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In the low-carbon martensite Dies Die steel usually used alloy tool steel, carbon steel and high-speed tool steel, After quenching his organization is the twin sub-structure, micro-cracks of the needle-like carbon, martensite sheet. Due to the higher carbon content, more elements to form carbide, steel mesh there will be inevitable, and the strip carbon chain, often caused by mold in the use of brittle fracture. Due to low-carbon martensite sub-structure is a mistake, a high intensity (hardness 45HRC ~ 50HRC, as the yield strength 1000MPa ~ 1300MPa), a good plastic (δ5 ≥ 10%, ψ ≥ 40%) and toughness (AKV ≥ 59J), as well as good cold, heat treatment and solderable distortion of small advantages. As a result, how to die steel quenched in more or even all low-carbon martensite, the mold is to improve the strength and toughness, the key to extend the service life of mold. At present, development is a low-carbon steel structure of the organization hope to be hardening all the lath martensite in order to ensure high strength and toughness; of high-carbon steel tend to reduce the carbon content or minimize the quenching temperature to reduce the number of twin martensite, To ensure that the toughness of the material; of carbon steel in high temperature quenching tend to be more or all of the low-carbon martensite organizations, to increase the fracture toughness. Low-carbon martensite in the plastic mold Application
1 low-carbon martensite carburizing steel-plastic mold Low-carbon steel, low carbon steel mold in the shape after carburizing, quenching and tempering temperature, so that the mold surface to be fine needle-like carbon tempered martensitic + + a small amount of granulated carbide retained austenite, the Department of Heart The main organization for low-carbon martensite. In order to ensure the mold surface with a high hardness (58HRC ~ 62HRC), the high wear-resistance, and the center has a high strength and toughness (30HRC ~ 45HRC), used in the manufacture of a variety of good wear-resistance requirements, complex shapes, and are subject to load High plastic forming die. 2 ultra-low carbon cold extruded plastic die steel
1 Foreign widely used ultra-low carbon steel cold extruded plastic mold manufacturing process. As the need for cold extrusion, with the exception of low carbon content, softened by annealing, the hardness of low (≤ 160HBS, complex cavity pressure when ≤ 130HBS), particularly suitable for cold plastic deformation. This type of steel in the cold extrusion after carburizing, quenching and tempering. Therefore, with high productivity, manufacturing cycle short, high precision molds. Typical of the kind of United States Steel P series of low-carbon steel mold, Germany X6CrMo4 Steel (≤ 0.07% C, mass fraction, the same below) and LJ-08Cr3NiMoV domestic steel (≤ 0.08% C).
3 martensite low-carbon steel (≤ 0.25% C) strength and toughness of steel-plastic mold Martensite low-carbon steel, including low-carbon carbon steel and alloy steel by low-carbon low-carbon martensitic hardening to deal with strong, high strength and toughness to be low-carbon martensite, quenched and tempered steel in place of or dealing with lowForgingRoughfinishing. For the heat treatment process: 920 ℃ heating, 10% NACL salt water quenching, 430 ℃ tempering. The technology not only eliminate the quenching soft, increase the hardenability die, and mold can improve the yield strength and toughness to ensure the service life of mold. After the above process, after the deduction section of cable-die forging, with an average hardness 40HRC, Kim Sang-lath martensite smaller organizations, successfully completed the task of the contract. (5) Q345B Steel Rivet die forging of a strong low-carbon martensitic hardening XKJ44.5mm ~ 48mm large sports complex for the steel cable-stayed-cable connector is a die-cast parts (quality 98.5KG), due to the volume is only 40 to choose thickness Q345B plate of 40mm, Rivet use of the technology approach, laminates made from 7 to 400mm × 400mm × 290mm of hot forging die. Process: CuttingrivetingMachiningrepair clamp. After Box 950 ℃ rapid heating furnace (20s/mm), saline cryogenic cooling quenching, tempering is not used directly. Die average hardness 46HRC, the completion of 40, can still continue to be used. Conclusion
(1) low-carbon martensite with high strength and toughness, die steel is the ideal organization quenching. (2) low-carbon martensitic steel (≤ 0.25% C) to carry out strong and hardening the surface of enhanced processing, can replace the steel mold manufacturing various types of mold. (3) in carbon steel die with high temperature quenching, can be more or even all low-carbon martensite organizations, significantly increase the strength and toughness of the mold. (4) high-carbon steel using low-temperature quenching die, will be more low-carbon martensite organizations, significantly improve the life of the mold. (5) die organization of low-carbon martensitic steel, die down carbon steel, low-carbon, and die steel heat treatment is an important trend.
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