U.S. patent application number 11/395322 was filed with the patent office on 2006-08-03 for low carbon alloy steel tube having ultra high strength and excellent toughness at low temperature and method of manufacturing the same.
This patent application is currently assigned to TENARIS CONNCECTIONS A.G. (a Liechtenstein Corporation). Invention is credited to Eduardo Altschuler, Edgardo Oscar Lopez.
Application Number | 20060169368 11/395322 |
Document ID | / |
Family ID | 38564023 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060169368 |
Kind Code |
A1 |
Lopez; Edgardo Oscar ; et
al. |
August 3, 2006 |
Low carbon alloy steel tube having ultra high strength and
excellent toughness at low temperature and method of manufacturing
the same
Abstract
A low carbon alloy steel tube and a method of manufacturing the
same, especially for a stored gas inflator pressure vessel, in
which the steel tube consists essentially of, by weight: about
0.06% to about 0.18% carbon, about 0.3% to about 1.5% manganese,
about 0.05% to about 0.5% silicon, up to about 0.015% sulfur, up to
about 0.025% phosphorous, and at least one of the following
elements: up to about 0.30% vanadium, upto t about 0.10% aluminum,
up to about 0.06% niobium, up to about 1% chromium, up to about
0.70% nickel, up to about 0.70% molybdenum, up to about 0.35%
copper, up to about 0.15% residual elements, and the balance iron
and incidental impurities. After a high heating rate of about
100.degree. C. per second; rapidly and fully quenching the steel
tubing in a water-based quenching solution at a cooling rate of
about 100.degree. C. per second. The steel has a tensile strength
of at least about 145 ksi and as high as 220 ksi and exhibits
ductile behavior at temperatures as low as -100.degree. C.
Inventors: |
Lopez; Edgardo Oscar; (Vera
Cruz, MX) ; Altschuler; Eduardo; (Bergamo,
IT) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
TENARIS CONNCECTIONS A.G. (a
Liechtenstein Corporation)
|
Family ID: |
38564023 |
Appl. No.: |
11/395322 |
Filed: |
April 3, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10957605 |
Oct 5, 2004 |
|
|
|
11395322 |
Apr 3, 2006 |
|
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Current U.S.
Class: |
148/332 ;
420/90 |
Current CPC
Class: |
C21D 8/00 20130101; C21D
8/10 20130101; C22C 38/02 20130101; C21D 9/08 20130101; C22C 38/20
20130101; C22C 38/04 20130101; C21D 9/50 20130101; C22C 38/06
20130101; C22C 38/24 20130101; C22C 38/28 20130101; C22C 38/22
20130101; C22C 38/44 20130101 |
Class at
Publication: |
148/332 ;
420/090 |
International
Class: |
C22C 38/20 20060101
C22C038/20 |
Claims
1. A low carbon alloy steel tube consisting essentially of, by
weight: about 0.06% to about 0.18% carbon; about 0.5% to about 1.5%
manganese; about 0.1% to about 0.5% silicon; up to about 0.015%
sulfur; up to about 0.025% phosphorous; up to about 0.50% nickel;
about 0.1% to about 1.0% chromium; about 0.1% to about 1.0%
molybdenum; about 0.01% to about 0.10% vanadium; about 0.01% to
about 0.10% titanium; about 0.05% to about 0.35% copper; about
0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to
about 0.15% residual elements; and the balance iron and incidental
impurities, wherein the steel tube has a tensile strength of at
least about 145 ksi and has a ductile-to-brittle transition
temperature below -60.degree. C.
2. The low carbon alloy steel tube of claim 1, wherein the steel
tube consists essentially of, by weight: about 0.07% to about 0.12%
carbon; about 1.00% to about 1.40% manganese; about 0.15% to about
0.35% silicon; up to about 0.010% sulfur; up to about 0.015%
phosphorous; up to about 0.20% nickel; about 0.55% to about 0.80%
chromium; about 0.30% to about 0.50% molybdenum; about 0.01% to
about 0.07% vanadium; about 0.01% to about 0.05% titanium; about
0.15% to about 0.30% copper; about 0.010% to about 0.050% aluminum;
up to about 0.05% niobium; up to about 0.15% residual elements; and
the balance iron and incidental impurities.
3. The low carbon alloy steel tube of claim 1, wherein the steel
tube consists essentially of, by weight: about 0.08% to about 0.11%
carbon; about 1.03% to about 1.18% manganese; about 0.15% to about
0.35% silicon; up to about 0.003% sulfur; up to about 0.012%
phosphorous; up to about 0.10% nickel; about 0.63% to about 0.73%
chromium; about 0.40% to about 0.45% molybdenum; about 0.03% to
about 0.05% vanadium; about 0.025% to about 0.035% titanium; about
0.15% to about 0.30% copper; about 0.010% to about 0.050% aluminum;
up to about 0.05% niobium; up to about 0.15% residual elements; and
the balance iron and incidental impurities.
4. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a yield strength of at least about 125 ksi.
5. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a yield strength of at least about 135 ksi.
6. The low carbon alloy steel tube of claim 1, wherein the steel
tube has an elongation at break of at least about 9%.
7. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a hardness of no more than about 40 HRC.
8. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a hardness of no more than about 37 HRC.
9. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a carbon equivalent of less than about 0.63%, the carbon
equivalent being determined according to the formula: Ceq=% C+%
Mn/6+(% Cr+% Mo+% V)/5+(% Ni+% Cu)/15.
10. The low carbon alloy steel tube of claim 9, wherein the steel
tube has a carbon equivalent of less than about 0.60%.
11. The low carbon alloy steel tube of claim 9, wherein the steel
tube has a carbon equivalent of less than about 0.56%.
12. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a maximum microinclusion content of 2 or less--thin
series--, and level 1 or less--heavy series--, measured in
accordance with ASTM E45 Standard-Worst Field Method (Method
A).
13. The low carbon alloy steel tube of claim 1, wherein the steel
tube has a maximum microinclusion content measured in accordance
with ASTM E45 Standard-Worst Field Method (Method A), as follows:
TABLE-US-00015 Inclusion Type Thin Heavy A 0.5 0 B 1.5 1.0 C 0 0 D
1.5 0.5
14. The low carbon alloy steel tube of claim 13, wherein oversize
inclusion content with 30 .mu.m or less in size is obtained.
15. The low carbon alloy steel tube of claim 14, wherein the total
oxygen content is limited to 20 ppm.
16. The low carbon alloy steel tube of claim 1, wherein the tube
has a seamless configuration.
