JP4552731B2 - Hot rolling method for steel strip - Google Patents

Hot rolling method for steel strip Download PDF

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JP4552731B2
JP4552731B2 JP2005099119A JP2005099119A JP4552731B2 JP 4552731 B2 JP4552731 B2 JP 4552731B2 JP 2005099119 A JP2005099119 A JP 2005099119A JP 2005099119 A JP2005099119 A JP 2005099119A JP 4552731 B2 JP4552731 B2 JP 4552731B2
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steel strip
cooling
bending
hot rolling
repeated bending
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JP2006272441A (en
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行宏 松原
敏樹 蛭田
栄二 遠山
聖司 太田
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JFE Steel Corp
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本発明は、従来に比べ高強度の熱延鋼帯を製造するための熱間圧延方法に関する。
The present invention relates to a hot rolling how for the production of hot rolled strip of high strength compared with the prior art.

鋼帯は、一般に、図3に示すような設備配置の熱間圧延ライン200にて熱間圧延される。
熱間圧延ライン200には、上流側から順に、加熱炉1、粗圧延機2、仕上圧延機3、水冷ゾーンを形成する冷却設備4、コイラ5a，5bが配置され、加熱炉1にて加熱後に抽出され、もしくは、加熱炉1を経ずに上工程から直送されてきたスラブ状の鋼片が、粗圧延機2にてシートバーと呼ばれる中間的な厚さ25ないし50ｍｍの鋼片にまで圧延され、しかる後に仕上圧延機3にて圧延されることで、熱延鋼帯10とされ、水冷ゾーンを形成する冷却設備４にて冷却が行われた後、5a，5bいずれか一方のコイラにコイル状に巻き取られる。符号11は、仕上圧延機3で加工された仕上圧延終了後の熱延鋼帯10（以下、鋼帯）の搬送方向である。 The steel strip is generally hot-rolled in a hot-rolling line 200 having an equipment arrangement as shown in FIG.
In the hot rolling line 200, a heating furnace 1, a rough rolling mill 2, a finish rolling mill 3, a cooling equipment 4 for forming a water cooling zone, and coilers 5a and 5b are arranged in order from the upstream side. The slab-like steel slab that was later extracted or sent directly from the upper process without going through the heating furnace 1 is turned into a steel slab having an intermediate thickness of 25 to 50 mm called a sheet bar in the roughing mill 2 After being rolled and then rolled in the finish rolling mill 3, it is made into a hot-rolled steel strip 10, cooled in the cooling equipment 4 that forms a water-cooling zone, and then one of the coilers 5a and 5b. Is wound into a coil. Reference numeral 11 denotes a conveyance direction of the hot-rolled steel strip 10 (hereinafter referred to as “steel strip”) after finishing rolling finished by the finish rolling mill 3.

このようにして製造される鋼帯の高強度化のため、従来から、結晶粒の微細化を図る熱間圧延方法が種々検討されている。その代表的なものとして、特許文献１などに開示されている、いわゆる制御圧延法がある。
制御圧延法の特徴は、再結晶温度よりも高温域にある段階にて、圧延を開始し、動的、あるいは、静的再結晶により、オーステナイト(以下、単にγと記す)粒を微細化すること、および、それよりも温度が低下しながらもいまだ未再結晶温度域にある段階にても、さらに圧延することで、γ粒内に転位などの格子欠陥を導入し、変態時にそこを起点とした変態核生成を促進させ、γ粒をさらに微細化すること、の2点により、変態後のフェライト(以下、単にαと記す)粒の結晶粒微細化を図る、というものである。 In order to increase the strength of steel strips manufactured in this way, various hot rolling methods for miniaturizing crystal grains have been studied. A typical example is a so-called controlled rolling method disclosed in Patent Document 1 or the like.
The feature of the controlled rolling method is that rolling is started at a stage where the temperature is higher than the recrystallization temperature, and austenite (hereinafter simply referred to as γ) grains are refined by dynamic or static recrystallization. In addition, even when the temperature is lower than that and still in the unrecrystallized temperature range, further rolling introduces lattice defects such as dislocations within the γ grains, and this is the starting point during transformation. The transformation nucleation is promoted, and the γ grains are further refined, whereby the ferrite grains after transformation (hereinafter simply referred to as α) grains are refined.

すなわち、γ→α変態時のα核生成場所であるγ粒界、あるいは、転位などの格子欠陥をより多量に導入することにより、γ→α変態時にα粒を数多く生成し、結晶粒の微細化を図るものである。
しかし、このような制御圧延法では、スラブ厚と製品厚が決まっている以上、圧延により導入できるひずみ量に限界があり、結晶粒径5μm程度までしか、結晶粒を微細化できない、と言われている。 In other words, by introducing a larger amount of lattice defects such as γ grain boundaries or dislocations, which are α nucleation sites during γ → α transformation, a large number of α grains are produced during γ → α transformation. It aims to make it easier.
However, with such a controlled rolling method, since the slab thickness and product thickness are determined, there is a limit to the amount of strain that can be introduced by rolling, and it is said that crystal grains can be refined only to a crystal grain size of about 5 μm. ing.

