The Effect of Carburization in Sodium on the Mechanical Properties of Austenitic Stainless Steels

Conventional mechanical properties tests (tensile, stress/rupture, and impact toughness) have been performed on annealed specimens of austenitic stainless steels (0.152 cm thick, 0.635 cm wide) which have been carburized in high temperature (538–593°C) sodium for times up to 2000 hr. Included in the work were alloys which might have been more resistant to carburization than conventional alloys, Type 310SS, 18-8-2, Uranus-S and Inconel-601. Results indicate that the tensile and stress rupture ductility of all the alloys decreased to less than 5 percent in tests at 538–593°C when the bulk carbon content of the specimens was 0.4 percent or greater. The decrease in ductility of surface-carburized specimens is much greater than that of alloys of the same nominal composition and same bulk carbon content but with the carbides homogeneously distributed throughout the specimen. It is shown that the brittle surface layer fractures in a transgranular, cleavage mode while the center of the specimens fail in the normal shear mode.