JP4844376B2 - Method for continuous casting of molten metal - Google Patents

Description

  The present invention relates to a continuous casting method in which a metal element can be added to molten metal at a high yield in the course of continuous casting of molten metal, and can be uniformly and stably dispersed in a slab.

  In order to add a metal element to the molten metal, a massive metal element is put on the molten metal surface, or a wire made of a simple metal element, a wire in which these metal elements are covered with aluminum or steel, etc. In addition, a method of adding with a wire made of an alloy containing these metal elements is employed. However, it is difficult to accurately add a metal element having a high vapor pressure and a low melting point, such as magnesium, bismuth, calcium, rare earth elements, tellurium, and lead, using these methods. The reason is that when a metal element having a high vapor pressure is added to the molten metal, the metal element is vaporized and diffused into the atmosphere near the molten metal surface. This is because it is difficult to control and the addition yield is lowered, and it is difficult to add uniformly.

  In addition, since the volume expansion when the metal element is vaporized is large, when the metal element is vaporized in the vicinity of the molten metal surface, the molten metal is severely scattered and it is difficult to ensure operational safety. Furthermore, when the melting point of the additive metal element is low, it becomes difficult to add a predetermined amount by softening or melting by the radiant heat of the molten metal before the addition. When a metal element having a density lower than that of the molten metal is added, the added metal is unevenly distributed only in the surface layer portion of the molten metal and does not enter the inside of the molten metal. In the case of adding a metal element having a high density, it is difficult to uniformly mix the entire molten metal only by settling into the molten metal from the addition position.

  In recent years, in order to improve mechanical properties of products, refinement of crystal grains and refinement of precipitates have been actively promoted. Pinning or heterogeneous nucleation by crystallization and precipitation of fine compounds is effective for refinement of crystal grains and precipitates. In order to obtain such an effect, it is important to add an appropriate amount of a metal element at an appropriate position.

  Patent Document 1 discloses a method in which bismuth is added to a molten steel stream that is moving out of the ladle and moving to the molten steel bath surface in the tundish. However, bismuth has a low boiling point and reacts explosively when it comes into contact with the molten steel stream, so it becomes a vapor and scatters in the atmosphere, so the addition yield is low, and it cannot be added uniformly into the molten steel, so it is a continuous cast slab. Not evenly distributed within.

  Patent Document 2 discloses a method in which lead, bismuth, or lead and bismuth-containing material is added to a molten steel in a ladle by injection using a lance, and gas is jetted from a porous plug at the bottom of the ladle and stirred. Has been. Even in the method disclosed in this document, when lead and bismuth having a low melting point or boiling point are added, an explosive reaction occurs when these metals come into contact with the molten steel, and the addition of the metal into the molten steel is uneven. And the yield is low, and the metal is not uniformly dispersed in the continuous cast slab. Moreover, it is difficult to arbitrarily adjust the reaction products of lead and bismuth added to the molten steel.

JP 2001-1116 (Claims and paragraph [0013]) JP-A-9-13119 (Claims and paragraphs [0004] and [0005]) JP 2004-249315 A (claims and paragraphs [0011] to [0015]) JP 2005-169404 A (Claims and paragraphs [0012] to [0015]) Japanese Patent Laying-Open No. 2005-219072 (Claims and paragraphs [0014] to [0017])

  The present invention has been made in view of the above problems, and the problem is that an appropriate amount of a low melting point or low boiling point metal element can be added to the molten metal, and the metal element is uniformly distributed in a continuous cast slab. And it is providing the continuous casting method which can be disperse | distributed stably.

  In order to solve the above-mentioned problems, the present inventors can add an appropriate amount of a low melting point or low boiling point metal element into the molten metal and uniformly and stably disperse it in the continuous cast slab. The possible continuous casting method was examined and the knowledge shown in the following (a) to (c) was obtained.

  (A) When adding a metal element into the molten metal by inserting a wire or rod containing the added metal element into the immersion lance immersed in the molten metal in the tundish, per unit time into the tundish The concentration of the metal element added to the molten metal can be made constant by controlling the supply speed of the metal wire or rod into the immersion lance according to the amount of molten metal supplied.

  (B) Depending on the depth of the molten metal in the tundish, by controlling the supply flow rate and / or pressure of the carrier gas (inert gas) used when supplying the metal wire, Splash) can be prevented.

