JPH11310846A - Steel plate with fatigue crack propagation inhibiting effect - Google Patents
Steel plate with fatigue crack propagation inhibiting effectInfo
- Publication number
- JPH11310846A JPH11310846A JP8551699A JP8551699A JPH11310846A JP H11310846 A JPH11310846 A JP H11310846A JP 8551699 A JP8551699 A JP 8551699A JP 8551699 A JP8551699 A JP 8551699A JP H11310846 A JPH11310846 A JP H11310846A
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- steel sheet
- steel
- fatigue crack
- fatigue
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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
進展特性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 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。[0004] 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. However, the effect of this method is limited to a low ΔK (ΔK: difference between the maximum stress intensity factor and the minimum stress intensity factor), that is, a case where the crack is not long and the stress level is low, and a certain amount of the heat generated from the weld is obtained. , And it is considered to be small for cracks in the middle ΔK region.
【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500 μm 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),
The effects of microstructure on fatigue endurance limit have been investigated in the field of mechanical structural steel as shown on pages 440 to 445, but in long cracks with a length of more than about 500 μm, It has been pointed out that it is hardly affected, and there is no knowledge to suppress the growth of relatively long cracks necessary for further improving the suppression of the growth of fatigue cracks.
【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 Patent Application Laid-Open No. 4-329848 discloses a hardness of a mother phase and a second phase in a two-phase structure regarding a hot-rolled steel sheet for various uses including an automobile wheel in which fatigue strength is an important property. Although it is shown that good fatigue strength can be obtained by limiting the area ratio and the particle size of the second phase, it cannot be said that the fatigue crack growth behavior has been sufficiently studied, and The effect of suppressing the growth of fatigue cracks, focusing on the difference in hardness between the 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)〜 (3) の疲労亀裂進展抑制効果を有する鋼板にあ
る。The gist of the present invention is as follows.
(1) to (3) a steel sheet having a fatigue crack growth suppressing effect.
【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）、M
o：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）、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、その組織は軟質部の素地とこの素地に分散した
硬質部とからなり、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), M
o: 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 (may be non-added), Ti: 0.1% or less (may be non-added) and V: 0.1% or less (may be non-added), and the balance is Fe and inevitable impurities. A steel sheet having a structure comprising a soft portion base and a hard portion dispersed in the base, and a hardness difference between the two portions is 150 or more in Vickers hardness.
【００１０】(2)硬質部の平均間隔が50μm 以下である
上記（1）の鋼板。(2) The steel sheet according to (1), wherein the average interval between the hard parts is 50 μm or less.
【００１１】(3)軟質部の平均粒径が50μm 以下である
上記（2）の鋼板。(3) The steel sheet according to the above (2), wherein the soft part has an average particle size of 50 μm or less.
【００１２】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。[0012] 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.
【００１３】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.
【００１４】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 on the fatigue behavior of the steel material, it is found that the fatigue crack is liable to be retained when the hardness of the composite structure is large. And this effect depends on the existence ratio (volume ratio) of the hard part and the soft part.
Not much affected.
【００１５】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。[0015] When the hardness difference 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 distance (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.
【００１６】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抑制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 one 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 growth suppressing property even in a corrosive environment can be expected.
【００１７】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 carbide is obtained, and the rate of fatigue crack propagation in the soft part decreases. .
【００１８】[0018]
【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%.
【００１９】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0.01％
以上とした。これを下回ると必要な強度と組織を確保す
るのが困難である。一方、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 required for applications of the steel sheet of the present invention, the C content is 0.01%.
It was above. Below this, it is difficult to secure the required strength and organization. On the other hand, the main use of steel sheets is always subjected to welding, so the upper limit of the C content is set to 0.3% in order to prevent the occurrence of welding cracks. A desirable range of the C content is 0.03 to 0.18%.
【００２０】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Si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. Si content is 0.
If less than 1%, this effect cannot be expected. On the other hand, if it exceeds 0.5%, the toughness of the steel is impaired. The desirable range of the Si content is 0.25 to 0.4%.
