JPS6035409B2 - Method for measuring properties of molten slag in converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the properties of molten slag in a converter.

Generally, in converter smelting, it is important to adjust the slag properties such as the degree of oxidation of the molten slag, or even the basicity, within an appropriate range.

Recently, the development of sublance equipment and the probes used for it has progressed, and it has become easier to obtain information on steel production, and the accuracy rate of C and T at the end of blowing has improved significantly. Regarding information on molten slag, there are very few rapid measurement methods that can use that information during blowing.

However, the composition of the molten slag in the converter naturally affects the degree of dephosphorization, and it also has a considerable effect on the decarburization rate through changes in the amount of granulated iron thrown out from the steel into the molten slag layer. This cannot be ignored as a controlling factor for burobukisen.

The present invention provides a method for rapidly determining the degree of oxidation of the slag phase in a converter blower, as well as the basicity, i.e., the properties of the slag.

It has become common to use sublances and probes to control the blowing end point of oxygen converters.

In other words, in the latter half of blowing, a sublance is immersed in a steel bath, a portion of the molten steel is flowed into the probe from the steel bath, and the solidification process is thermally analyzed to determine the C concentration of the steel grade, while the bath temperature is measured using a thermometer. Then, based on the above supplement information, .
This is a method of determining the amount of oxygen supply necessary to stop blowing at a target C concentration and steel grade temperature using an appropriate decarburization rate formula and temperature increase rate formula. By effectively utilizing this method, the control accuracy of the blowing end point is significantly improved, and the accuracy rate for the target is 70.
It has reached ~90%.

However, since various reactions in the converter are affected by various blowing sickle conditions, reproducibility is not necessarily good. Therefore, standardization of blowout conditions is often attempted with the intention of improving the accuracy of end point control, but this negates the converter's original function of removing impurities such as P. Unification cannot be carried out in factories that manufacture many types of steel in the same converter. On the other hand, a method of continuously measuring the amount of CO and CO2 in the exhaust gas escaping from the converter mouth and estimating the amount of decarburization of the steel grade, the so-called exhaust gas analysis method, is also common. Due to inaccuracies in the C concentration of input materials, especially in hot metal, and insufficient accuracy of C○, C02 analyzers and exhaust gas flowmeters, the Errors accumulate in the estimated value of the C concentration, making it unusable.

In addition, even in the method of estimating the C concentration in the steel alloy from time to time by exhaust gas analysis method after sublance charging based on the C concentration in the steel alloy estimated by suprance, switching of the converter exhaust gas recovery valve at the end of blowing, Disturbances such as the rise of the hood in the furnace section, which adjusts the amount of carbon mixed into the exhaust gas, cannot be fully processed by the time-delayed gas analysis and flow measurement system, resulting in a considerable error in the estimated C concentration in the steel bath. is included, and the accuracy rate for the target C concentration is only 90% at most.

As mentioned above, the reason why the accuracy rate is only 90% is that the information on sublance and exhaust gas is simply related to steel industry, and lacks information on the molten slag in the converter, which is closely related to the reaction in the furnace. It is.

That is, the molten slag in the converter mainly consists of oxidation products of Si, Mn, and Fe in the steel bath that are generated in the early stage of blowing, and Ca○ added as an auxiliary raw material, and is particularly closely related to the control of the end point of blowing. The concentration of iron oxide in the molten slag and the degree of iron oxidation are influenced by blowing conditions such as the shape of the blow sickle lance, the height of the lance from the scratched surface, the oxygen supply rate, the oxygen supply pressure, and the shape of the furnace wall. It is known that it depends not only on the slag generation situation, the amount of slag, the degree of forming in the furnace, but also on the degree of slagging of the lime supplied in lumps. As described above, there are many factors that control the oxidation concentration in the molten slag, and therefore there is poor reproducibility between the iron oxide concentration in the slag and the blowing time.

On the other hand, Ca0, which participates in the reaction in the converter, is supplied into the furnace in the form of lumps, but the melting point of Ca○ is high, and the reaction between Ca○ and Si02 in the slag causes the formation of father a○, Si02, *a○, S
Because i02 is strongly formed on the Ca○ surface, the homogenization of Ca○ into the slag tends to stagnate, and it is also known that it is unevenly distributed near the furnace wall due to the relationship with the circulation direction of molten steel. However, it is also known that the formation of Ca○ into slag is promoted by the presence of iron oxide in the slag. It's nice to see it change to Kamachu. Therefore, it is important to quantitatively understand two factors: iron oxide concentration in slag, which is closely related to decarburization reactions at the slag steel bath interface or grain iron interface, and Ca purulence, which is related to dephosphorization and desulfurization reactions. This can be considered indispensable for further increasing the end point control accuracy.

