Zhuojin Pipe Fitting Co., LtdMulti-Field Coupled Numerical Simulation of Submerged Arc Overlay Welding Process on Rolling Mill Rolls
Literature Overview
Published in the journal of Surface Engineering of China (Zhongguo Mianceng Gongcheng) in 2021, Vol. 34, No. 4, pp. 117–128, this paper by Li Chang, Huang Qingchun, Chen Xinxue, Liu Zhaotai, and Han Xing from Liaoning University of Science and Technology presents a comprehensive multi-field coupled numerical simulation of the submerged arc overlay welding process on rolling mill rolls. Supported by multiple funding sources including the National Natural Science Foundation, the Ministry of Public Security Fire Key Laboratory, and Liaoning Provincial Science and Technology programs, the research establishes a thermal-elastic-plastic-fluid multi-field coupled model to analyze the temperature field, stress field, and flow field evolution during the welding process.
Research Background and Motivation
Submerged arc overlay welding is a critical repair method for rolling mill rolls in the metallurgical industry. However, most existing research focuses on single-field analysis, examining either the temperature field or the stress field in isolation. The flow field within the weld pool, which is governed by the complex interplay of electromagnetic forces, temperature gradients, and fluid dynamics, has received minimal attention despite its significant influence on weld pool morphology, microstructure, and defect formation. This research addresses this gap by developing a multi-field coupled model that simultaneously captures the thermal, mechanical, and fluid dynamic aspects of the welding process.
Multi-Field Coupled Modeling Approach
The authors established a thermal-elastic-plastic-fluid multi-field coupled model based on the theory of thermo-elasto-plasticity and computational fluid dynamics (CFD). The model captures the evolution of three interrelated fields:
| Field | Governing Physics | Key Parameters | Impact on Weld Quality |
|---|---|---|---|
| Temperature field | Heat conduction, convection, radiation | Thermal conductivity, heat input, boundary conditions | Determines solidification rate, microstructure |
| Stress field | Elastic-plastic deformation, thermal expansion | Yield strength, elastic modulus, thermal expansion coefficient | Controls residual stress, cracking tendency |
| Flow field | Fluid dynamics, electromagnetic forces | Surface tension, electromagnetic force, buoyancy | Determines weld pool shape, mixing, microstructure homogeneity |
The multi-field coupling is achieved through the interaction between the fields: temperature gradients drive buoyancy-induced flow, electromagnetic forces generate Lorentz forces that drive flow, and the flow field influences heat and mass transfer within the weld pool. This coupled approach provides a more realistic representation of the welding process than single-field models.
Flow Field Analysis
The flow field within the submerged arc weld pool is governed by three primary driving forces: surface tension, electromagnetic force, and buoyancy. Each force contributes differently to the flow pattern and, consequently, to the weld pool morphology and microstructure.
Surface Tension Effect
Surface tension acts at the weld pool surface, driving flow from regions of high surface tension to regions of low surface tension. Since surface tension decreases with increasing temperature, this creates a flow pattern from the cooler regions of the pool toward the hotter center, known as Marangoni convection. The direction and magnitude of Marangoni convection depend on the surface tension coefficient and its temperature gradient.
Electromagnetic Force Effect
The electromagnetic force, or Lorentz force, is generated by the interaction between the welding current and the magnetic field it induces. This force acts primarily in the radial direction, driving flow outward from the center of the weld pool. The magnitude of the electromagnetic force is proportional to the square of the current density, making it a dominant driving force at high current densities.
Buoyancy Effect
Buoyancy is driven by density variations caused by temperature gradients within the weld pool. Hotter, less dense material rises while cooler, denser material sinks, creating a natural convection pattern. The buoyancy force is typically weaker than the electromagnetic and surface tension forces but contributes to the overall flow pattern.
| Driving Force | Direction | Magnitude Factor | Primary Effect |
|---|---|---|---|
| Surface tension (Marangoni) | Radial (outward or inward depending on temperature gradient) | Surface tension coefficient, temperature gradient | Controls surface flow, affects weld width |
| Electromagnetic force (Lorentz) | Radial outward | Current density squared | Drives deep penetration, central depression |
| Buoyancy | Vertical (upward for hot material) | Density difference, gravity | Contributes to natural convection |
Temperature Field and Stress Field Evolution
The temperature field simulation reveals the transient thermal behavior during submerged arc overlay welding on rolling mill rolls. The temperature distribution is asymmetric, with higher temperatures near the arc and cooler regions at the pool edges. The thermal cycle experienced by the weld pool and heat-affected zone is critical for determining the solidification microstructure and residual stress distribution.
