Economical steel plate for HRC36 plastic mold and production method thereof

Abstract

The invention discloses an economical steel plate for an HRC36 plastic mold, the thickness of the steel plate is 80-130 mm, and the steel plate is prepared from the following chemical components in percentage by mass (wt%): 0.43-0.46% of C, 0.20-0.40% of Si, 1.00-1.30% of Mn, less than or equal to 0.015% of P, less than or equal to 0.002% of S, 0.020-0.040% of Als, 1.80-2.00% of Cr, 0.020-0.030% of Nb, less than or equal to 0.030% of V, less than or equal to 0.30% of Ni, 0.15-0.20% of Mo, less than or equal to 0.020% of Ti and the balance of Fe and residual elements. The hardness of the steel plate is 34-38 HRC, and the hardness difference of the same plate is less than or equal to 4 HRC; the steel plate is reasonable in chemical component combination and uniform and stable in hardness performance, has the advantages of high hardness, high wear resistance and low cost, and can meet the actual production, processing and use requirements of the mold industry; the production method is simple, production organization in the technical field of wide and thick plate metallurgy is facilitated, and meanwhile the comprehensive performance can meet the use requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of wide and thick plate metallurgy, and specifically relates to an economical HRC36 steel plate for plastic moulds and a production method thereof. Background Art

[0002] Moulds are the foundation of industry, and moulds are also called "the mother of industry". Plastic moulds are the most widely used moulds at present, and their manufacturing materials are still mainly mould steel. Plastic moulds are consumable parts. As the number of times the mould is stamped increases, the product life will continue to decrease, and the mould needs to be replaced regularly. In addition, as the appearance of the product is updated and upgraded, the mould also needs to be constantly updated. Therefore, the market demand for mould steel is large and stable. According to market research data, the annual usage of plastic mould steel is about 1 million tons. For this reason, an economical steel for plastic film has been developed to reduce the economic cost of plastic products, which is of great significance to the development of my country's plastic industry.

[0003] Patent publication number CN 110565009 "An alloyed pre-hardened plastic mold steel and its preparation method", the HSTPM plastic mold steel produced by this method has a Mn content of 1.50-1.60, a Ni content of 0.9-1.1, and a Mo content of 0.40-0.50. The amount of high-value alloy added is large, and new alloy elements Ce and La rare earth elements are added at the same time, which greatly increases the cost; secondly, forging is adopted, and the number of heat treatment normalizing and quenching is not less than 2 times, and then tempering is performed. This method has high alloy cost and heat treatment, and the heat treatment process is cumbersome, making it difficult to apply and promote in the market.

[0004] Patent publication number CN 111172448 "A method for preparing thick and large-section highly homogeneous plastic mold steel" adopts high-purity and low-segregation electroslag remelting technology, but the cost of electroslag remelting technology is relatively high; and it requires forging and normalizing + quenching heat treatment, and the heat treatment cost is also relatively high.

[0005] Chinese patent 201510870739.2 discloses "an economical plastic mold steel plate and manufacturing method". The performance of the steel produced is HRC 28-33, the hardness is low, it is easy to wear, and the service life of the mold will not be too long.

[0006] In summary, the development of an economical HRC 36 mold steel plate with high hardness and low cost and its production method is of great significance to my country's mold manufacturing industry. Summary of the invention

[0007] In order to meet the above technical requirements, the purpose of the present invention is to provide an economical HRC 36 mold steel plate with high hardness and low cost. The chemical components of the steel plate are reasonably combined, the hardness performance is uniform and stable, and it has the advantages of high hardness, high wear resistance and low cost, which can meet the actual production, processing and use requirements of the mold industry; its production method is convenient for production organization in the field of wide and thick plate metallurgical technology, and at the same time, its comprehensive performance can meet the use requirements.

