JP6187270B2 - Steel material with excellent toughness at heat affected zone - Google Patents
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- 229910000831 Steel Inorganic materials 0.000 title claims description 101
- 239000010959 steel Substances 0.000 title claims description 101
- 239000000463 material Substances 0.000 title claims description 62
- 239000002131 composite material Substances 0.000 claims description 66
- 239000002245 particle Substances 0.000 claims description 41
- 229910052748 manganese Inorganic materials 0.000 claims description 15
- 229910052749 magnesium Inorganic materials 0.000 claims description 14
- 229910052782 aluminium Inorganic materials 0.000 claims description 11
- 239000012535 impurity Substances 0.000 claims description 8
- 239000000203 mixture Substances 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 7
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 238000003466 welding Methods 0.000 description 36
- 230000000694 effects Effects 0.000 description 35
- 229910001566 austenite Inorganic materials 0.000 description 26
- 239000011572 manganese Substances 0.000 description 21
- 229910052760 oxygen Inorganic materials 0.000 description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 16
- 239000001301 oxygen Substances 0.000 description 16
- 229910052761 rare earth metal Inorganic materials 0.000 description 14
- 238000010438 heat treatment Methods 0.000 description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 229910052799 carbon Inorganic materials 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- 230000003749 cleanliness Effects 0.000 description 6
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- 238000002844 melting Methods 0.000 description 6
- 230000008018 melting Effects 0.000 description 6
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 230000002411 adverse Effects 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 238000010276 construction Methods 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 229910052596 spinel Inorganic materials 0.000 description 4
- 239000011029 spinel Substances 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- 239000010953 base metal Substances 0.000 description 3
- 238000005261 decarburization Methods 0.000 description 3
- 238000007872 degassing Methods 0.000 description 3
- 238000000605 extraction Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 238000005096 rolling process Methods 0.000 description 3
- 229910052717 sulfur Inorganic materials 0.000 description 3
- 238000001816 cooling Methods 0.000 description 2
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 230000001629 suppression Effects 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910000532 Deoxidized steel Inorganic materials 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 229910020068 MgAl Inorganic materials 0.000 description 1
- 229910001122 Mischmetal Inorganic materials 0.000 description 1
- 229910016583 MnAl Inorganic materials 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical group [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
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- 238000009749 continuous casting Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
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- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
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- 230000008569 process Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000002407 reforming Methods 0.000 description 1
- 229910052706 scandium Inorganic materials 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 238000010407 vacuum cleaning Methods 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
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- Treatment Of Steel In Its Molten State (AREA)
Description
本発明は、溶接熱影響部(Heat Affected Zone)の靱性に優れた鋼材に関する。特に、近年要求の高まっている溶接入熱量が３００ｋＪ／ｃｍ以上の大入熱溶接を実施した場合であっても、溶接熱影響部において優れた靭性を有する鋼材に関するものである。 The present invention relates to a steel material excellent in toughness of a heat affected zone (Heat Affected Zone). In particular, the present invention relates to a steel material having excellent toughness in the weld heat-affected zone even when a high heat input welding with a heat input of 300 kJ / cm or more, which has been increasingly demanded in recent years, is performed.
建築、橋梁、造船、ラインパイプ、建設機械、海洋構造物、タンクなどの各種溶接鋼構造物に用いられる鋼材は、溶接部の破壊に対する安全性および信頼性を高めるため、靱性に対する要求が年々厳しさを増している。特に、母材鋼板の靭性と同様に、溶接熱影響部においてもより優れた靱性を有することが求められている。 Steel materials used in various types of welded steel structures such as buildings, bridges, shipbuilding, line pipes, construction machinery, offshore structures, tanks, etc., are increasingly demanding toughness year by year in order to improve safety and reliability against fracture of welds. It is increasing. In particular, similar to the toughness of the base steel sheet, it is required to have a better toughness in the weld heat affected zone.
溶接熱影響部は、溶融線近傍では１４００℃以上に加熱され、冷却後の組織中のオーステナイト(γ)粒が著しく粗大化する。その結果、溶接熱影響部の靱性が劣化する。この傾向は溶接入熱量が大きくなるほど顕著である。 The weld heat affected zone is heated to 1400 ° C. or more in the vicinity of the melting line, and austenite (γ) grains in the structure after cooling are significantly coarsened. As a result, the toughness of the weld heat affected zone deteriorates. This tendency becomes more prominent as the welding heat input increases.
一方で、この種の溶接鋼構造物において、溶接施工コストは、建造コストに占める割合が大きいため、高能率の溶接法が用いられるようになった。特に、溶接施工コストの低減には溶接パス数を減らすことが最も有効であるので、大入熱溶接を行うことが望ましい。しかし、大入熱溶接を行った場合、溶接熱影響部靭性が低下することは避けられない。したがって、靭性の要求が厳しい溶接鋼構造物に対しては、入熱を制限して溶接パス数を増やし、能率と経済性を犠牲にして溶接施工せざるを得ないという問題点があった。 On the other hand, in this type of welded steel structure, since the welding construction cost accounts for a large proportion of the construction cost, a highly efficient welding method has come to be used. In particular, reducing the number of welding passes is most effective for reducing the welding construction cost, so it is desirable to perform high heat input welding. However, when high heat input welding is performed, it is inevitable that the weld heat-affected zone toughness decreases. Therefore, for welded steel structures with severe toughness requirements, there has been a problem that the number of welding passes is limited by restricting heat input, and welding must be performed at the expense of efficiency and economy.
これらの問題を解決するため、大入熱溶接溶接熱影響部靱性を改善するための種々の対策が実施されてきた。 In order to solve these problems, various measures have been implemented to improve the toughness of the high heat input welding heat affected zone.
例えば、特許文献１には、粗大な旧オーステナイト粒の内部に、Ｔｉ酸化物あるいはさらにＴｉ窒化物との複合体を核とした粒内変態フェライトを積極的に生成させ、溶接熱影響部靱性の向上を図ることが開示されている。 For example, in Patent Document 1, intragranular ferrite with a core of a composite of Ti oxide or further Ti nitride is actively generated inside coarse prior austenite grains, and the toughness of the weld heat affected zone is improved. Improvements are disclosed.
特許文献２には、主として微細Ｔｉ２Ｏ３と微細ＴｉＮを核とした粒内変態フェライトを積極的に生成させ、溶接熱影響部靱性の向上を図ることが開示されている。 Patent Document 2 discloses that intragranular transformed ferrite mainly composed of fine Ti 2 O 3 and fine TiN is actively generated to improve the weld heat affected zone toughness.
特許文献３には、ＴｉＮとＭｎＳの複合析出物を核とした粒内変態フェライトを積極的に生成させ、溶接熱影響部靱性の向上を図ることが開示されている。 Patent Document 3 discloses that an intragranular ferrite having a composite precipitate of TiN and MnS as a nucleus is actively generated to improve the toughness of the weld heat affected zone.
特許文献４には、ＴｉとＲＥＭの複合添加により、異常に粗大な旧オーステナイト粒の発生を防止することで、溶接熱影響部靱性のバラツキを抑制することが開示されている。 Patent Document 4 discloses that the addition of Ti and REM prevents the generation of abnormally coarse prior austenite grains, thereby suppressing the variation in weld heat affected zone toughness.
特許文献５には、微細なＭｇＯを鋼中に分散させ、ピン止め効果、粒内変態を利用して、溶接熱影響部靱性の向上を図ることが開示されている。 Patent Document 5 discloses that fine MgO is dispersed in steel and the toughness of the weld heat affected zone is improved by utilizing the pinning effect and intragranular transformation.
特許文献６および７には、ＭｇＯを核としてその周辺にＴｉＮを有するＭｇＯ−ＴｉＮ複合介在物を鋼中に分散させ、ピン止め効果、粒内変態を利用して、溶接熱影響部靱性の向上を図ることが開示されている。 In Patent Documents 6 and 7, MgO-TiN composite inclusions with MgO as the core and TiN around them are dispersed in steel, and the pinning effect and intragranular transformation are utilized to improve the weld heat affected zone toughness. Is disclosed.
特許文献８には、ＭｇＯ、ＭｇＳおよびＭｇ（Ｏ、Ｓ）のうちの２種以上を鋼中に分散させ、ピン止め効果、粒内変態を利用して、溶接熱影響部靱性の向上を図ることが開示されている。 In Patent Document 8, two or more of MgO, MgS, and Mg (O, S) are dispersed in steel, and the toughness of the weld heat affected zone is improved by utilizing the pinning effect and intragranular transformation. It is disclosed.
特許文献９には、ＭｇＡｌ２Ｏ４を核としてその周辺にＴｉＮを有するＭｇＡｌ２Ｏ４−ＴｉＮ複合介在物を鋼中に分散させ、ピン止め効果、粒内変態を利用して、溶接熱影響部靱性の向上を図ることが開示されている。 In Patent Document 9, MgAl 2 O 4 —TiN composite inclusions having MgN 2 O 4 as a nucleus and TiN around the core are dispersed in steel, and the effect of welding heat is influenced by utilizing the pinning effect and intragranular transformation. It is disclosed to improve the toughness of the part.
