Plastic mold steel and heat treatment process

Abstract

The present application belongs to the field of heat treatment technology of plastic mold steel, and the present application discloses a plastic mold steel and a heat treatment process. The heat treatment process of the plastic mold steel in the present application includes the steps of melting and pouring raw materials into steel ingots, performing high temperature diffusion heat treatment on the steel ingots in sequence, hot rolling, annealing, isothermal quenching and air cooling, oil cooling and quenching, and tempering. The present application optimizes the component design and is equipped with an effective heat treatment process, while maintaining the cavity accuracy, finish and roughness, significantly improving the hardness and polishing performance of the mold and extending the service life of the mold.

Description

Technical Field

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

[0002] Plastic mold steel is an important mold material, widely used in various industries such as household appliances, electronic and communication equipment, plastic products, automobiles and motorcycles. With the development of the plastics industry, the demand for plastic product molding is increasing, and higher requirements are also put forward for the purity, polishing performance, fine grain structure, homogenization and corrosion resistance of plastic mold steel.

[0003] Plastic mold steel has high requirements for use, and deformation of the cavity is not allowed. The main process method currently used is to obtain martensitic structure by oil quenching after austenitization of steel, and tempering at a higher temperature to keep its hardness in the range of 30-45HRC, and then perform cavity machining, and directly apply it after machining. Although this treatment method solves the problem of deformation of the processing cavity, because the hardness of the mold workpiece is low, the corresponding mold service life is not high. If the hardness of the mold is to be improved, it will bring about the problem of processing difficulties. At the same time, the above method often causes a large difference in the microstructure and hardness of the mold core and the mold surface, causing the disadvantage of inconsistent mold surface roughness. These problems will limit the application scope of plastic mold steel.

[0004] How to significantly improve the hardness and polishing performance of the mold and extend the service life of the mold while maintaining the cavity accuracy, smoothness and roughness through component design optimization and effective heat treatment process under the existing equipment smelting technology level is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In order to develop a plastic mold steel with long service life, good polishing performance, and cavity accuracy, finish and roughness that meet the requirements of high-precision plastic molds, the present application provides a plastic mold steel and a heat treatment process.

[0006] In a first aspect, the present application provides a heat treatment process for plastic mold steel, comprising the following steps:

[0007] S1. Calculate the material ratio according to the design requirements of the composition of the plastic mold steel, place the raw materials in a vacuum induction furnace to melt into molten steel, and cast into steel ingots;

[0008] S2, heating the steel ingot obtained in step S1 to 1100-1190°C and keeping it warm for 8-15h;

[0009] S3, air-cooling the steel ingot heated in step S2 until the surface temperature is 860-980° C., and hot-rolling to obtain a steel plate;

[0010] S4, heating the steel plate obtained in step S3 to a surface temperature of 950-1100°C, keeping the temperature for 1-3h, cooling the steel plate in the furnace to a surface temperature of 600°C, and air cooling the steel plate out of the furnace to a surface temperature of 300-350°C;

[0011] S5, heating the steel plate treated in step S4 to a surface temperature of 880-950°C, keeping the temperature for 0.5-1h, and placing the steel plate in a 300-350°C salt bath furnace for isothermal quenching for 1.5-3.5h;

[0012] S6, heating the steel plate treated in step S5 to a surface temperature of 700-780°C and keeping the temperature for 10-15h, and quenching the steel plate by air cooling and oil cooling in sequence to reduce the surface temperature to 280-330°C;

[0013] S7, tempering the steel plate processed in step S6 to obtain plastic mold steel.

[0014] By adopting the above technical scheme, the present application promotes the formation of bainite structure by sequentially performing high-temperature diffusion heat treatment, hot rolling, annealing, austempering, air cooling, oil cooling combined quenching and tempering on the steel ingot, creating conditions for heterogeneous nucleation, structure refinement and toughness improvement of a large number of fine bainite ferrite. The present application performs staged quenching, including austempering and air cooling and oil cooling quenching. Austempering ensures that the core and surface temperatures of the die steel are consistent during quenching, which is beneficial to the release of stress after hot rolling and annealing of the steel plate, so that the transition layer on the surface and core of the steel plate transitions with a uniformly decreasing hardness gradient, preventing deformation or cracking of the metal material during heat treatment quenching.

