Modified high-carbon alloy steel as well as preparation method and application thereof

Abstract

The invention discloses modified high-carbon alloy steel and a preparation method and application thereof, and belongs to the technical field of high-carbon alloy steel for aluminum alloy forming dies. The preparation method disclosed by the invention comprises the following steps: carrying out electroslag remelting on a high-carbon alloy steel rod to obtain a casting blank; carrying out thermoplastic deformation on the casting blank to obtain a blank; the blank is annealed, so that carbides in the blank are eliminated or become fine particles, spherical graphite can be separated out, and the modified high-carbon alloy steel is obtained; the particle size of the fine particles is smaller than 10 microns. According to the method, coarse and large carbides which are difficult to eliminate in the high-carbon aluminum alloy forming die steel containing strong carbide forming elements such as Cr, Mo and V or medium-strong carbide forming elements are subjected to rapid and basic graphitization through a thermoplastic deformation and high-temperature graphitization combined process; the technical problem that carbide decomposition and graphite precipitation control are difficult to realize in the existing method is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of high-carbon alloy steel for aluminum alloy forming dies, specifically relating to a modified high-carbon alloy steel, its preparation method, and its application. Background Technology

[0002] There are two main types of aluminum alloy forming molds: extrusion forming and die casting forming. These two types of molds for forming aluminum alloys typically operate at around 500℃ and must withstand significant loads and intense friction during service (especially for extrusion molds). Therefore, aluminum alloy forming molds require good high-temperature strength, good toughness, high high-temperature hardness, heat resistance, and thermal conductivity. Simultaneously, to prevent aluminum adhesion during extrusion, reduce friction with the workpiece, and resist the erosion of the mold surface by molten aluminum during die casting, the molds also need excellent anti-aluminum adhesion properties, resistance to molten aluminum corrosion, and a low coefficient of friction with aluminum. To ensure the high-temperature strength, high-temperature hardness, wear resistance, and heat resistance required for steel molds during service, metallurgical theory dictates that mold steel needs to be alloyed with carbide-forming elements such as Cr, Mo, and V to improve thermal stability. The dispersed precipitation of carbides formed by these alloying elements enhances the mold's high-temperature strength, hardness, heat resistance, and wear resistance. Furthermore, to guarantee the mold's resistance to aluminum adhesion, resistance to molten aluminum corrosion, thermal conductivity, and low coefficient of friction with aluminum during service, materials science knowledge indicates that the presence of a graphite phase in the steel microstructure achieves these objectives. Therefore, steel containing alloying elements such as Cr, Mo, and V, and with a microstructure containing both carbides and numerous fine graphite spheres, is an ideal material for manufacturing aluminum alloy forming molds with high service performance and long service life.

[0003] Carbides in steel will form in the presence of carbon (C) and carbide-forming elements such as Cr, Mo, V, and W, according to the theory of phase formation in steel. However, graphite spheres in steel can only be formed through graphitization—first, the carbon in the steel forms carbides, and then the carbides decompose to form graphite. When steel contains medium- to strong carbide-forming elements such as Cr, Mo, and V, the time required for general thermal decomposition of carbides to form graphite is very long. For example, in traditional white cast iron containing only the weak carbide-forming element Fe and a relatively high amount of Si, a graphitizing element that promotes C graphitization, the time required for the free carbides (a collective term for primary and secondary carbides) to undergo thermal decomposition and graphitization at a temperature of 900–950°C is 60–80 hours. For steel, the Si content, a graphitizing element, is generally lower than that in cast iron. If the steel also contains medium- or strong carbide-forming elements such as Cr, Mo, and V, which stabilize carbides, the time required for complete graphitization of secondary carbides in the steel will be longer than that required for complete graphitization of carbides in white cast iron. For example, in experiments, for ductile iron with a composition of 3.6% C, 1.0~1.5% Mn, 0.5~1.0% Ni, 0.5~1.0% Cr, 1.5~2.5% Mo, 2.0% Si, 0.5~1.0% V, and the remainder being Fe and unavoidable impurities, even under conditions of holding at 1100℃ for 50 hours, a considerable portion of coarse free carbides failed to graphitize completely (see Appendix). Figure 2 Furthermore, the morphology of undecomposed carbides is undesirable (spherical or near-spherical morphology is preferred). Coarse free carbides are detrimental to improving the strength and toughness of steel and increasing the number of graphite spheres (thus improving the steel's resistance to aluminum melt corrosion and aluminum adhesion); at the same time, the long graphitization time of up to 50 hours is also detrimental to improving production efficiency and reducing production costs. Therefore, exploring methods to accelerate the decomposition of carbides in steel, while achieving controllable precipitation of graphite to obtain fine, high-density, and highly spherical graphite spheres, has important practical significance and economic value for the application of steel for aluminum alloy forming dies and for improving the service performance and lifespan of the corresponding dies. Summary of the Invention

