Austenite to ferrite transformation kinetics during continuous cooling

Technical Report · Sat Dec 31 04:00:00 EST 1994

DOI:https://doi.org/10.2172/34419· OSTI ID:34419

Militzer, M; Pandi, R; Hawbolt, E B ^[1]

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1. Univ. of British Columbia, Vancouver, British Columbia (Canada). Centre for Metallurgical Process Engineering

The austenite decomposition has been investigated in a hypo-eutectoid plain carbon steel under continuous cooling conditions using a dilatometer and a Gleeble 1500 thermomechanical simulator. The experimental results were used to verify model calculations based on a fundamental approach for the dilute ternary systems Fe-C-Mn. The austenite to ferrite transformation start temperature can be predicted from a nucleation model for slow cooling rates. The formation of ferrite nuclei takes place with equilibrium composition on austenite grain boundaries. The nuclei are assumed to have a pill box shape in accordance with minimal interfacial energy. For higher cooling rates, early growth has to be taken into account to describe the transformation start. In contrast to nucleation, growth of the ferrite is characterized by paraequilibrium; i.e. only carbon can redistribute, whereas the diffusion of Mn is too slow to allow full equilibrium in the ternary system. However, Mn segregation to the moving ferrite-austenite interface has to be considered. The latter, in turn, exerts a solute drag effect on the boundary movement. Thus, growth kinetics is controlled by carbon diffusion in austenite modified by interfacial segregation of Mn. Employing a phenomenological segregation model, good agreement has been achieved with the measurements.

• Research Organization: EG and G Idaho, Inc., Idaho Falls, ID (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States); American Iron and Steel Inst., Washington, DC (United States)
• DOE Contract Number: FC07-93ID13205
• OSTI ID: 34419
• Report Number(s): EGG-M--94205; CONF-940704--5; ON: DE95008582
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CARBON STEELS
COMPARATIVE EVALUATIONS
CRYSTAL-PHASE TRANSFORMATIONS
EXPERIMENTAL DATA
MANGANESE ADDITIONS
MATHEMATICAL MODELS
THEORETICAL DATA
TRANSITION TEMPERATURE