WO2021256243A1 - Continuous casting method - Google Patents
Continuous casting method Download PDFInfo
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- WO2021256243A1 WO2021256243A1 PCT/JP2021/020838 JP2021020838W WO2021256243A1 WO 2021256243 A1 WO2021256243 A1 WO 2021256243A1 JP 2021020838 W JP2021020838 W JP 2021020838W WO 2021256243 A1 WO2021256243 A1 WO 2021256243A1
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- slab
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- steel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/124—Accessories for subsequent treating or working cast stock in situ for cooling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
Definitions
- the present invention relates to a continuous steel casting method that suppresses the occurrence of surface cracks in slabs in continuous casting.
- the hot ductility of the alloy steel slab is significantly reduced at the temperature near the Ar 3 transformation point where the solidified structure is transformed from the austenite phase to the ferrite phase.
- the surface temperature of the slab is controlled by secondary cooling to correct the temperature above the transformation point, or the solidified structure of the slab is controlled to a structure that is hard to crack. Is commonly done.
- the spray pipe near the corner of the slab is generally closed and the spray width is cut without cooling.
- Patent Document 1 As a method of controlling the solidification structure, for example, Patent Document 1, to start the secondary cooling of the slab immediately after withdrawal of the slab from the rectangular mold, once Ar 3 transformation of the surface temperature of the slab The time and slab surface to keep the slab surface temperature below the Ar 3 transformation point when cooling to a temperature below the point and then reheating to a temperature above the Ar 3 transformation point and then straightening the slab.
- a technique has been disclosed in which the solidified structure from the surface of the slab to a depth of at least 2 mm is made into a mixed structure of ferrite and pearlite with an unclear austenite grain boundary by setting the minimum temperature at which the temperature reaches to an appropriate range. Is
- the technique of spray width cutting is to stop the spray from the spray near the corner of the slab and prevent the corner temperature from dropping.
- the width of the slabs is wide in response to various needs in recent years, there is a problem that a large amount of capital investment is required to properly spray the corners of the slabs of all sizes.
- the corners of the slab are cooled from the two sides of the slab on the long side and the short side, so that supercooling is likely to occur.
- the corner temperature is lowered by radiative cooling even if the cooling spray is not sprayed.
- Patent Document 1 there is a concern about the influence of dripping water flowing along the slab after being sprayed onto the slab from the secondary cooling spray.
- the dripping water affects the cooling of the slab surface, so that it may be difficult to quantitatively control the slab surface temperature, for example, by heat transfer calculation.
- the present invention has been made in view of such circumstances, and an object of the present invention is to prevent surface cracks in a slab which has not been sufficiently eliminated by controlling the temperature of the slab by secondary cooling alone.
- the purpose is to propose a continuous casting method that surely suppresses and produces high quality slabs without corner cracks in particular.
- the inventors have found that surface cracking of a slab can be suppressed by suppressing a temperature drop at a corner of a slab during secondary cooling while using a mold having a casting space having an appropriate shape, and have conceived the present invention. ..
- the continuous casting method of the present invention that advantageously solves the above problems is a method of continuously casting steel, using a mold in which the chamfered shape of the mold corner portion satisfies the following equation (1), and the slab corner portion. It is characterized in that the average secondary cooling water amount density from directly under the mold to the lower straightening is 20 to 60 L / (min ⁇ m 2). 0.09 ⁇ C / L ⁇ 0.20 ... (1)
- C corner chamfer amount (mm)
- L Short side length of slab (mm) Represents.
- the component composition of the steel is C: 0.05 to 0.25% and Mn: 1.0 to 4.0% in mass%, and further Nb: A more preferable solution is to optionally have at least one selected from 0.01 to 0.1%, V: 0.01 to 0.1%, and Mo: 0.01 to 0.1%. It is thought that it can be.
- the temperature of the corners of the slab is controlled by secondary cooling while using a mold in which a casting space having an appropriate shape is partitioned, so that corner cracking of the continuously cast slab is prevented and high quality is achieved. It will be possible to provide slabs.
- the steel continuous casting method (steel piece manufacturing method) according to the embodiment of the present invention includes a step of casting while supporting the slabs drawn from the continuous casting mold by a plurality of pairs of rolls facing each other.
