JP2002121640A - Steel sheet having suppressing effect on fatigue crack propagation - Google Patents
Steel sheet having suppressing effect on fatigue crack propagationInfo
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- JP2002121640A JP2002121640A JP2000315146A JP2000315146A JP2002121640A JP 2002121640 A JP2002121640 A JP 2002121640A JP 2000315146 A JP2000315146 A JP 2000315146A JP 2000315146 A JP2000315146 A JP 2000315146A JP 2002121640 A JP2002121640 A JP 2002121640A
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- hard
- steel sheet
- soft
- soft part
- hardness
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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、海洋構造物や装置及びラインパイプなどの素材と
して好適な、大気中及び腐食環境中において耐疲労亀裂
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 propagation resistance 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、溶接鋼構造物が大型化する傾向が
顕著となっている。このため、構造用鋼材の高強度化に
よる軽量化が望まれており、例えば、土木建築構造物や
船体に高張力鋼材の使用が拡大され始めている。しか
し、高強度鋼材を使用する場合、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, the tendency of welded steel structures to become larger has become remarkable. For this reason, it is desired to reduce the weight of structural steel materials by increasing the strength. For example, the use of high-tensile steel materials for civil engineering structures and hulls has begun to expand. However, when a high-strength steel material is used, the design stress increases, so that fatigue fracture becomes an important problem.
【０００３】一方、溶接構造用鋼材においては一般に溶
接施工が施されるため、溶接部を起点にして疲労亀裂が
発生することが多く、疲労亀裂の進展を抑制することが
できなければ重大な事故に発展する恐れがある。逆に、
溶接部から発生して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ことが
可能であるし、重大な事故を防止することができる。[0003] On the other hand, since welding work is generally performed on steel for welded structures, fatigue cracks often occur starting from a welded portion. If the propagation of fatigue cracks cannot be suppressed, serious accidents occur. There is a risk of developing. vice versa,
If the fatigue crack generated and propagated from the welded portion can be stopped by the steel material, the fatigue life of the structure can be extended and a serious accident can be prevented.
【０００４】特開平５−１４８５４１号公報には、疲労
亀裂の進展を抑制する方法として、疲労亀裂先端にマイ
クロクラックを発生させる技術が開示されている。しか
し、前記公報で提案された技術の効果は、△Ｋを最大応
力拡大係数と最小応力拡大係数との差として、低△Ｋ領
域、すなわち、亀裂が長くなく応力レベルが低い場合に
限られる。このため、溶接部から発生して或る程度の長
さを有する中△Ｋ領域における亀裂に対しては、前記技
術の効果は小さいものでしかない。Japanese Patent Application Laid-Open No. 5-148541 discloses a technique for generating a microcrack at the tip of a fatigue crack as a method for suppressing the growth of the fatigue crack. However, the effect of the technique proposed in the above publication is limited to a low ΔK region where ΔK is a 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. For this reason, the effect of the technique is only small for cracks in the medium K region having a certain length generated from the weld.
【０００５】特開平４−３２９８４８号公報には、疲労
強度が重要な特性となる自動車用ホイールを初めとする
各種用途の熱延鋼板に関して、２相組織中の母相と第２
相の硬さ、面積率及び第２相の粒径を限定する技術が開
示されている。この公報で提案された技術によれば、良
好な疲労強度が得られるものの、疲労亀裂の進展挙動に
関しては十分な配慮がなされておらず、したがって、必
ずしも疲労亀裂の進展を抑制できるものではない。これ
は、「疲労強度」が繰り返し荷重を受けた材料（鋼材）
の内部に数十μｍの疲労亀裂が発生するか否かに着目し
た強度特性でしかなく、疲労亀裂の進展抑制に及ぼす影
響は小さいからである。つまり、応力が集中する部分の
材料欠陥から発生した疲労亀裂が構造物中を進展して構
造物が耐え得る長さ（数ｍｍから数十ｍｍ）まで進展
し、その限界亀裂長さを超えて構造物の破断が生じる
が、構造物の疲労寿命のうちの大部分の期間は、この巨
視亀裂が進展する期間に相当し、たとえ疲労強度が低く
疲労亀裂が発生したとしても、破壊に至らなければ重大
な事故につながらない。このため、特に、大型溶接構造
物の場合には、疲労亀裂の発生以上にその進展抑制が重
要なのである。[0005] Japanese Patent Application Laid-Open 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 characteristic.
A technique for limiting the phase hardness, the area ratio, and the particle size of the second phase is disclosed. According to the technique proposed in this publication, good fatigue strength is obtained, but sufficient consideration is not given to the propagation behavior of fatigue cracks, and therefore, it is not always possible to suppress the growth of fatigue cracks. This is a material (steel material) whose "fatigue strength" is repeatedly loaded.
This is because it is only the strength characteristic that focuses on whether or not a fatigue crack of several tens of μm is generated inside the steel, and the influence on the suppression of the growth of the fatigue crack is small. In other words, the fatigue crack generated from the material defect in the portion where the stress is concentrated propagates in the structure and extends to a length (several mm to several tens mm) that the structure can withstand, and exceeds the limit crack length. Although the structure is ruptured, most of the fatigue life of the structure corresponds to the period during which the macrocrack propagates, and even if the fatigue strength is low and the fatigue crack occurs, the fracture must not occur. If it does not lead to a serious accident. For this reason, especially in the case of a large-sized welded structure, it is important to suppress the progress of fatigue cracks more than the occurrence of fatigue cracks.
【０００６】特開平７−１１３８３号公報には、第２相
の平均径を２０μｍ以下とすることで疲労限の向上を図
った「疲労特性に優れた複合組織鋼板」が開示されてい
る。しかし、この公報で提案された技術が対象とするの
は、ビッカース硬さで４００以上の高強度を有するもの
であり、したがって、鋼板の靱性が重視される厚鋼板の
場合に必ずしも適用できるものではない。Japanese Unexamined Patent Publication (Kokai) No. 7-11383 discloses a "composite structure steel sheet having excellent fatigue properties" in which the average diameter of the second phase is set to 20 μm or less to improve the fatigue limit. However, the technology proposed in this publication is intended for those having a high strength of 400 or more in Vickers hardness, and therefore not necessarily applicable to thick steel plates where the toughness of the steel plate is important. Absent.
【０００７】特開平７−９０４７８号公報には、「耐疲
労亀裂進展特性の良好な鋼板およびその製造法」が開示
されている。しかし、前記公報で提案された技術は、ビ
ッカース硬さで母相の硬さより３０％以上高い硬質の縞
状第２相が鋼板圧延方向に延在し、疲労亀裂の進展が上
記硬質相の存在によって抑制されるものである。このた
め、圧延方向に進展する疲労亀裂に対しては、必ずしも
進展抑制効果が発揮されるというものではない。[0007] Japanese Patent Application Laid-Open No. 7-90478 discloses "a steel sheet having good fatigue crack propagation resistance and a method for producing the same". However, in the technique proposed in the above publication, the hard striped second phase having a Vickers hardness of 30% or more higher than the hardness of the parent phase extends in the rolling direction of the steel sheet, and the progress of fatigue cracks is caused by the existence of the hard phase. It is controlled by. For this reason, the effect of suppressing the growth is not always exhibited for the fatigue cracks that grow in the rolling direction.
【０００８】特開平７−２４２９９２号公報には、硬質
部と軟質部の硬度差をビッカース硬さで１５０以上とし
た「疲労亀裂進展抑制効果を有する鋼板」が開示されて
いる。この公報で提案された鋼板は、前記した中△Ｋ領
域においても疲労亀裂進展特性に優れており、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
命を延長することができる。しかし、更に一層良好な疲
労亀裂進展特性が要求される場合には、前記公報で提案
された技術をもってしても必ずしも十分とはいえないよ
うなこともある。Japanese Patent Application Laid-Open No. 7-242992 discloses a "steel sheet having a fatigue crack growth suppressing effect" in which the difference in hardness between a hard part and a soft part is 150 or more in Vickers hardness. The steel sheet proposed in this publication has excellent fatigue crack growth characteristics even in the above-mentioned medium ΔK region, and can extend the fatigue life as compared with conventional steel even when a fatigue crack occurs from a welded portion. . However, if even better fatigue crack growth characteristics are required, the technique proposed in the above-mentioned publication may not always be sufficient.
