52100, 100Cr6, SUJ2 & GCr15 Bearing Steel

52100 is a material grade, not a complete bearing number

A search for 52100 bearing steel is a material query. A search for 608, 6204 or another complete bearing marking is a component query. Keep the two identities separate: a steel grade does not specify bore, outside diameter, width, seals, cage or precision.

A loose steel ball also needs its nominal ball diameter, ball grade and lot/gauge requirements. Those specifications are different from the dimensions and ABEC class of a complete bearing. “Chrome steel ball bearing” can mean either the assembled product or the loose rolling element; identify which one you need first.

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52100 vs 100Cr6 vs SUJ2 vs GCr15: related grades, not blanket approval

NSK describes the chemistry of SUJ2 as approximately corresponding to AISI 52100 and DIN 100Cr6. Ovako lists SAE 52100, 1.3505 and GCr15 among the related designations for its 100Cr6 family. This supports material identification, not an unconditional substitution of finished bearings or raw stock.

The ordering standard and revision, melt/cleanliness requirements, section size, heat treatment and inspection certificate still matter. Even two materials sold under the same broad international grade can have different supplier variants and measured properties.

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Bearing-steel chemical composition: keep the standard and source with the numbers

Mass percent (%). The first two columns reproduce factual ranges from NSK Table 12.1, A244; the third is the EN ISO 683-17 reference row published by Ovako, not a certificate for every Ovako variant or a replacement for the standard.

“Not listed” is not zero. Likewise, an upper limit is not a typical measured concentration. The source’s less-than wording is retained rather than silently changing it to a nominal value.

NSK’s later cross-standard Table 12.8 contains separately labelled older standard references and slightly different limits. Those entries are not merged into this table. Use the specification and revision governing the actual purchase or existing part when resolving a difference.

Supplier variants are a further qualification. Ovako 803F, for example, has a narrower published carbon range than the broad standard-reference row. Do not average several variants together and present the result as the composition of every 52100 bearing.

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52100 yield strength: four documented bar-stock conditions

Carpenter’s VIM-VAR 52100 sheet reports these typical properties for spheroidized-annealed bars in the listed conditions. The yield column uses the 0.2% offset method. Values are not guaranteed design minima and do not describe hardened bearing raceways.

For example, the 1 in turned-and-polished bar has a reported yield strength of 427 MPa; the cold-drawn row is 603 MPa. State the product form and condition when quoting either number. This table does not establish the yield strength of an unspecified 52100 bearing.

These are historical manufacturer reference data: the sheet prints edition date 06/01/1993. Use a current specification and batch certificate for acceptance or engineering design; this website has not independently tested the material.

The separate 100Cr6 table below illustrates different supplier conditions. It must not be relabelled as additional Carpenter 52100 test results.

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100Cr6 strength and bearing hardness: first ask “in which condition?”

There is no single condition-free strength or HRC value for a grade name. These are Ovako 100Cr6 variant 803F examples, not universal 52100 values and not allowable stresses for a finished bearing.

+SA identifies the spheroidized-carbide condition; +C is cold-work hardened; +Q/T(m) is quenched/tempered to martensite and +Q/T(b) to bainite. The manufacturer’s dimension string “24 < 190” is retained as printed; this page does not invent a new boundary interpretation or extend the row to every section size.

The table labels yield strength as a minimum and tensile strength and hardness as typical. Those are different kinds of statements. A typical hardness is not a guaranteed acceptance range, and a dash in the dimension field is not proof of unrestricted size applicability.

HB and HRC are different hardness scales. Do not treat 210 HB as 210 HRC or apply an unsourced fixed conversion. A finished ring or ball needs its own heat-treatment and inspection requirements.

A bulk-material tensile or yield value cannot replace a bearing’s catalogue dynamic/static load rating. Rolling contact, geometry, residual stresses, lubrication and fatigue verification are separate issues. Do not derive an allowable bearing load by multiplying one of these MPa values by a guessed area.

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Density, stiffness and thermal expansion: useful inputs with stated conditions

Typical physical values from Ovako’s 100Cr6 sheet. They describe the material reference, not the mass, stiffness or temperature rating of a complete bearing.

Illustrative thermal arithmetic: with α = 12×10⁻⁶/K, an unconstrained 50 mm steel dimension and an 80 K rise give ΔL = αLΔT = 0.048 mm. This is a calculated free-growth example, not a predicted running clearance for a bearing.

For a real fit, the shaft, bearing rings and housing may have different temperatures and materials. Compare their separate changes and constraints. Do not equate a 20–300°C property-reference interval with an approved bearing operating-temperature range.

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Rings, balls, rollers and cages need different material records

Through-hardening and case/carburizing hardening are different material-and-process choices. The latter aims for a hard working surface with a relatively softer core. A generic “carbon steel bearing” description leaves too much unresolved to approve a substitute.

Material cleanliness matters alongside chemistry. Supplier-specific melting and cleanliness controls should remain part of the material record; the familiar grade number does not by itself describe inclusions, processing quality or fatigue performance.

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Chrome steel vs stainless steel: chromium does not make them the same material

The chromium-bearing steels in the composition table are not the stainless grades listed separately by NSK. Its SUS440C reference, for example, has 16–18% chromium, compared with the approximately 1.3–1.6% ranges shown for these high-carbon bearing steels.

“Chrome steel” here describes an alloy; it is not evidence of chrome plating. Do not infer corrosion protection from the word chrome, and do not assume every stainless bearing is suitable for salt water, acid, washdown or dry running.

A material change also affects the rest of the selection problem. Check the actual load rating, closure, lubricant, cage and environment for the proposed bearing. A matching bore and a corrosion-related label are not enough to establish a replacement.

What to record before accepting a material equivalent

Keep the original name on the record even when a comparison identifies a related grade. If the supplier document omits a required condition or property, leave that field unknown until it is established. A website reference cannot turn an unspecified batch into certified bearing material.

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Use the material reference alongside model, dimension and ball-grade tools

For an assembled bearing, search the complete brand and model, then inspect which components have a recorded material specification. This guide does not retrospectively label every product in the database as 52100 or SUJ2.

For loose balls, carry the material choice into the precision-ball guide together with nominal diameter and grade. For a manufacturer/OEM assembly, also retain the original component reference and service procedure. A phrase such as “Tange Seiki 4T5-5 SUJ2” needs a matching maker record; the alloy name does not prove its dimensions or fitment.

Use thermal-expansion and mass calculations only after choosing inputs appropriate to the documented material and geometry. Their arithmetic does not certify a bearing selection.