ASTM B381 Titanium Forgings & Flanges: F-Grades, Ring Rolling & RFQ Guide

Published by Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd on 2026-10-21

ASTM B381 Titanium Forgings & Flanges: F-Grades, Ring Rolling, Flange Blanks & Procurement Guide

Table of Contents

• 1. What Is ASTM B381?
• 2. F-Grades: F-1/F-2/F-5/F-7/F-12 vs Gr.2/Gr.5
• 3. Forging Forms: Flange Blank, Ring, Disc, Block, Shaft
• 4. Open-Die, Closed-Die & Ring Rolling
• 5. Why Forged Flanges Beat Bar-Machined Flanges
• 6. Annealed, STA, Stress-Relieved
• 7. UT, PT, Grain-Flow & Dimensional Inspection
• 8. How to Write an ASTM B381 Forging RFQ
• 9. Forging Procurement Mistakes
• 10. Our Forging → Flange → Machining Chain
• 11. FAQs
• 12. Related Standards

1. What Is ASTM B381?

ASTM B381 is the standard specification for titanium and titanium alloy forgings. It covers annealed forgings in many grades — flanges, rings, discs, blocks, shafts, valve bodies, and custom pressure-part shapes. The ASME version is SB-381, used for code-stamped pressure equipment. [4](@ref)

A forging is not “a bar with a fancy shape”. The whole point of B381 is controlled hot deformation: the cast structure of the ingot/billet is broken down, the grain flow follows the part contour, and internal soundness improves versus saw-cut plate or machined bar.

B348 = bar/billet mill product.
B265 = plate/sheet/strip.
B381 = shaped, hot-worked part with directional grain flow.

2. F-Grades: F-1/F-2/F-5/F-7/F-12 vs Gr.2/Gr.5

ASTM B381 uses F-prefix grades (F-1, F-2, F-5, F-7, F-9, F-12…). Chemically they map to the familiar mill grades, but the mechanical basis comes from the forging or its prolongation, not from bar stock.

On a PO, writeASTM B381 F-2for the forging — not just “Gr.2”. If the customer means “Gr.2 chemistry”, fine; but forging inspection, reduction ratio, and test-coupon location are B381 matters. [1](@ref)

3. Forging Forms: Flange Blank, Ring, Disc, Block, Shaft

• Flange blank / flange forgings: WN, blind, slip-on, lap-joint, socket-weld blanks; later CNC-machined to ASME B16.5
• Seamless rolled ring: bearing housings, structural rings, gear blanks, large WN hubs
• Disc forging: turbine discs, tube-sheet blanks, thick round blocks
• Block forging: pump bodies, valve chambers, machined structural blocks
• Shaft forging: rotor shafts, actuator rods, high-fatigue cylindrical parts
• Custom die forging: valve bonnets, subsea connectors, aerospace brackets

Typical capability: forged rounds φ40–φ3000 mm, blocks up to ~1500 mm wide, single forgings from a few kg to several tonnes depending on press capacity. [2,5](@ref)

4. Open-Die, Closed-Die & Ring Rolling

For a large weld-neck flange hub, a ring-rolled or open-die preform + CNC finish usually beats a plate-cut disc: the grain flow around the bore reduces radial weakness.

5. Why Forged Flanges Beat Bar-Machined Flanges

• Grain flow: follows the flange contour instead of running straight through like bar
• Fatigue: better in cyclic-load and rotating-equipment service
• Internal soundness: porosity/stringers from cast structure are broken and healed by hot working
• Reduction of area: B381 forgings emphasize RA and directional properties more than plain bar
• Pressure parts: code reviewers prefer forged blanks for flanges, bonnets, and nozzle necks

Small low-pressure flanges can be machined from B348 bar. But for WN flanges, high-pressure classes, subsea, and rotating service, B381 forgings are the right call. [1,7](@ref)

6. Annealed, STA, Stress-Relieved

• Annealed: default for F-2/F-7/F-12; good ductility and corrosion resistance
• Stress-relieved: used after heavy machining to control distortion
• Solution treated + aged (STA): F-5 / F-23 high-strength condition; aerospace often references AMS 4928 / AMS 6931

For chemical/marine flanges, specify annealed. For aerospace Ti-6Al-4V forgings, the PO may require STA plus orientation-dependent tensile results.

