Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
Pure molybdenum has a melting point of 2,620°C, a boiling point of 4,650°C, and a density of 10.2 g/cm³. It is grayish-white in appearance.
Metallic molybdenum is produced by oxidatively roasting molybdenite concentrate, MoS₂, to obtain molybdenum trioxide, MoO₃. The oxide is then reduced with hydrogen at approximately 1,100°C:
MoO₃ + 3H₂ → 3H₂O + Mo
Although reduction takes place at a high temperature, the resulting molybdenum powder still contains a relatively high amount of oxygen. Consequently, sintered molybdenum bars made from this powder also contain residual oxygen, which should be considered when selecting charge materials for an alloy melting furnace.
The chemical composition of metallic molybdenum is listed in Table 4-4 of the source. It is mainly used for melting nickel-based high-temperature alloys, precision alloys, and other alloys with restricted iron contents.
2. Ferromolybdenum
Ferromolybdenum is an iron alloy containing 50%–65% molybdenum, together with impurities such as carbon, silicon, manganese, phosphorus, and sulfur. Ferromolybdenum containing 55% molybdenum has a density of approximately 9 g/cm³ and a melting point of about 1,750°C.
Most ferromolybdenum is produced by silicothermic or aluminothermic reduction. Molybdenum oxide concentrate, containing 80%–90% MoO₃, 3%–8% FeO, and 3%–10% SiO₂, is mixed with suitable quantities of iron ore, iron chips, and ferrosilicon powder or aluminum powder. The mixture is then reduced in a thermal reduction furnace.
Impurity oxides containing phosphorus, sulfur, and copper may also be reduced during the process, allowing these elements to enter the ferromolybdenum. Its chemical composition is listed in Table 4-5 of the source.
Ferromolybdenum is suitable for introducing molybdenum when producing molybdenum-bearing steels in an induction furnace. It can also be used for alloys that permit the presence of iron and other accompanying elements. Its relatively high copper, phosphorus, and sulfur contents require attention during charge selection.
Tungsten and Its Ferroalloys
Tungsten improves the hardness of steel at elevated temperatures and is an important alloying element in high-speed tool steels and heat-resistant steels. Tungsten-bearing charge materials include metallic tungsten, ferrotungsten, and tungsten concentrates.
1. Metallic Tungsten
Pure tungsten has a melting point of 3,410°C, a boiling point of 5,555°C, and a density of 19.32 g/cm³. It is dark gray in appearance.
Metallic tungsten is produced from wolframite, (Fe, Mn)WO₄, or scheelite, CaWO₄. Hydrometallurgical processing first produces tungsten trioxide, WO₃, which is then reduced with hydrogen at 800–1,200°C to obtain tungsten powder:
WO₃ + 3H₂ → 3H₂O + W
The tungsten powder is pressed and sintered to produce tungsten bars. Because the WO₃ feedstock has a relatively high purity, the resulting metallic tungsten is also highly pure. Its chemical composition is listed in Table 4-6 of the source.
Metallic tungsten is mainly used as a charge material for melting nickel-based high-temperature alloys, precision alloys, and other alloys with restricted iron contents.
2. Ferrotungsten
Ferrotungsten is an iron alloy containing 65%–80% tungsten, together with impurities such as copper, sulfur, and tin. Ferrotungsten containing 65%–70% tungsten has a density of approximately 16.4 g/cm³ and a melting range of 1,700–2,000°C. It is hard and difficult to break.
Ferrotungsten is produced by reducing wolframite concentrate with silicon, aluminum, or carbon in an electric arc furnace. The principal reactions are:
FeWO₄ + 4C → W + Fe + 4CO↑
2FeWO₄ + 4Si → 2W + 2Fe + 4SiO₂
3FeWO₄ + 8Al → 3W + 3Fe + 4Al₂O₃
Impurity oxides in the concentrate are also reduced and enter the ferrotungsten. Copper and tin are among the main impurities introduced in this way. The carbon, silicon, and manganese contents of the ferrotungsten described in the source do not materially affect the steel’s chemical composition.
The chemical composition of ferrotungsten is listed in Table 4-7 of the source. Grades with a high tungsten content can be used for melting nickel-based high-temperature alloys and precision alloys. Other grades are suitable for producing tungsten-bearing steels.
3. Tungsten Concentrates
Tungsten concentrates include wolframite concentrate and calcium tungstate concentrate, also known as scheelite concentrate. They can be used to produce tungsten-bearing alloy structural steels.
During melting, a measured quantity of concentrate powder is added to the slag layer. Aluminum powder or silicon–calcium alloy powder is then used to reduce the WO₃ in the slag, allowing the recovered tungsten to enter the molten steel in the steel melting furnace.
Wolframite concentrate contains approximately 75% WO₃ and 25% combined FeO and MnO. Its density is approximately 7.14–7.50 g/cm³, and its melting point is about 1,500°C.
Scheelite concentrate contains approximately 70%–80% WO₃, with the remainder mainly consisting of CaO. Its density is approximately 5.9–6.1 g/cm³. Pure WO₃ has a melting point of 1,473°C.
