Influence of microheterogeneity destruction on microstructure and crystal structure of Fe-12% Mn-1%C alloy ingots

Abstract

The results of comparative analysis of microstructure, crystal structure and mechanical properties in submicrovolumes of Fe-12%(wt.)Mn-1%(wt.)C alloys crystallized from the melt in different structural state: with destruction and without destruction of microheterogeneity are presented. Earlier, the authors found that overheating of the Fe-12%(wt.)Mn-1%(wt.)C melt to a temperature of 1700 °C leads to destruction of microheterogeneity, which changes the crystallization conditions of the ingot. Microheterogeneity means the presence in the melt of dispersed particles enriched in iron, which are suspended in an environment of a different composition and separated from it by a clear interfacial surface. The study of alloys was performed by scanning electron microscopy, energy dispersion analysis (EDS), the method of backscattered electron diffraction (EBSD) and nanoindentation. It was found that the destruction of the microheterogeneity of Fe-12%(wt.)Mn-1%(wt.)C melts during cooling and subsequent crystallization led to an increase in the dendritic parameter from 85 to 120 μm with increasing length of secondary branches of dendrites, crystallite size and small angle borders. Regardless of the crystallization conditions, manganese-enriched liquation layers with a thickness of L ~ 70–120 μm with a manganese content of 20 % (wt.) are formed on the surface of austenite dendrites, which leads to deformation inhomogeneity of the ingot. Based on the nanoindentation data, it is calculated that the adhesion of the manganese-enriched segregation layer to the body of austenite dendrites (Kint) for the sample crystallized after destruction of the microheterogeneous state increased by 1.2 times. The fracture energy along the boundary layer and the austenite dendrite body (Gc) also increased by 1.4 times. Average hardness values of the Young’s modulus of austenite dendrites did not change after the destruction of microheterogeneity. The mechanical characteristics of the ingot crystallized after the destruction of the microheterogeneity of the Fe-12%(wt.)Mn-1%(wt.)C melt under impact load generally improved. The equipment of the Ural Center for Shared Use "Modern nanotechnology" UrFU was used. The study was performed with the financial support of the Russian Foundation for Basic Research within the research project No. 19-33-90198.