JP4710150B2 - Hot rolling method for ultra low carbon steel - Google Patents

Description

【００２５】
ここで、ＨＳＢは、図２に示す如く、脱スケール装置１３の中でも、被圧延材の加熱炉抽出後の搬送履歴からして、最初に設けられたホットスケールブレーカ、Ｒ１−１、２、３は、それぞれ粗圧延機スタンドＲ１の１、２、３回目、Ｒ２−１、２、３は、それぞれ粗圧延機スタンドＲ２の１、２、３回目、Ｒ３は粗圧延機スタンドＲ３（１回目のみ）をそれぞれ示す。
【００２６】
本来この脱スケール装置の使用パターン（以下、脱スケールパターンと称する）は、該被圧延材１２の属性、主として材質、例えば金属中のＣ含有量が質量％で０．０１％未満の極低炭素鋼であるとか、同０．０１％以上０．１％未満の低炭素鋼であるとか、同０．１％以上０．５％未満の中炭素鋼であるとか、同０．５％以上の高炭素鋼であるとか、あるいはＣｒを含有量にして質量％で５％以上含有するとか、Ｎｉを０．５％以上含有するとかいった材質により、経験的に予め被圧延材１２の圧延前に適宜決定され、図１中に符号３８で示される設定装置内に設定され、記憶されている。そして該被圧延材１２が熱間圧延ラインに抽出されるごとに、個々の被圧延材１２の属性設定データとして紐付けされて、該被圧延材１２の搬送、圧延処理の進行とともに該被圧延材１２に伴って熱間圧延ライン上を仮想的に進行していく。該被圧延材１２が進行してくると、それが到着した設備においては、図示しないホットメタルディテクタ等により、これを捉え、前述の紐付けされた属性設定データに従って処理が行われる。脱スケール装置における脱スケール水の噴射はこれに従う。
【００２７】
ここでもしいま、表１（１）のような脱スケール装置の使用パターンで本来脱スケールが行われる極低炭素鋼の被圧延材１２が、加熱炉１０内で過加熱になったとする。本発明の実施の形態とは、１つはこの過加熱の程度に応じ、適宜、脱スケール水を噴射する箇所を増やす、というものである。
【００２８】
例えば、脱スケール水を噴射する箇所を１箇所増やすと、仕上圧延機の入側温度に換算して１０℃の被圧延材１２の温度降下が得られることが経験的にわかっていた、とすると、もしも、加熱炉からの抽出時点における被圧延材１２の温度が、仕上圧延機の入側温度に換算して、２０℃高くなると予測された場合、例えば表１（２）に示すように、脱スケール水を噴射する箇所を、本来の脱スケールパターンに対し、２箇所増やせば良い。逆に、加熱炉からの抽出時点における被圧延材１２の温度が、仕上圧延機の入側温度に換算して、２０℃低くなると予測された場合、例えば表１（３）に示すように、脱スケール水を噴射する箇所を、本来の脱スケールパターンに対し、２箇所減らせば良い。ここで１の位未満の端数は切り捨てるなり切り上げるなり適宜決定してよい。また、どこの脱スケール水を噴射する箇所を増やしたり減らしたりするか、は表１（２）や（３）の例に示すものに限るものではなく、適宜決めれば良い。また、ここでは３／４連続のタイプの熱間圧延ラインを例に取り説明したが、熱間圧延ラインは図５（ａ）（ｂ）（ｃ）のいずれによるものであっても、粗圧延のどの箇所、あるいはどの段階、あるいはどのパスで脱スケール水を噴射するしない、の脱スケールパターンの変更は適宜行うことができるから、熱間圧延ラインは図５（ａ）（ｂ）（ｃ）のいずれによるものであっても、各タイプに応じ、本発明の実施の形態は適宜修正して適用可能である。この設定が図１中４８で示される脱スケールパターン設定装置にて設定され、脱スケール装置の側は実際にそれに従って、脱スケール水の噴射、非噴射を制御される。
【００２９】
このような要領で、過加熱や加熱不足の程度に応じ、適宜、脱スケール水を噴射する箇所を増やしたり減らしたりしていくように脱スケールパターンを設定するのである。
【００３０】
ここで、加熱不足の際に脱スケール水を噴射する箇所を減らし過ぎると、ついには１箇所も脱スケール水を噴射する箇所がなくなって脱スケールが行われない、という事態を回避するため、最低１箇所とかｎ箇所とか、脱スケール水を噴射する箇所の最低数限度を設けた方が賢明である。
【００３１】
