800 MPa grade tear-resistant steel plate and production method thereof

Abstract

The invention provides a 800 MPa grade tear-resistant steel plate and a production method thereof, and relates to the technical field of steel plate production, the 800 MPa grade tear-resistant steel plate comprises the following chemical components by mass: 0.14-0.18% of C, less than or equal to 0.10% of Si, 1.3-1.5% of Mn, 0.4-0.6% of Cr, 0.15-0.18% of Ti, 0.020-0.045% of Al, 0.002-0.0035% of Ca, less than or equal to 0.002% of S, less than or equal to 0.012% of P, less than or equal to 0.004% of N, and the balance Fe and inevitable impurities; in the aspect of component design, Si is reduced, Cr is increased to replace part of Mn, and the hardenability is improved; and Ti microalloying optimization is carried out, the grain refinement effect of free Ti is ensured, ultra-low sulfur and calcium treatment is carried out, and the Ca / S ratio is controlled to realize inclusion spheroidization. The steel plate meets the Z35 level requirement; the welding performance is excellent; the obdurability matching is excellent.

Description

Technical Field

[0001] This invention relates to the field of steel plate production technology, and in particular to an 800MPa grade tear-resistant steel plate and its production method. Background Technology

[0002] Increasingly, applications demand steel plates with large thicknesses, high unit weights, high internal quality, and resistance to lamellar tearing. Currently, producing such steel often requires the addition of numerous expensive alloying elements such as Ni and Mo, but this is costly. Another approach is to use fewer alloying elements and produce 800MPa grade steel plates using the conventional DQ process, but this results in unstable Z-axis properties. Alternatively, adding elements such as Cu and Ni can improve performance, but this significantly increases costs and also results in relatively high carbon equivalents, which are detrimental to welding. However, without adding expensive alloying elements, while costs can be significantly reduced and weldability improved, insufficient hardenability makes it difficult to obtain a high-strength microstructure; insufficient low-temperature toughness; reduced resistance to lamellar tearing; and low reduction of area. For example, Chinese patent application number 202210571671.8 discloses a method for producing Q890D ultra-high strength steel medium-thick plates by online quenching. It uses higher contents of precious alloying elements, such as Mo (0.40-0.70%) and Ni (0.30-0.60%), and implements high-reduction rolling and online quenching processes. Its focus is on process execution and high strength, without emphasizing Z-axis performance indicators. Furthermore, the sulfur content control (<0.008%) is still detrimental to resistance to lamellar tearing, and the alloy cost advantage is insufficient. Another example is Chinese patent application number 202110596153.7, which discloses an online quenching method for producing 800MPa grade extra-thick steel plates for engineering machinery. It adopts a low-carbon design (C≤0.08%), but still adds alloying elements such as Mo, Ni, and Cu, and produces steel plates by optimizing steelmaking, rolling, and online quenching processes. Its sulfur content (<0.005%) is still too high, which is not conducive to ensuring Z-axis performance, and the alloy cost is still relatively high.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One of the objectives of this invention is to provide an 800MPa grade tear-resistant steel plate to solve the technical problem of the lack of a low-alloy steel plate with high tear resistance in the prior art.

[0005] The second objective of this invention is to provide a method for producing the aforementioned steel plate.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides an 800MPa grade tear-resistant steel plate, the steel plate comprising the following chemical composition by mass percentage: C: 0.14~0.18%, Si: ≤0.10%, Mn: 1.3~1.5%, Cr: 0.4~0.6%, Ti: 0.15~0.18%, Al: 0.020~0.045%, Ca: 0.002~0.0035%, S≤0.002%, P≤0.012%, N≤0.004%, carbon equivalent ≤0.55%, with the balance being Fe and unavoidable impurities; The mass percentage of the chemical composition of the steel plate simultaneously satisfies all conditions A1 to A4: A1, Mn+2Cr≥2.0%; A2, Ti-3.42N ≥ 0.08%; A3, 1.5≤Ca / S≤3.0; A4, Pcm=C+Si / 30+(Mn+Cr+Cu) / 20≤0.29%.

