As an important titanium semi-finished product, titanium rods are widely used in the aerospace, medical equipment, chemical industry, and high-end sports equipment sectors. The titanium rod manufacturing process involves multiple key steps. The selection and execution quality of the process route directly affect the performance, precision, and cost of the final product. In-depth understanding and control of the following core influencing factors are the key to ensuring high-quality titanium rod production:
1. Raw material selection: the basis of performance
The performance of titanium rods is based on the selected titanium alloy grade and its original state (such as sponge titanium, recycled materials, and intermediate alloy ratio). Different alloys (such as pure titanium, Ti-6Al-4V, Ti-3Al-2.5V, etc.) have significantly different compositions, phase compositions, mechanical properties (strength, plasticity, toughness) and process characteristics (such as forgeability and hardenability).
When selecting, the appropriate alloy grade, composition control range and impurity (such as O, N, Fe, C) content limit must be determined strictly based on the service environment requirements of the final product (such as strength, corrosion resistance, biocompatibility, high temperature performance) and subsequent processing requirements (such as weldability and cold formability). High purity or specific grades have extremely strict requirements on the purity of raw materials.
2. Melting and casting: the source of purity and uniformity
Melting is the core link that determines the metallurgical quality of titanium rods (purity, composition uniformity, low segregation). Common processes include **vacuum consumable arc melting (VAR) and cold hearth furnace melting (such as electron beam cold hearth furnace EBCHM, plasma arc cold hearth furnace PACHM).
Key control points:
Vacuum/inert atmosphere control: strictly prevent gas (O, N, H) contamination during melting.
Melting parameters: current, voltage, melting rate, etc. affect the depth of the molten pool, solidification rate and degree of segregation.
Electrode quality: The pressing density and uniformity of the consumable electrode affect the melting stability.
Casting ingot and cooling: determine the macro grain structure and potential defects (shrinkage, looseness) of the ingot. The cold hearth furnace has advantages in removing high-density inclusions (HDI) and low-density inclusions (LDI).
3. Heat treatment: regulating microstructure and properties
Heat treatment is the bridge between the molten cast billet and the final product performance, and runs through multiple stages of the titanium rod manufacturing process (such as ingot homogenization, after billeting, and before finished products).
Purpose and type:
Homogenization annealing: eliminate ingot component segregation and internal stress.
Recrystallization annealing: eliminate work hardening, restore plasticity, and refine grains.
Solution treatment + aging: For heat-treatable α+β and β titanium alloys, by controlling the heating temperature (usually near or below the β phase transformation point), holding time, cooling rate (water quenching, air cooling) and subsequent aging temperature and time, the α/β phase ratio, morphology, size and precipitation strengthening phase are precisely controlled to obtain the required comprehensive properties such as strength, toughness, fatigue, etc.
Stress relief annealing: remove residual stress from processing or welding.
4. Thermomechanical processing (finishing and forming): shaping and organization optimization
This stage is the core process of processing large-size ingots or billets into titanium bars of required specifications and performance through plastic deformation, which usually combines forging, rolling (hot rolling, warm rolling, cold rolling), stretching (drawing) and other processes.
Key roles and influencing factors:
Shaping: obtaining target diameter, length and tolerance.
Densification and defect healing: eliminating defects such as pores and looseness in the cast structure.
Microstructure control: The temperature, deformation amount (forging ratio, rolling reduction rate, stretching reduction rate), deformation rate and heat treatment system between passes of hot working jointly determine the crushing of grains, the degree of recrystallization, phase transformation and the formation of texture (anisotropy). This is crucial to the mechanical properties, isotropy and fatigue life of the final bar.
Surface quality control: Lubrication, die state and temperature control during processing directly affect surface finish, scratches and oxide layer.
5. Surface treatment: Improve performance and appearance
Surface treatment aims to improve the surface integrity, functionality and appearance of the titanium rod manufacturing process:
Common processes:
Pickling: Remove the oxide scale (α contamination layer) and slight surface contamination formed by hot working, which is the basis for subsequent processing or use.
Sandblasting/shot peening: Clean the surface to obtain a uniform matte effect, and introduce surface compressive stress to improve fatigue strength.
Mechanical polishing: Obtain a high-finish surface, often used for decoration or reducing fluid resistance.
Electrolytic polishing: Obtain a more uniform, clean, low-roughness mirror effect, often used in medical devices.
Anodizing: Form a dense, wear-resistant, corrosion-resistant oxide film, which can be colored (decorative), and improve biocompatibility or serve as a coating base.
6. Testing and quality control: Guarantee of performance and compliance
Strict testing and quality control throughout the entire manufacturing process are the lifeline to ensure that titanium rods meet design specifications, safety standards and customer requirements.
Key test items:
Chemical composition analysis: ensure that the alloy composition and impurity elements are within the allowable range (spectral analysis, ICP, etc.).
Mechanical properties test: tensile test (strength, elongation), hardness test, impact toughness, high temperature endurance/creep (specific requirements), etc.
Microstructure inspection: metallographic observation of α/β phase morphology, grain size, inclusions, etc.
Nondestructive testing (NDT): Ultrasonic flaw detection (UT) detects internal defects (inclusions, cracks, holes); eddy current testing (ET) or penetrant testing (PT) detects surface and near-surface defects; X-ray testing (RT) is used for specific applications.
Dimension and tolerance inspection: geometric accuracy such as diameter, length, roundness, straightness, etc. Surface quality inspection: visual or instrumental inspection of roughness, scratches, cracks, oxidation, etc.
Special requirements inspection: such as biocompatibility testing (medical), salt spray testing (corrosion resistance), hydrogen content analysis, etc.
Conclusion
The titanium rod manufacturing process is a complex and precise system engineering. Its final quality is the result of the synergy of many factors such as raw material quality, smelting purity, heat treatment system, thermomechanical processing parameters, surface treatment effect and strict quality control throughout the process**. Deeply understanding and accurately controlling these core influencing factors is the key to achieving stable production of high-performance, high-precision and high-reliability titanium rods. Manufacturers need to scientifically formulate and optimize the process route according to product specifications, application scenarios and standard requirements, and implement strict monitoring and inspection at each link.
