Сталь Дендрит Зростання

The crystal growth mode, that is, the way the solidification front advances, depends on the size of the undercooling formed by the solidification front. When the composition of undercooling increases from scratch and from small to large, the solidification front will evolve from a smooth and unorganized state to a cellular, dendritic, and endophytic growth. Under the actual solidification conditions of steel ingots, during most of the solidification period, the solidification front grows in a dendritic or endogenous state, ultimately obtaining the crystal structure of dendritic crystals. Crystals always come into contact with the liquid phase on the surface with the closest arrangement of atoms, in order to minimize surface energy. Face centered cubic lattice For Fe, the close packed plane is {111} plane, so the crystal that starts to precipitate is Octahedron shape. With the progress of crystallization, as fractional crystallization forms a solute enrichment layer at the front of solidification, the crystal will grow from the top of the Octahedron, the part with less solute concentration enrichment on the surface, along the direction [111], forming the primary axis (trunk) of the dendrite. Then, the primary axis grows and thickens preferentially along the edge of the Octahedron - the lower part of the solute concentration. When the composition undercooling at the surface of the primary axis further increases, the secondary dendrite secondary axis perpendicular to the primary axis will be formed at the Crystallographic defect of the primary axis. Subsequently, it is possible to form tertiary dendrites, quaternary dendrites, etc., with each crystal stem continuously growing thicker and producing higher order dendrites until they meet each other. Finally, the entire dendrite is filled between the branches, forming a grain.
Відповідність до різні зростання методи, три різні форми of dendrites can be obtained:
(1) columnar кристали. Тільки the the primary axis in one direction duces prorenent dendritic crystals. This primary axis is is called the spindle. When the composition is undercooled, columnar crystals are geted by dendritic growth, and secondary dendrites are not development, similar to to паличкоподібні кристали. As the композиція недоохолодження збільшення, the вищий порядок дендрити of columnar кристали поступово розвиваються.
(2) Equiaxed crystal. Dendritic crystals with relatively uniform development in all directions. Equiaxed crystals are only formed during during endogenetic growth.
(3) Granular crystals. Undeveloped dendritic crystals, also known as spherulites. Granular products can only be seen at the heat center of steel ingots and castings when the heat dissipation intensity is extremely low.