- the molten steel is primarily cooled with a mold.
- the slab is withdrawn from the mold at a predetermined drawing speed, and the slab is secondarily cooled while being supported by a plurality of pairs of rolls arranged in the casting direction to obtain a steel slab.
- a mold in which a casting space having an appropriate shape is partitioned is used, and it is appropriate in the cooling zone from directly under the mold to the bending back straightening point (lower straightening). It is important to go through a proper cooling pattern.
- the continuous casting machine used in the present embodiment is not particularly limited as long as it includes bending or bending back straightening from directly under the mold to carrying out the slab.
- the inventors observed surface cracks in the slabs cast by the curved continuous casting machine. Surface cracks in the slab were concentrated in and near the top corners. This is because tensile stress is generated during bending back correction.
- the upper surface side of the slab means the inside of the bending of the curved band of the curved continuous casting machine, that is, the long side surface side which is the upper surface of the horizontal band.
- the cracks were etched, the cracks propagated along the old austenite grain boundaries, so it was considered that the cracks occurred in the temperature range where the ferrite transformation started from austenite (generally called the embrittlement temperature), and the secondary cooling conditions were set. Experiments with various changes were conducted.
- the inventors focused on the shape of the slab. Since the conventional slab is rectangular and the corners are cooled from two surfaces, supercooling of the corners of the slab is likely to occur. We considered that changing the shape of the slab would change the cooling structure and suppress supercooling, and examined the appropriate slab shape by thermal stress analysis.
- the slab has a chamfered shape with the four corners of the rectangular cross section orthogonal to the casting direction removed, resulting in supercooling at the slab corners and stress load. It was found that the stress can be reduced. Then, in order to make the four corners of the slab into a chamfered shape, casting using a mold in which the four corners (right-angled portions) of the casting space, which is rectangular like a mold having a rectangular cross section, is removed into a right-angled triangular shape to form a chamfered shape. It is important to do.
- a mold having a casting space having such a chamfered shape is also referred to as a chamfer mold.
- the chamfered portion 4 of the chamfer mold is shown in the top view of the chamfer mold of FIG.
- the ratio of the right-angled triangle to the length a on the long side 2 side of the mold is the ratio b / a of the length b on the short side 3 side of the mold.
- a thermal analysis was performed on the effect of this ratio b / a on the overcooling of the corners of the slab. The calculation result is shown in FIG.
- this embodiment is suitable for application to steels having high embrittlement susceptibility to austenite to ferrite transformation.
- the composition of steel has C: 0.05 to 0.25% and Mn: 1.0 to 4.0% in mass%, and further Nb: 0.01 to 0.1%, V. It can be suitably applied when one or more selected from: 0.01 to 0.1% and Mo: 0.01 to 0.1% are arbitrarily possessed.
- the component composition is simply expressed as% in "mass%".
- Mn 1.0 to 4.0% If the Mn content is less than 1.0%, MnS, which is an embrittlement factor, is unlikely to be generated, so that there is no problem. If it is 1.0% or more, the embrittlement sensitivity becomes high, but if it exceeds 4.0%, the product becomes too strong, which is not desirable. Therefore, it is preferable to apply this embodiment in the case of a steel composition having a high embrittlement sensitivity and a Mn content of 1.0 to 4.0%.
- Nb 0.01 to 0.1%
- V 0.01 to 0.1%
- Mo 0.01 to 0.1%
- Nb, V and Mo contribute to the improvement of steel strength.
- the content of each element is less than 0.01%, it is difficult to form carbonitride which is an embrittlement factor, so that there is no problem.
- it exceeds 0.1% the price of the alloy becomes high and the cost rises, and the performance becomes excessive more than necessary. Therefore, it is not desirable to add more than 0.1%.
- Example 1 Using a curved continuous casting machine, in mass%, C: 0.18%, Si: 1.4%, Mn: 2.8%, P: 0.020% or less, S: 0.003% or less, And Ti: Steel having a predetermined composition containing 0.020% was cast.
- the Ar 3 transformation point of this steel is 805 ° C.
