U.S. patent application number 10/994551 was filed with the patent office on 2005-07-07 for welded joints with new properties and provision of such properties by ultrasonic impact treatment.
This patent application is currently assigned to UIT, L.L.C. Company. Invention is credited to Statnikov, Efim S..
Application Number | 20050145306 10/994551 |
Document ID | / |
Family ID | 36498419 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145306 |
Kind Code |
A1 |
Statnikov, Efim S. |
July 7, 2005 |
Welded joints with new properties and provision of such properties
by ultrasonic impact treatment
Abstract
Non-detachable welded joints with certain new or improved
properties and the provision of such non-detachable welded joints
by ultrasonic impact treatment, is described involving conforming
to select treatment parameters to control the formation of
predetermined properties and thus provide improved qualities and
reliability to a joint based on the task to be served by the welded
joint. The treatment parameters include repetition rate and length
of the ultrasonic impact, pressing force exerted on the ultrasonic
impact tool against the surface being treated, and impact
amplitude.
Inventors: |
Statnikov, Efim S.;
(Birmingham, AL) |
Correspondence
Address: |
Breiner & Breiner, L.L.C.
P.O. Box 19290
Alexandria
VA
22320-0290
US
|
Assignee: |
UIT, L.L.C. Company
Birmingham
AL
|
Family ID: |
36498419 |
Appl. No.: |
10/994551 |
Filed: |
November 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10994551 |
Nov 23, 2004 |
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10207859 |
Jul 31, 2002 |
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10207859 |
Jul 31, 2002 |
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09273769 |
Mar 23, 1999 |
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6289736 |
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10207859 |
Jul 31, 2002 |
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09653987 |
Sep 1, 2000 |
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6458225 |
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10207859 |
Jul 31, 2002 |
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09288020 |
Apr 8, 1999 |
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6338765 |
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09288020 |
Apr 8, 1999 |
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09145992 |
Sep 3, 1998 |
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6171415 |
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Current U.S.
Class: |
148/508 ;
148/320; 148/558; 148/902; 156/73.5 |
Current CPC
Class: |
B23K 20/106 20130101;
B06B 1/0253 20130101; C21D 11/00 20130101; C21D 10/00 20130101;
B23K 31/00 20130101; C21D 7/04 20130101; C21D 9/50 20130101; B23K
20/10 20130101; B23K 13/00 20130101; B23K 9/32 20130101; B23K 31/12
20130101; C21D 2201/00 20130101 |
Class at
Publication: |
148/508 ;
156/073.5; 148/558; 148/902; 148/320 |
International
Class: |
C21D 011/00 |
Claims
It is claimed:
1. An ultrasonic impact treated non-detachable welded joint
comprising at least one predetermined structural property resulting
from ultrasonic impact treatment of said welded joint, said at
least one predetermined structural property including at least one
of: surface roughness and relief of at least about 0.1 .mu.m; a
radius between surfaces of at least about 0.5 mm; a depth of a
groove along a weld toe line or line between any surfaces in a
stress concentration area of up to about 2 mm with a width of said
groove being up to about 10 mm; increase of material mechanical
properties in a stress concentration area, as to strength by at
least about 1.5 times and impact strength by at least about 1.2
times; plastic deformation, favorable compressive stresses and a
favorable relative change in microhardness to a depth of up to
about 7 mm; distribution of elastic compressive stresses due to
plastic deformation of material in section normal to a surface to a
depth of up to 10 mm; relaxation of process induced residual
stresses due to ultrasonic fluctuating stress wave with an
amplitude of at least about 0.05 of a material yield strength, to a
depth of up to about 12 mm; favorable residual stresses of a first
and a second kind on and under a surface to a predetermined depth
of at least material yield strength and ultimate strength based on
task application; compensation for residual process induced
deformations by at least about 40% of those occurring without
ultrasonic impact treatment application with increased stress
corrosion resistance by up to about 10 times; increase in
corrosion-fatigue strength by up to about 2.5 times and a life span
in a corrosion environment of up to about 20 times under variable
loading; increase in fatigue limit in air under repeated or
fluctuating stress by at least about 1.5 times and a life span by
at least about 10 times to increase joint strength by at least 1
category; or formation of a white layer and an amorphous structure
to a depth of at least about 50 .mu.m.
2. The ultrasonic impact treated non-detachable welded joint
according to claim 1, wherein said welded joint is made of a high
strength steel or alloy having a yield strength of .sigma.>500
MPa following ultrasonic impact treatment and has a fatigue limit
which is a minimum of about 30% greater than that of a steel or
alloy with .sigma.<500 MPa.
3. The ultrasonic impact treated non-detachable welded joint
according to claim 1, wherein said favorable compressive stresses
have a depth of about 2 mm, with a magnitude at a surface greater
than a yield strength and a fatigue limit of an untreated base
material of the welded joint by a factor of up to about 1.5.
4. The ultrasonic impact treated non-detachable welded joint
according to claim 1, wherein said welded joint has a level of
residual stresses of about 0.5 less of a yield strength of said
welded joint; residual welding deformations of about 100% or less
of a dimensional tolerance predetermined for said welded joint;
and/or fatigue resistance equal to or greater than that of an
untreated base material of said welded joint.
5. The ultrasonic impact treated non-detachable welded joint
according to claim 1, wherein said fatigue limit of a spot weld is
increased by at least about 1.3 times that of an untreated base
material and has increased fatigue resistance, yield point,
ultimate strength and impact strength to a level equal to or
greater than that of an untreated base metal material of the welded
joint.
6. The ultrasonic impact treated non-detachable welded joint
according to claim 1, wherein said fatigue limit of a tack weld is
at least about 1.3 times greater than that of an untreated base
material of the welded joint and fatigue resistance, ultimate
strength and impact strength are equal to or greater than that of
the untreated base material.
7. An ultrasonic impact treated non-detachable welded joint
comprising structural properties resulting from ultrasonic impact
treatment of said welded joint wherein parameters of said treatment
include oscillating system frequency of greater than zero to about
800 kHz, pressure on an ultrasonic impact tool of greater than zero
to about 50 kg, ultrasonic transducer vibrational amplitude during
impact of greater than 0 to about 120 .mu.m, ultrasonic frequency
in a range of greater than zero to about 2500 Hz, self-oscillation
amplitude of the impact tool of greater than zero to about 5 mm,
and an average duration of impact of said ultrasonic impact tool
being at least about 1 ms.
8. An ultrasonic impact treated non-detachable welded joint
comprising steel or steel alloy having a yield strength of
.sigma.>500 MPa, and structural properties resulting from
ultrasonic impact treatment of said welded joint wherein parameters
of said treatment include an oscillating system frequency of about
27 kHz, pressure on an ultrasonic impact tool of greater than zero
to about 10 kg, ultrasonic transducer vibrational amplitude during
impact of at least about 30 .mu.m, ultrasonic frequency in a range
of about 80-250 Hz, self-oscillation amplitude of the impact tool
of greater than zero to about 2 mm, indenter diameter of about
3-6.35 mm, and length of indenter being in a range of about 10-35
mm, wherein said welded joint has favorable compressive stresses to
a depth of at least 2 mm.
9. An ultrasonic impact treated non-detachable welded joint with
improved stress concentration comprising a groove in a transition
area between a weld material and a base material, said groove
having radiuses at a boundary of the groove of at least about 0.5
mm, widths greater than zero to about 10 mm and depth of greater
than zero to about 2 mm, and properties resulting from ultrasonic
impact treatment of the welded joint wherein parameters of said
treatment include ultrasonic vibration amplitude during impact of
greater than zero to about 50 .mu.m at a frequency of greater than
zero to about 80 kHz, ultrasonic frequency of greater than zero to
about 500 Hz, self-oscillation amplitude of an ultrasonic impact
tool of at least about 0.2 mm, an off-duty factor of impact
impulses of greater than zero to about 0.5, and pressure on the
ultrasonic impact tool of at least about 3 kg.
10. An ultrasonic impact treated non-detachable welded joint with
improved external loading properties comprising a joint metal of
carbon structural steel, stainless steel, or aluminum and titanium
alloys, and properties resulting from ultrasonic impact treatment
of the welded joint wherein parameters of said treatment include
ultrasonic vibration amplitude during impact of greater than zero
to about 50 .mu.m at a frequency of greater than zero to about 80
kHz, ultrasonic frequency of greater than zero to about 500 Hz with
average duration being at least about 1 ms, self-oscillation
amplitude of an ultrasonic impact tool of at least about 0.2 mm,
and pressure on the ultrasonic impact tool of at least about 3 kg,
whereby compressive stresses and strength in a stress concentration
area of the joint is greater than that present in the joint in the
absence of ultrasonic impact treatment to compensate for external
operational forces which cause in-service cracking.
11. The welded joint of claim 10 wherein said ultrasonic impact
treatment includes ultrasonic impact of a weld toe of said welded
joint and a load-carrying component on a loading side providing
during treatment plastic deformation to create and distribute said
compressive stresses.
12. An ultrasonic impact treated non-detachable welded joint
comprising a welded joint with compressive stresses in a plastic
deformation area to a depth of at least about 2 mm and
corresponding compressive stresses in an elastic deformation area
sufficient to compensate for residual effect of the tensile
stresses, and properties resulting from ultrasonic impact treatment
of the welded joint wherein parameters of the treatment include
pressure force of an ultrasonic impact tool of greater than zero to
about 10 kg, ultrasonic impact frequency of greater than zero to
about 500 Hz, average duration of ultrasonic impact of at least
about 1 ms, ultrasonic carrier frequency of greater than zero to
about 100 kHz, ultrasonic oscillation amplitude of an indenter
during impact of at least about 30 .mu.m, and impact amplitude of
at least about 0.2 mm.
13. An ultrasonic impact treated non-detachable welded joint
comprising deformation compensation within said joint to a value of
1>K.sub.o>-1 wherein K.sub.o is a toolmarks overlap
coefficient, and properties resulting from ultrasonic impact
treatment of the welded joint wherein parameters of the treatment
include pressure force of an ultrasonic impact tool of at least
about 4 kg, ultrasonic impact frequency of at least about 100 Hz,
impact amplitude of at least about 0.2 mm, average impact duration
of at least about 1 ms, carrier ultrasonic frequency of at least
about 15 kHz, ultrasonic vibration amplitude during impact of at
least about 30 .mu.m when said welded joint is made of steel or
steel alloy and about 30 .mu.m or less when said welded joint is
made of an aluminum alloy or metal with a yield strength of up to
about 235 MPa.
14. The welded joint according to claim 13 wherein said properties
include modification of residual welding deformations to create
rigid attachment with subsequent ultrasonic relaxation of residual
welding stresses, or ultrasonic plastic deformation and
redistribution of the weld metal.
15. An ultrasonic impact treated non-detachable welded joint
including residual stresses of not greater than 0.5 of the yield
strength of the welded joint, residual welding deformations of not
greater than 100% of dimensional tolerance specific to said welded
joint, and fatigue resistance of the welded joint is not less than
the fatigue resistance of a base metal in said welded joint,
wherein parameters of ultrasonic impact treatment of said welded
joint include pressure upon an ultrasonic impact tool with a steel
indenter is at least about 3 kg during manual treatment and greater
than zero to about 20 kg during mechanized treatment, ultrasonic
impact frequency of at least about 0.2 mm, carrier frequency of
indenter ultrasonic vibrations of at least about 15 kHz, and
ultrasonic vibration amplitude during impact of at least about 20
.mu.m when metal is above ambient temperature during treatment and
at least about 30 .mu.m when metal is at or about ambient
temperature during treatment.
16. An ultrasonic impact treated non-detachable welded joint
comprising a steel joint structured as a corner joint with obtuse
flank angles for a weld metal of the joint, said corner joint being
resistant to root cracking based on ultrasonic impact treatment of
said welded joint within parameters including pressure force of an
ultrasonic impact tool of at least about 3 kg during manual
treatment or at least about 25 kg during mechanized treatment,
ultrasonic frequency of greater than zero to about 800 Hz,
ultrasonic impact amplitude of at least about 0.2 mm, ultrasonic
vibration carrier frequency of at least about 18 kHz, ultrasonic
vibration amplitude during impact of greater than zero to about 20
.mu.m at a temperature above about 400.degree. C., and average
ultrasonic impact duration of at least about 1 ms, whereby weld
metal is redistributed between a flange and a web in the corner
joint.
17. The welded joint of claim 16 wherein said ultrasonic treatment
provides a meniscus and fuses sharp edges of said welded joint such
that upon solidification following said treatment smooth
transitions are provided between a weld and a base metal of said
welded joint increasing, to a level greater than said joint prior
to treatment, joint properties of resistance to stress
concentration and fatigue crack formation in a root of the
weld.
18. An ultrasonic impact treated non-detachable welded joint
comprising a carbon steel or aluminum alloy spot welded joint with
displaced tensile stress based on ultrasonic impact treatment of
said spot welded joint within parameters including ultrasonic
impact frequency of at least about 80 Hz, average impact duration
of least about 1 ms at an amplitude of at least about 0.2 mm,
indenter ultrasonic vibration carrier frequency during impact of
greater than zero to about 100 kHz, ultrasonic vibration amplitude
during impact in a range of from about 5-40 .mu.m, and pressure
force on an impact tool of from about 3-30 kg.
