Microstructure and microhardness of 12% chromium ferritic-martensitic steel sintered from elemental powders
摘要
The paper investigates the phase composition and microstructure of sintered cylindrical samples made of 12% chromium ferritic-martensitic steel, fabricated from elemental powders. The experimental characterization involves optical metallography, X‑ray diffraction (XRD), scanning and transmission electron microscopies. The investigation shows the formation of the typical highly defective lamellar martensitic structure. This matrix incorporates finely dispersed particles of cementite-type M3C carbides. The identified regions with retained austenite predominantly locate as thin interlayers along the prior austenite grain boundaries. Severely deformed localized zones are observed in the material with increased dislocation density and refined (sub-microcrystalline) grain-subgrain structure. According to the XRD microanalysis, a notable heterogeneity is observed in the elemental distribution across different structural regions. Specifically, Cr and Ni demonstrate significant changes in their concentration, which is likely attributed to micro-segregation during sintering and subsequent cooling. Regarding mechanical properties, the microhardness distribution across both the diameter and height of the cylindrical sample is relatively uniform, indicating to homogeneous overall processing. However, the observed localized spread in the microhardness values probably correlates with the chemical and microstructural heterogeneity.