Modified small-angle X-ray scattering technique for the analysis of different types of hardening precipitates in steel

This paper presents a modified small-angle X-ray scattering (SAXS) method for analyzing the size and shape of hardening particles in steels. Unlike the conventional SAXS approach, which typically analyzes alloy particles of only one morphology, the modified method enables simultaneous evaluation of various types of particles differing in both size and morphology. The essence of the modification to SAXS method is that it takes into account the contribution of the intensity of the separate types of particles with different morphologies to the total true intensity. For each type of particles, shape and structural coefficients are set taking into account their spatial distribution in the analyzed area. To detect the presence of particles of different morphologies in alloys, the experimental patterns are analyzed. First, based on the I(q−n) dependence, the morphology of the existing types of particles was traditionally identified (cylinder / needle (n =1), plate / disk (n = 2), and ellipsoid / sphere (n = 3, 4)). Subsequently, individual regions of the SAXS curve were analyzed in the context of optimizing the size and shape of various particles. The modified SAXS method was tested for analyzing the morphology and size of cementite particles in ferrite-pearlite steel subjected to annealing. As a result, it was shown that during the annealing process of steel, cementite particle morphology in pearlite grains undergoes a stepwise transformation according to the following scheme: lamellar → ellipsoidal → spherical. For the first time, quantitative characteristics of the change in particle size distribution were obtained for different morphologies. The transformation of cementite particle morphology was found to be accompanied by growth, which leads to a decrease in the contribution of dispersion hardening.