19. An ultrasonic impact treated non-detachable welded joint
comprising a joint of carbon steel or aluminum alloy with a tack
weld or a lap weld resistant to cracking at weld ends based on
ultrasonic impact treatment of said welded joint within parameters
including ultrasonic impact frequency of greater than zero to about
2000 Hz, average duration of ultrasonic impact of at least about 1
ms, impact amplitude of at least about 0.2 mm, indenter ultrasonic
vibration carrier frequency of at least about 18 kHz, indenter
ultrasonic vibration amplitude during impact of at least about 25
.mu.m for carbon steel and greater than zero to about 30 .mu.m for
aluminum alloy, and pressure force of an ultrasonic impact tool
against a treated surface of at least about 3 kg.
20. An ultrasonic impact treated non-detachable welded joint
comprising a corner welded joint of carbon steel or aluminum alloy
having increased fatigue limit by at least a factor of at least 1.3
based on ultrasonic impact treatment of said corner welded joint
within parameters including ultrasonic impact frequency of greater
than zero to about 1200 Hz, average duration of ultrasonic impact
of at least about 1 ms, ultrasonic impact amplitude of at least
about 0.2 mm, indenter ultrasonic vibration amplitude during impact
of at least about 25 .mu.m for carbon steel and not greater than
about 30 .mu.m for aluminum alloy, pressure of an ultrasonic impact
tool against a treated surface of said welded joint of at least
about 3 kg.
21. An ultrasonic impact treated non-detachable welded joint
comprising a welded joint having weld metal structure phase
homogeneity in all directions in the weld based on crystallization
and recrystallization of the weld metal based on ultrasonic impact
treatment of the welded joint within parameters including pressure
of an ultrasonic impact tool of from about 0.1-50 kg, ultrasonic
vibration carrier frequency at a transducer of from about 10-800
kHz, ultrasonic vibration amplitude under no-load conditions and
during impact of an ultrasonic tool at a carrier frequency of from
about 0.5-120 .mu.m, self-oscillation amplitude of ultrasonic
impact tool of from about 0.05-5 mm, and average duration of
ultrasonic impact of at least about 1 ms.
22. An ultrasonic impact treated non-detachable welded joint
comprising a joint of ferritic steel with a weld having activated
crystallization and resistance to brittle fracture based on
ultrasonic impact treatment of the welded joint within parameters
including ultrasonic impact frequency of greater than zero to about
2500 Hz, ultrasonic impact amplitude of at least about 0.2 mm,
average duration of ultrasonic impacts of at least about 1 ms,
ultrasonic vibration carrier frequency of at least about 15 kHz,
ultrasonic vibration amplitude during impact of at least about 15
.mu.m for metal not at ambient temperature and less than about 30
.mu.m for treatment of metal at or about ambient temperature, and
pressure force of an ultrasonic impact tool against a treated
surface of at least about 5 kg for manual treatment or at least
about 10 kg for mechanized treatment.
23. An ultrasonic impact treated non-detachable welded joint
comprising a joint modified by ultrasonic impact to increase
resistance to stress corrosion to a level greater than said joint
untreated by ultrasonic impact, based on ultrasonic impact
treatment of the welded joint within parameters including
ultrasonic impact frequency of greater than zero to about 500 Hz,
ultrasonic impact amplitude of at least about 0.5 mm, average
duration of ultrasonic impacts of at least about 1 ms, ultrasonic
vibration carrier frequency of at least about 15 kHz, ultrasonic
vibration amplitude during impact of at least about 20 .mu.m, and
pressure force on an ultrasonic impact tool against a treated
surface of at least about 5 kg.
24. The welded joint according to claim 23 wherein said joint has a
surface roughness of not less than about 5 .mu.m in a sampling
length of 0.8 mm, a waviness of not less than about 15 .mu.m at a
sampling length of 2.5 mm, compressive stresses not less than yield
strength of the joint, depth of plastic deformation and induced
residual stresses of not less than about 1.5 mm, corrosion
resistance of at least 2 times greater than in absence of the
treatment, and corrosion-fatigue strength of not less than about
1.3 times that of the joint in absence of the treatment of the
joint.
25. An ultrasonic impact treated non-detachable welded joint
comprising a welded joint structure containing at least one crack
arrest hole in said structure, said at least one crack arrest hole
having compressive stresses in the structure surrounding the at
least one hole, wherein parameters of ultrasonic impact treatment
of said welded joint structure containing said at least one crack
arrest hole include ultrasonic impact frequency of greater than
zero to about 500 Hz, ultrasonic impact amplitude of at least about
0.5 mm, average duration of ultrasonic impacts of at least about 1
ms, ultrasonic vibration carrier frequency of at least about 15
kHz, ultrasonic vibration amplitude during impact of at least about
30 .mu.m, and pressure force on an ultrasonic impact tool against a
treated surface of at least about 5 kg.
26. An ultrasonic impact treated non-detachable welded joint
comprising a structural combination including a welded joint with a
bracket and a panel, wherein a radius cutout is present between the
bracket and the panel, said structural combination has fatigue
resistance of at least 1.3 times that of the structural combination
when untreated by ultrasonic impact treatment, wherein said
ultrasonic impact treatment of said structural combination is
within parameters including ultrasonic impact frequency of greater
than zero to about 300 Hz, ultrasonic impact amplitude of at least
about 0.5 mm, average duration of ultrasonic impacts of at least
about 1 ms, ultrasonic vibration carrier frequency of at least
about 15 kHz, ultrasonic vibration amplitude during impact of at
least about 30 .mu.m, and pressure force on an ultrasonic impact
tool against a treated surface of at least about 3 kg.
27. An ultrasonic impact treated non-detachable welded joint
comprising a welded joint with reduced martensite decomposition
based on ultrasonic impact treatment of the welded joint within
parameters including ultrasonic impact frequency of greater than
zero to about 800 Hz, ultrasonic impact amplitude of at least about
0.5 mm, average duration of ultrasonic impacts of at least about 1
ms, ultrasonic vibration carrier frequency of at least about 15
kHz, ultrasonic impact of at least about 30 .mu.m, and pressure
force on an ultrasonic impact tool against a treated surface of at
least about 10 kg.
28. An ultrasonic impact treated non-detachable welded joint
comprising a welded joint having a coating thereon, said coating
being resistant to breakage upon ultrasonic impact treatment
wherein said treatment has parameters which include ultrasonic
impact frequency of greater than zero to about 1500 Hz, ultrasonic
impact amplitude of at least about 1 mm, average duration of
ultrasonic impacts of at least about 1 ms, ultrasonic vibration
carrier frequency of at least about 20 kHz, ultrasonic vibration
amplitude during impact of greater than zero to about 30 .mu.m,
contact pressure and stress gradient at a boundary between
individual ultrasonic impact tool marks of not greater than coating
breaking strength, and pressure force on an ultrasonic impact tool
against a surface of at least about 3 kg.
29. Process of analyzing and selecting an ultrasonic impact
treatment for treating a welded joint to have one or more
predetermined properties, comprising (1) defining pre-treatment
properties of material forming a weld of the joint and the welded
joint itself; (2) defining conformity of the properties of (1) to
post-treatment properties to be provided in the joint; (3) defining
physical factors having an effect on the joint in context of the
post-treatment properties to be provided in the joint; (4) defining
positive result criteria and effect of ultrasonic impact treatment
on providing the post-treatment properties in the joint; (5)
defining a manner of ultrasonic impact treatment for the joint in
context of providing the post-treatment properties in the joint,
including defining ultrasonic impact treatment conditions in
combination with parameters of a transducer, ultrasonic impact,
indenter, pressure, mechanical properties and acoustic
characteristics of the material to be treated; and (6) conducting
ultrasonic impact treatment on the joint in accordance with the
definitions established in (1) to (5).
30. Process according to claim 29, wherein said physical factors of
(3) comprise one or more of plastic deformation caused by low
frequency impact, ultrasonic plastic deformation during said impact
treatment, amplitude and attenuation of ultrasonic stress wave in
the material of the joint, and temperature and heat rejection rate
at a contact point during ultrasonic impact.
31. Process according to claim 29, wherein said post-treatment
properties of (2) comprise one or more of geometric accuracy,
residual deformations and nominal dimension tolerance thereof,
residual stresses equilibrated within volume of the joint and
structural segments of the material of the joint, acceptable stress
concentration level and configuration of stress raisers responsible
for load-carrying capacity of the joint, fatigue limit and fatigue
resistance under low-cycle and high-cycle reversal and fluctuating
loading, fatigue limit and resistance to corrosion and corrosion
fatigue failures in aggressive environment under the low-cycle and
high-cycle reversed and fluctuating loading and properties of the
welded joint.
32. Process according to claim 29, wherein the criteria of (4)
comprise one or more of induced residual stress and deformation
levels; relief, roughness and geometric modification of surface and
transitional areas of the joint and modification of properties of
the material in an area of treatment; relaxation and redistribution
of residual stresses produced during manufacture of the joint prior
to impact treatment; and modification of the joint as to type and
conditions of resistance to a service load.
33. Process according to claim 29, wherein the parameters of (5)
comprise one or more of pressure on an ultrasonic impact tool being
in a range of from about 0.1-50 kg; carrier ultrasonic frequency of
the transducer being between about 10-800 kHz; amplitude of
ultrasonic vibrations at said carrier frequency of between about
0.5-120 .mu.m; ultrasonic impact frequency and self-oscillation
frequency of the tool being between about 5-2500 Hz with duration
of random ultrasonic impact in a range of from about 2-50 vibration
periods at carrier ultrasonic frequency; self-oscillation amplitude
of the tool being between about 0.5-5 mm; level of connection
between a freely axially moving indenter and a transducer of the
tool being within the claimed parameters; free ultrasonic impacts
within said parameters selected in view of task, property and size
requirements of the material and the joint.
34. Process of treating a non-detachable welded structure
comprising: (a) subjecting at least a portion of a weld in a
non-detachable welded structure to repeated ultrasonic impact by an
ultrasonic impact tool to cause controlled plastic deformation in
said weld and modify surface and transitional areas of the weld of
said welded structure and thus modify one or more material
properties in the welded structure; (b) obtaining the material
properties of (a) by controlling one or more select parameters of
said repeated ultrasonic impact, said select parameters being
selected from one or more parameters of the group consisting of (1)
pressure on the ultrasonic impact tool being in a range of from
about 0.1-50 kg; (2) ultrasonic frequency of the ultrasonic impact
tool being from between about 10-800 kHz; (3) amplitude of
vibrations from said ultrasonic impact being from between about
0.5-120 .mu.m; (4) ultrasonic frequency of the ultrasonic impact
tool and self-oscillation frequency of the ultrasonic impact tool
being from between about 5-2500 Hz with a duration of ultrasonic
impact being in a range of from about 2-50 vibration periods at a
carrier ultrasonic frequency; (5) self-oscillation amplitude of the
ultrasonic impact tool being from between about 0.05-5 mm; (6) a
connection level between a freely axially moving indenter of the
ultrasonic impact tool and a transducer of the ultrasonic impact
tool acting within parameters (1)-(5); and (7) free ultrasonic
impacts falling within parameters (1)-(5) based on task, properties
and size of the welded structure.
35. Process of tuning ultrasonic impact for ultrasonic impact
treatment of a non-detachable welded joint comprising controlling
in combination parameters of free ultrasonic impact of the
treatment, wherein said parameters are of pressing, amplitude,
frequency, and duration of the free ultrasonic impact together with
control of transducer vibrations from said impact.
36. Process of structural rearrangement of a welded joint
comprising subjecting at least part of the welded joint to random
ultrasonic impact while controlling amplitude, length and
repetition rate of said ultrasonic impact in a manner to impact
energy at a repetitive rate with pauses between impacts, said
pauses being sufficient for relaxation of material condition and
availability for next impact with minimal resistance that does not
exceed internal losses in the material when the material is in a
quiet condition.
37. Process according to claim 34, wherein the welded structure is
selected from the group consisting of butt joints, fillet joints,
lap joints, narrow gap joints, spot joints and apertures in a joint
structure.
38. Process according to claim 35, wherein the welded structure is
selected from the group consisting of butt joints, fillet joints,
lap joints, narrow gap joints, spot joints and apertures in a joint
structure.
39. Process according to claim 36, wherein the welded structure is
selected from the group consisting of butt joints, fillet joints,
lap joints, narrow gap joints, spot joints and apertures in a joint
structure.
40. Process according to claim 34, wherein the material properties
affected are one or more properties selected from a group
consisting of surface roughness and relief, radius present between
surfaces, depth of groove at a weld toe line or a line between
surfaces of stress concentration area, width of said groove, impact
strength, plastic deformation, compressive stresses, ultrasonic
fluctuating stresses, residual stress, stress corrosion, white
layer/amorphous structure formation, and corrosion fatigue.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of U.S.
