STEEL WIRE ROD FOR HIGH STRENGTH AND HIGH TOUGHNESS SPRING HAVING EXCELLENT COLD WORKABILITY, METHOD FOR PRODUCING THE SAME AND METHOD FOR PRODUCING SPRING BY USING THE SAME

摘要

There is provided a steel wire rod for a high strength and high toughness spring having excellent cold workability, the steel wire rod having a composition comprising: in weight %, C: 0.4 to 0.7%, Si: 1.5 to 3.5%, Mn: 0.3 to 1.0%, Cr: 0.01 to 1.5%, Ni: 0.01 to 1.0%, Cu: 0.01 to 1.0%, B:0.005 to 0.02%, Al:0.1% or less, O: 0,0020% or less, P: 0.02% or less, S: 0.02% or less, N:0.02% or less, remainder Fe, and other unavoidable impurities, having an internal structure formed of ferrite and pearlite, the internal structure in which prior austenite grain size is 8 D or less.