RAYCHIN LIMITED

Molybdenum Lock Nuts – Design & Configurations

Critical Applications of Molybdenum Lock Nuts

International Standards & Global Designations – Molybdenum Lock Nuts

RAYCHIN LIMITED manufactures molybdenum lock nuts 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 Lock Nuts

Our molybdenum lock nuts 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 . Pure molybdenum lock nuts are typically supplied in stress-relieved condition (recrystallization temperature ~1100°C). 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 lock nuts must be used in vacuum, inert gas, or reducing atmospheres above 600°C to prevent catastrophic oxidation .

Complete Mechanical & Physical Properties – Molybdenum Lock Nuts (MPa / ksi)

Molybdenum lock nuts are supplied in various conditions (hard/stress relieved, soft/annealed) per ASTM B387. Data represent typical values based on industry standards and are compared with SUS304 stainless steel for reference .

Mechanical Properties – Pure Molybdenum vs. SUS304

Mechanical Properties – TZM Alloy Lock Nuts

Physical Properties – Molybdenum

High‑Temperature Performance of Molybdenum Lock Nuts

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 . Molybdenum has a melting point of 2620°C (4760°F), a low coefficient of thermal expansion and a high level of thermal conductivity . Because molybdenum lock nuts have the ability to withstand extremely high temperatures without changing shape, expanding or softening significantly, they are ideal for high strength / high temperature applications that are shielded from oxygen . However, exposing molybdenum lock nuts to oxygen above 600°C will cause them to readily oxidize, limiting use to vacuum, inert gas, or reducing atmospheres unless protected by coatings .

Elevated Temperature Capabilities

Molybdenum lock nuts support use with vacuum equipment in high-temperature environments. In oxidizing atmospheres above 600°C, rapid oxidation will occur; use is therefore recommended only in vacuum, inert gas, or reducing atmospheres . For air applications, protective coatings (MoSi₂, Al₂O₃, Y₂O₃) may be applied.

Corrosion Resistance of Molybdenum Lock Nuts

Molybdenum exhibits excellent resistance to many corrosive media, particularly in reducing environments and in the absence of oxidizing agents. It has considerably higher corrosion resistance than tungsten in high-temperature water environments .

• High-Temperature Water Corrosion: Mo shows a considerably higher corrosion resistance than W . At 180°C, corrosion rates are 0.022-0.029 mm/year for Mo . At 260°C, corrosion rates are 0.141-0.214 mm/year . At 320°C, significant attack occurs depending on the material . Mo–Re alloys may corrode more severely, with Mo–17.7%Re reaching 0.405 mm/year at 320°C .
• Oxidation Resistance: Molybdenum must be protected by a suitable coating to withstand temperatures above 500°C under an oxidizing environment . Exposing molybdenum to oxygen above 600°C will cause them to readily oxidize .
• Acid Resistance: Molybdenum is not resistant to acids . It has high solubility in concentrated sulphuric acid and nitric acid.
• Liquid Metals: Excellent resistance to liquid lithium, sodium, potassium, and bismuth, making it valuable in nuclear coolant systems.
• 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 .
• Low Vapor Pressure: Excellent low vapor pressure at high temperatures, making it ideal for vacuum applications .

Manufacturing Standards – Molybdenum Lock Nuts

All molybdenum lock nuts 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) available for oxidation protection. Cleanroom wash and cleanroom packaging available for semiconductor, medical, and aerospace applications – batch cleanroom packing provided for orders containing multiple items of the same size . Full traceability and destructive/non‑destructive testing available (UT, PMI, MPI). ISO 9001, AS9100D, ISO 13485 certified.