Views: 0 Author: Site Editor Publish Time: 2026-07-29 Origin: Site
If you are sourcing alloy steel balls for bearings, valves, linear motion systems, or heavy machinery, three grade names come up again and again: 52100 chrome steel, 100Cr6, and 8620. Two of them are actually the same steel under different standards — and the third works in a completely different way. Choosing the wrong grade can mean premature spalling, cracked balls under impact loads, or simply paying for precision you don't need.
This guide from an ISO 9001–certified precision steel ball manufacturer breaks down the chemical composition, hardness, heat treatment, and typical applications of each grade, with a side-by-side comparison table and a practical selection checklist — so you can specify the right bearing steel balls the first time.
Alloy steel balls are precision spheres made from steel that contains deliberate additions of alloying elements — most commonly chromium, nickel, molybdenum, and manganese — to improve hardenability, wear resistance, fatigue life, and toughness beyond what plain carbon steel balls can offer.
They are the workhorse of the rolling-element world. Every deep-groove ball bearing, ball screw, caster wheel, check valve, and ball transfer unit relies on hardened alloy steel balls to carry load with minimal friction. Depending on the grade, alloy steel balls are supplied in precision grades from G10 to G1000 (per ISO 3290 / ABMA Std 10) and diameters from about 0.5 mm up to 150 mm and beyond.
The two dominant families are:
Through-hardened high-carbon chromium bearing steels — 52100 / 100Cr6 / GCr15 / SUJ2 — hard all the way to the core.
Case-hardened (carburized) low-carbon alloy steels — such as AISI 8620 — with a hard wear-resistant surface over a tough, ductile core.
AISI 52100 is the world's most widely used bearing steel, and 52100 chrome steel balls are the default choice for precision ball bearings. It is a high-carbon, chromium-alloyed steel that through-hardens to an exceptionally high, uniform hardness with excellent rolling-contact fatigue life.
| Element | Content（%） |
| Carbon (C) | 0.93 – 1.05 |
| Chromium (Cr) | 1.35 – 1.60 |
| Manganese (Mn) | 0.25 – 0.45 |
| Silicon (Si) | 0.15 – 0.35 |
| Phosphorus (P) | ≤ 0.025 |
| Sulfur (S) | ≤ 0.025 |
Hardness: 60 – 66 HRC after oil quenching (≈840–860 °C) and low-temperature tempering — hard through the entire cross-section
Density: 7.81 g/cm³
Precision grades: commonly G10 – G100; grades to G5 or better available for instrument bearings
Working temperature: up to ~120–150 °C with standard tempering (higher with special stabilizing treatments)
Surface finish: mirror-lapped, typically Ra ≤ 0.02 µm for bearing grades
Here is the short answer buyers search for: 100Cr6 and 52100 are the same steel. 100Cr6 (material number 1.3505, per DIN / EN ISO 683-17) is simply the European designation for the high-carbon chromium bearing steel that the American AISI/ASTM system calls 52100. The name itself is the recipe — "100" for ~1.00% carbon, "Cr6" for chromium at 6/4 = 1.5%.
Composition ranges are virtually identical, with only minor differences in permissible trace-element limits between the standards. In practice, a reputable steel ball supplier will certify balls to either designation from the same melt, and a mill test certificate (EN 10204 3.1) can reference both.
| Country/Standard | Grade |
| USA — AISI / ASTM A295 | 52100 |
| Germany / EU — EN ISO 683-17 | 100Cr6 (1.3505) |
| China — GB/T 18254 | GCr15 |
| Japan — JIS G4805 | SUJ2 |
| UK — BS 970 | 535A99 (EN31) |
| France — AFNOR | 100C6 |
| Russia — GOST | ShKh15 |
AISI 8620 is a completely different animal. It is a low-carbon nickel-chromium-molybdenum alloy steel designed for carburizing (case hardening). Instead of being hard throughout, an 8620 steel ball has a hard, wear-resistant outer case over a softer, tough, shock-absorbing core — like a hard shell around a resilient center.
