JP5796379B2 - Steel for welded structure excellent in CTOD characteristics of high heat input weld heat affected zone - Google Patents
Steel for welded structure excellent in CTOD characteristics of high heat input weld heat affected zone Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 49
- 239000010959 steel Substances 0.000 title claims description 49
- 238000005204 segregation Methods 0.000 claims description 25
- 238000003466 welding Methods 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 14
- 238000001816 cooling Methods 0.000 claims description 13
- 238000004519 manufacturing process Methods 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 6
- 229910000746 Structural steel Inorganic materials 0.000 claims description 5
- 238000009749 continuous casting Methods 0.000 claims description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 230000008014 freezing Effects 0.000 claims description 4
- 238000007710 freezing Methods 0.000 claims description 4
- 238000005098 hot rolling Methods 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 238000012360 testing method Methods 0.000 description 26
- 230000000694 effects Effects 0.000 description 14
- 239000000463 material Substances 0.000 description 11
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 9
- 229910052748 manganese Inorganic materials 0.000 description 7
- 229910052698 phosphorus Inorganic materials 0.000 description 7
- 238000005096 rolling process Methods 0.000 description 7
- 229910001566 austenite Inorganic materials 0.000 description 6
- 238000007711 solidification Methods 0.000 description 6
- 230000008023 solidification Effects 0.000 description 6
- 229910052804 chromium Inorganic materials 0.000 description 5
- 229910052802 copper Inorganic materials 0.000 description 5
- 229910052759 nickel Inorganic materials 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 239000002131 composite material Substances 0.000 description 4
- 238000004453 electron probe microanalysis Methods 0.000 description 4
- 238000013507 mapping Methods 0.000 description 4
- 229910052750 molybdenum Inorganic materials 0.000 description 4
- 229910052721 tungsten Inorganic materials 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 238000011088 calibration curve Methods 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000003631 expected effect Effects 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229940045657 oxycide Drugs 0.000 description 1
- 238000013001 point bending Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- Heat Treatment Of Steel (AREA)
Description
本発明は、降伏強度が３９０Ｎ／ｍｍ２を超え、板厚が４０ｍｍ以上の溶接構造用鋼に関し、特に溶接入熱量が３００ｋＪ／ｃｍを超える大入熱溶接でも溶接熱影響部（以下、ＨＡＺということがある）のＣＴＯＤ特性に優れるものに関する。 The present invention relates to a welded structural steel having a yield strength exceeding 390 N / mm 2 and a plate thickness of 40 mm or more, and in particular, a welding heat-affected zone (hereinafter referred to as HAZ) even in high heat input welding where the welding heat input exceeds 300 kJ / cm. The CTOD characteristics are excellent).
鋼材の高強度化、厚肉化に伴い溶接施工に、サブマージアーク溶接、エレクトロガス溶接およびエレクトロスラグ溶接など生産能率に優れる大入熱溶接が適用されることが増加している。 With increasing strength and thickness of steel materials, high heat input welding with excellent production efficiency such as submerged arc welding, electrogas welding, and electroslag welding has been increasingly applied to welding construction.
鋼材において大入熱溶接された溶接熱影響部の靭性（以下、ＨＡＺの靭性、ＨＡＺ靭性ということがある）は低下するため、種々の大入熱溶接用鋼が提案され、例えば、ＴｉＮを鋼中に微細分散させ、溶接熱影響部のオーステナイト粒の粗大化を抑制したり、溶接熱影響部においてフェライト変態核として利用する技術が実用化されている。 Since the toughness of the heat-affected zone (hereinafter, sometimes referred to as HAZ toughness or HAZ toughness) which has been subjected to high heat input welding in steel materials is reduced, various high heat input welding steels have been proposed. A technique of finely dispersing in the steel to suppress coarsening of austenite grains in the weld heat affected zone, or to use as a ferrite transformation nucleus in the weld heat affected zone has been put into practical use.
また、Ｔｉ酸化物（オキシサイド）を溶接熱影響部に分散させたり（特許文献１）、更に、硫化物（サルファイド）の形態制御により溶接熱影響部の靭性を向上させるためＣａを添加したり（特許文献２）することが提案されている。 Moreover, Ti oxide (oxycide) is dispersed in the weld heat affected zone (Patent Document 1), and Ca is added to improve the toughness of the weld heat affected zone by controlling the form of sulfide (sulfide). (Patent Document 2) has been proposed.
しかしながら、ＴｉＮを主体に利用する場合、溶接熱影響部においてＴｉＮが溶解する
温度に加熱される領域はその効果が得られず、さらには地の組織が固溶Ｔｉおよび固溶Ｎにより脆化して靭性が著しく低下するという問題があった。
However, when TiN is mainly used, the effect is not obtained in the region heated to the temperature at which the TiN dissolves in the weld heat affected zone, and the ground structure becomes brittle due to the solute Ti and solute N. There was a problem that the toughness was significantly reduced.
