Refractory Metal Pure Nb RRR300 Annealed
Grade
UNS R04200 · ASTM B393 Type 1 · also Columbium
RRR300 Annealed = rRR ≥ 300, high-purity EB-melted and vacuum annealed
Specify 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.
Values for the RRR300 Annealed condition
Other Pure Nb tempers and conditions
Pure Nb is listed in 5 conditions; see the grade overview at Pure Nb.
- RRR300 Annealed
- Vacuum Annealed
- Stress Relieved
- As Rolled
- Cold Worked Hard
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
RRR300 AnnealedThis page RRR ≥ 300, high-purity EB-melted and vacuum annealed | Specify 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 | 180 | 50 | 48 HB | 12 % IACS |
Vacuum AnnealedDefault fully recrystallized (1100–1300 °C, high vacuum) | Default stocked condition: softest, most ductile and cleanest state for deep drawing, spinning, EB welding and SRF cavity fabrication. | 125 | 220 | 40 | 80 HB | 12 % IACS |
800–950 °C vacuum, partially recovered | Intermediate choice: removes cold-work stresses and hydrogen while keeping most of the cold-worked strength for dimensionally stable machined parts. | 280 | 350 | 22 | 105 HB | 11.5 % IACS |
cold rolled / cold worked, not annealed (~40–60 % reduction) | Pick 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 | 450 | 10 | 135 HB | 11.5 % IACS |
heavy reduction (>70 %) without anneal | Maximum room-temperature strength for springs, foil, thin wire and stiff diaphragms; very limited remaining ductility. | 570 | 620 | 5 | 10 HRC | 11.5 % IACS |
What is Pure Nb RRR300 Annealed?
Pure Nb RRR300 Annealed is Pure Nb in the RRR300 Annealed grade — specify 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. Pure Nb RRR300 Annealed has a yield strength of 70 MPa (10.2 ksi) and a tensile strength of 180 MPa (26.1 ksi) — weaker than 100% of refractory metal grades. Elongation at break is 50% and the elastic modulus is 105 GPa (15.2 Msi). Pure Nb RRR300 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). Vacuum Annealed is the default condition FabDigit quotes; RRR300 Annealed is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 92/100, better than 101% of refractory metal grades
- Ductile — tolerates forming and impact — 50%, better than 100% of refractory metal grades
- Readily welded — 85/100, better than 99% of refractory metal grades
- Forms and bends easily — 95/100, better than 99% of refractory metal grades
Limitations
- Low strength — 70 MPa (10.2 ksi), worse than 100% of refractory metal grades
Pure Nb RRR300 Annealed properties
Typical room-temperature values for Pure Nb RRR300 Annealed; 23 are specific to this condition. Other listed values are Pure Nb reference data and may not represent this condition. Bars are the position among refractory metal grades.
Physical3
Pure Nb RRR300 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 RRR300 Annealed has a yield strength of 70 MPa (10.2 ksi) and a tensile strength of 180 MPa (26.1 ksi) — weaker than 100% of refractory metal grades. Elongation at break is 50% and the elastic modulus is 105 GPa (15.2 Msi).
Thermal6
Pure Nb RRR300 Annealed is rated for continuous service to 400°C (752 °F). It conducts heat at 55 W/m·K (31.8 BTU/hr·ft·°F), better than 67% of refractory metal grades. Thermal expansion is 7.3 µm/m·K (4.06 µin/in·°F).
Electrical3
Pure Nb RRR300 Annealed conducts electricity at 12 % IACS, better than 67% of refractory metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (92/100), better than 86% of refractory metal grades.
Sustainability4
Producing a kilogram of Pure Nb RRR300 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 RRR300 Annealed's machinability is poor (25/100, worse than 65% of refractory metal grades); weldability excellent (85/100); formability excellent (95/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Pure Nb RRR300 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 RRR300 Annealed — frequently asked
What is Pure Nb RRR300 Annealed used for?
Pure Nb RRR300 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 RRR300 Annealed?
Pure Nb RRR300 Annealed has a typical yield strength of 70 MPa (10.2 ksi) and a tensile strength of 180 MPa (26.1 ksi) — weaker than 100% of refractory metal grades. Strength varies by condition: see the 5 listed tempers.
Is Pure Nb RRR300 Annealed easy to machine?
Not especially — machinability is rated poor (25/100, worse than 65% 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 RRR300 Annealed be welded?
Yes — weldability is rated excellent (85/100). 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 RRR300 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 RRR300 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 RRR300 Annealed?
Pure Nb RRR300 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.
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.