WO2004111277A1

WO2004111277A1 - Steel product reduced in alumina cluster

Info

Publication number: WO2004111277A1
Application number: PCT/JP2004/000139
Authority: WO
Inventors: Toshiaki Mizoguchi; Yoshiyuki Ueshima; Jun Yamaguchi; Yu Watanabe; Akira Mikasa; Hirotsugu Yasui
Original assignee: Nippon Steel Corporation
Priority date: 2003-06-12
Filing date: 2004-01-13
Publication date: 2004-12-23

Abstract

A steel product reduced in the inclusion of alumina clusters, which is produced by casting a molten steel prepared through the deoxidization using Al and then the addition of one or more of rare earth elements (REM) of Ce, La, Pr and Nd, characterized in that (a) the content of REM oxides in the oxide-based inclusions containing alumina and REM oxides as primary components is 0.5 to 15 mass % relative to said oxide-based inclusions, or (b) in addition to (a), the mass ratio of the total REM to the total oxygen (T.O), i.e., REM/T.O is 0.05 to 0.5, or (c) the total amount of REM is 0.1 ppm to less than 10 ppm, and the amount of REM forming a solid solution is less than 1 ppm.

Description

Description Steel material with the lowest alumina cluster [Technical field]

The present invention relates to a steel material having a small amount of alumina clusters suitable for a steel plate for automobiles, a structural steel plate, a thick plate for wear-resistant steel, a steel tube for oil country tubular goods, and the like.

(Background technology)

Rolled steel such as steel sheet is generally produced as aluminum-killed steel by deoxidizing undeoxidized molten steel in a converter with A1. Alumina generated during deoxidation is hard, easily clustered, and remains in the molten steel as inclusions of several hundred meters or more.

Therefore, if these inclusions are not sufficiently removed from the molten steel, slipper flaws (linear flaws) on thin plates, poor material quality on structural plates, low-temperature toughness on wear-resistant steel plates, oil wells This may cause UST defects in welds in pipe steel pipes (defects detected by Ultrasonic Testing). Furthermore, alumina adheres and accumulates on the inner wall of the immersion nozzle during continuous production, causing nozzle clogging.

The method of removing this alumina from the molten steel is as follows: (1) During dewatering in a converter, so that the time for alumina to coagulate, coalesce, float and separate from the molten steel is as long as possible after deoxidation. (2) CAS (Composition Ajustment by Sealed Argon) which is one of the secondary purification methods

B ubb 1 ing) or RH (R heinstah 1 H uttenwerkeund Heraeus) (vacuum degassing) Floating of the alumina by strongly stirring the molten steel, a method to facilitate separation, (3) adding C a to soluble steel in, alumina C a O of the low melting point inclusions - reformed to A 1 ₂ o ₃ There were methods of detoxification.

However, the flotation separation method of alumina by the above methods (1) and (2) cannot completely remove inclusions of several hundreds / zm or more, and cannot prevent slipper flaws generated on the steel sheet surface. .

According to the method for modifying inclusions by the method (3), the inclusions can be reduced in melting point to prevent the formation of clusters and to make the inclusions finer.

However, according to Shirota et al. (Materials and Processes, 4 (1991), p. 124, 14), in molten steel, alumina must be converted into a liquid-phase calcium aluminate by [ It is necessary to control [Ca] / [TO] in the range of 0.7 to 1.2.

For example, if T.O (total oxygen content in molten steel, the sum of dissolved oxygen and oxygen in inclusions) is 40 ppm, a large amount of 28-48 ppm C a Need to be added.

On the other hand, in the steel cords and the valve panel material for tires, inclusions, rolling processing during deformable low melting point _{C a O- S i 0 2 -} A 1 2 0 3 (-Mn O) type inclusions of It is generally known that the substance is reformed and rendered harmless.

However, in these methods, since Ca is usually added with an inexpensive Ca Si alloy, the production of automobile steel sheets and canned cold-rolled steel sheets in which the upper limit of the Si amount is strictly controlled is performed. The method (3) has not been put to practical use.

In the deoxidation of molten steel using EM such as Ce, La, etc., (1) A1 killed is assumed, and after A1 deoxidation, EM is used as a modifier for alumina. Or (2) do not use A 1, It is known to use as a deoxidizing agent in combination with Germany or Ca, Mg, or the like.

As a method based on the premise of A 1 killing, Japanese Patent Application Laid-Open No. 52-70918 discloses that after deoxidation of A 1 or A 1 —Si, Se, S b, La or C The interfacial tension between the molten steel and the alumina cluster is controlled by adding at least one of e from 0.001 to 0.05% or by combining it with molten steel stirring. A method for producing a clean steel with few nonmetallic inclusions, which removes an alumina cluster by floating separation, is disclosed.

Japanese Patent Application Laid-Open No. 2000-26842 also discloses that, after molten steel is deoxidized with A 1 and T i, Ca and Z or REM are added to the oxide-based steel. the size of the inclusions was less 5 0 mu m, and the composition of _{_{inclusions, a 1 2 O 3: 1}} 0~ 3 0 wt%, C a oxide and / or REM oxides: 5-3 A cold-rolled steel sheet excellent in surface properties and internal quality, in which the content is 0 wt% and the Ti oxide content is 50 to 90 wt%, and a method for producing the same are disclosed.

In addition, Japanese Patent Application Laid-Open No. H11-13324-26 discloses that A1, killed steel with no alumina clusters and few defects is produced by complex deoxidation by Al, REM and Zr. There is disclosed a production method for producing the same.

