Method for improving low-temperature toughness stability of center portion of TMCP thick marine steel plate

Abstract

This invention relates to a method for improving the low-temperature toughness and stability of the core of extra-thick TMCP marine engineering steel plates, belonging to the field of metallurgical technology. The process includes: composition design: carbon content ≤0.10%, Mn content ≤1.60%, S content ≤0.003%; rolling design: two-stage controlled rolling of roughing and finishing, with the compression ratio controlled according to the steel plate thickness; production organization: removing black ends according to the steel plate's production thickness, requiring ≥2.5T mm (T is the steel plate thickness) for 60-80mm thick steel plates, and ≥200mm for steel plates >80mm thick; grading the billet based on its low-magnification microstructure, and designing the billet furnace entry temperature, billet heating temperature, rolling temperature, and ACC cooling based on the billet grade and the steel plate's production thickness. This reduces abnormal microstructure transformation at billet segregation sites and promotes uniform and refined core microstructure, resulting in a core impact pass rate of over 99.3% for 60-120mm extra-thick steel plates at -40℃.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for improving the low-temperature toughness and stability of extra-thick marine steel. Background Technology

[0002] As my country's marine resource development continues to expand into the deep sea, open ocean, and polar regions, marine engineering structures are becoming increasingly larger and operating in harsher environments. Structural steel plates require not only great thickness, high strength and toughness, good weldability, and adaptability to low-temperature environments, but also excellent core low-temperature toughness stability to reduce the risk of weak points in complex welded structures, thus ensuring service safety in complex marine environments. However, the presence of defects such as segregation and porosity in the core of continuously cast billets, as well as the uneven core microstructure caused by the thickness effect of extra-thick steel plates, makes the core of extra-thick steel plates the weakest point in low-temperature toughness, highly susceptible to performance fluctuations, thus affecting the overall performance qualification rate of the steel plate. Once the core low-temperature toughness fails to meet the requirements, the steel plate usually has to be downgraded or re-judged, requiring re-production, which not only greatly increases production costs but also delays delivery, causing significant economic losses to both production and user companies.

[0003] Currently available invention patents related to "low-temperature toughness of the core in TMCP extra-thick steel plates" focus on composition optimization combined with conventional controlled rolling and cooling to improve the absolute value of core toughness. For example, Chinese patent application CN117403132A discloses an extra-thick 420MPa grade steel plate with good core impact toughness. Using a low-carbon equivalent composition design and combining controlled rolling with DQ / ACC processes, its impact energy at -20℃ (1 / 2 thickness) can reach over 243J, and at -40℃, it can reach over 207J. Existing technologies do not systematically address the stability control of core low-temperature toughness under mass production conditions, and therefore cannot effectively solve the problems of large performance fluctuations and low yield rates.

[0004] Therefore, developing a production method that can significantly reduce the low-temperature toughness fluctuation of the core of TMCP extra-thick marine engineering steel plates and improve batch performance stability and yield rate has important engineering value and economic significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine engineering steel plates. This method is particularly suitable for producing marine engineering steel plates with a thickness of 60-120mm, and the impact pass rate of the steel plate core at -40℃ can be stably maintained at over 99.3%.

[0006] The technical solution adopted by this invention to solve the above problems is as follows: a method for improving the low-temperature toughness stability of the core of TMCP extra-thick marine engineering steel plates, the method including composition design, production organization, and control of key process parameters in the production process, as detailed below: In actual mass production, the main reasons for the large fluctuations in the low-temperature toughness of the core of TMCP extra-thick steel plates are: first, the high composition at the center of the continuously cast billet segregation site easily leads to the formation of abnormal structures during the ACC cooling process after rolling; second, improper controlled rolling process results in mixed crystal structure in the core of the extra-thick steel plate; third, improper process control throughout the heating, rolling, and ACC processes leads to coarse core structure; and fourth, insufficient removal of blackheads at the beginning and end of the plates, resulting in unrepresentative sampling and fluctuations. Based on the above reasons for the large fluctuations in the low-temperature toughness of the core of TMCP extra-thick steel plates, the method of this application includes the following implementation technical features: To control the fluctuation of low-temperature toughness in the core caused by segregation in the center of the continuously cast billet, the composition design should focus on two aspects: First, the content of C and Mn, the elements with the strongest segregation tendency, should be minimized. Based on the thickness and strength grade of the rolled steel plate, the carbon content should be ≤0.10% and the Mn content should be ≤1.60%. Second, the S content should be controlled below 0.003% to reduce the tendency of MnS inclusions.

