Refractory Metal M5
M5 is a Framatome/AREVA Zr-1%Nb alloy whose oxide-forming microstructure is engineered for very low corrosion rates and low hydrogen pickup in PWR fuel cladding, and it is stocked as RXA, SRA, PRXA, CW and BQ material.
Reference datasheet — M5 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the RXA condition
M5 tempers and conditions
M5 is supplied in 5 conditions, soft to hard. RXA is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Beta-quenched | Specify as a process intermediate: the beta quench refines the structure and homogenises Nb distribution before final cold tube reduction and recrystallisation, giving the best corrosion microstructure. | 310 | 450 | 28 | 170 HB | 3 % IACS |
RXADefault Fully recrystallized annealed | Pick the fully recrystallized annealed state for PWR fuel cladding tubes: best corrosion, irradiation growth and creep behaviour with 30% elongation, at the lowest strength of 330 MPa yield. | 330 | 470 | 30 | 165 HB | 3.1 % IACS |
Partially recrystallized annealed | Use the partially recrystallized annealed state for spacer grid straps and some structural tubing, giving 420 MPa yield with more ductility and creep margin than the stress-relieved condition. | 420 | 530 | 20 | 184 HB | 3.1 % IACS |
Cold worked and stress-relief annealed | Choose cold worked and stress-relief annealed material for guide tubes and structural members needing 500 MPa yield at operating temperature, accepting lower ductility and creep resistance. | 500 | 590 | 15 | 198 HB | 3.1 % IACS |
Cold worked | Use only as an intermediate as-pilgered hollow, where strength peaks at 620 MPa yield / 700 MPa tensile with 8% elongation; residual stress and texture are unadjusted, so it is not a final delivery condition. | 620 | 700 | 8 | 21 HRC | 3 % IACS |
What is M5?
M5 is a Framatome/AREVA Zr-1%Nb alloy whose oxide-forming microstructure is engineered for very low corrosion rates and low hydrogen pickup in PWR fuel cladding, and it is stocked as RXA, SRA, PRXA, CW and BQ material. It is chosen where cladding corrosion and growth limit burnup, offering 330 MPa yield, 470 MPa tensile and 30% elongation with a corrosion rating of 90/100, normally as seamless cladding tube and assembly components. Service is capped near 400 °C, formability is moderate (65/100), and supply is licensed nuclear material. ZIRLO or E110 are the closest Zr-Nb alternatives. M5 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). M5 has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 470 MPa (68.2 ksi) — stronger than 50% of refractory metal grades. Elongation at break is 30% and the elastic modulus is 99 GPa (14.4 Msi).
What is M5 used for?
- PWR fuel rod cladding
- Fuel assembly guide tubes
- Fuel rod end plugs
- Spacer grid strip
- Nuclear fuel assembly components
Advantages
- Ductile — tolerates forming and impact — 30%, better than 86% of refractory metal grades
- Lightweight — 6.55 g/cm³ (0.237 lb/in³), better than 77% of refractory metal grades
Limitations
- Low stiffness — 99 GPa (14.4 Msi), worse than 79% of refractory metal grades
- Low electrical conductivity — 3.1 % IACS, worse than 78% of refractory metal grades
M5 properties
Typical room-temperature values for M5-RXA; bars are the position among refractory metal grades.
Physical3
M5 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
M5 has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 470 MPa (68.2 ksi) — stronger than 50% of refractory metal grades. Elongation at break is 30% and the elastic modulus is 99 GPa (14.4 Msi).
Thermal6
M5 is rated for continuous service to 400°C (752 °F). It conducts heat at 17.5 W/m·K (10.1 BTU/hr·ft·°F), worse than 72% of refractory metal grades. Thermal expansion is 5.8 µm/m·K (3.22 µin/in·°F).
Electrical3
M5 conducts electricity at 3.1 % IACS, worse than 78% of refractory metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (90/100), better than 75% of refractory metal grades.
Sustainability4
Producing a kilogram of M5 takes about 1,250 MJ of energy and emits 80 kg of CO₂ — more than 52% of refractory metal grades. Typical recycled content is 15%.
Manufacturability8
M5's machinability is poor (30/100, better than 54% of refractory metal grades); weldability very good (70/100); formability good (65/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the refractory metal family
Yield strength against density for every refractory metal grade FabDigit runs. M5 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with M5
Is M5 easy to machine?
