JP4617564B2

JP4617564B2 - Continuous casting method for different steel types

Info

Publication number: JP4617564B2
Application number: JP2000357329A
Authority: JP
Inventors: 健二大島; 芳幸田中; 博己藤井
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2000-11-24
Filing date: 2000-11-24
Publication date: 2011-01-26
Anticipated expiration: 2020-11-24
Also published as: JP2002153949A

Description

【０００１】
【発明の属する技術分野】
本発明は、異鋼種の連続鋳造方法に関する。
【０００２】
【従来の技術】
第１溶鋼の連続鋳造より鋼種の異なる第２溶鋼の連続鋳造に変換する場合、従来、なんらの手段をも講ぜず通常の方法によって鋼種の異なる第２溶鋼を鋳型に連続して注入する場合には、両者の境界部において異鋼種の混入鋳片が形成され、いずれの鋼種にも用いることができずスクラップとして廃却せざるを得ない。この廃却する長さは４〜５ｍに達し、溶鋼歩留りを悪化させる。そこで、従来、例えば特開昭51−112431号公報、特開昭52−30723 号公報、特公昭57−36059 号公報などに開示されるように、第１溶鋼注入終了後に鋳型内に隔離材を装入し、しかる後に第２溶鋼を注入することにより、異鋼種混合長さの短縮が図られている。この方法によれば、例えば特公昭57−36059 号公報では、タンディッシュを交換し、新たに異鋼種注入を行う操作により異鋼種混合長さが約50cmにまで短縮される。
【０００３】
【発明が解決しようとする課題】
しかし、見方を変えると、前記従来の技術では、50cm程度と短くはあっても異鋼種混合長さ部分が必然的に発生してその部分が廃却されることになるので、溶鋼歩留り面において未だ改善の余地がある。また、連鋳操業において鋳型への溶鋼注入を中断して鋳型内に隔離材を装入する工程が加わるという憂いがある。
【０００４】
そこで、本発明は、鋳型内への隔離材装入を伴わずに溶鋼歩留りを改善しうる異鋼種の連続鋳造方法を提供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、後工程で熱間圧延してＨ形鋼と成す鋳片を異鋼種連続鋳造するにあたり、異鋼種間の組成差に、異鋼種連鋳鋳片の継目部を後工程で処理したときにその処理成品が製品として充当できるようになる組成差の上限として、予め、第１、第２溶鋼の混合部となる継目部の溶鋼組成の濃度、濃度分布を求め、１種または２種以上の成分を選んでその成分について、Ｈ形鋼の各成分ごとの閾値を設けておき、異鋼種連鋳時の鋼種切り換えに際して、相前後して鋳型に注入される互いに鋼種の異なる第１溶鋼と第２溶鋼の組成差が前記閾値を超えるときのみ第１、第２溶鋼間に隔離材を装入し継目部は切断して屑化し、前記組成差が前記閾値以下となった継目部は後工程で熱間圧延して製品化することを特徴とする異鋼種の連続鋳造方法である。
【０００６】
【発明の実施の形態】
従来では、互いに鋼種の異なる第１溶鋼と第２溶鋼を相前後して鋳型に注入する際にはいかなる場合でも第１、第２溶鋼間に隔離材を装入していた。すなわち、図１（ａ）に示すように、相前後して鋳型に注入される第１、第２溶鋼が異鋼種であるか否かの判定を行い、異鋼種でない場合は隔離材を装入せずに連続鋳造し、継目部（湯の継目を含む鋳片部分）は非継目部と同様に適当な長さに切断して後工程で処理して製品化する。一方、異鋼種である場合は隔離材を装入して連続鋳造し、継目部は例えば長さ50cm程度に切断して屑（スクラップ）化する。
【０００７】
これに対し、本発明では、異鋼種間の組成差に閾値を設け、相前後して鋳型に注入される互いに鋼種の異なる第１溶鋼と第２溶鋼の組成差が前記閾値を超えるときのみ第１、第２溶鋼間に隔離材を装入するようにした。すなわち、図１（ｂ）に示すように、第１、第２溶鋼が異鋼種であるか否かの判定後にさらに、両溶鋼の組成差が閾値超か否かの判定を行い、否（閾値以下）の場合は隔離材を装入せずに連続鋳造し、継目部は非継目部と同様に適当な長さに切断して後工程で処理して製品化する。一方、閾値超の場合は隔離材を装入して連続鋳造し、継目部は例えば長さ50cm程度に切断して屑化する。
【０００８】
