A high-purity, corrosion-resistant plastic mold steel and its preparation method

Abstract

The present invention relates to a method for preparing high-purity, corrosion-resistant plastic mold steel, the main steps of which are as follows: S1, electric furnace smelting; S2, ladle refining furnace refining; S3, vacuum refining furnace refining; S4, casting electrode blanks; S5, electrode blank annealing; S6, electroslag remelting; S7, forging; S8, post-forging pretreatment; S9, ultrafine treatment. Using the above-mentioned preparation method, raw material quality control, electrode blank smelting and casting process optimization provide a full-process method for removing Class B inclusions in steel, thereby ensuring the purity of the electrode blank. This method solves the problem of low plastic mold steel polishing by controlling both material purity and carbide uniformity. The present invention also relates to high-purity, corrosion-resistant plastic mold steel.

Description

Technical Field

[0001] The present invention relates to the technical field of mold steel processing, and in particular to a high-purity, corrosion-resistant plastic mold steel and a preparation method thereof. Background Art

[0002] With the global economic and industrial restructuring, traditional industries such as manufacturing are shifting their focus to developing countries due to the increasing saturation of European and American markets, rising labor costs, declining profits, and a shift in focus to developing countries. After more than 30 years of transformation, upgrading, and innovative development, China's mold industry has become a major mold manufacturing and trading nation, and its transformation into a global mold powerhouse is accelerating.

[0003] With strong government support, a number of large, technologically advanced special steel companies have emerged in China, including Baosteel Special Steel, CITIC Pacific, Great Wall Special Steel, and Northeast Special Steel. These companies have made significant progress in composition design, alloying principles, and steelmaking technology, with some of their products reaching or approaching internationally advanced levels.

[0004] Currently, the mold manufacturing industry abroad is developing towards universalization, standardization, serialization, high efficiency, and short manufacturing cycles, and the application of CAD and CAM is becoming increasingly popular. To meet the needs of the mold manufacturing industry, mold materials are rapidly developing towards a variety of varieties, refinement, and productization. As mold working conditions become increasingly demanding, higher requirements are placed on mold quality, especially the purity and isotropy of the steel. To achieve this goal, electric furnaces and off-furnace refining processes are commonly used abroad to produce high-purity mold steel. Vacuum treatment is required for large-section forging modules and large steel products. For mold steels with higher purity requirements, most use electroslag remelting and vacuum self-consumption to further improve the purity, density, isotropy, and uniformity of the steel and reduce segregation.

[0005] Ultra-mirror stainless plastic mold steel requires high hardness uniformity, high density, and high purity. This places extremely high demands on the raw material application, smelting process, forging process, and heat treatment process. Domestic manufacturers are focusing on this area, conducting extensive research and development work in mold steel composition design and process optimization. However, the overall performance of mold steel is not very satisfactory, and further research and development of high-hardness uniformity, high density, and high-purity plastic mold steel is urgently needed. This project intends to produce the initial blank through raw material selection and smelting process optimization. The project will control key technical links such as high-temperature homogenization, three-dimensional forging, and ultra-fine heat treatment to improve the mold steel's internal composition, hardness uniformity, and polishing performance, significantly enhancing the actual level of domestically produced plastic mold steel. Summary of the Invention

[0006] The purpose of this invention is to provide a high-purity, corrosion-resistant plastic mold steel and its preparation method, so that its quality grade reaches the same or similar level as imported materials, gradually replacing imported products and better meeting the needs of downstream customers.

[0007] To achieve the above-mentioned purpose, the present invention provides a method for preparing high-purity corrosion-resistant plastic mold steel, the main steps of which are as follows:

[0008] S1. Electric furnace smelting:

[0009] The blast furnace molten iron, shear charge and bulk steel are proportioned according to the component content of the plastic mold steel, wherein the mass proportion of the blast furnace molten iron is ≥80%, and the mass proportion of Al in the shear charge and bulk steel is ≤0.01%. CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite are added, and the steel is melted and smelted in an electric furnace. After oxidation and slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added before tapping, and the tapping temperature is ≥1620℃.

[0010] The chemical composition content of the plastic mold steel is as follows: C 0.20-0.25%, Mn 0.30-0.60%, Si 0.80-1.00%, S ≤ 0.001%, P ≤ 0.010%, Cr 13.0-14.0%, Mo+V+Ni 1.00-1.50%, Cu ≤ 0.08%, and the remainder is Fe. The residual gas content is H ≤ 1.5 ppm, O ≤ 13 ppm, and N ≤ 140 ppm.

