52100 steel (G52986): properties, composition, equivalents
52100 steel (AISI/SAE 52100, UNS G52986, E52100): 1.0 % C, 1.5 % Cr bearing steel. Hardens to 60–67 HRC; 58–62 HRC in service. Composition, heat treatment, 52100 as knife steel, 100Cr6/SUJ2/GCr15/EN31 equivalents.
What is 52100?
AISI 52100 is the world's bearing steel: 1.0 % carbon and 1.5 % chromium, UNS G52986, melted to extreme cleanliness (oxygen ≤ 15 ppm, near-zero large inclusions) because every rolling-element bearing ball, roller and race is made from it or from its identical twins EN 100Cr6, JIS SUJ2, GB GCr15 and GOST ShKh15. After hardening from 840 °C in oil and tempering at 150–180 °C it reaches 60–64 HRC with a fine dispersion of chromium carbides that gives outstanding rolling-contact fatigue life and wear resistance, plus dimensional stability from the low retained-austenite content that the chromium addition and a cold treatment ensure.
Outside bearings, 52100 is a favourite of knifemakers and blacksmiths (very fine grain, keen edge, forgiving of forging), and it is used for rollers, cams, bushings, gauges, punches, needle valves and any small part that must be hard, precise and wear-resistant. Its hardenability is moderate — sections above about 20–30 mm need the Mn-Si variant 100CrMnSi6-4 (SUJ3) — and, with no ductility to speak of at 62 HRC, it must be machined in the spheroidized state and ground after hardening. Corrosion resistance is nil; stainless bearings use 440C.
52100 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.93 – 1.05 | |
| Mn | 0.25 – 0.45 | |
| P | ≤ 0.025 | |
| S | ≤ 0.015 | |
| Si | 0.15 – 0.35 | |
| Cr | 1.35 – 1.6 | |
| Ni | ≤ 0.25 | |
| Mo | ≤ 0.1 | |
| Cu | ≤ 0.3 | |
| Al | ≤ 0.05 | |
| O | ≤ 0.002 | 15 ppm oxygen max — inclusion control is the essence of bearing quality |
ASTM A295/A295M-21 (52100). 'E52100' = electric-furnace (all modern material). Compare EN 100Cr6 (1.3505): C 0.93–1.05, Cr 1.35–1.60, Mn 0.25–0.45, Si 0.15–0.35 — identical; JIS SUJ2 and GB GCr15 likewise.
52100 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Spheroidize annealed (delivery) — typical | ≈ 450 (≈ 65.3) | ≈ 680 (≈ 98.6) | 22 | ≤ 207 HB (typ. 180–200) |
| Normalized (900 °C) — typical | — | ≈ 1000 (≈ 145.0) | — | ≈ 290 HB |
| Hardened 840 °C oil + tempered 150 °C — bearing condition | ≈ 1700 (compressive yield ≈ 2000+) (≈ 246.6 (compressive yield ≈ 290.1+)) | ≈ 2200 (bend) (≈ 319.1 (bend)) | < 1 | 60–64 HRC |
| Hardened + tempered 200 °C | — | — | — | 58–61 HRC |
| Hardened + tempered 260 °C (knives, heavy-duty) | — | — | — | 56–59 HRC |
| Hardened + tempered 400 °C (springs, tools) | — | — | — | ≈ 50 HRC |
| As-quenched (oil, 840 °C) | — | — | — | 64–67 HRC |
Bearing steel is specified by chemistry, cleanliness (ASTM E45 / A295 inclusion ratings), decarburization limits and annealed hardness; hardened tensile values are typical and rarely used in design (contact fatigue governs). Rolling-contact fatigue life is the functional property.
Impact toughness
52100 requires a minimum Charpy V-notch energy of 8 J at 20 °C (typical, 60 HRC, unnotched ≈ 15–25 J). Low toughness at bearing hardness; bainitic hardening (austempered ≈ 58–60 HRC) or tempering to 56–58 HRC roughly doubles toughness for knives and rollers under shock.
