Abstract
The present study investigates the microstructural changes and corrosion behavior of 13Cr martensitic stainless steel (MSS), austenitized at 1040 °C followed by cooling to room temperature through oil-quenching, air-cooling and furnace-cooling. Oil-quenching and air-cooling produced a lath martensitic microstructure, while, the oil-quenched condition showed δ-ferrite stringers and quench cracks. The slow furnace-cooling produced a widmanstatten type ferrite with Cr-rich carbides. Air-cooled condition developed a higher hardness than that for the oil-quenched and furnace-cooled conditions due to martensitic structure and fine carbide precipitation along the prior austenitic grain boundaries (PAGB) during cooling from austenitization temperature. Double loop-electrochemical potentiokinetic reactivation (DL-EPR) tests and immersion tests followed by scanning electron microscope examination indicated that furnace-cooled and air-cooled conditions are susceptible to intergranular corrosion (IGC). Slow cooling is highly detrimental to IGC. Air-cooled condition showed preferential attack along the PAGB boundaries in both DL-EPR and immersion tests whereas furnace-cooled condition showed combined heavy uniform corrosion and IGC. No preferential attack is observed in oil-quenched condition, and it exhibited uniform corrosion. The present results show that the austenitization followed by cooling in air is sufficient to cause sensitization in 13Cr MSS. However, controlled (fast) air-cooling (avoiding sensitization during cooling) would be better a choice for austenitization heat treatment of 13Cr MSS.
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