【０００９】特開平１１−１７４２号公報には、フェラ
イト母相及び硬質の第２相についてそれぞれビッカース
硬さを規定するとともに、前記第２相のアスペクト比を
規定した「疲労き裂伝播特性の優れた鋼材及びその製造
方法」が開示されている。この公報で提案された技術に
よって疲労亀裂の進展を抑制することはできるものの、
第２相のアスペクト比が（長軸／短軸）＞３．４２であ
り、したがって、 鋼板方向で疲労亀裂進展速度や靱性
などの特性に差が生じることがある。Japanese Patent Application Laid-Open No. H11-1742 discloses a method of defining a Vickers hardness for each of a ferrite matrix phase and a hard second phase and defining an aspect ratio of the second phase. Steel material and its manufacturing method ". Although the technology proposed in this publication can suppress the growth of fatigue cracks,
The aspect ratio of the second phase is (long axis / short axis)> 3.42, and therefore, there may be a difference in properties such as fatigue crack growth rate and toughness in the steel sheet direction.
【００１０】[0010]
【発明が解決しようとする課題】本発明は、上記現状に
鑑みなされたもので、その目的は、土木建築構造物、船
体、海洋構造物や装置及びラインパイプなどの素材とし
て好適な、大気中や腐食環境中において耐疲労亀裂進展
特性に優れる鋼板、具体的には、後述の実施例における
評価で、大気中における亀裂進展速度ｄａ／ｄＮAVが
３．００×１０-6ｍｍ／サイクル以下、湿潤硫化水素中
又は人工海水中における亀裂進展速度ｄａ／ｄＮAVが１
２．００×１０-6ｍｍ／サイクル以下という優れた耐疲
労亀裂進展特性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 in view of the above-mentioned circumstances, and has as its object to provide an atmosphere suitable for use as a material for civil engineering building structures, hulls, marine structures and equipment, and line pipes. steel sheet excellent in fatigue crack growth properties in or corrosive environment, in particular, in the evaluation in the examples below, the crack growth rate da / dN AV in the atmosphere is 3.00 × 10 -6 mm / cycle or less, Crack growth rate da / dN AV in wet hydrogen sulfide or artificial seawater is 1
An object of the present invention is to provide a steel sheet having excellent fatigue crack propagation resistance of 2.00 × 10 −6 mm / cycle or less.
【００１１】[0011]
【課題を解決するための手段】本発明の要旨は、下記
（１）〜（４）に示す鋼板にある。The gist of the present invention resides in the following steel sheets (1) to (4).
【００１２】（１）質量％で、Ｃ：０．０３〜０．３０
％、Ｓｉ：０．０１〜０．５％、Ｍｎ：０．３〜２．０
％、ｓｏｌ．Ａｌ：０．００１〜０．１％、を含有し、
残部はＦｅ及び不純物からなる鋼板であって、その組織
が硬質部と軟質部とからなり、この２つの部分の組織に
占める割合及びビッカース硬さでの平均硬さが下記 (1)
式を満たす鋼板。(1) In mass%, C: 0.03 to 0.30
%, Si: 0.01 to 0.5%, Mn: 0.3 to 2.0
%, Sol. Al: 0.001 to 0.1%,
The remainder is a steel plate composed of Fe and impurities, and the structure is composed of a hard part and a soft part. The ratio of these two parts to the structure and the average hardness in Vickers hardness are as follows:
Steel plate that satisfies the formula.
【００１３】 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) （２）上記（１）に記載の成分に加えて更に、質量％
で、第１群：Ｃｕ：０．１〜１．５％、Ｎｉ：０．１〜
１．５％、Ｃｒ：０．１〜１．５％、Ｍｏ：０．１〜
１．０％のうちの１種以上、第２群：Ｖ：０．０１〜
０．１％、Ｎｂ：０．０１〜０．１％、Ｔｉ：０．０１
〜０．０５％のうちの１種以上、第３群：Ｂ：０．００
０５〜０．００３％、の１群以上をも含み、残部はＦｅ
及び不純物からなる鋼板であって、その組織が硬質部と
軟質部とからなり、この２つの部分の組織に占める割合
及びビッカース硬さでの平均硬さが下記 (1)式を満たす
鋼板。FA · HA−fB · HB ≧ −3500 (1) (2) In addition to the component described in the above (1), further, mass%
And the first group: Cu: 0.1 to 1.5%, Ni: 0.1 to
1.5%, Cr: 0.1 to 1.5%, Mo: 0.1 to
1.0% or more, second group: V: 0.01 to
0.1%, Nb: 0.01 to 0.1%, Ti: 0.01
At least one of -0.05%, third group: B: 0.00
0.05 to 0.003%, the balance being Fe
A steel sheet comprising a hard portion and a soft portion, wherein the ratio of the two portions to the structure and the average hardness in Vickers hardness satisfy the following formula (1).
【００１４】 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) （３）上記（１）又は（２）に記載の化学組成からなる
鋼板であって、その組織が硬質部の素地とこの素地に分
散した軟質部とからなり、軟質部の平均粒径が５０μｍ
以下で、且つ、前記２つの部分の組織に占める割合及び
ビッカース硬さでの平均硬さが下記 (1)式を満たす鋼
板。FA · HA−fB · HB ≧ −3500 (1) (3) A steel sheet having the chemical composition described in the above (1) or (2), wherein the structure is the same as the base material of the hard part. This soft part is dispersed in the base material, and the soft part has an average particle size of 50 μm.
A steel sheet having a ratio of the two parts to the structure and an average hardness in Vickers hardness satisfying the following formula (1).
【００１５】 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) （４）上記（１）又は（２）に記載の化学組成からなる
鋼板であって、その組織が硬質部の素地とこの素地に分
散した軟質部とからなり、硬質部の平均間隔が５０μｍ
以下で、且つ、前記２つの部分の組織に占める割合及び
ビッカース硬さでの平均硬さが下記 (1)式を満たす鋼
板。FA · HA−fB · HB ≧ −3500 (1) (4) A steel sheet having the chemical composition according to the above (1) or (2), wherein the structure is the same as the base material of the hard part. It consists of soft parts dispersed in this substrate, and the average interval of the hard parts is 50 μm.
A steel sheet having a ratio of the two parts to the structure and an average hardness in Vickers hardness satisfying the following formula (1).
【００１６】 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) ここで、前記のｆＡとｆＢは、それぞれ硬質部と軟質部
が組織に占める％単位での割合を指し、又、ＨＡとＨＢ
は、それぞれ硬質部と軟質部のビッカース硬さでの平均
硬さを指す。なお、組織に占める割合は、顕微鏡観察し
た場合の面積率とすればよい。FA · HA−fB · HB ≧ −3500 (1) Here, the above fA and fB indicate percentages of the hard portion and the soft portion in the tissue, respectively, in units of%. And HB
Indicates the average hardness of the hard part and the soft part in Vickers hardness. Note that the ratio in the tissue may be the area ratio when observed with a microscope.
【００１７】素地とは、組織に占める割合が５０％以上
の場合をいい、したがって、「硬質部の素地」とは、硬
質部が組織に占める割合が５０％以上であることを指
す。The base means a case where the ratio of the hard portion to the tissue is 50% or more. Therefore, the "base of the hard portion" means that the ratio of the hard portion to the structure is 50% or more.
【００１８】硬質部の平均間隔とは、軟質部を間にし
て、硬質部と軟質部との界面から隣の硬質部と軟質部と
の界面までの最短の直線距離の平均をいう。硬質部が素
地として連続している場合の平均間隔は０（ゼロ）であ
る。なお、素地の硬質相が連続しない場合としては、例
えば、オーステナイト粒界から析出したフェライトがオ
ーステナイト粒界を取り囲み、その内部にあったオース
テナイトがベイナイトやマルテンサイトといった硬質相
に変態した場合が挙げられる。なお、本明細書でいう
「硬質部」とは、マルテンサイト、ベイナイト、パーラ
イト及び焼戻しマルテンサイトの１種以上で構成される
組織を、「軟質部」とはフェライトから構成される組織
を意味する。The average interval between the hard portions means the average of the shortest linear distances between the interface between the hard portion and the soft portion and the interface between the adjacent hard portion and the soft portion with the soft portion therebetween. The average interval when the hard portion is continuous as a base is 0 (zero). The case where the hard phase of the base material is not continuous includes, for example, a case where ferrite precipitated from the austenite grain boundary surrounds the austenite grain boundary, and the austenite present therein is transformed into a hard phase such as bainite or martensite. . In the present specification, “hard part” means a structure composed of one or more of martensite, bainite, pearlite and tempered martensite, and “soft part” means a structure composed of ferrite. .
