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

440B stainless steel is a medium-carbon variant in the 440 series, with a carbon content of 0.75-0.95%. It has higher hardness and wear resistance than 440A, and better toughness than 440C. It is a "mid-range" option in the 440 series, suitable for components that require higher wear resistance than 440A but cannot sacrifice too much 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 (EN), UNS S44003 (ASTM)

Performance Advantages: Higher wear resistance than 440A; better toughness than 440C; good edge retention, suitable for cutting tools requiring sharpness retention; good dimensional stability after heat treatment; magnetic; moderate machinability.

Typical Applications: High-grade kitchen knives, hunting knives, tactical knives, bearing balls and races, high-pressure valve seats and stems, precision cutting tools, mold cores for wear-resistant requirements, marine hardware requiring wear resistance.

Practical Q&A

Q1: What is the difference between 440B and 440A/440C? A1: In terms of carbon content: 440A (0.60-0.75%) < 440B (0.75-0.95%) < 440C (0.95-1.20%). Corresponding hardness: 440A (55-57HRC) < 440B (57-59HRC) < 440C (60-62HRC). Toughness is the opposite: 440A > 440B > 440C. Choose according to the balance of wear resistance and toughness required.

Q2: What heat treatment process should be used for 440B to avoid brittleness? A2: Adopt quenching (1020-1060℃, oil cooling) + tempering (180-220℃, air cooling). Avoid tempering at 300-450℃, as this temperature range will cause temper brittleness, resulting in a significant decrease in impact toughness. For components subject to slight impact, tempering at 250-300℃ can be used to balance hardness and toughness.

Q3: Is 440B stainless steel 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℃), which is lower than austenitic stainless steel. It is suitable for high-precision components such as bearing races and mold cores that require strict dimensional tolerance.

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

Q5: Can 440B stainless steel be used for high-speed rotating components? A5: Yes, it is suitable for high-speed bearing rings and balls. Its high hardness (57-59HRC) and good wear resistance ensure long service life at high speeds. However, it is necessary to ensure sufficient lubrication to avoid dry friction, which will cause rapid wear and failure.