TC4 titanium alloy is the most widely used titanium alloy at present. It has high strength and good corrosion resistance, but it is difficult to see seamless titanium tubes made of TC4 material in the seamless titanium tube market.
TC4 titanium materials are mainly plates. The TC4 titanium tubes on the market are mainly high-strength, thick-walled tubes produced by hot extrusion or oblique drilling. The warm rolling process requires the improvement of traditional rollers, that is, the installation of induction heating devices on the tube rolling mill. This processing equipment has a complex structure, cumbersome process, and high production cost. The main reason is that the process strength of TC4 titanium alloy is high and the cold rolling deformation load is large. In order to solve the key technology of cold rolling deformation of TC4 seamless tubes, the school and the enterprise jointly conducted a series of studies. For example, direct cold rolling deformation is used to produce high-strength titanium alloy tubes, which not only greatly reduces the production cost but also meets the requirements of high-pressure applications of titanium alloys.
The tube billet is rolled into a tube with a total deformation of 70% by two and three passes, respectively. Vacuum annealing at 800℃×1h was performed between passes. The cooling method was furnace cooling to 500℃ and then immediate air cooling, and the changes in its organizational properties were observed.
The conclusions were:
In the case of small deformation billeting, the wall thickness deviation was small and the surface roughness increment was reduced; in the case of large deformation billeting, the wall thickness deviation was large, which would affect the wall thickness deviation of the pipe obtained by subsequent rolling.
Under the same total deformation, the more rolling passes, the greater the elongation and thickness of the pipe and the strength gain. The comprehensive performance is good.
When rolling with large deformation, the flow of the material is strip-shaped, and when rolling with small deformation, the flow of the material is bundle-shaped. Under the same heat treatment conditions between passes and subsequent rolling processes, the organizational distortion of the pipe obtained by billeting with large deformation is more serious.
Billeting with small deformation has little effect on the anisotropy of the pipe; there is a certain fluctuation in the anisotropy of mechanical properties in multi-pass rolling.
