梯度M_7C_3增强铁基堆焊涂层显微结构与耐磨性研究

Investigation on microstructure and abrasion resistance of gradient M_7C_3 reinforced arc hardfaced coatings

采用电弧堆焊工艺在Q235钢板表面制备了不同成分的M_7C_3增强铁基堆焊涂层,采用X射线衍射仪(XRD)、金相显微镜(OM)、扫描电子显微镜(SEM)对M7C3增强铁基堆焊涂层的物相和微观结构进行表征,并通过"绝热法"和定量金相方法对堆焊涂层中组成相进行定量统计。采用显微硬度计和纳米压痕仪对堆焊涂层的硬度梯度和微观硬度进行测试,采用自制磨粒磨损试验机和冲蚀磨损试验机对堆焊涂层的耐磨性进行评价。结果表明,M7C3增强铁基堆焊涂层显微组织主要由初生(Cr,Fe)7C3碳化物和共晶(Cr,Fe)_7C_3/γ-Fe+α-Fe基体组成。随堆焊涂层中碳含量上升,初生碳化物尺寸增大、体积占比增加、稀释区厚度降低。与此同时,堆焊涂层抵抗低应力磨粒磨损的耐磨性逐渐增强,抵抗高应力冲蚀磨损的耐磨性逐渐变差。碳化物分布及其与基体的匹配是决定涂层耐磨性的重要因素。涂层中六棱棒状结构的初生(Cr,Fe)7C3碳化物硬度为21.4±0.3GPa,而断续网状结构的共晶(Cr,Fe)_7C_3碳化物硬度为18.8±0.3 GPa。

The gradient M7C3 reinforced arc hardfaced coatings with different compositions is prepared on the surface of Q235 steel by arc welding process. The microstructure and wear resistance of M7C3 reinforced arc hardfaced coatings are characterized by using X-ray diffraction（ XRD）,metallographic microscope（ OM） and scanning electron microscopy（ SEM）. The phase of the coating are quantitatively analyzed by using a adiabatic method and a quantitative metallographic method. The microhardness tester and nanoindenter are used to measure the gradient hardness and microhardness of the coating. The abrasion resistance of the coating is evaluated by self-developed abrasive wear tester and erosion tester. The results show that the microstructure of gradient M7C3 reinforced arc hardfaced coating is mainly consisted of primary（ Cr,Fe）7C3 carbides and eutectic（ Cr,Fe）7C3/γFe ＋ α-Fe matrix. As the carbon content in the coating increases,the size and volume proportion of the primary carbides increases with the thickness of the dilution zone decreasing. Meanwhile,the abrasion resistance of the coating against low stress abrasive gradually increases,while the abrasive resistance against high stress erosion wear gradually deteriorates. The carbide distribution and the matrix matching are the important factors that determine the wear resistance of surfacing coatings. The hardness of（ Cr,Fe）7 C3 carbide with hexagonal rod shape is 21. 4 ± 0. 3 GPa,while the discontinuity mesh eutectic（ Cr,Fe）7C3 carbide hardness of 18. 8 ± 0. 3 GPa.