Die-casting die steel and manufacturing method thereof

Abstract

The present invention provides a die-casting die steel and a manufacturing method thereof, and relates to the field of metallurgical technology. The chemical composition of the die-casting die steel is obtained by adding an appropriate amount of Ni and adjusting it on the basis of 4Cr5Mo2V. Since the lattice constant of Ni is similar to that of γ-Fe, it can form a continuous solid solution, which is beneficial to improving the hardenability of steel. Ni can also reduce the critical point and increase the stability of austenite, improve the hardenability, and when Ni is combined with Cr and Mo, the hardenability can be particularly increased. The present invention also provides a manufacturing method for the above-mentioned die-casting die steel, specifically, after controlling the large steel ingot within the range of specific chemical composition, the electrode base material is die-cooled and stress-relieved annealed in a specific manner, and then the electrode base material is vacuum arc melted, and then die-cooled and stress-relieved annealed in a specific manner, and through specific heating and forging technology and heat treatment, qualified large die steel is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a die-casting die steel and a manufacturing method thereof. Background Art

[0002] The primary problem in mold manufacturing is mold materials. In recent years, with the rapid development of China's mold industry, a huge market has been provided for domestic mold steel, which has driven the improvement of the output, variety, specifications and quality level of domestic mold steel. At present, the annual output of domestic mold steel has reached about 600,000 tons, but domestic mold steel is still difficult to fully meet the needs of the domestic mold market in terms of variety and quality. With the continuous development of my country's mold industry, the import volume of high-end mold steel continues to rise. The import of mold steel mainly comes from Japan, Germany, Sweden and other countries. The specifications of imported mold steel are mainly large-sized forging modules (thickness 250~800mm)×(width 600~1200mm), which can only be produced by a few steel mills in China at present, and the price is expensive, generally 2~5 times that of domestic steel.

[0003] Lightweighting of new energy vehicles and "one-piece casting" have become a hot development direction in automobile manufacturing. The "one-piece casting" molding technology uses a large multi-directional die-casting machine of more than 6,000 tons for the frame structure, and uses a large mold to integrate dozens of parts on the frame into a whole and form them in one go. This method is not only conducive to integrated design, greatly reducing the number of components and achieving lightweighting, but also can reduce the number of supply chain supporting and processing equipment, shorten manufacturing time, reduce costs, and greatly improve production efficiency.

[0004] The mold used in "integrated casting" requires a thickness of 400-800mm, a width of 800-1300mm, and a unit weight of more than 10t. Due to its large size, complex shape, thin cavity wall, high stress and other characteristics, it is prone to problems such as uneven organization and mechanical properties, incomplete hardening, cracking, and insufficient impact resistance. At present, there is no die-casting mold steel product on the market that can fully meet the requirements of integrated large-scale mold conditions. 4Cr5MoSiV is generally used instead, and the ultimate life of the mold is short and unstable.

[0005] At present, the commonly used die-casting mold steels in the market are mainly 4Cr5MoSiV1 and 4Cr5Mo2V. Among them, 4Cr5MoSiV1 contains about 1.0% Si. The solid solution strengthening of Si makes the matrix toughness of the material poor, which is easy to produce fatigue thermal cracks and cracks; 4Cr5Mo2V increases the content of Mo on the basis of 4Cr5MoSiV1 to ensure the secondary hardening effect, reduces the content of Si and V to greatly improve the toughness, but its hardenability is insufficient for large die-casting molds. Die-casting mold steel mainly uses electroslag remelting to improve the purity of the material, but the effect is limited. At the same time, the oxygen content (≥15×10-6 ) and nitrogen content (≥90×10 -6 ), affecting the performance of the mold material.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The object of the present invention is to provide a die-casting die steel and a manufacturing method and a die thereof, so as to solve at least one of the above-mentioned technical problems.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] The first object of the present invention is to provide a die-casting die steel, comprising the following chemical components by mass fraction: C 0.33-0.40%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr 4.80-5.50%, Mo 1.90-2.60%, V 0.40-1.00%, Ni 0.10-0.80%, and the rest being Fe and unavoidable impurities.

[0010] Furthermore, based on the above technical solution of the present invention, the die-casting mold steel includes the following chemical components in mass fraction: C 0.33-0.40%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr4.80-5.50%, Mo1.90-2.30%, V 0.40-0.80%, Ni 0.10-0.80%, and the rest are Fe and unavoidable impurities.

[0011] A second object of the present invention is to provide a method for manufacturing a die-casting die steel, comprising the following steps:

[0012] S1. The raw material of the die-casting die steel is smelted, LF refined and RH degassed, and then cast under argon protection to obtain an electrode base material; the electrode base material is then subjected to mold cooling, stress relief annealing and surface grinding treatment; wherein the stress relief annealing temperature is 775 to 825°C;

[0013] S2. The electrode base material after the surface grinding treatment in step S1 is subjected to vacuum arc melting to obtain a steel ingot, and then the steel ingot is subjected to stress relief annealing; wherein the stress relief annealing temperature is 775 to 825°C;

[0014] S3. The steel ingot after stress relief annealing in step S2 is subjected to high temperature homogenization treatment and three-dimensional forging to obtain a forging; and then the forging is subjected to softening annealing treatment;

[0015] S4. The forgings after the softening annealing treatment in step S3 are subjected to solution treatment and isothermal spheroidizing treatment to obtain die casting die steel.

[0016] Further, on the basis of the above technical solution of the present invention, in step S1, the raw materials include blast furnace molten iron, ferroalloy and CrMo scrap steel;

[0017] And / or, in step S1, the mold cooling time is 8 to 12 hours;

[0018] And / or, in step S1, the stress relief annealing includes firstly placing the steel into an annealing furnace and heating it to 775-825°C, keeping the temperature at an effective diameter of 100 mm / 4h, and then slowly cooling it to no higher than 200°C and air cooling it out of the furnace.

[0019] Further, on the basis of the above technical solution of the present invention, in step S2, the melting rate of vacuum arc melting is 8.0-12.0 kg / min;

[0020] And / or, in step S2, the process conditions of the vacuum arc furnace used for vacuum arc melting include at least one of the following process parameters: vacuum degree of 0.1-0.3 mbar; melting current of 15000-20000 A; melting voltage of 20-25 V;

[0021] And / or, in step S2, during the vacuum arc melting process, the last 3 to 8% by weight of the electrode base material ingot is subjected to shrinkage feeding.

