JP2001316725A - Method for manufacturing steel excellent in resistance to propagating fatigue crack - Google Patents
Method for manufacturing steel excellent in resistance to propagating fatigue crackInfo
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- JP2001316725A JP2001316725A JP2000135313A JP2000135313A JP2001316725A JP 2001316725 A JP2001316725 A JP 2001316725A JP 2000135313 A JP2000135313 A JP 2000135313A JP 2000135313 A JP2000135313 A JP 2000135313A JP 2001316725 A JP2001316725 A JP 2001316725A
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- fatigue crack
- temperature
- steel
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- crack growth
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、疲労亀裂進展抵抗
性に優れた鋼材の製造方法に関する。より詳しくは、船
舶、海洋構造物、橋梁、建築物、タンクなど各種構造物
に用いられ、繰返し荷重を受けた場合でも良好な耐疲労
亀裂進展性を示す構造用鋼材の製造方法に関する。TECHNICAL FIELD The present invention relates to a method for producing a steel material having excellent fatigue crack propagation resistance. More specifically, the present invention relates to a method for producing a structural steel material used for various structures such as ships, marine structures, bridges, buildings, tanks, and the like, which exhibits good fatigue crack propagation resistance even under repeated loads.
【０００２】[0002]
【従来の技術】船舶、海洋構造物、橋梁、建築物、タン
クなど各種の構造物に使用される鋼材には、強度、靱性
などの機械的性質や溶接性に優れていることが要求され
る。上記構造物に対して構造上の安全性を確保させるた
めには、機械的性質の中でも特に耐疲労特性を高めるこ
とが極めて重要である。2. Description of the Related Art Steel materials used for various structures such as ships, marine structures, bridges, buildings, tanks, etc. are required to have excellent mechanical properties such as strength and toughness and weldability. . In order to ensure the structural safety of the above structure, it is extremely important to enhance the fatigue resistance among the mechanical properties.
【０００３】構造物が疲労損傷で破壊する過程について
は、従来、応力集中部における疲労亀裂の発生及びその
後の疲労亀裂進展の２つの過程に大きく分類した検討が
なされてきた。[0003] The process of fracture of a structure due to fatigue damage has conventionally been roughly classified into two processes: the generation of a fatigue crack at a stress concentration portion and the subsequent growth of a fatigue crack.
【０００４】構造物のうちでも特に溶接構造物の場合に
は、応力集中部となり得る溶接止端部が多数存在するの
で、疲労亀裂の発生を工業的規模で完全に防止すること
は技術的に不可能に近い。又、疲労亀裂の発生を完全に
防止することは検査費用の著しい上昇を招くため経済的
にも得策ではない。そこで、亀裂の進展寿命をいかに長
寿命化するかが重要となり、設計面からの工夫として、
荷重経路を多重化させる構造を採用することがある。こ
れは、荷重経路を多重化した場合には、構造物中のある
箇所に亀裂が発生して相当な長さにまで成長しても、剛
性の低下した亀裂を含む部分が分担していた荷重を、他
の部分が分担し合うことになり、その結果、亀裂を含む
部分での亀裂進展は抑制され、亀裂の発生・進展直後に
致命的な破壊に至ることを防ぐことができるからであ
る。[0004] In the case of a welded structure in particular, since there are many weld toes that can become stress concentration parts, it is technically necessary to completely prevent the occurrence of fatigue cracks on an industrial scale. Near impossible. Further, it is not economically advantageous to completely prevent the occurrence of fatigue cracks because the cost for inspection is significantly increased. Therefore, it is important how to extend the life of crack propagation.
A structure that multiplexes load paths may be employed. This is because when multiplexing the load path, even if a crack occurs at a certain point in the structure and grows to a considerable length, the load including the crack with reduced rigidity is shared. This is because other parts share each other, and as a result, crack growth in the part including the crack is suppressed, and it is possible to prevent fatal destruction immediately after the generation and propagation of the crack. .
【０００５】一方、現実問題としては、通常の構造物で
は経済性を優先させるため強度上の冗長度を多くとるこ
とには自ずと制約があり、上述の荷重経路の多重化とい
う設計手法による対応では効果に限界がある。したがっ
て、産業界からは鋼材自身の疲労亀裂進展抵抗性を増す
ことに対する要望が大きい。[0005] On the other hand, as a practical problem, there is naturally a limitation in increasing the degree of redundancy in strength in order to give priority to economy in ordinary structures. The effect is limited. Therefore, there is a great demand from the industry for increasing the fatigue crack propagation resistance of the steel material itself.
【０００６】鋼材の疲労亀裂進展抵抗性の向上に関する
技術が、例えば、特開平４−３３７０３７号公報、特開
平６−２７１９８５号公報や特開平６−２９９２３８号
公報に開示されている。[0006] Techniques for improving the fatigue crack propagation resistance of steel are disclosed in, for example, JP-A-4-337037, JP-A-6-271985 and JP-A-6-299238.
【０００７】このうち特開平４−３３７０３７号公報に
は、特定の化学組成を有する鋼を特定の条件で圧延、冷
却、巻取りして特定の最終組織を有する熱延鋼板を得る
「疲労強度と亀裂伝播抵抗の優れた良成形性熱延鋼板の
製造方法」が開示されている。しかし、この公報で提案
された技術の場合、改善の対象としている「疲労亀裂伝
播抵抗」は「亀裂進展下限界特性」に限定されたもので
あり、したがって、「疲労亀裂伝播停止特性」を記述す
る力学パラメータはΔＫｔｈのみで、亀裂の安定進展領
域は対象にはされていないので、外力が増すなどして疲
労亀裂先端での応力拡大係数範囲ΔＫがΔＫｔｈを超え
て疲労亀裂が進展し始めると、従来鋼と同じ疲労亀裂進
展速度で亀裂が成長してしまう。Among them, Japanese Patent Application Laid-Open No. 4-337037 discloses that a steel having a specific chemical composition is rolled, cooled and wound under specific conditions to obtain a hot-rolled steel sheet having a specific final structure. A method for producing a hot-rolled steel sheet having excellent formability having excellent crack propagation resistance "is disclosed. However, in the case of the technology proposed in this publication, the "fatigue crack propagation resistance" to be improved is limited to the "crack propagation lower limit characteristic", and therefore, describes the "fatigue crack propagation stop characteristic". The dynamic parameter to be performed is only ΔKth, and the stable growth region of the crack is not targeted.Therefore, when the external stress increases and the stress intensity factor range ΔK at the fatigue crack tip exceeds ΔKth, the fatigue crack starts to propagate. Cracks grow at the same fatigue crack growth rate as conventional steel.
