JP2004017147A

JP2004017147A - Continuous casting method for assuring quenchability of structural steel

Info

Publication number: JP2004017147A
Application number: JP2002180313A
Authority: JP
Inventors: Yoshiyuki Uejima; 上島　良之; Toshiaki Mizoguchi; 溝口　利明; Masayuki Kodama; 児玉　正行; Takanori Ishii; 石井　孝宣
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-06-20
Filing date: 2002-06-20
Publication date: 2004-01-22

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method, which can reduce the distortion of products after final heat treatment at a low cost without increasing stock removal for final finish machining, which requires a high machining cost, and without introducing a circular section continuous casting machine, and without carrying out the heat treatment for adding tension, in which the shapes of products are limited. <P>SOLUTION: The continuous casting machine for steel has an electromagnetic agitating device within a mold. The distortion of the product after the final heat treatment is reduced by reducing negative segregation and variation of concentration in a skin part of the ingot by controlling the operating intensity of the electromagnetic agitating device. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、焼入性を保証した構造用鋼の連続鋳造方法に関するものである。
【０００２】
【従来の技術】
通常、連続鋳造により製造されたブルーム鋳片を一旦加熱炉で均熱後、断面寸法の小さいビレットに圧延、その後製品寸法に応じた棒鋼に熱間圧延する。その後、棒鋼を再度加熱あるいは直接熱間で圧延または鍛造して製品形状に加工したのち、焼入れ焼戻し等の熱処理を施して所望の強度、靭性に調整される。
【０００３】
一般に、熱処理時の焼入れ性は、棒鋼のサイズ、成分、冷却速度で決まること、表面に濃度の不均一いわゆる偏析があると焼入性が変ることが知られている（例えば、日本鉄鋼協会編、鋼の熱処理、改訂５版、１９７４年、ｐ．１５〜ｐ．２８）。従って、熱間圧延あるいは鍛造加工後に、熱処理して強度と靭性を付与したあと最後に最終製品の寸法精度に切削などで仕上加工する。しかし、熱処理後に歪みが許容範囲以上に大きくなると製品不良率が増えるし、不良率を減らすために最終の仕上加工時の切削しろを増やすと当然コストが増す。
【０００４】
そこで、熱処理後の歪みを低減するために、鋼中析出物例えばＡｌＮ　などを利用して焼入前のオーステナイト状態における結晶粒を微細均一化して、材料を均一に焼入する方法は良く知られている。さらに、鋳片段階で丸断面形状に鋳造する方法も一部で採用されている。しかし、通常の角断面形状の連鋳材よりも表面縦割れが発生しやすく、特別なモールドテーパー形状を施す方法（特開平８−１３２１８４）やモールド表面に特殊な加工を施す方法（特開平９−１０３８４６）などにより割れ対策を講じる必要があり、いずれも特別な装置が必要で広く普及していないのが現状である。また、最終製品にテンションを掛けた状態で焼入れ焼戻しする方法（例えば特開平８−９２６５７）も知られている。しかし、テンションを付加した熱処理法は製品が真直の棒鋼、線材などの形状に限られ、これも特別な設備が必要になる。従って、これらの手段のような高額の特別な設備投資が不要で製品形状に限定されずに、安価な方法による製品熱処理時の歪低減方法が望まれていた。
【０００５】
【発明が解決しようとする課題】
本発明は、上記のコストの掛かる最終仕上加工しろの増加、丸断面連鋳機の新設、製品へのテンション付加を行わず、安価に最終熱処理後の製品の歪み量を低減するための連続鋳造方法を提案するものである。
【０００６】
【課題を解決するための手段】
