Preparation method of Cr12MoV die steel and Cr12MoV die steel

Abstract

The application relates to the alloy casting technical field, and particularly discloses a preparation method of Cr12MoV die steel and Cr12MoV die steel prepared by the method. According to the method, local transient heating in the solidification process is accurately controlled, strong thermal buoyancy is excited to realize self-stirring, columnar crystals and coarse dendrites are effectively broken, and equiaxed crystal nucleation and growth are promoted. Fine and uniform as-cast structures make carbides small and dispersedly distributed after subsequent forging and heat treatment. Finally, the die steel keeps high hardness and high wear resistance, and impact toughness is obviously improved, so that the problem that high-toughness of high-carbon and high-chromium die steel is difficult to be obtained is solved.

Description

Technical Field

[0001] This application relates to the field of alloy casting technology, and more specifically, to a method for preparing Cr12MoV mold steel, and to Cr12MoV mold steel with excellent as-cast microstructure and properties prepared by the method. Background Technology

[0002] Cr12MoV steel, a typical high-carbon, high-chromium ledeburitic cold work die steel, is widely used in manufacturing cold work dies with large cross-sections, complex shapes, and demanding working conditions, such as trimming dies, wire drawing dies, and cold stamping dies, due to its excellent hardness, wear resistance, and hardenability. However, its high-carbon, high-alloy characteristics also bring serious casting challenges. During the solidification process of traditional ingot casting, due to solute redistribution, alloying elements such as Cr, Mo, and V accumulate in the interdendritic space, leading to severe dendritic segregation and coarse eutectic carbide networks in the as-cast microstructure. Studies have shown that this uneven carbide distribution, especially the coarse network carbides in the core, severely disrupts the matrix, becoming stress concentration points and crack initiation sources. This results in a sharp decrease in the material's impact toughness, a significantly increased risk of quenching cracking, and a substantial reduction in the fatigue life and reliability of the die.

[0003] To improve the solidification structure and homogenization level of ingots, existing technologies mainly focus on applying external physical fields or altering the material composition. For example, Chinese patent application CN120796829A discloses a method for producing bars and wire rods using a continuous casting process for ledeburitic die steel Cr12MoV. This Cr12MoV uses a 150mm square billet for direct rolling into wire rods and bars, employing TX-2 protective slag. The 150mm continuous casting billet is continuously produced using a two-strand, two-crystal arc-shaped continuous casting machine. Secondary cooling with weak cooling water and electromagnetic stirring reduce core segregation in the continuous casting billet, while also mitigating the large carbide size and uneven carbide distribution caused by selective crystallization during casting, effectively achieving a fine and dispersed carbide distribution. However, electromagnetic stirring equipment is complex and energy-intensive. Furthermore, for high-viscosity, high-carbon, high-alloy steel melts, especially in the mushy region during the later stages of solidification, the electromagnetic force weakens due to the skin effect, making effective stirring of the melt core difficult. In addition, electromagnetically driven melt flow is mostly circumferential laminar flow, making it difficult to generate strong radial and axial convection to completely break up the dendritic framework.

[0004] Another approach is to use pulsed magnetic field technology. For example, Chinese patent application CN114749616A discloses an ingot mold and billet forming method for large steel ingots with high aspect ratios. By setting electromagnetic induction risers at the risers of the ingot mold, the billet in the solidification process is treated to refine the grains, improve the uniformity of the microstructure, and increase the ingot yield. However, its effect is more focused on grain refinement in the nucleation stage. It is difficult to effectively transport and mix the solute liquid that has accumulated in the pasty region in the middle and late stages of solidification over long distances, and the effect of improving segregation is limited. Moreover, the violent fluctuations in the melt caused by strong pulses pose a challenge to the stability of the die casting process.

[0005] Adding modifiers is a common metallurgical technique. For example, Chinese patent application CN107299190A discloses a composite modifier suitable for Cr12MoV and its preparation and application method, which refines carbides by adding rare earth, titanium, potassium, sodium, and other elements. While this method has some effect, it alters the chemical composition of the molten steel, potentially introducing new non-metallic inclusions and affecting the purity of the steel. Furthermore, it cannot fundamentally eliminate the macroscopic segregation trend determined by solidification thermodynamics, and its application is limited by cost and control precision.