[0011] S2, Ladle refining furnace refining:

[0012] After smelting in the electric furnace, the molten steel is transferred to a ladle and hoisted to a refining furnace. Slag materials such as CaO, CaF2, C-Si powder, and a silicon-calcium-barium composite deoxidizer are added for reduction to produce a primary white slag. Based on the deviation between the actual composition of the molten steel in the refining furnace and the target composition, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and the steel is reheated to a temperature of ≥1620°C. CaO, CaF2, C-Si powder, a silicon-calcium-barium composite deoxidizer, and red bricks are added to produce a secondary white slag.

[0013] S3, vacuum refining furnace refining:

[0014] The vacuum refining furnace is pumped in step by step, and the final vacuum degree is ≥70Pa. The vacuum time is maintained for more than 16 minutes twice, and the target value of residual gas nitrogen is ≤120ppm. After the degassing is completed, samples are taken for analysis, and argon gas is blown into the hanging bag after the composition is qualified.

[0015] S4. Casting electrode blanks:

[0016] Preheat the ingot mold to 50-80°C, and then open the argon protection device on the pouring gate before pouring the electrode blank. The entire process of pouring the electrode blank is carried out under argon atmosphere.

[0017] S5. Electrode blank annealing:

[0018] Annealing the electrode blank after demoulding in step S4;

[0019] S6, electroslag remelting:

[0020] The electrode blank obtained in step S5 is subjected to surface machining on a lathe to remove surface iron oxide scale; after preheating at 200-350° C., a dummy electrode is welded to the tail of the electrode blank, and then placed in an electroslag furnace for electroslag remelting;

[0021] S7, Forging:

[0022] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1250-1280° C., kept warm for 22-35 hours, subjected to high-temperature diffusion homogenization, and then forged to the finished product size;

[0023] S8. Post-forging pretreatment:

[0024] The forging blank obtained in step S7 is water-cooled to a core temperature of ≤450°C, and then placed in a heat treatment furnace for high-temperature tempering treatment;

[0025] S9, ultra-fine processing:

[0026] The workpiece obtained in step S8 is subjected to ultrafine processing.

[0027] Specifically, in step S1,

[0028] The addition amount of CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite per ton of steel is: CaO 25-40kg, CaF2 2-3kg, silicon calcium barium composite deoxidizer 2-3kg, dolomite 8-12kg;

[0029] After oxidation slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added. The addition amount of CaO, cleaning agent and silicon calcium barium composite deoxidizer per ton of steel is 20-25kg of CaO, 3-5kg of cleaning agent and 2-3kg of silicon calcium barium composite deoxidizer.

[0030] Specifically, in step S2, the amount of CaO added per ton of steel in the first white slag production is 20-25 kg, CaF2 2-3 kg, C-Si powder 3-4 kg, and silicon-calcium-barium composite deoxidizer 2-3 kg;

[0031] In the secondary white slag, the amount added per ton of steel is 20~25kg of CaO, 2~3kg of CaF2, 3~4kg of C-Si powder, 2~3kg of silicon calcium barium composite deoxidizer, and 2~3kg of red bricks.

[0032] Specifically, in step S5, the charging conditions are as follows: the outer surface of the electrode blank is cooled to 300-400°C, the annealing temperature is 870-890°C, the holding time is 3D-5D, D is the diameter of the electrode blank, the unit is dm, and it is cooled to 350°C before being taken out of the furnace. After annealing, the riser and ingot tail are sawed.

[0033] Specifically, in step S6, the electroslag is configured into a five-element slag using CaF2, Al2O3, MgO, CaO, and SiO2, and then the five-element slag is pre-melted and subjected to secondary refining and purification to make FeO ≤ 0.15%; and then cooled to room temperature under an argon protective atmosphere.

[0034] Furthermore, in the five-element slag, the addition amount per ton of steel is CaF2 44-50kg, Al2O3 16-22kg, MgO 4-6kg, CaO 12-16kg, and SiO2 14-16kg.

[0035] Specifically, in step S7, the specific steps of forging to the finished product size are: the intermediate billet is forged by two upsetting and two drawing, and then the intermediate billet is alternately cooled in water and air and then reheated to 1100-1200°C and kept warm for 6-12 hours, and then radially three upsetting and three drawing are performed, and the holding temperature before the last fire is 950-1100°C, and the last fire is four drawing, with a drawing ratio ≥2 to the finished product size.

[0036] Specifically, in step S8, the specific steps of high temperature tempering are: heating the forging billet to 680-720°C, keeping it at this temperature for 15-30 hours, then stopping the power supply and cooling the furnace to 300-350°C before taking it out of the furnace.

