Enhancing the resistance of steel against adiabatic shear band formation by alloy selection and heat treatment improvement

This thesis investigates pistons used in direct fastening tools, which are exposed to high dynamic loads in construction applications. The tips of the pistons are particularly susceptible to wear, which can ultimately lead to component failure. The aim was to reduce wear through the targeted selection of materials and optimized heat treatments, and to enhance the microstructural resistance against adiabatic shear band formation. The focus lies on the materials science-based relationships between microstructure, strength, toughness, and wear behavior under application-relevant loading conditions. The present wear mechanism that can lead to piston failure is the formation of adiabatic shear bands (ASBs). The theoretical section of this thesis provides a detailed explanation of how ASBs form and ultimately result in failure. Furthermore, it is examined what can be done to prevent the formation of ASBs. Based on this theoretical foundation, strategies are developed for four different tool steels in order to optimize properties such as toughness and yield strength. Building upon these strategies, various heat treatments were applied to the alloys to achieve the desired properties. The heat-treated samples were examined with respect to their mechanical properties and microstructure. The combinations of alloy and heat treatment that showed good mechanical characteristics, such as high yield strength or high toughness, were selected for application to pistons and subsequently tested under operating conditions. These application tests were designed to reliably reproduce the ASBs previously observed at the piston tip. The results of this thesis demonstrate that a high yield strength combined with sufficient toughness can significantly reduce the formation of adiabatic shear bands in the given application and thus considerably increase the service life of the piston.