JP3460687B2 - Steel continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
Casting of steel with little adhesion of Al oxide etc. in molten steel
Construction method. [0002] 2. Description of the Related Art When continuously casting molten steel deoxidized with Al,
Al oxide in molten steel adheres to the inner surface of the immersion nozzle
Therefore, the flow of the molten steel in the immersion nozzle is hindered. That
When using a normal immersion nozzle with two discharge holes
In addition, the discharge flow will not be uniform and one of the discharge flows will not be weak.
The flow of molten steel in the mold tends to be one-sided
No. Uneven flow causes uneven flow of molten steel in the mold
And the mold powder added to the molten steel surface in the mold
Entangled in molten steel or adhered to the inner surface of the immersion nozzle
Of aluminum oxide, etc., peeled off is caught in molten steel
It is. [0003] In this way, the steel is caught in the molten steel in the mold.
Mold powder and oxides of Al, etc.
It is trapped in the solid shell, and defects are likely to occur in the surface layer of the slab.
Defects in the surface layer of these slabs are caused by hot slabs
It causes surface or internal defects of the rolled product. The oxide of Al in molten steel is
Pass through the immersion nozzle to prevent grease from adhering
Method of blowing inert gas into molten steel
Have been. For example, Japanese Patent Application Laid-Open No. Hei 4-319055
Depends on the amount of molten steel passing through the immersion nozzle.
Methods for adjusting the amount of inert gas to be blown have been proposed.
You. However, depending on the amount of inert gas blown,
Bubbles of reactive gas are trapped in the solidified shell in the mold,
A bubble defect occurs in Bubble defects on the surface layer of this slab
Remains on the product and surface defects are likely to occur on the product. In addition, Ca is added to molten steel before casting to
Conventionally, the method of converting Al oxide in steel to low melting point oxide
Taken from. For example, Japanese Unexamined Patent Publication No. 9-192799
In the publication, Ca is added to molten steel after Al deoxidation,
A method for reducing the Ca content in the solution to 1 to 5 ppm has been proposed.
I have. However, adding Ca to molten steel is
Not only increase manufacturing costs, but also
, The mechanical properties are deteriorated by the addition of Ca. Further, Japanese Patent Application Laid-Open No. H10-305355
The material of the inner surface of the immersion nozzle is changed to Al oxide in molten steel.
A method of using a material that is difficult to adhere to has been proposed. Soak
The material of the refractory inside the pickling nozzle is SiO_Two And low C
By using a material such as spinel, Al in molten steel
Suppresses oxidation and adheres to the inner surface of the immersion nozzle
This is a method for minimizing the amount of Al oxide. But this
These refractory materials are typically used for immersion nozzles.
Poor thermal shock resistance compared to alumina graphite
Soaking nozzle breaks during preheating before casting or during casting
It's easy to do. In addition, a step is provided on the inner surface of the immersion nozzle.
A method for equalizing the flow velocity of molten steel passing through the immersion nozzle,
Space or insulation layer for heat insulation inside the immersion nozzle body
By maintaining the temperature of the inner surface of the immersion nozzle at a high temperature.
Of aluminum oxide etc. adhere to the inner surface of the immersion nozzle
A method of preventing such has been proposed. But soaked nose
Of aluminum oxide in molten steel on the inner surface of
The current situation is that it has not been prevented stably. [0008] In view of the above situation, inexpensive method,
Oxide of Al in molten steel stably on inner surface of immersion nozzle
There is a demand for a method capable of preventing the adhesion of odor. [0009] SUMMARY OF THE INVENTION The present invention provides an immersion nozzle
Inexpensive aluminum oxide etc. in the molten steel adhere to the inner surface
Can be prevented stably by the method
In the rolled product, mold powder, oxidation of Al
Products caused by defects in the surface layer of the slab due to objects, air bubbles, etc.
Continuous casting of steel to prevent surface or internal defects
The aim is to provide a method. [0010] The gist of the present invention is to provide an immersion nozzle.
Supplying molten steel from the tundish into the mold using chisel
In the continuous casting method,
Opening area S (m^Two ) And soaked nose
Cross section A of the part where molten steel in
(M^Two Use an immersion nozzle that satisfies the following formula (b)
To the molten steel inside the immersion nozzle defined by the following equation (c).
Casting under the condition that the head index H (m) satisfies the following equation (d).