また、Ｔｉ酸化物を利用する技術では、酸化物を均一微細に分散させることが困難であ
るという問題があった。これに対して、酸化物の複合化等の方法で分散能を改善すべく種々の検討が行われているが、入熱量が３００ｋＪ／ｃｍを超える大入熱溶接では、溶接熱影響部においてオーステナイト粒の成長を十分に抑制することは困難であった。
Further, the technology using Ti oxide has a problem that it is difficult to disperse the oxide uniformly and finely. On the other hand, various studies have been made to improve the dispersibility by a method such as compounding oxides. However, in high heat input welding where the heat input exceeds 300 kJ / cm, austenite is applied in the heat affected zone. It was difficult to sufficiently suppress grain growth.
一方、特許文献３、４では、溶接熱影響部でのフェライト変態を促進するＣａ系非金属介在物をＣａ、Ｏ、Ｓ含有量を適正に制御することで鋼中に分散させ、靭性を向上させることが開示されている。 On the other hand, in Patent Documents 3 and 4, Ca-based nonmetallic inclusions that promote ferrite transformation in the weld heat affected zone are dispersed in steel by appropriately controlling the Ca, O, and S contents, thereby improving toughness. Is disclosed.
また、特許文献５では鋼板の化学成分と、含有する複合酸化物の粒径と個数密度を規定した技術が提案されている。特に複合酸化物を粒内フェライトの生成核であるＴｉ（Ｎｂ）窒化物、Ｂ窒化物の析出サイトとして利用するために、円相当径０．００５〜０．５μｍの複合酸化物を１００〜３０００個／ｍｍ２含有することが有効であるとしている。 Patent Document 5 proposes a technique that defines the chemical components of the steel sheet and the particle size and number density of the composite oxide contained therein. In particular, in order to use the composite oxide as a precipitation site for Ti (Nb) nitride and B nitride which are the nuclei of intragranular ferrite, a composite oxide having an equivalent circle diameter of 0.005 to 0.5 μm is used in an amount of 100 to 3000. It is said that it is effective to contain pieces / mm 2 .
さらに、特許文献６では加熱されるオーステナイトの粒成長を抑制するために、複合酸化物の粒径と個数密度、組成を規定した技術が提案されている。すなわち、円相当径で０．００５〜２μｍの酸化物粒子を単位面積あたりの個数で１００〜５０００個／ｍｍ２含有し、その組成が少なくともＣａ、Ａｌ、Ｏを含みＯを除いた元素が質量比でＣａ：５％以上、Ａｌ：５％以上であることを特徴としている。 Further, Patent Document 6 proposes a technique that regulates the particle size, number density, and composition of the composite oxide in order to suppress the grain growth of heated austenite. That is, an oxide particle having a circle equivalent diameter of 0.005 to 2 μm is contained in a number per unit area of 100 to 5000 / mm 2 , and the element contains at least Ca, Al, O and excludes O. The ratio is Ca: 5% or more and Al: 5% or more.
ところで、溶接部の破壊靭性の評価には一般的にシャルピー試験が用いられるが、より厳密な破壊力学的評価法としてはＣＴＯＤ試験やディープノッチ試験が用いられる。これらの試験は材料の元厚（全板厚）で作成される試験片にノッチを入れて評価するため、板厚効果により厚肉材ほど厳しい試験となる。 By the way, a Charpy test is generally used for evaluating the fracture toughness of a welded portion, but a CTOD test or a deep notch test is used as a more strict fracture mechanics evaluation method. Since these tests are evaluated by putting a notch in a test piece created with the original thickness of the material (total plate thickness), the thicker the material, the more severe the test.
さらに、局所的な脆化部からの破壊に律速されるため、シャルピー試験と比較して試験値を向上させることが困難で、特許文献１〜６では、大入熱溶接継手部のＣＴＯＤ試験やディープノッチ試験の試験結果を安定して向上させることができなかった。 Furthermore, since it is rate-limited by the fracture from a local embrittlement part, it is difficult to improve a test value compared with a Charpy test. In patent documents 1-6, the CTOD test of a high heat input welded joint part or The test result of the deep notch test could not be improved stably.
そこで、本発明は、降伏強度が３９０Ｎ／ｍｍ２を超える、かつ板厚が４０ｍｍ以上の、溶接入熱量が３００ｋＪ／ｃｍを超える大入熱溶接でも溶接熱影響部で優れたＣＴＯＤ試験結果が得られる溶接構造用鋼およびその製造方法を提供することを目的とする。 Therefore, the present invention provides excellent CTOD test results in the heat affected zone even in high heat input welding where the yield strength exceeds 390 N / mm 2 and the plate thickness is 40 mm or more and the welding heat input exceeds 300 kJ / cm. It is an object of the present invention to provide a welded structural steel and a method for producing the same.
