1.3343 (M2) high-speed steel: properties, heat treatment, equivalents
1.3343 (HS6-5-2C) is AISI M2, the general-purpose high-speed steel: 64–66 HRC and red hardness to 600 °C. Composition, the 1190–1230 °C hardening window, triple tempering and M2/SKH51 equivalents.
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What is 1.3343?
1.3343 (HS6-5-2C) is the general-purpose high-speed steel — AISI M2 — and it is the steel most drills, taps, end mills, reamers, hobs, broaches and band-saw teeth in the world are made of. With 6 % tungsten, 5 % molybdenum, 4 % chromium and 2 % vanadium it hardens to 64–66 HRC and, crucially, holds about 50 HRC at 600 °C. That is the property that separates a high-speed steel from every other tool steel: not what it reads cold, but what it still reads when the cutting edge is glowing.
The price of that property is a hardening process with no margin for error. Austenitising is at 1190–1230 °C — within roughly ±10 °C of the chosen set point, barely below the melting range, held for two to five minutes only. Too cold and the alloy carbides do not dissolve, so the secondary hardening never happens; too hot or too long and the grain coarsens and the tool is brittle. Then come three tempers at 550–560 °C, each one transforming the retained austenite that the previous one released. A high-speed steel tool is a heat-treatment product in a way a cold-work tool is not; vacuum or salt-bath furnaces with tight pyrometry are the minimum, and this is not toolroom work.
Two things are commonly misread about the designation. The C in HS6-5-2C is the carbon level, not a quality mark: 0.86–0.94 % against 0.78–0.88 % for plain HS6-5-2, worth about one point of hardness and a useful gain in wear resistance. And M2 is not a cheap version of a carbide tool — it is the tougher one. Carbide holds its hardness far higher and cuts far faster, but it chips where M2 bends, which is why hand taps, long drills, thin saw blades and interrupted-cut tooling are still high-speed steel.
Where M2 runs out, the upgrades are well defined: 1.3243 (M35) adds 5 % cobalt for another 50 °C of hot hardness, 1.3344 (M3:2) adds vanadium for abrasive wear, and the powder-metallurgy high-speed steels sit above both. For most drilling, tapping and milling of carbon and alloy steel, none of that is needed.
1.3343 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.86 – 0.94 | |
| Si | ≤ 0.45 | |
| Mn | ≤ 0.4 | |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Cr | 3.8 – 4.5 | |
| Mo | 4.7 – 5.2 | |
| W | 5.9 – 6.7 | |
| V | 1.7 – 2.1 |
EN ISO 4957:2018, high-speed steels (HS6-5-2C). The **C suffix is the carbon level, not a quality grade**: HS6-5-2C carries 0.86–0.94 % C where plain HS6-5-2 carries 0.78–0.88 %. The extra carbon gives 1 HRC more working hardness and better abrasive wear resistance, at the cost of a little toughness, and it is the version normally supplied for drills, end mills and form tools. AISI M2 to ASTM A600 spans both: C 0.78–1.05, W 5.50–6.75, Mo 4.50–5.50, V 1.75–2.20.
1.3343 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| +A soft annealed (delivery) | — | ≈ 800–900 (typ.) (≈ 116.0–130.5 (typ.)) | — | ≤ 269 HB |
| Hardened 1210–1230 °C, as-quenched | — | — | — | 63–65 HRC |
| Tempered 3 × 550–560 °C | — | — | — | 64–66 HRC |
| Tempered 3 × 580 °C | — | — | — | 62–64 HRC |
| At 64 HRC, hot hardness at 600 °C | — | — | — | ≈ 50 HRC |
| Compressive yield at 64 HRC (typical) | ≈ 3000 (≈ 435.1) | ≈ 4000 (bend strength) (≈ 580.2 (bend strength)) | — | — |
EN ISO 4957 specifies the chemistry and the maximum annealed hardness; everything else is a heat-treatment result. The property that defines a high-speed steel is in the fifth row: **it still reads about 50 HRC at 600 °C**, where every cold-work and hot-work tool steel on this site is soft. That is what 'high speed' means — not the hardness at room temperature, which a plain 1 % carbon steel can almost match, but the hardness retained at the cutting edge while it is glowing.
