STEEL FOR MACHINE STRUCTURE EXCELLENT IN MACHINABILITY AND TOUGHNESS, AND MACHINE STRUCTURAL PARTS

摘要

PROBLEM TO BE SOLVED: To provide a steel for machine structure excellent in machinability, particularly in the life of a drill and treatability of chips and having the balance of good hardness and toughness, and to provide machine structural parts. ;SOLUTION: This steel for machine structure is a steel having a chemical compsn. contg., by mass, 0.05 to 0.55% C, 0.50 to 2.5% Si, 0.01 to 2.00% Mn, 0.005 to 0.080% S, ≤2.00% Cr, ≤0.035% P, ≤0.50% V, ≤0.0150% N, ≤0.04% Al, ≤2.0% Ni, ≤1.5% Mo, ≤0.01% B, ≤0.10% Bi, ≤0.05% Ca, ≤0.12% Pb, 0.04% Ti, 0.04% Zr, 0.04% Ti+Zr, ≤0.05% The, ≤0.05% Nd, ≤0.1% Nb, ≤1.5% Cu and ≤0.5% Se, satisfying 100C+11Si+18Mn+32Cr+45Mo+6 V≤100, -23C+Si(5-2Si)-4Mn-+104S-3Cr-9V+10≥0 and 3.2C+0.8Mn+5.2S +0.5Cr-120N+2.6Pb+4.1Bi-0.001α2+0.13α≥3.0, and consisting of the balance Fe with impurities, in which 10 to 80% in the area ratio of the structure is composed of a ferritic phase, and HV hardness is 160 to 350, where the elemental symbols in each inequality denote the contents by mass % of the elements, and α denotes the area ratio by % of the ferritic phase in the structure.;COPYRIGHT: (C)2000,JPO