JP2013082964A - Steel stock for welded joint excellent in anti-ductile crack development property and method for producing the same - Google Patents
Steel stock for welded joint excellent in anti-ductile crack development property and method for producing the same Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 60
- 239000010959 steel Substances 0.000 title claims abstract description 60
- 238000004519 manufacturing process Methods 0.000 title claims description 7
- 238000011161 development Methods 0.000 title abstract description 8
- 238000005482 strain hardening Methods 0.000 claims abstract description 15
- 239000000203 mixture Substances 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 239000000463 material Substances 0.000 claims description 35
- 238000001816 cooling Methods 0.000 claims description 18
- 238000001953 recrystallisation Methods 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 229910052719 titanium Inorganic materials 0.000 claims description 5
- 238000003466 welding Methods 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- 230000007547 defect Effects 0.000 abstract description 28
- 238000000034 method Methods 0.000 description 9
- 210000003371 toe Anatomy 0.000 description 8
- 238000006073 displacement reaction Methods 0.000 description 7
- 238000012360 testing method Methods 0.000 description 6
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- 229910052804 chromium Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 230000000977 initiatory effect Effects 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- 239000010953 base metal Substances 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 230000008439 repair process Effects 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 238000000137 annealing Methods 0.000 description 1
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
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- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
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- 238000001556 precipitation Methods 0.000 description 1
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- 239000002436 steel type Substances 0.000 description 1
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Abstract
Description
本発明は、耐延性亀裂進展特性に優れた溶接継手用鋼材およびその製造方法に関するものである。 The present invention relates to a steel material for welded joints having excellent ductile crack growth characteristics and a method for producing the same.
近年、パイプラインのコストダウンを図るべく、例えば特許文献１〜３に開示されているように、ＡＰＩ規格でＸ８０やＸ１００グレードの高強度鋼管が用いられている。一般的に鋼管は、高強度であることに加えて、不安定破壊特性としての脆性破壊特性や、延性的な不安定破壊特性である不安定延性破壊特性に対する耐久性に優れることが重要とされている。 In recent years, in order to reduce the cost of pipelines, for example, as disclosed in Patent Documents 1 to 3, high-strength steel pipes of X80 or X100 grade according to API standards have been used. In general, it is important for steel pipes to have excellent durability against brittle fracture characteristics as unstable fracture characteristics and unstable ductile fracture characteristics as ductile unstable fracture characteristics in addition to high strength. ing.
ところで、近年、鋼構造建築物や天然ガスパイプラインの建設は、地震地帯や凍土地帯まで拡大している。これらの地域に建設される鋼構造建築物には、地盤変動により大きな外力、すなわち大きな塑性変形力が作用することから、溶接止端部のような応力集中部あるいは溶接部に潜在する欠陥からの延性亀裂の発生・進展が問題となっている。 By the way, in recent years, the construction of steel structures and natural gas pipelines has expanded to earthquake zones and frozen land zones. Since steel structures constructed in these areas are subject to large external forces, that is, large plastic deformation forces, due to ground fluctuations, they are not subject to stress concentration parts such as weld toes or defects that exist in the welds. The occurrence and development of ductile cracks is a problem.
上記問題の対策として、非特許文献１に、延性亀裂発生に対する構造物の使用限界評価方法が提案されている。
この非特許文献１は、高強度鋼管円周溶接部の延性破壊クライテリオンに関するもので、Ｘ８０およびＸ１００グレード高強度鋼管の母材および円周溶接継手の延性破壊挙動を切欠丸棒試験片と表面切欠付広幅試験片によって調査する技術が開示されている。母材および円周溶接継手に共通して、切欠丸棒試験片で得られた亀裂発生限界歪み（限界相当の塑性歪み）に、表面切欠付広幅試験片のノッチ先端歪が達したときに延性亀裂が発生することから、限界相当塑性歪が試験片サイズに依存しない破壊クライテリオンとして有効であることが述べられている。
As a countermeasure against the above problem, Non-Patent Document 1 proposes a method for evaluating the limit of use of a structure against the occurrence of ductile cracks.
This non-patent document 1 relates to a ductile fracture criterion of a high strength steel pipe circumferential weld. The ductile fracture behavior of X80 and X100 grade high strength steel pipes and circumferential weld joints is measured with a round bar specimen and a surface notch. A technique for investigating with a wide specimen is disclosed. Common to base metal and circumferential welded joints, ductility when notch tip strain of wide test piece with surface notch reaches the crack initiation limit strain (plastic strain equivalent to the limit) obtained with notched round bar test piece Since cracks occur, it is stated that the critical equivalent plastic strain is effective as a fracture criterion that does not depend on the specimen size.
