Characterization of transition carbides in quench and partitioned steel microstructures by Mössbauer spectroscopy and complementary techniques

Quenching and partitioning (Q&P) produces steel microstructures with martensite and austenite that exhibit promising property combinations for third generation advanced high strength steels. Understanding the kinetics of reactions that compete for available carbon, such as carbide formation, is...

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Bibliographic Details
Published in:Acta materialia 2015-05, Vol.90 (C), p.417-430
Main Authors: Pierce, D.T., Coughlin, D.R., Williamson, D.L., Clarke, K.D., Clarke, A.J., Speer, J.G., De Moor, E.
Format: Article
Language:English
Subjects:
Austenite
Carbides
Carbon
MATERIALS SCIENCE
Microstructure
Mossbauer spectroscopy
Mössbauer spectroscopy
Partitioning
Quadratic programming
Quenching
Quenching and partitioning
Steels
Tempering
Transition carbides
Transmission electron microscopy
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Summary:Quenching and partitioning (Q&P) produces steel microstructures with martensite and austenite that exhibit promising property combinations for third generation advanced high strength steels. Understanding the kinetics of reactions that compete for available carbon, such as carbide formation, is critical for alloying and processing design and achieving austenite enrichment and retention during Q&P. Mössbauer effect spectroscopy (MES) was used to characterize Q&P microstructures in a 0.38C–1.54Mn–1.48Siwt.% steel after quenching to 225°C and partitioning at 400°C for 10 or 300s, with an emphasis on transition carbides. The recoilless fraction for η-carbide was calculated and a correction for saturation of the MES absorption spectrum was applied, making quantitative measurements of small amounts of η-carbide, including non-stoichiometric η-carbide, possible in Q&P microstructures. Complementary transmission electron microscopy confirmed the presence of η-carbides, and MES and X-ray diffraction were used to characterize the austenite. The amount of η-carbide formed during Q&P ranged from 1.4 to 2.4at.%, accounting for a substantial portion (∼24% to 41%) of the bulk carbon content of the steel. The amount (5.0at.%) of η-carbide that formed after quenching and tempering (Q&T) at 400°C for 300s was significantly greater than after partitioning at 400°C for 300s (2.4at.%), suggesting that carbon partitioning from martensite to austenite occurs in conjunction with η-carbide formation during Q&P in these specimens.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2015.01.024