Pre-hardened die steel with high heat conductivity coefficient and preparation process of pre-hardened die steel

Abstract

The invention belongs to the technical field of pre-hardened die steel, and particularly relates to pre-hardened die steel with a high heat conductivity coefficient and a preparation technology of the pre-hardened die steel. By optimizing the alloy component design and adopting the high-purity triple smelting process, the heat conduction performance is remarkably improved, the heat conductivity coefficient reaches 54 W / m * K, the mold steel with higher heat conductivity compared with traditional mold steel pre-hardened to 38-42 HRC is obtained, and meanwhile the excellent hardness and wear resistance are kept. The die steel not only has higher heat transfer speed and obviously shortens the injection molding cooling time, but also shows extremely high stability and durability in the use process, prolongs the service life of the die and reduces the production cost of enterprises. In addition, due to the excellent physical property, the mold can be suitable for a more complex and finer injection molding process.

Description

Technical Field

[0001] The invention belongs to the technical field of pre-hardened die steel, and in particular relates to a pre-hardened die steel with high thermal conductivity and a preparation process thereof. Background Art

[0002] With the continuous growth of the global manufacturing industry, especially the rapid development of the automotive, electronics, home appliances, medical and packaging industries, the demand for high-quality and efficient plastic products is growing. As one of the main methods of plastic processing, injection molding is directly related to the market competitiveness of the product in terms of production efficiency and product quality. As the key equipment in the injection molding process, the performance of the mold directly determines the molding quality, production efficiency and service life of the mold itself. Pre-hardened mold steel has been widely used in the field of injection molds due to its good mechanical properties, wear resistance, thermal fatigue resistance and easy processing.

[0003] Although the existing pre-hardened mold steel (such as Germany's 1.2738.02 and China Baosteel's SW718.TS) has excellent comprehensive performance, its thermal conductivity is relatively low (usually below 40W / (mk)), which has become a major bottleneck in the pursuit of efficient production in modern injection molding processes. Due to low thermal conductivity, the mold heats up quickly and cools slowly during the injection molding process, which directly leads to the extension of the injection molding cycle and the increase of production costs. In order to improve the thermal conductivity of the mold, some manufacturers use high-cost high-performance materials or carry out complex post-processing processes, such as using high-hardness beryllium copper as raw material, but beryllium copper is not only expensive, but more importantly, beryllium is a strong carcinogen, so it has been banned in Europe.

[0004] In response to the urgent need of the injection molding industry to shorten the production cycle, improve production efficiency and replace beryllium copper, the development of pre-hardened mold steel with higher thermal conductivity has become an industry consensus. Therefore, a method is proposed to improve the thermal conductivity of the mold by optimizing material composition, heat treatment process, etc., which can effectively shorten the injection molding cycle and reduce production costs. Summary of the invention

[0005] In view of the above problems, an object of the present invention is to provide a pre-hardened die steel with high thermal conductivity and a preparation process thereof.

[0006] The technical contents of the present invention are as follows:

[0007] The invention provides a pre-hardened die steel with high thermal conductivity. The chemical components of the pre-hardened die steel, measured by mass fraction, are carbon C accounting for 0.33-0.4%, manganese Mn accounting for 0.7-0.9%, molybdenum Mo accounting for 3.4-3.6%, vanadium accounting for 0.45-0.55%, silicon Si <0.15%, chromium Cr <0.3%, copper Cu <0.1%, phosphorus P <0.02%, sulfur S <0.005%, nickel Ni <0.2% and iron Fe as the remainder;

[0008] Preferably, the chemical composition of the pre-hardened die steel is 0.35% carbon, 0.07% silicon, 0.62% manganese, 0.08% chromium, 3.57% molybdenum, 0.49% vanadium, 0.02% copper, 0.009% phosphorus, 0.003% sulfur, 0.02% nickel, and the balance iron;

[0009] Preferably, the chemical composition of the pre-hardened die steel is 0.36% carbon, 0.06% silicon, 0.74% manganese, 0.08% chromium, 3.58% molybdenum, 0.49% vanadium, 0.02% copper, 0.009% phosphorus, 0.003% sulfur, 0.02% nickel, and the balance iron;

[0010] Preferably, the chemical composition of the pre-hardened mold steel is 0.35% carbon, 0.03% silicon, 0.75% manganese, 0.07% chromium, 3.61% molybdenum, 0.49% vanadium, 0.02% copper, 0.009% phosphorus, 0.003% sulfur, 0.02% nickel, and the balance is iron.

