HIGH STRENGTH HIGH DUCTILITY STEEL SHEET EXCELLENT IN PRODUCTION STABILITY, MANUFACTURING METHOD THEREOF AND COLD ROLLED ORIGINAL SHEET USED FOR MANUFACTURING HIGH STRENGTH HIGH DUCTILITY STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide a high strength high ductility steel sheet excellent in production stability, a manufacturing method thereof, and a cold rolled original sheet used for manufacturing the strength high ductility steel sheet.SOLUTION: A high strength high ductility steel sheet includes, by mass%, 0.07 to 0.15% C, 0% to 0.8% Si, 1.2 to 2.1% Mn, 0.5 to 2.1% Cr, over 0% to 0.02% or less P, over 0% to 0.01% or less S, over 0% to 0.15% or less Al, over 0% to 0.01% or less N, and 0.0005 to 0.01% B, and the balance Fe with inevitable impurities. The contents of the C, Si, Mn and Cr satisfy a formula (1) below, and a metallographic structure thereof includes ferrite of 20 to 40 area%, and tempered martensite: 140≤442×C-7.7×Si+53×Mn+31×Cr≤168 (1). In the formula (1), C, Si, Mn, and Cr denote the content of the respective components by mass%.SELECTED DRAWING: None