HIGH TENSILE STRENGTH HOT DIP GALVANIZED STEEL SHEET AND HIGH TENSILE STRENGTH HOT DIP GALVANNEALED STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide a high tensile strength hot dip galvanized or galvannealed steel sheet which contains large quantities of Si and Mn, has excellent plating adhesion, mechanical properties and a balance of strength-ductility, and also has excellent corrosion resistance.;SOLUTION: The steel sheet has a composition containing, by mass, 0.05 to 0.25% C, 0.50 to 2.00% Si, ≤3.5% Mn and 0.01 to 1.0% Al. The mass ratio of Mn/S in the steel is ≥2. The steel sheet also has a composite structure consisting of tempered martensite of ≥20% by volume fraction and retained austenite of ≥2%. The Al concentration (mass%) in a plated layer on the steel sheet satisfies the following inequality (1) in the case of a hot dip galvanized steel sheet and satisfies the following inequality (2) in the case of the hot dip galvannealed steel sheet, and the total of Si and Mn in the steel is ≥3%: 0.67-1/50(Mn/Si)≥[the Al concentration in the plated layer]≥0.37-1/50(Mn/Si) (1), and 0.5-1/50(Mn/Si)≥[the Al concentration in the plated layer]≥0.2-1/50(Mn/Si) (2).;COPYRIGHT: (C)2002,JPO