JP2004131794A - Method for dehydrogenation of steel sheet and method for manufacturing steel sheet using the same - Google Patents
Method for dehydrogenation of steel sheet and method for manufacturing steel sheet using the same Download PDFInfo
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、製鉄所における厚板等の鋼板製造工程における鋼板や、建築、造船、橋梁、建設機械、海洋構造物などの溶接構造物における溶接部周辺の鋼板に内在する水素を低減する鋼板の脱水素方法およびそれを用いた鋼板の製造方法に関する。
【０００２】
【従来の技術】
鋼板に内在する水素は、鋼板の靭性を低下させる。
特に、溶接部など、応力集中が発生し易い箇所は、この鋼板中に内在する水素が遅れ破壊の原因となるため、従来から、鋼板の脱水素方法が提案されている。
鋼中水素濃度の低減方法としては、溶鋼の脱ガス処理や、鋳込み後スラブの保温が実施され、さらに圧延後鋼板の加熱保温も行われる。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が可能であるが、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、鋳込み終了直後のスラブ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スラブ中の水素を表面まで拡散させて排除することによって行うことができる。この場合、厚いスラブ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、スラブの温度が低下してしまう。
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スラブを、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、水素起因の靭性低下や遅れ破壊が発生する危険性が増してくる。このため、圧延後の鋼板を積み重ねて徐冷のための場所、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（例えば、特許文献１参照。）。
なお、例えば、特許文献２に、溶接継手部に超音波振動を与えることによって、疲労強度を向上させる方法が開示されているが、超音波振動を鋼板の脱水素処理に利用することは開示されていない。
【０００３】
【特許文献１】特許第３２９８５１９号掲載公報
【特許文献２】米国特許第６，１７１，４１５号公報
【０００４】
【発明が解決しようとする課題】
本発明は、前述のような従来技術の問題点を解決し、鋼板の板厚方向に分散した水素を表層部に集めることによって、鋼板に内在する水素を十分に効率よく低減する鋼板の脱水素方法およびそれを用いた鋼板の製造方法を提供することを課題とする。
【０００５】
【課題を解決するための手段】
本発明は前述の課題を解決するために鋭意検討の結果なされたもので、鋼板の内部応力を増大させることによって、鋼板の板厚方向に分散した水素を表層部に誘導した後に加熱して、鋼板に内在する水素を十分に効率よく低減する鋼板の脱水素方法およびそれを用いた鋼板の製造方法を提供するものであり、その要旨とするところは特許請求の範囲に記載した通りの下記内容である。
【０００６】
（１）鋼板中に内在する水素を低減する鋼板の脱水素方法であって、前記鋼板の表層部の内部応力を増大させた後に、該表層部を１５０〜２２０℃に加熱することを特徴とする鋼板の脱水素方法。
（２）２００℃以下の前記鋼板の表面を、先端の径が５ｍｍ以上の超音波振動端子で打撃することにより、該鋼板の表層部の内部応力を増大させることを特徴とする（１）に記載の鋼板の脱水素方法。
（３）２００℃以下の前記鋼板の表面に、超音波振動を付与した鋼球を衝突させる超音波ショットピーニング処理を行うことにより、該鋼板の表層部の内部応力を増大させることを特徴とする（１）に記載の鋼板の脱水素方法。
（４）２００℃以下の前記鋼板の表層部を、誘導電流により加熱する誘導加熱装置を用いて加熱することを特徴とする（１）乃至（３）に記載の鋼板の脱水素方法。
（５）（１）乃至（４）に記載の鋼板の脱水素方法を用いることを特徴とする鋼板の製造方法。
【０００７】
【発明の実施の形態】
本発明の実施の形態について、以下に詳細に説明する。
まず、脱水素を行う前に、予め鋼板の表層部の内部応力を増大させる。
鋼板の板厚方向に分散している水素は、内部応力の高い部分に集まる性質があるので、鋼板の表層部の内部応力を増大させることによって、この部分に水素を誘導して偏在させることにより、水素を除去し易くすることができる。
【０００８】
本発明においては、鋼板表層部の内部応力を高める手段は問わないが、脱水素を行う箇所の鋼板表面を先端の直径が５ｍｍ以上の超音波振動端子（ハンマー）で打撃する方法（Ｕｌｔｒａｓｏｎｉｃ Ｉｍｐａｃｔ Ｔｒｅａｔｍｅｎｔ、ＵＩＴ）が好ましい。
鋼板表面を超音波振動端子で打撃することによって、鋼板表面に深さ数百μｍの圧痕を形成することができ、これによって、前述の鋼板表層部の内部応力を鋼板の降伏応力の約３０％以上に増加させることができる。