前記閾値は、異鋼種連鋳鋳片の継目部を後工程で処理したときにその処理成品が製品として充当できるようになる組成差の上限として予備実験等により決定される。すなわち、溶鋼の組成（化学組成）をなす成分には、Ｃ、Si、Mn、Ｐ、Ｓ、Al、Cu、Ni、Mo、Ti、Ｖ、Nb、Ca、REM 等々があるが、前記予備実験等でこれらのうちから第１、第２溶鋼の混合部となる継目部の溶鋼組成の濃度、濃度分布を求め、１種または２種以上の成分を選んでその成分について閾値を決定する。異鋼種連鋳時の鋼種切り換えに際しては、これら成分毎に第１溶鋼と第２溶鋼との濃度差（含有量の差）を求めて閾値との大小判定を行う。そして、混合部を生じる継目部の長さ、範囲を予め第１溶鋼、第２溶鋼の組合せの中で求めておき、発生する継目部の切断範囲を定める。この鋼種混合部の推定は容易であり、連鋳鋳型またはタンディッシュへの次鋼種注入開始に伴い、連鋳鋳型直下から引抜かれてくる連鋳鋳片のトラッキングを行い、引抜き連鋳鋳片の鋼種混合部を特定すること、および、次鋼種注入開始点を特定し、その前後を挟んでドリルサンプリング等により連鋳鋳片の成分分析を行うことにより、混合範囲を決定することができる。
【０００９】
よって、本発明によれば、異鋼種連鋳で発生する継目部のうち、第１、第２溶鋼の組成差が前記閾値以下になるものについては、切断した継目部の連鋳鋳片を後工程に回して製品化することができるようになるので、鋳型内への隔離材装入を伴わずに屑化量を減少させる、すなわち溶鋼歩留りを改善することができる。また、第１、第２溶鋼の混合を積極的に許容できるため、タンディッシュ交換を行わずとも、前溶鋼の注入に引続き次溶鋼の注入を開始できるので、連続鋳造操業の支障にもならない。
【００１０】
なお、前記閾値は、継目部を処理する後工程の種類に依存するが、この後工程としては、連鋳鋳片を素材に常用する熱間圧延が好適である。したがって、本発明では、異鋼種連鋳により発生させた継目部を素材とする熱間圧延成品について、その特性（寸法および機械的性質）が製品としての要求を満たす前記異鋼種間の組成差の上限を予備実験等により調査し、その結果を閾値として採用するのが好ましい。その場合、組成差が閾値以下となった継目部が熱間圧延されて製品化される。なお、いうまでもないが、継目部からの圧延製品と非継目部からのそれとは、要求特性が互いに異なる製品であってもよい。したがって、継目部の熱間圧延条件（加熱温度、圧延温度、圧下率など）は非継目部と同じにする必要はない。
【００１１】
本発明では、継目部を処理する後工程としての熱間圧延は、厚板圧延、薄板圧延、条鋼圧延などのいずれであってもよいが、本発明者らの調査によると、厚板圧延および薄板圧延の場合は継目部の熱間圧延成品を充当しうる製品の種類数が、化学組成範囲が狭いから、比較的少ないのに対し、条鋼圧延の場合は該製品の種類数が比較的多く、なかでもＨ形圧延の場合は、化学組成は比較的ゆるやかで成分範囲が広く、適用できる種類（鋼種）が最も多い。このため、本発明では、継目部の熱間圧延成品はＨ形圧延成品（Ｈ形鋼）とするのが最も好ましい。
【００１２】
すなわち、前記閾値は、鋳片の継目部を素材とした熱間圧延成品の特性、なかでも特にＨ形圧延成品であるＨ形鋼の特性を基に決定するのが好ましい。
【００１３】
【実施例】
（比較例）
Ａ溶鋼とＢ溶鋼を用いて異鋼種連鋳を行うにあたり、従来は特公昭57−36059 号公報記載の方法に従い、Ａ溶鋼注入停止→Ａ溶鋼で使用していたタンディッシュを退避→冷材装入（凝固シェル形成）→予熱して待機させていたＢ溶鋼用タンディッシュへ交換→Ｂ溶鋼注入を行って、発生した長さ50cm程度の継目部は屑化し、スクラップとしていた。
【００１４】
（実施例）
表１に示す組成になるＡ溶鋼とＢ溶鋼を用いて異鋼種連鋳を実施した。Ａ溶鋼の成分は490MPa級のＡグレード鋼（靱性保証なし）、Ｂ溶鋼の成分は490MPa級のＢグレード鋼（靱性保証有）で、ＪＩＳG3106 製品規格（記号）はＡ溶鋼がSM490A、Ｂ溶鋼がSM490Bに該当する。
【００１５】
ＪＩＳG3106 によるSM490AとSM490Bの組成範囲は、厚さ50mm以下の場合、SM490AではＣ：0.20mass％以下、Si：0.55mass％以下、Mn：1.60mass％以下、Ｐ：0.035 mass％以下、Ｓ：0.035 mass％以下であり、一方、SM490BではＣ：0.18mass％以下でSi，Mn，Ｐ，ＳはSM490Aと同一範囲であることから、鋼種混合を生じても混合部を再利用可能と判定し、以下の方法で連鋳操業を行った。
【００１６】
【表１】

