Deoxidation process of molten steel in EAF furnace
Due to the oxygen blowing process in EAF furnace, a large number of alloys are also oxidized, such as Cr2O3, MnO, FeO, and a large amount of free oxygen remains in the steel. EAF furnace deoxidation method includes precipitation deoxidation and diffusion deoxidation, the front is also known as deep deoxidation, refers to the deoxidizer directly and the oxygen in the steel reaction, play rapid deoxidation purpose, this method has the advantage of fast deoxidization speed, the disadvantage is that the deoxidization product removal is slow, such kind of deoxidizers have aluminum ingots, ferrosilicon, ferromangano and so on.
Diffusion deoxidation refers to the deoxidizer and the oxide reaction in the slag, , the advantage of this method is that the deoxidizer product is in the slag, will not pollute the liquid steel, the disadvantage is that the deoxidizer speed is slow, there are silicon calcium, silicon aluminum calcium barium, aluminum particles and other particle deoxidizer.
In order to achieve rapid deoxidation without contaminating liquid steel, the combination of precipitation deoxidation and diffusion deoxidation is generally adopted in EAF furnace process.
EAF furnace hot liquid, after decarbonization, static boiling for 5 to 10 minutes, directly inserted aluminum blocks for precipitation deoxidation, the oxygen in the steel is rapidly reduced, the aluminum content of the molten steel is controlled at 0.015% ~ 0.06%, and the tapping speed should be more than 8 tons/minute.
Deoxidation process of molten steel in LF furnace
Because there is a slag layer on the liquid steel surface in LF furnace, and the boiling point of Ca is 1484℃, it quickly becomes steam in the liquid steel, so the silica-aluminum-barium core-coated wire is used to improve the recovery rate of silica-aluminum-barium. At the same time, LF furnace will also use silicon calcium and other deoxidizers for deoxidation.
Since LF has entered the late refining stage, a large number of deoxidation products should not exist in the steel, so the LF furnace is generally diffused deoxidation to prevent deoxidation products from entering the steel.
LF furnace mainly uses a wire feeder to add the silica-aluminum-barium core-wire to the liquid steel, feed the silica-aluminum-barium core-wire according to the ratio of 1 ~ 4kg/ ton of molten steel, maintain the calcium content of molten steel 0.002% ~ 0.006%, and then add active lime. According to the oxygen activity, the silicon aluminum-calcium barium wire is added at any time to deoxidize and keep the oxygen activity of the molten steel < 5PPM. After the alloying is finished, the silicon aluminum-calcium barium wire is fed for a second time. At this time, the argon soft blowing operation is carried out to modify the inclusion and float the inclusion.
The amount of reductant added in LF furnace is controlled according to 2 ~ 3kg/ ton steel, to ensure that the residual calcium content in liquid steel is controlled to 0.002% ~ 0.006%, and the aluminum content in steel is generally controlled to 0.01% ~ 0.03%.
The content of reducing agent is low, indicating that the deoxidation is not complete, the content of reducing agent is high, and it is easy to react with the oxygen precipitated in the steel to produce oxides after pouring, and the oxides generated at this time are difficult to remove, which is extremely unfavorable to the quality of the casting, so the content of reducing agent elements in the steel should be strictly controlled.
