STEEL FOR NITRIDING TREATMENT, NITRIDING TREATED STEEL AND PRODUCTION METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide nitriding treated steel in which high strength and elongation properties can be reconciled, steel for nitriding treatment which is suitable as the stock for the nitriding treated steel, and to provide a production method therefor. SOLUTION: (1) The steel for nitriding treatment has a composition comprising≤0.01% C, 0.001 to 0.5% Si, 0.01 to 0.5% Mn, 0.001 to 0.1% P,≤0.015% S, 0.001 to 0.5% Al, 0.01 to 0.2% Ti, 0.02 to 0.1% Cr, 0 to 0.05% Nb, 0 to 0.005% B and≤0.005% N, and the balance Fe with impurities, and in which effect Ti=Ti-ä(N/14)+(S/32)+(C/12)}×48:0.01 to 0.08%, and 0.4×effective Ti≤0.1-Cr are satisfied, and is subjected to heat treatment so as to be held at 100 to 200°C for≥10 min after nitriding treatment. (2) Regarding the steel for nitriding treatment, the average chemical composition in the central region of the sheet thickness within the range from the center of the sheet thickness to 40% of the sheet thickness toward the surface is the same as the above composition in (1) except for≤0.03% C and 0.08 to 0.25% N, the hardness of the center of the sheet thickness is≥150 Hv hardness, and the number of pieces of iron nitride with a long side of≥5μm in the central region of the sheet thickness is≤10 pieces per 1×10-8m2. COPYRIGHT: (C)2006,JPO&NCIPI