JP2962134B2 - Steel plate with fatigue crack growth suppression effect - Google Patents
Steel plate with fatigue crack growth suppression effectInfo
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- JP2962134B2 JP2962134B2 JP3853894A JP3853894A JP2962134B2 JP 2962134 B2 JP2962134 B2 JP 2962134B2 JP 3853894 A JP3853894 A JP 3853894A JP 3853894 A JP3853894 A JP 3853894A JP 2962134 B2 JP2962134 B2 JP 2962134B2
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- steel sheet
- fatigue crack
- hardness
- soft
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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、海洋構造物や装置およびラインパイプ等の材料と
して好適な、大気中および腐食環境中において疲労亀裂
進展抑制特性（以下、単に疲労亀裂進展特性と記す）に
優れる鋼板に関する。TECHNICAL FIELD The present invention relates to a civil engineering building structure,
The present invention relates to a steel sheet having excellent fatigue crack growth suppression characteristics (hereinafter simply referred to as fatigue crack growth characteristics) in the atmosphere and in a corrosive environment, which is suitable as a material for hulls, marine structures and equipment, and line pipes.
【０００２】[0002]
【従来の技術】近年、土木建築構造物等は大型化および
軽量化が要求されており、このため、構造用鋼材の高強
度化が望まれている。船体用材料等でも、大型化および
コストダウンの観点から高張力鋼の使用が拡大され始め
ている。しかし、高強度鋼を使用する場合、当然設計応
力が上昇するために疲労破壊が重要な問題となる。2. Description of the Related Art In recent years, civil engineering and building structures and the like have been required to be large-sized and light-weight. For this reason, it has been desired to increase the strength of structural steel materials. For hull materials and the like, the use of high-tensile steel has begun to be expanded from the viewpoint of increasing the size and reducing costs. However, when high-strength steel is used, the design stress naturally increases, so that fatigue fracture is an important problem.
【０００３】一方、構造用鋼材等の厚鋼板では一般に溶
接施工が施されるため、溶接部から疲労亀裂が発生する
場合が多い。したがって、溶接部から発生進展する疲労
亀裂を鋼材で停留させることができれば、構造物の疲労
寿命を延長するのに有効である。On the other hand, since thick steel plates such as structural steel materials are generally welded, fatigue cracks often occur from welds. Therefore, if the fatigue crack generated and propagated from the welded portion can be stopped by the steel material, it is effective to extend the fatigue life of the structure.
【０００４】疲労亀裂の進展を停留させるためには、特
開平５−１４８５４１号公報にあるように疲労亀裂先端
にマイクロクラックを発生させる方法がある。しかし、
この方法の効果は、低ΔＫ（ΔＫ：最大応力拡大係数と
最小応力拡大係数との差）領域、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、溶接部から発生し
てある程度の長さを有しており、中ΔＫ領域にある亀裂
に関しては、少ないと考えられる。In order to stop the growth of fatigue cracks, there is a method of generating a microcrack at the tip of a fatigue crack as disclosed in Japanese Patent Application Laid-Open No. 5-148541. But,
The effect of this method is limited to the low ΔK (ΔK: difference between the maximum stress intensity factor and the minimum stress intensity factor), that is, the case where the crack is not long and the stress level is low. The cracks in the medium ΔK region are considered to be small.
【０００５】日本機械学会論文集Ａ編，ｖｏｌ．４５
（１９７９），Ｐ．４４０〜４４５にあるように、機械
構造用鋼の分野で疲労耐久限度におよぼす組織の影響が
調査されているが、長さが約５００μｍを超える長い亀
裂においては、その進展は組織の影響を受けにくいこと
が指摘されており、疲労亀裂の進展抑制をさらに向上さ
せようとする場合に必要な、比較的長い亀裂の進展を抑
制するための知見は示されていない。[0005] Transactions of the Japan Society of Mechanical Engineers A, vol. 45
(1979), p. As in 440 to 445, the influence of the structure on the fatigue endurance limit has been investigated in the field of steel for machine structural use. However, in a long crack having a length exceeding about 500 μm, the growth is affected by the structure. However, it is pointed out that it is difficult to suppress the growth of a relatively long crack, which is necessary for further improving the suppression of the growth of a fatigue crack.
【０００６】特開平４−３２９８４８号公報には、疲労
強度が重要な特性である自動車用ホイールをはじめとす
る各種用途の熱延鋼板に関して、二相組織中の母相と第
二相の硬さ、面積率および第二相の粒径を限定すれば、
良好な疲労強度が得られることが示されているものの、
疲労亀裂の進展挙動については十分に検討がなされてい
るとは言えず、また組織間の硬度差に着目した疲労亀裂
の進展抑制効果については明らかになっていない。Japanese Unexamined Patent Publication (Kokai) No. 4-329848 discloses a hot-rolled steel sheet for various uses such as an automobile wheel, in which the fatigue strength is an important property. If the area ratio and the particle size of the second phase are limited,
Although it has been shown that good fatigue strength can be obtained,
It cannot be said that the fatigue crack growth behavior has been sufficiently studied, and the effect of suppressing fatigue crack growth by focusing on the hardness difference between structures has not been clarified.
【０００７】[0007]
【発明が解決しようとする課題】本発明は上記課題を解
決するためになされたものであり、具体的な目的は、土
木建築構造物や船体、海洋構造物や装置、ラインパイプ
等の材料として使用される鋼材であって、疲労亀裂が進
展しにくい性質を有する鋼板を提供することにある。SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a specific object as a material for civil engineering construction structures and hulls, marine structures and equipment, line pipes and the like. It is an object of the present invention to provide a steel sheet which is used and has a property in which a fatigue crack does not easily propagate.