17. A stored gas inflator pressure vessel comprising the low carbon
alloy steel tube of claim 1.
18. An automotive airbag inflator comprising the low carbon alloy
steel tube of claim 1.
19. A low carbon alloy steel tube consisting essentially of, by
weight: about 0.08% to about 0.11% carbon; about 1.03% to about
1.18% manganese; about 0.15% to about 0.35% silicon; up to about
0.003% sulfur; up to about 0.012% phosphorous; up to about 0.10%
nickel; about 0.63% to about 0.73% chromium; about 0.40% to about
0.45% molybdenum; about 0.03% to about 0.05% vanadium; about 0.025%
to about 0.035% titanium; about 0.15% to about 0.30% copper; about
0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to
about 0.15% residual elements; and the balance iron and incidental
impurities, wherein the steel tube has a yield strength of at least
about 135 ksi, a tensile strength of at least about 145 ksi, an
elongation at break of at least about 9%, a hardness of no more
than about 37 HRC, and has a ductile-to-brittle transition
temperature below -60.degree. C.
20. The low carbon alloy steel tube of claim 19, wherein the tube
has a seamless configuration.
21. A stored gas inflator pressure vessel comprising the low carbon
alloy steel tube of claim 19.
22. An automotive airbag inflator comprising the low carbon alloy
steel tube of claim 19.
23. A method of manufacturing a length of steel tubing for a stored
gas inflator pressure vessel, comprising the following steps:
producing a length of tubing from a steel material consisting
essentially of, by weight: about 0.06% to about 0.18% carbon, about
0.5% to about 1.5% manganese, about 0.1% to about 0.5% silicon, up
to about 0.015% sulfur, up to about 0.025% phosphorous, up to about
0.50% nickel, about 0.1% to about 1.0% chromium, about 0.1% to
about 1.0% molybdenum, about 0.01% to about 0.10% vanadium, about
0.01% to about 0.10% titanium, about 0.05% to about 0.35% copper,
about 0.010% to about 0.050% aluminum, up to about 0.05% niobium,
up to about 0.15% residual elements, and the balance iron and
incidental impurities; subjecting the steel tubing to a
cold-drawing process to obtain desired dimensions; austenizing by
heating the cold-drawn steel tubing in an induction-type
austenizing furnace to a temperature of at least Ac3, at a heating
rate of at feast about 100.degree. C. per second; after the heating
step, quenching the steel tubing in a quenching fluid until the
tubing reaches approximately ambient temperature, at a cooling rate
of at least about 100.degree. C. per second; and after the
quenching step, tempering the steel tubing for about 2-30 minutes
at a temperature below Ac1.
24. The method of claim 23, wherein the steel tubing produced
consists essentially of, by weight: about 0.07% to about 0.12%
carbon, about 1.00% to about 1.40% manganese, about 0.15% to about
0.35% silicon, up to about 0.010% sulfur, up to about 0.015%
phosphorous, up to about 0.20% nickel, about 0.55% to about 0.80%
chromium, about 0.30% to about 0.50% molybdenum, about 0.01% to
about 0.07% vanadium, about 0.01% to about 0.05% titanium, about
0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum,
up to about 0.05% niobium, up to about 0.15% residual elements, and
the balance iron and incidental impurities.
25. The method of claim 23, wherein the steel tubing produced
consists essentially of, by weight: about 0.08% to about 0.11%
carbon, about 1.03% to about 1.18% manganese, about 0.15% to about
0.35% silicon, up to about 0.003% sulfur, up to about 0.012%
phosphorous, up to about 0.10% nickel, about 0.63% to about 0.73%
chromium, about 0.40% to about 0.45% molybdenum, about 0.03% to
about 0.05% vanadium, about 0.025% to about 0.035% titanium, about
0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum,
up to about 0.05% niobium, up to about 0.15% residual elements, and
the balance iron and incidental impurities.
26. The method of claim 23, wherein the finished steel tubing has a
yield strength of at least about 125 ksi.
27. The method of claim 23, wherein the finished steel tubing has a
yield strength of at least about 135 ksi.
28. The method of claim 23, wherein the finished steel tubing has a
tensile strength of at least about 145 ksi.
29. The method of claim 23, wherein the finished steel tubing has
an elongation at break of at least about 9%.
30. The method of claim 23, wherein the finished steel tubing has a
hardness of no more than about 40 HRC.
31. The method of claim 23, wherein the finished steel tubing has a
hardness of no more than about 37 HRC.
32. The method of claim 23, wherein the finished steel tubing has a
ductile-to-brittle transition temperature below -60.degree. C.
33. The method of claim 23, wherein in the austenizing heating
step, the steel tubing is heated to a temperature between about
920-1050.degree. C.
34. The method of claim 33, wherein in the austenizing heating
step, the steel tubing is heated at a rate of at least about
200.degree. C. per second.
35. The method of claim 23, wherein in the quenching step, the
steel tubing is cooled at a rate of at least about 200.degree. C.
per second.
36. The method of claim 23, wherein in the tempering step, the
steel tubing is tempered at a temperature between about
400-600.degree. C.
37. The method of claim 36, wherein in the tempering step, the
steel tubing is tempered for about 4-20 minutes.
38. The method of claim 23, further comprising a finishing step
wherein the tempered steel tubing is pickled, phosphated, and
oiled.
39. A method of manufacturing a length of steel tubing for a stored
gas inflator pressure vessel, comprising the following steps:
producing a length of tubing from a steel material consisting
essentially of, by weight: about 0.08% to about 0.11% carbon, about
1.03% to about 1.18% manganese, about 0.15% to about 0.35% silicon,
up to about 0.003% sulfur, up to about 0.012% phosphorous, up to
about 0.10% nickel, about 0.63% to about 0.73% chromium, about
0.40% to about 0.45% molybdenum, about 0.03% to about 0.05%
vanadium, about 0.025% to about 0.035% titanium, about 0.15% to
about 0.30% copper, about 0.010% to about 0.050% aluminum, up to
about 0.05% niobium, up to about 0.15% residual elements, and the
balance iron and incidental impurities; subjecting the steel tubing
to a cold-drawing process to obtain desired dimensions; austenizing
by heating the cold-drawn steel tubing in an induction-type
austenizing furnace to a temperature between about 920-1050.degree.
