JPH08325626A - Method for reducing and recovering valuable metal in slag improved in hit accuracy of molten steel component - Google Patents

Abstract

PURPOSE: To smelt molten steel having high component hit accuracy by adding a reducing agent in an optimum amt. of addition to the molten steel, thereby deoxidizing the molten steel. CONSTITUTION: The oxygen quantity of the easily reducing oxide in a slag is determined from the oxygen concn. in the molten steel or the decreased quantity of the Si concn. and Cr concn. before and after decarburization measured by an oxygen concn. battery or emission spectrochemical analysis method and the surface positions of the slag and the molten steel are detected at the time of reducing and recovering the valuable metals in the easily reducing oxide from the slag suspended on the surface of the molten steel to the molten steel. The thickness of the slag is calculated from the difference between the detected surface positions and the weight of the slag is determined in accordance with the slag thickness. The required addition amt. of the reducing agent is calculated from the oxygen quantity of the easily reducing oxide and the slag weight and the reducing agent is charged into the slag at the addition amt. which is the result of the calculation. As a result, the valuable metals, such as Fe, Mn and Cr, are recovered to the molten steel from the slag with the decreased consumption of the reducing agent. The molten steel having the compsn. coinciding with the target compsn. with high accuracy is thus smelted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention improves the precision of the composition of molten steel when reducing and recovering valuable metals in easily reducible oxides suspended in a slag layer covering the surface of molten steel after smelting into molten steel. A method for reducing and recovering valuable metals in slag.

[0002]

2. Description of the Related Art When decarburizing and refining alloy steel such as stainless steel in a converter, a vacuum degassing device, etc., carbon in molten steel reacts with blowing oxygen to form CO gas and is simultaneously removed from molten steel. A part of useful components such as Cr, Fe, and Mn is also oxidized according to the following reaction. 4 [Cr] + 3O ₂ → 2 (Cr ₂ O ₃ ) 2 [Fe] + O ₂ → 2 (FeO) 2 [Mn] + O ₂ → 2 (MnO) Metal elements such as Cr, Fe, Mn, etc. Migrates to the slag floating on the surface of the molten steel. The metal element in the slag is reduced from the oxide to a metal state in the final stage of steel making, and is recovered as molten metal in the molten steel. Recovery is Cr, F
Utilizing the fact that metallic elements such as e and Mn are easily reduced to a metallic state by Si, for example, a predetermined amount of Si is added to molten steel in a ladle during vacuum refining. The reduction reaction with Si is as follows. 2 (Cr ₂ O ₃ ) + 3Si → 4 [Cr] +3 (SiO
₂ ) 2 (FeO) + Si → 2 [Fe] + (SiO ₂ ) 2 (MnO) + Si → 2 [Mn] + (SiO ₂ ).

Cr, Fe, Mn, etc. in the metallic state are transferred to the molten steel, and as a result, the molten steel component concentration changes. In order to adjust the composition with high accuracy, it is necessary to quantitatively grasp the metal elements that migrate from the slag to the molten steel at the final stage. Recently, steel grades with extremely strict standards for Si content have begun to be used. In order to cope with such high-accuracy component adjustment and steel grades in which the Si content is strictly controlled, the amount of the easily reducible oxide reduced by Si contained in the slag is accurately grasped. It is necessary. The oxygen content of the easily reducible oxide contained in the slag is indicated by the proportion of the oxygen content and the slag content in the metal oxide such as Cr ₂ O ₃ , FeO, and MnO that is reduced by Si. The calculated amount of oxygen is the amount of Si required as a reducing agent.
It becomes the standard when determining the amount of addition of.

[0004]

A method of fluorescent X-ray analysis of a slag sample is known as a method for quantifying the oxygen concentration in a metal oxide. The fluorescent X-ray analysis requires 20 to 25 minutes from the weighing of the sample to the calculation of the analysis value in either the glass bead method or the press molding method. Moreover,
Assuming that the metal oxide contained in the sample is in the stoichiometric form, multiply the quantitative value of the metal element by the coefficient determined from the stoichiometric relationship between the metal and the oxide. Oxygen analysis value is calculated. Therefore, a measurement error is inevitably caused in a sample containing Cr, Fe, Mn and the like in a metallic state, or a sample containing a metal oxide having a different oxygen value. In order to eliminate such measurement error and shorten the analysis time, the inventors of the present invention, based on the oxygen concentration discharged to the outside of the system by the reaction between the sample collected from the steelmaking slag and the carbon source, steelmaking slag Developed a method for quantifying the oxygen concentration of easily reducible oxides contained in
Filed as No. 319364. According to this method,
Oxygen determination of the slag is possible in about 10 minutes with minimal analytical error.

