JP5157386B2 - Manufacturing method for thick-walled, high-strength, high-toughness steel pipe material - Google Patents

Description

  The present invention relates to a method for producing a steel material having excellent toughness, and particularly as a method for producing a steel pipe material for a line pipe produced by a UOE or press bend method having a strength level of API-5L X70 or more and a plate thickness of 20 mm or more. It relates to a suitable one.

  As the natural gas supply area becomes remote, the pipeline for natural gas transportation has become longer, and considering the increase in operating pressure for transportation efficiency, the pipe thickness of the line pipe is increased and a high strength grade is adopted. The demand for thick high-strength line pipe is increasing.

  In the case of a pipeline for transporting natural gas, it is desired that the ductile fracture surface ratio (SA (%)) in a test called DWTT (Drop Weight Tear Test) is high from the viewpoint of preventing brittle crack propagation.

  Generally, as the strength and thickness of a steel plate increase, the toughness tends to decrease. Therefore, as a technology for improving the toughness of a thick steel plate, TMCP technology such as controlled rolling, controlled cooling, and direct quenching-tempering technology, Online heat treatment techniques have been developed after rolling.

  It has been known that refinement of crystal grains is effective for improving toughness, and various studies have been made. In the case of grain refinement by adjusting the alloy design, the heating temperature during rolling, the rolling temperature, etc., the limit of the γ grain size of the thick steel plate obtained by rolling-cooling is about 20-30 μm.

  The grain size is larger than the crystal grain size obtained by reheating and quenching after rolling, and there is a limit to improving the toughness in the rolling-cooling or rolling-cooling-tempering process, particularly 20 mm. In the case of a thicker material exceeding this, it is difficult to satisfy the SA value during the DWTT test.

As a technique for promoting the refinement of a thick steel plate, for example, in Patent Document 1, the strain rate at each pass reduction in hot rolling is controlled to increase the one-pass reduction rate, and γ grains are obtained by dynamic recrystallization. A technique for reducing the diameter is disclosed.
Japanese Patent Application Laid-Open No. 08-225883

  However, since the rolling efficiency of the method described in Patent Document 1 is significantly reduced, it cannot be applied to the production of mass-produced materials such as line pipe materials, and the toughness can be reduced using a practical thick plate manufacturing process that does not impair the productivity. There is a demand for the development of new atomization technology for improvement.

  Therefore, the present invention achieves the refinement of γ grains that far surpasses that of conventional materials by using the rolling-accelerated cooling process suitable as a production method for steel pipe materials for line pipes, and by γ + α two-phase region rolling. It aims at providing the manufacturing method of steel which suppresses the generation | occurrence | production of a brittle fracture surface at the time of a DWTT test.

  In order to solve the above-mentioned problems, the present inventors have intensively studied paying attention to the heating / cooling / reduction pattern during rolling that affects the γ grain size, and after the recrystallization temperature range rolling, perform the non-recrystallization zone rolling, It was found that, when heated again to the recrystallization temperature range, fine γ was obtained, and excellent toughness and high strength were obtained by a combination of subsequent rolling and cooling conditions.

That is: The heating temperature during rolling and recrystallization zone rolling prevent coarsening of the initial γ grain size to obtain uniform γ grains, ensuring the cumulative rolling reduction of the subsequent non-recrystallization zone rolling, Ar without transformation _1. Fine recrystallization γ is obtained by heating in a short time from a temperature of ₃ or more to a recrystallization temperature range; Further, after that, by rolling the fine γ grains in a two-phase temperature range of γ + α, it was found that the structure was refined and excellent strength and toughness were obtained after accelerated cooling.

