JP6175911B2 - Method of adding titanium to molten iron - Google Patents

Description

  The present invention relates to a method for adding valuable metal titanium to a molten steel in a ladle for secondary refining mainly by a reduction reaction of an inexpensive titanium oxide in a steelmaking process.

  The titanium component in steel is a useful element that is added for the purpose of fixing and detoxifying C and N, interpenetrating elements of IF steel, improving the case hardening characteristics of products, and improving hardness by refining crystal grains. The contained steel product is manufactured through a casting and rolling process after adjusting the components of the molten steel manufactured in an electric furnace or converter in a ladle process of secondary refining by adding sponge titanium or the like.

  For this purpose, titanium metal such as sponge titanium to be added is very expensive. Therefore, if aluminum reduction of inexpensive titanium oxide can be performed with high reduction efficiency, it is extremely effective in terms of cost.

  Patent Documents 1 and 2 disclose a technique in which titanium oxide is added to a molten steel surface or slag existing thereon, and titanium is added to the molten steel.

Japanese Patent No. 3752892 JP 2001040404 A

  However, in the technique disclosed in Patent Document 1, since the addition of titanium oxide is performed on the molten steel surface or slag coexisting with the slag in the refining vessel, in order to reduce the titanium oxide with aluminum, in advance, In addition to limiting the slag composition in the refining vessel to a limited range, there are restrictions such as the need to define the stirring conditions at appropriate values.

Furthermore, in the technique disclosed in Patent Document 1, it is necessary to adjust the MgO concentration in the slag to a high level of 5 to 25% by mass in order to prevent refractory damage due to the addition of titanium oxide. In order not to be excessive, CaO / Al ₂ O ₃ needs to be 2.5 or less.

As a result, the Al ₂ O ₃ concentration in the slag is specified in the range of 15 to 55% by mass. It is recognized that the concentration of Al ₂ O ₃ decreases the titanium reduction yield, and this method has problems in terms of cost and reaction efficiency.

  Patent Document 2 describes means for simultaneously adding titanium oxide and calcium oxide (or calcium hydroxide) -containing material and metallic aluminum. In the embodiment at this time, briquette addition in which metallic aluminum is mixed with titanium oxide and calcium oxide is shown, but there is a special process in briquetting production, and there are restrictions such as the size of metallic aluminum that can be blended. It ’s a big one.

  There is no such restriction, and a simple method of adding titanium oxide, calcium oxide, and metal aluminum at the same time includes simultaneous injection with powder. The melting point of metal aluminum is 660 ° C., which is significantly lower than that of molten iron. Therefore, in general, in order to transport the molten iron surface or molten iron at a high temperature of 1500 ° C. or more, there are serious drawbacks such as causing an operation trouble that causes the aluminum particles to melt in the piping and block the piping.

  Patent Document 2 shows an operation example (in Table 1, Comparative Example 3) in which a mixed briquette containing only titanium oxide and calcium oxide is reduced with aluminum in steel, but the reduction efficiency remains low. ing. According to the investigation by the present inventors, the operating conditions at this time belong to a range where the blending ratio of titanium oxide and calcium oxide is inappropriate.

  In view of the above-mentioned problems of the prior art, the present invention aims to efficiently and economically add valuable metal titanium to molten steel and to provide an operational addition method for this purpose. To do.

  The inventors of the present invention have intensively studied a method for solving the above-described problems. As a result, it was found that the valuable metal titanium can be efficiently and economically added to molten steel by a reduction reaction of an inexpensive oxide raw material.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) The Al concentration in the molten iron is 0.005 to 0.80 mass%, and then contains 35 mass% or more of titanium, and contains titanium oxide and calcium oxide so as to satisfy the following formula (1). A method for adding titanium to molten iron, comprising adding a secondary material to the molten iron.
3 ≦ (mass% Ti) / (mass% Ca) ≦ 8 (1)
However,
(Mass% Ti): mass% of Ti contained as an oxide in the secondary material
(Mass% Ca): mass% of Ca contained as an oxide in the secondary material

  (2) The method for adding titanium to molten iron according to (1), wherein the secondary material is added to molten iron as a powder and is allowed to pass through the molten iron.

