Grade 2 vs Grade 5 Titanium (CP Titanium vs Ti-6Al-4V): Corrosion vs Strength, and How to Choose

Grade 2 is the grade you specify when a part has to survive a medium. Grade 5 is for parts that carry load. Once you know which of those two duties governs, the grade is close to settled, and the remaining work is product form, condition and documents.

Grade 2 is commercially pure titanium, UNS R50400, carrying only small controlled amounts of oxygen and iron. Grade 5 is the alloy Ti-6Al-4V, UNS R56400, with about 6 percent aluminium and 4 percent vanadium. Those additions buy a much higher strength level and give back some of the weldability and cold formability that make commercially pure titanium straightforward to turn into equipment.

Specifying Grade 5 for a corrosion duty that never sees a real load means paying for strength the part will never use, then fighting a harder alloy through every weld and every forming operation. The opposite error is worse. Grade 2 placed under a load path sized for Ti-6Al-4V yields.

Pure metal against alloy

Commercially pure titanium keeps the properties that make the metal attractive to fabricators: corrosion behaviour with no alloying complications, welds that stay ductile, and sheet that will take a cold form. Ti-6Al-4V trades part of that fabrication behaviour for strength and stiffness. Every difference below comes back to that one split.

The same split runs through properties nobody checks while making this comparison. Grade 5 carries electrical current and heat about three times worse than Grade 2, which matters on only a few parts but is settled the moment the grade is chosen. Resistivity and thermal conductivity by grade sets out the figures.

Strength, and what the comparison rests on

Grade 5 minimum tensile and yield requirements sit well above Grade 2 in routes where the two grades appear under the same product standard. Each minimum belongs to a specific standard, product form and condition, and the values that govern an order come from the table in the revision named on that order. Density is nearly identical, about 4.5 g/cm3 for Grade 2 and about 4.4 g/cm3 for Grade 5, so the alloy’s extra strength arrives at effectively the same weight.

The strength row stays qualitative on purpose. Figures lifted out of their context are how a plate value ends up on a bar acceptance argument, so read the numbers from the controlling standard and its revision, for the ordered form and condition, and report them against that order.

Corrosion: both grades passivate, one is bought for it

Both form the same protective oxide film, so both hold up in seawater, chlorides, oxidizing acids and many process media. What separates them is intent. Grade 2 reaches the drawing because corrosion governs and because commercially pure titanium welds into corrosion equipment without argument. Grade 5 reaches the drawing because something has to be carried, and its corrosion behaviour, good as it is, sits outside that decision. Aggressive reducing acids and hot crevice conditions defeat both plain grades; those duties belong with Grade 7 or Grade 12.

Welding, forming and machining

Grade 2 welds readily and the weld keeps its ductility, which is why fabricators commonly use it for welded titanium equipment. Grade 5 can be welded, but the process needs closer control, so welded Grade 5 fabrications turn up less often.

Forming splits the same way. Grade 2 cold-forms into sheet metal parts, tube and fabricated equipment. Grade 5 has limited cold formability and normally reaches its shape hot, or on a machine from solid.

Both grades machine. Grade 5 is harder on tooling, and a shop quoting a Ti-6Al-4V part will plan for more wear than the same geometry in Grade 2 would cause.

Fabricators commonly choose Grade 2 for heat exchangers, tanks, vessel linings and chemical equipment. These are welded and formed corrosion duties, so unused alloy strength can add fabrication work without improving the service decision.

Where each grade ends up

Grade 2 covers the duties led by corrosion service and fabrication:

• Heat exchangers, condensers and tubesheets.
• Chemical process equipment, tanks, reactors and vessel linings.
• Marine and seawater piping and components.
• Anodes, electrodes and electrochemical equipment.
• Welded or formed titanium fabrication in general.

Grade 5 covers the parts that carry the load:

• Aerospace structural parts, brackets and fittings.
• Fasteners, bolts, shafts and springs.
• High-strength machined components.
• Sporting and high-performance hardware where strength to weight leads the design.

Where a design needs both high strength and the best crevice or reducing-acid resistance, the answer is a more specific grade reviewed by a corrosion engineer, and neither of these two by default.

Product forms and the standard behind each one

The two grades do not share a single standards list, and merging them is where ordering errors start. Grade 2 (R50400) is supplied as sheet and plate to ASTM B265, tube to ASTM B338, and bar to ASTM B348. Grade 2 pipe follows a separate route: ASTM B861 for seamless pipe, ASTM B862 for welded pipe. Grade 5 (R56400) is supplied as bar to ASTM B348 or AMS 4928, plate to ASTM B265, and forgings to ASTM B381. ASTM B338 covers Grade 2 tube and does not include Grade 5, so a Grade 5 tube requirement cannot use that route.

Bar is the form where a material-level comparison runs out. Diameter, supplied condition, machining allowance and the enquiry lines that separate a Grade 2 bar order from a Grade 5 one belong in the titanium bar grade selection guide, which works through bar size, condition, machining and RFQ decisions rather than the material choice covered here.

What settles the enquiry

An enquiry naming a grade and nothing else leaves too much open to price against. Four things close it:

• The grade and UNS number with the controlling standard, and the revision where a drawing names one.
• Whether corrosion or mechanical load governs the part, which is what confirms the grade rather than the preference.
• Form and dimensions, with the condition and surface requirement taken from the drawing, controlling standard or purchase order.
• The inspection and document scope you need, including certificate type and the results to be reported, agreed for that order instead of assumed.

How Beiyu Titanium supplies Grade 2 and Grade 5

Beiyu supplies Grade 2 bar to ASTM B348, sheet and plate to ASTM B265, and tube to ASTM B338. Grade 5 routes include ASTM B348 or AMS 4928 bar, ASTM B265 sheet and plate, and ASTM B381 forgings. Lead the enquiry with the governing requirement, corrosion or load, then give the grade, form, dimensions, condition, controlling standard and the document scope you need. The available product route, traceability fields and reported results come back with the quotation for that order.

The comparison depends on figures, so the method behind them is part of it

A grade comparison is only as reliable as the numbers it compares. Two certificates quoting the same oxygen figure by different methods are not answering the same question, which is why ASTM B348 names the methods it relies on rather than leaving them to the mill.

Naming a method settles how a value was produced. It does not add an examination the order did not ask for, and it does not make a heat analysis and a later product analysis interchangeable.

What the comparison cannot settle for you

Picking between Grade 2 and Grade 5 answers the left column. The right column still has to be written onto the purchase order, whichever grade wins.

For a view of who else publishes this material and what each one states, see Grade 5 Titanium Fastener Suppliers: Five Company Pages Compared.

Specification detail with sources

The strength gap is set by ASTM B265, Table 2: Grade 2 must reach 345 MPa minimum tensile strength with 20% minimum elongation, while Grade 5 (Ti-6Al-4V) must reach 895 MPa with 10% minimum elongation. Grade 5 delivers roughly 2.6 times the strength floor; Grade 2 keeps twice the ductility floor.

Composition drives the rest of the trade: Grade 5 carries 5.50 to 6.75% Al and 3.50 to 4.50% V, per ASTM B265, Table 1, which brings density to 4.43 g/cm³ against 4.51 g/cm³ for Grade 2 (ASM Handbook, Vol. 2) but makes welding and cold forming more demanding than for the unalloyed grade.