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Characterization of Microstripping and Wear of Different Rolling Bearing Steels: Effects of Hardness and Heat Treatment

Release time:

2023-01-13

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Micro spalling or surface damage is a surface failure mechanism commonly found in modern mechanical components such as bearings and gears that are heavily loaded, non conformal, and roll slip contact. This type of damage is caused by rolling contact fatigue at the rough peak level, which occurs due to repeated rough peak stress fluctuations during rolling contact. It can be characterized by numerous microcracks and micro spalling formed on the rolling surface. It generally occurs under poor lubrication conditions (low λ values) where the oil film thickness is not sufficient to completely separate the rolling surface, and the load is borne by the rough peak rough peak contact and the lubricant, respectively. Because the current trend is to use thinner lubricants to maximize the efficiency of mechanical components, the focus is on understanding the phenomenon of micro spalling and designing rolling surfaces that are more resistant to micro spalling and withstand higher power density.

Nowadays, micro spalling has been identified as a surface contact fatigue phenomenon, which involves competition between mild wear and rough peak fatigue. By correcting the running in of the surface or removing the fatigue material layer, slight wear can reduce the formation of micro peeling pits. It has been confirmed that additives such as anti wear, anti friction, and extreme pressure have important effects on enhancing or delaying the formation of micro spalling. Additives that prevent rough rolling surface wear can enhance the formation of micro spalling pits, which generally maintain a high surface roughness amplitude, thus maintaining a high friction coefficient or increasing the friction coefficient, greatly increasing the risk of micro spalling. In contrast, additives that allow for a certain degree of running in wear or reduce friction coefficient often reduce the risk of micro peeling. The relevant literature focused on the role of ZDDP anti-wear additive, which is beneficial to Sliding friction, but may be harmful to rolling friction. A recent study has shown that the degree of micro peeling is more dependent on the degree of running in wear, rather than the thickness of the final formed friction film as described in reference [5]. In this case, sufficient running in wear will greatly reduce the risk of micro peeling.

However, in the absence of additives, other factors such as operating conditions, steel surface, and metallurgical properties receive more attention. If the Λ value is very low and there is a lack of anti wear additives, harsh contact conditions generally lead to a higher risk of micro peeling and even wear. Reference [13] suggests that the initiation and propagation of micro spalling are mainly controlled by working stress; Reference [14] suggests that increasing the slip to roll ratio will increase the sliding distance of growth, thereby accelerating micro spalling. Anyway, before reaching a certain threshold, slight wear dominates and can reduce micro peeling damage. In addition, it is generally believed that negative sliding (slower moving surfaces) is harmful to the occurrence and degree of microstripping damage, as it increases the pressure oil effect and helps to open cracks. Although some studies have shown the opposite conclusion, that due to less wear, positive sliding will cause microstripping damage to develop faster compared to negative sliding.

In addition to operating conditions, the focus was on studying the surface morphology and the role of materials. Research shows that surface roughness is the main cause of micro peeling, and rough smooth contact is harmful to smoother surfaces. In this case, the rough surface induces fatigue microcirculation on the smooth surface, thereby promoting micro delamination damage. Stress fluctuations caused by another surface roughness generally only occur on smooth surfaces. In addition, the rough peaks are relatively rolling