1. Open Die Forging

Its initial forging (open die) temperature is above the β transformation point, at 150-250°C, where the plasticity of the casting structure is good. Initially, light and quick strikes should be used to deform the ingot until the primary coarse crystal structure is broken. The degree of deformation must be maintained within the range of 20%-30%. The ingot is forged into the required cross-section and then cut into blanks of specified dimensions.

After the casting structure is broken, plasticity increases. Recrystallization intensifies with increasing temperature, prolonged holding time, and grain refinement. To prevent the occurrence of clustered recrystallization, the forging temperature must be gradually reduced as the grain refines, and the heating and holding time must also be strictly controlled.

2. Multi-directional Repeated Upsetting and Drawing

It starts forging at a temperature above the β transformation point, at 80-120°C, alternating between 2-3 cycles of upsetting and drawing, while also alternating the axis and edges. This allows the entire blank cross-section to achieve a very uniform recrystallized fine grain structure with β zone deformation characteristics. If the blank is rolled on a mill, this multi-directional upsetting and drawing may not be necessary.

3. Second Multi-directional Repeated Upsetting and Drawing

It is the same as the first multi-directional repeated upsetting and drawing method, but the initial forging temperature depends on whether the forged semi-finished product is a blank for the next process or a delivered product. If it is a blank for the next process, the initial forging temperature can be 30-50°C higher than the β transformation temperature; if it is a delivered product, the initial forging temperature should be 20-40°C below the β transformation temperature. Due to the low thermal conductivity of titanium, when upsetting or drawing the blank on free forging equipment, if the tool preheating temperature is too low, the equipment's impact speed is low, and the degree of deformation is large, an X-shaped shear band often forms on the longitudinal or transverse section. This is especially true during non-isothermal upsetting on a hydraulic press. This is because the tool temperature is low, causing the surface of the metal blank to cool rapidly upon contact with the tool, and during the deformation process, the deformation heat generated by the metal cannot conduct heat to the surroundings in time, resulting in a large temperature gradient from the surface to the center, leading to the formation of a strong flowing strain band in the metal. The greater the degree of deformation, the more pronounced the shear band becomes, ultimately leading to crack formation under the action of opposing tensile stresses. Therefore, when free forging titanium alloys, the impact speed should be faster, the contact time between the blank and the tool should be minimized, and the tool should be preheated to a higher temperature, while also appropriately controlling the degree of deformation within the first stroke.

During forging, the corners cool the fastest. Therefore, when drawing, the blank must be flipped multiple times, and the hammering force should be adjusted to avoid sharp angles. In the initial stage of hammer forging, light strikes should be used, with the degree of deformation not exceeding 5%-8%, and then the deformation amount can be gradually increased.

Die forging is usually used to manufacture blanks that are close in shape and size to the finished product, followed by only heat treatment and cutting processing. The forging temperature and degree of deformation are the basic factors that determine the alloy structure and performance. The heat treatment of titanium alloys is different from that of steel and does not play a decisive role in the alloy's structure. Therefore, the process specifications for the final step of titanium alloy die forging are particularly important.