HK1090957A1 - Method for a direct steel alloying - Google Patents

Abstract

The inventive direct steel alloying method relates to the iron and steel industry and can be used for steel production by means of a direct alloying process. Said direct steel alloying method consists in making steel in a steelmaking vessel, alloying the thus produced steel with manganese reduced from oxides during the supply of a manganese oxides-containing material and a reducing agent and the interaction thereof. The manganese reduction is carried out in association with the reduction of other alloying elements from a material containing non-metallic compounds thereof and supplied on the molten metal surface. The reducing agent is added when the height of the layer of the supplied material which contains the non-metallic compounds of alloying elements attains 0.1-0.15 of the total layer height. A reduction temperature is maintained at a level of the flowing temperature of the supplied material, a permanent contact of the molten part of the reducing element with the molten part of the supplied material containing non-metallic compounds of alloying elements being also maintained. The reducing element is supplied in a quantity ensuring the required thermal characteristics of the mixture of the supplied material and the reducing agent. Said method ensures a high recovery of alloying elements by metal, reduces steel contamination with non-metallic impurities and improves the quality thereof.

Description

Direct steel alloying method

Technical Field

The present invention relates generally to ferrous metallurgy and is applicable to the production of steel using a direct alloying process.

Technical Field

Worldwide, the trend to improve the quality of steel, in particular to produce steel with low or even ultra-low contents of carbon, gases and impurities, is increasingly important, in order to have the required parameters of the steel before casting, which makes changes in the existing melting processes, mainly the out-of-furnace (out-of-furnace) treatment. In this connection, it is strictly required that the steel has a predetermined composition while each element has a narrow content range. For this reason, the methods and process steps that enable controlled alloy recovery and modification additive recovery from the steel are of significant importance.

In view of the fact that in conventional steel production practice, regardless of the grade of steel to be produced, a low carbon product is melted in a steelmaking furnace and then the product is given the required parameters in the steel refining system, there is a necessity to subject the low carbon product to a deoxidation treatment prior to alloying. In this case, the metal inevitably contains saturated non-metallic impurities, oxidation products of the deoxidation reaction, and in order to modify or remove the oxidation products, additional measures that require energy and material consumption must be taken. The next step of the out-of-furnace treatment, the alloying of the steel, is also accompanied by the formation of a certain amount of non-metallic impurities. For the pre-deoxidation of steel, the use of materials that do not form non-metallic impurities, such as coke or coal, would lead to considerable heat losses, which must be compensated for by reheating the carbon-containing semifinished product before discharge, which leads to excessive costs and impairs the quality of the steel.

Conventional methods for alloying steel with manganese include: melting steel in a steelmaking furnace, tapping the steel into a ladle, charging alloying materials and blowing inert gas, wherein after metal tapping, low-phosphorus manganese-containing slag of ferroalloy industry, a reducing agent and lime are charged onto a molten surface in the ladle in such amounts that the basicity of the slag is 2.0 to 3.5, and then oxygen is injected onto the surface of the molten pool for 3 to 30 seconds (SU1044641, international classification No. C21C 7/00, 1983).

However, this conventional method is not suitable for the production of high quality steel because the oxide material containing alloying additives, manganese, a reducing agent and lime are simultaneously charged onto the surface of a semi-finished product containing carbon in a ladle after tapping from a steel furnace, and then oxygen is blown in, making it difficult to control the steel alloying process with manganese, thereby preventing the achievement of high recovery rate of manganese from steel and high desulfurization degree.

After deep pre-deoxidation of the metals, the sulphur content of the steel can be reduced by treatment with desulphurisation materials, which requires, for example, their maximum contact with the metals by vigorous stirring.

In the conventional method, the high-basicity slag, which is formed after direct alloying of steel with manganese and exhibits a certain sulfide content, cannot provide deep desulfurization of steel due to lack of strong stirring.

The process is therefore not suitable for obtaining low sulphur contents in steel.

When steel is directly alloyed with manganese, oxygen injected onto the surface of the metal increases the oxygen content in the metal, which increases the consumption of reducing agents, reduces the recovery rate of manganese from molten metal, deteriorates desulfurization conditions, and increases the contamination of steel with non-metallic impurities of oxides and sulfides, i.e., deteriorates the quality of steel.

The joint addition of raw materials to the ladle when tapping the carbonaceous semifinished product reduces the recovery of the alloying elements, manganese and this fact, together with the uncontrollable speed of the alloying process, impairs the quality of the steel.

When steel is produced according to the conventional method, the efficiency of the steel furnace will be reduced as compared with the method of alloying steel with iron alloy, because all raw materials are charged into a ladle when a carbon-containing semi-finished product is tapped from the ladle, which makes the alloying process longer because additional time is required to melt the charged raw materials.

Manganese in low-phosphorus manganese-containing slag in ferroalloy production is in the form of a chemically stable compound, MnSiO₃. When the consumed lime is used in an amount such that the basicity of the slag is 2.0 to 3.5 and added to the ladle together with the low-phosphorus manganese-containing slag before the reduction reaction of manganese starts, a stable compound having a high melting point (more than 1400 ℃) is formed in the slag together with calcium silicate and free lime. When manganese silicates are reduced with silicon, refractory calcium silicates Ca are still formed in the slag, although the presence of lime helps to break the chemical bonds of the manganese silicates₂SiO₄And Ca₃SiO₅And results in slag having a high melting point temperature, which increases slag viscosity, decreases recovery of manganese, increases the content of non-metallic impurities, and deteriorates the quality of steel.

Also, the manganese oxide-containing material used as an alloying material in the conventional method is expensive and energy-intensive because its production requires a large amount of electric energy to be consumed.

