The Effect of Sn on the Corrosion Resistance of 25Cr-6Ni Duplex Steel

Abstract

The effect of Sn addition on the corrosion resistance of 25Cr-6Ni duplex steel has been studied. Results obtained were summarized as follows.
(1), Corrosion rate of 25Cr-6Ni steel was decreased with small amounts of Sn addition in 5wt% H₂SO₄ solution at boiling temperature. (2), By addition of SnSO₄ in 5wt% H₂SO₄ at boiling temperature, the corrosion rate of 25Cr-6Ni steel was reduced. (3), Alloying of Sn made the passivation potential, E_p, less noble and reduced the critical current density, I_cr, in 5wt% H₂SO₄ solution. (4), Alloying of Sn had no influence on the corrosion rate in 65wt% HNO₃ solution except the case Sn bearing steels were reheated at 1200°C. In these reheated steels, the suscepitability of intergranular corrosion was increased with ferrite amounts. (5), Alloying of Sn had no effect in improving the corrosion rate of 25Cr-6Ni steel in 50g/l·FeCl₃+1/20N·HCl solution at 50°C and 70°C. In addition the pitting potential, V_c, was slightly more noble by Sn addition of 25Cr-6Ni steel in 0.5mol/l NaCl solution at 30°C.