Grade 440C
Martensitic stainless · AISI 440C / SAE 51440C, UNS S44004, EN 1.4125
Type 440C Ultra-High Carbon Martensitic Stainless (Bearing Steel), martensitic stainless steel.
Data sheet
| Designations | AISI 440C / SAE 51440C · UNS S44004 · EN 1.4125 (X105CrMo17) |
|---|---|
| Standards | ASTM A276, ASTM A580, AMS 5630 |
Metallurgy
Reference data for Type 440C Ultra-High Carbon Martensitic Stainless (Bearing Steel), against ASTM A276, ASTM A580, AMS 5630.
Elemental composition
X105CrMo17 to 1.4125
- Chromium 17,00%16,00–18,00%
- Molybdenum 0,50%max 0,75%
- Carbon 1,08%0,95–1,20%
- Other additions 1,04%Mn, Si, P, S
- Iron 80,39%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 | 80,39% |
| Carbon C | 0,95–1,20% | 1,08% |
| Chromium Cr | 16,00–18,00% | 17,00% |
| Molybdenum Mo | max 0,75%cap | 0,50% |
| 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 | 760 MPa110,2 ksi |
| Yield strength, 0,2% offset | 450 MPa65,3 ksi |
| Elongation at break | 14% |
| Hardness | 250 HBW / 98 HRB |
| Modulus of elasticity | 200 GPa29 Mpsi |
| Density | 7,65 g/cm³0,28 lb/in³ |
| Thermal conductivity | 24,2 W/(m·K)167,8 BTU·in/(hr·ft²·°F) |
| Thermal expansion | 10,2 µm/(m·K)5,7 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 18,65
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
Moderate; requires passivated and mirror-polished surface to withstand mild atmospheric halides.
Acidic and chemical media
Resistant to fresh water, domestic sewage, petroleum products, and mild acids.
Sensitisation and thermal behaviour
Large volume of primary chromium carbides (M7C3 and M23C6); not used in welded or sensitizing conditions.
Welding
Extremely Poor / Not Recommended; excessive hardenability causes catastrophic cracking without complex thermal procedures.
Machining and cold forming
Machinability index 35% relative to AISI 1212. Extremely low; limited to blanking/coining in fully spheroidize-annealed condition.
Where it is used
- Precision ball bearings, roller bearings, and instrument bearing races
- High-performance tactical knifemaking blades
- Valve seats, choke stems, and regulator needle valves
- Industrial rolling shear cutters and surgical chisels
Bearings & Precision Components · Cutlery & Tactical · Aerospace · Energy
Performance scores in full
The same six scores the profile plots, as numbers.
| Property | 440C |
|---|---|
| Corrosion resistance | 5.8 / 10 |
| Weldability | 1.5 / 10 |
| High-temperature resistance | 6.2 / 10 |
| Tensile strength | 9.8 / 10 |
| Cold formability | 2.5 / 10 |
| Machinability | 4 / 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.