The gist of the present invention is as follows.
1. % By mass, C: 0.03 to 0.09%,
Si: 0.01 to 0.50%,
Mn: 1.0 to 3.0%
P: 0.030% or less,
S: 0.010% or less,
sol. Al: 0.003 to 0.100%,
B: 0.0005% or less,
Nb: 0.005 to 0.1%,
Ti: 0.005 to 0.05%
In addition,
Cu: 0.01 to 1.0%,
Ni: 0.01 to 2.0%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
V: 0.003-0.1%
1 type or 2 types or more chosen from among,
Furthermore, the Ceq value calculated by the following equation (1) is 0.36 to 0.60,
A steel material having a composition comprising the balance of Fe and inevitable impurities,
Heat to 1000 ° C. or more and 1250 ° C. or less, and after rolling in the recrystallization temperature range, perform primary rolling for rolling at a cumulative reduction ratio of 40% or more in the non-recrystallization temperature range, and then from the temperature above the Ar ₃ transformation point After heating at a temperature increase rate of 2 ° C / sec or more above the recrystallization temperature, after cooling to a temperature not higher than Ar ₃ transformation point -50 ° C or higher after Ar ₃ transformation point, rolling is resumed, and cumulative reduction is performed in the two-phase temperature range. Production of a thick-walled, high-strength, high-toughness steel pipe material characterized by having a step of performing secondary rolling for rolling at a rate of 15% or more, and further accelerated cooling from a temperature above the Ar ₁ transformation point to 600 ° C. Method.
Ceq (%) = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (1)
Each element is a value in mass%.
2. The steel material is further
Ca: 0.0001 to 0.0060%,
Mg: 0.0001 to 0.0060%,
REM: 0.0001-0.0200%,
Zr: 0.0001 to 0.0100%
The method for producing a thick-walled, high-strength, high-toughness steel pipe material according to 1, which comprises one or more selected from among the above.
3. In primary rolling, before performing rolling with a cumulative reduction ratio of 40% or more in the non-recrystallization temperature range, performing water cooling during or after the recrystallization temperature range rolling and cooling to the non-recrystallization temperature range 3. A method for producing a thick-walled, high-strength, high-toughness steel pipe material according to 1 or 2,
4). The average γ grain size after recrystallization obtained after heating to a recrystallization temperature range from a temperature equal to or higher than the Ar ₃ transformation point after primary rolling is 15 μm or less, according to any one of 1 to 3, A manufacturing method for thick-walled, high-strength, high-toughness steel pipe materials.
5.1 to 4 produced by the method according to any one of claims 1 to 4, having an average γ grain size of 15 μm or less after recrystallization, a yield strength of 485 MPa or more and a tensile strength of 565 MPa or more, and a Charpy absorbed energy at −40 ° C. of 300 J or more. A steel pipe material for a line pipe, wherein the ductile fracture surface area SA value obtained by the DWTT test is 90% or more and the plate thickness is 20 mm or more.

  According to the present invention, using the process with rolling-accelerated cooling, compared to the conventional material, the temperature (SATT) at which 85% SA in the DWTT test is obtained has excellent toughness that is a low temperature of 20 ° C. or more. Thick materials exceeding 20 mm can be obtained without impairing productivity, and are extremely useful in industry.

The present invention performs non-recrystallized zone rolling with a cumulative reduction ratio of 40% or more after recrystallization zone rolling, and then rapidly heats again to the recrystallization temperature range, so that the γ grain size of 15 μm or less remains with rapid heating. Then, 15% or more of rolling is performed in the subsequent two-phase region of γ + α, and the ferrite that undergoes transformation during rolling is further refined. Hereinafter, the present invention will be described in detail. In addition,% in a component composition shall be mass%.
[Ingredient composition]
C: 0.03-0.09%
C is required to be at least 0.03% in order to secure a strength of APIX 70 or higher. On the other hand, if added over 0.09%, the hard phase formed after accelerated cooling becomes martensite, and the Charpy absorbed energy of the base material decreases, so 0.03% or more and 0.09% or less (hereinafter,. 03 to 0.09%).

