Author: Site Editor Publish Time: 2026-10-07 Origin: Site
52100, SUJ2 and 100Cr6 are not three different steels — they are three national designations for the same through-hardening bearing steel. AISI 52100 is the U.S. name (SAE J404, ASTM A295); SUJ2 is the Japanese name (JIS G4805); 100Cr6 is the European name (DIN EN 10089, Werkstoff 1.3505). China's GB/T 18254 calls the same composition GCr15. They are chemically and mechanically equivalent for 95% of bearing applications, and cross-grade substitution is normal procurement practice. The reasons one name is specified instead of another are usually regional (Japanese OEMs prefer SUJ2, European OEMs prefer 100Cr6, US OEMs prefer 52100) or traceability-driven (medical and aerospace bearings carry the specific national specification on the mill cert). This article lays out the chemistry, the heat treatment, the cleanliness standards, and the cross-grade substitution rules.
| Designation | Standard | Country / Region | Werkstoff |
|---|---|---|---|
| 52100 | ASTM A295/A295M, SAE J404 | USA | — |
| SUJ2 | JIS G4805 | Japan | — |
| 100Cr6 | DIN EN 10089 (formerly DIN 17230) | Europe | 1.3505 |
| GCr15 | GB/T 18254 | China | — |
| 100CrMo7-3 | DIN EN ISO 683-17 | Europe (higher-hardenability variant) | 1.3539 |
| Equivalent cross-reference | All four designations (52100 / SUJ2 / 100Cr6 / GCr15) describe essentially the same 1% carbon / 1.5% chromium through-hardening bearing steel | ||
| Property | 52100 (ASTM A295) | SUJ2 (JIS G4805) | 100Cr6 (DIN EN 10089) |
|---|---|---|---|
| Carbon, % | 0.93–1.05 | 0.95–1.10 | 0.90–1.05 |
| Silicon, % | 0.15–0.35 | 0.15–0.35 | 0.15–0.35 |
| Manganese, % | 0.25–0.45 | 0.50 max (often 0.95 max) | 0.25–0.45 |
| Chromium, % | 1.35–1.65 | 1.30–1.60 | 1.35–1.65 |
| Phosphorus, max % | 0.025 | 0.025 | 0.025 |
| Sulfur, max % | 0.025 | 0.025 | 0.025 |
| Other residuals | Mo + Ni + Cu ≤ 0.50 total (typical) | Mo + Ni + Cu ≤ 0.25 (typical) | Mo + Ni + Cu ≤ 0.25 (typical) |
| Hardenability (J660, mm) | ~10–15 mm | ~10–15 mm | ~10–15 mm |
| Working hardness after Q&T, HRC | 60–66 | 60–66 | 60–66 |
| Typical bearing ring hardness, HRC | 61–65 | 61–65 | 61–65 |
| Typical ball/roller hardness, HRC | 62–66 | 62–66 | 62–66 |
| Max service temperature (standard temper), °C | ~120 (150 °C temper limit) | ~120 | ~120 |
| Cross-substitution | Yes — interchangeable for the same bearing specification | Yes | Yes |
The chemistry differences are inside the noise band. The carbon range in SUJ2 runs slightly higher at the top end (up to 1.10%) — Japan historically targeted the high-carbon end for maximum ball hardness — but in practice JIS G4805 SUJ2 from any major mill ships at 0.98–1.05% C, overlapping 52100 and 100Cr6. For procurement, 52100, SUJ2 and 100Cr6 are the same steel, and the specification choice is driven by the buyer's national-standard requirement, not by metallurgy.
