The relationship between microstructure morphology and mechanical properties of the low-carbon steel(Fe-0.20C-2.59Mn-2.13Si)treated by different intercritical annealed quenching and partitioning(Q&P)processes was investigated through inter-rupted tensile tests plus quasi-situ electron backscatter diffraction measurements.Results show that size and distribution of retained austenite(RA)directly affect the sequence of deformation induced martensitic transformation.As strain increases,the equiaxed RA grains wrapped by ferrite transform first,followed by the equiaxed and film-like RA grains adjacent to martensite.Compared with traditional intercritical annealed Q&P steel with equiaxed structure,the steel with quenching pretreatment contains uniform lamellar structure and the relatively film-like type of RA,leading to the higher yield strength,tensile strength,and elongation,as well as the steady increase in dislocation density upon straining.