Preparation method of die steel for car lamp die

Abstract

The invention discloses a preparation method of die steel for a car lamp die, and belongs to the technical field of die steel preparation. The die steel is composed of matrix steel, a modified nano titanium carbide strengthening phase and a modified rare earth oxide complexing agent. The steel matrix comprises, by mass, 0.45% of carbon, 0.8% of silicon, 1.2% of manganese, 13.5% of chromium, 2.0% of molybdenum, 0.6% of vanadium, 1.5% of nickel and 0.3% of niobium. The other components comprise, by mass, 1.0% of a modified nano titanium carbide strengthening phase and 0.2% of a modified rare earth oxide complexing agent; and the balance of iron. According to the invention, the three materials of the matrix steel, the nano titanium carbide strengthening phase and the rare earth oxide complexing agent are synergistically modified, so that a three-in-one innovative system of'modified matrix + strengthening phase enhancement + rare earth regulation 'is constructed, and synchronous improvement of hardness, toughness, polishing performance and corrosion resistance is realized; the technical bottleneck that traditional die steel is poor in performance collaboration is solved.

Description

Technical Field

[0001] This invention relates to the field of mold steel preparation technology, and specifically to a method for preparing mold steel for automotive lamp molds. Background Technology

[0002] As a core component in automotive lighting production, automotive lighting molds place extremely high demands on the performance of mold steel. They not only need excellent hardness and wear resistance to ensure mold lifespan, but also good toughness, polishing properties, and corrosion resistance to guarantee high-precision forming and surface quality of the lighting products. Traditional automotive lighting molds often use conventional grades such as Cr12MoV and S136, and their manufacturing process typically involves a standard procedure of electric arc furnace smelting + forging + annealing + quenching and tempering. However, this process suffers from the following significant drawbacks: Poor performance synergy: Conventional mold steels are difficult to balance hardness and toughness. For example, Cr12MoV steel can reach a hardness of HRC60-62 after quenching and tempering, but its impact toughness is only 15-20J / cm². In the process of processing and using complex cavities of automotive lamp molds, chipping and cracking are likely to occur. Insufficient polishing performance: Traditional mold steel contains coarse carbide inclusions, mostly 5-10μm in size, which makes it difficult to achieve the surface roughness Ra≤0.02μm required for automotive lamp molds after polishing, thus affecting the light transmittance and appearance of automotive lamp products. Insufficient corrosion resistance: During use, automotive lamp molds come into contact with release agents, impurities in cooling water, etc. Conventional mold steel is prone to rust, which causes spots to appear on the surface of the mold cavity, thus affecting the quality of automotive lamp products and resulting in a short mold maintenance cycle (usually ≤6 months). Limited service life: Due to the contradiction between wear resistance and toughness, as well as the increased local wear caused by uneven distribution of carbides, the service life of traditional automotive lamp molds is usually only 50,000 to 80,000 cycles, which is difficult to meet the needs of large-scale production.

[0003] Existing Improvement Technologies and Limitations: To improve the performance of automotive headlight mold steel, researchers have proposed various optimization schemes, but all have shortcomings. For example, patent CN202010567890.3 discloses a method for preparing ultra-high hardness mold steel, which increases hardness by increasing the content of chromium and molybdenum, but this leads to a further decrease in toughness, with an impact toughness of only 12-16 J / cm². Patent CN201910876543.2 uses vacuum electric arc furnace smelting to improve the purity of molten steel, but it does not effectively control the morphology and distribution of carbides, resulting in limited improvement in polishing performance, with a surface roughness of only Ra0.03-0.04μm. Another technology improves wear resistance through surface nitriding treatment, but the nitrided layer thickness is uneven and prone to brittle cracking, failing to fundamentally solve the problem of insufficient matrix performance of mold steel.

[0004] The core problem with existing technologies is that they have not carried out systematic and collaborative innovation on the base steel, reinforcing phase, and preparation process of mold steel. Single modification or process optimization cannot achieve simultaneous improvement in hardness, toughness, polishing performance, and corrosion resistance. Furthermore, they have not been targeted at the specific application scenarios of automotive lighting molds, resulting in the overall performance of mold steel being unable to meet the needs of high-end automotive lighting production. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for preparing mold steel for automotive lamp molds. By targeting and modifying three materials—base steel, nano-titanium carbide reinforcing phase, and rare earth oxide composite agent—and optimizing the preparation process, a mold steel for automotive lamp molds with ultra-high hardness, excellent toughness, superior polishing performance, and corrosion resistance is obtained. This extends the service life of the mold, reduces production costs, and meets the high precision and high stability requirements of high-end automotive lamp production.

