JP3785376B2 - Manufacturing method of steel pipe and steel plate for steel pipe excellent in weld heat affected zone toughness and deformability - Google Patents

Description

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【発明の効果】
本発明によるＨＡＺ靭性に優れ、高い変形能を有する高強度鋼管（ＡＰＩ規格Ｘ１００以上）をパイプラインに採用することにより、パイプラインの安全性が著しく向上すると共に、輸送効率が飛躍的に改善された。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel pipe having high strength of X100 or more (yield strength of about 690 MPa or more, tensile strength of about 760 MPa or more) and excellent weld heat affected zone (HAZ) toughness and deformability as planned by the American Petroleum Institute (API). Is.
[0002]
[Prior art]
Line pipes used for pipelines that transport crude oil and natural gas over long distances are (1) increased in tension due to improved transport efficiency under high pressure and (2) improved local welding efficiency due to thinner walls. Tend to. Up to now, line pipes up to X80 in the API standard have been put into practical use, but there is a need for higher-strength line pipes. At present, high-strength line pipes of X100 or higher are manufactured by a method for producing X80 class line pipes (NKK Technical Report No. 138 (1992), pp. 24-31 and The 7th offshore Mechanical Arctic Engineering (1988), volume V, pp. 179). However, these line pipes have problems in terms of low-temperature toughness, particularly HAZ toughness, and a revolutionary high-strength steel pipe that overcomes these problems is desired. In addition, since a part of the frozen soil repeatedly melts and freezes in the pipeline laid on permafrost, there is a need for a steel tube with high deformability and excellent safety that can prevent the occurrence of ductile cracks by distorting the pipeline itself. It is rare.
[0003]
The HAZ toughness of low alloy steel is (1) grain size, (2) high carbon island martensite (M ^* ), dispersed state of hardened phase such as upper bainite (Bu), (3) grain boundary embrittlement. (4) It is governed by various metallurgical factors such as elemental microsegregation. Among them, the size of the HAZ crystal grains is known to have a great influence on the low temperature toughness, and many techniques for refining the HAZ structure have been developed and put into practical use.
[0004]
For example, a means to finely disperse TiN and improve the HAZ toughness during high heat input welding of 490 MPa class high-strength steel is disclosed (“Iron and Steel” (published in June 1979, Vol. 65, No. However, since these precipitates are exposed to high temperatures of 1400 ° C. or higher near the melting line, most of them are coarsened or dissolved, and the HAZ structure is coarsened to deteriorate the HAZ toughness. Have.
[0005]
In response to this problem, the HAZ structure near the melting line is refined by finely dispersing Ti oxide in steel and generating intragranular acicular ferrite (hereinafter referred to as IGF) in the HAZ during welding. It is disclosed in Japanese Patent Laid-Open Nos. 63-210235 and 1-15321 that HAZ toughness is improved.
[0006]
However, when the strength becomes higher than X100, the production of IGF from the Ti oxide is suppressed and the HAZ toughness deteriorates. Therefore, improvement of the HAZ toughness of the high strength steel of X100 or higher is strongly desired.
[0007]
On the other hand, regarding deformability, Japanese Patent Application Laid-Open No. 11-279700 discloses a steel pipe containing 10 to 50% of lower bainite in area fraction and excellent in buckling characteristics, and Japanese Patent Application Laid-Open No. 11-343542 has an average aspect ratio of 2. A steel pipe excellent in buckling resistance containing 2 to 15% of island-like martensite in an area fraction of ˜15 is disclosed.
However, none are intended for high-strength steel pipes of X100 or higher. Moreover, it aims at improving local buckling resistance about the base material of a steel pipe, and is not related with the steel pipe or pipeline containing a weld metal part.
[0008]
[Problems to be solved by the invention]
The present invention provides a high-strength steel pipe of X100 or higher having good HAZ toughness and excellent deformability and a method for producing the same.
[0009]
[Means for Solving the Problems]
The gist of the present invention is as follows.
[0010]
(1) In mass%,
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less]
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
Al: 0.05% or less,
N: 0.001 to 0.006%
And the balance is iron and inevitable impurities, and Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V
A base material having a Pb value defined in the range of 2.5 to 4.0;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in a tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more.
[0011]
(2) By mass%
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
Al: 0.05% or less,
N: 0.001 to 0.006%
In addition, Ni: 0.1-1.0%,
Cu: 0.1 to 1.2%,
Cr: 0.1 to 1.0%,
Mo: 0.1 to 1.0%,
V: 0.01 to 0.1%
Ca: 0.001 to 0.005%,
Mg: 0.0003 to 0.002%
And the balance consists of iron and inevitable impurities, and Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V
A base material having a Pb value defined in the range of 2.5 to 4.0;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in a tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more.
