Bainite: Mobility of the Transformation Interface

H. K. D. H. Bhadeshia

Abstract

Experimental evidence is provided to show that the interface responsible for the austenite to bainite transformation exhibits the essential characterisitics of a glissile, semi-coherent interface. The experiments involve a comparison between the rate of formation of bainite, and the mobility of an interface whose motion does not lead to the formation of invariant-plane strain surface relief effects. It is demonstrated that true thermally activated motion of the latter kind of interface is extremely slow at temperatures where bainite forms.

This research investigates the physical properties of the interface that facilitates the change from austenite to bainite in steel alloys. By comparing the speed of bainite growth against the much slower movement of diffusion-controlled boundaries, the author concludes that the transformation relies on a glissile, semi-coherent interface. Experimental data from a chromium-enriched steel alloy shows that while bainite forms rapidly, other structural perturbations take weeks to develop at the same temperature. The study asserts that the atomic movement during this process is more similar to martensitic transitions than to slow, thermally activated growth. Ultimately, these findings provide evidence that the mechanism of bainitic transformation is characterized by a specific type of conservative interfacial motion.

Journal de Physique, Colloque C4, No. 12, Vol. 43, 1982, pp. C4-437-441.

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