440A vs 440B Stainless Steel: Martensitic Hardness Grades

 

How do their compositions differ?

440A has 16-18% chromium, 0.6-0.75% carbon, and 0.4-0.6% molybdenum. 440B increases carbon to 0.75-0.95% while keeping chromium and molybdenum similar, allowing for greater hardness after heat treatment.

 

Which offers better hardness and wear resistance?

440B reaches 58-60 HRC after heat treatment, harder than 440A's 56-58 HRC. This makes 440B more wear-resistant, suitable for parts needing to maintain sharp edges under friction.

 

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 moist or salty conditions, with no significant difference between them.

 

What about their fabrication properties?

440A is slightly easier to machine and form than 440B due to lower carbon. Both require careful heat treatment (quenching and tempering) to achieve full hardness, with 440B needing more precise temperature control.

 

Where are 440A and 440B commonly used?

440A is in knife blades, bearings, and valve parts. 440B finds applications in high-performance cutting tools, precision bearings, and parts needing superior wear resistance.