MANUFACTURE OF COIL SPRING

PURPOSE:To simply manufacture a coil spring excellent in spring properties at low cost by subjecting wire rod for a spring to hardening, then forming it at a tempering temp., furthermore holding it to a specified temp. range and then executing setting treatment. CONSTITUTION:Wire rod for a spring is subjected to austenitizing treatment, is thereafter rapidly cooled and is subjected to hardening treatment. After that, the wire rod is heated to a tempering temp. of about 460 deg.C and is subjected to warm forming in this state. Successively, by utilizing the above tempering temp., this formed wire rod is held in the temp. range of 250 deg.C to the tempering temp. for >=30min. In this way, the effect equal to that of low temp. annealing treatment and aging treatment can be obtd. without requiring reheating. After that, hot setting is executed in the temp. range to subject the wire rod to setting treatment, and after that, shot peening treatment is executed.