ISSN   1004-0595

CN  62-1224/O4

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油润滑滚滑接触条件下轴承钢微点蚀的试验观察

An Experimental Study of Micropitting of Bearing Steel Under Oil Lubricated Rolling/Sliding Conditions

  • 摘要: 微点蚀作为1种表面起源型早期失效,严重制约了滚动轴承的精度寿命,目前对微点蚀的产生机理仍未完全揭示. 本研究使用微点蚀试验机研究了合成油润滑条件下滑滚比、卷吸速度和硫磷抗磨添加剂对GCr15轴承钢表面微点蚀的影响. 考察了数百万次循环应力下微点蚀表面形貌、微点蚀面积占比、摩擦系数与振动加速度的演化过程. 首先进行了不同滑滚比条件下轴承钢的微点蚀试验,发现在接近纯滚动时,由于其较小的剪切应力会导致轻微的微点蚀损伤;随着滑滚比增大,界面剪切应力增大,微点蚀损伤呈增大趋势;继续增大滑滚比导致滚子表面的磨损和抛光效应很大程度上抑制了微点蚀. 其次进行了不同卷吸速度条件下轴承钢的微点蚀试验,发现在裂纹产生之后,高的卷吸速度会导致封闭在裂纹中的润滑油难以排出,产生高的油压,从而加速裂纹的扩展和表层金属的剥落. 最后进行了硫化异丁烯和磷酸三甲酚酯作添加剂时对轴承钢微点蚀的影响,发现试验条件下2种添加剂对微点蚀的产生均起到了促进作用,但产生的微点蚀形貌存在较大的差异. 含硫的抗磨剂硫化异丁烯产生了孤立分布且剥落面积较大的微点蚀浅坑,分析认为在裂纹产生之后硫元素加速裂纹的扩展与表层金属的剥落. 含磷的抗磨剂磷酸三甲酚酯产生了密集的微裂纹和微凹坑,其在轴承钢表面形成的金属磷酸盐薄膜较薄且不均匀,不足以隔开粗糙峰的直接接触,从而促进了微点蚀的产生.

     

    Abstract: Micropitting, as a type of surface-originated early failure, restricts the precision and service performance of rolling bearings. The formation mechanism of micropitting has not been fully revealed. This study used a micropitting rig to investigate the influences of slide-roll ratio (SRR), rolling speed, and anti-wear additives on the micropitting of GCr15 bearing steel under synthetic oil lubrication conditions. The evolution process of micropitting in terms of variations of surface morphology, micropitting area proportion, friction coefficient and vibration acceleration was investigated under millions of stress cycles, and analyzed the causes of micropitting and the influence of anti-wear additives on micropitting. First, the effect of SRR on micropitting was studied experimentally. It was found that when approaching pure rolling, slight micropitting damage would occur due to the smaller shear stress at the tribological interfaces. With an increase in SRR, the interfacial shear stress increased, and the micropitting damage increased. Further increasing the SRR led to the wear and polishing effects of the roller surface, which inhibited micropitting. Micropitting exhibited a trend of initially increasing followed by a gradual decrease, ultimately stabilizing, which was influenced by the damage and the slide-roll ratio. Second, the effect of entrainment velocities on micropitting had been studied in boundary/mixed lubrication regimes. It was found that after initial surface crack formation, high rolling speed would cause the lubricant sealed in the crack to be difficult to discharge, resulting in high oil pressure and thus accelerating crack propagation and spalling of the surface material into micro-pits. Finally, the effects of sulfided isobutylene (SIB) and tricresyl phosphate (TCP) as additives on micropitting of bearing steel were carried out. And the film formation phenomenon of the early additives on the rollers was observed and measured using an optical microscope and an optical interference film thickness measurement instrument. It was found that both additives promoted the generation of micropitting under the used experimental conditions. However, there were large differences in the morphology of the generated micropitting. SIB produced isolated distributed shallow pits with large delaminating areas of micropitting, and it was thought that the sulfur element may accelerate crack propagation and delamination of surface material after crack formation. Through scanning electron microscopy and EDS elemental analysis, it was found that there were a considerable amount of sulfur (S) elements present within the micropitting, whereas the areas without micropitting did not contain sulfur (S) elements. TCP produced dense and more regular micro-cracks and later micro-pits, and its formed metal phosphate film on the bearing steel surface was thin and uneven, measured by the optical interference test apparatus, the formed phosphate film was approximately 40 nm thick, which may fail to separate direct contact between rough peaks, thereby promoting the generation of micropitting. This paper explored the operating conditions leading to micropitting and delved into the mechanism of S and P additives on micropitting, providing theoretical support for improving micropitting phenomena in engineering applications.

     

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