[0012]
(3) In mass%,
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.006%
The balance is made of iron and inevitable impurities, and Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo
A base material having a Qb value defined in the range of 2.0 to 3.5;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in the tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more.
[0013]
(4) By mass%
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.006%
In addition, Ni: 0.1-1.0%,
Cu: 0.1 to 1.2%,
Cr: 0.1 to 1.0%,
Mo: 0.1 to 1.0%,
V: 0.01 to 0.1%
Ca: 0.001 to 0.005%,
Mg: 0.0003 to 0.002%
And the balance is composed of iron and inevitable impurities, and Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo
A base material having a Qb value defined in the range of 2.0 to 3.5;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in the tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more.
[0014]
(5) The weld metal is further in mass%,
Cu: 0.1 to 1.0%
V: 0.01 to 0.1%
Ca: 0.001 to 0.005%
The steel pipe excellent in the weld heat affected zone toughness and deformability according to any one of the above (1) to (4), wherein one or more of them are contained.
[0020]
( 6 ) In mass%,
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
Al: 0.05% or less,
N: 0.001 to 0.006%
And the balance is made of iron and inevitable impurities, and Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V
After heating a slab having a Pb value defined by 2.5 to 4.0 to 950 to 1200 ° C., the reduction at 950 ° C. or less is set to 50% or more, and a temperature range of 700 to 850 ° C. After the rolling is finished, the weld heat affected zone toughness and deformation are characterized by cooling from a temperature range of 550 to 700 ° C. to an arbitrary temperature of 450 ° C. or less at a cooling rate of 2 ° C./second or more and then air cooling. A manufacturing method for steel plates for steel pipes with excellent performance.
[0021]
( 7 ) By mass%
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.006%
The balance is made of iron and inevitable impurities, and a slab having a Qb value defined by Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo in the range of 2.0 to 3.5 is 950 after heating to 1200 ° C., the reduction ratio at 950 ° C. or less and 50% or more, after completion of the rolling at a temperature range of 700-850 ° C., the cooling rate of 2 ° C. / sec or more from the temperature range of 550 to 700 ° C. A method for producing a steel plate for a steel pipe excellent in weld heat-affected zone toughness and deformability, characterized in that it is cooled to an arbitrary temperature of 450 ° C. or lower and then air cooled.
[0022]
( 8 ) The slab is further mass%,
Ni: 0.1 to 1.0%,
Cu: 0.1 to 1.2%,
Cr: 0.1 to 1.0%,
Mo: 0.1 to 1.0%,
V: 0.01 to 0.1%
Ca: 0.0005 to 0.005%,
Mg: 0.0003 to 0.002%
The manufacturing method of the steel plate for steel pipes excellent in the weld heat affected zone toughness and deformability as described in said (6) or (7) characterized by containing 1 type or 2 types or more.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Below, the high-strength steel pipe of this invention is demonstrated in detail.
[0024]
According to the study by the present inventors, the HAZ toughness largely depends on (1) the chemical composition of the steel and (2) the structure (the size of the crystal grains and the dispersion state of the hardened phase), and in order to improve the HAZ toughness Therefore, it is considered indispensable to optimize steel components and refine crystal grains, particularly to reduce the hardened phase such as M ^* . For steel pipes manufactured by welding inner and outer surfaces of steel plates (for example, UOE steel pipes), welding of one inner layer and one outer surface is applied from the viewpoint of reducing welding costs. In this case, it is considered that the toughness is most lowered in a region (coarse grains + Ac1 part) heated to 1400 ° C. or more in the vicinity of the melting line of the inner surface welding and reheated immediately above the Ac1 point by the subsequent outer surface welding. This is because carbon (C) is concentrated in a region transformed into austenite (ν) when reheated immediately above Ac1, and high carbon island martensite (M ^* ) containing a large amount of C in the subsequent cooling process. This is because a large amount of the cured phase is generated. Since M ^* contains a large amount of C, it is hard and easily becomes a point of occurrence of brittle fracture.
[0025]
In order to increase the strength of steel, it is inevitably necessary to increase the amount of alloying element added. However, the amount of M ^* produced increases in coarse grains and Ac1 part, and the HAZ toughness deteriorates greatly. Therefore, as a result of intensive studies on a method for suppressing the generation of M ^* in order to prevent the deterioration of toughness in the coarse particles and Ac1 part, the present inventors have (1) By reducing the C content of the steel pipe base material. It has been found that the amount of C concentrated in the region reheated immediately above Ac1 is reduced. Furthermore, in order to satisfy the target strength even when the temperature is made extremely low, the appropriate addition amount of the alloy element was examined. As a result, the Pb value in the case of B-free steel and the Qb in the case of B-added steel. It has been found that the strength can be ensured by limiting the value defined by the value to a predetermined range. However, when welding a base material of extremely low C steel, if the amount of C in the weld metal decreases, hot cracking due to δ solidification occurs. Moreover, when it contains C amount excessively, the low temperature toughness of a weld metal will deteriorate. Accordingly, the inventors have found an appropriate amount of C that prevents the hot cracking of the weld metal and satisfies the target strength of good low temperature toughness, and further an amount of alloying element added.