また、特許文献４には、溶接部からの延性亀裂発生に対する抵抗性に優れた高張力鋼溶接継手が提案されている。 Patent Document 4 proposes a high-strength steel welded joint that has excellent resistance to ductile cracking from the weld.
前記非特許文献１に記載された技術は、延性破壊の初期段階である微小延性亀裂の発生に基づいた鋼構造物の使用限界予測手法である。ところで、一般的に、欠陥部などの応力集中部から延性亀裂が発生・進展する場合には、内圧がかかるような鋼構造物の使用限界は、延性亀裂が板厚を貫通しリークが発生するまでであると考えられる。従って、延性亀裂発生点を内圧がかかる構造物の使用限界として予測するのは、過度に安全サイドに立つと考えられ、鋼構造物の経済径の観点からは疑問が残る。 The technique described in Non-Patent Document 1 is a method for predicting the use limit of a steel structure based on the occurrence of a micro-ductile crack, which is the initial stage of ductile fracture. By the way, in general, when a ductile crack is generated and propagates from a stress concentrated part such as a defect, the use limit of a steel structure to which an internal pressure is applied is that the ductile crack penetrates the plate thickness and a leak occurs. It is thought that. Therefore, it is considered that predicting the ductile crack generation point as the use limit of the structure to which the internal pressure is applied is considered to be excessively safe, and a question remains from the viewpoint of the economic diameter of the steel structure.
また、特許文献４に記載された技術は、延性破壊の初期段階である微小延性亀裂の発生の抵抗性を向上させようとする技術である。これは、ノッチのような比較的緩やかな応力集中からの延性亀裂発生の抵抗性を向上させる手段としては有効であるかも知れないが、実際の鋼構造物で問題となるのは鋭利な形状の溶接欠陥や先端半径の小さな疲労亀裂のような欠陥であり、すでに初期の延性亀裂が発生していると仮定できるような欠陥であることが多い。
従って、この技術は、実際に生じる延性破壊の対応策としてはやはり疑問が残る。
Moreover, the technique described in Patent Document 4 is a technique for improving the resistance to occurrence of a micro-ductile crack, which is an initial stage of ductile fracture. This may be effective as a means of improving the resistance of ductile cracking from a relatively moderate stress concentration such as a notch, but the problem with an actual steel structure is the sharp shape. It is often a defect such as a weld defect or a fatigue crack with a small tip radius, and it can be assumed that an initial ductile crack has already occurred.
Therefore, this technique still remains a question as a countermeasure for the ductile fracture that actually occurs.
本発明は、上記の現状に鑑み開発されたもので、地震地帯や不連続凍土地帯などに建設される鋼構造建築物で用いられる溶接継手について、大きな変形を受けた際に生じる応力集中部や欠陥からの延性亀裂の進展を効果的に抑制することができる耐延性亀裂進展特性に優れた溶接継手用鋼材を、その有利な製造方法と共に提案することを目的とする。 The present invention has been developed in view of the above-described situation, and a welded joint used in a steel structure building constructed in an earthquake zone, a discontinuous frozen land zone, etc. It aims at proposing the steel material for welded joints excellent in the ductile crack propagation characteristic which can suppress effectively the progress of the ductile crack from a defect with the advantageous manufacturing method.
さて、発明者等は、上記の問題を解決するために、種々の材料特性、中でも強度特性に優れた鋼材を用いて溶接継手を作製し、大変形を受けたときの溶接止端部での初期欠陥からの延性亀裂の発生・進展挙動について詳細に観察した。
その結果、溶接継手の溶接止端部欠陥からの延性亀裂は、欠陥最深部より発生し、板厚方向に進展し、最終的な亀裂が貫通することで破断に至るが、延性亀裂が進展する過程では亀裂とは反対側の板厚部位に局部的な材料くびれが発生し、この局所くびれにより板厚が減少することで、より亀裂の板厚貫通へと至り易い状況になっていることが判明した。
Now, in order to solve the above problems, the inventors made a welded joint using steel materials having various material characteristics, particularly strength characteristics, and at the toe of the weld when subjected to large deformation. The behavior of ductile crack initiation and propagation from initial defects was observed in detail.
As a result, the ductile crack from the weld toe defect of the welded joint occurs from the deepest part of the defect and propagates in the thickness direction, leading to fracture when the final crack penetrates, but the ductile crack develops. In the process, local material constriction occurs in the plate thickness part on the opposite side of the crack, and the plate thickness decreases due to this local constriction, so that it is more likely to lead to crack penetration. found.