【００１９】以下、上記の（１）〜（４）に記載のもの
をそれぞれ（１）〜（４）の発明という。Hereinafter, the inventions described in the above (1) to (4) are referred to as inventions (1) to (4), respectively.
【００２０】本発明者らは鋼材の疲労挙動に及ぼす材料
因子について種々検討し、下記の知見を得た。The present inventors have conducted various studies on the material factors affecting the fatigue behavior of a steel material and obtained the following findings.
【００２１】（ａ）疲労亀裂を停留させるためには、鋼
材の組織を構成組織間の硬さの差が大きい複合組織とす
ればよい。(A) In order to stop the fatigue crack, the structure of the steel material may be a composite structure having a large difference in hardness between the constituent structures.
【００２２】（ｂ）複合組織中の各組織間の硬さの差が
特定の値以上である場合、更に、これに加えて軟質部の
平均粒径が特定の値以下である場合又は、硬質部の平均
間隔が一定の値以下である場合には、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に、先端における
塑性変形が抑制されて、疲労亀裂の停留が起こる。(B) When the difference in hardness among the tissues in the composite structure is equal to or more than a specific value, and in addition, when the average particle size of the soft part is equal to or less than a specific value, or when the hardness is hard. When the average interval between the portions is equal to or less than a certain value, when the growing crack reaches the vicinity of the boundary between the hard portion and the soft portion, plastic deformation at the tip is suppressed, and the fatigue crack stops.
【００２３】（ｃ）硬質部と軟質部が組織に占める割合
と硬さの関係が特定の条件を満たすようにすることで、
耐疲労亀裂進展特性が極めて良好になり、亀裂進展速度
を大きく低下させることができる。(C) The relation between the ratio of the hard portion and the soft portion to the tissue and the hardness satisfies a specific condition.
The fatigue crack growth resistance becomes extremely good, and the crack growth rate can be greatly reduced.
【００２４】（ｄ）Ｃｕ、Ｎｉ、Ｃｒ及びＭｏのうちの
１種以上を少量含有させれば、鋼材の耐食性が向上する
ので、腐食環境中における耐疲労亀裂進展特性が高ま
る。(D) If a small amount of one or more of Cu, Ni, Cr and Mo is contained, the corrosion resistance of the steel material is improved, and the fatigue crack growth resistance in a corrosive environment is enhanced.
【００２５】（ｅ）Ｖ、Ｎｂ及びＴｉのうちの１種以上
を含有させれば、炭化物の形成によって軟質部（フェラ
イト）が強化するので、軟質部内を進展する疲労亀裂の
進展速度が低下する。(E) If one or more of V, Nb and Ti are contained, the soft part (ferrite) is strengthened by the formation of carbides, so that the growth rate of the fatigue crack that propagates in the soft part is reduced. .
【００２６】（ｆ）Ｂを適正量含有させれば、軟質部の
生成が抑制されて硬質部の生成が促進されるので、軟質
部と硬質部の占有比率が特定の範囲に制御され、耐疲労
亀裂進展特性が高まる。(F) When an appropriate amount of B is contained, the generation of the soft part is suppressed and the generation of the hard part is promoted, so that the occupation ratio of the soft part and the hard part is controlled to a specific range, and Increases fatigue crack growth characteristics.
【００２７】本発明は、上記の知見に基づいて完成され
たものである。The present invention has been completed based on the above findings.
【００２８】[0028]
【発明の実施の形態】以下、本発明の各要件について詳
しく説明する。なお、各元素の含有量の「％」表示は
「質量％」を意味する。 （Ａ）鋼板の化学組成 Ｃ：０．０３〜０．３０％ Ｃは、鋼の強度を高める作用を有し、特に、硬質部の強
度（硬さ）を高めるのに有効な元素である。しかし、そ
の含有量が０．０３％未満では硬質部硬さが十分な値に
ならず、耐疲労亀裂進展特性を高めることができない。
一方、その含有量が０．３０％を超えると溶接部の靱性
が劣化し、又、溶接割れが発生する。したがって、Ｃの
含有量を０．０３〜０．３０％とした。なお、Ｃ含有量
の上限は、０．２０％とすることが好ましく、０．１５
％とすれば一層好ましい。又、Ｃ含有量の下限は、０．
０５％とすることが好ましい。DESCRIPTION OF THE PREFERRED EMBODIMENTS Each requirement of the present invention will be described in detail below. In addition, "%" of the content of each element means "% by mass". (A) Chemical composition of steel sheet C: 0.03 to 0.30% C has an effect of increasing the strength of steel, and is an element that is particularly effective in increasing the strength (hardness) of a hard part. However, if the content is less than 0.03%, the hardness of the hard portion does not become a sufficient value, and the fatigue crack propagation resistance cannot be enhanced.
On the other hand, if the content exceeds 0.30%, the toughness of the welded portion deteriorates, and weld cracks occur. Therefore, the content of C is set to 0.03 to 0.30%. Note that the upper limit of the C content is preferably set to 0.20%, and 0.15%.
% Is more preferable. The lower limit of the C content is 0.
It is preferably set to 05%.
【００２９】Ｓｉ：０．０１〜０．５％ Ｓｉは、脱酸作用を有する。しかし、その含有量が０．
０１％未満では添加効果に乏しい。一方、Ｓｉの含有量
が０．５％を超えると鋼の靱性が損なわれるようにな
る。したがって、Ｓｉの含有量を０．０１〜０．５％と
した。なお、Ｓｉの含有量は０．２〜０．４％とするこ
とが望ましい。Si: 0.01 to 0.5% Si has a deoxidizing effect. However, when its content is 0.1.
If it is less than 01%, the effect of addition is poor. On the other hand, if the Si content exceeds 0.5%, the toughness of the steel will be impaired. Therefore, the content of Si is set to 0.01 to 0.5%. The content of Si is desirably 0.2 to 0.4%.
【００３０】Ｍｎ：０．３〜２．０％ Ｍｎは、鋼の強度を高める作用を有する。更に、硬質部
の生成を容易にするとともに硬質部の硬さを高める作用
も有している。こうした効果を発揮させるためには少な
くとも０．３％のＭｎを含有させる必要がある。一方、
Ｍｎの含有量が２．０％を超えると溶接熱影響部が硬化
して溶接部の靱性が劣化し、又、溶接割れが発生する。
したがって、Ｍｎの含有量を０．３〜２．０％とした。
なお、Ｍｎの含有量は０．８〜１．６％とすることが望
ましい。Mn: 0.3-2.0% Mn has the effect of increasing the strength of steel. Further, it has an effect of facilitating the generation of the hard portion and increasing the hardness of the hard portion. In order to exhibit such an effect, it is necessary to contain at least 0.3% of Mn. on the other hand,
If the Mn content exceeds 2.0%, the heat affected zone of the weld hardens and the toughness of the weld deteriorates, and weld cracks occur.
Therefore, the content of Mn is set to 0.3 to 2.0%.
The Mn content is desirably 0.8 to 1.6%.
