Bearing and Tool Steels: The Grades Behind the Hardest Jobs
Bearing steel and tool steel sit at the top of the carbon-and-chromium steel family — the grades where cleanliness, hardenability and heat-treatment discipline matter more than anywhere else in commodity steel. They are also the grades most often mis-specified and most often counterfeited. This guide covers the two families buyers actually encounter — through-hardening bearing steel (GCr15 / 100Cr6) and the cold-work, hot-work and plastic-mould tool steels — with the acceptance criteria that separate a good bar from a future warranty claim.
Bearing Steel: GCr15 and Its Equivalents
GCr15 (China GB/T 18253) is the world’s highest-volume bearing steel — chemically the same grade as 100Cr6 (Europe, EN ISO 683-17) and SUJ2 (Japan JIS G4805): roughly 1% carbon and 1.45% chromium. Larger sections use GCr15SiMn / 100CrMn7 for extra hardenability, and carburizing grades (G20CrNi2Mo ≈ SAE 4320) serve heavily loaded, shock-exposed bearings where a tough core and hard case are both needed.
What makes bearing steel special is not the chemistry — it is the cleanliness specification. A rolling contact fatigue failure starts at an oxide inclusion; the life of a bearing is therefore governed by how few and how small the non-metallic inclusions are, not by tensile strength.
The Three Acceptance Pillars of Bearing Steel
| Pillar | Typical Requirement | Why It Matters |
|---|---|---|
| Oxygen content | ≤ 12 ppm (premium ≤ 8 ppm), total O | Oxygen tracks oxide inclusion count — the fatigue limiter. Requires LF + vacuum degassing (VD/RH). |
| Inclusion rating | JK / ASTM E45 ratings; e.g. DS ≤ 0.5, thin-series ≤ 1.0–1.5, no soft inclusions > 2.0 | Method and acceptance class must be stated in the order — “clean steel” alone means nothing. |
| Carbide uniformity | Spheroidized annealed delivery; banding / network carbide limits per ISO 683-17 or GB/T 18253 | Carbide networks or heavy banding cause grinding burns and uneven hardness after quench. |
After heat treatment — spheroidize anneal, quench, temper — the target is 58–66 HRC depending on component, with case-hardened variants at 58–62 HRC surface over a 30–45 HRC core. Retained austenite control (typically < 10% for precision bearings) keeps dimensions stable over years of service.
Buying Checks for Bearing Steel Bars
- Melt route on the certificate: expect EAF or converter + LF + vacuum degassing. If the MTC is silent on vacuum degassing or total oxygen, the material is not bearing grade regardless of what the label says.
- Compression ratio: reputable mills declare total reduction from ingot/CC strand to bar (≥ 6:1 for bars; radial/axial forging for rings). Low-ratio material keeps centre porosity — fatal for rings.
- Surface condition: for turned and polished (peeled) bars, specify surface roughness (Ra ≤ 1.6 μm typical) and crack detection (eddy current per EN 10277-4 or UT). Bearing steel is quenched-and-tempered or spheroidized — verify delivery hardness on the MTC (typically 179–207 HB annealed for machining).
- Decarb limits on the bar surface (typically ≤ 1% of diameter per side for peeled stock) — decarburized skin ruins forged ring surfaces.
Tool and Die Steel: Choosing the Family First
Tool steel selection starts with a simpler question than grade numbers: hot, cold, or plastic?
| Family | Workhorse Grades (AISI / W-Nr) | Typical Duty |
|---|---|---|
| Cold-work | D2 / 1.2379 (12% Cr), O1 / 1.2510, A2 / 1.2363 | Blanking and forming dies, thread rolls, punches — wear is the enemy |
| Hot-work | H13 / 1.2344, H11 / 1.2343, H10 / 1.2365 | Die casting dies, forging dies, extrusion tooling — thermal fatigue is the enemy |
| Plastic mould | P20 / 1.2311 + 1.2312, 420-type / 1.2083, P21-type | Injection moulds — polishability and etching uniformity matter as much as hardness |
| High-speed | M2 / 1.3343, M35 / 1.3243 (Co) | Drills, taps, saws, milling cutters — red hardness |
The Specification Fields That Actually Change Performance
- Delivery condition: forged and annealed (EAF+ESR for D2/H13 class is standard premium practice). Electroslag remelting (ESR) dramatically reduces macro-inclusions — worth asking for on polishing-critical or fatigue-critical tooling.
- Annealed hardness: D2 ≈ ≤ 255 HB, H13 ≈ ≤ 229 HB, P20 delivered pre-hardened 28–34 HRC (1.2311) or 33–39 HRC (1.2312 higher sulphur for machinability). Verify on the MTC — “P20” without hardness is half a spec.
- UT quality class: per EN 10308 / SEP 1921 (e.g. ≥ 3/4 group for bars; q-classes for large blocks). Large die blocks live or die by centre soundness.
- Band/carbide distribution for D2 (often specified ≤ certain per GB/T 1299 or NADCA #207 for H13 die-casting quality — the NADCA standard is the one serious die casters write into POs).
- Hardened + double/ triple tempered state where the supplier delivers heat-treated: H13 typically quenched + 3 tempers around 550–600 °C to 44–48 HRC for die blocks; insist on temper curves, not just final hardness.
Mistakes That Cost Real Money
- Buying on grade name alone. 100Cr6 from an unverified source without oxygen/inclusion certificates is not bearing steel — it is 1% carbon steel with a bearing price. Counterfeit and downgraded bearing bar is one of the most common frauds in this family.
- Skipping ESR on polish-critical D2 — macro segregated carbides appear as streaks only after mirror polishing, discovered after machining is paid for.
- Wrong H13 temper window — single tempering or too-low temper leaves untempered martensite; dies crack on the first thermal cycle. NADCA-compliant triple temper is cheap insurance.
- Ignoring machinability of pre-hardened P20 variants — 1.2312 (higher S) machines ~30% faster than 1.2311 at equal hardness; for large mould plates the machine-time difference exceeds the steel premium.
How CREATEEL Supplies Bearing and Tool Steels
CREATEEL’s forged products line covers bearing steel bars and rings (GCr15/100Cr6 family with full oxygen and inclusion certification), cold-work and hot-work die steels including ESR-melted D2 and NADCA-compliant H13 blocks, pre-hardened P20 plates, and custom open-die blocks/bushings machined to drawing. Every delivery ships with EN 10204 3.1 certificates stating melt route, cleanliness method and results, delivery condition and hardness — the four fields that make these grades real. Machined, ground and NDT-inspected finished components are available from our mechanical division.
Need certified GCr15/100Cr6 bars, H13 die blocks or machined bearing components? CREATEEL supplies with full cleanliness certification and heat-treatment records. Request a quotation.
