Method for manufacturing a hot extrusion die steel having high impact toughness

Abstract

The application discloses a kind of high impact toughness hot extrusion die steel manufacturing method, including batching, melting, electroslag remelting, high temperature diffusion, forging, afterheat quenching-stress relief annealing, ultra-fining-spheroidizing annealing, finishing steps.The present application optimizes the existing hot working and heat treatment process by adjusting the material composition, hot working and heat treatment process, and the die steel bar after forging by the process of the present application has uniform structure, high hardenability and thermal cracking resistance, thereby improving the stability of the transverse impact energy of the steel.

Description

Technical Field

[0001] This invention relates to the field of hot extrusion technology, and more specifically to a method for manufacturing hot extrusion die steel with high impact toughness. Background Technology

[0002] Hot extrusion is the process of shaping a ductile metal billet into a profile or tube under pressure by passing it through an extrusion die cavity. Many non-ferrous metal and steel profiles, tubes, and special-shaped profiles are formed using hot extrusion.

[0003] Hot extrusion dies are specialized tools used to extrude and shape metal materials under high temperature and high pressure conditions. They are widely used in the production of profiles, pipes, and bars of metal materials such as aluminum profiles, copper alloys, and steel. These dies need to withstand high temperatures of 600-800℃, high pressure, and severe friction and wear, making their working conditions extremely harsh.

[0004] The existing heat treatment process for hot extrusion die steel has the following disadvantages: ① Conventional large-size H13 die steel materials usually have low impact toughness; ② The die steel produced by the existing hot working process has poor grain size and microstructure stability; ③ The existing heat treatment process often results in end crack propagation.

[0005] Therefore, there is an urgent need for a manufacturing method for hot extrusion die steel with high impact toughness (SD360Ni). Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for manufacturing hot extrusion die steel with high impact toughness, so as to solve the problems in the background art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0008] A method for manufacturing hot extrusion die steel with high impact toughness specifically includes the following steps: S1. Ingredients: Prepare high-carbon ferrochrome, low-nickel ferrochrome, medium-nickel ferrochrome, ferromolybdenum, ferrovanadium, scrap steel, and high-carbon ferromanganese; the mass percentage of each raw material is as follows: scrap steel 50%, low-nickel ferrochrome 36%, medium-nickel ferrochrome 4%, high-carbon ferrochrome 6%, ferromolybdenum 2%, ferrovanadium 1%, and high-carbon ferromanganese 1%. S2. Melting: The raw materials in step S1 are smelted using an electric furnace-AOD-LF-VD smelting process to obtain electrode billets. S3, Electroslag Remelting: The surface of the electrode blank from step S2 is polished to remove defects; then, an electroslag ingot is obtained through the electroslag remelting process. S4. High-temperature diffusion: The electroslag ingot is subjected to high-temperature diffusion at a temperature of 1270±10℃ for 30-35 hours. S5. Forging: The electroslag ingot from step S4 is transferred to the heating furnace of the forging station for heating. After heating to 1180±10℃ and holding for 5-7 hours, it is forged into a round bar. S6. Residual heat quenching-stress relief annealing: The round bars forged in S5 are subjected to residual heat quenching to make the final reheat temperature ≤300℃, and then stress relief annealing process is performed; the annealing temperature is 720-860℃, and the annealing holding time is 20-25h; then the head and tail hot working defects are removed. S7. Ultrafine-spheroidizing annealing: The round bar obtained after step S6 is subjected to ultrafine treatment, with a holding temperature of 1020±10℃ and a holding time of 5-6h. After being cooled to below 210℃ by alternating water and air cooling, the steel is subjected to spheroidizing annealing treatment. The steel is heated to 860±10℃ for through-firing and held for 20-25h, then cooled to 730±10℃ for through-firing and held for 25-30h, and then cooled to below 300℃ and air-cooled to room temperature to obtain the steel bar. S8. Finishing: The steel bar is cleaned and its dimensions are corrected according to the technical requirements to obtain mold steel.