[0037] Specifically, in step S9, the specific steps of the ultrafine treatment are: placing the workpiece obtained in step S8 into a heating furnace and heating it to 930-960°C with the furnace. After keeping warm, extreme cooling control is performed by direct quenching: the core temperature after cooling is ≤350°C; after cooling, the workpiece is placed in an annealing furnace, heated to 840-860°C, kept warm for 15-30 hours, cooled to 700-730°C in the furnace, kept warm for 25-50 hours for spheroidizing annealing.

[0038] A second object of the present invention is to provide a high-purity corrosion-resistant plastic mold steel prepared by the above-mentioned preparation method, wherein the chemical composition content by mass percentage is C 0.20-0.25%, Mn 0.30-0.60%, Si 0.80-1.00%, S ≤ 0.001%, P ≤ 0.010%, Cr 13.0-14.0%, Mo+V+Ni 1.00-1.50%, Cu ≤ 0.08%, and the remainder is Fe, and the residual gas content is H ≤ 1.5 ppm, O ≤ 13 ppm, and N ≤ 140 ppm.

[0039] The high-purity, corrosion-resistant plastic mold steel and its preparation method of the present invention have the following beneficial effects:

[0040] (1) The optimization of raw material quality control, electrode blank smelting and casting processes provides a full-process method for removing Class B inclusions in steel, ensuring the purity of the electrode blank; and solves the problem of low polishing degree of plastic mold steel from the two aspects of material purity and carbide uniformity control;

[0041] (2) The optimization of the electroslag ingot smelting process and the application optimization of the weakly alkaline five-element slag system provide a full-process method for removing D and Ds type inclusions in steel, ensuring the purity of the electroslag ingot;

[0042] (3) The optimization of high-temperature homogenization, multi-directional forging, post-forging heat treatment, and ultra-fine treatment processes provides a full-process method for carbide homogenization control, ensuring the uniformity of the organization. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The microstructure of the high-purity corrosion-resistant plastic mold steel obtained in Example 1;

[0044] Figure 2 The microstructure of the high-purity corrosion-resistant plastic mold steel obtained in Example 2;

[0045] Figure 3 This is the microstructure morphology of the high-purity corrosion-resistant plastic mold steel obtained in Example 3. DETAILED DESCRIPTION

[0046] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0047] Example 1

[0048] A method for preparing high-purity corrosion-resistant plastic mold steel, the main steps are as follows:

[0049] S1. Electric furnace smelting:

[0050] The blast furnace molten iron, shear charge and bulk steel are proportioned according to the component content of the plastic mold steel, wherein the mass proportion of the blast furnace molten iron is 85%, and the mass proportion of Al in the shear charge and bulk steel is 0.008%. CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite are added, and the steel is melted and smelted in an electric furnace. After oxidation and slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added before tapping, and the tapping temperature is 1650°C.

[0051] The chemical composition content of the plastic mold steel is shown in Table 1.

[0052] Table 1

[0053]

[0054] Note: The rest is Fe, and H≤1.5ppm, O≤10ppm, N≤140ppm.

[0055] S2, Ladle refining furnace refining:

[0056] After smelting in the electric furnace, the molten steel is transferred to a ladle and hoisted to a refining furnace. Slag materials such as CaO, CaF2, C-Si powder, and a silicon-calcium-barium composite deoxidizer are added for reduction to produce a primary white slag. Based on the deviation between the actual composition of the molten steel in the refining furnace and the target composition, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and the steel is reheated to a temperature of 1650°C. CaO, CaF2, C-Si powder, a silicon-calcium-barium composite deoxidizer, and red bricks are added to produce a secondary white slag.

[0057] S3, vacuum refining furnace refining:

[0058] The vacuum refining furnace is pumped in step by step, and the final vacuum degree is 70Pa. The vacuum time is maintained for 18 minutes twice, and the residual gas nitrogen is 100ppm. After the degassing is completed, samples are taken for analysis. If the composition is qualified, argon gas is blown into the hanging bag;

[0059] S4. Casting electrode blanks:

[0060] Preheat the ingot mold to 50-80°C, and then open the argon protection device on the pouring gate before pouring the electrode blank. The entire process of pouring the electrode blank is carried out under argon atmosphere.

[0061] S5. Electrode blank annealing:

[0062] Annealing the electrode blank after demoulding in step S4;

[0063] S6, electroslag remelting:

[0064] The electrode blank obtained in step S5 is subjected to surface machining on a lathe to remove surface iron oxide scale; after preheating at 200-350° C., a dummy electrode is welded to the tail of the electrode blank, and then placed in an electroslag furnace for electroslag remelting;

[0065] S7, Forging:

[0066] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1270° C., kept warm for 30 hours, subjected to high-temperature diffusion homogenization, and then forged to the finished product size;

[0067] S8. Post-forging pretreatment:

[0068] The forging blank obtained in step S7 is water-cooled to a surface temperature of 260° C., and then placed in a heat treatment furnace for high-temperature tempering treatment;

[0069] S9, ultra-fine processing:

[0070] The workpiece obtained in step S8 is subjected to ultrafine processing.

