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Atomic-scale investigation of carbon atom migration in surface induced white layers in high-carbon medium chromium (AISI 52100) bearing steel
RISE - Research Institutes of Sweden, Swerea, Swerea IVF AB, Tillverkningsprocesser. Chalmers University of Technology, Sweden; AB SKF, Sweden.ORCID-id: 0000-0001-9288-3872
Chalmers University of Technology, Sweden.
Chalmers University of Technology, Sweden.
Chalmers University of Technology, Sweden.
Vise andre og tillknytning
2017 (engelsk)Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 130, s. 155-163Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the Ac1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ-carbides (cementite). The APT results reveal that the original θ-carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (<0.1 at.%) is governed by the high dislocation density inside the grains, supported by the favorable binding energy between dislocations and C-atoms compared to C-atoms and Fe in carbides. No other evidence of redistribution of the substitutional alloying elements was observed. TEM analyses showed that T-WLs comprises of an equiaxed and nano-sized grains with well-defined cell boundaries, whereas the structure in the M-WLs comprised of elongated sub-grains formed via re-orientation of the original martensite followed by breakage/partitioning into elongated sub-grains.

sted, utgiver, år, opplag, sider
2017. Vol. 130, s. 155-163
Emneord [en]
Atom probe tomography; Carbon diffusion, Martensite, Nanocrystalline microstructure, White layer
HSV kategori
Identifikatorer
URN: urn:nbn:se:ri:diva-29401DOI: 10.1016/j.actamat.2017.03.030Scopus ID: 2-s2.0-85015817384OAI: oai:DiVA.org:ri-29401DiVA, id: diva2:1091283
Tilgjengelig fra: 2017-04-26 Laget: 2017-04-26 Sist oppdatert: 2019-01-03bibliografisk kontrollert

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