JPS6010086B2 - Steel manufacturing method - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing steel equivalent to rimmed steel without generating bubbles in a continuous casting process. Rimmed steel is a type of steel that is manufactured by intentionally performing almost no deoxidation during the refining process, generating a large amount of CO gas during ingot formation, and using the rimming action of the bubbles to wash away impurities at the solidification interface. If this is manufactured by a method such as continuous casting, in which the pieces are pulled out and moved as solidification progresses, if the generation of air bubbles is too intense, the movement of the molten metal in the mold will become active, resulting in It is dangerous because the bulging phenomenon occurs from deep within the steel, and even if the bubbles are weak, the solidification rate during continuous casting is fast, causing the problem of fine bubbles being trapped near the surface and causing pisohole defects in the product. Because of this, continuous casting of T-rimmed steel is rarely carried out.
Therefore, the types of steel that can be used for continuous casting are limited to killed steel and semi-killed steel that have been desilted with A or Si, but of course Si killed steel, A and killed steel, A〆-Sj killed steel as well as A [Sj] in the molten steel increases due to the ring element of Si02 in the refractory or the Si02 in the refractory, but the presence of such Si causes deterioration of deep drawability.
Quality problems such as deterioration of plating adhesion, occurrence of temper color, and buckling of colored steel sheets occurred, as well as problems in steel material processing such as deterioration of hole expandability and limitations on cold rolling rate. In addition, in particular, in the case of A and killed steel ~ A and town Si killed steel, “A〆2
03 There are operational issues such as deterioration in product costs due to the presence of oxidation products, problems with ladle or tundish nozzles due to deoxidation products, and cost issues such as high additive costs. exists. In this way Aku or Sj
Killed steel or semi-killed steel that has been deliquified by the process has disadvantages due to the presence of A or S furnaces, so restrictions in terms of use cannot be avoided. The reality is that rimmed steel is applied using the soul agglomeration method. However, the current trend is to expand the range of steel types to which the continuous casting method, which has a higher yield and better productivity than the ingot blooming method, is being applied. Naturally, continuous casting is also desired, and several attempts have been made in response to this.In order to reduce the disadvantages such as the deterioration of deep drawability as mentioned above, it is preferable that [Sj] be as low as possible. ``It is necessary to reduce the amount to at least 0.020% or less, which is accepted as rimmed steel.In addition, due to the cost of adding A, and the increase in [Sj] in molten steel caused by the reduction of Sj02 in the refractory, and the increase in [Sj] in the steel withdrawal nozzle or In order to prevent clogging of the sodish nozzle, it is preferable that the drumsticks T and [A] be lower. However, for example, in steel types such as hot-rolled steel plates that require fixation of nitrogen in the steel, "T. 0.010 to 0.020% is required, and when box dulling rolled steel sheets, etc., the amount of A required to prevent the generation of bubbles during continuous casting may be sufficient. If [at A] is 0.020% or less, it can be said that it shows a sufficient value as a product equivalent to rimmed steel.
i], it is thought that deoxidation will naturally become insufficient and tCO bubbles will be generated. Generally, the condition for the generation of bubbles in molten metal is that the internal pressure of the bubble is greater than the sum of the atmospheric pressure, the hydrostatic pressure of the lacquer bath at the bubble location, and the pressure exerted on the bubble by cohesive force. C produced by reaction of components in lacquered steel
If the sum of the gas pressures of O and N2 gases is smaller than the sum of atmospheric pressure, hydrostatic pressure, and pressure due to cohesive force, bubbles will not be generated.By the way, the partial pressure of N2 gas Because it is relatively small, ``To prevent bubbles from forming, CO
Gas generation must be suppressed, but ``the pinhole defects mentioned above are the result of small bubbles being trapped in the thin solidified shell inside the mold, so the hydrostatic pressure is extremely small, but the pressure exerted on the bubbles by cohesive force is Since a bubble of about 1 bar is small, in the end, in order to prevent bubble generation, it is sufficient to reduce the CO gas pressure to atmospheric pressure, that is, 1 atmosphere or less. It is produced by reacting as shown in the equation '1-~C0G=C○(g)...
...state {1-However, C3 C in molten steel Q free O in molten steel C ○ (g) Mi In CO gas equilibrium state, C concentration, free ○ concentration and pressure P of CO gas
If the equilibrium constant is K, then the relationship of equation (2) holds true between co and co. Pc. [C] If the concentration of [C] is as high as 0.43%,
o becomes 1 atm or less. Therefore, in the state where coagulation is progressing, "Freedom [0
] If the temperature is suppressed to 7 degrees or less, the generation of CO gas can naturally be suppressed. Then [SI], T. [A
When casting molten steel using a continuous casting method, it is possible to deoxidize using another method without relying on deoxidation using Si.

