STEEL PLATE SUBJECTED TO HEAT TREATMENT AND PROCESS FOR PRODUCING THE SAME

摘要

A steel plate subjected to heat treatment, consisting essentially of 0.05 to 0.09 mass% of C, 1 mass% or less of Si, 1.6 to 2.4 mass% of Mn, 0.02 mass% or less of P,0.02 mass% or less of S, 0.01 to 0.1 mass% of sol.Al, 0.005 mass% or less of N, 0.0003 to 0.003 mass% of B, Ti whose amount satisfies the relationship (48/32)S + (48/14)N <= Ti <= 2[(48/32)S + (48/14)N], and the remainder of Fe, wherein the average grain diameter of iron carbide deposited in the steel is 2 mum or less. This steel plate subjected to heat treatment is sequentially subjected to press forming and heat treatment. The resultant steel plate exhibits high strength and excellent delayed fracture resisting characteristics, so that it is suitable for use in automobile structural members.