420 Stainless Steel
metalmartensitic stainless steel
AISI 420UNS S42000EN 1.4021X20Cr13SUS420J1420 SS13Cr stainless
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 |
| P | — | 0.040 | |
| S | — | 0.030 | |
| Mo | — | 0.500 | Optional addition in some grades for improved corrosion and toughness |
| Ni | — | 0.750 |
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
Industries
toolingindustrialautomotivefood-processing
Compatible AM processes (1)
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Related calculators
NDT SelectorSelect the right non-destructive testing method for your AM part. Inputs: material class, defect focus, geometry, production volume, and criticality. Ranked scorecard across CT, X-ray, UT, FPI, MPI, eddy current, and visual inspection with detection limits and standard references.LPBF Porosity PredictorPredict lack-of-fusion and keyhole porosity from laser parameters. Maps VED and normalised enthalpy to relative density and flags dangerous regimes.Surface Treatment SelectorRank post-print surface treatments (shot peening, electropolishing, tumbling, PVD, and more) against Ra target, material, fatigue criticality, and corrosion requirements.Powder Characterisation TrackerScore a powder batch against key qualification metrics — particle size distribution, flowability, apparent/tap density, moisture, and oxygen content.HT AdvisorStandard stress-relief, solution, and aging cycles for AM metals (Ti-6Al-4V, IN718, 17-4PH, AlSi10Mg, 316L, CuCrZr) per AMS, ASTM F3301, and AMS 5664.
Last reviewed: 2026-05-13 · v1 · Sources: sandvik-420-am-2022, demir-2017-420ss-lpbf, jiang-2020-420ss-hardening
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