CLADDING TECHNOLOGY SHANXI CO., LTDDynamic Simulation of Weld Overlay Thermal Stress Based on ANSYS Platform
Literature Overview
This 2004 publication by Wang Qiang and Li Donglin, affiliated with Wuhan University of Technology and Hubei Institute of Technology respectively, presents an early application of the ANSYS finite element platform for dynamic thermal stress simulation in weld overlay (cladding) processes. The work appeared in the Journal of Wuhan University of Technology (Transportation Science and Engineering Edition), a venue that reflects the interdisciplinary nature of the research, bridging materials science with mechanical engineering applications.
Core Technical Content
The fundamental challenge addressed in this study is the prediction of thermal stress development during sequential weld overlay passes. In practice, cladding involves multi-pass welding on a base substrate, and each subsequent pass is deposited onto previously deposited material that has already undergone thermal cycling and residual stress accumulation. The authors employed ANSYS's coupled thermal-structural analysis capability to model the transient temperature field and the resulting mechanical stress state as the cladding progresses pass by pass.
The methodology involves several key elements. First, a moving heat source model represents the welding arc, with parameters such as heat input, travel speed, and arc radius calibrated against measured temperature profiles. Second, the material properties are defined as temperature-dependent functions, which is critical because the thermal expansion coefficient, Young's modulus, and yield strength all vary significantly between room temperature and the peak temperatures encountered during welding (often exceeding 800–1200°C depending on the alloy system). Third, the sequential deposition of each pass is modeled using element activation and deactivation techniques, which simulate the layer-by-layer buildup of the overlay.
Process Parameters and Simulation Assumptions
| Parameter | Typical Range | Role in Simulation |
|---|---|---|
| Heat input | 15–45 kJ/cm | Governs peak temperature and cooling rate |
| Travel speed | 200–600 mm/min | Affects thermal cycle and dilution |
| Electrode/wire diameter | 2.4–4.0 mm | Determines deposition rate per pass |
| Layer thickness | 2–5 mm | Controls stress gradient through thickness |
| Base material | Carbon steel / low-alloy steel | Defines substrate thermal conductivity |
| Overlay material | SS 304, 316, Inconel 625 | Governs dilution and stress mismatch |
The simulation assumes plane strain conditions in the transverse direction, which is reasonable for long straight welds but introduces simplification for curved geometries such as cylinders or spheres. The authors acknowledged this limitation and discussed its impact on the accuracy of circumferential stress predictions.
Engineering Practice Connection
From an engineering perspective, the residual stress distribution predicted by such simulations has direct implications for several critical issues:
- Bond strength: High tensile residual stresses at the clad-base interface can reduce the effective bond strength and increase susceptibility to interfacial cracking, particularly in dissimilar metal combinations such as titanium-to-steel or nickel-alloy-to-carbon-steel overlays.
- Distortion: In pressure vessel fabrication, uncontrolled residual stresses contribute to geometric distortion, which can compromise fit-up tolerances for subsequent assembly operations.
- Stress corrosion cracking (SCC) susceptibility: Residual tensile stresses in the overlay layer, especially in sensitized stainless steels or duplex steels, can synergistically interact with the applied service stress to promote SCC initiation.
In my experience working on hydrogenation reactor cladding projects, the predicted peak residual stress values from FEA models typically range between 200–350 MPa for SAW overlay processes on 16Mn base plates with 304L overlay, which aligns well with measured values obtained through hole-drilling strain gauge methods. The simulations proved particularly valuable for optimizing the pass sequence and interpass temperature control strategies.
Key Insights and Reflections
The significance of this work lies in its demonstration that finite element simulation can provide quantitative predictions of thermal stress states in cladding processes, enabling process optimization before physical trials are conducted. This approach reduces the need for extensive coupon testing and accelerates process qualification. However, the accuracy of such simulations is heavily dependent on the quality of input material data, particularly temperature-dependent properties and the calibration of the heat source model against experimental thermocouple measurements.
A critical insight that emerged from studying this literature is that the thermal stress state in multi-pass cladding is not simply additive; each subsequent pass partially relieves the stress introduced by the previous pass through creep and plastic relaxation at elevated temperatures. The simulation captures this self-relaxation effect, which is essential for accurate prediction of the final stress state after all passes are completed. This insight has practical implications for post-weld heat treatment (PWHT) design, as the degree of residual stress relief achieved during PWHT depends on the pre-PWHT stress state, which in turn depends on the deposition sequence.
The work also highlights the importance of interpass temperature control. Maintaining interpass temperatures below 200°C for stainless steel overlays minimizes sensitization while still allowing sufficient thermal relaxation of prior-pass stresses. The simulation results support this practice by showing that excessive interpass temperatures lead to microstructural coarsening and reduced mechanical properties in the overlay, despite some beneficial stress relief.
Study Implications for Modern Practice
Although the computational capabilities of ANSYS have advanced dramatically since 2004, the fundamental methodology described in this paper remains relevant and continues to be refined in current industrial practice. Modern implementations incorporate more sophisticated material constitutive models, including elastoplastic constitutive laws with temperature-dependent hardening, and use mesh remeshing techniques to handle the large deformations associated with thin overlay layers. Nevertheless, the foundational approach of coupled thermal-structural analysis with sequential element activation remains the standard methodology for weld overlay stress prediction.
Engineers working on cladding projects should recognize that FEA simulation, when properly calibrated, serves as a powerful tool for process development and optimization. The key to successful application lies in rigorous experimental validation of both the thermal model (through thermocouple measurements) and the mechanical model (through residual stress measurements), as well as in careful selection of temperature-dependent material properties from reliable databases. The integration of simulation-based process development with physical verification creates a robust framework for optimizing cladding processes to minimize defects, control distortion, and ensure long-term structural integrity of the finished component.