All you have to do is control [0]. From this point of view, the method for manufacturing coin coins that performs deoxidation is Tokuseki 53-? 3422, Samurai Seki Akihiro-9
3618 is known. These are subjected to vacuum degassing treatment after converter refining to reduce [C] and freedom [○].
This is a method of deoxidizing by adding Ti and Ti (the latter). Continuous casting of low port steel is possible. However, in these methods, "free oxidation in molten steel"

Splash is likely to occur because the vacuum is drawn in a state where [0] is high, and furthermore, the vacuum equipment is required to have a large evacuation capacity. Due to this splash, the base metal adhering to the furnace wall falls into the molten steel during vacuum treatment, so it is called "Freedom".

It also has drawbacks such as difficulty in controlling [0]. In addition, because the temperature drop during vacuum treatment is large, the tapping temperature of the converter has to be raised, which results in insufficient dephosphorization in the converter process, and there is also a problem of large melting loss of the converter refractories. There is. Furthermore, since the vacuum treatment requires a long time, there are significant restrictions on the process.There is also a drawback that the vacuum treatment equipment cost and the running cost of the vacuum treatment are high. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for producing a product equivalent to rimmed steel that can be continuously cast without generating bubbles even though it is not subjected to vacuum treatment. With the goal. The steel manufacturing method according to the present invention includes {1} converter (pure oxygen top-blown converter,
In a bottom blowing converter (also referred to as a so-called composite blowing furnace), blow the molten metal in step 2 to a melting container to reduce the concentration of [P] to at least the required concentration of the finished product. After removing the converter slag by tapping, the port water is further tapped into a converter (for example, a so-called compound blowing furnace) that allows gas to be introduced from below the surface. , either do not carry out oxygen blowing in the converter or carry out oxygen blowing without substantially adding a forming agent. ``In addition, if oxygen blowing is not performed, gas is introduced from below the steel bath surface after charging into the converter, and kasuzu refining is performed.``When slabs or blooms are cast using a continuous wind casting machine.'' During Sumizusa Seikama, during tapping from the converter to the ladle after rope refining, or at least during one of the periods after tapping, deoxidation is carried out by adding A-so.

[0] 70 skin or less ~ T. Molten steel containing 0.020% or less of [A and] and an unavoidable content of [S] is produced, and the molten steel is cast using a continuous casting machine, and a billet is cast using a continuous casting machine. In such cases, '1}～
(5') If necessary, during the offshore refining, during the tapping from the converter to the ladle after the overseas refining, or at least during one of the periods after the tapping, Deoxidizes by adding

[0] is 100 to 180 rods "(S amount) is melted steel having an unavoidable content" (6) When casting the molten steel with a continuous casting machine, the molten steel in the mold constituting the continuous casting machine By adding A solute into the mold and deoxidizing it, the molten steel is released in the mold.