前記鋼板の表層部は２００℃以下であることが好ましい。表層部の温度が２００℃を超えると、ＵＩＴで内部応力を高めようとしても鋼板が軟化しており容易に塑性変形してしまい、加工が板厚内部まで伝達しなくなるからである。
超音波振動端子の先端の径を５ｍｍ以上とするのは、先端の径が大きい方が鋼板表面の広い範囲を打撃することができ、より広範囲で深い範囲の内部応力を高めることができるからである。ただし、３０ｍｍを超えると、超音波源の出力が大きくなり過ぎて工業的に成り立たないので、超音波振動端子（ハンマー）の先端の直径は１０〜３０ｍｍが好ましい。
本発明においては、前述のハンマーで打撃する際の鋼板温度は、脱水素に影響が少ないので、省エネルギーの観点から１５０℃以下が好ましい。
【０００９】
また、本発明に使用する超音波発生装置は問わないが、２００ｗ〜３ｋｗの電源を用いて、トランスデューサによって１９Ｈｚ〜６０Ｈｚの超音波振動を発生させ、ウェーブガイドにて増幅させることにより、５ｍｍ〜３０ｍｍφのピンからなる超音波振動端子を２０〜６０μｍの振幅で振動させる装置が好ましい。
また、超音波振動端子の代わりに、超音波により振動を与えた直径１〜３ｍｍの鋼球を鋼板表面に衝突させる超音波ショットピーニング処理を行うことにより、より広い範囲の内部応力を増大させることができるので、製鉄所において、鋼板を製造する際に、圧延後脱水素処理を実施する際でも、鋼板表層部の内部応力を増大させ、水素を表層に集めてから、焼き戻し炉を短時間通過させれば、効率的に脱水素を行うことができる。
【００１０】
鋼板表層部の加熱温度は、１５０〜２２０℃とする。
水素は１５０〜２２０℃の範囲まで加熱すれば拡散し易くなり、鋼板表層部に集まった水素が大気中に放散されるからであり、１５０℃未満では鋼板中の水素の除去が不十分であり、２２０℃超まで加熱しても除去できる水素の量は飽和してしまううえ、鋼板温度が２５０℃以上になると青熱脆化を起こして靭性が劣化する場合があるほか、３００℃以上になると鋼板の強度が圧延ままの材料よりも低下してしまうからである。
ここに、加熱する鋼板の表層部は、脱水素を行う箇所の鋼板表面から板厚方向に４ｍｍ以上の深さまで、２０分以上加熱することが好ましい。
脱水素を行うためには、板厚方向により深く、長い時間加熱することが好ましいが、本発明においては鋼板の表層部に水素が集められているので、板厚方向に４ｍｍ以上の深さまで、２０分以上加熱することで十分に脱水素を行うことができる。
本発明においては、鋼板表層部の加熱方法は問わないので、前述のような焼き戻し炉を用いて加熱してもよいが、水素による遅れ破壊が懸念される応力集中部などに限定して加熱するためには、誘導電流により加熱する誘導加熱装置を用いて加熱することが好ましい。
なお、以上説明した鋼板の脱水素方法を用いて鋼板を製造することによって、鋼板に内在する水素が少なく、靭性の優れた鋼板を製造することができる。
【００１１】
【実施例】
本発明における鋼板の脱水素方法の実施例を表１乃至表４に示す。
表１および表２は、厚板の製造工程において脱水素処理を行った実施例を示す。
表１に示す化学成分および製造プロセスを用いた厚板に、超音波打撃処理（ＵＩＴ処理）と脱水素処理を行った結果を表２に示す。
脱水素の評価は、試験片に切欠き（ノッチ）を設けて、脆性の指標であるＫｃ値を測定するディープノッチ試験（金沢武、越賀房夫著、「脆性破壊２−破壊靭性試験−、破壊力学と材料強度講座８」，培風館，１９７７年９月２０日、ｐｐ８−１４参照。）により行い、切欠きの底部に水素性の脆性破面が無い場合を脱水素が良好とし、切欠きの底部に水素性の脆性破面が有る場合を脱水素が不良とした。
この水素性の脆性破面は、水素が一定量以上含まれている鋼材に負荷している最中に形成される破面であって、それが自然にき裂になるため、き裂先端の応力集中が増大し、１５０（Ｎ／ｍｍ１．５）以下の低いＫｃ値にて破断する。
【００１２】
ＮＯ．１〜ＮＯ．５は、本発明例であり、表１に示す化学成分のスラブを１０００〜１１００℃に加熱して圧延し、鋼板表面を先端の直径が１０〜３０ｍｍの超音波端子（ハンマー）で打撃した後、１８０〜２２０℃まで加熱して脱水素処理を行ったところ、本発明の条件を全て満足しているので、前述のディープノッチ試験の結果、切欠きの底部に水素性の破面は無く、脱水素は良好だった。
ＮＯ．６〜ＮＯ．１０は、比較例であり、表１に示す化学成分のスラブを１０００〜１１００℃に加熱して圧延し、本発明と異なる条件で脱水素処理を行う場合と、
脱水素処理を行わない場合について、前述のディープノッチ試験を行った。
【００１３】
ＮＯ．６は、ハンマーの直径が１ｍｍと小さいうえ、脱水素のための加熱温度が１００℃と低過ぎるので、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素は不良だった。
ＮＯ．７は、水素熱処理温度が２５０℃と高く青熱脆化が起こったために、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素も不良だった。
ＮＯ．８は、ＵＩＴプロセスでの処理温度が３００℃と高いため、ＵＩＴで内部応力を高めようとしても鋼板が軟化しており容易に塑性変形してしまい、加工が板厚内部まで伝達しないので、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素も不良だった。
ＮＯ．９およびＮＯ．１０は、脱水素処理を行わなかったので、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素は不良だった。
