主催: The Iron and Steel Institute of Japan
p. 88-95
The structures of carbon clusters and carbides in a low-carbon ferritic steel were investigated at atomic-scale by annular dark-field scanning transmission electron microscopy. In the low-carbon ferritic steel aged at 473 K for 1 h, some homogeneously dispersed ε-carbides were formed within the matrix as closely spaced granules aligned to <001> of the ferrite matrix, and others were heterogeneously formed on AlN precipitates. The ε-carbides formed on AlN precipitates were coexisted with carbon clusters with c/a ratio of 1.1, possibly formed via Zener-ordering. In-situ heating experiments showed that ε-carbides acted as precursors for θ-carbides via dissolution of ε-carbides. The microstructural evidence showed that the precipitation sequence of the low-carbon ferritic steels aged at 473 K is proposed as: supersaturated solid-solution → carbon clusters → ε-carbides → θ-carbides, suggesting that Zener-ordering should be the most fundamental step for the carbide precipitation sequence.