[0] less than 70 legs, T. [A〆]
is 0.020% or less, and [Sj] is made to be an unavoidable content. Hereinafter, the steel manufacturing method according to the present invention will be explained in detail, following the processing steps in the order of the numbers mentioned above. (1- In the present invention, first, in the converter, at least [P]
Oxygen blowing is carried out to reduce the concentration of ingredients to below the required concentration of the finished product. The use of alkali metal carbonates such as soda ash is effective for dephosphorization, but in the following slagless Fukisen or Takaazusa Refining [C], free

In order to easily control [0], it is preferable to stop blowing so that the end point [C] in this normal converter blowing sickle is 0.05% or more. If , the freedom at the end of the blowout

[0] becomes too high, and even if C is removed by Hinazusa Refining, which introduces gas from below the surface, it will not be sufficiently free.

[0] cannot be lowered, and further A in the subsequent process
This is because it is difficult to control freedom [0] to a predetermined value during deoxidation. In other words, in this normal converter coin,
Si] "[P]" [S] etc. are adjusted, especially for dephosphorization, and the blow-off is performed after [P] is dephosphorized to below the component concentration required for the product. At the same time [C
] is not decarburized to less than 0.05%,
Consider the blowing pressure, the amount of linking agent added, etc. In view of the nature of the product to be manufactured by the present invention as a rimmed steel substitute, it is preferable that the P to S concentrations of the finished product are both 0.030% or less. ] and [S] are both 0.030% or less. If low sulfur steel or low phosphorus steel is particularly required, preliminary treatment such as desulfurization or dephosphorization may be performed prior to the normal converter blowing. (2) In this way, the normal converter blowing sickle In order to use the fallen sun obtained in the slagless blowing or dark frame refining process described later,
The aim is to remove converter slag that is normally produced in converter slag. In order to perform this slag cutting more completely, the total molten metal is once tapped into a molten metal container. In other words, from the converter where converter blowing is normally performed, the port water is discharged into a ladle, which serves as a molten metal container, and then a slag-less blowing sickle or an ayago blowing mirror furnace, etc., which performs the slagless blowing kiln, which will be described later, is used. The slag is removed by the so-called LI ladle method, which is inserted into the converter.Normally, the slag is cut when the molten metal is tapped from the converter that has been blown into the converter. There is a method of filling the hole-shaped tap hole that is usually installed at the top with rags or scales.Also, as a method to prevent the slag from flowing out at the end of the taping stage, there is a method of filling the hole-shaped tap hole that is usually installed at the top with refractory spherical material (
From the slag ball method in which a slag ball (slag ball) is dropped onto the tap to block the tap to the slag dopper method in which the tap is closed with a stopper, quicklime powder is added to the slag near the tap that floats on the surface of the moat. A quicklime powder method and the like are known, in which the slag is solidified to prevent it from flowing out from the tap hole. Furthermore, as a method for preventing slag outflow both at the start of tapping and at the end of tapping, there is also known a sliding gate method in which a sliding valve is installed at the tap and the tap is controlled by opening and closing the sliding valve. In addition, when pouring hot water from a ladle to a converter such as a composite blowing bath furnace in the next step, there is a method of cutting slag by controlling the pouring of hot water by opening and closing a sliding valve or a stopper installed at the bottom of the ladle. In short, these methods can be adopted as appropriate during the relay process. In addition, in some cases, slag mixed in the inside of the converter where blowing sickle is normally performed or on the falling surface of the ladle, or the slag mixed into the converter where slagless blowing spindle or fly azusa refining is performed, may be removed using a slag draker, etc. You may take appropriate action. '3} The molten metal from which slag has been substantially removed in this way is charged into a converter, such as a composite blow sickle furnace, in which gas can be introduced from below the bath surface,
If [C] has decreased to a predetermined value in the above-mentioned normal converter blowing, the rope group refining described later is performed without oxygen blowing. In addition, if it is necessary to make [C] adjustment, oxygen blowing is carried out without substantially adding a forming agent; In addition, since there is virtually no slag, there is no oxygen supply stand from the slag to the molten steel during the blow saw, and the end point [C] and the end point are freely connected by the oxygen blowing key.

