JPH1060575A - Thick steel plate excellent in fatigue crack arrest characteristic - Google Patents
Thick steel plate excellent in fatigue crack arrest characteristicInfo
- Publication number
- JPH1060575A JPH1060575A JP22116396A JP22116396A JPH1060575A JP H1060575 A JPH1060575 A JP H1060575A JP 22116396 A JP22116396 A JP 22116396A JP 22116396 A JP22116396 A JP 22116396A JP H1060575 A JPH1060575 A JP H1060575A
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- Prior art keywords
- ferrite
- phase
- steel
- hard
- hardness
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、土木建築構造物、
船体、海洋構造物及びラインパイプ等の素材として好適
な、大気中又は腐食環境中において疲労亀裂進展抑制特
性に優れた厚鋼板及びその製造方法に関する。TECHNICAL FIELD The present invention relates to a civil engineering building structure,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate excellent in fatigue crack growth suppression characteristics in the atmosphere or in a corrosive environment, and a method for manufacturing the same, which is suitable as a material for a hull, an offshore structure, a line pipe, or the like.
【０００２】[0002]
【従来の技術】近年、鋼構造物全般の大型化及び軽量化
の傾向が著しく、このため、構造用厚鋼板の高強度化が
望まれている。船体用鋼板等でも、大型化及びコストダ
ウンの観点から高張力鋼の使用が拡大している。しか
し、高強度鋼板を溶接鋼構造物に使用しても、溶接部か
ら疲労亀裂が発生し進展してしまい、母材の高強度化に
見合って、溶接鋼構造物全体の高強度化が達成されない
場合が多い。従って、溶接部から発生し進展する疲労亀
裂を母材で停留させることができれば、構造物の疲労寿
命を延長することができる。2. Description of the Related Art In recent years, there has been a remarkable tendency to increase the size and weight of steel structures in general, and therefore, it has been desired to increase the strength of structural steel plates. For steel plates for hulls, the use of high-strength steel is increasing from the viewpoint of increasing the size and reducing costs. However, even when a high-strength steel plate is used for a welded steel structure, fatigue cracks are generated and propagated from the weld, and the entire welded steel structure has been strengthened in proportion to the strength of the base metal Often not. Therefore, if the fatigue crack generated and propagated from the weld can be stopped at the base material, the fatigue life of the structure can be extended.
【０００３】疲労亀裂の進展を停留させ疲労寿命の長期
化を図る方法として、疲労亀裂先端にマイクロクラック
を発生させる方法がある（特開平５−１４８５４１号公
報）。しかし、この方法の効果は、低いΔＫの範囲、す
なわち、亀裂が長くなく応力レベルが低い場合に限られ
る。ここに、△Ｋとは、疲労亀裂を発生し進展させる周
期的な負荷サイクルにおける最大応力拡大係数と最小応
力拡大係数との差をいう。なお、応力拡大係数は、応力
集中を考慮した亀裂先端での負荷状態をあらわす値であ
り、負荷応力と亀裂長さの平方根との積に比例する。As a method of prolonging the fatigue life by stopping the growth of the fatigue crack, there is a method of generating a microcrack at the tip of the fatigue crack (Japanese Patent Laid-Open No. 5-148541). However, the effect of this method is limited to the low ΔK range, ie, long cracks and low stress levels. Here, ΔK refers to the difference between the maximum stress intensity factor and the minimum stress intensity factor in a periodic load cycle in which a fatigue crack is generated and propagated. The stress intensity factor is a value representing a load state at the crack tip in consideration of stress concentration, and is proportional to the product of the applied stress and the square root of the crack length.
【０００４】このマイクロクラックを発生させることに
よる疲労亀裂進展速度の抑制方法は、溶接部から発生し
た亀裂がある程度の長さとなり、中程度のΔＫの範囲の
負荷サイクルを受ける亀裂に関しては、実効をあげにく
いと考えられる。[0004] This method of suppressing the growth rate of fatigue cracks by generating microcracks is effective for cracks generated from welds having a certain length and subject to a load cycle in a medium ΔK range. It is considered difficult to give.
【０００５】また、疲労強度が重要な特性である自動車
用ホイ−ルをはじめとする各種用途の熱延鋼板に関し
て、２相組織中の母相と第２相の硬度の差、各組織の体
積率、及び第２相の粒径を限定すれば、良好な疲労強度
が得られるとの提案がされている（特開平４−３２９８
４８号公報）。しかしながら、疲労亀裂の進展挙動につ
いて十分に検討がなされているとは言えず、疲労強度を
高める点で十分とはいいがたい。[0005] Further, regarding hot-rolled steel sheets for various uses such as wheels for automobiles in which fatigue strength is an important characteristic, the difference in hardness between the parent phase and the second phase in the two-phase structure and the volume of each structure. It has been proposed that if the ratio and the particle size of the second phase are limited, good fatigue strength can be obtained (JP-A-4-3298).
No. 48). However, it cannot be said that the fatigue crack propagation behavior has been sufficiently studied, and it is not sufficient to increase the fatigue strength.
【０００６】さらに、特開平７−１１３８３号公報には
第２相の平均径を２０μｍ以下とすることにより疲労限
の向上を図る鋼板が開示されているが、ビッカース硬さ
で４００以上という、極めて高い第２相の硬さが必要で
あり、鋼板の靭性が重視される厚鋼板では直ちに採用し
にくいところがある。[0006] Further, Japanese Patent Application Laid-Open No. 7-11383 discloses a steel sheet for improving the fatigue limit by setting the average diameter of the second phase to 20 µm or less, but it has a very high Vickers hardness of 400 or more. A high hardness of the second phase is required, and it is difficult to immediately adopt a thick steel plate in which the toughness of the steel plate is important.
【０００７】これまでのところ、上記のように疲労限度
に及ぼす組織の影響は調査されているが、５００μｍを
超えるような長い亀裂の進展速度については、材料の組
織の影響を受けにくいことが指摘されているのみで、進
展を抑制するための具体的方法は示されていないのが実
状である。So far, the influence of the structure on the fatigue limit has been investigated as described above. However, it has been pointed out that the growth rate of a long crack exceeding 500 μm is hardly affected by the structure of the material. In fact, no specific method has been shown to control progress.
【０００８】[0008]
【発明が解決しようとする課題】本発明の目的は、靭性
を具備したうえで疲労亀裂長さの短い範囲に限定され
ず、△Ｋの小〜中程度の範囲にわたって疲労亀裂進展抑
制特性に優れた厚鋼板、特に、土木建築構造物や船体、
海洋構造物、ラインパイプ等への使用に好適な厚鋼板及
びその製造方法を提供することにある。SUMMARY OF THE INVENTION An object of the present invention is not limited to a short range of fatigue crack length while having toughness, and it is excellent in fatigue crack growth suppressing properties over a small to medium range of ΔK. Steel plates, especially civil engineering structures and hulls,
An object of the present invention is to provide a thick steel plate suitable for use in an offshore structure, a line pipe, and the like, and a method for manufacturing the same.
【０００９】[0009]
【課題を解決するための手段】本発明は、疲労挙動に及
ぼす材料因子について得た次の〜の事項に基づいて
いる。SUMMARY OF THE INVENTION The present invention is based on the following items obtained on the material factors affecting the fatigue behavior.
