Abstract: Using 40Cr as the matrix material, the low temperature QPQ nitriding process at 450 ℃ was accelerated by applying direct current (DC) electric field and the corresponding mechanism was studied. The microstructure, thickness, hardness and phases of the nitriding layer of the treated samples were analyzed. The results show that when the DC electric field is applied and holding for 2 h, the compound layer thickness of the sample can reach 18 μm, which is similar to that of nitriding for 17 h without DC electric field. It means that the DC electric field significantly increases the nitriding speed. The surface hardness of the steel reaches 813 HV0.1 after applying DC electric field, which is 1.3 times of that without DC electric field. The DC electric field can make more CNO^- ions to exist around the anode sample, providing extra energy for the decomposition of CNO^- ions and obtaining more active nitrogen atoms required for nitriding, so as to achieve the accelerating effect of infiltration.

Key words: QPQ process, direct current electric field, accelerated nitriding, mechanism