[0004] The purpose of this invention is to provide a modified high-carbon alloy steel, its preparation method, and its application, in order to solve the technical problem that existing methods are difficult to achieve carbide decomposition while simultaneously controlling graphite precipitation.

[0005] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing modified high-carbon alloy steel, comprising the following steps: High-carbon alloy steel billets are electroslag remelted to obtain cast billets; The billet is subjected to thermoplastic deformation to obtain the billet material; Annealing the billet eliminates carbides or turns them into fine particles, and precipitates spherical graphite to obtain modified high-carbon alloy steel; the particle size of the fine particles is less than 10 μm.

[0006] Furthermore, by mass percentage, the composition of the high-carbon alloy steel bar satisfies: 1.3~1.6%C, 1.0~1.5%Si, 1.0~1.5%Mn, 0.5~1.0%Cr, 0.5~1.5%Ni, 1.5~2.5%Mo, 0.5~1.0%V, with the remainder being Fe and unavoidable impurities.

[0007] Furthermore, the composition of the billet, by mass percentage, satisfies the following: 1.3~1.6%C, 1.0~1.5%Si, 1.0~1.5%Mn, 0.5~1.0%Cr, 0.5~1.5%Ni, 1.5~2.5%Mo, 0.5~1.0%V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities.

[0008] Furthermore, the billet of the electroslag remelted casting is discharged from the furnace at a temperature of 900~1000℃, and immediately after being discharged from the furnace, it is placed in a heating furnace at a temperature of 550~600℃ and kept at that temperature for 4~6 hours, and then cooled to room temperature with the furnace.

[0009] Furthermore, the billet is subjected to thermoplastic deformation. The billet is heated to 980~1030℃ in an atmosphere furnace with a carbon potential of not less than 1.6 and held for 0.5~1h before thermoplastic deformation.

[0010] Furthermore, the thermoplastic deformation is performed sequentially in three directions, with at least two thermal deformation cycles in each direction, and each deformation amount is at least 40%, with a strain rate of 0.1~10 s⁻¹. -1 The total forging ratio is 4~8.

[0011] Furthermore, during the triaxial sequential thermoplastic deformation, if the forging temperature drops to 850℃ and the total forging ratio requirement is not met, the forging needs to be placed back into an atmosphere furnace at a temperature of 980~1030℃ and held for 0.5~1h before proceeding with the subsequent thermoplastic deformation according to the thermoplastic deformation requirements.

[0012] Furthermore, the billet that has completed thermoplastic deformation is immediately placed in a reducing atmosphere furnace at 950~1000℃ and held for 8~15 hours, then cooled to 600~650℃ for 8~10 hours, and then removed from the furnace and air-cooled to room temperature.

[0013] The present invention also discloses a modified high-carbon alloy steel prepared by the above preparation method.

