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This paper presents an investigation the effects of thermal cutting processon the fatigue life of selected structural elements. Thermal cutting process introduces aroughened surface on the cut edge and also changes in micro-structural properties ofmaterial in heat affected zone. A multi scale numerical approach for evaluation ofcrack initiation and propagation is presented. Crack initiation is dealt on micro scalemodel, while taking into account the effects of micro structural and geometricalchanges at the cut edges of selected structural element. Residual stresses induced by thethermal loading are neglected. Individual grains of synthetic microstructure aresimulated using Voronoi tessellation. Micro-crack initiation mechanism was based onTanaka-Mura model. Some improvements were added to this model. Crackpropagation is then solved on a macro scale model using linear elastic fracturemechanics approach. Some experimental testing was also performed so that theaccuracy of the numerical model was checked. The results of proposed computationalmodel show a reasonable correlation with experimental results.