In the process of cold extrusion of cemented carbide die, the main properties of the die material should include the following points:
1. High strength and toughness: The drawing die has to withstand complex loads such as extreme extrusion force, bending stress, and impact during the extrusion process. Therefore, it is required that the selected material should have high strength and toughness after heat treatment. Therefore, the drawing die material should have good hardenability, so as to ensure that the drawing die can be hardened and a uniform structure. Large carbides and serious deflection, fiber orientation and non-metallic inclusions and other internal defects will reduce the strength and toughness of the drawing die, or cause stress concentration when loaded, and cause early failure of the drawing die.
2. Good wear resistance: The drawing die should have high wear resistance to ensure normal service life and produce large quantities of qualified extrusions. Generally speaking, the hardness of steel is directly proportional to the wear resistance under certain conditions. Therefore, the drawing die material is required not only to have sufficient hardenability, but also high hardenability. However, in addition to hardness, the wear resistance of steel also determines the thickness, composition, excess and amount of carbide phases precipitated by the mouth fire after heat treatment, size, type, dispersion, and red hardness. For example, high-speed steel and low-alloy tool steel have the same hardness value after heat treatment. In actual use, the former has much higher wear resistance, while the wear resistance of cemented carbide with more than 80% WC is higher than that of steel. ten times. Therefore, in mass extrusion production, in order to obtain a long service life of the drawing die, high-speed steel and cemented carbide, which are expensive and complex in process, are still used as drawing die materials.
3. Sufficient thermal stability: During continuous production, the temperature rise of the drawing die sometimes reaches or exceeds 200°C. For drawing die materials that use 160~180°C as the tempering temperature, the strength and hardness will decrease, so it is used to compare the temperature rise. The high drawing die material should have good anti-tempering stability.
4. Good manufacturability: The cold extrusion die has a long manufacturing cycle, complex process and high precision requirements. Generally, they must undergo forging, cutting, heat treatment, grinding or other finishing. Therefore, only materials with relatively good manufacturability can meet the needs of production.
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