【０００８】特開平６−２７１９８５号公報には、特定
の組織を有する鋼板及びその鋼板を得るために鋼の化学
組成と圧延や冷却の条件を規定した「耐疲労伝播特性の
優れた鋼板およびその製造方法」が開示されている。し
かし、この公報で提案された技術の場合、島状マルテン
サイトの平均存在間隔、平均偏平比及び体積率を規定し
て疲労亀裂進展速度の抑制を実現しており、特に島状マ
ルテンサイトの体積率を０．５〜５％と規定している。
したがって、島状マルテンサイトを起点とする脆性破壊
が容易に発生し、疲労亀裂進展特性と破壊靱性とを両立
させることが困難である。特開平６−２９９２３８号公
報には、鋼の化学組成と圧延や冷却の条件を規定した
「耐疲労伝播特性と溶接熱影響部靱性の優れた鋼板の製
造方法」が開示されている。しかし、この公報で提案さ
れた技術の場合、Ｔｉで脱酸した後にＡｌを添加すると
いう複雑な製鋼工程が必須であり、したがって、製鋼コ
ストの上昇や他鋼種の製造工程への悪影響を避け難い。Japanese Unexamined Patent Publication No. Hei 6-271985 discloses a steel sheet having a specific structure and a steel sheet having excellent fatigue propagation resistance and a steel composition having a specified chemical composition and rolling and cooling conditions for obtaining the steel sheet. Manufacturing Method "is disclosed. However, in the case of the technology proposed in this publication, the average existence interval of the island-like martensite, the average aspect ratio and the volume ratio are specified to suppress the fatigue crack growth rate, and in particular, the volume of the island-like martensite is reduced. The rate is specified as 0.5 to 5%.
Therefore, brittle fracture starting from island martensite easily occurs, and it is difficult to achieve both fatigue crack growth characteristics and fracture toughness. Japanese Patent Application Laid-Open No. 6-299238 discloses a "method of manufacturing a steel sheet having excellent fatigue propagation resistance and toughness of a heat-affected zone of a weld" which defines the chemical composition of steel and conditions of rolling and cooling. However, in the case of the technique proposed in this publication, a complicated steelmaking process of adding Al after deoxidizing with Ti is essential, and therefore it is difficult to avoid an increase in steelmaking cost and an adverse effect on the manufacturing process of other steel types. .
【０００９】[0009]
【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、構造物の亀裂進展寿
命を延伸させて構造上の安全性を確保させるために、繰
返し荷重を受けた場合でも良好な耐疲労亀裂進展性を示
す構造用鋼材の製造方法を提供することである。SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to increase a crack propagation life of a structure to secure a structural safety by repeatedly applying a load. An object of the present invention is to provide a method for producing a structural steel material exhibiting good fatigue crack growth resistance even when it is subjected.
【００１０】[0010]
【課題を解決するための手段】本発明の要旨は、下記
（１）、（２）に示す疲労亀裂進展抵抗性に優れた鋼材
の製造方法にある。The gist of the present invention lies in a method for producing a steel material having excellent fatigue crack growth resistance as shown in the following (1) and (2).
【００１１】（１）質量％で、Ｃ：０．０２〜０．２５
％、Ｓｉ：０．０３〜０．６％、Ｍｎ：０．３０〜２．
０％、Ａｌ：０．０１０〜０．１０％、Ｎｂ：０．０１
０〜０．１０％、Ｔｉ：０．０１０〜０．１０％を含有
し、下記 (1)式で表されるＦＣＧ１の値が４．０以下を
満たし、残部がＦｅ及び不純物からなる鋼片を、１０５
０℃以上に加熱して１０４０〜７４０℃の圧延仕上げ温
度で熱間圧延し、その後、（Ｔｓ１＋５０）〜（Ｔｓ１
−２５）℃の温度から５〜５０℃／秒の冷却速度で少な
くとも５５０℃まで冷却することを特徴とする疲労亀裂
進展抵抗性に優れた鋼材の製造方法。ここで、Ｔｓ１は
下記(2)式から計算される温度である。(1) In mass%, C: 0.02 to 0.25
%, Si: 0.03-0.6%, Mn: 0.30-2.
0%, Al: 0.010 to 0.10%, Nb: 0.01
0-0.10%, Ti: 0.010-0.10%, the value of FCG1 represented by the following formula (1) satisfies 4.0 or less, and the balance is Fe and impurities. To 105
It is heated to 0 ° C. or more and hot-rolled at a rolling finishing temperature of 1040 to 740 ° C., and then (Ts1 + 50) to (Ts1
-25) A method for producing a steel material excellent in fatigue crack propagation resistance, comprising cooling from a temperature of ° C to at least 550 ° C at a cooling rate of 5 to 50 ° C / sec. Here, Ts1 is a temperature calculated from the following equation (2).
【００１２】 ＦＣＧ１＝（０．７＋Ｃ）／｛（Ｓｉ／２５）＋（Ｍｎ／５）＋（Ｎｂ／２５ ）＋Ｔｉ｝・・・・・ (1) Ｔｓ１＝（８２０−２００Ｃ−６０Ｓｉ−６００Ｎｂ＋２０００Ｔｉ）・・・ ・・ (2) なお、各式における元素記号はその元素の質量％での含
有量を示す。FCG1 = (0.7 + C) / {(Si / 25) + (Mn / 5) + (Nb / 25) + Ti} (1) Ts1 = (820-200C-60Si-600Nb + 2000Ti) (2) The symbol of each element in each formula indicates the content of the element in mass%.
【００１３】（２）上記（１）に記載の成分に加えて更
に、質量％で、 第１群：Ｃｕ：０．０２〜１．０％、Ｃｒ：０．０３〜
２．０％のうちの１種以上、 第２群：Ｎｉ：０．０５〜１．０％、Ｍｏ：０．０５〜
１．０％のうちの１種以上、 第３群：Ｖ：０．０１〜０．５％ の１群以上をも含み、下記 (3)式で表されるＦＣＧ２の
値が４．０以下を満たし、残部がＦｅ及び不純物からな
る鋼片を、１０５０℃以上に加熱して１０４０〜７４０
℃の圧延仕上げ温度で熱間圧延し、その後、（Ｔｓ２＋
５０）〜（Ｔｓ２−２５）℃の温度から５〜５０℃／秒
の冷却速度で少なくとも５５０℃まで冷却することを特
徴とする疲労亀裂進展抵抗性に優れた鋼材の製造方法。
ここで、Ｔｓ２は下記 (4)式から計算される温度であ
る。(2) In addition to the components described in the above (1), further, in mass%, the first group: Cu: 0.02 to 1.0%, Cr: 0.03 to
2.0% or more, 2nd group: Ni: 0.05 to 1.0%, Mo: 0.05 to
1.0% or more, 3rd group: V: 0.01 to 0.5% including one or more groups, and the value of FCG2 represented by the following formula (3) is 4.0 or less. Is satisfied, and the balance is heated to 1050 ° C. or higher by heating the steel slab consisting of Fe and impurities to 1040 to 740.
Hot rolling at a rolling finishing temperature of 200 ° C., and then (Ts2 +
50) A method for producing a steel material excellent in fatigue crack propagation resistance, comprising cooling from a temperature of (Ts2-25) ° C to at least 550 ° C at a cooling rate of 5 to 50 ° C / sec.
Here, Ts2 is a temperature calculated from the following equation (4).
【００１４】 ＦＣＧ２＝（０．７＋Ｃ）／｛（Ｓｉ／２５）＋（Ｍｎ／５）＋（Ｃｕ／５０ ）＋（Ｎｉ／５０）＋（Ｃｒ／２５）＋（Ｍｏ／２５）＋（Ｖ／５）＋（Ｎｂ／ ２５）＋Ｔｉ｝・・・・・ (3) Ｔｓ２＝（１＋０．１Ｖ）（８２０−２００Ｃ−６０Ｓｉ＋２００Ｃｕ＋５０ Ｎｉ−１００Ｃｒ＋６００Ｍｏ−６００Ｎｂ＋２０００Ｔｉ）・・・・・ (4) なお、各式における元素記号はその元素の質量％での含
有量を示す。FCG2 = (0.7 + C) / ｛(Si / 25) + (Mn / 5) + (Cu / 50) + (Ni / 50) + (Cr / 25) + (Mo / 25) + (V / 5) + (Nb / 25) + Ti｝ (3) Ts2 = (1 + 0.1V) (820-200C-60Si + 200Cu + 50 Ni-100Cr + 600Mo-600Nb + 2000Ti) (4) Indicates the content of the element in mass%.
