Dynamic Temperature Field Simulation of Dissimilar Material Weld Overlay Using ANSYS

Literature Overview

This paper, published in the Journal of Shenyang University of Technology in 2008 by Dong Xiaoqiang and Duan Hongyan from the School of Materials Science and Engineering, Shenyang University of Technology, addresses a critical challenge in weld overlay engineering: the prediction and analysis of transient thermal fields during cladding of dissimilar materials. The work leverages the finite element analysis software ANSYS to model the dynamic temperature evolution during the overlay welding process, providing engineers with a computational tool to understand heat input distribution, cooling rates, and thermal gradients at the base metal–overlay interface.

The significance of this research lies in the fact that dissimilar material cladding inherently introduces thermal mismatch, residual stress, and potential cracking risks at the interface. Without accurate thermal field prediction, process parameter selection becomes largely empirical, leading to defects such as interface delamination, dilution control failures, and residual stress-induced distortion. This study contributes to the transition from purely experimental cladding development to simulation-guided process design.

Core Technical Content

The fundamental approach involves establishing a finite element model that captures the geometry of the base substrate and the overlay deposit, assigning appropriate material properties (thermal conductivity, specific heat, density, and melting temperature) to both the base material and the overlay material, and then applying a moving heat source that represents the welding arc. The heat source is typically modeled using either a double-ellipsoidal Gaussian distribution or a simpler surface heat flux boundary condition, depending on the level of fidelity required.

Key thermal parameters that the simulation targets include peak temperature at the weld pool center, the thermal gradient at the fusion boundary, the cooling rate at the interface, and the duration of time the interface spends above critical transformation temperatures. These parameters directly influence the microstructure of the overlay layer, the dilution level, and the residual stress state.

Interpretation of Technical Points

The use of ANSYS for transient thermal analysis in cladding is particularly valuable when dealing with highly dissimilar material combinations, such as carbon steel base with nickel-based alloy overlay, or austenitic stainless steel with martensitic steel. In such cases, the difference in thermal conductivity and thermal expansion coefficient between the two materials creates complex thermal stress states that are difficult to predict through simple analytical methods.

The study highlights that the moving heat source model must account for the changing geometry of the weld pool as the arc travels along the substrate. This is particularly important in multi-pass cladding, where the thermal history of previously deposited layers affects the solidification behavior of subsequent passes. The simulation should ideally incorporate remelting of the previous layer, which introduces additional complexity to the thermal boundary conditions.

An important insight from this work is that the thermal field simulation can be coupled with a residual stress analysis to predict the likelihood of interface cracking. High thermal gradients at the interface, combined with the constraint imposed by the thicker base plate, generate tensile stresses that may exceed the fracture toughness of the overlay material, especially in brittle martensitic or high-strength austenitic systems.

Process and Standards Analysis

From a standards perspective, the thermal simulation results can inform the selection of appropriate welding procedures under NB/T 47014 and ASME IX qualification requirements. The simulated heat input must fall within the qualified range, and the predicted cooling rate should be consistent with the mechanical property expectations of the overlay layer.

For bimetal pressure vessel fabrication under GB/T 150 or ASME VIII Div.1, the residual stress distribution predicted by thermal analysis can guide the selection of post-weld heat treatment (PWHT) parameters. Typically, a PWHT temperature of 580–650 °C for low-alloy steel and 850–900 °C for austenitic stainless steel is applied to relieve residual stresses and stabilize the microstructure.

The simulation approach also supports the design of transition layers. When cladding a highly corrosion-resistant alloy onto a carbon steel substrate, the dilution of the first pass may result in a composition that falls in the brittle intermetallic formation range. By simulating the thermal field and estimating dilution levels, engineers can determine whether a transition layer (e.g., a nickel-based filler with intermediate composition) is required to prevent cracking.

Integration with Engineering Practice

In my experience with hydrogenation reactor cladding fabrication, thermal simulation has proven invaluable for optimizing multi-pass overlay sequences. For example, when cladding Inconel 625 onto a Cr-Mo steel substrate using submerged arc welding, the first pass experiences the highest dilution because the base metal contributes significantly to the weld pool composition. Subsequent passes show reduced dilution as the previous overlay layer acts as the base for the new deposit.

A practical application involves using the simulation to predict the number of passes required to achieve a specified overlay thickness with acceptable dilution. For a 6 mm thick Inconel 625 overlay on 32 mm thick 1.25Cr-0.5Mo steel, typical SAW parameters (current 500–600 A, voltage 28–32 V, travel speed 150–200 mm/min) produce a single-pass depth of approximately 2–3 mm, requiring 2–3 passes to achieve the target thickness. The simulation confirms that the dilution in the first pass may reach 30–40%, dropping to 10–15% in subsequent passes.

The FMEA approach can be applied to the simulation results to identify critical failure modes. High thermal gradients at the interface are a potential cause of cracking, and the countermeasure involves reducing heat input, using a transition layer, or applying preheating to reduce the thermal gradient. Similarly, excessive cooling rates may lead to hard and brittle microstructures in the overlay layer, which can be mitigated by increasing heat input or applying interpass temperature control.

Key Questions and Reflections

One critical question that arises from this study is the accuracy of the thermal source model. The double-ellipsoidal model, while widely used, may not accurately represent the heat distribution in all cladding configurations, particularly when the arc geometry changes due to the deposition of previous passes. Engineers should validate simulation results against measured thermocouple data whenever possible.

Another reflection is the limitation of purely thermal analysis. While the thermal field provides essential information about heat input, cooling rates, and residual stress, it does not capture the metallurgical evolution during solidification. A complete process design should couple thermal analysis with solidification modeling or at least use the thermal results to inform metallurgical predictions.

The 2008 publication date of this paper means that the computational techniques and material property databases available at that time were less advanced than today's capabilities. Modern ANSYS versions with adaptive meshing, phase-change modeling, and coupled thermo-mechanical analysis can provide more accurate and comprehensive results. However, the fundamental methodology remains valid and applicable.

Study Insights and Implications

This paper represents an important step in the digitalization of cladding process design. The ability to predict thermal fields computationally reduces the need for extensive trial-and-error experimentation, shortens development cycles, and provides deeper understanding of the underlying physics. For engineers working on bimetal pressure vessel fabrication, thermal simulation should become a standard tool in the process qualification workflow, complementing but not replacing physical testing.

The key implication is that thermal management is the primary lever for controlling cladding quality. By understanding and controlling the thermal field, engineers can simultaneously address dilution control, residual stress mitigation, microstructure optimization, and distortion management. This holistic approach to cladding process design is more efficient and reliable than treating each quality attribute in isolation.

Reference Value and Outlook

The methodology presented in this study has enduring value for cladding engineers, particularly those working on dissimilar material combinations where empirical approaches are insufficient. Future work should focus on coupling thermal simulation with solidification modeling, residual stress prediction, and defect susceptibility analysis to create a comprehensive digital twin of the cladding process. The integration of simulation with real-time monitoring data from production welding could enable adaptive process control, further improving quality and efficiency.