🚀 TITANIUM
Heat Treating Titanium: Stress Relief, Annealing, and Beta Aging for Grade 5 and Grade 23
Titanium heat treatment is governed by a phase transformation around the beta transus temperature and by an unforgiving sensitivity to oxygen, which means almost all of it happens in vacuum or inert atmosphere to avoid forming a brittle surface layer. What you can actually achieve depends entirely on whether the grade is an alpha alloy that won't age-harden or an alpha-beta alloy like Grade 5 that will.
AS9100NADCAPISO 13485
Alpha Case: The Contamination Layer That Drives Vacuum Furnace Use
Titanium is so reactive with oxygen at elevated temperature that any heat treatment in air forms alpha case, a hard, brittle, oxygen-enriched surface layer that cracks under load and destroys fatigue life. Above roughly 1100F in air, alpha case begins to form, and by the temperatures used for annealing it can grow thousandths of an inch deep. That layer is not a cosmetic problem, it is a crack-initiation site that disqualifies aerospace and medical parts.
This is why titanium heat treating is almost always done in a vacuum furnace or under high-purity argon. Vacuum protects the surface, gives bright clean parts, and is mandatory for fatigue-critical and biomedical components. If a part must be processed in air, the alpha case has to be removed afterward by chemical milling or grinding, which means leaving stock allowance and adds cost.
For buyers the rule is simple: specify vacuum heat treatment for titanium unless you have a deliberate plan and stock allowance to remove alpha case. Asking a shop to anneal titanium in an open atmosphere furnace because it is cheaper is how you scrap a lot of expensive parts.
Grade 2 Stress Relief and Annealing: Alpha Titanium Won't Harden
Grade 2 is commercially pure titanium, an alpha alloy with no beta phase to manipulate, so it cannot be hardened by heat treatment, just like austenitic stainless. The thermal treatments that matter for Grade 2 are stress relief (around 900 to 1100F) to remove machining and welding residual stresses, and annealing (around 1300F) to restore ductility after cold forming.
Grade 2 work-hardens during machining and forming, and stress relief is frequently specified after heavy machining to stabilize dimensions before final operations, particularly on thin or asymmetric parts that would otherwise distort over time. Because Grade 2 is used heavily in chemical processing, marine, and medical hardware for its corrosion resistance rather than strength, the goal of heat treatment is dimensional stability and formability, never added hardness.
Buyers should not expect a hardness spec on Grade 2 from heat treatment. If you need a stronger titanium part, you move to Grade 5, you don't try to heat-treat strength into commercially pure titanium.
Frequently Asked Questions
Titanium is extremely reactive with oxygen, nitrogen, and hydrogen at elevated temperatures, and if you heat it in an air atmosphere it forms alpha case, a hard, oxygen-enriched, brittle surface layer. Alpha case begins forming above roughly 1100F and grows deeper with time and temperature, reaching several thousandths of an inch during a typical anneal. That layer is not just a surface blemish, it is a network of crack-initiation sites that slashes fatigue strength and ductility, which is unacceptable for aerospace structural parts and medical implants where fatigue and fracture toughness are everything. Vacuum furnaces (or high-purity argon atmosphere furnaces) eliminate the oxygen source, so the part comes out bright, clean, and contamination-free with no alpha case to remove. If titanium must be processed in air for cost reasons, the alpha case has to be chemically milled or ground off afterward, which means leaving extra stock, adding an operation, and accepting dimensional uncertainty. For any fatigue-critical or biomedical titanium part, vacuum heat treatment is effectively mandatory, not optional.
No, Grade 2 commercially pure titanium cannot be hardened by heat treatment. It is an alpha-phase alloy with essentially no beta phase, and hardening titanium requires manipulating the alpha-beta phase transformation through solution treatment and aging, which only the alpha-beta and beta alloys like Grade 5 support. Heating and quenching Grade 2 simply does not produce a hardening transformation. The heat treatments that do apply to Grade 2 are stress relief, typically 900 to 1100F to relieve residual stress from machining, forming, or welding so the part stays dimensionally stable, and annealing around 1300F to restore ductility after cold work. Grade 2 is chosen for its excellent corrosion resistance, weldability, and formability rather than strength, so it serves chemical processing equipment, marine hardware, and medical components where those properties matter. If your application needs higher strength, the answer is to move up to Grade 5 (Ti-6Al-4V), which can be solution treated and aged, rather than attempting to heat-treat strength into Grade 2.
Mill annealed and solution-treated-and-aged (STA) are two heat treatment conditions for Ti-6Al-4V (Grade 5) that trade off strength against simplicity and toughness. Mill annealed is the default supplied condition, a stress-relieving anneal around 1300 to 1400F that produces a reliable, uniform structure with roughly 130 ksi yield, 138 ksi tensile, and good ductility regardless of section thickness, and it is what the large majority of structural and industrial Grade 5 parts use. STA solution treats the alloy near the beta transus (around 1750F), quenches, then ages at 900 to 1100F to precipitate strengthening phases, pushing yield up to roughly 150 to 160 ksi. The catch is that STA's strength gain depends on quench rate, so it only fully responds in thinner sections, thick parts cool too slowly in the core to harden, leaving you with a strength gradient. STA also costs more and carries more distortion risk. For most applications mill annealed is the right call, and STA is reserved for thinner, high-strength parts that genuinely need the extra capability.
Titanium heat treating costs more than steel because of the mandatory vacuum or inert-atmosphere processing and the certification overhead, expect roughly $4 to $12 per pound for vacuum annealing or stress relief of Grade 2 and Grade 5, with lot minimums commonly $400 to $800 at NADCAP-certified aerospace shops. Solution treat and age cycles on Grade 5 run higher still because of the extra furnace cycles, quench, and the distortion control required. Lead times are typically 7 to 15 business days for aerospace and medical work under AS9100 or ISO 13485, driven less by the furnace cycle (a stress relief is a few hours) and more by traceability, witnessed pyrometry, vacuum furnace scheduling, and per-lot testing. Vacuum furnace capacity is the real bottleneck, since these furnaces batch loads and the cleanliness requirements limit mixing of materials. Expedited service exists but at steep premiums because you may need to dedicate a furnace run. If parts require alpha-case removal or post-treatment straightening, add several days and machining cost.
Related Pages
Last updated: July 2026
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