【００２１】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、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. Mn content is 0.3
%, It is difficult to secure the strength required for the use of the steel sheet. However, Mn, like C, is a component that hardens the weld heat affected zone and causes welding cracks, and therefore has an upper limit on the content. That is, if it exceeds 2.0%, welding cracks are likely to occur. Desirable Mn content is 0.7-1.
4%.
【００２２】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 has a content of 0.005 as sol.Al for deoxidizing steel.
%. However, if the sol.Al content exceeds 0.1%, the cleanliness and toughness of the steel are impaired.
【００２３】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、0.020 ％以下に
抑えるのが望ましい。[0023] One of the steel sheets of the present invention includes, in addition to the above components,
The balance consists of Fe and inevitable impurities. P and S in the impurities are desirably suppressed to 0.025% or less and 0.020% or less, respectively.
【００２４】本発明の鋼板は上記の各成分に加えて、さ
らに、必要に応じて次の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 contain one or more of the following seven components, if necessary, in addition to the above components.
【００２５】Cr：1.5 ％以下 Crは、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 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 actively adding Cr
The content is desirably 0.01% or more. However, 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%.
【００２６】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組成変形の抑制に有
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 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. Therefore, when actively adding Mo
It is desirable that the lower limit of the content be 0.05%. But Mo
If the 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%.
【００２７】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 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, when actively adding Ni
It is desirable that the lower limit of the content be 0.1%. But Ni
If the content exceeds 0.5%, these effects are saturated and the strength of the steel is excessively increased, and the toughness is impaired. More preferably, it is in the range of 0.2-0.4%.
【００２８】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、Cu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.
It is desirable that the content be 0.1% or more. However, the Cu content is 1.
If it exceeds 0%, 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 0.3-0.5%.
【００２９】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 corrosion resistance, and together with this effect, the characteristic of suppressing the growth of fatigue cracks in a corrosive environment is improved.
【００３０】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0.01％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、Ti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, thereby suppressing fatigue crack growth in a corrosive environment. It is an effective component for improving characteristics. Therefore, when one or more of these three components are selected and positively added, the content is desirably 0.01% or more. However, if the content exceeds 0.1%, the above effect is saturated, and the strength of the steel excessively increases, so that the toughness is impaired. More preferably, Ti and Nb
Are in the range of 0.01 to 0.03%, and V is in the range of 0.02 to 0.05%.
【００３１】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) Difference in Structure and Hardness 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.
【００３２】本発明鋼板は、軟質部の素地とこの素地に
分散した硬質部と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。The steel sheet of the present invention has a composite structure composed of a soft portion base and hard portions dispersed in the base. 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.
【００３３】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 crack growth near the interface is obtained. 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.
【００３４】本発明鋼板の一つは、上記の軟質部の素地
とこの素地に分散した硬質部とからなる複合組織におい
て、さらに硬質部と軟質部との硬度の差をビッカース硬
度（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 is a composite structure comprising the above-described soft portion base and the hard portion dispersed in the base, and further, the difference in hardness between the hard portion and the soft portion is determined by Vickers hardness (hereinafter referred to as Hv). ) And 150 or more.
【００３５】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150 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 reason why the hardness difference between the soft part and the hard part is 150 or more in Hv is as follows. When the hardness difference is 150 or more, the dislocation movement at the crack tip is prevented at the interface between the soft part and the hard part, and the dislocations whose Burgers vector are perpendicular to the interface are arranged in the soft part near the interface between the two parts. Therefore, an inclined grain boundary is 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.
【００３６】本発明鋼板の他の一つは、その組織を軟質
部（素地）と硬質部（分散相）とからなるものとし、こ
の２部分の硬度差をＨv で150 以上、さらに分散相の硬
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、硬質部の平均間隔は中心間距離を指すも
のである。Another one of the steel sheets of the present invention has a structure comprising a soft portion (base material) and a hard portion (dispersed phase). The average interval (dispersion distance) of the hard portions is set to 50 μm or less. Here, the average interval of the hard portions indicates the center-to-center distance.