[0022] Further, on the basis of the above technical solution of the present invention, in step S2, after the smelting is completed, mold cooling is first performed, and then stress relief annealing is performed, and the mold cooling time is 2 to 5 hours;

[0023] And / or, in step S2, the stress relief annealing includes firstly placing the steel into an annealing furnace and heating it to 775-825°C, keeping the temperature at an effective diameter of 100 mm / 3h, and then slowly cooling it to no higher than 200°C and air cooling it out of the furnace.

[0024] Further, on the basis of the above technical solution of the present invention, in step S3, the high temperature homogenization treatment includes heating the steel ingot obtained in step S2 to 1260-1350° C., keeping the temperature at an effective diameter of 100 mm / 3 h, and then cooling it to 1150-1250° C. with the furnace;

[0025] And / or, in step S3, the three-dimensional forging includes using upper and lower large platforms to perform three-dimensional cross large deformation upsetting forging, each pressing amount is not less than 25-50%, 90° flipping to press another plane, three planes are pressed down in sequence, and the total forging ratio is not less than 8;

[0026] And / or, in step S3, the forging obtained by three-dimensional forging is cooled in a water gap after forging, the water cooling is stopped when the forging temperature reaches 450-500° C., air-cooled to no more than 300° C., and then softened and annealed;

[0027] And / or, in step S3, the softening annealing treatment includes heating the forging to 700-750° C. and keeping the temperature at an effective diameter of 100 mm / 5 h.

[0028] Further, on the basis of the above technical solution of the present invention, in step S4, the temperature of the solution treatment is 1000-1100° C.;

[0029] And / or, the solution treatment is performed by intermittent water entry, the temperature of the forging is reduced to 500-600°C for the first water entry, the temperature of the forging is reduced to 300-350°C for the second water entry, and the temperature of the forging is reduced to 150-200°C for the third water entry;

[0030] And / or, the isothermal spheroidizing treatment includes heating the forgings after solution treatment to 840-890°C in a furnace, cooling to 730-780°C at a rate of ≤30°C / h, then cooling to below 500°C at a rate of ≤50°C / h, and air cooling to room temperature after taking out of the furnace.

[0031] Furthermore, based on the above technical solution of the present invention, for large die-casting die steel with a thickness of 400 to 800 mm and a width of 800 to 1300 mm, the ultrasonic flaw detection can meet the GB / T6402-2008 standard level 4;

[0032] And / or, non-metallic inclusions are tested according to GB / T10561-2023 standard A method and are not greater than level 0.5;

[0033] and / or, oxygen content is not more than 8×10 -6 , nitrogen content is not more than 60×10 -6 ;

[0034] And / or, at a hardness of 45±1HRC, the transverse V-shaped impact energy KV2 of the core shall not be less than 25J, and the transverse 7×10mm unnotched impact energy KW2 of the core shall not be less than 400J.

[0035] The third object of the present invention is to provide a mold, which is made of the die-casting mold steel provided by the first object of the present invention or the die-casting mold steel made by the manufacturing method provided by the second object of the present invention.

[0036] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0037] (1) The present invention provides a die-casting die steel, which is obtained by adding an appropriate amount of Ni to 4Cr5Mo2V and making corresponding adjustments. The lattice constant of Ni is similar to that of γ-Fe, so it can form a continuous solid solution, which is beneficial to improving the hardenability of steel. Ni can also reduce the critical point and increase the stability of austenite, improve the hardenability, and when Ni is combined with Cr and Mo, the hardenability can be particularly increased. In addition, nickel-molybdenum steel also has a very high fatigue limit.

[0038] (2) The present invention provides a method for manufacturing the above-mentioned die-casting die steel, specifically, after controlling the chemical composition of the large steel ingot within a specific range, the electrode base material is die-cooled and stress-relief annealed in a specific manner, and then the electrode base material is vacuum arc melted to eliminate the instability of the smelting process. After die-cooling and stress-relief annealing in a specific manner, the steel ingot is subjected to specific heating and forging technology and heat treatment to obtain qualified large die-casting die steel. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0040] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0041] According to a first aspect of the present invention, a die-casting die steel is provided, comprising the following chemical components in mass fraction: C 0.33-0.40%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr 4.80-5.50%, Mo 1.90-2.60%, V 0.40-1.00%, Ni 0.10-0.80%, and the remainder being Fe and unavoidable impurities.

[0042] Wherein, the typical but non-limiting mass fraction of C is 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39% or 0.40%, etc.; the typical but non-limiting mass fraction of Si is 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45% or 0.50%, etc.; the typical but non-limiting mass fraction of Mn is 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65% or 0.70%, etc.; the typical but non-limiting mass fraction of Cr is 4.8%, 4.9%, 5.00%, 5.50%, 5.60%, 5.70%, etc. .10%, 5.20%, 5.30%, 5.40% or 5.50%; the typical but non-limiting mass fraction of Mo is 1.90%, 2.00%, 2.10%, 2.20%, 2.30%, 2.40%, 2.50% or 2.60%, etc.; the typical but non-limiting mass fraction of V is 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.85%, 0.90%, 0.95% or 1.00%, etc.; the typical but non-limiting mass fraction of Ni is 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70% or 0.80%, etc.

[0043] The die-casting die steel of the present invention is based on 4Cr5Mo2V, and a proper amount of Ni is added. The lattice constant of Ni is similar to that of γ-Fe, so it can form a continuous solid solution, which is beneficial to improving the hardenability of the steel. Ni can also reduce the critical point and increase the stability of austenite, improve the hardenability, and when Ni is combined with Cr and Mo, the hardenability can be increased. In addition, nickel-molybdenum steel also has a very high fatigue limit.

[0044] At the same time, the inventors also found that when the Ni content is too high (higher than 0.80%), it is easy to react chemically with the aluminum liquid, reducing the service life of the mold. At the same time, too high Ni will also increase the cost. When the Ni content is too low (lower than 0.10%), it cannot achieve the purpose of improving the impact toughness of the steel. Therefore, the Ni content needs to be limited to a certain numerical range.

