JP2007002271A - Steel with excellent fracture toughness in weld heat-affected zone, and its manufacturing method - Google Patents
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本発明は、小入熱溶接から中入熱溶接までの熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）に優れた鋼及びその製造方法に関するものである。 The present invention relates to a steel excellent in fracture toughness (CTOD) of a heat-affected zone (HAZ) from small heat input welding to medium heat input welding, and a method for producing the same.
従来、低合金鋼の熱影響部（ＨＡＺ）における靭性（ＨＡＺ靭性）は、（１）結晶粒子の大きさ（粒径）、（２）高炭素マルテンサイト（Ｍ＊）、上部ベイナイト（Ｂｕ）、フェライトサイドプレート（ＦＳＰ）等の硬化相の分散状態、（３）析出硬化状態、（４）粒界脆化の有無、（５）元素のミクロ偏析等、種々の要因に支配されることが知られている。そこで、これらの要因を制御することによりＨＡＺ靭性を改善した様々な低合金鋼が提案され、実用に供されている。
特に優れた低合金鋼としては、Ｔｉ酸化物によりミクロ組織を微細化し、さらにＴｉ、Ｏ、Ｎの各元素の含有量を適正化してＴｉＣの析出を抑制し、これにより析出硬化を低減し、靭性を向上させた低合金鋼が提案されている（特許文献１参照）。
Conventionally, the toughness (HAZ toughness) in the heat-affected zone (HAZ) of low alloy steel is (1) crystal grain size (grain size), (2) high carbon martensite (M * ), upper bainite (Bu). It is governed by various factors such as the dispersion state of the hardened phase of ferrite side plate (FSP), (3) precipitation hardened state, (4) presence / absence of grain boundary embrittlement, and (5) microsegregation of elements. Are known. Therefore, various low alloy steels having improved HAZ toughness by controlling these factors have been proposed and put into practical use.
As a particularly excellent low-alloy steel, the microstructure is refined with Ti oxide, and the content of each element of Ti, O, N is optimized to suppress the precipitation of TiC, thereby reducing the precipitation hardening, A low alloy steel with improved toughness has been proposed (see Patent Document 1).
この様な低合金鋼では、溶接熱影警部に発生する脆性に起因する亀裂等の破壊靭性は、上述したミクロ組織の影響と高炭素マルテンサイト（Ｍ＊）を含む硬化層の影響が大きく、この破壊靭性を改善するために、従来では、鋼組成にＮｉ、Ｃｕ等の元素を添加することが行われていた。
ところで、従来の低合金鋼では、Ｎｉ、Ｃｕ等の元素を添加することにより溶接熱影警部の破壊靭性（ＣＴＯＤ）特性は改善されるものの、小入熱溶接から中入熱溶接までの多層溶接においては、破壊靭性（ＣＴＯＤ）特性が不十分なものであり、小入熱溶接から中入熱溶接までの多層溶接における破壊靭性（ＣＴＯＤ）特性の改善が求められていた。
また、Ｎｉ、Ｃｕ等の高価な元素を添加した場合、低合金鋼の製造コストの増加を招き、破壊靭性（ＣＴＯＤ）特性に優れた鋼を製造・販売する際の障害になっていた。
By the way, in the conventional low alloy steel, although the fracture toughness (CTOD) characteristic of the welded thermal zone is improved by adding elements such as Ni and Cu, multilayer welding from small heat input welding to medium heat input welding is performed. However, the fracture toughness (CTOD) characteristic is insufficient, and improvement of the fracture toughness (CTOD) characteristic in multilayer welding from small heat input welding to medium heat input welding has been demanded.
In addition, when expensive elements such as Ni and Cu are added, the manufacturing cost of low alloy steel is increased, which has been an obstacle in manufacturing and selling steel having excellent fracture toughness (CTOD) characteristics.
本発明は、上記の事情に鑑みてなされたものであって、小入熱溶接から中入熱溶接までの多層溶接における熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性に優れた鋼及びその製造方法を提供することを目的とする。 The present invention has been made in view of the above circumstances, and is a steel excellent in fracture toughness (CTOD) characteristics of a heat-affected zone (HAZ) in multilayer welding from small heat input welding to medium heat input welding and its An object is to provide a manufacturing method.