仕上圧延機の入側温度に換算した値で決めることについては特に理由はなく、ここでは仕上圧延機の入側温度が当業者間で慣用されている被圧延材１２の温度管理指標だから、これで決めているにすぎず、以上の説明の例はあくまで一つの例である。よって、仕上圧延機の入側温度に限らず、加熱炉抽出時の被圧延材１２の温度のほか、使用者の都合によりまたはその他の状況に応じて適宜他の被圧延材１２の温度指標を使っても良い。いずれにせよ、バーニングスケールやエッジシームの発生の有無は、被圧延材１２の加熱温度と相関があることは過去の経験からわかっているため、何らかの被圧延材１２の粗圧延中温度に相関のある温度指標を使う。
【００３２】
ここでは、上記の説明の例に登場した被圧延材１２の仕上圧延機の入側温度を温度指標にするもの、として以下に話を続けるが、加熱炉１０からの抽出時点における被圧延材１２の温度が、仕上圧延機の入側温度に換算して、どれだけになるか、も経験的な方法、あるいは詳説しない前記搬送時間スケジュール予測装置３２により、予測する。
【００３３】
経験的な方法とは、例えば、加熱炉からの抽出時点における被圧延材１２の温度と、仕上圧延機の入側温度と、の実績的な値が、２つのケースで既知であったとすると、その中間の加熱炉からの抽出時点における被圧延材１２の温度である被圧延材１２がきた場合に、仕上圧延機の入側温度を線形補完して予測する、という方法である。例えば、
（１）加熱炉からの抽出時点における被圧延材１２の温度が１２４０℃である場合に仕上圧延機の入側温度が１０６０℃
（２）加熱炉からの抽出時点における被圧延材１２の温度が１１００℃である場合に仕上圧延機の入側温度が１０３０℃
であることが、実績的な値として経験的にわかっていた場合、もしも加熱炉からの抽出時点における被圧延材１２の温度が上記（１）（２）の中間である１１７０℃の被圧延材１２がきた場合には、仕上圧延機の入側温度も上記（１）（２）の中間である１０４５℃と予測するようにすることである。このロジックは簡単に数式化できるので省略するが、機能的には図１中４６で示される位置にくる。
【００３４】
ここで、加熱炉からの抽出時点における被圧延材１２の温度は、従来から使用されている、次に述べるような差分計算などの方法により求めるのが１つの方法である。図３に模式的に示すように、被圧延材１２は複数のスキッドレール２４上に該スキッドレール２４と直交する方向に配置され、被圧延材１２の幅方向（図１における炉内搬送方向を示す矢印方向）に、加熱炉入口から出口に向かってステップ的に進行するようになっている。そして、図示しない加熱炉内温度計は常時加熱炉の炉壁温度を測定している。一方、温度分布計算装置４４においては、例えば、図３に示すような仮想的なメッシュに被圧延材１２を分割した場合における各格子点２６上の温度を差分計算によって求め、図３中、被圧延材１２の中央部における各格子点２６の温度を全点で平均するなどして、最初にいった加熱炉からの抽出時点における被圧延材１２の温度とすればよい。もちろん、本発明の実施の形態に用いることのできる方法はこれに限るものではなく、メッシュ中のある代表点の温度を以って最初にいった加熱炉からの抽出時点における被圧延材１２の温度としてもよいし、あるいは考え方を変え、加熱炉内の抽出口近くに図示しない被圧延材１２の表面温度を実測するための温度計を別途設置し、これによる被圧延材１２の表面温度実測値を以って最初にいった加熱炉からの抽出時点における被圧延材１２の温度とするなどしてもよい。
【００３５】
尚、脱スケール水の圧力は、ポンプ圧で１０〜３０ＭＰaが好適であり、脱スケール装置１３の噴射位置から、被圧延材表面までの距離は１００〜３００ｍｍが好適である。
【００３６】
１０ＭＰa未満あるいは３００ｍｍ超では、脱スケール水の被圧延材表面への衝突圧が十分でなく、脱スケール性が悪化し、仕上圧延後の被圧延材にまでスケールが残存するため１０ＭＰa以上、３００ｍｍ以下がよい。
【００３７】
一方、３０ＭＰaを超えると、ポンプ電力が嵩んで経済的でなく、１００ｍｍを下回ると、被圧延材に反りが生じた場合に機械的に衝突し、脱スケール装置を破損する問題がある。よって、３０ＭＰa以下、１００ｍｍ以上がよい。
【００３８】
（実施例）
以下の実施例では、いずれも、質量％でＣ：０．００５％、Ｐ：０．０２５％、Ｓ：０．００８％、残部Ｆｅ及び不可避的不純物から成る鋼を被圧延材として使用した。
【００３９】
（実施例１）