[0045] As an optional embodiment of the present invention, the die-casting mold steel includes the following chemical components in mass fraction: C 0.33-0.40%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr 4.80-5.50%, Mo1.9-2.30%, V0.40-0.80%, Ni 0.1-0.8%, and the rest is Fe and unavoidable impurities.

[0046] By further optimizing the chemical composition of die-casting mold steel, the die-casting mold steel can achieve even better performance.

[0047] According to a second aspect of the present invention, there is also provided a method for manufacturing the above-mentioned die-casting die steel, comprising the following steps:

[0048] S1. The raw material of the die-casting die steel is smelted, LF refined and RH degassed, and then cast under argon protection to obtain an electrode base material; the electrode base material is then mold cooled, stress relieved annealed and surface ground;

[0049] S2. The electrode base material after the surface grinding treatment in step S1 is subjected to vacuum arc melting to obtain an ingot, and then the ingot is subjected to stress relief annealing;

[0050] S3. The steel ingot after stress relief annealing in step S2 is subjected to high temperature homogenization treatment and three-dimensional forging to obtain a forging; and then the forging is subjected to softening annealing treatment;

[0051] S4. The forgings after the softening annealing treatment in step S3 are subjected to solution treatment and isothermal spheroidizing treatment to obtain die casting die steel.

[0052] After in-depth research, the inventors of the present invention found that after controlling the chemical composition of large steel ingots within a specific range, the electrode base material is mold-cooled and stress-relief annealed in a specific manner, and then the electrode base material is vacuum arc melted to eliminate the instability of the smelting process. Then, after mold-cooling and stress-relief annealing in a specific manner, the steel ingot is subjected to specific heating and forging technology and heat treatment to obtain qualified large die steel.

[0053] As an optional embodiment of the present invention, in step S1, the raw materials include blast furnace molten iron, ferroalloy and CrMo scrap steel.

[0054] As an optional embodiment of the present invention, in step S1, the ferroalloy includes high carbon ferrochrome, low carbon ferrochrome, ferromolybdenum, ferrovanadium and ferronickel; the ferroalloy is melted evenly in an alloy melting furnace, and the tapping temperature is not lower than 1560°C.

[0055] As an optional embodiment of the present invention, in step S1, the mass content of phosphorus in the blast furnace molten iron is not higher than 0.020%, the total mass content of lead, arsenic, tin, antimony and bismuth is not greater than 0.020%, and the mass content of arsenic is not greater than 0.010%.

[0056] As an optional embodiment of the present invention, in step S1, an electric furnace is used to melt and dephosphorize molten iron from a blast furnace and CrMo scrap steel, the phosphorus content is not higher than 0.003%, and the tapping temperature is not lower than 1630°C.

[0057] As an optional embodiment of the present invention, in step S1, the molten steel from the alloy melting furnace and the electric furnace is added to the LF refining furnace for desulfurization to a mass content of no more than 0.002%, degassing, and removal of inclusions, and adjusted to the required composition for refining.

[0058] As an optional embodiment of the present invention, in step S1, after RH degassing (RH cycle degassing), the nitrogen mass content is not more than 70×10 -6 , oxygen mass content is not more than 10×10 -6 .

[0059] As an optional embodiment of the present invention, in step S1, the temperature of the molten steel ladle is 1520-1550°C (for example, 1520°C, 1525°C, 1530°C, 1535°C, 1540°C, 1545°C or 1550°C, etc.), and argon gas protection is used to cast not less than 10t of electrode base material.

[0060] As an optional embodiment of the present invention, in step S1, the mold cooling time is 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0061] In conventional production, the electrode base material is usually subjected to stress relief annealing at a high temperature of 850-950°C. During this process, tissue stress will be generated, which can easily lead to deformation or cracking. The stress relief annealing temperature used in the present invention is different from the conventional one. As an optional embodiment of the present invention, in step S1, the stress relief annealing temperature is 775-825°C. When stress relief annealing is performed at this temperature, the electrode base material will not undergo phase change, so there is no tissue stress.

[0062] As an optional embodiment of the present invention, in step S1, stress relief annealing includes first charging the steel ingot into an annealing furnace and heating it to 775-825°C (for example, 775°C, 780°C, 785°C, 790°C, 800°C, 810°C, 820°C or 825°C, etc.), keeping it warm at an effective diameter of 100 mm / 4h, and then slowly cooling it to no higher than 200°C and air cooling it out of the furnace.

[0063] It should be noted that "insulation according to effective diameter 100mm / 4h" means that the insulation time for every 100mm of effective diameter is 4h. For example, if the effective diameter is 300mm, the insulation time is 12h. If the effective diameter is 500mm, the insulation time is 20h, and so on.

[0064] As an optional embodiment of the present invention, in step S1, in order to ensure the purity of the molten steel, the electrode base material is first subjected to a cutting treatment and a surface grinding treatment. The cutting treatment is used to cut off the part of the base material that is poorly compensated for shrinkage, so as to prevent foreign inclusions from mixing into the molten steel during the smelting process; the surface grinding treatment is used to obtain an electrode base material with good surface quality, so as to prevent surface oxide scale and foreign inclusions from contaminating the molten steel.

[0065] As an optional embodiment of the present invention, in step S2, the melting rate of vacuum arc melting is 8.0-12.0 kg / min. The inventors have found in practice that if the melting rate is too fast, the molten pool is deep, the alloy elements are severely segregated during the solidification process, and the equiaxed crystal band in the center of the ingot is wide and the quality is poor; if the melting rate is too slow, the molten pool does not obtain enough heat, and cold shut defects are generated on the surface of the ingot, affecting the surface quality. In severe cases, the ingot will be directly scrapped. When the surface defects generated on the surface of the ingot are not serious, although the surface quality may be improved by processing, after forging and heat treatment, there is basically no effect on the internal quality, but this cost is abnormally high. Therefore, the typical but non-limiting melting rates in the vacuum arc melting process are 8.0 kg / min, 8.5 kg / min, 9.0 kg / min, 9.5 kg / min, 10.0 kg / min, 10.5 kg / min, 11.0 kg / min, 11.5 kg / min or 12.0 kg / min, etc.

