Microstructural response on the cracking resistance of alloy 600

Precipitation of chromium rich carbides promotes the development of a Cr-depleted zone which in turn provided a weak path for the intergranular crack propagation. The role of low temperature anneals on the intergranular cracking resistance (IGC) of alloy 600 was investigated using modified wedge opening loading specimens heat treated at 930, 800 and 600 °C and exposed to high purity water pressurized with hydrogen at 300 °C. Mill annealing at 930 °C did lead to IGC susceptible microstructures. In this condition the alloy 600 exhibited the least crack growth rates (da / dt) of the order of 1.86 × 10− 12 m/s and characterized the substantial work hardening ahead of the crack front. In contrast, annealing at 600 °C (HT600) resulted in increasing IGC susceptibilities. Under these conditions, crack growth rates, da / dt, as high as 7.10 × 10− 10 m/s were found (HT600). Accordingly, significant interactions between the slip bands and the crack path lead to crack bifurcation into the slip planes and cavity formation.