Fracture: Steel with superheated structure can refine austenite grain after reheating and quenching, but sometimes coarse granular fracture still appears. There are many controversies on the theory of fracture inheritance. It is generally believed that impurities such as MnS dissolved into austenite and enriched in the grain interface due to excessive heating temperature. These impurities precipitate along the grain interface when cooled, and are liable to fracture along the coarse austenite grain boundary when impacted.