A method for producing a super-thick mold block steel for injection molds

Abstract

The present application relates to a kind of production methods of special thick module steel for injection mold, preheating before welding of composite blank;Welding adopts the way of single wire gas-electric vertical welding, and blank assembling is carried out along the four edges of blank;After welding, heating;Two fire times heating is taken before forging;Composite blank is forged by adopting free forging;Heat treatment adopts water mist-air alternate control time quenching+tempering process.The composite module of 300-600mm thickness specification produced by the present application has good composite effect, the binding degree of matrix on both sides of composite interface is as high as 95.2% or more, internal quality meets GB / T6402 3-grade ultrasonic flaw detection standard, mechanical property meets SPI standard requirement, impact energy of composite surface reaches 50J or more, polishing grade meets PLASTICS A2 standard requirement, the production of special thick module for injection mold is realized, and traditional production process of high cost, low efficiency such as mold casting, electroslag is replaced.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, and specifically relates to a method for producing extra-thick modular steel for injection molds. Background Technology

[0002] Injection molds are widely used in the automotive and home appliance manufacturing industries. Injection mold steel is currently the mold steel with the largest consumption and output value. Large injection molded parts such as automotive bumpers and home appliance panels require molds to have large cross-sections, high uniformity, and high mirror polishability. This places new demands on the thickness specifications, steel purity, and uniform hardness of the entire cross-section of injection mold materials.

[0003] Due to limitations in the thickness specifications of continuously cast billets, the production of extra-thick injection molded modules currently typically employs die casting and electroslag remelting. Die casting yields large-sized steel ingots, ensuring a certain compression ratio for the production of extra-thick steel plates. However, the inherent defects of the die casting process lead to a series of problems, such as severe component segregation in the steel ingots, long casting time, high energy consumption, environmental pollution, and low rolling yield, generally not exceeding 70%, resulting in poor economic efficiency. Electroslag remelting can achieve a cleaner internal structure and alleviate the problem of billet segregation. However, electroslag remelting requires a secondary melting of the billet, which is inefficient, consumes a large amount of energy, and results in excessively high production costs.

[0004] Vacuum composite rolling technology is an effective method for producing extra-thick steel plates, solving the problem of limited thickness due to the thickness and compression ratio of continuously cast billets. Compared to traditional die casting, vacuum composite rolled products have better internal structure and properties, and a higher yield. Compared to electroslag remelting, it has higher production efficiency and lower cost, which is conducive to mass production. Currently, some steel mills in China have been able to manufacture high-quality extra-thick carbon low-alloy steel plates using vacuum composite rolling technology. However, for high-alloy injection mold steels such as 718 and 1.2738, weld cracking is highly likely during welding and post-weld cooling, and can even cause cracking of the billet itself. In addition, the production of composite steel plates using rolling processes has certain limitations: the composite interface is subjected to both vertical and transverse shear forces during rolling, weakening the composite effect; and the transmission of rolling force to the composite interface is insufficient.

[0005] Publication numbers CN101773931A ("A method for vacuum composite rolling of extra-thick plates"), CN103692166A ("A method for preparing extra-thick alloy steel plates"), CN101590596B ("A method for manufacturing extra-thick slabs using a cumulative stacking and welding process"), CN103028897A ("A method for producing extra-thick steel plates with high cold crack sensitivity"), and CN105252237A ("A method for producing CrMnNiMo series extra-thick mold composite billets") all employ vacuum electron beam welding technology to weld and assemble continuously cast billets, solving the production problem of high-alloy extra-thick steel plates. However, this process requires welding operations to be carried out in a sealed vacuum chamber, making it impossible to monitor the weld condition in real time; the weld can only be observed after the vacuum is broken following welding. For high-alloy mold steels, which have high sensitivity to welding cracks, cracking is extremely prone to occur during the welding process. Vacuum electron beam welding cannot provide timely repair welding, resulting in a decrease in the success rate of billet assembly. In addition, there is a problem of low bonding strength of the composite surface, which leads to problems such as delamination and cracking of the composite surface during subsequent heat treatment, processing and use. Summary of the Invention

[0006] This invention provides a method for producing extra-thick modular steel for injection molds. It uses continuously cast billets as the base material to produce extra-thick modules for injection molds with a thickness of 300-600 mm, excellent flaw detection and performance. This invention is low in cost, has a high yield, and is highly operable.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for producing extra-thick modular steel for injection molds, the method comprising:

[0009] 1) Composite billet processing:

[0010] The surface of the continuously cast billet to be composited after slow cooling and unstacking is milled to remove the oxide and rust layers and prevent it from hindering the diffusion and bonding of the matrix during subsequent heating and rolling. After milling, the gap between the billets is ≤2mm and the surface roughness Ra is ≤50μm.