Another conventional method of producing steel includes: melting, deoxidizing, alloying, producing molten metal containing silicon and aluminum as reducing agents, adding CaO/Mn to the molten metal in a steelmaking furnace_xO_yAdding an oxide mixture containing manganese oxide and calcium oxide at a ratio of 0.6 to 1.2, and treating the molten metal in a ladle with a slag formed when reducing manganese from silicon and aluminum dissolved in the metal, the treatment being performed while keeping the molten metal at a slag basicity of CaO/SiO₂0.7-1.8, and then further adding a silicon-containing reducing agent and an oxide mixture to the molten metal (RU 2096491C 1, international code No. C21C 7/00, 1997).

In the method, pre-deoxidation and alloying of the metal is carried out in a steelmaking furnace in the presence of oxidic slag and highly oxidised metal. This not only results in excessive consumption of oxidizing agents and alloying additives that can react with the iron oxides in the slag, but also increases the metal contamination by non-metallic impurities that are hardly removable, including silicates, aluminates and sulfides of manganese and iron. In this method, the metal is then treated with reduced manganese from the manganese oxide in a ladle while a silicon-containing reductant, a ferrosilicon alloy, is added to the ladle. The manganese reduction process is carried out in a diffused state, which inevitably requires additional time to carry out. In addition, since the silicate newly formed in the manganese reduction reaction is added, the amount of silicate, aluminate and sulfide previously formed in the steel making furnace increases. When there is no means for spheroidizing inclusions and there is high silica slag formed on the surface of the metal, the method cannot remove non-metallic inclusions from the metal body to form slag, which results in increased contamination of the metal with oxide and sulfide inclusions and deteriorates the quality of the metal.

This method creates unfavorable conditions for the reduction of manganese because the addition of the oxide mixture to the molten metal, wherein the amount of the ballast additive (CaO) is 1/2-2/3 of the total amount of the mixture, worsens the melting conditions, increases the time and heat required for its melting, which is considered to be of considerable importance when the reducing agent added together with the oxide mixture is a substance (silicon) having lower activity than aluminum. The use of silicon containing reducing agents is quite severe with possible local overheating of the mixture and reducing agent. The use of a siliceous reductant is associated with possible local overheating of the mixture and the reductant and, therefore, with its floating on the surface of the molten slag and with the oxygen in the atmosphere. Although the loss of siliceous reducing agent into the gas phase is negligible, the silicon oxides formed in the manganese reduction reaction worsen the thermodynamic conditions of manganese reduction, which leads to an increase in the consumption of calcium-containing oxides (lime) and an increase in the energy consumption for heating the oxide mixture. The thermal characteristics of the oxide mixture, even in combination with the aluminium and silicon previously added to the molten metal, do not provide a spontaneous reduction process and are due to the SiO in the slag₂The increase in part compromises manganese reduction performance by providing additional consumption of silicon-containing reductant to compensate for the heat of chemistry.

Disclosure of Invention

It is an object of the present invention to provide an improved method for direct alloying of steel by optimization of the preparation method. The invention ensures favorable physical, chemical and temperature conditions for simultaneous melting and reduction of the added raw materials, which improves recovery of alloying elements in the metal, reduces contamination of steel by non-metallic inclusions, and improves the quality of the steel.

The object of the present invention is to obtain a direct alloying method of steel comprising the following steps: melting steel in a steelmaking furnace; alloying of steel with manganese, said manganese being reduced from oxides of manganese during addition of raw materials comprising oxides of said manganese and reducing agents and during reaction of both, wherein according to the invention the reduction of manganese from oxides is carried out in combination with reduction of other alloying elements in raw materials from non-metallic compounds comprising alloying elements added onto the surface of the molten metal; and/or in combination with the reduction of manganese from the charged feedstock comprising other non-metallic manganese compounds; when the layer height of the added raw materials is 0.1-0.15 of the total layer height, adding a reducing agent; the reduction temperature is maintained at the melting temperature of the added raw materials and the reducing agent; the molten portion of the reducing agent is kept in continuous contact with the molten portion of the added raw material of the non-metallic compound containing the alloying element in an amount such that the mixture of the added raw material and the reducing agent is ensured to have the desired thermal characteristics.

The raw material of the non-metallic compound comprising the alloying element preferably comprises an oxide or a carbonate of the alloying element, or a combination thereof.

The reducing agent is preferably an aluminium-or silicon-containing, or carbon-containing material, or an alkaline earth metal-containing material, or a combination thereof.

The charging of the raw materials of the non-metallic compound containing the alloying element is preferably carried out continuously or in batches, each batch in an amount of not less than 0.1 of the total consumption amount.

In a direct steel alloying method in a steelmaking furnace, when the molten metal reaches a temperature higher than the tapping temperature by a value determined by the formula Δ t-33 [ Mn ], wherein: delta t is a value exceeding the tapping temperature, DEG C; [ Mn ] is the amount of reduced manganese, in weight percent; 33 is an empirical coefficient, it is preferable to further add a slag-forming material and a carbonaceous material serving as a reducing agent, and it is preferable to add: the raw material of the non-metallic compound containing alloying elements, the slag-forming material and the carbon-containing material are respectively in a ratio of 1: 0.18-0.20: 0.10-0.12, and preferably, the oxidized slag is removed from the steel furnace.

When alloying of steel is performed in a steelmaking furnace, it is preferable that raw materials of non-metallic compounds including alloying elements, slag forming materials, and carbonaceous materials are added in portions, and the weight of each portion including all supplied raw materials is 0.01 to 0.02 of the weight of molten metal.