[0011] The present invention also provides a preparation process of pre-hardened mold steel with high thermal conductivity, comprising the following steps:

[0012] 1) Melting: Steel and pure iron are used as the main raw materials, carbon, manganese, molybdenum and vanadium are added, and high-temperature smelting is performed to obtain high-temperature molten steel, which is then fully stirred to promote oxidation and decarburization smelting treatment, and alloying is performed to ensure uniform distribution of alloy elements;

[0013] In terms of mass percentage, the carbon accounts for 0.33-0.4%, the manganese accounts for 0.7-0.9%, the molybdenum accounts for 3.4-3.6%, the vanadium accounts for 0.45-0.55%, the scrap steel accounts for 18-22%, and the rest is iron;

[0014] Among them, scrap steel contains elements such as silicon, chromium, copper, phosphorus, sulfur and nickel. Their content in mold steel is controlled to be silicon < 0.15%, chromium < 0.3%, copper < 0.1%, phosphorus < 0.02%, sulfur < 0.005%, and nickel < 0.2%;

[0015] The temperature of the high temperature smelting is 1600-1800°C;

[0016] 2) Ladle refining: The high-temperature molten steel is poured into another ladle, and the VD process is used for degassing, deoxidation, desulfurization, removal of inclusions, and fine-tuning of alloy composition;

[0017] The deoxidation is carried out in the ladle to remove oxygen molecules in the molten steel to improve the mechanical properties and strength of the steel;

[0018] The desulfurization is carried out by refining the molten steel outside the furnace;

[0019] The removal of the inclusions is mainly achieved through floating and absorption by the slag layer. During the ladle refining process, gas or electromagnetic stirring of the molten steel is adopted to increase the collision between inclusions, so that small inclusion particles are aggregated into large particles, thereby increasing the inclusion removal rate. At the same time, the covering slag can absorb the inclusion particles that float to the steel-slag interface and further purify the molten steel. In addition, by controlling the refining process parameters, such as stirring intensity, refining time, etc., the inclusion removal effect can also be optimized;

[0020] 3) Vacuum degassing: The molten steel after refining in the ladle is transferred to a vacuum device. Under the vacuum negative pressure, the gas molecules in the molten steel will escape more easily and be pumped away, so that the gas dissolved in the molten steel (including hydrogen, oxygen, and nitrogen) is separated and treated, thereby improving the purity and mechanical properties of the mold steel;

[0021] 4) Ingot casting: The high-temperature molten steel after vacuum degassing is cast into the ingot mold through the bottom ingot casting process and solidified into a solid ingot to improve the purity and mechanical properties of the mold steel;

[0022] 5) Electroslag remelting: The solid steel ingot is remelted and purified through the PESR atmosphere protection electroslag remelting production line. The slag can absorb and dissolve impurities in the steel during the slag melting process, and the molten steel is further purified through the slag-steel reaction, which can improve the crystallization conditions of the steel, reduce segregation and inclusions in the steel, remove excess non-metallic inclusions inside the material, and re-solidify to form a new solid PESR steel ingot;

[0023] The remelting temperature is 1600-1800°C;

[0024] 6) High temperature diffusion: The solid ESR steel ingot is diffused at high temperature to homogenize and reduce segregation, and reduce the micro segregation of the mold steel ingot;

[0025] The high temperature is 1500-2000°C;

[0026] 7) Forging: After high-temperature diffusion, the high-temperature forging deformation is carried out by a forging hydraulic press. The solid ESR steel ingot is roughened and stretched to reach a certain forging ratio, so that sufficient extrusion deformation occurs inside the material, which increases the density of the core of the steel ingot. Forging makes the material into a stepped shape;

