JP2005002419A - Method for producing steel material with little alumina cluster - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel material which does not cause sliver flaw of a thin sheet for car and house electric appliance, defective quality of a thick plate for structural use, a reduction in low temperature toughness of the wear resistant thick plate and has little surface flaw and inner defect such as UST defect at welded part of a steel pipe for oil well pipe, etc., by preventing the coarse alumina cluster causing a defective product from being formed inside the molten steel and on the surface of Ar bubble. <P>SOLUTION: Mg/T.O (in a mass ratio) is made to be 0.01 to <0.5 by adding Mg into the molten steel after deoxidizing with Al or Al-Si. Oxide base inclusions in the steel material mainly contains Al<SB>2</SB>O<SB>3</SB>and MgO and the content of MgO by mass% is desirable to be 0.1-15%. Low melting point oxides of FeO and FeO-Al<SB>2</SB>O<SB>3</SB>existing as binder between the alumina grains of the cluster is reduced with Mg and thus, the coagulation and the coalesce of the alumina grains in the molten steel and on the Ar bubble surface, are restrained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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【発明の効果】
以上の説明から明らかなように、本発明によればクラスターのアルミナ粒子間にバインダーとして存在するＦｅＯ および ＦｅＯ・Ａｌ_２Ｏ_３の低融点酸化物がＭｇで還元され、溶鋼中およびＡｒ気泡表面でのアルミナ粒子の凝集・合体が抑制される。このため、Ａｌ脱酸、Ａｌ−Ｓｉ 脱酸鋼で、最終製品における表面疵や内部欠陥の原因となる粗大アルミナクラスターの生成を防止できる。よって、本発明は従来のＡｌ脱酸鋼やＡｌ−Ｓｉ 脱酸鋼における問題点を一掃したアルミナクラスターの少ない鋼材の製造方法として、産業の発展に寄与するところは極めて大である。さらに本発明によって、連続鋳造における溶鋼中アルミナの浸漬ノズルへの付着も防止可能である。したがって、浸漬ノズル閉塞防止に対する効果も大きい。
【図面の簡単な説明】
【図１】Ｍｇ／Ｔ．Ｏと最大アルミナクラスター径の関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel material with few alumina clusters suitable for automobile steel sheets, structural and wear-resistant steel plate, oil well pipe steel pipes, and the like.
[0002]
[Prior art]
[Patent Document 1] JP-A-4-333359 [Patent Document 2] JP-A-7-54103 [Patent Document 3] JP-A-9-192799 [Non-Patent Document 1] Materials and Processes, 4 (1991), p. 1214 (Hirota et al.)
[Non-patent document 2] Iron and steel, (1995), p. 17 (Annaka et al.)
[Non-Patent Document 3] ISIJ Int. , 37 (1997), p. 936 (H. Yin et al.)
[0003] Rolled steel materials such as steel plates are generally manufactured as aluminum killed steels in which undeoxidized molten steel melted in a converter is deoxidized with Al. Alumina produced during deoxidation is hard and easily clustered, and remains as inclusions of several hundred μm or more. Therefore, when removal from molten steel is insufficient, hot rolling with thin plates, sliver rods (wire rods) during cold rolling, poor material quality with structural planks, low temperature toughness reduction with wear-resistant steel planks, It causes weld defect UST defects in oil well pipe steel pipes.
[0004]
As a method of removing this alumina from molten steel, (1) after deoxidation, Al is added as a deoxidizing agent when leaving the steel in the converter so that the alumina aggregates, floats from the molten steel by coalescence, and the separation time is as long as possible. (2) A method in which molten steel is strongly stirred by CAS or RH treatment, which is one of the secondary refining methods, to promote the floating and separation of alumina, and (3) Alumina by adding Ca to the molten steel. Has been carried out, for example, by making the form of CaO—Al ₂ O ₃ of inclusions of low melting point controlled to be harmless.
