Chapter 7 | Forming and Soft Machining Bearing Metallurgy

Abstract

Bearing steel forming and shaping operations impact both cost and performance. Forming with raceway material (fiber) flow conformance is the preferred shaping method. High volume hot forging requires 52100 type steels to have a good homogeneity to avoid metallurgical integrity issues. Hot formability testing is described to define the optimum homogenization in the steelmaking process. Warm forming and ausforming are forming processes applied in specific bearing steels. Forming performed in the cold condition can have a beneficial influence on the rolling bearing functional properties. However, cold working of tubes or components negatively influences the hardening heat treatment distortion. The degree of forming reduction is an important consideration. A high amount of reduction increases the steelmaking and component process costs. Knowledge of the optimum is a profound consideration. The properties of formed bearing steel and components varies depending on the testing direction (i.e., transverse or longitudinal). The raceway incident angle of inclusions is a key issue and the metallurgically cleaner the steel the lower the effect of forming deformation and orientation. The so-called fiber flow can be quantified and defined in bearing steel component specifications. Good machinability is a requirement in efficient rolling bearing component manufacture. Turning tool life is generally used as the primary factor in assessing a softened bearing steel machinability. For metallurgical quality reasons low sulfur contents are applied in spheroidized annealed 52100 type steels and this has a negative effect on machinability. Carbon steels, such as 1055, used in hub bearing units, sometimes are resulfurized to improve the ring component machinability. Machinability and sulfur content is a particularly important consideration when drilling and taping operations are performed on the flanges of hub bearing units. Manufacturing process developments are in progress and tailored forming using composite steel combination and forming is an important future manufacturing development.