| Element (%) | 52100 (ASTM A295) | SUJ2 (JIS G4805) | 100Cr6 (DIN EN 10089 / 1.3505) | GCr15 (GB/T 18254) |
|---|---|---|---|---|
| Carbon | 0.93–1.05 | 0.95–1.10 | 0.90–1.05 | 0.95–1.05 |
| Manganese | 0.25–0.45 | 0.50 max (often up to 0.95) | 0.25–0.45 | 0.20–0.40 |
| Silicon | 0.15–0.35 | 0.15–0.35 | 0.15–0.35 | 0.15–0.35 |
| Chromium | 1.35–1.65 | 1.30–1.60 | 1.35–1.65 | 1.40–1.65 |
| Molybdenum | 0.10 max (typical, residual) | 0.25 max (typical) | 0.10 max (typical) | 0.10 max (typical) |
| Nickel | 0.25 max (typical) | 0.20 max (typical) | 0.25 max (typical) | 0.30 max |
| Copper | 0.30 max (typical) | 0.25 max (typical) | 0.30 max (typical) | 0.25 max |
| Phosphorus | 0.025 max | 0.025 max | 0.025 max | 0.025 max |
| Sulfur | 0.025 max | 0.025 max | 0.025 max | 0.020 max |
| Oxygen, ppm (premium bearing) | ≤15 (premium), ≤30 (standard) | ≤15 (premium) | ≤15 (premium) | ≤15 (premium) |
| Titanium, ppm (premium) | ≤30 (premium), ≤50 (standard) | ≤30 | ≤30 | ≤30 |
Three chemistry observations matter for procurement. First, phosphorus and sulfur caps at 0.025% are tighter than general alloy steel (typically 0.035–0.040%), reflecting the bearing industry's intolerance for inclusions that initiate fatigue spalls. Second, the residual caps (Mo, Ni, Cu) are loose — these are not intended alloying elements, they are residuals from scrap or from previous heats, and major mills hold them well below the standard maxima. Third, the oxygen and titanium levels in premium bearing steel are below 15 ppm and 30 ppm respectively, achieved via vacuum induction melting + vacuum arc remelting (VIM-VAR) or electroslag remelting (ESR). These trace elements are not in the printed specification but appear on premium-grade mill certs and are critical for fatigue life.
| Step | Standard practice |
|---|---|
| Spheroidize anneal (mill delivery) | 760–780 °C, slow cool to 650 °C, hold, furnace cool → 179–207 HB annealed (turned, ground, ready to machine) |
| Stress relief after machining | 550–650 °C × 2–4 h, slow cool |
| Austenitize | 800–850 °C (typ. 820–840 °C for through-hardening rings, 840–855 °C for balls) |
| Quench | Oil, 40–80 °C, with agitation (alternative: high-pressure gas quench in vacuum furnace for thin-section rings) |
| Wash and temper | 150–200 °C × 2–4 h (standard bearing temper), or 200–240 °C for high-temperature service |
| Surface temper (post-grind) | 150 °C × 2–3 h to relieve grinding stresses |
| Final hardness, ring | 61–65 HRC (typ. 62–64 HRC for automotive and industrial bearings) |
| Final hardness, ball | 62–66 HRC (typ. 64–66 HRC) |
| Retained austenite (typical) | 5–10% (standard temper); 10–15% (low-temperature temper, 150 °C) |
| Dimensional stability at service temperature | Up to 120 °C: stable. Above 150 °C: requires higher temper or specialty grade |
Two heat-treat principles define the bearing industry. First, spheroidize-annealed delivery condition. Bearing steel bar stock is shipped in a spheroidized annealed microstructure — carbide spheres embedded in a ferrite matrix, with hardness around 190 HB — which machines cleanly and forms the chip-breaking behavior needed for the high-volume turning and grinding of bearing rings. Hardening is done after machining. Second, low-temperature tempering. The 150–200 °C temper after oil quench preserves the maximum as-quenched hardness (64–66 HRC quenched, dropping to 62–64 HRC after temper), which is what gives the contact-fatigue resistance needed for bearing service. Tempering higher (above 250 °C) drops hardness and fatigue life — if higher service temperature is needed, the engineering answer is a dimensionally-stable bearing grade like 52100-3 (Si-Mo modified) or a tool steel like H13 hot work steel, not a higher temper on standard 52100.