本発明者らは上記課題を解決するために種々検討を行った結果、鋳型内に電磁攪拌を有する鋼の連続鋳造機において、鋳型内の溶鋼流速を調整して鋳片表面から必要深さまでの濃度低下を抑制することで、コストの掛かる最終仕上加工しろの増加、丸断面連鋳機の新設や製品へのテンション付加を行わずに、最終熱処理後の製品の歪み量を低減することに成功し、本発明を完成するに至った。本発明の要旨は以下のとおりである。
【０００７】
（１）鋳型に電磁攪拌装置を有する鋼の連続鋳造機において、鋳片表面からの深さ５〜５０ｍｍの範囲におけるデンドライト傾角の平均値θを１０°から２３°の範囲に入るように鋳型電磁攪拌強度を制御することを特徴とする焼入性を保証した構造用鋼の連続鋳造方法。
（２）上記（１）において、鋳片表面からの深さ５〜５０ｍｍの範囲におけるデンドライト傾角の平均値θを１５°から２１°の範囲に入るように鋳型電磁攪拌強度を制御することを特徴とする焼入性を保証した構造用鋼の連続鋳造方法。
【０００８】
【発明の実施の形態】
棒鋼用の鋳片はブルームあるいはビレット連続鋳造機で製造される。通常、鋳型内の湯面の皮張りを防止し、かつ中心偏析を低減して高品質の鋳片を安定に鋳造するために、鋳型内に電磁攪拌装置を設置して溶鋼を水平あるいは垂直方向に攪拌する。本発明者らは、熱間鍛造品の歪みが、連鋳鋳型内の溶鋼の電磁攪拌によって生じる軽微な負偏析に起因することを突き止めた。すなわち、凝固シェルが溶鋼に洗浄されると凝固シェル内の元素濃度が低下すること自体は「洗浄効果」と呼ばれ良く知られている現象である（高橋忠義ら：鉄と鋼、第６１年、１９７５年、第９　号、ｐ．２１９８〜２２１３）。しかし、連続鋳造鋳片の鋳型内電磁攪拌で生じる表面の軽微な負偏析と、熱間鍛造後の熱処理によって生じる製品寸法精度の低下との間の因果関係が全く知られていなかった。鋭意検討を重ねた結果、鋳造操業安定性と中心偏析度に影響を与えない範囲で、製品に歪みを防止する最適な溶鋼攪拌流速範囲を見出した。これにより、コストの掛かる最終仕上加工しろの増加、丸断面連鋳機の新設やテンション付加を行わずに、安価に製品寸法精度の高い熱処理製品を製造することに成功した。
【０００９】
従来技術は、鋳片の表面濃度不均一を前提として、コストの掛かる最終仕上加工しろの増加、丸断面連鋳機の新設やテンション付加熱処理を行っていたのが実状である。本発明は、発生原因が鋳片表面濃度不均一であることを突き止めこれを改善するものである。
【００１０】
次に、本発明の構成要件である鋳型内電磁攪拌流速とデンドライト傾角の限定理由について説明する。
電磁攪拌流速を高めるとデンドライト傾角が流れの上流側に向かって傾斜することが良く知られているので（例えば、岡野忍、西村隆ら：鉄と鋼、第６１年（１９７５）第１４号、ｐ．２９８２〜２９９０）、デンドライト傾角を電磁攪拌流速の指標として用いることとする。凝固界面の溶鋼流速が増すと、凝固シェルの濃度が低下する上、乱流による流速変動巾も増すので凝固シェルの濃度変動も増してくる。デンドライト傾角が２３°とする（１）の上限を超えて凝固界面の溶鋼流速が増すと、鋳片表面の成分濃度低下と変動巾が増加して加工後の最終製品の焼入れ性、硬度バラツキが生じ、歪みが発生することを本発明者らが実際の連続鋳造試験で鋭意検討して明らかにした。なお、デンドライト傾角を２１°とする（２）の上限は最終製品の歪みを厳格管理することが可能となり、より好ましいものである。（１）の下限を１０°とする理由は、安定操業を阻害する鋳型湯面の皮張りの防止と、中心偏析度を許容範囲内にするための必要流速である。（２）の下限は、より長時間安定して操業することが可能になり、より好ましいものである。なお、鋳型内に電磁攪拌装置を有する連続鋳造機の鋳造模式図を図１に、製造した鋳片横断面凝固組織とデンドライト傾角の模式図を図２に示す。
【００１１】
〔実施例１〕
焼入性を保証した構造用鋼鋼材（ＪＩＳＧ４０５２）のＳＣｒ４１５Ｈ　材を断面寸法３７０ｍｍ　×４８０ｍｍ　のブルーム連鋳機で鋳造速度０．５ｍ／ｍｉｎで製造した。鋳型内電磁攪拌電流値は５０〜４１０Ａの範囲である。鋳片を熱間圧延して一旦４０ｍｍ径の丸棒に加工したのち、同一鋳造チャージ内で３〜５個所から熱間鍛造により２５ｍｍ径の丸棒試験片を作成した。製品の熱処理時の歪みの中間指標値を測定するために、ジョミニ式一端焼入れ試験（ＪＩＳＧ０５６１）を行った。ジョミニ試験片の水冷端から１２．７ｍｍ位置でロックウエル硬度を表裏２個所測定して同一チャージ中の最大硬度差△Ｈ_ＲＣを測定した。この△Ｈ_ＲＣと最終製品の歪みと１　対１　対応することは別途確認しているので、△Ｈ_ＲＣを最終製品の歪みのバラツキ指標として用いた。結果を表１に示す。電磁攪拌装置の印加電流を３２０Ａ以下にした本発明材は、デンドライト傾角θを２３°以下であり最大硬度差が減少して歪み判定検査に全数合格した（表１中の歪み判定指数ＡとＢ）。これは鋳片表層の成分濃度の変動が極めて微小にできたことで硬度が安定したものである。表１には、表層深さを鋳片４０ｍｍ深さでＣ濃度を溶鋼平均Ｃ濃度で割ったＣ偏析度を複数点採取して±２σでバラツキを表した。
なお、電磁攪拌装置の電流値を５０Ａ　に下げたところ、鋳型の湯面に皮張りが発生して安定操業ができなくなったので試験を中止した。
【００１２】
【表１】