これに対し、発明者らは、特許文献２、特許文献３において、仕上圧延後の鋼帯に繰り返し曲げ加工を施すことで、スラブ厚及び製品厚を変更することなく、結晶粒を微細化し、高強度化を図る熱間圧延方法及び熱間圧延ラインを提案した。
図4に、特許文献２の熱間圧延ライン300を示すが、仕上圧延機3の下流に、繰り返し曲げ加工装置6を設置したことを特徴とする。 On the other hand, the inventors refined the crystal grains in Patent Document 2 and Patent Document 3 by repeatedly bending the steel strip after finish rolling without changing the slab thickness and product thickness, A hot rolling method and a hot rolling line for increasing the strength were proposed.
FIG. 4 shows a hot rolling line 300 of Patent Document 2, which is characterized in that a repetitive bending apparatus 6 is installed downstream of the finishing mill 3.

繰り返し曲げ加工装置(レベラとも言う)6は、図4に示すように、仕上圧延機3と水冷ゾーンを形成する冷却設備4との間に設置され、図5に要部を拡大して示すように、上下のワークロール6aを千鳥状に配列しており、上下のワークロール6aにて、通過中の熱延鋼帯10を挟圧しつつ、それら上下のワークロール6aを回転させることで、仕上圧延終了後の熱延鋼帯10に繰り返し曲げひずみを付与することができる。   As shown in FIG. 4, a repetitive bending apparatus (also referred to as a leveler) 6 is installed between the finish rolling mill 3 and the cooling equipment 4 that forms a water cooling zone, as shown in FIG. The upper and lower work rolls 6a are arranged in a zigzag pattern. Bending strain can be repeatedly applied to the hot-rolled steel strip 10 after the end of rolling.

また、熱間圧延ライン300には、図4に示すように、仕上圧延機3の最終圧延機（スタンド）と繰り返し曲げ加工装置6との間に冷却設備7を設置してもよく、冷却設備7で仕上圧延後の熱延鋼帯10の温度を制御することにより、結晶粒をさらに微細化することができる。
また、繰り返し曲げ加工装置6は、例えば、図5に示すように、バックアップロール6b、サイドガイド6c、などをさらに設置してもよく、あるいは、特許文献３の熱間圧延ライン400のように、スプレーノズル6dなどをさらに設置してもよい。 Further, in the hot rolling line 300, as shown in FIG. 4, a cooling facility 7 may be installed between the final rolling mill (stand) of the finishing mill 3 and the repeated bending apparatus 6, and the cooling facility By controlling the temperature of the hot-rolled steel strip 10 after finish rolling in 7, the crystal grains can be further refined.
Further, the repeated bending apparatus 6 may be further provided with a backup roll 6b, a side guide 6c, etc., as shown in FIG. 5, or like a hot rolling line 400 of Patent Document 3, A spray nozzle 6d and the like may be further installed.

また、このような繰り返し曲げ加工装置6は、新設の熱間圧延ラインに適用するだけではなく、既設の熱間圧延ラインに追設することもでき、設備費を安く抑えられるとともに、生産性の悪化等を招くこともない。
特開昭63-223124号公報 特開2003-220401号公報 特開2003-154403号公報 Moreover, such a repeated bending apparatus 6 can be applied not only to a new hot rolling line but also to an existing hot rolling line, so that the equipment cost can be reduced and productivity can be reduced. There will be no deterioration.
JP 63-223124 A Japanese Patent Laid-Open No. 2003-220401 JP 2003-154403 A

しかしながら、特許文献２、あるいは、特許文献３の方法では、いまだ結晶粒の微細化、引張強度の向上の余地が残されていた。
なぜなら、工業的に実現可能なワークロール直径や設備長さには限界があるため、曲げ加工により付与できる歪量にも限界があるからである。
本発明は、従来よりもさらに高強度の熱延鋼帯を製造することの可能な、熱間圧延方法を提供することを目的とする。
However, the method of Patent Document 2 or Patent Document 3 still leaves room for refinement of crystal grains and improvement of tensile strength.
This is because there is a limit to the amount of strain that can be applied by bending because there is a limit to the work roll diameter and equipment length that can be industrially realized.
The present invention is capable of producing a hot rolled strip of high strength yet than the conventional, and to provide a hot rolling how.

1. 鋼帯の熱間圧延に際し、前記鋼帯を仕上圧延終了後、1.5sec以内に、前記鋼帯に冷却と繰り返し曲げ加工を開始し、前記繰り返し曲げ加工終了時の前記鋼帯の温度を600℃以上に調整するとともに、前記繰り返し曲げ加工にて前記鋼帯に付与する歪を0.4以上とすることを特徴とする鋼帯の熱間圧延方法。 1. During hot rolling of steel strip, cooling and repeated bending of the steel strip are started within 1.5 seconds after finishing rolling of the steel strip, and the temperature of the steel strip at the end of the repeated bending is set. A method of hot rolling a steel strip, wherein the strain is adjusted to 600 ° C or higher and the strain applied to the steel strip by the repeated bending process is set to 0.4 or higher .