[0071] In this embodiment, in step S1,

[0072] The addition amount of CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite per ton of steel is: CaO 30kg, CaF2 2.5kg, silicon calcium barium composite deoxidizer 2.5kg, dolomite 10kg;

[0073] After oxidation slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added. The addition amount of CaO, cleaning agent and silicon calcium barium composite deoxidizer per ton of steel is 25kg of CaO, 4kg of cleaning agent and 2.5kg of silicon calcium barium composite deoxidizer.

[0074] Among them, in step S2, the amount of CaO 25kg, CaF2 2.5kg, C-Si powder 3.5kg, and silicon calcium barium composite deoxidizer 2.5kg are added per ton of steel in the first white slag production;

[0075] In the secondary white slag, the amount added per ton of steel is CaO 25kg, CaF2 2.5kg, C-Si powder 3.5kg, silicon calcium barium composite deoxidizer 2.5kg, and red brick 2.5kg.

[0076] In this embodiment, in step S5, the charging conditions are as follows: the outer surface of the electrode blank is cooled to 350°C, the annealing temperature is 880°C, the holding time is 4D, D is the diameter of the electrode blank, the unit is dm, and the electrode blank is cooled to 350°C and then taken out of the furnace. After annealing, the riser and ingot tail are sawed.

[0077] In this embodiment, in step S6, CaF2, Al2O3, MgO, CaO, and SiO2 are used to prepare a five-element slag, which is then pre-melted and subjected to secondary refining and purification to obtain a FeO content of 0.12%; and then cooled to room temperature under an argon protective atmosphere.

[0078] In this embodiment, the addition amount of CaF2 46kg, Al2O3 20kg, MgO 5kg, CaO 14kg, and SiO2 15kg per ton of steel in the five-element slag is.

[0079] In this embodiment, in step S7, the specific steps of forging to the finished product size are: the intermediate billet is forged by two upsetting and two drawing, and then the intermediate billet is alternately cooled in water and air and then reheated to 1150°C and kept warm for 10 hours, and then radially three upsetting and three drawing are performed, the holding temperature before the last tempering is 1050°C, and the last tempering and four drawing are performed, with a drawing length ratio of 2.3 to the finished product size.

[0080] In this embodiment, in step S8, the specific steps of high temperature tempering are: heating the forging billet to 700°C, keeping it at this temperature for 30 hours, then stopping the power supply to cool the furnace to 300°C and taking it out of the furnace.

[0081] In this embodiment, in step S9, the specific steps of the ultrafine treatment are: placing the workpiece obtained in step S8 into a heating furnace and heating it to 940°C with the furnace, and after keeping it warm, performing extreme cooling control by direct quenching: the surface temperature after cooling is 240°C; after cooling, placing the workpiece into an annealing furnace, heating it to 860°C, keeping it warm for 25 hours, cooling it to 720°C in the furnace, and keeping it warm for 40 hours to perform spheroidizing annealing.

[0082] Example 2

[0083] A method for preparing high-purity corrosion-resistant plastic mold steel is characterized by the following main steps:

[0084] S1. Electric furnace smelting:

[0085] The blast furnace molten iron, shear charge and bulk steel are proportioned according to the component content of the plastic mold steel, wherein the mass proportion of the blast furnace molten iron is 85%, and the mass proportion of Al in the shear charge and bulk steel is 0.008%. CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite are added, and the steel is melted and smelted in an electric furnace. After oxidation and slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added before tapping, and the tapping temperature is 1650°C.

[0086] The chemical component content of the plastic mold steel is shown in Table 2.

[0087] Table 2

[0088]

[0089] Note: The rest is Fe, and H≤1.5ppm, O≤10ppm, N≤140ppm.

[0090] S2, Ladle refining furnace refining:

[0091] After smelting in the electric furnace, the molten steel is transferred to a ladle and hoisted to a refining furnace. Slag materials such as CaO, CaF2, C-Si powder, and a silicon-calcium-barium composite deoxidizer are added for reduction to produce a primary white slag. Based on the deviation between the actual composition of the molten steel in the refining furnace and the target composition, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and the steel is reheated to a temperature of 1650°C. CaO, CaF2, C-Si powder, a silicon-calcium-barium composite deoxidizer, and red bricks are added to produce a secondary white slag.

