Atom probe tomography characterization of heavily cold drawn pearlitic steel wire.

Institut für Materialphysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany.
Ultramicroscopy (Impact Factor: 2.47). 11/2010; 111(6):628-32. DOI: 10.1016/j.ultramic.2010.11.010
Source: PubMed

ABSTRACT Atom Probe Tomography (APT) was used to analyze the carbon distribution in a heavily cold drawn pearlitic steel wire with a true strain of 6.02. The carbon concentrations in cementite and ferrite were separately measured by a sub-volume method and compared with the literature data. It is found that the carbon concentration in ferrite saturates with strain. The carbon concentration in cementite decreases with the lamellar thickness, while the carbon atoms segregate at dislocations or cell/grain boundaries in ferrite. The mechanism of cementite decomposition is discussed in terms of the evolution of dislocation structure during severe plastic deformation.

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    ABSTRACT: In order to investigate the thermodynamic driving force for the experimentally observed accumulation of C in ferritic layers of severely plastically deformed pearlitic wires, the stabilities of C interstitials in ferrite and of C vacancies in cementite are investigated as a function of uniaxial stain, using density-functional theory. In the presence of an applied strain along [1 1 0] or [1 1 1], the C interstitial in ferrite is significantly stabilized, while the C vacancy in cementite is moderately destabilized by the corresponding strain states in cementite [1 0 0] and ([0 1 0]). The enhanced stabilization of the C interstitial gives rise to an increase in the C concentration within the ferritic layers by up to two orders of magnitude. Our results thus suggest that in addition to the generally assumed non-equilibrium, dislocation-based mechanism, there is also a strain-induced thermodynamic driving force for the experimentally observed accumulation of C in ferrite.
    Acta Materialia 01/2013; 61. · 3.94 Impact Factor
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    ABSTRACT: A local electrode atom probe has been employed to analyze the redistribution of alloying elements including Si, Mn, and Cr in pearlitic steel wires upon cold-drawing and subsequent annealing. It has been found that the three elements undergo mechanical mixing upon cold-drawing at large strains, where Mn and Cr exhibit a nearly homogeneous distribution throughout both ferrite and cementite, whereas Si only dissolves slightly in cementite. Annealing at elevated temperatures leads to a reversion of the mechanical alloying. Si atoms mainly segregate at well-defined ferrite (sub)grain boundaries formed during annealing. Cr and Mn are strongly concentrated in cementite adjacent to the ferrite/cementite interface due to their lower diffusivities in cementite than in ferrite.
    Ultramicroscopy 11/2012; · 2.47 Impact Factor
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    ABSTRACT: Atom-probe tomography (APT) and first-principle calculations are employed to investigate the role of Si on the partitioning behavior of Mn in pearlitic steel. Mn is experimentally observed to partition preferentially to cementite, while Si prefers to bcc α-Fe by APT. The partitioning ratio of Mn in SWRS87BM steel (i.e., 8.17±1.57) is more pronounced than that in SWRS82B steel (i.e., 3.66±0.44), which is attributed to the higher content of Si in the former than in the latter. First-principle calculations illustrate that Si atoms, which strongly partition to bcc α-Fe phase, repulse Mn atoms into cementite phase and increase the Mn partitioning ratio.
    Materials Letters. 01/2014; 134:84–86.


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