【０００８】[0008]
【課題を解決するための手段】本発明の要旨は下記の
（１）〜（４）の鋼板にある。The gist of the present invention resides in the following steel sheets (1) to (4).
【０００９】（１）質量％で、Ｃ：０．０１〜０．３
％、Ｓｉ： ０．１〜０．５％、Ｍｎ：０．３〜２．０
％およびｓｏｌ．Ａｌ：０．００５〜０．１％、さら
に、Ｃｒ：１．５％以下（無添加でもよい）、Ｍｏ：
０．６％以下（無添加でもよい）、Ｎｉ：０．５％以下
（無添加でもよい）、Ｃｕ：１．０％以下（無添加でも
よい）、Ｎｂ：０．１％以下（無添加でもよい）、Ｔ
ｉ：０．１％以下（無添加でもよい）およびＶ：０．１
％以下（無添加でもよい）を含み、残部はＦｅと不可避
不純物からなる鋼板であって、その組織は硬質部の素地
とその素地に分散した軟質部とからなり、この２部分の
硬度差がビッカース硬度で１５０以上であることを特徴
とする疲労亀裂進展抑制効果を有する鋼板。(1) In mass%, C: 0.01 to 0.3
%, Si: 0.1 to 0.5%, Mn: 0.3 to 2.0
% And sol. Al: 0.005 to 0.1%, Cr: 1.5% or less (may not be added), Mo:
0.6% or less (no addition), Ni: 0.5% or less (no addition), Cu: 1.0% or less (no addition), Nb: 0.1% or less (no addition) Or T)
i: 0.1% or less (may not be added) and V: 0.1
% Or less include (which may be a non-additive), and the balance a steel sheet consisting of Fe and unavoidable impurities, the organization is hard portion matrix
And a soft portion dispersed in the base material, wherein the hardness difference between the two portions is not less than 150 in Vickers hardness.
【００１０】（２）上記（１）の成分の鋼板であって、
その組織は硬質部の素地とこの素地に分散した軟質部か
らなり、硬質部の素地と軟質部との硬度差がビッカース
硬度で１５０以上、軟質部の平均粒径が５０μｍ以下で
あることを特徴とする疲労亀裂進展抑制効果を有する鋼
板。(2) A steel sheet having the component (1),
The structure is composed of a hard part base and a soft part dispersed in the base, and the hardness difference between the hard part base and the soft part is 150 or more in Vickers hardness, and the average particle size of the soft part is 50 μm or less. Steel sheet having the effect of suppressing fatigue crack growth.
【００１１】（３）上記（１）の成分の鋼板であって、
その組織は硬質部の素地とこの素地に分散した軟質部か
らなり、この２部分の硬度差がビッカース硬度で１５０
以上、硬質部の平均間隔が５０μｍ以下であることを特
徴とする疲労亀裂進展抑制効果を有する鋼板。(3) A steel sheet having the component (1),
Is the structure a hard part base and a soft part dispersed in this base?
And the hardness difference between the two parts is 150 in Vickers hardness.
As described above, a steel sheet having an effect of suppressing fatigue crack growth, wherein the average interval of the hard portions is 50 μm or less.
【００１２】（４）上記（１）の成分の鋼板であって、
その組織は硬質部の素地とこの素地に分散した軟質部か
らなり、この２部分の硬度差がビッカース硬度で１５０
以上、硬質部の平均間隔が５０μｍ以下、かつ、軟質部
の平均粒径が５０μｍ以下であることを特徴とする疲労
亀裂進展抑制効果を有する鋼板。(4) The steel sheet having the component (1),
Is the structure a hard part base and a soft part dispersed in this base?
And the hardness difference between the two parts is 150 in Vickers hardness.
As described above, the steel sheet having the effect of suppressing the growth of fatigue cracks, wherein the average distance between the hard parts is 50 μm or less and the average particle diameter of the soft parts is 50 μm or less.
【００１３】ここでいう硬質部とは、マルテンサイト、
ベイナイト、パーライト、疑似パーライトおよび焼戻し
マルテンサイトの１種以上から、軟質部とはフェライト
から、それぞれ構成される組織を意味する。The hard portion referred to here is martensite,
The soft part means a structure composed of at least one of bainite, pearlite, pseudo pearlite and tempered martensite, and the soft part from ferrite.
【００１４】本発明は、疲労挙動に及ぼす材料因子につ
いて検討して得た次の〜の知見に基づいている。The present invention is based on the following findings obtained by examining the material factors affecting the fatigue behavior.
【００１５】鋼材の疲労挙動を調査した結果によれ
ば、複合組織であって、構成組織間の硬度差が大きい場
合、疲労亀裂が停留しやすいこと。そして、この効果
は、硬質部と軟質部との存在比率（体積率）によって、
あまり影響を受けないこと。According to the result of the investigation of the fatigue behavior of the steel material, it is found that fatigue cracks are liable to be retained in a composite structure having a large difference in hardness between the constituent structures. And this effect depends on the existence ratio (volume ratio) of the hard part and the soft part.
Not much affected.
【００１６】複合組織中の各組織間の硬度差をある値
以上にした場合、またこれに加えて軟質部の平均粒径を
一定値以下に抑制した場合、または、硬質部の平均間隔
（分散距離）を一定値以下に抑制した場合、進展する亀
裂が硬質部と軟質部の境界近傍に到達した際、先端にお
ける塑性変形が抑制されることにより、上述の疲労亀裂
の停留が起こること。When the difference in hardness between the respective structures in the composite structure is set to a certain value or more, in addition to this, when the average particle size of the soft part is suppressed to a certain value or less, or when the average interval (dispersion) When the distance) is suppressed to a certain value or less, when the growing crack reaches the vicinity of the boundary between the hard part and the soft part, plastic deformation at the tip is suppressed, so that the above-mentioned fatigue crack stops.
