A study of diffusion- and interface-controlled migration of the Austenite/Ferrite front during Austenitization of a case-hardenable alloy steel

Eric D. Schmidt, E. Buddy Damm, Seetharaman Sridhar

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Migrating austenite/ferrite interfaces in the ferrite regions of an alloy steel, containing 0.20 wt pct C, 0.87 wt pct Mn,and 0.57 wt pct Cr, with a ferrite/pearlite microstructure have been observed during austenitization by a high-temperature confocal scanning laser microscope in order to determine the mechanisms of transformation. The samples were subjected to isothermal (790 °C to 850 °C) and nonisothermal (0.5 °C to 20 °C/s) temperature profiles. The kinetic rates extracted from the observations were compared to models for long-range diffusion-controlled and interface reaction-controlled migration. The transition between the two mechanisms was found to occur at T0, which defines the temperature and composition at which a partitionless phase transformation is possible. Occurrence of the partitionless, interface-controlled transformation was confirmed by an analysis of carbon distribution and microstructure before and after a sample was subjected to a particular thermal profile. The mobility of such interfaces was found to be in the range 1.6·10-13 to 2·10-12 m4·J-1 ·s-1, which is consistent with previous studies on interface-controlled migration of the reverse reaction, α to γ, during cooling of dilute substitutional iron alloys. The diffusion-controlled migration, at temperatures belowT0, was found to occur in two stages: an initial stage, at which the growth rate can be predicted by a semi-infinite diffusion model; and a second stage, at which the growth slows more rapidly, possibly due to the overlap of diffusion fields.

Original languageEnglish (US)
Pages (from-to)698-715
Number of pages18
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume38
Issue number4
DOIs
StatePublished - Apr 2007
Externally publishedYes

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

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