去应力退火对薄壁钛管表面残余应力的影响

The evolution of surface residual stress in TA18 thin-walled tube was investigated before and after vacuum stress-relieving heat treatment by using X-ray diffraction technique. The results show that the cold-rolled TA18 tube has high compressive residual stress along rolling direction on the surface; and these stresses will be considerably reduced at different annealing temperatures and holding time. The degree of stress relaxation becomes better with increasing temperatures, while it reduces rapidly at first and goes to stabilization with increasing time. Within the scope of the orthogonal experiments, the surface residual stress of the pipe is mostly eliminated after heat treated at 450℃ for 2 h with furnace cooling. Calculated from the Zener-Wert-Avrami function, it is found that the behavior of residual stress relaxation is controlled by the recovery process, which is further confirmed by metallographic observation as no recrystallized grains being captured in the microstructure. In the present study, the crystallographic texture is stable in all stress-relieved tubes exhibiting a basal plane normal aligned parallel to the normal direction, thus making a slightly influence on residual stress measurement.