RAYCHIN LIMITED

Zirconium Hex Cap Screws – Complete Product Range

Critical Applications of Zirconium Hex Cap Screws

International Standards & Global Designations – Zirconium Hex Cap Screw Materials

RAYCHIN LIMITED manufactures Zirconium hex cap screws from material conforming to the most widely used national and international specifications. All material is traceable to the mill.

Chemical Composition (Weight %) – Zirconium Alloys for Hex Cap Screws

Our Zirconium hex cap screws are produced from material conforming to the limits of applicable ASTM, ASME, and ISO standards. Nuclear grades available with hafnium <0.01%.

Commercial Zirconium Grades – ASTM B493 / B550 / B551

Nuclear Grade Zirconium – ASTM B353 (Hf <0.01%)

Metallurgical note: Zirconium is a reactive metal that spontaneously forms a stable, adherent zirconium oxide (ZrO₂) layer in air or oxidizing media. This oxide film is self‑healing if damaged and provides exceptional corrosion resistance in most acids, including hydrochloric, sulfuric, and nitric acids. Zirconium has a hexagonal close-packed (α) structure at room temperature, with a melting point of 1855°C. The addition of niobium (2-3%) in Zr 705 increases strength through solid solution strengthening while maintaining excellent corrosion resistance. Nuclear grades (Zircaloy) are specified with hafnium content below 0.01% due to hafnium's high neutron absorption cross-section. Zirconium is non‑magnetic and exhibits good ductility even at cryogenic temperatures.

Complete Mechanical & Physical Properties – Zirconium Alloys for Hex Cap Screws (MPa / ksi)

Zirconium hex cap screws are supplied in appropriate conditions (annealed or stress relieved) per ASTM B493, ASTM B550, and customer specifications. Data represent typical values based on industry standards.

Commercial Zirconium – Mechanical Properties (minimum values)

Nuclear Grade Zirconium – Mechanical Properties (minimum values)

High‑Temperature Mechanical Properties – Zr 702 (representative)

Note: Zirconium maintains useful strength up to 800°C in inert or reducing atmospheres. In air, oxidation accelerates above 600°C; protective coatings may be required for long-term service above 600°C.

Physical Properties – Zirconium

High‑Temperature Performance of Zirconium Hex Cap Screws

Zirconium and its alloys maintain useful mechanical properties up to 800°C (1472°F), making them suitable for high‑temperature chemical processing and nuclear applications. Zirconium has a melting point of 1855°C, which is higher than steel and titanium. The alloy retains significant strength at elevated temperatures, as shown in the high‑temperature data. However, zirconium's high‑temperature service in air is limited by oxidation: above 600°C, the protective ZrO₂ layer begins to undergo phase transformations that may affect its protective properties. In inert atmospheres or reducing environments, zirconium can be used at much higher temperatures. Zircaloy‑4 and Zr‑2.5Nb alloys are specifically designed for high‑temperature service in nuclear reactors, where they operate at 300-400°C in high‑pressure water environments. For applications requiring extended service above 600°C in air, protective coatings (such as Cr or CrSi coatings) can significantly enhance oxidation resistance.

Elevated Temperature Capabilities

Note: Above 600°C in air, zirconium oxidizes forming ZrO₂; the oxide remains adherent but may spall under thermal cycling. Protective coatings available for higher temperature air service.

Exceptional Corrosion Resistance of Zirconium Hex Cap Screws

Zirconium is renowned for its outstanding corrosion resistance in a wide range of aggressive media, often exceeding that of nickel alloys and titanium. The protective ZrO₂ oxide film is stable in both oxidizing and reducing acids, and self‑heals rapidly if damaged. Zirconium is virtually immune to pitting and crevice corrosion in chloride environments.

• Hydrochloric Acid (HCl): Zirconium exhibits <0.13 mm/year corrosion rate (<5 mpy) in all concentrations of HCl up to boiling point. Even in 37% HCl, zirconium does not begin to show substantial corrosion until 130°C (266°F). This performance is unmatched by any other engineering metal except tantalum. Hastelloy C276 experiences 288 mpy in 10% HCl at boiling point, while zirconium has nil corrosion even when aerated.
• Sulfuric Acid (H₂SO₄): Excellent resistance up to 70% concentration at boiling point. Corrosion rates <0.13 mm/year in most concentrations. Only tantalum equals zirconium's performance in sulfuric acid.
• Nitric Acid (HNO₃): Outstanding resistance in all concentrations up to 90% and temperatures up to 200°C. Corrosion rate <0.1 mm/year.
• Phosphoric Acid: Excellent resistance comparable to Alloy 20, with corrosion rates <0.13 mm/year.
• Organic Acids: Completely resistant to acetic acid, formic acid, citric acid, and other organic acids at all concentrations and temperatures.
• Alkalis: Zirconium is attacked by strong alkalis (NaOH >40%) at elevated temperatures. In such environments, nickel alloys or Monel are recommended.
• Hydrofluoric Acid (HF): Rapidly attacked by HF and fluoride-containing media – not recommended.
• Oxidizing Chlorides: Ferric or cupric chlorides greatly decrease corrosion resistance; upstream equipment must be controlled to prevent oxidizing contaminants.
• Seawater: Corrosion rate <0.01 mm/year, outperforming titanium and nickel alloys. Immune to pitting and crevice corrosion in seawater.
• Galvanic Corrosion: Zirconium is cathodic to most metals; can accelerate corrosion of active metals (steel, aluminum) in contact. Isolation or coating recommended.

Manufacturing Standards – Zirconium Hex Cap Screws

All Zirconium hex cap screws are manufactured and tested to meet the following standards:

We offer surface finishes: plain (as‑machined), passivated, ground. Zirconium hex cap screws can be supplied with certified material traceability, dimensional inspection reports, and mechanical test certificates. Our manufacturing processes include CNC heading, thread rolling, and heat treatment (annealing or stress relief). We specialize in custom configurations including non‑standard lengths, special head markings, and proprietary thread forms. Cleanroom packaging available for pharmaceutical and semiconductor applications. All screws supplied with EN 10204 Type 3.1 or 3.2 certification. ISO 9001:2015 and AS9100D certified quality management system. Nuclear grades supplied with full traceability including hafnium content certification.