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Ti Grade 2 / UNS R50400 / AMS 4902 / AMS 4941

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Ti Grade 2 is another commercially pure form of titanium and is known as unalloyed titanium. Like Ti Grade 1 it offers very high purity, but it provides higher strength in terms of mechanical properties. It contains 99.2% titanium and stands out for its corrosion resistance, light weight and biocompatibility.

The commercially pure titanium grades have an excellent strength-to-density ratio and good corrosion resistance. These properties make commercially pure titanium suitable for the manufacture of components in weight-saving structures carrying low mass forces, and also for components requiring high corrosion resistance. In addition, because of the low thermal expansion of titanium, thermal stresses in titanium structures are lower than in other metallic materials. Together with this property, titanium components are increasingly becoming the material of choice in a widening range of sectors. The materials are also widely used in the medical sector because of their exceptional biocompatibility.​‌​​‌​

Application areas: chemical industry, aerospace industry, medical applications.

Machinability: Because it has somewhat higher mechanical properties than pure titanium, it is also somewhat more difficult to machine, but it can be processed with conventional machining techniques. Machinability depends on factors such as the hardness of the alloy, its high melting point and the need to work at elevated temperature.​‌​​‌​

Machining: It can be processed by operations such as milling, turning and drilling, but machining at low speed is recommended. Cutting tools should generally be a hard alloy or carbide, and cutting and cooling fluids should be used to prevent the titanium from overheating.

Welding: It can be welded by the TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) methods. Oxidation should be prevented during welding by using shielding gases such as argon.​‌​​‌​

Cold forming: Cold forming operations are suitable for Ti Grade 2, and plasma cutting and bending operations can generally also be carried out.

Hot forming: It is suitable for hot forming, but temperatures should not be too high. Working at the lower end of the temperature range is generally recommended for titanium alloys.​‌​​‌​

What Titanium Grade 2 Is — and Why It Is the De Facto Standard for Industrial Titanium​‌​​‌​

Titanium Grade 2 (UNS R50400 / W.Nr. 3.7035 / DIN Ti 2 / commonly sold as Ti 99.6) is the workhorse of unalloyed, commercially pure (CP) titanium. At room temperature it is single-phase HCP (α) titanium: no second phase, no precipitate, no hardening mechanism. It cannot be hardened by heat treatment. Its strength comes only from cold work and from interstitial atoms.​‌​​‌​

There is not a single deliberately added alloying element separating Grade 2 from Grade 1. Both are unalloyed titanium and their carbon, nitrogen and hydrogen ceilings are identical. Only two lines in the specification differ: oxygen (0.25 % versus 0.18 %) and iron (0.30 % versus 0.20 %). Those two lines take the minimum yield from 138 MPa to 275 MPa, roughly double — and that is what makes Grade 2 the only CP grade you can practically build a code calculation on.

What oxygen does — and why Grade 2 is the sweet spot

In titanium, oxygen is not an impurity — it is an alloying element. It sits interstitially in the HCP lattice, distorts it and blocks dislocation motion — solid solution strengthening in the strictest sense. Yield and tensile rise; elongation, formability and fracture toughness fall; the β transus shifts up (~888 °C in Grade 1, ~913 °C in Grade 2). Iron is a β stabiliser: it leaves a small amount of β at grain boundaries, and iron-rich regions are the weak points in reducing acid and in crevice corrosion.​‌​​‌​

Grade 2’s commercial dominance comes down to one sentence: its interstitial content holds the best balance between engineering-useful strength (275 MPa yield) and still-excellent ductility (20 % minimum, typically above 25 %). Grade 1 welds well but inflates wall thickness in a code calculation; Grades 3 and 4 give strength but cannot be formed and lose weld ductility. Grade 2 welds, forms AND passes the ASME calculation. No other unalloyed titanium grade does all three at once.

Standards by Product Form​‌​​‌​

Unlike the nickel alloys, titanium has an ASTM family numbered separately by product form — and Grade 2 is covered in EVERY specification in it. The table below can go straight onto a purchase order.

ASME Code Acceptance and MAXIMUM CODE TEMPERATURES

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The ceiling for titanium is strikingly low compared with the nickel alloys you are used to, and it is a CODE limit, not a metallurgical one. Grade 2 is metallurgically perfectly happy at 315 °C; the code stops there because there is no creep and long-term oxidation data behind it. Most of the family’s code lines were published through Grade 2 in the first place — it is the best-documented unalloyed titanium grade in ASME.

