Autogenous Laser Keyhole Welding of AISI 316LTi

Abstract

Effective autogenous full-penetration welding of 4 mm thick AISI 316LTi austenitic stainless steel bars was achieved using a CO₂ laser. The welding process parameters required to obtain an optimal and repeatable procedure giving the best quality welds were identified. The use of side jet of gas suppressing plasma formation was investigated, and it was discovered that there are optimal conditions that result in increased power transmission and improved repeatability. Tests were carried out on the final welds in the as-welded state and in the annealed state. These included microstructural and X-ray diffraction (XRD) analysis as well as potentiodynamic and salt spray corrosion tests. Microstructural analysis showed that solidification occurred in primary ferrite solidification (FA) mode. Application of a heat treatment to the welded samples dissolved the ferrite, but resulted in carbide precipitation diminishing resistance to pitting, and the corrosion tests carried out demonstrated that the corrosion-resistant properties of the material were not compromised by the welding process, and that a post-process heat treatment was unnecessary.

Keywords:

• Austenite
• Corrosion
• Keyhole
• Laser
• Plasma
• Stainless
• Steel
• Welding

ACKNOWLEDGMENTS

The authors gratefully acknowledge Mr. Daniel Vella for his precious help and advice. Further thanks go to Dr. Jian Chen, research fellow at the University of Birmingham, for conducting GDOES and XRD analysis.