MANUFACTURE OF GALVANNEALED STEEL SHEET EXCELLENT IN STRETCH FLANGING PROPERTY USING HIGH STRENGTH HOT ROLLED ORIGINAL STEEL SHEET

摘要

PURPOSE: To obtain the subjective high strength galvanized steel sheet having excellent workability superior to that of a hot rolled original steel sheet, particularly, excellent stretch flanging properties without executing cold rolling by using a high strength hot rolled steel sheet having ≥45kg tensile strength as an original sheet. ;CONSTITUTION: Steel having compn. contg., by weight, 0.02 to 0.30% C, ≤1.50% Si, 0.60 to 3.0% Mn, ≤0.20% P, ≤0.05% S and 0.01 to 0.10% Al, and the balance Fe with inevitable impurities is subjected to hot rolling at the Ac₃ point or above. This hot rolled steel sheet is picked, and after that, is held under heating to the Ac₁ point or above without executing cold rolling, in a continuous annealing and galvanizing line, and subsequently, is quenched to the Ms point or below during it reaches a hot dip zinc bath to produce partial or complete martensite in the steel sheet. Next the steel sheet is heated to the hot dip zinc bath temp. and galvannealing temp., i.e., the Ms point or above to produce partial or complete tempered martensite in the steel sheet.;COPYRIGHT: (C)1993,JPO&Japio