ＣＴＯＤ試験やディープノッチ試験はミクロ的な脆化組織に敏感であるため、本発明者らは大入熱溶接熱影響部におけるミクロ的な脆化組織である島状マルテンサイト組織（Ｍ−Ａ）について鋭意検討し、Ｍ−Ａの形成には平均的な化学成分のみならず、凝固偏析に起因する鋼板中のミクロ偏析の状態に依存し、特にＭｎとＰの偏析度が重要であることを見出した。本発明は得られた知見を基に更に検討を加えてなされたもので、すなわち、本発明は、
１．鋼組成が、質量％で
Ｃ：０．０３〜０．０９％
Ｓｉ：０．０２〜０．１５％
Ｍｎ：１．５〜２．５％
Ａｌ：０．００５〜０．０６％
Ｐ：０．０１２％以下
Ｓ：０．０００５〜０．００５０％
Ｎｂ：０．００５〜０．０２５％
Ｔｉ：０．００５〜０．０２％
Ｎ：０．００４０〜０．００７０％
Ｃａ：０．０００５〜０．００３０％
Ｂ：０．０００５〜０．００２５％
を含み、残部鉄および不可避的不純物からなり、板厚の１／４位置におけるＭｎの偏析度が１．２以下かつＰの偏析度が１．１以下であることを特徴とする大入熱溶接熱影響部のＣＴＯＤ特性に優れる溶接構造用鋼。
２．鋼組成として、更に質量％で
Ｖ：０．０４％以下
Ｎｉ：１．０％以下
Ｃｕ：１．０％以下
Ｃｒ：０．７％以下
Ｍｏ：０．７％以下
Ｗ：０．５％以下
の１種または２種以上を含有する１記載の大入熱溶接熱影響部の溶接熱影響部のＣＴＯＤ特性に優れる溶接構造用鋼。
３．鋼組成が、質量％で
Ｃ：０．０３〜０．０９％
Ｓｉ：０．０２〜０．１５％
Ｍｎ：１．５〜２．５％
Ａｌ：０．００５〜０．０６％
Ｐ：０．０１２％以下
Ｓ：０．０００５〜０．００５０％
Ｎｂ：０．００５〜０．０２５％
Ｔｉ：０．００５〜０．０２％
Ｎ：０．００４０〜０．００７０％
Ｃａ：０．０００５〜０．００３０％
Ｂ：０．０００５〜０．００２５％
を含み、残部が鉄および不可避的不純物からなる溶鋼を、連続鋳造法により鋳造し、その際の二次冷却における凝固点近傍から１２００℃までの冷却速度を０．１℃／ｓ超え、０．５℃／ｓ未満とし、得られた鋳片を１０００〜１２００℃に加熱後、熱間圧延することを特徴とする溶接構造用鋼の製造方法。
４．鋼組成として、更に質量％で
Ｖ：０．０４％以下
Ｎｉ：１．０％以下
Ｃｕ：１．０％以下
Ｃｒ：０．７％以下
Ｍｏ：０．７％以下
Ｗ：０．５％以下
の１種または２種以上を含有する３記載の溶接構造用鋼の製造方法。
Since the CTOD test and the deep notch test are sensitive to microscopic embrittlement structures, the present inventors have developed an island-like martensite structure (MA) that is a microscopic embrittlement structure in the heat-affected zone of high heat input welding. The formation of MA is dependent not only on the average chemical composition but also on the state of microsegregation in the steel sheet due to solidification segregation, and in particular the degree of segregation of Mn and P is important. I found it. The present invention was made by further study based on the obtained knowledge, that is, the present invention is
1. Steel composition by mass% C: 0.03-0.09%
Si: 0.02-0.15%
Mn: 1.5 to 2.5%
Al: 0.005-0.06%
P: 0.012% or less S: 0.0005 to 0.0050%
Nb: 0.005 to 0.025%
Ti: 0.005-0.02%
N: 0.0040 to 0.0070%
Ca: 0.0005 to 0.0030%
B: 0.0005 to 0.0025%
High heat input welding characterized in that the segregation degree of Mn at a 1/4 position of the plate thickness is 1.2 or less and the segregation degree of P is 1.1 or less. Steel for welded structure with excellent CTOD characteristics of heat affected zone.
2. As steel composition, V: 0.04% or less Ni: 1.0% or less Cu: 1.0% or less Cr: 0.7% or less Mo: 0.7% or less W: 0.5% or less The steel for welded structures which is excellent in the CTOD characteristic of the welding heat-affected zone of the high heat input welding heat-affected zone according to 1, which contains one or more of the above.
3. Steel composition by mass% C: 0.03-0.09%
Si: 0.02-0.15%
Mn: 1.5 to 2.5%
Al: 0.005-0.06%
P: 0.012% or less S: 0.0005 to 0.0050%
Nb: 0.005 to 0.025%
Ti: 0.005-0.02%
N: 0.0040 to 0.0070%
Ca: 0.0005 to 0.0030%
B: 0.0005 to 0.0025%
And the balance of iron and inevitable impurities is cast by a continuous casting method, and the cooling rate from the vicinity of the freezing point to 1200 ° C. in the secondary cooling at that time exceeds 0.1 ° C./s, 0.5 The manufacturing method of the steel for welded structures characterized by making it less than degrees C / s and hot-rolling the obtained slab after heating to 1000-1200 degreeC.
4). As steel composition, V: 0.04% or less Ni: 1.0% or less Cu: 1.0% or less Cr: 0.7% or less Mo: 0.7% or less W: 0.5% or less 3. A method for producing a welded structural steel according to 3, comprising one or more of the above.
本発明によれば、溶接入熱量が３００ｋＪ／ｃｍを超える大入熱溶接でも溶接熱影響部の靭性に優れ、降伏強度が３９０Ｎ／ｍｍ２以上でかつ板厚が４０ｍｍ以上の溶接構造用鋼が得られ産業上極めて有用である。 According to the present invention, there is provided a welded structural steel having excellent weld toughness in the heat affected zone, high yield strength of 390 N / mm 2 or more, and a plate thickness of 40 mm or more even in high heat input welding where the heat input of welding exceeds 300 kJ / cm. It is very useful in industry.
