420 vs 440A Stainless Steel: Martensitic Hardness Options

 

How do their compositions differ?​

420 has 12-14% chromium and 0.15-0.4% carbon. 440A ups the chromium to 16-18% and carbon to 0.6-0.75%, with a small molybdenum addition for extra wear resistance.​

 

Which offers better hardness and wear resistance?​

440A hits 56-58 HRC after heat treatment, harder than 420's 50-55 HRC. This makes 440A more wear-resistant, while 420 balances hardness with slightly better toughness.​

 

How do they stand up to corrosion?​

440A resists corrosion better than 420, thanks to higher chromium. Both handle dry environments well but can rust in moisture or salt-440A holds up a bit longer in mild humidity.​

 

What about machining and fabrication?​

420 is easier to machine in its annealed state, while 440A needs sharper tools due to higher carbon. Both require careful heat treatment to reach full hardness without brittleness.​

 

Where are 420 and 440A typically used?​

420 is in knife blades, surgical tools, and valve parts. 440A finds use in bearings, high-performance knives, and precision parts needing extra wear resistance.