Assessment of gas tungsten arc welding thermal cycles on Inconel 718 alloy

Heat moving source models along with transient heat analysis by finite element method were used to determine weld thermal cycles and isothermal sections obtained from the application of a gas tungsten arc welding beads on Inconel 718 plates. Analytical (Rosenthal's thick plate model) and finite element results show an acceptable approximation with the experimental weld thermal cycles. The isothermal sections determined by numerical simulation show a better approximation with the experimental welding profile for double-ellipse model heat distribution than Gauss model. To analyze the microstructural transformation produced by different cooling rates in the fusion and heat affected zones, Vickers microhardness measurements (profile and mapping representation) were conducted. A hardness decrement for the heat affected zone (similar to 200 HV0.2) and fusion zone (similar to 240 HV0.2) in comparison with base material (similar to 350 HV0.2) was observed. This behavior has been attributed to the heterogeneous solubilization process of the gamma '' phase (nickel matrix), which, according to the continuous-cooling-transformation curve, produced the Laves phase, delta and MC transition phases, generating a loss in hardness close to the fusion zone.