[0011] The length and width of a set of blanks to be composited differ by ≤10mm; then, the four sides of the surface to be composited are chamfered, with chamfer dimensions of 15~20mm×40~50°.

[0012] 2) Preheating of the composite billet before welding:

[0013] The finished continuous casting billets to be composited are aligned and stacked together. An electric heating asbestos pad is used to cover the billets around the chamfered edges and preheat them to reduce the temperature difference in the heat-affected zone and prevent weld cracking. The preheating temperature is 150-250℃ and the preheating time is 3-4 hours. The electric heating asbestos pad not only preheats the area near the chamfered edge, but also prevents the composited surface of the billets from oxidizing due to high temperature, which would affect the composite effect.

[0014] 3) Welding:

[0015] Welding was performed using single-wire electric gas welding (EGW) along the four sides of the billet. To ensure weld strength and take into account the characteristics of the steel composition, AWS A5.26 EG70T-2 flux-cored welding wire was selected. The wire speed was 24-32 m / min, CO2 gas flow rate was 40-50 L / min, cooling water flow rate was ≥3 L / min, welding current was 340-410 A, arc voltage was 45-52 V, and welding speed was 30-40 cm / min. A vent hole was reserved in the weld. Then, a vacuum pump was used to draw a vacuum from the vent hole to a vacuum level of ≤1 Pa. Finally, spot welding was used to seal the weld.

[0016] 4) Post-weld heating:

[0017] After welding, the weld area is covered and heated again with an electric heating asbestos pad to promote the escape of hydrogen in the weld, prevent delayed cracking, and reduce welding residual stress. The heating temperature is 100-200℃ and the heating time is 2-4 hours. After that, the composite billet is hoisted to the heating furnace for heating.

[0018] 5) Heated forging:

[0019] Two-stage heating forging is adopted, with a target heating temperature of 1230℃~1270℃. The heating time of the first stage is 1~1.5h / 100mm thickness. After the second stage is heated to the target heating temperature, the holding time is 2~3h to ensure that the composite billet is uniformly and thoroughly heated, while avoiding excessive heating time that would lead to coarse grains.

[0020] After the steel billet exits the furnace, its upper surface is cooled by water mist. The water mist temperature is ≤35℃, the water-to-air volume ratio in the water mist is 1:180~1:220, and the cooling temperature is 800~840℃, forming a "low-temperature hard shell" on the surface, thereby enhancing the penetration of forging force into the core of the steel billet during forging. A 3000-ton hydraulic press is used to forge the composite billet, with asymmetrical dimensions for the upper and lower hammers to further improve the forging penetration of the billet and strengthen the bonding of the composite interface. The upper hammer has a width W=0.4~0.5H and a length L= A flat hammerhead with a diameter of 1.5 to 1.8W′ is used. The width of the lower forging platform is ≥2.0W′, where H and W′ represent the height and width of the composite billet, respectively. The length direction of the upper hammerhead is perpendicular to the width direction of the lower platform and the billet feed direction. The forging direction is perpendicular to the composite interface of the billet. The initial forging temperature (at 1 / 2 of the billet thickness) is ≥1100℃, and the final forging temperature (at 1 / 2 of the billet thickness) is ≥800℃. The billet is forged in two passes, with a total forging ratio of 1.5 to 2. The single-pass forging feed is 0.8 to 1.0W. The billet is stacked and slowly cooled for more than 48 hours after forging.

[0021] 6) Heat treatment:

[0022] The heat treatment employs a water-mist-air alternating timed quenching + tempering process. This ensures that the core of the thick module receives a hardened structure, guaranteeing the uniformity of the cross-sectional properties and thus ensuring excellent polishing performance. It also reduces surface quenching stress, preventing surface cracks. The water-mist-air alternating timed quenching process is as follows: heating temperature 860–900℃, net holding time 1.8–2.2 min / mm, followed by air cooling for 10–15 min → water mist cooling for 20–30 min → air cooling for 30–40 min → water mist cooling for 40–50 min → air cooling to room temperature; tempering temperature 520℃–570℃, holding time 10–16 h.

