Multi-Field Coupled Numerical Simulation of Submerged Arc Hardfacing Process for Rolling Mill Rolls

Literature Overview

This study by Li Chang, Huang Qingchun, Chen Xinxue, Liu Zhaotai, and Han Xing from the School of Mechanical Engineering and Automation at Liaoning University of Science and Technology (2021, China Surface Engineering, Vol. 34, No. 4) presents a comprehensive multi-field coupled numerical simulation approach for the submerged arc hardfacing process of rolling mill rolls. The research addresses the limitation of existing studies that focus on single-field analysis by developing a coupled thermo-elastic-plastic-flow model that captures the evolution of temperature field, stress field, and fluid flow field during the hardfacing process, providing deeper insights into the molten pool dynamics and crack prevention mechanisms.

Research Background and Motivation

Submerged arc hardfacing is a widely used method for repairing and maintaining rolling mill rolls in the metallurgical industry. The rolls are subjected to extreme conditions during rolling operations, including high temperatures, heavy mechanical loads, and abrasive contact with hot metal, leading to surface wear, thermal fatigue cracking, and deformation. Hardfacing with appropriate alloy materials can restore the roll surface properties and extend the service life significantly. However, the quality of the hardfacing deposit is critical, as defects such as cracks, porosity, and poor dilution control can lead to premature failure of the roll.

The authors note that existing research on submerged arc hardfacing predominantly focuses on the temperature field or stress field in isolation, with very limited studies on the fluid flow field within the molten pool. The electromagnetic force, temperature gradient, and buoyancy force all contribute to the molten pool flow dynamics, which in turn affect the deposit geometry, microstructure, and defect formation. Understanding the coupled behavior of these multiple physical fields is essential for optimizing the hardfacing process and predicting potential failure modes.

Multi-Field Coupled Modeling Approach

The authors develop a coupled thermo-elastic-plastic-flow model based on thermo-elastic-plastic theory and computational fluid dynamics (CFD) methods. The model simultaneously solves the energy equation for the temperature field, the momentum equation for the flow field, and the constitutive equations for the stress field, capturing the complex interactions between these physical fields during the hardfacing process.

The electromagnetic force calculation is based on the Lorentz force equation, which considers the interaction between the welding current and the magnetic field generated by the current. The temperature gradient force is calculated from the Soret effect, where the temperature gradient drives the flow of the molten metal. The buoyancy force is calculated from the density difference caused by temperature variation within the molten pool.

The coupled model is implemented in a commercial finite element software package, with appropriate boundary conditions and material property functions that account for temperature-dependent behavior. The material properties include thermal conductivity, specific heat, density, viscosity, electrical resistivity, and mechanical properties such as yield strength and elastic modulus, all of which vary with temperature.

Molten Pool Flow Dynamics and Deposit Morphology

The simulation results reveal the complex flow patterns within the submerged arc hardfacing molten pool. The electromagnetic force, generated by the interaction between the welding current and the self-induced magnetic field, creates a downward flow pattern that promotes penetration of the molten metal into the substrate. The buoyancy force, caused by the density variation due to temperature differences, drives the hot, less dense molten metal upward and the cooler, denser metal downward. The surface tension force acts at the free surface of the molten pool, tending to minimize the surface area and creating a stabilizing effect on the pool geometry.

The relative magnitudes and directions of these forces determine the overall flow pattern within the molten pool, which in turn affects the deposit width, depth, and cross-sectional profile. The authors analyze how variations in welding parameters, such as current, voltage, travel speed, and wire feed rate, influence the balance of these forces and consequently the deposit morphology.

Crack Prevention and Process Optimization

One of the key practical outcomes of this study is the identification of process parameters and conditions that minimize the risk of hardfacing cracks. The coupled simulation provides insight into the residual stress distribution in the hardfacing deposit and the surrounding substrate, which is a critical factor in crack initiation and propagation. By optimizing the welding parameters to reduce the peak residual stresses and to promote a more uniform stress distribution, the crack tendency can be significantly reduced.

The authors also discuss the importance of the cooling rate in determining the microstructure and crack resistance of the hardfacing deposit. A slower cooling rate, achieved through appropriate preheating and controlled heat input, promotes the formation of a more ductile microstructure that is less susceptible to cracking. The simulation results provide quantitative guidance for setting the preheat temperature and interpass temperature to achieve the desired cooling rate.

Engineering Practice and Quality Assurance

The multi-field coupled simulation approach developed in this study provides a powerful tool for the optimization of submerged arc hardfacing processes for rolling mill rolls. By predicting the temperature field, stress field, and flow field evolution during the hardfacing process, engineers can identify potential problem areas before actual welding is performed, reducing the need for trial-and-error experimentation and improving the first-time quality of the hardfacing deposit.

The simulation results can be used to develop process windows that define the acceptable ranges of welding parameters for achieving the desired deposit quality. These process windows can be incorporated into the manufacturing quality assurance system to ensure consistent production quality. Additionally, the simulation model can be used to analyze the effect of material property variations on the hardfacing quality, providing guidance for material selection and procurement.

The study also highlights the importance of post-weld inspection and testing in verifying the quality of the hardfacing deposit. Non-destructive testing methods such as ultrasonic testing and magnetic particle inspection should be used to detect internal and surface defects, while metallographic examination and hardness testing should be performed on representative samples to verify the microstructure and mechanical properties of the deposit.

Study Insights and Future Directions

This study represents a significant advancement in the computational modeling of hardfacing processes by integrating multiple physical fields into a unified simulation framework. The coupled approach provides a more realistic representation of the hardfacing process than single-field models, capturing the complex interactions between thermal, mechanical, and fluid dynamic phenomena that govern the deposit quality.

Future research directions include the extension of the model to include solidification microstructure prediction, which would enable the simulation of the relationship between process parameters and the final microstructure of the hardfacing deposit. Additionally, the model could be enhanced to account for the effects of flux composition on the hardfacing process, as the flux plays a critical role in protecting the molten pool from atmospheric contamination and in modifying the deposit composition and properties. The development of real-time simulation capabilities that can be integrated with the welding control system would enable adaptive process control that automatically adjusts welding parameters to maintain optimal deposit quality throughout the hardfacing operation.

The practical value of this research extends beyond rolling mill roll repair to other hardfacing applications in the metallurgical, mining, and power generation industries, where submerged arc hardfacing is widely used for surface protection and component repair. The methodology and findings presented in this study provide a solid foundation for the development of more advanced simulation tools and process optimization strategies that can improve the reliability and efficiency of hardfacing operations across various industrial sectors.