Mechanism of austenite recrystallization induced by martensitic reversion in super invar cast alloy
Mechanism of austenite recrystallization induced by martensitic reversion in super invar cast alloy
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DOI：
10.1016/j.mtla.2020.100995
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发表时间：
2021-01-02
期刊：
影响因子：
3.4
通讯作者：
Nakada, Nobuo
中科院分区：
文献类型：
--
作者：
Rui, Bao;Sakaguchi, Naoki;Nakada, Nobuo
最近，据报道，通过由零度以下处理和随后的退火组成的新型热处理，在具有粗晶奥氏体结构的超级因瓦铸造合金中实现了显著的晶粒细化。利用电子背散射衍射分析了奥氏体晶粒细化机理。在低温处理后，沿着具有较低Ni浓度的枝晶观察到沿着的透镜状马氏体，然后，在退火时通过马氏体转变逆转为奥氏体。双向马氏体相变导致双相奥氏体组织的形成，该双相奥氏体组织由具有粗晶结构的未转变奥氏体和反转奥氏体组成。此外，由于在未转变的奥氏体与反转的奥氏体接触的区域处的原奥氏体晶界的凸出而形成再结晶晶粒。再结晶的奥氏体晶粒优选地朝向具有退火孪晶的反转奥氏体生长，这是由于反转奥氏体中的高位错密度，导致随机取向的细晶粒奥氏体结构。
Recently, significant grain refinement in super invar cast alloy having a coarse-grained austenitic structure was reportedly achieved through a novel heat treatment consisting of subzero treatment and subsequent annealing. We investigated the austenite grain refinement mechanism by microstructural analysis using electron backscatter diffraction. Lenticular martensite was observed along the dendrite having a lower Ni concentration after the subzero treatment, which then, reversed to austenite via martensitic transformation upon annealing. The bidirectional martensitic transformation led to the formation of duplex austenitic structure consisting of untransformed and reversed austenite having a coarse-grained structure. Furthermore, recrystallized grains were formed due to the bulging of the prior austenite grain boundaries at regions where untransformed austenite was in contact with reversed austenite. The recrystallized austenite grains preferred growing toward the reversed austenite having annealing twins due to the high dislocation density in the reversed austenite, resulting in a randomly oriented fine-grained austenitic structure.