By the way, in recent years, where the demand for stainless steel is increasing, it is necessary to increase the production amount per unit time in order to respond to the demand amount in the existing equipment, and shortening the tap time is an issue. Therefore, there is an urgent need to develop a technology for grasping the amount of easily reducing oxygen in slag in a shorter time. The present invention has been devised to meet such a demand, and is combined with a valuable metal in the slag from the amount of decrease in the molten steel oxygen concentration or the Cr concentration and Si concentration in the molten steel before and after decarburization refining. Easily and quickly grasp the oxygen concentration, determine the optimum addition amount based on this value and the separately obtained slag amount, and add the reducing agent to efficiently collect valuable metals in molten steel and to obtain high appropriate precision. The purpose is to obtain molten steel whose composition has been adjusted in 1.

[0006]

In order to achieve the object, the method for reducing and recovering valuable metals of the present invention recovers valuable metals in easily reducible oxides into the molten steel from slag floating on the surface of the molten steel. At this time, the molten steel oxygen value is measured using an oxygen concentration battery, and the oxygen concentration of the easily reducing oxide in the slag is estimated from the molten steel oxygen value, and the surface positions of the slag and the molten steel are detected, and the detected surface is detected. The thickness of the slag is calculated from the difference in position, the weight of the slag is calculated based on the thickness of the slag, and the oxygen concentration of the easily reducing oxide in the slag and the necessary addition amount of the reducing agent from the slag weight are calculated, It is characterized in that the reducing agent is added to the slag in the addition amount of the calculation result. As the molten steel oxygen value, the molten steel oxygen value measured by the emission spectroscopic analysis method when the oxygen concentration of the easily reduced oxide in the slag is obtained is used. When decarburizing and refining an alloy steel containing Si and Cr in a converter or a vacuum degassing apparatus, the reduction amount of Cr concentration and Si concentration in the molten steel before and after decarburization refining is used. Estimate oxygen concentration.

[0007]

[Operation] The easily reducible oxide contained in the steelmaking slag is
It is generated by blown oxygen during decarburization refining, and its oxygen value has a high correlation with the oxygen concentration in the molten steel. Further, according to the investigations and studies by the present inventors, it was found that there is a high correlation with the oxygen value of the easily reduced oxide calculated from the reduction amounts of Cr concentration and Si concentration in the molten steel before and after decarburization refining. As described above, the oxygen concentration of the easily reducing oxide contained in the steelmaking slag is obtained by measuring the oxygen concentration in the molten steel or the reduction amount of the Cr concentration and the Si concentration in the molten steel before and after decarburization refining. Suggest that it be done. The oxygen concentration of molten steel can be easily measured by an oxygen concentration cell or an emission spectrophotometer in about 2 minutes. Further, the reduction amounts of the Cr concentration and the Si concentration in the molten steel before and after the decarburization refining are the differences between the Si concentration and the Cr concentration in the molten steel before and after the decarburization refining, respectively. These concentration differences can be easily measured by an emission spectroscopic analyzer in only about 2 minutes. Therefore, when estimating the oxygen concentration of the steelmaking slag from the oxygen concentration in the molten steel or the Si concentration and the Cr concentration, a series of working time for obtaining the analytical value from the slag sampling operation and crushing is omitted, resulting in tap time. Can be significantly shortened.

