Effect of Microstructure on Pitting and Corrosion Fatigue of 17-4 PH Turbine Blade Steel in Chloride Environments

摘要

Depending on its heat treatment, 17-4 PH stainless steel may contain significant levels of reformed austenite and untempered martensite in a matrix of tempered martensite. Shot peening can cause changes in the microstructure of the surface layers by transforming the austenite to untempered martensite. The effect of these microstructural varations on the resistance of 17-4 PH stainless steel to pitting and corrosion fatigue has been determined in simulated steam turbine environments. The results of two electrochemical tests (large amplitude cyclic voltammetry and the pit propagation rate (PPR) test) indicate that tempering temperature and shot peening have only minor effects on resistance to pit initiation and propagation in any one of three aqueous chloride environments. However, the susceptibility of this stainless steel to corrosion fatigue in one of these environments (6 wt % FeCl sub 3 ) was reduced by increasing the tempering temperature from 538 exp 0 C (1000 exp 0 F) to 649 exp 0 C (1200 exp 0 F). (ERA citation 07:050846)