Abstract: Microstructural evolution in 0.2C-1.51Si-1.84Mn steel during partitioning process was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron microprobe analysis (EMPA). When partitioning at 400℃, carbon atoms have redistributed within 10 s, and the volume fraction of retained austenite is 13.4%. When the partitioning time increases, martensite is tempered and austenite decomposes, leading to the decrease of strength and elongation. However, when the partitioning time is 1 000 s, the tensile strength and elongation suddenly increase. The reason is that the elongation loss caused by decomposition of retained austenite is offset by tempered martensite, the precipitation of carbides and cementite impedes dislocation movement, and thus its tensile strength increases. EPMA results show that carbon atoms diffuse during partitioning process, and carbides and cementite precipitate when the partitioning time increases, which decreases the content of carbon in retained austenite.