Zhuojin Pipe Fitting Co., LtdHeat Source Modeling and Temperature Field Simulation of TIG Autogenous Welding of 12 mm 310S Austenitic Stainless Steel
Literature Overview
This paper by Liu Zhaoquan, Zhang Yutuo, and Dong Wenchao, published in the Journal of Shenyang Ligong University (2017, Vol. 36, No. 5, pp. 53-56), presents a numerical simulation study of the TIG autogenous welding process for 12 mm thick 310S austenitic stainless steel plates. The research was conducted using the SYSWELD finite element software, with the authors affiliated with Shenyang Ligong University and the Shenyang National Laboratory for Metal Materials at the Institute of Metal Research, Chinese Academy of Sciences. The work addresses a practical engineering challenge: predicting and controlling the thermal cycle and weld geometry for thick-section high-alloy stainless steel welding.
310S Stainless Steel: Material Characteristics and Welding Challenges
310S is a high-temperature austenitic stainless steel with a nominal composition of approximately 25% Cr and 20% Ni, with low carbon content (C ≤ 0.08%). This composition provides exceptional oxidation resistance at elevated temperatures (up to 1150 °C) but introduces significant welding challenges:
| Property | Typical Value | Welding Implication |
|---|---|---|
| Thermal conductivity | ~15 W/(m·K) | High heat input required; broad HAZ |
| Thermal expansion coefficient | ~18 × 10⁻⁶ /K | High residual stress and distortion |
| Solidification range | Narrow (austenitic) | Low hot cracking susceptibility |
| Recrystallization temperature | ~450 °C | Grain growth risk in HAZ |
| Carbon content | ≤ 0.08% | Reduced sensitization risk vs. 310 |
The 12 mm plate thickness represents a substantial section that requires either multi-pass welding or high-current single-pass welding, both of which produce significant thermal cycles that must be accurately predicted for process optimization.
SYSWELD Simulation Methodology
The authors established a comprehensive material property database for 310S stainless steel within the SYSWELD software environment. This database includes temperature-dependent thermal conductivity, specific heat capacity, density, and Young's modulus, which are critical inputs for accurate thermal and mechanical simulation.
Double-Ellipsoidal Heat Source Model
The heat source was modeled using a double-ellipsoidal distribution, which represents the TIG arc as two semi-ellipsoidal volumes: a front section (higher energy density) and a rear section (lower energy density). This model is widely accepted for TIG welding because it captures the characteristic deep, narrow weld profile produced by the constricted arc.
The key parameters of the double-ellipsoidal model include:
- Front ellipsoid semi-axes: a_f, b_f, c_f
- Rear ellipsoid semi-axes: a_r, b_r, c_r
- Energy distribution ratio: q_f and q_r (where q_f + q_r = 1)
- Total power input: Q (derived from welding current and voltage)
The front-to-rear energy ratio (q_f/q_r) is typically set between 0.5 and 0.8 for TIG welding, reflecting the asymmetric energy deposition where the arc concentrates more energy ahead of the travel direction due to the arc's tilting effect.
Boundary Conditions
The simulation incorporated convection and radiation as the primary heat exchange mechanisms between the workpiece and the surrounding environment. This is appropriate for TIG welding of thick plates where the arc is not shielded by a gas nozzle in the simulation domain, and the workpiece surface is exposed to ambient conditions.
Simulation Results and Validation
The simulation outputs were validated against experimental results through comparison of:
- Weld cross-sectional geometry: The simulated weld bead profile (width, depth, reinforcement) was compared with macrographically sectioned experimental welds.
- Welding thermal cycle curves: The simulated temperature-time histories at various locations (weld center, HAZ, base metal) were compared with thermocouple measurements from experimental welds.
The authors report that the double-ellipsoidal heat source model fitted the experimental data well, with reasonable parameter selections. This validation is critical because the accuracy of temperature field predictions directly affects the reliability of subsequent mechanical and metallurgical predictions.
Engineering Implications for Thick-Section 310S Welding
The temperature field simulation provides valuable insights for practical welding operations:
- Preheat temperature optimization: The simulation can predict the base metal temperature at the time of weld initiation, enabling preheat temperature selection to control the peak temperature and cooling rate.
- Interpass temperature control: For multi-pass welding, the simulation can predict the thermal state of previously deposited weld metal, guiding interpass temperature limits to prevent excessive grain growth.
- Distortion prediction: The temperature field serves as input for residual stress and distortion analysis, which is essential for thick-plate fabrication where angular and longitudinal distortion can exceed acceptable tolerances.
Key Questions and Reflections
The study demonstrates the value of numerical simulation for TIG welding process design, but several questions remain for practical application. First, the double-ellipsoidal model, while validated for the specific conditions studied, may not accurately capture the thermal behavior during full-position welding where arc force and gravity interact differently. Second, the material property database for 310S is relatively limited in the literature, and temperature-dependent properties above 1000 °C are particularly uncertain. Third, the simulation does not account for the effect of the tungsten electrode geometry on arc energy distribution, which can be significant for TIG welding.
For engineering practice, the key takeaway is that numerical simulation should be used as a complementary tool to experimental welding, not as a replacement. The simulation provides a framework for understanding thermal behavior, but actual welding trials remain essential for validating process parameters and ensuring weld quality.
Study Insights and Implications
This research contributes a validated thermal simulation model for TIG autogenous welding of thick-section 310S stainless steel, which is particularly valuable given the limited availability of material property data for this high-alloy grade. The successful application of the double-ellipsoidal heat source model demonstrates that standard finite element approaches can effectively predict the thermal behavior of TIG welding for high-temperature austenitic stainless steels. Engineers working on thick-plate 310S fabrication should consider incorporating numerical simulation into their process development workflow to reduce trial-and-error costs and improve first-pass weld quality.