Modified austempering effect on bending fatigue properties of Fe-0.6C-1.5Si-0.8Mn steel

The effect of a modified austemper coupled with interrupted quenching (IQ Aus) on the bending fatigue properties of Fe-0.6C-0.5Si-0.8Mn steel has been studied to determine the validity of using IQ Aus steel in possible environmentally conscious material applications. The bending fatigue stress of steel can be improved by IQ Aus: conventional austenitization at 1133 K followed by interrupted quenching a 533 K and then austempering at 673 K for a required time followed by subsequent water quenching and 473 K tempering. The IQ Aus steel had a triple structure consisting of carbide-free upper bainite, 26 vol.% retained austenite and 10 vol.% tempered martensite. Compared to the conventional austemper (Con Aus), the IQ Aus increased the bending fatigue limit stress. Compared to the quench and temper (QT), the IQ Aus showed a significantly decreased fatigue notch factor while there was little difference between the fatigue limit stress of both steels. The results are described and discussed in terms of fractography, etc..