RU2351659C2 - Technique of containment shell forming on surface of deoxidising agent of liquid steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy. Particularly it relates to forming of protective steel envelope on the surface of deoxidising agent of liquid steel, for instance, aluminium. In the capacity of material for protective envelope there are used residuals of steel shot in the form of steel particles with size 0.2-1.5 mm and metallic dust. Additionally protective envelope is formed by means of introduction into deoxidising agent surface residuals of steel shot and following its increasing by means of additional pasting, consisting of metallic dust and hydrocarbon binding agent, at mass ratio of deoxidising agent with protective envelope material 1:(0.2÷0.8).

EFFECT: reduction of deoxidising agent waste and costs for forming of protective envelope.

4 cl, 1 tbl

Description

The invention relates to metallurgy, in particular the development of a method for forming a protective shell on a deoxidizer used for deoxidation of steel, mainly in a melting unit. For example, when steel is smelted in an electric arc furnace (DSP) at the end of the oxidation and at the beginning of the recovery periods of the smelting, the oxygen content in the steel depends on the carbon content in it. Upon receipt of medium-carbon and high-carbon steels, the oxygen content in these periods is in the range of 0.01–0.02%, and in low-carbon steels it can reach 0.1–0.2% [1, p.224]. Deoxidation of the first two steels is carried out with silicon in the form of ferrosilicon, manganese in the form of metallic manganese or ferromanganese, and in the latter case, additionally with aluminum.

The aluminum consumption is determined by the oxygen content in the steel, which is associated with the oxidation of the final slag in the furnace and the carbon content [2, p.228]. Aluminum, like magnesium, calcium differs from other elements in the instability of assimilation due to the large difference in their physical properties compared to the base melt. Aluminum, having a density of about 3 times less than that of liquid steel, and less than that of liquid slag, floats on the surface of the slag. Most aluminum is oxidized by the furnace atmosphere and slag components. Having a greater affinity for oxygen, aluminum reduces silicon, manganese, and iron from their oxides - components of slag.

To eliminate this drawback, it is proposed to deoxidize steel with ferroaluminium, an alloy of iron with 30–50% aluminum. The density of the alloy (~ 5000 kg / m ³ ) is slightly lower than that of liquid steel (~ 7000 kg / m ³ ), but significantly higher than that of slag (~ 3000 kg / m ³ ). Ferroaluminium is more easily immersed in the volume of liquid steel and aluminum is more fully absorbed from it. However, such an alloy is more expensive than aluminum and its melting temperature (~ 1400 ° C) is much higher. Aluminum in it is in the form of intermetallic compounds, the assimilation of aluminum from ferroaluminium occurs more slowly and with less thermal effect [3, p. 178].

A particularly high consumption of aluminum is observed during the smelting of low-carbon high-chromium steels using oxygen in the oxidation period. After purging of the high-chromium melt, a large amount of slag is formed. According to [4, pp. 57-59] after the melting of the added waste of high-alloy scrap metal is deoxidized with lumpy 45% FS45 ferrosilicon (8 ÷ 12 kg / t) and aluminum (2 ÷ 3 kg / t), together with this, 10 ÷ 15 kg of lime and 3 ÷ 5 kg of fluorspar to increase slag basicity.

According to [5, p.159], after oxygen purging of high-chromium steel, the slag is 70–90% downloaded, 0.5% manganese and lump FS-45 0.2% silicon are planted in the furnace sequentially, and 4–5 silica-calcium kg / t and primary aluminum - 1 kg / t, then ferrochrome.

An analysis of the chemical composition of the metal showed that the aluminum content in the steel after its deoxidation in furnaces with a capacity of 0.3 ÷ 18 t is in the range of 0.005 ÷ 0.020% wt. Thus, the absorption of aluminum in medium-sized furnaces is only 5–10% when halves of standard aluminum ingots are introduced onto the metal surface.

The purpose of the invention: to increase the efficiency of deoxidation of liquid steel with a strong deoxidizer (for example, aluminum). The goal is achieved by developing a new method of forming a protective shell on the surface of the deoxidizer and the use of production waste (metal dust or crushed shots).

