Containing 15% to 30% chromium. The corrosion resistance, toughness and weldability increase with the increase of chromium content, resistance to chloride stress corrosion resistance is better than other types of stainless steel, belong to this category are Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and so on. Ferritic stainless steel because of high chromium content, corrosion resistance and oxidation resistance are better, but poor mechanical properties and process performance, and more for the acid structure is not used and for the use of anti-oxidation steel. This kind of steel can resist the corrosion of atmospheric, nitric acid and brine solution, and has high temperature oxidation resistance, thermal expansion coefficient is small, for nitric acid and food factory equipment, can also be made in high temperature work parts, such as gas turbine parts The