On the other hand, as a method for measuring the weight of the slag, the position X ₁ of the slag surface from the reference point and the position X _{2 of the} molten steel surface are measured.
Of the slag (X ₁ -X ₂
), The slag volume V _S is calculated from the inner diameter R of the vacuum degassing container, the ladle, etc., and the specific gravity ρ of the slag is multiplied to calculate the slag weight W _S. The surface position of the slag is detected by a range finder using eddy current, laser, microwave, radiation, etc., a touch type sensor that directly contacts the slag surface, a method of measuring the brightness of the slag, and the like. As an eddy current sensor,
It is preferable to use an eddy current sensor to which a high frequency alternating current having a frequency of 500 kHz or more and 1 MHz or less is supplied. A high-frequency alternating current with a frequency of 500 kHz or more and 1 MHz or less generates an eddy current only on the surface of the slag, so that the surface position of the slag can be detected.

The position of the molten metal surface under the slag is detected by using an eddy current type sensor, a pair of electrodes is immersed from the slag to the metal, and the difference in conductivity between the slag and the metal is electrically detected. The method is such that a gas probe in which a constant amount of gas always flows is dipped from the slag to the metal, and a change in back pressure in the gas probe caused by a difference in specific gravity between the slag and the metal is used for detection. For example, when using an eddy current sensor, a frequency of 0.5
A high frequency alternating current of up to 500 kHz is supplied to detect the surface position of the molten steel. By supplying a high-frequency alternating current with a frequency of 0.5 to 500 kHz, the error factor due to the eddy current caused by the metal droplets suspended in the slag layer is not taken into the receiving coil of the eddy current sensor, and the error is caused under the slag. The surface position of a certain molten steel is detected with high accuracy.

From the oxygen concentration of the molten steel measured as described above or the reduction amount of Cr concentration and Si concentration in the molten steel before and after decarburization refining and the weight of the slag, the required addition amount of the reducing agent according to the flow shown in FIG. Is calculated. When the reducing agent is added in this addition amount, the easily reducible oxide in the slag is reduced and is recovered in the molten steel in a metallic state. According to this method, since an excess reducing agent is not added, it is possible to reduce the excess reducing agent brought into the molten steel. That is, by adding the reducing agent in an amount determined based on the composition and weight of the slag, the reducing agent Si is not brought into the molten steel more than the standard component, and moreover, M
It is possible to obtain molten steel with improved precision of the content of alloying components such as n and Cr. The valuable metal reduced and recovered by the molten steel can be selected according to the reducing ability of the reducing agent used. For example, S
When i or ferrosilicon is used as a reducing agent, F
e, Mn and Cr are reduced and recovered in molten steel. Al, T
When i, Ca, Mg or an alloy thereof is used as a reducing agent, Fe, Mn, Cr and Si are reduced and recovered. A
When 1, l, Ca, Mg or their alloys are added as a reducing agent, Fe, Mn, Cr, Si and Ti are reduced and recovered in molten steel. In each case, the required addition amount of the reducing agent is determined from the oxygen amount of the easily reducing oxide in the slag and the weight of the slag. Molten steel can be obtained with high precision.

-Measurement of slag weight-The surface positions of slag and molten steel are distances X ₁ and X from the reference point.
Detected as ₂ . Since the surface position of the molten steel at the interface between the slag layer, the thickness of the slag layer is calculated as (X ₁ -X _2). On the other hand, since the inner radius R of a container such as a vacuum degassing container and a ladle is known in advance, the slag volume V _S is V _S =
.pi.R ² a × (X ₁ -X _2). The weight of the slag W _S is
By multiplying the volume V _S by the specific gravity ρ of the slag, W _S =
It is calculated as ρ × V _S = ρ × πR ² × (X ₁ −X ₂ ). The obtained slag weight W _S is a value directly calculated from the thickness of the slag layer without interposing the molten steel weight W _M. FIG. 1 shows the flow during this period. In this way, error factors are rarely taken in, and the slag weight W _S can be obtained with high accuracy.