- the casting conditions were in the range of a casting thickness of 220 mm, a casting width of 1000 to 1600 mm, and a casting speed of 1.20 to 1.80 m / min.
- the slab temperature when passing through the bent part (lower straightening) was confirmed by measuring with a thermocouple or a radiation thermometer.
- the slab After casting, the slab is subjected to color check (dye penetrant inspection) after removing oxides on the slab surface by shot blasting in order to facilitate observation of cracks on the slab surface. The presence or absence of cracks in the corners was investigated. Then, the corner crack occurrence rate was evaluated by the number of corner cracked slabs / the number of surveyed slabs ⁇ 100%. For the investigation of internal cracks, a cross-sectional sample perpendicular to the casting direction of the slab was cut out, milled, and then macro-etched with warm hydrochloric acid. The presence or absence of internal cracks was investigated using macro-etched photographs.
- Example 2 Next, in order to determine the relationship between the average secondary cooling water density applied to the corners of the slab until passing through the bent portion (lower straightening), corner cracks, and internal cracks, a test was conducted under the same steel grade and continuous casting conditions as in Example 1. Was carried out. The results are shown in Table 2.
- the average secondary cooling water density is less than 20 L / (min ⁇ m 2 ) (test Nos. 10 and 11), so that the corner temperature becomes Ar 3 or more and the corner cracks. Can be seen to be reduced.
- the thickness of the solidified shell near the corners is insufficient, causing internal cracking due to bulging. From this, it can be seen that it is not possible to suppress both corner cracking and internal cracking with a normal rectangular mold.
- a chamfer mold test Nos. 17 to 23
- Corner cracking could not be suppressed unless the density of the next cooling water was reduced to less than 20 L / (min ⁇ m 2 ), and internal cracking due to bulging could not be avoided.
- the chamfer molds (test Nos. 24 to 31) of the present embodiment were applied, the point that internal cracks occurred at less than 20 L / (min ⁇ m 2 ) (test Nos. 24 and 25) was the same. ..
- supercooling of the corners of the slab is suppressed in the average secondary cooling water density range (test No. 24 to 30) of 60 L / (min ⁇ m 2) or less, resulting in corner cracking. was able to prevent.
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- Organic Chemistry (AREA)
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Abstract
Description
すなわち、スプレー幅切りの技術は、鋳片コーナー部近傍のスプレーからの噴射を止め、コーナー温度の低下を防ぐものである。しかし、近年の様々なニーズに対応して鋳片の幅も多岐にわたるため、すべてのサイズの鋳片のコーナーを適切にスプレー幅切りするには多大な設備投資が必要になるという問題がある。それに加えて、鋳造速度が遅くなると、鋳片コーナー部はスラブの長辺側、短辺側の2面から冷却されるため過冷却になりやすい。そのうえ、連続鋳造機内での滞在時間が増えるため、冷却スプレーを噴射しなくとも輻射冷却によってコーナー温度が下がってしまうといった問題も生じる。 However, the above-mentioned prior art has the following problems.
That is, the technique of spray width cutting is to stop the spray from the spray near the corner of the slab and prevent the corner temperature from dropping. However, since the width of the slabs is wide in response to various needs in recent years, there is a problem that a large amount of capital investment is required to properly spray the corners of the slabs of all sizes. In addition, when the casting speed is slowed down, the corners of the slab are cooled from the two sides of the slab on the long side and the short side, so that supercooling is likely to occur. In addition, since the staying time in the continuous casting machine is increased, there is a problem that the corner temperature is lowered by radiative cooling even if the cooling spray is not sprayed.
0.09≦C/L≦0.20 ・・・(1)
ここで、C:コーナー面取り量(mm)、
L:鋳片短辺長さ(mm)
を表す。 The continuous casting method of the present invention that advantageously solves the above problems is a method of continuously casting steel, using a mold in which the chamfered shape of the mold corner portion satisfies the following equation (1), and the slab corner portion. It is characterized in that the average secondary cooling water amount density from directly under the mold to the lower straightening is 20 to 60 L / (min · m 2).
0.09 ≤ C / L ≤ 0.20 ... (1)
Here, C: corner chamfer amount (mm),
L: Short side length of slab (mm)
Represents.