[0007] In terms of rolling, a two-stage controlled rolling process is adopted based on the thickness range and low magnification microstructure of the steel plate to ensure that the core of the steel plate is fully deformed within a certain temperature range, so as to avoid mixed crystals caused by uneven deformation.

[0008] To obtain a fine core structure, comprehensive control is required from aspects such as billet entry into the furnace, heating temperature, rolling temperature, rolling deformation distribution, and ACC process control. First, the billet entry temperature should be ≤300℃ to avoid the continued growth of coarse austenite grains in the billet core due to direct heating in the furnace. Second, the heating temperature must be controlled according to the addition of microalloying elements, and a suitable temperature range should be set. Third, the rolling temperature and rolling deformation distribution must take into account the deformation temperature and deformation amount of the core structure to provide a suitable cumulative deformation austenite structure for subsequent ACC cooling. Fourth, post-rolling cooling must take into account the initial cooling temperature and cooling rate. This application adopts ACC laminar flow cooling.

[0009] The actual rolling conditions at the blackhead location of the steel plate differ greatly from those at other locations. To avoid fluctuations in the core properties of the blackhead location due to uncontrolled processes and microstructure, the amount of blackhead removal for 60-80mm thick steel plates needs to be ≥2.5T mm, where T is the thickness of the steel plate. For steel plates thicker than 80mm, the amount of blackhead removal needs to be ≥200mm.

[0010] Furthermore, to reduce fluctuations in the low-temperature toughness of the core during mass production, based on the aforementioned process design considerations, further optimization of production organization is necessary, as follows: The first-burner billet and the last-burner billet are usually the areas with the greatest low-magnification quality fluctuations in the casting process, requiring key control. First, steel of 355MPa and below should be prioritized for production in the first and last furnaces to reduce the tendency for abnormal microstructure transformation caused by excessive ACC cooling intensity of ultra-high strength steel plates. Second, the first-burner billet and the last-burner billet should be piled up for slow cooling for ≥48 hours and rolled in a concentrated manner at regular intervals to facilitate full-process control of heating, rolling, and ACC cooling.

[0011] The rolling compression ratio should be selected based on the thickness of the steel plate. For steel plates with a thickness of 60-80mm, a compression ratio of 3.0-5.0 can be selected to ensure sufficient core deformation and avoid exacerbating the segregation tendency caused by excessive thickness of the continuously cast billet. For steel plates with a thickness greater than 80mm, a compression ratio of 3.5-6.0 can be selected to ensure greater deformation accumulation in the core. This ensures that the core microstructure can obtain a uniform and fine microstructure with sufficient phase transformation driving force when the core cooling rate becomes slower and slower.

[0012] Under the premise of ensuring the compression ratio of steel plate rolling, the billet design is carried out according to the control rolling requirements of steel plates of different thicknesses and the requirements for the removal allowance of black ends. The size of the billet must ensure that the control rolling thickness of steel plates with a thickness of 60-80mm is ≥2.0T (T is the final thickness of steel plate), the control rolling thickness of steel plates with a thickness of >80-100mm is ≥2.2T, and the control rolling thickness of steel plates with a thickness of >100-120mm is ≥2.3T.