When the direct steel alloying method is performed in a ladle, it is preferable to previously add a carbonaceous material to the ladle; the reducing agent is preferably aluminum; in the alloying process, lime is preferably additionally added as a slagging material, and the following components are preferably adopted in percentage by weight: raw materials of non-metallic compounds containing alloying elements: 56-65 parts; aluminum: 12-16; carbon-containing material: 5-7; lime: and (4) the balance.

When alloying of the steel with chromium in the ladle, the non-metallic compound of the other element is preferably a chromium compound, which can be added to the ladle during tapping of the molten metal; in order to increase the manganese and chromium contents by 0.1% in the finished steel, the chromium oxide is preferably added in a manganese-chromium ratio of 1.1 to 1.2 in the material comprising the nonmetallic compounds of these elements, and the aluminum used as a reducing agent is preferably added together with calcium carbide in a ratio of 1: 2.9 to 3.2.

When the steel is alloyed with chromium in a ladle, the raw material containing chromium oxides is preferably converter slag in medium carbon ferrochrome production.

The process according to the invention relies on the principle of implementation according to which a reduction in the temperature of the reaction zone contributes to an increase in the equilibrium constant of the reaction and therefore to the completeness of the reaction; for this purpose, the method according to the invention ensures the following conditions:

1. the direct alloying process maintains a minimum temperature in the alloying element reduction reaction zone at a minimum viscosity to form slag, and has blast furnace slag adsorption capacity on the oxide products of the reduction reaction-the oxides of the active elements contained in the reductant.

2. The continued presence of the starting reaction components in the reaction zone throughout the reduction reaction: raw materials of the coating compound and a reducing agent.

3. The reduced alloying element is removed from the reaction zone of the reaction product, allowed to enter the metal body, and the formed oxide of the reducing agent active element is allowed to enter the slag phase.

Because the alloying elements are soluble in the molten iron, e.g., manganese is infinitely soluble in the molten iron, the reduced manganese particles can be immediately absorbed by the molten metal and convectively flowed, always present in the molten metal mass, removing the layer formed by the reduced elements enriched in the molten metal mass, thus averaging the composition with respect to the alloying elements, manganese. Other reducible alloying elements may also be strongly soluble in the metal body in the presence of the reduced manganese particles, since the reduction reaction takes place in liquid phase conditions and therefore does not prevent their dissolution in the molten metal.

The reducing agent is added in an amount capable of providing the desired thermal properties (thermal) to the feed mixture comprising manganese oxide, other alloying elements, and/or other non-metallic manganese compounds and the reducing agent.

For the spontaneous reaction of the reduction reaction of the elements from the oxides and carbonates, a specific potential heat source of a specific material mixture comprising non-metallic compounds of the alloying elements and reducing agents is required, which heat source not only melts the raw material and reduces the alloying elements, but also effectively separates the metals and the slag phase being formed. In direct steel alloying using materials comprising non-metallic compounds of alloying elements (the alloying elements being in the form of oxides and carbonates) and reducing agents, favourable thermal conditions for the reduction reaction process can be created, since together with the exothermic reduction reaction heat, the molten metal, the inner surfaces of the steel furnace, etc. can provide an additional heat source. In this case, together with a quantitative heat supplied to the reaction zone, conditions capable of preventing combustion of the highly active element, the reducing agent, and removing it to the gas phase can be provided. Thus, the thermal properties of each particular mixture can be selected experimentally to provide spontaneous reduction with minimal loss of reducing agent.

After the addition of the reducing agent, the surface of the reducing agent is first covered with slag and metal. But since the melting point of the reducing agent is lower than that of the metal and slag, the reducing agent melts and the process is accompanied by the rupture of the attached shell, thereby forming a continuous contact between the molten portion formed by the reducing agent and the homogeneous composition of the alloying material that has been melted, the contact being continuously maintained by the exothermic reaction heat of the reduction reaction of the alloying elements. This can provide a simultaneous process of melting of the added raw materials and reduction reaction of the alloying elements.

Detailed Description

The direct alloying method of steel is accomplished in the following manner.

Molten iron is charged into a steel-making furnace such as an oxygen converter, a shaft furnace, etc., and then slag-forming materials (lime, dolomite, spar) are added to blow oxygen into the melt. After the removal of the oxidic slag, a raw material comprising oxides of manganese, non-metallic compounds of other alloying elements, and/or comprising other non-metallic manganese compounds is charged onto the surface of the molten metal. The raw material containing the non-metallic compounds may be manganese ore, concentrate, slag produced from ferroalloy, etc. The non-metallic compound of the other alloying element may be a compound containing an oxide of the alloying element such as niobium, titanium, molybdenum, chromium, or a carbonate of the alloying element such as titanium oxycarbonitride, niobium carbonate, an alkaline earth metal, or the like, or a combination thereof. The raw materials of the non-metallic compound containing the alloying elements may be fed continuously or in batches, each batch in an amount of not less than 0.1 times the total consumption amount, according to the predetermined composition of the steel. The melting of the supplied raw materials is synchronized with the reduction of the alloying elements thereby, whereby the batch feeding of the raw materials containing the non-metallic compounds of the alloying elements is directed. Reducing the amount of raw material fed in a batch to less than 0.1 of the total consumption will hamper the melting process because the raw material is slagged to increase the melting time, resulting in an inefficient use of the reducing agent and a reduced recovery of molten metal of the elements obtained by reduction of the raw material comprising the alloying element compounds.

And when the layer height of the added raw material of the nonmetallic compound containing the alloying elements reaches 0.1-0.15 of the total height, starting to add the reducing agent, and continuing to add the reducing agent in the process of further adding the raw material.

