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Research Papers: Materials and Fabrication

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

[+] Author and Article Information
Michael L. Santella1

 Oak Ridge National Laboratory, Oak Ridge, TN 37831-6096santellaml@ornl.gov

1

Corresponding author.

J. Pressure Vessel Technol 134(2), 021404 (Jan 13, 2012) (5 pages) doi:10.1115/1.4005399 History: Received July 26, 2010; Revised February 17, 2011; Published January 13, 2012; Online January 13, 2012

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).

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Predicted A1 temperature ranges for SA387 Grade 91 (bottom) and SA213 Grade T92 (top). The vertical line indicates the reference temperature, 800 °C.

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Figure 2

Predicted A1 temperature range for SFA-5.23 B9 (20.04 version) weld metal. The vertical line indicates the reference temperature, 775 °C.

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Figure 3

Predicted A1 temperature range for SFA-5.23 B9 (2008) excluding compositions where Mn + Ni exceed 1.50 wt. %. The vertical line indicates the reference temperature, 790 °C.

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Figure 4

Variations of the A1 of midrange Grade 91 composition with concentrations of C, N, and Nb

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Figure 5

Variations of the A1 of midrange Grade 91 composition with concentrations of Mn, Mo, Ni, Si, and V

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Figure 6

Variations of the A1 with Cr concentrations for midrange compositions of Grade 91, Grade T92, and SFA-5.23 B9 (2004)

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Figure 7

Linear regression results for Grade 91

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Figure 8

Linear regression results for Grade T92

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Figure 9

Linear regression results for SFA-5.23 B9

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Figure 10

Comparison of AC1 dilation measurements with A1 predictions for heats of Grade 91. The line represents the predictions plotted against themselves.

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