Martensitic quenching and tempering of high carbon chromium bearing steel

**Martensitic Quenching and Tempering of High Carbon Chromium Bearing Steel** Home > Bearing Knowledge > Martensitic Quenching and Tempering of High Carbon Chromium Bearing Steel Source: China Bearing Network | Time: 2013-01-16 --- With the increasing speed and reduced weight of modern engines, the working conditions for bearings have become more demanding. The functional requirements for bearings are continuously rising, including smaller size, lighter weight, greater load capacity, longer service life, and improved reliability. In recent years, the lifespan and performance of domestic bearings have become key challenges in the industry. As a result, the development of advanced heat treatment techniques and the improvement of heat treatment quality have always been major focuses for bearing manufacturers and research institutions both domestically and internationally. --- ### 1. Annealing Process of High Carbon Chromium Bearing Steel The microstructure of high carbon chromium bearing steel after annealing is characterized by fine, uniform, and round carbide particles distributed on a ferrite matrix. This structure prepares the material for subsequent cold working and final quenching and tempering processes. Currently, most companies use single-channel pusher isothermal annealing furnaces with non-oxidizing atmospheres, except for a few that still use periodic equipment. These modern methods offer better control over the microstructure and hardness compared to traditional techniques. According to JB1255 specifications, the ideal microstructure should be 2–3 points of fine pearlite. However, these processes still face challenges such as high energy consumption and significant oxidation and decarburization after annealing. To address these issues, recent developments include oil-electric composite heating isothermal annealing furnaces and double-chamber isothermal furnaces, which show significant energy savings. These technologies should be widely adopted, especially when combined with blank forming processes and nitrogen-based atmosphere furnaces, to reduce oxidation and lower raw material and machining costs. --- ### 2. Martensitic Quenching and Tempering Process The development of martensitic quenching and tempering for high carbon chromium bearing steel mainly involves three aspects: - **Basic understanding of process parameters**: Studies focus on how quenching and tempering affect the microstructure, residual austenite content, and mechanical properties such as fatigue resistance. - **Process function research**: Investigations into the impact of quenching conditions on scale, deformation, and scale stability. - **Controlled atmosphere heating**: Moving away from oxidation and maintaining a controlled atmosphere during heating to improve overall quality. #### 2.1 Microstructure and Properties After Quenching and Tempering After martensitic quenching, the microstructure consists of martensite, residual austenite, and undissolved carbides. The carbon content of the martensite matrix is typically around 0.55%. The structure often appears as a mixture of lath and flake martensite or a central "jujube nucleus" shape. Cryptocrystalline and crystalline martensite are common, with substructures formed by dislocation entanglement and twin crystals. Increasing quenching temperature or holding time can lead to a transition from cryptocrystalline to fine needle-like martensite. An excessive amount of acicular martensite may indicate an improper microstructure and should be avoided. Studies have shown that quenching at 835–865°C and tempering at 150–180°C provides optimal mechanical properties and fatigue life. Higher quenching temperatures (e.g., 845°C) yield the highest crushing load and longest fatigue life. However, as tempering temperature and time increase, hardness decreases while strength and durability improve. For special applications or high-temperature environments, cold treatments between -40°C and -78°C can enhance dimensional stability, and isothermal quenching at 250°C followed by tempering at 180°C can further improve impact resistance. --- ### 2.2 Conventional Martensitic Quenching Conventional martensitic quenching is commonly performed using chain or mesh belt furnaces. While this method allows for precise control of the final microstructure and hardness, future improvements will focus on reducing distortion and optimizing residual stress and austenite levels. #### 2.3.1 Controlling Quenching Distortion Quenching distortion remains a critical issue in conventional martensitic quenching, especially in dustproof bearings where distortion can affect sealing performance. Advanced furnace technologies with controlled atmospheres help minimize decarburization and allow tighter machining tolerances. Proper placement of workpieces, selection of quenching oil, and oil temperature management are essential for achieving minimal or zero distortion. #### 2.3.2 Managing Residual Stress and Austenite Residual stress and retained austenite significantly influence the fatigue life and crack resistance of bearing components. While Chinese standards do not currently specify targets for these factors, many foreign companies integrate them into their heat treatment controls. Research into the effects of quenching and tempering on residual stress and austenite is ongoing, with the goal of tailoring these parameters to specific bearing applications. --- ### 3. Bainite Austempering Bainite austempering has become a hot topic in bearing research, particularly in China. Since the 1980s, the Luoyang Bearing Research Institute has collaborated with several factories to apply bainite austempering to railway and rolling mill bearings. This technique improves impact resistance, wear resistance, and dimensional stability, making it ideal for bearings in harsh environments such as railways, cranes, and mining machinery. SKF has successfully applied bainite austempering to various bearings, including railway and rolling mill bearings, using specialized steel grades like SKF24, SKF25, and 100Mo7. Their new grade 775V offers even better performance, with increased hardness and wear resistance. However, challenges remain in controlling the optimal bainite content and managing production costs associated with additional tempering steps. --- ### 4. Special Heat Treatment Techniques Special heat treatment methods such as carburizing, nitriding, and carbonitriding are used to improve surface properties and residual austenite stability. These techniques enhance wear resistance, fatigue life, and corrosion resistance. NSK and KOYO have developed advanced steel grades and heat treatment processes that significantly extend bearing life under polluted conditions. --- ### 5. Surface Modification Technologies Surface modification techniques like ion implantation and coating have also gained attention. Ion implantation, such as chromium or boron ion injection, enhances corrosion resistance and wear performance. Coating technologies like PVD and CVD deposit hard or soft films on bearing surfaces, improving wear resistance and reducing friction. --- ### Conclusion As the demand for higher-performance bearings continues to grow, advancements in heat treatment technologies—such as martensitic quenching, bainite austempering, and surface modification—are playing a crucial role in meeting these challenges. Ongoing research and development in these areas will ensure that bearings continue to perform reliably in increasingly demanding applications. --- **Related Articles:** - INA spherical roller bearings - Great Wall Heavy Industry jaw crusher bearings - Long-life bearing specifications - Understanding bearing oscillation levels - Surface treatment of SKF bearings For more information, visit [China Bearing Network](http://). Previous: *The Drive Shaft* Center Support Damage Discussion Next: Bearing Damage Conditions and Causes

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