Hot forming parameters research of bearing steel

The paper deals with an analysis of the hot forming parameters of the bearing steel 100Cr6 according to ČSN EN ISO 683-17, performed by means of the plastometer. Bearing steels belong to high carbon steels, generally alloyed by chromium, i.e. precipitation of carbides of type (FeCr)3C takes place. Uneven distribution of carbide phases, together with inclusions, deteriorates the resulting steel quality. Thus service properties, especially lifetime of bearings, are limited. Degradation of structure in the production process results mainly in carbide banding, carbide segregations and carbide network. By a suitable cooling rate it is possible to remove completely the carbide network after rolling; in addition, an appropriate structure for subsequent heat treatment may be prepared. Metallurgical process parameters, constitution and cleanliness of steel have significant influence on grain size and banding of the formed steel. Mainly correctly performed control of finishing rolling conditions and final cooling have considerable influence on quality of rolled products. Sufficiently fast cooling after forming decreases occurrence of carbide network, of course with danger of arising micro- and macro-cracks especially on weakened gamma-grains boundaries. This contribution illustrates selected results of the plastometric and metallographic investigation of deformation behaviour of high carbon steels alloyed with chromium, including bearing steel.