【００１５】本発明者らは、前記した課題を達成するた
めに鋼材の疲労亀裂進展挙動に及ぼす鋼の化学組成、圧
延条件、冷却条件の影響を検討し、下記の知見を得た。The present inventors have studied the effects of the chemical composition of steel, rolling conditions, and cooling conditions on the fatigue crack growth behavior of a steel material in order to achieve the above object, and have obtained the following findings.
【００１６】（ａ）疲労亀裂進展速度を抑制し、疲労亀
裂進展寿命を延伸させるためには、鋼材内の微視的な
領域で硬度差を設け、疲労亀裂伝播経路を微視的に屈曲
させて巨視亀裂進展速度を抑制させる方法、鋼材に繰
返し歪みが負荷された時の応力応答として繰返し軟化を
生ずる鋼材を準備し、疲労亀裂進展時の亀裂先端での応
力を緩和させることにより実質的な亀裂先端の応力を低
めて疲労亀裂進展速度を抑制させる方法、鋼材の降伏
強度に対する引張強度の比（降伏比）を低く押さえるこ
とにより、疲労亀裂先端に形成される塑性変形領域をよ
り広くして亀裂先端の局所的負荷を軽減し、結果として
疲労亀裂進展速度を抑制する方法があるが、これらのい
ずれの方法の場合にも、前記 (1)式で表されるＦＣＧ１
の値又は前記 (3)式で表されるＦＣＧ２の値を小さくす
ることが有効である。なお、以下の説明においては、前
記 (1)式で表されるＦＣＧ１及び前記 (3)式で表される
ＦＣＧ２をまとめてＦＣＧということもある。(A) In order to suppress the fatigue crack growth rate and extend the fatigue crack growth life, a hardness difference is provided in a microscopic region in the steel material, and the fatigue crack propagation path is microscopically bent. A method of suppressing the rate of macroscopic crack growth by preparing a steel material that repeatedly softens as a stress response when cyclic strain is applied to the steel material, and substantially alleviates the stress at the crack tip during fatigue crack growth. A method to reduce the stress at the crack tip to suppress the fatigue crack growth rate, and to keep the ratio of the tensile strength to the yield strength (yield ratio) of the steel material low, thereby expanding the plastic deformation region formed at the tip of the fatigue crack. There is a method of reducing the local load on the crack tip and consequently suppressing the fatigue crack growth rate. In any of these methods, the FCG1 represented by the above formula (1) is used.
Or the value of FCG2 represented by the above equation (3) is effective. In the following description, the FCG1 represented by the formula (1) and the FCG2 represented by the formula (3) may be collectively referred to as FCG.
【００１７】（ｂ）熱間圧延後の冷却開始温度は、鋼材
の疲労亀裂進展抵抗性に大きく影響し、疲労亀裂進展速
度が最小になる最適な冷却開始温度領域が存在する。(B) The cooling start temperature after hot rolling has a great effect on the fatigue crack growth resistance of the steel material, and there is an optimum cooling start temperature region where the fatigue crack growth rate is minimized.
【００１８】そこで、本発明者らは、種々の化学組成を
有する鋼材の疲労亀裂進展抵抗性と熱間圧延後の冷却開
始温度、冷却速度との関係について更に詳細な検討を加
えた。その結果、次の事項が明らかになった。Therefore, the present inventors have further studied the relationship between the fatigue crack growth resistance of steels having various chemical compositions and the cooling start temperature and cooling rate after hot rolling. As a result, the following matters became clear.
【００１９】（ｃ）いずれの鋼材においても熱間圧延後
の冷却開始温度を低温側から徐々に上昇させると、疲労
亀裂進展速度は漸減して行くが、その漸減割合は冷却開
始温度が高くなるにつれて段々と少なくなる。そして、
更に冷却開始温度を上昇させると却って疲労亀裂進展速
度が漸増して行く。つまり、疲労亀裂進展速度が最小に
なる最適な冷却開始温度が存在する。(C) In any of the steel materials, when the cooling start temperature after hot rolling is gradually increased from the low temperature side, the fatigue crack growth rate gradually decreases, but the rate of decrease gradually increases the cooling start temperature. As the number gradually decreases. And
Further, when the cooling start temperature is further increased, the fatigue crack growth rate gradually increases. That is, there is an optimum cooling start temperature at which the fatigue crack growth rate is minimized.
【００２０】（ｄ）上記の疲労亀裂進展速度漸増の割合
は、その漸減時の割合よりも緩やかであり、最適冷却開
始温度に対し疲労亀裂進展抵抗性がほぼ同等である冷却
開始温度は、最適冷却開始温度に対し、低温側に２５
℃、高温側に５０℃の７５℃の幅の領域である。 （ｅ）上記（ｃ）の疲労亀裂進展速度が最小になる最適
な冷却開始温度は、前記 (2)式で表されるＴｓ１又は前
記 (4)式で表されるＴｓ２と関係する。なお、以下の説
明においては、前記 (2)式で表されるＴｓ１及び前記
(4)式で表されるＴｓ２をまとめてＴｓということもあ
る。(D) The rate at which the fatigue crack growth rate gradually increases is slower than the rate at which the fatigue crack growth rate gradually decreases, and the cooling start temperature at which the fatigue crack growth resistance is almost equal to the optimum cooling start temperature is the optimum. 25 to the low temperature side relative to the cooling start temperature
It is an area of 75 ° C. width of 50 ° C. on the high temperature side. (E) The optimum cooling start temperature at which the fatigue crack growth rate in (c) is minimized is related to Ts1 represented by the above equation (2) or Ts2 represented by the above equation (4). In the following description, Ts1 represented by the above equation (2) and the
Ts2 represented by equation (4) may be collectively referred to as Ts.
【００２１】（ｆ）熱間圧延後の鋼材冷却速度の適正化
も、疲労亀裂進展速度を抑制し、疲労亀裂進展寿命を延
ばすのに有効である。本発明は、上記の知見に基づいて
完成されたものである。(F) Optimization of the cooling rate of the steel material after hot rolling is also effective in suppressing the fatigue crack growth rate and extending the fatigue crack growth life. The present invention has been completed based on the above findings.
