Annealing process of Gr38 titanium alloy

As a lightweight structural material, titanium alloy has excellent comprehensive properties, low density, high specific strength, good fatigue strength and crack propagation resistance, excellent corrosion resistance, good welding performance, etc., so it has increasingly broad application prospects in aviation, aerospace, automotive, shipbuilding, energy and other industries. Compared with Ti-6Al-4V alloy, Gr.38 alloy uses iron instead of higher-cost vanadium as a β stable element, its strength is comparable to Ti-6Al-4V alloy, and the elongation is comparable or slightly higher, but it is different from it that it can be both hot and cold processing, and can be made of thin sheets, coils, strips, precision hot-tied strips, thick plates, seamless pipes and castings and engineered products. In view of the excellent superplastic formability and open-hole fatigue properties of Gr.38 titanium alloy, and can also be used for friction agitation welding, it is very widely used, quite suitable for replacing steel, aluminum, composite materials, pure titanium and other titanium alloys, especially in aerospace and military defense systems have extremely broad application prospects. The effects of different annealing regimes on the microstructure, mechanical properties and tensile fracture morphology of Gr.38 titanium alloy rods were studied.

The main raw materials used for preparing Gr.38 titanium alloy are titanium sponge and alloying elements, which include aluminum-vanadium alloy, aluminum bean, iron nail and titanium dioxide. After mixing and electrode preparation, the ingot with Φ440mm was prepared by two vacuum smelting in vacuum consumable arc furnace. The phase transition point of Gr.38 titanium alloy is 970±5℃ by temperature metallography. After 8 rounds of forging, the Φ440mm ingot is finally hot rolled to the bar of Φ20mm, and the state is rolled. The annealing system is furnace cooling, water cooling and air cooling after holding at 830, 930, 950 and 1000℃ for 1h respectively.

The test rod with a length of 75mm was cut from the finished bar as the mechanical property sample, and the test rod with a length of 20mm was cut as the metallographic sample, and the test content was completed after annealing treatment. The main content of the experiment is to test the microstructure, tensile properties at room temperature and tensile fracture morphology under different annealing regimes. The test results show that:

(1) After being held at 930 ~ 950℃ for 1 hour and annealed by air cooling (or water cooling), Gr.38 alloy can obtain higher strength and better plasticity, and has good comprehensive mechanical properties.

(2) The yield strength of Gr.38 alloy is low after being held at 830℃ and annealed by air cooling for 1h, which is conducive to the subsequent processing of the material.

(3) The tensile fracture morphology of Gr.38 alloy at room temperature showed honeycomb ductile fracture characteristics. After annealing at 1000℃ for 1h, the dimble on the fracture was relatively small and shallow, and its plasticity was relatively poor.