Effect of Rare Earth/Stable Element Oxides on High Temperature Mechanical Properties of Low Chromium Nickel Ferritic Stainless Steel

409L stainless steel is a kind of low chromium nickel ferritic stainless steel commonly used in high efficiency engine and exhaust system. However, with the frequent start and stop of the engine, the coarse grain zone (CGZ) of the welded joint could appear hot cracks, and the high temperature mechanical properties of the welded joint decrease, finally result to thermal fatigue fracture. In order to solve this problem, when welding 409L ferritic stainless steel (FSS), rare earth oxide CeO2 and oxide of stabilizing element TiO2 were added which accounts for 0.3 and 1.2% respectively by mass of welding wire. The low frequency temperature cyclic load was applied to the specimens in the high temperature range (450–550 °C), the performance of the welded joint with the increase of the number of cycles was explored. The results show that adding a certain amount of rare earth/stable element oxides to 409L welds can achieve the purpose of refining grains and improving the tensile strength and plasticity of the specimens. Although the hardness decreases in the early stage of the test, it does not decrease much, and the hardness increases after more cycles. The overall thermal fatigue performance of the specimen is improved.