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

The sequence for adding ferroalloys is as follows: first, add those with weak deoxidizing power, then proceed to those with stronger deoxidizing power. Generally, alloy additions are made after slag removal has been completed and the carbon‑boosting operation has been finished, once a portion of the slag has been introduced to form a reducing slag. The specific requirements for adding different alloys are as follows:

(1) Addition of ferrosilicon

When smelting silicon steel, spring steel, or heat‑resistant steel, a substantial amount of ferrosilicon is added for alloying; this ferrosilicon must be preheated to red heat for an extended period. The primary reason is that ferrosilicon contains significant amounts of hydrogen, which can be eliminated by red‑heating, and preheating also accelerates its melting. Moreover, because ferrosilicon is relatively light, when added in large quantities to the furnace, some of the silicon will react with the slag as a deoxidizer, forming the acidic product silicon dioxide and reducing the local alkalinity of the slag—conditions that are detrimental to steel quality. To prevent this, an appropriate amount of lime should be introduced before and after adding ferrosilicon to maintain slag alkalinity, and the furnace should be energized at high voltage for several minutes to ensure thorough slag melting and favorable reactions, resulting in a uniform white slag. The recovery rate of ferrosilicon typically ranges from 90% to 98%.

During refining, once the chemical composition has been adjusted, the temperature is appropriate, and the slag is in good condition, ferrosilicon may be added. Steel should be tapped within 10 to 25 minutes after addition. If the time is too short, the ferrosilicon will not have sufficient time to melt completely, and silicon will be unevenly distributed throughout the steel. Conversely, if the tapping interval is too long, the molten steel is prone to absorbing gases, which can adversely affect steel quality.

(2) Addition of ferromanganese

Manganese‑iron can be added during the formation of the reducing slag, with its manganese content typically controlled at the lower limit of the specified range during the first addition. The recovery rate of manganese‑iron exceeds 95%.

(3) Addition of copper

When smelting weathering steel, copper enhances the steel’s hardenability and corrosion resistance. Because copper in the melt is resistant to oxidation, it can be added during charging or during the oxidation phase, with a recovery rate consistently above 95%. Given copper’s relatively high cost, it is generally advisable to incorporate copper‑bearing pig iron, copper‑containing scrap steel, or copper‑bearing iron ore in portions during the melting stage, with any remaining copper adjusted in the reduction phase, thereby minimizing the use of pure copper.

(4) Addition of ferrochrome

Ferrochrome is typically added at the very beginning of the reduction phase. Chromium has a stronger affinity for oxygen than iron, which is why it oxidizes more readily. If added during the melting or oxidation phases, chromium would be oxidized, leading to both alloy‑element losses and a thickening of the slag that impairs dephosphorization and smelting operations. Therefore, ferrochrome must be introduced during the reduction stage. After addition, if the slag turns green, this indicates insufficient deoxidation; the reduction process should be intensified to reduce the chromium oxide present in the slag. Once reduction is adequate, the slag will become white. Under white‑slag conditions during the reduction phase, the recovery rate of ferrochrome exceeds 95%.