Hardness Curves for 31CrMoV9 Steel after Gas Nitriding

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.