JP6693543B2 - Hot rolled steel sheet manufacturing method - Google Patents
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- 229910000831 Steel Inorganic materials 0.000 title claims description 79
- 239000010959 steel Substances 0.000 title claims description 79
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 238000005096 rolling process Methods 0.000 claims description 96
- 230000009467 reduction Effects 0.000 claims description 47
- 238000000034 method Methods 0.000 claims description 44
- 238000005098 hot rolling Methods 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052787 antimony Inorganic materials 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 229910052715 tantalum Inorganic materials 0.000 claims description 2
- 229910052718 tin Inorganic materials 0.000 claims description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 23
- 238000005336 cracking Methods 0.000 description 15
- 208000009205 Tinnitus Diseases 0.000 description 13
- 238000010438 heat treatment Methods 0.000 description 12
- 230000035882 stress Effects 0.000 description 11
- 229910052742 iron Inorganic materials 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 6
- 230000006355 external stress Effects 0.000 description 6
- 239000002436 steel type Substances 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 230000001186 cumulative effect Effects 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 230000037303 wrinkles Effects 0.000 description 3
- 238000005097 cold rolling Methods 0.000 description 2
- 230000001603 reducing effect Effects 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000011162 core material Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 210000005069 ears Anatomy 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 230000000452 restraining effect Effects 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000009966 trimming Methods 0.000 description 1
- 238000009489 vacuum treatment Methods 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Metal Rolling (AREA)
- Manufacturing Of Steel Electrode Plates (AREA)
Description
本発明は、熱延鋼板の製造方法に関する。本発明は、主として電磁鋼板で用いられる高Ｓｉを含有したスラブから熱延鋼板を製造する製造方法に関し、特に熱間圧延時における鋼板の割れを効率的に軽減し、圧延時の形状不良を軽減して歩留まりの向上を図れる熱延鋼板の製造方法に関する。 The present invention relates to a method for manufacturing a hot rolled steel sheet. TECHNICAL FIELD The present invention relates to a manufacturing method for manufacturing a hot-rolled steel sheet from a slab containing high Si, which is mainly used for electromagnetic steel sheets, and particularly efficiently reduces cracks in the steel sheet during hot rolling and reduces shape defects during rolling. The present invention relates to a method for manufacturing a hot-rolled steel sheet that can improve yield.
Ｓｉを多く含有した鋼板は主として、電磁鋼板として使用されている。電磁鋼板は変圧器及びその他の電気機器の鉄芯材料等として広く用いられており、そのため、製造時のコストダウンに対する要望も大きく、これに応えるため、歩留まり高く製品を製造する方法の開発が強く望まれている。 Steel sheets containing a large amount of Si are mainly used as electromagnetic steel sheets. Magnetic steel sheets are widely used as iron core materials for transformers and other electrical equipment, and there is a great demand for cost reduction during manufacturing.To meet this demand, development of a method for manufacturing products with high yield is strongly required. Is desired.
一般に鋼板中に多くのＳｉ（２．０〜４．０質量％）を添加することにより、優れた鉄損特性を示し、その結果として磁気特性に優れた電磁鋼板を得ることができる。しかしながらその一方で、鋼板中への多量のＳｉの添加は、本質的に鋼板の延性を著しく低下させるため、熱間圧延等の圧延時に表面割れあるいは耳割れといった鋼板の割れが発生する傾向が高く、操業上きわめて大きな問題となっている。 Generally, by adding a large amount of Si (2.0 to 4.0 mass%) to a steel sheet, an excellent iron loss characteristic is exhibited, and as a result, an electromagnetic steel sheet having excellent magnetic characteristics can be obtained. However, on the other hand, the addition of a large amount of Si into the steel sheet essentially significantly lowers the ductility of the steel sheet, so that there is a high tendency for cracks in the steel sheet such as surface cracks or edge cracks to occur during rolling such as hot rolling. , It has become a very big problem in operation.
鋼板の熱間圧延において表面割れが発生すると、この割れはその後の冷間圧延等でも解消することが難しく、製品板においてヘゲ疵となり歩留まりが悪くなる。また、耳割れが発生すると、その両端をトリマーでせん断する等のトリミング処理が必要となり、同じく歩留まりが悪くなる。 If surface cracks occur during hot rolling of a steel sheet, it is difficult to eliminate these cracks even in the subsequent cold rolling, etc., and the product sheet will be subject to bald defects and the yield will be poor. In addition, when the ear crack occurs, trimming processing such as shearing both ends of the ear crack with the trimmer is required, and the yield also deteriorates.
また、変形抵抗の軽減のため、熱間圧延前のスラブを１３００℃〜１４００℃という高温で加熱する処理が施される場合もあるが、高温状態の加熱により生じた異常成長粒は熱間圧延中にも十分に再結晶せずに荒い結晶粒を残した組織となる。この粗粒化した組織が存在することにより、変形が不均一となり不連続なしわ状の突起が形成され易く、形状が不安定となる。 Further, in order to reduce the deformation resistance, the slab before hot rolling may be subjected to a heating treatment at a high temperature of 1300 ° C. to 1400 ° C., but abnormally grown grains generated by heating in a high temperature state are hot rolled. The structure does not recrystallize sufficiently, leaving a rough crystal grain. Due to the presence of this coarse-grained structure, the deformation becomes non-uniform, and discontinuous wrinkle-shaped projections are easily formed, and the shape becomes unstable.
