JP3785940B2 - High toughness steel sheet pile having a web thickness of 15 mm or more and method for producing the same - Google Patents

Description

【０００５】
この新JISにおいては、母材の強度及び靭性の確保を組織の微細化や第２相の組織制御によって図る必要がある。そのような考え方は、例えば、特開平8-269622号公報や特開平10-1721号公報にも示されており、これらの提案にしたがえば溶接特性に優れた鋼矢板や水中溶接性と靱性に優れた鋼矢板の製造が可能とされている。
【０００６】
【発明が解決しようとする課題】
しかしながら、厚肉の鋼矢板、特にウェブ厚が15mmを超えるような厚肉鋼矢板では、その製造工程上の問題、特に中間圧延が比較的高温で完了するという問題に起因して母材の靱性が十分な値に達しないという問題があった。本発明は、水中溶接など極めて厳しい条件下で溶接を行っても溶接割れを発生することなく、かつ母材靭性が高く、容易に脆性破壊を起こさない厚肉の鋼矢板及びその製造方法を提案することを目的とする。
【０００７】
【課題を解決するための手段】
本発明者等は、C，Si，Mnおよび炭素当量の上限が規制された成分系とし、かつ鋼矢板のウェブ肉厚を15mm以上と大きくしたときでも、母材に高い靭性を付与しうる手段について検討を行い、鋼矢板製造工程中のブレークダウン圧延及び中間圧延においてオーステナイト結晶粒の再結晶を完全に行わせ、かつ該オーステナイト結晶粒から微細フェライト−パーライト組織が得られるようにすることが重要であることを見出して、本発明を完成した。
【０００８】
本発明のウェブ厚が15mm以上の高靭性鋼矢板は、質量比でC：0.05〜0.18%、Si：0.05〜0.55%、Mn：0.6〜1.5%、P：0.030%以下、S：0.020%以下、Al：0.1%以下、Ti：0.005〜0.025%、N：0.0060%以下、残部：Feおよび不可避的不純物からなるとともに該不可避的不純物としての Nb が 0.003% 以下に制限されている鋼組成を有し、かつ微細なフェライト−パーライトからなる組織を有する。
【０００９】
上記の鋼組成は、さらに質量比で(1) Cu：0.1〜0.6%、Ni：0.05〜0.5%、Cr：0.05〜0.5%、Mo：0.05〜0.5%、V：0.010〜0.10%から選んだ1種若しくは2種以上及び／又は(2) Ca：0.0010〜0.0050%、REM：0.003〜0.015%の1種若しくは2種を含有することが好ましい。
【００１０】
上記本発明のウェブ厚が15mm以上の高靭性鋼矢板を製造するに当たっては、鋼素材を1200〜1320℃に加熱後、ブレークダウン圧延、中間圧延、及び爪曲げ成形を含む仕上げ圧延を行う過程において、鋼素材を質量比でC：0.05〜0.18%、Si：0.05〜0.55%、Mn：0.6〜1.5%、P：0.030%以下、S：0.020%以下、Al：0.1%以下、Ti：0.005〜0.025%、N：0.0060%以下、残部：Feおよび不可避的不純物からなるものとするとともに該不可避的不純物としての Nb が 0.003% 以下に制限されているものとし、かつ前記中間圧延の終了温度を950℃以上とする。
【００１１】
上記において鋼素材は、さらに質量比で、(1) Cu：0.1〜0.6%、Ni：0.05〜0.5%、Cr：0.05〜0.5%、Mo：0.05〜0.5%、V：0.010〜0.10%の群から選んだ1種若しくは2種以上及び／又は(2) Ca：0.0010〜0.0050%、REM：0.003〜0.015%の1種若しくは2種を含有することとするのが好ましい。
【００１２】
【発明の実施の形態】
以下、本発明に係るウェブ厚が15mm以上の高靭性鋼矢板の実施形態を、その化学組成、圧延条件さらにその製造方法について具体的に説明する。
【００１３】
（化学組成）
C：0.05〜0.18%、(質量比、mass%、以下特に断らない限り同じ)
Cは強度確保の観点から0.05%以上必要であるが、0.18%を超えると溶接割れを惹起し、またHAZ靱性を低下させるのでその範囲を0.05〜0.18%に限定する。
【００１４】
Si：0.05〜0.55%
