JP2002066705A - Continuously cast slab, its casting method and manufacturing method of heavy plate therefrom - Google Patents
Continuously cast slab, its casting method and manufacturing method of heavy plate therefromInfo
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- JP2002066705A JP2002066705A JP2000249633A JP2000249633A JP2002066705A JP 2002066705 A JP2002066705 A JP 2002066705A JP 2000249633 A JP2000249633 A JP 2000249633A JP 2000249633 A JP2000249633 A JP 2000249633A JP 2002066705 A JP2002066705 A JP 2002066705A
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- slab
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、連続鋳造鋳片、そ
の鋳片の鋳造方法およびその鋳片を熱間で圧延すること
による耐水素誘起割れ性に優れた厚鋼板の製造方法に関
する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous cast slab, a method for casting the slab, and a method for producing a thick steel sheet having excellent resistance to hydrogen-induced cracking by hot rolling the slab.
【０００２】[0002]
【従来の技術】天然ガスおよび原油の採掘、精製、輸送
などに用いられるラインパイプなどは、連続鋳造鋳片を
熱間で圧延して得られる厚鋼板を素材として加工するこ
とにより製造されている。これらラインパイプなどの鋼
材では、水素誘起割れ（ＨＩＣ）によって油漏れなどの
事故が発生することが知られている。鋼材中の水素が、
非金属介在物（ＭｎＳ、クラスター状の酸化物、ＣａＳ
など）の周囲に集積し、水素ガスの圧力が高まるととも
に、非金属介在物の形状に基づく切欠き効果などによっ
て、非金属介在物を起点に水素誘起割れが発生する。そ
の際、Ｍｎ、Ｐなどが偏析する異常組織が存在している
と、その異常組織に沿って割れが伝播し、さらに大きな
割れが発生しやすい。2. Description of the Related Art Line pipes and the like used for mining, refining, and transporting natural gas and crude oil are manufactured by processing a thick steel plate obtained by hot rolling a continuous cast slab as a raw material. . It is known that hydrogen-induced cracking (HIC) causes accidents such as oil leakage in steel materials such as line pipes. Hydrogen in steel is
Non-metallic inclusions (MnS, cluster oxide, CaS
), The pressure of the hydrogen gas increases, and a hydrogen-induced crack originates from the nonmetallic inclusion due to a notch effect based on the shape of the nonmetallic inclusion. At this time, if there is an abnormal structure in which Mn, P, and the like are segregated, cracks propagate along the abnormal structure, and larger cracks are likely to occur.
【０００３】特開昭５４−３８２１４号公報には、Ｃ
ａ、ＲＥＭなどの添加によって、鋼材の水素誘起割れ感
受性を高める非金属介在物ＭｎＳの析出を抑制するとと
もに、ＭｎＳが球状となるように非金属介在物の形態を
制御する方法が提案されている。しかし、この方法で
は、Ｃａ、ＲＥＭなどの含有量の最適値が狭い範囲であ
るため、これらの添加量を適正に調整することが困難で
ある。これらＣａ、ＲＥＭなどの添加量が最適値より少
ないと、非金属介在物の形態制御の効果が発揮できず、
また添加量が多いと添加によって生成する硫化物、酸化
物などの量が多くなり、かえって鋼材の水素誘起割れ感
受性が高くなる。Japanese Patent Application Laid-Open No. 54-38214 discloses C
a, a method has been proposed in which the precipitation of non-metallic inclusions MnS, which enhances the hydrogen-induced cracking susceptibility of steel materials, is controlled by adding REM and the like, and the form of the non-metallic inclusions is controlled so that the MnS becomes spherical. . However, in this method, since the optimum values of the contents of Ca, REM, and the like are in a narrow range, it is difficult to appropriately adjust the amounts of these added. If the amount of addition of Ca, REM, etc. is less than the optimum value, the effect of controlling the form of nonmetallic inclusions cannot be exhibited,
Also, when the addition amount is large, the amount of sulfide, oxide and the like generated by the addition increases, and the susceptibility of the steel material to hydrogen-induced cracking increases.
【０００４】Ｍｎ、Ｐなどが偏析して発生する鋼材の異
常組織とは、連続鋳造鋳片に発生した中心偏析が、その
鋳片を熱間で圧延した鋼材にまで残存し、その部分の硬
度が高くなっている金属組織のことである。鋳片の中心
偏析は、凝固が進行する過程でデンドライト樹間に偏析
成分が濃化し、この濃化溶鋼が鋳片のバルジングなどに
より、デンドライト樹間より流出し、最終凝固部である
凝固完了点に向かって流動し、そのまま凝固して偏析成
分の濃化帯を形成するために発生する。[0004] The abnormal structure of a steel material caused by segregation of Mn, P and the like means that the central segregation generated in a continuously cast slab remains in a steel material obtained by hot rolling the slab, and the hardness of the portion Is a metal structure that has a high In the center segregation of the slab, segregation components are concentrated between dendrite trees in the process of solidification, and this concentrated molten steel flows out from between the dendrite trees due to bulging of the slab, and the solidification completion point which is the final solidification part , And flows to the solidified state to form a concentrated zone of segregated components.
【０００５】そこで、鋳片の中心偏析の防止対策とし
て、デンドライト樹間の偏析成分の濃化した溶鋼の移動
を防止し、また偏析成分の濃化した溶鋼の局所的な集積
を防ぐことが効果的であり、特開平９−５７４１０号公
報および特開平９−２０６９０３号公報には、未凝固部
を含む鋳片をバルジングさせ、最終凝固部の鋳造方向の
上流側で、バルジング量相当分を圧下する方法が提案さ
れている。しかし、これらの方法では、圧下する際の中
心固相率、圧下量などの圧下条件によっては、鋳造方向
の全長、鋳片の全幅にわたって中心偏析の発生を安定し
て抑制することが困難な場合がある。[0005] Therefore, as measures for preventing the center segregation of the slab, it is effective to prevent the movement of the molten steel in which the segregation component is concentrated between the dendrite trees and to prevent the local accumulation of the molten steel in which the segregation component is concentrated. Japanese Patent Application Laid-Open Nos. 9-57410 and 9-206903 disclose that a slab including an unsolidified portion is bulged, and a portion corresponding to the bulging amount is reduced upstream of the final solidified portion in the casting direction. A way to do that has been proposed. However, in these methods, depending on the rolling conditions such as the center solid phase ratio during rolling and the amount of rolling, it is difficult to stably suppress the occurrence of center segregation over the entire length in the casting direction and the entire width of the slab. There is.
【０００６】上記のような現状に鑑み、ラインパイプな
どの鋼材における水素誘起割れの発生を安定して抑制す
る連続鋳造鋳片およびその鋳片を得るための連続鋳造を
行う方法が望まれている。In view of the above situation, there is a demand for a continuously cast slab that stably suppresses the occurrence of hydrogen-induced cracking in steel materials such as line pipes, and a method of performing continuous casting to obtain the slab. .
【０００７】[0007]
【発明が解決しようとする課題】本発明は、ラインパイ
プなどの鋼材における水素誘起割れの発生を安定して抑
制できる鋼の連続鋳造鋳片、およびその鋳片を得るため
の連続鋳造方法を提供することを目的とし、さらに、こ
れらの鋳片を熱間で圧延することによる耐水素誘起割れ
性に優れた厚鋼板の製造方法を提供することを目的とす
る。SUMMARY OF THE INVENTION The present invention provides a continuous cast slab of steel capable of stably suppressing the occurrence of hydrogen-induced cracking in a steel material such as a line pipe, and a continuous cast method for obtaining the cast slab. Another object of the present invention is to provide a method for producing a thick steel plate having excellent resistance to hydrogen-induced cracking by hot rolling these slabs.
