Low cost,high strength and high elongation steel is always the major trends of steel development especially for automotive indus-try.However,raising strength usually brings about loss of ductility,which is known as the strength-ductility trade-off [1].Solving strength-ductility trade-off by increasing low cost carbon content is the century-long pursuit of researchers.Rashid [2] pointed out that investigation since 1900s indicates that the increase of carbon content leads to enhancing strength,but deteriorating ductility and other properties of steels.Krauss [3] also noted that for 41 ×× and 43×× series martensitic steels,increasing carbon con-tent results in the increase of strength and the decrease of ductility.