When the High alloy seamless steel pipe is cold drawn, due to defects such as cracks in the hot-rolled tube blank or after the high-precision cold-drawn pipe is made into a cylinder, there is almost no plastic deformation during use, and it is generally brittle fracture. Brittle fracture is caused by many reasons. For example: when there are precipitates on the grain boundary, no matter whether the strength of the high-pressure alloy tube is stronger or weaker than that of the matrix, it is the cause of cracks; the segregation of inclusions on the grain boundary is also the cause of fracture; in addition, even if it is far less than the yield Under extreme alternating load, fatigue fracture will also occur.

Generally speaking, the mechanical performance indicators used in the design of hydraulic (pneumatic) parts assume that the material is uniform, continuous, and isotropic. According to this method, it is considered safe design, and accidents sometimes occur. Fracture accident. Studies have found that in the process of low-stress brittle fracture that occurs 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, the brittle fracture of the high-pressure alloy tube is also related to the service temperature of the component. People have found through research 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, the design should be based on the working temperature of the component. Choose a high-pressure alloy tube material with a suitable cold-brittle transition temperature.
 High alloy seamless steel pipe selection considerations
There are many kinds of high alloy seamless steel pipe materials and their properties are different. Therefore, both ferrous and non-ferrous materials, or the non-metallic materials that will be discussed later, naturally have different applications. When selecting materials for High alloy seamless steel pipe products, it will be different due to the use situation (for example: strength requirements, environmental factors, cost considerations, etc.), and various materials have their appropriate uses due to their different structures. How to make the application of materials suitable for the material is the biggest criterion for material selection. This article will put forward several important considerations for material selection, and give specific explanations with examples.
1. The specification of the material should meet the needs of use　　
The most basic consideration for choosing High alloy seamless steel pipe material is to meet the characteristics and requirements of the product, such as tensile strength, machinability, and corrosion resistance. Many materials seem to be able to meet the needs of use, but if you choose materials that have orthographic marks or meet national standards, because their chemical composition and mechanical properties have been tested and have certain guarantees, the quality will be more guaranteed.
2. The price of materials should be reasonable　　
Price is another important factor in choosing materials. Because if the price of excellent materials is high, the cost of the product will inevitably increase, and the competitiveness will be reduced. Therefore, if the material is not the only choice, then a reasonable price of the same grade material or the development of a new product to replace it is a good solution.
3. The quality of alloy tube materials should be consistent 　　
If the product of High alloy seamless steel pipe is single, there is no need to consider the issue of consistency, but if it is a mass-produced product, the supply of materials must be stable and the quality must be certain, otherwise the product will be returned or compensated due to defective products. It is the loss of money and reputation that may be difficult to make up. Therefore, at the beginning of the selection of material supply, the consistency of material quality and source stability of High alloy seamless steel pipe are also important considerations. The choice is good, generally from the above three considerations.