JP2004195512A - Surface layer reforming method for steel cast slab, reformed cast slab, and processed product - Google Patents
Surface layer reforming method for steel cast slab, reformed cast slab, and processed product Download PDFInfo
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、鋼の連続鋳造鋳片の表層改質方法、およびそれを用いて得られる改質鋳片および加工製品に関する。
【0002】
【従来の技術】
性質の異なる2種類の金属を鋳片段階で製造することにより、複合された機能を有する複合材を通常の加工過程で製造することができる。発明者らは、鋳片表層と内層の成分が異なる鋳片の連続鋳造方法として、例えば連続鋳造する際に、2種類の溶鋼を同時に鋳造する方法を特許文献1に、また潤滑剤内に元素を混入させる方法を特許文献2にそれぞれ開示している。
【0003】
【特許文献1】
特開昭63−108947号公報
【特許文献2】
特開平07−26109号公報
【0004】
【発明が解決しようとする課題】
しかしながら、特許文献1に開示している様な、2種類の溶鋼を同時に鋳造する方法では、さまざまな組み合わせの複層鋳片を得ることができる反面、溶鋼段階で2種類の成分のものを準備する必要があり、かつ該溶鋼を入れる取鍋、それを鋳型に注入する際に必要となるタンディッシュやノズルなども2種類用意する必要があり、コスト的に高くなることが課題である。一方、特許文献2に開示している様な、潤滑剤内に元素を混入させる方法では、上記問題が解決され、コスト的に安価とできるものの、潤滑剤を通じて添加するために元素成分の付加範囲が安定しないことや、熱源の不足により量が限られる等の課題がある。
本発明は、鋼の連続鋳造鋳片表層を安価に確実に改質し、複合鋼材を製造することを目的とする。
【0005】
【課題を解決するための手段】
本発明は、
(1) 鋼鋳片の表層を誘導加熱、プラズマ加熱のいずれか一方または双方により溶融させ、溶融した鋼鋳片の表層部分に、添加元素もしくはその合金を添加することを特徴とする鋼鋳片の表層改質方法。
(2) 少なくとも誘導加熱を用いる場合、誘導加熱により発生する磁場の向きを、鋳片鋳造方向となるように発生させ、溶融部分を電磁力で保持することを特徴とする(1)に記載の鋼鋳片の表層改質方法。
(3) 少なくともプラズマ加熱を用いる場合、添加元素もしくはその合金を、プラズマ内に供給し、加熱または溶融してから、鋼の溶融した部分に供給することを特徴とする(1)または(2)に記載の鋼鋳片の表層改質方法。
(4) 誘導加熱、プラズマ加熱の双方を用いる場合、誘導加熱により鋳片表層と併せて添加元素もしくはその合金を予熱し、その後プラズマ加熱により該添加元素もしくはその合金を溶融化させることを特徴とする(1)に記載の鋼鋳片の表層改質方法。
(5) (1)〜(4)のいずれかに記載の方法により得られる表層改質鋼鋳片。
(6) (5)に記載の表層改質鋼鋳片を加工することにより得られる加工製品である。
【0006】
【発明の実施の形態】
本発明は、鋼の鋳片表層に添加元素もしくはその合金を溶着させる方法として、誘導加熱、プラズマ加熱のいずれか一方または双方を用いて鋼の鋳片表層を溶融させ、そこへ添加元素もしくはその合金を添加することで、安価に確実に複合鋼材を製造できることを見出した。以下にその詳細に説明する。
【0007】
本発明で対象とする鋼の鋳片について、その表層部分の厚さは、特に規定するものではないが、通常は0.5〜20mm程度である。これは、0.5mm未満の場合は通常の加熱・圧延工程で表面が酸化して失われてしまうこと、また20mm超の場合は一般に目的とする複合鋼材の製造において、特に要求がないことや、本プロセスによって溶融処理する上で、溶融処理コストが増大することが、その理由である。また、上記鋳片は連続鋳造により製造されたものが多い。
【0008】
本発明は、上記鋳片の表層部分に添加元素もしくはその合金を溶着させることで、複合鋼材を製造するものであるが、添加元素もしくはその合金については後述するとして、まず鋼の鋳片表層を溶融させる方法について説明する。
鋼の鋳片表層を溶融させる方法として、誘導加熱単独、プラズマ加熱単独、誘導加熱とプラズマ加熱の併用のいずれを用いても良い。
【0009】
誘導加熱単独で行う場合は、添加元素もしくはその合金を、ワイヤーやシートの形で鋳片表層溶融部に添加できる。具体的には、連続鋳造機で得られた鋳片は、切断後、溶融処理場に輸送され、鋳片を周回するように配置された誘導コイルにより加熱され、鋳片表層溶融部にワイヤーやシートを用いて添加元素もしくはその合金を添加して溶着される。誘導コイルは鋳片表層溶融部で電磁力により溶融部分を内面に向かって電磁力によって押さえつけることにより安定した溶融部表面を作り、その後再度冷却され凝固する。