【００１０】鋼材の組織をフェライトとマルテンサイ
ト等の硬質相からなる混合組織として硬質相の形態と大
きさを制御するか、又は、フェライトの形態と大きさを
制御したうえで、硬質相とフェライトの硬度差をある値
以上にすると、疲労亀裂進展速度が抑制される。このと
き、疲労亀裂はフェライト相中を伝搬しフェライトと硬
質相の界面近傍に到達すると、亀裂先端での塑性変形が
抑制され、疲労亀裂の停留が起こる。フェライト相と硬
質相の硬度差を大きくするほど、界面において疲労亀裂
の停留が生じやすい。[0010] The structure of the steel material is a mixed structure comprising ferrite and a hard phase such as martensite to control the form and size of the hard phase, or to control the form and size of the ferrite, When the hardness difference is more than a certain value, the fatigue crack growth rate is suppressed. At this time, when the fatigue crack propagates in the ferrite phase and reaches near the interface between the ferrite and the hard phase, plastic deformation at the crack tip is suppressed, and the fatigue crack stops. As the hardness difference between the ferrite phase and the hard phase is increased, retention of fatigue cracks is more likely to occur at the interface.
【００１１】Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏのいずれかを少
量添加することにより、鋼材の耐食性等を向上させる
と、腐食環境中においても疲労亀裂進展抑制特性を向上
させる効果が期待できる。When the corrosion resistance and the like of a steel material are improved by adding a small amount of any of Cu, Ni, Cr and Mo, an effect of improving the fatigue crack growth suppressing property even in a corrosive environment can be expected.
【００１２】Ｎｂ、Ｖのいずれかを含有させると、こ
れらの炭窒化物を生成することによりフェライトのマト
リックスが強化され、フェライト内を進展する疲労亀裂
進展速度が低下する。When any of Nb and V is contained, the formation of these carbonitrides strengthens the ferrite matrix and lowers the fatigue crack growth rate in the ferrite.
【００１３】本発明は、上記の諸事項を満たす鋼板につ
いて疲労試験を遂行することによって完成されたもの
で、下記の化学組成及び組織からなる厚鋼板及びその製
造方法を要旨とする。The present invention has been completed by performing a fatigue test on a steel sheet satisfying the above-mentioned various matters, and has a gist of a thick steel sheet having the following chemical composition and structure and a method of manufacturing the same.
【００１４】（１）重量％にて、Ｃ：０．０４〜０．２
５％、Ｓｉ：０．１〜０．５％、Ｍｎ：０．４〜２％、
sol.Ａｌ：０．００５〜０．１％、Ｎ：０．００１〜
０．００５％、Ｔｉ：０〜０．０３％、Ｂ：０〜０．０
０２５％、Ｃｕ：０〜１％、Ｎｉ：０〜０．５％、Ｃ
ｒ：０〜１％、Ｍｏ：０〜０．６％、Ｎｂ：０〜０．０
６％及びＶ：０〜０．１％を含み、残部はＦｅと不可避
不純物からなる化学組成を有し、その組織はフェライト
相及び１種以上の硬質相からなる混合組織の鋼であっ
て、フェライト相と各々の硬質相との硬度差がビッカー
ス硬さで１５０以上であり、１種以上の硬質相からなる
硬質相の集合体はフェライト相のなかで塊状であり、そ
の平均径が６〜５０μｍである疲労亀裂進展抑制特性に
優れた厚鋼板（〔発明１〕とする）。(1) C: 0.04 to 0.2% by weight
5%, Si: 0.1 to 0.5%, Mn: 0.4 to 2%,
sol. Al: 0.005 to 0.1%, N: 0.001 to
0.005%, Ti: 0 to 0.03%, B: 0 to 0.0
025%, Cu: 0 to 1%, Ni: 0 to 0.5%, C
r: 0 to 1%, Mo: 0 to 0.6%, Nb: 0 to 0.0
6% and V: 0 to 0.1%, with the balance having a chemical composition consisting of Fe and inevitable impurities, the structure of which is a mixed structure steel comprising a ferrite phase and at least one hard phase, The difference in hardness between the ferrite phase and each hard phase is Vickers hardness of 150 or more, and the aggregate of the hard phase composed of one or more hard phases is a lump in the ferrite phase and has an average diameter of 6 to A thick steel plate having excellent fatigue crack growth suppression properties of 50 μm (referred to as [Invention 1]).
【００１５】（２）〔発明１〕に記載する化学組成を有
しフェライト相及び１種以上の硬質相からなる混合組織
の鋼であって、フェライト相と各硬質相との硬度差がビ
ッカース硬さで１５０以上であり、１以上のフェライト
粒からなるフェライト粒の集合体は硬質相のなかで塊状
であり、その集合体の平均径が５０μｍ以下である疲労
亀裂進展抑制特性に優れた厚鋼板（〔発明２〕とす
る）。(2) A steel having the chemical composition described in [Invention 1] and having a mixed structure comprising a ferrite phase and at least one hard phase, wherein the hardness difference between the ferrite phase and each hard phase is Vickers hardness. Thick steel sheet excellent in fatigue crack growth suppression properties, wherein the aggregate of ferrite grains comprising at least one ferrite grain is a lump in a hard phase, and the average diameter of the aggregate is 50 μm or less. (Referred to as [Invention 2]).
【００１６】（３）〔発明１〕に記載する化学組成を有
する鋼をオーステナイト相とフェライト相の混合状態か
ら焼入れる処理を含む〔発明１〕又は〔発明２〕に記載
する疲労亀裂進展抑制特性に優れた厚鋼板の製造方法
（〔発明３〕とする）。(3) Fatigue crack growth inhibiting properties described in [Invention 1] or [Invention 2] including a process of quenching a steel having the chemical composition described in [Invention 1] from a mixed state of an austenitic phase and a ferrite phase. A method for manufacturing a thick steel plate excellent in quality (referred to as [Invention 3]).
【００１７】上記において、硬質相とは、マルテンサイ
ト、ベイナイト又はパーライトの諸相が対応する。In the above description, the hard phase corresponds to various phases of martensite, bainite or pearlite.
【００１８】フェライト相のなかで硬質相の集合体が
“塊状”とは、上記のマルテンサイト等からなる硬質相
の集合体とフェライトとの界面がそのマルテンサイト等
の硬質相の集合体の中心部からほぼ等方的に等しい距離
にあるような形状をいい、例えば薄片状のようにある一
定の方向だけ極端に短いものであってはならない。In the ferrite phase, the aggregate of the hard phase is "lumpy" when the interface between the hard phase aggregate of martensite and the ferrite is located at the center of the hard phase aggregate of martensite and the like. The shape is such that it is approximately isotropically at the same distance from the part, and should not be extremely short in a certain direction, for example, a flaky shape.
【００１９】“硬質相の集合体”とは、マルテンサイト
等のうち１相以上からなる集合体をさし、この集合体
は、フェライト相のなかにあって、互いに連結せずに個
々に存在するものをさす。The term "aggregate of hard phases" refers to an aggregate composed of one or more phases of martensite or the like, and this aggregate is present in the ferrite phase and exists individually without being connected to each other. What you do.