[0013] The TMCP extra-thick marine engineering steel plate involved in this invention comprises the following production processes: KR molten iron pretreatment, BOF converter smelting, LF furnace refining, RH vacuum degassing, slab continuous casting, continuous casting billet heating, and rolling. The technical improvement of this application lies in: based on the existing conventional production process of TMCP extra-thick marine engineering steel plates, simultaneously optimizing the billet furnace entry temperature, billet heating, controlled rolling, and ACC accelerated cooling processes to improve the stability of the low-temperature toughness of the steel plate core and significantly increase the production qualification rate. Specific process measures for each step are as follows: Billet is fed into the furnace: For extra-thick TMCP marine steel plates requiring low-temperature impact resistance in the core, the basic condition for billet entry into the furnace is a furnace temperature ≤300℃. Based on this, different low-magnification quality grades need to be marked to ensure graded control during subsequent heating, controlled rolling, and ACC cooling processes. Grade 1 is segregated C 0.5-1.0, Grade 2 is segregated C 1.5-2.0, and Grade 3 is segregated B 0.5-1.0. Billets with segregation of B 1.5 or worse need to be re-rolled into steel plates with other requirements and cannot be used to produce steel plates with low-temperature impact resistance in the core.

[0014] Billet heating: For the first-stage billet, the core segregation of the continuously cast billet is light. Based on the content of added alloying elements, the high-temperature section is controlled at 1100-1210℃ to reduce the tendency of coarse austenite grains in the continuously cast billet caused by excessive heating temperature. For the second-stage billet, the core segregation of the continuously cast billet is relatively heavy. The high-temperature section is controlled at 1140-1250℃, and the high-temperature section time is extended by 30 minutes. Higher temperature and longer high-temperature section time promote the diffusion of core segregation. For the third-stage billet, the core segregation of the continuously cast billet is the heaviest. Based on the heating technology of the second-stage billet, the high-temperature section time is extended by another 30 minutes.

[0015] Controlled rolling: A two-stage controlled rolling process is adopted. For the first-grade billet, the finishing rolling temperature range for 60-80mm thick steel plates is Ar3+ (20℃~60℃), with a controlled rolling thickness ≥2.0T (T is the final steel plate thickness); the finishing rolling temperature range for steel plates >80-100mm thick is Ar3+ (10~50℃), with a controlled rolling thickness ≥2.2T; and the finishing rolling temperature range for steel plates >100-120mm thick is Ar3+ (0℃~+30℃), with a controlled rolling thickness ≥2.3T. For the second and third-grade billets, the roughing stage ensures at least two passes with a single-pass deformation amount ≥50mm, and the initial rolling speed is reduced. This is achieved by increasing the core deformation and extending the deformation time to promote repeated recrystallization in the core, thus refining the grains. The finishing rolling start temperature is reduced by 10-20℃ compared to the first-grade billet to lower the core deformation temperature during the finishing rolling process.

[0016] ACC accelerated cooling: For 60-80mm thick steel plates, the ACC inlet temperature should be ≥740℃; for >80-100mm thick steel plates, the ACC inlet temperature should be ≥730℃; and for >100-120mm thick steel plates, the ACC inlet temperature should be ≥720℃. Based on the low-magnification quality of the continuously cast billets, the ACC inlet temperature for grades 2 and 3 needs to be controlled by the lower limit of the ACC inlet temperature plus (0-10℃) to avoid abnormal microstructure transformation caused by high ACC inlet temperatures in areas with heavy core segregation, which could affect the low-temperature toughness of the core.

[0017] The process design, production organization principles, and key process control points in the technical solution of this invention are formulated based on production practice. The low-temperature toughness stability of the core of TMCP extra-thick marine engineering steel plates is closely related to the chemical composition design, metallurgical quality of the continuously cast billet, heating process, controlled rolling process, and ACC process. Some internal metallurgical defects in the continuously cast billet, such as segregation and porosity, can be mitigated by optimizing the heating, controlled rolling, and ACC processes to reduce their adverse effects on the low-temperature toughness of the steel plate core. Conversely, if the heating, rolling, or post-rolling cooling processes are unreasonable, they will have a more adverse effect on the low-temperature toughness of the core of the finished steel plate. Therefore, improving the low-temperature toughness stability of the core of TMCP extra-thick marine engineering steel plates is a systematic project. It must be achieved stably by simultaneously taking optimization measures in multiple key processes of steel plate production, based on reasonable production arrangements, focusing on mitigating abnormal microstructure transformation at the segregation location of the billet and achieving uniform and refined microstructure in the core.

