Current situation and properties of ultra-high strength steel for automotive use in Japan

摘要

Governing factors of formability of ultra-high strength steel are different from those of mild steel. Homogeneity of microstructure is very important in bending, burring and drawing with small punch and die shoulder radius. Attention must be paid to delayed fracture that is caused by the existence of retained austenite. Several types of ultra-high strength steel are used in Japan, which are designed to possess required properties.