热处理对重载轴承材料耐磨性能的影响研究

发布时间：2018-09-09 15:34

【摘要】：面对科学技术的日新月异,材料将承受越来越多的极限工况,特别是轴承材料将面临极端的载荷作用,其摩擦磨损可能与在传统低载荷下的工况有所区别,导致其耐磨性能表现不佳。因此,研究轴承材料在重载条件下的耐磨性变得十分重要。本次实验对象选择使用最为广泛的GCr15轴承钢,主要研究淬火温度和表面渗氮对其耐磨性能的影响,并选择M2高速钢作为对比材料,从耐磨性角度讨论M2高速钢作为重载轴承用钢的可能性,在研究过程中主要讨论回火次数对其耐磨性能的影响。实验中采用了光学显微镜(OM)、扫描电镜(SEM)、能谱分析仪(EDS)和X射线衍射分析仪(XRD)等测试手段研究了热处理对轴承材料组织和性能的影响,利用旋转摩擦试验机测低载荷条件下材料的摩擦性能,利用高温重载摩擦试验机测重载条件下材料的摩擦性能,并通过力学性能测试和磨损形貌观察,探讨磨损机理,其结果表明:1)GCr15淬火时常常得到"黑白区"形貌。淬火后组织均为马氏体+碳化物+残余奥氏体,随着淬火温度的升高,马氏体形态由隐针状逐步变成粗针状,在860 ℃淬火硬度取最大值为HRC62.1,弹性模量为206.421 GPa。GCr15经渗氮后形成了三个区:氧化膜层、渗氮层和扩散层,渗氮层由γ-Fe4N和ε-Fe2-3N相组成,渗层厚度可达100μm,硬度从内部到表面逐渐升高,渗氮后表面硬度增加。M2高速钢淬火组织为马氏体+合金碳化物+残余奥氏体,碳化物主要为MC、M7C3、M3C2型碳化物,在高温回火过程中会发生二次硬化现象,二次回火后得到更多细小的碳化物,洛氏硬度和弹性模量分别为63.1和244.526 GPa,均比一次回火试样高。M2高速钢压缩屈服强度明显高于GCr15。2)在低载和重载条件下,热处理对GCr15耐磨性的影响相似。随着淬火温度从840 ℃升高到900 ℃,摩擦系数先减少后增加,经860 ℃淬火的试样摩擦系数与磨损率均最小。在同种热处理状态下,GCr15的摩擦系数随着接触应力的增大而减少,且减少幅度变小,磨损率随接触应力的增大而增大。材料的磨损率与硬度、弹性性模量有关,但并不是呈现简单的线性关系。在低载荷条件下,GCr15主要发生磨粒磨损,在重载条件下,GCr15主要发生严重的粘着磨损。3)表面渗氮对GCr15耐磨性的影响是复杂的。载荷较低时,GCr15表面渗氮能减小摩擦系数,降低磨损率,主要发生轻微擦伤,有少部分的剥离现象。在0.75 GPa、0.94 GPa、1.08 GPa的接触应力下,渗氮试样的磨损率较未渗氮试样分别降低46%、31%和28%。在重载条件下,表面渗氮对GCr15减磨效果变弱,在2.88 GPa下磨损60 min左右,化合物层被磨掉,且随着接触应力进一步增大后,在3.17 GPa下,渗氮试样的磨损率比未渗氮试样高8%,渗层失去减磨作用。4)对M2来说,在重载条件下摩擦虽然会产生大量的热,但氧化磨损并不严重。经二次回火后试样的摩擦系数与磨损率均比经一次回火的更小,相比于一次回火试样,二次回火试样的表面擦伤较轻。5)在已有的磨损率计算公式中,引入H/E表征材料的属性,来估算磨损率,并在随后的实验中,使用高速钢磨损率来讨论公式的误差,发现其结果误差较大,说明还有其他因素影响材料的磨损率。
[Abstract]:Facing the rapid development of science and technology, materials will bear more and more extreme working conditions, especially bearing materials will face extreme load. Its friction and wear may be different from the traditional low-load working conditions, resulting in poor wear resistance performance. Therefore, the study of bearing materials under heavy load conditions becomes very important. Important. This experiment selected the most widely used GCr15 bearing steel, mainly studied the influence of quenching temperature and surface nitriding on its wear resistance, and selected M2 high-speed steel as the contrast material, discussed the possibility of M2 high-speed steel as heavy-duty bearing steel from the wear resistance point of view, mainly discussed the tempering times on its wear resistance in the study process. The effects of heat treatment on the microstructure and properties of bearing materials were studied by means of optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The friction properties of bearing materials under low load were measured by rotary friction tester and high temperature and heavy load friction tester. The wear mechanism of GCr15 was studied by means of mechanical properties test and wear morphology observation. The results show that: 1) The morphology of "black and white zone" is often obtained during quenching of GCr15. The microstructure of GCr15 is martensite + carbide + retained austenite after quenching. With the increase of quenching temperature, the morphology of martensite gradually changes from crypto-acicular to coarse. Needle-like, the hardness of quenching at 860 C is HRC 62.1, and the elastic modulus is 206.421 GPa.GCr15. After nitriding, three zones are formed: oxide film, nitriding layer and diffusion layer. The nitriding layer consists of gamma-Fe4N and epsilon-Fe2-3N phases. The thickness of nitriding layer can reach 100 micron. The hardness increases gradually from inside to the surface, and the surface hardness increases after nitriding. The microstructure is martensite + alloy carbide + retained austenite, carbide is mainly MC, M7C3, M3C2 carbide, secondary hardening occurs during high temperature tempering, and more fine carbides are obtained after secondary tempering. Rockwell hardness and elastic modulus are 63.1 and 244.526 GPa, respectively, higher than that of the first tempering sample. The friction coefficient decreases first and then increases with the increase of quenching temperature from 840 to 900. The friction coefficient and wear rate of samples quenched at 860 are the smallest. Under the same heat treatment condition, the friction coefficient of GCr15 increases with contact stress. The wear rate is related to hardness and modulus of elasticity, but it does not show a simple linear relationship. Under low load conditions, GCr15 mainly occurs abrasive wear, and under heavy load conditions, GCr15 mainly occurs serious adhesion wear. 3) Surface nitriding. The influence of Nitriding on the wear resistance of GCr15 is complex. When the load is low, the friction coefficient and wear rate of GCr15 surface can be reduced, mainly slight abrasion and a few peeling phenomena occur. Under the contact stress of 0.75 GPa, 0.94 GPa and 1.08 GPa, the wear rate of nitriding sample is reduced by 46%, 31% and 28% respectively compared with that of non-nitriding sample. The wear reduction effect of surface nitriding on GCr15 is weakened, and the compound layer is abraded about 60 minutes at 2.88 GPa. With the further increase of contact stress, the wear rate of nitriding sample is 8% higher than that of non-nitriding sample at 3.17 GPa, and the nitriding layer loses the abrasion reduction effect. 4) For M2, friction under heavy load will produce a lot of heat, but oxidation. The friction coefficient and wear rate of the sample after secondary tempering are smaller than those after primary tempering, and the surface abrasion of the sample after secondary tempering is lighter than that of the sample after primary tempering. The error of the formula is discussed by wear rate, and it is found that the error of the result is large, indicating that there are other factors affecting the wear rate of the material.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.4;TG161

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