Friction welding has many merits such as energy efficiency, simple processing, etc butt difficult to obtain good weld at the welded interface and heat affected zone. To date, the continuum mechanics and fracture mechanics are utilized to analyse stresses at the interface and propagation of cracks. In this study. STS304 and SM15C are selected because they can be differentiated distinctively from metallic point of view and crack can be observed easily. It is ovserved during friction welding that STS304, rotary part is hatter than SH15C, fixed part. The last fracture occurs around the center because the surface of fatigue fracture has smooth regions, due to the separation phenomenon in plastic flows layers and striation dimple pattern.