U.S. patent application number 10/962943 was filed with the patent office on 2005-04-28 for method for producing line pipe.
Invention is credited to Merwin, Matthew J..
Application Number | 20050087269 10/962943 |
Document ID | / |
Family ID | 34526855 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087269 |
Kind Code |
A1 |
Merwin, Matthew J. |
April 28, 2005 |
Method for producing line pipe
Abstract
A method for producing steel line pipe having low yield strength
to tensile strength ratio in order to improve the capability of
steel line pipe to undergo reeling into coil form and unreeling
therefrom. The method includes (a) providing a steel pipe having a
composition consisting essentially of in weight percent: C 0.01 to
0.40, Mn 0.25 to 2.0, P residual to less than 0.5, S residual to
less than 0.020, Si residual to 2.0, Cu residual to 1.0, Ni
residual to 1.0, Cr residual to 2.0, Mo residual to 1.0, Al 0.010
minimum to less than 1.0, N residual to 0.030, V residual to less
than 0.5, B residual to less than 0.02, Ti residual to less than
0.3, and Nb residual to less than 0.3, balance iron and incidental
impurities. The pipe is heated to a temperature within the
intercritical A.sub.c1 to A.sub.c3 temperature range, cooled to a
temperature below the M.sub.s (martensite start) temperature in
order to obtain martensite, reheated to a temperature below the
A.sub.c1 temperature for a time sufficient to obtain the desired
yield strength, tensile strength and yield strength to tensile
strength ratio, and then air cooled.
Inventors: |
Merwin, Matthew J.;
(Murrysville, PA) |
Correspondence
Address: |
United States Steel Corporation
600 Grant Street - Room 1500
Pittsburgh
PA
15219
US
|
Family ID: |
34526855 |
Appl. No.: |
10/962943 |
Filed: |
October 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60513354 |
Oct 22, 2003 |
|
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|
Current U.S.
Class: |
148/590 |
Current CPC
Class: |
C21D 2211/008 20130101;
C21D 2211/005 20130101; C21D 1/185 20130101; C21D 9/08
20130101 |
Class at
Publication: |
148/590 |
International
Class: |
C21D 009/08 |
Claims
What is claimed is:
1. A method for the production of steel line pipe, comprising: (a)
providing a steel pipe having a composition consisting essentially
of in weight percent: C 0.01 to 0.40, Mn 0.25 to 2.0, P residual to
less than 0.5, S residual to less than 0.020, Si residual to 2.0,
Cu residual to 1.0, Ni residual to 1.0, Cr residual to 2.0, Mo
residual to 1.0, Al 0.010 minimum to less than 1.0, N residual to
0.030, V residual to less than 0.5, B residual to less than 0.02,
Ti residual to less than 0.3, and Nb residual to less than 0.3,
balance iron and incidental impurities; (b) heating the pipe to a
temperature within the intercritical A.sub.c1 to A.sub.c3
temperature range to obtain ferrite and austenite in the
microstructure; (c) cooling the heated pipe to a temperature below
the M.sub.s (martensite start) temperature at a cooling rate
sufficient to cause the austenite present to transform to
martensite; (d) after cooling from the intercritical annealing
temperature, reheating the pipe to a temperature below the A.sub.c1
temperature for a time sufficient to obtain the desired yield
strength, tensile strength and yield strength to tensile strength
ratio; and (e) then cooling the pipe to room temperature.
2. The method of claim 1, wherein the heating step comprises
heating the pipe to a temperature within the intercritical range
that is sufficient to obtain between 5 to 90 percent austenite in
the microstructure.
3. The method of claim 1, wherein said heating step comprises
heating the pipe to a temperature within the range of 1346 to
1562.degree. F. (730 to 850.degree. C.) for a time at temperature
within the range of 5 to 120 minutes.
4. The method of claim 1, wherein said cooling step (c) comprises
cooling the pipe at a rate within the range of 1.degree. C./second
to 200.degree. C./second.