Ser. No. 10/207,859 filed Jul. 31, 2002, which is a
continuation-in-part of both U.S. Ser. No. 09/273,769 filed Mar.
23, 1999 (now U.S. Pat. No. 6,289,736 B1) and U.S. Ser. No.
09/653,987 filed Sep. 1, 2000 (now U.S. Pat. No. 6,458,225 B1), the
latter in turn being a continuation-in-part of U.S. Ser. No.
09/288,020 filed Apr. 8, 1999 (now U.S. Pat. No. 6,338,765 B1)
which is a continuation-in-part of U.S. Ser. No. 09/145,992 filed
Sep. 3, 1998 (now U.S. Pat. No. 6,171,415 B1). Each of the parent
applications and patents issued thereon are incorporated herein by
reference.
FIELD OF INVENTION
[0002] The invention is directed to welded joints having new
strength and process induced properties and the process of
providing such properties to the welded joints by ultrasonic impact
treatment (UIT). The welded joint of the invention has specific
properties providing improved quality and reliability to the welded
joint. In a welded joint, the properties to be obtained or enhanced
are defined based on the task the welded joint is to serve, such as
in the areas of quality, reliability and fabricability.
BACKGROUND OF INVENTION
[0003] U.S. Pat. Nos. 6,171,415 B1 and 6,338,765 B1 describe
ultrasonic impact methods for treatment of welded structures using
pulse impact energy, in particular ultrasonic impact energy. These
patents teach fabrication and repair treatments for welded
structures based on stochastic ultrasonic impact treatment. The
frequency and amplitude of an ultrasonic transducer are basic
aspects of the impact. The striction feedback signal allows
selection of parameters sufficient and necessary to obtain a
specified treatment effect.
[0004] It has now been found to be desirous to customize properties
of a welded joint structure. This is in particular beneficial with
respect to welded joints in view of the particular task and
corresponding structure of the joint to further enhance quality and
reliability of the joint.
OBJECTS AND SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention is directed to
non-detachable welded joints with improved properties and the
provision of such properties to the welded joints when subjecting
the welded joint to ultrasonic impact treatment. New structural
properties are obtained in the welded joint in view of the
particular task to which the welded joint is intended to perform.
The description herein is set forth in relation to welded joints.
However, an equivalent non-detachable welded structure may also be
treated in accordance with the invention as described herein and
the engineering solutions described herein may be applied to any
other equivalent non-detachable welded joints and structures formed
thereby.
[0006] The invention also involves the selection of parameters for
ultrasonic impact application upon welded joints and structures
with new and predetermined properties.
[0007] As with the engineering solutions described in U.S. Pat.
Nos. 6,171,415 B1 and 6,338,765 B1, the present invention also
utilizes stochastic ultrasonic impact to treat welded joints. The
present invention, however, demonstrates that certain ultrasonic
impact treatment parameters in combination improve technical
properties of a welded structure, in particular a welded joint.
These parameters include (1) the repetition rate and length (or
duration) of the ultrasonic impact, (2) the pressure or pressing
force exerted on the ultrasonic impact tool against the surface
being treated and (3) the impact amplitude. The new conditions of
ultrasonic impact treatment of the invention also involve an
extension of ranges of standard parameters for exciting the
ultrasonic transducer that generates the carrier ultrasonic
oscillating frequency in the indenter of the ultrasonic impact
tool. A certain combination of these parameters make it possible to
obtain new properties or modify existing properties in welded
joints in view of the task the joint is to serve. The selected
parameters for the ultrasonic impact treatment control the
ultrasonic impact and create the necessary conditions in order to
define new quality and reliability criteria for welded structures
and obtaining welded structural properties suitable for serving
predetermined tasks of the welded structures.
[0008] The invention can be utilized for any type of non-detachable
welded structure, but primarily provides welded joints with
properties which result in significant performance enhancement.
Examples of welded joint structures of the invention include welded
joints in high-strength steels; welded joints with stress
concentration; welded joints subject to unbalanced loading, welded
joints having defects or damaged areas, such as cracks; welded
joints requiring predetermined manufacturing accuracy; repaired
welded joints; welded joints needing repair; lap welded joints;
tack welds for joints; corner welded joints; welded joints prone to
liquation, coarse grain and pore formation; welded joints made with
preliminary heating; welded joints having predetermined stress
corrosion resistance; welded joints with holes; welded joints in
brackets or stiffeners; and welded joints prone to martensite
formation.
DESCRIPTION OF DRAWINGS
[0009] FIG. 1 illustrates, in terms of amplitude and time,
vibrations of an ultrasonic transducer which cause ultrasonic
impact.
[0010] FIG. 2 illustrates, in terms of amplitude and time, the
force impulse randomly transferred by ultrasonic impact.
[0011] FIG. 3 illustrates, in terms of amplitude and time, the
lengthened ultrasonic impact obtained using the process of the
invention.
[0012] FIGS. 4a and 4b illustrate fatigue limits of high strength
steel untreated and treated according to the invention,
respectively.
[0013] FIG. 5 illustrates stress and deformation distribution in a
stress concentration area of material of a welded structure.
[0014] FIGS. 6a and 6b illustrate, as an example, girders and
loading conditions possible therewith, and the change in the
loading conditions as illustrated through change in the stress
concentration area following ultrasonic impact treatment which
compensates for dangerous effects of external factors.
[0015] FIGS. 7a, 7b and 7c illustrate a socket welded joint before
and after treatment according to the invention and the effect on
stress of the joint.
[0016] FIGS. 8a, 8b and 8c illustrate a defect retardation
mechanism for compressive stresses induced by ultrasonic impact.
FIG. 8a shows the joint before treatment, FIG. 8b during treatment
and FIG. 8c after treatment.
[0017] FIGS. 9a, 9b and 9c illustrate a technique of weld
deformation compensation using, as an example, a symmetric corner
welded joint taking into account directional weld shrinkage. FIG.
9a illustrates the welded joint and tolerances thereof before
ultrasonic impact treatment and FIG. 9b following treatment. FIG.
9c shows a schematic of deformation compensation direction
matching.
[0018] FIGS. 10a, 10b, 10c and 10d illustrate a mechanism of action
of a repair of a welded joint with crack and stress redistribution
due to ultrasonic impact treatment.
[0019] FIGS. 11a and 11b illustrate the formation of a weld joint
protected from root crack formation by positive flank angles of the
weld metal.
[0020] FIGS. 12a and 12b illustrate another weld joint formed to be
protected from root crack formation.
[0021] FIGS. 13a to 13e illustrate a spot welded joint before,
during and after ultrasonic impact treatment thereof.
[0022] FIG. 14a illustrates an untreated lap joint; FIG. 14b
illustrates a lap joint during treatment; and FIG. 14c illustrates
the lap joint subsequent to treatment.
[0023] FIGS. 15a and 15b illustrate a corner welded joint before
and after treatment in accordance with the invention,
respectively.
[0024] FIGS. 16a and 16b illustrate another corner welded joint
before and after ultrasonic impact treatment.
[0025] FIGS. 17a and 17b illustrated a weld joint's structural
phase homogeneity (enlarged portion) before and after ultrasonic
impact treatment, respectively.
[0026] FIGS. 18a and 18b illustrate a weld joint (including an
enlarged portion) untreated and after ultrasonic impact treatment
to provide activated crystallization (FIG. 18b) in the weld joint.
FIG. 18c graphically represents the treated and untreated weld
joints.
[0027] FIGS. 19a and 19b illustrate a weld joint without and with
ultrasonic impact treatment activated degassing, respectively.
[0028] FIGS. 20a and 20b illustrate a welded joint with and without
hydrogen content. FIG. 20c graphically compares a joint with a
permissible hydrogen content and a joint with minimization of
residual diffusion of hydrogen content following ultrasonic impact
treatment.
[0029] FIG. 21 graphically illustrates the corrosion rate of welded
joints of steel with high carbon content untreated and treated by
ultrasonic impact in accordance with the invention.
[0030] FIGS. 22a and 22b illustrate a welded joint with holes at
the tips of a crack before and during ultrasonic impact treatment,
respectively.
[0031] FIGS. 23a and 23b illustrate a welded bracket joint before
and after ultrasonic impact treatment, respectively.
[0032] FIG. 24 illustrates a diagram of supercooled austenite
decomposition in steel.
[0033] FIGS. 25a, 25b and 25c illustrate a welded joint before
coating and ultrasonic impact treatment (UIT), after application of
a protective coating and before UIT, and after UIT over the
coating, respectively.
[0034] FIG. 26 illustrates examples of welded joint structures
obtainable.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Ultrasonic impact treatment utilizes vibrations resulting
from excitation of an ultrasonic transducer. As shown in FIG. 1,
the vibrations occur at a certain amplitude over a defined time.
The vibrations can be forced when the transducer is activated or
free during a pause. The amplitude will lessen during free
vibration over time. As shown in FIG. 2, vibrations as illustrated
in FIG. 1 randomly transfer the force impulse to a freely axially
moving impacting element or indenter. The forced vibrations of the
ultrasonic transducer, as shown in FIG. 1, are interrupted to get
information about free vibrations of the ultrasonic transducer
under load and to correct the oscillator operating mode. The source
of this information is the feedback signal delivered from the
winding or electrodes of the active element during pause. It is
noted that this principle remains general for all types of active
materials used in ultrasonic transducers, specifically
magnetostrictive or piezoceramic. To analyze and correct the
operation of a generator, and hence a transducer, the striction
feedback signal is generally used (as described in Russian Patent
No. 817931 of Mar. 30, 1981). Thus, in order to select ultrasonic
impact treatment conditions in accordance with a task for a
particular welded joint, the striction feedback signal is used and
the technical system tuned for frequency and amplitude of
transducer vibrations under off-load and on-load conditions.
[0036] Besides ultrasonic transducer vibrational parameters, being
of importance in ultrasonic impact treatment, it has now been
determined that related parameters of the ultrasonic impact are
important in obtaining or modifying properties and, thus,
characteristics of non-detachable welded joints by ultrasonically
impacting material of the joint. Through selection of particular
parameters and optimization of these parameters, welded joints
having predetermined improved properties can be obtained. The
selection of ultrasonic transducer vibrational parameters and
ultrasonic impact parameters are based on the related
characteristics of the transducer-indenter-treated object
oscillating system wherein the characteristics are interdependent
with the pressure applied in treatment against the joint, physical
and mechanical properties of the joint material, and acoustic
properties of the joint itself. FIG. 3 illustrates how the
invention results in lengthening of the ultrasonic impacts, and
thus improving efficiency of the ultrasonic energy transfer to a
treated object in order to obtain new predetermined properties in
welded joints and structures. Accordingly, the ultrasonic impact
efficiency criteria are direct effects upon the joint material and
the associated length, frequency and amplitude parameters of the
ultrasonic impact.
[0037] Parameters of such an acoustic and mechanical system provide
the link for obtaining new or modified properties in welded joint
structures. The process of determining the correct combination of
select parameters involves:
[0038] (a) Defining the actual physical properties of the weld and
the material forming a welded joint,
[0039] (b) Defining conformity of the properties of (a) to
properties desired to meet quality and reliability requirements for
a specific joint,
[0040] (c) Defining the physical factors resulting from ultrasonic
impact treatment on the welded joint in context of providing the
desired properties to the joint,
[0041] (d) Defining criteria of the effect of ultrasonic impact
treatment on providing the desired joint properties,
[0042] (e) Defining conditions of the ultrasonic impact treatment
to provide the desired properties of the joint,
[0043] (f) Defining the ultrasonic impact treatment conditions in
combination with parameters of the transducer, ultrasonic impact,
indenter, pressure, mechanical properties and acoustic
characteristics of the treated joint material, and
[0044] (g) Carrying out ultrasonic impact treatment on the joint in
accordance with the definitions established above.
[0045] More particularly with respect to the above, to provide
non-detachable welded joints with predetermined new or modified
properties by ultrasonic impact treatment, the actual physical
properties of the welded joint to be treated are initially
determined by conventional testing techniques.
[0046] The properties desired in a welded joint following treatment
must then be defined and evaluated as to the difference thereof
from the properties of a welded joint before treatment. This may be
achieved by the present invention referred hereinafter as an
algorithm or series of procedural steps to achieve the desired end.
The algorithm generally includes (1) defining conformity of the
actual properties of the joint material to specified requirements;
(2) defining the physical factors and the mechanism of ultrasonic
impact treatment on a welded joint; (3) defining criteria in
determining desired weld joint quality and reliability; (4)
defining the basic criteria of the ultrasonic impact treatment on a
welded joint; (5) defining parameters of the ultrasonic impact
treatment for providing non-detachable welded joints with desired
properties, and (6) determining the results of the ultrasonic
impact treatment on a welded joint to provide predetermined
properties. The algorithm of the invention is described in further
detail hereafter. More particularly, the algorithm involves
initially determining conformity of the actual properties of the
non-detachable welded joint to be treated to the properties desired
in the joint in view of the task the joint is to serve, and
conforming to a set of ultrasonic impact treatment parameters
required to obtain the desired properties of the welded joint.
