SUS420 Stainless Steel: Corrosion Resistance & Hardness

Hardness

High Hardenability: It's a medium-carbon, high-hardenability steel designed for excellent hardness, reaching up to 50+ Rockwell C (HRC).

Heat Treatable: Achieves maximum hardness through hardening and tempering, providing superior wear resistance.

Corrosion Resistance

Good in Specific Conditions: Offers good resistance in fresh water, food, mild acids/alkalis, steam, and crude oil when hardened and polished.

Requires Surface Finish: Best corrosion resistance comes from a ground or polished surface; scale and dirt reduce protection.

Compromised at High Temps: Performance drops above 400°C (750°F), with strength loss and reduced corrosion resistance.

Applications

Cutlery & Tools: Knives, surgical/dental instruments, scissors.

Machinery: Pump/valve parts, gears, bearings, springs, shafts.

Key Takeaway

SUS420 balances hardness and corrosion resistance, but its high-carbon martensitic structure means you sacrifice some toughness and high-temp performance for extreme hardness, requiring specific finishing (polishing/hardening) for optimal protection.