Study Note on Three-Dimensional Dynamic Simulation of Weld Overlay Temperature Field

Literature Overview

This technical paper presents a comprehensive three-dimensional finite element analysis of the temperature field during weld overlay (cladding) operations. The study addresses the fundamental challenge of predicting thermal history, cooling rates, and residual stress distributions in overlay welding processes, which are critical for ensuring metallurgical compatibility and mechanical integrity of the cladding layer.

Core Technical Content

Simulation Methodology

The paper employs a coupled thermo-mechanical finite element model to simulate the temperature evolution during multi-pass overlay welding. The model incorporates moving heat source representations for various welding processes, including submerged arc welding (SAW), gas metal arc welding (GMAW), and plasma transferred arc (PTA) welding.

Temperature Field Characteristics

The three-dimensional simulation reveals several critical thermal phenomena:

1. Asymmetric thermal distribution: The heat source asymmetry in GMAW and PTA processes creates directional temperature gradients that influence solidification morphology and residual stress orientation.
2. Thermal history sensitivity: The cooling rate at the 800°C threshold temperature is the most critical parameter governing microstructural evolution in the overlay layer.
3. Multi-pass interaction: Subsequent passes partially reheat previously deposited material, modifying the thermal cycle and potentially causing grain growth in the heat-affected zone.

Dilution and Thermal Coupling

The simulation provides quantitative predictions of dilution factors that correlate with thermal input and travel speed. For nickel-based alloy overlays on carbon steel substrates, dilution exceeding 25% significantly compromises corrosion resistance and may introduce brittle intermetallic phases at the fusion boundary.

Engineering Practice Integration

Process Optimization Using Simulation Results

The simulation data directly informs several critical aspects of overlay welding process development:

Preheat temperature determination: For overlay welding of austenitic stainless steels on low-alloy steel substrates, the simulation indicates that preheat temperatures of 150-250°C effectively reduce the peak thermal gradient at the interface while maintaining acceptable dilution levels.

Interpass temperature control: The dynamic temperature simulation demonstrates that interpass temperatures exceeding 250°C for stainless steel overlays on carbon steel lead to excessive grain growth and reduced hardness in the overlay layer.

Travel speed optimization: The relationship between travel speed and cooling rate provides a practical framework for selecting parameters that achieve target microstructures without excessive dilution.

Application to Bimetal Pressure Vessel Fabrication

For clad plate pressure vessels fabricated according to NB/T 47002 and GB/T 150, the thermal simulation data is essential for:

• Determining qualified preheat and interpass temperature ranges for weld procedure qualification
• Predicting residual stress distributions that influence fatigue performance
• Optimizing welding sequences to minimize distortion in large-diameter vessels

Key Questions and Reflections

The most compelling aspect of this study is the demonstration that three-dimensional thermal modeling captures phenomena that one-dimensional or two-dimensional analyses fundamentally cannot predict. The interaction between adjacent weld passes, the influence of joint geometry on thermal flow, and the effect of backing bar configurations are all accurately represented in the three-dimensional model.

A significant practical challenge remains in correlating simulation predictions with actual metallurgical outcomes. The model assumes material properties that are well-characterized for pure metals but become increasingly uncertain in the dilution zone where composition varies continuously. Future work should integrate thermodynamic calculations with thermal simulation to predict local composition-dependent phase transformations throughout the overlay zone.

The simulation methodology described in this paper provides a powerful tool for reducing the number of expensive trial welds during procedure qualification. By predicting thermal cycles and dilution factors computationally, engineers can narrow the range of qualified parameters before committing to physical testing, thereby reducing development time and cost.