Continuous carbide films develop along the grain boundaries after proeutectoid carbide grains precipitate. When carbide films thicken, grain boundary allotriomorphs appear. The growth of Widmanstätten plates proceeds by either protrusions of the grain boundary allotriomorphs or by separate nucleation and growth of cementite plates in the austenite. The former produces Widmanstätten side-plates and the latter intragranular Widmanstätten plates [11]. Inverse bainites form with the ferrite plates attached to M3C Widmanstätten plates, and are the major structure in the austenite of hypereutectoid steels at sufficiently low temperatures [5], [6], [7], [8], [9] and [10].