[0009] To further optimize the technical solution, in step S1, the high-carbon ferrochrome is FeCr70C10.0, the ferromolybdenum is FeMo60-C, and the ferrovanadium is FeV60-B.

[0010] To further optimize the technical solution, in step S2, the melting temperature of the electric furnace is 1600-1640℃, and the carbon content of the steel tapped from the electric furnace is 1.5-2.0%.

[0011] Further optimize the technical solution. The AOD process in step S2 is as follows: the molten steel melted in the electric furnace is decarburized by blowing oxygen at a temperature of 1680-1740℃, ferrosilicon is added for reduction according to the oxygen consumption, and slag is removed.

[0012] Further optimize the technical solution. In step S2, the LF process is as follows: under argon protection, the furnace is heated to 1680-1700℃ for LF furnace refining.

[0013] To further optimize the technical solution, the VD process in step S2 is as follows: the VD furnace is evacuated to below 67 Pa and maintained for 20-25 minutes, followed by degassing.

[0014] To further optimize the technical solution, in step S3, the slag baking temperature is 600-800℃ and the baking time is ≥6h; the electroslag remelting uses a slag system of CaF2:Al2O3:CaO=60%:20%:20% for remelting, and after remelting, the φ920mm electroslag ingot is obtained by mold cooling and demolding.

[0015] To further optimize the technical solution, in step S5, the total forging ratio is ≥8, and the forging process is carried out at least twice to ensure that the steel is fully deformed. The heat preservation temperature is 1180℃, and the deformation amount of the final heat treatment should be greater than 40%.

[0016] To further optimize the technical solution, in step S8, the components of the mold steel, by mass percentage, include: C 0.35%-0.40%, Si 0-0.30%, Mn 0.30%-0.60%, P 0-0.015%, S 0-0.002%, Cr 5.00%-5.30%, Mo 1.40%-1.60%, V 0.65%-0.75%, Ni 1.00%-1.20%, with the remainder being Fe.

[0017] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0018] The present invention provides a method for manufacturing hot extrusion die steel with high impact toughness. The raw material contains a certain amount of Ni and has a low silicon content, which gives the die steel high impact toughness, excellent comprehensive mechanical properties and high tempering stability.

[0019] SD360 is a medium-carbon hot work die steel. After heat treatment, the matrix has high hardness but is relatively brittle and lacks impact toughness. Ni, as a non-carbide-forming austenite stabilizing and toughening element, can improve the toughness of the material from multiple dimensions, including microstructure and phase transformation behavior. Ni can expand the austenite phase region and lower the phase transformation temperature of steel. At the same time, it can pin and concentrate austenite grains at the grain boundaries, inhibiting abnormal growth of austenite grains, refining grains, increasing the number of crack propagation resistance sites such as grain boundaries and phase interfaces, and improving crack propagation resistance. This element is incorporated into the martensite and ferrite matrix in the form of substitutional solid solution, achieving matrix solid solution strengthening without sacrificing plasticity. It can significantly reduce the ductile-brittle transition temperature of the material, ensuring high impact toughness at room temperature and reducing the risk of mold chipping and cracking. Ni can also inhibit the diffusion and aggregation of elements such as Cr and C, weaken the tendency of eutectic carbides to precipitate in a network and stripe shape, and promote the distribution of carbides in a fine, dispersed, and spherical state, eliminating local stress concentration sources. In addition, Ni works synergistically with alloying elements such as Cr and Mo in steel to significantly improve hardenability, ensuring full-section hardenability of large-section SD360 workpieces, avoiding the formation of soft and brittle phases such as bainite in the core, and ensuring uniform overall strength and toughness. Therefore, Ni improves the impact toughness and anti-cracking performance of SD360 mold steel from the microstructure root through the synergistic effects of grain refinement, solid solution toughening matrix, optimization of carbide morphology distribution, and enhancement of hardenability.