  (3) Titanium to molten iron according to (1), wherein the secondary material is added to the molten iron surface that is blocked from the initial slag on the molten iron surface, and the interface between the secondary material and the molten iron is stirred. How to add.

  (4) The molten iron according to (1), (2), or (3), wherein the concentration of alumina at a reaction site in the reduction reaction of aluminum in the secondary material and molten iron is less than 10% by mass. Titanium addition method.

  According to the present invention, when manufacturing a steel product containing titanium, which is an important element for improving the properties of steel products, reduction of inexpensive titanium oxide without adding expensive metal titanium to molten iron, Titanium can be added with efficiency and stable operation.

It is a figure which shows typically implementation (addition of secondary material) of this invention by an injection system. It is a figure which shows typically implementation (addition of secondary material) of this invention by a CAS system.

The method for adding titanium to molten iron of the present invention (hereinafter sometimes referred to as “method of the present invention”) has an Al concentration in molten iron of 0.005 to 0.80 mass%, and then contains 35 mass% or more of titanium. In addition, a secondary material containing titanium oxide and calcium oxide so as to satisfy the following formula (1) is added to the molten iron.
3 ≦ (mass% Ti) / (mass% Ca) ≦ 8 (1)
However,
(Mass% Ti): mass% of Ti contained as an oxide in the secondary material
(Mass% Ca): mass% of Ca contained as an oxide in the secondary material

  An embodiment of the method of the present invention will be described based on FIG. Further, based on FIG. 2, an embodiment (one of desirable embodiments) different from the embodiment shown in FIG. 1 will be described.

  The embodiment of the method of the present invention is not limited to the embodiment shown in FIG. 1 and FIG. 2, and the method of the present invention can be applied as appropriate without departing from the scope of the means for solving the above problems. The embodiment can be adopted.

  FIG. 1 schematically shows the implementation of the present invention (addition of secondary materials) by the injection method.

  In the addition of the secondary material shown in FIG. 1, the injection lance 2 is inserted into the molten steel 7 in the molten steel pan 1, and titanium oxide and quick lime (both powders) are obtained from the titanium oxide hopper 3 and the quick lime hopper 4, respectively. A mixed flux 6 (secondary material) fed to the conveyance pipe 5 and mixed in the conveyance pipe 5 is blown into the molten steel 7 from the injection lance 2 together with a carrier gas (not shown).

  At this time, the molten steel 7 needs to contain 0.005-0.80 mass% of Al required as a reducing material of a titanium oxide in the molten steel manufactured with the converter, the electric furnace, etc. previously. The Al concentration of the molten steel will be described later.

  In addition, even if molten steel contains niobium, chromium, nickel, silicon, manganese, etc. as other components, there is no problem in carrying out the method of the present invention.

Titanium oxide (powder) in the mixed flux added to the molten steel is reduced by aluminum in the molten steel. As the titanium oxide, powders such as TiO ₂ , Ti ₂ O ₃ , and Ti ₂ O ₅ can be used regardless of the valence of the transition element titanium.

  Ilmenite ore present as an oxide and various mixtures can be used, but from the viewpoint of economy and reaction efficiency, the content of titanium oxide such as natural titanium ore is preferably 80% by mass or more. .

As calcium oxide constituting the mixed flux, quick lime (main component is CaO) is advantageous in terms of heat tolerance, but slaked lime (main component is (Ca (OH)) that changes to calcium oxide by a sublimation reaction. ₂ ) or limestone (the main component is CaCO ₃ ) or an oxide mixture such as slag with a high CaO content Titanium oxide and calcium oxide are necessarily mixed before addition and added to the molten iron There is no need.

  FIG. 2 schematically shows the implementation of the present invention (addition of secondary materials) by the CAS method.

  In the case of the addition of the secondary material shown in FIG. 2, titanium oxide and quicklime (both powders) are fed to the molten steel pan 8 from the titanium oxide hopper 9 and quicklime hopper 10, respectively, to the mixing container 11 and mixed additives. 11a (secondary material) is manufactured, and this mixed additive 11a is added to the area of the surface of the molten steel 13 in the CAS bell 12 that is cut off from the top slug 14.

  Then, the agitation gas 16 is blown from the porous plug 15 installed at the bottom 8a of the molten steel pan 8 to stir the secondary material and molten steel interface in the above-described region to promote the reduction reaction.

  In addition, the embodiment in which titanium oxide and calcium oxide are sequentially added to the surface of the molten iron, and the titanium oxide and calcium oxide are mixed on the surface of the molten iron so that substantially the same effect as the addition of the mixture is obtained on the surface of the molten iron, It is embodiment of the method of this invention.

The secondary material (for example, mixed flux, mixed additive) has a titanium content of 35% by mass or more in consideration of oxygen contained as an oxide, and the blending ratio of titanium oxide and calcium oxide is (1 ) Expression must be satisfied.
3 ≦ (mass% Ti) / (mass% Ca) ≦ 8 (1)
However,
(Mass% Ti): mass% of Ti contained as an oxide in the secondary material
(Mass% Ca): mass% of Ca contained as an oxide in the secondary material

For example, when titanium present as an oxide in the secondary material is tetravalent, that is, TiO ₂ , TiO ₂ is aluminum in the molten steel and is reduced according to the following formula (2), and titanium is used as an alloy component. It remains in the molten steel.

3TiO ₂ +4 Al → 3 Ti +2 Al ₂ O ₃ (2)
The underline indicates the alloy element in the molten steel.

  Here, the reason why the component composition of the secondary material is defined by the above formula (1) is that the following two conditions must be satisfied.

  Condition 1: Titanium oxide as a main component has a high melting point, which is disadvantageous for promoting the reaction. However, when calcium oxide is added, it has been found that the action of promoting the mass transfer of the reduction reaction is remarkable due to a decrease in the melting point. The blending ratio is (mass% Ti) / (mass% Ca) ≦ 8.

  Condition 2: In order to maintain a sufficient reaction driving force, it is necessary to have a composition that maintains the activity of titanium oxide at a high level. For this purpose, the titanium content is 35% by mass or more, and 3 ≦ (mass% Ti) / (mass% Ca).

  Hereinafter, Condition 1 and Condition 2 will be described.

  When reducing the high melting point titanium oxide that does not melt at the molten steel temperature with aluminum, unless a special operation technology is used that keeps the fine titanium oxide dispersed and in contact with the molten steel for a long time, The aluminum oxide produced by reducing the surface of the titanium oxide is interposed, so that the titanium oxide becomes agglomerated and a sufficient contact area between the molten steel and the titanium oxide, which is necessary for the reduction reaction, cannot be ensured.

  Therefore, the low-melting-point liquid phase (formed with titanium oxide and calcium oxide) formed with calcium oxide in the blending ratio specified in Condition 1 and the reaction kinetics (relaxation of mass transfer rate-controlled) due to the coexistence of titanium oxide. The effect was secured.

  In addition, the calcium oxide with the blending ratio specified in Condition 2 and the high titanium oxide content (35% or more) realizes a higher level of titanium oxide activity, ensuring a thermodynamic (high reaction driving force) effect. did.

  That is, the present inventors have found a condition capable of obtaining both the above-described kinetic effect and thermodynamic effect by detailed research and investigation.

  In addition, as for the substance to be blended with titanium oxide, calcium oxide was selected for the purpose of maintaining the activity of titanium oxide at a high level for the following reason.

  Similar to calcium oxide, there are several candidates for compounds that produce titanium oxide and a low melting point liquid phase. However, since a substance having a lower binding force with oxygen than titanium oxide is reduced preferentially over Ti, it is not applicable to the method of the present invention (eg, when MnO is blended, reduction with aluminum is MnO). Is not effective because the reduction is prioritized).

  From the viewpoint of oxygen bonding strength, oxides that can be applied to the method of the present invention are limited to several candidates, and for example, strontium oxide may be used. However, since the cost is several tens of times for industrial use, the compound used in the method of the present invention is limited to those mainly composed of calcium oxide.

  Next, the aluminum concentration (0.005-0.80 mass%) of molten steel required as a reducing material is demonstrated.

  If the aluminum concentration of the molten steel is less than 0.005% by mass, the oxygen activity necessary for the reduction of titanium oxide cannot be obtained, and the reduction efficiency of titanium oxide is insufficient. In addition, if the aluminum concentration is less than 0.005% by mass, in actual operation, the oxidation loss of titanium occurs due to the reduction of air and oxides in the refractory until continuous casting. It becomes difficult to manufacture stably.