【００１７】
まず、Ａ溶鋼を鋳込み、該Ａ溶鋼の注入末期のタンディッシュ内溶鋼残量が深さ200mm に減少した段階で、次溶鋼であるＢ溶鋼の注入を、タンディッシュを換えることなく、すなわちＡ溶鋼で使用していた同一タンディッシュに対して開始し、連続鋳造を継続した。
混合部で生じる混合部成分は、SM490A、SM490Bの双方を満足するＣ：0.18mass％以下であり、Si，Mnも問題はないため、継目である該混合部の５ｍ範囲を切断して、該切断鋳片を前記規格SM490A該当のＨ形鋼とするＨ形鋼圧延の素材として利用し、スクラップを発生させることなく、また、冷材装入等で連鋳を中断させることなく、Ｈ形鋼製品を得ることができた。
【００１８】
【発明の効果】
本発明によれば、異鋼種連鋳操業において隔離材装入を伴わずに、また、タンディッシュの交換を伴わずに溶鋼歩留りを向上させることができるという優れた効果を奏する。
【図面の簡単な説明】
【図１】従来（ａ）と本発明（ｂ）の比較対照図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for continuous casting of different steel types.
[0002]
[Prior art]
When converting from the continuous casting of the first molten steel to the continuous casting of the second molten steel having a different steel type, conventionally, when the second molten steel having a different steel type is continuously injected into the mold by a normal method without any means. Is formed with a mixture of different steel types at the boundary between them and cannot be used for any steel type, and must be discarded as scrap. The length to be discarded reaches 4 to 5 m, which deteriorates the molten steel yield. Therefore, conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 51-112431, Japanese Patent Application Laid-Open No. 52-30723, Japanese Patent Publication No. 57-36059, etc. The mixing length of the different steel types is shortened by charging and then injecting the second molten steel. According to this method, for example, in Japanese Examined Patent Publication No. 57-36059, the mixed length of the different steel types is reduced to about 50 cm by exchanging the tundish and newly injecting the different steel types.
[0003]
[Problems to be solved by the invention]
However, from a different perspective, in the conventional technique, even if it is as short as about 50 cm, a mixed length part of different steel types will inevitably occur and that part will be discarded, so in terms of molten steel yield There is still room for improvement. In addition, there is a concern that in the continuous casting operation, the process of interrupting the molten steel injection into the mold and introducing a separator into the mold is added.
[0004]
Then, an object of this invention is to provide the continuous casting method of the different steel types which can improve a molten steel yield, without being accompanied by the isolating material insertion in a casting_mold | template.
[0005]
[Means for Solving the Problems]
In the present invention, when continuously casting a slab formed of H-shaped steel by hot rolling in a subsequent process, the joint of the different steel type continuous cast slab is processed in the subsequent process due to the difference in composition between different steel types. Sometimes, as the upper limit of the compositional difference that allows the processed product to be used as a product, the concentration and concentration distribution of the molten steel composition of the seam portion that becomes the mixing portion of the first and second molten steels are obtained in advance, one or two types The above-mentioned components are selected and threshold values are set for the respective components of the H-section steel, and the first molten steel of different steel types injected into the mold before and after the different steel types during continuous casting. And only when the composition difference between the second molten steel exceeds the threshold value, a separator is inserted between the first and second molten steels, the seam portion is cut and scrapped, and the seam portion where the composition difference is equal to or less than the threshold value is This is a continuous casting method for different steel types characterized by hot rolling in the subsequent process to produce a product. That.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Conventionally, when the first molten steel and the second molten steel, which are different from each other, are poured into the mold in succession, a separator is inserted between the first and second molten steels in any case. That is, as shown in FIG. 1 (a), it is determined whether or not the first and second molten steels to be injected into the mold before and after are different steel types. Without casting, the seam portion (the slab portion including the seam seam) is cut into an appropriate length in the same manner as the non-seam portion and processed in a subsequent process to produce a product. On the other hand, in the case of a different steel type, a separator is inserted and continuously cast, and the seam is cut into, for example, a length of about 50 cm to be scrap (scrap).
[0007]
On the other hand, in the present invention, a threshold value is set for the composition difference between different steel types, and only when the composition difference between the first molten steel and the second molten steel, which are injected into the mold before and after, exceeds the threshold value. A separator was inserted between the first and second molten steels. That is, as shown in FIG. 1 (b), after determining whether or not the first and second molten steels are different steel types, it is further determined whether or not the composition difference between both molten steels exceeds a threshold value. In the case of the following), continuous casting is carried out without charging the separator, and the seam portion is cut to an appropriate length in the same manner as the non-seam portion and processed in a subsequent process to produce a product. On the other hand, in the case of exceeding the threshold value, the separator is inserted and continuously cast, and the joint portion is cut into a length of, for example, about 50 cm to be scrapped.
[0008]
