On the Carbon Solubility in Expanded Austenite and Formation of Hägg Carbide in AISI 316 Stainless Steel

Thomas Lundin Christiansen, Kenny Ståhl, Bastian Brink, Marcel A. J. Somers

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Abstract

The carbon solubility in expanded austenite is investigated by controlled low temperaturegaseous through-carburizing of AISI 316 stainless steel thin foils with thermogravimetry and synchrotron powder diffraction analysis. Carburizing is carried out in C2H2–H2–N2 and CO–H2–N2 atmospheres at 380–420 °C and 465–470 °C, respectively. Hägg carbide (x-M5C2)develops when the carbon content in the expanded austenite exceeds the metastable solubility limit; the transformation of carbon expanded austenite into Hägg carbide occurs irrespective of carburizing temperature in the investigated temperature range (380–470 °C). The maximum solubility of carbon in expanded austenite (380 °C) is found to correspond to an occupancy (yC) of 0.220 of the interstitial octahedral sites of the austenite lattice (i.e., 4.74wt%C). Decomposition of Hägg carbide into M7C3 occurs upon prolonged carburizing treatment orthermal exposure in inert atmosphere (in situ synchrotron experiments).
Original languageEnglish
JournalSteel Research International
Volume87
Issue number11
Pages (from-to)1395–1405
Number of pages11
ISSN1611-3683
DOIs
Publication statusPublished - 2016

Keywords

  • Carbon solubility
  • Expanded austenite
  • Thermogravimetry
  • Synchrotron diffraction
  • Hägg carbide

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