In 1956, Ruhr Steel Company and Hellas Company, both of which belong to Thyssen Company in Germany, successfully developed the RH vacuum steel liquid circulation degassing method, referred to as the RH method.
RH refining equipment mainly consists of vacuum chamber, immersion tube (riser, downcomer), vacuum degassing device (vacuum exhaust pipe), alloy feeding device, argon injection device for molten steel circulation, ladle and ladle lifting device, vacuum chamber preheating device and other parts.
RH furnace lining
RH furnace works under vacuum and high temperature. This slender container can be divided into several replaceable parts, upper, middle and lower, one part is immersed in molten steel. The service life of the refractory material depends on the installation position. The lower the service life, the shorter the service life, and the service life of the lifting tube is the shortest. According to the corrosion factor of the working lining of the RH furnace device, the lining material usually adopts high-quality magnesia-chrome bricks or alkaline ramming integral lining or adopts a comprehensive lining of partition lining according to the use conditions of different parts.
RH vacuum chamber upper part
The upper part of the RH vacuum chamber is not in direct contact with the molten steel, and there is no problem of molten steel scouring and slag erosion. It is a free space; the furnace lining has a relatively long life. However, due to vacuuming, blowing Ar, and blowing oxygen, the decarburization reaction of the molten steel produces CO bubbles, which causes the molten steel to splash, adhere to the furnace wall, and even form nodules. During the mid-maintenance, in order to remove the nodule cold steel, the refractory material of the furnace wall will be damaged.
In addition, when the upper part of the RH vacuum chamber is vacuumed, the oxygen partial pressure is low, and the air enters during the stop period, and the oxygen partial pressure is high, which causes the iron oxide in the magnesia-chrome brick to undergo a high-low valence state transformation and produce a volume effect. The upper part of the vacuum chamber is usually built with ordinary magnesia-chrome bricks, and it is obvious that general alumina-magnesia spinel bricks can also be used. However, magnesia-carbon bricks should not be used.
RH vacuum chamber lower part, bottom and throat
The refractory lining bricks used in the lower part, bottom and throat of the RH vacuum chamber are mainly subjected to the erosion of high-speed circulating molten steel. When smelting ultra-low carbon steel such as IF steel and silicon steel, it takes a long time to evacuate and blow oxygen to decarburize, which will form acidic slag with high iron oxide content, as well as the erosion and penetration of slag liquid with low melting point and good fluidity formed by spraying desulfurizer powder. Magnesium calcium bricks are not good at resisting the melting and penetration of iron oxide acidic slag, and their anti-erosion ability is not as good as that of magnesium chromium materials.
Therefore, magnesium carbon bricks should not be used for masonry in the lower part, bottom and throat of the vacuum chamber.
In terms of anti-erosion, anti-erosion and penetration of iron-silicon acidic slag and desulfurization slag, the better refractory material is the direct-bonded magnesia-chrome brick with high Cr₂O₃ content, among which the magnesia-chrome bricks bonded by electric melting are more suitable. Therefore, the lower part, bottom and throat of the vacuum chamber of the RH furnace should be built with high-temperature fired high-quality direct-bonded magnesia-chrome bricks.
RH furnace vacuum chamber
The vacuum chamber is generally preheated to about 1300℃ during operation, and the heating is stopped ten minutes before the molten steel is processed. A slag shield is added at the lower end of the lift pipe to prevent the molten steel in the ladle from entering the vacuum chamber. During degassing, the lift pipe is inserted into the molten steel to a depth of about 300mm. The temperature of the molten steel is 1650~1700℃, the processing time is 30~60min, and the vacuum degree is about 66.66Pa. Slag agent and alloy material are added during the degassing process for refining. The lining is affected by high temperature and vacuum, the lift pipe is in contact with the slag, and the use conditions are harsh. The RH-OB circulation method with oxygen blowing function improves the exhaust capacity, aggravates the splashing of molten steel in the vacuum chamber, strengthens the refining operation, and oxygen blowing aggravates the damage of refractory materials. The refractory materials in this part must have excellent corrosion resistance and thermal shock resistance.
Immersion pipe
Immersion pipe lining
The immersion pipe consists of a gas injection pipe, a steel structure supporting refractory materials, and refractory materials. The steel structure is fixed in the center, and the lining is made of high-temperature fired magnesia-chrome bricks, and the outside is castable.
In addition to being resistant to the erosion of high-speed flowing molten steel, the refractory materials used in the lining of the immersion pipe are required to be very good in terms of heat and structural spalling resistance, because the immersion pipe is not easy to keep warm during the stop period, and the temperature difference of temperature fluctuation is much larger than that in the vacuum chamber. The refractory materials used in the lining of the immersion pipe are now mostly built with magnesia-chrome bricks with good thermal shock resistance.
Outer wall of the dip tube
The strong thermal shock damage and slag erosion caused by the intermittent operation of the RH furnace caused the castable of the outer lining of the lift tube to be damaged due to severe cracking. At the same time, the refractory material of the outer wall of the dip tube is directly in contact with the alkaline slag in the ladle, and it is required to be resistant to alkaline slag erosion; in order to make the life of the castable synchronize with the life of the inner lining, low-cement or cement-free castables are developed, made of high-aluminum, corundum or aluminum-magnesium.