JP2010105007A - Continuous casting method of steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method for adding adequate amounts of metallic elements to molten steel in a high yield, uniformly stably dispersing them in a cast slab and suppressing the generation of coarse oxides of the metallic elements. <P>SOLUTION: In the continuous casting method, one or more of Bi alloy, Sn alloy, and Te alloy are added to the molten steel in a ladle, a tundish or a mold. The Bi alloy, the Sn alloy or the Te alloy is an alloy containing one or more of Al, Ca, Si, Mg, Ti, Mn and rare earth elements, respectively, and in the Bi alloy, the Sn alloy or the Te alloy, Bi, Sn or Te each is added in the content amount of ≥70 mass%. In the method, the Bi alloy, the Sn alloy or the Te alloy has a granular shape, a massive shape, or a wire-like shape, and preferably, the surfaces of them are covered with Fe or Al, and they are added to the molten steel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a continuous casting method capable of uniformly and stably dispersing a metal element in a slab by adding a metal element to molten steel at a high yield in a continuous casting process of steel.

  As a method of adding a metal element to molten steel, a massive metal element is introduced into the molten steel surface, or a wire made of a simple metal element, a wire in which these metal elements are coated with aluminum or steel, etc. For example, a method of adding a wire made of an alloy containing a metal element is adopted. However, using these methods, magnesium (Mg), bismuth (Bi), calcium (Ca), rare earth elements (REM), tellurium (Te), lead (Pb), etc. have high vapor pressure and low melting point. It is difficult to add a metal element with high accuracy. The reason is that when a metal element with a high vapor pressure is added to the molten steel, the metal element is vaporized and diffused into the atmosphere in the vicinity of the molten steel surface. This is because it is difficult to add uniformly and the addition yield is also lowered.

  Further, since the volume expansion when the metal element is vaporized is large, when the metal element is vaporized in the vicinity of the molten steel surface, the molten steel is severely scattered, making it 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 steel is added, the added metal is unevenly distributed only in the surface layer portion of the molten steel and does not penetrate into the molten steel. In the case of adding a metal element having a high density, it is difficult to uniformly mix the molten steel with the entire molten steel simply by settling into the molten metal from the addition position.

  In recent years, for the purpose of improving mechanical properties of products, refinement of crystal grains and refinement of precipitates have been actively promoted. To refine crystal grains and precipitates, it is effective to cause “pinning” or “heterogeneous nucleation” by crystallization or precipitation of minute compounds. It must be added at the proper position. In addition, in free-cutting steel, the addition of Bi is attracting attention in place of Pb from the viewpoint of product safety and work environment measures at the time of manufacture, and the use is expected to continue in the future. In an electrical steel sheet, it is necessary to concentrate Bi or the like at the grain boundaries in order to improve the magnetic properties. These steel materials are added with a metal element having a low melting point and a low boiling point and high density like Bi.

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

  Patent Document 2 discloses a method in which Pb, Bi, Pb and Bi-containing substances are 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. It is disclosed. Even in the method disclosed in this document, when Pb and Bi having a low melting point or low boiling point are added, an explosive reaction occurs when these metals come into contact with molten steel, and the addition of the metal into the molten steel is uneven. As a result, the yield decreases, and the added metal is not uniformly dispersed in the continuous cast slab. Moreover, it is difficult to arbitrarily adjust the reaction products of Pb and Bi added to the molten steel.

  Further, Patent Document 3 discloses a technique of adding into a molten steel using a Bi-containing alloy. And in the same literature, when Bi is alloyed, when added to molten steel, the melting reaction with molten steel is promoted, the vapor pressure is reduced, and the productivity of Bi-containing steel can be greatly increased. It is shown. However, by alloying Bi, the content ratio of Bi to be added is lowered, so it is necessary to increase the amount of Bi-containing alloy added to the molten steel accordingly. When the amount added is increased, the Bi-containing alloy becomes a cold material, and the temperature of the molten steel in the ladle, tundish, or mold is significantly lowered, which not only hinders continuous casting, but also the casting operation itself. May become difficult. In order to suppress the addition amount, it is necessary to increase the Bi content in the Bi-containing alloy, but the Bi content in the alloy in the method disclosed in the same document is not so high, and the addition amount of the Bi-containing alloy is large. Is the problem.

  By the way, when a metal element is added to molten steel, oxygen dissolved in the molten steel reacts with the metal element to form a coarse oxide. If this oxide is taken into the continuous cast slab and remains in the steel plate as the final product, the mechanical properties and electrical properties of the product are significantly impaired. However, in any of the above-mentioned Patent Documents 1, 2, and 3, no study has been made regarding the generation of oxide.

