Effect of strain rate on primary water stress corrosion cracking fracture mode and crack growth rate of nickel alloy and austenitic stainless steel

The primary water stress corrosion cracking (PWSCC) of Alloy 600 (UNS N06600), Type 304 (UNS S30400), and Type 316 (UNS S31600) stainless steels (SS) was studied at 360 degrees C and at nominal strain rates ranging from 1 x 10(-7) s(-1) to 1 x 10(-5) s(-1) using the slow strain rate tensile technique (SSRT). It was revealed that the PWSCC fracture mode of these materials changed with the strain rate, and the crack growth rate passes through a maximum with the strain rate. The total brittle fracture decreases with increasing strain rate; however, the fraction of transgranular (TG) mode in the brittle fracture increases with increasing strain rate, i.e., the fraction of intergranular (IG) fracture increases with decreasing strain rate. The fraction of TG increases in the following order. Alloy 600, Type 316, and Type 304 SS. The mechanism for the fracture mode change might possibly be explained by a similar mechanism of PWSCC and differences of stacking fault energy for these materials.