RAYCHIN LIMITED

Zirconium Lock Nuts – Comprehensive Product Range

Critical Applications of Zirconium Lock Nuts

International Standards & Global Designations – Zirconium Lock Nuts

RAYCHIN LIMITED manufactures zirconium lock nuts from vacuum arc remelted (VAR) or electron beam melted material conforming to the most widely used national and international specifications. All material is traceable to the mill with complete certifications.

Chemical Composition (Weight %) – Zirconium Alloys

Our zirconium lock nuts are produced from vacuum arc remelted (VAR) or electron beam melted material conforming to the limits of applicable ASTM B493 and B550 standards.

Zirconium 702 (UNS R60702) – Commercially Pure

Zirconium 705 (UNS R60705) – Zr-2.5%Nb Alloy

Metallurgical note: Zirconium is a refractory metal with a hexagonal close-packed crystal structure at room temperature. It exhibits exceptional corrosion resistance due to the formation of a stable, adherent, and self-healing oxide layer (ZrO₂) that provides protection in the most aggressive acidic environments. Zirconium is virtually immune to attack by hydrochloric acid at all concentrations up to boiling, outperforming all other engineering metals. In sulfuric acid, zirconium is resistant to concentrations up to 70% at temperatures well above boiling. It also exhibits excellent resistance to nitric acid, phosphoric acid, and most organic acids. Zirconium has the lowest thermal neutron absorption cross-section of all common structural metals (0.18 barns), making it the material of choice for nuclear reactor core components. The addition of 2-3% niobium in Zr 705 provides solid solution strengthening, increasing tensile strength by approximately 50% while maintaining excellent corrosion resistance. The apparent deformation activation energy of pure zirconium is 209 kJ mol⁻¹, indicating that cross-slip of dominant dislocation mechanisms controls the deformation process.

Complete Mechanical & Physical Properties – Zirconium Alloys (MPa / ksi)

Zirconium lock nuts are supplied in annealed condition per applicable ASTM specifications. Data represent typical values based on ASTM B493 and B550 standards.

Mechanical Properties – Zirconium Alloys (Annealed Condition)

Physical Properties – Zirconium Alloys

High-Temperature Mechanical Properties – Zr 705

Maximum continuous service temperature in corrosive environments: 400°C (752°F). Zirconium begins to oxidize rapidly above 500°C in air. High-temperature studies up to 1200°C are relevant for nuclear accident scenarios.

High‑Temperature Performance of Zirconium Lock Nuts

Zirconium is a refractory metal with excellent high-temperature strength and stability in vacuum or inert atmospheres. During hypothetical loss-of-coolant accident scenarios in nuclear reactors, zirconium alloy fuel claddings are exposed to steam at high temperatures up to 1200°C. The αZr(O) phase containing up to 7 wt.% oxygen shows substantial strengthening and embrittlement at these temperatures. For standard service in corrosive environments, zirconium lock nuts maintain useful mechanical properties up to 400°C (752°F). The apparent deformation activation energy of pure zirconium is 209 kJ mol⁻¹, indicating that cross-slip of dominant dislocation mechanisms controls the deformation process at elevated temperatures. Optimum processing conditions for zirconium are 700-900°C at 0.1-0.14 s⁻¹ and 905-950°C at 3-20 s⁻¹, with dynamic recrystallization occurring in these safe domains. In oxidizing atmospheres, zirconium forms a protective oxide layer (ZrO₂) at moderate temperatures but may oxidize above 500°C in air. Therefore, zirconium lock nuts with all-metal flexloc designs are typically specified for high-temperature applications in vacuum, inert gas, or reducing atmospheres.

Elevated Temperature Capabilities

Exceptional Corrosion Resistance of Zirconium Lock Nuts

Zirconium is renowned for its outstanding corrosion resistance, often outperforming all other engineering metals in aggressive acidic environments. The material forms a stable, adherent, and self-healing oxide layer (ZrO₂) that provides protection against a wide range of corrosive media. In 3.5% NaCl solution, zirconium exhibits corrosion potential of -198 mV, corrosion current density of 0.5 µA/cm², and film resistance of 63,000 Ω – all significantly better than titanium and 316L stainless steel.

Corrosion Resistance to Common Media

• Hydrochloric Acid: Zirconium lock nuts exhibit corrosion rates less than 5 mpy (0.13 mm/year) in 37% HCl at 130°C (266°F). This performance is unmatched by any other engineering metal with the exception of tantalum. In 10% HCl at boiling point, Hastelloy C276 experiences 288 mpy corrosion while zirconium exhibits nil corrosion even when aerated.
• Sulfuric Acid: Excellent resistance to sulfuric acid up to 70% concentration at temperatures well above boiling. Outperforms Alloy 20 and C-276 in sulfuric acid service.
• Nitric Acid: Zirconium can be used in all concentrations of nitric acid up to 90% and temperatures up to 200°C – comparable to tantalum and superior to most stainless steels.
• Organic Acids: Excellent resistance to acetic acid, formic acid, oxalic acid, and other organic acids at all concentrations up to boiling.
• Seawater Resistance: In 3.5% NaCl solution, zirconium demonstrates superior corrosion resistance compared to titanium and 316L stainless steel, with higher film resistance (63,000 Ω vs. 39,700 Ω for Ti and 3,150 Ω for 316L).
• Limitations: Zirconium is rapidly attacked by hydrofluoric acid, ferric chloride, cupric chloride, and other oxidizing halides. Even small amounts of oxidizing media will greatly decrease its corrosion resistance. Process control of upstream contaminants is critical for maintaining corrosion resistance.
• Galvanic Corrosion: Zirconium is noble (corrosion potential -198 mV in 3.5% NaCl) and can be safely coupled with most metals, but may accelerate corrosion of less noble materials. The current of Zr-Ti couple is 0.03 µA, whereas Zr-316L is 0.1 µA, indicating excellent compatibility with titanium.
• Nuclear Properties: Zirconium's low thermal neutron absorption cross-section (0.18 barns) makes it ideal for nuclear reactor applications.

Manufacturing Standards – Zirconium Lock Nuts

All zirconium lock nuts are manufactured and tested to meet the following standards:

We offer surface finishes: plain (as-machined), passivated, or electropolished. Controlled annealing processes per ASTM specifications ensure consistent mechanical properties. Specialized CNC machining and tapping for accurate lock nut geometry with reliable self-locking torque values. All-metal flexloc designs feature segmented collars that meet military standards for 15 cycles of prevailing torque. Class 2B/3B/6H thread fit. 100% inspection available including dimensional inspection, proof load testing, density verification, and non-destructive examination. Full traceability and material test reports (MTR) with mill certifications available. AS9100 and ISO 9001:2015 certified quality management. ISO 13485 certified for medical applications with cleanroom packaging available. Build-to-print specials to customer specifications are available.