  In order to stably manufacture a steel product, it is necessary to add aluminum again and add titanium by a reduction reaction to recover the oxidation loss of titanium. Therefore, the aluminum concentration of the molten steel is set to 0.005 mass% or more. Preferably it is 0.010 mass% or more.

  When the aluminum concentration of molten steel exceeds 0.80% by mass, the effect of promoting the reduction reaction of titanium does not increase. On the other hand, during continuous casting, slab cracks frequently occur as the aluminum concentration increases. Need to reduce speed significantly.

  Usually, the aluminum concentration required for titanium-containing ultra-low carbon steel products is 0.80% by mass or less. When the titanium oxide is reduced in molten steel having an aluminum concentration exceeding 0.80% by mass, it is necessary to reduce the aluminum alloy exceeding the specified value by the oxygen OB treatment.

  As a result, the processing steps become complicated and the aluminum alloy is wasted. Therefore, the aluminum concentration of the molten steel is 0.80% by mass or less. Preferably it is 0.50 mass% or less.

  In the addition of the secondary material by the injection method shown in FIG. 1, the secondary material can be added as a powder and allowed to pass through the molten iron, and in order to achieve the above effect, the reduction reaction specific surface area per volume of the secondary material is increased. Since it is possible to realize a transitory reaction that can be ensured, this is a particularly preferable mode of operation.

  In addition, this preferable operation form includes the operation form which sprays a secondary material (powder) on the molten steel surface in the vacuum tank of vacuum degassing apparatuses, such as RH system.

  In the operation mode shown in FIG. 2, the secondary material is added to the molten iron surface blocked from the initial slag of the molten iron surface in the molten steel pan, and the secondary material and the molten iron interface are stirred.

  In this mode of operation, in order to advantageously express the reduction characteristics, mixing of the top slag into the reaction site is efficiently and easily suppressed, while maintaining a high reaction driving force, and increasing the specific surface area due to interface disturbance. , Can promote mass transfer for the reaction. Therefore, although the said operation form differs from the injection system, it is a particularly preferable operation form.

  Moreover, in order to advance the said (2) formula efficiently in the reaction site in the reduction | restoration reaction of the aluminum in a secondary material and molten iron, reduction of an alumina activity is a particularly effective operating condition. As a result of experimental investigations by the present inventors, it was found that the alumina concentration at the reaction site is preferably less than 10% by mass.

  Note that the alumina concentration at the reaction site in the reduction reaction of aluminum in the secondary material and molten iron refers to the concentration of the alumina-containing material in the secondary material in the embodiment as shown in FIG. 1 that utilizes a transition reaction inside the molten iron. In the embodiment as shown in FIG. 2, in which the concentration is referred to and the top slag is cut off and agitation is used, the amount of unavoidably mixed slag in the blocked matter (in the CAS bell 12) after the addition of the auxiliary material is included. Refers to the alumina concentration.

  In the method of the present invention, in addition to the preferred embodiment shown in FIGS. 1 and 2, a mode in which a secondary material is added to a vacuum degassing tank, or a mode in which a secondary material is added in advance by removing the amount of slag on the surface of the molten steel. Even if is adopted, the effect of the method of the present invention can be obtained.

  In that case, the alumina concentration in the reaction site is the alumina concentration in the secondary material when adding the secondary material to the molten steel surface in the vacuum chamber, and is on the molten steel surface in the ladle without any obstruction such as a CAS bell. When adding a secondary material, it is the alumina density | concentration of hatching slag of the top slag after completion of secondary material addition.

  The economic effect of the method of the present invention can be appropriately obtained depending on the price and quality of titanium ore, the cost of the aluminum alloy, the required reduction concentration, etc., but the titanium ore with relatively high purity shown in the examples described later and metallic aluminum When Ti-added ultra-low carbon steel (target [Ti] is about 0.01 to 0.10% by mass), which is mainly used for steel sheets for automobiles, etc., ensure a Ti reduction rate of about 50% or more. If possible, the method of the present invention can be sufficiently utilized as an alternative technique for an inexpensive alloy.