[0005]
However, there is a limit to the measures for floating and separating alumina by the methods (1) and (2), and there is a problem that inclusions of several hundred μm or more cannot be completely removed, so that sliver flaws cannot be prevented. The modification of the oxide inclusions by Ca in (3) can prevent the formation of clusters and reduce the size by reducing the melting point of the inclusions. However, according to Non-Patent Document 1 described above, in order to convert alumina into liquid phase calcium aluminate in molten steel, [Ca] / [T. O] must be controlled in the range of 0.7 to 1.2. For this purpose, for example, T.W. It is necessary to add a large amount of Ca of O 2 at 40 ppm and 28 to 48 ppm. On the other hand, in steel cords and valve spring materials for tires, it is common to make inclusions harmless by controlling the inclusions to a low melting point CaO—SiO ₂ —Al ₂ O ₃ (—MnO) system that easily deforms during rolling. Well known. However, in these methods, since Ca is usually added as an inexpensive CaSi alloy, the present situation is that it has not been put to practical use in automotive steel plates and can cold-rolled steel plates with a strict upper limit of Si.
[0006]
In deoxidation of molten steel using REM such as Ce and La, (1) Al killing is premised, REM is used as an alumina modifier after Al deoxidation, and (2) REM without using Al. Is known, or a method of deoxidizing in combination with Ca, Mg or the like.
[0007]
As a method for reducing alumina clusters in Al killed steel, the above-mentioned Patent Document 1 describes that when melting Al killed steel, 0.1 kg / ts (corresponding to 100 ppm) or more of metal Mg is added to the molten steel. In addition, by controlling the form of alumina inclusions present in steel to Al ₂ O ₃ —MgO inclusions and finely dispersing them in the steel, product defects caused by clusters of alumina inclusions are prevented, A method for detoxifying inclusions in steel to prevent nozzle clogging during casting is shown. In Patent Document 2, C: 1.2% or less, Al: 0.01 to 0.1% by mass%, T.I. O: 005% or less; O × 0.5 ≦ T. Mg <T. An oxide-based inclusion ultrafine dispersion steel characterized by containing Mg satisfying the relationship of O × 7.0 is disclosed.
[0008]
In these methods, Al ₂ O ₃ is reduced with Mg to control the form of Al ₂ O ₃ .MgO (containing 28% MgO) or MgO, and each Al ₂ O ₃ particle is refined. To do. However, Al ₂ O ₃ .MgO particles themselves are easy to coalesce and it is difficult to suppress the formation of alumina clusters. Further, when Mg is added excessively, a large amount of Al ₂ O ₃ .MgO is generated due to the reaction with the slag at the top of the molten steel, and the cleanliness of the molten steel is deteriorated. It was. Furthermore, since Mg easily evaporates and the yield is poor, it is necessary to add a large amount of Mg alloy, which increases the manufacturing cost. Further, similarly to the modification of alumina with Ca, addition of Mg is usually an inexpensive SiMg alloy, so that it was difficult to apply it to automobile steel plates and can cold-rolled steel plates with strict Si upper limits.
[0009]
On the other hand, several generation mechanisms have been proposed for clustering alumina particles. For example, in the above-mentioned Patent Document 3, it is considered that P ₂ O ₅ in molten steel promotes agglomeration and coalescence of Al ₂ O ₃ particles, Ca is added to form nCaO · mP ₂ O _5, and Al ₂ O ₃ It has been shown that Al ₂ O ₃ adhesion to the immersion nozzle can be prevented by reducing the bonding strength of P ₂ O ₅ which is a binder. Moreover, according to the said nonpatent literature 2, it is guessed that the alumina particle capture | acquired by Ar gas used for the blockage | prevention of the immersion nozzle by continuous casting is the cause of the sliver flaw which generate | occur | produces in a cold-rolled steel plate. is doing. Further, Non-Patent Document 3 described above shows an observation result that the alumina particles trapped in the bubbles aggregate and coalesce on the surface of the bubbles due to the capillary effect. Although the microscopic formation mechanism of alumina clusters is being elucidated in this way, since the specific method for preventing clustering has not been clarified, inclusion defects due to alumina clusters are reduced to the required quality level. It was difficult to reduce.