加熱炉からの抽出時点における被圧延材１２の温度が、目標１１００℃に対し実績１１９３℃になって抽出された。仕上圧延機の入側温度に換算して、目標１０３０℃に対し、１０５０℃と、２０℃高くなると予測された。
【００４０】
ここで、本発明の実施の形態の脱スケールパターンである表１（２）を使用した。表１（２）に示すように、脱スケール水を噴射する箇所を、本来の脱スケールパターンである表１（１）に対し、２箇所増やした。
【００４１】
脱スケール水を噴射する箇所を１箇所増やすと、仕上圧延機の入側温度に換算して１０℃の被圧延材１２の温度降下が得られることが経験的にわかっていたからである。
【００４２】
その結果は、図４に示す如く、従来なら２７秒程度の待機・空冷時間が発生すべきところ、実際には待機・空冷時間は全く発生しなかった。また、従来１．７０％の割合で発生していたバーニングスケールが、本発明の適用により、０．２３％まで発生が抑制された。
【００４３】
（実施例２）
加熱炉からの抽出時点における被圧延材１２の温度が、目標１１００℃に対し実績１００７℃になって抽出された。仕上圧延機の入側温度に換算して、目標１０３０℃に対し、１０１０℃と、２０℃低くなると予測された。
【００４４】
ここで、本発明の実施の形態の脱スケールパターンである表１（３）を使用した。表１（３）に示すように、脱スケール水を噴射する箇所を、本来の脱スケールパターンである表１（１）に対し、２箇所減らした。
【００４５】
脱スケール水を噴射する箇所を１箇所減らすと、仕上圧延機の入側温度に換算して１０℃の被圧延材１２の温度上昇が得られることが経験的にわかっていたからである。
【００４６】
その結果は、従来０．４８％の割合で発生していたエッジシームが、本発明の適用により、０．１２％まで発生が抑制された。
【００４７】
なお、上記（実施例１）、（実施例２）においては、加熱炉からの抽出時点における被圧延材１２の温度である加熱温度実績としては、先述の差分法を用いたメッシュ格子の平均値や代表値を計算により求めて使用してもよいし、あるいは加熱炉内の抽出口近くに、図示しない被圧延材１２の表面温度を実測するための温度計を別途設置し、これによる被圧延材１２の表面温度実測値を使用してもよい。
【００４８】
【発明の効果】
本発明によれば、過加熱によるオシレーション待機・空冷時間の発生による生産能率の低下を抑制し、また、バーニングスケール、エッジシームといった表面品質不良が発生するのを抑制できる、という効果がある。
【図面の簡単な説明】
【図１】本発明を実施するための装置構成の例を示す、一部ブロック図を含む工程図
【図２】脱スケール装置の配置を示す図
【図３】加熱温度実績の計算法を説明するための斜視図
【図４】従来技術に対する本発明の効果を示すための線図
【図５】熱間圧延ラインの概要を説明するための工程図
【図６】加熱炉において過加熱が発生する状態を説明するための線図
【図７】エッジシームの発生メカニズムをイメージ的に示す斜視図
【符号の説明】
１０、１０Ａ〜１０Ｃ…加熱炉
１２、１２Ａ〜１２Ｉ…被圧延材
１３…脱スケール装置
１４…粗圧延機
Ｒ１〜Ｒ４…粗圧延機スタンド
１５…ファーネスコイラ
１６…仕上圧延機
Ｆ１〜Ｆ７…仕上圧延機スタンド
３０…冷却制御装置
３２…搬送時間スケジュール予測装置
３８…設定装置
４４…温度分布計算装置
４６…仕上圧延機入側温度予測装置
４８…脱スケールパターン設定装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for hot rolling of ultra-low carbon steel, and in particular, the temperature in hot rough rolling of ultra-low carbon steel that is a material to be rolled is adjusted using a descaling device, such as a burning scale and an edge seam. The present invention relates to a method for suppressing the occurrence of various quality defects.
