Corrosion-resistant high-polish plastic mold steel and method of making same

Abstract

The present application relates to the technical field of die steel manufacturing, and particularly relates to a corrosion-resistant high-polishing plastic die steel and a preparation method thereof, which comprises the following steps: S1, taking blast furnace molten iron, ferroalloy and scrap steel as raw materials, after smelting through an alloy melting furnace and an electric furnace, LF refining and VD degassing, pouring an electrode base material; S2, vacuum consumable smelting the electrode base material in a vacuum consumable furnace to obtain a steel ingot; S3, high-temperature homogenization treatment is performed on the steel ingot, and then multi-direction upsetting and drawing forging treatment is performed; S4, solid solution treatment is performed on the forged piece; and S5, spheroidizing annealing treatment is performed on the forged piece. By adopting the blast furnace molten iron and vacuum consumable smelting, the non-metallic inclusions in the plastic die steel are all not greater than 0.5 grade, and through the high-temperature homogenization treatment and subsequent solid solution + spheroidizing annealing treatment, the annealing structure of the plastic die steel reaches the A series within the GB / T35840.3-2018 standard.

Description

Technical Field

[0001] This invention relates to the field of mold steel manufacturing technology, and in particular to a corrosion-resistant, high-polish plastic mold steel and its preparation method. Background Technology

[0002] In recent years, with the rapid development of the plastics industry, increasingly stringent requirements have been placed on mold steel. It must not only possess high strength and toughness but also exhibit certain corrosion resistance. This is especially true in the molding process of plastic products made from raw materials such as polyvinyl chloride (PVC), fluoroplastics, and ABS with added flame retardants. In the molten state, plastics decompose and release corrosive gases such as hydrogen chloride, hydrogen fluoride, and sulfur dioxide, which can corrode the mold cavity. Molds used in the production of optical lenses require extremely high surface roughness. The surface roughness Ra of the injection mold cavity is required to be between 0.1 μm and 0.25 μm, with mirror finishes requiring Ra ≤ 0.063 μm and optical surfaces requiring Ra < 0.01 μm. Therefore, influenced by the working environment, plastic mold steels have a series of requirements, including wear resistance, strength, hardness, polishability, and corrosion resistance. Among these, polishability and corrosion resistance are the most important, as surface wear and corrosion account for approximately 50% of mold failure modes.

[0003] Polishing of molds, also known as mirror finishing, is standardized into four grades: A0 = Ra0.008μm, A1 = Ra0.016μm, A3 = Ra0.032μm, and A4 = Ra0.063μm. To meet the requirements for high-quality plastic molds, purity and uniformity are two key factors in the metallurgical quality of plastic mold steel. Currently, the commonly used corrosion-resistant plastic mold steel is 4Cr13NiVSi. This type of mold steel suffers from severe non-metallic inclusions and poor microstructure uniformity, failing to meet the demands for high-polish plastic mold steel. Summary of the Invention

[0004] To address the aforementioned shortcomings in existing technologies, the present invention aims to provide a corrosion-resistant, high-polish plastic mold steel and its preparation method. This invention uses blast furnace iron as raw material to reduce the inclusion content in the mold steel, and employs vacuum consumable smelting to further reduce the inclusion and gas content, thereby improving purity. This ensures that the non-metallic inclusions in the obtained plastic mold steel are all no greater than grade 0.5. The invention further improves the material microstructure and compositional segregation through high-temperature homogenization treatment, and obtains a fine and uniform spheroidized microstructure through subsequent solution treatment and spheroidizing annealing. Therefore, the annealed microstructure of the obtained plastic mold steel meets the requirements of series A as specified in GB / T35840.3-2018 standard.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing corrosion-resistant, high-polish plastic mold steel, the method comprising the following steps: S1. Using blast furnace iron, ferroalloys and scrap steel as raw materials, the electrode base material is cast under argon protection after being smelted in an alloy melting furnace and electric furnace, refined by LF, and degassed by VD. S2. The electrode base material is vacuum arc remelted in a vacuum arc remelting furnace to obtain steel ingots; S3. The steel ingot obtained in step S2 is subjected to high-temperature homogenization treatment, and then subjected to multi-directional upsetting and drawing forging treatment. S4. The forging obtained in step S3 is subjected to solution treatment, which includes heating the forging to the solution temperature and holding it at that temperature, followed by alternating water and air cooling to obtain martensite and lower bainite structures. S5. Perform spheroidizing annealing on the forgings obtained in step S4. The spheroidizing annealing includes heating the forgings obtained in step S4 in a furnace to 850~900℃, holding at that temperature, then reducing the temperature to 790~840℃ at a rate greater than 10℃ / h and not greater than 20℃ / h, then reducing the temperature to 660~700℃ at a rate of ≤10℃ / h, and then furnace cooling to ≤500℃ before removing from the furnace and air cooling.

[0006] Furthermore, by mass percentage, the phosphorus content in the blast furnace molten iron is no higher than 0.025%, and the total content of lead, arsenic, tin, antimony, and bismuth is no higher than 0.025%. And / or, the ferroalloy includes high-carbon ferrochrome, low-carbon ferrochrome, ferromolybdenum, ferrovanadium, and ferronickel; And / or, the scrap steel includes at least one of medium-sized scrap steel and heavy scrap steel.

[0007] Furthermore, in step S1, the ferroalloy is melted uniformly in the alloy melting furnace, and the tapping temperature is 1550~1650℃. And / or, in step S1, the electric furnace is used to melt and dephosphorize the blast furnace iron and the scrap steel, with the phosphorus content not exceeding 0.005 wt% and the tapping temperature being 1600~1680℃; And / or, in step S1, the molten steel from the alloy melting furnace and the electric furnace is added to the LF refining furnace for desulfurization to no more than 0.003 wt%, degassing, inclusion removal treatment, and adjustment to the required composition; subsequently, VD degassing treatment is performed, and the nitrogen content in the molten steel is no more than 70 × 10⁻⁶ by mass percentage. -6 Oxygen content not greater than 10×10 -6 ; And / or, in step S1, after the molten steel is degassed by the VD, it is poured into the consumable electrode mold at the consumable electrode casting station to cast the electrode base material. After mold cooling and demolding, the electrode base material is obtained. The temperature of the molten steel ladle is 1510~1560℃, and the mold cooling time is 2h~8h.