Siは固溶強化に有効な元素であり、脱酸剤としても有効であるが、0.05%未満では効果がない。一方0.55%を超えて合金しても、HAZの靱性を低下させるだけであるから、その合金量は0.05〜0.55%の範囲とする。
【００１５】
Mn：0.6〜1.5%
Mnも強度を上昇させるのに有効な元素であるが、0.6%未満ではその効果が小さく、逆に1.5%を超えると溶接割れを生ずる危険があるので0.6〜1.5%の範囲とする。
【００１６】
P：0.030%以下、S：0.020%以下
Pはその含有量が多いと、粒界に偏析し、脆化を促進させるので極力少ないことが望ましい。また、Sは主にMnと結合してMnSを形成し、母材の延性を低下させる。さらにHAZ靱性にも有害であるので極力少ないことが望ましい。これらの元素の含有量は、Pについては0.030%以下、Sについては0.020%以下に制限する。
【００１７】
Al：0.1%以下
Alは脱酸剤として有効であるのでAl脱酸を行うときには、0.1%の範囲で含有させる。しかし、Al脱酸に代えて、Si脱酸やTi，REM，Ca脱酸を行う場合は積極的に含有させる必要はない。
【００１８】
Ti：0.005〜0.025% 、N：0.0060%以下
TiはNをTiNとして固定し、鋼矢板が繰り返し歪みを受けたときに生ずる靱性の低下を抑制する効果があるので0.005%以上含有させる。しかし0.025%を超えて含有させてもその効果は飽和する。したがってTiは0.005〜0.025%の範囲で含有させる。また、Nは、鋼矢板が繰返し歪を受けたとき靱性を低下させる有害元素であるので極力低い方が望ましい。具体的にはその上限を0.0060%とする。
【００１９】
（残部：Fe及び不可避的不純物）
上記成分を除いた残部はFe及び不可避的不純物である。通常添加されるNbは添加しない。不可避的不純物としての存在は許容できるが、0.005%以下に留めるのが望ましい。本発明の適用されるウェブ厚の大きい鋼矢板においてNbが存在すると、その中間圧延時においてオーステナイトの再結晶を遅延し、その再結晶細粒化が抑制されて鋼組織が粗大化し、さらに上部ベイナイトの生成が促進されて母材の靱性が大きく低下するが、その制限により高靭性の付与が可能になる。そのことは次の実験結果から明かである。
【００２０】
0.14%C−0.3%Si−1.4%Mnを基本合金成分組成とし、これにNbを0.002%、0.015%および0.038%を含み、残部実質的にFeからなる鋼を溶製した。これらに対し厚肉鋼矢板のウェブ部の圧延に相当するラボ圧延を行い27mm厚の鋼板を製造した。なお、加熱温度は1300℃であり、中間圧延の圧下率/パスは10%以上とした。また、最終パス圧下量は10%、圧延仕上げ温度は1020℃とし、圧延終了後は空冷した。図1、図2に、得られた製品の強度と靱性のバランスをNb含有量をパラメータとして示す。図1、図2から分かるように実質的にNbを含有しない鋼ではvTrsが低く靭性が高いのに対して、Nbを添加した鋼では靱性が大きく低下している。
【００２１】
本発明では上記の成分バランスを保つことが必要であるが、さらに以下の諸元素を含有させることができる。
【００２２】
Cu：0.6%以下，Ni：0.5%以下，Cr：0.5%以上，Mo：0.5%以下，V：0.10%以下の1種又は2種以上
これらの元素は実質的にAr₃温度を低温化することにより強度上昇に寄与するので適量含有させることができる。しかし、過度に含有させてもコストが上昇するのでCuは0.6%以下、Niは0.5%以下、Crは0.5%以下、Moは0.5%以下、Vは0.10%以下の範囲とする。
【００２３】
Ca：0.0010〜0.0050%，REM：0.003〜0.015%の1種又は2 種
これらの元素は、HAZの靱性を一層向上させる。しかし過度の含有は鋼の清浄性を極端に低下させ、母材靱性を低下させる。したがって上限をCaについては0.0050%、REMについては0.015%とし、それらの効果が認められる範囲で含有させることができる。
【００２４】
Ceq：0.46%以下
低温溶接割れ抑制の観点から0.46%以下が望ましい。
【００２５】
(組織)
