Influence of Aging Heat Treatment on Pitting Corrosion Resistance of Martensitic Stainless Steel

Abstract

This research aim to study the influence of aging heat treatment on the pitting corrosion resistance of martensitic stainless steel (MSS), where a number of martensitic stainless steel specimens were subjected to solution treatment at 1100 oC for one hour followed by water quenching then aging in the temperatures range (500-750) oC for different holding times (1, 5, 10, 15 & 20) hr. Accelerated chemical corrosion test and immersion chemical corrosion test were performed on samples after heat treatment. The results of the research showed that the pitting corrosion resistance is significantly affected by the aging temperature. where samples that aged at 500 °C have the highest rate of corrosion due to an increase in the ratio of the Delta ferrite (δ-ferrite) and very soft precipitates from other phases of heterogeneous form in the basic martensitic phase; which leads to increase corrosion rate. From the other side, the aged samples in the temperature range (550–650) °C have the smaller rate of corrosion, this is due to the high volumetric ratio of remaining austenite. The aged samples at temperatures above 650 °C shows a medium corrosion rate. It was also found that the type of pits results from both the chemical corrosion tests and their shape were not related to the ferrite type and the carbides present in the microstructure.