JPH1180833A - Production of steel sheet for high strength line pipe excellent in hic resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce steel which is high strength material of APIX70 and X80 grades and excellent in HIC resistance by an economical producing method. SOLUTION: A slab having a compsn. contg., by weight, 0.03 to 0.08% C, 0.05 to 0.50% Si, 1.0 to 1.9% Mn, <=0.010% P, <=0.002% S, 0.005 to 0.05% Nb, 0.005 to 0.02% Ti, 0.01 to 0.07% Al and 0.0005 to 0.0040% Ca, also satisfying >=0.32 Ceq, and the balance Fe with inevitable impurities is subjected to slab heating at 1,000 to 1,200 deg.C, and accelerated cooling for the steel sheet after the completion of hot rolling is executed in such a manner that, at first, it is executed till the surface temp. of the steel sheet reaches <=500 deg.C, thereafter, the accelerated cooling is once stopped, it is reculerated till the surface temp. of the steel sheet reaches >=500 deg.C, and after that, the steel sheet is again subjected to accelerated cooling to >=600 deg.C at a cooling rate of 3 to 50 deg.C/s, where Ceq=C+Mn/64(Cu+Ni)/15+(Cr+Mo+V)/15.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet used as a material for a steel pipe for a line pipe having excellent resistance to hydrogen-induced cracking (HIC) and having a strength level of X70 grade or more, which is the American Petroleum Institute (API) standard. And a method for producing the same. In addition, the said steel plate is manufactured by a thick plate mill or a hot rolling mill. Further, the steel pipe is formed into a steel pipe by a method such as UOE, press bending, roll bending or the like in a cold state, and then manufactured by a method such as submerged arc welding or electric resistance welding, and is a line pipe for transporting crude oil or natural gas. It is used as

[0002]

2. Description of the Related Art In general, line pipes used for transporting crude oil and natural gas containing hydrogen sulfide have basic properties required for pipelines such as strength, toughness, weldability, and resistance to hydrogen-induced cracking (HIC resistance). Resistance) and stress corrosion cracking resistance (S
SCC resistance) is required. Here, HIC means that hydrogen ions generated by the corrosion reaction are adsorbed on the surface of the steel material and penetrate into the steel material as atomic hydrogen, and non-metallic inclusions such as MnS in the steel and a hard second phase structure Around the surface of the steel, and become molecular hydrogen, which means cracks generated by the internal pressure.

For this reason, the following methods have been disclosed to prevent the occurrence of HIC. 1) Morphological control of MnS inclusions (for example, see JP-A-54-1)
No. 10119) Since MnS in steel is elongated by rolling and HIC is generated and propagated along with it, by lowering the S content in the steel and simultaneously containing an appropriate amount of Ca or REM, This is a method of suppressing the generation and propagation of cracks by changing the form of inclusions from long elongated MnS to finely dispersed spheres with small stress concentration.

2) Reduction of segregated structure (for example, see
HIC is often generated at the central portion of the steel sheet corresponding to the central segregation zone of the continuous cast slab, and thus a hard island that can be a starting point of cracking. In addition to suppressing the formation of microstructure such as martensite, the formation of hardened structures such as martensite and bainite, which are likely to be crack propagation paths,
This is a method for improving the HIC resistance.

[0005] For this purpose, in addition to reducing elements that are easily segregated, such as C, Mn, and P, a soaking heat treatment that promotes diffusion of alloy elements in a slab heating step before rolling is employed, or cooling during rolling after rolling is performed. Accelerated cooling is employed to prevent the formation of a hardened structure caused by the diffusion of C accompanying the transformation.

3) Improvement of microstructure (for example, see Japanese Unexamined Patent Publication No.
JP-A-4-12782, JP-A-62-7819,
After the rolling, a microstructure having low crack susceptibility is obtained by performing a heat treatment of quenching and tempering after rolling, or by setting the finishing temperature of the rolling at a temperature equal to or higher than the recrystallization temperature of austenite to prevent wrought grains.

4) Formation of a protective film (for example, see
By including Cu in the steel, a Cu protective film is formed on the surface of the steel material to suppress intrusion of hydrogen into the steel.

