Effect of heat treatment on microstructure and mechanical properties of quenching and partitioning steel

In order to investigate the effect of microstructural characterization on the mechanical properties and retained austenite stability, a different type of quenching and partitioning steel (I-Q&P) through intercritical annealing before the quenching and partitioning process was designed, which can realize lamellar intercritical microstructure compared to the conventional quenching and partitioning (Q&P) process. The morphology of ferrite and martensite/retained austenite is lamellar in the I-Q&P steel while it is equiaxed after being heat-treated by conventional Q&P process. The I-Q&P steel is proved to have better formability and mechanical properties than conventional Q&P steel, which is due to the highervolume fraction of retained austenite in the I-Q&P steel and confirmed by electron backscattering diffraction patterns and X-ray diffraction. Furthermore, the stability of retained austenite in I-Q&P steel is also higher than that in conventional Q&P steel, which is investigated by tensile tests and differential scanning calorimetry.