JP7356025B2 - Hot width reduction rolling method for continuously cast slabs - Google Patents
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本発明は、連続鋳造鋳片の熱間幅圧下圧延方法に関する。 The present invention relates to a method for hot width reduction rolling of continuously cast slabs.
連続鋳造機で鋳造して得られた鋳片（スラブ）を所定長さに切断した後、すぐに当該鋳片を加熱し熱間幅圧下圧延するプロセスが行われる場合がある。このプロセスによれば、連続鋳造機で鋳造された鋳片の顕熱を利用して短時間の加熱で鋳片を圧延することができるため、工程の大幅な削減による生産性向上や省エネルギー化が可能となる。 After a slab obtained by casting with a continuous casting machine is cut into a predetermined length, the slab may be immediately heated and hot-width-reduced. According to this process, the sensible heat of the slab cast by a continuous casting machine can be used to roll the slab in a short time, resulting in improved productivity and energy savings by significantly reducing the number of processes. It becomes possible.
一方、連続鋳造鋳片には、鋳型内での凝固中に割れの芽が発生している。連続鋳造鋳片を熱間幅圧下圧延した際に、この割れの芽から鋳片に割れや疵が発生しやすいという課題がある。そこで、こうした課題を解決するため、これまで種々の方法が検討されてきた。 On the other hand, cracks appear in continuously cast slabs during solidification in the mold. When continuously cast slabs are subjected to hot width reduction rolling, there is a problem in that cracks and flaws are likely to occur in the slabs from the buds of these cracks. Therefore, various methods have been studied to solve these problems.
例えば、特許文献１には、連続鋳造された高温鋳片スラブをホットチャージ圧延する際に、（Ｆｅ，Ｍｎ）Ｓ、（Ｆｅ，Ｍｎ）Ｏ等の微細な準安定析出物がデンドライト界面やオーステナイト粒界面に析出して、熱間圧延による引張応力で発生する割れを防止するため、Ｏ，Ｓを所定量以下とし、Ｍｎ／Ｓを１０以上とすると共に冷却速度を規定し、９５０～１３００℃で少なくとも１０分間保温した鋳片スラブを熱間幅圧延する方法が開示されている。これにより、割れの原因となる微細な準安定析出物を粗大球状化すると共に、ＭｎＳを粒内に析出させて無害化し、割れ発生を防止できるとしている。
For example,
また、特許文献２記載の技術は、Ａｌキルド鋼鋳片を直送圧延する方法であって、連続鋳造中の二次冷却における冷却速度を規定してＡｒ１変態させ、復熱させてＡｃ３変態させることによって、金属組織の相変態を２度行わせ、割れの原因となる低融点のＦｅリッチな複合硫化物の析出位置を粒界とは異なるところに制御し、鋳片の表面疵を防止する方法が開示されている。
Further, the technology described in
連続鋳造鋳片を加熱し熱間幅圧下圧延するプロセスでは、鋳片の表面近傍に存在する微少な割れの芽が熱間幅圧下圧延時に開口して割れとなりやすい。特に、熱間幅圧下圧延時に温度が低下する鋳片の幅方向コーナー近傍では割れが発生しやすい。これをエッジ割れと呼んでおり、製品での疵の原因となるため、発生を抑制することが求められていた。 In the process of heating a continuously cast slab and hot width reduction rolling, minute crack buds that exist near the surface of the slab tend to open up and become cracks during hot width reduction rolling. In particular, cracks are likely to occur near the corners in the width direction of the slab where the temperature drops during hot width reduction rolling. This is called edge cracking, and since it causes defects in products, there has been a need to suppress its occurrence.
上記課題に対して、特許文献１に記載の方法で、ある程度はエッジ割れの発生を抑制できるものの、完全に防止することはできなかった。また、特許文献１の実施例に記載されているように、鋳片を１０５０～１２１０℃の温度で加熱すると、鋳片表面に厚いスケールが生成し、スケールを噛み込むスケール起因疵が発生するという新たな課題があった。
To address the above problem, although the method described in
特許文献２に記載の方法では、全体的に割れにくくすることはできるが、鋳片幅方向コーナー部は、温度が下がった後、復熱しにくいため本技術を適用できず、エッジ割れの防止はできなかった。
With the method described in
このように、先行技術では、連続鋳造鋳片を熱間幅圧下圧延する際に発生するエッジ割れとスケール起因疵を防止することはできていない。 As described above, in the prior art, it has not been possible to prevent edge cracks and scale-induced flaws that occur when continuously cast slabs are hot-width-reduced.
本発明はかかる事情に鑑みてなされたもので、連続鋳造鋳片を加熱し熱間幅圧下圧延するプロセスにおいて、鋳片のエッジ割れとスケール起因疵を共に防止することを目的とする。 The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent both edge cracking and scale-induced flaws in a continuously cast slab in the process of heating and hot width reduction rolling of a continuously cast slab.
上記目的を達成するため、本発明は、Ｃを０．０３～０．３０質量％、Ｓｉを０．０１～０．８０質量％、Ｍｎを０．５０～３．００質量％、Ｐを０．００５～０．０５０質量％、Ｓを０．０００１～０．０１５０質量％、Ａｌを０．０１～０．１０質量％含有する炭素鋼の溶鋼を連続鋳造機で幅１３５０ｍｍ～２０００ｍｍ、厚さ２５０ｍｍ～３００ｍｍに鋳造し、得られた鋳片を所定長さに切断した後、該鋳片を加熱し熱間幅圧下圧延する方法において、
１パス当たりの幅圧下量Ｗが０ｍｍ超３００ｍｍ以下のとき、熱間幅圧下圧延開始温度Ｔ（℃）が（１）式を満足し、且つ９９０℃未満であることを特徴としている。
Ｔ＞2.524×10８([Ｍｎ]・[Ｓ])３-7.429×106([Ｍｎ]・[Ｓ])２+7.130×104([Ｍｎ]・[Ｓ])+0.162Ｗ+724.3 （１）
ここで、[Ｍｎ]：Ｍｎの濃度（質量％）、[Ｓ]：Ｓの濃度（質量％）
In order to achieve the above object, the present invention contains 0.03 to 0.30% by mass of C, 0.01 to 0.80% by mass of Si, 0.50 to 3.00% by mass of Mn, and 0% by mass of P. Molten carbon steel containing 0.005 to 0.050 mass %, 0.0001 to 0.0150 mass % S, and 0.01 to 0.10 mass % Al is cast using a continuous casting machine to a width of 1350 mm to 2000 mm and a thickness. In the method of casting to 250 mm to 300 mm , cutting the obtained slab to a predetermined length, heating the slab and hot width reduction rolling,
It is characterized in that when the width reduction amount W per pass is more than 0 mm and 300 mm or less, the hot width reduction rolling start temperature T (°C) satisfies formula (1) and is less than 990°C.