[0020] The heat treatment process after forging in the manufacturing process of this invention adopts "residual heat quenching + stress relief annealing + ultrafine refining + spheroidizing annealing", which can effectively improve the uniformity of the material structure.

[0021] To address the defects in SD360 in both cast and forged states, such as coarse grains, uneven carbide distribution, and compositional segregation, a combined pretreatment process of forging residual heat quenching, stress-relieving annealing, ultrafine treatment, and spheroidizing annealing is adopted. This process enables homogenization and control of the microstructure throughout the entire process, laying a high-quality microstructure foundation for subsequent final heat treatment.

[0022] Forging residual heat quenching utilizes the high-temperature residual heat in the austenite region after final forging, directly and rapidly cooling without slow cooling. This freezes the coarse microstructure after forging into fine lath martensite, completely breaking the continuous network and banded coarse carbides, eliminating as-cast dendrite segregation, and constructing an ultra-fine, high dislocation density pre-treated initial microstructure. Stress-relief annealing is performed at a temperature below the austenite initiation temperature Ac1 to eliminate internal stress generated during forging and quenching, preventing deformation and cracking in subsequent processes. Simultaneously, it promotes martensite recovery and supersaturated carbon precipitation, achieving pre-dispersed carbide distribution and stabilizing the matrix microstructure. Ultra-fine treatment employs cyclic phase transformation or sub-temperature heat treatment, through repeated austenitization... - During the cooling process, the austenite nucleation rate is increased and grain growth is inhibited by the pinning effect of carbides, achieving dual ultrafine grains and carbides. This further homogenizes the carbide distribution, eliminates compositional segregation, and significantly improves the uniformity of the microstructure. The spheroidizing annealing is carried out at a temperature slightly lower than the austenite initiation temperature Ac1 for a long time and then slowly cooled. Relying on the interfacial energy reduction mechanism and Ostwald ripening, the angular and lamellar carbides are fully spheroidized and rounded, ultimately forming a stable microstructure with spheroids uniformly distributed on an equiaxed ferrite matrix. This completely solves the problems of uneven carbide morphology, size and distribution, and achieves uniform microstructure and strength-toughness balance in SD360 mold steel.

[0023] This invention optimizes existing hot working and heat treatment processes by adjusting material composition, hot working and heat treatment processes. The die steel bars forged by the process of this invention have a uniform structure, high hardenability and resistance to hot cracking, thereby improving the lateral impact stability of the steel. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a metallographic image of Embodiment 1 in this invention; Figure 3 This is a metallographic image of Example 2 in this invention; Figure 4 This is a metallographic image of Example 3 in this invention; Figure 5 This is the metallographic image of Comparative Example 1 in this invention; Figure 6 This is the metallographic image of Comparative Example 2 in this invention. Detailed Implementation

[0025] A method for manufacturing hot extrusion die steel with high impact toughness, combined with Figures 1 to 6 As shown, the specific steps include: S1. Ingredients: Prepare high-carbon ferrochrome, low-nickel ferrochrome, medium-nickel ferrochrome, ferromolybdenum, ferrovanadium, scrap steel, and high-carbon ferromanganese; the mass percentage of each raw material is as follows: scrap steel 50%, low-nickel ferrochrome 36%, medium-nickel ferrochrome 4%, high-carbon ferrochrome 6%, ferromolybdenum 2%, ferrovanadium 1%, and high-carbon ferromanganese 1%.

[0026] Since the mold steel prepared by this invention has a low nickel content, the production cost can be reduced by using a combination of low-nickel iron and medium-nickel iron in the raw materials. The proportion of nickel iron used is calculated according to the content: (nickel of low-nickel iron + nickel of medium-nickel iron) / total weight = 1.00%-1.20%.