【００２２】[0022]
【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、化学成分の含有量の「％」は「質
量％」を意味する。 （Ａ）鋼材の素材鋼の化学組成 Ｃ：０．０２〜０．２５％ Ｃは、構造部材の強度確保に有効な元素である。しか
し、その含有量が０．０２％未満では鋼材の組織に占め
るフェライト相の割合が極めて多く強度向上効果が得難
い。一方、Ｃの含有量が０．２５％を超えると溶接性が
低下するので溶接施工が困難となり、構造用鋼材として
の使用領域が著しく限定されてしまう。したがって、Ｃ
の含有量を０．０２〜０．２５％とした。なお、鋼材の
組織に占めるフェライト相の割合を抑えて大きな強度を
確保するとともに良好な溶接性をも確保するために、Ｃ
の含有量は０．０４〜０．１２％とすることが望まし
い。DESCRIPTION OF THE PREFERRED EMBODIMENTS Each requirement of the present invention will be described in detail below. In addition, “%” of the content of the chemical component means “% by mass”. (A) Chemical composition of steel material steel C: 0.02 to 0.25% C is an element effective for ensuring the strength of the structural member. However, when the content is less than 0.02%, the proportion of the ferrite phase in the structure of the steel material is extremely large, and it is difficult to obtain a strength improving effect. On the other hand, when the content of C exceeds 0.25%, weldability is reduced, so that welding is difficult, and a use region as a structural steel material is significantly limited. Therefore, C
Was set to 0.02 to 0.25%. In order to secure a large strength by suppressing the ratio of the ferrite phase in the structure of the steel material and to secure good weldability, C
Is desirably 0.04 to 0.12%.
【００２３】Ｓｉ：０．０３〜０．６％ Ｓｉは、脱酸作用を有する。しかし、その含有量が０．
０３％未満では添加効果に乏しい。一方、Ｓｉの含有量
が０．６％を超えると破壊靱性が低下するようになる。
したがって、Ｓｉの含有量を０．０３〜０．６％とし
た。なお、Ｓｉの含有量は０．２５〜０．５％とするこ
とが望ましい。Si: 0.03-0.6% Si has a deoxidizing effect. However, when its content is 0.1.
If it is less than 03%, the effect of addition is poor. On the other hand, when the content of Si exceeds 0.6%, the fracture toughness decreases.
Therefore, the content of Si is set to 0.03 to 0.6%. The content of Si is desirably 0.25 to 0.5%.
【００２４】Ｍｎ：０．３０〜２．０％ Ｍｎは、強度の確保に有効な元素である。しかし、その
含有量が０．３０％未満では添加効果に乏しい。一方、
Ｍｎの含有量が２．０％を超えると溶接性が低下するの
で溶接施工が困難となり、構造用鋼材としての使用領域
が著しく限定されてしまう。したがって、Ｍｎの含有量
を０．３０〜２．０％とした。なお、大きな強度を確保
するとともに良好な溶接性をも確保するために、Ｍｎの
含有量は０．５〜１．８％とすることが望ましい。Mn: 0.30 to 2.0% Mn is an element effective for securing strength. However, if the content is less than 0.30%, the effect of addition is poor. on the other hand,
When the content of Mn exceeds 2.0%, the weldability deteriorates, so that welding work becomes difficult, and the use region as a structural steel material is significantly limited. Therefore, the content of Mn is set to 0.30 to 2.0%. In addition, in order to ensure high strength and also ensure good weldability, the content of Mn is desirably 0.5 to 1.8%.
【００２５】Ａｌ：０．０１０〜０．１０％ Ａｌは、脱酸作用を有する。しかし、その含有量が０．
０１０％未満では添加効果に乏しく、一方、０．１０％
を超えると破壊靱性が低下するし、鋼の清浄性も悪くな
る。したがって、Ａｌの含有量を０．０１０〜０．１０
％とした。なお、Ａｌ含有量は０．０１０〜０．０５％
とすることが望ましい。Al: 0.010% to 0.10% Al has a deoxidizing effect. However, when its content is 0.1.
If it is less than 010%, the effect of the addition is poor, while 0.10%
If it exceeds 300, the fracture toughness decreases and the cleanliness of the steel deteriorates. Therefore, the content of Al is set to 0.010 to 0.10.
%. The Al content is 0.010 to 0.05%
It is desirable that
【００２６】Ｎｂ：０．０１０〜０．１０％ Ｎｂは、破壊靱性を確保するのに有効な元素であり、構
造材料として用いるために０．０１０％以上含有させる
必要がある。しかし、その含有量が０．１０％を超える
と却って破壊靱性が低下するようになる。したがって、
Ｎｂの含有量を０．０１０〜０．１０％とした。なお、
Ｎｂの含有量は０．０２０〜０．０５％とすることが望
ましい。Nb: 0.010% to 0.10% Nb is an element effective for securing fracture toughness, and must be contained at 0.010% or more in order to be used as a structural material. However, when the content exceeds 0.10%, the fracture toughness is rather lowered. Therefore,
The content of Nb was set to 0.010 to 0.10%. In addition,
The Nb content is desirably 0.020 to 0.05%.
【００２７】Ｔｉ：０．０１０〜０．１０％ Ｔｉは、破壊靱性を確保するのに有効な元素であり、構
造材料として用いるために０．０１０％以上含有させる
必要がある。しかし、その含有量が０．１０％を超える
と却って破壊靱性が低下するようになる。したがって、
Ｔｉの含有量を０．０１０〜０．１０％とした。なお、
Ｔｉの含有量は０．０１５〜０．０５％とすることが望
ましい。Ti: 0.010% to 0.10% Ti is an element effective for securing the fracture toughness, and it is necessary to contain 0.010% or more in order to use it as a structural material. However, when the content exceeds 0.10%, the fracture toughness is rather lowered. Therefore,
The content of Ti was set to 0.010 to 0.10%. In addition,
The content of Ti is desirably 0.015 to 0.05%.
【００２８】ＦＣＧ１：４．０以下 前記 (1)式で表されるＦＣＧ１の値が４．０以下の場合
に、疲労亀裂進展速度を抑制して疲労亀裂進展寿命を延
伸させることができる。したがって、ＦＣＧ１の値を
４．０以下とした。このＦＣＧ１の値は３．０以下とす
ることが好ましい。なお、ＦＧＣ１の下限値は、Ｃ、Ｓ
ｉ、Ｍｎ、Ｎｂ、Ｔｉの含有量がそれぞれ０．０２％、
０．６％、２．０％、０．１％、０．１％の場合の１．
３６である。FCG1: 4.0 or less When the value of FCG1 represented by the above formula (1) is 4.0 or less, the fatigue crack growth rate can be suppressed and the fatigue crack growth life can be extended. Therefore, the value of FCG1 was set to 4.0 or less. It is preferable that the value of FCG1 be 3.0 or less. The lower limit of FGC1 is C, S
i, Mn, Nb, Ti content is 0.02%,
0.6%, 2.0%, 0.1% and 0.1%
36.
【００２９】なお、本発明の疲労亀裂進展抵抗性に優れ
た鋼材の製造方法に用いられる素材鋼には、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良い。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 material steel used in the method for producing a steel material having excellent fatigue crack growth resistance according to the present invention further includes one of the first to third groups in addition to the above-mentioned respective component elements. More than a group may be included. The effects and desirable contents of these alloy elements are as follows.
