440B Stainless Steel: Medium-Carbon Martensitic Grade For Enhanced Wear Resistance

440B is a medium-carbon variant in the 440 series (C=0.75%-0.95%, Cr=16.0%-18.0%). It has higher hardness and wear resistance than 440A, and better toughness than 440C. As a mid-range option in the 440 series, it is suitable for components requiring high wear resistance and moderate toughness.

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: SUS440B (JIS), EN 1.4109, UNS S44003

Performance Advantages: Higher wear resistance than 440A; better toughness than 440C; good edge retention, suitable for cutting tools; good dimensional stability after heat treatment; moderate corrosion resistance in dry environments.

Typical Applications: High-grade kitchen knives, hunting knives, tactical knives, bearing balls and races, high-pressure valve seats, precision cutting tools, mold cores, marine hardware.

Practical Q&A

Q1: What is the difference between 440B and 440A/440C? A1: Carbon content: 440A (0.60-0.75%) < 440B (0.75-0.95%) < 440C (0.95-1.20%). Hardness: 440A (55-57HRC) < 440B (57-59HRC) < 440C (60-62HRC). Toughness is the opposite: 440A > 440B > 440C.

Q2: How to avoid brittleness during heat treatment of 440B? A2: Adopt quenching at 1020-1060℃, oil cooling + tempering at 180-220℃, air cooling. Avoid tempering at 300-450℃, as this temperature range will cause temper brittleness, significantly reducing impact toughness.

Q3: Is 440B suitable for high-precision components? A3: Yes. Its dimensional stability after heat treatment is good, with a linear expansion coefficient of 10.5×10⁻⁶/℃ (20-100℃), lower than austenitic stainless steel. It is suitable for bearing races and mold cores with strict dimensional tolerance.

Q4: How to improve the corrosion resistance of 440B? A4: After heat treatment, perform passivation with 20-30% nitric acid solution (20-30 minutes at room temperature) to thicken the oxide film; apply anti-rust oil in harsh environments; avoid contact with chloride ions and acidic media.

Q5: Can 440B be used for high-speed rotating components? A5: Yes. Its high hardness (57-59HRC) and good wear resistance ensure long service life for high-speed bearing rings and balls. Sufficient lubrication is required to avoid dry friction and rapid wear.