JP2000297315A - Method for decarburizing-refining molten stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decarburizing-refining method of molten stainless steel by which it is suppressed that the metal is spattered by splashing, the metal becomes fine grains by generating secondary burst and the fine grain metal is stucked to or deposited on a gas exhaust system and to perform stable decarburize-refining. SOLUTION: In the decarburizing-refining method of the molten stainless steel for executing the decarburizing-refining by dipping an immersion tube 13 into molten stainless steel 12 in a ladle 11, reducing the pressure in the inner part of the immersion tube 13 and blowing oxygen-containing gas from above the molten steel surface into the immersion tube 13 while supplying inert gas at 0.6-15.0 Nl/(min.ton of molten steel) from the bottom part of the ladle 11, the exhaust gas flow speed in the immersion tube 13 is regulated to 5-20 m/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for reducing the size of ingot produced by splashing during the decarburization and refining of molten stainless steel, and to prevent the ingot from adhering or accumulating on the exhaust system. The present invention relates to a method for decarburizing and refining stainless steel to be prevented.

[0002]

2. Description of the Related Art In the decarburization and refining of molten stainless steel,
Decarburization in which oxidation of chromium is suppressed by reducing the pressure in the vessel and blowing acid is performed.
The H-OB method is widely known. This RH-OB method
Both the riser and the downcomer are immersed in the molten steel in the ladle, the molten steel is sucked up by the gas lift action of the gas supplied from the riser, and discharged from the downcomer to circulate the molten steel in the ladle to the riser. Decarburization is performed by blowing an oxygen-containing gas from the provided nozzle. Japanese Patent Application Laid-Open No. 8-109410 discloses that an immersion pipe is immersed in molten steel in a ladle, the inside of the immersion pipe is evacuated and decompressed, and 0.6 to 15.0 is poured from the bottom of the ladle.
A decarburization and refining method for molten stainless steel has been proposed in which an oxygen-containing gas is blown from above an immersion pipe to decarburize while supplying an inert gas of N liter / (minute / ton of molten steel). This method has been put to practical use because it allows rapid decarburization by reducing the generation of Cr ₂ O ₃ (hereinafter referred to as chromium oxide) and the loss of chromium.

[0003]

However, in the above-mentioned RH-OB method, the immersion pipe is separated into an ascending pipe and a descending pipe, so that the molten stainless steel sucked from the ascending pipe returns to the ladle through the descending pipe. Because the time is short, when performing leaching acid decarburization refining of molten stainless steel, the chromium oxide once generated in the vacuum tank flows out of the vacuum tank instantaneously and is not affected by stirring. Ascend to the top. Since the chromium oxide floating on the upper part of the ladle hardly reacts with the carbon in the molten stainless steel, the efficiency of decarburization is low, causing an increase in chromium oxide and an increase in the amount of a reducing agent that reduces this chromium oxide. There are problems such as loss of chromium. Furthermore, since the molten steel is circulated by the action of the gas lift of the inert gas supplied to the riser, the absolute amount of gas blown from the riser increases, and the decarboxylation efficiency of the oxygen-containing gas blown decreases. Splash generation and secondary burst (the metal generated by the splash is reoxidized and refined) become intense. In Japanese Patent Application Laid-Open No. 8-109410, the molten steel in the ladle is blown with oxygen from above while the inert gas is blown from the bottom of the ladle to vigorously agitate the molten steel. A large amount of chromium oxide is formed on the surface. This chromium oxide rapidly reacts with carbon, and the CO gas generated at that time breaks on the surface of the molten steel to generate a splash and scatter the metal. The base metal generates a secondary burst and becomes finer, scatters along with the exhaust gas, and adheres and accumulates in the immersion pipe or the exhaust system. Also, because oxygen is blown onto the molten steel surface to decarburize,
Oxygen efficiency that works effectively for decarburization is reduced to 40-55%,
Oxygen that does not act on decarburization secondary-combustes in the immersion tube and promotes secondary burst of the scattered metal, so that fine-grain metal that adheres and accumulates on the exhaust system or the like increases. In particular, in molten stainless steel containing chromium in an amount of 5% by weight or more, the exhaust resistance of the ejector increases due to the adhesion and deposition of fine-grained metal in the exhaust system, and a high degree of vacuum cannot be obtained. As a result, there is a problem that chromium in the molten stainless steel is oxidized and chromium loss due to an increase in chromium oxide or a reducing agent such as Al for reducing chromium oxide increases.