7. UT, PT, Grain-Flow & Dimensional Inspection

• UT: internal soundness for rings/discs/large flanges; acceptance class must be stated — “100% UT” without criteria is not enough [6](@ref)
• PT: surface-breaking defects after rough/finish machining, not on heavy scale
• VT: 100% visual, no laps, cracks, folds, iron contamination
• Grain-flow / macroetch: for critical aerospace or directional-load parts
• Tensile: UTS, YS, elongation, sometimes reduction of area
• Hardness: supporting check, not a substitute for tensile/UT
• Certificate: EN 10204 3.1; 3.2 with TPI; heat/nozzle/lot traceability

UT is not automatic under B381. If you need it, the PO must name the procedure, coverage, calibration, and acceptance level. [6](@ref)

8. How to Write an ASTM B381 Forging RFQ

Weak: "Titanium flange 4 inch Gr2"

Strong: ASTM B381 F-2 forged WN flange blank, 4" 150# class envelope, OD 152 mm × hub length 90 mm, annealed, open-die preform + CNC finish to ASME B16.5, machining allowance 6 mm, UT per ASTM B594/AMS 2631 acceptance class A, PT after machining, EN 10204 3.1, heat no. on forging

Must specify:

1. Standard: ASTM B381 / ASME SB-381 + edition
2. Grade: F-2 / F-5 / F-7 / F-9 / F-12 / F-23
3. Form: flange blank, ring, disc, block, shaft, custom die
4. Forged dims + finished dims + machining allowance
5. Process: open-die / closed-die / ring-rolled
6. Condition: annealed / STA / stress-relieved
7. Surface: as-forged / pickled / rough-machined / finish-machined
8. NDE: UT procedure + class, PT timing, VT
9. Test coupon: location, orientation, represented lot
10. Marking + MTC: heat no., lot no., PO no.

9. Forging Procurement Mistakes

10. Our Forging → Flange → Machining Chain

• ASTM B381 / SB-381 F-2, F-5, F-7, F-9, F-12, F-23
• Open-die, closed-die, ring rolling; flange blanks & seamless rings
• From billet (B348) to forged blank to CNC-finished flange
• Finish to ASME B16.5 / B16.47 dimensions and facing
• UT per ASTM B594 / AMS 2631, PT after machining, 100% VT
• Annealed / stress-relieved / STA for Ti-6Al-4V
• Weld neck, blind, slip-on, lap-joint, socket-weld, custom nozzles
• Anti-mix control: titanium-only area, no carbon-steel grit
• Laser/dot-peen mark: grade + heat no. + PO + item no.
• EN 10204 3.1 / 3.2, dimensional report, heat-treat record

We don’t just forge titanium — we deliver machined, inspected, code-ready flange assemblies.

11. FAQs

Q: Is ASTM B381 F-2 the same as Gr.2?

Chemically yes, procedurally no. F-2 is the forging grade; Gr.2 is the mill-product grade. Forgings add grain-flow, reduction-ratio, and test-coupon rules.

Q: Do all titanium forgings need UT?

No. UT is specified by service criticality, size, code, or customer PO. “UT” without procedure and acceptance class is not a complete requirement. [6](@ref)

Q: Can a flange be machined from bar instead of forged?

Yes for small/low-pressure flanges. For WN flanges, high-pressure classes, and fatigue/subsea service, forged blanks are preferred.

Q: What’s better for a big WN flange — plate cut or ring rolled?

Ring-rolled/open-die forged: grain follows the ring, better fatigue and pressure performance. Plate-cut is cheaper but retains plate rolling structure.

Q: Can F-5 forgings be solution treated and aged?

Yes. Ti-6Al-4V forgings are often supplied STA for aerospace; commercial F-2/F-7 flanges are normally annealed.

12. Related Standards

• ASTM B348 Titanium Bar & Billet — billet feedstock for forgings
• ASTM B265 Titanium Plate, Sheet & Strip — plate-cut rings/blocks
• ASTM B861 Titanium Seamless Pipe — pipe matched to forged flanges
• ASTM B862 Titanium Welded Pipe — large welded lines + forged flanges
• ASTM B863 Titanium Wire — ERTi filler for flange/spool welding
• Titanium Standards Hub — all ASTM/ASME titanium articles
• ASTM B363 Titanium Fittings — elbows/tees/reducers, coming soon
• ASME B16.5 Titanium Flanges — flange dimensions & facing, coming soon

Request ASTM B381 Titanium Forging / Flange Quote

Send us:

• Standard + grade (ASTM B381 F-2 / F-5 / F-7 / F-12)
• Forging form (flange blank / ring / disc / block / shaft)
• Forged dims + finished drawing + machining allowance
• Process (open-die / closed-die / ring-rolled)
• Condition (annealed / STA / stress-relieved)
• NDE + certificate (UT class, PT, 3.1 / 3.2)

We reply within 4 business hours with forging route, inspection plan, and lead time.