Kinetics of the carburization--decarburization process of austenitic stainless steels in sodium

Abstract A mathematical analysis for the carburization-decarburization kinetics of austenitic stainless steels in high-temperature flowing sodium has been developed that incorporates 1. (1) the thermodynamic and kinetic information for carbon in the alloys, 2. (2) the thermal-mechanical treatment of the material (solution-annealed versus cold-worked) which influences the microstructure, and 3. (3) the carbon concentration in sodium and its dependence on sodium-system parameters. Carbon concentration-distance profiles in Types 304 and 316 stainless steel were generated as a function of time, temperature, and carbon concentration in sodium and compared with experimental data. The analysis was used to evaluate the carburization-decarburization behavior of Type 316 stainless steel fuel cladding exposed to sodium and to develop carbon-diffusion profiles in Type 304 stainless steel intermediate heat-exchanger piping upon exposure to primary and secondary system sodium for periods to 30 y.