【００３１】ｓｏｌ．Ａｌ：０．００１〜０．１％ Ａｌは、脱酸作用を有することに加えて、Ｏ（酸素）や
Ｎ（窒素）と結合した酸化物や窒化物がオーステナイト
粒を微細化するので、母材や溶接部の靱性を高める作用
もある。しかし、ｓｏｌ．ＡｌとしてのＡｌ含有量が
０．００１％未満では添加効果に乏しい。一方、ｓｏ
ｌ．ＡｌとしてのＡｌ含有量が０．１％を超えると、鋼
の清浄度及び靱性が著しく損なわれる。したがって、Ａ
ｌの含有量をｓｏｌ．Ａｌ量で０．００１〜０．１％と
した。なお、「ｓｏｌ．Ａｌ」とは所謂「酸可溶Ａｌ」
のことをいう。Sol. Al: 0.001 to 0.1% Al has a deoxidizing effect and an oxide or nitride combined with O (oxygen) or N (nitrogen) makes austenite grains finer. It also has the effect of increasing the toughness of materials and welds. However, sol. If the Al content as Al is less than 0.001%, the effect of addition is poor. On the other hand,
l. If the Al content as Al exceeds 0.1%, the cleanliness and toughness of the steel are significantly impaired. Therefore, A
l of sol. The Al content was 0.001 to 0.1%. Note that “sol. Al” is a so-called “acid-soluble Al”
Means
【００３２】（１）の発明に係る鋼板は、上記の各成分
元素のほか、残部がＦｅ及び不純物からなるものであ
る。なお、不純物中のＰ、Ｓ及びＮの含有量はそれぞれ
０．０２５％以下、０．０２０％以下、０．０１０％以
下とすることが好ましい。（２）〜（４）の発明に係る
鋼板には、上記の各成分元素に加えて更に、前記第１群
〜第３群のうちの１群以上を含んでいてもよい。これら
の合金元素の作用効果と望ましい含有量は下記のとおり
である。The steel sheet according to the first aspect of the present invention comprises, in addition to the above-mentioned constituent elements, the balance consisting of Fe and impurities. The contents of P, S, and N in the impurities are preferably set to 0.025% or less, 0.020% or less, and 0.010% or less, respectively. The steel sheet according to the inventions (2) to (4) may further include one or more of the first to third groups in addition to the above-described respective component elements. The effects and desirable contents of these alloy elements are as follows.
【００３３】Ｃｕ：０．１〜１．５％、Ｎｉ：０．１〜
１．５％、Ｃｒ：０．１〜１．５％、Ｍｏ：０．１〜
１．０％ Ｃｕ、Ｎｉ、Ｃｒ及びＭｏは、耐食性を高める作用を有
し、この効果と相俟って腐食環境下での疲労亀裂の進展
を抑制する作用を有する。更に、上記の各元素には軟質
部の転位構造を制御する作用と微視的塑性変形を抑制す
る作用もある。しかし、いずれの元素もその含有量が
０．１％未満では前記の効果が得難い。一方、Ｃｕを
１．５％を超えて、Ｎｉを１．５％を超えて、Ｃｒを
１．５％を超えて、又、Ｍｏを１．０％を超えて含有さ
せてもその効果は飽和してコストが嵩む。更に、強度が
大きくなりすぎるので靱性が劣化する。したがって、Ｃ
ｕ、Ｎｉ、Ｃｒ、Ｍｏの１種以上を添加する場合には、
Ｃｕの含有量を０．１〜１．５％、Ｎｉの含有量を０．
１〜１．５％、Ｃｒの含有量を０．１〜１．５％、Ｍｏ
の含有量を０．１〜１．０％とするのがよい。なお、Ｃ
ｕ、Ｎｉ、Ｃｒ、Ｍｏの１種以上を添加する場合におい
て、Ｃｕの含有量は０．１〜０．５％、Ｎｉの含有量は
０．２〜０．４％、Ｃｒの含有量は０．３〜１．０％、
Ｍｏの含有量は０．１〜０．３％とするのが一層好まし
い。Ｃｕの含有量は０．１〜０．３％とすれば極めて好
ましい。Cu: 0.1-1.5%, Ni: 0.1-
1.5%, Cr: 0.1 to 1.5%, Mo: 0.1 to
1.0% Cu, Ni, Cr and Mo have an effect of improving corrosion resistance, and together with this effect, have an effect of suppressing the growth of fatigue cracks in a corrosive environment. Further, each of the above elements has an effect of controlling the dislocation structure of the soft part and an effect of suppressing microscopic plastic deformation. However, if the content of any of the elements is less than 0.1%, it is difficult to obtain the above effects. On the other hand, even if Cu exceeds 1.5%, Ni exceeds 1.5%, Cr exceeds 1.5%, and Mo exceeds 1.0%, the effect is also increased. Saturation increases costs. Furthermore, the toughness deteriorates because the strength becomes too large. Therefore, C
When one or more of u, Ni, Cr, and Mo are added,
The Cu content is 0.1-1.5%, and the Ni content is 0.1%.
1-1.5%, Cr content 0.1-1.5%, Mo
Is preferably 0.1 to 1.0%. Note that C
When one or more of u, Ni, Cr, and Mo are added, the Cu content is 0.1 to 0.5%, the Ni content is 0.2 to 0.4%, and the Cr content is 0.3-1.0%,
The content of Mo is more preferably 0.1 to 0.3%. It is extremely preferable that the content of Cu be 0.1 to 0.3%.
【００３４】Ｖ：０．０１〜０．１％、Ｎｂ：０．０１
〜０．１％、Ｔｉ：０．０１〜０．０５％ Ｖ、Ｎｂ及びＴｉは、炭化物を形成することにより軟質
部を細粒化して強化し、腐食環境下での耐疲労亀裂進展
特性を高める作用を有する。しかし、いずれの元素もそ
の含有量が０．０１％未満では前記の効果が得難い。一
方、Ｖを０．１％を超えて、Ｎｂを０．１％を超えて、
又、Ｔｉを０．０５％を超えて含有させても上記効果は
飽和するし、強度が大きくなりすぎるので靱性が劣化す
る。したがって、Ｖ、Ｎｂ、Ｔｉの１種以上を添加する
場合には、Ｖの含有量を０．０１〜０．１％、Ｎｂの含
有量を０．０１〜０．１％、Ｔｉの含有量を０．０１〜
０．０５％とするのがよい。なお、Ｖ、Ｎｂ、Ｔｉの１
種以上を添加する場合において、Ｖの含有量は０．０２
〜０．０３％、Ｎｂの含有量は０．０１〜０．０２％、
Ｔｉの含有量は０．０１〜０．０２％とするのが一層好
ましい。V: 0.01-0.1%, Nb: 0.01
-0.1%, Ti: 0.01-0.05% V, Nb and Ti form a carbide to refine and soften the soft part, thereby improving fatigue crack propagation resistance in a corrosive environment. Has the effect of increasing. However, if the content of any of the elements is less than 0.01%, it is difficult to obtain the above effects. On the other hand, when V exceeds 0.1% and Nb exceeds 0.1%,
If the content of Ti exceeds 0.05%, the above effect is saturated, and the strength becomes too large, so that the toughness is deteriorated. Therefore, when adding one or more of V, Nb, and Ti, the content of V is 0.01 to 0.1%, the content of Nb is 0.01 to 0.1%, and the content of Ti is From 0.01 to
It is good to make it 0.05%. In addition, 1 of V, Nb, Ti
When adding more than one species, the content of V is 0.02
~ 0.03%, Nb content is 0.01 ~ 0.02%,
The content of Ti is more preferably 0.01 to 0.02%.
【００３５】Ｂ：０．０００５〜０．００３％ Ｂは軟質部の生成を抑制して硬質部の生成を促進し、軟
質部と硬質部の占有比率を制御して耐疲労亀裂進展特性
を高める作用がある。しかし、その含有量が０．０００
５％未満では前記の効果が得難い。一方、Ｂの含有量が
０．００３％を超えると軟質部の生成が困難となり、却
って耐疲労亀裂進展特性が劣化する場合がある。したが
って、Ｂを添加する場合には、その含有量を０．０００
５〜０．００３％とするのがよい。なお、Ｂを添加する
場合において、その含有量は０．０００５〜０．００１
５％とするのがより好ましい。 （Ｂ）鋼板の組織と硬さ （１）〜（４）の発明に係る鋼板は、硬質部と軟質部と
からなる複合組織を有するものでなければならない。こ
れは、硬質部と軟質部の２種類の組織を複合形成させな
ければ、その界面近傍において亀裂進展の停留効果が得
られないからである。B: 0.0005% to 0.003% B suppresses the formation of the soft part and promotes the formation of the hard part, and controls the occupation ratio of the soft part and the hard part to enhance the fatigue crack propagation resistance. There is action. However, its content is 0.000
If it is less than 5%, it is difficult to obtain the above effect. On the other hand, if the content of B exceeds 0.003%, it becomes difficult to form a soft part, and on the contrary, fatigue crack propagation resistance may deteriorate. Therefore, when B is added, the content is 0.000.
The content is preferably set to 5 to 0.003%. When B is added, the content is 0.0005 to 0.001.
