A method for producing a medium carbon hot work die steel

Abstract

This invention belongs to the field of special steel metallurgy technology, specifically relating to a production method of medium-carbon hot work die steel. The method includes the following steps in sequence: (1) forging: first, the steel ingot is subjected to high-temperature diffusion, and then cooled to the forging start temperature for forging; (2) online rapid cooling: the steel billet after forging in step (1) is directly water-cooled; (3) spheroidizing annealing: the steel billet after rapid cooling in step (2) is spheroidized annealed to obtain the medium-carbon hot work die steel. The production method provided by this invention simplifies the current heat treatment method for medium-carbon hot work die steel, which requires annealing, solution treatment and spheroidizing annealing in sequence after forging. The production method of this invention simplifies the production process, reduces costs and shortens the production cycle while ensuring the high strength and toughness of medium-carbon hot work die steel.

Description

Technical Field

[0001] This invention belongs to the field of special steel metallurgy technology, specifically relating to a method for producing medium carbon hot work die steel. Background Technology

[0002] Hot work die steels are the most widely used in the mold industry, with H13, SKD61, and A348 being the mainstream grades. A uniform annealed microstructure is a crucial prerequisite for ensuring the high strength and toughness of hot work die steels. After forging, medium-carbon hot work die steels typically undergo furnace cooling / annealing (to prevent stress cracking), followed by solution treatment (heating to a certain temperature, holding for a certain time, and then rapid cooling in a rapid cooling bath), and finally spheroidizing annealing to obtain a qualified annealed microstructure, network structure, and mechanical properties.

[0003] Medium-carbon hot work die steels often require rating of annealed microstructure (evaluated according to NADCA#207-90 spectrum, qualified grades A1~5, B1~4, C1~2, D1~2, E1) and banded (rated according to GB / T18254 Grade 8 diagram, qualified grade ≤3) and network carbides (rated according to GB / T1299 Grade 2 diagram, qualified grade 2). Therefore, such grades need to add a "forging furnace cooling / annealing + solution treatment" process before spheroidizing annealing to meet the standard requirements. This results in long production cycles and high costs for medium-carbon hot work die steels that can meet the corresponding ratings in the existing technology. Therefore, providing an efficient and low-cost heat treatment method for medium-carbon hot work die steels has very important industrial value. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for producing medium-carbon hot work die steel. This method simplifies the heat treatment methods for medium-carbon hot work die steel in existing technologies, shortens the production cycle by about one week, and reduces the process cost by about 600 yuan / ton.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for producing medium-carbon hot work die steel, the method comprising the following steps in sequence:

[0007] (1) Forging: First, the steel ingot is subjected to high-temperature diffusion, and then cooled to the forging start temperature for forging;

[0008] (2) Online rapid cooling: The uncooled steel billet after forging in step (1) is directly water-cooled;

[0009] (3) Spheroidizing annealing: The steel billet that has been rapidly cooled in step (2) is subjected to spheroidizing annealing to obtain the medium carbon hot work die steel.

[0010] In a preferred embodiment of the present invention, a rapid cooling pool is provided next to the forging cooling bed. The steel billet is placed in the rapid cooling pool and rapidly cooled using the residual heat from forging, thus achieving high-temperature quenching. In other words, the forged steel billet is placed directly into the rapid cooling pool for cooling without prior cooling, and the surface temperature of the steel billet is 800~950℃ when it enters the pool.

[0011] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (1), the temperature of the high temperature diffusion is 1220~1270℃ (e.g., 1230℃, 1240℃, 1250℃, 1260℃); preferably, the time of the high temperature diffusion is greater than 10 hours (e.g., 15h, 20h, 25h, 30h, 35h).

[0012] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (1), the forging starting temperature is 1180~1220℃ (e.g., 1185℃, 1190℃, 1195℃, 1200℃, 1210℃); preferably, the final forging temperature is greater than or equal to 950℃ (e.g., 975℃, 1000℃, 1025℃, 1050℃, 1075℃, 1100℃, 1200℃, 1300℃); preferably, the cooling method is furnace cooling; preferably, the forging ratio is >5.