Run low speed with heavy feed using sharp carbide tooling and ample water-based coolant. Chips form a combustible powder that must be collected separately; never grind or machine dry.
Can M5 be welded?
Use GTAW, electron-beam or laser welding (typical for end-plug closures) in a vacuum chamber or under full inert-gas shielding. Trace oxygen, nitrogen or hydrogen contamination causes embrittlement — an acceptable weld must stay bright silver.
Can M5 be formed, bent or molded?
Tube is made from extruded hollows by multi-pass cold pilgering with intermediate vacuum anneals. Room-temperature forming needs generous bend radii to avoid twin cracking and to control springback.
M5 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 |
|---|---|---|
| Nbmain alloying element; forms β-Nb precipitates | 0.8 – 1.2 | 1 |
| Osolid-solution strengthening, tightly controlled | 0.09 – 0.15 | 0.13 |
| Fecontrolled trace addition | 0.02 – 0.06 | 0.04 |
| Strace S improves creep resistance | 8×10⁻⁴ – 0 | 0 |
| SnSn-free design (residual only) | ≤ 0.01 | 0.01 |
| C | ≤ 0.02 | 0.01 |
| N | ≤ 0.01 | 0 |
| Hfnuclear grade: Hf removed to lower neutron absorption | ≤ 0.01 | 0.01 |
| Cr | ≤ 0.02 | 0.01 |
| Ni | ≤ 0.01 | 0 |
| Zr | balance |
What surface finishes work on M5?
HNO3/HF pickling for decontamination followed by polishing is standard. The protective oxide forms in service, so plating and coatings are normally omitted; remove all fluoride residues.
How much does M5 cost?
M5 is a high-cost refractory metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
M5 — frequently asked
What is M5 used for?
M5 is typically used for PWR fuel rod cladding, fuel assembly guide tubes, fuel rod end plugs, spacer grid strip and nuclear fuel assembly components. In short: lowest-corrosion Zr-Nb cladding; low in-reactor hydrogen pickup; high ductility, 30% elongation.
What is the yield strength of M5?
M5 has a typical yield strength of 330 MPa (47.9 ksi) and a tensile strength of 470 MPa (68.2 ksi) — stronger than 50% of refractory metal grades. Strength varies by condition: see the 5 listed tempers.
Is M5 easy to machine?
Not especially — machinability is rated poor (30/100, better than 54% of refractory metal grades). Run low speed with heavy feed using sharp carbide tooling and ample water-based coolant. Chips form a combustible powder that must be collected separately; never grind or machine dry.
Can M5 be welded?
Yes — weldability is rated very good (70/100). Use GTAW, electron-beam or laser welding (typical for end-plug closures) in a vacuum chamber or under full inert-gas shielding. Trace oxygen, nitrogen or hydrogen contamination causes embrittlement — an acceptable weld must stay bright silver.
What surface finishes work on M5?
HNO3/HF pickling for decontamination followed by polishing is standard. The protective oxide forms in service, so plating and coatings are normally omitted; remove all fluoride residues.
Can M5 be formed, bent or molded?
Tube is made from extruded hollows by multi-pass cold pilgering with intermediate vacuum anneals. Room-temperature forming needs generous bend radii to avoid twin cracking and to control springback.
What is the maximum service temperature of M5?
M5 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.
What is the difference between M5-RXA and M5-CW?
RXA is the default condition — pick the fully recrystallized annealed state for PWR fuel cladding tubes: best corrosion, irradiation growth and creep behaviour with 30% elongation, at the lowest strength of 330 MPa yield. CW: use only as an intermediate as-pilgered hollow, where strength peaks at 620 MPa yield / 700 MPa tensile with 8% elongation; residual stress and texture are unadjusted, so it is not a final delivery condition. Yield strength is 330 MPa in RXA versus 620 MPa in CW.
How much does M5 cost?
M5 is a high-cost refractory metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM B811 — Wrought Zirconium Alloy Seamless Tubes for Nuclear Reactor Fuel Cladding — ASTM International (2021)
- ASTM B350/B350M — Zirconium and Zirconium Alloy Ingots for Nuclear Application — ASTM International (2022)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys (Zirconium) — ASM International (1990)
- Thermophysical Properties of Materials for Nuclear Engineering (Zr alloys) — IAEA (2008)
- M5 fuel cladding alloy technical publications — Framatome (AREVA NP) (2018)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.