Si: 0.01 to 0.50%
Si is an element necessary for deoxidation, but if less than 0.01%, the effect is small, and if added over 0.50%, the weldability and base metal Charpy absorbed energy are remarkably lowered, so 0.01 to 0.50%.

Mn: 1.0-3.0%
Mn is necessary for securing the strength of the steel sheet in the same manner as C, and in particular, 1.0% or more is necessary for securing the strength of APIX 70 or higher. On the other hand, if it exceeds 3.0%, it is particularly concentrated in the segregated part inevitably formed at the time of casting, and this part causes the deterioration of DWTT characteristics.

P: 0.030% or less, S: 0.010% or less P and S are elements inevitably contained in the steel as impurities, and deteriorate the toughness of the steel base material and the weld heat affected zone. It is preferable to reduce as much as possible in consideration of economy, and P: 0.030% or less and S: 0.010% or less.

Al: 0.003 to 0.100%
Al is a deoxidizing element, and if it is less than 0.003%, its effect is not sufficient, and if added excessively, the toughness is deteriorated, so 0.003 to 0.100% or less. Al is sol. Al.

B: 0.0005% or less B may be contained in the steel as an impurity. In particular, when 0.0005% or more is contained, segregates at the γ grain boundary during hot rolling, and ferrite transformation from the grain boundary. It works to suppress. In the present application, as will be described later, since the fine γ grains are further rolled in a two-phase region of γ + α, the ferrite that is transformed during rolling is also refined to improve the DWTT characteristics. If it exists, this effect cannot be obtained sufficiently, so the upper limit of B is made 0.0005%.

Nb: 0.005 to 0.1%
Since Nb functions to expand the austenite non-recrystallization temperature range to the high temperature side, at least 0.005% or more is added in order to sufficiently secure a cumulative reduction ratio of 40% or more in the austenite non-recrystallization temperature range described later. There is a need to. At the same time, it has an effect of improving hardenability and strengthens the transformation of the second phase structure after accelerated cooling. However, when 0.1% or more is added, the second phase structure becomes too hard and the Charpy absorbed energy of the base material is increased. In order to bring about a fall, it is made 0.005 to 0.1%.

Ti: 0.005 to 0.05%
Ti forms nitrides in steel, and when 0.005% or more is added, it works to prevent the coarsening of γ grains due to the pinning effect of the nitride, so that the toughness of the base metal is secured and the heat affected zone of the weld This is effective from the viewpoint of securing toughness. If added over 0.05%, the toughness is significantly reduced, so 0.005 to 0.05%.

  In the present invention, one or more of Cu, Ni, Cr, Mo, and V are added as selective elements from the viewpoint of strength adjustment.

Cu: 0.01 to 1.0%
Cu is an element for increasing the strength and exerts its effect at 0.01% or more, and when added over 1.0%, the steel sheet surface properties deteriorate due to hot brittleness. 0.01 to 1.0%.

Ni: 0.01 to 2.0%
Ni can improve the toughness while increasing the strength of the base metal, and is effective at 0.01% or more. However, if it exceeds 2.0%, the effect is saturated and the economy is impaired. When it does, it is made 0.01 to 2.0%.

Cr: 0.01 to 1.0%
Cr is effective for increasing the strength, exhibits its effect at 0.01% or more, and deteriorates toughness when added over 1.0%. 0%.

Mo: 0.01 to 1.0%
Mo is effective for increasing the strength, exerts its effect at 0.01% or more, and adding over 1.0% significantly deteriorates toughness and impairs economy. 0.01 to 1.0%.

V: 0.003-0.1%
V is effective in increasing the strength due to carbide formation, and exhibits an effect when added in an amount of 0.003% or more. However, if it exceeds 0.1%, the amount of carbide becomes excessive and the toughness may be lowered. Therefore, when added, the content is made 0.003 to 0.1%.

