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Open AccessArticle

Determination of the Critical Stress Associated with Dynamic Phase Transformation in Steels by Means of Free Energy Method

1
Mechanical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
2
Federal Institute of Education, Science and Technology of Maranhao, Sao Luis 65075-441, Maranhao, Brazil
3
Materials Engineering, McGill University, Montreal, QC H3A 0C5, Canada
4
Département de Génie Mécanique, École de Technologie Supérieure, Montreal, QC H3C 1K3, Canada
*
Author to whom correspondence should be addressed.
Metals 2018, 8(5), 360; https://doi.org/10.3390/met8050360
Received: 30 April 2018 / Revised: 11 May 2018 / Accepted: 14 May 2018 / Published: 16 May 2018
The double differentiation method overestimates the critical stress associated with the initiation of dynamic transformation (DT) because significant amounts of the dynamic phase must be present in order for its effect on the work hardening rate to be detectable. In this work, an alternative method (referred to here as the free energy method) is presented based on the thermodynamic condition that the driving force is equal to the total energy obstacle during the exact moment of transformation. The driving force is defined as the difference between the DT critical stress (measured in the single-phase austenite region) and the yield stress of the fresh ferrite that takes its place. On the other hand, the energy obstacle consists of the free energy difference between austenite and ferrite, and the work of shear accommodation and dilatation associated with the phase transformation. Here, the DT critical stresses in a C-Mn steel were calculated using the free energy method at temperatures ranging from 870 °C to 1070 °C. The results show that the calculated critical stress using the present approach appears to be more accurate than the values measured by the double differentiation method. View Full-Text
Keywords: dynamic transformation; free energy method; critical stress; DT ferrite dynamic transformation; free energy method; critical stress; DT ferrite
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MDPI and ACS Style

Aranas, C., Jr.; Rodrigues, S.; Fall, A.; Jahazi, M.; Jonas, J. Determination of the Critical Stress Associated with Dynamic Phase Transformation in Steels by Means of Free Energy Method. Metals 2018, 8, 360.

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