| Element | Content（%） |
| Carbon (C) | 0.18 – 0.23 |
| Manganese (Mn) | 0.70 – 0.90 |
| Nickel (Ni) | 0.40 – 0.70 |
| Chromium (Cr) | 0.40 – 0.60 |
| Molybdenum (Mo) | 0.15 – 0.25 |
| Silicon (Si) | 0.15 – 0.35 |
The nickel and molybdenum give 8620 outstanding core toughness, which is exactly what through-hardened 52100 lacks. 8620 alloy steel balls excel where balls see shock, misalignment, debris, or point impact rather than clean rolling contact:
Large-diameter balls (roughly 1" / 25.4 mm up to 150 mm+), where uniform through-hardening becomes difficult
Ball transfer units and heavy conveyor tables
Mining, drilling, and oilfield equipment
Slewing rings and construction machinery
Agricultural equipment operating in dirty, high-impact environments
| Property | 521000（AISI） | 100Cr6（EN 1.3505） | 8620（AISI） |
| Steel type | High-carbon chromium bearing steel | Same steel, European standard | Low-carbon Ni-Cr-Mo carburizing steel |
| Carbon | 0.93 – 1.05% | 0.93 – 1.05% | 0.18 – 0.23% |
| Key alloys | Cr 1.35 – 1.60% | Cr 1.35 – 1.60% | Ni + Cr + Mo |
| Heat treatment | Through-hardening (quench + temper) | Through-hardening | Carburize + quench + temper |
| Surface hardness | 60 – 66 HRC | 60 – 66 HRC | 58 – 63 HRC |
| Core hardness | Same as surface | Same as surface | 30 – 45 HRC (tough) |
| Wear / fatigue resistance | Excellent | Excellent | Very good (surface) |
| Impact toughness | Moderate — brittle under shock | Moderate | Excellent |
| Typical precision | G5 – G100 | G5 – G100 | G100 – G1000 |
| Typical diameters | 0.5 – 100 mm | 0.5 – 100 mm | 25 – 150+ mm |
| Corrosion resistance | Low — oil protection required | Low | Low |
Work through four questions with your steel ball supplier:
Load character. Smooth, lubricated rolling contact → 52100 / 100Cr6. Shock, vibration, contamination, or point impact → 8620 case-hardened.
Ball diameter. Below ~25 mm, through-hardened chrome steel is economical and consistent. For very large diameter steel balls, carburized 8620 avoids the through-hardening limitations and brittleness of big 52100 sections.
Precision requirement. Instrument and spindle bearings need G10 or finer — the territory of 52100/100Cr6. Ball transfer and structural uses run happily on G100 – G1000. Our guide to steel ball precision grades explains the tolerance classes in detail.
Environment. None of these grades resists corrosion. For washdown, marine, food, or chemical exposure, step up to stainless steel balls (440C, 316, 304) instead.
Whether the grade is 52100, 100Cr6, or 8620, quality is built through the same tightly controlled sequence: cold heading of wire or bar into rough spheres, flash removal and filing, soft grinding, heat treatment (through-hardening for chrome steel, gas carburizing for 8620), hard grinding, and finally multi-stage lapping to achieve final sphericity and mirror surface finish. Each batch is then checked for diameter variation, waviness, surface defects, hardness, and — for bearing grades — crack detection on 100% of balls. Read the full walkthrough in our article on the steel ball manufacturing process.
Is 100Cr6 the same as 52100?
Yes. 100Cr6 (EN, material No. 1.3505) and AISI 52100 are the same high-carbon chromium bearing steel with ~1.0% C and ~1.5% Cr. Chinese GCr15 and Japanese SUJ2 are also equivalent grades. Only minor trace-element limits differ between the standards.
What is the hardness of 52100 chrome steel balls?
Through-hardened 52100 chrome steel balls reach 60 – 66 HRC uniformly from surface to core, which is what gives them their outstanding rolling-contact fatigue life in ball bearings.
What is the difference between 8620 and 52100 steel balls?
52100 is a high-carbon steel hardened all the way through (60 – 66 HRC) for maximum wear and fatigue resistance. 8620 is a low-carbon Ni-Cr-Mo steel that is carburized: hard on the surface (58 – 63 HRC) with a tough 30 – 45 HRC core that absorbs impact. Choose 52100 for precision rolling contact and 8620 for shock loads and large diameters.
Do alloy steel balls rust?
Yes. The ~1.5% chromium in 52100/100Cr6 improves hardenability, not corrosion resistance. Alloy steel balls are shipped with anti-rust oil and must be kept protected; for corrosive environments, specify stainless steel balls instead.
What precision grades are available for alloy steel balls?
Per ISO 3290 / ABMA Std 10, common grades run from G5/G10 (high-precision bearing balls) through G100 – G1000 (semi-precision and commercial balls). 52100/100Cr6 balls are routinely supplied at G10 – G40; carburized 8620 balls typically at G100 – G1000.
Which grade should I use for large-diameter steel balls?
For balls above roughly 25 – 50 mm that see heavy or impact loading — slewing rings, ball transfer units, mining equipment — case-hardened 8620 is usually the better choice, combining a wear-resistant surface with a crack-resistant core.