[0007] Furthermore, the metallographic structure of the steel plate is a multiphase structure composed of lath bainite and martensite.

[0008] Furthermore, in the multiphase structure, the volume ratio of lath bainite is 85-95%, and the volume ratio of martensite is 5-15%.

[0009] Furthermore, the original austenite grain size is ≥8.

[0010] Furthermore, the steel plate possesses at least one mechanical property selected from B1 to B5: B1. Yield strength ≥ 800 MPa; B2. Tensile strength ≥ 880 MPa; B3, elongation ≥14%; B4, Impact energy at -20℃ ≥60J; B5, Z-direction reduction of area ≥35%.

[0011] Secondly, the present invention provides a method for producing the aforementioned steel plate, comprising the following steps: S1. Smelting and continuous casting: The converter-LF-VD process is adopted, and the calcium treatment amount is 0.3~0.4 kg / t; S2. Heating: Heat the continuously cast billet to 1250~1300℃, and soak it for 50~80 minutes. S3. Rough rolling: Initial rolling temperature ≥1100℃, final rolling temperature 1030~1060℃, reduction rate per pass ≥15%; S4. Intermediate cooling: Rapid cooling to 830~800℃ using IC devices; S5, Finish rolling: Rolled in the non-recrystallization zone at 770~800℃, with a cumulative reduction rate ≥50%; S6. Online quenching: water immersion temperature 750~780℃, reddening temperature 330-380℃; S7. Tempering: Tempering temperature 560~600℃, calculated based on steel plate thickness, holding time is 3.5~4.0min / mm.

[0012] Furthermore, the thickness of the continuously cast billet is 250~350mm.

[0013] Furthermore, the control step of the reddening temperature of 330-380℃ includes adjusting the cooling rate to ≥60℃ / s.

[0014] Furthermore, the online quenching process includes the use of 12 sets of manifolds, with a total flow rate of 10000±100m³. 3 / h, water ratio 1.6, roller speed 0.40~0.45m / s.

[0015] Furthermore, the finishing rolling is carried out in the non-recrystallization zone, where the accumulated deformation energy provides a nucleation driving force for the bainitic phase transformation.

[0016] This invention provides an 800MPa tear-resistant steel plate. In terms of composition design, it is free of Ni and Mo, with reduced Si and increased Cr. Si ≤ 0.10% improves low-temperature impact toughness, and Cr partially replaces Mn to improve hardenability. Ti microalloying optimization is used, with Ti content at 0.15-0.18% and Ti-3.42N ≥ 0.08% to ensure grain refinement of free Ti. Ultra-low sulfur calcium treatment, with S ≤ 0.002% combined with Ca treatment, controls the Ca / S ratio to achieve inclusion spheroidization. The production method of this steel plate results in a Z-axis reduction of area ≥ 35%, meeting Z35 grade requirements; excellent weldability (Pcm ≤ 0.029%); and an impact energy ≥ 60J at -20℃, exhibiting excellent strength and toughness matching. Detailed Implementation

[0017] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0018] Unless otherwise stated, the methods and techniques of the present invention are generally carried out according to conventional methods well known in the art and as described in various general and more specific references, which are cited and discussed throughout this specification.

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides an 800MPa tear-resistant steel plate, the steel plate comprising the following chemical composition by mass percentage: C: 0.14~0.18%, Si: ≤0.10%, Mn: 1.3~1.5%, Cr: 0.4~0.6%, Ti: 0.15~0.18%, Al: 0.020~0.045%, Ca: 0.002~0.0035%, S≤0.002%, P≤0.012%, N≤0.004%, carbon equivalent ≤0.55%, with the balance being Fe and unavoidable impurities; The mass percentage of the chemical composition of the steel plate simultaneously satisfies all conditions A1 to A4: A1, Mn+2Cr≥2.0%; A2, Ti-3.42N ≥ 0.08%; A3, 1.5≤Ca / S≤3.0; A4, Pcm=C+Si / 30+(Mn+Cr+Cu) / 20≤0.29%.