  Next, the method of the present invention will be described based on examples, but the conditions in the examples are one condition example adopted for confirming the feasibility and effects of the method of the present invention. It is not limited to this one condition example. The method of the present invention can adopt various conditions as long as the object of the method of the present invention is achieved without departing from the gist of the method of the present invention.

(Example)
The experimental operation was carried out at a ladle processing station having a capacity of 150 t of secondary material addition function.

About 1650 ° C., [C]: 0.05% by mass, and the balance is inevitable impurity molten steel, 0.15% by mass of metal aluminum, and (a) 1 mm under rutile ore ( Main component TiO ₂ : Purity 95%) and 0.8mm under quick lime (Main component CaO: Purity 84.9% ) are mixed and added by the injection method, or (b) Pre-mixed and then added upward (bottom blowing) Argon stirring flow rate was 500 Nl / min).

  Table 1 shows the results of treatments performed at a level where the total amount of rutile ore was fixed at 250 kg and the amount of quicklime added was changed.

  In Examples 1, 3, and 4 in which the quick lime addition amount is 30 to 70 kg by the injection method, a very good reduction rate of 70% or more is obtained.

  Example 2 of the upward addition method is an example performed by the CAS method shown in FIG. A mixture of rutile ore and quicklime was added to the surface of the molten steel in the CAS bell from which the top slag was blocked, and the mixture was stirred with argon to accelerate the reduction reaction. In Example 2, a reduction rate equivalent to that of the injection method is obtained.

  On the other hand, in Comparative Example 1, the amount of quick lime added is insufficient, slag hatching is insufficient, and the reaction rate decreases. In Comparative Example 2, the compounding ratio of titanium oxide is low, and the activity is low. The reaction rate decreases, and the reduction rate is lower than 40%.

  In Table 2, the operation method is the same as Example 1, and the result of the operation test when the treated steel type is changed is shown.

  In Example 5, high alloy steel (SUS430 stainless steel) was targeted, and in Example 6, IF steel (very low carbon steel whose [C] was previously set to 20 ppm by vacuum degassing) was targeted. In both cases, as in Example 1, a high titanium reduction rate was obtained, and the method of the present invention can be widely applied to the manufacture of steel products such as high alloy steel and steel types that require vacuum degassing. It could be confirmed.

  Table 3 shows the results of the test operation carried out by changing the initial aluminum concentration of the steel.

  When the amount of titanium oxide added is constant, the effect of the method of the present invention cannot be quantitatively evaluated due to the influence of aluminum that decreases during the reduction reaction during the treatment. Therefore, the amount of titanium oxide to be added was changed in accordance with the initial aluminum concentration.

  That is, calculated from mass balance, the amount of rutile added is the amount of aluminum that can be reduced by aluminum so that even if the total amount is reduced, aluminum remains in the steel and the reduction ability is not lost. A reduction experiment was conducted such that 60% of the target was the target rutile addition amount, and the ratio of quicklime to the rutile was almost constant.

  When the initial aluminum concentration was 0.003% by mass, the titanium reduction rate was as low as about 33%. This is because aluminum remains in the steel, but the driving force for reduction is insufficient because the aluminum concentration is low.

  In addition, when the aluminum concentration is low, for example, it is possible to increase the reduction rate by adding a strong reducing element such as zirconium, but such a metal is more expensive than aluminum, and more generally, a metal More expensive than titanium.

  Therefore, except for very special steel types, the addition of titanium metal is simpler and more economical. Therefore, reduction treatment with an aluminum concentration of less than 0.005% by mass is excluded from the scope of the present invention.

  In an operation where the initial aluminum concentration is 0.005% by mass or more, a target reduction rate of 50% or more is obtained.

  On the other hand, in Comparative Example 4 in which the initial aluminum concentration exceeds 0.9% by mass, the aluminum concentration of the molten steel after the treatment is high. It became necessary to perform OB treatment (reduction of aluminum combustion by oxygen blowing) after the treatment. For this reason, problems such as an increase in the cost of aluminum addition, extension of operation time, and quality control of alumina generation by OB treatment have occurred.

