Heat Source Model and Temperature Field Simulation of 310S Austenitic Stainless Steel TIG Self-Fusion Welding

Literature Overview

This 2017 paper by Liu Zhao-quan, Zhang Yu-tuo, and Dong Wen-chao, published in the Journal of Shenyang Ligong University, presents a numerical simulation study of TIG self-fusion welding of 310S austenitic stainless steel. The work is conducted in collaboration between Shenyang Ligong University and the Shenyang Institute of Metal Research, Chinese Academy of Sciences. The study focuses on developing an accurate heat source model and simulating the temperature field during TIG welding without filler metal, which is a common practice for thin-section 310S components where dilution control is not required.

Core Technical Content

310S austenitic stainless steel is a high-temperature alloy with high chromium (24–26%) and nickel (19–22%) content, designed for service temperatures up to 1200 °C. Its application in furnace components, heat exchanger tubes, and high-temperature process equipment makes welding technology development critical. The TIG self-fusion welding process is particularly attractive for 310S because:

• It avoids the introduction of filler metal with potentially different thermal properties
• It maintains the chemical composition of the base metal in the weld zone
• It produces a narrow weld with minimal distortion

Heat Source Model Development

The paper develops a heat source model that captures the spatial and temporal distribution of energy input during TIG welding. The most common models used in welding simulations include:

The Goldak double-ellipsoidal model is particularly relevant for TIG welding because it accounts for the asymmetric heat distribution caused by the welding direction. The front half of the arc (in the direction of travel) receives less energy due to the arc being dragged backward by the motion, while the rear half receives more energy.

Temperature Field Simulation Results

The numerical simulation provides valuable insights into the thermal behavior during TIG self-fusion welding of 310S:

1. Peak temperature distribution: The peak temperature in the weld zone typically reaches 1800–2200 °C, well above the melting point of 310S (approximately 1400 °C). The temperature gradient extends several millimeters from the weld centerline.
2. Solidification time: The time spent above the solidus temperature (approximately 1350 °C) determines the grain structure and cooling rate. For TIG welding with typical parameters (100–150 A, 5–10 cm/min), the solidification time is on the order of 1–3 seconds.
3. Thermal cycles in the HAZ: The HAZ experiences thermal cycles with peak temperatures between 800–1350 °C, depending on distance from the weld. The region experiencing peak temperatures in the sensitization range (450–850 °C) is critical for intergranular corrosion resistance.
4. Residual stress distribution: The thermal simulation provides the basis for calculating residual stresses, which are typically tensile in the weld zone and compressive in the surrounding base metal.

Engineering Practice and Process Optimization

The simulation results have direct implications for welding process optimization:

• Travel speed control: Higher travel speeds reduce heat input and solidification time, leading to finer grain structures but potentially incomplete fusion at low currents.
• Current selection: The welding current directly affects the depth of penetration and the width of the weld. For 310S, currents of 100–150 A are typical for thin sections (2–4 mm), while thicker sections may require multi-pass welding with lower current per pass.
• Preheating and interpass temperature: Preheating reduces thermal gradients and residual stresses but must be carefully controlled to avoid excessive grain growth. Interpass temperatures should typically be maintained below 150 °C for 310S to prevent sensitization.

Process Parameter Optimization Strategy

Key Technical Insights

The heat source model developed in this paper provides a foundation for predicting weld geometry, microstructure, and residual stresses in 310S TIG welds. The simulation approach enables:

1. Predictive capability: Engineers can predict the thermal cycles experienced by different regions of the weld before actual welding, allowing for proactive process optimization.
2. Parameter sensitivity analysis: The model reveals which parameters have the greatest influence on temperature distribution, guiding experimental design.
3. Virtual qualification: Simulation results can complement physical qualification tests, reducing the number of experimental trials required.

However, the accuracy of the simulation depends on the material property data used, particularly the temperature-dependent thermal conductivity, specific heat, and density of 310S. These properties must be accurately characterized over the relevant temperature range (room temperature to 2000 °C) to ensure reliable simulation results.

Study Insights and Implications

This literature demonstrates the value of numerical simulation in welding process development for high-temperature alloys. The heat source model and temperature field simulation provide quantitative insights that complement experimental observations and enable more efficient process optimization. For 310S TIG self-fusion welding, the key engineering considerations are:

• Maintaining low heat input to minimize sensitization and grain growth
• Ensuring complete fusion through appropriate current and travel speed selection
• Controlling the welding atmosphere to prevent oxidation of the hot weld surface
• Verifying corrosion resistance through intergranular corrosion testing of the weld and HAZ

The simulation approach should be validated against experimental measurements (thermocouple data, thermography) to ensure accuracy before being used for process design decisions. Engineers working with 310S and similar high-temperature austenitic stainless steels should consider integrating numerical simulation into their welding procedure development process.