[0026]
In a pipeline laid on permafrost, it is said that a strain of about 3% is applied to the pipeline due to the melting and freezing of the frozen soil. In this case, it was found that if the uniform elongation in the tensile test in the tube axis direction of the base metal part and the weld metal part is 3% or more, the occurrence of ductile cracks can be prevented. Further, in order to increase the uniform elongation of the base metal, 5 to 50% of ferrite of 20 μm or less is contained, and in order to increase the uniform elongation of the weld metal, 1-15% of island martensite, preferably Has been found to contain 2 to 15%. Furthermore, when the yield strength in the tensile test in the base material circumferential direction is 689 MPa or more (X100 or more), the yield strength in the tensile test in the base material pipe axis direction is 0.9 times the yield strength in the tensile test in the circumferential direction. I found that there was no problem in practical use. Moreover, as a manufacturing method of the steel plate for steel pipes, rolling is finished in a temperature range of 650 to 800 ° C., and is cooled from a temperature range of 700 to 850 ° C. to an arbitrary temperature of 450 ° C. or less at a cooling rate of 2 ° C./second or more. Then, it was found that a steel sheet having both high strength and high uniform elongation can be obtained by air cooling thereafter, and the present invention has been achieved.
[0027]
That is, the feature of the present invention is that the alloy element addition amount is defined by the Pb value or the Qb value in order to ensure the target strength when applying an extremely low C—Nb—Ti-based component as the steel pipe base material. In order to limit the C amount from the viewpoint of preventing hot cracking and to satisfy the target strength, the alloy element addition amount is an appropriate range defined by Pw. In order to ensure excellent deformability, the uniform elongation in the tensile test in the tube axis direction of the base metal part and the weld metal part should be 3% or more, and in order to obtain a large uniform elongation The metal structure contains 5-50% ferrite having a particle size of 20 μm or less, the weld metal part contains 1-15%, preferably 2-15% of martensite on the island, and the circumference of the base material part. In direction tensile test Fushimi strength 689MPa or more, and in that the yield strength in the tensile test Hahazai section tube axis direction is not less than 0.9 times the yield strength in a tensile test in the circumferential direction.
[0028]
First, the reasons for limiting the components of the steel pipe base material will be described.
[0029]
In order to reduce the concentration of C in the region reheated immediately above Ac1, the C content of the base material must be 0.003% or less. This is because when the amount of C exceeds 0.003%, the amount of C enriched in austenite (ν) increases when heated just above Ac1, and high carbon island martensite (M ^{This is because *} ) is generated and becomes a point of occurrence of brittle fracture.
[0030]
In order to improve HAZ toughness, the C content of the base material must be 0.003% or less, but in order to satisfy the target strength of X100 or more, it is necessary to optimize the addition amount of the alloy element. is there. That is, in the case of B-free steel, the Pb value defined by the formula Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V must be in the range of 2.5 to 4.0. If the Pb value is less than 2.5, the target strength of X100 or more cannot be secured. On the other hand, when the Pb value exceeds 4.0, the generation of M ^* becomes remarkable and the HAZ toughness deteriorates. For this reason, the range of Pb value was limited to 2.5-4.0. On the other hand, in the case of B-added steel, the Qb value defined by the formula Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo must be in the range of 2.0 to 3.5. If the Qb value is less than 2.0, the target strength cannot be ensured. On the other hand, when the Qb value exceeds 3.5, the generation of M ^* becomes remarkable and the HAZ toughness deteriorates. For this reason, the range of Qb value was limited to 2.0-3.5.
[0031]
However, even if the amount of C is reduced as much as possible and the addition amount of the alloy element is limited to an appropriate range, excellent HAZ toughness cannot be obtained unless the basic components of the base material are appropriate. The reasons for limiting other basic components will be described below.
[0032]
Si is an element added for deoxidation and strength improvement, but if added in large amounts, the field weldability and the HAZ toughness deteriorate, so the upper limit was made 0.6%. For the deoxidation of steel, Ti alone is sufficient, and Si does not necessarily have to be added.
[0033]
Mn is an indispensable element for securing strength and low temperature toughness, and its lower limit is 0.8%. However, if Mn is too much, not only the hardenability of the steel is increased and the on-site weldability and HAZ toughness are deteriorated, but also the center segregation of continuously cast steel pieces is promoted and the low temperature toughness is also deteriorated. 5%.
