Chapter 5 | Remelt Special Steel Steelmaking Technologies

Abstract

Remelt steelmaking is one of the lesser understood bearing steel steelmaking technologies. It is applied when enhanced steel quality is required for demanding rolling bearing applications. The process and quality assurance costs are significantly higher than air-melt steelmaking as described in Chapter 4 of this book. Electroslag remelting (ESR) and vacuum arc remelting (VAR) are examples of remelt steelmaking processes. The VAR process is also referred to as the consumable electrode remelting process. Electroslag remelting can be performed under vacuum, under pressure or under a protective atmosphere. ESR remelting, under a nitrogen atmosphere, is particularly important in the production of high nitrogen stainless bearing steels. A combination of vacuum induction melting (VIM) and VAR remelted steel quality usually outperforms vacuum degassed air melt (AM) steels from the point of view of internal cleanliness and related rolling contact fatigue (RCF) strength. Vacuum induction melting (VIM) and casting under vacuum is an established methodology for ingot preparation for remelt steelmaking. The VIM ingot processing parameters, such as elimination of inclusion entrapment, are important for subsequent usage as electrodes in vacuum arc remelting. The remelting operation refines the steel particularly with respect to the absence of macrodefects such as exogenous nonmetallic inclusions. Additionally, the higher-alloyed high-speed steels would be too highly segregated if melted and cast in a normal fashion. The main parameters in remelt bearing steelmaking and the related specifications are summarized as: Precision and consistency of steel chemistry; avoidance of macrosegregation; and minimization of nonmetallic inclusions in the critical size range, typically ≥ 10 μm. Combinations of remelting, to improve the steel quality, are used, for example VIM-ESR-VAR, AM-ESR-VAR and VIM-VAR-VAR. Remelt rolling bearing steel qualities are made to the appropriate SAE AMS and SAE AS specifications using ASTM standard test methods and the specifications.