[0047] Physical factors and the mechanism of ultrasonic impact
treatment on a welded joint include plastic deformation caused by
the low-frequency impact; ultrasonic plastic deformation during the
impact; amplitude and attenuation (decrement of damping) of the
ultrasonic stress wave in the material of a given joint, while
ultrasonic vibrations of a layer saturated with plastic
deformations produced by low-frequency impact and ultrasonic
plastic deformation occur during the impact; and temperature and
heat rejection rate at the contact point during impacting.
[0048] Criteria in determining desired welded joint quality and
reliability include geometry accuracy; residual deformations and
their nominal dimension tolerance; residual stresses equilibrated
within the volume of the joint and structural segments of the joint
material; acceptable stress concentration level and configuration
of stress raisers responsible for the load-carrying capacity of the
joint; fatigue limit and fatigue resistance under low-cycle and
high-cycle reversed and fluctuating loading; and fatigue limit and
resistance to corrosion and corrosion-fatigue failures in
aggressive environment under low-cycle and high-cycle reversed and
fluctuating loading, and properties of the welded joint
material.
[0049] Basic criteria of the ultrasonic impact treatment effect on
a welded joint include the level of induced residual stresses and
deformations; relief, roughness and geometry modification of the
surface and transitional areas thereof and modification of material
properties in the treatment area; relaxation and redistribution of
residual stresses produced by the manufacturing technique of a
given joint prior to ultrasonic impact treatment; and modification
of the joint type and conditions of its resistance to service
loads.
[0050] Parameters of the ultrasonic impact treatment (UIT) for
providing non-detachable welded joints with properties desired
include (1) pressure on the ultrasonic impact tool in the range of
about 0.1 to 50 kg, (2) carrier ultrasonic frequency of the
transducer between about 10 and 800 kHz, (3) amplitude of
ultrasonic vibrations at carrier frequency between about 0.5 and
120 .mu.m, (4) ultrasonic impact frequency and self-oscillation
frequency of the tool-indenter system between about 5 and 2500 Hz
with duration of a random ultrasonic impact in the range of about 2
to 50 vibration periods at carrier ultrasonic frequency, (5)
self-oscillation amplitude of the tool between 0.05 and 5 mm, (6)
the level of connection between a freely axially moving indenter
and a transducer of the tool, which depends on the range of UIT
parameters described above, and (7) free ultrasonic impacts with
parameters set within above-mentioned ranges in accordance with the
task, properties and sizes of the material and welded joint.
[0051] The results of the ultrasonic impact treatment on a welded
joint to provide predetermined properties include at least one of
the following positive changes: surface roughness and relief of
about 0.1 .mu.m and above; a radius between surfaces of about 0.5
mm and above; the depth of the groove along the weld toe line or
line between any surfaces in the stress concentration area of up to
about 2 mm with the width of the groove being up to about 10 mm;
improvement of material mechanical properties in the stress
concentration area, as to strength by no less than about 1.5 times
and impact strength by no less than about 1.2 times; plastic
deformation, favorable compressive stresses and a favorable
relative change in microhardness to a depth of up to about 7 mm;
distribution of elastic compressive stresses due to plastic
deformation of material in section normal to the surface to the
depth of up to 10 mm; relaxation of process induced residual
stresses due to ultrasonic fluctuating stress wave with the
amplitude of no less than about 0.05 of the material yield
strength, to a depth of up to about 12 mm; favorable residual
stresses of the first and second kind on and under the surface to a
specified depth of no less than material yield strength and
ultimate strength depending on the task definition; compensation
for residual process induced deformations by not less than about
40% of those which occurred without UIT application with
improvement in stress corrosion resistance by up to about 10 times;
improvement in corrosion-fatigue strength by up to about 2.5 times
and a life span in a corrosion environment of up to about 20 times
under variable loading; improvement in fatigue limit in air under
repeated or fluctuating stress by no less than about 1.5 times and
a life span by no less than about 10 times, increasing the strength
of a joint by no less than 1 category; formation of a white layer
and an amorphous structure to a depth of no less than about 50
.mu.m.
[0052] The non-detachable welded joints can be made of any joined
material with the use of ultrasonic impact treatment with or
without fusion of the interface of the materials being joined, with
or without filler materials, and can contain in the aggregate or in
any combination the weld material, transition zone of a solid
solution of one material in another and zones altered relative to
joined and unjoined material structures and modes of deformation.
The non-detachable joints may be made by butt, fillet, lap,
narrow-gap or spot welding as well as welding along the aperture of
structural elements of any given shape with or without complete,
partial or incomplete penetration, with or without edge
preparation, and produced by varying means e.g. arc, resistance,
laser, electron beam, diffusion, friction, pressure, submerged arc,
shielded metal, gas shielded, open and submerged arc welding,
welding using filler material, open flame of ultrasonic welding,
soldering, and the like.
[0053] Particular welded joints of the invention will now be
described.
[0054] (A) Welded Joints in High-Strength Steels
[0055] In practice, the use of high-strength steels in the
fabrication of welded joints is limited by a low fatigue resistance
of the welded joints made from such steels as compared to low and
average-strength steels, namely, low-carbon and low-alloy steels
with yield strengths of a minimum two times as low and fatigue
limits up to two times as high as those of high-strength steels. It
is understood in the industry that the conditional boundary between
these steels is a yield strength or ultimate strength value of up
to 500 MPa.
[0056] The welded joints of high strength steel of the invention
obtained have a fatigue resistance which is at minimum twice as
high as that of low and average-strength steels. This is
graphically illustrated in FIGS. 4a and 4b. FIG. 4a shows the
fatigue limits of a high strength steel 1, a welded joint of low
carbon or low alloy steel 2 and a welded joint of high strength
steel without ultrasonic impact treatment 3. FIG. 4b shows the
fatigue limits of a welded joint of high strength steel after
ultrasonic impact treatment 4 and of a welded joint of low carbon
or low alloy steel after ultrasonic impact treatment 5. As shown,
the materials subjected to ultrasonic impact treatment in
accordance with the invention are significantly improved. The
welded joints made of high strength steels and alloy have a yield
strength of .sigma.>500 MPa following ultrasonic impact
treatment determined according to the invention and falling within
the parameters as set forth above to provide in the material of the
welded joint a fatigue limit which is a minimum of 30% greater than
that of steels and alloys with .sigma..ltoreq.500 MPa.
[0057] More specifically, to obtain the above, ultrasonic impact
treatment is applied to an area of hazardous stress concentration
at the toe of the weld. Thus, in accordance with the invention, the
characteristics of the as-welded joint and the base metal are first
determined. Taking into account the need to provide the fatigue
limit of the welded joint comparable to the strength of the base
metal of no less than 500 MPa, ultrasonic impact treatment
conditions are determined by calculating the impact energy that
suffices to create plastic deformations and compressive stresses.
Ultrasonic impact treatment conditions are then experimentally
verified and corrected to serve the task. At the oscillating system
frequency of about 27 kHz and a tool pressing force of up to about
10 kg, the ultrasonic impact treatment conditions to provide a
non-detachable welded joint with the desired properties are as
follows: ultrasonic transducer vibrational amplitude during impact
of not less than about 30 .mu.m, impact frequency in the range of
about 80 to 250 Hz, tool self-oscillation amplitude of up to about
2 mm, indenter diameter of about 3 to 6.35 mm, and the average
length or duration of the indenter being in a range of about 10-35
mm depending on the welded joint type. The above ultrasonic impact
treatment conditions are responsible for strengthening hazardous
tensile stress concentration area and creation therein of favorable
compressive stresses to a depth of no less than about 2 mm, whose
magnitude at the surface is greater than the yield strength and
fatigue limit of the base material by a factor of up to about 1.5.
In such a case, the stress concentration area after ultrasonic
impact treatment attains the configuration of a regular groove with
a depth up to about 1 mm, which is formed due to plastic
deformation caused by the ultrasonic impact and provides a smooth
transition between the weld and the base metal.
[0058] Thus, the inclusion of high-strength steels in the
fabrication of welded structures and in the resulting welded joint
is available.
[0059] (B) Welded Joints with Stress Concentration
[0060] Physical and mechanical properties of the material at a weld
toe of a joint, the nature of operating stresses and their
distribution at a stress concentration area are the basic strength
and fatigue resistance criteria for welded joints with stress
concentration together with the concentration factor that depends
on the geometry of the transition between the weld and base metal
at the weld toe.
[0061] Weld joints are obtained according to the invention by
ultrasonic impact treatment of the stress concentration area to
improve the strength, ductility and impact strength of the treated
welded joint material above nominal values relative to untreated
material forming the welded joint. In addition, the welded joint is
modified and adapted to external loads, since the ultrasonic impact
treatment of the stress concentration area performed induces
favorable residual compressive stresses in the treated area.
[0062] The condition, characteristics and properties of the treated
area are determined by the features of ultrasonic and impulse
plastic deformations, which are dependent on the amplitude and
length of ultrasonic impacts and their repetition rate during
ultrasonic impact treatment. As a result, the ultimate strength and
fatigue limit of the weld joint material in the stress
concentration area are greater than those of materials forming the
weld joint.
[0063] The mode of deformation of the weld joint under such
conditions is defined by the residual stresses and equivalent
plastic and elastic deformations. The favorable residual
compressive stresses in the area of ultrasonic plastic deformations
due to ultrasonic impact treatment are not less than the greater
nominal yield point of the materials. Elastic deformations and
respective elastic stresses decrease exponentially in the depth of
the treated material from the maximum of the residual compressive
stresses equilibrating the elastic stresses while the level and
distribution of the residual and elastic stresses on and under the
surface are established to compensate for environmental effect and
operational stresses.
[0064] Stress and deformation distribution in the stress
concentration area are shown in FIG. 5 together with the change in
material properties in this area as a result of ultrasonic impact
treatment performed in accordance with the algorithm described
herein.
[0065] It is well-known that hazardous stress concentration is
generally localized at a weld toe. This is due to the unfavorable
sharp transition between the weld and the base metal, the presence
in this zone of pronounced welding defects (such as overlaps,
irregularities, undercuts) as well as due to tensile residual
stresses caused by weld shrinkage on cooling.
[0066] In accordance with the invention, ultrasonic impact
treatment produces a smooth transition between a weld and a base
metal by forming a groove with radiuses at its boundaries of about
0.5 mm and greater, with widths of greater than zero and up to
about 10 mm and depths of greater than zero up to about 2 mm
depending on the metal thickness and the weld toe angle. Ultrasonic
impact treatment conditions define the relief, groove roughness
(not less than Ra=75 .mu.in), the magnitude and the nature of
induced compressive stresses (not less than the material's ultimate
strength), the effect thereof to a depth of not less than about 2
mm in the plastic deformation area and not less than about 5 mm in
the elastic deformation area, and residual welding stress
relaxation to a point not greater than about 20% of the original
state.
[0067] The parameters to provide the welded joint include an
ultrasonic vibration amplitude during impact of greater than zero
and up to about 50 .mu.m at a frequency of greater than zero and up
to about 80 kHz, impact frequency of greater than zero and up to
about 500 Hz, tool self-oscillation amplitude of about 0.2 mm and
greater, the off-duty factor of impact impulses of greater than
zero and up to about 0.5, a pressing force of at least about 3 kg
and as a consequence of the above, impact energy which is
equivalent and sufficient to create compressive stresses and modify
material ultimate strength properties in the stress concentration
area to be greater than the original stress and strength properties
and sufficient to compensate for external operational forces.
[0068] Ultrasonic impact treatment of carbon steels performed in
accordance with the method under the above-mentioned conditions
increases the fatigue limit of a welded joint as a result of a
combined action of the physical factors set forth above, as well as
the removal of welding defects by plastically deforming the welded
joint material.
[0069] (C) Welded Joints Subjected to Balanced and Unbalanced
Loading
[0070] A primary requirement that defines the ability of welded
joints to resist failure under balanced and unbalanced loading in
the original condition is the unbalanced nature of the load on
these joints after ultrasonic impact treatment to obtain properties
in accordance with the invention. However, the final stressed state
of the welded joint will always depend on the condition of external
loading on the weld joint. On this basis, ultrasonic impact
treatment of the weld joint is performed in accordance with the
algorithm of the invention concurrently with balanced or unbalanced
loading on the joint, which is close to actual loading.
[0071] The level and nature of external loading on a given weld
joint and related parameters of ultrasonic impact treatment
performed are determined and matched by the condition of adequacy
to compensate for the effect of factors causing crack formation
during operation of a given weld joint.
[0072] The procedure of rating the ultrasonic impact treatment
adequacy as a part of the invention can be as set forth below.
[0073] Initially, the varying loading, which is adequate to the
actual loading, is applied to a sample or the actual welded joint
in the as-welded condition and stresses or equivalent deformations
due to the loading are measured by any conventional means. By
calculating the required impact energy, the parameters of
ultrasonic impact treatment are then determined to compensate for
the stresses or deformations. Thereafter, ultrasonic impact
treatment is applied together with the varying loading and the
level of compensation for hazardous operational stresses or
deformations is established by the measuring procedure used before.