-Calculation of Required Addition Amount of Reducing Agent-The required addition amount of a reducing agent is determined by obtaining the concentration of easily reducing oxide contained in the slag and multiplying it by the weight of the slag. The concentration of easily reducible oxides contained in the slag was calculated from the oxygen concentration of the molten steel obtained using the oxygen concentration cell or the emission spectroscopy method or the decrease in the Cr concentration and Si concentration in the molten steel before and after decarburization refining. Determined. As a result of various experiments conducted by the present inventors, the oxygen concentration (O) of the easily reduced oxide in slag
It has been found that can be accurately estimated by the following equations. (O) = a · [O] + b (O) = c · ΔCr + d · ΔSi + e In the formula, a, b, c, d, and e represent coefficients or constants. Further, [O] represents the oxygen concentration of the molten steel obtained by the oxygen concentration battery or the emission spectroscopy, and ΔCr and ΔSi represent the reduction amounts of the Cr concentration and the Si concentration in the molten steel before and after decarburizing and refining, respectively. By multiplying the oxygen concentration (O) of the obtained easily reduced oxide in the slag by the slag weight W _S , the oxygen amount of the easily reduced oxide of the slag in the ladle can be obtained. Depending on the calculated oxygen amount, the amount of reducing agent input required for reduction is determined. When an amount of reducing agent adjusted in this way is added, Cr, Fe, Mn, etc. in the easily reducible oxides are recovered from the slag in a predetermined amount in the molten steel, and the amount of the reducing agent added is excessive. It will not be brought in. As a result, the reducing agent can be efficiently consumed, and the appropriateness of the molten steel components after melting is improved. In particular, it becomes possible to accurately manufacture a steel type that requires strict control regarding the Si content derived from the reducing agent.

[0013]

【Example】

Example 1: Cr content after completion of converter blowing is 11 to 20
A total of 100 charges of ferritic stainless steel and austenitic stainless steel in the weight% range (77
About 81 tons / charge), the oxygen concentration battery was immersed and the oxygen concentration was measured. At this time, the time until the oxygen concentration was obtained for all the charges was only 10 seconds.
Immediately after tapping the molten steel in the ladle, the positions of the slag surface and the molten metal surface were detected by using a sensor. The measurement time at this time is
It was about 1 minute. The position of the slag surface was measured using a touch-type sensor in direct contact, and the position of the molten metal surface was measured using an eddy current sensor. After measuring the slag thickness, the slag volume was calculated, and the slag weight was calculated by multiplying the slag specific gravity by a constant value. The total weight of easily reducible oxides in the slag was calculated from the obtained oxygen concentration and the slag weight, and the amount of the reducing agent required for the reduction was determined.

An example of 100 charges will be specifically described. The molten steel oxygen concentration determined by the oxygen concentration battery after the converter decarburization refining was 0.11% by weight. The oxygen concentration of the easily reducible oxide in the slag corresponding to this molten steel oxygen concentration is 12.4 wt% from the correlation diagram of FIG. In addition,
FIG. 2 shows a total of 100 charges (77 to 81 tons / charge) of ferritic stainless steel and austenitic stainless steel having Cr contents in the range of 11 to 20% by weight. It is a calibration curve which was obtained in advance by the carbon reduction method and was previously obtained from the relationship with the oxygen concentration in molten steel measured by an oxygen concentration battery.

On the other hand, the slag weight is the specific gravity of the slag which is previously determined to be 22.3 cm for the measured slag thickness of 3.5.
It was calculated to be 4.1 tons. Therefore, the oxygen concentration of the easily reducing oxide in the slag was 12.4% by weight x
The amount of Si required for recovering Cr, Fe, and Mn in molten steel was calculated to be 445 kg. After introducing ferrosilicon corresponding to 445 kg of pure Si, vacuum degassing and deoxidation were performed, slag was sampled again, and the oxygen concentration of the easily reducing oxide contained in the slag was measured. As a result, the oxygen concentration of the easily reducing oxide was 0.03% by weight. From this, it was confirmed that Cr, Fe and Mn were sufficiently recovered in the molten steel.

Example 2: A total of 100 ferritic stainless steels and austenitic stainless steels having a Cr content in the range of 11 to 20% by weight after completion of converter decarburization refining.
The oxygen concentration of the molten steel having a charge (77 to 81 tons / charge) was measured by an emission spectroscopy. At this time,
It took only about 2 minutes to obtain the measured oxygen concentration for all charges. After tapping molten steel in a ladle,
Immediately, the slag surface position was measured with a touch sensor, and the molten metal surface position was measured with an eddy current sensor. After measuring the slag thickness, the slag volume was calculated, and the slag weight was calculated by multiplying the slag specific gravity by a constant value. The total oxygen amount of the easily reducing oxide in the slag was calculated from the oxygen concentration of the easily reducing oxide in the obtained slag and the slag weight, and the input amount of the reducing agent necessary for the reduction was determined.

