Key Feature

The Premium Ultra-Hard Martensitic Piping Grade. Exceptionally high carbon content (0.95-1.20%) enables extreme hardness (up to 62 HRC) and superior wear/edge retention for critical applications in tubular form.

The hardest standard stainless steel in pipe form, used where maximum hardness and wear resistance are required.

Common Designations

UNS S44004
AISI 440C
ASTM A511 (Seamless Mechanical Tubing)EN 1.4125, X105CrMo17
JIS SUS440C

ASTM A511 is commonly used for seamless mechanical tubing applications.

Chemical Composition (Typical wt.%)

C: 0.95 - 1.20Cr: 16.0 - 18.0
Mo: 0.40 - 0.65Mn: ≤ 1.00
Si: ≤ 1.00
P: ≤ 0.040
S: ≤ 0.030

High carbon enables extreme hardness; molybdenum enhances hardenability and toughness.

Mechanical Properties (Annealed)

Tensile Strength: ≥ 750 MPa
Yield Strength: ≥ 450 MPa
Elongation: ≥ 10%
Hardness: ≤ 269 HB

Limited ductility even in annealed condition due to high carbon content.

Mechanical Properties (Hardened & Tempered)

Tensile Strength: Up to 1900 MPa
Yield Strength: Up to 1650 MPa
Hardness: Up to 62 HRCElongation: 2-5%
Impact Toughness: Low

Achieves the highest hardness of any standard stainless steel.

Physical Properties

Density: 7.70 g/cm³
Melting Range: 1370 - 1510 °C
Thermal Conductivity: 24.2 W/m·K
Strongly magnetic

High carbon content affects physical properties; always magnetic.

Heat Treatment Capability

Austenitizing: 1010-1065°C
Quenching: Oil (critical)
Tempering Range: 150-370°C
Sub-zero Treatment: Recommended
Annealing: 815-870°C, slow cool

Multiple tempering cycles often used; cryogenic treatment improves dimensional stability.

Pressure Applications

Not recommended for pressure pipingPrimarily mechanical/structuralLimited to low-pressure systems

High hardness makes it brittle and unsuitable for most pressure applications.

Corrosion Resistance

Moderate resistance to water, atmosphere, and mild chemicals. Inferior to 304/316. Requires proper passivation.

Better than tool steels but limited compared to lower-carbon stainless grades.

Welding Characteristics

Extremely difficult to weldHigh cracking susceptibilityPre-heat and Post-heat treatment mandatoryGenerally avoided for welded assemblies

Usually supplied as seamless and used in the heat-treated condition without welding.

Key Standards

ASTM A511: Seamless Mechanical Tubing
ASTM A268: General Service Pipe (limited)
AMS 5630 (Aerospace)
Custom specifications predominant

Often supplied to custom requirements rather than standard pipe specifications.

Common Applications

• Precision Bearings: Ball bearing races, roller bearing components
• Surgical Instruments: Orthopedic tool bodies, dental instrument shafts
• Cutlery Manufacturing: High-end knife barrels, razor blade components
• Industrial Components: Valve seat housings, pump shaft sleeves
• Mold Making: Plastic injection mold core tubes, high-wear inserts
• Aerospace/Defense: Aircraft bearing housings, specialized weapon components
• Food Processing: High-wear cutting system components

Where extreme hardness and wear resistance justify processing complexity in tubular form.