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1、Refractory material and tundish lining Session 14 1Dsseldorf, 27 June 1 July 2011The Tundish as a Metallurgical Reactor Dr. Patrick Tassot, Norbert Reichert, Christian Turrel Abstract: The role of the tundish in the continuous casting process has evolved from that of a buffer between the ladle and m
2、ould to being a grade separator, an inclusion removal device and a metallurgical reactor. For both grade separation and inclusion removal, the flow patterns inside the tundish play an important role. The separation of non-metallic inclusions at the interface between the steel and the slag in the tun
3、dish is to a great extent controlled by interfacial phenomena in the steelslag-inclusion system. One constant in the world of high purity, low residual and clean steels is the continual drive to reduce and control the frequency of the inclusions. For example, there are high purity, low residual clea
4、n steels such as IF-steel sheets for automobiles which require the absence of oxide inclusions with diameters larger than 100 micrometers. Strong efforts have been made to optimize the flow and turbulence in the tundish through weirs, dams or other systems. Furthermore a new system, the porous annul
5、ar well block for injecting argon, has been developed to optimize the bubble size and distribution and hence to achieve a high efficiency in trapping inclusions and in decreasing the hydrogen content in steel. Consequently, the steel quality is further improved in the tundish. Tested with success in
6、 a seamless steel shop, the new system gives results in agreement with the water models. 1. INTRODUCTION Continuous casting has gradually replaced ingot casting over the years, reaching 95% of carbon steels and specialty steels. Continuous casting offers many advantages including better premium cast
7、-metal yield, chemical homogeneity, and better inclusion cleanliness. In continuous casting process, the tundish plays an important role in linking the ladle with the continuous casting machine. The vessel is often divided into two sections: an inlet section, which generally has a pour box and where
8、 steel melt is fed from the ladle; and an outlet section from which melt is fed into the mould(s). Various flow control devices, such as dams, weirs, baffles with holes, etc., may be arranged along the length of the tundish. The tundish is intended to deliver the molten metal to the moulds evenly an
9、d at a designed throughput rate and temperature without causing contamination by inclusions. The oxidizing components, FeO, MnO, and SiO2, in ladle slag carried over to the tundish react with aluminium in the steel and form alumina clusters in steel slabs. The main causes for inclusion formation and
10、 contamination of the melt include reoxidation of the melt by air and carried over oxidizing ladle slag, entrainment of tundish and ladle slag, and emulsification of these slags into the melt. These inclusions should be floated out of the melt during its flow through the tundish before being teemed
11、into the mould. Fig 1. The tundish as reactor Refractory material and tundish lining Session 14 2Dsseldorf, 27 June 1 July 2011During transient periods (ladle change, ladle emptying), the incoming melt stream is heavily reoxidized by the ambient air and by the oxidizing ladle slag that is carried ov
12、er into the tundish with the melt. Both the reoxidation and the slag entrainment generate harmful macro oxide inclusions. The Al-deoxidized steel melt, even after removal of large particles of deoxidation product in the LF, contains a large number of suspended fine alumina particles. These particles
13、 were found to agglomerate by turbulent melt flow during the melt transfer from the ladle via the tundish to the mould, forming large alumina clusters. Non-metallic inclusions in steel are of two kinds, and each has its different mode of formation. - deoxidation of the steel melt. Most of these oxid
14、es are removed during refining and degassing of melt in the ladle, but some non-metallic oxide inclusions of small size remain suspended in the melt. - The other kind is exogenous inclusions, which form by reoxidation of deoxidized steel melt by air or by the entrained slag into the melt during the
15、melt transfer from ladle to mould. Usually, inclusions of exogenous origin are much larger than the indigenous ones, and hence are more harmful. Inclusions cause problems during the casting, rolling, and heat treating processes and sometimes result in failure of the steel during its application. Gen
16、erally speaking, steels with more demanding, processing and applications require inclusions smaller in size and number. Critical size of macro inclusions in cast semis after Ikeda1Flow control devices in the tundish increase the melt residence time and help in reducing macro inclusions originating from air reoxidation and slag emulsification. At the same time, clusters of agglomerated alumina inclusions are reduced by flotation of these inclusions. The beneficial effects of operatin