[0034]
Nb not only suppresses recrystallization of ν during controlled rolling and refines the crystal grains, but also contributes to precipitation hardening and hardenability, and has the effect of strengthening the steel and is essential in the present invention. Elements. In order to obtain this effect, a minimum of 0.01% Nb is required. However, if the amount of Nb is too large, the HAZ toughness deteriorates, so the upper limit value was limited to 0.05%.
[0035]
Ti forms fine TiN, suppresses coarsening of ν grains in slab reheating and HAZ, refines microstructure, improves low temperature toughness of base material and HAZ, and is an essential element in the present invention. It is. In order to exhibit this effect, addition of 0.005% or more is necessary. On the other hand, if it is too much, coarsening of TiN and precipitation hardening due to TiC occur and the low temperature toughness is deteriorated, so the upper limit value is limited to 0.03%.
[0036]
Al is an element added for deoxidation, but if added in a large amount, alumina-based nonmetallic inclusions increase and the cleanliness of the steel deteriorates, so the upper limit was made 0.05%.
[0037]
N forms TiN and suppresses coarsening of ν grains of HAZ during reheating of the slab and improves the low temperature toughness of the base material and HAZ. The minimum amount required for this is 0.001%. However, if the amount of N is too large, HAZ toughness is deteriorated due to slab surface flaws or solute N, so the upper limit value must be limited to 0.006%.
[0038]
In the present invention, the amounts of P and S, which are inevitable impurities, are set to 0.015% or less and 0.005% or less. The main reason is to further improve the low temperature toughness of the base material and the HAZ. The reduction of the P content reduces the center segregation of the continuously cast slab, prevents the grain boundary fracture and improves the low temperature toughness. Further, the reduction of the amount of S has the effect of reducing ductility and toughness by reducing MnS stretched by controlled rolling.
[0039]
Next, the reason for adding one or more of Ni, Cu, Cr, Mo, V, Ca, and Mg will be described. The main purpose of adding these elements as basic components is to improve properties such as strength and low-temperature toughness without impairing the characteristics of the steel of the present invention. Therefore, the amount added is of a nature that should be restricted by itself.
[0040]
Ni improves the strength and low temperature toughness of the base metal without adversely affecting weldability and HAZ toughness, but is less effective at 0.1% or less, and addition of 1.0% or more is not preferable for weldability. The upper limit value was 1.0%.
[0041]
Cu has substantially the same effect as Ni, and is also effective in corrosion resistance, resistance to hydrogen-induced cracking, and the like, and it is necessary to add 0.1% or more. However, when added excessively, Cu-cracks are generated during precipitation hardening due to precipitation hardening and HAZ toughness, and the upper limit value was set to 1.2%.
[0042]
Cr has the effect of increasing the strength of the base metal and the welded portion, and it is necessary to add 0.1% or more. However, if too much, field weldability and HAZ toughness are significantly deteriorated. For this reason, the upper limit of the Cr amount is set to 1.0%.
[0043]
Mo is an element that increases the strength of the base metal and the welded portion. However, if it exceeds 1.0%, the base metal, the HAZ toughness and the weldability are deteriorated similarly to Cr. In addition, the effect is small when 0.1% or less is added.
[0044]
V has substantially the same effect as Nb, but the effect is much weaker than Nb. In order to exhibit the effect, addition of 0.01% or more is necessary. Further, the upper limit is allowable up to 0.1% from the viewpoint of on-site weldability and HAZ toughness.
[0045]
Ca controls the carrying of sulfide (MnS) and improves low-temperature toughness (increase of absorbed energy in the Charpy test, etc.), and also exhibits a remarkable effect in improving sour resistance. If the amount is less than 0.001%, the effect is small, and if added over 0.005%, a large amount of CaO-CaS is formed, resulting in clusters and large inclusions. It also has an adverse effect. For this reason, the amount of Ca added is limited to 0.001 to 0.005%.
[0046]
Mg forms fine oxides of Al and Mg, and fine TiN is produced using this oxide as a production nucleus. Since this TiN is chemically stable even at a high temperature of 1400 ° C. or higher, it exhibits the effect of suppressing the coarsening of ν grains and improves the HAZ toughness. Less than 0.003% is less effective. Moreover, since the HAZ toughness is deteriorated when the amount of Mg added is too large, the upper limit is limited to 0.002%.
[0047]
B is a very small amount, which dramatically enhances the hardenability of the steel and provides good strength and toughness. In order to exert this effect, 0.0003% or more must be added. Moreover, since HAZ toughness will deteriorate when there is too much, the upper limit was limited to 0.002%.
[0048]
Next, the reasons for limiting the components of the weld metal will be described.