本発明者等は、鋭意検討した結果、小入熱溶接から中入熱溶接（板厚５０ｍｍで１．５〜６．０ｋＪ／ｍｍ）までの多層溶接における熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性（−６０℃程度の温度におけるＣＴＯＤ特性）は、極めて局部的な領域の靭性が支配的であり、この部分のミクロ組織の制御と脆化元素の添加量を低減することにより、小入熱溶接から中入熱溶接までの熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性を大幅に改善することができることを見出し、本発明を完成するに至ったものであり、本発明の要旨とするところは以下の通りである。 As a result of intensive studies, the present inventors have found that fracture toughness of heat affected zone (HAZ) in multi-layer welding from small heat input welding to medium heat input welding (plate thickness 50 mm, 1.5 to 6.0 kJ / mm) ( The CTOD) characteristic (CTOD characteristic at a temperature of about −60 ° C.) is dominated by toughness in a very local region. By controlling the microstructure in this part and reducing the amount of embrittlement element added, The present inventors have found that the fracture toughness (CTOD) characteristics of the heat affected zone (HAZ) from heat input welding to medium heat input welding can be greatly improved, and have completed the present invention. Is as follows.
（１） 質量％で、Ｃ：０．０４０〜０．０７５％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：１．７０〜２．５０％、Ｐ：０．００８％以下、Ｓ：０．００５％以下、Ａｌ：０．００４％以下、Ｔｉ：０．００５〜０．０１５％、Ｏ：０．００３５％以下、Ｎ：０．００３０〜０．００５０％を含有し、
残部が鉄および不可避不純物からなることを特徴とする溶接熱影響部の破壊靭性に優れた鋼。
(1) By mass%, C: 0.040 to 0.075%, Si: 0.10 to 0.30%, Mn: 1.70 to 2.50%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less, N: 0.0030 to 0.0050%,
A steel with excellent fracture toughness in the heat affected zone of welding, characterized in that the balance consists of iron and inevitable impurities.
（２） さらに、質量％で、Ｎｂ：０．０１５％以下、Ｖ：０．０３０％以下の群から選択された１種または２種を含有し、
かつ、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖで表されるＰＣＴＯＤが、質量％で０．０７５％以下であることを特徴とする上記（１）に記載の溶接熱影響部の破壊靭性に優れた鋼。
(2) Further, by mass%, Nb: 0.015% or less, V: containing 1 type or 2 types selected from the group of 0.030% or less,
And, P CTOD = C + Nb + 1 / P CTOD represented by 3V is excellent in fracture toughness of the heat affected zone according to the above (1), characterized in that not more than 0.075% in mass% steel.
（３） 質量％で、Ｃ：０．０４０〜０．０７５％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：１．７０〜２．５０％、Ｐ：０．００８％以下、Ｓ：０．００５％以下、Ａｌ：０．００４％以下、Ｔｉ：０．００５〜０．０１５％、Ｏ：０．００３５％以下、Ｎ：０．００３０〜０．００５０％を含有し、残部が鉄および不可避不純物からなる鋼を連続鋳造法によりスラブとし、次いで、このスラブを１１００℃以下の温度に再加熱し、その後、加工熱処理することを特徴とする溶接熱影響部の破壊靭性に優れた鋼の製造方法。 (3) By mass%, C: 0.040 to 0.075%, Si: 0.10 to 0.30%, Mn: 1.70 to 2.50%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less, N: 0.0030 to 0.0050%, the balance being iron Steel having excellent fracture toughness in the weld heat affected zone, characterized in that steel comprising inevitable impurities is made into a slab by a continuous casting method, then the slab is reheated to a temperature of 1100 ° C. or lower, and then heat-treated. Manufacturing method.
（４） 前記鋼は、さらに、質量％で、Ｎｂ：０．０１５％以下、Ｖ：０．０３０％以下の群から選択された１種または２種を含有し、かつ、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖで表されるＰＣＴＯＤが、質量％で０．０７５％以下であることを特徴とする上記（３）に記載の溶接熱影響部の破壊靭性に優れた鋼の製造方法。 (4) The steel further contains one or two kinds selected from the group of Nb: 0.015% or less and V: 0.030% or less by mass%, and P CTOD = C + Nb + 1 / PCTOD represented by 3V is 0.075% or less in mass%, and the method for producing steel excellent in fracture toughness of the weld heat affected zone according to (3) above.
