JP3288800B2 - Oxygen determination method for reduced oxides contained in steelmaking slag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantitatively analyzing the amount of oxygen contained in steelmaking slag produced by decarburization blowing at the steelmaking stage.

[0002]

2. Description of the Related Art When decarburizing and blowing alloy steel such as stainless steel in a converter or a vacuum degassing apparatus, carbon in the molten steel reacts with blowing oxygen and is removed from the molten steel as CO gas. At this time, some of the useful components such as Cr, Fe, and Mn are simultaneously 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)

[0003] Metal elements such as Cr, Fe and Mn that have become oxides migrate to slag floating on the surface of molten steel. The metal elements in the slag are reduced from oxides to a metal state in the final stage of steel making, and are recovered as molten metal in molten steel. The recovery reaction utilizes the fact that metal elements such as Cr, Fe, and Mn are easily reduced to a metal state by Si. For example, a predetermined amount of metallic Si source is added to molten steel in a ladle during vacuum refining, and the following reduction reaction is performed. Cr, Fe, Mn, etc. reduced to a metallic state are taken into molten steel. 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 ) From slag When refining while recovering Cr, Fe, Mn, etc. in molten steel, it is necessary to quantitatively grasp the metal elements that migrate from slag to molten steel in the final stage in order to adjust the composition of the molten steel with high accuracy. Also, recently, steel grades with strict standards for the Si content have begun to be manufactured. In order to obtain molten steel whose components are adjusted with high precision, and to respond to steel types whose Si content is strictly controlled, the amount of oxygen contained in the easily reducible metal oxide reduced by Si must be accurately determined. It is necessary to understand.

[0004] As a means for determining the amount of oxygen in a metal oxide, a method of performing X-ray fluorescence analysis of a slag sample is known. In the fluorescent X-ray analysis method, an analysis sample is prepared by a glass bead method, a press method, or the like from molten slag collected from a converter, an electric furnace, a ladle or the like during refining. Then, assuming that the oxides in the metal and metalloid element states contained in the sample are each in a specific oxide form, the oxygen determined by multiplying the quantitative value of the oxide by a coefficient determined from the stoichiometric relationship. Calculate analytical values. Therefore, in a sample containing metal-state Cr, Fe, Mn, or the like or a sample containing metal oxides having different oxygen values, the analysis value necessarily includes a measurement error. Then, the present inventors reacted the carbon source while continuously heating the sample in an inert atmosphere, and measured the amount of oxygen combined with carbon and discharged out of the system in time series, and measured the measured value. Is integrated, the Si contained in the sample and in the molten state
Found that the oxygen content of easily reducible metal oxides such as Cr, Fe, Mn, etc., reduced by oxygen is required, and proposed a method for quantifying oxygen in the easily reducible metal oxides in steelmaking slag (Japanese Patent Application No. Hei. -319364).

[0005]

In actual operation, when reducing oxides in slag to a metallic state, Al, Ti, Ca, Mg or an alloy thereof having an oxygen affinity higher than that of Si is used as a reducing agent. May be. When a reducing agent having a large oxygen affinity is used, C reduced by Si
In addition to easily reducible metal oxides such as r, Fe and Mn, elements having an oxygen affinity lower than that of the reducing agent used are simultaneously reduced. For example, when Al is used as a reducing agent, oxides such as SiO ₂ and TiO ₂ are also reduced according to the following reaction. 3 (SiO ₂ ) +4 Al → 3 [Si] +2 (Al ₂ O ₃ ) 3 (TiO ₂ ) +4 Al → 3 [Ti] +2 (Al ₂ O ₃ ) Therefore, in order to perform the reduction treatment with Al with high accuracy, It is not sufficient to grasp the amount of oxygen contained in easily reducible metal oxides such as Cr, Fe, and Mn, and the amount of oxygen in the hardly reducible metal oxide combined with Si, Ti, etc. Need to figure out. The present invention has been devised to solve such a problem, and is included in slag by combining a value obtained by carbon reduction analysis and a value obtained by X-ray fluorescence analysis. It is an object of the present invention to accurately and quickly determine the amount of a reducing agent necessary for reducing an oxide.