本発明によれば、従来よりもさらに高強度の熱延鋼帯を製造することが可能となる。   According to the present invention, it is possible to manufacture a hot-rolled steel strip having a higher strength than before.

本発明の特徴は、仕上圧延終了後、繰り返し曲げ加工を施すまでの時間と、鋼帯の冷却方法にある。
特許文献２、あるいは、特許文献３にもあるように、繰り返し曲げ加工を施す温度域としては、過冷γ域が最適であり、鋼帯組織がγであれば、鋼帯温度が低温になるほど有利になる。 The features of the present invention lie in the time required for repeated bending after finishing rolling and the method for cooling the steel strip.
As disclosed in Patent Document 2 or Patent Document 3, as the temperature range for repeated bending, the supercooled γ region is optimal, and if the steel strip structure is γ, the steel strip temperature becomes lower. Become advantageous.

発明者らは、これを実現しようと鋭意検討した結果、仕上圧延終了後、同一の設備にて、可及的速やかに鋼帯を冷却し、可及的速やかに鋼帯に曲げ加工を施すことが、非常に有効であることを知見し、本発明を完成させるに至った。
以下に、本発明を完成するに至った実験について述べる。
図１(a)は、本発明の熱間圧延ライン100を模した実験設備の設備列であり、圧延機41、冷却設備42、装置内に冷却装置44dを有する繰り返し曲げ加工装置44の順に設置している。 As a result of intensive studies to achieve this, the inventors have cooled the steel strip as soon as possible and finished bending the steel strip as soon as possible with the same equipment after finishing rolling. However, the present inventors have found that it is very effective and have completed the present invention.
Hereinafter, the experiment that led to the completion of the present invention will be described.
FIG. 1 (a) is an equipment row of the experimental equipment simulating the hot rolling line 100 of the present invention. The rolling mill 41, the cooling equipment 42, and the repeated bending apparatus 44 having the cooling equipment 44d in the equipment are installed in this order. is doing.

比較のために、特許文献２に相当する、従来の熱間圧延ライン300の設備列を模した実験設備を図１(b)に、特許文献３に相当する、従来の熱間圧延ライン400の設備列を模した実験設備を図1(c)に、それぞれ要部を拡大して示すが、それぞれ、圧延機41、冷却設備42、繰り返し曲げ加工装置43、あるいは、圧延機41、冷却設備42、装置内に冷却装置を有する繰り返し曲げ加工装置44の順に設置している。   For comparison, FIG. 1 (b) shows an experimental facility corresponding to Patent Literature 2 that simulates the equipment row of a conventional hot rolling line 300, and FIG. FIG. 1 (c) shows experimental equipment simulating equipment rows, with the main parts enlarged, respectively, but the rolling mill 41, cooling equipment 42, repeated bending apparatus 43, or rolling mill 41, cooling equipment 42 The repeated bending apparatus 44 having a cooling device in the apparatus is installed in this order.

図１(a)に示す、装置内に冷却装置44dを有する繰り返し曲げ加工装置44は、隣接する各ワークロール44a間に20〜50L/minの範囲で冷却水の流量を調整可能な冷却装置44d（スプレーノズル）を有し、各ノズルの開閉により、冷却水の総流量を調整し、繰り返し曲げ加工終了後の鋼帯の温度を調整することができる。
図１(a)では、冷却装置44d（スプレーノズル）は、隣接するワークロール44a間に設置しているが、本発明はこれに限るものではなく、鋼帯10を間接的にでも、冷却できればよく、この意味からは、例えば、ワークロールの直上に設置するなどしてもよい。 A repetitive bending apparatus 44 having a cooling apparatus 44d in the apparatus shown in FIG. 1 (a) has a cooling apparatus 44d capable of adjusting the flow rate of cooling water in the range of 20 to 50 L / min between adjacent work rolls 44a. (Spray nozzle), the total flow rate of the cooling water can be adjusted by opening and closing each nozzle, and the temperature of the steel strip after repeated bending can be adjusted.
In FIG. 1 (a), the cooling device 44d (spray nozzle) is installed between the adjacent work rolls 44a. However, the present invention is not limited to this, and the steel strip 10 can be cooled indirectly. In this sense, for example, it may be installed directly above the work roll.

