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The influence of N, W, Mo and Cu addition, alone or combined, on the active and passive corrosion behaviour of type 17Cr-13Ni stainless steels was investigated in de-aerated 2 N H 2 SO 4 solutions. Potentiodynamic polarization curves and current decay curves were determined in this medium. Surface characterization was examined by X-ray photo-electron spectroscopy (XPS).

Three austenitic stainless steels (a Fe-17Cr-13Ni-0.15N alloy, an ultra pure Fe-18Cr-10Ni alloy and a type 304 stainless steel) were used in this study in order to investigate the effect of nitrogen on the electrochemical behaviour and on the nature of the passive film formed on the steels in acidic solution (0.5 M H2SO4). The presence of nitrogen in the alloy does not apparently have a significant influence on the response of the material to anodic polarization in the acid electrolyte. Surface analysis of the alloys by XPS after passivation shows that nitrogen is enriched at the surface by anodic segregation during dissolution and passivation of the nitrogen-bearing alloys. After passivation of the alloys three chemical states of nitrogen are detected in the N 1s spectrum. The peak at low binding energy (397.7 ± 0.1 eV) corresponds to nitrogen bonded essentially to chromium under the form of a nitride which is incorporated in the passive film. The N 1s peaks observed at higher binding energies (400.2 ± 0.1 and 402 ± 0.1 eV) correspond to nitrogen species located on the surface of the passivated alloys, which are produced by reaction of the alloy surface with the solution.

Les lessiveurs plaques d’acier inoxydable utilises dans le procede Kraft sont depuis quelques annees tres serieusement endommages. Les phenomenes de projection des liqueurs et de calefaction au niveau des parois semblent etre responsables de cette corrosion comme le montrent des examens realises sur des autoclaves usages.Des essais de laboratoire realises dans des solutions industrielles montrent que l’agressivite de ces dernieres n’est pas seule responsable des corrosions observees. Des effets de parois chaudes provoques par un flux thermique sont necessaires pour retrouver en laboratoire des vitesses de corrosion similaires a celles observees sur les placages en acier austenitique AISI 316 Ti. Par ailleurs, la mise en evidence de risque de corrosion sous contrainte sur les nuances classiques et les bons resultats obtenus sur une nuance austeno-ferritique permettent de preconiser un nouveau placage inoxydable a structure biphasee.Un lessiveur neuf realise suivant ce principe se revele beaucoup plus resistant a la corrosion que les anciens lessiveurs plaques d’acier inoxydable austenitique. Des examens systematiques realises sur ce dernier, montrent bien que ces phenomenes de calefaction sont particulierement intenses sur des defauts geometriques. La bonne tenue d’une zone polie laisse esperer que ce nouveau placage avec un bon etat de surface ameliore sensiblement le comportement des lessiveurs utilises actuellement.

Presentation de quelques cas industriels typiques de corrosion provoquee par l'utilisation d'aciers inoxydables ou d'alliages base nickel en milieux chlorures: types de corrosion, essais experimentaux et industriels, remedes, choix des materiaux

The influence of sulphide ions on the corrosion resistance of some special stainless steels (Z2 CNDU 25-25, Z2 NCDU 25-20, Z2 CNDU 25-6, Z1 CN 25-20, Zl CD 29-4) in 40 wt % H 3 PO 4 with 330 ppm SO 4 2− and 1000 ppm Cl − at 80 °C has been investigated using electrochemical (polarisation curves) and spectrometric (SIMS) techniques. The corrosive effect of sulphide ions is confirmed: they increase the anodic current and shift the corrosion potential to more negative values. The presence in the solution of sufficient sulphide ions prevents the establishment of passivity. Critical sulphide ion concentrations above which the alloys Z2 CNDU 25-6, Z2 CNDU 25-25 and Z1 CD 29-4 are no longer able to passivate, are respectively, 1, 5 and 15 ppm S 2− ; so, the Z1 CD 29-4 alloy with high chromium content (29% Cr) and without nickel has good behaviour in such polluted phosphoric acid. In the passive state, in order of decreasing dissolution rate, the five steels are ranked as follows: Z1 CN 25-20, Z2 CNDU 25-6, Z2 NCDU 25-20, Z1 CD 29-4 and Z2 CNDU 25-25; sulphur is present in the films probably as sulphides or oxysulphides. Contrary to nickel, the presence of chromium and molybdenum is essential to increase the corrosion resistance of stainless steels in phosphoric acid with sulphides as impurities.