[0008] Furthermore, in step S1, after obtaining the electrode base material, the electrode base material is subjected to stress-relief annealing. The stress-relief annealing includes loading the electrode base material into an annealing furnace, heating it to 750~800℃, holding it at the effective diameter (2~4h) / 100mm, and then cooling it in the furnace to no higher than 200℃ before air cooling.

[0009] Furthermore, in step S1, after stress-relief annealing, the electrode substrate is subjected to cutting and surface finishing.

[0010] Furthermore, in step S2, the melting rate of the vacuum consumable melting is controlled at 6.0~12.0 kg / min; And / or, in step S2, feeding begins when the remaining weight of the electrode base material is 3% to 10% of the total weight of the initial electrode base material; And / or, in step S2, after obtaining the steel ingot, after cooling in the mold for 1 to 5 hours, the steel ingot is demolded and subjected to stress-relief annealing. The stress-relief annealing includes loading the steel ingot into an annealing furnace and heating it to 750 to 800°C, holding it at the effective diameter (2 to 4 hours) / 100 mm, and then cooling it in the furnace to a temperature not exceeding 200°C before air cooling.

[0011] Furthermore, in step S3, the high-temperature homogenization treatment includes holding the steel ingot obtained in step S2 at 1200~1300℃ for a period of time at an effective diameter of (2~4h) / 100mm to perform high-temperature homogenization treatment. And / or, in step S3, the multi-directional upsetting and drawing forging process includes: cooling the steel ingot after the high-temperature homogenization treatment to 1100~1200℃, performing multi-directional upsetting and drawing forging using an upper plate and a lower platform, with each reduction being 20~50%, flipping 90° to press another plane, pressing down on the three planes twice in sequence, with a total forging ratio of 6~12, controlling the final forging temperature to 800~900℃, and obtaining the forging.

[0012] Furthermore, in step S4, the solution temperature is 950~1050℃, and the heat preservation time is 2~5h; And / or, in step S4, during the water-air alternating cooling process, the water-air alternating cooling is performed twice. The initial water temperature is no higher than 40°C. The temperature of the forging drops to 450~550°C during the first water immersion. The forging is then air-cooled until it is dry during the first water immersion. The temperature of the forging drops to 250~350°C during the second water immersion. The final water temperature is no higher than 50°C. Finally, the forging is air-cooled to 100~200°C. And / or, in step S5, the forging obtained in step S4 is loaded into the furnace and heated to 850~900℃, and kept at the temperature according to the thickness (3-5h) / 100mm.

[0013] Furthermore, by mass percentage, the composition of the corrosion-resistant, high-polish plastic mold steel includes: C 0.35~0.45%, Si 0.50~1.20%, Mn 0.50-1.20%, Cr 12.5-14.5%, Mo 0.20~0.50%, V 0.20~0.50%, Ni 0.30~0.80%, with the remainder being Fe and unavoidable impurities.

[0014] In a second aspect, the present invention provides a corrosion-resistant, high-polish plastic mold steel, which is prepared by the preparation method described in the first aspect.

[0015] Compared with the prior art, the beneficial effects of the present invention include at least one of the following: (1) This invention uses blast furnace iron as raw material to reduce the inclusion content in mold steel and adopts vacuum self-consumption smelting to further reduce the inclusion and gas content in mold steel, thereby improving the purity. This results in non-metallic inclusions in the obtained plastic mold steel not exceeding grade 0.5. This invention improves the material structure and composition segregation by performing high-temperature homogenization treatment. Through subsequent solid solution + spheroidizing annealing treatment, a fine and uniform spheroidized structure is obtained, so that the annealed structure of the obtained plastic mold steel can reach the A series specified in GB / T35840.3-2018 standard.

[0016] (2) The oxygen mass percentage in the plastic mold steel prepared by this invention is not greater than 10 × 10⁻⁶. -6 The nitrogen content by mass is not greater than 60 × 10⁻⁶ -6 The liquid carbide content is zero, and the surface finish (polishability) reaches A1 (Ra0.016μm) and A0 (Ra0.008μm). After undergoing an acidic salt spray test in NaCl solution for 48 hours according to GB / T10125-2021, the defect area is 0 (no defects), and the appearance grade is 10 (highest). Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0018] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0019] In a first aspect, the present invention provides a method for preparing corrosion-resistant, high-polish plastic mold steel, the method comprising the following steps: S1. Using blast furnace iron, ferroalloys and scrap steel as raw materials, the electrode base material is cast under argon protection after being smelted in an alloy melting furnace and electric furnace, refined by LF, and degassed by VD. S2. The electrode base material is vacuum-melted in a vacuum arc remelting furnace to obtain qualified steel ingots. S3. The steel ingot obtained in step S2 is subjected to high-temperature homogenization treatment, and then subjected to multi-directional upsetting and drawing forging treatment. S4. The forging obtained in step S3 is subjected to solution treatment, which includes heating the forging to the solution temperature and holding it at that temperature, followed by alternating water and air cooling to obtain martensite and lower bainite structures. S5. Perform spheroidizing annealing on the forging obtained in step S4. The spheroidizing annealing includes heating the forging obtained in step S4 in a furnace to 850~900℃ (for example, 850℃, 870℃ or 900℃), holding it at that temperature, then reducing it to 790~840℃ (for example, 790℃, 810℃ or 840℃) at a rate greater than 10℃ / h and not greater than 20℃ / h, and then reducing it to 660~700℃ (for example, 660℃, 680℃ or 700℃) at a rate ≤10℃ / h, and then furnace cooling to ≤500℃ before removing it from the furnace and air cooling.

