Fatigue crack initiation and propagation in AISI 4130 steel exposed to neutral perchlorate solution

Abstract

In order to check whether recent results on the corrosion fatigue of copper single crystals may apply to a commercial metal, corrosion fatigue crack initiation and propagation in normalized AISI 4130 steel have been studied (1) in air, (2) in 0.1 M NaClO 4 solution in free corrosion and (3) in the same solution but at an imposed anodic potential of −0.555 V with respect to a saturated calomel electrode. As expected, crack initiation and propagation lives were reduced by the corrosive environment. Cracks initiated at inclusions in air, while in solution the first cracks initiated in grain boundaries and later in life they also initiated transgranularly. In solution, cracks propagated in a mixed intergranular and transgranular mode but mainly transgranular. When the test frequency was increased, the mode of cracking tended to change from intergranular to transgranular. Another effect of cyclic deformation in corrosive solution was to increase the rate and magnitude of the potential shift compared with the behavior in an unstressed specimen and the rate changes corresponded to the different stages of corrosion fatigue damage. Current transient behavior is similar to that observed in copper cycled under anodic conditions which produce oxide films. The intergranular cracking behavior is related to the homogeneity of slip which was promoted by the corrosive environment and to similar results found in copper and iron.