某CT机X射线防护箱体在安装过程中发现裂纹，为了找出裂纹产生的原因，利用体视显微镜、直读光谱仪、光学显微镜、扫描电子显微镜等仪器对箱体的断口形貌、化学成分和显微组织等进行了观察和分析。结果表明：该X射线防护箱体上的裂纹是在铸造后、热处理之前或热处理过程中产生的，裂纹的产生与该部位存在较严重的疏松缺陷和较发达的枝晶组织有关，这不仅降低了箱体材料的强度和韧性，而且增加了材料内部的残余应力。

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.