However, with these methods, it was difficult to reliably separate the alumina clusters by flotation, and inclusion defects could not be reduced to the required quality level.

As a method that does not use A 1, Patent No. 1150222 discloses that molten steel is deoxidized with a CaO-containing flux and then contains an alloy containing one or more of Ca, Mg, and EM. For example, 100 to 200 ppm is added, and the method for producing steel for steel, which lowers the melting point of the inclusions and softens it, has been developed. It is shown.

Patent No. 1266683 also discloses that after adjusting T.O. (total oxygen content) to 100 ppm or less with a deoxidizing agent other than A1, such as Mn and Si, air A method for producing a wire rod having good ultrafine drawability, in which 50 to 500 ppm of EM is added for the purpose of preventing oxidation due to urea.

However, these methods do not use inexpensive A1 as a deoxidizing agent, so that there is a problem that the cost of the deoxidizing agent is increased. Further, when deoxidizing with Si in these methods, it is difficult to apply the method to deoxidizing molten steel for thin sheet materials in which the upper limit of the Si amount is strictly controlled. On the other hand, several generation mechanisms have been proposed for clustering of anoremina particles.

Attachment For example, Japanese Unexamined 9 one '1 9 2 7 9 9 JP, aggregation P ₂ O ₅ in the molten steel is A 1 ₂ 0 ₃ particles, thought to promote coalescence, the C a molten steel pressurized to, yielding _{n C a O 'mP 2 O} 5, by lowering the bonding force p ₂ o ₅ is Painda one a 1 ₂ 0 _3, of a 1 ₂ Ο ₃ to immersion nozzle It is disclosed that adhesion can be prevented.

Annaka et al. (Iron and steel, (1995), p. 17) reported that alumina particles trapped in Ar gas bubbles used to prevent clogging of immersion nozzles in continuous construction. It is speculated that this is the cause of the slipper flaws generated on the cold-rolled steel sheet.

In addition, H.Y ineta 1. (ISIJI nt., 37 (1977), p. 936) showed that the alumina particles trapped in the bubbles caused the cavitation effect on the surface of the bubbles. The observation result of aggregation and coalescence is disclosed.

As described above, the formation mechanism of alumina clusters is being elucidated, but the specific method for preventing cluster unification is not clear, and inclusion defects due to alumina clusters can be reduced to the required quality level. Is difficult to reduce. [Disclosure of the Invention]

The present invention has been made in order to advantageously solve the conventional problems as described above, and may cause product defects in the manufacture of steel materials such as thin plates, thick plates, steel pipes, section steels, and steel bars. Prevents the formation of coarse alumina clusters in molten steel and on the surface of Ar bubbles, resulting in slipper flaws on thin plates for automobiles and home appliances, poor material quality on structural plates, and low temperatures on wear-resistant plates. It has been completed with the objective of providing a steel material with less surface defects such as UST defects and reduced internal defects such as UST defects in welds in oil country tubular goods.

Since the present inventors to solve the above problems, repeated experiments and studies, as a result of its, (i) is between alumina particles in clusters, F e O Contact and the _{F e O · A 1 2 0} 3 The presence of low-melting-point oxide as a binder, (ϋ) Reduction of this binder with an appropriate amount of REM suppresses aggregation and coalescence of alumina particles in molten steel and on the surface of Ar bubbles. (Iii) If more than the required amount of solid solution EM is left in the steel, the reaction between the molten steel and slag in the molten steel stage generates a large amount of composite oxide consisting of REM oxide and alumina. However, it was found that the purity of molten steel deteriorated.

The present invention has been made based on the above findings, and the gist is as follows. '

(1) A steel material produced by deoxidizing using A 1 and adding molten steel to which one or more rare earth elements (REM) of Ce, La, Pr and Nd are added,

The content of REM oxide in oxide-based inclusions mainly composed of alumina and REM oxide is 0.5% by mass based on the oxide inclusions. Not less than 15%

A steel material with less alumina clusters.

(2) A steel material obtained by deoxidizing using A1 and adding molten steel to which one or more rare earth elements (REM) of Ce, La, Pr and Nd are added,

Mass ratio of total REM to total oxygen (TO) in steel: REM / TO is 0.05 or more and 0.5 or less, and

Alumina: The content of REM oxide in oxide inclusions mainly composed of EM oxide is 0.5% or more and 15% or less by mass% based on the oxide inclusions.

A steel material having the least amount of alumina clusters.

(3) A steel material prepared by deoxidizing using A 1 and adding molten steel to which one or more rare earth elements (REM) of Ce, La, Pr and Nd are added,

The total amount of REM is 0.1 111 or more and less than 10 111, and the amount of solid solution REM is less than 1 ppm.

A steel material with less alumina clusters.

(4) The steel material is represented by mass%, C: 0.005 to 1.5%, Si: 0.05 to 1.2%, Mn: 0.05 to 3.0% , P: 0.001 to 0.1%, S: 0.00001 to 0.05%, A1: 0.005 to: 0.5%, T.O: 800 The steel material according to any one of (1) to (3), wherein the steel material contains less than ppm, and the balance is Fe and unavoidable impurities.

