JPS5837366B2 - Pretreatment method for molten metal - Google Patents

Description

[Detailed Description of the Invention] This invention aims to more completely remove impurities from molten metal such as hot metal in a ladle, which is performed during the process of charging hot metal tapped from a blast furnace to a converter. The present invention relates to a method for pretreatment of molten metal.

As is well known, for example, the sulfur content in hot metal depends on the raw material iron ore, the sulfur content in coke, and the blast furnace operating method.In order to reduce the sulfur content in hot metal, the coke ratio and solvent This is accompanied by an increase in ironmaking costs such as an increase in production costs and a decrease in productivity.

Furthermore, in order to improve the desulfurization efficiency in the converter furnace in a steel factory, the unit consumption of solvent increases and productivity decreases, and there is a limit to the desulfurization rate itself.

The quality requirements for products are becoming more sophisticated, and the demand for low-sulfur steel and ultra-low-sulfur steel is also increasing, so the development of an effective out-of-furnace desulfurization method is awaited. I'm here.

Conventionally, for example, hot metal tapped from a blast furnace is first received in a desulfurization treatment pot and scraped off from the surface before being charged into a converter.

The product is then transported to a desulfurization factory, where a desulfurization agent such as calcium carbide is put into a desulfurization treatment pot to desulfurize it, and the generated slag is scraped out.

The hot metal that has been pretreated in this way is charged into a mixed pig iron furnace or directly transferred to a converter charging ladle and charged into a converter.

Methods for scraping out the slag generated after adding the desulfurizing agent include using a slag drager, using a forklift, and manually, but in any of these methods, the slag in the processing pot is metal(
The slag on the surface of the hot metal is scraped using a slag scraping rod with an attachment attached to the tip of the arm, and in this slag scraping method, it is impossible to completely scrape out the slag. , a few percent of the slag will inevitably remain.

If an attempt is made to scrape out more completely, even the processed hot metal will be scraped out, resulting in an increase in iron loss.

The slag generated during this preliminary treatment contains a large amount of sulfur, phosphorus, etc. that have been separated and removed from the hot metal, and if even a small amount of this slag enters the converter, it will return to the steel due to resulfurization and rephosphorus phenomena. This results in

For example, in the case of desulfurization slag after desulfurization treatment, even if 5% of the slag remains without being scraped out, 1 to 5% of sulfur still exists in the slag, and this is absorbed by blowing into the converter. This causes the sulfur content in the steel to increase by 0.001 to 0.002%.

Sulfur content in hot metal after desulfurization treatment is 0.001 to 0.003
%, it was a big problem how to dispose of the remaining slag.

The present inventors have discovered that impurities such as sulfur and phosphorus in metallurgical furnaces such as converters, which are caused by incomplete slag scraping in conventional molten metal, especially hot metal pretreatment methods, as described above. As a result of conducting research to suppress the transfer of

In other words, (1) In slag scraping work, it is extremely difficult to completely scrape out slag without also scraping out molten metal;
Productivity is also extremely low.

(2) Therefore, even if an amount of slag that cannot be removed enters a metallurgical furnace such as a converter, sulfur from molten steel after blowing, etc.
In order to prevent an increase in impurities such as phosphorus, it is sufficient to reduce the impurities such as sulfur and phosphorus in the slag transferred into the converter, for example.

(3) To achieve this, by diluting the remaining slag after preliminary treatment such as desulfurization with a substance that does not have a negative effect on other steels, the amount of the above impurities remains as is, and the total amount of slag containing these impurities remains unchanged. After increasing the amount of slag, scraping may be performed again to remove the increased amount of slag and most of the impurities.

Therefore, this invention was made based on the above knowledge, and for example, when performing converter blowing work, desulfurization,
For molten metal such as hot metal after slag scraping etc.
After diluting the remaining slag by adding a new slag-forming agent and creating a mixed slag with the slag remaining in the molten metal, the mixed slag is discharged to obtain a molten metal with less impurities. It has characteristics.

The newly added sludge used in the pretreatment method of the present invention is preferably one with a low melting point, such as lime or soda ash. For example, in the case of steel, a slag-forming agent or desulfurization agent such as light calcined dolomite, slaked lime, and brick waste can be used.

Next, the present invention will be described by way of examples with reference to FIGS. 1 to 3.

170 tons of hot metal 1 tapped from the blast furnace is received in the desulfurization treatment ladle 2 (capacity 200 tons) as shown in Figure 1, and after normal desulfurization treatment is carried out (not shown in the figure). The desulfurization processing ladle 2 is tilted using tilting equipment to such an extent that the hot metal 1 does not flow out.

Next, the slag 3 is scraped out into the slag pan 6 installed on the sloping trolley 7 using a slag raking stick with an attachment 5 attached to the arm 4.

A small amount (approximately 50 kg) of slag 3 remained on hot metal 1 after slag removal, and it was impossible to scrape it out completely.

Next, as shown in FIG. 2, 500k49 lime 9 is charged in advance into a converter charging ladle 8, and the desulfurized hot metal 1 is transferred thereinto.

At this time, the lime 9 and what remains of the slag 3 after desulfurization are mixed by stirring the hot metal.

Thereafter, as shown in FIG. 3, scraping is carried out again to scrape out the mixed slag 10.

It is difficult to completely scrape out the mixed slag by this second slag scraping, but even if the amount of remaining slag is about the same as the amount of slag remaining after the first slag scraping, the sulfur content in the mixed slag 10 is It was less than 1/10 of the original slag 3, and even if it was directly blown in the converter, resulfurization was almost negligible.

Regarding the conventional pretreatment method and the pretreatment method of the present invention,
The treatment was carried out 10 times, and the average performance of the results is shown in Table 1.

In this way, compared to the conventional method, according to the method of the present invention, 0.0
0.1% of resulfurization could be prevented.

Further, when comparing the iron loss due to slag scraping, according to the present invention, iron loss could be reduced by about 130 kg by not forcing slag raking.

As described above, according to the present invention, the slag after preliminary treatment such as desulfurization treatment is diluted with a substance that does not adversely affect other molten metals, thereby making it easier to scrape off the slag, and removing sulfur and phosphorus in the remaining slag. Since impurities such as molten metal can be diluted, molten metal with less impurities can be obtained by this pretreatment.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic cross-sectional views showing embodiments of the method of the present invention, Figure 1 is a cross-sectional view showing the slag scraping mode after desulfurization, and Figure 2 is a cross-sectional view showing how hot metal is charged into a converter. FIG. 3 is a sectional view showing an embodiment of scraping again. In the drawings, 1... hot metal, 2... desulfurization treatment pot, 3... slag, 4... arm,
5... Attachment, 6... 7-mouth pan, 7... Noropan trolley, 8... Converter charging pot, 9... Lime, 10... mixed slag.

Claims (1)

[Claims] 1 Adding a new slag-forming agent to the molten metal after impurity removal treatment to create a mixed slag with the slag remaining in the molten metal, diluting the remaining slag, and then discharging the mixed slag. A molten metal pretreatment method characterized by obtaining molten metal with few impurities.