INFLUENCE OF THE PARTIAL SUBSTITUTION OF Si BY Al ON THE MICROSTRUCTURE OF HOT ROLLED TRIP STEELS BASED ON DYNAMIC TRANSFORMATION OF UNDERCOOLED AUSTENITE

The effect of A1 partially substituted Si on the microstructure of hot rolled TRIP (transformation induced plasticity)steels with identical contents of C and Mn on the basis of the dynamic transformation of undercooled austenite(DTUA)was investigated by uniaxial hot compression tests in a Gleeble-1500 simulation test machine.The results show that the partial replacement of Si with Al could reduce theγarea in the equilibrium phase diagram,increase the A_3 temperature and enlarge the range between A_3 and A_(r3).In addition,when the Si was partially replaced by Al,the kinetics of ferrite transformation during DTUA was accelerated and the optimum isothermal bainitic temperature was increased when the isothermal treatment was implemented.Moreover,the granular retained austenite in the C-Mn-Al-Si steel was more smaller and dispersive,and the carbon content in retained austenite was higher than that in C-Mn-Si steel,but the grains of ferrite were coarser in the C-Mn-Al-Si steel.