JPS5952922B2 - Steel manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention does not generate bubbles in the continuous casting process.
Equivalent to rimmed steel (7) T, CAI) (total
(Al content) and page Si) (Si content). 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 to be manufactured using a method such as continuous casting, in which the slab is pulled out and moved as solidification progresses, if the generation of air bubbles is too intense, the movement of the molten metal in the casting will become active.
Otherwise, it is dangerous because the bumping phenomenon occurs from the deep part of the unsolidified molten steel, and even if the generation of bubbles is weak, the solidification rate during continuous casting is fast, so fine bubbles are trapped near the surface and pinhole defects occur in the product. Continuous casting of rimmed steel is rarely carried out because of the problems that occur. Therefore, the steel types applicable to continuous casting are limited to guild steels and semi-killed steels that have been deoxidized with AI or Si, but of course Si-killed steels, Al guild steels,
-3i killed steel also increases (Si) in molten steel due to reduction of SiO2 in slag or refractory by AI,
The presence of such Si causes quality problems such as deterioration of deep drawability, deterioration of Zn plating adhesion, occurrence of temper color, and bending of the collar steel sheet, deterioration of hole expandability, restrictions on cold rolling rate, etc. There were also problems with steel processing. In particular, in the case of Al guild steel and Al-5i killed steel,
In addition to deterioration of slab quality due to the presence of Al2O3 clusters,
There are operational problems such as clogging of ladle nozzles or tundish nozzles due to AI deoxidation products, and cost problems such as the high cost of adding AI. Guild steel or semi-killed steel deoxidized by AI or Si has drawbacks due to the presence of AI or Si, so restrictions on usage cannot be avoided, and quality products that do not have the above drawbacks are required. The reality is that rimmed steel using the agglomeration and blooming method is used in these cases. However, the current trend is to expand the application of continuous casting, which has a higher yield and productivity than the ingot-blowing method, and the so-called rimmed equivalent steel types, which contain almost no Si and have a low Al content, are being introduced. Naturally, continuous casting is also desired, and several attempts have been made in response to this demand. In order to avoid the aforementioned drawbacks such as deterioration of deep drawability, it is preferable that [Si] be as low as possible, but it is necessary to keep it at least below 0.020%, which is acceptable as rimmed steel. In addition, in order to reduce the cost of adding AI and to prevent an increase in [Si] in molten steel caused by the reduction of SiO2 in the refractory and clogging of the ladle nozzle or tundish nozzle,
The lower the T and [AI], the better. However, in steel types that require fixation of nitrogen in the steel, such as hot-rolled steel sheets, T and [AI] are 0.010 to 0.
020%, and when box annealing a cold-rolled steel plate, the amount of AI added is sufficient to prevent the generation of bubbles during continuous casting. (If AI'l is 0.020% or less, it can be said to have a sufficient value as a product equivalent to rimmed steel. In general, for Al guild steel, T and [AI] are 0.030% or more. Therefore, T and [AI] are below these values. (If Si'l is suppressed, deoxidation will naturally be insufficient, and CO bubbles will be generated. Generally, bubbles are generated in molten metal. The condition is that the internal pressure of the bubble is greater than the sum of the atmospheric pressure, the hydrostatic pressure of the molten metal at the location of the bubble, and the pressure that the bubble receives due to cohesive force.In other words, C to be done
O5N2. If the total pressure of the gas such as N2 is lower than the total of the atmospheric pressure, hydrostatic pressure, and pressure due to cohesive force, bubbles will not be generated. By the way, the partial pressure of N2 gas and N2 gas is smaller than that of CO gas, so in order to prevent the generation of bubbles, it is necessary to suppress the generation of CO gas. However, the pinhole defect mentioned above is caused by the thin solidified shell inside the mold. Hydrostatic pressure is extremely small because it is a result of small bubbles being trapped, and the pressure that bubbles receive due to cohesive force is also small for bubbles of about 1 mm in diameter.In the end, CO gas pressure must be increased to prevent bubble generation. This means that it is sufficient to set the pressure to atmospheric pressure, that is, 1 atm or less. CO gas is generated by the reaction between C in molten steel and free O as shown in equation (1), and C+0=CO(f)
...(1) However, C: CO in molten steel O: Free 0 in molten steel CO (fI): In CO gas equilibrium state, C concentration, free C concentration, and pressure P of CO gas
When the equilibrium constant is K, the relationship shown in equation (2) holds true between CO and CO. However, [C]: C concentration in molten steel [C]: Free C concentration in molten steel In this equilibrium state, free C concentration

