| NI Jia,MA Heng,YU Minhua,HU Jing,AN Xulong,WEI Kunxia.Regulation of Structure and Properties of Nitriding Layer by Post Plasma Oxidation[J],53(17):170-175 |
| Regulation of Structure and Properties of Nitriding Layer by Post Plasma Oxidation |
| Received:August 24, 2023 Revised:January 08, 2024 |
| View Full Text View/Add Comment Download reader |
| DOI：10.16490/j.cnki.issn.1001-3660.2024.17.015 |
| KeyWord:42CrMo4 steel plasma nitriding post plasma oxidation hardness toughness corrosion resistance |
| Author | Institution |
| NI Jia |
Jiangsu Key Laboratory of Materials Surface Science and Technology,National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou , China |
| MA Heng |
Jiangsu Key Laboratory of Materials Surface Science and Technology,National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou , China |
| YU Minhua |
Jiangsu Key Laboratory of Materials Surface Science and Technology,National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou , China;Jiangsu Shuangliang Boiler Co., Ltd., Jiangsu Jiangyin , China |
| HU Jing |
Jiangsu Key Laboratory of Materials Surface Science and Technology,National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou , China;Huaide College, Changzhou University, Jiangsu Jingjiang , China |
| AN Xulong |
Jiangsu Key Laboratory of Materials Surface Science and Technology,National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou , China;Huaide College, Changzhou University, Jiangsu Jingjiang , China |
| WEI Kunxia |
Jiangsu Key Laboratory of Materials Surface Science and Technology,National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Jiangsu Changzhou , China;Huaide College, Changzhou University, Jiangsu Jingjiang , China |
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| Abstract: |
| Plasma nitriding is an environment-friendly and efficient surface modification technology. A nitrided layer composed of a compound layer on the top surface and a diffusion layer beneath can be formed on the surface of the sample treated by plasma nitriding, thus improving the performance of the sample. However, since the compound layer is hard and brittle, it has a strong tendency to crack while being subject to severe and heavy load, such as heavy load gears and impact molds. Therefore, it is necessary to avoid thicker compound layers for components that suffer severe impact and heavy load wear in order to prevent premature failure. At present, most factories use grinding to reduce the thickness of the compound layer, but this method has obvious disadvantage because it is difficult to control the grinding amount. Therefore, in order to obtain the required thickness of the effective hardened layer with fewer compound layers, it is crucial to find a technique to regulate the structure of the plasma nitriding layer, which has significant scientific research and application value. The work aims to explore and develop a novel method to regulate the structure of the plasma nitriding layer. The method was used to conduct post oxidation after plasma nitriding. The whole process was consisted of the following two steps:firstly, 42CrMo4 steel was subject to plasma nitriding at 500 ℃ for 5 hours and secondly, post oxidation was carried out at different temperatures for different time. The effect of the post oxidation temperature and time on the structure of the plasma nitriding layer was systematically investigated and the related mechanism was analyzed. The optical microscope, X-ray diffractometer, Vickers microhardness tester, and electrochemical workstation were used to examine and assess the microstructures, phase composition, hardness, toughness, and corrosion resistance of the nitriding layer. After the same plasma nitriding conditions of 500 ℃ for 5 hours, it was found that with the change of the post oxidation temperature and time, the compound layer formed by plasma nitriding gradually decomposed, and the thickness of the compound layer decreased from 9.41 μm to a minimum value of 3.62 μm. Meanwhile, the thickness of effective hardened layer and surface hardness after post oxidation were higher than that only by plasma nitriding without post oxidation. The thickness of effective hardened layer increased from 300 μm to a maximum value of 378 μm, and the sectional hardness increased from 765HV0.05 to 825HV0.05. An oxide film composed of Fe3O4 and Fe2O3 was formed on the surface of the compound layer, and the self-corrosion potential increased from −658.72 mV to −429.23 mV, which could prove that the corrosion resistance was improved. In all, after post oxidation treatment, the thickness of compound layer decreases significantly, while the thickness of effective hardened layer increases. At the same time, post oxidation can improve the hardness, toughness and corrosion resistance of 42CrMo4 steel. The maximum hardness and the best toughness and corrosion resistance are obtained by post oxidation at 400 ℃ for 2 hours. |
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