An imaging atom-probe combined with a high mass-resolution energy-compensated time-of-flight spectrometer has been used to study localised composition changes at the interfaces whose motion leads to the formation of bainite in steels. "Bulk" compositional analysis of retained austenite and bainitic-ferrite has also been carried out, and the results are interpreted in terms of a new thermodynamic analysis which allows a better distinction between diffusion-controlled growth involving the formation of bainitic-ferrite with a partial supersaturation of carbon, and that in which the ferrite grows with the precise composition of the parent austenite (i.e. in essence martensitic). The fine scale distribution of substitutional alloying elements (Si, Mn) has also been examined. It is believed that the results can be best understood in terms of the martensitic growth of bainite sub-units.
Acta Metallurgica, Vol. 30, 1982, 775-784.
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