Steel NAK55
NAK55 is a Ni-Cu-Al precipitation-hardening plastic mould steel supplied prehardened to about 37–43 HRC (typically 40 HRC), with hardness uniform through the section, so cavities can be machined and EDM'd and put into service without a further quench and the distortion that follows it.
Values for the Annealed condition
NAK55 tempers and conditions
NAK55 is supplied in 4 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault soft condition for heavy machining or re-heat-treatment | Rarely stocked; used only when very heavy stock removal or re-heat-treatment of a used block is planned, aging afterwards restores 40 HRC. | 560 | 800 | 20 | 24 HRC | — |
Pre-hardened | Standard commercial supply condition: machine and EDM directly, no further heat treatment or distortion risk. | 1,100 | 1,270 | 10 | 40 HRC | — |
prehard core plus gas/plasma nitrided case (~600–750 HV surface) | Use for abrasive glass- or mineral-filled resins and sliding faces; nitriding at 480–530 °C does not soften the aged core. | 1,100 | 1,270 | 8 | 40 HRC | 6.6 % IACS |
Quenched and tempered | Choose when a repaired, welded or annealed block must be restored to full working hardness; aging is a low-temperature, low-distortion treatment. | 1,120 | 1,290 | 9 | 41 HRC | 6.6 % IACS |
What is NAK55?
NAK55 is a Ni-Cu-Al precipitation-hardening plastic mould steel supplied prehardened to about 37–43 HRC (typically 40 HRC), with hardness uniform through the section, so cavities can be machined and EDM'd and put into service without a further quench and the distortion that follows it. A sulfur addition raises cutting rates well above P20/718 steels at equal hardness, suiting precision injection mould cavities, plates with moderate polish requirements and ejector or slide components. Sulfide inclusions lower mirror polishability, toughness and weldability compared with NAK80, corrosion resistance is that of a low-alloy steel, and service should stay below about 450 °C because the material softens near its ageing temperature. NAK55 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). NAK55 has a yield strength of 560 MPa (81.2 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 73% of steel grades. Elongation at break is 20% and the elastic modulus is 206 GPa (29.9 Msi).
What is NAK55 used for?
- Injection mould cavities and cores
- Mould inserts
- Mould cavity and bolster plates
- Ejector blocks and slides
- Textured-finish cosmetic mould components
- Precision gauge and fixture blocks
Advantages
- Easy to machine — 70/100, better than 96% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Low fracture toughness — 60 MPa·√m (54.6 ksi·√in), worse than 78% of steel grades
NAK55 properties
Typical room-temperature values for NAK55-Annealed; bars are the position among steel grades.
Physical3
NAK55 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
NAK55 has a yield strength of 560 MPa (81.2 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 73% of steel grades. Elongation at break is 20% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal5
NAK55 is rated for continuous service to 430°C (806 °F). It conducts heat at 39 W/m·K (22.5 BTU/hr·ft·°F), worse than 67% of steel grades. Thermal expansion is 12.4 µm/m·K (6.89 µin/in·°F).
Electrical2
NAK55 has an electrical resistivity of 2.6×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of NAK55 takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability6
NAK55's machinability is very good (70/100, better than 96% of steel grades); weldability fair (40/100); formability poor (30/100).
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. NAK55 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with NAK55
Is NAK55 easy to machine?
Machines readily at 37–43 HRC thanks to the sulfur addition — use coated carbide, moderate speeds and rigid setups; drilling/tapping is far easier than P20 at equal hardness, and EDM finishing needs a light polish of the recast layer.
Can NAK55 be welded?
TIG/laser repair with matched Ni-Cu-Al or maraging filler after preheat ~250 °C; re-age the area at 500–550 °C to recover hardness, expect somewhat lower toughness at sulfide-rich zones.
Can NAK55 be formed, bent or molded?
Supplied fully hardened — no cold forming or bending; shape only by machining, EDM or grinding, and stress-relieve at ~500 °C after heavy roughing on thin cores.
Manufacturability
The process limits FabDigit applies to NAK55. Every NAK55 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better70 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
NAK55 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 |
|---|---|---|
| Cproducer typical | 0.1 – 0.2 | 0.15 |
| Si | 0.15 – 0.5 | 0.3 |
| Mn | 1.2 – 1.8 | 1.5 |
| Niwith Cu+Al forms age-hardening precipitates | 2.5 – 3.5 | 3 |
| Cu | 0.8 – 1.3 | 1 |
| Al | 0.8 – 1.3 | 1 |
| Sintentional free-machining addition (absent in NAK80) | 0.04 – 0.12 | 0.08 |
| Presidual | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on NAK55?
Takes a good general polish (A2/B-grade texture and #4000 finish) but sulfide stringers can show as pinholes in mirror work — choose NAK80 for optical finishes; chrome/EN plating, nitriding and PVD all work, keep plating bake below 250 °C.
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).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
How much does NAK55 cost?
NAK55 is a standard-cost steel ($$), cheaper than about 59% 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.
NAK55 — frequently asked
What is NAK55 used for?
NAK55 is typically used for injection mould cavities and cores, mould inserts, mould cavity and bolster plates, ejector blocks and slides, textured-finish cosmetic mould components and precision gauge and fixture blocks. In short: premium mirror-polish mold.
What is the yield strength of NAK55?
NAK55 has a typical yield strength of 560 MPa (81.2 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 73% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is NAK55 easy to machine?
Yes — machinability is rated very good (70/100, better than 96% of steel grades). Machines readily at 37–43 HRC thanks to the sulfur addition — use coated carbide, moderate speeds and rigid setups; drilling/tapping is far easier than P20 at equal hardness, and EDM finishing needs a light polish of the recast layer.
Can NAK55 be welded?
With care — weldability is rated fair (40/100). TIG/laser repair with matched Ni-Cu-Al or maraging filler after preheat ~250 °C; re-age the area at 500–550 °C to recover hardness, expect somewhat lower toughness at sulfide-rich zones.
What surface finishes work on NAK55?
Takes a good general polish (A2/B-grade texture and #4000 finish) but sulfide stringers can show as pinholes in mirror work — choose NAK80 for optical finishes; chrome/EN plating, nitriding and PVD all work, keep plating bake below 250 °C.
Can NAK55 be formed, bent or molded?
Supplied fully hardened — no cold forming or bending; shape only by machining, EDM or grinding, and stress-relieve at ~500 °C after heavy roughing on thin cores.
What is the maximum service temperature of NAK55?
NAK55 is rated for continuous use to about 430°C (806 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between NAK55 Annealed and NAK55 Prehard?
Annealed is the default condition — rarely stocked; used only when very heavy stock removal or re-heat-treatment of a used block is planned, aging afterwards restores 40 HRC. Prehard: standard commercial supply condition: machine and EDM directly, no further heat treatment or distortion risk. Yield strength is 560 MPa in Annealed versus 1,100 MPa in Prehard.
How much does NAK55 cost?
NAK55 is a standard-cost steel ($$), cheaper than about 59% 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.
Can FabDigit make parts in NAK55?
Yes — NAK55 is available for CNC machining; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- NAK55 / NAK80 Pre-hardened Plastic Mold Steel data sheet — Daido Steel Co., Ltd. (2021)
- NAK55 free-machining prehardened mold steel technical bulletin — International Mold Steel (Daido distributor) (2020)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- Tool Steels, 5th ed. (mold steel chapters) — ASM International (1998)
- GB/T 1299 (mold and tool steels, 10Ni3MnCuAl class) — SAC (2014)
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.