The threshold value is determined by a preliminary experiment or the like as the upper limit of the composition difference that allows the processed product to be used as a product when the joint portion of the different steel type continuous cast slab is processed in a subsequent process. That is, the components (chemical composition) of the molten steel include C, Si, Mn, P, S, Al, Cu, Ni, Mo, Ti, V, Nb, Ca, REM, etc. From these, the concentration and concentration distribution of the molten steel composition of the seam portion that becomes the mixed portion of the first and second molten steel are obtained, and one or more components are selected and the threshold value is determined for the component. When the steel types are switched during continuous casting of different steel types, the concentration difference (content difference) between the first molten steel and the second molten steel is obtained for each of these components, and the magnitude of the threshold value is determined. And the length and range of the seam part which produces a mixing part are previously calculated | required in the combination of 1st molten steel and 2nd molten steel, and the cutting | disconnection range of the generated seam part is defined. It is easy to estimate the steel grade mixing part, and with the start of injection of the next steel grade into the continuous casting mold or tundish, the continuous casting slab drawn from directly under the continuous casting mold is tracked, and the The mixing range can be determined by specifying the steel type mixing part, specifying the next steel type injection start point, and performing component analysis of the continuous cast slab by drill sampling or the like across the front and rear.
[0009]
Therefore, according to the present invention, among the joint portions generated in the continuous casting of different steel types, those in which the composition difference between the first and second molten steels is equal to or less than the threshold value, the continuous cast slab of the cut joint portion is moved back. Since it can be turned into a product in the process, the amount of scrapping can be reduced without introducing the separating material into the mold, that is, the molten steel yield can be improved. Further, since the mixing of the first and second molten steels can be positively allowed, the injection of the next molten steel can be started subsequent to the injection of the previous molten steel without performing the tundish exchange, so that the continuous casting operation is not hindered.
[0010]
In addition, although the said threshold value is dependent on the kind of post process which processes a seam part, as this post process, the hot rolling which uses a continuous casting slab as a raw material is suitable. Therefore, in the present invention, the composition difference between the different steel types satisfying the requirements as a product for the hot-rolled product using the joint portion generated by different steel type continuous casting as a raw material. It is preferable to investigate the upper limit by a preliminary experiment or the like and adopt the result as a threshold value. In that case, the seam where the composition difference is equal to or less than the threshold value is hot-rolled to produce a product. Needless to say, the rolled product from the joint and the product from the non-joint may be products having different required characteristics. Accordingly, the hot rolling conditions (heating temperature, rolling temperature, rolling reduction, etc.) of the seam portion need not be the same as those of the non-seam portion.
[0011]
In the present invention, the hot rolling as a post-process for treating the joint portion may be any of thick plate rolling, thin plate rolling, strip rolling, etc., but according to the inventors' investigation, In the case of sheet rolling, the number of types of products that can be used for hot rolling products at the seam is relatively small because the chemical composition range is narrow, whereas in the case of strip rolling, the number of types of products is relatively large. In particular, in the case of H-shaped rolling, the chemical composition is relatively gradual and the component range is wide, and there are the most applicable types (steel types). For this reason, in the present invention, it is most preferable that the hot rolled product at the joint is an H-shaped rolled product (H-shaped steel).
[0012]
That is, the threshold value is preferably determined on the basis of the characteristics of a hot-rolled product made from the seam of the slab, in particular, the characteristics of an H-section steel that is an H-shaped rolled product.
[0013]
【Example】
(Comparative example)
Prior to continuous casting of different steel types using molten steel A and molten steel B, in accordance with the method described in Japanese Patent Publication No. 57-36059, the injection of molten steel A is stopped → the tundish used in molten steel A is evacuated. Insertion (formation of solidified shell)-> Change to T-dish for B molten steel that had been preheated and waited-> B molten steel was injected, and the generated seam with a length of about 50 cm was scrapped and scrapped.
[0014]
(Example)
Different steel type continuous casting was carried out using molten steel A and molten steel B having the compositions shown in Table 1. The component of molten steel A is 490MPa class A grade steel (without toughness guarantee), the component of molten steel B is 490MPa class B grade steel (with toughness guaranteed), and JIS G3106 product standard (symbol) is SM490A for molten steel A, Applicable to SM490B.
[0015]
The composition range of SM490A and SM490B according to JIS G3106 is as follows: when the thickness is 50 mm or less, C: 0.20 mass% or less, Si: 0.55 mass% or less, Mn: 1.60 mass% or less, P: 0.035 mass% or less, S: 0.035 On the other hand, in SM490B, C: 0.18 mass% or less, and Si, Mn, P, and S are in the same range as SM490A. The continuous casting operation was performed by the following method.
[0016]
[Table 1]

