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

Journal Article · Wed Apr 15 00:00:00 EDT 2015 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2015.02.020· OSTI ID:22476071

Hofer, Christina ^[1]; Leitner, Harald ^[2]; Winkelhofer, Florian ^[3]; Clemens, Helmut; Primig, Sophie ^[1]

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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)

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 with austenitic areas at the boundaries • Lower C content of M/A constituent explains its lower stability.

• OSTI ID: 22476071
• Journal Information: Materials Characterization, Vol. 102; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
• Country of Publication: United States
• Language: English

Related Subjects

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