Effect of Tempering Temperature on Ling-Life Fatigue Property in High Strength Steels

Abstract

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.