[0066] In step S2, in addition to limiting the melting rate of vacuum arc melting, the process conditions of the vacuum arc furnace used for vacuum arc melting are further optimized. The vacuum arc furnace adopts at least one of the following process parameters:

[0067] The vacuum degree is 0.1-0.3 mbar. Too high a vacuum degree will cause serious burning of volatile alloy elements, while too low a vacuum degree will affect the degassing and removal of inclusions. Therefore, the typical but non-restrictive vacuum degree is 0.1 mbar, 0.2 mbar, 0.3 mbar, etc.

[0068] The melting current is 15000-20000A, for example, 15000A, 16000A, 18000A or 20000A;

[0069] The melting voltage is 20 to 25 V, for example, 20 V, 21 V, 22 V, 24 V or 25 V.

[0070] As an optional embodiment of the present invention, in step S2, during the vacuum arc melting process, in order to obtain a steel ingot with better internal quality, the last 3 to 8% (for example, 3%, 4%, 5%, 6%, 7% or 8%, etc.) of the weight of the electrode base material ingot is subjected to shrinkage compensation to avoid the formation of larger shrinkage cavities in the last solidified part of the ingot.

[0071] As an optional embodiment of the present invention, in step S2, after the smelting is completed, mold cooling is first performed, and then stress relief annealing is performed, and the mold cooling time is 2 to 5 hours (for example, 2 hours, 3 hours, 4 hours or 5 hours, etc.).

[0072] Like the stress relief annealing temperature in step S1, the stress relief annealing temperature in step S2 is different from the stress relief annealing temperature (850-950°C) in conventional production. The stress relief annealing is performed at a relatively low temperature of 775-825°C (for example, 775°C, 780°C, 785°C, 790°C, 800°C, 810°C, 820°C or 825°C, etc.) to avoid deformation or cracking problems caused by the generation of new tissue stress.

[0073] As an optional embodiment of the present invention, in step S2, stress relief annealing includes firstly loading into an annealing furnace and heating to 775-825°C, keeping warm according to an effective diameter of 100 mm / 3h, and then slowly cooling to no higher than 200°C and air cooling out of the furnace.

[0074] It should be noted that "insulation according to effective diameter 100mm / 3h" means that the insulation time corresponds to 3h for every 100mm of effective diameter. For example, if the effective diameter is 300mm, the insulation time is about 9h. If the effective diameter is 500mm, the insulation time is about 15h, and so on.

[0075] As an optional embodiment of the present invention, in step S3, the high temperature homogenization treatment includes heating the steel ingot obtained in step S2 to 1260-1350°C (for example, 1260°C, 1270°C, 1280°C, 1290°C, 1300°C, 1310°C, 1320°C, 1340°C or 1350°C, etc.), keeping it warm at an effective diameter of 100 mm / 3h, and then cooling it with the furnace to 1150-1250°C (for example, 1150°C, 1160°C, 1180°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C or 1250°C, etc.).

[0076] High temperature homogenization treatment, especially high temperature homogenization treatment above 1260℃, can make various carbides fully melt, improve the original chemical composition and organization segregation of the steel ingot, and thus improve the quality of the steel ingot. If the high temperature homogenization treatment is lower than 1260℃, for example, 1200-1250℃, then various carbides may not be fully melted, the original chemical composition and organization of the steel ingot may be segregated, affecting the quality of the steel ingot.

[0077] In conventional production, forging adopts two-way back and forth upsetting, and the amount of each pressing is less than 25%, the core is difficult to compact, and there are defects such as looseness. The inventor has found through a lot of practice that the above problems can be effectively improved by improving the forging method, that is, introducing three-dimensional forging. As an optional embodiment of the present invention, in step S3, the three-dimensional forging includes using upper and lower large platforms to perform three-dimensional cross-large deformation upsetting forging, each time the amount of pressing is not less than 25-50% (for example, 25%, 28%, 30%, 35%, 40%, 42%, 45%, 48% or 50%, etc.), 90° flipping to press another plane, three planes are pressed down in sequence, the total forging ratio is not less than 8, and a forging with a thickness of 400-800mm and a width of 800-1300mm is obtained.

[0078] By further limiting the three-dimensional forging process parameters, the core of the forging can be fully deformed and the isotropy can be significantly improved.

[0079] As an optional embodiment of the present invention, in step S3, the forging obtained by three-dimensional forging is cooled in a water gap after forging, and the water cooling is stopped when the forging temperature reaches 450-500°C (450°C, 460°C, 470°C, 480°C, 490°C or 500°C, etc.), and after the above-mentioned water cooling, it is air-cooled to no more than 300°C, and then softening annealing treatment is performed.

[0080] As an optional embodiment of the present invention, in step S3, the softening annealing treatment includes heating the forging to 700-750°C (for example, 700°C, 710°C, 720°C, 730°C, 840°C or 850°C, etc.), and keeping the temperature at an effective diameter of 100 mm / 5h.

[0081] As an optional embodiment of the present invention, in step S4, the temperature of the solution treatment is 1000-1100°C (for example, 1000°C, 1020°C, 1040°C, 1050°C, 1060°C, 1080°C, or 1100°C, etc.).

[0082] As an optional embodiment of the present invention, in step S4, intermittent water entry is used during solution treatment, and the surface temperature of the forging is reduced to 500-600°C (for example, 500°C, 520°C, 540°C, 550°C, 560°C, 580°C or 600°C) for the first time, and the surface temperature of the forging is reduced to 300-350°C (for example, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C) for the second time, and the surface temperature of the forging is reduced to 150-200°C (for example, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C) for the third time.

[0083] "Interstitial water immersion" in solution treatment refers to quickly immersing the heated forgings in water, using the rapid cooling effect of water to inhibit the precipitation of the second phase, thereby obtaining the desired supersaturated solid solution structure (i.e., martensite and lower bainite structure).

