Refractory Metal Pure Nb · heat-treated state · default condition
Refractory Metal Pure Nb Vacuum Annealed
Properties of the Vacuum Annealed condition, compared with the other Pure Nb tempers.
Default stocked condition: softest, most ductile and cleanest state for deep drawing, spinning, EB welding and SRF cavity fabrication.
What is Pure Nb Vacuum Annealed?
Pure Nb Vacuum Annealed is Pure Nb heat treated to Vacuum Annealed — default stocked condition: softest, most ductile and cleanest state for deep drawing, spinning, EB welding and SRF cavity fabrication. Pure Nb Vacuum Annealed has a yield strength of 125 MPa (18.1 ksi) and a tensile strength of 220 MPa (31.9 ksi) — weaker than 97% of refractory metal grades. Elongation at break is 40% and the elastic modulus is 103 GPa (14.9 Msi). Pure Nb Vacuum Annealed has a density of 8.57 g/cm³ (0.31 lb/in³), heavier than 51% of refractory metal grades. It melts at 2,477°C (4,491 °F).
Advantages
- Polishes to a fine finish — 85/100, better than 100% of refractory metal grades
- Ductile — tolerates forming and impact — 40%, better than 96% of refractory metal grades
- Forms and bends easily — 92/100, better than 95% of refractory metal grades
- Readily welded — 80/100, better than 92% of refractory metal grades
Limitations
- Low strength — 125 MPa (18.1 ksi), worse than 97% of refractory metal grades
Pure Nb Vacuum Annealed properties
Typical room-temperature values for Pure Nb Vacuum Annealed — 16 properties are specific to this condition; the rest are grade-level values shared by every Pure Nb temper. Each bar shows where the value sits among the refractory metal grades in FabDigit's library — further right is higher.
Physical3
Pure Nb Vacuum Annealed has a density of 8.57 g/cm³ (0.31 lb/in³), heavier than 51% of refractory metal grades. It melts at 2,477°C (4,491 °F).
Mechanical13
Pure Nb Vacuum Annealed has a yield strength of 125 MPa (18.1 ksi) and a tensile strength of 220 MPa (31.9 ksi) — weaker than 97% of refractory metal grades. Elongation at break is 40% and the elastic modulus is 103 GPa (14.9 Msi).
Thermal6
Pure Nb Vacuum Annealed is rated for continuous service to 400°C (752 °F). It conducts heat at 53.7 W/m·K (31 BTU/hr·ft·°F), better than 64% of refractory metal grades. Thermal expansion is 7.3 µm/m·K (4.06 µin/in·°F).
Electrical3
Pure Nb Vacuum Annealed conducts electricity at 12 % IACS, better than 67% of refractory metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (90/100), better than 74% of refractory metal grades.
Sustainability4
Producing a kilogram of Pure Nb Vacuum Annealed takes about 500 MJ of energy and emits 32 kg of CO₂ — less than 70% of refractory metal grades. Typical recycled content is 25%.
Manufacturability8
Pure Nb Vacuum Annealed's machinability is poor (28/100, worse than 57% of refractory metal grades); weldability very good (80/100); formability excellent (92/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Pure Nb tempers and conditions
Pure Nb is also supplied in 4 other conditions. The full side-by-side table is on the Pure Nb overview.
- Vacuum AnnealedDefaultDefault stocked condition: softest, most ductile and cleanest state for deep drawing, spinning, EB welding and SRF cavity fabrication.125 MPa yield · 80 HB
- Cold Worked HardMaximum room-temperature strength for springs, foil, thin wire and stiff diaphragms; very limited remaining ductility.570 MPa yield · 90 HRB
- As RolledPick when higher strength and stiffness-per-thickness are wanted and only mild bending/machining follows; strength is lost on any anneal or hot service above ~800 °C.400 MPa yield · 135 HB
- RRR300 AnnealedSpecify for superconducting RF cavities and cryogenic magnets where high residual resistivity ratio, low interstitials and low Ta content control thermal conductivity at 2–4 K.70 MPa yield · 50 HV
Working with Pure Nb Vacuum Annealed
Is Pure Nb easy to machine?
Gummy and galling like soft stainless: use sharp positive-rake carbide or HSS, heavy flood of chlorinated/soluble oil, slow speeds (15–30 m/min), generous feed and no dwell to avoid smearing and work-hardened skin.
Can Pure Nb be welded?