本発明の溶接熱影響部の破壊靭性に優れた鋼によれば、質量％で、Ｃ：０．０４０〜０．０７５％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：１．７０〜２．５０％、Ｐ：０．００８％以下、Ｓ：０．００５％以下、Ａｌ：０．００４％以下、Ｔｉ：０．００５〜０．０１５％、Ｏ：０．００３５％以下、Ｎ：０．００３０〜０．００５０％を含有し、残部を鉄および不可避不純物とすることで、極めて局部的な領域のミクロ組織を制御するとともに、脆化元素であるＡｌを実質的に添加しないこととなり、小入熱溶接から中入熱溶接までの多層溶接における熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性を向上させることができる。 According to the steel excellent in fracture toughness of the weld heat affected zone of the present invention, C: 0.040 to 0.075%, Si: 0.10 to 0.30%, Mn: 1.70 to mass%. 2.50%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less, N: By containing 0.0030 to 0.0050% and the balance being iron and inevitable impurities, the microstructure of the extremely local region is controlled and Al, which is an embrittlement element, is not substantially added. Moreover, the fracture toughness (CTOD) characteristic of the heat affected zone (HAZ) in multilayer welding from small heat input welding to medium heat input welding can be improved.
本発明の溶接熱影響部の破壊靭性に優れた鋼の製造方法によれば、質量％で、Ｃ：０．０４０〜０．０７５％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：１．７０〜２．５０％、Ｐ：０．００８％以下、Ｓ：０．００５％以下、Ａｌ：０．００４％以下、Ｔｉ：０．００５〜０．０１５％、Ｏ：０．００３５％以下、Ｎ：０．００３０〜０．００５０％を含有し、残部が鉄および不可避不純物からなる鋼を連続鋳造法によりスラブとし、次いで、このスラブを１１００℃以下の温度に再加熱し、その後、加工熱処理するので、小入熱溶接から中入熱溶接までの多層溶接における熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性を向上させた鋼を容易かつ安価に製造することができる。 According to the manufacturing method of steel excellent in fracture toughness of the weld heat affected zone of the present invention, C: 0.040 to 0.075%, Si: 0.10 to 0.30%, Mn: 1 by mass%. 70 to 2.50%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less , N: 0.0030% to 0.0050% of steel, the balance being iron and inevitable impurities are made into a slab by a continuous casting method, and then this slab is reheated to a temperature of 1100 ° C. or less, and then processed. Since the heat treatment is performed, it is possible to easily and inexpensively manufacture steel with improved fracture toughness (CTOD) characteristics of the heat affected zone (HAZ) in multi-layer welding from small heat input welding to medium heat input welding.
本発明の溶接熱影響部の破壊靭性に優れた鋼及びその製造方法の一実施の形態について説明する。
なお、この実施の形態は、発明の趣旨をより良く理解させるために詳細に説明するものであるから、特に指定の無い限り、本発明を限定するものではない。
An embodiment of steel excellent in fracture toughness of the weld heat affected zone of the present invention and a method for producing the same will be described.
Note that this embodiment is described in detail for better understanding of the gist of the invention, and thus does not limit the present invention unless otherwise specified.
本発明の溶接熱影響部の破壊靭性に優れた鋼は、
質量％で、Ｃ：０．０４０〜０．０７５％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：１．７０〜２．５０％、Ｐ：０．００８％以下、Ｓ：０．００５％以下、Ａｌ：０．００４％以下、Ｔｉ：０．００５〜０．０１５％、Ｏ：０．００３５％以下、Ｎ：０．００３０〜０．００５０％を含有し、残部が鉄および不可避不純物からなるものである。
Steel excellent in fracture toughness of the weld heat affected zone of the present invention,
In mass%, C: 0.040-0.075%, Si: 0.10-0.30%, Mn: 1.70-2.50%, P: 0.008% or less, S: 0.005 %: Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less, N: 0.0030 to 0.0050%, the balance being iron and inevitable impurities It consists of
ここで、鋼の組成を上記の様に限定した理由について説明する。
Ｃは、鋼材の特性に最も顕著に効くもので、含有量を０．０４０〜０．０７５％の範囲に限定するものである。ここで、Ｃの含有量を上記の様に限定した理由は、０．０４０％未満では、高強度を得ることができないからであり、一方、０．０７５％を越えると、溶接熱影響部の靱性を劣化させ、−６０℃のＣＴＯＤ特性を満足させることができないからである。
Here, the reason for limiting the steel composition as described above will be described.
