440 Stainless Steel: High-Hardness Martensitic Stainless Steel For Wear-Resistant Applications

440 stainless steel is a high-carbon martensitic stainless steel series with 16%-18% chromium content. Its carbon content (0.60%-1.20%) is significantly higher than that of 420, enabling it to achieve extremely high hardness (up to 60HRC) after heat treatment. It has excellent wear resistance and edge retention, but relatively low toughness. According to carbon content differences, it is divided into 440A, 440B, 440C and 440F grades, suitable for high-wear and high-precision components.

Core Parameters (General for 440 Series)

Chemical Composition (wt%): C=0.60-1.20, Si≤1.00, Mn≤1.00, P≤0.040, S≤0.030, Cr=16.00-18.00, Fe=Balance (specific carbon content varies by sub-grade)

Mechanical Properties (Quenched & Tempered): Tensile Strength ≥795MPa, Yield Strength ≥550MPa, Elongation ≥12%, Hardness ≥55HRC

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

Equivalent Grades: SUS440 Series (JIS), EN 1.4125 (for 440C, EN), UNS S44002 (440A), S44003 (440B), S44004 (440C) (ASTM)

Performance Advantages: Ultra-high hardness and excellent wear resistance after heat treatment; good corrosion resistance in dry air and mild environments; excellent edge retention, suitable for cutting tools; good dimensional stability after heat treatment; magnetic.

Typical Applications: High-quality knife blades (chef's knives, hunting knives), bearings (stainless steel ball bearings), valve seats, nozzles, precision molds, surgical scalpels, measuring tools, textile machine components.

Practical Q&A

Q1: What is the difference in carbon content between 440A, 440B and 440C? A1: 440A (C=0.60-0.75%) has the lowest carbon content, with balanced hardness (55-57HRC) and toughness; 440B (C=0.75-0.95%) has medium carbon content, hardness 57-59HRC; 440C (C=0.95-1.20%) has the highest carbon content, hardness up to 60-62HRC, best wear resistance but lowest toughness.

Q2: What heat treatment process is required for 440 stainless steel to achieve high hardness? A2: Quenching at 1010-1070℃ (oil cooling or air cooling) + tempering at 150-200℃ (air cooling). This process maximizes hardness and wear resistance. Avoid tempering at 300-450℃, as it will cause temper brittleness and reduce toughness.

Q3: Is 440 stainless steel suitable for corrosion-prone environments? A3: Not suitable. Its high carbon content reduces corrosion resistance, and it is prone to pitting corrosion in chloride ion environments. It is only suitable for dry air or mild corrosion environments. For corrosive and wear-resistant applications, consider 17-4PH precipitation hardening stainless steel.

Q4: Can 440 stainless steel be cold worked? A4: Cold working is difficult in the hardened state due to high hardness. It should be cold worked in the annealed state (hardness ≤269HB), and then heat treated to achieve the required hardness. Cold working can improve strength but reduce toughness.

Q5: What is 440F stainless steel? A5: 440F is a free-cutting variant of 440, with added sulfur (S=0.15-0.30%) to improve machinability. Its hardness and wear resistance are slightly lower than 440C, but it is suitable for complex-shaped components that require high machining efficiency, such as precision bearing cages.