Core Process Analysis of pillow block Bearings: 

How Martensitic Heat Treatment Creates a “Hardcore” Bearing

In the manufacturing system of pillow block bearings, heat treatment is the decisive final step that determines the bearing’s ultimate performance. We use high-carbon chromium bearing steel (GCr15 series) as the core material and adopt martensitic quenching combined with low-temperature tempering as the final heat treatment process. This approach directly influences the balance between hardness, wear resistance, and dimensional stability.

Complete Process Analysis of Martensitic Heat Treatment

The essence of martensitic heat treatment lies in heating the bearing steel to its austenitizing temperature and then rapidly cooling it, preventing atomic diffusion and inducing a shear-type phase transformation to form high-hardness martensite. Our process consists of three critical stages.

Stage 1: Austenitizing Heating

The bearing rings or rolling elements are heated to a temperature range of 830–880°C and held for a specific duration, allowing carbides to fully dissolve into the austenite while maintaining an appropriate amount of undissolved carbide particles. This temperature window is crucial: too low, and the carbon and alloy content in austenite will be insufficient, resulting in inadequate hardness after quenching; too high, and austenite grain size increases, leading to coarse martensite needles and a sharp decline in toughness and fatigue strength. The holding time is precisely calculated based on the effective wall thickness of the workpiece to ensure uniform temperature distribution throughout the component.

Stage 2: Quenching and Martensitic Transformation

After holding, the bearing components are immediately immersed in oil for quenching. Oil quenching provides sufficient cooling capacity to complete the martensitic transformation below the Ms point, while avoiding the cracking risks associated with water quenching. The microstructure after quenching consists of martensite matrix, retained austenite, and undissolved carbides, achieving a hardness of HRC 64–67.

However, the quenched state is not the final condition. At this stage, the residual austenite content typically ranges from 6% to 15%. A moderate amount of retained austenite positively contributes to bearing toughness by enhancing crack propagation resistance. However, during service, residual austenite may undergo stress-induced transformation, causing dimensional changes. Therefore, tempering must follow quenching immediately.

Stage 3: Low-Temperature Tempering and Microstructural Stabilization

Immediately after quenching, the parts undergo low-temperature tempering at 150–180°C for 2–4 hours. This step serves three purposes: first, relieving internal stresses generated during quenching and reducing brittleness; second, precipitating nanoscale ε-carbides within the martensite matrix, thereby improving toughness without sacrificing hardness; third, further decomposing residual austenite to enhance dimensional stability.

For precision bearings requiring extremely tight dimensional tolerances, we additionally incorporate deep cryogenic treatment after quenching—cooling the parts to -60°C to -70°C to fully transform residual austenite into martensite before tempering. This allows us to achieve even tighter dimensional control.

The final tempered martensite structure achieves stable hardness within the range of HRC 61–65, fully meeting the requirements of Zhenkuai bearings under high-load, continuous operation conditions regarding hardness and wear resistance.

What Martensitic Heat Treatment Brings to pillow blocki Bearings

Following this martensitic quench-temper process, the contact fatigue strength of Zhenkuai bearings can exceed 1800 MPa, with wear resistance improved by 30%–50% compared to carbon tool steel. More importantly, the uniformly fine tempered martensite matrix combined with dispersed fine carbide particles enables the bearing to maintain high surface hardness under impact loads and cyclic stresses, while also providing sufficient matrix toughness to absorb energy, significantly reducing the risk of early spalling or fracture.

From materials to processing, martensitic heat treatment forms the technological foundation behind our promise of durability for pillow block bearings