[0092] S3, vacuum refining furnace refining:

[0093] The vacuum refining furnace is pumped in step by step, and the final vacuum degree is 70Pa. The vacuum time is maintained for 18 minutes twice, and the residual gas nitrogen is 100ppm. After the degassing is completed, samples are taken for analysis. If the composition is qualified, argon gas is blown into the hanging bag;

[0094] S4. Casting electrode blanks:

[0095] Preheat the ingot mold to 50-80°C, and then open the argon protection device on the pouring gate before pouring the electrode blank. The entire process of pouring the electrode blank is carried out under argon atmosphere.

[0096] S5. Electrode blank annealing:

[0097] Annealing the electrode blank after demoulding in step S4;

[0098] S6, electroslag remelting:

[0099] The electrode blank obtained in step S5 is subjected to surface machining on a lathe to remove surface iron oxide scale; after preheating at 200-350° C., a dummy electrode is welded to the tail of the electrode blank, and then placed in an electroslag furnace for electroslag remelting;

[0100] S7, Forging:

[0101] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1270° C., kept warm for 30 hours, subjected to high-temperature diffusion homogenization, and then forged to the finished product size;

[0102] S8. Post-forging pretreatment:

[0103] The forging blank obtained in step S7 is water-cooled to a surface temperature of 260° C., and then placed in a heat treatment furnace for high-temperature tempering treatment;

[0104] S9, ultra-fine processing:

[0105] The workpiece obtained in step S8 is subjected to ultrafine processing.

[0106] In this embodiment, in step S1,

[0107] The addition amount of CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite per ton of steel is: CaO 30kg, CaF2 2.5kg, silicon calcium barium composite deoxidizer 2.5kg, dolomite 10kg;

[0108] After oxidation slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added. The addition amount of CaO, cleaning agent and silicon calcium barium composite deoxidizer per ton of steel is 25kg of CaO, 4kg of cleaning agent and 2.5kg of silicon calcium barium composite deoxidizer.

[0109] Among them, in step S2, the amount of CaO 25kg, CaF2 2.5kg, C-Si powder 3.5kg, and silicon calcium barium composite deoxidizer 2.5kg are added per ton of steel in the first white slag production;

[0110] In the secondary white slag, the amount added per ton of steel is CaO 25kg, CaF2 2.5kg, C-Si powder 3.5kg, silicon calcium barium composite deoxidizer 2.5kg, and red brick 2.5kg.

[0111] In this embodiment, in step S5, the charging conditions are as follows: the outer surface of the electrode blank is cooled to 350°C, the annealing temperature is 880°C, the holding time is 4D, D is the diameter of the electrode blank, the unit is dm, and the electrode blank is cooled to 350°C and then taken out of the furnace. After annealing, the riser and ingot tail are sawed.

[0112] In this embodiment, in step S6, CaF2, Al2O3, MgO, CaO, and SiO2 are used to prepare a five-element slag, which is then pre-melted and subjected to secondary refining and purification to obtain a FeO content of 0.12%; and then cooled to room temperature under an argon protective atmosphere.

[0113] In this embodiment, the addition amount of CaF2 46kg, Al2O3 20kg, MgO 5kg, CaO 14kg, and SiO2 15kg per ton of steel in the five-element slag is.

[0114] In this embodiment, in step S7, the specific steps of forging to the finished product size are: the intermediate billet is forged by two upsetting and two drawing, and then the intermediate billet is alternately cooled in water and air and then reheated to 1150°C and kept warm for 10 hours, and then radially three upsetting and three drawing are performed, the holding temperature before the last tempering is 1050°C, and the last tempering and four drawing are performed, with a drawing length ratio of 2.3 to the finished product size.

[0115] In this embodiment, in step S8, the specific steps of high temperature tempering are: heating the forging billet to 700°C, keeping it at this temperature for 30 hours, then stopping the power supply to cool the furnace to 300°C and taking it out of the furnace.

[0116] In this embodiment, in step S9, the specific steps of the ultrafine treatment are: placing the workpiece obtained in step S8 into a heating furnace and heating it to 940°C with the furnace, and after keeping it warm, performing extreme cooling control by direct quenching: the surface temperature after cooling is 245°C; after cooling, placing the workpiece into an annealing furnace, heating it to 860°C, keeping it warm for 25 hours, cooling it to 720°C in the furnace, and keeping it warm for 40 hours to perform spheroidizing annealing.