[0004] The present invention has been made in view of the above circumstances, and in the decarburization and refining of molten stainless steel, the metal is scattered by splash and the secondary metal generates a secondary burst to become fine particles. It is an object of the present invention to provide a method for decarburizing and refining molten stainless steel capable of suppressing and preventing fine-grained metal from adhering and accumulating in an exhaust system, and performing stable decarburization and refining.

[0005]

According to the first aspect of the present invention, there is provided a method for decarburizing and refining molten stainless steel according to the first aspect of the present invention. While supplying an inert gas of 0.6 to 15.0 Nl / (min / ton of molten steel) from the bottom of the ladle,
In the decarburization and refining method for molten stainless steel in which decarburization and refining is performed by spraying an oxygen-containing gas from above the molten metal surface in the immersion pipe, the exhaust gas flow rate in the immersion pipe is set to 5 to 20 m / sec. By this method, the metal scattered by the splash is suppressed from being accompanied by the exhaust gas, and the fine metal is prevented from adhering or accumulating in the exhaust system. Stable decarburization refining can be performed. If the exhaust gas flow rate in the immersion tube is less than 5 m / sec, the amount of oxygen-containing gas blown is reduced or the degree of vacuum is reduced to an extremely low vacuum. Cannot be carried out, resulting in prolonged refining time and chrome loss. On the other hand, when the flow rate of the exhaust gas in the immersion pipe exceeds 20 m / sec, the metal scattered by the splash accompanies the exhaust gas, and secondary combustion is caused by oxygen remaining in the atmosphere to generate a secondary burst, and the fine particles are refined. The wrought metal adheres and accumulates in the exhaust system. For this reason, when the exhaust gas flow rate in the immersion pipe is set to 5 to 15 m / sec, a favorable result can be obtained because the decarburization refining time is extended, and adhesion and deposition of fine-grained metal to the exhaust system are prevented. If the amount of the inert gas supplied from the bottom of the ladle is less than 0.6 Nl / (min / ton of molten steel), the bubble active surface formed on the molten metal surface in the immersion tube becomes small, and the entire stainless steel molten steel is stirred. And the time for decarburization refining is extended. The amount of inert gas is 15.0
If it exceeds N liters / (minute / ton of molten steel), the stirring of the entire molten stainless steel becomes too strong, and the scatter of the metal increases due to the breakage of bubbles of the inert gas and the blowing acid on the molten metal surface in the immersion tube. .

Here, the flow rate of the exhaust gas can be adjusted by the amount of the oxygen-containing gas blown from above the molten metal surface in the immersion tube. This enhances the decarbonation efficiency of oxygen in the oxygen-containing gas sprayed onto the molten steel surface, suppresses the formation of chromium oxide, reduces secondary combustion in the immersion pipe, By suppressing the burst, fine metal can be prevented from being finely divided.

Further, the flow rate of the exhaust gas can be adjusted by the degree of vacuum in the immersion tube. As a result, the flow rate of the exhaust gas in the immersion pipe can be rapidly reduced, so that the fine metal ingot generated by the secondary burst can be prevented from being scattered to the exhaust system.

Further, the inner surface area of the molten steel immersion portion of the immersion tube can be set to 0.1 to 0.7 of the total molten steel surface area in the ladle. As a result, a bubble activated surface effective for decarburization (a state in which bubbles of inert gas are expanded, broken, and the molten metal surface is wavy)
, The oxygen efficiency that contributes to decarburization is increased, and a low carbon concentration can be achieved in a short time while suppressing secondary burst.
If the inner surface area of the molten steel immersion part of the dip tube is smaller than 0.1 of the total molten steel surface area in the ladle, the stirring power of the molten stainless steel is insufficient, the bubble active surface becomes narrow, the decarburization reaction is slowed, and the carbon The concentration cannot be lowered. On the other hand, when it is larger than 0.7, the gap between the inside of the ladle and the outer peripheral surface of the immersion tube becomes narrower,
The immersion of the immersion tube in the ladle becomes difficult due to the obstruction of sampling and the adhesion of chromium oxide or the like flowing out of the immersion tube.