【００３０】Ｃｕ：０．０２〜１．０％、Ｃｒ：０．０
３〜２．０％ Ｃｕ及びＣｒには耐食性を高める作用があるので、鋼材
が腐食環境下で使用される場合等に耐食性を確保する目
的で含有させるが、Ｃｕ含有量が０．０２％未満、Ｃｒ
含有量が０．０３％未満ではその効果が得難い。一方、
Ｃｕを１．０％を超えて、又、Ｃｒを２．０％を超えて
含有させると溶接性が低下するので溶接施工が困難とな
り、構造用鋼材としての使用領域が著しく限定されてし
まう。更に、Ｃｕを１．０％を超えて含有させた場合に
は、熱間加工性が低下して圧延で鋼材表面に疵が生じた
り、鋼材の表面や内部に割れが発生することがある。し
たがってＣｕ、Ｃｒの１種以上を添加する場合には、Ｃ
ｕの含有量を０．０２〜１．０％、Ｃｒの含有量を０．
０３〜２．０％とするのがよい。なお、Ｃｕ、Ｃｒの１
種以上を添加する場合、Ｃｕの含有量は０．１〜０．５
％、Ｃｒの含有量は０．２〜１．５％とするのが好まし
い。 Ｎｉ：０．０５〜１．０％、Ｍｏ：０．０５〜１．０％ Ｎｉ及びＭｏには鋼の破壊靱性を高めるとともに焼入れ
性を高める作用があるので、破壊靱性を確保したり鋼材
が大型構造物に使用される場合の焼入れ性を確保したり
する目的で含有させるが、Ｎｉ含有量が０．０５％未
満、Ｍｏ含有量が０．０５％未満ではその効果が得難
い。一方、Ｎｉを１．０％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コストが嵩む
ばかりである。したがってＮｉ、Ｍｏの１種以上を添加
する場合には、Ｎｉの含有量を０．０５〜１．０％、Ｍ
ｏの含有量を０．０５〜１．０％とするのがよい。 Ｖ：０．０１〜０．５％ Ｖには強度を高める作用があるので、構造物に大きな強
度を確保する目的で含有させるが、その含有量が０．０
１％未満ではその効果に乏しく、一方、０．５％を超え
て含有させてもその効果は飽和しコストが嵩むばかりで
ある。したがってＶを添加する場合には、０．０１〜
０．５％の含有量とするのがよい。Cu: 0.02 to 1.0%, Cr: 0.0
3 to 2.0% Since Cu and Cr have an effect of increasing corrosion resistance, they are included for the purpose of ensuring corrosion resistance when a steel material is used in a corrosive environment, but the Cu content is less than 0.02%. , Cr
If the content is less than 0.03%, the effect is difficult to obtain. on the other hand,
When Cu exceeds 1.0% and Cr exceeds 2.0%, the weldability deteriorates, so that welding becomes difficult, and a use region as a structural steel material is significantly limited. Further, when Cu is contained in an amount exceeding 1.0%, hot workability is reduced, and a flaw may be generated on a steel material surface by rolling, or a crack may be generated on the surface or inside of the steel material. Therefore, when one or more of Cu and Cr are added, C
The u content is 0.02 to 1.0% and the Cr content is 0.1%.
The content is preferably set to 03 to 2.0%. In addition, 1 of Cu and Cr
When adding more than one kind, the content of Cu is 0.1 to 0.5.
% And the content of Cr are preferably 0.2 to 1.5%. Ni: 0.05 to 1.0%, Mo: 0.05 to 1.0% Since Ni and Mo have the effect of increasing the fracture toughness of steel and increasing the hardenability, it is necessary to secure fracture toughness and to improve the steel material. Although it is contained for the purpose of securing hardenability when used for a large-sized structure, the effect is hardly obtained when the Ni content is less than 0.05% and the Mo content is less than 0.05%. On the other hand, Ni exceeds 1.0% and Mo exceeds 1.0%.
%, The effect is saturated and the cost increases. Therefore, when one or more of Ni and Mo are added, the content of Ni is 0.05 to 1.0%,
The content of o is preferably set to 0.05 to 1.0%. V: 0.01 to 0.5% V has an effect of increasing the strength, and is contained for the purpose of securing a large strength in the structure.
If the content is less than 1%, the effect is poor. On the other hand, if the content exceeds 0.5%, the effect is saturated and the cost is increased. Therefore, when V is added, 0.01 to
The content is preferably 0.5%.
【００３１】ＦＣＧ２：４．０以下 前記 (3)式で表されるＦＣＧ２の値が４．０以下の場合
に、疲労亀裂進展速度を抑制して疲労亀裂進展寿命を延
伸させることができる。したがって、ＦＣＧ２の値を
４．０以下とした。このＦＣＧ２の値は３．０以下とす
ることが好ましい。なお、ＦＧＣ２の下限値はは、Ｃ、
Ｓｉ、Ｍｎ、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ、Ｎｂ、Ｔｉ
の含有量がそれぞれ０．０２％、０．６％、２．０％、
１．０％、１．０％、２．０％、１．０％、０．５％、
０．１％、０．１％の場合の０．９１である。 （Ｂ）鋼材の製造条件 （Ｂ−１）熱間圧延前の加熱温度：１０５０℃以上 圧延前組織を整え、圧延加工が容易に行えるようにする
ために、加熱温度は１０５０℃以上とする必要がある。
したがって、上記（Ａ）に記載した化学組成を有する鋼
片の熱間圧延前の加熱温度を１０５０℃以上とした。な
お、加熱温度は１１００〜１２００℃とすることが好ま
しい。 （Ｂ−２）圧延仕上げ温度：１０４０〜７４０℃ 組織を粗大化させないために圧延仕上げ温度は１０４０
℃以下とする必要がある。しかし、圧延仕上げ温度が７
４０℃を下回ると、被圧延材の表面に加工が集中して、
鋼材の厚さ方向の機械的性質が不均一になってしまう。
したがって、熱間圧延仕上げ温度を１０４０〜７４０℃
とした。なお、圧延仕上げ温度は９５０〜８５０℃とす
ることが好ましい。 （Ｂ−３）熱間圧延後の冷却 疲労亀裂進展速度を抑制し、疲労亀裂進展寿命を延伸さ
せるためは、熱間圧延後の冷却開始を（Ｔｓ＋５０）〜
（Ｔｓ−２５）℃の温度から行う必要がある。冷却開始
温度が（Ｔｓ＋５０）℃を上回ったり、（Ｔｓ−２５）
℃を下回れば疲労亀裂進展速度が大きくなってしまう。
なお、上記のＴｓは鋼材の化学組成に応じて前記 (2)式
で表されるＴｓ１又は前記 (4)式で表されるＴｓ２を指
すものである。更に、上記温度領域からの冷却に際し、
その冷却速度を５〜５０℃／秒として少なくとも５５０
℃まで冷却する必要がある。冷却速度が５℃／秒未満の
場合には、鋼材内の微視的な領域で硬度差を設け、疲労
亀裂伝播経路を微視的に屈曲させて巨視亀裂進展速度を
抑制させることができず、一方、冷却速度が５０℃／秒
を超えると、鋼材の板厚方向に極めて大きな残留応力分
布が発生し、引張残留応力が形成される板厚中心部での
疲労亀裂進展速度が加速する。又、冷却終了温度が５５
０℃を超えると、鋼材の繰返し軟化特性が発現せず、亀
裂先端での応力が緩和されないので、結果として亀裂進
展速度を抑制できない。FCG2: 4.0 or less When the value of FCG2 represented by the formula (3) is 4.0 or less, the fatigue crack growth rate can be suppressed and the fatigue crack growth life can be extended. Therefore, the value of FCG2 was set to 4.0 or less. It is preferable that the value of FCG2 be 3.0 or less. The lower limit of FGC2 is C,
Si, Mn, Cu, Ni, Cr, Mo, V, Nb, Ti
Is 0.02%, 0.6%, 2.0%, respectively.