[0023] The water temperature of the water mist is ≤35℃, and the volume ratio of water to air in the water mist is 1:300~1:350.

[0024] To ensure internal quality, continuously cast billets located more than 3m from the head and tail of the billet are selected as the composite billets. After the billets are removed from the production line, they are stacked and cooled slowly to reduce the hardness of the billets and improve the efficiency of subsequent surface milling. The stacking temperature is ≥650℃ and the stacking time is ≥48h.

[0025] An extra-thick modular steel for injection molds, wherein the chemical composition of the steel by weight percentage is: C 0.30%–0.45%, Si 0.3%–0.8%, Mn 1.2%–2.0%, Cr 1.5%–2.5%, Ni 0.8%–1.6%, Mo 0.1%–0.5%, V 0.1%–0.2%, P≤0.030%, S≤0.080%, with the remainder being Fe and unavoidable impurities.

[0026] The finished thickness of the extra-thick modular steel used for injection molds is 300-600 mm.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention addresses the problems of high-grade injection mold steels such as 718, 1.2738, and XPM, which suffer from long production cycles, low yields, poor homogeneity of extra-thick modules, severe segregation leading to poor quality, and composite welding cracking and low bonding strength due to steel characteristics. It provides a low-cost, high-efficiency method for producing extra-thick modules, effectively solving the production problems of extra-thick modules for high-grade injection molds. This invention uses continuously cast billets as raw materials, which have superior internal quality compared to ingot-cast steel. It employs gas-electric vertical welding technology for billet assembly and welding. Through rational design of preheating and welding processes, a stable and smooth welding process is achieved, ensuring weld quality and improving welding efficiency. Combined with a 1.5-2 times low forging ratio, asymmetric deformation, and high interface penetration forging composite process, it achieves the production of high-homogeneity, high-interface bonding strength composite module steel. The yield reaches over 90%, far exceeding the 50% yield of ingot-cast steel and the 75% yield of electroslag remelted billets, resulting in a significant production cost advantage. The composite modules produced by this invention, with thicknesses ranging from 300 to 600 mm, exhibit excellent composite performance. The bonding strength between the substrates on both sides of the composite interface reaches over 95.2%. The internal quality meets the GB / T6402 Class 3 ultrasonic flaw detection standard, the mechanical properties meet the SPI standard requirements, the impact energy of the composite surface exceeds 50 J, and the polishing grade meets the PLASTICS A2 standard requirements. This invention enables the production of extra-thick modules for injection molds, replacing traditional high-cost and low-efficiency production processes such as die casting and electroslag remelting. Attached Figure Description

[0029] Figure 1 This is the core tissue of the 600mm thick composite extra-thick module of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] The chemical composition of the steel grades of the present invention is shown in Table 1; the processing parameters of the continuous casting billets of the embodiments are shown in Table 2; the process parameters of the gas-electric vertical welding billet assembly of the embodiments are shown in Table 3; the forging process of the embodiments is shown in Table 4; the heat treatment process of the embodiments is shown in Table 5; and the actual effects of the embodiments are shown in Tables 6 and 7.

[0032] Table 1. Chemical composition (wt%) of steel smelting in each embodiment.

[0033]

[0034]

[0035] Table 2 Processing parameters for continuous casting billets in each embodiment

[0036]

[0037] Table 3 Welding assembly process parameters for each embodiment

[0038]

[0039] Table 4 Forging process parameters for each embodiment

[0040]

[0041] Table 5 Heat treatment process parameters for each embodiment

[0042]

[0043]

[0044] Table 6. Actual Results of Each Embodiment

[0045] Table 7 Actual Effects of Each Embodiment

[0046]

[0047] See Figure 1 The metallographic structure diagram of Example 2 is shown below. Figure 1 It can be seen that no obvious dividing line was found in the composite interface of the extra-thick module of the present invention, and the structure of the composite interface is no different from that of the matrix, indicating that the composite interface achieves good metallurgical bonding.

