EFFECTS OF PASSIVATION AND CARBON-FILMS O N AUSTENITIC CRNIMO STEELS ON THEIR PITTING AND STRESS-CORROSION RESISTANCE

The influence of passive film and combinations of a passivation and a carbon layer on the resistance to pitting and SCC of austenitic CrNiMo steels has been investigated in physiological sodium chloride solutio n (Tyrode solution) at pH 6.9 to 7.4 at 37 +/- 1-degrees-C. The passiv e film was obtained after electrolytic polishing in H3PO4 + H2SO4 + C6 H5NHCOCH3 + oxalic acid + corrosion inhibitor CS by treatment with 40% nitric acid the carbon film was obtained by CVD. Impurities in the st eel (non-metallic inclusions) and the different metallic phases were i nvestigated and the chemical composition of the passive film was deter mined by quantitative analysis. The resistance to pitting of the steel with and without passive film was determined potentiodynamically in T yrode's solution at 37 +/- 1-degrees-C. The resistance to SCC was dete rmined in Tyrode's solution at 37 +/- 1-degrees-C, in neutral glycerol e and in boiling magnesium chloride solution at 154 +/- 1-degrees-C an d evaluated in terms of K(sigma) and K(tau).The corrosion damage was i nvestigated by optical and scanning electron microscopy. The investiga tions have revealed that the different surface conditions considerably improve the pitting and SCC resistance of the steels in the media use d in this work, so that they make possible the use of these materials as surgical implants.