[0027] The certain forging ratio is set according to the cross-sectional dimension tolerance range requirements of the product, and the surface quality of the forging such as the corners and sheet material flatness;

[0028] The forged material is then cut into blocks (modules);

[0029] 8) Annealing: The forged module is heat treated, and then the whole module is subjected to overall refinement annealing to obtain a uniform and fine annealed spherical pearlite structure;

[0030] Due to the high temperature treatment in the early stage, a black oxide layer is formed on the surface of the module. Flame dephosphorization treatment can be carried out as required to make the black surface slightly smooth;

[0031] 9) Trimming: Trim and remove possible quality problems, such as segregation and shrinkage holes;

[0032] 10) Quenching and tempering: The steel material is water quenched and tempered, hardened to 38-42HRC, and pre-hardened mold steel is obtained.

[0033] The beneficial effects of the present invention are as follows:

[0034] The pre-hardened mold steel with high thermal conductivity and its preparation process of the present invention achieve a significant improvement in thermal conductivity by optimizing the alloy composition design and adopting a high-purity triple smelting process. The thermal conductivity reaches 54W / m*K, and a mold steel with higher thermal conductivity than the traditional mold steel pre-hardened to 38-42HRC is obtained, while maintaining excellent hardness and wear resistance. This mold steel not only has a faster heat transfer speed and significantly shortens the injection cooling time, but also shows extremely high stability and durability during use, prolongs the service life of the mold, and reduces the production cost of the enterprise. In addition, its excellent physical properties enable the mold to be suitable for more complex and sophisticated injection molding processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a finished product diagram of the pre-hardened die steel of the present invention;

[0036] Figure 2 This is a graph showing the detection results of non-metallic inclusions in the pre-hardened die steel of the present invention;

[0037] Figure 3 This is a metallographic analysis result diagram of the pre-hardened die steel of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below through specific implementation cases and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art are all within the scope of the claims attached to this application.

[0039] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents from the conventional market.

[0040] Example

[0041] Preparation process of pre-hardened die steel with high thermal conductivity

[0042] 1) Melting: Using scrap steel and pure iron as the main raw materials, adding carbon, manganese, molybdenum, and vanadium, high-temperature smelting is performed to obtain high-temperature molten steel. Silicon and chromium exist in the recycled scrap steel, which need to be reduced as much as possible, and the smelting treatment is fully stirred to promote oxidation and decarburization, and alloying is performed to ensure uniform distribution of alloy elements;

[0043] In terms of mass percentage, the carbon accounts for 0.33-0.4%, the manganese accounts for 0.7-0.9%, the molybdenum accounts for 3.4-3.6%, the vanadium accounts for 0.45-0.55%, the scrap steel accounts for 18-22% (preferably 20%), and the rest is iron;

[0044] Among them, scrap steel contains elements such as silicon, chromium, copper, phosphorus, sulfur and nickel. Their content in mold steel is controlled to be silicon < 0.15%, chromium < 0.3%, copper < 0.1%, phosphorus < 0.02%, sulfur < 0.005%, and nickel < 0.2%;

[0045] The temperature of the high temperature smelting is 1600-1800°C;

[0046] 2) Ladle refining: The high-temperature molten steel is poured into another ladle, and the VD process is used for degassing, deoxidation, desulfurization, removal of inclusions, and fine-tuning of alloy composition;

[0047] The deoxidation is carried out in the ladle to remove oxygen molecules in the molten steel to improve the mechanical properties and strength of the steel;

[0048] The desulfurization is carried out by refining the molten steel outside the furnace;

[0049] The removal of the inclusions is mainly achieved through flotation and slag layer absorption;

[0050] During the ladle refining process, the molten steel is stirred by gas or electromagnetic stirring to increase the collision between inclusions, so that small inclusion particles are aggregated into large particles, thereby increasing the inclusion removal rate. At the same time, the covering slag can absorb the inclusion particles that float to the slag interface and further purify the molten steel. In addition, by controlling the refining process parameters, such as stirring intensity, refining time, etc., the inclusion removal effect can also be optimized;