However, as mentioned above, although it has been known that controlling the composition of molten slag in a converter is important, a method for obtaining information on the composition or similar information has not been clarified until now. Therefore, the inventors provided a slag inlet in the side wall of a cylindrical container made of a paper or wood compression molded product or a graphite molded product, sealed the container by gluing a thin metal plate or the like to its outer surface, and installed a thermocouple in the container. We developed a slug probe whose heat-sensitive end (thermal contact) protruded into a container and pre-filled the container with an appropriate amount of easily oxidizable metal, and conducted the following experiments.

That is, the above-mentioned probe was attached to the tip of the sublance and immersed in the molten slag layer in the converter, and an appropriate amount of slag was allowed to flow into the probe, thereby causing the easily oxidizable metal to react with the iron oxide in the slag. . This reaction is exothermic, and the temperature of the slag increases after the reaction starts, reaches a maximum value, and then decreases. Therefore, if this process is followed by a thermocouple, the heat of reaction for a given weight of easily oxidizable metal is Since it is proportional to the iron oxide content in the slag, the amount of iron oxide in the slag can be estimated by analyzing the measurement results under appropriate conditions.

The structural effects of this invention will be explained in detail below using specific examples.
Example 1 A cylindrical probe with an inner diameter of 2 mm and a height of 5 mm was manufactured from compression molded paper.

A willow hole with an inner diameter of 5 and a height of 4 is used as the slag inlet of the probe.
A copper foil with a thickness of 0.1 willow was pasted on the outside to seal it.

The thermocouple is Pt-13% Rh/Pt with a wire diameter of 0.2 ribs,
The two tip ends protruded into the probe. As an easily oxidizable metal, use N wire or N powder at 5% of the weight of the slag collected.
Slug the amount equivalent to beforehand.

It was loaded into the reaction chamber of the tube. For slag grade (here), 10k9 is melted in a twilight-impregnated magnesia crucible, and 15
Adjusted to 00o0.

Its composition is (%Fe○)t: 5-3 stops Ca○/Si0
221-4, %Mg025-10. When the reaction between this prepared slag and AI was followed, the reaction started in 2 to 5 seconds and a maximum value was produced in the temperature-time curve at 5 to 1 sand.

An example of the relationship between this temperature rise ΔT and (%Fe○)t is shown in FIG.

The parameter in the figure is the basicity of the slag. From this result, the iron oxide concentration in the slag can be estimated by measuring the temperature rise ΔT caused by the reaction.

In this case, as is clear from Figure 1, the basicity of the slag has some influence on the relationship between the temperature rise and iron oxide concentration, so
If the slag basicity at the time of measurement is roughly determined in advance in relation to the blow sickle conditions, the accuracy of determining the iron oxide concentration in the slag will be considerably improved.

The relationship shown in Figure 1 was established through experiments and chemical analysis of slag, and was then plotted in Figure 2 for cases where the amount of addition of slag was different (10%). Subsequently, an experiment was carried out to measure ΔT, and (%Fe○)t in the slag was estimated under various conditions. Table 1 shows the correspondence with the analytical values.

Table 1 Estimation of (poly Fe○)t in slack, A B addition amount 5
In that case, (%Fe0)3 in the table is the average basicity 2.4
Estimated value assuming (%Fe○) This is an estimated value of (%Fe○) in the slag using the estimated value of basicity determined by the milk blowing conditions.

What is noteworthy here is that by making full use of conventional rapid analysis methods,
Even with speedy sampling, it took at least 5 minutes to obtain information about the composition of the slag (Fe○
) Although it is only information about t, it has become possible to estimate it immediately by thermal analysis, opening the way for its application to high-speed processes such as converter blowing sickles.

Furthermore, if the temperature rise is measured for the same slag by changing the amount of addition of peaks, the basicity of the slag can also be estimated since the relationship between (%Fe0)t and ΔT is different in these two cases.

That is, for example, if the temperature increase when the amount of AI added is 5% and 10%, respectively, is △T, △L, then △T,
A relationship between (%Fe○)t and basicity that satisfies the following is determined, and on the other hand, a relationship different from that in the similar case of FIG. 1 is obtained in FIG.

