Stress corrosion crack growth behavior of a low alloy steel in 3.0% NaCl solution

Abstract

Stress corrosion crack growth behavior of a low alloy steel in 3.0% NaCl solution was studied. The investigation also examines the influence of initial stress intensity factor (K_i) and overload plastic zone size on the incubation period and stress corrosion crack growth rate. Compact tension specimens with (TL) orientation prepared from SAE 4140 steel in hardened and tempered condition were used. To examine the influence of overload, initially fatigue precracked specimens were overloaded to various levels, namely 10, 25, and 50% more than initial stress intensity levels (K_i) at two different (K_i) levels (K_i = 28 and 46 MPa√m) and unloaded. Stress corrosion crack growth behavior of these specimens was studied after reloading them to their initial stress intensity levels (i.e., K_i = 28 and 46 MPa√m, respectively) and keeping them submerged in 3.0% NaCl solution.

The results of the present investigation demonstrate that the incubation period for crack growth increases with increase in overload plastic zone size. The incubation period was found to decrease with increase in (K_i) level. Once the crack growth has started, the actual crack growth rate in the rest of the specimens was found to be higher in overloaded specimens than that in nonoverloaded specimens. The crack growth period, on the other hand, was found to decrease with increase in overload plastic zone size. This increase in incubation period in overloaded specimens can be attributed to the presence of residual compressive stresses in the crack tip region in overloaded specimens. The decrease in crack growth period (t _g) in overloaded specimens is due to the formation of stress induced martensites in these specimens.