If required, design parameters of ultrasonic impact treatment are
corrected to compensate for stresses or deformations as defined by
the task the weld joint is to perform.
[0074] The ultrasonic impact treatment of a welded joint applied in
parallel with the load can be performed in the free state on an
unfixed structure, in a rigid contour on a fixed structure, or
under constant, variable and balanced loading.
[0075] To solve problems as above described, the parameters of
ultrasonic impact treatment to provide welded joints made from
carbon structural and stainless steels, and aluminum and titanium
alloys with the desired properties includes ultrasonic vibration
amplitude during impact of greater than zero and up to about 50
.mu.m at a frequency of greater than zero and up to 80 kHz, the
impact frequency of greater than zero and up to 500 Hz with the
prevailing impact duration on average of no less than about 1 ms,
the tool self-oscillation amplitude of about 0.2 mm and greater,
the pressing force of no less than about 3 kg and as a consequence
of the above, the impact energy equivalent and sufficient to create
compressive stresses and modify material ultimate strength
properties in the stress concentration area to be greater than the
original compressive stresses and strength properties and are
sufficient to compensate for external operational forces.
[0076] The change in the loading condition as a result of
concurrent ultrasonic impact treatment which results in
compensation for the dangerous effects of external factors is shown
in FIGS. 6a and 6b through exemplary girder structures. FIG. 6a
shows girders under different stress loadings. Girder 10
illustrates a girder under static loading Fc. Girder 11 is under
cyclic, fluctuating or dynamic loading Fv. Girder 12 is under
complex loading, i.e., Fc+Fv. FIG. 6b shows the initial stressed
state in the stress concentration area for each of girders 10, 11
and 12 as compared to the stressed state in the same girder after
ultrasonic impact treatment.
[0077] Another exemplary structure is a so-called "socket weld
joint" as shown in FIG. 7a. In FIG. 7a, 20 indicates a socket
welded joint and 21 denotes the ultrasonic impact tool in treatment
of the weld for the joint. The feature of this "socket weld joint"
which is unique is that the joint is generally used in structures
having both fluctuating and alternating loading with a relatively
small thickness in the material forming the welded joint. In this
case, ultrasonic impact treatment of the stress concentration area
in accordance with the invention forms a groove of dimensions and
depth not greater than about 0.15 mm of thickness of the treated
material. FIG. 7b illustrates the joint before and after ultrasonic
impact treatment. Following treatment, the welded joint has a
radius 22 of a minimum of about 0.5 mm, width of greater than zero
and up to about 10 mm, depth of greater than zero and up to about 2
mm and about 0.15 mm of web thickness when the overall thickness is
about 4 mm.
[0078] Thus, the modification of the material properties in the
stress concentration area results in a specific level of
compressive stresses induced in the stress concentration area of
the joint. Conditions for creating such stresses and groove
dimensions related with weld joint dimensions and the thickness of
materials forming the socket weld joint give the socket weld joint
in the aggregate an excellent breaking strength under fluctuating
and cyclic loads that induce stresses above the yield strength of
the joint material in the stress concentration area. FIG. 7c
comparatively shows the cycle stress of the joint before and after
ultrasonic impact treatment. Accordingly, the loading condition and
ultrasonic impact treatment of the weld toe and the load-carrying
component on the side of constant loading and/or localization of
varying loading, initiate the ultrasonic plastic deformation,
creation and distribution of compressive stresses and formation of
a transition between the weld and the base metal so as to
compensate for the influence of static or cyclic or varying
stresses that cause the formation of in-service cracks due to the
stress concentration above the yield point of the base metal along
the weld toe and/or in the root.
[0079] (D) Welded Joints with Defects and Damaged Areas (Including
Cracks)
[0080] The practice of fabrication and operation of welded
structures presents an independent group of problems associated
with the improvement of the life and reliability of welded joints
which have welding defects, material structural defects,
meso-structure damages and cracks.
[0081] The benefits of ultrasonic impact treatment performed in
accordance with the invention makes it possible to provide
properties in welded joints in which the above defects are detected
so as to result in a reliable joint. Of importance for weld joint
modification in such instance are the ultrasonic plastic
deformation, deformations due to external force impulse (impact)
and residual compressive stresses that are introduced into the
material of the welded joint wherein such are within the
above-described parameters for these factors of ultrasonic impact
effect on the material condition.
[0082] Of critical importance in modifying defective welded joints
is ultrasonic plastic deformation, i.e., deformations caused by the
impact and residual compressive stresses introduced into the
material of the welded joint that cover the above-described defects
and retard their development under external forces due to
operational loads.
[0083] The crack is the most common example of a hazardous defect
in a welded joint material. Using differing crack sizes, in fact,
allows for defining the internal condition and simulating the
initial conditions or stages of failure produced by other types of
defects under external forces.
[0084] The hazardous area of all types of welding defects,
including cracks, is the stress concentration area, as shown in
FIGS. 8a-8c. Also shown in FIGS. 8a-8c is the defect retardation
mechanism in the field of compressive stresses caused by the
ultrasonic impact treatment. In FIG. 8a, 30 denotes a defective
welded joint containing a crack before ultrasonic impact treatment
and the stresses present in relation thereto. FIG. 8b illustrates
treatment of the defective area with an ultrasonic impact tool 31
to create a compressive field. FIG. 8c illustrates the welded joint
32 following ultrasonic impact treatment and the change in the
stresses present therein (compare FIGS. 8a and 8c).
[0085] A defect presents the severest hazard when the tension
vector is perpendicular to the plane on which the greatest defect
area is projected. In the case illustrated in FIGS. 8a-8c, the
crack periphery outlines the stress concentration area. When the
defect is subjected to the compressive stress field by means of
ultrasonic impact treatment in accordance with the invention, this
makes it possible to compensate for unfavorable tensile stresses in
the stress concentration area and displace them to a region of the
material where the stress concentration hazard is unlikely.
[0086] In this instance, ultrasonic impact treatment is localized
on the surface, whose dimensions suffice to displace possible
tensile stresses away from the possible stress concentration at a
distance sufficient to maintain resulting compressive stresses
under unfavorable conditions of external force action. The
dimensions of this surface are determined during simulating defect
development and retardation conditions as described herein.
Ultrasonic impact treatment parameters in this case to provide the
desired welded joint include the following: tool pressing force of
greater than zero and no greater than about 10 kg; ultrasonic
impact frequency of greater than zero and no greater than about 500
Hz; prevailing duration of ultrasonic impact of no less than an
average about 1 ms; ultrasonic carrier frequency of greater than
zero and up to about 100 kHz depending on the properties of the
material being treated and the surface condition requirements;
ultrasonic oscillation amplitude of the indenter during impact of
no less than about 30 .mu.m; and impact amplitude of no less than
about 0.2 mm. The impact energy defined in accordance with the
process and expressed by the above parameters and corresponding
indenter mass is set so as to produce compressive stresses in the
plastic deformation area to a depth of no less than about 2 mm and
in the elastic deformation area, to a depth that suffices to
compensate for the residual effect of tensile stresses.
[0087] New properties and welded joint material conditions so
obtained allow compensation for the effect of the dangerous
stresses resulting from operational loading on a given welded joint
and thus also the retardation of the defect development when the
joint is in service.
[0088] (E) Welded Joints with Specified Requirements to
Manufacturing Accuracy
[0089] Geometric accuracy of welded joints is a primary quality and
reliability characteristic. Ultrasonic impact treatment in
accordance with the invention is characterized by a system of
features that guarantees meeting this fundamental technical
requirement. These features essentially include ultrasonic
relaxation (of stresses and deformations), ultrasonic and impulse
plastic deformation (material redistribution), and creation of
compressive stresses (redistribution of tensile and compressive
stresses and deformations).
[0090] Thus, four ways to obtain a specified accuracy in a welded
joint are as follows: (1) ultrasonic impact treatment performed in
accordance with the invention using a rigid attachment (fixed
position) and ultrasonic relaxation of residual welding stresses
caused by fixation, (2) welding without fixation, ultrasonic and
impulse plastic deformation of the weld and base metal in the joint
area in accordance with the invention, material redistribution in
the joint, compensation for shrinkage and thus welding
deformations, (3) combining (1) and (2) above in the ultrasonic
impact treatment, and (4) dividing (differentiation of) weld
shrinkage by directions and ultrasonic impact treatment taking into
account compensation for joint deformations in these
directions.
[0091] The above examples of obtaining welded joints with specified
configuration accuracy requirements are applied over hot (above
ambient temperature) metal during welding or when the weld is
cooled down or over cold (at about ambient temperature) metal after
welding depending on the task and specific conditions of its
solution.
[0092] The technique of weld deformation compensation is shown in
FIGS. 9a, 9b and 9c using, as an example, a symmetric corner welded
joint taking into account a directional weld shrinkage. FIG. 9a
illustrates the welded joint 40 and the tolerances therein. FIG. 9b
illustrates the welded joint after ultrasonic impact treatment with
ultrasonic impact tool 41. Deformations and tolerances are denoted
in FIG. 9b as follows: a and f each indicate residual deformation
after ultrasonic impact treatment, b and e each indicate tolerance,
and c and d each indicate residual welding deformation. FIG. 9c
illustrates schematically deformation compensation direction
matching. While residual welding deformations in the joints are
compensated for by either creating a rigid attachment with
subsequent ultrasonic relaxation of residual welding stresses or
ultrasonic and impulse plastic deformation and redistribution of
the weld metal or by a combination of these effects, and, thus, in
so doing match the direction and magnitude of plastic deformation
of the weld metal with the ratio between its longitudinal and
transverse shrinkage depending on the welded joint type and welding
process.
[0093] During compensation for deformations in directions specified
by the task, the principle is used of selecting the ultrasonic
impact treatment tool marks overlap coefficient (K.sub.o). The
greatest value of K.sub.o corresponds to the direction of greater
residual deformations that should be compensated so as to provide
the specified accuracy, while the smallest value of K.sub.o
corresponds to the direction of smaller residual deformations. The
residual deformations in various directions correspond to the
shrinkage of weld metal and near-weld zone in these directions, and
deformation compensation corresponds to the sum of cumulative
displacements of local volumes of weld metal and near-weld zone
caused by plastic deformation due to ultrasonic impact treatment.
Taking K.sub.o to be positive and equal to the relationship between
the indentation diameter difference and the indentation
center-to-center distance when the surface is fully covered with
tool marks, and the ratio of interindentation distance to
indentation center-to-center distance corresponds to negative
overlap coefficients during intermittent treatment, then ultrasonic
impact treatment provides control of deformation compensation in
specified directions within the range of values, for which the
following is true: 1>K.sub.o>-1.
[0094] Thus, at a tool or workpiece travel speed of about 90 m/min,
K.sub.o becomes positive even at an ultrasonic impact frequency of
500 Hz and the indentation diameter of 3 mm. The actual ultrasonic
impact treatment speed, however, is within the range of greater
than zero and up to about 5 m/min. This emphasizes the reliability
of ultrasonic impact treatment in accordance with the method of the
invention and possible control of K.sub.o within the wide range of
treatment conditions, i.e., pressing force on the tool of about 4
kg and above, impact frequency of about 100 Hz and above, impact
amplitude of about 0.2 mm and above, impact duration of about 1 ms
and above, carrier ultrasonic frequency of no less than about 15
kHz, ultrasonic vibration amplitude during impact of no less than
about 30 .mu.m when steels and high-strength alloys are treated and
greater than zero and no greater than about 30 .mu.m when aluminum
alloys and metals with a yield strength of up to 350 MPa are
treated.
[0095] (F) Repaired Welded Joints
[0096] Repaired welded joints covers a wide area of fabrication and
operation of welded structures, e.g., repair of weld defects,
failures and cracks, strengthening structures and elements thereof,
as well as providing additional improvement in structural stability
and load-carrying capacity and correcting structural configuration
in the process of fabrication and operation. At the same time,
repairs of welded joints are a source of residual welding stress,
deformation, and stress concentration area and, thus, unregulated
metal fatigue.
[0097] Ultrasonic impact treatment conducted in accordance with the
invention solves these problems and results in welded joints
repaired to have improved properties, i.e., a level of residual
stresses not greater than about 0.5 of the yield strength of the
welded joint material, residual welding deformations not greater
than 100% of the dimensional tolerance specified for a given joint,
and fatigue resistance of not less than that of the base metal of
the given welded joint.
[0098] The mechanism of action on a repaired welded joint, and
cracks and stress redistribution due to ultrasonic impact treatment
are illustrated in FIGS. 10a to 10d.
[0099] As shown in FIG. 10a, the crack in a plane perpendicular to
tensile forces or in a spatial surface close to the plane creates a
concentration of stresses that is many times greater than normal
design stresses due to such forces.
[0100] A repaired welded joint somewhat improves the situation.
However, it produces a new residual tensile stress concentration at
the ends of the repair welding caused by the longitudinal shrinkage
of the weld deposition (FIG. 10b).
