Study Of Mechanical Properties And Corrosion Resistance Of Tin-containing Ferritic Stainless Steel

Considering of the lack of nickel and scrap resources, expanding the proportion of ferritic stainless steel is one of the major variety structure adjustments of stainless steels. Ferritic stainless steels can be said to be a resource-saving environmentally friendly materials. With the developing of smelting technology in recent years, ferritic stainless with low C, N content will play an increasingly important role in social production. Ferritic stainless inevitably face mechanics and corrosion problems in the process of production and use. This research was involved in mechanical properties and corrosion resistance of 430 ferritic stainless steels, based on the full investigation of on-site process and product quality, and combined with thermal simulation laboratory.Steel samples were 430 ferritic stainless containing 0.1% to 0.4% tin smelted by 10kg vacuum induction furnace, while the contrast steel was 430 ferritic stainless steel without tin.Cupping test and tensile test results showed that the addition of tin in 430 ferritic stainless steel causes the occurrence of a lattice distortion, increasing the tensile strength of steel by solid solution strengthening, slightly lowering the shaping, and improving the plastic strain ratio (r value). Under the experimental conditions, the higher tin content does not adversely affect the processing performance of ferritic stainless steel. As the stretching temperature increased, the recess shaping temperature of the tin-containing ferritic stainless steel is reduced, but the tin increases the shaping of stainless steels. The fractures of tin-containing stainless steel in 400℃ to 800℃ are a lot of dimples, behaving with good shaping. Ductile fractures occurred when steels are stretched. Tin added to 430 ferritic stainless steels improves the auxetic formability, plastic deformation and local formability.The results of the uniform corrosion immersion in 40% H2SO4 showed that, the amount of corrosion of tin-containing 430 ferritic stainless steels change linearly with time, which meant the corrosion rate is uniform. After adding a small amount of tin to 430 ferritic stainless steels, the corrosion rate decreases, and the uniform corrosion resistance of ferritic stainless steel containing tin would be improved. The lowest corrosion rate of 430 ferritic stainless steel is 0.3130 g·cm-2·h-1 with 0.3% Sn added.The results of potentiodynamic anodic polarization curves and electrochemical impedance spectroscopy showed that, after adding Sn, the pitting potential of 430 ferritic stainless steels rises and the best one with the maximum pitting corrosion resistance is the steel sample added 0.3% Sn; Cl" has a significant impact on pitting corrosion resistance points of the tin-containing 430 ferritic stainless steel. With the increasing of Cl- concentration, both of the pitting corrosion resistance and the polarization resistance significantly reduced; The pH of corrosive solution has a more significant impact on the resistant to points of tin-containing 430 ferritic stainless steels in the acidic environment. With the increase of H+ concentration, both of the polarization resistance and the resistance to pitting corrosion significantly reduced; In the alkaline environment, the pitting potential of tin-containing 430 ferritic stainless steels is higher than that of 430 stainless steel, performing better resistant to pitting; The temperature significantly affected pitting resistances of tin-containing 430 ferritic stainless steels, and with the increasing of test temperature, both of the resistance to pitting corrosion and polarization resistance significantly reduced.The results of immersion tests and potentiodynamic reactivation experiments showed that the rate of reactivation of the steel samples with 0.2% Sn is the lowest behaving the most outstanding resistance to intergranular corrosion, but the further addition of tin decreased resistance to intergranular corrosion.In the outer passivation film, the presence of Sn weak peaks can be detected, and the main component is SnO2. Sn exists in the inner membrane. When the inner oxide is destroyed, a tin oxide layer can be formed on the interface of metal oxide and metal, which can improve the stability of the membrane and prevent the damage of film and the occurrence of pitting corrosion.