STEEL WIRE FOR SPRING WITH SUPERIOR FATIGUE RESISTANCE

PURPOSE:To obtain a steel wire for a spring with improved settling resistance by hardening a wire rod and tempering it while producing a working strain. CONSTITUTION:A steel wire rod 2 is straightened almost perfectly with a straightener 4, fed to a heater 6, and heated to the hardening temp. decided in accordance with the kind of the steel. The heated rod 2 is cooled in a cooling vessel 7 to carry out hardening. The hardened rod 2 is fed to a heater 10 and heated to the tempering temp. so as to attain the required strength. While carrying out working with a working device 10 during the heating, the rod 2 is tempered, and it is cooled at once to ordinary temp. in a cooling vessel 12 and coiled around a coiler 14. The resulting steel wire 15 has improved settling resistance, so it can be used as the material of a spring for suspending a car, etc.