[0006] Technical solution: A mold steel for automotive headlight molds, comprising a base steel, a modified nano-titanium carbide reinforcing phase, and a modified rare earth oxide composite agent. The steel base includes the following components by mass fraction: carbon 0.45%, silicon 0.8%, manganese 1.2%, chromium 13.5%, molybdenum 2.0%, vanadium 0.6%, nickel 1.5%, and niobium 0.3%; the remaining components by mass fraction are: modified nano-titanium carbide reinforcing phase 1.0%, modified rare earth oxide composite agent 0.2%, and the balance being iron.

[0007] Preferably, the modified nano-titanium carbide reinforced phase is prepared as follows: industrial-grade titanium carbide powder is placed in a planetary ball mill, anhydrous ethanol is used as the ball milling medium, the ball-to-material ratio is 20:1, the ball milling speed is 400 r / min, and the ball milling time is 12 hours to obtain nano-titanium carbide powder with a particle size of 500 nm; the nano-titanium carbide powder is immersed in a 15% hydrochloric acid solution, stirred and reacted at 80°C for 2 hours, washed until neutral, and dried at 120°C for 4 hours; the dried nano-titanium carbide powder is mixed with aluminum powder at a mass ratio of 10:1, and sintered at 1200°C for 2 hours under an argon atmosphere to obtain the modified nano-titanium carbide reinforced phase.

[0008] Preferably, the modified rare earth oxide composite agent is prepared as follows: cerium oxide and lanthanum oxide are mixed at a mass ratio of 3:2 and added to a 20% nitric acid solution. The mixture is stirred and dissolved at 60°C for 30 minutes to form a rare earth nitrate solution. A 10% ammonium bicarbonate solution is added to the solution to adjust the pH to 8.5, generating a rare earth carbonate precipitate. After standing for 30 minutes, the precipitate is filtered and washed with deionized water until neutral. The precipitate is dried at 110°C for 6 hours and then calcined at 800°C for 3 hours to obtain a rare earth oxide composite powder. This powder is mixed with a silane coupling agent at a mass ratio of 100:3 and stirred at 1500 r / min for 20 minutes in a high-speed mixer to obtain the modified rare earth oxide composite agent. Preferably, the modified base steel is prepared by the following method: smelting in a vacuum induction furnace, adding electrolytic manganese and ferrosilicon to the molten steel for deoxidation and desulfurization pretreatment, then adding a pre-alloyed chromium-molybdenum-vanadium-nickel-niobium master alloy, controlling the smelting temperature at 1580℃, holding for 60 minutes, and introducing argon gas for stirring during the process, with an argon gas flow rate of 5L / min, to obtain a base steel molten steel with uniform composition.

[0009] Preferably, the original particle size of industrial-grade titanium carbide powder is 50 μm. After ball milling, acid washing and aluminum powder sintering modification, the particle size is refined to 500 nm, and a titanium trialuminide transition layer is formed on the surface.

[0010] Preferably, in the modified rare earth oxide composite, cerium oxide and lanthanum oxide are dissolved, precipitated, and calcined to refine the grain size to 1-2 μm, and the surface is coated with a silane coupling agent layer.

[0011] Preferably, the mold steel has a hardness of 63-65HRC, an impact toughness of 36-38J / cm², a surface roughness Ra≤0.014μm after polishing, a corrosion rate ≤0.004mm / a after 48 hours of salt spray testing, and a service life ≥160,000 cycles.