1.0%, 1.0%, 2.0%, 1.0%, 0.5%,
It is 0.91 for 0.1% and 0.1%. (B) Manufacturing conditions of steel materials (B-1) Heating temperature before hot rolling: 1050 ° C or more In order to prepare a structure before rolling and facilitate rolling, the heating temperature must be 1050 ° C or more. There is.
Therefore, the heating temperature of the steel slab having the chemical composition described in (A) before hot rolling was set to 1050 ° C. or higher. Note that the heating temperature is preferably set to 1100 to 1200 ° C. (B-2) Rolling finishing temperature: 1040 to 740 ° C. The rolling finishing temperature is 1040 in order not to coarsen the structure.
It is necessary to be below ° C. However, when the rolling finish temperature is 7
If the temperature falls below 40 ° C, the processing concentrates on the surface of the material to be rolled,
The mechanical properties in the thickness direction of the steel material become uneven.
Therefore, the hot rolling finishing temperature is set to 1040 to 740 ° C.
And In addition, it is preferable that the rolling finishing temperature is 950 to 850 ° C. (B-3) Cooling after hot rolling In order to suppress the fatigue crack growth rate and extend the fatigue crack growth life, the cooling start after hot rolling should be (Ts + 50) ~
It is necessary to start from a temperature of (Ts-25) ° C. The cooling start temperature exceeds (Ts + 50) ° C. or (Ts-25)
If the temperature is lower than ℃, the fatigue crack growth rate increases.
The above Ts indicates Ts1 represented by the above formula (2) or Ts2 represented by the above formula (4) according to the chemical composition of the steel material. Further, upon cooling from the above temperature range,
The cooling rate is at least 550 with 5 to 50 ° C./sec.
Need to cool down to ° C. If the cooling rate is less than 5 ° C./sec, a hardness difference is provided in a microscopic region in the steel material, and the fatigue crack propagation path cannot be microscopically bent to suppress the macroscopic crack growth rate. On the other hand, if the cooling rate exceeds 50 ° C./sec, an extremely large residual stress distribution is generated in the thickness direction of the steel material, and the fatigue crack growth rate at the center of the thickness where the tensile residual stress is formed is accelerated. The cooling end temperature is 55
If the temperature exceeds 0 ° C., the steel material does not exhibit the repetitive softening property, and the stress at the crack tip is not relaxed. As a result, the crack growth rate cannot be suppressed.
【００３２】したがって、熱間圧延後、（Ｔｓ＋５０）
〜（Ｔｓ−２５）℃の温度から５〜５０℃／秒の冷却速
度で少なくとも５５０℃まで冷却することとした。Therefore, after hot rolling, (Ts + 50)
It was decided to cool from a temperature of ~ (Ts-25) ° C to at least 550 ° C at a cooling rate of 5-50 ° C / sec.
【００３３】次に、実施例により本発明を更に詳しく説
明する。Next, the present invention will be described in more detail with reference to examples.
【００３４】[0034]
【実施例】（実施例１）表１〜３に示す化学組成を有す
る鋼を通常の方法によって試験炉溶製した。なお、表１
〜３には化学組成から計算されるＦＣＧ（つまり、ＦＣ
Ｇ１とＦＣＧ２）の値及びＴｓ（つまり、Ｔｓ１とＴｓ
２）の値も示した。EXAMPLES (Example 1) Steels having the chemical compositions shown in Tables 1 to 3 were melted in a test furnace by an ordinary method. Table 1
The FCG calculated from the chemical composition (that is, FCG)
G1 and FCG2) and Ts (ie, Ts1 and Ts)
The value of 2) is also shown.
【００３５】[0035]
【表１】 [Table 1]
【表２】 [Table 2]
【表３】 次いで、これらの鋼を通常の熱間鍛造によって厚さ１５
０ｍｍの鋼片とした後、１１００℃に加熱してから熱間
圧延した。なお、熱間圧延は、圧延仕上げ温度を８８０
℃として、板厚２５ｍｍに仕上げた。熱間圧延仕上げ後
は、鋼の化学組成に応じた（Ｔｓ＋１０）℃の温度から
４０℃／秒の冷却速度で５００℃まで冷却した。このよ
うにして得た板厚２５ｍｍの鋼板から各種試験片を採取
し、溶接性、清浄度、破壊靱性及び引張強度を測定し
た。すなわち、上記板厚２５ｍｍの鋼板の板厚中心部を
主に評価できるように、ｙ型溶接割れ試験片、ミクロ試
験片、JIS Z 2202(1998)に記載のＶノッチ衝撃試験片、
JIS Z 2201(1998)に記載の４号引張試験片を採取し、次
の各条件で溶接性、清浄度、破壊靱性及び引張強度を調
査した。[Table 3] The steels were then subjected to normal hot forging to a thickness of 15 mm.
After forming a 0 mm steel slab, it was heated to 1100 ° C. and then hot rolled. In the hot rolling, the rolling finishing temperature was 880.
It finished to board thickness 25mm at ℃. After hot rolling, the steel was cooled from a temperature of (Ts + 10) ° C. according to the chemical composition of the steel to 500 ° C. at a cooling rate of 40 ° C./sec. Various test pieces were sampled from the thus obtained steel plate having a thickness of 25 mm, and weldability, cleanliness, fracture toughness and tensile strength were measured. That is, the y-type weld crack test specimen, the micro test specimen, the V notch impact test specimen described in JIS Z 2202 (1998)
A No. 4 tensile test piece described in JIS Z 2201 (1998) was sampled, and weldability, cleanliness, fracture toughness and tensile strength were examined under the following conditions.
【００３６】ｙ型溶接割れ試験は、通常のサブマージア
ーク溶接用の溶接材料を用いて、試験片予熱温度が２５
℃、５０℃、７５℃、１００℃、１２５℃の各場合につ
いて、温度３０℃、湿度８０％の雰囲気で実施した。な
お、前記溶接材料を温度３０℃、湿度８０％の環境に１
時間放置してから試験を行った。各予熱温度に対する試
験数は２である。In the y-type welding crack test, a test piece preheating temperature was set to 25 using a normal welding material for submerged arc welding.
In each case of ° C, 50 ° C, 75 ° C, 100 ° C, and 125 ° C, the test was performed in an atmosphere at a temperature of 30 ° C and a humidity of 80%. The welding material was placed in an environment with a temperature of 30 ° C. and a humidity of 80%.
The test was performed after standing for a period of time. The number of tests for each preheating temperature is two.
【００３７】清浄度の評価は、JIS G 0555(1998)に則っ
て顕微鏡の倍率を４００倍とし、視野数６０で行った。The evaluation of cleanliness was carried out according to JIS G 0555 (1998) with a microscope magnification of 400 times and a visual field number of 60.
【００３８】破壊靱性試験は、板厚中心部から試験片の
長手方向が圧延方向に一致し、亀裂進展方向が鋼材の幅
方向に一致するように採取した前記JIS Z 2202(1998)に
記載のＶノッチ衝撃試験片を用い、各試験温度における
試験数を３としてシャルピー衝撃試験を行い、脆性−延
性の破面遷移温度（ｖＴｒｓ）を求めた。引張試験は、
板厚中心部から試験片の長手方向が圧延方向に一致する
ように採取したJIS Z 2201(1998)に記載の４号引張試験
片を用いて室温大気中で行った。なお、試験数は２とし
た。The fracture toughness test was conducted according to the above-mentioned JIS Z 2202 (1998) in which the specimen was sampled so that the longitudinal direction of the specimen coincided with the rolling direction and the crack propagation direction coincided with the width direction of the steel material from the center of the plate thickness. Using a V-notch impact test piece, a Charpy impact test was performed with the number of tests at each test temperature being 3, and a brittle-ductile fracture surface transition temperature (vTrs) was determined. The tensile test is
Using a No. 4 tensile test piece described in JIS Z 2201 (1998) sampled from the center of the sheet thickness such that the longitudinal direction of the test piece coincides with the rolling direction, the test was performed in the air at room temperature. The number of tests was 2.