When [0] is suppressed to 7Qppm or less, even if [C] is at a high concentration of about 0.3%, it becomes P. 0 becomes 1 atm or less. Therefore, in a state where solidification is progressing, if the free [0') is suppressed to 70 ppm or less, the generation of CO gas can naturally be suppressed. Then [Si), T. When casting molten steel with a low [AI] using the continuous casting method, it is possible to deoxidize using another method without relying on deoxidation using Si or AI.
It will be good to control O]. From this point of view, methods for producing slabs that perform deoxidation include JP-A-23-73422 and JP-A-54-93618.
is publicly known. These are subjected to vacuum degassing treatment after converter refining, and are converted into [C] and free

After reducing [0], deoxidation is performed by adding AI (the former) or AI and Ti (the latter), thereby reducing (Si). It is possible to continuously cast molten steel with low T and (AI). However, in these methods, the free molten steel is not deoxidized, and the free

Since the vacuum is drawn in a state where [0] is high, splash is likely to occur, and furthermore, the vacuum equipment is required to have a large exhaust capacity. It also has drawbacks such as difficulty in controlling free [O] because the base metal attached to the furnace wall due to splash etc. falls into the molten steel during vacuum treatment. In addition, because the temperature drop during vacuum treatment is large, the tapping temperature of the converter has to be raised, which leads to insufficient dephosphorization in the converter process and large melting loss of the converter refractories. There is. Further, since the vacuum treatment requires a long time, there are significant restrictions on the process, and there are also disadvantages in that the cost of the vacuum treatment equipment and the running cost of the vacuum treatment are high. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing 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) desiliconizing the hot metal prior to converter blowing in order to reduce the [Si] content of the hot metal charged into the converter to 0.30% or less, and (2) ) The hot metal, which has or has not been subjected to desiliconization treatment, is charged into a converter (for example, a so-called combined blowing furnace) that allows gas to be introduced from below the bath surface, and is heated in this converter for the entire period. Alternatively, oxygen blowing is performed while introducing gas from below the bath surface for a part of the time, and (3) after this oxygen blowing, gas is introduced from below the bath surface and stirring refining is performed. A slag-forming agent containing an alkali metal carbonate as a main component is added at an appropriate point from the oxygen blowing to the stirring refining. Next, when casting a slab or bloom with a continuous casting machine, (4) deoxidizing by adding A1 during and/or after tapping from the converter to the ladle after stirring and refining,
Free [O] is 70 ppm or less, T. Molten steel containing 0.020% or less of [Al] and an unavoidable content of (Si) is produced, and the molten steel is cast using a continuous casting machine, and a billet is cast using a continuous casting machine. If so, after performing steps (1) to (3),
41') If necessary, deoxidize by adding Al during and/or after tapping from the converter to the ladle after stirring and refining,
When melting molten steel with free [O] of 100 to 180 ppm and unavoidable content of (Si), and casting the molten steel with a continuous casting machine (5X), in the molten steel in the mold constituting the continuous casting machine, Deoxidation treatment is performed by adding Al, and the free [O] of the molten steel in the mold is set to 70 pIm or less, and the T and [AI] are set to 0.
0.020% or less, the (Si) content is made unavoidable. 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) For the reasons described later, the steelmaking method according to the present invention uses a slag-forming agent containing alkali metal carbonate as a main component to be added to the converter, especially soda ash (Na2CO3), which is highly economical.
). At this time, if the (Si) content of the hot metal is high, the Si in the hot metal
Or SiO2 and Na in the slag, which is an oxidation product of Si.
The reaction with 2CO3 occurs as shown in the following formulas (3) and (4), resulting in Na2CO3+5. Resistant Na2O-8iO2+o...
・(3) Na2CO3+SiO2→Na2O・SiO2
+C02 (Force... (4) However, Si, C: Si in the hot metal, CCCC02 (: Na2CO3, which should be involved in CO2 gas dephosphorization, decreases. Therefore, the amount of soda ash that should be added in the converter is large. Therefore, in order to achieve sufficient dephosphorization with the addition of a small amount of soda ash, the (Si) content of the hot metal charged to the converter should be 0.30% or less. For this reason, if the [Si] of the hot metal at the time of blast furnace tapping is 0.30% or more, prior to converter blowing,
Desiliconization treatment is performed until the content is 0% or less, preferably 0.20% or less. This desiliconization treatment is carried out by adding iron oxide to the hot metal in a blast furnace cast bed, torpedo car, hot metal pot, etc., or by spraying oxygen gas. (2), (3) The hot metal that has undergone such treatment as required is charged into a converter, such as a composite blowing furnace, which allows gas to be introduced from below the bath surface. In this converter, oxygen blowing is first performed (2), and then gas is introduced from below the bath surface to perform stirring and refining (3). For example, in the final stage of oxygen blowing, gas is introduced from below the bath surface to perform stirring and refining, so-called complex blowing. Then, a slag-forming agent containing an alkali metal carbonate as a main component is added at an appropriate point between the oxygen blowing and stirring refining. The entire amount of this slag-forming agent may be charged into the converter during oxygen blowing, but as will be clear from the reasons described below, 1. Part of the slag forming agent may be charged immediately after the start of oxygen blowing, and the remainder may be charged at the end of oxygen blowing. Alternatively, it is preferable to charge it at the start of stirring and refining. Now, the reason for stirring and refining is mainly (1), as will be explained later.
