SUS440B Stainless Steel: Medium-Carbon High-Carbon Martensitic Grade for Enhanced Wear Resistance

SUS440B is the medium-carbon variant in the SUS440 series (C=0.75-0.95%, Cr=16.0-18.0%), with higher hardness and wear resistance than SUS440A, and better toughness than SUS440C. As a mid-range product in the SUS440 series, it is suitable for components requiring high wear resistance and moderate toughness, filling the gap between SUS440A and SUS440C.

Core Parameters

Chemical Composition (wt%): C=0.75-0.95, 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 ≥860MPa, Yield Strength ≥620MPa, Elongation ≥12%, Hardness 57-59HRC

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

Equivalent Grades: EN 1.4109, UNS S44003, GB/T 8Cr17

Performance Advantages: Higher wear resistance than SUS440A; better toughness than SUS440C (impact toughness ≥18J); excellent edge retention, suitable for cutting tools and precision components; good dimensional stability after heat treatment; moderate corrosion resistance in dry environments; easy to grind and polish.

Typical Applications: High-grade kitchen knives, hunting knives, tactical knives, bearing rings and balls for medium-speed and medium-load, high-pressure valve seats and cores, precision cutting tools, mold cores for high-wear plastic molding, marine hardware, aerospace components with low impact requirements.

Practical Q&A

Q1: What is the performance difference between SUS440B and SUS440A/C? A1: Carbon content gradient: SUS440A (0.60-0.75%) < SUS440B (0.75-0.95%) < SUS440C (0.95-1.20%). Corresponding performance gradient: Hardness (55-57HRC < 57-59HRC < 60-62HRC), wear resistance (gradually increased), toughness (gradually decreased). SUS440B is a balanced choice between the three.

Q2: How to avoid temper brittleness during heat treatment of SUS440B? A2: Strictly control the tempering temperature, avoid the range of 300-450℃. The optimal tempering temperature is 180-220℃, which can ensure high hardness and avoid temper brittleness. After tempering, cool in air quickly to further reduce the risk of brittleness.

Q3: Is SUS440B suitable for high-precision bearing components? A3: Yes. Its good dimensional stability (linear expansion coefficient 10.5×10⁻⁶/℃) and high hardness (57-59HRC) make it suitable for medium-speed and medium-load bearing rings and balls. It can ensure the rotation accuracy and service life of bearings, and the cost is lower than SUS440C.

Q4: What measures can be taken to improve the corrosion resistance of SUS440B in humid environments? A4: After heat treatment, perform passivation treatment with 25% nitric acid + 2% hydrofluoric acid mixed solution (room temperature, 20 minutes) to form a thick and dense oxide film; apply anti-rust oil or ceramic coating on the surface; store in a dry and ventilated environment to avoid moisture accumulation.

Q5: Can SUS440B be used for high-speed rotating components? A5: It can be used for low-to-medium speed rotating components (rotating speed ≤3000r/min). For high-speed rotating components (rotating speed >3000r/min), it is recommended to use SUS440C with higher hardness and wear resistance, and ensure sufficient lubrication to reduce friction and wear.