The Effect of Ar and N2 Shielding Gas on Laser Weld Porosity in Steel, Stainless Steel, and Nickel
Journal Article
·
· Welding Journal
OSTI ID:1812143
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Aldermaston Weapons Establishment (United Kingdom)
Complete, or near complete, elimination of porosity in 304L stainless steel keyhole laser welds was observed when using N2 instead of Ar shielding gas. Partial penetration autogeneous welds made at intermediate power levels of 2-4 kW using a CW fiber laser at travel speeds of 8-11 mm/s where porosity often occurs when using inert shielding gas. To investigate this effect further, laser welds were made in N2 and Ar gas on three additional metals (A36 steel, 21-6-9 stainless steel, and pure nickel) that have varying properties and degrees of reactivity and solubilities with the shielding gasses. Optical metallography, x-ray radiography, and x-ray computed tomography were used to characterize the porosity levels in the welds. Results show that high levels of porosity occurred in nickel, regardless of shielding gas type, while low levels or no porosity was observed in 21-6-9 for either shielding gas. However, A36 and 304L exhibited porosity in all of the welds made with Ar, and very low or no porosity when made with N2. Computed tomography was used to quantify the porosity in selected welds, showing that the pore sizes are distributed in a monotonically decreasing trend that can be described by a two parameter Weibull relationship (β=0.5429, α=0.0366). Based on the results, it is believed that the reactivity of N2 with alloying elements, and/or its solubility in the liquid weld pool, play a significant role in reducing the amount of retained porosity in unstable keyhole welds as they solidify and cool to room temperature.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- Grant/Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1812143
- Report Number(s):
- LLNL-JRNL--663819; 785117
- Journal Information:
- Welding Journal, Journal Name: Welding Journal Vol. 2015; ISSN 0043-2296
- Publisher:
- American Welding SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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