[0006] Furthermore, subsequent thermomechanical treatments, such as large deformation forging or high-temperature homogenization annealing, are often used to improve the microstructure. For example, Chinese patent application CN108866299A discloses a forging heat treatment method for Cr12MoV steel, which solves the problems of eutectic carbide segregation and poor thermal conductivity in Cr12MoV steel during forging by combining a three-stage heating process with two light and one heavy forging heat treatment processes. This achieves carbide refinement and passivation, significantly improving the impact toughness and service life of the die. However, these are all remedial measures after ingot forming, which cannot optimize the initial as-cast microstructure, and the process is lengthy and energy-intensive, with particularly little effect on improving the core of large ingots.

[0007] In summary, existing technologies largely rely on continuously applying energy from the outside or altering the material's intrinsic composition by adding modifiers. A common shortcoming of these methods is their inability to easily and efficiently induce a strong and unified natural flow within the molten steel during the critical early solidification stage when a pasty region forms. This prevents them from fundamentally disrupting the growth of dendrite networks and the segregation of solute elements. Therefore, the industry urgently needs a new approach to obtain a uniform and fine-grained as-cast microstructure without altering the composition or significantly modifying the production line. Summary of the Invention

[0008] To address the issue of coarse and uneven microstructure in Cr12MoV ingots produced by traditional die casting processes and to achieve a refined and homogenized ingot microstructure, this application provides a method for preparing Cr12MoV die steel. This method does not rely on continuous external energy input but instead precisely controls the solidification path, triggering and amplifying the inherent hot solute convection within the melt during critical time windows. This achieves global self-stirring, fundamentally breaking down the dendritic framework, promoting equiaxed crystal formation, and resulting in a high-quality ingot with fine and uniformly distributed carbides. The final die obtained by this method exhibits high hardness and excellent toughness.

[0009] In a first aspect, this application provides a method for preparing Cr12MoV mold steel, comprising the following steps: S1. Smelting: According to the composition requirements of Cr12MoV steel, the steel is batched, smelted, refined and vacuum degassed to obtain molten steel; S2. Pouring and controlled cooling: Pouring molten steel into the mold; The bottom of the mold is integrated with an induction heating device, the heating area of ​​which covers 50%-70% of the bottom area of ​​the mold. The top of the mold is equipped with a cooling device, and a temperature monitoring device is located in the middle of the height direction of the mold. After the molten steel is poured, the temperature of the molten steel in the mold is monitored by the temperature monitoring device. When the monitored temperature drops to the first preset temperature T1, the induction heating device is started to heat the molten steel until the temperature of the molten steel in the bottom area of ​​the mold rises back to the second preset temperature T2. Then the heating is stopped and the molten steel is cooled and solidified to obtain a steel ingot. The first preset temperature T1 is lower than the liquidus temperature TL of molten steel and higher than the solidus temperature TS of molten steel; the second preset temperature T2 is lower than TL and higher than T1. S3. Forging: The steel ingot is forged to obtain a steel billet; S4. Heat treatment: The steel billet is subjected to annealing, quenching and tempering in sequence to obtain Cr12MoV mold steel.

[0010] The technical principle of this application lies in the following: when molten steel solidifies to the paste-like region (temperature T1), the bottom of the mold is locally and rapidly heated, causing the melt temperature in this region to rise rapidly and the density to decrease. This high-temperature, low-density melt generates strong thermal buoyancy in the gravitational field, forming an upward-moving melt flow. This upward flow strongly scours the dendrites growing in the paste-like region, causing them to melt and break. The broken dendrite fragments can serve as new equiaxed crystal nuclei, thereby significantly refining the grains and increasing the equiaxed crystal ratio. At the same time, the intense convection promotes the uniform distribution of the solute, effectively reducing macroscopic segregation and compositional inhomogeneity. Compared to traditional continuous electromagnetic stirring or overall heating, this method applies short-term, localized energy only during the critical solidification time window, resulting in high efficiency, low energy consumption, and more intense and deeper convection.

