Molybdenum
The following table shows various alloys and the meltstock Mo products they use.
| Super- alloys | Stainless Steel | Alloy Steel | Tool Steel & High Speed Steel | Cast Iron | |
|---|---|---|---|---|---|
| Roasted molybdenite concentrate (Technical Mo oxide) | x | x | x | ||
| Ferromolybdenum | x | x | x | x | |
| Mo metal pellets | x |
Stainless steel, alloy steel, tool steel, and high speed steel are typically melted in an electric arc furnace. The initial charge usually contains alloy steel scrap, pig iron, and a source of "Mo units" to attain the proper composition. Using scrap ensures that recycling provides an important share of the melt. Recycled material comes from in-house scrap, scrap collected from steel fabricators, and remelt stock purchased from recyclers. Depending on the steel grade and market factors, the share of molybdenum from recycled material can vary between 10 and 50%. Technical Mo oxide is usually added with the scrap charge to approach the specified Mo content. If only small amounts of new molybdenum are required, ferromolybdenum (FeMo) the normal alloy addition.
After meltdown, the liquid metal is usually transferred into an AOD vessel or a ladle furnace for further metallurgical treatment. Ferromolybdenum is added at this stage to adjust the composition to the specified Mo content.
FeMo is used exclusively as the source of molybdenum in cast iron. Superalloys, on the other hand, use only molybdenum pellets because of the alloys' requirement for high purity additions and vacuum melting.
Molybdenum metal scrap generated by mill product manufacturers is also used for alloy additions. The balance between metal and other addition sources depends upon the relative economics and availability of the various sources of Mo units.
Tech oxide is the principal product for adding molybdenum to alloy and stainless steels. It typically contains 56 - 58% Mo and a maximum of 0.5% Cu, and is available in the following forms and packaging options:
Product standards include:
Roasted molybdenum concentrate (Technical Mo oxide) powder (left) and briquettes
(Courtesy of Molymet, Chile)
FeMo can be used in any melting or refining unit to produce Mo-containing steel or cast iron. It is frequently used as ladle addition to achieve accurate final adjustment of composition. In steels with low Mo content (usually no more than 0.2% Mo) like High Strength Low Alloy (HSLA) steel, all of the Mo is added as FeMo.
FeMo typically contains 65 – 75% Mo and a maximum of 0.5% Cu.
The product is produced in size ranges between:
It is available as powder for special applications like welding electrodes.
Packaging is normally in steel drums or big bags.
Product standards include:
Ferromolybdenum
(Courtesy of Treibacher, Austria)
Pure Mo metal (Mo min. 99.9%) is used for superalloys to avoid contamination with trace elements.
The molybdenum powder is pressed into pellets and sintered in hydrogen to chemically reduce adsorbed oxygen and oxide films on the powder particle surfaces, densify the pressed pellets, and increase pellet strength. Sintering thus minimizes the amount of oxygen the pellets carry into the melt and increases ease of handling them in the melt shop.