【０００８】[0008]
【課題を解決するための手段】本発明の要旨は、下記の
（１）に示す連続鋳造鋳片、（２）に示す連続鋳造方
法、および（３）に示す厚鋼板の製造方法にある。 （１）鋳片の最終凝固部を厚さ方向の中央部に含む厚さ
中心部１０ｍｍ以内の領域において、Ｓ含有率が１０ｐ
ｐｍ以下であり、かつＭｎ含有率が２．０質量％以上の
面積率が０．２％未満であるＣａを含有する鋼の連続鋳
造鋳片。 （２）未凝固部を含む鋳片をバルジングさせた後、厚さ
中心部が凝固完了するまでの間に１つ以上の圧下ロール
対により圧下する方法において、中心固相率が０．２〜
０．７の鋳片の位置で、下記（Ａ）式で表される圧下率
Ｌｆが０．９〜１．５を満足する条件で鋳片を圧下する
上記（１）に記載の連続鋳造鋳片の鋳造方法。The gist of the present invention resides in a continuous cast slab shown in (1), a continuous casting method shown in (2), and a method for manufacturing a thick steel plate shown in (3). (1) In a region within a central portion of the thickness of 10 mm including the final solidified portion of the slab in the central portion in the thickness direction, the S content is 10 p.
A continuous cast slab of steel containing Ca of not more than pm and an Mn content of 2.0% by mass or more and an area ratio of less than 0.2%. (2) In a method in which the slab including the unsolidified portion is bulged and then reduced by one or more reduction roll pairs until the thickness center portion is completely solidified, the central solid phase ratio is 0.2 to
The continuous cast casting according to the above (1), wherein the slab is reduced at a position of a slab of 0.7 under a condition that a reduction ratio Lf represented by the following formula (A) satisfies 0.9 to 1.5. Piece casting method.
【０００９】Ｌｆ＝Ｄ１／Ｄ２ ・・・（Ａ） ここで、Ｄ１：未凝固部を含む鋳片の幅中央部における
圧下量（ｍｍ） Ｄ２：圧下開始時の固相率０．８以下の未凝固部の厚さ
（ｍｍ） （３）上記（１）に記載の連続鋳造鋳片を熱間で圧延す
る厚鋼板の製造方法。Lf = D1 / D2 (A) where D1: The amount of reduction (mm) at the center of the width of the slab including the unsolidified portion. D2: The solid phase ratio at the start of the reduction is 0.8 or less. Thickness of unsolidified portion (mm) (3) A method for producing a thick steel plate by hot rolling the continuous cast slab according to (1).
【００１０】本発明が対象とする連続鋳造鋳片は、横断
面形状が長方形の鋳片である。また、本発明で規定する
「鋳片の最終凝固部を厚さ方向の中央部に含む厚さ中心
部１０ｍｍ以内の領域」とは、次に示す鋳片の領域を意
味する。図１は、鋳片の横断面を示す模式図である。長
方形の鋳片２の最終凝固部Ｔｃは、厚さのほぼ１／２の
位置に相当するほぼ直線状の部分である。「鋳片の最終
凝固部を厚さ方向の中央部に含む厚さ中心部１０ｍｍ以
内の領域」とは、ほぼ直線状の最終凝固部Ｔｃの、図面
上で言えば、上側の５ｍｍの位置の直線Ｔ1 と下側の５
ｍｍの位置の直線Ｔ2 との間の鋳片の領域（図中に斜線
部で示す領域）のことである。長方形の鋳片の幅方向の
両側端部から、それぞれ１／２×Ｔ0 （Ｔ 0 は、鋳片厚
さを意味する）の距離までの間は、凝固の進行が速く、
最終凝固部とはならない。なお、図１では、Ｔ1 または
Ｔ2 とＴｃとの間隔は誇張して示している。[0010] The continuous cast slab to which the present invention is directed is a cross section.
The surface shape is a rectangular slab. Also, as defined in the present invention
"The thickness center including the final solidified part of the slab at the center in the thickness direction
"Area within 10 mm" means the following slab area.
To taste. FIG. 1 is a schematic view showing a cross section of a slab. Long
The final solidified portion Tc of the square slab 2 is approximately の of the thickness.
This is a substantially linear portion corresponding to the position. "The end of the slab
Thickness center 10mm or less including solidified part at center in thickness direction
The region in the figure is the drawing of the substantially solid final solidified portion Tc.
Speaking above, the straight line T at the upper 5 mm position1 And the lower 5
mm in a straight line TTwo The area of the slab between
(Area indicated by a part). In the width direction of the rectangular slab
1/2 × T from both ends0 (T 0 Is the slab thickness
Up to the distance), the coagulation progresses rapidly,
It does not become the final solidification part. In FIG. 1, T1 Or
TTwo The interval between Tc and Tc is exaggerated.
【００１１】鋳片の最終凝固部を厚さ方向の中央部に含
む厚さ中心部１０ｍｍ以内の領域において、Ｓ含有率が
１０ｐｐｍ以下とは、次のことを意味する。すなわち、
鋳片の横断面の上述の両端部近傍以外で、最終凝固部を
厚さ方向の中央部に含む厚さ中心部１０ｍｍ以内の領域
のいずれの位置でも、たとえば、直径３〜５ｍｍのドリ
ル刃により切り削を採取し、通常の高周波燃焼−赤外線
吸収法などにより分析したＳの値が１０ｐｐｍ以下であ
ることを意味する。The S content of 10 ppm or less in a region within a thickness center portion of 10 mm or less including the final solidified portion of the slab in the center portion in the thickness direction means the following. That is,
Except for the above-mentioned vicinity of both ends of the cross section of the slab, at any position within a thickness center portion of 10 mm or less including the final solidified portion in the center in the thickness direction, for example, with a drill blade having a diameter of 3 to 5 mm. It means that the value of S obtained by cutting out and analyzing by a normal high frequency combustion-infrared absorption method or the like is 10 ppm or less.
【００１２】また、鋳片の最終凝固部を厚さ方向の中央
部に含む厚さ中心部１０ｍｍ以内の領域において、Ｍｎ
含有率が２．０質量％以上の面積率が０．２％未満と
は、次のことを意味する。すなわち、鋳片の横断面の上
述の両端部近傍以外で、最終凝固部を厚さ方向の中央部
に含む厚さ中心部１０ｍｍ以内の領域のいずれの位置で
も、鋳片の幅方向にＷｍｍの範囲を、たとえば、５０μ
ｍビームサイズのＸ線マイクロアナライザを用いてＭｎ
含有率を測定する際に、Ｍｎ含有率が２．０質量％以上
となる測定点の数が、全測定点数の０．２％未満である
ことを意味する。たとえば、Ｗ＝２０ｍｍの場合には、
鋳片厚さ方向の測定点は２００点、幅方向の測定点は４
００点であり、全測定点は２００×４００＝８００００
点となる。Ｍｎ含有率が２．０質量％以上となる測定点
の数が、全測定点の０．２％未満、すなわち１６０点未
満であることを意味する。Further, in a region within a thickness center portion of 10 mm or less including a final solidified portion of the slab at a center portion in a thickness direction, Mn is
An area ratio of 2.0% by mass or more and less than 0.2% means the following. That is, except for the vicinity of both ends described above of the cross section of the slab, at any position within the thickness center portion 10 mm including the final solidified portion in the center in the thickness direction, Wmm in the width direction of the slab. Range, for example, 50μ
Mn using an X-ray microanalyzer with m beam size
When measuring the content, it means that the number of measurement points at which the Mn content is 2.0% by mass or more is less than 0.2% of the total number of measurement points. For example, when W = 20 mm,
200 measurement points in the slab thickness direction, 4 measurement points in the width direction
00 points, all measurement points are 200 × 400 = 80,000
Points. It means that the number of measurement points where the Mn content is 2.0% by mass or more is less than 0.2% of all the measurement points, that is, less than 160 points.
