EFFECTS OF TENSILE AND COMPRESSIVE STRESSES ON THE PASSIVE LAYERS FORMED ON A TYPE 302 STAINLESS STEEL IN A NORMAL SULPHURIC ACID BATH

摘要

Type 302 stainless steel samples were subjected to a U-bend test in a normal sulphuric acid bath at room temperature. The passive layers which subsequently grew on both sides of the sample, were studied by Auger electron spectroscopy. Each strained sample was immersed and passivated in a sulphuric acid solution under a voltage of + 450 mV/SCE and the anodic current density was studied as a function of the immersion time. The results obtained show that the anodic current density is higher for the strained specimens than for the unstrained specimen. Thus, passivation occurs more rapidly for an unstrained sample than for strained samples. There is also clear evidence that the decrease in the anodic current density is more rapid for an elastically strained sample than for a plastically strained one. The influence of the tensile and compressive stresses on the composition of the passive films was studied by comparing the elemental Auger depth profiles. The results obtained show that oxidation is more important on the tensile stressed side than on the compressive stressed one: whether the samples were elastically or plastically strained. Similarly, the width of the region affected by the chromium enrichment was enhanced by tensile straining and reduced by compressive straining, whether the samples were elastically or plastically strained. [References: 19]