There are two directions in matters of increasing the degree of assimilation of aluminum in particleboard.

1. To protect or significantly reduce the possibility of contact of the surface of aluminum ingots with the atmosphere of the furnace and liquid slag.

2. Create conditions for the rapid immersion of aluminum in molten steel.

A known method of forming on the surface of the deoxidizing agent of the slag shell [6]. This method was developed for small fractions of ferromanganese. For aluminum, it is unacceptable for the following reasons:

a) a piece of aluminum represents half or 1/3 of the standard ingots. Slag after pouring it onto aluminum and subsequent cooling will peel off from the flat and smooth surface of aluminum. Liquid slag when pouring ferroalloys fills the space between them, creating an inner frame that holds it from the outside;

b) when the surface of aluminum is heated to the temperature of liquid slag, it will be oxidized due to slag oxides - SiO ₂ , FeO, MnO. Therefore, this option is not used in production.

A known method of processing steel is that a deoxidizer is obtained in the form of a composite with aluminum as a low-melting matrix component and particles of an alloy based on iron as a high-melting reinforcing component, and the dissolution of the composite deoxidizer in liquid steel is started at a density ratio of at least 0, 5, continue with its continuous increase to 1.0 ÷ 1.1 and end at 0.9 ÷ 1.1. In the process of dissolution of aluminum, a composite deoxidizer disperses into individual fragments [7].

The same authors [8] indicate that the method is intended for the deoxidation of steel by aluminum. Aluminum in the composite acts as a deoxidizing agent, and particles of iron or an alloy based on it act as a weighting agent. Mass fractions of matrix and reinforcing components are within 25/75 ÷ 50/50, and the particle size of steel or cast iron is 0.5 ÷ 10 mm.

The application of the method described in both sources is limited. For example, by the ratio of the densities of the composite deoxidizer and liquid steel (1: 1), the mass of the reinforcing element can be calculated. The most common metal present in any production is St35, St45, having a carbon content of 0.32 ÷ 0.48%. For calculations, we take 0.35%. We carry out calculations by solving a system of equations with 2 unknowns:

where [Al] and [St35] are the fractions of aluminum and the reinforcing additive in the composite deoxidizer, 7.0 (g / cm ³ ) is the density of liquid steel.

Calculations showed: [St35] = 0.843; [Al] = 0.157 or 84.3% and 15.7%, respectively.

At the same time, we add carbon [C] to the steel with a minimum aluminum addition of 1 kg / t:

1 kg / t - 15.7% X = 84.3 · 1 / 15.7 = 5.37 kg [St35]

X kg / t - 84.3%

[C] = 5.37 kg · 0.35 = 1.88 kg or 0.18%, which is unacceptable in the production of low carbon steel.

If the mass fraction of the reinforcing component [7] is 75% of the mass of the composite deoxidizer, then the maximum density of the composite deoxidizer will be: ρ _to = 2.7 · 0.25 + 7.8 · 0.75 = 6.525 g / cm ³ . At 50% deoxidizer ρ _k = 2.7 · 0.5 + 7.8 · 0.5 = 4.25 g / cm ³ , which is lower than the density of liquid steel - 7.0 ÷ 7.2 g / cm ³ . The composite deoxidizer will not sink anyway, it will be oxidized by the atmosphere of the furnace, and when softened, the steel reinforcing elements having a density of 7.8 g / cm ³ will also fall apart and quickly drown in liquid steel.

A device for introducing additives into the melt [9] is known: a weighting agent (cast iron, steel, heavy metals, their alloys) is made with one or more holes filled with additives (Ti, B, Al, ЩЗМ, РЗМ), or the additive is mounted on a weighting agent and partially enclosed in a shell, or a weighting agent partially enclosed in a shell of an additive. The ratio of the mass of the additive to the mass of the weighting agent is 1: (2 ÷ 8).