1.3343 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| M2 | AISI / SAE | Identical | AISI M2 (UNS T11302, ASTM A600): C 0.78–1.05, W 5.50–6.75, Mo 4.50–5.50, Cr 3.75–4.50, V 1.75–2.20. The same steel. Because the ASTM carbon range covers both the plain and the high-carbon European versions, an M2 certificate should be read for its carbon level before it is matched to 1.3343 or to 1.3339. |
| W6Mo5Cr4V2 | GB/T (China) | Identical | GB/T 9943 W6Mo5Cr4V2 is the direct transcription and the most widely produced high-speed steel in China. W6Mo5Cr4V2Al adds aluminium for higher hot hardness. |
| R6M5 | GOST (Russia/CIS) | Identical | GOST 19265 R6M5: C 0.82–0.90, W 5.50–6.50, Mo 4.80–5.30, Cr 3.80–4.40, V 1.70–2.10. R6M5K5 is the 5 % cobalt version corresponding to M35. |
| SKH51 | JIS (Japan) | Identical | JIS G4403 SKH51: C 0.80–0.88, W 5.90–6.70, Mo 4.70–5.20, Cr 3.80–4.50, V 1.70–2.10 — the plain-carbon version, so about 1 HRC below HS6-5-2C at the same temper. |
| 1.3243 | EN (European) | Near | HS6-5-2-5 (M35): the same steel with 4.5–5.0 % cobalt. Cobalt raises hot hardness by about 50 °C and is the standard upgrade for stainless and high-temperature alloy machining; slightly more brittle and more expensive. |
| 1.3344 | EN (European) | Near | HS6-5-3 (M3:2): vanadium raised to 2.7–3.2 % and carbon to 1.15–1.25 %. Markedly better abrasive wear resistance for form tools and gear hobs, harder to grind. |
| 1.3355 | EN (European) | Functional | HS18-0-1 (T1): the original 18 % tungsten high-speed steel. Equivalent performance for general turning, but tungsten is heavier and dearer than molybdenum, so T1 has been displaced almost everywhere by M2. |
| 1.2379 | EN (European) | Functional | X153CrMoV12 (D2): comparable room-temperature hardness and abrasive wear resistance at a fraction of the cost, but it is soft by 300 °C. The right choice for cold blanking and the wrong one for any tool that cuts at speed. |
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 1.3343 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| S 6-5-2 | DIN 17350 (withdrawn) | The German short designation; same number 1.3343. The letters give the alloy content in order — 6 % W, 5 % Mo, 2 % V. |
| BM2 | BS 4659 (withdrawn) | The British designation. |
| Z85WDCV | NF A 35-590 | The French designation of the same steel. |
| S600 / HS6-5-2 | Böhler / trade names | Böhler S600, Erasteel EM2, Thyrapid 3343. Powder-metallurgy equivalents (ASP 2023, Böhler S390 class) are different steels, not versions of this one. |
Product forms and tolerance standards
Product forms: round bar (annealed, rolled or peeled), flat bar and strip, hollow bar and tube for hollow tooling, finished cutting tools (drills, taps, end mills, hobs, broaches), saw strip and bi-metal band-saw edge wire.
Dimensional tolerances: annealed round bar: EN 10060 or supplier tolerances, typically +0.5/+2 mm grinding allowance; ground stock: h6/h7 as agreed; finished cutting tools: tolerances from the relevant tool standard (ISO 235 for drills, ISO 529 for taps and so on), not from EN ISO 4957.
