M300 Tool Steel (18Ni-300 Maraging Steel)
metalmaraging steel — tooling grade (ultra-high-strength, precipitation-hardened)
EOS M30018Ni-300DIN 1.2709UNS K93120Maraging 300Vascomax 300 (wrought ref.)AMS 6514 (wrought ref.)
Composition — DIN 1.2709 / UNS K93120 / AMS 6514
| Element | Min % | Max % | Notes |
|---|---|---|---|
| Ni | 17.00 | 19.000 | High Ni for martensite transformation (no carbon hardening). Ni content controls martensite start temperature (Ms ~155°C for 18Ni-300) |
| Co | 8.50 | 9.500 | Promotes Mo precipitation on ageing by reducing Mo solubility in γ matrix; lowers Ms temperature slightly |
| Mo | 4.50 | 5.200 | Primary age-hardening precipitate Ni₃Mo; also Ni₄Mo. Controls ultimate hardness — 4.5–5.2% Mo is the 18Ni-300 specification |
| Ti | 0.50 | 0.800 | Forms Ni₃Ti precipitates; secondary contribution to peak hardness. Interacts with Al to form ordered Ni₃(Al,Ti) |
| Al | 0.05 | 0.150 | Deoxidiser during atomisation; promotes ordered phase formation on ageing |
| Fe | bal. | balance | |
| C | — | 0.030 | CRITICAL: must be below 0.03%. Carbon in martensite causes brittleness and reduces toughness. 'Maraging' = martensite + ageing — no carbon hardening involved |
| Mn | — | 0.100 | |
| Si | — | 0.100 | |
| P | — | 0.010 | |
| S | — | 0.010 | |
| Zr | — | 0.010 | |
| B | — | 0.003 | Grain boundary strengthener; suppresses grain boundary failure during ageing. Critical for fatigue life in injection moulding cyclic service |
Mechanical & thermal properties — 4 conditions
| Property | LPBF as-built (XY) — soft martensite | LPBF aged 490°C/6h (XY) — tooling condition | LPBF aged 490°C/6h (Z) | LPBF aged + nitrided surface (tooling production) |
|---|---|---|---|---|
| Elastic modulus | 170–190 GPa | — | — | — |
| Yield strength (0.2%) | 900–1100 MPa | 1900–2080 MPa | 1740–1960 MPa | — |
| Ultimate tensile strength | 1000–1200 MPa | 1960–2150 MPa | 1830–2050 MPa | — |
| Elongation at break | 8.0–16.0 % | 2.0–6.0 % | 1.5–5.0 % | — |
| Hardness (HV) | — | 530–600 HV10 | — | 900–1150 HV0.1 |
| Fatigue strength | — | 700–900 MPa | — | — |
| Density | 7.95–8.05 g/cm³ | — | — | — |
| Thermal conductivity | 16.0–18.5 W/m·K | — | — | — |
| CTE | 10.2–11.2 µm/m·K | — | — | — |
Values shown as min–max where a spread is reported, otherwise as typical ± unit. Ranges reflect inter-source variation, not single-sample scatter. All values are for AM-processed specimens unless noted.
Engineering considerations
- Ageing protocol for tooling: 490°C / 4–6h in vacuum furnace or nitrogen atmosphere. Peak hardness typically achieved at 5h. Do not exceed 500°C — hardness drops 2–3 HRC per 10°C over-temperature. Verify hardness with calibrated hardness tester on a coupon run with the tool batch.
- Sequence for tooling manufacture: LPBF → stress-relieve (300°C/1h, reduces distortion) → EDM/CNC machine cavity to within 0.1–0.2 mm of final dimension → age (490°C/5h) → finish grind/polish/EDM to final dimension → surface treat if required (nitriding, PVD).
- Conformal cooling channel design: minimum printable channel diameter 1.5 mm; standard tooling channel 3–6 mm. Minimum wall thickness between channel and cavity surface: 1.5–2 mm (verify by FEA at peak injection pressure). Spirolift, baffle, and turbulator geometries are printable — use optimisation to maximise flow turbulence and heat transfer coefficient.
- Distinguishing from Maraging MS1: when specifying for tooling vs. aerospace, explicitly state 'M300 (EOS tooling grade, 490°C/6h ageing)' rather than 'maraging steel' or '18Ni300' to ensure the correct material and heat treatment protocol is applied. The hardness target (50–54 HRC for M300 vs. 53–55 HRC for MS1) confirms the correct batch.