(5) The steel material is further represented by mass%, Cu: 0.1 to 1.5%, Ni: 0.1 to 10.0%, Cr: 0.1 to 10%. The steel material having a small amount of alumina clusters according to the above (4), characterized in that it contains one or more of 0% and Mo: 0.05 to 1.5%. (6) said steel further contains, by mass ^{_{0/0, N b: 0.}} 0 0 5~ 0. 1%, V: 0. 0 0 5~ 0. 3%, T i: 0. 0 0 1 ~ 0.25 ⁰ /. The steel material having a small amount of alumina clusters according to the above (4) or (5), characterized by containing one or more of the following.

(7) The steel according to any of (4) to (6), wherein the steel material further contains, by mass%, Β: 0.0005 to 0.0005%. A steel material having less alumina clusters as described.

(8) The steel material according to any one of (1) to (3), wherein the maximum diameter of the alumina cluster obtained by slime extraction of the steel material is 100 μππ or less. .

(9) In the alumina cluster, the number of alumina clusters of 20 μιη or more is two or less Zkg or less.

A steel material having a small amount of alumina clusters according to (8).

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the content of the REM oxide in the oxide-based inclusions and the diameter of the maximum alumina cluster.

FIG. 2 is a diagram showing the relationship between REMZT.O and the diameter of the largest alumina cluster.

Fig. 3 is a diagram showing the relationship between the total REM content in steel and the diameter of the largest alumina cluster.

Figure 4 is a diagram showing the relationship between the amount of solid-solution EM in steel and the state of clogging of the pan nozzle.

[Best mode for carrying out the invention]

Hereinafter, preferred embodiments of the present invention will be described.

In the present invention (1), (1), A 1 deoxidation or A 1 -Add one or more rare earth elements (R EM) selected from Ce, La, Pr, Nd, etc. to molten steel deoxidized using A1, such as Si deoxidation. The content of the REM oxide in the oxide-based inclusions mainly composed of alumina and the REM oxide is set to 0.5 to 15% by mass%.

Within the composition range of the EM oxide, it is possible to suppress aggregation and coalescence of alumina particles, and to prevent formation of coarse alumina clusters. The content of the REM oxide in the oxide-based inclusions is preferably 2 to 12% by mass.

In the present invention, the rare earth element refers to La of atomic number 57 to Lu of atomic number 71.

The upper limit of the content of REM oxides in oxide inclusions is set to 15%, as shown in Fig. 1, when the content of REM oxides exceeds 15% and increases. This is because the substances tend to aggregate and coalesce, and coarse clusters are formed.

On the other hand, the lower limit of the above content was set to 0.5%, as shown in FIG. 1, similarly, when the content of the REM oxide was less than 0.5%, there was no effect of the addition of the REM oxide, and the alumina particles had no effect. Clustering cannot be prevented.

In the present invention of the above (2) (the present invention (2)), in a molten steel deoxidized using A 1, such as A 1 deoxidation or A 1 -Si deoxidation, Ce,: L a The addition of one or more rare earth elements (R EM) selected from the group consisting of, Pr and N d to ensure the prevention of alumina clustering, the content of R EM oxide in oxide inclusions Is set to 0.5 to 1.5 mass%, and the mass ratio of all REM to total oxygen (TO) in the steel is set to 0.05 to 0.5.

Further, in order to further ensure the clustering of alumina, it is preferable that REM / T.0 = 0.15 to 0.4. The reason for setting the upper limit of R EM / T .O to 0.5 is that, as shown in Fig. 2, when R EM is added to exceed 0.5, clusters generated in ordinary A1 deoxidation are reduced. This is because a coarse RM oxide cluster of the same size is formed.

The reason for setting the lower limit of REMZT.O to 0.05 is that the addition of REM less than 0.05 has a sufficient effect of preventing clustering of alumina particles as shown in Fig. 2. As described above, T.O indicates the total of dissolved oxygen and oxygen in inclusions in the total amount of oxygen in the steel, as described above.

In the present invention of the above (3) (the present invention (3)), in the molten steel deoxidized using A 1 such as A 1 deoxidation or A 1 Si deoxidation, Ce, La, Add at least one rare earth metal (R EM) selected from Pr, Nd, etc. to make the total R EM 0.1-1! 1 or more and less than 10 111, and 1 ppm of solid solution R EM Less than

In the composition ranges of the total REM amount and the solid solution REM amount, the aggregation and coalescence of the alumina particles can be suppressed, and the formation of coarse alumina clusters can be prevented. The deterioration of the cleanliness of the molten steel due to the reaction with can be prevented.

By setting the total REM to less than 5 ppm, it is possible to more reliably prevent the formation of coarse alumina clusters.

As shown in Fig. 3, the upper limit of the total REM is set to less than 1 O ppm.As shown in Fig. 3, at 1 O ppm or more, the concentration of REM oxide in oxide-based inclusions increases, and alumina particles aggregate and coalesce. This is because coarse clusters are generated. On the other hand, the lower limit of the total REM was set to 0.1 ppm, as shown in Fig. 3, as shown in Fig. 3 below 0.1 ppm, there was no effect of the addition of REM, and the clustering of alumina particles could not be prevented. Because it is.

To more reliably prevent the formation of coarse alumina clusters, the total REM should be less than 5 ppm.

The reason why the solid-solution REM is less than 1 ppm is that if the concentration is 1 ppm or more, the slag and the solid-solution REM in the steel react at the molten steel stage, and a large amount of composite oxide consisting of REM oxide and alumina is generated. As a result, coarse clusters are formed and the cleanliness of the molten steel deteriorates. When the solid solution REM is 1 ppm or more, the pot nozzle closes as shown in Fig. 4.

