HIGH STRENGTH STEEL ARTIFACT SUPERIOR IN NOTCH FATIGUE STRENGTH, AND MANUFACTURING METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a high strength steel artifact consisting of ultrahigh-strength low-alloy TRIP steel (TBF steel) with high notch fatigue strength, manufactured by controlling a component addition amount of chemical composition and heat treatment condition without depending on a forging temperature, a forging processing rate and the like.;SOLUTION: The high strength steel artifact superior in notch fatigue strength includes 0.15 to 0.25% C, ≤2.5% Si (not including 0%), 0.5 to 2% Mn, 0.5 to 1.5% Cr, ≤0.5% Mo, ≤0.1% Nb, and remainder being Fe and unescapable impurities, and has a carbon equivalent (Ceq) of 0.65% or larger and less than 0.75%, which is determined by following formula. Moreover, in the metal structure of the high strength steel artifact, a mother phase includes not less than 65% of a Russ-like bainitic ferrite by volume rate to all the structure, and 5% or less in total of polygonal ferrite and granular bainitic ferrite by volume rate to all the structure, and a second phase includes 5 to 20% of remained austenite by volume rate to all the structure and 10% or less of martensite by volume rate to all the structure. The carbon equivalent is determined by the formula: Ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14.;COPYRIGHT: (C)2012,JPO&INPIT