309S, the national plate number is: 0cr23ni13, and the usable temperature is 900~1000 degrees Celsius. 309S is a free-cutting stainless steel containing sulfur (Si) for applications where free-cutting and high surface finish are primarily required. 309S (23Cr-13Ni) stainless steel has excellent corrosion resistance and strength, and is suitable for parts with a working temperature of 1000 °C. Due to this high temperature resistance, it is also known as: high alloy stainless steel, which has excellent high temperature acid resistance and high temperature strength. Its use is generally widely used in exhaust machines, heat treatment furnaces and heat exchangers.