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Ti Grade 1 / UNS R50250 / AMS 4940

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Commercially pure titanium – low oxygen. Ti Grade 1 is the purest form of titanium and is known as unalloyed titanium. The alloy contains 99.5% titanium and is known for its very high corrosion resistance, excellent biocompatibility, low density and good mechanical properties.

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: Being pure titanium, some difficulties can arise in terms of machinability, but machining is generally possible. The following are some important points regarding the machinability of Ti Grade 1.​‌​​‌​

Machining: It can be processed by conventional methods such as milling, turning and drilling. During the machining of titanium, however, it is important to allow for high temperatures and to use appropriate cutting tools. Machining at low speed and the use of cutting fluids are necessary, because titanium can generate high temperatures during cutting operations.

Welding: It can be welded by the TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) methods. It is important to use shielding gases such as argon during welding in order to prevent oxidation of the titanium. Post-weld heat treatment may be required, since some change in properties can occur in the weld zone.​‌​​‌​

Cold forming: Cold forming is generally suitable for Ti Grade 1. Operations such as plasma cutting and bending can also be carried out, but care should be taken during the process.

Hot forming: Hot forming is generally suitable for Ti Grade 1 and working at lower temperatures is recommended. It should be remembered that temperatures must not be too high.​‌​​‌​

What Titanium Grade 1 Is — and the ONE Thing That Separates It From Grade 2​‌​​‌​

Titanium Grade 1 (UNS R50250 / W.Nr. 3.7025 / DIN Ti 1 / commonly sold as Ti 99.8) is the softest and most ductile grade of unalloyed, commercially pure (CP) titanium. At room temperature it is single-phase HCP (α) titanium — there is no second phase, no precipitate and no hardening mechanism in it. It cannot be hardened by heat treatment. Its strength comes from exactly two sources: cold work and interstitial atoms.

There is not a single deliberately added alloying element separating Grade 1 from Grade 2. Both are unalloyed titanium; both carry the same carbon, nitrogen and hydrogen ceilings. Only two lines in the specification differ: oxygen and iron. Those two lines set the strength, the ductility, the bend radius, the welding behaviour, the price and what code calculation you are allowed to do. Everything else on this page follows from that one fact.​‌​​‌​

What oxygen and iron actually do​‌​​‌​

In titanium, oxygen is not an impurity — it is an alloying element. It sits interstitially in the octahedral sites of 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. Going from Grade 1 to Grade 2 oxygen rises by only 0.07 percentage points, and in exchange the minimum yield goes from 138 MPa to 275 MPa — roughly double. Iron is capped for a different reason: 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 acids and in crevice corrosion. Grade 1’s 0.20 % ceiling means a cleaner single phase and noticeably better ductility.

The sentence worth publishing: Grade 1 is not a “purer” Grade 2. It is the grade chosen for a different engineering purpose. Grade 2 exists for strength and code calculability; Grade 1 exists for formability, weld ductility and cladding adhesion. Ordering the wrong one is expensive in both directions: put Grade 1 in a pressure vessel and your wall thickness grows for nothing; put Grade 2 into a deep-draw die and it tears.​‌​​‌​

Standards by Product Form

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Unlike the nickel alloys, titanium has an ASTM family numbered separately by product form, and it covers Grade 1 almost completely. The table below can be used directly on 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. Unalloyed titanium is metallurgically perfectly happy at 315 °C; the code stops there because there is no creep and long-term oxidation data behind it.

What an “H” grade is, and why Grade 1 was left out

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; the only difference is that the minimum tensile is guaranteed at 400 MPa (58 ksi) instead of 345 MPa (50 ksi). Yield is 275 MPa and elongation 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. Grade 1 is outside this programme — because Grade 1 is not bought for strength in the first place.​‌​​‌​

Product Forms With NO Standard — the Commercially Valuable Section

Titanium has fewer gaps than the nickel alloys, but they sit in different places and cost more when you hit them. 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​‌​​‌​

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Never mix specification minima with typical mill values. Purchasing works from the minima; typicals are a guarantee of nothing and, if substituted for the specification, cause trouble on the first certificate.

