Refractory Metal Zr-2.5Nb CWSR
Heat-treated state
UNS R60901 · ASTM B350/B353
Standard high-strength condition for pressure tubes and thin-wall tubing: highest creep resistance and yield strength with acceptable residual ductility.
Values for the CWSR condition
Other Zr-2.5Nb tempers and conditions
Zr-2.5Nb is listed in 5 conditions; see the grade overview at Zr-2.5Nb.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault alpha-annealed / recrystallised (typ. 550–650 °C) | Pick for plate, sheet, bar and general fabrication where formability, weld ductility and dimensional stability matter more than peak strength. | 430 | 610 | 20 | 185 HB | 3.1 % IACS |
Beta quenched and aged (~500 °C) without cold work | Choose for forgings and thick sections needing strength above annealed levels where cold working is impractical; omega/beta-Nb decomposition provides the strengthening. | 550 | 700 | 15 | 21 HRC | 3 % IACS |
CWSRThis page cold worked ~20–30 % and stress relieved (~400 °C/24 h) | Standard high-strength condition for pressure tubes and thin-wall tubing: highest creep resistance and yield strength with acceptable residual ductility. | 620 | 760 | 14 | 22 HRC | — |
Beta quenched, cold worked and stress relieved | Reactor pressure-tube specification route: beta quench refines the Nb-enriched beta phase, then cold pilgering plus 400 °C stress relief gives maximum in-reactor creep and growth resistance. | 650 | 800 | 13 | 250 HB | — |
Cold worked | Cold-worked (typically 20–30 % CW, stress-relieved ~400 °C) Zr-2.5Nb as used for CANDU-type pressure tubing — much higher strength and creep resistance with reduced ductility and anisotropic texture. | 680 | 850 | 14 | 24 HRC | 3.1 % IACS |
What is Zr-2.5Nb CWSR?
Zr-2.5Nb CWSR is Zr-2.5Nb heat treated to CWSR — standard high-strength condition for pressure tubes and thin-wall tubing: highest creep resistance and yield strength with acceptable residual ductility. Zr-2.5Nb CWSR has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 84% of refractory metal grades. Elongation at break is 14% and the elastic modulus is 97 GPa (14.1 Msi). Zr-2.5Nb CWSR has a density of 6.55 g/cm³ (0.237 lb/in³), lighter than 77% of refractory metal grades. It melts at 1,840°C (3,344 °F). Annealed is the default condition FabDigit quotes; CWSR is available on request or by drawing note.
Advantages
- High strength — 620 MPa (89.9 ksi), better than 84% of refractory metal grades
- Tough — resists crack growth — 70 MPa·√m (63.7 ksi·√in), better than 84% of refractory metal grades
- Lightweight — 6.55 g/cm³ (0.237 lb/in³), better than 77% of refractory metal grades
Limitations
- Low stiffness — 97 GPa (14.1 Msi), worse than 91% of refractory metal grades
- Limited service temperature — 350°C (662 °F), worse than 89% of refractory metal grades
- Low electrical conductivity — 3.1 % IACS, worse than 78% of refractory metal grades
- Poor heat conductor — 17.1 W/m·K (9.88 BTU/hr·ft·°F), worse than 76% of refractory metal grades
Zr-2.5Nb CWSR properties
Typical room-temperature values for Zr-2.5Nb CWSR; 18 are specific to this condition. Other listed values are Zr-2.5Nb reference data and may not represent this condition. Bars are the position among refractory metal grades.
Physical3
Zr-2.5Nb CWSR has a density of 6.55 g/cm³ (0.237 lb/in³), lighter than 77% of refractory metal grades. It melts at 1,840°C (3,344 °F).
Mechanical16
Zr-2.5Nb CWSR has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 84% of refractory metal grades. Elongation at break is 14% and the elastic modulus is 97 GPa (14.1 Msi).
Thermal6
Zr-2.5Nb CWSR is rated for continuous service to 350°C (662 °F). It conducts heat at 17.1 W/m·K (9.88 BTU/hr·ft·°F), worse than 76% of refractory metal grades. Thermal expansion is 6.3 µm/m·K (3.5 µin/in·°F).
Electrical3
Zr-2.5Nb CWSR conducts electricity at 3.1 % IACS, worse than 78% of refractory metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (86/100), better than 59% of refractory metal grades.
Sustainability4
Producing a kilogram of Zr-2.5Nb CWSR takes about 1,300 MJ of energy and emits 80 kg of CO₂ — more than 57% of refractory metal grades. Typical recycled content is 10%.
Manufacturability8
Zr-2.5Nb CWSR's machinability is poor (32/100, better than 67% of refractory metal grades); weldability good (55/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Zr-2.5Nb CWSR
Is Zr-2.5Nb easy to machine?