T＞2.524×10 8 ([Mn]・[S]) 3 -7.429×10 6 ([Mn]・[S]) 2 +7.130×10 4 ([Mn]・[S])+0.162W+724.3 (1)
Here, [Mn]: concentration of Mn (mass%), [S]: concentration of S (mass%)
本発明者らは、鋳片のエッジ割れの起点が、鋳片の表面近傍の割れの芽に析出したＭｎＳ非金属介在物であることを発見した。因って、鋳片を熱間幅圧下圧延するときにＭｎＳ非金属介在物が析出していないようにできれば、鋳片のエッジ割れを防止することができる。 The present inventors have discovered that the origin of edge cracks in slabs is MnS nonmetallic inclusions deposited in the buds of cracks near the surface of the slab. Therefore, if it is possible to prevent the precipitation of MnS nonmetallic inclusions when the slab is hot-width-reduced, edge cracking of the slab can be prevented.
本発明では、鋳片に含まれるＭｎとＳの濃度積と幅圧下量に応じて決まる温度で鋳片を熱間幅圧下圧延する。具体的には、１パス当たりの幅圧下量Ｗが０ｍｍ超３００ｍｍ以下のとき、熱間幅圧下圧延開始温度Ｔが（１）式を満足すると、ＭｎＳ非金属介在物の析出量を、幅圧下量に応じて決まるエッジ割れに影響しないレベルまで低減でき、鋳片のエッジ割れが防止される。
また、熱間幅圧下圧延開始温度Ｔが９９０℃以上となる温度まで加熱炉で加熱すると、鋳片表面にスケールが大量に生成して表面疵の原因となるので、熱間幅圧下圧延開始温度Ｔは９９０℃未満とする。
In the present invention, a slab is hot width-reduced at a temperature determined according to the concentration product of Mn and S contained in the slab and the amount of width reduction. Specifically, when the width reduction amount W per pass is more than 0 mm and 300 mm or less, and the hot width reduction rolling start temperature T satisfies formula (1), the amount of precipitation of MnS nonmetallic inclusions is reduced by the width reduction. Edge cracking, which is determined depending on the amount, can be reduced to a level that has no effect, and edge cracking of slabs is prevented.
In addition, if the hot width reduction rolling start temperature T is heated in a heating furnace to a temperature of 990°C or higher, a large amount of scale will be generated on the surface of the slab and cause surface flaws. T is less than 990°C.
本発明に係る連続鋳造鋳片の熱間幅圧下圧延方法では、熱間幅圧下圧延開始温度を制御することにより、ＭｎＳ非金属介在物を析出させないようにして鋳片のエッジ割れを防止すると共に、スケールの過剰な生成を抑制してスケール起因疵を防止することができる。 In the hot width reduction rolling method for continuously cast slabs according to the present invention, by controlling the hot width reduction rolling start temperature, MnS nonmetallic inclusions are not precipitated and edge cracking of the slab is prevented. , it is possible to suppress excessive production of scale and prevent scale-induced flaws.
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態について説明し、本発明の理解に供する。 Next, embodiments embodying the present invention will be described with reference to the attached drawings to provide an understanding of the present invention.
［本発明の考え方］
本発明者らは、炭素鋼を連続鋳造機で鋳造し、得られた鋳片（スラブ）を所定長さに切断した後、当該鋳片を加熱し、サイジングミルを用いて熱間幅圧下圧延したものについて割れ等の調査を実施した。
[Concept of the present invention]
The present inventors cast carbon steel using a continuous casting machine, cut the obtained slab into predetermined lengths, heated the slab, and then hot-width-reduced it using a sizing mill. We conducted an investigation on the cracks etc.
炭素鋼はＣ－Ｓｉ－Ｍｎ系の成分組成を有する鋼種とし、鋼中のＳを２０ｐｐｍ～１００ｐｐｍの低濃度から高濃度まで変化させた各鋳片について熱間幅圧下圧延を行った。そして、熱間幅圧下圧延後の鋳片から全幅で１００ｍｍ程度の長さでサンプリングして、まずは目視でエッジ割れの有無を確認した。 The carbon steel was a steel type having a C--Si--Mn composition, and hot width reduction rolling was performed on each slab in which the S concentration in the steel was varied from a low concentration of 20 ppm to 100 ppm to a high concentration. Then, a sample having a total width of about 100 mm was taken from the slab after hot width reduction rolling, and the presence or absence of edge cracking was first visually confirmed.
熱間幅圧下圧延後にエッジ割れが発生した鋳片から、エッジ割れ部位を１００ｍｍ角×１０ｍｍ厚みの詳細観察用の試験片を切り出して、金属組織、非金属介在物の調査、解析を行った。
電界放出形走査電子顕微鏡（ＦＥ－ＳＥＭ）を用いて観察した結果、エッジ割れが発生した周囲には、割れに沿ってまだ結合していない微細な亀裂が多数並んで分布していることが確認された。また、その微細な亀裂の内部に多数の介在物が存在しており、エネルギー分散型Ｘ線分析装置（ＥＤＳ）を用いて非金属介在物を同定した結果、ＭｎＳ非金属介在物であることがわかった。これらの観察結果から推定されるエッジ割れ発生メカニズムは以下の通りである。
A 100 mm square x 10 mm thick specimen for detailed observation of the edge crack site was cut out from a slab in which edge cracks had occurred after hot width reduction rolling, and the metallographic structure and nonmetallic inclusions were investigated and analyzed.
As a result of observation using a field emission scanning electron microscope (FE-SEM), it was confirmed that around the edge crack, there were many fine cracks that were not yet bonded and distributed along the crack. It was done. In addition, there were many inclusions inside the microscopic cracks, and as a result of identifying the nonmetallic inclusions using an energy dispersive X-ray spectrometer (EDS), it was determined that they were MnS nonmetallic inclusions. Understood. The mechanism of edge crack occurrence estimated from these observation results is as follows.