In the molten steel passing through the immersion nozzle
Inert gas amount W (m^Three (Normal) / s)
(E) Continuous casting method for steel cast under conditions that satisfy formula
is there. S = Q / ｛ρ × (2gh)^1/2 } ···(I) 2 <A / S <5 (b) H = (2g)^-1× (ρc)^-2× (Q / A)^Two   ... (c) 0.08 <H <0.5 (d) 1 × 10^-6 <W / Q <5 × 10^-6    ... (e) Here, Q: molten steel flow passing through the immersion nozzle per unit time
Amount (kg / s) ρ: density of molten steel (kg / m^Three) g: Gravitational acceleration (m / s^Two) h: Depth of molten steel inside tundish (m) c: Channel coefficient (-) The above equation (a) is an equation obtained from the law of conservation of energy.
The opening cross-sectional area S of the outlet of the tundish defined by the formula
Is to supply molten steel from a tundish into an immersion nozzle.
Means the cross-sectional area of the opening of the tundish outlet
You. That is, the numerator on the right side of the equation (a) is per unit time
Is the flow rate of molten steel into the mold, and the denominator is a tundish
The depth of the molten steel in h, that is, the loss head h of molten steel
Means the flow speed of molten steel at the time. Therefore, the unit time
Flow rate of molten steel into the mold
The right side of equation (a) divided by the flow rate of molten steel at the time of
Means the opening cross-sectional area of the outlet of the dish. For example, casting
Change the flow rate Q of molten steel into the mold by changing the casting speed
When this is done, this cross-sectional area S changes. Further, the immersion nozzle defined by the above equation (c)
The molten steel head index H (m) inside the nozzle is
Height of molten steel surface formed in the mold and height of molten steel surface in mold
And the difference. Molten steel flow through the immersion nozzle,
By setting the cross-sectional area of the immersion nozzle
Molten steel flowing from the outlet of the tundish
It falls on the molten steel surface formed inside the immersion nozzle. That
In this case, the above equation (c) is similar to the above equation (a) in energy conservation.
The difference from equation (a), which is obtained from the law of existence, is that
The point is that the flow path coefficient c is given. This channel coefficient c
Is the speed head generally used in Bernoulli's formula.
Means the reciprocal of the correction coefficient. Here, the value of the density ρ of the molten steel is 7000
(Kg / m^Three ), 9.8 (m /
s^Two ) Can be used. Also, the inside of the immersion nozzle
The flow discharged into the molten steel in the mold of the molten steel is turbulent.
Since it is good to handle, use 0.9 as the channel coefficient c.
Can be FIG. 1 shows the inside of a tundish and a soaked tip.
It is a schematic diagram which shows the situation of the molten steel in a furnace. FIG. 1 (b)
FIG. 2 is an enlarged view of a cross section taken along line A1-A2 in FIG.
is there. The opening cross-sectional area S of the outlet of the tundish 2 (described above)
(Cross-sectional area defined by equation (a)), molten steel 1 in immersion nozzle 1
0 crosses the cross-sectional area A, inside the tundish
Depth h of molten steel and index of molten steel head inside immersion nozzle
H and the like are schematically shown. Symbol 3 is a sliding game
4, reference numeral 4 denotes a discharge hole, reference numeral 8 denotes a meniscus, reference numeral 9 denotes a model.
Mold powder, reference numeral 11 is mold, and reference numeral 12 is solidification.
Show the shell. The present inventors have solved the above-mentioned problems as follows.
Based on the knowledge of the above, the problem was solved by taking the following measures. Fig. 2 shows the situation where deposits adhere to the inner surface of the immersion nozzle.
FIG. Reference numeral 5 denotes a tande into the immersion nozzle 1.
Near the exit of the
6 attached to the vicinity of the immersion nozzle
The adhered matter attached to the portion, symbol 7 is attached near the discharge hole 4.
Deposits. Reference numeral 10 is molten steel, reference numeral 11 is a mold, and
And reference numeral 12 indicates a solidified shell. An ordinary immersion nozzle having two discharge holes is provided.
When used, the discharge flow is not uniform and the flow of molten steel in the mold
The one-sided flow is caused by the deposit 7 near the discharge hole 4.
It is easy to occur when many are formed. Two discharge holes
The size of each deposit in the vicinity is often different
And the flow velocity and direction of each discharge flow from the two discharge holes
Are not the same, and a so-called one-sided flow occurs.