【００１７】Ｃｒ、Ｍｏ、ＮｉおよびＣｕ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、腐食環境中においても疲労亀裂進展特性を向上させ
る効果が期待できること。By adding a small amount of any of Cr, Mo, Ni and Cu, the effect of improving the corrosion resistance and the like of the steel material and the effect of improving the fatigue crack propagation characteristics even in a corrosive environment can be expected.
【００１８】また、Ｎｂ、ＴｉおよびＶのいずれかを添
加すれば、炭化物を生成することにより軟質部（フェラ
イト）を強化する効果が得られ、軟質部内を進展する疲
労亀裂進展速度は低下すること。Further, if any one of Nb, Ti and V is added, the effect of strengthening the soft part (ferrite) by forming carbides is obtained, and the rate of fatigue crack propagation in the soft part is reduced. .
【００１９】[0019]
【発明の実施の形態】以下、本発明の鋼板の化学組成、
その組織および軟質部と硬質部の硬度差の限定理由を作
用効果とともに説明する。％は質量％を意味する。BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the chemical composition of the steel sheet of the present invention,
The structure and the reason for limiting the difference in hardness between the soft part and the hard part will be described together with the function and effect. % Means mass%.
【００２０】１）鋼板の化学組成 Ｃ：０．０１〜０．３％ Ｃは鋼の強度を高める成分である。本発明鋼板の用途に
必要な強度レベルを保持するために、Ｃ含有量は０．０
１％以上とした。これを下回ると本発明の鋼板の用途に
必要な強度と組織を確保するのが困難である。一方、本
発明の鋼板の主要な用途では必ず溶接施工を受けるの
で、溶接割れの発生を防止するために、Ｃ含有量の上限
は０．３％とした。望ましいＣ含有量の範囲は０．０３
〜０．１８％である。1) Chemical composition of steel sheet C: 0.01 to 0.3% C is a component that increases the strength of steel. In order to maintain the strength level necessary for the use of the steel sheet of the present invention, the C content is 0.0
1% or more. Below this, it is difficult to secure the strength and structure required for the use of the steel sheet of the present invention. On the other hand, since the steel sheet of the present invention is always subjected to welding in the main use, the upper limit of the C content is set to 0.3% in order to prevent the occurrence of welding cracks. Desirable C content range is 0.03
０．１0.18%.
【００２１】Ｓｉ：０．１〜０．５％ Ｓｉは鋼の脱酸のために必要な成分である。Ｓｉ含有量
が０．１％未満ではこの効果が期待できない。一方、
０．５％を超えると鋼の靱性が損なわれる。望ましいＳ
ｉ含有量の範囲は０．２５〜０．４％である。Si: 0.1-0.5% Si is a necessary component for deoxidizing steel. If the Si content is less than 0.1%, this effect cannot be expected. on the other hand,
If it exceeds 0.5%, the toughness of the steel is impaired. Desirable S
The range of the i content is 0.25 to 0.4%.
【００２２】Ｍｎ：０．３〜２．０％ Ｍｎは鋼の強度を向上させる成分である。Ｍｎ含有量が
０．３％未満では本発明の鋼板の用途に必要な強度を確
保するのが困難である。しかし、ＭｎもＣと同様、溶接
熱影響部を硬化させ溶接割れをもたらす成分であること
から、その含有量には上限がある。すなわち、２．０％
を上回ると溶接割れが発生しやすくなる。望ましいＭｎ
の含有量は０．７〜１．４％である。Mn: 0.3 to 2.0% Mn is a component for improving the strength of steel. If the Mn content is less than 0.3%, it is difficult to secure the strength required for the use of the steel sheet of the present invention. However, Mn, like C, is a component that hardens the weld heat affected zone and causes welding cracks, and thus has an upper limit on the content. That is, 2.0%
If the ratio exceeds the range, welding cracks are likely to occur. Desirable Mn
Is 0.7 to 1.4%.
【００２３】ｓｏｌ．Ａｌ：０．００５〜０．１％ Ａｌは、鋼の脱酸のためにｓｏｌ．ＡｌとしてＡｌ含有
量が０．００５％以上となるようする必要がある。しか
し、ｓｏｌ．Ａｌ含有量が０．１％を上回ると鋼の清浄
度および靱性が損なわれる。Sol. Al: 0.005 to 0.1% Al is sol. It is necessary that the Al content be 0.005% or more as Al. However, sol. If the Al content exceeds 0.1%, the cleanliness and toughness of the steel are impaired.
【００２４】本発明の鋼板の一つは、上記の成分の外、
残部がＦｅと不可避不純物からなるものである。不純物
の中のＰとＳは、それぞれ０．０２５％以下、０．０２
０％以下に抑えるのが望ましい。One of the steel sheets of the present invention is, in addition to the above components,
The balance consists of Fe and inevitable impurities. P and S in the impurities are 0.025% or less and 0.02% or less, respectively.
It is desirable to keep it at 0% or less.
【００２５】本発明の鋼板は必要に応じて上記の各成分
に加えてさらに、次の７種類の成分の中の１種または２
種以上を含むものであってもよい。The steel sheet of the present invention may further comprise one or more of the following seven components, if necessary, in addition to the above components.
It may contain more than one species.
【００２６】Ｃｒ：１．５％以下 Ｃｒは、腐食環境下での疲労亀裂進展特性の改善および
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
な成分である。したがって、積極的に添加する場合Ｃｒ
含有量は０．０１％以上とするのが望ましい。しかし、
Ｃｒ含有量が１．５％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。より望ましいのは０．３〜１．０％の範囲である。Cr: 1.5% or less Cr is a component effective for improving fatigue crack growth characteristics in a corrosive environment, controlling the dislocation structure of the soft part, and suppressing microscopic plastic deformation. Therefore, when aggressively added Cr
The content is desirably 0.01% or more. But,
When the Cr content exceeds 1.5%, these effects are saturated, and the strength of the steel is excessively increased, so that the toughness is impaired. More preferably, it is in the range of 0.3 to 1.0%.
