SU1775478A1 - Slag-forming mixture - Google Patents

Description

The invention relates to ferrous metallurgy, in particular to the compositions of slag-forming mixtures used to protect

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metal during continuous casting of steel. The essence of the invention is to improve the quality of continuously-cast billet by reducing scrap on longitudinal cracks, increasing the assimilating ability with respect to non-metallic inclusions and improving the macrostructure of the metal. Slag-forming mixture contains graphite cryolite and a material based on a two-component system: sodium and silicon oxides, in the following ratio of components, May. %: graphite 12-28: cryolite 3-10; a material based on a two-component system: oxides of sodium and silicon 12-28, dump slag of low-carbon ferrochrome - the rest. 1 hp f-ly, 2 tab.

about

The invention relates to ferrous metallurgy, in particular to the compositions of slag-forming mixtures used to protect the metal during continuous casting of steel.

The purpose of the invention is to reduce the prevalence of cast billet surface defects, increasing the assimilating ability in relation to non-metallic inclusions and the improvement of the macrostructure.

This goal is achieved by the fact that the mixture additionally contains cryolite and a material based on a two-component system: sodium and silicon oxides - in the following ratio of components, May. %:

Graphite 12-28

Cryolite 3-10

Material based on a two-component

systems - oxides

sodium and silicon 12-28

Dump slag

low carbon

ferrochrome rest

In addition, the proposed slag-forming mixture as a material based on a two-component system - oxides of sodium and silicon contains silicate lump or soda and quartz sand in a ratio of 1: (1-1.5).

A feature of the proposed slag-forming mixture is that graphite is introduced into the composition of the slag-forming mixture in the amount of 12-28% to increase the insulating properties of slag, creating a reducing atmosphere above the metal mirror and eliminating

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the possibility of foam slag garnissage on the walls of the mold.

The minimum value of the content of graphite is limited by the fact that with a decrease in its value the necessary positive effect is not achieved. With an increase in the content of more than 28%, the carburization of the metal of the billets sharply increases, which dramatically affects the quality of the metal. ten

Cryolite is required in the mixture in the amount of 3-10% to obtain fluorine in the slag composition, which reduces the viscosity and melting point of the slag due to the formation of low-melting solutions based on 15 MaA15U4-NoA151zO8-KA12512O8 ^_ CaA12512O8 with partial replacement of oxygen by fluorine.

With an increase in the content of cryolite above the upper limit, an energetic release of volatile alkali fluoride fluoride metals begins, which adversely affects the sanitary and hygienic working conditions at the working site.

As a material based on a two-component oxide system - sodium and silicon oxides 25, the slag-forming mixture contains silicate lump or soda and quartz sand in a ratio of 1: (1-1.5).

Quartz sand is introduced into the composition of the mixture to create a basic slag-forming mixture close to one and obtain vitreous slag. Reducing the content of quartz sand below the lower limit leads to an increase in the basicity of the slag, a decrease in the melting range of 35 and, as a consequence, a high incidence of slag inclusions on the surface of the cast billet. An increase in the content of quartz sand above the upper limit leads to a decrease in the basicity, an increase in viscosity at the casting temperature and, as a result, to the impact of the surface of the cast billet by longitudinal cracks.

Soda mixture contained in the slag-forming mixture contains sodium oxides 45 and potassium, which reduce the surface tension of the slag, which increases its fluidity, which has a positive effect on the quality of the surface of the ingot.

The limits of the content of silicate lump 50 or quartz sand and soda have been established experimentally, with higher soda content corresponding to higher values of the speed of extrusion.

Waste slag from the production of low-carbon ferrochrome serves as a source of oxides of calcium, silicon, magnesium, and aluminum. Its amount of 34-73% provides the slag with the necessary assimilating capacity (properties) and the necessary basicity.

The slag-forming mixture used dump slag of the following chemical composition, May. %: CaO 44.0; MDO 5.3; 5102 21.3; MpO 4.8; A1 ₂ 0z 4.2; 5 0.14: eeOz 17.9; P2O5 0.4.

Dump slag has the following physical and mechanical properties:

Average density, g / cm ³ 3.20 Fragility,% 8.6 Activity, MPa 1.9 Structure stability,% 1.7 Metal content cobalt impurities,% 4.6 Frost resistance, Mrz 100 The resulting melt

As a result, the slag has a melting point of less than 1200 ° C, a viscosity of less than 10 poise, which ensures high quality of the ingots being cast.

In tab. 1 shows some of the compositions of slag-forming mixtures, and their physico-chemical properties in the table. 2

The mixture was tested in the casting of blooms of 250 x 300 grades of steel: Stu; St35; 70K; 70KK; 20XTNM; 40XMFA at a pull rate of up to 0.8 m / min. The casting process is stable. No harmful gas emissions are noted. Cast billets have a defect-free surface and are distinguished by high purity of the metal by non-metallic inclusions.

The use of this mixture can improve the quality of continuously cast billets and reduce the cost of the mixture compared to the known mixture.

Claims (2)

Claim 1. Slag-forming mixture for steel casting, including graphite, waste slag for the production of low-carbon ferrochrome, characterized in that, in order to reduce the incidence of cast billet surface defects, increase the assimilating ability in relation to non-metallic inclusions and improve the macrostructure, it additionally contains cryolite and material the basis of a two-component system - oxides of sodium and silicon - in the following ratio of components, May. %: Graphite 12-28 Cryolite 3-10 Material based two-component oxide systems sodium and silicon 12-28 Dump slag low carbon ferrochrome rest five 1775478 6 2. A mixture of pop. 1, characterized in that as a material based on a two-component oxide system - oxides of sodium and silicon - it contains silicate lump or soda and quartz sand in a ratio of 1: 1-1.5. Table 1 Component The content of components, wt.%, In the mixture one 2 3 G raffit 28 23 12 Cryolite ten eight 3 Soda 28 sixteen 12 Quartz sand in the ratio 1: (1-1,5) Dump slag 34 53 73 table 2 Physicochemical properties Composition № 1 №2 Number 3 Melting point, ° С Start 1190 1190 1190 end 1290 1290 1290 Viscosity, P. at 1300 ° С 4.8 4.8 4.8 Surface tension, MJ / m ² 430 430 430 Stripping percentage. % on surface cracks 20-30 20-30 20-30 on slag inclusions 12-16 12-16 • 12-16 Number of defects mm defects / meter billet 2.8-5.0 2.8-5.0 2.8-5.0 Depth of cracks ·, mm 0.5-1.8 0.5-1.8 0.5-1.8 Depth of inclusion, mm 0.7-1.9 0.6-1.9 0.7-1.9