[0014] The present invention also discloses the application of the above-mentioned modified high-carbon alloy steel in the preparation of aluminum alloy forming dies.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing modified high-carbon alloy steel. Through high-temperature plastic deformation, coarse carbides in cast aluminum alloy forming die steel are refined and uniformly distributed in the matrix. Simultaneously, plastic deformation refines the crystals, increases the number of grain boundaries, and generates numerous dislocations in the metal matrix, providing rapid pathways for the diffusion of C and alloy atoms during the subsequent high-temperature graphitization process. Furthermore, the grain boundaries and dislocations formed during plastic deformation provide more nucleation sites and favorable conditions for graphite formation during the volume expansion graphitization process, thereby accelerating the carbide decomposition and graphite precipitation. This method removes coarse, difficult-to-eliminate carbides in high-carbon aluminum alloy forming die steel containing strong or medium-strong carbide-forming elements such as Cr, Mo, and V through high-temperature plastic deformation. The combination of plastic deformation and high-temperature graphitization process enables rapid and near-fundamental graphitization. Simultaneously, it refines the size and sphericity of the resulting graphite spheres, transforming the previously coarse and irregularly shaped graphite obtained solely through thermal decomposition into fine, high-density, and more spherical graphite. This significantly simplifies the manufacturing process of the aluminum alloy forming die steel, substantially reduces the manufacturing cost of the steel and its dies, and significantly improves the strength, toughness, hardness, thermal stability, resistance to aluminum melt corrosion, and resistance to aluminum adhesion of the aluminum alloy forming die steel. Consequently, it significantly improves the service performance of the aluminum alloy forming dies made of this steel, greatly extends the service life of the dies, and reduces the manufacturing cost. This has significant implications for the advancement and application of aluminum alloy die preparation technology and aluminum alloy forming technology. Attached Figure Description

[0016] Figure 1 The image shows the metallographic microstructure of the modified high-carbon alloy steel prepared according to this invention. Figure 2 The image shows the microstructure of a Mo and V-containing ductile iron sample obtained by air cooling after holding at 1100℃ for 50 hours. Detailed Implementation

[0017] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0018] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0019] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0020] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0021] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0022] This invention refines coarse carbides in cast aluminum alloy forming die steel through high-temperature plastic deformation, distributing them evenly within the matrix. Simultaneously, plastic deformation refines the crystal structure, increases the number of grain boundaries, and generates numerous dislocations in the metal matrix, providing rapid pathways for the diffusion of carbon and alloy atoms during the subsequent high-temperature graphitization process. Furthermore, the grain boundaries and dislocations formed during plastic deformation provide more nucleation sites and favorable conditions for graphite formation during the volume expansion graphitization process, thereby accelerating carbide decomposition and graphite precipitation. Simultaneously, the refinement and uniform distribution of carbides within the matrix through plastic deformation is beneficial for the subsequent in-situ decomposition of carbides into graphite, and for controlling the size and shape of graphite spheres. The increased nucleation sites provided by plastic deformation for graphite formation further contribute to the refinement and uniform distribution of precipitated graphite. Therefore, by subjecting as-cast aluminum alloy forming die steel to appropriate plastic deformation at suitable temperatures, the decomposition of carbides in the as-cast aluminum alloy forming die steel can be accelerated and the graphite precipitation can be controlled, resulting in fine, high-density, and highly spherical graphite. This allows for the efficient and low-cost preparation of aluminum alloy die-casting die steel with no coarse free carbides and a large number of fine graphite spheres in its microstructure.

[0023] First, in a medium-frequency induction melting furnace, a mold steel billet with the following alloy composition is smelted and prepared: 1.3~1.6% C, 1.0~1.5% Si, 1.0~1.5% Mn, 0.5~1.0% Cr, 0.5~1.5% Ni, 1.5~2.5% Mo, 0.5~1.0% V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities (unless otherwise specified, all percentages in this document are by mass). Then, the billet is purified of S, P, and other impurity elements using electroslag remelting technology to obtain a mold steel billet with S<0.02% and P<0.025%. The billet is heated to 980~1030℃ in a controlled atmosphere furnace and held for 0.5~1h. Then, it is subjected to straining in three directions at a rate of 0.1~10 on a press. S-1, plastic deformation with a total forging ratio of 4~8, followed by holding in a reducing atmosphere furnace at 950~1000℃ for 8~15 hours (depending on the workpiece size), then cooling to 600~650℃ for 8~10 hours before air cooling to room temperature, completes the rapid decomposition of carbides and the controllable graphitization precipitation of carbon in the steel. This process eliminates carbides in the original billet that could not be eliminated even after holding at 1100℃ for 50 hours, effectively decomposing them into fine spherical graphite under the above conditions. Simultaneously, it avoids the irregular graphite formed under thermal decomposition conditions (instead, the graphite appears primarily as fine spherical shapes). This solves the problems of high heat treatment costs and high performance improvement costs for high-carbon alloy steel used in aluminum alloy forming die steel, which are caused by the difficulty in eliminating carbides in aluminum alloy forming die steel through graphitization and the uncontrollable graphite morphology resulting from conventional graphitization treatment.

