Anodic behaviour of mild steel during yielding in nitrate solutions

Abstract

The anodic behaviour of mild steel during yielding, at constant potential in various hotnitrate solutions, has been studied. The influence of solution composition, pH, strain rate and electrode potential, has been examined. Yielding of oxide-covered steel is accompanied by a large increase in anodic current density. This increase is almost independent of strain rate and is a linear function of percentage strain; the anodic c.d. on the yielding metal bared by rupture of the oxide layer can be as high as 2A/cm 2. At low strain rates stress corrosion “cracking” can be observed. The rate of “crack” propagation was estimated microscopically as up to ∼ 0·25cm/h, which is equivalent to an anodic dissolution of the advancing edge of the “crack” of up to ∼ 2A/cm 2. The stress corrosion “crack” is therefore considered to be a fissure of which the yielding advancing edge is bared metal that can dissolve anodically at up to 2A/cm 2 while the static sides become oxide-covered so that the anode c.d. there is many times smaller.