【0010】
この方法によると、鋳片表層の溶融部温度を液相線温度(鉄は他の成分を含むため、融点のように1つの温度では溶融状態が決まらず、凝固が始まる温度を固相線温度、全て液体となる温度を液相線温度と呼ぶ)よりもわずかに高い温度に保持し、添加後に急速に冷却凝固させることにより凝固組織を小さくでき、結晶粒のサイズを小さくすることにより、添加元素の溶融処理部内での均一性が増し、また圧延時にも割れなどの欠陥を生じにくくなるという利点がある。
【0011】
また、鋳片表層溶融部に添加元素もしくはその合金を添加して溶着させる場合、鋳片の酸化を防止することが好ましいため、誘導コイルはチャンバー内で不活性ガス雰囲気(例えばアルゴン、窒素等)で溶融改質するのが好ましく、さらにより確実に酸化を防止するためには、不活性ガス雰囲気中に約2容量%程度の水素を含んで溶融改質することが好ましい。
ここで、誘導コイルによる電磁力の力の発生原理を図3に示す。誘導コイル3が発生する磁場と、導体である鋳片に誘導した電流の相互作用により、溶融部には電磁力が作用する。この電磁力はピンチ力と呼ばれる溶融部を圧縮する作用があり、溶融部表面の安定化に寄与する。
【0012】
次に連続鋳造機端、すなわち連続鋳造後の鋳片が水平に移動している際に、本発明方法を適用する場合について説明する。この場合、鋳片は一般の湾曲型もしくは垂直部を鋳型下数mにわたって有する垂直曲げ型連鋳機において、一般には曲げ戻しを受けたあと、ガスカットされる前に水平部を有することから、この部分に配置する。誘導コイルは鋳片を周回するように配置されている。この方式の場合、図6、7に示す様に鋳片上部は誘導コイルによる加熱により鋳片表層部が溶融しても、重力による滴下が起こらないため、容易に処理される。また鋳片下部の溶融部は、図3に示す原理に基づいた電磁力の作用により保持され、重力による滴下や再凝固後の表面形状が悪化することを防止できる。この処理は、ガスカット後に鋳片反転装置を用いて180度反転させることで、片面づつ処理することもできる。鋳片端部については、上記鋳片反転装置を用いて±90度反転させることで、処理することができる。
【0013】
さらに連続鋳造機内、すなわち鋳片が垂直に移動している際に、本発明方法を適用する場合について説明する。連続鋳造機内において、鋳型を出た鋳片は、2次冷却帯内において、誘導コイルにより加熱される。誘導コイルは溶融部の電磁力による保持を受けて、溶融部分が重力により滴下することなく、下部の誘導コイルを通過後に再度冷却され凝固する。ここで、鋳片溶融部分は溶融部の下部側が重力の作用によってより滴下しやすくなるため、誘導コイルは図5に示す様に、上部コイルよりは下部コイルを鋳片近くに設置することで、溶融部の下部側がより強い電磁力を発生して溶融部が漏れることを防止できるため好ましい。
【0014】
また、プラズマ加熱単独で行う場合は、プラズマ内に添加元素もしくはその合金を供給し、鋼の溶融した部分に供給することで鋳片表層溶融部に添加できる。プラズマは一般に軸対称な形をしているため、連続的に鋳片の表面を処理するには、プラズマトーチを鋳片幅方向にスキャンさせる方法か、特開昭54−1421545号公報のプラズマを鋳片幅方向に電磁力を使って扁平な往復運動させる方法等を用いることができる。
【0015】
連続鋳造機で得られた鋳片は、切断後、溶融処理場に輸送され、添加元素もしくはその合金をプラズマに供給することで、プラズマで鋳片表層を溶融しつつ、添加元素もしくはその合金を供給し、鋼の溶融した部分に供給することで、溶着される。その後再度冷却され凝固する。
【0016】
この方法でも、鋳片表層の溶融部温度を液相線温度(鉄は他の成分を含むため、融点のように1つの温度では溶融状態が決まらず、凝固が始まる温度を固相線温度、全て液体となる温度を液相線温度と呼ぶ)よりもわずかに高い温度に保持し、添加後に急速に冷却凝固させることにより凝固組織を小さくでき、結晶粒のサイズを小さくすることにより、添加元素の溶融処理部内での均一性が増し、また圧延時にも割れなどの欠陥を生じにくくなるという利点がある。
また、鋳片表層溶融部に添加元素もしくはその合金を添加して溶着させる場合、鋳片の酸化を防止することが好ましいため、チャンバー内のガス雰囲気は上記と同様であることが好ましい。
【0017】
次に連続鋳造機端、すなわち連続鋳造後の鋳片が水平に移動している際に、本発明方法を適用する場合について説明する。この場合、鋳片は一般の湾曲型もしくは垂直部を鋳型下数mにわたって有する垂直曲げ型連鋳機において、一般には曲げ戻しを受けたあと、ガスカットされる前に水平部を有することから、この部分に配置する。この方式の場合、誘導コイルを用いた場合の様に電磁力の力で溶融部を保持することができないため、水平処理で上面側のみの処理をまず行い、ガスカット後に鋳片を180度反転して処理するなどの対応をすることが必要になる。また鋳片端部については、±90度反転させることで、処理することができる。
【0018】
さらに、誘導加熱とプラズマ加熱を併用して行う場合について、図1〜4に基づいて説明する。