[0051] 3) Vacuum degassing: The molten steel after refining in the ladle is transferred to a vacuum device. Under the vacuum negative pressure, the gas molecules in the molten steel will escape more easily and be pumped away, so that the gas dissolved in the molten steel (including hydrogen, oxygen, and nitrogen) is separated and treated, thereby improving the purity and mechanical properties of the mold steel;

[0052] 4) Ingot casting: The high-temperature molten steel after vacuum degassing is cast into the ingot mold through the bottom ingot casting process and solidified into a solid ingot to improve the purity and mechanical properties of the mold steel;

[0053] 5) Electroslag remelting: The solid steel ingot is remelted and purified through the PESR atmosphere protection electroslag remelting production line. The slag can absorb and dissolve impurities in the steel during the slag melting process, and the molten steel is further purified through the slag-steel reaction, which can improve the crystallization conditions of the steel, reduce segregation and inclusions in the steel, remove excess non-metallic inclusions inside the material, and re-solidify to form a new solid PESR steel ingot;

[0054] The remelting temperature is 1600-1800°C;

[0055] 6) High temperature diffusion: The solid ESR steel ingot is diffused at high temperature to homogenize and reduce segregation, and reduce the micro segregation of the mold steel ingot;

[0056] The high temperature is 1500-2000°C;

[0057] 7) Forging: After high-temperature diffusion, the high-temperature forging deformation is carried out by a forging hydraulic press. The solid ESR steel ingot is roughened and stretched to reach a certain forging ratio, so that sufficient extrusion deformation occurs inside the material, which increases the density of the core of the steel ingot. Forging makes the material into a stepped shape;

[0058] The certain forging ratio is set according to the cross-sectional dimension tolerance range requirements of the product, and the surface quality of the forging such as the corners and sheet material flatness;

[0059] The forged material is then cut into blocks (modules);

[0060] 8) Annealing: The forged module is heat treated, and then the whole module is subjected to overall refinement annealing to obtain a uniform and fine annealed spherical pearlite structure;

[0061] Due to the high temperature treatment in the early stage, a black oxide layer is formed on the surface of the module. Flame dephosphorization treatment can be carried out as required to make the black surface slightly smooth;

[0062] 9) Trimming: Trim and remove possible quality problems, such as segregation and shrinkage holes;

[0063] 10) Quenching and tempering: The steel material is water quenched and tempered, hardened to 38-42HRC, and pre-hardened mold steel is obtained.

[0064] Three embodiments were set up to prepare pre-hardened die steels, and the process was the same as above, except that the chemical composition and temperature were different. The specific temperature is shown in Table 1, and the chemical composition of the pre-hardened die steels of different embodiments is shown in Table 2.

[0065] Table 1 Process temperature of the embodiment

[0066] High temperature melting / ℃ Remelting / ℃ High temperature diffusion / ℃ Example 1 1800 1800 2000 Example 2 1600 1700 1800 Example 3 1800 1600 1500

[0067] Comparative Example 1

[0068] MFR x5 Sonder tool steel (1.2738.02 from Saarschmiede forging factory, Saarland, Germany).

[0069] Comparative Example 2

[0070] Collex die steel (1.2083 from Saarschmiede forging steelworks, Germany).

[0071] The pre-hardened die steel prepared above was tested as follows:

[0072] 1. Chemical composition detection

[0073] By adjusting the addition amount of different raw materials, the content of each component in the embodiment is controlled within the required range. Since there are residual elements such as silicon, chromium, copper, phosphorus, sulfur and nickel in the scrap steel, and their contents are controlled during the preparation process of the pre-hardened mold steel, silicon is less than 0.15%, chromium is less than 0.3%, copper is less than 0.1%, phosphorus is less than 0.02%, sulfur is less than 0.005%, and nickel is less than 0.2%.

