Crystallographic similarity between the lath martensite and lower bainite in medium-carbon alloy steels

Progress in the crystallography of lath martensitic and lower bainitic transformations is briefly reviewed, followed by a presentation of the experimentally measured crystallographic characteristics of both lath martensite and lower bainite formed in medium-carbon steels containing Si, Mn and Mo. It is found that the bainite plates relate to each other by a relative rotation of 54. 7 degrees or 60 degrees about the normal to their common close-packed planes {110} (h), which ensures a pseudo-{112} (b) twin relationship between two adjacent plates, and that all bainite variants for med in a single packet keep a unique G-T orientation relationship with the austenite matrix. These two types of OR of lower bainite are similar to that of the lath martensite, respectively. Furthermore, the measured habit planes of both the lower bainite and lath martensite are all {335} (f) type, which can verify the crystal lographic similarity between the lath martensite and lower bainite.