連続鋳造機1で連続鋳造を完了した鋳片5は、切断後、溶融処理場に輸送され、図1のように誘導コイル3により加熱され、さらに添加元素もしくはその合金をプラズマ2に供給することで、鋳片表層溶融部に添加元素もしくはその合金を添加して溶着させる。誘導コイル3は鋳片表層溶融部8で電磁力によるより溶融部分を内面に向かって電磁力によって押さえつけることにより安定した溶融部表面を作り、その後再度冷却され凝固する。
【0019】
この様に上記方法を併用した場合でも、鋳片表層への熱負荷が従来技術よりも小さくできるため、得られる表層改質鋳片の溶融部温度を液相線温度(鉄は他の成分を含むため、融点のように1つの温度では溶融状態が決まらず、凝固が始まる温度を固相線温度、全て液体となる温度を液相線温度と呼ぶ)よりもわずかに高い温度に保持し、添加後に急速に冷却凝固させることにより凝固組織を小さくでき、結晶粒のサイズを小さくすることにより、添加元素の溶融処理部内での均一性が増し、また圧延時にも割れなどの欠陥を生じにくくなるという利点がある。
また、鋳片表層溶融部に添加元素もしくはその合金を添加して溶着させる場合、鋳片の酸化を防止することが好ましいため、チャンバー内のガス雰囲気は上記と同様であることが好ましい。さらに、誘導コイルによる電磁力は先に記載している通り、作用する。
【0020】
次に連続鋳造機端、すなわち連続鋳造後の鋳片が水平に移動している際に、本発明方法を適用する場合について説明する。この場合、鋳片は一般の湾曲型もしくは垂直部を鋳型下数mにわたって有する垂直曲げ型連鋳機において、一般には曲げ戻しを受けたあと、ガスカットされる前に水平部を有することから、この部分に配置する。誘導コイルは鋳片を周回するように配置されており、プラズマも上下側端に配置されている。この方式の場合、図2に示す様に鋳片上部は誘導コイルによる加熱により鋳片表層部が溶融しても、重力による滴下が起こらないため、容易に処理される。また鋳片下部の溶融部は、図3に示す原理に基づいた電磁力の作用により保持され、重力による滴下や再凝固後の表面形状が悪化することを防止できる。この処理は、ガスカット後に鋳片反転装置を用いて180度反転させることで、片面づつ処理することもできる。鋳片端部については、上記鋳片反転装置を用いて±90度反転させることで、処理することができる。
【0021】
さらに連続鋳造機内、すなわち鋳片が垂直に移動している際に、本発明方法を適用する場合について説明する。連続鋳造機内において、鋳型を出た鋳片5は、2次冷却帯内において、誘導コイル3により加熱され、さらに添加元素もしくはその合金をプラズマ2に供給することで、鋳片表層溶融部に添加元素もしくはその合金を添加して溶着させる。誘導コイルは溶融部の電磁力による保持を受けて、溶融部分が重力により滴下することなく、下部の誘導コイルを通過後に再度冷却され凝固する。ここで、鋳片溶融部分は溶融部の下部側が重力の作用によってより滴下しやすくなるため、誘導コイル3は図5に示す様に、上部コイルよりは下部コイルを鋳片近くに設置することで、溶融部の下部側がより強い電磁力を発生して溶融部が漏れることを防止できるため好ましい。
【0022】
なお、添加元素の成分としては、鋼材の特性を変化させるために用いられるものとして、炭素、シリコン、マンガン、リン、硫黄、ニッケル、クロム、モリブデン、銅、金、アルミニウム、マグネシウム、レアアースメタル等が挙げられる。また、添加元素の合金としては、上記添加元素の複数成分の合金に加え、添加元素成分と酸素あるいは窒素との化合物なども含まれる。
【0023】
以下に添加元素について説明する。
炭素:鋼材の強度を上げる働きがある。例えば、極低炭素鋼の表層のみに炭素を添加することにより、加工性を内部の鋼で維持し、表層で強度を増すことにより強度の双方に優れる鋼板の製造が可能である。
ニッケル、クロム:鋼材の耐食性を向上させる作用がある。例えば、低炭素鋼の表層にニッケル、クロムを添加することにより、表層をステンレスとすることができる。
モリブデン:上記のニッケル、クロムに加えてモリブデンを添加することで、さらに耐食性を向上させる作用がある。
シリコン、マンガン:特に鉄系合金に対して強度を向上させる作用がある。
リン:極低炭素鋼に添加して、強度を上げる作用がある。
硫黄:鋼の切削性を高める作用がある。
銅:極低炭素鋼にニッケルと併せて添加することにより加工性と強度を同時に増すことができる。
金:鋼に抗菌作用を付加することができる。
アルミニウム:普通鋼に添加することにより、耐食性を増すことができる。
マグネシウム、レアアースメタル:鋼中の酸素や硫黄と結びつき、微細な酸化物や硫化物を生成して、鋼材の組織を小さくし、また鋼管材など溶接される材料に用いられる場合、溶接の熱影響部では組織が粗くなって強度が低下するが、これを微細な化合物で抑制することなどができる。
【0024】
また、添加元素の合金については、上記添加元素の複数成分の合金であれば特に規定するものではないが、通常はフェロマンガン、フェロニッケル、フェロリンその他合金鉄等が用いられる。
