A carbide-free bainitic steel with high-ductility by dynamic transformation during coiling process

A new hot-rolled alloy of carbide-free bainite has been proposed for heavy trucks frames. It involves dynamic bainite transformation during the prolonged cooling of the coiling process after hot-rolling. The new hot-rolled Fe-0.5C-2.9Mn-2.3Al (in wt-%) steels exhibit tensile strength of 1110?MPa with a combined total elongation of 35%. The alloy has been re-heat-treated with one step and two steps isothermal bainitic transformation to study the effect of microstructure evolution and microstructure-property relationship. The transformation-induced plasticity (TRIP) effect of retained austenite has been discussed and revealed as the main contributor for the high ductility of bainitic steels. The formation of the cracks at fracture regions after tensile deformation, which is associated with the austenite stability and morphology, has been observed and discussed.