Erosion and wear resistance of steel can be enhanced by incorporating a ceramic powder in the surface. This aspect of surface engineering has applications in areas such as mining, agriculture and transport. An economic alternative to laser for melting the surface is by using a tungsten inert gas torch. The process requires shielding gas to protect the melted and re-solidified track from oxygen and hydrogen in the environment, which often have a deleterious effect on the mechanical properties of the modified surface. During the melting process, the heat produced is conducted to the substrate ahead of the torch; this has been described as ‘preheat’ giving a temperature several hundred degrees higher than the area under the torch. To reduce the number of trial and error experiments for determining the optimal conditions to modify the surface, a mathematical model, based on the Rosenthal approach, was developed. Experiments using TIG technique were conducted on microalloyed steel using argon, helium and nitrogen shielding gases to obtain heating and cooling curves from positions along the melted track. The data for argon was compared with the model. This first attempt to validate the model was satisfactory, showing a deviation of 6% (35oC) between experimental and numerical values.