This is to promote C deoxidation according to the formula, but if there is a large amount of converter slag on the steel bath surface during stirring refining, a large amount of oxygen is supplied from the slag to the molten steel, and the C deoxidation during stirring refining is Impairs the deoxidizing effect. In order to substantially avoid the effects of oxygen supply from converter slag to molten steel, the amount of converter slag should be kept at 40 kg or less per ton of molten steel. was clarified as a result of research by the inventors of the present application. Conventionally, quicklime (Cab) was usually used as a slag-forming agent added to a converter, and CaO was the main component in the slag and was involved in dephosphorization and desulfurization reactions. However, in order to achieve sufficient dephosphorization and desulfurization with quicklime, the amount of quicklime added must be 30 to 60 kg per molten steel. It was impossible to satisfy the condition that the amount of slag be 40 kg or less per molten steel. However, when using an alkali metal carbonate such as soda ash (Na2CO3) in the converter slag as in the steelmaking method according to the present invention, it is possible to remove Phosphorus and desulfurization are sufficiently carried out. Figure 1 shows the relationship between the amount of soda ash added and the dephosphorization rate, with the horizontal axis representing the amount of soda ash participating in the dephosphorization reaction (effective amount of soda ash), and the vertical axis representing the dephosphorization rate. It is. As is clear from the figure, when the effective amount of soda ash is 15 to 25 kg per 1 molten steel, a coalescence rate of 90% or more is obtained. Therefore, in order to suppress the amount of converter slag as much as possible and perform dephosphorization efficiently, in the present invention, soda ash is used as the slag forming agent added to the converter. In addition, when using soda ash, T, Fe
(total Fe) content is extremely low compared to when quicklime or limestone is used, and the end point (C, l is 0.05%)
When the steel is blown to a certain degree, the T and Fe contents are about 5 to 8% at most. Therefore, during C deoxidation by stirring refining, which will be described later, the supply of oxygen from the slag is extremely small and C deoxidation can be carried out efficiently. In general, looking at the behavior of each element during oxygen blowing in a converter, first of all, Si is rapidly oxidized in the early stage of blowing, and SiO
2 and the slag is discharged offshore, and after (Si) decreases, the decarburization rate increases, and the supplied oxygen reaches approximately 10
It reaches the middle stage of blowing, when nearly 0% is consumed for decarburization. In the final stage of blowing, the decarburization rate decreases due to a decrease in Ca, and the free [O] in the molten steel and the FeO concentration in the slag increase. Therefore, first, immediately after the start of oxygen blowing, soda ash necessary for the reaction of formula (4) to proceed is added for the purpose of turning 5i02 produced at the beginning of oxygen blowing into slag. In addition, when [Ca] in the molten metal is high, such as in the early or middle stages of oxygen blowing, the soda ash that should be involved in dephosphorization is consumed according to the reaction of equation (5), so Na2CO3+ 2C → 2Na(g)+ 3CO (f
) ... (5) However, Na (ri), C0 (y)
, - N discharged from the molten metal and slag as gases, respectively.
a. The addition of soda ash for the purpose of CO1 dephosphorization and desulfurization is preferably carried out under conditions of as low [Ca] as possible. It will be added during stirring and refining. In short, [Ca is 0.10% or less, (Si) is 0.3
0% or less (However, in converter blowing, under conditions where [Ca is 0.10%, [si, 1 is a very small amount]), [P] of hot metal is 0.100~ If it is about 0.150%, add 20 to 30 kg of soda ash per 1 molten steel.
By adding, the effective amount of soda ash increases from 15 to 2 as mentioned above.
5 kg, and a dephosphorization rate of 90 or more can be obtained. Further, when the [S] content of the hot metal is 0.030%, it is possible to desulfurize it to about 0.010%. Considering the nature of the product manufactured by the present invention as a rimmed steel substitute, the P and S concentrations of the finished product are both 0.030.
% or less, but normally [P] during tapping is 0. ．． 1.
00 to 0.150%, and since [S] is around 0.03%1, there is no need for preliminary treatment such as dephosphorization and desulfurization prior to the converter process, and dephosphorization and desulfurization are performed by soda ash treatment in the converter. Desulfurization is sufficient. In addition, [S] is 0.0 due to the soda ash treatment in the converter.
It is possible to desulfurize up to about 10%, but the S required for the product is
If the concentration is particularly low, prior to desiliconization treatment or converter blowing,
KR method, in which a desulfurizing agent such as quicklime or soda ash is added to hot metal in a hot metal ladle, and the hot metal and desulfurizing agent are mixed by the rotation of an impeller, or injection method, in which gas in which the desulfurizing agent is suspended is blown into the hot metal and mixed. It goes without saying that a preliminary desulfurization treatment may be performed separately by a method or the like. In addition, the method of adding soda ash in a converter is to add it from the auxiliary material input hopper, which is the same as the normal slag adding method, but when adding it during stirring and refining for the purpose of dephosphorization and desulfurization, it is necessary to add soda ash below the bath surface. By adopting a method in which the stirring scum that is introduced into the molten steel is blown into the molten steel as a carrier gas, the treatment can be performed more effectively. Now, during an appropriate period during oxygen blowing (all or part of the period) and after oxygen blowing, an inert gas such as Ar is introduced below the bath surface to stir the steel bath. It compensates for the drop in stirring power at the final stage of forging, efficiently decarburizes through oxygen blowing, and improves freedom in molten steel.

