Purpose. To investigate the possibility of martensite nucleation on magnetic (concentration) inhomogeneities of chrome-nickel steels austenite. Research methods. Generalization of experimental and theoretical studies of the strong magnetic field effect on the martensitic transformation in steels and iron alloys, taking into account the magnetic state of austenite Results. The analysis of the magnetic state of austenite and the abnormally large strong magnetic field effect on the martensite point displacement in 40X2H20 steel indicates that the transformation of austenite into martensite in it is a “magnetic first order phase transition”. Scientific novelty. Some features of the martensitic transformation in steels and iron alloys are explained. It is assumed that martensite during the “magnetic γ→α- transition” originates on magnetic inhomogeneities with a disoriented magnetic structure of the spin glass type. Forced magnetostriction during paraprocess and spontaneous magnetostriction below the Curie point lead to the emergence of collinear ferromagnetism with a change in the coordination number from 12 to 8. High all-round pressure leads to the occurrence of collinear antiferromagnetism and the γ-phase stabilization. In paramagnetic austenite the nucleation of α-martensite occurs on dislocation nuclei, the sizes of which have the same order of magnitude (by volume) as the magnetic inhomogeneities in the Fe-Ni system. Practical value. The results obtained in the work expand the concept of martensitic transformation in steels and provide grounds for explaining some kinetic features in them.

Purpose. Establishing effective and correct techniques for detecting the grain structure in structural medium-carbon steels taking into account the recommendations of modern standards (ДСТУ ISO, ASTM, ГОСТ) with the aim of reliably determining the austenitic grain size and putting into operation of metal with the well-known and required, according to the normative technical documentation (technical requirements, drawings) quality. Research methods. Metallographic analysis of microstructure and evaluation of the austenitic grain size were carried out by comparing the image revealed on polished and etched using various chemical reagents microsections of heat-treatable steel 40KHN2МА-Ш with etalon of scale of standard. Results. Studies of structural alloyed steel 40ХН2МА-Ш found that the most effective etchant reagent, which best detects initial austenitic grain boundaries in medium-carbon alloyed steels, is a standard reagent - a saturated aqueous solution of picric acid. As a result of etching in this reagent, a visible image of the grain structure is formed in the form of a clear contrast of light areas of the grain body and dark lines of the grain boundaries, which allows a correct comparison of the structure with the images of the standards on the scales. Scientific novelty. On the example of heat- treatable steel 40ХН2МА-Ш, the ways of further development of ideas regarding the choice of an effective chemical reagent are considered for the purpose of detecting and forming a visible grain structure in accordance with the requirements of methodical standards in structural medium-carbon steels, proper and reliable estimation of austenitіс grain size using standard scale. Practical value. A correct procedure for detecting the initial austenite grain is proposed, which allows to reliably determine the grain size and quality from this parameter of various structural steels including for the production of responsible parts of aircraft and spacecraft.

Purpose. It consists in establishing regularities of the influence of alloying elements on the thermophysical characteristics of nickel-based superalloys of equiaxial crystallization, which allows to optimize the manufacturing and heat treatment processes. Research methods. The experimental values were processed by mathematical methods to obtain correlation dependencies of the "parameter-property" type and establish regression models that optimally describe these dependencies. Results. The regularities of the influence of the chemical composition of nickel-based superalloys on thermophysical characteristics have been established. We have obtained ratios that allow us to take into account the criteria of competition (cooperation) of chemical elements and obtain diagrams by which it is possible to determine critical temperatures. Scientific novelty. The established ratios of Kg¢, Kg, KMC and KM23C6 allow taking into account the criteria of competition (cooperation) of chemical elements in the chemical composition of nickel-based superalloys of equiaxial crystallization. Thanks to the obtained ratios, a diagram was obtained with the help of which it is possible to establish thermophysical characteristics for the alloys of the specified group. Practical value. An effective solution for establishing the main critical temperatures of nickel-based superalloys of equiaxial crystallization is proposed, which made it possible to optimize the temperatures of production, heat treatment and operation.

CONSIDERATION OF THE ENERGETICS OF SOLID PHASE DEFECTS (MAINLY INTERNAL GRAIN BOUNDARIES) IN CIGAR-SHAPED DIAGRAMS OF TWO-PHASE STRUCTURES