Refractory Metal Ta-40Nb-SR (Stress relieved)
Heat-treated state
UNS R05240 · ASTM B365
Pick when moderate strength with retained ductility and flatness/dimensional stability is needed (thermowells, tube, machined parts).
Values for the SR condition
Other Ta-40Nb tempers and conditions
Ta-40Nb is listed in 3 conditions; see the grade overview at Ta-40Nb.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault vacuum recrystallization annealed (sheet, plate, rod, tube) | Standard stocked condition: softest, most ductile, for forming, deep drawing and welded chemical-process fabrication. | 220 | 330 | 27 | 130 HV | — |
SRThis page Stress relieved | Pick when moderate strength with retained ductility and flatness/dimensional stability is needed (thermowells, tube, machined parts). | 370 | 450 | 15 | 165 HB | 4.2 % IACS |
Cold worked | Highest strength/stiffness-limited sections such as rupture discs, springs, diaphragms and thin strip that will not be recrystallized after forming. | 570 | 620 | 6 | 20 HRC | 4.1 % IACS |
What is Ta-40Nb-SR?
Ta-40Nb-SR is Ta-40Nb heat treated to SR — pick when moderate strength with retained ductility and flatness/dimensional stability is needed (thermowells, tube, machined parts). Ta-40Nb-SR has a yield strength of 370 MPa (53.7 ksi) and a tensile strength of 450 MPa (65.3 ksi) — stronger than 60% of refractory metal grades. Elongation at break is 15% and the elastic modulus is 138 GPa (20 Msi). Ta-40Nb-SR has a density of 12.1 g/cm³ (0.437 lb/in³), heavier than 74% of refractory metal grades. It melts at 2,650°C (4,802 °F). Annealed is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Readily welded — 80/100, better than 92% of refractory metal grades
Limitations
- Limited service temperature — 300°C (572 °F), worse than 95% of refractory metal grades
- High embodied carbon — 160 kg CO₂/kg, worse than 84% of refractory metal grades
Ta-40Nb-SR properties
Typical room-temperature values for Ta-40Nb-SR; 21 are specific to this condition. Other listed values are Ta-40Nb reference data and may not represent this condition. Bars are the position among refractory metal grades.
Physical3
Ta-40Nb-SR has a density of 12.1 g/cm³ (0.437 lb/in³), heavier than 74% of refractory metal grades. It melts at 2,650°C (4,802 °F).
Mechanical12
Ta-40Nb-SR has a yield strength of 370 MPa (53.7 ksi) and a tensile strength of 450 MPa (65.3 ksi) — stronger than 60% of refractory metal grades. Elongation at break is 15% and the elastic modulus is 138 GPa (20 Msi).
Thermal6
Ta-40Nb-SR is rated for continuous service to 300°C (572 °F). It conducts heat at 31 W/m·K (17.9 BTU/hr·ft·°F), worse than 59% of refractory metal grades. Thermal expansion is 6.8 µm/m·K (3.78 µin/in·°F).
Electrical3
Ta-40Nb-SR conducts electricity at 4.2 % IACS, worse than 64% of refractory metal grades.
Chemical & Environmental2
Corrosion resistance is excellent (90/100), better than 75% of refractory metal grades.
Sustainability3
Producing a kilogram of Ta-40Nb-SR takes about 2,800 MJ of energy and emits 160 kg of CO₂ — more than 84% of refractory metal grades. Typical recycled content is 25%.
Manufacturability8
Ta-40Nb-SR's machinability is poor (30/100, better than 54% of refractory metal grades); weldability very good (80/100); formability good (55/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Ta-40Nb-SR
Is Ta-40Nb easy to machine?
Turn/mill slowly with sharp, positive-rake carbide or HSS tooling, heavy flood of chlorinated or sulfurized oil and generous depth of cut — the alloy is gummy, work-hardens and galls, so avoid dwelling and rubbing.
Can Ta-40Nb be welded?
GTAW with high-purity argon/helium and full trailing plus back-purge chambers, EB or laser welding in vacuum; keep O, N, H and carbon pickup near zero as interstitials cause embrittlement, and never weld in air or use flux.
Can Ta-40Nb be formed, bent or molded?
Annealed sheet cold-forms, deep draws, spins and explosively/roll clads readily; use clean lubricants and non-ferrous or coated dies to avoid iron pickup, and vacuum-anneal (~1200–1400 °C) between heavy reductions.
