CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation and Residual Stress Study of Multi-Pass Multi-Layer Overlay Forming
Literature Overview
This paper by Zhang Xue, Xia Yufeng, Teng Haihao, Peng Mengxia, and Jin Li, published in the Journal of Mechanical Science and Technology in 2023, presents a comprehensive numerical simulation study of multi-pass multi-layer overlay welding forming processes. The research was conducted at the School of Materials Science and Engineering, Chongqing University, and was supported by the National Natural Science Foundation of China (Project No. 51775068). The work addresses the critical challenge of predicting and controlling residual stresses in multi-pass overlay welds, which directly affect the service life and reliability of cladded components.
Core Technical Content and Simulation Methodology
The numerical simulation employs a coupled thermal-mechanical finite element analysis approach, which is essential for accurately capturing the complex stress evolution in multi-pass overlay welding. The simulation methodology involves several key components:
Simulation Parameters and Material Properties
| Parameter | Value / Range | Notes |
|---|---|---|
| Welding current | 250-350 A | GMAW overlay |
| Arc voltage | 25-32 V | GMAW overlay |
| Travel speed | 350-500 mm/min | Multi-pass |
| Number of passes per layer | 4-8 | Depends on width |
| Number of layers | 3-10 | Depends on thickness |
| Heat source model | Double-ellipsoidal (Goldak) | Accounts for front/rear heat distribution |
| Thermal conductivity | Temperature-dependent | Base metal and overlay metal |
| Yield strength | Temperature-dependent | Elastic-plastic analysis |
| Thermal expansion coefficient | Temperature-dependent | Residual stress calculation |
The simulation employs a Goldak double-ellipsoidal heat source model that accounts for the asymmetric heat distribution in GMAW welding. The front half of the heat source has a smaller radius and higher intensity than the rear half, which accurately represents the actual heat input distribution in arc welding. The material properties are temperature-dependent, incorporating the effects of thermal softening, phase transformations, and plastic deformation.
Residual Stress Distribution Patterns
The simulation results reveal several important residual stress patterns in multi-pass multi-layer overlay welds:
- Longitudinal residual stresses: Compressive stresses develop in the weld metal centerline, while tensile stresses appear at the weld edges. The magnitude of tensile stresses can reach 200-350 MPa in the overlay layer, depending on the number of passes and layers.
- Transverse residual stresses: These are generally lower than longitudinal stresses but can still reach 100-250 MPa. The transverse stress distribution is more symmetric about the weld centerline.
- Through-thickness stress gradients: The stress distribution varies significantly through the overlay layer thickness, with the highest tensile stresses typically occurring near the surface and at the interface between the overlay layer and base metal.
- Stress relaxation effects: Subsequent passes partially relax the residual stresses from previous passes, but the cumulative effect of multiple passes leads to a complex stress state that is not simply additive.
Key Simulation Results
| Parameter Variation | Effect on Peak Residual Stress | Effect on Compressive Stress Zone |
|---|---|---|
| Increasing current (250→350 A) | Peak stress increases 15-25% | Compressive zone widens |
| Increasing travel speed (350→500 mm/min) | Peak stress decreases 10-20% | Compressive zone narrows |
| Increasing number of layers (3→10) | Peak stress increases 20-30% | Stress distribution becomes more complex |
| Increasing overlap ratio (0.4→0.6) | Peak stress decreases 5-10% | More uniform stress distribution |
| Post-weld stress relief (600°C/2h) | Peak stress reduces 40-60% | Compressive zone preserved |
Engineering Practice and Residual Stress Management
For overlay welding engineers, the simulation results provide critical guidance for residual stress management in multi-pass overlay operations. The following strategies are recommended based on the simulation findings:
- Weld sequence optimization: Welding from the center outward or using a symmetric sequence can reduce peak residual stresses by distributing heat input more evenly.
- Interpass temperature control: Maintaining interpass temperatures between 150-250°C allows for partial stress relaxation without excessive grain growth.
- Post-weld heat treatment: A stress relief treatment at 600°C for 2 hours can reduce residual stresses by 40-60% while preserving the overlay layer microstructure.
- Peening and rolling: Mechanical post-weld treatments can introduce beneficial compressive surface stresses that improve fatigue resistance.
The simulation also highlights the importance of the overlay-base metal interface. The coefficient of thermal expansion mismatch between the overlay layer and base metal creates interfacial stresses that can lead to delamination or cracking. For example, a stainless steel overlay on carbon steel produces interfacial stresses of approximately 150-250 MPa, while a nickel-based overlay on carbon steel can produce stresses exceeding 300 MPa due to the larger thermal expansion coefficient difference.
Comparison of Stress Relief Methods
| Method | Temperature (°C) | Time (h) | Stress Reduction (%) | Risk of Overlay Degradation |
|---|---|---|---|---|
| Furnace stress relief | 550-650 | 2-4 | 50-70 | Low if properly controlled |
| Induction stress relief | 500-600 | 0.5-1 | 30-50 | Medium |
| Shot peening | N/A | N/A | 20-40 (compressive) | Low |
| Vibratory stress relief | N/A | 1-2 | 20-35 | Low |
| Water quenching (local) | N/A | N/A | 10-20 | High risk of cracking |
Critical Reflections and Study Insights
This numerical simulation study provides valuable insights into the residual stress behavior of multi-pass multi-layer overlay welds. The coupled thermal-mechanical approach is essential for capturing the complex stress evolution, and the results are consistent with experimental measurements reported in the literature. However, several important limitations must be considered.
First, the simulation assumes perfect material properties and does not account for microstructural evolution during welding, such as grain growth, phase transformations, and precipitate coarsening. These microstructural changes significantly affect the mechanical properties and, consequently, the residual stress distribution. Second, the model assumes elastic-plastic behavior but does not incorporate viscoplastic effects, which are important at high temperatures during welding. Third, the simulation does not account for the effects of hydrogen diffusion, which can contribute to residual stress through hydrogen-induced cracking and delayed cracking mechanisms.
The practical implication is that numerical simulation should be used as a complementary tool to experimental measurement and non-destructive testing. Engineers should validate simulation results with residual stress measurements using X-ray diffraction, neutron diffraction, or hole-drilling methods on actual overlay welds. The combination of simulation and experimental verification provides the most reliable basis for overlay welding process optimization and quality control.
This study exemplifies the growing importance of computational methods in overlay welding technology. As simulation capabilities continue to advance, engineers will be able to design and optimize overlay welding processes with greater confidence and reduced trial-and-error costs. The integration of simulation with real-time process monitoring and adaptive control systems represents the future direction of intelligent overlay welding technology.