また、図１(a)では、冷却設備42（図4に示す従来の熱間圧延ライン300にいう冷却設備7に相当）を、繰り返し曲げ加工装置44内に設置した冷却装置44d（スプレーノズル）とは別に設置しているが、繰り返し曲げ加工装置44内に設置した冷却装置44d（スプレーノズル）から鋼帯10に向けて供給される冷却水の流量が、十分に確保できれば、冷却設備42は、省略することもできる。   Further, in FIG. 1 (a), a cooling device 44d (spray nozzle) in which a cooling device 42 (corresponding to the cooling device 7 in the conventional hot rolling line 300 shown in FIG. 4) is repeatedly installed in the bending device 44. However, if the flow rate of cooling water supplied from the cooling device 44d (spray nozzle) installed in the bending device 44 to the steel strip 10 is sufficiently secured, the cooling equipment 42 It can be omitted.

各設備列にて、0.15mass%のC、0.01mass%のSi、0.75mass%のMnを含有し、残部Feおよび不可避的不純物からなる供試鋼（γ→α変態点温度Ar1=723℃）を、圧延機41の出側温度が850℃、あるいは、800℃となるように、厚さ3mmに仕上圧延し、引き続き、表1に示す各条件で、冷却、並びに、曲げ加工を施し、その後、空冷した。
図１(b)の、従来の熱間圧延ライン300の設備列を模した実験設備、図１(a)の、本発明の熱間圧延ライン100の設備列を模した実験設備、の両者とも、繰り返し曲げ加工装置43a、44は、ワークロール本数23本、ワークロール直径70mm、ワークロール中心軸間隔90mmとした。 In each equipment row, test steel containing 0.15 mass% C, 0.01 mass% Si, 0.75 mass% Mn, the balance Fe and inevitable impurities (γ → α transformation temperature Ar 1 = 723 ° C ), And finish-rolling to a thickness of 3 mm so that the exit temperature of the rolling mill 41 is 850 ° C. or 800 ° C., and then, under each condition shown in Table 1, cooling and bending are performed, Then it was air cooled.
Both the experimental equipment simulating the equipment row of the conventional hot rolling line 300 in FIG. 1 (b) and the experimental equipment simulating the equipment row of the hot rolling line 100 of the present invention in FIG. 1 (a). The repeated bending apparatuses 43a and 44 have 23 work rolls, a work roll diameter of 70 mm, and a work roll central axis interval of 90 mm.

なお、上下のワークロールで鋼帯10を挟んだ状態から、上ワークロールを押し込んだ距離で定義される、ロール締め込み量を種々変更することにより、繰り返し曲げ歪の量を調整した。
得られた各供試鋼について、結晶粒径および引張強さの調査を行った。結晶粒径については、JIS G 0552に準拠して結晶粒の平均断面積を求め、それを円形と仮定して平均結晶粒径を算出した。引張強さについては、JIS Z 2201に準拠して5号試験片を切り出して引張試験を行い、引張強さをその値とした。 Note that the amount of repeated bending strain was adjusted by variously changing the amount of roll tightening defined by the distance by which the upper work roll was pushed from the state in which the steel strip 10 was sandwiched between the upper and lower work rolls.
About each obtained test steel, the crystal grain size and the tensile strength were investigated. As for the crystal grain size, the average cross-sectional area of the crystal grain was determined according to JIS G 0552, and the average crystal grain size was calculated assuming that it was circular. Regarding the tensile strength, a No. 5 test piece was cut out in accordance with JIS Z 2201 and subjected to a tensile test, and the tensile strength was defined as the value.

結果を表1にあわせて示す。特許文献２に相当する、図１（ｂ）の、従来の熱間圧延ライン300の設備列を模した実験設備では、No.2に示すように、冷却設備42で鋼帯10を冷却し、過冷γ域である750〜730℃で繰り返し曲げ加工を施すことが有効であり、No.3に示すように、冷却設備42で700℃まで冷却した場合、繰り返し曲げ加工を施す前にγ→α変態しているために、曲げ加工を施す効果が小さくなっていた。   The results are shown in Table 1. In the experimental equipment simulating the equipment row of the conventional hot rolling line 300 in FIG. 1 (b) corresponding to Patent Document 2, as shown in No. 2, the steel strip 10 is cooled by the cooling equipment 42, It is effective to repeatedly perform bending at 750 to 730 ° C, which is the supercooled γ region, and as shown in No. 3, when cooling to 700 ° C with the cooling equipment 42, γ → Because of the α transformation, the effect of bending was small.

Figure 0004552731
Figure 0004552731

これに対し、特許文献３に相当する、図１（ｃ）の、従来の熱間圧延ライン400の設備列を模した実験設備では、No.15に示すように、繰り返し曲げ加工装置44内で鋼帯10を冷却することにより、繰り返し曲げ加工を終了する温度が650℃の場合も、過冷γ域であり、No.2に比べ、効果的に結晶粒を微細化することができていた。これは、γ→α変態点温度近傍での鋼帯10の冷却速度が大きいため、過冷γ域をより低温まで拡大できたためと考えられる。   On the other hand, in the experimental equipment simulating the equipment row of the conventional hot rolling line 400 of FIG. 1 (c) corresponding to Patent Document 3, as shown in No. 15, in the repeated bending apparatus 44. By cooling the steel strip 10, even when the temperature at which the repeated bending process is finished is 650 ° C., it is in the supercooled γ region, and compared to No. 2, the crystal grains could be effectively refined. . This is thought to be because the supercooled γ region could be expanded to a lower temperature because the cooling rate of the steel strip 10 near the γ → α transformation point temperature was high.

