Zhuojin Pipe Fitting Co., LtdDynamic and Residual Stress Analysis During Overlay Welding of Large Frame Structures
Literature Overview
This paper by Zhong Zhiyong et al., published in the Transactions of the China Welding Institution (Volume 31, Issue 6, 2010, pages 93-96), investigates the dynamic stress evolution and residual stress distribution during overlay welding processes on large-scale frame structures at Baosteel Equipment Maintenance Co. The study compares two distinct overlay techniques—large-area laser cladding and MIG (Metal Inert Gas) overlay welding—focusing on how each process influences structural integrity through dynamic stress generation and post-weld residual stress accumulation. This work is particularly relevant for engineers dealing with heavy structural repair and surface hardening applications in the steel industry, where understanding stress behavior is critical to preventing premature failure.
Core Technical Findings
The research reveals a fundamental difference in stress-inducing capability between the two overlay processes. Laser cladding generates relatively low dynamic stresses that remain well below the yield strength of the base structure, making it a thermally gentle process suitable for precision surface modification. In contrast, MIG overlay welding produces significantly higher dynamic stresses, with the maximum tensile stress reaching 311.27 MPa at the mid-position of vertical columns—exceeding the yield strength of the material. This critical finding has direct implications for process selection in repair scenarios where dimensional stability and structural integrity are paramount.
Post-weld dimensional measurements confirmed that the structure width increased by 0.4 mm after MIG overlay welding, demonstrating measurable thermal distortion. This dimensional change, though seemingly small, can be significant in precision structural applications where fit-up tolerances are tight. The blind hole method was employed to measure residual stresses both before and after overlay welding, revealing that local residual stresses in the overlay layer increased substantially compared to original stress levels, with maximum values reaching approximately 220 MPa for both processes.
Process Comparison and Engineering Implications
| Parameter | Laser Cladding | MIG Overlay Welding |
|---|---|---|
| Dynamic stress magnitude | Low (below yield strength) | High (311.27 MPa max) |
| Stress location | Distributed | Column mid-position |
| Post-weld dimensional change | Minimal | +0.4 mm width increase |
| Residual stress increase | ~220 MPa max | ~220 MPa max |
| Thermal input | Low | High |
| Applicable area | Large surface areas | Large surface areas |
The data indicates that while both processes produce comparable residual stress levels in the overlay layer, the dynamic stress behavior during the welding process differs markedly. This distinction is crucial because dynamic stresses during welding can trigger immediate plastic deformation, crack initiation in susceptible materials, or fatigue damage accumulation. For large frame structures in the steel industry—such as blast furnace supports, rolling mill frames, or continuous casting equipment—selecting laser cladding over MIG welding may be justified when dimensional stability is a priority.
Residual Stress Management Considerations
The residual stress values of approximately 220 MPa measured post-overlay welding represent a significant concern for long-term structural performance. In service, these residual stresses superimpose on operational loads, potentially accelerating fatigue crack initiation and propagation. Engineers must consider post-weld stress relief measures, including:
- Controlled furnace stress relief annealing at appropriate temperatures for the base material
- Mechanical peening or shot peening to introduce compressive surface stresses
- Vibration stress relief (VSR) as a practical field method
- Process optimization through welding sequence planning to minimize stress accumulation
The blind hole method used in this study is a well-established technique for residual stress measurement, though it is destructive and labor-intensive. For field applications, ultrasonic methods or X-ray diffraction techniques may offer more practical alternatives for quality assurance purposes.
Study Insights and Practical Recommendations
This literature provides valuable quantitative data that supports the engineering judgment that laser cladding, despite higher equipment costs, offers superior thermal management for large structural overlay applications. The 311.27 MPa dynamic stress in MIG welding exceeding yield strength is a red flag for engineers planning repair operations on critical structures. The dimensional increase of 0.4 mm, while modest, demonstrates that even "low-energy" processes can produce measurable distortion in large frames.
For engineering practice, the following recommendations emerge from this study: First, laser cladding should be the preferred process for overlay welding on precision-critical large structures. Second, when MIG welding is unavoidable, careful welding sequence planning and interpass temperature control are essential. Third, residual stress measurement and relief should be integral components of the repair specification, not afterthoughts. The approximately 220 MPa residual stress values warrant post-weld stress relief treatment in most service applications to ensure long-term structural reliability.