【００２０】硬質相の集合体の平均径とは、フェライト
相と硬質相の集合体との界面で区切られる硬質相の集合
体の平均径をさし、光学顕微鏡の視野中で直線の切断距
離を平均化する通常の方法により求められる。The average diameter of the aggregate of the hard phase means the average diameter of the aggregate of the hard phase divided at the interface between the ferrite phase and the aggregate of the hard phase. Is determined by a normal method of averaging.
【００２１】硬さの測定は、荷重１ｋｇのビッカース硬
さ測定法により求める。The hardness is measured by a Vickers hardness measurement method with a load of 1 kg.
【００２２】上記〔発明２〕において、“１以上のフェ
ライト粒からなるフェライト粒の集合体が塊状”とは、
フェライト粒の集合体の中心部からフェライト粒集合体
と硬質相との界面までの距離が等方的で各方向にほぼ等
しく、フェライト粒の集合体は連結しないで個々に存在
していることをさす。ウィドマンステッテンフェライト
等は塊状のフェライトには該当しない。In the above [Invention 2], "the aggregate of ferrite grains comprising one or more ferrite grains is a lump"
The distance from the center of the ferrite grain aggregate to the interface between the ferrite grain aggregate and the hard phase is isotropic and almost equal in each direction, and the ferrite grain aggregates exist individually without being connected. As expected. Widmanstatten ferrite and the like do not correspond to massive ferrite.
【００２３】フェライト粒の集合体の平均径が５０μｍ
以下であるとは、硬質相の集合体の平均径を求める測定
方法と同じ方法で求めた平均径が５０μｍ以下であるこ
とをいう。The average diameter of the aggregate of ferrite grains is 50 μm.
The following means that the average diameter determined by the same method as the measurement method for determining the average diameter of the aggregate of the hard phase is 50 μm or less.
【００２４】上記〔発明３〕において、オーステナイト
とフェライトの混合組織は、１００％オーステナイトの
高温から、例えば空冷してフェライトを部分的に生成し
た状態でもよいし、又は低温から昇温して部分的にオー
ステナイトを変態させた状態でもよい。In the above [Invention 3], the mixed structure of austenite and ferrite may be in a state in which ferrite is partially formed from a high temperature of 100% austenite, for example, by air cooling, or may be partially increased by raising the temperature from a low temperature. Austenite may be transformed.
【００２５】[0025]
【発明の実施の形態】以下、本発明の各限定理由につい
て実験結果等に基づいて詳述する。BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, each reason for limitation of the present invention will be described in detail based on experimental results and the like.
【００２６】１．化学組成 まず、鋼の組成の限定理由について説明する。1. Chemical Composition First, the reasons for limiting the steel composition will be described.
【００２７】Ｃ：０．０４〜０．２５％ Ｃは、鋼の強度を高める成分であり、本発明の用途に必
要な強度レベルを保持するために、０．０４％以上とす
る。０．０４％未満では本発明において必要なフェライ
トとベイナイト又はマルテンサイトといった硬質組織と
の硬度差を確保するのが困難である。一方、本発明に係
る鋼板は必ず溶接施工を受け、Ｃが０．２５％を超える
と溶接割れの危険性が高くなるので０．２５％以下とす
る。溶接割れの危険性を小さくして、より一層高強度を
確保するのに望ましい範囲は０．０６〜０．１８％であ
る。C: 0.04 to 0.25% C is a component for increasing the strength of steel, and is set to 0.04% or more in order to maintain the strength level required for the use of the present invention. If the content is less than 0.04%, it is difficult to secure a difference in hardness between ferrite and a hard structure such as bainite or martensite required in the present invention. On the other hand, the steel sheet according to the present invention is always subjected to welding, and if C exceeds 0.25%, the risk of welding cracks increases, so the content is set to 0.25% or less. A desirable range for reducing the risk of welding cracks and ensuring higher strength is 0.06 to 0.18%.
【００２８】Ｓｉ：０．１〜０．５％ Ｓｉは鋼の脱酸のために必要な成分である。Ｓｉが０．
１％未満では、脱酸効果が期待できないので０．１％以
上必要である。一方、０．５％を超えると鋼の靱性が損
なわれるので上限を０．５％とする。良好な靭性を確保
して十分脱酸効果をあげるために、より望ましい範囲は
０．１５〜０．３％ある。Si: 0.1-0.5% Si is a necessary component for deoxidizing steel. Si is 0.
If it is less than 1%, a deoxidizing effect cannot be expected, so 0.1% or more is necessary. On the other hand, if it exceeds 0.5%, the toughness of the steel is impaired, so the upper limit is made 0.5%. In order to secure good toughness and sufficiently enhance the deoxidizing effect, a more desirable range is 0.15 to 0.3%.
【００２９】Ｍｎ：０．４〜２％ Ｍｎは鋼の強度を向上させるが、０．４％未満では本発
明に係る厚鋼板の用途に必要な強度を確保するのが困難
なので０．４％以上必要である。一方、２％を超えると
溶接熱影響部を硬化させ溶接割れをもたらすので、２％
以下とする。溶接割れを回避して十分な強度を確保する
のに、より望ましい範囲は０．７〜１．４％である。Mn: 0.4 to 2% Mn improves the strength of steel, but if it is less than 0.4%, it is difficult to secure the strength required for the use of the steel plate according to the present invention, so that Mn is 0.4%. It is necessary. On the other hand, if it exceeds 2%, the heat affected zone is hardened and weld cracks are caused.
The following is assumed. A more desirable range is 0.7 to 1.4% to avoid welding cracks and secure sufficient strength.
【００３０】sol.Ａｌ：０．００５〜０．１％ Ａｌは鋼の脱酸のために必要であり、sol.Ａｌとして
０．００５％未満では脱酸が十分ではないので、sol.Ａ
ｌとして０．００５％以上含有させる。一方、０．１％
を超えると鋼の清浄度及び靱性が損なわれるので０．１
％以下とする。Sol. Al: 0.005 to 0.1% Al is necessary for deoxidizing steel, and if less than 0.005% as sol. Al, deoxidation is not sufficient.
The content is 0.005% or more as l. On the other hand, 0.1%
Exceeds 0.1, the cleanliness and toughness of the steel are impaired.
% Or less.
【００３１】Ｔｉ：０〜０．０３％ Ｔｉは添加しなくてもよい。しかし、Ｔｉは炭窒化物を
形成することにより組織の粒径を制御し、また強度上昇
により疲労亀裂進展抑制特性を改善する。さらに次に述
べるＢによる焼入性を発揮させるためにも重要な成分で
ある。従って、より一層疲労強度を高める場合には添加
する。０．００５％未満では上記の効果が明白に得られ
ないので、含有させる場合には０．００５％以上とする
ことが望ましい。一方、０．０３％を超えると溶接割れ
が発生しやすくなるので、０．０３％以下とする。溶接
割れの危険を懸念しないで疲労強度を高める範囲として
０．０１〜０．０２％とするのが望ましい。Ti: 0 to 0.03% Ti need not be added. However, Ti controls the grain size of the structure by forming carbonitrides, and improves the fatigue crack growth suppression characteristics by increasing the strength. Further, it is an important component for exhibiting the hardenability by B described below. Therefore, it is added when the fatigue strength is further increased. If the content is less than 0.005%, the above-mentioned effects cannot be obtained clearly, so if it is contained, the content is preferably 0.005% or more. On the other hand, if it exceeds 0.03%, welding cracks are likely to occur, so the content is made 0.03% or less. It is desirable that the range for increasing the fatigue strength is 0.01 to 0.02% without concern about the danger of welding cracks.