JP 2001-1116 A (claims, paragraphs [0013] and [0014]) JP-A-9-13119 (Claims [0004] and [0005]) JP 2002-363683 A `` Binary Alloy Phase Diagrams (second edition) '' The Materials International Society, 1990, USA, p.129, p.2816, p.3406

  The present invention has been made in view of the above-mentioned problems, and its task is to add an appropriate amount of a metal element to molten steel at a high yield in the continuous casting process of steel, and to make it uniform and stable in the slab. It is an object of the present invention to provide a continuous casting method that can suppress the generation of coarse oxides of metal elements.

  The inventors of the present invention have added a proper amount of a metal element in molten steel in a continuous casting process of steel at a high yield, and uniformly and stably dispersed in a slab, thereby generating a coarse oxide of the metal element. Research has been conducted on a continuous casting method capable of suppressing the above, and the following knowledge has been obtained.

(1) Increase in melting point due to alloying of metal elements and increase in concentration of metal elements in alloy When a metal element having a high vapor pressure or a metal element having a low melting point is added to molten steel, the added metal contacts the molten steel. Or receives radiant heat from the molten metal and melts or vaporizes. If the metal elements are melted or vaporized before or at the moment of addition to the molten metal, it is difficult to add these metal elements uniformly into the molten steel with a good yield.

  It is effective to increase the melting point or boiling point of the metal element to be added in order to suppress melting of the metal element before addition to the molten steel, or melting or vaporization at the moment of addition. In order to increase the melting point or boiling point of a metal element, an alloy with a metal that raises the melting point may be produced and added to the molten metal.

  At this time, when a large amount of alloy is added to the molten steel, the amount of heat required for melting the alloy increases, and the temperature of the molten steel is significantly reduced. In order to keep the temperature of the molten steel constant, it is only necessary to raise the temperature of the molten steel by the temperature drop when the alloy is added, but not only a large amount of heat is required to raise the molten steel temperature, but also the temperature The increase in the amount of oxygen increases the vaporization of the alloy at the time of alloy addition, making it difficult to add the alloy. In order to solve this problem, the content of the metal element in the alloy may be increased.

(2) Suppression of formation of coarse oxide of metal element When a metal element is added to molten steel, the metal element reacts with oxygen in the molten steel to produce a coarse oxide of the metal element, which is continuously cast slab or It is taken into the ingot and remains in the final product. Since such an oxide becomes a defect of a product, it is indispensable to suppress the generation of the oxide, and the suppression of the generation of the oxide is a problem that must be solved together with the uniform addition of the metal element.

  For example, in order to improve the free-cutting property of steel materials, conventionally, Pb has been added. However, Pb is said to have an adverse effect on the human body, and regulations are becoming stricter from the viewpoint of reducing the environmental load. For this reason, Bi has been added as well as Pb, which is excellent in free-cutting properties, has no adverse effects on the human body, and has a low environmental impact. In this case, in order to ensure free-cutting properties, it is necessary to suppress the generation of Bi oxide in the slab and disperse Bi particles.

  Bi may also be added to the electromagnetic steel sheet. Electrical steel sheets are used for transformers, motors, etc., and magnetic steel sheets are required to have high magnetic flux density and low iron loss. For this reason, a technique is used in which a fine precipitate-dispersed phase is uniformly generated in the steel sheet to suppress the growth of crystal grains. In order to further enhance this effect, Bi, Sn, Te, and the like are added, and the magnetic characteristics are improved by segregating these elements to the crystal grain boundaries. In order to establish these technologies, it is essential to suppress the formation of oxides of metal elements such as Bi.

  In order to suppress the formation of coarse oxides of metal elements added to the molten steel, a metal having a strong deoxidizing power may be added to the molten steel. Moreover, in order to produce an alloy with a metal element, it is necessary to select a metal having a metal content for deoxidation as low as possible and having a large increase in melting point. As a result, the temperature drop of the molten steel due to the addition of the metal element alloy into the molten steel can be suppressed, the amount of the alloy added can be reduced, the formation of coarse oxides of the metal element can be suppressed, and the molten steel can be added. It is possible to prevent the molten steel from being scattered when the metal element is added, and the yield is improved.

