JPS6027726B2 - Method for refining molten steel using a ladle - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for refining molten steel using a ladle, which can reduce the content of phosphorus P, sulfur S, hydrogen, oxygen, etc., and has a high ability to adjust the components. Conventionally, a converter blowing method has been known as a means for obtaining low P steel. As the converter blow sickle method, the normal blowing method, soft blow method, double slug method, and double tapping method are known, but in these methods, the P content in the molten steel is 1
It can only be lowered to about 50, 100, 80 and 70 (skin). The reason why the P content of molten steel cannot be lowered in this way is as follows. In other words, converter fusen is mainly controlled by decarburization processing time, and since the processing time is short,
It is not possible to take enough time for deP treatment to obtain low P steel. In addition, if the slag volume (amount) for dephosphorization is increased, there is a risk of slag blowing out, etc., and there are problems with workability, so there is a limit to the slag volume for dephosphorization. Therefore, in the converter blowing mirror, it was not possible to lower the P content of the molten steel. On the other hand, in order to obtain steel with low P and also low S, it is necessary to refining molten steel by taking steel as in the powder injection method, and also to obtain low P steel.
Therefore, in order to obtain steel whose composition can be reliably adjusted by reducing the H content to 0, it is necessary to refine (process) the molten steel, such as vacuum treatment using a ladle, for example, RH degassing treatment. Therefore, when trying to obtain steel with a low content of P, S, 0, etc. through ladle refining, the tapping temperature of the steelmaking furnace must be increased, taking into account the temperature drop of the molten steel in the ladle. Must be (for example, around 1740-176000)
. As a result, in the steelmaking furnace, a problem occurs in that the P content does not decrease, the amount of erosion of the refractory increases, and the yield decreases. Therefore, this invention was made to provide a method for refining molten steel in a ladle that solves the above-mentioned problems. Then, the tip of the heating electrode is immersed in the slag on the molten steel in the ladle to heat the molten steel in the ladle. Next, an oxidizing refining flux is added to the molten steel in the ladle, and then a refining gas is blown into the molten steel in the ladle from above through a lance, so that the molten steel is heated in an oxidizing gas atmosphere. Then, the molten steel in the ladle, the molten steel, and the slag on the port steel are concentrated, the slag on the molten steel in the ladle is removed, and the molten steel in the ladle is vacuum-treated. Next, a flux for reduction refining is added to the molten steel in the ladle, and then an inert gas is blown into the molten steel from the lance, so that the molten steel in the ladle is heated under an inert gas atmosphere. Then, the port steel and the slag on the molten steel are ignited, and if necessary, following the step ``H'', a flux for reduction refining is added to the molten steel in the steel taking process, Next, by blowing an inert gas into the molten steel from the lance, the molten steel in the ladle, the molten steel, and the slag on the molten steel are mixed together in an inert gas atmosphere. removing slag on the molten steel in the ladle;
佽′ The feature is that the face steel inside the ladle is then subjected to vacuum treatment. As the slag for dipping the heating electrode, steelmaking furnace slag may be used, or a synthetic crab-forming agent may be used. There are two types of heating using heating electrodes: electric arc heating and resistance heating.The advantages of heating in this way are:
This means that the tapping temperature of the steelmaking furnace can be lowered. That is, the first
Figure 2 shows the relationship between the refractory corrosion coefficient of a steelmaking furnace (converter) and its tapping temperature, and Figure 2 shows the [P] (P) of raw steel obtained in a steelmaking furnace (converter). As can be seen from the diagrams showing the relationship between the concentration of steel (concentration of The lower the value, the lower the port loss coefficient of the refractory, and the lower [P] (therefore, it is advantageous for refining in a ladle), further improving the yield. Another advantage of only heating being performed (that is, the catalytic treatment and heat treatment are separated) is that there is less variation in the surface of the molten steel in the ladle. (because the electrode rod is not heated), heating can be performed stably and the life of the electrode rod can be extended. As is well known, when heating is performed using a heating electrode, a lance that is immersed in the molten steel in the ladle from above prevents gas (such as impurities such as sulfur and sulfur) from entering the steel to promote heating. gas (e.g., 02, Ar, gas, etc.),
It is injected into the molten steel to improve the heating efficiency of the heating electrode by blowing into the molten steel (the amount of injection is 0.00000000000000 yen per ton of steel
It is preferable that the speed is 4N/min or more and less than 4N/min. The reason for this is that if the heating rate is less than 0.4 so/min, it will take a long time to heat, making it impractical in terms of heating efficiency.On the other hand, if the heating rate is more than 0.4 so/min, the base metal will adhere to the electrode due to molten steel scattering. This is because the life of the electrode will be shortened. ). Also,
After heating, the heating electrode is raised to separate its tip from the slag in the ladle. The gas for refining carried out under an oxidizing atmosphere can be a gas that does not introduce impurities such as S, S, etc. into the steel, such as ~02 gas, and it can also be carried out under an inert gas atmosphere. An inert gas such as Ar can be used as the gas for worship (refining), and the flow rate of these gases should be at least 100 ton/min to prevent the refining efficiency from decreasing. Preferably,
The molten steel surface rises too much due to gas injection, and the so-called free board in the ladle must be made large, making it impractical.