[0] can be controlled with high precision. {43 Next, when performing this oxygen blowing, during and after the oxygen blowing sickle (slugless blowing coin) ~ Also, if oxygen blowing is not performed, from below the bath surface even after placing the bag in the converter. An inert gas such as Ar gas is introduced to weaken the steel. This compensates for the decline in crossing power at the end of the oxygen blowing sickle phase in Nadayo during the oxygen blowing mirror, allowing efficient decarburization with the oxygen blowing sickle.

[0] is prevented from increasing, and when only Takaazusa refining is performed, C deoxidation is promoted. This C deoxidation is also possible when an inert gas such as A is used as the gas for the steel bath because the CO gas partial pressure in the bubbles in the steel bath is diluted by the inert gas and becomes low. C and freedom Q
This occurs due to the reaction according to the formula {1}. In other words, the CO bubbles generated by the formula 0} are diluted with an inert gas to lower the CO gas partial pressure ~ the generation of CO is promoted by the formula {1}, or the Ar bubbles are distributed in large quantities in the molten steel {1}. The CO generated by the reaction in the lacquered steel is diluted and mixed into the A bubbles to be discharged from the lacquered steel to promote the reaction in the {i} type.

[0] is lowered. Through this refining, [C] and free [Q] in the molten steel
] will be in equilibrium with c. is less than 1 atm. The introduction of the hatch frame car x can be done by using a normal converter and inserting a lance for Nada Azusa gas into the steel bath of the converter, but as shown in Fig. Even if you use an Enokiai blowing sickle furnace with a feather pupil installed at the bottom of the hearth, it is most efficient to introduce the fly gas from this tuyere and use it to feed the steel.Also, this tuyere It goes without saying that the same effect can be obtained even if it is installed at the bottom of the furnace wall.The oxidation gas is preferably an inert gas such as Xr or Xe. may be CO or CO2, but ``CO cannot lower the partial pressure of CO gas during C deoxidation, and CO2 decomposes into CO and 02 to generate CO and 02, so it is still free [0
] cannot be lowered.
However, it is not preferable for steel types where absorption of N in molten steel is a problem.Also, when N2 is used during oxygen blowing...
It is better to change to a gas that does not contain N2, such as a boat, or perform denitrification by using a gas that does not contain N2, such as A, after blowing. teeth"
02 may also be used. It is also possible to use a combination of these gases. Gas flow rate is molten steel lt (tons)
It takes more than his share of 0.0 harvest per hit. If it is less than 0.0 min, the fly-pull effect will be small, and since the deliquification rate is slow, the treatment time will be prolonged, and a drop in the temperature of the minato steel during treatment will become a problem. In slagless combined blowing, in which Kenazusa refining as described above is combined with slagless blowing, the decrease in the frame force at the end of the oxygen blowing process is compensated for, and decarburization is performed efficiently.

As mentioned above, [0] may increase unnecessarily. In addition, since there is virtually no slag, there is no supply of oxygen from the slag to the twill steel during the taka-azusa process, and the flow rate of the taka-azusa gas can be adjusted to provide freedom during blow-off.

[0] can be controlled with high precision. Figure 2 shows the end point [C] on the horizontal axis and the free end point [C] on the vertical axis.
0] and perform normal pure oxygen top blowing (LD), the end point [C] and the free end point

The relationship with [0] is shown in the shaded area.

After the relationship with [0] is indicated by △), slagless composite blowing (end point [C] and end point free

This is a graph in which the effect when the relationship with [0] is indicated by a circle is shown by an open arrow. Generally, decarburization progresses by oxygen injection, but the freedom [0] in molten steel increases. Therefore, at the end point [C
〕×

The smaller [0] is, the better the refining method is.
) free compared to

[0] continues to be low, and it is necessary to deoxidize the same [C] in the subsequent process.

It has the advantage of having less [0]. In addition, the solid line in the figure indicates Pco: 1 atm "160"
[C] in the equilibrium state in the case of 000 and

The relationship with [0] is shown. In fact, C02 is also generated, so this solid line is the free line between [C] in the equilibrium state when Pco + Pco2 = 1 atm.

