52100 Steel
Also: AISI 52100, SAE 52100, E52100, UNS G52986, 100Cr6, 1.3505, SUJ2 (JIS), EN31 / 535A99 (BS 970), GCr15 (GB), ShKh15 (GOST), chrome steel, bearing steel
52100 is the classic bearing steel: 1% carbon, 1.5% chromium, through-hardened to 58-64 HRC for balls, rings and rollers. Values annealed and hardened.
Sourcing 52100 parts or stock?
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At a glance
| Density | 7.81 g/cm³ (0.282 lb/in³) |
|---|---|
| Tensile strength | About 650-725 MPa (95-105 ksi) spheroidize annealed; roughly 2,000-2,200 MPa (290-320 ksi) hardened to 60-62 HRC, rarely tested in tension |
| Yield strength | About 400-500 MPa (58-73 ksi) spheroidize annealed; roughly 1,700-2,000 MPa (245-290 ksi) hardened, with little plastic range before fracture |
| Hardness | About 180-210 HB (roughly 88-95 HRB) spheroidize annealed; 58-64 HRC hardened and tempered (bearing rings usually 60-64 HRC) |
| Elongation | About 20-25% spheroidize annealed; under 2% hardened |
| Modulus of elasticity | 210 GPa (30.5 Msi) |
| Thermal | Melts at about 1,400-1,480 °C (2,550-2,700 °F); thermal conductivity ~45 W/m·K; standard low tempers hold size in service to about 120-150 °C (250-300 °F) |
| Composition | Fe, 0.93-1.10% C, 1.30-1.60% Cr, 0.25-0.45% Mn, 0.15-0.35% Si, low P and S (bearing quality) |
Typical values, Spheroidize annealed (as stocked) and hardened and tempered at about 150-180 °C (300-350 °F) to 58-64 HRC; both given.. Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- About 40% of the 1212 benchmark spheroidize annealed: rough and semi-finish soft with carbide. Hardened, it is hard turned with CBN or ground.
- WeldabilityNot recommended
- At 1% carbon the weld and heat-affected zone form brittle martensite and crack. Do not weld it; bolt, press fit or shrink fit instead.
- FormabilityFair
- Spheroidized wire and rod cold head into ball and roller blanks; rings are hot forged and ring rolled. Bar and plate are not bent.
- Corrosion resistancePoor
- About 1.5% chromium is far from stainless. Keep it oiled or greased; for wet or corrosive service use 440C.
52100 is a high-carbon chromium steel, about 1.0% carbon and 1.5% chromium, and the standard material for ball and roller bearings worldwide (100Cr6 in Europe, SUJ2 in Japan). Hardened and tempered to 58-64 HRC, it combines very high hardness, compressive strength and rolling-contact fatigue life with fine, evenly spread carbides, which is exactly what a raceway or a ball needs. Bearing-quality 52100 is made to tight cleanliness limits because inclusions start the fatigue spalls that end a bearing life.
It is bought spheroidize annealed, at roughly 180-210 HB, where it machines at about 40% of the free-machining benchmark. Parts are turned and milled soft with grind stock left, hardened in oil or salt, often given a sub-zero treatment to transform retained austenite, tempered low and then ground or hard turned to size. Outside bearings it is used for precision spindles, gauges, cam followers, punches and knife blades, anywhere a hard, stable, wear-resistant surface through the whole section is wanted.
The limits are clear. It cannot practically be welded. It is not stainless: bearings live in oil or grease, and wet or corrosive service calls for 440C. Standard low tempers keep its size stable only to about 120-150 °C (250-300 °F); warmer service needs a stabilizing temper at some cost in hardness. And at 60+ HRC it is brittle in tension, so sharp corners and thin sections crack in the quench.
Heat treatment
Stocked spheroidize annealed for machining. Harden by austenitizing at about 830-860 °C (1,525-1,575 °F), in vacuum or a protective atmosphere to prevent decarburization, then quench in oil, or marquench in hot oil or salt to reduce distortion. Temper at 150-180 °C (300-350 °F) for 60-64 HRC. A sub-zero treatment between quench and temper transforms retained austenite so gauges and precision rings do not grow in service. Higher stabilizing tempers, roughly 200-250 °C (400-480 °F), allow warmer service at a cost of a few HRC. Austempering to lower bainite gives about 58-60 HRC with less distortion and better toughness. Induction hardening is used for raceways built into shafts.