Claims

1. A method for producing extra-thick modular steel for injection molds, characterized in that, The methods and steps include the following: 1) Preheating of the composite billet before welding: The finished continuous casting billets are aligned and stacked together. An electric heating asbestos pad is used to cover the billets around the perimeter and preheat them. The preheating temperature is 150-250℃ and the preheating time is 3-4 hours. 2) Welding: Welding is performed using single-wire gas-electric vertical welding. Welding is carried out along the four sides of the billet by welding bevels. The wire speed is 24-32 m / min, the CO2 gas flow rate is 40-50 L / min, the cooling water flow rate is ≥3 L / min, the welding current is 340-410 A, the arc voltage is 45-52 V, and the welding speed is 30-40 cm / min. A pre-reserved evacuation hole is made in the weld. Then, a vacuum pump is used to draw a vacuum from the evacuation hole in the weld until the vacuum degree is ≤1 Pa. Finally, spot welding is used to complete the sealing. 3) Post-weld heating: After welding, the weld area is covered and heated again with an electric heating asbestos pad at a temperature of 100-200℃ for 2-4 hours. After that, the composite billet is hoisted to the heating furnace for heating. 4) Heated forging: The forging process is carried out by two heating cycles, with a target heating temperature of 1230℃~1270℃. The heating time for the first heating cycle is 1~1.5h / 100mm thickness, and the holding time for the second heating cycle is 2~3h after the temperature is raised to the target heating temperature. After the steel billet exits the furnace, its upper surface is cooled by water mist. The water mist temperature is ≤35℃, the volume ratio of water to air in the water mist is 1:180~1:220, and the cooling temperature is 800~840℃. A 3000-ton hydraulic press is used to forge the composite billet. The upper and lower hammers are asymmetrical in size. The upper hammer uses a flat hammer head with a width W=0.4~0.5H and a length L=1.5~1.8W′, and the lower forging platform is ≥2.0W′ wide. H and W′ are the height and width of the composite billet, respectively. The initial forging temperature is ≥1100℃ at 1 / 2 of the billet thickness, and the final forging temperature is ≥800℃ at 1 / 2 of the billet thickness. The billet is forged in two passes with a total forging ratio of 1.5~2. The single-pass forging feed is 0.8~1.0W. After forging, the billet is stacked and slowly cooled for more than 48 hours. 5) Heat treatment: The heat treatment adopts a water mist-air alternating timed quenching + tempering process. The water mist-air alternating timed quenching process is as follows: heating temperature 860~900℃, net holding time 1.8~2.2min / mm, followed by air cooling for 10~15min after removal from the furnace → water mist cooling for 20~30min → air cooling for 30~40min, water mist cooling for 40~50min → air cooling to room temperature; tempering temperature 520℃~570℃, holding time 10~16h. The chemical composition of the steel, by weight percentage, is as follows: C 0.30%–0.45%, Si 0.3%–0.8%, Mn 1.2%–2.0%, Cr 1.5%–2.5%, Ni 0.8%–1.6%, Mo 0.1%–0.5%, V 0.1%–0.2%, P≤0.030%, S≤0.080%, with the remainder being Fe and unavoidable impurities; The finished thickness of the extra-thick modular steel used for injection molds is 300-600 mm.

2. The method for producing extra-thick modular steel for injection molds according to claim 1, characterized in that, Before preheating before welding, the surface of the continuously cast billet to be composited after slow cooling and unstacking is milled to remove the oxide layer and rust layer; after milling, the gap between the billet assemblies is ≤2mm and the surface roughness Ra is ≤50µm.

3. The method for producing extra-thick modular steel for injection molds according to claim 2, characterized in that, Chamfer the four sides of the composite surface to be processed, with chamfer dimensions of (15~20mm)×(40~50)°.

4. The method for producing extra-thick modular steel for injection molds according to claim 1, characterized in that, The water mist in step 5) above has a water temperature ≤35℃ and a water-to-air volume ratio of 1:300 to 1:

350.

5. The method for producing extra-thick modular steel for injection molds according to claim 1, characterized in that, Select continuously cast billets that are more than 3m away from the head and tail of the continuously cast billet as the billet to be composited. After the continuously cast billets are removed from the line, they are stacked and cooled slowly. The stacking temperature is ≥650℃ and the stacking time is ≥48h.

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