Effect of carbon content on microstructure and intergranular corrosion susceptibility of C-276 alloy

Samples of different carbon content C-276 alloy plate were selected. The samples were solution treated first, and then sensitized at 900 ℃ for different times. The method A of ASTM G28 was used to test the intergranular corrosion of C-276 samples with solution and sensitization. The results showed that the annual corrosion rate of C-276 alloy increased with the increase of sensitization time, and the intergranular corrosion sensitivity of C-276 alloy increased with the increase of sensitization time. The intergranular corrosion sensitivity of high carbon type C-276 alloy is higher than that of low carbon type C-276 alloy in solid solution state. After sensitization at 900 ℃ for 30 minutes, low carbon C-276 alloy shows higher intergranular corrosion sensitivity. The effect of carbon content on the microstructure of C-276 alloy was studied by metallographic microscope and scanning electron microscope (SEM). In the solution state microstructure of low carbon C-276 alloy, no obvious precipitates were found at the grain boundary and inside the grains. In the solution state microstructure of high carbon C-276 alloy, the precipitated phase μ phase rich in Mo is distributed in part of the grain boundary and inside the grain. No matter low carbon or high carbon C-276 alloy, the precipitated phase in sensitization process is Mo rich M6C carbide. In the high carbon C-276 alloy, the precipitation rate of Mo rich carbides is slowed down due to the pinning effect of μ on Mo. Therefore, low carbon C-276 alloy has higher intergranular corrosion sensitivity after sensitization.