Fatigue and wear behavior of pearlitic and bainitic microstructures with the same chemical composition and hardness using twin-disc tests

Abstract

Railway transport companies in Brazil and worldwide have become more productive and efficient by increasing the weight transported and using faster locomotives. These actions have caused the premature exchange of wheels and rails due to excessive wear and rapid growth of rolling contact fatigue (RCF) cracks, and both consequences have been minimized by the improvement of pearlitic steels of wheels and rails. However, these pearlitic materials have already shown that there is a limit to the optimization of their mechanical properties. The bainitic microstructure could replace the pearlitic one, however few studies on the bainitic microstructure variants have been carried out, which still makes its behavior in rolling and sliding wear – especially in high carbon microalloyed steels – a matter of debate. Those studies are far from reaching a consensus, and, therefore, an important question arises regarding the materials used in the wheel-rail contact: which microstructure has better tribological and fatigue properties being produced from the same steel, having the same hardness, and being influenced by the same tribological variables: bainite or pearlite? In order to answer this question, twin-disc tests were performed on forged railway wheel microalloyed steel (7NbMo) with pearlitic and bainitic microstructures with the same bulk hardness and on high carbon steel (7C) with tempered martensite. The results revealed that the microstructure had a significant role in wear and RCF performance. The bainitic microalloyed steel (7NbMo–B) showed lower wear rates and greater resistance to RCF than the pearlitic one (7NbMo–P). Similar behavior was observed for their counter-bodies, indicating that the use of bainite in rolling and sliding wear applications would cause the joint benefit of the body and counter-body.