しかし、特許文献１〜４に記載の鋼材では、溶接入熱量が３００ｋＪ／ｃｍ以上となって、加熱温度が１４００℃にもなる溶融線近傍では、炭化物や窒化物が溶解・粗大化し、旧オーステナイト粒界の移動をピンニングする力が低下し、旧オーステナイト粒の成長を十分に抑えることはできなかった。したがって、このような大入熱溶接溶接熱影響部においては、十分な靱性を得ることが困難であった。 However, in the steel materials described in Patent Documents 1 to 4, carbide and nitride are dissolved and coarsened in the vicinity of the melting line where the heat input of welding is 300 kJ / cm or more and the heating temperature is 1400 ° C. The force for pinning the movement of grain boundaries was reduced, and the growth of prior austenite grains could not be sufficiently suppressed. Therefore, it has been difficult to obtain sufficient toughness in such a high heat input welding heat affected zone.
また、特許文献５〜９に記載の鋼材では、溶融線近傍での加熱温度が１４００℃以上となっても、Ｍｇ系介在物は安定な酸化物である。このため、溶接入熱量が３００ｋＪ／ｃｍ以上となる大入熱溶接により溶融線近傍での加熱温度が１４００℃にも及んでも、これらのＭｇ系介在物からなる酸化物が上昇しても消失することはない。その結果、旧オーステナイト粒界の移動をピンニングする力は低下しない。しかし、これらのＭｇ系介在物からなる酸化物では、十分なピンニング効果は得られず、旧オーステナイト粒の粗大化を十分に抑制できないことが分かった。 Moreover, in the steel materials described in Patent Documents 5 to 9, even if the heating temperature in the vicinity of the melting line is 1400 ° C. or higher, the Mg-based inclusion is a stable oxide. For this reason, even if the heating temperature in the vicinity of the melting line reaches 1400 ° C. due to high heat input welding with a welding heat input of 300 kJ / cm or more, it disappears even if the oxides composed of these Mg-based inclusions rise. Never do. As a result, the force for pinning the movement of the prior austenite grain boundaries does not decrease. However, it has been found that oxides composed of these Mg-based inclusions cannot obtain a sufficient pinning effect and cannot sufficiently suppress coarsening of prior austenite grains.
本発明は、このような課題に鑑みてなされたものであって、溶接入熱量が３００ｋＪ／ｃｍ以上となる大入熱溶接を実施した場合であっても、旧オーステナイト粒の粗大化を抑制し、もって優れた溶接熱影響部靭性を有する鋼を提供することを目的とする。 The present invention has been made in view of such problems, and suppresses coarsening of prior austenite grains even when high heat input welding is performed in which the heat input of welding is 300 kJ / cm or more. Therefore, an object of the present invention is to provide a steel having excellent weld heat affected zone toughness.
本発明者等は、３００ｋＪ／ｃｍ以上の大入熱溶接したときであっても、より安定した旧オーステナイト粒の粗大化抑制効果を発現し、溶接熱影響部における靱性を確保するために、種々の検討と実験を行った。その結果、次の(a)〜(d)に示す知見を得た。 In order to secure the toughness in the weld heat affected zone, the present inventors have exhibited a more stable effect of suppressing the coarsening of prior austenite grains even when high heat input welding of 300 kJ / cm or more is performed. Were examined and experimented. As a result, the following findings (a) to (d) were obtained.
(a) １４００℃以上の高温でも熱的に安定である（ＭｎＳ＋Ｍｎ、Ｍｇ系スピネル）複合介在物、具体的には、ＭｇとＭｎとＡｌからなる酸化物とＭｎＳからなる複合介在物を鋼中に分散させる。この複合介在物は、溶接入熱量が３００ｋＪ／ｃｍ以上となる大入熱溶接により鋼材温度が上昇しても、消失することはない。このため、旧オーステナイト粒界の移動をピンニングする力は低下しないので、この複合介在物によるピン止め効果と粒内変態を利用すれば、溶接熱影響部靱性の向上を図ることができる。 (a) A composite inclusion that is thermally stable even at a high temperature of 1400 ° C. or higher (MnS + Mn, Mg-based spinel), specifically, an oxide comprising Mg, Mn, and Al and a composite inclusion comprising MnS in steel. To disperse. This composite inclusion does not disappear even if the steel material temperature rises due to high heat input welding with a welding heat input of 300 kJ / cm or more. For this reason, the force for pinning the movement of the prior austenite grain boundaries does not decrease. Therefore, if the pinning effect and intragranular transformation by this composite inclusion are used, the weld heat affected zone toughness can be improved.
(b) ただし、この複合介在物は微細かつ多量に分散・生成させることによってはじめて十分なピンニング効果が得られることが分かった。具体的には、粒径０．６μｍ未満の複合介在物が鋼中に１×１０６個／ｍｍ３以上で存在する必要がある。複合介在物は、粒径０．６μｍ未満のものが鋼中に１×１０６個／ｍｍ３以上で存在していればよく、この複合介在物の粒径が０．６μｍ以上のものが存在しても構わない。ただし、複合介在物の個数が多く生成しすぎると一旦生成した複合介在物が凝集して粗大な複合介在物になりやすくなる。その結果、粒径０．６μｍ未満の個数が１×１０６個／ｍｍ３未満となりやすく、この場合、旧オーステナイト粒界の移動を十分にピンニングすることはできない。 (b) However, it has been found that a sufficient pinning effect can be obtained only by dispersing and generating this complex inclusion in a fine and large amount. Specifically, composite inclusions having a particle size of less than 0.6 μm need to be present in steel at 1 × 10 6 pieces / mm 3 or more. Composite inclusions with a particle size of less than 0.6 μm need only be present in steel at 1 × 10 6 pieces / mm 3 or more, and those with a composite inclusion particle size of 0.6 μm or more exist. It doesn't matter. However, if the number of composite inclusions is too large, the composite inclusions once generated tend to aggregate and become coarse composite inclusions. As a result, the number of particles having a particle size of less than 0.6 μm tends to be less than 1 × 10 6 / mm 3 , and in this case, the movement of the prior austenite grain boundaries cannot be sufficiently pinned.
(c) この複合介在物を鋼中に微細かつ多量に分散・生成させるためには、鋼中のＳ、Ｓｉ、Ｏ（酸素）の各含有量の制御に加えて、鋼中の酸不溶性Ａｌ（以下、「Insol.Ａｌ」と略記する。）、酸可溶性Ａｌ（以下、「sol.Ａｌ」と略記する。）、酸不溶性Ｍｇ（以下、「Insol.Ｍｇ」と略記する。）および酸可溶性Ｍｇ（以下、「sol.Ｍｇ」と略記する。）の各含有量を適正範囲に制御すると、微細なＭｇとＭｎとＡｌからなる酸化物の上に微細ＭｎＳを析出させてなる微細な複合介在物を鋼中に微細かつ多量に分散して析出させることができ、オーステナイト変態した直後の旧オーステナイト初期粒径の微細化効果を発現するので、旧オーステナイト粒の粗大化を抑制できることが分かった。 (c) In order to disperse and produce this composite inclusion in steel in a fine and large amount, in addition to controlling the contents of S, Si and O (oxygen) in steel, acid-insoluble Al in steel (Hereinafter abbreviated as “Insol.Al”), acid-soluble Al (hereinafter abbreviated as “sol.Al”), acid-insoluble Mg (hereinafter abbreviated as “Insol.Mg”), and acid-soluble When the content of Mg (hereinafter abbreviated as “sol.Mg”) is controlled within an appropriate range, a fine composite interposition formed by precipitating fine MnS on fine Mg, Mn, and Al oxides. It was found that the material can be finely dispersed in a large amount in the steel and precipitated, and the effect of refinement of the initial grain size of the prior austenite immediately after the austenite transformation is exhibited, so that the coarsening of the prior austenite grains can be suppressed.
(d)さらにＮｂを適切な量添加し、粒径０．６μｍ未満のＮｂ炭化物を鋼中に１×１０５個／ｍｍ３以上存在させることができる。Ｎｂ炭化物は、加熱温度が１４００℃なる溶融線近傍では、一部炭化物が溶解・粗大化するが、上記複合介在物の効果に加えてさらに粗大化抑制効果が高まることがわかった。 (d) Further, an appropriate amount of Nb can be added, and Nb carbide having a particle size of less than 0.6 μm can be present in steel at 1 × 10 5 pieces / mm 3 or more. It has been found that Nb carbide partially dissolves and coarsens in the vicinity of the melting line where the heating temperature is 1400 ° C., but in addition to the effect of the composite inclusion, the coarsening suppression effect is further increased.
本発明は、このような知見に基づいて完成したものであり、その要旨は、下記の(1)〜(5)の溶接熱影響部靱性に優れた鋼材にある。 The present invention has been completed on the basis of such knowledge, and the gist thereof is the steel material excellent in the weld heat affected zone toughness of the following (1) to (5).