さらに、添加元素成分と窒素との化合物については、例えば窒化鉄の様な窒素を合金の形で添加することで、結晶粒を小さくする作用があるため、圧延時の表面粗さが均一に保たれ鋼の表面形状を良好にできる。また、添加元素成分と酸素との化合物については、例えばマグネシウム酸化物の様な酸素を合金の形で添加することで、組織を微細化する作用があるため、加工割れの防止や溶接時の強度低下防止などができる。
【0025】
また、誘導加熱、プラズマ加熱の双方を併用する場合の別の形態として、誘導加熱により鋳片表層と併せてワイヤーやシートの形で鋳片表層部に添加した添加元素もしくはその合金を予熱し、その後プラズマ加熱により該添加純金属または合金を溶融合金化させる方法を用いても良い。
これは、誘導加熱は単に予熱機能として使用し、その後のプラズマ加熱で添加元素もしくはその合金を溶融合金化させるものであり、プラズマで一般に加熱溶融するには添加元素もしくはその合金の形状がパウダー状であり、プラズマ内に吹き込むのが一般的であるのに対し、この方法の場合には添加元素もしくはその合金の形状にかかわらず実施できるという利点がある。
【0026】
上記方法により得られた表層改質複合鋼材鋳片は、表層と内部の性質が異なる鋼の特性を併せ持つ、低コスト鋼材であるという利点がある。
従って、上記の表層改質複合鋼材鋳片を加工することにより得られる加工製品について、表層と内部の性質が異なる鋼の特性を併せ持つ低コスト製品が得られる。加工製品とは薄板、厚板等の鋼板、形鋼、鋼管等が挙げられるが、通常の鉄鋼プロセスで鋳片を加工して得られる鉄鋼製品すべてを対象とする。また、熱延コイル等の半製品も含まれる。
【0027】
【実施例】
(実施例1)
図1、2に示すような、連続鋳造を完了した鋳片を切断後に、誘導加熱とプラズマ加熱を併用して溶融改質処理を行う方法を用いて、幅1500mm、厚さ250mm、長さ10mの0.01%C−0.03%Si−0.24%Mn−0.01%P−0.01%S(単位は質量%)の連続鋳造鋳片の表層20mmを溶融処理し、プラズマを用いて炭素、珪素、マンガン、ニッケル、クロム合金の添加を行い、0.04%C−0.49%Si−1.01%Mn−0.01%P−0.01%S−18.1%Cr−8.5%Ni(質量ベース)の表層ステンレス鋳片とした。
得られた鋳片は、断面分析したところ、深さ方向のばらつきプラスマイナス1mm、元素成分のばらつきは5%以内であった。本鋳片を加工することにより、表面がステンレスの特性すなわち高い耐食性、美観を有する薄板用鋼板を、安価に製造することができた。
【0028】
(実施例2)
図6、7に示すような、連続鋳造を完了した鋳片を切断後に、誘導加熱により溶融改質処理する方法を用いて、幅1500mm、厚さ250mm、長さ10mの0.001%C−0.11%Mn−0.01Si−0.007%P−0.009%S−0.045%Al−0.049%Ti(単位は質量%)の連続鋳造鋳片の表層20mmを溶融処理し、合金ワイヤーを用いて炭素合金添加を行い、表層の炭素成分のみ0.03質量%とした。
得られた鋳片は、断面分析したところ、深さ方向のばらつきプラスマイナス1mm、元素成分のばらつきは3%以内であった。本鋳片を加工することにより、疲労強度に優れ、同時に良好な加工性を有する薄板用鋼板を得ることができた。
【0029】
【発明の効果】
以上説明したように本発明の表層改質方法を用いれば、複層鋳片が、安価に製造可能となる。
【図面の簡単な説明】
【図1】本発明の方法の構成の一例(鋳片切断後あるいは連鋳機端での処理)を示す断面模式図。
【図2】本発明の方法の構成を示すもので、図1の鋳片表層の処理部分詳細図。
【図3】誘導コイルによる電磁力発生の原理の説明図。
【図4】本発明の方法の構成の他の例(機内処理)を示す断面模式図。
【図5】本発明の方法の構成(機内処理)および力のバランスの説明図(図4の処理部分詳細図)。
【図6】電磁誘導のみを用いた本発明の方法の構成例(鋳片切断後あるいは連鋳機端での処理)を示す断面模式図。
【図7】電磁誘導のみを用いた本発明の方法の構成(図6の処理部分詳細図)。
【符号の説明】
1:連続鋳造機
2:元素を溶融添加する機能を保有したプラズマ
3:電磁誘導コイル
4:サポートロール
5:鋳片
6:不活性ガス雰囲気をつくる容器
7:凝固部
8:溶融した部分
9:未凝固部
10:連続引抜もしくは移動方向
11:コイル電流
12:交流電流
13:時間
14:電気伝導体
15:磁場
16:未溶融の加熱部
17:添加元素が富化された部分
18:電磁力の方向と強さ
19:重力(静鉄圧)の方向と強さ
20:元素を添加するワイヤー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for modifying a surface layer of a continuously cast slab of steel, and a modified slab and a processed product obtained by using the method.
