U.S. patent application number 11/047589 was filed with the patent office on 2005-09-15 for nanocrystalline bolt and method for manufacturing same.
Invention is credited to Murakami, Yuichi.
Application Number | 20050201886 11/047589 |
Document ID | / |
Family ID | 34917882 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050201886 |
Kind Code |
A1 |
Murakami, Yuichi |
September 15, 2005 |
Nanocrystalline bolt and method for manufacturing same
Abstract
A nanocrystalline bolt, which serves as a high-strength bolt, is
manufactured by the steps of compacting powder formed of
nanocrystalline metal particles having a nanometer-scale grain
size, extruding a resultant compact so as to obtain a rod stock,
and subjecting the rod stock to a bolt-forming process (heading,
machining, and form rolling) without involvement of heat treatment.
Examples of metal material include JIS SUS410,
precipitation-hardening-type 13Cr-8Ni-2Mo, and other stainless
steels.
Inventors: |
Murakami, Yuichi;
(Fujisawa-shi, JP) |
Correspondence
Address: |
LORUSSO, LOUD & KELLY
3137 Mount Vernon Avenue
Alexandria
VA
22305
US
|
Family ID: |
34917882 |
Appl. No.: |
11/047589 |
Filed: |
February 2, 2005 |
Current U.S.
Class: |
419/67 ;
704/E11.006; 704/E21.012; 704/E21.013 |
Current CPC
Class: |
G10L 21/028 20130101;
G10L 25/90 20130101; G10L 21/0272 20130101 |
Class at
Publication: |
419/067 |
International
Class: |
B22F 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2004 |
JP |
2004-045327 |
Claims
What is claimed is:
1. A nanocrystalline bolt manufactured by compacting powder formed
of nanocrystalline metal particles having a nanometer-scale grain
size, extruding a resultant compact so as to obtain a rod stock,
and forming the rod stock into a bolt shape without involvement of
heat treatment.
2. A nanocrystalline bolt according to claim 1, wherein the metal
powder is of stainless steel.
3. A method for manufacturing a nanocrystalline bolt, comprising
the steps of: compacting powder formed of nanocrystalline metal
particles having a nanometer-scale grain size; extruding a
resultant compact so as to obtain a rod stock; and forming the rod
stock into a bolt shape without involvement of heat treatment.
4. A method for manufacturing a nanocrystalline bolt according to
claim 3, wherein the metal powder is of stainless steel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a nanocrystalline bolt,
which serves as a high-strength bolt, and a method for
manufacturing the nanocrystalline bolt. More particularly, the
invention relates to a nanocrystalline bolt having high strength
and high toughness and being able to be manufactured without need
for heat treatment, as well as to a method for manufacturing the
nanocrystalline bolt.
[0003] 2. Description of the Related Art
[0004] Conventionally, high-strength bolts having high strength and
high toughness for use in, for example, aircraft are manufactured
from 13Cr-8Ni stainless steel or the like by the steps of formation
of head portions of bolts by heading, heat treatment, machining,
and form rolling (as disclosed in, for example, Japanese Patent
Application Laid-Open (kokai) No. H05-247593). In this manner, the
manufacture of conventional high-strength bolts indispensably
involves heat treatment. Accordingly, conventional high-strength
bolts are poor in productivity and high in manufacturing cost.
SUMMARY OF THE INVENTION
[0005] An object of the present invention is to solve the
above-mentioned problems in the conventional high-strength bolt and
in the method for manufacturing the conventional high-strength bolt
and to provide a high-strength bolt (nanocrystalline bolt) that can
be manufactured without involvement of heat treatment and can
exhibit high strength and high toughness equivalent to those of a
high-strength bolt manufactured from an alloy steel with
involvement of heat treatment, and thus can be manufactured with
high productivity and low cost, as well as to provide a method for
manufacturing the high-strength bolt (nanocrystalline bolt).
[0006] To achieve the above object, the present invention provides
a nanocrystalline bolt manufactured by compacting powder formed of
nanocrystalline metal particles having a nanometer-scale grain
size, extruding a resultant compact so as to obtain a rod stock,
and forming the rod stock into a bolt shape without involvement of
heat treatment.
