jats:titleAbstract</jats:title> jats:pI have on previous occasions shown how we can be surprised and delighted by new discoveries in steels, which at the same time may be useful. However, my focus in this lecture is purely on some basic science so that a well-founded understanding of mechanisms can lead to ever greater advances. The composite structure that is known colloquially as bainite is arguably the most interesting of all of the essential microstructures that occur in steels, where the manner in which atoms move is seminal to the design of steels. Therefore, I take the liberty to indulge myself and talk only of theory on this occasion.</jats:p>