The Bainite Transformation in Steel

In 1930, Davenport and Bain published micrographs of partially transformed specimens showing units of bainite in a matrix of martensite. They described the possible increase of the carbon content of bainitic ferrite with decreasing temperature. In 1934, Bain’s staff at US Steel started to use the term bainite. In 1952, Ko and Cottrell presented a work that has been the basis of two conflicting hypotheses considering the mechanism of bainite formation. Their observation of surface relief has been taken as support of the rapid displacive mechanism without diffusion of carbon while their observation of slow growth has been taken as support of the diffusional mechanism. It is amazing that such a controversy has not been resolved after more than 60 years. There should now be sufficient information to resolve the controversy. An attempt to examine available information will here be presented.