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A thermodynamic study of inverse bainitic transformation

A thermodynamic study of inverse bainitic transformation The effect of Cr, Mn, and the isothermal holding temperature on inverse bainitic transformation in hypereutectoid steels is investigated. Thermodynamic driving force is calculated for the onset of nucleation of cementite and ferrite from parent austenite, Hultgren extrapolation of A e3 and A cm phase boundaries, and the molar Gibbs energy change for austenite to ferrite transformation. For a given carbon concentration above the eutectoid carbon concentration, inverse bainite is favored at a lower Cr and higher Mn concentrations in the steel. With the increase in Cr concentration, the inverse bainitic start temperature has been found to increase. Cr partitioning from parent austenite to form Cr7C3 or Cr23C6 occurs only at prolonged transformation time (10000 s and above), by when the inverse bainitic transformation is complete. Cementite is the favored carbide nucleating from parent austenite during the inverse bainitic transformation. With the increase in Mn concentration, both the inverse bainitic start and finish temperatures have been found to decrease. For a given chemical composition, inverse bainite is generally favored below the pearlitic transformation temperature. Inverse bainitic transformation gets suppressed when the isothermal transformation temperature is lowered, in which case conventional upper/lower bainite is the favored transformation product. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Materials Science Springer Journals

A thermodynamic study of inverse bainitic transformation

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References (39)

Publisher
Springer Journals
Copyright
Copyright © 2018 by Springer Science+Business Media, LLC, part of Springer Nature
Subject
Materials Science; Materials Science, general; Characterization and Evaluation of Materials; Polymer Sciences; Continuum Mechanics and Mechanics of Materials; Crystallography and Scattering Methods; Classical Mechanics
ISSN
0022-2461
eISSN
1573-4803
DOI
10.1007/s10853-018-2541-8
Publisher site
See Article on Publisher Site

Abstract

The effect of Cr, Mn, and the isothermal holding temperature on inverse bainitic transformation in hypereutectoid steels is investigated. Thermodynamic driving force is calculated for the onset of nucleation of cementite and ferrite from parent austenite, Hultgren extrapolation of A e3 and A cm phase boundaries, and the molar Gibbs energy change for austenite to ferrite transformation. For a given carbon concentration above the eutectoid carbon concentration, inverse bainite is favored at a lower Cr and higher Mn concentrations in the steel. With the increase in Cr concentration, the inverse bainitic start temperature has been found to increase. Cr partitioning from parent austenite to form Cr7C3 or Cr23C6 occurs only at prolonged transformation time (10000 s and above), by when the inverse bainitic transformation is complete. Cementite is the favored carbide nucleating from parent austenite during the inverse bainitic transformation. With the increase in Mn concentration, both the inverse bainitic start and finish temperatures have been found to decrease. For a given chemical composition, inverse bainite is generally favored below the pearlitic transformation temperature. Inverse bainitic transformation gets suppressed when the isothermal transformation temperature is lowered, in which case conventional upper/lower bainite is the favored transformation product.

Journal

Journal of Materials ScienceSpringer Journals

Published: Jun 6, 2018

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