[0008] The object of the present invention is to provide a method for producing an economical HRC 36 mold steel plate with high hardness and low cost. The specific scheme is as follows:

[0009] To achieve the above object, the technical solution adopted by the present invention is: an economical HRC 36 steel plate for plastic molds, the thickness of the steel plate is 80-130 mm, and the chemical composition (wt%) of the following mass percentage is adopted: C: 0.43-0.46%, Si: 0.20-0.40%, Mn: 1.00-1.30%, P: ≤0.015%, S: ≤0.002%, Als: 0.020-0.040%, Cr: 1.80-2.00%, Nb: 0.020-0.030%, V: ≤0.030%, Ni: ≤0.30%, Mo: 0.15-0.20%, Ti: ≤0.020%, and the balance is Fe and residual elements; the hardness of the steel plate is 34-38 HRC, and the hardness difference of the same plate is ≤4 HRC;

[0010] The composition design idea of ​​the present invention is:

[0011] C is the main interstitial solid solution strengthening element, which can significantly improve the strength and hardness of steel. However, when the C content is too high, it will reduce the Bs point and cause the precipitation of granular carbides. In addition, the increase in C content will also increase the risk of steel plate bursting. Therefore, it is most appropriate to control the C content of plastic mold steel in the middle limit of 0.43-0.46%.

[0012] Si can increase the activity of C and the precipitation tendency of primary carbides, stabilize ferrite, and increase yield strength. Si can also improve the tempering stability and fatigue resistance of steel. In addition, adding Si can increase the critical point of steel, thereby increasing the quenching temperature of steel. However, when the Si content is greater than 1%, the steel plate is prone to banded structure, the longitudinal and transverse properties are quite different, the tempering brittleness increases, and the impact toughness decreases. Therefore, the Si content is generally not more than 0.4%.

[0013] Mn can eliminate the harmful effects of S and improve the hot working properties of steel. Mn also has the effect of solid solution strengthening, which can improve the hardenability of steel, reduce Ms point, and stabilize residual austenite. Secondly, manganese, like chromium, can improve the hardenability of mold steel, make the structure of mold steel in quenching and tempering heat treatment more uniform, and avoid grain growth during heating to a certain extent. At the same time, manganese can increase the wear resistance of mold steel without reducing the toughness of mold steel, so as to extend the service life of mold steel.

[0014] Nb mainly refines grains. During rolling, it can significantly increase the temperature of the non-recrystallized zone and prevent the core grains from growing and coarsening. It is used to eliminate the problem of uneven hardness caused by coarse grains and affecting processing. Secondly, it forms Nb (C, N) with C and N, which can improve the hardness and wear resistance of the steel plate.

[0015] Cr is a commonly used alloying element in die steel, which can improve the hardenability and tempering resistance of steel, and improve the oxidation resistance and impact toughness of steel. Cr can be dissolved in the matrix to play a solid solution strengthening role, and can also form chromium carbon compounds with C to improve wear resistance. In addition, the addition of Cr can also promote bainite and martensite phase transformation.

[0016] Mo is a medium-strong carbide-forming element, which mainly exists in the form of carbides in steel and has a significant secondary hardening effect. Mo can also effectively refine the cast structure in steel, improve the section uniformity and tempering stability, and slow down the precipitation of carbides at the grain boundaries of the martensitic plate matrix during the phase transformation process, thereby improving the impact toughness and comprehensive performance of the steel.

[0017] Ni plays a role in solid solution strengthening and improving hardenability. It refines the iron grains and improves the plasticity and toughness of steel, especially low-temperature toughness, under the same strength conditions. When used in combination with chromium, molybdenum, etc., it improves the thermal strength and corrosion resistance of steel. In mold steel, Ni gives it good polishing and etching properties.

[0018] During the solidification process, P and S in steel form phosphides and sulfides that precipitate at the grain boundaries, thus causing intergranular brittleness and reducing the plasticity of the steel. This not only causes cracks in the segregation zone during ingot rolling, but also reduces the mechanical properties of the steel. Therefore, the P and S content in steel should be reduced as much as possible.

[0019] The production method of the above-mentioned economical HRC 36 steel plate for plastic molds includes smelting, controlled rolling and controlled cooling, and tempering heat treatment, which is as follows:

[0020] 1) Smelting: In the converter smelting process, 42CrMo, Cr13, Mo1 scrap steel or steel scrap base materials containing Cr and Mo are used to reduce the alloy cost; it should be noted that in the chemical composition of an economical HRC34-38 steel plate for plastic molds, V: ≤0.030%, Ni: ≤0.30%. Cr, V, Ni, and Mo in alloy scrap steel are inherent in scrap steel. Although the price of alloy scrap steel is slightly higher than that of ordinary scrap steel, the cost is still relatively low compared to special alloying, and the alloy content is low, which has a significant cost advantage.

