Study Of The Nonmetallic Inclusions In The Continuous Casting Slab Q195

The characters of the inclusions in the liquid steel, especially oxide inclusions produced during deoxidizing processes affect the quality of the steel directly. Therefore, it is one of the key problems of producing the clean steel to control the deoxidization and deoxidizing products of the liquid steel. The oxide inclusions appeared in the steel are mainly coming from three parts: One is called the firstly deoxidizing products appeared at the time of alloying and final deoxidization with aluminum; one is called the secondly deoxidizing products that appear at the time of cooling steel from refine temperature to liquid temperature; another is called thirdly deoxidizing products that appear at the time of cooling the steel from liquid phase line temperature to solid phase line temperature. The nature of the firstly deoxidizing products cannot be controlled, but the quantity of them can be controlled, which is decided by the content of aluminum in the liquid steel. The composition of the secondly and thirdly deoxidizing products can be controlled through controlling the content of aluminum and calcium of the strong deoxidizing elements, making them have good distortion ability in hot work. This way not only decreases the total amount of the oxide inclusions but also reduces the size of the oxide inclusions. This is the basic technical idea to control the composition and form of the oxide inclusions.In this paper, first the inclusions of the Q195 steel continuous cast slab are researched including the type, form, quantity, size and distribution of the inclusions made by LD Ar injection treatment CC of Weiyuan Iron and Steel Company. Second, thermodynamic calculation has been carried out for the deoxidizing ability of the alkaline-earth metal alloy, at the same time the principle of control on deoxidizing products has been discussed. The relation between the composition of secondly deoxidizing products and the molten steel has been calculated, the molten steel condition of making the secondly deoxidizing products having good distortion ability is conformed; Third the influence of the liquid steel flowing on the eliminating of firstly deoxidizing products is studied; finally the distribution of the inclusion in the cast slab is discussed.According to the experiment and the thermodynamic calculation, the results are as follow:1) The nonmetal inclusions in the continuous cast slab produced by Weiyuan Ironand Steel company are mostly spherical which are oxide inclusions, the thimbleful is regular forms such as triangle which are silicate inclusions. The size is mainly smaller than 10m, accounting for more than 80%, there is less large inclusion.2) The inclusions in the cast slab are mainly aluminum silicate, the basis is Al2O3 and SiO2, there is also the oxide of Mn Ca Ti and Mg. There is little sulfide inclusion. There is also large complex inclusion, in which the centre relies mainly on AI2O3 and the periphery surrounded by a layer of aluminum silicate. The inclusions are mainly origin from the deoxidizing products and the not rising inclusions produced in the solidify course because of the balance moving.3) The distribution of inclusions in the cast slab has certain regularity. On thickness the inclusions gather in the place of 1/3 and 1/4 from surface, on the both ends inclusion relatively little; on width the inclusions gather at 1/4 from surface too, the distribution of other positions is more even.4) Because alkaline-earth metal has mutual effect, on the one hand the nature and form of the inclusions should be controlled in order to make inclusions become plasticity inclusions that are harmless to the steel. On the other hand the surface tension among inclusions and liquid steel should increased, which benefits the rise and removing of the inclusions.5) According to the thermodynamic calculation, it indicates that the area of producing liquid deoxidizing products is quite wide using SiAlCa alloy deoxidization. But the area of making the chemical compound CaO Al2O3 2SiO2-the biggest formulation ability is relativel...