1. Cold working characteristics of titanium alloy bars and wires
In the production process of semi-finished products (sheets, bars, and tubes) of titanium and titanium alloys, the processing of titanium alloy bars and wires often adopts the method of rolling first and then drawing. Titanium alloys exhibit high strength and low plasticity at room temperature, so most processing processes must be carried out after heating. However, to obtain a uniform and consistent fine-grained structure, cold deformation is sometimes required at 40-50°C below the phase transition point.
Cold deformation, hot deformation, and warm deformation are the three main methods of titanium alloy bar and wire processing. Cold deformation is carried out below the recovery temperature. At this time, the metal mainly undergoes work hardening, plasticity decreases, and deformation resistance increases. Hot deformation is carried out at high temperatures. Although it can reduce deformation resistance, the metal is severely oxidized, affecting the surface quality and mechanical strength of the product. Warm deformation is between the two, usually carried out at 0.4-0.6 melting point temperature, which can reduce the deformation resistance of the metal while maintaining a certain plasticity.
2. Effect of cold working on titanium alloy rods and wires
Improved mechanical properties: During the cold drawing process, the titanium alloy's grains are deformed, the lattice is distorted, and the grains are broken, resulting in work hardening of the material and a significant increase in strength. This provides a way to improve the strength of materials that cannot be strengthened by heat treatment.
High dimensional accuracy: Cold-drawn materials are drawn under cold deformation conditions. Compared with hot-worked materials, they have higher dimensional accuracy and smaller absolute values of dimensional tolerances, reducing the allowance for subsequent mechanical processing.
Good surface finish: The surface finish of materials processed under cold working conditions is good, which is an effect that is difficult to achieve with hot working.
Microstructure changes: During the cold drawing process, the internal grains of the titanium alloy are elongated, the lattice is distorted, and the grains are broken, forming obvious fibrous structures, making the material anisotropic.
Producing deformation texture: When the cold drawing deformation is large, the orientation of the internal grains of the material will be roughly consistent, forming a "deformation texture", which has the characteristics of preferential orientation.
Work hardening and performance changes: Cold work hardening increases the strength of titanium alloys, but reduces plasticity. At the same time, the physical and physicochemical properties of the material after cold drawing, such as electrical conductivity, thermal conductivity, and magnetism, will also change.
3. Application of cold working in the production of titanium alloy bars and wires
Although cold working increases the energy consumption during deformation and the number of intermediate annealing times, it is still an important means of producing titanium alloy bars and wires because it can obtain products with smooth surfaces, fine dimensions, and regular shapes to meet the different needs of industry for materials. Especially in the production of fine wires, cold working is an indispensable technology.
In summary, the cold working characteristics and their influences on titanium alloy bars and wires are multifaceted, and various factors need to be comprehensively considered in actual production to formulate reasonable processing technology and parameters.