52100 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 535A99 (EN31) | BS (superseded British) | Identical | BS 970 535A99: C 0.95–1.10, Cr 1.20–1.60. |
| 100Cr6 | EN (European) | Identical | 1.3505 (EN ISO 683-17): C 0.93–1.05, Cr 1.35–1.60, Mn 0.25–0.45, Si 0.15–0.35 — identical; dual-certified. |
| GCr15 | GB/T (China) | Identical | GB/T 18254 GCr15: C 0.95–1.05, Cr 1.40–1.65, Mn 0.25–0.45, Si 0.15–0.35. |
| ShKh15 | GOST (Russia/CIS) | Identical | GOST 801 ShKh15: C 0.95–1.05, Cr 1.30–1.65, Mn 0.20–0.40, Si 0.17–0.37. |
| SUJ2 | JIS (Japan) | Identical | JIS G4805 SUJ2: C 0.95–1.10, Cr 1.30–1.60, Mn ≤ 0.50, Si 0.15–0.35. |
| 100CrMnSi6-4 | EN (European) | Near | 1.3520 (SUJ3 / GCr15SiMn / ShKh15SG): Mn 1.0–1.2, Si 0.5–0.7 — higher hardenability for rings > 30 mm wall. |
| 100CrMo7-3 | EN (European) | Near | 1.3536 (SUJ5-type): Mo-bearing for large bearings and high-temperature use. |
| 1095 | AISI / SAE | Functional | Plain 0.95 % C: similar hardness, much lower hardenability, no chromium carbides — cheaper knife/spring alternative. |
| O1 / 1.2510 | AISI / SAE | Functional | Oil-hardening tool steel: similar heat treatment window, more W/V carbides for wear; preferred for dies. |
| 440C | AISI / SAE | Functional | Stainless bearing steel (S44004) for corrosive environments at similar hardness. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for 52100 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| E52100 | AISI | E = electric-furnace melted; all current 52100 is E52100. |
| G52986 | UNS | |
| 100Cr6 / 1.3505 | EN ISO 683-17 / DIN 17230 | European twin; 100CrMnSi6-4 (1.3520) for larger sections. |
| 535A99 / EN31 | BS 970 | EN31 remains the common Indian/UK name. |
| SUJ2 | JIS G4805 | Japanese twin; SUJ3 = higher Mn/Si. |
| GCr15 | GB/T 18254 | Chinese twin. |
| ShKh15 | GOST 801 | Russian twin. |
Product forms and tolerance standards
Product forms: bar and rod (ASTM A295, A29) — spheroidize-annealed, tube for bearing rings (A295 / A534), wire for balls and rollers (A295), forgings, ring blanks; ground flat stock for knifemakers, powder / ESR variants for aerospace bearings (AMS 6440/6444).
Dimensional tolerances: bar: ASTM A295 / A29; cold-finished: ASTM A108; aerospace: AMS 6440 (bar), AMS 6444 (premium).
Key property values
52100 hardness
As-quenched 64–67 HRC; bearing condition (tempered 150–180 °C) 60–64 HRC; knives 58–61 HRC (200 °C temper); tools 56–59 HRC; annealed (spheroidized) ≤ 207 HB, typically 180–200 HB. Bainite-hardened (austempered 230–250 °C) 58–60 HRC with better toughness.
52100 strength (hardened)
Tensile ≈ 2200 MPa in bending, compressive yield > 2000 MPa, contact stress capability ≈ 4 GPa; elongation < 1 %. Annealed: ≈ 450 MPa yield / 680 MPa tensile, 22 % elongation.
Heat treatment
Spheroidize anneal 780–800 °C, slow cool 10–20 K/h to 650 °C (delivery condition). Harden 830–860 °C (1525–1575 °F), 20–30 min, oil quench (thin sections may be salt-quenched or air-cooled in fast-quench variants); sub-zero −70 to −80 °C for dimensional stability (bearings); temper 150–180 °C for bearings, 200–260 °C for knives/tools, 2 h. Stress relieve after grinding 120–150 °C. Ac1 ≈ 745 °C, Ms ≈ 220 °C. Retained austenite 5–15 % after quench, < 5 % after cold treatment.