本発明鋼は、微細なフェライト−パーライトからなる組織を有する。これにより母材の靭性が確保される。上部ベーナイトの生成は母材の靭性を著しく低下させるので避けなければならない。なお、鋼矢板として必要な強度及び靭性を得るためには金属組織は微細であることが好ましく、フェライト結晶粒度番号6以上とするのがよい。なお、パーライトについては生成すれば十分であるので、その大きさについては特に限定しない。
【００２６】
（製造方法）
本発明のウェブ厚が15mm以上の高靭性鋼矢板は、図3に示すようにブレークダウン圧延、中間圧延、及び爪曲げ成形を含む仕上げ圧延によって製造されるが、その際以下の点に留意するのが望ましい。まず、素材の加熱温度は1200〜1320℃とするのがよい。これはブレークダウン圧延および中間圧延時の圧下量を10%/パス以上確保し、オーステナイト結晶粒の再結晶とその細粒化を図るためである。加熱温度を1200℃以上でないと変形抵抗が大きくなりすぎ、一方、1320℃を超えると、スケールロスや加熱炉原単位の増加を招く。
【００２７】
中間圧延を950℃以上で完了させ、その後爪曲げ成形圧延を行う。爪曲げ成形前の中間圧延温度が950℃未満となると、Nbを実質的に含有しない鋼であってもオーステナイトの完全再結晶化が抑制され、靱性が低下する。したがって中間圧延温度を950℃以上とする。中間圧延温度の上限は特に設ける必要はないが、オーステナイトの粒成長を抑制させる観点から1100℃以下とすることが好ましい。なお、ブレークダウン圧延は中間圧延に先行するので、上記中間圧延条件を遵守すれば十分である。また、上記中間圧延時の最終パス圧下量は10%以上とするのがよい。これにより母材の靭性の確保が一層確実になる。
【００２８】
上記中間圧延後、爪曲げ圧延が行われる。その工程は常法に従えばよいが、その終了後空冷することが望ましい。これにより微細なフェライト＋パーライト組織の形成が行われ、母材靱性が高められる。なお、爪曲げ成形圧延の際に、ウェブを水冷することも可能であり、これにより母材の強度上昇を図り得る。ただし靱性に有害な上部ベーナイトの生成を抑える条件の選定が必要で、冷却停止温度500℃以上として靱性および延性の確保を図らなければならない。
【００２９】
【実施例】
表2に示す組成を有する素材を表3に示す条件で処理してウェブ厚24.3mm、5Lサイズの厚肉鋼矢板を製造した。得られた製品鋼矢板のウェブ高さ1/4部より全厚引張試験片および1/4部よりシャルピー衝撃試験片を採取し、その機械的性質を調査した。その結果は表4に示すとおりである。ここに示すように、発明例（A〜E）では、0℃での吸収エネルギー（vE₀）が100J以上と高く、靱性に優れた鋼矢板となっている。たとえば、発明例はCおよび炭素当量が低く、溶接性やHAZ靱性を向上させた成分系となっている。これに対し比較例（F,G）及び従来例（H）ではともにvE₀が低く、護岸用厚肉鋼矢板としては性能が不十分であった。
【００３０】
【表２】

【００３１】
【表３】

【００３２】
【表４】

【００３３】
【発明の効果】
本発明の厚肉鋼矢板は水中溶接など極めて厳しい条件下で溶接を行っても溶接割れを発生することなく、かつ母材靭性が高く、容易に脆性破壊を起こさないののであるので、これを利用して地震等の災害時によく耐える岸壁の護岸工事をより確実に行えるようになる。
【図面の簡単な説明】
【図１】 厚肉鋼矢板の靭性（vTrs）と強度（TS）に及ぼすNb含有量の影響を示すグラフである。
【図２】 厚肉鋼矢板の靭性（vTrs）と強度（YP）に及ぼすNb含有量の影響を示すグラフである。
【図３】 本発明による鋼矢板の製造工程の概略模式図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel sheet pile used as a structural member for rivers and harbors, and a method for manufacturing the steel sheet pile, and more particularly to a steel sheet pile having excellent HAZ toughness and base material toughness with a web thickness of 15 mm or more and a method for manufacturing the steel sheet pile.
