R60702
I. Standard System and Brand Code
- Core Execution Standards
- International mainstream: ASTM SB – 551 (specifies zirconium and zirconium alloy plates, rods, and tubes, such as reactor structural components);
- Chinese national standard: GB/T 26314 (grade Zr – 3, completely equivalent to R60702);
- Nuclear power dedicated: ASME BPVC Section III (nuclear pressure vessel components, such as fuel cladding).
- Global Grade Correspondence
| System/Region | Grade | Description |
|---|---|---|
| American UNS | UNS R60702 | Core identification (benchmark of commercial pure zirconium) |
| Chinese National Standard | Zr-3 | Consistent chemical composition with R60702 |
| European EN | W. Nr. 3534 | Equivalent to commercial pure zirconium |
II. Chemical composition (mass fraction%, ASTM standard)
R60702 achieves performance breakthrough through “ultra-high-purity zirconium+micro-alloying”, with precise element function;
| Element | Content range | Core role |
|---|---|---|
| Zr + Hf | ≥ 99.2 | Main element, providing basic corrosion resistance and nuclear compatibility |
| Hf | ≤ 4.5 | Natural associated element of zirconium, with no significant effect on performance |
| Fe + Cr | ≤ 0.20 | Optimize workability and assist in stabilizing the oxide film |
| C | ≤ 0.05 | Strictly control carbides to avoid intergranular corrosion |
| N | ≤ 0.025 | Inhibit the precipitation of zirconium nitride and maintain toughness |
| H | ≤ 0.005 | Prevent hydrogen embrittlement (a key requirement in nuclear environments) |
| O | ≤ 0.16 | Control interstitial elements to balance strength and plasticity |
Key characteristics:
- Thermal neutron absorption cross – section: Only 0.18 barn (much lower than 2.5 barn of stainless steel), which is the core advantage for nuclear reactor structural materials.
- Density: 6.5 g/cm³ (only 83% of nickel – based alloys, with significant lightweighting).
III. Mechanical properties (annealed state, room temperature)
R60702 is superior to titanium alloy in properties and machinability because of pure zirconium matrix and low gap elements;
| Performance Index | Typical Value (ASTM Requirement) | Comparison with Ti-6Al-4V (Titanium Alloy) |
|---|---|---|
| Tensile Strength | ≥380 MPa | 25% lower (Ti-6Al-4V ≥500 MPa) |
| Yield Strength | ≥205 MPa | 30% lower (Ti-6Al-4V ≥345 MPa) |
| Elongation (δ₅) | ≥16% | Slightly lower (Ti-6Al-4V ≥10%) |
| Hardness | 120~150 HB | 40% lower (Ti-6Al-4V ≈200 HB) |
| High-Temperature Performance | 300℃ tensile strength ≥250 MPa | Better than titanium alloy (Ti-6Al-4V strength decreases by 50% at 300℃) |
Physical properties:
- Melting point: 1852℃ (better high-temperature resistance than most stainless steels)5;
- Thermal conductivity: 22 W/(m·K) (close to carbon steel, suitable for heat exchange scenarios)7.
IV. Heat Treatment Requirements (Activated Corrosion Resistance and Machinability)
- Annealing Treatment (Mandatory):
- Temperature: 704 – 760°C (hold for 1 – 2 hours to eliminate cold working stress and restore plasticity);
- Cooling: Air cooling or water cooling (avoid high – temperature oxidation and keep the surface 光洁 (smooth));
- Function: Optimize formability and lay the foundation for processing such as deep drawing and rolling ⁷.
- Solution Strengthening (Optional):
- Temperature: 850 – 900°C (hold for 0.5 – 1 hour to dissolve the second phase);
- Cooling: Rapid water cooling (inhibit the precipitation of harmful phases and increase strength by 15% – 20%);
- Applicable scenarios: Nuclear reactor structural components requiring high strength (such as fuel rod positioning grids) ⁷.
- Welding Process:
- Welding material: Select ERZr – 3 welding wire (match chemical composition to ensure weld corrosion resistance);
- Process: Use Gas Tungsten Arc Welding (GTAW), strictly control heat input (avoid grain coarsening), and stress relief annealing at 650°C after welding is required (eliminate residual stress in welds) .
V. Main application fields (extreme corrosion+nuclear radiation scene)
R60702, relying on “corrosion resistance × nuclear compatibility × lightweight”, dominates the following fields (performance exceeds titanium alloy, and the cost is only 1/5 of tantalum):
- Nuclear Industry:
- Nuclear reactors (fuel cladding tubes, control rod guide tubes): Resistant to 300°C high – temperature and high – pressure water corrosion, resistant to neutron radiation embrittlement (service life exceeds 40 years) ¹¹⁰;
- Nuclear waste treatment (storage containers, transport tanks): Resistant to radioactive media + long – term stability (replace stainless steel, weight reduced by 30%).
- Chemical Industry and Pharmaceutical Industry:
- Strong acid and strong alkali reaction kettles (hydrochloric acid, sulfuric acid, sodium hydroxide): Corrosion rate < 0.025 mm/a (better than Hastelloy, cost reduced by 60%) ³⁹;
- Pharmaceutical – grade equipment (high – purity solvent pipelines): Compliant with sanitary regulations, 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%).
- High – end Manufacturing:
- Aerospace (engine corrosion – resistant parts): Lightweight + resistant to jet fuel corrosion (replace titanium alloy, weight reduced by 20%);
- Medical implants (artificial joints, dental implants): Excellent biocompatibility, resistant to body fluid corrosion (service life exceeds 20 years) ⁷¹⁰.
Key Summary
- Core Advantages:
- Corrosion resistance: Corrosion rate < 0.025 mm/a in 70% sulfuric acid and boiling hydrochloric acid, better than titanium alloy and 90% nickel – based alloy ³⁹;
- Nuclear compatibility: Extremely low thermal neutron absorption cross – section, the “only choice” for nuclear reactor structural materials;
- Cost – performance ratio: Performance is close to tantalum, and the cost is only 1/5 of it, with cost – performance far exceeding titanium alloy.
- Limitations:
- Long – term service temperature ≤ 350°C (prone to oxidation at high temperatures, ceramic coating needs to be applied);
- High cold work hardening rate (multiple annealing processes required, processing cost increased by 10% – 15%).
R60702(UNS R60702/Zr-3) is a “golden material for nuclear industry”. It breaks through the performance bottleneck of titanium alloy and stainless steel through ultra-high purity zirconium design, and becomes an “irreplaceable ultimate solution” in the fields of nuclear reactors, extremely corrosive chemical equipment, high-end medical devices and so on, redefining the benchmark of cost performance of corrosion-resistant materials.