[0117] Example 3

[0118] A method for preparing high-purity corrosion-resistant plastic mold steel is characterized by the following main steps:

[0119] S1. Electric furnace smelting:

[0120] The blast furnace molten iron, shear charge and bulk steel are proportioned according to the component content of the plastic mold steel, wherein the mass proportion of the blast furnace molten iron is 85%, and the mass proportion of Al in the shear charge and bulk steel is 0.008%. CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite are added, and the steel is melted and smelted in an electric furnace. After oxidation and slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added before tapping, and the tapping temperature is 1650°C.

[0121] The chemical component contents of the plastic mold steel are shown in Table 3.

[0122] Table 3

[0123]

[0124] Note: The rest is Fe, and H≤1.5ppm, O≤10ppm, N≤140ppm.

[0125] S2, Ladle refining furnace refining:

[0126] After smelting in the electric furnace, the molten steel is transferred to a ladle and hoisted to a refining furnace. Slag materials such as CaO, CaF2, C-Si powder, and a silicon-calcium-barium composite deoxidizer are added for reduction to produce a primary white slag. Based on the deviation between the actual composition of the molten steel in the refining furnace and the target composition, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and the steel is reheated to a temperature of 1650°C. CaO, CaF2, C-Si powder, a silicon-calcium-barium composite deoxidizer, and red bricks are added to produce a secondary white slag.

[0127] S3, vacuum refining furnace refining:

[0128] The vacuum refining furnace is pumped in step by step, and the final vacuum degree is 70Pa. The vacuum time is maintained for 18 minutes twice, and the residual gas nitrogen is 100ppm. After the degassing is completed, samples are taken for analysis. If the composition is qualified, argon gas is blown into the hanging bag;

[0129] S4. Casting electrode blanks:

[0130] Preheat the ingot mold to 50-80°C, and then open the argon protection device on the pouring gate before pouring the electrode blank. The entire process of pouring the electrode blank is carried out under argon atmosphere.

[0131] S5. Electrode blank annealing:

[0132] Annealing the electrode blank after demoulding in step S4;

[0133] S6, electroslag remelting:

[0134] The electrode blank obtained in step S5 is subjected to surface machining on a lathe to remove surface iron oxide scale; after preheating at 200-350° C., a dummy electrode is welded to the tail of the electrode blank, and then placed in an electroslag furnace for electroslag remelting;

[0135] S7, Forging:

[0136] The electroslag ingot obtained in step S6 is heated to a heating temperature of 1270° C., kept warm for 30 hours, subjected to high-temperature diffusion homogenization, and then forged to the finished product size;

[0137] S8. Post-forging pretreatment:

[0138] The forging blank obtained in step S7 is water-cooled to a surface temperature of 260° C., and then placed in a heat treatment furnace for high-temperature tempering treatment;

[0139] S9, ultra-fine processing:

[0140] The workpiece obtained in step S8 is subjected to ultrafine processing.

[0141] In this embodiment, in step S1,

[0142] The addition amount of CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite per ton of steel is: CaO 30kg, CaF2 2.5kg, silicon calcium barium composite deoxidizer 2.5kg, dolomite 10kg;

[0143] After oxidation slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added. The addition amount of CaO, cleaning agent and silicon calcium barium composite deoxidizer per ton of steel is 25kg of CaO, 4kg of cleaning agent and 2.5kg of silicon calcium barium composite deoxidizer.

[0144] Among them, in step S2, the amount of CaO 25kg, CaF2 2.5kg, C-Si powder 3.5kg, and silicon calcium barium composite deoxidizer 2.5kg are added per ton of steel in the first white slag production;

[0145] In the secondary white slag, the amount added per ton of steel is CaO 25kg, CaF2 2.5kg, C-Si powder 3.5kg, silicon calcium barium composite deoxidizer 2.5kg, and red brick 2.5kg.

[0146] In this embodiment, in step S5, the charging conditions are as follows: the outer surface of the electrode blank is cooled to 350°C, the annealing temperature is 880°C, the holding time is 4D, D is the diameter of the electrode blank, the unit is dm, and the electrode blank is cooled to 350°C and then taken out of the furnace. After annealing, the riser and ingot tail are sawed.

[0147] In this embodiment, in step S6, CaF2, Al2O3, MgO, CaO, and SiO2 are used to prepare a five-element slag, which is then pre-melted and subjected to secondary refining and purification to obtain a FeO content of 0.12%; and then cooled to room temperature under an argon protective atmosphere.

[0148] In this embodiment, the addition amount of CaF2 46kg, Al2O3 20kg, MgO 5kg, CaO 14kg, and SiO2 15kg per ton of steel in the five-element slag is.

