Plastic mold steel and production process

Abstract

The present application belongs to the technical field of steel forging and heat treatment, and the present application discloses a plastic mold steel and a production process. The chemical composition of the plastic mold steel in the present application includes elements such as C, Mn, Si, Cr, Mo and Ni, and also includes trace amounts of Ce and Y elements. The toughness, polishing effect and corrosion resistance of the plastic mold steel are improved, and the hardenability of the steel is improved so that the hardness distribution along the cross section is uniform. The preparation method of the plastic mold steel in the present application includes smelting, vacuum degassing, heat preservation, forging, normalizing, roughening and drawing, and heat treatment steps. The plastic mold steel prepared in the present application has a uniform hardness distribution along the cross section and strong corrosion resistance. The prepared plastic mold steel has good sawing processing performance and is suitable for making plastic molds with strict dimensional accuracy requirements and complex cavities.

Description

Technical Field

[0001] The present application relates to the technical field of steel forging and heat treatment, and in particular to a plastic mold steel and a production process. Background Art

[0002] The plastic products industry is developing very rapidly, and its output and consumption are growing relatively steadily. At the same time, it has also brought about the rapid development of plastic mold steel. my country's plastic mold steel industry is currently in the early stage of development. The number of special steel types for plastic molds is small and relatively scarce. High-precision mold steels such as P20 and 718 pre-hardened plastic mold steel modules and high-precision flat steel are particularly scarce. There are still problems such as long delivery time, poor quality and incomplete varieties and specifications in China. Plastic mold steel made by traditional technology has poor toughness, poor mirror polishing effect, and weak corrosion resistance. At present, the plastic mold steel industry is developing towards large-scale and precision; therefore, it is required that the mold steel plate has uniform hardness in the cross-section direction, excellent cutting processability, mirror polishing, pattern etching, and good basic properties such as wear resistance, electrospark processing, welding, and plastic product corrosion resistance. Therefore, how to develop a plastic mold steel with excellent cutting processability and polishing, and simplify its production process is of great significance to improving the comprehensive performance of the mold and promoting the development of the mold industry. Summary of the invention

[0003] In order to solve the above technical problems, a plastic mold steel with uniform hardness distribution, strong polishability and corrosion resistance is developed. The present application provides a plastic mold steel and a production process.

[0004] In the first aspect, the present application provides a plastic mold steel, the chemical composition of the plastic mold steel and its mass percentage are: C: 0.6-0.8%, Mn: 1.6-3.9%, Si: 0.4-0.8%, Cr: 1.2-2 parts, Mo: 0.5-0.8 parts, Ni: 0.5-1.3%, P≤0.02%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0005] Furthermore, the chemical composition of the plastic mold steel and its mass percentage are: C: 0.6-0.8%, Mn: 1.6-3.9%, Si: 0.4-0.8%, Cr: 1.2-2%, Mo: 0.5-0.8%, Ni: 0.5-1.3%, Ce: 0.01-0.04%, Y: 0.005-0.015%, P≤0.02%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0006] Furthermore, the chemical composition of the plastic mold steel and its mass percentage are: C: 0.74%, Mn: 3.1%, Si: 0.68%, Cr: 1.5%, Mo: 0.55%, Ni: 0.82%, Ce: 0.018%, Y: 0.01%, P≤0.02%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0007] By adopting the above technical scheme, the present application improves the composition of plastic mold steel. On the one hand, manganese, chromium, molybdenum and nickel are added to form the matrix material of the steel alloy to improve the toughness, polishing effect and corrosion resistance of the plastic mold steel. On the other hand, trace amounts of cerium and yttrium elements are added to improve the hardenability of the steel, improve the organizational stability and uniformity of the plastic mold steel, and make the hardness distribution along the cross section uniform, which is suitable for making plastic molds with strict requirements on dimensional accuracy and surface roughness and complex cavities. Further, the raw materials of the plastic mold steel include carbon powder, ferromanganese, ferrosilicon, ferrochromium, ferromolybdenum, electrolytic nickel, CeO2, Y2O3 and iron blocks.