【００１３】図２は、厚鋼板の水素誘起割れ面積率に及
ぼす鋳片の厚さ中心部近傍１０ｍｍ以内の領域における
ＳおよびＭｎの含有率の影響を示す図である。以下の内
容の試験を行った結果を示す図である。FIG. 2 is a diagram showing the effect of the S and Mn contents in a region within 10 mm near the center of the thickness of the slab on the hydrogen-induced cracking area ratio of a thick steel plate. It is a figure which shows the result of having performed the test of the following contents.
【００１４】すなわち、鋳片の最終凝固部を厚さ方向の
中央部に含む厚さ中心部１０ｍｍ以内におけるＳ含有率
およびＭｎ含有率２．０質量％以上の面積率が、それぞ
れ種々の値を有する厚さ２３０ｍｍの鋳片サンプルを実
機の連続鋳造機で鋳造して準備し、これら鋳片サンプル
を実験室規模の圧延装置を用いて熱間で厚さ１９ｍｍの
鋼板に圧延した。得られた鋼板から試験片を採取し、５
質量％ＮａＣｌおよび０．５質量％ＣＨ3 ＣＯＯＨを含
む飽和Ｈ2 ＳのＮＡＣＥ腐食液（ｐＨ：約３．０）中に
９６時間浸漬し、水素誘起割れの発生状況を調査した結
果を示す。図中に示す水素誘起割れ面積率（％）とは、
超音波探傷（探傷子；ポイントフォーカス型、５０ＭＨ
ｚ）により割れ発生と判定される部分の面積を超音波探
傷した鋼板の試験片の全表面積で除した割合のことであ
る。That is, the S content and the Mn content within an area of 10 mm or less including the final solidified portion of the slab at the center in the thickness direction have an area ratio of 2.0% by mass or more, respectively. The cast slab samples having a thickness of 230 mm were prepared by casting using a continuous caster of an actual machine, and these cast slab samples were hot-rolled into a 19-mm-thick steel plate using a laboratory-scale rolling device. A test piece was collected from the obtained steel sheet, and 5
The results of investigating the state of occurrence of hydrogen-induced cracking by immersing for 96 hours in a NACE corrosion solution (pH: about 3.0) of saturated H 2 S containing mass% NaCl and 0.5 mass% CH 3 COOH are shown. The hydrogen-induced cracking area ratio (%) shown in the figure is
Ultrasonic flaw detection (flaw detector; point focus type, 50 MH
This is a ratio obtained by dividing the area of a portion determined to be cracked by z) by the total surface area of a test piece of a steel plate subjected to ultrasonic flaw detection.
【００１５】図２から、つぎのことがわかる。つまり、
Ｃａを含有させて、非金属介在物ＭｎＳの析出を抑制す
るとともに、ＭｎＳを球状化させても、鋳片の最終凝固
部を厚さ方向の中央部に含む厚さ中心部１０ｍｍ以内の
領域におけるＳ含有率が１０ｐｐｍを超えると、これら
の領域におけるＭｎ含有率が２．０質量％以上の面積率
が零でも、水素誘起割れが発生する。The following can be seen from FIG. That is,
Ca is contained to suppress the precipitation of the nonmetallic inclusions MnS, and even when the MnS is spheroidized, even in a region within a thickness central portion of 10 mm or less including the final solidified portion of the slab in the central portion in the thickness direction. If the S content exceeds 10 ppm, hydrogen-induced cracking occurs even if the Mn content in these regions is 2.0 mass% or more and the area ratio is zero.
【００１６】また、鋳片の最終凝固部を厚さ方向の中央
部に含む厚さ中心部１０ｍｍ以内の領域におけるＳ含有
率を１０ｐｐｍ以下にしても、Ｃａを含有させないと、
これらの領域におけるＭｎ含有率が２．０質量％以上の
面積率が０．２％未満でも、水素誘起割れが発生する。Further, even if the S content in a region within a thickness central portion of 10 mm or less including the final solidified portion of the slab at the center in the thickness direction is 10 ppm or less, if Ca is not contained,
Even if the Mn content in these regions is less than 0.2% when the Mn content is 2.0% by mass or more, hydrogen-induced cracking occurs.
【００１７】さらに、鋳片の最終凝固部を厚さ方向の中
央部に含む厚さ中心部１０ｍｍ以内の領域におけるＳ含
有率を１０ｐｐｍ以下にし、Ｃａを含有させ、これらの
領域におけるＭｎ含有率が２．０質量％以上の面積率を
０．２％未満とすると、水素誘起割れの発生を抑制でき
る。これらの領域に存在する非金属介在物ＭｎＳの析出
量が少なく、かつ存在するＭｎＳの形状が安定して球状
となっているので、これらの領域の硬度は均一になる。
そのため、鋼材の水素誘起割れの発生を抑制できるので
ある。Further, the S content in a region within a thickness center portion of 10 mm or less including the final solidified portion of the slab in the center in the thickness direction is set to 10 ppm or less, Ca is contained, and the Mn content in these regions is reduced. When the area ratio of 2.0% by mass or more is less than 0.2%, the occurrence of hydrogen-induced cracking can be suppressed. Since the amount of nonmetallic inclusions MnS existing in these regions is small and the shape of the existing MnS is stable and spherical, the hardness of these regions becomes uniform.
Therefore, the occurrence of hydrogen-induced cracking of the steel material can be suppressed.
【００１８】本発明の連続鋳造方法では、未凝固部を含
む鋳片をバルジングさせた後に、厚さ中心部が凝固完了
するまでの間に鋳片を圧下するので、鋳片の厚さ中心部
近傍を効果的に圧下できる。In the continuous casting method of the present invention, after the slab including the unsolidified portion is bulged, the slab is lowered until the thickness center portion is completely solidified. The vicinity can be effectively reduced.
【００１９】さらに、中心固相率が０．２〜０．７の鋳
片の位置で、前述の（Ａ）式で表される圧下率Ｌｆが
０．９〜１．５を満足する条件で鋳片を圧下するので、
圧下効果が鋳片の厚さ中心部にまで効果的に及び、最終
凝固部近傍に存在する偏析成分の濃化した溶鋼を鋳造方
向の上流側に速い速度で排出することができる。そのた
め、圧下により圧着される鋳片の厚さ方向の両側の凝固
界面に偏析成分の濃化した溶鋼が捕捉されることがない
ので、ＳおよびＭｎの含有率の低い領域が鋳造方向の全
長、鋳片の全幅にわたって、安定して生成する。Further, at the position of the slab having the center solid phase ratio of 0.2 to 0.7, under the condition that the rolling reduction Lf represented by the above-mentioned formula (A) satisfies 0.9 to 1.5. Since the slab is reduced,
The rolling effect is effectively extended to the center of the thickness of the cast slab, and the molten steel having a segregated component concentrated near the final solidified portion can be discharged at a high speed to the upstream side in the casting direction. Therefore, since the molten steel in which the segregation component is concentrated is not captured at the solidification interface on both sides in the thickness direction of the slab to be pressed by pressing, the region where the content of S and Mn is low is the entire length in the casting direction, Produces stably over the entire width of the slab.