What an “H” grade is, and whether Grade 2H is worth buying

An H grade is a grade with identical chemistry but a raised minimum tensile strength. Grade 2H has exactly the same composition as Grade 2 — same UNS number, same O, Fe, C, N and H ceilings. The only difference is that the minimum tensile is guaranteed at 400 MPa (58 ksi) instead of 345 MPa (50 ksi); yield stays at 275 MPa and elongation at 20 % for both.
The justification is statistical. The Materials Technology Institute and the International Titanium Association reviewed first more than 400 commercial heats and later more than 5,200 commercial test reports, and showed that over 99 % already met the 58 ksi minimum. So an H grade is not a new material — it is strength that already existed being accepted into the code. In one published example, using Grade 2H under Section VIII Div. 2 (Class 2) rules gives roughly a 14 % material saving over Div. 1.
The practical answer: if you are building a thick-walled, large-diameter vessel and the design can move to Div. 2, ask for 2H — same metal, similar price, thinner wall. In thin sheet, exchanger tube and general piping the difference disappears in practice; there, specifying 2H only narrows your supplier pool.​‌​​‌​

Product Forms With NO Standard — the Commercially Valuable Section

Grade 2 is the most widely covered titanium grade; the gaps are few but expensive. This is the section your sales engineers should memorise.​‌​​‌​

Chemical Composition​‌​​‌​

For unalloyed titanium, “composition” means writing down the interstitial ceilings. There are five lines on the certificate; two of them (oxygen, iron) define the grade.

Mechanical Properties​‌​​‌​

Never mix specification minima with typical mill values. Purchasing works from the minima; typicals guarantee nothing.​‌​​‌​

Physical Properties

Heat Treatment and Thermal Stability

The most important sentence first: Grade 2 cannot be hardened by heat treatment. In single-phase α titanium there is no solution treat plus age, no martensite, no precipitate. The purpose of heat treatment is to soften, to relieve stress and to stabilise dimensions.​‌​​‌​

Welding

Welding titanium is not difficult; welding it CLEAN is. Grade 2 welds easily in metallurgical terms — single phase, no hardening, no preheat, no cracking. The entire risk is in one place: molten and hot titanium absorbs oxygen, nitrogen and hydrogen greedily.​‌​​‌​

Machining

Grade 2 is the easiest unalloyed grade in the titanium family to machine — but “easy” is a relative word here. Its higher oxygen makes it break chips more cleanly than Grade 1; even so, Grade 2 work hardens the instant it is rubbed, concentrates heat at the cutting edge and destroys a dull tool quickly.​‌​​‌​

Corrosion — Why It Is Good, and WHERE IT FAILS

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All of titanium’s corrosion resistance rests on one thing: the spontaneously formed TiO₂ passive film. That film is extremely stable, tightly adherent and self-healing — but only if oxygen or water is present. If the environment feeds the film, titanium is close to untouchable; if it cannot, titanium is an ordinary active metal. Grade 1 and Grade 2 behave practically identically in corrosion; the grade is chosen for strength and code, not for corrosion.​‌​​‌​

Frequently Asked Questions

The customer wants Grade 2H. We have Grade 2 in stock. Can we certify it as 2H?​‌​​‌​

Chemically yes; mechanically only if that heat’s tensile value genuinely meets it. Grade 2H has exactly the same chemistry and the same UNS number (R50400) as Grade 2; it is not a separate material. The difference is one line: the minimum tensile is guaranteed at 400 MPa (58 ksi) instead of 345 MPa. Yield (275 MPa) and elongation (20 %) are unchanged.
The good news: in practice most Grade 2 heats already exceed that. The published statistic is clear — over 99 % of more than 5,200 commercial test reports met the 58 ksi minimum, which is exactly why the H grade exists. A typical mill value is of the order of ~483 MPa (70 ksi) at 20 °C.
But procedure matters. If the actual tensile value on the heat’s original certificate meets 400 MPa and the mill dual-marked it as 2H, there is no problem. If it does not — or if the certificate only states “≥345 MPa” without the actual value — you cannot sell the material as 2H; ask the supplier for the actual tensile value or for a new certificate dual-marked as 2H.
And ask one more question: does the customer actually need 2H? Its only benefit is a higher code allowable stress, hence a thinner wall. On a thick-walled, large-diameter Div. 2 vessel that is meaningful — one published example gives ~14 % material saving over Div. 1. In thin sheet, exchanger tube and general piping the difference disappears, and there the 2H requirement only narrows the supplier pool.