[0024] This invention discloses a method for preparing modified high-carbon alloy steel, specifically comprising the following steps: S1: A high-carbon alloy steel billet for preparing aluminum alloy forming dies; S2: Electroslag remelting of high-carbon alloy steel billets to obtain castings of mold steel; S3: Perform thermoplastic deformation on the cast billet to obtain the blank for the mold; S4: Annealing the thermoplastically deformed billet eliminates carbides in the mold steel billet after thermoplastic deformation, turning them into particles with a diameter of less than 10 μm; at the same time, a large number of fine, small-spaced spherical graphite are precipitated, thereby eliminating the precipitation of carbides and graphite spheres in the steel, and thus improving the service performance of the steel / mold and increasing the service life of the mold.

[0025] Preferably, in S1, the composition of the high-carbon alloy steel bar satisfies: 1.3~1.6%C, 1.0~1.5%Si, 1.0~1.5%Mn, 0.5~1.0%Cr, 0.5~1.5%Ni, 1.5~2.5%Mo, 0.5~1.0%V, with the remainder being Fe and unavoidable impurities.

[0026] Preferably, in S2, the composition of the billet satisfies: 1.3~1.6%C, 1.0~1.5%Si, 1.0~1.5%Mn, 0.5~1.0%Cr, 0.5~1.5%Ni, 1.5~2.5%Mo, 0.5~1.0%V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities.

[0027] Preferably, in S2, the billet of the electroslag remelted casting is discharged from the furnace at a temperature of 900~1000℃. After being discharged from the furnace, it is immediately placed in a heating furnace at a temperature of 550~600℃ and kept at that temperature for 4~6 hours. Then, it is cooled to room temperature with the furnace to prevent the billet from cracking during the cooling process.

[0028] Preferably, before thermoplastic deformation of the billet, the billet needs to be heated to 980~1030℃ in an atmosphere furnace with a carbon potential of not less than 1.6 and held for 0.5~1h before thermoplastic deformation of the billet.

[0029] Preferably, the hot plastic deformation of the cast billet needs to be carried out sequentially in three directions, with no less than two hot deformations in each direction, and the deformation amount in each deformation being no less than 40%, with a strain rate of 0.1~10 s. -1 The total forging ratio is 4~8.

[0030] Preferably, when the forging temperature drops to 850°C and the total forging ratio requirement is not met, the forging needs to be placed back into an atmosphere furnace at a temperature of 980~1030°C and held for 0.5~1h before proceeding with the subsequent thermoplastic deformation according to the above-mentioned thermoplastic deformation requirements.

[0031] Preferably, the billet that has completed thermoplastic deformation is immediately placed in a reducing atmosphere furnace at 950~1000℃ and kept at that temperature for 8~15 hours, then cooled to 600~650℃ for 8~10 hours, and then removed from the furnace and air-cooled to room temperature.

[0032] like Figure 1 As shown, after the above steps, the carbides in the steel billet for the mold are basically eliminated / become particles with a particle size of less than 10 μm; at the same time, a large amount of fine, small-spaced spherical graphite is precipitated.