[0018] Compared with the prior art, the advantages of the present invention are as follows: This invention relates to a method for improving the low-temperature toughness and stability of the core of extra-thick TMCP marine engineering steel plates. The method includes a complete set of production process technologies encompassing process design, production organization principles, and control of key processes throughout the entire process. The advantage of this invention is that it is based on long-term production practice, comprehensively analyzes the key production processes of the steel plate to address the main influencing factors affecting the low-temperature toughness of the core of extra-thick TMCP marine engineering steel plates, and proposes a systematic solution, including reasonable process design, production organization principles, and key control points for key processes throughout the entire process.

[0019] The 60-120mm extra-thick steel plates produced using the technical solution of this invention have a core impact pass rate of over 99.3% at -40℃. The production process is simple, highly operable, and suitable for mass production. Attached Figure Description

[0020] Figure 1 This is a 200x magnification microstructure of the 110mm thick steel plate at the 1 / 4 width and 1 / 2 thickness position of the head section. The billet comes from the first furnace head billet. The low-magnification segregation of the billet is C1.5, belonging to the second-grade billet. The microstructure in the non-segregated position is ferrite + pearlite, with a size of 10-25 micrometers. The microstructure in the segregated position is blocky lower bainite and fine granular bainite. The blocky lower bainite is 20-40 micrometers in size, and the granular bainite is arranged in discontinuous dispersed clusters with a microstructure size of 5-15 micrometers within the clusters.

[0021] Figure 2The microstructure is a 200x magnification analysis of a 110mm thick S460MLO steel plate with the same composition as in Example 3, processed using conventional methods. The billet also originated from the first furnace. The low-magnification segregation of the billet is C1.5, classifying it as a second-grade billet. The microstructure in the non-segregated areas is ferrite + pearlite, with a size of 12-45 micrometers; the microstructure in the segregated areas is blocky upper bainite, with a block size of 25-120 micrometers. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. Example 1

[0023] The 70-80mm thick TMCP extra-thick marine engineering steel plate S355MLO in this embodiment has the following chemical composition by weight percentage: C 0.06-0.08%, Mn 1.30-1.45%, Nb 0.010-0.025%, S 0.0007-0.003%. The steel plate is produced using 360mm thick continuously cast billets, involving 43 smelting furnace numbers and a total of 347 large plates. The key production processes and technical parameters for this batch of steel plates are as follows: Billet loading: The billet loading temperature is 200-298℃. In the low magnification mass of the billet, there are a total of 39 heats (315 billets) of first-stage segregation, 3 heats (24 billets) of second-stage segregation, and 1 heat (8 billets) of third-stage segregation.

[0024] Heating of continuously cast billets: For the first stage of segregation, a total of 39 heats (315 billets) were conducted, with the high-temperature section at 1100-1210℃ and a total time of 141-152 min; for the second stage of segregation, 3 heats (24 billets) were conducted, with the high-temperature section at 1140-1250℃ and a total time of 175-184 min; for the third stage of segregation, 1 heat (8 billets) was conducted, with a total time of 210-223 min.

[0025] Controlled rolling: For the first stage of segregation, a total of 39 heats (315 billets) were rolled to a controlled thickness of 2.0T-2.4T. For the second stage of segregation, 3 heats (24 billets) and the third stage of segregation, 1 heat (8 billets), the roughing stage had 3 passes with single-pass deformation >50mm, namely 60mm, 58mm and 55mm, respectively. At the same time, the rolling speed was reduced to 1.1-1.3m / s, and the controlled rolling thickness was 2.1T-2.4T.

[0026] ACC accelerated cooling: For the first stage of segregation, a total of 39 heats (315 billets) were conducted, and the steel plate entered the ACC at a temperature of 751-758℃; for the second stage of segregation, 3 heats (24 billets) and the third stage of segregation, 1 heat (8 billets) were conducted, and the steel plate entered the ACC at a temperature of 740-749℃. Example 2

[0027] The 82-95mm thick TMCP extra-thick offshore wind power steel plate S420ML in this embodiment has the following chemical composition by weight percentage: C 0.05-0.08%, Mn: 1.40-1.60%, Nb: 0.030-0.045%, Cr: 0.10-0.25%, S: 0.0005-0.002%. The steel plate is produced using 360mm thick continuously cast billets, involving 21 smelting furnace numbers and a total of 158 large plates. The key production processes and technical parameters for this batch of steel plates are as follows: Billet loading: The billet loading temperature is 150-213℃. The first stage of segregation in the low magnification of the billet is 20 heats (151 billets), and the second stage of segregation is 1 heat (7 billets).

