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目的：研究低温盐浴氮化17-4PH不锈钢经中温时效处理后氮化层组织性能的变化情况。方法采用光学显微镜（OM）分析氮化层的厚度和显微组织，利用X射线衍射仪（XRD）检测渗氮层的相组成，利用显微硬度计测定渗层的硬度，利用冲刷腐蚀实验评价渗层的耐腐蚀性能。结果17-4PH 不锈钢氮化后在425~475℃时效保温处理，其渗层厚度随时效时间的延长而增加。时效处理使渗层中N原子的浓度发生改变，过饱和扩展奥氏体发生分解，析出与其结构同为面心立方结构的Fe4N、Fe2N和CrN。时效温度的升高能加速扩展奥氏体的分解，促进CrN析出及氧化物的生成。经过渗氮时效后，渗层深度可达27.4μm。根据热力学公式计算出N原子在时效过程中的扩散激活能为216.2 kJ/mol，表面显微硬度在初期显著升高，达到了近1150HV0.1，随后逐渐降低。在475℃、50 d的时效条件下，冲刷腐蚀中的失重率达到最大值30.3 mg/(h·dm2)。结论不锈钢氮化后在一定的温度和时间内时效处理会达到最大表面硬度，在随后的保温过程中硬度开始下降。时效处理后17-4PH不锈钢的耐冲刷腐蚀性能下降。

ABSTRACT:Objective To study the change of the microstructures and properties of 17-4PH stainless steel after low temper-ature salt bath nitriding treatment and mid-temperature aging treatment.Methods The thickness and microstructure of the ni-triding layer were analyzed using optical microscope (OM) , the phase composition of the nitriding layer was determined by X-ray diffractometer (XRD), the hardness of the nitriding layer was measured by microhardness tester, and the corrosion resis-tance of the nitriding layer was evaluated by erosion-corrosion experiment.Results The thickness of the nitriding layer in- creased with the extension of aging time. The change of nitrogen concentration in nitriding layer during the aging treatment re-duced Gibbs free energy. This led to decomposition of expanded supersaturated austeinite into Fe4N with face-centred cubic structure. When it went up to a certain concentration, some Fe2N precipitated out. The decomposition rate of expanded auste-inite increased with rising temperature. Then, extension of aging time and rise of aging temperature promoted CrN to sepa-rate out. The depth of the nitrided layer was increased to 27.4μm; The active energy of nitrogen-atoms in 17-4PHstainless steel was 216.2 kJ/mol ascalculated form Thermodynamics formula; The surface microhardness significantly increased to nearly 1150HV0.1, and then gradually reduced; The erosion-corrosion mass loss rate of 17-4PH stainless steel reached its maximum value of 30.3 mg/(h·dm2) after 50 days of 475℃ aging treatment.Conclusion17-4PH stainless steel after nitriding could reach its maximum surface hardness after aging treatment at 425~475℃ for some time. Then, with the increasing aging time, its surface hardness and erosion-corrosion resistant performance reduced.