[0101] Ultrasonic impact treatment in accordance with the invention
(FIG. 10c) redistributes unfavorable residual tensile stresses that
are replaced by compressive stresses in the hazardous weld
deposition area (FIG. 10d). As this takes place, tensile stresses
move into the region of normal stresses that is safe for the welded
joint load-carrying capacity and can be calculated using standard
procedures.
[0102] Ultrasonic impact treatment of a repaired welded joint, as
defined by the task served by the joint, is applied in the course
of welding to the metal being cooled and to the cold metal.
[0103] Thus, to improve the quality of the weld metal and its
resistance to structural defect formation, ultrasonic impact
treatment in accordance with the invention is done during welding.
In order to compensate for residual welding deformations and
stresses localized in the repair welded area, ultrasonic impact
treatment in accordance with the invention is done upon the metal
being cooled. Ultrasonic impact treatment is done on the cold
(ambient temperature) metal to harden welded joint metal, create
favorable compressive stresses in hazardous areas, and replace and
relax hazardous tensile stresses.
[0104] In doing so to provide the welded joint, the pressure upon
the ultrasonic tool during manual treatment of steels is about 3 kg
and above, which may increase up to 20 kg in the case of mechanized
treatment, the impact frequency is not less than about 80 Hz, the
impact frequency is not less than about 0.2 mm, the impact length
is not less than on average about 1 ms, the carrier frequency of
indenter ultrasonic vibrations is about 15 kHz and above, the
ultrasonic vibration amplitude during impact is not less than about
20 .mu.m when hot (above ambient temperature) metal is treated and
not less than about 30 .mu.m when treating metal being cooled and
cold metal. When weld deposits of aluminum alloys are treated, the
ultrasonic vibration frequency is reduced by up to 40% subject to
the strength of material.
[0105] (G) Corner Joints with Incomplete Penetration Protected from
Root Cracking
[0106] A welded joint protected against root cracking and having a
load-carrying capacity is obtained by selecting type and dimensions
of a weld joint with complete, partial or incomplete penetration.
Achieving such is particularly difficult when the joint has partial
or incomplete penetration.
[0107] The cause of root crack formation is primarily associated
with the flank angle of the weld metal with the web end and flange
plane in a gap between them, as may be exemplified by a corner
joint. In the case of a negative (acute) flank angle, the crack
formation directly results from the stress concentration in this
area of the welded joint.
[0108] Ultrasonic treatment of a weld joint, performed during
welding, solves this problem by changing heat exchange conditions
at the boundary between the molten metal and the solid metal in the
root of the weld. This phenomenon may be explained as follows.
Ultrasonic impact during welding causes an impulse and ultrasonic
stress wave to propagate in the weld metal and thus the molten
metal. As a result, strong acoustic flows are formed at the
molten-solid metal boundary in the weld root that contribute to
heat exchange activation and hence greater penetration of the
surface of metal forming the gap between web and flange in this
area. Thus, based on the procedure invention, an instrument to
control the penetration configuration of the web and flange metal
in the weld root may be provided, thereby resulting in a
substantially new appearance of a welded joint having positive
(obtuse) flank angles of the weld metal with the flange surface and
web end, which, in turn, insure that a given welded joint is
resistant to stress concentration and fatigue crack formation in
the weld root.
[0109] The formation of a weld joint protected from root crack
formation by positive (obtuse) flank angles of the weld metal with
the web and flange metal in the gap between them is shown in FIGS.
11a and 11b. FIG. 11a illustrates a weld 50 made without ultrasonic
impact treatment. FIG. 11b illustrates a weld 51 subjected to
ultrasonic impact treatment using an ultrasonic impact tool in an
initial operating position 52 during welding and a continuing
operating position 53.
[0110] The selection of the tool angle and ultrasonic impact
treatment areas, as shown in FIGS. 11a and 11b, allow formation in
the molten pool of acoustic flows specifically directed relative to
the pool boundaries. This, in turn, offers possibilities for
control of the flange and web metal fusion penetration intensity in
directions where the weld metal favorably meets the base metal.
[0111] Thus, when the flange side face is subjected to ultrasonic
impact treatment (operating position 53 FIG. 11b), the
prerequisites are created for better fusion of the flange metal as
compared to the web. A close effect can be obtained by increasing
the tool angle relative to the flange plane by more than 450 (the
position 52 in FIG. 11b). A choice of treatment conditions, tool
angles and positions during treatment depends on the welding
process, material and dimensions of a welded joint. The
above-mentioned preferred ultrasonic impact treatment conditions to
provide welded joints of this type made of carbon steels include:
tool pressing force of about 3 kg and above during manual
treatment, greater than zero and up to about 25 kg during
mechanized treatment; impact frequency of greater than zero and up
to about 800 Hz; impact amplitude of about 0.2 mm and above;
ultrasonic vibration carrier frequency of about 18 kHz and above;
ultrasonic vibration amplitude during impact of greater than zero
and up to 20 .mu.m in a temperature range of above about
400.degree. C. and not less than about 30 .mu.m in a temperature
range below about 400.degree. C.; and ultrasonic impact duration of
on average of not less than about 1 ms.
[0112] With favorable redistribution of the weld metal between the
flange and the web, ultrasonic impact treatment in accordance with
the invention reduces residual welding stresses by a minimum of 40%
of standard mode of deformation of the as-welded joint.
[0113] Concurrent with the heat exchange activation effect
described above, the ultrasonic impact in accordance with the
invention initiates a surface tension reduction effect for the
molten metal and, as a consequence of this phenomenon, increases
the fluidity of the molten metal. That is, ultrasonic and impulse
stress waves are transferred to materials being welded through the
weld metal as a result of the ultrasonic impact treatment and
increase the yielding and hence the flowability of the molten metal
on the web and flange ends in the gap between them. The temperature
of the molten pool, activated by the acoustic flow, additionally
fuses the edges, forming a concave meniscus similar to that in
capillary as shown in FIGS. 12a and 12b. It was established that
the molten metal fluidity increases within a wide range of
ultrasonic vibration carrier frequencies of up to 300 kHz and
ultrasonic impact repetition rates of up to 2500 Hz. Ultrasonic
impact treatment parameters are defined in accordance with the
process of the invention depending on the properties of welded
materials and consumables, the type and sizes of welded joints, the
welding process and conditions. In the schematic representation of
a welded joint as shown in FIGS. 12a and 12b, FIG. 12a shows a weld
60 not subjected to ultrasonic impact treatment and the crack
formed therein. FIG. 12b shows a weld 61 subjected to ultrasonic
impact treatment. The meniscus in the weld root is denoted by 62.
The ultrasonic impact tool is shown in an initial operating
position 63 on the weld and in a continuing operating position 64
during treatment of the weld. The corner welded joint, with
incomplete and/or partial penetration, made with ultrasonic impact
treatment conducted within the parameters of the invention during
making a root run over the weld metal, flange or web, results in
the molten metal filling the gap (under ultrasonic impacting)
between the stiffener or web end and the flange or web plant with
or without diffusion or adhesion bonds between the weld and the
base metal in the gap producing a meniscus 62 and fusing of the
sharp edges upon solidification from smooth transitions between
base and weld metals, thereby increasing the resistance of a given
welded joint to stress concentration effect and fatigue crack
formation in the root of the weld.
[0114] Thus, one further mechanism makes possible positive (obtuse)
flank angles of the weld metal with the web end and flange surface
as a result of ultrasonic impact treatment in accordance with the
invention. This explains how a new welded joint is formed that is
protected from root crack formation due to stress concentration and
fatigue.
[0115] (H) Spot Welded Joints
[0116] A specific task associated with the need to increase quality
and reliability of a welded joint based on fatigue resistance
criterion relates to spot welding. A primary problem is that the
danger zone in the weld joint area is inaccessible for conventional
stress concentration treatment techniques. This necessitates
modifying a mode of deformation of a welded joint across the whole
thickness of the materials being welded. Thus, the dangerous heat
affected zone must be considered to include stress raisers and
represent a circle or ring with an average diameter that is equal
to the diameter of a circle along the boundary of a welded
joint.
[0117] A spot welded joint made using ultrasonic impact treatment
in accordance with the invention features a high level of
ultrasonic plastic and impulse deformation across the whole metal
thickness in the weld area, the fatigue limit being a minimum of
about 1.3 times greater than that of an untreated joint and having
an ultimate strength of not less than that of the base metal.
[0118] A schematic representation of a spot welded joint is shown
in FIGS. 13a-13e. FIG. 13a illustrates at 70 an untreated spot
welded joint and stresses in relation thereto. FIG. 13b shows an
ultrasonic impact tool 71 in treatment of a spot weld in
conjunction with a stop plate 73. In FIG. 13c, two ultrasonic
impact tools 71 and 72 are utilized in relation to a spot weld.
FIG. 13d is a close-up of the point of contact of impact from a
stop plate or tool 74 and tool 75 as to the spot weld. FIG. 13e
shows at 76 a treated joint and stresses in relation thereto.
[0119] Ultrasonic impact treatment of a spot welded joint can be
done during welding (when the welding electrode at the same time
presents the vibration velocity concentrator or indenter) and after
welding. The indenter can have a round, flat and circumferential
working surface depending on the welded joint size and its
post-welding condition.
[0120] In fact, ultrasonic impact treatment can be applied using
passive or active resonance acoustic decoupling, passive
non-resonance acoustic decoupling and a rigid stop block serving as
an "anvil". It means that plastic deformations in the welded joint
area may be formed sequentially from each side and simultaneously
from both sides.
[0121] As shown in FIG. 13a, the risk area of the spot welded
joint, where the maximum tensile stresses operate, is localized at
the "spot weld" boundary and is positioned in the operational
stress critical concentration zone.
[0122] Ultrasonic impact treatment in accordance with the invention
completely subjects the welded joint to the favorable compressive
stress area and displaces the tensile stress area to the zone
without any structural prerequisites for stress concentration.
[0123] Thus, based on the experimental data, ultrasonic impact
treatment in accordance with the invention, increases the fatigue
limit of a spot weld by at least about 1.3 times and improves the
fatigue resistance, yield points, ultimate strengths and impact
strength to the level not below that of the base material.
[0124] To obtain spot welded joints made of carbon steels and
aluminum alloys, ultrasonic impact treatment conditions include the
following and vary within the described amounts based on the joint
type and material: ultrasonic impact frequency of not less than
about 80 Hz, impact duration of not less than on average about 1 ms
at an amplitude of not less than about 0.2 mm, indenter ultrasonic
vibration carrier frequency during impact of greater than zero and
up to about 100 kHz, ultrasonic vibration amplitude during impact
in a range of from about 5 to 40 .mu.m, and tool pressure from
about 3 to 30 kg. The stabilization of the resonance frequency of
the system "tool-welded joint within a structure" during welding
with ultrasonic impact treatment or during ultrasonic impact
treatment is the method treatment termination criterion for such
types of welded joints.
[0125] (I) Lap Welded Joints and Tack Welds
[0126] Lap or tack welded joints are extremely prone to cracking at
weld ends with cracks quickly propagating on short weld portions.
Crack formation in these joints is mainly due to welding defects,
unfavorable weld toe angles, stress concentration, the loss of the
local stability and strength of a joint, and fatigue. These
problems can be solved by creating a welded joint, which is
subjected to ultrasonic impact treatment in accordance with the
invention to result in the formation of a smooth transition between
the weld and base metal. At the same time, such transitions at the
tack weld end and along the weld toe line are subjected to
ultrasonic plastic deformation, while the fatigue limit of the tack
weld is a minimum about 1.3 times greater as compared to the
untreated condition, and the fatigue resistance, ultimate strength
and impact strength are not less than that of the base metal. A
schematic representation of a welded joint and the mode of
deformation thereof due to ultrasonic impact treatment is shown in
FIGS. 14a to 14c. FIG. 14a shows an untreated lap joint and
stresses 80 in relation thereto. FIG. 14b illustrates a lap joint
during treatment with an ultrasonic impact tool 82 to create
compressive stress areas as denoted thereon. FIG. 14c illustrates
the treated lap joint 84 and the stresses associated therewith.
[0127] More specifically, FIG. 14a shows that maximum tensile
stresses are localized at tack weld ends due to longitudinal and,
to a lesser extent, transverse weld shrinkage. This situation is
aggravated by the fact that the tack weld end area coincides with
the operational stress concentration area.
[0128] Ultrasonic impact treatment in accordance with the invention
changes the nature of the welded joint mode of deformation,
redistributes tensile stresses, replaces these by compressive
stresses and displaces tensile stresses due to operational loads to
the welded joint region where stress concentration is unlikely to
occur. Ultrasonic impact treatment in accordance with the invention
improves the resistance of a given welded joint to formation of
cracks caused by the stress concentration due to design features of
a given joint and metal fatigue under the unfavorable nature of
variable and reversed loading cycles.
[0129] Thus, in parallel with residual stress redistribution, the
improvement of a given welded joint resistance to crack formation
is also achieved by modifying material properties of the welded
joint during ultrasonic plastic deformation thereof, as shown in
FIGS. 14a-14c.
