Research On Microstructure And Properties Of Low-cost Cold-rolled Dual Phase Steel

Due to the combination of high strength, excellent formability and good impact resistance, DP steel is widely used in automobile industry, even becoming the first choice. According to the present state of automobile and steel industry in our country, cold-rolled DP steel with high strength was emphatically studied. This study will contribute to explore the experience of advanced high strength steel production and combine the research and production.Although the production and application of Q345has been researched through several decades, the study of develop DP steel from Q345by using cold-rolled and heat treated was seldom reported. Without any micro-alloy elements addition, hot-rolled Q345steel was taken as raw material which was heat treated by continuous annealing simulator after cold rolling. DP steel with excellent comprehensive mechanical properties was developed and make a study of the ability of welding as well. This study included the following main parts:(1) Simulation test was conducted in the continuous annealing simulator CAS-300Ⅱto study the effect of continuous annealing process parameters on microstructure and mechanical properties of DP steel. The heating temperature, holding time of annealing, slow cooling rate, quenching temperature, rapid cooling rate, and overaging temperature were emphatically studied.(2) Combining different detect result by using optical microscopy, scanning electron microscope and transmission electronic microscopy, the microstructure,morphology distribution, fine structure of martensite under different production process were observed.(3) Through the anlysis of the microstructure and mechanical properties after diferent processes of annealing, the effect of continuous annealing on the comprehensive properties of dual phase steel was studied to achieve appropriate production process.(4) The weldability of tested dual phase steel after continuous annealing was studied. The principles of phase transformation and weldability of the joints were emphatically studied, which were treated by different welding methods, including electronic beam welding, laser welding, and argon arc welding. The formability of equal thickness and different thickness tailor-welded blanks were simulated by FEM, including punch bulging simulation and hydro forming simulation.