Regarding the relationship with [0], [C] is 0.
In the case of 1%, CO2 can be ignored since it is less than 2% of CO+C02. Now, unlike the present invention, the end point [C] and the free end point in the case of the Enoki blowing mirror, which uses a condensing agent and combines the oxygen blowing key with rope and western refining.

The relationship with [0] is shown by eclipses. As is clear from the figure, even in the case of this type of Enoki blowing mirror, compared to normal blowing, [C] ×

[0] is significantly lower, Pc
. = Close to the equilibrium state at 1 atm, but in the case of a slugless post-agifukisen like the one of the present invention (marked 0), it is further [C] ×

[0] is low and Pc is balanced. is less than 1 atm. This indicates that the hawking effect is not diminished because there is no oxygen supply from the slag to the molten steel during the hawking process. In this way, slagless composite blowing can be said to be an extremely excellent refining method. Now, the results of Hinaazusa refining after slagless composite blowing coins are shown in Figure 2. Furthermore, equilibrium occurs when Pco = 0.5 atm and Pc = 0.3 atm [C]. The relationship with freedom [0] is shown by a broken line and a dashed-dotted line, respectively.As is clear from the figure, the decarburization and deoxidation effects of slag are remarkable, and slag is substantially deposited on the surface of the molten steel. Because there is no “Hashih frame” effect, the
[C] in molten steel, free

Pc in equilibrium with [0]. is 0.3
C deoxidation progresses to about atmospheric pressure. Therefore, A
This means that the amount of A added in the final demelting process can be extremely small. In addition, when blowing is stopped so that [C] is about 0.05% with a normal converter blowing key, the subsequent slagless slag-less blowing and slag refining are performed until [C] becomes about 0.02%. Can be decarburized. '5}, (5), (6) Next, when the lacquered steel is cast in a continuous casting machine, it is deoxidized by the addition of A to free the free molten steel in the mold constituting the continuous casting machine. [0
] to a stiffness of 7 or less. In this step, if the nozzle diameter of the ladle or tundish is small (15 side or less) as in a continuous billet casting machine, the nozzle is likely to be clogged by the A-deoxidized product A-203. Specifically, the free material in the port steel in the ladle and tundish obtained by deoxidizing by adding A

When [0] is less than 100 skins, nozzle clogging occurs frequently. Therefore, when continuously casting billets, the stage up to tundish is free.

[0] was adjusted by 100 to 18 degrees to avoid nozzle clogging, and after that, the free space in the lacquered steel in the mold was

[0]
Deoxidation is performed by adding A solute to the molten steel in the mold so that the amount of steel is 7 or less. In addition, it is free at the tundish stage.

[0]
The reason for setting 180 legs or less is that if this value is exceeded, the amount of A added to the molten steel in the mold becomes too large, and the free

This is because it becomes difficult to control the amount of [0] and A added. Freedom again [
0] exceeds 18 degrees, the damage to the tundish nozzle becomes severe, resulting in an increase in inclusions caused by the eroded refractory, and in some cases, steel leakage from the tundish nozzle. cause inconvenience. As a method of adding A grains, A grains may be added, but as described later, it is easier and freer to add if the space between the tundish and the mold is sealed with an inert gas.

[0] Easy to adjust A
The finishing line feeding method is preferred. On the other hand, when the ladle nozzle and the nozzle diameter of the tasso dish nozzle are 15 or more, as in a continuous slab/bloom casting machine, there is no need to separate the deoxidation treatment into two stages, and the free for any period

Deoxidation treatment may be performed by adding the minimum amount of A necessary to reduce [0] to 7 or less. The place where this is added is inside the converter (Enoki Abuki Furnace) during the Nada Azusa refining mentioned in (4) above, or during tapping from the converter to the ladle, or inside the ladle after tapping. It may be done in the tundish, or even in the mold, or in multiple places.

[0] is determined by measuring it with an oxygen probe that utilizes an electrochemical phenomenon such as a solid-state battery, but since the steel has already been deoxidized at the Takatomo Refining process in (■), an extremely small amount of A is present. Freedom in Minato Steel with its addition

[0] can be deoxidized to below 7Q stiffness.
[A〆] is 0, which is required for quality as a steel equivalent to rimmed steel.
It can be kept sufficiently below 0.020%. In addition, when adding soybean into the converter or ladle, there is no slag in the slag.