[0020] Martensite is a supersaturated solid solution of carbon in α-Fe. Lower bainite is a mechanical mixture of supersaturated lamellar ferrite and cementite precipitated within it. Both structures contain sufficient carbon to rapidly precipitate and form spheroidizing nuclei during subsequent spheroidization, resulting in a uniform spheroidized structure.

[0021] During the spheroidizing annealing process, the second cooling rate is lower than the first cooling rate. The main purpose is to reduce the degree of supercooling and allow the carbides to precipitate and grow uniformly.

[0022] This invention reduces the inclusion content in mold steel by using blast furnace iron as raw material and employing vacuum consumable smelting to eliminate instability in the smelting process, further reducing the inclusion and gas content in the mold steel, thereby improving purity. This results in non-metallic inclusions in the obtained plastic mold steel not exceeding grade 0.5. The invention also improves the material microstructure and compositional segregation through high-temperature homogenization treatment, and obtains a fine and uniform spheroidized microstructure through subsequent solution treatment and spheroidizing annealing. Therefore, the annealed microstructure of the obtained plastic mold steel meets the requirements of series A as specified in GB / T35840.3-2018.

[0023] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional implementation, the phosphorus content in the blast furnace molten iron, by mass percentage, is no higher than 0.025%, and the total content of lead, arsenic, tin, antimony, and bismuth is no higher than 0.025%. Phosphorus is a harmful element in steel, causing component segregation and affecting the uniformity of the microstructure; the higher the content, the greater the impact. Therefore, it is necessary to limit the phosphorus content to no more than 0.025%. Lead, arsenic, tin, antimony, and bismuth are all low-melting-point trace elements. If their content is too high, they segregate at grain boundaries, affecting material properties and hot working.

[0024] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, the ferroalloy includes high-carbon ferrochrome, low-carbon ferrochrome, ferromolybdenum, ferrovanadium, and ferronickel; preferably, the phosphorus content in the high-carbon ferrochrome is not greater than 0.025 wt%, and the phosphorus content in the low-carbon ferrochrome is not greater than 0.025 wt%.

[0025] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, the scrap steel includes at least one of medium-sized scrap steel and heavy scrap steel.

[0026] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S1, the iron alloy is melted uniformly in the alloy melting furnace, and the tapping temperature is 1550~1650℃, for example, 1550℃, 1570℃, 1590℃, 1610℃, 1630℃ or 1650℃.

[0027] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S1, the electric furnace is used to melt and dephosphorize the blast furnace molten iron and the scrap steel, the phosphorus content is not higher than 0.005 wt%, and the tapping temperature is 1600~1680℃ (for example, it can be 1600℃, 1620℃, 1640℃, 1660℃ or 1680℃).

[0028] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S1, the molten steel from the alloy melting furnace and the electric furnace is added to an LF refining furnace for desulfurization to no more than 0.003 wt%, degassing, inclusion removal treatment, and adjustment to the required composition; subsequently, VD degassing treatment is performed, and the nitrogen content in the molten steel is no more than 70 × 10⁻⁶ by mass percentage. -6 Oxygen content not greater than 10×10 -6 .

[0029] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S1, after the molten steel undergoes the VD degassing treatment, it is poured into the consumable electrode mold at the consumable electrode casting station to cast the electrode base material. After mold cooling and demolding, the electrode base material is obtained. The temperature of the molten steel ladle is 1510~1560℃ (for example, it can be 1510℃, 1530℃ or 1560℃), and the mold cooling time is 2h~8h (for example, it can be 2h, 4h, 6h or 8h).

[0030] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S1, after obtaining the electrode base material, the electrode base material is subjected to stress-relief annealing. The stress-relief annealing includes loading the electrode base material into an annealing furnace, heating it to 750~800℃ (for example, 750℃, 770℃ or 800℃), holding it at an effective diameter of (2~4h) / 100mm, and then cooling it in the furnace to no higher than 200℃ before air cooling.

[0031] Here, the effective diameter = 1 / 2 × (diameter of the upper base + diameter of the lower base).

[0032] (2~4h) / 100mm / refers to the heat preservation time of 2-4h per 100mm of the effective diameter of the electrode base material. For example, if the effective diameter of the electrode base material is 200mm, then the heat preservation time is 4-8h.

[0033] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S1, to ensure the purity of the molten steel, after stress-relief annealing, the electrode base material is subjected to a cutting process and a surface finishing process. The cutting process is used to remove the poorly fed portions of the electrode base material to prevent foreign inclusions from being mixed into the molten steel during the smelting process; the surface finishing process is used to obtain an electrode base material with good surface quality and to prevent surface oxide scale and foreign inclusions from contaminating the molten steel.

[0034] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S2, the melting rate of the vacuum consumable melting is controlled at 6.0~12.0 kg / min (for example, it can be 6 kg / min, 8 kg / min, 10 kg / min or 12.0 kg / min). If the melting rate is too fast, the molten pool is too deep, resulting in severe segregation of alloying elements during solidification, and a wide equiaxed grain zone at the center of the ingot, leading to poor quality. If the melting rate is too slow, the molten pool does not receive enough heat, causing cold shut defects on the surface of the steel ingot, affecting the surface quality.

[0035] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional implementation, in order to obtain a steel ingot with better internal quality, feeding is started when the weight of the remaining electrode base material is 3% to 10% of the total weight of the initial electrode base material (for example, it can be 3%, 5%, 7% or 10%), so as to avoid large shrinkage cavities formed in the last solidified part of the steel ingot.

[0036] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S2, after obtaining the steel ingot, it is mold-cooled for 1h~5h (for example, 1h, 3h or 5h) and then demolded to perform stress-relief annealing on the steel ingot. The stress-relief annealing includes loading the steel ingot into an annealing furnace and heating it to 750~800℃ (for example, 750℃, 770℃ or 800℃), holding it at an effective diameter of (2~4h) / 100mm, and then cooling it in the furnace to no higher than 200℃ before air cooling.