An example of 100 charges will be specifically described. The molten steel oxygen concentration measured by emission spectroscopy after the converter decarburization refining was 0.09% by weight. The oxygen concentration of the easily reducible oxide in the slag corresponding to this molten steel oxygen concentration obtained by spectroscopy is the molten steel oxygen concentration obtained by using the oxygen concentration battery shown in FIG. 2 and the easily reduced oxide in the slag. Since it matches the relationship with the oxygen concentration, it can be seen from the correlation diagram of FIG. 2 that 11.1 wt% corresponding to the molten steel oxygen concentration of 0.09 wt% is the oxygen concentration of the easily reducing oxide in the slag. . On the other hand, the slag weight is 5.4 by multiplying the measured slag thickness of 29.3 cm by the specific gravity of 3.5 of the slag obtained in advance.
Calculated as tons. Therefore, the oxygen concentration of the easily reducing oxide in the slag was 11.1% by weight × 5.4 tons = 60.
The amount of Si was 0 kg, and the amount of Si required to recover Cr, Fe, and Mn in molten steel was calculated to be 525 kg. After introducing ferrosilicon equivalent to 525 kg of this Si pure content,
Vacuum degassing and deoxidation treatment were performed, the slag was sampled again, and the oxygen concentration of the easily reducing oxide contained in the slag was measured. As a result, the oxygen concentration of the easily reducing oxide is
It was 0.02% by weight. From this, it was confirmed that Cr, Fe and Mn were sufficiently recovered in the molten steel.

Example 3: A total of 100 ferritic stainless steels and austenitic stainless steels having a Cr content in the range of 11 to 20% by weight after completion of converter decarburization refining.
For molten steel with a charge (77 to 81 tons / charge), the reduction amount of Cr concentration and Si concentration in the molten steel before and after the converter decarburization refining, that is, the difference in the concentration of Cr and Si in the molten steel before and after the converter decarburization refining It was measured by optical emission spectroscopy. At this time, it took only about 2 minutes for all the charges to obtain the measured values showing the reduction amounts of the Cr concentration and Si concentration in the molten steel before and after the converter decarburization refining. Immediately after tapping the molten steel in the ladle, the position of the slag surface was measured by the touch type sensor, and the position of the molten metal surface was measured by the eddy current type sensor. After measuring the slag thickness, the slag volume was calculated, and the slag weight was calculated by multiplying the slag specific gravity by a constant value. The total oxygen amount of the easily reducing oxide in the slag was calculated from the oxygen concentration of the easily reducing oxide in the obtained slag and the slag weight, and the input amount of the reducing agent necessary for the reduction was determined.

An example of 100 charges will be specifically described. Decarburization refining in a converter, Cr concentration and S before and after decarburization refining
The i concentration was measured by optical emission spectroscopy. Cr concentration and Si
The oxygen concentration of the easily reduced oxide in the slag estimated from the amount of decrease in concentration was 10.7% by weight, and the oxygen of the easily reduced oxide in the slag obtained from this estimated value based on the correlation diagram of FIG. The concentration was 10.8% by weight. In addition, FIG.
Total 1 of ferritic stainless steel and austenitic stainless steel whose content is in the range of 11 to 20% by weight
Oxygen concentration of easily reduced oxide in slag estimated by using reduction amount of Cr concentration and Si concentration in molten steel before and after decarburization refining for 00 charge (77 to 81 ton / charge) molten steel and carbon reduction method It is a calibration curve obtained from the relationship with the oxygen concentration of easily reducing oxide in slag.