What surface finishes work on Ta-40Nb?
Degrease and pickle in HNO3/HF-free acid mixes carefully (HF attacks the metal); mechanical polishing and electropolishing give bright passive surfaces, plating/painting is unnecessary since the native oxide provides the corrosion protection.
Ta-40Nb 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 |
|---|---|---|
| Nbnominal 40 wt% Nb solid-solution addition | 39 – 41 | 40 |
| Cimpurity max | ≤ 0.01 | 0.01 |
| Oimpurity max | ≤ 0.03 | 0.02 |
| Nimpurity max | ≤ 0.01 | 0.01 |
| Himpurity max | ≤ 0 | 5×10⁻⁴ |
| Feimpurity max | ≤ 0.01 | 0 |
| Tiimpurity max | ≤ 0.01 | 0 |
| Wimpurity max | ≤ 0.05 | 0.01 |
| Moimpurity max | ≤ 0.02 | 0.01 |
| Niimpurity max | ≤ 0.01 | 0 |
| Siimpurity max | ≤ 0.01 | 0 |
| Tabalance, nominally 60 wt% | balance | — |
Ta-40Nb-SR — frequently asked
What is Ta-40Nb-SR used for?
Ta-40Nb-SR is typically used for chemical process components, corrosion-resistant fasteners, electron tube parts and capacitor anode alternatives. In short: lower-cost tantalum substitute; lower density than tantalum; ductile and readily weldable.
What is the yield strength of Ta-40Nb-SR?
Ta-40Nb-SR has a typical yield strength of 370 MPa (53.7 ksi) and a tensile strength of 450 MPa (65.3 ksi) — stronger than 60% of refractory metal grades. Strength varies by condition: see the 3 listed tempers.
Is Ta-40Nb-SR easy to machine?
Not especially — machinability is rated poor (30/100, better than 54% of refractory metal grades). Turn/mill slowly with sharp, positive-rake carbide or HSS tooling, heavy flood of chlorinated or sulfurized oil and generous depth of cut — the alloy is gummy, work-hardens and galls, so avoid dwelling and rubbing.
Can Ta-40Nb-SR be welded?
Yes — weldability is rated very good (80/100). GTAW with high-purity argon/helium and full trailing plus back-purge chambers, EB or laser welding in vacuum; keep O, N, H and carbon pickup near zero as interstitials cause embrittlement, and never weld in air or use flux.
What surface finishes work on Ta-40Nb-SR?
Degrease and pickle in HNO3/HF-free acid mixes carefully (HF attacks the metal); mechanical polishing and electropolishing give bright passive surfaces, plating/painting is unnecessary since the native oxide provides the corrosion protection.
Can Ta-40Nb-SR be formed, bent or molded?
Annealed sheet cold-forms, deep draws, spins and explosively/roll clads readily; use clean lubricants and non-ferrous or coated dies to avoid iron pickup, and vacuum-anneal (~1200–1400 °C) between heavy reductions.
What is the maximum service temperature of Ta-40Nb-SR?
Ta-40Nb-SR is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Ta-40Nb Annealed and Ta-40Nb-CW?
Annealed is the default condition — standard stocked condition: softest, most ductile, for forming, deep drawing and welded chemical-process fabrication. CW: highest strength/stiffness-limited sections such as rupture discs, springs, diaphragms and thin strip that will not be recrystallized after forming. Yield strength is 220 MPa in Annealed versus 570 MPa in CW.
Sources
- ASTM B708 — Tantalum and Tantalum Alloy Plate, Sheet, and Strip — ASTM International (2021)
- ASTM B365 — Tantalum and Tantalum Alloy Rod and Wire — ASTM International (2018)
- ASTM B364 — Tantalum and Tantalum Alloy Ingots — ASTM International (2018)
- ASTM B521 — Tantalum and Tantalum Alloy Seamless and Welded Tubes — ASTM International (2018)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (refractory metals) — ASM International (1990)
- ASM Handbook Vol.3 — Alloy Phase Diagrams (Nb-Ta system) — ASM International (1992)
- Tantalum and tantalum alloy (Ta-2.5W, Ta-40Nb) semi-finished product data — H.C. Starck / Plansee (2022)
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.