[0011] The term "liquidity line" as used in this application refers to the critical temperature at which Cr12MoV molten steel begins to solidify during the cooling process, i.e., when the solid phase begins to precipitate; the term "pasty zone" as used in this application refers to the temperature range in which the two phases coexist between the liquidity line and the solidity line.

[0012] More preferably, in step S2, the temperature difference between TL and T1 is 20-50℃, and the temperature difference between TL and T2 is 5-10℃.

[0013] By heating to temperatures close to the liquidus line, the solid-phase ratio in the mushy region of the heated area decreases while the liquid-phase fluidity significantly increases. At this point, the melt viscosity drops dramatically, but it is not yet completely liquid. This state allows the thermal expansion and density reduction effects generated by heating to be most effectively converted into a strong upward flow, thereby violently agitating the entire mushy region, achieving the goal of breaking dendrites and homogenizing the solute. Temperatures below the liquidus line, on the other hand, preserve the potential for grain refinement and achieve the lowest energy consumption and most stable control.

[0014] More preferably, in step S2, the heating area of ​​the induction heating device covers 50%-60% of the bottom area of ​​the mold.

[0015] This coverage area is one of the key aspects of this application. If the heating area is too small (<50%), the intensity of the generated thermal buoyancy flow is limited, the convection range is insufficient, and it is difficult to achieve effective global "stirring" of the entire ingot cross-section. If the heating area is too large (>70%), it is close to uniform heating of the entire bottom, making it difficult to form a sufficiently steep temperature gradient and density difference locally. The thermal buoyancy convection effect is weakened, and it is more like heat preservation or slow heating, resulting in a significant decrease in grain refinement effect. A coverage area of ​​50%-60% can form a strong but limited heat source at the bottom, most effectively stimulating strong convection that spreads upward and outward, achieving an optimal balance between global stirring and energy consumption.

[0016] More preferably, in step S2, the induction heating device is an induction heating coil, and its power and heating duration are configured such that the temperature of the molten steel in the bottom area of ​​the mold can be raised from T1 to T2 within 30-60 seconds.

[0017] Rapid heating can create a large instantaneous temperature gradient near the solidification interface in a very short time, thereby rapidly stimulating intense thermal buoyancy convection. Slow heating cannot produce this impactful convection effect. This rapid heating process, matched with the solidification process, precisely intervenes in the growth of the dendrite network and is a key operating parameter for achieving efficient "self-stirring".

[0018] More preferably, in step S2, the cooling device is a cooling water jacket disposed on the upper part of the mold.

[0019] By installing a cooling device on the upper part of the mold, the axial temperature gradient of the ingot from top to bottom can be strengthened, promoting sequential solidification.

[0020] More preferably, in step S3, the forging process is upset forging, and the forging temperature is 1050-1100℃.

[0021] The aforementioned forging conditions can further break down any remaining carbides in the as-cast microstructure and improve their distribution. Furthermore, the excellent as-cast microstructure obtained in this application provides a good foundation for forging, reducing the forging ratio requirement and minimizing the risk of cracking.

[0022] More preferably, in step S4, the annealing process includes: holding the forging at 870-940°C for 4 hours, followed by three-stage isothermal spheroidizing annealing.

[0023] The aforementioned heat treatment process is used to obtain a spheroidal pearlite structure, reduce hardness, facilitate subsequent processing, and prepare for final quenching and tempering. Because the original microstructure is uniform, the carbide spheroidization in this process will be more complete and uniform.

[0024] Secondly, this application provides a Cr12MoV steel ingot, which is prepared by the above-mentioned method, and the equiaxed crystal ratio of the as-cast macrostructure of the Cr12MoV steel ingot is not less than 48%. A high equiaxed crystal ratio means that the as-cast microstructure is more uniform and more isotropic, which provides a fundamental guarantee for subsequent processing and final performance.