When one-sided flow occurs, mold powder or the inner surface of the immersion nozzle
The mold from which the oxides of Al etc. adhered to
As described above, it is easy to get caught in the molten steel inside.
You. The reason why the deposit is formed in the vicinity of the discharge hole is as follows.
If the pressure of molten steel immediately before flowing out of the discharge port is high,
This is because swirl is likely to occur in the flow of molten steel above the outlet.
You. When eddy currents occur, oxides of Al and the like in the molten steel are impregnated.
Oxidation of Al
Objects easily adhere to the inner surface of the immersion nozzle. Vortex below
The situation where the flow occurs will be further described. [0017] The present inventors have studied the flow of molten steel in an immersion nozzle.
In order to investigate the flow of the discharge flow,
A Dell experiment was performed. By using a 1/1 scale model
The number of Reynolds and fluid at the same time
There is an advantage that it can be made the same as steel. As a result,
Whirlpools are likely to occur above the hole because molten steel is inside the immersion nozzle.
And the pressure of molten steel just before flowing out of the discharge port.
When the depth of the molten steel in the tundish acts.
I found it to be true. At that time, the molten
The pressure of the steel is determined by the difference in height between the molten steel surface in the mold and the discharge hole.
It drops sharply to the corresponding pressure. Therefore, the discharge hole
Above, the molten steel is sucked into the discharge hole,
A vortex is generated in the direction. The inside of the immersion nozzle is not filled with molten steel,
Molten steel flowing in from the outlet of the
If it falls on the molten steel surface formed in
The pressure of the molten steel just before flowing out of the
The height difference between the surface and the molten steel surface in the mold.
is there. Therefore, the pressure of molten steel just before flowing out of the discharge port
The difference between the force and the pressure of the molten steel flowing out of the discharge port is small.
To suck molten steel into the discharge hole above the discharge hole, and
And eddy currents are prevented. According to the method of the present invention, the above equation (A) is used.
The opening cross-sectional area S (m^Two )
And the part where the molten steel in the immersion nozzle passes from top to bottom
Cross sectional area A (m^Two ) Satisfies the above formula (b)
Use a nozzle. And the immersion defined by the above equation (c).
The molten steel head index H (m) inside the pickling nozzle is the same as (d) above.
Cast under conditions that satisfy the formula. Therefore, the inside of the immersion nozzle is filled with molten steel.
Molten steel flowing from the outlet of the tundish
As it falls onto the molten steel surface formed inside the nozzle, it discharges
The pressure of the molten steel just before flowing out of the outlet is
Equivalent to the height difference between the molten steel surface in the mold and the molten steel surface in the mold
And the difference from the pressure of molten steel flowing out of the discharge port is
Since it becomes smaller, eddy currents above the discharge holes are less likely to occur.
Since eddy currents are unlikely to occur, A
l oxides and the like hardly adhere. Further, in the method of the present invention, the inside of the immersion nozzle
Of inert gas blown per unit time into molten steel passing through
(M^Three (Normal) / s) satisfies the above (e)
In other words, the appropriate amount of inertness for the amount of molten steel passing through
Since gas is blown, oxidation in molten steel inside the immersion nozzle
Prevents adhesion of objects and is inert to the solidified shell in the mold
Gas bubbles can also be prevented from being trapped. [0022] DETAILED DESCRIPTION OF THE INVENTION The process of the present invention
For continuous casting of molten steel containing Al oxide in the molten steel
Suitable for application. However, the solution deoxidized with Al
Not limited to steel. The method of the present invention can be applied to an acid such as Ti or Zr.
And other sulfides and nitrides are present in the molten steel
It is also effective for continuous casting of molten steel. The method of the present invention can be applied to wide cast slabs,
It is suitable to be applied when casting a lab slab. this
When casting such a slab, for example, from two discharge holes
The flow velocity and direction of each discharge flow are not uniform,
When flow occurs, the flow of molten steel in the mold becomes uneven.
Oxidization adhering to the mold powder and the immersion nozzle
Is it easy to get the peeled material into the molten steel in the mold?
It is. The larger the slab width, the more one-sided such discharge flows
Slab width is more than 1000mm
In this case, it is preferable to apply the method of the present invention.
Apply the method of the present invention to the case of 1200 mm or more
More preferably, The number of discharge holes of the immersion nozzle is an even number of two or more.
