Titanium alloy bar and its TC4 alloy bar's initial forging (opening) temperature is 150~250℃ above the beta transition point, a this time, the casting structure is the best plasticity. At the beginning, the ingot should be deformed by light or quick strike until the coarse grain structure is broken. The degree of deformation must be kept within 20% ~ 30%. The ingot is forged to the required section and then cut into a size blank.
The plasticity increases after the casting structure is broken. Aggregation recrystallization is intensified with the increase of temperature, longer holding time and grain refinement. In order to prevent aggregation recrystallization, the forging temperature must be gradually reduced with grain refinement, and the heating and holding time should also be strictly controlled.
2, Multi-directional repeated pull
It starts forging at 80 ~ 120℃ above the temperature of beta transition point, and carries out upsetting and drawing for 2 ~ 3 times alternately, and changes the axis and edge alternately at the same time. In this way, the whole blank cross section can obtain very uniform recrystallization fine grain structure with deformation characteristics in the beta region. If the blank is rolled on the mill, it is unnecessary to do this kind of upsetting.
3, The second multi-directional repeated pull
It is the same as the first repeated upsetting, but the initial forging temperature depends on whether the semi-finished product is the blank of the next process or the delivered product. If the blank of the next process is done, the initial forging temperature is 30 ~ 50℃ higher than the beta transition temperature; If the product is delivered, the initial forging temperature is 20 ~ 40℃ below the beta transition temperature. Due to the low thermal conductivity of titanium, when upsetting or drawing the blank on the free forging equipment, if the preheating temperature of the tool is too low, the strike speed of the equipment is low, and the degree of deformation is large, the x-shaped shear band is often formed on the longitudinal section or cross section. This is especially true for non - isothermal upsetting on hydraulic presses. This is because the tool temperature is low, and the contact between the blank and the tool causes surface surface cooling of the metal blank. In the process of deformation, the deformation heat generated by the metal has no time to conduct heat around, and a large temperature gradient is formed from the surface to the center, resulting in the metal forming a strong flow strain band. The greater the deformation degree is, the more obvious the shear zone is, and finally cracks are formed under the action of tensile stress with opposite signs. Therefore, in the free forging of titanium alloy, the strike speed should be faster, as far as possible to shorten the blank and tool contact time and as far as possible to preheat the tool to a higher temperature, but also properly control the degree of deformation within a stroke.