This study investigates the formation of the layer hardened on a cylindrical workpiece by grinding-hardening using the traverse grinding method. A finite element heat transfer model, that took into account the helical trajectory of the of the grinding heat source movement, was developed. The hardened layer was found featuring a wavy profile as a result of the heat conduction from an adiabatic plane crossing the middle of the trajectory pitch. The accumulation of the grinding heat within a small pitch can lead to the welding of the molten material with the base material. Enlarging the pitch by reducing the workpiece speed will increase the time of heating, allowing the heat to penetrate deeper and to expand wider in the workpiece, thus thickening the hardened layer.