It is preferred that The method of the present invention uses a so-called slab
Since it is preferable to target the case of casting a slab,
The number of discharge holes of the immersion nozzle is two
Good, or even two or more, such as four
No. The discharge flow from each half of the discharge holes is
Almost facing each other in the opposite short sides of the mold
It should just be. The total cross-sectional area of these discharge holes is
2-3 of the cross-sectional area A of the part through which the molten steel inside the nozzle passes
Preferably it is twice. Moreover, it is 2.2 to 2.6 times.
Is more preferable. The molten steel in the immersion nozzle passes from above to below
The cross-sectional shape of the part to be
preferable. In addition, from the top of the immersion nozzle to the bottom
Preferably, the inner diameter is constant. However,
Due to the production of the pickling nozzle,
In this case, the inner diameter is reduced by about 5 to 10 mm. This
If the inside diameter is changed as in
The cross-sectional area corresponding to the portion of
I just need. In the method of the present invention, the above-described equation (A) is used.
Of the opening of the outlet of the tundish
Crossing the part where molten steel in the pickling nozzle passes from top to bottom
The ratio A / S of the area A is more than 2 and less than 5. When the value of the ratio A / S is 5 or more, tundish
Cross-sectional area of the outlet of the nozzle, i.e. supply into the immersion nozzle
Cross section in the immersion nozzle compared to the cross section of the molten steel
The molten steel along the inner wall of the immersion nozzle in a specific direction
Easy to flow. Therefore, the strength of the discharge flow
It tends to differ depending on the hole, the discharge flow will be uneven, and the mold
The flow of molten steel inside is likely to be one-sided. In extreme cases
Represents the surface of molten steel in the mold on the left and right
The molten steel surface on either side, that is, the molten metal surface
The phenomenon that the level becomes high occurs. Ratio A / S value is 2 or more
Below, the cross-sectional area through which molten steel passes through the immersion nozzle is compared.
Is almost completely filled with molten steel inside the immersion nozzle.
Down. Therefore, the molten steel immediately before flowing out of the discharge port
A molten steel head corresponding to the depth of molten steel in the dish is formed.
As described above, a vortex is generated above the discharge hole
Oxidation of Al in molten steel occurs on the inner surface of the immersion nozzle
Easy to adhere. In the method of the present invention, the above-described equation (C) is used.
The value of the molten steel head index H inside the immersion nozzle is set to 0.
More than 08m and less than 0.5m. If the value of H is 0.5 m or more, the flow
Since the pressure of molten steel immediately before discharging increases,
Vortices are likely to occur at H value is less than 0.08m
In this case, the inside diameter of the immersion nozzle must be extremely large or
It corresponds to the case of extremely slow production speed,
The amount of molten steel supplied is small. Therefore, immersion from molten steel
Since the amount of heat supply to the nozzle is reduced, the temperature of the immersion nozzle
And metal becomes easy to adhere to the inner surface of the immersion nozzle.
In extreme cases, clogging of the immersion nozzle may occur and
It becomes difficult to continue. In the method of the present invention, the immersion nozzle
The flow rate of molten steel Q (kg / s)
Inert gas amount W (m^Three (Norma
l) / s) W / Q (m^Three (Normal) / kg) is 1 × 1
0^-6m^Three (Normal) / kg over 5 × 10^-6m^Three (Nor
mal) / kg. The ratio W / Q is 5 × 10^-6m^Three (Normal) / kg
Above, the amount of inert gas is too large,
Bubbles are easily captured by the solidified shell in the mold. Also extreme
In such cases, the molten steel surface in the mold
It is easy to get powder into the molten steel in the mold,
Mold powder easily adheres to the solidified shell inside. Also, 1
× 10^-6m^Three (Normal) / kg or less, the inner surface of the immersion nozzle
Oxide in molten steel easily adheres to steel. Inert gas is introduced into the molten steel passing through the immersion nozzle.
The immersion nozzle is located at the bottom of the tundish
Near opening to sliding gate and immersion nose
It is good to blow in from at least one of the tools. [0033] DESCRIPTION OF THE PREFERRED EMBODIMENTS Vertical bending type continuous casting machine having two strands
And a C content of 0.001 to 0.003% by mass.
Low carbon steel with thickness 270mm, width 1200mm or 1
Casting at a speed of 1.3 to 1.6 m / min into a 600 mm slab
did. The depth of molten steel in the tundish is 0.96 to 2.