そこで、次に、かかる局所くびれの発生状況と継手鋼材の強度特性を詳細に比較したところ、鋼板の加工硬化特性のうち、３〜６％の塑性ひずみ領域での加工硬化率を大きくすることによって、この局所くびれの発生を抑制することができ、その結果、大きな変形を受けた際に生じる応力集中部や欠陥からの延性亀裂の進展を効果的に抑制できることの知見を得た。
本発明は、上記の知見に立脚するものである。
Then, next, when the occurrence state of such local constriction and the strength characteristics of the joint steel were compared in detail, among the work hardening characteristics of the steel sheet, by increasing the work hardening rate in the plastic strain region of 3 to 6%. As a result, it has been found that the occurrence of this local constriction can be suppressed, and as a result, it is possible to effectively suppress the development of a ductile crack from a stress concentrated portion or a defect that occurs when subjected to a large deformation.
The present invention is based on the above findings.
すなわち、本発明の要旨構成は次のとおりである。
１．質量％で、
Ｃ：０．０３〜０．１５％、
Si：０．０１〜１％及び
Mn：０．５〜２％
を含有し、残部はFeおよび不可避的不純物からなる鋼材であって、３〜６％の塑性ひずみ領域において、次式(1)で示される加工硬化率ｎが0.12以上を満足することを特徴とする耐延性亀裂進展特性に優れた溶接継手用鋼材。
σ＝Ｋ・εn
ここで、σ：真応力（MPa）
ε：真塑性ひずみ（−）
Ｋ：定数
ｎ：加工硬化率（％）
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.03-0.15%,
Si: 0.01-1% and
Mn: 0.5-2%
The balance is a steel material composed of Fe and inevitable impurities, and the work hardening rate n expressed by the following formula (1) satisfies 0.12 or more in a plastic strain region of 3 to 6%. Steel material for welded joints with excellent ductile crack growth characteristics.
σ = K · ε n
Where σ: True stress (MPa)
ε: True plastic strain (-)
K: Constant
n: Work hardening rate (%)
２．前記鋼材が、質量％で、さらに
Ｎｂ：０．００５〜０．１％、
Ｖ：０．００５〜０．１％及び
Ｔｉ：０．００５〜０．１％
の群から選択された１種または２種以上を含有することを特徴とする上記１に記載の耐延性亀裂進展特性に優れた溶接継手用鋼材。
2. The steel material is mass%, and Nb: 0.005 to 0.1%,
V: 0.005-0.1% and Ti: 0.005-0.1%
The steel material for welded joints having excellent ductile crack growth characteristics as described in 1 above, which comprises one or more selected from the group consisting of:
３．前記鋼材が、質量％で、さらに
Ｃｕ：０．０５〜０．５％、
Ｎｉ：０．０５〜０．５％、
Ｃｒ：０．０５〜０．５％及び
Ｍｏ：０．０５〜０．５％
の群から選択された１種または２種以上を含有することを特徴とする上記１または２に記載の耐延性亀裂進展特性に優れた溶接継手用鋼材。
3. The steel material is mass%, and Cu: 0.05 to 0.5%,
Ni: 0.05 to 0.5%,
Cr: 0.05-0.5% and Mo: 0.05-0.5%
The steel material for welded joints having excellent ductile crack growth characteristics as described in 1 or 2 above, which comprises one or more selected from the group consisting of
４．前記１〜３のいずれかに示す種々の成分組成になる鋼スラブを、1000〜1200℃に加熱し、未再結晶温度域での熱間圧延を行い、熱間圧延された鋼板をＡｒ3〜（Ａｒ3−８０℃）の温度域から、５℃／秒以上の平均冷却速度で、５００℃以下２５０℃以上の温度域まで冷却することを特徴とする耐延性亀裂進展特性に優れた溶接継手用鋼材の製造方法。 4). Steel slabs having various component compositions shown in any one of 1 to 3 are heated to 1000 to 1200 ° C., hot-rolled in a non-recrystallization temperature range, and the hot-rolled steel sheet is converted to Ar 3 to (Ar 3 -80 ° C.) Welded joint with excellent ductile crack growth characteristics, characterized by cooling to a temperature range of 500 ° C. or lower and 250 ° C. or higher at an average cooling rate of 5 ° C./second or higher. Steel manufacturing method.
本発明によれば、大きな変形を受けた際に生じる応力集中部や欠陥からの延性亀裂の進展を効果的に抑制することができる溶接継手用鋼材を提供することができる。
従って、本発明によれば、鋼構造物が大きな外力（変形量）を受けた場合にも、応力集中部や欠陥からの延性亀裂の進展を効果的に抑制して、鋼構造物の機能維持を図ると共に、許容欠陥寸法（点検・補修に必要な欠陥寸法）を大きくすることが可能となるため、補修等のメンテナンスの長期化も達成でき、鋼構造物の長寿命化および維持コストの削減にも偉効を奏する。
ADVANTAGE OF THE INVENTION According to this invention, the steel material for welded joints which can suppress effectively the progress of the ductile crack from the stress concentration part and defect which arise when receiving big deformation can be provided.
