Tests of refractories in stream vacuum degassing of steel with teeming in continuous casting machines

Abstract

The largest unit in the world for stream vacuum degassing of steel with teeming in a Progress continuous casting machine has been installed and placed in use in No. 2 Oxygen Converter Shop of Novolipetsk Metallurgical Combine [i, 2].In the "Progress" unit the processes of stream vacuum degassing and continuous casting of steel melted in 350-ton converters are rationally combined. The principle of its action is chown schematically in Fig. i. The metal from the steel teeming ladle I enters the vacuum chamber 2 where under the action of the vacuum degassing and refining of both the open stream and of the layer of metal on the bottom of the chamber occurs. The metal treated in the vacuum passes through the tube 3 into the pony ladle 4 and then into the mold 5 of the continuous casting machine.The advantage of such a process of vacuum degassing over batch, circulation, or ladle type units used at present is the universality and teh reduction in the time of the steel in the steel teeming ladle, which eliminates the necessity of superheating of it in the steel melting furnace. This also reduces the interaction of the metal being degassed with the ladle lining and secondary impregnation of the metal by gases during teeming.Before building at Novolipetsk Metallurgical Combine of Zhe unit for vacuum degassing of steel experience in the creation of a production lining for degassing of converter steel in equipment of this type was lacking. This article presents the results of investigations on selection of the most resistant refractories in vacuum degassing steels primarily of types 08Yu, 08GSYuT, 03KhGYu, 08ps, 06KhGSYu, etc.The temperature of the molten metal before vacuum degassing varies within limits of 1570-1600~ the rate of teeming is 0.8-0.9 m/min, and the time for teeming a single heat is 70-85 min. The protective slag in the pony ladle in contact with the outer lining of the tube is characterized by a comparatively low basicity and a high aluminum oxide content. A typical oxide content in the slag in wt.% is 23. 6-24.2 CaO, 20.1-22.7 SiO2, 35.5-39.9 A1203, 3.9-5.9 Fe203, 2.0-3.6 MgO, 7.1-8.9 MnO, and 0.7-0.9 TiO 2.The outer lining of the tube was made of MKN-94 hydraulically hardening corundum compound to Technical Specification 14-8-359-80 produced by Borovichi Refractory Combine.For the purpose of selection of the most wear resistant variation of the inner lining of the tube and of the vacuum chamber comparative tests were made in these zones of refractories of corundum and magnesia compositions. The inner lining of hte tube was made of refractory rings and the working lining of the bottom and the walls of the vacuum chamber was laid of straight and trapezoidal brick, respectively.