It was 2 m. The immersion nozzle is made of alumina graphite.
Nozzle made of refractory material and having two holes of normal downward 30 °
And The cross-sectional area of one discharge hole is 0.008m^Two , Molten steel
The effective height of the part through which is passed is constant at 930 mm
And the inner diameter of the part where molten steel passes from top to bottom is 70
The test was performed with a change of 〜120 mm. Immersion nozzle lower end
The immersion depth in the molten steel in the mold shall be 250-300mm.
Was. Ar gas is supplied from the sliding gate to 6
7 × 10^-6~ 500 × 10^-6m^Three (Normal) / s (about 4 ~
30 liters (Normal) / min) through the immersion nozzle
Blown into the molten steel. Approximately 280 tons of molten steel in one heat was fed
Subsequently, casting was performed, and the immersion nozzle was recovered after the casting. Collect
The immersion nozzle, and check if there is any
With nothing, the adhesion thickness was investigated. The surface of the obtained slab was treated with oxygen gas so-called
Wrapping of mold powder by scarfing
Nookami scratches or vertical splits on the surface layer of the slab due to penetration
The scratches were visually inspected. Using the obtained slab as a raw material, a thickness of 4 to 5 mm
Hot rolled into steel strip, then pickled and then cold rolled to thickness
It was rolled to a steel strip of 0.8 to 1.0 mm. Product steel strip surface
The occurrence of flaws was visually inspected. Part where surface flaws occurred
And cut the total amount by the cold rolling amount to obtain the product
It was evaluated as a flaw occurrence rate. Table 1 shows the test conditions.
Are shown in Table 2. [0039] [Table 1] [Table 2]Test No. 1 and No. In 2, slab width 1600mm
And the casting speed was 1.6 m / min. Test N
o. In No. 3, the slab width was 1200 mm and the casting speed was 1.
3 m / min. For these tests, the tundish
The depth h of the molten steel at the part is 1.8 m or 2.0 m,
The opening cross-sectional area S of the dish outlet is 11.2 × 10^-Four~
19.4 × 10^-Fourm^Two And the molten steel in the immersion nozzle passes
The cross sectional area A of the part to be formed is 47.8 × 10^-Fourm^Two Or 6
3.6 × 10^-Fourm^Two By setting the ratio A / S to 2.
Tested as 60-4.26. The value of these ratios A / S
Is a value within the range defined by the method of the present invention.
In addition, since the casting speed was set to the above-mentioned speed corresponding to the slab width,
The flow rate Q of the molten steel passing through the immersion nozzle during the storage time is 49.1
4 kg / s or 80.64 kg / s.
Index of molten steel head inside immersion nozzle defined by equation (c)
H became 0.136 m-0.365 m. These molten steels
The value of the head index H is within the range of the conditions defined by the method of the present invention.
The value in the box. In addition, molten steel passing through the immersion nozzle
The amount of inert gas W to be blown per unit time is 200 × 10
^-6~ 333 × 10^-6m^Three (Normal) / s, so unit
Molten steel flow rate Q passing through the immersion nozzle
The ratio W / Q of the amount of inert gas W that is blown in per unit time is
3.10 × 10^-6~ 4.13 × 10^-6m^Three (Normal) / k
g. These values of the ratio W / Q are defined by the method of the present invention.
It is a value within the range of the condition to be specified. Test No. In 1, the inner surface of the immersion nozzle
No deposit was generated. Test No. 2 and N
o. In No. 3, a thickness of 2 mm or 3 mm is provided near the discharge hole.
Deposits were observed, but the thickness was very slight. Ma
In addition, in these tests, norokami scratches were found on the slab surface.
It was not possible, and the casting work was going well. In addition, product flaws
The birth rate is as low as 0.1 to 0.3%, which is a good result.
Was. Test No. In 4, pass through the immersion nozzle
The amount of inert gas W blown into the molten steel per unit time is 500
× 10^-6m^Three (Normal) / s.
