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

摘要

A drawn and heat-treated steel wire for a high-strength spring, which comprises, in mass%, not less than 0.67% and less than 0.9% of C, 2.0-3.5% of Si, 0.5-1.2% of Mn, 1.3-2.5% of Cr, 0.003-0.007% of N, 0.0005-0.003% of Al, Si and Cr in such amounts that the following formula: 0.3 ≤ Si-Cr ≤ 1.2 is fulfilled, and a reminder made up by iron and unavoidable impurities, wherein P and S are contained as the impurities in amounts of 0.025% or less and 0.025% or less, respectively, an undissolved spherical carbide has an equivalent circle diameter of less than 0.2 μm, at least a remaining austenite is present as a metal structure at a volume ratio of more than 6% and not more than 15%, the prior austenitic grain size number is 10 or greater, and the undissolved spherical carbide has an equivalent circle diameter of less than 0.2 μm.