The reducing agent is an aluminum-containing, or silicon-containing, or carbon-containing material, or a group of alkaline earth metals, or a combination thereof. The flake composition may vary from 1.0-3.0mm to 20-50mm or more depending on the reducing agent selected. The reducing agent is added in an amount that provides the desired thermal properties to the mixture of added feedstock and reducing agent.

The addition of non-metallic compounds containing oxides of manganese, other alloying elements, and/or raw materials containing other non-metallic manganese compounds is directed by bringing the temperature of the raw materials being melted to a temperature lower than the temperature of the raw materials already melted.

When a uniform composition of the molten raw material is formed and the reducing agent is added at an appropriate time, these measures can ensure the concentration of the reduction process and the simultaneous melting of the supplied raw material and reduction of the alloying elements, which improves the recovery rate of the alloying elements in the metal, reduces the contamination of the steel by the nonmetallic inclusions, and improves the quality of the steel. The reducing agent can be effectively utilized by melting the raw material of the nonmetallic compound containing the alloying element and the reducing agent at the same time. This promotes the intensive performance of the liquid-phase reduction reaction of the alloying elements.

The reducing reaction can be started early by adding the reducing agent during the addition of the raw material of the non-metallic compound containing the alloying element, the contact between the molten portion of the reducing agent and the homogeneous composition of the formed molten raw material of the non-metallic compound containing the alloying element is continued, and the melting and reducing reactions of the supplied raw material are synchronized, thereby preventing the transition of the reducing process to a diffusion state accompanied by a low-speed and complete reducing process, an increase in consumption of the reducing agent, contamination of metal by non-metallic inclusions, and a reduction in steel quality.

It is preferable to start the addition of the reducing agent when the layer height of the added alloying material reaches 0.1 to 0.15 of the total layer height because the melting point of the reducing agent is lower than that of the raw material of the non-metallic compound containing the alloying element. When the addition of the reducing agent is started before the layer height of the raw material reaches 0.1 of the total layer height, the raw material will not have time to melt to form a uniform phase, and thus the molten reducing agent cannot participate in the reduction reaction, which may result in its insufficient utilization. The addition of a reducing agent when the raw material layer height of the alloying element-containing compound is greater than 0.15 of the total layer height is also undesirable because the concentrated formation of a homogeneous phase of the added alloying materials will interfere with the synchronous manner of melting and reduction reactions of the alloying materials, which can lead to a reduction in the recovery of the alloying elements from the molten metal, contamination of the metal by non-metallic inclusions and impairment of the steel quality.

The reduction of the alloying elements is carried out at the melting temperature of the non-metallic compounds comprising manganese oxides, other alloying elements, and/or the feedstock comprising other non-metallic manganese compounds.

This can be guided by the fact that: the fact that the completeness of the reduction reaction is increased and the temperature is minimized in the presence of the homogeneous composition of the alloying raw materials and the molten portion of the reducing agent contributes to the recovery of the alloying elements of the metal, reduces the contamination of the metal by non-metallic inclusions, and improves the quality of the steel. According to the method of the present invention, the temperature is not increased above the melting temperature of the raw materials because the reduction reaction is substantially completed when the melting of the added raw materials is completed.

According to the method of the present invention, it is desirable to maintain continuous contact between the molten portion of the reducing agent and the homogeneous composition of the molten feedstock of non-metallic compounds containing alloying elements to maintain a high rate and completeness of the reduction process.

When the direct steel alloying process is performed in a steel making furnace such as a converter, the oxidized slag is taken out when the refining blast period is terminated and a molten metal temperature exceeding the tapping temperature is reached. Supplemental heating of the molten metal is directed by reducing the viscosity of the oxidized slag before tapping and compensating for the heat loss caused by the endothermic reaction of carbothermic reduction of the alloying elements from the raw material comprising the non-metallic compounds of the alloying elements. For each particular steel grade, the value at which the molten metal temperature should exceed the nominal tapping temperature is determined by the following formula: Δ t ═ 33[ Mn ], where: delta t is a value exceeding the tapping temperature, DEG C; [ Mn ] is the amount of reduced manganese, mass percent; 33 is an empirical coefficient. When the molten metal is heated to the desired temperature value, the oxidic slag is removed and the resulfurization and rephosphorization of the metal in the steelmaking furnace can be minimized with the following process. Then, a raw material of a non-metallic compound containing an alloying element, a slag-forming material such as lime, and a carbonaceous material serving as a reducing agent are added to the steel-making furnace in batches, each batch being 0.01 to 0.02 by weight of the molten metal. The raw material of the non-metallic compound containing the alloying elements is lump ore, concentrate, sintered ore, preferably 20-50mm fragment component, and the added carbonaceous material used as the reducing agent is coke, coal, silicon carbide, calcium carbide, or a combination thereof. The amount of carbonaceous material added is selected from the following proportions: the raw material of the non-metallic compound containing the alloy material, the slagging material and the carbon-containing material are respectively 1 to (0.18-0.20) to (0.10-0.12). The proportion must be guided in such a way that direct steel alloying is carried out continuously. An increase in consumption of slagging raw materials and carbonaceous raw materials will decrease the amount of raw materials of non-metallic compounds containing alloying elements added to the steelmaking furnace, decrease the recovery rate of alloying elements in the molten metal, increase the non-uniformity of slag, worsen the process of heat exchange and mass exchange, all of which impair the quality characteristics of steel by increasing the content of non-metallic inclusions. When the added raw material is reduced to a ratio of less than 1: (0.18-0.20): (0.10-0.12), the amount of CaO added to the steel furnace is reduced, the physical and chemical state of the reduction process is deteriorated, the recovery rate of reduced alloying elements in the molten metal is reduced, and the quality of steel is impaired.

