Morphology of carbide precipitates in solution quenched PH13-8 Mo stainless steel: A small-angle neutron scattering investigation

This article reports the small-angle neutron scattering (SANS) and the transmission electron microscopy (TEM) investigations on solution quenched PH13-8 Mo stainless steel. The metallic carbide precipitates of parallelepiped like morphology, as revealed by TEM, have been mainly responsible for the strong scattering signal in SANS measurements. Scattering signal from the needle like austenites, which have been also identified by TEM, remains insignificant because of the poor scattering contrast between the austenites precipitates and the martensite matrix. Shape of the normalized scattering profile varies significantly with the specimen thickness. These variations of the scattering profiles could arise due to the two factors, namely: (i) the multiple scattering of the neutrons at small-angles and (ii) the double Bragg reflections. In the present case, it has been established that the contribution in the scattering signal due to the double Bragg reflection is quite insignificant compared to that from the multiple scattering. The single scattering profile, extracted from the multiple scattered profiles of the samples, has been analyzed in the light of polydisperse cylindrical particle model as well as with polydisperse parallelepiped particle model, assuming fixed aspect ratio of the precipitates, in order to obtain the size distribution of the precipitates.