JP3617295B2 - Control method of secondary cooling zone in continuous casting - Google Patents
Control method of secondary cooling zone in continuous casting Download PDFInfo
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- JP3617295B2 JP3617295B2 JP08111398A JP8111398A JP3617295B2 JP 3617295 B2 JP3617295 B2 JP 3617295B2 JP 08111398 A JP08111398 A JP 08111398A JP 8111398 A JP8111398 A JP 8111398A JP 3617295 B2 JP3617295 B2 JP 3617295B2
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- cooling
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Description
【０００１】
【発明の属する技術分野】
本発明は、連続鋳造における２次冷却帯の制御方法に係り、特に、１流体によるスプレー冷却あるいは水と空気の２流体によるミスト冷却が行われている、連続鋳造の２次冷却帯に用いるのに好適な、鋳造速度を低下させることなく、広い範囲にわたって２次冷却帯の冷却能力（即ち熱伝達係数）を変化させることが可能な、連続鋳造における２次冷却帯の制御方法に関する。
【０００２】
【従来の技術】
鉄鋼の連続鋳造において、溶鋼は、取鍋からタンディッシュを経て鋳型に入り１次冷却され、鋳型内で鋳片の表面のみ凝固した状態で、２次冷却帯に引き出され、１流体によるスプレー冷却もしくは水と空気の２流体によるミスト冷却により冷却され、内部まで凝固する。
【０００３】
この２次冷却に際しては、鋳片の内部割れを防止するためには、冷却を強くする必要がある。そのためには、鋳造速度を低下させることが効果的であるが、生産性が阻害される。
【０００４】
鋳造速度を低下させない方法としては、冷却水量を増加して冷却能力を向上させることが考えられるが、設備の制約上の問題から、無制限に冷却水量を増やすことはできない。
【０００５】
逆に、鋼種によっては、鋳片表面の割れが問題になることが多い。この表面割れを防止する対策としては、２次冷却において緩冷却を実施する必要がある。その手段の１つとして、ミストスプレーによる冷却が行われることも多いが、冷却水量が多くなった場合には、ミストと水スプレーの差異が小さくなり、結果的に表面割れ防止効果は小さくなってしまう。
【０００６】
従って、表面割れ防止のための緩冷却方法としては、冷却水量を減じることにより冷却能力を低下させている。しかしながら、冷却水量を減じた場合には、ノズルの特性によっては水量分布の均一性が保てなくなり、鋳片の不均一冷却が生じる。又、鋳造速度によっては内部割れが生じることとなるため、鋳造速度を低下させる必要が生じ、生産性を阻害することとなる。
【０００７】
冷却能力の指標である熱伝達係数αとスプレー水の水量密度Ｗｄの関係については、例えば日本鉄鋼協会 共同研究会 熱経済技術部会 冷却技術研究小委員会報告書「鉄鋼製造プロセスにおける冷却技術」（昭和６３年８月）の第１１３頁〜第１２２頁に、図３に例示する如く、前記熱伝達係数αがスプレー水の水量密度Ｗｄの関数であり、水量密度Ｗｄが大きいほど熱伝達係数α、即ち、冷却能力が高くなることが示されている。
【０００８】
又、スプレー水の水温（冷却水温）Ｔｗが熱伝達係数αに与える影響に関しては、「鉄と鋼」第５２年（１９６６）第１０号の第８７頁〜第８９頁に、水量密度６００ｌ／ｍ２ ・分レベルにおいて、図４及び次式に示す如く、冷却水温Ｔｗが高くなると熱伝達係数αが小さくなる（１℃上昇で０．７５％低下）ことが示されている。
【０００９】
α∝（１−０．００７５Ｔｗ） …（１）
【００１０】
【発明が解決しようとする課題】
しかしながら、前者では、冷却水温の影響が考慮されておらず、又、後者においては、水量密度の範囲が狭く、一般的には適用できないという問題点を有していた。
【００１１】
本発明は、前記従来の問題点を解決するべくなされたもので、鋳造速度を低下させることなく、広い範囲に亘って２次冷却帯の冷却能力を制御することを課題とする。
【００１２】
【課題を解決するための手段】
本発明は、目標の熱伝達係数αが得られるよう、次式
α∝１−（β0＋γ×ｌogＷｄ）×ΔＴｗ…（２）
（ここで、Ｗｄは、水量密度、ΔＴｗは、基準水温Ｔｗｏとの温度差、β0は、熱伝達係数αに対する冷却水温Ｔｗの影響度を表わす影響係数βの基準値、γは、該影響係数βの傾き）
