The rolled steel and its production mannered null mass which are superior in weather resistance and resistance

摘要

PROBLEM TO BE SOLVED: To improve weatherability to sea salt grains and fatigue resistance by adding slight amounts of Ni, Cu, and Mo to steel components and controlling the concentration ratio of Ni/Cu, the thickness of an internal oxidation layer in the surface of the steel, and the thickness of an Ni-, Cu-, and Mo-concentrated layer on the internal oxidation layer, respectively. ;SOLUTION: The steel has a composition which consists of, by weight, 0.02-0.20% C, ≤0.1% Mn, ≤0.1% Si, ≤0.1% Cr, ≤0.1% Al, ≤0.1% Ti, 0.8-3.0% Ni, 0.8-2.0% Cu, 0.4-0.7% Mo, 0.001-0.01% N, ≤0.1% P, ≤0.006% S, and the balance Fe and in which the concentration of Ni/Cu is regulated to ≥0.8. A cast billet of the steel is reheated to 1100 to 1300°C, rolled, and subjected to rolling where cumulative draft at ≤950°C becomes ≥40%, and hot rolling is finished at ≥900°C. By this procedure, the thickness of an internal oxidation layer in the surface of the steel is regulated to ≤2 μm in an as-hot-rolled state, and an Ni-, Cu-, and Mo-concentrated layer of ≥2 μm thickness is formed on the internal oxidation layer, and the sum of concentrations of these elements is regulated to ≤7.0%.;COPYRIGHT: (C)2000,JPO