本発明における鋼板の脱水素方法の実施例を表１乃至表４に示す。
表３および表４は、溶接部に脱水素処理を行った実施例を示す。
表３に示す化学成分および製造プロセスを用いた厚板に、種々の溶接方法にて溶接した溶接継手に、部超音波打撃処理（ＵＩＴ処理）と脱水素処理を行った結果を表４に示す。
脱水素の評価は、前述の厚板の実施例と同様である。
【００１４】
ＮＯ．１１〜ＮＯ．１５は、本発明例であり、表１に示す化学成分の厚板同士を種々の溶接方法にて溶接した継手表面を先端の直径が１０〜３０ｍｍの超音波端子（ハンマー）で打撃した後、１８０〜２２０℃まで加熱して脱水素処理を行ったところ、本発明の条件を全て満足しているので、前述のディープノッチ試験の結果、切欠きの底部に水素性の破面は無く、脱水素は良好だった。
ＮＯ．１６〜ＮＯ．２０は、比較例であり、表１に示す化学成分の厚板同士を種々の溶接方法にて溶接し、本発明と異なる条件で脱水素処理を行う場合と、脱水素処理を行わない場合について、前述のディープノッチ試験を行った。
【００１５】
ＮＯ．１６は、ハンマーの直径が１ｍｍと小さいうえ、脱水素のための加熱温度が１００℃と低過ぎるので、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素は不良だった。
ＮＯ．１７は、水素熱処理温度が２５０℃と高く青熱脆化が起こったために、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素も不良だった。
ＮＯ．１８は、ＵＩＴプロセスでの処理温度が３００℃と高いため、ＵＩＴで内部応力を高めようとしても鋼板が軟化しており容易に塑性変形してしまい、加工が板厚内部まで伝達しないので、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素も不良だった。
ＮＯ．１９およびＮＯ．２０は、脱水素処理を行わなかったので、Ｋｃ値が低く、切欠きの底部に水素性の破面が認められたので、脱水素は不良だった。
なお、本実施例におけるＵＩＴ処理は、超音波振動端子で鋼板表面を打撃する方法としたが、直径１〜３ｍｍの鋼球を鋼板表面に衝突させる超音波ショットピーニング処理に代えても効果は変わらない。
【００１６】
【発明の効果】
本発明によれば、鋼板の内部応力を増大させることによって、鋼板の板厚方向に分散した水素を表層部に誘導した後に加熱して、鋼板に内在する水素を十分に効率よく低減する鋼板の脱水素方法およびそれを用いた鋼板の製造方法を提供することができ、産業上有用な著しい効果を奏する。
【表１】
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steel plate in a steel plate manufacturing process such as a thick plate in a steel mill, and a steel plate for reducing hydrogen contained in a steel plate around a welded portion in a welded structure such as a building, a shipbuilding, a bridge, a construction machine, and a marine structure. The present invention relates to a dehydrogenation method and a method for producing a steel sheet using the same.
[0002]
[Prior art]
Hydrogen present in the steel sheet reduces the toughness of the steel sheet.
In particular, in places where stress concentration is likely to occur, such as welds, hydrogen present in the steel sheet causes delayed fracture, and therefore, a method of dehydrogenating a steel sheet has been conventionally proposed.
As a method for reducing the hydrogen concentration in steel, degassing of molten steel, heat retention of the slab after casting, and heat retention of the steel sheet 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 degassing time.However, if the processing time is long, the processing cost increases, and the time is limited by the continuous casting cycle. is there. A more sufficient reduction in the hydrogen concentration is to stack the slabs immediately after