| METALS AND METAL MATRIX COMPOSITES |
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Effect of NH3 and CO Flow of Gas Nitrocarburizing on Microstructure and
Properties of Nitrocarburized Layers of Low-carbon Steel |
| XU Qiang, HONG Yue, LI Nan, WU Cuilan
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| College of Material Science and Engineering,Hunan University,Changsha 410082 |
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Abstract The microstructure and properties of the nitrocarburized layer are greatly affected by the nitriding potential and carbon potential in the atmosphere which can be directly controlled by the flow rate of NH3 and CO during nitrocarburizing. The effects of NH3 and CO flow on the microstructure and properties of the compound layer were investigated by scanning electron microscopy, X-ray diffractometer, microhardness tester and electrochemical analyzer. The results show that the thickness and porosity of the compound layer increases with the increasing NH3 flow du-ring gas nitrocarburizing. With the rising of CO flow, the compound layer becomes more compact, but the thickness of the compound layer increases first and then decreases. The addition of C in the nitrocarburized layer can restrain the formation of γ′ phase forming and promote the formation of ε phase. While the excess C would result in the emerging of θ phase. Fortunately, the permeated C show limited impact on the corrosion behavior of the compound layer. The combined effects of NH3 and CO on nitrocarburized layers can be realized through raising the flow rate of NH3 and the corresponding flow rate of CO appropriately, thus a thicker and compact compound layer with good corrosion-resistance can be formed successfully.
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Published: 31 January 2019
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| Fund:This work was financially supported by the National Natural Science Foundation of China (11427806,51671082,51471067). |
| About author:: Qiang Xu received his M.S. degrees in June 2018 from Hunan University in Material Science and Engineering. From September 2015 to June 2018, he stu-died the process and microscopic characterization of nitriding and nitrocarburizing of low carbon steel at the Institute of High Resolution Electron Microscope Center of Hunan University.Cuilan Wu, professor and doctoral supervisor of Hunan University,graduated from South China University of Technology in June 2005 with a doctorate in materials science. The design, microstructures, properties and heat treatment control of high strength steel, aluminium alloy and magnesium alloy are mainly studied. Metal materials (aluminium alloy, steel, magnesium alloy, titanium alloy) and non-metallic materials (SiC, foam) are studied by means of electron microscopy (including scanning electron microscopy, conventional transmission electron microscopy, high resolution transmission electron microscopy, etc.). The structure and interface of defects and precipitates in stone and chrysanthemum stone are measured by nano materials. |
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2019, Vol. 33 
