低炭素鋼の塑性変形されたオーステナイトの粒界から生成するフェライト粒の形,大きさと結晶方位

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The influence of plastic strain on the shape, size and crystallographic orientation of ferrite (α) grains formed at the grain boundaries of the deformed austenite (γ) was studied in a 0.17C-0.3Si-1.5Mn steel. Specimens with a coarse γ grain size of 300μm were compressed at 1023K and cooled at 10K/s. When the plastic strain increased to 0.4, the shape of α grains changed from plate like to equiaxed, and the average length of α grains decreased from 12 to 6μm. However, the average length did not change in the larger plastic strains up to 1.1. On the other hand, the average thickness of α grains was constant regardless of the plastic strain. The crystallographic orientations of the α grains formed at one γ grain boundary were almost the same when the plastic strain was smaller than 0.2 and the α grain shape was plate like. However, the orientations were widely distributed, and most of the α/α boundaries were high angle ones, when the plastic strain was larger than 0.4 and the α grain shape was equiaxed. The shape change and α grain refinement by the deformation resulted from the wide distribution of crystallographic orientations of α grains rather than from the increase in the nucleation rate. The wide distribution of crystallographic orientation of α grains is closely associated with the serrated austenite grain boundaries induced by the deformation.
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