Carbonitrided Mancrodur for heavy-duty operating conditions

For many years, materials engineers have been trying to make rolling bearing steels more resistant to mixed friction or contamination which includes foreign particles. These conditions typically occur in the steel industry, in mining and in rail technology. Significant reductions in bearing operating life or premature failure can have consequential costs. Two conflicting objectives have to be reconciled. On the one hand, the raceways must be very hard, wear-resistant and capable of supporting loads. On the other, they should be able to tolerate the deformations caused by hard foreign particles during overrolling and, if necessary, level these out. Schaeffler has demonstrably resolved these conflicting objectives between hardness and a sufficient ductility with the Mancrodur rolling bearing steel combined with carbonitriding heat treatment.

Carbonitrided Mancrodur has a combination of characteristics which make this rolling bearing material particularly suitable for extremely demanding environmental conditions. By using a combination of carbonization and nitriding for the heat treatment, the surfaces of Mancrodur bearings are, on the one hand, hard and wear-resistant.

On the other, fine, spheroidal carbides form in carbonitrided Mancrodur which are uniformly distributed in the material and are less concentrated at the grain boundaries. This reduces the risk of localized weak spots. The raceway surface is therefore not only harder and more wear-resistant but also more ductile.
Mancrodur is, therefore, able to level out ridges in the raceway caused by embedded foreign particles, despite its high surface hardness. Material fatigue is considerably reduced, the formation of cracks prevented and the operating life significantly extended.

In applications with poor lubrication, the local temperature of the material increases due to increased friction. Compared to other steels, the reduction in strength in Mancrodur due to temperature is less which considerably reduces the danger of local overloading due to inadequate lubrication.

In applications with poor lubrication, the local temperature of the material increases due to increased friction. Compared to other steels, the reduction in strength in Mancrodur due to temperature is less which considerably reduces the danger of local overloading due to inadequate lubrication.

Under normal lubrication conditions (full lubrication), carbonitrided Mancrodur increases basic load ratings by 30% compared to standard materials which equate to an increase in the nominal rating life of 240%. A rating life up to six times longer has been verified in tests when using carbonitrided Mancrodur with full lubrication.

Double the operating life
In the uncompromising environments encountered above all in railway technology, mining and the steel industry, tests in actual adverse conditions are vital. The first test bearings from the four row carbonitrided Mancrodur FAG tapered roller bearing range have been installed at a steel producer in the work rolls on a hot strip mill. The test bearings have achieved twice the standard operating life in this application.

Mancrodur is particularly suitable where greater machine capacity is required under tough operating conditions. In addition to the application areas already tested in steel works, this new high-performance steel has proven itself to be the material of choice in areas such as highly-loaded axlebox bearings in freight cars, planetary bearings in wind turbines and bearings in pumps and compressors. The trend towards downsizing means that, in many machines, the bearing supports are approaching the limits of their load carrying capacity. Mancrodur’s significantly higher load carrying capacity, and its insensitivity to poor lubrication conditions and contaminants makes it an outstanding material choice for bearings in transmissions in agricultural and construction machinery, automobiles and trucks as well as ships’ propulsion systems.

Schaeffler
www.schaeffler.com