EFFECTS OF PHOSPHORUS SEGREGATED AT GRAIN-BOUNDARIES ON STRESS-CORROSION CRACK INITIATION AND PROPAGATION OF ROTOR STEEL IN BOILING 40 WT PERCENT NAOH SOLUTION

Abstract

The effects of phosphorus segregated at grain boundaries on intergranular corrosion have been investigated by an electrochemical method. The stress corrosion crack initiation and propagation of rotor steels was studied as a function of applied stress in boiling 40 wt.% NaOH solution at an applied passive potential of -530 mV(SHE) using the electrical potential method. Phosphorus segregation leads to intergranular corrosion susceptibility. Intergranular attack by anodic dissolution is responsible for the crack initiation, irrespective of the applied stress and phosphorus doping. The decrease in stress corrosion crack propagation time due to phosphorus segregated at grain boundaries is enhanced with increasing applied stress and is presumably related to crack branching. Fringe patterns on the intergranular facets of the fracture surface are found to be associated with martensite lath boundaries and are inferred to be caused by strain-induced dissolution.