Effect of local texture and precipitation on the ductility dip cracking of ERNiCrFe-7A Ni-based overlay

Abstract

The multi-pass ERNiCrFe-7A overlay depositions, produced by cold wire feed (CWF) or hot wire feed (HWF) gas tungsten arc welding (GTAW) process with typical parameters, were employed to investigate the effects of different micro-characteristics on ductility-dip cracking (DDC) susceptibility. The results show that, the HWF-produced deposit exhibited the texture with larger quantity of 〈001〉 oriented grains in the pass region (away from the fusion line), while the CWF-produced deposit was weakly textured with increased crystallographic misorientation for the higher heat input per unit volume. Crystal misorientation also increased in the interpass region (near the fusion line) of both the overlays. Results of strain-to-fracture (STF) tests indicated that the overall DDC resistance in the deposit CWF was lower than that in the deposit HWF. And the interpass region exhibited higher DDC susceptibility than the pass region. The intergranular cracking is found to be triggered by the strain accumulation between differently oriented grains. Meanwhile, both the over 30° misorientation angle and melting of Cr-rich M23C6 carbides reduced the grain boundary (GB) strength and promoted the cracking. Therefore, the DDC resistance would be increased by decreasing the GBs those have misorientation angles over 30°, as well as the carbides distributed on the GBs.