The TEM analysis of the M3C carbide in the austenite of the steel after 100-h isothermal holding at 1023 K. (a) The BF image revealing the grain-boundary M3C carbide (γ: austenite; C: M3C), (b) another BF image showing a dark Widmanstätten cementite in the austenite, (c) the accompanying SAD pattern from the [1View the MathML source1] direction of M3C carbide in (a), and (d) the [01View the MathML source] SAD pattern of the light colored austenite adjacent to the M3C carbide grain in (a). (T: transmitted beam).