[0049]
In order to prevent hot cracking of the weld metal, the C content needs to be 0.035% or more. If it is less than 0.035%, δ solidification occurs in the process of solidification after welding, and hot cracking occurs. However, if the C content exceeds 0.08%, the low temperature toughness of the weld metal deteriorates, so the upper limit value was made 0.08%.
[0050]
Si is an element added for deoxidation and strength improvement, but if added in a large amount, the low temperature toughness and on-site weldability deteriorate, so the upper limit was made 0.6%.
[0051]
Mn is an essential element for securing strength and low temperature toughness, and its lower limit is 1.5%. However, if there is too much Mn, the hardenability of the steel increases and the low temperature toughness and on-site weldability deteriorate, so the upper limit was made 2.2%.
[0052]
The purpose of adding Ni is to increase the strength without deteriorating the low temperature toughness and on-site weldability. However, if the addition amount is too large, not only the economical efficiency but also the low temperature toughness is deteriorated. Therefore, the upper limit is set to 2.5% and the lower limit is set to 1.0%.
[0053]
Cr increases the strength, but if it is too much, the low temperature toughness and on-site weldability deteriorate significantly. For this reason, the upper limit of the Cr amount is 1.5%, and the lower limit is 0.3%.
[0054]
The reason for adding Mo is to improve the hardenability of the steel. In order to obtain this effect, Mo needs to be at least 0.3%, preferably 0.5%. However, excessive addition of Mo deteriorates low temperature toughness and on-site weldability, so the upper limit was made 1.5%.
[0055]
Nb has an effect of strengthening steel and needs to be 0.01% or more. However, adding 0.1% or more of Nb adversely affects on-site weldability and low-temperature toughness, so the upper limit was made 0.1%.
[0056]
Ti addition forms fine TiN and improves low temperature toughness. In order to exhibit such an effect of TiN, it is necessary to add at least 0.005% Ti. However, if the amount of Ti is too large, TiN coarsening and precipitation hardening due to TiC occur and the low temperature toughness deteriorates, so the upper limit must be limited to 0.03%.
[0057]
B is an element that greatly increases the hardenability of steel in a very small amount. In order to obtain such an effect, B must be at least 0.0003%. On the other hand, if added excessively, not only the low temperature toughness is deteriorated, but also the effect of improving the hardenability of B may be lost, so the upper limit was made 0.002%.
[0058]
Al usually has an effect as a deoxidizing element. However, if the Al content exceeds 0.05%, Al-based non-metallic inclusions increase to impair the cleanliness of the steel, so the upper limit was made 0.05%.
[0059]
N forms TiN and improves low temperature toughness. The minimum amount required for this is 0.001%. However, if the amount is too large, the low temperature toughness is deteriorated, so the upper limit must be suppressed to 0.01%.
[0060]
O forms an oxide in the weld metal, acts as a nucleus of intragranular transformed ferrite, and is effective in refining the structure. However, if the amount is too large, the low temperature toughness of the weld metal deteriorates and welding defects such as slag entrainment occur. For this reason, the lower limit of the amount of O is set to 0.015%, and the upper limit is set to 0.045%.
[0061]
Further, in the present invention, the amounts of impurity elements P and S are set to 0.015% or less and 0.005% or less, respectively. The main reason is to further improve the low temperature toughness. Reduction of the P content prevents grain boundary fracture and improves low temperature toughness. Moreover, reduction of the amount of S has the effect of reducing MnS and improving ductility.
[0062]
Next, the reason for adding one or more of Cu, V, and Ca will be described.
[0063]
In addition to the basic components, the main purpose of adding these elements as necessary is to improve properties such as strength and low temperature toughness of the weld metal without impairing the excellent characteristics of the steel of the present invention. Therefore, the amount of addition is a property that should be restricted by itself.
[0064]
Cu, like Ni, increases strength without deteriorating low-temperature toughness and on-site weldability. However, if added excessively, the low temperature toughness deteriorates, so the upper limit was made 1.0%. The lower limit of 0.1% of Cu is the minimum value at which the effect on the material due to addition becomes remarkable.
[0065]
V has almost the same effect as Nb, but the effect is weaker than that of Nb. V causes strain-induced precipitation and increases the strength. The lower limit is 0.01%, and the upper limit is acceptable up to 0.1% from the viewpoint of on-site weldability and low temperature toughness.
[0066]
Ca controls the form of sulfide (MnS) and improves low-temperature toughness (such as an increase in absorbed energy in the Charpy test). However, when the Ca content is 0.001% or less, there is no practical effect. When the Ca content exceeds 0.005%, a large amount of CaO—CaS is generated and a weld defect is generated. For this reason, Ca addition amount was limited to 0.001 to 0.005%.