C., at a heating rate of at least about 200.degree. C. per second;
after the heating step, quenching the steel tubing in a water-based
quenching solution until the tubing reaches approximately ambient
temperature, at a cooling rate of at least about 200.degree. C. per
second; and after the quenching step, tempering the steel tubing
for about 4-20 minutes at a temperature between about
450-550.degree. C., a finishing step wherein the tempered steel
tubing is pickled, phosphated, and oiled, wherein the finished
steel tubing has a yield strength of at least about 135 ksi, a
tensile strength of at least about 145 ksi, an elongation at break
of at least about 9%, a hardness of no more than about 37 HRC, a
ductile-to-brittle transition temperature below -60.degree. C. and
a good surface appearance.
40. A method of manufacturing a length of steel tubing for a stored
gas inflator pressure vessel, comprising the following steps:
producing a length of tubing from a steel material consisting
essentially of, by weight: about 0.06% to about 0.18% carbon, about
0.3% to about 1.5% manganese, about 0.05% to about 0.5% silicon, up
to about 0.015% sulfur, up to about 0.025% phosphorous, and at
least one of the following elements: up to about 0.30% vanadium, up
to about 0.10% aluminum, up to about 0.06% niobium, up to about 1%
chromium, up to about 0.70% nickel, up to about 0.70% molybdenum,
up to about 0.35% copper, up to about 0.15% residual elements, and
the balance iron and incidental impurities; subjecting the steel
tubing to a cold-drawing process to obtain desired dimensions;
austenizing by heating the cold-drawn steel tubing in an
induction-type austenizing furnace to a temperature of at least
Ac3, at a heating rate of at least about 100.degree. C. per second;
after the heating step, quenching the steel tubing in a quenching
fluid until the tubing reaches approximately ambient temperature,
at a cooling rate of at least about 100.degree. C. per second,
wherein the steel tube has a tensile strength of at least about 145
ksi and has a ductile-to-brittle transition temperature below
-60.degree. C.
41. The method of claim 40, wherein the steel tubing produced
consists essentially of, by weight: about 0.07% to about 0.12%
carbon, about 0.60% to about 1.40% manganese, about 0.05% to about
0.40% silicon, up to about 0.010% sulfur, up to about 0.02%
phosphorous, and at least one of the following elements: up to
about 0.20% vanadium, up to about 0.07% aluminum, up to about 0.04%
niobium, up to about 0.8% chromium, up to about 0.50% nickel, up to
about 0.50% molybdenum, up to about 0.35% copper, up to about 0.15%
residual elements, and the balance iron and incidental impurities,
wherein the steel tube has a tensile strength of at least about 160
ksi and has a ductile-to-brittle transition temperature below
-60.degree. C.
42. The method of claim 40, wherein the steel tube has a carbon
equivalent of less than about 0.52%, the carbon equivalent being
determined according to the formula: Ceq=% C+% Mn/6+(% Cr+% Mo+%
V)/5+(% Ni+% Cu)/15.
43. The method of claim 41, wherein the steel tube has a carbon
equivalent of less than about 0.48%, the carbon equivalent being
determined according to the formula: Ceq=% C+% Mn/6+(% Cr+% Mo+%
V)/5+(% Ni+% Cu)/15.
44. The method of claim 40, wherein the finished steel tubing has
an elongation at break of at least about 9%.
45. The method of claim 40, wherein in the austenizing heating
step, the steel tubing is heated to a temperature between about
860-1050.degree. C.
46. The method of claim 40, wherein in the austenizing heating
step, the steel tubing is heated at a rate of at least about
200.degree. C. per second.
47. The method of claim 40, wherein in the quenching step, the
steel tubing is cooled at a rate of at least about 200.degree. C.
per second.
48. A method of manufacturing a length of steel tubing for a stored
gas inflator pressure vessel, comprising the following steps:
producing a length of tubing from a steel material consisting
essentially of, by weight: about 0.07% to about 0.12% carbon, about
0.60% to about 1.40% manganese, about 0.05% to about 0.40% silicon,
up to about 0.010% sulfur, up to about 0.02% phosphorous, maximum
0.20% vanadium, up to about 0.07% aluminum, up to about 0.04%
niobium, up to about 0.8% chromium, up to about 0.50% nickel, up to
about 0.50% molybdenum, up to about 0.35% copper, up to about 0.15%
residual elements, and the balance iron and incidental impurities;
subjecting the steel tubing to a cold-drawing process to obtain
desired dimensions; austenizing by heating the cold-drawn steel
tubing in an induction-type austenizing furnace to a temperature
between about 860-1050.degree. C., at a heating rate of at least
about 200.degree. C. per second; after the heating step, quenching
the steel tubing in a water-based quenching solution at a cooling
rate of at least about 200.degree. C. per second; wherein the
finished steel tubing has a tensile strength of at least about 160
ksi, an elongation at break of at least about 9%, and a
ductile-to-brittle transition temperature below -60.degree. C. and
preferably below 100.degree. C.
Description
RELATED APPLICATION
[0001] This application is a Continuation-in-part of U.S.
Nonprovisional patent application Ser. No. 10/957,605, filed on
Oct. 5, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to low carbon alloy steel
tubes having ultra high strength and excellent toughness at low
temperature and also to a method of manufacturing such a steel
tube. The steel tube is particularly suitable for making components
for containers for automotive restraint systems, an example of
which is an automotive airbag inflator.
[0004] In addition, alternative steel compositions in the low
carbon, low alloy category and different heat treatment processes
were developed and tested in order to decrease the manufacturing
cost.
[0005] 2. Brief Description of the Prior Art
[0006] Japanese Publication No. 10-140249 [Application date Nov. 5,
1996] and Japanese Publication No. 10-140283 [Application date Nov.
12, 1996] illustrate in general terms steel chemistry considered
useful for an automotive airbag inflator. These documents mention
as a final condition the absence of heat treatment, a stress
relieving, and a normalizing or a quenching and tempering. These
publications do not mention the possibility of just a quenching as
a heat treatment step. No mechanical properties are mentioned in
the claims. In the various examples, only in example #21 is the
steel quenched and tempered, but the reported UTS is only 686 MPa
(99 ksi). Even the highest stated mechanical properties, in example
#26, are relatively low, with a maximum UTS of 863 MPa (125 ksi).
Hence, these publications relate to grades which are relatively low
(the intended target is 590 MPa (86 ksi). In addition these
publications show ductility at low temperature with a flattening
drop-weight (DW) type test at -40.degree. C. The currently accepted
test for demonstrating ductility at low temperature is the burst
test, which is more efficient in showing brittleness. It is
believed that most of the examples shown in these documents that
are alleged to be ductile after a DW test, would in fact not show
ductile behavior at low temperature in a burst test and, therefore,
would not qualify for certain airbag inflator applications due to a
lack of compliance with governmental regulations (e.g. US DOT).