[0074] According to the detection method in GB / T 4336-2016 “Determination of multi-element content of carbon steel and medium and low alloy steel - Spark discharge atomic emission spectrometry”, the composition of the pre-hardened die steel prepared by the present invention was detected, and the detection results are shown in Table 2.

[0075] Table 2 Chemical composition test results (%)

[0076] C Si Mn P S Cr Ni Mo Cu V Example 1 0.35 0.07 0.62 0.009 0.003 0.08 0.02 3.57 0.02 0.49 Example 2 0.36 0.06 0.74 0.009 0.003 0.08 0.02 3.58 0.03 0.49 Example 3 0.35 0.03 0.75 0.009 0.002 0.07 0.02 3.61 0.02 0.49 Comparative Example 1 0.25 0.20 1.45 0.009 0.003 1.30 1.10 0.60 0.05 0.10 Comparative Example 2 0.40 0.45 0.35 0.01 0.002 13.00 0.20 1.80 0.05 0.30

[0077] 2. Non-metallic inclusion detection

[0078] According to the detection method in GB / T 10561-2023 "Standard Rating Chart Microscopic Examination Method for Determination of Non-Metallic Inclusion Content in Steel", the pre-hardened die steel prepared by the present invention was tested for non-metallic inclusions, and the test results are shown in Table 3.

[0079] Table 3 Non-metallic inclusion detection results

[0080]

[0081] The metallographic microscope (BX53M, polished state 100×) was used to observe the Figure 2 Combined with Table 2, it can be seen that it contains only 0.5 D-level inclusions, and the others are basically 0. It can be seen that there are very few non-metallic inclusions in the prepared pre-hardened mold steel, indicating that the purity is extremely high.

[0082] 3. Metallographic analysis and testing

[0083] According to the detection methods in GB / T 13298-2015 "Methods for Testing Metal Microstructures" and GB / T6394-2017 "Methods for Determining Average Grain Size of Metals", metallographic analysis was performed on the pre-hardened die steel prepared by the present invention.

[0084] Chemical etching was used to observe the microstructure. Figure 3 As shown, tempered martensite + fine-grained carbides can be seen, and the grain size reaches level 8.5.

[0085] 4. Hardness and thermal conductivity testing

[0086] According to the testing method in GB / T230.1-2008 "Rockwell Hardness Test for Metallic Materials", the hardness of the obtained die steel is tested;

[0087] According to the test method in GB / T 22588-2008 "Flash Method for Measurement of Thermal Diffusivity or Thermal Conductivity", a thermal conductivity meter (LFA467) was used to test the thermal conductivity (25°C). The results are shown in the following table:

[0088] Table 4 Hardness and thermal conductivity

[0089] Quenching hardness / HRC Tempering hardness / HRC Thermal conductivity (W / m*K) Example 1 45 38 54.181 Example 2 50 42 53.538 Example 3 47 40 53.495 Comparative Example 1 50 40 38.239 Comparative Example 2 49 42 27.117

[0090] It can be seen from the results in Table 4 that, through the composition ratio and high-purity triple smelting process of the present invention, a mold steel with higher thermal conductivity than the traditional mold steel pre-hardened to 38-42HRC can be obtained, and the thermal conductivity coefficient is as high as 54W / m*K, which will help shorten the production cycle of injection molding when the mold is used.

Claims

1. A pre-hardened die steel with high thermal conductivity, characterized in that: In the pre-hardened die steel, by mass fraction, carbon accounts for 0.33-0.4%, manganese accounts for 0.7-0.9%, molybdenum accounts for 3.4-3.6%, vanadium accounts for 0.45-0.55%, silicon is less than 0.15%, chromium is less than 0.3%, copper is less than 0.1%, phosphorus is less than 0.02%, sulfur is less than 0.005%, nickel is less than 0.2% and iron is the remainder.

