440A Stainless Steel: Balanced Hardness & Toughness Martensitic Grade for Utility Tools

440A is a low-carbon variant in the 440 series martensitic stainless steel (C=0.60%-0.75%, Cr=16.0%-18.0%). It has balanced hardness and toughness, with hardness reaching 55-57HRC after heat treatment, and is suitable for making utility tools that require both wear resistance and impact resistance.

Core Parameters

Chemical Composition (wt%): C=0.60-0.75, 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 ≥795MPa, Yield Strength ≥550MPa, Elongation ≥12%, Hardness 55-57HRC

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

Equivalent Grades: SUS440A (JIS), EN 1.4104, UNS S44002

Performance Advantages: Balanced hardness and toughness; good wear resistance and edge retention; easier heat treatment and machining than 440B/440C; moderate corrosion resistance in dry environments; magnetic.

Typical Applications: Household kitchen knives, utility knives, scissors, bearing rings, valve cores, precision molds, textile machine needles, measuring tools.

Practical Q&A

Q1: What is the optimal heat treatment process for 440A? A1: Quenching at 1010-1050℃, oil cooling + tempering at 180-220℃, air cooling. This process achieves hardness of 55-57HRC, with the best balance of wear resistance and toughness. For higher toughness, temper at 300-350℃, but hardness will decrease to 48-52HRC.

Q2: How does 440A compare with SUS420J2? A2: 440A has higher carbon and chromium content, with higher hardness (55-57HRC vs. 52-57HRC) and better wear resistance. It is more suitable for high-wear tools, while SUS420J2 is more cost-effective for general applications.

Q3: Is 440A suitable for food contact tools? A3: Yes. After heat treatment and passivation, its surface oxide film is stable, meeting food safety standards. However, it should not be soaked in acidic detergents for a long time to avoid corrosion.

Q4: Can 440A be polished to a mirror finish? A4: Yes. Use 120#→240#→400#→600# abrasive belts for dry polishing, then use polishing paste for fine polishing. The polished surface can reach a mirror finish with a roughness Ra≤0.05μm.

Q5: What is the service life of 440A in wear applications? A5: In general wear environments (textile machine needles), its service life is 2-3 times that of SUS420J2. In high-load wear environments, it is recommended to use 440C with higher hardness.