The objectives of this work were to characterise and understand the effects of circular magnetic arc deflection (arc stirring) on grain structure refinement of gas tungsten arc weld beads made in Inconel 690 substrates. Welds were made at various arc stirring frequencies (1?5-50 Hz), and microstructures were analysed using optical and electron backscattered diffraction microscopy. Optimum refinement of grain size occurred at a stirring frequency of ,7 Hz. Analysis of computational fluid flow, heat transfer and solidification model results suggested that grain detachment was the primary mechanism for grain refinement.
The formation of a columnar grain structure in high chromium nickel based alloy welds can be associated with cracking and poor resolution for ultrasonic non-destructive examination. The objective of this research was to characterise the effects of circular magnetic arc deflection (arc stirring) on grain structure of gas tungsten arc weld overlays made on Inconel 690 substrates with 52M filler wire. Welds and weld overlays were made at various arc stirring frequencies, and microstructures were analysed using optical and electron backscattered diffraction microscopy. Significant refinement of grain size occurred at a stirring frequency of 7 Hz. Ultrasonic nondestructive examination confirmed 100% improvement in signal/noise ratio in weld overlays made with magnetic stirring.
High chromium nickel-base weld filler metals 52 (ERNiCrFe-7) and 52M (ERNiCrFe-7A) have in recent years replaced filler metal 82 (ERNiCr-3) for new fabrication and for repair applications in commercial nuclear power plants. Filler metals 52 and 52M are selected because they have excellent resistance to primary water stress corrosion cracking (PWSCC). Unfortunately, filler metals 52 and 52M exhibit a higher susceptibility to ductility-dip cracking (DDC) compared to filler metal 82. Filler metal 52MSS (ERNiCrFe-13) is a new high chromium nickel-base alloy with Nb and Mo added to improve resistance to ductility-dip cracking. Increasing Nb has in previous research been shown to widen the solidification temperature range in nickel-base alloys. A wider solidification temperature range can potentially increase susceptibility to hot cracking. This study investigated the solidification behavior and hot cracking susceptibility of three heats of 52MSS and compared the results to a heat of filler metal 52M and a heat of filler metal 52i. The solidification behavior and hot cracking susceptibility were investigated by an optimized Transvarestraint test and by a next generation Cast Pin Tear Test (CPTT). The solidification temperature range and eutectic transformations were measured by a patented Single Sensor Differential Thermal Analysis (SS-DTA) technique. This study showed that filler metal 52MSS was slightly more susceptible to hot cracking than 52M and 52i. This study also demonstrated that the next generation CPTT and SS-DTA technique are effective methods for evaluating the solidification behavior and hot cracking susceptibility of high chromium nickel-base weld filler metals.
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