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Influence of Chemical Compositions on Lower Ferrite-Austenite Transformation Temperatures in 9Cr Steels

[+] Author Affiliations
Michael Santella

Oak Ridge National Laboratory, Oak Ridge, TN

Paper No. PVP2010-25748, pp. 871-877; 7 pages
  • ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference
  • ASME 2010 Pressure Vessels and Piping Conference: Volume 6, Parts A and B
  • Bellevue, Washington, USA, July 18–22, 2010
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 978-0-7918-49255 | eISBN: 978-0-7918-3878-5
  • Copyright © 2010 by ASME


Computational thermodynamics approach was used to predict the ranges of the lower ferrite-austenite transformation temperatures, A1 ’s, in three 9% Cr steels. The predicted A1 ranges were: 766–856°C for SA387 Grade 91, 775–863°C for SA213 Grade T92, and 676–862°C for the weld metal SFA-5.23 B9 (2004). For Grade 91 and Grade T92 using the highest tempering temperature permitted by ASME Code, 800°C, would permit certain alloys conforming to the chemical composition specification to be tempered above their A1 , thereby risking the formation of untempered martensite. Similar circumstances exist for weld metal conforming to the SFA-5.23 B9 specification. Linear regression analyses were performed to develop simplified expressions capable of representing the thermodynamically predicted relationships between chemical compositions and A1 ’s. These are, Grade 91/SFA-5.23 B9 (2004): 805°C + 2.5(%Cr) + 18.1(%Mo) + 19.1(%Si) + 37.1(%V) + 19.2(%Nb) − 63.7(%C) − 130.6(%N) − 60.5(%Mn) − 72.3(%Ni); Grade T92: 778°C + 4.9(%Cr) + 22.6(%Mo) + 10.8(%W) + 22.9(%Si) + 43.6(%V) + 20.2(%Nb) − 80.6(%C) − 150.7(%N) − 55.1(%Mn) − 68.0(%Ni).

Copyright © 2010 by ASME



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