Analysis of Heat Treatment Techniques for Bearings

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Heat treatment is a crucial process in the manufacturing of bearings, yet many people don’t fully understand how to apply it effectively. In this article, I’ll provide an in-depth analysis of the heat treatment techniques used in bearings and their benefits. (1) **Expanding the Application of GCR15 Steel**: Typically, GCR15 steel is quenched using M (oil) quenching for wall thicknesses up to 12mm. However, with BL (bainite) quenching, which uses nitrate salt as a cooling medium, the effective wall thickness can be extended to around 28mm. This is achieved through methods like mixing, stringing, or adding water, allowing for more versatile applications. (2) **Stable and Uniform Hardness**: BL quenching is a slower process compared to traditional methods. For example, GCR15 steel usually requires 4 hours, while GCR18MO needs about 5 hours. During this time, the ferrule undergoes isothermal treatment in nitrate salt, ensuring uniform microstructure changes. As a result, the hardness after BL quenching typically ranges from 59–61 HRC, with a uniformity of no more than 1 HRC. This is a significant improvement over oil quenching, where larger wall thicknesses may lead to soft spots and uneven hardness. (3) **Reducing Quenching and Grinding Cracks**: In the production of large bearings used in railways and rolling mills, quenching and grinding cracks are common issues. Oil quenching can make the material brittle, leading to microcracks. However, BL quenching produces a better bainite structure, creating surface compressive stresses of up to -400 to -500 MPa. These compressive stresses help reduce crack formation and offset grinding stresses, significantly lowering the risk of grinding cracks. (4) **Improving Bearing Service Life**: Bearings used in high-impact environments, such as railway and rolling mill systems, often fail due to inner ring cracking during installation or outer ring fragmentation during use after M quenching. Austempered bearings, however, offer better impact resistance and surface compressive stress, reducing the likelihood of these failures. As a result, isothermal quenching improves both the average lifespan and reliability of bearings compared to traditional M quenching.

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**Recommended Reading** - Common Terms and Definitions of Bearings (Part 2) - Analysis of National Watch Comparison Tests - Hub Bearing Seal Layout and Rolling Bearing Manufacturing - Bearing Wear Analysis and Ferrule Grinding & Superfinishing - Small Four-Wheel Tractor Bearings This article is linked from: http:// Please cite China Bearing Network: http:// Previous: Bearing Inspection Test: Professional Bearing Treatment Plan Next: High-Speed Thrust Angular Contact Ball Bearing

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