The pitting corrosion resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 ℃ to 1200 ℃ for 24 h has been investigated by means of potentiostatic critical pitting temperature (CPT). The microstructural evolution and pit morphologies of the specimens were studied through optical microscopy and scanning electron microscopy. The potentiostatic CPT measurements show that the CPT was elevated with the annealing temperature increased from 1050 ℃ to 1150℃ and decreased as the temperature further increased to 1200 ℃. The specimens annealed at 1150 ℃ exhibited the highest CPTand the best pitting corrosion resistance. The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases. The results were explained by the variation of pitting resistance equivalent number (PREN) of ferrite and austenite phases as the annealing temperature was varied.
The intergranular corrosion (IGC) character of tin-added B316LX and the influence of tin addition on IGC susceptibility were investigated by DL-EPR, oxalic acid etch test and transmission electron microscopy. IGC susceptibility of B316LX is mainly caused by the precipitation of M23C6 carbide and intermetallic Laves phase. DL-EPR test is unsuitable to evaluate the IGC susceptibility of B316LX with long-time sensitization, because more carbides and inter- metallic phases are formed at grain boundaries and inside the grains, which induce more severe IGC and pits attacks. Tin addition increases the IGC susceptibility, maybe due to diffusion of tin toward grain boundaries.
Min SunYuan-Yuan YangMing LuoLai-Zhu JiangYi-Ming JiangJin Li
The effect of tin on general and pitting corrosion behaviors of the austenitic stainless steel in sulfuric acid and sodium chloride solutions was investigated by potentiostatic critical pitting temperature, cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electron microscopy. The results showed that there is an optimal tin addition which is around (0.062-0.1) wt%, and the general corrosion resistance of B316LX with 0.08 wt% tin addition in boiling H2SO4 increased remarkably with a corrosion rate of an order of magnitude lower than that of 316L. Hydrolyzation of tin ions induces more metastable pit occurrence on the material surface. However, the pitting resistance of B316LX increases because tin oxides improve the density and uniformity of the passive film, and hydroxide and oxide of tin inhabit the process of pit growing. The effect of tin on pitting corrosion process is illustrated schematically.
Min SunMing LuoChao LuTian-Wei LiuYan-Ping WuLai-Zhu JiangJin Li