More preferably, it is set to 5%. (B) Structure and Hardness of Steel Sheet The steel sheets according to the inventions (1) to (4) must have a composite structure including a hard part and a soft part. This is because the effect of stopping the crack growth in the vicinity of the interface cannot be obtained unless the two types of structures of the hard part and the soft part are formed.
【００３６】なお、「硬質部」が、マルテンサイト、ベ
イナイト、パーライト及び焼戻しマルテンサイトの１種
以上からなる組織を指し、「軟質部」がフェライト組織
を指すことは既に述べたとおりである。前記（Ａ）項で
述べた化学組成を有する鋼板の硬質部と軟質部のビッカ
ース硬さでの平均硬さＨＡとＨＢは、それぞれ２３０〜
３６０程度、８０〜１８０程度である。As described above, the "hard portion" refers to a structure composed of at least one of martensite, bainite, pearlite, and tempered martensite, and the "soft portion" refers to a ferrite structure. The average hardnesses HA and HB in the Vickers hardness of the hard part and the soft part of the steel sheet having the chemical composition described in the above section (A) are 230 to 230, respectively.
It is about 360 and about 80 to 180.
【００３７】（１）〜（４）の発明に係る鋼板は、ｆＡ
とｆＢを、それぞれ硬質部と軟質部が組織に占める％単
位での割合として、更に、「ｆＡ・ＨＡ−ｆＢ・ＨＢ≧
−３５００」で表される前記 (1)式をも満たす必要があ
る。この規定を設ける理由は以下のとおりである。The steel sheets according to the inventions (1) to (4) have fA
And fB as percentages of the hard part and the soft part in the tissue, respectively, in units of%, and further, “fA · HA−fB · HB ≧
-3500 ”must be satisfied. The reasons for this provision are as follows.
【００３８】軟質部と硬質部の硬さの差が大きいほど、
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。上記傾角粒界は粒界一次転位のみに
よって構成されるため、粒界凝集力が高く、破壊の抵抗
となりやすい。更に、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、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。上記集
合部は亀裂進展の抵抗となり、鋼板の亀裂が進展するの
を抑制する効果を高めるので、軟質部と硬質部の硬さの
差が大きいほど亀裂の進展を抑制する効果は大きくな
る。ところが、軟質部と硬質部の硬さの差が大きすぎる
場合には、前記硬さの差が単に大きいだけでは、靱性の
劣化が著しくなるし、更に、上記した亀裂先端と軟質部
−硬質部界面との干渉効果が十分に発揮されず、良好な
耐疲労亀裂進展特性が得られない場合もある。As the difference in hardness between the soft part and the hard part increases,
Movement of dislocations at the crack tip is prevented at the interface between the soft part and the hard part, and dislocations whose Burgers vector are perpendicular to the interface are arranged in the soft part near the interface between the two parts, so that an inclined grain boundary is formed. . Since the tilt grain boundaries are composed only of grain boundary primary dislocations, the grain boundary has a high cohesive force and tends to be resistant to fracture. Further, since dislocations do not easily enter into the formed tilt boundaries, when a repeated stress is applied continuously, new tilt boundaries are formed on the soft part side adjacent to the grain boundaries, and such steps are repeated. As a result, an aggregate of the tilt grain boundaries having a large volume is formed. The aggregated portion serves as resistance to crack growth and enhances the effect of suppressing the growth of cracks in the steel sheet. Therefore, the greater the difference in hardness between the soft portion and the hard portion, the greater the effect of suppressing crack growth. However, if the difference between the hardness of the soft part and the hardness of the hard part is too large, the mere difference in the hardness will significantly deteriorate the toughness, and further, the crack tip and the soft part-hard part will be described. In some cases, the effect of interference with the interface is not sufficiently exhibited, and good fatigue crack propagation resistance cannot be obtained.
【００３９】しかし、（Ａ）項で述べた化学組成を有す
る鋼板の硬質部と軟質部の硬さの差がたとえ極めて大き
い場合であっても、 (1)式を満たすことによって、良好
な靱性と優れた耐疲労亀裂進展特性（すなわち十分な亀
裂進展の抑制効果）とを確保できる。したがって、
（１）〜（４）の発明に係る鋼板に対して、前記 (1)式
をも満たすように規定した。However, even if the difference between the hardness of the hard portion and the hardness of the soft portion of the steel sheet having the chemical composition described in the section (A) is extremely large, the satisfactory toughness can be obtained by satisfying the expression (1). And excellent fatigue crack growth resistance (that is, sufficient crack growth suppressing effect). Therefore,
The steel plates according to the inventions (1) to (4) are defined so as to satisfy the above-mentioned expression (1).
【００４０】（３）の発明に係る鋼板は、更に、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を
有し、軟質部の平均粒径が５０μｍ以下のものである。The steel sheet according to the invention (3) further has a structure composed of a base material of a hard part and a soft part dispersed in the base material, and the soft part has an average particle size of 50 μm or less.
【００４１】上記軟質部の分散形態は、ランダム状、点
列ネットワーク状、複数で平行する点列状、複数で平行
する連続状及び連続ネットワーク状などいずれでもよい
が、軟質部が平行な縞状に存在する場合には、軟質部の
縞模様と平行に進展する疲労亀裂については界面との干
渉の効果が小さいので、軟質部の分散形態は、ランダム
状、ネットワーク状であることが好ましい。The dispersion mode of the soft portion may be any of a random shape, a dot sequence network shape, a plurality of parallel dot sequence shapes, a plurality of parallel continuous shapes, and a continuous network shape. , The effect of interference with the interface is small with respect to fatigue cracks that grow in parallel with the stripe pattern of the soft part, and therefore the dispersion form of the soft part is preferably a random shape or a network shape.
【００４２】軟質部の平均粒径が５０μｍ以下の場合、
短範囲で結晶方位が変化するので結晶粒内の転位の移動
が抑制できるし、更に、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
化が生じて、粒界転位が残留して粒界を強化することが
できる。このため、一層高い亀裂進展抑制効果が得られ
る。したがって、軟質部の平均粒径は５０μｍ以下とす
るのがよい。なお、軟質部の平均粒径は強度・靱性確保
の点から小さければ小さいほど好ましい。When the average particle size of the soft part is 50 μm or less,
Since the crystal orientation changes in a short range, the movement of dislocations in the crystal grain can be suppressed.In addition, even when the dislocation reaching the grain boundary moves into the adjacent crystal grain, the Burgers vector changes, and the grain boundary changes. Dislocations remain to strengthen grain boundaries. For this reason, a higher crack growth suppressing effect can be obtained. Therefore, the average particle size of the soft part is preferably set to 50 μm or less. The smaller the average particle size of the soft part is, the better the strength and toughness are ensured.
【００４３】（４）の発明に係る鋼板は、更に、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を
有し、硬質部の平均間隔が５０μｍ以下のものである。The steel sheet according to the invention (4) further has a structure composed of a base material of a hard part and a soft part dispersed in the base material, and the average interval between the hard parts is 50 μm or less.
【００４４】硬質部の平均間隔が５０μｍ以下の場合、
軟質部内の微視的な塑性変形が抑制され、亀裂進展抑制
効果が極めて顕著になる。したがって、硬質部の平均間
隔は５０μｍ以下とするのがよい。なお、硬質部の平均
間隔の下限値は、軟質部を優先的に進行してきた亀裂が
いずれの方向を向いていようとも軟質部と硬質部との界
面にぶつかってその進行が抑制されるように０（ゼロ）
であることが好ましい。なお、既に述べたように、硬質
部の平均間隔とは、軟質部を間にして、硬質部と軟質部
との界面から隣の硬質部と軟質部との界面までの最短の
直線距離の平均をいい、硬質部が素地として連続してい
る場合の平均間隔は０（ゼロ）である。When the average interval between the hard portions is 50 μm or less,
Microscopic plastic deformation in the soft part is suppressed, and the effect of suppressing crack growth becomes extremely significant. Therefore, the average interval between the hard portions is preferably set to 50 μm or less. The lower limit of the average interval of the hard portion is such that the crack that has preferentially progressed through the soft portion hits the interface between the soft portion and the hard portion regardless of which direction the crack is directed, so that its progress is suppressed. 0 (zero)
It is preferable that As described above, the average interval between the hard parts is the average of the shortest linear distances from the interface between the hard part and the soft part to the interface between the adjacent hard part and the soft part with the soft part in between. The average interval is 0 (zero) when the hard portion is continuous as a base.
