ISSN   1004-0595

CN  62-1224/O4

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1种高速钢轧辊材料高温氧化与摩擦磨损行为研究

High Temperature Oxidation, Friction and Wear Behavior of a High Speed Steel Roll Material

  • 摘要: 为了探究高速钢轧辊材料的高温氧化与摩擦行为,将高速钢样品分别在600℃下进行高温氧化(恒温氧化和循环氧化)试验和摩擦试验,考察其氧化动力学,分析其氧化表面和横截面的显微组织,并探讨氧化层的机械性能和摩擦磨损行为. 结果表明:恒温氧化和循环氧化动力学曲线都符合抛物线规律;恒温氧化和循环氧化过程中的产物分别以Fe2O3和Fe3O4为主,但是在循环氧化条件下会存在CaCO3,从而降低氧化层表面的光洁度和硬度;循环氧化条件下,氧化膜厚度更厚,氧化膜与基体的结合力更高,但由于CaCO3和裂缝的存在,延长循环氧化时间会造成氧化膜过早破坏. 高速钢摩擦磨损机制主要为氧化磨损、磨粒磨损和黏着磨损,在摩擦过程中出现材料转移现象;磨损产物与氧化产物类似,但磨损产物以Fe3O4为主.

     

    Abstract: Due to the processing conditions of high speed steel (HSS) work rolls is harsh (high temperature, high stress, relative sliding with rolled material, and other special working conditions), the work roll will inevitably suffer oxidation, wear and tear. The oxide film may influence the tribological properties and vice versa. Accordingly, investigating the oxidation and tribological behaviors of HSS roll materials at high temperature and elucidating the oxidation kinetics, the wear mechanism, and the mechanism of friction reduction and anti-wear of roll materials and counterparts will be helpful to reduce wear and increase the life of roll materials, improve the quality of rolled materials, and heighten the production efficiency. In this paper, the high temperature oxidation (isothermal oxidation and cyclic oxidation) and friction experiment of one kind of HSS samples were carried out at 600 ℃, and the oxidation kinetics, the microstructure on oxidation surface and cross-section were analyzed, as well as the wear mechanism were explored. The original HSS sample mainly contains Fe-based solid solution and carbides (VC, Cr7C3 and Mo2C). Although the cyclic oxidation rate was much larger than the isothermal oxidation rate, the oxidation kinetics under both conditions conform to the parabolic law, indicating that the oxidation was controlled by the ion diffusion process. The products were mainly Fe2O3 and V2O5 for isothermal oxidation, while Fe3O4 and CaCO3 dominated the cyclic oxidation, no V2O5 could be detected during cyclic oxidation. Few Cr7C3 and Mo2C carbides were oxidized due to the better oxidation resistance. With the proceeding of the cyclic oxidation, the CaCO3 segregate at grain boundary firstly and then cover the surface. During cyclic oxidation, due to the difference of thermal conductivity between matrix and carbide, the cracks initiated and propagated at carbides. The presences of CaCO3 and cracks facilitated the inward diffusion of oxygen, thus speeds up the oxidation. Under cyclic oxidation, the oxide film was thicker, and the bonding strength between the oxide film and the substrate was higher. However, due to the presence of CaCO3 and cracks, prolonging the cycle oxidation time may have caused premature destruction of the oxide film. The friction coefficient leveled off and stabilized at about 0.47 after a short running-in, and the wear rate of HSS pin and counterpart Q235 steel disk was low and even negative wear 1.855×10−7 g/(N·m) and −1.496×10−7 cm3/(N·m), respectively. The wear products of HSS pin were similar with the isothermal oxidation, with the iron oxide (Fe3O4 and Fe2O3), Fe matrix, vanadium oxide (V2O5) and carbides can be observed. Compared to the Fe2O3 main phase after isothermal oxidation, the dominant products were Fe3O4 after wear, which was contributed to the less oxygen partial pressure during the wear test. The grooves, spalling pit, wear debris existed on the wear surface of HSS pin, indicating the wear mechanisms of pin are mainly oxidative, abrasive and adhesive wear. For the counterpart disc, the wear products are Fe2O3, Fe3O4, V2O5, Fe matrix and carbide, which was same with the pin. On the wear surface of Q235 disc, the oxidation zones, wear debris zones and tribolayer containing V and Cr could be observed. Because the Q235 is free of V, Cr, Mo, the detected V, Cr, Mo element should come from the pin. The presence of tribolayer proves the occurrence of material transfer, and the tribolayer could separate the direct contact of the HSS pin and Q235 disc, which was beneficial for reducing the friction coefficient and wear rate. The material transfer was responsible for the negative wear of the counterpart disc, also may account for the reduction of rolled material quality. The wear mechanism of the Q235 counterpart disc was oxidative and adhesive wear.

     

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