C is most effective for the properties of the steel material and limits the content to a range of 0.040 to 0.075%. Here, the reason why the content of C is limited as described above is that if the content is less than 0.040%, high strength cannot be obtained. This is because the toughness is deteriorated and the CTOD characteristic of −60 ° C. cannot be satisfied.
Ｓｉは、良好なＨＡＺ靭性を得るためには少ない方が好ましいが、本発明鋼では同様の脱酸効果を有するＡｌの含有量が０．００４％以下であるから、脱酸上０．１０％以上は必要である。しかしながら、０．３０％超ではＨＡＺ靭性を害するため、０．３０％を上限とした。 Si is preferably less in order to obtain good HAZ toughness, but in the steel of the present invention, the content of Al having the same deoxidation effect is 0.004% or less. The above is necessary. However, if it exceeds 0.30%, the HAZ toughness is impaired, so 0.30% was made the upper limit.
Ｍｎは、ミクロ組織を適正化する効果が大きく、ＨＡＺ靭性を害しないものであるから、添加することが好ましいが、２．５０％超では、靭性に有害なベイナイトが生成し易くなるので、２．５０％を上限とした。また、１．７０％未満では、ミクロ組織を適正化する効果が小さくなるので、１．７０％を下限とした。 Since Mn has a great effect of optimizing the microstructure and does not impair the HAZ toughness, it is preferable to add Mn. However, if it exceeds 2.50%, bainite harmful to toughness is likely to be generated. .50% was made the upper limit. Further, if it is less than 1.70%, the effect of optimizing the microstructure becomes small, so 1.70% was made the lower limit.
Ｐ、Ｓは、本発明の鋼においては不純物であり、母材靭性、ＨＡＺ靭性の点から共に少ないほど好ましい。しかし、必要以上に含有量を低減することは、製鋼工程に対する負荷増となり、生産性やコストの面で得策ではない。そこで、Ｐの上限を０．００８％、Ｓの上限を０．００５％とした。
Ａｌは、脱酸元素として最も一般的なものであるが、Ｔｉと共存した場合、Ｔｉ酸化物あるいはＴｉ及びＡｌを含む複合酸化物を生成させるため少ない方が好ましいが、工業生産的に制約があり、０．００４％が上限である。
P and S are impurities in the steel of the present invention, and are preferably as small as possible in terms of base metal toughness and HAZ toughness. However, reducing the content more than necessary increases the load on the steelmaking process and is not a good measure in terms of productivity and cost. Therefore, the upper limit of P is set to 0.008%, and the upper limit of S is set to 0.005%.
Al is the most common deoxidation element, but when coexisting with Ti, it is preferable to use a small amount to produce a Ti oxide or a composite oxide containing Ti and Al, but there are restrictions on industrial production. Yes, the upper limit is 0.004%.
Ｔｉは、Ｏと結合してＴｉ２Ｏ３、ＴｉＯ２等のＴｉ酸化物を形成し、ミクロ組織を微細化させるが、Ｔｉの含有量が多過ぎると、Ｃと結合してＴｉＣを生成し、ＨＡＺ靭性を劣化させる虞があるため、含有量の適正な範囲を０．００５〜０．０１５％とした。
Ｏは、Ｔｉ酸化物の生成に必要であるが、含有量が０．００３５％超では粗大なＴｉ酸化物が生成されることで靭性が極端に劣化するので、上限を０．００３５％とした。
Ｎは、Ｔｉ窒化物の生成に必要であるが、含有量が０．００３％未満では効果が小さく、また、０．００５％超では、鋼片製造時に表面皮が発生するため、Ｎの含有量の範囲を０．００３０〜０．００５０％とした。
Ti combines with O to form a Ti 2 O 3, TiO Ti oxides such as 2, but is finer microstructure, when the content of Ti is too large, combine to generate TiC and C Since there is a possibility that the HAZ toughness is deteriorated, an appropriate range of the content is set to 0.005 to 0.015%.
O is necessary for the production of Ti oxide, but if the content exceeds 0.0035%, the toughness is extremely deteriorated due to the production of coarse Ti oxide, so the upper limit was made 0.0035%. .
N is necessary for the formation of Ti nitride, but if the content is less than 0.003%, the effect is small, and if it exceeds 0.005%, a surface skin is generated during the production of a steel slab. The range of the amount was 0.0030 to 0.0050%.
