Numerical Simulation of Wire-Fed TIG Welding of Stainless Steel

Literature Overview

This paper by Yang Wenfei and Liu Aiguo from the School of Materials Science and Engineering at Shenyang Ligong University, published in the Journal of Shenyang Ligong University (2021, Vol. 40, No. 6, pp. 71–76), presents a numerical simulation study of wire-fed TIG (GTAW with filler metal) welding of 2 mm thick 304 stainless steel plates using the Simufact Welding finite element software. The study employs a double-ellipsoid heat source model to characterize the welding process and investigates the effects of welding parameters on temperature field, stress field, and weld deformation. This work is classified under TG444 and contributes to the growing body of computational welding mechanics literature.

Core Technical Content and Simulation Methodology

The simulation focuses on a simplified physical model of 2 mm thick 304 stainless steel plate welded by wire-fed TIG process. The double-ellipsoid heat source model is selected to represent the asymmetric heat distribution characteristic of TIG welding, where the keyhole region and the back side of the weld pool have different heat deposition characteristics. The simulation varies welding current (120 A to 160 A) and welding speed (12 cm/min to 16 cm/min) to examine their influence on thermal and mechanical responses.

Simulation Parameters and Results Summary

A key finding from the simulation is that the stress concentration region remains virtually unchanged regardless of current or speed variations. The stress is most concentrated at the weld start position, which is consistent with the known behavior of weld initiation where thermal expansion is constrained by the already-solidified weld metal. This observation has practical implications for weld sequence planning, where initiating welds from positions of lower constraint can reduce overall distortion.

Thermal and Mechanical Analysis

The temperature field analysis reveals the typical characteristics of thin-plate TIG welding, with the peak temperature occurring in the weld pool region and rapidly decreasing in the base metal. For 304 stainless steel, the thermal conductivity is relatively low (approximately 16 W/m·K at room temperature), which contributes to higher peak temperatures and more localized heat concentration compared to carbon steels. The phase transformation behavior of 304 stainless steel is relatively simple compared to martensitic steels, as the austenitic microstructure does not undergo martensitic transformation during cooling. However, sensitization (chromium carbide precipitation at grain boundaries) can occur in the 450–850°C range, which is relevant for the HAZ microstructure.

Stress Field Characteristics

The residual stress distribution in the simulated weld shows characteristic patterns:

• Maximum tensile residual stress in the transverse direction at the weld centerline
• Longitudinal tensile stress near the weld that transitions to compressive stress with increasing distance from the weld
• Lower longitudinal tensile stress at the weld center compared to the regions immediately adjacent to the weld

These stress patterns are consistent with the general understanding of residual stress development in thin-plate welds, where the cooling of the weld metal causes contraction that is resisted by the surrounding base metal, generating tensile stresses in the weld region and compensating compressive stresses in the base metal.

Engineering Practice Implications

For practical welding of 2 mm thick 304 stainless steel, the simulation results provide guidance on parameter selection. The relatively low deformation values (maximum 0.33 mm for the studied range) suggest that thin-plate TIG welding of 304 stainless steel is generally manageable from a distortion control perspective, provided that appropriate fixturing and welding sequence strategies are employed. The finding that welding speed has a more pronounced effect on deformation than welding current (0.33 mm vs. 0.06 mm change) suggests that speed optimization should be prioritized in welding procedure development for distortion-sensitive applications.

Practical Parameter Recommendations Based on Simulation

The simulation also highlights the importance of weld start position stress concentration, which in practice can be mitigated by using back-step welding, tack welds, or welding from the center outward on symmetric joints. For pipe applications, where circumferential welds are common, the initiation and termination of the weld often create stress concentrations that can be problematic in fatigue-critical service.

Study Insights and Reflections

This numerical simulation study provides valuable quantitative insights into the welding behavior of thin stainless steel plates, though it is limited by the simplified physical model and the assumption of a double-ellipsoid heat source. In practice, wire-fed TIG welding involves additional complexities such as filler wire feeding dynamics, gas shielding effects, and potential spatter that are not fully captured in the simulation. The results nonetheless offer a useful framework for understanding parameter sensitivity and can guide experimental welding procedure development. For pipe welding applications, where the geometry is cylindrical rather than planar, additional geometric effects on stress and deformation would need to be considered. The study demonstrates the value of computational methods in welding engineering, complementing experimental approaches and reducing the need for extensive trial welding in procedure qualification.