How Ferromolybdenum Is Produced: From Ore to FeMo Alloy
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Overview of the Ferromolybdenum Production Route
Ferromolybdenum (FeMo) is an iron-molybdenum alloy used to add molybdenum to steel and cast iron. Most of the world's ferromolybdenum is supplied by China, the United States and Chile. The core production principle is simple: molybdenum is first mined and concentrated, converted into molybdenum (VI) oxide (MoO3), mixed with iron oxide and aluminum oxide, and then reduced in a thermite reaction to produce the alloy. The crude product can be purified by electron beam melting or packaged as-is for metallurgical use.
Step 1: Mining and Concentration
Molybdenum ore, principally molybdenite (MoS2), is mined and processed by flotation to produce a concentrate containing roughly 45-57% molybdenum. The concentrate is the raw feed for roasting and must meet limits on copper, lead and other impurities that would otherwise carry into the alloy.
Step 2: Roasting to Molybdenum Trioxide
The concentrate is roasted in a multi-hearth or fluidized-bed furnace at about 550-650 °C, where sulfur is driven off and molybdenum sulfide is converted to molybdenum trioxide (MoO3). The roasted oxide is then blended with iron oxide (scale), aluminum powder and ferrosilicon as reducing agents, together with lime for slag conditioning.
Step 3: Thermite (Aluminothermic) Reduction
The blend is charged into a refractory-lined vessel and ignited. The strongly exothermic reaction reduces the oxides to metal: aluminum and silicon react with MoO3 and iron oxide, producing molten ferromolybdenum that settles below a fluid slag layer. The high heat of reaction melts both metal and slag without external energy. After cooling, the alloy block is crushed and sized into lumps or powder as specified.
Step 4: Refining and Packaging
For applications requiring very low gas and impurity content, the crude alloy can be refined by electron beam melting, which removes volatiles and further purifies the metal. For standard metallurgical use, the alloy is crushed, screened, magnetically separated and packed directly. Fine ferromolybdenum powder is commonly shipped in bags or sealed drums to prevent oxidation and contamination.
Standard Grades and Chemical Composition
| Grade | Mo min % | Si max % | S max % | P max % | C max % | Cu max % | Sb max % | Sn max % |
|---|---|---|---|---|---|---|---|---|
| FeMo70 | 65.0-75.0 | 1.5 | 0.10 | 0.05 | 0.10 | 0.5 | -- | -- |
| FeMo70Cu1 | 65.0-75.0 | 2.0 | 0.10 | 0.05 | 0.10 | 1.0 | -- | -- |
| FeMo70Cu1.5 | 65.0-75.0 | 2.58 | 0.20 | 0.10 | 0.10 | 1.5 | -- | -- |
| FeMo60-A | 55.0-65.0 | 1.0 | 0.10 | 0.04 | 0.10 | 0.50 | 0.04 | 0.04 |
| FeMo60-B | 55.0-65.0 | 1.5 | 0.10 | 0.05 | 0.10 | 0.50 | 0.05 | 0.06 |
| FeMo60-C | 55.0-65.0 | 2.0 | 0.15 | 0.05 | 0.20 | 1.0 | 0.08 | 0.08 |
| FeMo60 | ≥60.0 | 2.0 | 0.10 | 0.05 | 0.15 | 0.05 | 0.04 | 0.04 |
| FeMo55-A | ≥55.0 | 1.0 | 0.10 | 0.08 | 0.20 | 0.5 | 0.05 | 0.06 |
| FeMo55-B | ≥55.0 | 1.5 | 0.15 | 0.10 | 0.25 | 1.0 | 0.08 | 0.08 |
FAQ
1. Why is molybdenum added to steel?
Molybdenum increases hardenability, high-temperature strength, creep resistance and corrosion resistance, which is why it is used in tool steels, stainless steels and heat-resistant alloys.
2. What is the thermite reaction?
It is a self-sustaining exothermic reduction in which aluminum and ferrosilicon reduce metal oxides to molten metal. In ferromolybdenum production it converts MoO3 and iron oxide into the alloy without external heating.
3. What is the difference between FeMo60 and FeMo70?
FeMo70 contains 65.0-75.0% molybdenum and FeMo60 contains 55.0-65.0%. Higher molybdenum content means more alloying power per kilogram but a more demanding production route and higher cost.
4. Why is copper limited in ferromolybdenum?
Copper is an impurity that can cause hot shortness in steel and is difficult to remove once present. Its limit depends on the target steel specification, so grades such as FeMo70Cu1 and FeMo70Cu1.5 exist for applications that tolerate higher copper.
5. How is ferromolybdenum usually packaged?
Lumps are typically packed in 250 kg steel drums or big bags on pallets, while fine powder is packed in sealed bags or drums. Packaging is confirmed with the supplier to match handling and melting practice.