[0084] Each time the forgings are taken out of the water, they must be air-cooled. When they are just out of the water, the surface temperature of the forgings is very low, and they need to be returned to a given temperature (i.e. the surface temperature of the forgings drops to 500-600°C for the first time, 300-350°C for the second time, and 150-200°C for the third time) before they are put into the water again. Air cooling and temperature measurement are performed between the water outflow and water inflow, and the next step is carried out after reaching the temperature.

[0085] By further limiting the process parameters in the solution treatment, it is ensured that as much martensite + lower bainite structure as possible is obtained, providing a good preparatory structure for the spheroidizing treatment.

[0086] As an optional embodiment of the present invention, in step S4, the isothermal spheroidizing treatment includes heating the forgings after the solution treatment to 840-890°C (for example, 840°C, 850°C, 860°C, 870°C, 880°C or 890°C, etc.), and cooling to 730-780°C (for example, 730°C, 740°C, 750°C, 760°C, 770°C or 780°C, etc.) at a speed of ≤30°C / h (for example, 30°C / h, 25°C / h, 20°C / h or 15°C / h, etc.), and then cooling to below 500°C in the furnace at a speed of ≤50°C / h (for example, 50°C / h, 40°C / h, 30°C / h or 20°C / h, etc.), and air cooling to room temperature after taking out of the furnace.

[0087] The large die-casting mold steel with a thickness of 400-800 mm and a width of 800-1300 mm obtained by the above method can meet the level 4 of GB / T6402-2008 standard for ultrasonic flaw detection; the non-metallic inclusions are not greater than level 0.5 according to the method A of GB / T10561-2023 standard; the oxygen content is not greater than 8×10 -6 、Nitrogen content measured according to GB / T20124-2006 is not more than 60×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is not less than 25J, and the transverse 7×10mm unnotched impact energy KW2 of the core is not less than 400J.

[0088] According to a third aspect of the present invention, there is also provided a die, which is made of the above-mentioned die-casting die steel or the die-casting die steel made by the above-mentioned manufacturing method.

[0089] In view of the advantages of the die-casting mold prepared by the present invention, it has good application prospects in the field of mold manufacturing.

[0090] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0091] Example 1

[0092] The present embodiment provides a large-size die-casting mold steel, in which the components are designed to include chemical components with the following mass percentages: C 0.36%, Si 0.20%, Mn 0.38%, Cr 5.10%, Mo1.95%, V 0.60%, Ni0.18%, and the rest are Fe and unavoidable residual elements and impurities.

[0093] The manufacturing method of the large-size die-casting die steel of this embodiment comprises the following steps:

[0094] S1. The ferroalloy (high carbon ferrochrome, low carbon ferrochrome, ferromolybdenum, ferrovanadium and ferronickel) is melted uniformly in an alloy melting furnace, and the tapping temperature is 1570°C;

[0095] The blast furnace molten iron and CrMo scrap steel are melted and dephosphorized in an electric furnace, with a phosphorus content of 0.002% and a tapping temperature of not less than 1640°C;

[0096] The molten steel from the alloy melting furnace and the electric furnace is added to the LF refining furnace for desulfurization to 0.002%, degassing, and inclusion removal, and then adjusted to the required composition;

[0097] Then RH cycle degassing treatment was carried out, and the nitrogen content was 70×10 -6 , oxygen content is 8×10 -6 ;

[0098] The temperature of the molten steel ladle is 1525℃, and argon gas is used to protect the casting of 12t electrode base material;

[0099] The mold cooling time is 8 hours, and then it is placed in an annealing furnace and heated to 800±25℃, kept warm for 33 hours, and then slowly cooled to 180℃ and air-cooled out of the furnace to obtain an electrode base material with good quality.

[0100] S2. The electrode base material is first subjected to cutting and surface grinding treatment, and then placed in a vacuum arc furnace for vacuum arc melting, with the melting rate controlled at 8-10 kg / min, the vacuum degree at 0.15 mbar, the melting current at 15000-16000 A, the melting voltage at 20-25 V, and the last 4% by weight of the electrode base material ingot is subjected to shrinkage compensation; after smelting, the mold cooling time is 3 hours, and then the electrode base material is placed in an annealing furnace and heated to 800±25°C, kept warm for 28 hours, and then slowly cooled to 180°C and air-cooled out of the furnace for stress relief annealing to obtain a steel ingot of good quality.

[0101] S3. The steel ingot is kept at 1300±10℃ for 28h for high temperature homogenization treatment, and then cooled to 1190±10℃ with the furnace; three-dimensional cross large deformation upsetting forging is carried out using upper and lower large platforms, with the pressing amount each time not less than 30-50%, and another plane is pressed by turning 90°. The three planes are pressed down in sequence, with a total forging ratio of 9, and then a forging with a thickness of 450mm and a width of 1100mm is obtained.

[0102] After forging, the forgings are cooled in a water gap. When the forging temperature reaches 450°C, water cooling is stopped and the forgings are air-cooled to 250°C. The forgings are placed in a gas annealing furnace and kept at 730±10°C for 34 hours for softening annealing treatment.

[0103] S4. The forgings after the above softening annealing treatment are solution treated at 1080℃, the temperature of the forgings entering water for the first time is reduced to 550℃, the temperature of the forgings entering water for the second time is reduced to 310℃, and the temperature of the forgings entering water for the third time is reduced to 160℃; then they are charged into a furnace for isothermal spheroidizing treatment, specifically, they are heated to 870±10℃, and cooled to 730±10℃ at a rate of ≤28℃ / h, and then furnace-cooled to below 400℃ at a rate of 48℃ / h, and air-cooled to room temperature after being taken out of the furnace to obtain large-size die-casting mold steel.

[0104] The ultrasonic flaw detection of the large die-casting mold steel prepared by the above method can meet and exceed the level 4 of GB / T6402-2008 standard, and there is no dense area with an equivalent diameter of 1mm, which indicates that the structure of each part of the mold steel is uniform and the mechanical properties are uniform; the non-metallic inclusions are tested according to the method A of GB / T10561-2023 standard, and the A (sulfide), B (alumina), C (silicate), D (spherical oxide), and Ds (large particle spherical oxide) are all level 0; the oxygen content is 4×10 -6 According to GB / T20124-2006, the nitrogen content is 32×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 32J, and the transverse 7×10mm unnotched impact energy KW2 of the core is 448J.