本発明では成分組成を規定する。以下の説明において％は質量％とする。
Ｃ：０．０３〜０．０９％
Ｃは鋼の強度を向上する元素であり、本発明では、所望の強度を確保するため０．０３％以上の含有を必要とするが、０．０９％を超えると、溶接性が劣化するばかりか靭性にも悪影響がある。このため、０．０３〜０．０９％、好ましくは０．０４〜０．０８％とする。
In the present invention, the component composition is defined. In the following description, “%” means “mass%”.
C: 0.03-0.09%
C is an element that improves the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure a desired strength. However, if it exceeds 0.09%, weldability is deteriorated. There is also an adverse effect on toughness. For this reason, it is 0.03 to 0.09%, preferably 0.04 to 0.08%.
Ｓｉ：０．０２〜０．１５％
Ｓｉは脱酸元素として、また、鋼の強化元素として有効であるが、０．０２％未満の含有量ではその効果がない。一方、０．１５％を超えると鋼の表面性状を損なうばかりか靭性が極端に劣化する。従って０．０２〜０．１５％とする。
Si: 0.02-0.15%
Si is effective as a deoxidizing element and as a steel strengthening element, but if the content is less than 0.02%, the effect is not obtained. On the other hand, if it exceeds 0.15%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, it is set to 0.02 to 0.15%.
Ｍｎ：１．５〜２．５％
Ｍｎは強化元素として有効であるが、１．５％より少ないとその効果が不十分で、一方、２．５％を超えると溶接性が劣化し、鋼材コストも上昇するため、１．５〜２．５％とする。
Mn: 1.5 to 2.5%
Mn is effective as a strengthening element, but if it is less than 1.5%, its effect is insufficient. On the other hand, if it exceeds 2.5%, the weldability deteriorates and the steel material cost also increases. 2.5%.
Ｐ：０．０１２％以下
Ｐは、不純物元素として鋼材に不可避的に含有されるもので、靭性に悪影響を及ぼす。本発明では含有量とともに偏析度も規定するが、０．０１２％を超えて含有すると、偏析度を低下させても溶接部の靭性劣化が大きいので、その上限を０．０１２％とする。
P: 0.012% or less P is unavoidably contained in steel as an impurity element, and adversely affects toughness. In the present invention, the segregation degree is specified together with the content. However, if the content exceeds 0.012%, the toughness of the welded portion is greatly deteriorated even if the segregation degree is lowered, so the upper limit is made 0.012%.
Ｓ：０．０００５〜０．００５０％
Ｓは、ＨＡＺ靭性の向上に有効な分散粒子であるＣａ（ＯＳ）の構成元素として必要で、０．０００５％以上含有させる。一方、０．００５０％を超えて含有すると、母材および溶接部の靭性を劣化させるため、０．０００５〜０．００５０％とする。
S: 0.0005 to 0.0050%
S is necessary as a constituent element of Ca (OS), which is a dispersed particle effective for improving the HAZ toughness, and is contained in an amount of 0.0005% or more. On the other hand, if the content exceeds 0.0050%, the toughness of the base metal and the welded portion is deteriorated, so the content is made 0.0005 to 0.0050%.
Ａｌ：０．００５〜０．０６％
Ａｌは、脱酸剤として作用するため０．００５％以上の含有を必要とするが、０．０６％を超えて含有すると、靭性を低下させるとともに、溶接した場合に、溶接金属部の靭性を低下させる。このため、Ａｌは、０．００５〜０．０６％、好ましくは、０．０２〜０．０５％とする。
Al: 0.005-0.06%
Since Al acts as a deoxidizer, it needs to be contained in an amount of 0.005% or more. However, if contained in excess of 0.06%, the toughness is lowered and, when welded, the toughness of the weld metal part is reduced. Reduce. For this reason, Al is 0.005 to 0.06%, preferably 0.02 to 0.05%.
Ｎｂ：０．００５〜０．０２５％
Ｎｂは制御圧延を行う本発明鋼では不可欠な元素であり、制御圧延による鋼の強化のため０．００５％以上を含有させる。しかし、０．０２５％を超える多量の含有は析出硬化によりＨＡＺ靭性を低下させるので、０．００５〜０．０２５％とする。
Nb: 0.005 to 0.025%
Nb is an indispensable element in the steel of the present invention that performs controlled rolling, and is contained in an amount of 0.005% or more for strengthening the steel by controlled rolling. However, a large content exceeding 0.025% reduces the HAZ toughness by precipitation hardening, so 0.005 to 0.025%.
Ｔｉ：０．００５〜０．０２％
Ｔｉは凝固時およびその後の鋳片の冷却時にＴｉＮとなって析出し、溶接部でのオーステナイト粒の粗大化抑制に有効に作用し高靭性化に寄与する。０．００５％未満ではその効果が少なく、０．０２％を超えるとＴｉＮ粒子の粗大化によって期待する効果が得られなくなるため、０．００５〜０．０２％とする。
Ti: 0.005-0.02%
Ti precipitates as TiN during solidification and subsequent cooling of the slab, and effectively acts to suppress coarsening of austenite grains in the welded portion, thereby contributing to high toughness. If it is less than 0.005%, the effect is small, and if it exceeds 0.02%, the expected effect cannot be obtained due to the coarsening of TiN particles, so 0.005 to 0.02%.
