440C Stainless Bearing Steel — Hardness, Corrosion and Limits

440C sits at the high-carbon end of the martensitic stainless family. The chromium forms a passive oxide layer that stops rust, and the carbon allows the steel to harden — but carbon also ties up chromium as carbide, which removes it from the passive layer and creates chromium-depleted zones around each carbide. That is why 440C resists fresh water well and pits in chlorides: chloride attacks exactly those depleted zones.

Compared with 52100 the fatigue limit is slightly lower and the price is roughly three times. What you buy is the ability to run without grease as a rust barrier — the single biggest cause of bearing failure in wet plants is water in the grease, not load.

• Food and beverage machinery: washdown, caustic cleaning, H1 greases, condensation on stop-start duty.
• Medical and laboratory equipment: autoclave-adjacent positions, instrument trays, sterilisation cycles.
• Outdoor and marine-adjacent equipment: fresh water spray, humidity, occasional rain — not direct salt spray.
• Packaging and printing: ink mist, water-based adhesives, frequent cleaning.
• Pharmaceutical and cleanroom: corrosion-free surfaces that can be wiped down.

First, chlorides: seawater, brine, hypochlorite sanitisers and pool water. Second, stagnant wet contact: a bearing that sits in a puddle with no rotation loses its passive layer and crevice-corrodes under the seal. Third, high load at temperature: 440C softens above about 250 °C faster than 52100 and has less retained hardness for shock duty.

• Pits in chlorides — seawater, brine, hypochlorite. Not a marine material.
• Crevice corrosion under seals where water sits and the bearing does not rotate.
• Roughly 10–15% less dynamic capacity than 52100; a marginal selection becomes a short life.
• Higher cost means counterfeit and mis-declared “stainless” product is common — insist on the certificate.
• Softer at temperature than 52100 above 250 °C, so shock duty at heat is a poor fit.

1. Say “440C to ASTM A276 / EN 1.4125” and ask for the mill certificate — not just “stainless”.
2. Name the fluid: fresh water, food residue and chloride are three different answers.
3. Specify the seal: a 2RS contact seal keeps water out but adds torque; a shield does not seal.
4. Pair the material with an NSF H1 grease if there is any chance of food contact.