Titanium Forging: Grade 2, Ti-6Al-4V and Grade 23

Every titanium forging decision orbits the beta-transus temperature, the point at which the metal transforms fully to the body-centered-cubic beta phase. For Ti-6Al-4V that line sits near 1820°F. Forge below it (alpha-beta or sub-transus forging) and you get a fine, equiaxed alpha-beta microstructure with excellent strength and fatigue life. Forge above it (beta forging) and you develop a lamellar, transformed-beta structure that gives better fracture toughness and creep resistance but lower fatigue strength. The forge shop chooses the route to hit the property spec, and they need pyrometry accurate to within a few degrees to stay on the right side of that line. This is also why titanium forging is slow and deliberate. The metal has poor thermal conductivity, so it heats and cools unevenly, and it has a narrow forgeable window before it cools out of range. Strain rate matters enormously: forge too fast and the localized heating from deformation can locally cross the transus, while forging too cold causes cracking. Isothermal and hot-die forging, where the dies are heated close to the workpiece temperature, exist specifically to solve titanium's tendency to chill against cold tooling and to allow slow, controlled strain rates for near-net shapes. Get any of this wrong and you do not find out until destructive testing or fatigue failure in service. That is why aerospace and medical titanium forgings carry mandatory microstructure and mechanical lot testing.

At forging temperature titanium grabs oxygen, nitrogen and hydrogen from the atmosphere with enthusiasm. Oxygen and nitrogen diffuse into the surface and create alpha case, a hard, brittle, oxygen-stabilized layer that is a fatigue-crack nursery. Alpha case must be removed, typically 0.005-0.020 in. per surface, by machining or chemical milling after forging, and stock allowances are set to guarantee its removal. Leave it on a fatigue-critical part and you have built in a crack initiation site. Hydrogen pickup is the other reactivity hazard. Absorbed hydrogen embrittles titanium, so descaling and pickling must avoid hydrogen-charging acids, and hydrogen content is controlled to low limits (often 0.0125-0.015% max) and verified. This is not a material you forge in a dirty shop with sloppy atmosphere control. Galling against the dies is a constant nuisance. Titanium loves to stick to and seize on steel tooling, so forging requires generous, well-applied lubricants (glass-based and graphite coatings), and the workpiece is often coated to protect both the part and the dies. All of this adds process steps and cost relative to steel.

Grade 2 is commercially pure titanium, soft, ductile and corrosion-proof in seawater and chemical environments. It forges easily relative to the alloys and is used for chemical-process and marine forgings where corrosion resistance trumps strength. It is not heat-treatable to high strength, so you choose it for environment, not load. Grade 5, Ti-6Al-4V, is the workhorse and accounts for the majority of titanium forged worldwide. It is an alpha-beta alloy reaching roughly 130-145 ksi tensile, with an excellent strength-to-weight ratio, and it can be solution-treated and aged for a further strength bump in thinner sections. Forged Ti-6Al-4V dominates aerospace structure, engine fan blades and discs, and high-load fittings. It is the default unless a requirement pushes you elsewhere. Grade 23 is Ti-6Al-4V ELI (Extra Low Interstitials), with tightened oxygen and iron limits that buy improved fracture toughness and ductility at a small strength cost. That toughness and its biocompatibility make Grade 23 the standard for forged medical implants, orthopedic components and fracture-critical aerospace parts. The forging behavior is nearly identical to Grade 5; the difference is purity control and lot certification, which is why ELI forgings carry tighter chemistry verification and ISO 13485 traceability.

Titanium forging is expensive at every stage. The raw metal costs many times more than steel, the buy-to-fly ratio on machined-from-forging parts is scrutinized to the gram, isothermal and hot-die tooling (often made from nickel superalloys to survive the heat) is costly, and the mandatory alpha-case removal, microstructure testing and chemistry verification add processing and calendar time. First-article aerospace titanium forgings commonly run 16-30 weeks from a cold start once you include die development, NADCAP heat treat and source inspection. Forging wins for titanium specifically because grain flow dramatically improves fatigue life, and for high-volume aerospace parts where machining from a solid billet would scrap 80-90% of very expensive metal. The closer to net shape you forge, the more titanium you save, which is why precision and isothermal forging are economically justified here even though they are exotic elsewhere. When is forging the wrong call? For one-off prototypes, low volumes, or geometrically simple parts, machining Grade 5 from plate or bar is faster and avoids the die cost, even with the chip loss. And if a part needs to be welded into a complex assembly, you may be better served by forged-plus-welded sub-elements or additive manufacturing. Forging is the answer when fatigue performance and material utilization at volume both point the same direction.