【００３２】Ｂ：０〜０．００２５％ Ｂは添加しなくてもよい。Ｂはオーステナイト粒界に固
溶状態で偏析することにより、フェライトの生成を抑制
し、鋼の強度を向上させる成分である。したがって高強
度鋼の場合には添加してもよいが、０．０００３％未満
では十分な効果が期待できないので含有させる場合は
０．０００３％以上とする。一方、０．００２５％を超
えると溶接割れが発生しやすくなる。溶接割れの危険性
がなく強度上昇が図れる望ましい範囲は、０．０００８
〜０．００１５％である。B: 0 to 0.0025% B may not be added. B is a component that segregates in the austenite grain boundary in a solid solution state, thereby suppressing the formation of ferrite and improving the strength of steel. Therefore, it may be added in the case of high-strength steel, but if it is less than 0.0003%, a sufficient effect cannot be expected. On the other hand, if it exceeds 0.0025%, welding cracks are likely to occur. A desirable range in which the strength can be increased without danger of weld cracking is 0.0008.
~ 0.0015%.
【００３３】Ｃｕ：０〜１％ Ｃｕは添加しなくてもよい。Ｃｕは腐食環境下での疲労
亀裂進展抑制の改善及び軟質部の転位構造の制御と微視
的塑性変形の抑制に有効である。したがって、腐食環境
等で使用する鋼には含有させるが、０．１％未満ではそ
の効果が小さいので、０．１％以上とするのが望まし
い。一方、１％を超えるとこれらの効果が飽和する上に
鋼の強度が過剰に上昇しすぎ、靱性が損なわれるので１
％以下とする。良好な靭性を確保してより一層腐食環境
での疲労亀裂進展を抑制するには、０．３〜０．５％の
範囲が望ましい。Cu: 0 to 1% Cu need not be added. Cu is effective in improving the suppression of fatigue crack growth in a corrosive environment, controlling the dislocation structure of a soft part, and suppressing microscopic plastic deformation. Therefore, although it is contained in steel used in a corrosive environment or the like, if its content is less than 0.1%, its effect is small. On the other hand, if it exceeds 1%, these effects are saturated and the strength of the steel excessively increases, and the toughness is impaired.
% Or less. In order to secure good toughness and further suppress the fatigue crack growth in a corrosive environment, the range of 0.3 to 0.5% is desirable.
【００３４】Ｎｉ：０〜０．５％ Ｎｉは添加しなくてもよい。しかし、Ｎｉは腐食環境下
での疲労亀裂進展抑制特性の改善及び軟質部の転位構造
及び微視的塑性変形の抑制に有効な成分である。したが
って疲労亀裂進展抑制効果をさらに向上させたい場合に
は添加するが、０．１％未満ではその効果が小さいの
で、０．１％以上とするのが望ましい。一方、０．５％
を超えるとこれらの効果が飽和し、コストアップに見合
うだけの性能改善が得られないので０．５％以下とす
る。疲労進展抑制とコスト上昇の均衡をはかる観点から
より望ましいのは、０．２〜０．４％の範囲である。Ni: 0 to 0.5% Ni may not be added. However, Ni is an effective component for improving the fatigue crack growth suppression characteristics in a corrosive environment and for suppressing the dislocation structure and microscopic plastic deformation of the soft part. Therefore, when it is desired to further improve the effect of suppressing the fatigue crack growth, it is added if the content is less than 0.1%, and the effect is small. On the other hand, 0.5%
If these values exceed, these effects are saturated and the performance improvement corresponding to the cost increase cannot be obtained. A more desirable range from the viewpoint of balancing fatigue growth suppression and cost increase is in the range of 0.2 to 0.4%.
【００３５】Ｃｒ：０〜１％ Ｃｒは添加しなくてもよい。Ｃｒは腐食環境下での疲労
亀裂進展抑制特性の向上及び軟質部の転位構造及び微視
的塑性変形の抑制に有効なので、さらに疲労亀裂進展を
抑制する場合には添加する。含有させる場合、０．１％
未満ではその効果が小さいので、０．１％以上とするこ
とが望ましい。一方、１％を超えるとこれらの効果が飽
和する上に鋼の強度が過剰に上昇しすぎ、靱性が損なわ
れるので１％以下とする。靭性を確保したうえで疲労亀
裂進展を一層抑制するのに望ましいのは、０．３〜０．
５％の範囲である。Cr: 0 to 1% Cr need not be added. Cr is effective for improving the fatigue crack growth suppression property in a corrosive environment and for suppressing the dislocation structure and microscopic plastic deformation of the soft part. Therefore, Cr is added when further suppressing the fatigue crack growth. 0.1% if included
Since the effect is small when it is less than 0.1%, it is desirable to make it 0.1% or more. On the other hand, if it exceeds 1%, these effects are saturated, and the strength of the steel excessively increases, and the toughness is impaired. Desirable for further suppressing the fatigue crack growth while securing the toughness is 0.3 to 0.5 mm.
The range is 5%.
【００３６】Ｍｏ：０〜０．６％ Ｍｏは添加しなくてもよい。しかし、Ｍｏは腐食環境下
での疲労亀裂進展を抑制するのに有効なので、より一層
疲労亀裂進展を抑制する場合には添加する。含有させる
場合、０．１％未満ではその効果が小さいので、０．１
％以上とするのが望ましい。一方、０．６％を超える
と、この効果が飽和する上、鋼の強度が過剰に上昇しす
ぎ、靱性が損なわれるので０．６％以下とする。靭性を
確保したうえでより一層疲労亀裂の進展を抑制するのに
望ましいのは、０．２〜０．４％の範囲である。Mo: 0 to 0.6% Mo may not be added. However, Mo is effective in suppressing the growth of fatigue cracks in a corrosive environment. Therefore, Mo is added to further suppress the growth of fatigue cracks. When it is contained, if the content is less than 0.1%, the effect is small.
% Is desirable. On the other hand, if it exceeds 0.6%, this effect is saturated, and the strength of the steel excessively increases, and the toughness is impaired. The range of 0.2 to 0.4% is desirable for further suppressing the growth of fatigue cracks while ensuring toughness.
【００３７】Ｎｂ：０〜０．０６％ Ｎｂは添加しなくてもよい。Ｎｂは炭窒化物を形成する
ことにより、フェライトを細粒化して強化するので、腐
食環境下での疲労亀裂進展の抑制に有効な成分なので、
より一層疲労亀裂進展を抑制する場合には添加する。
０．０１％未満では効果が明瞭でないので、含有させる
場合は０．０１％以上にすることが望ましい。一方、
０．０６％を超えると上記効果が飽和する上に鋼の強度
が過剰に上昇しすぎ靱性が損なわれるとともに、溶接割
れが発生しやすくなるので０．０６％以下とする。溶接
割れの懸念がなく、より一層疲労亀裂進展を抑制するの
に望ましいのは０．０１〜０．０４％の範囲である。Nb: 0 to 0.06% Nb may not be added. Since Nb forms carbonitrides and refines and strengthens ferrite, it is an effective component for suppressing the growth of fatigue cracks in a corrosive environment.