[0015] Furthermore, in step S1, the element composition of the steel ingot includes, by weight percentage: C: 0.45-0.60; Si: 1.20-1.40; Mn: 0.35-0.45; Cr: 1.60-2.60; Mo: 0.60-0.80; V: 0.22-0.50; Ni: 0.8-1.3; Zr: 0.10-0.22; La: 0.01-0.03; Ce: 0.01-0.02; P≤0.01; S≤0.005, and the remainder is Fe and unavoidable impurities.

[0016] By adopting the above technical scheme, on the basis of accurately understanding the control principle of the content of multiple alloying elements C, Si, Mn, Cr, Ni, V, Mo, Zr, La and Ce in die steel, the chemical components of low-temperature bainite hot working die steel are reasonably designed and controlled. The Mn element has a solid solution strengthening effect, which can improve the strength, hardness and hardenability of ferrite and austenite; the Si element can reduce the diffusion rate of carbon in ferrite, making it difficult for carbides precipitated during tempering to aggregate, thereby increasing the tempering stability; the Mo element combines with the C element during tempering to precipitate Mo in martensite.2 C can form secondary hardening and improve the tempering stability of steel; the combined use of Ni, Cr and Mo can improve the thermal strength of plastic mold steel; La and Ce elements are helpful for grain refinement and inclusion modification, improving mechanical properties and extending service life. La and Ce can form stable oxides or sulfides, which are beneficial to the dispersion of carbides and improving the wear resistance of steel.

[0017] Furthermore, in step S3, in the hot rolling process, the starting rolling temperature is ≤960°C, the final rolling temperature is ≥875°C, and the pass deformation rate is 10-15%.

[0018] Furthermore, in step S3, the thickness of the steel ingot before hot rolling is 250-330 mm, and the thickness of the steel plate after hot rolling is 55-80 mm.

[0019] Furthermore, in step S6, the air cooling time is 10-15 minutes, and the oil cooling time is 70-100 minutes.

[0020] Furthermore, in step S6, when the insulated steel plate is air-cooled to a surface temperature of 420-460° C., the steel plate is placed in quenching oil for oil cooling.

[0021] Furthermore, in step S7, when the steel plate is tempered, the tempering temperature is 250-300° C., the tempering time is 1-2 hours, and then air-cooled to room temperature.

[0022] Furthermore, tempering is performed twice in step S7.

[0023] In a second aspect, the present application provides a plastic mold steel prepared by the above-mentioned heat treatment process for the plastic mold steel.

[0024] In summary, the present invention includes at least one of the following beneficial technical effects:

[0025] The plastic mold steel heat treatment process provided by the invention improves the uniformity of the structure and hardness of the plastic mold steel, ensures the service life and quality of the mold steel, and can also effectively control the precision and roughness of the plastic mold steel. DETAILED DESCRIPTION

[0026] This application designs a heat treatment process for plastic mold steel, comprising the following steps:

[0027] S1. Calculate the material ratio according to the design requirements of the composition of the plastic mold steel, place the raw materials in a vacuum induction furnace to melt into molten steel, and cast into steel ingots;

[0028] S2, heating the steel ingot obtained in step S1 to 1100-1190°C and keeping it warm for 8-15h;

[0029] S3, air-cooling the steel ingot heated in step S2 until the surface temperature is 860-980° C., and hot-rolling to obtain a steel plate;

[0030] S4, heating the steel plate obtained in step S3 to a surface temperature of 950-1100°C, keeping the temperature for 1-3h, cooling the steel plate in the furnace to a surface temperature of 600°C, and air cooling the steel plate out of the furnace to a surface temperature of 300-350°C;

[0031] S5, heating the steel plate treated in step S4 to a surface temperature of 880-950°C, keeping the temperature for 0.5-1h, and placing the steel plate in a 300-350°C salt bath furnace for isothermal quenching for 1.5-3.5h;

[0032] S6, heating the steel plate treated in step S5 to a surface temperature of 700-780°C and keeping the temperature for 10-15h, and quenching the steel plate by air cooling and oil cooling in sequence to reduce the surface temperature to 280-330°C;

[0033] S7, tempering the steel plate processed in step S6 to obtain plastic mold steel.

