STEEL WIRE FOR HIGH-STRENGTH SPRING

摘要

Disclosed is a steel wire for a high strength spring. The wire is characterised by including, by mass%, at least 0.67% but less than 0.75% of C, 2.0-2.5% of Si, 0.5-1.2% of Mn, 0.8-1.3% of Cr, 0.03-0.20% of V, 0.05-0.25% of Mo, 0.05-0.30% of W and 0.003-0.007% of N, where the total content of Mn and V is 0.70%?Mn+V?1.27%, the total content of Mo and W is 0.13%?Mo+W?0.35%, P is limited to 0.025% or less, S is limited to 0.025% or less, Al is limited to 0.003% or less and the remainder consists of iron and unavoidable impurities. Said steel wire is also characterised in that: the metallographic structure consists of tempered martensite and retained austenite with a volume fraction of more than 6% but not more than 15%; the former austenite grain size number is not smaller than 10; the density of spherical carbides with a circle-equivalent diameter of 0.2-0.5µm is 0.06 particles/µm2 or less; the density of spherical carbides with a circle-equivalent diameter exceeding 0.5µm is 0.01particles/µm2 or less; and the tensile strength is 2100-2350MPa.