[0027] S2. Melting: The raw materials in step S1 are smelted using an electric furnace-AOD-LF-VD smelting process to obtain electrode blanks.

[0028] Specifically: The raw materials from step S1 are added to an electric furnace. The melting temperature of the electric furnace is 1600-1640℃, and the carbon content of the steel tapped from the electric furnace is 1.5-2.0%.

[0029] The AOD process involves blowing oxygen to decarburize molten steel smelted in an electric furnace at a temperature of 1680-1740℃, adding ferrosilicon for reduction according to oxygen consumption, and removing slag.

[0030] The LF process is as follows: the furnace is heated to 1680-1700℃ under argon protection for LF furnace refining.

[0031] The VD process involves evacuating the VD furnace to below 67 Pa and maintaining this vacuum for 20-25 minutes.

[0032] S3. Electroslag Remelting: The surface of the electrode blank from step S2 is polished to remove defects; then the electrode blank is transferred to the electroslag remelting station for electroslag remelting. A slag system of CaF2:Al2O3:CaO = 60%:20%:20% is selected for remelting. After remelting, the blank is demolded to obtain a φ920mm electroslag ingot. The slag baking temperature is 600~800℃, and the baking time is ≥6h; the electroslag ingot is obtained after the electroslag remelting process.

[0033] S4. High-temperature diffusion: The electroslag ingot is subjected to high-temperature diffusion at a temperature of 1270±10℃ for 30-35 hours.

[0034] S5. Forging: The electroslag ingot from step S4 is transferred to the heating furnace at the forging station for heating. After heating to 180±10℃ and holding for 5-7 hours, it is forged into a round bar.

[0035] S6. Residual heat quenching-stress relief annealing: The round bar forged by S5 is subjected to residual heat quenching so that the final reheat temperature is ≤300℃, and then stress relief annealing process is performed; the annealing temperature is 720-860℃, and the annealing holding time is 20-25h; then the head and tail hot working defects are removed.

[0036] S7. Ultrafine Refining-Spheroidizing Annealing: The round bar obtained after step S6 is subjected to ultrafine refining treatment. The holding temperature is 1020±10℃, and the holding time is 5-6 hours. After being removed from the furnace, it is cooled by alternating water and air to below 210℃. Then, spheroidizing annealing treatment is performed. The steel is heated to 860±10℃, and after thorough firing, it is held for 20-25 hours. The temperature is then lowered to 730±10℃, and after thorough firing, it is held for 25-30 hours. After being cooled to below 300℃, it is removed from the furnace and air-cooled to room temperature to obtain the steel bar.

[0037] S8. Finishing: The steel bars are surface-cleaned and dimensionally corrected according to technical requirements to obtain mold steel.

[0038] The components of the mold steel, by mass percentage, include: C 0.35%-0.40%, Si 0-0.30%, Mn 0.30%-0.60%, P 0-0.015%, S 0-0.002%, Cr 5.00%-5.30%, Mo 1.40%-1.60%, V 0.65%-0.75%, Ni 1.00%-1.20%, with the remainder being Fe.

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example 1:

[0040] S1. Ingredients: Prepare high-carbon ferrochrome, low-nickel ferrochrome, medium-nickel ferrochrome, ferromolybdenum, ferrovanadium, scrap steel, and high-carbon ferromanganese; the mass percentage of each raw material is as follows: scrap steel 50%, low-nickel ferrochrome 36%, medium-nickel ferrochrome 4%, high-carbon ferrochrome 6%, ferromolybdenum 2%, ferrovanadium 1%, and high-carbon ferromanganese 1%.

[0041] S2. Melting: The raw materials in step S1 are smelted using an electric furnace-AOD-LF-VD smelting process to obtain electrode blanks.

[0042] Specifically: The raw materials from step S1 are added to the electric furnace. The melting temperature of the electric furnace is 1640℃, and the carbon content of the steel tapped from the electric furnace is 2.0%.