Therefore, according to the present invention, even when the steel structure receives a large external force (deformation amount), it is possible to effectively suppress the progress of ductile cracks from the stress concentration portion and the defect, thereby maintaining the function of the steel structure. As well as increasing the permissible defect dimensions (defect dimensions necessary for inspection and repair), it is possible to extend the maintenance time for repairs, etc., extending the life of steel structures and reducing maintenance costs. Also has a great effect.
以下、本発明を具体的に説明する。
前述したとおり、溶接継手の溶接止端部欠陥からの延性亀裂は、欠陥最深部より発生し、この亀裂が板厚方向に進展して、最終的に板厚を貫通することで破断に至るが、この延性亀裂が進展する過程で亀裂とは反対側の板厚位置に局部的な材料くびれが発生する。
この現象を、図１に示す。
図１は、切欠（初期欠陥）を付与した小型試験片に対し引張試験を行ったときの断面の状態を模式的に示したもので、１が小型試験片であり、１０で切欠（初期欠陥）、１０ａで切欠最深部、２０で延性亀裂、３０で局所くびれを示す。また、δeffは有効開口変位、ａ0は初期欠陥深さ、Δａは延性亀裂長さ、Ｒaは局所くびれ量を表わす。
Hereinafter, the present invention will be specifically described.
As described above, the ductile crack from the weld toe defect of the weld joint occurs from the deepest part of the defect, and this crack propagates in the plate thickness direction and eventually breaks through the plate thickness. In the course of the development of the ductile crack, a local material constriction occurs at the plate thickness position opposite to the crack.
This phenomenon is shown in FIG.
FIG. 1 schematically shows a cross-sectional state when a tensile test is performed on a small test piece provided with a notch (initial defect). 1 is a small test piece, and 10 is a notch (initial defect). ) 10a indicates the deepest notch, 20 indicates a ductile crack, and 30 indicates a local constriction. Also, δ eff represents the effective opening displacement, a 0 represents the initial defect depth, Δa represents the ductile crack length, and R a represents the amount of local constriction.
さて、本発明の特徴は、溶接継手に使用する鋼材の応力−ひずみ曲線における特定ひずみ域での加工率を所定に範囲に制限することにより、溶接止端部から発生し板厚方向へ伝播する延性亀裂の進展を抑制するところにある。
具体的は、３〜６％の塑性ひずみ領域において、次式(1)
σ＝Ｋ・εn --- (1)
ここで、σ：真応力（MPa）
ε：真塑性ひずみ（−）
Ｋ：定数
ｎ：加工硬化率（％）
で示される加工硬化率ｎを0.12以上に規定することである。
The feature of the present invention is that it is generated from the weld toe and propagates in the plate thickness direction by limiting the processing rate in a specific strain region in the stress-strain curve of the steel material used for the welded joint to a predetermined range. This is to suppress the development of ductile cracks.
Specifically, in the plastic strain region of 3-6%, the following formula (1)
σ = K ・ ε n --- (1)
Where σ: True stress (MPa)
ε: True plastic strain (-)
K: Constant
n: Work hardening rate (%)
Is defined as 0.12 or more.
上記したように、式(1)で示される加工硬化率ｎ、特に塑性ひずみが３〜６％の領域における加工硬化率ｎを0.12以上とすることにより、延性亀裂が進展していく際の亀裂発生側とは反対側の板厚位置における局部的な材料くびれの発生が効果的に抑制され、その結果、板厚方向へ伝播する延性亀裂の進展速度を低減することが可能になるのである。 As described above, when the work hardening rate n represented by the formula (1), particularly the work hardening rate n in the region where the plastic strain is 3 to 6%, is set to 0.12 or more, the crack when the ductile crack progresses. Occurrence of local material constriction at the plate thickness position opposite to the generation side is effectively suppressed, and as a result, it is possible to reduce the rate of progress of ductile cracks propagating in the plate thickness direction.
図２に、有効開口変位（δeff）量と（Δａ＋Ｒa）/ｔとの関係について調べた結果を示す。ここに、ｔは、初期の板厚（Ｔ）と初期欠陥深さ（ａ0）との差（Ｔ−ａ0）である。
このデータは、溶接部止端部の表面欠陥から延性亀裂が進展するときの延性亀裂の開口変位と進展量の関係について考察したものである。
同図に示したとおり、（Δａ＋Ｒa）/ｔが大きくなると有効開口変位（δeff）量も次第に増大する。
FIG. 2 shows the result of examining the relationship between the effective aperture displacement (δ eff ) amount and (Δa + R a ) / t. Here, t is the difference (T−a 0 ) between the initial plate thickness (T) and the initial defect depth (a 0 ).
