Spray-Formed Bearing Steel with High Oxide Cleanliness and Small and Fine Dispersed Inclusions*

Abstract

Abstract Rolling contact bearings belong to the most highly-stressed components in mechanical engineering. This demands high quality of the bearing steels, especially high-fatigue strength. Today bearing steels are produced by ingot casting or continuous casting. The premium quality is achieved by refining technologies, e. g. vacuum-arc remelting. In this point spray forming opens up another promising technology. Billets and rings from the bearing steel 100CrMnMoSi8-4-6 (W7) have been spray-formed on a laboratory plant with weight up to 80 kg and were analyzed. The spray-formed materials were hot-worked to round bars and rings. Microstructure, the size and distribution of inclusions and the chemical composition were analyzed. Rolling-contact fatigue tests and rotary-bending tests were performed. The results are compared with standard bearing steels. Core porosity of the spray-formed billets is low but because of increased rim porosity this material must be removed to avoid cracking during hot working. Hot working is required to close inner porosity. Rings could be ring-rolled immediately. The cleanliness is much better than typical for high quality conventional bearing steel of similar composition. Despite low degree of deformation no carbide network and no carbide stringers are visible. In the rolling-fatigue tests spray-formed W7 during hot working reaches similar values as a conventionally variant. Thus, beside reduced size of inclusions the removal of residual porosity is the dominating factor on enhanced fatigue resistance of spray-formed bearing steel.