Steel NAK80 · heat-treated state
Steel NAK80 Prehard
Properties of the Prehard condition, compared with the other NAK80 tempers.
Standard stock condition: machine straight to finished cavity, no heat treatment and no distortion risk.
What is NAK80 Prehard?
NAK80 Prehard is NAK80 heat treated to Prehard — standard stock condition: machine straight to finished cavity, no heat treatment and no distortion risk. NAK80 Prehard has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). NAK80 Prehard has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F). Annealed is the default condition FabDigit quotes; Prehard is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 95/100, better than 100% of steel grades
- High strength — 1,150 MPa (167 ksi), better than 94% of steel grades
Limitations
- High embodied carbon — 2.6 kg CO₂/kg, worse than 86% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Poor heat conductor — 30 W/m·K (17.3 BTU/hr·ft·°F), worse than 83% of steel grades
- Low electrical conductivity — 5.7 % IACS, worse than 80% of steel grades
- Low fracture toughness — 60 MPa·√m (54.6 ksi·√in), worse than 79% of steel grades
NAK80 Prehard properties
Typical room-temperature values for NAK80 Prehard — 11 properties are specific to this condition; the rest are grade-level values shared by every NAK80 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical2
NAK80 Prehard has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
NAK80 Prehard has a yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
NAK80 Prehard is rated for continuous service to 400°C (752 °F). It conducts heat at 30 W/m·K (17.3 BTU/hr·ft·°F), worse than 83% of steel grades. Thermal expansion is 12.5 µm/m·K (6.94 µin/in·°F).
Electrical3
NAK80 Prehard conducts electricity at 5.7 % IACS, worse than 80% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of NAK80 Prehard takes about 36 MJ of energy and emits 2.6 kg of CO₂ — more than 88% of steel grades. Typical recycled content is 30%.
Manufacturability7
NAK80 Prehard's machinability is good (55/100, better than 62% of steel grades); weldability fair (50/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other NAK80 tempers and conditions
NAK80 is also supplied in 3 other conditions. The full side-by-side table is on the NAK80 overview.
- AnnealedDefaultRarely stocked; used when very heavy roughing or cold work is needed before re-solution-treating and aging back to 40 HRC.700 MPa yield · 28 HRC
- Q&TRe-heat-treatment route after weld repair or after machining in the soft state; restores full pre-hard properties.1,180 MPa yield · 41 HRC
- PrehardStandard stock condition: machine straight to finished cavity, no heat treatment and no distortion risk.1,150 MPa yield · 40 HRC
Working with NAK80 Prehard
Is NAK80 easy to machine?
Machine directly at 40 HRC with coated carbide (or CBN for finishing); rigid setups, 60–120 m/min, light radial engagement — EDM and engraving behave well and no post-heat-treat distortion allowance is needed.
Can NAK80 be welded?
Repairable by TIG or laser with matching NAK80/maraging-type filler; preheat 250–350 °C, low heat input, then re-age ~500 °C ×3–5 h to recover cavity hardness and colour match.
Can NAK80 be formed, bent or molded?
Supplied in the hardened condition, so no cold forming — shape by milling, EDM, grinding; hot working (1100→900 °C forge) only at the mill followed by solution + aging.
What surface finishes work on NAK80?
Excellent mirror polishability (Ra <0.01 µm achievable, #10000 attainable) thanks to low sulfur and fine uniform structure; accepts texturing/etching, hard chrome or electroless nickel for corrosive resins, and nitriding or PVD for wear.
NAK80 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 |
|---|---|---|
| C | 0.1 – 0.2 | 0.15 |
| Si | 0.1 – 0.5 | 0.3 |
| Mn | 1.2 – 1.8 | 1.5 |
| Niwith Al and Cu forms the precipitation-hardening system | 2.5 – 3.5 | 3 |
| Cu | 0.8 – 1.2 | 1 |
| AlNi-Al intermetallic aging response | 0.8 – 1.2 | 1 |
| Mo | 0.15 – 0.4 | 0.3 |
| Skept low (non-free-cutting) for mirror polishability, unlike NAK55 | ≤ 0.01 | 0.01 |
| P | ≤ 0.03 | 0.02 |
| Fe | balance | — |
NAK80 Prehard — frequently asked
What is NAK80 Prehard used for?
NAK80 Prehard is typically used for injection moulds for high-gloss transparent parts, optical lens moulds, precision cavity and core inserts, cosmetic and consumer housing moulds, photo-etched and textured cavity plates and medical device moulds. In short: premium mirror-polish mold.
What is the yield strength of NAK80 Prehard?
NAK80 Prehard has a typical yield strength of 1,150 MPa (167 ksi) and a tensile strength of 1,300 MPa (189 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is NAK80 Prehard easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine directly at 40 HRC with coated carbide (or CBN for finishing); rigid setups, 60–120 m/min, light radial engagement — EDM and engraving behave well and no post-heat-treat distortion allowance is needed.
Can NAK80 Prehard be welded?
With care — weldability is rated fair (50/100). Repairable by TIG or laser with matching NAK80/maraging-type filler; preheat 250–350 °C, low heat input, then re-age ~500 °C ×3–5 h to recover cavity hardness and colour match.
What surface finishes work on NAK80 Prehard?
Excellent mirror polishability (Ra <0.01 µm achievable, #10000 attainable) thanks to low sulfur and fine uniform structure; accepts texturing/etching, hard chrome or electroless nickel for corrosive resins, and nitriding or PVD for wear.
Can NAK80 Prehard be formed, bent or molded?
Supplied in the hardened condition, so no cold forming — shape by milling, EDM, grinding; hot working (1100→900 °C forge) only at the mill followed by solution + aging.
What is the maximum service temperature of NAK80 Prehard?
NAK80 Prehard 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.
What is the difference between NAK80 Annealed and NAK80 Prehard?
Annealed is the default condition — rarely stocked; used when very heavy roughing or cold work is needed before re-solution-treating and aging back to 40 HRC. Prehard: standard stock condition: machine straight to finished cavity, no heat treatment and no distortion risk. Yield strength is 700 MPa in Annealed versus 1,150 MPa in Prehard.
Can FabDigit make parts in NAK80 Prehard?
Yes — NAK80 Prehard is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- NAK80 Pre-hardened Mirror-finish Plastic Mold Steel — Daido Steel (2020)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- Tool Steels, 5th ed. — ASM International (1998)
- Mold steel comparison tables (NAK80 / P20 / 718H) — Ensinger–Hasco style tooling data compilations (2022)
- (NAK80/718H/P20) (2025)
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.