Here, in the present invention, the steel material to be deoxidized using A 1 is, in mass%, C: 0.0005 to 1.5%, S i: 0.005 to 1.2%, Mn: 0.05 to 3.0%, P: 0.01 to 0.1%, S: 0.00001 to 0.05%, A1: 0.005 to 1.5%, T. 0: 80 ppm or less, and, if necessary, (a) Cu: 0.1-1.5%, Ni: 0.1 to 10. 0%, Cr: 0.1 to 10.0%, Mo: 0.05 to: 1.5% or more of one or more types, (b) Nb: 0.005 to 0 1%, V: 0.005 to 0.3%, Ti: 0.01 to 0.25%, 1 or more kinds, and (c) B: 0.00 It is made of molten steel containing one or more element groups selected from the three element groups of 0 to 0.05%, with the balance being Fe and unavoidable impurities, and By performing the necessary rolling, it can be processed into thin plates, thick plates, steel pipes, sections, bars, etc. The reason that the above composition range is preferable is as follows.

Since C is a basic element for improving the strength of steel, its content is adjusted in the range of 0.0005 to 1.5% according to the desired strength. In order to ensure the desired strength or hardness, it is desirable to contain at least 0.005%, but if it exceeds 1.5%, toughness is impaired. Therefore, 1.5% or less is good.

The reason why Si is set to 0.005 to 1.2% is that if the value is less than 0.05%, a large cost burden is imposed on the reduction of the Si amount, and the economic efficiency is impaired. If the content is more than 2%, when plating is applied, a metal plating is generated, and the surface properties and corrosion resistance of the steel material are deteriorated.

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 longer and the economic efficiency is impaired, whereas if it is more than 3.0%, the workability of the steel material is increased. Is greatly deteriorated.

The reason why P is set to 0.001 to 0.1% is that if it is less than 0.01%, it takes time and cost to pre-treat the hot metal, and the economic efficiency is impaired, while 0.1% If more, the workability of the steel material will be greatly deteriorated.

The reason why S is set to 0.00001 to 0.05% is that if it is less than 0.001%, pretreatment of the hot metal takes time and costs, and the economic efficiency is impaired. If the content is more than 0.5%, the workability and corrosion resistance of the steel material are significantly deteriorated.

The reason that A 1 is set to 0.005 to .1.5% is that if it is less than 0.05%, N is trapped as A 1 N and solute N cannot be reduced. On the other hand, if it is more than 1.5%, the surface properties and workability of the steel material deteriorate.

The reason for setting T.O to 80 ppm or less is that if it is more than 80 ppm, the collision frequency of the alumina particles increases and the cluster becomes coarse. On the other hand, if T.O is more than 80 ppm, the amount of REM added required for reforming alumina increases, and economic efficiency is impaired. The present invention comprises the above components as basic components. In addition to the basic components, one or more of (a) Cu, Ni, Cr, Mo, (B) One or more of Nb, V, Ti And (c) one or more of the three element groups of B can be selected and contained.

Cu, Ni, Cr, and Mo are all elements that improve the hardenability of steel, and Cu, Ni, and Cr are 0.1% or more, and Mo is 0%. By adding 0.5% or more, the strength of the steel material can be increased. ,

However, if Cu and Mo exceed 1.5%, and Ni and Cr exceed 10%, toughness and workability may be impaired. 1,5%, Ni and Cr are both 0.110%, and Mo is 0.05-5: L: 5%.

Nb, V, and Ti are all elements that improve the strength of the steel by precipitation strengthening.Nb and V are ◦ .05% or more, and Ti is 0.0. By containing 0.1% or more, the strength of steel can be increased.

However, if Nb exceeds 0.1%, V exceeds 0.3%, and Ti exceeds 0.25%, the toughness may be impaired. Is 0.005 to 0.1%, V is 0.005 to 0.3%, and Ti is 0.0001 to 0.25%.

B is an element that improves the hardenability of the steel and increases the strength. By containing 0.0005% or more, the strength of the steel can be increased.

However, if added in excess of 0.05%, the precipitates of B may increase and the toughness may be impaired. Therefore, B is set to 0.0005% to 0.05%.

Further, in the present invention, the maximum diameter of the alumina cluster obtained by extracting the slime of the pieces is preferably 100 / xm or less. This means that when the maximum diameter of the aluminum cluster is greater than 100 μππι, This is because it causes surface defects and internal defects to be formed after processing into products.

In the present invention, the number of alumina clusters of 20 m or more obtained by slime extraction of a piece is preferably two or less Z kg. This is because if the above number is more than 2 / 'kg, surface defects and internal defects may occur after rolling.

The addition of REM to the molten steel is performed, for example, after deoxidizing the molten steel using a secondary refiner, a CAS refiner or an RH refiner. : EM may be any of pure metals such as Ce and La, alloys of REM metals or alloys with other metals, and the shape may be massive, granular, or wire.

Since the amount of REM added is extremely small, in order to make the REM concentration in the molten steel uniform, it must be added to the refluxed molten steel in the RH type refining tank, or added in a ladle, and then Ar gas It is desirable to stir with such as. It is also possible to add REM to molten steel in a tundish or a type II.

〔Example〕

(Example 1).