に従って、冷却水温Ｔｗを変化させることにより、連続鋳造における２次冷却帯の冷却能力を制御するようにして、前記課題を解決したものである。
【００１５】
発明者等が、ミスト冷却能力を評価するオフライン実験を行った際に、図１に示す如く、冷却水温Ｔｗを変化させたときに、冷却能力の指標となる熱伝達係数αが変化し、その程度は、水量密度Ｗｄに依存することが明らかになった。これらの関係を解析したところ、水量密度Ｗｄが大きいほど、冷却水温Ｔｗによる冷却能力の変化が大きく、図２に示す如く、熱伝達係数αに対する冷却水温Ｔｗの影響度を表わす影響係数βも大きくなることが判明した。図１の縦軸は、基準温度Ｔｗｏ＝４０℃における熱伝達係数を基準とした場合のαの比率である。
【００１６】
（２）式は、この図１及び図２に示すような関係に基づいて導出したものである。
【００１７】
【発明の実施の形態】
以下、本発明の実施形態を詳細に説明する。
【００１８】
本実施形態は、連続鋳造の２次冷却にあたり、冷却を強くしなければならない場合には、（２）式に従って、冷却水の水温Ｔｗを低くして冷却に使用することにより、熱伝達係数αを大きくし、冷却能力を向上させる。又、緩冷却をしなければならない場合には、冷却水温Ｔｗを（２）式に従って高くして冷却に使用することにより、熱伝達係数αを小さくし、冷却能力を低下させる。
【００１９】
このようにして、冷却水温Ｔｗを調整することによって、冷却能力を調整する。
【００２０】
【実施例】
鋳片厚２２０ｍｍ、鋳片幅８００〜１９００ｍｍで、炭素含有量０．０８重量％から０．２重量％の中炭素鋼スラブを連続鋳造設備で鋳造する際に、スプレー水量密度５０〜１００００ｌ／分・ｍ２ 、気水比５〜３０に調整可能な２次冷却帯での２次冷却において、従来は、コーナーかぎ割れ＋コーナー近傍表面疵を含むコーナー部割れ発生率が、５０枚中５枚、即ち１０％であり、内部割れ発生率は、５０枚中３枚、即ち６％であったのが、本発明を適用したところ、コーナー部割れ発生率及び内部割れ発生率、共に、５０枚中１枚、即ち２％に大幅に低減できた。
【００２１】
【発明の効果】
本発明によれば、鋳造速度を低下させることなく、広い範囲に亘って２次冷却帯の冷却能力を調整することが可能となる。従って、生産性を阻害することなく、鋳片の内部割れや表面割れを防止して、良好な鋳片を得ることが可能となる。
【図面の簡単な説明】
【図１】本発明の原理を説明するための、水量密度を変えたときの冷却水温と、基準温度における熱伝達係数αを基準とした場合のαの比率の関係の例を示す線図
【図２】同じく、水量密度と熱伝達係数に対する冷却水温の影響度の関係を示す線図
【図３】従来から知られていた水量密度と熱伝達係数の関係の例を示す線図
【図４】同じく、ある水量密度における冷却水温と熱伝達係数の関係の例を示す線図
【符号の説明】
α…熱伝達係数
Ｗｄ…水量密度
Ｔｗ…冷却水温
β…熱伝達係数αに対する冷却水温Ｔｗの影響度を表わす影響係数
γ…影響係数βの傾き[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling a secondary cooling zone in continuous casting, and more particularly, to a secondary cooling zone for continuous casting in which spray cooling with one fluid or mist cooling with two fluids of water and air is performed. It is related with the control method of the secondary cooling zone in continuous casting which can change the cooling capacity (namely, heat transfer coefficient) of a secondary cooling zone over a wide range, without reducing the casting speed.
[0002]
[Prior art]
In continuous casting of steel, molten steel enters the mold through a tundish from a ladle, is primarily cooled, and is drawn into the secondary cooling zone in a state where only the surface of the slab is solidified in the mold. Or it cools by the mist cooling by two fluids, water and air, and it solidifies to the inside.
