Zhuojin Pipe Fitting Co., LtdComputer Simulation of Residual Stress Field in Overlay Welding
Literature Overview
This paper by Yang Qingxiang, Li Yanli, Zhao Yanhui, and Yao Mei from Yanshan University (2001) presents a combined experimental and numerical investigation into the residual stress distribution in overlay welds deposited on 60CrMnMo steel substrates. The work was funded by the Doctoral Point Fund of Higher Education Institutions and the State Key Laboratory of Modern Welding Production Technology. The study employs X-ray diffraction measurement (AST-type analyzer) for experimental validation and ANSYS finite element analysis for simulation, incorporating the effects of martensitic phase transformation, temperature-dependent elastic modulus, and thermal expansion.
Core Technical Findings
The most striking experimental observation is the presence of two distinct residual tensile stress peaks: one at the center of the overlay weld metal and another in the heat-affected zone near the fusion boundary. This dual-peak phenomenon is not trivial—it reflects the complex interplay between thermal contraction of the weld metal, plastic deformation in the base metal near the fusion line, and the austenite-to-martensite phase transformation in the 60CrMnMo substrate.
The finite element model considered several physically significant factors that distinguish it from simpler thermal stress calculations:
| Parameter Considered | Physical Significance |
|---|---|
| Martensitic transformation | Accommodates volumetric expansion during phase change, modifying stress state |
| Temperature-dependent Young's modulus | Captures elastic stiffness variation during heating and cooling cycles |
| Thermal expansion coefficient | Accounts for differential contraction between weld and base metal |
| Plastic deformation | Models irreversible strain accumulation during thermal cycling |
The comparison between simulated and measured residual stress fields showed good agreement, validating the model. A particularly useful parametric study examined how specimen dimensions influence the residual stress distribution. The results demonstrated that as specimen size increases, the peak residual stress magnitude increases and the peak location shifts—this is directly attributable to the reduced constraint effect in larger specimens, allowing more localized plastic deformation near the weld.
Technical Interpretation and Engineering Relevance
The dual-peak residual stress pattern has direct implications for service performance. The tensile peak near the fusion boundary is particularly concerning because it coincides with the zone most susceptible to hydrogen-induced cracking and stress-corrosion cracking in 60CrMnMo-type steels. In engineering practice, this means that post-weld heat treatment (PWHT) or mechanical peening strategies should be specifically targeted at the fusion line region.
The dimension effect finding is practically important for component design. When overlay welding is applied to large, thick-walled components (such as turbine disks or pressure vessel heads), the higher constraint leads to elevated residual stresses that may exceed the material's yield strength in the as-welded condition. Engineers must account for this in residual stress management strategies—either through design modifications (stress-relief notches, reduced weld size) or through post-processing (PWHT at 600-650°C for 2-4 hours for this steel grade).
Key Questions and Reflections
Several questions emerge from this study that remain relevant to modern practice. First, the model treats the overlay as a single-layer deposition, whereas actual multi-pass overlay welding creates a more complex thermal history with interpass heating effects. Second, the study does not address the effect of welding sequence on the final stress state—a critical factor when overlaying large areas. Third, the material model for the base metal appears to use a simplified approach to the phase transformation, which may not fully capture the kinetics of martensite formation during the non-equilibrium cooling rates encountered in welding.
The study's methodology—combining X-ray measurement with finite element simulation—remains a gold standard for residual stress characterization. Modern FEA codes offer more sophisticated material models (such as the Koçak model for phase transformation plasticity), but the fundamental approach of this paper remains valid and instructive.
Study Insights and Implications
This paper serves as an excellent example of how computational modeling can supplement limited experimental measurement. In industrial settings, X-ray stress measurement is time-consuming and spatially limited; finite element simulation provides the full three-dimensional stress field and enables parametric studies that would be impractical experimentally. For engineers working on overlay repair of critical components—such as pump impellers, valve trim, or nuclear reactor internals—understanding the residual stress state is essential for predicting service life and preventing premature failure. The validated model developed here provides a framework that can be adapted to modern software platforms with improved material constitutive laws, making it a valuable foundation for contemporary residual stress analysis in overlay welding applications.