連続鋳造時の鋳片、特に温度が低下しやすい幅方向コーナー部で、割れの芽となるＭｎＳ非金属介在物が多数発生する。これら割れの芽部位は、局部的に延性が劣るため、その後、熱間幅圧下圧延時の引張応力によって、ＭｎＳ非金属介在物が破壊したり、ボイドが生成したりして、多数の微細な亀裂となる。そして、これら多数の微細な亀裂が結合して割れとなり、鋳片表面に開口したものがエッジ割れとなる。 During continuous casting, a large number of MnS nonmetallic inclusions that become crack buds are generated in slabs during continuous casting, especially at the corners in the width direction where the temperature tends to drop. Since the ductility of these crack buds is locally poor, the MnS nonmetallic inclusions are destroyed and voids are generated due to the tensile stress during hot width reduction rolling, resulting in a large number of fine particles. It becomes a crack. These many fine cracks combine to form cracks, and those that open on the surface of the slab become edge cracks.
連続鋳造時の鋳片では、最初は固体鉄中にＭｎ、Ｓも固溶している。この固溶した状態では、固体鉄中で非金属介在物を形成していないので、圧延によって鉄が延ばされて変形しても全く悪影響がない。しかし、鋳片温度が、ある温度よりも低下すると、固体鉄中に固溶するＭｎとＳの濃度積が固溶限を上回り（固溶する限界の固溶限は、鋳片温度が低下すると徐々に小さくなる。）、固体鉄中に固溶しているＭｎ、Ｓが反応してＭｎＳ非金属介在物を形成し析出する。鋳片温度が低くなればなるほど、また、ＭｎとＳの濃度積が大きければ大きいほど、ＭｎＳ非金属介在物が多く形成される。 In the slab produced during continuous casting, Mn and S are initially dissolved in solid iron. In this state of solid solution, no nonmetallic inclusions are formed in the solid iron, so even if the iron is stretched and deformed by rolling, there is no adverse effect at all. However, when the slab temperature drops below a certain temperature, the concentration product of Mn and S dissolved in solid iron exceeds the solid solubility limit (the solid solubility limit, which is the limit of solid solubility, ), Mn and S dissolved in solid iron react to form MnS nonmetallic inclusions and precipitate. The lower the slab temperature and the greater the concentration product of Mn and S, the more MnS nonmetallic inclusions are formed.
熱間幅圧下圧延によって鋳片に引張応力が作用すると、析出したＭｎＳ非金属介在物は、鉄中で異物としてそれ自身が破壊したり、鉄とＭｎＳ非金属介在物の変形抵抗が異なるため、鉄との界面でボイドを形成する。ＭｎＳ析出物が多く形成されるほど、鉄とＭｎＳ非金属介在物の異相界面が形成され、多数の微細な亀裂の原因となる。そして、これら多数の微細な亀裂が結合して、鋳片表面に開口しエッジ割れとなる。 When tensile stress is applied to the slab by hot width reduction rolling, the precipitated MnS nonmetallic inclusions may themselves break as foreign matter in the iron, and the deformation resistance of iron and MnS nonmetallic inclusions is different. Forms voids at the interface with iron. The more MnS precipitates are formed, the more different phase interfaces between iron and MnS nonmetallic inclusions are formed, causing a large number of fine cracks. Then, these many fine cracks combine and open on the surface of the slab, resulting in edge cracks.
上記のエッジ割れ発生メカニズムより、本発明者らは、エッジ割れを防止するためには、熱間幅圧下圧延時のＭｎＳ非金属介在物の析出量を低減することが重要であるとの考えに到達した。そこで、エッジ割れの発生状況が異なる複数の鋼種について、熱間幅圧下圧延時のＭｎＳ非金属介在物の析出量とエッジ割れ発生率の関係を幅圧下量別に整理した。なお、熱間幅圧下圧延開始温度が約９５０℃のものについて整理した。 Based on the above edge crack generation mechanism, the present inventors believe that in order to prevent edge cracks, it is important to reduce the amount of MnS nonmetallic inclusions precipitated during hot width reduction rolling. Reached. Therefore, the relationship between the precipitation amount of MnS nonmetallic inclusions and the edge crack occurrence rate during hot width reduction rolling was organized by width reduction amount for multiple steel types with different edge crack occurrence conditions. In addition, the hot width reduction rolling start temperature was arranged at about 950°C.
熱間幅圧下圧延時のＭｎＳ非金属介在物の析出量は、Ｍｎ、Ｓの鉄中の濃度と温度の関数であり、熱力学平衡計算によって求まる。そこで、９５０℃における熱力学平衡計算によるＭｎＳ非金属介在物析出量（以降、「計算ＭｎＳ析出量」と呼ぶ。）を、熱力学平衡計算ソフトsolgasmix Ver.3.1を用いて算出した。また、それぞれの条件の鋳片各２０枚のエッジ割れの有無を調査し、エッジ割れが発生した鋳片の枚数割合をエッジ割れ発生率とした。 The amount of MnS nonmetallic inclusions precipitated during hot width reduction rolling is a function of the concentration of Mn and S in iron and temperature, and is determined by thermodynamic equilibrium calculation. Therefore, the amount of precipitated MnS nonmetallic inclusions based on thermodynamic equilibrium calculation at 950° C. (hereinafter referred to as "calculated amount of MnS precipitated") was calculated using thermodynamic equilibrium calculation software solgasmix Ver. 3.1. In addition, the presence or absence of edge cracks was investigated for each of 20 slabs under each condition, and the ratio of the number of slabs in which edge cracks occurred was defined as the edge crack occurrence rate.