[0002]
[Prior art]
Hot rolling means that a metal material is heated to several hundred to several hundreds of degrees Celsius, then extracted onto a hot rolling line and rolled with a roller while being conveyed. The hot rolling line is a type called a stickel mill shown in FIG. 5 (a), a type called semi-continuous shown in FIG. 5 (b), and a rough rolling mill 14 and a finishing rolling mill 16 are separately provided. The rolling mill performs reciprocating rolling, and the finishing rolling mill performs unidirectional rolling, and the type referred to as 3/4 continuous shown in (c), and includes a plurality of rough rolling mills 14 of the type (b) (in many cases) 4), some of which (one in many cases) are reciprocally rolled, and the rest are unidirectionally rolled (3 out of 4 are not limited to unidirectional, for example 3 2 of the two are unidirectional, etc.).
[0003]
These hot rolling lines are generally provided with a descaling device 13 for the purpose of removing oxide scale that continues to be generated on the surface of the rolled material 12 during rolling of the rolled material 12 due to the self-heating of the rolled material. It is. In many cases, a plurality of descaling apparatuses are installed as appropriate in order to remove scales generated one after another as the rolled material 12 is rolled, and the principle is mostly high-pressure water jets.
[0004]
In the figure, 10A, 10B and 10C are heating furnaces, 12 is a material to be rolled, 15 is a furnace coiler, R1 to R4 are rough rolling mill stands, F1 to F7 are finishing mill stands, and 18A and 18B are coilers.
[0005]
Here, although it moves to the talk about the problem which became the opportunity of this invention, generally in hot rolling, as shown in FIG. 6, several to-be-rolled material 12A, 12B ... 12I ... is in the heating furnace 10. As shown in FIG. Is heated continuously. On the other hand, the heating temperature target for each material to be rolled is set individually for each material to be rolled in order to ensure the mechanical quality such as elongation and strength of each material to be rolled and the quality required for surface properties. The
[0006]
Therefore, as shown in the figure, for example, when the material to be rolled 12E to 12I having a heating temperature target of 1100 ° C. is heated following the material to be rolled 12A to 12D having a heating temperature target of 1150 ° C. at the time of extraction. Occurs. Then, even if the setting of the furnace temperature is changed in the material to be rolled (for example, 12E, 12F) in which the heating temperature target is rapidly changed, the heating temperature result of the material to be rolled does not immediately follow, and the heating temperature target is set. It becomes an overheating state exceeding.
[0007]
In addition, even when the entire hot rolling line has been interrupted for a long time due to an unexpected trouble, the material to be rolled is still overheated.
[0008]
The overheating at the time of extraction in the heating furnace is also increased and deviated even at the temperature of the material to be rolled on the entry side of the finishing mill after leaving the roughing mill. In this way, when the temperature of the material to be rolled on the entrance side of the finish rolling mill exceeds a certain temperature, it is finish-rolled at a temperature higher than planned as it is, and the above-mentioned mechanical quality of the product after finish rolling can be ensured. In addition to the fact that the oxide scale is generated on the surface of the material to be rolled due to recuperation during finish rolling and finish rolling in that state, the oxide scale is pushed into the material to be rolled. There may be a case where the surface quality is called poor.
[0009]
Therefore, conventionally, after passing through the final stand of the roughing mill, the material to be rolled is put on standby by oscillation that causes the rolled material after rough rolling (hereinafter also referred to as a sheet bar) to reciprocate on the entry side of the finishing mill. After the finish rolling, the material to be rolled is air-cooled to an appropriate temperature at which good mechanical quality of the product can be obtained, and then the material to be rolled is subjected to finish rolling. Therefore, the conveyance of the material to be rolled is delayed by the time required for the oscillation, and the rolling efficiency is greatly reduced.
[0010]
Now, the following is the opposite case. For example, the rolled materials 12E to 12I having a heating temperature target of 1150 ° C. may be heated following the rolled materials 12A to 12D having a heating temperature target of 1100 ° C. Arise. Then, in the material to be rolled (for example, 12E, 12F) where the heating temperature target becomes discontinuous, the heating temperature result after the heating temperature target change does not immediately follow, and is in a state of insufficient heating below the heating temperature target. .