[0006]

In order to achieve the object, the oxygen determination method of the present invention reacts a sample collected from steelmaking slag with a carbon source while continuously heating the sample in an inert atmosphere to obtain a carbon source. And the amount of oxygen discharged out of the system in combination with the time is measured in a time series, and the amount of oxygen of the easily reducible metal oxide contained in the sample and reduced by Si in a molten state is obtained from the integrated value of the measurement result. Similarly, a sample collected from steelmaking slag is irradiated with X-rays, the fluorescent X-ray intensity of the component element of the hardly reducible metal oxide generated is measured, and the oxygen compounded with the component element is determined. And quantitatively analyzing the oxygen content of the oxide contained in the steelmaking slag from the oxygen content of the easily reducible metal oxide and the hardly reducible metal oxide. As easily reducible metal oxides in actual operation,
There are oxides such as Cr, Ni, Fe, and Mn. Examples of the non-reducible metal oxide include oxides such as Si, Ti, Al, Ca, and Mg.

Hereinafter, the present invention will be described specifically. -Oxygen determination of easily reducible metal oxide-The easily reducible metal oxide reduced by Si in the slag is obtained by filling a sample taken from the slag together with a carbon source such as activated carbon or carbide into a graphite crucible, and supplying an inert atmosphere. Oxygen can be quantified by continuously heating and raising the temperature in the inside, and measuring CO gas generated by a reduction reaction with carbon by an infrared absorption method or the like. Carbon reduction starts with an element having a low oxygen affinity and gradually shifts to an element having a high oxygen affinity. The easily reducible metal oxides such as Cr, Fe, and Mn contained in the sample slag initiate a reduction reaction at a relatively low temperature, and oxygen separated from the metal element is extracted. On the other hand, non-reducible metal oxides such as Si, Al, Ti, Ca, and Mg that cannot be reduced by Si start a reduction reaction at a high temperature. Therefore, after the extraction of oxygen from the easily-reducible metal oxide ends, the oxygen extraction of the hardly-reducible metal oxide starts.

[0008] CO generated by carbon reduction of sample slag
When the gas is quantified by the infrared absorption method, an oxygen extraction curve shown in FIG. 1 is obtained. The oxygen extraction curve rises with the analysis time and the heating time, but once decreases at a temperature T ₁ near 1800 ° C., which reaches the time point t ₁ , and then rises again, and then the oxygen intensity becomes zero at the time point t ₂ . Minimum value I ₁ of the analytical oxygen intensity at time t ₁ is clearly detected. Therefore, the reduction reaction of the easily reducible metal oxide is clearly distinguished from the reduction reaction of the hardly reducible metal oxide. Analysis start time t
CO gas discharged in the period from ₀ to time t ₁ is derived from the easily reducible metal oxides, CO gas discharged in the period from time t ₁ to time t ₂ is derived from the irreducible metal oxide I do. Therefore, by integrating the oxygen intensity during the period (t ₀ → t ₁ ) and converting the area of the shaded area shown in FIG. 1 to the concentration, the amount of oxygen extracted from the easily reducible metal oxide can be obtained. .

-Oxygen determination of non-reducible metal oxide-Metal elements such as Si, Al, Ti, Ca, and Mg, which have a high oxygen affinity, are different from easily-reducible metal oxides in normal converter operation. Not present as metals or metalloids, all present in slag as oxide form. Therefore, Si, A
X-ray fluorescence analysis can be applied to the determination of oxygen in hardly reducible metal oxides such as l, Ti, Ca, and Mg without introducing measurement errors caused by the metal or metalloid state. The sample used for the fluorescent X-ray analysis method is prepared by a press molding method, a glass bead method or the like as shown in FIG. Among them, the press molding method is advantageous in that a sample can be prepared in a short time, unlike the glass bead method which requires accurate weighing of an analysis sample and a flux. In the press molding method, an appropriate amount of the collected slag is filled in an aluminum cap, and is subjected to pressure molding with a 15 to 20 ton press to produce an analysis sample. At this time, since the sample slag is sufficiently pulverized, the analysis error caused by the dispersion of the particles is eliminated, so that a highly reliable analysis result can be obtained by one measurement using the same sample. Analytical results are obtained in a short time of less than 10 minutes.