Ｎ：０．００４０〜０．００７０％
Ｎは、ＴｉＮが上述した効果を発揮するための必要量を確保するうえで必要な元素であり、本発明では０．００４０％未満では十分なＴｉＮ量が得られず、０．００７０％を超えると溶接熱サイクルによってＴｉＮが溶解する溶接ボンド部近傍の領域における固溶Ｎ量の増加のために靭性を著しく低下させるため、０．００４０〜０．００７０％とする。
N: 0.0040 to 0.0070%
N is an element necessary for securing a necessary amount for TiN to exert the above-described effects. In the present invention, a sufficient TiN amount cannot be obtained if it is less than 0.0040%, and it exceeds 0.0070%. In order to significantly reduce the toughness due to an increase in the amount of solid solution N in the region near the weld bond where TiN is dissolved by the welding heat cycle, the content is made 0.0040 to 0.0070%.
Ｃａ：０．０００５％〜０．００３０％
Ｃａは、溶接熱影響部でのフェライト変態を促進するＣａ系非金属介在物（酸硫化物）の構成元素として必須の元素である。このような効果を発揮させるには少なくとも０．０００５％は含有することが必要であるが、０．００３０％を超えて含有しても効果が飽和するため、０．０００５％〜０．００３０％とする。
Ca: 0.0005% to 0.0030%
Ca is an essential element as a constituent element of Ca-based non-metallic inclusions (oxysulfides) that promote ferrite transformation in the weld heat affected zone. In order to exert such an effect, it is necessary to contain at least 0.0005%, but even if it exceeds 0.0030%, the effect is saturated, so 0.0005% to 0.0030% And
Ｂ：０．０００５〜０．００２５％
Ｂは溶接熱影響部でＴｉＮが溶解して放出されるＮをＢＮとして固定し、溶接部靭性の劣化を抑制する。また、ＢＮはフェライト生成核となって、組織の微細化とＭ−Ａの生成を抑し、溶接部靭性の向上に寄与する。さらに、焼入性を向上させ母材の強度確保に有効に寄与する。それらの効果は０．０００５％以上の添加で発揮され、また、０．００２５％以上添加してもその効果は飽和するため、０．０００５〜０．００２５％とする。
B: 0.0005 to 0.0025%
B fixes N which is released by dissolution of TiN in the weld heat affected zone as BN, and suppresses deterioration of toughness of the weld zone. Further, BN serves as a ferrite nuclei, suppresses the refinement of the structure and the formation of MA, and contributes to the improvement of the weld joint toughness. Furthermore, it improves hardenability and contributes effectively to securing the strength of the base material. These effects are exhibited by addition of 0.0005% or more, and even if 0.0025% or more is added, the effect is saturated, so 0.0005 to 0.0025%.
以上が本発明の基本成分組成であるが、更に特性を向上させるため、Ｖ、Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ、Ｗの一種または二種以上を含有することが可能である。 The above is the basic component composition of the present invention, but in order to further improve the characteristics, it is possible to contain one or more of V, Ni, Cu, Cr, Mo, W.
Ｖ、Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ、Ｗの一種または二種以上
Ｖ、Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ、Ｗはいずれも鋼の焼入れ性を高める元素である。圧延後の強度上昇に直接寄与するとともに、靭性、高温強度、あるいは耐候性などの機能向上のために添加するが、過度の添加は靭性や溶接性を劣化させるため、添加する場合は、それぞれ上限をＶ：０．０４％、Ｎｉ：１．０％、Ｃｕ：１．０％、Ｃｒ：０．７％、Ｍｏ：０．７％、Ｗ：０．５％とする。一方、Ｖ、Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ、Ｗの添加量はそれぞれが０．０１％未満であるとその効果が現れないため、０．０１％以上の添加とする。
One or more of V, Ni, Cu, Cr, Mo, and W V, Ni, Cu, Cr, Mo, and W are all elements that enhance the hardenability of steel. It contributes directly to the strength increase after rolling, and is added to improve functions such as toughness, high-temperature strength, or weather resistance, but excessive addition degrades toughness and weldability. V: 0.04%, Ni: 1.0%, Cu: 1.0%, Cr: 0.7%, Mo: 0.7%, W: 0.5%. On the other hand, if the added amount of V, Ni, Cu, Cr, Mo, W is less than 0.01%, the effect does not appear.
板厚の１／４位置（板厚１／４ｔ部ともいう）におけるＭｎの偏析度が１．２以下かつＰの偏析度が１．１以下
さらに本発明においては、大入熱溶接熱影響部におけるミクロ的な脆化組織である島状マルテンサイト組織（Ｍ−Ａ）の生成を抑制するため、鋼板の板厚の１／４位置の凝固偏析によるＭｎの偏析度を１．２以下かつＰの偏析度を１．１以下とする。
Mn segregation degree is 1.2 or less and P segregation degree is 1.1 or less at a 1/4 position of the plate thickness (also referred to as a 1/4 t portion of the plate thickness). In order to suppress the formation of island-like martensite structure (MA), which is a microscopic embrittlement structure, the segregation degree of Mn by solidification segregation at 1/4 position of the thickness of the steel sheet is 1.2 or less and P The segregation degree is 1.1 or less.