According to a second aspect of the present invention, there is provided a method for decarburizing and refining molten stainless steel according to a second aspect of the present invention, in which a dip tube is immersed in stainless steel in a ladle, the inside of the dip tube is depressurized, and the bottom of the ladle is depressed. While supplying an inert gas of 0.6 to 15.0 Nl / (min./ton of molten steel) from the lance disposed above the molten metal surface in the immersion tube, and blowing an oxygen-containing gas toward the molten metal surface. In the decarburization and refining method for molten stainless steel for decarburization and refining, the oxygen-containing gas includes the following (1):
The cavity depth L obtained by the equation (2) is 210 to 5
Spray so as to be 00 mm. L = Lh × 10 ^{(−780H / Lh)} (1) Lh = 0.894 × (Q ² / S × n) ^1/3 (2) where L Is the cavity depth (mm), H is the distance (m) from the tip position of the lance to the stationary metal surface, and Lh is H = 0.
, The cavity depth (mm), Q is the flow rate of the oxygen-containing gas (Nm ³ ), S is the cross-sectional area of the narrowest portion of the lance discharge port (m ² ), and n is the number of lance discharge ports. The cavity depth L is 21 due to the oxygen-containing gas sprayed on the molten steel surface.
Since the blowing acid is hard blown so as to be 0 to 500 mm, the decarburization reaction at the flash point of the blowing acid and its vicinity,
Promotes the reaction of the generated Cr ₂ O ₃ with carbon in the molten steel,
Decarbonization efficiency including oxygen consumed for decarburization and combustion (secondary combustion) of the generated CO gas above the hot water surface can be improved, and the size of the metal scattered by the blowing acid can be increased. Exposure of the metal to the jet of oxygen can be suppressed to prevent secondary bursts.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. FIG. 1 is a conceptual diagram of a decarburizing refining apparatus applied to a method for decarburizing stainless steel molten steel according to one embodiment of the present invention, and FIG. 2 is an exhaust gas during blowing acid decarburizing refining using the decarburizing refining apparatus. FIG. 3 is a graph showing changes in flow velocity, acid supply amount, exhaust gas flow rate, and degree of vacuum, FIG. 3 is a graph showing a relationship between a lance type and a metal deposition speed on an exhaust duct, and FIG. It is an enlarged view. As shown in FIG. 1, a decarburizing and refining apparatus 10 applied to a method for decarburizing and refining stainless steel molten steel according to one embodiment of the present invention includes a ladle 11 and a stainless steel molten steel 12 received by the ladle 11. A dipping tube 13 of a straight body type to be dipped by an elevating device (not shown), a porous plug 14 for blowing an inert gas into the molten stainless steel 12 and stirring the molten steel 12 at the bottom of the ladle 11, and a stainless steel in the dipping tube 13. A lance 16 provided with a flow rate control valve 15 for setting the flow rate of the oxygen-containing gas to be blown on the molten metal surface 12 a of the molten steel 12 is provided above the immersion pipe 13. The immersion pipe 13 is provided with an exhaust duct 17 communicating with an ejector (not shown) for reducing the pressure inside. In this exhaust duct 17,
A vacuum gauge 18 for measuring the degree of vacuum inside the immersion tube 13 and an exhaust gas flow meter 19 are provided. Further, the inner surface area of the molten steel immersion part of the immersion tube 13 is set to be 0.1 to 0.7 with respect to the total molten steel surface area of the stainless steel molten steel 12 in the ladle 11. In the drawing, reference numeral 20 denotes a chute for adding an auxiliary material such as alloyed iron or quick lime into the immersion tube 13, and 21 denotes a storage hopper for auxiliary material such as alloyed iron or quick lime.

