Ferro tungsten series (with tungsten content of 70%-80%) is an alloy composed of tungsten and iron used as an alloy additive in steelmaking. The commonly used ferro tungsten includes two types containing 70% and 80% tungsten, respectively. Ferro tungsten is produced by carbon reduction of tungsten manganese iron ore in an electric furnace. It is mainly used as an alloying element in tungsten-containing alloys such as high-speed steel (HSS).
A track mobile open-hearth electric furnace with detachable upper section is utilized in this method, and carbon is used as a reducing agent. A mixed furnace charge composed of tungsten concentrate, pitch coke (or petroleum coke), and slag-making agent (alumina) is added to the furnace in batches, and the produced metal in the furnace is generally in a viscous state, and gradually solidifies from the bottom as the thickness increases. After the furnace is filled, it is stopped and the furnace body is pulled out to allow the clumps to cool and condense. Then the clumps are removed, crushed, and refined; the edges, slag-containing parts and unqualified parts are picked out for remelting. The product contains about 80% tungsten and less than 1% carbon in its composition.
This is suitable for smelting ferro tungstens with lower tungsten (70%) and lower melting point. Silicon and carbon are used as reducing agents; the operation is divided into three stages: reduction stage, refining stage, and iron acquisition stage. During the reduction stage, the furnace contains slag with a lager WO3 content of over 10% left from the previous iron-collecting, and the tungsten concentrate is added to the furnace in batches. Then silicon iron with 75% silicon content and a small amount of pitch coke (or petroleum coke) are added for reduction smelting. When the WO3 content in the slag falls below 0.3%, the slag is discharged.
Then it enters the refining stage. During this stage, tungsten concentrate and pitch coke mixture is added in batches, and high voltage is applied for refining and removing impurities such as silicon and manganese at high temperatures. After taking samples for testing and confirming the composition is qualified, the iron is collected. During the iron collecting period, tungsten concentrate and pitch coke are added according to the furnace conditions.
In order to utilize waste hard alloy powder to separate cobalt and recycle carbide tungsten, an aluminum-thermal ferro tungsten process was developed, using recycled carbide tungsten and iron as raw materials and aluminum as a reducing agent. The thermal energy generated by the carbon and aluminum combustion in carbide tungsten is used to transform tungsten and iron in the raw materials into ferro tungsten. This can save a significant amount of electrical energy and reduce costs. At the same time, because the impurities in carbide tungsten raw materials are much lower than those in tungsten concentrate, the product quality is higher than that of ferro tungstens produced from tungsten concentrates. The tungsten recovery rate is also higher than that of processes using tungsten concentrates as raw materials.
Tungsten is expensive, and in the production process, it is necessary to pay attention to improving the recovery rate. Unqualified products and slag iron should be collected for recycling, and the electric furnace should have an efficient flue gas dust removal facility to recover tungsten-containing dust.