An 8% cobalt high-speed steel (AISI M42) with the highest hardenability and hardness of the common HSS grades — up to about 70 HRC. It is the choice for the toughest cutting jobs on hard, abrasive and high-strength materials.
What Is M42 High-Speed Steel?
M42 is an 8% cobalt molybdenum high-speed steel. The very high cobalt and vanadium let it reach 67 – 70 HRC and keep that hardness at the high temperatures of aggressive cutting, so it outlasts M35 and M2 on the hardest alloys.
It is used for the most demanding drills, end mills, taps and broaches, often with a TiN or AlTiN coating. It is more brittle than lower-cobalt grades, so it needs rigid machines and correct parameters.
Supply Forms and Sizes
Every form is available soft-annealed (for further forming and machining) or heat-treated to your hardness window.
| Form | Condition | Size Range | Typical Use |
|---|---|---|---|
| Round bar / rod | Annealed | 3 – 100 mm | Tool blanks, drills |
| Flat bar | Annealed | 5 – 60 mm | Milling cutters, blades |
| Ground rod | Pre-ground | 3 – 40 mm | Precision tool stock |
| Saw & blade stock | Annealed | 2 – 20 mm | HSS saw blanks |
Chemical Composition (AISI M42)
| C | W | Mo | Cr | V | Co | P max | S max |
|---|---|---|---|---|---|---|---|
| 1.05 – 1.15 | 1.15 – 1.85 | 9.00 – 10.00 | 3.50 – 4.25 | 0.95 – 1.35 | 7.75 – 8.75 | 0.030 | 0.030 |
Heat analysis is reported on the mill certificate for every lot. If your drawing calls for tighter limits than the standard, flag it at enquiry — ladle-refined heats usually meet it without a surcharge.
Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Elastic modulus (E) | ~200 GPa |
| Shear modulus (G) | ~79 GPa |
| Thermal conductivity | ~40 W/m·K at room temperature |
| Coefficient of thermal expansion | ~12 ×10⁻₆ /K (20 – 200 °C) |
Mechanical Properties
Typical as-hardened and tempered values. The mill certificate is the binding document.
| Condition | Hardness | Red-hardness* | Transverse strength | Notes |
|---|---|---|---|---|
| Annealed | ≤ 269 HB | — | — | For machining |
| H&T 68 HRC | 67 – 70 HRC | ~600 °C | ~3000 MPa | Max hardness |
| Triple tempered | 67 – 69 HRC | ~600 °C | ~3100 MPa | Stable edge |
Equivalent Grades
| Standard | Designation |
|---|---|
| USA AISI | M42 |
| Europe EN | HS2-9-1-8 (similar) |
| Japan JIS G4403 | SKH59 (similar) |
| China GB/T 9943 | W2Mo9Cr4VCo8 (similar) |
Heat Treatment and Processing
Preheat slowly, then raise to the grade forging range. Work above the lower limit and cool slowly after forging to avoid cracks.
800 – 860 °C, slow furnace cool. Delivers soft condition for machining.
1170 – 1210 °C, oil or salt, then triple temper.
Around 540 – 560 °C, three tempers, to reach 67 – 69 HRC with stable austenite.
After machining or forming, 200 – 350 °C for 1 – 2 hours, air cool, to stabilise dimensions and relieve residual stress.
Heat-treated bars and plates are supplied with the hardness and test certificate you specify. For critical parts we can control decarburisation depth and supply a spheroidized or soft-annealed structure on request.
Applications of M42 High-Speed Steel
Deep-hole and hard-material drilling.
Tough cutting of hardened and high-strength alloys.
Maximum wear and edge retention.
TiN/AlTiN-coated M42 for aerospace alloys.
Cutting hard or abrasive bar and tube.
Where the hardest HSS edge is required.
M42 High-Speed Steel vs Alternative Grades
| Grade | vs M42 High-Speed Steel | Choose It When |
|---|---|---|
| M42 | — | Hardest, highest red-hardness; toughest cutting jobs. |
| M35 | Lower Co, slightly less hard | General cobalt HSS at lower cost |
| M2 (no Co) | Cheaper, lower red-hardness | Routine cutting where heat is moderate |
| T15 | Highest wear, lower toughness | Very abrasive work only |
Quality Control and Mill Certificates
Every shipment ships with an EN 10204 3.1 mill certificate covering heat chemical analysis, hardness and the mechanical test on record. On request we add: ultrasonic test on heavy bar and plate, magnetic particle inspection on machined surfaces, and third-party inspection (SGS / BV) before loading. Dimensional tolerances follow the relevant EN / ASTM / JIS standard or your drawing.
Frequently Asked Questions
What is M42 high-speed steel?
An 8% cobalt HSS reaching up to ~70 HRC, used for the most demanding drills, end mills, taps and broaches on hard alloys.
M42 vs M35?
M42 has more cobalt and vanadium and reaches higher hardness and red-hardness; M35 is a more general-purpose cobalt HSS.
What hardness does M42 reach?
Typically 67 – 70 HRC after hardening and triple tempering.
Is M42 brittle?
It is harder and more brittle than lower-cobalt grades, so it needs rigid set-ups and correct speeds and feeds.
What is the minimum order quantity?
Mill lots typically start at 200 kg per item; common sizes are often from stock.
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