To remarkably increase the residual compressive stress of the body to be heated and to exceedingly improve its fatigue strength by subjecting the body to be worked such as a carbon steel to ultra rapid heating at a specified heating rate by induction heating to heat it in an ultra short time to regulate its temp. to a hardening temp. and thereafter executing rapid cooling and hardening.
The body to be heated such as steel is preheated at ≤800°C which is the transition temp. as necessary, is thereafter heated to a hardening temp. by ultra short time heating at a heating rate of 2000 to 20000°C/sec by induction heating, is thereafter rapidly cooled and is hardened. The above preheating is executed by either an induction heating furnace or a radiation type heating furnace, and by this preheating, the increase of the heating rate can be made easy. The depth of a surface effective hardened layer formed by this induction hardening is preferably regulated to 0.3 to 1.5 mm. In this way, the residual compressive stress in the surface part of the body to be heated is remarkably increased to about 2000 to 3000 MPa to impart high strength and high toughness thereto, by which its fatigue strength can remarkably be improved.
KIYOZAWA YUTAKA
KAWASAKI KAZUHIRO
YAMAZAKI TAKAO
SHIMIZU MASAO
KOMOTORI JIYUN