本発明の溶接熱影響部の破壊靭性に優れた鋼は、上記の組成に加えて、
さらに、質量％で、Ｎｂ：０．０１５％以下、Ｖ：０．０３０％以下の群から選択された１種または２種を含有し、
かつ、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖで表されるＰＣＴＯＤが、質量％で０．０７５％以下であることが好ましい。
Ｎｂ及びＶそれぞれの含有量を上記の様に限定したのは、母材強度の向上に有効であり、かつ、ＨＡＺ靭性を大きく害しない範囲とするためである。そこで、Ｎｂの含有量の上限を０．０１５％、Ｖの含有量の上限を０．０３０％とした。
In addition to the above composition, the steel excellent in fracture toughness of the weld heat affected zone of the present invention,
Furthermore, it contains 1 type or 2 types selected from the group of Nb: 0.015% or less and V: 0.030% or less in mass%,
And it is preferable that PCTOD represented by PCTOD = C + Nb + 1 / 3V is 0.075% or less by mass%.
The reason why the respective contents of Nb and V are limited as described above is that they are effective in improving the strength of the base material and do not greatly impair the HAZ toughness. Therefore, the upper limit of the Nb content is 0.015%, and the upper limit of the V content is 0.030%.
ここで、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖで表されるＰＣＴＯＤが、質量％で０．０７５％以下とした点について説明する。
本発明者等は、実際の溶接熱履歴（板厚５０ｍｍの潜弧溶接（ＳＡＷ）５ｋＪ／ｍｍの多層溶接）をシミュレートした実験を多数実施し、−６０℃のＣＴＯＤ特性が満足できる条件を検討した。なお、熱サイクルは、異なる温度を計３回付与することとし、１回目を１４００℃、２回目を７６０℃、３回目を５００℃とした。
Here, P CTOD represented by P CTOD = C + Nb + 1 / 3V is explained point not more than 0.075% in mass%.
The present inventors have conducted a number of experiments simulating actual welding heat history (multilayer welding with 50 mm plate thickness submerged arc welding (SAW) 5 kJ / mm), and satisfying the condition that the CTOD characteristic at −60 ° C. can be satisfied. investigated. In addition, the heat cycle gave a different temperature 3 times in total, 1400 degreeC for the 1st time, 760 degreeC for the 2nd time, and 500 degreeC for the 3rd time.
この実験結果に基づき、ミクロ組織で靭性を劣化させると見られる粒界フェライトやフェライトサイドブレートおよびベイナイト組織の多さを指標にミクロ組織評点を算出した。図１にミクロ組織評点とＣＴＯＤ特性（Ｔδc0.1（℃））の関係を示す。この図によれば、ミクロ組織評点とＣＴＯＤ特性の関係は認められるが、ブロードなバンド（弱い負の相関）であり、他に大きな要因が存在することが分かった。
そこで、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖで表されるＰＣＴＯＤとＣＴＯＤ特性（Ｔδc0.1（℃））の関係を調べたところ、図２に示すように、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３ＶとＣＴＯＤ特性の関係は明瞭で、−６０℃のＣＴＯＤ特性を達成するためには、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖを０．０７５％以下とすることが必須であることが分かった。
Based on the results of this experiment, the microstructure score was calculated based on the number of grain boundary ferrites, ferrite side brates, and bainite structures, which are considered to deteriorate toughness in the microstructure. FIG. 1 shows the relationship between the microstructure score and CTOD characteristics (Tδc0.1 (° C.)). According to this figure, the relationship between the microstructure score and the CTOD characteristic is recognized, but it is a broad band (weak negative correlation), and it has been found that there are other major factors.
Then, when the relationship between P CTOD represented by P CTOD = C + Nb + 1 / 3V and the CTOD characteristic (Tδc0.1 (° C.)) was examined, as shown in FIG. 2, the relationship between P CTOD = C + Nb + 1 / 3V and the CTOD characteristic was obtained. In order to achieve a CTOD characteristic of −60 ° C., it was found that P CTOD = C + Nb + 1 / 3V is 0.075% or less.
次に、本発明の溶接熱影響部の破壊靭性に優れた鋼の製造方法について説明する。
この製造方法は、質量％で、Ｃ：０．０４０〜０．０７５％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：１．７０〜２．５０％、Ｐ：０．００８％以下、Ｓ：０．００５％以下、Ａｌ：０．００４％以下、Ｔｉ：０．００５〜０．０１５％、Ｏ：０．００３５％以下、Ｎ：０．００３０〜０．００５０％を含有し、残部が鉄および不可避不純物からなる鋼を連続鋳造法によりスラブとし、次いで、このスラブを１１００℃以下の温度に再加熱し、その後、加工熱処理する方法である。
Next, the manufacturing method of steel excellent in the fracture toughness of the welding heat affected zone of the present invention will be described.
