Effect of Low-Temperature Aging on the Mechanical Properties of Cast Stainless Steels

摘要

The significance of in-service embrittlement of cast duplex stainless steels under light-water operating conditions was investigated. Mechanical property data are presented from Charpy-impact, tensile, and J-R curve tests for several heats of cast stainless steel aged up to 10,000 h at 450, 400, 350, 320, and 290 deg C. Thermal aging increased the tensile strength and decreased the impact energy, J/sub IC/, and tearing modulus of the steels. Also, the ductile-to-brittle transition curve shifted to higher temperatures. Fracture toughness results were consistent with the Charpy-impact data. The ferrite content and concentration of C in the steel had a strong effect on the overall process of low-temperature embrittlement. The low-carbon CF-3 steels were the most resistant and Mo-containing CF-8M steels were most susceptible to embrittlement. Weakening of the ferrite/austenite phase boundaries by carbide precipitates had a significant effect on the kinetics and extent of embrittlement of the high-carbon CF-8 and CF-8M steels, particularly after aging at temperatures greater than or equal to 400 deg C. The influence of N content and distribution of ferrite on loss of toughness are discussed. Data also indicate that existing correlations do not accurately represent the embrittlement behavior over the temperature range 280 to 450 deg C. 16 refs., 22 figs., 2 tabs. (ERA citation 13:009035)