STRESS-CORROSION CRACKING OF ARMCO IRON IN PHOSPHATE SOLUTIONS

The stress corrosion cracking of Armco iron was examined in 0.033 and 1.0 M sodium orthophosphate solutions of pH 4.0, 7.0, and 9.0 at 25-100°C in constant strain-rate tests. In 1 M solution of pH 4.0 there formed in Armco iron deep intergranular cracks at potentials - 150 to - 50 mV (SCE) and anodic currents of 0.4-8 A/m2, and also shallow transgranular cracks at ca. - 250 to - 50 mV and 1-30 A/m2. Intergranular cracking has been associated with the presence of the oxide passivating film of moderate protectiveness and it was ascribed to deterioration of this film on grain boundaries of the metal by segregated admixtures. Transgranular cracking has been associated with the presence of less protective layers and their rupture along deformation bands. © 1979.