Titanium Grade 2 vs Grade 5 (Ti-6Al-4V): Selecting on Strength, Corrosion and Cost

Titanium Grade 2 and Grade 5 account for the large majority of all titanium sold, and they are compared constantly - usually by someone who has a strength problem and is looking at Grade 5, or a corrosion problem and is looking at Grade 2. The two grades are not variations on a theme. Grade 2 is commercially pure titanium whose properties come from interstitial control; Grade 5 is the alloy Ti-6Al-4V, whose properties come from an aluminium-vanadium two-phase structure. That difference produces a factor of three in strength and, just as importantly, a factor of two in thermal conductivity.

What is the metallurgical difference between Grade 2 and Grade 5?

Grade 2 has no deliberate alloying additions at all; its strength comes from interstitial elements, chiefly oxygen, and that is why oxygen is the element with the tightest practical control in commercially pure titanium. Grade 5 is alloyed with aluminium, which stabilises the alpha phase, and vanadium, which stabilises the beta phase. The result is a two-phase microstructure that can be strengthened further by heat treatment - something no single-phase commercially pure grade can ever do.

How much stronger is Grade 5 than Grade 2?

Yield strength differs by a factor of three, and that gap cannot be closed by adding thickness in any design where weight matters. The thermal conductivity row is the one that surprises engineers who have only worked with steel: Grade 5 conducts heat at roughly 40% of the rate of Grade 2, so cutting heat stays at the tool edge instead of flowing away into the chip and the workpiece. That single property, combined with triple the yield strength, is why machining Grade 5 costs far more than machining Grade 2.

How do the two grades differ in fabrication?

• Cold forming: Grade 2 deep draws, spins and bends readily and is the standard choice for cold-formed tube, strip and expanded heat-exchanger tube. Grade 5 has limited room-temperature formability and usually needs hot forming or superplastic forming.
• Welding: both need inert shielding until the joint has cooled below about 400 C, because titanium reacts with oxygen, nitrogen and hydrogen above that temperature. A weld shielded only on the top face will oxidise on the underside while looking sound from outside.
• Weld colour is the field indicator - silver is acceptable, straw and blue are not, and a discoloured weld has lost ductility.
• Machining: practical cutting speeds for Grade 5 are roughly half those used on Grade 2 - about 30-45 m/min against 60-90 m/min with carbide tooling - and both need low speeds, abundant coolant and care to avoid chip ignition.
• Inspection: both grades are non-magnetic, so magnetic particle inspection cannot be used; dye penetrant or ultrasonic testing is required.
• Galling: titanium galls against itself, so threaded connections need lubrication, dissimilar material pairing or surface treatment.

Which grade resists corrosion better?

Both grades rely on the same tenacious titanium dioxide passive film, so in seawater, chlorides and oxidising media they are close - and Grade 2 is usually marginally better because it has no aluminium addition to compromise the film. The important row is the last one: titanium is outstanding in oxidising service and poor in reducing service, and it reacts dangerously with dry chlorine gas, fuming nitric acid and anhydrous methanol. Where the medium is a hot reducing acid, titanium is the wrong family entirely and a nickel alloy such as C-276 is the correct answer. The grade cross-reference helps locate that boundary.

What standards and product forms apply?

A single specification covers many grades, so ordering to ASTM B265 alone does not define the grade - the grade designation must be stated separately. Ordering Grade 2 and receiving Grade 5, or the reverse, is a real and expensive risk when only the standard number is quoted.

What about Grade 7, Grade 12 and Grade 23?

These three are the answers to the questions Grade 2 and Grade 5 cannot answer. Grade 7 and Grade 12 solve crevice corrosion in hot chlorides - see Grade 2 vs Grade 7 and Grade 2 vs Grade 12. Grade 23 trades a little strength for a large gain in fracture toughness - see Grade 5 vs Grade 23.

How do the two grades compare on cost?

Grade 2 is the cheapest titanium product, with the widest stock range and the shortest lead times. Grade 5 typically costs 30-60% more per kilogram because of the aluminium and vanadium content and the harder hot working, and the gap widens substantially in finished parts because machining time is roughly double. For a welded process component, Grade 2 will normally be the cheaper finished article by a wide margin; for an aerospace bracket, the weight saving justifies both premiums.

Which grade should you specify?

The rule is short. If the requirement is corrosion allowance, Grade 2 is almost always the answer and it costs less. If the requirement is a stress value that pure titanium cannot reach, Grade 5 is the only option in this pair. Hangbo supplies both grades in plate, sheet, strip, bar, tube, forgings and machined parts - see the Grade 2 and Grade 5 data sheets, or Grade 5 vs Inconel 718 for the point where titanium stops being the light answer.

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