[0034] The present application designs a plastic mold steel prepared by the heat treatment process of the above-mentioned plastic mold steel.

[0035] The technical problem solved by this application is that although the existing heat treatment process for plastic mold steel solves the problem of deformation of the processing cavity, the mold workpiece has a low hardness and the corresponding mold service life is not high. If the hardness of the mold is to be improved, it will bring about the problem of processing difficulties. At the same time, the above method often causes a large difference in the microstructure and hardness of the mold core and the mold surface, causing the disadvantage of inconsistent mold surface roughness. These problems will limit the application scope of plastic mold steel. This application significantly improves the hardness and polishing performance of the mold and extends the service life of the mold while maintaining the cavity accuracy, finish and roughness through component design optimization and an effective heat treatment process.

[0036] The present application is further described in detail below in conjunction with specific embodiments.

[0037] Example 1

[0038] The heat treatment process of the plastic mold steel in Example 1 comprises the following steps:

[0039] S1. According to the mass percentage of each element in the prepared steel ingot: C: 0.55; Si: 1.28; Mn: 0.42; Cr: 1.89; Mo: 0.66; V: 0.39; Ni: 1.16; Zr: 0.18; La: 0.002; Ce: 0.012; P: 0.006; S: ​​0.002; the balance is Fe as a benchmark, and combined with the actual loss of each element during the smelting process, the raw material feeding ratio is calculated; all the raw materials are placed in a vacuum high-frequency induction furnace for smelting and electroslag remelting, and the obtained molten steel is cast into a steel ingot with a thickness of about 320 mm.

[0040] S2, heating the steel ingot obtained in step S1 to 1140° C. and keeping the temperature for 12 hours;

[0041] S3, air-cooling the steel ingot heated in step S2 to a surface temperature of 950°C, and hot-rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 950°C, the final rolling temperature is set to 890°C, and the pass deformation rate is controlled to be 12%;

[0042] S4, heating the steel plate obtained in step S3 to a surface temperature of 1050°C, keeping the temperature for 2.5 hours, cooling the steel plate in a furnace to a surface temperature of 600°C, and air cooling the steel plate out of the furnace to a surface temperature of 350°C;

[0043] S5, heating the steel plate treated in step S4 to a surface temperature of 920°C, keeping the temperature for 1 hour, and placing the steel plate in a 350°C salt bath furnace for isothermal quenching for 3 hours;

[0044] S6, heating the steel plate treated in step S5 to a surface temperature of 750°C and keeping it for 12 hours, quenching it in turn by air cooling and oil cooling, the air cooling time is controlled to be 13 minutes, air cooling the steel plate to a surface temperature of 430°C and then oil cooling, the oil cooling time is controlled to be 80 minutes, until the surface temperature of the steel plate drops to 290°C, and then air cooling it to room temperature;

[0045] S7, tempering the steel plate treated in step S6 twice, during the first tempering process, the tempering temperature is 300° C., and the tempering time is 1 hour; during the second tempering process, the tempering temperature is 250° C., and the tempering time is 2 hours; and plastic mold steel is obtained.

[0046] Example 2

[0047] The heat treatment process of the plastic mold steel in Example 2 comprises the following steps:

[0048] S1. According to the mass percentage of each element in the prepared steel ingot: C: 0.45; Si: 1.40; Mn: 0.45; Cr: 1.60; Mo: 0.60; V: 0.22; Ni: 1.3; Zr: 0.1; La: 0.01; Ce: 0.02; P: 0.006; S: ​​0.002; the balance is Fe as a benchmark, and combined with the actual loss of each element during the smelting process, the raw material feeding ratio is calculated; all the raw materials are placed in a vacuum high-frequency induction furnace for smelting and electroslag remelting, and the obtained molten steel is cast into a steel ingot with a thickness of about 320 mm.

