Stuty Of Phase Composition And Performance Of Gas Nitrided25Cr2MoVA Steel

25Cr2MoVA steel is pearlitic steel and mediun carbon alloy structural steel with high strength and toughness.25Cr2MoVA steel has wide applications, which is used to make the stem, shaft, rotor, gear and so on. Due to the presence of Cr, Mo, V and other elements, it can be nitrided well. In order to meet the performance requirements in practical application, we have nitrided the steel via one-step gas nitriding method for the purpose of further improving the surface hardness and wear resistance. Samples got the γsingle-phase compound layer by adjusting the nitriding parameters. The surface wear resistance are further improved.The micro structures were discussed and analyzed by means of metallography, to determine porosity and permeability level of nitrided layer. The phase composition of compound layer was analyzed by means of X-ray diffraction. Surface hardness, brittleness, nitrided layer depth, compound layer thickness were analyzed by means of microhardness tester. Wear resistance were analyzed using MM200wear tester. Surface morphology of the samples after wear were discussed by means of field-emission scanning electron microscope, in order to analyzed wear mechanisms of nitrided layer. Through the above analysis and discussion, we studied the effects of nitrogen potential, nitriding time, nitriding temperature for25Cr2MoVA steel performance. The goal was to obtain optimal parameter.Microstructure and XRD showed that the compound layer thickness increased with rising of nitrogen potential, nitriding temperature, nitriding time. The compound layer thickness obviously increased when nitrogen potential was less than1. Phase composition of compound layer was determined mainly by nitrogen potential. The y’ single-phase compound layer was closely obtained when nitrogen potentials were0.5,0.2.The content of increased with increasing of nitrogen potential nitriding temperature and nitriding time has little impact on ε-phase content.Microhardness test demonstrated that the surface hardness markedly enhanced after nitriding. The hardness increased with rising of nitrogen potential, nitriding temperature. The depth of the nitrided layer was evaluated by means of hardness method. It was indicated that the depth increased with rising of nitriding temperature, nitriding time, yet had less to do with nitrogen potential. Microhardness of nitrided layer formed gradient from high to low from surface to interior. The surface topography of the samples showed that the surface of original sample had large size peeling and tearing. Shallow scratches or smaller pits were observed on the surface of nitrided samples. It followed fatigue wear characteristics. The hard particles occurred plastic deformation of, but there were no peeling.Wear test results showed that the wear scar width changed gently. The wear scar width of the nitrided samples followed the general law for the weariness of nitrided layer, i.e., running-in and steady-state wear stages after wear90min. Wear scar width of nitride samples are smaller than the original sample specimen, i.e., the wear resistance of nitrided samples is significantly increased. We suggested that the optimum wear resistance could be obtained when the nitriding process was T=520℃, KN=0.5, t=5h by the comparison of wear depth, wear volume.