The raw material of the non-metallic compound containing the alloying element (e.g. manganese) applied to the surface of the molten metal and lime are melted and a chemical reaction takes place between carbon as reducing agent and oxygen of the slag-metal two-phase system, for example:

(FeO)+C＝[Fe]+CO (1)，

(MnO)+C＝[Mn]+CO (2)，

[O]+C＝CO (3)。

the gaseous product of all three reactions is carbon monoxide, which can bubble slag and strengthen its refining capacity and upper metal layer, thus contributing to the strong absorption of the reduced elements by the base metal.

The endothermic nature of the reaction between the metal and the carbon and oxygen contained in the slag does not inhibit the reaction, since the metal has been preheated to a temperature above the tapping temperature before the start of the direct alloying process, depending on the desired amount of reduced metal, such as manganese.

The reduction process must be performed uniformly, and the weight of the raw material added to each batch is controlled to be 0.01 to 0.02 of the weight of the molten metal. When the weight of the batch is reduced to less than 0.01 of the weight of the molten metal, the thermal condition of the reduction process is deteriorated and thus the mass exchange process is deteriorated because the amount of gaseous carbon monoxide bubbling on the slag and the surface layer of the molten metal formed during the deoxidation process of the molten metal and the reduction of the alloying element with carbon is reduced, which impairs the completeness of the reduction reaction of the alloying element and impairs the refining process, and the quality of the resulting metal is deteriorated due to the increase of the content of non-metallic inclusions.

It is also undesirable to increase the weight of each batch to more than 0.02 of the weight of the molten metal because it interferes with the heat exchange process and causes the deterioration of the slagging process due to the large addition of the slagging material contained in the charged raw material, which results in the thickening of the slag, increases the non-uniformity of the slag, decreases the recovery rate of alloying elements, and impairs the refining process, and thus, the amount of non-metallic inclusions in the metal increases and the quality of the steel deteriorates.

In the direct alloying process carried out, the low-oxide metal is taken out of the steelmaking furnace. Thus, the process of providing the metal with the predetermined composition can be adjusted for small and pre-measured amounts of oxygen dissolved in the metal. This significantly reduces the number of repeated observations to be made for a narrow range of content of any one alloying or modifying element.

When the direct alloying process is performed in a ladle, when molten metal is tapped from a steelmaking furnace, a carbonaceous material is first added to the ladle, and then a raw material of a non-metallic compound containing an alloying element, a reducing agent such as aluminum, and a slag-forming material such as lime are added in the following weight percentages: raw materials of non-metallic compounds containing alloying elements: 56-65 parts; aluminum: 12-16; carbon material: 5-7; lime: and (4) the balance.

The addition of carbonaceous material, such as coke or coal, to the ladle in an amount of 5 to 7% by weight of the total consumption of raw materials added to the ladle provides a deoxidation of the metal to bring the oxygen content of the finished steel to the desired value.

Furthermore, combining the deoxidation and alloying processes with tapping the metal into the ladle shortens the alloying time, thereby reducing the melting cycle. A reduction in the content of carbonaceous material in the feed material to the ladle does not result in the desired level of deoxygenation, however an increase in the content to over 7% results in cooling of the metal in the ladle because the heat generated by the exothermic reaction is not sufficient to compensate for the heat loss caused by the endothermic reaction between carbon and oxygen in the metal.

The raw material of the non-metallic compound containing the alloying element is added in an amount of 56 to 65 wt%, so that a predetermined concentration of the alloying element in the steel can be ensured. The addition of the raw material of the non-metallic compound containing alloying elements in an amount of less than 56 wt.% increases the consumption of the reducing agent (aluminum) and the consumption of the reducing agent for additional metal deoxidation reaction accompanied by the formation of non-metallic aluminate inclusions which are difficult to remove, which deteriorates the casting process of steel and deteriorates the quality of steel. Increasing the raw material consumption to more than 65 wt.% will decrease the recovery rate of the alloying elements recovered thereby.

The consumption of aluminum in an amount of 12 to 16 wt.% provides a high recovery rate of the alloy material without substantially forming AlO and Al contaminating the workshop environment₂O₃The temperature in the reaction zone is reduced compared to the metal temperature of the reaction gas product. Al produced in the reaction of aluminum oxide₂O₃Combine with CaO to form a readily removable compound.

The direct steel alloying process with chromium is accomplished in the following manner. During tapping of molten metal from a steelmaking furnace, a raw material of a non-metallic compound containing other elements in the form of chromium oxide is added to a ladle together with manganese oxide and other non-metallic manganese compounds.

Because chromium oxide has a high melting point, the presence of manganese oxide and other non-metallic manganese compounds in the added raw materials improves the thermal balance and physical and chemical conditions of the reduction reaction of the alloying elements by lowering the melting temperature of the added raw materials. The melting of the refractory components comprising chromium oxide must be accelerated, according to which the joint addition of the components to the ladle during the tapping of the metal is directed, which improves the homogenization of the slag phase and the reduction of the alloying elements.

