In Situ Study on Interrupted Growth Behavior and Crystallography of Bainite

The growth behavior and crystallographic orientation of bainite in a low carbon steel were investigated by a combination of in situ observation and electron backscattered diffraction. The intersection of different bainitic ferrite (BF) laths was analyzed in detail. The results show that the growth of a given lath stops when it runs into a preexisting lath of bainitic ferrite. Growth resumes, after a short stasis, through the nucleation of a new lath on the other side of the obstructing lath. The newly nucleated lath has been termed BF-clone because it shares the same crystallographic orientation with the prior bainitic lath. The nucleation of the BF-clone is promoted by the accumulated transformation strain in the region where the growing lath intersected the pre-existing lath. During the growth of the bainitic ferrite laths, the transformation strain was accommodated through the formation of twin-related variant pairs, which formed one after another with the identical lengthening rates.