HIC and SCC Corrosion Behavior of the ۱۷-۴ PH Stainless Steel in Double Over Aged Condition

This research studied the effect of two-stage over aging treatment on the ۱۷-۴ PH stainless steel corrosion behavior. First, the steel was solution annealed at ۱۰۳۵ °C for ۱h, then it was subjected to a two-stage over aging treatment known as H۱۱۵۰-M treatment. Hydrogen induced cracking and stress corrosion cracking standard tests were carried out under annealed and over aged conditions. Microhardness tests were conducted to evaluate the mechanical properties under different testing conditions. Microstructural examinations were performed by the optical microscope and field emission scanning electron microscope. The results showed that under annealed condition, the microstructure consisted of lath and coarse martensite and interdendritic δ-ferrite that transferred to severely tempered and layered martensite after over aging treatment with the formation of reversed austenite. In the latter case, the reversed austenite was about ۲۶% compared to ۷% before over aging treatment. Under the hydrogen induced cracking test, the over aged ۱۷-۴ PH steel exhibited no cracking, unlike the annealed condition. The results also showed that ۱۷-۴ PH steel under both annealing and over aging conditions, is suspectable to stress corrosion cracking; meanwhile, time to failure was substantially higher in the latter condition.