This data considers the relationship between the opening displacement of a ductile crack and the amount of progress when the ductile crack progresses from a surface defect at the weld toe.
As shown in the figure, as (Δa + R a ) / t increases, the amount of effective aperture displacement (δ eff ) gradually increases.
また、図３に、塑性ひずみが３〜６％のときのｎ値とＲa/ｔとの関係について調べた結果を示す。
同図に示したとおり、ｎ値が大きくなるほどＲa/ｔ比すなわち局所くびれ量は小さくなり、延性亀裂の進展部の抵抗を高めることができる。特にｎ値が0.12以上になる場合は局所くびれ比（Ｒa/ｔ）0.11以下となり、溶接継手の板厚に対してくびれ量が10％以下となる優れた値を得ることができた。
FIG. 3 shows the results of examining the relationship between the n value and R a / t when the plastic strain is 3 to 6%.
As shown in the figure, as the n value increases, the Ra / t ratio, that is, the amount of local constriction decreases, and the resistance of the ductile crack progressing portion can be increased. In particular, when the n value was 0.12 or more, the local neck ratio ( Ra / t) was 0.11 or less, and an excellent value that the necking amount was 10% or less with respect to the plate thickness of the welded joint could be obtained.
また、本発明において、加工硬化率ｎを規定すべき塑性ひずみの領域を３〜６％の範囲に制限した理由は、溶接継手の溶接止端部欠陥からの延性亀裂が進展する過程では亀裂とは反対側の板厚部位に局部的な材料くびれが発生するが、この局所くびれが発生するまでの３〜６％の塑性ひずみ領域での材料の加工硬化性能が当該部での均一なひずみ分布に影響を与えるからである。 In the present invention, the reason why the plastic strain region in which the work hardening rate n should be defined is limited to a range of 3 to 6% is that cracks are generated in the process of the development of ductile cracks from weld toe defects in weld joints. Although local material constriction occurs in the opposite thickness, the work hardening performance of the material in the plastic strain region of 3-6% until this local constriction occurs is uniform strain distribution in the part It is because it affects.
次に、本発明の鋼材の好適成分組成について説明する。
本発明の溶接継手用鋼材は、４９０MPa以上の高強度材であることが好ましいので、成分組成もそれに見合う組成とする必要がある。なお、鋼材中の元素の含有量の単位は何れも「質量％」であるが、以下、特に断らない限り単に「％」で示す。
Next, the preferred component composition of the steel material of the present invention will be described.
Since the steel material for welded joints of the present invention is preferably a high-strength material of 490 MPa or more, the component composition must be commensurate with it. In addition, although the unit of content of the element in steel materials is all "mass%", unless otherwise indicated below, it shows only by "%".
本発明では、基本成分として、Ｃ：０．０３〜０．１５％、Si：０．０１〜１％及びMn：０．５〜２％を含有させる必要がある。
また、本発明では、その他にも、Ｎｂ：０．００５〜０．１％、Ｖ：０．００５〜０．１％及びＴｉ：０．００５〜０．１％の群から選択された１種または２種以上、さらにはＣｕ：０．０５〜０．５％、Ｎｉ：０．０５〜０．５％、Ｃｒ：０．０５〜０．５％及びＭｏ：０．０５〜０．５％の群から選択された１種または２種以上を適宜含有させることができる。
In the present invention, it is necessary to contain C: 0.03 to 0.15%, Si: 0.01 to 1%, and Mn: 0.5 to 2% as basic components.
In the present invention, in addition, one type selected from the group of Nb: 0.005 to 0.1%, V: 0.005 to 0.1%, and Ti: 0.005 to 0.1% Or two or more, further Cu: 0.05-0.5%, Ni: 0.05-0.5%, Cr: 0.05-0.5% and Mo: 0.05-0.5% 1 type (s) or 2 or more types selected from the group of these can be contained suitably.
以下、上記した各成分の限定理由について説明する。
Ｃ：０．０３〜０．１５％
Ｃは、鋼材の強度を確保するとともに、島状マルテンサイトの生成を促進するために必要な元素である。しかしながら、含有量が０．０３％未満では島状マルテンサイトの量が不足し、一方０．１５％を超えて添加すると溶接性が劣化するので、Ｃ量は０．０３〜０．１５％とする。
Hereinafter, the reason for limitation of each component described above will be described.
