RAYCHIN LIMITED

Molybdenum Button Head Cap Screws – Design & Configurations

Critical Applications of Molybdenum Button Head Cap Screws

International Standards & Global Designations – Molybdenum Button Head Cap Screws

RAYCHIN LIMITED manufactures molybdenum button head cap screws 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 Button Head Cap Screws

Our molybdenum button head cap screws 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 button head cap screws 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 button head cap screws should be handled with care due to limited ductility at room temperature, becoming more ductile above ductile-to-brittle transition temperature (DBTT). Vented versions are available for UHV applications .

Complete Mechanical & Physical Properties – Molybdenum Button Head Cap Screws (MPa / ksi)

Molybdenum button head cap screws 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 Button Head Screws

Physical Properties – Pure Molybdenum

High‑Temperature Performance of Molybdenum Button Head Cap Screws

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 2623°C (4743°F) and a low coefficient of thermal expansion (5.1 x 10⁻⁶ /K), making it ideal for the highest temperature environments . It offers load bearing capabilities up to 1600°C . However, molybdenum oxidizes rapidly above 600°C in air, forming volatile MoO₃, limiting use to vacuum, inert gas, or reducing atmospheres unless protected by coatings . In semiconductor manufacturing equipment, molybdenum screws are designed to withstand interior temperatures of 500-1000°C in ion generators, light sources, and processing chambers .

Elevated Temperature Capabilities

Molybdenum button head cap screws support use with vacuum equipment in high-temperature environments. In oxidizing atmospheres above 600°C, sublimation 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. The low-profile design of button head screws is particularly suitable for applications where clearance is limited in high-temperature systems .

Corrosion Resistance of Molybdenum Button Head Cap Screws

Molybdenum exhibits excellent resistance to many corrosive media, particularly in reducing environments and in the absence of oxidizing agents. It has good resistance to corrosion in molten glass and can withstand corrosion and erosion at high temperatures . However, rapid oxidation occurs in air above 600°C . Its stability in various chemical environments makes it suitable for specialized applications.

• Oxidation Resistance: Forms volatile MoO₃ above 600°C in air; requires protective atmosphere or coating for high-temperature air service .
• Glass Corrosion: Outstanding resistance to molten glass, widely used in glass melting electrodes and stirrers . Molybdenum withstands corrosion and erosion in molten glass at high temperatures, with load bearing capabilities up to 1600°C .
• Acid Resistance: One of the few metals that has some resistance to hydrofluoric acid . Excellent resistance to hydrochloric acid (HCl) at moderate temperatures. High solubility in concentrated sulphuric acid and nitric acid. Resists most non-oxidizing mineral acids .
• 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.
• Halogens: Resistant to fluorine, chlorine, and bromine at moderate temperatures; forms halides at higher temperatures.
• Bimetallic Corrosion: Can be safely connected to tungsten, tantalum, and graphite. Avoid direct contact with aluminum, zinc, and copper at high temperatures due to eutectic formation.
• Low Vapor Pressure: Excellent low vapor pressure at high temperatures, making it ideal for vacuum applications .

Manufacturing Standards – Molybdenum Button Head Cap Screws

All molybdenum button head cap screws 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.