439 stainless steel reduces the content of C on the basis of ordinary ferritic material (430) and adds stabilizing elements such as Ti to improve the intergranular corrosion resistance, formability and weldability of the steel. Compared with 304 steel, although the elongation is low (about 30%), the strength and corrosion resistance are equivalent, and the corrosion resistance is better than 200 series materials. Chromium content is 12% ~ 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its chloride stress corrosion resistance is better than that of stainless steel.