CN101643822B - Ultrahigh basicity low aluminum fluorine-free refining slag and preparation method and use method thereof - Google Patents

Abstract

The invention belongs to the technical field of steelmaking and refining, and is an ultra-high alkalinity, low-aluminum, fluorine-free pre-melted ladle refining slag, a preparation method and a use method. The chemical composition is (mass%): CaO 85-95%, _{B2O 3} 2-10%, MgO 2-10%, Al ₂ O ₃ 1-10%, impurities less than 5%, especially harmful impurities such as sulfur and phosphorus, the lower the better. It is prepared from industrial reagents: active lime, boric anhydride, magnesia, aluminum ash, pre-melted at 1350-1450 ℃, and broken into 2-10mm after cooling, and packed in moisture-proof packaging. The slag system can be used for refining slag making of LF, RH and CAS, etc. After pre-deoxidation of molten steel and reduction treatment of ladle residue, the refining slag is put into the ladle during the argon blowing process. The refining slag of the present invention has strong desulfurization and phosphorus capabilities, no pollution, improved ability to absorb inclusions produced by deoxidation, improved steel deoxidation effect, good spreadability, reduced gas absorption and oxidation of molten steel, no slag sticking to refining equipment, simple preparation process, and convenient storage and use.

Description

An ultra-high alkalinity, low-aluminum, fluorine-free refining slag and its preparation method and use method

technical field

The invention relates to a fluorine-free pre-melted ladle refining slag with ultra-high alkalinity and a preparation method and a use method thereof, which belong to the field of refining outside a steelmaking furnace and are suitable for slagging refining process in a ladle.

Background technique

With the development of social economy, users put forward higher and higher requirements for the quality of steel products. As an important production process in the modern steelmaking process, extra-furnace refining plays a pivotal role in the entire steel production process. Among many refining processes, synthetic slag refining has the functions of desulfurization, dephosphorization, deoxidation and absorption of inclusions in steel, and has been widely used and developed.

At present, the refining slag outside the steelmaking furnace mainly includes the following basic series: CaO-CaF ₂ slag series; CaO-Al ₂ O ₃ slag series; CaO-Al ₂ O ₃ -CaF ₂ slag series. Among the three basic slag systems, the component that really plays a role in desulfurization and phosphorus refining is mainly CaO. CaO is cheap and has a strong ability to remove sulfur and phosphorus. However, due to the very high melting point of CaO, it is necessary to add a relatively large amount of auxiliary Flux CaF ₂ , that is, CaO-CaF ₂ slag system, due to the high-temperature instability of CaF ₂ , causes serious fluorine pollution, and the single use of CaF ₂ , the stability of the slag is poor, which is not conducive to smooth operation. This is the consensus of the metallurgical industry . After realizing the harm of CaF ₂ as a fluxing agent, CaO-Al ₂ O ₃ slag system was used for slag making outside the furnace, which eliminated fluorine pollution. However, due to the weak fluxing effect of Al ₂ O ₃ , the Al ₂ O ₃ occupies a larger component, which dilutes the role of CaO as a desulfurization and phosphorus component, making the metallurgical properties of the slag system poor. On the basis of the CaO-CaF ₂ slag system and the CaO-Al ₂ O ₃ slag system, the study adopts the CaO-Al ₂ O ₃ -CaF ₂ slag system, and uses Al ₂ O ₃ and CaF ₂ to adjust the metallurgical properties of the slag. This slag system is currently widely used in the refining slag system outside the furnace. However, with the improvement of human health and environmental protection requirements, the use of CaF ₂ is strictly limited, and the use of Al ₂ O ₃ in slag has to be increased. The refining slag system has better melting performance, so that the maximum amount of CaO in the slag system can only be about 60%, which limits the improvement of the desulfurization and phosphorus capabilities of the CaO-Al ₂ O ₃ -CaF ₂ slag system, and also This limits the absorption capacity of the refining slag to the aluminum deoxidation product, namely Al ₂ O ₃ . Recently, some researchers have proposed to replace some or all of CaO with BaO, Na ₂ O, Li ₂ O, SrO, etc., which can reduce the amount of flux used and improve the desulfurization and phosphorus capabilities, but BaO and Na ₂ O will pollute the environment. , The erosion of equipment is no less harmful than that caused by fluorine pollution, and Li ₂ O and SrO are very rare resources. Therefore, the current refining slagging outside the furnace can only use CaO, which is cheap and has strong desulfurization and phosphorus capabilities. As a basis, but to overcome the above-mentioned shortcomings of the current CaO-CaF ₂ slag system, CaO-Al ₂ O ₃ slag system and CaO-Al ₂ O ₃ -CaF ₂ slag system, while ensuring the melting performance of slag, make the slag Keep the content of CaO as high as possible in order to improve the ability of refining slag to desulfurize, absorb inclusions and deoxidation products, and control the phosphorus return of molten steel.