The oxides with a manganese-chromium ratio of 1.1-1.2, which are consumed to increase the contents of both manganese and chromium in the resulting steel by 0.1%, in the added raw materials of the non-metallic compounds containing these elements, can provide the optimum recovery rates (about 90%) of the alloying elements chromium and manganese in the metal, thereby improving the chemical homogeneity of the steel, reducing the oxidation level of the metal, reducing the amount of non-metallic inclusions, and improving the quality of the steel. A reduction of the manganese-chromium ratio in the added raw material below 1.1 worsens the process parameters for chromium and manganese reduction due to worsening of the kinetic conditions of the reduction process and high non-uniformity of the slag formed, caused by the increase in viscosity caused by the molten liquid phase oxide raw material. This impairs the ability to recover alloying elements from the oxides, reduces the slag adsorption capacity for nonmetallic inclusions, and increases the contamination of metals with nonmetallic inclusions. Increasing the manganese-chromium ratio in excess of 1.2 in the added feedstock will result in dilution of the slag with the chromium oxide containing feedstock, reducing the absolute amount of feedstock containing non-metallic manganese compounds and thus reducing the recovery of manganese and chromium in the metal, which will result in a reduction of the chemical homogeneity of the alloying elements manganese and chromium in the metal body and impair the quality of the steel.

Adding aluminum and calcium carbide which are used as reducing agents into a casting ladle together in a ratio of 1: 2.9-3.2. The thermal and kinetic conditions for the reduction of chromium and manganese, from each alloying element of the raw materials with different melting points, must be optimized, according to which the chosen proportions of the raw materials are guided. The recovery of molten metal from the alloying elements of the added raw materials is improved due to the simultaneous presence of an endothermic reaction between the carbon of the calcium carbide and the oxygen of the molten raw material and an exothermic reaction between the aluminium and the oxygen from the raw material and dissolved in the metal, thus providing the correct heat balance. In addition, an exothermic reaction occurs between calcium contained in the calcium carbide and oxygen and sulfur dissolved in the metal, thereby generating CaO and CaS, respectively. This also contributes to the stabilization of the heat balance during the reduction. The reaction between carbon and oxygen of the calcium carbide is accompanied by the formation of carbon monoxide bubbles which bubble the molten slag and improve the recovery of non-metallic inclusions by the slag, thereby reducing their content in the metal and improving the quality of the steel.

Calcium contained in calcium carbide is not only an effective deoxidizer and desulfurizer but also promotes spheroidization of aluminate formed on the metal surface layer as a result of a combination of metal deoxidation with aluminum and reduction of alloying elements from its oxide. The use of surface slag allows for the active recovery of spheroidized aluminates, which contributes to the reduction of non-metallic inclusions and improves the quality of the steel. Part of the calcium added to the ladle reacts with the sulphides formed in the metal, typically MnS and FeS, changing their morphology and forming simple sulphides (CaS) and complex calcium-passivated manganese and silicon sulphides, reducing the amount of non-metallic sulphide inclusions and the sulphur content in the metal and improving the quality of the steel. Increasing the calcium carbide fraction to more than 3.2 impairs the characteristics of the reduction reaction process and the characteristics of the sulfur removal refining of metals due to the deterioration of the thermal state, increases the non-uniformity of slag, reduces the adsorption capacity for non-metallic inclusions, increases the chemical non-uniformity of metals, chromium and manganese of alloying elements, and impairs the quality of steel. Lowering the calcium carbide fraction below 2.9 will raise the temperature of the reduction reaction zone and may accompany the molten aluminum floating on the molten slag surface due to AlO and Al₂Incomplete oxidation of aluminum of O causes aluminum to react with oxygen in the atmosphere, and a gas oxide is generated in the gas phase after the oxidation reaction. This changes the heat balance, deteriorates the reduction process characteristics of alloying elements from its oxides and the process characteristics of sulfur removal refining of metals with calcium, and damages the plant environment. Due to the increase in the non-uniformity of the slag and the decrease in the strength of the slag stirred with carbon monoxide bubbles, changing the ratio of the reducing agent component according to the present invention deteriorates the dynamic state of the reduction reaction and the metal refining process, which impairs the recovery ability of the slag for non-metallic inclusions and increases the non-metallic inclusionsContamination of the metal with substances. All these factors with respect to the content of alloying elements impair the chemical homogeneity of the steel, deteriorate the desulfurization effect, increase the content of non-metallic inclusions in the metal, and impair the quality of the steel.

The above-described embodiments of the method according to the invention do not exclude other embodiments comprised within the scope of the claims and may be carried out in any vessel with molten metal, such as an open hearth furnace, ladle furnace or the like.

Example 1

The process for the direct alloying of steel with manganese and chromium is carried out in a converter with a capacity of 250 t. Charging molten iron to the converter with slag-forming material lime, the molten iron comprising, in weight percent: c-4.42; si-0.82; s-0.020; p-0.095; iron-balance. The lime comprises the following components in percentage by weight: CaO-92.0; MgO-6.5; other Side Impurities (OSI) -balance.

The material comprising oxides of manganese and other non-metallic compounds of manganese was 44.6% by weight of the total content of manganese, calculated as net element. The material of the non-metallic compound containing the other alloying elements is a material containing 70.81 wt% Cr₂O₃Of (4) chromium oxide. The reducing agent is an aluminum-containing material and a carbonaceous material. The aluminium-containing material is an undersized slag in aluminium production comprising, in weight percent: al (Al)_Metal-44.8; volatile-balance; the carbonaceous material is coke comprising, in weight percent: c-85.9; s-0.47; volatiles-balance. After charging molten pig iron and slag forming materials into the converter, the metal is charged at 940N m³Oxygen was blown in at a flow rate/min for 8 minutes and the oxidic slag was taken off. Then, raw materials containing manganese oxide and other non-metallic manganese compounds were fed at a feed rate of 14.0kg/t (3500kg), and raw materials containing chromium oxide, both in pieces of 10 to 20mm, were fed at a feed rate of 12kg/t (3000kg), and continuously charged onto the surface of the molten metal in the converter. When the layer height of the supplied raw material is 0.1-0.15 of the total height, 1785kg of reducing agent, that is, 20-30 mmSlag with insufficient size in aluminum production of chips and 465kg of coke with 10-20 mm chips in order to obtain the thermal properties required for the mixed-in raw materials. The reduction reaction of the alloying elements is carried out under conditions such that the molten portion of the reducing agent is maintained in continuous contact with the molten portion of the charged raw materials throughout the reduction reaction at the melting temperature at which the charged raw materials are mixed. To produce steel with the desired composition, the required alloying additives (copper and nickel) are added to the converter, while a deoxidizer, ferrosilicon, is added to the ladle.

