亜包晶炭素鋼のオーステナイト結晶粒形成とそれに及ぼす炭素およびフェライト安定化元素の影響

概要

論文の詳細を見る
In order to investigate the formation process from δ dendrite to γ grain in a hypo-peritectic carbon steel, an unidirectionally solidifying carbon steel sample is quenched from a temperature above the solidus temperature. Three zones of primary dendrite, fine columnar grain and coarse columnar grain are observed in the sample. The dendritic zone consists of (L+δ) phase, the fine columnar grain is both phases of (L+δ+γ) and (δ+γ), and the coarse columnar grain is γ phase. The width of the fine columnar grain agrees with the primary arm spacing of the δ dendrite and it is the same result as that for a hyper-peritectic carbon steel. The γ grain boundary in the zone of the fine columnar grain forms at the skeleton of the δ dendrite, while that for a hyper-peritectic carbon steel forms at the position between the δ dendrites. Since transition from the fine columnar grain to the coarse one occurs immediately after the disappearance of δ phase, the δ phase prevents the coarsening of the fine columnar grain. A length of the zone of the fine columnar grain decreases with increasing carbon concentration. The length extends according to the addition of ferrite-stabilizing elements. The extended effect becomes stronger in the sequence of Nb>V>Mo, while Ni as an austenite-stabilizing element have no influence on the length.