(1) 質量％で、
Ｃ：０．０２〜０．２５％、
Ｓｉ：０．０００１〜０．４％、
Ｍｎ：０．５〜２．０％、
Ｓ：０．００１〜０．０５０％、
Ｏ：０．００１〜０．００５％、
Insol.Ａｌ：０．０００１〜０．００５％、
sol.Ａｌ：０．０００１〜０．０００５％、
Insol.Ｍｇ：０．０００１〜０．００５％、
sol.Ｍｇ：０．０００１〜０．０００５％、
Ｎｂ：０．０１〜０．０５％、
Ｃｕ：０〜１．０％、
Ｎｉ：０〜１．０％、
Ｃｒ：０〜０．５％、
Ｍｏ：０〜０．５％、
Ｖ：０〜０．２％、
Ｂ：０〜０．０００５％、
Ｃａ：０〜０．００５％、
ＲＥＭ：０〜０．００５％、
Ｔｉ：０〜０．０２％、
Ｓｎ：０〜０．５％、
残部：Ｆｅおよび不純物、
不純物としてのＰおよびＮが
Ｐ：０．０３％以下、
Ｎ：０．００６％以下、
である化学組成を有し、
粒径が０．６μｍ未満である、ＭｇとＭｎとＡｌからなる酸化物およびＭｎＳからなる複合介在物が鋼材中に１×１０６個／ｍｍ３以上存在し、かつ、
粒径が０．６μｍ未満であるＮｂ炭化物が鋼材中に１×１０5個／ｍｍ３以上存在する、
溶接熱影響部の靱性に優れた鋼材。
(1) By mass%
C: 0.02 to 0.25%,
Si: 0.0001 to 0.4%,
Mn: 0.5 to 2.0%
S: 0.001 to 0.050%,
O: 0.001 to 0.005%,
Insol.Al: 0.0001 to 0.005%,
sol.Al: 0.0001 to 0.0005%,
Insol.Mg: 0.0001 to 0.005%,
sol.Mg: 0.0001 to 0.0005%,
Nb: 0.01-0.05%
Cu: 0 to 1.0%
Ni: 0 to 1.0%,
Cr: 0 to 0.5%,
Mo: 0 to 0.5%,
V: 0 to 0.2%,
B: 0 to 0.0005%,
Ca: 0 to 0.005%,
REM: 0 to 0.005%,
Ti: 0 to 0.02%,
Sn: 0 to 0.5%,
Balance: Fe and impurities,
P and N as impurities are P: 0.03% or less,
N: 0.006% or less,
Having a chemical composition of
1 × 10 6 particles / mm 3 or more exist in the steel material in which the particle diameter is less than 0.6 μm, and the composite inclusion composed of an oxide composed of Mg, Mn and Al and MnS, and
Nb carbide having a particle size of less than 0.6 μm is present in the steel material at 1 × 10 5 pieces / mm 3 or more,
Steel material with excellent toughness of weld heat affected zone.
(2) さらに、質量％で、
Ｃｕ：０．０１〜１．０％、
Ｎｉ：０．０１〜１．０％、
Ｃｒ：０．０１〜０．５％、
Ｍｏ：０．０１〜０．５％、
Ｖ：０．０１〜０．２％および
Ｂ：０．０００１〜０．０００５％
から選択される１種以上を含有する、
上記(1)の溶接熱影響部靱性に優れた鋼材。
(2) Furthermore, in mass%,
Cu: 0.01 to 1.0%,
Ni: 0.01 to 1.0%,
Cr: 0.01 to 0.5%
Mo: 0.01 to 0.5%,
V: 0.01 to 0.2% and B: 0.0001 to 0.0005%
Containing one or more selected from
Steel material with excellent weld heat affected zone toughness (1).
(3) さらに、質量％で、
Ｃａ：０．０００５〜０．００５％および
ＲＥＭ：０．０００５〜０．００５％
から選択される１種または２種を含有する、
上記(1)または(2)の溶接熱影響部靱性に優れた鋼材。
(3) Furthermore, in mass%,
Ca: 0.0005 to 0.005% and REM: 0.0005 to 0.005%
Containing one or two selected from
(1) or (2) a steel material having excellent weld heat affected zone toughness.
(4) さらに、質量％で、
Ｔｉ：０．００１〜０．０２％
を含有する、
上記(1)〜(3)のいずれかの溶接熱影響部靱性に優れた鋼材。
(4) Furthermore, in mass%,
Ti: 0.001 to 0.02%
Containing
A steel material having excellent weld heat affected zone toughness according to any one of (1) to (3) above.
(5) さらに、質量％で、
Ｓｎ：０．０５〜０．５％
を含有する、
上記(1)〜(4)のいずれかの溶接熱影響部靱性に優れた鋼材。
(5) Furthermore, in mass%,
Sn: 0.05-0.5%
Containing
A steel material having excellent weld heat affected zone toughness according to any one of (1) to (4) above.
本発明によれば、溶接熱影響部の靱性に優れた鋼板を提供することができる。特に、溶接入熱量が３００ｋＪ／ｃｍ以上の大入熱溶接を実施した場合であっても、旧オーステナイト粒の粗大化を抑制することができ、もって優れた溶接熱影響部靭性を有する鋼を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the steel plate excellent in the toughness of a welding heat affected zone can be provided. In particular, even when high heat input welding with a heat input of 300 kJ / cm or more is carried out, it is possible to suppress the coarsening of prior austenite grains and to provide steel having excellent weld heat affected zone toughness can do.
１．本発明に係る鋼材の化学組成について
以下、本発明に係る鋼材の化学組成について説明する。なお、含有量に関する「％」は、質量％を意味する。
1. About the chemical composition of the steel materials which concern on this invention Hereinafter, the chemical composition of the steel materials which concern on this invention is demonstrated. In addition, "%" regarding content means the mass%.
Ｃ：０．０２〜０．２５％
Ｃは母材および溶接部の強度および靱性を確保するのに有効な元素であるが、その含有量が０．０２％未満ではその効果が得られない。しかし、０．２５％を超えると溶接性を劣化させる。したがって、Ｃの含有量は０．０５〜０．２５％とする。Ｃの含有量の好ましい下限は０．０４％であり、好ましい上限は０．１８％である。
C: 0.02-0.25%
C is an element effective for ensuring the strength and toughness of the base metal and the welded portion, but if the content is less than 0.02%, the effect cannot be obtained. However, if it exceeds 0.25%, the weldability is deteriorated. Therefore, the C content is 0.05 to 0.25%. The minimum with preferable content of C is 0.04%, and a preferable upper limit is 0.18%.
Ｓｉ：０．０００１〜０．４％
Ｓｉは、脱酸のために鋼に含有される。この効果を得るために、Ｓｉを０．０００１％以上含有させる必要がある。しかし、多すぎると溶接性および溶接熱影響部靱性が劣化する。したがって、Ｓｉの含有量は０．０００１〜０．４％とする。Ｓｉ含有量の好ましい下限は０．０１％であり、好ましい上限は０．２％である。
Si: 0.0001 to 0.4%
Si is contained in the steel for deoxidation. In order to acquire this effect, it is necessary to contain Si 0.0001% or more. However, if too much, weldability and weld heat affected zone toughness deteriorate. Therefore, the Si content is 0.0001 to 0.4%. The minimum with preferable Si content is 0.01%, and a preferable upper limit is 0.2%.
Ｍｎ：０．５〜２．０％
Ｍｎは母材および溶接部の強度および靱性の確保に不可欠であり、０．５％以上必要とする。しかし、Ｍｎが多すぎると溶接熱影響部靱性の劣化およびスラブの中心偏析を助長し、溶接性を劣化させる。したがって、Ｍｎの含有量は０．５〜２．０％とする。Ｍｎ含有量の好ましい下限は１．０％であり、好ましい上限は１．５％である。
Mn: 0.5 to 2.0%
Mn is indispensable for securing the strength and toughness of the base material and the welded portion, and is required to be 0.5% or more. However, too much Mn promotes deterioration of the weld heat affected zone toughness and center segregation of the slab, and deteriorates the weldability. Therefore, the Mn content is set to 0.5 to 2.0%. The minimum with preferable Mn content is 1.0%, and a preferable upper limit is 1.5%.
Ｐ：０．０３％以下
Ｐは鋼材中に含まれる不純物元素である。Ｐを低減すると、スラブの中心偏析の軽減を通じて母材および溶接熱影響部の機械的性質を改善し、さらには、溶接熱影響部の粒界破壊を抑制する。このため、Ｐは少ないほど望ましいが、経済性を考慮してＰの含有量は０．０３％以下とする。
P: 0.03% or less P is an impurity element contained in the steel material. When P is reduced, the mechanical properties of the base material and the weld heat affected zone are improved by reducing the center segregation of the slab, and further, the grain boundary fracture of the weld heat affected zone is suppressed. For this reason, the smaller the amount of P, the better. However, considering the economy, the P content is set to 0.03% or less.