また、多くのＳｉを含有することによって本質的に鋼の延性が低く、さらに粗粒化した組織により発生するしわが局所的な応力集中の起点として作用し、容易に割れが発生する。そのためＳｉを多く含有した鋼板は、優れた鉄損特性を示すものの、熱延時の歩留まりが悪く、コスト削減のため歩留まりの向上が望まれていた。 Further, since a large amount of Si is contained, the ductility of steel is essentially low, and the wrinkles generated by the coarse-grained structure act as a starting point of local stress concentration, and cracks easily occur. Therefore, although a steel sheet containing a large amount of Si exhibits excellent iron loss characteristics, the yield during hot rolling is poor, and improvement in yield has been desired for cost reduction.
歩留まり向上のため、高Ｓｉ含有鋼の熱間圧延工程における耳割れを防止する技術が開発されている。 In order to improve the yield, a technique for preventing edge cracks in the hot rolling process of high Si content steel has been developed.
例えば、特許文献１には、仕上げ圧延中の温度低下を２２０℃以内にすることによって耳割れを防止する技術が開示されている。しかしこの技術では、粗圧延時や仕上げ圧延の前段階で発生する耳割れは防止できない。 For example, Patent Document 1 discloses a technique for preventing ear cracking by controlling the temperature decrease during finish rolling to 220 ° C or less. However, this technique cannot prevent edge cracking that occurs during rough rolling or before finish rolling.
また、特許文献２には、仕上げ圧延以降の圧下率を制御することによって耳割れを防止する技術が開示されている。しかしこの技術も、粗圧延時や仕上げ圧延の前段階で発生する耳割れは防止できない。 Further, Patent Document 2 discloses a technique for preventing ear cracking by controlling the rolling reduction after finish rolling. However, this technique cannot prevent the edge cracks that occur during rough rolling or in the stage before finish rolling.
一方、特許文献３、特許文献４、特許文献５および特許文献６には、仕上げ圧延１パス目の入側および／または出側にてシートバーの側面の形状を整えることで耳割れを防止する技術が開示されている。つまり、側面の形状が悪い場合には粗大に成長した結晶の粒界でノッチ状の凹部が生じ、これが耳割れの起点となることを考慮して、側面の形状を整えることによって耳割れの防止を図るものである。これらの技術は軽度な耳割れの防止には有効である。しかしシートバーの側面に深いノッチ状の凹部が存在する場合には、凸部の倒れ込みを発生させてしまい、特に歩留まりや操業に悪影響を与える重度の耳割れにはほとんど効果がなかった。 On the other hand, in Patent Document 3, Patent Document 4, Patent Document 5 and Patent Document 6, ear cracking is prevented by adjusting the shape of the side surface of the sheet bar on the entry side and / or the exit side of the first pass of finish rolling. The technology is disclosed. In other words, if the shape of the side surface is bad, a notch-shaped recess is created at the grain boundary of the coarsely grown crystal, and considering that this becomes the starting point of the ear crack, it is possible to prevent the ear crack by adjusting the shape of the side surface. Is intended. These techniques are effective in preventing mild ear cracking. However, when there is a deep notch-shaped concave portion on the side surface of the seat bar, the convex portion collapses, and there is little effect particularly on severe ear cracking which adversely affects yield and operation.
さらに、特許文献７には粗圧延の最終パスの圧下率を規定することによって耳割れを防止する技術、特許文献８には鋳込み組織を制御することによって耳割れを防止する技術、および特許文献９にはスラブの断面形状を特殊な形状にすることによって耳割れを防止する技術が開示されている。これらの技術は、粗圧延における幅圧下が多大な影響を及ぼすので、安定した効果を得ることは難しく、耳割れ防止に有効な技術とは言えなかった。 Further, Patent Document 7 discloses a technique for preventing ear cracks by defining the rolling reduction in the final pass of rough rolling, and Patent Document 8 discloses a technique for preventing ear cracks by controlling the cast structure, and Patent Document 9. Discloses a technique for preventing ear cracking by changing the cross-sectional shape of the slab to a special shape. Since the width reduction in rough rolling has a great influence on these techniques, it is difficult to obtain a stable effect, and it cannot be said that these techniques are effective for preventing ear cracking.
特許文献１０には、粗圧延にて５〜４０％の幅圧下を行なうことによって耳割れを防止する技術が開示されている。この技術によれば、大きな耳割れ（たとえば長さ２０〜４０ｍｍ）は認められなかった。しかし、１０ｍｍ程度の耳割れは依然として残存していた。 Patent Document 10 discloses a technique for preventing ear cracking by performing a width reduction of 5 to 40% by rough rolling. According to this technique, no large ear crack (for example, 20 to 40 mm in length) was observed. However, the ear crack of about 10 mm still remained.
これらの技術が耳割れを防止できない原因は、高温かつ長時間の加熱によってスラブに生成した粗大な結晶粒を破壊して再結晶させることができない、あるいは粗大な結晶粒を破壊するために幅圧下を大きくするとロールバイトの噛み込み時に表層に引張応力が作用し、かえって粒界割れを引き起こしてしまうことにあった。また、粗粒化した組織が存在することにより、変形が不均一となり不連続なしわ状の突起が形成され易く、しわが局所的な応力集中の場所として作用し、鋼板に割れが発生する。 The reason why these technologies cannot prevent ear cracking is that the coarse crystal grains generated in the slab by heating at high temperature for a long time cannot be destroyed and recrystallized, or the width reduction due to the coarse crystal grain destruction is caused. If the value is increased, a tensile stress acts on the surface layer when the roll bite is bitten, which rather causes intergranular cracking. Further, due to the presence of the coarse-grained structure, the deformation becomes nonuniform and discontinuous wrinkle-shaped projections are easily formed, and the wrinkles act as local stress concentration sites, and cracks occur in the steel sheet.