[0013] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (2), the water cooling is to immerse the forged steel billet in cooling water. Preferably, the temperature of the cooling water is less than 30°C (e.g., 10°C, 15°C, 20°C, 25°C).

[0014] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (2), the cooling rate of the water cooling is 70~100℃ / min (e.g. 75℃ / min, 80℃ / min, 85℃ / min, 90℃ / min, 95℃ / min); preferably, the steel billet is cooled to a surface temperature of 180~250℃ (e.g. 190℃, 200℃, 210℃, 220℃, 230℃, 240℃) and then discharged from the water.

[0015] In this invention, the steel billet is cooled in cooling water to a surface temperature of 180~250°C and then discharged. This allows the surface temperature of the steel billet to be controlled to not exceed 300°C after being discharged from the water.

[0016] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (3), the spheroidizing annealing includes the following steps in sequence: furnace feeding, heating, first heat preservation, first cooling, second heat preservation, second cooling and furnace cooling.

[0017] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (3), the steel billet that has undergone rapid cooling in step (2) is first cooled to the furnace temperature and then annealed. The furnace temperature is 50~200℃ (e.g. 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃); preferably, the cooling method is air cooling.

[0018] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (3), the heating is performed at a rate of 40~60℃ / h (e.g., 45℃ / h, 50℃ / h, 55℃ / h) to heat the billet to the temperature for the first holding; preferably, the temperature for the first holding is 850~870℃ (e.g., 855℃, 860℃, 865℃); preferably, the holding time is 16~30h (e.g., 20h, 22.5h, 25h, 27.5h); preferably, the cooling is performed at a rate of 10~30℃ / h (e.g., 15℃ / h, 20 ... The billet is cooled to the secondary holding temperature at a rate of 730~750℃ (e.g., 735℃, 740℃, 745℃) at a rate of 25℃ / h; preferably, the secondary holding time is 20~30h (e.g., 22h, 24h, 26h, 28h); preferably, the secondary cooling is performed at a rate of 10~30℃ / h (e.g., 15℃ / h, 20℃ / h, 25℃ / h) to the furnace exit temperature; preferably, the furnace exit temperature of the billet during the secondary cooling is less than or equal to 250℃; preferably, the furnace exit cooling is air cooling.

[0019] In the above-mentioned production method of medium carbon hot work die steel, as a preferred embodiment, in step (1), the steel ingot is of type H13, SKD61 or A348;

[0020] Preferably, the chemical composition of the H13 is: C: 0.32~0.45wt%, Si: 0.80~1.2wt%, Mn: 0.25~0.50wt%, P≤0.020wt%, S≤0.01wt%, Cr: 4.75~5.50wt%, Mo: 1.20~1.75wt%, V: 0.85~1.2wt%; Cu≤0.20wt%, with the remainder being iron and unavoidable impurities;

[0021] Preferably, the chemical composition of the SKD61 is as follows: C: 0.37~0.42wt%, Si: 0.80~1.2wt%, Mn: 0.25~0.50wt%, P≤0.015wt%, S≤0.003wt%, Cr: 5.00~5.50wt%, Mo: 1.30~1.50wt%, V: 0.80~1.00wt%, Ni≤0.20wt%, Cu≤0.20wt%, Ti≤0.010wt%, with the remainder being iron and unavoidable impurities;

[0022] Preferably, the chemical composition of the A348 is as follows: C: 0.35~0.40wt%, Si: 0.10~0.30wt%, Mn: 0.30~0.60wt%, P≤0.015wt%, S≤0.005wt%, Cr: 5.20~5.50wt%, Mo: 2.40~2.60wt%, V: 0.85~1.2wt%, Ni≤0.15wt%, Cu≤0.20wt%, with the remainder being iron and unavoidable impurities.