[0007] Japanese Publication No. 2001-49343 [Application date Oct.
8, 1999] is said to address only steels for use in making
electric-resistance-welded tubes (the ERW process). The claims
specify various aspects of the ERW process and an optional heat
treatment for a normalizing or quench and temper, an optional
ulterior cold drawing, an optional ulterior heat treatment
(normalizing or quench and temper). This document addresses only
two different, very general steel chemistry, one being a low carbon
steel, the other noting common limits in various alloying elements.
This document does not suggest the possibility of just a quenching
heat treatment. Various examples are given for a quench and temper
material, but mechanical properties obtained are relatively low.
The maximum result achieved is 852 MPa (123 ksi) in the quench and
temper test #18.
[0008] It is believed that the steel "chemistry" put forth by
Sumitomo in each of JP 10-140249 JP 10-140283; JP 2001-49343; as
well as the chemistry later identified in Kondo et al., U.S. Pat.
No. 6,878,219 B2, or the continuation published as US 2005/0039826
A1, actually define steels with such broad ranges so as to include
SAE 1010 general purpose steel as made and sold in the US since
long prior to 1990. Applicants are aware that for several years a
SAE 1010 steel grade manufactured with modern technologies normally
guarantees that a P amount will be below 0.025 and an S amount will
be below 0.01 as described in the mentioned application.
[0009] Additional documents illustrating the state of the prior art
in steels for air bag applications include Erike, U.S. Pat. No.
6,386,583 B2 and various published continuations thereof, including
US 2004/0074570 A1 and US 2005/0061404 A1. These documents do not
suggest any advantage as taught herein from an extremely rapid
induction austenitizing and an ulterior ultra fast water quenching,
let alone using just such a rapid quench and not thereafter using a
tempering step. In addition JP 10-140283 discloses overlapping
chemistry with U.S. Pat. No. 6,878,219 B2, with only a slightly
lower maximum for P (0.02) and a slightly higher maximum for S
(0.02). While Patent Publication US20020033591A1 broadly suggests
the possibility of quenching without tempering, claims 6 and 7 do
not mention the necessity of quenching in order to achieve the
mechanical properties claimed and instead these claims require at
least two heat treatments.
[0010] Airbag inflators for vehicle occupant restraint systems are
required to meet strict structural and functional standards.
Therefore, strict procedures and tolerances are imposed on the
manufacturing process. While field experience indicates that the
industry has been successful in meeting past structural and
functional standards, improved and/or new properties are necessary
to satisfy the evolving requirements, while at the same time a
continuous reduction in the manufacturing costs is also
important.
[0011] Airbags or supplemental restraint systems are an important
safety feature in many of today's vehicles. In the past, air bag
systems were of the type employing explosive chemicals, but they
are expensive, and due to environmental and recycling problems, in
recent years, a new type of inflator has been developed using an
accumulator made of a steel tube filled with argon gas or the like,
and this type is increasingly being used.
[0012] The above-mentioned accumulator is a container which at
normal times maintains the gas or the like at a high pressure which
is blown into an airbag at the time of the collision of an
automobile, in a single or multiple stage burst. Accordingly, a
steel tube used as such an accumulator is to receive a stress at a
high strain rate in an extremely short period of time. Therefore,
compared with a simple structure such as an ordinary pressure
cylinder, the above-described steel tube is required to have
superior dimensional accuracy, excellent workability, and
weldability, and above all must have high strength, toughness, and
excellent resistance to bursting. Dimensional accuracy also is
important to ensure a very precise volume of gas will blow into the
airbag.
[0013] Cold forming properties are very important in tubular
members used to manufacture accumulators since they are formed to
final shape after the tube is manufactured.
[0014] Different shapes depending on the vessel configuration shall
be obtained by cold forming. It is crucial to obtain pressure
vessels without cracks and superficial defects after cold forming.
Moreover, it is also vital to have very good toughness even at low
temperatures after cold forming.
[0015] The steels disclosed herein have very good weldability, and
do not require, for air bag accumulator applications, either a
preheating prior to welding, or a post weld heat treatment. The
carbon equivalent, as defined by the formula, Ceq=% C+% Mn/6+(%
Cr+% Mo+% V)/5+(% Ni+% Cu)/15 should be less than about 0.63% in
order to obtain the required weldability. As Ceq diminishes,
weldability improves. In the preferred embodiment of this
invention, the carbon equivalent as defined above should be less
than about 0.60%, preferably less than about 0.56%, and most
preferably less than about 0.52%, or even less than about 0.48%, in
order to better guarantee weldability.
[0016] To produce a gas container, a cold-drawn tube made according
to the present invention is cut to length and then cold formed
using different known technologies (such as crimping, swaging, or
the like) in order to obtain the desired shape. Alternatively, a
welded tube could be used. Subsequently, to produce the
accumulator, an end cap and a diffuser are welded to each end of
the container by any suitable technology such as friction welding,
gas tungsten arc welding or laser welding. These welds are highly
critical and as such require considerable labor, and in certain
instances testing to assure weld integrity throughout the pressure
vessel and airbag deployment. It has been observed that these welds
can crack or fail, thus, risking the integrity of the accumulator,
and possibly the operation of the airbag.
[0017] The inflators are tested to assure that they retain their
structural integrity during airbag deployment. One of such tests is
the so-called burst test. This is a destructive-type test in which
a canister is subjected to internal pressures significantly higher
than those expected during normal operational use, i.e., airbag
deployment. In this test, the inflator is subjected to increasing
internal pressures until rupture occurs.
[0018] In reviewing the burst test results and studying the test
canister specimens from these tests, it has been found that
fracture occurs through different alternative ways: ductile
fracture, brittle fracture, and sometimes a combination of these
two modes. It has been observed that in ductile fracture an
outturned rupture exemplified by an opened bulge (such as would be
exhibited by a bursting bubble) occurs. The ruptured surface is
inclined approximately 45 degrees with respect to the tube outer
surface, and is localized within a subject area. In a brittle
fracture, on the other hand, a non-arresting longitudinal crack
along the length of the inflator is exhibited, which is indicative
of a brittle zone in the material. In this case, the fracture
surface is normal to the tube outer surface. These two modes of
fracture have distinctive surfaces when observed under a scanning
electron microscope--dimples are characteristic of ductile
fracture, while cleavage is an indication of brittleness.
