A QUANTITATIVE-ANALYSIS OF SOLUTION NITROGEN IN CR-NI-MO AUSTENITIC STEELS BY ELECTRON-PROBE MICROANALYSIS

Five 20 approximately 25Cr-Ni-Mo austenitic steels were prepared with a nickel concentration range between 5 and 28 mass% and a molybdenum concentration range between zero and 4 mass% . Five series of Cr-Ni-Mo austenitic steels with different nitrogen concentrations ranging from 0.01 to 0.76 mass% were prepared by nitrogenizing under different nitrogen gas pressures at 1523 K without changing the matrix composition. They were used to make calibration curves between the nitrogen concentrations and NK-alpha intensities. A coated multi-layer X-ray dispersion element, specifically designed for measuring NK-alpha intensities, was used as an analyzing crystal. Correlation between the nitrogen concentrations and the NK-alpha intensities was represented by a straight line. Gradients and background intensities for five calibration curves are all the same within the present experimental accuracy. Nitrogen partitioning between ferrite and austenite in duplex stainless steels was determined by utilizing the calibration curves for five Cr-Ni-Mo austenitic steels. Nitrogen in solution both in ferrite and austenite was analyzed with an accuracy of +/- 0.02 mass%.