Application of X-ray Technique to Study the Structure of Ultrafine-Grained Ferritic/Martensitic Steel
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JMEPEG https://doi.org/10.1007/s11665-019-04440-1
Application of X-ray Technique to Study the Structure of Ultrafine-Grained Ferritic/Martensitic Steel V.D. Sitdikov, R.K. Islamgaliev, M.A. Nikitina, and G.F. Sitdikova (Submitted April 17, 2019; in revised form October 22, 2019) In this work, x-ray diffraction and transmission electron microscopy (TEM) analyses have been applied to study the structure of ultrafine-grained (UFG) ferritic/martensitic steel as compared to coarse-grained samples subjected to standard treatment. The x-ray phase analysis of diffraction patterns taken in the ‘‘transmission’’ mode allowed determining the volume fraction and phase composition of particles in the UFG samples. The lattice parameter, the size of coherent scattering domains, the averaged dislocation density, and the fraction of edge and screw dislocations of the ferritic phase in steel were determined according to the diffraction patterns taken in the ‘‘reflection’’ mode. The small-angle x-ray scattering (SAXS) technique was used to study the quantitative characteristics of the size, shape, and distribution of precipitates in the UFG samples. The TEM investigations were performed on the same foils to confirm the results of SAXS. The quantitative evaluations of dispersion and dislocation hardenings in ferritic/martensitic steel were conducted on the basis of the results obtained. Keywords
ferritic/martensitic steel, transmission electron microscopy, ultrafine-grained structure, x-ray diffraction
1. Introduction It is known that 12Cr-2W ferritic/martensitic steels are used at elevated temperatures due to their excellent creep and oxidation resistance, but their strength after quenching and tempering usually does not exceed 900 MPa (Ref 1). The strength of ferritic/martensitic steels is ensured by both the martensitic transformation after quenching and additional dispersion hardening after subsequent tempering (Ref 1-4). The recent studies showed that the strength of ferritic/martensitic steels could be significantly enhanced via refining the grain structure by severe plastic deformation (SPD) techniques (Ref 5). The grain size of the ultrafine-grained (UFG) structure as well as the volume fraction and size of precipitates are conventionally determined through analyzing a microstructure by TEM techniques. The contributions of various strengthening mechanisms are usually calculated on the basis of the TEM results (Ref 6). As, during thermomechanical treatment of steels, a considerable contribution to strength is made by precipitates, the estimation of their contribution to hardening should be made
V.D. Sitdikov, Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, 12 K. Marx Str., Ufa, Russia 450000; and Laboratory for Mechanics of Bulk Nanomaterials, Saint Petersburg State University, 28 Universitetsky pr., Saint Petersburg, Russia 198504; and R.K. Islamgaliev, M.A. Nikitina, and G.F. Sitdikova, Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, 12 K. Marx Str., Ufa, R
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