The specification says “Titanium Grade 2, ASME Section VIII, 400 °C design temperature”. Can we supply it?​‌​​‌​

Not as a pressure-retaining component — and the reason is a code limit, not a metallurgical one. Do not confuse the two.
Metallurgically Grade 2 is untroubled at 400 °C: no phase transformation, no embrittlement window, the β transus far away (~913 °C). The material simply gets weaker — published typical data show tensile falling from ~483 MPa at 20 °C to ~228 MPa at 300 °C, while elongation rises to 43 %.
The problem is code coverage, and the ceiling is surprisingly low: 315 °C (600 °F). That figure applies to unalloyed titanium for all applications — VIII Div. 1 and Div. 2, III Class 2/3, Section XII. Above it there is no code allowable stress, so you have no number to design with at 400 °C.
And the most forgotten item is flanges. ASME B16.5 does not cover titanium. A titanium flange is made to B16.5 dimensions but its rating must be calculated per Annex A; “Class 300 titanium flange” is not a rating on its own — and a significant part of the price difference in the quotation comes from that engineering work.
Realistic answers: get the design temperature brought down to 315 °C; if 400 °C is genuinely required, leave the titanium family for a nickel alloy with code coverage above it (alloy 825, C-276); or use the titanium as a non-pressure-retaining lining or cladding on a code-approved backing — on the seawater and chloride side this is a very common and very economical solution. What you must not do is quote “titanium is good to 500 °C” from a catalogue and let it turn into a design temperature.

We are using Grade 2 tube in a seawater exchanger. What should we watch for?​‌​​‌​

Grade 2 is the world’s de facto standard for this duty — but there are three traps, and all three are about system design, not corrosion data.
First, galvanic coupling, and it runs the opposite way to most people’s intuition. Titanium is passive in seawater and is not attacked itself; but it accelerates the other member of the couple. Connect a titanium tube bundle to a carbon steel tubesheet, to aluminium bronze or to ordinary stainless, and what corrodes is not the titanium but the other metal — and because the titanium cathode area is large, the effect is severe. The fix is to make the whole wetted surface titanium, to use insulation or coating, or to design a deliberate sacrificial anode scheme.
Second, cathodic protection and hydrogen. If you try to solve the galvanic problem with impressed-current cathodic protection, you make the titanium a cathode and generate hydrogen on its surface. Above 77 °C and in the pH <3 or >12 region that leads to hydrogen embrittlement; in near-neutral brine the threshold quoted is a potential more negative than −0.70 V (SCE). Do not over-protect the titanium.
Third, temperature and crevices. Grade 2’s general corrosion resistance in seawater is outstanding, but crevice corrosion is a real risk above ~82 °C (180 °F) and low pH pulls the threshold down further. The risky places are under gaskets, in the tube-to-tubesheet roll zone and under deposits. If there is hot brine, the right answer is not Grade 2 but Grade 7 / Grade 16 (palladium-bearing) or Grade 12.
And a bonus — the most common real cause of failure in the field: titanium’s modulus is 105 GPa, half that of steel, which means twice the deflection and a lower natural frequency at the same geometry. In seawater exchangers flow-induced vibration and support spacing cause more failures than corrosion does. Choose the tube wall thickness for vibration, not for corrosion allowance — in titanium the corrosion allowance is effectively zero anyway.

