Steel NAK55 · heat-treated state
Steel NAK55 Q&T
Properties of the Q&T condition, compared with the other NAK55 tempers.
Choose when a repaired, welded or annealed block must be restored to full working hardness; aging is a low-temperature, low-distortion treatment.
What is NAK55 Q&T?
NAK55 Q&T is NAK55 heat treated to Q&T — choose when a repaired, welded or annealed block must be restored to full working hardness; aging is a low-temperature, low-distortion treatment. NAK55 Q&T has a yield strength of 1,120 MPa (162 ksi) and a tensile strength of 1,290 MPa (187 ksi) — stronger than 93% of steel grades. Elongation at break is 9% and the elastic modulus is 206 GPa (29.9 Msi). NAK55 Q&T 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; Q&T is available on request or by drawing note.
Advantages
- High strength — 1,120 MPa (162 ksi), better than 93% of steel grades
Limitations
- Limited ductility — 9%, worse than 93% of steel grades
- 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 79% of steel grades
NAK55 Q&T properties
Typical room-temperature values for NAK55 Q&T — 8 properties are specific to this condition; the rest are grade-level values shared by every NAK55 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
NAK55 Q&T 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 Q&T has a yield strength of 1,120 MPa (162 ksi) and a tensile strength of 1,290 MPa (187 ksi) — stronger than 93% of steel grades. Elongation at break is 9% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal5
NAK55 Q&T 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 66% of steel grades. Thermal expansion is 12.4 µm/m·K (6.89 µin/in·°F).
Electrical2
NAK55 Q&T 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 Q&T 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 Q&T's machinability is fair (52/100, better than 52% of steel grades); weldability fair (40/100); 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 NAK55 tempers and conditions
NAK55 is also supplied in 3 other conditions. The full side-by-side table is on the NAK55 overview.
- AnnealedDefaultRarely stocked; used only when very heavy stock removal or re-heat-treatment of a used block is planned, aging afterwards restores 40 HRC.560 MPa yield · 24 HRC
- Q&TChoose when a repaired, welded or annealed block must be restored to full working hardness; aging is a low-temperature, low-distortion treatment.1,120 MPa yield · 41 HRC
- PrehardStandard commercial supply condition: machine and EDM directly, no further heat treatment or distortion risk.1,100 MPa yield · 40 HRC
Working with NAK55 Q&T
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.
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.
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 | — |
NAK55 Q&T — frequently asked
What is NAK55 Q&T used for?
NAK55 Q&T 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 Q&T?
NAK55 Q&T has a typical yield strength of 1,120 MPa (162 ksi) and a tensile strength of 1,290 MPa (187 ksi) — stronger than 93% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is NAK55 Q&T easy to machine?
Reasonably — machinability is rated fair (52/100, better than 52% 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 Q&T 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 Q&T?
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 Q&T 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 Q&T?
NAK55 Q&T 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.
Can FabDigit make parts in NAK55 Q&T?
Yes — NAK55 Q&T is available for CNC machining with instant online pricing. 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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.