[0012] A method for preparing mold steel for automotive headlight molds includes the following steps: S1. Base steel smelting: 99.9% pure industrial iron, electrolytic manganese, ferrosilicon, and chromium-molybdenum-vanadium-nickel-niobium pre-alloy master alloy are added to a vacuum induction furnace, the vacuum is evacuated to a vacuum degree of 0.001MPa, the temperature is raised to 1580℃, and the temperature is held for 60 minutes. During the process, argon gas with a flow rate of 5L / min is introduced for stirring to obtain molten base steel. S2. Addition of reinforcing phase and modifier: The modified nano-titanium carbide reinforcing phase is uniformly added to the matrix steel liquid and kept at the temperature for 30 minutes, during which time it is stirred with argon gas at a flow rate of 3L / min; then the modified rare earth oxide composite agent is added and kept at the temperature for 20 minutes, while the argon gas stirring rate remains unchanged; S3. Casting: Under argon protection, the uniformly mixed molten steel is poured into a mold preheated to 300°C at a pouring speed of 50 mm / min, and then naturally cooled to room temperature to obtain a mold steel ingot. S4. Forging process: Heat the ingot to 1150℃ and hold for 2.5 hours, then perform three-dimensional forging with a forging ratio of 5:1. The forging reduction is 10mm each time to ensure that the internal structure of the forging is dense and free from porosity and defects. Hold for 30 minutes after each forging to finally forge a plate with a thickness of 50mm. The cooling rate is controlled at 5℃ / min during the forging process. S5. Annealing treatment: Heat the forged plate to 860℃, hold for 4 hours, then cool to 500℃ at a cooling rate of 2℃ / min, and then air cool to room temperature; S6. Quenching treatment: Heat the annealed plate to 1050℃ and hold for 1.5 hours. Then, use oil quenching at a cooling rate of 30℃ / min and control the quenching oil temperature at 50℃ to ensure uniform cooling and avoid deformation and cracking of the steel parts. S7. Tempering treatment: The quenched steel parts are heated to 220℃ and held for 3 hours, then air-cooled to room temperature. The tempering treatment is carried out three times, and after each tempering, the parts are air-cooled to room temperature to finally obtain the mold steel for car headlight molds. Beneficial effects

[0013] 1. This invention constructs a three-in-one innovative system of "modified matrix + strengthening phase + rare earth regulation" by synergistically modifying three materials: matrix steel, nano-titanium carbide reinforcing phase, and rare earth oxide composite agent. This system achieves simultaneous improvement in hardness, toughness, polishing performance, and corrosion resistance, and solves the technical bottleneck of poor performance synergy of traditional mold steel.

[0014] 2. The matrix steel is precisely designed in terms of composition and modified by vacuum smelting to ensure the uniform distribution of alloying elements, laying the foundation for subsequent strengthening phase loading and performance optimization. The modified nano-titanium carbide strengthening phase is refined by ball milling, pickling to remove impurities, and modified by aluminum powder sintering. Not only is the particle size refined to 500nm, but the interfacial bonding force with the matrix steel is also significantly improved, ensuring increased hardness while avoiding a decrease in toughness. The modified rare earth oxide composite agent is refined by dissolution precipitation, calcination, and silane coupling agent modification, resulting in significantly improved dispersibility. It can effectively refine grains, purify molten steel, and reduce carbide inclusions.

[0015] 3. The mold steel prepared by this invention has a hardness of HRC63-65, an impact toughness of 35-40 J / cm², a surface roughness Ra≤0.015μm after polishing, good corrosion resistance (no rust after 48 hours of salt spray test), and a service life of 150,000-180,000 mold cycles. All its properties are superior to those of traditional automotive lamp mold steel.

[0016] 4. The preparation process is stable and controllable. By precisely controlling key aspects such as smelting temperature, forging parameters, and heat treatment processes, the consistency of mold steel performance is ensured. The industrial production cost is reduced by 10-15% compared to traditional processes. It can be widely used in the manufacturing of high-end automotive lighting molds. The mold steel prepared by this invention has excellent performance and extends the service life of the mold. Attached Figure Description

[0017] Figure 1 This is a graph showing the performance test results of the embodiment and the comparative example; Figure 2 This is a process flow diagram for preparing mold steel. Detailed Implementation

