The influence of steel microstructure in high-speed high-load bearing applications

Abstract

In the bearings’ segment of machine tools, there is a strong demand for high-performance steel solutions. The bearings may operate under severe conditions of contact pressures of up to 3 GPa; rotating at speed factors in excess of 3 million ndm. Such conditions pose a high risk of bearing seizure failure. Improving lubrication conditions is complex as the bearing operating temperature must be well controlled. Adhesive wear was found to occur in hybrid steel-ceramic contacts. Another relevant failure mode is micropitting. It is demonstrated that macroscopic hardness is insufficient to predict the resistance of steel microstructures to surface-initiated fatigue. In this regard, strain-hardening and the breadth of the range of hardness values of microstructure phases play an important role.

Application of a Rolling Bearing Life Model with Surface and Subsurface Survival to Hybrid Bearings in High-Load and High-Speed Applications

“…The results show that it is possible to adapt the hybrid bearing life model to account for the particular performance of different steels with the limitations load-speed also given by the particular materials considered in the bearing design. As discussed in [9,11] the PM1 steel has high thermal conductivity and high fatigue strength, which make it a very successful material for conditions of high speed and high load as the ones pursued in these applications if compared with the earlier results for hybrid bearings [8] as shown in Fig. 7.…”

“…The hybrid bearings endurance tested here are angular contact ball bearings of designation 7209 with ISO internal geometry and a nominal contact angle of 25 deg. The bearing rings are made of PM1 powder metallurgy steel in bars with basic information and composition given in [9,11] and the rolling elements of bearing grade silicon nitride (Si 3 N 4 ). The bearings were all manufactured and heat treated in-house.…”

“…For this, minimum-life endurance tests are carried out under high-speed and high-load conditions. Besides this, the methodology for life calculation will be applied as a showcase to a new tougher steel based on powder metallurgy (here it will be refered as PM1) used to manufacture the hybrid bearings [9,11]. Hence also full fatigue endurance tests to measure the fatigue strength of the bearings are carried out to validate the life model with this material.…”

Evaluation of hybrid spindle bearings with nitriding raceway steels under high rotational speeds

“…In a new calculation approach, the fatigue strength of various bearing steels could then be determined with the exact material parameters in good agreement with experimental results [6]. In particular, the microstructure of the raceway steels has a strong influence on the fatigue strength under extreme conditions, which was demonstrated by tribometer tests [7]. Furthermore, powder metallurgical steels show good frictional heating resistance under high loads compared to conventional steels, which also has a positive effect on fatigue strength [8].…”

“…Raceway back bearing On the other hand, it is evident that the temperature level in the bearing can favour chemical reactions between the raceway and the lubricant. A comparison of the raceways in Figure 6 with the classification in [7] shows that the bearing steel has good micropitting resistance.…”