[0105] Example 2

[0106] The present embodiment provides a large-size die-casting mold steel, in which the components are designed to include chemical components with the following mass percentages: C 0.37%, Si 0.30%, Mn 0.50%, Cr 5.00%, Mo2.28%, V 0.50%, Ni0.40%, and the rest are Fe and unavoidable residual elements and impurities.

[0107] The manufacturing method of the large-size die-casting die steel of this embodiment comprises the following steps:

[0108] S1. The ferroalloy (high carbon ferrochrome, low carbon ferrochrome, ferromolybdenum, ferrovanadium and ferronickel) is melted uniformly in an alloy melting furnace, and the tapping temperature is 1560°C;

[0109] The blast furnace molten iron and CrMo scrap steel are melted and dephosphorized in an electric furnace, with a phosphorus content of 0.003% and a tapping temperature of not less than 1660°C;

[0110] The molten steel from the alloy melting furnace and the electric furnace is added to the LF refining furnace for desulfurization to 0.001%, degassing, and inclusion removal, and then adjusted to the required composition;

[0111] Then RH cycle degassing treatment was carried out, and the nitrogen content was 65×10 -6 , oxygen content is 7×10 -6 ;

[0112] The temperature of the molten steel ladle is 1535℃, and argon gas is used to cast 24t of electrode base material;

[0113] The mold cooling time is 12 hours, and then it is placed in an annealing furnace and heated to 800±25℃, kept warm for 44 hours, and then slowly cooled to 150℃ and air-cooled out of the furnace to obtain an electrode base material with good quality.

[0114] S2. The electrode base material is first subjected to cutting and surface grinding treatment, and then loaded into a vacuum arc furnace for vacuum arc melting, with the melting rate controlled at 10-12 kg / min, the vacuum degree at 0.20 mbar, the melting current at 16000-18000 A, the melting voltage at 20-25 V, and the last 6% by weight of the electrode base material ingot is subjected to shrinkage compensation; after smelting, the mold cooling time is 5 hours, and then the electrode base material is loaded into an annealing furnace and heated to 800±25°C, kept warm for 36 hours, and then slowly cooled to 180°C and air-cooled out of the furnace for stress relief annealing to obtain a steel ingot of good quality.

[0115] S3. The above steel ingot is kept at 1270±10℃ for 36h for high temperature homogenization treatment, and then cooled to 1230±10℃ with the furnace; three-dimensional cross large deformation upsetting forging is carried out using upper and lower large platforms, with the pressing amount each time not less than 25-40%, and another plane is pressed by 90° flipping, and the three planes are pressed down in sequence, with a total forging ratio of 11, and then a forging with a thickness of 700mm and a width of 1200mm is obtained.

[0116] After forging, the forgings are cooled in a water gap. When the forging temperature reaches 480°C, water cooling is stopped and the forgings are air-cooled to 280°C. The forgings are placed in a gas annealing furnace and kept at 720±10°C for 53 hours for softening annealing treatment.

[0117] S4. The forgings after the above softening annealing treatment are solution treated at 1030℃, the temperature of the forgings entering water for the first time is reduced to 580℃, the temperature of the forgings entering water for the second time is reduced to 330℃, and the temperature of the forgings entering water for the third time is reduced to 180℃; then they are charged into a furnace for isothermal spheroidizing treatment, specifically, heating to 850±10℃, and cooling to 740±10℃ at a rate of ≤25℃ / h, and then furnace cooling to below 300℃ at a rate of 42℃ / h, and air cooling to room temperature after being taken out of the furnace to obtain large-size die-casting mold steel.

[0118] The ultrasonic flaw detection of the large die-casting die steel prepared by the above method can meet and exceed the level 4 of GB / T6402-2008 standard, and there is no dense area with an equivalent diameter of 1mm, which indicates that the structure of each part of the die steel is uniform and the mechanical properties are uniform; the non-metallic inclusions are detected according to the A method of GB / T10561-2023 standard, among which the fine system of class D (spherical oxide type) is 0.5, and the other classes A (sulfide type), class B (alumina type), class C (silicate type), class D (spherical oxide type) coarse system and Ds (large particle spherical oxide type) are all 0; the oxygen content is 6×10 -6 According to GB / T20124-2006, the nitrogen content is 48×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 28J and the transverse 7×10mm unnotched impact energy KW2 of the core is 413J when tested in accordance with GB / T229-2020.

[0119] Example 3

[0120] This embodiment provides a large-size die-casting mold steel, and the content of each component in the steel is designed to be consistent with that in Example 1.

[0121] The manufacturing method of the large-size die-casting mold steel in this embodiment is the same as that in the first embodiment except that the melting rate of the vacuum arc melting is adjusted from 8 to 10 kg / min to 14 to 15 kg / min in step S2. The remaining manufacturing steps and process parameters are the same as those in the first embodiment.

[0122] The ultrasonic flaw detection of the large die-casting die steel prepared by the above method cannot meet the level 4 of GB / T6402-2008 standard, and there are local dense areas with an equivalent of φ1mm. The non-metallic inclusions are tested according to the method A of GB / T10561-2023 standard, and the A (sulfide), B (alumina), C (silicate), D (spherical oxide) and Ds (large particle spherical oxide) are all level 0. The oxygen content is 5×10 -6 According to GB / T20124-2006, the nitrogen content is 30×10-6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 23J and the transverse 7×10mm unnotched impact energy KW2 of the core is 362J when tested in accordance with GB / T229-2020.

[0123] Comparative Example 1

[0124] This comparative example provides a large-size die-casting die steel, except that its chemical composition does not contain Ni, the contents of other components are designed to be consistent with those of Example 1.

[0125] The manufacturing method of the large-size die-casting mold steel in this comparative example is the same as that of Example 1 except that the iron alloy in step S1 does not contain nickel iron. The remaining manufacturing steps and process parameters are the same as those of Example 1.