[0007] According to the present invention, a rod stock
(nanocrystalline material) used to form the nanocrystalline bolt is
formed by extruding a compact that is formed by compacting powder
formed of naoncrystalline metal particles having a nanometer-scale
grain size. The rod stock itself has high strength and high
toughness. Therefore, without involvement of heat treatment, by
merely subjecting the rod stock to a conventional bolt-forming
process (heading, machining, and form rolling), a yielded
high-strength bolt; i.e., a nanocrystalline bolt, exhibits strength
and toughness equivalent to those of a high-strength bolt that is
manufactured from an alloy steel with involvement of heat
treatment. In the case where the nanocrystalline bolt assumes the
form of a headed bolt having a long length, manufacture thereof
does not require a corrective straightening process effected by
heat treatment. Thus, the high-strength bolt can be manufactured
with high productivity and low cost.
[0008] Preferably, the metal powder used in the present invention
is of stainless steel.
[0009] By virtue of the above feature, a nanocrystalline bolt,
which is a high-strength bolt having excellent corrosion
resistance, high toughness, and high strength, can be readily
manufactured from a general material. Particularly, the
nanocrystalline bolt can serve as a high-strength bolt suited for
use in a plant where stress-corrosion cracking is highly likely to
occur.
[0010] The present invention also provides a method for
manufacturing a nanocrystalline bolt, comprising the steps of
compacting powder formed of nanocrystalline metal particles having
a nanometer-scale grain size, extruding a resultant compact so as
to obtain a rod stock, and forming the rod stock into a bolt shape
without involvement of heat treatment.
[0011] According to the method of the present invention, a rod
stock (nanocrystalline material) used to form the nanocrystalline
bolt is formed by extruding a compact that is formed by compacting
powder formed of naoncrystalline metal particles having a
nanometer-scale grain size. The rod stock itself has high strength
and high toughness. Therefore, without involvement of heat
treatment, by merely subjecting the rod stock to a conventional
bolt-forming process (heading, machining, and form rolling), there
can be manufactured a nanocrystalline bolt; i.e., a high-strength
bolt that exhibits strength and toughness equivalent to those of a
high-strength bolt that is manufactured from an alloy steel with
involvement of heat treatment. In the case where the
nanocrystalline bolt assumes the form of a headed bolt having a
long length, the method does not involve a corrective straightening
process effected by heat treatment. Thus, the high-strength bolt
can be manufactured with high productivity and low cost.
[0012] Preferably, the metal powder used in the method of the
present invention is of stainless steel.
[0013] By virtue of the above feature, the method of the present
invention can readily manufacture, from a general material, a
nanocrystalline bolt, which is a high-strength bolt having
excellent corrosion resistance, high toughness, and high strength.
Particularly, the method can manufacture a high-strength bolt
suited for use in a plant where stress-corrosion cracking is highly
likely to occur.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Various other objects, features and many of the attendant
advantages of the present invention will be readily appreciated as
the same becomes better understood by reference to the following
detailed description of the preferred embodiment when considered in
connection with the accompanying drawings, in which:
[0015] FIG. 1 is a side view of a nanocrystalline bolt according to
an embodiment of the present invention;
[0016] FIG. 2 is a side view of the nanocrystalline bolt as viewed
after subjection to a tensile test;
[0017] FIG. 3 is a side view of the nanocrystalline bolt as viewed
after subjection to a bifacial shearing test;
[0018] FIG. 4 is a side view of the nanocrystalline bolt as viewed
after subjection to a fatigue test; and
[0019] FIG. 5 is a table comparing the results of the tensile and
shearing tests conducted on the test samples of the embodiment with
corresponding values of a standard material.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] An embodiment of the present invention will next be
described in detail with reference to the drawings.
[0021] A stainless steel equivalent to JIS SUS410 is used to make a
nanocrystalline material. The stainless steel is pulverized into
fine particles having a particle size of tens of .mu.m. Next, the
particles are further pulverized to a nano-pulverizer, such as a
medium-stirring mill, to thereby be formed into finer particles
having a nanometer-scale (nm-scale) particle size.
[0022] The powder having a nanometer-scale particle size is
compacted. The resultant compact is hot-extruded into a
nanocrystalline stainless steel rod stock (nanocrystalline
material). In the course of the hot extrusion, Zr contained in the
powder material suppresses grain growth, thereby controlling the
grains size to a value on a predetermined order. Such a
nanocrystalline powder is supplied by Japan Ultra-high Temperature
Materials Research Center.