これに対し、図１（a）の、本発明の熱間圧延ライン100の設備列を模した実験設備では、No.5，6，7，9，10，14に示すように、圧延終了後、1.5sec以内に、鋼帯10の冷却と繰り返し曲げ加工を開始し、かつ、繰り返し曲げ加工終了時の鋼帯10の温度が600℃以上、繰り返し曲げ歪が0.4以上では、従来に比べ、結晶粒を格段に微細化できており、非常に有効であることが分かる。   On the other hand, in the experimental equipment simulating the equipment row of the hot rolling line 100 of the present invention shown in FIG. 1 (a), as shown in Nos. 5, 6, 7, 9, 10, and 14, Within 1.5 sec, cooling of the steel strip 10 and repeated bending are started, and when the temperature of the steel strip 10 at the end of repeated bending is 600 ° C or higher and the repeated bending strain is 0.4 or higher, the It can be seen that the grains can be remarkably refined and are very effective.

本発明が結晶粒の微細化に格段に有効である理由は、明らかではないが、圧延により扁平したままのγ粒に、直ちに、繰り返し曲げ歪を付与した場合、その後のα変態の際に、α粒の核生成が促進されるからである可能性がある。
また、圧延終了後、冷却した後、繰り返し曲げ加工を施す場合、時間とともにγ→α変態は進行してしまうため、過冷γ域にある状態とするのにも限界があったのに対し、冷却と曲げ加工を同一の設備にて施すことにより、γ→α変態が進行する前に繰り返し曲げ加工を施すことが可能となり、より低温の過冷γ域で繰り返し曲げ加工を施すことができるようになった効果も大きい。 The reason why the present invention is remarkably effective for refining crystal grains is not clear, but when γ grains that have been flattened by rolling are immediately subjected to repeated bending strain, during the subsequent α transformation, This may be because nucleation of α grains is promoted.
Moreover, after rolling, after cooling, when repeatedly bending, the γ → α transformation proceeds with time, so there was a limit to the state in the supercooled γ region, By performing cooling and bending with the same equipment, it becomes possible to repeatedly perform bending before the γ → α transformation progresses, and it is possible to repeatedly perform bending in the lower-temperature supercooled γ region. The effect that became.

これは、従来の熱間圧延ライン400の設備列を模した実験設備では、曲げ加工出側温度が650℃の場合に最も効果的に結晶粒を微細化できていたのに対し、本発明の熱間圧延ライン100の設備列を模した実験設備では、曲げ加工出側温度が600℃の場合に最も効果的に結晶粒を微細化できていることと対応する。
本発明において、仕上圧延後、鋼帯10への繰り返し曲げ加工を開始するまでの時間を1.5 sec以内に限定したのは、上記したように、γ→α変態が進行する前に繰り返し曲げ加工を施すためであり、1.5 secを越えると、γ→α変態が進行しやすいため、繰り返し曲げ加工を施す効果が小さくなるからである。 This is because, in the experimental equipment simulating the equipment row of the conventional hot rolling line 400, the crystal grains were most effectively refined when the bending process outlet temperature was 650 ° C. In the experimental equipment simulating the equipment line of the hot rolling line 100, this corresponds to the fact that the crystal grains can be most effectively refined when the bending process outlet temperature is 600 ° C.
In the present invention, after finishing rolling, the time until the start of repeated bending to the steel strip 10 is limited to within 1.5 sec, as described above, the repeated bending is performed before the γ → α transformation proceeds. This is because if the time exceeds 1.5 sec, the γ → α transformation is likely to proceed, so that the effect of repeated bending is reduced.

一方、通常、仕上圧延終了後の温度は、900℃内外である。繰り返し曲げ加工に最適な温度域は、750℃以下の過冷γ域であるため、鋼帯を強制冷却することなく、1.5 sec以内に繰り返し曲げ加工を施した場合、850℃を越える温度域内外で繰り返し曲げ加工を施すことになり、歪の回復、再結晶により、蓄積効果が小さくなるため、結晶粒微細化効果は小さくなる。このため、従来、700℃内外まで冷却した後に、繰り返し曲げ加工を施していたが、この場合、繰り返し曲げ加工を施すまでに時間を要し、そのため、γ→α変態が進行する時間を与えてしまうことになり、十分な結晶粒の微細化効果を得ることができていなかったようである。   On the other hand, the temperature after finish rolling is usually 900 ° C. inside or outside. The optimum temperature range for repeated bending is the supercooled γ range of 750 ° C or less. Therefore, if the bending process is repeated within 1.5 seconds without forced cooling of the steel strip, the temperature range above 850 ° C is exceeded. In this case, the bending effect is repeatedly applied and the accumulation effect is reduced by strain recovery and recrystallization. For this reason, conventionally, after bending to 700 ° C inside and outside, repeated bending was performed, in this case, it took time until repeated bending was performed, and therefore the time for the γ → α transformation to proceed was given. Thus, it seems that a sufficient crystal grain refining effect could not be obtained.