[0021] In terms of composition design, it is free of Ni and Mo, with Si reduced and Cr increased. Si ≤ 0.10% improves low-temperature impact toughness, and Cr replaces part of Mn to improve hardenability. Ti microalloying is optimized, with Ti content of 0.15-0.18% and Ti-3.42N ≥ 0.08% to ensure the grain refinement effect of free Ti. Ultra-low sulfur calcium treatment, with S ≤ 0.002% combined with Ca treatment, controls the Ca / S ratio to achieve inclusion spheroidization.

[0022] The steel plate has a single austenitic structure at high temperatures. When the cooling rate is between the formation of bainite and martensite, the austenitic structure transforms into a mixed structure of bainite and martensite. In some specific embodiments, the metallographic structure of the steel plate is a multiphase structure composed of lath bainite and martensite. In some specific embodiments, the volume ratio of lath bainite in the multiphase structure is 85-95%, and the volume ratio of martensite is 5-15%. In some specific embodiments, the original austenite grain size is ≥8.

[0023] The mechanical properties of 800MPa grade tear-resistant steel plates meet the following requirements: yield strength ≥ 800MPa; tensile strength ≥ 880MPa; elongation ≥ 14%; impact energy at -20℃ ≥ 60J; Z-direction reduction of area ≥ 35%.

[0024] According to another aspect of the present invention, a method for producing the above-described steel plate is also provided, comprising the following steps: S1. Smelting and continuous casting: The converter-LF-VD process is adopted, and the calcium treatment amount is 0.3~0.4 kg / t; S2. Heating: Heat the continuously cast billet to 1250~1300℃, and soak it for 50~80 minutes. S3. Rough rolling: Initial rolling temperature ≥1100℃, final rolling temperature 1030~1060℃, reduction rate per pass ≥15%; S4. Intermediate cooling: Rapid cooling to 830~800℃ using IC devices; S5, Finish rolling: Rolled in the non-recrystallization zone at 770~800℃, with a cumulative reduction rate ≥50%; S6. Online quenching: water immersion temperature 750~780℃, reddening temperature 330-380℃; S7. Tempering: Tempering temperature 560~600℃, calculated based on steel plate thickness, holding time is 3.5~4.0min / mm.

[0025] This production method involves heating the continuously cast billet to 1250~1300℃ for 50~80 minutes to ensure sufficient dissolution of alloying elements and avoid overheating. The billet is then removed from the furnace, descaled, and enters the roughing mill. The exit temperature of the roughing mill is controlled at 1030~1060℃. Large reduction rolling is used in the roughing stage, with a reduction rate ≥15% per pass, effectively breaking down the original as-cast structure. After roughing, an IC device is used for cooling, rapidly cooling to 830~800℃ before entering the finishing mill. The temperature at the end of the finishing mill is controlled at 770~800℃. Controlling the finishing temperature within this range facilitates rolling in the non-recrystallized zone. By rolling with large deformation in the non-recrystallized zone, an ideal microstructure is created for the subsequent phase transformation process, thus inducing bainite transformation. On the other hand, the steel plate enters the online quenching device directly after exiting the rolling mill, with the water temperature controlled at 750~780℃, lower than the water temperature of the traditional DQ process, to retain more nucleation cores. By dynamically adjusting the parameters of the online quenching device, the steel plate's red-hot temperature is controlled between 330–380℃, thereby obtaining a multiphase structure mainly composed of lath bainite with a suitable amount of martensite, ensuring excellent strength and toughness. Finally, the quenched steel plate is immediately subjected to tempering heat treatment, with the tempering temperature set at 560~600℃ and the holding time calculated according to the steel plate thickness, at T = 3.5~4.0 min / mm, to obtain a stable tempered structure with stress relief.

[0026] The above-mentioned steel plate contains no precious elements such as Ni and Mo, which reduces the alloy cost by more than 30%; the production method of the steel plate results in a Z-direction section reduction rate of ≥35%, meeting the Z35 grade requirement; it has excellent weldability (Pcm≤0.29%); and its impact energy at -20℃ is ≥60J, with excellent strength and toughness matching.

[0027] In some specific embodiments, the thickness of the continuously cast billet is 250~350mm.