Physical Properties​‌​​‌​

Heat Treatment and Thermal Stability​‌​​‌​

The most important sentence first: Grade 1 cannot be hardened by heat treatment. In single-phase α titanium there is no solution treat plus age, no martensite, no precipitate. Heat treatment has three purposes and all three are to soften, to relieve stress and to stabilise dimensions.

Welding​‌​​‌​

Welding titanium is not difficult; welding it CLEAN is. Metallurgically Grade 1 is the easiest of the family to weld — single phase, no hardening, no preheat, no cracking tendency. The entire risk sits in one place: molten and hot titanium absorbs oxygen, nitrogen and hydrogen greedily.

Machining​‌​​‌​

Grade 1 is the hardest grade in the titanium family to machine — and because that is counter-intuitive, it is constantly planned wrong. Being soft does not make it easier; on the contrary it goes “gummy”: the chip smears onto the tool instead of breaking, forms a built-up edge (BUE) and ruins the surface. Grade 2, with its higher oxygen, breaks chips more cleanly.

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 — the critical point — self-healing, but only if oxygen or water is present in the environment. Every piece of good news and every piece of bad news below follows from that one sentence. 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 — both build the same TiO₂ film. Grade 1’s slightly lower iron gives a marginal edge in some environments; do not turn that into a sales argument.​‌​​‌​

Frequently Asked Questions

Is oxygen really the only difference between Grade 1 and Grade 2? Then why does the price run the other way?​‌​​‌​

Yes — only two lines in the specification differ: oxygen and iron. Grade 1 is O ≤0.18 % and Fe ≤0.20 %; Grade 2 is ≤0.25 % and ≤0.30 %. The carbon, nitrogen and hydrogen ceilings are identical, and there is no deliberately added alloying element in either.
The consequence is not small: that 0.07 percentage point of oxygen roughly doubles the minimum yield, from 138 MPa to 275 MPa. The price is that minimum elongation falls from 24 % to 20 % and the bend radius goes from 1.5T–2T to 2T–2.5T.
The reason the price runs the other way is volume, not metallurgy. Grade 2 is the overwhelming majority of industrial titanium consumption and is stocked at every service centre; Grade 1 is melted to a narrower oxygen window and is usually a smaller batch. So its price per kilo is often above Grade 2’s, its lead time is longer and the thickness range is narrower.
Practical advice: if the reason is deep drawing, explosive cladding, an anode substrate or a very tight bend radius, Grade 1 is a genuine requirement. If the reason is “purer, therefore better corrosion resistance”, the reason is weak: both grades build the same TiO₂ film and behave the same in practice. In that case Grade 2 is faster, cheaper and more useful in a code calculation.

The customer specification says “Titanium Grade 1, 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.
Metallurgically unalloyed titanium is untroubled at 400 °C: no phase transformation, no embrittlement window, the β transus far away (~888 °C). The material simply gets weaker — published typical data for Grade 2 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. There is no code allowable stress above it.
A second coverage problem: most of the code rows on this page were verified through Grade 2; that Grade 1 (R50250) is separately listed in the same sections could not be independently verified. Confirm the R50250 line in Section II Part D before ordering. In practice most designers move to Grade 2 anyway: a 138 MPa minimum yield inflates the wall thickness.
The third and most forgotten item is flanges. ASME B16.5 does not cover titanium. There is no ready-made pressure–temperature table; a titanium flange is made to B16.5 dimensions but its rating has to be calculated per B16.5 Annex A. “Class 300 titanium flange” is not a rating on its own.
Realistic answers: get the design temperature brought down to 315 °C; move to Grade 2 or Grade 2H for strength (2H guarantees 400 MPa minimum tensile on identical chemistry, and in one published example gives a 14 % material saving under Div. 2 Class 2 rules); or use the titanium as a non-pressure-retaining lining on a code-approved backing material. 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 want Grade 1 plate for explosive cladding onto steel. Why not Grade 2?​‌​​‌​

