440C vs 440B Stainless Steel: High-Hardness Martensitic Grades

 

How do their compositions differ?

440B contains 16-18% chromium, 0.75-0.95% carbon, and 0.4-0.6% molybdenum. 440C increases carbon to 0.95-1.20% and molybdenum to 0.4-0.7%, enabling higher hardness after heat treatment.

 

Which offers better hardness and wear resistance?

440C reaches 58-60 HRC after heat treatment, harder than 440B's 56-58 HRC. This makes 440C more wear-resistant, ideal for high-speed bearings and cutting tools needing to maintain sharp edges.

 

How do they compare in corrosion resistance?

Both offer similar moderate corrosion resistance in dry environments, with chromium forming a protective oxide layer. They resist rust in indoor settings but may corrode in moisture or salt, with no significant difference between them.

 

What about their fabrication properties?

440B is slightly easier to machine and polish than 440C due to lower carbon. Both require careful heat treatment (quenching and tempering) to avoid brittleness, with 440C needing stricter temperature control.

 

Where are 440C and 440B commonly used?

440B is in precision bearings and high-quality knife blades. 440C finds applications in industrial cutting tools, valve seats, and parts needing maximum wear resistance under friction.