the end of casting at intervals, cover them with a cover, etc. to keep them warm, and prolong the high-temperature time to diffuse hydrogen in the slabs to the surface and eliminate them. Can be done by In this case, the diffusion of hydrogen takes a long time in a thick slab, so that it needs to be left for several days or more, and the temperature of the slab decreases.
In recent years, from the viewpoint of efficient use of energy and shortening of the manufacturing process, the hot slab immediately after casting is immediately adjusted to the required temperature without cooling, and hot-rolling or rolling is performed directly to the product dimensions. Many 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. The danger of reduced toughness and delayed fracture increases. For this reason, it is inevitable that there is a problem in the process, such as a place for stacking rolled steel sheets for slow cooling, a heating and heat keeping facility, and an increase in the required time due to such a place (for example, see Patent Document 1).
In addition, for example, Patent Literature 2 discloses a method of improving fatigue strength by applying ultrasonic vibration to a welded joint. However, it is disclosed that ultrasonic vibration is used for dehydrogenation of a steel sheet. Not.
[0003]
[Patent Document 1] Japanese Patent No. 3298519 [Patent Document 2] US Pat. No. 6,171,415
[Problems to be solved by the invention]
The present invention solves the problems of the prior art as described above, and collects hydrogen dispersed in the thickness direction of the steel sheet in the surface layer, thereby sufficiently efficiently reducing the hydrogen present in the steel sheet. It is an object to provide a method and a method for manufacturing a steel sheet using the method.
[0005]
[Means for Solving the Problems]
The present invention has been made as a result of intensive studies to solve the above-mentioned problems, by increasing the internal stress of the steel sheet, by heating the hydrogen dispersed in the thickness direction of the steel sheet to the surface layer and then heating, It is intended to provide a method for dehydrogenating a steel sheet and a method for manufacturing a steel sheet using the same, in which hydrogen contained in the steel sheet is sufficiently and efficiently reduced, and the gist thereof is as described in the claims below. It is.
