抄録
In order to investigate the effect of tempering temperature on the fatigue properties of high strength steels and surface hardened steels in the super-long life range (N≥1×(10)^7), cantilever type rotating bending fatigue tests were carried out for SNCM439 specimens which tempered by the tempering temperature of four kind of 160℃, 300℃, 500℃ and 620℃. As a result of fatigue tests, all specimens tempered at 500℃ and 620℃ were "surface crack origin type". For the case of tempering temperature of 300℃, one specimen was "internal crack origin type" and other specimens were "surface crack origin type". For the case of tempering temperature of 300℃, 500℃ and 620℃, the tendency in which the S-N curves decreased again in the very long life regime over (10)^7 cycles could not be observed.