C: 0.03-0.15%
C is an element necessary for ensuring the strength of the steel material and for promoting the formation of island martensite. However, if the content is less than 0.03%, the amount of island martensite is insufficient. On the other hand, if the content exceeds 0.15%, weldability deteriorates, so the C content is 0.03 to 0.15%. To do.
Si：０．０１〜１％
Ｓｉは、強度を高めるため、また製鋼工程における脱酸剤として添加する。しかしながら、含有量が０．０１％未満ではその効果が十分でなく、一方１％を超えて添加すると溶接部の靭性が劣化するので、Si量は０．０１〜１％とする。
Si: 0.01 to 1%
Si is added to increase the strength and as a deoxidizer in the steel making process. However, if the content is less than 0.01%, the effect is not sufficient. On the other hand, if the content exceeds 1%, the toughness of the welded portion deteriorates, so the Si content is 0.01 to 1%.
Mn：０．５〜２％
Ｍｎは、強度を高めるために添加する。しかしながら、含有量が０．５％未満では強度が不足し、一方２％を超えて添加すると母材と溶接部の靭性、さらには溶接性が劣化するので、Mn量は０．５〜２％とする。
Mn: 0.5-2%
Mn is added to increase the strength. However, if the content is less than 0.5%, the strength is insufficient. On the other hand, if the content exceeds 2%, the toughness of the base metal and the welded portion and further the weldability deteriorate, so the Mn content is 0.5-2%. And
Ｃｕ：０．０５〜０．５％、Ｎｉ：０．０５〜０．５％、Ｃｒ：０．０５〜０．５％、Ｍｏ：０．０５〜０．５％
Ｃｕ，Ｎｉ，Ｃｒ及びＭｏは、選択元素であり、強度を高める場合に１種または２種以上を添加する。しかしながら、いずれの元素も、含有量が０．０５％未満では効果がなく、一方０．５％を超えると溶接性が劣化するので、これらの元素は単独添加または複合添加いずれの場合も０．０５〜０．５％とする。
Cu: 0.05-0.5%, Ni: 0.05-0.5%, Cr: 0.05-0.5%, Mo: 0.05-0.5%
Cu, Ni, Cr and Mo are selective elements, and one or two or more are added to increase the strength. However, any element has no effect when the content is less than 0.05%, while weldability deteriorates when the content exceeds 0.5%. 05 to 0.5%.
Ｎｂ：０．００５〜０．１％、Ｖ：０．００５〜０．１％、Ｔｉ：０．００５〜０．１％
Ｎｂ，Ｖ及びＴｉは、選択元素であり、靭性および強度を高める場合に１種または２種以上を添加する。しかしながら、いずれの元素も、含有量が０．００５％未満では効果がなく、一方０．１％を超えると溶接部の靭性が劣化するので、これらの元素は単独添加または複合添加いずれの場合も０．００５〜０．１％とする。
Nb: 0.005-0.1%, V: 0.005-0.1%, Ti: 0.005-0.1%
Nb, V, and Ti are selective elements, and one or two or more are added to increase toughness and strength. However, any element has no effect if the content is less than 0.005%, whereas if it exceeds 0.1%, the toughness of the welded portion deteriorates. Therefore, these elements can be added individually or in combination. 0.005 to 0.1%.
本発明は、上記に規定した元素を含有していればその効果が得られ、不純物元素としてのＰ，Ｓ、脱酸剤として添加されるＡｌ、及びその他の元素を含んでいても、その効果は何ら損なわれることはない。 The present invention is effective if it contains the elements specified above, and even if it contains P and S as impurity elements, Al added as a deoxidizer, and other elements. Will not be damaged at all.
次に、本発明鋼材の製造方法について説明する。
上記の好適成分組成に調整した溶鋼を、好ましくは連続焼鈍によってスラブとする。ついで得られた鋼スラブを、１０００〜１２００〜℃に加熱する。加熱温度が１０００℃に満たないと効率低下により製造コストが上昇することになり、一方１２００℃を超えるとミクロ組織の粗大化の問題が生じる。上記のスラブ加熱後、未再結晶温度域において熱間圧延を行ったのち、Ａｒ3〜（Ａｒ3−８０℃）の温度域から５℃／秒以上の平均冷却速度で５００℃以下２５０℃以上の温度域まで冷却する。
ここに、熱間圧延温度を未再結晶温度域としたのは、最終的なミクロ組織微細化し強度と靱性を両立する理由による。なお、本発明の鋼種における未再結晶温度は概ね950℃〜Ａｒ3の範囲である。また、冷却開始温度を、Ａｒ3〜（Ａｒ3−８０℃）の温度域としたのは、冷却開始温度がＡｒ3より高い場合、冷却前のフェライトの析出量が少なくn値を確保できなくなるからであり、一方（Ａｒ3−８０℃）より低くなるとパーライトが生成するようになり鋼材の強度が低くなるからである。上記の温度域からの平均冷却速度を５℃／秒以上としたのは、平均冷却速度が５℃／秒に満たないとパーライトが生成するようになり鋼材の所定の強度が確保できなくなるからである。さらに、上記の制御冷却停止温度を５００℃以下２５０℃以上の範囲としたのは、制御冷却停止温度が５００℃超ではフェライト主体の組織となりｎ値を確保するために必要な高強度組織の分率が低下するためであり、一方２５０℃未満では鋼材の延性が低下するからである。
Next, the manufacturing method of this invention steel material is demonstrated.
