Three-Dimensional Temperature Field Analysis of TIG Welding on Thin Stainless Steel Plate Using SYSWELD

Literature Overview

This 2007 study from China University of Petroleum, authored by Li Ruiying, Zhao Ming, and Sun Yongxing, presents a finite element analysis (FEA) of the three-dimensional temperature field during TIG welding of thin stainless steel plate. The research was supported by the China University of Petroleum Doctoral Research Fund (Y070305) and was published in the Heat Processing Technology journal (热加工工艺). The use of the SYSWELD software package represents a significant advancement in welding simulation capabilities, moving beyond two-dimensional approximations to capture the true three-dimensional thermal behavior of the weld process.

Core Technical Content and Methodology

The SYSWELD software is a specialized finite element package for welding simulation that incorporates a moving heat source model, material property databases, and coupled thermal-mechanical analysis capabilities. The three-dimensional temperature field analysis is critical for understanding the weld pool geometry, solidification behavior, and residual stress distribution in thin plate welds.

The double-ellipsoidal heat source model is particularly important for TIG welding because it captures the asymmetry of the weld pool — the front part of the pool (in the direction of welding travel) is deeper and narrower due to the momentum of the arc, while the back part is shallower and wider due to the slower cooling rate.

Microstructural Implications of Temperature Field Analysis

The three-dimensional temperature field analysis provides critical information for predicting the microstructural evolution during welding:

1. Cooling rate: The cooling rate from 800°C to 500°C (t₈₀₀₋₅₀₀) is a key parameter that determines the grain structure and phase transformations in the HAZ. For thin stainless steel plate, the cooling rate is typically high (50–200°C/s), leading to fine grain structures in the HAZ.
2. Peak temperature: The peak temperature at any point in the plate determines the extent of grain growth and precipitation dissolution. Points experiencing peak temperatures above 1300°C undergo complete austenitization, while points below 900°C experience minimal microstructural change.
3. Solidification rate: The solidification rate (G/R, where G is the temperature gradient and R is the growth rate) determines the dendrite arm spacing in the weld metal. Higher solidification rates produce finer dendrite structures, which generally improve mechanical properties.

Engineering Practice and Connection to Pressure Vessel Fabrication

The three-dimensional temperature field analysis has direct applications in the fabrication of bimetal pressure vessels:

• Thick-to-thin transition welding: In pressure vessel fabrication, it is common to weld thin clad plates to thicker base plates. The temperature field analysis helps predict the weld pool geometry and dilution rate at these transitions, which is critical for ensuring adequate bond strength and corrosion resistance.
• Residual stress prediction: The temperature field data serves as input for coupled thermal-mechanical analysis, which predicts the residual stress distribution in the weld joint. High residual stresses can lead to distortion, fatigue cracking, or stress corrosion cracking in pressure vessels.
• Process optimization: By varying the welding parameters in the simulation, engineers can identify optimal process windows that minimize distortion, residual stress, and defect formation before committing to expensive experimental trials.

Key Questions and Reflections

A fundamental question addressed by this research is the accuracy of the three-dimensional temperature field prediction compared to experimental measurements. The study demonstrates that the SYSWELD software, with appropriate calibration of the heat source model parameters, can predict the temperature field with reasonable accuracy (within 10–15% of experimental measurements). However, the prediction accuracy depends heavily on the quality of the input data, including material properties, boundary conditions, and heat loss coefficients.

Another important consideration is the computational efficiency of the three-dimensional analysis. While the three-dimensional model provides more accurate results than two-dimensional models, it requires significantly more computational resources and time. For industrial applications where rapid process optimization is needed, a hybrid approach — using two-dimensional models for initial parameter screening and three-dimensional models for final validation — may be the most practical strategy.

Study Insights and Implications

The three-dimensional temperature field analysis represents a powerful tool for understanding and optimizing the TIG welding process for thin stainless steel plate. For engineers involved in bimetal pressure vessel fabrication, the ability to predict the thermal behavior of the weld process with high accuracy enables more informed decision-making regarding process parameter selection, quality control, and defect prevention. The integration of numerical simulation with experimental validation provides a robust framework for developing and implementing welding procedures in complex manufacturing environments.