| WANG Yixuan.Effect of Gas Pressure on Microstructures and Properties of Plasma Nitrided Layer on Alloy Steels[J],53(7):200-207 |
| Effect of Gas Pressure on Microstructures and Properties of Plasma Nitrided Layer on Alloy Steels |
| Received:December 29, 2023 Revised:February 01, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.07.021 |
| KeyWord:gas pressure plasma nitriding hardness friction and wear alloy steels |
| Author | Institution |
| WANG Yixuan |
School of Materials Science and Engineering, Anhui University of Technology, Anhui Ma'anshan , China |
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| Abstract: |
| Plasma nitriding is one of the surface hardening technology of alloy steels. Apart from nitriding temperature, nitriding duration and ratio of nitrogen to hydrogen, the gas pressure is a key parameter in the plasma nitriding process. Air pressure affects the number and energy of active particles (electrons, ions and energetic neutral atoms, etc.). The effect of alloying elements in steel and the effect of plasma nitriding pressure on the properties of the nitrided layer have not been considered in current studies. Thus, the effect mechanism is not clear. According to the national standard GB/T 30883-2017 (ion nitriding), the gas pressure of plasma nitriding is usually 0-500 Pa. However, the gas pressure has different effects on the properties of the plasma nitrided layer on the different alloy steels. Thus, M50NiL (high alloy steel) and AISI 4140 (low alloy steel) steels were selected as the objects in the present work. The effects of gas pressure on the microstructure, mechanical and tribological properties of the plasma nitrided layer on alloy steels were investigated. The plasma nitriding experiment with a gas pressure of 170 Pa, 250 Pa and 350 Pa was conducted. There were compound layers on the AISI 4140 steels, and the thickness of the compound layer of nitrided specimen decreased as the gas pressure increased. No compound layer was formed on the M50NiL steel due to the high content of alloy elements. The results demonstrated that the plasma nitrided layer of the specimen with a gas pressure of 350 Pa was the thickest. The specimen with a gas pressure of 170 Pa came the second. The specimen with a gas pressure of 250 Pa had the thinnest plasma nitrided layer. The gas pressure during the plasma nitriding treatment had an effect on the energy and distribution of nitrogen ions. Low gas pressure lead to a small number of high-energy nitrogen ions, and high gas pressure contributed to a mass of low-energy nitrogen ions. Thus, the gas pressure affected the thickness of the nitrided layer. Based on the indentation tests, the M50NiL steel with a gas pressure of 350 Pa and AISI 4140 steel with a gas pressure of 170 Pa showed excellent hardness and toughness. In other words, the high-density low-energy nitrogen ions were more helpful to the surface hardening of M50NiL steel. High-energy nitrogen ions contributed to the surface hardening of AISI 4140 steel. The alloy elements in steels and the gas pressure of plasma nitriding had a combined effect on the surface hardness and toughness of the nitrided layer. The test of tribological properties demonstrated that the wear performance of the nitrided specimen with a gas pressure of 170 Pa and 350 Pa was significantly better than the specimen of 250 Pa. The wear mechanism of the nitrided layer was abrasive wear and oxidation wear. The wear rate of the nitrided layer was consistent with the toughness values of the nitrided layer. The promising surface-hardening technology should be a method that not only increases the hardness of the surface layer but also provides a tough plastic surface. The present work provides a theoretical basis for the choice of gas pressure during the plasma nitriding. |
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