A forging-rolling integrated manufacturing method of high-toughness thick steel plate

Abstract

The application discloses a forging-rolling integrated manufacturing method of high-toughness heavy steel plate, and belongs to the technical field of heavy steel plate manufacturing methods.The steel ingot is obtained through molten steel smelting-mold casting, then 1-2 times of forging and 1 time of hot rolling are carried out to obtain multiple heavy steel plates, the heart loose defects of the steel ingot are forged through the forging process, the material density is improved, meanwhile, the multidirectional staggered metal flow lines are constructed in the blank, and the as-cast structure directionality is eliminated; the hot rolling process improves the forming efficiency, reduces the steel plate allowance, retains the transverse flow line structure of the blank, realizes the homogeneity of the full-section material of the heavy steel plate and the refinement of the structure, and makes the strength and toughness match optimal. The method can greatly reduce the manufacturing cost, realizes the balance control of quality and cost, the ultrasonic flaw detection of the manufactured heavy steel plate can meet the grade I requirement of the NB / T47013.3 standard, meanwhile, the mechanical properties in each direction of the steel plate are relatively uniform, the longitudinal and transverse tensile strength and impact energy deviation are small, and the stability and reliability of the heavy steel plate are ensured.

Description

Technical Field

[0001] This invention relates to the technical field of manufacturing methods for extra-thick steel plates, and in particular to an integrated forging and rolling manufacturing method for high-strength and high-toughness extra-thick steel plates. Background Technology

[0002] High-strength and high-toughness extra-thick steel plates are widely used in energy, marine engineering, and national defense, with demand increasing year by year. They have become a fundamental material for achieving energy security and the high-end development of large-scale engineering equipment. Currently, my country's high-strength steel plate specifications provide manufacturing requirements for steel plates with a thickness of 30-100mm, but do not cover high-strength and high-toughness steel plates with a thickness of ≥120mm. For a long time, the manufacturing processes for high-strength and high-toughness extra-thick steel plates with a thickness of ≥120mm have generally adopted continuous casting-rolling, die casting flat ingot-rolling, and die casting-free forging processes, but the manufacturing results of these processes are not ideal.

[0003] The continuous casting or ingot casting-rolling process offers high production efficiency, high yield, and low manufacturing cost. However, there are certain limitations in the manufacturing of large-section billets. The billets inevitably have defects such as central porosity, shrinkage cavities, and segregation, which are easily inherited by extra-thick steel plates after rolling. This results in more impurities in the center of the steel plate, insufficient density and uniformity, and obvious directional mechanical properties. Consequently, flaw detection and mechanical properties cannot meet the requirements, making it unsuitable for extreme working conditions.

[0004] The die casting-free forging manufacturing process effectively removes impurities from the molten steel through the sequential solidification of the die casting ingot and the removal of water riser material. Free forging effectively compacts and welds the large deformation and defects such as porosity and shrinkage cavities at the center of the ingot, improving the metallurgical quality of the slab center material. Its mechanical properties are superior to those of the continuous casting / die casting flat ingot-rolling manufacturing scheme. However, ultra-thick steel plates formed by single forging have problems such as multiple forging processes, low forming efficiency, large allowance, low material utilization, and difficulties in subsequent processing, resulting in high costs and hindering the sustainable development of ultra-thick high-strength plates.

[0005] Therefore, ensuring the overall quality of extra-thick steel plates over 120mm while appropriately reducing manufacturing costs, and ensuring that these extra-thick steel plates possess high strength and toughness in all directions to meet the requirements of heavy-load and high-speed impact applications, is an urgent industry challenge to be solved. Summary of the Invention

[0006] To address the problems of insufficient central strength and toughness, anisotropy, high manufacturing cost, and high energy consumption in existing methods for manufacturing extra-thick steel plates, this invention provides an integrated forging and rolling manufacturing method for high-strength and high-toughness extra-thick steel plates.

