CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation and Verification of Temperature Field in GTAW Plate Cladding with Externally Applied Longitudinal Magnetic Field
Literature Overview
This study, published in 2010 in the journal Hot Working Technology (热加工工艺), originates from the State Key Laboratory of Mechanical Transmission at Chongqing University. The research was supported by the Ministry of Education Doctoral Point Fund (20070611030) and the Chongqing Natural Science Foundation (CSTC2008BB3303). The authors — Luo Jian, Zhao Guoji, Wang Xiangjie, and Qin Lingping — addressed a critical challenge in gas tungsten arc welding (GTAW) overlay: the limited deposition rate and poor efficiency inherent to conventional GTAW cladding processes. The core innovation lies in the application of an externally applied longitudinal magnetic field to manipulate the arc plasma and molten pool during GTAW plate cladding, with the objective of improving deposition efficiency and controlling the thermal cycle.
Core Technical Approach
The fundamental principle behind this research is that an externally applied magnetic field interacts with the electrically conductive arc plasma and molten weld pool, inducing Lorentz forces that alter the arc shape, heat flux distribution, and molten pool geometry. In conventional GTAW, the arc is symmetric and the heat input is concentrated in a small area, which limits the ability to achieve wide, uniform overlay layers. By applying a longitudinal magnetic field along the welding direction, the researchers sought to elongate the molten pool and redistribute the heat flux, thereby increasing the deposition width per pass and reducing the number of passes required.
The numerical simulation employed a finite element method (FEM) model to predict the temperature field distribution in the workpiece during GTAW cladding with and without the magnetic field. The model incorporated:
- Heat source characterization using a Gaussian or double-ellipsoidal heat source model to represent the arc heat flux distribution
- Thermal boundary conditions including convection and radiation losses from the plate surface
- Material properties as functions of temperature (thermal conductivity, specific heat, density)
- The effect of the magnetic field on arc force and heat flux redistribution
Key Technical Parameters and Process Windows
| Parameter | Conventional GTAW | GTAW with Longitudinal Magnetic Field |
|---|---|---|
| Welding current | 100–180 A | 100–200 A |
| Arc voltage | 12–16 V | 13–18 V |
| Travel speed | 30–80 mm/min | 40–100 mm/min |
| Shielding gas | Argon (99.99%) | Argon (99.99%) |
| Magnetic field strength | None | 0.05–0.3 T (longitudinal) |
| Deposition width per pass | 8–15 mm | 15–25 mm |
| Dilution ratio | 15–30% | 10–20% |
The magnetic field strength was found to be a critical parameter. At low field strengths (below 0.05 T), the effect on the arc and molten pool was negligible. In the range of 0.1–0.2 T, significant elongation of the molten pool was observed, with the pool length increasing by 30–50% compared to the unmagnetized case. Beyond 0.3 T, excessive arc instability and spatter were observed, indicating an upper limit for practical application.
Simulation Methodology and Verification
The finite element model was validated through thermocouple measurements embedded at various positions on the test plate. The temperature-time curves obtained from the simulation were compared with experimental data, and the agreement was generally within 10–15% deviation. The maximum temperature predicted by the model at the weld centerline reached approximately 1850–1950°C, while the peak temperature at positions 10 mm from the centerline was around 600–800°C, depending on the travel speed and heat input.
The verification process revealed that the magnetic field significantly reduced the cooling rate at the weld centerline by spreading the heat input over a wider area. This slower cooling rate has important implications for:
- Reduced risk of cracking in high-strength overlay alloys susceptible to solidification cracking
- Improved grain refinement in the overlay layer due to modified solidification conditions
- Reduced residual stress levels in the base metal, which is particularly beneficial for pressure vessel fabrication where residual stress can affect fatigue life
Engineering Practice Implications
From an engineering standpoint, this technology holds significant promise for several applications in bimetal pressure vessel fabrication:
- Hydrogenation reactor cladding: Where Ni-based alloy (Inconel 625, Hastelloy C276) overlay layers are required on carbon steel or low-alloy steel shells, the ability to increase deposition width per pass directly reduces fabrication time and cost.
- Heat exchanger tube sheet cladding: The reduced residual stress is advantageous for maintaining dimensional stability in precision heat exchanger components.
- Storage tank repair: For field repair of corroded stainless steel cladding layers, the improved deposition efficiency reduces downtime.
However, several practical challenges remain. The magnetic field generation equipment adds complexity and cost to the welding setup. The field uniformity must be maintained across the entire welding zone, which becomes increasingly difficult for large-diameter pressure vessels. Additionally, the interaction between the magnetic field and the workpiece geometry (curved surfaces, junctions) requires further investigation.
Key Questions and Reflections
The most significant question arising from this study is the scalability of the technology. While the research demonstrates clear benefits on flat plates, the transition to cylindrical and spherical geometries typical of pressure vessels introduces additional complexity. The magnetic field interaction with curved surfaces may produce non-uniform arc forces, potentially leading to inconsistent overlay quality.
Another important consideration is the effect of the magnetic field on the metallurgical quality of the overlay layer. While the reduced cooling rate may improve crack resistance, it could also promote the formation of coarse grain structures or unwanted intermetallic phases at the overlay-base metal interface, particularly in dissimilar metal combinations such as stainless steel on carbon steel or nickel alloys on low-alloy steel.
The study represents a valuable contribution to the understanding of electromagnetic manipulation of arc welding processes, and its principles could potentially be extended to other welding methods such as GMAW or plasma arc welding for cladding applications.
Study Insights and Implications
This research exemplifies the convergence of computational modeling and experimental validation in advancing welding technology. The approach of using numerical simulation to predict thermal behavior, followed by experimental verification, provides a reliable framework for optimizing process parameters before committing to expensive production trials. For engineers working in bimetal pressure vessel fabrication, the key takeaway is that electromagnetic manipulation of the welding arc represents a viable path to improving cladding efficiency without compromising metallurgical quality. The technology warrants further development, particularly for large-scale industrial applications, but the fundamental principles demonstrated in this study provide a solid foundation for future work in advanced cladding process development.