[0019] At times, a combination of these two fracture modes can be
observed, and brittle cracks can propagate from the ductile,
ruptured area. Because the whole system, including the airbag
inflator, may be utilized in vehicles operating in very different
climates, it is crucial that the material exhibits ductile behavior
over a wide temperature range, from very cold up to warm
temperatures.
SUMMARY OF THE INVENTION
[0020] First, the present invention first relates to certain novel
low carbon alloy steels suitable for cold forming having more than
high tensile strength (UTS 145 ksi minimum) and preferably ultra
high tensile strength (UTS 160 ksi minimum and possibly 175 ksi or
220 ksi), and, consequently, a very high burst pressure. Moreover,
the steel has excellent toughness at low temperature, with
guaranteed ductile behavior at -60.degree. C., i.e., a
ductile-to-brittle transition temperature (DBTT) below 60.degree.
C., and possibly as low as -100.degree. C.
[0021] Second, the present invention also relates to a process of
manufacturing such a steel tube which essentially comprises a novel
rapid induction austenizing/high speed quench/no temper technique.
In a preferred method, there is an extremely rapid induction
austenizing with an ultra fast water quenching step that eliminates
any tempering step, so as to create a low carbon alloy steel tube
that also is suitable for cold forming having ultra high tensile
strength (UTS 145 ksi minimum and up to 220 ksi), and,
consequently, a very high burst pressure. Moreover, the steel has
excellent toughness at low temperature, with guaranteed ductile
behavior at -60.degree. C., i.e., a ductile-to-brittle transition
temperature (DBTT) that is below -60.degree. C., and possibly even
as low as -100.degree. C.
[0022] The material of the present invention has particular utility
in components for containers for automotive restraint system
components, an example of which is an automotive airbag inflator.
The chemistry used to create each of the steels disclosed herein is
novel, hereafter will be identified as Steel A, Steel B, Steel C,
Steel D and Steel E, with the compositions for each being
summarized in the following Table I: TABLE-US-00001 Steel C Mn S P
Cr Mo Ni V A 0.10 1.23 0.002 0.008 0.11 0.05 0.34 0.002 B 0.10 1.09
0.001 0.011 0.68 0.41 0.03 0.038 C 0.11 1.16 0.001 0.010 0.64 0.47
0.03 0.053 D 0.11 1.07 0.002 0.008 0.06 0.04 0.03 0.083 E 0.10 0.47
0.001 0.011 0.04 0.02 0.05 0.001 Steel Ti Si Cu Al Carbon. eq A
0.023 0.27 0.24 0.035 0.38 B 0.025 0.28 0.22 0.035 0.52 C 0.026
0.25 0.22 0.028 0.55 D 0.001 0.08 0.06 0.033 0.33 E 0.002 0.19 0.07
0.027 0.20
[0023] Test results using each of these steels in a novel rapid
induction austenizing/high speed quench/no temper technique
revealed surprising and differing results, among the five steel
compositions, as summarized in the following Table II:
TABLE-US-00002 Yield UTS Elong. Hardness Flatten Burst Steel (MPa)
(ksi) (MPa) (ksi) (%) (HRC) (DOT) -60.degree. C. -100.degree. C. A
920 133 1230 178 22 42 OK ductile ductile B 940 136 1217 176 22 41
OK ductile N/A C 997 144 1260 183 20 42 OK ductile N/A D 781 113
1184 172 19 32 OK ductile N/A E 552 80 827 120 26 17 OK ductile
N/A
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Preferred embodiments of the invention are described in
detail below, by example only, with reference to the accompanying
drawings, wherein:
[0025] FIG. I is a core microstructure for a high speed quench on
Steel E;
[0026] FIG. II shows burst tests at -60 C for a high speed quench
on Steel E.
[0027] FIG. III shows microstructure for a normal quench on Steel
E;
[0028] FIG. IV shows a high speed quench core microstructure on
Steel D;
[0029] FIG. V shows burst test at -60 C for a high speed quench on
Steel D.
[0030] FIG. VI shows micro-structure for a normal quench on Steel
D
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] While the present invention is susceptible of embodiment in
various forms, it will hereinafter be described a presently
preferred embodiment with the understanding that the present
disclosure is to be considered an exemplification of the invention
and is not intended to limit the invention to the specific
embodiment illustrated.
[0032] The present invention relates to steel tubing to be used for
stored gas inflator pressure vessels. More particularly, the
present invention relates to a low carbon ultra high strength steel
grade for seamless pressure vessel applications with guaranteed
ductile behavior at -60.degree. C., i.e., a ductile-to-brittle
transition temperature below -60.degree. C., and possibly even as
low as -100.degree.
[0033] More particularly, the present invention relates to a
chemical composition and a manufacturing process to obtain a
seamless steel tubing to be used to manufacture an inflator.
[0034] A schematic illustration of a method of producing the
seamless low carbon ultra high strength steel could be as
follows:
1. Steel making
2. Steel casting
3. Tube hot rolling
4. Hot-rolled hollow finishing operations
5. Cold drawing
6. Austenizing with Quenching (without tempering)
7. Cold-drawn tube finishing operations
[0035] One of the main objectives of the steel-making process is to
refine the iron by removal of carbon, silicon, sulfur, phosphorous,
and manganese. In particular, sulfur and phosphorous are
prejudicial for the steel because they worsen the mechanical
properties of the material. Ladle metallurgy is used before or
after basic processing to perform specific purification steps that
allow faster processing in the basic steel making operation.
[0036] The steel-making process is performed under an extreme clean
practice in order to obtain a very low sulfur and phosphorous
content, which in turn is crucial for obtaining the high toughness
required by the product. Accordingly, the objective of an inclusion
level of 2 or less--thin series--, and level 1 or less--heavy
series--, under the guidelines of ASTM E45 Standard-Worst Field
Method (Method A) has been imposed. In the preferred embodiment of
this invention, the maximum microinclusion content as measured
according to the above-mentioned Standard should be: TABLE-US-00003
Inclusion Type Thin Heavy A 0.5 0 B 1.5 1.0 C 0 0 D 1.5 0.5
[0037] Furthermore, the extreme clean practice allows obtaining
oversize inclusion content with 30 .mu.m or less in size. These
inclusion contents are obtained limiting the total oxygen content
to 20 ppm.
[0038] Extreme clean practice in secondary metallurgy is performed
by bubbling inert gases in the ladle furnace to force the inclusion
and impurities to float. The production of a fluid slag capable of
absorbing impurities and inclusions, and the inclusions' size and
shape modification by the addition of SiCa to the liquid steel,
produce high quality steel with low inclusion content.
