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The order of adding ferroalloys is that the deoxidization ability is weak first, and then the deoxidization ability is strong. Generally, the carburizing operation of the alloy is completed after slag scraping, and the reduction slag is added after adding some slag. The addition requirements of different alloys are as follows:

(1) The addition of ferrosilicon

In the smelting of silicon steel or spring steel and heat resistant steel, a large amount of ferrosilicon is added for alloying, and the ferrosilicon added must be roasted red for a long time. The main reason is that ferrosilicon contains more hydrogen, which can be removed after roasting, and preheated ferrosilicon can also accelerate melting; moreover, because ferrosilicon is lighter, when a large number of ferrosilicon is added into the furnace, it will inevitably deoxidize some silicon and slag, and produce acidic product silicon dioxide, which reduces the basicity of local slag, thus affecting the quality of steel. It's bad. In order to prevent the occurrence of this situation, appropriate amount of lime should be added before and after adding ferrosilicon to maintain slag basicity, and high voltage power transmission for several minutes, so that slag melts and reacts well and becomes uniform white slag. The recovery of ferrosilicon is between 90% and 98%.

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(2) Ferromanganese addition

Ferromanganese can be added at the same time as reducing slag, and the composition control of manganese is generally controlled at the lower limit for the first time. The recovery of ferromanganese is over 95%.

(3) Copper addition

When smelting weatherproof steel, copper in steel can improve the hardenability and corrosion resistance of steel. Copper in steel is not easy to oxidize, so it can be added during charging or oxidation period, and the recovery rate is stable at more than 95%. Because copper is more expensive, it is generally better to add a part of pig iron containing copper, scrap iron containing copper or copper-bearing iron ore in the melting period, and adjust a small amount of copper in the reduction period to minimize the consumption of pure copper.

(4) Addition of ferrochromium

Ferrochrome is usually added at the beginning of reduction period. The affinity between chromium and oxygen is greater than that between iron and oxygen, that is to say, chromium is easier to oxidize than iron. If chromium is added during the melting and oxidation periods, it will be oxidized, which will not only cause the loss of alloy elements, but also make the slag thicker, which will affect the dephosphorization and smelting operations, so ferrochromium should be added during the reduction period. If the slag turns green after adding, it shows that the deoxidization of the slag is not good, reduction must be strengthened to reduce the chromium oxide in the slag. After good reduction, the residue will turn white. The recovery of ferrochromium is more than 95% under the condition of white slag in reduction period.

(5) The addition of ferrovanadium

Iron vanadium should be added during the reduction period. Vanadium and oxygen have high affinity and are easy to oxidize, so they can not be added in the oxidation stage, but only after the slag and molten steel deoxidize well in the reduction stage. As the addition of ferrovanadium makes it easy for molten steel to absorb nitrogen in the air and affects the quality of steel, it can not be added prematurely, but only before tapping. However, the melting of ferrovanadium takes a certain time, so it should be added 10-35 minutes before tapping. When the amount of adding is small, the time should be controlled in the lower limit, and when the amount of adding is large, the time should be controlled in the upper limit. The recovery of ferrovanadium is close to that of ferrosilicon.

(6) Addition of ferromolybdenum

Iron molybdenum is a refractory alloy, which is usually added at the beginning of the reduction period to ensure complete melting and uniform composition. If the molybdenum and iron are added in the later stage, it will not melt completely in a few minutes before tapping, which may cause uneven distribution in molten steel and increase smelting time. The recovery of ferromolybdenum is generally more than 98%.

(7) The addition of ferroniobium

Niobium is an element with weak affinity to oxygen, so it is easy to control and master in the smelting process. Generally, steel can be tapped only after 20 minutes of addition at the early stage of reduction period, so as to promote its melting uniformity. When non-oxidation process is adopted, niobium can also be added during charging, and the recovery of niobium is generally more than 95%.

(8) Addition of ferrotungsten

FeW is characterized by high density and high melting point. After adding, it sinks into the bottom of the furnace and is not easy to melt. Compared with nickel and molybdenum, tungsten has higher affinity with oxygen. When tungsten is added in the melting period, it will oxidize and exist in the slag in the form of calcium tungstate, resulting in loss of tungsten, which makes it more difficult to control the composition of tungsten. Therefore, ferrotungsten can not be added at the early stage of reduction period or at the later stage of refining. Because ferrotungsten is difficult to melt, a large amount of ferrotungsten is added at the later stage of refining, which will affect the smelting time. At the same time, the distribution of ferrotungsten in molten steel is uneven. Most ferrotungsten should be added at the early stage of reduction period, leaving only a small amount of adjustment at the later stage of reduction period. Moreover, the added ferrotungsten should be small in size and must be roasted red to facilitate melting. The recovery of ferrotungsten is generally over 95%.

