The bearing rig tests performed in this study, demonstrate superior bearing performance of Cronidur 30 steel over conventional bearing steels. In these tests the L10 life of Cronidur 30 steel as calculated by the DIN/ISO 281 method was 80 times the unfactored L10 life under full lubrication conditions. In boundary lubrication conditions, the Cronidur 30 steel demonstrated the L10 life capability typical of EHD lubrication conditions, whereas the other steels showed a drastically reduced lives. In tests with predamaged races and boundary lubrication conditions, Cronidur 30 demonstrated 8 times the calculated L10 life, whereas the conventional steels exhibited further debit in lives as compared to the boundary lubrication testing whithout predamage. The improved performance of Cronidur 30 steel over conventional bearing steels is attributed to its unique compositional formulation and microstructure that results in provision of balanced properties in the alloy – hardness, toughness and corrosion resistance.

For pricing reasons the extent of metallurgical treatment often is questioned about its influence on bearing performance. In this paper steels with three different quality levels are compared with regards to cleanliness and fatigue resistance.

Schlüsselworte: Austenitischer Stahl, Wälzlager, warmbestän-dig, hohe Härte, nicht rostend, nicht magnetisierbar A low cost austenitic chromium manganese steel with about 1 mass% of carbon and nitrogen was molten under normal pressure which reveals an amazing combination of properties. Starting from a yield strength of about 600 MPa it is cold work hardened to 60 HRC. This high hardness is brought about for the first time without a martensitic microstructure which is usual for roller bearings. In addition this steel is stainless, non-magnetic and heating resistant up to about 500 C, i.e. a material to serve under complex loading. Manufacturing by ingot metallurgy, ESR, hot working, solution annealing and machining was carried out on an industrial scale. The investigation of the structure was carried out on several scales, beginning with the electronic structure, the TEM structure, the light optical microscopy up to macro-etchings. In this manner an extensive understanding of the outstanding combination of properties of the steel named CARNIT was derived.

A new process, duplex hardening, was developed, for two steels which are already widely used for aerospace applications, M50 and M50 NiL. The rolling contact fatigue and sliding wear performance of duplex hardened bearing components were evaluated on M50 and M50NiL steels. The rolling contact fatigue and sliding wear tests performed under the development program demonstrate superior performance of duplex hardened M50 and M50 NiL over conventional treated M50 and M50NiL bearing components. The bearing rig tests performed in this study also demonstrate superior bearing performance of duplex hardened M50 and M50NiL steels over conventional heat treated M50 resp. M50NiL steels. Under boundary lubricating conditions, the duplex hardened M50 and M50NiL bearings did not even fail after 1500 hrs. In tests with predamaged races, duplex hardened M50 bearing races demonstrated more than ten times the calculated L10-life. The tests on duplex hardened M50NiL bearings were interrupted after 1.500 hrs. runtime with no bearing failure.

White etching cracks (WECs), or white structure flaking, is a failure phenomenon that has been reported as emerging in rolling bearing parts for more than the past two decades. This failure mode appears only if, in addition to the normal Hertzian load, a so-called additional load is applied. WECs can occur regardless of the bearing type and size and in both oil- and grease-lubricated bearings. By modifying the testing conditions of an FE8 type test rig, it is possible to alter the failure mechanism from classical wear failures to WEC formations. This allows for easy, fast, and reproducible testing of materials and heat treatment variants to check their WEC formation propensity. This paper explains the methodology of testing on a FE8 test rig, the subsequent failure analysis, and the testing results. The tested components are produced from a wide range of commonly used bearing materials that in these tests are through hardened variants of low and high alloyed steels, case carburized steel with high retained austenite content, and inductive hardened quenched and tempered steel. In addition to the spread in the base materials with different contents of carbon and alloying elements, the variations in materials and heat treatments offer the possibility of significantly varying the content of retained austenite and the residual stress distribution. The results show that all the tested low alloyed materials fail with the WEC mechanism, whereas a significant increase in lifetime can be observed in terms of inductive hardened quenched and tempered steel. Only the nitrogen alloyed stainless steel Cronidur 30 demonstrates an outstanding performance without WEC formation.

The substitution of nitrogen for carbon distinctly improves the corrosion resistance of martensitic stainless steels with about 15% chromium and 1% molybdenum. In addition, this property becomes more stable with respect to tempering. Together with a raise in secondary hardening, the new high-nitrogen steels combine improved hot hardness and corrosion resistance for service at elevated temperatures. The new steels show better mechanical properties and bearing life as compared to conventional stainless bearing steels. Pressurized electroslag remelting allows for partial substitution of nitrogen for carbon. A full substitution is possible by powder metallurgy. Further investigations are in process.

No abstract

The rings of rolling bearings are either through hardened with a martensitic or bainitic structure or case hardened. They differ in cleanliness, structure and residual stresses. The over-rolling fatigue resistance mirrors these differences. Typical results are given for over-rolling conditions causing classical fatigue, surface-initiated failure or failure by white etching cracking. This paper is part of a Themed Issue on Recent developments in bearing steels.