[0067]
Furthermore, in order to satisfy the strength of X100 or more in the weld metal, it is necessary to optimize the addition amount of the alloy element. That is, the Pw value defined by Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb must be limited to a range of 0.2 to 0.35. When the Pw value is less than 0.2, the weld strength of X100 or more cannot be ensured. On the other hand, when the Pw value exceeds 0.35, the generation of M ^* becomes remarkable, the toughness is deteriorated, and low temperature cracking occurs. For this reason, the range of Pw value was limited to 0.2-0.35.
[0068]
Next, the reason for limitation for obtaining high deformability will be described below.
[0069]
First, in a pipeline laid on permafrost, when a strain of about 3% is applied to the pipeline due to the melting and freezing of the frozen soil, it is uniform in the tensile test in the tube axis direction of the base metal part and the weld metal part. If the elongation is 3% or more, even if a strain of 3% is applied, the branching of ductile cracks will not occur, and the occurrence of ductile cracks can be prevented, so the uniform elongation of the base metal part and the weld metal part is 3% or more. Limited to.
[0070]
In order to increase the uniform elongation of the base material, it is necessary to contain 5-50% of ferrite of 20 μm or less. This is because if it exceeds 20 μm, the toughness of the base material is significantly reduced. This is because when the ferrite fraction is less than 5%, the effect of improving uniform elongation cannot be obtained. Moreover, since sufficient intensity | strength is not obtained when it exceeds 50%, content of the ferrite fraction was limited to 5 to 50%.
[0071]
In order to increase the uniform elongation of the weld metal, it is necessary to contain 1 to 15%, preferably 2 to 15% of island martensite. By containing island martensite, the SS curve in a tensile test becomes a round type, and uniform elongation improves. If island-like martensite is less than 1%, the effect of improving uniform elongation cannot be obtained, and if it exceeds 15%, the low temperature toughness of the weld metal part deteriorates, so the range was limited to 1 to 15%.
[0072]
When the yield strength in the tensile test in the circumferential direction of the base metal is 689 MPa or more (X100 or more), the yield strength in the tensile test in the direction of the base pipe axis must be 0.9 times the yield strength in the tensile test in the circumferential direction. is there. When ferrite is introduced into the base material to improve uniform elongation, a decrease in yield strength is observed. Although the strength in the circumferential direction is determined by the internal pressure, there is no practical problem as long as the yield strength in the tube axis direction is 0.9 times or more the yield strength in the circumferential direction. For this reason, the yield strength in the tensile test in the base tube axis direction is limited to 0.9 times the yield strength in the tensile test in the circumferential direction.
[0073]
As a manufacturing method of a steel plate used for a steel pipe, after heating a slab to 950 to 1200 ° C., setting the rolling reduction at 950 ° C. or less to 50% or more and finishing rolling in a temperature range of 700 to 850 ° C., 550 It is necessary to cool from a temperature range of ˜700 ° C. to an arbitrary temperature of 450 ° C. or less at a cooling rate of 2 ° C./second or more.
[0074]
First, the reheating temperature is limited to a range of 950 to 1200 ° C. The reheating temperature must be 950 ° C. or higher in order to dissolve Nb precipitates, refine the structure during rolling, and obtain excellent low temperature toughness. However, when the reheating temperature exceeds 1200 ° C., the ν grains become extremely coarse and cannot be completely miniaturized even by rolling, so that excellent low temperature toughness cannot be obtained. For this reason, the upper limit of the reheating temperature was set to 1200 ° C.
[0075]
Furthermore, the cumulative rolling reduction at 950 ° C. or less must be 50% or more, and the rolling end temperature must be 700 to 850 ° C. This is because the ν grains refined by recrystallization zone rolling are stretched by low-temperature rolling, and the crystal grains are thoroughly refined to improve low-temperature toughness. If the cumulative rolling reduction is less than 50%, the extension of the ν structure is insufficient and fine crystal grains cannot be obtained. Further, if the rolling end temperature is 850 ° C. or higher, fine crystal grains cannot be achieved even if the cumulative rolling reduction is 50% or higher, for example. Further, if the rolling temperature is too low, excessive ν / α2 phase rolling occurs and the low temperature toughness deteriorates, so the lower limit of the rolling end temperature was set to 700 ° C.
[0076]
After rolling, it is essential to cool the steel plate at an accelerated rate. Accelerated cooling allows for increased strength and improved uniform elongation based on microstructure control without compromising low temperature toughness. As a condition for accelerated cooling, it must be cooled from a temperature range of 550 to 700 ° C. after rolling to an arbitrary temperature of 450 ° C. or lower at a cooling rate of 2 ° C./second or higher, and then air-cooled. When the temperature at which cooling starts exceeds 700 ° C., the uniform elongation decreases. Further, when the temperature at which cooling is started is 550 ° C. or less, sufficient strength cannot be obtained. Therefore, the temperature range which starts cooling was limited to 550-700 degreeC. Further, if the cooling rate is too low or the cooling stop temperature is too high, the effect of accelerated cooling cannot be obtained sufficiently, and sufficient strength cannot be obtained.