[0023] Secondly, the present invention provides medium carbon hot work die steel obtained by the above-described method for producing medium carbon hot work die steel.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] The production method of this invention can improve the compositional segregation, homogenize the microstructure, and refine the grains of medium-carbon hot work die steel to ultimately obtain a uniform annealed microstructure and good mechanical properties. Specifically, it utilizes the residual heat after forging the medium-carbon hot work die steel to directly place the forged steel billet in cold water for rapid cooling, thereby achieving high-temperature quenching. This replaces the traditional "furnace cooling / annealing + solution treatment after forging," achieving cost reduction (reducing process costs by approximately 600 yuan / ton), shortening the production cycle by about one week, reducing the labor intensity of workers, and ensuring product quality.

[0026] The annealed microstructure (assessed according to NADCA#207-2011 chart, qualified grades A1~5, B1~4, C1~2, D1~2, E1) and banded (graded according to GB / T18254 eighth level chart, qualified grade ≤3), network carbides (graded according to GB / T1299 second level chart, qualified grade ≤2) and mechanical properties of the medium carbon hot work die steel produced by the production method of this invention meet the standard requirements respectively.

[0027] Since March 2022, the forging plant has implemented "online rapid cooling" to replace the traditional offline "furnace cooling / annealing + solution treatment" process for medium carbon hot work die steel. The quality of the approximately 1,000 tons / month of medium carbon hot work die steel produced has all passed the quality test. This has overcome the problems of long production cycle, high cost and high labor intensity of offline "furnace cooling / annealing + solution treatment", resulting in a monthly cost reduction and profit of more than 600,000 yuan. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0029] Example 1

[0030] A method for producing medium carbon hot work die steel. In this embodiment, the die steel obtained is a high-quality hot work die steel of type H13, with dimensions of φ280mm×9500mm (diameter×length).

[0031] (1) 5.0t steel ingots are heated in a bogie-type gas furnace for high-temperature diffusion. The high-temperature diffusion temperature is 1250±10℃ and the diffusion time is 15h. After high-temperature diffusion, the temperature of the steel ingots is reduced to 1190±10℃ to start forging. The forging adopts the "upsetting-drawing" process to forge to φ280mm specification. The total forging ratio is 5.94 and the final forging temperature is 950℃.

[0032] (2) After forging, the forged billet is directly transferred to a cold water tank for rapid cooling. Before the billet is put into the water, the billet temperature is 880±50℃, the water temperature is controlled below 30℃, and the billet surface temperature is cooled to 220±30℃ before being taken out of the water. The billet surface temperature is not exceeded 300℃ within 5 minutes after being taken out of the water.

[0033] (3) The billet that has been rapidly cooled is subjected to spheroidizing annealing. The spheroidizing annealing process includes the following steps: furnace feeding, heating, first heat preservation, first cooling, second heat preservation, second cooling and furnace cooling.

[0034] After rapid cooling, the steel billet is further cooled to 120±60℃ and then placed in an annealing furnace for heating at a rate of 50±10℃ / h. It is heated to a first holding temperature of 860±10℃ and then held for 20 hours. Next, it is cooled at a rate of 20±10℃ / h to a second holding temperature of 740±10℃ and held for 20 hours. Finally, it is cooled at a rate of 20±10℃ / h to 250℃ and then air-cooled to obtain the medium-carbon hot work die steel.

[0035] According to the North American Die Casting Association's (NADCA) Acceptance Standard for High-Quality Die Steel and Die Casting Mold Heat Treatment (NADCA#207-2011), the annealed microstructure of the medium-carbon hot work die steel prepared in this embodiment is AS4. According to GB / T18254, the banded microstructure of the medium-carbon hot work die steel prepared in this embodiment is grade 3. According to the German Hot Work Tool Steel Microscopic Inspection Standard (SEP1614-1996), the banded microstructure of the medium-carbon hot work die steel prepared in this embodiment is SA2. According to GB / T1299, the medium-carbon hot work die steel prepared in this embodiment has no carbide precipitation or network carbides, meeting the standard requirements.

[0036] Example 2

[0037] A method for producing a medium-carbon chromium-molybdenum-vanadium hot work die steel. The die steel obtained in this embodiment is SKD61 forged round steel with dimensions of φ400mm×9000mm (diameter×length).

