Numerical Simulation of Submerged Arc Overlay Welding Considering Phase Transformation Induced Plasticity

Literature Overview

This paper, published in Surface Technology in 2021 by Huang Qingchun, Li Chang, Zhang Dacheng, Gao Hexin, Han Xing, and Li Yunfei from Liaoning University of Science and Technology and China Energy Engineering Dongfang Electric Corporation, presents a comprehensive numerical simulation methodology for submerged arc overlay welding that incorporates phase transformation induced plasticity (TRIP) effects. The study uses CALPHAD thermodynamic calculations to determine temperature-dependent material properties and the COMSOL multiphysics platform to simulate the transient temperature field, martensite phase fraction, and TRIP stress evolution during the overlay welding of failed rolling mills. The research was supported by multiple funding sources including the National Natural Science Foundation of China.

Methodology and Computational Framework

The numerical simulation methodology integrates three key computational approaches:

1. CALPHAD thermodynamic calculations: Used to compute temperature-dependent material properties including specific heat capacity, thermal conductivity, elastic modulus, and phase transformation kinetics for the overlay welding material system.
2. Dual ellipsoid heat source model: Represents the asymmetric thermal distribution of the submerged arc welding process, where the heat source is elongated in the welding direction with a leading and trailing component.
3. Multiphysics coupling in COMSOL: Simultaneously solves the heat transfer equation, phase transformation kinetics, and mechanical equilibrium equations to capture the coupled thermal-metallurgical-mechanical behavior.

The TRIP effect is a critical consideration in this simulation because the volume expansion associated with martensitic transformation (from austenite to martensite) can generate significant internal stresses that either add to or partially relieve the thermally induced tensile stresses. This phenomenon is particularly important in high-carbon and high-alloy overlay welding applications where the cooling rates are sufficient to produce substantial martensite formation.

Simulation Results and Key Findings

The numerical results provide several important quantitative findings:

The simulation reveals that the heat transfer rate is higher near the substrate side of the weld compared to the overlay layer itself, which causes the martensite transformation to occur more rapidly in this region. This rapid transformation results in a broader distribution of TRIP stress values near the substrate interface. During cooling, the martensitic transformation causes a gradual decrease in stress values in the heat-affected zone, which is a beneficial effect that partially offsets the thermally induced tensile stresses.

The experimental validation using Zeiss Sigma HD field emission scanning electron microscopy (SEM) confirmed the accuracy of the numerical model, providing confidence in the predictive capability of the simulation methodology.

Engineering Applications and Process Optimization

The simulation methodology developed in this study has direct applications for the overlay welding repair of rolling mills, which are critical components in steel production facilities. Rolling mills experience severe wear and deformation during operation, and overlay welding is the standard repair method. The ability to predict residual stress distributions and microstructural evolution enables process optimization through the following approaches:

• Preheating temperature selection: The simulation can predict the effect of preheating on cooling rates and martensite formation, allowing for optimized preheating temperatures that minimize residual stresses while maintaining adequate hardness.
• Interpass temperature control: By predicting the thermal history of each pass, the simulation can guide the selection of interpass temperatures to minimize the cumulative effect of thermal cycling.
• Post-weld heat treatment design: The predicted residual stress distribution and phase transformation behavior provide a basis for designing effective stress relief and tempering treatments.
• Crack prevention: Understanding the TRIP stress contribution to the overall stress state enables the identification of critical stress concentrations and the development of countermeasures.

Study Insights and Methodological Significance

The most significant contribution of this study is the integration of TRIP effects into the numerical simulation framework, which provides a more complete picture of the stress state during and after overlay welding. Traditional thermal-mechanical simulations that ignore phase transformation effects may overestimate residual stresses because they do not account for the stress-relieving contribution of martensitic transformation. The CALPHAD-based approach to determining material properties is also noteworthy because it provides thermodynamically consistent property data across the full temperature range of the welding process, eliminating the need for empirical interpolation of property data. For engineers involved in overlay welding applications, this methodology represents a significant advancement in the ability to predict and control weld quality through numerical simulation.