The order of adding ferroalloys is as follows: first, ferroalloys with a weaker deoxidizing capacity are added, and then with a stronger deoxidizing capacity. Alloys are usually added after the slag removal is completed, the carburizing operation is completed, and some slag is added to obtain the reducing slag. The requirements for adding different alloys are as follows:
(1) Addition of Ferrosilicon
In the smelting of siliconic, spring, and heat-resistant steel, a large amount of ferrosilicon must be added for alloying, and the added ferrosilicon must be burned red-hot for a long time. The main reason is that ferrosilicon contains a lot of hydrogen, which can be removed after baking red, and preheating ferrosilicon can also speed up melting; In addition, because ferrosilicon is light, when a large amount of ferrosilicon is added to the furnace, some of the silicon inevitably deoxidizes with the slag, forming an acidic product called silica, which reduces the alkalinity of the local slag, which is not good for the quality of steel. To prevent this from happening, before and after adding ferrosilicon, it is necessary to add an appropriate amount of lime to maintain the alkalinity of the slag, and also use high voltage for a few minutes to melt the slag and react well to turn into a uniform white slag. The degree of ferrosilicon recovery is from 90 to 98%.
During refining, when the chemical composition is adjusted, the temperature is suitable, and the slag is good, ferrosilicon can be added. Once added, the steel can be poured for 10-25 minutes. If the time is too short, the ferrosilicon will not have time to melt completely, and the silicon will not be evenly distributed in the steel. If the time is too long, the molten steel will easily absorb the gas, which will affect the quality of the steel.
(2) Addition of Ferromanganese
Ferromanganese can be added in the manufacture of reducing slag. Manganese content is usually controlled at the lower limit for the first time. The recovery rate of ferromanganese is more than 95%.
(3) Addition of copper
: In the smelting of weathered steel, the copper in the steel can improve the hardenability and corrosion resistance of steel. Copper in steel is not easily oxidized, so it can be added during the charging or oxidation period, while the reduction factor is also stable and is more than 95%. Because copper is expensive, it is usually best to add some copper-bearing iron, copper-bearing steel scrap, or copper-bearing iron ore during the smelting period, and a small amount of copper is adjusted during the recovery period to minimize the amount of pure copper.
(4) Ferrochrome
Addition Ferrochrome is usually added at the beginning of the recovery period. Chromium has a greater affinity for oxygen than iron, which means that chromium is more easily oxidized than iron. If it is added during the melting and oxidation period, the chromium will be oxidized, which will not only lead to the loss of alloying elements, but also make the slag thicker, which will affect dephosphorization and melting operations. Therefore, ferrochrome should be added during the recovery period. If the slag turns green after being added, it means that the slag is poorly deoxidized. RestoredIt should be strengthened to reduce the chromium oxide content of the slag. After a good recovery, the slag will turn white. The ferrochrome recovery rate is more than 95% under the condition of white slag during the recovery period.
(5) Ferrovanadium
Addition Ferrovanadium should be added during the recovery period. Vanadium has a high affinity for oxygen and is easily oxidized. Therefore, it should not be added during the oxidation period. It can only be added during the recovery period after the slag and molten steel are well oxidized. Since when ferrovanadium is added, molten steel easily absorbs nitrogen in the air, which affects the quality of the steel, it should not be added too early, but only before steel smelting. However, ferrovanadium takes some time to melt, so it should be added 10-35 minutes before casting steel. With a small amount of ferrovanadium added, the time should be controlled according to the lower limit, and with a large amount - according to the upper and middle limit. The recovery rate of ferrovanadium is close to the recovery rate of ferrosilicon.
(6) Addition of ferromolybdenum
Ferromolybdenum is a refractory alloy. It is usually added at the beginning of the recovery period to ensure complete melting and a uniform composition. If it is added later, within a few minutes of pouring the steel, the ferromolybdenum will not have time to melt completely, which can lead to an uneven distribution in the molten steel and an increase in smelting time. The recovery rate of ferromolybdenum usually exceeds 98%.
(7) Addition of Ferroniobium
Niobium is an element with a weak affinity for oxygen, so it is relatively easy to control and master in the smelting process. It is usually added at the beginning of the recovery period, and the steel can be tapped 20 minutes after addition to promote its uniform melting. If the non-oxidative method is used for smelting, niobium can also be added during charging. The recovery rate of niobium is usually greater than 95%.
(8) Addition of Ferrotungsten
Ferrotungsten is characterized by high density and melting point. Once added, it settles to the bottom of the furnace and does not melt easily. Compared to nickel and molybdenum, tungsten has a greater affinity for oxygen. If it is added during the smelting period, the tungsten will oxidize and exist in the slag in the form of calcium tungstat, which will lead to a loss of tungsten and complicate the control of the tungsten composition. Therefore, tungsten ferro-tungsten must be added at the beginning of the recovery period and cannot be added during the smelting or late refining period. Since ferrotungsten is difficult to melt, adding a large amount of it in the late refining period will affect the smelting time and will also be unevenly distributed in the molten steel. Most of the tungsten ferro-tungsten should be added at the beginning of the recovery period, leaving only a small amount for adjustment at the end of the recovery period. In addition, the added ferrotungsten must be small in size and must be red-roasted to facilitate melting. The recovery rate of ferrotungsten is typically greater than 95%.