Investigation and modeling of the effect of pre-deformation of austenite on the kinetics of ferritic transformation

A.A. Vasilyev, D.F. Sokolov, S.F. Sokolov show affiliations and emails
Received  06 October 2020; Accepted  11 December 2020
Citation: A.A. Vasilyev, D.F. Sokolov, S.F. Sokolov. Investigation and modeling of the effect of pre-deformation of austenite on the kinetics of ferritic transformation. Lett. Mater., 2021, 11(1) 90-94
BibTex   https://doi.org/10.22226/2410-3535-2021-1-90-94

Abstract

Based on the obtained experimental data a physically motivated model is formulated for the ferritic transformation with allowance for the effects of deformation and concurrent recovery of austenite. The model is first to evaluate variation of nucleation barriers owing to the hydrostatic component of internal stresses at austenite grain boundaries.The kinetics of transformation of undeformed and deformed austenite during continuous cooling has been investigated on several industrial steels. Dimensions of both prior austenite grains and ferrite grains in ferrite-pearlite structures obtained for various states of the parent austenite and cooling rates have been determined. At low cooling rates, no notable effect of austenite deformation on the temperature of the onset of ferritic transformation has been found. This effect gains in significance at higher cooling rates that is seemingly due to a weaker recovery of the deformed austenite. Similarly, the deformation of austenite influences the temperature of the transformation finish, although in this case the effect of the cooling rate on the increase of this temperature is lesser. As expected, the pre-deformation of the austenite shifts the transformation range to higher temperatures. Based on the obtained experimental data, a physically motivated model is formulated for the ferritic transformation with allowance for the effects of deformation and concurrent recovery of austenite. To predict properly the nucleation rate, the variation of nucleation barriers at the austenite grain boundaries is considered, which is due to the hydrostatic component of the deformation-induced internal stresses. The present model is first to allow for this effect exponentially increasing the nucleation rate. The simulated kinetics of the ferritic-pearlitic transformation in the investigated steels satisfactorily comply with the experiments. Experimental verification of the ferrite grain sizes predicted for both undeformed and deformed austenite is satisfactory as well. The relative errors of these predictions averaged over all considered steels, are 10.8 and 13.2 %, respectively.

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Funding

1. Russian Science Foundation - Project No. 19-19-00281