(9) Addition of Aluminum as Alloy Element

Aluminum is easy to be duplicated, so it is usually added before tapping. For steel grades with different aluminium content, the adding method is slightly different: steel grades with less than 02% aluminium content can generally be inserted into the furnace 2-5 minutes before tapping without slag scraping. The recovery of aluminium is about 50%. If titanium is contained in steel, the recovery rate is slightly higher, up to 55%. For steels with high aluminium content, in order to prevent slag from returning to silicon after a large amount of aluminium addition and to make the finished silicon higher than the requirement of composition, all slag removal methods are adopted. The reduced slag is removed completely, then aluminium blocks are added. After aluminium blocks are added, then lime with liquid steel weight of 2%-3% and fluorite with low silica content are added. After uniform delivery of electrolyte slag, the slag is shaken out again. In steel, the recovery of aluminium in this case ranges from 65% to 88%.

(10) Addition of ferroboron

Boron is easy to combine with oxygen and nitride in steel. It is usually added before tapping, and proper amount of Al and Ti must be added to steel before adding boron in order to deoxidize and stabilize nitrogen. Eight methods of adding boron:

1) Boron iron is usually added to ladle in the process of tapping. At this time, the tapping operation first needs to pick large tapping port, shake the furnace at a faster speed, and at the same time carry out slag blocking operation. The molten steel must first flow into the ladle, and when about one third of the molten steel in the ladle, boron iron (put or insert) must be added. Then let the slag flow out. The method of slag stopping in front of the furnace: first, a few shovels of lime can be added at the outlet of the steel, and then the slag-picking sawdust rake can be used to block the outlet of the steel, and then the steel can be swiftly shaken out of the furnace.

2) After adding aluminium or titanium, iron boron is inserted in front of the furnace, stirred, and then tapped. At this time, ferroboron should be firmly fastened on the iron bar, wrapped in aluminium sheet or horse manure paper, and inserted into molten steel as quickly as possible to avoid the loss of boron oxidation in slag.

The boron recovery rates of the above two methods are about the same, generally 45%-85%, which will be higher in some cases. From the homogeneity of boron in steel and the internal quality of steel, the latter method is better.

(11) Addition of ferrotitanium

Titanium has a great affinity with oxygen and nitrogen, and is easily oxidized and nitrided to become inclusions in steel. Therefore, titanium is usually added under the condition of white slag and melted completely before tapping, that is, steel is usually required within 5 to 15 minutes after adding. Titanium iron should be added near the furnace entrance to avoid approaching the arc as far as possible in order to reduce burning loss. If the quantity is small, there is no need to push the slag after joining. After adding ferrotitanium, staying in the furnace for too long will not only reduce the recovery rate, but also decrease the quality of molten steel. In addition, because of the low density of ferrotitanium, it floats on the slag steel surface when it is added into the furnace, and then melts into molten steel gradually, so the recovery fluctuates greatly and the influencing factors are complex.

The main factors affecting titanium recovery are:

1) The influence of slag quantity in furnace. The burning loss of titanium is mainly caused by slag, so when there is less slag in the furnace, the effect is small and the recovery rate is relatively stable. When the slag quantity is large and the slag deoxidizes well and the fluidity is appropriate, the burning loss of titanium is small and stable. If the slag quantity is large and the slag condition is bad, the burning loss of titanium is large and extremely unstable; if the slag is too thin, the interaction between ferrotitanium and slag will be strengthened, so the recovery rate will decrease, but if the slag is too sticky, the burning loss of ferrotitanium on the slag surface will be large, and the recovery rate will also be reduced; the slag deoxidization is poor, the content of iron oxide in the slag is high, and the oxidation loss of titanium will be reduced. The higher the temperature, especially the slag temperature, causes the loss of ferrotitanium and the lower the recovery rate. Titanium content in steel is high, and the recovery rate is also high: when there are many other deoxidizing elements in steel, the recovery rate is also high. If aluminium and titanium are inserted before adding titanium, the recovery rate can also be improved and stable. Titanium and iron can be directly added into molten steel because of gravity effect, and the recovery rate is also improved.

(2) The effect of Ti-Fe lumpness. As long as it is not all fragments, it is generally not the main factor, but if it is powdered, the recovery of ferrotitanium will be greatly reduced, sometimes less than 25%.

(3) The effect of adding methods. Titanium iron is added after slag pushing operation, even after slag sticking with iron rake, when the reduction slag in the door area of the furnace is pushed open and the exposed molten steel can be seen, Titanium iron is added immediately. Recovery (such as stainless steel) can be stabilized at 60% - 65% (slag condition and temperature have little effect). Generally, structural steels containing silicon and vanadium have higher deoxidization degree than stainless steels, so the recovery rate can be up to about 70%.

Electric energy is used as heat source in electric arc furnace steelmaking to avoid the pollution of sulphur content in gas heat source to steel; flexible operation process, slag and furnace gas can be adjusted to oxidize or reduce; strong reducibility can make the precious elements chromium, nickel, tungsten, molybdenum, vanadium, titanium contained in furnace charge very little burning loss; furnace temperature is high, easy to control, and reduce. The product quality is high.

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