【００３９】表４に上記の各試験結果を示す。なお、表
２におけるマーク「○」と「×」はそれぞれ次の区分に
基づくものである。Table 4 shows the results of the above tests. The marks “マ ー ク” and “X” in Table 2 are based on the following categories.
【００４０】すなわち、「溶接性」は予熱温度２５℃で
割れを生じない場合を「○」、割れを生じないために５
０℃以上の予熱を必要とした場合を「×」とした。「清
浄度」は、現状のＡ級の船級規格鋼を基準に判断し、こ
れと同等以上の清浄度である場合を「○」、それを下回
る場合を「×」とした。「破壊靱性」は破面遷移温度
（ｖＴｒｓ）が−２０℃未満の場合を「○」、−２０℃
以上の場合を「×」とした。又、「引張強度」は４００
ＭＰａ以上の公称引張強度が得られた場合を「○」、４
００ＭＰａを下回る場合を「×」とした。That is, “weldability” is “○” when no crack is generated at a preheating temperature of 25 ° C., and 5 when no crack is generated.
A case where a preheating of 0 ° C. or more was required was evaluated as “×”. The “cleanliness” was determined based on the current A-class marine grade standard steel, and was evaluated as “度” when the cleanliness was equal to or higher than this, and “x” when the cleanliness was lower than this. “Fracture toughness” is “○” when the fracture surface transition temperature (vTrs) is lower than −20 ° C., and −20 ° C.
The above case was marked as “×”. The “tensile strength” is 400
When the nominal tensile strength of not less than MPa was obtained,
The case where the pressure was lower than 00 MPa was evaluated as “x”.
【００４１】[0041]
【表４】 表４から、鋼材の化学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た鋼２８〜４１を用いた場合に
は、溶接性、清浄度、破壊靱性、引張強度のいずれかが
目標に達していないことが明らかである。[Table 4] From Table 4, when any one of the chemical components of the steel material used steels 28 to 41 out of the range of the content specified in the present invention, any one of the weldability, cleanliness, fracture toughness, and tensile strength was obtained. It is clear that the goal has not been reached.
【００４２】次いで、溶接性、清浄度、破壊靱性、引張
強度のいずれもが目標に達した鋼１〜２７の板厚２５ｍ
ｍの鋼板の全厚での疲労亀裂進展特性を評価するため
に、ＬＴ方向でＣＴ試験片を採取し、負荷条件として繰
返し速度２５Ｈｚ、応力比０．１の下、室温大気中でＡ
ＳＴＭ規格（Ｅ６４７）に則って疲労亀裂進展試験を行
った。疲労亀裂進展速度は、亀裂先端における応力拡大
係数範囲ΔＫが２０ＭＰａ・ｍ1/2 における進展速度で
代表させて求めた。なお、一般鋼材における疲労亀裂進
展速度のレベルを参照して、目標とする疲労亀裂進展速
度はその上限を４．０×１０-5ｍｍ／サイクルとした。
表５に、疲労亀裂進展試験の結果を示す。Next, the steel thickness of 25 to 25 m of the steels 1 to 27 in which all of the weldability, cleanliness, fracture toughness, and tensile strength reached the target.
In order to evaluate the fatigue crack growth characteristics of the steel sheet having a total thickness of m, a CT specimen was taken in the LT direction, and subjected to A in a room temperature atmosphere under a repetition rate of 25 Hz and a stress ratio of 0.1 as load conditions.
A fatigue crack growth test was performed according to the STM standard (E647). The fatigue crack growth rate was determined by representing the growth rate when the stress intensity factor range ΔK at the crack tip was 20 MPa · m 1/2 . The upper limit of the target fatigue crack growth rate was set to 4.0 × 10 −5 mm / cycle with reference to the level of the fatigue crack growth rate in the general steel material.
Table 5 shows the results of the fatigue crack growth test.
【００４３】[0043]
【表５】 表５から、鋼材に含まれる各元素が本発明で規定する含
有量の範囲内の場合でもＦＧＣの値が本発明で規定する
範囲から外れた鋼１〜４、鋼８及び鋼１３を用いた場合
には、疲労亀裂進展速度が目標とする値を超え、疲労亀
裂進展抵抗性に劣ることが明らかである。 （実施例２）前記実施例１で溶製した鋼の一部を用い
て、疲労亀裂進展速度に及ぼす冷却開始温度の影響を詳
細に調査した。[Table 5] From Table 5, steels 1 to 4, steel 8 and steel 13 whose FGC values were out of the range specified in the present invention were used even when each element contained in the steel material was within the range of the content specified in the present invention. In this case, it is clear that the fatigue crack growth rate exceeds the target value and the fatigue crack growth resistance is poor. (Example 2) Using a part of the steel melted in Example 1, the effect of the cooling start temperature on the fatigue crack growth rate was investigated in detail.
【００４４】すなわち、鋼６、鋼７及び鋼２０につい
て、通常の方法で熱間鍛造して作製した厚さ１５０ｍｍ
の鋼片を、１１００℃に加熱してから熱間圧延した。な
お、熱間圧延は、圧延仕上げ温度を９５０〜７５０℃と
して、板厚２５ｍｍに仕上げた。熱間圧延仕上げ後は、
鋼の化学組成に応じて表６に記載の各種の温度から４０
℃／秒の冷却速度で５００℃まで冷却した。That is, steel 6, steel 7, and steel 20 were formed by hot forging by a usual method to a thickness of 150 mm.
Was heated to 1100 ° C. and then hot-rolled. The hot rolling was performed at a rolling finish temperature of 950 to 750 ° C. and a plate thickness of 25 mm. After hot rolling,
Depending on the chemical composition of the steel, from the various temperatures listed in Table 6 to 40
It was cooled to 500 ° C at a cooling rate of ° C / sec.
【００４５】[0045]
【表６】 このようにして得た板厚２５ｍｍの鋼板の全厚での疲労
亀裂進展特性を評価するために、ＬＴ方向でＣＴ試験片
を採取し、前記実施例１と同じ条件で疲労亀裂進展試験
を行い、亀裂先端における応力拡大係数範囲ΔＫが２０
ＭＰａ・ｍ1/2における進展速度で代表させて疲労亀裂
進展速度を求めた。なお、本実施例においても、目標と
する疲労亀裂進展速度はその上限を４．０×１０-5ｍｍ
／サイクルとした。疲労亀裂進展試験の結果は表６に示
したとおりである。[Table 6] In order to evaluate the fatigue crack growth characteristics of the thus obtained steel sheet having a thickness of 25 mm at the entire thickness, a CT specimen was taken in the LT direction, and a fatigue crack growth test was performed under the same conditions as in Example 1 above. , The stress intensity factor range ΔK at the crack tip is 20
The fatigue crack growth rate was determined by representing the growth rate at MPa · m 1/2 . In this embodiment, the target fatigue crack growth rate has an upper limit of 4.0 × 10 −5 mm.
