目的 提高20CrMnTi钢表面硬度及耐磨性能。方法 采用粉末包埋法在20CrMnTi钢表面制备了碳铌复合渗层。粉末渗铌剂组成为铌粉、氧化镧、氧化铝及氯化铵，渗铌温度为950 ℃，保温时间为5 h。通过光学显微镜、扫描电子显微镜、显微硬度计、能谱仪、X射线衍射仪及微动摩擦磨损试验机，研究了不同La2O3添加量条件下，碳铌复合渗层的硬度、厚度、组织、物相组成及摩擦系数。结果 不同La2O3添加量条件下，复合渗层主要由NbC相组成，厚度为23~28 mm，硬度为2250~2950HV0.5。随着La2O3添加量的增加，复合渗层物相组成变化不明显，渗层晶粒尺寸先增大后减小，厚度逐渐下降，硬度先上升后逐渐下降，摩擦系数基本是先上升后下降。稀土添加量（质量分数）为0.5%时，其摩擦系数较低。结论 粉末包埋复合渗铌渗剂中，La2O3的最佳添加量为0.5%，能细化渗层晶粒尺寸，有利于提高20CrMnTi表面碳铌复合渗层的致密性及硬度。

This work aims to improve surface hardness and wear resistance of 20CrMnTi steel. Composite carbon-niobiumizing coatings were prepared on 20CrMnTi steel surface in powder packing method. The niobiumizing agent was composed of Nb powder, La2O3, Al2O3 and NH4Cl. Treating temperature was 950 ℃ and holding time was 5 h. Microhardness, thickness, microstructure, phase composition and friction coefficient of the carbon-niobiumizing coatings with different content of La2O3 (0%, 0.5%, 1%, 2%) were characterized with OM, SEM, microhardness tester, EDS, XRD and fretting tribotester. Main phase of the prepared coatings with different content of La2O3 was NbC. The thickness and microhardness of carbon-niobiumizing coatings was 23~28 mm and 2250~2950HV0.5, respectively. With the increase of La2O3 content, phase composition of the carbon-niobiumizing coating was similar, both microhardness and grain size of carbon-niobiumizing coatings first increased and then decreased, while the thickness decreased gradually. With the increase of La2O3 content, friction coefficient of carbon-niobiumizing coatings first increased and then decreased. The friction coefficient was the lowest when the La2O3 content was 0.5wt%. In summary, the optimum content of La2O3 in powder-packed composite niobiumizing agent is 0.5wt%. Addition of 0.5wt%La2O3 can refine grains size of carbon-niobiumizing layer, and improve hardness and density of composite carbon-niobiumizing coatings on 20CrMnTi surface.