The Comparison of Cracking Susceptibility of IN52M and IN52MSS Overlay Welds

Abstract

Overlay-welding of IN52M and IN52MSS onto CF8A stainless steel (SS) was conducted by a gas tungsten arc welding process in multiple passes. An electron probe micro-analyzer (EPMA) was applied to determine the distributions and chemical compositions of the grain boundary microconstituents, and the structures were identified by electron backscatter diffraction (EBSD). The hot cracking of the overlay welds was related to the microconstituents at the interdendritic boundaries. The formation of γ-intermetallic (Ni 3 (Nb,Mo)) eutectics was responsible predominantly for the hot cracking of the 52M and 52MSS overlays. The greater Nb and Mo contents in the 52MSS overlay enhanced the formation of coarser microconstituents in greater amounts at the interdendritic boundaries. Thus, the hot cracking sensitivity of the 52MSS overlay was higher than that of the 52M overlay. Moreover, migrated grain boundaries were observed in the 52M and 52MSS overlays but did not induce ductility dip cracking (DDC) in this study. amount of interdendritic phases [25]. Coarse (Nb,Ti)C precipitates in 52M overlays will enhance the formation of Laves phases and increase their size [25,26], leading to increased hot crack sensitivity of the overlay welds.Besides the occurrence of hot cracking, Ni-based deposits for repair-welding of nuclear reactor components can be susceptible to ductility dip cracking (DDC) [27][28][29]. DDC in a Ni-based alloy weld mainly occurs in the reheated weld at elevated temperatures, and it is related to grain boundary (GB) sliding, impurity segregation at GBs, and intergranular precipitation [30]. GB sliding is responsible for the DDC of 52M deposits in strain-to-fracture tests [31]. Moreover, ductility dip cracks are initiated due to the combined effects of the strain concentration on the concave side of the grain boundary, the orientation of the GB to the loading direction, and GB disorientation [32]. In a prior study, IN52 alloy is reported to be more susceptible to DDC than IN82 alloy [33]. Adding Nb and Ti into IN52 alloy can reduce its DDC susceptibility due to the precipitation of NbC and TiC at the GBs [30]. It was reported that the DDC of a 52MSS weld, which was modified from 52M by adding 2.5% Nb and 3.0% Mo, can be alleviated even after multi-pass welding [34,35].In this study, IN52M and IN52MSS fillers were employed to perform overlay-welding on CF8A SS substrate. The microstructures and chemical compositions of the microconstituents at the solidified boundaries of the overlay welds were investigated. The hot cracking tendency and DDC of 52M and 52MSS overlays were evaluated by inspecting the interior microfissures carefully. Grain boundary micro-constituents were analyzed by electron backscatter diffraction (EBSD) to identify the complex phases. Furthermore, the relationships between microstructural features and the cracking tendencies of the overlay welds were correlated with those interdendritic precipitates.

Welding Metallurgy and Weldability of Superalloys

“…Researchers were invited to submit innovative research papers in the areas of welding metallurgy, weldability, and associated topics of superalloys. In total, six research papers were published in this Special Issue of Metals, entitled "Welding Metallurgy and Weldability of Superalloys", which presents some of the research trends in the field [1][2][3][4][5][6]. All six research papers were related to weld cracking in some aspect, with the strongest focus on hot cracking [1][2][3][4]6], followed by strain age cracking [5].…”

“…In total, six research papers were published in this Special Issue of Metals, entitled "Welding Metallurgy and Weldability of Superalloys", which presents some of the research trends in the field [1][2][3][4][5][6]. All six research papers were related to weld cracking in some aspect, with the strongest focus on hot cracking [1][2][3][4]6], followed by strain age cracking [5]. The major part of the submission in terms of material was associated with Alloy 718, the "work horse" within the group of superalloys in the aero-engine industry [2][3][4].…”

“…al. [1] contributed with a paper on Ni-based weld fillers, IN52M and IN52MSS, where its weld performance on a stainless steel (SS) substrate was investigated [1]. The overlay-welding of IN52M and IN52MSS onto CF8A SS was conducted by a TIG welding process in multiple passes.…”