[0006]
(1) A method for dehydrogenating a steel sheet for reducing hydrogen present in the steel sheet, wherein after increasing the internal stress of the surface part of the steel sheet, the surface part is heated to 150 to 220 ° C. Steel sheet dehydrogenation method.
(2) The internal stress of the surface layer of the steel sheet is increased by hitting the surface of the steel sheet at a temperature of 200 ° C. or less with an ultrasonic vibration terminal having a tip diameter of 5 mm or more. A method for dehydrogenating a steel sheet as described in the above.
(3) The internal stress of the surface layer portion of the steel sheet is increased by performing an ultrasonic shot peening process in which a steel ball to which ultrasonic vibration is applied collides with the surface of the steel sheet at 200 ° C or lower. The method for dehydrogenating a steel sheet according to (1).
(4) The method for dehydrogenating a steel sheet according to any one of (1) to (3), wherein the surface layer of the steel sheet at a temperature of 200 ° C. or lower is heated using an induction heating device that heats the steel sheet by an induction current.
(5) A method for producing a steel sheet, comprising using the method for dehydrogenating a steel sheet according to any one of (1) to (4).
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described in detail below.
First, before performing dehydrogenation, the internal stress of the surface layer of the steel sheet is increased in advance.
Hydrogen dispersed in the thickness direction of the steel sheet has the property of gathering in parts with high internal stress, so by increasing the internal stress in the surface layer of the steel sheet, hydrogen is induced in this part and unevenly distributed , And can easily remove hydrogen.
[0008]
In the present invention, a means for increasing the internal stress of the surface layer of the steel sheet is not limited, but a method of hitting the surface of the steel sheet at a location to be dehydrogenated with an ultrasonic vibration terminal (hammer) having a tip diameter of 5 mm or more (Ultrasonic Impact Treatment). , UIT) are preferred.
By hitting the surface of the steel sheet with an ultrasonic vibration terminal, an indentation having a depth of several hundred μm can be formed on the surface of the steel sheet, thereby reducing the internal stress of the surface layer of the steel sheet to about 30% of the yield stress of the steel sheet. It can be increased above.
It is preferable that the surface portion of the steel sheet is 200 ° C. or lower. If the temperature of the surface layer exceeds 200 ° C., the steel sheet is softened and easily plastically deformed even if an attempt is made to increase the internal stress in the UIT, so that the work is not transmitted to the inside of the sheet thickness.
The reason why the diameter of the tip of the ultrasonic vibration terminal is set to 5 mm or more is that a larger tip diameter can hit a wider range of the steel sheet surface and can increase the internal stress in a wider range and a deeper range. is there. However, if it exceeds 30 mm, the output of the ultrasonic source becomes too large to be industrially feasible. Therefore, the diameter of the tip of the ultrasonic vibration terminal (hammer) is preferably 10 to 30 mm.
In the present invention, the temperature of the steel sheet at the time of hitting with the above-mentioned hammer is preferably 150 ° C. or less from the viewpoint of energy saving because it has little effect on dehydrogenation.
[0009]
Also, the ultrasonic generator used in the present invention is not limited, and the ultrasonic vibration of 19 Hz to 60 Hz is generated by a transducer using a power supply of 200 w to 3 kw, and amplified by a waveguide, thereby obtaining 5 mm to 30 mm φ. It is preferable to use an apparatus that vibrates an ultrasonic vibration terminal composed of a pin having an amplitude of 20 to 60 μm.
In addition, instead of the ultrasonic vibration terminal, the internal stress in a wider range is increased by performing an ultrasonic shot peening process in which a steel ball having a diameter of 1 to 3 mm vibrated by ultrasonic waves collides against a steel sheet surface. In steel mills, when producing steel sheets, even when performing dehydrogenation treatment after rolling, the internal stress of the steel sheet surface layer is increased, hydrogen is collected on the surface layer, and then the tempering furnace is operated for a short time. If it is passed, dehydrogenation can be performed efficiently.