[0028] Heating of continuously cast billets: For the first stage of segregation, a total of 20 heats (151 billets) were conducted, with the high-temperature section at 1100-1210℃ and a total time of 145-159 min; for the second stage of segregation, 1 heat (7 billets) was conducted, with the high-temperature section at 1140-1250℃ and a total time of 172-189 min.

[0029] Controlled rolling: For the first stage of segregation, a total of 20 heats (151 billets) were rolled to a controlled thickness of 2.2T-2.4T. For the second stage of segregation, 1 heat (7 billets) was rolled, with two passes in the roughing stage where the single-pass deformation was greater than 50mm, specifically 58mm and 55mm. At the same time, the rolling speed was reduced to 1.1-1.3m / s, and the controlled thickness was 2.2T-2.4T.

[0030] ACC accelerated cooling: For the first stage of segregation, a total of 20 heats (151 billets) were conducted, and the steel plate entered the ACC at a temperature of 743-755℃; for the second stage of segregation, 1 heat (7 billets) was conducted, and the steel plate entered the ACC at a temperature of 731-738℃. Example 3

[0031] The 105-120mm thick TMCP extra-thick offshore wind power steel plate S460MLO in this embodiment has the following chemical composition by weight percentage: C 0.04-0.07%, Mn: 1.48-1.65%, Nb: 0.035-0.045%, Cr: 0.10-0.25%, Ni: 0.15-0.35%, S: 0.0007-0.002%. The steel plate is produced using 450mm thick continuously cast billets, involving 63 smelting furnace numbers and a total of 364 large plates. The key production processes and technical parameters for this batch of steel plates are as follows: Billet loading: The billet loading temperature is 100-243℃. The first-stage segregation in the low-magnification mass of the billet is 62 heats (358 billets), and the second-stage segregation is 1 heat (6 billets).

[0032] Heating of continuously cast billets: For the first stage of segregation, a total of 62 heats (358 billets) were conducted, with the high-temperature section at 1100-1210℃ and a total time of 221-242 min; for the second stage of segregation, 1 heat (6 billets) was conducted, with the high-temperature section at 1140-1250℃ and a total time of 261-282 min.

[0033] Controlled rolling: For the first stage of segregation, a total of 62 heats (358 billets) were rolled to a controlled thickness of 2.3T-2.4T. For the second stage of segregation, 1 heat (6 billets) was rolled, with two passes in the roughing stage where the single-pass deformation was greater than 50mm, specifically 56mm and 53mm. At the same time, the rolling speed was reduced to 1.1-1.3m / s, and the controlled thickness was 2.3T-2.4T.

[0034] ACC accelerated cooling: For the first stage of segregation, a total of 62 heats (358 billets) were conducted, and the steel plate entered the ACC at a temperature of 741-752℃; for the second stage of segregation, 1 heat (6 billets) was conducted, and the steel plate entered the ACC at a temperature of 724-731℃.

[0035] As shown in Table 1, before the implementation of this technical solution, the pass rate of low-temperature toughness of the core of the TMCP extra-thick marine steel plate was about 95%. After the implementation of this technical solution, the pass rate of low-temperature toughness of the core of the TMCP extra-thick marine steel plate reached over 99.3%, a significant improvement, indicating that the implementation effect of the technical solution of this invention is very significant.

[0036] Table 1. Low-temperature toughness results of the steel plate core in each embodiment and comparison of low-temperature toughness before and after implementation of the technical solution of the present invention.

[0037] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine engineering steel plates, characterized in that: The implementation process includes, Composition design: Carbon content ≤0.10%, Mn content ≤1.60%, S content ≤0.003%; Rolling design: Two-stage controlled rolling is adopted, with roughing and finishing rolling, and the compression ratio is controlled according to the thickness of the steel plate; Production organization: Remove the blackheads at the beginning and end according to the production thickness of the steel plate. For steel plates with a thickness of 60-80mm, the amount of blackheads removed is ≥2.5T mm, where T is the thickness of the steel plate. For steel plates with a thickness of >80mm, the amount of blackheads removed is ≥200mm.

2. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 1, characterized in that: Used for producing marine engineering steel plates with a thickness of 60-120mm, the core impact test pass rate at -40℃ is over 99.3%.

3. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine engineering steel plates according to claim 1, characterized in that: Rolling design includes selecting the rolling compression ratio based on the steel plate thickness. For producing steel plates 60-80mm thick, the compression ratio is 3.0-5.0; for producing steel plates >80mm thick, the compression ratio is 3.5-6.

0.

4. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 1, characterized in that: Production organization includes the production of steel with a yield strength of 355MPa and below in the first and last furnaces; the first billets from the first furnace and the last billets from the last furnace are piled up for slow cooling for ≥48 hours and rolled in a concentrated manner at regular intervals. During rolling, the controlled rolling thickness for finishing is determined based on the thickness of the steel plate. For steel plates with a thickness of 60-80mm, the controlled rolling thickness for finishing is ≥2.0T; for steel plates with a thickness of >80-100mm, the controlled rolling thickness for finishing is ≥2.2T; and for steel plates with a thickness of >100-120mm, the controlled rolling thickness for finishing is ≥2.3T, where T is the target steel plate thickness.

5. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 1, characterized in that: Rolling design also involves billet loading into the furnace, billet heating, rolling temperature, and ACC cooling. The billet is graded based on its low-magnification microstructure. The furnace loading temperature, billet heating temperature, rolling temperature, and ACC cooling are designed considering both the billet grade and the production thickness of the steel plate. Referring to YB / T 4003-2016, the low-magnification quality of the billet is graded: Grade 1 is segregated C0.5-1.0, Grade 2 is segregated C1.5-2.0, and Grade 3 is segregated B0.5-1.

0. Billets with segregation of B1.5 or worse are repurposed for rolling other types of steel plates and cannot be used to produce steel plates requiring low-temperature impact toughness in the core.

6. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 5, characterized in that: For Grade 1, 2, and 3 billets, the preheating temperature before rolling is ≤300℃.

7. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 5, characterized in that: For the first-stage casting, a high-temperature zone of 1100-1210℃ is set; for the second-stage casting, the high-temperature zone is 1140-1250℃, and the temperature is extended. High temperature section The holding time is 30 minutes; for the third-grade billet, the holding time in the high-temperature section is extended by another 30 minutes based on the heating process of the second-grade billet.

8. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 5, characterized in that: A two-stage controlled rolling process is adopted. For the first-grade billet, the finishing rolling temperature range for 60-80mm thick steel plates is Ar3+ (20℃~60℃), with a controlled rolling thickness ≥2.0T, where T is the final steel plate thickness. For steel plates >80-100mm thick, the finishing rolling temperature range is Ar3+ (10~50℃), with a controlled rolling thickness ≥2.2T. For steel plates >100-120mm thick, the finishing rolling temperature range is Ar3+ (0~+30℃), with a controlled rolling thickness ≥2.3T. For the second and third-grade billets, the single-pass deformation amount is set to ≥50mm in more than two passes during the roughing stage. Compared with the first-grade billet, the roller speed is reduced, and the finishing rolling start temperature is also reduced by 10-20℃ compared with the first-grade billet.

9. The method for improving the low-temperature toughness stability of the core of extra-thick TMCP marine steel plates according to claim 5, characterized in that: After rolling, the steel is cooled in the ACC. For the first-grade billet, the ACC water inlet temperature for 60-80mm thick steel plates is ≥740℃; for steel plates >80-100mm thick steel plates, the ACC water inlet temperature is ≥730℃; and for steel plates >100-120mm thick steel plates, the ACC water inlet temperature is ≥720℃. According to the low-multiplier quality of the continuously cast billet, the ACC water inlet temperature for the second and third-grade billets is controlled at the lower limit of the ACC control temperature plus (0~10℃).

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