EFFECT OF OVERSTRESSING ON FATIGUE BEHAVIOR OF AUSTEMPERED DUCTILE IRON

Studies have been conducted on the effect of overstressing in rotary b ending fatigue on the fatigue properties of an annealed and austempere d ductile iron containing 1.5 Ni-0.3 Mo. For various R ratios S-N curv es were determined and the fatigue limit estimated. It was found that the fatigue limit was a function of the level of overstressing and cyc le ratio. In the case of austempered samples a beneficial effect of ov erstressing was observed at a certain level of overstressing. This was related to the work hardening behaviour of the austenite phase. In an nealed samples, a reduction in the fatigue limit was observed at all l evels of overstressing.