Zr702 vs Zr705: Which Zirconium Alloy Is Right for Your Application?
At FULLERKREG, we supply precision fasteners and engineered components in reactive and refractory metals, including zirconium alloys. Zr702 (R60702) and Zr705 (R60705) are the two most widely specified commercial zirconium grades — both offering exceptional corrosion resistance in aggressive chemical environments, but with meaningfully different strength levels and alloy compositions.
Zirconium alloys are among the most corrosion-resistant materials available, outperforming even titanium and most nickel alloys in hydrochloric acid, sulfuric acid, and many oxidizing environments. They are also the material of choice for nuclear fuel cladding due to their extremely low neutron absorption cross-section.
This guide provides a direct technical comparison of Zr702 and Zr705 per ASTM B550, covering chemical composition and mechanical properties to support your material selection decision.
Alloy Overview
- Zr702 (R60702) — Commercially pure zirconium with a minimum Zr+Hf content of 99.2%. Excellent corrosion resistance in a wide range of acids, alkalis, and salt solutions. Lower strength than Zr705 but superior formability and weldability. Governed by ASTM B550 R60702.
- Zr705 (R60705) — A zirconium-niobium alloy with 2–3% niobium addition for significantly improved strength while retaining the outstanding corrosion resistance of commercially pure zirconium. The preferred grade where higher mechanical strength is required alongside corrosion resistance. Governed by ASTM B550 R60705.
Chemical Composition Comparison (ASTM B550)
All values are weight percent (%). Min = minimum required; Max = maximum allowed.
Zr702 — R60702 (ASTM B550)
| Zr + Hf (%) | Hf (%) | Fe + Cr (%) | H (%) | N (%) | C (%) | O (%) | |
|---|---|---|---|---|---|---|---|
| Min | 99.2 | — | — | — | — | — | — |
| Max | — | 4.5 | 0.2 | 0.005 | 0.025 | 0.05 | 0.16 |
Balance: Zirconium (Zr). Hafnium (Hf) is a naturally occurring companion element in zirconium ores and is counted within the Zr+Hf total. For nuclear applications, low-Hf grades are specified separately.
Zr705 — R60705 (ASTM B550)
| Zr + Hf (%) | Hf (%) | Fe + Cr (%) | H (%) | N (%) | C (%) | O (%) | Nb (%) | |
|---|---|---|---|---|---|---|---|---|
| Min | 95.5 | — | — | — | — | — | — | 2.0 |
| Max | — | 4.5 | 0.2 | 0.005 | 0.025 | 0.05 | 0.18 | 3.0 |
Balance: Zirconium (Zr) + Niobium (Nb). The 2–3% Nb addition is the key differentiator from Zr702, providing solid-solution strengthening without significantly compromising corrosion resistance.
Mechanical Properties Comparison (ASTM B550)
| Grade | UNS | Standard | Tensile Strength Rm (N/mm²) min | Yield Strength Rp0.2 (N/mm²) min | Elongation A (%) min |
|---|---|---|---|---|---|
| Zr702 | R60702 | ASTM B550 | ≥380 | ≥205 | ≥16 |
| Zr705 | R60705 | ASTM B550 | ≥550 | ≥380 | ≥16 |
Note: Both grades maintain the same minimum elongation of 16%, demonstrating that the niobium addition in Zr705 improves strength without sacrificing ductility.
