NAK80 | P21 | Pre-Hardened Mirror-Finish Plastic Mold Steel

NAK80 is a high-grade precipitation-hardening plastic mold steel from Japan, serving as the benchmark for high-gloss and mirror-finish molds. Its typical composition is 0.15% C, 3.00% Ni, 1.00% Cu and 1.00% Al. Supplied pre-hardened at 38–42 HRC, it delivers uniform hardness from surface to core and requires no post-machining heat treatment. Compared with P20 at the same hardness, NAK80 steel achieves 10–15% faster machining, finer polishing (Ra ≤ 0.05 μm) and better EDM performance.

Different from conventional quenched-and-tempered mold steels, NAK80 material gains hardness via aging precipitation, forming a uniform, dense microstructure without hardness gradient. It provides excellent dimensional stability and good weldability. Its heat-affected zone softens instead of hardening and can be re-aged for hardness recovery, while EDM recast layers are easy to remove.

NAK80 tool steel corresponds to international grades: modified AISI P21, DIN 1.2796, GB 10Ni3MnCuAl/15Ni3Mn and KS 10Ni3MnCuAl.

Supply Range of NAK80

1. Round Bar

Hot Rolled / Forged: Diameter Φ10mm – Φ500mm
Forged: Diameter Φ50mm – Φ400mm (larger sizes available upon request)
Length: 2000mm – 5800mm (customizable)
Tolerances: Compliant with AISI P21 or DIN 1.2796
Surface conditions: Black skin, peeled, turned, or ground finish

Flat Bar / Plate

3. Forgings / Custom Shapes of NAK80

Mold inserts, core pins, mirror-polish cavity plates, and complex geometries – all manufactured from your prints
Full dimensional flexibility: thickness, width, length, and shape all tailored to batch order requirements
Maximum weight per piece: up to 10 tons
Sample Testing: 1–10 pieces available for evaluation before formal production

Keyspark Steel offers precision plate component machining of NAK80 steel, specializing in steel plate milling and precision hole finishing. Custom-made to your drawings.

We also provide our overseas customers with assembly services for various CNC machined parts.

Our team does rough and fine machining for all kinds of forging ring parts. We provided rough turning service like slewing bearing rings and gear rings to many European construction machinery partners. Keyspark Steel have strong custom ability and an engineer teams. We make products from your drawings and are very flexible.

Keyspark Steel also offers importing clients custom cold drawn steel round bars, steel square bars and hexagon steel bars in different sizes with cold drawing dies as supporting items. The material have tight tolerance, smooth surface and stable material performance. And also cold drawing dies as supporting items.

NAK80 Material Equivalent

Standard System	Country/Region	Equivalent Grade	Common Search Terms
JIS	Japan	NAK80	NAK80 steel, NAK80 mold steel, NAK80 material, NAK80 tool steel
AISI / ASTM	USA	P21, UNS T51621	P21 steel, P21 mold steel
DIN / EN	Germany	1.2796	1.2796 steel, DIN 1.2796
GB	China	10Ni3MnCuAl, 15Ni3Mn	10Ni3MnCuAl steel, 15Ni3Mn
KS	Korea	10Ni3MnCuAl	KS 10Ni3MnCuAl steel

NAK80 Steel Composition

Element	C	Si	Mn	P	S	Ni	Cu	Mo	Al
Content	0.12–0.18	≤0.40	1.40–1.70	≤0.030	≤0.030	2.80–3.40	0.80–1.20	0.20–0.50	0.70–1.20

The nickel, aluminum, and copper additions in NAK80 steel are essential for the precipitation-hardening reaction. Molybdenum enhances hardenability and temper resistance.

NAK80 Properties

MECHANICAL PROPERTY	METRIC VALUE	IMPERIAL VALUE
Hardness (Solution Treated)	29 – 32 HRC	29 – 32 HRC
Hardness (Aged / Pre-hardened)	38 – 42 HRC	38 – 42 HRC
Tensile Strength (σb)	1264 MPa	183.4 ksi
Yield Strength (σ0.2)	1018 MPa	147.6 ksi
Elongation (δ5)	16.1 %	16.1 %
Reduction of Area (ψ)	41.9 %	41.9 %
Impact Toughness (KV, 20°C, Longitudinal)	11.0 J	8.1 ft·lb

Delivery Condition of NAK80

Black Surface, Bright Surface, Turned Surface, Grinded Surface, Poblished surface.

NAK80 Application

NAK80 steel is the preferred choice for high-gloss, mirror-finish molds and precision components:

Optical Molds: Eyeglass lenses, camera lens elements, light guides, optical diffusers.
Transparent Parts: Molds for PMMA, PC, PS, and other transparent plastics.
Automotive Lighting: Headlight lenses, tail light covers, reflector housings.
Consumer Electronics: Mobile phone covers, computer housings, display bezels.
Cosmetic Packaging: High-gloss cosmetic boxes, compacts, and containers.
Medical Devices: Syringe molds, connector molds, pharmaceutical packaging.
Food-Grade Packaging: Caps, closures, containers meeting hygiene requirements.
CD/DVD/Blu-ray Molds: Stamper-backing plates and cavity inserts.
Mold Components: Core pins, ejector sleeves, slides, and inserts for multi-cavity tools.
Precision Jigs & Fixtures: Measuring fixtures requiring dimensional stability.