A due to [0] Because there is no loss, "freedom in molten steel"

[0] can be controlled with high precision. Furthermore, if slag is present on the surface of the molten steel when A slag is added, the slag component Si02 is partially reduced by the slag and the so-called S pick-up occurs, which increases the [Si] in the twill steel. is similarly unaffected by this. On the other hand, Si from the Si02 component in the refractory
It is conceivable that the amount of Si in the molten steel increases slightly due to Si contained in the pick-up or A so metal. With its addition, the increase in [SI] is extremely small and remains an unavoidable content.The adjustment of alloying elements such as Mn, which is required depending on the application of the steel material, This is done by adding an alloy to the inside of the converter, during tapping from the converter to the ladle, or into the ladle after tapping.Also, molten steel is air oxidized during tapping from the converter to the ladle. In order to prevent this, it is desirable to seal the area around the molten steel with an inert gas such as Ar during tapping.Furthermore, since the surface of the molten steel tapped into the ladle is in contact with air, it is necessary to prevent heat radiation and prevent air oxidation. From the above point of view, it is preferable to introduce flux or rice husks, etc.In addition, in the above-mentioned series of steps, the processing time will be longer by the time required to perform the fly azusa refining than the steps required in the stage before normal continuous casting. "The temperature of the molten steel does not need to be particularly higher than that of normal continuous casting. is cast using a continuous casting machine, but there is no freedom in the lacquered steel.

Since [0] satisfies the above-mentioned condition of 7.0 cm or less, no CO bubbles are generated and key pieces without defects such as pinholes can be stably produced. During continuous casting, measures are taken to prevent re-oxidation of molten steel. ~It is desirable to take known measures such as sealing the space between the molds with an inert gas such as Ar.Q
Next, an embodiment of the present invention will be described in detail for producing a slab with a thickness of 25 mm and a billet with a thickness of 116 mm. 1st table tr; trace 2nd table tr; trace When manufacturing a 25 mm thick slab first, use Table 1 column A (
Preliminary deflow treatment was carried out on 27 plates of twill pig iron having the component concentrations and temperatures described in (Before treatment). This means that the [S] of the hot metal is 0.023%, which means that the [S] is 0.023%.
This is because low sulfur steel was particularly required. Desulfurization treatment is carried out using the KR method, in which soda ash Na2C03 is added to the molten iron in a hot metal ladle and mixed with the molten iron by the rotation of an in-vehicle (the KR method, in which a gas in which soda ash Na2C03 is suspended is blown into port pig iron and mixed). (The injection method may also be used.) The concentrations of each component after this desulfurization treatment were as shown in column B of Table 1 (after desulfurization treatment).
After removing the slag produced in the desulfurization treatment, the hot metal was charged into a 27-type converter, quicklime (or soda ash) was added, and ordinary oxygen blowing was performed. As a result, as stated in column C of Table 1 (after converter blowing),
[P] became the required component concentration, that is, 0.030% or less. Further, [C] remained at a value of 0.10%, slightly higher than 0.05%. Next, after receiving the molten steel obtained by using this continuous converter blowing sickle into a ladle, slag cutting was performed using the reidle method.
It was loaded into In this converter 2, slagless Enoki-Aibuki coins were made using pure oxygen Kamifuki bran and Enoki refining in combination without using a forging agent. This composite blowing mirror uses a so-called rear blowing sickle furnace as shown in Fig. 1, and the blade □1 placed at the bottom has an inner diameter of 12.7 ribs. It has a double tube structure with a gap of 1.1 ribs between the inner and outer tubes, and the inner tube is made of Cu and the outer tube is made of stainless steel. Hydrocarbon gas was transfused to cool the tip of the blade.The oxygen delivery rate of the oxygen blower was 40,
It was 0000 hours, and the blowing speed of the fly Azusa was about the same as in the state. As shown in column D of Table 1 (after slagless blowgun), [C] was 0.07% and free.