Ｍｎの偏析度を１．２以下かつＰの偏析度を１．１以下とすることによりＭ−Ａはほとんど形成されず、優れたＣＴＯＤ試験結果やディープノッチ試験結果が得られる。 When the segregation degree of Mn is 1.2 or less and the segregation degree of P is 1.1 or less, MA is hardly formed, and excellent CTOD test results and deep notch test results are obtained.
偏析度の測定方法は以下の通りである。Ｍｎ、Ｐの標準試料を準備するため、小型の溶解炉でＰの含有量とＭｎの含有量を少なくとも３種類に変化させた鋼を作製する。その後、この鋼片を１２５０℃で４８時間以上保持して、ミクロ偏析を拡散させて、その後のＥＰＭＡ測定の標準試料とする。 The method for measuring the degree of segregation is as follows. In order to prepare standard samples of Mn and P, steel in which the content of P and the content of Mn are changed to at least three types in a small melting furnace is produced. Then, this steel piece is hold | maintained at 1250 degreeC for 48 hours or more, a microsegregation is diffused, and it is set as the standard sample of subsequent EPMA measurement.
偏析度を評価する鋼板の板厚の１／４ｔ部より試験片を採取して鏡面に研磨する。まず、測定条件を定め、標準試料のＥＰＭＡ分析を行ない、信号強度とＰ、Ｍｎの含有量の関係を採取し、いわゆる検量線を作成する。電子ビームのスポット径は１μｍが好ましい。 A test piece is sampled from a 1/4 t portion of the thickness of the steel plate to be evaluated for the degree of segregation and polished to a mirror surface. First, measurement conditions are determined, EPMA analysis of a standard sample is performed, a relationship between signal intensity and P and Mn contents is collected, and a so-called calibration curve is created. The spot diameter of the electron beam is preferably 1 μm.
次に偏析度を評価するサンプルについて同一条件にてＥＰＭＡ分析を０．５ｍｍ×０．５ｍｍの領域をスポット径１μｍ、１μｍステップで元素マッピングを行い、Ｍｎ、Ｐの信号強度の測定を行なう。 Next, EPMA analysis is performed on the sample for evaluating the degree of segregation under the same conditions, elemental mapping is performed in an area of 0.5 mm × 0.5 mm in steps of a spot diameter of 1 μm and 1 μm, and the signal intensity of Mn and P is measured.
得られた信号強度の値を検量線によりＭｎ、Ｐ濃度に変換し、マッピングした中の最大濃度と鋼板の平均濃度との比をとり偏析度とする。 The obtained signal intensity value is converted into Mn and P concentrations using a calibration curve, and the ratio between the maximum concentration in the mapping and the average concentration of the steel sheet is taken as the segregation degree.
本発明に係る鋼板は以下の製造方法で製造することが可能である。 The steel plate according to the present invention can be manufactured by the following manufacturing method.
上記成分組成の溶鋼を、転炉等で溶製し、連続鋳造等で鋼素材（スラブ）とする際、二次冷却における凝固点近傍から１２００℃までの冷却速度をを０．１℃／ｓ超え、０．５℃／ｓ未満とする。 When the molten steel having the above composition is melted in a converter or the like and made into a steel material (slab) by continuous casting or the like, the cooling rate from the vicinity of the freezing point to 1200 ° C in the secondary cooling exceeds 0.1 ° C / s. And less than 0.5 ° C./s.
ミクロ偏析は凝固時に不可避的に形成されるが、凝固後は元素の拡散により偏析度は小さくなる。この効果は凝固後、高温での滞留時間が長いほど大きく、１２００℃以下では合金元素の拡散係数が小さく偏析低減効果が大きくないので、凝固点近傍〜１２００℃での冷却条件を０．１℃／ｓ超え、０．５℃／ｓ未満とする。 Microsegregation is unavoidably formed during solidification, but the degree of segregation decreases after solidification due to element diffusion. This effect is greater as the residence time at high temperature is longer after solidification, and at 1200 ° C. or less, the diffusion coefficient of the alloy element is small and the effect of reducing segregation is not significant. More than s and less than 0.5 ° C./s.
冷却速度が０．５℃／ｓ以上であると、１２００℃以上の滞留時間が少なく、拡散が不十分でＭｎの偏析度が１．２以下かつＰの偏析度が１．１以下にならない。一方、冷却速度が０．１℃／ｓ以下であると鋳造の能率が下がるとともに、ＴｉＮが粗大化してピンニング効果が十分得られず溶接部でのオーステナイト粒が粗大化しＨＡＺ靭性が低下する。 When the cooling rate is 0.5 ° C./s or more, the residence time of 1200 ° C. or more is small, the diffusion is insufficient, the segregation degree of Mn is 1.2 or less, and the segregation degree of P is not 1.1 or less. On the other hand, when the cooling rate is 0.1 ° C./s or less, the casting efficiency is lowered, TiN is coarsened, and a pinning effect is not sufficiently obtained, and austenite grains in the welded portion are coarsened and HAZ toughness is lowered.