Ｓ：０．００１〜０．０５０％
Ｓは、本発明において重要な元素である。粒内フェライト変態核として、ＭｇとＭｎとＡｌからなる酸化物の上に、ＭｎＳを複合析出してなる複合介在物を分散・生成させるために、０．００１％以上含有させる必要がある。しかし、Ｓが０．０５０％を超えると母材および溶接熱影響部の靱性が劣化する。したがって、Ｓの含有量は０．００１〜０．０５０％とする。
S: 0.001 to 0.050%
S is an important element in the present invention. As an intragranular ferrite transformation nucleus, it is necessary to contain 0.001% or more in order to disperse and generate a composite inclusion formed by complex precipitation of MnS on an oxide composed of Mg, Mn and Al. However, if S exceeds 0.050%, the toughness of the base metal and the weld heat affected zone deteriorates. Therefore, the content of S is set to 0.001 to 0.050%.
Ｏ：０．００１〜０．００５％
Ｏ（酸素）は、ピンニング粒子であり、上記複合介在物の個数を制御する上で重要である。Ｏが０．００１％未満の場合、上記複合介在物の個数が不足し、溶接熱影響部靱性が劣化する。一方、Ｏが０．００５％を超える場合、鋼の清浄度が低下して機械的性質が劣化する。したがって、Ｏの含有量は０．００１〜０．００５％とする。
O: 0.001 to 0.005%
O (oxygen) is a pinning particle and is important in controlling the number of the composite inclusions. When O is less than 0.001%, the number of the composite inclusions is insufficient, and the weld heat affected zone toughness deteriorates. On the other hand, when O exceeds 0.005%, the cleanliness of the steel decreases and the mechanical properties deteriorate. Therefore, the content of O is set to 0.001 to 0.005%.
Ｎ：０．００６％以下、
Ｎは不純物として存在する。母材靭性の低下、溶接時に希釈による溶接金属中への混入から溶接金属の靭性低下を招くため、Ｎの含有量の上限を０．００６％とする。
N: 0.006% or less,
N exists as an impurity. In order to reduce the toughness of the weld metal due to a decrease in the base metal toughness and mixing into the weld metal due to dilution during welding, the upper limit of the N content is set to 0.006%.
Insol.
Ａｌ：０．０００１〜０．００５％
sol. Ａｌ：０．０００１〜０．０００５％
Insol. Ａｌは、旧オーステナイト粒成長のピンニング粒子である上記複合介在物の個数を１×１０６個／ｍｍ３以上存在するように制御する上で重要である。Insol. Ａｌが０．０００１％未満の場合、上記複合介在物の個数が１×１０６個／ｍｍ３未満になってしまい、旧オーステナイト粒が十分に細粒化されず、良好な溶接熱影響部靱性が得られない。また、Insol. Ａｌが０．００５％を超えると、上記複合介在物の個数が多く生成しすぎる。その結果、一旦生成した複合介在物が凝集して粗大な複合介在物になりやすくなる。その結果、粒径０．６μｍ未満の複合介在物の個数が１×１０６個／ｍｍ３未満となりやすく、この場合、旧オーステナイト粒界の移動を十分にピンニングすることはできない。また、粗大な複合介在物が形成されると、それに起因した溶接熱影響部靱性の劣化が起こる。したがって、Insol. Ａｌの含有量は０．０００１〜０．００５％とする。
Insol.
Al: 0.0001 to 0.005%
sol. Al: 0.0001 to 0.0005%
Insol. Al is important in controlling the number of composite inclusions, which are pinning particles for the prior austenite grain growth, to be 1 × 10 6 / mm 3 or more. When Insol. Al is less than 0.0001%, the number of the composite inclusions is less than 1 × 10 6 / mm 3 , and the prior austenite grains are not sufficiently refined, and the effect of welding heat is good. The toughness cannot be obtained. On the other hand, if Insol. Al exceeds 0.005%, too many composite inclusions are generated. As a result, the composite inclusions once generated tend to aggregate and become coarse composite inclusions. As a result, the number of composite inclusions having a particle size of less than 0.6 μm tends to be less than 1 × 10 6 / mm 3 , and in this case, the movement of prior austenite grain boundaries cannot be sufficiently pinned. Further, when coarse composite inclusions are formed, the weld heat affected zone toughness is deteriorated due to the inclusion. Therefore, the content of Insol. Al is set to 0.0001 to 0.005%.
次に、sol. Ａｌは上記の微細な複合介在物を分散させる上で、マイナスに働く。sol.Ａｌの含有量が増加して０．０００５％を超えると、鋼中のＡｌの総量が増加すると、上記複合介在物が粗大化してしまい、旧オーステナイト粒が十分に細粒化されず、良好な溶接熱影響部靱性が得られない。したがって、sol. Ａｌの含有量の上限は０．０００５％とする。ただし、sol. Ａｌの含有量が０．０００１％未満では十分な脱酸効果が得られないので、その下限を０．０００１％とする。 Next, sol. Al works negatively in dispersing the fine composite inclusions. If the content of sol.Al increases and exceeds 0.0005%, the total amount of Al in the steel increases, the composite inclusions become coarse, and the prior austenite grains are not sufficiently refined, Good weld heat-affected zone toughness cannot be obtained. Therefore, the upper limit of the sol. Al content is 0.0005%. However, if the content of sol. Al is less than 0.0001%, a sufficient deoxidation effect cannot be obtained, so the lower limit is made 0.0001%.
Insol.Ｍｇ：０．０００１〜０．００５％
sol.Ｍｇ：０．０００１〜０．０００５％
Insol.Ｍｇは、旧オーステナイト粒成長のピンニング粒子である上記複合介在物の個数を１×１０６個／ｍｍ３以上存在するように制御する上で重要である。Insol.Ｍｇが０．０００１％未満の場合、上記複合介在物の個数が１×１０６個／ｍｍ３未満になってしまい、旧オーステナイト粒が十分に細粒化されず、良好な溶接熱影響部靱性が得られない。また、Insol.Ｍｇが０．００５％を超えると、上記複合介在物の個数が多く生成しすぎる。その結果、一旦生成した複合介在物が凝集して粗大な複合介在物になりやすくなる。その結果、粒径０．６μｍ未満の複合介在物の個数が１×１０６個／ｍｍ３未満となりやすく、この場合、旧オーステナイト粒界の移動を十分にピンニングすることはできない。また、粗大な複合介在物が形成されると、それに起因した溶接熱影響部靱性の劣化が起こる。したがって、Insol.Ｍｇの含有量は０．０００１〜０．００５％とする。
Insol.Mg: 0.0001 to 0.005%
sol.Mg: 0.0001 to 0.0005%
Insol.Mg is important in controlling the number of composite inclusions, which are pinning particles for the prior austenite grain growth, to be 1 × 10 6 / mm 3 or more. When Insol.Mg is less than 0.0001%, the number of the composite inclusions is less than 1 × 10 6 pieces / mm 3 , and the prior austenite grains are not sufficiently refined, resulting in good welding heat effect. The toughness cannot be obtained. On the other hand, if Insol.Mg exceeds 0.005%, the number of the composite inclusions is excessively generated. As a result, the composite inclusions once generated tend to aggregate and become coarse composite inclusions. As a result, the number of composite inclusions having a particle size of less than 0.6 μm tends to be less than 1 × 10 6 / mm 3 , and in this case, the movement of prior austenite grain boundaries cannot be sufficiently pinned. Further, when coarse composite inclusions are formed, the weld heat affected zone toughness is deteriorated due to the inclusion. Therefore, the content of Insol.Mg is set to 0.0001 to 0.005%.
次に、sol.Ｍｇは上記の微細な複合介在物を分散させる上で、マイナスに働く。sol.Ｍｇの含有量が０．０００５％を超えて、鋼中のＭｇの総量が増加すると、上記複合介在物が粗大化してしまい、旧オーステナイト粒が十分に細粒化されず、良好な溶接熱影響部靱性が得られない。したがって、sol.Ｍｇの含有量の上限は０．０００５％とする。ただし、sol. Ｍｇの含有量が０．０００１％未満では上記の微細な複合介在物を分散させるのに必要なInsol. Ｍｇを確保できないので、その下限を０．０００１％とする。 Next, sol.Mg works negatively in dispersing the fine composite inclusions. If the content of sol.Mg exceeds 0.0005% and the total amount of Mg in the steel increases, the composite inclusions become coarse, and the prior austenite grains are not sufficiently refined, and good welding is achieved. Heat affected zone toughness is not obtained. Therefore, the upper limit of the content of sol.Mg is set to 0.0005%. However, if the content of sol.Mg is less than 0.0001%, Insol.Mg necessary for dispersing the fine composite inclusions cannot be secured, so the lower limit is made 0.0001%.
Ｎｂ：０．０１％〜０．０５％以下
Ｎｂは、ピン止め効果により旧オーステナイト粒の粗大化を抑制し、母材組織の微細化に有効な元素である。このため、Ｎｂの含有量を０．０１％以上とする。しかし、Ｎｂの含有量が０．０５％を超えると、溶接熱影響部靱性が悪化するので、Ｎｂ含有量は０．０５％以下とする。０．０４％以下とするのが好ましい。なお、Ｎｂ含有量は、０．０２％以上とするのが好ましい。
Nb: 0.01% to 0.05% or less Nb is an element that suppresses the coarsening of the prior austenite grains due to the pinning effect and is effective in refining the base material structure. For this reason, the Nb content is set to 0.01% or more. However, if the Nb content exceeds 0.05%, the weld heat affected zone toughness deteriorates, so the Nb content is set to 0.05% or less. It is preferable to set it to 0.04% or less. In addition, it is preferable that Nb content shall be 0.02% or more.