[0049] S2, heating the steel ingot obtained in step S1 to 1140° C. and keeping the temperature for 12 hours;

[0050] S3, air-cooling the steel ingot heated in step S2 to a surface temperature of 950°C, and hot-rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 950°C, the final rolling temperature is set to 890°C, and the pass deformation rate is controlled to be 12%;

[0051] S4, heating the steel plate obtained in step S3 to a surface temperature of 1050°C, keeping the temperature for 2.5 hours, cooling the steel plate in a furnace to a surface temperature of 600°C, and air cooling the steel plate out of the furnace to a surface temperature of 350°C;

[0052] S5, heating the steel plate treated in step S4 to a surface temperature of 920°C, keeping the temperature for 1 hour, and placing the steel plate in a 350°C salt bath furnace for isothermal quenching for 3 hours;

[0053] S6, heating the steel plate treated in step S5 to a surface temperature of 750°C and keeping it for 12 hours, quenching it in turn by air cooling and oil cooling, the air cooling time is controlled to be 13 minutes, air cooling the steel plate to a surface temperature of 430°C and then oil cooling, the oil cooling time is controlled to be 80 minutes, until the surface temperature of the steel plate drops to 290°C, and then air cooling it to room temperature;

[0054] S7, tempering the steel plate treated in step S6 twice, during the first tempering process, the tempering temperature is 300° C., and the tempering time is 1 hour; during the second tempering process, the tempering temperature is 250° C., and the tempering time is 2 hours; and plastic mold steel is obtained.

[0055] Example 3

[0056] The heat treatment process of the plastic mold steel in Example 3 comprises the following steps:

[0057] S1. According to the mass percentage of each element in the prepared steel ingot: C: 0.60; Si: 1.20; Mn: 0.35; Cr: 2.60; Mo: 0.80; V: 0.50; Ni: 0.8; Zr: 0.22; La: 0.03; Ce: 0.01; P: 0.006; S: ​​0.002; the balance is Fe as a benchmark, and combined with the actual loss of each element during the smelting process, the raw material feeding ratio is calculated; all the raw materials are placed in a vacuum high-frequency induction furnace for smelting and electroslag remelting, and the obtained molten steel is cast into a steel ingot with a thickness of about 320 mm.

[0058] S2, heating the steel ingot obtained in step S1 to 1140° C. and keeping the temperature for 12 hours;

[0059] S3, air-cooling the steel ingot heated in step S2 to a surface temperature of 950°C, and hot-rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 950°C, the final rolling temperature is set to 890°C, and the pass deformation rate is controlled to be 12%;

[0060] S4, heating the steel plate obtained in step S3 to a surface temperature of 1050°C, keeping the temperature for 2.5 hours, cooling the steel plate in a furnace to a surface temperature of 600°C, and air cooling the steel plate out of the furnace to a surface temperature of 350°C;

[0061] S5, heating the steel plate treated in step S4 to a surface temperature of 920°C, keeping the temperature for 1 hour, and placing the steel plate in a 350°C salt bath furnace for isothermal quenching for 3 hours;

[0062] S6, heating the steel plate treated in step S5 to a surface temperature of 750°C and keeping it for 12 hours, quenching it in turn by air cooling and oil cooling, the air cooling time is controlled to be 13 minutes, air cooling the steel plate to a surface temperature of 430°C and then oil cooling, the oil cooling time is controlled to be 80 minutes, until the surface temperature of the steel plate drops to 290°C, and then air cooling it to room temperature;

[0063] S7, tempering the steel plate treated in step S6 twice, during the first tempering process, the tempering temperature is 300° C., and the tempering time is 1 hour; during the second tempering process, the tempering temperature is 250° C., and the tempering time is 2 hours; and plastic mold steel is obtained.

[0064] Example 4

[0065] Example 4 is based on Example 1, with the difference being that step S3 of Example 4 is changed to: air-cooling the steel ingot heated in step S2 to a surface temperature of 975°C, and hot-rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 975°C, the final rolling temperature is set to 860°C, and the pass deformation rate is controlled to 12%.

