Overview
SS440C (AISI 440C Stainless Steel) is the highest-carbon grade within the 440 Series Martensitic Stainless Steel Family. It is renowned for its exceptional hardness, outstanding wear resistance, superior edge retention, and excellent dimensional stability after heat treatment.
SS440C is often considered the premium bearing-grade stainless steel and one of the hardest stainless steels available. It is extensively used in high-performance bearings, surgical instruments, knife blades, aerospace components, molds, valve parts, and precision engineering applications.
Compared with SS440A and SS440B, SS440C offers the highest hardness and wear resistance, although with slightly reduced toughness and corrosion resistance.
Material Specification
| Property | Value |
|---|---|
| Material Designation | AISI 440C |
| Material Family | High Carbon Martensitic Stainless Steel |
| UNS Number | S44004 |
| EN Grade | 1.4125 |
| Density | 7.70–7.75 g/cm³ |
| Magnetic Property | Magnetic |
| Standard Forms | Bar, Rod, Plate, Sheet, Forgings |
Chemical Composition
| Element | Content (%) |
|---|---|
| Iron (Fe) | Balance |
| Chromium (Cr) | 16.0–18.0 |
| Carbon (C) | 0.95–1.20 |
| Manganese (Mn) | ≤1.00 |
| Silicon (Si) | ≤1.00 |
| Phosphorus (P) | ≤0.040 |
| Sulfur (S) | ≤0.030 |
| Molybdenum (Mo) | ≤0.75 |
| Nickel (Ni) | ≤0.75 |
Mechanical Properties
Annealed Condition
| Property | Value |
|---|---|
| Tensile Strength | 760–950 MPa |
| Yield Strength | ≥450 MPa |
| Elongation | ≥10% |
| Hardness | ≤285 HB |
| Elastic Modulus | 200 GPa |
Hardened & Tempered Condition
| Property | Value |
|---|---|
| Tensile Strength | 1500–1900 MPa |
| Yield Strength | 1200–1600 MPa |
| Hardness | 58–62 HRC |
| Wear Resistance | Outstanding |
| Contact Fatigue Resistance | Outstanding |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.74 g/cm³ |
| Melting Point | 1450–1510°C |
| Thermal Conductivity | 24.2 W/m·K |
| Electrical Resistivity | 0.60 μΩ·m |
| Thermal Expansion Coefficient | 10.2 × 10⁻⁶/K |
| Specific Heat Capacity | 460 J/kg·K |
Corrosion Resistance
| Environment | Performance |
|---|---|
| Indoor Environment | Excellent |
| Atmospheric Exposure | Good |
| Fresh Water | Good |
| Food Contact Applications | Good |
| Industrial Environment | Moderate |
| Marine Environment | Fair |
| Chloride Environment | Limited |
SS440C provides the highest hardness among stainless steels but slightly lower corrosion resistance than SS440A because of its higher carbon content.
Proper polishing and passivation can significantly improve corrosion performance.
Heat Treatment
Annealing
| Parameter | Value |
|---|---|
| Temperature | 850–900°C |
| Cooling Method | Furnace Cool |
Hardening
| Parameter | Value |
|---|---|
| Temperature | 1010–1070°C |
| Quenching | Oil or Air |
Tempering
| Parameter | Value |
|---|---|
| Temperature | 150–370°C |
| Purpose | Improve Toughness & Stability |
Typical Hardness
| Condition | Hardness |
|---|---|
| Annealed | 255–285 HB |
| Hardened | 58–62 HRC |
| Cryogenic Treated | Up to 63 HRC |
International Equivalent Grades
| Standard | Equivalent Grade |
|---|---|
| ASTM / AISI (USA) | 440C |
| UNS | S44004 |
| EN (Europe) | 1.4125 |
| DIN (Germany) | X105CrMo17 |
| JIS (Japan) | SUS440C |
| GB/T (China) | 9Cr18Mo |
| ISO | X105CrMo17 |
Available Forms
| Product Type | Availability |
|---|---|
| Round Bar | Yes |
| Flat Bar | Yes |
| Stainless Plate | Yes |
| Stainless Sheet | Yes |
| Precision Ground Bar | Yes |
| Bearing Grade Bar | Yes |
| Forgings | Yes |
Typical Applications
Bearing Industry
- Ball Bearings
- Roller Bearings
- Bearing Races
- Precision Bearing Components
- Aerospace Bearings
Knife Manufacturing
- Premium Kitchen Knives
- Tactical Knives
- Outdoor Knives
- Hunting Knives
- Industrial Cutting Blades
Medical Industry
- Surgical Instruments
- Dental Instruments
- Orthopedic Tools
- Medical Cutting Equipment
Aerospace Industry
- Precision Shafts
- Wear Components
- Control System Parts
- High Precision Bearings
Valve & Pump Industry
- Valve Seats
- Mechanical Seals
- Wear Rings
- Pump Components
Mold & Tool Industry
- Injection Mold Components
- Precision Dies
- Measuring Instruments
- Gauge Components
Manufacturing Characteristics
| Manufacturing Process | Rating |
|---|---|
| CNC Turning | Good |
| CNC Milling | Good |
| Precision Grinding | Outstanding |
| Heat Treatment | Outstanding |
| Polishing | Excellent |
| Forging | Excellent |
| Drilling | Moderate |
| EDM Machining | Excellent |
| Welding | Poor |
Advantages
Exceptional Hardness
Can achieve up to 62 HRC after heat treatment.