FIG. 3 shows an oxygen determination method using X-ray fluorescence of a hard-to-reduce metal oxide contained in slag, using Si as an example.
Shown in In the X-ray fluorescence analysis method, since a plurality of elements can be simultaneously quantified, the amount of oxygen combined with Al, Ti, Ca, Mg, etc. other than Si is measured simultaneously. When X-rays are irradiated on the press-formed surface of the slag sample, Si atoms are excited. When the excited Si atom returns to a stable level,
X-rays unique to Si are generated. The fluorescent X-rays of Si are separated by a spectral crystal, and the X-ray intensity is measured by a gas flow type proportional counter. The measured X-ray intensity is proportional to the Si content of the slag. This indicates that all the Si in the slag exists in an oxide state. Therefore, the SiO ₂ concentration of the slag sample is calculated by substituting the measured value of the X-ray intensity into the calibration curve (FIG. 4) previously obtained from the relationship between the SiO ₂ content and the X-ray intensity.

The Si in the slag is in an oxide state without being present in a metal state. Therefore, by converting the SiO ₂ concentration determined with reference to the calibration curve of FIG. 4 to O ₂ , quick and accurate oxygen quantification becomes possible. The oxygen combined with Si obtained by the fluorescent X-ray analysis is calculated, for example, as follows for the sample A in Table 1. Theoretical calculation oxygen content = SiO ₂ × (O ₂ / SiO ₂ ) = 18.31 × (32 / 60.1) = 9.8 An analysis system using both the carbon reduction analysis method and the fluorescent X-ray analysis method is shown in FIG. Show. The amount of oxygen extracted from the easily reducible metal oxide is measured by the carbon reduction analysis method, and the amount of oxygen combined with Si, Al, Ti, Ca, Mg, etc. is quickly and accurately determined by a fluorescent X-ray analyzer. Measured. From these two types of oxygen amounts, the total oxygen amount in the slag is determined. As a result, during refining using a reducing agent having a large oxygen affinity, it is necessary to reduce the metal oxide having a smaller oxygen affinity than the added reducing agent together with the easily reducible metal oxide contained in the slag. The amount of the reducing agent added can be determined accurately.

[0012]

【Example】

Example 1 Four types of stainless steel converter slag whose compositions are shown in Table 1 were used as slags to be subjected to oxygen determination. In addition, the theoretical calculation value of the amount of easily reduced oxygen in Table 1 is a value obtained by multiplying a measurement value obtained by X-ray fluorescence analysis after separating and removing metal in slag with iodine alcohol.

[0013]

[Table 1]

An analytical sample was weighed in an amount of 0.05 g, and the same amount of a carbonaceous reducing agent was added to an empty-baked 2.5-ml double crucible and heated at a heating rate of 4 ° C./sec. The oxygen intensity detected during the period (t ₀ → t ₁ ) shown in FIG. 1 was integrated, and the oxygen concentration of the easily reducible metal oxide was measured. As is evident from Table 2 showing the measurement results, the oxygen concentration measured in this way matched the theoretical calculation value with high accuracy.

[0015]

[Table 2]

The carbon reduction of the easily reducible metal oxide hardly proceeds in a low temperature range of 800 ° C. or lower as shown in FIG. Therefore, rapid heating that instantaneously passes through the low-temperature region
After the temperature was raised to 00 ° C, activated carbon was added as a reducing agent,
Thereafter, heating was performed at a heating rate of 4 ° C./sec. Under this heating condition, the oxygen concentration of the easily reducible metal oxide was measured in the same manner.
As is clear from Table 3 showing the measurement results, the measured values at this time also had high consistency with the theoretically calculated values.

[0017]

[Table 3]

Example 2 An analysis sample was prepared by filling an analysis sample into an aluminum cup and press-forming with a 15 to 20 ton press. When fluorescent X-ray analysis was performed under the conditions of tube voltage: 50 kV, tube current: 55 mA, and integration time: 40 seconds, the oxygen amounts of Si, Al, Ti, Mg, and Ca shown in Table 4 were calculated. These oxygen amounts were in good agreement with the theoretically calculated oxygen amounts calculated by the wet analysis method.

