HIGH YIELD RATIO AND HIGH STRENGTH HOT ROLLED STEEL PLATE AND HIGH YIELD RATIO AND HIGH STRENGTH GALVANIZED STEEL PLATE EXCELLENT IN WELDABILITY AND DUCTILITY, AND HIGH YIELD RATIO AND HIGH STRENGTH ALLOYED GALVANIZED STEEL PLATE AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high yield ratio and high strength hot rolled steel plate and a high yield ratio and high strength galvanized steel plate, both having excellent weldability and ductility, and to provide a high yield ratio and high strength alloyed galvanized steel plate and its manufacturing method.;SOLUTION: The high yield ratio and high strength hot rolled steel plate having excellent weldability and ductility is a steel containing, by mass%, over 0.030 to less than 0.10 of C, 0.35 to 0.80 of Si, 1.7 to 3.2 of Mn, 0.001 to 0.02 of P, 0.0001 to 0.006 of S, 0.060 of Al, 0.0001 to 0.0070 of N, 0.01 to 0.055 of Ti, 0.012 to 0.055 of Nb, 0.07 to 0.55 of Mo, 0.0005 to 0.0040 of B and the balance of iron and inevitable impurities, and the steel has the yield ratio of 0.68 or more and less than 0.92, 1.0 X-ray intensity ratio on a {110} plane in a layer at a depth corresponding to 1/8 thickness of the steel plate and parallel to the plate face, and 780 MPa highest tensile strength (TS).;COPYRIGHT: (C)2005,JPO&NCIPI