Tempers and conditions
- Spheroidize annealed (as stocked)
- Hardened and tempered 58-64 HRC
- Hardened, sub-zero treated and tempered (dimensionally stabilized)
- Austempered (bainitic), about 58-60 HRC
- Vacuum-degassed or vacuum-remelted bearing quality
Stock forms
- Round bar (spheroidize annealed)
- Seamless bearing tube
- Wire and rod for balls and rollers
- Forged and ring-rolled rings
- Hardened and ground rod
Relative cost
Tier 3 of 5. Commercial bar prices between 4140 and 4340; bearing-quality vacuum-degassed or remelted bar costs more. Grinding usually dominates part cost.
Typical applications
- Ball and roller bearing rings
- Bearing balls, rollers and needle rollers
- Precision spindles, gauge pins and gauges
- Cam followers, track rollers and bushings
- Raceways built into shafts and housings
- Punches, dies and knife blades for light-duty cutting
Process compatibility
How 52100 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Turning | GoodGood | Rings and rollers are turned soft with grind stock left; hardened parts are hard turned with CBN. |
| CNC Machining | FairFair | Mills acceptably when spheroidized, at about 40% of 1212; leave stock for grinding after hardening. |
| CNC Grinding | ExcellentExcellent | Raceways and bores are ground to micron tolerances after hardening; specify burn inspection. |
| Centerless Grinding | ExcellentExcellent | The standard finish for rollers, pins and hardened rod; holds roundness and size in volume. |
| Heat Treating | ExcellentExcellent | Oil or salt quench and a low temper for 58-64 HRC; add sub-zero treatment for dimensional stability. |
| Vacuum Heat Treating | GoodGood | Hardening in vacuum avoids decarburization on precision parts and cuts cleanup grinding. |
| Induction Hardening | GoodGood | Hardens raceways on shafts to about 60 HRC while the rest stays soft and tough. |
| Forging | GoodGood | Bearing rings are hot forged and ring rolled, then spheroidize annealed for machining. |
| Wire EDM | GoodGood | Cuts hardened 52100 for punches, gauges and slots; remove the recast layer on wear faces. |
| Black Oxide | GoodGood | Used on bearing rings for smearing resistance and mild corrosion protection with oil. |
| Nitriding | PoorPoor | Nitriding runs at 500 °C or more, which tempers hardened 52100 far below bearing hardness. |
| Welding | Not recommendedNot recommended | At 1% carbon the weld and heat-affected zone crack; join by press fit, shrink fit or fasteners. |
Design and sourcing tips
- Rough and semi-finish soft and leave about 0.2-0.5 mm (0.008-0.020") per side for grinding or hard turning after hardening; the part will move.
- Specify hardness as a range (for example 60-64 HRC) and, for gauges or precision rings, a sub-zero treatment and a stabilizing temper; state the maximum service temperature.
- Require grinding-burn inspection (temper etch) on bearing and wear surfaces.
- Radius every corner and keep walls even: at 60+ HRC, sharp corners, thin sections and nearby cross holes crack in the quench.
- If the part will see water or corrosive fluid, use 440C instead; 52100 must be oiled or sealed.
Frequently asked questions
- What is the hardness of 52100 steel?
- Hardened and tempered for bearings, 52100 is 58-64 HRC, most often 60-64 HRC. As bought, spheroidize annealed, it is roughly 180-210 HB, soft enough to machine. Stabilizing tempers for warmer service bring it down a few points.
- Is 52100 stainless steel?
- No. It has about 1.5% chromium, far below the roughly 10.5% needed to be stainless, and it rusts quickly unless oiled or greased. For bearings or wear parts in wet or corrosive service, 440C is the usual stainless alternative.
- Can 52100 be welded?
- Not practically. At about 1% carbon the weld and heat-affected zone turn to brittle martensite and crack, even with preheat. Design 52100 parts to be press fit, shrink fit or bolted, and weld only the mild-steel parts around them.
- What is the difference between 52100 and 440C?
- Both are high-carbon bearing steels hardened to about 58-62 HRC and above. 52100 has about 1.5% chromium and is not stainless, but it is cheaper, easier to grind and has excellent rolling-contact fatigue life. 440C has about 17% chromium, so it resists corrosion, at higher cost and with coarser carbides. Use 52100 in oiled bearings and 440C where water or chemicals are present.
- Can you machine hardened 52100?
- Yes, but not with conventional tools. At 58-64 HRC it is ground, hard turned with CBN inserts, or cut by wire EDM. The usual route is to machine it spheroidize annealed, harden it, then grind or hard turn only the critical surfaces.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A295 (high-carbon bearing steel) and ISO 683-17 (100Cr6)
- AMS 6440 and AMS 6444 (aerospace bearing steel)
- ASM Handbook Vol. 1 (properties) and Vol. 4 (heat treating)
- Bearing steel producer data sheets for 52100 and 100Cr6
