Abstract
The microsegregation behavior of alloy filler metal 52 (FM 52) was studied using microprobe analysis on two different solidification processes. First, microsegregation was characterized in samples manufactured by directional solidification, and then by gas tungsten arc welding (GTAW). The experimental results were compared with Thermo-Calc calculations to verify their accuracy. It was confirmed that the thermodynamic database predicts most alloying elements well. Once this data had been determined, several tip undercooling calculations were carried out for different solidification conditions in terms of fluid flow and thermal gradient values. These calculations allowed the authors to develop a parametrization card for the constants of the microsegregation model, according to the process parameters (e.g., convection in melt pool, thermal gradient, and growth velocity). A new model of microsegregation, including convection and tip undercooling, is also proposed. The Tong–Beckermann microsegregation model was used individually and coupled with a modified Kurz-Giovanola-Trivedi (KGT) tip undercooling model, in order to take into account the convection in the fluid flow at the dendrite tip. Model predictions were compared to experimental results and showed the microsegregation evolution accurately.
Highlights
The first pressurized water reactor (PWR) components were manufactured from stainless steel and nickel A600 alloys
The microsegregation profiles for the quenched directional solidification (QDS) and gas tungsten arc welding (GTAW) experiments are given for Fe, Cr, Ti and
11 of the different microsegregation profiles for one QDS experiment, along with the microsegregation predicted by the TB model, lever rule and Scheil rule
Summary
The first pressurized water reactor (PWR) components were manufactured from stainless steel and nickel A600 alloys. The importance of back-diffusion to reduce solidification cracking has recently been shown [25], along with the fact that microsegregation in gas tungsten arc welding (GTAW) can be somewhat controlled by the use of pulsed current [26]. It is critical for development and application, to thoroughly understand how segregation occurs and how to model it. The intense convection that occurs in the weld pool may affect the solutal build-up associated with solidification, and thereby modify the dendrite tip undercooling This is not taken into account in the Scheil description, and may affect the initial conditions for microsegregation. These results are discussed, and rules for better use of microsegregation models are proposed
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