Key property values
1.3343 hardness and red hardness
Annealed ≤ 269 HB. As-quenched 63–65 HRC; after triple tempering at 550–560 °C the working hardness is 64–66 HRC — a secondary-hardening gain, so the steel comes out of tempering harder than it went in. Hot hardness is the real specification: roughly 62 HRC at 400 °C, 58 HRC at 500 °C and 50 HRC at 600 °C. Compare the cold-work grade 1.2379, which is below 45 HRC by 400 °C.
Heat treatment — the narrow window
Soft anneal 820–870 °C, very slow cool (≤ 15 K/h). Preheat in two stages, 450–500 °C and 850–900 °C. Austenitise 1190–1230 °C, held only 2–5 minutes at temperature, in vacuum, a neutral salt bath or a protective atmosphere; the window is about ±10 °C around the set point. Quench in oil, salt at 500–550 °C, or vacuum gas; interrupt at 50–70 °C. Temper three times for at least 1 h at 550–560 °C, cooling to room temperature between tempers. Deep freezing after the quench is sometimes used but does not replace the third temper. Ms ≈ 220 °C.
Why three tempers
A quenched high-speed steel contains 20–30 % retained austenite. Each temper converts part of it to fresh, untempered martensite on cooling; the next temper tempers that martensite and converts more austenite. After three cycles the retained austenite is below a few per cent. Skipping the third temper leaves an unstable structure that changes dimension in storage and chips in service — the classic cause of a tool that was correct on inspection and failed in the first hour.
Coating
Nearly all production high-speed steel tooling is coated. TiN (gold, 2300 HV, deposited at 450–500 °C) is the general case; TiCN for abrasive work, TiAlN/AlTiN for dry and high-speed cutting because its oxide layer insulates the edge, and CrN for aluminium and copper alloys. PVD temperatures sit below the 550 °C tempering temperature, so the substrate keeps its hardness — that compatibility is a direct consequence of the secondary-hardening temper and is why high-speed steel takes coatings while oil-hardening grades cannot. Coating a tool typically doubles to quadruples its life; it does not repair a bad edge geometry.
Wear resistance and grinding
Carbide volume is around 10 %, including hard MC vanadium carbides. That makes the steel abrasion resistant in service and difficult to grind: use soft, open aluminium-oxide wheels or CBN, generous coolant, light passes, and watch for grinding burn — a blue edge is a soft edge, because the surface has been tempered past 600 °C. Re-sharpening a coated tool removes the coating on the ground face; the edge still works, but the gain is partly lost unless it is re-coated.
Physical properties
Density 8.10 g/cm³ — noticeably heavier than ordinary tool steel because of the tungsten. E = 230 GPa, higher than any other steel on this site, which is part of why high-speed steel drills deflect less than their stiffness-to-diameter ratio suggests. Thermal conductivity ≈ 19 W/m·K, low, so heat stays at the edge and coolant matters. Expansion 10.1 × 10⁻⁶/K (20–100 °C), 11.5 × 10⁻⁶/K (20–600 °C).
Weldability
Not a weldable steel in any structural sense, but flash and friction welding of a high-speed steel tip to a plain-steel shank is standard industrial practice — most drills above about 13 mm diameter and every bi-metal band saw are made this way, which is why a cheap long drill has a hardened flute section and a soft shank. Repair welding of a damaged tool is uneconomic and unreliable: preheat 500 °C, matching filler, immediate triple temper, and the result is still a crack risk. Do not weld a hardened high-speed steel tool as a repair.
Machining, forming and heat treatment
Annealed machinability ≈ 35–40 % relative to 1 % C free-cutting steel: the hard carbides are abrasive even in the annealed state, so carbide tooling, moderate speeds and rigid set-ups are required. Finished tool geometry is almost always produced by grinding after hardening, not by machining before it — flutes, lands and reliefs are ground on CNC tool grinders, which is why a high-speed steel cutter is a ground product. EDM is possible and used for form tools; the white layer must be removed because it is untempered. Hard turning at 64 HRC is impractical. Nitriding (steam or salt, 'blue' finish) at 480–520 °C is applied to taps and some drills for extra surface hardness and lubricity.
