What is the difference between 304 and 309 stainless steel?

First of all, from the perspective of chemical composition, the main components of 304 stainless steel include chromium (Cr) 18%-20% and nickel (Ni) 8%-10.5%, and the carbon (C) content does not exceed 0.08%. 309 stainless steel contains higher chromium and nickel content, and also contains a small amount of molybdenum (Mo) and nitrogen (N) elements, which increase its corrosion resistance and high temperature performance. ‌
In terms of corrosion resistance, 304 stainless steel has good corrosion resistance and is suitable for general atmosphere and fresh water environments, but the corrosion resistance may be reduced in chloride ion or acidic environments. In contrast, 309 stainless steel has better corrosion resistance due to its higher chromium and nickel content and a small amount of molybdenum, and is particularly suitable for high temperature and high corrosion environments. ‌
In terms of high temperature performance, 304 stainless steel is suitable for general high temperature environments, but its high temperature performance is relatively limited. 309 stainless steel is mainly used in high-temperature applications, such as chemical, electric power, metallurgy and other fields, and it can maintain stable performance and strength at high temperatures.
Finally, in terms of application areas, 304 stainless steel is widely used in construction, furniture, food processing, medical and other fields. 309 stainless steel is mainly used in high-temperature equipment, heat exchangers, stoves and other fields that require high temperature resistance and corrosion resistance.