And casting the finished steel into a steel ingot of 12.5t, rolling the steel ingot into a plate with the thickness of 10-20 mm, and carrying out metallographic analysis.

The finished steel had the following composition in weight percent: c-0.11; si-0.24; mn-0.57; s-0.010; p-0.007; al-0.025; cr-0.60; ni-0.70; cu-0.46; fe-balance.

The recovery of manganese from the molten metal was 92.7% and the recovery of chromium was 89.8%. Contamination of the steel with non-metallic inclusions (in percent) is as follows: 1.4 of oxide; 1.2 parts of sulfide; silicate 1.3.

Example 2 (carried out for comparison with the closest prior art (RU 2096491))

The melting was carried out in a 250t converter together with deoxidation and alloying of the metal in the converter. The slag-free metal tapped from the converter at 1690 c contains aluminium and silicon. During tapping, CaO to Mn_xO_yManganese ore (Mn-48.0%; SiO) in a ratio of 1: 1₂-3.5％；Fe-3.4％；CaO-1.5％；Al₂O₃-2.5%; p-0.05%) and lime (CaO-90%); a mixture of carbon ferrochrome of the phi X-650(FeCr650) grade and ferrosilicon of the phi C-65(FeSi 65) grade are simultaneously added to the ladle. As in the process of the invention, nickel and copper are added to the converter in order to produce steel having the desired composition. When the time is 10 minutes and the CaO/SiO of the slag is obtained₂1.3, the finished steel has the following composition, in weight percent: c-0.15; mn-0.51; si-0.27; al-0.003; cr-0.54; ni-0.72; cu-0.55; s-0.017; p-0.015; fe-balance.

The molten metal recovered 71.2% manganese, 67.8% chromium, and contamination of the steel with non-metallic inclusions (in percent) was as follows: 3.5 of oxide; 2.8 parts of sulfide; silicate 2.0.

The method of the invention can provide high recovery rate of alloying elements and reduce the pollution of non-metallic inclusions to steel.

Example 3

1630 deg.C; the carbon content is 0.03-0.05%, and the manganese content is 0.055%. 146t of pig iron were poured into a converter. The temperature of the added pig iron is 1410 ℃, and the pig iron comprises the following components in percentage by weight: c-4.2; si-0.85; mn-0.57; s-0.016; p-0.021. The melt is treated with oxygen at 120Nm³Purging for 22 minutes at a flow rate of one minute until the temperature of the melt reaches a value higher than the tapping temperature according to the specification by the formula Δ t-33 [ Mn []Temperature of the determined value: Δ t ═ 33[ Mn]Wherein: delta t is a value exceeding the tapping temperature, DEG C; [ Mn ]]Is the amount, weight percent, of manganese reduced from a feedstock comprising a non-metallic manganese compound; 33 is an empirical coefficient. Determining the formula Δ t 33[ Mn ] based on the specifications of the melt]Middle [ Mn ]]The value is obtained. In the embodiment, when the carbon content is 0.03-0.05%, the manganese content before tapping should be 0.55%. At such a carbon content, the manganese content is usually 0.05 to 0.07% (considered as 0.05%) at the end of purging. Thus, [ Mn ] was determined]The value was 0.55-0.05-0.50%. By the formula Δ t 33[ Mn]The Δ t value was determined to be 16.5%. For this reason, purging was performed until the melting temperature was 1647 ℃. Then, the oxide slag is taken out of the converter, and a mixture of a raw material (lime) containing manganese oxide and other nonmetallic inclusions and coke as a carbonaceous reducing agent is added in the proportions of 1 to (0.18 to 0.20) to (0.10 to 0.12), respectively, and the weight of each batch including all the supplied raw materials is 0.01 to 0.02 of the weight of the molten metal. The temperature of the molten metal before tapping when the direct alloying process was terminated was 1630 ℃. Before tapping, the metals comprise, in weight percent: c-0.05; mn-0.54; p-0.006；S-0.005。

Table 1 shows the process characteristics and results of the process.

The molten metal tapped into the ladle exhibits a low oxidation coefficient and low sulphur and phosphorus content, which reduces contamination of the steel by non-metallic inclusions and contributes to improving the quality of the finished steel. The manganese recovery of the molten metal was 81.7%.

Example 4

Melting a steel having the following composition, in weight percent: c: 0.09-0.12; mn: 0.40 to 0.65; si: 0.17 to 0.34; s: 0.20; p: 0.20. molten metal produced in the steelmaking furnace was tapped in a non-oxidized form into a ladle having a capacity of 5 t. During tapping of the molten metal, a carbonaceous material; coke; a material comprising oxides of manganese and a material comprising other non-metallic manganese compounds, the total manganese content of the material being 44% by weight on a net elemental basis; aluminum and lime as reducing agents were added to the ladle. The raw materials are charged into the ladle in the proportions according to the invention. The metal was cast into a 1t ingot. Metal samples were taken for chemical analysis before and after the addition of the raw materials to the ladle. Samples were also taken from rolled products made from ingots to determine the percentage of non-metallic inclusions.

The steel prepared by the direct alloying method of the invention shows high recovery of alloying elements in the metal (95.4%) manganese and low pollution of non-metallic inclusions.

