JP4768526B2 - Thick steel plate with excellent high heat input HAZ toughness and low temperature base metal toughness - Google Patents
Thick steel plate with excellent high heat input HAZ toughness and low temperature base metal toughness Download PDFInfo
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Description
本発明は、例えば船舶および海洋構造物などの溶接構造物に適用される厚鋼板に関し、殊に５０ｋＪ／ｍｍ以上の超大入熱溶接後の熱影響部（Ｈｅａｔ Ａｆｆｅｃｔｅｄ Ｚｏｎｅ、ＨＡＺ）の靭性に優れると共に、低温母材靱性に優れた厚鋼板に関するものである。 The present invention relates to a thick steel plate applied to a welded structure such as a ship and an offshore structure, and is particularly excellent in the toughness of a heat affected zone (HEAT Affected Zone, HAZ) after super large heat input welding of 50 kJ / mm or more. In addition, the present invention relates to a thick steel plate having excellent low-temperature base material toughness.
近年、例えばコンテナ船等の大型化が進められ、板厚が６０ｍｍ以上の厚鋼板が用いられることがある。このような厚鋼板を効率良く溶接するために、入熱量が５０ｋＪ／ｍｍ以上である超大入熱溶接を行うことが求められている。 In recent years, for example, a container ship or the like has been increased in size, and a thick steel plate having a thickness of 60 mm or more may be used. In order to weld such a thick steel plate efficiently, it is required to perform super large heat input welding with a heat input of 50 kJ / mm or more.
しかし超大入熱溶接を行うと、ＨＡＺが高温のオーステナイト領域まで加熱されてから徐冷されるため、その組織が粗大化し、ＨＡＺ靱性が著しく劣化するという問題があった。そのため従来では、溶接入熱量の制限を余儀なくされていた。 However, when super-high heat input welding is performed, the HAZ is heated to a high temperature austenite region and then gradually cooled, so that the structure becomes coarse and the HAZ toughness deteriorates significantly. For this reason, conventionally, the welding heat input has to be limited.
このような超大入熱溶接で良好なＨＡＺ靱性を達成するために、例えば特許文献１は、厚鋼板中のＣ含有量を低減させると共に、不可避的に混入してくるＰの含有量を制限し、加えてＮｂおよびＢの含有量を適切な範囲に制御することを提案している（殊に特許請求の範囲および段落００１０参照）。また特許文献２は、鋼材にＮを比較的多量に添加し、且つＴｉとＢの添加バランスを適切に制御することを提案している（殊に特許請求の範囲および段落００１３参照）。さらに特許文献３は、溶接用鋼中に存在するＴｉＮ系介在物の中に積極的にＮｂを含有させることを提案している（殊に特許請求の範囲および段落０００９参照）。
しかし溶接の分野では、ＨＡＺ靱性のさらなる改良が求められている。さらに上記特許文献のいずれも、低温母材靱性（以下、「低温靱性」と省略することがある）について考慮していない。従って本発明が解決しようとする課題は、５０ｋＪ／ｍｍ以上の超大入熱溶接でも良好なＨＡＺ靱性を示すと共に、低温靱性に優れた厚鋼板を提供することである。 However, further improvements in HAZ toughness are sought in the field of welding. Furthermore, none of the above-mentioned patent documents considers low-temperature base material toughness (hereinafter sometimes abbreviated as “low-temperature toughness”). Therefore, the problem to be solved by the present invention is to provide a thick steel plate exhibiting good HAZ toughness even in super high heat input welding of 50 kJ / mm or more and excellent in low temperature toughness.
上記課題を解決し得た本発明の厚鋼板とは、Ｃ：０．０３０〜０．１０％（質量％の意味、以下同じ）、Ｓｉ：１．０％以下（０％を含まない）、Ｍｎ：０．８〜２．０％、Ｐ：０．０３％以下（０％を含まない）、Ｓ：０．０１％以下（０％を含まない）、Ａｌ：０．０１〜０．１０％、Ｎｂ：０．０１５〜０．０３５％、Ｔｉ：０．０１５〜０．０３％、Ｂ：０．００１５〜０．００３５％、およびＮ：０．００５５〜０．０１％を含有し、さらにＣｕ：２．０％以下（０％を含む）、Ｎｉ：２．０％以下（０％を含む）、Ｃｒ：１％以下（０％を含む）、Ｍｏ：０．５％以下（０％を含む）およびＶ：０．１％（０％を含む）以下を含有し、残部がＦｅおよび不可避不純物からなり、且つ下記式（１）および（２）を満足することを特徴とするものである。
２≦［Ｔｉ］／［Ｎ］≦４ ・・・ （１）
４０≦Ｘ値 ・・・ （２）
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］
（式中、［ ］は各元素の含有量（質量％）を表す。）
The thick steel plate of the present invention that has solved the above problems is C: 0.030 to 0.10% (meaning mass%, the same shall apply hereinafter), Si: 1.0% or less (not including 0%), Mn: 0.8 to 2.0%, P: 0.03% or less (not including 0%), S: 0.01% or less (not including 0%), Al: 0.01 to 0.10 %, Nb: 0.015-0.035%, Ti: 0.015-0.03%, B: 0.0015-0.0035%, and N: 0.0055-0.01%, Further, Cu: 2.0% or less (including 0%), Ni: 2.0% or less (including 0%), Cr: 1% or less (including 0%), Mo: 0.5% or less (0 %) And V: 0.1% (including 0%) or less, the balance being Fe and inevitable impurities, and satisfying the following formulas (1) and (2) It is an.
2 ≦ [Ti] / [N] ≦ 4 (1)
40 ≦ X value (2)
X value = 500 [C] +32 [Si] +8 [Mn] -9 [Nb]
+14 [Cu] +17 [Ni] -5 [Cr] -25 [Mo] -34 [V]
(In the formula, [] represents the content (% by mass) of each element.)
本発明の厚鋼板の中で、良好な低温靱性およびＨＡＺ靱性の観点から、（Ｉ）δ域の温度範囲が４０℃以下であるもの、および／または（ＩＩ）深さｔ／４の位置（ｔ＝板厚）において、Ｔｉ系炭窒化物の平均粒子径が４０ｎｍ以下であり、Ｎｂ系炭窒化物の平均粒子径が６０ｎｍ以下であるものが好ましい。 Among the thick steel plates of the present invention, from the viewpoint of good low temperature toughness and HAZ toughness, (I) the temperature range of the δ region is 40 ° C. or less, and / or (II) the position at the depth t / 4 ( t = plate thickness), the average particle diameter of the Ti-based carbonitride is preferably 40 nm or less, and the average particle diameter of the Nb-based carbonitride is preferably 60 nm or less.