In addition to preventing an increase in [0],
This is done to promote C deoxidation. This C deoxidation occurs when an inert gas such as Ar is used as a stirring gas, because the CO gas partial pressure in the bubbles in the steel bath is diluted by the inert gas and becomes lower. This is caused by a reaction with O according to formula (1). That is, the CO bubbles generated by equation (1) are diluted with an inert gas to lower the CO gas partial pressure and the CO bubbles generated by equation (1) are reduced.
or by distributing a large amount of Ar bubbles in the molten steel, the CO generated by the reaction of equation (1) can be
r Diluted and mixed into bubbles and discharged from the molten steel (1)
It promotes the reaction of the formula and reduces the free [O] in molten steel. Through this stirring and refining, P is in equilibrium with [C] and free [O] in the molten steel. . is less than 1 atm. The stirring gas may be introduced by using a normal converter and inserting a lance for the stirring gas into the molten steel in the converter, but as shown in Figure 2, a tuyere 1 at the bottom of the furnace It is most efficient to stir the steel bath by introducing stirring gas through the tuyere 1 using a composite blowing furnace equipped with a steel bath. Moreover, it goes without saying that the same effect can be obtained even if this panel is installed at the lower part of the furnace wall. The stirring gas is preferably an inert gas such as Ar, Kr, or Xe. CO or CO2 may be used to compensate for the decrease in stirring power during oxygen blowing, but CO can lower the partial pressure of CO gas during C deoxidation, and CO2 decomposes into CO and 02 to produce CO2. and 02, which can also reduce freedom (0),
Both are unfavorable during C deoxidation. Although N2 may be used, it is not preferable for steel types where absorption of N in molten steel is a problem. Also, when using N2 during oxygen blowing, Ar
Either change to a gas that does not contain N2, such as, or use A after blowing.
It is preferable to perform denitrification by stirring with a gas that does not contain N2, such as r. Furthermore, 0° may be used as the stirring gas during oxygen blowing. It is also possible to use a combination of these gases. The gas flow rate is required to be 0.03 Nm''/min or more per molten steel. If it is less than 0.038 m3/min, the stirring effect will be small and the deoxidation rate will be slow, resulting in a long treatment time and Decreasing the temperature of molten steel is a problem. Generally, decarburization progresses by oxygen injection, but the freedom (0') in molten steel increases. In the so-called combined blowing, which is carried out using a combination of oxygen blowing and argon gas stirring, [Cax[O] at the end of blowing is smaller than in normal converter blowing. The relationship between [C] and free [O] at the end point in the case of combined blowing is shown by the black circle, and the relationship between normal pure oxygen top blowing (
LD) is a graph in which the relationship between [C] and freedom [O] at the end point is shown in the shaded area. Also, the solid line in the figure indicates P. 0 is 1 atm, the wavy line is P. 0 is 0.5 atm, dashed line is P
. The relationship between [C] and free [O] in an equilibrium state of 1600°C when 0 is 0.3 atm is shown. In reality, CO2 is also produced, so the relationship between these curves is P. 0 + P This is the relationship between [C] and free [O] in an equilibrium state when CO2 is at a predetermined atmospheric pressure, but when [C] is 0.1%, CO2 is C
It is less than 2% of O+CO2, and is so small that it can be ignored. As is clear from this figure, the free [O] is lower in the case of compound blowing than in normal blowing (LD), and the same [C
] must be deoxidized in the post-process [O
] has the advantage of being small. In addition, in the case of compound blowing, the relationship between [C] and free [O] is P. P is close to the equilibrium state when o = 1 atm. By controlling 0 and the end point [C], [O
] is almost uniquely controlled, and composite blowing is advantageous in this respect as well. Next, only stirring is performed to measure C deoxidation, but in order not to impair this C deoxidation effect, oxygen blowing in combined blowing is performed at a [C] content of 0.05% or more. stop. If C'l is less than 0.05%, free [O
) becomes too high and cannot be sufficiently deoxidized by stirring, and deoxidation with a small amount of AI (described later) is difficult to control free (0'l) to a predetermined value.In this way, The results of stirring and refining the molten steel obtained by composite blowing using Ar are shown in Figure 3 by white circles.As is clear from this figure, the decarburization and deoxidation effects of stirring are remarkable.
PCO in equilibrium with [C] and free [O] in molten steel is 0.3
It has been deoxidized to a pressure of ~0.5 atm. Also, if the oxygen blowing end point [C] is 0.05% or more, it is free.