図１に、９５０℃における熱力学平衡計算によるＭｎＳ析出量とエッジ割れ発生率の関係を幅圧下量別に示す。幅圧下量ごとにエッジ割れ発生率が急激に上昇するＭｎＳ析出量が存在することが同図よりわかる。以降では、エッジ割れ発生率が上がり始める計算ＭｎＳ析出量を「エッジ割れ発生限界となる計算ＭｎＳ析出量」という。
幅圧下量に応じたエッジ割れ発生限界となる計算ＭｎＳ析出量は、図２に示す１パス当たりの幅圧下量とエッジ割れ発生限界となる計算ＭｎＳ析出量の関係より（２）式で求めることができる。
Ｌ＝-0.0013Ｗ+1.214 （２）
ここで、Ｌ：エッジ割れ発生限界となる計算ＭｎＳ析出量（mol/1000kg鋼）、Ｗ：１パス当たりの幅圧下量（ｍｍ）
なお、１パス当たりの幅圧下量Ｗは０ｍｍ超３００ｍｍ以下である。
FIG. 1 shows the relationship between the amount of MnS precipitation and the edge crack occurrence rate based on thermodynamic equilibrium calculations at 950° C. for each width reduction amount. It can be seen from the figure that there is a precipitated amount of MnS at which the edge crack occurrence rate increases rapidly for each width reduction amount. Hereinafter, the calculated MnS precipitation amount at which the edge crack occurrence rate begins to increase will be referred to as the "calculated MnS precipitation amount that becomes the edge crack occurrence limit."
The calculated amount of MnS precipitation, which is the limit for edge crack occurrence according to the amount of width reduction, can be determined by equation (2) from the relationship between the amount of width reduction per pass shown in FIG. 2 and the calculated amount of MnS precipitation, which is the limit for edge crack occurrence. I can do it.
L=-0.0013W+1.214 (2)
Here, L: Calculated MnS precipitation amount (mol/1000 kg steel) that is the limit for edge cracking, W: Width reduction amount per pass (mm)
Note that the width reduction amount W per pass is more than 0 mm and less than 300 mm.
図３に、Ｍｎ濃度を一定とした際のＳ濃度と計算ＭｎＳ析出量の関係を温度別に示す。温度が低下し、Ｓ濃度が上昇すると、計算ＭｎＳ析出量が上昇することが同図よりわかる。従って、計算ＭｎＳ析出量をエッジ割れ発生限界以下とするためには、Ｓ濃度に応じて温度を変える必要があるが、実際のところＭｎ濃度も変化するため、Ｍｎ濃度とＳ濃度に応じた熱間幅圧下圧延開始温度とする必要がある。 FIG. 3 shows the relationship between the S concentration and the calculated amount of MnS precipitation at different temperatures when the Mn concentration is constant. It can be seen from the figure that as the temperature decreases and the S concentration increases, the calculated amount of MnS precipitation increases. Therefore, in order to keep the calculated amount of MnS precipitation below the edge crack generation limit, it is necessary to change the temperature according to the S concentration, but in reality the Mn concentration also changes, so the temperature must be adjusted according to the Mn and S concentrations. It is necessary to set the width reduction rolling start temperature.
図４は、幅圧下量とエッジ割れが発生する計算限界温度の関係を[Ｍｎ]・[Ｓ]濃度積別に示したものである。幅圧下量とエッジ割れが発生する計算限界温度の関係は一次関数で表すことができることが同図よりわかる。
また、図５は、[Ｍｎ]・[Ｓ]濃度積とエッジ割れが発生する計算限界温度の関係を幅圧下量別に示したグラフである。[Ｍｎ]・[Ｓ]濃度積とエッジ割れが発生する計算限界温度の関係は三次関数で表すことができることが同図よりわかる。
FIG. 4 shows the relationship between the width reduction amount and the calculation limit temperature at which edge cracking occurs, for each [Mn]/[S] concentration product. The figure shows that the relationship between the amount of width reduction and the calculation limit temperature at which edge cracking occurs can be expressed as a linear function.
Further, FIG. 5 is a graph showing the relationship between the [Mn] and [S] concentration product and the calculation limit temperature at which edge cracking occurs, for each width reduction amount. It can be seen from the figure that the relationship between the [Mn]/[S] concentration product and the calculation limit temperature at which edge cracking occurs can be expressed by a cubic function.
そこで、熱間幅圧下圧延開始温度ＴをＭｎとＳの濃度積の三次関数、幅圧下量の一次関数と仮定し、熱力学平衡計算による計算ＭｎＳ析出量が(２)式となるデータに対して回帰分析を実施し、以下の関係式（３）を得た。なお、熱間幅圧下圧延開始温度としたのは、熱間幅圧下圧延の１パス目でエッジ割れが発生するかどうかが決まると推定されるためである。
Ｔ＞2.524×10８([Ｍｎ]・[Ｓ])３-7.429×106([Ｍｎ]・[Ｓ])２+7.130×104([Ｍｎ]・[Ｓ])+0.162Ｗ+724.3 （３）
ここで、[Ｍｎ]：Ｍｎの濃度（質量％）、[Ｓ]：Ｓの濃度（質量％）
ただし、１パス当たりの幅圧下量Ｗは０ｍｍ超３００ｍｍ以下である。
Therefore, assuming that the hot width reduction rolling start temperature T is a cubic function of the concentration product of Mn and S and a linear function of the width reduction amount, the calculated MnS precipitation amount by thermodynamic equilibrium calculation is based on data such that the amount of MnS precipitation is expressed by equation (2). A regression analysis was carried out, and the following relational expression (3) was obtained. The hot width reduction rolling start temperature is used because it is estimated that whether or not edge cracking occurs is determined in the first pass of hot width reduction rolling.
T＞2.524×10 8 ([Mn]・[S]) 3 -7.429×10 6 ([Mn]・[S]) 2 +7.130×10 4 ([Mn]・[S])+0.162W+724.3 (3)
Here, [Mn]: concentration of Mn (mass%), [S]: concentration of S (mass%)
However, the width reduction amount W per pass is more than 0 mm and less than 300 mm.
１パス当たりの幅圧下量Ｗが０ｍｍ超３００ｍｍ以下のとき、（３）式を満足する熱間幅圧下圧延開始温度で鋳片を熱間幅圧下圧延することにより、エッジ割れの無い鋳片を製造することができる。 When the width reduction amount W per pass is more than 0 mm and less than 300 mm, a slab without edge cracks can be obtained by hot width reduction rolling the slab at a hot width reduction rolling start temperature that satisfies equation (3). can be manufactured.