【００４５】以下、本発明を実施例によって更に詳しく
説明する。Now, the present invention will be described in further detail with reference to Examples.
【００４６】[0046]
【実施例】表１、表２に示す化学組成を有する鋼を連続
鋳造して厚さ２００ｍｍのスラブを作製した。表１にお
ける鋼１〜１１は化学組成が本発明で規定する範囲内に
あるものである。一方、表２における鋼Ｘ１〜Ｘ８は少
なくとも成分のいずれかが本発明で規定する含有量の範
囲から外れるものである。EXAMPLE A steel having the chemical composition shown in Tables 1 and 2 was continuously cast to produce a 200 mm thick slab. Steels 1 to 11 in Table 1 have a chemical composition within the range specified in the present invention. On the other hand, in steels X1 to X8 in Table 2, at least one of the components is out of the range of the content specified in the present invention.
【００４７】[0047]
【表１】 [Table 1]
【表２】 次いで、上記のスラブに表３に示すＡ〜Ｉの処理を施
し、厚さ１５〜７５ｍｍの鋼板を得た。各スラブに対し
て施した処理を具体的に表３〜６に示す。[Table 2] Next, the slab was subjected to the treatments A to I shown in Table 3 to obtain a steel plate having a thickness of 15 to 75 mm. Tables 3 to 6 specifically show the processing performed on each slab.
【００４８】なお、Ａの処理は、スラブを加熱後熱間圧
延し、圧延を９５０℃で仕上げ、その後空冷する通常の
熱間圧延処理である。The process A is a normal hot rolling process in which the slab is heated and then hot-rolled, the rolling is finished at 950 ° C., and then air-cooled.
【００４９】Ｂの処理は、スラブを加熱後熱間圧延し、
圧延を９００℃で仕上げ、その後水で加速冷却する処理
である。In the treatment of B, the slab is heated and then hot-rolled,
This is a process of finishing rolling at 900 ° C. and then accelerated cooling with water.
【００５０】Ｃの処理は、スラブを加熱後熱間圧延し、
圧延を９５０℃で仕上げ、その後空冷した通常の熱間圧
延鋼板を、更にオーステナイトとフェライトとの２相域
温度（以下、単に２相域温度という）である８００℃に
加熱した後水冷する処理である。In the treatment C, the slab is heated and then hot-rolled,
Rolling is finished at 950 ° C., and then the air-cooled normal hot-rolled steel sheet is further heated to 800 ° C., which is the two-phase temperature of austenite and ferrite (hereinafter simply referred to as the two-phase temperature), and then water-cooled. is there.
【００５１】Ｄの処理は、スラブを加熱後熱間圧延し、
圧延を９５０℃で仕上げ、その後空冷した通常の熱間圧
延鋼板を、更にオーステナイト域温度である８８０℃に
加熱した後空冷する処理である。In the process of D, the slab is heated and then hot-rolled,
This is a process of finishing the rolling at 950 ° C., then heating the ordinary hot-rolled steel sheet that has been air-cooled to 880 ° C., which is the austenite region temperature, and then air-cooling.
【００５２】Ｅの処理は、スラブを加熱後熱間圧延し、
圧延を９５０℃で仕上げ、その後空冷した通常の熱間圧
延鋼板を、更に２相域温度である８００℃に加熱した後
空冷し、次いで、６００℃で焼戻しを行った後水冷する
処理である。In the treatment E, the slab is heated and then hot-rolled,
This is a process in which a normal hot-rolled steel sheet which has been subjected to rolling at 950 ° C. and then air-cooled is further heated to 800 ° C. which is a two-phase region temperature, air-cooled, then tempered at 600 ° C. and then water-cooled.
【００５３】Ｆの処理は、スラブを加熱後熱間圧延し、
圧延を２相域温度の８００℃で仕上げ、その後水で加速
冷却する処理である。In the treatment of F, the slab is heated and then hot-rolled,
This is a process in which rolling is finished at a two-phase temperature of 800 ° C. and then accelerated cooling with water.
【００５４】Ｇの処理は、スラブを加熱後熱間圧延し、
圧延をオーステナイトの再結晶域温度である１１００℃
で仕上げ、その直後に水冷する処理である。In the processing of G, the slab is heated and then hot-rolled,
Rolling was performed at 1100 ° C, which is the temperature of the recrystallization zone of austenite.
And water cooling immediately after.
【００５５】Ｈの処理は、スラブを加熱後熱間圧延し、
圧延を９５０℃で仕上げ、その後空冷した通常の熱間圧
延鋼板を、更にオーステナイト域温度である９００℃に
加熱した後水焼入れする処理である。In the treatment of H, the slab is hot-rolled after heating,
This is a process of finishing the rolling at 950 ° C., then heating the air-cooled normal hot-rolled steel sheet to 900 ° C., which is the austenite region temperature, and then water quenching.
【００５６】Ｉの処理は、上記Ｈの処理の後、更に６０
０℃で焼戻ししてから水冷する処理である。The processing of I is performed after the processing of H described above for another 60 hours.
This is a process of tempering at 0 ° C. and then cooling with water.
【００５７】[0057]
【表３】 上記厚さ１５〜７５ｍｍの鋼板の板厚中央部位置から１
５ｍｍ×１５ｍｍ×１０ｍｍの試験材を切り出し、組織
観察と微小領域のビッカース硬さ測定を行った。又、各
鋼板の板厚中央部位置で亀裂進行方向がＣ方向になるよ
うに、ASTM E 647に記載のＣＴ試験片を切り出して、耐
疲労亀裂進展特性の調査を行った。[Table 3] 1 from the central position of the steel plate having a thickness of 15 to 75 mm
A test material of 5 mm × 15 mm × 10 mm was cut out, and the structure was observed and the Vickers hardness of a minute area was measured. Further, a CT test piece described in ASTM E 647 was cut out so that the direction of crack propagation was the C direction at the central position of the thickness of each steel sheet, and the fatigue crack propagation characteristics were investigated.
【００５８】組織観察と微小領域のビッカース硬さ測定
は以下のようにして行った。すなわち、ナイタールで腐
食した後、倍率２００〜５００倍で光学顕微鏡観察して
組織判定を行った。又、光学顕微鏡上の各１０視野につ
いて、切片法にて長さを測定することで、軟質部の平均
粒径と、硬質部の平均間隔を測定した。なお、硬質部の
平均間隔は板厚の中心部でランダムに１０視野を測定し
て測定した。The structure observation and the measurement of the Vickers hardness of the minute area were performed as follows. That is, after corrosion with nital, the structure was determined by observation with an optical microscope at a magnification of 200 to 500 times. The average particle size of the soft part and the average interval of the hard part were measured by measuring the length of each of the ten visual fields on the optical microscope by the section method. The average interval between the hard portions was measured by randomly measuring 10 visual fields at the center of the plate thickness.
【００５９】ビッカース硬さは、硬質部、軟質部ともに
ランダムに測定し、それぞれ硬質部と軟質部の平均硬さ
を求めた。The Vickers hardness was measured randomly for both the hard and soft parts, and the average hardness of the hard and soft parts was determined.
【００６０】耐疲労亀裂進展特性は、サーボパルサ装置
を用いて、繰り返し速度（ｆ）を３０Ｈｚ、応力比
（Ｒ）を０．１として、室温で疲労試験を行って調査し
た。なお、疲労試験の雰囲気は、大気、水１０％を
含む懸濁させた原油に、硫化水素が１体積％で残りが窒
素からなる混合ガスを試験期間中常時吹き込む湿潤硫化
水素環境、ASTM D-1141-52 で規定する人工海水、の
３条件とした。The fatigue crack growth resistance was investigated by performing a fatigue test at room temperature with a repetition rate (f) of 30 Hz and a stress ratio (R) of 0.1 using a servo pulser device. The atmosphere of the fatigue test was a wet hydrogen sulfide environment in which a mixed gas containing 1% by volume of hydrogen sulfide and the remainder of nitrogen was constantly blown into suspended crude oil containing 10% of water and water during the test. Artificial seawater specified in 1141-52.