これに対し、本発明では、圧延後、鋼帯10への繰り返し曲げ加工を施すとともに、鋼帯10の強制冷却を開始するので、γ→α変態が進行する時間をさして与えることなく、過冷γ域での繰り返し曲げ加工を施すことができるようになり、顕著な結晶粒の微細化効果を得られるのである。
繰り返し曲げ加工終了後の鋼帯10の温度を600℃以上に限定したのは、繰り返し曲げ加工終了後の鋼帯10の温度が600℃未満の場合、No.8にも示すように、鋼帯10の組織がベイナイト組織となるからである。ベイナイト組織は、延性、低温靭性が低化するため、好ましくない。また、ベイナイト組織は、結晶が粒状ではないため、結晶粒径がうまく測定できない。No.8はその例である。 On the other hand, in the present invention, after rolling, the steel strip 10 is subjected to repeated bending processing and forced cooling of the steel strip 10 is started. It becomes possible to repeatedly perform bending in the γ region, and a remarkable crystal grain refinement effect can be obtained.
The temperature of the steel strip 10 after repeated bending is limited to 600 ° C or higher when the temperature of the steel strip 10 after repeated bending is less than 600 ° C, as shown in No.8. This is because 10 structures become bainite structures. A bainite structure is not preferable because ductility and low temperature toughness are reduced. Further, in the bainite structure, the crystal grain size cannot be measured well because the crystal is not granular. No. 8 is an example.

繰り返し曲げ歪を0.4以上に限定したのは、No.13にも示すように、曲げ歪が小さいと、結晶粒の微細化に有効でないからである。なお、繰り返し曲げ歪(ε)は、ワークロール中心軸間隔(2L)、ワークロール数(N)、ロール締め込み量(δ)、板厚(t)を用い、以下の式により、算出される。
ε=(N-2)2tδ/L2
なお、本発明では、当然ながら、熱間圧延ライン100における仕上圧延機3の下流に、仕上圧延終了後、1.5sec以内に、繰り返し曲げ加工を開始可能なように、繰り返し曲げ加工装置44を設置する。鋼帯10の仕上圧延機3の出側における搬送速度には範囲があるが、本発明の方法が対象とするような、従来よりもさらに高強度の熱延鋼帯を製造する場合の搬送速度の際に、仕上圧延終了後、1.5sec以内に、繰り返し曲げ加工を開始可能なように、繰り返し曲げ加工装置44を設置すればよい。 The reason why the repeated bending strain is limited to 0.4 or more is that, as shown in No. 13, if the bending strain is small, it is not effective for refining crystal grains. The repeated bending strain (ε) is calculated by the following formula using the work roll center axis interval (2L), the number of work rolls (N), the roll tightening amount (δ), and the plate thickness (t). .
ε = (N-2) 2tδ / L 2
In the present invention, of course, the repeated bending apparatus 44 is installed downstream of the finishing mill 3 in the hot rolling line 100 so that repeated bending can be started within 1.5 seconds after finishing rolling. To do. Although there is a range in the conveyance speed on the exit side of the finish rolling mill 3 of the steel strip 10, the conveyance speed in the case of manufacturing a hot-rolled steel strip having higher strength than the conventional one, which is the method of the present invention In this case, the repeated bending apparatus 44 may be installed so that the repeated bending process can be started within 1.5 seconds after finishing rolling.

本発明の効果を実証するため、図3に示す従来の熱間圧延ライン200に追設する形で、各水準を設け、以下の実験を行った。本発明の場合は、装置内に冷却装置44dを有する繰り返し曲げ加工装置44を、従来の熱間圧延ライン200に追設して、以下の実験を行った。
本発明の、装置内に冷却装置44dを有する繰り返し曲げ加工装置44を、従来の熱間圧延ライン200に追設した熱間圧延ライン100では、仕上圧延機3の最終圧延機（スタンド）のワークロール中心と、装置内に冷却装置44dを有する繰り返し曲げ加工装置44の第1番目のノズルまでの距離、及び、仕上圧延機3の最終圧延機（スタンド）のワークロール中心と、装置内に冷却装置44dを有する繰り返し曲げ加工装置44の第1番目のワークロール中心までの距離は、いずれも8mである。 In order to verify the effect of the present invention, the following experiments were conducted by providing each level in the form of being added to the conventional hot rolling line 200 shown in FIG. In the case of the present invention, the following experiment was conducted by adding a repeated bending apparatus 44 having a cooling apparatus 44d in the apparatus to the conventional hot rolling line 200.
In the hot rolling line 100 in which the repetitive bending apparatus 44 having the cooling device 44d in the apparatus is added to the conventional hot rolling line 200, the work of the final rolling mill (stand) of the finish rolling mill 3 is provided. Cooling in the center of the roll, the distance to the first nozzle of the repetitive bending device 44 having the cooling device 44d in the device, the center of the work roll of the final rolling mill (stand) of the finishing mill 3 The distance to the center of the first work roll of the repeated bending apparatus 44 having the apparatus 44d is 8 m.