The present inventors have further studied and obtained specific findings shown in the following (a) to (c).
(A) It is effective to add the metal element added to the molten steel to the molten steel in the form of an alloy. And when producing an alloy of metal elements, for example, refer to Non-Patent Document 1, etc., so that the liquidus temperature of the alloy in the equilibrium diagram is higher than the liquidus temperature of the added metal element alone. It is necessary to make an alloy. However, if the liquidus temperature of the alloy of the metal element added to the molten steel is higher than the temperature of the molten steel, the alloy does not melt, so the metal element cannot be added to the molten steel.

  Therefore, the melting point may be adjusted by changing the content of the metal element in the alloy so that the melting point of the alloy is lower than the melting point of the molten steel. For this purpose, it is necessary to select a region where the liquidus temperature in the equilibrium diagram of the alloy varies depending on the content of the added metal element.

  FIG. 1 shows an equilibrium diagram of the Al—Bi system described in Non-Patent Document 1. According to the figure, in the region where the Bi content is 70% by mass or more, the liquidus temperature can be changed by the Bi content, and the melting point 271 ° C. in the case of Bi alone can be increased to 1030 ° C. or more. it can.

  FIG. 2 shows an equilibrium diagram of the Ti—Sn system described in the same document. In the region where the Sn content is 70% by mass or more, the liquidus temperature can be changed by the Sn content, and the melting point 232 ° C. in the case of Sn alone can be increased to about 1490 ° C.

  Similarly, FIG. 3 shows an equilibrium diagram of the Nd—Te system. In the region where the Te content is 70% by mass or more, the liquidus temperature can be changed by the Te content, and the melting point 450 ° C. in the case of Te alone can be increased to 1100 ° C. or more.

  As shown in FIGS. 1, 2 and 3, the liquidus temperature of the alloy can be greatly changed by setting the contents of Bi, Sn, and Te in the alloy to 70% by mass or more. Therefore, by setting the content of Bi, Sn and Te in the alloy to a high value of 70% by mass or more, the amount of the alloy added can be reduced, and this becomes a cold material when the alloy is added, and the temperature of the molten steel Can be suppressed.

  (B) As a metal which forms an alloy with the metal element added in molten steel, it is necessary to use a metal with high deoxidation capability in molten steel. In producing an alloy with an additive metal element including one or more selected from Bi, Sn, and Te, which is a subject of the present invention, Al, Ca, Si, Mg, Ti, Mn are used as metals having a strong deoxidizing power. It is appropriate to use a metal containing one or more selected from rare earth elements containing Nd or Ce. Both are metal elements having a low standard free energy for formation of oxides.

  (C) In the actual operation of continuous casting of steel, it is appropriate to add the alloy of the metal element to the ladle, the tundish or the molten steel in the mold. In addition, these alloys are preferably added continuously in the form of particles, lumps or wires, and are added using a metal addition device. An alloy containing an additive metal may be oxidized during storage, or may collapse due to brittleness in the course of addition to molten steel by a metal addition device. From the viewpoint of preventing the above oxidation or collapse, the additive metal alloy is preferably coated with Fe or Al.

  The present invention has been completed based on the above findings, and the gist of the present invention is the continuous casting method of steel shown in the following (1) and (2).

  (1) A continuous casting method in which one or more of a Bi alloy, a Sn alloy, and a Te alloy are added to molten steel in a ladle, a tundish, or a mold, wherein the Bi alloy, the Sn alloy, or Each Te alloy is an alloy with one or more of Al, Ca, Si, Mg, Ti, Mn, and rare earth elements, and the content of Bi, Sn, or Te in the alloy is 70% by mass or more. A continuous casting method of steel, characterized by being added as:

  (2) In the above (1), the Bi alloy, Sn alloy or Te alloy is in the form of particles, lumps or wires, and the surfaces thereof are coated with Fe or Al and added to the molten steel. The continuous casting method of the described steel.

  In the following description of the present specification, “%” representing the steel composition or alloy composition represents “mass%”.

  According to the continuous casting method of the present invention, in the continuous casting process of steel, an appropriate amount of a metal element is added to the molten steel at a high yield, and is uniformly and stably dispersed in the slab. Oxide generation can also be suppressed. As a result, the method of the present invention is a technology that can greatly contribute in the field of continuous casting as a method for producing high-quality slabs for producing steel products having excellent mechanical properties such as strength and toughness as well as electrical properties. .

  As described above, the method of the present invention is a continuous casting method in which one or more of Bi alloy, Sn alloy, and Te alloy are added to molten steel in a ladle, in a tundish, or in a mold. The alloy, Sn alloy or Te alloy is an alloy with at least one of Al, Ca, Si, Mg, Ti, Mn and rare earth elements, and the content of Bi, Sn or Te in the alloy Is added as 70% by mass or more, and is a continuous casting method for steel.

