440C
440C is the highest-carbon martensitic stainless steel grade. It delivers extreme hardness and outstanding wear resistance after quenching and tempering, paired with moderate corrosion resistance.
Typical Chemical Composition
- Chromium (Cr): 16.0%–18.0% – Provides stainless passive film for basic anti-corrosion performance
- Carbon (C): 0.95%–1.20% – Ultra-high carbon is the core element for achieving ultra-high hardness post quenching
- Manganese (Mn): ≤1.00%
- Silicon (Si): ≤1.00%
- Molybdenum (Mo): 0.40%–0.70% – Improves wear resistance and hardenability
- Balance: Iron
Core Material Properties
- Ultra-High Hardness & Superior Wear Resistance After full quenching and low-temperature tempering, hardness can reach 58–62 HRC, ranking top among standard stainless steels. Perfect for components subject to long-term sliding friction and abrasion.
- Moderate Corrosion Resistance Better rust resistance than 420 martensitic steel, yet far inferior to 304/316 austenitic stainless steel. It withstands dry air, fresh water and mild organic media, but will corrode under salt spray, acid or continuous sweat exposure.
- Fully Heat-Treatable Soft and machinable in annealed condition; quenching plus tempering drastically boosts hardness, yield strength and abrasion resistance.
- Ferromagnetic Property Magnetic in all metallurgical states, unsuitable for electronic assemblies sensitive to magnetic interference.
- Low Ductility High carbon and chromium carbides reduce toughness. It is prone to cracking during heavy cold forming; strict sintering parameter control is required for MIM manufacturing.
- Temperature Limitation Long-term operating temperature is limited below 200°C; sustained high temperature will cause hardness loss and structural softening.
Machining & MIM Process Adaptability
- Metal Injection Molding (MIM) 440C powder is available for fabricating tiny complex high-hardness functional parts. Sintering atmosphere must be precisely regulated to avoid decarburization or excess carbide precipitation. Widely used for miniature bearings, cutting tips and precision sliding cores.
- Compatible Surface Treatments Supports mirror polishing, sandblasting, passivation and PVD coating. Mirror polishing yields ultra-smooth surfaces for precision contact components.
- Standard Heat Treatment Route Full annealing (softening for forming) → high-temperature quenching → low-temperature tempering to eliminate quenching stress while retaining maximum hardness.
Advantages & Disadvantages
Advantages
- Highest attainable hardness and wear resistance among common stainless steel grades
- Better corrosion resistance than 410 / 420 martensitic stainless steel
- Excellent polishing performance for ultra-smooth precision contact surfaces
- High surface compressive strength, long service life under continuous friction
Disadvantages
- Poor corrosion resistance against salt, acid and coastal humid environments
- Low toughness and ductility, easy to crack under impact load
- Strong magnetism, cannot be used for magnetic-sensitive equipment
- Strict sintering atmosphere control required for MIM to prevent carbon imbalance defects
- Higher raw material cost than grade 420
Typical Applications
- Precision Wear Parts: Miniature bearing components, high-hardness sliding valve cores, gear friction inserts
- Cutting & Medical Tools: Micro cutting blades, hard-tip surgical instruments with low corrosion demand
- Consumer Hardware: High-end watch bearing parts, precision lock cores
- Industrial Precision Components: Meter valve spools, wear-resistant miniature mold inserts
