Stress Corrosion Cracking of Type 403 Stainless Steel in Sodium Chloride at 95°C Under Different Heat Treatment Conditions

Slow strain rate tests were used to evaluate the effect of heat treatment on the stress corrosion cracking (SCC) susceptibility of type AISI 403 (UNS S40300) martensitic stainless steel in 20% sodium chloride (NaCl) at 95°C. Heat treatments included water-quenched, quenched, and tempered at 200°C, 400°C, and 600°C and annealed at 850°C. When tested in oil (90°C), the highest loss in ductility was shown by the quenched specimen, and the lowest by the annealed specimen. Between these two specimens, there were specimens tempered at 200°C, 400°C, and 600°C, respectively. When tested in 20% NaCl (wt%) at pH 7, 6, and 5, all specimens were embrittled by the environment, the most severe one being the solution with pH 5, showing at least 50% reduction in the elongation exhibited in oil. Fracture morphology was completely intergranular along the prior austenite for the quenched specimen and completely transgranular for the annealed specimen. The percentage of intergranular cracking decreased as the tempering temperature increased from 200°C to 600°C, and as the pH increased from 5 to 7. The fracture mechanism was thought to be hydrogen embrittlement.