CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation of Stress Field During Plug Cladding Welding Process Using ANSYS
Literature Overview and Methodology
Residual stress is one of the most critical factors affecting the service performance of cladding welds, particularly in thick-section components such as hydraulic plugs, valve bodies, and pump housings where high-integrity cladding is applied. This study employs finite element analysis (FEA) using ANSYS software to simulate the thermal-mechanical behavior during the plug cladding welding process, providing quantitative predictions of residual stress distribution that can guide process optimization and post-weld treatment decisions.
The numerical model couples thermal analysis with structural analysis to capture the sequential heating and cooling cycles inherent in multi-pass cladding welding. The thermal analysis computes temperature field evolution, while the structural analysis calculates plastic strain accumulation and residual stress development based on the temperature-dependent material properties.
Model Configuration
| Model Parameter | Description | Value / Setting |
|---|---|---|
| Geometry | Cylindrical plug, 200 mm diameter, 150 mm length | Axisymmetric 2D model |
| Cladding thickness | 6 mm total, 3 passes | Each pass 2 mm |
| Base material | 42CrMo steel | E = 206 GPa, α = 12×10⁻⁶/°C |
| Cladding material | Stellite 6 (Co-Cr-W alloy) | E = 210 GPa, α = 13×10⁻⁶/°C |
| Heat source | Double-ellipse Goldak model | q = 2.5 kW |
| Travel speed | 400 mm/min | — |
| Element type | 8-node quadratic solid (SOLID90/SOLID186) | — |
| Mesh density | 0.5 mm near weld, 2 mm far field | ~15,000 elements |
| Boundary conditions | Symmetry on axis, fixed base | — |
Core Technical Findings
Thermal Field Analysis
The thermal simulation reveals that the peak temperature at the weld pool center reaches approximately 1650°C during the first pass, decreasing to 1480°C for subsequent passes due to heat accumulation effects. The cooling rate at the weld centerline is estimated at 15–25°C/s for the first pass and 35–45°C/s for the final pass, which is critical for predicting microstructural evolution in the heat-affected zone (HAZ).
The thermal cycle at the weld toe exhibits a slower cooling rate of 8–12°C/s, which influences the dilution layer microstructure and the formation of carbide phases at the interface between the Stellite 6 overlay and the 42CrMo base metal. The temperature gradient across the cladding layer is approximately 50–80°C/mm, creating significant thermal stresses during solidification.
Residual Stress Distribution
The simulated residual stress distribution shows a characteristic pattern typical of welding processes:
- Longitudinal stress: Compressive stress develops at the weld centerline (up to -280 MPa) transitioning to tensile stress in the HAZ and base metal (up to +320 MPa).
- Circumferential stress: The circumferential stress is predominantly tensile near the weld surface, reaching +250 MPa, with compressive stress developing in the deeper base metal regions.
- Radial stress: The radial stress component is generally lower in magnitude but shows significant variation near the cladding-base metal interface, with peak values of ±180 MPa.
The multi-pass welding sequence significantly influences the final residual stress state. Each subsequent pass partially relieves the residual stress from the previous pass through thermal cycling, but the overall stress level increases with each pass due to the cumulative plastic strain accumulation.
| Stress Component | Pass 1 | Pass 2 | Pass 3 | Unit |
|---|---|---|---|---|
| Longitudinal (peak tensile) | +185 | +265 | +320 | MPa |
| Longitudinal (peak compressive) | -145 | -210 | -280 | MPa |
| Circumferential (peak tensile) | +155 | +210 | +250 | MPa |
| Radial (peak magnitude) | +95 | +140 | +180 | MPa |
Effect of Process Parameters on Residual Stress
The study systematically varies key welding parameters to assess their influence on residual stress magnitude:
- Heat input: Increasing heat input from 8 kJ/cm to 15 kJ/cm reduces peak residual stress by approximately 25–35% due to lower cooling rates and reduced thermal gradients, but increases distortion.
- Travel speed: Higher travel speeds (600 mm/min vs. 400 mm/min) increase residual stress by 20–30% due to steeper thermal gradients and faster cooling rates.
- Preheating temperature: Preheating from 100°C to 250°C reduces peak tensile stress by 15–20% by lowering the temperature differential between the weld pool and base metal.
- Interpass temperature: Maintaining interpass temperature between 150–200°C provides optimal stress relief without excessive grain coarsening in the HAZ.
Post-Weld Treatment Optimization
Based on the simulation results, post-weld stress relief treatment was evaluated to determine the optimal parameters for residual stress reduction:
| Treatment Condition | Peak Tensile Stress After Treatment | Stress Reduction (%) | Recommended |
|---|---|---|---|
| No treatment | 320 MPa | 0% | — |
| 500°C / 2h | 210 MPa | 34% | Marginal |
| 550°C / 2h | 165 MPa | 48% | Acceptable |
| 600°C / 4h | 95 MPa | 70% | Optimal |
| 650°C / 4h | 80 MPa | 75% | Risk of temper embrittlement |
The simulation confirms that stress relief at 600°C for 4 hours provides the best balance between stress reduction and avoidance of undesirable microstructural changes in the 42CrMo base metal. Temper embrittlement risk increases significantly above 620°C for this steel grade, making 600°C the practical upper limit.
Validation and Engineering Implications
The numerical simulation results were validated against experimental measurements obtained through X-ray diffraction (XRD) residual stress measurement and hole-drilling method on actual cladded plugs. The agreement between simulated and measured residual stresses was within ±40 MPa for the majority of measurement locations, confirming the reliability of the model for engineering predictions.
From an engineering practice standpoint, the key implications are:
- The predicted residual stress levels of 250–320 MPa in the cladding weld zone are significant relative to the yield strength of the base material (approximately 950 MPa for 42CrMo), representing a stress ratio of 0.26–0.34 that can influence fatigue life.
- The multi-pass welding strategy should be optimized to minimize stress accumulation, potentially through back-step welding sequences or skip welding patterns.
- Post-weld stress relief at 600°C/4h is strongly recommended to reduce residual stress below 100 MPa, significantly improving fatigue performance and dimensional stability.
- The simulation approach can be extended to predict distortion, which is critical for maintaining the geometric tolerances of precision hydraulic components after cladding.
Study Insights and Reflections
This literature demonstrates the significant value of coupled thermal-mechanical FEA in cladding welding process development. The ability to predict residual stress distributions without conducting full-scale physical experiments substantially reduces development costs and accelerates the qualification process. However, the accuracy of the simulation depends critically on the quality of input data, including temperature-dependent material properties, accurate heat source characterization, and appropriate boundary condition modeling.
A key reflection is that the simulation reveals the complex interplay between welding sequence, heat input, and residual stress development that is difficult to capture through experimental methods alone. The insight that each subsequent pass partially relieves stress from the previous pass, while simultaneously adding new stress, provides a nuanced understanding of multi-pass welding that directly informs welding sequence optimization. The practical implication is that welding sequence design should not be treated as a minor procedural detail but as a critical process variable that significantly affects the final residual stress state and, consequently, the service performance of the cladded component.
The study also underscores the importance of post-weld stress relief as a necessary step in the cladding process chain, particularly for thick-section components where residual stresses can approach or exceed the proportional limit of the base material. Without proper stress relief, the cladded component may be susceptible to stress corrosion cracking, hydrogen-assisted cracking, and premature fatigue failure under cyclic loading conditions.
In summary, this numerical simulation study provides a powerful analytical tool for cladding process optimization, enabling engineers to predict residual stress states, evaluate process parameter effects, and design effective post-weld treatment protocols with confidence, ultimately leading to improved component reliability and reduced qualification costs in industrial applications.