Patent ID: 7789974

Claim:
A spring steel wire having a high strength and toughness after heat treatment suitable for use in springs for cars, characterized by: the spring steel wire consisting essentially of, in mass, C: 0.4-1.2%, Si: 0.9-3.0%, Mn: 1-2.0%, P≦0.015%, S: <0.015%, Cr 1.07-2.5%, N: 0.001-0.015%, Mg: 0.0004-0.01%, W: 0.05-1.0% with a balance of Fe and unavoidable impurities; and wherein steel for spring steel wire has been subjected to heating at 1200° C. or more for an effective amount of time to dissolve coarse carbide in the steel followed by hot rolling; and wherein globular cementite carbides observed in a microscopic visual field satisfy the density of globular cementite carbides of 0.2 to 3 μm in circle-equivalent diameter is 0.5 piece/μm 2 or less and the density of globular cementite carbides of over 3 μm in circle-equivalent diameter is 0.005 piece/μm 2 or less.