1. The Raw Material Chain
The raw material for smelting ferromolybdenum is mainly molybdenite (MoS2) concentrate. Before smelting, the molybdenum concentrate is oxidized and roasted in a multi-hearth furnace to obtain roasted molybdenum ore with a sulfur content of less than 0.07%. The low residual sulfur is essential because sulfur would otherwise enter the alloy and harm steel quality.
2. The Outside-Furnace Smelting Method
Ferromolybdenum smelting generally adopts the outside-furnace method. The furnace is a cylinder placed on a sand base and lined with clay bricks. Ferrosilicon containing 75% silicon, together with a small amount of aluminum particles, is used as the reducing agent. After the charge is added into the furnace barrel at one time, it is smelted by the upper ignition method, using an initiator such as saltpeter, aluminum chips or magnesium chips on the material surface.
3. Reaction, Slag Removal and Cooling
After ignition, the charge reacts violently, then calms, and the slag is released before the furnace barrel is removed. The ferromolybdenum ingots are first cooled in the sand nest, then sent to the cooling room to be flushed with water for cooling, and finally crushed and finished. The metal recovery rate is 92 to 99% depending on the charge practice and ore quality. In the steelmaking industry in recent years, molybdenum oxide briquettes have been widely used to replace ferromolybdenum in some applications.
4. Metallurgical Use in Steel
Ferromolybdenum is an alloy of molybdenum and iron, and its main use is as an additive for molybdenum in steelmaking. Adding molybdenum to steel produces a uniform fine-grained structure, improves the hardenability of the steel, and helps eliminate temper brittleness. In high-speed steel, molybdenum can replace part of the tungsten, lowering cost while preserving cutting performance. Molybdenum is widely used with other alloying elements to produce stainless steel, heat-resistant steel, acid-resistant steel and tool steel, as well as alloys with special physical properties.
5. Use in Cast Iron and Other Applications
Molybdenum is added to cast iron to increase its strength and wear resistance, supporting heavy-duty castings such as gears, rolls and machine frames. Beyond steel and iron, molybdenum alloys serve aerospace, chemical processing, energy and electronics industries where high-temperature strength, corrosion resistance and wear performance are required.
6. FAQ
Q1: What is the raw material for ferromolybdenum? Molybdenite (MoS2) concentrate, which is oxidized and roasted to reduce sulfur below 0.07% before smelting.
Q2: How is ferromolybdenum smelted? By the outside-furnace method, in which ferrosilicon and aluminum reduce the roasted ore in a clay-lined barrel furnace ignited from the top.
Q3: What is the metal recovery rate? Typically 92 to 99%, depending on the ore quality and smelting practice.
Q4: What is the main use of ferromolybdenum? As a molybdenum additive in steelmaking, to refine grain, improve hardenability, eliminate temper brittleness and support alloy steel production.
Q5: Can molybdenum replace tungsten in high-speed steel? Yes, part of the tungsten can be replaced by molybdenum while preserving cutting performance, which reduces alloy cost.
Q6: What are molybdenum oxide briquettes? A briquetted form of roasted molybdenum oxide used in steelmaking as a practical alternative to ferromolybdenum for molybdenum addition.