[0077]
The present invention is most preferably applied to a thick plate mill, but can also be applied to a hot coil (in this case, the steel sheet after rolling and cooling is wound and cooled). Moreover, since the steel plate manufactured by this method is excellent in low temperature toughness, it can be applied to a pressure vessel as well as a pipeline in a cold region.
[0078]
【Example】
Examples of the present invention will be described. Steel tubes manufactured from steel pieces of various steel components by a converter-continuous casting method were used to manufacture steel pipes, and various properties were investigated. The characteristics of the steel pipe welded part were evaluated using a Charpy test piece taken from a 1/2 t part of the steel sheet after performing SAW (submerged arc welding) of one layer on the inner and outer surfaces. The notch positions were the center of the weld metal and HAZ (1 mm from the point where the weld metal of the inner surface welding and the outer surface welding intersected). The tensile test used a round bar tensile test piece having a diameter of 12.7 mm and a gauge length of 50.8 mm. Tables 1 to 7 show the test conditions and results. Tables 1 to 4 show the chemical composition of the steel pipe base material and the weld metal, Tables 5 and 6 show the steel plate manufacturing conditions, structure and mechanical properties of the steel pipe base material, and Table 7 shows the mechanical properties of the steel pipe weld. Showed the nature. As is clear from the table, the steel pipe of the present invention has excellent strength (YS, TS), uniform elongation (uEl), low temperature toughness, and weld zone toughness. On the other hand, the chemical composition of the comparative steel is not appropriate, and any of the characteristics is inferior.
[0079]
Steel 13 is inferior in HAZ toughness because the amount of C in the base material is too large. Steel 14 is inferior in HAZ toughness because the amount of Al in the base material is too large. Steel 15 does not satisfy the target strength because the Pb value of the base material is too low. Steel 16 is inferior in HAZ toughness because the Pb value of the base material is too high. Steel 17 does not satisfy the target strength because the Qb value of the base material is too low. Steel 18 is inferior in HAZ toughness because the Qb value of the base material is too high. Since the steel 19 has a small amount of C in the weld metal, hot cracking of the weld metal occurs. Since the steel 20 has too much C amount of the weld metal, the low temperature toughness of the weld metal is inferior. Since the Pw value of the weld metal is too low, the strength of the welded portion is low. Steel 22 is inferior in toughness of the weld metal because the Pw value of the weld metal is too high. Steel 23 has a ferrite fraction of 20 μm or less and less than 5%, so that sufficient uniform elongation cannot be obtained. In steel 24, the ferrite fraction of 20 μm or less exceeds 50%, so that sufficient strength cannot be obtained. In Steel 25, the island-like martensite fraction of the weld metal is less than 1%, so that sufficient uniform elongation cannot be obtained. In steel 26, the welded metal toughness deteriorates because the island-like martensite fraction of the weld metal exceeds 15%. Steel 27 was buckled when laying the pipeline because the yield strength in the tensile test in the tube axis direction of the base metal part was 0.9 times or less than the yield strength in the tensile test in the circumferential direction. Since the steel 28 has a slab reheating temperature of 950 ° C. or lower, sufficient strength and low temperature toughness cannot be obtained. Since the slab reheating temperature of the steel 29 exceeds 1200 ° C., excellent low temperature toughness cannot be obtained. Steel 30 cannot obtain good low temperature toughness because the amount of reduction at 950 ° C. or less is less than 50%. Since the rolling end temperature of steel 31 exceeds 850 ° C., good low temperature toughness cannot be obtained. Since the rolling end temperature of the steel 32 is less than 700 ° C., good low temperature toughness cannot be obtained. The steel 33 cannot obtain a uniform elongation because its cooling start temperature exceeds 700 ° C. Since the steel 34 has a cooling start temperature of less than 550 ° C., sufficient strength cannot be obtained. Steel 35 cannot obtain sufficient strength because the cooling stop temperature exceeds 450 ° C. Since the steel 36 has a low cooling rate, sufficient strength cannot be obtained.
[0080]
[Table 1]

[0081]
[Table 2]

[0082]
[Table 3]

[0083]
[Table 4]

[0084]
[Table 5]

[0085]
[Table 6]

[0086]
[Table 7]

[0087]
【The invention's effect】
By adopting a high strength steel pipe (API standard X100 or higher) having excellent HAZ toughness and high deformability according to the present invention in the pipeline, the safety of the pipeline is remarkably improved and the transportation efficiency is dramatically improved. It was.

