Grade 420
Martensitic stainless · AISI 420 / SAE 51420, UNS S42000, EN 1.4021
Type 420 High-Carbon Martensitic Stainless (Cutlery Grade), martensitic stainless steel.
Data sheet
| Designations | AISI 420 / SAE 51420 · UNS S42000 · EN 1.4021 (X20Cr13) |
|---|---|
| Standards | ASTM A276, EN 10088-3 |
Metallurgy
Reference data for Type 420 High-Carbon Martensitic Stainless (Cutlery Grade), against ASTM A276, EN 10088-3.
Elemental composition
X20Cr13 to 1.4021
- Chromium 13,00%12,00–14,00%
- Carbon 0,20%0,15–0,25%
- Other additions 1,04%Mn, Si, P, S
- Iron 85,77%Balance
Proportions use the normalised midpoint of each specified range. The midpoint is a derived figure, not something the standard states: read the table for what is actually specified.
Performance profile
Comparative scores out of ten, for weighing one grade against another
These are relative ratings, not measured properties, and they carry no units. Use them to narrow a shortlist, then work from the specified values.
Composition as specified
| Element | Specified | Nominal |
|---|---|---|
| Iron Fe | Balance | 85,77% |
| Carbon C | 0,15–0,25% | 0,20% |
| Chromium Cr | 12,00–14,00% | 13,00% |
| Manganese Mn | max 1,00%cap | 0,50% |
| Silicon Si | max 1,00%cap | 0,50% |
| Phosphorus P | max 0,040%cap | 0,020% |
| Sulphur S | max 0,030%cap | 0,015% |
A cap is a ceiling, not a quantity: a heat may contain far less. The nominal column is the midpoint of each range, used for the chart's proportions only.
Mechanical and physical properties
| Property | Value |
|---|---|
| Tensile strength, ultimate | 650 MPa94,3 ksi |
| Yield strength, 0,2% offset | 340 MPa49,3 ksi |
| Elongation at break | 20% |
| Hardness | 215 HBW / 95 HRB |
| Modulus of elasticity | 200 GPa29 Mpsi |
| Density | 7,75 g/cm³0,28 lb/in³ |
| Thermal conductivity | 24,9 W/(m·K)172,6 BTU·in/(hr·ft²·°F) |
| Thermal expansion | 10,5 µm/(m·K)5,8 µin/(in·°F) |
Test condition not yet confirmed. These figures are typical values for the grade; the condition a bar was supplied in changes them materially, so ask us for the mill certificate before designing to a number.
Pitting resistance
PREN 13
Cr + 3,3 Mo + 16 N, across the full specified composition
- Freshwater0–20
- Brackish20–32
- Seawater32–40
- Extreme offshoreover 40
A standard states its elements as ranges, so a grade has a window rather than a single score. The bar is that window; the tick is the midpoint.
Corrosion and fabrication
Chloride and marine service
Poor; requires clean, polished, fully hardened/stress-relieved condition for optimum corrosion resistance.
Acidic and chemical media
Resistant to fresh water, steam, blood, urine, food acids, and mild petroleum products.
Sensitisation and thermal behaviour
Corrosion resistance severely degraded if tempered between 425°C–600°C due to chromium carbide precipitation.
Welding
Very Poor; rarely welded due to severe martensitic cracking; requires 250°C preheat and immediate post-weld annealing.
Machining and cold forming
Machinability index 50% relative to AISI 1212. Poor; formed exclusively in the soft annealed state.
Where it is used
- Surgical instruments (scalpels, forceps, surgical scissors)
- Professional cutlery, hunting knives, and shear blades
- Needle valves, valve balls, and plunger bushings
- Brake discs for motorcycles and mountain bikes
Medical / Surgical · Cutlery & Tooling · Motorsports · Oil & Gas
Performance scores in full
The same six scores the profile plots, as numbers.
| Property | 420 |
|---|---|
| Corrosion resistance | 5.3 / 10 |
| Weldability | 3 / 10 |
| High-temperature resistance | 6 / 10 |
| Tensile strength | 8.5 / 10 |
| Cold formability | 4.5 / 10 |
| Machinability | 5.8 / 10 |
This page is guidance for selecting a grade, not a specification. Design to the governing standard and the mill certificate for the heat you are supplied.
The specifications and data on this site are provided for general information only. Verify any real-world project with a qualified metallurgist before relying on these figures. We take no responsibility for the use and application of this information.