[0011]
Due to insufficient heating at the time of extraction in the heating furnace, the temperature of the material to be rolled during rough rolling is lowered. Thus, when the temperature of the material to be rolled during rough rolling is low, surface quality defects called edge seams may occur due to the following actions.
[0012]
This defect is particularly prominent in hot rolling of extremely low carbon steel. The difference is clear when compared to low carbon steel (mild steel). The cause of the occurrence of the edge seam is that, when the actual heating temperature is low, as shown in FIG. 7, the corner portion 12Z of the material 12 to be rolled is locally strongly cooled and lowered in the rough rolling initial stage. Furthermore, by locally strongly cooling with descaling water, the portion is transformed and the crystal grains are coarsened, and as a result of the subsequent rough rolling, the material to be rolled 12 is elongated in the longitudinal direction by the roll 14R. It is said that a difference in elongation occurs compared to the crystal, resulting in a streak shape.
[0013]
In the case of ultra-low carbon steel, the transformation temperature is higher than that of low-carbon steel, and the corner part is likely to undergo local transformation even when roughly rolled at the same temperature as low-carbon steel (soft steel), and directly above and below the transformation temperature. The difference in deformation resistance is large, the difference in elongation in the longitudinal direction of the material to be rolled is conspicuous at the corner portion and the portion that is not, and the scale growth rate in the air is small, and the portion where the edge seam occurs is difficult to peel off, It is estimated that the edge seam generated by the rough rolling is likely to remain in the finished rolled product.
[0014]
As a prior art regarding such a problem, there is JP-A-51-86050. In JP-A-51-86050, using a spray cooling device installed in the rough rolling process, the material to be rolled is cooled in the range of 50 to 100 ° C., and the standby and air cooling time on the finishing mill entry side is greatly increased. It has been proposed to shorten it.
[0015]
[Problems to be solved by the invention]
However, the method according to Japanese Patent Application Laid-Open No. 51-86050 is limited to the production of high-strength steel sheets, and the cooling conditions are, for example, setting of a flag for injecting or not injecting cooling water, Since the conditions such as the passing speed are also set and fixed in advance, the heating temperature target discontinuity generated by the connection method of the material to be rolled in the heating furnace as described in FIG. There was a problem that it was not possible to cope with overheating, etc. that occurred due to long interruptions in the entire rolling line.
[0016]
The present invention has been made to solve the problems of the prior art, and one is rolling with high efficiency by reducing wasted time lost due to standby and air cooling due to oscillation at the entry side of the finishing mill. The problem is to enable operation, and the other is to suppress the occurrence of surface quality defects such as burning scales and edge seams.
[0017]
[Means for Solving the Problems]
In the hot rolling of ultra-low carbon steel, the present invention changes the descaling pattern in the rough rolling with respect to the initial setting, and in the case of overheating, the location where the descaling water is injected is initially set and stored. Increased with respect to the descaling pattern that has been achieved, and in the case of insufficient heating, the portion to which descaling water is sprayed is reduced with respect to the descaling pattern that is set and stored in the initial stage , thereby solving the above problem It is.
Here, a lower limit can be provided in the number of locations where the descaling water is injected.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
First, the ultra-low carbon steel is steel composed of C: less than 0.01%, P: 0.050% or less, S: 0.050% or less, the balance Fe and unavoidable impurities. The mass% of C is the same as the chemical composition of the hot-rolled mild steel sheet and steel strip specified in JIS G 3131 except that the content is one digit lower than that of general steel (also called low carbon steel) called mild steel. You may think.
[0020]
As the hot rolling line, a 3/4 continuous type hot rolling line (derivative of the type shown in FIG. 5C) as shown in FIG.
[0021]
In FIG. 1, 30 is a conveyance time schedule prediction device 32 called mill pacing among parties, a setting device 38 for initial setting of a finish rolling mill entry side rolling material temperature target value and a descaling pattern, and a temperature distribution calculation device. 44, a cooling control device including a finishing rolling mill entry side temperature prediction device 46 and a descaling pattern setting device 48.
[0022]
The point of the present invention is how to use the descaling device as indicated by reference numeral 13 in FIG.
[0023]
If it has just been heated to an appropriate temperature, descaling is originally performed using the descaling device usage pattern as shown in Table 1 (1) (initial setting: stored in the setting device 38 in FIG. 1). It is assumed that there is a material 12 to be rolled. This is just an example of a very low carbon steel.