[0038] (1) 10.0t steel ingots are heated in a bogie-type gas furnace for high-temperature diffusion. The high-temperature diffusion temperature is 1250±10℃ and the high-temperature diffusion time is 24h. After high-temperature diffusion, the temperature of the steel ingots is reduced to 1190±10℃ and forging is started to φ400mm. The forging adopts the "upsetting-drawing" process, the total forging ratio is 6.3, and the final forging temperature is 950℃.

[0039] (2) After forging, the billet is quickly cooled in a water tank using the residual heat after forging. Before the billet is put into the water, the billet temperature is 880±50℃ and the cooling water temperature is controlled below 30℃. The billet surface temperature is measured to be cooled to 220±30℃ before being taken out of the water. The billet surface temperature is not more than 300℃ after 5 minutes of being taken out of the water.

[0040] (3) The billet that has been rapidly cooled is subjected to spheroidizing annealing. The spheroidizing annealing process includes the following steps: furnace feeding, heating, first heat preservation, first cooling, second heat preservation, second cooling and furnace cooling.

[0041] The rapidly cooled steel billet is further air-cooled to 120±60℃, then placed in an annealing furnace and heated at a rate of 50±10℃ / h. After heating to a first holding temperature of 860±10℃, it undergoes a first holding for 20 hours. Then, it is cooled at a rate of 20±10℃ / h to a second holding temperature of 740±10℃, followed by a second holding for 20 hours. Finally, it undergoes a second cooling at a rate of 20±10℃ / h to 250℃ before being removed from the furnace and air-cooled, thus obtaining the medium-carbon hot work die steel.

[0042] According to the North American Die Casting Association's (NADCA) Acceptance Standard for High-Quality Die Steel and Die Casting Mold Heat Treatment (NADCA#207-2011), the annealed microstructure of the medium-carbon hot work die steel prepared in this embodiment is AS3. According to the German Hot Work Tool Steel Microscopic Examination (SEP1614-1996), the banded microstructure of the medium-carbon hot work die steel prepared in this embodiment is SA3. According to GB / T18254, the banded microstructure of the medium-carbon hot work die steel prepared in this embodiment is grade 3. According to GB / T1299, the medium-carbon hot work die steel prepared in this embodiment shows no carbide precipitation or network carbides, meeting the standard requirements.

[0043] Example 3

[0044] A method for producing a medium-carbon chromium-molybdenum-vanadium hot work die steel. The die steel obtained in this embodiment is of type A348, with dimensions of 300mm (thickness) × 700mm (width) × 2000mm (length).

[0045] (1) 10t steel ingots are heated in a bogie-type gas furnace for high-temperature diffusion. The high-temperature diffusion temperature is 1260±10℃ and the high-temperature diffusion time is 22h. After high-temperature diffusion, the steel ingot temperature is reduced to 1210±10℃ to start forging. The forging adopts the "upsetting-drawing" process. The total forging ratio is 6.69 and the final forging temperature is controlled at 950℃.

[0046] (2) After forging, the billet is rapidly cooled in a water bath using the residual heat from forging. Before the billet is immersed in the water, the billet temperature is 880±50℃, and the cooling water temperature is controlled below 30℃. The billet is taken out of the water after cooling to 220±30℃. The surface temperature of the billet does not exceed 300℃ within 5 minutes after being taken out of the water.

[0047] (3) The billet that has been rapidly cooled is subjected to spheroidizing annealing. The spheroidizing annealing process includes the following steps: furnace feeding, heating, first heat preservation, first cooling, second heat preservation, second cooling and furnace cooling.

[0048] The rapidly cooled steel billet is further air-cooled to 120±60℃, then placed in an annealing furnace and heated at a rate of 50±10℃ / h. After heating to a first holding temperature of 860±10℃, it undergoes a first holding for 20 hours. Then, it is cooled at a rate of 20±10℃ / h to a second holding temperature of 740±10℃, followed by a second holding for 20 hours. Finally, it undergoes a second cooling at a rate of 20±10℃ / h to 250℃ before being removed from the furnace and air-cooled, thus obtaining the medium-carbon hot work die steel.

