Discussion on the Cleanliness of GCr15 Bearing Steel Produced by the Converter Process

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The production of GCr15 bearing steel using the converter, LF (Ladle Furnace), RH (Rhodius) and continuous casting process has been studied in detail. This research focused on analyzing the total oxygen content (T[O]) and non-metallic inclusions throughout the various stages of the process, including the converter, LF furnace, RH, tundish, and billet. The study aimed to evaluate the cleanliness of the final product and determine if a high-purity level could be achieved through this process. The results showed that the average total oxygen content in the billet was 12×10⁻⁶, while in the wire rod it was reduced to 9×10⁻⁶. The amount of macro-inclusions in the billet was found to be 2.68 mg/10kg. These findings suggest that the converter process, when properly controlled, can produce high-quality GCr15 bearing steel with excellent cleanliness levels. Key words: Converter; Bearing steel; Inclusions; Cleanliness Authors: JIA Nan¹, WU Huajie¹, BAO Yanping¹, XUE Zhengxue², WU Xun¹, MA Fuping² ¹University of Science and Technology Beijing, ²Xingtai Iron & Steel Co., Ltd. --- ### 1. Introduction With the advancement of modern technology, there is an increasing demand for bearings with longer lifespan, higher stability, and greater reliability. This requires minimizing impurities in bearing steel. One of the key factors affecting the performance and life of bearings is the cleanliness of the steel, which refers to both the oxygen content and the presence, size, and distribution of non-metallic inclusions. Cleanliness is crucial for the quality of bearing steel. Impurities such as oxides, sulfides, and other non-metallic inclusions can significantly reduce the mechanical properties and service life of bearings. Therefore, understanding and controlling these impurities is essential for producing high-performance bearing steel. --- ### 2. Production Process and Research Method The production process of GCr15 bearing steel follows the route: blast furnace → top and bottom combined blowing converter → LF → RH → continuous casting. Molten iron from the blast furnace and scrap steel are melted in the converter, followed by deoxidation and alloying operations. The LF process uses white slag to refine the steel, while the RH process performs vacuum degassing. Continuous casting is carried out using a four-stream curved caster with electromagnetic stirring in the mold. Sampling was conducted at different stages: converter, LF furnace, RH, tundish, and billet. Metallographic samples were prepared by grinding and polishing, then analyzed under an optical microscope. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the composition and morphology of inclusions. Additionally, the large sample electrolysis method was employed to analyze inclusions larger than 50 μm in the casting billet. --- ### 3. Results and Discussion #### 3.1 Changes in T[O] and [N] Content During the sampling process, the total oxygen (T[O]) and nitrogen ([N]) content were measured at each stage. The T[O] value at the end of the converter was 56×10⁻⁶, which decreased to 16×10⁻⁶ after tapping, indicating effective deoxidation. Further reduction occurred during the LF and RH processes, with T[O] reaching 11×10⁻⁶ and finally 9×10⁻⁶ in the wire rod. The nitrogen content was lowest at the end of the converter (20×10⁻⁶). However, it increased during subsequent steps, especially in the LF and tundish stages. After RH treatment, nitrogen levels dropped slightly, but they rose again during casting. The final nitrogen content in the wire rod was 30×10⁻⁶, which is within acceptable limits for bearing steel. #### 3.2 Analysis of Non-Metallic Inclusions Several types of non-metallic inclusions were identified during the process: - **Al₂O₃** (Aluminum Oxide): Mainly formed during deoxidation. - **MnS** (Manganese Sulfide): Often associated with deoxidizers and alloying agents. - **Calcium Aluminate**: Formed due to the recovery of residual aluminum. - **Calcium Aluminate + Sulfide Composite**: A combination of the above two. Before LF treatment, Al₂O₃ inclusions were dominant, with sizes ranging up to 5 μm. After LF treatment, the number of Al₂O₃ inclusions decreased, and the size of other inclusions remained around 5 μm. During RH and casting, the inclusions became smaller, and the number of large particles (>10 μm) was significantly reduced. In the billet, three main types of inclusions were observed: calcium aluminate, calcium aluminate + sulfide composite, and Ti-rich inclusions. Most of these were less than 5 μm in size, although some larger ones (over 10 μm) were also present. These larger inclusions may have originated from slag entrapment during casting. --- ### 4. Conclusion 1. The converter → LF → RH → continuous casting process is capable of producing GCr15 bearing steel with a cleanliness level suitable for high-performance applications. The final T[O] content in the steel reached 9×10⁻⁶, which is well below the national standard requirement of 12×10⁻⁶. 2. The main types of inclusions in GCr15 bearing steel include Al₂O₃, MnS, calcium aluminate, and calcium aluminate + sulfide. Their size typically ranges between 5–10 μm. The formation of these inclusions is closely related to the use of deoxidizers and the recovery of residual elements in the steel. 3. The presence of Ti-rich inclusions in the billet indicates the need for further optimization of the casting process to minimize slag entrapment and improve overall cleanliness. --- ### Recommended Reading - Analysis of the preload of the thrust spherical roller bearing - Analysis of the new specification of the wind turbine bearing - Analysis of the thrust bearing and the device - NTN imported bearing work – early damage and avoidance of key engine sliding bearings (2) This article is sourced from China Bearing Network. For more information, visit [http://www.chinabearing.net](http://www.chinabearing.net). Previous: Bearing support seals Next: About the selection of bearings

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