Steel SKH51
JIS SKH51 · AISI/SAE M2
SKH51 is the JIS molybdenum-type high-speed steel equivalent to AISI M2, hardened by W-Mo-Cr-V carbides and secondary hardening, and the default general-purpose HSS for cutting tools.
Reference datasheet — SKH51 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Annealed condition
SKH51 tempers and conditions
SKH51 is supplied in 6 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault soft (spheroidize) annealed, ≤255 HB | Standard stock condition for bar/plate — machine to shape, then harden and temper. | 550 | 850 | 20 | 22 HRC | 2.9 % IACS |
Hardened, tempered and surface nitrided / steam-tempered | Post-hardening surface treatment adding ~1000–1200 HV case for taps and drills on abrasive work. | 1,950 | 2,100 | 0.5 | 63 HRC | 2.6 % IACS |
Hardened & tempered to 64–66 HRC | High austenitising temperature for maximum wear resistance on form tools and gear cutters; toughness is minimal. | 2,000 | 2,200 | 0.5 | 65 HRC | 2.6 % IACS |
Hardened & tempered to 58–60 HRC | Lower austenitising / higher tempering temperature for shock-loaded punches and cold-forming tools. | 2,100 | 1 | 59 HRC | — | |
Hardened & tempered to 60–62 HRC | Balanced hardness/toughness for taps, broaches, cold-work punches and dies. | 2,300 | 0.5 | 61 HRC | — | |
Hardened & triple tempered to 62–64 HRC | Normal delivery hardness for drills, end mills and hobs — best wear/red-hardness compromise. | 2,500 | 0.3 | 63 HRC | — |
Supply forms, finishes and certifications
Ways SKH51 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
Cold Drawn Ground | Annealed, cold drawn / centreless ground bar | Surface finish |
What is SKH51?
SKH51 is the JIS molybdenum-type high-speed steel equivalent to AISI M2, hardened by W-Mo-Cr-V carbides and secondary hardening, and the default general-purpose HSS for cutting tools. Engineers choose it for the balance of hot hardness, toughness and grindability at working hardnesses of 58–66 HRC; it is widely stocked as round bar, flat bar, cold-drawn ground stock, nitrided blanks and finished tool bodies. It is machinable only in the annealed condition at about 240 HB, has no corrosion resistance and is listed to roughly 400 °C; where higher hot hardness is required at extra cost and lower toughness, cobalt SKH59 (M42) is the next step. SKH51 has a density of 8.16 g/cm³ (0.295 lb/in³), heavier than 98% of steel grades. It melts at 1,370°C (2,498 °F). SKH51 has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 71% of steel grades. Elongation at break is 20% and the elastic modulus is 217 GPa (31.5 Msi).
What is SKH51 used for?
- drills
- end mills
- taps
- reamers
Advantages
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Low fracture toughness — 30 MPa·√m (27.3 ksi·√in), worse than 96% of steel grades
- Poor heat conductor — 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- High embodied carbon — 3.2 kg CO₂/kg, worse than 92% of steel grades
- Difficult to machine — 30/100, worse than 89% of steel grades
SKH51 properties
Typical room-temperature values for SKH51-Annealed; bars are the position among steel grades.
Physical3
SKH51 has a density of 8.16 g/cm³ (0.295 lb/in³), heavier than 98% of steel grades. It melts at 1,370°C (2,498 °F).
Mechanical17
SKH51 has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 71% of steel grades. Elongation at break is 20% and the elastic modulus is 217 GPa (31.5 Msi).
Thermal6
SKH51 is rated for continuous service to 400°C (752 °F). It conducts heat at 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades. Thermal expansion is 11 µm/m·K (6.11 µin/in·°F).
Electrical3
SKH51 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (16/100), better than 79% of steel grades.
Sustainability4
Producing a kilogram of SKH51 takes about 45 MJ of energy and emits 3.2 kg of CO₂ — more than 93% of steel grades. Typical recycled content is 45%.
Manufacturability7
SKH51's machinability is poor (30/100, worse than 89% of steel grades); weldability poor (20/100); formability poor (15/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SKH51 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SKH51
Is SKH51 easy to machine?
Machine only in the annealed condition with rigid setups, cobalt-HSS or coated carbide, low speed and heavy feed; once hardened above ~55 HRC, use grinding, EDM or CBN.
Can SKH51 be welded?
Not a structural weld metal — repair weld only with matched HSS filler, 500–550 °C preheat, immediate post-weld temper; otherwise cracking is certain.
Can SKH51 be formed, bent or molded?
Hot forge 1100→900 °C with slow furnace cooling to soft-anneal (≈860 °C, slow cool); cold forming is impractical.
SKH51 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CJIS G4403 SKH51 | 0.8 – 0.88 | 0.85 |
| Si | ≤ 0.45 | 0.3 |
| Mn | ≤ 0.4 | 0.3 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Cr | 3.8 – 4.5 | 4.1 |
| Mo | 4.7 – 5.2 | 5 |
| W | 5.9 – 6.7 | 6.3 |
| V | 1.7 – 2.1 | 1.9 |
| Curesidual | ≤ 0.25 | |
| Niresidual | ≤ 0.25 | |
| Fe | balance |
What surface finishes work on SKH51?
Harden at 1180–1230 °C, oil/vacuum/salt quench, then triple temper 540–560 °C; finish by grinding and protect with black oxide, steam oxide, phosphate or PVD TiN/TiAlN coating.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SKH51 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- M2
How much does SKH51 cost?
SKH51 is a premium-cost steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SKH51 — frequently asked
What is SKH51 used for?
SKH51 is typically used for drills, end mills, taps and reamers. In short: default general-purpose HSS; AISI M2 equivalent; best HSS cost-toughness balance.
What is the yield strength of SKH51?
SKH51 has a typical yield strength of 550 MPa (79.8 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 71% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SKH51 easy to machine?
Not especially — machinability is rated poor (30/100, worse than 89% of steel grades). Machine only in the annealed condition with rigid setups, cobalt-HSS or coated carbide, low speed and heavy feed; once hardened above ~55 HRC, use grinding, EDM or CBN.
Can SKH51 be welded?
Not readily — weldability is rated poor (20/100). Not a structural weld metal — repair weld only with matched HSS filler, 500–550 °C preheat, immediate post-weld temper; otherwise cracking is certain.
What surface finishes work on SKH51?
Harden at 1180–1230 °C, oil/vacuum/salt quench, then triple temper 540–560 °C; finish by grinding and protect with black oxide, steam oxide, phosphate or PVD TiN/TiAlN coating.
Can SKH51 be formed, bent or molded?
Hot forge 1100→900 °C with slow furnace cooling to soft-anneal (≈860 °C, slow cool); cold forming is impractical.
What is the maximum service temperature of SKH51?
SKH51 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does SKH51 cost?
SKH51 is a premium-cost steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- JIS G4403 High Speed Tool Steel Steels — JSA (2015)
- ASTM A600 Tool Steel High Speed — ASTM (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Böhler S600 (M2) / Erasteel ASP-M2 datasheet — voestalpine Böhler / Erasteel (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.