The simplest calculations show that when the weight of the weighting agent is 8 times the mass of aluminum, the average density of the component (7.2 g / cm ³ ) will be approximately equal to the density of liquid steel. Thus, these deoxidation devices do not provide a quick immersion of the deoxidizer in the melt. This virtually eliminates the use of the third type of device when the weighting agent is coated with aluminum. More favorable is the second type of device, when the additive (aluminum) is mounted on the weighting agent and, thus, partially enclosed in the shell of the weighting agent. This partially eliminates the contact of aluminum with the atmosphere of the furnace and liquid slag. The weighting agent can be fixed with wire, but it will burn immediately and the components will separate. If welding is used to fasten steel plates, this increases the cost of steel.

Closest to the proposed first type of device, when the weighting agent is made with one or more holes filled with aluminum. In this case, almost completely the contact of aluminum with the atmosphere of the furnace and slag is excluded.

The disadvantage of this device is the high cost of its manufacture, which consist of the following factors:

1. Purchase of metal of a certain chemical composition and profile, for example, rolled metal, or its manufacture.

2. The complexity of machining (drilling) and the cost of the tool.

3. Organization of an additional redistribution for the melting of primary aluminum or waste from the production of aluminum castings and pouring it into a weighting agent (additional redistribution).

4. Loss on aluminum slag during smelting.

5. Large energy costs.

The deoxidation efficiency is ultimately determined by the cost of obtaining 1 ton of molten steel or steel billet.

Thus, at present, there is no effective way to protect the active deoxidizer (aluminum) of steel in the working space of the melting unit from surface oxidation by the furnace atmosphere and liquid slags.

The proposed method of forming a protective shell of steel is that an aluminum piece (ingot) is preliminarily coated with waste steel fractions at a mass ratio of 1: (0.2 ÷ 0.8). The density of such a deoxidizer is in the range of 3.5 ÷ 5.6 g / cm ³ , which is higher than the density of the slag and allows the deoxidizer to be immersed through the slag to a metal level. Shot wastes after shot blasting operations for cleaning castings and forgings are steel particles, as a rule, of a flattened shape of 0.2 ÷ 1.5 mm in size and metal dust. This waste is mixed with scale and sand and taken to a landfill. It is possible to separate metal components from non-metallic ones with the help of a magnetic washer available at any metallurgical enterprise, while the cost of waste removal is reduced.

A protective layer is formed in two ways.

1. Metal waste fractions are poured into a steel container, an aluminum ingot is placed horizontally inside, rammed and the container is placed in a thermal furnace. Exposure is carried out at a temperature of the onset of softening of aluminum 660 ° C (melting point of pure aluminum). If a load is placed on the surface of a heated shot, the weight of which provides pressure on the surface of an aluminum ingot 2 ÷ 3 kg / cm ² , then the metal particles are fused into the aluminum surface in a continuous layer. The exposure time of a container with a wall thickness of 10 mm, when it contains an ingot of aluminum weighing 8 ÷ 8.2 kg, and the thickness of the layer of waste fractions is 50 ÷ 70 mm, only 4 hours, while the energy consumption is much less than during the remelting process of aluminum.

2. The pellets are driven by impact method into the surface of the ingot of primary aluminum. Paste can be made from metal dust, where sulfide-yeast mash (SDB) can be used as a binder. This liquid is a solution of hydrocarbon compounds in water with a density of 1.24 ÷ 1.27 g / cm ³ . The paste can easily be applied to the surface of small grains, and the pores will be well filled with dusty metal particles. SDB dries in a thin layer with virtually no heat.

An important advantage of the proposed method is the lack of influence of the chemical composition of the steel material due to its small amount: 1.25–5 times less, in the analogue 2–8 times more than the deoxidizing agent.

We tested various deoxidizing agents in steel 20 smelting in an 6T steel arc furnace.

After the oxidation period, slag was downloaded by 70–80%, steel was deoxidized in small portions of ferrosilicon and ferromanganese to their calculated content of 0.2% wt. each until the end of the visible bale. Then, a piece of aluminum weighing 6-6.3 kg was thrown into the middle of the bath at the rate of 1 kg / t. In option 1, aluminum was without a shell, and in options 2 and 3 - in shells. Five minutes later, samples were taken for analysis. The results are shown in the table.

