The formation reason and process of tensile crack casting defect are different from that of shrinkage crack casting defect.
1) When the molten steel is poured into the casting cavity, the surface of the steel casting near the sand mold begins to solidify first and forms a solidification layer.
2) When the solidified layer becomes a dendrite skeleton with certain strength, the dendrite skeleton begins to shrink with the continuous decrease of temperature, but the shrinkage is hindered by the mold, core and sprue, resulting in stress and strain. When the generated stress or strain is greater than the fracture strength or strain strength of the metal at that temperature, the metal is first pulled apart at the position with dense sulfide and low thermal strength and forms a micro crack casting defect. With the continuous increase of stress, the micro crack expands. At this time, if there is no liquid steel feeding crack, a tensile crack casting defect is formed.
3) During the solidification process of steel castings, the solidification layer is continuously thickened, and the tensile crack casting defects also gradually expand inward. In this way, the stress caused by the blocked shrinkage of steel castings gradually decreases, and the crack casting defects become the form of large surface opening and small internal opening.