JP3298519B2 - Steel sheet free of hydrogen defects and method for producing the same - Google Patents

Steel sheet free of hydrogen defects and method for producing the same

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Publication number
JP3298519B2
JP3298519B2 JP27561598A JP27561598A JP3298519B2 JP 3298519 B2 JP3298519 B2 JP 3298519B2 JP 27561598 A JP27561598 A JP 27561598A JP 27561598 A JP27561598 A JP 27561598A JP 3298519 B2 JP3298519 B2 JP 3298519B2
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JP
Japan
Prior art keywords
hydrogen
steel
slab
thickness
segregation
Prior art date
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Expired - Fee Related
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JP27561598A
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Japanese (ja)
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JP2000102848A (en
Inventor
大悟郎 大瀧
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Sumitomo Metal Industries Ltd
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Priority to JP27561598A priority Critical patent/JP3298519B2/en
Publication of JP2000102848A publication Critical patent/JP2000102848A/en
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Publication of JP3298519B2 publication Critical patent/JP3298519B2/en
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Expired - Fee Related legal-status Critical Current

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Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【0001】[0001]

【発明の属する技術分野】本発明は、連続鋳造法による
鋼の鋳片を圧延して製造する内部に水素性欠陥のない厚
鋼板およびその製造方法に関するものである。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate having no hydrogen defects therein and manufactured by rolling a steel slab by a continuous casting method, and a method of manufacturing the same.

【0002】[0002]

【従来の技術】連続鋳造法により鋳片を鋳込み、これを
圧延して厚鋼板とする場合、水素に基づくと考えられる
超音波探傷にて検出される欠陥が見出されることがあ
る。ここではこれを水素性欠陥と呼ぶことにするが、圧
延後の冷却の過程で、鋼中に固溶している水素が介在物
や成分偏析部で気体となり、その圧力で鋼内部に亀裂を
生じさせ欠陥として検出されるためと考えられている。
したがってこの欠陥発生に対し、鋼中の水素をできるだ
け低下させること、および水素による割れ発生に対する
鋼の耐性を向上させること、などの対策が必要である。
2. Description of the Related Art When a slab is cast by a continuous casting method and rolled into a thick steel plate, defects detected by ultrasonic flaw detection considered to be based on hydrogen may be found. Here, this is referred to as a hydrogen defect.In the process of cooling after rolling, hydrogen dissolved in the steel becomes gas at inclusions and component segregation parts, and the pressure causes cracks inside the steel. This is considered to be caused and detected as a defect.
Therefore, it is necessary to take measures such as reducing hydrogen in steel as much as possible and improving the resistance of steel to cracking caused by hydrogen.

【0003】鋼中水素濃度の低減方法としては、溶鋼の
脱ガス処理や、鋳込み後鋳片の保温が実施され、さらに
は圧延後鋼板の加熱保温もおこなわれる。連続鋳造の場
合、不純物除去や成分調整の目的もあって、溶鋼の多く
が脱ガス処理されるが、これには主としてRH脱ガス法
が採用されている。溶鋼中の水素は、この脱ガス処理の
時間を長くすることにより十分な低減は可能であるが、
処理時間が長くなると処理コストが増し、連続鋳造のサ
イクルによる時間の制約もあるため、限界がある。より
十分な水素濃度低下は、鋳込み終了直後の鋳片を間隔を
あけて積み重ねカバーで覆うなどして保温し、高温にあ
る時間を長くして鋳片中の水素を表面にまで拡散させ排
除することによっておこなうことができる。この場合、
厚い鋳片では水素の拡散に時間がかかるので数日以上の
放置を要し、しかも、鋳片の温度が低下してしまう。
[0003] As a method for reducing the hydrogen concentration in steel, degassing of molten steel, heat retention of cast slabs after casting, and heat insulation of steel sheets after rolling are also performed. In the case of continuous casting, most of the molten steel is degassed for the purpose of removing impurities and adjusting the components. For this purpose, the RH degassing method is mainly used. Hydrogen in molten steel can be sufficiently reduced by lengthening the time of this degassing process,
As the processing time increases, the processing cost increases, and the time is limited by the cycle of continuous casting, so that there is a limit. More sufficient reduction in hydrogen concentration is achieved by keeping the slabs immediately after pouring at intervals and covering them with a cover, keeping them warm, and extending the high temperature time to diffuse hydrogen in the slabs to the surface and eliminate them. It can be done by doing. in this case,
Thick slabs require a few days or more to stand because the diffusion of hydrogen takes time, and the temperature of the slabs decreases.

【0004】近年、エネルギーの効率的利用および製造
工程短縮の観点から、鋳込み直後の高温の鋳片を、冷却
することなく直ちに所要温度に調整して、製品寸法にま
で圧延してしまうホットチャージないしは直接圧延の製
造方法が多く採用されるようになってきた。この場合鋳
造過程で鋼中に残存した水素は、十分除去されないまま
圧延され厚鋼板形状となるので、圧延後の冷却過程にお
いて温度の高い間に水素を放出させ低下させなければ、
水素性欠陥が発生する危険が増してくる。このため、圧
延後の鋼板を積み重ねて徐冷したり、加熱して保温する
必要が生じ、徐冷のための場所、加熱保温設備、さらに
はそれらによる所要時間の増大など、工程上の問題は避
けられない。
[0004] In recent years, from the viewpoint of efficient use of energy and shortening of the manufacturing process, a hot charge or a hot cast slab immediately after casting is immediately adjusted to a required temperature without cooling and rolled to a product size. Many direct rolling manufacturing methods have been adopted. In this case, the hydrogen remaining in the steel during the casting process is rolled into a thick steel plate shape without being sufficiently removed, so in the cooling process after rolling, if hydrogen is not released and lowered while the temperature is high,
The danger of hydrogen deficiency increases. For this reason, it is necessary to stack the rolled steel sheets and gradually cool them down, or to heat them to keep them warm, and there are problems in the process, such as the place for slow cooling, heating and heat keeping equipment, and the increase in the required time due to them. Inevitable.

【0005】水素による割れ発生に対する鋼の耐性を向
上させる手段としては、水素割れの起点となる介在物の
低減やその生成抑止、および中心偏析など局所的硬化の
抑止などが考えられる。MnSや酸化物のクラスター状
介在物は、圧延された鋼中で帯状に拡がって存在し、こ
れに沿って鋼中に溶けていた水素が気体となって水素割
れを引き起こす。これらの介在物は、中心偏析部など鋼
中の成分、組織、硬さなどの不均質な部分に発生しやす
く、鋼板の水素性欠陥は、主として鋼板の中心偏析部に
発生する。
As means for improving the resistance of steel to cracking caused by hydrogen, it is conceivable to reduce inclusions serving as starting points of hydrogen cracking, suppress the formation thereof, and suppress local hardening such as center segregation. Cluster-like inclusions such as MnS and oxides are present in the form of a band in the rolled steel, along which hydrogen dissolved in the steel becomes gas and causes hydrogen cracking. These inclusions are likely to occur in non-homogeneous portions of the steel, such as the center segregation, such as components, structure, and hardness, and hydrogen defects of the steel sheet mainly occur in the center segregation of the steel.