2. A process for preparing the pre-hardened die steel with high thermal conductivity as claimed in claim 1, characterized in that: The steps include: 1) Melting: Using scrap steel and pure iron as the main raw materials, adding carbon, manganese, molybdenum and vanadium, high-temperature smelting is performed to obtain high-temperature molten steel, and after sufficient stirring to promote oxidation and decarburization smelting treatment, alloying is performed to ensure uniform distribution of alloy elements; Among them, scrap steel contains elements such as silicon, chromium, copper, phosphorus, sulfur and nickel; In terms of mass percentage, the carbon accounts for 0.33-0.4%, the manganese accounts for 0.7-0.9%, the molybdenum accounts for 3.4-3.6%, the vanadium accounts for 0.45-0.55%, the scrap steel accounts for 18-22%, and the rest is iron; 2) Ladle refining: The high-temperature molten steel is poured into another ladle, and the VD process is used for degassing, deoxidation, desulfurization, removal of inclusions, and fine-tuning of alloy composition; 3) Vacuum degassing: The molten steel after ladle refining is transferred to the VD vacuum device. Under the vacuum negative pressure, the gas molecules in the molten steel will escape more easily and be pumped away, so that the gas dissolved in the molten steel (including hydrogen, oxygen, and nitrogen) is separated and treated to improve the purity and mechanical properties of the mold steel; 4) Ingot casting: The high-temperature molten steel after vacuum degassing is cast into the ingot mold through the bottom ingot casting process and solidified into a solid ingot to improve the purity and mechanical properties of the mold steel; 5) Electroslag remelting: The solid steel ingot is remelted and purified through the PESR atmosphere protection electroslag remelting production line. The slag can absorb and dissolve impurities in the steel during the slag melting process, and the molten steel is further purified through the slag-steel reaction, which can improve the crystallization conditions of the steel, reduce segregation and inclusions in the steel, remove excess non-metallic inclusions inside the material, and re-solidify to form a new solid PESR steel ingot; 6) High temperature diffusion: The solid ESR steel ingot is diffused at high temperature to homogenize and reduce segregation, and reduce the micro segregation of the mold steel ingot; 7) Forging: After high-temperature diffusion, the high-temperature forging deformation is carried out by a forging hydraulic press. The solid ESR steel ingot is roughened and stretched to reach a certain forging ratio, so that sufficient extrusion deformation occurs inside the material, which increases the density of the core of the steel ingot. Forging makes the material into a stepped shape; The forged material is then cut into blocks / modules; 8) Annealing: The forged module is heat treated, and then the whole module is subjected to overall refinement annealing to obtain a uniform and fine annealed spherical pearlite structure; 9) Trimming: Trim and remove possible quality problems, such as segregation and shrinkage holes; 10) Quenching and tempering: The steel material is water quenched and tempered, hardened to 38-42HRC, and pre-hardened mold steel is obtained.

3. The process for preparing the pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: Step 1) The scrap steel contains silicon, chromium, copper, phosphorus, sulfur and nickel in the mold steel, with silicon <0.15%, chromium <0.3%, copper <0.1%, phosphorus <0.02%, sulfur <0.005% and nickel <0.2%.

4. The process for preparing the pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: The temperature of the high temperature smelting in step 1) is 1600-1800°C.

5. The process for preparing pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: Step 2) The deoxidation is performed in a ladle to remove oxygen molecules in the molten steel to improve the mechanical properties and strength of the steel; The desulfurization is carried out by refining the molten steel outside the furnace; The removal of the inclusions is mainly achieved through flotation and slag layer absorption.

6. The process for preparing pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: Step 5) The remelting temperature is 1600-1800°C.

7. The process for preparing pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: Step 6) The high temperature is 1500-2000°C.

8. The process for preparing pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: The certain forging ratio in step 7) is set according to the cross-sectional dimension tolerance range requirements of the product, and the surface quality of the forging such as the corners and sheet material flatness.

9. The process for preparing pre-hardened die steel with high thermal conductivity according to claim 2, characterized in that: Step 8) Due to the high temperature treatment in the early stage, a black oxide skin is formed on the surface of the module. Flame dephosphorization treatment can be performed as required to make the black skin on the surface slightly smooth.

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