Microstructure of High-Chromium Ferritic-Martensitic Steels for Next-Generation Reactors

High-chromium steels are key alloys used for the construction of technological devices in industry. Stainless steels are suitable for components that are exposed to a corrosive environment for a long time because chromium has anticorrosion properties due to segregation of chromium and the formation of a passivation layer. The physicochemical properties of the surface and the bulk of the material as well are determined by microstructure. Herein, steel NS219 is focused on, where the chromium concentration is around 13.5 wt%. In order to study the microstructure of steel, Mossbauer spectroscopy is used. Experimental results are evaluated using the binomial distribution model of the probability distribution of atoms in the nearest neighbor of the resonant atom 57Fe. Obtained spectral parameters, viz., the average magnetic hyperfine field, the average isomer shift, and the probability of the atomic configuration with no impurity atoms in the two-shell vicinity of the iron atoms, reach saturation values from which the solubility limit of chromium in iron can be determined. On the other hand, the solubility limit of iron in Cr-rich phase can be estimated from the value of the isomer shift of the single-line in the spectrum annealed for the longest time. Steels are used for the construction of components of nuclear power plants. Microstructure of materials determines properties and must be studied especially in the case of high-chromium steels. Mossbauer spectroscopy is used to describe changes during annealing at 475 degrees C and Mossbauer spectra of the analyzed steel contain magnetic and paramagnetic components, and the spectral parameters provide information on recrystallization.image (c) 2023 WILEY-VCH GmbH