  Below, the preferable aspect in the continuous casting method of the steel of this invention and the reason are added.

  As described above, it is preferable to coat the alloy of the additive metal with Fe or Al. And when coat | covering with Fe, it is preferable that the coating thickness shall be 0.1-2.0 mm, and when coat | covering with Al, the coating thickness shall be 0.5-3.0 mm Is preferred.

  The reason is that if the coating thickness is less than 0.1 mm in the case of coating with Fe, or if the coating thickness is less than 0.5 mm in the case of coating with Al, the coating is caused by mechanical impact or thermal influence. This is because there is a possibility that the metal alloy is broken and softened, melted or evaporated before the additive metal alloy is supplied into the molten steel, and it becomes difficult to supply an appropriate amount of the additive metal into the molten steel. In addition, the addition yield tends to decrease. On the other hand, if the coating thickness exceeds 2.0 mm in the case of coating with Fe or exceeds 3.0 mm in the case of coating with Al, the dissolution of the additive metal alloy in the molten steel is delayed, and the metal element is changed. It becomes difficult to mix and disperse uniformly in the molten steel.

  When coating a granular additive metal alloy, the method of coating with Al is inexpensive in terms of production cost. In this case, since the alloy of the additive metal is immersed in molten Al to cover the surface of the alloy, it is necessary that the melting point of the additive metal alloy is higher than the melting point of Al. The particle diameter of the additive metal alloy is preferably in the range of 2 to 50 mm. When the particle size is less than 2 mm, clogging may occur, which is not preferable in terms of operation. On the other hand, when the particle size exceeds 50 mm, the alloy addition apparatus becomes large and equipment costs increase, which is not preferable.

  When the alloy of the additive metal is a lump, the metal alloy is loaded into the inside of a 2-50 mm long Fe tube or Al tube, and both ends of the tube are crimped to cover the additive metal alloy. It is preferable. If the length of the tube made of Fe or Al is less than 2 mm, clogging may occur, which is not preferable in terms of operation. On the other hand, if the length of the tube exceeds 50 mm, the alloy addition device Is unfavorable because it increases in size and increases the equipment cost.

  When the alloy of the additive metal is formed into a wire shape, an alloy wire is obtained by loading the metal alloy into an Fe tube or an Al tube. The alloy wire diameter (the outer diameter of the Fe tube or Al tube forming the wire) is preferably in the range of 2 to 20 mm. If the diameter of the alloy wire is less than 2 mm, it is not preferable because the wire buckles and it becomes difficult to supply. On the other hand, if the diameter of the wire exceeds 20 mm, the alloy adding device becomes large and equipment costs increase, which is not preferable.

  In the method of the present invention, when the oxidation of the additive metal alloy is negligibly small, and when problems such as lack of mechanical strength, lack of thermal strength, and collapse due to brittleness do not occur, the additive metal is added. It can also be added as a granular, massive or wire-like alloy.

  In order to confirm the effect of the continuous casting method of the present invention, the following tests were conducted and the results were evaluated.

1. Continuous casting conditions Molten steel: Carbon steel having the composition shown in Table 1 to be described later Molten steel temperature: 1580 ° C
Casting speed: 1.0 to 1.8 m / min Mold size: thickness 240 mm x (width 900 to 1800 mm)
Molten steel amount: 320 tons Additive alloy: Al-80% Bi (referred to as Al-80Bi), Ti-70% Bi (Ti-70Bi),
Mg-85% Bi (Mg-85Bi), Mn-75% Sn (Mn-75Sn),
Si-85% Te (Si-85Te) or Ni-55% Bi (Ni-55Bi)
In some of the tests of the comparative example, the additive metal element was added alone.
Addition position: ladle, tundish, or mold Addition method: granular, lump, Fe-coated lump, wire, Fe-coated wire, or Al coating
Covered wire supply method

  Tables 1 and 2 collectively show the test conditions such as steel composition, additive alloy type, alloy addition position, and addition method for each test.

  As shown in the above examples, for each molten steel in a ladle, tundish, or mold, an alloy in the form of granular, lump, Fe-coated lump, wire, Fe-coated wire or Al-coated wire is added. did.

2. Evaluation method of test results The yield of the additive metal element in the continuous cast slab produced under the above casting conditions, the uniformity of the content distribution of the additive metal element, and the oxide ratio in the inclusions are determined by the following method, Casting operation and slab quality were evaluated.

