After stress relief heat treatment, the test results of steel tube are analyzed and the conclusion is drawn.


1. The geometric accuracy of steel tube is basically unchanged.


2. The elongation, section shrinkage and surface roughness of steel pipe meet the technical requirements.


3. Compared with the cold working state, the impact energy of the steel tube increases by 83%, but it still fails to meet the technical requirements of the hydraulic cylinder.


4. On the basis of cold working, the tensile strength, yield strength and hardness of steel pipe are greatly reduced.


5. Compared with the cold working condition, the metallographic structure of the steel tube is slightly improved, but far less than the technical requirements of the hydraulic cylinder.


Since stress relief annealing is mainly to eliminate the internal stress of metal, the heating temperature does not exceed the phase transformation temperature of the material during heat treatment, but is close to the recrystallization temperature, the microstructure of the metal material does not change significantly during stress relief annealing. When the material performance, impact toughness and fatigue strength of the hydraulic cylinder used in general environment are low, it can be produced by the above heat treatment process.