This production method is, in mass%, C: 0.040 to 0.075%, Si: 0.10 to 0.30%, Mn: 1.70 to 2.50%, P: 0.008% or less, S: 0.005% or less, Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less, N: 0.0030 to 0.0050%, the balance Is a method in which steel composed of iron and inevitable impurities is made into a slab by a continuous casting method, and then this slab is reheated to a temperature of 1100 ° C. or lower, followed by a thermomechanical treatment.
この製造方法は、工業的には連続鋳造法で製造することが必須である。
その理由は、溶鋼の凝固冷却連度が速く、スラブ中に微細なＴｉ酸化物とＴｉ窒化物を多量に生成することが可能なためである。
スラブを圧延するに際しては、その再加熱温度を１１００℃以下とする必要がある。その理由は、再加熱温度が１１００℃を超えると、Ｔｉ窒化物が異常粒成長することにより粗大化し、母材の靭性劣化を生じさせる虞があり、また、ＨＡＺ靭性の改善効果が期待できないからである。
Industrially, it is essential to manufacture this manufacturing method by a continuous casting method.
The reason is that the solidification and cooling of molten steel is fast, and a large amount of fine Ti oxide and Ti nitride can be generated in the slab.
When rolling the slab, the reheating temperature needs to be 1100 ° C. or less. The reason for this is that when the reheating temperature exceeds 1100 ° C., the Ti nitride becomes coarse due to abnormal grain growth, which may cause toughness deterioration of the base material, and the improvement effect of HAZ toughness cannot be expected. It is.
この再加熱後では、加工熱処理が必須である。
その理由は、再加熱後では母材の靭性が劣ったものとなっているので、優れたＨＡＺ靭性が得られても、母材の靭性が劣っていると鋼材としては不十分なものだからである。
加工熱処理の方法としては、（１）制御圧延法、（２）制御圧延−加速冷却法、（３）圧延後直接焼入れ−焼戻し法、等が挙げられるが、好ましくは、（２）制御圧延−加速冷却法である。
なお、この鋼を製造した後、脱水素等の目的でＡｒ３変態点以下の温度に再加熱しても、本発明の特徴を損なうものではない。
After this reheating, a work heat treatment is essential.
The reason is that the toughness of the base metal is inferior after reheating, so even if excellent HAZ toughness is obtained, it is insufficient as a steel material if the toughness of the base material is inferior. is there.
Examples of the heat treatment method include (1) controlled rolling method, (2) controlled rolling-accelerated cooling method, (3) direct hardening after rolling-tempering method, etc., preferably (2) controlled rolling- This is an accelerated cooling method.
Incidentally, this was prepared steel, even if reheated to purposes Ar 3 following transformation point temperature of the dehydrogenation and the like, it does not impair the features of the present invention.
次に、本発明の鋼を実施例１〜１５及び比較例１６〜２０にて説明する。
転炉により、表１に示す様々な組成の鋼スラブを溶製し、次いで、表２に示す製造方法により、表２に示す板厚（４０〜６５ｍｍ）の厚鋼板を作製した。
製造方法は、制御圧延（ＣＲ）、加速冷却（ＡＣＣ）、圧延直後焼入−焼戻（ＤＱＴ）の群から１種を適用した。
Next, the steel of this invention is demonstrated in Examples 1-15 and Comparative Examples 16-20.
Steel slabs having various compositions shown in Table 1 were melted by a converter, and then steel plates having a thickness (40 to 65 mm) shown in Table 2 were produced by the manufacturing method shown in Table 2.
The manufacturing method applied 1 type from the group of controlled rolling (CR), accelerated cooling (ACC), and quenching-tempering (DQT) immediately after rolling.