Typical applications
- Twist drills, centre drills and reamers
- Hand and machine taps, thread chasers and thread-rolling tools
- End mills, slot drills, side-and-face cutters and slitting saws
- Gear hobs, shaper cutters and shaving tools
- Broaches and keyway cutters
- Bi-metal band-saw and hacksaw blades (edge wire)
- Turning and planing tool bits for interrupted or low-speed work
- Cold-work punches needing red hardness, hot shear blades
Frequently asked questions
Is 1.3343 the same as M2?
Yes. 1.3343 (HS6-5-2C, EN ISO 4957) and AISI M2 (UNS T11302, ASTM A600) are the same tungsten-molybdenum high-speed steel. The ASTM carbon range, 0.78–1.05 %, covers both the standard and the high-carbon European versions, so an M2 certificate should be read for its actual carbon content: 1.3343 is the high-carbon one at 0.86–0.94 %, and 1.3339 is the plain version.
What does the C in HS6-5-2C mean?
Carbon. HS6-5-2C carries 0.86–0.94 % carbon against 0.78–0.88 % for plain HS6-5-2, which is worth roughly one point of working hardness — 64–66 HRC instead of 63–65 — and a useful gain in abrasive wear resistance for a small loss of toughness. It is not a quality or purity designation. The numbers in the name are the tungsten, molybdenum and vanadium contents.
What hardness does M2 reach?
64–66 HRC after hardening from 1210–1230 °C and triple tempering at 550–560 °C. More to the point, it retains about 58 HRC at 500 °C and 50 HRC at 600 °C, which no cold-work or hot-work tool steel does. The room-temperature number is not what the steel is bought for.
Why does high-speed steel need three tempers?
Because a quenched high-speed steel holds 20–30 % retained austenite. Each tempering cycle converts part of it to fresh untempered martensite as it cools, which the next cycle then tempers. Three cycles bring the retained austenite down to a few per cent. A tool tempered only once or twice is dimensionally unstable and chips in service, even though it measures correctly on inspection.
M2 or carbide — which should I use?
Carbide cuts several times faster and holds hardness far higher, so for stable, rigid, high-volume machining it wins on cost per part. M2 is tougher: it bends where carbide chips. Hand taps, small and long drills, thin slitting saws, interrupted cuts, unstable set-ups, old low-speed machines and anything that may be shock-loaded are still high-speed steel for that reason, and coating closes part of the speed gap.
What is the difference between M2 and M35?
Cobalt. M35 (1.3243, HS6-5-2-5) is the same steel with 4.5–5.0 % cobalt, which raises hot hardness by roughly 50 °C and makes it the standard choice for drilling stainless steel, nickel alloys and titanium. It is slightly more brittle and more expensive, and it brings no benefit on ordinary carbon steel.
Can M2 tools be re-sharpened?
Yes, and they are designed to be — that is part of the economics of high-speed steel tooling. Grind with soft open wheels or CBN, with plenty of coolant and light passes, and watch the colour: a blue edge has been tempered above 600 °C and is soft, so it must be ground back further. Re-sharpening removes the coating on the ground face, so a re-ground coated tool performs between the coated and uncoated levels unless it is re-coated.
Why is a cheap long drill hard at the tip and soft at the shank?
Because it is two steels friction or flash welded together: a high-speed steel cutting section joined to a plain-steel shank. It is normal manufacturing practice above about 13 mm diameter, not a defect, and the same construction gives bi-metal band-saw blades a hard tooth edge on a flexible backing.
Related grades
Verified against EN ISO 4957:2018; EN ISO 4957:2018, high-speed steels; ASTM A600-92a (M2 comparison); JIS G4403:2015 (SKH51 comparison); GOST 19265-73 (R6M5 comparison). Last checked: October 2026.