Molybdenum and Molybdenum Alloys
Molybdenum melts at 2,623 °C, weighs 10.2 g/cm³ — half of tungsten — and combines a modulus of 320 GPa with thermal conductivity of 138 W/m·K and expansion of only 5 ppm/K. Stress-relieved pure molybdenum yields 400–550 MPa at room temperature and is the only refractory metal that machines and forms without much drama. TZM adds titanium, zirconium and carbon for roughly twice the strength at 1,200 °C and a recrystallization temperature near 1,400 °C; Mo-La and MHC push creep resistance further. All of them oxidize fast above 500 °C in air, so they live in vacuum, hydrogen or inert gas.
Popular molybdenum grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Pure Mo | 590 | 700 | 10.22 | Fair | Poor | Furnace hardware, targets, electrodes |
| TZM | 760 | 900 | 10.22 | Fair | Poor | Hot dies, anodes and loaded fixtures to 1,400 °C |
| Mo-La | 560 | 700 | 10.2 | Fair | Poor | Sag-resistant elements and boats |
| MHC | 800 | 900 | 10.2 | Poor | Poor | Extrusion and die-casting tooling beyond TZM |
| Mo-30W | 620 | 760 | 11.9 | Poor | Poor | Molten zinc and glass contact parts |
| Mo-47.5Re | 1,000 | 1,240 | 13.5 | Poor | Very good | Ductile, weldable molybdenum for formed parts |
| Mo1/Mo2 | 580 | 700 | 10.22 | Fair | Poor | National-standard purity grades on drawings |
Choose molybdenum for
Vacuum- and hydrogen-furnace hot zones — elements, racks, boats, shields, sintering trays — glass-melting electrodes and stirrers, sputter targets and semiconductor hardware, X-ray rotating anodes, hot-forging and die-casting inserts, and any high-temperature part that must be machined to tolerance and does not have to survive air above 500 °C.
Look elsewhere when
The part runs in air when hot (a nickel or cobalt superalloy such as L605 or Inconel 601, or a ceramic), the temperature exceeds about 1,600 °C where only Pure W or Ta-10W hold up, the environment is a hot acid rather than a furnace (Pure Ta or Zr 702), the design needs a welded or cold-bent joint in a thick section (Mo-47.5Re or Pure Nb), or a stainless steel fixture survives the duty at a fraction of the cost below 1,000 °C.
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Molybdenum by application
- Furnace hot zones
- Pure Mo racks, boats, shields and hearth plates to about 1,600 °C in vacuum or hydrogen; Mo-La for elements and thin shields that would sag or embrittle after recrystallization.
- Hot-work tooling
- TZM for isothermal forging dies, hot-extrusion mandrels, die-casting cores and piercing tools that carry load at 1,000–1,400 °C; MHC where die life in aluminum die casting or copper extrusion is the limit.
- Glass and molten-metal contact
- Pure Mo and Mo-30W electrodes, stirrers and thermocouple sheaths in molten glass; Mo-30W in molten zinc, which attacks most other metals.
- Targets and X-ray components
- Pure Mo and Mo (Grade 360) sputter targets and backing plates; TZM rotating-anode substrates with a tungsten-rhenium focal track.
Working with molybdenum
- Machining
- Machines like a hard, abrasive gray cast iron: carbide tooling, sharp edges, moderate speed and positive feeds, with chamfered exits because the metal chips rather than burrs. Stress-relieved bar is preferred; recrystallized stock cracks at the edges. TZM and MHC cut the same way at slightly lower speed.
- Forming
- Sheet bends warm, 150–300 °C for thin gauges and hotter for plate, and only in the stress-relieved condition. Deep draws and spinning are done hot with intermediate stress relief. Boats and shields are folded and riveted with molybdenum rivets rather than welded.
- Welding and joining
- Fusion welds in pure Mo and TZM are brittle recrystallized zones — use electron beam under vacuum, keep joints out of bending loads, or specify Mo-47.5Re, which welds ductile. Brazing to steel with nickel, titanium or palladium fillers and mechanical fastening are the everyday joints.
- Heat treatment and coatings
- Stress-relieve at 900–1,000 °C in hydrogen or vacuum after heavy machining; never recrystallize a part that will be flexed cold. MoSi₂ coatings allow short excursions in air at temperature; otherwise the part must stay in vacuum or protective gas above 500 °C.
Other refractory metal series
Molybdenum and Molybdenum Alloys — frequently asked
What is molybdenum?
Molybdenum melts at 2,623 °C, weighs 10.2 g/cm³ — half of tungsten — and combines a modulus of 320 GPa with thermal conductivity of 138 W/m·K and expansion of only 5 ppm/K. Stress-relieved pure molybdenum yields 400–550 MPa at room temperature and is the only refractory metal that machines and forms without much drama. TZM adds titanium, zirconium and carbon for roughly twice the strength at 1,200 °C and a recrystallization temperature near 1,400 °C; Mo-La and MHC push creep resistance further. All of them oxidize fast above 500 °C in air, so they live in vacuum, hydrogen or inert gas.
Which grade of molybdenum should I use?
Pure Mo for furnace racks, boats, heat shields, sputter targets, glass-melting electrodes and any machined part that is not heavily loaded when hot — Mo (Grade 360) is the ASTM B386 designation for the same unalloyed metal, and Mo1/Mo2 the national-standard purity grades. TZM for hot-work tooling, isothermal forging dies, die-casting cores, rotating X-ray anodes and loaded fixtures at 1,000–1,400 °C. Mo-La for heating elements, sintering boats and shields that must not sag after long exposure: its lanthanum-oxide dispersion keeps an elongated grain structure and ductility after recrystallization. MHC (Mo-1.2Hf-0.1C) out-performs TZM in extrusion and die-casting tooling; Mo-30W resists molten zinc and glass. Mo-41Re and Mo-47.5Re are the weldable, room-temperature-ductile molybdenum for formed and welded assemblies.
Which grade of molybdenum is the strongest?
Mo-47.5Re has the highest yield strength in the series at 1,000 MPa; TZC follows at 930 MPa. Values are for each grade's default condition.
Which grade of molybdenum is easiest to machine?
TZM (machinability fair, 45/100), then Mo (Grade 360) (40/100).
Pure Mo or TZM?
Pure Mo unless the part carries load above about 1,000 °C. It is cheaper, more available, easier to machine and form, and strong enough for racks, boats, shields and electrodes. TZM roughly doubles the strength and creep resistance at 1,200 °C and recrystallizes about 300 °C later, for the same density and thermal properties — it is the die, mandrel, anode and loaded-fixture alloy. Both oxidize the same way in air, so the choice is purely mechanical.
Can molybdenum be welded?
Not usefully in the pure metal or TZM: the weld and heat-affected zone recrystallize, oxygen and nitrogen pickup embrittle them, and the joint fails in bending at room temperature. Electron-beam welding in vacuum gives the best of a poor set of options for sealed assemblies. Where a welded structure is really needed, Mo-41Re or Mo-47.5Re weld ductile, or the design switches to rivets, threads and interlocking tabs, which is how most molybdenum furnace hardware is built.