[0037] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S3, the high-temperature homogenization treatment includes holding the steel ingot obtained in step S2 at 1200~1300℃ (for example, 1200℃, 1220℃, 1240℃, 1260℃, 1280℃, or 1300℃) at an effective diameter of (2~4h) / 100mm to improve the original chemical composition and microstructure segregation of the steel ingot. If the temperature is too low, the diffusion rate of alloying elements is slow, and the homogenization effect cannot be achieved; if the temperature is too high, the steel ingot will overheat or burn, reducing the performance of the steel and even rendering it unusable.

[0038] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S3, the multi-directional upsetting and drawing forging process includes: cooling the steel ingot after the high-temperature homogenization treatment to 1100~1200℃ (e.g., 1100℃, 1120℃, 1140℃, 1160℃, 1180℃ or 1200℃), performing multi-directional upsetting and drawing forging using an upper plate and a lower platform, with each reduction being 20~50% (e.g., 20%, 30%, 40% or 50%), flipping it 90° to press another plane, pressing down on the three planes twice in sequence, with a total forging ratio of 6~12 (e.g., 6, 8, 10 or 12), ensuring that the core of the forging is sufficiently deformed, and controlling the final forging temperature to 800~900℃ (e.g., 800℃, 820℃, 840℃, 860℃, 880℃ or 900℃), to obtain a forging with uniform properties and microstructure. If the final forging temperature is too high, the grain size will be coarse; if the final forging temperature is too low, the surface of the forging will be prone to cracking. The calculation method for the forging ratio depends on the specific forging process. The forging ratio during drawing is the ratio of the cross-sectional area before and after drawing, while the forging ratio during upsetting is the ratio of the height before and after upsetting. The total forging ratio is obtained by adding the forging ratios of each process. In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S4, the solution treatment temperature is 950~1050℃ (for example, it can be 950℃, 1000℃, or 1050℃), and the heat preservation time is 2~5h (for example, it can be 2h, 3h, or 5h).

[0039] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S4, during the water-air alternating cooling process, water-air alternating cooling is performed twice. The initial water temperature is no higher than 40°C. During the first immersion in water, the forging temperature drops to 450-550°C (e.g., 450°C, 500°C, or 550°C). After the first immersion in water, the forging temperature is air-cooled until dry. During the second immersion in water, the forging temperature drops to 250-350°C (e.g., 250°C, 300°C, or 350°C). The final water temperature is no higher than 50°C, and finally, air cooling is performed to 100-200°C (e.g., 100°C, 120°C, 140°C, 160°C, 180°C, or 200°C). If the initial water temperature is too high, the cooling rate decreases, failing to achieve the purpose of preventing carbide precipitation. If the final water temperature is too high, the cooling capacity decreases, the cooling time is prolonged, and martensite or lower bainite structures cannot be obtained. This invention, through water-air alternating cooling, makes the forging less prone to cracking.

[0040] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, in step S5, the forging obtained in step S4 is heated in a furnace to 850~900℃ and held at a temperature of (3-5h) / 100mm. (3-5h) / 100mm means that the forging thickness is maintained for 3-5 hours per 100mm. For example, if the forging thickness is 200mm, the holding time is 6-10 hours.

[0041] In the above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel, as an optional embodiment, the composition of the corrosion-resistant, high-polish plastic mold steel, by mass percentage, includes: C 0.35~0.45%, Si 0.50~1.20%, Mn 0.50-1.20%, Cr 12.5-14.5%, Mo 0.20~0.50%, V 0.20~0.50%, Ni 0.30~0.80%, with the remainder being Fe and unavoidable impurities. This invention improves the corrosion resistance of the mold steel and reduces liquid carbide precipitation by adding molybdenum.

[0042] In a second aspect, the present invention provides a corrosion-resistant, high-polish plastic mold steel, which is prepared by the preparation method described in the first aspect.

[0043] Currently, the commonly used corrosion-resistant plastic mold steel on the market is 4Cr13NiVSi, which has poor resistance to chloride ion corrosion. The steel grade of this invention is based on 4Cr13NiVSi, with the addition of an appropriate amount of Mo to improve the steel's corrosion resistance and prevent pitting corrosion in chloride solutions. Simultaneously, molybdenum has a solid solution strengthening effect on ferrite and also improves the stability of carbides, thereby increasing the steel's strength. Molybdenum also plays a significant role in improving the steel's ductility, toughness, and wear resistance. Furthermore, by increasing the C and Si content, this invention achieves higher hardness and superior polishability in the mold steel.

[0044] The corrosion-resistant, high-polish plastic mold steel provided by this invention has non-metallic inclusions of no more than 0.5 grade and an oxygen mass percentage of no more than 10 × 10⁻⁶. -6 The nitrogen content by mass is not greater than 60 × 10⁻⁶ -6 The annealed microstructure meets the requirements of the A series as specified in GB / T35840.3-2018, with zero carbide precipitation and a surface finish of A1 (Ra 0.016 μm) and A0 (Ra 0.008 μm). After undergoing an acidic salt spray test in NaCl solution for 48 hours according to GB / T10125-2021, the defect area is 0 (no defects), and the appearance grade is 10 (highest).

[0045] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0046] Example 1 A corrosion-resistant, high-polish plastic mold steel has the following chemical composition and mass percentage: C 0.40%; Si 0.70%; Mn 0.50%; Cr 13.60%; Mo 0.30%; V 0.25%; Ni 0.40%; the remainder being Fe and unavoidable impurities.