【００２０】前述の（Ａ）式において、圧下開始時の鋳
片の未凝固部の厚さＤ２を、鋳片内部の厚さ方向の両側
の固相率０．８の凝固界面の間の厚さとする理由は、こ
のような固相率が０．８以下の厚さの領域では、圧下力
が伝達しないからであり、この領域を未凝固部とする。
この固相率０．８の凝固界面は、鋳片サイズ、溶鋼過熱
度、鋳造速度、二次冷却比水量などが決まれば、通常用
いられている凝固伝熱解析方法を用いて計算できる。In the above formula (A), the thickness D2 of the unsolidified portion of the slab at the start of the reduction is defined as the thickness between the solidification interfaces with a solid fraction of 0.8 on both sides in the thickness direction inside the slab. The reason is that the rolling force is not transmitted in such a region where the solid phase ratio is 0.8 or less, and this region is defined as an unsolidified portion.
The solidification interface having a solid phase ratio of 0.8 can be calculated using a commonly used solidification heat transfer analysis method if the slab size, molten steel superheat, casting speed, secondary cooling specific water amount, and the like are determined.
【００２１】さらに、本発明の厚鋼板の製造方法では、
前述の鋼の連続鋳造鋳片を用いて熱間圧延する。Further, in the method for manufacturing a thick steel plate according to the present invention,
Hot rolling is performed using the continuous cast slab of the steel described above.
【００２２】[0022]
【発明の実施の形態】本発明では、質量％で、Ｍｎ含有
率が１．０〜２．５％、Ｓ含有率が０．０００１〜０．
００６０％である炭素鋼および低合金鋼を対象とするの
に好適である。この程度のＭｎおよびＳを含有する炭素
鋼および低合金鋼では、連続鋳造鋳片に中心偏析が発生
しやすく、その鋳片を素材とする厚鋼板などに、水素誘
起割れが発生しやすいからである。BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the Mn content is 1.0 to 2.5% and the S content is 0.0001 to 0.
It is suitable for targeting carbon steel and low alloy steel of 0060%. In carbon steel and low alloy steel containing Mn and S of this degree, center segregation is apt to occur in a continuous cast slab, and hydrogen-induced cracking is likely to occur in a thick steel plate or the like using the slab as a material. is there.
【００２３】さらに、本発明ではＣａを含有する鋼を対
象とする。鋼のＣａ含有率は、質量％で１０〜５０ｐｐ
ｍとするのが望ましい。１０ｐｐｍ未満では、Ｃａを添
加することによる非金属介在物ＭｎＳの形態制御の効果
が発揮されにくく、また５０ｐｐｍを超えると、Ｃａ添
加によって生成した硫化物、酸化物などが多くなりす
ぎ、かえって水素誘起割れ感受性が高くなる。Further, the present invention is directed to a steel containing Ca. The Ca content of the steel is 10 to 50 pp in mass%.
m is desirable. If it is less than 10 ppm, the effect of controlling the form of the nonmetallic inclusion MnS by adding Ca is difficult to exert, and if it exceeds 50 ppm, sulfides and oxides generated by the addition of Ca become too large, and on the contrary hydrogen-induced The crack sensitivity increases.
【００２４】本発明の連続鋳造鋳片は、鋳片の最終凝固
部を厚さ方向の中央部に含む厚さ中心部１０ｍｍ以内の
領域において、Ｓ含有率が１０ｐｐｍ以下であり、か
つ、Ｍｎ含有率が２．０質量％以上の面積率が０．２％
未満である鋳片とする。In the continuous cast slab of the present invention, the S content is 10 ppm or less and the Mn content is 10 ppm or less in a region within a thickness center portion of 10 mm including a final solidified portion of the slab in a center portion in a thickness direction. Area ratio of 2.0% by mass or more is 0.2%
Less than the slab.
【００２５】鋳片の最終凝固部を厚さ方向の中央部に含
む厚さ中心部１０ｍｍ以内の領域とするのは、鋼材の水
素誘起割れの発生の起点が多い領域に相当する鋳片の領
域であるからである。The region within the center of the thickness of 10 mm or less including the final solidified portion of the slab in the center in the thickness direction is defined as the region of the slab corresponding to the region where the starting point of hydrogen-induced cracking of the steel material is large. Because it is.
【００２６】また、Ｍｎ含有率が２．０質量％以上の面
積率を規定するのは、Ｍｎ含有率が２．０質量％以上に
なると、その鋼材の硬度が３３０Ｈｖに達し、水素誘起
割れが発生しやすくなるからである。その際、Ｍｎ含有
率の上限は、とくに限定しない。ただし、本発明が対象
とする鋼が、前述のとおり、Ｍｎ含有率が１．０〜２．
５質量％の炭素鋼または低合金鋼であるので、たとえ
ば、前述の５０μｍビームサイズのＸ線マイクロアナラ
イザを用いて分析する際、Ｍｎ含有率が３．８質量％程
度となる場合がある。いずれにせよ、Ｍｎ含有率が２．
０質量％以上である面積率を求めるものとする。The reason why the area ratio when the Mn content is 2.0% by mass or more is that when the Mn content becomes 2.0% by mass or more, the hardness of the steel material reaches 330 Hv, and hydrogen-induced cracking occurs. This is because it easily occurs. At that time, the upper limit of the Mn content is not particularly limited. However, the steel targeted by the present invention has a Mn content of 1.0 to 2.
Since it is 5 mass% of carbon steel or low alloy steel, for example, when analyzed using the above-mentioned X-ray microanalyzer having a beam size of 50 μm, the Mn content may be about 3.8 mass%. In any case, the Mn content is 2.
An area ratio of 0% by mass or more is determined.
【００２７】さらに、上述の鋳片の領域におけるＳ含有
率およびＭｎ含有率が２．０質量％以上の面積率をそれ
ぞれ上限を規定する理由は、これらの鋳片の領域に存在
する非金属介在物ＭｎＳの析出量が少なくなるからであ
る。Ｃａを含有させることによるＭｎＳの形態制御の効
果も合わさって、これらの鋳片の領域の硬度は均一にな
り、鋼材の水素誘起割れの発生を抑制できる。Further, the reason why the upper limit is set for the area ratios of the S content and the Mn content of 2.0% by mass or more in the above-described slab regions is that the non-metallic intervening existing in these slab regions. This is because the precipitation amount of the substance MnS decreases. The effect of controlling the morphology of MnS by containing Ca is also combined, so that the hardness of these cast slab regions becomes uniform, and the occurrence of hydrogen-induced cracking of the steel material can be suppressed.