[0066] Example 5

[0067] Example 5 is based on Example 1, with the difference being that step S3 of Example 5 is changed to: air-cooling the steel ingot heated in step S2 to a surface temperature of 930°C, and hot-rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 930°C, the final rolling temperature is set to 890°C, and the pass deformation rate is controlled to 12%.

[0068] Example 6

[0069] Example 6 is based on Example 1, except that the thickness of the steel plate obtained after hot rolling in step S3 of Example 6 is changed to 55 mm.

[0070] Example 7

[0071] Example 7 is based on Example 1, except that the thickness of the steel plate obtained after hot rolling in step S3 of Example 7 is changed to 80 mm.

[0072] Example 8

[0073] Example 8 is based on Example 1, with the difference being that step S6 of Example 8 is changed to: heating the steel plate treated in step S5 to a surface temperature of 750°C and keeping it warm for 12 hours, quenching it in turn by air cooling and oil cooling, with the air cooling time controlled at 10 minutes, air cooling the steel plate to a surface temperature of 460°C and then oil cooling it, with the oil cooling time controlled at 80 minutes, until the surface temperature of the steel plate drops to 330°C, and then air cooling it to room temperature.

[0074] Example 9

[0075] Example 9 is based on Example 1, with the difference that step S6 of Example 9 is changed to: heating the steel plate treated in step S5 to a surface temperature of 750°C and keeping it warm for 12 hours, quenching it in turn by air cooling and oil cooling, with the air cooling time controlled to 15 minutes, air cooling the steel plate to a surface temperature of 420°C and then oil cooling it, with the oil cooling time controlled to 80 minutes, until the surface temperature of the steel plate drops to 280°C, and then air cooling it to room temperature.

[0076] Example 10

[0077] Example 10 is based on Example 1, with the difference being that step S7 of Example 10 is changed to: tempering the steel plate treated in step S6 once, during which the tempering temperature is 300° C. and the tempering time is 1 hour, thereby obtaining plastic mold steel.

[0078] Embodiment 11

[0079] Example 11 is based on Example 1, with the difference being that step S7 of Example 11 is changed to: tempering the steel plate treated in step S6 once, during which the tempering temperature is 250° C. and the tempering time is 2 h, thereby obtaining plastic mold steel.

[0080] Comparative Example 1

[0081] Comparative Example 1 is based on Example 1, except that: the plastic mold steel in Comparative Example 1 does not undergo step S4 during the heat treatment process, that is, the heat treatment process of the plastic mold steel in Comparative Example 1 includes the following steps:

[0082] S1. According to the mass percentage of each element in the prepared steel ingot: C: 0.55; Si: 1.28; Mn: 0.42; Cr: 1.89; Mo: 0.66; V: 0.39; Ni: 1.16; Zr: 0.18; La: 0.002; Ce: 0.012; P: 0.006; S: ​​0.002; the balance is Fe as a benchmark, and combined with the actual loss of each element during the smelting process, the raw material feeding ratio is calculated; all the raw materials are placed in a vacuum high-frequency induction furnace for smelting and electroslag remelting, and the obtained molten steel is cast into a steel ingot with a thickness of about 320 mm.

[0083] S2, heating the steel ingot obtained in step S1 to 1140° C. and keeping the temperature for 12 hours;

[0084] S3, air-cooling the steel ingot heated in step S2 to a surface temperature of 950°C, and hot-rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 950°C, the final rolling temperature is set to 890°C, and the pass deformation rate is controlled to be 12%;

[0085] S4, heating the steel plate treated in step S3 to a surface temperature of 920°C, keeping the temperature for 1 hour, and placing the steel plate in a 350°C salt bath furnace for isothermal quenching for 3 hours;

[0086] S5, heating the steel plate treated in step S4 to a surface temperature of 750°C and keeping it for 12 hours, quenching it in turn by air cooling and oil cooling, the air cooling time is controlled to be 13 minutes, air cooling the steel plate to a surface temperature of 430°C and then oil cooling, the oil cooling time is controlled to be 80 minutes, until the surface temperature of the steel plate drops to 290°C, and then air cooling it to room temperature;

[0087] S6. Temper the steel plate treated in step S5 twice. During the first tempering process, the tempering temperature is 300° C. and the tempering time is 1 hour; during the second tempering process, the tempering temperature is 250° C. and the tempering time is 2 hours; and plastic mold steel is obtained.

