440C (ASTM A276; GB 10Cr17Mo) is a high-carbon martensitic stainless round bar with properties that contrast sharply with 304:
Tensile strength: 1790–2000 MPa (far higher than 304's 515 MPa), due to its high carbon (0.95–1.20% vs. 304's ≤0.08%).
Hardness: 58–60 HRC after quenching (1010–1070°C) and tempering (150–300°C)-making it one of the hardest stainless steels, ideal for cutting tools.
Corrosion resistance: Moderate (resists freshwater but not saltwater), lower than 304 but superior to carbon steel.
Ductility: 10–12% elongation (much lower than 304's 40%), limiting its use to non-forming applications.
440C is used in bearings, valve seats, and surgical instruments-applications requiring both wear resistance and moderate corrosion resistance. It is more expensive than 304 but cheaper than tool steel, making it a popular compromise.