次いで、実施例１〜１５及び比較例１６〜２０各々の厚鋼板について、表２に示す母材強度および溶接継手の靭性の評価を行った。
溶接は、一般的に試験溶接として用いられている、潜弧溶接（ＳＡＷ）法で、溶接溶け込み線（ＦＬ）が垂直になるようにＫ開先とし、溶接入熱は４．５〜５．０ｋＪ／ｍｍで実施した。
ＣＴＯＤ試験は，試験片の大きさをｔ（板厚）×２ｔの大きさとし、ノッチは５０％疲労亀裂でＦＬ位置（３本）で実施した。
表１に鋼組成を示し、表２に厚鋼板の製造方法及び諸特性を示す。
なお、ＣＴＯＤ試験については、３本のＦＬ位置それぞれにおける値及び最小値（ｍｉｎ）を示した。
Next, the base steel strength and the toughness of the welded joint shown in Table 2 were evaluated for each of the thick steel plates of Examples 1 to 15 and Comparative Examples 16 to 20.
Welding is a submerged arc welding (SAW) method, which is generally used as test welding, with a K groove so that the weld penetration line (FL) is vertical, and the welding heat input is 4.5-5. The test was performed at 0 kJ / mm.
In the CTOD test, the size of the test piece was t (plate thickness) × 2 t, and the notch was 50% fatigue cracked at the FL position (three).
Table 1 shows the steel composition, and Table 2 shows the manufacturing method and various characteristics of the thick steel plate.
In addition, about the CTOD test, the value and minimum value (min) in each of three FL positions were shown.
これらの評価結果によれば、実施例１〜１５は、いずれも降伏強度（ＹＳ）が４２０Ｎ／ｍｍ２以上で、−４０℃でのＣＴＯＤ値が０．７４ｍｍ以上の良好な破壊靭性を示した。
一方、比較例１６〜２０は、母材強度は実施例１〜１５と同等であるが、ＣＴＯＤ値が劣っており、厳しい環境下で使用される鋼板としては、適切でないことが分かった。
According to these evaluation results, Examples 1 to 15 all exhibited good fracture toughness with a yield strength (YS) of 420 N / mm 2 or more and a CTOD value at −40 ° C. of 0.74 mm or more. .
On the other hand, Comparative Examples 16 to 20 have the base material strength equivalent to that of Examples 1 to 15, but the CTOD value is inferior, and it was found that the steel plates used in harsh environments are not suitable.
比較例１６では、Ｎｂの含有量が多すぎ、Ｃ＋Ｎｂの値も０．０８９％と多すぎ、さらに、Ａｌの含有量も多すぎるために、ＣＴＯＤ値が低い値であった。
比較例１７では、Ｃ、Ｎｂが多すぎ、Ｃ＋Ｎｂ＋Ｖの値も０．１１２％と多すぎるため、ＣＴＯＤ値が低い値であった。
比較例１８では、Ｃ、Ｎｂ等は実施例１〜１５と同様であるが、Ｏの含有量が多すぎるため、ＣＴＯＤ値が低い値であった。
比較例１９では、主な鋼成分は実施例１〜１５と同様であるが、Ａｌの含有量が多すぎるため、ＣＴＯＤ値が低い値であった。
比較例２０では、主な鋼成分は実施例１〜１５と同様であるが、Ｔｉの含有量が多すぎるため、ＣＴＯＤ値が低い値であった。
In Comparative Example 16, the content of Nb was too high, the value of C + Nb was too high at 0.089%, and the content of Al was too high, so the CTOD value was low.
In Comparative Example 17, the amount of C and Nb was too large, and the value of C + Nb + V was too large at 0.112%, so the CTOD value was low.
In Comparative Example 18, C, Nb, and the like are the same as in Examples 1 to 15, but the CTOD value was low because the O content was too large.
In Comparative Example 19, the main steel components were the same as in Examples 1 to 15, but the CTOD value was low because the Al content was too high.
In Comparative Example 20, the main steel components were the same as those in Examples 1 to 15, but the CTOD value was low because the Ti content was too high.
本発明は、小入熱溶接から中入熱溶接までの多層溶接における熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性を支配する極めて局部的な領域のミクロ組織の制御と脆化元素の添加量を低減することにより、小入熱溶接から中入熱溶接までの熱影響部（ＨＡＺ）の破壊靭性（ＣＴＯＤ）特性を大幅に改善することができたものであるから、海洋構造物、耐震性建築物等の厳しい環境下で使用される高強度の鋼材として広く適用可能であり、その産業上の利用価値は極めて大きい。 The present invention relates to the control of the microstructure in the extremely local region governing the fracture toughness (CTOD) characteristics of the heat affected zone (HAZ) in multi-layer welding from low heat input welding to medium heat input welding, and addition of embrittlement elements. By reducing the amount, the fracture toughness (CTOD) characteristics of the heat affected zone (HAZ) from small heat input welding to medium heat input welding could be greatly improved. It can be widely applied as a high-strength steel material used in harsh environments such as building materials, and its industrial utility value is extremely large.