【００２７】Ｍｏ：０．６％以下 Ｍｏも、腐食環境下での疲労亀裂進展抑制特性の改善お
よび軟質部の転位構造の制御と微視的塑性変形の抑制に
有効な成分である。したがって、積極的に添加する場合
Ｍｏ含有量の下限は０．０５％とするのが望ましい。し
かし、Ｍｏ含有量が０．６％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。より望ましいのは０．１〜０．４％の範囲で
ある。Mo: 0.6% or less Mo is also an effective component for improving the fatigue crack growth suppression characteristics in a corrosive environment, controlling the dislocation structure of the soft part, and suppressing microscopic plastic deformation. Therefore, in the case of positive addition, the lower limit of the Mo content is preferably set to 0.05%. However, when the Mo content exceeds 0.6%, these effects are saturated, and the strength of the steel is excessively increased, so that the toughness is impaired. More preferably, it is in the range of 0.1 to 0.4%.
【００２８】Ｎｉ：０．５％以下 Ｎｉも、腐食環境下での疲労亀裂進展抑制特性の改善お
よび軟質部の転位構造の制御と微視的塑性変形の抑制に
有効な成分である。したがって、積極的に添加する場合
Ｎｉ含有量の下限は０．１％とするのが望ましい。しか
し、Ｎｉ含有量が０．５％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。より望ましいのは０．２〜０．４％の範囲であ
る。Ni: 0.5% or less Ni is also a component effective for improving the fatigue crack growth suppression characteristics in a corrosive environment, controlling the dislocation structure of the soft part, and suppressing microscopic plastic deformation. Therefore, when adding positively, the lower limit of the Ni content is desirably 0.1%. However, when the Ni content exceeds 0.5%, these effects are saturated, and the strength of the steel is excessively increased, so that the toughness is impaired. More preferably, it is in the range of 0.2 to 0.4%.
【００２９】Ｃｕ：１．０％以下 Ｃｕも、腐食環境下での疲労亀裂進展抑制特性の改善お
よび軟質部の転位構造の制御と微視的組成変形の抑制に
有効な成分である。ただし、Ｃｕ含有量が０．１％未満
ではその効果が小さいので、積極的に添加する場合Ｃｕ
含有量は０．１％以上とするのが望ましい。しかし、Ｃ
ｕ含有量が１．０％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。より望ましいのは、０．３〜０．５％の範囲であ
る。Cu: 1.0% or less Cu is also a component effective for improving the fatigue crack growth suppression characteristics in a corrosive environment, controlling the dislocation structure of the soft part, and suppressing the microscopic composition deformation. However, if the Cu content is less than 0.1%, the effect is small.
The content is desirably 0.1% or more. But C
If the u content exceeds 1.0%, these effects are saturated, and the strength of the steel is excessively increased, so that the toughness is impaired. More desirable is a range of 0.3-0.5%.
【００３０】以上のＣｒ、Ｍｏ、ＮｉおよびＣｕは、い
ずれも耐食性を向上させる作用を有し、この効果も相俟
って腐食環境下での疲労亀裂進展抑制特性が改善され
る。The above-mentioned Cr, Mo, Ni and Cu all have an effect of improving the corrosion resistance, and together with this effect, the fatigue crack growth suppression characteristics in a corrosive environment are improved.
【００３１】Ｎｂ、Ｔｉ、Ｖ：いずれも０．１％以下 Ｎｂ、ＴｉおよびＶは、いずれも炭化物を生成すること
により、軟質部を細粒化して強化するため、腐食環境下
での疲労亀裂進展抑制特性の改善に有効な成分である。
したがって、これらの３種類の成分から１種以上を選ん
で積極的に添加する場合には、含有量はいずれも０．０
１％以上とするのが望ましい。しかし、含有量が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。より望ましいのは、Ｔ
ｉおよびＮｂでともに０．０１〜０．０３％、Ｖで０．
０２〜０．０５％の範囲である。Nb, Ti, V: not more than 0.1% Nb, Ti, and V all form carbides to refine and soften the soft part by generating carbides, so that fatigue cracks in a corrosive environment It is a component that is effective for improving the growth suppression characteristics.
Therefore, when one or more of these three components are selected and positively added, the contents are all 0.0%.
It is desirable that the content be 1% or more. However, when the content is 0.1
%, The above effect is saturated, and the strength of the steel is excessively increased, so that the toughness is impaired. More preferably, T
Both 0.01 and 0.03% for i and Nb, and 0.1 for V.
The range is from 02 to 0.05%.
【００３２】２）鋼板の組織および硬度差 上記の化学組成を有する本発明鋼板は、通常の溶製、鋳
造（連続鋳造またはインゴット鋳造）の後、熱間鍛造ま
たは熱間圧延を行い、熱処理を施す製造工程で得ること
ができる。2) Structure and hardness difference of steel sheet The steel sheet of the present invention having the above chemical composition is subjected to normal forging or casting (continuous casting or ingot casting), followed by hot forging or hot rolling, followed by heat treatment. It can be obtained in the manufacturing process.
【００３３】本発明鋼板は、硬質部の素地とこの素地に
分散した軟質部からなる複合組織を有するものである。
硬質部はマルテンサイト、ベイナイト、パーライト、疑
似パーライトおよび焼戻しマルテンサイトの１種以上か
らなる組織、軟質部はフェライト組織である。[0033] The steel sheet of the present invention comprises a base material of a hard part and a base material
It has a composite structure composed of dispersed soft parts .