【００３７】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 is also composed of both hard and soft parts, and has an appropriate difference in hardness, so that the effect of stopping crack growth near the interface can be obtained.
【００３８】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 the crack stopping effect becomes remarkable.
If the average interval of the hard portions exceeds 50 μm, the remarkable effect cannot be obtained.
【００３９】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 hardness difference are maintained, and both the conditions that the average particle size of the soft part is 50 μm or less and the average interval of the hard part is 50 μm or less are satisfied,
A more favorable effect can be obtained.
【００４０】[0040]
【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 formed 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.
【００４１】[0041]
【表１】 [Table 1]
【００４２】[0042]
【表２】 [Table 2]
【００４３】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, etc. for each of the steel Nos. 1 to 24, various structures, the difference in hardness between the soft part and the hard part, and the average of the soft part A steel sheet having a particle size, an average distance between hard parts (dispersion distance), 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.
【００４４】これらの鋼板から採取した試験材を試番１
〜56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
The structure, the average grain size of the soft part, the average interval of the hard part, the difference in hardness, and the fatigue crack growth suppression properties were investigated.
【００４５】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.
【００４６】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 (b) shows the investigation of the fatigue crack growth suppression characteristics.
(A) and a fatigue test method using a servo pulser device shown in FIG. 1 (a).
【００４７】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.
【００４８】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50〜300 kgf/mm3/2)における
第２領域で、 Paris則〔Trans.ASME,Ser.D.85.523 (196
3)) 〕、すなわちda/dN=C( ΔＫ) m 、ただし、〔Δ
Ｋ〕：kgf/mm3/2 ，〔da/dN 〕：mm/cycleが成り立つこ
とが判明した。したがって、疲労亀裂進展抑制特性は、
この中ΔＫ領域のΔＫ＝50および100kgf/mm3/2におけ
る、亀裂進展速度da/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 (crude oil with 10% water suspended, hydrogen sulfide concentration 1%, The remainder is continuously blown with a mixed gas of nitrogen during the test period. According to the results of the fatigue test in artificial seawater and in the atmosphere specified in ASTM, D-1141-52, according to the results of the fatigue test in any of the test specimens, the medium ΔK region (this test) In the second region at about 50 to 300 kgf / mm 3/2 ), the Paris rule (Trans.ASME, Ser.D.85.523 (196
3))], that is, da / dN = C (ΔK) m , where [Δ
K]: kgf / mm 3/2 and [da / dN]: mm / cycle were found to hold. Therefore, the fatigue crack growth suppression properties are:
The average value of the crack growth rate da / dN (mm / cycle) at ΔK = 50 and 100 kgf / mm 3/2 in the ΔK region (da / dN) m
It was decided to evaluate. Tables 3 to 6 show the results of the above investigation, measurement and fatigue test.
【００４９】[0049]
【表３】 [Table 3]
【００５０】[0050]
【表４】 [Table 4]
【００５１】[0051]
【表５】 [Table 5]
【００５２】[0052]
【表６】 [Table 6]
【００５３】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.１〜37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、疲労亀裂進展特性は改善されて
いない。As can be seen from the (da / dN) m of each test piece,
In Test Nos. 1 to 37, which are examples of the present invention, (da / dN) m is small, and has high fatigue crack growth resistance. On the other hand, in Test Nos. 38 to 56 in which the difference in hardness was out of the range defined by the present invention, (da / dN) m was large, and the fatigue crack growth characteristics were not improved.
【００５４】[0054]
【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 specimen, 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 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideaki Yukiaki 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Hideharu Okaguchi 4-chome, Kitahama, Chuo-ku, Osaka-shi, Osaka 5-33 Sumitomo Metal Industries Co., Ltd. (72) Inventor Takeshi Ichinose 4-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture 5-33 Sumitomo Metal Industries Co., Ltd. (72) Inventor Takahiro Kushida Osaka-shi, Osaka 4-7-33 Kitahama-ku, Sumitomo Metal Industries Co., Ltd. (72) Inventor Noboru Yoshida 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries Co., Ltd.
