The precipitation hardening mechanisms in high strength maraging steels have been studied in detail by many
investigators [1-3], but limited information is available on the formation of austenite during aging [4-6]. Some
investigations [6,7] have been concerned with the understanding of the effect of reverted austenite formed during aging
on the mechanical properties. However, only a few investigations [5,8,9] have been reported on the morphology and
crystallographic feature of austenite. Shiang and Wayman [5] first reported the twin-related and coupled morphology of
Widmamt~tten austenite plates which were frequently observed in maraging steel. In addition, Ameyama et al. [9]
reported the morphology and crystallographic features of austenite formed in ferrite grain during aging in a two-phase
stainless steel, and found that each side of the austenite pair of twins satisfies the Kurdjumov-Sachs (K-S) orientation
relationship with the parent phase.