[0043] The AOD process involves blowing oxygen to decarburize molten steel smelted in an electric furnace at a temperature of 1740℃, adding ferrosilicon for reduction according to oxygen consumption, and removing slag.

[0044] The LF process is as follows: the furnace is heated to 1700℃ under argon protection for LF furnace refining.

[0045] The VD process is as follows: the VD furnace is evacuated to 67 Pa and held for 25 minutes for degassing.

[0046] S3. Electroslag Remelting: The surface of the electrode blank from step S2 is polished to remove defects; then the electrode blank is transferred to the electroslag remelting station for electroslag remelting. A slag system of CaF2:Al2O3:CaO = 60%:20%:20% is selected for remelting. After remelting, the blank is demolded to obtain a φ920mm electroslag ingot. The slag baking temperature is 700℃, and the baking time is 6 hours. The electroslag ingot is obtained after the electroslag remelting process.

[0047] S4. High-temperature diffusion: The electroslag ingot is subjected to high-temperature diffusion at 1270℃ for 35 hours.

[0048] S5. Forging: The electroslag ingot from step S4 is transferred to the heating furnace of the forging station for heating. After heating to 1180℃ and holding for 7 hours, it is forged into a round bar after three upsetting and drawing processes.

[0049] S6. Residual heat quenching-stress relief annealing: The S5 forged round bar is subjected to residual heat quenching to a final reheat temperature of 300℃, and then stress relief annealing is performed; the annealing temperature is 860℃ and the annealing holding time is 25h; then the head and tail hot working defects are removed.

[0050] S7. Ultrafine-spheroidizing annealing: The round bar obtained after step S6 is subjected to ultrafine treatment, with a holding temperature of 1030℃ and a holding time of 5h. After being cooled to below 210℃ by alternating water and air cooling, the steel is subjected to spheroidizing annealing treatment. The steel is heated to 870℃ for through-firing and held for 20h, then cooled to 730℃ for through-firing and held for 28h, and finally cooled to below 300℃ and air-cooled to room temperature to obtain the steel bar.

[0051] S8. Finishing: The steel bar is cleaned and its dimensions are corrected according to the technical requirements to obtain mold steel.

[0052] The mold steel prepared in this embodiment comprises the following components by mass percentage: C 0.38%, Si 0.10%, Mn 0.40%, P 0.01%, S 0.001%, Cr 5.30%, Mo 1.60%, V 0.65%, Ni 1.00%, with the remainder being Fe; its metallographic structure is as follows: Figure 2 As shown. Example 2:

[0053] S1. Ingredients: Prepare high-carbon ferrochrome, low-nickel ferrochrome, medium-nickel ferrochrome, ferromolybdenum, ferrovanadium, scrap steel, and high-carbon ferromanganese; the mass percentage of each raw material is as follows: scrap steel 50%, low-nickel ferrochrome 36%, medium-nickel ferrochrome 4%, high-carbon ferrochrome 6%, ferromolybdenum 2%, ferrovanadium 1%, and high-carbon ferromanganese 1%.

[0054] S2. Melting: The raw materials in step S1 are smelted using an electric furnace-AOD-LF-VD smelting process to obtain electrode blanks.

[0055] Specifically: The raw materials from step S1 are added to an electric furnace. The melting temperature of the electric furnace is 1600℃, and the carbon content of the steel tapped from the electric furnace is 1.8%.

[0056] The AOD process involves blowing oxygen to decarburize molten steel smelted in an electric furnace at a temperature of 1680℃, and then adding ferrosilicon for reduction and slag removal based on the oxygen consumption.

[0057] The LF process is as follows: the furnace is heated to 1680℃ under argon protection for LF furnace refining.

[0058] The VD process is as follows: the VD furnace is evacuated to 66 Pa and held for 25 minutes for degassing.