【００１３】
註１）デンドライト傾角θの測定方法
鋳片Ｃ断面において、ピクリン酸を主成分とする腐食液で顕出した凝固組織プリントを使って巾中央部の５０ｍｍ巾を長辺、短辺４個所で、それぞれ鋳片表面から５、１０、２０、３０、４０、５０ｍｍ深さでデンドライト傾角を各深さごとに５本、４面全部で２０本、５つの深さ全部で１００　本測定して、その平均値をデンドライト傾角θとした。傾角は、鋳片巾中央部の表面の基準線に直角の線を傾角０度、この直角線とデンドライト主軸間の角度を傾角と定義した。本方法による傾角θの測定誤差は１度以下である。本発明では、水平方向の電磁攪拌装置を有する連続鋳造機で試験したので鋳片Ｃ断面で傾角を測定している。もし、垂直方向の電磁攪拌装置を有する場合は鋳片巾方向中央のＬ断面のデンドライト傾角を測定する。なお、デンドライト傾角測定の鋳片表面の基準線は巾中央部５０ｍｍ巾の内、半分以上を占める平坦面で決めた。
【００１４】
註２）Ｃ偏析度
鋳片Ｃ断面の巾中央部で表面からの深さ４０ｍｍ±１０ｍｍの位置で深さ方向に５ｍｍ間隔で５個所、４面合計で２０個所、コーナー部の深さ６０±１０ｍｍで５ｍｍ間隔の位置で５個所、４角合計で２０個所、全部で４０個所の測定点のＣ濃度の分析値の平均を溶鋼濃度で割ってＣ　偏析度を測定した。標準偏差σを使って±２σでＣ偏析度のバラツキを表している。
【００１５】
註３）歪み判定指数
Ａは厳格材において歪み不良発生なし、Ｂは一般材において歪み不良発生なし、Ｃは歪み不良一部発生、Ｄは歪み不良相当数発生したことを示す。
【００１６】
〔実施例２〕
焼入性を保証した構造用鋼鋼材（ＪＩＳＧ４０５２）のＳＣＭ４２０Ｈ　材を断面寸法３７０ｍｍ　×４８０ｍｍ　のブルーム連鋳機で鋳造速度Ｖｃ＝０．４５〜０．５５ｍ／ｍｉｎ　で製造した。鋳型内電磁攪拌電流値の水準は１８０　〜４５０Ａの範囲である。熱間圧延により２５ｍｍ径の丸棒に加工して、製品の熱処理時の歪みを測定するために、ジョミニ式一端焼入れ試験（ＪＩＳＧ０５６１）を行った。ジョミニ試験片の水冷端から１２．７ｍｍ位置のロックウエル硬度最大差△Ｈ_ＲＣを測定した。結果を表２に示す。鋳造速度を変えても、デンドライト傾角θが２３°以下になるように電磁攪拌装置の電流値を制御すると、ジョミニ試験片の最大硬度差が減少して歪み判定検査に合格した。
【００１７】
【表２】

