High Temperature Characteristics of Lap Joint of 15Cr Ferritic Stainless Steel

Abstract

Ferritic stainless steels have excellent stress corrosion resistance and a low coefficient of thermal expansion compared to austenitic stainless steels. Ferritic stainless steels of the 400 series have been available for automotive exhaust systems, heat exchangers, radiators etc. in various industries. Automotive exhaust manifolds especially require good heat resistance because the typical operation temperature(800°C) of the exhaust system is exposed to during engine operation. In this study, the effects of high temperature(800°C) characteristics on the mechanical and microstructure properties were investigated for lap joint of ferritic stainless steel(STS 429) mainly used as the automotive exhaust manifolds. The microstructure of lap joint was characterized by optical microscopy(OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The mechanical property of lap joint was evaluated by tensile test. The tensile test results show that a significant decrease in ultimate tensile strength(between 82 and 85%) was observed for aged STS 429 when tested at the evaluated temperature(800°C). The tensile strength was significantly influenced by growth of grain in the heat affected zone(HAZ). The XRD results show that chromium carbide and chromium nitride phases such as Cr23C6, Cr7C3, Cr2N and TiN were precipitated in the heat affected zone(HAZ).