[0] is on the 32■ side, and this [C]×

[0] is lower than the equilibrium state when Pco=1 atm, as shown in FIG. Next, after oxygen blowing, .about. was blown into the molten steel for 5 minutes at a rate of 2 sails/minute from each inner tube of two vanes □1 for 5 minutes to carry out tomato refining. As a result, as shown in column E of Table 1 (after fly refining), free

[0] was removed to 137 pods.
Next, when tapping the steel from the composite blowing furnace to the ladle, the rod-shaped A-shaped steel in the molten steel is heated to 43k9 (approximately 0.16kg per lt of molten steel).
), and at the same time HCFe-Mn (
An appropriate amount of Fe-Mn alloy) was added. In addition, in order to promote the floating of A-203 type inclusions generated by A-so deoxidation, after the ladle was covered, a immersion lance was inserted into the molten steel and irradiation with Ar was performed. The concentrations of each component after the deoxidation treatment of A are shown in column F of Table 1 (after the deoxidation treatment of A). [Si] is 0.009%, T. [A evening] is 0.0
19%, which is a sufficient value as a steel type equivalent to IJ Mudo steel, and has even more freedom.

[0] indicates 50 Yanagi, which has no risk of generating bubbles during continuous casting. Next, in a continuous slab casting machine with a thickness of 25 mm, the space between the tap steel and the tundish was sealed with Ar, and a long nozzle was used for the L-thread steel mezzle, and a dipping nozzle was used for the tundish nozzle, and the drawing speed was 1.2 m/s. Although it was cast in minutes, there were no air bubbles or pinholes, and a key piece with good surface quality was manufactured.Next, we will discuss the case of manufacturing a pilet with i16 skin L. 77 tons of molten iron having the component concentration and temperature listed in Table A column (before treatment) was desulfurized using the KR method with the addition of soda ash in a molten iron pot.The concentrations of each component after desulfurization were
The results were as shown in column B of Table (after desulfurization treatment). After removing the slag produced in the desulfurization treatment, the hot metal was charged into a 7-meter converter, quicklime (or soda ash) was added, and ordinary oxygen blowing was performed. As a result, as described in column C of Table 2 (after converter blowing), [P] reached the required component concentration. Also, [C] is 0.
The value remained slightly higher than 0.09% and 0.05%. Next, the molten steel obtained by this normal converter blowing sickle is received in a ladle, cut into slag, and then charged in the next process into a 7-piece composite blowing furnace with a structure similar to that shown in Figure 1. However, here, we carried out Enoki-bukisen without using a birch agent.The oxygen supply rate was 11,000N/hour. The inner tube is made of Cu and the outer tube is made of stainless steel, which is the same as in the case shown in Fig. 1, but the inner diameter of the inner tube is 7.75mm. As shown in column D of Table 2 (after slug-less blowing sickle), [C] is 0.07 due to composite blowing coins.
% freedom

[0] becomes 341 legs, which is Pc as shown in Figure 2. = Close to the equilibrium state when the pressure is 1 atm. Next, after oxygen blowing, Ar was blown into the molten steel for 5 minutes from each inner pipe of the two tuyeres at a total rate of Isohin to perform rope refining. As a result, as shown in column E of Table 2 (after fly refining), free

[0] decreased to 156 legs. When producing billets, part of the deoxidation adjustment is done in the mold of the continuous casting machine.
At the tundish stage, there is no freedom in the molten steel.

