Numerical Simulation of Temperature and Stress Fields in Medium-High Carbon Steel Surfacing Before and After Heat Source Removal

Literature Overview

This research paper by Yang Qingxiang, Gao Jun, Li Da, and Chen Xiaojun, published in the Transactions of the China Welding Institute in 2006 (Volume 27, Issue 5, pages 52-56), presents a finite element analysis (FEA) study of the temperature and stress fields during and after the surfacing of medium-high carbon steel 60CrMnMo. The work was conducted at the State Key Laboratory of Metastable Materials Preparation Technology and Science at Yanshan University, with funding from the Hebei Province Science and Technology Project and the Ministry of Education Overseas Research Fund.

Numerical Simulation Methodology

The study employs a coupled thermo-mechanical finite element model to simulate the surfacing process. The simulation captures two critical phases: the welding phase (with active heat source) and the cooling phase (after heat source removal). The 60CrMnMo steel is a medium-high carbon alloy steel commonly used in applications requiring high strength and wear resistance, such as bearing rings, shafts, and gear components.

The finite element model incorporates temperature-dependent material properties, including thermal conductivity, specific heat, elastic modulus, and thermal expansion coefficient, to accurately represent the thermomechanical behavior of the material during the surfacing process.

Temperature Field Analysis Results

The temperature field simulation reveals important characteristics of heat transfer during and after the surfacing process:

During welding (at 16 seconds): The temperature distribution shows a concentrated high-temperature zone at the surfacing location, with rapid temperature gradients extending into the surrounding base metal. The peak temperature at the weld pool surface reaches the melting range, while the heat-affected zone (HAZ) experiences temperatures sufficient to induce microstructural transformations.

After heat source removal: The temperature field distribution changes dramatically after the heat source is removed at 16 seconds. Heat rapidly propagates toward the lower surface and the boundaries of the specimen. The temperature gradient at the weld pool surface reverses direction as heat flows away from the surface.

At 180 seconds: The specimen temperature field approaches an equilibrium state, with heat transfer essentially ceasing. At this point, the temperature peak has shifted to the region near the lower surface center, and the temperature difference between the inner and outer regions becomes relatively small. This demonstrates the transient nature of the thermal cycle and the importance of considering post-weld cooling in residual stress analysis.

Stress Field Analysis and Residual Stress

The stress field simulation, based on the temperature field results, reveals critical findings about residual stress development:

The stress peak occurs at the interface between the heat-affected zone and the base metal region, with a significant jump in stress values across this boundary. This interface represents a critical location for potential cracking, as the stress concentration combined with microstructural changes in the HAZ creates favorable conditions for crack initiation and propagation.

The excellent agreement between the simulated and experimentally measured residual stress fields validates the numerical model and confirms its applicability for predicting residual stress in surfacing operations. This validation is crucial for using the model as a predictive tool in process optimization and quality control.

Engineering Implications for Surfacing Practice

The findings of this study have direct practical significance for engineers working with medium-high carbon steel surfacing applications:

Residual stress management: The high tensile residual stresses at the HAZ-base metal interface pose a risk of cracking, particularly in thick surfacing deposits or when the base metal has limited ductility. Stress-relief heat treatment or in-process techniques such as interpass tempering should be considered for critical applications.

Crack susceptibility: The stress concentration at the interface, combined with the hard microstructure of medium-high carbon steel, creates conditions favorable for cracking. Preheating the base metal to reduce the cooling rate, using filler metals with lower carbon content, and controlling the heat input per pass are effective countermeasures.

Process parameter optimization: The temperature field simulation provides guidance for optimizing process parameters to minimize residual stresses. Lower heat input, slower travel speeds, and multi-pass strategies with interpass temperature control can reduce peak temperatures and thermal gradients, thereby reducing residual stress magnitudes.

Application to pipe and fitting surfacing: For engineers working on surfacing operations on piping components, the understanding of temperature and stress field evolution is particularly relevant. Thin-walled pipe components are more susceptible to distortion and cracking due to their limited thermal mass and geometric constraints. The simulation approach can be adapted to predict residual stress in pipe surfacing operations and guide process parameter selection.

Key Questions and Study Insights

A fundamental question addressed by this research is how the removal of the heat source affects the subsequent evolution of temperature and stress fields. The answer is clear: the post-weld cooling phase is equally important as the welding phase itself in determining the final residual stress state. The rapid heat propagation after heat source removal creates thermal gradients that drive the development of residual stresses, particularly at the HAZ-base metal interface.

This study demonstrates the power of numerical simulation as a tool for understanding and predicting surfacing process outcomes. For industrial applications, the ability to simulate temperature and stress fields before performing actual surfacing operations enables process optimization, reduces trial-and-error costs, and improves the reliability of surfacing deposits. The validated model can serve as a foundation for developing process windows that ensure acceptable residual stress levels for specific applications, thereby enhancing the quality and reliability of surfaced components in demanding service environments.