MU37 cont. - Postdoc continuation of Charmec Phd project MU37 Postdoc: Björn Andersson Railway rails and wheels are subjected to extreme thermo-mechanical loading conditions, combining multiaxial stresses with elevated temperatures from braking, sliding, or welding. If sufficiently heated and rapidly cooled, the steel microstructure may undergo phase transformations to austenite or martensite, leading to detrimental changes in mechanical performance. To improve predictive maintenance and extend rail service life, the PhD project MU37 developed advanced thermo-metallurgical-mechanical material models and implemented these in finite element simulations of critical rail and wheel scenarios subjected to thermal and mechanical loads. Building directly on this simulation framework, the postdoctoral project "MU37 cont." continues the work, with an expanded focus on new rail steel grades and rail maintenance operations. Within MU37, a phenomenological material model was established for pearlitic steels, incorporating cyclic plasticity, phase transformation kinetics, and analytically based multi-phase homogenisation. Key achievements include demonstrating the decisive influence of homogenisation strategy on predicted stress–strain states, identifying the self-consistent method as most physically accurate, and showing the importance of accounting for material state recovery during cyclic melting and solidification. Moreover, the project also delivered a computationally efficient simulation methodology for railhead repair welding, integrating the new material model. This framework enables detailed evaluation of repair weld procedures with reduced reliance on full-scale testing. Numerical studies highlighted, for instance, the benefits of powerful final zig-zag passes, chamfered cut-out geometries, and inward-oriented trapezoid cuts for robust rail repair performance. Simulations further clarified how shallow repairs promote rapid cooling, high martensite content, and surface-near tensile stresses, all raising fatigue crack initiation risk, which agrees with field observations. The continuation of this work in "MU37 cont." will further develop and apply the modeling framework in collaboration with the Swedish Transport Administration (Trafikverket). A particular focus is the characterization and performance of welds in newly introduced rail steel grades in heavily loaded track sections, where repair welding remains a crucial maintenance strategy. Moreover, the simulation framework will be extended to other rail maintenance operations, such as grinding, which involve similar thermo-mechanical-metallurgical interactions. By coupling advanced material modeling with realistic thermo-mechanical load simulations, "MU37 cont." aims to provide scientifically grounded and computationally efficient tools to support CHARMEC and Trafikverket in optimizing repair and maintenance procedures. Ultimately, this work contributes to safer, more durable rail infrastructure and reduced life-cycle costs for the railway system.