A Study of Diffusion- and Interface-Controlled Migration of the Austenite/Ferrite Front during Austenitization of a Case
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DOI: 10.1007/s11661-007-9208-4 The Minerals, Metals & Materials Society and ASM International 2007
Erratum to: METALLURGICAL AND MATERIALS TRANSACTIONS A, Vol. 38A, No. 2, February 2007, pp. 244–60 DOI: 10.1007/s11661-006-9029-x
THE color figures in this article were inadvertently printed in black and white in the printed issue. The article is reprinted in its entirety on the following pages.
ERIC D. SCHMIDT, Graduate Student, and SEETHARAMAN SRIDHAR, Professor, are with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA. Contact e-mail: [email protected] E. BUDDY DAMM, Principal Materials Engineer, is with The Timken Corporation, Canton, OH 44706-0930, USA. The online version of the original article can be found under doi:10.1007/s11661-006-9029-x. Article published online May 30, 2007. 698—VOLUME 38A, APRIL 2007
METALLURGICAL AND MATERIALS TRANSACTIONS A
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, and SEETHARAMAN SRIDHAR 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 1.6Æ10)13 to 2Æ10)12 m4ÆJ)1Æs)1, which is consistent with previous studies on interface-controlled migration of the reverse reaction, a to c, during cooling of dilute substitutional iron alloys. The diffusioncontrolled migration, at temperatures below T0, 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. DOI: 10.1007/s11661-006-9029-x The Minerals, Metals & Materials Society and ASM International 2007
I.
INTRODUCTION
THE austenitization of medium to low-alloy carbon steels is an important part of many industrial heat treating procedures. It has not, however, received the more rigorous treatment that has been accorded to austenite decomposition into its several products (e.g., Refe
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