The law of growth of nitrided layers produced by gaseous nitriding of 31CrMoV9 alloy steel at different process parameters is described. 31CrMoV9 steel specimens were subjected to nitriding process in ammonia gas at three different temperatures: 510, 550 and 590• C, and for each temperature four different nitriding times were used. This way twelve specimens were produced. Nitrided specimens were investigated with optical microscopy, electron probe micro-analysis and x-ray diffraction. The nitrogen depth concentration profiles, deduced from electron probe micro-analysis, in conjunction with results of optical microscopy, were used to determine the thickness of the nitrided layers, i.e. the diffusion depth of nitrogen. From the dependence of the nitrided layer thickness on process parameters (temperature and time) it was possible to deduce the law that governs the growth of the nitrided layer for 31CrMoV9 alloy steel. Through this law, then, it is possible to predetermine the layer thickness for every real process parameter in nitriding of 31CrMoV9 steel, which is very important for technological applications.
This work is an experimental study of the hardness curve in the zone of diffusion for the gas nitriding process of 31CrMoV9 steel. 12 samples were subjected to gas nitriding at three different temperatures -510• C, 550• C, and 590• C -and for each temperature four different nitriding times were used. Hardness was measured with an automatic microhardness tester PCE from LECO with a load of HV0.1 (0.9807N), and the distance between the points was 50 µm. It was found that the hardness of the diffusion layer changed from 602 HV to 787 HV. The maximum surface hardness was found at 510• C after nitriding for 16 h. Depending on the process parameters, the depth of the diffusion layer ranged from 270 µm to 700 µm. From the results we can draw conclusions for the gradient curve of nitriding parameters, and from each curve we can find the depth of the diffusion of nitrogen in steel.
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