D. D. Satskii, S. V. Soloveva, A. E. Ustinov, V. Y. Yarkov, M. L. Lobanov

DETERMINATION OF AUSTENITE GRAIN SIZE IN FERRITIC-MARTENSITIC STAINLESS STEEL BY ORIENTATION MICROSCOPY METHODS

The development of chromium stainless steels is caused by the need for creating materials showing an optimal combination of physical, mechanical, and chemical properties when used in aggressive environments. Currently, for the production of industrial tubular articles functioning under load at high temperatures, it is promising to use stainless steels of the ferritic-martensitic and martensitic classes, strengthened by additional alloying. The achievement of a given set of properties in steels and alloys is determined by the homogeneity of the chemical and phase compositions, microstructure and crystallographic texture. The formation of these parameters for heat-treated materials is mainly determined by the characteristics of the grains of austenite formed during heat treatment before quenching. The size and shape of austenite grains determine the morphology and dispersion of the products of γ→α′(α) phase transformation. Orientation microscopy methods based on backscattered electron diffraction are used to study the restorability of high-temperature austenite grains for samples of a low-carbon high-alloy stainless steel of the ferritic-martensitic class, with ~12 wt% Cr, additionally alloyed with Ni, Mo, W, Nb, and V. After heat treatment, the samples have a ferrite-martensite and ferrite-bainite structure. When restoring austenite grains, we used the orientation relationships (ORs) of Kurdyumov–Sachs (K–S), Nishiyama–Wasserman (N–W), Greninger–Troyan (G–T), and new ORs proposed by V. S. Kraposhin (ORK). The fundamental possibility of restoring pre-existing austenite grains is shown. The restoration is based on the crystallographic features of both ferrite-martensite and ferrite-bainite structures. The most valid results in austenite grain recovery were obtained when OR K–S and ORK were used.

Acknowledgment: The research was supported by the Russian Science Foundation, grant No. 23-29-00615, https://rscf.ru/project/23-29-00615/.

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