EB welding in high vacuum or GTAW inside an inert glovebox/trailing shield; any air, oxygen or nitrogen pickup embrittles the weld, and cleanliness plus post-weld vacuum degassing are essential.
Can Pure Nb be formed, bent or molded?
Outstanding cold formability — deep drawing, spinning and 180° bends in the annealed state; interstage vacuum anneals at 1100–1200 °C restore ductility, and tooling must be non-galling (bronze/coated dies with dry-film lube).
What surface finishes work on Pure Nb?
Pickle in HNO3/HF mixtures, then buff-and-electropolish (HF-H2SO4) for SRF or vacuum surfaces; anodizing gives decorative interference colours, and a thin Nb2O5 or silicide/aluminide coating is required for any use in air above ~400 °C.
Pure Nb chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| TaRRR/SRF grades typically ≤ 0.05 % | ≤ 0.1 | 0.05 |
| W | ≤ 0.05 | — |
| Mo | ≤ 0.02 | — |
| Zr | ≤ 0.02 | — |
| Ti | ≤ 0.02 | — |
| Hf | ≤ 0.02 | — |
| Fe | ≤ 0.01 | — |
| Ni | ≤ 0.01 | — |
| Si | ≤ 0.01 | — |
| Ointerstitial; controls hardness/RRR | ≤ 0.03 | 0.01 |
| N | ≤ 0.01 | 0 |
| C | ≤ 0.01 | 0 |
| Hhydrogen embrittlement limit | ≤ 0 | — |
| Nbcommercially pure / reactor grade R04200 | ≥ 99.8 (balance) | — |
Pure Nb Vacuum Annealed — frequently asked
What is Pure Nb Vacuum Annealed used for?
Pure Nb Vacuum Annealed is typically used for superconducting RF cavities, cryogenic vessels and bellows, nuclear reactor core components, chemical process linings and thermowells, sputtering targets and anodized jewellery and medical implants. In short: superconductor-grade niobium.
What is the yield strength of Pure Nb Vacuum Annealed?
Pure Nb Vacuum Annealed has a typical yield strength of 125 MPa (18.1 ksi) and a tensile strength of 220 MPa (31.9 ksi) — weaker than 97% of refractory metal grades. Strength varies by condition: see the 5 listed tempers.
Is Pure Nb Vacuum Annealed easy to machine?
Not especially — machinability is rated poor (28/100, worse than 57% of refractory metal grades). Gummy and galling like soft stainless: use sharp positive-rake carbide or HSS, heavy flood of chlorinated/soluble oil, slow speeds (15–30 m/min), generous feed and no dwell to avoid smearing and work-hardened skin.
Can Pure Nb Vacuum Annealed be welded?
Yes — weldability is rated very good (80/100). EB welding in high vacuum or GTAW inside an inert glovebox/trailing shield; any air, oxygen or nitrogen pickup embrittles the weld, and cleanliness plus post-weld vacuum degassing are essential.
What surface finishes work on Pure Nb Vacuum Annealed?
Pickle in HNO3/HF mixtures, then buff-and-electropolish (HF-H2SO4) for SRF or vacuum surfaces; anodizing gives decorative interference colours, and a thin Nb2O5 or silicide/aluminide coating is required for any use in air above ~400 °C.
Can Pure Nb Vacuum Annealed be formed, bent or molded?
Outstanding cold formability — deep drawing, spinning and 180° bends in the annealed state; interstage vacuum anneals at 1100–1200 °C restore ductility, and tooling must be non-galling (bronze/coated dies with dry-film lube).
What is the maximum service temperature of Pure Nb Vacuum Annealed?
Pure Nb Vacuum Annealed is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in Pure Nb Vacuum Annealed?
Yes — Pure Nb Vacuum Annealed is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM B393 — Niobium and Niobium Alloy Strip, Sheet and Plate — ASTM International (2020)
- ASTM B392 — Niobium and Niobium Alloy Bar, Rod and Wire — ASTM International (2020)
- ASM Handbook Vol. 2 — Properties of Refractory Metals and Alloys — ASM International (1990)
- ASM Handbook Vol. 13B — Corrosion: Materials (Niobium and Tantalum) — ASM International (2005)
- CRC Handbook of Chemistry and Physics — physical constants of niobium — CRC Press (2022)
- Niobium sheet, rod and RRR SRF-grade material data — ATI / Plansee / (OTIC) (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.