904LWhen stainless steel is cold-drawn, the stainless steel billet may have defects such as cracks. For instance, after high-precision cold-drawn tubes are formed into oil cylinders, the fractures that occur during use show almost no plastic deformation and are generally brittle fractures. Brittle fracture is caused by a variety of reasons. For example, when there are precipitates at the grain boundaries, regardless of whether their strength is stronger or weaker than that of the matrix, it is the cause of cracks. The segregation of inclusions at grain boundaries is also a cause of fracture; Furthermore, even at the intersection points far below the yield upper limit, fatigue fracture will occur under variable loads.

　　Generally speaking, the mechanical performance indicators used in the design of hydraulic (pneumatic) parts assume that the materials are uniform, continuous and isotropic. According to this method, the design is considered risk-free and accidents may occur sometimes. Damage accident. Research has found that during the low-stress brittle fracture process of high-strength metallic materials, the material structure is far from homogeneous and isotropic. Structural defects such as cracks, inclusions and pores may occur, which can be regarded as microcracks in the material.

　　In addition, brittle fracture is also related to the service temperature of the component. Through research, it is found that when the temperature drops below a certain value, the material will transform into a brittle state, and its impact absorption energy will significantly decrease. This phenomenon is called cold brittleness. Therefore, when designing, the operating temperature of the components should also be taken into account. Select materials with an appropriate cold brittleness transition temperature.