Machine like austenitic stainless but slower: rigid setups, sharp carbide or HSS tools, positive rake, heavy flood coolant, no dwelling — fine chips and dust are pyrophoric, so collect wet and never use water-only extinguishers on burning fines.
Can Zr-2.5Nb be welded?
GTAW or EBW with high-purity argon/helium chamber or full trailing and back shielding; keep oxygen, nitrogen and moisture out (any straw/blue/grey tint means embrittling contamination), no flux processes, and stress relieve cold-worked tube after welding.
Can Zr-2.5Nb be formed, bent or molded?
Form in the annealed condition, preferably warm (200–400 °C) for tight bends because of strong hcp texture and springback; cold-worked pressure-tube stock has little remaining formability and is finished by pilgering.
What surface finishes work on Zr-2.5Nb?
Pickle in HNO3/HF to remove oxide and any alpha-case, then passivate or grow an anodic/thermal oxide for galling resistance; the natural oxide is protective, so paint and plating are rarely used.
Zr-2.5Nb 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 |
|---|---|---|
| Nbprimary strengthener, beta-Zr stabiliser | 2.4 – 2.8 | 2.5 |
| Ocontrolled interstitial strengthener (900–1600 ppm) | 0.09 – 0.16 | 0.12 |
| Feresidual | ≤ 0.15 | 0.05 |
| Crresidual | ≤ 0.02 | — |
| C | ≤ 0.03 | 0.01 |
| N | ≤ 0.01 | 0 |
| Hhydride embrittlement control | ≤ 0 | 8×10⁻⁴ |
| Hfnuclear grade: Hf must be removed for low neutron capture | ≤ 0.01 | 0.01 |
| Zr | balance | — |
Zr-2.5Nb CWSR — frequently asked
What is Zr-2.5Nb CWSR used for?
Zr-2.5Nb CWSR is typically used for CANDU reactor pressure tubes, nuclear structural tubing and high-strength reactor components. In short: strongest common Zr alloy; CANDU pressure-tube grade; best Zr creep resistance.
What is the yield strength of Zr-2.5Nb CWSR?
Zr-2.5Nb CWSR has a typical yield strength of 620 MPa (89.9 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 84% of refractory metal grades. Strength varies by condition: see the 5 listed tempers.
Is Zr-2.5Nb CWSR easy to machine?
Not especially — machinability is rated poor (32/100, better than 67% of refractory metal grades). Machine like austenitic stainless but slower: rigid setups, sharp carbide or HSS tools, positive rake, heavy flood coolant, no dwelling — fine chips and dust are pyrophoric, so collect wet and never use water-only extinguishers on burning fines.
Can Zr-2.5Nb CWSR be welded?
Yes — weldability is rated good (55/100). GTAW or EBW with high-purity argon/helium chamber or full trailing and back shielding; keep oxygen, nitrogen and moisture out (any straw/blue/grey tint means embrittling contamination), no flux processes, and stress relieve cold-worked tube after welding.
What surface finishes work on Zr-2.5Nb CWSR?
Pickle in HNO3/HF to remove oxide and any alpha-case, then passivate or grow an anodic/thermal oxide for galling resistance; the natural oxide is protective, so paint and plating are rarely used.
Can Zr-2.5Nb CWSR be formed, bent or molded?
Form in the annealed condition, preferably warm (200–400 °C) for tight bends because of strong hcp texture and springback; cold-worked pressure-tube stock has little remaining formability and is finished by pilgering.
What is the maximum service temperature of Zr-2.5Nb CWSR?
Zr-2.5Nb CWSR is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Zr-2.5Nb Annealed and Zr-2.5Nb-CW?
Annealed is the default condition — pick for plate, sheet, bar and general fabrication where formability, weld ductility and dimensional stability matter more than peak strength. CW: cold-worked (typically 20–30 % CW, stress-relieved ~400 °C) Zr-2.5Nb as used for CANDU-type pressure tubing — much higher strength and creep resistance with reduced ductility and anisotropic texture. Yield strength is 430 MPa in Annealed versus 680 MPa in CW.
Sources
- ASTM B350/B350M — Zirconium and Zirconium Alloy Ingots for Nuclear Application — ASTM International (2022)
- ASTM B351/B351M — Hot-Rolled and Cold-Finished Zirconium and Zirconium Alloy Bars, Rod and Wire for Nuclear Application — ASTM International (2021)
- ASTM B353 — Wrought Zirconium and Zirconium Alloy Seamless and Welded Tubes for Nuclear Service — ASTM International (2017)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (Zirconium and Hafnium) — ASM International (1990)
- IAEA TECDOC series on Zr-alloy pressure tube and fuel channel behaviour (Zr-2.5Nb property compilations) — IAEA (2010)
- Zirconium alloy mill product and corrosion data (Zr702/Zr705/Zr-2.5Nb) — ATI / Wah Chang (2020)
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.