Effect of TIG welding on corrosion behavior of 316L stainless steel

摘要

316L stainless steel (SS) is one of the most consumable materials in orthopedic implants. Certain types of orthopedic implants such as mono-bloc hip stems are often made of two elements welded together. In this study, effect of TIG welding on corrosion behavior of 316L stainless steel in physiological solution was investigated. In this method, filler metal wasn't used due to the small thickness of samples and it was welded to lap form. Corrosion behavior in physiological solution at 37℃ was investigated with potentiodynamic polarization curves. Microstructure of base metal (BM) and weld metal (WM) was studied with scanning electronic microscopy (SEM). The corrosion behavior of weld metal, base metal and couple (BM and WM together) was compared together. For detecting microstructure and phases in BM and WM, X-ray diffraction analysis was done. Finally, post-weld heat treatment (PWHT) was performed on as-welded samples. Results indicated that corrosion behavior of WM was better than the BM. This phenomenon was attributed to secondary phases that were present in the BM. Secondary phases in the weld metal are dissolved when the base metal is melting due to the welding process. Based on the results of electrochemical analysis, it was determined that the corrosion rate of a couple was more than of other parts. Heat affected zone (HAZ) is responsible for this phenomenon. The adjacent zones of the weld metal are classically less corrosion resistant, thereby being attacked preferentially when the steel is exposed to corrosive environments. PWHT decreased the corrosion rate of the couple.