High-Strength Bainitic Steels

With careful design, mixed microstructures consisting of fine plates of upper bainitic ferrite separated by thin films of stable retained austenite have exhibited impressive combinations of strength and toughness in highsilicon bainitic steels. The silicon suppresses the precipitation of brittle cementite leading to an improvement in toughness. The essential principles governing the optimisation of such microstructures are well established, particularly that large regions of unstable high-carbon retained austenite must be avoided. The aim of the present work was to see how far these concepts can be extended to achieve the highest ever combination of strength and toughness in bulk-samples, consistent with certain hardenability and processing requirements.