Microstructure of laser metal deposited duplex stainless steel: Influence of shielding gas and heat treatment
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RESEARCH PAPER
Microstructure of laser metal deposited duplex stainless steel: Influence of shielding gas and heat treatment Maria Asuncion Valiente Bermejo 1 & Karthikeyan Thalavai Pandian 1 & Björn Axelsson 2 & Ebrahim Harati 1,3 & Agnieszka Kisielewicz 1 & Leif Karlsson 1 Received: 31 August 2020 / Accepted: 21 November 2020 # The Author(s) 2020
Abstract This research work is the first step in evaluating the feasibility of producing industrial components by using Laser Metal Deposition with duplex stainless steel Wire (LMDw). The influence of Ar and N2 shielding gases was investigated in terms of nitrogen loss and in the microstructure and austenite content of different deposited geometries. The evolution of the microstructure in the build-up direction of the Ar and N2-shielded blocks was compared in the heat-treated and as-deposited conditions. The susceptibility for oxygen pick-up in the LMDw deposits was also analyzed, and oxygen was found to be in the range of conventional gas-shielded weldments. Nitrogen loss occurred when Ar-shielding was used; however, the use of N2-shielding prevented nitrogen loss. Austenite content was nearly doubled by using N2-shielding instead of Ar-shielding. The heat treatment resulted in an increase of the austenite content and of the homogeneity in the microstructure regardless of the shielding gas used. The similarity in microstructure and the low spread in the phase balance for the as-deposited geometries is a sign of having achieved a stable and consistent LMDw process in order to proceed with the build-up of more complex geometries closer to industrial full-size components. Keywords Duplex stainless steels . Additive manufacturing . Laser metal deposition . Directed energy deposition . Laser beam additive manufacturing
1 Introduction Additive manufacturing (AM) has the potential to revolutionize the industry worldwide for several reasons: minimal material wastage, short time-to-market, flexibility in the geometry and design of the components produced, and the possibility to improve their functionality, by for example producing functionally graded materials. The European Union, aware of the importance of AM, has been supporting its establishment through research projects funded by the Horizon 2020 Program [1–3]. Recommended for publication by Commission IX - Behaviour of Metals Subjected to Welding * Maria Asuncion Valiente Bermejo [email protected] 1
Department of Engineering Science, University West, 461 86 Trollhättan, Sweden
2
Alfa Laval Tumba AB, 147 80 Tumba, Sweden
3
ITW Welding AB, 433 25 Partille, Sweden
However, there are still important technological and scientific challenges ahead in connection to the industrial implementation of the technique, for example, the in-process monitoring and control, the reduction of post-processing steps, the simulation and measurement of thermal gradients and residual stresses, and very importantly and connected to the previous challenges, the control of the resulting microstructure. Because of the difficulty to predict an
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