The Investigation of fatigue strength of stainless steels to AISI 4340 steel welded by friction welding

ABSTRACT Master Thesis THE INVESTIGATION OF FATIGUE STRENGTH OF STAINLESS STEELS TO AISI 4340 STEEL WELDED BY FRICTION WELDING Engin ÜNAL Firat University Graduate School of Science Department of Mechanical Education 2003, Page: 115 The high stresses appeared in discontinuities resulting from material or local geometric effects according to process conditions in conventional welding methods play significant role in failure process of join welded. In this study, weldability of ferritic (AISI 430), martenzitic (AISI 440) and austenitic (AISI 304) stainless steels to AISI 4340 steel by friction welding and fatigue strength of specimens welded have been investigated according to different rotation speeds. In experiments, the welding zones of specimens joined in 1500, 1800 and 2100 cycle per minute by friction welding using a direct-drive friction welding machine were examined optic and Scanning Electron Microscopy (SEM) and analyzed by EDAX. The microhardness distributions on welding zone were determined at Vickers scale. The fatigue test and tensile test were performed to welded specimens in order to determine mechanical endurance. The fatigue tests were performed using a rotational bending fatigue test machine. In addition, fracture types were determined from fractographic examinations. The study is consisting of six chapters. In the first chapter, importance of this subject and relevant literatures were explained. In the second chapter the mechanism of fatigue, the factors effecting to fatigue and basic concept presented. In the third chapter, the friction welding, various friction welding methods were explained. In fourth chapter the aim of study, material and method were presented. In fifth chapter results were discussed, and sixth and final chapter, general results were concluded and recommendations were given. Keywords: Friction Welding, Fatigue, Stainless Steel, AISI 4340 Steel. IX