[0019]

[Table 4]

Example 3 Oxygen determination of reduced oxides contained in steelmaking slag by using a converter slag having the composition shown in Table 5 together with carbon reduction analysis and X-ray fluorescence analysis did. Each of the compositions shown in Table 5 is a value quantitatively analyzed by a wet method. The value obtained by the iodine alcohol method for the metal component and the value obtained by the wet analysis for the oxide were multiplied by the stoichiometric coefficient.

[0021]

[Table 5]

The analysis values of Samples H and I were compared with the theoretically calculated oxygen amount converted to oxygen amount, and the carbon reduction analysis method and fluorescence X
Table 6 shows the amount of oxygen determined by the combined use of the line analysis method.

[0023]

[Table 6]

According to the fluorescent X-ray method, the oxygen content of the hardly reducible metal oxide was able to be separated for each element, and each of them was in good agreement with the theoretical calculation value of the oxygen content. However, Cr,
Since Fe, Mn, and the like are present in the slag in the form of a metal in addition to the oxide, the oxygen content of the easily reducible metal oxide is high, and an error has occurred as compared with the theoretical calculation value. On the other hand, according to the carbon reduction analysis method, although the oxygen amount of the easily reducible metal oxide was in good agreement with the theoretical calculation value, the oxygen amount of the hardly reducible metal oxide could not be measured. Therefore, the oxygen content of the easily reducible metal oxide is obtained by the carbon reduction analysis method, and the oxygen content of the hardly reducible metal oxide is obtained by the fluorescent X-ray analysis method. The obtained oxygen amount was obtained. When determining the amount of the reducing agent to be added to molten steel during refining based on this oxygen amount, molten steel whose components are adjusted with high precision can be obtained.

[0025]

As described above, in the present invention, by combining the carbon reduction analysis method and the fluorescent X-ray analysis method, the oxides to be reduced contained in the steelmaking slag can be quickly and accurately determined. Oxygen can be determined and stable steelmaking operation is possible. For example, Cr, F contained in slag
When reducing easily-reducible metal oxides such as e and Mn with Al, Si, Ti, and the like, which have a lower oxygen affinity than Al, are reduced. Therefore, it is necessary to grasp the amount of oxygen bonded to Si, Ti, and the like. Is required. In such a case, the present invention is applied, and the addition amount of a reducing agent such as Al, an Al alloy, or an Al compound required for the reduction reaction can be accurately obtained. As a result, the recovery rate of Cr, Fe, Mn and the like and the medium accuracy of the components such as Si and Ti are improved without requiring an excessive reducing agent.

[Brief description of the drawings]

FIG. 1 is an oxygen extraction curve obtained when carbon slag is reduced while heating a converter slag at a rate of 4 ° C./sec in an inert gas atmosphere.

Fig. 2 Sample preparation process used for X-ray fluorescence analysis

Fig. 3 Measurement principle of X-ray fluorescence analysis

FIG. 4 Calibration curve of SiO ₂ in X-ray fluorescence analysis

FIG. 5 is a steelmaking slag analysis system according to the present invention.

(56) References JP-A-6-148167 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 31/00 C21C 5/00 G01N 23/223 G01N 33 / 20

Claims (2)

(57) [Claims] 1. A sample collected from a steelmaking slag is reacted with a carbon source while continuously heating in an inert atmosphere, and the amount of oxygen combined with carbon and discharged out of the system is measured in a time series. The amount of oxygen in the easily reducible metal oxide contained in the sample and reduced by Si in the molten state is determined from the integrated value of the measurement results, and the sample similarly collected from steelmaking slag is irradiated with X-rays to generate The fluorescent X-ray intensity of the component element of the hardly reducible metal oxide to be measured is measured, the oxygen combined with the component element is quantified, and the oxygen content of the easily reducible metal oxide and the hardly reducible metal oxide is determined. A quantitative analysis of the oxygen content of the oxides contained in the steelmaking slag from the above. 2. The easily reducible metal oxide according to claim 1, wherein
An oxygen determination method in which an oxide such as r, Ni, Fe, and Mn is used, and the non-reducible metal oxide is an oxide such as Si, Ti, Al, Ca, and Mg.