Why Heat Treatment Decides Bearing Life

No other step influences a bearing's load capacity and service life as much as heat treatment. It is the process that turns ordinary alloy steel into a microstructure capable of supporting heavy rolling loads for millions of revolutions without failing.

Austenitising, Quenching and Tempering

For through-hardened bearing steel the sequence is: heat to the austenitising temperature (commonly 830-870°C), then quench rapidly in oil or gas so the structure transforms to hard, brittle martensite. A subsequent temper at 150-200°C relieves internal stress and restores toughness, settling the part at about 60-64 HRC - hard enough to resist wear, tough enough to avoid cracking.

Precipitation (Age) Hardening - 17-4PH

Stainless grades such as 17-4PH harden differently. After a solution anneal the alloy is aged: reheating causes finely dispersed copper/niobium precipitates to form inside the martensitic matrix, pinning dislocations and raising strength without the very high carbon content of 440C. The result is a balanced combination of corrosion resistance and hardness (around HRC 42-48) - ideal for food, marine and chemical duty where plain martensitic stainless would rust.

Cryogenic Treatment and Stability

Some high-precision programs add a cryogenic step (cooling below -70°C) to convert retained austenite into martensite. Leftover retained austenite can transform later in service and change dimensions, so driving it out improves dimensional stability - important for spindles and instruments.

Case Carburising for Tough Cores

Low-carbon steels used in large or impact-loaded bearings are often carburised: carbon is diffused into the surface layer, then the part is quenched and tempered so the case is hard while the core stays tough. This "hard surface, tough core" structure resists both wear and shock loading.

How KMK Bearing Applies This

At KMK Bearing (SINO BEARINGS, KMK brand) these principles guide every order we manufacture in Chengdu, China. Our in-house process chain - forging, heat treatment, precision grinding, superfinishing and cleanroom assembly - is built to the standards described above, whether the part is a standard catalog bearing or a custom-engineered solution.

• 20+ years of precision bearing manufacturing
• Materials from chrome steel to 17-4PH stainless steel and full ceramic (ZrO2, Si3N4)
• In-house heat treatment and metrology to P4/P2 (ABEC 7/9) precision
• Custom designs and low-MOQ prototyping from drawings or samples

Discuss your application with kevin@sinoti.com or browse our bearing catalog.

SINO BEARINGS (KMK) - Perfect Quality -- Great Service -- Customized.

Source: SINO BEARINGS