図６は、熱間幅圧下圧延開始温度とスケール起因疵発生率の関係を示したグラフである。実際の熱間圧延後のスケール起因疵発生率を調査して、温度との関係を求めたものである。なお、それぞれの条件の鋳片各２０枚を調査し、スケール起因疵が発生した鋳片の割合をスケール疵発生率とした。
熱間幅圧下圧延開始温度が９９０℃以上になると、スケール起因疵発生率が急激に上昇し、熱間幅圧下圧延開始温度の上昇に伴い、スケール起因疵発生率がさらに増大することが同図よりわかる。
FIG. 6 is a graph showing the relationship between hot width reduction rolling start temperature and scale-induced flaw occurrence rate. The scale-induced flaw occurrence rate after actual hot rolling was investigated and the relationship with temperature was determined. In addition, 20 pieces of slabs under each condition were investigated, and the proportion of slabs in which scale-induced defects occurred was defined as the scale defect occurrence rate.
When the hot width reduction rolling start temperature becomes 990°C or higher, the scale-induced flaw occurrence rate increases rapidly, and as the hot width reduction rolling start temperature rises, the scale-induced flaw occurrence rate further increases. I understand more.
図７は、 [Ｍｎ]・[Ｓ]濃度積と熱間幅圧下圧延開始温度の関係におけるエッジ割れ発生の有無を幅圧下量別に示したグラフである。なお、図中の実線と一点鎖線は（３）式で示される、[Ｍｎ]・[Ｓ]濃度積及び幅圧下量に応じた熱間幅圧下圧延開始温度の限界温度を示す線を示しており、それぞれ幅圧下量が１００ｍｍと３００ｍｍの場合の線である。また、図中の破線はスケール起因疵が発生する限界温度９９０℃を示している。
熱間幅圧下圧延開始温度が限界温度以下になると、エッジ割れが発生することが同図よりわかる。また、熱間幅圧下圧延開始温度が限界温度を超えていればエッジ割れは発生しないが、９９０℃以上になると、スケール起因疵が発生することがわかる。
FIG. 7 is a graph showing the presence or absence of edge cracking in the relationship between the [Mn] and [S] concentration product and the hot width reduction rolling start temperature for each width reduction amount. In addition, the solid line and the dashed-dotted line in the figure indicate the limit temperature of the hot width reduction rolling start temperature according to the [Mn]/[S] concentration product and width reduction amount, which is shown by equation (3). These are the lines when the width reduction amount is 100 mm and 300 mm, respectively. Further, the broken line in the figure indicates the limit temperature of 990° C. at which scale-induced flaws occur.
It can be seen from the figure that edge cracking occurs when the hot width reduction rolling start temperature falls below the limit temperature. Further, it can be seen that if the hot width reduction rolling start temperature exceeds the limit temperature, edge cracking does not occur, but when the temperature exceeds 990° C., scale-induced flaws occur.
［本発明の一実施の形態に係る連続鋳造鋳片の熱間幅圧下圧延方法］
転炉で吹錬して、更に真空脱ガス装置を用いて精錬した溶鋼中に、Ｃ、Ｓｉ、Ｍｎ等の合金を添加して撹拌し、脱酸と成分調整を行う。Ｓについては、必要なＳ上限まで溶銑予備処理あるいは二次精錬工程で脱硫を行う。また、Ａｌやその他、必要な合金を添加して成分調整を行う。このようにして溶製された溶鋼を連続鋳造して鋳片を製造する。連続鋳造では、例えば、２５０ｍｍ～３００ｍｍ厚程度のスラブ連続鋳造で実施する。
その後、連続鋳造鋳片を所定長さに切断して加熱炉に装入する。加熱炉では、熱間幅圧下圧延開始温度Ｔが（３）式を満足し、且つ９９０℃未満となるようにして鋳片を３０分から５０分程度加熱した後、熱間幅圧下圧延を行う。１パス当たりの幅圧下量は０ｍｍ超３００ｍｍ以下とする。この時、同時にサイジングミルを用いて厚み圧下を行ってもよい。
[Hot width reduction rolling method for continuously cast slab according to an embodiment of the present invention]
Alloys such as C, Si, and Mn are added to molten steel that has been blown in a converter and further refined using a vacuum degassing device and stirred to perform deoxidation and component adjustment. Regarding S, desulfurization is carried out in the hot metal pretreatment or secondary refining process up to the required upper limit of S. In addition, Al and other necessary alloys are added to adjust the composition. The molten steel produced in this manner is continuously cast to produce slabs. Continuous casting is carried out, for example, by continuous slab casting with a thickness of about 250 mm to 300 mm.
Thereafter, the continuously cast slab is cut into a predetermined length and charged into a heating furnace. In the heating furnace, the slab is heated for about 30 to 50 minutes so that the hot width reduction rolling start temperature T satisfies equation (3) and is less than 990° C., and then hot width reduction rolling is performed. The amount of width reduction per pass shall be more than 0 mm and less than 300 mm. At this time, thickness reduction may be performed simultaneously using a sizing mill.
本発明が対象とする鋼種は、熱間圧延用薄板鋼種、厚板鋼種で、ＭｎＳが生成しやすく、熱間幅圧下によるエッジ割れが生成する課題が顕著な鋼種成分を対象とする。これら対象鋼種の溶鋼に含まれる主要成分の範囲は以下の通りである。 The steel types targeted by the present invention are thin plate steel types for hot rolling and thick plate steel types, which are steel types in which MnS is likely to be generated and have a remarkable problem of edge cracking due to hot width reduction. The range of the main components contained in the molten steel of these target steel types is as follows.
＜Ｃ：０．０３～０．３０質量％＞
Ｃは、鋼の焼き入れ性と強度を制御する最も基本的な元素である。鋼板の強度を確保するために必須の元素であり、少なくとも０．０３質量％が必要である。しかし、Ｃ濃度が０．３０質量％を超えると、加工性ならびに溶接性が劣化する。そのため、本実施の形態では、Ｃ濃度を０．３０質量％以下とする。
＜Ｓｉ：０．０1～０．８０質量％＞
Ｓｉは主要な脱酸元素の一つであり、伸びを大きく損なうことなく鋼の強度を向上することができる。そのため、Ｓｉ濃度を０．０１質量％以上とする必要がある。一方、Ｓｉ濃度が高すぎると、靭延性が極端に悪くなり、スケールの固着を促進する。そのため、本実施の形態では、Ｓｉ濃度の上限を０．８０質量％とする。
<C: 0.03 to 0.30% by mass>
C is the most fundamental element that controls the hardenability and strength of steel. It is an essential element to ensure the strength of the steel plate, and at least 0.03% by mass is required. However, when the C concentration exceeds 0.30% by mass, workability and weldability deteriorate. Therefore, in this embodiment, the C concentration is set to 0.30% by mass or less.