本発明の厚鋼板は、さらに、（イ）Ｃａ：０．００５％以下（０％を含まない）および／またはＭｇ：０．００５％以下（０％を含まない）、（ロ）Ｚｒ：０．１％以下（０％を含まない）および／またはＨｆ：０．０５％以下（０％を含まない）、および／または（ハ）Ｃｏ：２．５％以下（０％を含まない）および／またはＷ：２．５％以下（０％を含まない）を含有していても良い。本発明の厚鋼板は、大型のコンテナ船等の製造に適した４９０ＭＰａ以上の引張強度を有する高張力鋼板であることが望ましい。
なお本明細書において「炭窒化物」は、窒化物も含む意味で使用する。
The thick steel plate according to the present invention further comprises (a) Ca: 0.005% or less (excluding 0%) and / or Mg: 0.005% or less (excluding 0%), (b) Zr: 0 1% or less (not including 0%) and / or Hf: 0.05% or less (not including 0%), and / or (c) Co: 2.5% or less (not including 0%) and / Or W: It may contain 2.5% or less (excluding 0%). The thick steel plate of the present invention is desirably a high-tensile steel plate having a tensile strength of 490 MPa or more suitable for manufacturing a large container ship or the like.
In the present specification, “carbonitride” is used to mean including nitride.
驚くべきことに、各化学成分の量を適切な範囲内に収めると共に、上記式（１）および（２）を満たすように化学成分組成を調整することにより、超大入熱溶接でも優れたＨＡＺ靱性を示すと共に、低温靱性に優れた厚鋼板を得ることができる。 Surprisingly, the amount of each chemical component is within an appropriate range, and by adjusting the chemical component composition so as to satisfy the above formulas (1) and (2), excellent HAZ toughness is achieved even in super large heat input welding. A thick steel plate having excellent low-temperature toughness can be obtained.
本発明者らは、Ｔｉ系炭窒化物を微細化することによって、超大入熱溶接でも良好なＨＡＺ靱性を達成することを試みた。従来のＴｉ系炭窒化物の分散状態は、溶鋼凝固時の冷却速度が一定であれば、Ｔｉ、Ｎの添加バランスのみにより定まるものと考えられてきた。しかし本発明者らが鋭意検討した結果、鋼の状態図において表されるδ域の温度範囲を縮小させることにより、同じＴｉ、Ｎ添加量でも、Ｔｉ系炭窒化物を微細分散させ得ることを見出した。 The inventors of the present invention attempted to achieve good HAZ toughness even in super-high heat input welding by refining Ti-based carbonitrides. It has been considered that the dispersion state of a conventional Ti-based carbonitride is determined only by the balance of addition of Ti and N if the cooling rate during solidification of molten steel is constant. However, as a result of diligent investigations by the present inventors, it is possible to finely disperse Ti-based carbonitrides even with the same Ti and N addition amounts by reducing the temperature range of the δ region represented in the phase diagram of steel. I found it.
ここで「δ域」とは、鋼の状態図においてδ鉄が含まれる領域を意味する。この「δ鉄が含まれる領域」は、δ鉄のみの領域の他にも、δ＋γの２相領域など、δ鉄と他の状態が含まれる領域も包含する。そして「δ域の温度範囲」とは、δ鉄が含まれる温度範囲（δ域の上限温度と下限温度との差）をいう。ここで特定組成の鋼において、例えばδ鉄のみの温度範囲とδ＋γ鉄の温度範囲がある場合、これらの温度範囲の合計が、δ域の温度範囲である。このδ域の温度範囲は、総合熱力学計算ソフトウェア（Ｔｈｅｒｍｏ−ｃａｌｃ、ＣＲＣ総合研究所から購入可能）に、鋼板の化学成分組成を入力することにより計算することができる。 Here, the “δ region” means a region containing δ iron in the steel phase diagram. The “region including δ iron” includes not only a region including δ iron but also a region including δ iron and other states such as a two-phase region of δ + γ. The “temperature range in the δ range” refers to a temperature range including δ iron (difference between the upper limit temperature and the lower limit temperature in the δ range). Here, in the steel having a specific composition, for example, when there is a temperature range of only δ iron and a temperature range of δ + γ iron, the sum of these temperature ranges is the temperature range of the δ region. The temperature range of the δ region can be calculated by inputting the chemical composition of the steel sheet into the comprehensive thermodynamic calculation software (Thermo-calc, available from CRC Research Institute).
このδ鉄中ではＴｉの拡散速度が速いため、δ域の温度範囲が広いと、δ鉄が存在する時間が長くなり、粗大なＴｉ系炭窒化物が形成され易くなると考えられる。そこで化学成分組成を調整してδ域の温度範囲を縮小することにより、Ｔｉ系炭窒化物を微細化することを検討した。そのためにＴｈｅｒｍｏ−ｃａｌｃの計算にて、特定成分を基準に化学成分量の１つだけを変更することにより、各化学成分のδ域の温度範囲への影響を調べた。そのような検討により、δ域の温度範囲と相関関係にあり、化学成分組成の関数で表されるＸ値を定めた：
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］
（式中、［ ］は各元素の含有量（質量％）を表す。）
Since the diffusion rate of Ti is fast in this δ iron, it is considered that when the temperature range in the δ region is wide, the time during which the δ iron exists becomes longer and coarse Ti-based carbonitrides are easily formed. Therefore, the refinement of the Ti-based carbonitride was studied by adjusting the chemical composition and reducing the temperature range in the δ region. For this purpose, in Thermo-calc calculation, the influence of each chemical component on the temperature range in the δ region was examined by changing only one of the chemical component amounts based on the specific component. As a result of such studies, an X value correlated with the temperature range of the δ region and expressed as a function of the chemical composition was determined:
X value = 500 [C] +32 [Si] +8 [Mn] -9 [Nb]
+14 [Cu] +17 [Ni] -5 [Cr] -25 [Mo] -34 [V]
(In the formula, [] represents the content (% by mass) of each element.)
