High-strength oil-tempered steel wire with excellent spring fabrication

Abstract

A high-strength oil-tempered steel wire with excellent spring fabrication property that is made of spring low-alloy steel, having a decarburized layer of reduced hardness extending to a depth of not greater than 200 .mu.m from the wire surface, a wire surface hardness in the range from an Hv (Vickers hardness) of 420 to an Hv of 50 below the Hv of the wire interior, and an Hv at the interior of the wire beyond the depth of the decarburized layer of not less than 550. The spring low-alloy steel can preferably comprise, in weight percent, 0.45-0.80% C, 1.2-2.5% Si, 0.5-1.5% Mn, 0.5-2.0% Cr and the balance of Fe and unavoidable impurities. The method for producing the foregoing steel wire comprises the steps of continuously passing and heating a starting material low-alloy steel wire fed through a furnace body through-pipe of a continuous heating furnace for oil tempering, decarburizing the low-alloy steel wire under regulation of a dew point of a decarburizing atmosphere in the pipe by introducing into the pipe from its inlet side or a desired intermediate point thereof hydrogen gas or a mixed gas of hydrogen gas and an inert gas and, to form steam by reaction therewith, oxygen gas or an oxygen-containing gas and controlling the amount of oxygen gas or oxygen-containing gas introduced, and thereafter quenching and annealing the low-alloy steel wire.