Numerical Simulation of Residual Stress Field in Weld Overlay Specimens Containing Rare Earth Oxides

Literature Overview

This study presents a finite element analysis (FEA) of residual stress fields in weld overlay layers fabricated with filler metals containing rare earth oxide (REO) additions. The research addresses a critical gap in understanding how REO additions—commonly used to improve weldability, refine microstructure, and reduce cracking susceptibility—affect the thermomechanical behavior of overlay welds. The authors employed a coupled thermo-mechanical model to simulate the welding process and subsequent cooling, comparing residual stress distributions in overlays made with and without REO-containing fillers.

Methodology and Model Configuration

The numerical model was built in ABAQUS using an Eulerian-Lagrangian moving heat source approach. The welding process was simulated as a sequential deposition of multiple beads, with each bead modeled as a heat source followed by a plastic deformation event. The material properties were defined as temperature-dependent, incorporating elastic modulus, thermal expansion coefficient, and yield stress as functions of temperature.

Model Parameter	Specification
Geometry	200 mm × 100 mm × 20 mm base plate with 3-layer overlay
Element Type	8-node quadrilateral element (DC2D4 for thermal, CPS4R for mechanical)
Heat Source	Double-ellipsoidal Goldak model
REO Content	0.05 wt% La2O3 and CeO2 in filler wire
Welding Process	Submerged Arc Welding (SAW) with flux
Base Material	Q345R low-alloy steel
Overlay Material	316L stainless steel with REO addition
Preheat Temperature	150°C

The key innovation in this model was the incorporation of REO-specific material property modifications. The authors assumed that REO additions reduce the thermal conductivity of the weld metal by approximately 8–12% due to increased phonon scattering, and decrease the coefficient of thermal expansion by 3–5% due to the formation of rare earth-rich phases. These assumptions were validated against experimental measurements from the literature.

Results and Key Findings

The simulation results demonstrated that REO addition significantly altered the residual stress distribution in the overlay. The peak longitudinal residual stress in the REO-free overlay reached 320 MPa, while the REO-containing overlay exhibited a peak of only 265 MPa—a reduction of approximately 17%. The stress reduction was attributed to two mechanisms: (1) the refined grain structure resulting from REO-induced nucleation, which reduced transformation plasticity effects, and (2) the modified thermal properties that led to a more uniform cooling profile.

Condition	Peak Longitudinal Stress (MPa)	Peak Transverse Stress (MPa)	Stress Gradient at Interface
Without REO	320	185	45 MPa/mm
With 0.05% La2O3	265	158	32 MPa/mm
With 0.05% CeO2	258	152	29 MPa/mm

The interface region between the overlay and base plate was identified as the critical zone for stress concentration. In the REO-free case, the stress gradient at the interface reached 45 MPa/mm, which exceeds the cracking threshold for many overlay systems. With REO addition, this gradient dropped to 29–32 MPa/mm, substantially reducing the risk of interfacial cracking.

Discussion and Engineering Relevance

The study provides quantitative evidence that REO additions can be used as a process control variable to manage residual stresses in cladding operations. This finding has direct implications for the fabrication of bimetal pressure vessels, where residual stress management is critical for preventing stress corrosion cracking (SCC) and hydrogen-induced cracking (HIC). The authors recommend incorporating REO-containing filler metals in overlay applications where the substrate-overlay combination has a high thermal expansion mismatch, such as titanium/steel or nickel alloy/carbon steel systems.

A notable limitation of the study is the simplification of REO effects to bulk material property modifications. In reality, REO additions influence microstructure at the grain scale, and their effects on phase transformation kinetics and precipitation behavior are more complex than the linear property modifications assumed in the model. Nevertheless, the directional conclusions are robust: REO additions reduce residual stresses and improve the stress state at critical interfaces.

Study Insights and Reflections

This study represents a valuable contribution to the field of computational welding mechanics applied to cladding. The approach of incorporating material-specific modifications into FEA models is a practical strategy for engineers who need to predict residual stress effects without conducting exhaustive experimental campaigns. However, I note that the model assumes perfect bond between layers and does not account for potential partial delamination or interfacial sliding, which can occur in real weld overlay joints. Future work should explore the coupling of REO effects with multi-pass welding strategies, where the thermal history from previous passes modifies the base material properties before subsequent passes are deposited. The practical takeaway is that REO-containing filler metals should be considered as a standard option in cladding process qualification, particularly for applications governed by ASME Section IX or NB/T 47014 where residual stress control is a critical acceptance criterion.