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Title: 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 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-1.48Si wt.% steel after quenching to 225 °C and partitioning at 400 °C for 10 or 300 s, 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 2.4 at.%, accounting for a substantial portion (~24% to 41%) of the bulk carbon content of the steel. The amount (5.0 at.%) of η-carbide that formed after quenching and tempering (Q&T) at 400 °C for 300 s was significantly greater than after partitioning at 400 °C formore » 300 s (2.4 at.%), suggesting that carbon partitioning from martensite to austenite occurs in conjunction with η-carbide formation during Q&P in these specimens.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [2] ;  [1] ;  [1]
  1. Colorado School of Mines, Golden, CO (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
OSTI Identifier:
1193479
Report Number(s):
LA-UR--14-28509
Journal ID: ISSN 1359-6454; PII: S1359645415000282
Grant/Contract Number:
AC52-06NA25396; EE0005765
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 90; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE quenching and partitioning; tempering; transition carbides; Mossbauer spectroscopy; transmission electron microscopy