本発明に係る鋼材は、上記の元素を含有し、残部がＦｅおよび不純物からなる。ここで、不純物とは、鋼材を工業的に製造する際に、鉱石、スクラップ等の原料その他の要因により混入する成分を意味する。 The steel material according to the present invention contains the above elements, with the balance being Fe and impurities. Here, an impurity means the component mixed by raw materials and other factors, such as an ore and a scrap, when manufacturing steel materials industrially.
本発明に係る鋼材には、必要に応じて、下記の元素を含有させることができる。 The steel material according to the present invention may contain the following elements as necessary.
Ｃｕ：０〜１．０％、
Ｃｕを含有させると、溶接性および溶接熱影響部靱性に悪影響を及ぼすことなく母材の強度と靭性を向上させることができるので、含有させてもよい。しかし、その含有量が１．０％を超えると、逆に母材の強度と靭性を低下させる。したがって、Ｃｕの含有量は１．０％以下とする。なお、Ｃｕによる効果を得たい場合には、Ｃｕを０．０１％以上含有させることが好ましい。
Cu: 0 to 1.0%
When Cu is contained, the strength and toughness of the base material can be improved without adversely affecting the weldability and the weld heat affected zone toughness, and thus may be contained. However, if the content exceeds 1.0%, the strength and toughness of the base material are reduced. Therefore, the Cu content is 1.0% or less. In addition, when obtaining the effect by Cu, it is preferable to contain Cu 0.01% or more.
Ｎｉ：０〜１．０％、
Ｎｉは、溶接性および溶接熱影響部靱性に悪影響を及ぼすことなく母材の強度と靭性を確保するために有効な元素であるので、含有させてもよい。しかし、Ｎｉの含有量が１．０％を超えると、逆に母材の強度と靭性を低下させる。したがって、Ｎｉの含有量は１．０％以下とする。なお、Ｎｉによる効果を得たい場合には、Ｎｉを０．０１％以上含有させることが好ましい。
Ni: 0 to 1.0%,
Ni is an element effective for ensuring the strength and toughness of the base material without adversely affecting the weldability and the weld heat affected zone toughness, and may be contained. However, if the Ni content exceeds 1.0%, the strength and toughness of the base material are conversely reduced. Therefore, the Ni content is 1.0% or less. In addition, when obtaining the effect by Ni, it is preferable to contain Ni 0.01% or more.
Ｃｒ：０〜０．５％、
Ｃｒは、溶接性および溶接熱影響部靱性に悪影響を及ぼすことなく母材の強度と靭性を確保するために有効な元素であるので、含有させてもよい。しかし、Ｃｒの含有量が０．５％を超えると、逆に母材の強度と靭性を低下させる。したがって、Ｃｒの含有量は０．５％以下とする。なお、Ｃｒによる効果を得たい場合には、Ｃｒを０．０１％以上含有させることが好ましい。
Cr: 0 to 0.5%,
Cr is an element effective for ensuring the strength and toughness of the base material without adversely affecting the weldability and weld heat affected zone toughness, and therefore may be contained. However, if the Cr content exceeds 0.5%, the strength and toughness of the base material are conversely reduced. Therefore, the Cr content is 0.5% or less. In addition, when obtaining the effect by Cr, it is preferable to contain Cr 0.01% or more.
Ｍｏ：０〜０．５％、
Ｍｏは、溶接性および溶接熱影響部靱性に悪影響を及ぼすことなく母材の強度と靭性を確保するために有効な元素であるので、含有させてもよい。しかし、Ｍｏの含有量が０．５％を超えると、逆に母材の強度と靭性を低下させる。したがって、Ｍｏの含有量は０．５％以下とする。なお、Ｍｏによる効果を得たい場合には、Ｍｏを０．０１％以上含有させることが好ましい。
Mo: 0 to 0.5%,
Mo is an element effective for ensuring the strength and toughness of the base material without adversely affecting the weldability and the weld heat-affected zone toughness, and therefore may be contained. However, if the Mo content exceeds 0.5%, the strength and toughness of the base material are reduced. Therefore, the Mo content is 0.5% or less. In addition, when obtaining the effect by Mo, it is preferable to contain Mo 0.01% or more.
Ｖ：０〜０．２％、
Ｖは、母材の靱性を向上させるのに有効な元素である。しかし、Ｖの含有量が０．２％を超えると、逆に母材の靭性を低下させるので、含有させてもよい。したがって、Ｖの含有量は０．２％以下とする。なお、Ｖによる効果を得たい場合には、Ｖを０．０１％以上含有させることが好ましい。
V: 0 to 0.2%,
V is an element effective for improving the toughness of the base material. However, if the content of V exceeds 0.2%, the toughness of the base material is conversely reduced, so it may be contained. Therefore, the V content is 0.2% or less. In addition, when obtaining the effect by V, it is preferable to contain V 0.01% or more.
Ｂ：０〜０．０００５％、
Ｂは、焼入れ性を高めて母材や溶接熱影響部の機械的性質を向上させるのに有効な元素であるので、含有させてもよい。しかし、Ｂの含有量が０．０００５％を超えると、逆に溶接熱影響部靱性や溶接性を低下させる。したがって、Ｂの含有量は０．０００５％以下とする。なお、Ｂによる効果を得たい場合には、Ｂを０．０００１％以上含有させることが好ましい。
B: 0 to 0.0005%,
B is an element effective for enhancing the hardenability and improving the mechanical properties of the base material and the weld heat affected zone, and therefore may be contained. However, if the B content exceeds 0.0005%, the weld heat affected zone toughness and weldability are conversely reduced. Therefore, the B content is 0.0005% or less. In addition, when obtaining the effect by B, it is preferable to contain B 0.0001% or more.
Ｃａ：０〜０．００５％、
Ｃａは、硫化物の形態を制御し、熱間加工性を増加させ、低温靭性を確保するために有効であるので、含有させてもよい。しかし、Ｃａの含有量が０．００５％を超えると、大型介在物やクラスターを生成して鋼の清浄度を害するので、Ｃａ含有量は０．００５％以下とする。なお、Ｃａによる効果を得たい場合には、Ｃａの含有量を０．０００５％以上とするのが好ましい。
Ca: 0 to 0.005%,
Ca is effective for controlling the form of sulfide, increasing hot workability, and ensuring low temperature toughness, so Ca may be contained. However, if the Ca content exceeds 0.005%, large inclusions and clusters are generated to impair the cleanliness of the steel, so the Ca content is set to 0.005% or less. In addition, when acquiring the effect by Ca, it is preferable to make content of Ca 0.0005% or more.
ＲＥＭ：０〜０．００５％、
ＲＥＭは、Ｃａと同様に、硫化物の形態を制御し、熱間加工性を増加させ、低温靭性を確保するために有効であるので、含有させてもよい。しかし、ＲＥＭの含有量が０．００５％を超えると、大型介在物やクラスターを生成して鋼の清浄度を害するので、ＲＥＭ含有量は０．００５％以下とする。なお、ＲＥＭによる効果を得たい場合には、ＲＥＭの含有量を０．０００５％以上とするのが好ましい。ここで、ＲＥＭとは、ランタノイドの１５元素にＹおよびＳｃを合わせた１７元素の総称であり、これらの元素のうちの１種または２種以上を含有させることができる。ＲＥＭの混合体であるミッシュメタルを添加することでＲＥＭを含有させてもよい。なお、ＲＥＭの含有量はこれらの元素の合計含有量を意味する。
REM: 0 to 0.005%,
REM, like Ca, is effective for controlling the form of sulfides, increasing hot workability, and ensuring low temperature toughness, so REM may be included. However, if the REM content exceeds 0.005%, large inclusions and clusters are generated and the cleanliness of the steel is impaired, so the REM content is set to 0.005% or less. In addition, when obtaining the effect by REM, it is preferable to make content of REM 0.0005% or more. Here, REM is a general term for 17 elements in which Y and Sc are combined with 15 elements of lanthanoid, and one or more of these elements can be contained. REM may be contained by adding misch metal which is a mixture of REM. Note that the content of REM means the total content of these elements.
Ｔｉ：０〜０．０２％、
Ｔｉは、窒化物を生成し、鋼中の固溶Ｎ量を低減するとともに析出したＴｉＮは作用を有するので、含有させてもよい。しかしながら、この含有量が０．０２％を超えると、上記複合介在物の生成に必要なＯ量の低減を招くため、ピン止め効果が低減し溶接熱影響部靭性が悪化するので、Ｔｉ含有量は０．０２％以下とする。なお、Ｔｉによる効果を得たい場合には、Ｔｉの含有量を０．００１％以上とするのが好ましい。
Ti: 0 to 0.02%,
Ti generates nitrides, reduces the amount of solute N in the steel, and precipitated TiN has an action, so it may be contained. However, if this content exceeds 0.02%, the amount of O necessary for the generation of the composite inclusions is reduced, so the pinning effect is reduced and the weld heat affected zone toughness deteriorates. Is 0.02% or less. In addition, when obtaining the effect by Ti, it is preferable to make content of Ti 0.001% or more.
