R60705
R60705 (core code UNS R60705, commercial name Zr – 5 zirconium – niobium alloy) is a niobium (Nb) – strengthened zirconium – based alloy. It achieves the synergy of high strength × extreme corrosion resistance × nuclear compatibility through “Nb precipitated phase + dual – phase structure (α – Zr + β – Nb)”. The following is a systematic analysis from six dimensions:
I.Standard System and Grade Codes
1 Core Execution Standards
- International General:
- ASTM B551 (zirconium and zirconium alloy plates, tubes, regulating the performance of formed workpieces);
- ASTM B351 (zirconium and zirconium alloy forgings, covering high – pressure equipment structural parts);
- Chinese National Standard:
- GB/T 30568 – 2014 (zirconium and zirconium alloy forgings, equivalent to ASTM B351);
- GB/T 26314 (zirconium and zirconium alloy bars, plates, specifying composition and performance);
- Nuclear Power Extension: ASME BPVC Section III (nuclear – grade component certification, requiring higher purity).
2 Grades and Codes
- Core Identification: UNS R60705 (American Unified Numbering System);
- Commercial Name: Zr – 5 (zirconium – niobium alloy) (because it contains ~2.5% Nb for strengthening, formerly known as HZr705);
- Welding Matching: Welding wire corresponds to ERZr – 5 (composition matching, ensuring weld strength and corrosion resistance).
II. Chemical composition (mass fraction%, ASTM standard)
Through the design of “Zr+Hf matrix+Nb precipitation strengthening”, R60705 has precise elements:
| Element | Content range | Core role |
|---|---|---|
| Zr + Hf | ≥ 95.5 | Matrix element, providing corrosion resistance and nuclear compatibility |
| Nb | 2.0 – 3.0 | Key strengthening phase! Precipitates β-Nb particles, improving strength |
| Fe + Cr | ≥ 0.20 | Refines grains and assists in stabilizing the oxide film |
| C | ≤ 0.05 | Strictly controls carbides to avoid intergranular corrosion |
| N | ≤ 0.025 | Inhibits the precipitation of zirconium nitride and maintains toughness |
| O | ≤ 0.18 | Interstitial strengthening, balancing strength and plasticity |
| H | ≤ 0.005 | Prevents hydrogen embrittlement (a key requirement in nuclear/chemical environments) |
III. Mechanical properties (heat treatment state)
The performance of R60705 is far ultra-pure zirconium (R60702) due to Nb strengthening and dual-phase structure;
| State | Tensile strength (MPa) | Yield strength (MPa) | Elongation (%) | Hardness (HB) | Core characteristics |
|---|---|---|---|---|---|
| Annealed state | ~450 | ~250 | ~12 | 150 – 160 | Easy to process (cutting, welding) |
| Quenched + aged state | ~550 | ~350 | ~15 | 180 – 200 | Balance of strength and toughness (equipment main shaft) |
Physical properties:
- Density: 6.51 g/cm³ (only 83% of nickel – based alloys, significant lightweighting);
- Melting point: ≥1800℃ (better high – temperature resistance than most stainless steels);
- Thermal neutron absorption cross – section: ~0.18 barn (close to pure zirconium, with nuclear compatibility advantages).
IV. Heat treatment requirements (activating the strengthening potential of Nb)
- Solution Quenching (Refining Structure):
- Temperature: 850 – 870°C (hold for 1 – 2 hours to fully dissolve β-Nb phase);
- Cooling: Rapid water cooling (inhibit coarsening of β-Nb, retain fine dual-phase structure);
- Function: Lay a structural foundation for age strengthening.
- Age Strengthening (Precipitation of Nb Phase):
- Temperature: 550 – 570°C (hold for 0.5 – 1 hour to precipitate dispersed β-Nb particles);
- Effect: Strength increases by more than 20%, and plasticity is improved at the same time (precipitates pin dislocations and inhibits deformation concentration);
- Applicable scenarios: High – stress equipment (such as main shafts of chemical reactors, nuclear auxiliary pipelines).
- Welding and Post – treatment:
- Welding material: Select ERZr – 5 welding wire (match Nb composition to ensure weld corrosion resistance);
- Process: GTAW (Gas Tungsten Arc Welding) with high – purity argon (99.999%) protection is required, and O₂, N₂, and H₂ contamination are prevented throughout the process (zirconium is extremely easy to absorb impurities at high temperatures, leading to embrittlement);
- Post – treatment: Stress relief annealing at 650°C after welding (eliminate residual stress in welds and restore corrosion resistance).
V. Main application fields (medium and high stress+strong corrosion scenario)
R60705, relying on “Nb – strengthened corrosion resistance + nuclear compatibility”, dominates the following fields (performance exceeds titanium alloy, and the cost is only 1/5 of it):
- Chemical Industry and Pharmaceutical Industry:
- Strong acid and strong alkali equipment (hydrochloric acid, sulfuric acid, sodium hydroxide reaction kettles/pipelines): Corrosion rate < 0.025 mm/a (better than Hastelloy, cost reduced by 60%);
- Pharmaceutical – grade heat exchangers: Sanitary platforms, resistant to chloride ion stress corrosion cracking (replace titanium alloy, cost reduced by 40%).
- Energy and Environmental Protection:
- Geothermal power generation (high – temperature brine pipelines): Resistant to 250°C high – salinity solution corrosion (service life is 5 times that of 316L stainless steel);
- Waste incineration (acidic waste gas treatment system): Resistant to Cl⁻ + SO₂ composite corrosion (replace nickel – based alloy, cost reduced by 70%).
- Nuclear Industry Auxiliary:
- Nuclear auxiliary systems (non – core structural parts, such as coolant pipelines): Resistant to radiation + high – temperature water corrosion (Nb does not significantly affect neutron absorption, better than Ti – containing alloys);
- Nuclear waste transportation tanks: Resistant to radioactive media + long – term stability (replace stainless steel, weight reduced by 30%).
- High – end Manufacturing:
- Aerospace (engine corrosion – resistant parts): Lightweight + resistant to jet fuel corrosion (replace titanium alloy, weight reduced by 15%);
- Medical devices (artificial joints, dental implants): Excellent biocompatibility, resistant to body fluid corrosion (service life exceeds 20 years).
Key Summary
- Core Advantages:
- Strength: More than 20% higher than pure zirconium, suitable for medium and high – stress scenarios;
- Corrosion resistance: Corrosion rate < 0.025 mm/a in boiling hydrochloric acid and 70% sulfuric acid, better than titanium alloy;
- Cost – effectiveness: Performance is close to nickel – based alloy, and the cost is only 1/3 of it.
- Limitations:
- Long – term service temperature ≤ 350°C (prone to Nb embrittlement phase precipitation at high temperatures, temperature control required);
- Welding/processing has extremely high requirements for the environment (dust – free, oxygen – free, and water – free protection required).
R60705 (Zr – 5) is the “benchmark of Nb – strengthened zirconium alloy”. It breaks through the strength bottleneck of pure zirconium through niobium alloying, and becomes the “cost – effective alternative to titanium alloy” in fields such as chemical corrosion resistance, nuclear auxiliary systems, and high – end equipment, redefining the strength upper limit of zirconium – based materials.