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       When steel pipes are cold drawn, due to defects such as cracks in the hot-rolled pipe blanks or the fractures that occur during use after the high-precision cold-drawn pipes are made into oil cylinders, almost no plastic deformation occurs and are generally brittle fractures. Brittle fracture is caused by a variety of reasons.
    For example: when there are precipitates on the grain boundaries, regardless of whether their strength is stronger or weaker than the matrix strength, it is the cause of cracks; the segregation of inclusions on the grain boundaries is also the cause of fracture; in addition, even under the action of alternating loads that are far less than the yield limit, fatigue fracture will also occur.

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  Precision boring and rolling tube

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  Precision cold drawn steel pipe

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  Precision cold drawn tube

   
Generally speaking, the mechanical performance indicators used in the design of hydraulic (pneumatic) parts assume that the material is uniform, continuous, and isotropic. Analysis based on this method is considered to be a safe design, but accidental fractures sometimes occur. Research has found that in the process of low-stress brittle fracture occurring in high-strength metal materials, the material structure is far from uniform and isotropic.
    There will be cracks, inclusions, pores and other defects in the structure. These defects can be regarded as micro-cracks in the material. In addition, brittle fracture is also related to the service temperature of the component. Through research, people have found that when the temperature is lower than a certain temperature value, the material will transform into a brittle state, and its impact absorption energy will decrease significantly. This phenomenon is called cold brittleness. Therefore, materials with a suitable cold brittleness transition temperature must be selected according to the working temperature of the component during design.