Ceq (%): 0.36 to 0.60
Ceq (%) = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5), each element is a content (mass%), and a steel plate having a thickness of 25 mm achieves a strength of not less than APIX 70, 0.36 or more And On the other hand, if the addition is performed such that Ceq (%) exceeds 0.60, the weldability deteriorates, and in particular, it becomes impossible to prevent low-temperature cracking during circumferential welding of the pipe, so the upper limit is set to 0.60. The element not added is 0.

  The basic component composition of the present invention is as described above, but if necessary, Ca: 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, REM: 0.0001 to 0.0200%, Zr: One or more selected from 0.0001 to 0.0100% can be contained.

  Ca, Mg, REM, and Zr have a function of fixing S in steel and improving the toughness of the steel sheet, and are effective when added in an amount of 0.0001% or more. On the other hand, if the addition exceeds 0.0060%, 0.0060%, 0.0200%, and 0.0100%, the amount of inclusions in the steel increases and the toughness deteriorates. Therefore, when added, Ca: 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, REM: 0.0001 to 0.0200%, Zr: 0.0001 to 0.0100% And

  The balance other than the components described above consists of Fe and inevitable impurities.

[Production conditions]
The molten steel having the above composition is melted by a conventional method using a melting means such as a converter or an electric furnace, and is made into a steel material such as a slab by a conventional method using a continuous casting method or an ingot-bundling method. The melting method and the casting method are not limited to the methods described above. Thereafter, the sheet is rolled into a desired shape under specific conditions, and cooled or heated under specific conditions during or after rolling.

1. After slab heat casting, after the slab temperature is lowered to room temperature or in a high temperature state, it is inserted into a heating furnace and heated to 1000 ° C. or higher.

  The heating temperature is preferably lower from the viewpoint of securing toughness, but if it is less than 1000 ° C., there is a possibility that unthickened zaku in the middle of the slab thickness may remain and deteriorate the 1 / 2t performance, and Nb, V, etc. In order to dissolve sufficiently, the temperature is set to 1000 ° C. or higher.

  On the other hand, when heated to a temperature exceeding 1250 ° C., the initial γ grains become coarse and the toughness deteriorates, so the upper limit is set to 1250 ° C.

The rolling is rolling performed at Ar ₃ or higher (primary rolling) and rolling performed in a two-phase region of γ + α (secondary rolling). After the primary rolling, rapid heating and again heating to the recrystallization temperature range, Cool and perform secondary rolling.

2.1 Primary rolling Primary rolling is performed to make a steel material such as a slab into a desired shape, and the rolling is performed for one pass or more at the recrystallization temperature, and then the cumulative rolling reduction is performed at the non-recrystallization temperature. Roll 40% or more.

  Recrystallization zone rolling is necessary to uniformly refine the γ grains during heating to a certain extent, and the reduction is performed for one pass or more, preferably 20% or more cumulatively.

  In the non-recrystallized zone rolling, if the rolling reduction is small, the effect of refining the microstructure after rapid heating that reheats to the recrystallized zone after that cannot be exhibited, so 40% or more is secured. A higher rolling reduction is preferable, but about 80% is the upper limit industrially.

  In addition, after recrystallization zone rolling, it may wait by natural cooling (air cooling) up to the start temperature of non-recrystallization zone rolling, but it may be cooled by water during or after recrystallization zone rolling and wait until the start of non-recrystallization zone rolling. Shortening the time is preferable from the viewpoint of efficiency and the effect of suppressing the growth of recrystallization γ, and is effective by miniaturization.

_3. After primary rolling, after rapid rolling and non-recrystallization zone rolling, the temperature range from the Ar ₃ transformation point to the recrystallization temperature range is heated at a rate of temperature rise of 2 ° C./sec or more. The heating method is not particularly limited, but a high-frequency heating device is preferable. There is no need to perform holding or the like after heating.

When the heating start temperature is lower than the Ar ₃ transformation point, ferrite transformation occurs, and γ is refined by reverse transformation during reheating. However, the heating temperature cost at the time of subsequent heating is increased, efficiency and economy are impaired, precipitation and coarsening of Nb carbide and the like are promoted, and a mixed grain structure is easily formed and toughness is reduced.