[0021] 2) Controlled rolling and controlled cooling: Two-stage rolling is adopted, in which high-pressure water is used for each rough rolling pass, and the reduction in the first three passes is increased, with a reduction of 40mm in the first pass, 45mm in the second pass, and 50mm in the third pass. In the actual rolling process, the inventors found that the use of equal or decreasing reduction in rough rolling will make it difficult for the rolling force to penetrate into the core of the steel plate, and problems such as grooves appearing on the edges; secondly, it will make the density and dislocation density of the surface and core inconsistent, resulting in a large difference in hardness between the surface and the core. However, by using increasing reduction, as the temperature decreases, the reduction will gradually penetrate into the core through the surface, making the core of the steel plate more dense and the hardness more uniform.

[0022] After the rough rolling, the steel is dried at a controlled temperature. The specific steel thickness and finishing rolling process are as follows:

[0023]

[0024] After rolling, the steel plate enters ACC controlled cooling. The ACC header is opened at intervals, that is, one group is opened and one group is closed. The water volume is controlled at 80-100m 3 / h, the roller speed is 1.2m / s, and it is cooled only once; the purpose of controlled cooling is to prevent the core grain coarsening of the steel plate under high temperature state; the second is to retain the dislocation in the controlled rolling process to improve hardness and wear resistance; the purpose of interval opening is to avoid the steel plate from being continuously cooled, resulting in excessive cooling intensity and increasing the risk of cracking; after the steel plate returns to red for 90s after leaving ACC and is heated, it enters the straightening machine for straightening.

[0025] 3) Tempering heat treatment: After the steel plate is finished, asbestos is used for heat insulation so that the temperature is ≥100℃ before entering the tempering furnace. Asbestos insulation can avoid cracking caused by excessive fire cutting stress after fire cutting. Stacking and slow cooling after tempering can further eliminate residual stress and improve the easy cutting performance of the steel plate. Secondly, because the surface temperature drop of the steel plate is large and the core temperature drop is small, this will cause a large difference in hardness between the surface and the core of the steel plate. Through stacking and slow cooling, the cooling rate of the surface and the core of the steel plate can be kept consistent as much as possible, which can significantly improve the uniformity of the cross-section hardness. The specific tempering process is as follows:

[0026]

[0027] After the steel plates are unstackered, they are inspected for hardness, surface and internal flaw detection before being put into storage.

[0028] The steel plate obtained according to this scheme has a reasonable match between chemical composition and matrix structure, can have high hardness and good wear resistance at the same time, and has a simple production process and meets the requirements of industrial production and the needs of the mold industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0030] Figure 1 This is the surface metallographic structure diagram of the HRC 36 plastic mold steel with a thickness of 110 mm according to the present invention.

[0031] Figure 2 It is a metallographic structure diagram of a quarter of the thickness of the 110 mm thick HRC 36 plastic mold steel of the present invention.

[0032] Figure 3 This is the metallographic structure diagram of the core of the 110 mm thick HRC 36 plastic mold steel of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0034] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0035] Example 1

[0036] This embodiment 1 provides an HRC 36 steel plate with a thickness of 85 mm, including the following chemical components in mass percentage: C0.43, Si0.25, Mn1.25, P0.012, S0.002, Als0.030, Cr1.93, Nb0.025, V0.018, Ni0.23, Mo0.19, Ti0.016, and the balance is Fe and residual elements.

[0037] The production method includes:

[0038] 1) Smelting: After KR stirring and desulfurization, the S content of the molten iron is 0.007%. The converter scrap steel uses 42CrMo steel scrap base material containing Cr and Mo, Cr13, Mo1, etc. The amount of aluminum block added to the converter steel deoxidizer is 200Kg, and the amount of lime added to the steel tapping is 500Kg. The argon station blows argon for 8 minutes, the amount of lime added during the LF smelting process is 12kg / t, the white slag is kept for 25 minutes, and the total LF time is 53 minutes. The VD arrival temperature is 1603℃, the departure temperature is 1565℃, the pressure holding time is 17 minutes, and the soft blowing after breaking the air is 9 minutes, [H] ≤ 0.82PPm.

