440A vs 440C Martensitic Stainless Steels: Hardness vs Corrosion Balance

 

440A has 0.60-0.75% C, 16-18% Cr, 0.75% max Mo-heat-treatable to 56 HRC, balancing wear resistance and basic corrosion protection.440C contains 0.95-1.20% C, 16-18% Cr, 0.75% max Mo-reaches 60 HRC, with dense carbides for superior wear resistance but lower corrosion resistance.Both require quenching + tempering to achieve full hardness; 440C needs triple tempering to eliminate retained austenite.

440A suits low-wear tools (kitchen knives, scissors) and small bearings-tolerates mild moisture without heavy rusting.440C is the top choice for high-wear parts: surgical scalpels, precision bearing races, industrial saw blades-demands edge retention.440C's brittleness limits use in impact-loaded parts (e.g., axes), while 440A offers better toughness for general cutting tools.

440A has the best corrosion resistance in the 440 family-tolerates dry indoor conditions and light outdoor exposure with maintenance.440C's high carbon disrupts the chromium passive film-prone to rust in humid/coastal settings; protective coatings are mandatory for outdoor use.Neither grade works in marine/chemical environments-use 17-4 PH for high-strength, better corrosion resistance.

For 440A: Quench at 1010-1060°C (oil), temper at 150-200°C to balance hardness/toughness-avoid over-tempering.For 440C: Quench at 1010-1070°C (oil), triple-temper at 150-200°C to maximize hardness and eliminate brittleness.Temper immediately after quenching for both grades to prevent cracking from residual stress.