[0024]
[Table 1]

[0025]
Here, as shown in FIG. 2, the HSB is a hot scale breaker first provided in the descaling apparatus 13 based on the conveyance history after extraction of the material to be rolled in the heating furnace, R1-1, 2, 3 Are the first, second, and third times of the roughing mill stand R1, and R2-1, 2, and 3 are the first, second, and third times of the roughing mill stand R2, and the R3 is the roughing mill stand R3 (only the first time, respectively). ) Respectively.
[0026]
Originally, the use pattern of this descaling apparatus (hereinafter referred to as descaling pattern) is attributed to the material 12 to be rolled, mainly material, for example, extremely low carbon whose C content in the metal is less than 0.01% by mass%. Steel, low carbon steel of 0.01% or more and less than 0.1%, medium carbon steel of 0.1% or more and less than 0.5%, or 0.5% or more of the same. Depending on the material such as the high carbon steel, or the Cr content of 5% or more by mass, or the Ni content of 0.5% or more, the material to be rolled 12 is empirically pre-rolled beforehand. And is set and stored in the setting device denoted by reference numeral 38 in FIG. Each time the material to be rolled 12 is extracted to the hot rolling line, it is linked as attribute setting data of each material to be rolled 12, and the material to be rolled is conveyed along with the conveyance of the material to be rolled 12 and the progress of the rolling process. Along the material 12, it virtually proceeds on the hot rolling line. When the material to be rolled 12 advances, the facility where it arrives catches this with a hot metal detector (not shown) and the like, and processing is performed according to the above-described attribute setting data associated with the material. The spray of descaling water in the descaling device follows this.
[0027]
Here, it is assumed that the material 12 to be rolled of ultra-low carbon steel that is originally descaled in the usage pattern of the descaling apparatus as shown in Table 1 (1) is overheated in the heating furnace 10. One of the embodiments of the present invention is to increase the number of places to which descaling water is jetted, depending on the degree of overheating.
[0028]
For example, suppose that it has been empirically known that, when the number of places to which descaling water is injected is increased by one, a temperature drop of the rolled material 12 of 10 ° C. can be obtained in terms of the inlet temperature of the finishing mill. If the temperature of the material to be rolled 12 at the time of extraction from the heating furnace is predicted to increase by 20 ° C. in terms of the entry side temperature of the finishing mill, for example, as shown in Table 1 (2), What is necessary is just to increase the location which injects descaling water 2 places with respect to an original descaling pattern. Conversely, when the temperature of the material to be rolled 12 at the time of extraction from the heating furnace is predicted to be 20 ° C. lower when converted to the entry side temperature of the finishing mill, for example, as shown in Table 1 (3), What is necessary is just to reduce the location which injects descaling water two places with respect to an original descaling pattern. Here, the fraction less than 1 may be appropriately determined by rounding down or rounding up. In addition, the location where the descaling water is increased or decreased is not limited to those shown in the examples of Table 1 (2) and (3), and may be determined as appropriate. In addition, although a description has been given here taking a 3/4 continuous type hot rolling line as an example, the hot rolling line is roughly rolled regardless of which of FIGS. 5A, 5B, and 5C. Since the descaling pattern in which the descaling water is not sprayed in any part, in any stage, or in any pass of the hot rolling line can be appropriately performed, the hot rolling line is shown in FIGS. 5 (a) (b) (c). The embodiment of the present invention can be applied with appropriate modifications according to each type. This setting is set by a descaling pattern setting device indicated by 48 in FIG. 1, and the descaling device side is actually controlled to inject and uninject descaling water accordingly.
[0029]
In such a manner, the descaling pattern is set so as to increase or decrease the number of locations where the descaling water is jetted as appropriate according to the degree of overheating or insufficient heating.
[0030]
Here, in order to avoid a situation in which descaling is not performed because there is no place to inject descaling water when there is too few places to inject descaling water at the time of insufficient heating. It is wise to set a minimum number of places where one or n places or descaling water is injected.
