Shape, Size and Crystallographic Orientation of the Ferrite Grains Formed at Grain Boundaries of Deformed Austenite in a Low Carbon Steel

摘要

The influence of plastic strain on the shape, size and crystallographic orientation of ferrite (#alpha#) grains formed at the grain boundaries of the deformed austenite (#gamma#) was studied in a 0.l7C-0.3Si-l.5Mn steel. Specimens with a coarse #gamma# grain size of 300 #mu#m were compressed at 1023K and cooled 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 #alpha# grains decreased from 12 to 6 #mu#m. However, the average length did not change in the larger plastic strains up to 1.1. On the other hand, the average thickness of #alpha# grains was constant regardless of the plastic strain. The crystallographic orientations of the #alpha# grains formed at one #gamma# grain 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 widely distributed (and most of the #alpha#/#alpha# boundaries were high angle ones, when the plastic strain was larger than 0.4 and the #alpha# grain shape was equiaxed. The shape change and #alpha# grain refinement by the deformation resulted from the wide distribution of crystallographic orientations of #alpha# grains rather than from the increase in the nucleation rate. The wide distribution of crystallographic orientation of #alpha# grains is closely associated with the serrated austenite grain boundaries induced by the deformation.