Numerical Simulation of Residual Stress Field in Rare Earth Oxide Modified Overlay Welding Deposits

Literature Overview

This 2003 study by Yang Qingxiang and Yao Mei from Yanshan University, supported by the State Key Laboratory of Modern Welding Production Technology, investigates the influence of rare earth oxide additions in welding flux on the residual stress field in overlay deposits on medium-to-high carbon steel substrates. The research combines experimental measurements using infrared thermography and X-ray stress analysis with two-dimensional finite element modeling to understand how rare earth oxides and metallic nickel affect the martensitic transformation temperature and consequently the residual stress distribution in overlay welds.

Experimental Methodology and Measurement Techniques

The study employed a dual measurement approach to capture both the transient thermal field and the final residual stress state. Infrared thermography was used to record the temperature field during the welding process, providing the boundary conditions for the finite element model. X-ray diffraction stress analysis was then applied to the completed welds to measure the residual stress distribution at the surface.

The finite element model was constructed using the experimentally measured temperature field as input, along with the physical and mechanical properties of the materials involved. The model specifically accounted for the volumetric expansion associated with the austenite-to-martensite transformation, which is a critical factor in determining the residual stress state in martensitic overlay welds.

Key Findings on Rare Earth Effects

The most significant finding of this research is that the addition of rare earth oxides and metallic nickel in the welding flux reduces the martensitic transformation temperature (Ms temperature) of the overlay deposit. This reduction in Ms temperature has a direct and beneficial effect on the residual stress field: a lower Ms temperature means that the martensitic transformation occurs at a lower temperature, when the thermal contraction of the surrounding material is less severe, resulting in reduced residual tensile stress at the weld surface.

The mechanism is physically intuitive but requires careful quantification. When the martensitic transformation occurs at a higher temperature, the transformation-induced expansion happens while the surrounding material is still relatively hot and therefore more compliant. However, the subsequent cooling from the transformation temperature to ambient temperature creates additional thermal contraction stresses. When the transformation temperature is lowered, the transformation expansion occurs closer to room temperature, partially compensating for the thermal contraction that occurs during final cooling, thereby reducing the net residual tensile stress.

Engineering Significance and Practical Applications

The practical implication of this research is substantial for engineers designing overlay welds for components subject to cyclic loading or stress-corrosion cracking environments. High residual tensile stresses at the weld surface are detrimental to fatigue life, stress-corrosion cracking resistance, and can promote cracking during welding itself. By incorporating rare earth oxides into the welding consumable, it is possible to reduce these detrimental stresses without changing the welding process parameters.

For the steel pipe and pipe fitting industry, this finding has implications for overlay welding of corrosion-resistant or wear-resistant layers on carbon and low-alloy steel substrates. Medium-to-high carbon steels, which are commonly used in high-pressure piping and flanges, are particularly susceptible to welding-induced cracking due to the combination of high carbon content and residual stresses. The use of rare earth modified consumables could provide a practical solution to this problem.

The study also highlights the value of combining experimental measurements with numerical simulation in understanding complex welding phenomena. The finite element model serves as a predictive tool that can be used to optimize consumable design before expensive experimental trials are conducted. This approach represents a mature engineering methodology that should be adopted in advanced welding process development programs.

This research provides a solid foundation for the development of next-generation welding consumables that incorporate rare earth elements to improve weld integrity and service performance, and the methodology employed remains a benchmark for computational welding mechanics studies.