Phase transformation of Cu‐rich precipitates from 9R to 3R variant via ledges mechanism in ferritic steel containing copper

Summary Precipitates and solute enrich in aged ferritic steel containing copper were examined using high‐resolution electron microscopy, high‐angle annular dark‐field scanning transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. Two ledges with one‐atom and two‐atom layers height in the 9R/3R interface were observed. The enrichment of copper into two successive closed‐packed planes with an interval of Fe‐rich close‐packed plane was detected. The passage of the Shockley partial, or the shearing, changes the stacking sequence of closed‐packed planes. Finally, 9R Cu variant transformed into 3R Cu variant.