Heat treatment causing very high strength leads to susceptibility to chloride SCC in which grade?

• A. Martensitic
• B. Ferritic
• C. Austenitic
• D. Precipitation Hardened

Answer: (D)

When a stainless steel gains very high strength through a heat-treating or aging process, its toughness and ductility can decrease. For precipitation-hardening (PH) stainless steels, aging builds up hard, finely dispersed precipitates that raise strength dramatically, but this also can reduce the material’s ability to accommodate and blunt cracks, especially under tensile stresses in a chloride-containing environment. Chloride ions destabilize protective films and promote localized attack, so once a PH stainless steel is made very strong, the combination of high residual and applied stresses with increased susceptibility to localized corrosion makes it more prone to chloride-induced stress corrosion cracking.

Martensitic and ferritic grades don’t typically exhibit this same pattern under heat treatment aimed at maximizing strength, and austenitic grades, while generally more resistant to SCC, are not the ones singled out for this high-strength, chloride-SCC behavior. Precipitation-hardening stainless steels thus stand out as the grade where very high strength from heat treatment correlates with increased chloride SCC susceptibility.