[0007] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a method for integral forging and rolling of high-strength and tough extra-thick steel plates, wherein the thickness of the extra-thick steel plate is H mm, and H > 120 mm, comprising the following steps: S1. The raw materials are subjected to electric furnace primary refining, ladle refining, vacuum treatment, and die casting to obtain steel ingots, and the residual material in the steel ingot water riser is removed; S2. Heat the steel ingot to 1150℃-1240℃ and hold it at that temperature for a duration of {(0.4~1.2)×H1 / 100} hours, where H1 is the maximum cross-sectional dimension of the hot steel ingot in mm. S3. Using the free forging method, the steel ingot is upset longitudinally by 30%~50%, and then drawn longitudinally with a wide anvil to obtain a square bar billet. The thickness of the square bar billet is (5~10)×H, the anvil width ratio is 0.6-0.75, the reduction rate is 20%, and the single reduction amount does not exceed 25% of the original height. S4. Rotate the square billet 90° and flatten it laterally to obtain a flat billet. The thickness of the flat billet is (2.5~5.5)×H, and the width is the design width of the extra-thick steel plate. S5. Rotate the flat billet 90° again, and draw and finish it longitudinally to obtain a forging blank. The thickness of the forging blank is H2 = (1.8~3.0) × H, and the width is the finished width of the extra-thick steel plate. S6. Heat the forging blank to 860℃-940℃ and hold it for {(1.5~3.0)×H2 / 100} hours, then air cool it after holding. Then heat the forging blank to 600℃-650℃ and hold it for {(2.0~5.0)×H2 / 100} hours, then air cool it after holding. S7. Heat the forging blank to 1100℃-1200℃ and hold it at that temperature for {(1.2~2.0)×H2 / 100} hours; S8. Rough rolling: After cleaning the oxide scale on the surface of the forging blank, multiple rolling passes are used. The reduction in the first pass is 20%-30%, and the reduction in subsequent passes gradually decreases. The rolling speed is 0.5~2m / s. S9. Finish rolling: The reduction per pass is 5%-15%, and the rolling speed is 3~10m / s to obtain an extra-thick steel plate with a thickness of H. S10. After air cooling, the extra-thick steel plate is divided into multiple pieces along its length. S11. Quenching: Heat the extra-thick steel plate to 800℃-900℃ and hold it at that temperature for {(1.2~2.0)×H / 100} hours; S12. Immerse the extra-thick steel plate in a water tank for water cooling for a duration of {(3.0~6.0)×H / 100} minutes; S13. Tempering: The extra-thick steel plate is heated to 180℃-300℃ for tempering, and then air-cooled to room temperature, thus completing the manufacturing of the extra-thick steel plate.

[0008] Preferably, in S1, the molten steel ingot riser is removed by gas cutting or hot cutting.

[0009] Preferably, in S3-S5, the forging compression ratio is ≥2.5, and the forging deformation process is completed in one to two forging passes.

[0010] Preferably, in S8-S9, the rolling compression ratio is 1.8~3.0, and the rolling deformation process is completed within one heat treatment.

[0011] Preferably, the ultrasonic testing of the manufactured extra-thick steel plate meets the Class I requirements of NB / T47013.3 standard, and the deviations in longitudinal and transverse tensile strength and impact energy are all less than 5%.

[0012] According to the above technical solution, the beneficial effects of the present invention are: This invention consists of 1-2 heating cycles and 1 hot rolling cycle. The forging process combines forging to eliminate defects such as porosity in the steel ingot core, while simultaneously constructing multi-directional interlaced metal flow lines within the billet, eliminating the directional nature of the as-cast structure. The hot rolling process improves forming efficiency, reduces steel plate allowance, and retains the transverse flow line structure of the billet, achieving homogeneity and microstructure refinement across the entire cross-section of the extra-thick steel plate. This results in optimal strength and toughness matching. Compared to the 4-5 heating cycles and 30-50mm forging allowance of the free forging method, this invention can significantly reduce manufacturing costs and achieve a balance between quality and cost control.

