Precision seamless steel tubes should be kept at a certain temperature (usually below the phase transition temperature or recrystallization temperature) for a period of time and then slowly cooled to eliminate the stress during the annealing process of various precision seamless steel tubes.


During stamping, casting, welding, heat treatment, cutting, etc., the product may generate internal stress. In most cases, the metal retains a portion of the residual stress at the end of the process. Residual stress can cause fracture, deformation or dimensional change of the workpiece. Residual stress also increases the chemical activity of the metal, and is particularly susceptible to fracture caused by intergranular corrosion in the residual tensile stress. Therefore, residual stress can affect the performance of precision seamless steel tubes or lead to premature failure of the workpiece.


When the stress is less than the yield strength of the material, the stress is lower than the yield strength of the material, and when the stress relaxation temperature is lower than the yield strength of the material, the stress relaxation achieves the purpose of eliminating the residual stress. During stress relief annealing, the workpiece is generally slowly heated to a lower temperature (500 to 550 ° C for gray cast iron, 500 to 650 ° C for precision seamless steel pipe, and less than the recrystallization temperature for nonferrous metal alloy stampings). Then slowly cool to prevent new residual stresses.


Stress relief annealing does not completely eliminate residual stresses inside precision seamless steel tubes, but largely eliminates residual stresses. In order to completely eliminate residual stress, precision seamless steel tubes need to be heated to a higher temperature. In this case, changes in other organizations may be brought about, jeopardizing the performance of seamless use of seamless steel tubes.