5. The method of claim 4, wherein said cooling step comprises water
quenching the pipe.
6. The method of claim 1, wherein said reheating step (c) comprises
reheating the pipe to a temperature within the range of 572 to
1292.degree. F. (300 to 700.degree. C.).
7. The method of claim 1, wherein said cooling step (d) comprises
air cooling the pipe to room temperature.
8. The method of claim 1, wherein said pipe has a yield/tensile
ratio of 0.40 to 0.85 after cooling step (d).
9. The method of claim 1, wherein steps (b), (c) and (d) are
performed in-line on a seamless pipe mill.
10. The method of claim 1, wherein steps (b), (c) and (d) are not
performed in-line on a pipe mill.
11. The method of claim 1 which further comprises reeling said
steel line pipe into coil form.
12. The method of claim 1 wherein said steel line pipe is in coil
form, said method further comprising unreeling said steel line
pipe.
13. A method for the production of steel line pipe, comprising: (a)
providing a steel pipe having a composition consisting essentially
of in weight percent: C 0.01 to 0.40, Mn 0.25 to 2.0, P residual to
less than 0.5, S residual to less than 0.020, Si residual to 2.0,
Cu residual to 1.0, Ni residual to 1.0, Cr residual to 2.0, Mo
residual to 1.0, Al 0.010 minimum to less than 1.0, N residual to
0.030, V residual to less than 0.5, B residual to less than 0.02,
Ti residual to less than 0.3, and Nb residual to less than 0.3,
balance iron and incidental impurities; (b) heating the pipe to a
temperature within the temperature range of 1346 to 1562.degree. F.
(730 to 850.degree. C.) for a time at temperature within the range
of 5 to 120 minutes in order to obtain ferrite and austenite in the
microstructure; (c) cooling the heated pipe to a temperature below
the M.sub.s (martensite start) temperature at a cooling rate
sufficient to cause the austenite present to transform to
martensite; (d) after cooling from the intercritical annealing
temperature, reheating the pipe to a temperature reheating the pipe
to a temperature within the range of 572 to 1292.degree. F. (300 to
700.degree. C.) in order to obtain the desired yield strength,
tensile strength and yield strength to tensile strength ratio; and
(e) then air cooling the pipe to room temperature.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for producing
steel line pipe having low yield strength to tensile strength
ratio, and particularly to a method for producing steel line pipe
by intercritical annealing, quenching and tempering. The invention
includes a method for improving the capability of steel line pipe
to undergo reeling into coil form and unreeling therefrom which
includes reeling steel line pipe into coil form which has been
produced by intercritical annealing, quenching and tempering.
BACKGROUND OF THE INVENTION
[0002] Customers for steel line pipe are interested in acquiring
pipe having relatively low yield strength to ultimate tensile
strength ratios. The low yield to tensile strength ratio is thought
to aid coiling of the pipe for transport. Typically it is desired
that the pipe have a yield strength of less than 85 percent of the
tensile strength. This requirement is specified so as to
accommodate the pipe reeling and unreeling operations. Normally in
prior art commercial production, steel line pipe is heat treated by
annealing at a temperature above the A.sub.c3 temperature to fully
austenitize the steel, water quenching and then reheating to a
temperature below the A.sub.c1 temperature to temper the steel.
Most current line pipe steels are produced with microalloyed high
strength low alloy compositions and frequently result in yield to
tensile ratios approaching, and in some cases exceeding, the 0.85
yield to tensile ratio requirement.