[0028] In some specific embodiments, the step of controlling the reddening temperature of 330-380℃ includes adjusting the cooling rate to ≥60℃ / s. In some specific embodiments, the online quenching includes using 12 sets of manifolds with a total flow rate of 10000±100m³. 3 / h, water ratio 1.6, roller speed 0.40~0.45m / s.

[0029] In some specific embodiments, the finishing rolling is carried out in the non-recrystallization zone, where the accumulated deformation energy provides a nucleation driving force for the bainitic phase transformation.

[0030] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0031] Example 1 An 800MPa grade tear-resistant steel plate is formulated with the following mass percentages: C: 0.14%, Si: 0.10%, Mn: 1.3%, Cr: 0.4%, Ti: 0.15%, Al: 0.030%, Ca: 0.003%, S: 0.001%, P: 0.012%, N: 0.003%, with the balance being Fe and unavoidable impurities.

[0032] The specific production process is as follows: 1) The smelting adopts the converter-LF-VD process, the calcium processing amount is 0.3kg / t, the continuous casting process adopts electromagnetic stirring technology, and the thickness of the continuous casting billet is 300mm.

[0033] 2) Heat the continuously cast billet to 1280℃ and soak it for 60 minutes.

[0034] 3) The billet is fed into the roughing mill for roughing. The initial reduction of each pass in the roughing stage is 50 mm, and the reduction rate of subsequent passes is controlled at ≥15%. At the end of the roughing stage, the billet thickness is 80 mm and the billet temperature is 1000~1040℃.

[0035] 4) After rough rolling, the material is quickly fed into the IC device for cooling, and rapidly cooled to 830~800℃.

[0036] 5) The rolling mill is used for finishing rolling. The reduction rate of each finishing rolling pass is ≥10%. Finishing rolling ends at a temperature of 790℃. 6) After exiting the rolling mill, the steel plate directly enters the online quenching device with an inlet water temperature of 765℃. Twelve manifolds are activated for online quenching, with a total flow rate of 10000±100m³. 3 / h, water ratio 1.6, roller speed 0.45m / s, final cooling temperature 350℃, and reddening temperature controlled at 380℃; 7) The quenched steel plate is subjected to tempering heat treatment in a continuous furnace at a tempering temperature of 570℃ and a holding time of 160min.

[0037] The final steel plate has a thickness of 40 mm, a longitudinal yield strength of 845 MPa, a tensile strength of 915 MPa, an elongation of 14%, an average impact energy of 65 J at -20℃, Z-direction tensile properties meeting the Z35 grade requirements, and a section reduction rate of 38%. Specific properties are shown in Table 1.

[0038] Example 2 Molten steel is prepared according to the following mass percentages: C: 0.18%, Si: 0.25%, Mn: 1.5%, Cr: 0.6%, Ti: 0.18%, Al: 0.040%, Ca: 0.003%, S: 0.0015%, P: 0.010%, N: 0.002%, with the balance being Fe and unavoidable impurities.

[0039] The specific production process is as follows: 1) The smelting adopts the converter-LF-VD process, the calcium processing amount is 0.4kg / t, the continuous casting process adopts electromagnetic stirring technology, and the thickness of the continuous casting billet is 300mm.

[0040] 2) Heat the continuously cast billet to 1270℃ and soak it for 50 minutes.

[0041] 3) The billet is fed into the roughing mill for roughing. The initial reduction of each pass in the roughing stage is 50 mm, and the reduction rate of subsequent passes is controlled at ≥15%. At the end of the roughing stage, the billet thickness is 100 mm and the billet temperature is 1000~1040℃.

[0042] 4) After rough rolling, the material is quickly fed into the IC device for cooling, and rapidly cooled to 830~800℃.

[0043] 5) Enter the finishing mill for finishing rolling. The reduction rate of each finishing rolling pass is ≥10%. Finishing rolling ends at 800℃.