[0059] S3. Electroslag Remelting: The surface of the electrode blank from step S2 is polished to remove defects; then the electrode blank is transferred to the electroslag remelting station for electroslag remelting. A slag system of CaF2:Al2O3:CaO = 60%:20%:20% is selected for remelting. After remelting, the blank is demolded to obtain a φ920mm electroslag ingot. The slag baking temperature is 700℃, and the baking time is 6 hours. The electroslag ingot is obtained after the electroslag remelting process.

[0060] S4. High-temperature diffusion: The electroslag ingot is subjected to high-temperature diffusion at 1280℃ for 30 hours.

[0061] S5. Forging: The electroslag ingot from step S4 is transferred to the heating furnace of the forging station for heating. After heating to 1190℃ and holding for 5 hours, it is forged into a round bar after three upsetting and drawing processes.

[0062] S6. Residual heat quenching-stress relief annealing: The S5 forged round bar is subjected to residual heat quenching to a final reheat temperature of 290℃, and then stress relief annealing is performed; the annealing temperature is 720℃ and the annealing holding time is 20h; then the head and tail hot working defects are removed.

[0063] S7. Ultrafine-spheroidizing annealing: The round bar obtained after step S6 is subjected to ultrafine treatment, with a holding temperature of 1020℃ and a holding time of 5h. After being cooled to below 210℃ by alternating water and air cooling, the steel is subjected to spheroidizing annealing treatment. The steel is heated to 850℃ for through-firing and held for 25h, then cooled to 740℃ for through-firing and held for 25h, and finally cooled to below 300℃ and air-cooled to room temperature to obtain the steel bar.

[0064] S8. Finishing: The steel bar is cleaned and its dimensions are corrected according to the technical requirements to obtain mold steel.

[0065] The mold steel prepared in this embodiment comprises the following components by mass percentage: C 0.35%, Si 0.30%, Mn 0.60%, P 0.015%, S 0.001%, Cr 5.20%, Mo 1.50%, V 0.75%, Ni 1.10%, with the remainder being Fe; its metallographic structure is as follows: Figure 3 As shown. Example 3:

[0066] S1. Ingredients: Prepare high-carbon ferrochrome, low-nickel ferrochrome, medium-nickel ferrochrome, ferromolybdenum, ferrovanadium, scrap steel, and high-carbon ferromanganese; the mass percentage of each raw material is as follows: scrap steel 50%, low-nickel ferrochrome 36%, medium-nickel ferrochrome 4%, high-carbon ferrochrome 6%, ferromolybdenum 2%, ferrovanadium 1%, and high-carbon ferromanganese 1%.

[0067] S2. Melting: The raw materials in step S1 are smelted using an electric furnace-AOD-LF-VD smelting process to obtain electrode blanks.

[0068] Specifically: The raw materials from step S1 are added to the electric furnace. The melting temperature of the electric furnace is 1620℃, and the carbon content of the steel tapped from the electric furnace is 1.5%.

[0069] The AOD process involves blowing oxygen to decarburize molten steel smelted in an electric furnace at a temperature of 1700℃, and then adding ferrosilicon for reduction and slag removal according to the oxygen consumption.

[0070] The LF process is as follows: the furnace is heated to 1690℃ under argon protection for LF furnace refining.

[0071] The VD process is as follows: the VD furnace is evacuated to 65 Pa and held for 25 min for degassing.

[0072] S3. Electroslag Remelting: The surface of the electrode blank from step S2 is polished to remove defects; then the electrode blank is transferred to the electroslag remelting station for electroslag remelting. A slag system of CaF2:Al2O3:CaO = 60%:20%:20% is selected for remelting. After remelting, the blank is demolded to obtain a φ920mm electroslag ingot. The slag baking temperature is 700℃, and the baking time is 6 hours. The electroslag ingot is obtained after the electroslag remelting process.

[0073] S4. High-temperature diffusion: The electroslag ingot is subjected to high-temperature diffusion at 1260℃ for 33 hours.

