Development and introduction of energy saving materials for steel pouring

The amount of steel poured into molds has been reduced considerably. Nonetheless, in some metallurgical enterprises and within the engineering complex, the method of pouring steel into a mold remains the basic one. Currently with bottom pouring of various steel grades, including alloy steels, various methods are used for action on molten metal in order to achieve some required surface quality for the ingot obtained and its microstructure. In particular, so-called readily-melting slag-forming mixes are used, which between the area of ingot solidification and the mold internal surface form a thixotropic layer reducing interphase tension. Heat insulation material is used in order to overcome shrinkage defects within the top of an ingot, as a result of whose action there is effective retention of physical heat of the melt for quite a long period [1, pp. 284 – 290]. Sometimes heat insulation material is replaced by exothermic mixes, compensating for heat loss [2]. There is a well-known method for warming the head part of a steel ingot with a heat insulating cover, not touching liquid metal, and a simultaneous supply of an exothermic mix to the steel surface [3]. The disadvantages of the method are the labor content, caused by introduction of two additional operations, and ineffective heat insulation. There is also a method [4] used during steel pouring employing heat insulation material containing 88 – 92 wt.% thermal power station ash and 8 – 12% of fuel shale. The drawback of this method is organization of three operations for material supply, its quite high consumption (3.6 kg/ton), increased gas content of an area of the melt, low heat insulation capacity, and also the possibility of impregnating the metal with hydrogen from fuel shale volatiles. It should be noted that supply of heat insulation material in the period of filling a mold, for example suspension of a container with materials within a mold, makes the process of slag formation difficult in its bottom part. Therefore an ingot surface, corresponding to this part of a mold, contains a considerable amount of surface defects. As a mold is filled with liquid metal the heat insulation material starts to float, and this gives rise to a requirement for using an exothermic mix. Its action develops during some quite considerable time (3 – 5 min), i.e., when the metal is almost filling a mold, and the heat insulation material is warmed to red heat and loses its heat insulation properties. It is apparent that with this method there is ineffective use of the exothermic mix itself. Colleagues of OOO Ogneupor Trade Group have developed a method [5] for use of heat insulation and slag forming materials during steel pouring into a mold. The technical results of its application consist of a marked increase in slag forming mix melting rate, and as a consequence of this a reduction in surface defects and defects of the macrostructure of an ingot formed without application of an exothermic mix, but a simultaneous reduction in heat insulation material. The heat insulation material used is Isotherm-1600. The slag forming mix is supplied in a polyethylene package to the bottom of a mold before entry of liquid metal. The operation of adding heat insulation material is accomplished in parts. The first small part is during 3 – 10 sec after entry of metal into a mold to the outer solid surface with a polyethylene shell. The second, larger part, is supplied to a layer of liquid slag or to the residual layer of heat insulation material remaining on the molten slag surface after its ascent into the top of a mold. Refractories and Industrial Ceramics Vol. 52, No. 4, November, 2011