[0088] Comparative Example 2

[0089] Comparative Example 2 is based on Example 1, except that: the order of step S3 and step S4 is replaced during the heat treatment of the plastic mold steel in Comparative Example 2, that is, the heat treatment process of the plastic mold steel in Comparative Example 2 includes the following steps:

[0090] S1. According to the mass percentage of each element in the prepared steel ingot: C: 0.55; Si: 1.28; Mn: 0.42; Cr: 1.89; Mo: 0.66; V: 0.39; Ni: 1.16; Zr: 0.18; La: 0.002; Ce: 0.012; P: 0.006; S: ​​0.002; the balance is Fe as a benchmark, and combined with the actual loss of each element during the smelting process, the raw material feeding ratio is calculated; all the raw materials are placed in a vacuum high-frequency induction furnace for smelting and electroslag remelting, and the obtained molten steel is cast into a steel ingot with a thickness of about 320 mm.

[0091] S2, heating the steel ingot obtained in step S1 to 1140° C. and keeping the temperature for 12 hours;

[0092] S3, heating the steel ingot from step S2 to a surface temperature of 1050°C, keeping the temperature for 2.5 hours, furnace cooling to a surface temperature of 600°C, and air cooling to a surface temperature of 350°C after being taken out of the furnace;

[0093] S4, heating the steel ingot in step S3 to a surface temperature of 950°C, and hot rolling to obtain a steel plate with a thickness of about 72 mm; the starting rolling temperature is set to 950°C, the final rolling temperature is set to 890°C, and the pass deformation rate is controlled to be 12%;

[0094] S5, heating the steel plate treated in step S4 to a surface temperature of 920°C, keeping the temperature for 1 hour, and placing the steel plate in a 350°C salt bath furnace for isothermal quenching for 3 hours;

[0095] S6, heating the steel plate treated in step S5 to a surface temperature of 750°C and keeping it for 12 hours, quenching it in turn by air cooling and oil cooling, the air cooling time is controlled to be 13 minutes, air cooling the steel plate to a surface temperature of 430°C and then oil cooling, the oil cooling time is controlled to be 80 minutes, until the surface temperature of the steel plate drops to 290°C, and then air cooling it to room temperature;

[0096] S7, tempering the steel plate treated in step S6 twice, during the first tempering process, the tempering temperature is 300° C., and the tempering time is 1 hour; during the second tempering process, the tempering temperature is 250° C., and the tempering time is 2 hours; and plastic mold steel is obtained.

[0097] Comparative Example 3

[0098] Comparative Example 3 is based on Example 1, with the difference that during the heat treatment of the plastic mold steel in Comparative Example 3, step S5 is changed to: heating the steel plate treated in step S4 to a surface temperature of 920°C, keeping it warm for 1 hour, and oil quenching (i.e., oil cooling) until the surface temperature of the steel plate reaches 350°C.

[0099] Comparative Example 4

[0100] Comparative Example 4 is H13 steel.

[0101] Comparative Example 5

[0102] Comparative Example 5 is based on Example 1, except that: in the process of preparing the steel ingot in step S1 of the plastic mold steel in Comparative Example 5, the raw materials corresponding to the La element and the Ce element are not added.

[0103] Performance Testing

[0104] 1. Roughness (Ra) and wear performance (wear weight loss %) of the plastic mold steel in Examples 1-11 and Comparative Examples 1-5.

[0105] 2. According to the standard GB / T 230.1, the Rockwell hardness (HRC) of the plastic mold steel samples in Examples 1-11 and Comparative Examples 1-5 was measured at two points on the surface and the center of the thickness section.