[0010]
The heating temperature of the surface layer of the steel sheet is 150 to 220 ° C.
Hydrogen is easily diffused when heated to the range of 150 to 220 ° C., because hydrogen collected on the surface layer of the steel sheet is diffused into the atmosphere. At less than 150 ° C., the removal of hydrogen in the steel sheet is insufficient. , The amount of hydrogen that can be removed even when heated to over 220 ° C. saturates, and when the steel sheet temperature exceeds 250 ° C., blue heat embrittlement may occur and the toughness may deteriorate. This is because the strength of the steel sheet is lower than that of the as-rolled material.
Here, it is preferable that the surface layer portion of the steel sheet to be heated is heated from the surface of the steel sheet at the location where dehydrogenation is performed to a depth of 4 mm or more in the thickness direction for 20 minutes or more.
In order to perform dehydrogenation, it is preferable to heat deeper in the sheet thickness direction and for a long time, but in the present invention, since hydrogen is collected in the surface layer portion of the steel sheet, to a depth of 4 mm or more in the sheet thickness direction, Dehydrogenation can be sufficiently performed by heating for 20 minutes or more.
In the present invention, since the heating method of the surface layer portion of the steel sheet does not matter, the heating may be performed using the above-described tempering furnace, but the heating is limited to the stress concentrated portion where delayed fracture due to hydrogen is a concern. In order to perform the heating, it is preferable to perform heating using an induction heating device that heats by an induction current.
In addition, by manufacturing a steel sheet using the above-described steel sheet dehydrogenation method, it is possible to manufacture a steel sheet having less hydrogen contained in the steel sheet and having excellent toughness.
[0011]
【Example】
Tables 1 to 4 show examples of the method for dehydrogenating steel sheets in the present invention.
Tables 1 and 2 show examples in which the dehydrogenation treatment was performed in the manufacturing process of the thick plate.
Table 2 shows the results obtained by performing an ultrasonic impact treatment (UIT treatment) and a dehydrogenation treatment on a thick plate using the chemical components and the production process shown in Table 1.
The evaluation of dehydrogenation was performed by a notch (notch) in the test piece and a deep notch test in which a Kc value as an index of brittleness was measured (taken by Takeshi Kanazawa and Fumio Koshiga, "brittle fracture 2-fracture toughness test- Destruction Mechanics and Material Strength Course 8 ", Baifukan, September 20, 1977, pp. 8-14.) Dehydrogenation is considered to be good if there is no brittle brittle fracture surface at the bottom of the notch. When there was a brittle brittle fracture surface at the bottom of the sample, the dehydrogenation was regarded as poor.
This hydrogen brittle fracture surface is a fracture surface formed during loading on a steel material containing a certain amount of hydrogen or more. Stress concentration increases, and fracture occurs at a low Kc value of 150 (N / mm 1.5 ) or less.
[0012]
NO. 1 to NO. 5 is an example of the present invention, in which a slab of a chemical component shown in Table 1 is heated to 1000 to 1100 ° C., rolled, and the steel plate surface is hit with an ultrasonic terminal (hammer) having a tip diameter of 10 to 30 mm. When heated to 180 to 220 ° C. and subjected to dehydrogenation treatment, all the conditions of the present invention are satisfied. As a result of the above-described deep notch test, there is no hydrogenated fracture surface at the bottom of the notch, Dehydrogenation was good.
NO. 6 to NO. Reference numeral 10 denotes a comparative example, in which a slab of a chemical component shown in Table 1 is heated to 1000 to 1100 ° C., rolled, and dehydrogenated under conditions different from those of the present invention;
The above-described deep notch test was performed in the case where the dehydrogenation treatment was not performed.
