Reason of Fracture of S136 Steel Die

S136 steel die broke and failed during service. Through chemical composition analysis, fracture analysis, microstructure observation and hardness test, the reason for fracture of this S136 steel die was analyzed. The results showed that the fracture of S136 steel die was mainly dimple morphology, a large number of granular carbides could be seen in dimples, and a small amount of microcracks appear red at grain boundary. Microstructure of S136 steel die was tempered martensite, with a large number of micron carbide particles distributed at grain boundary. The carbide hardness was about 11 GPa, and matrix hardness was about 5 GPa. Comprehensive analysis showed that the reason for fracture of S136 steel die was the large amount of carbides existing at grain boundary, which led to increase brittleness of material.