309S+ is a variant of 309 stainless steel with a lower carbon content, used in places where welding is required. The lower carbon content minimizes the precipitation of carbides in the heat-affected zone near the weld, and the precipitation of carbides may cause intergranular corrosion (welding erosion) of stainless steel in certain environments.

It can withstand repeated heating below 980°C, and has high high-temperature strength, oxidation resistance, and carburization resistance.

The Chinese grade corresponding to 309S is 0Cr23Ni13, and the American standard S30908 (American AISI, ASTM) features and uses: corrosion resistance and heat resistance are better than 0Cr19Ni9. 309s is a variant of 309 stainless steel with a lower carbon content, used in places where welding is required. The lower carbon content minimizes the precipitation of carbides in the heat-affected zone near the weld, and the precipitation of carbides may cause intergranular corrosion (welding erosion) of stainless steel in certain environments.