1) Yield of additive metal elements and uniformity of content distribution Chips were collected from continuous cast slabs and analyzed for additive metal elements. The sampling position of the chip for analysis is a position in the slab thickness direction 1/4, a position in the slab width direction 1/2, a position in the slab width direction 1/4, and 20 mm from the slab short side. The three positions were

  The yield of the additive metal element is obtained by calculating the average content of the above-mentioned three metal elements, and dividing the mass of the metal element in the slab obtained from the average content of the metal element by the additive mass of the metal element as a percentage ( %).

  The uniformity of the content distribution of the additive metal element was evaluated by determining the deviation of the metal element content. The deviation of the metal element content is obtained by calculating the difference between the maximum value and the minimum value of the metal element content at the three locations, and dividing this value by the average content of the metal elements at the three locations. ).

2) Oxide ratio The oxide ratio is 20 mm from the slab thickness direction 1/4 position, the slab width direction 1/2 position, the slab width direction 1/4 position, and the slab short side. Samples of 10 mm square were collected from three locations at the position, and the number of observed oxides was divided by the total number of inclusions to obtain a percentage (%).

  Here, the number of oxides of the metal element was measured by the following method. One surface of the 10 mm square sample was mirror-polished using an abrasive of diamond abrasive grains having a particle diameter of 1 μm and anhydrous alcohol as a lubricant. About this mirror-polished sample, the inclusions were observed at a magnification of 1000 using a scanning electron microscope with a composition analyzer (SEM with EDX) to confirm the presence or absence of metal element oxides. And based on the result, the ratio (%) of the inclusion of the added metal element in the total number of inclusions was calculated.

3. Test results Table 2 shows the yield of the additive metal element, the deviation of the content of the additive metal, and the ratio of the oxide, together with the test conditions. Test numbers H1 to H13 are tests for examples of the present invention that satisfy the conditions defined in the present invention, and test numbers C1 to C5 are tests for comparative examples that do not satisfy the conditions defined by the present invention. .

  In the inventive examples of test numbers H1 to H13, the yield of the additive metal element is as high as about 70% or more, and the deviation of the content distribution in the slab of the metal element is also as small as 5% or less. It can be seen that it can be added at a high yield, and that uniform dispersion within the slab can be achieved. In addition, since the additive metal is an alloy with a metal having strong deoxidizing power in the molten steel and added to the molten steel, the oxide ratio of the metal element is about 1% or less, which is extremely low. Cleanliness is also good.

  On the other hand, in the comparative examples of test numbers C1 to C5, the yield of the additive metal element is low, and the deviation of the content distribution of the metal element is large. This was because a metal element having a low melting point or low boiling point was added to the molten steel alone or as an alloy, but the melting point of the alloy was high and it was difficult to add and disperse uniformly in the molten steel. by. Further, the generation ratio of the metal element oxide is high, which is because the added metal was not added in the form of an alloy or was added as an alloy with a metal having a weak deoxidizing power. From the above results, in order to suppress the formation of oxides, it was confirmed that it was effective to use an additive metal as an alloy with a metal having a strong deoxidizing power in molten steel and to add this to the molten steel.

  According to the continuous casting method of the present invention, in the continuous casting process of steel, an appropriate amount of a metal element is added to the molten steel at a high yield, and is uniformly and stably dispersed in the slab. Oxide generation can also be suppressed. As a result, the continuous casting method of the present invention is widely applied in the continuous casting process as a method for producing high-quality slabs for producing steel products having excellent mechanical properties such as strength and toughness as well as electrical properties. be able to.

It is an equilibrium diagram of an Al-Bi system (page 129 of Non-Patent Document 1). It is a Ti-Sn system equilibrium diagram (page 2816 of Non-Patent Document 1). FIG. 3 is an equilibrium diagram of an Nd—Te system (page 3406 of Non-Patent Document 1).

Claims (2)

  A continuous casting method in which one or more of Bi alloy, Sn alloy and Te alloy are added to molten steel in a ladle, tundish or mold, wherein Bi alloy, Sn alloy or Te alloy is And an alloy with one or more of Al, Ca, Si, Mg, Ti, Mn, and rare earth elements, respectively, and a Bi, Sn, or Te content in the alloy is added as 70% by mass or more. A continuous casting method for steel characterized by the above.   2. The steel according to claim 1, wherein the Bi alloy, the Sn alloy, or the Te alloy is in a granular shape, a lump shape, or a wire shape, and the surface thereof is coated with Fe or Al and added to the molten steel. Continuous casting method.

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