[0002]
[Prior art]
Steel sheet piles are indispensable members for civil engineering work, harbor revetment work, etc., and when used for revetment quay walls, electrodes for cathodic protection are often attached by welding. Since this welding is mainly performed by underwater welding after the steel sheet pile is set up, the welded part is subjected to a very severe thermal history and the HAZ hardens, so that a weld crack occurs or the steel sheet pile starts from that crack. May lead to brittle fracture. In fact, during the 1993 Hokkaido Kushiro-oki earthquake, the steel sheet pile used for the revetment quay suffered brittle fracture from the welded part of the cathodic protection fixture.
[0003]
In response to this, the performance improvement of steel sheet piles was reviewed from the viewpoint of earthquake resistance, and a new JIS (steel sheet pile for welding) was announced in November 2000. In this new JIS, the upper limit of C, Si, Mn and carbon equivalent is restricted from the viewpoint of cold weld cracking property, and the lower limit of toughness of the base metal is set in order to suppress the brittle fracture of the base metal. In addition, an upper limit of the amount of solute N is provided in order to suppress a decrease in toughness due to repeated strain received during an earthquake. Specifically, it is as shown in Table 1.
[0004]
[Table 1]

[0005]
In this new JIS, it is necessary to ensure the strength and toughness of the base material by refining the structure or controlling the structure of the second phase. Such a concept is also shown in, for example, Japanese Patent Application Laid-Open Nos. 8-269622 and 10-1721. According to these proposals, steel sheet piles with excellent welding characteristics and underwater weldability and toughness It is possible to manufacture steel sheet piles excellent in
[0006]
[Problems to be solved by the invention]
However, for thick steel sheet piles, especially thick steel sheet piles with a web thickness of more than 15 mm, the toughness of the base metal is due to problems in the manufacturing process, especially the fact that intermediate rolling is completed at a relatively high temperature. There was a problem that did not reach a sufficient value. The present invention proposes a thick-walled steel sheet pile that does not generate weld cracks even under welding under extremely severe conditions such as underwater welding, has high base metal toughness, and does not easily cause brittle fracture, and a method for manufacturing the same. The purpose is to do.
[0007]
[Means for Solving the Problems]
The present inventors have a component system in which the upper limits of C, Si, Mn and carbon equivalent are regulated, and even when the web thickness of the steel sheet pile is increased to 15 mm or more, means capable of imparting high toughness to the base material It is important to completely recrystallize austenite grains in breakdown and intermediate rolling during the steel sheet pile manufacturing process and to obtain a fine ferrite-pearlite structure from the austenite grains As a result, the present invention was completed.
[0008]
The high toughness steel sheet pile having a web thickness of 15 mm or more according to the present invention has a mass ratio of C: 0.05 to 0.18%, Si: 0.05 to 0.55%, Mn: 0.6 to 1.5%, P: 0.030% or less, S: 0.020% or less. , Al: 0.1% or less, Ti: 0.005~0.025%, N: 0.0060% or less, the balance being with Fe and unavoidable impurities have a steel composition which Nb is limited to 0.003% or less as the unavoidable impurities And has a structure composed of fine ferrite-pearlite.
[0009]
The above steel composition was further selected from (1) Cu: 0.1-0.6%, Ni: 0.05-0.5%, Cr: 0.05-0.5%, Mo: 0.05-0.5%, V: 0.010-0.10% by mass ratio. It is preferable to contain 1 type or 2 types and / or (2) 1 type or 2 types of Ca: 0.0010-0.0050%, REM: 0.003-0.015%.