【００１８】
【発明の効果】
以上に述べたように本発明により、鋳型に電磁攪拌を有する鋼の連続鋳造機において、鋳型内の電磁攪拌流速に上限値を設けて鋳片表面から必要深さまでの濃度低下を抑制することにより、コストの掛かる最終仕上加工しろの増加、丸断面連鋳機の新設やテンション付加を一切行わずに、最終熱処理後の製品の歪み量を低減することが可能となる。よって本発明は従来の問題点を一掃した焼入性を保証した構造用鋼の連続鋳造方法として産業の発展に寄与するところは極めて大である。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for continuously casting structural steel in which hardenability is guaranteed.
[0002]
[Prior art]
Normally, bloom cast slabs produced by continuous casting are once soaked in a heating furnace, then rolled into billets having a small cross-sectional dimension, and then hot-rolled into steel bars according to the product dimensions. After that, the steel bar is again heated or directly hot rolled or forged, processed into a product shape, and then subjected to a heat treatment such as quenching and tempering to adjust to a desired strength and toughness.
[0003]
In general, it is known that the hardenability during heat treatment is determined by the size, composition, and cooling rate of the steel bar, and that the hardenability changes when the surface has non-uniform concentration, so-called segregation (for example, edited by the Iron and Steel Institute of Japan). , Heat Treatment of Steel, 5th revised edition, 1974, pp. 15-28). Therefore, after hot rolling or forging, heat treatment is performed to impart strength and toughness, and finally, finishing is performed by cutting or the like to the dimensional accuracy of the final product. However, if the strain becomes larger than the allowable range after the heat treatment, the product defect rate increases, and if the cutting margin at the time of final finishing is increased to reduce the defect rate, the cost naturally increases.
[0004]
Therefore, in order to reduce the strain after the heat treatment, a method for uniformly quenching the material by making the crystal grains in the austenite state before quenching fine and uniform by using precipitates in steel, such as AlN, is well known. ing. Further, a method of casting into a round cross-section at the slab stage is also partially adopted. However, surface vertical cracks are more likely to occur than a continuous cast material having a regular square cross-section, and a method of applying a special mold taper shape (Japanese Patent Application Laid-Open No. 8-132184) or a method of performing special processing on the mold surface (Japanese Patent Application Laid-Open No. It is necessary to take countermeasures against cracking due to, for example, -103846), etc. All of them require special devices and are not widely used at present. There is also known a method of quenching and tempering a final product with tension applied thereto (for example, JP-A-8-92657). However, the heat treatment method with added tension is limited to products such as straight bars and wires, which also require special equipment. Therefore, there is a need for a method of reducing distortion during heat treatment of a product by an inexpensive method without requiring expensive special equipment investment such as these means and not being limited to a product shape.
[0005]
[Problems to be solved by the invention]
The present invention provides a continuous casting method for reducing the amount of distortion of a product after final heat treatment at a low cost without increasing the final finishing work margin which requires the above cost, newly installing a round section continuous caster, and adding tension to the product. It proposes a method.
[0006]
[Means for Solving the Problems]
The present inventors have conducted various studies to solve the above problems, and as a result, in a continuous casting machine for steel having electromagnetic stirring in the mold, the molten steel flow rate in the mold was adjusted to a required depth from the slab surface. Suppressing the decrease in concentration, successfully reducing the amount of distortion of the product after final heat treatment without increasing the cost of final finishing work, installing a round section continuous caster and adding tension to the product Thus, the present invention has been completed. The gist of the present invention is as follows.
[0007]
(1) In a continuous steel casting machine having an electromagnetic stirring device in the mold, the mold electromagnetic force is adjusted so that the average value θ of the dendrite inclination angle in the range of 5 to 50 mm depth from the slab surface falls within the range of 10 ° to 23 °. A continuous casting method for structural steel that guarantees hardenability, characterized by controlling stirring strength.
(2) In the above (1), the electromagnetic stirring strength of the mold is controlled so that the average value θ of the dendrite inclination angle in the range of 5 to 50 mm in depth from the slab surface falls within the range of 15 ° to 21 °. Continuous casting method for structural steel with guaranteed hardenability.