Steels: overall transformation kinetics @bhadeshia123

Uploaded February 2022 | Updated September 2026, 2 weeks ago

In calculating a volume fraction of transformation as a function of time, temperature and chemical composition, it is necessary to possess models for nucleation and growth of each of the product phases, based on their respective mechanisms of transformation. However, this is not sufficient to estimate the volume fraction, because growing particles will eventually collide and the nucleation of new particles cannot occur in already transformed regions. This "hard impingment" is taken into account in Avrami theory by calculating first, an extended volume where particles can grow into each other, and then correcting that by multiplying by the fraction of untransformed austenite. This theory is then generalised to multiple, simultaneous transformations and applied to continuous cooling transformation. A case study is presented at the end of how to use such knowledge to design a hydrogen-resistant steel.

Associated teaching materials can be found on:
phase-trans.msm.cam.ac.uk/teaching.html
H. K. D. H. Bhadeshia

$Steels: overall transformation kinetics In calculating a volume fraction of transformation as a function of time, temperature and chemical composition, it is necessary to possess models for nucleation and growth of each of the product phases, based on their respective mechanisms of transformation. However, this is not sufficient to estimate the volume fraction, because growing particles will eventually collide and the nucleation of new particles cannot occur in already transformed regions. This hard impingment is taken into account in Avrami theory by calculating first, an extended volume where particles can grow into each other, and then correcting that by multiplying by the fraction of untransformed austenite. This theory is then generalised to multiple, simultaneous transformations and applied to continuous cooling transformation. A case study is presented at the end of how to use such knowledge to design a hydrogen-resistant steel. Associated teaching materials can be found on: http://www.phase-trans.msm.cam.ac.uk/teaching.html H. K. D. H. Bhadeshia$

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