[0018] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1

[0020] The mold steel for automotive lamp molds is prepared according to the above technical solution, and the specific parameters are as follows: 1. Modification of the base steel: The smelting temperature in the vacuum induction furnace is 1580℃, the holding time is 60 minutes, the argon flow rate is 5L / min, and the mass fraction of each component of the base steel is 0.45% carbon, 0.8% silicon, 1.2% manganese, 13.5% chromium, 2.0% molybdenum, 0.6% vanadium, 1.5% nickel, 0.3% niobium, and the balance is iron. 2. Modified nano-titanium carbide reinforced phase: ball milling speed 400 r / min, ball milling time 12 hours, hydrochloric acid concentration 15%, pickling temperature 80℃, pickling time 2 hours, titanium carbide to aluminum powder mass ratio 10:1, sintering temperature 1200℃, sintering time 2 hours. 3. Modified rare earth oxide composite: Cerium oxide to lanthanum oxide mass ratio 3:2, nitric acid concentration 20%, dissolution temperature 60℃, ammonium bicarbonate solution concentration 10%, pH value 8.5, calcination temperature 800℃, calcination time 3 hours, rare earth oxide to silane coupling agent mass ratio 100:3, stirring speed 1500 r / min, stirring time 20 minutes; 4. Preparation process: pouring speed 50mm / min, mold preheating temperature 300℃, forging temperature 1150℃, holding for 2.5 hours, forging ratio 5:1, annealing temperature 860℃, holding for 4 hours, quenching temperature 1050℃, holding for 1.5 hours, tempering temperature 220℃, holding for 3 hours, three tempering cycles.

[0021] Example 2

[0022] The difference from Example 1 lies in the preparation parameters of the modified nano-titanium carbide reinforced phase; all other parameters are the same. Modified nano-titanium carbide reinforced phase: ball milling speed 450 r / min, ball milling time 10 hours, hydrochloric acid concentration 18%, pickling temperature 75℃, pickling time 2.5 hours, titanium carbide to aluminum powder mass ratio 11:1, sintering temperature 1150℃, sintering time 2.5 hours.

[0023] Example 3

[0024] The difference from Example 1 lies in the preparation parameters of the modified rare earth oxide composite agent; all other parameters are the same. Modified rare earth oxide composite: Cerium oxide to lanthanum oxide mass ratio 2:1, nitric acid concentration 22%, dissolution temperature 55℃, ammonium bicarbonate solution concentration 12%, pH value 8.0, calcination temperature 850℃, calcination time 2.5 hours, rare earth oxide to silane coupling agent mass ratio 100:4, stirring speed 1400 r / min, stirring time 25 minutes.

[0025] Comparative Example 1

[0026] The traditional Cr12MoV mold steel is used, and the manufacturing process is conventional electric arc furnace smelting + forging + annealing + quenching and tempering. The specific parameters are: electric arc furnace smelting temperature 1600℃, forging temperature 1100℃, forging ratio 3:1, annealing temperature 830℃, holding for 3 hours, quenching temperature 980℃, holding for 1 hour, tempering temperature 200℃, holding for 2 hours, without any material modification steps.

[0027] Comparative Example 2

[0028] The difference from Example 1 is that only the base steel is modified, and the composite agent of nano-titanium carbide reinforcing phase and rare earth oxide is not modified. Specifically: The nano-titanium carbide reinforcing phase was not modified by ball milling, acid washing, or aluminum powder sintering; it was directly added using industrial-grade titanium carbide powder (particle size 50 μm). The rare earth oxide composite agent was not modified by dissolution precipitation, calcination, or silane coupling agent; it was directly added by mixing cerium oxide and lanthanum oxide at a mass ratio of 3:2. The rest of the preparation process was the same as in Example 1.

[0029] Comparative Example 3

[0030] The difference from Example 1 is that only the nano-titanium carbide reinforcing phase is modified, and the matrix steel and rare earth oxide composite agent are not modified. Specifically: The base steel was smelted in a conventional electric arc furnace without argon stirring or precise composition control; the rare earth oxide composite agent was not dissolved, precipitated, calcined, or modified with silane coupling agent, but was directly added by mixing cerium oxide and lanthanum oxide at a mass ratio of 3:2, and the rest of the preparation process was the same as in Example 1.

[0031] Performance testing methods:

[0032] Hardness test: The hardness of the mold steel was tested using a Rockwell hardness tester according to GB / T230.1-2018 Metallic materials Rockwell hardness test - Part 1: Test method. Five test points were used, and the average value was taken. Impact toughness test: According to GB / T229-2020 Metallic Materials Charpy Pendulum Impact Test Method, Charpy V-notch impact specimens were used to test the impact toughness. Three specimens were tested and the average value was taken. Polishing performance test: According to the surface roughness parameters and values ​​of the surface structure profile method in the product geometric technical specification (GB / T1031-2009), the mold steel sample was polished step by step using a polishing machine (400#, 800#, 1200#, 2000#, 5000# sandpaper), and finally polished with diamond polishing paste. The surface roughness Ra after polishing was tested. Corrosion resistance test: The salt spray test of artificial atmosphere corrosion test was conducted in accordance with GB / T10125-2021. The test was conducted with neutral salt spray for 48 hours. The rust on the sample surface was observed and the corrosion rate was calculated by weighing. Service life test: The mold steel is processed into the cavity of the car lamp mold and put into actual production trial. The number of times the mold shows obvious wear, chipping or product quality failure is recorded, which is the service life of the mold.

