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Effect of nitrogen in shielding gas of keyhole GTAW on properties of duplex and superduplex welds

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Abstract

Keyhole gas tungsten arc welding (GTAW) is a relatively new variant used for fabrication of pressure equipment where up to 10-mm-thick material can be autogenously welded in one pass. As the shielding gas used for keyhole mode is typically Ar + 5% H2, the suitability of this method for welding of duplex stainless steels has been investigated. Duplex UNS S31803 and superduplex UNS S32750 schedule 40 seamless pipe was welded using a closed square butt joint configuration. Shielding gas compositions were applied with increasing nitrogen content in argon or argon-hydrogen mixtures. An investigation of the completed welds included examinations of the microstructure, corrosion and mechanical properties of the weld metal. All shielding gases resulted in high-quality welds free from defects, showed high strength and excellent corrosion resistance. Hydrogen additions increased the weld metal nitrogen loss and resulted in lower austenite formation. Ar + 5% H2 showed up to 20 vol.% less austenite than the gas types containing nitrogen and also showed the lowest impact toughness. At least 2% nitrogen would be recommended for optimizing the phase balance and impact toughness. Taking all aspects into account, Ar + 2% N2 is the preferred shielding gas for welding duplex and superduplex with the keyhole GTAW process.

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Authors and Affiliations

  1. K-TIG, Building 5/9 William Street, Mile End, Adelaide, SA, 5031, Australia

    A. M. Sales & B. L. Jarvis

  2. voestalpine Böhler Welding, Böhler Welding Str. 1, 8605, Kapfenberg, Austria

    E. M. Westin

Authors
  1. A. M. Sales
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  2. E. M. Westin
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  3. B. L. Jarvis
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Correspondence to A. M. Sales.

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Recommended for publication by Commission IX - Behaviour of Metals Subjected to Welding

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Sales, A.M., Westin, E.M. & Jarvis, B.L. Effect of nitrogen in shielding gas of keyhole GTAW on properties of duplex and superduplex welds. Weld World 61, 1133–1140 (2017). https://doi.org/10.1007/s40194-017-0486-1

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