Therefore, the temperature rise is started from a temperature equal to or higher than the Ar ₃ transformation point. The heating temperature needs to be higher than the recrystallization temperature, and is preferably a low temperature of the recrystallization temperature + 100 ° C. or lower. This is because γ grains grow when the temperature increases, and the effect of refinement of γ grains cannot be obtained.

  The heating rate is 2 ° C./sec or more. If it is 2 ° C./sec or less, recovery of the processed structure or processing-induced precipitation of carbides such as Nb and Ti occurs before recrystallization, and toughness deteriorates. Although holding after heating may be performed, grain re-growth occurs after completion of recrystallization. Therefore, holding more than necessary should not be performed, and a short time is preferable.

  By controlling the initial γ grains at the slab heating temperature and securing the cumulative rolling rate of non-recrystallized zone rolling and rapidly reheating to the recrystallization temperature range, the refinement of γ is achieved. Γ grains having a diameter of 15 μm or less or 10 μm or less are obtained. In the present invention, the average grain size of γ grains after recrystallization is referred to as the average γ grain size after recrystallization.

4. Secondary rolling Rolling (secondary rolling) performed after rapid heating in the recrystallization region and cooling to the two-phase region of γ + α is set to a cumulative reduction ratio of 15% or more. First, the steel sheet with γ grains refined to 15 μm or less by rapid heating to the recrystallization zone is air-cooled or water-cooled to the two-phase zone of γ + α, and then rolling is resumed, but the temperature at which rolling is resumed is Ar ₃ transformation. When the temperature exceeds the point, sufficient two-phase region rolling cannot be performed, and conversely, when the temperature at which the rolling is resumed is lower than the Ar ₃ transformation point −50 ° C., the rolling load is remarkably increased and the rolling cannot be performed. Therefore, the temperature at which the rolling is restarted is set to Ar ₃ transformation point or lower and Ar ₃ transformation point −50 ° C. or higher. Thereafter, when rolling at a rolling reduction of at least 15% in total is performed, the ferrite grains transformed during the rolling are refined and the DWTT characteristics are improved.

  The cumulative rolling reduction is preferably 20% or more in order to obtain the effect of refining ferrite grains over the center of the plate thickness.

5. In the accelerated cooling and accelerated cooling, the second phase is formed into a bainite structure in order to secure the strength of APIX 70 or higher, and the cooling start temperature is set to the Ar ₁ transformation point or higher and the cooling stop temperature is set to 600 ° C. or lower. When cooling is started from a temperature below the Ar ₁ transformation point, ferrite that is not refined by rolling is transformed between the end of rolling and the start of accelerated cooling, and these ferrites are not sufficiently refined so that the DWTT characteristics deteriorate. To do.

  On the other hand, when the cooling stop temperature is 600 ° C. or higher, the second phase becomes pearlite, and it becomes difficult to ensure the strength of APIX 70 or higher. The cooling rate is preferably strong cooling of 10 ° C./sec.

In the above description, the steel material temperature is the average temperature of the surface and the center of the steel material. The recrystallization temperature and the Ar ₃ , Ar ₁ transformation point vary depending on the components, and within the range of the chemical composition of the steel specified in the present application, the recrystallization temperature (the limit temperature causing recrystallization) is approximately in the range of 800 to 950 ° C. The Ar ₃ transformation point is approximately in the range of 700 to 800 ° C., and the Ar ₁ transformation point is approximately in the range of 600 to 700 ° C.

  The slab having the composition shown in Table 1 was formed into a thick steel plate having a thickness of 20 to 38 mm according to the hot rolling conditions shown in Table 2.

  In Table 1, the steel type No. One of the component compositions of the G, H, I, J, K, and L test steels is outside the scope of the present invention.