【0006】連続鋳造特有の中心偏析の発生原因は、凝
固にともない成分濃化した溶鋼が局部的に移動集積する
こと、すなわち凝固末期におけるデンドライト間の残溶
鋼が溶鋼の凝固収縮や凝固シェルのバルジングにより、
最終凝固部の凝固完了点に向けて移動し、そこで凝固す
るためである。これに対する防止策としては、バルジン
グの発生を極力抑える方法、さらには凝固完了点にて圧
下を加える方法などが開発され、さらに最近では連続鋳
造中に積極的にバルジングを生じさせた後、圧下を加え
てバルジングを生じた分を元へ押し戻す方法も提案され
ている。
The cause of the center segregation peculiar to continuous casting is that the molten steel whose components have been enriched due to solidification moves and accumulates locally, that is, the residual molten steel between the dendrites in the final stage of solidification causes solidification shrinkage of the molten steel and bulging of the solidified shell. By
This is for moving to the solidification completion point of the final solidification part and solidifying there. As measures to prevent this, a method of minimizing the occurrence of bulging, a method of applying reduction at the solidification completion point, and the like have been developed.More recently, after bulging has been actively generated during continuous casting, the reduction is reduced. In addition, a method has been proposed in which the bulging is pushed back.

【0007】従来連続鋳造材の中心偏析対策は、厚鋼板
の溶接時などの板厚の中心部割れや、例えばH2Sを含
む酸性環境(サワー環境)にてその鋼板がラインパイプ
やタンク類などとして使用される際の水素誘起割れ(H
IC)に対して種々検討されてきた。このHICは、工
場出荷後の鋼中水素が極めて低いレベルになっている鋼
板の使用中において発生する割れであり、表面の腐食等
により生じ鋼中に侵入した水素が原因であるが、割れ発
生部位以外の水素量はごくわずかである。これに対し、
ここで対象とするのは鋼板圧延後に見出される超音波探
傷にて検出される欠陥で、欠陥の発生位置は中心偏析位
置に集中しており、水素が関与しているという点におい
て共通しているが、欠陥の発生する時点における鋼中水
素の量ははるかに大きい。したがって、従来の中心偏析
とは異なる観点からの対策が必要である。
Conventionally, the countermeasures against center segregation of continuous cast materials are to crack the central part of the plate thickness at the time of welding of a thick steel plate or the like, for example, when the steel plate is used for line pipes and tanks in an acidic environment (sour environment) containing H 2 S. Hydrogen-induced cracking (H
Various studies have been made on IC). This HIC is a crack that occurs during use of a steel sheet having a very low level of hydrogen in the steel after shipment from the factory. The HIC is caused by the corrosion of the surface or the like and the hydrogen that has entered the steel. The amount of hydrogen outside the site is negligible. In contrast,
The target here is a defect detected by ultrasonic flaw detection found after rolling a steel sheet, the defect generation position is concentrated at the center segregation position, and it is common in that hydrogen is involved However, the amount of hydrogen in the steel at the time of the occurrence of the defect is much larger. Therefore, it is necessary to take measures from a viewpoint different from the conventional center segregation.

【0008】[0008]

【発明が解決しようとする課題】本発明の目的は、連続
鋳造にて鋳片を製造しこれを圧延して厚鋼板とする場合
に、鋳片または圧延直後の鋼板において、徐冷や保温な
どのなどの脱水素処理を必要としない鋼板、およびその
製造方法の提供であり、とくに鋳片を冷却することなく
加熱炉に投入して温度を調整後圧延するダイレクトチャ
ージ法、または鋳片をそのまま直ちに圧延する直接圧延
法、などによって製造される鋼板の水素性欠陥を防止す
ることにある。
SUMMARY OF THE INVENTION An object of the present invention is to produce a slab by continuous casting and roll it into a thick steel plate. The present invention provides a steel sheet that does not require a dehydrogenation treatment, and a method for producing the same.In particular, a direct charge method in which a slab is put into a heating furnace without cooling the slab and the temperature is adjusted and then rolled, or the slab is directly used as it is. An object of the present invention is to prevent hydrogen-based defects in a steel sheet manufactured by a direct rolling method of rolling.

【0009】[0009]

【課題を解決するための手段】本発明者は、厚板にて発
生する、水素に基づくと考えられる超音波探傷にて検出
される欠陥、すなわち水素性欠陥に関し、その発生を抑
制する対策について種々検討をおこなった。この超音波
探傷で検出される欠陥は、鋳片を連続鋳造後一旦冷却
し、再加熱して圧延した場合はほとんど発生せず、鋳片
を鋳造後直ちに加熱して圧延するダイレクトチャージ法
に多く発生し、これに圧延終了後、放冷など比較的速く
冷却する場合が重畳すると、とくに多く発生する。した
がって水素が関係していると推定されるので、鋼板中の
水素量と欠陥発生の状況を調査したところ、約2ppmを超
えるようになると欠陥発生の頻度が急速に増してくるこ
とがわかった。この水素は、溶鋼の脱ガス処理にて十分
低下できなかったものが、そのまま鋼板にまで持ち来さ
れたものと推定され、脱ガス処理を確実におこなえば解
消できると思われた。しかし、通常の溶鋼の脱ガス処理
においては、1〜2ppm程度までは容易に下げることがで
きるが、それ以下に確実に低下、ことに1ppmを下回る量
にまで低下させようとすると、脱ガス処理時間を大幅に
増さねばならなくなり、処理時間増加による工程管理
や、コスト上昇が問題となる。このことは、見方を変え
れば、もし1〜2ppm程度水素が含まれていたとしても、
水素性欠陥の発生を十分に抑止することができれば、脱
ガス処理工程に対する負担を軽減でき、処理時間の合理
化が可能になる筈である。
Means for Solving the Problems The present inventor has proposed a measure for suppressing the occurrence of a defect which is generated in a thick plate and is detected by ultrasonic flaw detection which is considered to be based on hydrogen, that is, a hydrogen defect. Various studies were conducted. Defects detected by this ultrasonic flaw detection hardly occur when the slab is cooled once after continuous casting, then reheated and rolled, and the direct charge method in which the slab is heated immediately after casting and rolled is common. This occurs particularly when cooling is performed at a relatively high speed such as cooling after the completion of rolling. Therefore, since it is presumed that hydrogen is involved, the amount of hydrogen in the steel sheet and the state of the occurrence of defects were investigated, and it was found that the frequency of the occurrence of defects increased rapidly when the concentration exceeded about 2 ppm. This hydrogen, which could not be sufficiently reduced by the degassing treatment of the molten steel, was presumed to have been brought to the steel sheet as it was, and it was thought that it could be eliminated if the degassing treatment was performed reliably. However, in ordinary molten steel degassing, it can be easily reduced to about 1 to 2 ppm, but if it is surely reduced to less than 1 ppm, especially if it is tried to lower it to less than 1 ppm, degassing treatment The time must be greatly increased, and the process management and the cost increase due to the increase in the processing time become problems. From a different point of view, this means that even if it contains about 1 to 2 ppm hydrogen,
If the generation of hydrogen defects can be sufficiently suppressed, the burden on the degassing process can be reduced, and the processing time should be rationalized.