On the other hand, the slag weight is the specific gravity of the slag, which is previously determined to be 31.2 cm for the measured slag thickness of 3.5.
Was calculated to be 5.8 tons. Therefore, the oxygen concentration of the easily reducing oxide in the slag was 10.8% by weight ×
5.8 tons = 626 kg, and the amount of Si required to recover Cr, Fe, and Mn into molten steel was calculated to be 548 kg. After introducing ferrosilicon corresponding to this Si pure content of 548 kg, vacuum degassing and deoxidation treatment were performed, the slag was sampled again, and the oxygen concentration of the easily reducing oxide contained in the slag was measured. As a result, the oxygen concentration of the easily reducing oxide was 0.03% by weight. From this, it was confirmed that Cr, Fe and Mn were sufficiently recovered in the molten steel.

In Table 1, the oxygen concentration of the easily reducing oxide in the slag is determined from the amount of the molten steel oxygen concentration of 100 charges or the reduction amount of Cr concentration and Si concentration in the molten steel before and after converter decarburization refining. When determined, and when the amount of ferrosilicon to be input is determined by directly analyzing the slag to obtain the oxygen concentration of the easily reducible oxide, the average value of the appropriate percentage of Si content in each molten steel and the average of working time It is shown in comparison with the value. As shown in the results of Table 1, Si in the molten steel when the oxygen concentration of the easily reducing oxide in the slag was calculated from the oxygen concentration of the molten steel and the amount of ferrosilicon added was determined
Regarding the average value of the appropriate ratio of the content, the work required time was shortened by about 10 minutes as compared with the case where the amount of ferrosilicon added was determined by directly analyzing the slag and determining the oxygen concentration of the easily reducible oxide. This shortening time is equivalent to an increase in monthly production of 9,600 tons, assuming a line producing 80 tons of crude steel per hour, and it can be seen that this leads to a significant increase in production. Further, it was found that the variation in working time was within ± 1 minute.

[0022]

[0023]

As described above, in the present invention, the optimum addition amount of the reducing agent can be known in the shortest time,
By adding a reducing agent in an optimum amount, the easily reducing oxides such as Fe, Mn, and Cr contained in the slag are reduced to a metallic state and recovered in molten steel, and due to the excessive addition of the reducing agent. Suppresses the increase of Si content, Al content, etc. in the molten steel after the heat treatment. As a result, the working time is drastically shortened, and molten steel having a high predictive value for the target composition is smelted. Further, since the consumption amount of the reducing agent can be minimized, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a flow of determining a required amount of a deoxidizer according to the present invention.

FIG. 2 is a graph showing that there is a close relationship between the oxygen concentration of molten steel measured by an oxygen concentration battery and the oxygen concentration of easily reducible oxide in slag obtained by the carbon reduction method.

[Fig. 3] Oxygen concentration of easily reduced oxide in slag estimated from reduction amount of Si concentration and Cr concentration in molten steel oxidized before and after decarburization refining and oxygen concentration of easily reduced oxide in slag obtained by carbon reduction method Graph showing that there is a close relationship with the analysis value

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Yamauchi 4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nisshin Steel Co., Ltd.

Claims (3)

[Claims] 1. When the valuable metal in an easily reducible oxide is reduced and recovered to the molten steel from the slag floating on the surface of the molten steel, the oxygen concentration of the molten steel is measured by using an oxygen concentration battery, and the oxygen value of the molten steel is measured in the slag. While estimating the oxygen concentration of the easily reducing oxide, the surface position of the slag and the molten steel is detected, the thickness of the slag is calculated from the difference between the detected surface positions, and the slag is based on the thickness of the slag. Obtaining the weight, the oxygen concentration of the easily reducing oxide in the slag and the required addition amount of the reducing agent from the slag weight is calculated, and the reducing agent is added to the slag with the addition amount of the calculation result. A method for reducing and recovering valuable metals in slag with improved precision in the composition. 2. A method for reducing and recovering valuable metals in slag, wherein the molten steel oxygen value measured by optical emission spectroscopy is used as the molten steel oxygen value according to claim 1 when determining the oxygen concentration of the easily reduced oxide in the slag. 3. When the alloy steel containing Si and Cr is subjected to decarburization refining in a converter or a vacuum degassing device, the reduction amount of Cr concentration and Si concentration in the molten steel before and after decarburization refining is used to facilitate reduction in slag. A method for reducing and recovering valuable metals in slag by estimating the oxygen concentration of oxides.