[0013] Compared with completely free forging billets, it saves the processes of billet heating, press forging, and machining, saving more than half of the energy and reducing the overall cost. Compared with completely hot rolled billets, forging and rolling integral forming can avoid the uneven structure and obvious anisotropy of mechanical properties in completely hot rolled extra-thick steel plates, which leads to relatively low transverse strength and plasticity. Due to multi-directional deformation, the extra-thick steel plates formed by forging and rolling integral forming have high structural density and more uniform mechanical properties in all directions, which can ensure the stability and reliability of the steel plates. Detailed Implementation

[0014] A method for integral forging and rolling of high-strength and high-toughness extra-thick steel plate, wherein the thickness of the extra-thick steel plate is H mm, and H > 120, the method includes the following steps: S1. The raw materials are subjected to electric furnace primary refining, ladle refining, vacuum treatment, and die casting to obtain steel ingots. The remaining material at the water riser of the steel ingots is removed by gas cutting or hot cutting.

[0015] S2. Heat the steel ingot to 1150℃-1240℃ and hold it at that temperature for a duration of {(0.4~1.2)×H1 / 100} hours, where H1 is the maximum cross-sectional dimension of the hot steel ingot in mm.

[0016] S3. Using the free forging method, the steel ingot is upset 30%~50% along the longitudinal direction, and then a wide anvil is used to draw it into a square shape along the longitudinal direction to obtain a square bar billet. The thickness of the square bar billet is (5~10)×H, the anvil width ratio is 0.6-0.75, the reduction rate is 20%, and the single reduction amount does not exceed 25% of the original height.

[0017] S4. Rotate the square billet 90° and flatten it laterally to obtain a flat billet. The thickness of the flat billet is (2.5~5.5)×H, and the width is the design width of the extra-thick steel plate.

[0018] S5. Rotate the flat billet 90° again, and draw and finish it longitudinally to obtain a forging blank. The thickness of the forging blank is H2 = (1.8~3.0) × H, and the width is the finished width of the extra-thick steel plate.

[0019] In S3-S5, the forging compression ratio is ≥2.5, and the forging deformation process is completed in one to two forging passes.

[0020] S6. Heat the forging blank to 860℃-940℃ and hold it for {(1.5~3.0)×H2 / 100} hours, then air cool it after holding. Then heat the forging blank to 600℃-650℃ and hold it for {(2.0~5.0)×H2 / 100} hours, then air cool it after holding.

[0021] S7. Heat the forging blank to 1100℃-1200℃ and hold it at that temperature for {(1.2~2.0)×H2 / 100} hours.

[0022] S8. Rough rolling: After cleaning the oxide scale on the surface of the forging blank, multiple rolling passes are used. The reduction in the first pass is 20%-30%, and the reduction in subsequent passes gradually decreases. The rolling speed is 0.5~2m / s.

[0023] S9. Finish rolling: The reduction per pass is 5%-15%, and the rolling speed is 3~10m / s, to obtain an extra-thick steel plate with a thickness of H.

[0024] In S8-S9, the rolling compression ratio is 1.8~3.0, and the rolling deformation process is completed in one heat.

[0025] S10. After air cooling, the extra-thick steel plate is divided into multiple pieces along its length.

[0026] S11. Quenching: Heat the extra-thick steel plate to 800℃-900℃ and hold it at that temperature for a duration of {(1.2~2.0)×H / 100} hours.

[0027] S12. Immerse the extra-thick steel plate in a water tank for water cooling for a duration of {(3.0~6.0)×H / 100} minutes.

[0028] S13. Tempering: The extra-thick steel plate is heated to 180℃-300℃ for tempering, and then air-cooled to room temperature, thus completing the manufacturing of the extra-thick steel plate.