[0] is easily deoxidized to about 150 ppm, and the amount of Ai added in the AI deoxidation treatment described later can be extremely small. Note that those whose oxygen blowing end point [C] is about 0.05% can be deoxidized to about 0.03% by stirring and refining. As described above, if a large amount of converter slag exists on the surface of the steel bath during stirring refining, a large amount of oxygen is supplied from the slag into the molten steel, impairing the C deoxidizing effect during stirring refining. However, in the steel manufacturing method according to the present invention, soda ash is used as a slag forming agent added to the converter, so as mentioned above, a sufficient dephosphorization effect can be obtained with an addition amount of 20 to 30 kg per 1 molten steel. Since the amount of slag during stirring and refining is 40 kg or less per molten steel, the C deoxidizing effect is not impaired. In addition, from the early to middle stages of oxygen blowing, only a small amount of soda ash is added immediately after the start of blowing for the purpose of turning SiO□ into slag, so during the decarburization stage in the middle stage of oxygen blowing, converter slag is Only a small amount of Na2O-8iO2 is present in formulas (3) and (4), and therefore the decarburization efficiency is excellent, and together with the composite blowing effect, free [O] and FeO in the slag at the end of blowing are
The increase in concentration is kept extremely small. The T and Fe content of this slag containing FeO is [C]
Even when the content is 0.05%, it is extremely low at 5 to 8% or less, but the low T and Fe contents also contribute to making the C deoxidation effect during stirring refining effective. (4), ((1), ((to)) Next, when casting the molten steel in a continuous casting machine, deoxidation is performed by adding AI to free the unsolidified molten steel in the mold that constitutes the continuous casting machine.

[0] to 7
Reduce it to below 0 ppm. In this step, if the nozzle diameter of the ladle or tundish is small (15 mm'6 or less) as in a continuous billet casting machine, the nozzle is likely to be clogged by the A1 deoxidation product Al2O3. Specifically, the freedom in the molten steel in the ladle and tundish obtained by deoxidizing with the addition of AI

When [0] is less than 1100 pp, nozzle clogging occurs frequently. Therefore, when continuously casting billets, the free [O] force f'' in the molten steel in the mold should be adjusted to 100 to 180 pp to avoid nozzle clogging in the stage up to the tundish. AI is added to the molten steel in the mold to deoxidize it so that it is less than IOppm.

[0] iso pμs
The reason for the following is that if this value is exceeded, A will enter the molten steel in the mold.
This is because too much I is added, making it difficult to control the amounts of free [O] and Al added. As for the AI addition method, it is possible to add A1 grains, but as described later, it is easier to add when the gap between the tundish and the mold is sealed with an inert gas, and it is easier to adjust the free [O] using AI cotton wire. The feeding method is preferred. Meanwhile ladle nozzle, like slab, bloom continuous casting machine
If the nozzle diameter of the tangent nozzle is 15mmφ or more, there is no need to divide the AI deoxidation treatment into two stages as described above, and the AI deoxidation treatment can be carried out at any time before casting.
0] is below 70pIIT1.
It was possible to perform deoxidation treatment by adding a large amount of chlorine. The addition location may be during tapping from the converter (combined blowing furnace) to the ladle as described in (2) above, in the ladle after tapping, in the tundish, or even in the mold. You can go anywhere. The amount of AI added is free in the molten steel before addition.