It is added to further suppress the fatigue crack growth.
If the content is less than 0.01%, the effect is not clear. on the other hand,
If it exceeds 0.06%, the above effect is saturated, and the strength of the steel is excessively increased, so that the toughness is impaired and weld cracks are easily generated. The range of 0.01 to 0.04% is preferable in order to eliminate the possibility of weld cracking and to further suppress fatigue crack growth.
【００３８】Ｖ：０〜０．１％ Ｖは添加しなくてもよい。Ｖはフェライトを細粒化して
強化するため、腐食環境下での疲労亀裂の進展を抑制す
るのに有効なので、より一層疲労亀裂の進展を抑制する
場合には添加する。０．０３％未満では効果が小さいの
で、含有させる場合は０．０３％以上にすることが望ま
しい。しかし、０．１％を超えると上記効果が飽和する
上に鋼の強度が過剰に上昇しすぎ靱性が損なわれるので
０．１％以下とする。靭性を確保したうえで、疲労亀裂
の進展を抑制するには０．０３〜０．０５％とするのが
望ましい。V: 0 to 0.1% V may not be added. V is effective in suppressing the growth of fatigue cracks in a corrosive environment because it refines and strengthens ferrite, and is added when further suppressing the growth of fatigue cracks. If the content is less than 0.03%, the effect is small. However, if it exceeds 0.1%, the above effect is saturated and the strength of the steel is excessively increased, so that the toughness is impaired. In order to suppress the growth of fatigue cracks while ensuring toughness, the content is preferably set to 0.03 to 0.05%.
【００３９】本発明の鋼板は、上記の合金成分のほか、
残部がＦｅと不可避不純物からなるものである。不純物
のうちのＰとＳは、それぞれ０．０２５％以下、０．０
２％以下に抑えるのが望ましい。[0039] The steel sheet of the present invention, in addition to the above alloy components,
The balance consists of Fe and inevitable impurities. P and S of impurities are 0.025% or less and 0.025% or less, respectively.
It is desirable to keep it to 2% or less.
【００４０】次ぎに鋼板の組織及び硬度差について詳述
する。Next, the structure and hardness difference of the steel sheet will be described in detail.
【００４１】２．組織及び硬度差 本発明に係る鋼板は、上記の化学組成を有し、通常の溶
製を経て鋳造の後、熱間鍛造又は熱間圧延をおこない、
熱処理を施す製造工程により得ることができ、フェライ
ト及びフェライトとの硬度差がビッカース硬さで１５０
以上の１種以上の硬質相からなる混合組織を有するもの
である。硬質相とは、上述したようにマルテンサイト、
ベイナイト又はパーライトを意味するが、とくにマルテ
ンサイト又はベイナイトが対象となる。2. Microstructure and hardness difference The steel sheet according to the present invention has the above chemical composition, and is subjected to hot forging or hot rolling after casting through normal melting.
It can be obtained by a manufacturing process of performing heat treatment, and the difference in hardness between ferrite and ferrite is 150 in Vickers hardness.
It has a mixed structure composed of one or more hard phases described above. The hard phase is, as described above, martensite,
It means bainite or pearlite, especially martensite or bainite.
【００４２】これは、フェライトと硬質組織の混合組織
とすることにより、その界面近傍において亀裂進展の停
留効果を得るためであり、硬度差はビッカース硬さで１
５０以上必要である。This is because a mixed structure of ferrite and a hard structure is used to obtain an effect of stopping the propagation of cracks in the vicinity of the interface. The difference in hardness is 1 Vickers hardness.
50 or more are required.
【００４３】硬度差をビッカース硬さで１５０以上にす
る理由は次の通りである。The reason for setting the hardness difference to Vickers hardness of 150 or more is as follows.
【００４４】ビッカース硬さで硬度差が１５０以上にな
ると、亀裂先端の転位の移動がフェライトと硬質組織の
界面で阻止され、バーガーズベクトルが界面に直交する
転位が界面近傍のフェライト内部に集積し、傾角粒界が
形成される。この傾角粒界は、粒界一次転位のみにより
構成されるため、粒界凝集力が高く、破壊の抵抗とな
る。形成されたこの傾角粒界には転位が突入しにくいた
め、引き続き繰り返し応力が作用する場合には、粒界に
隣接するフェライト側に新しい傾角粒界が順次形成され
る。このようなステップを繰り返すことにより、大きな
体積を有する傾角粒界の集合が形成される。この集合は
亀裂進展の抵抗となり、疲労亀裂の進展を抑制する作用
を向上させる。When the hardness difference in Vickers hardness is 150 or more, the movement of dislocations at the crack tip is stopped at the interface between the ferrite and the hard structure, and the dislocations whose Burgers vector are perpendicular to the interface accumulate inside the ferrite near the interface. An inclined grain boundary is formed. Since the tilt grain boundaries are constituted only by the grain boundary primary dislocations, the grain boundary agglomeration force is high and the fracture boundaries have resistance to fracture. Since dislocations do not easily enter the formed tilt grain boundaries, new tilt grain boundaries are successively formed on the ferrite side adjacent to the grain boundaries when the stress is continuously applied. By repeating such steps, a set of tilt boundaries having a large volume is formed. This set serves as crack propagation resistance and improves the action of suppressing fatigue crack growth.
【００４５】これら硬質相全体の体積率は４０〜７０％
とすることが望ましい。The volume ratio of these hard phases is 40 to 70%.
It is desirable that
【００４６】これは疲労亀裂の進展をフェライトと硬質
相の界面で十分な頻度で阻止するためにこの程度の体積
率で硬質相が存在することが望ましいからである。This is because it is desirable that the hard phase be present at such a volume ratio in order to prevent the growth of fatigue cracks at the interface between the ferrite and the hard phase with sufficient frequency.
【００４７】上記の硬度差に加えて、〔発明１〕及び
〔発明２〕の場合、それぞれつぎの組織上の要因が付加
される。In addition to the above hardness difference, in the case of [Invention 1] and [Invention 2], the following structural factors are added.
【００４８】（ａ）〔発明１〕の場合 硬度差につけ加えて硬質相の集合体の形状は塊状でなけ
ればならない。その理由は次の通りである。亀裂先端が
硬質相に衝突すると進展が停留し、亀裂は硬質相を迂回
する。このため、亀裂の進展が抑制されるのであるが、
塊状でない場合、例えば薄片状の場合は亀裂が硬質相を
突き抜けることが想定されること、及び薄片の面に平行
に亀裂が進行する場合は後記する迂回路の延長距離はほ
とんど長くならないからである。(A) In the case of [Invention 1] In addition to the hardness difference, the shape of the aggregate of the hard phase must be massive. The reason is as follows. When the crack tip collides with the hard phase, the growth stops and the crack bypasses the hard phase. For this reason, crack growth is suppressed,
This is because, if it is not a lump, for example, in the case of a flake, it is assumed that the crack penetrates the hard phase, and if the crack progresses in parallel to the plane of the flake, the extension distance of the detour described later is hardly long .
【００４９】さらに上記につけ加えて塊状の硬質相の平
均径は６〜５０μｍとする。硬質相の集合体の平均径が
６μｍ未満の場合には、迂回した亀裂の進展経路は十分
長くならず、疲労亀裂の進展を十分に抑制することはで
きない。In addition to the above, the average diameter of the massive hard phase is 6 to 50 μm. When the average diameter of the aggregate of the hard phase is less than 6 μm, the bypass crack propagation path is not sufficiently long, and the growth of fatigue cracks cannot be sufficiently suppressed.
