Reviewed by the Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd.
ASTM B381 covers annealed titanium and titanium-alloy forgings for general industrial, chemical, marine, aerospace, and pressure-equipment service. It is the material standard for forged flanges, valve bodies, hubs, rings, discs, blocks, and custom pressure-retaining parts.
The standard lists 39 grades — F-1 through F-38, including F-2H / F-7H / F-16H / F-26H high-UTS variants for pressure-vessel use. For industrial procurement, F-2, F-5, F-7, F-12 cover the large majority of orders; F-23 is added for medical/aerospace fracture-critical parts.[4](@ref)
B381 defines chemistry, tensile properties (extracted from the forging or its prolongation), heat treatment, marking, and certification. It does not define flange dimensions (that is ASME B16.5 / B16.47) and it does not cover bar (B348), plate (B265), or castings (B367).
The one sentence that prevents 80% of procurement disputes: B381 is the material-and-process standard; B16.5 is the dimension standard. A complete titanium flange spec cites both — "ASME B16.5 dimensions, ASTM B381 F-2 forging." Citing only B16.5 lets a supplier deliver a bar-machined part to B16.5 dimensions, which is not a code forging.
| Grade | UNS | Chemistry | Typical forged part | Relative cost index |
|---|---|---|---|---|
| F-1 | R50250 | CP Ti, 0.18% O max | High-formability liners, medical preforms | 1.0 |
| F-2 | R50400 | CP Ti, 0.25% O max | Flanges, valve bodies, fittings, agitator hubs (workhorse) | 1.0–1.1 |
| F-3 / F-4 | R50550 / R50700 | CP Ti, higher O | Higher-yield CP parts, implant preforms | 1.1–1.3 |
| F-5 | R56400 | Ti-6Al-4V | Aerospace flanges, subsea connectors, high-strength fastener blanks | 1.8–2.2 |
| F-7 | R52400 | CP Ti + 0.12–0.25% Pd | Reducing-acid valve stems, chlor-alkali flanges, crevice-service hubs | 1.5–1.8 |
| F-9 | R56320 | Ti-3Al-2.5V | Cold-headed forged fasteners, hydraulic forged bodies | 1.6–2.0 |
| F-12 | R53400 | Ti-0.3Mo-0.8Ni | Elevated-temperature valve bodies, sour-service flanges | 1.4–1.7 |
| F-23 | R56407 | Ti-6Al-4V ELI | Medical implants, fracture-critical aerospace forgings | 2.5–3.0 |
Cost index relative to F-2; Pd/Mo/V/Al surcharges dominate the delta.
Rule of thumb: F-2 for general corrosive service; F-7 when crevice/reducing-acid resistance is the failure mode; F-12 when service temperature exceeds ~150°C with chlorides; F-5 only when yield strength >800 MPa is required and corrosion is secondary.
| Element | F-2 max | F-5 | F-7 max | F-12 max |
|---|---|---|---|---|
| N | 0.03% | 0.05% | 0.03% | 0.03% |
| C | 0.08% | 0.08% | 0.08% | 0.08% |
| H | 0.015% | 0.015% | 0.015% | 0.015% |
| Fe | 0.30% | 0.40% max | 0.30% | 0.30% |
| O | 0.25% | 0.20% max | 0.25% | 0.25% |
| Al | — | 5.5–6.75% | — | — |
| V | — | 3.5–4.5% | — | — |
| Pd | — | — | 0.12–0.25% | — |
| Mo / Ni | — | — | — | 0.2–0.4% / 0.6–0.9% |
| Ti | Balance | Balance | Balance | Balance |
Procurement note: F-2 and F-7 share everything except Pd. The MTR must show Pd in range for F-7 — visual inspection cannot. PMI (XRF) every heat of F-7/F-12 before machining; confusion with F-2 in inventory is the most common grade-mix incident.
| Grade | Tensile, min (MPa) | Yield 0.2% offset, min (MPa) | Elongation, min (%) | Reduction of Area, min (%) |
|---|---|---|---|---|
| F-2 | 345 | 275 | 20 | 30 |
| F-5 | 895 | 828 | 10 | 25 |
| F-7 | 345 | 275 | 20 | 30 |
| F-12 | 483 | 345 | 18 | 25 |
| F-23 | 828 | 760 | 10 | 25 |
Per ASTM B381; tensile coupon taken from forging or prolongation, not from bar stock.
Why RA matters: Reduction of Area is mandatory on forgings and is the clearest signal that the coupon represents forged (not bar) material. A bar tensile can pass; a forged RA value proves directional integrity through the hub/fillet.
B381 permits open-die, closed-die, ring-rolling, and isothermal forging. Three metallurgical controls decide whether the part is code-grade:
Bar-machined ≠ forged: A B348 bar turned to flange dimensions has axial grain crossing the hub fillet transversely. ASME B31.3 / Section VIII do not accept it as a forged flange. The MTR must say "forged" with reduction ratio — otherwise the inspector rejects it.
B381 treats NDE as a purchaser-specified requirement — if you don't ask, you don't get it. For critical service, specify:
| Test | Standard | When to require |
|---|---|---|
| Ultrasonic (volumetric) | ASTM A388 / AMS 2630 | Large forgings, billet-fed flanges, valve bodies |
| Magnetic particle / dye penetrant | ASTM E709 / E165 | Surface-breaking defects after machining |
| Macro-etch | Internal practice | Grain-flow verification on first-article |
| PMI (XRF) | ASTM E572 | Every heat of F-7 / F-12 / F-16 |
| Ferroxyl (free iron) | ASTM A380 | After machining, chloride service |
| Microstructure | Project spec | Aerospace / medical / fracture-critical |
Weld repairs, if allowed, must be written into the PO. For titanium pressure forgings, repair welding requires argon shielding on root and cap until <320°C; blue/purple heat tint = oxygen pickup = re-pickle or reject.
Top failure modes:
Maintained by the Engineering Team at Shaanxi Qianyi Tuoda Technology Co., Ltd. Data per ASTM B381 / ASME SB-381. Procurement support: sales@sxqytd.com.
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