[0033] This invention utilizes a thermoplastic transformation combined with high-temperature graphitization to rapidly and efficiently eliminate coarse, difficult-to-remove carbides in high-carbon aluminum alloy forming die steel containing strong or medium-strong carbide-forming elements such as Cr, Mo, and V. Simultaneously, it improves the production of coarse, unevenly distributed, and poorly shaped graphite from thermally decomposed carbides, controlling the precipitation of fine, high-density, uniformly distributed, and highly spherical graphite. This has significant practical implications for the efficient and economical preparation of aluminum alloy forming die steel and aluminum alloy forming dies with excellent service performance and long service life.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0036] Example 1 A method for preparing modified high-carbon alloy steel, which achieves rapid elimination of carbides and controllable precipitation of graphite spheres in high-carbon alloy steel, specifically includes the following steps: S1: A high-carbon alloy steel billet for preparing aluminum alloy forming dies; S2: Electroslag remelting of high-carbon alloy steel billets to obtain castings of mold steel; S3: Perform thermoplastic deformation on the cast billet to obtain the blank for the mold; S4: Annealing the thermoplastically deformed billet to basically eliminate / replace the carbides in the mold steel billet after thermoplastic deformation into particles with a particle size of less than 10um; at the same time, a large number of fine, small-spaced spherical graphite are precipitated, thereby eliminating the precipitation of carbides and graphite spheres in the steel, and thus achieving the purpose of improving the service performance of the steel / mold and increasing the service life of the mold. In S1, the composition of the high-carbon alloy steel bar for aluminum alloy forming dies meets the following requirements: 1.3%C, 1.0%Si, 1.0%Mn, 0.5%Cr, 0.5%Ni, 1.5%Mo, 0.5%V, with the remainder being Fe and unavoidable impurities. In S2, the composition of the high-carbon alloy steel billet for aluminum alloy forming molds meets the following requirements: 1.3%C, 1.0%Si, 1.0%Mn, 0.5%Cr, 0.5%Ni, 1.5%Mo, 0.5%V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities; In S2, the billet of the electroslag remelted casting is delivered at a temperature of 900℃. After being delivered, it is immediately placed in a heating furnace at a temperature of 550℃ and kept at that temperature for 4 hours. Then, it is cooled to room temperature with the furnace to prevent the billet from cracking during the cooling process. In S3, before the billet undergoes thermoplastic deformation, it needs to be heated to 980°C in an atmosphere furnace with a carbon potential of not less than 1.6 and held for 0.5 hours before thermoplastic deformation is performed. In S3, the hot plastic deformation of the billet needs to be carried out sequentially in three directions, with each direction undergoing hot deformation twice, and each deformation amount being 40%, with a strain rate of 0.1 s⁻¹. -1 The total forging ratio is 4; In S3, when the forging temperature drops to 850℃ and the total forging ratio requirement is not met, the forging needs to be placed back into an atmosphere furnace at 980℃ for 0.5h and then subjected to subsequent thermoplastic deformation according to the above-mentioned thermoplastic deformation requirements. In S4, the billet that has completed thermoplastic deformation is immediately placed in a reducing atmosphere furnace at 950°C and held for 8 hours, then cooled to 600°C for 8 hours, and then taken out of the furnace and air-cooled to room temperature to obtain modified high-carbon alloy steel. After optimization and the above steps, the carbides in the steel billet for the mold are basically eliminated / become particles with a particle size of less than 10 μm; at the same time, a large amount of fine, closely spaced and highly rounded spherical graphite is precipitated.

