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Kinetics of austenite-ferrite and austenite-pearlite transformations in a 1025 carbon steel

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Abstract

Isothermal and continuous-cooling transformation kinetics have been measured dilatometrically for the γ → α+ γ′ and γ′→ P reactions in a 1025 steel. The isothermal transformation of austenite for each reaction was found to fit the Avrami equation after the fraction transformed was normalized to unity at the completion of the reaction and a transformation-start time was determined. The transformation kinetics under isothermal conditions therefore were characterized in terms of then andb parameters from the Avrami equation together with the transformation-start times. The parametern was found to be independent of temperature over the range studied (645 to 760 ‡C) and to have values of 0.99 and 1.33 for the ferrite and pearlite reactions, respectively. This indicates that the nucleation condition is essentially constant and site saturation occurs early in the transformation process. The continuous-cooling experiments were conducted at cooling rates of 2 to 150 ‡C per second to determine the transformation-start times for the ferrite and pearlite reactions and the completion time for transformation to pearlite under CCT conditions. Both reactions were found to obey the Additivity Principle for continuous cooling provided that the incubation (pre-transformation) period was not included in the transformation time. The isothermal transformation data and CCT transformation-start times have been incorporated in a mathematical model to predict continuous-cooling transformation kinetics that agree closely with measurements made at three cooling rates.

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Authors and Affiliations

  1. The Centre for Metallurgical Process Engineering, Department of Metallurgical Engineering, The University of British Columbia, V6T 1W5, Vancouver, BC, Canada

    E. B. Hawbolt (Professor), B. Chau (Research Engineer) & J. K. Brimacombe (Stelco Professor of Process Metallurgy)

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  1. E. B. Hawbolt
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  2. B. Chau
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  3. J. K. Brimacombe
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Hawbolt, E.B., Chau, B. & Brimacombe, J.K. Kinetics of austenite-ferrite and austenite-pearlite transformations in a 1025 carbon steel. Metall Trans A 16, 565–578 (1985). https://doi.org/10.1007/BF02814230

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