[0010]
[Problems to be solved by the invention]
The present invention has been made in order to advantageously solve the above-described conventional problems, and it is possible to obtain coarse alumina clusters that cause product defects in steel materials such as thin plates, thick plates, steel pipes, shaped steels, and steel bars. By preventing formation at the surface of molten steel and Ar bubbles, thin sliver rods for automobiles and household appliances, poor structural plate materials, low-temperature toughness of wear-resistant thick plates, welded UST defects in oil well pipes The present invention has been completed for the purpose of providing a method for producing a steel material with few surface defects and internal defects.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the inventor repeated experiments and examinations. As a result, (1) low melting point oxides of FeO and FeO.Al ₂ O ₃ exist as binders between the alumina particles of the cluster. {Circle around (2)} It was found that agglomeration and coalescence of alumina particles in molten steel and on the surface of Ar bubbles was suppressed by reducing this binder with an appropriate amount of Mg. The present invention has been completed on the basis of the above-mentioned findings. By adding Mg to Al deoxidized or Al-Si deoxidized molten steel, Mg / T. O is 0.01 or more and less than 0.5. Moreover, it is preferable that the oxidation type inclusions in the steel material are mainly composed of Al ₂ O ₃ and MgO, and the content of MgO is 0.1% to 15% by mass%.
[0012]
In addition, the component of steel is the mass% C: 0.0005-1.5%, Si: 0.005-1.2%, Mn: 0.05-3.0%, P: 0.001-0. 1%, S: 0.0001-0.05%, Al: 0.005-1.5%, or (a) Cu: 0.1-1.5%, Ni: 0.1-10. 1% or more of 0%, Cr: 0.1 to 10.0%, Mo: 0.05 to 1.5%, or (b) Nb: 0.005 to 0.1%, V: 0 0.005 to 0.3%, Ti: 0.001 to 0.25%, or (c) B: 0.0005 to 0.005% (a), (b), ( c) It is preferable that any one or two or more are contained and the balance is Fe and inevitable impurities.
[0013]
Furthermore, it is preferable that the maximum diameter of the alumina cluster obtained by slime extraction of the slab is 100 μm or less, and the number of alumina clusters of 20 μm or more obtained by slime extraction of the slab is 2 pieces / kg or less. It is preferable.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
In the present invention, by adding Mg to Al deoxidized or Al-Si deoxidized molten steel, Mg / T. O is 0.01 or more and less than 0.5. As a result, the low melting point oxides of FeO and FeO.Al ₂ O ₃ existing as binders between the alumina particles of the cluster are reduced with Mg, and aggregation and coalescence of alumina particles in the molten steel and on the surface of Ar bubbles are suppressed. . As shown in FIG. In the composition range where O is 0.01 or more and less than 0.5, aggregation and coalescence of alumina particles can be suppressed, and formation of coarse alumina clusters can be prevented. Mg / T. The reason why the upper limit of O is less than 0.5 is that when 0.5 or more of Mg is added, coarse Al ₂ O ₃ .MgO clusters of the same degree as Al deoxidation are usually generated. Further, because a large amount of Al ₂ O ₃ .MgO is generated by reaction with the slag, the molten steel cleanliness is deteriorated and the continuous casting immersion nozzle is closed. The lower limit is set to 0.01 because the effect of preventing clustering of alumina particles cannot be obtained if the lower limit is less than this. T. O is the total amount of oxygen in the steel and means the total of dissolved oxygen and oxygen in inclusions.
[0015]
According to claim 2, it had a content of MgO of _Al 2 _{O 3} and MgO main component oxide-based inclusions was 0.1 to 15 percent, tends inclusions are aggregated, coalesced with more, This is because coarse clusters are generated, and if it is less than this, the effect of Mg addition is lost and clustering of alumina particles cannot be prevented.