[0025] Thirdly, this application provides a Cr12MoV mold steel, which is prepared by the above-described method. The Cr12MoV mold steel has a fine and uniform microstructure, thus exhibiting excellent comprehensive mechanical properties, with a hardness reaching over 60.03 HRC, while also possessing good toughness.

[0026] In summary, this application has the following beneficial effects: This application utilizes precise control of localized instantaneous heating during the solidification process to induce strong thermal buoyancy and "self-stirring," effectively breaking down columnar crystals and coarse dendrites, and promoting equiaxed crystal nucleation and growth. The steel ingot prepared in Example 1 achieved an equiaxed crystal ratio of 53%, far superior to traditional processes. Thanks to the fine and uniform as-cast microstructure, the carbides can be finely and dispersedly distributed after subsequent forging and heat treatment. The resulting mold steel maintains high hardness and high wear resistance while significantly improving impact toughness, solving the problem of achieving both high strength and toughness in high-carbon, high-chromium mold steel. The method provided in this application involves short-duration (30-60 seconds) localized heating only during the critical solidification period, resulting in concentrated energy and high efficiency. Compared to continuous electromagnetic stirring or prolonged homogenization annealing, energy consumption is significantly reduced. Closed-loop control is achieved through temperature monitoring, ensuring good process stability and easy integration into existing production lines. Attached Figure Description

[0027] Figure 1 This is a micrograph of the annealed state of the material obtained in Example 1 of this application.

[0028] Figure 2 This is a micrograph of the annealed state of the material obtained in Comparative Example 1 of this application. Detailed Implementation

[0029] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application.

[0030] Furthermore, it should be understood that the one or more method steps mentioned in this application do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of the method steps or limit the scope of implementation of this application. Changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered as within the scope of implementation of this application.

[0031] In this application, unless otherwise specified, 'Cr12MoV steel' generally refers to a steel grade (material) having the standard chemical composition of that grade. 'Cr12MoV steel ingot' specifically refers to a steel ingot in a cast state prepared by the method of this application; 'Cr12MoV steel billet' specifically refers to the material obtained by forging the steel ingot; 'Cr12MoV mold steel' specifically refers to the material obtained by heat treatment of the steel billet, which can be used to manufacture molds; 'mold' specifically refers to the final product processed from the mold steel.

[0032] The raw material composition control requirements and measured values ​​used in the embodiments and comparative examples of this application are shown in Table 1. The liquidus temperature TL is approximately 1420℃.

[0033] Table 1. Raw material composition control requirements and actual measurements (wt%) Control requirements 1.45-1.7 ≤0.4 ≤0.4 ≤0.03 ≤0.005 11-12.5 0.4-0.6 0.15-0.3 Actual measurement 1.63 0.351 0.38 0.021 0.004 11.5 0.42 0.17

[0034] The balance is Fe and unavoidable impurities. Example 1

[0035] This embodiment is a baseline embodiment, using 50% bottom heating area, T1=TL-30℃ (1390℃), T2=TL-5℃ (1415℃).

[0036] S1, Smelting

[0037] Electric arc furnace smelting: Prepare the raw materials according to the composition shown in Table 1 and add them to the electric arc furnace for smelting. Tap-out temperature ≥1590℃, P≤0.03%.

[0038] LF smelting: Lime and fluorite are added, slag is formed by passing electricity through the slag, and deoxidation is carried out using ferrosilicon deoxidizer.

[0039] VD vacuum treatment: Hold under ultimate vacuum ≤67Pa for 30 minutes, with ladle pouring temperature T=1435℃.

[0040] S2, Pouring and Cooling Control

[0041] Molten steel is poured into a square mold with a cross-section of 400mm × 400mm. A platinum-rhodium thermocouple is installed in the middle of the mold along its height for real-time temperature measurement. A medium-frequency induction heating coil is integrated at the bottom of the mold, and the heating area covers 50% of the bottom area of ​​the mold. A cooling water jacket is installed at the top of the mold for water cooling to enhance the temperature gradient from top to bottom.