In the existing technology of eliminating fluorine pollution and promoting slagging, Chinese invention patent: (application number: 200910029247.5) a ladle refining slagging agent and its preparation method and slag adjusting method proposes the use of quicklime, aluminum ash, magnesia and boron The anhydride is prepared according to CaO 30-60%, Al ₂ O ₃ 30-60%, MgO 2-10%, B ₂ O ₃ 2-10%, to prepare a pre-melted slagging agent. This invention has good slagging effect and no fluorine pollution And other advantages, as a slagging agent, when used in combination with quicklime, etc., it has a better refining effect. But this invention is only a slag adjusting agent used in the refining process, and cannot be used alone as refining slag. In other words, the deficiencies or essential defects when it is used as refining slag are mainly: (1), the content of CaO in this invention is relatively low , the desulfurization and dephosphorization capabilities are limited, and even reduce the suction capacity of acidic deoxidation products such as SiO ₂ , Al ₂ O ₃ , affecting the deep deoxidation effect of molten steel; (2), the content of Al ₂ O ₃ in this invention is relatively high, Although it is beneficial to slag, it reduces the ability of refining slag to absorb and accommodate _Al2O3 , the product of aluminum deoxidation in molten steel, which is not conducive to the discharge of _Al2O3 in molten steel, and forms inclusions in steel _, so it is not suitable for the _production of super pure steel.

Chinese Invention Patent: (Application No.: 200910029248.X) An anti-sticking slag-free fluorine-free slagging agent for ladle refining and its preparation method and use method, which proposes to use quicklime, aluminum ash, magnesia and boric anhydride by CaO 75-85% , Al ₂ O ₃ 10-20%, MgO 0-8%, B ₂ O ₃ 5-15%, prepare pre-melted slagging agent, the main function of this invention is to prevent the refining equipment from sticking slag, of course, this invention is very important for improving the refining effect It also has a certain effect, such as being beneficial to desulfurization, controlling phosphorus return, etc., but similarly, this invention is only a slag adjusting agent used in the refining process, and the shortcomings when used as refining slag alone are also the two points mentioned above: That is, the content of CaO is low, the refining capacity is insufficient, and the content of Al ₂ O ₃ is high, which is not conducive to the deoxidation of molten steel and the absorption of inclusions. Therefore, it is not suitable for the production of super pure steel as refining slag alone.

To sum up, in order to improve the desulfurization and dephosphorization ability of slag, the basicity of slag must be increased as much as possible, that is, the content of CaO in slag is high and the content of acidic components is low. The amount of Al ₂ O ₃ in slag. In industrial production, in order to ensure refining efficiency, this high-alkalinity and low-aluminum refining slag must be combined with a flux that can promote lime melting more effectively than CaF ₂ and Al ₂ O ₃ in order to achieve a good refining effect.

