High voltage electron microscopy observations of microdeformation in alloy 600 tubing

Alloy 600 tubing was obtained in the mill-annealed (MA) and thermally treated (TT) conditions. Heat bulk composition of the major elements in weight percent was 0.03 C, 76.2 Ni, 15.4 Cr, 7.6 Fe, 0.25 Mn, 0.2 Si, 0.37 AI, 0.26 Ti, 0.26 Cu, 0.001 S, 0.009 P and 0.003 B. Details concerning fabrication, mechanical properties and SCC resistance have been reported. (7) Mill-annealed tubing was quite susceptible to IGSCC, while TT tubing did not show cracking in primary-water environments, Thermal treatment was performed at 704°C for 15 hours. HVEM tensile specimens were prepared by cutting longitudinal strips from the tubes and surface grinding the curved slices to flat rectangular slabs approximately 150 ~m thick. The ends of the specimens were lacquered and a jet polisher used to remove material across the entire specimen width. Jet po|ishing was performed from both sides by reversing the specimen in the jet every 30 seconds until 10 to 20 um of material remained in the center. A 20% perchloric acid-80% methanol solution cooled to -55°C and an applied voltage of 425 V was used for the jet polish bath.