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Microstructure and segregation behaviour of directionally solidified tungsten bearing 25Cr-35Ni-Nb heat-resistant stainless steels

Attarian, M ; Sharif University of Technology | 2017

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  1. Type of Document: Article
  2. DOI: 10.1080/13640461.2016.1261519
  3. Publisher: Taylor and Francis Ltd , 2017
  4. Abstract:
  5. Two series of heat-resistant 25Cr-35Ni-Nb stainless steels with tungsten addition and Nb/C ratio of ≈2.6 and 3.9 were directionally solidified under two cooling rates of 23–6 °C s−1, respectively. EDS analysis, electron backscatter diffraction (EBSD), differential thermal analysis (DTA) and field emission scanning electron microscopy (FESEM) tests were carried out to show that tungsten as a carbide phase nucleant promoted weak coupled eutectic growth of γ/ M7C3 and decreased the lamellar eutectic colonies. Substantial negative segregation of Ni and Fe and positive segregation of Nb and Cr in tungsten-bearing alloys stimulated the γ/M23C6 reaction and the M23C6 possessed a dendritic morphology. Two morphologies of MC carbides consisted of Widmanstätten and dendritic with a wavy surface were detected depending on the cooling rate and tungsten addition. The partition coefficient of Nb was determined as 0.31 and 0.52 for the alloy with and without tungsten, respectively. © 2016 Informa UK Limited, trading as Taylor & Francis Group
  6. Keywords:
  7. Directionally solidified ; heat-resistant stainless steel ; MC carbide ; tungsten effect ; Carbides ; Cooling ; Differential thermal analysis ; Eutectics ; Field emission microscopes ; Nickel ; Niobium ; Scanning electron microscopy ; Thermoanalysis ; Tungsten ; Tungsten carbide ; Dendritic morphology ; Differential thermal analyses (DTA) ; Electron back scatter diffraction ; Field emission scanning electron microscopy ; Heat resistant ; Negative segregations ; Partition coefficient ; Stainless steel
  8. Source: International Journal of Cast Metals Research ; Volume 30, Issue 2 , 2017 , Pages 112-122 ; 13640461 (ISSN)
  9. URL: https://www.tandfonline.com/doi/abs/10.1080/13640461.2016.1261519?journalCode=ycmr20