[0049] According to the North American Die Casting Association's (NADCA) Acceptance Standard for High-Quality Die Steel and Die Casting Mold Heat Treatment (NADCA#207-2011), the annealed microstructure of the medium-carbon hot work die steel prepared in this embodiment is AS3. According to the German Hot Work Tool Steel Microscopic Examination (SEP1614-1996), the banded microstructure of the medium-carbon hot work die steel prepared in this embodiment is SA3. According to GB / T18254, the banded microstructure of the medium-carbon hot work die steel prepared in this embodiment is grade 3. According to GB / T1299, the medium-carbon hot work die steel prepared in this embodiment shows no carbide precipitation or network carbides, meeting the standard requirements.

[0050] Comparative Example 1

[0051] A method for producing a medium-carbon chromium-molybdenum-vanadium hot work die steel. The die steel obtained in this embodiment is of type A348, with dimensions of 300mm (thickness) × 700mm (width) × 2000mm (length), and is prepared by a process of "forging + annealing + solution treatment + spheroidizing annealing".

[0052] (1) Forging: 10.0t steel ingots are heated in a bogie-type gas furnace at a high temperature diffusion temperature of 1260±10℃ and a high temperature diffusion time of 22h. After high temperature diffusion, the steel ingots are cooled to 1210±10℃ to start forging. The forging adopts the "upsetting-drawing" process to forge to 300mm (thickness)×700mm (width)×2000mm (length), with a total forging ratio of 6.69. The final forging temperature is controlled at 950℃.

[0053] (2) Annealing: After forging, the obtained steel billet is air-cooled to 350℃, then air-cooled to 250±10℃ before entering the annealing furnace for softening annealing. The softening annealing process is as follows: the steel billet is heated to 780±10℃ at a heating rate of 70±10℃ / h, held for 12h, and then cooled at a cooling rate of 20±10℃ / h to 400℃ before being taken out of the furnace and air-cooled.

[0054] (3) Solution treatment:

[0055] 3.1 The softened and annealed steel billet is heated and held at a temperature in a bogie-type gas furnace: the steel billet is heated to 850±10℃ at a heating rate of 50±10℃ / h and held for 3~5h; then the steel billet is heated to 1060±10℃ at a heating rate of 70±10℃ / h for solution treatment, held for 6h and then removed from the furnace and air-cooled until the center temperature of the large surface is 900℃.

[0056] 3.2 Water Cooling: After solution treatment, the steel billet is water-cooled. Before immersion in water, the billet temperature is 880±50℃, and the cooling water temperature is controlled below 30℃. The billet is removed from the water after cooling to 220±30℃. The surface temperature of the billet does not exceed 300℃ within 5 minutes after removal from the water.

[0057] (5) Spheroidizing annealing: Spheroidizing annealing is performed on the steel billet after rapid cooling. Spheroidizing annealing includes furnace feeding, heating, first heat preservation, first cooling, second heat preservation, second cooling and furnace cooling.

[0058] The rapidly cooled steel billet was further air-cooled to 120±60℃, then placed in an annealing furnace and heated at a rate of 50±10℃ / h. After heating to a first holding temperature of 860±10℃, it underwent a first holding for 20 hours. Then, it was cooled at a rate of 20±10℃ / h to a second holding temperature of 740±10℃, followed by a second holding for 20 hours. Finally, it was cooled a second time at a rate of 20±10℃ / h to 250℃ before being removed from the furnace and air-cooled, thus obtaining the medium-carbon chromium-molybdenum-vanadium hot work die steel.

[0059] According to the North American Die Casting Association's (NADCA) Acceptance Standard for High-Quality Die Steel and Die Casting Mold Heat Treatment (NADCA#207-2011), the annealed microstructure of the medium-carbon hot work die steel prepared in this comparative example is AS3. According to the German Hot Work Tool Steel Microscopic Examination (SEP1614-1996), the banded microstructure of the medium-carbon hot work die steel prepared in this comparative example is SA3. According to GB / T18254, the banded microstructure of the medium-carbon hot work die steel prepared in this comparative example is grade 3. According to GB / T1299, the medium-carbon hot work die steel prepared in this comparative example shows no carbide precipitation or network carbides, meeting the standard requirements.

