During the course of our research on the quantitative design of steels [1, 2], an exciting discovery was made, in which carbide–free bainite was obtained by transformation at incredibly low temperatures, as low as 125◦ C [3]. To put this into context, the random jump distance of an iron atom at that temperature is only 10− 17 m over a period of three weeks. The consequence of the low transformation–temperature was to reduce the scale of the microstructure to such an extent, that it became possible to achieve a strength of 2300 MPa with signs of considerable ductility. The work described in what follows was carried out to understand and design this extraordinary bainite, which is incredibly strong, tough and cheap. The combination of properties achieved has never before been reported for bainite.