High-resolution electron microscopy characterization of 2H and 9R variant in the ferritic steels containing copper

Ferritic steels containing copper have been studied as model systems for cluster/precipitate formation in reactor pressure vessel steels. The samples were aged at 400 °C for 2000 h and subsequently analyzed using high-resolution electron microscopy. Direct evidence was found that, besides the 9R structure occurring, there exist also 2H variant and stacking faults in local regions of the same Cu precipitate. The 2H variant has a hexagonal unit cell with lattice parameters a = b = 0.254 nm and c = 0.417 nm and axial ratio c/a = 1.642.