【００６１】疲労試験結果の検討によれば、いずれの試
験条件の場合も中△Ｋ領域（本試験では約１５．５〜９
３ＭＰａ・ｍ0.5 ）における第２領域で所謂「Ｐａｒｉ
ｓ則」、すなわち、疲労亀裂進展速度（ｄａ／ｄＮ：繰
り返し荷重１サイクル当たりの亀裂進展量）と応力拡大
係数範囲（ΔＫ＝Ｋmax −Ｋmin ：１サイクル中の応力
拡大係数Ｋの最大値と最小値の差）との間にＣ及びｍを
材料、環境、応力比などに依存する定数として、ｄａ／
ｄＮ＝Ｃ・（ΔＫ）m の関係式が成立することが判明し
た。。According to the examination of the fatigue test results, the medium ΔK region (about 15.5 to 9 in this test) was obtained under any of the test conditions.
In the second region at 3 MPa · m 0.5 ), the so-called “Pari
s-law ”, that is, fatigue crack growth rate (da / dN: crack growth amount per cycle of repeated load) and stress intensity factor range (ΔK = K max -K min : maximum value of stress intensity factor K during one cycle) And the minimum value), C and m are defined as constants depending on the material, environment, stress ratio, etc., and da /
It has been found that the relational expression of dN = C · (ΔK) m holds. .
【００６２】したがって、耐疲労亀裂進展特性は、この
中△Ｋ領域の△Ｋが１５．５ＭＰａ・ｍ0.5 及び３１Ｍ
Ｐａ・ｍ0.5 における疲労亀裂進展速度ｄａ／ｄＮ（ｍ
ｍ／サイクル）の平均値であるｄａ／ｄＮAVで評価する
こととした。Therefore, the fatigue crack growth resistance of the △ K region is 15.5 MPa · m 0.5 and 31M.
Fatigue crack growth rate at Pa · m 0.5 da / dN (m
was be evaluated in da / dN AV is the average value of m / cycle).
【００６３】表４〜９に組織観察結果、ビッカース硬さ
測定結果及び耐疲労亀裂進展特性の調査結果を併せて示
す。耐疲労亀裂進展特性調査結果は、表４〜７に大気中
の調査結果を、表８、表９に湿潤硫化水素中と人工海水
中での調査結果を示す。なお、試験番号２２〜２６及び
Ｘ２１〜Ｘ２３が湿潤硫化水素中、試験番号２７〜３２
及びＸ２４〜Ｘ２６が人工海水中での調査結果である。Tables 4 to 9 also show the results of structure observation, results of Vickers hardness measurement, and results of investigation of fatigue crack growth resistance. Tables 4 to 7 show the results of the investigation on the fatigue crack propagation characteristics in the atmosphere, and Tables 8 and 9 show the results of the investigation in the wet hydrogen sulfide and in the artificial seawater. In addition, the test numbers 22-26 and X21-X23 are the test numbers 27-32 in wet hydrogen sulfide.
And X24 to X26 are the results of investigations in artificial seawater.
【００６４】[0064]
【表４】 [Table 4]
【表５】 [Table 5]
【表６】 [Table 6]
【表７】 [Table 7]
【表８】 [Table 8]
【表９】 表４〜９の組織欄において、Ｆはフェライト組織を指
し、塊状、針状など形態を問わないものである。既に述
べたように、本発明でいう軟質部とはフェライト組織の
ことをいう。[Table 9] In the microstructure columns of Tables 4 to 9, F indicates a ferrite microstructure, which may be in any form such as a lump or a needle. As described above, the soft part in the present invention refers to a ferrite structure.
【００６５】Ｂはベイナイト組織を指し、羽毛状の所謂
「上部ベイナイト組織」、針状の所謂「下部ベイナイト
組織」などすべてのベイナイト組織を含むものである。
Ｍはマルテンサイト組織を指す。ＴＭはマルテンサイト
を焼戻しした組織を指す。Ｐはパーライト組織を指し、
セメンタイト層が連続状の層状パーライト、セメンタイ
ト層が不連続の擬似パーライトの双方を含むものであ
る。既に述べたように、本発明でいう硬質部とは、ベイ
ナイト、マルテンサイト、焼戻しマルテンサイト及びパ
ーライトの１種以上からなる組織のことをいう。B denotes a bainite structure, and includes all bainite structures such as a so-called “upper bainite structure” having a feather shape and a so-called “lower bainite structure” having a needle shape.
M indicates a martensite structure. TM refers to a structure obtained by tempering martensite. P refers to pearlite structure,
The cementite layer contains both continuous layered pearlite and the cementite layer contains both discontinuous pseudo pearlite. As described above, the hard part in the present invention refers to a structure composed of at least one of bainite, martensite, tempered martensite, and pearlite.
【００６６】表３〜６における式１は前記 (1)式におけ
る「ｆＡ・ＨＡ−ｆＢ・ＨＢ」を指す。Equation 1 in Tables 3 to 6 indicates “fA · HA−fB · HB” in the above equation (1).
【００６７】表４〜７から、本発明の規定を満たす試験
番号１〜２１の場合には、大気中における疲労亀裂進展
速度ｄａ／ｄＮAVが２．５×１０-6ｍｍ／サイクル以下
という優れた耐疲労亀裂進展特性を有することが明らか
である。[0067] From Table 4-7, in the case of Test No. 1 to 21 which satisfy the requirements of the present invention is excellent in that fatigue crack growth rate da / dN AV in the atmosphere is 2.5 × 10 -6 mm / cycle or less It is evident that the steel has excellent fatigue crack growth resistance characteristics.
【００６８】上記試験番号の中でも、軟質部の平均粒径
が５０μｍ以下の場合には、上記疲労亀裂進展速度ｄａ
／ｄＮAVが１．６×１０-6ｍｍ／サイクル以下で一層優
れた耐疲労亀裂進展特性を有しており、更に、硬質部の
平均間隔が５０μｍ以下の場合には、上記疲労亀裂進展
速度ｄａ／ｄＮAVが１．０×１０-6ｍｍ／サイクル以下
で極めて優れた耐疲労亀裂進展特性を有している。これ
に対して、試験番号Ｘ１〜Ｘ２０の場合には、本発明で
規定する条件を満たさないので大気中における疲労亀裂
進展速度ｄａ／ｄＮAVは２．５×１０-6ｍｍ／サイクル
を超え、目標性能に達していない。Among the above test numbers, when the average particle size of the soft part is 50 μm or less, the fatigue crack growth rate da
/ DN AV is has more excellent fatigue crack growth resistance characteristics below 1.6 × 10 -6 mm / cycle, further, when the average distance between the hard portion is less 50μm, said fatigue crack growth rate da / dN AV has extremely excellent fatigue crack growth properties below 1.0 × 10 -6 mm / cycle. In contrast, in the case of Test No. X1~X20 fatigue crack growth rate da / dN AV in the atmosphere does not satisfy the conditions defined by the present invention is greater than 2.5 × 10 -6 mm / cycle, The target performance has not been reached.
【００６９】又、表８及び表９から、本発明の規定を満
たす試験番号２２〜３２の場合には、湿潤硫化水素中又
は人工海水中における亀裂進展速度ｄａ／ｄＮAVが１
２．０×１０-6ｍｍ／サイクル以下という優れた耐疲労
亀裂進展特性を有することが明らかである。上記試験番
号の中でも、軟質部の平均粒径が５０μｍ以下の場合に
は、上記疲労亀裂進展速度ｄａ／ｄＮAVが７．０×１０
-6ｍｍ／サイクル以下で一層優れた耐疲労亀裂進展特性
を有しており、更に、硬質部の平均間隔が５０μｍ以下
の場合には、上記疲労亀裂進展速度ｄａ／ｄＮAVが５．
０×１０-6ｍｍ／サイクル以下で極めて優れた耐疲労亀
裂進展特性を有している。これに対して、試験番号Ｘ２
１〜Ｘ２６の場合には、本発明で規定する条件を満たさ
ないので潤硫化水素中又は人工海水中における疲労亀裂
進展速度ｄａ／ｄＮAVは１２．０×１０-6ｍｍ／サイク
ルを超え、目標性能に達していない。[0069] Further, Table 8 and Table 9, in the case of Test No. 22 to 32 that satisfy the requirements of the present invention, the crack growth rate da / dN AV in the wet sulfide hydrogen or artificial seawater is 1
It is clear that it has excellent fatigue crack growth resistance of 2.0 × 10 −6 mm / cycle or less. The Among the test number, when the average particle diameter of the soft portion is 50μm or less, the fatigue crack growth rate da / dN AV is 7.0 × 10
-6 has mm / cycle more excellent fatigue crack growth characteristics below, further, when the average distance between the hard portion is 50μm or less, the fatigue crack growth rate da / dN AV 5.
