Abstract
Linear Friction Welding (LFW) was applied to medium-high carbon steel S55C, which had difficulty for arc welding process, and fatigue strength of welded joints were evaluated. In LFW process, peak temperature can be easily controlled by applied pressure and fatigue strength of welded joints for two level of peak temperature are compared. As a result of fatigue test, the harmful welding defects are not detected in the joints. Sound welded joints can be fabricated by LFW. Because, the fatigue crack initiated at the surface of interface between joint area and base material, not in the joint area itself. A remarkable difference was recognized for the hardness distribution between two level of peak temperature, and low peak temperature joint has low and almost flat distribution. Low peak temperature joint came to have almost equivalent fatigue strength to that of a base material. The reason why the fatigue strength of LWF joints is maintained at the same level as the base material is because compressive residual stress is generated on the joint surface, which is the initiation site of fatigue crack. This compressive residual stress is thought to be due to the tensile plastic deformation of the surface due to uneven temperature distribution within the cross section during the air cooling process after welding.