The hard part has a structure composed of one or more of martensite, bainite, pearlite, pseudo pearlite and tempered martensite, and the soft part has a ferrite structure.
【００３４】これは、硬質部と軟質部の２種類の組織を
複合形成させて、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る。この効果は、硬質部と軟質部と
の存在比率（体積率）によって、あまり影響を受けな
い。したがって、本発明鋼板では、上記の存在比率は特
に限定されない。This is because two types of structures, ie, a hard part and a soft part, are formed in a composite manner, and the effect of stopping the propagation of cracks is obtained in the vicinity of the interface. This effect is not significantly affected by the existence ratio (volume ratio) of the hard part and the soft part. Therefore, in the steel sheet of the present invention, the above-mentioned existence ratio is not particularly limited.
【００３５】本発明鋼板の一つは、上記の組織におい
て、さらに硬質部と軟質部との硬度の差をビッカース
（以下、Ｈｖという）で１５０以上としたものである。One of the steel sheets of the present invention has a structure in which the difference in hardness between the hard part and the soft part is 150 or more in Vickers (hereinafter referred to as Hv) in the above structure.
【００３６】軟質部と硬質部との硬度差をＨｖで１５０
以上にする理由は次のとおりである。この硬度差が１５
０以上になると、亀裂先端の転位の移動が軟質部と硬質
部との界面で阻止されるとともに、バーガースベクトル
が界面に直交する転位が、両部の界面近傍の軟質部内に
配列するため、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、破壊の抵抗となりやすい。さらに、形成され
た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、粒界に隣接する軟質部側
に新しい傾角粒界が形成される。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
合部が形成される。この集合部は亀裂進展の抵抗とな
り、鋼材の亀裂進展抑制特性を向上させるのである。The hardness difference between the soft part and the hard part is 150 in Hv.
The reason for the above is as follows. This hardness difference is 15
If it becomes 0 or more, the dislocation movement at the crack tip is blocked at the interface between the soft part and the hard part, and the dislocation whose Burgers vector is orthogonal to the interface is arranged in the soft part near the interface between the two parts, so the tilt angle is increased. Grain boundaries are formed. Since this tilt grain boundary is constituted only by the grain boundary primary dislocation, the grain boundary has a high cohesive force and is likely to be resistant to fracture. Further, since dislocations do not easily enter the formed tilt grain boundary, when a repeated stress continuously acts, a new tilt grain boundary is formed on the soft part side adjacent to the grain boundary. By repeating such a step, an aggregate of inclined grain boundaries having a large volume is formed. This aggregate serves as resistance to crack growth, and improves the crack growth suppressing properties of the steel material.
【００３７】本発明鋼板の他の一つは、硬質部の素地と
この素地中に分散した軟質部とからなる組織とし、硬質
部の素地と分散した軟質部との硬度差をＨｖで１５０以
上、さらに軟質部の平均粒径を５０μｍ以下としたもの
である。Another one of the steel sheets of the present invention has a structure composed of a base of a hard part and a soft part dispersed in the base, and the difference in hardness between the base of the hard part and the dispersed soft part is 150 or more in Hv. Further, the average particle size of the soft portion is set to 50 μm or less.
【００３８】軟質部の分散形態としては、ランダム状、
複数で平行する点列状および点列ネットワーク状または
からまった点列ネットワーク状、複数で平行する連続状
および連続ネットワーク状またはからまった連続ネット
ワーク状などがある。これらの軟質部はフェライトであ
り、この平均粒径を５０μｍ以下とするのである。The dispersion form of the soft part may be random,
There are a plurality of parallel point trains and a point train network or a tangled point network, a plurality of parallel continuous and a continuous network or a continuous network. These soft parts are ferrite, and the average particle size is set to 50 μm or less.
【００３９】このような複合組織と硬度差においても、
硬質部と軟質部との界面近傍において亀裂進展の停留効
果を得ることができる。Even in such a composite structure and hardness difference,
In the vicinity of the interface between the hard part and the soft part, the effect of stopping the crack growth can be obtained.
【００４０】軟質部の平均粒径を５０μｍ以下に制御す
る理由とその効果は、次のとおりである。The reason for controlling the average particle size of the soft part to 50 μm or less and the effect thereof are as follows.
【００４１】この制御により、短範囲で結晶方位を変化
させ結晶粒内の転位の移動を抑制するとともに、粒界に
到達した転位が隣接結晶粒内へ移動する場合においても
バーガースベクトルに変化が生じるために、粒界転位が
残留して粒界を強化することができ、高い亀裂停留効果
が発現する。軟質部の平均粒径が５０μｍを超えると高
い亀裂停留効果が得られない。By this control, the crystal orientation is changed in a short range to suppress the movement of dislocations in the crystal grain, and the Burgers vector changes even when the dislocation reaching the grain boundary moves into the adjacent crystal grain. Therefore, grain boundary dislocations remain to strengthen the grain boundaries, and a high crack arresting effect is exhibited. If the average particle size of the soft part exceeds 50 μm, a high crack stopping effect cannot be obtained.
【００４２】本発明鋼板のさらに他の一つは、その組織
を硬質部（素地）と軟質部（分散相）とからなるものと
し、その２部分の硬度差をＨｖで１５０以上、さらに硬
質部の平均間隔（分散距離）を５０μｍ以下としたもの
である。ここで、硬質部の平均間隔とは中心間距離を指
すものである。Still another steel sheet according to the present invention has a structure comprising a hard part (base material) and a soft part (dispersed phase), and the difference in hardness between the two parts is 150 or more in Hv. The average distance (dispersion distance) is set to 50 μm or less. Here, the average interval of the hard portions indicates the center-to-center distance.
