【摘要】 研究了M50NiL齿轮钢渗碳后的等离子渗氮温度对脉状组织形成的影响。利用金相显微镜、扫描电镜和自动显微硬度计等分析了碳氮复合渗层的碳氮化物、元素分布、显微硬度等。结果表明：随着离子渗氮温度的降低，表面白亮层厚度逐渐减少，在520、495和470℃离子渗氮时白亮层厚度分别约为10、3.6和2.7μm。渗碳试样的渗碳层厚度接近1900μm,表层硬度为740 HV0.2,经离子渗氮后试样表层硬度接近1200 HV0.2,比渗碳试样提高62%。经520℃离子渗氮后，M50NiL钢复合渗层中存在大量脉状析出物，主要为碳氮化物并在晶界位置聚集。离子渗氮温度由520℃降低到470℃时，碳氮化物析出相形态进一步改善为以圆形及椭圆形为主，少量以短棒状形态存在，脉状组织基本消除。这种复合渗层组织具有超高硬度，可进一步增加材料表面残余压应力，并且使用时可以避免在脉状组织聚集的晶界快速萌生裂纹，有利于提高构件的接触疲劳和弯曲疲劳强度。更多还原

【Abstract】 Effect of plasma nitriding temperature on the formation of vein-like structures in carburized M50NiL gear steel was investigated. Metallographic microscopes, scanning electron microscopes(SEM) and automatic microhardness tester were used to analyze the carbonitrides, element distribution and microhardness of the combined carburizing-nitriding layer. The results show that as the plasma nitriding temperature decreases, the thickness of the surface white layer gradually reduces, which is approximately 10, 3.6 and 2.7 μm at the plasma nitriding temperature of 520, 495 and 470 ℃, respectively. The carburized layer thickness of the carburized specimens is close to 1900 μm, with a surface hardness of 740 HV0.2. After plasma nitriding, the surface hardness of the specimens reaches nearly 1200 HV0.2, by an increase of 62% compared to the carburized specimens. After plasma nitriding at 520 ℃, a large number of vein-like precipitates appear in the combined layer of the M50NiL steel, which is primarily carbonitrides and mainly accumulate at grain boundaries. When the plasma nitriding temperature is reduced from 520 ℃ to 470 ℃, the morphology of carbonitride precipitates is further improved to exhibit a circular or elliptical shape, with a small amount in a short rod-like form, and the vein-like structures are basically eliminated. This combined carburizing-nitriding layer structure possesses ultra-high hardness, which further increases the surface residual compressive stress of the material and can prevent the rapid initiation of cracks at grain boundaries where vein-like structures tend to accumulate during service, thereby contributing to the improvement of the contact fatigue strength and bending fatigue strength of components.更多还原