CHARACTERIZATION OF 9CR-1MOVNB STEEL BY ANOMALOUS SMALL-ANGLE X-RAY-SCATTERING

The size distribution and volume fraction of Cr23C6 precipitates in 9Cr-1MoVNb steel have been isolated from the distributions of all other precipitates by the technique of anomalous small-angle X-ray scattering. Three X-ray wavelengths near the Cr K absorption edge were used to vary the scattering contrast of Cr23C6 while that of the other precipitates was left unchanged. Size distributions calculated from each scattering curve using a maximum entropy method were combined by a scattering contrast gradient analysis to isolate the volume-fraction size distribution of the chromium carbides. Behavior of these carbides was studied as a function of isothermal aging temperature. Mean diameter is smallest and Cr23C6 number density is highest after aging at 811 K. Above 811 K, the mean diameter of the chromium carbides increases with increasing aging temperature.