Near‐Atomic Investigation on the Elemental Redistribution During Coprecipitation of Nano‐Sized Kappa‐Type and B2 Precipitates in an Al‐Alloyed Lightweight Steel

In the present study, correlative transmission Kikuchi diffraction‐transmission electron microscopy (correlative TKD‐TEM) measurements, atom probe tomography (APT) and density functional theory (DFT) calculations are used to reveal the elemental redistribution during coprecipitation of nano‐sized kappa ( κ ) and B2 phases in the face‐centered cubic (FCC) matrix of an Al‐alloyed Fe10Al7Mn6Ni1C (wt.%) dual phase (FCC/body‐centered cubic) steel. Upon aging at 1073 K for 15 min, two co‐nanoprecipitation pathways are observed: within the FCC matrix, B2 forming in direct contact with κ ‐type precipitates or isolated B2 precipitates forming separately. APT reveals that the B2 precipitate next to κ (referred to as B2 I ) is close to an FeAl‐type phase, while the isolated B2 precipitate (referred to as B2 II ) is close to a NiAl‐type phase. The κ precipitates maintain a nearly constant Al content (≈18.4 at.%) regardless of whether they precipitate adjacent to B2 or not. DFT confirms that κ may accommodate limited Ni substitution at Fe sites without losing structural stability, and that Fe–Ni atoms exchange between κ and B2 is thermodynamically favorable at 1073 K. This exchange drives the B2 phase to evolve from NiAl‐type toward FeAl‐type, improving the stability of both phases during coprecipitation. These results provide understanding of κ –B2 interactions and offer insights for designing nanosized intermetallic‐strengthened microstructures in Al‐alloyed lightweight steels.