[0042] After casting is completed, the control system continuously monitors the temperature of the molten steel. When the thermocouple shows that the temperature drops to T1 (1390℃), the bottom induction heating coil is immediately activated. Within 45 seconds, the temperature of the molten steel in the bottom area of ​​the mold is rapidly raised back to T2 (1415℃). Heating is then stopped, and the steel ingot is naturally cooled and solidified to obtain the steel ingot.

[0043] S3, Forging

[0044] The steel ingot is upsetting and forging at a temperature of 1050-1100℃ to obtain a steel billet.

[0045] S4, Heat Treatment

[0046] Annealing treatment: Hold the forging at 950-970℃ for 2 hours, remove from the furnace and air cool to room temperature (20-30℃), hold for 3 hours, raise the temperature to 870-940℃ and hold for 4 hours; then cool in the furnace to 700-720℃ and perform three-stage isothermal spheroidizing annealing (700-720℃→730-750℃→700-720℃), each stage for 2 hours; finally, cool in the furnace to ≤300℃ and remove from the furnace.

[0047] Quenching and tempering treatment: Quenching at 950-1000℃ and oil cooling at 20-60℃; then tempering at 500-550℃ 3 times, holding for 2 hours each time, to obtain Cr12MoV mold steel. Example 2

[0048] This embodiment verifies the technical effects of different T1 (1370℃) and T2 (1410℃) temperatures and heating times (60s), while the remaining parameters are the same as in Embodiment 1.

[0049] The difference from Example 1 is that in step S2, induction heating is started when the temperature shown by the thermocouple drops to T1 (1370°C), the heating duration is 60s, and heating is stopped when the temperature of the molten steel in the bottom area of ​​the mold rises back to T2 (1410°C).

[0050] The other steps and parameters are the same as in Example 1. Example 3

[0051] This embodiment verifies the technical effects of different T1 (1400℃) and T2 (1415℃) temperatures and heating times (30s), while the remaining parameters are the same as in Embodiment 1.

[0052] The difference from Example 1 is that in step S2, induction heating is started when the temperature shown by the thermocouple drops to T1 (1400°C), the heating duration is 30s, and heating is stopped when the temperature of the molten steel in the bottom area of ​​the mold rises back to T2 (1415°C).

[0053] The other steps and parameters are the same as in Example 1. Example 4

[0054] This embodiment verifies the technical effect of heating area of ​​70%, and the remaining parameters are the same as in embodiment 1.

[0055] The difference from Example 1 is that in step S2, the heating area of ​​the medium-frequency induction heating coil integrated at the bottom of the mold covers 70% of the bottom area of ​​the mold.

[0056] The other steps and parameters are the same as in Example 1. Example 5

[0057] This embodiment verifies the technical effect of heating area of ​​60%, and the remaining parameters are the same as in embodiment 1.

[0058] The difference from Example 1 is that in step S2, the heating area of ​​the medium-frequency induction heating coil integrated at the bottom of the mold covers 60% of the bottom area of ​​the mold.

[0059] The other steps and parameters are the same as in Example 1.

[0060] Comparative Example

[0061] Comparative Example 1

[0062] This comparative example uses the traditional die casting process and does not employ an induction heating device.

[0063] S1, Smelting

[0064] Same as Example 1.

[0065] S2, Pouring and Cooling

[0066] Molten steel is poured into a square mold with a cross-section of 400mm × 400mm and allowed to cool and solidify naturally to obtain a steel ingot. The mold is not equipped with an induction heating device or a top cooling water jacket.

[0067] S3, Forging

[0068] Same as Example 1.

[0069] S4, Heat Treatment

[0070] Same as Example 1.

[0071] Comparative Example 2

[0072] This embodiment verifies the technical effect of heating area of ​​100%, and the other parameters are the same as those in embodiment 1.

[0073] The difference from Example 1 is that in step S2, the heating area of ​​the integrated medium-frequency induction heating coil at the bottom of the mold covers 100% of the bottom area of ​​the mold, that is, the entire bottom plane is heated.

[0074] The other steps and parameters are the same as in Example 1.

