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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

  1. 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.
  2. 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.
  3. Fully Heat-Treatable Soft and machinable in annealed condition; quenching plus tempering drastically boosts hardness, yield strength and abrasion resistance.
  4. Ferromagnetic Property Magnetic in all metallurgical states, unsuitable for electronic assemblies sensitive to magnetic interference.
  5. 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.
  6. 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

  1. 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.
  2. Compatible Surface Treatments Supports mirror polishing, sandblasting, passivation and PVD coating. Mirror polishing yields ultra-smooth surfaces for precision contact components.
  3. 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

  1. Precision Wear Parts: Miniature bearing components, high-hardness sliding valve cores, gear friction inserts
  2. Cutting & Medical Tools: Micro cutting blades, hard-tip surgical instruments with low corrosion demand
  3. Consumer Hardware: High-end watch bearing parts, precision lock cores
  4. Industrial Precision Components: Meter valve spools, wear-resistant miniature mold inserts