The Study On High Temperature Deformation Behavior Of Si-Mn Hot-rolled Dual-phase Steel

The demands for automotive plates are being increased dramatically with the national economy development. There are many merits( advantages) of Dual-phase steel, such as continuity yield, low yield strength and tensile strength ratio, high work-hardening exponent, high elongation, etc. Dual-phase steel is in the front edge of the development of high strong low alloy, and provides a good way to reduce the weight of automotive, produce high toughness pressing part and simplify the impact pressing process.In this paper, the hot deformation behavior and mechanical properties of Dual-phase steel were studied on Gleeble-1500 thermo-mechanical simulator. The main contents are given as follows:1. By single-pass compression test, the behavior of dynamic softening was studied for Si-Mn Dual-phase steel. The results indicate that dynamic recrystallization occurred when the deformation temperature was 1000℃. The behavior of recrystallization became esier and the flow stress became smaller when the deformation temperature increasing. When deformation at 850℃ or 1000℃, the flow stress increased with the increasing of deformation rate.2. According to true stress-strain curves of single-pass compression, the resistance mathematic model of Si-Mn Dual-phase steel were established:σ=9813.61481· (ε)^0.62570(ε|·)^0.03804 exp(-0.00246T-1.04907ε) and then calculated the austenite activation energy by Z-hollomen parameters: Q =301.158kJ/mol.3. By double-pass compression test, the static softening behavior of Si-Mn Dual-phase steel was studed. The static softening rate became bigger under the condition of high deformation temperature, long holding time, and large deformation amount; Besides that, the seize of grain became bigger and the patterns of martensite lath changed. Through Z-hollomen parameters, we calculate the static rate, and got the static recrystallize activation energy is 99.971KJ/mol, the results indicated that the recrystallize behavior of the steel in this paper was liable to happened.4. The CCT curve of Si-Mn Dual-phase steel was determined, the behavior of γ→α transformation and the microstucture were studied during the continues cooling process. Based on the CCT curve we had got, it was feasible to dual-phase steel, and established...