Ｘ値の上記式中の係数は、特定成分の鋼から、各化学成分を変化させた場合のδ域の温度範囲の変化量に対応する。具体的には、例えば［Ｃ］の係数の「５００」は、Ｃ量を０．０１％だけ増大させたときに、Ｔｈｅｒｍｏ−ｃａｌｃの計算にてδ域の温度範囲が約５℃減少することを意味する。そしてＸ値とδ域の温度範囲とは、ほぼ反比例の関係（Ｘ値が増大すれば、δ域の温度範囲は減少するという関係）にある。 The coefficient in the above formula of the X value corresponds to the amount of change in the temperature range in the δ region when each chemical component is changed from the specific component steel. Specifically, for example, when the coefficient of [C] is “500”, when the C content is increased by 0.01%, the temperature range in the δ region decreases by about 5 ° C. in the calculation of Thermo-calc. Means. The X value and the temperature range in the δ region are in an inversely proportional relationship (the relationship that the temperature range in the δ region decreases as the X value increases).
このような考えに基づいて、様々なＸ値を有する鋼板を製造して調べたところ、Ｘ値を増大させることで、Ｔｉ系炭窒化物の平均粒子径を微細化でき、ＨＡＺ靱性を向上させ得ることを見出した。 Based on this idea, steel sheets having various X values were manufactured and investigated, and by increasing the X value, the average particle diameter of the Ti-based carbonitride could be refined and the HAZ toughness was improved. Found to get.
そしてＸ値を増大させることで、さらに、鋼板の低温靱性も向上することを見出した。この現象は、Ｘ値を増大させることで、Ｔｉ系炭窒化物の平均粒子径の減少と共に、Ｎｂ系炭窒化物の平均粒子径が減少したことによるものと推定される。またＮｂ系炭窒化物の平均粒子径が減少したのは、Ｔｉ系炭窒化物が微分散されたためであると考えられる。なぜならＮｂ系炭窒化物のほとんどは、Ｔｉ系炭窒化物を核に析出するからである。 And it discovered that the low temperature toughness of a steel plate was further improved by increasing X value. This phenomenon is presumed to be due to the decrease in the average particle size of the Nb-based carbonitride along with the decrease in the average particle size of the Ti-based carbonitride by increasing the X value. Moreover, it is thought that the average particle diameter of Nb type carbonitride decreased because Ti type carbonitride was finely dispersed. This is because most of the Nb-based carbonitrides precipitate Ti-based carbonitrides as nuclei.
上記のように本発明の鋼板は、その化学成分組成が下記式（２）：
４０≦Ｘ値 ・・・ （２）
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］
（式中、［ ］は各元素の含有量（質量％）を表す。）
を満たしている点に、大きな特徴がある。但し本発明は、上記のような推定理由（δ域の温度範囲の減少による炭窒化物の平均粒子径の減少、平均粒子径の減少によるＨＡＺ靱性および低温靱性の向上など）には制限されず、本発明の範囲は、特許請求の範囲により定められる。即ち特許請求の範囲に規定する構成要件を満たす厚鋼板は、本発明の範囲内に包含される。
As described above, the chemical composition of the steel sheet of the present invention has the following formula (2):
40 ≦ X value (2)
X value = 500 [C] +32 [Si] +8 [Mn] -9 [Nb]
+14 [Cu] +17 [Ni] -5 [Cr] -25 [Mo] -34 [V]
(In the formula, [] represents the content (% by mass) of each element.)
There is a major feature in that However, the present invention is not limited to the above estimation reasons (decrease in average particle diameter of carbonitride due to decrease in temperature range of δ region, improvement of HAZ toughness and low temperature toughness due to decrease in average particle diameter, etc.). The scope of the present invention is defined by the claims. That is, a thick steel plate that satisfies the structural requirements defined in the claims is included within the scope of the present invention.
各化学成分量が適正範囲内であれば、Ｘ値が大きくなるほど、Ｔｉ系炭窒化物およびＮｂ系炭窒化物の平均粒子径、並びにＨＡＺ靱性および低温靱性が向上する。このＸ値の下限は、４０、好ましくは４５、より好ましくは５０である。Ｘ値の上限は、各化学成分の適正量から定められ、１６０程度である。硬質相ＭＡ組織（マルテンサイト−オーステナイトの混合組織）の生成抑制の観点から、Ｘ値の好ましい上限は、７５以下である。 If the amount of each chemical component is within an appropriate range, the average particle diameter, the HAZ toughness and the low temperature toughness of the Ti-based carbonitride and the Nb-based carbonitride improve as the X value increases. The lower limit of this X value is 40, preferably 45, more preferably 50. The upper limit of the X value is determined from an appropriate amount of each chemical component and is about 160. From the viewpoint of suppressing generation of a hard phase MA structure (mixed structure of martensite and austenite), the preferable upper limit of the X value is 75 or less.
本発明の厚鋼板では、Ｘ値が４０以上となるように化学成分組成を調整することにより、Ｔｉ系およびＮｂ系炭窒化物を微細にしている。しかしＴｉ量とＮ量とのバランスが崩れると、鋼板の靱性、特にＨＡＺ靱性が劣化する。具体的には［Ｔｉ］／［Ｎ］が４を超える場合は、Ｔｉ系炭窒化物が粗大になり、ＨＡＺ靱性が低下する。逆に２未満であれば、過剰Ｎの影響で、低温靱性およびＨＡＺ靱性が低下する。よって本発明の鋼板は、Ｘ値を規定する上記式（２）に加えて、下記式（１）：
２≦［Ｔｉ］／［Ｎ］≦４ ・・・ （１）
（式中、［ ］は各元素の含有量（質量％）を表す。）
を満たすように、Ｔｉ量とＮ量とのバランスが図られていることも特徴の１つとする。この［Ｔｉ］／［Ｎ］の好ましい下限は２．５であり、好ましい上限は３．５である。
In the thick steel plate of the present invention, the Ti-based and Nb-based carbonitrides are made fine by adjusting the chemical composition so that the X value is 40 or more. However, when the balance between the Ti content and the N content is lost, the toughness of the steel sheet, particularly the HAZ toughness, deteriorates. Specifically, when [Ti] / [N] exceeds 4, the Ti-based carbonitride becomes coarse and the HAZ toughness decreases. On the other hand, if it is less than 2, low temperature toughness and HAZ toughness decrease due to the influence of excess N. Therefore, the steel sheet of the present invention has the following formula (1):
2 ≦ [Ti] / [N] ≦ 4 (1)
(In the formula, [] represents the content (% by mass) of each element.)
