Case Hardening (Carburising)

Diffusing carbon into the surface of a low carbon steel at 880-950 °C, then quenching, to produce a hard wear-resistant case over a tough core.

The two-property trick

A gear tooth needs a surface that resists contact fatigue and a core that absorbs shock. No single carbon level does both. Carburising raises surface carbon to 0.8-1.0% so the case quenches to 58-62 HRC, while the core stays at its original 0.15-0.20% and remains tough at 150-200 HB.

Case depth

Effective case depth — usually measured to 550 HV — runs 0.3 mm on small parts to 1.5 mm on heavy gears, controlled by time at temperature. Deeper is not better: too deep a case makes the tooth brittle and prone to spalling.

Related terms

Decarburisation
Jominy Hardenability
Through Hardening

Where this applies

Case Hardening & Bearing Steel Bars

Need help applying this?

Stancor Bright Bars engineers answer specification questions directly. Contact us.