The single most important quality variable in bearing steel is non-metallic inclusion content. Inclusions act as fatigue initiation sites — under cyclic contact stress, a 10 µm alumina inclusion will start a spall after 10⁶–10⁷ cycles. The cleaner the steel, the longer the bearing life. The major standards measure this with three methods:
| Method | Standard | Measurement | Acceptance for premium bearing |
|---|---|---|---|
| JK chart, Method A | ASTM E45 | Worst field per inclusion type (A sulfides, B alumina, C silicates, D globular oxides) | Thin & Thick: A ≤ 2.0, B ≤ 1.5, C ≤ 1.0, D ≤ 1.5; max total severity ≤ 5.0 |
| JK chart, Method D | ASTM E45 (modern) | Statistical, 100 fields at 100×, mean and max | Thin & Thick: same targets |
| Micrograph | DIN 50602 | Method K (extrapolated) | K1 ≤ 30 (premium), K4 ≤ 20 |
| Inclusion rating | JIS G0555 | Method A (worst field) | A ≤ 2.0, B+C ≤ 1.5, D ≤ 1.5 |
| ISO 19497 | ISO | Statistical | Same JK-equivalent targets |
The premium bearing grades (designated by suffixes like "-1" or "-3" in SAE J404, or "E" in Chinese GB) hold the ASTM E45 Method A worst field at A ≤ 1.5, B ≤ 1.0, C ≤ 0.5, D ≤ 1.0 — half the maximum allowed in standard bearing steel. These premium grades are made via vacuum induction melting + vacuum arc remelting (VIM-VAR) or via electroslag remelting (ESR), and are specified for aerospace bearings, wind turbine bearings, high-speed rail bearings, and any bearing with design life above 10⁹ cycles.
Bearing steel cleanness procurement rule: specify the application and the L10 life (cycles at which 10% of bearings fail by fatigue). For automotive and industrial bearings, standard ASTM A295 52100 from a major mill is adequate. For aerospace or wind turbine bearings, specify ESR or VIM-VAR premium grade with ASTM E45 Method A targets and oxygen below 15 ppm.
| Application | Service condition | Recommended grade / quality | Reasoning |
|---|---|---|---|
| Automotive wheel hub bearings | Moderate cyclic load, 150 °C max | Standard 52100 / SUJ2 / 100Cr6 (oil-quenched, 62–64 HRC) | Through-hardened rings; ball bearing steel standard |
| Automotive transmission bearings | High cyclic load, moderate impact | Standard 52100 / SUJ2 / 100Cr6 | Same as above; higher cleanliness spec for fleet trucks |
| Electric motor bearings (low noise) | High RPM, low vibration | Premium ESR 52100 (low inclusion) | Inclusions cause noise and vibration; ESR cuts inclusions |
| Wind turbine mainshaft bearings | Very high cyclic load, 30-year life | Premium ESR or VIM-VAR 52100 | Design life 10⁹+ cycles; requires top cleanliness |
| Aerospace bearings (landing gear, engines) | High load, high reliability | VIM-VAR 52100, sometimes 52100-3 (Si-Mo) | Aviation-grade cleanness; dimensional stability at 150–200 °C |
| High-speed machine tool spindle bearings | Very high RPM, accuracy | Premium ESR 52100, retain austenite controlled | Sub-micron inclusions; tight dimensional stability |
| High-temperature bearings (oven conveyors) | Service 200–300 °C | 52100-3 (Si-Mo) or Cr4Mo4V (M50) tool steel | Standard 52100 softens above 150 °C; need stabilized grade |
| Railway axle box bearings | High cyclic load, vibration | Premium ESR SUJ2 (Japanese OEM) or 52100 (US) | 30-year design life; tight inclusions |
| Tapered roller bearings (heavy truck) | High load, moderate impact | Standard 52100 / 100Cr6, slightly lower hardness 60–63 HRC | Trade some hardness for impact toughness |
| Thrust ball bearings (low-speed) | Static or low-cycle load | Standard 52100 / SUJ2 / 100Cr6 | Low cycle count, standard grade adequate |
| Linear motion bearings (precision rails) | High repetition, low load | Premium ESR 52100, ground and superfinished | Low friction, fine surface finish |
The selection logic: standard 52100 / SUJ2 / 100Cr6 from a major mill covers 80% of bearing applications. Premium ESR or VIM-VAR covers the high-fatigue-life, high-reliability tier. High-temperature or aerospace-stability applications step up to modified grades (52100-3, M50, Cr4Mo4V). For high-temperature, high-stress bearing service above 200 °C, 4140 alloy steel in carburized form is sometimes used for low-speed applications, and M50 tool steel is the aerospace default.
