Intergranular Corrosion Susceptibility of Alloy 600 after Autogenous Tungsten Inert Gas and Laser Beam Welding using Electrochemical Technique

Abstract

Intergranular corrosion and intergranular stress corrosion cracking is influenced by precipitation of chromium carbides at grain boundaries and formation of chromium depletion regions. The present study focuses on understanding the carbide precipitation and subsequent sensitization in the weldments of Alloy 600 using two different welding techniques. The effect of heat input on microstructure and IGC susceptibility was measured using electrochemical reactivation test. The SEM studies were done to evaluate the presence of chromium depleted regions. The carbide was indentified to be Cr7C3 using TEM. The laser beam weldments showed an increased resistance to IGC as compared to TIG weldments.

The Performance of Different Etchants on the Carbides of Ni600 and Ni625

“…The SEM figure of Ni600 with the finely polished sample surface revealed black phases on the GBs that were considered to be chromium carbides [29], as is shown in Figure 3. The presence of these carbides can lead to intergranular corrosion and stress corrosion cracking [30]. The formation of chromium carbides is influenced by precipitations at GBs and the formation of chromium depletion regions.…”

Susceptibility of Dissimilar IN600 Welded Joints to Stress Corrosion Cracking Using Slow Strain Rate Test in Sodium Electrolytes

“…Lim et al [6] observed that the precipitation of Cr carbides occurred preferentially in high-energy zones at the grain boundaries. In his study, Abraham [7] corroborated that the mechanism of precipitation was principally due to the low solubility of C in the Ni matrix and the high thermodynamic affinity of Cr to form compounds of different stoichiometry with C. The formation of Cr-rich carbides in IN600 may reduce the solid solution strengthening mechanism and lead to a loss in the intergranular corrosion resistance (IGCR) of the alloy. Yoo et al [8] reported that the precipitation of chromium carbides, namely, Cr7C3 and Cr23C6, in IN600 occurred in the temperature range of 550-1050 °C, but it might also occur at lower temperatures after very long exposures during service.…”

“…Yoo et al [8] reported that the precipitation of chromium carbides, namely, Cr7C3 and Cr23C6, in IN600 occurred in the temperature range of 550-1050 °C, but it might also occur at lower temperatures after very long exposures during service. The behavior and microstructural characterization of IN600 welds have been studied using a variety of filler materials and welding processes [2,7,[9][10][11][12]. When alloys are welded, a variety of microstructural changes take place at the base material (BM), leaving a heat affected zone (HAZ) with different microstructural features at each side of the welded joint.…”