Patent ID: 6224686
Filing Date: 2001-05-01
Classification: C21D,C22C,Y10S

Abstract:
A high-strength valve spring formed by subjecting an oil-tempered steel wire made from a steel material composition containing 0.5-0.8 wt % C, 1.2-2.5 wt % Si, 0.4-0.8 wt % Mn, 0.7-1.0 wt % Cr, balance Fe and inevitable impurities, where, in the inevitable impurities, Al is no more than 0.005 wt % and Ti is no more than 0.005 wt %, and the largest non-metallic inclusion is 15 .mu.m, to hardening treatment at a heating temperature between 950-1100.degree. C. followed by cooling; tempering treatment followed by cooling; coiling; and nitriding, wherein the oil-tempered wire comprises 1-5 vol % residual austenite after hardening and tempering and the density of carbides larger than 0.05 .mu.m in diameter is no more than 5 pieces/.mu.m.sup.2 in the microscopic photograph of the oil-tempered wire.