Examples Using Low Carbon, Alloy Steels
[0039] The chemical composition of the obtained steel shall be as
follows, in each case "%" means "mass percent":
Carbon (C)
[0040] C is an element that inexpensively raises the strength of
the steel, but if its content is less than 0.06% it is difficult to
obtain the desired strength. On the other hand, if the steel has a
C content greater than 0.18%, then cold workability, weldability,
and toughness decrease. Therefore, the C content range is 0.06% to
0.18%. A preferred range for the C content is 0.07% to 0.12%, and
an even more preferred range is 0.10 to 0.12%.
Manganese (Mn)
[0041] Mn is an element which is effective in increasing the
hardenability of the steel, and therefore it increases strength and
toughness. If it content is less than 0.3% it is difficult to
obtain the desired strength, whereas if it exceeds 1.5%, then
banding structures become marked, and toughness decreases.
Accordingly, the Mn content is 0.3% to 1.5%, with a preferred Mn
range of 0.60 to 1.40%.
Silicon (Si)
[0042] Si is an element which has a deoxidizing effect during steel
making process and also raises the strength of the steel. If Si
content is less than 0.05%, the steel is susceptible to oxidation,
on the other hand if it exceeds 0.50%, then both toughness and
workability decrease. Therefore, the Si content is 0.05% to 0.5%,
and a preferred Si range of 0.05% to 0.40%.
Sulfur (S)
[0043] S is an element that causes the toughness of the steel to
decrease. Accordingly, the S content is limited to 0.015% maximum.
A preferred maximum value is 0.010%
Phosphorous (P)
[0044] P is an element that causes the toughness of the steel to
decrease. Accordingly, the P content is limited to 0.025% maximum.
A preferred maximum value is 0.02%,
Nickel (Ni)
[0045] Ni is an element that increases the strength and toughness
of the steel, but it is very costly, therefore for cost reasons Ni
is limited to 0.70% maximum. A preferred maximum value is
0.50%.
Chromium (Cr)
[0046] Cr is an element which is effective in increasing the
strength, toughness, and corrosion resistance of the steel. If it
exceeds 1% the toughness at the welding zones decreases markedly.
Accordingly, the Cr content is limited to 1.0% maximum, and a
preferred Cr maximum content is 0.80%,
Molybdenum (Mo)
[0047] Mo is an element which is effective in increasing the
strength of the steel and contributes to retard the softening
during tempering, but it is very costly. Accordingly, the Mo
content is limited to 0.7% maximum, and a preferred Mo maximum
content is 0.50%
Vanadium (V)
[0048] V is an element which is effective in increasing the
strength of the steel, even if added in small amounts, and allows
to retard the softening during tempering. However, this ferroalloy
is expensive, forcing the necessity to lower the maximum content.
Therefore, V is limited to 0.3% maximum, with a preferred maximum
of 0.20%
[0049] Preferred ranges for other elements not listed above are as
follows: TABLE-US-00004 Element Weight % Aluminum 0.10% max Niobium
0.06% max Sn 0.05% max Sb 0.05% max Pb 0.05% max As 0.05% max
[0050] Residual elements in a single ladle of steel used to produce
tubing or chambers shall be: Sn+Sb+Pb+As.ltoreq.0.15% max, and
S+P.ltoreq.0.025
[0051] The next step is the steel casting to produce a solid steel
bar capable of being pierced and rolled to form a seamless steel
tube. The steel is cast in the steel shop into a round solid
billet, having a uniform diameter along the steel axis.
[0052] The solid cylindrical billet of ultra high clean steel is
heated to a temperature of about 1200.degree. C. to 1300.degree.
C., and at this point undergoes the rolling mill process.
Preferably, the billet is heated to a temperature of about
1250.degree. C., and then passed through the rolling mill. The
billet is pierced, preferably utilizing the known Manessmann
process, and subsequently the outside diameter and wall thickness
are substantially reduced while the length is substantially
increased during hot rolling. For example, a 148 mm outside
diameter solid bar is hot rolled into a 48.3 mm outside diameter
hot-rolled tube, with a wall thickness of 3.25 mm.
[0053] The cross-sectional area reduction, measured as the ratio of
the cross-sectional area of the solid billet to the cross-sectional
area of the hot-rolled tube, is important in order to obtain a
refined microstructure, necessary to get the desired mechanical
properties. Therefore, the minimum cross-sectional area reduction
is about 15:1, with preferred and most preferred minimum
cross-sectional area reductions of about 20:1 and about 25:1,
respectively.
[0054] The seamless hot-rolled tube of ultra high clean steel so
manufactured is cooled to room temperature. The seamless hot-rolled
tube of ultra high clean steel so manufactured has an approximately
uniform wall thickness, both circumferentially around the tube and
longitudinally along the tube axis.
[0055] The hot-rolled tube is then passed through different
finishing steps, for example cut in length into 2 to 4 pieces, and
its ends cropped, straightened at known rotary straightening
equipment if necessary, and non-destructively tested by one or more
of the different known techniques, like electromagnetic testing or
ultrasound testing.
[0056] The surface of each piece of hot-rolled tube is then
properly conditioned for cold drawing. This conditioning includes
pickling by immersion in acid solution, and applying an appropriate
layer of lubricants, like the known zinc phosphate and sodium
estearathe combination, or reactive oil. After surface
conditioning, the seamless tube is cold drawn, pulling it through
an external die that has a diameter smaller than the outside
diameter of the tube being drawn. In most cases, the internal
surface of the tube is also supported by an internal mandrel
anchored to one end of a rod, so that the mandrel remains close to
the die during drawing. This drawing operation is performed without
the necessity of previously heating the tube above room
temperature.
[0057] The seamless tube is so cold drawn at least once, each pass
reducing both the outside diameter and the wall thickness of the
tube. The cold-drawn steel tube so manufactured has a uniform
outside diameter along the tube axis, and a uniform wall thickness
both circumferentially around the tube and longitudinally along the
tube axis. The so cold-drawn tube has an outside diameter
preferably between 10 and 70 mm, and a wall thickness preferably
from 1 to 4 mm.