Next, a method for decarburizing and refining stainless steel melt according to the present embodiment using the decarburizing and refining apparatus 10 will be described. First, a ladle 11 receives 150 tons of molten stainless steel 12 containing 5% by weight or more of chromium, and a immersion tube 13 is inserted into the ladle 11 so that the tip of the immersion tube 13 has a depth from the surface of the molten stainless steel 12 in the ladle 11. It was immersed so as to reach a position of 600 mm, and the inside of the immersion tube 13 was evacuated from the exhaust duct 17 by an ejector (not shown) to reduce the pressure. Immersion tube 13
An argon gas, which is an example of an inert gas, is supplied from the porous plug 14 of the ladle 11 to the hot water surface 12a in the inner space 12a.
By supplying 5.0 Nl / (min / ton of molten steel), a bubble activated surface is formed, and the degree of vacuum in the immersion tube 13 is 200
After reaching torr, the lance 16
From a height of 2800 mm to 3000 Nm ³ / hr
By blowing oxygen, which is an example of an oxygen-containing gas (blowing acid)
Decarburization refining was performed. In the initial stage of the decarburization refining, that is, immediately after the start of the blowing acid, since the metal Al for heating is added into the immersion pipe 13, oxygen is consumed in the combustion of the metal Al, and the amount of generated exhaust gas is small. When the combustion of the metal Al is completed, oxygen and chromium in the molten stainless steel 12 positively generate Cr ₂ O ₃ by the reaction of the formula (3), and this Cr ₂ O ₃ is combined with carbon (4) in the molten stainless steel 12. Decarburization is carried out by reacting as shown in the formula (1). 2Cr + 3 / 2O ₂ → Cr ₂ O ₃ (3) Cr ₂ O ₃ + 3C → 2Cr + 3CO (4) At this time, if the degree of vacuum is low, chromium in the stainless steel melt 12 is oxidized. Rapidly occurs, and excessive Cr ₂ O ₃ is generated,
An abnormal reaction such as bumping or oxidization loss of chromium is caused.

Therefore, as shown in FIG. 2, in order to suppress the excessive production of Cr ₂ O _3, a vacuum
The operation is performed by adjusting the exhaust amount of an ejector (not shown) so that the value of “” becomes a high vacuum degree of about 100 torr. The flow rate of the exhaust gas including the generated CO gas and the secondary-combusted CO ₂ gas (shown by two-dot hatching in the figure) is measured by an exhaust gas flow meter 19 provided in the exhaust duct 17. It rapidly increases with the start of the decarburization reaction, and the exhaust gas flow rate (shown by a thick solid line in the figure) also rises following the increase in the exhaust gas flow rate. Therefore, the degree of vacuum (indicated by a broken line in the figure) is set to 100
The exhaust volume of an ejector (not shown) is adjusted from a high vacuum of torr to a low vacuum of 150 torr, and the exhaust gas flow rate is set in a range of 8 to 12 m / sec. Assuming that the exhaust gas flow rate (m / sec) is V, V can be obtained by equation (5). V = Q ÷ S × (P ₀ / P) × (T / T ₀ ) (5) Here, Q is the exhaust gas flow rate (Nm ³ / hr), and S is the area of the immersion tube in the diameter direction. (M ² ), P ₀ is the standard atmospheric pressure (101
325 Pa), P is the internal pressure of the immersion tube (Pa), T is the exhaust gas temperature (K), and T ₀ is the standard temperature (K).

Further, in the middle stage in which the decarburization reaction of the stainless steel molten steel 12 proceeds, the exhaust gas flow rate further increases, the indication of the exhaust gas flow meter 19 becomes about 3500 Nm ³ / hr, and the exhaust gas flow rate exceeds 12 m / sec. So the degree of vacuum is 1
While maintaining the pressure at 50 torr, the opening of the flow control valve 15 is adjusted to reduce the oxygen amount of the blowing acid, that is, the acid supply amount (shown by a solid line in the figure) to 2500 Nm ³ / hr, and the exhaust gas flow rate to 8 to 12 m. / Sec range. At the end of the decarburization refining, the exhaust gas flow rate decreases due to the decrease in the carbon concentration in the stainless steel molten steel 12, so that the inside of the immersion pipe 13 is changed from a low vacuum of 150 torr to a high vacuum of 5 to 2 torr in accordance with the decrease in the exhaust gas flow rate. Perform decarburization refining. As described above, the acid flow rate and the degree of vacuum are adjusted to reduce the flow rate of the exhaust gas rising in the immersion tube 13, so that fine-grained metal generated by the secondary burst of the metal generated by the splash is reduced. It can be prevented from scattering along with the flow of the exhaust gas and adhering to or accumulating on the exhaust duct 17, and it is possible to eliminate the trouble of increasing the exhaust resistance and processing the accumulated metal.