[0016]
In addition, the steel materials manufactured by Al deoxidation and Al-Si deoxidation in the present invention are C: 0.0005 to 1.5%, Si: 0.005 to 1.2%, and Mn: 0 in mass%. .05 to 3.0%, P: 0.001 to 0.1%, S: 0.0001 to 0.05%, Al: 0.005 to 1.5%, T.I. O ≦ 80 ppm, or (a) Cu: 0.1 to 1.5%, Ni: 0.1 to 10.0%, Cr: 0.1 to 10.0%, Mo: 0.05 to 1 1% or 2 or more of 5%, or (b) Nb: 0.005 to 0.1%, V: 0.005 to 0.3%, Ti: 0.001 to 0.25% Or two or more, or (c) B: 0.0005 to 0.005% (a), (b), (c) any one or two or more, the balance being Fe and inevitable impurities This carbon steel can be applied to a thin plate, a thick plate, a steel pipe, a shape steel, a steel bar, etc. by applying necessary rolling to the steel material. The reason why this range is preferable is as follows.
[0017]
Since C is a basic element that improves the strength of steel most stably, the content is adjusted in the range of 0.0005 to 1.5% depending on the strength of the desired material. In order to ensure strength or hardness, it is desirable to contain 0.0005% or more, but if it exceeds 1.5%, the toughness is impaired, so 1.5% or less is preferable.
[0018]
The reason why Si is 0.005 to 1.2% is that if it is less than 0.005%, a pretreatment is required, which imposes a large cost burden on refining and impairs economic efficiency. If it exceeds 1.2%, plating is performed. This is because defects occur and surface properties and corrosion resistance deteriorate.
[0019]
The reason why Mn is set to 0.05 to 3.0% is that, if it is less than 0.05%, the refining time becomes long and the economic efficiency is impaired. If it exceeds 3.0%, the workability of the steel material is greatly deteriorated. It is to do.
[0020]
The reason why P is 0.001 to 0.1% is that if it is less than 0.001%, the hot metal pretreatment takes time and cost, and the economic efficiency is impaired. If it exceeds 0.1%, the workability of the steel material is greatly deteriorated. It is to do.
[0021]
If S is 0.0001 to 0.05%, if less than 0.0001%, the hot metal pretreatment takes time and cost, and the economic efficiency is impaired. If it exceeds 0.05%, the workability and corrosion resistance of the steel material are impaired. This is because of a significant deterioration.
[0022]
The reason why Al is 0.005 to 1.5% is that when it is less than 0.005%, N is trapped as AlN and solid solution N cannot be reduced. On the other hand, if it exceeds 1.5%, surface properties and workability deteriorate, so 1.5% or less is preferable.
[0023]
T.A. The reason why O 2 is set to 80 ppm or less is that if it exceeds 80 ppm, the collision frequency of alumina particles increases, and the cluster may become coarse. Further, since the amount of REM added for reforming alumina is increased, cost is increased and economic efficiency is also impaired. Here, T.W. O represents the total amount of dissolved oxygen and inclusion oxygen in terms of the total amount of oxygen in the steel.
[0024]
The above is the basic component system, but in the present invention, in addition to these, (a) one or more of Cu, Ni, Cr, and Mo, (b) one of Nb, V, and Ti, depending on each application As described above, (c) any one or two or more of (a), (b) and (c) of B 1 can be contained.
[0025]
Cu, Ni, Cr, and Mo are all elements that improve the hardenability of the steel, and Cu, Ni, and Cr contain 0.1% or more, and Mo contains 0.05% or more. As shown, Cu is 1.5 and Mo is 1.5%, and Ni and Cr are added in excess of 10%, so that the toughness and workability may be impaired. And Cr is limited to 0.1 to 10%, and Mo is limited to a range of 0.05 to 1.5%.
