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Ferrite (iron)
About: Ferrite (iron) is a research topic. Over the lifetime, 20700 publications have been published within this topic receiving 234474 citations.
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TL;DR: In this paper, the nanostructure and the phase composition in UIC 860V pearlitic steel, deformed by high pressure torsion in the shear stress range from 62 to 430, were studied.
393 citations
TL;DR: In this paper, the authors performed density-functional theory (DFT) calculations of carbon dissolution and diffusion in iron, the latter being a typical example of interstitial diffusion, and they found that a supercell with 128 Fe atoms and one C atom is sufficient for describing dilute concentrations of carbon in bcc Fe.
Abstract: We perform density-functional theory (DFT) calculations of carbon dissolution and diffusion in iron, the latter being a typical example of interstitial diffusion. The Kohn-Sham equations are solved with periodic boundary conditions and within the projector-augmented-wave formalism, using the generalized gradient approximation for electron exchange and correlation. With the solution enthalpy as an indication of cell size convergence, we find a supercell with 128 Fe atoms and one C atom is sufficient for describing dilute concentrations of carbon in bcc Fe. The solution enthalpy of carbon in an octahedral site in ferrite is predicted to be 0.74 eV, i.e., the dissolution of carbon in bcc ferromagnetic (FM) Fe is an endothermic process. Using the Fe128C1 periodic cell, we find that the minimum-energy path (MEP) of carbon diffusion from one octahedral site to another (via a tetrahedral site) has a barrier of 0.86 eV, in excellent agreement with the experimental value of 0.87 eV. This encouraging benchmark result prompted us to investigate carbon diffusion in austenite, whose electronic structure is less well characterized experimentally. Cell size convergence results show that a supercell with 32 Fe atoms and one C atom is sufficient. The calculated solution enthalpy is $\ensuremath{-}0.17$ eV, which indicates that the dissolution of carbon in fcc Fe is exothermic, consistent with the known greater solubility of C in austenite compared to ferrite. The MEP shows that carbon moves linearly from an octahedral site to another, contrary to the common notion of an off-plane diffusion path. The diffusion barrier is calculated to be 0.99 eV. Since we model austenite with the FM high-spin phase, the diffusion barrier we obtain is not directly comparable to the experiments in which austenite is usually paramagnetic. However, this prediction is relevant for C incorporation into Fe thin films, since FM high-spin fcc Fe can be obtained by epitaxial growth of thin Fe films on a Cu substrate.
379 citations
TL;DR: In this article, differently heat treated samples of a low alloyed TRIP steel have been investigated using electron diffraction techniques in SEM and TEM, and the results showed that the mechanical properties of these samples are most strongly influenced by the amount and distribution of carbon in the retained austenite and by the degree of recovery in bainite and martensite.
378 citations
TL;DR: In this article, a study of the mechanical properties of dual phase (martensite plus ferrite) structures produced when Fe-Mn-C alloys are quenched from the austenite and ferrite phase field, so as to give a series of alloys with constant ferrite and martensite compositions but varying percent martensites, was made.
Abstract: A study has been made of the mechanical properties of dual phase (martensite plus ferrite) structures produced when Fe-Mn-C alloys are quenched from the austenite plus ferrite phase field, so as to give a series of alloys with constant ferrite and martensite compositions but varying percent martensites. It is found that the strength of a dual phase structure is dependent on the ferrite grain size and the volume fraction of martensite, and is independent of the composition and strength of the martensite. In agreement with previous work the ductility of these steels is superior to that for standard HSLA steels at the same tensile strength. As shown in a previous paper the strength and ductility as a function of percent martensite are in agreement with Mileiko’s theory of composites of two ductile phases. This theory and the results indicate that the superior ductility of dual phase steels is largely a consequence of the high strength (fine grained), highly ductile (low interstitial content) ferrite matrix.
373 citations
TL;DR: In this article, two Fe-0.2C-1.5Si steels with and without the addition of 0.039Nb were studied using laboratory rolling-mill simulations of controlled thermomechanical processing and the microstructures of all samples were characterized by optical metallography, X-ray diffraction, and transmission electron microscopy (TEM).
Abstract: Two Fe-0.2C-1.55Mn-1.5Si (in wt pct) steels, with and without the addition of 0.039Nb (in wt pct), were studied using laboratory rolling-mill simulations of controlled thermomechanical processing. The microstructures of all samples were characterized by optical metallography, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The microstructural behavior of phases under applied strain was studied using a heat-tinting technique. Despite the similarity in the microstructures of the two steels (equal amounts of polygonal ferrite, carbide-free bainite, and retained austenite), the mechanical properties were different. The mechanical properties of these transformation-induced-plasticity (TRIP) steels depended not only on the individual behavior of all these phases, but also on the interaction between the phases during deformation. The polygonal ferrite and bainite of the C-Mn-Si steel contributed to the elongation more than these phases in the C-Mn-Si-Nb-steel. The stability of retained austenite depends on its location within the microstructure, the morphology of the bainite, and its interaction with other phases during straining. Granular bainite was the bainite morphology that provided the optimum stability of the retained austenite.
356 citations