Ferrite nucleation and growth during continuous cooling

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02649814· OSTI ID:264074

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 two hypoeutectoid plain carbon steels under continuous cooling conditions using a dilatometer on a Gleeble 1500 thermomechanical simulator. The experimental results were used to verify model calculations based on a fundamental approach for the dilute ternary system, Fe-C-Mn. The austenite-to-ferrite transformation start temperature can be predicted from a nucleation model for slow cooling rates and small austenite grain sizes, where ferrite nucleates at austenite grain corners. The nuclei are assumed to have an equilibrium composition and a pillbox shape in accordance with minimal interfacial energy. For higher cooling rates or larger austenite grain sizes, early growth has to be taken into account to describe the transformation start, and nucleation is also encouraged at the remaining sites of the austenite grain boundaries. 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 draglike effect on the boundary movement. Thus, growth kinetics are 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.

• Sponsoring Organization: USDOE
• OSTI ID: 264074
• Report Number(s): CONF-941016--
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 6 Vol. 27; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AUSTENITE
CARBON STEELS
DIFFUSION
ENERGY
GRAIN BOUNDARIES
GRAIN SIZE
INTERFACES
KINETICS
MATHEMATICAL MODELS
PHASE TRANSFORMATIONS
PREDICTION EQUATIONS
TEMPERATURE DEPENDENCE
VERIFICATION