[0002]
[Prior art]
By producing two kinds of metals having different properties at the slab stage, a composite material having a composite function can be produced in a normal working process. The inventors have disclosed in Patent Document 1 a method of continuously casting two types of molten steel at the time of continuous casting, for example, as a continuous casting method of a slab having different components of a slab surface layer and an inner layer. Are disclosed in
[0003]
[Patent Document 1]
JP-A-63-108947 [Patent Document 2]
JP 07-26109 A
[Problems to be solved by the invention]
However, in the method of simultaneously casting two types of molten steel as disclosed in Patent Document 1, it is possible to obtain a multilayer slab of various combinations, but on the other hand, preparing two types of components in the molten steel stage. It is necessary to prepare two types of ladle for placing the molten steel, a tundish and a nozzle required for pouring the ladle into a mold, and the problem is that the cost becomes high. On the other hand, a method of mixing an element into a lubricant as disclosed in
An object of the present invention is to produce a composite steel material by reliably and inexpensively modifying the surface layer of a continuously cast slab of steel.
[0005]
[Means for Solving the Problems]
The present invention
(1) A steel slab characterized in that a surface layer of a steel slab is melted by one or both of induction heating and plasma heating, and an additional element or an alloy thereof is added to a surface layer portion of the molten steel slab. Surface modification method.
(2) The method according to (1), wherein at least when induction heating is used, the direction of the magnetic field generated by the induction heating is generated so as to be in the slab casting direction, and the molten portion is held by electromagnetic force. A method for modifying the surface layer of steel slabs.
(3) When using plasma heating at least, the additional element or its alloy is supplied into the plasma, heated or melted, and then supplied to the molten portion of the steel (1) or (2). The method for modifying the surface layer of a steel slab according to the above.
(4) When both induction heating and plasma heating are used, the additional element or its alloy is preheated together with the slab surface layer by induction heating, and then the additional element or its alloy is melted by plasma heating. (1) The method for modifying a surface layer of a steel slab according to (1).
(5) A surface modified steel slab obtained by the method according to any one of (1) to (4).
(6) A processed product obtained by processing the surface-modified steel slab according to (5).
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention, as a method of welding an additive element or an alloy thereof to the surface layer of steel slab, induction heating, one or both of plasma heating to melt the surface layer of steel slab, the additional element or its It has been found that composite steel can be reliably manufactured at low cost by adding an alloy. The details will be described below.
[0007]
The thickness of the surface layer of the steel slab to be used in the present invention is not particularly limited, but is usually about 0.5 to 20 mm. This is because when the thickness is less than 0.5 mm, the surface is oxidized and lost in a normal heating / rolling process, and when the thickness is more than 20 mm, there is no particular requirement in the production of a target composite steel material. The reason is that the melt processing cost increases in the melt processing by the present process. In addition, the slabs are often manufactured by continuous casting.
[0008]
The present invention is to produce a composite steel material by welding an additive element or an alloy thereof to the surface layer portion of the slab, the additional element or its alloy will be described later, first, the steel slab surface layer The method of melting will be described.
As a method of melting the surface layer of the steel slab, any of induction heating alone, plasma heating alone, and a combination of induction heating and plasma heating may be used.
[0009]
When induction heating is performed alone, the additive element or an alloy thereof can be added to the slab surface layer molten portion in the form of a wire or sheet. Specifically, the slab obtained by the continuous casting machine, after cutting, is transported to a melting treatment plant, heated by an induction coil arranged so as to go around the slab, and a wire or An additional element or an alloy thereof is added and welded using a sheet. The induction coil forms a stable molten portion surface by pressing the molten portion toward the inner surface by the electromagnetic force at the surface layer of the slab by the electromagnetic force, and then cools and solidifies again.