[0037] Example 2 A method for preparing modified high-carbon alloy steel, which achieves rapid elimination of carbides and controllable precipitation of graphite spheres in high-carbon alloy steel, specifically includes the following steps: S1: A high-carbon alloy steel billet for preparing aluminum alloy forming dies; S2: Electroslag remelting of high-carbon alloy steel billets to obtain castings of mold steel; S3: Perform thermoplastic deformation on the cast billet to obtain the blank for the mold; S4: Annealing the thermoplastically deformed billet to basically eliminate / replace the carbides in the mold steel billet after thermoplastic deformation into particles with a particle size of less than 10um; at the same time, a large number of fine, small-spaced spherical graphite are precipitated, thereby eliminating the precipitation of carbides and graphite spheres in the steel, and thus achieving the purpose of improving the service performance of the steel / mold and increasing the service life of the mold. In S1, the composition of the high-carbon alloy steel bar for aluminum alloy forming dies meets the following requirements: 1.6%C, 1.5%Si, 1.5%Mn, 1.0%Cr, 1.5%Ni, 2.5%Mo, 1.0%V, with the remainder being Fe and unavoidable impurities. In S2, the composition of the high-carbon alloy steel billet for aluminum alloy forming molds meets the following requirements: 1.6%C, 1.5%Si, 1.5%Mn, 1.0%Cr, 1.5%Ni, 2.5%Mo, 1.0%V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities; In S2, the billet of the electroslag remelted casting is discharged from the furnace at a temperature of 1000℃. After being discharged from the furnace, it is immediately placed in a heating furnace at a temperature of 600℃ and kept at that temperature for 6 hours. Then it is cooled to room temperature with the furnace to prevent the billet from cracking during the cooling process. In S3, before the billet undergoes thermoplastic deformation, it needs to be heated to 1030℃ in an atmosphere furnace with a carbon potential of not less than 1.6 and held for 0.1h before the billet undergoes thermoplastic deformation. In S3, the hot plastic deformation of the billet needs to be carried out sequentially in three directions, with each direction undergoing hot deformation three times, and each deformation amount being 50%, with a strain rate of 10 s. -1 The total forging ratio is 8; In S3, when the forging temperature drops to 850℃ and the total forging ratio requirement is not met, the forging needs to be placed back into an atmosphere furnace at 1030℃ for 1 hour and then subjected to subsequent thermoplastic deformation according to the above-mentioned thermoplastic deformation requirements. In S4, the billet that has completed thermoplastic deformation is immediately placed in a reducing atmosphere furnace at 1000℃ and held for 15 hours, then cooled to 650℃ for 10 hours, and then taken out of the furnace and air-cooled to room temperature to obtain modified high-carbon alloy steel. After optimization and the above steps, the carbides in the steel billet for the mold are basically eliminated / become particles with a particle size of less than 10 μm; at the same time, a large amount of fine, closely spaced and highly rounded spherical graphite is precipitated.

[0038] Example 3 A method for preparing modified high-carbon alloy steel, which achieves rapid elimination of carbides and controllable precipitation of graphite spheres in high-carbon alloy steel, specifically includes the following steps: S1: A high-carbon alloy steel billet for preparing aluminum alloy forming dies; S2: Electroslag remelting of high-carbon alloy steel billets to obtain castings of mold steel; S3: Perform thermoplastic deformation on the cast billet to obtain the blank for the mold; S4: Annealing the thermoplastically deformed billet to basically eliminate / replace the carbides in the mold steel billet after thermoplastic deformation into particles with a particle size of less than 10um; at the same time, a large number of fine, small-spaced spherical graphite are precipitated, thereby eliminating the precipitation of carbides and graphite spheres in the steel, and thus achieving the purpose of improving the service performance of the steel / mold and increasing the service life of the mold. In S1, the composition of the high-carbon alloy steel bar for aluminum alloy forming dies meets the following requirements: 1.5%C, 1.2%Si, 1.3%Mn, 0.8%Cr, 1.0%Ni, 2.0%Mo, 0.7%V, with the remainder being Fe and unavoidable impurities. In S2, the composition of the high-carbon alloy steel billet for aluminum alloy forming molds meets the following requirements: 1.5%C, 1.2%Si, 1.3%Mn, 0.8%Cr, 1.0%Ni, 2.0%Mo, 0.7%V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities; In S2, the billet of the electroslag remelted casting is delivered at a temperature of 980℃. After being delivered, it is immediately placed in a heating furnace at a temperature of 580℃ and kept at that temperature for 5 hours. Then, it is cooled to room temperature with the furnace to prevent the billet from cracking during the cooling process. In S3, before the billet undergoes thermoplastic deformation, it needs to be heated to 1000℃ in an atmosphere furnace with a carbon potential of not less than 1.6 and held for 0.8h before thermoplastic deformation is performed. In S3, the hot plastic deformation of the billet needs to be carried out sequentially in three directions, with four hot deformations in each direction, and the deformation amount in each deformation being 50%, with a strain rate of 4 s. -1 The total forging ratio is 6; In S3, when the forging temperature drops to 850℃ and the total forging ratio requirement is not met, the forging needs to be placed back into an atmosphere furnace at 1000℃ for 0.8h and then subjected to subsequent thermoplastic deformation according to the above-mentioned thermoplastic deformation requirements. In S4, the billet that has completed thermoplastic deformation is immediately placed in a reducing atmosphere furnace at 980°C and held for 12 hours, then cooled to 630°C for 9 hours, and then removed from the furnace and air-cooled to room temperature. After optimization and the above steps, the carbides in the steel billet for the mold are basically eliminated / become particles with a particle size of less than 10 μm; at the same time, a large amount of fine, closely spaced and highly rounded spherical graphite is precipitated.