By adopting these methods, the resistance to H
The IC properties have been improved, and line pipes requiring sour resistance up to the strength level API standard X65 grade have been mass-produced. However, in recent years, the need for higher-strength steel pipes has increased in order to improve transportation efficiency and reduce pipe laying costs, and high-strength steel pipes of X70 and X80 grades have been required for line pipes used in sour environments. It became so. On the other hand, HIC has a higher cracking sensitivity with an increase in strength and is more likely to generate HIC. Therefore, it has become difficult to completely suppress the generation of HIC by the above methods 1) to 4).

That is, in the case of high-strength materials such as X70 and X80 grades, cracking susceptibility to HIC is remarkably increased, so that cracks may be generated from spherical inclusions whose shape is controlled in the above 1). Even if the countermeasure for reducing the influence of the central segregation of 2) is taken, cracks will occur in portions other than the central portion of the sheet thickness. On the other hand, microstructure control by quenching-tempering treatment or rolling finish in the recrystallization temperature range or higher in 3) is a promising method for high-strength materials. However, mass production of steel sheets for line pipes requires cost and efficiency. It is inappropriate and it is difficult to obtain sufficient low-temperature toughness.

[0010] Furthermore, the effect of the Cu film of 4) cannot be expected in an environment having a low pH.
Of 5% NaCl + 0.5% CH saturated with hydrogen sulfide
With a 3COOH aqueous solution (so-called NACE solution), the effect of the film is not obtained.

To cope with such a problem, recently, several methods for producing a sour-resistant X80 grade steel sheet for line pipe have been disclosed. The main feature is that while adding Ca to the ultra-low S steel to control the morphology of the inclusions, it also controls the Mn content, which tends to segregate in the central segregation zone of continuous cast slabs, in addition to the low C, resulting in a reduction in strength. To
A method of supplementing with the addition of Cr (JP-A-5-9575),
A method of supplementing with the addition of r-Mo (JP-A-5-271766, JP-A-7-109519) or Ni-
This is a method of supplementing with the addition of Cr-Mo (JP-A-7-173536), in which accelerated cooling is performed after rolling is completed.

However, any of the prior arts relating to the production method of these X80 grade steel sheets is characterized by the HI of the central segregation zone.
Although it is an effective method for preventing the generation of C, regarding the prevention of HIC generated in a portion other than the central segregation zone,
There is no concrete cracking measure. That is, when the strength level of the steel pipe used in the sour environment rises, HIC is more likely to occur even if the form control of the inclusions of the steel plate as the material and the structure control of the central segregation part at the center of the plate thickness are performed, When accelerated cooling is applied, HIC is likely to be generated not only at the central segregation portion but also on the surface side in the thickness direction.
Preventing the generation of C is a major issue.

[0013]

According to the present invention, such an AP is used.
It is an object of the present invention to make it possible to manufacture a steel material having high strength of IX70 and X80 grades and excellent in HIC resistance by an economical manufacturing method.

[0014]

Means for Solving the Problems The present inventors varied the alloy composition of high-strength steel for line pipes, the manufacturing conditions of steel plates, especially the conditions of accelerated cooling, to thereby change the strength, toughness and HI resistance of steel plates.
A survey was conducted on the relationship with the C property. As a result, X7
Even with a high-strength material of 0 or X80, accelerated cooling is effective in improving the HIC resistance of the central segregation portion. But,
In the conventional accelerated cooling method, a hardened structure such as bainite is generated near the surface of the steel sheet and the hardness increases, so that HIC is easily generated at the boundary between these structures. In particular, X7
This tendency is remarkable in high-strength materials such as 0 and X80 because the amount of alloying elements added is large. On the other hand, by making the accelerated cooling method a so-called intermittent type, even in the case of high-strength materials of X70 and X80 grades, it is possible to suppress an increase in hardness in the vicinity of the surface of the steel sheet, thereby preventing the occurrence of HIC. Found that it is possible.

That is, the gist of the present invention resides in that the accelerated cooling method is a so-called intermittent type. This method will be described below in comparison with the conventional accelerated cooling method. FIG. 1 and FIG. 2 schematically show the temperature histories during the accelerated cooling process of a hot-rolled steel sheet in the conventional method and the method of the present invention.

In the conventional method, when accelerated cooling is performed on a rolled steel sheet, cooling is performed from the front and back surfaces of the steel sheet. Therefore, naturally, a predetermined accelerated cooling stop is performed while maintaining a temperature distribution in the sheet thickness direction. It is accelerated to a temperature (generally around 500 ° C.), and then cooled to room temperature by air cooling while reducing this temperature distribution. Therefore, in the high-strength materials of X70 and X80 grades, due to the high cooling rate near the surface of the steel sheet, bainite or martensite transformation is likely to occur on the surface side, and a hard structure is generated. As a result, even if HIC in the central part of the plate thickness could be prevented,
Is more likely to occur.