Therefore, the present invention proposes to adopt ultra-high basicity, low-aluminum, and fluorine- _free refining slag, that is, to increase the content of CaO in the slag, and reduce the amount of _Al2O3 in the refining slag at the same time, thereby increasing the concentration of free CaO in the slag and increasing the concentration of slag. Desulfurization and phosphorus ability, overcome the problem of insufficient desulfurization and phosphorus ability caused by a large amount of Al ₂ O ₃ slag adjustment. In addition, there is a large amount of free CaO in the slag, which increases the impact of refining slag on residual deoxidation products in steel such as Al ₂ O ₃ , SiO ₂ The absorption capacity of substances such as fluorine is beneficial to improve the deoxidation effect of molten steel; at the same time, in order to promote lime melting, B ₂ O ₃ is used as flux instead of CaF ₂ , thereby eliminating fluorine pollution and improving slagging speed and smelting stability.

Contents of the invention

The purpose of the present invention is to provide a fluorine-free refining slag with ultra-high alkalinity, low aluminum, and overcome the fluorine pollution caused by the desulfurization, low phosphorus capacity, easy saturation of the ability to absorb inclusions and fluorite as a flux in the current refining slag. , serious corrosion of refractory materials and other key issues, better play the metallurgical function of slag refining outside the furnace, improve the quality of molten steel, smelting efficiency and the life of refining equipment.

The purpose of the present invention is achieved through the following technical solutions:

An ultra-high alkalinity, low-aluminum, fluorine-free refining slag, characterized in that: the composition is calculated by mass percentage, CaO 85-95%, B ₂ O ₃ 2-10%, MgO 2-10%, Al ₂ O ₃ 1-10%, the impurities in the refining slag should be less than 5%, especially the lower the harmful impurities such as sulfur and phosphorus, the better.

In the above refining slag, impurities include SiO ₂ , sulfur, phosphorus and their compounds.

The preparation method of the refining slag of the above composition is characterized in that: the industrial reagents: active lime, boric anhydride, magnesia, aluminum ash are prepared according to the above given composition, the lower the impurity content in the raw material, the better, and the selected material The principle is that impurities such as SiO ₂ , sulfur and phosphorus should be less than 5% after batching. The raw materials should be fully dried before weighing, weighed and batched, crushed into pieces below 2mm, and pre-melted after mixing. Coke heating, gas heating or electric heating are used for pre-melting. The pre-melting temperature is 1350-1400°C. After melting evenly, it is discharged from the furnace. The liquid slag is cooled after being released from the furnace and crushed. The particle size is 2-10mm and kept in a dry state. Next, moisture-proof packaging for use.

The refining method using the refining slag is as follows: after pre-deoxidation and alloying treatment of molten steel, enter the refining station, add reducing agent to reduce the ladle residue, put the pre-melted refining slag into the mirror area of molten steel during the argon blowing process, and the subsequent refining process and The conventional refining slags currently used are exactly the same, and this slag can be used in refining processes such as LF refining, RH refining and CAS refining. For LF refining, because arc heating needs to create foam slag, the pre-melted slag can be mixed with foaming agent and put into ladle, and then opened to the electric heating station for refining, or it can be packaged for use during the refining process. For RH refining and CAS refining, the refining slag can be poured into the mirror area of molten steel after argon blowing and slag removal in the ladle, and then the dipping tube or isolation cover is refined, and it can also be packaged for use during the refining process. The amount of refining slag used is determined according to the amount of desulfurization. Adding 15Kg of pre-melted slag per ton of molten steel, LF refining for 30 minutes, can reduce the sulfur content in molten steel from 0.010% to 0.001%, and the desulfurization rate reaches about 90%. If you want to continue deep desulfurization , then appropriately increase the amount of slag or prolong the refining time.

The principle of matching optimization between the refining slag composition and refining requirements of the invention is as follows:

(1) CaO is the main desulfurization and dephosphorization component, and it is also the main component for absorbing deoxidation products (Al ₂ O ₃ , SiO ₂ and their combinations) in steel. This is why this slag adopts high CaO content The fundamental reason, therefore, when the desulfurization task is heavy, the amount of residual steelmaking slag in the ladle is relatively large, and the amount of deoxidation in the ladle is large to generate a large amount of deoxidation products such as Al ₂ O ₃ and SiO ₂ , when the pre-melted slag of the present invention is used, The CaO content in the slag can take the upper limit or a higher value close to the upper limit; on the contrary, the CaO content in the pre-melted slag can take a lower limit or a lower value close to the lower limit;

(2) B ₂ O ₃ is the main flux. When the content of CaO and MgO in the slag is high and the content of Al ₂ O ₃ is low, the content of B ₂ O ₃ should be a larger value close to the upper limit to make the refining The slag has better metallurgical effects; on the contrary, when the content of CaO and MgO in the slag is low and the content of Al ₂ O ₃ is high, the content of B ₂ O ₃ can take a smaller value close to the lower limit to save costs and ensure the slag desulfurization capacity.

