RAYCHIN LIMITED

Molybdenum Hex Bolts – Design & Configurations

Critical Applications of Molybdenum Hex Bolts

International Standards & Global Designations – Molybdenum Hex Bolts

RAYCHIN LIMITED manufactures molybdenum hex bolts from vacuum arc melted (VAR) or powder metallurgy (PM) material conforming to the most widely used national and international specifications. All material is traceable to the mill.

Chemical Composition (Weight %) – Molybdenum Alloys for Hex Bolts

Our molybdenum hex bolts are produced from vacuum arc melted (VAR) or powder metallurgy (PM) material conforming to ASTM B386/B387 and industry standards.

Pure Molybdenum (Grade 360 / 361) – Mo ≥99.95%

TZM Alloy (Grade 363 / 364) – Mo-0.5Ti-0.08Zr-0.02C

MoLa Alloy (Mo with Lanthanum Oxide)

Metallurgical note: Molybdenum is a refractory metal with a body-centered cubic (BCC) crystal structure, atomic number 42, atomic weight 95.94. Pure molybdenum hex bolts are typically supplied in stress-relieved condition (recrystallization temperature ~1100°C) or soft/annealed condition. TZM alloy offers significantly higher recrystallization temperature (~1400°C) and improved creep strength through carbide dispersion strengthening. MoLa (lanthanated molybdenum) maintains ductility after high-temperature exposure due to oxide dispersion pinning grain boundaries. All molybdenum hex bolts should be handled with care due to limited ductility at room temperature, becoming more ductile above ductile-to-brittle transition temperature (DBTT).

Complete Mechanical & Physical Properties – Molybdenum Hex Bolts (MPa / ksi)

Molybdenum hex bolts are supplied in various conditions (hard/stress relieved, soft/annealed) per ASTM B387. Data represent typical values based on industry standards.

Mechanical Properties – Pure Molybdenum Hex Bolts

Mechanical Properties – TZM Alloy Hex Bolts

Physical Properties – Molybdenum

High‑Temperature Performance of Molybdenum Hex Bolts

Molybdenum and its alloys are renowned for exceptional high-temperature strength and stability. Pure molybdenum maintains useful mechanical properties up to 1700°C (3090°F) in vacuum or reducing atmospheres, with TZM extending capability further through carbide strengthening. The yield stress of molybdenum is sensitive to test temperature and strain rate, with strength decreasing predictably as temperature increases. However, molybdenum oxidizes rapidly above 600°C in air, forming volatile MoO₃, limiting use to vacuum, inert gas, or reducing environments unless protected by coatings.

Elevated Temperature Capabilities

Molybdenum alloys are capable of long-time operation at temperatures of 1200-1300°C under low loads. For applications requiring protection against oxidation in air above 600°C, protective coatings such as MoSi₂, Al₂O₃, Y₂O₃, or Cr-Ni double layer deposits may be applied. Molybdenum is considered a main structural material for nuclear thermionic converters due to its low vapor pressure in vacuum.

Corrosion Resistance of Molybdenum Hex Bolts

Molybdenum exhibits excellent resistance to many corrosive media, particularly in reducing environments and in the absence of oxidizing agents. It is insoluble in water but has high solubility in concentrated sulphuric acid and nitric acid. Its stability in various chemical environments makes it suitable for chemical processing equipment and research applications.

• Acid Resistance: Excellent resistance to hydrochloric acid (HCl) at moderate temperatures. High solubility in concentrated sulphuric acid and nitric acid. The beneficial action of Mo against pitting corrosion in neutral chloride solutions is attributed to its presence as MoO₄²⁻ or HMoO₄⁻ in the passive film, not to an insoluble Mo-oxide.
• Chloride Solutions: Molybdenum containing alloys have superior resistance against pitting attack in 0.1 M NaCl solutions up to 200°C. Above 200°C, pitting attack may degenerate into different kinds of localized or general attack at rather high potentials.
• Alkalis: Stable in alkaline solutions, resisting corrosion effectively.
• Liquid Metals: Excellent resistance to liquid lithium, sodium, potassium, and bismuth, making it valuable in nuclear coolant systems. Resists molten aluminum and zinc.
• Oxidation: Forms volatile MoO₃ above 490-600°C in air; requires protective atmosphere or coating for high-temperature air service.
• Hydrogen: Excellent resistance to hydrogen attack even at high temperatures.
• Glass Corrosion: Outstanding resistance to molten glass, widely used in glass melting electrodes and stirrers.
• Environmental Stability: Molybdenum occurs naturally in fresh water at 0.03-10 µg/L and sea water at 4-10 µg/L as MoO₄²⁻ in oxidised environments.

Manufacturing Standards – Molybdenum Hex Bolts

All molybdenum hex bolts are manufactured and tested to meet the following standards:

We offer surface finishes: black (as-machined), chemical cleaned, ground, polished, and passivated. Special coatings (MoSi₂, Al₂O₃, Y₂O₃, Cr-Ni double layer) available for oxidation protection. Full traceability and destructive/non‑destructive testing available (UT, PMI, MPI). ISO 9001, AS9100D, ISO 13485 certified with cleanroom packaging available for semiconductor and medical applications.