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Title: Structural characterization of “carbide-free” bainite in a Fe–0.2C–1.5Si–2.5Mn steel

Low-alloyed, low C containing carbide-free bainitic steels are attractive candidates for applications in the automotive industry due to their well-balanced combination of high strength and ductility achieved in an economic way. In this work, their complex microstructure consisting of a mixture of bainitic ferrite, austenite with different morphologies and stabilities, martensite, M/A constituent and a few carbides has been investigated with metallographic and high-resolution techniques. After specific isothermal heat treatments in a dilatometer, a combination of LePera and Nital etching was applied to distinguish between bainite and martensite. Site-specific atom probe tips were prepared by means of scanning electron microscopy, electron backscatter diffraction and focused ion beam, revealing that “carbide-free” bainite consists of C depleted bainitic ferrite, C enriched retained austenite and occasional ε-carbides. Furthermore, it was found that the M/A constituent is highly dislocated and mainly martensitic. Its C content is increased compared to the nominal composition, but below the values obtained for retained austenite, explaining the lower transformation resistance. - Highlights: • Detailed top-down characterization of low C “carbide-free” bainitic steel • APT of all constituents in “carbide-free” bainite • Identification of ε-carbide based on its C content determined by APT • M/A constituent is mainly martensitic withmore » austenitic areas at the boundaries • Lower C content of M/A constituent explains its lower stability.« less
Authors:
 [1] ;  [2] ;  [3] ; ;  [1]
  1. Department of Physical Metallurgy and Materials Testing, Montanuniversitaet Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria)
  2. Böhler Edelstahl GmbH & Co KG, Mariazeller Straße 25, 8605 Kapfenberg (Austria)
  3. voestalpine Stahl Linz GmbH, voestalpine-Straße 3, 4020 Linz (Austria)
Publication Date:
OSTI Identifier:
22476071
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 102; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AUSTENITIC STEELS; BAINITE; CARBON COMPOUNDS; DIFFRACTION; ETCHING; FERRITES; HEAT TREATMENTS; ION BEAMS; IRON COMPOUNDS; LOW ALLOY STEELS; MANGANESE COMPOUNDS; MARTENSITIC STEELS; METALLOGRAPHY; MICROSTRUCTURE; RESOLUTION; SCANNING ELECTRON MICROSCOPY; SILICON COMPOUNDS