[0033] The performance test results of the above embodiments and comparative examples are as follows: Figure 1 As shown. The mold steels for automotive lamp molds prepared in Examples 1-3 exhibit excellent properties, with a hardness of 63-65 HRC, an impact toughness of 36-38 J / cm², a surface roughness Ra≤0.014 μm, a corrosion rate of only 0.003-0.004 mm / a, and a service life of 160,000-180,000 mold cycles, fully demonstrating the technical advantages of synergistic modification of the three materials; Comparative Example 1 (traditional Cr12MoV steel) has the worst performance in all aspects. Its hardness is only 61HRC, its impact toughness is less than 20J / cm², its surface roughness is difficult to meet the requirements of automotive lamp molds, its corrosion rate is 5 times that of Example 1, and its service life is only 60,000 mold cycles, highlighting the performance shortcomings of traditional mold steel. Comparative Example 2 (modified base steel only) did not modify the nano-titanium carbide reinforcing phase and rare earth oxide composite agent. The nano-titanium carbide was unevenly dispersed and had poor bonding with the matrix. The rare earth oxide could not effectively refine the grains and purify the molten steel. As a result, the hardness, toughness, polishing performance and service life were significantly lower than those of Examples 1-3. The hardness was 6 HRC lower than that of Example 1 and the impact toughness was 13 J / cm² lower. Comparative Example 3 (modified only with nano-titanium carbide reinforcing phase) suffers from poor compositional uniformity due to the rudimentary smelting process of the base steel and insufficient dispersion due to the lack of modification of rare earth oxides, thus failing to fully exert the synergistic reinforcing effect. Its performance is still significantly different from that of Examples 1-3, and its service life is only 90,000 cycles, less than 60% of that of Example 1.

[0034] In summary, this invention, through precise modification of three materials—base steel, nano-titanium carbide reinforcing phase, and rare earth oxide composite agent—combined with optimized preparation process, successfully prepared a high-performance mold steel for automotive lighting molds. This solves the problem of insufficient performance of traditional mold steels and provides an efficient and long-lasting solution for the manufacturing of high-end automotive lighting molds.

[0035] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A mold steel for automotive headlight molds, characterized in that, It is composed of a base steel, a modified nano-titanium carbide reinforcing phase, and a modified rare earth oxide composite agent. The steel base includes the following components by mass fraction: carbon 0.45%, silicon 0.8%, manganese 1.2%, chromium 13.5%, molybdenum 2.0%, vanadium 0.6%, nickel 1.5%, and niobium 0.3%; the remaining components by mass fraction are: modified nano-titanium carbide reinforcing phase 1.0%, modified rare earth oxide composite agent 0.2%; and the balance is iron.

2. The mold steel for automotive lamp molds according to claim 1, characterized in that, The modified nano-titanium carbide reinforced phase is prepared as follows: industrial-grade titanium carbide powder is placed in a planetary ball mill, anhydrous ethanol is used as the ball milling medium, the ball-to-material ratio is 20:1, the ball milling speed is 400 r / min, and the ball milling time is 12 hours to obtain nano-titanium carbide powder with a particle size of 500 nm; the nano-titanium carbide powder is immersed in a 15% hydrochloric acid solution, stirred and reacted at 80°C for 2 hours, washed until neutral, and dried at 120°C for 4 hours; the dried nano-titanium carbide powder is mixed with aluminum powder at a mass ratio of 10:1, and sintered at 1200°C for 2 hours under an argon atmosphere to obtain the modified nano-titanium carbide reinforced phase.