  About the obtained thick steel plate, the full thickness tensile test piece based on API-5L was extract | collected, the tensile test was implemented, and the yield strength, the tensile strength, and the yield ratio (ratio of yield strength and tensile strength) were calculated | required.

  For Charpy impact test, a V-notch standard size Charpy impact test piece conforming to JIS Z 2202 (1998 revised version) was sampled from the position in the thickness direction 1/4, and JIS Z 2242 (1998 revised version) was obtained. In accordance with the Charpy impact test at -40 ° C., the absorbed energy was determined.

  Moreover, the DWTT test piece based on API-5L was extract | collected, the test was performed at -40 degreeC, and SA value was calculated | required.

  After the non-recrystallized zone rolling, the average γ grain size after recrystallization is the same as the rolling conditions in Table 2 until the reheating, and after the holding time of 10 seconds after the reheating, A small rolled sample for gamma particle size measurement was taken from a part.

  A sample for microstructural observation is taken from the position of the plate thickness ¼ of the sample, and the plate thickness direction cross section of the sample is mirror-polished and then subjected to picric acid etching treatment, and then in a range of 400 to 1000 times using an optical microscope. Then, a photograph showing the γ grain boundary was taken, and the average particle size was calculated by image analysis.

  Table 3 shows the average γ grain size and mechanical properties after recrystallization of the investigated thick steel plates.

  In this example, the range of the present invention is that the lower limit yield strength of APIX70 is 485 MPa and the lower limit tensile strength is 565 MPa or more, the Charpy absorbed energy at −40 ° C. is 300 J or more, and the ductile fracture surface area SA value obtained in the DWTT test is 90% or more. And

  Invention Example No. 1 suitable for the present invention. Nos. 1 to 9 all have an average γ grain size of 15 μm or less after recrystallization, and have achieved high strength exceeding the lower limit yield strength of 485 MPa and the lower limit tensile strength of 565 MPa of APIX70, and further −40 ° C. Excellent toughness with a Charpy absorbed energy of 300 J or more and a ductile fracture surface area SA value obtained by a DWTT test of 90% or more was recognized. APIX70 shall refer to API-5L X70.

  On the other hand, in Comparative Example 10, although the chemical composition of the steel is suitable, the γ + α two-phase region rolling is subsequently performed without performing the rapid reheating after the non-recrystallization region rolling at the time of hot rolling, and thereafter accelerated cooling. As a result, the average γ grain size after recrystallization exceeded the range of the present invention. As a result, the Charpy absorbed energy and the SA value of the DWTT test were low.

  In Comparative Example 11, the heating rate in the reheating after the non-recrystallization zone rolling was slower than the range of the present invention, and the γ grains partially recovered during the reheating, and the recrystallization during the reheating was insufficient. Therefore, the average γ grains after recrystallization were coarse, and Charpy absorbed energy and the SA value of the DWTT test were low.

  In Comparative Example 12, the cumulative reduction ratio during rolling in the non-recrystallized zone was below the lower limit of the present invention, and sufficient processing was not performed to recrystallize during reheating, so the average γ grain after recrystallization was coarse, Similarly, the Charpy absorbed energy and the SA value of the DWTT test were low.

  On the other hand, in Comparative Example 13, since the cumulative rolling reduction during the two-phase rolling performed after the reheating treatment was below the lower limit of the present invention, the average γ grains after recrystallization were fine, but subsequent refinement of ferrite was sufficient In addition, the SA value of the DWTT test was a low value.

  In Comparative Example 14, the cooling stop temperature of the accelerated cooling exceeded the upper limit of the present invention, so that the second phase was not sufficiently bainite, and did not reach the lower limit of the strength of APIX70.

  In Comparative Example 15, the steel C content was lower than the lower limit of the present invention, and as a result, the lower limit of the Ceq value was also lower, so the strength was similarly low.