<Si: 0.01 to 0.80% by mass>
Si is one of the main deoxidizing elements and can improve the strength of steel without significantly impairing elongation. Therefore, it is necessary to set the Si concentration to 0.01% by mass or more. On the other hand, if the Si concentration is too high, the toughness and ductility will be extremely poor and the fixation of scale will be promoted. Therefore, in this embodiment, the upper limit of the Si concentration is set to 0.80% by mass.
＜Ｍｎ：０．５０～３．００質量％＞
Ｍｎは、製綱段階での脱酸に有用な元素であり、Ｃ、Ｓｉと共に鋼板の高強度化に有効な元素である。このような効果を得るためには、Ｍｎ濃度を０．５０質量％以上とする必要がある。しかしながら、Ｍｎを３．００質量％を超えて含有させると、Ｍｎの偏析や固溶強化の増大により鋼の延性が低下する。また、溶接性や母材靭性も劣化するので、Ｍｎ濃度の上限は３．００質量％とする。
＜Ｓ：０．０００１～０．０１５０質量％＞
Ｓは、不純物として偏析し、熱延製品としたときに、ＭｎＳ系の延伸介在物を形成して加工性を劣化させる。そのため、Ｓ濃度の上限を０．０１５０質量％とした。Ｓは、極力低濃度であることが望ましく、二次精錬において脱硫負荷をかけすぎると、脱硫コストが高くなり、コストが高くなる。従って、Ｓ濃度の下限は０．０００１質量％とする。
<Mn: 0.50 to 3.00% by mass>
Mn is an element useful for deoxidizing in the steel manufacturing stage, and is an element effective for increasing the strength of steel sheets together with C and Si. In order to obtain such an effect, the Mn concentration needs to be 0.50% by mass or more. However, when Mn is contained in excess of 3.00% by mass, the ductility of the steel decreases due to Mn segregation and solid solution strengthening. Furthermore, since weldability and base metal toughness are also deteriorated, the upper limit of the Mn concentration is set to 3.00% by mass.
<S: 0.0001 to 0.0150% by mass>
S segregates as an impurity, and when a hot-rolled product is produced, it forms MnS-based drawn inclusions and deteriorates workability. Therefore, the upper limit of the S concentration was set to 0.0150% by mass. It is desirable that the concentration of S be as low as possible, and if too much desulfurization load is applied in the secondary refining, the desulfurization cost will increase and the cost will increase. Therefore, the lower limit of the S concentration is 0.0001% by mass.
＜Ｐ：０．００５～０．０５０質量％＞
ＰはＦｅ原子よりも小さな置換型固溶強化元素として作用する点において有効である。しかし、Ｐ濃度が０．０５０質量％を超えると、オーステナイトの粒界に偏析し、粒界強度を低下させることにより、ねじり疲労強度を低下させ、加工性の劣化を引き起こす原因にもなりえる。そのため、Ｐ濃度の上限を０．０５０質量％とする。一方、固溶強化の必要がなければＰを添加する必要はなく、Ｐ濃度の下限値は０．００５質量％とする。
＜Ａｌ：０．０１～０．１０質量％＞
Ａｌは、一般に鋼の脱酸に用いられる元素である。その酸化物がクラスター化して粗大になり易く、加工性を劣化させるため、極力抑制することが望ましい。しかしながら、安価で有効な脱酸元素であるため、Ａｌ濃度の下限は０．０１質量％とした。一方、ハイテンの鋼種によっては、Ｓｉを使わずＡｌで強度を出す場合もあるため、Ａｌ濃度の上限は０．１０質量％とする。
<P: 0.005 to 0.050% by mass>
P is effective in that it acts as a substitutional solid solution strengthening element smaller than Fe atoms. However, if the P concentration exceeds 0.050% by mass, P will segregate at the grain boundaries of austenite, lowering the grain boundary strength, thereby lowering the torsional fatigue strength and possibly causing deterioration of workability. Therefore, the upper limit of the P concentration is set to 0.050% by mass. On the other hand, if there is no need for solid solution strengthening, there is no need to add P, and the lower limit of the P concentration is set to 0.005% by mass.
<Al: 0.01 to 0.10% by mass>
Al is an element commonly used for deoxidizing steel. Since the oxide tends to cluster and become coarse, which deteriorates workability, it is desirable to suppress this as much as possible. However, since Al is a cheap and effective deoxidizing element, the lower limit of Al concentration was set at 0.01% by mass. On the other hand, depending on the type of high-strength steel, strength may be achieved with Al without using Si, so the upper limit of the Al concentration is set to 0.10% by mass.
なお、上記溶鋼は、さらに以下の成分を含んでいてもよい。
＜Ｔｉ：０～０．０４５質量％＞
Ｔｉは主要な脱酸元素の一つであると共に、炭化物、窒化物、炭窒化物を形成し、結晶粒の微細化・高強度化機能を担う。コストが高くなることと、０．０４５質量％を超えてＴｉを含有すると、粗大な炭化物、窒化物、炭窒化物を形成してしまい、かえって材質の劣化を招き、含有量に見合う効果が期待できない。このため、本実施の形態では、Ｔｉ濃度の上限を０．０４５質量％とする。一方、ハイテン鋼の鋼種によっては、Ｔｉを添加せず、他の安価な高強度化元素、例えば、Ｃ，Ｓｉ，Ｍｎを使用する場合もあることから０を下限とする。
Note that the molten steel may further contain the following components.
<Ti: 0 to 0.045% by mass>
Ti is one of the main deoxidizing elements, forms carbides, nitrides, and carbonitrides, and plays a role in making crystal grains finer and stronger. The cost will be high, and if Ti is contained in excess of 0.045% by mass, coarse carbides, nitrides, and carbonitrides will be formed, leading to deterioration of the material, and the effect commensurate with the content is not expected. Can not. Therefore, in this embodiment, the upper limit of the Ti concentration is set to 0.045% by mass. On the other hand, depending on the type of high-tensile steel, Ti may not be added and other inexpensive high-strength elements such as C, Si, and Mn may be used, so 0 is set as the lower limit.