【0010】この水素性欠陥の発生場所を調査したとこ
ろ、ほとんどすべてが板厚tの中央位置、すなわち1/2
tの位置の近傍にて見出されることがわかった。またそ
の発生場所は、いわゆる中心偏析部と言われるMn濃度
の高いMn偏析度、すなわち取鍋分析値に対する濃度
比、が1を大きく超える部分であることも明らかであっ
た。したがって、もしこのMn濃度の高い部分がなくな
れば、割れを発生し始める鋼板の水素濃度、すなわち割
れ発生臨界水素濃度を高くすることができると思われ
た。そこで、板厚中央部のMn偏析度が1.0を超えない
ようにした連続鋳造による鋳片を作製し、水素性欠陥の
発生を調べてみたが、必ずしもその効果ははっきりしな
かった。
[0010] When the location of the hydrogen defect was investigated, almost all of them were found to be located at the center of the plate thickness t, that is, 1/2.
It was found that it was found near the position of t. It was also apparent that the place of occurrence was a so-called center segregation part where the Mn segregation degree of high Mn concentration, that is, the concentration ratio to ladle analysis value greatly exceeded 1. Therefore, if the portion having a high Mn concentration disappeared, it was thought that the hydrogen concentration of the steel sheet at which cracking began to occur, that is, the critical hydrogen concentration at which cracking occurred, could be increased. Thus, a slab was produced by continuous casting in which the degree of Mn segregation at the center of the sheet thickness did not exceed 1.0, and the occurrence of hydrogen defects was examined. However, the effect was not always clear.

【0011】HICに対する種々の検討結果によれば、
MnSなどの介在物が割れ発生の起点になるとされてい
る。介在物はこの水素性欠陥においても割れ発生の起点
となるに違いないので、さらにMn量およびS量と水素
性欠陥発生の関係を調べた。その結果、板厚中央部のM
n偏析度が1.0を超えない場合でも、Mn量とS量との
積(以下重量%で示される含有量をそれぞれ[Mn]ま
たは[S]と表示し、その積は[Mn]×[S]と示
す)が0.005を超えると水素性欠陥が現れるようにな
り、[Mn]×[S]が0.005以下で、かつMn偏析度
を1.0以下にすれば、水素が1〜2ppm程度含まれていたと
しても、水素性欠陥が発生しないことが明らかになった
のである。
According to various examination results on HIC,
It is said that inclusions such as MnS are the starting points of crack generation. Since inclusions must be a starting point of crack generation even in this hydrogen defect, the relationship between the Mn content and the S content and the hydrogen defect generation was further examined. As a result, M
Even when the degree of n segregation does not exceed 1.0, the product of the amount of Mn and the amount of S (hereinafter, the content represented by weight% is expressed as [Mn] or [S], and the product is [Mn] × [S ] Exceeds 0.005), hydrogen defects appear, and if [Mn] × [S] is 0.005 or less and the Mn segregation degree is 1.0 or less, about 1-2 ppm of hydrogen is contained. Even so, it became clear that no hydrogen defects were generated.

【0012】水素性欠陥は、熱間圧延終了後の冷却の過
程で、冷却速度が比較的速く、水素が鋼表面にまで拡散
して鋼中濃度が十分低下できないままに温度が低下する
とき、MnSなどの介在物周辺でこれが核となって水素
がガス化して、局所的に圧力が高くなり、Mnなどが偏
析した硬く脆い部分で割れが発生することによると推定
される。鋼中のMnとSとは、その含有量が高い場合、
すなわち[Mn]×[S]が大きい場合、溶鋼が凝固す
る過程でMnSが形成され、介在物となって熱間圧延に
より引き延ばされた形になり、水素のガス化の核にな
る。
[0012] Hydrogen defects occur during the cooling process after the completion of hot rolling, when the cooling rate is relatively high, and when the temperature decreases without diffusion of hydrogen to the steel surface to sufficiently reduce the concentration in the steel, It is presumed that this becomes a nucleus around inclusions such as MnS and hydrogen gasifies to locally increase the pressure, causing cracks to occur in hard and brittle portions where Mn and the like are segregated. When the content of Mn and S in steel is high,
That is, when [Mn] × [S] is large, MnS is formed during the process of solidification of the molten steel, becomes an inclusion, is elongated by hot rolling, and becomes a core of gasification of hydrogen.

【0013】これに対し[Mn]×[S]が小さい場合
は、凝固の段階では固溶状態にあり、その後の温度低下
とともに、次第に微細に析出してくるようになる。[M
n]×[S]が0.005以下であることは、このMnSが
大きな介在物にはならず、微細な析出物となって鋼中に
分散する状態となる濃度であると推定される。大きな介
在物とはならないので、水素のガス化のための核にはな
らず、割れの発生が抑止されるのである。単に中心偏析
をなくし、Mnの偏析度を1.0以下にしただけでは水素
性欠陥を抑止できないのは、このような理由によると考
えられる。
On the other hand, when [Mn] × [S] is small, it is in a solid solution state at the stage of solidification, and gradually becomes finer as the temperature decreases. [M
The fact that n] × [S] is 0.005 or less is presumed to be a concentration at which this MnS does not become a large inclusion but becomes a fine precipitate and is dispersed in the steel. Since it does not become a large inclusion, it does not become a nucleus for gasification of hydrogen and generation of cracks is suppressed. It is considered that hydrogen-induced defects cannot be suppressed only by eliminating center segregation and reducing the degree of Mn segregation to 1.0 or less.