[0058] The cold-drawn tube is then heat treated in an austenizing
furnace at a temperature of at least the upper austenizing
temperature, or Ac3 (which, for the specific chemistry disclosed
herein, is about 880.degree. C.), but preferably above about
920.degree. C. and below about 1050.degree. C. This maximum
austenizing temperature is imposed in order to avoid grain
coarsening. This process can be performed either in a fuel furnace
or in an induction-type furnace, but preferably in the latter. The
transit time in the furnace is strongly dependent on the type of
furnace utilized. It has been found that the high surface quality
required by this application is better obtained if an induction
type furnace is utilized. This is due to the nature of the
induction process, in which very short transit times are involved,
precluding oxidation to occur. Preferably, the austenizing heating
rate is at least about 100.degree. C. per second, but more
preferably at least about 200.degree. C. per second. The extremely
high heating rate and, as a consequence, very low heating times,
are important for obtaining a very fine grain microstructure, which
in turn guarantees the required mechanical properties.
[0059] Furthermore, an appropriate filling factor, defined as the
ratio of the round area defined by the outer diameter of the tube
to the round area defined by the coil inside diameter of the
induction furnace, is important for obtaining the required high
heating rates. The minimum filling factor is about 0.16, and a
preferred minimum filling factor is about 0.36.
[0060] At or close to the exit zone of the furnace the tube is
quenched by means of an appropriate quenching fluid. The quenching
fluid is preferably water or water-based quenching solution. The
tube temperature drops rapidly to ambient temperature, preferably
at a rate of at least about 100.degree. C. per second, more
preferably at a rate of at least about 200.degree. C. per second.
This extremely high cooling rate is crucial for obtaining a
complete microstructure transformation.
[0061] In a technique where a tempering step is employed, the steel
tube is then tempered with an appropriate temperature and cycle
time, at a temperature below Ac1. Preferably, the tempering
temperature is between about 400-600.degree. C., and more
preferably between about 450-550.degree. C. Alternatively, the
tempering temperature may be between 200.degree. C. to 600.degree.
C. and more preferably between 250.degree. C. to 550.degree. C. The
soaking time shall be long enough to guarantee a very good
temperature homogeneity, but if it is too long, the desired
mechanical properties are not obtained. This tempering step is
performed preferably in a protective reducing or neutral atmosphere
to avoid decarburizing and/or oxidation of the tube.
[0062] In a preferred method, the tempering step is eliminated and
only a high speed quench using water or water based solutions, as
described above, is employed.
[0063] In order to achieve a high speed quench, the following
equipment is preferred, but not required.
[0064] A Quenching line with a full capacity of 2200 kg per hour,
follows an induction furnace with a maximum power of inductor
settled at 500 Kw. A head quencher employs 42 lines with 12 nozzles
on each line. Water quenching flow is adjusted into a range of 10
to 60 m3 per hour, and the advance speed of the tube is controlled
from 5 to 25 meters per minute. Additionally, following pinch
rollers are set up to produce a rotation over the tube.
[0065] The ultra high strength steel tube so manufactured is passed
through different finishing steps, straightened at known rotary
straightening equipment, and non-destructively tested by one or
more of the different known techniques. Preferably, for this kind
of applications tubes should be tested by means of both known
ultrasound and electromagnetic techniques.
[0066] The tubing after heat treatment can be chemically processed
to obtain a tube with a desirable appearance and very low surface
roughness. For example, the tube could be pickled in a sulfuric
acid and hydrochloric acid solution, phosphated using zinc
phosphate, and oiled using a petroleum-based oil, a water-based
oil, or a mineral oil.
[0067] A steel tube obtained by the first or second described
methods have the following minimum mechanical properties:
TABLE-US-00005 Yield Strength about 110 ksi (758 MPa) minimum
Tensile Strength about 145 ksi (1000 MPa) minimum Elongation about
9% minimum
[0068] The yield strength, tensile strength, and elongation are to
be performed according to the procedures described in the Standards
ASTM E8. For the tensile test, a full size specimen for evaluating
the whole tubular section is preferred.
[0069] Flattening testing shall conform to the requirements of
Specification DOT 39 of 49 CFR, Paragraph 178.65. Therefore, a tube
section shall not crack when flattened with a 60 degree angled
V-shaped tooling, until the opposite sides are 6 times the tube
wall thickness apart. This test is fully met by the steel
developed.
[0070] In order to obtain a good balance between strength and
toughness, the prior (sometimes referred to as former) austenitic
grain size shall be preferably 7 or finer, and more preferably 9 or
finer, as measured according to ASTM E-112 Standard. This is
accomplished thanks to the extremely short heating cycle during
austenitizing.
[0071] The steel tube obtained by the described method shall have
the stated properties in order to comply with the requirements
stated for the invention.
[0072] The demand of the industry is continuously pushing roughness
requirements to lower values. The present invention has a good
visual appearance, with, for example, a surface finish of the
finished tubing of 3.2 microns maximum, both at the external and
internal surfaces. This requirement is obtained through cold
drawing, short austenizing times, reducing or neutral atmosphere
tempering, and an adequate surface chemical conditioning at
different steps of the process.
[0073] A hydroburst pressure test shall be performed by sealing the
ends of the tube section, for example, by welding flat steel plates
to the ends of the tube. It is important that a 300 mm tube section
remains constraint free so that full hoop stress can develop. The
pressurization of the tube section shall be performed by pumping
oil, water, alcohol or a mixture of them.
[0074] The burst test pressure requirement depends on the tube
size. When burst tested, the ultra high strength steel seamless
tube has a guaranteed ductile behavior at -60.degree. C. Tests
performed on the samples produced show that this grade has a
guaranteed ductile behavior at -60.degree. C., with a
ductile-to-brittle transition temperature below -60.degree. C.
[0075] The inventors have found that a far more representative
validation test is the burst test, performed both at ambient and at
low temperature, instead of Charpy impact test (according to ASTM
E23). This is due to the fact that relatively thin wall thicknesses
and small outside diameter in these products are employed,
therefore no standard ASTM specimen for Charpy impact test can be
machined from the tube in the transverse direction. Moreover, in
order to get this subsize Charpy impact probe, a flattening
deformation has to be applied to a curved tube probe. This has a
sensible effect on the steel mechanical properties, in particular
the impact strength. Therefore, no representative impact test is
obtained with this procedure.
Examples Using Alternative, Low Carbon, Low Alloy Steels
[0076] Applicants have discovered that a high speed quench without
a temper is a critical aspect of the present invention. Steels
which are lower alloy and less expensive than prior art chemistries
when treated by a particular heating and high speed quench can meet
or exceed the standards discussed hereinbefore.
[0077] The above defined, novel Steels A, B, C, D and E are
alternative steels that were analyzed using the preferred method,
wherein a very fast induction furnace austenizing with a high speed
quench was used instead of adding a tempering step. Surprisingly,
when control testing was done with certain of these novel steels
wherein less than a high speed quench, i.e, a normal quenching
process was employed or a tempering step, as described
hereinbefore, was employed, the tests showed significantly poorer
characteristics.