Ｓｎ：０〜０．５％、
Ｓｎは耐食性を改善するために有効であるので、含有させてもよい。しかし、Ｓｎの含有量が０．５％を超えると、母材および熱影響部靭性が低下するので、Ｓｎの含有量は０．５％以下とする。Ｓｎの好ましい含有量は０．４％以下である。なお、Ｓｎの効果を得たい場合には、Ｓｎの含有量を０．００２％以上とするのが好ましく、０．０５％以上とするのがより好ましい。
Sn: 0 to 0.5%,
Since Sn is effective for improving the corrosion resistance, it may be contained. However, if the Sn content exceeds 0.5%, the base material and the heat-affected zone toughness deteriorate, so the Sn content is set to 0.5% or less. The preferable content of Sn is 0.4% or less. In addition, when obtaining the effect of Sn, the Sn content is preferably 0.002% or more, and more preferably 0.05% or more.
２．本発明に係る複合介在物について
本発明においては、粒径が０．６μｍ未満である、ＭｇとＭｎとＡｌからなる酸化物とＭｎＳからなる複合介在物が鋼材中に１×１０６個／ｍｍ３以上存在することが必要である。以下、その理由を詳述する。
2. About the composite inclusion according to the present invention In the present invention, the composite inclusion made of Mg, Mn, Al oxide and MnS having a particle size of less than 0.6 μm is 1 × 10 6 pieces / mm in the steel material. There must be 3 or more. The reason will be described in detail below.
１４００℃以上の高温でも熱的に安定である（ＭｎＳ＋Ｍｎ、Ｍｇ系スピネル）複合介在物、具体的には、ＭｇとＭｎとＡｌからなる酸化物とＭｎＳからなる複合介在物を鋼中に微細に分散させると、溶接入熱量が３００ｋＪ／ｃｍ以上となる大入熱溶接により鋼材温度が上昇しても、消失することはない。ここで、ＭｇとＭｎとＡｌからなる酸化物とＭｎＳからなる複合介在物とは、スピネル構造のマンガンスピネルＭｎＡｌ２Ｏ４のＭｎの一部がＭｇで置換された酸化物と、Ｍｎ：Ｓが１：１のＮａＣｌ構造のＭｎＳからなる複合介在物をいう。 Composite inclusions that are thermally stable even at a high temperature of 1400 ° C. or higher (MnS + Mn, Mg-based spinel), specifically, oxides composed of Mg, Mn and Al, and composite inclusions composed of MnS are finely formed in steel. When dispersed, even if the steel material temperature rises due to high heat input welding with a welding heat input of 300 kJ / cm or more, it does not disappear. Here, the composite inclusion consisting of an oxide composed of Mg, Mn and Al and MnS is an oxide in which a part of Mn of manganese spinel MnAl 2 O 4 having a spinel structure is substituted with Mg, and Mn: S A composite inclusion composed of MnS having a NaCl structure of 1: 1.
このような複合介在物が存在すると、旧オーステナイト粒界の移動をピンニングするので、溶接熱影響部靱性を向上できる。しかし、この複合介在物は微細かつ多量に分散・生成させることによってはじめて十分なピンニング効果が得られる。具体的には、粒径０．６μｍ未満の複合介在物が鋼中に１×１０６個／ｍｍ３以上で存在する必要がある。粒径が０．６μｍ以上の複合介在物では旧オーステナイト粒界の移動を十分にピンニングすることはできないおそれがあるからであり、そして、粒径０．６μｍ以上の複合介在物が存在してもその個数が鋼中に１×１０６個／ｍｍ３未満ではやはり十分なピンニング効果を得ることができず、溶接熱影響部の粒界が大きくなり靭性が低下してしまうからである。ここで、粒径はいわゆる円相当粒径であり、複合介在物を円に換算した場合の円の粒径をいう。 When such composite inclusions exist, the movement of the prior austenite grain boundaries is pinned, so that the weld heat affected zone toughness can be improved. However, a sufficient pinning effect can be obtained only when the composite inclusions are finely dispersed and produced in large quantities. Specifically, composite inclusions having a particle size of less than 0.6 μm need to be present in steel at 1 × 10 6 pieces / mm 3 or more. This is because there is a possibility that the migration of the prior austenite grain boundary cannot be sufficiently pinned with a composite inclusion having a particle size of 0.6 μm or more, and even if a composite inclusion having a particle size of 0.6 μm or more exists. This is because if the number is less than 1 × 10 6 pieces / mm 3 in the steel, a sufficient pinning effect cannot be obtained, and the grain boundary of the weld heat affected zone becomes large and the toughness is lowered. Here, the particle size is a so-called equivalent circle particle size, which is the particle size of a circle when the composite inclusion is converted into a circle.
複合介在物の粒径の下限は特に規定しないが、ピンニングの効果を十分に得たい場合には、その粒径を０．０１μｍ以上とするのが好ましい。また、複合介在物の数が多いほどピンニング効果は大きくなるので上限は規定しない。しかし、鋼中に存在するＭｇ、Ｍｎ、ＡｌおよびＳの含有量から計算すると、この複合介在物の個数は１×１０８個／ｍｍ３が上限となる。なお、複合介在物は、粒径０．６μｍ未満のものが鋼中に１×１０６個／ｍｍ３以上で存在していればよく、この複合介在物の粒径が０．６μｍ以上のものが存在しても構わない。ただし、粒径が大きな複合介在物が多く存在すると０．６μｍ未満の複合介在物を１×１０６個／ｍｍ３以上確保し難くなる。 The lower limit of the particle size of the composite inclusion is not particularly defined. However, when a sufficient pinning effect is desired, the particle size is preferably 0.01 μm or more. Further, since the pinning effect increases as the number of complex inclusions increases, no upper limit is defined. However, when calculated from the contents of Mg, Mn, Al and S present in the steel, the upper limit of the number of composite inclusions is 1 × 10 8 pieces / mm 3 . In addition, composite inclusions having a particle size of less than 0.6 μm may be present in steel at 1 × 10 6 pieces / mm 3 or more, and the composite inclusions have a particle size of 0.6 μm or more. May be present. However, when there are many composite inclusions having a large particle size, it is difficult to secure 1 × 10 6 composite inclusions of less than 0.6 μm / mm 3 or more.
さらに、本発明においては、粒径０．６μｍ未満のＮｂ炭化物が鋼材中に１×１０5個／ｍｍ３以上存在をすることが必要である。
Nbを適切な量添加することにより、粒径０．６μｍ未満のNb炭化物が鋼中に１×１０5個／ｍｍ３以上で存在させることができる。加熱温度が１４００℃にもなる溶融線近傍では、一部炭化物が溶解・粗大化するが、上記複合介在物の効果に加えてさらに粗大化抑制効果が高まる。
Furthermore, in the present invention, it is necessary that Nb carbide having a particle size of less than 0.6 μm be present in the steel material at 1 × 10 5 pieces / mm 3 or more.
By adding an appropriate amount of Nb, Nb carbide having a particle size of less than 0.6 μm can be present in the steel at 1 × 10 5 pieces / mm 3 or more. In the vicinity of the melting line where the heating temperature is as high as 1400 ° C., some carbides are dissolved and coarsened, but in addition to the effects of the composite inclusions, the coarsening suppression effect is further increased.
なお、Ｎｂ炭化物は、粒径０．６μｍ未満のものが鋼中に１×１０5個／ｍｍ３以上で存在していればよく、その他のＮｂ炭化物の粒径が０．６μｍ以上のものが存在しても構わない。ただし、粒径が大きなＮｂ炭化物が多く存在すると０．６μｍ未満のＮｂ炭化物を１×１０5個／ｍｍ３以上確保し難くなる。０．６μｍ未満のＮｂ炭化物を１×１０5個／ｍｍ３以上確保するためには、スラブを高温で保持する時間を短くすることが好ましい。例えば、スラブを加熱炉から抽出した後１２０秒以内に圧延を開始することが好ましい。この理由は時間が長いと、Ｎｂ炭化物の結晶粒径が粗大化してしまうためである。 Nb carbides having a particle size of less than 0.6 μm may be present in steel at 1 × 10 5 pieces / mm 3 or more, and other Nb carbides having a particle size of 0.6 μm or more. May be present. However, when a large amount of Nb carbide having a large particle size is present, it is difficult to secure 1 × 10 5 pieces / mm 3 or more of Nb carbide of less than 0.6 μm. In order to secure 1 × 10 5 pieces / mm 3 or more of Nb carbide of less than 0.6 μm, it is preferable to shorten the time for holding the slab at a high temperature. For example, it is preferable to start rolling within 120 seconds after extracting the slab from the heating furnace. This is because, if the time is long, the crystal grain size of Nb carbide becomes coarse.
