Titanium Block

The Processing Technology Of Forging Titanium Billet

1. Type Of Forging Process

Open Forging (Open Die Forging)

It is used in the roughing stage to process titanium ingots by repeated hammering or pressure to eliminate casting defects (e.g. porosity, segregation). For example, titanium billets are free-forged in the β phase zone (approx. 950-1050°C) with a single deformation of 50%-70% and a significant reduction in grain size (from millimeters to microns).

Die Forging (Closed Die Forging)

It is suitable for precision forming, and the final shape is controlled by a mold. For example, aero engine blade die forging needs to be carried out in the α+β two-phase region (850-950 °C), and the isothermal forging technology (the same temperature as the die and the blank) can reduce surface oxidation and improve dimensional accuracy (tolerance ± 0.2 mm).

Isothermal Superplastic Forging

For complex thin-walled parts, the elongation can exceed 500% in the titanium alloy superplastic temperature range (approx. 750-900°C) at very low strain rates (10⁻⁴-10⁻³ s⁻¹). For example, Dynamet uses this process to manufacture Ti-6Al-4V special-shaped parts for aerospace, and the material utilization rate is increased by 30%.

2. Key Process Parameters

Temperature Control

β Forging: Forging above the β phase change temperature (e.g., Ti-6Al-4V about 995 °C) to form a lamellar structure and improve the fracture toughness (KIC up to 60 MPa·m¹/²).

α+β Forging: forging below the phase change point (e.g., 900°C) to obtain an equiaxed α+β bistate structure, taking into account both strength (tensile strength ≥1100 MPa) and plasticity (elongation ≥10%).

Deformation Rate vs. Path

Multi-directional forging (e.g. three-way compression) refines grains down to the sub-micron level (<1 μm), e.g. by increasing the yield strength of TC4 alloy to 1200 MPa by 80% cumulative deformation in 4 passes.

Cooling Method

After Forging, air-cooled, water-cooled or oil-cooled control structure:

Air-Cooled: Forms a α+β dual-state structure, which is suitable for high fatigue strength parts.

Water Quenching: retain more metastable β phases, and subsequent aging treatment (such as 550°C×4h) is required to precipitate α phases to improve the strength.

3. Supporting Post-Processing Technology

Heat Treatment

Annealing: Eliminate residual stress at 700-800°C and stabilize the structure (e.g., ≥strength of 895 MPa after annealing of aircraft-grade Ti-6Al-4V).

Solution Aging (STA): For β titanium alloys (such as Ti-5Al-5Mo-5V-3Cr), the secondary α phase is precipitated by solution (750°C×1h water quenching) and then aged (500°C×8h) to precipitate the secondary  phase, and the hardness is increased to more than HRC 40.

Surface Cleaning

The oxide scale is removed by sandblasting (alumina sand particles), pickling (HF+HNO₃ mixture), or laser cleaning (1064 nm wavelength laser) to achieve a micron-level clean surface.

Non-Destructive Testing

Ultrasonic flaw detection (UT) detects internal defects (sensitivity Φ0.8 mm flat-bottomed holes), and X-ray diffraction (XRD) analyzes the residual stress distribution.

The Application Field Of Forged Titanium Billet

1. Aerospace

Structural parts: aircraft landing gear forgings (such as Boeing 787 using Ti-10V-2Fe-3Al forging billet, weight reduction of 20%), rocket engine shell (Ti-6Al-4V after β forging tensile strength ≥ 1100 MPa).

Engine parts: high-pressure compressor blades (isothermal forged Ti-6242S alloy, creep life of more than 1000 hours at 650°C).

2. Military And Marine

Armor Plate: Ti-6Al-4V forging billet is forged in multiple directions for grain refinement (ASTM Class 12) and has better ballistic performance than conventional steel armor.

Submarine Parts: seawater corrosion-resistant titanium alloy (such as Ti-3Al-2.5V) forged into pump valve parts, service life of more than 30 years.

3. Energy & Chemicals

Nuclear power equipment: Ti-35V-15Cr flame retardant titanium alloy forgings are used in the cooling system of nuclear reactors, which are resistant to high-temperature oxidation (oxidation weight gain < 5 mg/cm² at 600°C).

Chemical Containers: Ti-Pd alloys (such as Grade 7) are forged into corrosion-resistant reactors that can withstand 98% sulfuric acid (50°C) corrosion rate < 0.1 mm/year.

4. Biomedical

Orthopedic Implants: Ti-13Nb-13Zr forging billet is treated with surface sandblasting + acid etching (SLA), and the osseointegration strength is increased by 30%.

Surgical Instruments: ultra-fine-grained Ti-6Al-4V forgings (grain size 0.5 μm) to make minimally invasive surgical forceps, which have both high strength and fatigue resistance.

5. High-End Equipment

Racing Parts: The connecting rod of the F1 car is made of Ti-5Al-5V-5Mo-3Cr forgings, with a specific strength of 300 kN·m/kg.

3C Electronic Mold: forged pure titanium (Grade 2) is used for mobile phone middle frame die-casting mold, and the wear resistance life is 5 times longer than that of steel mold.

3. Technical Challenges And Development Trends

Uniformity Control Of Large-Size Forging Billets (e.g., the temperature difference of billets above Φ500 mm needs to be <20°C);

The Deformation Resistance Of High-Strength β Titanium Alloy Is Large (for example, the flow stress of Ti-5553 exceeds 200 MPa at 900 °C), and large-tonnage forging equipment (≥ 50,000 tons of hydraulic presses) needs to be developed;

Near-Net Shape Technology For Complex Shapes (e.g., hollow turbine disc forgings need to be controlled within 3%).

Numerical Simulation Optimization: the temperature field and stress field in the forging process can be predicted through DEFORM or QForm software, and the number of mold trials can be reduced (the cost can be reduced by 30%).

Composite Process: Forging + additive manufacturing (such as forging billet local 3D printing strengthening), forging + rolling (continuous forming of long-size profiles);

Green Forging: Induction heating (energy efficiency > 80%) instead of gas furnaces to reduce carbon emissions.