Hardenability and section size
Ideal critical diameter ≈ 25–35 mm in oil; rings with wall > 20–30 mm use 100CrMnSi6-4 / SUJ3 / GCr15SiMn, and large bearings (> 100 mm wall) use 100CrMo7-3/7-4 or carburizing steels.
Cleanliness and fatigue
Bearing quality requires ASTM A295 / ISO 683-17 inclusion limits (E45 method A: A ≤ 2.5, B ≤ 1.5, C ≤ 0.5, D ≤ 1.0 thin) and oxygen ≤ 15 ppm (≤ 8 ppm premium); L10 rolling-contact life scales strongly with cleanliness — the reason vacuum-degassed or ESR 52100 is specified for aerospace.
Physical properties
Density 7.81 g/cm³, E = 210 GPa, expansion 11.9 × 10⁻⁶/K (20–100 °C), conductivity ≈ 46 W/m·K; ferromagnetic; not corrosion-resistant despite 1.5 % Cr (all chromium is in carbides).
Weldability
Not weldable in the practical sense (CE > 1.2): hardens and cracks on cooling. Repair welding only with 300–400 °C preheat, immediate annealing and full re-hardening; forge-welding for damascus is common in knifemaking (1100–1200 °C, flux, then normalize several times and spheroidize).
Machining, forming and heat treatment
Machinability ≈ 40 % of B1112 in the spheroidized condition (hard Cr carbides): carbide tooling, moderate speed, generous coolant. All machining, drilling and rough grinding in the annealed state; after hardening only grinding (CBN/soft wheels, avoid burn), honing, lapping and superfinishing. Hot forging 1050–850 °C followed by normalizing 870–900 °C and spheroidizing. Surface treatments: black oxide, thin dense chrome (bearings), no plating without hydrogen bake.
Typical applications
- Ball and roller bearing rings, balls, rollers and needle rollers (the dominant use)
- Linear bearing rails, ball screws and guide shafts
- Cams, cam followers, rollers, tappets, bushings and sleeves
- Knife blades, forged blades and damascus (with 15N20)
- Gauges, plug gauges, measuring pins, precision spindles
- Punches, dies, thread-rolling dies and small wear parts
- Valve balls and seats, needle valves, injection-pump components
Frequently asked questions
Is 52100 the same as 100Cr6?
Yes. 52100 (ASTM A295), EN 100Cr6 (1.3505), JIS SUJ2, GB GCr15, GOST ShKh15 and BS 535A99/EN31 share the 1.0 % C / 1.5 % Cr analysis and are dual-certified worldwide; only the cleanliness and inspection clauses differ by standard.
How hard is 52100?
60–64 HRC as used in bearings (tempered 150–180 °C), 64–67 HRC as-quenched. Knifemakers usually run it at 58–61 HRC for a balance of edge retention and toughness.
Is 52100 a good knife steel?
Yes — it forges well, has very fine grain, takes a razor edge and holds it well, and is tougher than 1095 at equal hardness thanks to its Cr carbides and hardenability. It is not stainless: blades need oil or a patina.
How do you heat-treat 52100?
Austenitize 830–860 °C (soak 20–30 min), oil quench, optional cold treatment at −70 °C, temper 150–180 °C (bearings) or 200–260 °C (knives) for 2 h, twice. Spheroidize at 780–800 °C with slow cooling before machining or if the steel has been forged.
Why is 52100 not stainless with 1.5 % chromium?
Practically all the chromium is bound in (Fe,Cr)₃C carbides, leaving almost none in the matrix to form a passive film; stainless behaviour needs ≥ 10.5 % dissolved Cr. 440C (17 % Cr) is the stainless bearing steel.
What is the difference between 52100 and SUJ3 / 100CrMnSi6-4?
SUJ3 (1.3520, GCr15SiMn) adds ~1.1 % Mn and 0.6 % Si to raise hardenability for bearing rings with wall thickness above 20–30 mm; otherwise the same steel and heat treatment.
Related grades
Verified against ASTM A295/A295M-21; ASTM A295/A295M-21 Tables 1–3; EN ISO 683-17:2023 (100Cr6 comparison); ASM Handbook Vol. 4 (heat treating); AMS 6440 / 6444. Last checked: September 2026.