[0008] In a second aspect, the present application provides a method for preparing the above-mentioned plastic mold steel, comprising the following steps:

[0009] S1, smelting the iron block to obtain molten steel, transferring the molten steel into the LF furnace, adding the remaining raw materials for smelting, refining, deoxidizing and desulfurizing the molten steel;

[0010] S2, vacuum degassing is performed, and after degassing is completed, a steel ingot is cast in a protective gas atmosphere;

[0011] S3, keeping the steel ingot at 1260-1300° C. for 15-18 hours, and forging the steel ingot after keeping the temperature to obtain a forging blank;

[0012] S4, cooling the forging blank obtained in step S3 and then performing normalizing treatment;

[0013] S5. The forging blank after the normalizing treatment in step S4 is subjected to roughening and drawing processes, the roughening ratio of the roughening is 2-5, and the compression ratio of the drawing is 1.1-1.3, and then heat treatment is performed to obtain plastic mold steel; the heat treatment includes heat preservation, quenching and tempering.

[0014] Furthermore, in the step S2, when vacuum degassing is performed, the vacuum degree is controlled at 50-80 Pa, and the degassing time is 10-20 min.

[0015] Furthermore, in the step S3, the steel ingot after heat preservation is forged, the initial forging temperature is 1100-1180°C, the final calcination temperature is 720-820°C, and the forging ratio is 4-8.

[0016] Furthermore, in step S4, when the forging blank is subjected to normalizing treatment, it is kept at 850-880° C. for 6-9 hours and air-cooled to room temperature.

[0017] Furthermore, in step S5, the heat treatment includes: keeping the forged billet after the roughening and drawing process in step S4 at 800-900°C for 8-9h, quenching to a surface temperature of 200-250°C, charging into a tempering furnace for tempering, the tempering temperature is 580-640°C, the tempering time is 10-14h, and air cooling for 20-40min after being taken out of the furnace to obtain plastic mold steel.

[0018] Preferably, in step S5, tempering is performed multiple times, and the tempering-air cooling process is repeated 2-4 times.

[0019] By adopting the above technical solution, vacuum degassing can fully remove the gas in the molten steel to obtain high-purity molten steel, which is conducive to the uniform distribution of manganese, chromium, molybdenum, nickel, cerium and yttrium elements in the molten steel, which is conducive to improving the hardenability of the steel; the steel ingot is kept at 1260-1300℃ before forging to make carbon, silicon, manganese, chromium, molybdenum, nickel, cerium and yttrium elements fully dissolved and evenly distributed in the high-temperature austenite, creating conditions for obtaining a homogenized steel plate, and at the same time preventing the excessive growth of the high-temperature austenite from affecting Steel properties: During the forging process, the initial forging temperature and the final forging temperature are strictly controlled to prevent the steel plate from cooling down too fast, forming a martensitic structure, and exceeding the hardness standard. The superposition of thermal stress and structural stress brings the risk of cracks or even rupture in the steel ingot. Before heat treatment, the forging billet after normalizing treatment is subjected to roughening and drawing processes, which is beneficial to reduce the segregation of low-melting-point solutes inside the ingot, and the carbide distribution in the structure is dispersed and uniform, so as to obtain a homogenized forging billet. In the subsequent heat treatment process, the hardness of the steel structure can be within a reasonable range.

