HIGH STRENGTH STEEL SHEET AND HIGH STRENGTH GALVANIZED STEEL SHEET EXCELLENT IN SHAPEABILITY AND METHODS OF PRODUCTION OF SAME

摘要

High strength steel sheet and high strength galvanized steel sheet which are excellent in shapeability which secure a tensile maximum strength 900 MPa or more high strength while obtaining excellent ductility and stretch flangeability, which sheets have predetermined compositions of ingredients, have steel sheet structures which contain volume fraction 1 to 20% of residual austenite phases, and which have martensite transformation points of the residual austenite phases of −60° C. or less.

主权项

1. High strength steel sheet which is excellent in shapeability which contains, by mass %,
C: 0.075 to 0.300%, Si: 0.70 to 2.50%, Mn: 1.30 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.005 to 1.500%, N: 0.0001 to 0.0100%, and O: 0.0001 to 0.0100%, which contains, as optional elements, one or more of Ti: 0.005 to 0.150%, Nb: 0.005 to 0.150%, B: 0.0001 to 0.0100%, Cr: 0.01 to 2.00%, Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Mo: 0.01 to 1.00%, V: 0.005 to 0.150%, and one or more of Ca, Ce, Mg, Zr, Hf, and REM: total 0.0001 to 0.5000%, and has a balance of iron and unavoidable impurities, wherein the structure of the steel sheet contains, by volume fraction, 2 to 20% of residual austenite phase, and said residual austenite phase has a martensite transformation point of −60° C. or less.