[0044] 6) After exiting the rolling mill, the steel plate directly enters the online quenching device with an inlet water temperature of 780℃. Twelve manifolds are activated for online quenching, with a total flow rate of 10000±100m³. 3 / h, water ratio 1.6, roller speed 0.40m / s, final cooling temperature 340℃, and reddening temperature controlled at 370℃; 7) The quenched steel plate is subjected to tempering heat treatment in a continuous furnace at a tempering temperature of 600℃ and a holding time of 200min.

[0045] The final steel plate has a thickness of 50 mm, a longitudinal yield strength of 868 MPa, a tensile strength of 929 MPa, an elongation of 16%, an average impact energy of 126 J at -20℃, Z-direction tensile properties that meet the Z35 grade requirements, and a section reduction rate of 40%. Specific properties are shown in Table 1.

[0046] Comparative Example 1 Unlike Example 1, after rough rolling, air cooling was used to reduce the temperature to 880℃; then, it entered the finish rolling mill, and the temperature at the end of the finish rolling was controlled at 860℃; it then directly entered the online quenching device, with an inlet water temperature of 840℃. Ten sets of manifolds were opened for online quenching, with a total flow rate of 8500±100m³. 3 The water ratio is 1.2, the roller speed is 0.40 m / s, the final cooling temperature is 450℃, and the reddening temperature is controlled at 480℃. The quenched steel plate is then subjected to tempering heat treatment in a continuous furnace at a tempering temperature of 580℃ and a holding time of 160 min.

[0047] The final steel plate has a thickness of 40 mm, a longitudinal yield strength of 868 MPa, a tensile strength of 910 MPa, an elongation of 11%, an average impact energy of 25 J at -20℃, unqualified Z-direction performance, and a section reduction rate of only 15%. Specific properties are shown in Table 1.

[0048] Comparative Example 2 Unlike Example 2, the roughing mill exit temperature was controlled at 1070℃, with a pass reduction rate of 13% during the roughing stage. After roughing, air cooling was used to lower the temperature to 870℃. Then, the mill entered the finishing mill, with a finishing temperature of 865℃. Next, the mill entered the DQ online quenching device with a water inlet temperature of 830℃. Twelve manifolds were opened for online quenching, with a total manifold flow rate of 8900 m³ / h. 3 The water ratio is 1.15, the roller speed is 0.38 m / s, the final cooling temperature is 340℃, and the red-hot temperature is controlled at 370℃. The quenched steel plate is then subjected to tempering heat treatment in a continuous furnace at a tempering temperature of 600℃ and a holding time of 140 min.

[0049] The final steel plate has a thickness of 40 mm, a longitudinal yield strength of 858 MPa, a tensile strength of 942 MPa, an elongation of 10%, an average impact energy of 41 J at -20℃, unqualified Z-direction properties, and a section reduction rate of only 16%. Specific properties are shown in Table 1.

[0050] Comparative Example 3 Unlike Example 1, the composition design simultaneously increases the content of Si and Cr. The steel plate composition is prepared according to the following mass percentages: C: 0.15%, Si: 0.35%, Mn: 1.40%, Cr: 0.75%, Ti: 0.16%, Al: 0.035%, Ca: 0.0035%, S: 0.0015%, P: 0.011%, N: 0.003%, with the balance being Fe and unavoidable impurities. The production method is the same as in Example 1.

[0051] Comparative Example 4 Unlike Example 1, the Ti content was reduced in the composition design. The steel plate composition was prepared according to the following mass percentages: C: 0.16%, Si: 0.09%, Mn: 1.35%, Cr: 0.55%, Ti: 0.06%, Al: 0.035%, Ca: 0.0020%, S: 0.0010%, P: 0.010%, N: 0.003%, with the balance being Fe and unavoidable impurities. The production method was the same as in Example 1.

[0052] Comparative Example 5 Unlike Example 1, the Ca / S ratio is < 1.5 in this composition design. The steel plate composition is prepared according to the following mass percentages: C: 0.16%, Si: 0.10%, Mn: 1.50%, Cr: 0.60%, Ti: 0.17%, Al: 0.025%, Ca: 0.0015%, S: 0.0020%, P: 0.011%, N: 0.003%, with the balance being Fe and unavoidable impurities. The production method is the same as in Example 1.