[0020] In summary, the present invention includes at least one of the following beneficial technical effects:

[0021] The plastic mold steel prepared by the present application has uniform hardness distribution along the cross section and strong corrosion resistance. The prepared plastic mold steel has good sawing processing performance and is suitable for making plastic molds with strict dimensional accuracy requirements and complex cavities. DETAILED DESCRIPTION

[0022] The present application designs a plastic mold steel, the chemical composition of the plastic mold steel and its mass percentage are: C: 0.6-0.8%, Mn: 1.6-3.9%, Si: 0.4-0.8%, Cr: 1.2-2 parts, Mo: 0.5-0.8 parts, Ni: 0.5-1.3%, P≤0.02%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0023] The chemical composition of the plastic mold steel and its mass percentage are: C: 0.6-0.8%, Mn: 1.6-3.9%, Si: 0.4-0.8%, Cr: 1.2-2%, Mo: 0.5-0.8%, Ni: 0.5-1.3%, Ce: 0.01-0.04%, Y: 0.005-0.015%, P≤0.02%, S≤0.01%, and the balance is iron and unavoidable impurities.

[0024] The plastic mold steel of the present application is prepared by the following method, comprising the following steps:

[0025] S1, smelting the iron block to obtain molten steel, transferring the molten steel into the LF furnace, and adding the remaining raw materials for smelting;

[0026] S2, vacuum degassing is performed, and after degassing is completed, a steel ingot is cast in a protective gas atmosphere;

[0027] S3, keeping the steel ingot at 1260-1300° C. for 15-18 hours, and forging the steel ingot after keeping the temperature to obtain a forging blank;

[0028] S4, cooling the forging blank obtained in step S3 and then performing normalizing treatment;

[0029] S5. The forging blank after the normalizing treatment in step S4 is subjected to roughening and drawing processes, the roughening ratio of the roughening is 2-5, and the compression ratio of the drawing is 1.1-1.3, and then heat treatment is performed to obtain plastic mold steel; the heat treatment includes heat preservation, quenching and tempering.

[0030] The technical problem solved by the present application is that plastic mold steel has poor toughness, poor mirror polishing effect, and weak corrosion resistance. In order to meet the requirements of existing plastic mold steel for processability, corrosion resistance and wear resistance, the present application adds manganese, chromium, molybdenum and nickel to the formula to form a base material of the steel alloy, adds trace amounts of cerium and yttrium elements, and uses a specific sequence of production processes to obtain a plastic mold steel with uniform hardness distribution, strong corrosion resistance, and good sawing processing performance, which is suitable for making plastic molds with strict dimensional accuracy requirements and complex cavities.

[0031] The present application is further described in detail below in conjunction with specific embodiments.

[0032] Examples 1-6

[0033] Examples 1-6 are plastic mold steels with different element contents. The specific chemical compositions and mass percentages are shown in Table 1.

[0034] Table 1

[0035]

[0036]

[0037] As described in Table 1, in addition to the above elements and proportions listed in Table 1, in Examples 1-6, P≤0.02%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0038] The raw materials used in Examples 1-6 are carbon powder, ferromanganese, ferrosilicon, ferrochromium, ferromolybdenum, electrolytic nickel, CeO2, Y2O3 and iron blocks, respectively.

[0039] The preparation method of the plastic mold steel in Examples 1-6 comprises the following steps:

[0040] S1, move the iron block into an electric furnace for smelting to obtain molten steel, move the molten steel into an LF furnace, add the remaining raw materials for smelting, and refine, deoxidize and desulfurize the molten steel;

[0041] S2, vacuum degassing, the vacuum degree is controlled at 60Pa, and the degassing time is 15min; after the degassing is completed, the steel ingot is cast in an argon atmosphere;

[0042] S3, keeping the steel ingot at 1280° C. for 16 hours, forging the steel ingot after keeping the temperature, setting the initial forging temperature to 1160° C., the final calcination temperature to 790° C., and the forging ratio to 7, to obtain a forging blank;

[0043] S4, cooling the forging blank obtained in step S3, performing normalizing treatment, keeping the temperature at 870° C. for 8 hours, and air cooling to room temperature;

[0044] S5. The forging blank after the normalizing treatment in step S4 is subjected to one upsetting and one drawing process, the upsetting ratio of the upsetting is set to 3, and the compression ratio of the drawing is set to 1.3, and then a heat treatment is performed, the forging blank after the upsetting and drawing process is kept at 880° C. for 8 hours, and quenched to a surface temperature of 200° C.; the quenched forging blank is tempered: the forging blank is loaded into a tempering furnace for tempering, the tempering temperature is 620° C., the tempering time is 12 hours, and the furnace is air-cooled for 30 minutes. The tempering treatment is performed only once to obtain a plastic mold steel.