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The slab for the steel bar is manufactured by a bloom or billet continuous casting machine. Normally, in order to prevent hot skin in the mold and reduce center segregation and stably cast high-quality slabs, an electromagnetic stirrer is installed in the mold to move molten steel horizontally or vertically. And stir. The present inventors have found that the distortion of a hot forged product is caused by slight negative segregation caused by electromagnetic stirring of molten steel in a continuous casting mold. In other words, the fact that the concentration of elements in the solidified shell decreases when the solidified shell is washed into molten steel is a well-known phenomenon called "cleaning effect" (Takayoshi Takahashi et al .: Iron and Steel, 61 , 1975, No. 9, pp. 2198-2213). However, a causal relationship between slight negative segregation of the surface caused by electromagnetic stirring in the mold of the continuous cast slab and reduction in product dimensional accuracy caused by heat treatment after hot forging was not known at all. As a result of intensive studies, we have found the optimal range of molten steel agitation flow rate to prevent distortion of products within the range that does not affect the stability of casting operation and the degree of center segregation. As a result, it has succeeded in producing a heat-treated product with high product dimensional accuracy at low cost without increasing the cost of final finishing work margin, installing a round section continuous caster or adding tension.
[0009]
In the prior art, on the premise that the surface concentration of the slab is non-uniform, the actual situation is that a costly increase in the final finishing work margin, a new round section continuous casting machine, and heat treatment with tension addition were performed. The present invention is to find out that the cause is uneven slab surface concentration, and to improve this.
[0010]
Next, the reasons for limiting the electromagnetic stirring flow rate in the mold and the dendrite inclination angle, which are constituent elements of the present invention, will be described.
It is well known that when the electromagnetic stirring flow rate is increased, the dendrite inclination angle inclines toward the upstream side of the flow (for example, Shino Okano, Takashi Nishimura et al .: Iron and Steel, 61 (1975) No. 14, pp. 2982-2990), the dendrite tilt angle is used as an index of the electromagnetic stirring flow rate. As the flow velocity of the molten steel at the solidification interface increases, the concentration of the solidification shell decreases, and the fluctuation speed of the flow velocity due to turbulence also increases, so that the concentration fluctuation of the solidification shell also increases. When the molten steel flow rate at the solidification interface increases beyond the upper limit of (1) where the dendrite inclination angle is 23 °, the component concentration on the slab surface decreases and the fluctuation range increases, and the hardenability and hardness variation of the final product after processing are reduced. The inventors of the present invention have intensively studied in an actual continuous casting test and found out that the deformation and the occurrence of distortion occur. Note that the upper limit of (2) in which the tilt angle of the dendrite is 21 ° is more preferable because the distortion of the final product can be strictly controlled. The reason why the lower limit of (1) is set to 10 ° is prevention of skinning of the mold surface which hinders stable operation, and the required flow rate for keeping the degree of center segregation within an allowable range. The lower limit of (2) allows more stable operation for a longer time, and is more preferable. FIG. 1 is a schematic diagram of a continuous casting machine having an electromagnetic stirring device in a mold, and FIG. 2 is a schematic diagram of a cross-sectional solidification structure and a dendrite inclination angle of a manufactured slab.
[0011]
[Example 1]
An SCr415H material of structural steel material (JIS G4052) whose hardenability was guaranteed was manufactured at a casting speed of 0.5 m / min by a bloom continuous caster having a cross-sectional dimension of 370 mm × 480 mm. The electromagnetic stirring current value in the mold is in the range of 50 to 410A. The cast slab was hot-rolled and once processed into a round bar having a diameter of 40 mm, and a round bar test piece having a diameter of 25 mm was prepared by hot forging from 3 to 5 locations within the same casting charge. In order to measure an intermediate index value of distortion during heat treatment of the product, a Jomini-type one-end quenching test (JISG0561) was performed. It was measured maximum hardness difference △ H _RC in the same charge from water cooling end of Jomini specimen front to back two positions measured Rockwell hardness 12.7mm position. Since it is separately confirmed that the △ H _RC and the final product of the strain and one-to-one correspondence, with △ H _RC as the dispersion index of the distortion of the final product. Table 1 shows the results. The material of the present invention in which the applied current of the electromagnetic stirrer was set to 320 A or less, the dendrite inclination angle θ was 23 ° or less, the maximum hardness difference decreased, and all passed the strain judgment inspection (the strain judgment indexes A and B in Table 1). ). This is because the fluctuation of the component concentration in the surface layer of the slab was extremely small and the hardness was stable. In Table 1, a plurality of points of C segregation obtained by dividing the surface layer depth by a slab 40 mm depth and the C concentration by the average C concentration of molten steel were sampled, and the variation was expressed by ± 2σ.
When the current value of the electromagnetic stirrer was lowered to 50 A, the test was stopped because skinning occurred on the mold surface and stable operation became impossible.
[0012]
[Table 1]

