HIGH YIELD RATIO AND HIGH-STRENGTH THIN STEEL SHEET SUPERIOR IN WELDABILITY AND DUCTILITY, HIGH-YIELD RATIO HIGH-STRENGTH HOT-DIP GALVANIZED THIN STEEL SHEET, HIGH-YIELD RATIO HIGH-STRENGTH HOT-DIP GALVANNEALED THIN STEEL SHEET, AND METHODS OF PRODUCTION OF SAME

摘要

High yield ratio high-strength thin steel sheetsuperior in weldability and ductility characterized by;being comprised of steel containing, by mass%,C: over 0.030 to less than 0.10%, Si: 0.30 to 0.80%, Mn:1.7 to 3.2%, P: 0.001 to 0.02%, S: 0.0001 to 0.006%, Al:0.060% or less, N: 0.0001 to 0.0070%, containing furtherTi: 0.01 to 0.055%, Nb: 0.012 to 0.055%, Mo: 0.07 to0.55%, B: 0.0005 to 0.0040%, and simultaneouslystatisfying 1.1 = 14xTi(%) + 20xNb(%) + 3xMo(%) + 300xB(%) =3.7,the balance comprised of iron and unavoidable impurities,andhaving a yield ratio of 0.64 to less than 0.92,a TSxE1 of 3320 or more, an YRxTSxE1 1/2 of 2320 or more,and a maximum tensile strength (TS) of 780 MPa or more.