[0039] 2) Continuous casting: continuous casting speed 0.825m / min; light pressure reduction position: 11-12 stage, pressure reduction 2.5mm, electromagnetic stirring parameters: 550A / 5Hz. After cutting, the billet is stacked and slowly cooled for 20h, and the billet is cleaned with heat at a temperature of 230-250℃.

[0040] 3) Heating: The billet charging temperature is 150-200°C. 90 minutes before entering the heating furnace, the first heating temperature is controlled at 847°C, the second heating temperature is 1236°C, the soaking section is 1233°C, and the total heating time is 12.5min / cm.

[0041] 4) Controlled rolling and controlled cooling: The first pass of rough rolling of steel billet is carried out with a reduction of 40mm, the second pass is carried out at 45mm, and the third pass is carried out at 50mm; the thickness of steel is 120mm, the finishing rolling starts at 886℃, and the final rolling is 865℃. Then the steel plate enters the AC interval cooling, the header opens one group and closes one group, and the header water volume is controlled at 85m 3 / h, the roller speed is 1.2m / s, and it is cooled once. After the steel plate leaves ACC, it returns to red for 90s and then enters the straightening machine for straightening three times.

[0042] 5) Stack cooling and finishing: After the steel plate is straightened, it is cooled to 320℃ on the cooling bed and then stacked for slow cooling. After 10 hours of slow cooling, the stack is removed. After the stack is removed, the steel plate is finished with warm fire cutting at a temperature of 156℃.

[0043] 6) Tempering heat treatment: After the steel plate is finished, asbestos is used for heat preservation. The temperature before tempering is 105℃. Tempering is stable at 570℃, and the tempering time is 3.5min / mm. After the steel plate is taken out of the furnace, it is stacked and slowly cooled. The temperature in the slow cooling pit is 300~350℃, and the slow cooling time is ≥24h.

[0044] Example 2

[0045] This embodiment 2 provides a HRC 36 steel plate with a thickness of 110 mm, including the following chemical components in mass percentage: C0.45, Si0.30, Mn1.19, P0.011, S0.001, Als0.033, Cr1.95, Nb0.026, V0.015, Ni0.25, Mo0.19, Ti0.015, and the remainder is Fe and residual elements.

[0046] The production method of the 110 mm HRC 36 steel plate is different from that in Example 1 in that the S content of the molten iron after KR stirring and desulfurization is 0.006%. The LF white slag is kept for 26 minutes, and the total LF time is 55 minutes. The VD arrival temperature is 1598°C, and the departure temperature is 1566°C. After the VD is broken, the soft blowing is 8 minutes, and [H]≤0.79PPm.

[0047] The billet is cleaned with temperature at 220-260℃. The billet charging temperature is 160-200℃. 90min before entering the heating furnace, the first heating temperature is controlled at 839℃, the second heating temperature is 1235℃, and the soaking temperature is 1228℃.

[0048] The thickness of the steel is 140mm, the finishing rolling temperature is 878℃, the final rolling temperature is 856℃, and after the steel plate is straightened, it is cooled to 330℃ on the cooling bed and then stacked for slow cooling. The finishing temperature of the steel plate with warm fire cutting is 163℃. The temperature of the steel plate before tempering is 108℃. The tempering is stable at 565℃, and the tempering time is 3.8min / mm. After the steel plate is taken out of the furnace, it is stacked for slow cooling, and the temperature in the slow cooling pit is 300~350℃, and the slow cooling time is ≥24h.

[0049] Example 3

[0050] This embodiment 3 provides a HRC 36 steel plate with a thickness of 130 mm, including the following chemical components in mass percentage: C0.46, Si0.35, Mn1.28, P0.011, S0.001, Als0.033, Cr1.93, Nb0.028, V0.018, Ni0.28, Mo0.20, Ti0.017, and the balance is Fe and residual elements.

