PRODUCTION OF HOT-DIP ALUMINUM COATED STEEL SHEET FOR DEEP DRAWING, EXCELLENT IN THERMAL DISCOLORATION RESISTANCE

摘要

PURPOSE: To combine thermal discoloration resistance with superior workability by subjecting a steel, containing specific amounts of C, N, Mn, Si, P, Al, N, and Fe, to nitriding treatment at specific temp. and then applying hot-dip aluminum coating to it. ;CONSTITUTION: A steel, having a composition consisting of, by weight, ≤0.05% C, ≤0.005% N, ≤1.5% Mn, ≤0.5% Si, ≤0.1% P, 5×N to (5×N+0.05)% Al, and the balance essentially Fe, is used. This steel is finish-rolled at a temp. not lower than the Ar₃ transformation point, coiled at 650-780°C, cold-rolled, and recrystallization-annealed in a continuous annealing furnace. Then, nitriding treatment is done in a nitriding atmosphere at 600-800°C under the condition where the product of NH³ concentration (%) and time of stay (sec) becomes 20 to 500. Subsequently, hot-dip aluminum coating is done, followed by heat treatment at 300-450°C for 2-100hr.;COPYRIGHT: (C)1995,JPO