Numerical Simulation of Pulsed TIG Welding of 06Cr18Ni11Ti Stainless Steel Thin Plate

Literature Overview

This 2022 study by Huang Wenxiang, Zhang Chun, Li Hui, and Meng Lei from the 724th Research Institute of China Shipbuilding Industry Corporation investigates the numerical simulation of pulsed TIG welding of 06Cr18Ni11Ti (equivalent to UNS S321) stainless steel thin plate. Published in the journal Thermal Processing Technology, the research addresses the challenges of welding thin stainless steel plates in shipbuilding applications, where dimensional accuracy, corrosion resistance, and mechanical integrity are critical.

06Cr18Ni11Ti is a stabilized austenitic stainless steel containing titanium, which provides resistance to intergranular corrosion in the sensitized temperature range (450–850°C). This material is widely used in marine environments, chemical processing equipment, and heat exchangers where both corrosion resistance and mechanical strength are required.

Core Technical Approach

The numerical simulation employs a three-dimensional finite element model to predict the thermal field, fluid flow, and solidification behavior during pulsed TIG welding of 06Cr18Ni11Ti thin plate. The model incorporates:

• A double-ellipsoidal heat source to represent the TIG arc
• Pulsed current characteristics to capture the dynamic weld pool behavior
• Coupled thermal-fluid analysis to model weld pool convection and solidification
• Material properties that vary with temperature and phase state

Simulation Parameters

The pulsed TIG process is particularly advantageous for thin plate welding because it allows precise control of the heat input, reducing the risk of burn-through while maintaining adequate penetration. The pulse parameters (peak current, background current, and frequency) can be optimized to achieve the desired weld geometry and microstructure.

Key Technical Points

Thermal Field Analysis

The numerical simulation reveals several important characteristics of the thermal field during pulsed TIG welding:

1. Temperature distribution: The peak temperature in the weld pool reaches 1800–2000°C, with the solidification front located at approximately 1450–1500°C (the melting point of austenitic stainless steel).
2. Heat input distribution: The pulsed current creates a periodic variation in the heat input, with the peak current producing a deeper and wider weld pool and the background current maintaining the arc and preventing re-solidification.
3. Thermal cycle: The cooling rate at the weld center is approximately 50–150°C/s, which is significantly higher than in conventional DC TIG welding due to the reduced heat input.

Fluid Flow and Solidification

The fluid flow analysis shows that the weld pool exhibits complex convection patterns driven by:

• Thermocapillary convection: Surface tension gradients drive fluid flow from the hot center to the cooler edges of the weld pool.
• Buoyancy-driven convection: Density differences due to temperature variations create natural convection currents.
• Electromagnetic stirring: The Lorentz force generated by the interaction of the arc current with the magnetic field stirs the molten weld pool.

The solidification analysis predicts a columnar dendritic microstructure in the weld center and an equiaxed grain structure near the fusion line. This microstructure is consistent with the rapid cooling rates and high temperature gradients characteristic of thin plate welding.

Residual Stress and Distortion

The simulation also predicts the residual stress distribution and angular distortion:

• Residual stress: The maximum longitudinal residual stress reaches 200–350 MPa, with tensile stresses concentrated in the weld center and compressive stresses in the surrounding base material.
• Angular distortion: The predicted angular distortion is 0.5–2.0 degrees for 1.0 mm thick plate and 0.3–1.0 degrees for 2.0 mm thick plate, depending on the heat input and welding speed.

Engineering Practice Implications

The numerical simulation provides valuable insights for optimizing the pulsed TIG welding process for 06Cr18Ni11Ti thin plate:

• Burn-through prevention: The pulse parameters can be adjusted to maintain a stable weld pool without excessive penetration, reducing the risk of burn-through in thin plates.
• Microstructure control: The cooling rate and solidification behavior can be influenced by the pulse parameters, allowing optimization of the weld microstructure for improved mechanical properties and corrosion resistance.
• Distortion control: The predicted residual stress and distortion can be used to design appropriate fixturing and welding sequences to minimize dimensional deviations.

Process Optimization Recommendations

Study Insights and Reflections

This research demonstrates the value of numerical simulation in understanding and optimizing the pulsed TIG welding process for thin stainless steel plates. The key insight is that the pulse parameters have a profound influence on the thermal field, fluid flow, and solidification behavior, which in turn determine the weld geometry, microstructure, and residual stress distribution.

The study also highlights the importance of accurate material property data in numerical simulations. The thermal and mechanical properties of 06Cr18Ni11Ti vary significantly with temperature and phase state, and these variations must be accurately captured in the simulation to produce reliable predictions.

In conclusion, the numerical simulation of pulsed TIG welding provides a powerful tool for process optimization and quality control in thin plate welding applications. By predicting the thermal field, fluid flow, and solidification behavior, the simulation enables the selection of optimal process parameters that achieve the desired weld geometry, microstructure, and mechanical properties while minimizing distortion and residual stress.