Steel SKH51 Nitrided
Finish state
JIS SKH51 · AISI/SAE M2
Post-hardening surface treatment adding ~1000–1200 HV case for taps and drills on abrasive work.
Values for the Nitrided condition
Other SKH51 tempers and conditions
SKH51 is listed in 6 conditions; see the grade overview at SKH51.
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 |
NitridedThis page 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 | — |
What is SKH51 Nitrided?
SKH51 Nitrided is SKH51 supplied in the Nitrided condition — post-hardening surface treatment adding ~1000–1200 HV case for taps and drills on abrasive work. SKH51 Nitrided has a yield strength of 1,950 MPa (283 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 230 GPa (33.4 Msi). SKH51 Nitrided 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). Annealed is the default condition FabDigit quotes; Nitrided is available on request or by drawing note.
Advantages
- High strength — 1,950 MPa (283 ksi), better than 100% of steel grades
- High service temperature — 560°C (1,040 °F), better than 96% of steel grades
- Good corrosion resistance — 25/100, better than 92% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Limited ductility — 0.5%, worse than 100% of steel grades
- Low fracture toughness — 15 MPa·√m (13.7 ksi·√in), worse than 100% of steel grades
- Difficult to machine — 3/100, worse than 100% of steel grades
- Difficult to weld — 5/100, worse than 100% of steel grades
- Limited formability — 1/100, worse than 100% of steel grades
SKH51 Nitrided properties
Typical room-temperature values for SKH51 Nitrided; 21 are specific to this condition. Other listed values are SKH51 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SKH51 Nitrided 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 Nitrided has a yield strength of 1,950 MPa (283 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 230 GPa (33.4 Msi).
Thermal6
SKH51 Nitrided is rated for continuous service to 560°C (1,040 °F). It conducts heat at 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades. Thermal expansion is 11 µm/m·K (6.11 µin/in·°F).
Electrical3
SKH51 Nitrided conducts electricity at 2.6 % IACS, worse than 97% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (25/100), better than 92% of steel grades.
Sustainability4
Producing a kilogram of SKH51 Nitrided 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 Nitrided's machinability is not recommended (3/100, worse than 100% of steel grades); weldability not recommended (5/100); formability not recommended (1/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SKH51 Nitrided
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.
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.
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 | — |
SKH51 Nitrided — frequently asked
What is SKH51 Nitrided used for?
SKH51 Nitrided 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 Nitrided?
SKH51 Nitrided has a typical yield strength of 1,950 MPa (283 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 100% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SKH51 Nitrided easy to machine?
Not especially — machinability is rated not recommended (3/100, worse than 100% 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 Nitrided be welded?
Not readily — weldability is rated not recommended (5/100). 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 Nitrided?
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 Nitrided 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 Nitrided?
SKH51 Nitrided is rated for continuous use to about 560°C (1,040 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.