[0149] In this embodiment, in step S7, the specific steps of forging to the finished product size are: the intermediate billet is forged by two upsetting and two drawing, and then the intermediate billet is alternately cooled in water and air and then reheated to 1150°C and kept warm for 10 hours, and then radially three upsetting and three drawing are performed, the holding temperature before the last tempering is 1050°C, and the last tempering and four drawing are performed, with a drawing length ratio of 2.3 to the finished product size.

[0150] In this embodiment, in step S8, the specific steps of high temperature tempering are: heating the forging billet to 700°C, keeping it at this temperature for 30 hours, then stopping the power supply to cool the furnace to 300°C and taking it out of the furnace.

[0151] In this embodiment, in step S9, the specific steps of the ultrafine treatment are: placing the workpiece obtained in step S8 into a heating furnace and heating it to 940°C with the furnace, and after keeping it warm, performing extreme cooling control by direct quenching: the surface temperature after cooling is 260°C; after cooling, placing the workpiece into an annealing furnace, heating it to 860°C, keeping it warm for 25 hours, cooling it to 720°C in the furnace, and keeping it warm for 40 hours to perform spheroidizing annealing.

[0152] In order to verify the mechanical properties of the plastic mold steel provided by the preparation method of the present invention, the inventors took samples of the mold steel obtained in Examples 1 to 3 for microstructure testing. Figures 1 to 3 As shown; the performance test data are shown in Table 4 and Table 5

[0153] Table 4

[0154]

[0155] Table 5

[0156]

[0157] From this we can see that

[0158] 1. By Figures 1 to 3 As shown, it can be concluded that the uniformity of carbides can be controlled through high-temperature homogenization, multi-directional forging, and ultra-fine treatment, so that the microstructure of the mold material in the spheroidized annealed state is uniform, and the spheroidal carbides are distributed on the ferrite matrix. According to the North American Die Casting Association NADCA #229-2022 standard, it is rated at level 3-4;

[0159] 2. Based on the composition and inclusion test data of Examples 1-3, it can be concluded that by controlling the quality of raw materials and reducing the Al and O contents in the steel, it is beneficial to control the types and levels of inclusions, which can significantly improve the purity of the material. The levels of all types of inclusions are ≤ 0.5;

[0160] 3. After pre-hardening, the mold material is polished and tested. The polishing score is above 90 points under the 16000# polishing grade, and the polishing quality is excellent.

[0161] In summary, the plastic mold steel prepared by this preparation method has high purity, high structural uniformity and high polishing performance.

[0162] The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the described embodiments. Those skilled in the art may make various equivalent modifications or substitutions without departing from the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for preparing high-purity corrosion-resistant plastic mold steel, characterized in that: The main steps are as follows: S1. Electric furnace smelting: The blast furnace molten iron, shear charge and bulk steel are proportioned according to the component content of the plastic mold steel, wherein the mass proportion of the blast furnace molten iron is ≥80%, and the mass proportion of Al in the shear charge and bulk steel is ≤0.01%. CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite are added, and the steel is melted and smelted in an electric furnace. After oxidation and slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added before tapping, and the tapping temperature is ≥1620℃. The chemical composition content of the plastic mold steel is as follows: C 0.20-0.25%, Mn 0.30-0.60%, Si 0.80-1.00%, S ≤ 0.001%, P ≤ 0.010%, Cr 13.0-14.0%, Mo+V+Ni 1.00-1.50%, Cu ≤ 0.08%, and the remainder is Fe. The residual gas content is H ≤ 1.5 ppm, O ≤ 13 ppm, and N ≤ 140 ppm. S2, Ladle refining furnace refining: After smelting in the electric furnace, the molten steel is transferred to a ladle and hoisted to a refining furnace. Slag materials such as CaO, CaF2, C-Si powder, and a silicon-calcium-barium composite deoxidizer are added for reduction to produce a primary white slag. Based on the deviation between the actual composition of the molten steel in the refining furnace and the target composition, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation is completed, the white slag is removed, and the steel is reheated to a temperature of ≥1620°C. CaO, CaF2, C-Si powder, a silicon-calcium-barium composite deoxidizer, and red bricks are added to produce a secondary white slag. S3, vacuum refining furnace refining: The vacuum refining furnace is pumped in step by step, and the final vacuum degree is ≥70Pa. The vacuum time is maintained for more than 16 minutes twice, and the target value of residual gas nitrogen is ≤120ppm. After the degassing is completed, samples are taken for analysis, and argon gas is blown into the hanging bag after the composition is qualified. S4. Casting electrode blanks: Preheat the ingot mold to 50-80°C, and then open the argon protection device on the pouring gate before pouring the electrode blank. The entire process of pouring the electrode blank is carried out under argon atmosphere. S5. Electrode blank annealing: Annealing the electrode blank after demoulding in step S4; S6, electroslag remelting: The electrode blank obtained in step S5 is subjected to surface machining on a lathe to remove surface iron oxide scale; after preheating at 200-350° C., a dummy electrode is welded to the tail of the electrode blank, and then placed in an electroslag furnace for electroslag remelting; In step S6, the electroslag is configured into a five-element slag using CaF2, Al2O3, MgO, CaO, and SiO2, and then the five-element slag is pre-melted and subjected to secondary refining and purification to make FeO ≤ 0.15%; and then cooled to room temperature under an argon protective atmosphere; In the five-element slag, the addition amount per ton of steel is CaF2 44-50kg, Al2O3 16-22kg, MgO 4-6kg, CaO 12-16kg, SiO2 14-16kg; S7, Forging: The electroslag ingot obtained in step S6 is heated to a heating temperature of 1250-1280° C., kept warm for 22-35 hours, subjected to high-temperature diffusion homogenization, and then forged to the finished product size; In step S7, the specific steps of forging to the finished product size are as follows: the intermediate billet is forged by two upsetting and two drawing, and then the intermediate billet is alternately cooled in water and air and then reheated to 1100-1200°C and kept warm for 6-12 hours, and then radially upsetting and drawing three times, with the holding temperature before the last tempering being 950-1100°C, and finally tempering and drawing four times, with the drawing ratio ≥2 to the finished product size; S8. Post-forging pretreatment: The forging blank obtained in step S7 is water-cooled to a core temperature of ≤450°C, and then placed in a heat treatment furnace for high-temperature tempering treatment; In step S8, the specific steps of high temperature tempering are: heating the forging billet to 680-720°C, holding the billet at this temperature for 15-30 hours, then cooling the billet to 300-350°C after power off; S9, ultra-fine processing: The workpiece obtained in step S8 is subjected to ultrafine processing.