【００４３】このような複合組織も、硬質、軟質の両部
からなり、適正な硬度差を有するため、その界面近傍で
亀裂進展の停留効果を得ることができる。Such a composite structure also comprises both hard and soft parts and has an appropriate difference in hardness, so that the effect of stopping the propagation of cracks near the interface can be obtained.
【００４４】硬質部の平均間隔が５０μｍ以下で分散す
るように制御した場合には、この制御により軟質部内の
微視的な塑性変形を抑制し、亀裂停留効果が顕著にな
る。硬質部の平均間隔が５０μｍを超えると、その顕著
な効果が得られなくなる。When control is performed such that the average interval between the hard portions is dispersed to be 50 μm or less, this control suppresses microscopic plastic deformation in the soft portion and makes the crack stopping effect remarkable. When the average interval of the hard portions exceeds 50 μm, the remarkable effect cannot be obtained.
【００４５】本発明鋼板では、前記の複合組織と硬度差
を維持し、さらに軟質部の平均粒径が５０μｍ以下と硬
質部の平均間隔が５０μｍ以下との両方の条件を満たせ
ば、一層好ましい効果を得ることができる。In the steel sheet of the present invention, if the above-mentioned composite structure and the difference in hardness are maintained, and if the average grain size of the soft part is 50 μm or less and the average interval of the hard part is 50 μm or less, both effects are more preferable. Can be obtained.
【００４６】[0046]
【実施例】表１に示す化学組成の鋼を連続鋳造により厚
さ１６０ｍｍのスラブとし、熱間で直送して熱間圧延に
供し、厚さ４０ｍｍの鋼板とした。得られた鋼板の組織
と硬度差を制御するため、これらの鋼板に表２に示す条
件で加工熱処理を施した。EXAMPLE A steel sheet having a chemical composition shown in Table 1 was cast into a slab having a thickness of 160 mm by continuous casting, directly fed hot, and subjected to hot rolling to obtain a steel sheet having a thickness of 40 mm. In order to control the structure and hardness difference of the obtained steel sheets, these steel sheets were subjected to a working heat treatment under the conditions shown in Table 2.
【００４７】[0047]
【表１】 [Table 1]
【００４８】[0048]
【表２】 [Table 2]
【００４９】すなわち、鋼番１〜２４の各鋼に対し、加
熱温度、圧延条件、冷却速度等を適切に制御することに
よって、種々の組織、軟質部と硬質部の硬度差、軟質部
の平均粒径、硬質部の平均間隔（分散距離）を有し、引
張強度が４１〜８６ｋｇｆ／ｍｍ２の範囲の鋼板とし
た。比較例として、焼入れ後、表２に記載の条件で焼戻
し処理をおこなった鋼板も評価した。That is, by appropriately controlling the heating temperature, rolling conditions, cooling rate, and the like for each of steel Nos. 1 to 24, various structures, a difference in hardness between the soft part and the hard part, and an average soft part. A steel sheet having a particle size, an average interval (dispersion distance) between hard portions, and a tensile strength in a range of 41 to 86 kgf / mm 2 was used. As a comparative example, a steel sheet which was tempered under the conditions shown in Table 2 after quenching was also evaluated.
【００５０】これらの鋼板から採取した試験材を試番１
〜５４とし、組織、軟質部の平均粒径、硬質部の平均間
隔、硬度差及び疲労亀裂進展抑制特性を調査した。The test materials collected from these steel sheets were designated as Test No. 1
And to 54, the tissue was examined an average particle diameter of the soft portion, the average distance between the hard portion, the hardness difference and fatigue crack growth inhibiting properties.
【００５１】鋼板の組織調査と硬度の測定は、サンプル
をエポキシ樹脂に埋め込み、切断、断面の研磨、エッチ
ングを施して、顕微鏡観察および微小領域の硬度測定を
行うことにより行った。The structure of the steel sheet was examined and the hardness was measured by embedding the sample in an epoxy resin, cutting, polishing the cross section, and etching, observing the sample with a microscope, and measuring the hardness of a minute area.
【００５２】疲労亀裂進展抑制特性の調査は、図１
（ｂ）に示すＣＴ試験片１と図１（ａ）に示すサーボパ
ルサ装置を用いる疲労試験法によった。FIG. 1 shows the investigation of the fatigue crack growth suppression characteristics.
A fatigue test method using a CT test piece 1 shown in (b) and a servo pulser device shown in FIG.
【００５３】図１（ａ）に示す装置では、１はＣＴ試験
片、２は試験溶液槽、３は溶液循環ポンプ、４はロード
セル、５は油圧シリンダー、６は油圧源、７はサーボバ
ルブ、８は波形発生器、９は負荷制御器であり、試験溶
液槽２中で試験片１に油圧シリンダー５により繰返し応
力を負荷することができる。疲労試験条件は次のとおり
である。In the apparatus shown in FIG. 1A, 1 is a CT test piece, 2 is a test solution tank, 3 is a solution circulation pump, 4 is a load cell, 5 is a hydraulic cylinder, 6 is a hydraulic source, 7 is a servo valve, Reference numeral 8 denotes a waveform generator, and 9 denotes a load controller, which can repeatedly apply a stress to the test piece 1 in the test solution tank 2 by the hydraulic cylinder 5. The fatigue test conditions are as follows.