As shown in FIG. 3, in the case of a straight nozzle having a generally used discharge port, the lance 16 used for blowing acid has a gas jet which spreads and becomes a soft blow, so that oxygen for decarburization is removed. The efficiency decreases, and the sliver generated by the splash causes secondary combustion with the oxygen present in the atmosphere to generate a secondary burst. However, in the case of hard blowing using a Laval nozzle that blows out from the discharge port at a speed higher than the speed of sound, the oxygen efficiency of decarburization increases, and the secondary burst of the slab generated by splash can be suppressed. This tendency is more effective in suppressing the secondary burst since the use of single-hole Laval than the use of three-hole Laval allows hard blow. That is, as shown in FIG. 4, the cavity depth (dent) of the molten metal surface 12a obtained from the above-described equations (1) and (2), which are generally used under the condition of hard blow using a single-hole Laval. Depth) L value is 2
By setting the thickness to 10 to 500 mm, in the vicinity of the flash point A, decarburization is performed by the reaction between oxygen and carbon in the molten steel 12, and oxygen and chromium (Cr) react to form Cr ₂ O _3.
Generate In addition, since the cavity depth L is within a predetermined range, when the generated Cr ₂ O ₃ floats,
Oxygen efficiency which is reduced by carbon in the upper part of the stainless steel melt 12 in the immersion pipe 13 and contributes to decarburization can be improved. Further, if the blowing force at the time of blowing acid is increased to make the cavity depth L as deep as the above range, the amount of the metal scattered from the molten metal surface 12a increases, and the metal particles Is relatively large. However, by making the blowing acid a hard blow, the spread of the oxygen jet is reduced, and the amount of metal exposed to the oxygen jet can be reduced.
It is possible to suppress the miniaturization due to the secondary burst (fine grains indicated by dotted lines in the figure). The Cr ₂ O ₃ near the fire point
Synergistic actions such as improvement of decarbonation efficiency including reduction of metal, coarsening of metal, and suppression of spread of oxygen jet prevent the fine metal from accumulating in exhaust ducts, etc. Operation. When the blow acid is soft blown and the cavity depth L is smaller than 210 mm, a secondary burst of the metal occurs, and the metal adheres to the exhaust system duct and the like. The blowing power during blowing acid is too strong,
When the cavity depth L is larger than 500 mm, the scattering of the metal becomes extremely large, and the refractory near the fire point is worn. Therefore, the cavity depth L value is 300-45.
If it is set to 0 mm, more preferable results are obtained.

[0015]

Next, an embodiment to which the method for decarburizing and refining stainless steel molten steel according to the present invention will be described. The molten steel immersion part has an inner surface area of 0.3 of the total molten steel surface area in the ladle after 150 tons of molten stainless steel containing 13% by weight of chromium is melted and received in a ladle by a converter. The tip of is dipped 600 mm deep from the surface of the stainless steel molten steel of the ladle, and the inside of the dipping tube is decompressed to a degree of vacuum of 100 mm.
After reaching torr, decarburization and refining were performed by blowing acid from above the dip tube through a lance, and the exhaust gas flow rate, the presence or absence of exhaust duct metal deposits, and the presence or absence of fluctuations in the degree of vacuum during operation were investigated.
As shown in Table 1, in Example 1, the cavity depth during blowing acid was set to 300 mm, and at the beginning of the blowing acid decarburization refining, 3000 Nm ³ / hr of oxygen was sprayed onto the surface of the molten metal using single-hole Laval. In the middle stage, the degree of vacuum is reduced to 150 NTorr and the oxygen is reduced to 2500 Nm ³ / hr.
This is a case where the vacuum is sequentially increased from 0 torr to 50 torr, the exhaust gas flow rate can be made 8 m / sec on average, there is no accumulation of metal in the exhaust duct, and there is no fluctuation in the degree of vacuum during operation, and stable decarburization refining is performed. The evaluation was good (◎) as the overall evaluation. Further, in Example 2, the cavity depth at the time of the blowing acid was set to 450 mm, and at the initial stage of the blowing acid decarburization refining, 3000 Nm ³ / hr of oxygen was sprayed on the molten metal surface using a single-hole laval. Oxygen was reduced to 2500 Nm ³ / hr by reducing the vacuum degree to 120 torr, and at the end of the blowing acid decarburization refining, the vacuum degree was increased to 120 without changing the blowing acid amount.
A high vacuum of 50 torr is applied sequentially from torr, the exhaust gas flow rate can be 10 m / sec on average, there is no accumulation of metal in the exhaust duct, and there is no fluctuation in the degree of vacuum during operation, and stable decarburization and refining is performed. The evaluation was good (◎) as the overall evaluation. In Example 3, the cavity depth at the time of blowing acid was set to 210 mm, and at the beginning of the blowing acid decarburization refining, 3000 Nm ³ / hr of oxygen was sprayed on the molten metal surface using a single-hole laval. Oxygen is reduced to 2500 Nm ³ / hr by reducing the pressure to 150 torr, and at the end of the blowing acid decarburization refining, the oxygen amount is the same as in the middle stage and only the degree of vacuum is set to 150 Nm ³ / hr.
A high vacuum of 50 torr sequentially from torr was applied, the exhaust gas flow rate could be 8 m / sec on average, the amount of metal in the exhaust duct was extremely small, and there was no fluctuation in the degree of vacuum during operation. Refining could be performed, and a good (○) result was obtained as an overall evaluation.