High Speed Quench and no Temper Process with Alternative Including
Lower Cost Steels According to the Preferred Method
[0078] The parameters used for high speed quench tests on Steel E
samples were as follows: Water flow of 40 m3/hr ; Speed advance
tube of 20 m/min.; Inductor power of 80% Austenitizing temperature:
880-940.degree., aim 920.degree.; Martensite transformation on OD
surface and core material was observed.
[0079] FIG. 1 shows core material with 100% Martensite
transformation for Steel E.
[0080] Steel E, which has chemistry similar to a low alloy SAE 1010
grade steel, did not achieved minimum expected values. when
subjected to high speed quenching.
[0081] Test results were as follows: TABLE-US-00006 YS YS % UTS UTS
Sample (Mpa) (Psi) Elo (Mpa) (Psi) 20476 561 81414 26 835 121140
20477 570 82680 32 827 119988 20478 538 78086 32 802 116446 20479
552 80177 32 831 120613
[0082] Likewise, burst tests at low temperature (-60.degree. C.)
were performed in order to observe the behavior and type of crack.
FIG. II shows tested burst samples for Steel E. Both presented a
ductile behavior.
[0083] A control test on Steel E involved a normal quenching
process was performed, results as follows: TABLE-US-00007 YS YS UTS
Sample (Mpa) (Psi) % Elo (Mpa) UTS (Psi) 20480 478 69367 28 721
104683 20481 469 68059 32 713 103531 20482 497 72226 32 714 103574
20483 478 69367 32 703 102009
[0084] FIG. III presents the core structures for Steel E using
normal quenching process. Some ferrite structure is observed along
the wall thickness.
[0085] Steel D was discovered to be very promising because of the
high performance to cost value it presented. Steel D was selected
to manufacture tubing according to the preferred method. Measured
chemical composition of samples of Steel D that were used for high
speed quench tests were as follows: TABLE-US-00008 Element % Value
C 0.11 Mn 1.07 S 0.002 P 0.008 Si 0.08 V 0.08 Al 0.03 Nb 0.008
[0086] The parameters used for the high speed quench tests on
samples of Steel D were as follows:
Quenching process was conducted controlling austenite temperature
into 920-940.degree. C.
Water flow of 40 m3/hr
Speed advance tube of 10 m/min.
Inductor power of 62% total capacity (500 Kw)
A rotation over the tube was given with an angle of pinch rolls of
17.degree.
[0087] Test results for high speed quenched on samples of Steel D,
were as follows: TABLE-US-00009 YS YS % UTS UTS Sample (Mpa) (Psi)
Elo (Mpa) (Psi) 19605 860 124810 20 1209 175388 19606 781 113360 19
1184 171860
[0088] FIG. IV shows that a high speed quench Steel D
microstructure that presents Martensite at 100% and a completely
quenched transformation.
[0089] Likewise, burst tests at low temperature (-60.degree. C.)
were performed in order to observe the behavior and type of crack.
Figure V shows tested burst samples for Steel D. Both presented a
ductile behavior.
[0090] A control test on Steel D involving a normal quenching
process was performed, results as follows: TABLE-US-00010 YS YS UTS
Sample (Mpa) (Psi) % Elo (Mpa) UTS (Psi) 19609 618 89635 24 861
124952 19610 586 85060 24 882 127967
[0091] FIG. VI presents the core structures for Steel D using
normal quenching process.
[0092] Steel B was selected to manufacture tubing according to the
preferred method. Measured chemical composition of samples of Steel
B that were used for high speed quench tests were as follows:
TABLE-US-00011 Element % Value C 0.10 Mn 1.09 S 0.001 P 0.011 Si
0.28 V 0.038 Al 0.035 Cr 0.68 Mo 0.41 Nb 0.005
[0093] The parameters used for the high speed quench tests on
samples of Steel B were as follows:
Quenching process was conducted controlling austenite temperature
into 920-940.degree. C. Water flow of 40 m3/hr
Speed advance tube of 10 m/min.
Inductor power of 70% total capacity (500 Kw)
A rotation over the tube was given with an angle of pinch rolls of
17.degree.
[0094] Test results for high speed quenched on samples of Steel B,
were as follows: TABLE-US-00012 YS YS % UTS Sample (Mpa) (Psi) Elo
(Mpa) UTS (Psi) 25222 940 136 22 1217 176 25002 914 132 24 1206
175
[0095] Likewise, burst tests at low temperature (-60.degree. C.)
were performed on Steel B in order to observe the behavior and type
of crack, both presented a ductile behavior.
[0096] Steel A was selected to manufacture tubing according to the
preferred method. Measured chemical composition of samples of Steel
A that were used for high speed quench tests were as follows:
TABLE-US-00013 Element % Value C 0.10 Mn 1.23 S 0.002 P 0.008 Si
0.27 V 0.002 Al 0.035 Cr 0.11 Mo 0.05 Ni 0.34
[0097] The parameters used for the high speed quench tests on
samples of Steel A were as follows:
Quenching process was conducted controlling austenite temperature
into 920-940.degree. C.
Water flow of 50 m3/hr
Speed advance tube of 20 m/min.
Inductor power of 90% total capacity (500 Kw)
A rotation over the tube was given with an angle of pinch rolls of
17
[0098] Test results for high speed quenched on samples of Steel A,
were as follows: TABLE-US-00014 YS YS % UTS Sample (Mpa) (Psi) Elo
(Mpa) UTS (Psi) 20313 920 133 22 1230 178 21442 883 128 20 1195
173
[0099] Likewise, burst tests at low temperature (-60.degree. C. and
-100.degree. C.) were performed on Steel A in order to observe the
behavior and type of crack, both presented a ductile behavior.
Control Tests with a High Quench Followed by a Temper Process with
Alternative Lower Cost Steels
[0100] Once samples of the preferred Steel D were found to yield
surprising mechanical values upon using a high speed quenching
according to the preferred method, a tempering then was performed
in order to determine the effect of adding a temper upon the
mechanical properties.
[0101] A tempering heat treatment was conducted at 580.degree. C.
for total time of 15 minutes. The UTS average was 116 Ksi (805
MPa), which do not meet the expected values
[0102] While preferred embodiments of our invention have been shown
and described in order to comply with the description and
enablement requirements of 35 USC .sctn.112, it is to be understood
that the scope of the invention is not limited to any embodiment
that has been described, but solely is to be defined by the scope
of the appended claims.
* * * * *