Titanium Grade 2 (UNS R50400) and Titanium Grade 5 (UNS R56400, also written Ti-6Al-4V) are the two most widely used titanium grades, and they sit at opposite ends of the same alloy family. Grade 2 is commercially pure titanium used for corrosion resistance; Grade 5 is an alpha-beta alloy used for strength. The difference in minimum yield strength between them is a factor of three, so the choice is a design decision rather than a preference.
What is the chemical difference between Grade 2 and Grade 5?
| Element | Grade 2 (R50400) | Grade 5 (R56400) |
|---|---|---|
| Ti | Balance | Balance |
| Al | - | 5.5-6.75 |
| V | - | 3.5-4.5 |
| Fe (max) | 0.30 | 0.40 |
| O (max) | 0.25 | 0.20 |
| C (max) | 0.08 | 0.08 |
| N (max) | 0.03 | 0.05 |
| H (max) | 0.015 | 0.015 |
Grade 2 has no deliberate alloying additions at all; its properties come from interstitial control, chiefly oxygen. Grade 5 is alloyed with aluminium, which stabilises the alpha phase and strengthens it, and vanadium, which stabilises the beta phase. The result is a two-phase microstructure that can be strengthened further by heat treatment - something a single-phase commercially pure grade can never do.
How much stronger is Grade 5 than Grade 2?
| Property | Grade 2 | Grade 5 |
|---|---|---|
| Tensile strength (MPa) | 345 | 895 |
| Yield strength, 0.2% (MPa) | 275 | 828 |
| Elongation in 50 mm (%) | 20 | 10 |
| Reduction of area (%) | 30 | 25 |
| Density (g/cm3) | 4.51 | 4.43 |
| Elastic modulus (GPa) | 102 | 114 |
| Thermal conductivity (W/mK) | 16.4 | 6.7 |
The last row is the one that surprises people who have only worked with steel. Grade 5 conducts heat at roughly 40% of the rate of Grade 2, so cutting heat concentrates at the tool edge instead of flowing into the chip and the workpiece. Combined with a yield strength three times higher, this is why machining Grade 5 is dramatically slower and more tool-hungry - and why a shop that quotes Grade 2 work at Grade 5 prices loses money on every part.
Which grade should be chosen for corrosion service?
Grade 2 is the corrosion grade, and it is the correct starting point for almost every process application. Commercially pure titanium forms a tenacious passive oxide film that resists seawater, chlorides, wet chlorine, hypochlorite, nitric acid and most oxidizing acid service. It is used for heat exchanger tubing to ASTM B338, seawater piping, anodes, desalination plant and chemical process vessels.
Grade 5 is also corrosion resistant, but it is not the better corrosion choice despite being the more expensive alloy. The aluminium addition slightly reduces resistance in some oxidizing media, and the two-phase structure makes it more susceptible to hydrogen pickup in cathodic protection and sour service. Where the problem is corrosion, Grade 2 usually wins. Where the problem is strength at low weight, Grade 5 wins.
Why is Grade 5 so much harder to machine and weld?
- Low thermal conductivity concentrates cutting heat in the tool, so cutting speeds for Grade 5 are roughly half those used on Grade 2 - around 30 to 45 m/min against 60 to 90 m/min with carbide tooling.
- Titanium reacts with oxygen, nitrogen and hydrogen above about 400 C, so both grades require inert gas shielding until the weld cools below that temperature - and Grade 5 is less tolerant of contamination.
- Grade 5 responds to heat input with alpha-prime martensite formation in the weld zone, so qualified procedures control interpass temperature tightly.
- Both grades are non-magnetic, so magnetic particle inspection cannot be used - dye penetrant or ultrasonic testing is required.
- Grade 2 is the more formable of the two by a wide margin and is the usual choice for cold-formed tube, strip and expanded heat exchanger tube.
The welding requirement applies to both grades equally, and it is the most common source of titanium fabrication failures: a weld that was adequately protected on the top face but not on the underside will oxidise and lose ductility while looking perfectly sound from the outside. Weld colour is the field indicator - silver is acceptable, straw and blue are not.
Which product standards apply to each grade?
| Product form | Specification | Notes |
|---|---|---|
| Plate, sheet, strip | ASTM B265 | Covers Grades 1 to 4, 5, 7 and 12 in one document |
| Seamless and welded tube | ASTM B338 | Heat exchanger and condenser tubing |
| Bar and billet | ASTM B348 | Bar, forging stock and billet |
| Forgings | ASTM B381 | Conventional and beta forged |
| Fittings | ASTM B363 | Titanium fittings for corrosion service |
| Surgical implants | ASTM F136 | Applies to Grade 23, the ELI variant of Grade 5 |
Note how the standards are organised: a single specification covers many grades, exactly as the nickel alloy product standards do. ASTM B265 plate can be supplied as Grade 1, 2, 3, 4, 5, 7 or 12, so the grade designation must be stated separately on the order. Ordering Grade 2 and receiving Grade 5, or the reverse, is a real risk when only the standard is quoted.