[0010]
In producing a high toughness steel sheet pile having a web thickness of 15 mm or more according to the present invention, the steel material is heated to 1200 to 1320 ° C. and then subjected to finish rolling including breakdown rolling, intermediate rolling, and nail bending. Steel material by mass ratio: C: 0.05 to 0.18%, Si: 0.05 to 0.55%, Mn: 0.6 to 1.5%, P: 0.030% or less, S: 0.020% or less, Al: 0.1% or less, Ti: 0.005 to 0.025% N: 0.0060% or less, the balance with a made of Fe and unavoidable impurities shall Nb as the unavoidable impurities is limited to 0.003% or less, and the end temperature of the intermediate rolling 950 ℃ or more.
[0011]
In the above, the steel material further has a mass ratio of (1) Cu: 0.1 to 0.6%, Ni: 0.05 to 0.5%, Cr: 0.05 to 0.5%, Mo: 0.05 to 0.5%, V: 0.010 to 0.10% It is preferable to contain one or two or more selected from (1) and / or (2) Ca: 0.0010 to 0.0050%, REM: 0.003 to 0.015%.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a high toughness steel sheet pile having a web thickness of 15 mm or more according to the present invention will be specifically described with respect to its chemical composition, rolling conditions, and its production method.
[0013]
(Chemical composition)
C: 0.05 to 0.18% (mass ratio, mass%, the same unless otherwise specified)
C needs to be 0.05% or more from the viewpoint of securing strength, but if it exceeds 0.18%, weld cracking is caused and HAZ toughness is lowered, so the range is limited to 0.05 to 0.18%.
[0014]
Si: 0.05-0.55%
Si is an element effective for solid solution strengthening, and is also effective as a deoxidizing agent, but it is ineffective at less than 0.05%. On the other hand, alloying over 0.55% only reduces the toughness of HAZ, so the alloy content is in the range of 0.05 to 0.55%.
[0015]
Mn: 0.6-1.5%
Mn is also an element effective for increasing the strength. However, if it is less than 0.6%, its effect is small, and conversely if it exceeds 1.5%, there is a risk of causing weld cracking, so the range is 0.6 to 1.5%.
[0016]
P: 0.030% or less, S: 0.020% or less
If the P content is large, it is segregated at the grain boundaries and promotes embrittlement, so it is desirable that P be as small as possible. S mainly combines with Mn to form MnS, which lowers the ductility of the base material. Furthermore, since it is also harmful to HAZ toughness, it is desirable that it be as small as possible. The content of these elements is limited to 0.030% or less for P and 0.020% or less for S.
[0017]
Al: 0.1% or less
Since Al is effective as a deoxidizer, it is contained in the range of 0.1% when Al deoxidation is performed. However, it is not necessary to actively contain Si deoxidation, Ti, REM, or Ca deoxidation instead of Al deoxidation.
[0018]
Ti: 0.005-0.025%, N: 0.0060% or less
Ti fixes N as TiN, and has an effect of suppressing a decrease in toughness caused when a steel sheet pile is repeatedly strained, so 0.005% or more is contained. However, the effect is saturated even if it exceeds 0.025%. Therefore, Ti is contained in the range of 0.005 to 0.025%. Further, N is a harmful element that lowers toughness when the steel sheet pile is repeatedly strained, so it is desirable that N be as low as possible. Specifically, the upper limit is set to 0.0060%.
[0019]
(Remainder: Fe and inevitable impurities)
The balance excluding the above components is Fe and inevitable impurities. Normally added Nb is not added. The presence as an inevitable impurity is acceptable, but it is desirable to keep it at 0.005% or less. When Nb is present in a steel sheet pile having a large web thickness to which the present invention is applied, the recrystallization of austenite is delayed during the intermediate rolling, the recrystallization fine graining is suppressed, the steel structure becomes coarse, and the upper bainite The toughness of the base material is greatly reduced due to the generation of the toughness, but the toughness can be imparted by the limitation. This is clear from the following experimental results.
