Influence of the Geometry of Cast Products on Orientation of Dendritic Crystals Growth and Formation of Hot Cracks

The results of studies of hot cracks formed in cast shapes from low-alloy steel G21Mn5 are presented. Macroand microstructural analyses are carried out. Fractography studies of samples cut from castings used in the production of railway freight cars are performed. The criteria used to assess the susceptibility of alloys to hot brittleness are considered. It is shown that the orientation of dendritic crystals affects significantly the formation of hot cracks, and the direction of the dendrite growth is determined by the conditions of heat dissipation, which are influenced in their turn by the geometry of the casting. The phenomenon of coalescence under the conditions of misorientation of neighbor dendrites and its effect on the formation of hot cracks is studied. A modified RDG criterion is suggested, which allows for the influence of the geometry of the cast product on the formation of hot cracks through the angle of misorientation of neighbor crystals.