【００５４】 ｆ（繰返し速度）＝３０Ｈｚ Ｒ（応力比）＝０．１ Ｔ（試験温度）＝室温 試験雰囲気：湿潤硫化水素環境中 （水１０％を含む懸濁させた原油に、硫化水素濃度１
％、残りは窒素の混合ガスを試験期間中常時吹き込み） ＡＳＴＭ，Ｄ−１１４１−５２で規定する人工海水中 大気中 疲労試験結果の検討によれば、いずれの試験片の場合も
中ΔＫ領域（本試験では約５０〜３００ｋｇｆ／ｍｍ
３／２）における第２領域で、Ｐａｒｉｓ則〔Ｔｒａｎ
ｓ．ＡＳＭＥ，Ｓｅｒ．Ｄ．８５．５２３（１９６
３）〕、すなわちｄａ／ｄＮ＝Ｃ（ΔＫ） ｍ 、ただし、
〔ΔＫ〕：ｋｇｆ／ｍｍ ３／２ ，〔ｄａ／ｄＮ〕：ｍｍ
／ｃｙｃｌｅが成り立つことが判明した。したがって、
疲労亀裂進展特性は、この中ΔＫ領域のΔＫ＝５０およ
び１００ｋｇｆ／ｍｍ ３／２ における、亀裂進展速度ｄ
ａ／ｄＮ（ｍｍ／ｃｙｃｌｅ）の平均値（ｄａ／ｄＮ）
ｍ で評価することとした。表３〜表６に上記の調査、測
定および疲労試験の結果を示す。F (repetition rate) = 30 Hz R (stress ratio) = 0.1 T (test temperature) = room temperature Test atmosphere: in a wet hydrogen sulfide environment (hydrogen sulfide concentration in suspended crude oil containing 10% water) 1
%, The rest being continuously blown with a mixture of nitrogen during the test period) According to the results of the fatigue test in artificial seawater and air specified by ASTM, D-1141-52, the medium ΔK region ( In this test, about 50-300kgf / mm
3/2 ), the Paris rule [Tran
s. ASME, Ser. D. 85.523 (196
3)], that is, da / dN = C (ΔK) m , where
[ΔK]: kgf / mm 3/2 , [da / dN]: mm
/ Cycle was found to hold. Therefore,
The fatigue crack growth characteristics are determined by the crack growth rate d at ΔK = 50 and 100 kgf / mm 3/2 in the ΔK region.
Average value of a / dN (mm / cycle) (da / dN)
m . Tables 3 to 6 show the results of the above investigation, measurement and fatigue test.
【００５５】[0055]
【表３】 [Table 3]
【００５６】[0056]
【表４】 [Table 4]
【００５７】[0057]
【表５】 [Table 5]
【００５８】[0058]
【表６】 [Table 6]
【００５９】各試験片の（ｄａ／ｄＮ）ｍからわかるよ
うに、本発明例である試験Ｎｏ．１〜３５では（ｄａ／
ｄＮ）ｍが小さく、高い疲労亀裂進展抵抗を有してい
る。一方、硬度差が本発明で定める範囲外にある試験
Ｎｏ．３８〜５６の場合では（ｄａ／ｄＮ）ｍが大き
く、疲労亀裂進展抑制特性は改善されていない。As can be seen from the (da / dN) m of each test piece, test No. In 1 to 35, (da /
dN) m is small and has high fatigue crack growth resistance. On the other hand, a test in which the hardness difference is out of the range defined by the present invention
No. In the case of 38 to 56, (da / dN) m is large, and the fatigue crack growth suppressing property is not improved.
【００６０】[0060]
【発明の効果】本発明の鋼板は、中ΔＫ領域においても
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、従来鋼に比べて疲労寿命の延長
が期待できる。したがって、土木建築構造物、船体、海
洋構造物、海洋装置およびラインパイプなどに用いられ
る鋼材として適している。The steel sheet of the present invention is excellent in fatigue crack growth suppression characteristics even in the medium ΔK region, and can prolong the fatigue life as compared with conventional steel even when a fatigue crack occurs from a weld. Therefore, it is suitable as a steel material used for civil engineering building structures, hulls, marine structures, marine equipment, line pipes, and the like.
【図１】（ａ）は試験装置の概要を示す図、（ｂ）は疲
労試験片の形状を示す図である。FIG. 1A is a diagram showing an outline of a test apparatus, and FIG. 1B is a diagram showing a shape of a fatigue test piece.
１：ＣＴ試験片、 ２：試験溶液槽、 ３：溶液循環
ポンプ、 ４：ロードセル、 ５：油圧シリンダー、６：油圧源、 ７：サーボバルブ、８：波形発生器、 ９：負荷制御
器1: CT test piece, 2: Test solution tank, 3: Solution circulation pump, 4: Load cell, 5: Hydraulic cylinder, 6: Hydraulic source, 7: Servo valve, 8: Waveform generator, 9: Load controller
───────────────────────────────────────────────────── フロントページの続き (72)発明者 幸 英昭 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (72)発明者 岡口 秀治 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (72)発明者 一ノ瀬 威 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (72)発明者 櫛田 隆弘 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (72)発明者 誉田 登 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (56)参考文献 特開 昭64−87746（ＪＰ，Ａ) 特開 平７−11383（ＪＰ，Ａ) 特開 平４−337026（ＪＰ，Ａ) 特開 平４−329848（ＪＰ，Ａ) (58)調査した分野(Int.Cl.6，ＤＢ名) C22C 38/00 - 38/60 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Hideaki Yuki, Inventor 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries Co., Ltd. (72) Hideharu Okaguchi 4-5-Kitahama, Chuo-ku, Osaka City, Osaka Prefecture No. 33 Sumitomo Metal Industries Co., Ltd. (72) Inventor Takeshi Ichinose 4-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture Sumitomo Metal Industries Co., Ltd. (72) Inventor Takahiro Kushida 4, Kitahama, Chuo-ku, Osaka-shi, Osaka No. 5-33 Sumitomo Metal Industries, Ltd. (72) Inventor Noboru Shoda 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (56) References JP-A-64-87746 (JP) JP-A-7-11383 (JP, A) JP-A-4-337026 (JP, A) JP-A-4-329848 (JP, A) (58) Fields investigated (Int. Cl. 6 , DB Name) C22C 38/00-38/60
Claims (4)
ｉ：０．１〜０．５％、Ｍｎ：０．３〜２．０％および
ｓｏｌ．Ａｌ：０．００５〜０．１％、さらに、Ｃｒ：
１．５％以下（無添加でもよい）、Ｍｏ：０．６％以下
（無添加でもよい）、Ｎｉ：０．５％以下（無添加でも
よい）、Ｃｕ：１．０％以下（無添加でもよい）、Ｎ
ｂ：０．１％以下（無添加でもよい）、Ｔｉ：０．１％
以下（無添加でもよい）およびＶ：０．１％以下（無添