この問題を解決するために、高Ｓｉ含有のスラブの高温加熱を行なう前に、予め歪を与えることによって耳割れを防止する技術が開示されている。 In order to solve this problem, a technique has been disclosed in which ear cracking is prevented by pre-straining a slab having a high Si content before heating at a high temperature.
例えば、特許文献１１には、高温加熱を行なう前のスラブに６０ｍｍ以上の幅圧下を付与することによって耳割れを防止する技術、特許文献１２には圧下率が１〜２０％の水平圧下や圧下率が１〜２０％の幅圧下を付与することによって耳割れを防止する技術が開示されている。これらの技術は、高温加熱を行なう前のスラブに歪が与えられることによって、高温加熱の際に再結晶が進行して結晶粒の粗大化を抑制して、幅方向端部の形状を良好に維持でき、耳割れ防止が可能となる。しかし、耳割れを防止するためには幅圧下を大きくする必要がある。幅圧下を大きくすると、スラブの表層部に表面割れが発生し易くなる。つまり特許文献１１、特許文献１２に開示された技術では、耳割れを防止することは可能ではあるが、表面割れにより鋼板が割れ、その結果、歩留りの低下、ひいては製造コストの上昇を招く。 For example, Patent Document 11 discloses a technique for preventing ear cracking by applying a width reduction of 60 mm or more to a slab before high temperature heating, and Patent Document 12 discloses horizontal reduction or reduction with a reduction rate of 1 to 20%. A technique for preventing ear cracking by applying a width reduction of 1 to 20% is disclosed. In these techniques, strain is applied to the slab before high temperature heating, so that recrystallization progresses during high temperature heating to suppress coarsening of the crystal grains and improve the shape of the widthwise end portion. It can be maintained and the ear crack can be prevented. However, it is necessary to increase the width reduction in order to prevent ear cracking. When the width reduction is increased, surface cracks are likely to occur in the surface layer portion of the slab. In other words, with the techniques disclosed in Patent Documents 11 and 12, it is possible to prevent ear cracks, but surface cracks cause the steel sheet to crack, resulting in a decrease in yield and an increase in manufacturing cost.
特許文献１３には、仕上げ圧延の圧延時に後段３スタンドの累積圧下率を５０％以上かつ、最終パスの圧下率を３０％以下かつ板幅減少率を０．０４以下とすることで、耳割れを防止する技術が開示されている。しかしながら、高Ｓｉ化した鋼における圧延において同様の基準で圧延した場合、１０ｍｍ程度の耳割れが残存する場合があった。さらに、表面割れが発生する場合があった。 In Patent Document 13, when the rolling of finish rolling is performed, the cumulative rolling reduction of the latter three stands is 50% or more, the rolling reduction of the final pass is 30% or less, and the strip width reduction rate is 0.04 or less, thereby cracking the ears. A technique for preventing the above is disclosed. However, when rolling on the steel having a high Si content, the edge cracks of about 10 mm may remain when rolled on the same basis. Furthermore, surface cracks may occur.
本発明は、高Ｓｉ含有のスラブを熱間圧延する際に生じる鋼板の割れを効果的に軽減して、歩留まり高く熱延鋼板を製造することができる熱延鋼板の製造方法を提案することを目的とする。
なお、本発明において、高Ｓｉ含有のスラブとは、Ｓｉを２．０〜４．０質量％含有するスラブを意味する。
The present invention proposes a method for producing a hot-rolled steel sheet, which can effectively reduce cracks in the steel sheet that occur during hot rolling of a slab having a high Si content and can produce a hot-rolled steel sheet with high yield. To aim.
In the present invention, the slab having a high Si content means a slab containing 2.0 to 4.0 mass% of Si.
上記課題を解決するに当たり、本発明者らは高Ｓｉを含有したスラブの熱間圧延時に割れが発生するコイルの熱延条件を詳細に調査した。その結果、熱間圧延前のスラブの加熱温度が同じであっても、各圧延スタンドの圧下率に応じて、鋼板に割れが発生しやすいケースと発生しにくいケースがあることが判明した。 In solving the above problems, the present inventors have investigated in detail the hot rolling conditions of a coil in which cracks occur during hot rolling of a slab containing high Si. As a result, it was revealed that even if the heating temperature of the slab before hot rolling is the same, there are cases where cracks easily occur in the steel sheet and cases where cracking does not occur easily depending on the rolling reduction of each rolling stand.
各圧延スタンドの圧下率が異なると、各圧延時の圧延荷重が異なり、一般には圧下率を大きく設定すると、圧延荷重が大きくなる。詳細に各圧延スタンドの圧下率を調べると、ある圧延スタンドの圧下率が大きい、すなわち圧延荷重が大きくなるケースで鋼板に割れが発生していることを見出した。 When the rolling reduction of each rolling stand is different, the rolling load at each rolling is different. Generally, when the rolling reduction is set to be large, the rolling load becomes large. When the rolling reduction of each rolling stand was examined in detail, it was found that the steel sheet was cracked in the case where the rolling reduction of a certain rolling stand was large, that is, the rolling load was large.
そこで発明者らは操業性を損なわずに圧延荷重を低減する効率的な方法を検討した。各圧延スタンドの圧延荷重を低減すれば、熱間圧延中に割れが生じない。しかしその一方で、鋼板に割れが発生しないよう各圧延スタンドの圧延荷重を小さくしすぎると、目的とする最終仕上げの厚みに達しない可能性が生じる。したがって、製造する鋼板ごとに割れが発生しない荷重の限度が個々の圧延スタンドごとにわかれば、それ以下の荷重で圧延することで効率的に最終仕上げ厚みを達することができる。それには、鋼板そのものの変形抵抗力が求まればよい。そこで本発明者らは、熱間圧延時の変形抵抗力を以下に示す方法であらかじめ求めることによって、割れを発生しないパススケジュールを操業条件とする方法を見出した。 Therefore, the inventors examined an efficient method for reducing the rolling load without impairing the operability. If the rolling load of each rolling stand is reduced, cracking does not occur during hot rolling. On the other hand, however, if the rolling load of each rolling stand is too small so that cracks do not occur in the steel sheet, there is a possibility that the target final finish thickness may not be reached. Therefore, if the limit of the load that does not cause cracking for each steel sheet to be manufactured is known for each rolling stand, the final finished thickness can be efficiently reached by rolling with a load less than that. For that purpose, the deformation resistance of the steel plate itself may be obtained. Therefore, the present inventors have found a method in which a pass schedule that does not cause cracking is set as an operating condition by previously obtaining the deformation resistance during hot rolling by the method described below.
本発明では次の技術により、鋼板の変形抵抗力を下記の手順により算出する。 In the present invention, the deformation resistance of the steel sheet is calculated by the following procedure by the following technique.
バルク鉄中に固溶原子であるＳｉ原子をランダムに分散させ、そのマトリクス中の転位運動時の変形抵抗力（σin(y,z))を下記（５）式から算出する工程と、ある一定の外部応力（σapp）を加えたうえで転位運動を下記（６）式から計算する工程と、転位が止められることなく運動するときの外部応力を変形抵抗力とみなす工程で、変形抵抗力を算出する。 There is a step of randomly dispersing solid solution Si atoms in bulk iron and calculating the deformation resistance force (σ in (y, z)) in dislocation motion in the matrix from the following formula (5). In the process of calculating the dislocation motion from the following equation (6) after applying a constant external stress (σ app ) and the process of considering the external stress when the dislocation moves without being stopped as the deformation resistance force, Calculate the force.
具体的に、変形抵抗力を算出する方法を図１を用いて説明する。 Specifically, a method of calculating the deformation resistance will be described with reference to FIG.
図１の［１］は、バルク鉄を示している。図１の［２］は、バルク鉄中に固溶原子であるＳｉ原子をランダムに一定の数を分散させたときの様子を示した図である。図１の［３］は、バルク鉄中にＳｉ原子をランダムに分散させた後に転位を導入した様子を示している。なお、この手順は逆でも良く、転位を導入した後にＳｉ原子をランダムに分散させても良い。［２］・［３］の手順終了後、（５）式を計算した後、（６）式へ代入し、外部応力（σapp）がゼロの下で（６）式を解き、転位の初期位置を求める。 [1] in FIG. 1 indicates bulk iron. [2] of FIG. 1 is a diagram showing a state in which a fixed number of Si atoms, which are solid solution atoms, are randomly dispersed in bulk iron. [3] in FIG. 1 shows a state in which dislocations are introduced after randomly dispersing Si atoms in bulk iron. Note that this procedure may be reversed, and Si atoms may be randomly dispersed after introducing dislocations. After the procedure of [2] and [3] is completed, after calculating the equation (5), it is substituted into the equation (6), and the equation (6) is solved when the external stress (σ app ) is zero, and the initial dislocation Find the position.
転位の初期位置を求めた後、図１の［４］に示すように、ある一定の外部応力（σapp）を加え（５）式と（６）式を連立して解くことで転位の位置を求める。転位の位置を求めた後、外部応力を少し大きくし、再度（５）式と（６）式を連立して解く。
そして、上記計算を繰り返して、転位が止まらずに動き続けるときの外部応力を変形抵抗力とする（図１の［５］）。
After obtaining the initial position of the dislocation, as shown in [4] of FIG. 1, a certain external stress (σ app ) is added to solve the positions of the dislocation by solving the equations (5) and (6) simultaneously. Ask for. After obtaining the position of dislocation, increase the external stress a little and solve the equations (5) and (6) simultaneously.
Then, the above calculation is repeated, and the external stress when the dislocation continues to move without stopping is defined as the deformation resistance ([5] in FIG. 1).
表１に示した鋼種から上記方法で算出した変形抵抗力とJIS５号試験片を作成し、単軸の引張試験を行うことで測定した引張強さ（変形抵抗力）の実測値との比較を図２に示す。
図２に示すように、上記方法で算出した変形抵抗力は、引張試験により測定した変形抵抗力の実測値と良好に一致することが確認できた。
The deformation resistance calculated from the steel types shown in Table 1 and JIS No. 5 test pieces were created and compared with the measured values of tensile strength (deformation resistance) measured by performing a uniaxial tensile test. As shown in FIG.
As shown in FIG. 2, it was confirmed that the deformation resistance calculated by the above method was in good agreement with the measured value of the deformation resistance measured by the tensile test.
上記変形抵抗の算出式（（５）式、（６）式）を本発明の高Ｓｉ鋼に適用し、Ｓｉ原子の組成に依存する形で、以下の手順で簡略化すると下記（１）式の右辺が得られる。 The deformation resistance calculation formulas ((5) and (6)) are applied to the high Si steel of the present invention, and the formula (1) is simplified as follows depending on the composition of Si atoms. The right side of is obtained.
スラブ中のＳｉの含有量をcsi（原子％）として、前述した［１］〜［５］の手順により、Ｓｉ含有量の異なる各スラブについて、各Ｓｉの含有量に対する変形抵抗力を求め、各Ｓｉの含有量に対する変形抵抗力、すなわちcsi（原子％）に対する変形抵抗力を、
k√csiの形式に簡略化することで（１）式の右辺が得られる。
With the content of Si in the slab as c si (atomic%), the deformation resistance with respect to the content of each Si is obtained for each slab having different Si content by the procedure of [1] to [5] described above. The deformation resistance with respect to the content of each Si, that is, the deformation resistance with respect to c si (atomic%),
The right side of equation (1) can be obtained by simplifying to the form of k√c si .
この方法により、各Ｓｉの含有量に対する引張試験片を作成することなく、あらかじめ２．０〜４．０％Ｓｉの高Ｓｉ鋼の変形抵抗力が推定できるので、それを用いて割れを発生させない各圧延スタンドの最大圧下率rmを下記（１）式より決定し、機械的かつ簡便に熱延条件を決定することが可能になった。なお、下記（１）式の左辺は、各圧延スタンドにおいて、鋼板割れが発生しやすくなる場合と抑制しやすくなる場合との閾値となる荷重（最大荷重）を示している。 With this method, the deformation resistance of high Si steel of 2.0 to 4.0% Si can be estimated in advance without creating tensile test pieces for each Si content, so that cracking does not occur using it. the maximum reduction ratio r m of the rolling stands determined from the following equation (1), it made it possible to determine the mechanical and simple hot rolling conditions. In addition, the left side of the following formula (1) indicates a load (maximum load) that is a threshold value in each of the rolling stands when the steel plate crack is likely to occur and when it is easily suppressed.
すなわち、本発明の要旨構成は次のとおりである。
［１］スラブを圧延スタンドで熱間圧延して熱延鋼板を製造する熱延鋼板の製造方法であって、質量％で、Ｓｉ：２．０〜４．０％を含有するスラブを圧延スタンドで熱間圧延するに際し、各圧延スタンドにおいて上記（１）式により求めた最大圧下率rmを超えない圧下率で圧延する、熱延鋼板の製造方法。
［２］前記スラブは、質量％で、Ｃ：０．１２０％以下、Ｓｉ：２．０〜４．０％、Ｍｎ：０．００５〜３．０％、Ｐ：０．００１〜０．４０％、Ｓ：０．１０％以下を含有し、残部がＦｅおよび不可避的不純物からなる組成を有する、［１］に記載の熱延鋼板の製造方法。
That is, the gist of the present invention is as follows.
[1] A hot-rolled steel sheet manufacturing method for hot-rolling a slab in a rolling stand to produce a hot-rolled steel sheet, wherein a slab containing Si: 2.0 to 4.0% in mass% is rolled. upon hot rolling in, rolling in the above (1) maximum rolling reduction rolling reduction not exceeding r m obtained by equation at each rolling stand, a manufacturing method of hot-rolled steel sheet.
[2] The slab, in mass%, is C: 0.120% or less, Si: 2.0 to 4.0%, Mn: 0.005 to 3.0%, P: 0.001 to 0.40. %, S: 0.10% or less, and the balance is Fe and inevitable impurities. The method for producing a hot-rolled steel sheet according to [1].
本発明の圧延鋼板の製造方法を用いれば、鋼板割れのリスクを軽減した高Ｓｉ含有の熱延鋼板が製造される。また、ある温度における鋼板割れが起こる各圧延スタンドの最大圧下率がわかるため、従来の技術に比べ比較的低温のスラブ加熱で、かつ予め鋼板に歪を与えることなく鋼板割れを低減し、歩留まり高く熱延鋼板を製造することができる。 By using the method for producing a rolled steel sheet according to the present invention, a hot-rolled steel sheet having a high Si content and reduced risk of steel sheet cracking is produced. In addition, since the maximum rolling reduction of each rolling stand at which a steel plate crack occurs at a certain temperature can be known, the steel plate crack can be reduced by heating the slab at a relatively low temperature as compared with the conventional technology and without predistorting the steel plate, thus increasing the yield. A hot rolled steel sheet can be manufactured.
以下、本発明を具体的に説明する。まず、本発明において、素材であるスラブの成分組成を限定した理由について説明する。なお、成分に関する「％」表示は特に断らない限り質量％（ｍａｓｓ％）を意味する。 Hereinafter, the present invention will be specifically described. First, the reason for limiting the component composition of the slab as a raw material in the present invention will be described. In addition, the "%" display regarding components means mass% (mass%) unless otherwise specified.
Ｓｉ：２．０〜４．０％
Ｓｉは、鋼の比抵抗を高めて鉄損を低減する有効成分であるが、含有量が４．０％を超えると延性が損なわれ、割れやすくなる。一方２．０％に満たないと高い比抵抗が得られず、十分な鉄損低減効果が得られないので、Ｓｉの含有量は２．０〜４．０％の範囲に限定した。
Si: 2.0-4.0%
Si is an effective component that increases the specific resistance of steel and reduces iron loss, but if the content exceeds 4.0%, the ductility is impaired and cracking easily occurs. On the other hand, if it is less than 2.0%, a high specific resistance cannot be obtained and a sufficient iron loss reducing effect cannot be obtained, so the Si content is limited to the range of 2.0 to 4.0%.
また、本発明の製造方法を適用するスラブは、Ｓｉに加えて、以下の成分を含有する組成を有することが好ましい。 Further, the slab to which the manufacturing method of the present invention is applied preferably has a composition containing the following components in addition to Si.
Ｃ：０．１２０％以下
Ｃの含有量が０．１２０％を超えると、後続の脱炭焼鈍工程にて長時間を要するという不利が生じる。したがって、Ｃの含有量は０．１２０％以下とすることが好ましい。より好ましくはＣの含有量は０．０８０％以下である。
C: 0.120% or less When the content of C exceeds 0.120%, there is a disadvantage that a long time is required in the subsequent decarburization annealing step. Therefore, the C content is preferably 0.120% or less. More preferably, the C content is 0.080% or less.
Ｍｎ：０．００５〜３．０％
Ｍｎは、Ｓｉと同様に電気抵抗を高めて鉄損を低減させる元素である。また、製造時の熱間加工性を向上させる効果も有する。その効果を得るためにはＭｎを０．００５％以上含有させることが好ましい。一方、Ｍｎの含有量が３．０％を超えると磁束密度の低下を招くおそれがある。よって、Ｍｎの含有量を０．００５〜３．０％の範囲とすることが好ましい。
Mn: 0.005-3.0%
Mn is an element that increases electric resistance and reduces iron loss, similar to Si. It also has the effect of improving hot workability during manufacturing. In order to obtain the effect, Mn is preferably contained in an amount of 0.005% or more. On the other hand, if the Mn content exceeds 3.0%, the magnetic flux density may be reduced. Therefore, it is preferable to set the Mn content in the range of 0.005 to 3.0%.
Ｐ：０．００１〜０．４０％
Ｐは、鋼板素材の強度を上昇させる効果があるので、０．００１％以上含有することが好ましい。しかしながら、多量添加は冷間圧延性が低下する。また、Ｐは、鋼中で偏析する傾向が強く、溶接部の脆化を招く。このため、Ｐの含有量の上限を０．４０％とすることが好ましい。Ｐの含有量は、より好ましくは０．３０％以下である。
P: 0.001 to 0.40%
Since P has the effect of increasing the strength of the steel sheet material, it is preferable to contain 0.001% or more. However, the addition of a large amount lowers the cold rolling property. Further, P has a strong tendency to segregate in the steel and causes embrittlement of the welded portion. Therefore, the upper limit of the P content is preferably 0.40%. The P content is more preferably 0.30% or less.
Ｓ：０．１０％以下
Ｓは、鋼中で主として介在物として存在し耐食性を低下させるため、極力低減することが望ましいが、０．１０％までであれば許容できるため、本発明では、Ｓ量の含有量の上限を０．１０％とすることが好ましい。より好ましくはＳ量の含有量は０．０５％以下である。一方、Ｓを低減するためには、製造コストが上昇する。また、製鋼能力の点からも難しい。よって、Ｓの含有量の下限は０．００１％程度とすることが好ましい。
S: 0.10% or less S is mainly present as inclusions in the steel and lowers the corrosion resistance, so it is desirable to reduce it as much as possible, but up to 0.10% is acceptable, so in the present invention, S The upper limit of the amount content is preferably 0.10%. More preferably, the content of S is 0.05% or less. On the other hand, in order to reduce S, the manufacturing cost increases. It is also difficult in terms of steelmaking ability. Therefore, the lower limit of the S content is preferably about 0.001%.
残部はＦｅおよび不可避的不純物であることが好ましい。
本願の対象は、上記記載の成分に限られるものではなく、電磁気特性の改善のために以下の添加元素を用いることは妨げない。Ｓｅ、Ａｌ、Ｎ、Ｓｎ、Ｓｂ、Ｍｏ、Ｃｒ、Ｎｉ、Ｃｕ、Ｂｉ、Ｂ、Ｎｂ、Ｔａを合計で０．５％以下の範囲内で添加することができる。
The balance is preferably Fe and inevitable impurities.
The subject matter of the present application is not limited to the components described above, and the use of the following additive elements for improving electromagnetic characteristics is not hindered. Se, Al, N, Sn, Sb, Mo, Cr, Ni, Cu, Bi, B, Nb, and Ta can be added within a range of 0.5% or less in total.
次に、本発明の熱延鋼板の製造工程について説明する。
上記の成分組成に調整した溶鋼を、転炉、電気炉などを用いる公知の方法で精錬し、必要があれば真空処理などを施したのち、通常の造塊法や連続鋳造法を用いてスラブを製造する。また、直接鋳造法を用いて１００ｍｍ以下の厚さの薄鋳片を直接製造してもよい。
Next, the manufacturing process of the hot rolled steel sheet of the present invention will be described.
Molten steel adjusted to the above component composition is smelted by a known method using a converter, an electric furnace, etc. and, if necessary, subjected to a vacuum treatment, etc., and then a slab is formed using a usual ingot-making method or continuous casting method. To manufacture. Further, a thin cast piece having a thickness of 100 mm or less may be directly manufactured by using the direct casting method.
スラブを熱間圧延するに際して行うスラブ加熱（スラブ再加熱）は、ガス燃焼炉または電気式加熱炉あるいはその両方を用いてよい。加熱炉で加熱したスラブは、熱間粗圧延を行い、引き続き熱間仕上げ圧延を行って熱延鋼板とする。この熱間圧延における割れを防止するため、本発明では次に述べる手順に従い、各圧延スタンドの圧下率を制御することで熱間圧延を実施する。 The slab heating (slab reheating) performed when hot rolling the slab may use a gas combustion furnace, an electric heating furnace, or both. The slab heated in the heating furnace is subjected to hot rough rolling and then hot finish rolling to obtain a hot rolled steel sheet. In order to prevent the cracks in the hot rolling, hot rolling is performed in the present invention by controlling the rolling reduction of each rolling stand according to the procedure described below.
すなわち、本発明では、スラブを圧延スタンドで熱間圧延する際の圧下率を、各圧延スタンド（各圧延パス）において上記（１）式により求めた最大圧下率rmを超えない範囲のパススケジュールで制御する。
なお、本発明では、少なくとも仕上げ圧延の各圧延スタンドにおいて上記制御を行う必要がある。好ましくは、粗圧延と仕上げ圧延の各圧延スタンドにおいて上記制御を行う。
以上により、熱間圧延時の鋼板の割れを軽減した、高Ｓｉ含有の熱延鋼板が製造される。
That is, in the present invention, the rolling schedule when hot rolling the slab in the rolling stand is a pass schedule in a range not exceeding the maximum rolling reduction r m obtained by the above formula (1) in each rolling stand (each rolling pass). Control with.
In the present invention, it is necessary to perform the above control at least in each rolling stand for finish rolling. Preferably, the above control is performed in each rolling stand of rough rolling and finish rolling.
As described above, a hot-rolled steel sheet having a high Si content in which cracking of the steel sheet during hot rolling is reduced is manufactured.
（実施例１）
表２に示す組成を有する鋼Ｎｏ．ＡおよびＢの溶鋼から厚さ２４０ｍｍのスラブを連続鋳造により製造した。ついで、これらスラブを、ガス燃焼炉で１２００℃に加熱したのち、粗圧延で板厚４０．０ｍｍのシートバーとし、引き続き仕上げ圧延により３．０ｍｍ厚の熱延鋼板とした。表３中、Ａ−Ｉ、Ａ−ＩＩは、鋼Ｎｏ．Ａから製造した熱延鋼板であり、Ｂ−Ｉ、Ｂ−ＩＩは、鋼Ｎｏ．Ｂから製造した熱延鋼板である。
(Example 1)
Steel No. having the composition shown in Table 2 A slab having a thickness of 240 mm was produced by continuous casting from the molten steels A and B. Then, these slabs were heated to 1200 ° C. in a gas combustion furnace, rough-rolled into a sheet bar having a plate thickness of 40.0 mm, and subsequently subjected to finish rolling into a hot-rolled steel plate having a thickness of 3.0 mm. In Table 3, A-I and A-II are steel Nos. It is a hot rolled steel sheet manufactured from A, B-I and B-II are steel No. It is a hot rolled steel sheet manufactured from B.
その際、各仕上げ圧延スタンド（第１スタンドから順にＦ１、Ｆ２、…、Ｆ５）の圧下率rを表３となるようにロール位置の調整を行った。表３中のＡ−ＩＩ、Ｂ−ＩＩがそれぞれ鋼Ｎｏ．ＡおよびＢのスラブから本発明による圧延方法で製造した熱延鋼板である。また、図３と図４にそれぞれ各鋼種のスラブから圧延鋼板を製造した際の、各圧延スタンドにおける（１）式中の左辺から右辺を引いた応力差を示す（なお、この際の左辺は、rmに変えて上記圧下率rを用いて計算）。この応力差が正のほうへと大きくなるほど、鋼板割れの危険度が大きくなる。なお、表３に、（１）式により求めた最大圧下率rm以下の圧下率rで圧延した場合を圧延条件○、前記rmを超えた圧下率rで圧延した場合を圧延条件×で示した。 At that time, the roll position was adjusted so that the rolling reduction r of each finish rolling stand (F1, F2, ..., F5 from the first stand) was as shown in Table 3. A-II and B-II in Table 3 are steel Nos. It is a hot-rolled steel sheet manufactured by the rolling method according to the present invention from the slabs of A and B. Further, FIGS. 3 and 4 show stress differences obtained by subtracting the right side from the left side in the formula (1) in each rolling stand when manufacturing a rolled steel sheet from slabs of each steel type (the left side at this time is , R m instead of, and calculated using the above reduction ratio r). As the stress difference increases toward the positive side, the risk of steel plate cracking increases. In Table 3, the rolling condition is ○ when rolling is performed at a rolling reduction r that is equal to or less than the maximum rolling reduction r m obtained by the equation (1), and the rolling condition is x when rolling is performed at a rolling reduction r that exceeds the r m. Indicated.
得られた鋼板の耳割れ最大深さ及び表面割れの有無について調べた結果を、表３に併記する。なお、表３の表面割れについては、表面割れが観察されたケースを×、観察されなかったケースを○と記載した。表３から明らかなように、本発明の製造方法により製造した熱延鋼板は、いずれも耳割れ深さが５ｍｍ以下であり、耳割れの発生が格段に軽減されている。また、表面割れも防ぐことができている。一方、比較例ではいずれも１５ｍｍを超える耳割れの発生が余儀なくされ、鋼種Ａにいたっては表面割れも確認された。
また、発明例では、鋼板の加熱温度を１２００℃と比較的低温にしたため、不連続なしわ状の突起がなく、その結果、しわ部に発生する局所的な応力集中による割れも見られなかった。
Table 3 also shows the results of examining the maximum depth of edge cracks and the presence or absence of surface cracks of the obtained steel sheet. Regarding the surface cracks in Table 3, the case where the surface cracks were observed was described as x, and the case where the surface cracks were not observed was described as o. As is clear from Table 3, the hot-rolled steel sheets produced by the production method of the present invention all have a crack depth of 5 mm or less, and the occurrence of crack edges is significantly reduced. Also, surface cracks can be prevented. On the other hand, in each of the comparative examples, the occurrence of edge cracks of more than 15 mm was unavoidable, and surface cracks were also confirmed for steel type A.
Further, in the invention examples, since the heating temperature of the steel sheet was set to a relatively low temperature of 1200 ° C., there were no discontinuous wrinkle-like projections, and as a result, cracks due to local stress concentration generated in the wrinkles were not observed. ..
（実施例２）
Ｃ：０．０６質量％、Ｓｉ：３．６質量％、Ｍｎ：０．０７質量％、Ｓ：０．０２質量％、Ｐ：０．００３質量％を含有し、残部がＦｅおよび不可避的不純物から成る組成を有する鋼（鋼Ｎｏ．Ｃ）の溶鋼から厚さ２２０ｍｍのスラブを連続鋳造により製造した。ついで、前記スラブを、ガス燃焼炉で１２００℃に加熱した後、粗圧延で４０．０ｍｍのシートバーとし、引き続き計７つのスタンドの仕上げ圧延により２．２ｍｍ厚の熱延鋼板とした。
(Example 2)
C: 0.06% by mass, Si: 3.6% by mass, Mn: 0.07% by mass, S: 0.02% by mass, P: 0.003% by mass, the balance being Fe and unavoidable impurities A slab having a thickness of 220 mm was produced by continuous casting from a molten steel of a steel (steel No. C) having a composition of. Next, the slab was heated to 1200 ° C. in a gas combustion furnace, rough-rolled to a sheet bar of 40.0 mm, and then finish-rolled with a total of seven stands to obtain a hot-rolled steel sheet having a thickness of 2.2 mm.
その際、各仕上げ圧延スタンド（第１スタンドから順にＦ１、Ｆ２、…、Ｆ７）の圧下率rをそれぞれ表４となるようにロール位置の調整を行った。なお、このとき最終スタンド（Ｆ７）における板幅減少率を０．０４とした。図５に、上記スラブから圧延鋼板を製造した際の、各圧延スタンドにおける（１）式中の左辺から右辺を引いた応力差を示す（なお、この際の左辺は、rmに変えて上記圧下率rを用いて計算）。この応力差が正のほうへと大きくなるほど、鋼板割れの危険度が大きくなる。また、表４に、（１）式により求めた最大圧下率rm以下の圧下率rで圧延した場合を圧延条件○、前記rmを超えた圧下率rで圧延した場合を圧延条件×で示した。さらに、表４には後段３スタンド（Ｆ５〜Ｆ７）における累積圧下率を示した。なお、表４の比較例Ｃ−Ｉは、特許文献１３の圧延条件を満たすように圧延を行ったものである。 At that time, the roll position was adjusted so that the rolling reductions r of the finish rolling stands (F1, F2, ..., F7 in order from the first stand) are as shown in Table 4. At this time, the plate width reduction rate in the final stand (F7) was set to 0.04. FIG. 5 shows a stress difference obtained by subtracting the right side from the left side in the formula (1) in each rolling stand when a rolled steel sheet is manufactured from the above slab (note that the left side at this time is changed to r m as described above). Calculation using the rolling reduction r). As the stress difference increases toward the positive side, the risk of steel plate cracking increases. Further, in Table 4, the rolling condition is ○ when rolling is performed at a rolling reduction r that is equal to or less than the maximum rolling reduction r m obtained by the equation (1), and the rolling condition is x when rolling is performed at a rolling reduction r that exceeds the r m. Indicated. Further, Table 4 shows the cumulative reduction ratios in the latter three stands (F5 to F7). In addition, Comparative Example CI of Table 4 was rolled such that the rolling conditions of Patent Document 13 were satisfied.
得られた鋼板の耳割れ最大深さ及び表面割れの有無について調べた結果を、表４に併記する。なお、表４の表面割れについては、表面割れが観察されたケースを×、観察されなかったケースを○と記載した。表４から明らかなように、比較例Ｃ−Iでは、特許文献１３の圧延条件（後段３スタンドの累積圧下率を５０％以上、最終パスの圧下率を３０％以下）を満たすように圧延を行ったが、耳割れ及び表面割れが観察された。一方で、本発明により求めた基準をもとに圧延した場合（発明例Ｃ−ＩＩ）、後段３スタンドの累積圧下率５０％以上を満たさない条件でＳｉを３．６質量％含有する鋼を圧延した場合においても耳割れ及び表面割れが発生しなかった。このように本発明の技術によれば、仕上熱延の各スタンド間の圧下率の関係を拘束することなく、また、板幅減少率とも関係なく耳割れおよび表面割れ欠陥の少ない熱間圧延を実施することができた。 Table 4 also shows the results of examining the maximum depth of edge cracks and the presence or absence of surface cracks of the obtained steel sheet. Regarding the surface cracks in Table 4, the case where the surface cracks were observed was described as x, and the case where the surface cracks were not observed was described as o. As is clear from Table 4, in Comparative Example C-I, rolling was performed so as to satisfy the rolling conditions of Patent Document 13 (cumulative reduction of the latter three stands of 50% or more and final pass reduction of 30% or less). After that, ear cracks and surface cracks were observed. On the other hand, when rolled based on the criteria determined by the present invention (Invention Example C-II), a steel containing 3.6 mass% of Si under the condition that the cumulative rolling reduction of 50% or more of the subsequent three stands is not satisfied. Even when rolled, no ear cracks or surface cracks occurred. As described above, according to the technique of the present invention, hot rolling with less edge cracking and surface cracking defects is performed without restraining the relationship of the reduction ratio between the stands for finish hot rolling, and regardless of the strip width reduction rate. It was possible to carry out.
Claims (2)
質量％で、Ｃ：０．１２０％以下、Ｓｉ：２．０〜４．０％、Ｍｎ：０．００５〜３．０％、Ｐ：０．００１〜０．４０％、Ｓ：０．１０％以下を含有し、残部がＦｅおよび不可避的不純物からなる組成を有するスラブを圧延スタンドで熱間圧延するに際し、
各圧延スタンドにおいて下記（１）式により求めた最大圧下率rmを超えない圧下率で圧延する、熱延鋼板の製造方法。
% By mass, C: 0.120% or less, Si: 2.0 to 4.0%, Mn: 0.005 to 3.0%, P: 0.001 to 0.40%, S: 0.10. % Or less, with the balance being Fe and unavoidable impurities , when hot rolling a slab having a composition of a rolling stand,
Rolling below (1) reduction ratio that does not exceed the maximum reduction ratio r m obtained by equation at each rolling stand, a manufacturing method of hot-rolled steel sheet.
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