One of the characteristics is that the balance between the Ti amount and the N amount is achieved so as to satisfy the above. The preferable lower limit of [Ti] / [N] is 2.5, and the preferable upper limit is 3.5.
靱性の観点から、本発明の厚鋼板中のＴｉ系およびＮｂ系炭窒化物は微細であることが好ましい。よって本発明の厚鋼板中のＴｉ系炭窒化物は、好ましくは４０ｎｍ以下、より好ましくは３５ｎｍ以下、さらに好ましくは３０ｎｍ以下であり、Ｎｂ系炭窒化物は、好ましくは６０ｎｍ以下、より好ましくは５５ｎｍ以下、さらに好ましくは５０ｎｍ以下である。 From the viewpoint of toughness, the Ti-based and Nb-based carbonitrides in the thick steel plate of the present invention are preferably fine. Therefore, the Ti-based carbonitride in the thick steel plate of the present invention is preferably 40 nm or less, more preferably 35 nm or less, still more preferably 30 nm or less, and the Nb-based carbonitride is preferably 60 nm or less, more preferably 55 nm. Hereinafter, it is more preferably 50 nm or less.
本発明におけるＴｉ系炭窒化物およびＮｂ系炭窒化物の平均粒子径の値は、以下のようにして測定した値である：まず、鋼板の熱履歴を代表する部分として深さｔ／４の位置（ｔ＝板厚）を、透過型電子顕微鏡（ＴＥＭ）で、観察倍率６万倍以上、観察視野２．０×２．０μｍ以上、観察箇所５箇所以上の条件で観察する。そしてその視野中の各炭窒化物の面積を測定し、この面積から各炭窒化物の円相当径を算出する。この各炭窒化物の円相当径を算術平均（相加平均）して得られる値を、本発明におけるＴｉ系またはＮｂ系炭窒化物の平均粒子径とする。 The value of the average particle diameter of the Ti-based carbonitride and the Nb-based carbonitride in the present invention is a value measured as follows: First, at a depth t / 4 as a portion representing the thermal history of the steel sheet. The position (t = plate thickness) is observed with a transmission electron microscope (TEM) under the conditions of an observation magnification of 60,000 times or more, an observation visual field of 2.0 × 2.0 μm or more, and five or more observation places. Then, the area of each carbonitride in the field of view is measured, and the equivalent circle diameter of each carbonitride is calculated from this area. The value obtained by arithmetically averaging (arithmetic average) the equivalent circle diameters of the carbonitrides is defined as the average particle diameter of the Ti-based or Nb-based carbonitrides in the present invention.
なおＴｉ系炭窒化物またはＮｂ系炭窒化物のいずれであるかの判別は、各炭窒化物粒子の主体となる成分（炭素および窒素以外で最大の含有量（質量％）である成分）によって定まり、これはエネルギー分散型Ｘ線検出器（ＥＤＸ）によって決定することができる。なお、あまりに微細な炭窒化物は測定できないため、本発明における炭窒化物とは、５ｎｍ以上のものに限定する。 In addition, it is discriminate | determined whether it is Ti type carbonitride or Nb type carbonitride by the component (component which is the largest content (mass%) other than carbon and nitrogen) of each carbonitride particle. This can be determined by an energy dispersive X-ray detector (EDX). In addition, since a very fine carbonitride cannot be measured, the carbonitride in the present invention is limited to those of 5 nm or more.
上記のように本発明の厚鋼板は、その化学成分組成が上記式（１）および（２）の関係を満たすことを特徴とする。しかし上記式（１）および（２）の関係を満たしても、それぞれの化学成分（各元素）の含有量が適正範囲内になければ、優れたＨＡＺ靱性および低温靱性を達成することができない。よって本発明の厚鋼板は、上記式（１）および（２）を満たすことに加えて、それぞれの化学成分の量が、以下に記載するような適正範囲内にあることも特徴とする。以下、化学成分について個々に説明する。 As described above, the thick steel plate of the present invention is characterized in that the chemical component composition satisfies the relationship of the above formulas (1) and (2). However, even if the relations of the above formulas (1) and (2) are satisfied, excellent HAZ toughness and low temperature toughness cannot be achieved unless the content of each chemical component (each element) is within an appropriate range. Therefore, in addition to satisfying the above formulas (1) and (2), the thick steel plate of the present invention is also characterized in that the amount of each chemical component is within an appropriate range as described below. Hereinafter, chemical components will be described individually.
［Ｃ：０．０３０〜０．１０％］
Ｃは、鋼板の強度を確保するために必要な元素であり、また鋼の状態図におけるδ域の温度範囲を縮小させるために有効な元素である。Ｃ量が０．０３０％未満では強度を確保することができなくなる。一方、Ｃ量が０．１０％を超えると、硬質の第２相ＭＡ組織が多くなりすぎて、母材靱性およびＨＡＺ靭性が低下する。そこでＣ量を０．０３０〜０．０１０％と定めた。Ｃ量の好ましい下限は０．０４０％であり、好ましい上限は０．０８０％である。
[C: 0.030 to 0.10%]
C is an element necessary for ensuring the strength of the steel sheet, and is an effective element for reducing the temperature range in the δ region in the steel phase diagram. If the C content is less than 0.030%, the strength cannot be secured. On the other hand, if the amount of C exceeds 0.10%, the hard second-phase MA structure becomes too much, and the base material toughness and the HAZ toughness are lowered. Therefore, the C amount is set to 0.030 to 0.010%. The preferable lower limit of the amount of C is 0.040%, and the preferable upper limit is 0.080%.
［Ｓｉ：１．０％以下（０％を含まない）］
Ｓｉは、鋼板の強度を確保するために有効な元素であり、そのためには、０．１０％以上添加することが好ましい。しかしＳｉを過剰に添加すると、ＭＡ組織が多く生成し、母材靱性およびＨＡＺ靭性が低下するため、その上限を１．０％とする必要がある。Ｓｉ量の好ましい上限は０．８％であり、より好ましくは０．６％以下である。
[Si: 1.0% or less (excluding 0%)]
Si is an effective element for securing the strength of the steel sheet, and for that purpose, it is preferable to add 0.10% or more. However, when Si is added excessively, a large amount of MA structure is generated, and the base material toughness and the HAZ toughness are lowered. Therefore, the upper limit needs to be 1.0%. The upper limit with the preferable amount of Si is 0.8%, More preferably, it is 0.6% or less.