On the other hand, in the intermittent accelerated cooling method of the present invention, the accelerated cooling of the steel sheet having a temperature distribution in the thickness direction by the first accelerated cooling after rolling is temporarily interrupted, and air-cooled for a certain time. Due to this air cooling treatment, the temperature of the steel sheet surface side is regained by the heat retained in the central part of the steel sheet that has not yet been sufficiently cooled, the temperature distribution is made uniform, and the hardened structure generated on the surface side is tempered. Receive processing. Then, accelerated cooling is performed again from the regained temperature range to obtain a predetermined strength.

At this time, the surface temperature at which the accelerated cooling is interrupted is set at a value of 50 to sufficiently advance the transformation near the surface.
It is necessary that the temperature be 0 ° C. or less. Further, the reheat temperature of the steel sheet surface needs to be 500 ° C. or higher in order to reduce the hardness of the surface by self-tempering. Further, the final accelerated cooling is performed to 600 ° C. or less in order to secure necessary strength. The temperature control in such intermittent accelerated cooling can be performed by controlling the transport speed of the steel sheet passing through the accelerated cooling device, controlling the amount of water in each cooling zone, measuring the temperature in the middle, and the like.

In addition to the above basic concept, the following invention was made by limiting the chemical composition and the like in order to obtain high strength, high toughness and weldability required for steel for line pipes. That is, in the first invention, C: 0.03 to 0.0% by weight.
8%, Si: 0.05 to 0.50%, Mn: 1.0 to
1.9%, P: 0.010% or less, S: 0.002% or less, Nb: 0.005 to 0.05%, Ti: 0.005
-0.02%, Al: 0.01-0.07%, Ca:
0.0005-0.0040%, and Ce
q: A slab that slabs a slab satisfying 0.32 or more, the balance being Fe and other unavoidable impurities, at 1000 to 1200 ° C., accelerates cooling of the steel sheet after hot rolling is completed, After cooling to 500 ° C. or less, accelerated cooling is temporarily interrupted, and the steel sheet is re-heated until the surface temperature of the steel sheet becomes 500 ° C. or more, and then the steel sheet is cooled again at a cooling rate of 3 ° C./s or more and 50 ° C./s or less. A method for producing high-strength linepipe steel excellent in HIC resistance, characterized by accelerated cooling to a temperature of not more than ° C. Here, Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr
+ Mo + V) / 15 By adopting the so-called intermittent cooling type accelerated cooling of the present invention, it is possible to obtain a predetermined strength while suppressing an increase in hardness near the surface of the steel sheet, thereby improving the HIC resistance of the high-strength material. It is possible to do.

According to a second aspect of the present invention, the steel further comprises:
And Cu: 0.50% or less, Ni: 0.50% or less, C
r: 0.50% or less, Mo: 0.50% or less, V: 0.
A method for producing a high-strength linepipe steel excellent in HIC resistance, characterized by containing one or more of 1% or less. According to the present invention, the degree of freedom in selecting an alloy component is increased, so that toughness and weldability can be further improved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the reasons for limiting the alloy components, steel plate manufacturing conditions and accelerated cooling conditions in the present invention will be described. First, the reasons for limiting the essential elements in the present invention are shown below.

C: C is required as a steel strengthening element,
In order to ensure the predetermined strength of the X70 and X80 grades, the content must be 0.03% or more. On the other hand, if it is contained excessively, the toughness and the HIC resistance of the steel sheet are deteriorated, and the C content is also reduced from the viewpoint of weldability and sulfide stress corrosion cracking resistance.
Since it is desirable to reduce the amount, the upper limit is set to 0.08%.

Si: Si is added for deoxidation, and
If it is less than 05%, a sufficient deoxidizing effect cannot be obtained, while excessive content causes deterioration of toughness and weldability, so the upper limit is made 0.50%.

Mn: Mn is contained as a basic element effective for improving the strength and brittleness of steel, but if its content is less than 1.0%, its effect is small, and if it exceeds 1.9%, weldability and HIC resistance are exceeded. The range is 1.0 to
1.9%. In addition, since Mn tends to segregate in the central segregation part, there is a prior art in which the content of the upper limit is limited lower, but within the scope of the present invention, the harmful effect is obtained by optimizing accelerated cooling conditions. Can be prevented.

