Thread Content
Given the previous background regarding intergranular corrosion of stainless steels used in nuclear industrial reactors, preventive measures against intergranular corrosion of nuclear-grade stainless steels can be implemented from three aspects: material selection, process control, and operation & maintenance monitoring. 1. Optimization of material composition: Select ultra-low-carbon nuclear-grade stainless steels such as 304L and 316L, keeping the carbon content below 0.03% to minimize the precipitation of chromium carbides at the source； Stabilizing elements such as titanium and niobium are added, preferentially combining with carbon to form TiC and NbC, thereby preventing chromium from being consumed and the formation of chromium-deficient regions. 2. Regulation of the heat treatment process: After solution treatment at 1050–1150°C, rapid water quenching is performed to completely dissolve the chromium carbides that have precipitated along the grain boundaries, thereby inhibiting any subsequent precipitation ； Perform desensitization annealing on sensitized components to restore the chromium content at grain boundaries through chromium diffusion, thereby eliminating the tendency to corrode. 3. Control of hot processing procedures: During welding, a low-heat-input process is employed to increase the cooling rate, enabling the components to quickly pass through the sensitization temperature range of 450–850°C and avoiding prolonged exposure to this range ； It is strictly prohibited to increase the welding heat input to prevent excessive slow cooling from exacerbating the precipitation of chromium carbide. 4. Control of operating environment: Regularly monitor the pH value and chloride ion concentration of the coolant to prevent excessive levels of these substances in the medium ； Apply corrosion-resistant coatings or cathodic protection to critical components to reduce the erosion of corrosion media on grain boundaries.