[0045] Embodiment 7-8

[0046] Example 7 is based on Example 5, with the difference that: step S3 of the method for preparing plastic mold steel in Example 7 is changed to: keeping the steel ingot at 1260° C. for 18 hours, and forging the steel ingot after keeping the temperature.

[0047] Example 8 is based on Example 5, with the difference that step S3 of the method for preparing plastic mold steel in Example 8 is changed to: keeping the steel ingot at 1300° C. for 15 hours, and forging the steel ingot after keeping the temperature.

[0048] Examples 9-10

[0049] Example 9 is based on Example 5, with the difference that step S3 of the method for preparing plastic mold steel in Example 9 is changed to: the initial forging temperature during forging is set to 1100°C, the final calcination temperature is set to 820°C, the forging ratio is set to 4, and a forging blank is obtained.

[0050] Example 10 is based on Example 5, with the difference that step S3 of the method for preparing plastic mold steel in Example 10 is changed to: the initial forging temperature during forging is set to 1180°C, the final calcination temperature is set to 720°C, the forging ratio is set to 8, and a forging blank is obtained.

[0051] Examples 11-13

[0052] Example 11 is based on Example 5, with the difference that the tempering-air cooling process in step S5 of the method for preparing plastic mold steel in Example 11 is performed twice.

[0053] Example 12 is based on Example 5, with the difference that the tempering-air cooling process in step S5 of the method for preparing plastic mold steel in Example 12 is performed three times.

[0054] Example 13 is based on Example 5, with the difference that the tempering-air cooling process in step S5 of the method for preparing plastic mold steel in Example 13 is performed 5 times.

[0055] Comparative Example 1

[0056] Comparative Example 1 is based on Example 5, except that the chemical composition and mass percentage of the plastic mold steel in Comparative Example 1 are: C: 0.74%, Mn: 3.1%, Si: 0.68%, Cr: 1.6%, Mo: 0.55%, Ni: 1.9%, Ce: 0.018%, Y: 0.01%, P≤0.02%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0057] Comparative Example 2

[0058] Comparative Example 2 is based on Example 5, with the difference that: in the preparation method of the plastic mold steel in Comparative Example 2, the roughing and drawing processes are not performed before the heat treatment in step S5, that is, step S5 is changed to: heat treating the forging blank after the normalizing treatment in step S4, keeping the forging blank at 880°C for 8h, quenching to a surface temperature of 200°C; loading into a tempering furnace for tempering, the tempering temperature is 620°C, the tempering time is 12h, and the furnace is air-cooled for 30min. The tempering-air-cooling process is performed only once to obtain a plastic mold steel.

[0059] Comparative Example 3

[0060] Comparative Example 3 is based on Example 5, except that: in the preparation method of the plastic mold steel in Comparative Example 3, the normalizing treatment is changed to the annealing treatment in step S4. That is, step S4 is changed to: the forging blank prepared in step S3 is cooled and then annealed, kept at 660°C for 25h, slowly cooled to 450°C at a rate of 5°C / min, and air-cooled after being taken out of the furnace.

[0061] Performance Testing

[0062] 1. Referring to the polishing process in standard GB / T6060.1-2009, the surface roughness Ra value (μm) of the plastic mold steel prepared in Examples 1-13 and Comparative Examples 1-3 was measured.

[0063] 2. With reference to standard GB / T 10125-1997 "Artificial atmosphere corrosion test salt spray test", the corrosion resistance of the plastic mold steels prepared in Examples 1-13 and Comparative Examples 1-3 was measured, and the corrosion rate was determined by spraying with a 5% NaCl aqueous solution for 72 hours.

