Strain, stress and damage evolution in alloys during cyclic loading considering interplay of microstructure, surface hardening and overload

Engineering components are frequently subjected to random cyclic loading and occasional stress overloads during service, significantly affecting fatigue behavior. The resulting stress and strain evolution is further complicated by interactions between surface hardening treatments and microstructure. To optimize fatigue performance and durability, especially in components such as automotive gears, a detailed understanding of these interactions is essential. This proposal aims to use neutron Bragg edge imaging (BEI) to investigate the evolution of localized strain and phase distributions in surface-hardened steels under cyclic loading, including overload effects. The study will focus on 20MnCr5 case-hardened steel specimens provided by Ovako and used by Scania, examined in the as-treated state, after 1000 and 2000 fatigue cycles, and after an overload followed by 1000 cycles. BEI will capture strain and phase changes, particularly retained austenite content, across the surface using a high-resolution Timepix 2 detector. A total of 18 measurements will be conducted, covering various surface treatments and loading histories. The resulting data will clarify how retained austenite transforms under loading and how it influences local stress concentrations and fatigue crack resistance. These insights will guide the design of microstructures and surface treatments for enhanced fatigue life and lightweighting of critical steel components.