Effect of tempering-induced microstructural evolution on the corrosion behaviour of high chromium cast iron

This study investigated the effect of tempering heat treatment on the corrosion behaviour of high chromium cast iron (HCCI) in a solution of 0.5 mol dm^-3 H₂SO₄ and 0.01 mol dm^-3 HCl. After tempering, microstructural analyses revealed that the primary γ phase transformed into the α phase, accompanied by the precipitation of fine carbides and changes in the composition of the eutectic carbides. Electrochemical and surface analyses demonstrated that the galvanic effect, driven by the area ratio and distance between the carbides and the α phase, accelerated selective corrosion in heat-treated specimens compared to as-casted samples. The preferential dissolution was initiated in either the γ or α phase and propagated towards the eutectic γ phase or inter-eutectic carbides (α) for as-casted and heat-treated HCCI, respectively. Consequently, heat treatment accelerated the corrosion rate by intensifying galvanic interactions.