Gr1 Titanium Rod

 

 

In the production process of titanium and titanium alloy semi-finished products (plates, bars, tubes), some special properties need to be considered, such as high chemical reactivity at high temperatures; corrosion resistance in many corrosive media; high strength and slightly low plasticity; polymorphic transformation within the most suitable temperature range for hot deformation; low thermal conductivity, etc. The processing of titanium alloy bars and wires generally adopts the method of rolling first and then drawing. The drawing process is divided into hot deformation, cold deformation and warm deformation. Titanium alloys have high strength and low plasticity at room temperature, and most of the processing is carried out by heating to make semi-finished products. The larger the cross-sectional area of the alloy and the higher the content of alloying elements, the smaller the equipment power, and the higher the required heating temperature. High-temperature deformation in the β single-phase region will form a macroscopic and microscopic structure with large grains and low mechanical properties. To obtain a uniform and fine-grained structure, deformation should be carried out at a temperature 40-50℃ below the phase transformation point to destroy the coarse-grained structure formed by casting. Due to the high temperature of hot deformation, metal oxidation is severe, and the surface quality, dimensional accuracy and mechanical strength of the products are worse than those of cold deformation. Therefore, in actual production, hot deformation and cold deformation are used in combination. The finishing of finished products and semi-finished products is mainly completed by cold deformation or incomplete cold deformation. Warm deformation includes incomplete hot deformation and incomplete cold deformation. The warm drawing of titanium alloys is generally carried out at 0.4-0.6 of the melting point temperature (550-720℃). The characteristics of warm drawing are that the strengthening of the wire during the drawing process is reduced, and a large total reduction and pass reduction can be adopted. During incomplete hot deformation, in addition to work hardening, dynamic recovery and partial dynamic recrystallization also occur. After deformation, there are two different types of microstructures: equiaxed grains that have recrystallized and elongated grains that have not recrystallized, which increases the deformation non-uniformity, resulting in a decrease in the plasticity of the metal and a higher residual stress value, affecting the performance of the product. Incomplete cold deformation is deformation carried out at a temperature higher than the recovery temperature, without recrystallization but with the recovery process taking place. It is also commonly referred to as warm deformation. During the plastic deformation of metals, in addition to hardening, there is also a partial softening process (recovery), which can significantly eliminate internal stress, improve plasticity and reduce work hardening. Warm deformation not only reduces the number of intermediate annealing required for metals, increases productivity, but also reduces energy consumption and saves energy. Cold deformation is carried out at a temperature lower than the recovery temperature, and only work hardening occurs during deformation, with no recovery or recrystallization. In this case, the deformation resistance of the metal is high, while the plasticity is low. During cold deformation, the resistance of the metal to deformation continuously increases with the increase in the degree of deformation, while the plasticity gradually decreases. Cold deformation of metals is generally carried out several times, and each time a certain amount of total deformation is completed according to the properties of the metal and specific process conditions. Annealing treatment is required between deformations to restore the plasticity of the blank. By appropriately using the cold deformation-annealing cycle, metals can be processed into products of any shape, size and degree of hardening or softening. Cold-drawn materials are made from hot-rolled materials and have the following advantages: ① High mechanical properties. This is the result of grain deformation, lattice distortion and grain fragmentation during the cold drawing deformation process, which leads to work hardening of the material. Through cold drawing, the strength of titanium alloys can usually be increased to a higher level, which can fully utilize the material and also provides a way to increase the strength of materials that cannot be strengthened by heat treatment. ② High dimensional accuracy. Cold-drawn materials are drawn under cold deformation conditions, and compared with hot-processed materials, they have higher dimensional accuracy. Compared with hot-drawn materials, the absolute value of the allowable dimensional tolerance of cold-drawn materials is relatively small, reducing the machining allowance of the material during mechanical processing. ③ Good surface finish. This is the characteristic of the material when processed in a cold working state. After cold drawing, the microstructure of the material changes: ① Microstructure changes. The shape change of the material during the drawing process is actually the sum of the internal grain changes. After cold drawing deformation, the shape and size of the material change, and the internal grains change accordingly, that is, the grains are elongated in the drawing direction. In the case of large deformation, obvious fibrous structure may appear, making the material anisotropic. ② Lattice distortion and grain fragmentation. Cold drawing plastic deformation causes a large number of dislocations and vacancies in the material, and makes the atoms deviate from their equilibrium positions in the lattice, that is, the lattice is distorted and disordered. Some grains are even crushed and split into many small grains, which are called fragmented grains or subgrains. ③ Deformation texture is produced. When the cold drawing deformation is large, the orientation of the internal grains of the material tends to be consistent. This microstructure in which the grains have a preferred orientation due to plastic deformation is called "deformation texture". The deformation texture formed during the drawing process is called "wire texture". Its characteristic is that a certain crystal direction of each grain is parallel or nearly parallel to the drawing force direction. The properties of the material change after cold drawing: ① Work hardening. The cold working hardening of the material is caused by the microstructure changes during the deformation process. The increase in the material's strength is due to lattice distortion and subgrains. During continuous deformation, in addition to being hindered by the original grain boundaries, the material is also hindered by the distorted lattice and subgrain boundaries, which requires an increase in external force, manifested as an increase in tensile strength and deformation resistance, while the plasticity decreases due to the increase in internal defects after cold drawing, and further deformation may cause cracks or fractures. Work hardening can be used to increase the strength of the material and improve its mechanical properties, but it also brings difficulties to cold drawing processing. Intermediate heat treatment can be used to eliminate the influence of work hardening. ② Changes in other properties. After cold drawing, the physical and physicochemical properties of the material, such as electrical conductivity, thermal conductivity, magnetic properties, potential, specific gravity, density, and corrosion resistance, will all change. Although cold drawing increases the energy consumption during deformation and the number of intermediate annealing, cold working is still an important means of manufacturing many materials, especially for fine wire production. It can obtain products with smooth surfaces, precise dimensions, and regular shapes to meet the different needs of industry for materials, which is difficult to achieve by hot working.