Investigation on Impact of Heat Input on Microstructural, Mechanical, and Intergranular Corrosion Properties of Gas Tungsten Arc-Welded Ti-Stabilized 439 Ferritic Stainless Steel

In the present study, gas tungsten arc welding was employed to weld Ti-stabilized 439 ferritic stainless steel using 308L austenitic stainless steel filler electrode with varying heat input, i.e., low heat input (LHI) and high heat input (HHI). The optical microstructure revealed the formation of retained austenite (RA) and ferrite in the weld zone (WZ), whereas the peppery structure consisting of chromium-rich carbides were observed in the heat-affected zone for both the weldments. The volumetric fraction of RA was calculated using X-ray diffraction analysis. The RA’s content decreased, whereas grain size in WZ increased with an increase in heat input. The local misorientation and grain boundary distribution in the welded region was investigated by electron backscattered diffraction. The LHI weldment depicted the higher micro-hardness and tensile strength attributed to the higher content of RA as compared to HHI; however, the opposite trend was observed for the intergranular corrosion resistance.

Potentiodynamic corrosion behavior and microstructural features of gas tungsten constricted arc (GTCA)-welded superalloy 718 joints

The gas tungsten constricted arc welding (GTCAW) process was used to join thin Su-718 alloy sheets to minimize alloying segregation and Laves phase precipitation in the fusion zone (FZ). The potentiodynamic corrosion behavior of GTCAW Su-718 alloy joints was studied and correlated to the microstructural features of welds. The potentiodynamic corrosion test was done in a 3.56 wt.-% NaCl solution to determine the corrosion rate of Su-718 alloy joints. The optical microscopy (OM) technique was used to analyze the microstructure of corroded weldments. The scanning electron microscopy (SEM) technique was used to study the Laves phase development in FZ. The SEM X-ray energy dispersive spectroscopy (EDS) technique was used to for elemental mapping of FZ. The corrosion resistance of Su-718 joints is inversely proportional to the precipitation of Laves phase in FZ. The GTCA welded Su-718 alloy joints disclosed superior corrosion resistance for the joints with lower Laves phase precipitation. It is correlated to the refining of FZ microstructure, which aids in minimizing the Laves phase precipitation. The joints with higher Laves phase precipitation revealed inferior corrosion resistance. It is attributed to coarsening of FZ microstructure, which raises the alloying segregation and leads to depletion of alloying elements in FZ. The dendritic core regions showed severe corrosion compared to the interdendritic regions. The corrosion resistance of GTCA welded Su-718 joints is better than that of CC-GTAW and PC-GTGAW joints and comparable to that of EBW and LBW joints. It refers to the arc constriction and high frequency current pulsation.

Effect of Heat Input on Distortions and Residual Stresses Induced by Gas Tungsten Arc Welding in SS 316L to INCONEL625 Multipass Dissimilar Welded Joints

In the present study, distortion and residual stresses in the multipass welded joint were analyzed with respect to heat input. The welded joint was produced using the gas tungsten arc welding (GTAW) process with dissimilar Ni-based filler of ERNiCrMo-3. This dissimilar joint is essential in power generating nuclear and thermal plants operating at elevated temperatures. The distortion and residual stress measurements were taken using the Vernier height gauge and XRD method. To evaluate the mechanical properties, tensile testing was carried out at room temperature. The welded joint qualified the tensile test with an average value of 593 MPa. In the weld metal, a significant variation of residual stresses is measured on the top surface of the weldment along with the thickness with peak magnitude of 145 MPa to 180 MPa at the fusion zone.

Residual stresses in gas tungsten arc welding: a novel phase-field thermo-elastoplasticity modeling and parameter treatment framework

The fusion welding process of metallic components, such as using gas tungsten arc welding (GTAW), is often accompanied by detrimental deformations and residual stresses, which affect the strength and functionality of these components. In this work, a phase-field model, usually used to track the states of phase-change materials, is embedded in a thermo-elastoplastic finite element model to simulate the GTAW process and estimate the residual stresses. This embedment allows to track the moving melting front of the metallic material induced by the welding heat source and, thus, splits the domain into soft and hard solid regions with a diffusive interface between them. Additionally, temperature- and phase-field-dependent material properties are considered. The J2 plasticity model with isotropic hardening is considered. The coupled system of equations is solved in the FE package FEniCS, whereas two- and three-dimensional initial-boundary-value problems are introduced and the results are compared with reference data from the literature.