[0029] The ultrasonic testing of the manufactured extra-thick steel plates meets the Class I requirements of NB / T47013.3 standard, with deviations in longitudinal and transverse tensile strength and impact energy all below 5%.

[0030] Example 1: A high-strength and tough extra-thick steel plate of 150×3000×3000mm, the material grade selected is 30CrMnSiNi2A, the chemical composition of which, by mass percentage, includes: carbon (C): 0.31%; silicon (Si): 1.03%; manganese (Mn): 1.10%; chromium (Cr): 1.05%; nickel (Ni): 1.55%; the remainder is iron (Fe) and unavoidable impurities.

[0031] 32t steel ingots were prepared through processes such as primary refining, refining, vacuum degassing, and die casting. The water riser residue was removed and the ingots were heated to 1220℃ in a furnace. The cast metal of the ingot body was then subjected to forging operations such as upsetting and drawing to form a flat square billet with dimensions of 380×3000×2750mm.

[0032] The steel is hot-rolled to a yield of 85-90%. After hot rolling along the longitudinal direction, the hot-rolled metal has a specification of 150×3000×6300mm. Two extra-thick steel plates of 150×3000×3000mm are obtained by cutting.

[0033] The austenitizing temperature is 880℃, and the temperature is water-cooled. The tempering temperature is 220℃, and the temperature is air-cooled.

[0034] For the 30CrMnSiNi2A high-strength and high-toughness extra-thick steel plate manufactured in Example 1, ultrasonic testing met the Class I standard of NB / T47013.3; the strength and toughness were tested at T / 4 of the steel plate, and the deviations of longitudinal and transverse tensile strength and impact energy were 3.13% and 4.07%, respectively. The performance indicators are shown in Table 1. Table 1 Mechanical properties of 30CrMnSiNi2A high-strength and high-toughness extra-thick steel plates Example 2: A high-strength and tough extra-thick steel plate of 160×3000×3000mm, the material grade selected is 30Cr2Ni2Mo, the chemical composition of which, by mass percentage, includes: carbon (C): 0.31%; silicon (Si): 0.25%; manganese (Mn): 0.60%; chromium (Cr): 2.0%; nickel (Ni): 2.1%; molybdenum (Mo): 0.4%; the remainder is iron (Fe) and unavoidable impurities.

[0035] 35t steel ingots are prepared through processes such as primary refining, refining, vacuum degassing, and die casting. The water riser residue is removed and the ingot is heated to 1230℃ in a furnace. The cast metal of the ingot body is then subjected to forging operations such as upsetting and drawing to forge a flat square billet with dimensions of 400×3000×2940mm.

[0036] The steel is hot-rolled to a yield of 85-90%. After hot rolling along the longitudinal direction, the hot-rolled metal has a size of 160×3000×6450mm. Two extra-thick steel plates of 160×3000×3000mm are obtained by cutting.

[0037] The austenitizing temperature is 860℃, and the temperature is cooled by water. The tempering temperature is 220℃, and the temperature is cooled by air.