【0014】中心偏析を少なくする方法として、鋳片の
凝固完了の直前に圧下を加え、厚さ中央部の、成分が濃
化した溶鋼を押し戻す方法がある。さらに押し戻す溶鋼
量をより多くする方法として、鋳込み中の表面凝固層が
発達する過程で鋳片の厚みを増すバルジングを積極的に
おこなわせ、凝固終了点近くで圧下して厚さを減少さ
せ、凝固層の厚さの合計が当初の鋳型の短辺長さにまで
到達するところで圧下を終了する、と言う技術が開発さ
れている。このように、中心部の成分濃化溶鋼を押し戻
すことにより、鋳片厚さの中央部、または鋳片の1/2厚
付近のMn偏析度を1.0以下とすることが可能である。
しかしながら、凝固層の発達は必ずしも均一ではなく、
とくに幅方向中央部はエッジ部に比較し凝固層の発達が
遅れ、鋳片を圧下して当初鋳型の短辺長さに圧下する
際、エッジに近い部分は成分濃化溶鋼が排除されるが、
幅中央部には残存することがある。凝固層は一旦できて
しまうと変形は困難なので、幅方向には不均一となり、
偏析は低減されているが一部にMnの偏析度が1.0を超
えるところが生じることになる。Mnの濃度が増すと、
S量が同じならその部分で[Mn]×[S]が大きくな
り、MnS介在物が生じ、水素性欠陥が現れる結果とな
る。
As a method for reducing the center segregation, there is a method in which a reduction is applied immediately before the solidification of the slab to complete the molten steel in the central part of the thickness, in which the components are concentrated. As a method to further increase the amount of molten steel to be pushed back, positively perform bulging to increase the thickness of the slab in the process of developing a surface solidification layer during casting, reduce the thickness by rolling down near the solidification end point, A technique has been developed in which the reduction is stopped when the total thickness of the solidified layer reaches the length of the short side of the original mold. In this way, by pushing back the component-concentrated molten steel in the central portion, the degree of Mn segregation in the central portion of the slab thickness or in the vicinity of 1/2 thickness of the slab can be reduced to 1.0 or less.
However, the development of the solidified layer is not always uniform,
In particular, the development of the solidified layer is slower at the center in the width direction than at the edge, and when the slab is pressed down to the length of the short side of the mold initially, the concentrated steel is removed from the portion close to the edge. ,
It may remain at the center of the width. Once formed, the solidified layer is difficult to deform, so it becomes uneven in the width direction,
Although segregation is reduced, a part where the degree of segregation of Mn exceeds 1.0 occurs. As the concentration of Mn increases,
If the amount of S is the same, [Mn] × [S] is increased in that portion, MnS inclusions are generated, and a hydrogen defect appears.

【0015】そこで、板幅のできるだけ広い範囲にわた
って板厚中央部にMnの偏析度が1.0を超える領域が現
れない鋳造方法を検討した。その結果、バルジングをあ
る程度凝固層が発達してからおこなわせ、次いで圧下を
凝固が完了するよりも早い段階で、できるだけ短時間に
大圧下を加える条件でおこなわせると、Mnの偏析度が
1.0以下である領域が確実に得られ、しかも板幅方向の
全幅に近い範囲にわたってその領域が得られるることが
わかった。このような結果になる理由は必ずしも明確で
はないが、バルジング開始の時期を遅らせることによ
り、未凝固域が幅方向に十分広げられることになって、
幅方向での不均一性が減少し、短時間の大圧下によって
成分濃化溶鋼の移動量が大きくなって確実に偏析度が1.
0以下に低下するのではないかと思われる。ただし、板
厚中央近傍に偏析度が1.0の領域が増加することによっ
て、中央部以外の部分に多少偏析度が1.0を超える部分
が生じたり、鋳込みの初期の鋳片に比し、後期の鋳片の
平均Mn量が多少増加する傾向が見られるが、いずれも
ばらつきの範囲内にあることが確かめられた。
Therefore, a casting method in which a region where the degree of segregation of Mn exceeds 1.0 does not appear in the center of the plate thickness over the widest possible range of the plate width was studied. As a result, when bulging is performed after the solidified layer has developed to some extent, and then the reduction is performed at a stage earlier than the completion of the solidification and under the condition of applying the large reduction in the shortest possible time, the degree of segregation of Mn is reduced.
It was found that an area of 1.0 or less was reliably obtained, and that the area was obtained over a range close to the entire width in the plate width direction. The reason for such a result is not always clear, but by delaying the timing of the start of bulging, the unsolidified region will be sufficiently widened in the width direction,
Non-uniformity in the width direction is reduced, and the amount of movement of the component-enriched molten steel is increased by short-time large pressure, and the degree of segregation is reliably 1.
It is thought that it will be reduced to 0 or less. However, due to the increase in the area where the segregation degree is 1.0 near the center of the sheet thickness, a part where the segregation degree slightly exceeds 1.0 may occur in parts other than the center part, and in the later casting compared to the slab at the beginning of casting. The average Mn content of the pieces tended to increase somewhat, but it was confirmed that each of them was within the range of variation.

【0016】以上のような検討結果に基づき、さらにそ
の条件や範囲の限界を確認し本発明を完成させた。本発
明の要旨は次のとおりである。
Based on the above-described examination results, the conditions and the limits of the range were further confirmed, and the present invention was completed. The gist of the present invention is as follows.

【0017】(1) 鋼板の板厚をtとするとき、Mnの偏
析度が1.0以下である厚さ0.20t以下の領域が、板厚の1
/2t位置を中心とする±0.2tの範囲内に存在し、かつ
鋼組成の重量%で示すMnとSの含有量が Mn(%)×S(%)≦0.005 であることを特徴とする厚鋼板。
(1) Assuming that the thickness of the steel sheet is t, a region having a thickness of 0.20 t or less in which the degree of segregation of Mn is 1.0 or less is 1% of the sheet thickness.
The content of Mn and S in the range of ± 0.2t centered on the / 2t position and represented by wt% of the steel composition is Mn (%) × S (%) ≦ 0.005. Steel plate.

【0018】なお、ここで±0.2tの範囲というのは、
板厚の中心を0として、その上下の0.2tまでの部分であ
る。
Here, the range of ± 0.2t is defined as
With the center of the plate thickness set to 0, the upper and lower parts are portions up to 0.2t.

【0019】(2) 鋳造中の中央部未凝固の鋳片にてバル
ジングを生ぜしめ、その後鋳造ライン内に設けた圧下ロ
ールを用い、元の鋳型の短辺長さまで圧下する鋳片の連
続鋳造方法において、中央部固相率が0.5〜0.7の範囲で
バルジングを生じさせて鋳片の最大厚さを鋳型短辺長さ
の110〜150%とし、次いで鋳片の中央部固相率が0.7〜
0.8の範囲で、1対の圧下ロール当たり前記鋳型短辺長
さの10%以上の圧下を加えて、厚鋼板の圧延素材となる
鋳片とすることを特徴とする、上記(1)の厚鋼板の製造
方法。
(2) Continuous casting of slabs in which bulging is caused by unsolidified slabs in the center during casting, and then reduced to the short side length of the original mold using a reduction roll provided in a casting line. In the method, bulging is caused in the range of 0.5 to 0.7 of the center solid phase ratio so that the maximum thickness of the slab is 110 to 150% of the length of the short side of the mold. ~
In the range of 0.8, a reduction of at least 10% of the length of the short side of the mold per pair of reduction rolls is applied to obtain a slab that becomes a rolled material of a thick steel plate. Steel plate manufacturing method.