[0130] Parameters of ultrasonic impact treatment in accordance with
the invention which provide the desired welded joint include the
following: ultrasonic impact frequency of greater than zero and up
to about 2000 Hz, ultrasonic impact length of not less than on
average about 1 ms, impact amplitude of not less than about 0.2 mm,
indenter ultrasonic vibration carrier frequency of about 18 kHz and
above, indenter ultrasonic vibration amplitude during impact of not
less than about 25 .mu.m for carbon steels and not greater than
about 30 .mu.m for aluminum alloys, tool pressure against a treated
surface of about 3 kg and above.
[0131] (J) Corner Welded Joints
[0132] It is a difficult technical problem to obtain manufacturing
accuracy and high fatigue resistance of corner welded joints with a
groove varying along the joint perimeter, as well as with a varying
flank angle of less than 90.degree. and complete weld penetration.
This problem is aggravated by specific welding stress and
deformation distribution present, as well as the joint fatigue
limit dependence on the geometric conditions of the formation of a
complex oriented in the space joint along the weld perimeter.
[0133] Ultrasonic impact treatment performed in accordance with the
invention during welding and over cold metal makes possible a
specified dimensional accuracy along the perimeter of such a
complex joint and increases fatigue limit at a minimum by a factor
of 1.3. A schematic representation of a corner welded joint with a
groove varying along the perimeter and an angle of less than
90.degree. treated by ultrasonic impact treatment is shown in FIGS.
15a and 15b. The welded joint is denoted as 90 and the weld as 91.
The ultrasonic impact tool 93 is shown in different weld treatment
positions.
[0134] Corner welded joints with an angle between the web and
flange of <90.degree. and with a through or incomplete
penetration are widely used, which brings to the forefront the
problem of technical cost minimization, providing therewith a
dimensional accuracy and appropriate fatigue limit and life span.
Ultrasonic impact treatment in accordance with the invention solves
this problem by ultrasonic and impulse compensation for
longitudinal and transverse weld shrinkage, symmetric angle
deformation of the flange relative to the web, material properties
and condition modification in the stress concentration area. This
provides for a weld joint wherein the angles between the web and
flange are <90.degree., and obtaining a specified joint
dimensional accuracy as well as increased fatigue limit and life
span not less than a factor of 1.3 and 10 respectively.
[0135] A schematic representation of a welded corner joint in
accordance with the invention is shown in FIGS. 16a and 16b. FIG.
16a shows the work pieces 100 for forming a corner prior to
welding. FIG. 16b illustrates the work pieces including corner
welds 101 being treated by ultrasonic impact tools 102. Following
ultrasonic impact treatment, modifications are present in the
properties of the treated material. Deviation from specified
dimensions after ultrasonic impact treatment is within the
tolerances for longitudinal and cross deformations. The fatigue
limit of the welded corner joint after treatment is a minimum of
1.3 times greater over that of a welded corner joint in an
untreated condition. The life span of the welded corner joint after
treatment is a minimum of 10 times greater than that of the welded
corner joint in an untreated condition.
[0136] Thus, the fabrication and maintenance of corner welded
joints with varying and "constant" groove beveling angles, as shown
in FIGS. 15a-15b and 16a-16b, is associated with the need to search
for engineering solutions that through minimum production costs
provide, on one hand, the requisite accuracy of such joints and on
the other hand, a specified life thereof.
[0137] The accuracy of corner welded joints should ensure their
service reliability, design load-carrying capacity and external
loading resistance. The endurance of the welded joints should
ensure a life time expressed through the resistance of the welded
joints to varying and reversed loads.
[0138] The welded joint accuracy is generally achieved by heat
treatment and using a costly conductor tool set. The endurance of
the welded joint is achieved through special approaches to
selection of the base metal and welding consumables, greater weld
dimensions and the heat treatment for residual stress
reduction.
[0139] Ultrasonic impact treatment in accordance with the invention
minimizes production costs, eliminates the need for heat treatment
and the use of large amounts of weld metal in the weld. This is
achieved through ultrasonic relaxation and redistribution of
residual welding stresses and deformations, as well as by modifying
welded joint material properties to be at the level of the base
material in the area affected by ultrasonic plastic deformations of
the welded joint material.
[0140] Ultrasonic impact treatment in accordance with the invention
may be applied to the hot metal during welding, to the metal during
cool down or to cold metal after welding, depending on the
production conditions and welding process.
[0141] The results of the ultrasonic impact application in
accordance with the invention are obtained by layer treatment of
the weld metal, formation of the deconcentration groove in the
stress concentration area, and in-process or on-line control of the
ultrasonic impact treatment results in the course of treatment.
[0142] Ultrasonic impact treatment conditions for corner welded
joints in accordance with the invention include: ultrasonic impact
frequency of up to about 1200 Hz, ultrasonic impact length of not
less than about 1 ms, impact amplitude of not less than about 0.2
mm, indenter ultrasonic vibration carrier frequency of about 18 kHz
and above, indenter ultrasonic vibration amplitude during impact of
not less than about 25 .mu.m for carbon steels and not greater than
30 .mu.m for aluminum alloys, tool pressure against the treated
surface of about 3 kg and above subject to manual or mechanized
treatment.
[0143] (K) Liquation, Grain Size, Degassing and Pores
[0144] Welded joints made with a high volume of a molten pool under
conditions of long duration and long cooling of the weld metal are
prone to liquation. This phenomenon is mainly explained by the
growth of large grains and the direction of molten pool
crystallization from its boundaries with the base metal to the
center.
[0145] Ultrasonic impact treatment concluded within the parameters
of the invention during welding and cooling down of the weld metal
solve this problem on the basis of the volume ultrasonic
crystallization of the molten metal and the ultrasonic and impulse
recrystallization of large grains. Volume crystallization in the
molten pool occurs due to acoustic flows and enhanced cavitation
caused by ultrasonic vibrations originating from the ultrasonic
wave propagating along the weld as a result of the effect thereupon
of ultrasonic impacts. Weld metal and near-weld area are
recrystallized under direct action of the ultrasonic impact upon
the weld and the near-weld metal being cooled down. This provides
specified weld metal phase homogeneity across the weld section in
all directions. A weld joint with structural phase homogeneity can
be formed in accordance with the schematic representation as shown
in FIGS. 17a and 17b wherein representative portions are enlarged.
FIG. 17a illustrates a weld having liquation 110 in the center of
the weld. FIG. 17b illustrates an ultrasonic impact tool 112
treating the weld within the parameters of the invention to provide
a weld with ultrasonic impact activated crystallization 111. Impact
is provided across the weld shown in FIG. 17b as indicated by the
arrows and the tool 112 shown in solid and broken lines.
[0146] The most important characteristics responsible for weld
joint reliability, such as impact strength, yield and ultimate
strengths, stringiness and crack resistance at sub-zero, and high
and ambient temperatures, depend on the grain size. Ultrasonic
impact treatment performed within the parameters of the method at a
distance from the arc corresponding to the maximum sensitivity of a
molten metal to the crystallization center formation and
solidifying metal to grain recrystallization in the process of a
grain growth successfully solves this problem. A new type of weld
joint is thus created which meets the stringent mechanical strength
requirements and possesses specified physical and mechanical
properties because of the fine grain structure of the weld metal
and heat affected zone. A schematic representation of how such a
joint is obtained is shown in FIGS. 18a and 18b. FIG. 18c
graphically illustrates the mechanical strength and impact
strength, which results from ultrasonic impact treatment, for the
joints. FIG. 18a shows a weld 120 (with enlarged portion for
illustration) which was not subjected to ultrasonic impact
treatment. FIG. 18b shows a weld 121 with ultrasonic impact
activated crystallization (shown in the illustrative enlarged
portion) by treatment with an ultrasonic impact tool 122 which
moves across the weld in accordance with the arrows and tool shown
in solid and broken lines. FIG. 18c sets forth data as to weld 120
and weld 121.
[0147] One of the basic quality criteria for a welded joint is the
presence or absence of pores in the weld metal. This property is
chiefly determined by the molten pool degassing efficiency in the
process of welding. Ultrasonic impact treatment in accordance with
the invention makes an effective solution for this problem possible
based on the initiation of molten pool ultrasonic degassing in the
process of welding.
[0148] This effect is achieved by ultrasonic impact treatment
performed over the weld metal or associated metal using the
parameters set forth above at a distance from the arc that
corresponds to a molten pool liquid phase, which is equivalent to
the minimum solubility of gas inclusions in the weld metal. The
welded joint and a schematic representation of its degassing are
shown in FIGS. 19a and 19b. FIG. 19a illustrates a weld 130 not
subjected to ultrasonic impact treatment and having visible pores
in the root area of the weld. In FIG. 19b, the weld 131 was treated
with ultrasonic impact to activate degassing so no pores are
visible. Treatment with an ultrasonic impact tool 132 is across the
weld as indicated by the arrows and the tool 132 shown in solid and
broken lines.
[0149] Thus, described are three possible applications of
ultrasonic impact treatment in accordance with the invention during
welding that are directed toward producing welded joints with new
properties such as liquation resistance at great volumes of molten
metal, reliable recrystallization and fine-grain structure
formation, and weld metal resistance to pore formation.
[0150] Effects of ultrasonic impact treatment in accordance with
the invention upon the molten metal's behavior, structure and
properties of the weld metal and the joint as a whole are based on
the corresponding method choice of the distance of the ultrasonic
impact area from the molten pool and the ultrasonic impact
parameters. In each specific case the selection criteria of the
ultrasonic impact treatment area location performed in accordance
with the invention relative to the welding area are the temperature
ranges of effective crystallization and recrystallization of the
molten metal and weld metal respectively, as well as the
temperature range of the minimum gas solubility in the molten pool.
In this case, the parameters of ultrasonic impact treatment in
accordance with the invention, subject to properties of the treated
material and the temperature at the ultrasonic impact treatment
area, are set within the following ranges: tool pressure from about
0.1 to 50 kg, ultrasonic vibration carrier frequency at the
transducer of from about 10 to 800 kHz, ultrasonic vibration
amplitude under no-load conditions and during impact at a carrier
frequency of from about 0.5 to 120 .mu.m, tool self-oscillation
amplitude of from about 0.05 to 5 mm, and the average ultrasonic
impact duration of not less than about 1 ms.
[0151] (L) Diffusion Hydrogen
[0152] Welded joints with stringent brittle fracture resistance
requirements made of steels, specifically ferritic steels, are
preliminarily or concurrently heated before and during welding to
expel diffusion hydrogen from the joint metal. This results in a
high temperature at the operator's work place, pollution of the
environment and an increase in residual welding deformations caused
by the added heating of the structure.
[0153] Ultrasonic impact treatment performed in accordance with the
invention during welding at a distance from a molten pool and/or
over cold metal of edges or after welding with intensity and
spectrum of ultrasonic impact that jointly correspond to the
maximum mobility of diffusion hydrogen produces a welded joint with
high resistance to brittle fracture. Thus, preliminary and
concurrent heating requirements are minimized.
[0154] A schematic representation of a welded joint is shown in
FIGS. 20a and 20b. FIG. 20c is a graph showing the minimization of
residual diffusion hydrogen content in the metal of the joint after
ultrasonic impact treatment. FIG. 20a shows a weld 140 (with an
illustrative enlarged section) not subjected to ultrasonic impact
treatment and thus has visible pores. FIG. 20b shows weld 141 (with
illustrative enlarged section) with activated crystallization (no
pores) due to the cooling down or cold edge preparation being
accompanied by ultrasonic impact treatment using tool 142 which is
moved across the weld during treatment in accordance with the
arrows and the ultrasonic impact tool 142 shown in solid and broken
lines. Treatment occurs within the parameters described below. FIG.
20c shows permissible hydrogen content limits for steel. It is
conventional that prior to welding, the permissible level of
residual hydrogen in the welded joint metal should not exceed 5
cm.sup.3/100 g for steel. FIG. 20c shows the hydrogen content for
the welds shown in FIGS. 20a and 20b as indicated by the
corresponding reference numbers.
[0155] Ultrasonic impact treatment of welded joints in accordance
with the invention is performed, with consideration for the fact
that the metal is prone to hydrogen saturation, in any production
conditions: over cold edges before welding or over edges some
distance ahead of the molten pool during welding, or over the weld
metal some distance following the welding pool during welding, or
over the weld metal after welding within a certain temperature
range in fabrication of new structures, reengineering thereof,
preventive maintenance or repair.
[0156] For all conditions referenced above, prior to treatment in
accordance with the process of the invention, the temperature range
or temporary conditions are determined that provide for effective
diffusion hydrogen removal and maintaining metal in this state.
[0157] From the saturation diagram shown in FIG. 21, it can be seen
that ultrasonic impact treatment in accordance with the invention
reduces the content of diffusion hydrogen within a wide temperature
range by at least 2 times.
[0158] Parameters of ultrasonic impact treatment in accordance with
the invention that ensure the results presented above include:
ultrasonic impact frequency of up to about 2500 Hz, ultrasonic
impact amplitude of not less than about 0.2 mm, average statistical
length of ultrasonic impacts of not less than about 1 ms,
ultrasonic vibration carrier frequency of about 15 kHz and above,
ultrasonic vibration amplitude during impact of not less than about
15 .mu.m depending on the temperature and grade of the metal being
treated and not less than about 30 .mu.m when cold metal is
treated, pressing force on the tool against a treated surface of
not less than about 5 kg for manual treatment and not less than
about 10 kg during mechanized treatment.
