Manabu Tanaka1, Ohmi Miyagawa2 and Dai Fujishiro3
1Graduate School, Tokyo Metropolitan University, Tokyo
The crystallography of the grain boundary reaction nodule has been investigated for several austenitic heat resisting steels including a 21-4 N engine value steel (21%Cr-4%Ni-9%Mn-0.5%C-0.4%N) by means of optical and transmission electron microscopy.
It was revealed that the orientation of the austenite matrix in the nodule formed by grain boundary reaction was generally the same as that of the neighboring grain but different from that of the grain in front of the nodule. This relationship was confirmed for two kinds of steels which have M23C6 or Cr2N as grain boundary reaction precipitate.
In high chromium-nickel heat resisting steels with high nitrogen and extremely low carbon contents, only Cr2N (hcp) was formed by the grain boundary reaction and the following orientation relationship was found between Cr2N and matrix in the grain boundary reaction nodule: (00⋅1)Cr_2N//( 11)γ, and [11⋅0]Cr_2N//γ, i.e. the close packed plane of Cr2N is parallel to 111γ.
Please do not copy without permission.