Cross-substitution between 52100, SUJ2 and 100Cr6 is normal procurement practice. The rules:
Standard bearing applications (automotive, industrial machinery, consumer goods): all three grades are fully interchangeable. Specify the national standard the customer's drawings call for; supply the equivalent if needed.
Premium bearing applications (wind turbine, aerospace, railway): the cross-substitution has to match the cleanliness spec, not just the chemistry. Premium 52100 (ASTM A295 with ESR or VIM-VAR suffix) substitutes for premium SUJ2 (JIS G4805 with cleanliness spec per JIS G0555) and premium 100Cr6 (DIN EN 10089 with cleanliness per DIN 50602). The mill cert has to carry the cleanliness data on all three.
Regulated industries (aerospace, medical, nuclear): substitution requires the customer's engineering approval. The original equipment manufacturer (OEM) typically specifies a single national standard and a single heat — substitution is approved at the engineering level, not the procurement level.
China-origin material: GB/T 18254 GCr15 is fully equivalent in chemistry, and major Chinese mills produce to cleanness levels matching ASTM A295. For premium cleanness (oxygen <15 ppm, titanium <30 ppm), specify the ESR or VIM-VAR route on the purchase order.
| Designation | Standard | Country | Title |
|---|---|---|---|
| 52100 | SAE J404 | USA | SAE standard grade designation |
| 52100 | ASTM A295/A295M | USA | Standard specification for bearing steel (high-carbon, anti-friction bearing) |
| 52100.1 | ASTM A295 | USA | Standard grade with tighter inclusion limits via ESR/VAR (formerly "Aerospace grade") |
| 52100.3 | SAE J404 | USA | Si-Mo modified grade for dimensional stability up to 200–250 °C |
| SUJ2 | JIS G4805 | Japan | High carbon chromium bearing steel |
| 100Cr6 | DIN EN 10089 (replaces DIN 17230) | Europe | Through-hardenable bearing steel (Werkstoff 1.3505) |
| 100CrMnSi6-4 | DIN EN ISO 683-17 | Europe | Through-hardenable with higher Mn, deeper hardening (1.3503) |
| 100CrMo7-3 | DIN EN ISO 683-17 | Europe | Higher-hardenability variant for large bearings (1.3539) |
| GCr15 | GB/T 18254 | China | High-carbon chromium bearing steel |
| GCr15SiMn | GB/T 18254 | China | Mn-Si modified, deeper hardening |
| ShKh15 | GOST 801 | Russia | Russian bearing steel, equivalent to 52100 |
| ShKh15SG | GOST 801 | Russia | Mn-Si modified variant |
For through-hardened bearings up to 25 mm section, all four major designations (52100 / SUJ2 / 100Cr6 / GCr15) are interchangeable. For larger sections, the higher-hardenability variants (52100H, 100CrMo7-3, GCr15SiMn) come into play — the standard 1% carbon / 1.5% chromium composition does not through-harden in oil above about 15 mm section.
The most common mistake is specifying the chemistry but not the cleanliness. A standard ASTM A295 52100 mill cert meets the chemistry table, but the inclusion content (ASTM E45 Method A) can vary by a factor of 5× between mills. For a 100,000-cycle L10 life bearing, that's a non-issue. For a 10⁹-cycle wind turbine bearing, it's the difference between a 5-year failure rate and a 25-year design life. Specify the cleanliness target on the purchase order — not just the chemistry.
The second mistake is specifying the hardness without specifying the temper. A 62 HRC 52100 ring could be tempered at 160 °C (standard, dimensionally stable to 120 °C in service) or at 220 °C (dimensionally stable to 200 °C, but with 15% lower fatigue life). The hardness reading is the same; the service behavior is different. Specify the temper temperature range on the heat-treat drawing.
