Effects of Temperature on Crack Growth Rate in Sensitized Type 304 Stainless Steel and Alloy 600

Effects of temperature on stress corrosion crack growth rates were studied on three heats of sensitized type 304 (UNS S30400) stainless steel (SS) and one heat of sensitized alloy 600 (UNS N06600). Data were obtained using reversed direct current (DC) potential drop crack length monitoring on 25-mm compact-type (CT) specimens in 25°C to 288°C water, usually containing 200 ppb oxygen (O2). Most data were obtained in 0.3 μM sulfuric acid (0.267 μS/cm). In one heat, 0.1 μM hydrochloric acid (HCl) (0.076 μS/cm), 0.5 μM HCl (0.224 μS/cm), and air-saturated water (≈ 8,800 ppb O2 and ≈ 0.5 μS/cm) also were evaluated. All heats and materials had similar temperature dependence and showed a peak in crack growth rate at ≈ 200°C in these water chemistries, which typically was a factor of 30 to 100 times higher than at 288°C or 25°C. Growth rates decreased rapidly above 250°C compared to those between 25°C and 200°C. In many cases, similar rates were observed at 25°C and 288°C. Data were compared with the literature on fracture mechanics and slow strain rate specimens. Issues in determining the value and origin of apparent activation energies also were discussed.