【００２８】鋳片の最終凝固部を厚さ方向の中央部に含
む厚さ中心部１０ｍｍ以内の領域から、たとえば直径３
ｍｍ〜５ｍｍのドリル刃により切り削を採取してＳ含有
率を分析するに際し、鋳片幅中央部および幅の１／４部
の少なくとも２カ所から切り削を採取するのが好まし
い。また、Ｍｎ含有率を、たとえば、５０μｍビームサ
イズのＸ線マイクロアナライザを用いて分析するに際
し、鋳片幅中央部および幅の１／４部の少なくとも２カ
所において、鋳片の幅方向にＷ＝２０ｍｍ程度の領域を
測定するのが好ましい。図３は、本発明の連続鋳造方法
を実施するための連続鋳造機の例を示す模式図である。
浸漬ノズル４を経て鋳型１内に注入された溶鋼３は、鋳
型で冷却されて凝固する。形成された凝固殻２ａは、鋳
型の下方のノズル群（図示していない）から噴射される
冷却水により冷却され、その厚さが増していく。内部に
未凝固部２ｂを含む鋳片２は、ガイドロール５により支
持、案内されながら、ピンチロール７により引き抜かれ
る。その際、未凝固部を含む鋳片を、ガイドロールの鋳
片厚さ方向の間隔を拡げることにより、バルジングゾー
ン８内でバルジングさせる。さらに、バルジングさせた
鋳片を、厚さ中心部が凝固完了するまでの間の圧下ゾー
ン９で、圧下ロール対６を用いて圧下する。図３では、
２つの圧下ロール対を用いて鋳片を圧下する例を示す。
本発明の連続鋳造方法では、未凝固部を含む鋳片をバル
ジングさせた後、厚さ中心部が凝固完了するまでの間
の、中心固相率が０．２〜０．７の鋳片の位置で、１つ
以上の圧下ロール対を用いて鋳片を圧下する。From a region within a central portion of 10 mm in thickness including a final solidified portion of the slab at a central portion in a thickness direction, for example, a diameter of 3 mm
In analyzing the S content by extracting a cut with a drill blade having a diameter of 5 mm to 5 mm, it is preferable to collect a cut from at least two places, that is, the center of the slab width and 1/4 of the width. Further, when analyzing the Mn content using, for example, an X-ray microanalyzer having a beam size of 50 μm, at least two locations, ie, the central part of the slab width and １ ／ part of the width, W = W in the width direction of the slab. It is preferable to measure an area of about 20 mm. FIG. 3 is a schematic view showing an example of a continuous casting machine for performing the continuous casting method of the present invention.
The molten steel 3 injected into the mold 1 through the immersion nozzle 4 is cooled by the mold and solidified. The formed solidified shell 2a is cooled by cooling water injected from a group of nozzles (not shown) below the mold, and its thickness increases. The slab 2 including the unsolidified portion 2 b therein is pulled out by the pinch roll 7 while being supported and guided by the guide roll 5. At this time, the slab including the unsolidified portion is bulged in the bulging zone 8 by increasing the interval between the guide rolls in the slab thickness direction. Further, the bulged slab is reduced using the pair of reduction rolls 6 in the reduction zone 9 until the thickness center portion is completely solidified. In FIG.
The example which reduces a cast slab using two reduction roll pairs is shown.
In the continuous casting method of the present invention, after bulging the slab including the unsolidified portion, until the thickness center portion is completely solidified, the center solid phase ratio of the slab of 0.2 to 0.7 At the location, the slab is reduced using one or more reduction roll pairs.
【００２９】未凝固部を含む鋳片をバルジングさせた後
に鋳片を圧下するので、鋳片の厚さ中心部近傍を効果的
に圧下できる。中心固相率が０．２未満では、圧下時期
が早すぎて、未凝固部の厚さが厚く、圧下率Ｌｆを０．
９以上とするためには圧下量を過大に大きくする必要が
あり、実際にはこのような大きな圧下量を確保すること
は困難である。また、中心固相率が０．７を超えると、
圧下時期が遅すぎるため未凝固部の溶鋼の流動性が悪い
ので、偏析成分の濃化した溶鋼を鋳造方向の上流側に完
全に排出できず、局所的に偏析成分の濃化した溶鋼が残
存する。Since the slab is reduced after bulging the slab including the unsolidified portion, the vicinity of the center of the thickness of the slab can be reduced effectively. When the central solid phase ratio is less than 0.2, the rolling period is too early, the thickness of the unsolidified portion is large, and the rolling ratio Lf is set to 0.1.
In order to make it 9 or more, it is necessary to make the rolling reduction excessively large, and it is actually difficult to secure such a large rolling reduction. Also, when the center solid fraction exceeds 0.7,
Because the rolling time is too late, the fluidity of the molten steel in the unsolidified part is poor, so the molten steel with concentrated segregation components cannot be completely discharged upstream in the casting direction, and the molten steel with locally concentrated segregation components remains. I do.
【００３０】本発明の連続鋳造方法では、前述の（Ａ）
式で表される圧下率Ｌｆが０．９〜１．５を満足する条
件で鋳片を圧下する。In the continuous casting method of the present invention, the aforementioned (A)
The slab is reduced under the condition that the reduction ratio Lf represented by the formula satisfies 0.9 to 1.5.
【００３１】圧下率Ｌｆが０．９未満では、圧下量が小
さいので、偏析成分の濃化した溶鋼が鋳造方向の上流側
に排出される量が少なくなったり、その排出速度が遅く
なる。したがって、偏析成分の濃化した溶鋼が鋳片の厚
さ中心部近傍に取り残されやすい。圧下率Ｌｆが１．５
を超えると、圧下量が過大に大きくなり、実際にはこの
ような大きな圧下量を確保することは困難である。If the rolling reduction Lf is less than 0.9, the rolling reduction is small, so that the amount of molten steel in which the segregated component is concentrated is discharged to the upstream side in the casting direction, or the discharging speed is reduced. Therefore, the molten steel in which the segregation component is concentrated is likely to be left near the center of the thickness of the slab. Reduction ratio Lf is 1.5
When it exceeds, the reduction amount becomes excessively large, and it is actually difficult to secure such a large reduction amount.
【００３２】さらに、圧下量はバルジング量の５０％以
上とするのが望ましい。５０％以上の場合に、鋳片の厚
さ中心部近傍をより効果的に圧下できる。Further, it is desirable that the amount of reduction be 50% or more of the bulging amount. When it is 50% or more, the vicinity of the center of the thickness of the slab can be reduced more effectively.
【００３３】圧下ロール対は１対を１台とすれば、１台
以上で圧下する。複数台で圧下する場合は、それぞれの
圧下ロール対ごとに、前述の（Ａ）式で表される圧下率
Ｌｆが０．９〜１．５となる条件で圧下する。Assuming that one pair of reduction rolls is one, the reduction is performed by one or more rolls. In the case of rolling down by a plurality of rolls, rolling down is performed under the condition that the rolling-down rate Lf represented by the above-mentioned formula (A) is 0.9 to 1.5 for each rolling roll pair.
【００３４】図３の模式図では、垂直型連続鋳造機を示
しているが、湾曲型連続鋳造機、垂直曲げ型連続鋳造機
にも本発明の方法を適用できる。Although the vertical type continuous casting machine is shown in the schematic diagram of FIG. 3, the method of the present invention can be applied to a curved type continuous casting machine and a vertical bending type continuous casting machine.
【００３５】耐水素誘起割れ性に優れた厚鋼板は、本発
明の連続鋳造鋳片を熱間で圧延して製造することができ
る。鋳片の加熱温度、在炉時間、圧延温度などは、通常
の同様な化学組成の連続鋳造鋳片を熱間で圧延する場合
と同じ条件で構わない。A steel plate having excellent resistance to hydrogen-induced cracking can be produced by hot rolling the continuous cast slab of the present invention. The heating temperature, the in-furnace time, the rolling temperature, etc. of the slab may be the same conditions as in the case of hot rolling a continuous cast slab having a similar chemical composition.