【0020】[0020]

【発明の実施の形態】Mnの偏析度が1.0を超えると、
その場所はMnSの介在物が存在しやすくなり、硬化す
るので水素性欠陥が発生しやすい。通常、連続鋳造法に
よる鋳片では中心偏析の傾向を示し、厚さ方向の中央近
傍にMn濃度の高い偏析度が1.0を超える部分が生じる
が、これは鋼板に圧延による変形にともない、そのまま
伸ばされて残り、鋼板の板厚中央付近の位置に板面と平
行で幅および長さ方向に拡がった状態で存在する。水素
性欠陥の抑止には、このMn濃度の高い部分がなく、む
しろこの部分のMn濃度が、その上下部と同等かそれよ
り低いことが必要である。ただし、MnはCと共存する
ことにより鋼の強度に重要な役割をはたす元素であり、
このMn濃度の低い偏析度1.0以下の部分が増すこと
は、鋼板の強度確保ができなくなるおそれがあるので、
この領域の厚さは0.2t以内とする。また偏析度1.0以下
の領域の厚さは、実質的に鋼板の板厚中央部近傍に偏析
度が1.0を超える部分がなければ、0tであってもかまわ
ない。また偏析度1.0以下である領域の位置は、鋳造設
備の構造により必ずしも板厚の中央位置とは一致しない
ことがあるが、板厚の中央位置が相対的に水素の影響を
受けやすいことから、偏析度1.0以下である領域は、板
厚の1/2tの位置を中心とする±0.2tの範囲内、すなわ
ち板厚のほぼ中央部にある必要がある。
DESCRIPTION OF THE PREFERRED EMBODIMENTS When the segregation degree of Mn exceeds 1.0,
At that location, inclusions of MnS are likely to be present and harden, so that hydrogen defects are likely to occur. Normally, slabs produced by continuous casting show a tendency of segregation at the center, and there is a portion near the center in the thickness direction where the degree of segregation with a high Mn concentration exceeds 1.0. And exists in a position near the center of the thickness of the steel sheet in a state of being spread in the width and length directions parallel to the sheet surface. In order to suppress the hydrogen defect, there is no portion having a high Mn concentration, but it is necessary that the Mn concentration in this portion is equal to or lower than the upper and lower portions. However, Mn is an element that plays an important role in the strength of steel by coexisting with C,
An increase in the portion of the Mn concentration having a low segregation degree of 1.0 or less is likely to make it impossible to secure the strength of the steel sheet.
The thickness of this region shall be within 0.2t. The thickness of the region having a segregation degree of 1.0 or less may be 0t as long as there is substantially no portion where the segregation degree exceeds 1.0 near the center of the thickness of the steel sheet. In addition, the position of the region where the segregation degree is 1.0 or less may not always coincide with the center position of the plate thickness due to the structure of the casting equipment, but since the center position of the plate thickness is relatively easily affected by hydrogen, The region where the segregation degree is 1.0 or less needs to be within a range of ± 0.2 t centered on the position of 1/2 t of the plate thickness, that is, substantially in the center of the plate thickness.

【0021】板厚中央部におけるMnの偏析度と鋼板の
水素濃度、およびその鋼板の水素性欠陥の有無について
調べた結果を図1に示す。この場合、鋳片はホットチャ
ージで熱間圧延後放冷として、水素性欠陥を意図して出
やすくしている。図1からわかるように、Mnの偏析度
が1.0を超えると、水素濃度の高い場合はいずれも水素
性欠陥を生じている。偏析度が1.0以下になると、水素
濃度1〜2ppmの範囲、さらには2ppmを超えても水素性欠
陥の認められないものが現れてくる。次に、このMn偏
析度1.0以下のものについて、[Mn]×[S]に対す
る水素濃度および水素性欠陥の関係を見ると、図2の結
果が得られた。これからMn偏析度を1.0以下とし、2pp
m程度の水素濃度にて水素性欠陥を抑止するには[M
n]×[S]を0.005以下にすればよいことがわかる。
FIG. 1 shows the results obtained by examining the degree of segregation of Mn at the center of the sheet thickness, the hydrogen concentration of the steel sheet, and the presence or absence of hydrogen defects in the steel sheet. In this case, the slab is left to cool after hot rolling by hot charging, thereby making it easier to cause hydrogen defects. As can be seen from FIG. 1, when the segregation degree of Mn exceeds 1.0, a hydrogen defect occurs in any case where the hydrogen concentration is high. When the segregation degree is 1.0 or less, a hydrogen concentration is in the range of 1 to 2 ppm, and even if the hydrogen concentration exceeds 2 ppm, ones having no hydrogen defect appear. Next, when the relationship between the hydrogen concentration and the hydrogen defect with respect to [Mn] × [S] was examined for those having a Mn segregation degree of 1.0 or less, the results shown in FIG. 2 were obtained. From this, the Mn segregation degree is set to 1.0 or less, and 2pp
To suppress hydrogen defects at a hydrogen concentration of about m
It can be seen that n] × [S] should be set to 0.005 or less.

【0022】すなわち本発明は、Mnの偏析度が1.0以
下で板面と平行に拡がる厚さ0.20t以下の領域が、板厚
tの1/2位置を中心とする±0.2tの範囲内に存在し、か
つ鋼組成のMnとSの含有量が重量%でMn(%)×S
(%)≦0.005である厚鋼板である。この鋼板は、とく
に鋳造後の鋳片を冷却することなく、直ちに圧延するか
圧延用の加熱炉に投入して圧延する製造方法において、
水素性欠陥の発生を抑止することができる。なお、Mn
の偏析度が1.0以下で厚さ0.20t以下の領域は、板幅の
全幅にわたって存在する必要はなく、板幅の80%以上あ
れば、水素性欠陥のない鋼板が得られる。
That is, according to the present invention, the region having a segregation degree of Mn of 1.0 or less and a thickness of 0.20 t or less extending parallel to the plate surface is within a range of ± 0.2 t centered on a half position of the plate thickness t. Mn (%) × S
(%) ≦ 0.005. This steel plate, in particular, without cooling the slab after casting, in the manufacturing method of rolling immediately or rolling into a heating furnace for rolling,
Generation of hydrogen defects can be suppressed. Note that Mn
A region having a segregation degree of 1.0 or less and a thickness of 0.20 t or less does not need to exist over the entire width of the sheet, and if it is 80% or more of the sheet width, a steel sheet without hydrogen defects can be obtained.