また、比較のため、従来例として、図4に示すような、特許文献２の熱間圧延ライン300も用いた。仕上圧延機3の最終圧延機（スタンド）のワークロール中心と冷却設備7の第1番目のノズルまでの距離は8m、仕上圧延機3の最終圧延機（スタンド）のワークロール中心と繰り返し曲げ加工装置6の第1番目のワークロール中心までの距離は30mである。
本発明例、従来例のいずれの場合も、ワークロール本数27、ワークロール直径190mm、ワークロール中心軸間隔200mmとした繰り返し曲げ加工装置を用い、繰り返し曲げ加工にて鋼帯10に付与する曲げ歪を1.2〜0.4とした。また、装置内に冷却装置を有する繰り返し曲げ加工装置の冷却装置には、スリットタイプの冷却ノズルを用いた。 For comparison, a hot rolling line 300 of Patent Document 2 as shown in FIG. 4 was also used as a conventional example. The distance from the work roll center of the final rolling mill (stand) of the finishing mill 3 to the first nozzle of the cooling facility 7 is 8 m, and the bending of the work roll center of the final rolling mill (stand) of the finishing mill 3 is repeated. The distance to the first work roll center of the device 6 is 30 m.
In both cases of the present invention and the conventional example, a bending strain applied to the steel strip 10 by repeated bending using a repeated bending apparatus with a work roll number of 27, a work roll diameter of 190 mm, and a work roll central axis interval of 200 mm. Was set to 1.2 to 0.4. A slit type cooling nozzle was used as a cooling device of a repetitive bending apparatus having a cooling device in the apparatus.

0.15mass%のC、0.01mass%のSi、0.75mass%のMnを含有し、残部Feおよび不可避的不純物からなる供試鋼を用い、仕上圧延機3の出側における鋼帯10の温度が850℃、仕上圧延機3の出側における鋼帯10の搬送速度が750m/minとなるように、3mmに仕上圧延した。
本発明例では、仕上圧延後、0.64sec後に冷却と繰り返し曲げ加工を開始し、繰り返し曲げ加工装置44の出側での鋼帯10の温度が650℃となるよう、繰り返し曲げ加工装置44の出側での鋼帯10の温度の実績を、図示しない制御装置にフィードバックし、繰り返し曲げ加工装置から鋼帯10に向けて供給される冷却水の流量を調整した。 Using test steel containing 0.15 mass% C, 0.01 mass% Si, 0.75 mass% Mn, the balance Fe and unavoidable impurities, the temperature of the steel strip 10 on the exit side of the finishing mill 3 is 850 Finish rolling was performed at 3 ° C. so that the conveying speed of the steel strip 10 on the exit side of the finish rolling mill 3 was 750 m / min.
In the example of the present invention, after finishing rolling, cooling and repeated bending are started after 0.64 seconds, and the temperature of the steel strip 10 on the exit side of the repeated bending device 44 is set to 650 ° C. The actual temperature of the steel strip 10 on the side was fed back to a control device (not shown), and the flow rate of the cooling water supplied from the repeated bending device toward the steel strip 10 was adjusted.

従来例では、仕上圧延後、0.64sec後に冷却を開始し、750℃まで冷却した後、仕上圧延後、2.4sec後に繰り返し曲げ加工を開始した。
いずれも、繰り返し曲げ加工終了後、冷却設備4にて600℃まで冷却し、その後、コイラ5aにて巻き取った。
本発明例、従来例の両者について、巻き戻した鋼帯10の長手方向中央部、幅方向中央部において、JIS Z 2201に準拠して、5号試験片を10個切り出し、引張試験を行った。引張強さは、引張試験により得られた引張強さの平均値とした。 In the conventional example, after finishing rolling, cooling was started after 0.64 sec, after cooling to 750 ° C., after finishing rolling, repeated bending processing was started after 2.4 sec.
In either case, after the repeated bending process was completed, it was cooled to 600 ° C. with the cooling equipment 4, and then wound up with the coiler 5a.
For both the inventive example and the conventional example, in the central part in the longitudinal direction and the central part in the width direction of the rewound steel strip 10, 10 test pieces were cut out according to JIS Z 2201 and subjected to a tensile test. . The tensile strength was an average value of the tensile strength obtained by the tensile test.

結果を図2に示す。本発明例では、従来例に比べ、格段に高強度の熱延鋼帯を得られることがわかる。   The result is shown in figure 2. In the example of the present invention, it can be seen that a hot-rolled steel strip with much higher strength can be obtained than in the conventional example.

