LAUSR

ABSTRACT An intercritical annealing pre-treatment was added before the conventional two-step heat treatment process, and the effect of the isothermal bainitic transformation (IBT) time on the steel's microstructure and mechanical properties were investigated. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, while the mechanical properties were evaluated using tensile testing. The microstructure of the three-step hot-dip galvanised transformation induced plasticity (TRIP) steel consists of ferrite, bainite, retained austenite, and martensite. The mechanical properties of the steel after the three-step heat treatment process are excellent, with a tensile strength above 770 MPa and elongation above 29%. The effect of IBT time on the mechanical properties was insignificant because the intercritical annealing pre-treatment increases the bainitic transformation rate.