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

Literature Overview

This paper, published in the Journal of Shenyang Ligong University in 2017 by researchers from Shenyang Ligong University and the State Key Laboratory of Metal Science at the Institute of Metal Research, Chinese Academy of Sciences, addresses the thermal modelling of TIG self-melting welding on 310S austenitic stainless steel. The study establishes a finite element heat source model and simulates the temperature field evolution during the welding process. This work is particularly relevant to engineers working on weld overlay and cladding applications where 310S or similar high-chromium austenitic grades are deposited onto carbon steel or low-alloy steel substrates for high-temperature corrosion resistance.

Core Technical Points

The key contribution of this study is the development of a realistic heat source model that captures the non-uniform energy distribution characteristic of TIG welding. Unlike simplified point-source or Gaussian models, the authors account for the conical shape of the tungsten electrode and the spatial distribution of arc energy. The temperature field simulation reveals critical thermal parameters including peak temperature, cooling rate, and the extent of the heat-affected zone.

The 310S grade contains approximately 25% Cr and 20% Ni, with carbon content limited to 0.08% maximum to reduce sensitization risk. The simulation shows that the thermal cycle produces a narrow but deep heat-affected zone where grain boundary carbide precipitation is minimized due to the low carbon content. This is critical for engineers specifying 310S overlay layers in hydrogenation reactors and high-temperature heat exchangers where intergranular corrosion resistance is paramount.

Process and Standards Analysis

From a standards perspective, the thermal parameters derived in this simulation align with qualification requirements under NB/T 47014 and ASME IX. The cooling rate range of 5–30 °C/s falls within the acceptable window for weld overlay qualification procedures. Engineers should note that the simulated temperature field can be used to predict the dilution ratio between the 310S overlay and the base metal, which directly affects the final composition of the weld metal.

The heat input range of 15–25 kJ/cm corresponds to typical TIG welding parameters of 150–250 A with travel speeds of 3–8 cm/min. For multi-pass overlay applications, the interpass temperature should be maintained below 150 °C to prevent excessive grain coarsening in the overlay layer. The simulation also highlights the importance of preheating control — excessive preheat above 200 °C can lead to intergranular cracking in the 310S weld metal due to the high nickel content promoting sigma phase formation during slow cooling.

Integration with Engineering Practice

In practical cladding operations, the temperature field data from this study can be applied to optimize welding sequences for clad plate fabrication. For example, when applying 310S overlay to 16MnR or SA-516 Gr.70 base plates, the simulated thermal gradients help predict the bond strength at the interface. The study's findings support the use of a lower heat input for the first pass (15–18 kJ/cm) to ensure metallurgical bonding without excessive dilution, followed by subsequent passes at moderate heat input (20–25 kJ/cm) to build up the overlay thickness.

Engineers should also consider the implications for post-weld heat treatment. The thermal simulation indicates that a solution treatment at 1050–1100 °C followed by rapid water quenching can effectively dissolve any carbide precipitation at grain boundaries. This is essential for ensuring the overlay layer meets intergranular corrosion test requirements per ASTM A263 or EN 10028-7.

Key Questions and Reflections

One notable aspect of this study is the validation approach — the authors compare simulated temperature profiles with thermocouple measurements taken during actual welding trials. This experimental validation is crucial for building confidence in the model's predictive capability. However, the study does not extensively address the effect of tungsten electrode condition (dressing, contamination) on the heat source distribution, which is a practical concern in production environments.

The research also raises an important question about the applicability of the model to multi-layer overlay scenarios where thermal history accumulates from previous passes. In engineering practice, the thermal cycle experienced by the final overlay pass differs significantly from a single-pass simulation. Future work should extend the model to incorporate multi-pass sequential welding with proper thermal coupling between passes.

Study Insights and Implications

This literature provides a solid foundation for understanding the thermal behavior of 310S TIG welding, which is directly applicable to weld overlay qualification and process optimization in pressure vessel fabrication. The finite element modelling approach demonstrated here can be adapted for other austenitic grades such as 304, 316, and 347, with appropriate adjustments to thermal conductivity and specific heat. For engineers involved in bimetal pressure vessel design per GB/T 150 or ASME VIII Div.1, the ability to predict thermal fields enables more accurate assessment of residual stress distribution and potential distortion. The work underscores the value of computational modelling as a complementary tool to experimental qualification, reducing the number of physical trials required for process development while maintaining engineering rigor.