engleski

Influence of thermal oxides on pitting corrosion of stainless steel in chloride solutions

X-ray diffraction analysis, Auger electron spectroscopy, X-ray photoelectron spectrometry, optical micrography, and spot potential measurements were used for characterisation of AISI 316L stainless steel specimens with oxide films formed by heating in air isothermally (at 200-1000 oC) or in temperature gradient. Pitting liability of such specimens was tested by exposure to FeCl3 solution and determination of 9 topographic criteria. Testing was performed also on previously heated specimens after removal of thermal oxides by pickling. It is proven that thermal oxides facilitate pits nucleation but they do not influence pits propagation. Effect on nucleation is caused by stresses and lattice defects in oxide film and in metal substrate. Maximum pitting liability is established after heating at 600 oC. Removal of thermal oxides formed at 200-800 oC improves pitting resistance but initial stability is never attained because of residual stresses and lattice defects on cleaned metal surface. After heating at 1000 oC pitting liability is even increased by pickling.

AISI 316L stainless steel; oxide films; topographical criteria; pickling; pitting corrosion

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