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Requirement on the weight saving of automobiles has further been energetic for global environment and for saving natural resources.The steel which has tensile strength ( TS) more than 1,000 MPa and TS multiplied by total elongation ( El) TS × El is more than 30 000 MPa ·% ( El type) has been studied.By taking other applications into consideration,better notch toughness has also been studied ( Toughness type).TRIP steel seems to be better for El type and grain refined Martensite based steel ( M steel) is better for Toughness type.Mn can stabilize Austenite ( γ) during cooling from γ area as Retained Austenite ( γR ) and can lower Ms temperature.Grain refining prior to Austenite→Martensite ( γ→M),Austenite→Retained Austenite ( γ→γR ) and Austenite→Bainite ( γ→β) should be effective to modify transformation behavior and transformed structure.Middle Mn steel having 5 % Mn with 0.05 % Nb and hot control-rolled was studied by changing C content and the condition of heat treatment after rolling.TRIP steel having TS.El≥30 000 MPa · % and M steel having Absorbing Energy ( AE) at - 100℃ of 8.2 Joule,and 50% FATT of -70 ~ -90℃ were obtained.