[0038] For the 30Cr2Ni2Mo high-strength and high-toughness extra-thick steel plate manufactured in Example 2, ultrasonic testing met the NB / T47013.3 standard Class I; the strength and toughness were tested at T / 4 of the steel plate, and the deviations of longitudinal and transverse tensile strength and impact energy were controlled within 5%. The performance indicators are shown in Table 2. Table 2. Mechanical properties of 30Cr2Ni2Mo high-strength and high-toughness extra-thick steel plates As can be seen from Examples 1 and 2, the extra-thick steel plate formed by forging and rolling has high microstructure density due to multi-directional deformation, and its mechanical properties are relatively uniform in all directions, which can ensure the stability and reliability of the steel plate. At the same time, multi-directional interlaced metal flow lines are constructed inside the billet, eliminating the directionality of the cast microstructure. The hot rolling process improves the forming efficiency, reduces the steel plate allowance, retains the transverse flow line structure of the billet, and realizes the homogeneity of the material and the refinement of the microstructure of the extra-thick steel plate across the entire cross section, so that the strength and toughness are optimally matched.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for integral forging and rolling of a high-strength and high-toughness extra-thick steel plate, wherein the thickness of the extra-thick steel plate is H mm, and H > 120 mm, characterized in that... Includes the following steps: S1. The raw materials are subjected to electric furnace primary refining, ladle refining, vacuum treatment, and die casting to obtain steel ingots, and the residual material in the steel ingot water riser is removed; S2. Heat the steel ingot to 1150℃-1240℃ and hold it at that temperature for a duration of {(0.4~1.2)×H1 / 100} hours, where H1 is the maximum cross-sectional dimension of the hot steel ingot in mm. S3. Using the free forging method, the steel ingot is upset longitudinally by 30%~50%, and then drawn longitudinally with a wide anvil to obtain a square bar billet. The thickness of the square bar billet is (5~10)×H, the anvil width ratio is 0.6-0.75, the reduction rate is 20%, and the single reduction amount does not exceed 25% of the original height. S4. Rotate the square billet 90° and flatten it laterally to obtain a flat billet. The thickness of the flat billet is (2.5~5.5)×H, and the width is the design width of the extra-thick steel plate. S5. Rotate the flat billet 90° again, and draw and finish it longitudinally to obtain a forging blank. The thickness of the forging blank is H2 = (1.8~3.0) × H, and the width is the finished width of the extra-thick steel plate. S6. Heat the forging blank to 860℃-940℃ and hold it for {(1.5~3.0)×H2 / 100} hours, then air cool it after holding. Then heat the forging blank to 600℃-650℃ and hold it for {(2.0~5.0)×H2 / 100} hours, then air cool it after holding. S7. Heat the forging blank to 1100℃-1200℃ and hold it at that temperature for {(1.2~2.0)×H2 / 100} hours; S8. Rough rolling: After cleaning the oxide scale on the surface of the forging blank, multiple rolling passes are used. The reduction in the first pass is 20%-30%, and the reduction in subsequent passes gradually decreases. The rolling speed is 0.5~2m / s. S9. Finish rolling: The reduction per pass is 5%-15%, and the rolling speed is 3~10m / s to obtain an extra-thick steel plate with a thickness of H. S10. After air cooling, the extra-thick steel plate is divided into multiple pieces along its length. S11. Quenching: Heat the extra-thick steel plate to 800℃-900℃ and hold it at that temperature for {(1.2~2.0)×H / 100} hours; S12. Immerse the extra-thick steel plate in a water tank for water cooling for a duration of {(3.0~6.0)×H / 100} minutes; S13. Tempering: The extra-thick steel plate is heated to 180℃-300℃ for tempering, and then air-cooled to room temperature, thus completing the manufacturing of the extra-thick steel plate.

2. The method for integrated forging and rolling of high-strength and high-toughness extra-thick steel plates according to claim 1, characterized in that: In S1, gas cutting or hot cutting methods are used to remove the water riser of the steel ingot.

3. The method for integrated forging and rolling of high-strength and high-toughness extra-thick steel plates according to claim 1, characterized in that: In S3-S5, the forging compression ratio is ≥2.5, and the forging deformation process is completed in one to two forging passes.

4. The method for integrated forging and rolling of high-strength and high-toughness extra-thick steel plates according to claim 1, characterized in that: In S8-S9, the rolling compression ratio is 1.8~3.0, and the rolling deformation process is completed in one heat.

5. The method for integrated forging and rolling of high-strength and high-toughness extra-thick steel plates according to claim 1, characterized in that: The ultrasonic testing of the manufactured extra-thick steel plates meets the Class I requirements of NB / T47013.3 standard, with deviations in longitudinal and transverse tensile strength and impact energy all below 5%.

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