[0039] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing modified high-carbon alloy steel, characterized in that, Includes the following steps: High-carbon alloy steel billets are electroslag remelted to obtain cast billets; The billet is subjected to thermoplastic deformation to obtain the billet material; The billet is annealed to eliminate carbides or reduce them to fine particles, and spherical graphite is precipitated to obtain modified high-carbon alloy steel; the particle size of the fine particles is less than 10 μm.

2. The method for preparing modified high-carbon alloy steel according to claim 1, characterized in that, The high-carbon alloy steel bar composition, by mass percentage, satisfies the following: 1.3~1.6%C, 1.0~1.5%Si, 1.0~1.5%Mn, 0.5~1.0%Cr, 0.5~1.5%Ni, 1.5~2.5%Mo, 0.5~1.0%V, with the remainder being Fe and unavoidable impurities.

3. The method for preparing modified high-carbon alloy steel according to claim 1, characterized in that, The composition of the billet, by mass percentage, satisfies the following: 1.3~1.6%C, 1.0~1.5%Si, 1.0~1.5%Mn, 0.5~1.0%Cr, 0.5~1.5%Ni, 1.5~2.5%Mo, 0.5~1.0%V, S<0.02%, P<0.025%, with the remainder being Fe and unavoidable impurities.

4. The method for preparing modified high-carbon alloy steel according to claim 1, characterized in that, The billet produced by electroslag remelting is delivered at a temperature of 900~1000℃. Immediately after delivery, it is placed in a heating furnace at a temperature of 550~600℃ and kept at that temperature for 4~6 hours, and then cooled to room temperature with the furnace.

5. The method for preparing modified high-carbon alloy steel according to claim 1, characterized in that, The billet is subjected to thermoplastic deformation by heating it to 980~1030℃ in a furnace with a carbon potential of not less than 1.6 and holding it at that temperature for 0.5~1h before thermoplastic deformation.

6. The method for preparing modified high-carbon alloy steel according to claim 1, characterized in that, The thermoplastic deformation is performed sequentially in three directions, with at least two thermal deformations in each direction, and each deformation being at least 40%, with a strain rate of 0.1~10 s⁻¹. -1 The total forging ratio is 4~8.

7. The method for preparing modified high-carbon alloy steel according to claim 6, characterized in that, When performing triaxial sequential thermoplastic deformation, if the forging temperature drops to 850℃ and the total forging ratio requirement is not met, the forging needs to be placed back into an atmosphere furnace at a temperature of 980~1030℃ and held for 0.5~1h before proceeding with subsequent thermoplastic deformation according to the thermoplastic deformation requirements.

8. The method for preparing modified high-carbon alloy steel according to claim 6, characterized in that, Immediately place the completed thermoplastic deformation billet into a reducing atmosphere furnace at 950~1000℃ and hold it for 8~15 hours. Then cool it to 600~650℃ for 8~10 hours and then remove it from the furnace and air cool it to room temperature.

9. A modified high-carbon alloy steel, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. The application of the modified high-carbon alloy steel according to claim 9 in the preparation of aluminum alloy forming dies.

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