【００３６】[0036]
【実施例】垂直曲げ型連続鋳造機を用いて、合計１２ヒ
ートの鋳造試験を行った。鋳片サイズは、いずれも厚さ
２３０ｍｍ、幅２３００ｍｍとし、１ヒートの単鋳で鋳
造した。１ヒートは約２５０ｔｏｎである。表１に、用
いた鋼の化学組成を示す。用いた鋼は、Ｍｎ含有率が
１．５０質量％、Ｎｂ含有率が０．０４２質量％で、Ｃ
ａ含有率が０．００２５質量％の厚鋼板用の鋼とした。EXAMPLE Using a vertical bending type continuous casting machine, a casting test was conducted for a total of 12 heats. Each of the cast pieces had a thickness of 230 mm and a width of 2300 mm, and was cast by single casting with one heat. One heat is about 250 tons. Table 1 shows the chemical composition of the steel used. The steel used had a Mn content of 1.50% by mass, a Nb content of 0.042% by mass, and C
The steel for thick steel plates having a content of 0.0025% by mass was used.
【００３７】[0037]
【表１】 タンディッシュ内における溶鋼の過熱度は２５〜３５℃
とした。鋳造速度は０．９０〜１．１３ｍ／分とし、ま
た二次冷却比水量は１．２〜１．５リットル／ｋｇ−鋼
とし、これら鋳造速度、二次冷却比水量を変更すること
により、圧下開始時の中心固相率を変化させて試験し
た。中心固相率は、通常の凝固伝熱解析方法を用いて計
算により求めた。[Table 1] Superheat degree of molten steel in tundish is 25-35 ° C
And The casting speed is 0.90 to 1.13 m / min, and the secondary cooling specific water amount is 1.2 to 1.5 liter / kg-steel. By changing the casting speed and the secondary cooling specific water amount, The test was performed by changing the center solid phase ratio at the start of reduction. The center solid fraction was determined by calculation using an ordinary solidification heat transfer analysis method.
【００３８】圧下前のバルジング量は鋳片幅中央部で２
０ｍｍとし、その後、直径４００ｍｍの１つの圧下ロー
ル対で未凝固部を含む鋳片を圧下した。この圧下ロール
対は溶鋼のメニスカスから２１ｍの位置に配置した。鋳
造方向で長さ１００ｍｍの鋳片横断面サンプルを採取し
た。この横断面サンプルの厚さ中心部で、鋳片幅方向中
心部および幅の１／４部から、直径３ｍｍのドリル刃に
より切り削を採取してＳを分析し、その平均値を求め
た。また、ドリル刃で切り削を採取した部分を外して、
鋳片幅方向中心部および幅の１／４部から、幅方向に２
０ｍｍで全厚のサンプルを切り出し、Ｘ線マイクロアナ
ライザを用いて、５０μｍビームサイズでＭｎ含有率を
測定した。その際、Ｍｎ含有率が２．０質量％以上とな
る測定点の数を、全測定点数で除した面積率を求めた。
測定サンプル毎の全測定点は２００×４００＝８０００
０点である。The bulging amount before the reduction is 2 at the center of the slab width.
After that, the slab including the unsolidified portion was reduced by one reduction roll pair having a diameter of 400 mm. This rolling roll pair was arranged at a position 21 m from the meniscus of the molten steel. A slab cross section sample having a length of 100 mm in the casting direction was collected. At the center of the thickness of this cross-sectional sample, a cut was taken from the center of the slab in the width direction of the slab and １ ／ of the width with a drill blade having a diameter of 3 mm, S was analyzed, and the average value was obtained. Also, remove the part where the cut was collected with the drill blade,
From the center in the slab width direction and 1/4 of the width, 2
A sample having a total thickness of 0 mm was cut out, and the Mn content was measured using an X-ray microanalyzer with a beam size of 50 μm. At that time, the area ratio was obtained by dividing the number of measurement points at which the Mn content was 2.0% by mass or more by the total number of measurement points.
All measurement points for each measurement sample are 200 × 400 = 8000
0 points.
【００３９】また、得られた鋳片を素材として厚さ１９
ｍｍの厚鋼板に圧延し、厚鋼板の引張強度を調査した。
また、縦１００ｍｍ、横１５０ｍｍの厚鋼板サンプルを
採取し、５質量％ＮａＣｌおよび０．５質量％ＣＨ3 Ｃ
ＯＯＨを含む飽和Ｈ2 ＳのＮＡＣＥ腐食液（ｐＨ：約
３．０）中に９６時間浸漬し、水素誘起割れの発生状況
を調査した。水素誘起割れの発生の有無は、超音波探傷
（感度８ｄＢ）により調査した。超音波探傷した厚鋼板
サンプルの面積に対して、水素誘起割れの発生している
領域の面積の割合を、水素誘起割れ面積率として求め
た。試験条件および試験結果を表２に示す。The obtained cast slab is used as a raw material and has a thickness of 19 mm.
mm, and the tensile strength of the steel plate was investigated.
In addition, a thick steel plate sample having a length of 100 mm and a width of 150 mm was sampled, and 5% by mass of NaCl and 0.5% by mass of CH 3 C were collected.
It was immersed in a saturated H 2 S NACE etchant containing OOH (pH: about 3.0) for 96 hours, and the state of occurrence of hydrogen-induced cracking was examined. The presence or absence of hydrogen-induced cracking was examined by ultrasonic testing (8 dB sensitivity). The ratio of the area of the region where the hydrogen-induced cracking occurred to the area of the steel plate sample subjected to ultrasonic flaw detection was determined as the hydrogen-induced cracking area ratio. Table 2 shows the test conditions and test results.
【００４０】[0040]
【表２】 試験Ｎｏ．１では、鋳造速度を１．０ｍ／分、二次冷却
の比水量を１．４リットル／ｋｇ−鋼、圧下量Ｄ１を２
０ｍｍとした。圧下開始時の、中心固相率は０．５、未
凝固部の厚さＤ２は２０ｍｍとなるので、圧下率Ｌｆは
１．０であった。また、試験Ｎｏ．２では、鋳造速度を
０．９５ｍ／分、二次冷却の比水量を１．３リットル／
ｋｇ−鋼、圧下量Ｄ１を２０ｍｍとした。圧下開始時
の、中心固相率は０．７、未凝固部の厚さＤ２は１５ｍ
ｍとなるので、圧下率Ｌｆは１．３であった。これら試
験Ｎｏ．１およびＮｏ．２での中心固相率および圧下率
Ｌｆは、それぞれ本発明で規定する条件の範囲内の値で
ある。[Table 2] Test No. In No. 1, the casting speed was 1.0 m / min, the specific water volume of the secondary cooling was 1.4 L / kg-steel, and the rolling reduction D1 was 2
0 mm. At the start of the reduction, the center solid phase ratio was 0.5, and the thickness D2 of the unsolidified portion was 20 mm. Therefore, the reduction ratio Lf was 1.0. Test No. In No. 2, the casting speed was 0.95 m / min, and the specific water volume of the secondary cooling was 1.3 liters / minute.
kg-steel and the amount of reduction D1 were 20 mm. At the start of the reduction, the central solid phase ratio is 0.7, and the thickness D2 of the unsolidified portion is 15 m.
m, the rolling reduction Lf was 1.3. These test Nos. 1 and No. The center solid phase ratio and the rolling reduction Lf in 2 are values within the range of the conditions defined in the present invention, respectively.