The molten steel adjusted to the above suitable component composition is preferably made into a slab by continuous annealing. The steel slab obtained is then heated to 1000-1200 ° C. If the heating temperature is less than 1000 ° C., the production cost will increase due to the decrease in efficiency, while if it exceeds 1200 ° C., the problem of coarsening of the microstructure occurs. After the above slab heating, after hot rolling in the non-recrystallization temperature range, the average cooling rate of 5 ° C./second or more from the temperature range of Ar 3 to (Ar 3 −80 ° C.) is 500 ° C. or less and 250 ° C. or more. Cool to the temperature range.
The reason why the hot rolling temperature is set to the non-recrystallization temperature range is that the final microstructure is refined to achieve both strength and toughness. The non-recrystallization temperature in the steel type of the present invention is generally in the range of 950 ° C. to Ar 3 . The reason why the cooling start temperature is in the temperature range of Ar 3 to (Ar 3 -80 ° C.) is that when the cooling start temperature is higher than Ar 3 , the precipitation amount of ferrite before cooling is small and the n value cannot be secured. This is because when the temperature is lower than (Ar 3 -80 ° C.), pearlite is generated and the strength of the steel material is lowered. The reason why the average cooling rate from the above temperature range was set to 5 ° C./second or more is that pearlite is generated when the average cooling rate is less than 5 ° C./second, and the predetermined strength of the steel material cannot be secured. is there. Furthermore, the above-described controlled cooling stop temperature is set to a range of 500 ° C. or lower and 250 ° C. or higher because the controlled cooling stop temperature exceeds 500 ° C. and becomes a structure mainly composed of ferrite. This is because the ductility of the steel material is lowered at a temperature lower than 250 ° C.
上記したように、本発明に従う成分組成の鋼スラブを、再結晶温度域で熱間圧延したのち、Ａｒ3〜（Ａｒ3−８０℃）の温度域から所定の温度まで制御冷却を行うことにより、３〜６％の塑性ひずみ領域における加工硬化率ｎが0.12以上の鋼材を得ることができる。
なお、本発明の鋼材は、溶接継手として使用されるものであるため、板厚は１２〜５０mm程度とするのが好適である。
As described above, the steel slab having the composition according to the present invention is hot-rolled in the recrystallization temperature region, and then controlled cooling from the temperature range of Ar 3 to (Ar 3 -80 ° C.) to a predetermined temperature. Thus, a steel material having a work hardening rate n in a plastic strain region of 3 to 6% of 0.12 or more can be obtained.
Since the steel material of the present invention is used as a welded joint, the plate thickness is preferably about 12 to 50 mm.
以下、実施例により、本発明をさらに詳細にするが、 本発明は、以下の例に何ら限定されるものではない。
実施例１
表１に示す種々の成分組成になる鋼スラブを、加熱後、未再結晶温度域で熱間圧延したのち、Ａｒ3〜（Ａｒ3−８０℃）の温度域から、種々の平均冷却速度で、５００℃以下２５０℃以上の温度域まで冷却して鋼板を作製した。スラブ加熱温度、冷却開始温度、冷却速度および冷却停止温度を表２に示す。
得られた鋼板から、同じ溶接材料および溶接条件の下に溶接継手を作製した。この溶接継手の止端部に表面欠陥として長さ：３０mm、深さ：４mmの予亀裂を導入し、大変形を与えたときの欠陥からの延性亀裂発生・進展に伴う、くびれの発生およびその成長の様子を観察した。
上記した延性亀裂発生・進展試験にて得られた結果を表２に併記する。
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the following examples at all.
Example 1
Steel slabs having various component compositions shown in Table 1 are heated and then hot-rolled in the non-recrystallization temperature range, and then at various average cooling rates from the temperature range of Ar 3 to (Ar 3 -80 ° C.). The steel sheet was manufactured by cooling to a temperature range of 500 ° C. or lower and 250 ° C. or higher. Table 2 shows the slab heating temperature, cooling start temperature, cooling rate, and cooling stop temperature.