Claims (4)
残部が鉄および不可避不純物からなることを特徴とする溶接熱影響部の破壊靭性に優れた鋼。 In mass%, C: 0.040-0.075%, Si: 0.10-0.30%, Mn: 1.70-2.50%, P: 0.008% or less, S: 0.005 %: Al: 0.004% or less, Ti: 0.005 to 0.015%, O: 0.0035% or less, N: 0.0030 to 0.0050%,
A steel with excellent fracture toughness in the heat affected zone of welding, characterized in that the balance consists of iron and inevitable impurities.
かつ、ＰＣＴＯＤ＝Ｃ＋Ｎｂ＋１／３Ｖで表されるＰＣＴＯＤが、質量％で０．０７５％以下であることを特徴とする請求項１記載の溶接熱影響部の破壊靭性に優れた鋼。 Furthermore, it contains 1 type or 2 types selected from the group of Nb: 0.015% or less and V: 0.030% or less in mass%,
The steel having excellent fracture toughness of the weld heat-affected zone according to claim 1, wherein P CTOD represented by P CTOD = C + Nb + 1 / 3V is 0.075% by mass or less.
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008075443A1 (en) * | 2006-12-20 | 2008-06-26 | Nippon Steel Corporation | Steel excelling in toughness at region affected by welding heat |
| JP2008169429A (en) * | 2007-01-11 | 2008-07-24 | Nippon Steel Corp | Steel having excellent ctod in weld heat-affected zone and method for producing the same |
| WO2009072663A1 (en) | 2007-12-07 | 2009-06-11 | Nippon Steel Corporation | Steel with weld heat-affected zone having excellent ctod properties and process for producing the steel |
| WO2010134323A1 (en) | 2009-05-19 | 2010-11-25 | 新日本製鐵株式会社 | Steel material for welding and method for producing same |
| WO2013077022A1 (en) | 2011-11-25 | 2013-05-30 | 新日鐵住金株式会社 | Steel material for welding |
| US8920713B2 (en) | 2009-05-21 | 2014-12-30 | Nippon Steel & Sumitomo Metal Corporation | Steel for welded structure and producing method thereof |
| US9403242B2 (en) | 2011-03-24 | 2016-08-02 | Nippon Steel & Sumitomo Metal Corporation | Steel for welding |
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2006
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008075443A1 (en) * | 2006-12-20 | 2008-06-26 | Nippon Steel Corporation | Steel excelling in toughness at region affected by welding heat |
| JP2008169429A (en) * | 2007-01-11 | 2008-07-24 | Nippon Steel Corp | Steel having excellent ctod in weld heat-affected zone and method for producing the same |
| WO2009072663A1 (en) | 2007-12-07 | 2009-06-11 | Nippon Steel Corporation | Steel with weld heat-affected zone having excellent ctod properties and process for producing the steel |
| JP4547037B2 (en) * | 2007-12-07 | 2010-09-22 | 新日本製鐵株式会社 | Steel excellent in CTOD characteristics of weld heat affected zone and method for producing the same |
| JPWO2009072663A1 (en) * | 2007-12-07 | 2011-04-28 | 新日本製鐵株式会社 | Steel excellent in CTOD characteristics of weld heat affected zone and method for producing the same |
| US8361248B2 (en) | 2007-12-07 | 2013-01-29 | Nippon Steel Corporation | Steel superior in CTOD properties of weld heat-affected zone and method of production of same |
| WO2010134323A1 (en) | 2009-05-19 | 2010-11-25 | 新日本製鐵株式会社 | Steel material for welding and method for producing same |
| US8668784B2 (en) | 2009-05-19 | 2014-03-11 | Nippon Steel & Sumitomo Metal Corporation | Steel for welded structure and producing method thereof |
| US8920713B2 (en) | 2009-05-21 | 2014-12-30 | Nippon Steel & Sumitomo Metal Corporation | Steel for welded structure and producing method thereof |
| US9403242B2 (en) | 2011-03-24 | 2016-08-02 | Nippon Steel & Sumitomo Metal Corporation | Steel for welding |
| WO2013077022A1 (en) | 2011-11-25 | 2013-05-30 | 新日鐵住金株式会社 | Steel material for welding |
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| JP4303703B2 (en) | 2009-07-29 |
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