Can we offer Grade 2 for our hydrochloric acid line?​‌​​‌​

Most probably not — and this is the most common way titanium gets misapplied.
Titanium’s window in HCl is narrow: useful resistance runs to about 7 % at room temperature. At boiling, above 2 % the corrosion rate reaches the order of 280 mpy (~7.1 mm/y) — the material effectively dissolves. In sulphuric the window is narrower still: ~5 % at room temperature, ~20 % at 0 °C, and high corrosion at boiling with as little as 0.5 %.
The reason in one sentence: to heal itself the TiO₂ film needs oxygen or an oxidant in the environment, and a deaerated, hot, reducing acid does not have one.
But there is an important exception, and you have to ask the right question: is there ferric or cupric ion in the stream? In titanium, Fe³⁺ and Cu²⁺ are not a threat but INHIBITORS — they passivate titanium in reducing acid; published data show ferric or cupric ion preventing corrosion in 20 % sulphuric. A real process line with carbon steel upstream often generates those ions already. This is the exact opposite of the Hastelloy B family, where the same ions are the number one cause of failure.
A practical route: ask the customer in writing for concentration, temperature, aeration state and a ferric/cupric analysis. If the acid is dilute, cold and carries an oxidant, Grade 2 can work — but write those conditions into the order acknowledgement. If the acid is hot, concentrated or deaerated, the right answer is Grade 7 or Grade 16 (palladium-bearing titanium), or outside the family altogether Hastelloy B-3. And if there is hydrofluoric acid or fluoride in the stream, no titanium grade works — that one is not negotiable.

Common datasheet errors — check these before you order​‌​​‌​

1. “Grade 2H is a different alloy” — WRONG. Its chemistry and UNS number (R50400) are identical to Grade 2. The only difference is that the minimum tensile is guaranteed at 400 MPa instead of 345; yield and elongation are unchanged.
2. The AMS-T-9046 / MIL-T-9046 “CP” numbering runs INVERSE. CP-3 = Grade 2, CP-4 = Grade 1, CP-1 = Grade 4. Assuming “CP-1 must be the purest” is the most common and most expensive misreading.
3. Material-number confusion. 3.7035 = DIN 17850 Ti 2 (base metal), 3.7034 = WL/aerospace, 3.7036 = welding FILLER wire. Several mill sheets print the base metal as 3.7034 [D].
4. The ASTM minimum and the DIN range get mixed. ASTM B265 Grade 2 gives only Rm ≥345 MPa; DIN Ti 2 sets both a lower and an UPPER limit at Rm 390–540 MPa. A heat conforming to ASTM may fail DIN — from below or from above.
5. The YIELD MAXIMUM gets overlooked. ASTM B265 Grade 2 yield is 275–450 MPa; 450 MPa is an upper limit and it is enforced. Over-cold-worked, “stronger” Grade 2 does not conform.
6. ASTM B337 is still quoted as the pipe specification — it was WITHDRAWN in 1997. The correct references are B861 (seamless) and B862 (welded).
7. “ASME B16.5 Class 150 titanium flange” is taken for a rating — it is NOT. B16.5 does not cover titanium. The flange is made to B16.5 dimensions; the rating is calculated per Annex A.
8. Thermal conductivity gets copied from the wrong family. The ~7 W/m·K figure is for Ti-6Al-4V; the band published for unalloyed titanium is ~16–22 W/m·K [sources diverge across 16.4 · 20.8 · 21.8 · 22].
9. Ferric and cupric ions are taken for a threat — in titanium they are INHIBITORS. Fe³⁺ and Cu²⁺ passivate titanium in reducing acid; this is the exact opposite of the Hastelloy B family.
10. “Titanium does not corrode” — WRONG and dangerous. It dissolves in HF at every concentration, ignites in dry chlorine, burns in pure oxygen, cracks in anhydrous methanol, forms a pyrophoric product in RFNA, embrittles with hydrogen above 77 °C under cathodic charging and suffers crevice corrosion in seawater above 82 °C.
11. Hardness scale, carbon ceiling and modulus. Grade 2 is ~80 HRB (~145 HV); reading “80” as HRC produces nonsense. The carbon ceiling is often printed as 0.10 % — the current ASTM B265 value is 0.08 %. And the modulus is 105 GPa, roughly half that of steel — twice the deflection at the same section, which is why flow-induced vibration causes more seawater-exchanger failures than corrosion.
12. Hardening by heat treatment gets offered. Grade 2 is single-phase α titanium; it cannot be hardened. For surface hardness the route is anodising, nitriding or coating.
13. Allowable stresses get taken from a distributor sheet. ASME Section II Part D values are updated edition to edition. Always take the design value from the code edition in force.
14. “Grade 2 is NACE approved” gets published as a one-liner. One source states that Grade 2 is approved for sour service under NACE MR-01-75, but this is single-sourced and could not be verified against the current ISO 15156-3 text. Before taking on H₂S work, read the table in force yourself, including its temperature, chloride and pH limits.

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