The order of adding various ferroalloys during steelmaking—once you see it, you’ll be amazed! (II)

(5) Addition of ferrovanadium

Vanadium‑iron should be added during the reduction phase. Due to vanadium’s strong affinity for oxygen, it readily oxidizes; therefore, it cannot be introduced during the oxidation phase and must be added only after the slag and molten steel have been effectively deoxidized in the reduction stage. Moreover, the addition of vanadium‑iron makes the molten steel highly susceptible to absorbing atmospheric nitrogen, which can degrade steel quality; hence, it should not be added prematurely but rather just before tapping. However, since vanadium‑iron requires a certain amount of time to melt, it should be charged 10–35 minutes prior to tapping. When the charge is small, the timing should be set toward the lower end of this range; for larger charges, the upper-middle range is appropriate. The recovery rate of vanadium‑iron is comparable to that of ferrosilicon.

(6) Addition of ferromolybdenum

Ferro‑molybdenum is a refractory alloy that is typically added during the early stages of the reduction phase to ensure complete melting and uniform composition. If added later, with only a few minutes remaining before tapping, the ferro‑molybdenum may not have sufficient time to melt fully, leading to uneven distribution in the molten steel and prolonging the smelting process. The recovery rate of ferro‑molybdenum is generally above 98%.

(7) Addition of niobium iron

Niobium is an element with relatively weak affinity for oxygen, making it easier to control and manage during the smelting process. It is typically added at the early stage of the reduction phase; after 20 minutes of addition, steel can be tapped to ensure uniform melting. When employing a non-oxidizing smelting method, niobium may also be charged directly during the charging process, with a recovery rate generally exceeding 95%.

(8) Addition of ferrotungsten

Ferro‑tungsten is characterized by its high density and high melting point. When added, it sinks to the bottom of the furnace and is difficult to melt. Compared with nickel and molybdenum, tungsten exhibits a stronger affinity for oxygen; if introduced during the melting stage, it will oxidize, forming calcium tungstate that remains in the slag, leading to tungsten losses and complicating compositional control. Therefore, ferro‑tungsten should be charged at the very beginning of the reduction phase and not during melting or in the later refining stages. Because it is refractory, adding large quantities in the final refining stage can extend the smelting time and result in uneven distribution in the molten steel. Consequently, most of the ferro‑tungsten is best introduced early in the reduction phase, with only a small portion reserved for fine adjustments toward the end. Furthermore, the charge should consist of small lumps and must be preheated until red‑hot to facilitate melting. The recovery rate of ferro‑tungsten typically exceeds 95%.

(10) Addition of boron and iron

Boron readily combines with oxygen and nitrogen in steel; it is typically added just before tapping. Prior to boron addition, appropriate amounts of aluminum and titanium must be introduced into the steel to deoxidize it and stabilize nitrogen. Methods for adding boron include:

1) Typically, boron‑iron is added to the ladle during the steel‑tapping process. At this stage, the tapping operation begins by first clearing the tap hole, slightly increasing the furnace‑tilting speed, and simultaneously performing slag‑blocking. It is essential to allow the molten steel to flow into the ladle first; once the ladle is about one‑third full, the boron‑iron is introduced—either by pouring it in or by inserting it—and then the slag is allowed to exit. As for slag‑blocking at the furnace front, one can initially throw several shovelfuls of lime into the tap hole, use a wooden slag‑removal rake to block the opening, and then quickly tilt the furnace to pour out the steel.

2) After adding aluminum or titanium, insert the ferroboron into the molten steel at the furnace front, stir thoroughly, and then tap out the steel immediately. At this point, the ferroboron should be securely fastened to an iron rod, wrapped externally with aluminum foil or manure paper, and inserted into the molten steel as quickly as possible to minimize boron oxidation losses in the slag.