2020 Volume 51 Pages 147-156
Rietveld texture analysis with the use of neutron diffraction is a promising analytical method to observe microstructural evolution of steels in high-temperature processes. Phase fraction and texture evolution can be analyzed from diffraction intensities in the Rietveld texture analysis. However, since the diffraction intensities can vary with the isotropic temperature factor, Biso, which is a parameter of the atomic thermal vibration, the analytical accuracy of Biso would affect the texture and phase fraction analyses. We examined the influence of the divergence of Biso on the analytical accuracy of phase fraction and texture in Rietveld texture analysis by using neutron diffraction data of steels. It was confirmed that the decrease in diffraction intensities at high reflection indices became significant with an increase in temperatures, as a result of the increase in the atomic thermal vibration. By observing the clear attenuation of diffraction intensities from low to high reflection indices, the Biso equivalent to the literature value was successfully estimated, and appropriate phase fraction of ferrite and cementite phases were obtained. When the Biso was intentionally changed in Rietveld texture analysis, the estimated phase fraction deviated from the actural value while the texture results was affected little. We also examined the number of diffraction peaks necessary for obtaining appropriate Biso. It was confirmed that 11 or more diffraction peaks are required for estimating an appropriate Biso value, so that phase fraction of ferrite and cementite phases is to be analyzed correctly.
