Steel SKH51 Annealed
Temper · default condition
JIS SKH51 · AISI/SAE M2
Standard stock condition for bar/plate — machine to shape, then harden and temper.
Values for the Annealed 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 |
|---|---|---|---|---|---|---|
AnnealedDefaultThis page 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 | — |
What is SKH51 Annealed?
SKH51 Annealed is SKH51 in the Annealed temper — standard stock condition for bar/plate — machine to shape, then harden and temper. SKH51 Annealed 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). SKH51 Annealed 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).
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 Annealed properties
Typical room-temperature values for SKH51 Annealed; 23 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 Annealed 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 Annealed 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 Annealed 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 Annealed 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 Annealed 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 Annealed'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. Confirm any required mill or lot documentation when quoting.
Working with SKH51 Annealed
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 Annealed — frequently asked
What is SKH51 Annealed used for?
SKH51 Annealed 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 Annealed?
SKH51 Annealed 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 Annealed 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 Annealed 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 Annealed?
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 Annealed 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 Annealed?
SKH51 Annealed 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.
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.