Ｎｂ、Ｖは、ＣもしくはＮと複合炭化物、複合窒化物、複合炭窒化物を形成して母材組織の細粒化を促進し、靭性向上に寄与する。
＜Ｎｂ：０～０．０４５質量％＞
複合炭化物、複合窒化物等を得るため、Ｎｂを含有させることが好ましいが、Ｎｂ濃度が０．０４５質量％を超えると、母材組織の細粒化の効果が飽和し、製造コストが高くなる。このため、Ｎｂ濃度は０．０４５質量％を上限とする。一方、ハイテン鋼の鋼種によっては、Ｎｂを添加せず、他の安価な高強度化元素、例えば、Ｃ，Ｓｉ，Ｍｎを使用する場合もあることから０を下限とする。
＜Ｖ：０～０．０３４質量％＞
上述した複合炭化物、複合窒化物等を得るためにはＶを含有させることが好ましいが、Ｖ濃度が０．０３４質量％を超えると、効果が飽和し、製造コストが高くなる。このため、Ｖ濃度は０．０３４質量％を上限とする。一方、ハイテン鋼の鋼種によっては、Ｖを添加せず、他の安価な高強度化元素、例えば、Ｃ，Ｓｉ，Ｍｎを使用する場合もあることから０を下限とする。
Nb and V form composite carbides, composite nitrides, and composite carbonitrides with C or N, promote grain refinement of the base material structure, and contribute to improving toughness.
<Nb: 0 to 0.045% by mass>
In order to obtain composite carbides, composite nitrides, etc., it is preferable to include Nb, but if the Nb concentration exceeds 0.045% by mass, the effect of grain refinement of the base metal structure is saturated and the manufacturing cost increases. . Therefore, the upper limit of the Nb concentration is 0.045% by mass. On the other hand, depending on the type of high-tensile steel, Nb may not be added and other inexpensive high-strength elements such as C, Si, and Mn may be used, so 0 is set as the lower limit.
<V: 0 to 0.034% by mass>
In order to obtain the above-mentioned composite carbide, composite nitride, etc., it is preferable to include V, but when the V concentration exceeds 0.034% by mass, the effect is saturated and the manufacturing cost increases. Therefore, the upper limit of the V concentration is 0.034% by mass. On the other hand, depending on the type of high-tensile steel, V may not be added and other inexpensive high-strength elements such as C, Si, and Mn may be used, so 0 is set as the lower limit.
Ｚｒは、硫化物の形態制御により、粒界を強化し、加工性を向上するために、必要に応じて含有することができる。
＜Ｚｒ：０～０．０１３質量％＞
Ｚｒは、上述した硫化物を球状化して母材の靭性を改善する効果を得るために、濃度を高くすることが好ましい。しかし、Ｚｒを多量に含有すると、かえって鋼の清浄性を損ない、延性を劣化させる。そのため、Ｚｒ濃度は０．０１３質量％を上限とする。一方、求められる靭性によっては、Ｚｒの添加を必要としない場合もあることから０を下限とする。
Zr can be contained as necessary in order to strengthen grain boundaries and improve workability by controlling the form of sulfides.
<Zr: 0 to 0.013% by mass>
It is preferable to increase the concentration of Zr in order to obtain the above-mentioned effect of spheroidizing the sulfide and improving the toughness of the base material. However, when Zr is contained in a large amount, it actually impairs the cleanliness of the steel and deteriorates its ductility. Therefore, the upper limit of the Zr concentration is 0.013% by mass. On the other hand, depending on the required toughness, it may not be necessary to add Zr, so 0 is set as the lower limit.
＜Ｃａ：０～０．００５質量％＞
Ｃａは、ハイテンの加工性を損なうＳを固定するために有効な元素であるが、Ｃａを多量に含有させても効果が飽和し、かえって鋼の清浄性を損ない、延性を劣化させる。そのため、Ｃａ濃度は０．００５質量％を上限とする。一方、Ｃａを添加せず、極低濃度まで脱硫することで、Ｃａ添加を省くことができる。従って、Ｃａ濃度の下限は０とする。
<Ca: 0 to 0.005% by mass>
Ca is an effective element for fixing S, which impairs the workability of high tensile strength steel, but even if a large amount of Ca is contained, the effect is saturated, and instead impairs the cleanliness of the steel and deteriorates its ductility. Therefore, the upper limit of the Ca concentration is 0.005% by mass. On the other hand, by desulfurizing to an extremely low concentration without adding Ca, the addition of Ca can be omitted. Therefore, the lower limit of Ca concentration is set to 0.
以上、本発明の一実施の形態について説明してきたが、本発明は何ら上記した実施の形態に記載の構成に限定されるものではなく、特許請求の範囲に記載されている事項の範囲内で考えられるその他の実施の形態や変形例も含むものである。 Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and within the scope of the claims. It also includes other possible embodiments and modifications.
本発明の効果について検証するために実施した検証試験について説明する。
表１～表３に試験条件及び試験結果の一覧を示す。
A verification test conducted to verify the effects of the present invention will be described.
Tables 1 to 3 show a list of test conditions and test results.
本試験では、表１～表３に示す化学成分の溶鋼を転炉で吹錬し、更に真空脱ガス装置を用いて精錬した溶鋼中に、Ｃ、Ｓｉ、Ｍｎ等の合金を添加して撹拌し、脱酸と成分調整を行った。Ｓについては、各試験ケースＳ濃度となるまで溶銑予備処理あるいは二次精錬工程により脱硫を行った。また、Ａｌやその他、必要な合金を添加して成分調整を行った。このようにして溶製された溶鋼を連続鋳造して鋳片を製造した。連続鋳造では、２８０ｍｍ厚程度のスラブ連続鋳造で実施した。 In this test, molten steel with the chemical composition shown in Tables 1 to 3 was blown in a converter, and alloys such as C, Si, and Mn were added to the molten steel, which was further refined using a vacuum degassing device and stirred. Then, deoxidation and component adjustment were performed. Regarding S, desulfurization was performed by hot metal pretreatment or secondary refining process until the S concentration was reached in each test case. In addition, Al and other necessary alloys were added to adjust the composition. The thus produced molten steel was continuously cast to produce slabs. Continuous casting was carried out by continuous slab casting with a thickness of about 280 mm.
