The Role of Microstructural Variables in Fatigue Behaviour of High V-Cr-Ni Cast Irons

Abstract

This paper describes the fatigue behaviour of high V-Cr-Ni cast irons with different micro-structures. Rotary bending fatigue tests have been performed using smooth specimens in laboratory air at ambient temperature in order to understand the role of microstructural variables in fatigue behaviour. The microstructure of the cast irons consisted of austenitic matrix microstructure, lamellar microstructure consisting of austenitic microstructure and V and Cr carbides, and isolated vanadium carbides (VC) dispersed within them. Although the area fraction of VC increased with increasing the amount of V and C addition, its dependence of fatigue strength was not observed. Instead, there existed a good correlation between fatigue limit and the constituent phases of the microstructure. Fatigue limit increased as the area fraction of the lamellar microstructure increased or the area fraction of the matrix microstructure decreased, indicating that the area fraction of lamellar microstructure was a most important microstructural variable controlling fatigue strength. Fatigue crack initiation was often related to VC, but dispersed VC was a microstructural parameter of secondary importance.