Effects of microstructural parameters on the mechanical properties of eutectoid rail steels

A study was made of the effects of microstructural variations, as produced by differences in heat treatment and the addition of Nb, on the mechanical properties of eutectoid pearlitic carbon steels. The pearlite interlamellar spacing increased with an increase in autenitizing temperature and, to a lesser extent, with the addition of Nb. The tensile strength depended strongly on microstructure, being higher for larger prior austensite grain size and for smaller pearlite interlamellar spacings. Ductility increased with a decrease in austenite grain size. In fatigue, the interlamellar spacing is an important variable with respect to crack initiation, the material with the largest spacing having the lowest resistance to initiation, despite the fact that it does not have the lowest yield stress. Fatigue crack propagation in stage II was found to be insensitive to variations in interlamellar spacing.