加でもよい）を含み、残部はＦｅと不可避不純物からな
る鋼板であって、その組織は硬質部の素地とこの素地に
分散した軟質部とからなり、この２部分の硬度差がビッ
カース硬度で１５０以上であることを特徴とする疲労亀
裂進展抑制効果を有する鋼板。C .: 0.01 to 0.3% by mass, S:
i: 0.1 to 0.5%, Mn: 0.3 to 2.0%, and sol. Al: 0.005 to 0.1%, and Cr:
1.5% or less (no addition), Mo: 0.6% or less (no addition), Ni: 0.5% or less (no addition), Cu: 1.0% or less (no addition) Or N)
b: 0.1% or less (may not be added), Ti: 0.1%
Or less (may be not added) and V: 0.1% or less include (may be not added), and the balance a steel sheet consisting of Fe and unavoidable impurities, into a green body and the green body of the tissue rigid portion
A steel sheet having a fatigue crack growth suppressing effect, comprising a dispersed soft part, and a hardness difference between the two parts being 150 or more in Vickers hardness.
であって、その組織は硬質部の素地とこの素地に分散し
た軟質部からなり、硬質部の素地と軟質部との硬度差が
ビッカース硬度で１５０以上、軟質部の平均粒径が５０
μｍ以下であることを特徴とする疲労亀裂進展抑制効果
を有する鋼板。2. A steel sheet having the chemical composition according to claim 1 , wherein the structure is composed of a base material of a hard part and a soft part dispersed in the base material, and a difference in hardness between the base material of the hard part and the soft part is obtained. Vickers hardness is 150 or more, average particle size of soft part is 50
A steel sheet having an effect of suppressing fatigue crack growth, which is not more than μm.
であって、その組織は硬質部の素地とこの素地に分散し
た軟質部とからなり、この２部分の硬度差がビッカース
硬度で１５０以上、硬質部の平均間隔が５０μｍ以下で
あることを特徴とする疲労亀裂進展抑制効果を有する鋼
板。3. A steel sheet having the chemical composition according to claim 1 , wherein the structure is composed of a base material of a hard part and a structure dispersed in the base material.
A steel sheet having a fatigue crack growth suppressing effect, comprising a soft portion having a hardness difference of 150 or more in Vickers hardness and an average interval of 50 μm or less of the hard portion.
あって、その組織は硬質部の素地とこの素地に分散した
軟質部とからなり、この２部分の硬度差がビッカース硬
度で１５０以上、硬質部の平均間隔が５０μｍ以下、か
つ、軟質部の平均粒径が５０μｍ以下であることを特徴
とする疲労亀裂進展抑制効果を有する鋼板。 4. A steel sheet having the chemical composition according to claim 1, wherein a structure of the steel sheet has a structure of a hard part and a structure dispersed in the base material.
The fatigue crack suppression characterized by comprising a soft portion, wherein the hardness difference between the two portions is 150 or more in Vickers hardness, the average interval between the hard portions is 50 μm or less, and the average particle size of the soft portion is 50 μm or less. Steel sheet with effect.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3853894A JP2962134B2 (en) | 1994-03-09 | 1994-03-09 | Steel plate with fatigue crack growth suppression effect |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3853894A JP2962134B2 (en) | 1994-03-09 | 1994-03-09 | Steel plate with fatigue crack growth suppression effect |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP08551699A Division JP3298544B2 (en) | 1999-03-29 | 1999-03-29 | Steel plate with fatigue crack growth control effect |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07242992A JPH07242992A (en) | 1995-09-19 |
| JP2962134B2 true JP2962134B2 (en) | 1999-10-12 |
Family
ID=12528068
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3853894A Expired - Lifetime JP2962134B2 (en) | 1994-03-09 | 1994-03-09 | Steel plate with fatigue crack growth suppression effect |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2962134B2 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3849244B2 (en) * | 1997-09-16 | 2006-11-22 | Ｊｆｅスチール株式会社 | Steel material excellent in ductile crack growth resistance under repeated large deformation and its manufacturing method |
| CN1809648B (en) * | 2003-06-19 | 2010-07-21 | 住友金属工业株式会社 | Steel product excellent in characteristics of resistance to fatigue crack extension and method for production thereof |
| JP5633374B2 (en) * | 2011-01-05 | 2014-12-03 | 新日鐵住金株式会社 | Welded joint |
| CN106811696B (en) * | 2015-12-02 | 2018-02-27 | 鞍钢股份有限公司 | A kind of big thickness ocean engineering 390MPa levels steel plate and its manufacture method |
| KR102557520B1 (en) | 2019-01-23 | 2023-07-20 | 제이에프이 스틸 가부시키가이샤 | Steel plate and method of producing same |
| KR20240021260A (en) | 2021-07-16 | 2024-02-16 | 제이에프이 스틸 가부시키가이샤 | Heavy steel plate and manufacturing method of thick steel plate |
-
1994
- 1994-03-09 JP JP3853894A patent/JP2962134B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH07242992A (en) | 1995-09-19 |
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