[0016]

[Table 1]

On the other hand, in the comparative example, the cavity depth during blowing acid was set to 150 mm, and 3,000 Nm ³ / hr of oxygen was blown onto the molten metal surface using a 3-hole Laval lance during the entire period of blowing acid decarburization refining. The case where the degree of vacuum is increased from 100 torr in the initial stage to 60 torr in the middle stage and to 50 torr in the last stage, and the exhaust gas flow rate becomes as fast as 27 m / sec.
Metal deposits occurred in the exhaust duct, and the degree of vacuum during operation fluctuated, resulting in unstable decarburization and refining. The overall evaluation was poor (x).

The embodiment of the present invention has been described above.
The present invention is not limited to the above-described embodiment, and all changes in conditions that do not depart from the gist are within the scope of the present invention. For example, in the above embodiment, decarburization and refining of molten stainless steel has been described, but the present invention can also be applied to decarburization and refining of general molten steel containing carbon. Further, as the shape of the immersion tube, a shape in which a diameter of an intermediate portion corresponding to an upper portion of a molten metal surface to which an oxygen-containing gas is blown is enlarged, in addition to a straight body type, can be used. In addition, decarburization refining can be performed using a gas obtained by mixing argon gas, carbon dioxide gas, or the like with oxygen as the oxygen-containing gas.

[0019]

The method for decarburizing and refining molten stainless steel according to any one of claims 1 to 4 is to immerse the immersion pipe in the molten stainless steel in the ladle to reduce the pressure inside the immersion pipe and to reduce the pressure from the bottom of the ladle. In the decarburization and refining method for molten stainless steel, in which an oxygen-containing gas is blown from above the immersion pipe to perform decarburization and refining while supplying an inert gas at 6 to 15.0 Nl / (min. 5 to 20 m / sec.
It is possible to suppress the scattering of the fine-grained metal generated by the secondary burst of the metal generated by the splash, bumping, etc., to prevent the fine metal from sticking or accumulating on the exhaust system duct, etc., and to perform a stable operation.

In particular, in the method for decarburizing and refining molten stainless steel according to claim 2, since the exhaust gas flow rate is adjusted by the amount of oxygen-containing gas blown from above the immersion pipe, the secondary combustion of the CO gas generated by the decarburization reaction is prevented. Thus, it is possible to efficiently suppress the secondary burst of the ingot caused by splash, bumping or the like.

In the method for decarburizing and refining stainless steel melt according to the third aspect, the flow rate of the exhaust gas is adjusted by the degree of vacuum in the immersion pipe, so that the flow rate of the exhaust gas can be rapidly reduced, and the fine-grained metal is reduced in the flow of the exhaust gas. It is possible to prevent accompanying scattering.