３．製造方法
微細酸化物を確実に得るには、酸化物を凝固段階で生成させる手法が最適である。凝固段階で溶存酸素をもとに酸化物が晶出した場合、凝集や成長が抑制されるため、溶鋼段階で生成される酸化物よりも微細なまま鋼材中に留まることになる。このため、製鋼段階では溶鋼中の粗大酸化物が少ない、すなわち溶鋼清浄度が高く、かつ、溶存酸素が高い状態にする必要がある。
3. Manufacturing method In order to obtain fine oxides with certainty, the technique of generating oxides in the solidification stage is optimal. When oxides crystallize based on dissolved oxygen in the solidification stage, aggregation and growth are suppressed, so that the oxide remains in the steel material while being finer than the oxide produced in the molten steel stage. For this reason, at the steelmaking stage, it is necessary to make the state that there are few coarse oxides in the molten steel, that is, the cleanliness of the molten steel is high and the dissolved oxygen is high.
上記した溶鋼を溶製するには、ＲＨ等の環流型真空脱ガス装置にて、脱炭反応を用いると良い。すなわち、Ａｌ等の脱酸剤を用いると、溶鋼の清浄度が悪化することに加え、溶存酸素が必要以上に低下してしまう。弱脱酸鋼を減圧処理すると、溶存酸素は炭素との脱酸平衡に向かって脱酸が生じることになる。溶存酸素の低下速度は、溶鋼中の炭素濃度と真空槽内の圧力で決まるため、鋼種によって処理時間を制御することで、溶存酸素を高めに制御できる。この時、溶鋼中に存在するＡｌ２Ｏ３といった酸化物は熱力学的に不安定となるので、成長が抑制されるが、ＲＨにおける介在物除去効果は変わらないため、溶鋼の清浄度を高めつつ、溶存酸素が高い溶鋼を効率的に溶製できる。 In order to melt the above molten steel, it is preferable to use a decarburization reaction in a reflux type vacuum degassing apparatus such as RH. That is, when a deoxidizer such as Al is used, the cleanliness of the molten steel is deteriorated and the dissolved oxygen is lowered more than necessary. When the weakly deoxidized steel is subjected to reduced pressure treatment, the dissolved oxygen is deoxidized toward the deoxidation equilibrium with carbon. The rate of decrease in dissolved oxygen is determined by the carbon concentration in the molten steel and the pressure in the vacuum chamber. Therefore, the dissolved oxygen can be controlled to be higher by controlling the treatment time depending on the steel type. At this time, oxides such as Al 2 O 3 present in the molten steel become thermodynamically unstable, so that growth is suppressed, but the inclusion removal effect in RH does not change, so the cleanliness of the molten steel is increased. Meanwhile, molten steel with high dissolved oxygen can be efficiently produced.
上記考えのもと、微細介在物を多量に分散させるために、本発明において、以下の処理を行う。溶鋼は、製鋼路から取鍋に出向された後、環流型脱ガス装置にて減圧処理される。取鍋に出鋼される時点もしくは出鋼された後から環流型脱ガス装置に搬送されるまでの間に、合金や造滓材等を添加して成分調整しても良い。また、脱硫やスラグ改質等を目的に、撹拌操作を加えても良い。成分調整後、環流型脱ガス装置にて減圧清浄化処理を行うに当たり、真空槽内圧力を低下させ、溶鋼中の酸素濃度よりも、溶鋼中の炭素濃度と真空槽内圧力から求まる酸素濃度を低い状態にすることで脱炭脱酸反応を生じさせる。 Based on the above idea, the following treatment is performed in the present invention in order to disperse a large amount of fine inclusions. The molten steel is seconded from the steelmaking path to the ladle and then subjected to a reduced pressure treatment with a circulating degassing device. Components may be adjusted by adding an alloy, a slagging material, or the like at the time when the steel is taken out to the ladle or after it is taken out until it is conveyed to the reflux degassing device. A stirring operation may be added for the purpose of desulfurization, slag reforming, or the like. After component adjustment, when performing vacuum cleaning treatment with a recirculation type degassing device, the pressure inside the vacuum chamber is reduced, and the oxygen concentration obtained from the carbon concentration in the molten steel and the pressure in the vacuum chamber is determined from the oxygen concentration in the molten steel. A decarburization deoxidation reaction is caused by making it low.
溶鋼中の炭素濃度、真空槽内圧力から求まる酸素濃度は、下記の（１）式から算出できる。ＣＯ分圧と真空槽内圧力が大きく異なることは無いため、狙いの炭素濃度に合わせて真空槽内圧力を５０〜１３×１０３Ｐａ程度の範囲で調整すれば良い。
ｌｏｇ Ｋ＝ｌｏｇ（ＰＣＯ／（ａＣ・ａＯ））＝１１６０／Ｔ＋２．００３ ・・・（１）
ここで、ＫはＣ＋Ｏ＝ＣＯ（ｇ）反応の平衡定数、ＰＣＯはＣＯ分圧、ａＣ、ａＯはそれぞれ炭素、酸素の活量、Ｔは温度（Ｋ）である。
The oxygen concentration obtained from the carbon concentration in the molten steel and the pressure in the vacuum chamber can be calculated from the following equation (1). Since the CO partial pressure and the pressure in the vacuum chamber are not significantly different, the pressure in the vacuum chamber may be adjusted in the range of about 50 to 13 × 10 3 Pa according to the target carbon concentration.
log K = log (P CO / (a C · a O )) = 1160 / T + 2.003 (1)
Here, K is the equilibrium constant of the C + O = CO (g) reaction, P CO is the CO partial pressure, a C and a O are the activities of carbon and oxygen, respectively, and T is the temperature (K).
この処理を１０〜２５分間行う。炭素以外の脱酸剤（Ａｌ， Ｓｉ， Ｍｎ， Ｔｉ， Ｍｇ， Ｃａ）は脱炭脱酸反応を生じさせる前に済ませておくことが望ましい。また、溶存酸素濃度を調整する目的で、適宜酸素濃度プローブで溶鋼の溶存酸素を測定しても良い。 This treatment is performed for 10 to 25 minutes. It is desirable that deoxidizers other than carbon (Al, Si, Mn, Ti, Mg, Ca) be completed before the decarburization deoxidation reaction occurs. Moreover, you may measure the dissolved oxygen of molten steel with an oxygen concentration probe suitably for the purpose of adjusting a dissolved oxygen concentration.
なお、厚板の製造プロセスについては、通常の製造方法でよい。 In addition, about the manufacturing process of a thick board, a normal manufacturing method may be sufficient.
表１に示す４４種類の化学組成を有する試験鋼から上記製造法に記載したような条件で連続鋳造法によりスラブを作製し、このスラブを複数枚重ねることにより脱水素を行った。その後、加熱炉に装入して１１５０〜１２００℃まで加熱した後、スラブを加熱炉から取り出し、生成したスケールに高圧水をかけて完全に除去し、加熱炉抽出から６０秒後に圧延を開始し、続けてスラブを１パスあたり５％以上の圧下量で圧延して厚さ５５ｍｍの鋼材とした。圧延後の鋼材の温度が８００〜９００℃程度に低下した後、続いて５℃/秒以上の冷却温度で４００〜５００℃まで水冷した。このような工程を経て得た鋼材から機械加工により板両面を５ｍｍずつ切削して、厚さ５５ｍｍの平滑な鋼板とした。 Slabs were produced from test steels having 44 kinds of chemical compositions shown in Table 1 by the continuous casting method under the conditions described in the above production method, and dehydrogenation was performed by stacking a plurality of the slabs. Then, after charging in a heating furnace and heating to 1150-1200 ° C., the slab is removed from the heating furnace, and the generated scale is completely removed by applying high-pressure water, and rolling is started 60 seconds after extraction from the heating furnace. Subsequently, the slab was rolled at a reduction amount of 5% or more per pass to obtain a steel material having a thickness of 55 mm. After the temperature of the steel material after rolling dropped to about 800 to 900 ° C, it was subsequently water-cooled to 400 to 500 ° C at a cooling temperature of 5 ° C / second or more. A steel plate obtained through such a process was cut by 5 mm on both sides of the plate by machining to obtain a smooth steel plate having a thickness of 55 mm.
このようにして得た各鋼材について、側面の一方を１０°に加工し、２枚の鋼板を突き合わせることにより、２０°Ｖ開先としてエレクトロスラグ溶接を実施した。溶接入熱は３００ｋＪ／ｃｍ、ワイヤはＤＷＳ−１ＬＧ、電流４００Ａ、電圧４２Ｖ、溶接速度は３．４ｃｍ／ｍｉｎとした。 About each steel material obtained in this way, one of the side surfaces was processed to 10 °, and two steel plates were abutted to perform electroslag welding with a 20 ° V groove. The welding heat input was 300 kJ / cm, the wire was DWS-1LG, the current was 400 A, the voltage was 42 V, and the welding speed was 3.4 cm / min.