P: P is an impurity element that deteriorates the weldability and the HIC resistance, and it is desirable to reduce P as much as possible. However, excessive removal of P causes an increase in manufacturing cost, so the upper limit is made 0.010%.

S: Mn containing Ca and extending inclusions
Even if form control is performed from S to spherical CaS-based, in the case of a high-strength material, finely dispersed CaS-based inclusions can also be the starting points of cracking. Therefore, the S content is 0.002%
It is necessary to reduce to below, and reduce the starting point of crack.

Nb: In addition to the increase in strength due to precipitation hardening, Nb suppresses austenite recrystallization and reduces the size of crystal grains, particularly in hot rolling, so that Nb has sufficient brittleness as a line pipe steel. It is an essential component to give. However, if it is less than 0.005%, the effect is not sufficient, and if it exceeds 0.05%, the effect is almost saturated and the brittleness of the heat affected zone is deteriorated. 0.05%.

Ti: Ti has the effect of forming TiN, suppressing grain growth during slab heating, and bringing about microstructural refinement, thereby improving the brittleness. However, if the content is less than 0.005%, the effect is insufficient, while if it exceeds 0.02%, the brittleness is adversely deteriorated.
To 0.02%.

Al: Al is mainly contained as a deoxidizing agent in line pipe steel. If the content is less than 0.01%, the effect is not stable. On the other hand, if the content exceeds 0.07%, the cleanliness of the steel is reduced and the HIC resistance is deteriorated. 07%.

Ca: Ca is an element indispensable for controlling the form of sulfide-based inclusions, and its effect is recognized at 0.0005% or more. On the other hand, if the content exceeds 0.0040%, the effect is saturated, and conversely, the cleanliness of the steel is reduced and the HIC resistance is deteriorated. Therefore, the range is set to 0.0005 to 0.0040%.

Ceq: In order to stably obtain a strength of X70 grade or more by the production method of the present invention, Ceq is 0.3.
Since 2% or more is required, the lower limit is set to 0.32%. The upper limit does not need to be particularly limited from the viewpoint of HIC resistance. However, from the viewpoint of weldability, Ceq is preferably as low as possible, and thus is generally determined by a balance between strength and requirements for weldability. Ceq is expressed by the following equation. Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr
+ Mo + V) / 15

In the present invention, the following elements can be contained in addition to the above elements. The reason for the limitation is shown below. C
u: Cu is one of the elements effective in improving the toughness and increasing the strength, but if the content exceeds 0.50%, Cu
Since flaws are likely to occur, the upper limit is 0.50%
And

Ni: Ni is one of the elements effective in improving the toughness and increasing the strength. However, if the content exceeds 0.50%, the effect is saturated and stress corrosion cracking in a sour environment occurs. Because it easily occurs, the upper limit is 0.50%
And

Mo: Mo is one of the elements effective for improving the toughness and increasing the strength, but when the content exceeds 0.50%, the effect is saturated and the weldability and HIC resistance are impaired. Therefore, the upper limit is set to 0.50%.

Cr: Cr, together with Mo, is a low C type X
Although it is an element effective for obtaining sufficient strength as 70 and 80 grades, if the content exceeds 0.50%, the weldability is impaired, so the upper limit is set to 0.50%.

V: Since an appropriate amount of V can increase strength without deteriorating brittleness, weldability and sour resistance,
It is an element effective for obtaining sufficient strength as a low C type X70, 80 grade. However, if it exceeds 0.10%, the weldability is significantly impaired, so the upper limit is made 0.10%.

Next, the reasons for limiting the rolling conditions and accelerated cooling conditions will be described. Slab heating temperature: 1000-1200 ° C. When the slab heating temperature is lower than 1000 ° C., the solid solution of Nb becomes insufficient, and the precipitation effect is small and sufficient strength cannot be obtained. On the other hand, if the heating temperature exceeds 1200 ° C., the austenite crystal grains become coarse, so that good toughness cannot be obtained. Although the rolling end temperature is not particularly limited, an excessive reduction in a low temperature range is not preferable in terms of HIC resistance, and therefore it is preferable that the rolling end temperature is equal to or higher than the Ar3 transformation temperature.