[0159] (M) Aggressive Environment--Stress Corrosion (Treatment
Before and During)
[0160] Resistance of a weld joint to stress corrosion damage or
failures under fluctuating loading defines the reliability and life
of a loaded structure with a long operational cycle. Main pipelines
and offshore platforms are examples of such structures. Their
protection against stress corrosion is very costly.
[0161] Treatment to provide new properties in accordance with the
invention solves this problem. Described below are the main
parameters of ultrasonic impact treatment effect on a metal surface
in aggressive environment under stressed conditions or fluctuating
loading:
[0162] a roughness which is not less than 5 .mu.m at a sampling
length of 0.8 mm and waviness which is not less than 15 .mu.m at a
sampling length of 2.5 mm,
[0163] compressive stresses in the area of ultrasonic and impulse
deformation which are not less than the material yield
strength,
[0164] depth of plastic deformation and introduced residual
compressive stresses which are not less than 1.5 mm, and
[0165] amorphous microstructure modification with the formation of
a white layer depending on the material properties which is not
less than 50 .mu.m.
[0166] Since surface and material properties are transformed,
stress corrosion resistance of the joint is increased at least by a
factor of 2 ultimate corrosion-fatigue strength increased by at
least 1.3 times and the life increased by at least 7 times under
various loading in a corrosive environment as compared to the joint
in an untreated condition. It is significant that these properties
pertain equally to newly welded joints and welded joints in
operation.
[0167] The results and properties of welded joints made of steel
with high carbon content and subjected to ultrasonic impact
treatment are shown in FIG. 21. It is shown in FIG. 21 that
following the irregular corrosion, which is typical to occur on the
surface of any material, the stable process occurs, wherein the
corrosion rate of the layer treated by ultrasonic impact treatment
in accordance with the process is a minimum of 4 times less than
that of the as-welded metal based on the experimental data. A
minimum equivalent time during which the carbon steel treated by
ultrasonic impact treatment in accordance with the invention
resists stress corrosion in sea water is 10 years.
[0168] Parameters of ultrasonic impact treatment in accordance with
the invention that ensure the results presented above include:
ultrasonic impact frequency of up to about 500 Hz, ultrasonic
impact amplitude of not less than about 0.5 mm, average duration of
ultrasonic impacts of not less than about 1 ms, ultrasonic
vibration carrier frequency of about 15 kHz and above, ultrasonic
vibration amplitude during impact of not less than about 20 .mu.m,
and pressing force on the tool against a treated surface of not
less than about 5 kg.
[0169] (N) Holes in Welded Joints
[0170] The practice of welded structure operation is associated to
a certain extent with the need to use holes as a crack arrest means
in an area near or within a welded joint. Damage in such joints may
develop not only from the crack stopped by such holes, but also
from the holes themselves. The reason is in the surface tearing
produced during making of the holes, which become stress
concentration areas in operation which in turn cause fatigue.
[0171] To obtain a reliable welded joint with crack arrest holes,
ultrasonic impact treatment in accordance with the invention is
first applied to both crack sides and then to the hole. A hole is
treated where the metal is damaged during the making of the hole at
the entrance and exit regions, but not less than 1/5 of the hole
depth from the damaged side. Residual compressive stresses, not
less than the material yield strength, are formed in the layer
subjected to ultrasonic and impulse plastic deformation. It is
noted that the indenter shape in this case is chosen to provide
free access to the damaged portions of the hole.
[0172] A schematic diagram of a welded joint with holes and the
results of the treatment are shown in FIGS. 22a and 22b. FIG. 22a
illustrates a crack between two holes in a weld 150 prepared using
conventional tip drilling which results in known associated
stresses. FIG. 22b illustrates a crack between two holes in a weld
151 prepared with conventional tip drilling followed by ultrasonic
impact treatment with an impact tool 152. Associated stresses which
result from the tip drilling are altered due to formation of the
compressive stress area 153. FIG. 22b also illustrates the needle
indenter 154 of the ultrasonic impact tool 152 and the manner of
treating the holes 155 and edges of holes 156 to result in the
tearing of material in the holes at the end of the cracks. It is
shown that tensile stresses in the hole area after drilling thereof
are replaced by compressive stresses and possible tensile stresses
are displaced into the region of the structure where operational
stress concentration and hence fatigue crack initiation is unlikely
to occur.
[0173] Parameters of ultrasonic impact treatment in accordance with
the invention that ensure the results presented above for a widest
range of metals include: ultrasonic impact frequency of up to about
500 Hz, ultrasonic impact amplitude of not less than about 0.5 mm,
average duration of ultrasonic impacts of not less than about 1 ms,
ultrasonic vibration carrier frequency of 15 kHz and above,
ultrasonic vibration amplitude during impact of not less than about
30 .mu.m, pressing force on the tool against a treated surface of
not less than about 5 kg.
[0174] (O) Brackets
[0175] Weld joints of brackets with a radius cutout where a bracket
plane intersects the main weld are a typical welded joint that is
extensively used in the fabrication of welded structures. The most
dangerous components of such a structure are the weld ends in the
cutout area and the weld toe line when the bracket is welded to a
panel. Dimensional accuracy in such a joint also presents a very
significant problem.
[0176] Ultrasonic impact treatment of the weld along the bracket
and weld end in a radius cutout when within the parameters of the
invention results in a weld joint that meets dimensional accuracy
requirements with a minimum increase in fatigue resistance of 1.3
times that of an untreated joint.
[0177] A schematic representation of a bracket welded joint prior
to and after ultrasonic impact treatment are shown in FIGS. 23a and
23b. The bracket panels 160 have cracks 161 in the areas of bracket
welding in the absence of ultrasonic impact treatment. The bracket
plane intersects the main weld wherein a connection with the panel
is made by longitudinal fillet welds relative to the bracket end in
a radius cutout. FIG. 23b shows a bracket treated by ultrasonic
impact to provide treatment zones 162. Ultrasonic impact treatment
of the weld along the bracket and at the weld end in the radius
cutout insures that the welded joint meets dimensional accuracy
requirements and results in a minimum increase in fatigue
resistance of 1.3 times as compared to the same properties in an
untreated bracket structure.
[0178] When the weld end in the cutout area is treated by
ultrasonic impact treatment in accordance with the invention
special tool heads are used to provide an access for the indenter
to this area.
[0179] Parameters of ultrasonic impact treatment in accordance with
the process of the invention which ensure the results presented
above for a widest range of metals include: ultrasonic impact
frequency of up to about 300 Hz, ultrasonic impact amplitude of not
less than about 0.5 mm, average duration of ultrasonic impacts of
not less than about 1 ms, ultrasonic vibration carrier frequency of
about 15 kHz and above, ultrasonic vibration amplitude during
impact of not less than about 30 .mu.m, pressing force on the tool
against the treated surface of not less than about 3 kg.
[0180] (P) Welded Joints Prone to Martensite Formation
[0181] When residual welding deformation should be minimized,
intense forced cooling of a welded joint immediately following the
welding process is used in some specific cases. This causes a
well-known hardening effect, especially in carbon steels, that is
accompanied by expelling martensite and the formation of a joint
having limited ductility. Martensite decomposition is achieved by
additional forced heating of the joint and soaking of the joint for
a long time within a narrow specified temperature range. This
procedure has a large energy consumption, is complex as regards
achieving the conditions of heating and soaking within the narrow
temperature range and is characterized by insufficient consistency
of results.
[0182] Ultrasonic impact treatment of this type of joint within the
parameters of the invention at a distance from the heating arc
corresponding to the temperature of martensite decomposition and
its replacement by sorbite or tempered martensite, changes the
welded joint structure in a temperature range which is a minimum of
1.5 times greater than the bottom boundary of this range, while the
range itself is a minimum 2 times greater than that required in
welding to reduce the likelihood of martensite formation under the
above-mentioned conditions in the absence of ultrasonic impact
treatment. As this takes place, the martensite decomposition time
is reduced by at least 10 times. This produces a weld joint with a
radically increased process temperature range of martensite
decomposition, while the average temperature of the range is
reduced relative to standard conditions required to solve this
problem.
[0183] A diagram of supercooled austenite (martensite)
decomposition is shown in FIG. 24 for an exemplary sample of steel
12XH3. Lines 1 indicate martensitic transformation at a temperature
T1 for a sample not subjected to ultrasonic treatment. A sample, as
indicated by lines 2, subjected to ultrasonic impact treatment
according to the invention has martensitic transformation at
temperature T2. T1>T2. It is shown in FIG. 24 that the
martensite decomposition process during standard heat treatment can
occur within the temperature range from 495.degree. to 430.degree.
C. for a minimum of 3 hours. During ultrasonic impact treatment in
accordance with the invention the same process can last for 3-4
min. within the temperature range of 260.degree. to 39020 C.
[0184] Parameters of ultrasonic impact treatment in accordance with
the invention that ensure the results presented above for a widest
range of metals include: ultrasonic impact frequency of up to about
800 Hz, ultrasonic impact amplitude of not less than about 0.5 mm,
average duration of ultrasonic impacts of not less than about 1 ms,
ultrasonic vibration carrier frequency of about 15 kHz and above,
ultrasonic vibration amplitude during impact of not less than about
30 .mu.m, pressing force on the tool against a treated surface of
not less than about 10 kg.
[0185] This produces a weld joint with a radically increased
process temperature range of martensite decomposition, while the
average temperature of the range is reduced relative to a standard
conditions required to solve this problem within a period of the
actual flow-line automatic or computer-aided production of welded
structures.
[0186] (Q) Welded Joints with Protective and/or Hardening
Coating
[0187] The maintenance of welded joints is associated in many
respects with the need for their protection or hardening by using
various metallic or nonmetallic coatings. In such a case, the use
of any type of mechanical operation, including the known methods of
plastic deformation of the weld, near-weld area and weld toe, is
limited by the coating integrity required.
[0188] Treating with ultrasonic impact in accordance with the
invention solves the above problem and makes it possible to produce
welded joints with specified new properties since the ultrasonic
impact treatment can be conducted over the coating. In this case,
the integrity and improvement in properties of protective or
hardening coatings are obtained along with specified properties in
the welded joint.
[0189] An example of such a welded joint is shown in FIGS. 25a, 25b
and 25c. FIG. 25a illustrates a weld before coating and ultrasonic
impact treatment. FIG. 25b illustrates the same weld after a
coating 170 is applied and before ultrasonic impact treatment of
the coated weld. In FIG. 25c, the coated weld is shown following
ultrasonic impact treatment. The groove and stress raiser
modification in the weld is denoted by 171 over the coating 170. In
the weld joint of FIG. 25c, the radius is a minimum of 0.5 mm, the
width is up to 10 mm, the depth is up to 2 mm, and the coating
thickness is 0.15 mm when the web thickness is 4 mm. It is shown in
FIGS. 25a-25c that ultrasonic impact treatment in accordance with
the invention makes possible the process of producing a welded
joint with specified properties due to the use of special coating
in the following order: fabrication of a joint by welding,
application of the protective or hardening coating, and ultrasonic
impact treatment in accordance with the invention.
[0190] To maintain the coating integrity, the conditions of
ultrasonic impact treatment in accordance with the invention are
selected so that the contact pressure on the coated surface and
pressure gradients in the ultrasonic impact treatment area are not
greater than the breaking strength of the coating.
[0191] Parameters of ultrasonic impact treatment in accordance with
the invention that ensure the results presented above for a widest
range of metals include: ultrasonic impact frequency of up to about
1500 Hz, ultrasonic impact amplitude of not less than about 1 mm,
average duration of ultrasonic impacts of not less than about 1 ms,
ultrasonic vibration carrier frequency of not less than about 20
kHz, ultrasonic vibration amplitude during impact of not greater
than about 30 .mu.m, contact pressure and stress gradient at the
boundary between individual ultrasonic impact treatment tool marks
of not greater than the coating breaking strength, pressing force
on the tool against a treated surface of not less than about 3
kg.
[0192] (R) Welded Structures
[0193] The above described welded joints, and processes for
obtaining the joints, make possible the creation of welded
structures that meet high quality and reliability requirements. A
structural representation is schematically shown in FIG. 26 to
illustrate various welded joints 180 obtainable under the
invention. Such structures in aggregate or in any combination of
elements, details, joints and materials may include: panels,
cylindrical elements with continuous or varying bevel angle that
are welded perpendicularly or at an angle to the panel, flat
structural elements, webs, brackets, corner joints, lap joints,
etc. The quality and reliability of the welded joints are improved
by provision of improved properties in the joints through
ultrasonic impact treatment of the joints in accordance with the
invention.
[0194] As will be apparent to one skilled in the art, various
modification can be made within the scope of the aforesaid
description. Such modifications being within the ability of one
skilled in the art form a part of the present invention and are
embraced by the appended claims.
* * * * *