[0] is determined by measuring it with an oxygen probe that utilizes an electrochemical phenomenon such as a solid-state battery, but since the molten steel has already been deoxidized in the stirring refining step (3), an extremely small amount of By adding AI, the free [O] in molten steel can be deoxidized to 70 ppm or less, and the T and [AI) in molten steel after adding AI can be sufficiently kept below 0.020%, which is required for quality as steel equivalent to rimmed steel. be able to. In addition, since the T and Fe contents contained in the converter slag are low, and the supply of oxygen from the slag is small, there is no loss of AI when adding AI, so the free [O] in molten steel can be controlled with high precision. Since the (Si) content of the hot metal charged into the converter is adjusted to 0.03% or less, preferably 0.20% or less, the SiO2 component in the slag is small, and the SiO2 component in the slag is reduced by adding A1. The effect of so-called Si pick-up, where (Si:) increases in molten steel due to reduction of the Freedom (0) can be controlled with high precision.Also, it is possible that [Si:) in the molten steel increases slightly due to Si pickup from the SiO2 component in the refractory or Si contained in the AI metal. , as mentioned above, [AI] is approximately 0.020%.
When added, the increase in (Si) is extremely small and remains at an unavoidable content. Further, adjustment of alloying elements such as Mn required depending on the use of the steel material is carried out by adding the alloy to the ladle during or after tapping from the converter to the ladle. Furthermore, in order to prevent the molten steel from being oxidized by air during tapping from the converter to the ladle, 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 the air, it is preferable to add 7 lacs or rice husks from the viewpoint of preventing heat radiation and air oxidation. In addition, in the series of steps described above, the processing time is longer by the time required for stirring and refining than the steps required before normal continuous casting, but it is significantly shorter than when performing the vacuum processing as described above. Next, the molten steel that has been subjected to such deoxidation treatment is cast in a continuous casting machine, but free particles in the molten steel

[0] is the aforementioned 70pp
Since the condition of less than m is satisfied, CO is not generated and slabs without defects such as pinholes can be stably produced. During continuous casting, measures are taken to prevent re-oxidation of molten steel: a long nozzle is used as the ladle nozzle, a submerged nozzle is used as the tundish nozzle, and the space between the ladle and the tundish and between the tundish and the casting is heated with Ar, etc. It is desirable to take known measures such as sealing with an inert gas. Next, an example of the present invention was prepared using a 250 mm thick slab and a 116 mm thick slab.
The case of manufacturing mmmm billets will be described in detail. First, when manufacturing a 250 mm thick slab, Table 1 A
Hot metal 270 with the component concentration and temperature listed in the column (before treatment)
t was placed in a hot metal ladle of a desiliconization treatment facility shown in FIG. 4 and subjected to desiliconization treatment. 4 in Fig. 4 is a water-cooled quadruple pipe Laval type lance,
FIG. 5 shows its lower end surface. This lance 4 has a center hole and three holes located at three equal intervals around the center hole. Quicklime powder is supplied from the center hole at a rate of 25 kg/min using N2 as a carrier gas, and from the three peripheral holes. 02 at 3ONm3/min (0.ll per 1 hot metal
The oxygen was sprayed onto the molten steel at an oxygen delivery rate of Nm3/min). Immersion type graphite lance 5 to effectively perform desiliconization treatment at the same time.
N2 was introduced into the molten steel and stirred. As a result of carrying out such treatment for 21 minutes, the concentrations of each component in the hot metal became as shown in column B of Table 1 (after desiliconization treatment). That is, (Si) was 0.17%, which was 0.30% or less. After that, the slag generated in the desiliconization process is removed, and the hot metal is charged into a 270-ton converter (compound blowing furnace) 2 shown in Fig. 2 for complex blowing. Immediately after the start of blowing, soda ash is Hot metal 1
7 kg of each was added. Note that the tuyere 1 has an inner tube inner diameter of 12.7 mm' and a gap between the inner and outer tubes of 1.
It has a 1mm double tube structure, with an inner tube made of Cu and an outer tube made of stainless steel.Ar is discharged from the inner tube for stirring, and the outer tube is used to cool the tip of the slats. Hydrocarbon gas is passed through. The oxygen blowing rate during oxygen blowing was 40,00 ONm3/hour, and the stirring Ar blowing rate was 9Nm3/min. As shown in Column C of Table 1 (after combined blowing), the combined blowing resulted in a 325p riverbed with [C] of 0.07% (free CO), which is Pco-1 as shown in Figure 3. Close to the equilibrium state at atmospheric pressure. Note that [P] and [S] do not decrease at all because the amount of added soda ash is small. Next, after composite blowing, soda ash is added to molten steel (1 kg) 20 kg
Then, Ar was blown into the molten steel for 5 minutes from each inner tube of the two tuyeres 1 at a total rate of 2ONm3/min to perform stirring and refining. As a result, as shown in the first table (after stirring and refining), free