[0075] Performance testing

[0076] Measurement of equiaxed crystal ratio in steel ingots: Samples were taken from the cross-section at the middle of the height direction of the steel ingot. After grinding, polishing and etching, the area ratio of equiaxed crystal regions was statistically analyzed using image analysis software.

[0077] Mechanical property testing of mold steel:

[0078] Hardness: Measured using a fully automatic Brinell hardness tester (model: THBS-3000MD-AZF).

[0079] Abrasion resistance: Tested using an MM-P2 abrasion tester. The machine speed was set to 400 r / min, the load to 1200 N, and the wear time to 20 h. The weight of the steel sample before and after wear was measured, and the wear rate was calculated. Wear rate = [(Weight of steel sample before wear - Weight of steel sample after wear) / Weight of steel sample before wear] × 100%

[0080] Impact toughness: determined according to GB / T 229-2020, using unnotched Charpy impact specimens with dimensions of 10mm×10mm×55mm.

[0081] As shown in Table 2, Example 1 achieved the highest equiaxed crystal ratio (53%), significantly better than traditional molds (Comparative Example 1, 39%) and bottom-mounted heating (Comparative Example 2, 38%). This indicates that the thermal buoyancy "self-stirring" effect induced by localized instantaneous heating is key to refining the as-cast microstructure; a heating area coverage of 50%-70% (Examples 1, 4, 5) can form a sufficiently steep temperature gradient, generating strong thermal buoyancy convection; an excessively large heating area (Comparative Example 2, 100%) tends to result in a gentler temperature gradient, weakened convection intensity, and a decrease in the equiaxed crystal ratio of the ingot.

[0082] The final mold steel of Example 1 has a hardness of 63.02 HRC, a 20-hour wear rate of 0.01%, and an impact toughness of 41.1 J. While maintaining high hardness and high wear resistance, the impact toughness is about 30% higher than that of traditional casting mold (Comparative Example 1, 31.6 J), achieving a good match between strength and toughness of high carbon and high chromium mold steel.

[0083] Table 2 Performance test results of Cr12MoV steel heating area 50% 50% 50% 70% 60% - 100% T1 settings TL-30℃ TL-50℃ TL-20℃ TL-30℃ TL-30℃ - TL-30℃ T2 settings TL-5℃ TL-10℃ TL-5℃ TL-5℃ TL-5℃ - TL-5℃ Heating time 45s 60s 30s 45s 45s - 45s Equiaxed crystallinity / % 53 52 52 50 48 39 38 Hardness HRC 63.02 62.98 62.88 61.51 60.03 58.11 57.65 Wear rate / % 0.01 0.01 0.02 0.03 0.09 0.28 0.26 Impact toughness / J 41.1 40.3 39.7 38.1 37.5 32.3 31.6

[0084] Figure 1 and Figure 2 The images show the microstructure of steel ingots obtained in Example 1 and Comparative Example 1 of this application after annealing heat treatment.

[0085] Figure 1The metallographic structure shows that the carbide particles are small, uniformly and dispersed, and numerous. This excellent annealed structure directly stems from the fine as-cast structure obtained by the patented method. In step S2, the strong thermal buoyancy "self-stirring" generated by the localized instantaneous heating at the bottom effectively breaks down the primary columnar crystals and coarse dendrites, significantly increasing the equiaxed crystal ratio (53%) and greatly improving the uniformity of alloying elements and carbon distribution. This uniform and refined initial as-cast structure allows for more complete and uniform dissolution, diffusion, and re-precipitation of carbides during subsequent annealing, thus forming... Figure 1 The morphology of the carbides shown is illustrated.

[0086] In comparison, Figure 2 In the metallographic structure, the undissolved carbide particles are noticeably large and unevenly distributed, with a relatively small number of particles. This is because, under traditional casting processes, solidification is dominated by columnar crystals (equiaxed crystal ratio of only 39%), resulting in severe dendritic segregation and significant enrichment of carbon and alloying elements between dendrites. During subsequent annealing, these locally enriched areas are prone to forming large undissolved carbides or agglomerating, while the barren areas have fewer carbides, ultimately resulting in... Figure 2 The diagram shows a carbide distribution with poor uniformity.