C含有量が0.05~0.25%では特にオーステナイト粒が粗大化しやすい。したがって、脆化感受性の高い、C含有量が0.05~0.25%の鋼組成の場合に本実施形態を適用することが好ましい。 C: 0.05-0.25%
When the C content is 0.05 to 0.25%, the austenite grains are particularly liable to become coarse. Therefore, it is preferable to apply this embodiment in the case of a steel composition having a high embrittlement sensitivity and a C content of 0.05 to 0.25%.
Mn含有量が1.0%未満では脆化因子であるMnSが生成しにくいため問題にならない。1.0%以上では脆化感受性が高くなるが、4.0%超えでは製品が高強度になりすぎるため望ましくない。したがって、脆化感受性の高い、Mn含有量が1.0~4.0%の鋼組成の場合に本実施形態を適用することが好ましい。 Mn: 1.0 to 4.0%
If the Mn content is less than 1.0%, MnS, which is an embrittlement factor, is unlikely to be generated, so that there is no problem. If it is 1.0% or more, the embrittlement sensitivity becomes high, but if it exceeds 4.0%, the product becomes too strong, which is not desirable. Therefore, it is preferable to apply this embodiment in the case of a steel composition having a high embrittlement sensitivity and a Mn content of 1.0 to 4.0%.
Nb、VおよびMoは鋼の強度向上に寄与する元素であるが、その含有量がそれぞれ0.01%未満では脆化因子である炭窒化物を生成しにくいため問題とならない。一方で、0.1%超えでは、合金の値段が高くなりコストが上昇するうえ、必要以上に過剰性能となるため0.1%より多く添加することは望ましくない。 One or more selected from Nb: 0.01 to 0.1%, V: 0.01 to 0.1% and Mo: 0.01 to 0.1% Nb, V and Mo contribute to the improvement of steel strength. However, if the content of each element is less than 0.01%, it is difficult to form carbonitride which is an embrittlement factor, so that there is no problem. On the other hand, if it exceeds 0.1%, the price of the alloy becomes high and the cost rises, and the performance becomes excessive more than necessary. Therefore, it is not desirable to add more than 0.1%.
湾曲型連続鋳造機を用いて、質量%で、C:0.18%、Si:1.4%、Mn:2.8%、P:0.020%以下、S:0.003%以下、およびTi:0.020%を含有した所定の成分組成を持つ鋼を鋳造した。この鋼のAr3変態点は805℃である。鋳造条件は、鋳造厚み220mm、鋳造幅1000~1600mmおよび鋳造速度1.20~1.80m/minの範囲であった。なお、曲げ部(下部矯正)通過時の鋳片温度は、熱電対や放射温度計を用いて測定することで確認した。鋳造後の鋳片は、鋳片表面の割れの観察を容易にするために、ショットブラストにより鋳片表面の酸化物を除去し、その後、カラーチェック(染色浸透探傷試験)を行って、鋳片コーナー部の割れ有無を調査した。そして、コーナー割れ発生率として、コーナー割れ鋳片本数/調査鋳片本数×100%で評価した。内部割れの調査に関しては、鋳片の鋳造方向に垂直な断面サンプルを切り出し、フライス仕上げののち、温塩酸によりマクロエッチングを実施した。マクロエッチングの写真にて内部割れの有無を調査した。 (Example 1)
Using a curved continuous casting machine, in mass%, C: 0.18%, Si: 1.4%, Mn: 2.8%, P: 0.020% or less, S: 0.003% or less, And Ti: Steel having a predetermined composition containing 0.020% was cast. The Ar 3 transformation point of this steel is 805 ° C. The casting conditions were in the range of a casting thickness of 220 mm, a casting width of 1000 to 1600 mm, and a casting speed of 1.20 to 1.80 m / min. The slab temperature when passing through the bent part (lower straightening) was confirmed by measuring with a thermocouple or a radiation thermometer. After casting, the slab is subjected to color check (dye penetrant inspection) after removing oxides on the slab surface by shot blasting in order to facilitate observation of cracks on the slab surface. The presence or absence of cracks in the corners was investigated. Then, the corner crack occurrence rate was evaluated by the number of corner cracked slabs / the number of surveyed slabs × 100%. For the investigation of internal cracks, a cross-sectional sample perpendicular to the casting direction of the slab was cut out, milled, and then macro-etched with warm hydrochloric acid. The presence or absence of internal cracks was investigated using macro-etched photographs.
