Effects of zinc addition on corrosion behavior of 316L stainless steel and Stellite 6 cobalt-based alloy in PWR primary water

The effects of zinc addition on general corrosion of 316L austenitic stainless steel and Stellite 6 cobalt-based alloy were investigated in simulated PWR primary water with 0, 10 and 40 ppb zinc additions. The corrosion rate and the metal release rate of the two materials were calculated by weight loss method. The surface and cross-sectional morphology, thickness and element distribution of the oxide film were analyzed by SEM and TEM-EDS. The results show that the corrosion rate of 316L stainless steel decreased with the increase in zinc concentrations. For cobalt-based alloy, the corrosion rate and corrosion product release rate decreased with the increase in zinc concentrations. The microstructural analysis of the oxide film indicates that Zn2+ promotes the denser outer oxide film formation by forming the zinc-incorporated spinel, which retards the outward diffusion of metal ions and the inward diffusion of oxygen ions, reduces the oxygen partial pressure at oxide/metal (O/M) interface, and promotes the formation of continuous protective Cr2O3 inner oxide film, and thus significantly suppressing the corrosion and metal release of 316L austenitic stainless steel and Stellite 6 cobalt-based alloy in high temperature water.