The molten steel was blown in a converter of 270 t, and thereafter, the steel was adjusted to a predetermined carbon concentration and tapped. After adjusting to the target molten steel composition in the secondary refining and deoxidizing in A 1; EM, Ce, La, misch metal (for example, mass ⁰ /. Ce: 45%, La : 35%, Pr: 6%, Nd: 9%, alloy composed of unavoidable impurities), or alloy of misted metal, Si and Fe (Fe-Si—30% REM) ). Table 1 shows the resulting composition of molten steel.

The molten steel having the composition shown in Table 1 was produced by a vertical bending type continuous forming machine. Forging speed 1.0 to 1.8 m / min, temperature of molten steel in tundish 1520 to 1580 ° C, forging 245 mm thickness XI 200 to 220 mm A piece of width was manufactured.

Thereafter, the strip was subjected to hot rolling, pickling, and if necessary, cold rolling, and a quality survey was conducted. The thickness after hot rolling is 2 to 100 mm, and the thickness after cold rolling is 0.2 mm.

(4) The maximum diameter of one cluster, the number of clusters, the average inclusion composition, the defect occurrence rate, etc. were investigated for the samples taken from the pieces. The results are shown in Table 2.

From Table 2, it can be confirmed that the present invention significantly reduces product defects caused by alumina clusters.

The meanings of * 1 to * 7 in Tables 1 and 2 are as follows.

* 1: REM is the sum of Ce, La, Pr, and Nd.

* 2: MM: Missing metal. An alloy consisting of 45% by mass of Ce, 35% by mass of La, 6% by mass of Pr, 9% by mass of Nd, and unavoidable impurities by mass%. MM S i: R EM— S i — Fe alloy. Composition: REM: 30%, Si: 30%, balance Fe.

* 3: Average value of the composition of 10 inclusions arbitrarily extracted from the mirror section. The composition was identified by SEM with EDX (ScanningElectntronMicroscope).

* 4: The method for measuring the maximum cluster diameter is as follows: Inclusions extracted from (1 ± 0.1) kg pieces by slime electrolysis (using a minimum mesh of 20 μm) are photographed with a stereoscopic microscope ( Then, the average value of the major axis and minor axis of the photographed inclusion was calculated for all the inclusions, and the maximum value of the average was defined as the maximum cluster diameter.

The number of clusters is slime electrolysis from (1 ± 0.1) kg pieces. The number of inclusions extracted by the method (using a minimum mesh of 20 μm), and the number of all inclusions of 20 μππι or more observed with an optical microscope (100 × magnification) Is converted to the number of

* 5: The defect rate is calculated by the following formula.

Thin plate: Slipper flaw generation rate on the plate surface [= (total length of slipper flaws / coil length) X 100 (%)].

Thick plate: UST defect occurrence rate or separation occurrence rate on the product sheet [= (number of sheets with defects Z total number of sheets inspected) XI 0 0 (%) In addition, in the fracture surface observation after the Charpy test, It was confirmed whether separation occurred.

In the column of the defect occurrence rate of the thick plate, if the defect is a UST defect, (UST) is indicated, and if the defect is a separation defect, (SPR) is indicated.

Steel pipe: UST defect occurrence rate at the welded portion of the oil country tubular goods [= (number of defective pipes / total number of inspected pipes) X 100 (%)].

* 6: V-notch Charpy impact test value in the rolling direction at 120 ° C. Average value of 5 test pieces.

* 7: Aperture value in the thickness direction of the product plate at room temperature [= (cross-sectional area of fractured part after tensile test / cross-sectional area of test specimen before test) X I 0 0 (%)

} o

91

6ειοοο contract zdf / iDd LLZWi OZ OAV Table 2

No. Inclusion composition * 3, inass% Maximum cluster-diameter Class-number Defect incidence Impact absorption Plate thickness direction

A1 ₂ 0 ₃ REM oxides # 4, mu * 4, number / kg * 5,% Energy / gravel ,, ^ Seung 6, J aperture * 7,% Invention Example A1 96.3 0.5 62 1.2 0.20 one invention example A2 96.6 2.4 ≤20 0.0 0.11 '--Invention A3 94.3 3.9 ≤20 0.0 0.08-One Invention A4 84.8 6.4 ≤20 0.0 0.26--Invention A5 90.3 7.3 ≤20 0.0 0.18-Invention A6 87.1 9.8 ≤20 0.0 0.22- one

A7 87.8 11.3 ≤20 0.0 0.25--Invention example A8 83.8 14.4 52 0.7 0.10--Invention example A9 90.7 0.5 65 2.0 '0.23--Invention example A10 91.0 6.6 ≤20 0.0 0.26--Invention example All 96.2 0.6 48 1.1 0.21- I Invention example A12 96.8 2.3 ≤20 0.0 0.20

Invention example A13 94.3 3.9 ≤20 0.0 0.09-One Invention example A14 84.8 6.4 ≤20 0.0 0.15-Invention example A15 91.6 6.0 ≤20 0.0 0.11--Invention example A16 88.4 8.4 ≤20 0.0 0.12 One-Invention example A17 90.0 9.0 ≤20 0.0 0.16 1-1 Invention example A18 87.1 11.1 ≤20 0.0 0.08--Invention example A19 78.6 12.6 31 0.1 0.11 1-1

