The grade behind the bearing in nearly every machine
EN31, known internationally as AISI/SAE 52100 or DIN 100Cr6, is the standard high-carbon chromium bearing steel, chosen wherever a component needs to survive millions of repeated load cycles without fatigue cracking or surface wear. If a machine shop is reconditioning bearings, machining precision shafts, or making bushings and pins for industrial equipment, there's a good chance EN31 is the grade already in use or the one they should be asking for.
What through-hardening actually means
EN31 runs a high 0.95 to 1.10% carbon and 1.30 to 1.60% chromium, with manganese (0.25 to 0.45%) and silicon (0.15 to 0.35%) rounding out the alloy. That's high enough carbon and chromium content that the whole cross-section hardens uniformly through conventional quench and temper, no carburizing, no case-and-core structure like 8620. That's "through-hardening": the entire part reaches a consistent, high hardness, typically 60 to 66 HRC, from surface to center, which matters for a bearing race or a precision shaft where surface fatigue resistance and dimensional stability under load both come from the same uniform microstructure rather than a hardened shell over a softer core.
Against the 30 to 70 HRC span covered in this catalogue.
60 to 66 HRC for high-carbon chromium bearing steel
Hardness depends on the heat treatment applied. Confirm the condition before specifying.
Why bearings fail differently than other parts
A bearing race or roller doesn't fail the way a gear tooth or a shaft typically fails. It fails from rolling contact fatigue, microscopic subsurface cracks that develop under millions of repeated load cycles at the contact point between the rolling element and the race, eventually working their way to the surface as spalling. Resisting that requires more than surface hardness, it requires a clean, uniform, fully hardened microstructure through the load-bearing depth of the part, exactly what EN31's high carbon content is formulated to deliver.
Where it's specified
Ball and roller bearings first and foremost, but also precision shafts, high-wear pins, and bushings, anywhere rolling contact fatigue resistance is the deciding property rather than toughness or weldability. It's not a structural or forging steel in the way 4140 or 8620 are, it's chosen specifically for components where dimensional precision and fatigue life under rolling contact matter more than impact resistance or machinability.
Typical published ranges, percent by weight
- Cr1.3 to 1.6%
- C0.95 to 1.1%
- Mn0.25 to 0.45%
- Si0.15 to 0.35%
0%2%
Ranges are typical published values, not guaranteed for a specific batch. Confirm against the mill test certificate.
A narrower, more technical buyer than general alloy steel
EN31 isn't a general forging steel like 4140 or 8620. The natural customer is a bearing reconditioning shop or a precision machine shop making replacement shafts and bushings for industrial machinery, a distinct segment from the automotive forging trade even though both fall under "alloy steel" broadly. These buyers tend to order in smaller, more specification-driven quantities than a forging shop ordering stock for a production run, and they usually know exactly which grade they want by the time they call, worth stocking separately and marketing to that specific buyer rather than lumping it in with general forging steel inquiries.
A note on local demand
This is one of the grades where the research behind the Pakistani context is more general than specific, no single named cluster the way Sialkot's surgical instruments or Wazirabad's cutlery trade have one. Karachi and Lahore machine shops doing bearing and precision shaft work are the logical buyer, worth refining with direct customer conversations rather than treating as settled fact the way the cluster-backed grades in this catalog are.
Need EN31 for a bearing or precision shaft job? Get in touch with your specification.