[0051] The production method of the 130 mm HRC 36 steel plate is different from that in Examples 1 and 2 in that the S content of the molten iron after KR stirring and desulfurization is 0.005%. The LF white slag is kept for 28 minutes, and the total LF time is 60 minutes. The VD temperature at the station is 1608°C and that at the station is 1567°C. After the VD is broken through the air, the soft blowing is performed for 8 minutes, and [H]≤0.76PPm.

[0052] The billet is cleaned with temperature at 230-260℃. The billet charging temperature is 170-210℃. 90min before entering the heating furnace, the first heating temperature is controlled at 846℃, the second heating temperature is 1239℃, and the soaking temperature is 1229℃.

[0053] The thickness of the steel is 150mm, the finishing rolling temperature is 866℃, the final rolling temperature is 853℃, and after the steel plate is straightened, it is cooled to 339℃ on the cooling bed and then stacked for slow cooling. The finishing temperature of the steel plate with warm fire cutting is 185℃. The temperature of the steel plate before tempering is 125℃. The tempering is stable at 560℃, and the tempering time is 4.2min / mm. After the steel plate is taken out of the furnace, it is stacked for slow cooling, and the temperature in the slow cooling pit is 300~350℃, and the slow cooling time is ≥24h.

[0054] Example Performance

[0055] The HRC 36 steel plates obtained in Examples 1, 2, and 3 were used as the tested products, and the hardness test results of the steel plates are shown in the following table.

[0056] The following table shows the test results

[0057] Steel Type Thickness / mm Surface diagonal five-point hardness Cross-sectional three-point hardness HRC36 85 36、37、36、35、35 36、35、37 HRC36 110 34、36、35、37、37 35、38、36 HRC36 130 35、37、38、36、34 37、36、35

[0058] It can be seen from the above table that the HRC 36 steel plate provided in the embodiment of the present application has uniform and stable hardness in all parts.

[0059] The steel plate obtained in Example 2 was tested, and the surface structure, quarter thickness structure, and core structure after tempering were as follows: Figure 1 , 2 As shown in Figure 3, the structure is a uniform bainite tempered structure.

[0060] In addition, the pass rate of surface inspection and internal flaw detection of steel plates reached 100.00%.

[0061] In summary, the chemical composition, production process, and internal organization of the HRC 36 steel plate provided by this application are reasonable, and can have good hardness performance at the same time. Its production method meets the organizational production of the metallurgical industry, can achieve the quality of HRC36 steel plate, and improve its performance.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An economical HRC 36 steel plate for plastic molds, characterized in that: The thickness of the steel plate is 80-130 mm, and the chemical composition (wt%) is as follows: C: 0.43-0.46%, Si: 0.20-0.40%, Mn: 1.00-1.30%, P: ≤0.015%, S: ≤0.002%, Als: 0.020-0.040%, Cr: 1.80-2.00%, Nb: 0.020-0.030%, V: ≤0.030%, Ni: ≤0.30%, Mo: 0.15-0.20%, Ti: ≤0.020%, and the balance is Fe and residual elements; the hardness of the steel plate is 34-38 HRC, and the hardness difference of the same plate is ≤4 HRC.

2. The method for producing an economical HRC 36 steel plate for a plastic mold according to claim 1, characterized in that: Including smelting, controlled rolling and controlled cooling, tempering heat treatment, as follows: 1) Smelting: In the converter smelting process, 42CrMo, Cr13, Mo1 scrap steel or steel chips containing Cr and Mo are used as base materials to reduce alloy costs; 2) Controlled rolling and controlled cooling: Two-stage rolling is adopted, in which high-pressure water is used for each rough rolling. The reduction in the first three passes increases, with the first pass reducing 40mm, the second pass reducing 45mm, and the third pass reducing 50mm. After the rough rolling, the steel is air-dried at controlled temperature. The specific steel thickness and finishing rolling process are as follows: After rolling, the steel plate enters ACC controlled cooling. The ACC header is opened at intervals, that is, one group is opened and one group is closed. The water volume is controlled at 80-100m 3 / h, the roller speed is 1.2m / s, and it is cooled only once. After the steel plate returns to red after leaving ACC for 90s, it enters the straightening machine for straightening; 3) Tempering heat treatment: After the steel plate is finished, asbestos is used for heat preservation so that the temperature is ≥100℃ before entering the tempering furnace. The specific tempering process is as follows:

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