[0017]
First, molten steel A is cast, and when the remaining amount of molten steel in the tundish at the end of injection of the molten steel A is reduced to a depth of 200 mm, the molten steel B, which is the next molten steel, is injected without changing the tundish, that is, Started with the same tundish used in, and continued casting.
The mixing part component generated in the mixing part is C: 0.18 mass% or less satisfying both SM490A and SM490B, and there is no problem with Si and Mn, so the 5m range of the mixing part which is a seam is cut, Using the cut slab as a raw material for H-section steel rolling, which is H-section steel corresponding to the standard SM490A, without generating scrap and without interrupting continuous casting due to cold material charging, etc. I was able to get the product.
[0018]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, there exists an outstanding effect that a molten steel yield can be improved, without the isolation | separation material charging in a different steel type continuous casting operation, and without exchanging a tundish.
[Brief description of the drawings]
FIG. 1 is a comparative view of the prior art (a) and the present invention (b).

Claims

When continuously casting a slab made of H-shaped steel by hot rolling in a subsequent process, the difference in composition between the different steel types is processed when the joint of the continuous cast slab is processed in the subsequent process. As an upper limit of the compositional difference that allows the product to be used as a product, the concentration and concentration distribution of the molten steel composition of the seam portion that becomes the mixing portion of the first and second molten steels are obtained in advance, and one or more components are added. For each of the selected components, a threshold value is set for each component of the H- section steel, and the first molten steel and the second molten steel, which are different from each other, are injected into the mold at the same time when the steel types are switched during continuous casting of different steel types. Only when the composition difference exceeds the threshold value, a separator is inserted between the first and second molten steels, the seam portion is cut and scrapped, and the seam portion where the composition difference becomes less than the threshold value is heated in a later step. A continuous casting method for different steel types, characterized in that it is rolled into a product .