The stress field analysis, based on the thermo-elasto-plastic theory, captures the evolution of residual stresses during and after welding. The thermal expansion during heating is constrained by the surrounding cooler material, generating compressive stresses. During cooling, the contracting weld metal is again constrained, generating tensile residual stresses. The distribution and magnitude of these residual stresses directly influence the susceptibility to cracking and the long-term fatigue behavior of the overlay weld.
Material Characterization and Process Analysis
The research includes material characterization of the overlay welds to validate the simulation results. The microstructural analysis reveals that the multi-field coupled simulation accurately predicts the weld pool morphology and solidification pattern. The flow field analysis provides insights into the mixing behavior within the weld pool, which affects the homogeneity of the microstructure and the distribution of alloying elements.
The simulation results demonstrate that the electromagnetic force is the dominant driving force for weld pool flow at typical submerged arc welding current densities. The surface tension effect modulates the flow pattern near the pool surface, while buoyancy contributes a secondary flow component. The combined effect of these forces determines the final weld pool shape, which directly influences the overlay weld geometry and quality.
Practical Significance for Crack Prevention
One of the key practical outcomes of this research is the ability to predict and prevent overlay weld cracking. The multi-field coupled model identifies the regions and conditions where cracking is most likely to occur, based on the combination of high residual stress, unfavorable microstructure, and inadequate plasticity. By understanding the flow field dynamics, engineers can optimize the welding parameters to promote favorable solidification conditions that minimize cracking susceptibility.
| Cracking Factor | Simulation Insight | Prevention Strategy |
|---|---|---|
| High residual stress | Stress field analysis identifies critical regions | Optimize welding sequence, reduce heat input |
| Unfavorable microstructure | Flow field affects solidification pattern | Control cooling rate through parameter optimization |
| Inadequate plasticity | Temperature field determines phase transformations | Select appropriate filler material, control heat input |
Engineering Practice Implications
For engineers in the metallurgical industry responsible for rolling mill roll maintenance, this research provides a comprehensive framework for understanding and controlling the submerged arc overlay welding process. The multi-field coupled approach enables the prediction of weld pool behavior, residual stress distribution, and microstructural evolution, allowing for proactive process optimization and quality control.
The identification of electromagnetic force as the dominant flow driving force has practical implications for process parameter selection. Since the electromagnetic force is proportional to the current density squared, small changes in welding current can significantly alter the flow pattern and, consequently, the weld quality. Engineers should carefully calibrate the welding parameters to achieve the desired flow regime and weld pool geometry.
Key Reflections
The development of multi-field coupled models for welding simulation represents a significant advancement in computational welding engineering. The ability to simultaneously capture thermal, mechanical, and fluid dynamic phenomena provides a holistic understanding of the welding process that single-field models cannot achieve. For submerged arc overlay welding on rolling mill rolls, where the process parameters and material properties are well-characterized, the multi-field coupled approach offers a powerful tool for process optimization and quality improvement.
The research also highlights the importance of flow field analysis in understanding weld quality. The flow within the weld pool influences heat and mass transfer, which in turn affects the solidification microstructure and residual stress distribution. By understanding and controlling the flow field, engineers can achieve more uniform microstructures and lower residual stresses, leading to improved weld performance.
Summary
This paper presents a comprehensive multi-field coupled numerical simulation of submerged arc overlay welding on rolling mill rolls, integrating thermal, elastic-plastic, and fluid dynamic analyses. The research identifies electromagnetic force as the dominant driving force for weld pool flow, with surface tension and buoyancy contributing secondary effects. The multi-field coupled model enables the prediction of weld pool morphology, residual stress distribution, and microstructural evolution, providing valuable insights for process optimization and crack prevention. For engineers in the metallurgical industry, this work demonstrates the power of multi-field simulation as a tool for understanding and controlling complex welding processes, ultimately leading to improved overlay weld quality and extended roll service life.