Forging Temperature Ranges for TA7, TA13, TC4, TC6 and TC11 Titanium Alloys

Why the Forging Window Is Narrower for Titanium Than for Steel

Titanium has a hexagonal close-packed alpha phase at room temperature and a body-centred cubic beta phase above a composition-dependent beta transus. Almost every property that matters in a forged part - the alpha/beta ratio, grain size, crystallographic texture and the balance between strength and damage tolerance - is fixed by how the metal is worked relative to that transus. Titanium also conducts heat poorly, strain-hardens quickly and begins to absorb oxygen above roughly 600 °C, so the usable window is much narrower than for carbon or alloy steel. Heat a billet too far above the transus and beta grain growth becomes irreversible; finish a pass too cold and surface cracking, adiabatic shear bands or die overload follow.

This reference gives the practical forging temperature ranges for the grades most often specified under GB/T 3620.1 - TA7, TA13, TC4, TC6 and TC11 - together with the beta transus values behind them and the process rules that keep a forging inside specification.

Beta Transus and Phase Family by Grade

The beta transus is the reference line for every forging schedule. Strong alpha stabilisers such as aluminium, oxygen and nitrogen raise it; beta stabilisers such as molybdenum, vanadium, chromium, iron and silicon lower it.

Note on TA7: tabulated values of 930-970 °C for this grade normally describe a practical alpha+beta working band, not the transus itself. Ti-5Al-2.5Sn is strongly alpha-stabilised, its transus sits close to 1040 °C, and ingot breakdown therefore has to start well above that line. Using 930-970 °C as a transus leads to oversized beta grains and a coarse Widmanstatten structure.

Forging Temperature Ranges in Practice

For alpha+beta grades the finishing pass conventionally ends 30 - 50 °C below the transus. That is what produces the fine equiaxed or bimodal structure that gives TC4, TC6 and TC11 their combination of tensile strength, fatigue life and fracture toughness. TA13, being a low-alloy alpha grade, is worked in a lower band because its transus is correspondingly low.

Deformation Degree, Heating and Transfer Practice

Respect the allowable deformation per pass. For TA7 the accepted range is 30 - 50 %; exceeding it in a single stroke produces internal shear cracking that is invisible on the finished surface.

Heat slowly through the alpha+beta field. A steep thermal gradient between surface and core causes thermal stress cracking during breakdown of large ingots.

Limit furnace time. Long holds above 600 °C build an oxygen-rich alpha case that must later be removed by machining; excessive hold time also coarsens beta grains above the transus.

Keep transfer time short. Because titanium loses heat slowly but surface temperature drops quickly against cold dies, the die contact window is short; shop practice is to move small billets from furnace to press in the few seconds available and to pre-heat dies.

Use glass-based anti-oxidation coatings and lubricants on billets intended for press forging, and remove them before heat treatment or welding.

Never finish below roughly 700 °C. Below that level flow stress rises sharply and the risk of surface tearing becomes unacceptable for all five grades.

Heat treat after forging in accordance with the applicable forging specification; titanium alloy forgings are generally supplied per ASTM B381 or the equivalent national standard, with the alloy grade and condition stated on the certificate.

Common Misconceptions

"Hotter is always easier." Above the transus titanium flows more readily, but beta grain growth is not reversed by later working, and the finished part may fail toughness requirements.

"Beta forging always gives better properties." Beta working suits some thick-section and damage-tolerant parts, but it is a deliberate process with controlled cooling, not a shortcut for hard-to-fill dies.

"One window fits all grades." TC4, TC6 and TC11 look similar on paper but their transus values, aluminium contents and silicon additions shift the practical bands.

"Furnace setting equals billet temperature." Poor conductivity means the core can lag the surface by tens of degrees; the schedule should be written around measured billet temperature.

"Alpha case can be forged off." The hardened, oxygen-enriched layer must be removed mechanically; forging it into the surface buries a brittle layer in the finished part.

FAQ

Q: What is the forging temperature of TC4 titanium alloy?
TC4 (Ti-6Al-4V) is normally broken down from 1200 to 850 °C, pre-formed between 1000 and 800 °C and finish forged between 980 and 800 °C, with the last pass finishing below its 980 - 1010 °C beta transus.

Q: Why is the beta transus so important?
It separates the alpha+beta field from the beta field, so it defines whether a pass refines or coarsens the structure. Forging temperature, finishing temperature and cooling rate are all written relative to it.

Q: Is Ti-5Al-2.5Sn forged above its transus?
Only for ingot breakdown. Production passes for TA7 are completed in the alpha+beta field so that the alpha phase remains the dominant constituent in the finished forging.

Q: How much deformation is allowed in one pass?
For TA7 the accepted figure is 30 - 50 %. For the alpha+beta grades the permitted reduction depends on die design, press capacity and billet section, and is set in the process route rather than by a single universal number.

Q: What happens if a forging is finished below 700 °C?
Flow stress rises steeply and the material loses ductility. Surface tearing and internal cracking become likely, and the defect cannot be repaired by subsequent heat treatment.

Q: Does the same schedule apply to bar and to large forgings?
No. Large sections need slower heating, longer equalising holds and smaller per-pass reductions because the temperature difference between surface and core is much greater.