3. The mold steel for automotive lamp molds according to claim 1, characterized in that, The modified rare earth oxide composite agent is prepared as follows: cerium oxide and lanthanum oxide are mixed at a mass ratio of 3:2 and added to a 20% nitric acid solution. The mixture is stirred and dissolved at 60°C for 30 minutes to form a rare earth nitrate solution. A 10% ammonium bicarbonate solution is added to the solution to adjust the pH to 8.5, generating a rare earth carbonate precipitate. After standing for 30 minutes, the precipitate is filtered and washed with deionized water until neutral. The precipitate is dried at 110°C for 6 hours and then calcined at 800°C for 3 hours to obtain a rare earth oxide composite powder. This powder is mixed with a silane coupling agent at a mass ratio of 100:3 and stirred at 1500 r / min for 20 minutes in a high-speed mixer to obtain the modified rare earth oxide composite agent.

4. The mold steel for automotive lamp molds according to claim 1, characterized in that, The modified base steel is prepared by the following method: smelting in a vacuum induction furnace, adding electrolytic manganese and ferrosilicon to the molten steel for deoxidation and desulfurization pretreatment, then adding a pre-alloyed chromium-molybdenum-vanadium-nickel-niobium master alloy, controlling the smelting temperature at 1580℃, holding for 60 minutes, and introducing argon gas for stirring during the process, with an argon gas flow rate of 5L / min, to obtain a base steel molten steel with uniform composition.

5. The mold steel for automotive lamp molds according to claim 1, characterized in that, The original particle size of the industrial-grade titanium carbide powder was 50 μm. After ball milling, acid washing and aluminum powder sintering modification, the particle size was refined to 500 nm, and a titanium trialuminide transition layer was formed on the surface.

6. The mold steel for automotive lamp molds according to claim 1, characterized in that, In the modified rare earth oxide composite, cerium oxide and lanthanum oxide are dissolved, precipitated, and calcined to refine the grain size to 1-2 μm, and the surface is coated with a silane coupling agent layer.

7. The mold steel for automotive lamp molds according to claim 1, characterized in that, The mold steel has a hardness of 63-65HRC, an impact toughness of 36-38J / cm², a surface roughness Ra≤0.014μm after polishing, a corrosion rate ≤0.004mm / a after 48 hours of salt spray testing, and a service life ≥160,000 cycles.

8. A method for preparing mold steel for automotive lamp molds as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Base steel smelting: 99.9% pure industrial iron, electrolytic manganese, ferrosilicon, and chromium-molybdenum-vanadium-nickel-niobium pre-alloy master alloy are added to a vacuum induction furnace, the vacuum is evacuated to a vacuum degree of 0.001MPa, the temperature is raised to 1580℃, and the temperature is held for 60 minutes. During the process, argon gas with a flow rate of 5L / min is introduced for stirring to obtain molten base steel. S2. Addition of reinforcing phase and modifier: The modified nano-titanium carbide reinforcing phase is uniformly added to the matrix steel liquid and kept at the temperature for 30 minutes, during which time it is stirred with argon gas at a flow rate of 3L / min; then the modified rare earth oxide composite agent is added and kept at the temperature for 20 minutes, while the argon gas stirring rate remains unchanged; S3. Casting: Under argon protection, the uniformly mixed molten steel is poured into a mold preheated to 300°C at a pouring speed of 50 mm / min, and then naturally cooled to room temperature to obtain a mold steel ingot. S4. Forging process: Heat the ingot to 1150℃ and hold for 2.5 hours, then perform three-dimensional forging with a forging ratio of 5:

1. The forging reduction is 10mm each time to ensure that the internal structure of the forging is dense and free from porosity and defects. Hold for 30 minutes after each forging to finally forge a plate with a thickness of 50mm. The cooling rate is controlled at 5℃ / min during the forging process. S5. Annealing treatment: Heat the forged plate to 860℃, hold for 4 hours, then cool to 500℃ at a cooling rate of 2℃ / min, and then air cool to room temperature; S6. Quenching treatment: Heat the annealed plate to 1050℃ and hold for 1.5 hours. Then, use oil quenching at a cooling rate of 30℃ / min and control the quenching oil temperature at 50℃ to ensure uniform cooling and avoid deformation and cracking of the steel parts. S7. Tempering treatment: The quenched steel parts are heated to 220℃ and held for 3 hours, then air-cooled to room temperature. The tempering treatment is carried out three times, and after each tempering, the parts are air-cooled to room temperature to finally obtain the mold steel for car headlight molds.

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