［Ｍｎ：０．８〜２．０％］
Ｍｎは、焼入れ性を向上させ、鋼板の強度を確保するのに有効な元素である。Ｍｎ量が０．８％未満では、強度確保の作用が充分に発揮されない。一方、Ｍｎ量が２．０％を超えると、母材靱性およびＨＡＺ靭性が低下する。そこでＭｎ量を、０．８〜２．０％と定めた。Ｍｎ量の好ましい下限は１．００％であり、より好ましくは１．５０％以上である。一方、Ｍｎ量の好ましい上限は１．８０％である。
[Mn: 0.8 to 2.0%]
Mn is an element effective for improving the hardenability and ensuring the strength of the steel sheet. When the amount of Mn is less than 0.8%, the effect of securing the strength is not sufficiently exhibited. On the other hand, when the amount of Mn exceeds 2.0%, the base material toughness and the HAZ toughness are lowered. Therefore, the amount of Mn is set to 0.8 to 2.0%. The minimum with the preferable amount of Mn is 1.00%, More preferably, it is 1.50% or more. On the other hand, the preferable upper limit of the amount of Mn is 1.80%.
［Ｐ：０．０３％以下（０％を含まない）］
不純物元素であるＰは、母材靱性およびＨＡＺ靭性に悪影響を及ぼすため、その量は、できるだけ少ないことが好ましい。よってＰ量は、０．０３％以下、好ましくは０．０１０％以下である。しかし工業的に、鋼中のＰ量を０％にすることは困難である。
[P: 0.03% or less (excluding 0%)]
Since the impurity element P adversely affects the base material toughness and the HAZ toughness, the amount is preferably as small as possible. Therefore, the amount of P is 0.03% or less, preferably 0.010% or less. However, industrially, it is difficult to reduce the P content in steel to 0%.
［Ｓ：０．０１％以下（０％を含まない）］
Ｓは、ＭｎＳを形成して延性を低下させる元素であり、特に高張力鋼において悪影響が大きくなるため、その量は、できるだけ少ないことが好ましい。よってＳ量は、０．０１％以下、好ましくは０．００５％以下である。しかし工業的に、鋼中のＳ量を０％にすることは困難である。
[S: 0.01% or less (excluding 0%)]
S is an element that forms MnS and lowers the ductility, and the adverse effect is large particularly in high-strength steel. Therefore, the amount is preferably as small as possible. Therefore, the amount of S is 0.01% or less, preferably 0.005% or less. However, industrially, it is difficult to reduce the amount of S in steel to 0%.
［Ａｌ：０．０１〜０．１０％］
Ａｌは、脱酸、およびミクロ組織の微細化により母材靱性を向上させる効果を有する元素である。このような効果を充分に発揮させるため、Ａｌを０．０１％以上添加する。もっともＡｌを過剰に添加すると、かえって母材靱性およびＨＡＺ靱性が低下するため、上限を０．１０％とする。Ａｌ量の好ましい下限は０．０２０％である。一方、その好ましい上限は０．０６０％であり、より好ましくは０．０４０％以下である。
[Al: 0.01 to 0.10%]
Al is an element having an effect of improving the base material toughness by deoxidation and refinement of the microstructure. In order to sufficiently exhibit such effects, 0.01% or more of Al is added. However, when Al is added excessively, the base material toughness and the HAZ toughness are lowered, so the upper limit is made 0.10%. A preferable lower limit of the amount of Al is 0.020%. On the other hand, the preferable upper limit is 0.060%, more preferably 0.040% or less.
［Ｎｂ：０．０１５〜０．０３５％］
Ｎｂは、素地の焼入れ性を向上させて鋼板の強度を高めるために有効な元素である。このような効果を充分に発揮させるために、Ｎｂ量は０．０１５％以上であることが必要である。しかしＮｂを過剰に添加すると、母材靱性およびＨＡＺ靭性が低下するため、その上限量を０．０３５％と定めた。Ｎｂ量は、好ましくは０．０２０％以上であり、好ましくは０．０３０％以下、より好ましくは０．０２５％以下である。
[Nb: 0.015 to 0.035%]
Nb is an effective element for improving the hardenability of the substrate and increasing the strength of the steel sheet. In order to sufficiently exhibit such an effect, the Nb amount needs to be 0.015% or more. However, when Nb is added excessively, the base material toughness and the HAZ toughness are lowered, so the upper limit was set to 0.035%. The Nb amount is preferably 0.020% or more, preferably 0.030% or less, more preferably 0.025% or less.
［Ｔｉ：０．０１５〜０．０３％］
Ｔｉは、Ｎと微細な窒化物を形成し、溶接時におけるＨＡＺのオーステナイト粒の粗大化を抑制することにより（いわゆるピンニング効果）、ＨＡＺ靭性を向上させるために有効な元素である。このような効果を充分に発揮させるため、Ｔｉを０．０１５％以上添加する。しかしＴｉ量が過剰であると、かえってＨＡＺ靭性が劣化するため、Ｔｉ量の上限を０．０３％と定めた。Ｔｉ量は、好ましくは０．０１８％以上、０．０２５％以下である。
[Ti: 0.015-0.03%]
Ti is an effective element for improving HAZ toughness by forming fine nitrides with N and suppressing the coarsening of austenite grains of HAZ during welding (so-called pinning effect). In order to sufficiently exhibit such an effect, 0.015% or more of Ti is added. However, if the Ti amount is excessive, the HAZ toughness deteriorates, so the upper limit of the Ti amount is set to 0.03%. The amount of Ti is preferably 0.018% or more and 0.025% or less.