[0003] U.S. Pat. No. 3,655,465 discloses steel pipe for oil country
goods applications, such as tubing and casing, that has over 90 ksi
yield strength and which is rendered less susceptible to sulfide
corrosion cracking in sour oil wells through an intercritical
heating and tempering treatment. The steel is heated to a
temperature within the intercritical A.sub.c1 to A.sub.c3
temperature range. Then it is cooled to below the M.sub.s
(martensite start) temperature and preferably below the M.sub.f
(martensite finish) temperature, reheated to a tempering
temperature below the A.sub.c1 temperature and finally cooled to
room temperature. Cooling can be conducted by air, oil quenching,
water quenching, etc. Steels containing Ni were found to actually
increase in strength after the tempering treatment, more
particularly those which also contain at least one temper resistant
element, such as up to Mo up to 3%, Cr up to 4%, Si up to 3%, V up
to 3%, and W. Tests conducted on C 75, AISI 4140 and 4340 steels,
as well as 3.5% Ni and 9% Ni alloys, showed a significant increase
in sulfide stress corrosion cracking resistance after the
intercritical heating and tempering treatment described above.
[0004] U.S. Pat. No. 4,354,882 discloses a process for improving
sulfide stress cracking resistance of steel pipe comprising
extruding a steel tube of AISI 4130 composition, intercritically
annealing the steel tube, cooling, cold sizing and surface
grinding, intercritically annealing again, and then reheating to
fully austenitize, quench and temper the steel tube.
[0005] U.S. Pat. No. 4,938,266 discloses a method of producing
steel plate having a low yield ratio, high strength and a
dual-phase mixed microstructure of ferrite and second-phase
carbide. The method includes heating a slab of low carbon steel or
low carbon low alloy steel to a temperature of 950 to 1250.degree.
C., hot rolling the slab to plate, rapid cooling the plate to a
temperature not exceeding 250.degree. C., reheating to a
temperature of A.sub.c1+20.degree. C. to A.sub.c1+80.degree. C.,
water cooling and then tempering at a temperature in the range of
200 to 600.degree. C. The reference requires rapid cooling after
hot rolling to a temperature not exceeding 250.degree. C. prior to
reheating to the intercritical temperature range.
[0006] Various line pipe steel compositions are disclosed in U.S.
Pat. Nos. 3,692,514 and 3,955,971. Various methods for producing
line pipe steels with low yield ratio are disclosed in Abstracts of
JP 63-014815, JP 63-250418, JP 63-227715, JP 3-097809, JP 5-098350
and JP 8-337816. JP63-014815 discloses heating steel line pipe to
the A.sub.c3 temperature or above, rapid cooling, stopping cooling
when the average temperature in the pipe wall in the thickness
direction is between 350 C. to 550 C., and then air cooling. The
pipe has low maximum hardness, good sour resistance and low yield
ratio. JP63-250418 discloses subjecting seamless pipe after finish
hot rolling to water cooling from less than or equal to 600 C. to
room temperature at 5-30 C/sec. A yield ratio less than or equal to
85% can be obtained. JP63-227715 discloses production of hot rolled
sheet for line pipe. A slab is heated to 1180-1300 C, rough rolled
at 950-1050 C. and finish rolled at 760-800 C. The hot rolled sheet
is air cooled at 5-20 C/sec to 670 C. and coiled. A yield ratio of
less than or equal to 85% is obtained. JP3-097809 discloses
seamless pipe after finish hot rolling at a temperature between Ar3
and 900 C. is allowed to cool, and then cooled rapidly from a
temperature between just under the Ar1 point and 400 C. down to
room temperature. Or finished pipe may be cooled to room
temperature, reheated to the austenitizing temperature, allowed to
cool, and then cooled rapidly from a temperature between the Ar1
point and 400 C. JP5-098350 discloses subjecting pipe in the final
stage of hot piercing continuous rolling to working at 900-700 C.
with 3-15% reduction of area. The pipe has a temperature between
Ar3-100 C. and Ar3+50 C. after this operation. The pipe is reheated
to 900 to 1000 C and subjected to hot finish rolling with an Ar3+50
C. finishing temperature. The resulting pipe is subjected to air
cooling from greater than or equal to the Ar3 temperature, or is
subjected, after air cooling to heating up to less than or equal to
Ac3 and air cooled to undergo a tempering treatment. JP 8-337816
discloses production of low yield ratio steel sheet for line pipe.