Heat Treatment & Processing of NAK80 Tool Steel

Heat Treatment

NAK80 steel is typically supplied pre-hardened (38–42 HRC). The following information covers the aging treatment used during production and for post-weld re-aging.

Solution Treatment: Heat to 840–900°C, hold adequately, then quench. This dissolves alloying elements for subsequent precipitation.
Aging (Precipitation Hardening): Heat to 490–530°C, hold for 3–5 hours, then air cool. NAK80 material achieves 38–42 HRC through this aging treatment. Hardness is uniform from surface to center.
Stress Relieving: Not required for NAK80 under normal machining conditions. The pre-hardened condition eliminates the need for post-machining stress relief.

Processing Guide:

Machining: Pre-hardened NAK80 steel (38–42 HRC) machines 10–15% faster than P20 at 30 HRC. Carbide tools recommended. Excellent chip formation and tool life.
Polishing: NAK80 material offers outstanding polishability. Achieves mirror finish of Ra ≤ 0.05 μm. Step polish with SiC paper #240 to #2000, followed by diamond paste.
EDM (Electrical Discharge Machining): NAK80 mold steel features excellent EDM performance. The recast layer is thinner and easier to remove compared to conventional mold steels. Dense, smooth EDM surfaces can replace pear-skin texturing.
Welding: NAK80 tool steel is highly weldable. The heat-affected zone (HAZ) softens rather than hardens, and can be re-age hardened to restore 40 HRC. No preheating required.
Nitriding: Gas or plasma nitriding can be applied at 470–530°C for enhanced surface hardness and wear resistance. Note that nitriding may slightly reduce corrosion resistance.
Corrosion Resistance: Moderate. Material NAK80 offers better corrosion resistance than P20 but is not a stainless grade. Protective treatment recommended for humid environments.

Quality Control

Full-process control:

Raw material and manufacturer control
Test : Chemical composition, mechanical properties, UT(ultrasonic testing), specification, surface condition, straightness, etc.
Packing: Wooden case or pallet or VCI plastic film

Why Purchase NAK80 Mold Steel from Keyspark Steel?

Fully Customizable: Dimensions, heat treatment, and hardness – all adjustable per batch order.
Certified Quality: Each batch comes with MTC certificate (EN 10204 3.1/3.2) , full chemical and mechanical test report.
ESR Option: Premium quality with Electro-Slag Remelting available for critical applications.
Stable Production: Large forging and rolling capacity ensures consistent quality across orders.
Long-Term Supply: Reserved production slots for regular customers – no interruptions.
Neutral Packaging: Oiled, wrapped, and strapped.

FAQ of NAK80

Q1: What is NAK80?

A: NAK80 material is a Ni-Al-Cu precipitation hardening pre-hardened plastic mold steel developed by Daido Steel in Japan. Its delivery hardness is 37–43 HRC. It is refined by vacuum degassing and ESR remelting, with dense structure and high purity. It can be machined directly without heat treatment.

Q2: Why does NAK80 not require heat treatment before use?

A: NAK80 steel has finished solution and aging treatment at steel mill and is supplied in pre-hardened state. It gains hardness from dispersed precipitation of Ni-Al-Cu intermetallic compounds, not traditional quenched martensite strengthening. Users can directly cut, EDM and polish the steel. It removes quenching and tempering steps, and avoids heat treatment deformation and cracking risk.

Q3: Why is NAK80 suitable for mirror-polishing applications?

A: NAK80 uses low carbon design (C 0.10–0.20%). It greatly reduces carbide segregation, and prevents pinholes and polishing lines on finished surface. With high purity from vacuum melting, it can reach #8000 and above mirror finish. It fits molds for transparent parts and high-gloss appearance parts.

Q4: How does NAK80 behave during EDM compared to conventional pre-hardened steels?

A: The surface hardness of NAK80 tool steel stays stable after EDM, and will not rise. No extra work to remove hardened layer, so later processing becomes easier. This feature comes from its precipitation hardening mechanism. Base hardness comes from aged precipitates instead of quenched martensite. EDM will not form hard white layer on surface.

Q5: What happens to NAK80 after welding, and how is hardness restored?

A: NAK80 mold steel has good weldability. Its heat affected zone softens instead of turning hard and brittle like traditional quenched steel. After welding, re-aging treatment (hold around 500°C) can recover hardness to 40 HRC by secondary hardening effect. This is its special advantage over Cr-Mo pre-hardened steel such as P20 and 718H.

Q6: How does NAK80 compare with P20 and 718H in performance positioning?

A: Performance ranking: NAK80＞738H＞718H＞P20. P20 and 718H are Cr-Mo pre-hardened steels with limited polishing limit and wear resistance. NAK80 uses unique Ni-Al-Cu precipitation hardening route. Its mirror finish ability and wear resistance are better, but its overall toughness is slightly lower than 738H. Choose 738H for large thick plates or high-impact cavities. Choose NAK80 for high-gloss transparent parts and precision appearance part molds.