[0010]
According to this method, the melting point temperature of the surface layer of the slab is determined by the liquidus temperature (since iron contains other components, the melting state is not determined at one temperature such as the melting point, and the temperature at which solidification starts is the solidus temperature. (The temperature at which all liquids are formed is called the liquidus temperature.) The solidification structure can be reduced by rapidly cooling and solidifying after the addition, and the crystal grain size can be reduced. There is an advantage that the uniformity of the element in the melt-processed portion is increased, and defects such as cracks are less likely to occur during rolling.
[0011]
In addition, when an additional element or an alloy thereof is added to and fused to the surface layer of the cast slab, it is preferable to prevent oxidation of the cast slab. Therefore, the induction coil is provided in an inert gas atmosphere (eg, argon, nitrogen, etc.) In order to more reliably prevent oxidation, melt reforming is preferably performed by containing about 2% by volume of hydrogen in an inert gas atmosphere.
Here, the principle of generation of the electromagnetic force by the induction coil is shown in FIG. Due to the interaction between the magnetic field generated by the
[0012]
Next, the case where the method of the present invention is applied when the end of the continuous casting machine, that is, the slab after continuous casting is moving horizontally, will be described. In this case, the slab is a general bending type or a vertical bending type continuous casting machine having a vertical portion extending over several m below the mold, and generally has a horizontal portion before being gas-cut after being bent back, Place it in this part. The induction coil is arranged to go around the slab. In this method, as shown in FIGS. 6 and 7, the upper portion of the slab is easily treated because even if the slab surface layer is melted by heating by the induction coil, dripping by gravity does not occur. Further, the molten portion below the slab is held by the action of electromagnetic force based on the principle shown in FIG. 3, and it is possible to prevent the surface shape after dripping by gravity or resolidification from deteriorating. This process can be performed one by one by inverting 180 degrees using a slab reversing device after gas cutting. The slab end can be processed by reversing ± 90 degrees using the slab reversing device described above.
[0013]
Further, a case where the method of the present invention is applied in a continuous casting machine, that is, when the slab is moving vertically, will be described. In the continuous casting machine, the slab leaving the mold is heated by the induction coil in the secondary cooling zone. The induction coil receives the holding by the electromagnetic force of the melting portion, and the melted portion is cooled again and solidified after passing through the lower induction coil without dripping by gravity. Here, since the lower portion of the molten portion of the slab is more likely to drip due to the action of gravity, the induction coil is disposed closer to the slab than the upper coil, as shown in FIG. This is preferable because it is possible to prevent the lower portion of the fusion zone from generating a stronger electromagnetic force and to prevent the fusion zone from leaking.
[0014]
When plasma heating is performed alone, an additional element or an alloy thereof is supplied into the plasma and supplied to a molten portion of steel, so that the additional element or the alloy can be added to the surface layer of the slab. Since plasma generally has an axially symmetric shape, in order to continuously treat the surface of a slab, a method in which a plasma torch is scanned in the width direction of the slab or a method disclosed in Japanese Patent Application Laid-Open No. Sho 54-142545 is used. A flat reciprocating motion using electromagnetic force in the slab width direction can be used.
[0015]
After cutting, the slab obtained by the continuous casting machine is transported to a melting treatment plant, and by supplying the additional element or its alloy to the plasma, while melting the slab surface layer with plasma, the additional element or its alloy is Supply and supply to the molten portion of the steel to be welded. Thereafter, it is cooled again and solidified.
[0016]
Also in this method, the melting temperature of the surface layer of the slab is determined by the liquidus temperature (since iron contains other components, the melting state is not determined at one temperature such as the melting point, and the temperature at which solidification starts is the solidus temperature, (The temperature at which all liquids are formed is called the liquidus temperature.) The solidification structure can be reduced by rapidly cooling and solidifying after the addition, and the size of the crystal grains can be reduced. This has the advantage that the uniformity in the melt-processed portion is increased, and defects such as cracks are less likely to occur during rolling.
In addition, when an additional element or an alloy thereof is added to the slab surface layer fusion portion and welded, it is preferable to prevent the slab from being oxidized. Therefore, the gas atmosphere in the chamber is preferably the same as described above.
[0017]
Next, the case where the method of the present invention is applied when the end of the continuous casting machine, that is, the slab after continuous casting is moving horizontally, will be described. In this case, the slab is a general bending type or a vertical bending type continuous casting machine having a vertical portion extending over several m below the mold, and generally has a horizontal portion before being gas-cut after being bent back, Place it in this part. In the case of this method, the molten portion cannot be held by the force of the electromagnetic force as in the case of using an induction coil. Therefore, only the upper surface is first processed by horizontal processing, and the slab is turned 180 degrees after gas cutting. It is necessary to take measures such as processing. The end of the slab can be processed by reversing ± 90 degrees.
[0018]
Further, a case where induction heating and plasma heating are performed in combination will be described with reference to FIGS.
