RU2175278C1 - Slag-forming mixture for continuous casting of steel - Google Patents

Abstract

FIELD: metallurgy, particularly, continuous casting of steel. SUBSTANCE: mixture comprises components, wt.%: carbon-containing material, 15-25; fluorite, 7-20; calcined soda, 3-15; feldspar, 7-20; sand, 15-25; slag-portland cement, the balance. Use of mixture makes it possible to prepare layer of lining slag between walls of crystallizer and semifinished product thus improving quality of semifinished products. EFFECT: improved properties of the slag-forming mixture. 2 tbl

Description

 The invention relates to ferrous metallurgy, and in particular to the composition of slag-forming mixtures for continuous casting of steel.

 Known slag-forming mixture for continuous casting of steel containing carbon-containing material, fluorspar and sand (SU 1254026 A1, C 21 C 5/54, 08/30/1986).

 The disadvantage of this slag-forming mixture is that, due to the low content in the fluxes, slag-metal "cakes" are formed on the surface of the melt in the mold, which leads to the formation of surface defects on the cast billets, and sometimes to the suspension of billets and breakthrough of liquid metal.

 The desired technical result is to improve the surface of the continuously cast billet by lowering the viscosity, the melting temperature of the mixture and providing a continuous layer of slag between the walls of the mold and the surface of the billet.

This is achieved by the fact that the slag-forming mixture for continuous casting of steel, containing carbon-containing material, fluorspar and sand, according to the invention additionally contains soda ash, feldspar and slag Portland cement in the following ratio, wt.%:
carbon-containing material - 15-25
fluorspar - 7-20
soda ash - 3-15
feldspar - 7-20
sand - 12-25
Portland cement slag - 20-35
The ratio of the components is selected in such a way that when the mixture contacts the liquid metal, a relatively low-melting slag (liquidus t = 1100-1250 ^o C) is formed, which has high refining ability and good wettability with respect to the walls of the mold.

 Slag Portland cement and sand are used as a filler in the mixture. When the content of cement and sand is within the specified limits, the basicity of the slag is equal to 0.75-0.9, and the liquid state of the slag.

 When the cement content is below 20% and with a sand fraction of more than 25%, as well as a cement fraction of more than 35% and sand of less than 12%, slag of the required composition cannot be formed.

 Fluorspar (fluorspar concentrate) is the main element that lowers the melting temperature and viscosity of the slag-forming mixture. It should be noted that fluorspar is a powerful slag thinner.

 To accurately obtain the desired melting point and viscosity, feldspar is introduced into the mixture.

 Within the specified limits of the content of fluorspar together with feldspar, the specified melting temperature and viscosity of the slag are achieved, which ensures the normal technological casting of steel with obtaining a high-quality surface of the workpieces.

 When the proportion of fluorspar is more than 20% and the specified range of feldspar content, the resulting slag is characterized by high fluidity, which leads to its high costs and deterioration of the surface quality of the workpieces.

 When the proportion of fluorspar is less than 7%, the slag viscosity rises sharply, which leads to poor slag performance and gross surface defects due to non-metallic inclusions and cracks.

 Carbon-containing material (coke, graphite, etc.) is introduced to control the SCO penetration rate, create a reducing atmosphere above the metal and slag mirror, and partially compensate for heat losses due to heat generation due to oxidation of carbon by atmospheric oxygen.

 The content of carbon-containing material in the specified range of 15-25% provides the required SCO penetration rate. When the content of carbon-containing material in the SCO is more than 25%, carburization of the metal is observed, which leads to the rejection of finished products by carbon content.

 When the graphite content is less than 15%, SCO penetration occurs in an unstable mode with the formation of slag "cakes", which leads to a deterioration of the surface of the cast billet.

 Feldspar in its composition contains oxides of alkaline earth metals, which, on the one hand, contribute to the refinement of metal from non-metallic inclusions, and on the other hand, reduce interfacial voltage, i.e. increase the wettability of the mold walls by slag, which contributes to the formation of a uniform (in thickness and in time) layer (skull) between the mold walls and the body of the workpiece.

 In the specified range of feldspar content, together with fluorspar, they provide narrowly specified viscosity and melting temperature of the mixture.

 When the content of feldspar is more than 20%, the slag melt becomes very fluid, which sharply increases the specific consumption of slag and leads to exposure of the meniscus.

 When the content of feldspar is less than 7% due to the increase in viscosity, the continuity of the skull is disrupted, which leads to local sharp cooling of the surface sections of the workpiece and the formation of surface cracks.

 Soda ash is a fluxing material; it promotes the assimilation of non-metallic inclusions, especially solid oxides (corundum) and aluminates.

 Within the specified limits, soda provides the required degree of assimilation of non-metallic inclusions. When the content of soda ash in the mixture is more than 15%, a noticeable increase in assimilation is not observed.

 With a soda content of less than 3%, the amount of non-metallic inclusions remains constant.

 The slag-forming mixture was tested during continuous casting of blooms with a section of 300x360 mm from St10, St5 steel, rail steel and workpieces with a diameter of 430 from wheel steel at drawing speeds of 0.4-0.6 m / min. The consumption of the mixture is 0.6-0.7 kg / t of steel. The process of continuous casting during use is stable. Table 1 shows some of the compositions of slag-forming mixtures, table 2 sorting of the workpieces.

 Sorting by surface defects of the workpieces cast under the proposed slag-forming mixture is 2 times less than under the prototype mixture.

 The technical effect of using the present invention consists in the formation of a uniform slag layer (skull), continuous in thickness and time, between the walls of the mold and the body of the workpiece, which determines the technological continuous casting of steel to produce workpieces of high macro-, microstructure and surface.

Sources of information
1. Japan patent N 52-17486, 1977

 2. Auth. USSR certificate N 1252353, 03/23/1986

Claims (1)

Slag-forming mixture for continuous casting of steel, containing carbon-containing material, fluorspar and sand, characterized in that it additionally contains soda ash, feldspar and slag Portland cement in the following ratio, wt.%:
Carbon-containing material - 15 - 25
Fluorspar - 7 - 20
Soda Ash - 3 - 15
Feldspar - 7 - 20
Sand - 12 - 25
Slag Portland cement - 20 - 35u

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