High-Temperature Softening Characteristics And Forging Control Of Titanium Alloys

High-temperature softening is the core physical law of titanium alloy forging. Increasing temperature intensifies atomic thermal motion and reduces dislocation resistance, leading to a significant drop in material strength and deformation resistance. This is the foundation for the plastic forming of titanium alloys, yet it also tends to cause process issues such as grain coarsening, uneven performance, and forming defects.

 

 

1. Physical Softening

Elevated temperature enhances lattice atomic vibration and weakens atomic bonding, markedly reducing the resistance to dislocation motion. Titanium alloys have high deformation resistance at room temperature, retaining over 65% of their strength at 400℃, and dropping rapidly above 600℃. In this stage, flow stress decreases continuously with temperature rise, conforming to the common law of metals.

 

2. Phase Transformation Softening

α+β two-phase region: Deformation is dominated by α-phase slip and β-phase coordinated deformation, with softening accompanied by dynamic recovery where dislocations rearrange but cannot fully eliminate hardening.

 

β single-phase region: Good plasticity and low deformation resistance, but β grains are prone to coarsening, resulting in a substantial decline in the strength and toughness of forgings.

 

Near-phase-transformation region: Optimal softening and plasticity effects, suitable for precision forging, but with a very narrow process control window.

 

3. Dynamic Softening

Dynamic recovery: Mostly occurs at medium-low temperatures and high strain rates. Dislocations rearrange via slip and climb, with limited softening effect and residual work hardening.

 

Dynamic recrystallization: Mostly occurs at high temperatures and low strain rates. New grains nucleate and grow, completely eliminating hardening and refining the microstructure. For example, when Gr5 is deformed at 920–950℃ and 0.01s⁻¹, dynamic recrystallization is sufficient, and grains can be refined to 5–10μm.

 

Superplastic softening: Under specific temperature ranges and extremely low strain rates, deformation is dominated by grain boundary sliding, with elongation exceeding 1000%, suitable for forming complex precision components.

 

 

1. Commercially Pure Titanium

Softening characteristics: Stable performance below 300℃, rapid strength reduction above 350℃, and deformation resistance at 600℃ is only 1/5 of that at room temperature.

 

Process points: Forging temperature 800–900℃, protection against high-temperature oxidation required; good formability, suitable for open die forging and conventional closed die forging.

 

2. α+β Type

Softening characteristics: The most widely used, high strength at 400–500℃, obvious softening above 600℃, and phase transformation temperature Tβ about 980–1020℃.

 

Key differences:

Forging in α+β region: Forms a duplex microstructure with balanced strength-toughness and optimal fatigue performance.

Forging in β region: Prone to β grain coarsening and greatly reduced fatigue life, only used for large-size blanks.

 

3. Near-α Type High-Temperature

Softening characteristics: Containing elements such as Sn, Zr, Si, with strong softening resistance at 600–650℃ and excellent creep properties.

Process points: Forging temperature 950–1000℃, control β phase proportion below 30% to ensure high-temperature stability.

 

4. β Type

Softening characteristics: High content of Mo and V, high phase transformation temperature, low high-temperature deformation resistance, and good hardenability.

 

Process points: Adopt β region forging, low strain rate to promote dynamic recrystallization, and avoid uneven α phase precipitation.

 

 

1. Forging Temperature

Temperature range: Conventional forging in α+β region; precision/isothermal forging in near-phase-transformation region; β forging only for large blank cogging, followed by α+β region finish forging.

 

Temperature control requirements: Heating in vacuum/atmosphere furnace, temperature control ±5℃, holding for 1–2h; temperature fluctuation of die and billet in isothermal forging ±5℃, temperature drop in conventional forging not exceeding 50℃; final forging temperature ≥850℃ to prevent cracking.

 

2. Deformation Rate

Low rate: For isothermal/superplastic forging, uniform microstructure, suitable for aerospace precision parts.

Medium rate: For conventional closed die forging, balancing efficiency and quality.

High rate: Only for simple parts, prone to overheating, coarse grains, and cracking.

 

3. Deformation Degree and Mode

Deformation amount: Single pass 40–60%, total deformation ≥70% to refine microstructure.

Deformation mode: Isothermal forging with high precision; multi-directional forging to improve isotropy; radial forging suitable for long shaft parts.

 

4. High-Temperature Protection

Vacuum/argon protection, oxygen content <10ppm;

Use protective coating for friction reduction and oxidation resistance;

Shorten high-temperature holding time and operate continuously.

 

5. Dies and Equipment

Dies: Molybdenum/nickel-based dies for isothermal forging, preheated to over 80% of billet temperature, die repair when wear exceeds 0.2mm.

Equipment: Adopt servo hydraulic press with infrared temperature measurement closed-loop temperature control.

 

6. Digital Simulation

Use DEFORM, ABAQUS to simulate field variables and microstructure evolution, reducing scrap rate by 20% and improving microstructure uniformity by 30%.

 

 

Ruihang is a technology and innovation enterprise that integrates R&D, production and sales into one integrated system.If you have purchasing needs on hand, feel free to contact us: Sam.Rui@bjrh-titanium.com.