[0047] The preparation method of the above-mentioned corrosion-resistant, high-polish plastic mold steel includes the following steps: S1. High-carbon ferrochrome (with a phosphorus content of 0.018 wt%), low-carbon ferrochrome (with a phosphorus content of 0.023 wt%), ferromolybdenum, ferrovanadium, and ferronickel are uniformly melted in an alloy melting furnace at a tapping temperature of 1570℃. Blast furnace hot metal (with a phosphorus content of 0.021 wt% and a total content of lead, arsenic, tin, antimony, and bismuth of 0.018 wt%) and medium-sized scrap steel are melted and dephosphorized in an electric furnace to a phosphorus content of 0.002 wt% at a tapping temperature of 1640℃. The molten steel from the alloy melting furnace and the electric furnace is then added to an LF refining furnace for desulfurization to 0.002 wt%, degassing, inclusion removal, and adjustment to the required composition. Subsequently, VD degassing treatment is performed, resulting in a nitrogen content of 70 × 10⁻⁶ by mass percentage in the molten steel. -6 Oxygen content is 8×10 -6 After the molten steel undergoes VD degassing treatment, it is poured into the consumable electrode mold at the consumable electrode casting station using an argon gas shield. A 6t electrode base material is then poured, followed by mold cooling and demolding to obtain the electrode base material. The ladle temperature is 1525℃, and the mold cooling time is 4 hours. After obtaining the electrode base material, it is placed in an annealing furnace and heated to 780℃. It is then held at this temperature for 24 hours at a ratio of 4h / 100mm effective diameter. The furnace is then shut off, and the material is cooled to 180℃ before being air-cooled to obtain a high-quality electrode base material. The obtained electrode base material is then subjected to trimming and surface finishing.

[0048] S2. The above-mentioned electrode base material is placed in a vacuum arc remelting furnace for vacuum arc remelting to obtain steel ingots. During the vacuum arc remelting process, the melting rate is controlled at 6~8 kg / min. Feeding begins when the remaining weight of the electrode base material is 4% of the initial total weight (feeding begins when the last 4% of the electrode base material weight is obtained). After obtaining the steel ingot, it is molded and cooled for 2 hours, then demolded and placed in an annealing furnace and heated to 780℃. It is held at this temperature for 20 hours according to an effective diameter of 4h / 100mm, then the furnace is turned off and cooled to 180℃ before being removed from the furnace and air-cooled to obtain high-quality steel ingots.

[0049] S3. The above steel ingot is subjected to high-temperature homogenization treatment at 1230℃ for 20 hours with an effective diameter of 4h / 100mm. Then, it is cooled in the furnace to 1160℃ and subjected to multi-directional upsetting forging using an upper plate and a lower platform. Each pressing is 30%, and the ingot is flipped 90° to press another plane. The three planes are pressed twice in sequence. The total forging ratio is 7.5, and the final forging temperature is 810℃. A forging with a thickness of 200mm × width of 810mm × length of 3500mm and uniform properties and structure is obtained.

[0050] S4. Load the above forgings into the furnace and heat them to the solution temperature of 1020℃. Hold them at this temperature for 2 hours. Cool them twice with alternating water and air. The initial water temperature is 28℃. The temperature of the forging drops to 480℃ after the first water immersion. The forging is then air-cooled until it is dry after the first water immersion. The temperature of the forging drops to 270℃ after the second water immersion. The final water temperature is 35℃. Then, the forging is air-cooled to 160℃.

[0051] S5. The above forgings are heated in the furnace to 870°C and held for 6 hours at a rate of 3h / 100mm thickness. Then, the temperature is reduced to 830°C at a rate of 15°C / h, and then reduced to 690°C at a rate of 10°C / h. After furnace cooling to 480°C, the parts are removed from the furnace and air-cooled to obtain mold steel.

[0052] The properties of the corrosion-resistant, high-polish plastic mold steel prepared by the above method were tested. The non-metallic inclusions were as follows: Class A (sulfide coarse series), Class A (sulfide fine series), Class B (alumina coarse series), Class B (alumina fine series), Class C (silicate coarse series), Class C (silicate fine series), Class D (spherical oxide coarse series), and Ds (large particle spherical oxide) were all grade 0; the Class D (spherical oxide) fine series was grade 0.5. The oxygen content, by mass percentage, was 6 × 10⁻⁶. -6 Nitrogen content 50×10 -6 The annealed structure meets the A2 standard specified in GB / T35840.3-2018; the carbide precipitation is zero according to GB / T18254 test; the surface finish (polishability) reaches A0 (Ra0.008μm); after undergoing acidic salt spray test in NaCl solution for 48h according to GB / T10125-2021, the defect area is 0 (no defects), and the appearance grade is 10 (highest).

[0053] Example 2 A corrosion-resistant, high-polish plastic mold steel has the following chemical composition and mass percentage: C 0.42%; Si 0.50%; Mn 0.60%; Cr 13.00%; Mo 0.35%; V 0.35%; Ni 0.60%; the remainder being Fe and unavoidable impurities.

[0054] The above-mentioned method for preparing corrosion-resistant, high-polish plastic mold steel includes the following steps: S1. High-carbon ferrochrome (with a phosphorus content of 0.018 wt%), low-carbon ferrochrome (with a phosphorus content of 0.023 wt%), ferromolybdenum, ferrovanadium, and ferronickel are uniformly melted in an alloy melting furnace at a tapping temperature of 1590℃. Blast furnace hot metal (with a phosphorus content of 0.021 wt% and a total content of lead, arsenic, tin, antimony, and bismuth of 0.018 wt%) and medium-sized scrap steel are melted and dephosphorized in an electric furnace to a phosphorus content of 0.003 wt% at a tapping temperature of 1660℃. The molten steel from the alloy melting furnace and the electric furnace is then added to an LF refining furnace for desulfurization to 0.001 wt%, degassing, inclusion removal, and adjustment to the required composition. Subsequently, VD degassing treatment is performed, resulting in a nitrogen content of 60 × 10⁻⁶ by mass percentage in the molten steel. -6 Oxygen content is 7×10 -6 After the molten steel undergoes VD degassing treatment, it is poured into the consumable electrode mold at the consumable electrode casting station using an argon gas shield. A 12t electrode base material is then poured, followed by mold cooling and demolding to obtain the electrode base material. The ladle temperature is 1535℃, and the mold cooling time is 6 hours. After obtaining the electrode base material, it is placed in an annealing furnace and heated to 760℃. It is then held at this temperature for 32 hours at a rate of 4h / 100mm effective diameter, followed by furnace cooling to 150℃ before air cooling to obtain a high-quality electrode base material. The obtained electrode base material is then subjected to trimming and surface finishing.