(3) The main function of MgO is to reduce the erosion of the magnesia-carbon refractory material at the ladle slag line by the refining slag, so as to prolong the service life of the refractory material. Practice has proved that: 4% to 6% MgO in the refining slag can effectively reduce the erosion of the ladle lining. When the ladle lining is seriously corroded, the MgO in the slag can be increased (the upper limit is 10%), but it is easy to cause slag sticking and crusting in the lining.

(4) The main function of Al ₂ O ₃ is to adjust the viscosity of the slag. For steel types that require a large amount of aluminum and silicon deoxidation in the ladle, since deoxidation will generate a large amount of Al ₂ O ₃ and other substances, the prepared refining slag should be Reduce the content of Al ₂ O ₃ to increase the absorption capacity of the refining slag to the deoxidation products Al ₂ O ₃ and SiO ₂ ; conversely, for steel types with low deoxidation in the ladle, the prepared refining slag can be appropriately increased in Al ₂ O 3 The content of ₃ makes the refining slag have good metallurgical properties.

(5) Impurities in the slag should be less than 5%, among which _SiO2 will significantly reduce the desulfurization and phosphorus capacity of the slag, and sulfur, phosphorus and their compounds will directly pollute the molten steel, so the lower the impurity content, the better.

Compared with prior art, main advantage of the present invention is summarized as follows:

(1) The refining slag has ultra-high alkalinity, strong desulfurization ability, and can control the rephosphorization of molten steel;

(2) Using B ₂ O ₃ as flux, eliminating the fluorine pollution caused by CaF ₂ as flux;

(3), B ₂ O ₃ has a strong fluxing effect, the melting speed of slag is fast, the melting point is low, and the metallurgical properties of slag are improved;

(4) The content of Al ₂ O ₃ , the slag-adjusting component in slag, is greatly reduced, which improves the absorption capacity of refining slag to Al ₂ O ₃ inclusions in steel, and also increases the concentration of free CaO, desulfurization and control of steel The ability of liquid phosphorus return is significantly improved;

(5) There is no SiO ₂ or the content of SiO ₂ is very low in the slag, which improves the absorption capacity of the refining slag to silicon deoxidation products and silicate inclusions, so the deoxidation effect of steel is improved, and the inclusions produced by deoxidation in steel be effectively controlled.

(6) The refining slag adopts the form of pre-melting treatment, which improves the stability and metallurgical effect of the refining slag, and improves the working environment of the operation site at the same time.

In summary, compared with the prior art, the present invention has the advantages of no pollution, strong desulfurization and phosphorus capabilities, and improved ability to absorb inclusions produced by steel deoxidation, improving the deoxidation effect of steel, and solving the problem of the current steelmaking furnace. The key problem of slagging refining is that, in addition, the refining slag has good spreadability, reduces the gas absorption and oxidation of molten steel, the refining equipment does not stick to slag, the preparation process is simple, and it is convenient for storage, transportation and use.

Detailed ways

Implementation example

The present invention will be further elaborated below in conjunction with embodiment. Examples are only used to illustrate the present invention, but not to limit the present invention in any way

(1) Preparation of premelted refining slag

The raw materials that embodiment adopts are as follows, and when referring to percentage below, all are percentage by weight:

The chemical composition _of active lime is: 100%>CaO≥90.0, 5%≥MgO>0, 2.5% _≥SiO2 >0, and the rest are trace impurities such as _Al2O3 ;

Chemical composition of boric anhydride: 100%>B ₂ O ₃ ≥85.0, 5%≥CaO>0, 3%≥MgO>0, 3%≥SiO ₂ >0, and the rest are trace impurities;

