AISI 440C Stainless Steel
AISI 440C is the standard martensitic stainless steel for industrial cutting tools, bearings and food-contact blades. High-carbon, 17 % Cr.
AISI 440C (UNS S44004) is the highest-carbon standard martensitic stainless steel, hardened by a population of large M₂₃C₆ primary carbides in a tempered martensite matrix. It is the default grade for industrial cutting tools that need corrosion resistance with high achievable hardness.
Standard composition: C 0.95–1.20 %, Cr 16.0–18.0 %, Mo ≤ 0.75 %, Mn ≤ 1.00 %, Si ≤ 1.00 %, Ni ≤ 0.75 %, balance Fe.
Hardness: Annealed HB 220–255; hardened HRC 58–60 (typical), maximum practical HRC 60.
Heat treatment: Austenitise 1,040–1,070 °C, oil or pressurized-gas quench, sub-zero (−80 °C) treatment to convert retained austenite, temper 160–200 °C to avoid sensitisation. Avoid tempering above 250 °C (chromium-carbide precipitation in the 400–500 °C range reduces corrosion resistance).
Properties: Best combination of corrosion resistance and hardness in the standard martensitic stainless family. Lower toughness than D2 (Charpy 6–10 J).
Applications: Food slicer blades, meat-bone granulator rotors (food recycling), surgical instruments, food-contact slitter blades, marine and outdoor cutting applications, ball bearings and valve seats.
Cross-reference: ≈ JIS SUS440C, DIN 1.4125, GB 11Cr17 (close: 9Cr18MoV / 1.4112). Note: 9Cr18MoV carries 0.1–0.2 % V and 1.0–1.3 % Mo that 440C does not, making it tougher but slightly less hard. See 9Cr18MoV vs 440C for the field differences.
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