渗碳工艺对高速液压翻转犁犁尖部件耐磨性的影响

针对在犁尖部件的局部区域堆焊硬质合金层仍无法解决现有国产犁尖整体耐磨性不足的问题，该研究对高速液压翻转犁犁尖部件整体采用渗碳-淬火-回火处理，并探讨了该工艺对犁尖微观组织与耐磨性的影响机制。研究结果表明，经渗碳-淬火-回火（Carburizing-Quenching-Tempering）工艺处理后的犁尖（CQT态犁尖）近表层最大碳质量分数约为0.70%，渗层深度约为2.5 mm，其表层组织为针状马氏体（高硬度）+残余奥氏体+少量碳化物，芯部组织则以板条马氏体（高强韧性）为主，这与经淬火-回火（Quenching-Tempering）工艺处理后的犁尖（QT态犁尖）中的板条马氏体+先共析铁素体组织明显不同，微观组织的改善使CQT态犁尖近表层的显微硬度较QT态犁尖提高56%。同时，与QT态犁尖相比，CQT态犁尖芯部的屈服强度和抗拉强度分别提升16%和20%。摩擦磨损试验及田间试验表明，CQT态犁尖的平均摩擦系数较QT态犁尖下降约22%，耕作120 hm2后的CQT态犁尖的磨损量较QT态犁尖降低37%，这主要归因于渗碳层中含有高硬度针状马氏体及残余奥氏体的应变诱导马氏体相变的综合强化作用。此外，与QT态犁尖相比，CQT态犁尖的耐磨性更高，使其具有更大的表面积，这有利于通过减小犁尖单位面积上的载荷和摩擦放热量来减轻待磨层材料蠕变软化的倾向，从而提高CQT态犁尖的耐磨性。上述研究结果可望为改善农机触土部件的耐磨性提供可行的技术方案。

Effects of carburizing process on the wear resistance of plow tips of high speed hydraulic reversible plough

Abstract: In this work, the Carburizing-Quenching-Tempering (CQT) process was employed to tackle the problem of insufficient wear resistance of domestic plow tips fabricated by 33MnCrB5 steel with hard alloy coatings, aiming at elucidating the influence mechanism of the process on the microstructure and wear resistance of carburized plow tips. It is found that the maximum near-surface carbon content and the depth of the carburized layer of 33MnCrB5 plow tips treated by CQT process have been determined to be 0.70 % and 2.5 mm, respectively. The surface carbon content is significantly higher than that of the plow tip treated by Quenching-Tempering (QT) process.. In addition, the surface microstructure of the CQT plow tip is composed of plate martensite (high hardness), retained austenite and a small amount of carbides, while the core microstructure is mainly lath martensite (high strength and toughness), which is different from the microstructure of lath martensite and pro-eutectoid ferrite in the QT plow tip. The microhardness and tensile strength of CQT 33MnCrB5 plow tips are greatly enhanced due to the improvement of microstructure. Compared with the QT plow tip, the yield strength and tensile strength of the carburized plow tip in the core region are raised to 1584 MPa and 1898 MPa respectively, and the surface microhardness is increased to 699 HV1. Among them, the yield strength and tensile strength are increased by 198 MPa and 314 MPa,and the surface microhardness increased by 252 HV1. The friction tests show that in comparison to those of the QT plow tip (0.37), the CQT plow tip (0.29) exhibits lower friction coefficient but higher abrasive resistance.which is mainly attributed to the fact that the carburized layer produces abrasive chips containing high hardness carbide tissue during wear, increasing the contact area between the carburized layer and the friction substrate.Furthermore, the field tests indicated that the total wear of the CQT plow tip after 120 hm2 of operation (91 g) is significantly lower than that of the QT plow tip (144 g), which is confirmed by its profile dimensions in the length, width and thickness directions. It is noteworthy that the carbide layer on both CQT plow tip and QT plow tip had completely failed, which further indicates that the method of overlaying carbide layer is not able to protect the tips for a long time.This can be contributed to the combined strengthening effect of high hardness plate martensite and strain-induced martensitic transformation in the carburized layer.The high hardness plate martensite and diffusely distributed carbide organization in the carburized layer can effectively hinder the abrasive particles from pressing into the substrate, weaken the cutting effect of abrasive particles on the plow tip material, and improve the local resistance of the material to destructive deformation. At the same time, the residual austenite in the near-surface layer of the carburized layer produces significant strengthening due to dislocation strengthening and strain-induced martensitic phase transformation during the frictional wear of the plow tip. The strengthening layer can transfer the external load to a greater depth, triggering dislocation movement at stresses above the yield point. As a result, the strain-induced martensite will appear within the slip band, so that the internal microhardness gradient of the sample inward development, resulting in significant work hardening, to further improve the wear resistance of the CQT plow tip.Moreover, the surface area of the CQT plow tip after wear is significantly larger than that of the QT plow tip, which can reduce the load and friction heat release per unit area of the CQT plow tip to reduce the creep softening tendency of the material to be worn, to improve the wear resistance of the CQT plow tip. Our results might shed light on improving the wear resistance of key soil-engaging components in the agricultural machinery manufacturing industry.