Abstract
A study has been made of the effects of chemical composition and coiling temperature on the mechanical properties of as-hot-rolled Tri-phase steel which possesses combined advantageous properties of both dual-phase steel and ferrite-bainite steel.
At least 2% of martensite in volume fraction is necessary to obtain low yield ratio of less than 0.7, and low yield point elongation of less than 1%. On the other hand, the volume fraction of martensite has to be controlled less than 10% in order to get high stretch flangeability.
Tri-phase steel sheets composed of ferrite, bainite and 2-10% of martensite exhibit low yield ratio, low yield point elongation and good stretch flangeability, and are able to be produced by lowering the coiling temperature under than 250°C using C-Si-Mn steels. The steels used in this experiment are mainly Cr free steels, because the addition of Cr results in the deterioration of paintability and increases the production cost.