[0013]
NO. In No. 6, since the diameter of the hammer was as small as 1 mm and the heating temperature for dehydrogenation was too low at 100 ° C., the Kc value was low, and a hydrogen-based fracture surface was observed at the bottom of the notch. Was bad.
NO. In No. 7, since the hydrogen heat treatment temperature was as high as 250 ° C. and blue heat embrittlement occurred, the Kc value was low, and a hydrogen-based fracture surface was recognized at the bottom of the notch, and the dehydrogenation was also poor.
NO. In No. 8, since the processing temperature in the UIT process is as high as 300 ° C., the steel sheet is softened and easily plastically deformed even if an attempt is made to increase the internal stress in the UIT. Dehydrogenation was poor because of the low value and the presence of a hydrogen rupture at the bottom of the notch.
NO. 9 and NO. In No. 10, since the dehydrogenation treatment was not performed, the Kc value was low, and a hydrogen-based fracture surface was observed at the bottom of the notch, so that the dehydrogenation was poor.
Tables 1 to 4 show examples of the method for dehydrogenating steel sheets in the present invention.
Tables 3 and 4 show Examples in which a dehydrogenation treatment was performed on the welded portion.
Table 4 shows the results of partial ultrasonic impact treatment (UIT treatment) and dehydrogenation treatment on a welded joint obtained by welding to a thick plate using the chemical components and manufacturing processes shown in Table 3 by various welding methods. .
Evaluation of dehydrogenation is the same as that of the above-mentioned thick plate example.
[0014]
NO. 11 to NO. Reference numeral 15 denotes an example of the present invention, in which a joint surface obtained by welding thick plates of the chemical components shown in Table 1 by various welding methods is hit with an ultrasonic terminal (hammer) having a tip diameter of 10 to 30 mm. When the dehydrogenation treatment was performed by heating to 180 to 220 ° C., all the conditions of the present invention were satisfied. As a result of the above-described deep notch test, there was no hydrogen fracture surface at the bottom of the notch, and The quality was good.
NO. 16 to NO. Reference numeral 20 denotes a comparative example, in which thick plates having the chemical components shown in Table 1 are welded to each other by various welding methods and dehydrogenation treatment is performed under conditions different from those of the present invention, and when dehydrogenation treatment is not performed The deep notch test described above was performed.
[0015]
NO. In No. 16, since the diameter of the hammer was as small as 1 mm and the heating temperature for dehydrogenation was too low at 100 ° C., the Kc value was low, and a hydrogen-based fracture surface was observed at the bottom of the notch. Was bad.
NO. In No. 17, since the hydrogen heat treatment temperature was as high as 250 ° C. and blue heat embrittlement occurred, the Kc value was low, and a hydrogen-based fracture surface was observed at the bottom of the notch, and the dehydrogenation was also poor.
NO. In No. 18, since the processing temperature in the UIT process is as high as 300 ° C., the steel sheet is softened and easily plastically deformed even if an attempt is made to increase the internal stress in the UIT. Dehydrogenation was poor because of the low value and the presence of a hydrogen rupture at the bottom of the notch.
NO. 19 and NO. Sample No. 20 was not dehydrogenated, and had a low Kc value, and a hydrogen-based fracture surface was observed at the bottom of the notch, so that dehydrogenation was poor.
Although the UIT treatment in the present embodiment was a method of hitting the steel sheet surface with an ultrasonic vibration terminal, the effect does not change even when the ultrasonic shot peening treatment in which a steel ball having a diameter of 1 to 3 mm collides with the steel sheet surface is performed. Absent.
[0016]
【The invention's effect】
According to the present invention, by increasing the internal stress of the steel sheet, the hydrogen dispersed in the thickness direction of the steel sheet is heated after being guided to the surface layer, and the hydrogen present in the steel sheet is sufficiently efficiently reduced. A dehydrogenation method and a method for producing a steel sheet using the same can be provided, and a remarkable industrially useful effect is achieved.
[Table 1]
Claims (5)
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