2. The method for preparing high-purity corrosion-resistant plastic mold steel according to claim 1, characterized in that: In step S1, The addition amount of CaO, CaF2, silicon calcium barium composite deoxidizer and dolomite per ton of steel is: CaO 25-40kg, CaF2 2-3kg, silicon calcium barium composite deoxidizer 2-3kg, dolomite 8-12kg; After oxidation slagging, CaO, cleaning agent and silicon calcium barium composite deoxidizer are added. The addition amount of CaO, cleaning agent and silicon calcium barium composite deoxidizer per ton of steel is 20-25kg of CaO, 3-5kg of cleaning agent and 2-3kg of silicon calcium barium composite deoxidizer.

3. The method for preparing high-purity corrosion-resistant plastic mold steel according to claim 1, characterized in that: In step S2, the amount of CaO added per ton of steel in the first white slag production is 20-25 kg, CaF2 2-3 kg, C-Si powder 3-4 kg, and silicon-calcium-barium composite deoxidizer 2-3 kg; In the secondary white slag, the amount added per ton of steel is 20~25kg of CaO, 2~3kg of CaF2, 3~4kg of C-Si powder, 2~3kg of silicon calcium barium composite deoxidizer, and 2~3kg of red bricks.

4. The method for preparing high-purity corrosion-resistant plastic mold steel according to claim 1, characterized in that: In step S5, the charging condition is that the outer surface of the electrode blank is cooled to 300-400°C, the annealing temperature is 870-890°C, and the electrode blank is cooled to 350°C before being taken out of the furnace. After annealing, the riser and ingot tail are sawed.

5. The method for preparing high-purity corrosion-resistant plastic mold steel according to claim 1, characterized in that: In step S9, the specific steps of the ultrafine treatment are as follows: placing the workpiece obtained in step S8 into a heating furnace and heating it to 930-960°C with the furnace. After keeping warm, the workpiece is subjected to extreme cooling control by direct quenching: the core temperature after cooling is ≤350°C; after cooling, the workpiece is placed in an annealing furnace, heated to 840-860°C, kept warm for 15-30 hours, cooled to 700-730°C in the furnace, kept warm for 25-50 hours for spheroidizing annealing.

6. A high-purity corrosion-resistant plastic mold steel prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The chemical components are as follows: C 0.20-0.25%, Mn 0.30-0.60%, Si 0.80-1.00%, S≤0.001%, P≤0.010%, Cr 13.0-14.0%, Mo+V+Ni 1.00-1.50%, Cu≤0.08%, and the rest is Fe. The residual gas content is: H≤1.5ppm, O≤13ppm, and N≤140ppm.

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