[0026]
Nb, V, and Ti are all elements that improve the strength of the steel by precipitation strengthening. Nb and V are 0.005% or more, and Ti is contained by 0.001% or more. , Nb is 0.1%, V is 0.3%, and if Ti is added over 0.25%, the toughness may be impaired, so Nb is 0.005 to 0.1% and V is 0.005. -0.3%, Ti is limited to the range of 0.001-0.25%.
[0027]
B is an element that improves the hardenability of the steel and increases the strength. By adding 0.0005% or more, it shows an effect of improving the strength. However, if added over 0.005%, the precipitate of B increases. Therefore, the toughness may be impaired, so the content is limited to 0.0005 to 0.005%.
[0028]
The combined use of Ca lowers the effect of suppressing the formation of alumina clusters due to the addition of Mg in order to facilitate partial dissolution and coalescence of the alumina surface. Therefore, it is desirable to prevent Ca from entering from slag and refractory as much as possible.
[0029]
Further, the reason that the maximum diameter of the alumina cluster obtained by slime extraction of the slab is 100 μm or less is that when it is larger than 100 μm, it leads to surface defects and internal defects in the product. The reason why the number of alumina clusters of 20 μm or more obtained by the slime extraction of the slab was 2 / kg or less is that when it exceeds 2 / kg, it leads to surface defects and internal defects after rolling.
[0030]
Addition of Mg into the molten steel is performed after Al deoxidation of the molten steel using, for example, CAS or RH of a secondary refining apparatus. Mg may be a pure metal or an alloy with another metal, and the shape may be a lump, granule, wire, or the like. Since the addition amount is very small, in order to make the Mg concentration in the molten steel uniform, addition to the refluxing molten steel in the RH tank or stirring with Ar gas after addition of the ladle is desirable. Moreover, Mg can also be added to tundish and molten steel in a mold. Next, examples of the present invention will be described.
[0031]
【Example】
After blowing in a 270 t converter, the steel was adjusted to a predetermined carbon concentration and produced. It adjusted to the target molten steel component by secondary refining, Mg was added as Si-10% Mg alloy and Si-3% Mg alloy after Al deoxidation. The results are shown in Tables 1 and 2. Comparative examples are shown in Tables 3 and 4. Table 2 is a continuation of Table 1, and Table 4 is a continuation of Table 3. The molten steel in the table was subjected to a vertical bending type continuous casting machine, and the slab size was 245 mm thick × 1200 to 2200 mm wide, the casting speed was 1.0 to 1.8 m / min, and the molten steel temperature in the tundish was 1520 to 1580 ° C. The slab was manufactured. Thereafter, the slab was hot-rolled, pickled, and further cold-rolled as necessary to conduct a quality survey. The plate thickness after hot rolling was 2 to 100 mm, and the plate thickness after cold rolling was 0.2 to 1.8 mm.
[0032]
The maximum cluster diameter, number of clusters, average inclusion composition, defect generation rate, etc. of the samples taken from the slab are as shown in Tables 2 and 4, and the present invention greatly reduces product defects caused by alumina clusters. It was confirmed that the product exhibited excellent productivity.
[0033]
The meanings of * 1 to * 7 in the table are as follows.
* 1: Mg and T.I. O is the analytical value of the molten steel sample taken 1 minute after the addition of Mg.
* 2: Si10Mg: Si-10% Mg alloy, Si3Mg: Si-3% Mg alloy.
* 3: Average value of 10 inclusion compositions arbitrarily extracted from the slab cross section. The composition was identified by SEM with EDS.
* 4: The maximum cluster diameter is measured using a stereomicroscope (40x magnification) of inclusions extracted from a slab weighing 1 kg ± 0.1 kg with a slime electrolytic extraction (using a minimum mesh of 20 μm). The average value of the major axis and the minor axis of the object was obtained for all the inclusions, and the maximum value of the average value was taken as the maximum inclusion diameter. The number of clusters is inclusion of 1 ± 0.1 kg of slime electro-extracted (using a minimum mesh of 20 μm), and all inclusions of 20 μm or more observed with an optical microscope (100 times) were converted to 1 kg units. .