A20 82.8 14.8 42 0.8 0.12-Invention example A21 94.9 1.9 43 1.0-1 39.8-1 Invention example A22 96.6 2.4 ≤20 0.0-40.2-Invention example A23 93.1 5.1 ≤20 0.0-1 36.5-Invention example A24 84.3 6.9 ≤20 0.0 9. l (UST)-one invention A25 86.0 11.6 23 0.1 4.8 (SPR)--invention A26 82.4 14.4 43 0.6 one 58.5 invention A27 98.5 0.5 59 1.0 0-one invention A28 93.7 4.5 ≤20 0.0 0.0-one invention A29 83.3 7.9 ≤20 0.0 0.2-One Invention A30 85.0 12.6 46 0.2 0.1--Invention A31 83.5 13.3 31 0.2 0.2 One Invention A32 84.0 15.0 65 1.2 0.2-One Comparative Bl 98.2 0.0 172 5.6 0.8-One Comparative B2 91.0 0.2 115 3.1 0.6--Comparative example B3 80.4 17.3 105 3.5 1.2-One Comparative example B4 74.9 22.0 284 7.5 1.4--Comparative example B5 83.7 13.1 152 3.3 0.7 One

Comparative Example B6 99.0 0.0 181 6.8 1 21.6

Comparative Example B7 98.0 0.2 103 2.5 26.5

Comparative Example B8 72.1 19.2 172 4.8 22.3

Comparative Example B9 99.0 0.0 186 7.3 21.5 (UST)

Comparative example BIO 98.0 0.2 108 3.0 13.6 (SPR)

Comparative example Bll 72.1 19.2 167 4.3 31.0 Comparative example B12 97.6 0.0 126 5.7 1.2

Comparative Example B13 91.1 0.2 101 2.9 1.4

Comparative Example B14 80.7 16.9 168 3.7 1.1 (Example 2 ')

The molten steel was blown in a converter of 270 t, and thereafter, the steel was adjusted to a predetermined carbon concentration and tapped. After adjusting to the target molten steel composition in the secondary refining and deoxidizing in A1, the EM, Ce, La, and misted metal (for example, mass ⁰ /. Ce: 45%, La : 35%, Pr: 6%, Nd: 9%, alloy consisting of unavoidable impurities) or alloy of misch metal, Si and Fe (Fe-Si—30% REM) ). Table 3 shows the resulting composition of molten steel.

The molten steel with the component composition shown in Table 3 was produced by a vertical bending type continuous forming machine at a forming speed of 1.0 to 1.8 mZmin and the molten steel temperature in the tundish.

It was manufactured under the condition of 20 to 580 ° C. to produce a piece having a thickness of 245 mm and a width of 200 to 220 mm.

(4) The maximum diameter of one cluster, the number of clusters, and the clogging status of the immersion nozzle after fabrication were investigated for the sample taken from the piece. The results are as shown in Table 4.

Table 4 confirms that the present invention significantly reduces product defects caused by alumina clusters.

The meanings of * 1 to * 4 in Tables 3 and 4 are as follows.

* 1: R EM (all R EM) is the sum of Ce, La, Pr, and Nd. R EM and T.O are the analysis values of the molten steel sample collected within 1 minute after the addition of R EM.

* 2: MM: Missing metal. In mass%, Ce: 45%, La:

An alloy consisting of 35%, Pr: 6%, Nd: 9%, and unavoidable impurities. MMS i: REM—Si—Fe alloy. Composition: REM: 30%, Si: 30%, balance Fe.

* 3: The maximum cluster diameter measurement method is (1 ± 0.1) kg kg The inclusions extracted from the piece by slime electrolysis (using a minimum mesh of 20 μm) were photographed with a stereoscopic microscope (× 40), and the average of the major and minor diameters of the photographed inclusions was calculated for all The maximum value of the average value obtained from inclusions was defined as the maximum cluster diameter.

The number of clusters is the number of inclusions extracted (by using a minimum mesh of 20 μπι) from pieces of (1 ± 0.1) kg by slime electrolysis and observed with an optical microscope (100 ×). The number of all inclusions of 20 / Ζm or more was converted to the number per 1 kg.

* 4: After fabrication, the thickness of the inclusions on the inner wall of the immersion nozzle was measured. Based on the average value of the thickness at 10 points in the circumferential direction, the nozzle clogging status was classified into the following levels.

〇: Adhesion thickness less than 1 mm

△: Adhesion thickness l to 5 mm

X: Adhesion thickness more than 5 mm

Table 3

Table 4

No. Maximum cluster-diameter Cluster-number Immersion nozzle * 3, μm * 3, pieces / kg Blocking status * 4 Invention example A1 62 1.2 O Invention example A2 ≤20 0.0 O Invention example A3 ≤20 0.0 〇 Invention example A4 ≤20 0.0 O Invention A5 ≤20 0.0 発明 Invention A6 ≤20 0.0 O Invention A7 ≤2Q 0.0 O Invention A8 52 0.7 〇 Invention A9 65 0.9 発明 Invention A10 ≤20 0.0 〇 Invention All 48 1.1発明 Invention A12 ≤20 0.0 〇 Invention A13 ≤20 0.0 〇 Invention A14 ≤Z0 0.0 発明 Invention A15 ≤20 0.0 O Invention A16 ≤20 0.0 〇 Invention A17 ≤20 0.0 〇 Invention A18 ≤20 0.0 o Invention example A19 31 0.1 〇 Invention example A20 42 0.8 〇 Invention example A21 43 1.0 発明 Invention example A22 ≤20 0.0 〇 Invention example A23 ≤20 0.0 発明 Invention example A24 ≤20 0.0 〇 Invention example A25 23 0.1 o Invention example A26 43 0.6 o Invention A27 59 1.0 〇 Invention A28 ≤20 0.0 発明 Invention A29 ≤20 0.0 発明 Invention A30 46 0.2 発明 Invention A31 31 0.2 o Invention A32 65 1.2 〇 Comparative Bl 172 5.6 X Comparative B2 115 3.1 △ Comparative example B3 105 3.5 △ Comparative example B4 284 7.5 X Comparative example B5 181 6.8 X Comparative example B6 103 2.5 Δ Comparative example Β7 172 4.8 X Comparative example B8 176 6.3 X Comparative example B9 98 2.0 △ Comparative example BIO 177 5.3 X Comparative example Bll 126 5.7 X Comparative Example B12 101 2.9 Δ Comparative example B13 168 3.7 X (Example 3)