溶接後に、鋼材母材から電解抽出により、母材を０．５ｇ溶かし、ピンニング粒子がフィルター上に乗った試料を作製し、これを３００００倍以上の倍率で２５０μｍ２の面積にわたって走査型電子顕微鏡（ＳＥＭ）で観察することによって、ピンニング粒子である複合介在物、Ｎｂ炭化物のサイズと個数をカウントし、その存在密度を求めた。また、電解抽出時に鋼材母材の溶けた量から、ＳＥＭ観察で求めた存在密度を鋼材母材中での存在密度に換算し直した。なお、ＭｇとＭｎとＡｌからなる酸化物とＭｎＳからなる複合介在物、Ｎｂ炭化物の同定は、ＳＥＭに付属するエネルギー分散型Ｘ線分光法（ＥＤＳ）による組成分析により行った。このようにして求めた鋼材母材中での複合介在物の存在密度（換算値）を表２に示した。 After welding, 0.5 g of the base material is melted by electrolytic extraction from the steel base material, and a sample in which pinning particles are placed on the filter is prepared. This is a scanning electron microscope over an area of 250 μm 2 at a magnification of 30000 times or more ( By observing with SEM), the size and number of composite inclusions and Nb carbides as pinning particles were counted, and the existence density was determined. Moreover, the existing density calculated | required by SEM observation was converted into the existing density in a steel base material from the quantity which the steel base material melted at the time of electrolytic extraction. In addition, the composite inclusion which consists of the oxide which consists of Mg, Mn, and Al, MnS, and Nb carbide | carbonized_material were identified by the compositional analysis by the energy dispersive X-ray spectroscopy (EDS) attached to SEM. Table 2 shows the existence density (converted value) of the composite inclusions in the steel base material thus obtained.
また、溶接後に、溶接熱影響部にJIS４号に基づいてノッチを形成した試験片を作製し、JISZ2242金属シャルピー衝撃試験方法に基づいて試験を行うことによって、靱性を調査した。その結果は、表２のシャルピー衝撃値(vE-30)で示したとおりである。 Further, after welding, a test piece in which a notch was formed in the weld heat affected zone based on JIS No. 4 was prepared, and the toughness was investigated by performing a test based on the JIS Z2242 metal Charpy impact test method. The result is as shown by the Charpy impact value (vE- 30 ) in Table 2.
表２に示すように、本発明に係る化学組成の範囲内にある本発明鋼（鋼No.１〜２７）は、いずれも粒径０．６μｍ未満の複合介在物が鋼材中に１×１０６個／ｍｍ３以上で、かつ粒径０．６μｍ未満のＮｂ炭化物が鋼材中に１×１０5個／ｍｍ３以上存在しており、シャルピー衝撃値(vE-30)が高く、優れた溶接熱影響部靭性を示すことが分かる。 As shown in Table 2, the steels of the present invention (steel Nos. 1 to 27) within the range of the chemical composition according to the present invention each have a composite inclusion with a particle size of less than 0.6 μm in the steel material at 1 × 10. Nb carbide with a particle size of 6 pieces / mm 3 or more and a particle size of less than 0.6 μm is present in the steel material at 1 × 10 5 pieces / mm 3 or more, has a high Charpy impact value (vE -30 ), and is excellent in welding It can be seen that the heat-affected zone toughness is exhibited.
これに対して、本発明に係る化学組成の範囲外にある比較鋼（鋼No.２８〜４４）は、いずれも粒径０．６μｍ未満の複合介在物が鋼材中に１×１０６個／ｍｍ３未満であり、特に鋼No.４０〜４４は、粒径０．６μｍ未満のＮｂ炭化物が鋼材中に１×１０5個／ｍｍ３未満であり、シャルピー衝撃値(vE-30)が低く、溶接熱影響部靱性が劣ることが分かる。 On the other hand, the comparative steels (steel Nos. 28 to 44) outside the range of the chemical composition according to the present invention each have 1 × 10 6 composite inclusions in the steel material with a particle size of less than 0.6 μm. less than mm 3, in particular steel No.40~44 is less than 1 × 10 5 cells / mm 3 Nb carbide having a particle size of less than 0.6μm is in the steel material, the Charpy impact value (vE -30) is low It can be seen that the weld heat-affected zone toughness is inferior.
本発明によれば、溶接入熱量が３００ｋＪ／ｃｍ以上の大入熱溶接を実施した場合であっても、旧オーステナイト粒の粗大化を抑制することができ、もって優れた溶接熱影響部靭性を有する鋼材を提供することができる。 According to the present invention, even when high heat input welding with a heat input of 300 kJ / cm or more is carried out, it is possible to suppress the coarsening of the prior austenite grains and thus to have excellent weld heat affected zone toughness. The steel material which has can be provided.
Claims (5)
Ｃ：０．０２〜０．２５％、
Ｓｉ：０．０００１〜０．４％、
Ｍｎ：０．５〜２．０％、
Ｓ：０．００１〜０．０５０％、
Ｏ：０．００１〜０．００５％、
Insol.Ａｌ：０．０００１〜０．００５％、
sol.Ａｌ：０．０００１〜０．０００５％、
Insol.Ｍｇ：０．０００１〜０．００５％、
sol.Ｍｇ：０．０００１〜０．０００５％、
Ｎｂ：０．０１〜０．０５％、
Ｃｕ：０〜１．０％、
Ｎｉ：０〜１．０％、
Ｃｒ：０〜０．５％、
Ｍｏ：０〜０．５％、
Ｖ：０〜０．２％、
Ｂ：０〜０．０００５％、
Ｃａ：０〜０．００５％、
ＲＥＭ：０〜０．００５％、
Ｔｉ：０〜０．０２％、
Ｓｎ：０〜０．５％、
残部：Ｆｅおよび不純物、
不純物としてのＰおよびＮが
Ｐ：０．０３％以下、
Ｎ：０．００６％以下、
である化学組成を有し、
粒径が０．６μｍ未満である、ＭｇとＭｎとＡｌからなる酸化物およびＭｎＳからなる複合介在物が鋼材中に１×１０６個／ｍｍ３以上存在し、かつ、
粒径が０．６μｍ未満であるＮｂ炭化物が鋼材中に１×１０5個／ｍｍ３以上存在する、
溶接熱影響部の靱性に優れた鋼材。 % By mass
C: 0.02 to 0.25%,
Si: 0.0001 to 0.4%,
Mn: 0.5 to 2.0%
S: 0.001 to 0.050%,
O: 0.001 to 0.005%,
Insol.Al: 0.0001 to 0.005%,
sol.Al: 0.0001 to 0.0005%,
Insol.Mg: 0.0001 to 0.005%,
sol.Mg: 0.0001 to 0.0005%,
Nb: 0.01-0.05%
Cu: 0 to 1.0%
Ni: 0 to 1.0%,
Cr: 0 to 0.5%,
Mo: 0 to 0.5%,
V: 0 to 0.2%,
B: 0 to 0.0005%,
Ca: 0 to 0.005%,
REM: 0 to 0.005%,
Ti: 0 to 0.02%,
Sn: 0 to 0.5%,
Balance: Fe and impurities,
P and N as impurities are P: 0.03% or less,
N: 0.006% or less,
Having a chemical composition of
1 × 10 6 particles / mm 3 or more exist in the steel material in which the particle diameter is less than 0.6 μm, and the composite inclusion composed of an oxide composed of Mg, Mn and Al and MnS, and
Nb carbide having a particle size of less than 0.6 μm is present in the steel material at 1 × 10 5 pieces / mm 3 or more,
Steel material with excellent toughness of weld heat affected zone.
Ｃｕ：０．０１〜１．０％、
Ｎｉ：０．０１〜１．０％、
Ｃｒ：０．０１〜０．５％、
Ｍｏ：０．０１〜０．５％、
Ｖ：０．０１〜０．２％および
Ｂ：０．０００１〜０．０００５％
から選択される１種以上を含有する、
請求項１の溶接熱影響部靱性に優れた鋼材。 Furthermore, in mass%,
Cu: 0.01 to 1.0%,
Ni: 0.01 to 1.0%,
Cr: 0.01 to 0.5%
Mo: 0.01 to 0.5%,
V: 0.01 to 0.2% and B: 0.0001 to 0.0005%
Containing one or more selected from
The steel material excellent in weld heat-affected zone toughness according to claim 1.
Ｃａ：０．０００５〜０．００５％および
ＲＥＭ：０．０００５〜０．００５％
から選択される１種または２種を含有する、
請求項１または２に記載の溶接熱影響部靱性に優れた鋼材。 Furthermore, in mass%,
Ca: 0.0005 to 0.005% and REM: 0.0005 to 0.005%
Containing one or two selected from
The steel material excellent in the weld heat affected zone toughness according to claim 1 or 2.
Ｔｉ：０．００１〜０．０２％
を含有する、
請求項１から３までのいずれかに記載の溶接熱影響部靱性に優れた鋼材。 Furthermore, in mass%,
Ti: 0.001 to 0.02%
Containing
The steel material excellent in the weld heat affected zone toughness according to any one of claims 1 to 3.
Ｓｎ：０．０５〜０．５％
を含有する、
請求項１から４までのいずれかに記載の溶接熱影響部靱性に優れた鋼材。 Furthermore, in mass%,
Sn: 0.05-0.5%
Containing
The steel material excellent in the weld heat affected zone toughness according to any one of claims 1 to 4.
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