日本金属学会誌

J. Japan Inst. Metals, Vol. 41, No. 11 (1977),
pp. 1145-1153

Electron Microscopic Observation of Cr2N Precipitated in 25%Cr-28%Ni-2%Mo Austenitic Steels Containing Nitrogen

Tohru Tanaka1, Makoto Kikuchi2 and Ryohei Tanaka2

1Graduate School, Tokyo Institute of Technology, Tokyo
2Department of Metallurgy, Faculty of Engineering, Tokyo Institute of Technology, Tokyo

Abstract:

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)Cr_2N. The orientation relationship between the austenitic matrix and the precipitates of Cr2N was 00{⋅1}Cr_2N//111γ and < 11⋅0 > Cr_2N//< 110 > 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.


(Received 1977/04/9)

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