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研究了纯铁及38CrMoAlA钢分别在500℃、0~0.4 MPa压力和510℃、0~0.5 MPa压力条件下的氨气渗氮行为.提高渗氮压力可显著加速气体渗氮动力学过程,纯铁在500℃和0.4 MPa下气体渗氮处理5 h后渗氮层厚度(1160μm)可同比达到常规渗氮层厚度(205μm)的5倍以上,而38CrMoAlA钢经510℃和0.5 MPa压力下渗氮5 h后的渗氮层厚度(400μm)几乎与常规渗氮50 h所得硬化层厚度(440μm)相当.同时,纯铁及38CrMoAlA钢渗氮层中ε-Fe2-3 N与γ′-Fe4 N的相比例、氮势及表层硬度均随压力的提高呈现先增加后降低的变化趋势.提出了一种合金结构钢表面高强高韧渗氮层快速复合制备工艺(增压渗氮+冷轧).与一段式常规渗氮及增压渗氮工艺相比,复合工艺处理表层硬度及韧性均较优良,尤其高剪切应力磨损条件下复合处理表层的耐磨性能最优,在20~600℃热循环处理10~300次条件下复合处理表层的耐热疲劳性能最佳.研究了42CrMo钢在既定的渗氮周期内(6 h)以NH3为介质,530℃及不同压力循环次数条件下的气体渗氮行为.在渗氮温度和总时间相同条件下,循环压力气体渗氮样品化合物层随压力循环次数的增加逐渐减薄,渗氮层整体厚度随压力循环次数的增加逐渐增加,同时渗氮表层韧性随压力循环次数的增加逐渐增强.

Gas nitriding of pure iron and 38CrMoAlA steel were performed in flowing NH3 at 500 ℃ for 5 h under nitriding pressures ranging from 0 to 0.4 MPa,and at 510 ℃ for 5 h under nitriding pressures ranging from 0 to 0.5 MPa,respectively.The results showed that,the increase in nitriding pressure markedly accelerated the gas nitri-ding kinetic process.Increasing the nitriding pressure from 0 MPa to 0.4 MPa significantly increased the thickness of nitrided layer in pure Fe from 205μm to 1160μm,and the thickness (400μm)of the nitrided layer in 38CrMoAlA sample nitrided under 0.5 MPa for 5 h was almost equal to that (440μm)of the conventional gas nitriding at 510 ℃for 50 h.The ratios of theε-Fe2-3 N phase toγ′-Fe4 N phase,nitriding potential and the surface hardness of nitrided pure iron and 38CrMoAlA steel first increased with increasing nitriding pressure and then decreased to a low level. The combined treatment of pressurized gas nitriding and cold rolling was proposed as a new approach to rapid prepara-tion of a strong and tough nitrided layer for steel 38CrMoAlA.The surface layer nitrided by the combined process showed better wear resistance under heavy loads and thermal fatigue resistance in comparison with that obtained by the conventional gas nitrding and pressurized gas nitriding treatment.The gas nitriding behaviors of 42CrMo steel in flo-wing NH3 gas at 530 ℃ for 6 h with cyclic pressures were investigated.Under the same nitriding temperature and du-ration,the thickness of the compound layer was decreased,whereas the total thickness of the nitrided layer and sur-face toughness were increased with increasing the pressure cycle numbers.