The effect of microstructure on fatigue crack propagation in pearlitic eutectoid steels

The paper describes the results of a study of the effect of microstructure on the fatigue crack propagation (FCP) rate in fully pearlitic eutectoid rail steel. Variations both in austenitizing temperature and time, and in isothermal transformation temperature have been used to alter and control both the prior austenite grain size and the pearlite lamellae spacing in compact tension specimens. The rate offatigue crack growth has been measured in these specimens from threshold (da/dN ~ 10^-10 m/cycle) to nearly the end of the power law region. It has been found that increasing pearlite lamellae spacing and increasing austenite grain size both reduce FCP rate, however, the latter variable is more important. Scanning electron fractography has been used to examine the fracture surfaces of the failed specimens. The FCP results are discussed in light of the microstructural changes and the fractographic observations.