[0053] Comparative Example 6 Unlike Example 1, the Ca / S ratio is greater than 3.0 in this case. The steel plate composition is prepared according to the following mass percentages: C: 0.16%, Si: 0.10%, Mn: 1.45%, Cr: 0.55%, Ti: 0.17%, Al: 0.030%, Ca: 0.0045%, S: 0.0010%, P: 0.011%, N: 0.003%, with the balance being Fe and unavoidable impurities. The production method is the same as in Example 1.

[0054] Table 1

[0055] In summary, compared with the loose sulfur control and extensive process used in the comparative example, the embodiment of the present invention, through the synergistic process of "medium carbon design - ultra-low sulfur calcium treatment - low temperature controlled rolling - toughening tempering", successfully improved the Z-direction performance from severely unqualified (15%) to the excellent level of Z35 grade (38%) while ensuring high strength and high toughness, achieving a breakthrough in comprehensive performance under low alloy cost.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tear-resistant steel plate with a strength of 800 MPa, characterized in that, The steel plate comprises the following chemical composition by mass percentage: C: 0.14~0.18%, Si: ≤0.10%, Mn: 1.3~1.5%, Cr: 0.4~0.6%, Ti: 0.15~0.18%, Al: 0.020~0.045%, Ca: 0.002~0.0035%, S≤0.002%, P≤0.012%, N≤0.004%, carbon equivalent ≤0.55%, with the balance being Fe and unavoidable impurities; The mass percentage of the chemical composition of the steel plate simultaneously satisfies all conditions A1 to A4: A1, Mn+2Cr≥2.0%; A2, Ti-3.42N ≥ 0.08%; A3, 1.5≤Ca / S≤3.0; A4, Pcm=C+Si / 30+(Mn+Cr+Cu) / 20≤0.29%.

2. The steel plate according to claim 1, characterized in that, The metallographic structure of the steel plate is a multiphase structure composed of lath bainite and martensite.

3. The steel plate according to claim 2, characterized in that, In the multiphase microstructure, the volume ratio of lath bainite is 85-95%, and the volume ratio of martensite is 5-15%.

4. The steel plate according to claim 3, characterized in that, The original austenite grain size is ≥8.

5. The steel plate according to any one of claims 1 to 4, characterized in that, The steel plate possesses at least one mechanical property selected from B1 to B5: B1. Yield strength ≥ 800 MPa; B2. Tensile strength ≥ 880 MPa; B3, elongation ≥14%; B4, Impact energy at -20℃ ≥60J; B5, Z-direction reduction of area ≥35%.

6. A method for producing steel plates according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Smelting and continuous casting: The converter-LF-VD process is adopted, and the calcium treatment amount is 0.3~0.4 kg / t; S2. Heating: Heat the continuously cast billet to 1250~1300℃, and soak it for 50~80 minutes. S3. Rough rolling: Initial rolling temperature ≥1100℃, final rolling temperature 1030~1060℃, reduction rate per pass ≥15%; S4. Intermediate cooling: Rapid cooling to 830~800℃ using IC devices; S5, Finish rolling: Rolled in the non-recrystallization zone at 770~800℃, with a cumulative reduction rate ≥50%; S6. Online quenching: water immersion temperature 750~780℃, reddening temperature 330-380℃; S7. Tempering: Tempering temperature 560~600℃, calculated based on steel plate thickness, holding time is 3.5~4.0min / mm.

7. The production method according to claim 6, characterized in that, The thickness of the continuously cast billet is 250~350mm.

8. The production method according to claim 6, characterized in that, The control steps for the reddening temperature of 330-380℃ include adjusting the cooling rate to ≥60℃ / s.

9. The production method according to claim 8, characterized in that, The online quenching process includes the use of 12 manifolds with a total flow rate of 10000±100m³. 3 / h, water ratio 1.6, roller speed 0.40~0.45m / s.

10. The production method according to claim 6, characterized in that, The finishing rolling is carried out in the non-recrystallization zone, where the accumulated deformation energy provides the nucleation driving force for the bainitic phase transformation.

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