得られたスラブを、１０００〜１２００℃の温度に加熱してから熱間圧延を行う。加熱温度が１０００℃未満であると、圧延能率が低下し、一方、１２００℃超えであるとオーステナイト粒が粗大化し、靭性の低下を招くばかりか、酸化ロスが顕著となり、歩留が低下するので、加熱温度は１０００〜１２００℃とする。 The obtained slab is heated to a temperature of 1000 to 1200 ° C. and then hot-rolled. When the heating temperature is less than 1000 ° C., the rolling efficiency is lowered. On the other hand, when it is more than 1200 ° C., the austenite grains become coarse, leading to a decrease in toughness, leading to a significant oxidation loss and a decrease in yield. The heating temperature is 1000 to 1200 ° C.
靭性の観点から好ましい加熱温度の範囲は１０５０〜１１５０℃、より好ましくは１０５０〜１１００℃である。 The range of preferable heating temperature from the viewpoint of toughness is 1050 to 1150 ° C, more preferably 1050 to 1100 ° C.
その後、熱間圧延により所望の板厚に圧延するが、強度とともに母材靭性も要求されることが多いので制御圧延を行い、仕上温度は９００〜６５０℃の範囲が好ましく、より好ましくは、８００〜７００℃の範囲である。さらに、高強度化のためには圧延後に適宜、加速冷却を適用する。 Then, although it rolls to desired plate | board thickness by hot rolling, since a base material toughness is often requested | required with intensity | strength, a controlled rolling is performed and the finishing temperature has the preferable range of 900-650 degreeC, More preferably, 800 It is the range of -700 degreeC. Furthermore, accelerated cooling is applied as appropriate after rolling to increase the strength.
表１に示す種々の組成の溶鋼（鋼記号Ａ〜Ｗ）を、転炉で溶製後、連続鋳造法で２８０ｍｍ厚の鋼素材（スラブ）とし、熱間圧延により板厚５０〜７０ｍｍの厚鋼板とした後、種々の条件で冷却しＮｏ．１〜２３の供試鋼を得た。 The molten steels (steel symbols A to W) having various compositions shown in Table 1 are melted in a converter and then made into a steel material (slab) having a thickness of 280 mm by a continuous casting method, and a thickness of 50 to 70 mm is obtained by hot rolling. After making the steel plate, it was cooled under various conditions and No. Sample steels 1 to 23 were obtained.
表２に連続鋳造の場合の二次冷却条件として凝固点近傍から１２００℃の冷却速度、鋼素材（スラブ）の加熱条件、圧延条件および冷却条件を示す。 Table 2 shows the cooling rate at 1200 ° C. from the vicinity of the freezing point, the heating condition of the steel material (slab), the rolling condition, and the cooling condition as secondary cooling conditions in the case of continuous casting.
得られた厚鋼板について、板厚の１／４部よりΦ１４のＪＩＳ１４Ａ号試験片を採取し、引張試験を行い、降伏点（ＹＳ）、引張強さ（ＴＳ）を測定し、板厚の１／４部よりＪＩＳ４号衝撃試験片を採取し、シャルピー試験を行って、破面遷移温度（ｖＴｒｓ）を求めた。 About the obtained thick steel plate, Φ14 JIS14A test piece was collected from 1/4 part of the plate thickness, subjected to a tensile test, and measured for yield point (YS) and tensile strength (TS). A JIS No. 4 impact test piece was collected from / 4 part, and a Charpy test was performed to determine the fracture surface transition temperature (vTrs).
また、板厚１／４ｔ部より試験片を採取して鏡面に研磨し、ＥＰＭＡ分析により０．５ｍｍ×０．５ｍｍの領域をスポット径１μｍ、１μｍステップで元素マッピングを行い、Ｍｎ、Ｐの濃度分布の測定を行った。マッピングした中の最大濃度と鋼板の平均濃度との比をとり偏析度とした。 In addition, a test piece was collected from a 1/4 t part of the plate thickness, polished to a mirror surface, and subjected to elemental mapping in an area of 0.5 mm × 0.5 mm with a spot diameter of 1 μm and 1 μm steps by EPMA analysis, and the concentrations of Mn and P Distribution measurements were taken. The ratio between the maximum concentration in the mapping and the average concentration of the steel sheet was taken as the degree of segregation.
さらに、各鋼板から採取した継手用試験板に、Ｖ開先を施し、エレクトロガスアーク溶接（溶接入熱450ｋJ/cm)により大入熱溶接継手を作製した。これら溶接継手からノッチ位置をボンド部とするＣＴＯＤ試験片を採取し、ＢＳ７４４８にしたがい、３点曲げＣＴＯＤ試験を実施した。試験は−１０℃で３体行い、その最低値を求めた。 Furthermore, V groove was given to the joint test plate taken from each steel plate, and a large heat input welded joint was produced by electrogas arc welding (welding heat input 450 kJ / cm). From these welded joints, CTOD test pieces having the notch position as the bond portion were sampled and subjected to a three-point bending CTOD test in accordance with BS7448. Three tests were performed at -10 ° C, and the minimum value was determined.