連続鋳造後、連続鋳造鋳片を所定長さに切断して、加熱炉に装入した。鋳片を３０分から５０分程度加熱した後、加熱炉から抽出し、サイジングミルを用いて表１～表３に示す熱間幅圧下圧延開始温度で熱間幅圧下圧延を行った。その後、鋳片のエッジ割れ及びスケール起因疵の有無について調査した。 After continuous casting, the continuously cast slab was cut into a predetermined length and charged into a heating furnace. After heating the slab for about 30 to 50 minutes, it was extracted from the heating furnace and hot width reduction rolling was performed using a sizing mill at the hot width reduction rolling start temperature shown in Tables 1 to 3. Thereafter, the slab was investigated for edge cracks and scale-induced flaws.
割れの評価方法は、先ず目視で行い、エッジ割れが見られた場合はエッジ割れについて×とした。目視でエッジ割れが不明な場合は、鋳片の上下面スカーフ溶削を２～４ｍｍ行い、エッジ割れが見られた場合はエッジ割れについて×とした。鋳片の上下面スカーフ溶削を行っても不明な場合は、鋳片からＣ断面（鋳片の長手方向と直交する断面）サンプルを切り出し、表面を研磨してカラーチェックを行い、エッジ割れが見られた場合は×、見られない場合は○とした。また、目視観察でスケール起因疵が見られた場合はスケール起因疵について×、見られない場合はスケール起因疵について○とした。 The evaluation method for cracks was first visually observed, and if edge cracks were observed, the edge cracks were rated as x. If edge cracking is not visible by visual inspection, scarf cutting is performed on the upper and lower surfaces of the slab by 2 to 4 mm, and if edge cracking is observed, the edge cracking is marked as ×. If it is unclear even after carrying out scarf cutting on the top and bottom surfaces of the slab, cut out a sample of the C section (a cross section perpendicular to the longitudinal direction of the slab) from the slab, polish the surface, check the color, and check for edge cracks. If it was seen, it was marked ×; if it was not, it was marked ○. In addition, when scale-induced flaws were observed by visual observation, the scale-induced flaws were marked as ×, and when no scale-induced flaws were observed, the scale-induced flaws were marked as ○.
表１は全て発明例であり、エッジ割れもスケール起因疵も発生しなかった。
表２は、本発明に係る熱間幅圧下圧延開始温度範囲より低い温度で熱間幅圧下圧延を行った比較例であり、エッジ割れが発生した。
表３は、本発明に係る熱間幅圧下圧延開始温度範囲より高い温度で熱間幅圧下圧延を行った比較例であり、エッジ割れはないものの、スケール起因疵が発生した。
Table 1 shows all the invention examples, and neither edge cracks nor scale-induced flaws occurred.
Table 2 shows a comparative example in which hot width reduction rolling was performed at a temperature lower than the hot width reduction rolling start temperature range according to the present invention, and edge cracking occurred.
Table 3 shows a comparative example in which hot width reduction rolling was performed at a temperature higher than the hot width reduction rolling start temperature range according to the present invention, and although there was no edge cracking, scale-induced flaws occurred.
Claims (1)
１パス当たりの幅圧下量Ｗが０ｍｍ超３００ｍｍ以下のとき、熱間幅圧下圧延開始温度Ｔ（℃）が次式を満足し、且つ９９０℃未満であることを特徴とする連続鋳造鋳片の熱間幅圧下圧延方法。
Ｔ＞2.524×10８([Ｍｎ]・[Ｓ])３-7.429×106([Ｍｎ]・[Ｓ])２+7.130×104([Ｍｎ]・[Ｓ])+0.162Ｗ+724.3
ここで、[Ｍｎ]：Ｍｎの濃度（質量％）、[Ｓ]：Ｓの濃度（質量％）
C 0.03 to 0.30% by mass, Si 0.01 to 0.80% by mass, Mn 0.50 to 3.00% by mass, P 0.005 to 0.050% by mass, S Molten carbon steel containing 0.0001 to 0.0150% by mass and 0.01 to 0.10% by mass of Al is cast using a continuous casting machine into a width of 1350mm to 2000mm and a thickness of 250mm to 300mm. In a method of cutting a slab into a predetermined length, heating the slab and hot width reduction rolling,
A continuously cast slab characterized in that when the width reduction amount W per pass is more than 0 mm and 300 mm or less, the hot width reduction rolling start temperature T (°C) satisfies the following formula and is less than 990 °C. Hot width reduction rolling method.
T＞2.524×10 8 ([Mn]・[S]) 3 -7.429×10 6 ([Mn]・[S]) 2 +7.130×10 4 ([Mn]・[S])+0.162W+724.3
Here, [Mn]: concentration of Mn (mass%), [S]: concentration of S (mass%)
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000042703A (en) | 1998-07-24 | 2000-02-15 | Nippon Steel Corp | Production of steel slab without developing surface defect due to width reduction |
| JP2002066601A (en) | 2000-08-29 | 2002-03-05 | Nippon Steel Corp | Method for preventing surface cracking of continuous cast slab under large reduction of hot rolled width |
| JP2002346602A (en) | 2001-05-22 | 2002-12-03 | Nippon Steel Corp | Production method of billet without crack defect |
| CN106319389A (en) | 2015-06-17 | 2017-01-11 | 宝山钢铁股份有限公司 | Low-cost high-machinability steel for engineering machine and manufacturing method of steel |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000042703A (en) | 1998-07-24 | 2000-02-15 | Nippon Steel Corp | Production of steel slab without developing surface defect due to width reduction |
| JP2002066601A (en) | 2000-08-29 | 2002-03-05 | Nippon Steel Corp | Method for preventing surface cracking of continuous cast slab under large reduction of hot rolled width |
| JP2002346602A (en) | 2001-05-22 | 2002-12-03 | Nippon Steel Corp | Production method of billet without crack defect |
| CN106319389A (en) | 2015-06-17 | 2017-01-11 | 宝山钢铁股份有限公司 | Low-cost high-machinability steel for engineering machine and manufacturing method of steel |
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