[0055] S2. The above-mentioned electrode base material is placed in a vacuum arc remelting furnace for vacuum arc remelting to obtain steel ingots. During the vacuum arc remelting process, the melting rate is controlled at 8~10Kg / min. Feeding begins when the remaining weight of the electrode base material is 8% of the initial total weight (feeding begins when the last 8% of the electrode base material weight is reached). After obtaining the steel ingot, the mold cooling time is 3h, followed by demolding. The steel ingot is then placed in an annealing furnace and heated to 770℃. It is held at this temperature for 27h according to an effective diameter of 3h / 100mm. After that, the furnace is turned off and cooled to 160℃ before being removed from the furnace and air-cooled to obtain a high-quality steel ingot.

[0056] S3. The above steel ingot is subjected to high-temperature homogenization treatment at 1270℃ for 27 hours with an effective diameter of 3h / 100mm. Then, it is cooled in the furnace to 1150℃ and subjected to multi-directional upsetting forging using an upper plate and a lower platform. Each pressing is 45%, and the ingot is flipped 90° to press another plane. The three planes are pressed twice in sequence. The total forging ratio is 10.2, and the final forging temperature is 850℃. A forging with uniform properties and structure with a thickness of 350mm × width of 1010mm × length of 3280mm is obtained.

[0057] S4. Load the above forgings into the furnace and heat them to the solution temperature of 1000℃. Hold them at this temperature for 4 hours. Cool them twice with alternating water and air. The initial water temperature is 25℃. The temperature of the forging drops to 500℃ during the first water immersion. The forging is then air-cooled until it is dry during the first water immersion. The temperature of the forging drops to 290℃ during the second water immersion. The final water temperature is 33℃. Then, the forging is air-cooled to 130℃.

[0058] S5. The above forgings are heated in the furnace to 890°C and held for 12 hours. Then the temperature is reduced to 820°C at a rate of 18°C / h, and then reduced to 660°C at a rate of 8°C / h. After furnace cooling to 450°C, the parts are removed from the furnace and air-cooled to obtain mold steel.

[0059] The properties of the corrosion-resistant, high-polish plastic mold steel prepared by the above method were tested. The non-metallic inclusions were as follows: Class D (spherical oxides) fine series was grade 0.5; other inclusions including Class A (sulfide), Class A (sulfide), Class B (alumina), Class B (alumina), Class C (silicate), Class C (silicate), Class D (spherical oxide), and Ds (large-particle spherical oxides) were all grade 0. The oxygen content, by mass percentage, was 4 × 10⁻⁶. -6 Nitrogen content 38×10 -6 The annealed structure meets the A2 standard specified in GB / T35840.3-2018; the carbide precipitation is zero according to GB / T18254 test; the surface finish (polishability) meets the A1 standard (Ra0.016μm); after undergoing acidic salt spray test in NaCl solution for 48 hours according to GB / T10125-2021, the defect area is 0 (no defects), and the appearance grade is 10 (highest).

[0060] Example 3 A corrosion-resistant, high-polish plastic mold steel has the following chemical composition and mass percentage: C 0.42%; Si 0.90%; Mn 0.80%; Cr 13.30%; Mo 0.40%; V 0.40%; Ni 0.50%; the remainder being Fe and unavoidable impurities.

[0061] The preparation method of the above-mentioned corrosion-resistant, high-polish plastic mold steel includes the following steps: S1. High-carbon ferrochrome (with a phosphorus content of 0.018 wt%), low-carbon ferrochrome (with a phosphorus content of 0.023 wt%), ferromolybdenum, ferrovanadium, and ferronickel are uniformly melted in an alloy melting furnace at a tapping temperature of 1600℃. Blast furnace hot metal (with a phosphorus content of 0.021 wt% and a total content of lead, arsenic, tin, antimony, and bismuth of 0.018 wt%) and medium-sized scrap steel are melted and dephosphorized in an electric furnace to a phosphorus content of 0.003 wt% at a tapping temperature of 1660℃. The molten steel from the alloy melting furnace and the electric furnace is then added to an LF refining furnace for desulfurization to 0.002 wt%, degassing, inclusion removal, and adjustment to the required composition. Subsequently, VD degassing treatment is performed, resulting in a nitrogen content of 70 × 10⁻⁶ by mass percentage in the molten steel. -6 Oxygen content is 8×10 -6 After the molten steel undergoes VD degassing treatment, it is poured into the consumable electrode mold at the consumable electrode casting station using an argon gas shield. A 6t electrode base material is then poured, followed by mold cooling and demolding to obtain the electrode base material. The ladle temperature is 1540℃, and the mold cooling time is 5 hours. After obtaining the electrode base material, it is placed in an annealing furnace and heated to 780℃. It is then held at this temperature for 24 hours at an effective diameter of 4h / 100mm, followed by furnace cooling to 180℃ before air cooling to obtain a high-quality electrode base material. The obtained electrode base material is then subjected to trimming and surface finishing.

[0062] S2. The above-mentioned electrode base material is placed in a vacuum arc remelting furnace for vacuum arc remelting to obtain steel ingots. During the vacuum arc remelting process, the melting rate is controlled at 6~8 kg / min. Feeding begins when the remaining weight of the electrode base material is 6% of the initial total weight (feeding begins when the last 6% of the electrode base material weight is obtained). After obtaining the steel ingot, it is molded and cooled for 3 hours, then demolded, and the steel ingot is placed in an annealing furnace and heated to 780℃. It is held at this temperature for 20 hours according to an effective diameter of 4h / 100mm, then the furnace is turned off and cooled to 180℃ before being removed from the furnace and air-cooled to obtain high-quality steel ingots.