The method of (c) above (a) and (b), the magnesium in the molten steel, bismuth, silver, calcium, tellurium, lead, manganese, lithium, Itte Le Biumu, neodymium, lanthanum, cerium, VA potassium, strontium and This is effective when one or more selected from thallium are added.

  The present invention has been completed on the basis of the above findings, and the gist thereof resides in a molten metal continuous casting method shown in the following (1) and (2).

  (1) A wire or rod containing a metal element to be added to the molten metal is inserted into the immersion lance immersed in the molten metal in the tundish, and the vapor of metal element and / or near the lower tip inside the immersion lance. Alternatively, it is a continuous casting method in which particles are generated and the generated metal vapor and / or metal particles are added into the molten metal together with an inert gas, and is immersed in the tundish according to the amount of molten metal supplied per unit time. Continuous casting of molten metal characterized by controlling the feed rate of the inert gas and / or the pressure according to the depth of the molten metal in the tundish while controlling the feeding speed of the wire or rod into the lance Method.

(2) said molten metal is molten steel, magnesium the metal element is added to the molten metal, bismuth, silver, calcium, tellurium, lead, manganese, lithium, Itte Le Biumu, neodymium, lanthanum, cerium, Ba potassium The method for continuously casting a molten metal according to (1), wherein the metal contains one or more selected from strontium and thallium.

  In the present invention, “metal vapor and / or metal particles” means metal vapor and / or metal particles present due to insufficient evaporation, or metal particles formed by condensation of metal vapor. The “metal” includes pure metals and metal alloys.

  In addition, the “inert gas” means a gas such as helium, neon, or argon which is a group 18 element in the periodic table.

  According to the molten metal continuous casting method of the present invention, the amount of molten metal scattering in the tundish is remarkably reduced, and the concentration fluctuation of the additive metal element in the slab is suppressed to a very low level. An appropriate amount of a metal element having a melting point or a low boiling point can be stably added to the molten metal with a good yield, and can be uniformly dispersed in the continuous cast slab.

(1) Basic configuration of the invention When a metal element having a high vapor pressure or a metal element having a low melting point is added to the molten metal, the added metal comes into contact with the molten metal or receives radiant heat from the molten metal and melts. Do or vaporize. If the metal elements are melted or vaporized before or at the moment of addition to the molten metal, it is difficult to uniformly add these metal elements to the molten metal with good yield. Further, in order to uniformly add the metal element into the continuous cast slab, the method of adding to the molten metal in the tundish near the continuous cast mold or in the continuous cast mold is optimal.

  The inventors previously proposed a method of adding a vapor of a metal element or a compound of a metal element into molten metal in a tundish or a continuous casting mold in Patent Document 3, Patent Document 4, and Patent Document 5. . By these methods, it has become possible to add a metal element or a compound of a metal element uniformly to the molten metal with good yield.

  As described above, the present invention that has further solved the problem and improved the present invention controls the supply speed of the wire or rod into the immersion lance according to the amount of molten metal supplied per unit time into the tundish, A molten metal continuous casting method characterized in that the supply flow rate and / or pressure of an inert gas is controlled in accordance with the depth of the molten metal in the dish.

  FIG. 1 is a diagram showing an example of the continuous casting method of the present invention. The molten metal 1 supplied from the ladle 3 to the tundish 2 is injected into the mold 8 via the immersion nozzle 6 and forms a solidified shell 7 while being drawn downward to form a cast piece. A metal wire 50 containing an additive metal element is inserted into an immersion lance 4 immersed in the molten metal 1 in the tundish 2, and the additive metal element finally becomes a metal vapor and melts in the tundish 2. Supplied in metal 1.

  The upper end of the immersion lance 4 is connected to the wire feeder 5. A wire reel 51 is loaded in the metal wire feeder 5, and the metal wire 50 is inserted into the immersion lance 4 by a wire feeding roll 52 whose feeding speed is controlled by the wire feeding speed control device 11. A carrier gas 9 is introduced into the metal wire feeder 5 and is supplied into the immersion lance 4 together with the metal wire 50. Hereinafter, the case where the molten metal 1 is molten steel will be described in detail.