Example 5

According to the invention, the steel is melted together with chromium by direct alloying in a 100t electric steelmaking furnace.

Molten metal is tapped from a steelmaking furnace into a ladle at 1650 ℃ and during tapping a feed stock comprising alloying elements, non-metallic compounds of chromium in the form of converter slag in the production of medium carbon ferrochrome is added in an amount of 1200kg, the chromium content of the feed stock being 48.99% by weight calculated as net elements, and a feed stock comprising oxides of manganese and other non-metallic manganese compounds in an amount of 1400kg, the total manganese content of the feed stock being 44% by weight calculated as net elements. 370kg of grade AB-86 recycled aluminium and 1100kg of calcium carbide were also added to the ladle in a ratio of 1: 3.

And casting the finished steel into a steel ingot of 12.5t, rolling the steel ingot into a plate with the thickness of 10-20 mm, and performing metallographic analysis.

The finished steel had the following composition in weight percent: c-0.11; si-0.17; mn-0.54; s-0.006; p-0.007; al-0.023; cr-0.61; ni-0.70; cu-0.53; fe-balance.

The composition of the raw materials added to the ladle and the test results of the product steel are shown in table 2.

TABLE 2

Number of melts	1	2	3
				Raw material composition, weight%: feedstock of non-metallic compounds containing alloying elements	56.0	60.0	65.0
Coke	5.0	6.0	7.0
				Aluminium	12.0	14.0	12.0
Lime	27.0	20.0	12.0
				Recovery rate of manganese%	96.8	97.0	98.0
Desulfurization rate%	64.2	58.4	61.0
				Maximum percentage of non-metallic inclusions: oxides in the form of inclusions in the form of strips	1.9	1.8	1.8
Dot oxide	1.4	1.6	1.5
				Sulfide compound	2.3	2.5	2.4

In this example, the recovery of molten metal was: 91.2% chromium and 93.2% manganese.

The use of the direct steel alloying method with the chromium oxide consumption according to the invention can provide steel with a high degree of chemical homogeneity of the main alloying elements, a high degree of desulphurization and a low contamination of the steel with non-metallic inclusions.

Claims (9)

1. A method of direct alloying of steel, the method comprising: melting steel in a steelmaking furnace; alloying of steel with manganese, said manganese being reduced from oxides of manganese during addition of a feed material comprising said oxides of manganese and a reducing agent and during reaction of both, said method being characterized in that the reduction of manganese is carried out in combination with the reduction of other alloying elements in the feed material from non-metallic compounds comprising said alloying elements added to the surface of the molten metal; and/or in combination with the reduction of manganese from the charged feedstock comprising other non-metallic manganese compounds; when the layer height of the added raw materials is 0.1-0.15 of the total layer height, starting to add the reducing agent; the reduction temperature is maintained at the melting temperature of the added raw materials and the reducing agent; the molten portion of the reducing agent is kept in continuous contact with the molten portion of the added raw material of the non-metallic compound containing the alloying element, the amount of the reducing agent added being such as to ensure that the mixture of the added raw material and the reducing agent has the desired thermal characteristics.

2. The method of claim 1, wherein the feedstock of non-metallic compounds comprising alloying elements contains an oxide or carbonate of the alloying elements, or a combination thereof.

3. The method of claim 1, wherein the reducing agent is an aluminum-containing, or silicon-containing, or carbon-containing material, or an alkaline earth metal-containing material, or a combination thereof.

4. The method of claim 1, wherein the addition of the feedstock of non-metallic compounds containing alloying elements is performed continuously or in batches, each batch in an amount greater than or equal to 0.1 of the total consumption.

5. The method as set forth in any one of claims 1 to 4, wherein, in the direct steel alloying process performed in the steel making furnace, when the molten metal reaches a temperature higher than the tapping temperature by a value determined by the formula Δ t ═ 33[ Mn ], a slag forming material and a carbonaceous material serving as a reducing agent are further added to the steel making furnace in such amounts that the ratio of the raw material of the non-metallic compound containing the alloying element, the slag forming material and the carbonaceous material is 1: (0.18 to 0.20) to (0.10 to 0.12), respectively; and taking the oxidized slag out of the steelmaking furnace, wherein: Δ t is the value exceeding the tapping temperature in ° c, [ Mn ] is the amount of manganese reduced, in weight percent, 33 is an empirical coefficient.

6. The method according to claim 5, wherein the raw materials of the non-metallic compound containing the alloying element, the slag-forming material and the carbonaceous material are added in portions, and the weight of each portion containing all the added raw materials is 0.01 to 0.02 of the weight of the molten metal.

7. A method as claimed in any one of claims 1 to 3, wherein during direct steel alloying in a ladle, a carbonaceous material is additionally added to the ladle; the reducing agent added is aluminum; in the alloying process, lime is additionally added as a slagging agent; the following components are adopted in the following proportion by weight percentage: the raw material of the non-metallic compound containing alloying elements is as follows: 56-65 parts; aluminum: 12-16; carbon-containing material: 5-7; lime: and (4) the balance.

8. A method according to claim 1 or 3, wherein when alloying of the steel with chromium in the ladle, the non-metallic compound of the other element is chromium oxide added to the ladle during tapping of the molten metal; in order to increase the contents of both manganese and chromium in the finished steel by 0.1%, chromium oxide is added to the material containing the nonmetallic compounds of these elements in a manganese-chromium ratio of 1.1-1.2, and aluminum used as a reducing agent is added together with calcium carbide in a ratio of 1: 2.9-3.2.

9. The process of claim 8, wherein the chromium oxide containing feedstock is converter slag in the production of medium carbon ferrochrome.