[0126] The ultrasonic flaw detection of the large die-casting die steel prepared by the above method can meet and exceed the level 4 of GB / T6402-2008 standard, and there is no dense area with an equivalent diameter of 1mm; the non-metallic inclusions are tested according to the method A of GB / T10561-2023 standard, and the types A (sulfide), B (alumina), C (silicate), D (spherical oxide) and Ds (large particle spherical oxide) are all level 0; the oxygen content is 5×10 -6 According to GB / T20124-2006, the nitrogen content is 30×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 23J and the transverse 7×10mm unnotched impact energy KW2 of the core is 380J when tested in accordance with GB / T229-2020.

[0127] Comparative Example 2

[0128] This comparative example provides a large-size die-casting mold steel. Except for the Ni content, the contents of other components are designed to be consistent with those in Example 1, including the following chemical components in mass percentage: C 0.36%, Si 0.20%, Mn 0.38%, Cr 5.10%, Mo 1.95%, V 0.60%, Ni 1.00%, and the rest are Fe and unavoidable residual elements and impurities.

[0129] The ultrasonic flaw detection of the large die-casting mold steel prepared by the above method cannot meet the level 4 of GB / T6402-2008 standard, mainly because the Ni content is too high, which makes the steel ingot prone to white spot defects; the non-metallic inclusions are tested according to the A method of GB / T10561-2023 standard, and the A (sulfide), B (alumina), C (silicate), D (spherical oxide) and Ds (large particle spherical oxide) are all level 0; the oxygen content is 7×10 -6 According to GB / T20124-2006, the nitrogen content is 46×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 20J and the transverse 7×10mm unnotched impact energy KW2 of the core is 354J when tested in accordance with GB / T229-2020.

[0130] Comparative Example 3

[0131] This comparative example provides a large-size die-casting mold steel. Except for the Ni content, the contents of other components are designed to be consistent with those in Example 1, including the following chemical components in mass percentage: C 0.36%, Si 0.20%, Mn 0.38%, Cr 5.10%, Mo 1.95%, V 0.60%, Ni0.05%, and the rest are Fe and unavoidable residual elements and impurities.

[0132] The ultrasonic flaw detection of the large die-casting die steel prepared by the above method can meet and exceed the level 4 of GB / T6402-2008 standard, and there is no dense area with an equivalent diameter of 1mm; the non-metallic inclusions are tested according to the method A of GB / T10561-2023 standard, and the types A (sulfide), B (alumina), C (silicate), D (spherical oxide) and Ds (large particle spherical oxide) are all level 0; the oxygen content is 5×10 -6 According to GB / T20124-2006, the nitrogen content is 30×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 21J and the transverse 7×10mm unnotched impact energy KW2 of the core is 389J when tested in accordance with GB / T229-2020.

[0133] Comparative Example 4

[0134] This comparative example provides a large-size die-casting mold steel, in which the components are designed to include the following chemical compositions in mass percentage: C 0.36%, Si 0.20%, Mn 0.38%, Cr 5.10%, Mo1.95%, V 0.60%, Ni0.18%, and the rest are Fe and unavoidable residual elements and impurities.

[0135] The manufacturing method of the large-size die-casting die steel of this comparative example comprises the following steps:

[0136] S1. The ferroalloy (high carbon ferrochrome, low carbon ferrochrome, ferromolybdenum, ferrovanadium and ferronickel) is melted uniformly in an alloy melting furnace, and the tapping temperature is 1570°C;

[0137] The blast furnace molten iron and CrMo scrap steel are melted and dephosphorized in an electric furnace, with a phosphorus content of 0.002% and a tapping temperature of not less than 1640°C;

[0138] The molten steel from the alloy melting furnace and the electric furnace is added to the LF refining furnace for desulfurization to 0.002%, degassing, and inclusion removal, and then adjusted to the required composition;

[0139] Then RH cycle degassing treatment was carried out, and the nitrogen content was 70×10 -6 , oxygen content is 8×10 -6 ;

[0140] The temperature of the molten steel ladle is 1525℃, and argon gas is used to protect the casting of 12t electrode base material;

[0141] The mold cooling time is 8h, then it is placed in an annealing furnace and heated to 800±25℃, kept warm for 33h, and then slowly cooled to 180℃ and air-cooled to obtain the electrode base material.

[0142] S2. The electrode base material is first subjected to cutting and surface grinding treatment, and then loaded into a vacuum arc furnace for vacuum arc melting, with the melting rate controlled at 8-10 kg / min, the vacuum degree at 0.15 mbar, the melting current at 15000-16000 A, the melting voltage at 20-25 V, and the last 4% by weight of the electrode base material ingot is subjected to shrinkage compensation; after smelting, the mold cooling time is 3 hours, and then the electrode base material is loaded into an annealing furnace and heated to 800±25°C, kept warm for 28 hours, and then slowly cooled to 180°C and air-cooled out of the furnace for stress relief annealing to obtain a steel ingot.

[0143] S3. The steel ingot is kept at 1220±10℃ for 28h for high temperature homogenization treatment, and then cooled to 1190±10℃ in the furnace; two-way back and forth upsetting is adopted, and the reduction amount each time is less than 25%, and then a forging with a thickness of 450mm and a width of 1100mm is obtained.

[0144] After forging, the forgings are cooled in a water gap. When the forging temperature reaches 450°C, water cooling is stopped and the forgings are air-cooled to 250°C. The forgings are placed in a gas annealing furnace and kept at 730±10°C for 34 hours for softening annealing treatment.

[0145] S4. The forgings after the above softening annealing treatment are solution treated at 1080℃, the temperature of the forgings entering water for the first time is reduced to 550℃, the temperature of the forgings entering water for the second time is reduced to 310℃, and the temperature of the forgings entering water for the third time is reduced to 160℃; then they are charged into a furnace for isothermal spheroidizing treatment, specifically, they are heated to 870±10℃, and cooled to 730±10℃ at a rate of ≤28℃ / h, and then furnace-cooled to below 400℃ at a rate of 48℃ / h, and air-cooled to room temperature after being taken out of the furnace to obtain large-size die-casting mold steel.