Because explosive cladding is a forming process, and Grade 1 is the most formable grade in the family. A thin titanium plate is driven onto the backing plate at very high velocity by explosive energy; a metallurgical bond forms at the interface, but the price is very high local plastic deformation in the impact zone. Grade 1’s minimum elongation is 24 % and its bend radius 1.5T–2T; Grade 2, at 20 % and 2T–2.5T, is markedly stiffer and more prone to cracking at the wave front. The same logic applies to deep drawing, spinning, pressing plate-heat-exchanger plates and tank lining.
Three warnings. (1) If the backing steel is to be stress relieved after cladding, make sure the temperature suits the titanium side too: 538–593 °C is safe; an anneal at 650 °C or above carried out in air produces alpha case on the titanium surface. (2) No steel tool may touch the clad surface — free iron contamination starts local corrosion in service. (3) Seam welds are made with ERTi-1 under full argon shielding and back purge; an unshielded root pass is scrap, not a repair.
And let us be honest: if the part will not be formed, the premium you pay for Grade 1 buys nothing. For flat plate, pipe, flanges and pressure vessels, Grade 2 is the better choice on every count.

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

1. “Grade 1 and Grade 2 have the same chemistry” — WRONG. Two lines differ: oxygen (0.18 / 0.25 %) and iron (0.20 / 0.30 %). Those two lines double the minimum yield.
2. The AMS-T-9046 / MIL-T-9046 “CP” numbering runs INVERSE. CP-4 = Grade 1, CP-3 = Grade 2, CP-1 = Grade 4. Assuming “CP-1 must be the purest” is the most common and most expensive misreading.
3. AMS number confusion. Grade 1’s aerospace sheet specification is AMS 4940 (“25.0 ksi yield”); AMS 4901 is Grade 4 at 70 ksi yield; AMS 4902 is Grade 2. Some distributor tables assign AMS 4901 to both Grade 1 and Grade 4 and thereby contradict themselves in the same table.
4. The material-number triplet. 3.7025 = DIN 17850 Ti 1 (base metal), 3.7024 = WL/aerospace, 3.7026 = welding FILLER wire. The same triplet exists on the Grade 2 side: 3.7035 / 3.7034 / 3.7036.
5. The ASTM minimum and the DIN range get mixed. ASTM B265 Grade 1 gives only Rm ≥240 MPa; DIN Ti 1 sets both a lower and an UPPER limit at Rm 290–410 MPa. A heat that conforms to ASTM may fail DIN — from below or from above.
6. The YIELD MAXIMUM gets overlooked. ASTM B265 Grade 1 yield is 138–310 MPa; 310 MPa is an upper limit and it is enforced. There is no such product as “high-strength Grade 1”.
7. There is no “Grade 1H”. The ASME-approved H grades are 2H, 7H, 16H, 26H.
8. ASTM B337 is still quoted as the pipe specification — it was WITHDRAWN in 1997. The correct references are B861 (seamless) and B862 (welded).
9. “B16.5 Class 150 titanium flange” is taken for a rating — it is NOT. B16.5 does not cover titanium; the rating is calculated per Annex A.
10. 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].
11. 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.
12. “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 red fuming nitric acid, embrittles with hydrogen above 77 °C under cathodic charging and suffers crevice corrosion in seawater above 82 °C.
13. Hardness scale and carbon ceiling. Grade 1 is ~70 HRB (~120 HV); reading “70” as HRC produces nonsense. And the carbon ceiling is often printed as 0.10 % — the current ASTM B265 value is 0.08 %.
14. Hardening by heat treatment gets offered. Grade 1 is single-phase α titanium; it cannot be hardened. For surface hardness the route is anodising, nitriding or coating.
15. The modulus is assumed to be steel-like. It is 103–105 GPa, roughly half that of steel — twice the deflection at the same section. In titanium design stiffness almost always governs before strength.

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