Recent studies on the hot rolling of Grade 5 titanium sheets (Ti-6Al-4V) provide improved data for temperature windows, reduction schedules, and coiling parameters that stabilize microstructure and surface quality. Advantages include corrosion resistance, high specific strength, good stability, and low density, making Grade 5 a leading choice for aerospace skins, structural brackets, and high-performance components. Yet the development of titanium alloys is limited by the disadvantages of low thermal conductivity, high deformation resistance, low yield rate and difficulty in rolling forming. These intrinsic hurdles extend high-temperature dwell, promote uneven β→α transformation, and amplify residual stresses and shape defects.
Taking Grade 5 titanium alloy plate as the research object, by improving the hot rolling process, it is proposed that the processing safety temperature of Grade 5 titanium alloy plate is 890℃-1000℃, and the instability zone range is 700℃-850℃. Within this optimized window, finishing near the lower end of the safe range with moderate per-pass reductions and controlled coiling suppresses β-grain growth and α-case, while avoiding the flow instabilities and surface damage that arise in the 700–850 ℃ band. Complementary controls—accurate reheating, thorough descaling, and post-roll annealing—improve thickness tolerance, flatness, and downstream formability, helping overcome the alloy’s low thermal conductivity and high deformation resistance to raise yield and consistency.
1. Experimental materials and procedures
1.1 Materials
· Alloy: Grade 5 titanium alloy (Ti-6Al-4V, Grade 5)
· Geometry: Plate specimens of 100 mm × 30 mm × 9 mm
1.2 Rolling and characterization methods
· Hot rolling temperatures: 800–1000 °C
· Pass reductions: 20% and 40%
· Work roll diameter: 200 mm
· Experimental plan: Single-pass rolling at designated temperatures and reductions to acquire real-time rolling force and exit surface temperature. Multiple rolled Grade 5 titanium alloy samples were reserved for process trials.
· Metallography: Microstructural observations performed with a ZEISS Axio Observer optical microscope to evaluate α/β morphology, spheroidization, and dynamic recrystallization (DRX) behavior.
2. Results and analysis
2.1 Experimental results
Rolling force measurements at 20% reduction:
· 800 °C: 252 kN
· 850 °C: 221 kN
· 900 °C: 197 kN
· 950 °C: 146 kN
· 1000 °C: 99 kN
Rolling force measurements at 40% reduction:
· 800 °C: 425 kN
· 850 °C: 405 kN
· 900 °C: 350 kN
· 950 °C: 333 kN
· 1000 °C: 262 kN
Exit surface temperatures at 20% reduction:
· From 800, 850, 900, 950, 1000 °C entry: 660, 695, 760, 826, 929 °C respectively
Exit surface temperatures at 40% reduction:
· From 800, 850, 900, 950, 1000 °C entry: 620, 650, 710, 760, 860 °C respectively
Trends:
· At fixed reduction, the measured rolling force decreases as rolling temperature increases, while the exit surface temperature increases.
· At fixed temperature, higher reduction increases rolling force but lowers exit surface temperature.
Metallurgical interpretation:
· Under the same temperature, increasing reduction intensifies deformation and strain rate in the bite zone. In Grade 5 titanium alloy, lamellar α colonies undergo progressive spheroidization and dynamic recrystallization as total strain increases, leading to greater grain fragmentation. At around 900 °C, further temperature elevation enhances DRX kinetics and the uniformity of α spheroidization, improving the homogeneity of the microstructure and thereby the quality of the resulting Grade 5 Titanium sheets and Titanium plates.
2.2 Measured rolling force versus theoretical predictions
Comparative analysis between measured rolling forces and model-based theoretical/simulation results shows consistent trends and similar magnitudes. This agreement indicates that the constitutive parameters and boundary conditions used in the rolling model capture the Grade 5 titanium alloy interaction forces during deformation, supporting its use for process planning and scaling to production mills.
2.3 Measured surface temperature versus theoretical predictions
Temperature exerts a first-order effect on the internal microstructure and properties of Grade 5 titanium alloy. Accurate prediction and control of temperature are thus critical when defining the rolling process route. In the single-pass trials:
· At constant reduction, exit surface temperature rises with higher entry rolling temperature.
· At constant entry temperature, exit surface temperature decreases as reduction increases due to enhanced deformation work and shorter contact time before exit radiation/convective losses.
The measured exit temperatures follow the same variation pattern as thermal–mechanical simulation outputs, with small errors, validating that the selected hot rolling conditions and data acquisition are reasonable and suitable for guiding titanium alloy production.
3. Improvements to the hot rolling process
A processing map study was established using flow stress data at true strains of 0.2, 0.3, and 0.4. Power dissipation maps and instability maps were overlaid to delineate safe and unstable regimes.
Key observations across strain levels:
· The stable–safe and unstable regions show broadly similar locations across strains, while the area of instability grows slightly with increasing strain.
· At strain ε = 0.2:
o Instability temperature range: 700–800 °C
o Associated strain rate range: 0.1 s⁻¹ to 0.55 s⁻¹
o Safe temperature band: 700–730 °C with higher strain rates of 4 s⁻¹ to 20 s⁻¹
o In this condition, the alloy exhibits higher susceptibility to flow instabilities; resulting microstructures may contain defects and degraded overall properties if operated within or near the unstable zone.
· At strain ε = 0.3:
o Instability temperature range: 700–850 °C
o Strain rate range (instability): 0.1 s⁻¹ to 0.55 s⁻¹
o Safe temperature band: around 700–730 °C at higher strain rates of 4 s⁻¹ to 20 s⁻¹ (with reference to a high-temperature boundary near 1050 °C)
o The location of peak flow instability shifts more substantially, narrowing the practical process window and elevating forming difficulty for Grade 5 Titanium sheets.