* 5: Defect occurrence rate is according to the following formula.
For thin plates, the occurrence rate of sliver wrinkles on the plate surface (= total sliver wrinkles / coil length x 100,%).
Thick plate is UST defect generation rate or separation generation rate on product plate (= number of defective plates / total number of inspection plates × 100,%). The occurrence of separation was confirmed by observation of the fracture surface after the Charpy test.
In addition, in the thick plate material defect occurrence rate of Table 2, it was described as (UST) when the defect was a UST defect, and (SPR) when it was a separation defect.
For steel pipes, UST defect rate at oil well pipe welds (= number of defect-generated pipes / total number of inspection pipes x 100,%).
* 6: V-notch Charpy impact test value in the rolling direction at −20 ° C. Average value of 5 test pieces.
* 7: Thickness direction drawing value of the product plate at room temperature (= cross-sectional area of the fractured portion after the tensile test / cross-sectional area of the test piece before the test × 100,%).
[0034]
[Table 1]

[0035]
[Table 2]

[0036]
[Table 3]

[0037]
[Table 4]

[0038]
【The invention's effect】
As is clear from the above description, according to the present invention, the low melting point oxides of FeO and FeO.Al ₂ O ₃ existing as binders between the alumina particles of the clusters are reduced with Mg, and in the molten steel and on the surface of the Ar bubbles. Aggregation and coalescence of alumina particles are suppressed. For this reason, Al deoxidation and Al-Si deoxidized steel can prevent generation of coarse alumina clusters that cause surface defects and internal defects in the final product. Therefore, the present invention contributes greatly to the development of the industry as a method for producing a steel material with few alumina clusters that eliminates the problems associated with conventional Al deoxidized steel and Al—Si deoxidized steel. Further, according to the present invention, it is possible to prevent adhesion of alumina in molten steel to the immersion nozzle in continuous casting. Accordingly, the effect of preventing the immersion nozzle from being blocked is great.
[Brief description of the drawings]
FIG. 1 shows Mg / T. It is a graph which shows the relationship between O and the maximum alumina cluster diameter.

Claims (8)

By adding Mg to Al deoxidized or Al-Si deoxidized molten steel, Mg / T. A method for producing a steel material with few alumina clusters, wherein O is 0.01 or more and less than 0.5. The oxide-based inclusions in the steel material are mainly composed of Al ₂ O ₃ and MgO, and the content of MgO is 0.1 to 15% by mass%. A method for producing a small amount of steel. Steel material component in mass%, C: 0.0005-1.5%, Si: 0.005-1.2%, Mn: 0.05-3.0%, P: 0.001-0.1% , S: 0.0001 to 0.05%, Al: 0.005 to 1.5%, T.I. The method for producing a steel material with few alumina clusters according to claim 1 or 2, wherein O: 80 ppm or less, with the balance being Fe and inevitable impurities. In mass%, Cu: 0.1 to 1.5%, Ni: 0.1 to 10.0%, Cr: 0.1 to 10.0%, Mo: 0.05 to 1.5% Or the 2 or more types is further contained, The manufacturing method of the steel materials with few alumina clusters of Claim 3 characterized by the above-mentioned. It is characterized by further containing one or more of Nb: 0.005 to 0.1%, V: 0.005 to 0.3%, Ti: 0.001 to 0.25% in mass%. The manufacturing method of steel materials with few alumina clusters of Claim 3 or 4. The method for producing a steel material with few alumina clusters according to claim 3, wherein B: 0.0005 to 0.005% is further contained in mass%. The method for producing a steel material with few alumina clusters according to any one of claims 1 to 6, wherein the maximum diameter of the alumina clusters obtained by slime extraction of a slab is 100 µm or less. The method for producing a steel material with less alumina clusters according to claim 7, wherein the number of alumina clusters of 20 µm or more obtained by slime extraction of a slab is 2 pieces / kg or less.

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