In the case of No. 5, this inert gas amount W is set to 67 × 10^-6m^Three (Norma
l) / s. Other test conditions
Experiment No. 1 or No. The conditions were almost the same as those in 2. N
o. In 4, the molten steel flow passing through the immersion nozzle per unit time
Inert gas amount blown per unit time into molten steel with respect to amount Q
The ratio W / Q of W is 6.20 × 10^-6m^Three (Normal) / kg
No. 5, the ratio W / Q is 0.83 × 10^-6
m^Three (Normal) / kg. The values of these ratios W / Q are:
The upper or lower limit of the condition specified by the method of the present invention
The values were out of range. 1. The ratio A / S in these tests
46 and the value of 0.365m of the molten steel head index H
The value was within the range specified by the method of the invention. Test No. In 4, blow in unit time during molten steel
Since the amount of inert gas to be injected was large, the discharge of the immersion nozzle
Only deposits with a thickness of 1 mm were generated near the holes.
However, since the amount of inert gas blown is large,
Because the level of the molten metal in the mold fluctuated greatly,
Many pinhole flaws and norokami flaws were generated. Further
In addition, products have pinhole flaws on the slab surface
Many linear flaws are generated due to flaws, and the product flaw generation rate is 2.
3% was bad. Test No. In 5, blow inert gas
Because of the small amount of clogging, clogging of the immersion nozzle during the second heat
Balls occurred, casting was performed at a reduced casting speed,
Since the deterioration of the slab quality due to the lower casting speed was predicted,
The casting was stopped. Thickness 1
A deposit of 5 mm was generated. On the slab surface,
Many flaws were generated. In the mold due to clogging of the immersion nozzle
Molten steel flow is not stable,
This is because a change has occurred. Norokami scratches on the slab surface
Product flaws are generated, and the product flaw occurrence rate is 5.7%
It was bad. Test No. 6. In the tundish,
By making the steel depth h as shallow as 0.96 m, the ratio A / S
Was reduced to 1.80 and tested. Other test conditions
Is the test No. 1 or No. With almost the same conditions as 2
Was. The value of the ratio A / S is determined by the conditions specified by the method of the present invention.
Was out of the lower limit. Index W / Q 3.10 × 10
^-6m^Three (Normal) / kg and molten steel head index H0.36
Each value of 5 m is the value of the condition defined by the method of the present invention.
The value was within the range. Test No. At 6, exit tundish
Because the inner diameter of the immersion nozzle is smaller than the opening cross-sectional area of
The inside of the immersion nozzle is filled with molten steel, and vortex flows above the discharge port
Presumed to have occurred, and the immersion nozzle clogged
Then, on the inner surface of the immersion nozzle after casting, a deposit with a thickness of 8 mm
Had occurred. Also, the clogging of the immersion nozzle
Fluctuation of the molten steel level in the molten steel caused
It was terrible. Therefore, the surface of the slab often has nookami flaws.
Occurred. There are many product flaws due to noro flaws on the slab surface
The product flaw occurrence rate was 3.2%, which was bad. Test No. In 7, the solution in the tundish
Making steel depth h as deep as 2.2 m, and immersion nozzle
Part of the immersion nozzle through which molten steel passes
Cross section A of 63.6 × 10^-Fourm^Two And make it bigger
The test was carried out by increasing the ratio A / S to 5.16. So
The other test conditions are as follows: With almost the same conditions as 3
Was. The value of the ratio A / S is determined by the conditions specified by the method of the present invention.
Was out of the upper limit. Index W / Q 2.94 × 10
^-6m^Three (Normal) / kg and molten steel head index H0.10
Each value of 2 m is the value of the condition defined by the method of the present invention.
The value was within the range. Test No. At 7, exit the tundish
The inner diameter of the immersion nozzle is larger than the opening cross-sectional area of
The thickness of the deposit on the inner surface of the immersion nozzle after casting was 3 mm.
However, molten steel passing through the immersion nozzle
Flow along the inner wall of the pickling nozzle,
One-sided flow occurred in the molten steel. As a result, the level change
It became large, and sliver cracks occurred on the slab surface. Slab table
Product flaws caused by norokami flaws on the surface, resulting in product flaws
The rate was 1.8%. Test No. 8, the inner diameter of the immersion nozzle is 12
Because it was enlarged to 0 mm, the molten steel head inside the immersion nozzle
The index H decreased to 0.065 m. Other test articles
For the test No. 1 or No. With almost the same conditions as 2
Was. The value of the molten steel head index H is defined by the method of the present invention.
It is a value that falls outside the lower limit of the condition for performing Index W / Q 2.48
× 10^-6m^Three (Normal) / kg and ratio A / S4.76
Each value is within the range defined by the method of the present invention.
