摘要
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,CQT)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,QT)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,从而具有更大的表面积,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。上述研究结果可为改善农机触土部件的耐磨性提供可行的技术方案。
Wear resistance of plow tips has been one of the most important issues in a high-speed hydraulic reversible plough.In this study, the Carburizing-Quenching-Tempering(CQT) process was employed to improve the wear resistance of plow tips fabricated by the 33MnCrB5 steel with the hard alloy coatings. A systematic investigation was also made to elucidate the influence mechanism of the process on the microstructure and wear resistance of carburized plow tips. The results show that the maximum content of near-surface carbon and the depth of the carburized layer were 0.70 % and 2.5 mm, respectively, for the 33MnCrB5 plow tips after CQT process. The surface carbon content of the plow tip was significantly higher than that treated by Quenching-Tempering(QT) process. In addition, the surface microstructure of the CQT plow tip was composed of plate martensite(high hardness), retained austenite, and a small amount of carbide. Specifically, the core microstructure was mainly lath martensite(high strength and toughness), which was 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 were greatly enhanced, due to the evolution of the microstructure. The yield strength and tensile strength of the carburized plow tip in the core region reached up to 1 584 and 1 898 MPa, respectively, while, the surface microhardness reached 699 HV1. Among them, the yield strength, tensile strength, and surface microhardness increased by 198 and 314 MPa, and 252 HV1, respectively,compared with the QT plow tip. The friction tests show that the CQT plow tip(0.29) presented a lower friction coefficient, but a higher abrasive resistance, compared with the QT plow tip(0.37). The improvement was attributed to the fact that the carburized layer was produced into the abrasive chips with the higher hardness carbides during wear, thus 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) was significantly lower than that of the QT plow tip(144 g), in terms of the profile dimensions in the length, width and thickness directions. Nevertheless, the carbide layer on both CQT and QT plow tips was completely fractured, indicating that the overlaying carbide layer failed to protect the tips for a long time. The combined strengthening was achieved to integrate the high hardness plate martensite and strain-induced martensitic transformation in the carburized layer. The high hardness of plate martensite and diffusely distributed carbide organization in the carburized layer effectively hindered the abrasive particles from pressing into the substrate, and then weakened the cutting of abrasive particles on the plow tip material, particularly for the higher local resistance of the material to destructive deformation. At the same time,the residual austenite in the near-surface layer of the carburized layer produced significant strengthening, due to the dislocation strengthening and strain-induced martensitic phase transformation during the frictional wear of the plow tip. The strengthening layer was used to transfer the external load into a greater depth, thus triggering the dislocation movement at stresses above the yield point. As a result, the strain-induced martensite appeared within the slip band. As such, the internal microhardness gradient of the sample inward development resulted in significant work hardening, especially for the higher wear resistance of the CQT plow tip. Moreover, the surface area of the CQT plow tip after wear was significantly larger than that of the QT one.Correspondingly, there was a decrease in the load and friction heat release per unit area of the CQT plow tip, in order to reduce the creep softening tendency of the material to be worn. The higher wear resistance of the CQT plow tip was finally achieved in this case. The finding can shed light on the wear resistance of key soil-engaging components in the agricultural machinery and manufacturing industry.
作者
沈宝国
黄豪
郭顺
倪豪豪
常亚南
汪东发
鞠玉琳
袁志钟
Shen Baoguo;Huang Hao;Guo Shun;Ni Haohao;Chang Yanan;Wang Dongfa;Ju Yulin;Yuan Zhizhong(Key Laboratory of Modern Agricultural Equipment and Technolog,Ministry of Education,Zhenjiang 212013,China;Jiangsu Aviation Technical College,Zhenjiang 212134,China;School of Materials Science and Engineering,Jiangsu University,Zhenjiang 212013,China;Zhengzhou Longfeng Agricultural Machinery and Equipment Manufacturing Co.,Ltd.,Zhengzhou 450041,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2022年第14期35-42,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家自然科学基金项目(52175410)
江苏大学农业装备学部项目(NZXB20200101)。
关键词
显微组织
硬度
耐磨性
渗碳工艺
犁尖
microstructure
hardness
wear resistance
carburizing process
plow tip