440B vs 440C Martensitic Stainless Steels: Mid-Hardness vs Maximum Wear Resistance

 

What are their core compositions and mechanical property differences?

440B has 0.75–0.95% C, 16–18% Cr, 0.75% max Mo, achieving a maximum hardness of 58 HRC after heat treatment. It balances wear resistance with moderate corrosion protection for dry environments.440C contains 0.95–1.20% C, 16–18% Cr, 0.75% max Mo, reaching 60 HRC-one of the hardest standard stainless steels. Its high carbon forms dense chromium carbides, delivering superior wear resistance but lower corrosion resistance than 440B.Both grades are magnetic and require precise quenching and tempering to achieve their full hardness potential.

How do their hardness and wear resistance translate to end-use applications?

440B is suited for medium-wear cutting tools and mechanical parts: garden shears, industrial blades for non-abrasive materials, and small bearing races that require a balance of hardness and toughness.440C is the top choice for high-wear applications: surgical scalpels, precision bearing races for heavy loads, industrial saw blades for hard materials, and firearm components that demand maximum edge retention.440C's high carbide density makes it resistant to abrasion but more brittle than 440B, limiting its use in impact-loaded parts like axes or hammers.

How do their corrosion resistances compare in different environments?

440B has better corrosion resistance than 440C, tolerating dry indoor conditions and short-term exposure to mild humidity without significant rusting. Proper maintenance (e.g., oiling) can extend its service life in semi-outdoor settings.440C's high carbon content disrupts the chromium passive film, making it prone to rust in humid or coastal environments-protective coatings (e.g., DLC coating) are mandatory for outdoor use.Neither grade is recommended for marine, chemical, or food-processing applications; precipitation-hardening grades like 17-4 PH are better alternatives for these scenarios.

What are the critical heat treatment tips for these grades?

For 440B: Austenitize at 1010–1060°C, quench in oil, then temper at 150–200°C to balance hardness and toughness. Tempering above 200°C will reduce hardness significantly but improve ductility.For 440C: Austenitize at 1010–1070°C, quench in oil, then perform triple tempering at 150–200°C to eliminate retained austenite and maximize hardness. This triple tempering step is critical to avoid brittleness.Both grades must be tempered immediately after quenching to prevent cracking from residual stress.

What are the key limitations and application guidelines?

440B and 440C have poor weldability-welding causes carbide precipitation at grain boundaries, leading to brittleness and cracking in the heat-affected zone. Mechanical joining (threading, press-fitting) is preferred.440C is more expensive than 440B due to tighter carbon content control during production, so it should only be used when maximum wear resistance is critical.Choose 440B for medium-wear, low-corrosion applications; select 440C only when ultra-high wear resistance is required and corrosion exposure is minimal.