[0020]
0.14% C-0.3% Si-1.4% Mn was used as the basic alloy component composition, and steel containing Nb of 0.002%, 0.015%, and 0.038% and the balance being substantially Fe was melted. These were subjected to laboratory rolling corresponding to the rolling of the web portion of the thick steel sheet pile to produce a 27 mm thick steel plate. The heating temperature was 1300 ° C., and the rolling reduction / pass for intermediate rolling was 10% or more. Further, the final pass reduction amount was 10%, the rolling finishing temperature was 1020 ° C., and air cooling was performed after rolling. Fig. 1 and Fig. 2 show the balance between strength and toughness of the obtained product using Nb content as a parameter. As can be seen from FIGS. 1 and 2, the steel containing substantially no Nb has low vTrs and high toughness, whereas the steel to which Nb is added has greatly reduced toughness.
[0021]
In the present invention, it is necessary to maintain the above-mentioned component balance, but the following various elements can be further contained.
[0022]
One or more of Cu: 0.6% or less, Ni: 0.5% or less, Cr: 0.5% or more, Mo: 0.5% or less, V: 0.10% or less These elements substantially lower the Ar ₃ temperature. Since this contributes to an increase in strength, it can be contained in an appropriate amount. However, since the cost increases even if it is excessively contained, Cu is 0.6% or less, Ni is 0.5% or less, Cr is 0.5% or less, Mo is 0.5% or less, and V is 0.10% or less.
[0023]
Ca: 0.0010~0.0050%, REM: 0.003~0.015 % of one or these elements, to further improve the HAZ toughness. However, excessive content extremely reduces the cleanliness of the steel and lowers the base material toughness. Therefore, the upper limit is 0.0050% for Ca and 0.015% for REM, and the upper limit can be included within the range where these effects are recognized .
[0024]
Ceq: 0.46% or less From the viewpoint of suppressing low-temperature weld cracking, 0.46% or less is desirable.
[0025]
(Organization)
The steel of the present invention has a structure composed of fine ferrite-pearlite. This ensures the toughness of the base material. The formation of upper bainite must be avoided because it significantly reduces the toughness of the base metal. In order to obtain the strength and toughness required for the steel sheet pile, the metal structure is preferably fine, and the ferrite crystal grain size number 6 or more is preferable. Since it is sufficient to generate pearlite, the size is not particularly limited.
[0026]
(Production method)
The high toughness steel sheet pile having a web thickness of 15 mm or more according to the present invention is manufactured by finish rolling including breakdown rolling, intermediate rolling, and claw bending as shown in FIG. 3, but pay attention to the following points. Is desirable. First, the heating temperature of the material is preferably 1200 to 1320 ° C. This is to secure a reduction amount of 10% / pass or more during breakdown rolling and intermediate rolling, and to recrystallize and refine the austenite crystal grains. If the heating temperature is not 1200 ° C. or higher, the deformation resistance becomes too high. On the other hand, if it exceeds 1320 ° C., the scale loss and the heating furnace basic unit increase.
[0027]
Intermediate rolling is completed at 950 ° C or higher, and then nail bending forming rolling is performed. When the intermediate rolling temperature before nail bending is less than 950 ° C., even if the steel does not substantially contain Nb, complete recrystallization of austenite is suppressed and toughness is reduced. Therefore, the intermediate rolling temperature is set to 950 ° C or higher. The upper limit of the intermediate rolling temperature is not particularly required, but is preferably set to 1100 ° C. or lower from the viewpoint of suppressing austenite grain growth. Since breakdown rolling precedes intermediate rolling, it is sufficient to observe the above-described intermediate rolling conditions. In addition, the final pass reduction amount during the intermediate rolling is preferably 10% or more. This further ensures the toughness of the base material.
