Titanium alloy rolling blanks are usually larger-sized forged rods. Due to different cooling rates, the structure of the forged rod at room temperature is a β-transformation structure in the form of needle-like, fine flakes or thick flakes.
This structure has high creep resistance and fracture toughness, but low fatigue strength and tensile plasticity. The processing of titanium alloy rods usually hopes to obtain an equiaxed structure with good tensile and fatigue properties. However, the lamellar structure of the forged rod is very stable at room temperature, and it can only be made equiaxed through strong deformation in the two-phase zone, so The high deformation resistance and difficulty in deformation of titanium alloys at room temperature are one of the reasons that restrict the rolling forming of titanium alloys. Therefore, the rolling forming of titanium alloys is usually performed at a certain temperature.
The large amount of rolling deformation is beneficial to refining the structure and improving the mechanical properties; the small amount of rolling deformation only causes dynamic recovery during the rolling process. However, titanium alloy has poor plasticity and small deformation in each pass. Therefore, the coarse structure of titanium alloy due to small deformation in passes is an important feature of roll forming.
Another characteristic of titanium alloy roll forming is that the rolling process requires multiple annealings. In an open rolling environment, the heat transfer between alloy, air, rolls, etc. causes the surface temperature of the rolled piece to drop rapidly. The temperature at the center of the rolled piece rises instead due to deformation and heat generation, forming a larger temperature between the surface and the center. Gradient, surface cracks are prone to occur during the rolling process.
In order to ensure that rolling is within the set temperature range and that the temperature of the rolled piece is uniform, the rolled piece needs to be heated between passes. In addition, due to the accumulation of twins and texture and work hardening during the rolling process, rolling deformation becomes increasingly difficult. Therefore, in order to continue deformation, the rolled piece needs to be heated between passes to cause a large number of twins to occur. Recrystallization improves the plasticity of the material and prevents the material from cracking during subsequent rolling.