【００５０】一方、硬質相の集合体の平均径が５０μｍ
を超える場合には、母材の靱性が低下してしまい、靭性
が重視される厚鋼板にとっては無視することができない
短所となる。従って、硬質相の集合体の平均径は６〜５
０μｍとする。On the other hand, the average diameter of the aggregate of the hard phase is 50 μm.
If it exceeds, the toughness of the base material is reduced, which is a disadvantage that cannot be ignored for a thick steel plate in which toughness is important. Therefore, the average diameter of the aggregate of the hard phase is 6 to 5
0 μm.
【００５１】残りの組織を構成しているフェライト相に
ついては形状や結晶粒径にとくに制限を設けない。The shape and crystal grain size of the ferrite phase constituting the remaining structure are not particularly limited.
【００５２】（ｂ）〔発明２〕の場合 〔発明２〕の場合は、マトリックスである硬質相の中
に、平均径５０μｍ以下のフェライト粒の集合体が分布
する混合組織とする。フェライト集合体の平均径を５０
μｍ以下に制御する理由と効果は次の通りである。(B) In the case of [Invention 2] In the case of [Invention 2], a mixed structure in which an aggregate of ferrite grains having an average diameter of 50 μm or less is distributed in a hard phase as a matrix. The average diameter of the ferrite aggregate is 50
The reason and effect of controlling the thickness to less than μm are as follows.
【００５３】この限定により、フェライト粒の集合体か
ら硬質相へと亀裂が進展する際に硬質相が高い亀裂進展
抑制効果を発揮し、疲労亀裂は平均径５０μｍ以下のフ
ェライト粒の集合体のなかに閉じこめられる。疲労亀裂
が５０μｍ以下であれば応力拡大係数からみて、容易に
この亀裂が硬質相のなかを進展することがない。According to this limitation, when a crack propagates from the aggregate of ferrite grains to the hard phase, the hard phase exerts a high crack growth suppressing effect, and the fatigue crack is formed in the aggregate of ferrite grains having an average diameter of 50 μm or less. Trapped in If the fatigue crack is 50 μm or less, the crack does not easily propagate in the hard phase in view of the stress intensity factor.
【００５４】また、フェライト粒の集合体を構成する各
フェライト粒の径は当然５０μｍより微細である。この
ため、あるフェライト粒に発生した疲労亀裂が隣接フェ
ライト粒に進展しようとしても、隣接粒内へ移動する転
位のバーガースベクトルが変化し、粒界転位が残留して
粒界を強化するので、高い亀裂停留効果が発現する。こ
の結果、フェライト粒の集合体の平均径が５０μｍを超
えると高い亀裂停留効果が得られない。The diameter of each ferrite grain constituting the aggregate of ferrite grains is naturally smaller than 50 μm. For this reason, even if a fatigue crack generated in a certain ferrite grain attempts to propagate to an adjacent ferrite grain, the Burgers vector of the dislocation moving into the adjacent grain changes, and the grain boundary dislocation remains and strengthens the grain boundary. The crack arrest effect appears. As a result, when the average diameter of the aggregate of ferrite grains exceeds 50 μm, a high crack stopping effect cannot be obtained.
【００５５】フェライト粒の集合体の平均径は、後記す
る製造方法によって実現できる最小の大きさを考慮し、
また、あまり小さくなると硬質相の破壊の単位が大きく
なり靭性が劣化するので１０μｍ程度を下限とすること
が望ましい。The average diameter of the aggregate of ferrite grains is determined in consideration of the minimum size that can be realized by the manufacturing method described later.
Further, if it is too small, the unit of fracture of the hard phase becomes large and the toughness is deteriorated. Therefore, the lower limit is preferably set to about 10 μm.
【００５６】３．製造方法（〔発明３〕） オーステナイト相とフェライト相が混合状態にある鋼を
焼入れる処理を含むこととするのは、この状態から焼入
れることによりオーステナイトから硬質相を生成させる
ためである。この結果、フェライトと硬質相の硬度差を
容易にビッカース硬さで１５０以上とすることができ
る。3. Manufacturing method ([Invention 3]) The reason for including the treatment of quenching steel in which the austenite phase and the ferrite phase are in a mixed state is to form a hard phase from austenite by quenching from this state. As a result, the hardness difference between the ferrite and the hard phase can be easily increased to Vickers hardness of 150 or more.
【００５７】オーステナイトとフェライトの混合組織
は、完全オーステナイト状態から圧延中、又は圧延終了
後に初析フェライトを部分的に生成させ、その後加速冷
却もしくは加速冷却後途中停止するか、又は直接焼入れ
し、残っているオーステナイトをマルテンサイト又はベ
イナイト等の硬質相に変態させるのが一つの法である。The mixed structure of austenite and ferrite is obtained by partially forming pro-eutectoid ferrite during rolling from the completely austenite state or after rolling, and then stopping after accelerated cooling or accelerated cooling, or directly quenching One method is to transform austenite into a hard phase such as martensite or bainite.
【００５８】もう一つの方法は、フェラトとパーライ
ト、ベイナイト、又はマルテンサイト組織の鋼をＡｃ1
点以上に加熱して、部分的にオーステナイトを生成し、
それに焼入れ処理を施す方法である。この場合、オース
テナイト以外の部分、すなわちフェライトにセメンタイ
ト等の炭化物が残る場合があるが、炭化物が残存してい
ても、本発明の効果は変わらない。Another method is to use a ferrite and pearlite, bainite or martensitic steel in Ac 1
Heating above the point to partially form austenite,
This is a method of performing a quenching process. In this case, carbides such as cementite may remain in portions other than austenite, that is, ferrite, but the effects of the present invention do not change even if carbides remain.
【００５９】〔発明３〕は上記のどちらの方法をとって
もよい。また、靭性の確保のため上記の焼入れ後に３０
０〜６００℃の温度域で焼戻しを施してもよく、加速冷
却後途中停止する場合以外は、むしろそのほうが普通で
ある。[Invention 3] may employ any of the above methods. In addition, 30 seconds after the above quenching to ensure toughness.
Tempering may be performed in a temperature range of 0 to 600 ° C., and this is rather normal except when the cooling is stopped halfway after accelerated cooling.
【００６０】[0060]
【実施例】つぎに実施例により本発明の効果を説明す
る。EXAMPLES Next, the effects of the present invention will be described with reference to examples.
【００６１】表１は実験に供した鋼の化学成分を示す。Table 1 shows the chemical composition of the steel subjected to the experiment.
【００６２】[0062]
【表１】 [Table 1]
【００６３】これらの鋼のスラブに表２に示す加工熱処
理を与え、鋼の組織、硬度差を制御した。The slabs of these steels were subjected to the thermomechanical treatment shown in Table 2 to control the structure and hardness difference of the steels.
【００６４】[0064]
【表２】 [Table 2]
【００６５】これら鋼板からＡＳＴＭ Ｅ３９９に規定
されるＣＴ試験片（Compact Tension ）を採取し、サー
ボパルサを用いて疲労試験をおこなった。疲労試験条件
は以下の通りである。From these steel plates, CT specimens (Compact Tension) specified in ASTM E399 were collected and subjected to a fatigue test using a servo pulser. The fatigue test conditions are as follows.
