Commonly used heat treatment methods for titanium alloy seamless pipes are annealing, solid solution and aging treatment. Annealing is to eliminate internal stress, improve plasticity and structural stability, and obtain better overall performance. Generally, the annealing temperature of α alloy and (α+β) alloy is selected at 120～200℃ below the (α＋β)-→β phase transformation point; the solution and aging treatment are rapid cooling from the high temperature zone to obtain martensite α′ phase and metastable Then the meta-stable phases are decomposed by heat preservation in the middle temperature zone, and the fine and dispersed second-phase particles such as the α phase or compounds are obtained to achieve the purpose of strengthening the alloy.
The heat treatment process of titanium alloy seamless pipe can be summarized as:
(1) Solution treatment and aging: The purpose is to improve its strength. α titanium tubes and stable β titanium tubes cannot be strengthened heat treatment, and only annealing is carried out in production. α+β titanium tube and metastable β titanium tube containing a small amount of α phase can further strengthen the alloy through solution treatment and aging.
(2) Complete annealing: the purpose is to obtain good toughness, improve processing performance, facilitate reprocessing and increase the stability of size and structure.
(3) Stress relief annealing: the purpose is to eliminate or reduce the residual stress generated during processing. Prevent chemical attack and reduce deformation in some corrosive environments.
In addition, in order to meet the special requirements of the workpiece, the industrial titanium alloy seamless pipe also adopts metal heat treatment processes such as double annealing, isothermal annealing, β heat treatment, and deformation heat treatment.