[0074] S5. Forging: The electroslag ingot from step S4 is transferred to the heating furnace of the forging station for heating. After heating to 1170℃ and holding for 6 hours, it is forged into a round bar after two upsetting and drawing processes.

[0075] S6. Residual heat quenching-stress relief annealing: The S5 forged round bar is subjected to residual heat quenching to a final reheat temperature of 290℃, and then stress relief annealing is performed; the annealing temperature is 800℃ and the annealing holding time is 22h; then the head and tail hot working defects are removed.

[0076] S7. Ultrafine-spheroidizing annealing: The round bar obtained after step S6 is subjected to ultrafine treatment, with a holding temperature of 1010℃ and a holding time of 6 hours. After being cooled to below 210℃ by alternating water and air cooling, the steel is subjected to spheroidizing annealing treatment. The steel is heated to 860℃ for through-firing and held for 22 hours, then cooled to 720℃ for through-firing and held for 30 hours. Finally, it is cooled to below 300℃ and air-cooled to room temperature to obtain the steel bar.

[0077] S8. Finishing: The steel bar is cleaned and its dimensions are corrected according to the technical requirements to obtain mold steel.

[0078] The mold steel prepared in this embodiment comprises the following components by mass percentage: C 0.40%, Si 0.05%, Mn 0.30%, P 0.005%, S 0.001%, Cr 5.00%, Mo 1.40%, V 0.7%, Ni 1.20%, with the remainder being Fe; its metallographic structure is as follows: Figure 4 As shown.

[0079] Comparative Example 1:

[0080] The difference between Comparative Example 1 and Example 1 is that after completing the forging process in step S5, the round bar forged in S5 is subjected to residual heat quenching so that the final reheat temperature is ≤300℃. The resulting round bar is then subjected to ultrafine treatment, with a holding temperature of 1020±10℃ and a holding time of 5-6 hours. After being removed from the furnace and cooled alternately by water and air to below 210℃, it undergoes spheroidizing annealing treatment. The steel is heated to 860±10℃ for through-firing and then held for 20-25 hours. After being cooled to 730±10℃ for through-firing and then held for 25-30 hours, it is cooled to below 300℃ and then air-cooled to room temperature to obtain the steel bar.

[0081] The mold steel prepared in this comparative example comprises the following components by mass percentage: C 0.36%, Si 0.20%, Mn 0.40%, P 0.01%, S 0.001%, Cr 5.32%, Mo 1.58%, V 0.66%, Ni 0.6%, with the remainder being Fe; its metallographic structure is as follows. Figure 5 As shown.

[0082] Comparative Example 2:

[0083] The difference between Comparative Example 2 and Example 1 is that step S1 does not include low-nickel iron or medium-nickel iron, while the other process steps are the same.

[0084] The mold steel prepared in this comparative example comprises the following components by mass percentage: C 0.381%, Si 0.11%, Mn 0.42%, P 0.01%, S 0.001%, Cr 5.28%, Mo 1.59%, V 0.66%, with the remainder being Fe; its metallographic structure is as follows. Figure 6 As shown.

[0085] The mold steels obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to transverse impact energy, banded structure, microstructure, and grain size tests, respectively. The test results are shown in the table below:

[0086] The above comparison shows that this application incorporates a certain amount of Ni into the raw materials to improve the impact toughness of the material; the heat treatment process after forging adopts: residual heat quenching + stress relief annealing + ultrafine refining + spheroidizing annealing to improve the uniformity of the structure; the manufacturing method of hot extrusion die steel with high impact toughness provided by this application can effectively improve the impact toughness and structural stability of hot extrusion die steel (SD360Ni material) with high impact toughness.

