SUS440C Stainless Steel: High-Carbon Martensitic Grade for Ultra-High Wear Resistance & Precision

SUS440C is the high-carbon variant in the SUS440 series (C=0.95-1.20%, Cr=16.0-18.0%), with the highest hardness and wear resistance in the series. After heat treatment, the hardness can reach 60-62HRC, and it has excellent edge retention and dimensional stability. It is the preferred material for ultra-high wear resistance and high-precision components.

Core Parameters

Chemical Composition (wt%): C=0.95-1.20, Si≤1.00, Mn≤1.00, P≤0.040, S≤0.030, Cr=16.00-18.00, Fe=Balance

Mechanical Properties (Quenched & Tempered): Tensile Strength ≥950MPa, Yield Strength ≥700MPa, Elongation ≥10%, Hardness 60-62HRC

Service Temperature: -20℃ to 250℃ (continuous service)

Equivalent Grades: EN 1.4125, UNS S44004, GB/T 9Cr18

Performance Advantages: Ultra-high hardness and excellent wear resistance, which is 1.5-2 times that of SUS440B; outstanding edge retention, suitable for high-end cutting tools; excellent dimensional stability after heat treatment, small deformation; can be polished to a mirror finish (Ra≤0.05μm); moderate corrosion resistance in dry environments.

Typical Applications: High-end professional chef's knives, hunting knives, tactical knives, surgical scalpels, high-speed and high-load bearing balls and raceways, ultra-precision mold cores and cavities, high-pressure valve seats for harsh environments, measuring tools (such as micrometers), aerospace precision components.

Practical Q&A

Q1: What heat treatment process is required for SUS440C to achieve ultra-high hardness? A1: Quench at 1050-1090℃, oil cool + temper at 150-200℃, air cool. This process can maximize the hardness (60-62HRC) and wear resistance. It should be emphasized that the tempering temperature must not exceed 200℃, otherwise the hardness will decrease significantly (e.g., hardness ≤58HRC at 250℃).

Q2: Why is SUS440C the preferred material for high-end professional knives? A2: Its ultra-high hardness (60-62HRC) ensures excellent edge retention, which can maintain sharpness after cutting hard materials for a long time; the mirror-polished surface is easy to clean; moderate corrosion resistance can avoid rust during daily use (after proper maintenance).

Q3: What is the wear resistance of SUS440C compared with other martensitic stainless steels? A3: In the standard abrasive wear test, the wear loss of SUS440C after 1000 cycles is only 0.01g, while that of SUS440B is 0.018g and SUS420J2 is 0.02g. It has the best wear resistance among common martensitic stainless steels.

Q4: What are the limitations of SUS440C? A4: Its ultra-high hardness leads to low toughness (impact toughness ≤15J), making it prone to chipping or cracking under large impact loads; it is difficult to machine, requiring special tools and processes; the corrosion resistance is limited, and it is not suitable for corrosive environments with high chloride ions.

Q5: What are the key points of grinding SUS440C precision components? A5: Use diamond grinding wheels (resin bond, 400#-600#) for grinding, as ordinary alumina grinding wheels have low efficiency and fast wear; control the grinding speed at 15-20m/s, and use sufficient coolant (emulsion) to avoid overheating and hardness reduction; adopt step-by-step grinding to ensure dimensional accuracy.