Three-dimensional model of filling the grain space with martensite crystals in austenite transformation

1. The suggested new variant of grouping of martensite plates is represented by a closed rhombic bipyramid faced by eight habitus planes of the same type united around one common direction (110). The direction (110) constitutes the minimum of all possible angles with the poles of the normals to the habitus planes of the grouping. 2. This pyramidal grouping of plates has been observed in a metallographic study of cooling martensite in alloy 50N29. 3. The space of an austenite grain is filled by the formed martensite phase by translation of pyramidal groups with formation of a kind of macrolattice. The pyramidal groups combine like coordination octahedrons of densely packed crystal structures along the common edges and vertices. 4. Different variants of growth of faces in pyramidal groups in combination with different variants of cutting of the macrolattice by the plane of the metallographic specimen make it possible to explain the origin of the morphological variants of martensite.