[0031]
There is no particular reason for deciding on the value converted into the inlet side temperature of the finishing mill. Here, the inlet side temperature of the finishing mill is a temperature management index of the material 12 to be rolled, which is commonly used by those skilled in the art. The above description is just an example. Therefore, not only the entrance temperature of the finishing mill, but also the temperature of the material to be rolled 12 when extracting from the heating furnace, the temperature index of the other material to be rolled 12 is appropriately set according to the convenience of the user or according to other circumstances. You can use it. In any case, since it is known from past experience that the occurrence of burning scale and edge seam has a correlation with the heating temperature of the material 12 to be rolled, there is a correlation with the temperature during rough rolling of the material 12 to be rolled. Use temperature index.
[0032]
Here, the following description will be continued on the assumption that the temperature at the entry side of the finish rolling mill of the rolled material 12 that has appeared in the example described above is used, but the rolled material 12 at the time of extraction from the heating furnace 10 is used. It is predicted by an empirical method or the transport time schedule prediction device 32 that will not be described in detail how much the temperature is converted to the inlet side temperature of the finishing mill.
[0033]
The empirical method is, for example, that the actual values of the temperature of the material 12 to be rolled at the time of extraction from the heating furnace and the entry side temperature of the finish rolling mill are known in two cases. In this method, when the material to be rolled 12, which is the temperature of the material to be rolled 12 at the time of extraction from the intermediate heating furnace, comes, the entrance temperature of the finishing mill is linearly complemented and predicted. For example,
(1) When the temperature of the material 12 to be rolled at the time of extraction from the heating furnace is 1240 ° C., the entry side temperature of the finishing mill is 1060 ° C.
(2) When the temperature of the material 12 to be rolled at the time of extraction from the heating furnace is 1100 ° C., the entrance side temperature of the finishing mill is 1030 ° C.
If it is empirically known as the actual value, the material to be rolled at 1170 ° C. in which the temperature of the material to be rolled 12 at the time of extraction from the heating furnace is intermediate between the above (1) and (2) When 12 comes, the entry side temperature of the finishing mill is predicted to be 1045 ° C., which is intermediate between the above (1) and (2). Since this logic can be easily expressed as a mathematical expression, it is omitted, but functionally, it is located at a position indicated by 46 in FIG.
[0034]
Here, one method is to obtain the temperature of the material to be rolled 12 at the time of extraction from the heating furnace by a method such as a difference calculation described below, which has been conventionally used. As schematically shown in FIG. 3, the material to be rolled 12 is arranged on a plurality of skid rails 24 in a direction orthogonal to the skid rail 24, and the width direction of the material to be rolled 12 (the in-furnace conveyance direction in FIG. In the direction indicated by the arrow), the process proceeds stepwise from the entrance to the exit of the heating furnace. A heating furnace thermometer (not shown) constantly measures the furnace wall temperature of the heating furnace. On the other hand, in the temperature distribution calculation device 44, for example, the temperature on each lattice point 26 when the material to be rolled 12 is divided into virtual meshes as shown in FIG. What is necessary is just to make it the temperature of the to-be-rolled material 12 at the time of extraction from the first heating furnace by averaging the temperature of each lattice point 26 in the center part of the rolled material 12 at all points. Of course, the method that can be used in the embodiment of the present invention is not limited to this, and the material 12 to be rolled at the time of extraction from the heating furnace first with the temperature of a certain representative point in the mesh is used. Alternatively, a thermometer for actually measuring the surface temperature of the material to be rolled 12 (not shown) may be installed near the extraction port in the heating furnace, and the surface temperature of the material to be rolled 12 may be actually measured. It may be set as the temperature of the material 12 to be rolled at the time of extraction from the first heating furnace with a value.
[0035]
The pressure of descaling water is preferably 10 to 30 MPa in terms of pump pressure, and the distance from the spray position of the descaling apparatus 13 to the surface of the material to be rolled is preferably 100 to 300 mm.
[0036]
If the pressure is less than 10 MPa or more than 300 mm, the impact pressure of the descaling water on the surface of the rolled material is not sufficient, the descaling property deteriorates, and the scale remains on the rolled material after finish rolling. Is good.
[0037]
On the other hand, if it exceeds 30 MPa, the pump power is bulky and not economical, and if it is less than 100 mm, there is a problem that when the material to be rolled is warped, it mechanically collides and damages the descaling device. Therefore, 30 MPa or less and 100 mm or more are preferable.
[0038]
(Example)
In the following examples, in each case, steel consisting of C: 0.005%, P: 0.025%, S: 0.008%, the balance Fe and unavoidable impurities was used as the material to be rolled.
