Self-stabilization of untransformed austenite by hydrostatic pressure via martensitic transformation
Self-stabilization of untransformed austenite by hydrostatic pressure via martensitic transformation
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DOI：
10.1016/j.actamat.2016.03.048
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发表时间：
2016-05-15
期刊：
影响因子：
9.4
通讯作者：
Takaki, Setsuo
中科院分区：
文献类型：
--
作者：
Nakada, Nobuo;Ishibashi, Yuji;Takaki, Setsuo
为了提高对钢中奥氏体稳定性的认识，从宏观和微观两方面评价了马氏体相变产生的未转化奥氏体的静水压力，并在Fe-27%Ni奥氏体合金中研究了静水压力对奥氏体稳定性的影响。x射线衍射分析表明，只有当马氏体成为主导相时，未转变奥氏体的晶格参数才会通过马氏体转变而不断降低。这表明未转变奥氏体受到周围马氏体晶粒的各向同性压缩，即在马氏体转变后期，未转变奥氏体动态产生静水压力。另一方面，利用电子背散射衍射技术进行的微观应变映射表明，更细的未转变奥氏体晶粒具有更高的静水压力，而在靠近奥氏体/马氏体界面的未转变奥氏体中，由于具有非热弹性马氏体转变特征的晶格不变剪切，也引入了高密度的位错。实验结果表明，静水压力稳定了未转变奥氏体；然而，单纯的奥氏体稳定效应不足以完全解释钢中马氏体起始和结束温度之间的巨大差距。(C) 2016材料学报Elsevier Ltd.出版。版权所有。
For improving the understanding of austenite stability in steel, hydrostatic pressure in untransformed austenite that is generated via martensitic transformation was evaluated from macro- and micro-viewpoints, and its effect on austenite stability was investigated in a Fe-27%Ni austenitic alloy. X-ray diffractometry revealed that the lattice parameter of untransformed austenite is continuously decreased via martensitic transformation only when martensite becomes the dominant phase in the microstructure. This suggests that the untransformed austenite is isotropically compressed by the surrounding martensite grains, i.e., hydrostatic pressure is generated in untransformed austenite dynamically at a later stage of martensitic transformation. On the other hand, microscopic strain mapping using the electron backscatter diffraction technique indicated that a finer untransformed austenite grain has a higher hydrostatic pressure, while a high density of dislocations is also introduced in untransformed austenite near the austenite/martensite interface because of lattice-invariant shear characterized by non-thermoelastic martensitic transformation. Furthermore, it was experimentally demonstrated that the hydrostatic pressure stabilizes the untransformed austenite; however, the austenite stabilization effect alone is not large enough to fully explain a large gap between martensite start and finish temperatures in steel. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.