[0060] The production method of the present invention (forging, online rapid cooling, spheroidizing annealing) used in Example 3 is basically the same as that used in Comparative Example 1, which uses the preparation process of "forging + post-forging annealing + solution treatment + spheroidizing annealing". The annealed structure, banded structure, carbide liquid precipitation, network carbides and mechanical properties are basically the same. It overcomes the problems of long production cycle, high cost and high labor intensity of offline "furnace cooling / annealing + solution treatment + spheroidizing treatment" and achieves significant cost reduction results.

[0061] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., 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 of producing a medium carbon hot work die steel, characterized by, The method sequentially comprises the following steps: (1) forging: firstly, high-temperature diffusion is performed on the ingot, and then the ingot is cooled to a forging starting temperature for forging, and the final forging temperature is greater than or equal to 950 DEG C; (2) on-line fast cooling: the steel blank after forging in step (1) is directly subjected to water cooling without cooling; The water cooling is to immerse the steel blank after forging in cooling water, the temperature of the cooling water used in the water cooling is less than 30 DEG C, the cooling speed of the water cooling is 70-100 DEG C / min, and the steel blank is water cooled to a surface temperature of 180-250 DEG C and then taken out of water; (3) spheroidizing annealing: the steel blank after fast cooling in step (2) is subjected to spheroidizing annealing to obtain the medium-carbon hot work die steel, The spheroidizing annealing sequentially comprises the following steps: furnace charging, heating, first holding, first cooling, second holding, second cooling and furnace cooling; The furnace charging comprises firstly cooling the steel blank after fast cooling in step (2) to a furnace charging temperature and then performing annealing, and the furnace charging temperature is 50-200 DEG C; The heating is to heat the steel blank to the temperature of the first holding at a speed of 40-60 DEG C / h; The temperature of the first holding is 850-870 DEG C; The time of the first holding is 16-30 h; The first cooling is to cool the steel blank to the temperature of the second holding at a speed of 10-30 DEG C / h; The temperature of the second holding is 730-750 DEG C; The time of the second holding is 20-30 h; The second cooling is to cool the steel blank to the furnace discharge temperature at a speed of 10-30 DEG C / h; The furnace discharge temperature of the steel blank is less than or equal to 250 DEG C; The furnace cooling is air cooling after furnace discharge; In step (1), the type of the ingot is H13, SKD61 or A348; The chemical composition of the H13 is: C: 0.32-0.45wt%, Si: 0.80-1.2wt%, Mn: 0.25-0.50wt%, P≤0.020wt%, S≤0.01wt%, Cr: 4.75-5.50wt%, Mo: 1.20-1.75wt%, V: 0.85-1.2wt%, Cu≤0.20wt%, and the rest is iron and inevitable impurities; The chemical composition of the SKD61 is: C: 0.37-0.42wt%, Si: 0.80-1.2wt%, Mn: 0.25-0.50wt%, P≤0.015wt%, S≤0.003wt%, Cr: 5.00-5.50wt%, Mo: 1.30-1.50wt%, V: 0.80-1.00wt%, Ni≤0.20wt%, Cu≤0.20wt%, Ti≤0.010wt%, and the rest is iron and inevitable impurities; The chemical composition of the A348 is: C: 0.35-0.40wt%, Si: 0.10-0.30wt%, Mn: 0.30-0.60wt%, P≤0.015wt%, S≤0.005wt%, Cr: 5.20-5.50wt%, Mo: 2.40-2.60wt%, V: 0.85-1.2wt%, Ni≤0.15wt%, Cu≤0.20wt%, and the rest is iron and inevitable impurities.

2. The production method according to claim 1, wherein In step (1), the temperature of the high-temperature diffusion is 1220-1270℃; And / or, in step (1), the time of the high-temperature diffusion is greater than 10 hours; And / or, in step (1), the starting temperature of the forging is 1180-1220℃; And / or, in step (1), the cooling mode is furnace cooling; And / or, in step (1), the forging ratio of the forging is >5.

3. The medium-carbon hot-work die steel produced by the production method of any one of claims 1-2.