Fe－1．83C马氏体中碳的有序化──Ⅰ．普通有序相的晶体结构

CARBON ORDERING IN Fe-1.83C MARTENSITE Ⅰ. Crystal Structure of a Conventional Ordered Phase

采用电子衍射方法对Ｆｅ－１．８３Ｃ马氏体室温时效时产生的有序相结构进行研究，确定其结构为偏离化学计量成分Ｆｅ_４Ｃ的γ′－Ｆｅ_４结构，称为γ′－Ｆｅ_ｘＣ（Ⅰ）（ｘ＝４－１１）。碳原子位于单胞的１／２，１／２，１／２位置。该有序相单胞尺寸为：（ａ_Ｍ，ｃ_Ｍ分别为马氏体单胞的ａ和ｃ轴长度），它与母相完全共格，位向关系为（００１）_Ⅰ∥（００１）_Ｍ，［１００］_Ⅰ∥［１１０］_Ｍ。根据γ′－Ｆｅ_ｘＣ（Ⅰ）晶体结构计算出的有序相衍射花样与实验得到的衍射花样全部吻合。

Electron diffraction technique is applied to determine the crystal structure of a conventional ordered phase found in an aged high carbon(1.83%) martensite. Experimental data of good quality are obtained to ensure the reliability of the structure determination. The ordered phase is found to be an off-stoichiometric compound isomorphic with γ'-Fe_4N, it is thus called γ'-Fe_xC (I)(x= 4-11). Its cell dimension is (a_M and c_M are the length of a and c axis of martensite unit cell, respectively). The ordered phase is coherent with martensite, their orientation relationship is (001)Ⅰ∥(001)M,[100]Ⅰ∥[110]M. Diffraction patterns calculated based on γ'-Fe_xC (I) are in agreement with experimental observations.