When should Grade 2 be selected and when should Grade 5 be selected?
| Application | Typical grade | Reason |
|---|---|---|
| Heat exchanger tubing, seawater | Grade 2 | Corrosion resistance and formability |
| Chemical process piping | Grade 2 | Corrosion resistance, weldability, cost |
| Desalination and chlorination plant | Grade 2 | Chloride and hypochlorite resistance |
| Anodes and cathodic protection | Grade 2 | Stable passive film |
| Aerospace airframe structure | Grade 5 | Strength-to-weight ratio |
| Fasteners and fittings above 500 MPa | Grade 5 | Cannot be met by any pure grade |
| Medical implants and instruments | Grade 5 or Grade 23 | Strength with biocompatibility |
| Motorsport and bicycle components | Grade 5 | Weight reduction at high strength |
The selection rule is short: if the requirement is a 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. The grades are not interchangeable in either direction, because the strength gap cannot be closed by thickness alone in weight-sensitive designs.
How do the two grades compare on cost?
Grade 5 typically costs more per kilogram than Grade 2, and the gap widens significantly in finished parts because machining time for Grade 5 is roughly double. For a welded process component, Grade 2 will usually be the cheaper finished article by a wide margin. For an aerospace bracket, the weight saving justifies both the material premium and the machining cost.
There is a third position worth knowing about. Grade 5 is available in an extra-low interstitial form, Grade 23 (UNS R56407), which trades a little strength for much better fracture toughness and is the grade used for surgical implants and some aerospace fracture-critical parts. The comparison Grade 5 vs Grade 23 covers that trade in detail, and Grade 2 vs Grade 7 covers the palladium-modified version of Grade 2 for more aggressive reducing acid service.
Continue reading
- Titanium Grade 2 vs Grade 7: When Palladium Makes the DifferenceTitanium Grade 7 (UNS R52400) is Grade 2 (UNS R50400) with 0.12-0.25% palladium, raising resistance to reducin
- Titanium Grade 5 vs Grade 23: Ti-6Al-4V vs ELI for Medical and AerospaceGrade 5 (Ti-6Al-4V) is the workhorse titanium alloy; Grade 23 is its Extra Low Interstitial variant, offering
- Titanium Grade 5 (Ti-6Al-4V) vs Inconel 718: Lightweight Titanium vs Heat-Resistant SuperalloyTitanium Grade 5 (Ti-6Al-4V) delivers an exceptional strength-to-weight ratio for lightweight structures. Inco
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Frequently asked questions
What is the main difference between titanium Grade 2 and Grade 5?
Grade 2 is commercially pure titanium with a minimum yield strength of 275 MPa used for corrosion resistance and formability, while Grade 5 is the alloy Ti-6Al-4V with a minimum yield strength of 828 MPa used where strength-to-weight ratio matters, so the two grades are separated mainly by a factor of three in strength.
Is Grade 5 titanium stronger than Grade 2?
Yes, Grade 5 is roughly three times stronger: ASTM sets minimum yield strength at 828 MPa for Grade 5 against 275 MPa for Grade 2, and minimum tensile strength at 895 MPa against 345 MPa, because the aluminium and vanadium additions in Grade 5 produce a two-phase structure that can also be strengthened by heat treatment while pure titanium cannot.
Why is Grade 5 harder to machine than Grade 2?
Grade 5 conducts heat at about 6.7 W/mK compared with 16.4 W/mK for Grade 2, so cutting heat concentrates at the tool edge instead of dispersing, and its yield strength is three times higher, which together reduce practical cutting speeds to roughly half those used on Grade 2 and shorten tool life considerably.
Can Grade 2 and Grade 5 be substituted for each other?
No, they cannot be substituted without a design re-check, because the minimum yield strength differs by a factor of three and the grades are not interchangeable in either direction - substituting Grade 2 for Grade 5 leaves the part below its design strength, and substituting Grade 5 for Grade 2 adds cost and machining difficulty without improving corrosion performance.
Which grade is used for heat exchanger tubing?
Grade 2 is the standard choice for heat exchanger and condenser tubing to ASTM B338, because the application needs chloride and seawater corrosion resistance plus the formability to be expanded into tubesheets, and its strength is more than adequate for the tube wall thicknesses involved.
Are both grades non-magnetic?
Yes, both Grade 2 and Grade 5 are non-magnetic, which means magnetic particle inspection cannot be used on either grade, and surface defects must be found by dye penetrant or ultrasonic testing instead.