[0] was deoxidized to 141 p1m, and dephosphorization and desulfurization were also performed, so that [P] and [S] were each 0.015. 0.01
It decreased to 1%. Next, the steel was tapped from the converter to the ladle, and during this tapping, 80 kg of rod-shaped AI was added to the molten steel (approximately 0.0 kg per 1 molten steel).
．． 3 kg) and at the same time added HCFe to adjust the Mn component.
An appropriate amount of -Mn (Fe-Mn alloy) was added. In addition, in order to promote the floating of A1□03-based inclusions generated by AI deoxidation, after the ladle was covered, an immersion lance was inserted into the molten steel, and the steel was stirred with Ar at a pressure of 3 kg/cm2 for 5 minutes. . The concentrations of each component after this AI deoxidation treatment are shown in Table 1, column E (after AI deoxidation treatment). [Si] is 0.010%, T, [
A1] is 0.016%, which is a sufficient value for molten steel for products equivalent to rimmed steel, and even more free.

[0] indicates 5Qppm, which is not likely to generate bubbles during continuous casting. Then, in a continuous slab casting machine with a thickness of 250 ROM, the spaces between the ladle and the tundish and between the tundish and the mold were sealed with Ar, and a long nozzle was used for the ladle nozzle, and a submerged nozzle was used for the tundish nozzle, and the drawing speed was 1. Although casting was carried out at a speed of .2 m/min, there was no generation of air bubbles or pinholes, and a slab with good surface quality could be produced. Next, the case of manufacturing a 116 mm billet will be described. 77 tons of hot metal having the component concentration and temperature listed in column A (before treatment) of Table 2 was transferred to a hot metal ladle 6 as shown in FIG. 6, and subjected to desiliconization treatment by the KR method. That is, the tip of the impeller 7 was immersed in the hot metal, and while stirring the hot metal by rotating the impeller 7 at 5 Qr, p, m, the immersion lance 8 was used to feed oxygen at a rate of 12 Nm3/min (0.15 Nm3/min per 1 piece of hot metal). 02 in molten steel at 22 min)
I blew it for a minute. In addition, in order to perform the desiliconization process efficiently, 150 kg (approximately 2 kg per 1 hot metal
g) quicklime was added. The concentration of each component in the hot metal after this desiliconization treatment is as shown in column B of Table 2 (after desiliconization treatment), and [Si] is 0.21% and 0.
．． It decreased to 30% or less. After that, the slag generated in the desiliconization process is removed, and this hot metal is charged into a composite blowing furnace with a structure similar to that shown in Figure 2 for composite blowing. Immediately after the start of blowing, soda ash is added to the hot metal. 1 was added in an amount of 7 kg per portion. The oxygen supply rate was 11゜00ONm3/hour, and the stirring Ar
The blowing speed is 4 Nm3/min. The material of the tuyeres is the same as in the case of Fig. 2, with the inner tube being Cu and the outer tube being stainless steel, but the shape is slightly smaller, with the inner diameter of the inner tube being 7.75 mmφ and the gap between the inner and outer tubes being 0.8 mm. As shown in column C of Table 2 (after composite blowing), [C amount is 0.10%, free

[0] is 250ppm
As shown in Fig. 3, this is close to the equilibrium state when Pco is 1 atm.Dephosphorization and desulfurization are hardly performed.Next, after combined blowing, soda ash is applied to molten steel 1. )) 20k
Ar was injected into the molten steel for 5 minutes at a rate of 8 Nm/7 minutes from the inner tube of the two sidings to perform stirring and refining. As a result, as shown in the second table column (after stirring and refining), C
PU and [S) are 0.013% and 0.009%, respectively.
Dephosphorized and desulfurized until

[0] also decreased to 110 spots. When producing billets, part of the deoxidation adjustment is performed in the mold of a continuous casting machine, so at the tundish stage, the free [O] in the molten steel must be reduced to 100 to 180'1)IIITI
However, in this example, stirring and refining is used to remove free particles in the molten steel.