  Furthermore, in order to evaluate the influence of the size and type of the additive (secondary material), the results of the test operation performed with the upper addition and the Ar stirring are shown in Table 4 under the same conditions as in Example 2 in Table 1. Shown in

When the rutile and quicklime sizes are added in bulk (about 50 mm in size) (Example 11), the type of titanium oxide is changed, and more inexpensive ilmenite (main component FeTiO ₃ ) is mixed into rutile by 30%. When used (Ti content is changed to 40.8% by mass with mixing: Example 12), and the type of calcium oxide is changed to slaked lime (main component Ca (OH) ₂ ), limestone (main component CaCO ₃ ) It can be confirmed that good reduction characteristics can be obtained in all cases (Examples 13, 14, and 15) where a converter rod (main component CaO—SiO ₂ -iron oxide) was used.

In the test using the agglomerated soot (main component CaO—Al ₂ O ₃ ) as the calcium oxide source in the additive (substituent material (mass% Ti / mass% Ca) = about 4) (Example 16), The alumina in the blended material was 11% by mass. The reduction rate is 53.7%, and a result exceeding 50% of the target value is obtained, but it is lower than the other levels.

  This is probably because the alumina concentration in the additive was relatively high, so the activity of alumina was high, and the reaction of formula (2) was stagnant.

  When carrying out the method of the present invention by the upper addition method, in order to confirm that it can be operated without a CAS bell, using a slag dart at the time of steelmaking in the converter, carrying out the waste in the ladle, Even in Example 17, where the effect of the ladle slag amount was thoroughly removed until the error range of the additive component was reached, good Ti reduction characteristics were obtained.

  In this case, it can be confirmed that the method of the present invention can be carried out even if there is no equipment measure for installing the CAS bell. However, since the work load is increased and the treatment time is extended by removal, it is necessary to add Ti to the manufactured product at the steelworks. The CAS method is more advantageous in terms of running cost, except that the ratio of steel types required to be added is small.

Furthermore, based on the conditions of Example 15, the additive contained silica sand (over 95% SiO ₂ , 2 mm under) to change the Ti content. At that time, Ti (mass%) / Ca (mass%) was constant. The results are shown in Table 5.

  In Examples 18 to 20 (in the range where the Ti content is 35% by mass or more), the target Ti reduction rate of 50% or more is obtained, but the conditions (Comparative Examples 5, 6 and Ti, in which a large amount of silica sand is added) are obtained. In a range of less than 35% by mass, the Ti reduction rate was remarkably lowered, and a reduction rate of 50% could not be secured.

  As described above, according to the present invention, when manufacturing a steel product by adding it to molten iron containing titanium, which is an important element for improving characteristics, inexpensive titanium can be used without adding expensive titanium metal to the molten iron. Reduction of the oxide can be carried out with high efficiency and stable operation, and titanium can be added to the molten iron. Therefore, titanium-containing steel products can be produced economically, is easy in operation, has a very high industrial value in terms of cost, and has high applicability in the steel industry.

DESCRIPTION OF SYMBOLS 1 Molten steel pan 2 Injection lance 3 Titanium oxide hopper 4 Quick lime hopper 5 Conveying piping 6 Mixed flux 7 Molten steel 8 Molten steel ladle 8a Bottom 9 Titanium oxide hopper 10 Quick lime hopper 11 Mixing container 11a Mixed additive 12 CAS bell 13 Molten steel 14 Top slag 15 Porous Plug 16 Stir gas

Claims (4)

The secondary material contains Al in the molten iron in an amount of 0.005 to 0.80 mass%, then contains 35 mass% or more of titanium, and contains titanium oxide and calcium oxide so as to satisfy the following formula (1). Is added to molten iron. A method for adding titanium to molten iron.
3 ≦ (mass% Ti) / (mass% Ca) ≦ 8 (1)
However,
(Mass% Ti): mass% of Ti contained as an oxide in the secondary material
(Mass% Ca): mass% of Ca contained as an oxide in the secondary material   2. The method of adding titanium to molten iron according to claim 1, wherein the secondary material is added to the molten iron as a powder and passed through the molten iron.   2. The method of adding titanium to molten iron according to claim 1, wherein the secondary material is added to the molten iron surface that is blocked from the initial slag on the molten iron surface, and the interface between the secondary material and the molten iron is agitated.   4. The method for adding titanium to molten iron according to claim 1, wherein the concentration of alumina at a reaction site in the reduction reaction of aluminum in the secondary material and molten iron is less than 10 mass%. .

Images