Dilution control in Gas-tungsten arc welds involving superaustenitic stainless steels and nickel-based alloys
Stephen W. Banovic, J N. DuPont, A R. Marder
Dissimilar metal welds were prepared between a super austenitic stainless steel, AL-6XN alloy, and two Ni-base filler metals, IN625 and IN622, using the Gas Tungsten Arc Welding (GTAW) process. Fusion zone compositions over the full range of dilution levels (0 % to 100 %) were produced by varying the independent welding parameters of arc power and volumetric filler metal feed rate. Microstructural characterization of the welds was conducted via light optical microscopy with quantitative chemical information obtained through electron probe microanalysis (EPMA). The dilution level of each weld was determined from the EPMA data as well as through geometric measurements of the weld cross-sectional areas. The dilution level was observed to decrease with increasing filler metal feed rate and decreasing arc power. These effect are quantitatively interpreted based on a previously proposed processing model. The model is used to demonstrate that, in terms of welding parameters, the dilution level can be correlated exclusively to the ratio of volumetric filler metal feed rate (Vfm) to arc power (VI), i.e., the individual values of Vfm and VI are not important in controlling dilution and resultant weld metal composition. Good agreement is obtained between experimental and calculated dilution values using the model. It is also demonstrated that the melting enthalpies of the filler metal and substrate have onkly a minor influence on dilution at dilution levels in the 40 % to 100 % range. The knowledge facilitates estimates of dilution levels in this range when the substrate and filler metal thermal properties are not accurately known. The results presented from this study provide guideleines for controlling weld metal composition in these dissimilar metal weld combinations.
Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science