本発明あるいは従来の、熱間圧延ラインを模した実験設備の設備列の要部を拡大して示した図である。It is the figure which expanded and showed the principal part of the equipment row | line of the experimental equipment which imitated this invention or the conventional hot rolling line. 本発明の効果を示す図である。It is a figure which shows the effect of this invention. 従来の熱間圧延ラインの設備列を模式的に示した図である。It is the figure which showed typically the installation row | line | column of the conventional hot rolling line. 従来の熱間圧延ラインの設備列を模式的に示した図である。It is the figure which showed typically the installation row | line | column of the conventional hot rolling line. 従来の熱間圧延ラインの設備列を模式的に示した図である。It is the figure which showed typically the installation row | line | column of the conventional hot rolling line.

符号の説明Explanation of symbols

１ 加熱炉
２ 粗圧延機
３ 仕上圧延機
3a 仕上圧延機最終スタンド
４ 冷却設備
5a、5b コイラ
６、43、44 繰り返し曲げ加工装置
6a 44a ワークロール
6b バックアップロール
6c サイドガイド
6d スプレーノズル
７ 冷却設備
10 熱延鋼帯（鋼帯）
11 熱延鋼帯（鋼帯）の搬送方向
41 圧延機
42 冷却設備
44d 冷却装置
200、300、400 熱間圧延ライン 1 Heating furnace 2 Rough rolling mill 3 Finishing mill
3a Finishing mill final stand 4 Cooling equipment
5a, 5b Coiler 6, 43, 44 Repeat bending machine
6a 44a Work roll
6b Backup roll
6c Side guide
6d Spray nozzle 7 Cooling equipment
10 Hot-rolled steel strip (steel strip)
11 Transport direction of hot-rolled steel strip (steel strip)
41 Rolling mill
42 Cooling equipment
44d cooling system
200, 300, 400 Hot rolling line

Claims (1)

鋼帯の熱間圧延に際し、前記鋼帯の仕上圧延終了後、1.5sec以内に、前記鋼帯に冷却と繰り返し曲げ加工を開始し、前記繰り返し曲げ加工終了時の前記鋼帯の温度を600℃以上に調整するとともに、前記繰り返し曲げ加工にて前記鋼帯に付与する歪を0.4以上とすることを特徴とする鋼帯の熱間圧延方法。
Upon hot rolling of the steel strip, cooling and repeated bending are started on the steel strip within 1.5 seconds after finishing rolling of the steel strip, and the temperature of the steel strip at the end of the repeated bending is 600 ° C. A hot rolling method for a steel strip characterized by adjusting the strain to be applied to the steel strip by the repeated bending process to 0.4 or more .
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DE102008010062A1 (en) * 2007-06-22 2008-12-24 Sms Demag Ag Process for hot rolling and heat treatment of a strip of steel
JP5434040B2 (en) * 2008-10-08 2014-03-05 Ｊｆｅスチール株式会社 Manufacturing method of high formability and high strength steel sheet with excellent chemical conversion
JP5673370B2 (en) * 2011-06-07 2015-02-18 新日鐵住金株式会社 Method for cooling hot-rolled steel sheet
US9186710B2 (en) 2011-06-07 2015-11-17 Nippon Steel & Sumitomo Metal Corporation Method for cooling hot-rolled steel sheet
US9566625B2 (en) 2011-06-07 2017-02-14 Nippon Steel & Sumitomo Metal Corporation Apparatus for cooling hot-rolled steel sheet
US9211574B2 (en) 2011-07-27 2015-12-15 Nippon Steel & Sumitomo Metal Corporation Method for manufacturing steel sheet

Citations (5)

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Publication number Priority date Publication date Assignee Title
JPS627247B2 (en) * 1982-04-03 1987-02-16 Nippon Steel Corp
JP2003154402A (en) * 2001-11-15 2003-05-27 Kawasaki Steel Corp Hot rolling line and hot-rolling method
JP2003220401A (en) * 2000-12-28 2003-08-05 Jfe Steel Kk Hot rolling method and hot rolling line
JP2004122133A (en) * 2002-09-30 2004-04-22 Jfe Steel Kk Hot-rolling method
JP2004130375A (en) * 2002-10-15 2004-04-30 Jfe Steel Kk Method and equipment for manufacturing hot-rolled steel strip

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS627247B2 (en) * 1982-04-03 1987-02-16 Nippon Steel Corp
JP2003220401A (en) * 2000-12-28 2003-08-05 Jfe Steel Kk Hot rolling method and hot rolling line
JP2003154402A (en) * 2001-11-15 2003-05-27 Kawasaki Steel Corp Hot rolling line and hot-rolling method
JP2004122133A (en) * 2002-09-30 2004-04-22 Jfe Steel Kk Hot-rolling method
JP2004130375A (en) * 2002-10-15 2004-04-30 Jfe Steel Kk Method and equipment for manufacturing hot-rolled steel strip

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