The slab 5 that has been continuously cast by the continuous casting machine 1 is cut, transported to a melting treatment plant, heated by the
[0019]
As described above, even when the above method is used in combination, the heat load on the surface layer of the slab can be made smaller than that of the conventional technique. Therefore, the melting state is not determined at one temperature, such as the melting point, and the temperature at which solidification begins is called the solidus temperature, and the temperature at which all liquids are formed is called the liquidus temperature). The solidification structure can be made smaller by rapid cooling and solidification after the addition, and the size of the crystal grains is made smaller, so that the uniformity of the added element in the melt-processed portion is increased, and defects such as cracks are less likely to occur during rolling. There is an advantage.
In addition, when an additional element or an alloy thereof is added to the slab surface layer fusion portion and welded, it is preferable to prevent the slab from being oxidized. Therefore, the gas atmosphere in the chamber is preferably the same as described above. In addition, the electromagnetic force from the induction coil acts as described above.
[0020]
Next, the case where the method of the present invention is applied when the end of the continuous casting machine, that is, the slab after continuous casting is moving horizontally, will be described. In this case, the slab is a general bending type or a vertical bending type continuous casting machine having a vertical portion extending over several m below the mold, and generally has a horizontal portion before being gas-cut after being bent back, Place it in this part. The induction coil is arranged to go around the slab, and the plasma is also arranged at the upper and lower ends. In the case of this method, as shown in FIG. 2, the upper portion of the slab is easily processed because even if the slab surface layer is melted by heating by the induction coil, dripping by gravity does not occur. Further, the molten portion below the slab is held by the action of electromagnetic force based on the principle shown in FIG. 3, and it is possible to prevent the surface shape after dripping by gravity or resolidification from deteriorating. This process can be performed one by one by inverting 180 degrees using a slab reversing device after gas cutting. The slab end can be processed by reversing ± 90 degrees using the slab reversing device described above.
[0021]
Further, a case where the method of the present invention is applied in a continuous casting machine, that is, when the slab is moving vertically, will be described. In the continuous casting machine, the slab 5 coming out of the mold is heated by the
[0022]
In addition, as a component of the additive element, carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, copper, gold, aluminum, magnesium, rare earth metal, etc., which are used to change the properties of the steel material No. In addition, the alloy of the additive element includes a compound of the additive element component and oxygen or nitrogen, in addition to the alloy of a plurality of components of the additive element.
[0023]
Hereinafter, the additional elements will be described.
Carbon: works to increase the strength of steel. For example, by adding carbon only to the surface layer of ultra-low carbon steel, the workability is maintained by the inner steel, and the strength is enhanced by increasing the surface layer, thereby making it possible to produce a steel sheet having both excellent strength.
Nickel, chromium: has the effect of improving the corrosion resistance of steel. For example, the surface layer can be made of stainless steel by adding nickel and chromium to the surface layer of low carbon steel.
Molybdenum: Addition of molybdenum in addition to the above nickel and chromium has the effect of further improving corrosion resistance.
Silicon, manganese: has the effect of improving strength, especially for iron-based alloys.
Phosphorus: Adds to extremely low carbon steel to increase strength.
Sulfur: has the effect of improving the machinability of steel.
Copper: Workability and strength can be increased at the same time by adding it together with nickel to ultra-low carbon steel.
Gold: An antibacterial effect can be added to steel.
Aluminum: Corrosion resistance can be increased by adding it to ordinary steel.
Magnesium and rare earth metals: Combine with oxygen and sulfur in steel to form fine oxides and sulfides, reduce the structure of steel materials, and when used for materials to be welded such as steel pipe materials, the thermal effects of welding In the part, the structure becomes coarse and the strength decreases, but this can be suppressed with a fine compound.
[0024]
The alloy of the additive element is not particularly limited as long as it is an alloy of a plurality of components of the additive element. Usually, ferromanganese, ferronickel, ferroline, and other alloyed irons are used.
Furthermore, as for the compound of the additive element component and nitrogen, the addition of nitrogen such as iron nitride in the form of an alloy has the effect of reducing crystal grains, so that the surface roughness during rolling is kept uniform. The surface shape of the drop steel can be improved. In addition, as for the compound of the additive element component and oxygen, the addition of oxygen such as magnesium oxide in the form of an alloy has the effect of refining the structure, thereby preventing work cracking and improving the strength during welding. Prevention of drop is possible.
[0025]
In addition, as another form when both induction heating and plasma heating are used in combination, preheating the additive element or its alloy added to the slab surface layer in the form of a wire or sheet together with the slab surface layer by induction heating, Thereafter, a method of melting the added pure metal or alloy by plasma heating may be used.
This is because induction heating is simply used as a preheating function, and then the added element or its alloy is melt-alloyed by plasma heating.In general, the shape of the added element or its alloy is powder-like for heating and melting by plasma. In contrast to the general method of blowing into plasma, this method has an advantage that the method can be performed irrespective of the shape of an additive element or an alloy thereof.
[0026]
The surface layer modified composite steel slab obtained by the above method has the advantage of being a low-cost steel material having the characteristics of steel having different surface and internal properties.
