Study On Preparation Process Of Low Carbon And High Strength Q&P Steel

Q&P steel as a new generation of automotive steel, whose good performance of highstrength and plasticity, and strengthen the plasticizing mechanism has become a hotspotof Q&P steel. The test first to ordinary low carbon Si-Mn steel as the research object,with the traditional Q&P heat treatment process, study the effect of partitioning time onmicrostructure and mechanical properties, then on this basis, to add the right amount of Belements, by intercritical insulation, let Mn element diffusion into the austenite, andcombine it with the traditional Q&P one-step and two-step method heat treatmentrespectively, and design a new type of Q&P heat treatment process, study quenchingtemperature of new process, and study the new process and traditional Q&P processeffect on the microstructure and mechanical properties of steel. The results showed that:Low carbon Si-Mn steel got the best mechanical properties in the partition time30safter Q&P processing, tensile strength was1340MPa, elongation was20%.Test steel increases its hardenability with a small amount of B element added. Afterthe traditional Q&P one-step process, the microstructure was mainly composed of platestrip martensite, a small amount of carbide particles and residual austenite, there are alsosome massive secondary martensite structure; by intercritical heating insulation at760℃,Mn content of austenite reached the maximum when the holding time at1300s, but themicrostructure was mainly the plate strip martensite after the Q&P one-step process, themassive martensite significantly reduced, ultimate tensile strength was1310MPa,elongation was12%.When the test steel processed by I&Q&P two-step treatment, in the intercritical720℃insulation1500s or760℃insulation1300s, after the new process, tensile strengthwas1240~1480MPa, elongation was12.9%~23.3%, product of strength and elongationwas more than25000MPa%, comprehensive mechanical performance superior to thetraditional Q&P Steel.