High-Alumina ramming bodies for lining steel casting ladles having provision for vacuum refining

Abstract

Ladle treatment of steel using a synthetic slag, vacuum treatment, and blowing with inert gases (lancing) made the working conditions of the walls, the bottom portions, and the cavities of the nozzles of the steel casting (teeming) ladles more severe. Using chamotte refractory pieces (for example, the MKRAP-45 and KShU-39 products) and Siliceous ramming bodies based on quartzite or natural half-dark sands does not ensure the required stability of the ladle lining under these conditions. Steel casting ladles having a capacity of 130 ton are being used in the electric steelmaking shop of the Cherepovetsk Steel Plant. Molten steel existing in the ladles is subjected to argon lancing for a period of 20-25 min and is vacuum treated for a period of 8-12 rain under a vaccum of 2.0-2.7 kPa. The temperature of the steel poured from the furnace into the ladle amounts to 1650-1720"C (occasionally, 1750~ depending on the grade of the steel. The duration of residence of the steel in the ladle ranges from 50 rain up to 2.5 h depending on the method of casting (pouring into an ingot mold or continuous casting).Previously, for lining the cavities of such ladles, the MLM-1 (according to TU 14-8-119--74) and MMK-65 (TU 14-8-337--80) mullite ramming bodies produced by the Semiluksk Refractories Factory were being used (with clay additions). Relining of the cavity was carried out whenever the nozzle is replaced, i.e., after two fillings, because of the destruction of the rammed lining.Replacing these bodies with the high-strength MK-90 (TU 14-8-457--84) corundum body produced by the 'Kazogneupor' factory made it possible to carry out ramming of the cavity of the nozzle only once during the campaign of the working layer of the base made from ladle bricks. The MK-90 body does not contain clay and the rammed lining made from it has a significantly higher density and strength than the mullitic bodies. This can be attributed to the presence of finely dispersed corundum which imparts satisfactory ramming properties and ensures the required sinterability of the body. The high strength of the rammed lining made from the MK-90 body makes it possible to change the steel casting nozzle without destructing the cavity. The MK-90 body is also used for lining the ladle base under the working layer (instead of brick lining).Using the MK-90 body for ramming the ladle base made it possible to exclude the passage of molten steel through the joints of the brick lining and the burn places (holes) of the jacket which is particularly important during continuous casting of steel. Using the MK-90 body, the rammed lining of the base is made by pneumatic ramming maintaining compressed air at a pressure of 0.5-0.6 MPa. A metallic reinforcing network (grid) is used for holding the rammed lining. After obtaining dense ramming of the base, a layer consisting of refractory pieces is placed on it. Until sintering of the lining is completed, this layer protects the rammed lining against erosion due to the stream of molten steel falling on it.When the rammed lining o...

Results of the discussion

“…2 Converter Shop of Novolipetsk Metallurgical Combine in the use of type MMK-88 compound from Semiluki Plant in 350-ton steel teeming ladles [4]. investigations [5] established that addition of 10% of crushed grinding wheels for the purpose of economy in alumina does not have a detremental effect on the service properties of the compound.Tests of mullite-corundum parts in 150-ton steel teeming ladles of the Electric Malt Shop of Oskol' Electrometallurgical Combine showed [6] that the life of unfired and fired refractories is practically the same and increases by 20-30% with the addition of chrome ore.in [7] the advantages of Kazakh Refractory Plant type MK-90 corundum compound in the service of the wells and bottoms of Cherepovets Metallurgical Combine steel teeming ladles were shown. In the opinion of the authors this is the result of the fact that the compound does not contain clay and the presence of finely dispersed corundum provides higher density and strength in comparison with mullite compounds.…”

“…In this case the service life of the bottom lining increases by four times [7]. Experi--ence in the preparation and repair of bottoms with concrete silica compounds was considered in [8].…”