Claims

1. A method for manufacturing high-impact toughness hot extrusion die steel, characterized in that, Specifically, the following steps are included: S1. Ingredients: Prepare high-carbon ferrochrome, low-nickel ferrochrome, medium-nickel ferrochrome, ferromolybdenum, ferrovanadium, scrap steel, and high-carbon ferromanganese; the mass percentage of each raw material is as follows: scrap steel 50%, low-nickel ferrochrome 36%, medium-nickel ferrochrome 4%, high-carbon ferrochrome 6%, ferromolybdenum 2%, ferrovanadium 1%, and high-carbon ferromanganese 1%. S2. Melting: The raw materials in step S1 are smelted using an electric furnace-AOD-LF-VD smelting process to obtain electrode billets. S3, Electroslag Remelting: The surface of the electrode blank from step S2 is polished to remove defects; then, an electroslag ingot is obtained through the electroslag remelting process. S4. High-temperature diffusion: The electroslag ingot is subjected to high-temperature diffusion at a temperature of 1270±10℃ for 30-35 hours. S5. Forging: The electroslag ingot from step S4 is transferred to the heating furnace of the forging station for heating. After heating to 1180±10℃ and holding for 5-7 hours, it is forged into a round bar. S6. Residual heat quenching-stress relief annealing: The round bars forged in S5 are subjected to residual heat quenching to make the final reheat temperature ≤300℃, and then stress relief annealing process is performed; the annealing temperature is 720-860℃, and the annealing holding time is 20-25h; then the head and tail hot working defects are removed. S7. Ultrafine Refining-Spheroidizing Annealing: The round bar obtained after step S6 is subjected to ultrafine refining treatment. The holding temperature is 1020±10℃ and the holding time is 5-6 hours. After being removed from the furnace, the bar is cooled to below 210℃ by alternating water and air cooling. Then, the bar is subjected to spheroidizing annealing treatment. The steel is heated to 860±10℃, and after thorough firing, it is held for 20-25 hours. The temperature is then lowered to 730±10℃, and after thorough firing, it is held for 25-30 hours. The temperature is then lowered to below 300℃ and removed from the furnace. The bar is then air cooled to room temperature to obtain the steel bar. S8. Finishing: The steel bar is cleaned and its dimensions are corrected according to the technical requirements to obtain mold steel.

2. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that: In step S1, the high-carbon ferrochrome is FeCr70C10.0, the ferromolybdenum is FeMo60-C, and the ferrovanadium is FeV60-B.

3. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that: In step S2, the melting temperature of the electric furnace is 1600-1640℃, and the carbon content of the steel tapped from the electric furnace is 1.5-2.0%.

4. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that, The AOD process in step S2 is as follows: the molten steel melted in the electric furnace is decarburized by blowing oxygen at a temperature of 1680-1740℃, and ferrosilicon is added for reduction and slag removal according to the oxygen consumption.

5. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that, The LF process in step S2 is as follows: the furnace is heated to 1680-1700℃ under argon protection for LF furnace refining.

6. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that, The VD process in step S2 is as follows: the VD furnace is evacuated to below 67 Pa and held for 20-25 minutes for degassing.

7. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that, In step S3, the slag baking temperature is 600-800℃ and the baking time is ≥6h; the electroslag remelting uses a slag system of CaF2:Al2O3:CaO=60%:20%:20% for remelting, and after remelting, the φ920mm electroslag ingot is obtained by mold cooling and demolding.

8. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that, In step S5, the total forging ratio is ≥8, and the forging process is carried out at least twice to ensure that the steel is fully deformed. The final firing temperature is reduced to 1160℃, and the deformation amount of the final firing should be greater than 40%.

9. The method for manufacturing high impact toughness hot extrusion die steel according to claim 1, characterized in that, In step S8, the components of the mold steel, by mass percentage, include: C 0.35%-0.40%, Si≤0.30%, Mn 0.30%-0.60%, P≤0.015%, S≤0.002%, Cr 5.00%-5.30%, Mo 1.40%-1.60%, V 0.65%-0.75%, Ni 1.00%-1.20%, with the remainder being Fe.

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