窒素を含む25%Cr-28%Ni-2%Moオーステナイト鋼中に析出するCr₂Nの透過電子顕微鏡観察

抄録

The precipitation morphology of Cr₂N with hcp structure in 25%Cr-28%Ni-2%Mo austenitic steels containing 0.30, 0.36 and 0.63 wt% nitrogen was studied. In the steels with a 0.3% concentration level of nitrogen, only intergranular precipitates were observed. The coherent twin boundary was not a site favorable for the Cr₂N precipitation. In the steel containing 0.63% nitrogen, intragranular precipitates were also observed. The intragranular precipitates of Cr₂N were formed on {111} matrix planes as thin plates with a broad face of (00·1)_Cr2N. The orientation relationship between the austenitic matrix and the precipitates of Cr₂N was {00·1}_Cr2N\varparallel{111}_γ and ⟨11·0⟩_Cr2N\varparallel⟨\bar110⟩_γ. The growth of the Cr₂N precipitates at about 700°C was accompanied by the generation of dislocations.
Density of the Cr₂N precipitates on isolated dislocations was far much smaller than that of precipitates of other interstitial compounds, such as M₂₃C₆, in austenitic steels. In the cold rolled steel with 0.63% nitrogen, thin plates of Cr₂N precipitated on deformation bands consisting of the planar array of dislocations. At higher aging temperatures where the recrystallization followed by the precipitation took place, the shape of the plate precipitates changed into that of the globular ones with no special orientation relationship with the recrystallized grain after the passage of through a recrystallizing interface.