/ Cycle. The results of the fatigue crack growth test are as shown in Table 6.
【００４６】表６から、鋼材に含まれる各元素が本発明
で規定する含有量の範囲内にあり、しかもＦＧＣの値が
本発明で規定する範囲内にあっても、冷却開始温度が本
発明で規定する範囲（すなわち（Ｔｓ＋５０）〜（Ｔｓ
−２５）℃）から外れた場合には、疲労亀裂進展速度が
目標とする値を超え、疲労亀裂進展抵抗性に劣ることが
明らかである。From Table 6, it can be seen that even if each element contained in the steel material falls within the range defined by the present invention and the value of FGC falls within the range defined by the present invention, the cooling start temperature falls within the range defined by the present invention. (Ts + 50) to (Ts
When the temperature is out of (−25) ° C.), it is clear that the fatigue crack growth rate exceeds the target value and the fatigue crack growth resistance is poor.
【００４７】[0047]
【発明の効果】本発明によれば、疲労亀裂進展抵抗性に
優れた鋼材が得られるので、船舶、海洋構造物、橋梁、
建築物、タンクなど各種構造物に用いることができる。According to the present invention, a steel material having excellent resistance to fatigue crack growth can be obtained, so that ships, marine structures, bridges,
It can be used for various structures such as buildings and tanks.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 有持 和茂 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 Ｆターム(参考） 4K032 AA01 AA04 AA05 AA11 AA14 AA16 AA19 AA22 AA23 AA31 AA35 AA36 BA01 CA02 CC02 CC03 CC04 CD02 CD03 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazushige Mochimo 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. F-term (reference) 4K032 AA01 AA04 AA05 AA11 AA14 AA16 AA19 AA22 AA23 AA31 AA35 AA36 BA01 CA02 CC02 CC03 CC04 CD02 CD03
Claims (2)
ｉ：０．０３〜０．６％、Ｍｎ：０．３０〜２．０％、
Ａｌ：０．０１０〜０．１０％、Ｎｂ：０．０１０〜
０．１０％、Ｔｉ：０．０１０〜０．１０％を含有し、
下記 (1)式で表されるＦＣＧ１の値が４．０以下を満た
し、残部がＦｅ及び不純物からなる鋼片を、１０５０℃
以上に加熱して１０４０〜７４０℃の圧延仕上げ温度で
熱間圧延し、その後、（Ｔｓ１＋５０）〜（Ｔｓ１−２
５）℃の温度から５〜５０℃／秒の冷却速度で少なくと
も５５０℃まで冷却することを特徴とする疲労亀裂進展
抵抗性に優れた鋼材の製造方法。ここで、Ｔｓ１は下記
(2)式から計算される温度である。 ＦＣＧ１＝（０．７＋Ｃ）／｛（Ｓｉ／２５）＋（Ｍｎ／５）＋（Ｎｂ／２５ ）＋Ｔｉ｝・・・・・ (1) Ｔｓ１＝（８２０−２００Ｃ−６０Ｓｉ−６００Ｎｂ＋２０００Ｔｉ）・・・ ・・ (2) なお、各式における元素記号はその元素の質量％での含
有量を示す。C .: 0.02 to 0.25% by mass, S
i: 0.03 to 0.6%, Mn: 0.30 to 2.0%,
Al: 0.010% to 0.10%, Nb: 0.010%
0.10%, Ti: 0.010 to 0.10%,
The value of FCG1 represented by the following formula (1) satisfies 4.0 or less, and the balance consisting of Fe and impurities was 1050 ° C.
The above heating is performed and hot rolling is performed at a rolling finishing temperature of 1040 to 740 ° C., and thereafter, (Ts1 + 50) to (Ts1-2)
5) A method for producing a steel material excellent in fatigue crack growth resistance, wherein the steel material is cooled from a temperature of ° C to at least 550 ° C at a cooling rate of 5 to 50 ° C / sec. Here, Ts1 is
This is the temperature calculated from equation (2). FCG1 = (0.7 + C) / {(Si / 25) + (Mn / 5) + (Nb / 25) + Ti} (1) Ts1 = (820-200C-60Si-600Nb + 2000Ti) ...・ ・ (2) The symbol of each element in each formula indicates the content of the element in mass%.
％で、 第１群：Ｃｕ：０．０２〜１．０％、Ｃｒ：０．０３〜
２．０％のうちの１種以上、 第２群：Ｎｉ：０．０５〜１．０％、Ｍｏ：０．０５〜
１．０％のうちの１種以上、 第３群：Ｖ：０．０１〜０．５％ の１群以上をも含み、下記 (3)式で表されるＦＣＧ２の
値が４．０以下を満たし、残部がＦｅ及び不純物からな
る鋼片を、１０５０℃以上に加熱して１０４０〜７４０
℃の圧延仕上げ温度で熱間圧延し、その後、（Ｔｓ２＋
５０）〜（Ｔｓ２−２５）℃の温度から５〜５０℃／秒
の冷却速度で少なくとも５５０℃まで冷却することを特
徴とする疲労亀裂進展抵抗性に優れた鋼材の製造方法。
ここで、Ｔｓ２は下記 (4)式から計算される温度であ
る。 ＦＣＧ２＝（０．７＋Ｃ）／｛（Ｓｉ／２５）＋（Ｍｎ／５）＋（Ｃｕ／５０ ）＋（Ｎｉ／５０）＋（Ｃｒ／２５）＋（Ｍｏ／２５）＋（Ｖ／５）＋（Ｎｂ／ ２５）＋Ｔｉ｝・・・・・ (3) Ｔｓ２＝（１＋０．１Ｖ）（８２０−２００Ｃ−６０Ｓｉ＋２００Ｃｕ＋５０ Ｎｉ−１００Ｃｒ＋６００Ｍｏ−６００Ｎｂ＋２０００Ｔｉ）・・・・・ (4) なお、各式における元素記号はその元素の質量％での含
有量を示す。2. The composition according to claim 1, further comprising, in mass%, a first group: Cu: 0.02 to 1.0%, Cr: 0.03 to 0.03%.
2.0% or more, 2nd group: Ni: 0.05 to 1.0%, Mo: 0.05 to
1.0% or more, 3rd group: V: 0.01 to 0.5% including one or more groups, and the value of FCG2 represented by the following formula (3) is 4.0 or less. Is satisfied, and the balance is heated to 1050 ° C. or higher by heating the steel slab consisting of Fe and impurities to 1040 to 740.
Hot rolling at a rolling finishing temperature of 200 ° C., and then (Ts2 +
50) A method for producing a steel material excellent in fatigue crack propagation resistance, comprising cooling from a temperature of (Ts2-25) ° C to at least 550 ° C at a cooling rate of 5 to 50 ° C / sec.
Here, Ts2 is a temperature calculated from the following equation (4). FCG2 = (0.7 + C) / ｛(Si / 25) + (Mn / 5) + (Cu / 50) + (Ni / 50) + (Cr / 25) + (Mo / 25) + (V / 5) + (Nb / 25) + Ti｝ (3) Ts2 = (1 + 0.1V) (820-200C-60Si + 200Cu + 50 Ni-100Cr + 600Mo-600Nb + 2000Ti) (4) Element symbol in each formula Indicates the content in mass% of the element.
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