Chapter 4 | Steelmaking, Casting, Rolling—Air (Open) Melt Steel Grades

Abstract

Bearing steel technologists need to be aware of air-melt bearing steelmaking process developments and the market demands for cheaper and better rolling bearings, and reduced CO2 emissions. Primary steelmaking in electric arc or basic oxygen furnaces is described together with the development of linked or separate ladle refining and vacuum degassing technologies. The choice of aluminum or silicon (nonaluminum) deoxidation is explained as a function of the applied casting methodology, end product requirement, and the prevailing ethos. The variety of steelmaking combinations are explained and relationships of the processes with the metallurgical quality illustrated. The technologies applied in bearing steel casting operations have a profound effect on quality and costs and this is described. High carbon bearing steel compositions present special problems with respect to segregation and a need for homogenization treatments. Continuous casting of bearing steels is established, but ingot casting is required for higher alloyed steels. Ingot casting remains an excellent way of making high-quality bearing steels. Both billet and bloom continuous casting are economically attractive provided the bearing steels in question can be cast in suitable sequences. The use of post-casting homogenization treatments are explained particularly for the large-size bearing steel grades produced by radial-axial hot ring rolling. Control of hot-working process temperatures and adiabatic heating effects, particularly for high carbon-alloy steels, is described. Nondestructive testing cannot detect all internal metallurgical defects which means that hot ring rolling must not introduce undetectable, or difficult to detect, internal void defects. It is explained that careful homogenization of steels for radial and axial ring rolling needs to be performed in order to ensure that the rings have full metallurgical integrity (i.e., they are free of voids/porosity).