The presented results show that the degree of assimilation of aluminum in options 2 and 3 are quite comparable, but the costs of manufacturing a deoxidizer are very different.

The use of operations of melting and casting aluminum, drilling holes in the weighting agent is 2–3 times more expensive than the operation of holding it in a thermal furnace.

The amount of assimilation of aluminum during deoxidation of steel by various deoxidants No. p / p Deoxidizer The content of elements,% wt. The amount of assimilation of aluminum,% FROM Si Mn Al one Standard 0.09
0.08
0.10
0.10
0.09 0.15
0.17
0.19
0.20
0.18 0.29
0.31
0.25
0.28
0.27 0.005
0.010
0.005
0.015
next 5
10
5
fifteen
0 2 Analogue 0.10
0.11
0.09
0.08
0.10 0.18
0.21
0.17
0.16
0.17 0.26
0.30
0.28
0.28
0.29 0,035
0,035
0,030
0,025
0,030 35
35
thirty
25
thirty 3 Proposed 0.09
0.08
0.09
0.09
0.08
0.08
0.10
0.09 0.16
0.18
0.17
0.15
0.17
0.16
0.17
0.18 0.26
0.30
0.28
0.29
0.31
0.28
0.29
0.31 0,030
0,035
0,025
0,025
0,030
0,035
0,035
0,020 thirty
35
25
25 *
thirty
35
35
twenty* * - a method of stuffing fractions and applying paste.

LITERATURE

1. Kramarov AD, Sokolov AN, Electrometallurgy of steel and ferroalloys. M .: Metallurgy, 1976, 376 p.

2. Trubin N.G., Oyks G.N. Metallurgy of steel. M .: Metallurgy, 1970, 621 p.

3. Ten E.B., Petrovsky P.V. Iron-aluminum composite liquid steel deoxidizer. / Proceedings of the V Congress of Foundry Workers of Russia, Moscow, RAL, 2001, p.178-180.

4. Murakhovsky I.M., Kulakov Yu.A., Dashevsky V.D. and others. Improving the technology of smelting stainless steel in electric furnaces of medium capacity. // Sat "Production of electric steel", No. 8, 1980; M .: Minchermet, p. 57-60.

5. Borodulin G.M., Moshkevich E.I. Stainless steel, M .: Metallurgy, 1973, 319 p.

6. Application No. 2005128231/20 (031701) Stadnichuk V.I., Stadnichuk A.V., Merker E.E. The method of deoxidation and alloying of metal melts (not published).

7. Patent No. 2208053. Teng E.B. The method of processing steel, BIMP No. 19, 2003, S. 684.

8. Patent No. 2192495. Teng E.B. Deoxidizing agent. BIMP No. 31, 2002, S. 464.

9. Patent No. 26054. A device for introducing additives into the melt. Krinochkin E.V., Karpov A.A., Scherbakov S.A. and other BIMP No. 31, 2002, S. 573.

Claims (4)

1. The method of forming a protective steel shell on the surface of a deoxidizer of liquid steel, characterized in that the material of the protective shell using waste steel shot in the form of steel particles with a size of 0.2-1.5 mm and metal dust, while the protective shell is formed by the introduction into the surface of the deoxidizer of waste steel fractions and the subsequent increase in its thickness by additional coating with a paste consisting of metal dust and a hydrocarbon binder, with a mass ratio of deoxidizer to the protective material hydrochloric shell 1: (0,2 ÷ 0,8). 2. The method according to claim 1, characterized in that the introduction of the particles of the fraction is carried out during the aging of the deoxidizer at the temperature of the beginning of its melting in the layer of particles of steel shot with a thickness of 50 ÷ 70 mm for 4 hours under a pressure of 2 ÷ 3 kg / cm ² . 3. The method according to claim 1, characterized in that the introduction of particles of steel shot when using a milder deoxidizer is carried out in the surface of the deoxidizer by the impact method. 4. The method according to claim 3, characterized in that aluminum is used as a deoxidizing agent.