The effects of isothermal transformation on the fatigue strength of austempered ductile iron

Abstract

The fatigue strength of austempered ductile irons was studied. Austempering was carried out by initial austenitising at temperatures of 850, 900 and 950°C for 1 hour followed by rapid quenching and holding in a salt bath maintained at temperatures of 280, 300, and 350°C for different time intervals (15,30,60,90 or 120 minutes). Fatigue test was prepared to standard and the number of cycles to failure for each specimen was plotted against the bending stresses for the specimen. Results showed that at low austenitising and low austempering temperatures, the fatigue limits were generally low. Increasing the austenitising temperature to 950°C while maintaining the austempering temperature at 3500C, the fatigue limits of both medium silicon and high silicon alloys increased. The highest fatigue strength 450Nmm-2 was obtained from alloy austenitised at 950°C and austempered at 350°C for 90 minutes.

Keywords: fatigue, austempered ductile cast iron

Botswana Journal of Technology Vol. 14(2) 2005: 21-25