Claims (3)
0.5 ％、Mn:0.3〜2.0 ％およびsol.Al：0.005 〜0.1
％、さらに、Cr：1.5 ％以下、Mo：0.6 ％以下、Ni：0.
5 ％以下、Cu：1.0 ％以下、Nb：0.1 ％以下、Ti：0.1
％以下およびＶ：0.1 ％以下を含み、残部はFeと不可避
不純物からなる鋼板であって、その組織は軟質部の素地
とこの素地に分散した硬質部とからなり、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: 0.3-2.0% and sol.Al: 0.005-0.1
%, Cr: 1.5% or less, Mo: 0.6% or less, Ni: 0.
5% or less, Cu: 1.0% or less, Nb: 0.1% or less, Ti: 0.1
% And V: 0.1% or less, the balance being a steel sheet comprising Fe and inevitable impurities, the structure of which is composed of a soft part base and a hard part dispersed in the base, and the hardness difference between the two parts is small. A steel sheet having a Vickers hardness of 150 or more and having an effect of suppressing fatigue crack growth.
を特徴とする請求項１に記載の疲労亀裂進展抑制効果を
有する鋼板。2. The steel sheet according to claim 1, wherein the average interval between the hard portions is 50 μm or less.
を特徴とする請求項２に記載の疲労亀裂進展抑制効果を
有する鋼板。3. The steel sheet according to claim 2, wherein the average grain size of the soft part is 50 μm or less.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08551699A JP3298544B2 (en) | 1999-03-29 | 1999-03-29 | Steel plate with fatigue crack growth control effect |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08551699A JP3298544B2 (en) | 1999-03-29 | 1999-03-29 | Steel plate with fatigue crack growth control effect |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3853894A Division JP2962134B2 (en) | 1994-03-09 | 1994-03-09 | Steel plate with fatigue crack growth suppression effect |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11310846A true JPH11310846A (en) | 1999-11-09 |
| JP3298544B2 JP3298544B2 (en) | 2002-07-02 |
Family
ID=13861086
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP08551699A Expired - Lifetime JP3298544B2 (en) | 1999-03-29 | 1999-03-29 | Steel plate with fatigue crack growth control effect |
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| Country | Link |
|---|---|
| JP (1) | JP3298544B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004033144A1 (en) | 2002-10-08 | 2004-04-22 | Nippon Steel Corporation | Boxing joint with excellent fatigue strength, method of manufacturing the boxing joint, and welded structure |
| EP2105516A1 (en) * | 2008-03-28 | 2009-09-30 | Kabushiki Kaisha Kobe Seiko Sho | High-strength steel sheet excellent in resistance to stress-relief annealing and in low-temperature joint toughness |
-
1999
- 1999-03-29 JP JP08551699A patent/JP3298544B2/en not_active Expired - Lifetime
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004033144A1 (en) | 2002-10-08 | 2004-04-22 | Nippon Steel Corporation | Boxing joint with excellent fatigue strength, method of manufacturing the boxing joint, and welded structure |
| JP2004130316A (en) * | 2002-10-08 | 2004-04-30 | Nippon Steel Corp | Boxing joint of excellent fatigue strength, boxing joint manufacturing method, and welded structure |
| US7695825B2 (en) | 2002-10-08 | 2010-04-13 | Nippon Steel Corporation | Circularly welded joint featuring excellent fatigue strength, method of producing circularly welded joint and welded structure |
| JP4537649B2 (en) * | 2002-10-08 | 2010-09-01 | 新日本製鐵株式会社 | Rotating welded joint, manufacturing method of Rotated welded joint, and welded structure |
| EP2105516A1 (en) * | 2008-03-28 | 2009-09-30 | Kabushiki Kaisha Kobe Seiko Sho | High-strength steel sheet excellent in resistance to stress-relief annealing and in low-temperature joint toughness |
| US8394209B2 (en) | 2008-03-28 | 2013-03-12 | Kobe Steel, Ltd. | High-strength steel sheet excellent in resistance to stress-relief annealing and in low-temperature joint toughness |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3298544B2 (en) | 2002-07-02 |
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