【００６６】ｆ(繰り返し速度)＝３０Ｈｚ Ｒ(応力比)＝０．１ （片振りの最小応力と最大応力の
比） Ｔ(試験温度)＝室温 いずれの試験片も中程度のΔＫの範囲（本試験では約５
０〜３００ｋｇｆ／ｍｍ3/2）における第２領域でＰａ
ｒｉｓ則（Trans.ASME,Ser.D,85,523(1963)）が成り立
つことが明らかとなった。Ｐａｒｉｓ則とは、ａを亀裂
長さ、Ｎを応力負荷回数、△Ｋを応力拡大係数、Ｃ及び
ｍを常数とするとき、亀裂が安定して進展する中程度の
△Ｋの範囲で、亀裂進展速度ｄａ／ｄＮについて、ｄａ
／ｄＮ＝Ｃ（ΔＫ）m が成り立つことをさす。ここに、
△Ｋ等の単位は、［ΔＫ］：ｋｇｆ／ｍｍ3/2 ，［ｄａ
／ｄＮ］：ｍｍ／ｃｙｃｌｅである。F (repetition rate) = 30 Hz R (stress ratio) = 0.1 (ratio of minimum and maximum stresses in pulsation) T (test temperature) = room temperature All of the test pieces have a medium ΔK range ( About 5 in this test
0 to 300 kgf / mm 3/2 ) in the second region.
It became clear that the ris rule (Trans.ASME, Ser. D, 85, 523 (1963)) holds. The Paris rule is that when a is the crack length, N is the number of stress loads, △ K is the stress intensity factor, and C and m are constants, the crack can be cracked in a moderate △ K range in which the crack can grow stably. For the progress rate da / dN, da
/ DN = C (ΔK) m . here,
The unit such as ΔK is [ΔK]: kgf / mm 3/2 , [da
/ DN]: mm / cycle.
【００６７】また、Ｃは試験片によらずほぼ一定で約
５．０×１０-14 であった。従って疲労亀裂進展特性は
ｍ値の大小で評価することができる。ｍ値が小さいほど
亀裂進展速度が遅く、亀裂の進展を抑制する効果が高い
ことを示す。なお、供試鋼の軟質相、硬質相の体積率や
平均粒径は、供試鋼をエポシキ樹脂に埋め込み、切断
後、断面を研磨、エッチングし顕微鏡観察をおこなうこ
とにより求めた。C was almost constant irrespective of the test piece and was about 5.0 × 10 -14 . Therefore, the fatigue crack growth characteristics can be evaluated by the magnitude of the m value. The smaller the m value is, the slower the crack growth rate is, indicating that the effect of suppressing the crack growth is high. The volume fraction and average particle size of the soft phase and the hard phase of the test steel were determined by embedding the test steel in epoxy resin, cutting, polishing and etching the cross section, and performing microscopic observation.
【００６８】表２はこれら供試鋼の組織の特徴と疲労試
験結果を示す。表２の塊状組織の種類がフェライト
（Ｆ）の場合は、フェライト平均粒径が５０μｍ以下の
とき硬度差等を満足すれば〔発明２〕に該当し、一方、
ベイナイト（Ｂ）とマルテンサイト（Ｍ）との硬質相の
集合体の場合は、この集合体の平均径が６〜５０μｍな
らば硬度差等を満足することを条件に〔発明１〕に該当
する。Table 2 shows the structural characteristics of these test steels and the results of the fatigue tests. In the case where the type of the bulk structure in Table 2 is ferrite (F), if the ferrite average particle size is 50 μm or less, if the hardness difference or the like is satisfied, it corresponds to [Invention 2].
In the case of an aggregate of a hard phase of bainite (B) and martensite (M), the invention corresponds to [Invention 1] on the condition that a difference in hardness or the like is satisfied if the average diameter of the aggregate is 6 to 50 μm. .
【００６９】[0069]
【表２】 [Table 2]
【００７０】各試験番号のｍ値からわかるように、本発
明鋼である試験番号１〜６では、ｍ値が小さく亀裂進展
抵抗を有することがわかる。特に硬度差の大きい試験番
号１では、ｍ値が特に小さく、組織の制御が極めて効果
的であることがわかる。As can be seen from the m value of each test number, in the test numbers 1 to 6, which are the steels of the present invention, it is understood that the m value is small and the steel has crack propagation resistance. In Test No. 1 having a particularly large difference in hardness, the m value is particularly small, and it can be seen that the control of the structure is extremely effective.
【００７１】一方、フェライトと硬質相との硬度差や平
均粒径又は平均径が本発明で規定する範囲外にある場合
はｍ値は大きく、疲労亀裂伝播停止特性は改善されてい
ない。On the other hand, when the hardness difference between ferrite and the hard phase, or the average particle diameter or the average diameter is out of the range specified in the present invention, the m value is large, and the fatigue crack propagation stopping characteristics are not improved.
【００７２】[0072]
【発明の効果】本発明は、靭性を具備したうえで中程度
のΔＫの範囲においても疲労亀裂進展抑制特性に優れて
おり、溶接部から疲労亀裂が発生した場合でも、従来の
鋼に比べて疲れ寿命の延長が十分に期待できるため、関
連業界に各種鋼構造物の製造に有用な厚鋼板及びその製
造方法を提供するものである。The present invention has excellent toughness and excellent fatigue crack growth suppression characteristics even in a moderate range of ΔK. An object of the present invention is to provide a steel plate useful for manufacturing various steel structures and a method of manufacturing the steel plate to related industries, since the fatigue life can be sufficiently extended.
Claims (3)
Ｓｉ：０．１〜０．５％、Ｍｎ：０．４〜２％、sol.Ａ
ｌ：０．００５〜０．１％、Ｎ：０．００１〜０．００
５％、Ｔｉ：０〜０．０３％、Ｂ：０〜０．００２５
％、Ｃｕ：０〜１％、Ｎｉ：０〜０．５％、Ｃｒ：０〜
１％、Ｍｏ：０〜０．６％、Ｎｂ：０〜０．０６％及び
Ｖ：０〜０．１％を含み、残部はＦｅと不可避不純物か
らなる化学組成を有し、その組織はフェライト相及び１
種以上の硬質相からなる混合組織の鋼であって、フェラ
イト相と各々の硬質相との硬度差がビッカース硬さで１
５０以上であり、１種以上の硬質相からなる硬質相の集
合体はフェライト相のなかで塊状であり、その平均径が
６〜５０μｍであることを特徴とする疲労亀裂進展抑制
特性に優れた厚鋼板。(1) C: 0.04 to 0.25% by weight
Si: 0.1-0.5%, Mn: 0.4-2%, sol.A
l: 0.005 to 0.1%, N: 0.001 to 0.00
5%, Ti: 0 to 0.03%, B: 0 to 0.0025
%, Cu: 0 to 1%, Ni: 0 to 0.5%, Cr: 0 to 0%
1%, Mo: 0 to 0.6%, Nb: 0 to 0.06%, and V: 0 to 0.1%, with the balance having a chemical composition of Fe and unavoidable impurities, and the structure thereof being ferrite. Phase and 1
A steel having a mixed structure consisting of at least one kind of hard phase, wherein the hardness difference between the ferrite phase and each hard phase is 1 Vickers hardness.