[0064] 3. A wear test was conducted using a rubber wheel wear tester to determine the wear resistance of the plastic mold steels prepared in Examples 1-13 and Comparative Examples 1-3: relative loss was measured.

[0065] 4. The Rockwell hardness and homogeneity of the core of the plastic mold steel prepared in Examples 1-13 and Comparative Examples 1-3 were measured.

[0066] The measurement results are shown in Table 2.

[0067] surface

[0068]

[0069] By analyzing the data in Table 2 and comparing the various performance indicators of Examples 1-13 with those of Comparative Examples 1-3, it can be seen that the plastic mold steel prepared in the present application has excellent wear resistance, high hardness and uniform hardness distribution, and at the same time, its polishability and corrosion resistance are both strong, and it is suitable for making plastic molds with strict dimensional accuracy requirements and complex cavities.

[0070] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing plastic mold steel, characterized in that: The following steps are involved: S1, smelting the iron block to obtain molten steel, transferring the molten steel into the LF furnace, adding the remaining raw materials for smelting, refining, deoxidizing and desulfurizing the molten steel; S2, vacuum degassing is performed, and after degassing is completed, a steel ingot is cast in a protective gas atmosphere; S3, keeping the steel ingot at 1260-1300° C. for 15-18 hours, and forging the steel ingot after keeping the temperature to obtain a forging blank; S4, cooling the forging blank obtained in step S3 and then performing normalizing treatment; S5, subjecting the forged blank after the normalizing treatment in step S4 to roughening and drawing processes, wherein the roughening ratio of the roughening is 2-5 and the compression ratio of the drawing is 1.1-1.3, and then subjecting the same to heat treatment to obtain a plastic mold steel; wherein the heat treatment includes heat preservation, quenching and tempering; The chemical composition and mass percentage of the plastic mold steel are: C: 0.6-0.8%, Mn: 1.6-3.9%, Si: 0.4-0.8%, Cr: 1.2-2%, Mo: 0.5-0.8%, Ni: 0.5-1.3%, Ce: 0.01-0.04%, Y: 0.005-0.015%, P≤0.02%, S≤0.01%, and the balance is iron and unavoidable impurities; In the step S3, the steel ingot after heat preservation is forged, the initial forging temperature is 1100-1180°C, the final calcination temperature is 720-820°C, and the forging ratio is 4-8; In the step S5, the heat treatment includes: keeping the forged billet after the roughening and drawing process at 800-900°C for 8-9h, quenching to a surface temperature of 200-250°C, placing it in a tempering furnace for tempering, the tempering temperature is 580-640°C, the tempering time is 10-14h, and air cooling is performed for 20-40min after being taken out of the furnace to obtain a plastic mold steel; In step S5, tempering is performed multiple times, and the tempering-air cooling process is repeated 2-4 times.

2. The method for preparing plastic mold steel according to claim 1, characterized in that: The chemical composition of the plastic mold steel and its mass percentage are: C: 0.74%, Mn: 3.1%, Si: 0.68%, Cr: 1.5%, Mo: 0.55%, Ni: 0.82%, Ce: 0.018%, Y: 0.01%, P≤0.02%, S≤0.01%, and the balance is iron and unavoidable impurities.

3. The method for preparing plastic mold steel according to claim 1, characterized in that: The raw materials of the plastic mold steel include carbon powder, ferromanganese, ferrosilicon, ferrochrome, ferromolybdenum, electrolytic nickel, CeO2, Y2O3 and iron block.

4. The method for preparing plastic mold steel according to claim 1, characterized in that: In the step S2, when vacuum degassing is performed, the vacuum degree is controlled at 50-80 Pa, and the degassing time is 10-20 min.

5. The method for preparing plastic mold steel according to claim 1, characterized in that: In the step S4, when the forging blank is subjected to normalizing treatment, it is kept at 850-880° C. for 6-9 hours and then air-cooled to room temperature.

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