A steel slab is heated and hot rolled with a finishing temperature
of Ar3+30 C. to Ar3, cooled at a mild cooling rate of less than or
equal to 10 C./sec for 5 to 10 seconds. The hot rolled sheet is
subsequently cooled at a cooling rate of greater than or equal to
15 C./sec and coiled at 400 to 500 C.
DISCLOSURE OF THE INVENTION
[0007] According to the present invention a method for the
production of steel line pipe includes providing a steel pipe
having a composition consisting essentially of in weight percent: C
0.01 to 0.40, Mn 0.25 to 2.0, P residual to less than 0.5, S
residual to less than 0.020, Si residual to 2.0, Cu residual to
1.0, Ni residual to 1.0, Cr residual to 2.0, Mo residual to 1.0, Al
0.010 minimum to less than 1.0, N residual to 0.030, V residual to
less than 0.5, B residual to less than 0.02, Ti residual to less
than 0.3, and Nb residual to less than 0.3, balance iron and
incidental impurities. The pipe is heated to a temperature within
the intercritical A.sub.c1 to A.sub.c3 temperature range to obtain
ferrite and austenite in the microstructure. Preferably the pipe is
heated to a temperature within the intercritical range that is
sufficient to obtain between 5 to 90 percent austenite in the
microstructure. Most preferably the pipe is heated to a temperature
within the range of 1346 to 1562.degree. F. (730 to 850.degree. C.)
for a time at temperature within the range of 5 to 120 minutes. The
pipe is water quenched to a temperature below the M.sub.s
(martensite start) temperature at a cooling rate sufficient to
cause the austenite present to transform to martensite. Depending
on the alloy content of the steel, appropriate cooling rates may
range from 1.degree. C./second to 200.degree. C./second. After
cooling from the intercritical annealing temperature, the pipe is
reheated to a temperature below the A.sub.c1 temperature for a time
sufficient to obtain the desired yield strength, tensile strength
and yield strength to tensile strength ratio. The pipe is then air
cooled to room temperature. The advantages provided by treating
pipe according to the method of the invention are: creation of
microstructures capable of achieving yield/tensile ratios of 0.40
to 0.85, while employing commonly available heat treatment
facilities.
[0008] In one embodiment the steps of heating to a temperature
within the intercritical temperature range, water quenching and
reheating to a tempering temperature are performed in-line on a
seamless pipe mill. However, the method of the invention may be
performed off-line. The method may also be performed on line pipe
manufactured by other pipe manufacturing processes.
[0009] The invention also includes a method for improving the
capability of steel line pipe to undergo reeling into coil form and
unreeling therefrom which includes reeling steel line pipe into
coil form which has been produced by intercritical annealing,
quenching and tempering.
DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a graph of yield strength, as defined by the 0.5%
Extension Under Load (EUL) method, vs. tempering temperature for
the Example 1 steel after intercritical annealing at three
different temperatures, followed by water quenching to room
temperature and then tempering at the various tempering
temperatures indicated.
[0011] FIG. 2 is a graph of ultimate tensile strength vs. tempering
temperature for the Example 1 steel after intercritical annealing,
quenching and tempering as referred to with respect to FIG. 1.
[0012] FIG. 3 is a graph of the 0.5% EUL yield strength to ultimate
tensile strength ratio vs. tempering temperature of the Example 1
steel after intercritical annealing, quenching and tempering as
referred to with respect to FIG. 1.
[0013] FIG. 4 is a graph of the CVN energy absorbed at 32.degree.
F. (0.degree. C.) in foot-pounds vs. tempering temperature for the
Example 1 steel after intercritical annealing followed by tempering
as referred to with respect to FIG. 1.
[0014] FIG. 5 is a graph of the CVN energy absorbed at -40.degree.
