THE CORROSION-RESISTANCE OF NITROGEN BEARING MARTENSITIC STAINLESS-STEELS

It has been mentioned that nitrogen enhances the corrosion resistance of the martensitic stainless steels. In this work, by means of electro chemical and mass loss tests, the corrosion resistance of three experi mental martensitic stainless steels, with partial substitution of carb on by nitrogen were investigated. Martensitic stainless steels type AI Sl 410 and AISl 420 were also tested, for comparison, and all steels w ere tested in both hardened and tempered conditions. The resistance to general corrosion in 0.5 M H2SO4 was evaluated by mass loss tests and by potentiodynamic polarization tests, the last through the critical current density and the passive current density. The resistance to pit ting corrosion was evaluated by potentiodynamic polarization tests in 0.01 M NaCl + 0.01 M Na2SO4, through the pitting potential. The result s of both general corrosion and pitting corrosion tests show that the nitrogen, when present in the solid solution condition, improves the c orrosion resistance. it was observed that with the partial substitutio n of carbon by nitrogen, the passive current densities were lower, in 0.5 M H2SO4, and the pitting potentials were higher, in the 0.01 M NaC l + 0.01 M Na2SO4 solution. The results are discussed basically throug h the different chemical composition of the steels and the microstruct ure observed in each sample.