HS6-5-2-5
1.3243Standard cobalt high speed steel with 5% Co — the most widely used cobalt HSS grade. Also known as M35 or HSS-E/HSSE. Better hot hardness and cutting performance than M2, lower cost than M42. HRC 64-66 hardened. The "go-to upgrade" when M2 performance is insufficient. Used for drill bits (HSS-Co branded), taps, end mills, saw blades, and general-purpose cutting tools for stainless steel and medium-hard alloys.
International equivalents
| Flag | Standard | Country | Grade | Number | Match |
|---|---|---|---|---|---|
| 🇺🇸 | AISI | USA | AISI M35 / UNS T11335 | T11335 | REF |
| 🇪🇺 | EN | Europe | HS6-5-2-5 / 1.3243 | 1.3243 | 100% |
| 🇯🇵 | JIS | Japan | SKH55 | — | 100% |
Sources: ASTM A600, EN ISO 4957, JIS G4403
Chemical composition comparison (wt%)
Side-by-side: HS6-5-2-5 (EN) (EN ISO 4957) vs HS6-5-2-5 / 1.3243 (EN) (EN ISO 4957)
| Element | HS6-5-2-5 (EN) | HS6-5-2-5 / 1.3243 (EN) | Overlap |
|---|---|---|---|
| C | 0.86–0.94% | 0.86–0.94% | OK |
| Si | 0–0.45% | 0–0.45% | OK |
| Mn | 0–0.4% | 0–0.4% | OK |
| Cr | 3.75–4.5% | 3.75–4.5% | OK |
| Mo | 4.5–5.5% | 4.5–5.5% | OK |
| V | 1.75–2.2% | 1.75–2.2% | OK |
| W | 5.5–6.75% | 5.5–6.75% | OK |
| Co | 4.5–5.5% | 4.5–5.5% | OK |
Mechanical properties
Hardened Tempered
| Property | Value | Unit |
|---|---|---|
| Hardness HRC | 64–66 | HRC |
| Elastic Modulus | ≥ 210 | GPa |
| Density | ≥ 8.08 | g/cm3 |
Annealed
| Property | Value | Unit |
|---|---|---|
| Hardness HB | ≤ 280 | HB |
Heat treatment
| Process | Temperature | Medium | Holding Time | Notes |
|---|---|---|---|---|
| hardening | 1200–1240 °C | salt bath or vacuum | short hold | — |
| tempering | 540–580 °C | air | 3x 1h minimum | Triple temper — secondary hardness peak |
Compatibility verdict
HS6-5-2-5 and HS6-5-2-5 / 1.3243: 100% composition match
Close equivalents but NOT identical.
Related materials
P20 / 40CrMnMo7
1.2311Pre-hardened plastic mold steel (usually delivered at 28-34 HRC). The most widely used mold base steel globally. Good machinability in pre-hardened condition, good polishability. Used for injection molds, die-casting dies, extrusion tooling, and structural mold components.
M2 / HS6-5-2
1.3343The most widely used high-speed steel worldwide. W-Mo-Cr-V composition gives excellent red hardness (cuts at temperatures up to 600°C). Used for twist drills, end mills, taps, reamers, bandsaw blades, and general-purpose cutting tools. The benchmark HSS grade.
X45NiCrMo4
1.2767Nickel cold-work tool steel with exceptional toughness from ~4% Ni content. Excellent through-hardenability, polishability, and impact resistance. Used for plastic injection molds (high-gloss), embossing dies, scrap shear blades, punches, cutlery dies, and bending tools.
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