Therefore, as for the processed product obtained by processing the above-described surface-modified composite steel slab, a low-cost product having the characteristics of steel having different surface and internal properties can be obtained. The processed product includes a steel plate such as a thin plate and a thick plate, a shaped steel, a steel pipe, and the like, and includes all steel products obtained by processing a slab by a normal steel process. Also, semi-finished products such as hot rolled coils are included.
[0027]
【Example】
(Example 1)
As shown in FIGS. 1 and 2, after cutting a slab that has been subjected to continuous casting, using a method of performing a melt reforming treatment using both induction heating and plasma heating, the width is 1500 mm, the thickness is 250 mm, and the length is 10 m. Of 20% of a continuous cast slab of 0.01% C-0.03% Si-0.24% Mn-0.01% P-0.01% S (unit: mass%) , An alloy of carbon, silicon, manganese, nickel and chromium is added, and 0.04% C-0.49% Si-1.01% Mn-0.01% P-0.01% S-18. A surface stainless steel slab of 1% Cr-8.5% Ni (mass basis) was used.
The obtained slab was subjected to cross-sectional analysis and found to have a variation in the depth direction of plus or minus 1 mm and a variation in elemental component within 5%. By processing this cast slab, a steel sheet for a thin plate having a stainless steel surface, that is, high corrosion resistance and aesthetic appearance, could be manufactured at low cost.
[0028]
(Example 2)
As shown in FIGS. 6 and 7, a slab that has been subjected to continuous casting is cut and then subjected to a melt reforming process by induction heating to obtain a 1500 mm wide, 250 mm thick, and 10 m long 0.001% C- The surface layer 20mm of the continuous cast slab of 0.11% Mn-0.01Si-0.007% P-0.009% S-0.045% Al-0.049% Ti (unit is mass%) is melted. Then, a carbon alloy was added using an alloy wire, and only the carbon component in the surface layer was adjusted to 0.03% by mass.
The obtained slab was subjected to a cross-sectional analysis, and found to have a variation in the depth direction of ± 1 mm and a variation in the element component within 3%. By processing this cast slab, it was possible to obtain a steel sheet for a thin sheet having excellent fatigue strength and good workability at the same time.
[0029]
【The invention's effect】
As described above, the use of the method for modifying a surface layer of the present invention makes it possible to produce a multilayer cast piece at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the method of the present invention (processing after slab cutting or at the end of a continuous casting machine).
FIG. 2 is a view showing a configuration of a method of the present invention, and is a detailed view of a treatment portion of a surface layer of a slab of FIG. 1;
FIG. 3 is an explanatory diagram of a principle of generation of an electromagnetic force by an induction coil.
FIG. 4 is a schematic sectional view showing another example (in-machine processing) of the configuration of the method of the present invention.
FIG. 5 is an explanatory view of the configuration (in-machine processing) of the method of the present invention and the balance of forces (details of the processing in FIG. 4).
FIG. 6 is a schematic cross-sectional view showing an example of the configuration of the method of the present invention using only electromagnetic induction (processing after slab cutting or at the end of a continuous casting machine).
FIG. 7 is a configuration of the method of the present invention using only electromagnetic induction (processing part detailed view of FIG. 6).
[Explanation of symbols]
1: Continuous casting machine 2: Plasma having a function of melting and adding elements 3: Electromagnetic induction coil 4: Support roll 5: Slab 6: Container for creating an inert gas atmosphere 7: Solidification part 8: Melted part 9: Unsolidified part 10: Continuous drawing or moving direction 11: Coil current 12: AC current 13: Time 14: Electric conductor 15: Magnetic field 16: Unmelted heating part 17: Part enriched with added element 18: Electromagnetic force Direction and strength 19: gravity (static iron pressure) direction and strength 20: wire to which element is added
Claims (6)
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JP2008284582A (en) * | 2007-05-17 | 2008-11-27 | Nippon Steel Corp | Surface layer treatment apparatus for cast slab and surface treatment method for cast slab |
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JP2009095879A (en) * | 2007-10-19 | 2009-05-07 | Nippon Steel Corp | Apparatus for surface melting treatment and starting method for surface melting treatment |
JP2009255140A (en) * | 2008-04-18 | 2009-11-05 | Nippon Steel Corp | Surface melting treatment apparatus of cast steel slab |
JP2010279992A (en) * | 2009-06-08 | 2010-12-16 | Nippon Steel Corp | Double layered steel sheet excellent in corrosion resistance, and method of manufacturing the same |
KR20180066175A (en) | 2015-10-30 | 2018-06-18 | 신닛테츠스미킨 카부시키카이샤 | Continuous casting equipment and continuous casting method of multi-layer casting |
US10987730B2 (en) | 2015-10-30 | 2021-04-27 | Nippon Steel Corporation | Continuous casting apparatus and continuous casting method for multilayered slab |
CN109576698A (en) * | 2018-10-31 | 2019-04-05 | 昆明理工大学 | A kind of method and device preparing composite material using region remelting |
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