【0023】本発明の鋼板は、Mn量とS量とが[M
n]×[S]≦0.005を満足している限りにおいては、
とくにその組成を規制するものではないが、現実に鋼板
を製造する場合、以下のような範囲の化学組成であるこ
とが好ましい。
The steel sheet of the present invention has an Mn content and an S content of [M
n] × [S] ≦ 0.005,
The composition is not particularly limited, but when a steel sheet is actually produced, the chemical composition preferably has the following range.

【0024】Cは鋼の強度を決定する重要な元素であ
り、通常の用途において0.05%以上の含有が必要である
が、多すぎると厚板としては必須である溶接性を劣化す
るので、多くても含有量は0.2%以下とするのがよい。
C is an important element that determines the strength of steel, and it must be contained in an amount of 0.05% or more in ordinary applications. However, if it is too much, the weldability, which is essential for a thick plate, is deteriorated. However, the content is preferably 0.2% or less.

【0025】MnはSによる熱間脆性の抑止に必須の元
素であり、またCととも含有することにより強度向上さ
せる元素であるので、これらの目的のため含有させる。
その範囲は0.2〜2.5%がよいが、これは0.2%を下回る
とその効果がなく、2.5%を超える場合は鋼板の靱性が
劣化してくるからである。
Mn is an element essential for suppressing hot embrittlement by S, and is an element that improves the strength by being contained together with C. Therefore, Mn is contained for these purposes.
The range is preferably 0.2 to 2.5%, but if it is less than 0.2%, the effect is not obtained, and if it exceeds 2.5%, the toughness of the steel sheet is deteriorated.

【0026】Siは溶鋼の脱酸を目的として含有させ
る。そのためには0.05%以上の添加が必要であるが、多
くなると鋼板の表面性状を劣化させるので、上限の含有
量を0.60%までとする。
Si is contained for the purpose of deoxidizing molten steel. For that purpose, the addition of 0.05% or more is necessary, but if it is increased, the surface properties of the steel sheet are deteriorated. Therefore, the upper limit content is set to 0.60%.

【0027】Pは鋼の不可避的不純物の一つであり、鋼
の靱性を劣化させるので、その含有は少なければ少ない
ほどよい。その悪影響が顕著でない範囲として、多くて
も0.20%以下とするのが望ましい。
P is one of the unavoidable impurities of steel and degrades the toughness of steel, so the smaller the content, the better. The range in which the adverse effect is not remarkable is desirably at most 0.20% or less.

【0028】Sは鋼の不可避的不純物の一つであり、靱
性その他の鋼の特性を劣化するのでその含有は少なけれ
ばすく何ほどよい。Mnの存在はその悪影響を低減する
が、多くなるとMnS介在物を増加させるので、0.01%
以下とする。なお、前述のように[Mn]×[S]は0.
005%以下でなければならない。
S is one of the unavoidable impurities of steel and degrades the toughness and other properties of the steel. The presence of Mn reduces its adverse effects, but increasing it increases MnS inclusions, so 0.01%
The following is assumed. [Mn] × [S] is 0.
005% or less.

【0029】Alは溶鋼の脱酸のために含有させる。ま
た鋼の細粒化に効果がある。この効果を得るためには、
少なくとも0.001%以上の含有が必要であるが、多く添
加してもその効果は飽和し、コスト上昇を招くだけなの
で、0.20%以下とするのがよい。
Al is contained for deoxidizing molten steel. It is also effective in reducing the grain size of steel. To get this effect,
At least 0.001% or more must be contained. However, even if a large amount is added, the effect is saturated and only the cost is increased, so it is preferable to set the content to 0.20% or less.

【0030】Cu、Ni、CrおよびMoは、熱処理に
よる組織の改善により鋼の強度を向上させる元素であ
り、添加しなくてもよいが、必要に応じ1.0%までの範
囲で含有させる。1.0%を超える含有は、靱性劣化を来
したり、効果が飽和しコスト上昇を招くだけの結果とな
るからである。なお、Cuは強度向上の他、耐食性を向
上させる効果もある。
Cu, Ni, Cr and Mo are elements that improve the strength of the steel by improving the structure by heat treatment, and do not need to be added, but may be contained up to 1.0% as necessary. If the content exceeds 1.0%, the toughness is degraded, and the effect is saturated, resulting in cost increase. Note that Cu has an effect of improving corrosion resistance in addition to improving strength.

【0031】Nb、VおよびTiは、少量の添加で結晶
粒の微細化および析出強化の作用があり、添加しなくて
もよいが、このような効果を得たい場合には、0.10%以
下の範囲で含有させる。0.10%を超える含有は鋼の靱性
を劣化させるおそれがある。
Nb, V and Ti have the effect of refining the crystal grains and strengthening the precipitation with a small amount of addition, and need not be added. However, if such an effect is desired, 0.10% or less is required. It is contained in the range. If the content exceeds 0.10%, the toughness of the steel may be deteriorated.

【0032】鋳片の厚さ中央部にMnの偏析度が1.0以
下の部分を形成させ、圧延後において板厚tに対し0.2
t以下の厚さのMn濃度の高くない領域を持つ鋼板を製
造するためには、厚板の素材となる鋳片を連続鋳造法に
て製造する際に、積極的にバルジングを生じさせ、その
後圧下する方法を用いる。この場合、鋳片の中央部固相
率が0.5〜0.7の範囲であるときに、バルジングを生じさ
せ、鋳片の最大厚みを鋳型の短辺長さの110〜150%にす
る。その後、鋳片中央部の固相率が0.7〜0.8となったと
き、圧下して鋳片を元の鋳型の短辺長さと同じ厚さに戻
すが、その際の圧下に用いる圧下ロール1対当たりの圧
下量を、鋳型の短辺長さの10%以上とする。
A portion where the degree of segregation of Mn is 1.0 or less is formed at the center of the thickness of the slab.
In order to manufacture a steel sheet having a region with a thickness of not more than t and not having a high Mn concentration, when producing a slab as a material of a thick plate by a continuous casting method, bulging is actively generated, and then Use the method of rolling down. In this case, when the solid fraction in the center of the slab is in the range of 0.5 to 0.7, bulging occurs, and the maximum thickness of the slab is 110 to 150% of the short side length of the mold. Thereafter, when the solid fraction of the slab central portion becomes 0.7 to 0.8, the slab is lowered to return the slab to the same thickness as the short side length of the original mold. The amount of reduction per hit shall be 10% or more of the short side length of the mold.