  In Comparative Example 16, since the C amount exceeded the upper limit of the present invention, the strength of APIX70 or higher was exhibited, but the Charpy absorbed energy was extremely low.

  In Comparative Example 17, since the amount of Si in the steel exceeded the upper limit of the present invention, the Charpy absorbed energy was low. Moreover, since the Mn amount of steel exceeded the upper limit of this invention, the SA value of the DWTT test was remarkably low in the comparative example 18.

  In Comparative Example 19, since the amount of B in the steel exceeded the upper limit of the present invention, the ferrite transformation was suppressed, and ferrite could not be sufficiently refined during rolling in the two-phase region, and the SA of the DWTT test The value was low.

  In Comparative Example 20, since the Nb content of the steel was below the lower limit of the present invention, even when the austenite non-recrystallization temperature range was narrow and the cumulative rolling reduction was sufficiently performed, a recovery phenomenon occurred during rolling, and recrystallization occurred. The γ-grain recrystallization during reheating to the region was not sufficient, and the average γ-grain after coarse recrystallization resulted in low Charpy absorbed energy and SA value in the DWTT test.

Claims (5)

% By mass, C: 0.03 to 0.09%,
Si: 0.01 to 0.50%,
Mn: 1.0 to 3.0%
P: 0.030% or less,
S: 0.010% or less,
sol. Al: 0.003 to 0.100%,
B: 0.0005% or less,
Nb: 0.005 to 0.1%,
Ti: 0.005 to 0.05%
In addition,
Cu: 0.01 to 1.0%,
Ni: 0.01 to 2.0%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
V: 0.003-0.1%
1 type or 2 types or more chosen from among,
Furthermore, the Ceq value calculated by the following equation (1) is 0.36 to 0.60,
A steel material having a composition comprising the balance of Fe and inevitable impurities,
Heat to 1000 ° C. or more and 1250 ° C. or less, and after rolling in the recrystallization temperature range, perform primary rolling for rolling at a cumulative reduction ratio of 40% or more in the non-recrystallization temperature range, and then from the temperature above the Ar ₃ transformation point After heating at a temperature increase rate of 2 ° C / sec or more above the recrystallization temperature, after cooling to a temperature not higher than Ar ₃ transformation point -50 ° C or higher after Ar ₃ transformation point, rolling is resumed, and cumulative reduction is performed in the two-phase temperature range. Production of a thick-walled, high-strength, high-toughness steel pipe material characterized by having a step of performing secondary rolling for rolling at a rate of 15% or more, and further accelerated cooling from a temperature above the Ar ₁ transformation point to 600 ° C. Method.
Ceq (%) = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (1)
Each element is a value in mass%.
The steel material is further
Ca: 0.0001 to 0.0060%,
Mg: 0.0001 to 0.0060%,
REM: 0.0001-0.0200%,
Zr: 0.0001 to 0.0100%
The method for producing a thick-walled, high-strength, high-toughness steel pipe material according to claim 1, comprising one or more selected from among the above.   In primary rolling, before performing rolling with a cumulative reduction ratio of 40% or more in the non-recrystallization temperature range, performing water cooling during or after the recrystallization temperature range rolling and cooling to the non-recrystallization temperature range The method for producing a thick-walled, high-strength, high-toughness steel pipe material according to claim 1 or 2, characterized by the above. The average γ grain size after recrystallization obtained after heating from the temperature not lower than the Ar ₃ transformation point to the recrystallization temperature range after primary rolling is 15 μm or less. The manufacturing method of the thick-walled high strength high toughness steel pipe material as described.   It is manufactured by the method according to any one of claims 1 to 4, and after recrystallization, the average γ grain size is 15 µm or less, the yield strength is 485 MPa or more, the tensile strength is 565 MPa or more, and the Charpy absorbed energy at -40 ° C is 300 J or more. A steel pipe material for a line pipe, wherein the ductile fracture surface area SA value obtained by the DWTT test is 90% or more and the plate thickness is 20 mm or more.