· At strain ε = 0.4:
o Instability temperature range: 700–850 °C
o Strain rate range (instability): 0.1 s⁻¹ to 0.55 s⁻¹
o Safe temperature band: approximately 700–730 °C at 4 s⁻¹ to 20 s⁻¹ (upper temperature reference near 1050 °C)
o Again, the shifting of instability loci increases forming difficulty if operations drift toward the unstable field.
Overall conclusion from processing maps and hot compression flow data:
· Processing safety temperature for Grade 5 (Grade 5) during hot rolling is 890–1000 °C, with corresponding practical strain rates of 0.1 s⁻¹ to 20 s⁻¹.
· The instability zone spans 700–850 °C at strain rates of 0.1 s⁻¹ to 0.55 s⁻¹.
These boundaries align with the experimental force–temperature trends and the microstructural observations. Operating in the safe window enhances DRX uniformity, curbs α-case, and promotes balanced strength–ductility, while avoiding the instability zone reduces the risk of flow localization, surface damage, and edge cracking.
4. Microstructural characterization of the titanium alloy
Optical microscopy (ZEISS Axio Observer) revealed:
· At lower temperatures (≤850 °C) and low reduction, lamellar α within transformed β matrix remains relatively intact, with limited spheroidization.
· With higher temperature (≈900–1000 °C) and/or higher reduction (40%), increased DRX of the β phase and α-spheroidization lead to finer, more equiaxed microstructures. The distribution becomes more homogeneous, indicating improved workability and formability for subsequent passes or downstream cold-rolling.
· The correlation between reduced rolling force and elevated temperature mirrors the transition toward more favorable slip and DRX mechanisms within the titanium alloy, explaining improved surface quality and reduced tendency for flow defects.
5. Implications for Titanium plates and Titanium sheets production
· Parameter selection: Maintaining entry temperatures in the 890–1000 °C window while choosing reductions that balance load and DRX initiation is essential for Grade 5 titanium alloy. For the tested geometry and roll diameter, 20–40% single-pass reductions deliver useful contrast in load and microstructure without entering instability bands.
· Shape and surface: Higher temperatures within the safe window reduce rolling force and improve surface integrity. Exit temperature monitoring provides a rapid proxy for thermal history, aiding in real-time control of flatness and α-case mitigation.
· Scale-up: The agreement between measured and simulated rolling force and temperature suggests that plant-scale mills can apply the same process maps, with adjustments for mill stiffness, friction, and inter-pass timing, to produce Titanium sheets with consistent gauge and properties.
6. Conclusions
· Single-pass hot rolling data for Grade 5 titanium alloy demonstrate that rolling force declines with temperature and rises with reduction, while exit surface temperature shows the opposite trends at fixed parameters.
· Processing maps built from flow stress at ε = 0.2–0.4 define a safe processing temperature of 890–1000 °C at 0.1–20 s⁻¹, and an instability zone of 700–850 °C at 0.1–0.55 s⁻¹.
· Measured rolling forces and exit temperatures closely track theoretical simulations, supporting the reasonableness of the selected hot rolling schedule for Titanium plates and Titanium sheets made from Grade 5 titanium alloy.
· Operating within the safe window promotes uniform DRX and α spheroidization, improving downstream formability, surface quality, and final mechanical properties.
Frequently Asked Questions and Answers
Q1: What key hot rolling parameters (e.g., heating temperature, rolling speed, pass reduction ratio) are critical in titanium sheets hot rolling data, and how do these data points influence the final grain structure and mechanical properties (e.g., yield strength, ductility) of the sheets?
A1: Heating temperature governs phase state and DRX kinetics; higher temperatures within the safe window reduce flow stress and foster equiaxed grains, elevating ductility. Pass reduction ratio controls strain and stored energy, triggering α spheroidization and DRX when sufficient; overly high reductions can approach instability. Rolling speed (and thus strain rate) shifts the balance between work hardening and recovery/DRX—moderate to high strain rates in the safe window refine grains without inducing flow localization. Together, these data determine texture, grain size, and the strength–ductility balance.
Q2: How do hot rolling data (e.g., temperature profiles, rolling force, exit thickness) differ when producing thin-gauge titanium sheets (<2 mm) versus thick-gauge sheets (>10 mm), and what adjustments to data collection are needed for each scenario?
A2: Thin gauges cool faster, show lower absolute rolling forces, and are more sensitive to temperature transients and frictional heating; precise pyrometry and shorter sampling intervals are needed to capture rapid thermal changes. Thick gauges retain heat, produce higher forces, and develop larger through-thickness temperature gradients; embedded thermocouples or multi-wavelength pyrometry, along with load cell data at higher sampling rates, help resolve gradient effects. Exit thickness control for thin sheet relies on higher mill stiffness and faster feedback; thick plate requires compensation for bulging and crown.
Q3: What role does titanium sheets hot rolling data play in optimizing process efficiency, and how is this data used to reduce defects like edge cracking or thickness variation during large-scale production?
A3: High-fidelity rolling data calibrate constitutive models and processing maps, enabling mills to select safe temperature–strain-rate windows and optimal reductions. Real-time force–temperature–thickness feedback supports adaptive control of speed, lubrication, and cooling to stabilize bite and shape. Data-driven adjustments—such as trimming reductions near instability bands, tweaking entry temperature to sustain DRX, and balancing roll gap/coolant—lower edge cracking incidence, minimize thickness variation and crown, and improve yield, throughput, and surface quality across large coils of Grade 5 titanium alloy Titanium sheets.
