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Process
Titanium Forging: The Parameters That Decide the Billet's Future
Titanium forging is a narrow-window process. Heat it too far above the beta transus and the beta grain grows without a limit that later working can undo. Work it too little and the structure stays coarse. Transfer it too slowly and the surface contaminates before the die ever touches it. The parameters are not independent and they are not forgiving.
Forging is a narrow-window process. Send the drawing with the property callout and the inspection requirement, and the route is stated back to you in writing. Request a forging quote
The transus and the two windows
Every titanium alloy has a beta transus — the temperature at which the hexagonal alpha phase transforms fully to body-centred cubic beta. For the workhorse alpha-beta alloy Ti-6Al-4V it sits near 995 °C, and the exact figure shifts with interstitial content, which is one reason a heat's chemistry matters as much as its grade.
Where the forging is done relative to that line is the first decision, and it is a genuine trade rather than a preference.
| Alpha-beta forging (below the transus) | Beta forging (above the transus) | |
|---|---|---|
| Structure produced | Equiaxed or bimodal alpha in a transformed beta matrix | Coarse, fully transformed beta grains, colonised |
| Strength and ductility balance | The strongest room-temperature combination; the usual choice for structural parts | Higher creep resistance and better fracture toughness in the right direction; lower ductility |
| Forming loads | Higher — the alloy is less forgiving and resists flow | Lower — beta is softer and flows more easily, which suits intricate die shapes |
| Risk | Under-forging, with the work never reaching the core | Uncontrolled grain growth, which is not recoverable by subsequent alpha-beta working |
| Where it is chosen | Most structural forgings, discs, hubs | Parts where creep or damage tolerance dominates, and thick sections where die filling is the limit |
Reduction ratio
An ingot's cast structure has to be broken down before it is worth anything as a forging. The measure is the cumulative reduction ratio from ingot to finished billet, and it matters because it is the mechanism that closes porosity, refines the structure and homogenises the chemistry.
- The reduction is a total, accumulated across the whole conversion sequence — not the last press stroke. Upsetting and drawing in alternating directions is what breaks the cast structure down in three dimensions; repeated working in one direction only aligns and elongates it.
- A billet with insufficient conversion cannot be rescued downstream. No final forging pass recovers a structure that was never refined.
- For critical parts the reduction ratio is specified on the purchase order and verified from the mill's route card, not inferred from the finished dimensions.
Temperature control, and the minutes between furnace and die
The furnace is the easy part. The hard part is everything that happens after the door opens.
- Furnace uniformity. A soak that is correct at the thermocouple and cold at the back of the load produces a forging that is partly in one window and partly in another. Uniformity surveys and correct thermocouple placement matter more than the setpoint.
- Transfer time. The billet surface cools quickly, and hot titanium absorbs oxygen. A slow transfer produces alpha case on the surface before the die touches it — a hard, brittle layer that has to be removed and that can be pushed into the surface if it is worked instead.
- Die temperature. Cold dies chill the billet surface and raise the flow stress where contact is first made, which is exactly where the die detail is. Die heating is not a comfort measure.
- Multiple heats. Each reheating cycle adds grain growth and adds oxide. The number of heats is a process decision with a structural consequence.
Cooling and what follows
Cooling rate from the finishing temperature sets how much beta is retained and how the phases partition, and it is therefore part of the specification rather than an afterthought. Air cooling is normal for alpha-beta forgings; faster cooling changes the structure and, with it, the subsequent ageing response. What follows — annealing, stress relief, or solution treatment and ageing — is chosen to match the forging route, not applied as a default. A heat treatment written for a wrought bar is not automatically correct for the same alloy as a forging.
Open die and closed die
- Open die produces a worked blank: bar, disc or block, with the structure refined by reduction but the shape still to be established by machining. It is the right route for one-offs, for large parts, and for anything where the finished shape is not yet fixed.
- Closed die produces near-net shape with grain flow that follows the part contour. It needs tooling, a press of adequate capacity, and a batch large enough to carry both. Flash, draft and corner radii all have to be designed for a material that resists flow at forging temperature far more than steel does at its own.
What the finished part inherits
The reason all of this belongs on the enquiry rather than in the supplier's workshop is that the forging route sets properties the drawing will later test for but cannot create: through-thickness ductility, fatigue initiation resistance at the surface, and the directionality of toughness. If those are requirements, they have to be met by the route — and the route has to be chosen before the billet is cut.
Send the drawing with the property callout, the inspection requirement and the quantity, and we will state the route and its basis in writing with the quotation. Material forms and available stock are listed on the titanium forgings page.
FAQ
Common questions
What is the beta transus and why does it matter for forging?
It is the temperature at which the alpha phase transforms completely to beta — near 995 °C for Ti-6Al-4V, shifting with interstitial content. Forging below it produces a fine equiaxed or bimodal structure with the strongest room-temperature strength and ductility balance. Forging above it makes the metal flow more easily, which suits intricate dies, but the beta grain grows rapidly and the resulting coarse structure cannot be recovered by later working. It is the first decision in any forging route.
Why is reduction ratio specified on a forging order?
Because it is what breaks down the ingot's cast structure. Porosity closes and the structure refines in proportion to how much the material has been worked, and working must be in alternating directions to do it in three dimensions rather than elongate it in one. A billet that has not had enough conversion cannot be fixed by a final forging pass, so for critical parts the ratio is stated on the order and verified from the mill's route card.
Why does transfer time from furnace to press matter so much?
Because hot titanium absorbs oxygen from the air. A slow transfer lets an oxidised, hard surface layer form before the die contacts the billet — alpha case. If that layer is then forged into the surface rather than cleaned off, it becomes an inclusion of brittle, oxygen-enriched material at the surface of the finished part, which is exactly where fatigue cracks initiate.
Can a forged part be heat treated the same way as bar of the same grade?
Not automatically. The correct heat treatment follows the forging route and the cooling rate from the finishing temperature, because those already set how the phases are distributed. A cycle written for wrought bar can leave a forging with the wrong balance, or with properties that vary from surface to centre. Where heat treatment matters, state the required properties and let the route and cycle be specified together.
Ask about Titanium forging
Send the drawing with the grade and the governing specification. We will confirm the material form, the process route, the inspection plan and a date in writing with the quotation.