Bainite in Silicon Steels: A New Composition-Property approach. Part I

H. K. D. H. Bhadeshia and D. V. Edmonds

Abstract

Recent work on the mechanism of the bainite transformation has shown that the extent of transformation to bainitic ferrite, and the carbon content of the remaining austenite, can be estimated thermodynamically. This paper is concerned with the application of this work to the development of a quantitative relationship between the composition and some important mechanical properties of silicon containing steels, which can be transformed isothermally to an aggregate of bainitic ferrite and carbon enriched retained austenite only. It is demonstrated that the method has predictive capabilities, and forms the basis of further work (Part 2 of this study) on the theoretical design, optimization and testing of two promising steel compositions.

This research details the thermodynamic and mechanical principles governing the formation of bainite in silicon-rich steels. By using silicon to suppress the precipitation of brittle carbides, the researchers demonstrate how to create a microstructure consisting of bainitic ferrite and carbon-enriched retained austenite. This specific combination of phases is shown to provide enhanced toughness and strength compared to traditional heat-treated steels. The study emphasises that the morphology of the austenite, particularly the presence of thin films rather than large blocks, is critical for achieving superior mechanical stability. Ultimately, the authors present a predictive model that allows for the design of economical, high-performance alloys based on the chemical composition and transformation temperature.

Metal Science, Vol. 17, 1983, pp. 411-419.

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