[0063] S3. The above steel ingot is subjected to high-temperature homogenization treatment at 1230℃ for 20 hours with an effective diameter of 4h / 100mm. Then, it is cooled in the furnace to 1160℃ and subjected to multi-directional upsetting and drawing forging using an upper plate and a lower platform. Each pressing is 30%, and the ingot is flipped 90° to press another plane. The three planes are pressed twice in sequence. The total forging ratio is 7.5, and the final forging temperature is 810℃. A forging with a thickness of 200mm × width of 810mm × length of 3500mm and uniform properties and structure is obtained.

[0064] S4. Load the above forgings into the furnace and heat them to the solution temperature of 1020℃. Hold them at this temperature for 2 hours. Cool them alternately with water and air. The initial water temperature is 28℃. The temperature of the forging drops to 500℃ after the first water immersion. The forging is then air-cooled until it is dry after the first water immersion. The temperature of the forging drops to 300℃ after the second water immersion. The final water temperature is 33℃. Then, the forging is air-cooled to 160℃.

[0065] S5. The above forgings are heated in the furnace to 870°C and held for 8 hours at a thickness of 4h / 100mm. Then the temperature is reduced to 830°C at a rate of 15°C / h, and then reduced to 690°C at a rate of 10°C / h. After furnace cooling to 480°C, the parts are removed from the furnace and air-cooled to obtain mold steel.

[0066] The properties of the corrosion-resistant, high-polish plastic mold steel prepared by the above method were tested. The non-metallic inclusions were as follows: Class A (sulfide coarse series), Class A (sulfide fine series), Class B (alumina coarse series), Class B (alumina fine series), Class C (silicate coarse series), Class C (silicate fine series), Class D (spherical oxide coarse series), and Ds (large particle spherical oxide) were all grade 0; the Class D (spherical oxide) fine series was grade 0.5. The oxygen content, by mass percentage, was 8 × 10⁻⁶. -6 Nitrogen content 40×10 -6 The annealed structure meets the A2 standard specified in GB / T35840.3-2018; the carbide precipitation is zero according to GB / T18254 test; the surface finish (polishability) reaches A0 (Ra0.008μm); after undergoing acidic salt spray test in NaCl solution for 48h according to GB / T10125-2021, the defect area is 0 (no defects), and the appearance grade is 10 (highest).

[0067] As can be seen from Examples 1-3, the present invention reduces the inclusion content in mold steel by using blast furnace iron as raw material and further reduces the inclusion and gas content in mold steel by using vacuum self-consumption smelting, thereby improving the purity. The non-metallic inclusions in the obtained plastic mold steel are all no greater than grade 0.5. The present invention improves the material structure and compositional segregation by high-temperature homogenization treatment at 1200~1300℃. Through subsequent solution treatment and spheroidizing annealing, a fine and uniform spheroidized structure is obtained, so that the annealed structure of the obtained plastic mold steel can reach the A series specified in GB / T35840.3-2018 standard.

[0068] Comparative Example 1 The corrosion-resistant, high-polish plastic mold steel provided in this comparative example has the following chemical composition and mass percentage: C 0.40%; Si 0.70%; Mn 0.50%; Cr 13.60%; Mo 0.30%; V 0.25%; Ni 0.40%; the remainder being Fe and unavoidable impurities.

[0069] The preparation method of corrosion-resistant, high-polish plastic mold steel is basically the same as that in Example 1, except that: In step S2, the electrode base material is smelted by electroslag remelting. The specific process is as follows: 70wt% CaF2 + 30wt% CaO electroslag system is added at 5% of the weight of the electrode base material, the filling ratio is 0.70, the melting rate is 0.7Kg / h of the crystallizer diameter (in mm) (if the crystallizer diameter is A mm, then the melting rate is A × 0.7Kg / h), and argon gas protection is used throughout the process.

[0070] The properties of the corrosion-resistant, high-polish plastic mold steel prepared by the above method were tested. The non-metallic inclusions were as follows: Class A (sulfides) coarse and fine series were both grade 0.5; Class B (alumina) coarse and fine series were both grade 1.0; Class C (silicates) coarse and fine series were both grade 0; Class D (spherical oxides) coarse and fine series were both grade 1.0; and Ds (large-particle spherical oxides) was grade 1.0. The annealed microstructure reached A2 as specified in GB / T35840.3-2018. According to GB / T18254, the carbide liquefaction grade was 0.5. The surface finish (polishability) reached A4 (Ra 0.063 μm). After undergoing an acidic salt spray test in NaCl solution for 48 hours according to GB / T10125-2021, the defect area was 0.25 < A ≤ 0.5, and the appearance grade was 7.

[0071] As can be seen from the comparison, the metallurgical method of electroslag remelting has limited ability to remove non-metallic inclusions. Moreover, during the electroslag remelting process, the increased content of gases such as oxygen, nitrogen and hydrogen leads to the formation of new inclusions to a certain extent, resulting in the material's purity failing to meet the polishing requirements of mirror and optical surfaces.

[0072] Comparative Example 2 The corrosion-resistant, high-polish plastic mold steel provided in this comparative example has the following chemical composition and mass percentage: C 0.40%; Si 0.70%; Mn 0.50%; Cr 13.60%; Mo 0.30%; V 0.25%; Ni 0.40%; the remainder being Fe and unavoidable impurities.

[0073] The preparation method of corrosion-resistant high-polish plastic mold steel is basically the same as that in Example 1, except that in step S5, the above forging is heated to 870°C in a furnace and held for 6 hours at a thickness of 3h / 100mm. Then, the temperature is reduced to 690°C at a rate of 15°C / h, and then the furnace is cooled to 480°C before being removed from the furnace and air-cooled to obtain mold steel.

[0074] The properties of the corrosion-resistant, high-polish plastic mold steel prepared by the above method were tested. The non-metallic inclusions were as follows: Class A (sulfide coarse series), Class A (sulfide fine series), Class B (alumina coarse series), Class B (alumina fine series), Class C (silicate coarse series), Class C (silicate fine series), Class D (spherical oxide coarse series), and Ds (large particle spherical oxide) were all grade 0, and Class D (spherical oxide) fine series was grade 0.5. The annealed microstructure reached B2 as specified in GB / T35840.3-2018. According to GB / T18254, carbide precipitation was 0. The surface finish (polishability) reached A3 (Ra 0.032 μm). After undergoing an acidic salt spray test in NaCl solution for 48 hours according to GB / T10125-2021, the defect area was 0.1 < A ≤ 0.25, and the appearance grade was 8.

