Numerical Simulation of Weld Overlay on Dissimilar Metals Between Low Alloy Steel and Stainless Steel

Literature Overview

The research by Jiang Xiaohua, Dai Deping, Cai Jianpeng, and Deng De'an from the School of Materials Science and Engineering at Chongqing University, published in Thermal Processing Technology in 2016 and supported by the National Natural Science Foundation of China (Grant No. 51275544), presents a finite element numerical simulation study of weld overlay cladding between low alloy steel and stainless steel. This work addresses a critical engineering challenge in the fabrication of bimetallic components, where the dissimilar metal interface is susceptible to cracking, distortion, and residual stress concentration.

Core Technical Framework

The authors employed a coupled thermo-mechanical finite element model to simulate the multi-pass weld overlay process. The simulation incorporated a moving heat source model based on the double-elliptical heat flux distribution, which accounts for the asymmetric temperature field characteristic of arc welding processes. The material properties were defined as temperature-dependent, including thermal conductivity, specific heat, elastic modulus, and yield strength for both the base low alloy steel and the stainless steel overlay material.

The key technical contribution of this work lies in the accurate prediction of residual stress and deformation patterns at the dissimilar metal interface. The authors identified that the coefficient of thermal expansion mismatch between the low alloy steel substrate (approximately 12.0 x 10^-6 /K) and the stainless steel overlay (approximately 17.0 x 10^-6 /K) generates significant interface stresses during cooling. These stresses can exceed the yield strength of the softer material, leading to plastic deformation and potential cracking.

Key Findings and Technical Interpretation

The simulation results revealed several important phenomena. First, the maximum residual tensile stress was concentrated at the weld interface and at the trailing edge of the weld bead, with values reaching up to 420 MPa in the high heat input condition. This is significantly above the yield strength of 304 stainless steel at room temperature (approximately 205 MPa), indicating substantial plastic deformation in the overlay layer near the interface.

Second, the angular distortion of the substrate plate was found to increase with heat input, reaching values of 0.8-1.5 degrees for a 10 mm thick plate with a 5-pass overlay. The authors proposed that preheating the substrate to 200-300 degrees Celsius and employing a lower heat input per pass (below 3.0 kJ/mm) could effectively reduce both residual stresses and distortion.

Third, the simulation predicted a critical interface temperature window. If the interface temperature exceeded 1500 degrees Celsius, excessive dilution of the stainless steel overlay would occur, reducing its corrosion resistance. Conversely, if the interface temperature was below 900 degrees Celsius, incomplete bonding and potential lack of fusion defects could result. The optimal interface temperature range was identified as 1000-1400 degrees Celsius.

Process Optimization and Engineering Application

Based on the simulation results, the authors recommended a multi-pass welding strategy with alternating welding directions to minimize angular distortion. The first pass should be deposited with a low heat input to establish a strong metallurgical bond without excessive dilution, followed by subsequent passes with progressively higher heat inputs to build up the overlay thickness efficiently.

The numerical simulation approach presented in this paper offers significant advantages for engineering practice. By predicting residual stress distributions and deformation patterns before actual welding, manufacturers can optimize process parameters, reduce trial-and-error costs, and improve the first-pass quality rate. The simulation results also provide a basis for determining post-weld stress relief requirements, which is essential for components subject to fatigue loading or corrosion-resistant service conditions.

Study Reflections

This paper exemplifies the growing importance of computational methods in welding engineering. The coupled thermo-mechanical simulation provides insights that are difficult to obtain through physical experimentation alone, particularly regarding the internal stress state at the dissimilar metal interface. However, the accuracy of such simulations depends critically on the quality of input material data and the appropriateness of constitutive models. In practice, simulation results should always be validated against experimental measurements before being used for production decisions. The work also underscores the need for standardized simulation protocols to ensure comparability of results across different studies and organizations.