【0033】バルジングを生じさせる時に、鋳片の中央
部固相率を0.5〜0.7の範囲とするのは、凝固層をある程
度発達させてから、凝固層間の溶鋼部分の間隔を広げる
ことにより、Mnの偏析度1.0以下の領域が板の幅方向
にできるだけ均一に、かつ幅方向の範囲をできるだけ大
きくするためである。中央部固相率が0.5を下回るとき
は偏析度が1.0以下の領域の厚さが不均一になり、1.0を
超えるところが出てくるおそれがある。中央部固相率が
0.7を超えてからバルジングを生じさせると、バルジン
グが十分生じず、偏析度が1.0を超えてしまう。したが
って、中央部固相率が0.5〜0.7の範囲にてバルジングを
生じさせる。バルジングの厚さは、鋳型の短辺長さの11
0%を下回る場合は、Mn偏析度が1.0以下にすることが
できなくなる。この場合のバルジングは大きい方が望ま
しいが、150%を超えると側面のブレークアウトの危険
性があり、また圧下して元の厚さに戻すためにはより多
くの圧下力が必要となる。したがって鋳型の短辺長さの
110〜150%とする。
When the bulging is caused, the solid phase ratio in the central portion of the slab is set in the range of 0.5 to 0.7 because the solidified layer is developed to some extent and then the interval between the molten steel portions between the solidified layers is increased. The reason for this is that a region having a segregation degree of 1.0 or less is as uniform as possible in the width direction of the plate and the range in the width direction is as large as possible. When the solid fraction in the central portion is less than 0.5, the thickness of the region where the degree of segregation is 1.0 or less becomes uneven, and there is a possibility that a portion exceeding 1.0 may appear. The solid fraction in the center is
If bulging occurs after exceeding 0.7, bulging does not sufficiently occur, and the degree of segregation exceeds 1.0. Therefore, bulging occurs when the solid fraction at the center is in the range of 0.5 to 0.7. The bulging thickness is 11
If it is less than 0%, the Mn segregation degree cannot be reduced to 1.0 or less. In this case, it is preferable that the bulging is large. However, if the bulging exceeds 150%, there is a risk of side breakout, and more rolling force is required to reduce the pressure to the original thickness. Therefore, the short side length of the mold
110% to 150%.

【0034】バルジングを生じさせた後、中央部固相率
が0.7〜0.8となったとき、圧下して鋳片を元の鋳型の短
辺長さと同じ厚さに戻す。これは0.7未満ではMn偏析
度を1.0以下にできなくなるからであり、0.8を超えると
凝固層が厚くなりすぎ、元の鋳型の短辺長さまで圧下で
きなくなるからである。圧下する際、圧下ロール1対当
たりの圧下量を、鋳型の短辺長さの10%以上とするの
は、圧下を急激に生じさせ、成分の濃化した溶鋼をでき
るだけ効果的に押し戻すためで、圧下ロール1対当たり
の圧下量がこれを下回ると、Mn偏析度1.0を下回る領
域の形成が不十分となるためである。
After the bulging occurs, when the solid fraction in the center becomes 0.7 to 0.8, the slab is reduced to return the cast slab to the same thickness as the short side length of the original mold. This is because if it is less than 0.7, the Mn segregation degree cannot be reduced to 1.0 or less, and if it exceeds 0.8, the solidified layer becomes too thick, and it cannot be reduced to the short side length of the original mold. The reason why the amount of reduction per pair of reduction rolls is set to 10% or more of the length of the short side of the mold during the reduction is to cause the reduction rapidly and to push back the molten steel with the concentrated components as effectively as possible. If the amount of reduction per pair of reduction rolls is less than this, the formation of a region below the Mn segregation degree of 1.0 becomes insufficient.

【0035】[0035]

【実施例】鋳型直下から引き抜き方向に配列されたガイ
ドロールが鋳片厚さ方向の間隔が可変であり、凝固完了
点近傍にて鋳片の厚さを減じ得る圧下ロールを供えた連
続鋳造装置を用い、表1に示す組成の鋼の鋳片を鋳込ん
だ。鋳型の短辺は235mm、長辺は2260mmである。鋳込み
は、はじめ鋳型の厚さとし、凝固層を形成させてからバ
ルジングを生ぜしめ、さらに凝固層を発達させ、次いで
1対のロールにより圧下を加えて元の鋳型の短辺厚さと
した。バルジング開始時の固相率、バルジング厚さ、バ
ルジ圧下開始時の固相率等を表2に示す。得られた鋳片
は直ちに加熱炉に投入して1200℃に均熱後、炉より取り
出して熱間圧延をおこない、約900℃にて40mm厚に仕上
げた後、放冷した。
DESCRIPTION OF THE PREFERRED EMBODIMENTS A continuous casting apparatus provided with a rolling roll in which guide rolls arranged in a drawing direction from immediately below a mold are variable in a thickness direction of a slab and can reduce the thickness of a slab near a solidification completion point. , A steel slab having the composition shown in Table 1 was cast. The short side of the mold is 235 mm and the long side is 2260 mm. In the casting, the thickness of the mold was first set, a solidified layer was formed, bulging was caused, the solidified layer was further developed, and then a reduction was applied by a pair of rolls to the short side thickness of the original mold. Table 2 shows the solid phase ratio at the start of bulging, the bulging thickness, the solid phase ratio at the start of bulging reduction, and the like. The obtained slab was immediately put into a heating furnace, soaked at 1200 ° C., taken out of the furnace, subjected to hot rolling, finished at 40 ° C. at about 900 ° C., and allowed to cool.

【0036】[0036]

【表1】 [Table 1]

【0037】[0037]

【表2】 [Table 2]

【0038】各鋼番ともチャージのほぼ中央に相当する
位置から採取した、長さ10mの鋼板を対象に調査をおこ
なった。Mnの偏析度、および水素濃度は、幅方向の1
/4位置において、被調査鋼板の頭部、中央部、尾部の
3ヶ所で分析し、結果を平均した。超音波探傷は被調査
鋼板全面でおこない、水素性欠陥が1ヶでも見出された
場合は、欠陥ありと判定した。これらの結果も併せて表
2に示す。
Each steel number was examined for a steel plate having a length of 10 m, which was collected from a position substantially corresponding to the center of the charge. The segregation degree of Mn and the hydrogen concentration are 1 in the width direction.
At the / 4 position, analysis was performed at three locations: the head, center, and tail of the steel plate to be inspected, and the results were averaged. Ultrasonic flaw detection was performed on the entire surface of the steel sheet to be inspected, and when even one hydrogen defect was found, it was determined that there was a defect. Table 2 also shows these results.

