Microstructure, properties and process optimization of laser nitrogen alloyed coating on 45 steel
Li Haitao, Fan Shuaiqi, Zhang Leitao, Dai Jiaoyan, Xu Jinfu
2021, 46(8):
209-213.
doi:10.13251/j.issn.0254-6051.2021.08.040
Abstract
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Nitrogen alloyed layer was prepared on the surface of 45 steel by using laser alloying technology, and the alloying process parameters were optimized by orthogonal test, then the microstructure and properties of the alloyed layer obtained by the optimized process treatment were studied by means of OM, XRD, microhardness tester and friction-abrasion testing machine. The results show that with the increase of laser power and scanning speed, the hardness of alloyed layer increases at first and then decreases, reaching the maximum values of 782 HV0.3 and 725 HV0.3 at 1.0 kW and 500 mm·min-1, respectively. With the increase of overlap ratio, the hardness of alloyed layer decreases gradually, and the optimal process is as follows: laser power of 1.0 kW, scanning speed of 500 mm·min-1 and overlap ratio of 30%. The microstructure of the alloyed zone after optimized process treatment is composed of solid solution phases and compounds such as γ-(Fe, N), γ-(Fe, C), acicular martensite, γ′(Fe4N), ε(Fe2N) and Fe3C, mainly consisting of columnar and cellular crystals, with a thickness of about 120 μm and an average hardness of about 816 HV0.3. The microstructure of the heat affected zone is composed of a small amount of acicular martensite and retained austenite. The thickness is about 200 μm, and the hardness is graded from 768 HV0.3 to 242 HV0.3. The friction coefficient of the alloyed layer is about 0.4827, and the wear rate is 8.218×10-15 m3·N-1·m-1.