- Dimensional change on ageing: typical linear shrinkage 0.05–0.10% — account for this in pre-age final machining allowance when tolerances are ±0.01 mm or tighter.
- Surface finish for mould cavities: as-built M300 Ra 8–15 µm. Typical finishing sequence: coarse EDM → fine EDM (Ra ~1 µm) → hand polishing or abrasive blasting → final polish to Ra <0.1 µm (SPI A1 grade) for optical surfaces.
- Wear resistance for abrasive resins: glass-filled (GF) and talc-filled polymers cause accelerated cavity wear on uncoated steel. For >20% GF content, apply plasma nitriding (0.2 mm case depth, ~1050 HV) or PVD TiAlN coating (4–6 µm, 3200 HV). Both are compatible with M300.
- Fatigue life in high-cycle tooling: typical injection mould tool sees 10⁷–10⁸ cycles over lifetime. Design to <30% of endurance limit (~800 MPa) at gate/runner stress concentration points. Use FEA to verify cavity face stresses during peak injection. Gate area is the primary fatigue initiation site.
Advantages
- Near-zero dimensional change on ageing (<0.1% linear): machine cavity to tight tolerance in soft as-built state (~32 HRC), then age to 50–54 HRC — eliminates distortion risk of H13 quench-and-temper
- Achieves injection mould specification hardness (50–54 HRC) without the complex thermal management required for H13 through-hardening
- LPBF enables conformal cooling channels impossible in machined H13/P20 tooling: can reduce injection moulding cycle time 20–40%
- Uniform hardness through section thickness — superior to H13 which has through-hardening gradients in sections >100 mm
- Highest strength of any standard LPBF metal in tooling condition: UTS ~2050 MPa — withstands injection pressures up to 200 MPa without plastic deformation
- Good machinability in as-built state (32 HRC): conventional carbide machining and excellent EDM machinability enable finishing of complex cavity geometry
- Can be nitrided after ageing for enhanced wear resistance against abrasive-filled polymers (surface hardness up to 1100 HV)
- Laser micro-weld repair with matching maraging filler wire — enables cavity repair without full tooling replacement
Limitations
- Very low ductility after ageing (2–6%) — not suitable for impact-loaded structures; only for tooling predominantly under compressive or low-tensile stress
- Ageing is mandatory for tooling use — as-built 32 HRC is insufficient for production injection moulding
- High raw powder cost: M300 powder is 4–6× more expensive per kg than H13 tool steel powder. Cost-justified only for complex conformal cooling geometries where cooling efficiency improvements outweigh the material cost
- Over-ageing above 510°C causes hardness reduction via precipitate coarsening — temperature control to ±5°C is critical; record and verify every oven batch
- Susceptible to hydrogen embrittlement: avoid acid pickling without pre-bake at 200°C/4h; prohibit electroless nickel plating without special HE relief procedures
- Limited corrosion resistance vs. stainless — suitable for dry conditions; for humid or chemical environments, apply PVD TiN or CrN surface coating
- M300 is frequently confused with Maraging MS1 in quotation and procurement: both are 18Ni-300, but M300 has a tooling-specific data package and is distinguished by its ageing optimisation (490°C vs. 480°C). Always specify by EOS material code to avoid mix-up
- Limited fracture toughness data: unlike aerospace alloys, standardised KIC values for LPBF M300 are sparse — use wrought 18Ni-300 data (KIC ~70–80 MPa√m aged) as conservative estimate
Typical applications
Injection mould inserts with conformal cooling channels (automotive, consumer goods)Die-casting tooling for aluminium and zinc alloy casting insertsHigh-pressure press forming dies and deep-drawing toolsInjection mould hot-runner manifold componentsPrecision jigs, fixtures, and gauges requiring high dimensional stabilityMotorsport gear and drivetrain components requiring extreme strengthAerospace structural brackets and fasteners (ultra-high-strength, non-fracture-critical)Textile machinery and packaging equipment tooling (wear-resistant)
Industries
toolingaerospacemotorsportindustrial
Standards & certifications
Compatible AM processes (1)
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Last reviewed: 2026-05-13 · v1 · Sources: eos-m300-datasheet-2022, bai-2021-m300-lpbf, vieira-2020-maraging-tooling, kempen-2011-ms1, ASTM-E8, ASTM-E18
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