去应力退火对薄壁钛管表面残余应力的影响

Effect of stress relieving annealing on surface residual stress of thin-walled Ti pipe

在不同退火温度和保温时间下对冷轧TA18薄壁管进行真空去应力退火处理,通过X射线衍射分析了无缝管表面轴向残余应力在退火前后的变化规律。结果表明:冷轧TA18管外表面轴向保留了较大的残余压应力;经真空去应力退火处理后,残余应力有了大幅下降。其应力松弛随退火温度的提高,效果变佳;随保温时间的延长,残余应力先快速下降后趋于稳定。在正交实验范围内,经450℃保温2h并随炉冷却后,管材外表面轴向上的残余应力已基本消除,且仍为压应力状态。经Zener-Wert-Avrami公式计算后表明,管材退火时的应力松弛受回复过程控制,从金相组织观察中进一步证实了在实验范围内没有出现再结晶。去应力退火阶段,TA18管织构基本不变,仍保留着冷轧时沿TD方向倾斜的双峰基面织构状态,进一步降低了织构对残余应力测定所带来的影响。

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.