Mechanism of the bainite transformation: a turning point

The 99th Edward de Mille Campbell Memorial Lecture

H. K. D. H. Bhadeshia

Abstract

Some aspects of the theory for iron and its alloys have a chequered history, witness the β-iron controversy, the notion that molecules can move through iron, and not least, the mechanism of the bainite transformation. There was a period in which bainite was designated a non-lamellar eutectoid with no participation of shear, even though the deformation was there for all to see. We have come a long way since, so much so, that calculations have led the creation of new steels that are now commercial, including the world's first bulk nanostructured steel, and transportation infrastructure that has seen more than a billion gross-tonnes of traffic. My goal in this lecture is to highlight the depth of quantitative understanding and to resolve a few oddities. This does not minimise the wonderful experiments that have flourished, not just in establishing reality, but in stimulating discoveries such as the tetragonality of the crystal structure of bainitic ferrite, emulating the discovery made originally by Fink and Campbell of asymmetric martensite, exactly 100 years ago.

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