Cause Analysis on Cracks of an X-ray Protection Box Used for CT Machines

Cracks were discovered on an X-ray protection box used for CT machines during installation. To find out the causes of the cracks, instruments such as stereo microscope, direct reading spectrometer, optical microscope and scanning electron microscope were used to analyze the fracture morphology, chemical compositions and microstructure of the box. The results show that the cracks formed after casting and before heat treatment or during heat treatment. And the formation of cracks was related to the existence of serious casting porosity defects and more developed dendrite structure which not only reduced the strength and toughness of the box material, but also increased the internal residual stress of the material.