At 0 × 10 −6 mm / cycle or less, it has extremely excellent fatigue crack growth resistance. On the other hand, test number X2
In the case of 1~X26 fatigue crack growth rate da / dN AV during Jun hydrogen sulfide or artificial seawater does not satisfy the conditions defined by the present invention is greater than 12.0 × 10 -6 mm / cycle, the target Performance has not been reached.
【００７０】[0070]
【発明の効果】本発明の鋼板は、中△Ｋ領域においても
良好な耐疲労亀裂進展特性を有するので、溶接部から疲
労亀裂が発生した場合でも従来の鋼板に比べて疲労寿命
を延長することができる。このため、本発明の鋼板は、
土木建築構造物、船体、海洋構造物や装置及びラインパ
イプなどの素材として適している。The steel sheet of the present invention has good fatigue crack propagation resistance even in the middle ΔK region, so that even if a fatigue crack is generated from the weld, the fatigue life can be extended as compared with the conventional steel sheet. Can be. For this reason, the steel sheet of the present invention
It is suitable as a material for civil engineering structures, hulls, marine structures and equipment, line pipes, and the like.
─────────────────────────────────────────────────────
────────────────────────────────────────────────── ───
【手続補正書】[Procedure amendment]
【提出日】平成１２年１０月１７日（２０００．１０．
１７）[Submission date] October 17, 2000 (2000.10.
17)
【手続補正１】[Procedure amendment 1]
【補正対象書類名】明細書[Document name to be amended] Statement
【補正対象項目名】００６４[Correction target item name] 0064
【補正方法】変更[Correction method] Change
【補正内容】[Correction contents]
【００６４】[0064]
【表４】 [Table 4]
【表５】 [Table 5]
【表６】 [Table 6]
【表７】 [Table 7]
【表８】 [Table 8]
【表９】 表４〜９の組織欄において、Ｆはフェライト組織を指
し、塊状、針状など形態を問わないものである。既に述
べたように、本発明でいう軟質部とはフェライト組織の
ことをいう。[Table 9] In the microstructure columns of Tables 4 to 9, F indicates a ferrite microstructure, which may be in any form such as a lump or a needle. As described above, the soft part in the present invention refers to a ferrite structure.
Claims (4)
ｉ：０．０１〜０．５％、Ｍｎ：０．３〜２．０％、ｓ
ｏｌ．Ａｌ：０．００１〜０．１％、を含有し、残部は
Ｆｅ及び不純物からなる鋼板であって、その組織が硬質
部と軟質部とからなり、この２つの部分の組織に占める
割合及びビッカース硬さでの平均硬さが下記 (1)式を満
たす鋼板。 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) ここで、ｆＡとｆＢは、それぞれ硬質部と軟質部が組織
に占める％単位での割合を指し、ＨＡとＨＢは、それぞ
れ硬質部と軟質部のビッカース硬さでの平均硬さを指
す。(1) In terms of mass%, C: 0.03 to 0.30%, S
i: 0.01 to 0.5%, Mn: 0.3 to 2.0%, s
ol. Al: 0.001 to 0.1%, the balance being a steel plate composed of Fe and impurities, the structure of which is composed of a hard part and a soft part. The ratio of these two parts to the structure and Vickers Steel sheet whose average hardness satisfies the following formula (1). fA · HA−fB · HB ≧ −3500 (1) Here, fA and fB indicate percentages of the hard portion and the soft portion in the tissue, respectively, in units of%, and HA and HB respectively indicate the hard portion. And Vickers hardness of the soft part.
％で、第１群：Ｃｕ：０．１〜１．５％、Ｎｉ：０．１
〜１．５％、Ｃｒ：０．１〜１．５％、Ｍｏ：０．１〜
１．０％のうちの１種以上、第２群：Ｖ：０．０１〜
０．１％、Ｎｂ：０．０１〜０．１％、Ｔｉ：０．０１
〜０．０５％のうちの１種以上、第３群：Ｂ：０．００
０５〜０．００３％、の１群以上をも含み、残部はＦｅ
及び不純物からなる鋼板であって、その組織が硬質部と
軟質部とからなり、この２つの部分の組織に占める割合
及びビッカース硬さでの平均硬さが下記 (1)式を満たす
鋼板。 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) ここで、ｆＡとｆＢは、それぞれ硬質部と軟質部が組織
に占める％単位での割合を指し、ＨＡとＨＢは、それぞ
れ硬質部と軟質部のビッカース硬さでの平均硬さを指
す。2. The composition according to claim 1, further comprising, by mass%, a first group: Cu: 0.1 to 1.5%, Ni: 0.1%.
-1.5%, Cr: 0.1-1.5%, Mo: 0.1-
1.0% or more, second group: V: 0.01 to
0.1%, Nb: 0.01 to 0.1%, Ti: 0.01
At least one of -0.05%, third group: B: 0.00
0.05 to 0.003%, the balance being Fe
A steel sheet comprising a hard part and a soft part, wherein the ratio of these two parts to the structure and the average hardness in Vickers hardness satisfy the following formula (1). fA · HA−fB · HB ≧ −3500 (1) Here, fA and fB indicate percentages of the hard portion and the soft portion occupying the tissue, respectively, and HA and HB respectively indicate the hard portion. And Vickers hardness of the soft part.
鋼板であって、その組織が硬質部の素地とこの素地に分
散した軟質部とからなり、軟質部の平均粒径が５０μｍ
以下で、且つ、前記２つの部分の組織に占める割合及び
ビッカース硬さでの平均硬さが下記 (1)式を満たす鋼
板。 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) ここで、ｆＡとｆＢは、それぞれ硬質部と軟質部が組織
に占める％単位での割合を指し、ＨＡとＨＢは、それぞ
れ硬質部と軟質部のビッカース硬さでの平均硬さを指
す。3. A steel sheet having the chemical composition according to claim 1 or 2, wherein the structure is composed of a base material of a hard part and a soft part dispersed in the base material, and the soft part has an average particle size of 50 μm.
A steel sheet having the following two ratios and the average hardness in Vickers hardness satisfying the following formula (1). fA · HA−fB · HB ≧ −3500 (1) Here, fA and fB indicate percentages of the hard portion and the soft portion occupying the tissue, respectively, and HA and HB respectively indicate the hard portion. And Vickers hardness of the soft part.
鋼板であって、その組織が硬質部の素地とこの素地に分
散した軟質部とからなり、硬質部の平均間隔が５０μｍ
以下で、且つ、前記２つの部分の組織に占める割合及び
ビッカース硬さでの平均硬さが下記 (1)式を満たす鋼
板。 ｆＡ・ＨＡ−ｆＢ・ＨＢ≧−３５００・・・(1) ここで、ｆＡとｆＢは、それぞれ硬質部と軟質部が組織
に占める％単位での割合を指し、ＨＡとＨＢは、それぞ
れ硬質部と軟質部のビッカース硬さでの平均硬さを指
す。4. A steel sheet comprising the chemical composition according to claim 1 or 2, wherein the structure comprises a base material of a hard part and a soft part dispersed in the base material, and the average interval between the hard parts is 50 μm.
A steel sheet having the following two ratios and the average hardness in Vickers hardness satisfying the following formula (1). fA · HA−fB · HB ≧ −3500 (1) Here, fA and fB indicate percentages of the hard portion and the soft portion occupying the tissue, respectively, and HA and HB respectively indicate the hard portion. And Vickers hardness of the soft part.
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|---|---|---|---|
| JP2000315146A JP2002121640A (en) | 2000-10-16 | 2000-10-16 | Steel sheet having suppressing effect on fatigue crack propagation |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000315146A JP2002121640A (en) | 2000-10-16 | 2000-10-16 | Steel sheet having suppressing effect on fatigue crack propagation |
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|---|---|
| JP2002121640A true JP2002121640A (en) | 2002-04-26 |
Family
ID=18794293
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
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