[0] is adjusted by 100 to 18 Masaiso, but in this example, the freeness in the molten steel is

Since [0] was 156 legs and within this range, the Mn component was only adjusted by adding HCFe-Mh without adding A to the tundish stage. When the molten steel produced in this way is cast in a continuous billet casting machine with a capacity of 116 mm, ~ 200 lbs.
The A warp wire was supplied to the molten steel in the mold at a rate of 500 ml. Even though the drawing speed was 2.2 times, in order to prevent re-oxidation of the molten steel, sealing was performed between the drawing steel and the tundish and between the tundish and the mold.6 As a result, air bubbles were generated. In addition, there were no pinholes, and coins with good surface quality were manufactured.The concentrations of each component in the molten steel in the mold are shown in column F of Table 2 (molten steel in the mold).
Since no deoxidation was performed, [Si] was 0.010%.
Of course this is a low word, but T. [A so] is also 0.010
%, which is extremely low compared to 0.030% or more of conventional A-killed steel, and is a sufficient value as a steel equivalent to trimmed steel. Even more freedom

[0] was also extremely low at just 4 winds, so naturally no bubbles were generated. The above two examples are both about products equivalent to low carbon rimmed steel with a C content of about 0.03 to 0.10%;
It goes without saying that the present invention is also applicable to products equivalent to high carbon rimmed steel with a JI of about 0.25%.

[0] is low, but the subsequent deoxidizing treatment is mild. As explained in detail above, a series of steel manufacturing methods centered on slagless composite blowing and slag refining according to the present invention are capable of producing A
It is possible to continuously cast molten steel with minimal deoxidation, and to obtain key pieces equivalent to rimmed steel without defects such as pinholes at a high yield and with high efficiency. In addition, since vacuum treatment is not performed, the equipment does not need to be large-scale, and the time required for the entire process is shorter than when deoxidizing using the vacuum treatment method, so the drop in molten steel temperature is small and operation is possible. As described above, the steel manufacturing method according to the present invention can produce low [AZ], [Si] steel L, that is, a product equivalent to rimmed steel, which was previously considered impossible, without significantly changing the conventional steel manufacturing process. This made continuous casting possible, and it can be said to be a revolutionary contribution to this type of technology.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal cross-sectional view of a rear-blow sickle furnace, and FIG. 2 is a graph showing the effects of the slag-less composite blow sickle and rope azusa refining. Turtle...tuyere, 2...converter. Diamond Diagram Diamond Diagram 2

Claims (1)

[Scope of Claims] 1. Blowing is performed in a converter to reduce the concentration of [P] to at least the component concentration required for the finished product, and after the blown molten metal is poured into a molten metal container, it is further heated from below the bath surface. When oxygen blowing is carried out by charging the material into a converter into which gas can be introduced, and oxygen blowing is not performed in the converter, or oxygen blowing is performed without substantially adding a slag-forming agent. During the oxygen blowing and/or after the oxygen blowing, or if oxygen blowing is not performed, after charging into the converter, gas is introduced from below the surface of the steel bath to perform stirring refining. Deoxidation by adding Al is performed during tapping from the converter to the ladle after refining, or at least during one period after tapping, and free [O] is 70 ppm or less, T. A steel manufacturing method characterized by producing molten steel containing 0.020% or less of [Al] and an unavoidable content of [Si], and casting the molten steel using a continuous casting machine. 2 In the converter, blowing is performed to reduce the concentration of [P] to at least the component concentration required for the finished product, and after the blown molten metal is tapped into a molten metal container, gas is further introduced from below the bath surface. The material is charged into a converted converter, and oxygen blowing is not performed in the converter, or oxygen blowing is performed without substantially adding a slag-forming agent, and if oxygen blowing is performed, during the oxygen blowing. And/or after oxygen blowing, or if oxygen blowing is not performed, after charging into the converter, gas is introduced from below the surface of the steel bath to perform stirring refining, and if necessary, during stirring refining and after stirring refining. Deoxidation is performed by adding Al during or at least one period after tapping the steel from the converter to the ladle, and the free [O] is 10.
When melting molten steel with an unavoidable Si content of 0 to 180 ppm and casting the molten steel using a continuous casting machine, Al is added to the molten steel in the mold constituting the continuous casting machine to remove Al. Perform acid treatment to reduce the free [O] of molten steel in the mold to 70p
pm or less, T. [Al] 0.020% or less, [Si]
A steel manufacturing method characterized by making the content of