Morphology analysis of hot tears casting defects

The appearance characteristics of hot tears casting defects are that the tears propagates along the grain boundary, the appearance is tortuous, the surface has oxidation color, is not smooth, the surface is wide and the interior is narrow. It usually occurs in the hot spot where the section thickness of the casting is abrupt or the local solidification is slow, as well as the final solidification. Hot tears casting defects not only reduce the mechanical properties of the metal, but also cause stress concentration. When in use, the tears propagation will lead to the fracture of the casting, resulting in safety accidents and great harm.

1. Macro morphology analysis of hot tears casting defects

Observe the macro morphology of hot tears casting defects. One kind of hot tears is irregular dendritic solidification surface, as shown in Figure 1. If the two sides of the tears are close together, the two sides will not completely coincide. The surface of this tears is similar to the shrinkage cavity surface, which is called “shrinkage tears”.

The tears shown in Figure 2 is obviously different from the “shrinkage tears”, which is a sawtooth hot tears casting defect with concave convex compensation broken along the grain boundary. If the two sides of the tears are combined and close together, the sawteeth on both sides can basically coincide to form a complete whole. We also call this kind of tears “tensile tears”.

2. Micro morphology analysis of hot tears casting defects

There are great differences in the macro appearance of hot tears casting defects of steel castings because of the different causes of formation. In order to further analyze the causes of hot tears casting defects, it is necessary to understand and analyze the micro morphology of tears. The micro morphology is shown in figures 3 and 4.

It can be clearly seen from microscopic figures 3 and 4 that shrinkage tears are accompanied by shrinkage porosity and small cavities, while tensile tears are accompanied by tearing microcracks and casting defects.

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