A lecture given by Sundaranam Babu, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. The interpretation of bainitic microstructures that develop very rapidly during flash processing. An innovative rapid heat-treating process (flash processing) that uses rapid heating to austenite phase field and quenching has been developed to produce high strength steels. Flash processing lead to tensile strengths greater than 1600 MPa and uniform elongation greater than 7%. In order to rationalise the microstructure evolution, the microstructures before and after processing were characterised. The initial microstructure contained ferrite and spherodised cementite. The final microstructure, after processing, contained a mixture of bainite and martensite with interspersed un-dissolved cementite particles. The above microstructure evolution was evaluated with computational thermodynamic and kinetic models. Interface motion between M3C diffusion couple, subjected to linear heating, supported the above microstructure evolution. The calculations show that the rapid dissolution of M3C in Fe-C system, in contrast to sluggish dissolution in Fe-Cr-C system. Generality of flash processing for wider range of steel systems is explored.