The molten steel was blown in a converter of 270 t, and thereafter, the steel was adjusted to a predetermined carbon concentration and tapped. After adjusting to the target molten steel composition by secondary refining and deoxidizing with A1, REM, Ce, La, misch metal (for example, mass ⁰ /. Ce: 45%, La: 35%, Pr: 6%, Nd: 9%, alloy consisting of unavoidable impurities), or alloy of misted metal, Si and Fe · (Fe—Si—30% REM) Was added in the form of Table 5 shows the resulting composition of molten steel.

The molten steel having the composition shown in Table 5 was produced by a vertical bending continuous casting machine at a forming speed of 1.0 to: 1.8 mZm in, and the temperature of the molten steel in the tundish was 150 to 180 ° C. Under these conditions, a piece having a thickness of 245 mm and a width of 1200 to 220 mm was produced.

Thereafter, the strip was subjected to hot rolling, pickling, and, if necessary, cold rolling, and a quality inspection was performed. The thickness after hot rolling is 2 to 100 mm, and the thickness after cold rolling is 0.2 to 1.8 mm. (4) The maximum diameter of one cluster, the number of clusters, the defect occurrence rate, the pot nozzle clogging status, etc. were investigated for the samples taken from the pieces. The results are as shown in Table 6.

Table 6 confirms that the present invention significantly reduces product defects caused by alumina clusters.

The meanings of * 1 to * 7 in Tables 5 and 6 are as follows. '

* 1: Total REM is the sum of REM present in inclusions and REM dissolved in steel. A 1-g sample was cut out from the center of a molten steel sample 30 mm in diameter and 60 mm in height collected by a tundish, and then inductively coupled plasma-mass spectrometer (ICP-MS: Inductively Coupled Plasma M) ass S p REM (total of Ce, La, Pr, and Nd) was analyzed by ectrometry, and this was taken as the total REM.

The lower limit of analysis of the mass spectrometer is 0.1 lpm.

* 2: Solid solution EM was analyzed as follows. That is, after the inclusions in the steel are discharged to the sample surface by cold crucible melting, the sample lg is cut out from the center of the sample without inclusions by a drill, and REM (C e, La, Pr, Nd) was analyzed, and this was defined as the solid-solution REM.

A 90 g steel slab was cut out from the center of a molten steel sample with a diameter of 30 mm and a height of 60 mm sampled with a tundish and melted with a cold crucible. The dissolution was performed in Ar—2% H ₂ gas. The case where the EM element is qualitatively detected even below the lower limit of analysis is shown in the table as <0.1 ppm.

The details of cold crucible lysis are reported in, for example, CAMP-ISIJ, 14 (201), p. 817.

* 3: The method for measuring the maximum cluster diameter is as follows: (1) 0.1 kg of a piece of slime was extracted by slime electrolysis (using a minimum mesh of 20 μm) and photographed with a stereomicroscope. Then, the average value of the major axis and minor axis of the photographed inclusion was calculated for all the inclusions, and the maximum value of the average was defined as the maximum cluster diameter.

The number of clusters is the number of inclusions extracted by using the slime electrolysis method (using a minimum mesh of 20 μm) from a piece of (1 ± 0.1) kg, and observed with an optical microscope (100 times). The number of all inclusions of 20 μm or more was converted to the number per kg.

* 4: The defect rate is calculated by the following formula.

Thin plate: Slipper flaw generation rate on the plate surface [= (total length of slipper flaw coil length) X 100 (%)]. Thick plate: UST defect occurrence rate or separation occurrence rate on product sheet [= (number of sheets with defects 総数 total number of inspected sheets) XI 0 0 (%) In addition, in the fracture surface observation after the Charpy test, It was confirmed whether separation occurred.

Steel pipe: U S で defect occurrence rate [= (number of defective pipes 総数 total number of inspected pipes) X I 00 (%)] at the welded portion of the oil country tubular goods.

* 5: V-notch impact test value in the rolling direction at-20 ° C. Average value of 5 test pieces.

* 6: Draw value in the thickness direction of the product plate at room temperature [-(Cross-sectional area of fractured part after tensile test Z Cross-sectional area of test specimen before test) X I 0 0 (%)

* 7: Pot nozzle clogging conditions were as follows: なし was not blocked, △ was blocked but 铸 did not reduce the production speed, and X decreased the production speed due to blockage.