(2) Carrier gas flow rate and pressure control and metal wire feed rate control In continuous casting of steel, the molten steel 1 is supplied from the ladle 3 to the tundish 2 in continuous casting, and the immersion nozzle is used when the amount of molten steel reaches a predetermined level. The molten steel 1 is supplied into the mold through 6 and continuous casting is started. When the height position of the immersion lance 6 is fixed after the molten steel 1 starts to be supplied to the tundish 2 and reaches a predetermined amount, the pressure in the immersion lance 4 rises, and as a result, the immersion lance The amount of metal vapor and / or metal particles and carrier gas 9 ejected from 4 changes. This is because the static iron pressure (static pressure by the molten steel head) applied to the tip of the immersion lance 4 increases until the molten steel 1 reaches a predetermined amount.

  If the flow rate and pressure of the carrier gas 9 supplied to the immersion lance 4 are set to be constant in advance, the amount of carrier gas with respect to the immersion depth of the immersion lance 4 is increased until the molten steel in the tundish 2 reaches a predetermined amount. Too much molten steel 1 scatters and adheres to the refractories on the side and upper surfaces of the tundish 2. When the tundish 2 is reused hot, it is necessary to remove this splash, which causes a reduction in operating efficiency. In addition, since the molten steel 1 is vigorously stirred, oxygen in the atmosphere gas in the tundish 2 reacts with the molten steel 1 to generate an oxide, and this oxide is taken into the molten steel 1. As a result, the molten steel 1 is cleaned. Remarkably deteriorates. A similar phenomenon occurs even when the amount of molten steel in the tundish 2 decreases before the end of continuous casting.

  In order to prevent such scattering of the molten steel 1, the flow rate and / or pressure of the carrier gas 9 supplied from the immersion lance 4 into the molten steel 1 is appropriately controlled according to the depth of the molten steel in the tundish. That's fine. Specifically, for example, the molten steel depth calculated from the measured value of the molten steel surface position by the molten steel level meter 21 or the measured value by the molten steel weight measuring device 22, the measured pressure value by the pressure gauge 55, and the flow rate by the flow meter 54. A measured value is input to the flow rate pressure control device 10 and supplied to the molten steel 1 from the immersion lance 4 by controlling the flow rate control valve 53 and / or the pressure control valve 56 according to a command from the flow rate pressure control device 10. The flow rate and / or pressure of the carrier gas 9 may be controlled within an appropriate range.

  When the supply speed of the metal wire 50 or the metal rod is constant and the amount of molten steel in the tundish 2 before the start or end of continuous casting is small, the amount of metal element added is relatively large relative to the amount of molten steel. It will pass. Further, when the casting speed changes during the continuous casting, if the supply speed of the metal wire 50 or the metal rod is constant, the concentration of the metal element in the slab changes. In order to prevent such a change in concentration, the mass feed rate of molten steel into the tundish 2 calculated based on the measured value by the weight measuring device 22 or the weight measuring device 31 is input to the wire feed speed control device 11. The supply speed of the metal wire 50 or the metal rod may be controlled within an appropriate range by a command from the wire feed speed control device 11 according to the molten steel supply speed.

In order to confirm the effects of the continuous casting method and continuous casting apparatus of the present invention, the following continuous casting test was performed and the results were evaluated.
[Example 1]
1. Casting test conditions Molten metal: Low carbon steel (mass%, C: 0.16%, Si: 0.15%, Mn: 0.5%, P: 0.02%, S: 0.001%, Ti : 0.15%)
Molten metal amount: Continuous casting at 5 tons / min Addition metal: Magnesium (Mg) or Silver (Ag) is added individually Addition method: Metal wire with a diameter of 3 mmφ Wire feed rate: Reference value 2 m / min Addition position: Carrier gas in the tundish: Argon gas, standard value 10 L / min Pressure: standard value 0.03 MPa
In accordance with the method shown in FIG. 1, a continuous casting test was performed in which a metal wire was inserted into the immersion lance to generate a vapor of the added metal element, and this was supplied into the molten metal together with an inert gas.

  FIG. 2 shows the operating conditions employed in this casting test. The figure (a) shows the transition of the molten steel depth (molten steel amount) in each casting period, the figure (b) shows the transition of the casting speed (molten steel supply per unit time) in each casting period, and the figure (C) shows the transition of the metal wire supply speed, the carrier gas flow rate, and the pressure in each casting period.

