Abstract
The local composition of small, coherent Cu-rich precipitates with a metastable body-centered cubic structure in a ferritic α-Fe matrix of a high-strength low-carbon steel was studied by conventional atom-probe tomography. The average diameter, 〈D〉, of the precipitates is 2.5 ± 0.3 nm at a number density of (1.1 ± 0.3) × 10 24 m-3 after direct aging at 490°C for 100 min to a near-peak hardness condition, yielding a value of 84 Rockwell G. Besides Cu, the precipitates contain 33 ± 1 at.% Fe and are enriched in Al (0.5 ± 0.1 at.%). Nickel and Mn are significantly segregated at the α-Fe matrix/precipitate heterophase interfaces. The Gibbsian interfacial excesses relative to Fe and Cu are 1.5 ± 0.4 atoms nm-2 for Ni and 1.0 ± 0.3 atoms nm-2 for Mn. The reduction of the interfacial free energy, calculated utilizing the Gibbs adsorption isotherm, is 16 mJ m -2 for Ni and 11 mJ m-2 for Mn.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 841-849 |
| Number of pages | 9 |
| Journal | Acta Materialia |
| Volume | 54 |
| Issue number | 3 |
| DOIs | |
| State | Published - Feb 2006 |
Funding
The authors thank Dr. Shrikant P. Bhat, Ispat-Inland Inc., for the provision of the steel used in this study and the bulk chemical composition. The atom-probe tomographic experiments were performed in the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The instruments in this Center were purchased with funds from the Office of Naval Research and the National Science Foundation’s instrumentation programs. Financial support by the Office of Naval Research, Grant Nos. N000014-03-1-0252 and N00014-99-1-0601, Drs. George Yoder and Julie Christodoulou, program directors, is gratefully acknowledged.
Keywords
- Ferritic steels
- Gibbsian interfacial excess
- Interface segregation
- Nanostructure
- Precipitation hardening
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys