JP3952954B2 - Method of ingot rolling of continuous cast slab - Google Patents
Method of ingot rolling of continuous cast slab Download PDFInfo
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- JP3952954B2 JP3952954B2 JP2003006183A JP2003006183A JP3952954B2 JP 3952954 B2 JP3952954 B2 JP 3952954B2 JP 2003006183 A JP2003006183 A JP 2003006183A JP 2003006183 A JP2003006183 A JP 2003006183A JP 3952954 B2 JP3952954 B2 JP 3952954B2
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- 238000005096 rolling process Methods 0.000 title claims description 96
- 238000000034 method Methods 0.000 title claims description 20
- 239000000463 material Substances 0.000 claims description 22
- 238000007711 solidification Methods 0.000 claims description 3
- 230000008023 solidification Effects 0.000 claims description 3
- 229910000831 Steel Inorganic materials 0.000 description 22
- 239000010959 steel Substances 0.000 description 21
- 238000010438 heat treatment Methods 0.000 description 14
- 230000007547 defect Effects 0.000 description 8
- 238000001514 detection method Methods 0.000 description 7
- 239000000047 product Substances 0.000 description 6
- 238000002791 soaking Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000011265 semifinished product Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000012423 maintenance Methods 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000002788 crimping Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000002706 hydrostatic effect Effects 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は、連続鋳造鋳片の分塊圧延方法に関し、詳しくは、鋳片の内部欠陥であるポロシティが圧着して内部品質に優れ、超音波探傷での合格率に優れた鋼片を製造するための連続鋳造鋳片の分塊圧延方法に関する。
【０００２】
【従来の技術】
連続鋳造鋳片、すなわち連続鋳造法によって鋳込まれたブルーム、スラブ等には、その横断面の中心部において長辺面と平行に凝固時に生成されるポロシティが存在する。鋳片の内部欠陥である上記ポロシティは、その後の製造工程で圧着されると製品品質には悪影響を及ぼすことはないが、圧着されないままで残存すると、強度や靱性が低下する原因となり、場合によっては致命的な欠陥になってしまう。
【０００３】
このため、特許文献１、特許文献２及び特許文献３に、熱間加工の段階でポロシティを除去する技術が開示されている。
【０００４】
すなわち、特許文献１には、上下一対のロールによって、低い歪速度と大きな圧下力で圧延する「熱間圧延方法」が開示されている。しかし、この公報で提案された技術の場合には、圧延能率が低下するため生産効率が低いという問題があった。
【０００５】
特許文献２には、鋼材の圧延中に作用する鋼材中心部の静水圧応力を規定した「内部欠陥の少ない鋼材の製造法」が開示されている。しかし、応力は被圧延材の変形抵抗、したがって被圧延材の化学組成に依存する。このため、応力での規定は必ずしも絶対的な基準とはならないし、被圧延材の断面に対して同じ方向から圧延し、その際の鋼材中心部圧下応力を大きくするだけでは内質欠陥であるポロシティが必ずしも圧着できるというものでもなく、したがって超音波探傷での高い合格率を確保できるというものではなかった。
【０００６】
特許文献３には、特定サイズの中断面ブルームである連続鋳造鋳片を特定の条件で２〜４パスで圧延する「条鋼用鋼片の製造方法とその装置」が開示されている。しかし、この公報で提案された技術は２〜４パスという少ないパス数で所望の鋼片に加工するものであるため、鋳片横断面のサイズ及び形状を一辺が１４０〜３００ｍｍである正方形又は、これと等価な断面積を有する長辺対短辺の比が１．６以下である矩形にする必要があり、生産性が低いという問題があった。更に、条鋼圧延に供される半製品としては適用できても、総圧下比が小さく圧延後にそのサイズのまま製品として用いることが難しい場合もあった。
【０００７】
なお、上記圧延における総圧下比とは下記の▲３▼式で表される値をいう。
【０００８】
総圧下比＝鋳片の断面積／圧延後の鋼片の断面積 ・・・▲３▼。
【０００９】
【特許文献１】
特開平３−１７４９０１号公報
【特許文献２】
特開平５−２２８５０２号公報
【特許文献３】
特開平１０−３０５３０１号公報
【００１０】
【発明が解決しようとする課題】
本発明は、上記現状に鑑みてなされたもので、その目的は、圧延能率を低下させることなく、鋳片の内部欠陥であるポロシティが圧着して内部品質に優れ、超音波探傷での合格率に優れた鋼片が得られるとともに、圧延後にその鋼片を半製品としてだけではなく、そのサイズのまま製品として用いることができる大断面の連続鋳造鋳片を分塊圧延する方法を提供することである。
【００１１】
【課題を解決するための手段】
本発明の要旨は、下記（１）及び（２）に示す連続鋳造鋳片の分塊圧延方法にある。
【００１２】
（１）横断面の寸法が一辺３３０ｍｍ以上の正方形又はこれと等価な断面積を有する矩形で、凝固完了後の表面温度が７００℃以上である連続鋳造ままの鋳片に、％単位での圧下率ｒが下記▲１▼式を満たす厚み方向及び幅方向の圧延を少なくとも各１パスずつ施し、且つ、全てのパスが下記▲２▼式を満たすことを特徴とする連続鋳造鋳片の分塊圧延方法。
【００１３】
２５．５≦ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲１▼、
ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲２▼。
【００１４】
ここで、ｒ＝｛１−（ｈnO／ｈni）｝×１００、Ｄn はｎ回目の圧延時のロール直径（ｍｍ）、ｈniとｈnOはそれぞれｎ回目の圧延前後の被圧延材の厚み（ｍｍ）、である。
【００１５】
（２）横断面の寸法が一辺３３０ｍｍ以上の正方形又はこれと等価な断面積を有する矩形の凝固を完了した連続鋳造鋳片を表面温度を１１００℃以上、且つ、鋳片表面と鋳片内部との温度差を２００℃以内として加熱した後、１回目の圧延前の鋳片表面温度を７００℃以上として、その鋳片に％単位での圧下率ｒが下記▲１▼式を満たす厚み方向及び幅方向の圧延を少なくとも各１パスずつ施し、且つ、全てのパスが下記▲２▼式を満たすことを特徴とする連続鋳造鋳片の分塊圧延方法。
【００１６】
２５．５≦ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲１▼、
ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲２▼。
【００１７】
ここで、ｒ＝｛１−（ｈnO／ｈni）｝×１００、Ｄn はｎ回目の圧延時のロール直径（ｍｍ）、ｈniとｈnOはそれぞれｎ回目の圧延前後の被圧延材の厚み（ｍｍ）、である。
【００１８】
なお、鋳片に「厚み方向及び幅方向の圧延を少なくとも各１パスずつ施す」とは、圧延前の鋳片で見た場合の「厚み」方向と「幅」方向とに対して、少なくとも各１パスずつの圧延を施すことを意味する。
【００１９】
上記の「Ｄn ／ｈni」はいわゆる「ロール径比」と称されるものであり、以下の説明においてはこの用語を用いることもある。
【００２０】
なお、上記（１）は、連続鋳造鋳片を均熱炉や加熱炉で加熱することなく鋳片の有する顕熱を利用して分塊圧延する方法であり、一方、上記（２）は、連続鋳造鋳片を均熱炉や加熱炉で加熱した後に分塊圧延する方法である。
【００２１】
【発明の実施の形態】
本発明者らは、前記した目的を達成するために、応力のように被圧延材の化学組成に依存することがなく、しかも通常の３次元剛塑性有限要素解析（以下、単にＦＥＭ解析という）によって比較的容易に求めることができる被圧延材中心部の圧下方向に対する圧縮歪に着目して種々の検討を行った。その結果、下記（ａ）〜（ｅ）の知見が得られた。
【００２２】
（ａ）図１に示すように圧延方向をｚ、被圧延材の横断面における圧下方向をｙ及び圧下方向に垂直な方向（つまり、ロール軸に平行な方向）をｘとして圧延する場合、ポロシティ圧着のためには被圧延材中心部に対して連続する多パス圧延の異なる２方向からの圧延によりそれぞれのパスでのｙ方向に圧縮歪が加わるように、換言すれば、元の被圧延材のｙ方向とｘ方向に圧縮歪が加わるようにすればよい。上記の場合、被圧延材中心部に対するｚ方向の歪はポロシティの圧着には影響を及ぼさない。これは、たとえｚ方向に引張歪が作用しても、ｙ方向及びｘ方向に圧縮歪が加わっておりさえすれば、ポロシティが圧着されるからである。なお、実施例の説明においては、上記のｙ方向及びｘ方向に関する被圧延材の寸法をそれぞれ「厚み」及び「幅」という。
【００２３】
（ｂ）被圧延材の原寸法と最終仕上げ寸法が固定されている場合、多パス圧延における合計の圧縮歪が一定であっても、圧下率の配分を変えて１つ以上のパスにおいて強圧下圧延することでｙ方向へのポロシティ圧着効果を増大させることができる。
【００２４】
（ｃ）ｙ方向に強圧下を加えても、ｘ方向への引張り歪の増大に基づくポロシティの拡大を生じない場合がある。
【００２５】
（ｄ）ロール径比はポロシティの圧着効果と相関を有する。
【００２６】
（ｅ）ポロシティを圧着させるとともに鋼片の表面性状をも高めるためには、連続鋳造鋳片の温度を管理することが重要になる。
【００２７】
本発明は、上記の知見に基づいて完成されたものである。
【００２８】
以下、本発明の各要件について詳しく説明する。
（Ａ）連続鋳造鋳片横断面の寸法
本発明においては、分塊圧延したサイズのままで製品としても用いるために、横断面の寸法が一辺３３０ｍｍ以上の正方形又はこれと等価な断面積を有する矩形の大断面連続鋳造鋳片を対象とする。上記の横断面寸法とすることによって、分塊圧延だけで大きな総圧下比が確保でき、したがって、分塊圧延したサイズのままでも製品として十分用いることが可能となる。
【００２９】
なお、横断面寸法の上限は、一辺５００ｍｍの正方形又はこれと等価な断面積を有する矩形とするのがよい。又、横断面形状が矩形の場合、その長辺と短辺の比は１．８以下とするのがよい。
（Ｂ）連続鋳造鋳片の温度
（Ｂ−１）均熱炉や加熱炉で加熱することなく鋳片の有する顕熱を利用して分塊圧延する場合：
連続鋳造した鋳片を均熱炉や加熱炉で加熱することなく鋳片の有する顕熱を利用して分塊圧延し、ポロシティを圧着させるとともに鋼片の表面性状をも高めるためには、連続鋳造鋳片が凝固完了後に表面温度７００℃以上の状態で後述する（Ｃ）項に記載の条件で分塊圧延する必要がある。表面温度が７００℃を下回ると、鋼片に生じる表面疵が多くなって手入れに多大の工数を要するし、圧延時の変形抵抗も大きくなる。
（Ｂ−２）均熱炉や加熱炉で加熱した後に分塊圧延する場合：
連続鋳造した鋳片を均熱炉や加熱炉で加熱した後に分塊圧延し、ポロシティを圧着させるとともに鋼片の表面性状をも高めるためには、表面温度を１１００℃以上、且つ、鋳片表面と鋳片内部との温度差を２００℃以内として加熱した後、１回目の圧延前の鋳片表面温度を７００℃以上として、後述する（Ｃ）項に記載の条件で分塊圧延する必要がある。加熱時の表面温度が１１００℃を下回ったり１回目の圧延前の鋳片表面温度が７００℃を下回ると、鋼片に生じる表面疵が多くなって手入れに多大の工数を要するし、圧延時の変形抵抗も大きくなるからである。更に、鋳片表面と鋳片内部との温度差が２００℃を超える場合には内部欠陥が圧着し難いし、圧延時の変形抵抗も大きくなる。なお、加熱時の表面温度の上限は１３５０℃とすればよい。
（Ｃ）圧延条件
本発明においては、％単位での圧下率ｒが前記▲１▼式を満たす厚み方向及び幅方向の圧延を少なくとも各１パスずつ施し、且つ、全てのパスが前記▲２▼式を満たすようにする。
【００３０】
２５．５≦ｒ×（Ｄn ／ｈni）0.07 の条件から外れる、つまり、％単位での圧下率ｒが２５．５×（Ｄn ／ｈni）-0.07 未満の場合には、厚み方向への十分なポロシティ圧着効果が得られない。
【００３１】
一方、ｒ×（Ｄn ／ｈni）0.07 ≦３１．０の条件から外れる、つまり、％単位での圧下率ｒが３１．０×（Ｄn ／ｈni）-0.07 を超える場合には、被圧延材の形状が矩形から平行四辺形に変化して後続の圧延ができなくなったり、ポロシティが開口したりする場合がある。
【００３２】
したがって、本発明おいては、％単位での圧下率ｒが前記▲１▼式を満たす厚み方向及び幅方向の圧延を少なくとも各１パスずつ施し、更に、圧延における全てのパスが前記▲２▼式を満たすこととした。ここで、Ｄn 、ｈni及びｈnOは、既に述べたように、それぞれｎ回目の圧延時のロール直径（ｍｍ）、ｎ回目の圧延前の被圧延材の厚み（ｍｍ）、ｎ回目の圧延後の被圧延材の厚み（ｍｍ）を指す。
【００３３】
以下、実施例により本発明を更に詳しく説明する。
【００３４】
【実施例】
表１に示す化学組成を有する鋼を通常の方法で溶製し、横断面の寸法が長辺４００ｍｍで短辺３００ｍｍである矩形状に連続鋳造した。
【００３５】
【表１】
次いで、長さ４５００ｍｍに切断した上記の鋳片について、（イ）鋳片の有する顕熱を利用して分塊圧延する、（ロ）加熱炉で加熱してから分塊圧延する、の２つの場合について圧延テストを行った。
【００３７】
なお、（イ）の場合において、分塊圧延前の各供試鋳片の表面温度はほぼ９００℃であった。一方、（ロ）の場合には、鋳片の表面温度がほぼ１２００℃で、鋳片表面と鋳片内部との温度差がほぼなくなるまで十分に加熱し、各供試鋳片の表面温度がほぼ１０４０℃の状態で分塊圧延の１回目の圧延（１パス目の圧延）に供した。
分塊圧延は次のようにして行った。すなわち、２Ｈｉリバース分塊圧延機を用いて総圧下比が３．０となるように粗圧延して２００ｍｍ角にし、続いてＶＨミルで６パスの仕上げ圧延を施して１６０ｍｍ角に仕上げた。
【００３８】
ここで、上記の粗圧延における総圧下比とは下記の▲４▼式で表される値をいう。
【００３９】
総圧下比＝鋳片の断面積／粗圧延後の鋼片の断面積 ・・・▲４▼。
【００４０】
なお、上記の２Ｈｉリバース分塊圧延機を用いた粗圧延は、３００ｍｍの短辺側を「厚み」、４００ｍｍの長辺側を「幅」として１パス目の圧延を行い、２パス目以降はその詳細を表２〜５に示す「ケース１」から「ケース４」までの各条件で圧延した。ここで、各ケースの圧延は、「ケース１」が％単位での圧下率ｒが▲１▼式を満たすパスが全くない場合、「ケース２」が上記ｒが▲１▼式を満たすパスを１回だけ行う場合、「ケース３」が上記ｒが▲１▼式を満たすパスを圧延前の鋳片で見た場合の「幅」方向に対して２回行う場合、「ケース４」が上記ｒが▲１▼式を満たすパスを圧延前の鋳片で見た場合の「厚み」方向と「幅」方向とに対して各１回行う場合で、「ケース４」が本発明に係る圧延である。１６０ｍｍ角への圧延は各鋼の各条件についてそれぞれ５０回行った。なお、各表における「ターン」とは圧延の「厚み」方向と「幅」方向とを変えたこと、つまり被圧延材を９０度回転させたことを意味する。又、各表の備考欄における「○」印は、上記％単位での圧下率ｒが▲１▼式を満たすことを示す。
【００４１】
【表２】
【表３】
【表４】
【表５】
上記のようにして得た１６０ｍｍ角鋼片について、先ず、表面を目視で検査して表面性状を調査した。その結果、粗圧延前の鋳片はいずれも本発明の温度条件を満たすものであり、したがって、いずれの鋼片にも疵の発生は認められなかった。
【００４６】
次いで、通常の条件で超音波探傷を行った。表６に超音波探傷の結果を示す。
【００４７】
【表６】
表６から、本発明の方法である「ケース４」で分塊圧延した１６０ｍｍ角鋼片は超音波探傷の合格率が極めて高いことが明らかである。
【００４９】
【発明の効果】
本発明によれば、圧延能率を低下させることなく、鋳片の内部欠陥であるポロシティが圧着して内部品質に優れ、超音波探傷での合格率に優れた鋼片が得られる。又、本発明の分塊圧延における総圧下比は大きいので、圧延後にその鋼片を半製品としてだけではなく、そのサイズのまま製品として用いることができる。
【図面の簡単な説明】
【図１】圧延における座標軸を説明する図である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method of rolling a continuous cast slab. Specifically, the porosity, which is an internal defect of a slab, is pressure-bonded to produce a steel slab having excellent internal quality and excellent acceptance rate in ultrasonic flaw detection. The present invention relates to a method for split rolling of continuous cast slabs.
[0002]
[Prior art]
A continuous cast slab, that is, a bloom, a slab, or the like cast by a continuous casting method, has a porosity generated during solidification in parallel with the long side surface at the center of the cross section. The porosity, which is an internal defect of the slab, will not adversely affect the product quality when it is crimped in the subsequent manufacturing process, but if it remains unbonded, it will cause a decrease in strength and toughness. Becomes a fatal defect.
[0003]
For this reason, Patent Literature 1, Patent Literature 2 and Patent Literature 3 disclose techniques for removing porosity at the stage of hot working.
[0004]
That is, Patent Document 1 discloses a “hot rolling method” in which rolling is performed at a low strain rate and a large reduction force by a pair of upper and lower rolls. However, in the case of the technique proposed in this publication, there is a problem that the production efficiency is low because the rolling efficiency is lowered.
[0005]
Patent Document 2 discloses a “method for manufacturing a steel material with few internal defects” that defines the hydrostatic stress at the center of the steel material that acts during rolling of the steel material. However, the stress depends on the deformation resistance of the material to be rolled and thus the chemical composition of the material to be rolled. For this reason, the definition of stress is not necessarily an absolute standard, and rolling from the same direction with respect to the cross-section of the material to be rolled is an internal defect simply by increasing the steel center rolling stress at that time. Porosity is not necessarily capable of being crimped, and therefore, it has not been possible to ensure a high pass rate in ultrasonic flaw detection.
[0006]
Patent Document 3 discloses a “manufacturing method and apparatus for a steel strip for steel bars” in which a continuous cast slab that is a medium-section bloom of a specific size is rolled in 2 to 4 passes under a specific condition. However, since the technique proposed in this publication is to process a desired steel slab with a small number of passes of 2 to 4 passes, the size and shape of the slab cross section is a square whose side is 140 to 300 mm, or There is a problem in that productivity is low because it is necessary to form a rectangle having a long side to short side ratio of 1.6 or less having an equivalent cross-sectional area. Furthermore, even if it can be applied as a semi-finished product used for strip rolling, it may be difficult to use it as a product after rolling because the total reduction ratio is small.
[0007]
The total rolling reduction ratio in the rolling refers to a value represented by the following formula (3).
[0008]
Total rolling ratio = cross-sectional area of slab / cross-sectional area of steel slab after rolling (3).
[0009]
[Patent Document 1]
JP-A-3-174901 [Patent Document 2]
JP-A-5-228502 [Patent Document 3]
Japanese Patent Laid-Open No. 10-305301
[Problems to be solved by the invention]
The present invention has been made in view of the above situation, and its purpose is to reduce the rolling efficiency, the porosity, which is an internal defect of a slab, is excellent in internal quality, and the pass rate in ultrasonic flaw detection. To provide a method of performing batch rolling of a continuous cast slab having a large cross section that can be used as a product as it is, not only as a semi-finished product but also as a semi-finished product after rolling. It is.
[0011]
[Means for Solving the Problems]
The gist of the present invention resides in the method for ingot rolling of continuous cast slabs shown in the following (1) and (2).
[0012]
(1) Reduction in units of% to a continuous cast slab having a cross-sectional dimension of a square with a side of 330 mm or more or a rectangle having an equivalent cross-sectional area and a surface temperature after solidification of 700 ° C. or more. Ingot of continuous cast slab characterized in that at least one pass each of rolling in the thickness direction and width direction satisfying the following formula (1) is satisfied, and all passes satisfy the following formula (2) Rolling method.
[0013]
25.5 ≦ r × (D n / h ni ) 0.07 ≦ 31.0 (1),
r × (D n / h ni ) 0.07 ≦ 31.0 (2).
[0014]
Here, r = {1− (h nO / h ni )} × 100, D n is the roll diameter (mm) at the n-th rolling, h ni and h nO are the rolled material before and after the n-th rolling, respectively. The thickness (mm).
[0015]
(2) A continuous cast slab that has been solidified in a square having a cross-sectional dimension of 330 mm or more on a side or a rectangle having a cross-sectional area equivalent to that of a square, has a surface temperature of 1100 ° C. or more, and the slab surface and the inside of the slab After the temperature difference of 200 ° C. is heated, the slab surface temperature before the first rolling is 700 ° C. or more, and the slab has a reduction ratio r in% units satisfying the following formula (1): A method of performing ingot rolling of a continuous cast slab, wherein at least one pass is applied in each direction in the width direction, and all passes satisfy the following formula (2).
[0016]
25.5 ≦ r × (D n / h ni ) 0.07 ≦ 31.0 (1),
r × (D n / h ni ) 0.07 ≦ 31.0 ··· ▲ 2 ▼.
[0017]
Here, r = {1− (h nO / h ni )} × 100, D n is the roll diameter (mm) at the n-th rolling, h ni and h nO are the rolled material before and after the n-th rolling, respectively. The thickness (mm).
[0018]
Note that “perform at least one pass each in rolling in the thickness direction and width direction” on the slab is at least each of the “thickness” direction and the “width” direction when viewed in the slab before rolling. This means rolling one pass at a time.
[0019]
The above “D n / h ni ” is a so-called “roll diameter ratio”, and this term may be used in the following description.
[0020]
In addition, said (1) is a method of carrying out partial rolling using the sensible heat which a slab has, without heating a continuous cast slab with a soaking furnace or a heating furnace, On the other hand, said (2) is This is a method in which a continuous cast slab is heated in a soaking furnace or a heating furnace and then subjected to split rolling.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
In order to achieve the above-mentioned object, the present inventors do not depend on the chemical composition of the material to be rolled like stress, and are ordinary three-dimensional rigid-plastic finite element analysis (hereinafter simply referred to as FEM analysis). Various studies were conducted focusing on the compressive strain in the rolling direction at the center of the material to be rolled, which can be determined relatively easily by the above. As a result, the following findings (a) to (e) were obtained.
[0022]
(A) When rolling with z as the rolling direction, y as the rolling direction in the cross section of the material to be rolled and x as the direction perpendicular to the rolling direction (that is, the direction parallel to the roll axis) as shown in FIG. For the crimping, the multi-pass rolling that is continuous with respect to the center of the material to be rolled is subjected to rolling from two different directions so that compressive strain is applied in the y direction in each pass, in other words, the original material to be rolled. The compressive strain may be applied in the y direction and the x direction. In the above case, the strain in the z direction with respect to the center of the material to be rolled does not affect the pressure bonding of the porosity. This is because even if tensile strain acts in the z direction, the porosity is pressure-bonded as long as compressive strain is applied in the y direction and the x direction. In the description of the examples, the dimensions of the material to be rolled in the y direction and the x direction are referred to as “thickness” and “width”, respectively.
[0023]
(B) When the original dimensions and final finish dimensions of the material to be rolled are fixed, even if the total compressive strain in the multi-pass rolling is constant, the reduction of the rolling reduction is changed and one or more passes are strongly reduced. Rolling can increase the effect of porosity bonding in the y direction.
[0024]
(C) Even if a strong pressure is applied in the y direction, the expansion of the porosity based on an increase in tensile strain in the x direction may not occur.
[0025]
(D) The roll diameter ratio correlates with the pressure-bonding effect of porosity.
[0026]
(E) In order to press the porosity and improve the surface properties of the steel slab, it is important to control the temperature of the continuous cast slab.
[0027]
The present invention has been completed based on the above findings.
[0028]
Hereinafter, each requirement of the present invention will be described in detail.
(A) Continuous cast slab cross-sectional dimensions In the present invention, in order to use as a product in the form of a piece-rolled, the cross-sectional dimension is a square having a side of 330 mm or more or a cross-sectional area equivalent thereto. The object is a rectangular large-section continuous cast slab. By setting the above-mentioned cross-sectional dimensions, a large total reduction ratio can be ensured only by the partial rolling, and therefore, it can be sufficiently used as a product even with the partial rolled size.
[0029]
The upper limit of the cross-sectional dimension is preferably a square having a side of 500 mm or a rectangle having an equivalent cross-sectional area. When the cross-sectional shape is rectangular, the ratio of the long side to the short side is preferably 1.8 or less.
(B) Temperature of continuous cast slab (B-1) When performing batch rolling using sensible heat of the slab without heating in a soaking furnace or heating furnace:
In order to increase the surface properties of the steel slab, the continuous cast slab is rolled in pieces using the sensible heat of the slab without heating it in a soaking furnace or heating furnace. After the cast slab has been solidified, it is necessary to carry out partial rolling under the conditions described in the section (C) described later in a state where the surface temperature is 700 ° C. or higher. When the surface temperature is lower than 700 ° C., surface flaws generated in the steel slab increase, and a great number of man-hours are required for maintenance, and deformation resistance during rolling increases.
(B-2) When heating in a soaking furnace or heating furnace and then rolling in pieces:
In order to heat a continuous cast slab in a soaking furnace or a heating furnace, and then roll it into pieces, press the porosity, and improve the surface properties of the steel slab, the surface temperature is 1100 ° C. or more, and the slab surface And the temperature difference between the inside of the slab and the inside of the slab is heated to within 200 ° C, and the surface temperature of the slab before the first rolling is set to 700 ° C or more, and it is necessary to carry out the partial rolling under the conditions described in the section (C) described later. is there. If the surface temperature during heating is lower than 1100 ° C or the slab surface temperature before the first rolling is lower than 700 ° C, surface flaws generated in the steel slab increase, requiring a lot of man-hours for maintenance. This is because the deformation resistance also increases. Furthermore, when the temperature difference between the slab surface and the inside of the slab exceeds 200 ° C., internal defects are difficult to press and deformation resistance during rolling increases. Note that the upper limit of the surface temperature during heating may be 1350 ° C.
(C) Rolling conditions In the present invention, rolling in the thickness direction and the width direction satisfying the above formula (1) with a reduction ratio r in% unit is performed at least one pass each, and all passes are the above (2). Try to satisfy the formula.
[0030]
25.5 ≦ r × (D n / h ni ) 0.07 is not satisfied, that is, when the rolling reduction ratio r in% unit is less than 25.5 × (D n / h ni ) −0.07 , the thickness direction A sufficient porosity pressing effect cannot be obtained.
[0031]
On the other hand, when the condition r × (D n / h ni ) 0.07 ≦ 31.0 is not satisfied, that is, when the rolling reduction ratio r in% unit exceeds 31.0 × (D n / h ni ) −0.07 , In some cases, the shape of the material to be rolled changes from a rectangle to a parallelogram, and subsequent rolling cannot be performed or porosity is opened.
[0032]
Therefore, in the present invention, at least one pass of rolling in the thickness direction and the width direction satisfying the above formula (1), where the rolling reduction ratio r in% unit is applied, and all the passes in rolling are the above described (2). It was decided to satisfy the formula. Here, as described above, D n , h ni and h nO are respectively the roll diameter (mm) at the n-th rolling, the thickness (mm) of the material to be rolled before the n-th rolling, and the n-th rolling. It refers to the thickness (mm) of the material to be rolled after rolling.
[0033]
Hereinafter, the present invention will be described in more detail with reference to examples.
[0034]
【Example】
Steel having the chemical composition shown in Table 1 was melted by an ordinary method and continuously cast into a rectangular shape having a cross-sectional dimension of 400 mm long side and 300 mm short side.
[0035]
[Table 1]
Next, the above-mentioned slab cut to a length of 4500 mm is divided into two pieces: (b) slabbing using the sensible heat of the slab, and (b) slabbing after heating in a heating furnace. A rolling test was performed on the case.
[0037]
In the case of (A), the surface temperature of each specimen slab before the block rolling was approximately 900 ° C. On the other hand, in the case of (b), the surface temperature of the slab is approximately 1200 ° C., and it is heated sufficiently until there is almost no temperature difference between the slab surface and the inside of the slab. It used for the 1st rolling (rolling of the 1st pass) of partial rolling in the state of 1040 degreeC.
Split rolling was performed as follows. That is, using a 2Hi reverse block mill, rough rolling was performed to 200 mm square so that the total reduction ratio was 3.0, followed by 6-pass finish rolling with a VH mill to finish 160 mm square.
[0038]
Here, the total rolling reduction ratio in the above rough rolling means a value represented by the following formula (4).
[0039]
Total reduction ratio = Cross-sectional area of slab / Cross-sectional area of steel slab after rough rolling (4).
[0040]
In the rough rolling using the above 2Hi reverse block mill, the first pass is rolled with the 300 mm short side as the “thickness” and the 400 mm long side as the “width”. The details were rolled under the conditions from “Case 1” to “Case 4” shown in Tables 2-5. Here, in rolling of each case, when “Case 1” has no pass where the reduction ratio r in% unit satisfies the formula (1), “Case 2” has a pass where r satisfies the formula (1). When performed only once, “Case 3” is performed twice in the “width” direction when the path satisfying the above equation (1) is viewed in the slab before rolling. In the case where r is performed once for each of the “thickness” direction and the “width” direction when a path satisfying the formula (1) is viewed with the slab before rolling, “case 4” is the rolling according to the present invention. It is. Rolling to 160 mm square was performed 50 times for each condition of each steel. “Turn” in each table means that the “thickness” direction and “width” direction of rolling are changed, that is, the material to be rolled is rotated by 90 degrees. In addition, “◯” in the remarks column of each table indicates that the rolling reduction ratio r in the above% unit satisfies the expression (1).
[0041]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
About the 160 mm square steel piece obtained as mentioned above, the surface property was first examined by visually inspecting the surface. As a result, all the slabs before rough rolling satisfy the temperature condition of the present invention, and therefore no flaws were observed in any steel slab.
[0046]
Next, ultrasonic flaw detection was performed under normal conditions. Table 6 shows the results of ultrasonic flaw detection.
[0047]
[Table 6]
From Table 6, it is apparent that the 160 mm square steel slab rolled in the “case 4” which is the method of the present invention has a very high pass rate of ultrasonic flaw detection.
[0049]
【The invention's effect】
According to the present invention, the porosity, which is an internal defect of the slab, is pressed to reduce the rolling efficiency, and the steel slab is excellent in internal quality and in the pass rate in ultrasonic flaw detection. Moreover, since the total reduction ratio in the partial rolling of the present invention is large, the steel slab can be used not only as a semi-finished product but also as a product as it is after rolling.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating coordinate axes in rolling.
Claims (2)
２５．５≦ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲１▼
ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲２▼
ここで、
ｒ＝｛１−（ｈnO／ｈni）｝×１００、
Ｄn はｎ回目の圧延時のロール直径（ｍｍ）、
ｈniとｈnOはそれぞれｎ回目の圧延前後の被圧延材の厚み（ｍｍ）、
である。A slab with a cross-sectional dimension of a square having a side of 330 mm or more or a rectangle having an equivalent cross-sectional area and a surface temperature after solidification of 700 ° C. or more is continuously cast and has a reduction ratio r in% units. A piecewise rolling method for continuously cast slabs characterized in that at least one pass each of rolling in the thickness direction and width direction satisfying the following formula (1) is applied, and all passes satisfy the following formula (2).
25.5 ≦ r × (D n / h ni ) 0.07 ≦ 31.0 (1)
r × (D n / h ni ) 0.07 ≦ 31.0 (2)
here,
r = {1− (h nO / h ni )} × 100,
D n is the roll diameter (mm) during the n-th rolling,
h ni and h nO are the thickness (mm) of the material to be rolled before and after the n-th rolling, respectively.
It is.
２５．５≦ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲１▼
ｒ×（Ｄn ／ｈni）0.07 ≦３１．０ ・・・▲２▼
ここで、
ｒ＝｛１−（ｈnO／ｈni）｝×１００、
Ｄn はｎ回目の圧延時のロール直径（ｍｍ）、
ｈniとｈnOはそれぞれｎ回目の圧延前後の被圧延材の厚み（ｍｍ）、
である。The surface temperature of a continuous cast slab that has been solidified to be a square having a cross-sectional dimension of 330 mm or more on one side or a rectangle having a cross-sectional area equivalent to this is 1100 ° C. or more, and the temperature difference between the slab surface and the inside of the slab Is heated to 200 ° C. or less, the slab surface temperature before the first rolling is set to 700 ° C. or more, and the slab has a rolling reduction ratio r in% units satisfying the following formula (1): A method of split rolling a continuous cast slab, wherein the rolling is performed at least one pass each and all passes satisfy the following formula (2).
25.5 ≦ r × (D n / h ni ) 0.07 ≦ 31.0 (1)
r × (D n / h ni ) 0.07 ≦ 31.0 (2)
here,
r = {1− (h nO / h ni )} × 100,
D n is the roll diameter (mm) during the n-th rolling,
h ni and h nO are the thickness (mm) of the material to be rolled before and after the n-th rolling, respectively.
It is.
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