HIGH-TENSILE-STRENGTH HOT-DIP GALVANIZED HOT-ROLLED STEEL SHEET WITH LOW YIELD RATIO AND COMPOSITE STRUCTURE SUPERIOR IN EXTENSION FLANGE, AND MANUFACTURING METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a high-tensile-strength hot-dip galvanized hot-rolled steel sheet with a low yield ratio and a composite structure superior in extension flange, which is suitable for a material for automotive parts, and to provide a manufacturing method therefor.;SOLUTION: The high-tensile-strength hot-dip galvanized hot-rolled steel sheet with the low yield ratio and the composite structure superior in extension flange has a steel composition comprising, by mass%, 0.01-0.2% C, 0.5% or less Si, 0.5-3.0% Mn, 0.10% or less P, 0.02% or less S, 0.005-0.2% Al, 0.02% or less N and the balance Fe with unavoidable impurities; and has the composite structure comprising ferrite, tempered martensite and martensite, so as to make the tempered martensite occupy 50% or more and the martensite 5% or more by a volume fraction.;COPYRIGHT: (C)2005,JPO&NCIPI