According to the tempering temperature range of the brittleness of precision tubes, it can be divided into low-temperature tempering brittleness and high-temperature tempering brittleness.

Precision tube low-temperature tempering brittleness After the martensite structure is obtained by quenching the alloy steel, the steel is embrittled by tempering in the temperature range of 250~400 °C, and its toughness-brittleness conversion temperature increases significantly. The embrittlementized precision tube can no longer be eliminated by the method of low-temperature tempering heating, so it is also called "irreversible tempering brittleness". It mainly occurs in steel grades such as alloy structural steel and low-alloy ultra-high strength precision tubes. The fracture of the embrittlementized precision tube is either a per-crystal fracture or a mixed aquarium and quasi-cleavage fracture. The reasons for the brittleness of low-temperature tempering are generally believed to be: (1) It is closely related to the precipitation of cementite in the form of thin flakes in the grain boundaries of the original austenite during low-temperature tempering, resulting in the embrittlement of grain boundaries. (2) The segregation of impurity elements phosphorus in the grain boundaries of the original austenite is also one of the reasons for the brittleness of low-temperature tempering. High-purity precision tubes with a phosphorus content of less than 0.005% do not produce low-temperature tempering brittleness. Phosphorus undergoes segregation at austenite grain boundaries when heated by fire, and is retained after quenching. Phosphorus is precipitated at the original austenite grain boundaries during segregation at the original austenite grain boundaries and cementite tempering, which cause brittleness along the crystalline and contribute to the occurrence of low-temperature tempering brittleness.

The alloying elements in the precision tube have a great influence on the brittleness of low-temperature tempering. Chromium and manganese promote the segregation of impurity elements phosphorus in austenite grain boundaries, thereby promoting low-temperature tempering brittleness, tungsten and vanadium basically have no effect, molybdenum reduces the toughness of low-temperature tempering precision tubes-brittleness conversion temperature, but it is not enough to inhibit low-temperature tempering brittleness. Silicon can delay the precipitation of cementite during tempering and increase its formation temperature, so it can increase the temperature at which low-temperature tempering brittleness occurs in precision tubes.