Effect of pressurized solution nitriding on phase changes and mechanical properties of ferritic Fe-22.7Cr-2.4Mo stainless steel
Effect of pressurized solution nitriding on phase changes and mechanical properties of ferritic Fe-22.7Cr-2.4Mo stainless steel
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DOI：
10.1016/j.msea.2013.10.103
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发表时间：
2014-01-13
期刊：
影响因子：
6.4
通讯作者：
Akbari, Alireza
中科院分区：
文献类型：
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作者：
Mohammadzadeh, Roghayeh;Akbari, Alireza
研究了铁素体Fe-22.7Cr-2.4Mo不锈钢在压力为0.25 MPa、1200℃的氮气中不同时间的加压渗氮。采用x射线衍射、光学显微镜、扫描电镜和拉伸试验对其组织和力学性能进行了表征。随着渗氮时间的延长，铁素体向奥氏体的相变从试样表面开始，并进一步向芯部扩展。2 mm厚的板材渗氮9 h后获得了完全的奥氏体组织。氮化12 h后，在样品边缘发现了形态不连续的条状氮化铬析出物。根据晶格参数计算，估计奥氏体相的平均溶质氮含量在1.25 ~ 1.75 wt%之间。屈服强度在900 MPa以上随PSN时间的增加而单调增加。溶液氮化6 h后试样具有较高的断裂伸长率（30%以上）和较高的抗拉强度（1000 MPa以上）。渗氮使断裂模式由延性断裂转变为晶间和穿晶混合脆性断裂。平面滑移带的形成是导致奥氏体相脆性断裂的主要原因。氮化铬的析出有利于脆性断裂。为了抑制氮化铬的析出，应优化PSN的时间。(C) 2013 Elsevier B.V.版权所有
Pressurized solution nitriding (PSN) of ferritic Fe-22.7Cr-2.4Mo stainless steel at 1200 degrees C in nitrogen gas under pressure of 0.25 MPa for different times has been investigated. The structure and mechanical properties were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy and tensile testing. Phase transformation of ferrite to austenite starts from the sample surface and grows further into the core with increasing nitriding time. A fully austenitic structure was achieved after 9 h nitriding for plates of 2 mm thick. Strip-like chromium nitride precipitates with discontinuous morphology are found in the edges of the sample nitrided for 12 h. The average solute nitrogen content of austenite phase was estimated based on lattice parameter calculations to vary from 1.25 to 1.75 wt%. The yield strength is monotonically increased above 900 MPa with increasing the PSN time. The solution nitrided samples for 6 h exhibit high elongation to fracture (above 30%) and high tensile strength (above 1000 MPa). Solution nitriding changes the fracture mode from ductile to a mixed mode inter-granular and trans-granular brittle fracture. Formation of the planar slip bands plays a major role in brittle fracture of the austenite phase. Brittle fracture is favored with precipitation of chromium nitrides. The time of the PSN should be optimized to suppress chromium nitride precipitation. (C) 2013 Elsevier B.V. All rights reserved.