In this case, since the slags to be measured are the same, only one set of (%Fe◯)t and basicity that satisfies the above two relationships is determined. Examples in that case are shown in Table 2. The estimated value corresponds well to the analytical value, and the determination accuracy is (%Fe○)t.
．． 0%, basicity is considered to be about ±0.2. Table 2 Example of estimating (poly Fe○)t and basicity in slag 2 As a structure that can be attached to a sub-lance for a converter, two slag probes described in Example 1 are installed in the same structure, and the slag inlet has a high Compressed paper probes with the same diameter and an inlet port offset by 1800 were manufactured and tested in a 16-ratio converter operation.

Of the two slag probes, one was charged with AI at 5% of the weight of the collected slag, and the other one was charged with AI at 10%. The position of the steel bath surface was determined by measuring the scratch surface in front of the blowing mirror, and the depth of the dent directly under the blowing iron oxygen lance determined by the blowing coin conditions was also taken into account, and the immersion position of the slag probe was determined so that the slag inlet was 2 points below the steel grade. It was determined that it would be within the slag layer above Qianfan or 8qi Cape. The thickness of the slag layer is usually equal to or greater than the low gunwale of a blow sickle, and the above-mentioned position was the optimal position because it prevented the steel grate from entering the slag probe and the slag from getting mixed into the upper probe.

Approximately 2 to 4 minutes before the scheduled end of blowing, the slag probe was attached to the tip of the sublance and lowered to immerse it in the slag layer.

As a result, as in Example 1, the temperature -
A local maximum occurred in the time curve. When we determined the relationship between this temperature rise and the slag composition, we found that the relationship was substantially the same as that in Figures 1 and 2. Using this relationship, we used (%F
When e○)t and basicity were estimated, the standard deviation of the difference between the estimated value and the analytical value of basicity was (%Fe○).
・t=10-25 basicity 1.5 each in the range of 2-4
,0.2. The number of measurements in this case is 28.

However, regarding measurement number 2, it was found that there were cases where the reaction between the mountain and slag was not completed within the probe.
In addition to N, Mn02 was added as an oxidizing agent to 1 of the amount of AI in advance.
Example 1 shows that the reaction is completed when 0% is added.
This was confirmed in 50 experiments using similar experiments. It has been found that with this amount of Mn02 added, the relationship between the temperature rise and (%Fe◯)t shown in FIGS. 1 and 2 is substantially maintained. In the above-described embodiments, N was described as the easily oxidizable metal pre-loaded in the slag probe, but in the present invention, in addition to AI, Ca, rare earth metals, Cr, Sj, Ti, Zr, etc. can be used.
Also, oxidizing agents that replace Mn02 are C2, Cr03, Fe2
03 etc. are suitable. When measuring the basicity of molten slag in a converter together with the degree of oxidation according to this invention, in addition to using two slag probes, using a slag probe having two independent reaction chambers will make the bonding operation even simpler. .

By carrying out this invention, the above-mentioned problems and problems can be advantageously solved, and the properties of the molten slag in the converter can be detected immediately, so that the oxidation degree and basicity of the slag can be easily determined accordingly. Can be adjusted.

However, it must be noted that if the probe immersion position is not appropriate, proper measured values will not be obtained. This invention is of course applicable to all refining processes that use oxide slag.

[Brief explanation of the drawing]

The figure shows the temperature rise due to the reaction inside the probe and the (F) in the slag.
e0) The relationship between the t content and the influence of basicity on it. Figure 1 shows N at 5% of the slag weight, Figure 2 shows N at 10
% addition is a graph. Figure 1 Figure 2

Claims (1)

[Claims] 1. During blowing in an oxygen converter, a probe is immersed into the molten slag layer in the converter from the upper part of the converter mouth to allow the slag to flow into the probe. The degree of oxidation of the molten slag in the converter is determined by causing the slag to react with the oxidizable metal loaded in advance, and thermally analyzing the reaction heat generated by the reaction detected by a heat-sensitive element installed in the probe. Characteristic method for measuring the properties of molten slag in a converter. 2. During blowing in an oxygen converter, probes loaded with different amounts of easily oxidizable metals are immersed into the molten slag layer in the converter from the upper part of the converter mouth to each reaction chamber. The oxidation degree and basicity of the molten slag in the converter are determined by allowing slag to flow in and detecting and thermally analyzing the heat of reaction between the slag and an oxidizable metal using a heat-sensitive element installed in each reaction chamber. A method for measuring the properties of molten slag in a converter.