Aggregates of hard phases composed of one or more types of hard phases are at least 50, and are excellent in fatigue crack growth suppression characteristics characterized by being a lump in a ferrite phase and having an average diameter of 6 to 50 μm. Steel plate.
イト相及び１種以上の硬質相からなる混合組織の鋼であ
って、フェライト相と各硬質相との硬度差がビッカース
硬さで１５０以上であり、１以上のフェライト粒からな
るフェライト粒の集合体は硬質相のなかで塊状であり、
その集合体の平均径が５０μｍ以下であることを特徴と
する疲労亀裂進展抑制特性に優れた厚鋼板。2. A steel having a mixed structure comprising a ferrite phase and one or more hard phases having the chemical composition according to claim 1, wherein a difference in hardness between the ferrite phase and each hard phase is Vickers hardness. 150 or more, the aggregate of ferrite grains consisting of one or more ferrite grains are massive in the hard phase,
A thick steel plate having excellent fatigue crack growth suppression characteristics, wherein the average diameter of the aggregate is 50 μm or less.
オーステナイト相とフェライト相の混合状態から焼入れ
る処理を含むことを特徴とする請求項１又は請求項２に
記載する疲労亀裂進展抑制特性に優れた厚鋼板の製造方
法。3. The method according to claim 1, further comprising quenching the steel having the chemical composition according to claim 1 from a mixed state of an austenitic phase and a ferrite phase. A method for manufacturing thick steel plates with excellent properties.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22116396A JPH1060575A (en) | 1996-08-22 | 1996-08-22 | Thick steel plate excellent in fatigue crack arrest characteristic |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22116396A JPH1060575A (en) | 1996-08-22 | 1996-08-22 | Thick steel plate excellent in fatigue crack arrest characteristic |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH1060575A true JPH1060575A (en) | 1998-03-03 |
Family
ID=16762466
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP22116396A Pending JPH1060575A (en) | 1996-08-22 | 1996-08-22 | Thick steel plate excellent in fatigue crack arrest characteristic |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH1060575A (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005054533A1 (en) * | 2003-12-01 | 2005-06-16 | Sumitomo Metal Industries, Ltd. | Steel product excellent in fatigue characteristics and method for production thereof |
| JP2005240177A (en) * | 2004-01-30 | 2005-09-08 | Jfe Steel Kk | Method for manufacturing steel material having uniform strength in sheet thickness direction and superior fatigue-crack propagation resistance |
| JP2007314819A (en) * | 2006-05-23 | 2007-12-06 | Kobe Steel Ltd | Steel sheet having excellent fatigue crack propagation resistance |
| JP2008121092A (en) * | 2006-11-15 | 2008-05-29 | Jfe Steel Kk | Steel material with excellent fatigue crack propagation resistance, and its manufacturing method |
| JP2008174766A (en) * | 2007-01-16 | 2008-07-31 | Jfe Steel Kk | Steel having reduced residual stress and excellent fatigue crack propagation resistance charactristic |
| JP2008255469A (en) * | 2007-03-09 | 2008-10-23 | Jfe Steel Kk | Fatigue crack propagation delayed steel and its manufacturing method |
| JP2008255468A (en) * | 2007-03-09 | 2008-10-23 | Jfe Steel Kk | Fatigue crack propagation delayed steel and its manufacturing method |
| JP2011025270A (en) * | 2009-07-23 | 2011-02-10 | Sumitomo Metal Ind Ltd | Weld joint |
| JP2012102402A (en) * | 2011-11-29 | 2012-05-31 | Jfe Steel Corp | Manufacturing method of steel member having excellent resistance property in fatigue crack propagation |
| CN103820708A (en) * | 2014-03-05 | 2014-05-28 | 江苏常宝钢管股份有限公司 | Preparation method of boron-containing seamless pipeline for marine petroleum and natural gas exploitation |
| WO2015029873A1 (en) | 2013-08-26 | 2015-03-05 | 株式会社神戸製鋼所 | Thick steel sheet having excellent fatigue properties, and method for producing same |
| KR20160144439A (en) | 2014-05-22 | 2016-12-16 | 가부시키가이샤 고베 세이코쇼 | Thick steel plate |
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1996
- 1996-08-22 JP JP22116396A patent/JPH1060575A/en active Pending
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005054533A1 (en) * | 2003-12-01 | 2005-06-16 | Sumitomo Metal Industries, Ltd. | Steel product excellent in fatigue characteristics and method for production thereof |
| JP4670371B2 (en) * | 2004-01-30 | 2011-04-13 | Ｊｆｅスチール株式会社 | Manufacturing method of steel with excellent strength uniformity in the thickness direction and fatigue crack propagation characteristics |
| JP2005240177A (en) * | 2004-01-30 | 2005-09-08 | Jfe Steel Kk | Method for manufacturing steel material having uniform strength in sheet thickness direction and superior fatigue-crack propagation resistance |
| JP2007314819A (en) * | 2006-05-23 | 2007-12-06 | Kobe Steel Ltd | Steel sheet having excellent fatigue crack propagation resistance |
| JP2008121092A (en) * | 2006-11-15 | 2008-05-29 | Jfe Steel Kk | Steel material with excellent fatigue crack propagation resistance, and its manufacturing method |
| JP2008174766A (en) * | 2007-01-16 | 2008-07-31 | Jfe Steel Kk | Steel having reduced residual stress and excellent fatigue crack propagation resistance charactristic |
| JP2008255468A (en) * | 2007-03-09 | 2008-10-23 | Jfe Steel Kk | Fatigue crack propagation delayed steel and its manufacturing method |
| JP2008255469A (en) * | 2007-03-09 | 2008-10-23 | Jfe Steel Kk | Fatigue crack propagation delayed steel and its manufacturing method |
| JP2011025270A (en) * | 2009-07-23 | 2011-02-10 | Sumitomo Metal Ind Ltd | Weld joint |
| JP2012102402A (en) * | 2011-11-29 | 2012-05-31 | Jfe Steel Corp | Manufacturing method of steel member having excellent resistance property in fatigue crack propagation |
| WO2015029873A1 (en) | 2013-08-26 | 2015-03-05 | 株式会社神戸製鋼所 | Thick steel sheet having excellent fatigue properties, and method for producing same |
| CN103820708A (en) * | 2014-03-05 | 2014-05-28 | 江苏常宝钢管股份有限公司 | Preparation method of boron-containing seamless pipeline for marine petroleum and natural gas exploitation |
| KR20160144439A (en) | 2014-05-22 | 2016-12-16 | 가부시키가이샤 고베 세이코쇼 | Thick steel plate |
| KR20180115352A (en) | 2014-05-22 | 2018-10-22 | 가부시키가이샤 고베 세이코쇼 | Thick steel plate |
| JP2019214752A (en) * | 2018-06-12 | 2019-12-19 | 日本製鉄株式会社 | Low-yield-ratio thick steel plate |
| CN109371326A (en) * | 2018-12-05 | 2019-02-22 | 江苏科技大学 | A kind of anti-H2S/CO2Low-alloy steel material of corrosion and the preparation method and application thereof |
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