【0039】表1の化学組成および表2の鋼板の調査結
果から明らかなように、[Mn]×[S]が0.005以下
で、かつ板厚中央部のMn偏析度が1以下の、試験番号
1、2および5の鋼板は、いずれも水素性欠陥が見いだ
せなかった。これに対し、試験番号3および4は、[M
n]×[S]が0.005を超えており、鋼板の水素濃度が
他の試験番号の鋼板より低く、Mn偏析度が1以下であ
るにもかかわらず、水素性欠陥が生じている。また、試
験番号6〜10は、バルジングまたはバルジ圧下の条件
が、本発明の範囲を逸脱しており、いずれも板厚中央部
のMn偏析度が1を超えている。このため、[Mn]×
[S]は0.005以下ではあるが、水素性欠陥が生じてい
る。
As is clear from the examination results of the chemical composition in Table 1 and the steel sheet in Table 2, the test numbers in which [Mn] × [S] is 0.005 or less and the degree of Mn segregation at the center of the sheet thickness is 1 or less. No hydrogen defects were found in any of the steel sheets 1, 2, and 5. In contrast, Test Nos. 3 and 4 indicate [M
n] × [S] exceeds 0.005, the hydrogen concentration of the steel sheet is lower than that of the steel sheets of other test numbers, and hydrogen defects are generated even though the Mn segregation degree is 1 or less. In Test Nos. 6 to 10, the conditions of bulging or bulging pressure deviated from the scope of the present invention, and the Mn segregation degree at the center of the plate thickness exceeded 1 in all cases. For this reason, [Mn] ×
Although [S] is 0.005 or less, hydrogen deficiency has occurred.

【0040】[0040]

【発明の効果】本発明の厚鋼板は、製造時における水素
性欠陥の発生し難い鋼板であり、連続鋳造にて鋳片を製
造しこれを圧延して厚鋼板とする場合、鋳片または圧延
直後の鋼板において、徐冷や保温などの脱水素処理を必
ずしも必要としない鋼板である。とくに近年、省エネル
ギーや工程簡略化のため、連続鋳造後の鋳片を冷却する
ことなく加熱炉に投入して温度を調整後圧延するダイレ
クトチャージ法や、鋳片をそのまま直ちに圧延する直接
圧延法が多く採用されるようになっているが、その場合
に発生しやすい鋼板の水素性欠陥の抑制に効果的であ
る。
The steel plate according to the present invention is a steel plate in which hydrogen defects are unlikely to occur during production. When a slab is manufactured by continuous casting and rolled into a thick steel plate, the slab or the rolled steel plate is used. The steel sheet immediately after the steel sheet does not necessarily require dehydrogenation treatment such as slow cooling and heat retention. In recent years, in order to save energy and simplify the process, in recent years, the direct charging method, in which a slab after continuous casting is put into a heating furnace without cooling and the temperature is adjusted and then rolled, or the direct rolling method in which the slab is immediately rolled as it is, without cooling, has been adopted. Although it is increasingly used, it is effective in suppressing hydrogen-induced defects in the steel sheet, which are likely to occur in such cases.

【図面の簡単な説明】[Brief description of the drawings]

【図1】鋼板のMn偏析度および鋼板の水素濃度と、鋼
板の水素性欠陥の有無との関係を示す図である。
FIG. 1 is a view showing the relationship between the degree of Mn segregation of a steel sheet and the hydrogen concentration of the steel sheet, and the presence or absence of hydrogen defects in the steel sheet.

【図2】鋼のMn濃度(%)とS濃度(%)との積およ
び鋼板の水素濃度と、鋼板の水素性欠陥の有無との関係
を示す図である。
FIG. 2 is a diagram showing the relationship between the product of the Mn concentration (%) and the S concentration (%) of steel, the hydrogen concentration of the steel sheet, and the presence or absence of hydrogen defects in the steel sheet.

フロントページの続き (56)参考文献 特開 平9−314298(JP,A) 特開 平9−57410(JP,A) 特開 平4−305350(JP,A) 特開 平10−244349(JP,A) 特開 平11−179489(JP,A) 特開 平11−61328(JP,A) 特開 平9−253703(JP,A) 特開 平6−179910(JP,A) 特開 昭63−20142(JP,A) (58)調査した分野(Int.Cl.7,DB名) B22D 11/16 B22D 11/128 350 B22D 11/20 C22C 38/00 301 Continuation of front page (56) References JP-A-9-314298 (JP, A) JP-A-9-57410 (JP, A) JP-A-4-305350 (JP, A) JP-A-10-244349 (JP) JP-A-11-179489 (JP, A) JP-A-11-61328 (JP, A) JP-A-9-253703 (JP, A) JP-A-6-179910 (JP, A) 63-20142 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) B22D 11/16 B22D 11/128 350 B22D 11/20 C22C 38/00 301

Claims (2)

(57)【特許請求の範囲】(57) [Claims] 【請求項1】鋼板の板厚をtとするとき、Mnの偏析度
が1.0以下である厚さ0.20t以下の領域が、板厚の1/2t
位置を中心とする±0.2tの範囲内に存在し、かつ鋼組
成の重量%で示すMnとSの含有量が Mn(%)×S(%)≦0.005 であることを特徴とする厚鋼板。
When the thickness of a steel sheet is represented by t, a region having a thickness of 0.20 t or less in which the degree of segregation of Mn is 1.0 or less is t t of the sheet thickness.
A thick steel plate which is present within a range of ± 0.2 t centered on the position, and wherein the content of Mn and S expressed by weight% of the steel composition is Mn (%) × S (%) ≦ 0.005. .
【請求項2】鋳造中の中心部未凝固の鋳片にてバルジン
グを生ぜしめ、その後鋳造ライン内に設けた圧下ロール
を用いて元の鋳型の短辺長さまで圧下する鋳片の連続鋳
造方法において、中心部固相率が0.5〜0.7の範囲でバル
ジングを生じさせて鋳片の最大厚さを鋳型短辺長さの11
0〜150%とし、次いで鋳片の中心部固相率が0.7〜0.8の
範囲で、1対の圧下ロール当たり前記鋳型短辺長さの10
%以上の圧下を加えて、厚鋼板の圧延素材となる鋳片と
することを特徴とする、請求項1に記載の厚鋼板の製造
方法。
2. A continuous casting method for casting slabs in which bulging is caused in a slab that is not solidified in the center during casting, and then reduced to the short side length of the original mold by using a reduction roll provided in a casting line. In, the bulging occurs in the center solid phase ratio in the range of 0.5 to 0.7, the maximum thickness of the slab is set to 11 of the short side length of the mold.
0 to 150%, and then, when the solid phase ratio in the center of the slab is in the range of 0.7 to 0.8, the length of the short side of the mold is 10 per pair of reduction rolls.
The method for producing a thick steel plate according to claim 1, wherein a slab that is a rolling material of the thick steel plate is formed by applying a reduction of at least%.
JP27561598A 1998-09-29 1998-09-29 Steel sheet free of hydrogen defects and method for producing the same Expired - Fee Related JP3298519B2 (en)

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