  When the immersion lance 4 was immersed by the molten steel 1 supplied from the ladle 3 to the tundish 2, supply of the metal wire 50 and the carrier gas 9 was started. Since the amount of molten steel increases from when the immersion lance 4 is immersed in the molten steel 1 in the tundish 2 until the casting start depth is reached, it is necessary to increase the supply amount of the wire 50, and the immersion lance 4 As a result, the pressure in the immersion lance 4 increases, so that the pressure and flow rate of the carrier gas 9 must be increased. When the molten steel amount in the tundish reaches a predetermined amount (predetermined depth), the casting speed (molten steel supply amount per unit time) reaches the reference value, so the supply speed of the metal wire 50 and the flow rate of the carrier gas 9 The pressure and the pressure were also controlled to be the reference values at that time.

  On the other hand, at the end of casting, the supply amount of the molten steel 1 from the ladle 3 to the tundish 2 is reduced or is not supplied. Therefore, the amount of molten steel in the tundish (the depth of molten steel) must be reduced and the casting speed must be reduced. Accordingly, the supply speed of the metal wire 50, the flow rate of the carrier gas 9 and the pressure thereof must be reduced. is there. Before the end of casting, since the immersion lance 4 is exposed from the upper surface of the molten steel 1, the supply of the metal wire 50 and the carrier gas 9 was stopped. Even if the metal wire 50 is stopped, the addition of the metal element to the molten steel 1 in the tundish 2 by the metal wire 50 has already been performed.

2. Casting test results Table 1 shows control conditions and test results in the casting test.

  In the same table, the splash occurrence index measures the area where the splash adheres to the side and top surfaces of the tundish, and uses this to control the flow rate of the carrier gas, control the pressure of the carrier gas, and control the supply speed of the metal wire. It was obtained by dividing by the splash adhesion area in test number 4 of the comparative example which was not performed.

  In addition, the concentration fluctuation index in the slab measures the concentration of the additive metal element magnesium or silver at a plurality of locations in the casting direction of the slab, and determines the maximum concentration difference of either the magnesium or silver element as the carrier gas. The flow rate control, the carrier gas pressure control, and the metal wire supply rate control were all divided by the maximum concentration difference in the same test number 4 where the control was performed and indexed. Here, the concentration measurement of the additive element in the initial stage of casting is performed at five intervals from the tip of the slab to the casting method at intervals of 500 mm, and the concentration measurement in the stationary casting period is performed at intervals of 5000 mm in the casting direction at the steady casting portion of the slab. Concentration measurement at 5 locations and at the end of casting was performed by collecting analytical samples from 5 locations at intervals of 500 mm from the rear end of the slab in the direction opposite to the casting direction, and conducting these elemental analyzes. did.

  Test number 1 is a test for the present invention example in which the supply flow rate and / or pressure of the carrier gas is controlled and the supply speed of the metal wire is controlled as specified in the present invention. This is a test for a comparative example that does not satisfy at least one of the control conditions defined in the invention.

  In Test No. 1, which is an example of the present invention, the amount of splashing is remarkably reduced both in the initial stage and the final stage of continuous casting, and the concentration fluctuation of the additive element in the slab is extremely low, resulting in good quality. A slab was obtained.

On the other hand, in the test number 2 of the comparative example in which the flow rate and pressure of the carrier gas were controlled but the supply speed of the metal wire was not controlled, the amount of splash generated in both the initial and final stages of continuous casting However, the concentration fluctuation of the additive element in the slab was almost the same as in the case of test number 4, and was not improved at all. In addition, in the test number 3 of the comparative example in which the supply speed of the metal wire was controlled but the flow rate and pressure of the carrier gas were not controlled, the variation in the concentration of the additive element in the slab was reduced, but the amount of splash generated was This was the same as in the case of test number 4, and was not improved at all.
[Example 2]
1. Casting test conditions Molten metal: Low carbon steel (mass%, C: 0.12%, Si: 0.13%, Mn: 1.2%, P: 0.018%, S: 0.002%, Ti : 0.12%)
Molten metal amount: Continuous casting at 5 tons / min Addition metal: Magnesium or strontium (Sr) added individually Addition method: Metal wire with a diameter of 3 mmφ Wire feed speed: Reference value 2 m / min Addition position: in tundish Carrier gas: Argon gas, standard value 10 L / min Pressure: standard value 0.03 MPa
A casting test was conducted in the same manner as in Example 1 according to the method shown in FIG. Further, the control conditions for the supply speed of the metal wire and the flow rate and pressure of the carrier were in accordance with the conditions shown in FIG.