Surface temperature at which accelerated cooling is interrupted: 500 ° C. or less. If accelerated cooling is interrupted at a temperature where the surface temperature exceeds 500 ° C., transformation near the surface has not sufficiently progressed, so that the material is transformed into a structure such as bainite when accelerated cooling is performed again after reheating. Therefore, by reducing the hardness near the surface of the steel sheet by interrupting the accelerated cooling and reheating, the gist of the present invention cannot be achieved.
It should be below ° C.

On the other hand, if the surface temperature at which the accelerated cooling is interrupted is too low, the central part of the sheet thickness is also supercooled, so that subsequent reheating is not sufficiently performed. Therefore, the surface temperature at the time of interrupting the accelerated cooling needs to be equal to or higher than the temperature at which the reheat temperature of 500 ° C. or higher is ensured. Specifically, it is set in consideration of the cooling curve of the surface of the steel sheet and the central part of the sheet thickness determined by the thickness of the steel sheet and the cooling method.

Surface reheat temperature: 500 ° C. or higher. Recuperation means that the surface temperature is reduced to 500 ° C. or less by accelerated cooling, bainite transformation is performed in the vicinity of the surface, and then self-tempering is performed by the heat held in the central portion of the steel plate, thereby reducing the surface hardness. have. Therefore, if the recuperation temperature of the surface is lower than 500 ° C., the tempered portion of the transformed surface layer is not sufficiently tempered, so that the hardness does not decrease and causes HIC, so the surface recuperation temperature is set to 500 ° C. or higher.

Accelerated cooling stop temperature: 600 ° C. or less. The final accelerated cooling is performed in order to secure a predetermined strength over the entire thickness of the sheet.
If the temperature exceeds the above, sufficient strength may not be obtained in some cases. Therefore, the cooling stop temperature of the accelerated cooling is set to 600 ° C. or less. In the present invention, since so-called intermittent accelerated cooling is performed, an excessively hardened portion is not generated near the surface.
Therefore, if the accelerated cooling stop temperature is 600 ° C. or less,
No special restrictions need to be added. That is, cooling to the room temperature by accelerated cooling is also permitted.

Cooling rate: 3 ° C./s or more and 50 ° C./s or less. If the cooling rate is less than 3 ° C./s, a predetermined strength may not be obtained due to insufficient structural change due to accelerated cooling. On the other hand, when the temperature exceeds 50 ° C./s, a martensite structure is generated, and the strength is excessively increased, which results in deterioration of HIC resistance. Therefore, the cooling rate should be between 3 ° C./s and 50 ° C./s.
The following is assumed.

As long as the above manufacturing conditions are satisfied, the HIC resistance
The rolling conditions of other steel sheets are not particularly limited, because a high-strength steel having excellent properties can be manufactured. The method of forming the steel pipe is not particularly limited as long as it is cold.

[0044]

EXAMPLES Examples obtained by the present invention will be described below in comparison with invention steels and comparative steels. Table 1 shown as FIG.
It shows the chemical composition of the test steel. Here, steel A ~
K is steel within the range of the chemical composition of the present invention. On the other hand, steel L is Ceq, steel O is Mn content and Ceq, steel Q
Has an Nb content below the range of the present invention. The steel N has a C content, the steel P has a P and S content, and the steel R has a Ca content and a Ni content each exceeding the scope of the present invention. Further, the steel M has a lower C content and a higher Mn content than the present invention.

For these steels, Table 2 shown in FIG.
Under the conditions of hot rolling and accelerated cooling shown in
m of steel plates were manufactured. Table 2 also shows the mechanical properties of the steel sheet, the hardness difference between the steel sheet surface and the center of the sheet thickness, the HIC resistance, and the weldability. Regarding the strength and toughness, considering the application of the steel of the present invention, the case where the yield strength was 448 MPa or more and the fracture surface transition temperature in the Charpy impact test was 160 ° C. or less was regarded as good. Further, the mechanical properties of the steel sheet and the hardness difference between the steel sheet surface and the center of the sheet thickness are expressed by the hardness (H
v10) and the hardness at the center of the sheet thickness were measured at five points each, and the difference was determined from the difference between the average values.

The HIC test was conducted in a 5% NaCl + 0.5% CH3COOH aqueous solution (commonly called NACE solution) saturated with hydrogen sulfide having a pH of about 3, and the crack length ratio (CLR)
Was 15% or less, the HIC resistance was judged to be good.

