Shape, size and crystallographic orientation of the ferrite grains formed at grain boundaries of deformed austenite in a low carbon steel

The influence of plastic strain on the shape, size and crystallographic ori entation of ferrite (alpha) grains formed at the grain boundaries of the de formed austenite (gamma) was studied in a 0.17C-0.3Si-1.5Mn steel, Specimen s with a coarse gamma grain size of 300 mum were compressed at 1023K and co oled at 10K/s. When the plastic strain increased to 0.4, the shape of alpha grains changed from plate like to equiaxed, and the average length of a gr ains decreased from 12 to 6 mum. However, the average length did not change in the larger plastic strains up to 1.1. On the other hand, the average th ickness of alpha grains was constant regardless of the plastic strain. The crystallographic orientations of the alpha grains formed at one gamma train boundary were almost the same when the plastic strain was smaller than 0.2 and the alpha grain shape was plate like. However, the orientations were w idely distributed and most of the alpha/alpha boundaries were high angle on es, when the plastic strain was larger than 0.4 and the alpha grain shape w as equiaxed. The shape change and alpha grain refinement by the deformation resulted from the wide distribution of crystallographic orientations of al pha grains rather than from the increase in the nucleation rate. The wide d istribution of crystallographic orientation of alpha grains is closely asso ciated with the serrated austenite grain boundaries induced by the deformat ion.