[0039]
Example 1
The temperature of the material 12 to be rolled at the time of extraction from the heating furnace reached 1193 ° C. with respect to the target 1100 ° C., and was extracted. It was predicted that it would be 20 ° C higher than 1050 ° C with respect to the target of 1030 ° C when converted to the inlet temperature of the finishing mill.
[0040]
Here, Table 1 (2), which is the descaling pattern of the embodiment of the present invention, was used. As shown in Table 1 (2), the number of locations where the descaling water was injected was increased by two locations relative to Table 1 (1), which is the original descaling pattern.
[0041]
This is because it has been empirically known that when the number of places where the descaling water is injected is increased by one, a temperature drop of the material to be rolled 12 of 10 ° C. can be obtained in terms of the entrance temperature of the finishing mill.
[0042]
As a result, as shown in FIG. 4, in the past, standby / air cooling time of about 27 seconds should be generated, but actually no standby / air cooling time occurred at all. In addition, the burning scale, which was generated at a rate of 1.70% in the past, was suppressed to 0.23% by the application of the present invention.
[0043]
(Example 2)
The temperature of the material 12 to be rolled at the time of extraction from the heating furnace was 1007 ° C. with respect to the target 1100 ° C. and extracted. It was predicted that the temperature would be 1010 ° C. and 20 ° C. lower than the target 1030 ° C. in terms of the inlet temperature of the finishing mill.
[0044]
Here, Table 1 (3), which is a descaling pattern according to the embodiment of the present invention, was used. As shown in Table 1 (3), the number of places where the descaling water was jetted was reduced by two from Table 1 (1), which is the original descaling pattern.
[0045]
This is because it has been empirically known that if one place where the descaling water is injected is reduced, the temperature rise of the rolled material 12 of 10 ° C. can be obtained in terms of the inlet temperature of the finishing mill.
[0046]
As a result, the generation of edge seams, which conventionally occurred at a rate of 0.48%, was suppressed to 0.12% by the application of the present invention.
[0047]
In the above (Example 1) and (Example 2), the average value of the mesh grid using the above-mentioned difference method is used as the heating temperature record that is the temperature of the material 12 to be rolled at the time of extraction from the heating furnace. Or a representative value may be obtained by calculation or used, or a thermometer for actually measuring the surface temperature of the material to be rolled 12 (not shown) is installed near the extraction port in the heating furnace, and the material to be rolled by this Actual surface temperature values of the material 12 may be used.
[0048]
【The invention's effect】
According to the present invention, there is an effect that it is possible to suppress a decrease in production efficiency due to generation of oscillation standby / air cooling time due to overheating, and it is possible to suppress the occurrence of surface quality defects such as a burning scale and an edge seam.
[Brief description of the drawings]
FIG. 1 is a process diagram including a partial block diagram showing an example of an apparatus configuration for carrying out the present invention. FIG. 2 shows an arrangement of a descaling apparatus. FIG. 3 explains a method for calculating a heating temperature record. FIG. 4 is a diagram for illustrating the effect of the present invention over the prior art. FIG. 5 is a process diagram for explaining the outline of a hot rolling line. FIG. 6 is that overheating occurs in a heating furnace. [Fig. 7] A perspective view conceptually showing an edge seam generation mechanism [Explanation of symbols]
DESCRIPTION OF SYMBOLS 10, 10A-10C ... Heating furnace 12, 12A-12I ... Rolled material 13 ... Descaling device 14 ... Rough rolling mill R1-R4 ... Rough rolling mill stand 15 ... Furnace coiler 16 ... Finishing mill F1-F7 ... Finishing Rolling mill stand 30 ... cooling control device 32 ... conveying time schedule prediction device 38 ... setting device 44 ... temperature distribution calculation device 46 ... finishing mill entry side temperature prediction device 48 ... descaling pattern setting device

Claims (2)

In the hot rolling of ultra-low carbon steel, the descaling pattern in the rough rolling is changed from the initial setting, and in the case of overheating, the location where the descaling water is injected is set at the initial setting and stored. Increased with respect to the scale pattern, in the case of insufficient heating, the location where the descaling water is jetted is reduced with respect to the descaling pattern set and stored in the initial stage. Rolling method.   The hot rolling method for ultra-low carbon steel according to claim 1, wherein a lower limit is provided for the number of locations to which the descaling water is injected.

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