[0028]
After the intermediate rolling, claw bending rolling is performed. The process may be performed in accordance with a conventional method, but it is desirable to cool by air after the process is completed. Thereby, a fine ferrite + pearlite structure is formed, and the base material toughness is enhanced. In addition, it is also possible to water-cool the web during claw bending forming rolling, thereby increasing the strength of the base material. However, it is necessary to select conditions that suppress the formation of upper bainite, which is harmful to toughness, and to ensure toughness and ductility at a cooling stop temperature of 500 ° C or higher.
[0029]
【Example】
A material having the composition shown in Table 2 was processed under the conditions shown in Table 3 to produce a thick steel sheet pile having a web thickness of 24.3 mm and a size of 5 L. Full thickness tensile specimens were collected from 1/4 part of the web height of the product steel sheet pile and Charpy impact specimens were taken from 1/4 part, and the mechanical properties were investigated. The results are shown in Table 4. As shown here, in the inventive examples (A to E), the absorbed energy (vE ₀ ) at 0 ° C. is as high as 100 J or more, and the steel sheet pile is excellent in toughness. For example, the inventive examples have low C and carbon equivalents and have a component system with improved weldability and HAZ toughness. On the other hand, in the comparative examples (F, G) and the conventional example (H), vE ₀ was low, and the performance as a thick steel sheet pile for revetment was insufficient.
[0030]
[Table 2]

[0031]
[Table 3]

[0032]
[Table 4]

[0033]
【The invention's effect】
Since the thick steel sheet pile of the present invention does not generate weld cracks even when welding under extremely severe conditions such as underwater welding, and has high base metal toughness, it does not easily cause brittle fracture. By using it, it will be possible to more reliably carry out revetment work for quay walls that can withstand earthquakes and other disasters.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of Nb content on toughness (vTrs) and strength (TS) of thick steel sheet piles.
FIG. 2 is a graph showing the influence of Nb content on the toughness (vTrs) and strength (YP) of thick steel sheet piles.
FIG. 3 is a schematic diagram showing a manufacturing process of a steel sheet pile according to the present invention.

Claims (4)

By mass ratio: C: 0.05 to 0.18%, Si: 0.05 to 0.55%, Mn: 0.6 to 1.5%, P: 0.030% or less, S: 0.020% or less, Al: 0.1% or less, Ti: 0.005 to 0.025%, N : 0.0060% or less, the balance being with Fe and unavoidable impurities has a steel composition that Nb is limited to 0.003% or less as the unavoidable impurities, and fine ferrite - to have a made of pearlite High toughness steel sheet pile with a characteristic web thickness of 15mm or more. Steel composition is further selected by mass ratio (1) Cu: 0.1-0.6%, Ni: 0.05-0.5%, Cr: 0.05-0.5%, Mo: 0.05-0.5%, V: 0.010-0.10% 2 or more and / or (2) one or two of Ca: 0.0010 to 0.0050%, REM: 0.003 to 0.015%, high-toughness steel having a web thickness of 15 mm or more Sheet pile. In manufacturing steel sheet piles with a web thickness of 15 mm or more by finishing rolling including breakdown rolling, intermediate rolling, and claw bending after heating the steel material to 1200-1320 ° C,
By mass ratio, the steel material is C: 0.05 to 0.18%, Si: 0.05 to 0.55%, Mn: 0.6 to 1.5%, P: 0.030% or less, S: 0.020% or less, Al: 0.1% or less, Ti: 0.005 to 0.025% N: 0.0060% or less, the balance with a made of Fe and unavoidable impurities shall Nb as the unavoidable impurities is limited to 0.003% or less, and the end temperature of the intermediate rolling 950 A method for producing a high toughness steel sheet pile having a web thickness of 15 mm or more, characterized in that the temperature is set to ℃ or higher. In steel material further mass ratio, (1) Cu: 0.1~0.6% , Ni: 0.05~0.5%, Cr: 0.05~0.5%, Mo: 0.05~0.5%, V: selected from 0.010 to 0.10% 1 4 or more types and / or (2) Ca: 0.0010-0.0050%, REM: 0.003-0.015% 1 type or 2 types are contained, The web thickness of Claim 3 characterized by the above-mentioned. A method for producing a tough steel sheet pile.

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