Session: 04-24-05: Materials Processing and Characterization V

Paper Number: 165656

Microstructural Changes and Mechanical Properties of Friction Stir Welded 316l Stainless Steel 

Microstructural changes and mechanical properties of AISI 316L stainless steel in the 1/8 hard initial state were thoroughly investigated after friction stir welding (FSW) in this study. The research utilized the bead-on-plate FSW technique to simulate the butt welding process of AISI 316L stainless steel, which necessitated the use of a tungsten carbide (WC) welding tool and the application of high welding parameters. Microstructure and mechanical property evaluations were carried out on the parent material as a reference to compare the effects of the welding process.

The first step in the study involved determining the optimal welding parameters, which was crucial to achieving a successful weld. Once the ideal parameters were established, the cross-section of the welded plate was carefully examined using metallographic methods to ensure that the weld had fully penetrated through the entire thickness of the material. It was also important to verify that no defects or WC particles from the welding tool had contaminated the FSW’ed material. Optical microscopy and Scanning Electron Microscopy (SEM) were used for detailed metallographic characterization of the weld. Additionally, microhardness tests were conducted across different zones of the welded joint, including the parent material, the heat-affected zone (HAZ), the thermomechanically affected zone (TMAZ), and the stir zone.

Both the parent material and the FSW’ed material underwent tensile tests to evaluate their mechanical strength, and fractography studies were performed to investigate the nature of the fractures. For the parent material, minimal differences were observed between specimens when comparing those whose longitudinal axis was parallel to the rolling direction of the plates versus those whose longitudinal axis was normal to the rolling direction. However, the FSW’ed specimens exhibited an increase in both microhardness and yield strength compared to the parent material. Despite these improvements, the fracture consistently occurred within the stir zone, indicating the localized nature of the material’s mechanical properties.

To further understand the underlying microstructural changes induced by the welding process, advanced techniques like Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) were employed. These methods provided detailed insights into the crystallographic and structural changes occurring during welding. The study carefully analyzed the influence of these microstructural modifications on the overall mechanical properties of the welded material. The occurrence of changes in the microstructure during welding and their direct impact on the material’s performance were comprehensively discussed, providing a deeper understanding of the relationship between processing conditions, microstructure, and mechanical properties in FSWed AISI 316L stainless steel.

Presenting Author: Michael Regev Braude College of Engineering

Presenting Author Biography: Prof. Michael Regev has a B.Sc. degree in Mechnical Engineering, M.Sc. and Ph. D. in Materials Engineering. Serves as VP for Academic Affairs of Braude College of Engineering, Karmiel, Israel.

Authors:

Michael Regev Braude College of Engineering
Stefano Spigarelli DIISM, Università Politecnica delle Marche