A simple method, in terms of gaseous equilibration, has been developed to prepare specimens of Cr-Ni austenitic steels with various combinations of carbon and nitrogen concentration. Specimens were first nitrogenized up to the desired nitrogen concentration under the controlled nitrogen pressure with the aid of experimental studies on the activity of nitrogen in Cr-Ni austenitic steels. The nitrogenized specimens were carburized in a sealed quartz capsule, using hydrogen as a carrier and a plain carbon steel as a carbon supply. In this method, the carbon concentration in the Cr-Ni austenitic steels can be controlled within ±0.01% at the concentration level of 0.3% with very rough estimate of carbon activity in the specimen.
The method was successfully applied to a study of the effect of nitrogen on the precipitation morphology of M23C6 in a 25%Cr-28%Ni-2%Mo austenitic steel.