In the method for decarburizing and refining molten stainless steel according to claim 4, since the inner surface area of the molten steel immersion portion of the immersion pipe is set to 0.1 to 0.7 of the total molten steel surface area in the ladle, the exhaust gas flow rate is reduced. The oxygen concentration that contributes to decarburization can be increased, secondary burst can be suppressed, and the carbon concentration can be reduced in a short time.

According to a fifth aspect of the present invention, there is provided a method for decarburizing and refining molten stainless steel, comprising: dipping a dip tube in molten stainless steel in a ladle;
While depressurizing the inside of the immersion tube, 0.6 mm from the bottom of the ladle
In a decarburization refining method for molten stainless steel, a decarburization refining method is performed in which an oxygen-containing gas is sprayed from above the surface of the molten metal in the immersion pipe to supply deactivated carbon while supplying an inert gas of up to 15.0 Nl / (min./ton of molten steel). Since the contained gas is blown such that the cavity depth L is within a predetermined range, the decarburization reaction near the ignition point of the blowing acid and the reaction between Cr ₂ O ₃ and carbon are promoted, and the oxygen efficiency is improved. It is possible to prevent the metal scattered by the blowing acid from being secondary-bursted and to be miniaturized, to prevent the metal from being deposited on the exhaust duct, and to perform a stable operation.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a decarburization refining apparatus to which a method for decarburization of molten stainless steel according to an embodiment of the present invention is applied.

FIG. 2 is a graph showing changes in an exhaust gas flow rate, an acid supply amount, an exhaust gas flow rate, and a degree of vacuum during blowing acid decarburization refining using the decarburization refining apparatus.

FIG. 3 is a graph showing a relationship between a type of a lance and an adhesion speed of a metal to an exhaust duct.

FIG. 4 is a partially enlarged view of the vicinity of a fire point during blowing acid.

[Explanation of symbols]

10: decarburization refining equipment, 11: ladle, 12: stainless steel, 12a: hot water, 13: immersion pipe, 14: porous plug, 15: flow control valve, 16: lance, 17: exhaust duct, 18: vacuum Meter, 19: exhaust gas flow meter, 20: chute, 21: storage hopper

Claims (5)

[Claims] 1. An immersion tube is immersed in molten stainless steel in a ladle, the inside of the immersion tube is depressurized, and 0.6 to 15.0 Nl / (min./ton of molten steel) is applied from the bottom of the ladle. In the decarburization and refining method for molten stainless steel, in which an oxygen-containing gas is blown from above the surface of the molten metal in the immersion pipe to perform decarburization while supplying an inert gas, the exhaust gas flow rate in the immersion pipe is reduced to 5 to 20 m / sec. A method for decarburizing and refining molten stainless steel. 2. The decarburizing and refining method for molten stainless steel according to claim 1, wherein the flow rate of the exhaust gas is adjusted by the amount of oxygen-containing gas blown from above the molten metal surface in the immersion pipe. 3. The method for decarburizing and refining stainless steel melt according to claim 1, wherein the flow rate of the exhaust gas is adjusted by a degree of vacuum in the immersion pipe. 4. The method for decarburizing and refining molten stainless steel according to any one of claims 1 to 3, wherein the inner surface area of the molten steel immersion portion of the immersion tube is 0.1% of the total molten steel surface area in the ladle.
A decarburization refining method for molten stainless steel of 1 to 0.7. 5. An immersion pipe is immersed in molten stainless steel in a ladle, and the inside of the immersion pipe is depressurized, and 0.6 to 15.0 Nl / (min./ton of molten steel) is applied from the bottom of the ladle. In the decarburizing and refining method for stainless steel molten steel, in which an oxygen-containing gas is blown toward the molten metal surface from a lance disposed above the molten metal surface in the immersion pipe to perform decarburization while supplying an inert gas, The method for decarburizing and refining molten stainless steel, wherein the gas is blown so that the cavity depth L determined by the following equation is 210 to 500 mm. L = Lh × 10 ^{(−780H / Lh)} Lh = 0.894 × (Q ² / S × n) ^1/3 where L is the cavity depth (mm), H is the stationary hot water from the tip of the lance. Distance to the surface (m), Lh is H = 0
, The cavity depth (mm), Q is the flow rate of the oxygen-containing gas (Nm ³ ), S is the cross-sectional area of the narrowest portion of the lance discharge port (m ² ), and n is the number of lance discharge ports.