F. (-40.degree. C.) in foot-pounds vs. tempering temperature for
the Example 1 steel after intercritical annealing followed by
tempering as referred to with respect to FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] ) According to the present invention a method for the
manufacture of steel line pipe includes providing a steel pipe
having a composition consisting essentially of in weight percent: C
0.01 to 0.40, Mn 0.25 to 2.0, P residual to less than 0.5, S
residual to less than 0.020, Si residual to 2.0, Cu residual to
1.0, Ni residual to 1.0, Cr residual to 2.0, Mo residual to 1.0, Al
0.010 minimum to less than 1.0, N residual to 0.030, V residual to
less than 0.5, B residual to less than 0.02, Ti residual to less
than 0.3, and Nb residual to less than 0.3, balance iron and
incidental impurities. The pipe may be made by a seamless process
or various other pipe manufacturing processes. The process for
manufacturing the pipe is not in and of itself critical. Also, the
pipe may have been subjected to various prior heat treatments.
[0016] The pipe is heated to a temperature within the intercritical
A.sub.c1 to A.sub.c3 temperature range to obtain ferrite and
austenite in the microstructure. Preferably the pipe is heated to a
temperature within the intercritical range that is sufficient to
obtain between 5 to 90 percent austenite in the microstructure.
Most preferably the pipe is heated to a temperature within the
range of 1346 to 1562.degree. F. (730 to 850.degree. C.) for a time
at temperature within the range of 5 to 120 minutes. It is
desirable to have austenite within the above range in order to
achieve the low yield/tensile ratio, while maintaining yield and
tensile strength requirements dictated in common line pipe
specifications. With austenite contents outside this specified
range, the effect of martensite in reduction of the yield/tensile
ratio will not be reliably achieved. Generally, a range of
austenite between 5 to 50 percent is satisfactory.
[0017] After cooling from the intercritical anneal temperature, the
pipe is reheated to a temperature below the A.sub.c1 temperature
for a time sufficient to obtain the desired yield strength, tensile
strength and yield strength to tensile strength ratio. Preferably
the pipe is reheated to a temperature within the range of 572 to
1292.degree. F. (300 to 700.degree. C.). The pipe is then air
cooled to room temperature.
[0018] An example of the composition in weight percent of a steel
treated in the laboratory according to the invention is set forth
in Table 1 below:
1TABLE 1 C Mn P S Si Cu Ni Cr Mo Al N V B Ti Cb 0.14 0.98 0.01
0.002 0.24 0.013 0.01 0.06 0.1 0.022 0.004 0.047 0.0001 0.002
0.001
[0019] This steel was commercially produced by the basic oxygen
process and ladle refinement. It was continuously cast as round
billets, and subsequently rolled to seamless pipe product.
[0020] Samples of the pipe were heat treated in the laboratory in
accordance with the invention described herein. Samples were
exposed to three intercritical soaking temperatures, 1450.degree.
F. (788.degree. C.), 1475.degree. F. (802.degree. C.) and
1500.degree. F. (816.degree. C.), and subsequently water-quenched
to room temperature. After quenching the samples were sectioned for
examination in the as-quenched condition or for tempering. Several
tempering temperatures were employed to determine the material
response to this process.
[0021] FIGS. 1-5 illustrate the performance of the example 1 steel
as related to the thermal treatments employed. FIGS. 1 and 2 show
that yield strength and tensile strength decline with increasing
tempering temperature. FIG. 3 shows that the yield-tensile ratio
increases with increasing temperature. However, in all cases the
example 1 steel treated in accordance with the invention
demonstrated yield-tensile ratio substantially below that of the
typical range in prior art commercial production of the alloy
employed in this study. The tempering procedure was found to be
necessary to achieve acceptable impact toughness performance, as
shown in the graph of Charpy V-Notch energy absorbed at a
32.degree. F. (0.degree. C.) test temperature. Many customers
require 50 foot-pounds energy absorbed, or more, for line pipe
products. For the composition of steel employed in this study,
tempering temperatures in the range of 1050 to 1150.degree. F. (565
to 620.degree. C.) provided the best combination of strength, and
toughness, while maintaining a yield-tensile ratio substantially
less than commonly available with the examined steel chemistry.
* * * * *