Z

Cl000 / l700Zdf / X3d ■ n contract OA Table 6

No. Maximum class diameter Turaster-Number of defects Occurrence of absorption Impact absorption Plate thickness direction Pot nozzle's occlusion * 3, μm * 3, fli / kg * 4,% Energy '-* 5, J Aperture value * 6,% Status * 7 Invention example A1 200.0 0.20 1-〇 Invention example A2 20 0.0 0.11--O Invention example A3 200.0 0.08--o Invention example A4 25 0.2 0.26-〇 Invention example A5 46 0.7 0.18 1 o Invention example A6 81 1.6 0.22 one o Invention example A7 42 0.6 0.25 one-o Invention example A8 20 0.0 0.10 one-o Invention example A9 23 0.1 0.23-one o Invention example A10 <20 0.0 0.26--〇 Invention example All 31 0.4 0.21 --o Invention example A12 200.0 0.20 1-〇 Invention example A13 20 0.0 0.09--o Invention example A14 21 0.2 0: 15-発明 Invention example A15 65 1.1 0.11-発明 Invention example M6 21 0.3 0.12 1 o Invention Example A17 48 0.5 0.16--〇 Inventive example A18 20 20 0.0 0.08--o Inventive example A19 20 0.0 0.11 11 o Inventive example A20 20 0.0 0.12-o Inventive example A21 24 0.4-39.8 1 o Inventive example A22 20 0.0-40.2-o Invention example A23 <20 0.0-36.5-〇 Invention example A24 2 5 0.3 4.6 (UST) 1-〇 Invention A25 49 0.7 9.3 (SPR)--o Invention A26 93 1.8-58.5 発明 Invention A27 38 0.5 0.00--〇 Invention A28 200.0 0.00 1-〇 Invention A29 gu 20 0.0 0.20-〇 Invention example A30 gu 20 0.0 0.10 one 一 Invention example A31 27 0.2 0.20 one-発明 Invention example A32 gu 20 0.0 0.20 one-比較 Comparative example Bl 152 5.6 0.80-one Δ Comparative example B2 115 3.1 0.60 --Δ Comparative example B3 127 2.5 0.56--△ Comparative example B4 158 3.9 0.60--X Comparative example B5 232 3.3 0.70--X Comparative example B6 134 6.8 1 21.6, 1mm Comparative example B7 193 2.5 '-26.5 Example B8 155 4.8 22.3 X Comparative B9 122 2.1 16.3 (UST) Δ Comparative BIO 201 3.0 23.6 (SP) X Comparative Bll 172 4.3 31.0 Δ Comparative B12 166 5.7 1.7 Δ Comparative B13 120 2.9 1.4 X Comparative B14 152 3.5 1.6 mm Comparative Example B15 217 3.7 1.1 X [Industrial applicability]

According to the present invention, it is possible to obtain a steel material that has been deoxidized using A 1 and that has very few surface flaws and internal defects due to coarse alumina clusters in the final product.

Further, according to the present invention, it is possible to prevent the alumina in the molten steel from adhering to the immersion nozzle in the continuous production.

Therefore, the present invention is to provide a steel material with few alumina clusters that has eliminated the conventional problems in steel deoxidized using A 1, and greatly contributes to industrial development.

Claims

The scope of the claims

1. A steel material that has been deoxidized using A1 and made of molten steel to which one or more rare earth elements (REM) of Ce, La, Pr, and Nd have been added. hand,

The content of the REM oxide in the oxide inclusions mainly composed of the EM oxide with alumina is 0.5% or more and 15% or less in mass% based on the oxide inclusions.

A steel material with less alumina clusters. .

2. A steel material which is deoxidized using A1 and is made of molten steel to which one or more rare earth elements (REM) of Ce, La, Pr and Nd are added. ,

The content of the REM oxide in the oxide-based inclusions mainly composed of alumina and the REM oxide is 0.5% or more and 15% or less by mass% based on the oxide inclusions.

A steel material with less alumina clusters.

3. A steel material that has been deoxidized using A1 and forged into molten steel to which one or more rare earth elements (REM) of Ce, La, Pr, and Nd have been added. hand,

The total amount of REM is at least 0.1 ppm and less than 10 ppm, and the amount of solid solution REM is less than 1 ppm

A steel material with less alumina clusters.

4. The steel material is represented by mass%, C: 0.005 to 1.5%, Si: 0.05 to 1.2%, Mn: 0.05 to 3.0%, P: 0.001 to 0.1%, S: 0.01 to 0.05%, A1: 0.00 5 to; L. 5%, T. O: 80 ppm or less, with the balance being Fe and inevitable wood pure matter. A steel material having less alumina clusters as described.

5. The steel material further contains, by mass%, Cu: 0:! To 1.5%, Ni: 0.1 to 10.0%, Cr: 0.1 to: LO 0.0%. 5. The steel material having a small amount of alumina clusters according to claim 4, comprising one or more of Mo: 0.05 to 1.5%.

6. The steel material further contains, by mass%, Nb: 0.05 to 0.1%, V: 0.05 to 0.3%, Ti: 0.001 to 0. 6. The steel material having a small amount of alumina clusters according to claim 4 or 5, wherein the steel material contains 25% of one or more kinds.

7. The steel according to any one of claims 4 to 6, wherein the steel material further contains B: 0.0005 to 0.005% by mass%. Steel material with less alumina cluster.

8. The steel material according to any one of claims 1 to 3, wherein the maximum diameter of the alumina cluster obtained by slime extraction of the steel material is 100 µππ or less.

9. The steel material having a small amount of alumina clusters according to claim 8, wherein in the alumina clusters, the number of alumina clusters of 20 μπι or more is 2 / kg or less.