420 Stainless Steel

metal

martensitic stainless steel

AISI 420UNS S42000EN 1.4021X20Cr13SUS420J1420 SS13Cr stainless

420 Stainless Steel 3D printed component

Density

7.75 g/cm³

YS (LPBF as-built (XY) — soft martensite)

950–1250 MPa

UTS (LPBF as-built (XY) — soft martensite)

1200–1600 MPa

Elongation (LPBF as-built (XY) — soft martensite)

1.0–7.0 %

Elastic modulus

190–210 GPa

Thermal conductivity

22.0–28.0 W/m·K

Composition — UNS S42000 / AISI 420

Element	Min %	Max %	Notes
Fe	bal.		balance
Cr	12.00	14.000	Provides corrosion resistance via Cr₂O₃ passive film. Minimum 11.5% to be defined as 'stainless'. Higher Cr in 420 vs carbon steels is the key corrosion advantage over H13.
C	0.15	0.400	Higher C than 410 SS (max 0.15%). Carbon enables martensitic hardening to HRC 50–52. Critical to control during LPBF to avoid carbide precipitation at grain boundaries.
Mn	—	1.000
Si	—	1.000	Deoxidiser; improves oxidation resistance

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Mechanical & thermal properties — 2 conditions

Property	LPBF as-built (XY) — soft martensite	LPBF hardened + tempered (1025°C oil quench + 150–200°C / 2h)
Elastic modulus	190–210 GPa	200 GPa
Yield strength (0.2%)	950–1250 MPa	1400–1750 MPa
Ultimate tensile strength	1200–1600 MPa	1600–1950 MPa
Elongation at break	1.0–7.0 %	1.0–6.0 %
Charpy impact	—	8.0–18.0 J
Density	7.75 g/cm³	—
Relative density	98.5–99.8 %	—
Thermal conductivity	22.0–28.0 W/m·K	—
CTE	9.8–10.8 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

Use 420 SS over H13 when corrosion from moulded resin or environment is a concern — H13 corrodes in PVC moulding without coating
Use H13 over 420 SS when thermal shock resistance or elevated temperature toughness is required (die casting, extrusion dies)
Machine conformal cooling channels in as-built condition (HRC ~40) before final hardening to avoid tool wear in hard material
Design cooling channels with wall thickness ≥3 mm from cavity surface to avoid thermal gradient cracking on hardening
Stress relief at 600–650°C before hardening is strongly recommended to minimise quench distortion in LPBF parts
EDM is the preferred method for final cavity geometry fine-tuning in hard condition (post Q+T) — conventional machining becomes difficult above HRC 48
For PVC moulding: chrome plating or PVD TiN coating on top of hardened 420 SS is standard practice to further protect against Cl⁻ attack from HCl outgassing
Minimum wall thickness: ≥1.0 mm for structural integrity; ≥0.5 mm for non-load-bearing features

Advantages

Highest hardness achievable in a corrosion-resistant stainless steel (HRC 50–52 after Q+T)
Superior corrosion resistance over H13 and P20 tool steels in humid, acidic, or halide environments
Ideal for injection moulding of corrosive resins (PVC, PTFE-filled, FR grades) where H13 would corrode
LPBF enables conformal cooling channels inaccessible in conventional tool steel machining
As-built condition is machinable (HRC ~40) — EDM and grinding possible before final hardening
Good wear resistance after hardening — suitable for high-production moulding (>1 million shots)

Limitations

Low toughness in hardened condition (Charpy ~12 J) — avoid impact loading; design out stress concentrations
Quenching distortion risk — oil quench from 1025°C causes dimensional change; design for grind allowance
Hot cracking susceptibility in LPBF due to C content (0.15–0.40%) — requires preheat (100–200°C) and optimised scan strategy
Limited elevated temperature performance — loses hardness above ~300°C; not suitable for die casting (use H13)
Stress relief before hardening is mandatory for LPBF parts — skipping causes excessive distortion on quench
Carbon content variation in LPBF can lead to inhomogeneous hardness distribution — characterise hardness across build height
Limited LPBF supplier ecosystem compared to H13 and maraging steels — fewer qualified powder suppliers
Corrosion resistance, while better than H13, is still below austenitic grades (316L) — not for seawater immersion

Typical applications

Injection mould tooling inserts for corrosive resins (PVC, fire-retardant, glass-filled)Injection mould tooling in humid or wet environments where H13 would corrodeCutting tools and blades requiring corrosion resistance alongside hardnessPump components and valve seats in corrosive fluid handlingMedical surgical instruments (non-implantable, sterilisation-compatible)Food processing equipment requiring hardness and corrosion resistancePlastic injection mould cores and cavities for corrosive chemical environmentsConformal-cooled tooling inserts for faster cycle times in mould production

420 Stainless Steel

Composition — UNS S42000 / AISI 420

Mechanical & thermal properties — 2 conditions

Engineering considerations

Advantages

Limitations

Typical applications

Industries

Compatible AM processes (1)

Other metal materials

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