Microstructure and mechanical properties of two quenched and tempered steels for industrial undercarriage track links: A preliminary comparison

Thanks to their resistance to static and fatigue loads, quenched and tempered (Q&T) steels are widely used to produce track links for undercarriage systems of industrial machines, which operate under severe mechanical and environmental conditions. This preliminary study investigates the fatigue properties of two Q&T forged steels: the 27MnCrB5-2 steel subjected to a low-temperature tempering treatment to reduce the environmental impact of industrial production, and the carbon-neutral 36CTR4 steel tempered at a higher temperature. Tensile and rotating bending fatigue tests were carried out on specimens directly extracted from heat-treated track links. Static properties enabled a preliminary calibration of the stress amplitude levels for fatigue testing, while microstructural characterization by optical microscopy (OM) and scanning electron microscopy (SEM) was performed to understand the influence of microstructure on the fatigue properties of the investigated steels. Preliminary fatigue data were analyzed using a bi-conditional probability–stress–life (P-S-N) model, enabling a robust statistical evaluation of fatigue resistance. The results confirmed the effectiveness of the selected heat treatments in ensuring reliable mechanical performance.