It is preferably n or less. Note that such a large amount of gas blown can only be obtained by a lance structure in which the lance is immersed into the molten steel from above. The manner in which the gas is ejected from the lance into the molten steel is preferably within a range of 1y in the vertical direction with respect to the horizontal direction. This is because the gas ejected from the lance first spreads horizontally and then rises vertically, so the gas trapped in the molten steel is used extremely effectively for attack, resulting in high wear efficiency. Further, the shape of the gas flow passage of the lance for this purpose is as shown in FIG.
The T-shaped two-hole type with the nozzle la located at one location, and the L-shaped one-hole type with the nozzle 1'a located at one location at the tip of the lance 1' as shown in the opening of Figure 3. Preferably. By using such a lance, it is possible to flow the molten steel from the side wall of the ladle toward the center of the ladle, as shown in the figure, so that the slag and molten steel are mixed uniformly on the steel surface and The refining flux added after the electrode heating is easily converted into molten steel by contact mixing with the molten steel by the gas supplied from the lance, and electrode heating for oxidation is therefore not necessary. In addition, the flux (slag) that has become grooved in a short time continues to come into contact with the molten steel and mix vigorously, so that the slag-metal reaction progresses quickly and a high quality smelter is obtained. 4A and 4B are cross-sectional views showing an example of a ladle for carrying out the present invention, FIG. 4A shows a heating mode using a heating electrode, and FIG. 4B shows a refining mode using a lance. ing. As shown in the figure, 2 is the ladle main body, 2a is the ladle lid, 3 is the molten steel, 4 is the slag at the time of immersion in the heating electrode, 4' is the slag after adding the refining flux, and the ladle lid is In 2a,
A V supply pipe 5 for gas for adjusting the atmosphere inside the ladle and a hopper 6 for additives into the ladle are attached, and a heating electrode 7 that can be raised and lowered and a lance for blowing gas are attached to the ladle lid 2a. 8 is passing through. Reference numeral 9 denotes a sealing material (for example, kaoru) having excellent heat resistance, airtightness, and plasticity and is interposed between the upper end of the ladle main body 2 and the lower end of the ladle lid 2a. Note that the arrow in the figure indicates molten steel 3 due to gas injection from lance 8.
It shows the flow. Next, embodiments of this invention will be described. The molten steel from the 250 ton converter, which has been refined at a molten steel temperature of 1640 qo, is transferred to a 25 ton converter with the structure shown in Figure 4 A and 4.
The steel was poured into a ladle. At that time, it is possible to prevent converter slag from flowing into the tapped steel, and at the end of tapping, Ca046%, S
A synthetic flux containing 79% of iO2, 4% of AI2Q, and 1% of impurities was added to the molten steel to produce ladle slag (slag for heating electrode immersion).Then, a ladle lid was attached to the ladle body. The tip of the heating electrode for electric arc heating is immersed in the ladle slag to start energizing, and at the same time a T-shaped two-hole lance is immersed in the molten steel to produce an Ar of 0.5 mm/min.