Claims (8)

% By mass
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
Al: 0.05% or less,
N: 0.001 to 0.006%
And the balance is iron and inevitable impurities, and Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V
A base material having a Pb value defined in the range of 2.5 to 4.0;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in a tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more. % By mass
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
Al: 0.05% or less,
N: 0.001 to 0.006%
In addition, Ni: 0.1-1.0%,
Cu: 0.1 to 1.2%,
Cr: 0.1 to 1.0%,
Mo: 0.1 to 1.0%,
V: 0.01 to 0.1%
Ca: 0.001 to 0.005%,
Mg: 0.0003 to 0.002%
And the balance consists of iron and inevitable impurities, and Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V
A base material having a Pb value defined in the range of 2.5 to 4.0;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in a tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more. % By mass
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.006%
The balance is made of iron and inevitable impurities, and Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo
A base material having a Qb value defined in the range of 2.0 to 3.5;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in the tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more. % By mass
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.006%
In addition, Ni: 0.1-1.0%,
Cu: 0.1 to 1.2%,
Cr: 0.1 to 1.0%,
Mo: 0.1 to 1.0%,
V: 0.01 to 0.1%
Ca: 0.001 to 0.005%,
Mg: 0.0003 to 0.002%
And the balance is composed of iron and inevitable impurities, and Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo
A base material having a Qb value defined in the range of 2.0 to 3.5;
C: 0.035 to 0.08%,
Si: 0.6% or less,
Mn: 1.5-2.2%,
P: 0.015% or less,
S: 0.005% or less,
Ni: 1.0-2.5%,
Cr: 0.3 to 1.5%,
Mo: 0.3 to 1.5%,
Nb: 0.01 to 0.1%,
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.01%,
O: 0.015-0.045%
And the balance consists of iron and inevitable impurities, and Pw = C + 0.11Si + 0.03Mn + 0.02Ni + 0.04Cr + 0.07Mo + 1.46Nb
Having a weld metal part with a Pw value defined in the range of 0.2 to 0.35,
The metal structure of the base material part contains 5-50% of ferrite having a particle size of 20 μm or less,
The island martensite containing 1-15% more weld metal,
The yield strength in the tensile test in the circumferential direction of the base metal part is 689 MPa or more, and the yield strength in the tensile test in the pipe axis direction of the base metal part is 0.9 times or more of the yield strength in the tensile test in the circumferential direction,
A steel pipe excellent in weld heat affected zone toughness and deformability, characterized in that the uniform elongation in the tensile test in the pipe axis direction of the base metal part and the weld metal part is 3% or more. The weld metal is further mass%,
Cu: 0.1 to 1.0%
V: 0.01 to 0.1%
Ca: 0.001 to 0.005%
The steel pipe excellent in the weld heat affected zone toughness and deformability according to any one of claims 1 to 4, wherein one or more of them are contained. % By mass
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
Al: 0.05% or less,
N: 0.001 to 0.006%
And the balance is made of iron and inevitable impurities, and Pb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V
After heating a slab having a Pb value defined by 2.5 to 4.0 to 950 to 1200 ° C., the reduction at 950 ° C. or less is set to 50% or more, and a temperature range of 700 to 850 ° C. After the rolling is finished, the weld heat affected zone toughness and deformation are characterized by cooling from a temperature range of 550 to 700 ° C. to an arbitrary temperature of 450 ° C. or less at a cooling rate of 2 ° C./second or more and then air cooling. A manufacturing method for steel plates for steel pipes with excellent performance. % By mass
C: 0.03% or less,
Si: 0.6% or less,
Mn: 0.8 to 2.5%
P: 0.015% or less,
S: 0.005% or less,
Nb: 0.01-0.05%
Ti: 0.005 to 0.03%,
B: 0.0003 to 0.002%,
Al: 0.05% or less,
N: 0.001 to 0.006%
The balance is made of iron and inevitable impurities, and a slab having a Qb value defined by Qb = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + 2Mo in the range of 2.0 to 3.5 is 950 after heating to 1200 ° C., the reduction ratio at 950 ° C. or less and 50% or more, after completion of the rolling at a temperature range of 700-850 ° C., the cooling rate of 2 ° C. / sec or more from the temperature range of 550 to 700 ° C. A method for producing a steel plate for a steel pipe excellent in weld heat-affected zone toughness and deformability, characterized in that it is cooled to an arbitrary temperature of 450 ° C. or lower and then air-cooled. The slab is more mass%,
Ni: 0.1 to 1.0%,
Cu: 0.1 to 1.2%,
Cr: 0.1 to 1.0%,
Mo: 0.1 to 1.0%,
V: 0.01 to 0.1%
Ca: 0.0005 to 0.005%,
Mg: 0.0003 to 0.002%
The manufacturing method of the steel plate for steel pipes excellent in the weld heat affected zone toughness and deformability of Claim 6 or Claim 7 characterized by containing 1 type (s) or 2 or more types of these.