[0087] The comparison of the two metallographic structures visually demonstrates the superiority of this patented technology at the microscopic level. The fine, dispersed, and uniform carbide distribution obtained in Example 1 is the microstructural basis for achieving high hardness (63.02 HRC), high wear resistance (wear rate 0.01%), and high impact toughness (41.1 J) simultaneously after subsequent quenching and tempering. This structure effectively avoids the cutting of the matrix by coarse carbides, reduces stress concentration points and crack initiation tendency, thus successfully solving the problem of achieving both strength and toughness in high-carbon, high-chromium mold steel.

[0088] The above description is merely a preferred embodiment of this application and does not constitute any limitation on this application in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of this application, and these improvements and additions should also be considered within the scope of protection of this application. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of this application are equivalent embodiments of this application; furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of this application still fall within the scope of the technical solution of this application.

Claims

1. A method for preparing Cr12MoV mold steel, characterized in that, Includes the following steps: S1. Smelting: According to the composition requirements of Cr12MoV steel, the steel is batched, smelted, refined and vacuum degassed to obtain molten steel; S2. Pouring and controlled cooling: Pouring molten steel into the mold; The bottom of the mold is integrated with an induction heating device, the heating area of ​​which covers 50%-70% of the bottom area of ​​the mold. The top of the mold is equipped with a cooling device, and a temperature monitoring device is located in the middle of the height direction of the mold. After the molten steel is poured, the temperature of the molten steel in the mold is monitored by the temperature monitoring device. When the monitored temperature drops to the first preset temperature T1, the induction heating device is started to heat the molten steel until the temperature of the molten steel in the bottom area of ​​the mold rises back to the second preset temperature T2. Then the heating is stopped and the molten steel is cooled and solidified to obtain a steel ingot. The first preset temperature T1 is lower than the liquidus temperature TL of molten steel and higher than the solidus temperature TS of molten steel; the second preset temperature T2 is lower than TL and higher than T1. S3. Forging: The steel ingot is forged to obtain a steel billet; S4. Heat treatment: The steel billet is subjected to annealing, quenching and tempering in sequence to obtain Cr12MoV mold steel.

2. The method for preparing Cr12MoV mold steel according to claim 1, characterized in that, In step S2, the temperature difference between TL and T1 is 20-50℃, and the temperature difference between TL and T2 is 5-10℃.

3. The method for preparing Cr12MoV mold steel according to claim 1, characterized in that, In step S2, the heating area of ​​the induction heating device covers 50%-60% of the bottom area of ​​the mold.

4. The method for preparing Cr12MoV mold steel according to claim 1, characterized in that, In step S2, the induction heating device is an induction heating coil, and its power and heating duration are configured to raise the temperature of the molten steel in the bottom area of ​​the mold from T1 to T2 within 30-60 seconds.

5. The method for preparing Cr12MoV mold steel according to claim 1, characterized in that, In step S2, the cooling device is a cooling water jacket installed on the upper part of the mold.

6. The method for preparing Cr12MoV mold steel according to claim 1, characterized in that, In step S3, the forging process is upset forging, and the forging temperature is 1050-1100℃.

7. The method for preparing Cr12MoV mold steel according to claim 1, characterized in that, In step S4, the annealing process includes: holding the forging at 870-940°C for 4 hours, followed by three-stage isothermal spheroidizing annealing.

8. A Cr12MoV steel ingot, characterized in that, The Cr12MoV steel ingot is prepared by steps S1 and S2 of the preparation method according to any one of claims 1 to 7, and the equiaxed crystal ratio is not less than 48%.

9. A Cr12MoV mold steel, characterized in that, It is prepared by any one of claims 1 to 7.

10. The Cr12MoV mold steel according to claim 9, characterized in that, The Cr12MoV mold steel has a hardness of not less than 60.03 HRC, a wear rate of not more than 0.09%, and an impact toughness of not less than 37.5J.

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