Rotary friction welding is a solid-state technique for combining two materials together by using the heat energy generated by the friction at the interface region between them with help of an external axial force. The main goals of this work-study were, to look to the researches works that studied RFW, to understand their thermal models of the RFW process, see mathematical, simulation models and the assumptions taken into account, and compare with the experimental results of their works if exist. The results we obtained from previous researches were as follows: The rise in the temperature of materials during the welding process leads to a change in their properties, so the heat generated during the process is not constant. The heat generated is divided into two parts, heat generated by rotating and sliding friction, and heat generated during plastic deformation. With the temperature rising, the yield stress reduces until it became less than flow stress, and then the plastic deformation starts. The heat transfer throw the solid work pieces is analyzed by Fourier heat conduction law. Compared the simulation results with the experimental results of the researches we can say that, the welding process can be represented numerically through software programs.