［Ｂ：０．００１５〜０．００３５％］
Ｂは、超大入熱溶接の際に、ＨＡＺ、殊にボンド部の付近で、ＢＮを核にした粒内フェライトを生成させると共に、固溶Ｎの固定作用も有し、ＨＡＺ靭性改善に重要な元素である。本発明では、その効果を充分に発揮させるためにＢを、通常の厚鋼板中の含有量よりも多く、０．００１５％以上含有させている。しかしＢ量が過剰であると、超大入熱溶接の際に粗大なベイナイト組織が形成されるため、かえってＨＡＺ靱性が劣化する。そのためＢ量の上限を０．００３５％と定めた。Ｂ量は、好ましくは０．００２０％以上、０．００３０％以下である。
[B: 0.0015 to 0.0035%]
B produces HAG, especially in the vicinity of the bond part, in the vicinity of the bond part, and generates intragranular ferrite with BN as the nucleus, and also has a fixing action of solute N, which is important for improving HAZ toughness. It is an element. In this invention, in order to fully exhibit the effect, B is contained more than the content in a normal thick steel plate, 0.0015% or more. However, if the amount of B is excessive, a coarse bainite structure is formed during super-high heat input welding, so that the HAZ toughness deteriorates. Therefore, the upper limit of the B amount is set to 0.0035%. The amount of B is preferably 0.0020% or more and 0.0030% or less.
［Ｎ：０．００５５〜０．０１％］
Ｎは、Ｔｉと結合して微細な炭窒化物を形成し、超大入熱溶接の際にオーステナイト粒の粗大化を抑制し、ＨＡＺ靭性を向上させる効果を有する元素である。Ｎ量が少なすぎると、上記効果が充分に発揮されないため、その下限を０．００５５％と定めた。一方、Ｎ量が過剰であると、母材靱性およびＨＡＺ靭性に悪影響を及ぼすため、その上限を０．０１％と定めた。Ｎ量の好ましい下限は０．００６０％であり、より好ましくは０．００７０％以上である。またＮ量の好ましい上限は０．００９０％であり、より好ましくは０．００８０％以下である。
[N: 0.0055 to 0.01%]
N combines with Ti to form fine carbonitrides, suppresses coarsening of austenite grains during super-high heat input welding, and has an effect of improving HAZ toughness. If the amount of N is too small, the above effect is not sufficiently exhibited, so the lower limit was set to 0.0055%. On the other hand, if the amount of N is excessive, the base material toughness and the HAZ toughness are adversely affected, so the upper limit was set to 0.01%. The minimum with the preferable amount of N is 0.0060%, More preferably, it is 0.0070% or more. Moreover, the upper limit with preferable N amount is 0.0090%, More preferably, it is 0.0080% or less.
［Ｃｕ：２．０％以下（０％を含む）］
Ｃｕは、焼入れ性を高めて強度向上に寄与する元素であり、必要に応じて添加することができる。またＣと同様にδ域の温度範囲を縮小させて、Ｔｉ系炭窒化物を微細化する効果を有すると考えられる。このような効果を充分に発揮させるために、Ｃｕ量は、好ましくは０．２０％以上、より好ましくは０．４０％以上であることが推奨される。しかしＣｕ量が過剰であると、母材靱性およびＨＡＺ靱性が低下する傾向があるため、その上限を２．０％と定めた。Ｃｕ量は好ましくは１．０％以下である。
[Cu: 2.0% or less (including 0%)]
Cu is an element that enhances hardenability and contributes to strength improvement, and can be added as necessary. Further, like C, it is considered that the temperature range in the δ region is reduced to refine the Ti-based carbonitride. In order to sufficiently exhibit such effects, it is recommended that the amount of Cu is preferably 0.20% or more, more preferably 0.40% or more. However, if the amount of Cu is excessive, the base material toughness and the HAZ toughness tend to decrease, so the upper limit was set to 2.0%. The amount of Cu is preferably 1.0% or less.
［Ｎｉ：２．０％以下（０％を含む）］
Ｎｉも、Ｃｕと同様に、焼入れ性を高めて強度向上に寄与し、δ域の温度範囲を縮小させるために有効な元素であり、必要に応じて添加することができる。このような効果を充分に発揮させるために、Ｎｉ量は、好ましくは０．２０％以上、より好ましくは０．４０％以上であることが推奨される。しかしＮｉ量が過剰であると、母材靱性およびＨＡＺ靱性が低下する傾向があるため、その上限を２．０％と定めた。Ｎｉ量は好ましくは１．０％以下である。
[Ni: 2.0% or less (including 0%)]
Ni, like Cu, is an element effective for increasing the hardenability and contributing to strength improvement, and reducing the temperature range in the δ region, and can be added as necessary. In order to sufficiently exhibit such an effect, it is recommended that the amount of Ni is preferably 0.20% or more, more preferably 0.40% or more. However, if the amount of Ni is excessive, the base material toughness and the HAZ toughness tend to decrease, so the upper limit was set to 2.0%. The amount of Ni is preferably 1.0% or less.
［Ｃｒ：１％以下（０％を含む）］
Ｃｒも、Ｃｕと同様に、焼入れ性を高めて強度向上に寄与する元素であり、必要に応じて添加することができる。このような効果を充分に発揮させるために、Ｃｒ量は、好ましくは０．２０％以上、より好ましくは０．４０％以上であることが推奨される。しかしＣｒ量が過剰であると、母材靱性およびＨＡＺ靱性が低下するので、その上限を１％と定めた。Ｃｒ量の好ましい上限は０．８０％である。
[Cr: 1% or less (including 0%)]
Cr, like Cu, is an element that increases the hardenability and contributes to strength improvement, and can be added as necessary. In order to sufficiently exhibit such effects, it is recommended that the Cr amount is preferably 0.20% or more, more preferably 0.40% or more. However, if the Cr amount is excessive, the base material toughness and the HAZ toughness are lowered, so the upper limit was set to 1%. The upper limit with preferable Cr amount is 0.80%.
［Ｍｏ：０．５％以下（０％を含む）］
Ｍｏは、焼入れ性を高めて強度を向上させることに加えて、焼戻し脆性を防止するために有効な元素であり、必要に応じて添加することができる。このような効果を充分に発揮させるために、Ｍｏ量は、好ましくは０．０５％以上、より好ましくは０．１０％以上であることが推奨される。しかしＭｏ量が過剰であると、母材靱性およびＨＡＺ靭性が劣化するため、その上限を０．５％と定めた。Ｍｏ量は、好ましくは０．３０％以下である。
[Mo: 0.5% or less (including 0%)]
Mo is an element effective for improving hardenability and improving strength and preventing temper embrittlement, and can be added as necessary. In order to sufficiently exhibit such an effect, the Mo amount is preferably 0.05% or more, more preferably 0.10% or more. However, if the amount of Mo is excessive, the base material toughness and the HAZ toughness deteriorate, so the upper limit was set to 0.5%. The amount of Mo is preferably 0.30% or less.