The weldability was evaluated by performing submerged arc welding corresponding to seam welding of an actual steel pipe, and examining the presence or absence of high-temperature cracking and low-temperature cracking by observing the cross section of the welded portion. When there was no crack in the weld, the weldability was judged to be good.

As shown in Table 2, when the steel of the present invention was subjected to the hot rolling and accelerated cooling of the present invention, sufficient strength, toughness, good HIC resistance, and weldability were obtained. . On the other hand, even if the steel A of the present invention is used, the steel sheets (A-1, A-2, A
-3, A-5, and A-6) did not provide sufficient performance.

That is, A-1 is a case where the heating temperature is low, and the strength is insufficient. A-2 is a case where the heating temperature is high, and although sufficient strength is obtained, toughness is insufficient. A-3 has a low recuperation temperature,
The hardness difference between the surface of the steel sheet and the center of the thickness is large, and the HIC performance is insufficient. A-5 is a case where the cooling rate of the accelerated cooling is extremely high, and also in this case, the hardness difference between the surface of the steel sheet and the center of the thickness is large, and the HIC performance is insufficient.
A-6 is a case where the cooling rate of the accelerated cooling is slow, and the strength is insufficient.

On the other hand, steel sheets (L-1, Q, -1, R-1) obtained by subjecting a non-invented steel to the rolling accelerated cooling of the present invention,
Alternatively, a steel sheet (M-1, N-1, 0-1, P-1) obtained by performing rolling accelerated cooling which is not the invention of the present invention on steel not of the invention.
Does not provide sufficient performance.

That is, the steel sheet L-1 having a Ceq below the range of the present invention has insufficient strength and does not contain Nb.
-1 has insufficient toughness, and steel sheet R-1 having Ca content and Ni content exceeding the range of the present invention has poor HIC resistance and weldability. Further, the steel sheet M-1 having a high Mn content and a high heating temperature has poor toughness, HIC resistance, and weldability. The steel sheet N-1 having a high C content and a high accelerated cooling interruption temperature has poor HIC resistance and weldability.
The steel sheet O-1 having a low Mn content and Ceq and a low recuperation temperature has insufficient strength, HIC resistance, and weldability.
Further, the steel sheet P-1 having high P and S and having a high final accelerated cooling stop temperature has insufficient strength and HIC resistance.

[0052]

According to the present invention, an AP having excellent HIC resistance is provided.
It has become possible to economically and stably produce high-strength steel sheets for line pipes of the I standard X70 and X80 grades. As a result, in a sour environment containing hydrogen sulfide, safety against HIC and reliability against stress corrosion cracking in a state where stress is applied are remarkably improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a temperature history in an accelerated cooling process after hot rolling in a conventional accelerated cooling method.

FIG. 2 is a diagram schematically showing a temperature history in an accelerated cooling process after hot rolling in the method of the present invention.

FIG. 3 is a table showing chemical compositions of test steels used in Examples and Comparative Examples of the present invention as Table 1.

FIG. 4 is a table showing the results of hot rolling conditions, accelerated cooling conditions, mechanical properties, HIC resistance, and weldability of a test steel sheet as Table 2.

Continuation of front page (72) Inventor Ryuji Muraoka 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (2)

[Claims] (1) C: 0.03 to 0.08% by weight,
Si: 0.05 to 0.50%, Mn: 1.0 to 1.9
%, P: 0.010% or less, S: 0.002% or less, N
b: 0.005 to 0.05%, Ti: 0.005 to 0.
02%, Al: 0.01 to 0.07%, Ca: 0.00
0.05 to 0.0040%, and Ceq: 0.3
A slab of a steel slab that satisfies 2% or more and the balance is Fe and other unavoidable impurities is slab-heated at 1000 to 1200 ° C., and accelerated cooling of the steel sheet after the completion of hot rolling is performed. After that, accelerated cooling is temporarily interrupted, and the steel sheet is re-heated until the surface temperature of the steel sheet becomes 500 ° C. or more. A method for producing a high-strength linepipe steel sheet having excellent HIC resistance, characterized by accelerated cooling to a temperature. Here, Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr
+ Mo + V) / 15 2. The steel according to claim 1, further comprising:
0.50% or less, Ni: 0.50% or less, Cr: 0.5
0% or less, Mo: 0.50% or less, V: 0.1% or less.
A method for producing a high-strength linepipe steel sheet having excellent HIC resistance according to claim 1. [0001]