A welded joint was produced from the obtained steel plate under the same welding material and welding conditions. Introducing a precrack of length 30mm and depth 4mm as a surface defect at the toe of this welded joint, the occurrence of constriction accompanying the occurrence and propagation of ductile cracks from the defect when large deformation is applied, and The state of growth was observed.
The results obtained in the above-described ductile crack initiation / propagation test are also shown in Table 2.
表２に示したとおり、発明例はいずれも、３〜６％の塑性ひずみ領域における加工硬化率ｎ：0.12以上を満足し、その結果、局所くびれの発生量が少なく、局所くびれ比（Ｒa/ｔ）は0.11以下という極めて低い値を呈していた。 As shown in Table 2, all of the inventive examples satisfy a work hardening ratio n: 0.12 or more in a plastic strain region of 3 to 6%. As a result, the amount of local necking is small, and the local necking ratio (R a / t) exhibited an extremely low value of 0.11 or less.
１ 小型試験片
１０ 切欠（初期欠陥）
１０ａ 切欠最深部
２０ 延性亀裂
３０ 局所くびれ
ａ0 初期欠陥深さ
Δａ 延性亀裂長さ
Ｒa 局所くびれ量
ｔ 初期の板厚と初期欠陥深さとの差
Ｔ 初期の板厚
δeff 有効開口変位
1
10a
Claims (4)
Ｃ：０．０３〜０．１５％、
Si：０．０１〜１％及び
Mn：０．５〜２％
を含有し、残部はFeおよび不可避的不純物からなる鋼材であって、３〜６％の塑性ひずみ領域において、次式(1)で示される加工硬化率ｎが0.12以上を満足することを特徴とする耐延性亀裂進展特性に優れた溶接継手用鋼材。
σ＝Ｋ・εn --- (1)
ここで、σ：真応力（MPa）
ε：真塑性ひずみ（−）
Ｋ：定数
ｎ：加工硬化率（％） % By mass
C: 0.03-0.15%,
Si: 0.01-1% and
Mn: 0.5-2%
The balance is a steel material composed of Fe and inevitable impurities, and the work hardening rate n expressed by the following formula (1) satisfies 0.12 or more in a plastic strain region of 3 to 6%. Steel material for welded joints with excellent ductile crack growth characteristics.
σ = K ・ ε n --- (1)
Where σ: True stress (MPa)
ε: True plastic strain (-)
K: Constant
n: Work hardening rate (%)
Ｎｂ：０．００５〜０．１％、
Ｖ：０．００５〜０．１％及び
Ｔｉ：０．００５〜０．１％
の群から選択された１種または２種以上を含有することを特徴とする請求項１に記載の耐延性亀裂進展特性に優れた溶接継手用鋼材。 The steel material is mass%, and Nb: 0.005 to 0.1%,
V: 0.005-0.1% and Ti: 0.005-0.1%
The steel material for welded joints having excellent ductile crack growth characteristics according to claim 1, comprising one or more selected from the group of the above.
Ｃｕ：０．０５〜０．５％、
Ｎｉ：０．０５〜０．５％、
Ｃｒ：０．０５〜０．５％及び
Ｍｏ：０．０５〜０．５％
の群から選択された１種または２種以上を含有することを特徴とする請求項１または２に記載の耐延性亀裂進展特性に優れた溶接継手用鋼材。 The steel material is mass%, and Cu: 0.05 to 0.5%,
Ni: 0.05 to 0.5%,
Cr: 0.05-0.5% and Mo: 0.05-0.5%
The steel material for welded joints having excellent ductile crack growth characteristics according to claim 1 or 2, comprising one or more selected from the group of the above.
A steel slab having various component compositions according to any one of claims 1 to 3 is heated to 1000 to 1200 ° C, hot-rolled in a non-recrystallization temperature range, and the hot-rolled steel sheet is converted to Ar 3. Welding with excellent ductile crack growth characteristics characterized by cooling from a temperature range of ~ (Ar 3 -80 ° C) to a temperature range of 500 ° C or lower and 250 ° C or higher at an average cooling rate of 5 ° C / second or higher. Manufacturing method of steel for joints.
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| KR101839227B1 (en) | 2016-09-12 | 2018-03-16 | 주식회사 포스코 | Steel sheet for pipe having excellent fatigue resistance, method for manufacturing the same, and welded steel pipe using the same |
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| CN106756517A (en) * | 2017-02-17 | 2017-05-31 | 上海海事大学 | A kind of steel plate and its manufacture method for polar region ship |
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