[0003]
In this secondary cooling, it is necessary to strengthen the cooling in order to prevent internal cracking of the slab. For this purpose, it is effective to reduce the casting speed, but the productivity is hindered.
[0004]
As a method that does not decrease the casting speed, it is conceivable to increase the cooling water amount to improve the cooling capacity. However, the amount of cooling water cannot be increased without limitation due to the problem of equipment limitations.
[0005]
Conversely, depending on the steel type, cracking of the slab surface often becomes a problem. As a measure for preventing this surface crack, it is necessary to perform slow cooling in the secondary cooling. As one of the means, cooling by mist spray is often performed, but when the amount of cooling water increases, the difference between mist and water spray becomes small, and as a result, the effect of preventing surface cracking becomes small. End up.
[0006]
Therefore, as a slow cooling method for preventing surface cracks, the cooling capacity is reduced by reducing the amount of cooling water. However, when the amount of cooling water is reduced, the uniformity of the water amount distribution cannot be maintained depending on the characteristics of the nozzles, resulting in uneven cooling of the slab. Further, depending on the casting speed, internal cracks occur, so that it is necessary to reduce the casting speed, which impedes productivity.
[0007]
Regarding the relationship between the heat transfer coefficient α, which is an index of cooling capacity, and the water density Wd of the spray water, for example, the Japan Steel Association Joint Research Group Thermal Economic Technology Subcommittee Report “Cooling Technology in Steel Manufacturing Processes” ( As shown in FIG. 3, the heat transfer coefficient α is a function of the water flow density Wd of the spray water, and the heat transfer coefficient α increases as the water flow density Wd increases. That is, it is shown that the cooling capacity is increased.
[0008]
Regarding the influence of the water temperature (cooling water temperature) Tw of the spray water on the heat transfer coefficient α, “Iron and Steel” 52nd (1966) No. 10, pages 87 to 89, the water density is 600 l / At the m 2 · min level, as shown in FIG. 4 and the following equation, it is shown that the heat transfer coefficient α decreases as the cooling water temperature Tw increases (lowers by 1 ° C. by 0.75%).
[0009]
α∝ (1-0.0075Tw) (1)
[0010]
[Problems to be solved by the invention]
However, in the former, the influence of the cooling water temperature is not taken into consideration, and in the latter, the range of the water density is narrow and there is a problem that it cannot be generally applied.
[0011]
The present invention has been made to solve the above-described conventional problems, and an object thereof is to control the cooling capacity of the secondary cooling zone over a wide range without reducing the casting speed.
[0012]
[Means for Solving the Problems]
In the present invention, in order to obtain the target heat transfer coefficient α, the following equation αｄ1- (β0 + γ × logWd) × ΔTw (2)
(Wd is the water density, ΔTw is the temperature difference from the reference water temperature Two, β0 is the reference value of the influence coefficient β representing the degree of influence of the cooling water temperature Tw on the heat transfer coefficient α, and γ is the influence coefficient. β slope)
Accordingly by changing the cooling water temperature Tw, in the so that to control the cooling capacity of the secondary cooling zone in a continuous casting, is obtained by solving the above problems.
[0015]
When the inventors conducted an off-line experiment for evaluating the mist cooling capacity, as shown in FIG. 1, when the cooling water temperature Tw is changed, the heat transfer coefficient α serving as an index of the cooling capacity is changed. It became clear that the degree depends on the water density Wd. As a result of analysis of these relationships, the greater the water density Wd, the greater the change in cooling capacity due to the cooling water temperature Tw, and the larger the influence coefficient β representing the degree of influence of the cooling water temperature Tw on the heat transfer coefficient α, as shown in FIG. Turned out to be. The vertical axis in FIG. 1 is the ratio of α when the heat transfer coefficient at the reference temperature Two = 40 ° C. is used as a reference.
[0016]
Equation (2) is derived based on the relationship as shown in FIGS.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0018]
In the present embodiment, when the cooling must be strengthened in the secondary cooling of the continuous casting, the heat transfer coefficient α is obtained by lowering the cooling water temperature Tw and using it for cooling according to the equation (2). Increase the cooling capacity. In the case where slow cooling is required, the cooling water temperature Tw is increased according to the equation (2) and used for cooling, thereby reducing the heat transfer coefficient α and reducing the cooling capacity.
[0019]
In this way, the cooling capacity is adjusted by adjusting the cooling water temperature Tw.
