Development of Ti-Microalloyed 600 MPa Hot Rolled High Strength Steel

A high strength steel with yield strength on the order of 600 MPa was developed successfully with only addition of titanium alloying element based on a low-carbon steel. The results showed that the hot deformation accelerated ferrite and pearlite transformation and retarded bainite transformation under continuous cooling condition. The microstructure of this steel was mainly composed of fine grained ferrite and carbides distributing along the ferrite grain boundaries. The yield and tensile strengths of steels were about 620—650 MPa and 720 — 740 MPa, respectively, and the values of strain hardening exponent and plastic strain ratio were 0. 12 and 0. 80, respectively, thereby providing a good combination of strength with toughness. In short, the fine grained ferrite and TiC precipitation strengthening contributed to a high strength.