Was the value of Test No. In 8, the immersion nozzle inner diameter is extremely
The amount of molten steel supplied into the immersion nozzle
And the temperature of the immersion nozzle decreased,
A large amount of metal adhered to the inner surface of the nozzle. Therefore, 3 heat
In the middle of the eyes, clogging of the immersion nozzle occurred remarkably, and the casting speed
Casting at a reduced temperature, but eventually the casting was stopped
Was. On the inner surface of the recovered immersion nozzle, a 18 mm thick metal
Had adhered. Noroka flaws occur on the slab surface
Was. Single flow occurs in molten steel in mold due to clogging of immersion nozzle
This is due to fluctuations in the surface level. Slab surface
Many product flaws caused by norokami flaws occur, and product flaws
The birth rate was 4.3%, which was bad. Test No. In No. 9, the inner diameter of the immersion nozzle was 70
mm, so the molten steel head finger inside the immersion nozzle
The number H increased to 0.563 m. The index A / S
Was a small value of 1.98. Other test conditions are
Test No. 1 or No. The conditions were almost the same as those in 2. This
The value of the molten steel head index H of the steel
The value is outside the upper limit. Also, the value of this ratio A / S
Is a value outside the lower limit of the condition specified by the method of the present invention.
You. Index W / Q 2.48 × 10^-6m^Three (Normal) / kg
The value is a value within the range defined by the method of the present invention.
Was. Test No. In No. 9, the inner diameter of the immersion nozzle is small.
To increase the molten steel head index H inside the immersion nozzle
Therefore, the pressure of molten steel immediately before flowing out of the discharge port increases.
As a result, a vortex was generated above the discharge hole. Therefore,
The pickling nozzle is clogged, causing a single flow in the molten steel in the mold
did. As a result, the fluctuation of the molten metal level increases,
Norokami scratches occurred on the surface. Norokami scratches on the slab surface
Product flaws, and the product flaw occurrence rate was 2.8%.
Was. [0051] According to the method of the present invention, the immersion nozzle
Inexpensive aluminum oxide etc. in the molten steel adhere to the inner surface
Can be prevented stably by the method
In the rolled product, mold powder, oxidation of Al
Products caused by defects in the surface layer of the slab due to objects, air bubbles, etc.
The occurrence of surface defects or internal defects can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the state of molten steel in a tundish and an immersion nozzle. FIG. 2 is a schematic diagram showing a situation in which a deposit adheres to an inner surface of a immersion nozzle. [Explanation of Signs] 1: Immersion nozzle 2: Tundish 3: Sliding gate 4: Discharge hole 5: Deposits attached near the sliding gate 6: Deposits attached to the body of the immersion nozzle 7: Adhesion near the discharge holes 8: Meniscus 9: Mold powder 10: Molten steel 11: Mold 12: Solidified shell S: Cross-sectional area of opening of tundish outlet A: Cross-sectional area of portion through which molten steel passes in the immersion nozzle h: Inside of tundish Molten steel depth H: Index of molten steel head inside immersion nozzle

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/10 330 B22D 11/10 360 B22D 41/50 520 B22D 11/10 320 B22D 41/58

Claims (1)

(57) [Claims] 1. Casting from a tundish using an immersion nozzle
A continuous casting method for supplying molten steel in a mold, comprising:
The opening cross section of the outlet of the tundish defined by equation (a)
Product S (m ^Two ) And the molten steel in the immersion nozzle
Cross-sectional area A (m^Two ) Satisfies the following expression (b)
Immersion nozzle defined by the following formula (c)
The molten steel head index H (m) inside the pickling nozzle is expressed by the following formula (d).
Casting under conditions that satisfy
Amount of inert gas W (m ^Three (N
ormal) / s) is cast under the condition satisfying the following formula (e).
A continuous casting method for steel. S = Q / ｛ρ × (2gh)^1/2 } ···(I) 2 <A / S <5 (b) H = (2g)^-1× (ρc)^-2× (Q / A)^Two   ... (c) 0.08 <H <0.5 (d) 1 × 10^-6 <W / Q <5 × 10^-6    ... (e) Here, Q: molten steel flow passing through the immersion nozzle per unit time
Amount (kg / s) ρ: density of molten steel (kg / m^Three) g: Gravitational acceleration (m / s^Two) h: Depth of molten steel inside tundish (m) c: Channel coefficient (-)