【００４１】試験Ｎｏ．１では、鋳片の厚さ中心部近傍
１０ｍｍ以内の領域において、Ｓ含有率は９ｐｐｍ、Ｍ
ｎ含有率が２．０質量％以上の面積率は０．１％で低い
値であった。また、試験Ｎｏ．２では、鋳片の厚さ中心
部近傍１０ｍｍ以内の領域において、Ｓ含有率は７ｐｐ
ｍ、Ｍｎ含有率が２．０質量％以上の面積率は０．０５
％で低い値であった。これら試験Ｎｏ．１およびＮｏ．
２でのＳ含有率、およびＭｎ含有率が２．０質量％以上
の面積率は、本発明で規定する条件の範囲内である。厚
さ中心部にまで圧下の効果が効果的に及んだので、鋳片
の厚さ方向の両側の凝固界面に、偏析成分の濃化した溶
鋼が捕捉されることがなく、ＳおよびＭｎの含有率の低
い領域が安定して生成した。さらに、これら試験Ｎｏ．
１およびＮｏ．２の鋳片を素材とする厚鋼板には、水素
誘起割れは発生しなかった。また、これら厚鋼板の引張
強度は５９０ＭＰａまたは５９１ＭＰａであった。この
引張強度は目標とする強度の範囲内である。なお、目標
とする厚鋼板の引張強度は、前述の表１に示す化学組成
の鋼であるので、５００Ｍｐａ以上である。Test No. In No. 1, the S content was 9 ppm in the region within 10 mm near the center of the thickness of the slab,
The area ratio where the n content was 2.0% by mass or more was a low value of 0.1%. Test No. In No. 2, the S content was 7 pp in a region within 10 mm near the center of the thickness of the slab.
The area ratio where the m and Mn content is 2.0% by mass or more is 0.05.
% Was a low value. These test Nos. 1 and No.
The S content and the Mn content of 2.0 in the area ratio of 2.0% by mass or more are within the range defined by the present invention. Since the effect of the reduction was effectively applied to the center of the thickness, the solidified interface on both sides in the thickness direction of the slab did not capture the molten steel in which the segregated component was concentrated. A region with a low content was formed stably. Further, in these test nos.
1 and No. No hydrogen-induced cracking occurred in a thick steel plate made of the cast slab No. 2. The tensile strength of these thick steel plates was 590 MPa or 591 MPa. This tensile strength is within the target strength range. Note that the target tensile strength of the thick steel plate is 500 Mpa or more because the steel plate has the chemical composition shown in Table 1 described above.
【００４２】試験Ｎｏ．３では、鋳造速度を１．０５ｍ
／分、二次冷却の比水量を１．４リットル／ｋｇ−鋼、
圧下量Ｄ１を２０ｍｍとした。圧下開始時の、中心固相
率は０．３、未凝固部の厚さＤ２は２５ｍｍとなるの
で、圧下率Ｌｆは０．８であった。また、試験Ｎｏ．４
では、鋳造速度を０．９５ｍ／分、二次冷却の比水量を
１．３リットル／ｋｇ−鋼、圧下量Ｄ１を１０ｍｍとし
た。圧下開始時の、中心固相率は０．７、未凝固部の厚
さＤ２は１５ｍｍとなるので、圧下率Ｌｆは０．７であ
った。これら試験Ｎｏ．３およびＮｏ．４での圧下率Ｌ
ｆは、それぞれ本発明で規定する条件を外れて小さな値
である。Test No. In 3, the casting speed was 1.05m
/ Min, the specific water volume of the secondary cooling is 1.4 liter / kg-steel,
The rolling reduction D1 was set to 20 mm. At the start of the reduction, the central solid phase ratio was 0.3, and the thickness D2 of the unsolidified portion was 25 mm. Therefore, the reduction ratio Lf was 0.8. Test No. 4
In this test, the casting speed was 0.95 m / min, the specific water volume of the secondary cooling was 1.3 liter / kg-steel, and the reduction D1 was 10 mm. At the start of the reduction, the center solid phase ratio was 0.7, and the thickness D2 of the unsolidified portion was 15 mm. Therefore, the reduction ratio Lf was 0.7. These test Nos. 3 and No. 3 Reduction ratio L at 4
f is a small value outside the conditions defined in the present invention.
【００４３】試験Ｎｏ．３では、鋳片の厚さ中心部近傍
１０ｍｍ以内の領域において、Ｓ含有率は１３ｐｐｍ、
Ｍｎ含有率が２．０質量％以上の面積率は０．５％であ
った。また、試験Ｎｏ．４では、鋳片の厚さ中心部近傍
１０ｍｍ以内の領域において、Ｓ含有率は１４ｐｐｍ、
Ｍｎ含有率が２．０質量％以上の面積率は０．８％であ
った。これら試験Ｎｏ．３およびＮｏ．４でのＳ含有
率、およびＭｎ含有率が２．０質量％以上の面積率は、
本発明で規定する条件を外れた大きな値である。圧下率
Ｌｆが小さい値であったので、厚さ中心部にまで圧下の
効果が十分及ばなかったためである。さらに、これら試
験Ｎｏ．３およびＮｏ．４の鋳片を素材とする厚鋼板に
は、水素誘起割れが発生し、これらの水素誘起割れ面積
率は７．６％または９．２％であった。また、これら厚
鋼板の引張強度は５８９ＭＰａまたは５９２ＭＰａであ
った。Test No. In 3, the S content was 13 ppm in a region within 10 mm near the center of the thickness of the slab,
The area ratio where the Mn content was 2.0% by mass or more was 0.5%. Test No. In 4, the S content was 14 ppm in a region within 10 mm near the center of the thickness of the slab,
The area ratio where the Mn content was 2.0% by mass or more was 0.8%. These test Nos. 3 and No. 3 4, the S content and the Mn content are 2.0% by mass or more in area ratio.
This is a large value outside the conditions defined in the present invention. This is because the rolling reduction Lf was a small value, and the rolling reduction effect did not sufficiently reach the center of the thickness. Further, in these test nos. 3 and No. 3 Hydrogen-induced cracks occurred in the thick steel plate using the slab of No. 4 as a material, and the hydrogen-induced cracking area ratio was 7.6% or 9.2%. Further, the tensile strength of these thick steel plates was 589 MPa or 592 MPa.
【００４４】試験Ｎｏ．５では、鋳造速度を１．１３ｍ
／分、二次冷却の比水量を１．５リットル／ｋｇ−鋼、
圧下量Ｄ１を２０ｍｍとした。圧下開始時の、中心固相
率は０．１、未凝固部の厚さＤ２は３５ｍｍとなるの
で、圧下率Ｌｆは０．５７であった。また試験Ｎｏ．６
では、鋳造速度を０．９ｍ／分、二次冷却の比水量を
１．２リットル／ｋｇ−鋼、圧下量Ｄ１を２０ｍｍとし
た。圧下開始時の、中心固相率は０．８、未凝固部の厚
さＤ２は１１ｍｍとなるので、圧下率Ｌｆは１．８であ
った。これら試験Ｎｏ．５およびＮｏ．６での圧下開始
時の中心固相率、および圧下率Ｌｆは、それぞれ本発明
で規定する条件を外れて、小さいかまたは大きな値であ
る。Test No. In 5, the casting speed was 1.13 m
/ Min, the specific water volume of the secondary cooling is 1.5 liter / kg-steel,
The rolling reduction D1 was set to 20 mm. At the start of the reduction, the center solid phase ratio was 0.1, and the thickness D2 of the unsolidified portion was 35 mm. Therefore, the reduction ratio Lf was 0.57. Test No. 6
In the test, the casting speed was 0.9 m / min, the specific water volume of the secondary cooling was 1.2 liter / kg-steel, and the reduction D1 was 20 mm. At the start of the reduction, the center solid phase ratio was 0.8, and the thickness D2 of the unsolidified portion was 11 mm. Therefore, the reduction ratio Lf was 1.8. These test Nos. 5 and No. 5 The center solid phase ratio at the start of rolling and the rolling ratio Lf at 6 are smaller or larger values, respectively, outside the conditions defined in the present invention.
