Explanation

Also known as shrinkage crack, a crack caused by uneven shrinkage (such as solidification shrinkage and solid shrinkage) of various parts when a metal or alloy cools down from high temperature, is a serious casting defect and a serious casting defect. After the casting is completely solidified, it continues to cool to elasticity state. When it is close to room temperature or room temperature, the crack is caused by the stress in the casting exceeding the tensile strength of the metal due to the external resistance of the mold or the shrinkage resistance of the casting structure itself. The shape of shrinkage crack is straight or smooth curve, and it often passes through crystal rather than fracture along grain boundary. The fracture surface has a metallic luster, sometimes showing a slight oxidation color. shrinkage crack often occurs at the tensile part of castings, especially at the stress concentration. Large castings with complex shapes are prone to shrinkage crack. Due to the large residual stress in the castings, shrinkage crack may also occur during handling or cleaning vibration. The composition and melting quality of alloy have great influence on shrinkage crack. For example, when the phosphorus content in steel exceeds 0.1%, the shrinkage crack tendency increases significantly; Poor deoxidation of cast steel and more non-metallic inclusions in steel also increase the tendency of shrinkage crack.

Classification