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 stu died on three heats of sensitized type 304 (UNS S30400) stainless stee l (SS) and one heat of sensitized alloy 600 (UNS N06600). Data were ob tained using reversed direct current (DC) potential drop crack length monitoring on 25-mm compact-type (CT) specimens in 25-degrees-C to 288 -degrees-C water, usually containing 200 ppb oxygen (O2). Most data we re obtained in 0.3 muM sulfuric acid (0.267 muS/cm). In one heat, 0.1 muM hydrochloric acid (HCl) (0.076 muS/cm), 0.5 muM HCl (0.224 muS/cm) , and air-saturated water (almost-equal-to 8,800 ppb O2 and almost-equ al-to 0.5 muS/cm) also were evaluated. All heats and materials had sim ilar temperature dependence and showed a peak in crack growth rate at almost-equal-to 200-degrees-C in these water chemistries, which typica lly was a factor of 30 to 100 times higher than at 288-degrees-C or 25 -degrees-C. Growth rates decreased rapidly above 250-degrees compared to those between 25-degrees-C and 200-degrees-C. In many cases, simila r rates were observed at 25-degrees-C and 288-degrees-C. Data were com pared with the literature on fracture mechanics and slow strain rate s pecimens. Issues in determining the value and origin of apparent activ ation energies also were discussed.