Study Of Vacuum Annealing Process For Gr5 Alloy Plates

Gr5 titanium domestic also known as TC4, TC4 titanium alloy contains 6% of α-stabilizing element Al and 4% of β-stabilizing element V, belonging to the Ti-Al-V system typical α+-β titanium alloy. Titanium alloy series of alloys accounted for about 40% of the market use, cold processing is very difficult, the main reason is the alloy's plasticity, flexural strength ratio, and its mechanical properties and performance depends largely on the metallurgical organization, the metallurgical organization depends mainly on the heat treatment process, the vacuum annealing process of the different effects on the performance of the subsequent processing will play a decisive role.

In addition, it is also necessary to study the dehydrogenation effect of different vacuum annealing to reduce the hydrogen content of the surface layer of titanium alloys to a safe concentration, eliminating the possibility of hydrogen embrittlement and avoiding processing cracks.
Titanium sponge, high purity aluminum (99.99%) and aluminum-vanadium alloys are melted in a vacuum self-melting furnace in a certain ratio. 3.7mm semi-finished sheet is made by forging and rolling.

The heating temperature was 980°C to 1020°C during hot working. It was observed that the microstructure obtained from the thermal deformation with a deformation rate of 95% had very obvious primitive β grain boundaries, very obvious α phases in the grain boundaries, and coarser α phases in the crystals, which were needle-like. and periodic. The main reason for this organization is that the original billet is heated or deformed in the β-phase region, or the original billet is carried out in the β-phase region, while the deformation occurs in the α+β-phase region. Smaller.

The grain boundaries are not recrystallized due to lack of deformation. The microstructure has poor plasticity and high strength. Intermediate recrystallization annealing is required to improve its plasticity and strength and create favorable deformation conditions for cold working. It is also found that the grains in the fully deformed area are fine and obviously elongated.

The original 3.7mm samples were annealed in a vacuum annealing furnace, and the four samples with the worst plasticity were selected. The annealing treatments were 780°C±2°C, 800°C±2°C, 820°C±2°C, 830°C±2°C, vacuum ≤0.02 Pa for 2 hours, and 200°C out of the furnace. The tensile properties and hydrogen content at room temperature were measured. The test results showed that:

(1) Annealing regime of 800°C±2°C and holding time of 2 hours results in lower yield strength and highest plastic properties.

(2) An annealing regime of 800°C±2°C and 2 h of holding time results in a stable α+β phase network.

(3) According to the existing vacuum furnace vacuum ≤ 0.02Pa, at 800 ℃ ± 2 ℃, holding time of 2 hours, the average hydrogen content of 0.009% lower than the original sample to achieve the effect of dehydrogenation, to achieve the following cold working effect will not produce hydrogen embrittlement (chronic fracture) of the safety level.