次に曲げ部(下部矯正)通過時までの鋳片コーナー部にかかる平均2次冷却水量密度とコーナー割れ、内部割れの関係を決定すべく実施例1と同様の鋼種、連続鋳造条件にて試験を実施した。結果を表2に示す。 (Example 2)
Next, in order to determine the relationship between the average secondary cooling water density applied to the corners of the slab until passing through the bent portion (lower straightening), corner cracks, and internal cracks, a test was conducted under the same steel grade and continuous casting conditions as in Example 1. Was carried out. The results are shown in Table 2.
2 長辺
3 短辺
4 面取り部 1
Claims (2)
- 鋼を連続鋳造する方法であって、鋳型コーナー部の面取り形状が下記(1)式を満足するような鋳型を用い、鋳片コーナー部にかかる鋳型直下から下部矯正までの平均2次冷却水量密度を20~60L/(min・m2)とすることを特徴とする連続鋳造方法。
0.09≦C/L≦0.20 ・・・(1)
ここで、C:コーナー面取り量(mm)、
L:鋳片短辺長さ(mm)
を表す。 This is a method of continuous casting of steel, using a mold whose chamfering shape at the corners of the mold satisfies the following formula (1), and the average secondary cooling water volume density from directly under the mold to the lower straightening applied to the corners of the slab. Is 20 to 60 L / (min · m 2 ), which is a continuous casting method.
0.09 ≤ C / L ≤ 0.20 ... (1)
Here, C: corner chamfer amount (mm),
L: Short side length of slab (mm)
Represents. - 前記鋼の成分組成が、質量%で、C:0.05~0.25%およびMn:1.0~4.0%を有し、さらに、Nb:0.01~0.1%、V:0.01~0.1%およびMo:0.01~0.1%のうちから選ばれる1種以上を任意に有することを特徴とする請求項1に記載の連続鋳造方法。 The composition of the steel is C: 0.05 to 0.25% and Mn: 1.0 to 4.0% in mass%, and further, Nb: 0.01 to 0.1%, V. The continuous casting method according to claim 1, wherein one or more selected from 0.01 to 0.1% and Mo: 0.01 to 0.1% are arbitrarily contained.
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KR1020227042643A KR20230006903A (en) | 2020-06-18 | 2021-06-01 | continuous casting method |
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CN202180040196.5A CN115697587A (en) | 2020-06-18 | 2021-06-01 | Continuous casting method |
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Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2002307149A (en) | 2001-04-11 | 2002-10-22 | Sumitomo Metal Ind Ltd | Continuous casting method |
JP2007331000A (en) * | 2006-06-15 | 2007-12-27 | Kobe Steel Ltd | Mold for continuous casting |
JP2015503450A (en) * | 2011-12-27 | 2015-02-02 | ポスコ | Continuous casting mold |
JP2015128776A (en) * | 2014-01-06 | 2015-07-16 | 三島光産株式会社 | Continuous casting mold |
JP2020066018A (en) * | 2018-10-23 | 2020-04-30 | 日本製鉄株式会社 | Mold for continuous casting and method for steel continuous casting |
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WO2006025349A1 (en) * | 2004-08-30 | 2006-03-09 | Showa Denko K.K. | Method and device for manufacturing metal material, and metal material and metal working material |
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Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2002307149A (en) | 2001-04-11 | 2002-10-22 | Sumitomo Metal Ind Ltd | Continuous casting method |
JP2007331000A (en) * | 2006-06-15 | 2007-12-27 | Kobe Steel Ltd | Mold for continuous casting |
JP2015503450A (en) * | 2011-12-27 | 2015-02-02 | ポスコ | Continuous casting mold |
JP2015128776A (en) * | 2014-01-06 | 2015-07-16 | 三島光産株式会社 | Continuous casting mold |
JP2020066018A (en) * | 2018-10-23 | 2020-04-30 | 日本製鉄株式会社 | Mold for continuous casting and method for steel continuous casting |
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