[0106] The measurement results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] By analyzing the data in Table 1, it can be seen that the roughness, wear resistance, hardness and uniformity of the plastic mold steel prepared by the present application by sequentially subjecting the steel ingot to high temperature diffusion heat treatment, hot rolling, annealing, isothermal quenching and air cooling, oil cooling with quenching and tempering steps and combining the specific element ratio are well controlled; by comparing Example 1 with Examples 4-5, Examples 6-7, Examples 8-9, and Examples 10-11, it can be seen that the hot rolling parameter control, steel plate thickness control, annealing temperature control after hot rolling, air cooling, oil cooling with quenching parameter control during the heat treatment process have a significant effect on the roughness, wear resistance and uniformity of the obtained plastic mold steel. For example, when Example 1 is compared with Example 4, although the hardness of Example 4 is higher, the hardness values ​​of Example 4 are quite different, and it can be seen that its uniformity is significantly worse than that of Example 1. By comparing Example 1 with Comparative Examples 1-5, it can be seen that the uniformity of the plastic mold steel prepared in Comparative Examples 1-5 is significantly worse than that of Example 1, and the roughness is significantly greater than that of Example 1. Therefore, the heat treatment process of the plastic mold steel in this application has excellent uniformity and surface properties.

[0111] 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 heat treatment process for plastic mold steel, characterized in that: The following steps are involved: S1. Calculate the feed ratio according to the design requirements of the composition of the plastic mold steel, place the raw materials in a vacuum induction furnace to melt into molten steel, and cast into steel ingots; S2, heating the steel ingot obtained in step S1 to 1100-1190°C and keeping the temperature for 8-15h; S3, air-cooling the steel ingot heated in step S2 until the surface temperature is 860-980° C., and hot-rolling to obtain a steel plate; S4, heating the steel plate obtained in step S3 to a surface temperature of 950-1100°C, keeping the temperature for 1-3h, cooling the steel plate in a furnace to a surface temperature of 600°C, and air cooling the steel plate out of the furnace to a surface temperature of 300-350°C; S5, heating the steel plate treated in step S4 to a surface temperature of 880-950°C, keeping the temperature for 0.5-1h, and placing the steel plate in a 300-350°C salt bath furnace for isothermal quenching for 1.5-3.5h; S6, heating the steel plate treated in step S5 to a surface temperature of 700-780°C and keeping it at that temperature for 10-15h, quenching it in turn by air cooling and oil cooling to reduce the surface temperature to 280-330°C, and then air cooling it to room temperature; S7, tempering the steel plate treated in step S6 to obtain plastic mold steel; In the step S1, the element composition of the steel ingot includes, by weight percentage: C: 0.45-0.60; Si: 1.20-1.40; Mn: 0.35-0.45; Cr: 1.60-2.60; Mo: 0.60-0.80; V: 0.22-0.50; Ni: 0.8-1.3; Zr: 0.10-0.22; La: 0.01-0.03; Ce: 0.01-0.02; P≤0.01; S≤0.005, and the remainder is Fe and unavoidable impurities.

2. The heat treatment process for plastic mold steel according to claim 1, characterized in that: In step S3, in the hot rolling process, the starting rolling temperature is ≤960°C, the final rolling temperature is ≥875°C, and the pass deformation rate is 10-15%.

3. The heat treatment process for plastic mold steel according to claim 1, characterized in that: In the step S3, the thickness of the steel ingot before hot rolling is 250-330 mm, and the thickness of the steel plate after hot rolling is 55-80 mm.

4. The heat treatment process for plastic mold steel according to claim 1, characterized in that: In step S6, the air cooling time is 10-15 minutes, and the oil cooling time is 70-100 minutes.

5. The heat treatment process for plastic mold steel according to claim 1, characterized in that: In the step S6, when the insulated steel plate is air-cooled to a surface temperature of 420-460° C., the steel plate is placed in quenching oil for oil cooling.

6. The heat treatment process for plastic mold steel according to claim 1, characterized in that: In the step S7, when the steel plate is tempered, the tempering temperature is 250-300° C. and the tempering time is 1-2 hours.

7. The heat treatment process for plastic mold steel according to claim 1, characterized in that: In step S7, tempering is performed twice.

8. A plastic mold steel prepared by the heat treatment process of the plastic mold steel according to any one of claims 1 to 7.

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