［Ｖ：０．１％以下（０％を含む）］
Ｖは、少量の添加により、焼入れ性および焼戻し軟化抵抗を高める効果を有する元素であり、必要に応じて添加することができる。このような効果を充分に発揮させるために、Ｖ量は、好ましくは０．０１％以上、より好ましくは０．０２％以上であることが推奨される。しかしＶ量が過剰であると、母材靱性およびＨＡＺ靭性が劣化するため、その上限を０．１％と定めた。Ｖ量は、好ましくは０．０５％以下である。
[V: 0.1% or less (including 0%)]
V is an element having an effect of enhancing hardenability and temper softening resistance by addition of a small amount, and can be added as necessary. In order to sufficiently exhibit such effects, it is recommended that the V amount is preferably 0.01% or more, more preferably 0.02% or more. However, if the amount of V is excessive, the base metal toughness and the HAZ toughness deteriorate, so the upper limit was set to 0.1%. The amount of V is preferably 0.05% or less.
本発明の厚鋼板は、上記成分の他は基本的に、Ｆｅおよび不可避不純物からなる。しかし本発明は、他の元素が含有される厚鋼板を排除するものではなく、本発明の範囲には、本発明の効果が損なわれない範囲で、他の成分元素を含有している厚鋼板も含まれる。 The thick steel plate of the present invention basically comprises Fe and inevitable impurities in addition to the above components. However, the present invention does not exclude thick steel plates containing other elements, and within the scope of the present invention is a thick steel plate containing other component elements as long as the effects of the present invention are not impaired. Is also included.
例えば本発明の厚鋼板には、上記成分の他、必要に応じて、（イ）Ｃａ：０．００５％以下（０％を含まない）および／またはＭｇ：０．００５％以下（０％を含まない）、（ロ）Ｚｒ：０．１％以下（０％を含まない）および／またはＨｆ：０．０５％以下（０％を含まない）、および／または（ハ）Ｃｏ：２．５％以下（０％を含まない）および／またはＷ：２．５％以下（０％を含まない）、等を含有させることも有効であり、含有させる成分の種類に応じて、鋼板の特性がさらに改善される。 For example, in the thick steel plate of the present invention, in addition to the above components, if necessary, (i) Ca: 0.005% or less (not including 0%) and / or Mg: 0.005% or less (0% (B) Zr: 0.1% or less (not including 0%) and / or Hf: 0.05% or less (not including 0%), and / or (c) Co: 2.5 % Or less (not including 0%) and / or W: 2.5% or less (not including 0%), etc. are also effective, and depending on the type of component to be included, the characteristics of the steel sheet Further improvement.
［Ｃａ：０．００５％以下および／またはＭｇ：０．００５％以下］
ＣａおよびＭｇは、ＨＡＺ靭性を向上させる効果を有する元素である。詳しくは、Ｃａは、ＭｎＳを球状化するという介在物の形態制御による異方性を低減させることによって、ＨＡＺ靭性を向上させる。一方、Ｍｇは、ＭｇＯを形成し、ＨＡＺのオーステナイト粒の粗大化を抑制することによってＨＡＺ靭性を向上させる。このような効果を充分に発揮させるために鋼板中に、Ｃａを好ましくは０．０００５％以上、および／またはＭｇを０．０００１％以上含有させることが好ましい。しかしこれらの量が過剰であると、かえって母材靱性およびＨＡＺ靱性を劣化させるので、Ｃａおよび／またはＭｇを含有させる場合の上限を、それぞれ０．００５％と定めた。Ｃａ量の好ましい上限は０．００３０％であり、Ｍｇ量の好ましい上限は０．００３５％である。
[Ca: 0.005% or less and / or Mg: 0.005% or less]
Ca and Mg are elements having an effect of improving the HAZ toughness. Specifically, Ca improves HAZ toughness by reducing anisotropy due to inclusion shape control of spheroidizing MnS. On the other hand, Mg improves the HAZ toughness by forming MgO and suppressing the coarsening of the HAZ austenite grains. In order to sufficiently exhibit such effects, the steel sheet preferably contains Ca of 0.0005% or more and / or Mg of 0.0001% or more. However, if these amounts are excessive, the base material toughness and the HAZ toughness are deteriorated, so the upper limit when Ca and / or Mg is contained is set to 0.005%. A preferable upper limit of the Ca amount is 0.0030%, and a preferable upper limit of the Mg amount is 0.0035%.
［Ｚｒ：０．１％以下および／またはＨｆ：０．０５％以下］
ＺｒおよびＨｆは、Ｔｉと同様に窒化物を形成し、溶接時におけるＨＡＺのオーステナイト粒の粗大化を抑制するので、ＨＡＺ靭性の改善に有効な元素である。このような効果を充分に発揮させるため、Ｚｒ量は、好ましくは０．００１％以上、Ｈｆ量は、好ましくは０．０００５％以上であることが推奨される。しかしこれらの量が過剰であると、かえって母材靱性およびＨＡＺ靭性が低下させるので、これらを含有させる場合、Ｚｒ量の上限を０．１％、Ｈｆ量の上限を０．０５％と定めた。
[Zr: 0.1% or less and / or Hf: 0.05% or less]
Zr and Hf are effective elements for improving the HAZ toughness because they form nitrides like Ti and suppress the coarsening of the austenite grains of the HAZ during welding. In order to sufficiently exhibit such effects, it is recommended that the amount of Zr is preferably 0.001% or more and the amount of Hf is preferably 0.0005% or more. However, if these amounts are excessive, the toughness of the base metal and the HAZ toughness are lowered. Therefore, when these are included, the upper limit of the Zr amount is set to 0.1% and the upper limit of the Hf amount is set to 0.05%. .
［Ｃｏ：２．５％以下および／またはＷ：２．５％以下］
ＣｏおよびＷは、焼入れ性を向上させ、鋼板の強度を高める効果を有する元素である。このような効果を充分に発揮させるため、これらの１つまたは両方を、それぞれ０．２％以上で含有させることが好ましい。しかしこれらの量が過剰であると、母材靱性およびＨＡＺ靭性が劣化するため、これらの量の上限を、それぞれ２．５％と定めた。
[Co: 2.5% or less and / or W: 2.5% or less]
Co and W are elements having an effect of improving hardenability and increasing the strength of the steel sheet. In order to fully exhibit such an effect, it is preferable to contain one or both of these in an amount of 0.2% or more. However, if these amounts are excessive, the base material toughness and the HAZ toughness deteriorate, so the upper limit of these amounts was set to 2.5%.