Since [0] had been deoxidized to 110 pn, no AI was added until the tundish stage, and only the Mn component was adjusted by adding HCFe-Mn. When casting the molten steel produced in this way using a 116 mm billet continuous casting machine, molten steel 1 is cast at a rate of 200 m
Al wire was supplied to the molten steel in the mold at the same rate. The drawing speed was 2.2 m for 7 minutes, and Ar sealing was performed to prevent re-oxidation of the molten steel. As a result, there was no generation of air bubbles or pinholes, and a slab with good surface quality could be produced. The concentration of each component of the molten steel in the mold is shown in Table 2 column E (molten steel in the mold), but since no Si deoxidation was performed, (Si)
It is natural that T is as low as 0.009%. (AI) is also 0.013%, which is 0.0 of conventional A1 guild steel.
This is extremely low compared to 30% or more, and is sufficient for molten steel equivalent to rimmed steel. Furthermore, since the free COI was extremely low at 53 ppm, naturally no bubbles were generated. In both examples of soil and mud, the amount of C in the product was 0.0.
This is about a product equivalent to low carbon rimmed steel with a carbon concentration of about 3 to 0.10%, but the C concentration in the finished product is 0.11 to 0.25%.
It goes without saying that the present invention is also applicable to products equivalent to high carbon rimmed steel to a certain degree. [This is because the higher the C content, the freer the end point of oxygen blowing (0, 1 is lower, and the subsequent deoxidation treatment is light.) As detailed above, the composite blowing using soda ash according to the present invention A series of steelmaking methods centered on stirring and refining have made it possible to continuously cast molten steel with no Si deoxidation and only slight AI deoxidation, making it possible to cast molten steel equivalent to rimmed steel without pinhole defects. This method makes it possible to obtain pieces at a high yield and with high efficiency, and since vacuum treatment is not performed, the equipment does not require manual labor, and compared to deoxidation using vacuum treatment. As described above, the steel manufacturing method according to the present invention can achieve low A
I), (Si) steel, that is, a product equivalent to rimmed steel, has been made possible to be continuously cast, and can be said to be an epoch-making contribution to this type of technology.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the effective amount of soda ash and the dephosphorization rate, Figure 2 is a schematic longitudinal cross-sectional view of a composite blowing furnace, and Figure 3 is a graph showing the relationship between the effective amount of soda ash and the dephosphorization rate. Graph showing the effect, Figure 4 is a schematic vertical cross-sectional view of the desiliconization treatment equipment, Figure 5 is a diagram schematically showing the lower end surface of a water-cooled quadruple-pipe Laval type lance, and Figure 6 is a diagram showing the KR method desiliconization treatment. FIG. 2 is a schematic vertical cross-sectional view of the silica equipment. 1...tuyere, 2...converter, 3,6...
... Hot metal pot, 4 ... Water-cooled quadruple pipe Laval type lance, 5 ... Immersion type graphite lance, 7 ...
... Impeller, 8... Lance, 9...
・Hopper.

Claims (1)

[Claims] 1. If necessary, the hot metal can be desiliconized to reduce the Si content to 0.30% or less, and gas can be introduced from below the bath surface into the hot metal with or without the desiliconization treatment. Oxygen blowing is performed by charging into a converter with a similar structure, and stirring and refining is performed by introducing gas from below the bath surface for an appropriate period during oxygen blowing and after oxygen blowing. A slag-forming agent mainly composed of alkali metal carbonate is added at an appropriate point leading to refining, and during and/or after tapping from the converter to the ladle after stirring and refining, the addition of AI Deoxidize and free [0] force QOOpp
m or less, T, [Al] is 0.020% or less, [Si]
1. A steel manufacturing method characterized by producing molten steel having an unavoidable content of molten steel and casting the molten steel using a continuous casting machine. 2 In short, the hot metal is desiliconized so that the page Si) is 0.30% or less, and the hot metal with or without the desiliconization treatment is placed in a converter that allows gas to be introduced from below the bath surface. After the oxygen blowing, gas is introduced from below the surface of the bath to perform stirring and refining, and at appropriate times from oxygen blowing to stirring and refining. A slag-forming agent containing an alkali metal carbonate as a main component is added, if necessary, during tapping from the converter to the ladle after stirring and refining.
Or, after tapping the steel, perform deoxidation by adding A1 to produce molten steel with a free [0] of 100 to 180p and an unavoidable content of [Si], and when casting the molten steel with a continuous casting machine, Al is added to the molten steel in the mold constituting the continuous casting machine to perform deoxidation treatment, and the free [0] of the mold self-melting steel is reduced to 70
pIrn or less, T, (AI) 0.020% or less,
A steel manufacturing method characterized by making [Si] an unavoidable content.