DRAWN AND HEAT-TREATED STEEL WIRE FOR HIGH-STRENGTH SPRING, AND UNDRAWN STEEL WIRE FOR HIGH-STRENGTH SPRING

摘要

Drawn heat treated steel wire for high strength spring use is provided containing, by mass %, C: 0.67% to less than 0.9%, Si: 2.0 to 3.5%, Mn: 0.5 to 1.2%, Cr: 1.3 to 2.5%, N: 0.003 to 0.007%, and Al: 0.0005% to 0.003%, having Si and Cr satisfying the following formula: 0.3%SiCr1.2%, and having a balance of iron and unavoidable impurities, having as impurities, P: 0.025% or less and S: 0.025% or less, furthermore having a circle equivalent diameter of undissolved spherical carbides of less than 0.2 m, further having, as a metal structure, at least residual austenite in a volume rate of over 6% to 15%, having a prior austenite grain size number of #10 or more, and having a circle equivalent diameter of undissolved spherical carbides of less than 0.2 m.