Thermal pulses on pearlitic steels: Influence of laser heat scanning parameters on surface layers transforming to martensite

Artikel i vetenskaplig tidskrift, 2025

Industrial processes like grinding and welding impose cyclic heating and rapid cooling on steel surfaces, affecting material properties and residual stresses. This study examines how intense localised surface heating influences pearlitic railway steels using laser welding equipment as a precisely controlled heat source, without added filler materials. Two steels were studied: high-carbon rail steel (R260) and medium-carbon wheel steel (ER7T). The findings reveal that applied power is the key factor affecting thermal gradients and material transformations, rather than laser scanning speed. Under identical thermal loads, R260 fully transformed to martensite at lower temperatures, creating pronounced shear stresses, while ER7T experienced partial transformation and more hydrostatic tensile stresses. Numerical simulations, validated by experimental results, highlight the interplay between melted and non-melted material. The thermal contraction of the melted material induced tensile stresses in the otherwise compressive stress-dominated non-melted martensitic regions. These results demonstrate the potential of laser welding equipment for studying high-energy heating effects on railway steels. Insights highlight the importance of controlled heat input for optimising microstructures and stress states, informing advanced rail maintenance strategies like repair welding and grinding. This work contributes to improving the performance, safety, and sustainability of railway components.