Key Feature

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

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

Common Designations

UNS S44004
AISI 440C
ASTM A276 (Stainless Steel Bars)
EN 1.4125, X105CrMo17
JIS SUS440C

Part of 440 series: 440A (lower carbon), 440B, 440C (highest carbon).

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
Machinability: 40% of B1112 steel

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.

Available Forms

Rounds: 6mm - 150mm diameter
Squares: 6mm - 75mm
Flats: Various sizes
Hexagons: 6mm - 50mm
Billets: For forging applications

Generally available in smaller sizes suitable for precision components.

Surface Conditions

Hot Rolled: Black bar
Cold Drawn: Bright bar
Centerless Ground: Precision ground
Polished: Mirror finishes available
Peeled/Turned: For improved machining

High-quality surface finishes required for many 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.

Machining Characteristics

• Very difficult to machine when hardened
• Best machined in annealed condition• High tool wear due to carbides
• Requires specialized tooling• Cryogenic treatment improves machinability

Typically machined in soft condition, then heat treated; hardened material is extremely difficult to machine.

Key Standards

ASTM A276 440C: Stainless Steel Bars
ASTM A484: General Requirements
AMS 5630 (Aerospace)
EN 10088-3: Stainless Steel Bars
JIS G4303: Stainless Steel Bars

Often supplied to custom requirements and heat treatment specifications.

Common Applications

• Precision Bearings: Ball bearing races, roller bearing components
• Cutlery Manufacturing: High-end knife blades, surgical scalpels, razor blades
• Surgical Instruments: Orthopedic tools, dental instruments, specialized implants
• Industrial Components: Valve seats, pump shafts, measuring tools, gauges
• Mold Making: Plastic injection mold cores, high-wear inserts
• Aerospace/Defense: Aircraft bearing components, specialized weapon parts
• Food Processing: High-wear cutting blades, slicers, specialized cutters

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