The third mistake is ignoring retained austenite. A ring quenched and tempered at 150 °C holds 10–15% retained austenite, which slowly transforms in service and causes dimensional growth. For a precision spindle bearing running at tight clearance, this growth can close the bearing clearance and cause failure. The fix is either a higher temper (200–220 °C) or a sub-zero treatment between quench and temper to convert the retained austenite. For standard automotive and industrial bearings, neither is needed; for precision bearings, both are mandatory.
The fourth mistake is using 52100 above 150 °C without a dimensional stability plan. Standard 52100 tempered at 150 °C starts to soften above 120 °C in service and grows dimensionally as retained austenite transforms. For service at 150–250 °C, step up to 52100-3 (Si-Mo modified) or to a tool steel grade like M50 or H13 hot work tool steel for extreme temperature.
Q: Are 52100, SUJ2 and 100Cr6 really the same steel?
Chemically and mechanically, yes — the compositions overlap, the heat-treatment response is identical, the cleanliness standards are aligned across national specifications, and cross-substitution is standard practice. The differences are in the national certification and the mill's traceability language. Specify the national standard your customer's drawings call for.
Q: What is the difference between 52100 and 52100.3?
52100.3 (also written 52100-3) is a Si-Mo modified version with 0.65–0.90% silicon and 0.10–0.20% molybdenum, designed for dimensional stability at 200–250 °C in service. It's specified for high-temperature bearings (oven conveyors, jet engine accessories). Standard 52100 is for service below 120 °C.
Q: Can I substitute GCr15 for 52100?
Yes, for the vast majority of bearing applications. GCr15 is the Chinese GB/T 18254 designation for the same composition, and major Chinese mills produce to cleanness levels matching ASTM A295. For aerospace and premium bearings, specify the ESR or VIM-VAR route and confirm the cleanliness on the mill cert.
Q: Why is bearing steel spheroidize-annealed for delivery?
The 1% carbon matrix in 52100 forms hard, brittle lamellar pearlite in the as-rolled condition — too hard to machine cleanly. Spheroidize annealing (heating to 760–780 °C and slow-cooling) converts the carbides to spherical particles in a soft ferrite matrix, dropping the hardness to 179–207 HB and giving the chip-breaking behavior needed for high-volume bearing ring machining. After machining, the rings are hardened to 62–64 HRC.
Q: What is L10 life and how does it relate to bearing steel quality?
L10 is the cycle count (or hours of operation) at which 10% of a population of bearings fail by fatigue. It's calculated per ISO 281 or ABMA Std 9. Bearing steel cleanness directly determines L10 — every 50% reduction in inclusion severity roughly doubles L10 life. This is why premium ESR or VIM-VAR 52100 is specified for high-reliability bearings: the cleanliness premium pays back in life.
Q: Can I induction-harden 52100 instead of through-hardening?
For bearing applications, no. The contact stresses in bearing service (1500–2500 MPa Hertzian stress) require through-hardened martensite to a depth that exceeds the maximum shear stress depth — typically 0.5–1.0 mm below the raceway surface. Induction hardening can produce this case, but the substrate needs to be a carburizing or through-hardening grade; standard 52100 induction hardens well but is rarely used this way because the through-hardening oil quench is cheaper and more uniform.
If you are sourcing bearing steel and need to specify the right grade — 52100, SUJ2, 100Cr6 or GCr15; standard cleanness or ESR premium; for automotive, wind, aerospace or industrial application — send the specification, the cleanliness target and the bearing type. Qilu Metal supplies high-carbon chromium bearing steel to ASTM A295, JIS G4805, DIN EN 10089 (1.3505) and GB/T 18254 (GCr15), with conventional, ESR and VIM-VAR routes, oxygen and titanium controlled for premium applications, full mill test reports and traceability. Email enquiry@qilumetal.com and our metallurgy team will quote the grade, the quality level and the heat-treatment recommendation matched to your bearing design life.