By starting to blow gas into the molten steel, the molten steel was heated to a temperature of 1,650 qo in 18 minutes from the start of energization and gas injection. When 15 minutes have elapsed since the start of energization, the heating electrode is pulled up from the slag, 5 tons of sodium metasilicate is added from the additive hopper, and at the same time, the amount of Ar gas blown into the lance is set to 1/min, and the inside of the ladle is filled with air. Air is supplied from the gas supply pipe for adjusting the atmosphere inside the pot. Refining (gas blowing) was performed for 8 minutes in a state where the inside of the ladle was made into an oxidizing atmosphere by supplying gas at a rate of 1/min. Next, the steel slag is discharged (removed), the molten steel in the ladle is subjected to RH degassing treatment as a well-known vacuum treatment, and after deoxidizing by adding ferroalloy to the molten steel, quicklime 1
．． 5 tons, and 750 kg of a synthetic regulating agent containing 048% Ca, 49% SiQ, 2033% A, and 1% impurities were added onto the molten steel in the ladle. Next, 2.0N Hinoki from Lance/
Ar gas of min. is started to be blown into the molten steel in the ladle, and at the same time, Ar gas of min. Refining (gas blowing) was performed for 20 minutes while supplying Ar gas at a rate of 1/min to create an inert gas atmosphere inside the ladle. As a result, as shown in Table 1, P, S, day, and T

A steel with extremely low [0] was obtained. In addition, the above-mentioned [
E, [mouth}, shiichi, 8, moth, H', 'to', combined',
and 're} process, that is, before performing vacuum treatment,
When refining was carried out under an inert gas atmosphere, it was found that the composition was almost the same as that of the above example, but P, S, day, and T,

A steel with less [0] was obtained. As explained above, in this invention, extremely
It is possible to obtain a refining method that can inexpensively and easily obtain steel with a low content of P, S, day, and 0.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the corrosion coefficient of refractories in a steelmaking furnace (converter) and its tapping temperature, and Figure 2 shows the [P] of Qin steel obtained in a steelmaking furnace (converter) and its Figure 3A shows the relationship with tapping temperature; Figure 3A shows a sectional view of a lance immersed in molten steel in the ladle; It is a sectional view showing an example. 1, 1', 8... Lance, 2... Ladle body, 28...
Ladle lid, 3...molten steel, 4,4'...slag, 5...
- Gas supply pipe for adjusting the atmosphere inside the steel processing, 6... hopper, 7... heating electrode, 9... sealing material. Figure 3: Younger brother Figure 4: Figure 2

Claims (1)

[Claims] 1. Molten steel refined in a steelmaking furnace is poured into a ladle that has a sealing lid and into which gas can be blown, and then the slag above the molten steel in the ladle is poured into The tip of the heating electrode is immersed to heat the molten steel in the ladle, then an oxidation refining flux is added to the molten steel in the ladle, and then a lance is immersed into the molten steel in the ladle from above, By blowing in a stirring gas, the molten steel in the ladle and the molten steel and the slag on the molten steel are stirred in an oxidizing gas atmosphere, and then the slag on the molten steel in the ladle is removed. Then, by vacuum treating the molten steel in the ladle, adding flux for reduction refining to the molten steel in the ladle, and then blowing an inert gas into the molten steel from the lance, A method for refining molten steel using a ladle, comprising stirring the molten steel in the ladle and the molten steel and slag on the molten steel in an inert gas atmosphere. 2. Transfer the molten steel refined in the steelmaking furnace to a ladle that has a sealing lid and into which gas can be blown, and then insert the tip of the heating electrode onto the slag above the molten steel in the ladle. immersion to heat the molten steel in the ladle, then add oxidation refining flux to the molten steel in the ladle, and then blow stirring gas from a lance immersed into the molten steel in the ladle from above. by stirring the molten steel in the ladle, the molten steel, the molten steel, and the slag on the molten steel in an oxidizing gas atmosphere, and then removing the slag on the molten steel in the ladle, Next, flux for reduction refining is added to the molten steel in the ladle, and then an inert gas is blown into the molten steel from the lance, so that the molten steel in the ladle and A method for refining molten steel using a ladle, comprising: stirring the molten steel and slag on the molten steel; then removing the slag on the molten steel in the ladle; and then subjecting the molten steel in the ladle to vacuum treatment.