| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a workpiece made of a high strength steel which is composed of a low alloy TRIP type annealed martensitic steel (TAM steel) having high hardenability and high notch fatigue strength by controlling the componential addition of the chemical composition and heat treatment conditions without depending on forging temperature, forging ratio or the like. <P>SOLUTION: The workpiece has a composition comprising 0.1 to 0.7% C, ≤2.5% Si, 0.5 to 2% Mn, ≤1.5% Al, one or more kinds selected from Nb, Ti and V by 0.01 to 0.3% in total, ≤2.0% Cr, ≤0.5% Mo, ≤1.0% Ni, Cr, and Mo and Ni by ≤2.0% in total and ≤0.005% B, and in which the concentration of carbon in retained austenite is 0.7 to 1.5 mass%, and a value(Ceq*) obtained by removing the C content from carbon equivalent (Ceq) is 0.3 to <0.6%, and the balance Fe with inevitable impurities: the value(Ceq*) is Ceq*=Ceq-C=Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14. <P>COPYRIGHT: (C)2011,JPO&INPIT |