表３にＭｎ、Ｐの偏析度と母材機械的特性の試験結果と大入熱溶接継手のＣＴＯＤ試験結果を併せて示す。表より、製造Ｎｏ．１〜１６の本発明鋼は−１０℃での限界ＣＴＯＤが０．２５ｍｍ以上と優れた破壊靭性値を示したが、製造Ｎｏ．１７〜２３の比較例はいずれも０．１ｍｍ以下であった。 Table 3 shows the test results of the segregation degree of Mn and P, the base material mechanical properties, and the CTOD test results of the high heat input welded joint. From the table, production No. Inventive steels Nos. 1 to 16 showed excellent fracture toughness values of 0.25 mm or more at the critical CTOD at -10 ° C. The comparative examples 17-23 were all 0.1 mm or less.
Claims (4)
Ｃ：０．０３〜０．０９％
Ｓｉ：０．０２〜０．１５％
Ｍｎ：１．５〜２．５％
Ａｌ：０．００５〜０．０６％
Ｐ：０．０１２％以下
Ｓ：０．０００５〜０．００５０％
Ｎｂ：０．００５〜０．０２５％
Ｔｉ：０．００５〜０．０２％
Ｎ：０．００４０〜０．００７０％
Ｃａ：０．０００５〜０．００３０％
Ｂ：０．０００５〜０．００２５％
を含み、残部鉄および不可避的不純物からなり、板厚の１／４位置におけるＭｎの偏析度が１．２以下かつＰの偏析度が１．１以下であることを特徴とする大入熱溶接熱影響部のＣＴＯＤ特性に優れる溶接構造用鋼。 Steel composition by mass% C: 0.03-0.09%
Si: 0.02-0.15%
Mn: 1.5 to 2.5%
Al: 0.005-0.06%
P: 0.012% or less S: 0.0005 to 0.0050%
Nb: 0.005 to 0.025%
Ti: 0.005-0.02%
N: 0.0040 to 0.0070%
Ca: 0.0005 to 0.0030%
B: 0.0005 to 0.0025%
High heat input welding characterized in that the segregation degree of Mn at a 1/4 position of the plate thickness is 1.2 or less and the segregation degree of P is 1.1 or less. Steel for welded structure with excellent CTOD characteristics of heat affected zone.
Ｖ：０．０４％以下
Ｎｉ：１．０％以下
Ｃｕ：１．０％以下
Ｃｒ：０．７％以下
Ｍｏ：０．７％以下
Ｗ：０．５％以下
の１種または２種以上を含有する請求項１記載の大入熱溶接熱影響部のＣＴＯＤ特性に優れる溶接構造用鋼。 As steel composition, V: 0.04% or less Ni: 1.0% or less Cu: 1.0% or less Cr: 0.7% or less Mo: 0.7% or less W: 0.5% or less The steel for welded structures which is excellent in the CTOD characteristic of the high heat input welding heat-affected zone according to claim 1, comprising one or more of the above.
鋼組成が、質量％で
Ｃ：０．０３〜０．０９％
Ｓｉ：０．０２〜０．１５％
Ｍｎ：１．５〜２．５％
Ａｌ：０．００５〜０．０６％
Ｐ：０．０１２％以下
Ｓ：０．０００５〜０．００５０％
Ｎｂ：０．００５〜０．０２５％
Ｔｉ：０．００５〜０．０２％
Ｎ：０．００４０〜０．００７０％
Ｃａ：０．０００５〜０．００３０％
Ｂ：０．０００５〜０．００２５％
を含み、残部が鉄および不可避的不純物からなる溶鋼を、連続鋳造法により鋳造し、その際の二次冷却における凝固点近傍から１２００℃までの冷却速度を０．１℃／ｓ超え、０．５℃／ｓ未満とし、得られた鋳片を１０００〜１２００℃に加熱後、熱間圧延することを特徴とする溶接構造用鋼の製造方法。 A method for producing a welded structural steel according to claim 1 or 2,
Steel composition by mass% C: 0.03-0.09%
Si: 0.02-0.15%
Mn: 1.5 to 2.5%
Al: 0.005-0.06%
P: 0.012% or less S: 0.0005 to 0.0050%
Nb: 0.005 to 0.025%
Ti: 0.005-0.02%
N: 0.0040 to 0.0070%
Ca: 0.0005 to 0.0030%
B: 0.0005 to 0.0025%
And the balance of iron and inevitable impurities is cast by a continuous casting method, and the cooling rate from the vicinity of the freezing point to 1200 ° C. in the secondary cooling at that time exceeds 0.1 ° C./s, 0.5 The manufacturing method of the steel for welded structures characterized by making it less than degrees C / s and hot-rolling the obtained slab after heating to 1000-1200 degreeC.
Ｖ：０．０４％以下
Ｎｉ：１．０％以下
Ｃｕ：１．０％以下
Ｃｒ：０．７％以下
Ｍｏ：０．７％以下
Ｗ：０．５％以下の１種または２種以上を含有する請求項３記載の溶接構造用鋼の製造方法。 As steel composition, V: 0.04% or less Ni: 1.0% or less Cu: 1.0% or less Cr: 0.7% or less Mo: 0.7% or less W: 0.5% or less The manufacturing method of the steel for welded structures of Claim 3 containing 1 type, or 2 or more types of these.
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