ISSUE 2/2010

/// 01
Fraś, E.; Kawalec, M.; Lopez, H. F.
Solidification microstructures and mechanical properties of high-vanadium Fe-C-V and Fe-C-V-Si alloys

Fe-C-V and Fe-C-V-Si alloys of various C, V and Si compositions were investigated in this work. It was found that the phases present in both of these alloy systems were alloyed ferrite, alloyed cementite, and VCx carbides. Depending on the alloy composition, the solidified microstructural constituents were granular pearlite-like, lamellar pearlite, or mixtures of alloyed ferrite + granular pearlite-like or granular pearlite-like + lamellar pearlite. In addition, it is shown that in Fe-C-V alloys the C/V ratio influences a) the type of matrix, b) the fraction of vanadium carbides, fv and c) the eutectic cell count, NF. In Fe-C-V alloys, a relationship between the alloy content corresponding to the eutectic line was experimentally determined and can be described by Ce = 7,91 Ve-0.635 where Ce and Ve are the carbon and vanadium composition of the eutectic. Moreover, in the Fe-C-V alloys (depending on the alloy chemistry), the primary VCx carbides crystallize with nonfaceted or nonfaceted/faceted interfaces, while the eutectic morphology is nonfaceted/nonfaceted with regular fiber-like structures, or it possesses a dual morphology (nonfaceted/nonfaceted with regular fiber-like structures + nonfaceted/faceted with complex regular structures). In the Fe-C-V-Si system, the primary VCx carbides solidify with a nonfaceted/faceted interface, while the eutectic is nonfaceted/faceted with complex regular structures. In particular, spiral eutectic growth is observed when Si is present in the Fe-C-V alloys. In general, it is found that as the matrix constituent shifts from predominantly ferrite to lamellar pearlite, the hardness, yield and tensile strengths exhibit substantial increases at expenses of ductility. Moreover, Si additions lead to alloy strengthening by solid solution hardening of the ferrite phase and/or through a reduction in the eutectic fiber spacings with a decrease in the alloy ductility.




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