【００４５】試験Ｎｏ．５では、鋳片の厚さ中心部近傍
１０ｍｍ以内の領域において、Ｓ含有率は１３ｐｐｍ、
Ｍｎ含有率が２．０質量％以上の面積率は２．１％であ
った。また、試験Ｎｏ．６では、鋳片の厚さ中心部近傍
１０ｍｍ以内の領域において、Ｓ含有率は１６ｐｐｍ、
Ｍｎ含有率が２．０質量％以上の面積率は６．３％であ
った。これら試験Ｎｏ．５およびＮｏ．６でのＳ含有
率、およびＭｎ含有率が２．０質量％以上の面積率は、
本発明で規定する条件を外れた大きな値である。試験Ｎ
ｏ．５では、中心固相率および圧下率Ｌｆがともに小さ
く、厚さ中心部にまで圧下の効果が十分及ばなかったた
めである。また、試験Ｎｏ．６では、中心固相率および
圧下率Ｌｆがともに大きく、厚さ中心部にまで圧下の効
果が十分及ばなかったためである。さらに、これら試験
Ｎｏ．５およびＮｏ．６の鋳片を素材とする厚鋼板に
は、水素誘起割れが発生し、これらの水素誘起割れ面積
率は２６．８％または３２．２％であった。また、これ
ら厚鋼板の引張強度は５９０ＭＰａまたは５９２ＭＰａ
であった。Test No. 5, the S content was 13 ppm in a region within 10 mm near the center of the thickness of the slab,
The area ratio where the Mn content was 2.0% by mass or more was 2.1%. Test No. In 6, the S content was 16 ppm in a region within 10 mm near the center of the thickness of the slab,
The area ratio where the Mn content was 2.0% by mass or more was 6.3%. These test Nos. 5 and No. 5 6, the S content and the Mn content are 2.0% by mass or more in area ratio.
This is a large value outside the conditions defined in the present invention. Test N
o. In No. 5, both the central solid phase ratio and the reduction ratio Lf were small, and the reduction effect did not sufficiently reach the center of the thickness. Test No. In No. 6, both the central solid phase ratio and the reduction ratio Lf were large, and the reduction effect did not sufficiently reach the center of the thickness. Further, in these test nos. 5 and No. 5 Hydrogen-induced cracking occurred in a thick steel plate made of the cast slab No. 6, and the hydrogen-induced cracking area ratio was 26.8% or 32.2%. Further, the tensile strength of these thick steel plates is 590 MPa or 592 MPa.
Met.
【００４６】[0046]
【発明の効果】本発明の連続鋳造鋳片、その鋳片の鋳造
方法およびその鋳片を熱間圧延する厚鋼板の製造方法の
適用により、ラインパイプ、油井管などの用途に適した
耐水素誘起割れ性に優れた厚鋼板などを得ることができ
る。According to the present invention, the continuous cast slab, the method for casting the slab, and the method for producing a thick steel plate obtained by hot rolling the slab are applied to hydrogen-resistant steel suitable for use in line pipes and oil country tubular goods. It is possible to obtain a thick steel plate or the like having excellent induced cracking properties.
【図１】鋳片の横断面を示す模式図である。FIG. 1 is a schematic view showing a cross section of a slab.
【図２】厚鋼板の水素誘起割れ面積率に及ぼす鋳片の厚
さ中心部近傍１０ｍｍ以内の領域におけるＳおよびＭｎ
の含有率の影響を示す図である。FIG. 2 shows the effect of S and Mn in a region within 10 mm near the center of the thickness of a slab on the hydrogen-induced cracking area ratio of a thick steel plate.
It is a figure which shows the influence of the content rate of.
【図３】本発明の連続鋳造方法を実施するための連続鋳
造機の例を示す模式図である。FIG. 3 is a schematic view showing an example of a continuous casting machine for performing the continuous casting method of the present invention.
１：鋳型 ２：鋳片 ２ａ：凝固殻 ２ｂ：未凝固部 ３：溶鋼 ４：浸漬ノズル ５：ガイドロール ６：圧下ロール対 ７：ピンチロール ８：バルジングゾーン ９：圧下ゾーン Ｔｃ：ほぼ直線状の最終凝固部 Ｔ1 ：Ｔｃの上側の５ｍｍの位置の直線 Ｔ2 ：Ｔｃの下側の５ｍｍの位置の直線 Ｔ0 ：鋳片厚さ1: mold 2: cast slab 2a: solidified shell 2b: unsolidified portion 3: molten steel 4: immersion nozzle 5: guide roll 6: reduction roll pair 7: pinch roll 8: bulging zone 9: reduction zone Tc: substantially linear Final solidified portion T 1 : straight line at 5 mm above Tc T 2 : straight line at 5 mm below Tc T 0 : slab thickness
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｂ２２Ｄ 11/16 Ｂ２２Ｄ 11/16 Ｃ ──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. 7 Identification symbol FI theme coat ゛ (Reference) B22D 11/16 B22D 11/16 C
Claims (3)
む厚さ中心部１０ｍｍ以内の領域において、Ｓ含有率が
１０ｐｐｍ以下であり、かつＭｎ含有率が２．０質量％
以上の面積率が０．２％未満であることを特徴とするＣ
ａを含有する鋼の連続鋳造鋳片。An S content is 10 ppm or less and a Mn content is 2.0% by mass in a region within a thickness center portion of 10 mm including a final solidified portion of a slab in a center portion in a thickness direction.
C, wherein the above area ratio is less than 0.2%.
Continuous cast slab of steel containing a.
後、厚さ中心部が凝固完了するまでの間に１つ以上の圧
下ロール対により圧下する方法において、中心固相率が
０．２〜０．７の鋳片の位置で、下記（Ａ）式で表され
る圧下率Ｌｆが０．９〜１．５を満足する条件で鋳片を
圧下することを特徴とする請求項１に記載の連続鋳造鋳
片の鋳造方法。 Ｌｆ＝Ｄ１／Ｄ２ ・・・（Ａ） ここで、Ｄ１：未凝固部を含む鋳片の幅中央部における
圧下量（ｍｍ） Ｄ２：圧下開始時の固相率０．８以下の未凝固部の厚さ
（ｍｍ）2. A method in which a slab including an unsolidified portion is bulged and then reduced by one or more pairs of reduction rolls until solidification of a thickness central portion is completed. The slab is reduced at a position of the slab of 2 to 0.7 under a condition that a reduction ratio Lf represented by the following formula (A) satisfies 0.9 to 1.5. The method for casting a continuous cast slab according to item 1. Lf = D1 / D2 (A) Here, D1: The amount of reduction (mm) at the center of the width of the slab including the unsolidified portion. D2: The unsolidified portion having a solid phase ratio of 0.8 or less at the start of the reduction. Thickness (mm)
延することを特徴とする厚鋼板の製造方法。3. A method for producing a thick steel plate, comprising hot rolling the continuous cast slab according to claim 1.
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|---|---|---|---|---|
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|---|---|---|---|---|
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| JP4548231B2 (en) * | 2005-06-10 | 2010-09-22 | 住友金属工業株式会社 | Steel continuous casting method and continuous cast slab |
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