The Effect of Cooling Rate on the Microstructure and Mechanical Properties of the Plastic Injection Molds

In this research, the effect of cooling rate on the microstructure, hardness and impact energy of a plastic injection mold made of X210Cr12 steel was investigated. The microstructural studies showed that with increasing cooling rate, the amount of residual austenite (Ar) decreases until it is completely removed. Statistical analysis showed that the size and volume fraction of chromium stabilized with block carbides decreases with increasing cooling rate. As the cooling rate increased, bainites were observed in the microstructure. The hardness decreased via increasing the cooling rate and austenitization time due to the reduced interaction of carbides with dislocations. Martensitic structure prevented a significant reduction in hardness. These factors increased the toughness of the X210Cr12 and led to the ductile failure. Cryogenic treatment modified the structure via distribution of fine carbides into the stable lath martensite. With optimizing the hardness and toughness to withstand the impact of the die, toughness increased to 125 j and hardness decreased to 624 H.V.