Stress relaxation in structural titanium alloys

Conclusions

• 1. For structural titanium alloys there are minimal stresses below which the stress does not decrease at a given annealing temperature. The original residual stresses determine the annealing time but do not affect the value of the retained stress.

• 2. The relaxation resistance of alloys with a coarse-grained structure is 10–35% higher than for alloys with a fine-grained structure at the temperatures tested. More intensive annealing is required to remove residual stresses in weldments than in material with a fine-grained structure.

• 3. The relaxation resistance increases with increasing stability and decreasing extent to which the structure is heterophase. Other conditions being equal, the relaxation capacity is highest for heterophase titanium alloys of the VT22 type, with a substantial quantity of unstable β_M phase.

• 4. As much as 50–75% of the original stress is removed in the heating stage during annealing under the conditions tested. The heating rate has a considerable effect on stress relaxation.

• 5. Annealing of alloys OT4-1, VT5-1, and VT22, respectively, at 600–650°, 750–800°, and 650–675° for 0.5–1 h and zonal induction annealing of weldments at 650° for 3–10 min, 800° for 10 min, and 700° for 5 min provide almost complete elimination of residual stress.