[0146] The ultrasonic flaw detection of the large die-casting die steel prepared by the above method cannot meet the GB / T6402-2008 standard level 4, and there are φ3mm point defects in some parts that exceed the standard; the non-metallic inclusions are tested according to the GB / T10561-2023 standard A method, and the A (sulfide), B (alumina), C (silicate), D (spherical oxide) and Ds (large particle spherical oxide) are all level 0; the oxygen content is 7×10 -6 According to GB / T20124-2006, the nitrogen content is 40×10 -6 ; The Rockwell hardness is tested in accordance with GB / T230.1-2020. At a hardness of 45±1HRC, the transverse V-type impact energy KV2 of the core is 20J and the transverse 7×10mm unnotched impact energy KW2 of the core is 366J when tested in accordance with GB / T229-2020.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A die-casting die steel, characterized in that: The chemical composition includes the following mass fractions: C 0.33-0.40%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr 4.80-5.50%, Mo 1.90-2.60%, V 0.40-1.00%, Ni 0.10-0.80%, and the rest are Fe and unavoidable impurities.

2. The die-casting die steel according to claim 1, characterized in that: The chemical composition includes the following mass fractions: C 0.33-0.40%, Si 0.10-0.50%, Mn 0.30-0.70%, Cr 4.80-5.50%, Mo 1.90-2.30%, V 0.40-0.80%, Ni 0.10-0.80%, and the rest are Fe and unavoidable impurities.

3. The method for manufacturing a die casting die steel according to claim 1 or 2, characterized in that: The following steps are involved: S1. The raw material of the die-casting die steel is smelted, LF refined and RH degassed, and then cast under argon protection to obtain an electrode base material; the electrode base material is then subjected to mold cooling, stress relief annealing and surface grinding treatment; wherein the stress relief annealing temperature is 775 to 825°C; S2. The electrode base material after the surface grinding treatment in step S1 is subjected to vacuum arc melting to obtain a steel ingot; and then the steel ingot is subjected to stress relief annealing; wherein the stress relief annealing temperature is 775 to 825°C; S3. The steel ingot after stress relief annealing in step S2 is subjected to high temperature homogenization treatment and three-dimensional forging to obtain a forging; and then the forging is subjected to softening annealing treatment; S4. The forgings after the softening annealing treatment in step S3 are subjected to solution treatment and isothermal spheroidizing treatment to obtain die casting die steel.

4. The method for manufacturing die-casting die steel according to claim 3, characterized in that: In step S1, the raw materials include blast furnace molten iron, ferroalloy and CrMo scrap steel; And / or, in step S1, the mold cooling time is 8 to 12 hours; And / or, in step S1, the stress relief annealing includes firstly placing the steel into an annealing furnace and heating it to 775-825°C, keeping the temperature at an effective diameter of 100 mm / 4h, and then slowly cooling it to no higher than 200°C and air cooling it out of the furnace.

5. The method for manufacturing die-casting die steel according to claim 3, characterized in that: In step S2, the melting rate of vacuum arc melting is 8.0-12.0 kg / min; And / or, in step S2, the process conditions of the vacuum arc furnace used for vacuum arc melting include at least one of the following process parameters: vacuum degree of 0.1-0.3 mbar; melting current of 15000-20000 A; melting voltage of 20-25 V; And / or, in step S2, during the vacuum arc melting process, the last 3 to 8% by weight of the electrode base material ingot is subjected to shrinkage feeding.

6. The method for manufacturing die-casting die steel according to claim 3, characterized in that: In step S2, after the smelting is completed, mold cooling is first performed, and then stress relief annealing is performed, and the mold cooling time is 2 to 5 hours; And / or, in step S2, the stress relief annealing includes firstly placing the steel into an annealing furnace and heating it to 775-825°C, keeping the temperature at an effective diameter of 100 mm / 3h, and then slowly cooling it to no higher than 200°C and air cooling it out of the furnace.

7. The method for manufacturing die-casting die steel according to claim 3, characterized in that: In step S3, the high temperature homogenization treatment includes heating the steel ingot obtained in step S2 to 1260-1350° C., keeping the temperature at an effective diameter of 100 mm / 3 h, and then cooling it to 1150-1250° C. with the furnace; And / or, in step S3, the three-dimensional forging includes using upper and lower large platforms to perform three-dimensional cross large deformation upsetting forging, each pressing amount is not less than 25-50%, 90° flipping to press another plane, three planes are pressed down in sequence, and the total forging ratio is not less than 8; And / or, in step S3, the forging obtained by three-dimensional forging is cooled in a water gap after forging, the water cooling is stopped when the surface temperature of the forging reaches 450-500°C, air-cooled to no more than 300°C, and then softened and annealed; And / or, in step S3, the softening annealing treatment includes heating the forging to 700-750° C. and keeping the temperature at an effective diameter of 100 mm / 5 h.

8. The method for manufacturing die-casting die steel according to claim 3, characterized in that: In step S4, the temperature of the solution treatment is 1000-1100°C; And / or, the solid solution treatment is performed by intermittent water entry, the surface temperature of the forging is reduced to 500-600°C for the first water entry, the surface temperature of the forging is reduced to 300-350°C for the second water entry, and the surface temperature of the forging is reduced to 150-200°C for the third water entry; And / or, the isothermal spheroidizing treatment includes heating the forgings after solution treatment to 840-890°C in a furnace, cooling to 730-780°C at a rate of ≤30°C / h, then cooling to below 500°C at a rate of ≤50°C / h, and air cooling to room temperature after taking out of the furnace.

9. The method for manufacturing a die-casting die steel according to any one of claims 3 to 8, characterized in that: For large die-casting die steel with a thickness of 400-800mm and a width of 800-1300mm, its ultrasonic flaw detection can meet the GB / T6402-2008 standard level 4; And / or, non-metallic inclusions are tested according to GB / T10561-2023 standard A method and are not greater than level 0.5; and / or, oxygen content is not more than 8×10 -6 , nitrogen content is not more than 60×10 -6 ; And / or, at a hardness of 45±1HRC, the transverse V-shaped impact energy KV2 of the core shall not be less than 25J, and the transverse 7×10mm unnotched impact energy KW2 of the core shall not be less than 400J.

10. A mold, characterized in that: The die-casting die steel is made of the die-casting die steel described in claim 1 or 2 or the die-casting die steel produced by the manufacturing method described in any one of claims 3-9.