[0075] As can be seen from the comparative example, in step S5, when only high-speed cooling is used, the uniformity of the microstructure is reduced and the polishing performance is reduced.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a corrosion-resistant, high-polish plastic mold steel, characterized in that, The preparation method includes the following steps: S1. Using blast furnace iron, ferroalloys and scrap steel as raw materials, the electrode base material is cast under argon protection after being smelted in an alloy melting furnace and electric furnace, refined by LF, and degassed by VD. S2. The electrode base material is vacuum arc remelted in a vacuum arc remelting furnace to obtain steel ingots; S3. The steel ingot obtained in step S2 is subjected to high-temperature homogenization treatment, and then subjected to multi-directional upsetting and drawing forging treatment. S4. The forging obtained in step S3 is subjected to solution treatment, which includes heating the forging to the solution temperature and holding it at that temperature, followed by alternating water and air cooling to obtain martensite and lower bainite structures. S5. Perform spheroidizing annealing on the forgings obtained in step S4. The spheroidizing annealing includes heating the forgings obtained in step S4 in a furnace to 850~900℃, holding at that temperature, then reducing the temperature to 790~840℃ at a rate greater than 10℃ / h and not greater than 20℃ / h, then reducing the temperature to 660~700℃ at a rate of ≤10℃ / h, and then furnace cooling to ≤500℃ before removing from the furnace and air cooling. In step S3, the multi-directional upsetting and drawing forging process includes: cooling the steel ingot after the high-temperature homogenization treatment to 1100~1200℃ in a furnace, performing multi-directional upsetting and drawing forging using an upper plate and a lower platform, with each reduction being 20~50%, flipping it 90° to press another plane, pressing down on the three planes twice in sequence, with a total forging ratio of 6~12, and controlling the final forging temperature at 800~900℃ to obtain the forging; In step S4, the solution temperature is 950~1050℃, and the heat preservation time is 2~5h; In step S4, during the water-air alternating cooling process, the water and air are alternately cooled twice. The initial water temperature is no higher than 40°C. The temperature of the forging drops to 450~550°C during the first water immersion. The forging is then air-cooled until it is dry during the first water immersion. The temperature of the forging drops to 250~350°C during the second water immersion. The final water temperature is no higher than 50°C. Finally, the forging is air-cooled to 100~200°C. The composition of the corrosion-resistant, high-polish plastic mold steel, by mass percentage, includes: C 0.35~0.45%, Si 0.50~1.20%, Mn 0.50-1.20%, Cr 12.5-14.5%, Mo 0.20~0.50%, V 0.20~0.50%, Ni 0.30~0.80%, with the remainder being Fe and unavoidable impurities.

2. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 1, characterized in that, The phosphorus content in the blast furnace molten iron, by mass percentage, is not higher than 0.025%, and the total content of lead, arsenic, tin, antimony, and bismuth is not higher than 0.025%. The ferroalloys include high-carbon ferrochrome, low-carbon ferrochrome, ferromolybdenum, ferrovanadium, and ferronickel; The scrap steel includes at least one of medium-sized scrap steel and heavy scrap steel.

3. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 1, characterized in that, In step S1, the ferroalloy is melted uniformly in the alloy melting furnace, and the tapping temperature is 1550~1650℃. In step S1, the electric furnace is used to melt and dephosphorize the blast furnace iron and the scrap steel, with the phosphorus content not exceeding 0.005 wt% and the tapping temperature being 1600~1680℃. In step S1, the molten steel from the alloy melting furnace and the electric furnace is added to the LF refining furnace for desulfurization to no more than 0.003 wt%, degassing, inclusion removal, and adjustment to the required composition; subsequently, VD degassing treatment is performed, and the nitrogen content in the molten steel is no more than 70 × 10⁻⁶ by mass percentage. -6 Oxygen content not greater than 10×10 -6 ; In step S1, after the molten steel undergoes the VD degassing treatment, it is poured into the consumable electrode mold at the consumable electrode casting station to cast the electrode base material. After mold cooling and demolding, the electrode base material is obtained. The temperature of the molten steel ladle is 1510~1560℃, and the mold cooling time is 2h~8h.

4. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 1, characterized in that, In step S1, after obtaining the electrode base material, the electrode base material is subjected to stress-relief annealing. The stress-relief annealing includes loading the electrode base material into an annealing furnace, heating it to 750~800℃, holding it at the effective diameter (2~4h) / 100mm, and then cooling it in the furnace to no higher than 200℃ before air cooling.

5. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 4, characterized in that, In step S1, after stress-relief annealing, the electrode substrate is cut off and surface-finished.

6. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 1, characterized in that, In step S2, the melting rate of the vacuum consumable melting is controlled at 6.0~12.0 kg / min; In step S2, feeding begins when the remaining weight of the electrode base material is 3% to 10% of the total weight of the initial electrode base material; In step S2, after obtaining the steel ingot, it is molded for 1 to 5 hours and then demolded to perform stress-relief annealing. The stress-relief annealing includes loading the steel ingot into an annealing furnace and heating it to 750 to 800°C, holding it at the effective diameter (2 to 4 hours) / 100 mm, and then cooling it in the furnace to no more than 200°C before air cooling.

7. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 1, characterized in that, In step S3, the high-temperature homogenization treatment includes holding the steel ingot obtained in step S2 at 1200~1300℃ for a period of time at an effective diameter of (2~4h) / 100mm to perform high-temperature homogenization treatment.

8. The method for preparing corrosion-resistant, high-polish plastic mold steel according to claim 1, characterized in that, In step S5, the forging obtained in step S4 is loaded into the furnace and heated to 850~900℃, and kept at the temperature according to the thickness (3-5h) / 100mm.