[0020]
【Example】
When casting a medium carbon steel slab with a cast slab thickness of 220 mm and a cast slab width of 800 to 1900 mm and a carbon content of 0.08 wt% to 0.2 wt% in a continuous casting facility, the spray water density is 50 to 10,000 l / min.・ In secondary cooling in a secondary cooling zone that can be adjusted to m 2 and a steam-water ratio of 5 to 30, conventionally, the incidence of corner cracks + corner cracks including surface flaws in the vicinity of corners is 5 out of 50 sheets. That is, 10%, and the internal crack occurrence rate was 3 out of 50 sheets, that is, 6%. When the present invention was applied, both the corner crack generation rate and the internal crack generation rate were 50 sheets. One of them, that is, 2% can be greatly reduced.
[0021]
【The invention's effect】
According to the present invention, the cooling capacity of the secondary cooling zone can be adjusted over a wide range without reducing the casting speed. Therefore, it is possible to obtain a good slab by preventing internal cracks and surface cracks of the slab without impairing productivity.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a relationship between a cooling water temperature when a water amount density is changed and a ratio of α when a heat transfer coefficient α at a reference temperature is a reference for explaining the principle of the present invention; FIG. 2 is a diagram showing the relationship between the water density and the degree of influence of the cooling water temperature on the heat transfer coefficient. FIG. 3 is a diagram showing an example of the relationship between the water density and the heat transfer coefficient known from the past. Similarly, a diagram showing an example of the relationship between cooling water temperature and heat transfer coefficient at a certain water density [Explanation of symbols]
α ... heat transfer coefficient Wd ... water density Tw ... cooling water temperature β ... influence coefficient γ representing the degree of influence of cooling water temperature Tw on heat transfer coefficient α ... inclination of influence coefficient β
Claims (1)
α∝１−（β0＋γ×ｌogＷｄ）×ΔＴｗ
（ここで、Ｗｄは、水量密度、ΔＴｗは、基準水温Ｔｗｏとの温度差、β0は、熱伝達係数αに対する冷却水温Ｔｗの影響度を表わす影響係数βの基準値、γは、該影響係数βの傾き）
に従って、冷却水温Ｔｗを変化させることにより、連続鋳造における２次冷却帯の冷却能力を制御することを特徴とする連続鋳造における２次冷却帯の制御方法。In order to obtain the target heat transfer coefficient α, the following equation α∝1- (β0 + γ × logWd) × ΔTw
(Wd is the water density, ΔTw is the temperature difference from the reference water temperature Two, β0 is the reference value of the influence coefficient β representing the degree of influence of the cooling water temperature Tw on the heat transfer coefficient α, and γ is the influence coefficient. β slope)
The control method of the secondary cooling zone in the continuous casting is characterized by controlling the cooling capacity of the secondary cooling zone in the continuous casting by changing the cooling water temperature Tw according to the above.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08111398A JP3617295B2 (en) | 1998-03-27 | 1998-03-27 | Control method of secondary cooling zone in continuous casting |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08111398A JP3617295B2 (en) | 1998-03-27 | 1998-03-27 | Control method of secondary cooling zone in continuous casting |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11277208A JPH11277208A (en) | 1999-10-12 |
| JP3617295B2 true JP3617295B2 (en) | 2005-02-02 |
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| JP08111398A Expired - Fee Related JP3617295B2 (en) | 1998-03-27 | 1998-03-27 | Control method of secondary cooling zone in continuous casting |
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| JP5094154B2 (en) * | 2007-02-19 | 2012-12-12 | 株式会社神戸製鋼所 | Slab cooling method in continuous casting machine |
| JP4924104B2 (en) * | 2007-03-02 | 2012-04-25 | Ｊｆｅスチール株式会社 | Method for producing high Ni content steel slab |
| JP5907334B2 (en) * | 2011-09-05 | 2016-04-26 | Ｊｆｅスチール株式会社 | Continuous casting method for cast slabs |
| CN106270438B (en) * | 2016-08-30 | 2018-06-22 | 东北大学 | A kind of shell thickness Forecasting Methodology and system |
| CN113102714B (en) * | 2020-07-30 | 2021-12-03 | 北京科技大学 | Continuous casting cooling method for controlling peritectic steel slab corner cracks |
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1998
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| JPH11277208A (en) | 1999-10-12 |
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