Key Differences at a Glance
| Parameter | Zr702 (R60702) | Zr705 (R60705) |
|---|---|---|
| UNS designation | R60702 | R60705 |
| Governing standard | ASTM B550 | ASTM B550 |
| Zr + Hf min (%) | 99.2 | 95.5 |
| Nb content (%) | — (none) | 2.0–3.0 |
| O max (%) | 0.16 | 0.18 |
| Tensile Strength min (N/mm²) | 380 | 550 (+45%) |
| Yield Strength min (N/mm²) | 205 | 380 (+85%) |
| Elongation min (%) | 16 | 16 |
| Strengthening mechanism | Commercially pure (interstitial) | Solid solution (Nb) |
| Formability | Excellent | Good |
| Weldability | Excellent | Good (requires inert atmosphere) |
| Corrosion resistance | Outstanding | Outstanding (equivalent to Zr702) |
| Nuclear neutron absorption | Very low (suitable for nuclear) | Very low (suitable for nuclear) |
| Relative cost | Lower | Higher (Nb addition) |
| Primary applications | Chemical process equipment, nuclear cladding | High-strength chemical plant, nuclear structural |
Corrosion Resistance of Zirconium Alloys
Both Zr702 and Zr705 share the same outstanding corrosion resistance profile, which is one of the broadest of any engineering metal:
- Hydrochloric acid (HCl) — Resistant at all concentrations up to boiling point. Outperforms titanium and most nickel alloys.
- Sulfuric acid (H₂SO₄) — Resistant up to ~70% concentration at boiling. Excellent in dilute sulfuric acid environments.
- Nitric acid (HNO₃) — Resistant at all concentrations and temperatures. Widely used in nuclear fuel reprocessing.
- Acetic acid and organic acids — Excellent resistance across a wide range of concentrations.
- Alkalis (NaOH, KOH) — Good resistance in dilute solutions; limited in concentrated hot alkalis.
- Seawater and chloride solutions — Excellent resistance; no pitting or crevice corrosion observed under normal conditions.
- Limitation — Zirconium is attacked by hydrofluoric acid (HF) and concentrated sulfuric acid above ~70% at elevated temperatures. Not suitable for dry chlorine gas above 200°C.
Application Selection Guide
Choose Zr702 (R60702) when:
- Maximum corrosion resistance in aggressive acid environments is the primary requirement and strength is secondary
- Excellent formability and weldability are needed for complex fabricated components
- Nuclear fuel cladding or reactor internals require the lowest possible neutron absorption
- Cost optimization is important — Zr702 is the more economical grade
- Typical applications: chemical process heat exchangers, reactor vessels for HCl and H₂SO₄ service, nuclear fuel rod cladding (Zircaloy variants), pharmaceutical process equipment, acetic acid plant components
Choose Zr705 (R60705) when:
- Higher mechanical strength is required alongside the corrosion resistance of commercially pure zirconium
- Structural components in chemical plants must withstand higher pressures or mechanical loads
- Fasteners, bolts, and nuts in corrosive environments require yield strength above what Zr702 can provide
- Typical applications: high-pressure chemical reactor fasteners, nuclear structural components, pump shafts and valve stems in aggressive acid service, high-strength corrosion-resistant bolting for chemical plant flanges
Important Handling Notes for Zirconium
- Machining — Zirconium is machinable but requires sharp tools, adequate cooling, and care to avoid ignition of fine chips or turnings.
- Welding — Must be performed under inert gas (argon) shielding to prevent oxidation. Contamination with oxygen or nitrogen significantly reduces ductility.
- Fire hazard — Fine zirconium powder and thin chips are flammable. Bulk material is not a fire hazard under normal conditions.
- Hafnium content — For nuclear applications, low-Hf grades (Hf <100 ppm) are specified separately from commercial grades (Hf ≤4.5%).
FULLERKREG Supply Capabilities
FULLERKREG supplies precision fasteners and engineered components in Zr702 and Zr705:
- Material Test Certificates (MTC) — EN 10204 3.1 / 3.2 available on request
- ASTM B550 compliance — rod and bar forms for fastener and structural applications
- Zirconium fasteners to DIN, ISO, and custom specifications — hex bolts, studs, nuts, and socket head cap screws
- Low-Hf nuclear-grade zirconium — available on request with full traceability documentation
- Bulk wholesale pricing — OEM and MRO procurement with competitive lead times
- Global shipping — from our manufacturing base in China to customers worldwide
Need a quote or technical consultation for Zr702 or Zr705 fasteners? Contact FULLERKREG with your specification and our engineering team will respond promptly.
FULLERKREG — Precision Fasteners. Global Standards. Reliable Supply.