The chemical composition of magnesia: 100%>MgO≥90.0, 5%≥CaO>0, 3%≥Al ₂ O ₃ >0, 1%≥SiO ₂ >0, and the rest are trace impurities;

Chemical composition of aluminum ash: 100%>Al ₂ O ₃ ≥90.0, 5%≥CaO>0, 3%≥MgO>0, 1.5%≥SiO ₂ >0, and the rest are trace impurities;

Take the above-mentioned raw materials and weigh them after baking at 100-150°C, and mix according to the three ingredients in Table 1. Crumble each raw material to less than 1mm, mechanically mix it, add it to a new ladle, heat it with gas to melt it at 1380°C, and release it from the furnace after melting evenly, cool the liquid slag after it comes out of the furnace, and crush it The size is 2 ~ 10mm, keep it in a dry state, and pack it in a moisture-proof package for use. (Note: The steelworks need to bake the new ladle before using it. In order to save energy, this embodiment uses the ladle to bake while pre-melting the slag material. After the slag material is melted and poured out, the ladle can continue to be baked to use temperature).

Table 2 is the compositional analysis results of the prepared pre-melted slag

Table 1 Pre-melted slag batching scheme

Table 2 Analysis results of prepared pre-melted slag components

(2) Use of premelted refining slag

Take the above-mentioned pre-melted slag, and carry out industrial test on a 30-ton LF ladle refining furnace. The process test conditions and main technical and economic indicators are shown in Table ₃ . The slag is thrown into the mirror area of the molten steel, and then the ladle is opened to the electrified station for heating and refining.

Table 3 Process test conditions and main technical and economic indicators

It can be known from the above results that after refining by the present invention, the sulfur, oxygen content and inclusions in the steel all reach the standard of high-grade high-quality steel. In particular, the sulfur, phosphorus, and oxygen contents are all below 10ppm, which meets the standard of high-grade pure steel, and the control level of inclusions reaches the standard of high-quality and special high-quality steel. From the point of view of the refining process, the slag is in good condition, there is no crusting and slag sticking, and there is no obvious erosion of the refractory material at the ladle slag line.

Claims (5)

1. A method for using ultra-high alkalinity, low-aluminum, fluorine-free pre-melted ladle refining slag, the components of the refining slag are, by mass percentage, CaO 85-95%, B ₂ O ₃ 2-10%, MgO 2- 10%, Al ₂ O ₃ 1～10%, the impurity in the refining slag should be less than 5%, it is characterized by: used for LF refining, RH refining and CAS refining, specifically: pre-deoxidation of molten steel and after ladle residue reduction treatment , during the argon blowing process, the pre-melted refining slag is put into the mirror area of molten steel, and 15kg of pre-melted slag is added per ton of molten steel. The subsequent refining process is exactly the same as the current refining process using conventional refining slag. 2. A method for using ultra-high alkalinity, low-aluminum, fluorine-free pre-melted ladle refining slag as claimed in claim 1, characterized in that: for LF refining, the pre-melted slag and blowing agent are mixed and put into The ladle is then opened to the electric heating station for refining; or it is put into a bag during the refining process. 3. A method for using ultra-high alkalinity, low-aluminum, fluorine-free pre-melted ladle refining slag as claimed in claim 1, characterized in that: for RH refining and CAS refining, the refining slag is removed after the ladle is blown with argon Put it into the mirror area of molten steel, and then drop the dip tube or isolation cover for refining; or throw it into the package during the refining process. 4. A method for using ultra-high alkalinity, low-aluminum, fluorine-free pre-melted ladle refining slag as claimed in claim 1, characterized in that: the desulfurization rate reaches 90%, and the rephosphorization of molten steel can be completely controlled, and the steel The content of sulfur and phosphorus in the medium is controlled below 0.0010%. 5. A method for using ultra-high basicity, low-aluminum, fluorine-free pre-melted ladle refining slag as claimed in claim 1, characterized in that the impurities include SiO ₂ , sulfur, phosphorus and their compounds.