Outstanding Wear Resistance
One of the most wear-resistant stainless steels available.
Superior Edge Retention
Maintains sharp cutting edges for extended periods.
Excellent Bearing Performance
Industry-standard stainless bearing material.
Good Corrosion Resistance
Better than tool steels and carbon steels.
Excellent Dimensional Stability
Ideal for precision engineering applications.
Limitations
Lower Toughness Than SS440A
High hardness reduces impact resistance.
More Difficult to Machine
Requires rigid tooling and optimized machining strategies.
Poor Weldability
Generally not recommended for welded structures.
Limited Marine Performance
Not suitable for prolonged saltwater immersion.
Comparison with Other Stainless Steels
| Property | SS440C | SS440B | SS440A | SS420 | SS304 |
|---|---|---|---|---|---|
| Hardness | Outstanding | Very High | High | High | Medium |
| Wear Resistance | Outstanding | Outstanding | Excellent | Excellent | Moderate |
| Edge Retention | Outstanding | Excellent | Good | Good | Poor |
| Corrosion Resistance | Moderate | Good | Better | Moderate | Excellent |
| Toughness | Lower | Good | Better | Good | Excellent |
| Heat Treatable | Yes | Yes | Yes | Yes | No |
Comparison with Common Blade & Bearing Materials
| Material | Hardness (HRC) | Wear Resistance | Corrosion Resistance |
|---|---|---|---|
| SS440C | 58–62 | Outstanding | Moderate |
| SS440B | 56–60 | Excellent | Good |
| SS440A | 54–58 | Good | Better |
| VG10 | 60–61 | Outstanding | Excellent |
| D2 Tool Steel | 58–62 | Outstanding | Fair |
| M390 | 60–62 | Exceptional | Excellent |
Available Surface Finishes
Mill Finishes
- Ground Finish
- Bright Finish
- Cold Finished Surface
Decorative Finishes
- Mirror Polish
- Satin Finish
- Hairline Finish
- Brushed Finish
Functional Finishes
- Passivation
- Electropolishing
- DLC Coating
- PVD Coating
- Black Oxide Coating
- Cryogenic Treatment
Frequently Asked Questions (FAQ)
What is SS440C stainless steel?
SS440C is a high-carbon martensitic stainless steel known for its exceptional hardness, wear resistance, and bearing-grade performance.
What is SS440C used for?
Typical applications include:
- Bearings
- Knife Blades
- Surgical Instruments
- Valve Components
- Aerospace Parts
- Precision Mechanical Components
Is SS440C magnetic?
Yes. SS440C is fully magnetic in both annealed and hardened conditions.
Can SS440C be heat treated?
Yes. SS440C is specifically designed for hardening and tempering and can achieve hardness levels up to 62 HRC.
What is the difference between SS440C and SS440A?
| Property | SS440C | SS440A |
|---|---|---|
| Hardness | Higher | Lower |
| Wear Resistance | Better | Lower |
| Corrosion Resistance | Lower | Better |
| Toughness | Lower | Better |
What is the difference between SS440C and D2 Tool Steel?
| Property | SS440C | D2 |
|---|---|---|
| Corrosion Resistance | Better | Lower |
| Wear Resistance | Similar | Similar |
| Toughness | Better | Lower |
| Stainless | Yes | No |
Is SS440C good for bearings?
Yes. SS440C is the most commonly used stainless bearing steel in aerospace, medical, and industrial applications.
Can SS440C rust?
Although it offers good corrosion resistance, prolonged exposure to saltwater or aggressive chemicals may cause corrosion.
Why is SS440C popular for premium knives?
Because it combines:
- Exceptional Hardness
- Outstanding Edge Retention
- Good Corrosion Resistance
- High Wear Resistance
making it one of the most respected traditional knife steels.
Does GCNOV provide custom manufacturing services for SS440C?
Yes. GCNOV provides:
- CNC Machining
- Precision Grinding
- Heat Treatment
- Bearing Component Manufacturing
- Knife Component Manufacturing
- Surface Finishing
- Passivation
- Cryogenic Treatment
- Prototype Development
- Low-Volume Production
- Mass Production