2. Casting test results Table 2 shows control conditions and test results in the casting test.

  In the same table, as in the case of Example 1, the splash occurrence index indicates the splash adhesion area obtained in each test, the flow control of the carrier gas, the pressure control of the carrier gas, and the supply speed control of the metal wire. It is a value obtained by dividing by the splash adhesion area in test number 8 of the comparative example that was not performed. Further, the concentration fluctuation index in the slab was measured in the same manner as in Example 1 by measuring the concentration of magnesium or strontium as an additive metal element at a plurality of locations in the casting direction of the slab, and obtained in each test. Or, it is a value obtained by dividing the maximum concentration difference of any element of strontium by the maximum concentration difference in Test No. 8 to make an index.

  Test number 5 is a test for the present invention example in which the supply flow rate and / or pressure of the carrier gas is controlled and the supply speed of the metal wire is controlled as specified in the present invention. This is a test for a comparative example that does not satisfy at least one of the control conditions defined in the invention.

  In Test No. 5, which is an example of the present invention, the amount of splashing is significantly reduced both in the initial and final stages of continuous casting, and the concentration fluctuation of the additive element in the slab is extremely small, and good results are obtained. Obtained.

  On the other hand, in the test number 6 of the comparative example in which the flow rate and pressure of the carrier gas were controlled but the supply speed of the metal wire was not controlled, in the slab at both the initial and final stages of continuous casting. The concentration variation of the additive element was almost the same as the value in Test No. 8, and was not improved at all. In addition, in the test number 7 of the comparative example in which the supply rate of the metal wire was controlled but the flow rate and pressure control of the carrier gas were not controlled, the amount of splash was almost the same as the value in the test number 8, which is completely improved. Was not.

  From the results shown in Examples 1 and 2 above, according to the continuous casting method of the present invention, the amount of splash is significantly reduced in the initial and final stages of continuous casting, and the amount of added metal elements in the slab is reduced. It was confirmed that the present invention can greatly contribute to the improvement of casting operability and the stability of the slab quality because the concentration fluctuation is suppressed very well. In the above embodiment, the case where the molten metal is molten steel has been described as an example. However, the present invention exhibits the same effect even when another molten metal is used.

  According to the molten metal continuous casting method of the present invention, the amount of splash of molten metal in the tundish is remarkably reduced and the concentration fluctuation of the additive metal element in the slab is suppressed to a very low level. A metal element having a melting point or a low boiling point can be stably added to the molten metal with a good yield, and can be uniformly dispersed in the continuous cast slab. Therefore, the continuous casting method of the present invention can be widely applied to uniform slab quality including the distribution of additive metal elements in the slab, and further to improving the quality of castings and processed products.

It is a figure which shows an example of the continuous casting method of this invention. It is a figure which shows typically an example of the operating conditions of the continuous casting method of this invention, The figure (a) shows transition of the molten steel depth in each casting period, The figure (b) shows the casting speed in each casting period. FIG. 3C shows the transition of the metal wire supply speed, the carrier gas flow rate, and the pressure in each casting period.

Explanation of symbols

1: Molten metal, molten steel, 2: Tundish, 21: Molten steel level meter,
22: weight measuring device, 3: ladle, 31: weight measuring device, 4: immersion lance,
5: Metal wire feeder, 50: Metal wire, 51: Wire reel,
52: Wire feed roll, 53: Flow control valve, 54: Flow meter, 55: Pressure gauge, 56: Pressure control valve, 6: Immersion nozzle, 7: Solidified shell, 8: Continuous casting mold,
9: inert gas, carrier gas, 10: flow pressure controller
11: Wire feed speed control device,

Claims (2)

A wire or rod containing a metal element to be added to the molten metal is inserted into the immersion lance immersed in the molten metal in the tundish,
A continuous casting method in which vapor and / or particles of the metal element are generated near the lower tip inside the immersion lance, and the generated metal vapor and / or metal particles are added to the molten metal together with an inert gas. There,
Controlling the supply speed of the wire or rod into the immersion lance according to the amount of molten metal supplied per unit time into the tundish;
A method for continuously casting a molten metal, wherein the flow rate and / or pressure of the inert gas is controlled in accordance with the depth of the molten metal in the tundish. Is said molten metal is molten steel, magnesium the metal element is added to the molten metal, bismuth, silver, calcium, tellurium, lead, manganese, lithium, Itte Le Biumu, neodymium, lanthanum, cerium, VA potassium, strontium and The molten metal continuous casting method according to claim 1, wherein the molten metal is one or more metals selected from thallium.

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