[0023] Next, the rod stock is cut into pieces each having a
predetermined length. Each of the cut pieces is subjected to a
conventional bolt-forming process (heading, machining, and form
rolling) to thereby be finished to a bolt (nanocrystalline bolt) 1
as shown in FIG. 1. In the bolt 1, the metallographic grain size is
controlled to a nanometer scale. Heat treatment is not performed
before and after the bolt-forming process.
EXAMPLE
[0024] The bolts 1 of the present embodiment were manufactured as
test samples from the above-mentioned rod stock having a diameter
of 5 mm. Each of the test sample bolts 1 has a head portion 2 and a
long bolt body portion 3. A threaded portion 3a is formed on the
bolt body portion 3 while extending along a predetermined length
from an end portion of the bolt body portion 3. The test sample
bolts 1 have the dimensions shown in FIG. 1. The threaded portion
3a has threads of #10-32UNJF-3A. The test sample bolts 1 were
subjected to the tensile, shearing, and fatigue tests.
[0025] The tensile test was conducted in accordance with American
Standard MIL-STD-1312 TEST No. 8. The threaded portion 3a was
ruptured at a load of 17.50 kN (see FIG. 2).
[0026] The shearing test was conducted in accordance with American
Standard MIL-STD-1312 TEST No. 13, which specifies a bifacial
shearing test. Shear fracture occurred at a load of 28.55 kN (see
FIG. 3).
[0027] The fatigue test was conducted in accordance with American
Standard MIL-STD-1312 TEST No. 11. The test was conducted under the
following cycle test conditions: fatigue high-load: 40% of tensile
break load (7 kN); fatigue low-load: 0.1% of fatigue high-load (0.7
kN); and frequency: 30 Hz. Thread rupture occurred at 3,994,900
cycles (see FIG. 4).
[0028] Since no criteria were available for the above test results,
the test results were compared with corresponding values of JIS
SUS410 serving as a standard material.
[0029] JIS G4303 SUS410 has a tensile strength of at least 540
N/mm.sup.2 as measured in a quenched and tempered condition. A
tensile strength of the standard material as reduced to an
effective cross-sectional area of 12.73 mm.sup.2 of the threaded
portion 3a of the test sample bolt 1 is calculated as 540
N/mm.sup.2.times.12.73 mm.sup.2=6.88 kN.
[0030] A shearing strength of the standard material as reduced to a
bolt diameter of 4.801 mm of the test sample bolt 1 is calculated
as 540 N/mm.sup.2.times.0.6.times.18.09 mm.sup.2=5.87 kN. The
bifacial shearing strength is two times of 5.87 kN; i.e., 11.74
kN.
[0031] The above results are shown in the TABLE 1.
[0032] As is apparent from the TABLE 1, the nanocrystalline bolt 1
of the present embodiment, which is manufactured from a stainless
steel equivalent to SUS410, has a tensile strength and a shearing
strength that are two times or more of those of the standard
material JIS SUS410.
[0033] The above-mentioned high-strength feature is attained
because the rod stock (nanocrystalline material), which is
manufactured by compacting a nanocrystalline powder of stainless
steel and extruding the resultant compact, itself has high strength
and high toughness. Furthermore, since the nanocrystalline bolt 1
is manufactured from a stainless steel, the nanocrystalline bolt 1
has excellent corrosion resistance and particularly can serve as a
high-strength bolt suited for use in a plant where stress-corrosion
cracking is highly likely to occur.
[0034] Even when the nanocrystalline bolt (high-strength bolt) 1
assumes the form of a headed bolt having a long length, the method
for manufacturing the nanocrystalline bolt 1 does not need to
involve a corrective straightening process effected by heat
treatment.
[0035] Since the manufacturing process does not involve heat
treatment as mentioned above, the nanocrystalline bolt
(high-strength bolt) 1 can be manufactured with high productivity
and low cost.
[0036] The test sample bolts used in the above tests were
manufactured by subjecting a rod stock of nanocrystalline stainless
steel to a bolt-forming process (heading, machining, and form
rolling) without involvement of heat treatment. Accordingly, the
test revealed that the test sample bolts were equivalent in
strength to heat-treated bolts used widely in general aircraft and
having a tensile strength of 1,240 MPa (180 KSI (Kp/in.sup.2)).
[0037] The present invention is not limited to the above
embodiment, but may be embodied in various other forms without
departing from the scope of the invention.
[0038] For example, the metal material is not limited to JIS
SUS410. Other stainless steels, such as
precipitation-hardening-type 13Cr-8Ni-2Mo, may be used as
appropriate.
* * * * *