1 Effect of mold temperature
During die casting, the speed is very high, the pressure is very high, the surface of the mold is subjected to a strong impact load, and the surface of the mold is in contact with the high-temperature melt, and its temperature is up to 8700C. Under such high temperature and rapid heating, the surface of the mold generates compressive thermal stress. Before each die-casting, the lubricant is sprayed in the mold for rapid cooling, and tensile stress is generated on the surface of the mold. When this alternating thermal stress exceeds the yield strength of the mold surface, thermal fatigue microcracks are generated on the surface, which diffuse rapidly and spread toward the center to form tortoises. crack. It will cause casting strain and mold sticking, and seriously cause early cracking of the mold.
2 Basic properties of materials
Die-casting works in a rapidly hot and rapidly cooling die-casting environment, and has the following requirements for die-casting mold materials:
(1) Good resistance to thermal fatigue and thermal shock, not easy to crack.
(2) Good toughness and ductility, improving the impact resistance of sharp corners and protruding parts of the mold.
(3) Good thermal hardness, heat strength, hardenability, wear resistance and high temperature oxidation resistance.
(4) Heat treatment deformation is small, thermal expansion coefficient is small, etc. The hot work die steel 3Cr2W8V and H13 steel (4Cr5MoSiVl) mainly used in die-casting molds are mainly chromium, tungsten and molybdenum. At present, H13 steel is mostly used for die-casting molds. It is a hot work die steel mainly composed of alloying element chromium. It has good toughness, thermal fatigue resistance and oxidation resistance. After proper surface treatment, its service life can reach a very high level. , has become a mature die-casting mold steel and has been widely used. More than 90% of die-casting cavity molds abroad are made of H13 steel. Mold material control is very important. The H13 steel used in the die-casting mold must be clean steel, uniform structure, slight segregation, high-quality steel with good isotropy. A series of advanced technologies are adopted in the production process of foreign high-quality H13 steel, such as vacuum degassing, electroslag remelting and other refining technologies to improve cleanliness, and then through multi-directional rolling or repeated pier forging and ultra-fine processing technology , so that H13 steel has excellent intrinsic quality. Using advanced smelting technology to provide more high-purity die-casting die steel is the future direction.
EN 
