24 research outputs found
On the spheroidized carbide dissolution and elemental partitioning in a high carbon bearing steel 100Cr6
We report on the characterization of high carbon bearing steel 100Cr6 using
electron microscopy and atom probe tomography in combination with
multi-component diffusion simulations (DICTRA). Scanning electron micrographs
show that around 14 vol.% spheroidized carbides are formed during soft
annealing and only 3 vol.% remain after dissolution into the austenitic matrix
by austenitization at 1123 K (850 {\deg}C) for 300 s. The spheroidized
particles are identified as (Fe, Cr)3C by transmission electron microscopy.
Atom probe analyses reveal the redistribution and partitioning behaviors of
elements, i.e. C, Si, Mn, Cr, Fe in both, the spheroidized carbides and the
bainitic matrix in the sample isothermally heat-treated at 773 K (500 {\deg}C)
after austenitization. A homogeneous distribution of C and gradual gradient of
Cr was detected within the spheroidized carbides. Due to its limited
diffusivity in (Fe, Cr)3C, Cr exhibits a maximum concentration at the surface
of spheroidized carbides (16 at.%) and decreases gradually from surface towards
the core down to a level of about 2 at.%. The atom probe results also indicate
that the partially dissolved spheroidized carbides during austenitization may
serve as nucleation sites for intermediate temperature cementite within
bainite, which results in a relatively softer surface and harder core in
spheroidized particles. This microstructure may contribute to the good wear
resistance and fatigue propertie
Ordnungsumwandlungen in kubisch raumzentrierten Mischkristallen : Modellvorstellungen und Messmethoden ; [mit] Tabellen
Ordnungsumwandlungen in kubisch raumzentrierten Mischkristallen : Modellvorstellungen und Messmethoden ; [mit] Tabellen
Thermodynamic self-consistency issues related to the Cluster Variation Method: The case of the BCC Cr-Fe (Chromium-Iron) system
The Cluster Variation Method (CVM), introduced over 50 years ago by Prof. Dr. Ryoichi Kikuchi, is applied to the thermodynamic modeling of the BCC Cr-Fe system in the irregular tetrahedron approximation, using experimental thermochemical data as initial input for accessing the model parameters. The results are checked against independent data on the low-temperature miscibility gap, using increasingly accurate thermodynamic models, first by the inclusion of the magnetic degrees of freedom of iron and then also by the inclusion of the magnetic degrees of freedom of chromium. It is shown that a reasonably accurate description of the phase diagram at the iron-rich side (i.e. the miscibility gap borders and the Curie line) is obtained, but only at expense of the agreement with the above mentioned thermochemical data. Reasons for these inconsistencies are discussed, especially with regard to the need of introducing vibrational degrees of freedom in the CVM model. (C) 2008 Elsevier Ltd. All rights reserved.Sao Paulo State Research Funding Agency (FAPESP, Sao Paulo-SP, Brazil)[2006/024700]Brazilian National Research Council (CNPq, Brasilia-DF, Brazil)[301392/2004-8