[0013]
Note 1) Measurement method of dendrite inclination angle θ In the cross section of cast slab C, a 50 mm width at the center of the width was measured using a solidification structure print exposed with a corrosive solution containing picric acid as the main component at the four long and short sides. The dendrite inclination was measured at 5, 10, 20, 30, 40, and 50 mm depths from the slab surface at each depth of 5, 5, 20 on all 4 surfaces, and 100 on all 5 depths. The average value was defined as the dendrite inclination angle θ. The inclination was defined as a line perpendicular to the reference line on the surface at the center of the slab width at an inclination of 0 °, and the angle between the perpendicular and the main axis of the dendrite was defined as the inclination. The measurement error of the inclination angle θ by this method is 1 degree or less. In the present invention, since the test was performed using a continuous casting machine having a horizontal electromagnetic stirrer, the inclination angle was measured in the section C of the slab. If the apparatus has a vertical electromagnetic stirrer, the dendrite inclination angle of the L section at the center in the slab width direction is measured. The reference line of the slab surface for the measurement of the inclination of the dendrite was determined by a flat surface occupying more than half of the width of 50 mm at the center of the width.
[0014]
Note 2) Degree of C segregation: 5 locations at 5 mm intervals in the depth direction at a depth of 40 mm ± 10 mm from the surface at the center of the width of the cross section of the slab C, 20 locations in total on 4 sides, and a depth of 60 ± 60 The C segregation degree was measured by dividing the average of the analytical values of the C concentration at the measurement points at 5 points at 10 mm intervals at 5 mm intervals and at 20 points in total, and 40 points in total, by the molten steel concentration. The deviation of the C segregation degree is represented by ± 2σ using the standard deviation σ.
[0015]
Note 3) Strain determination index A indicates no occurrence of distortion failure in strict materials, B indicates no occurrence of distortion failure in general materials, C indicates partial occurrence of distortion failure, and D indicates that a considerable number of distortion defects occurred.
[0016]
[Example 2]
SCM420H material of structural steel material (JIS G4052) whose hardenability was guaranteed was produced by a bloom continuous caster having a cross-sectional dimension of 370 mm × 480 mm at a casting speed Vc = 0.45 to 0.55 m / min. The level of the electromagnetic stirring current value in the mold is in the range of 180 to 450A. The product was processed into a round bar having a diameter of 25 mm by hot rolling, and a Jomini-type one-end quenching test (JISG0561) was performed in order to measure distortion during heat treatment of the product. It was measured Rockwell hardness maximum difference △ _{H RC} of 12.7mm position from the water-cooling end of Jomini specimen. Table 2 shows the results. Even when the casting speed was changed, when the current value of the electromagnetic stirrer was controlled such that the dendrite inclination angle θ was 23 ° or less, the maximum hardness difference of the Jomini test piece was reduced and the strain passed the strain determination test.
[0017]
[Table 2]

[0018]
【The invention's effect】
As described above, according to the present invention, in a steel continuous casting machine having electromagnetic stirring in the mold, by providing an upper limit value to the electromagnetic stirring flow rate in the mold to suppress the concentration decrease from the slab surface to the required depth In addition, it is possible to reduce the distortion amount of the product after the final heat treatment without increasing the cost of the final finishing work, newly installing a round section continuous caster or adding tension. Therefore, the present invention greatly contributes to the development of industry as a continuous casting method for structural steel that has eliminated hardening problems and has guaranteed hardenability.

Claims

In a continuous caster of steel having an electromagnetic stirring device in the mold, the electromagnetic stirring intensity of the mold is set so that the average value θ of the dendrite inclination angle in the range of 5 to 50 mm in depth from the slab surface falls within the range of 10 ° to 23 °. A continuous casting method for structural steel, which is characterized by controlling hardenability.

The quenching method according to claim 1, wherein the electromagnetic stirring strength of the mold is controlled so that the average value? Of the inclination angle of the dendrite in the range of 5 to 50 mm from the surface of the slab falls within the range of 15 to 21 degrees. Continuous casting method for structural steel with guaranteed performance.