本発明の厚鋼板は、上記化学成分量、［Ｔｉ］／［Ｎ］およびＸ値の要件を満たす鋼を、通常の溶製法によって溶製し、この溶鋼を冷却してスラブとした後、通常の条件で加熱および熱間圧延を行い、次いで焼入れ（場合により焼入れ・焼戻し）を行うことにより製造することができる。 The thick steel plate of the present invention is usually prepared by melting steel satisfying the above-mentioned chemical component amounts, [Ti] / [N] and X value by a normal melting method, and cooling the molten steel into a slab. It can manufacture by performing a heating and hot rolling on these conditions, and then quenching (it quenching and tempering depending on the case).
本発明の厚鋼板は、Ｘ値を制御してδ域の温度範囲を狭くさせているので、溶鋼を通常の条件で冷却（例えば１５００℃から１１００℃までを０．１〜２．０℃／秒の冷却速度で冷却）してスラブを形成することにより、充分に小さいＴｉ系およびＮｂ系炭窒化物の平均粒子径を形成することができる。但し、より微細な炭窒化物を形成させるために、鋳造機の冷却水量や冷却方法を変更させて、凝固時の冷却速度を向上させることが好ましい。 Since the thick steel plate of the present invention controls the X value to narrow the temperature range in the δ region, the molten steel is cooled under normal conditions (for example, from 1500 ° C. to 1100 ° C. at 0.1 to 2.0 ° C. / By cooling at a cooling rate of 2 seconds) to form a slab, sufficiently small average particle diameters of Ti-based and Nb-based carbonitrides can be formed. However, in order to form a finer carbonitride, it is preferable to improve the cooling rate during solidification by changing the amount of cooling water and the cooling method of the casting machine.
本発明は厚鋼板に関するものであり、該分野において厚鋼板とは、ＪＩＳで定義されるように、一般に板厚が３．０ｍｍ以上であるものを指す。しかし本発明の厚鋼板の板厚は、好ましくは２０ｍｍ以上、好ましくは４０ｍｍ以上、さらに好ましくは６０ｍｍ以上である。なぜなら本発明の厚鋼板は、入熱量が５０ｋＪ／ｍｍである超大入熱溶接であっても良好なＨＡＺ靱性を示すので、板厚が厚くても、入熱量を増大させることで効率よく溶接できるからである。 The present invention relates to a thick steel plate. In this field, a thick steel plate generally refers to one having a plate thickness of 3.0 mm or more as defined by JIS. However, the thickness of the steel plate of the present invention is preferably 20 mm or more, preferably 40 mm or more, and more preferably 60 mm or more. This is because the thick steel plate of the present invention exhibits good HAZ toughness even with super-high heat input welding with a heat input of 50 kJ / mm, so even if the plate thickness is large, it can be efficiently welded by increasing the heat input. Because.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより以下の実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples as a matter of course, and appropriate modifications are made within a range that can meet the purpose described above and below. Of course, it is also possible to implement them, and they are all included in the technical scope of the present invention.
表１に示す組成の鋼を、通常の溶製法によって溶製し、この溶鋼を０．１〜２．０℃／分の冷却速度で１５００℃から１１００℃まで冷却してスラブとした後、１１００℃に加熱して熱間圧延を行い、および場合により焼戻しを行い、板厚６０ｍｍの高張力鋼板を製造した。 The steel having the composition shown in Table 1 was melted by a normal melting method, and this molten steel was cooled from 1500 ° C. to 1100 ° C. at a cooling rate of 0.1 to 2.0 ° C./min to form a slab. A high-tensile steel sheet having a thickness of 60 mm was manufactured by heating to 0 ° C. and hot rolling, and optionally tempering.
鋼板の化学成分組成から計算した［Ｔｉ］／［Ｎ］およびＸ値、並びにＴｈｅｒｍｏ−ｃａｌｃから計算したδ域の温度範囲の値（表中で「δ域」と記載）を、表２に示す。
また上記のようにして製造した鋼板について、下記要領でＴｉ系炭窒化物の平均粒子径、Ｎｂ系炭窒化物の平均粒子径、鋼板の引張強度、低温靱性およびＨＡＺ靱性を測定した。これらの結果を表２に示す。
Table 2 shows the [Ti] / [N] and X values calculated from the chemical composition of the steel sheet, and the value of the temperature range in the δ range calculated from Thermo-calc (described as “δ range” in the table). .
Further, with respect to the steel sheet produced as described above, the average particle diameter of the Ti-based carbonitride, the average particle diameter of the Nb-based carbonitride, the tensile strength of the steel sheet, the low temperature toughness and the HAZ toughness were measured in the following manner. These results are shown in Table 2.
［Ｔｉ系炭窒化物およびＮｂ系炭窒化物の平均粒子径］
深さｔ／４の位置（ｔ＝板厚）を、透過型電子顕微鏡（ＴＥＭ）で、観察倍率６万倍、観察視野２．０×２．０μｍ、観察箇所５箇所の条件で観察した。そしてその視野中の各炭窒化物の面積を測定し、この面積から各炭窒化物の円相当径を算出した。この各炭窒化物の円相当径を算術平均（相加平均）して、各鋼板におけるＴｉ系またはＮｂ系炭窒化物の平均粒子径を算出した。
[Average particle diameter of Ti-based carbonitride and Nb-based carbonitride]
A position at a depth t / 4 (t = plate thickness) was observed with a transmission electron microscope (TEM) under the conditions of an observation magnification of 60,000 times, an observation field of view 2.0 × 2.0 μm, and five observation locations. Then, the area of each carbonitride in the field of view was measured, and the equivalent circle diameter of each carbonitride was calculated from this area. The circle equivalent diameter of each carbonitride was arithmetically averaged (arithmetic average), and the average particle size of Ti-based or Nb-based carbonitride in each steel plate was calculated.
［引張強度］
深さｔ／４の位置（ｔ＝板厚）でＪＩＳ４号試験片を採取し、引張試験を行うことにより、引張強度を測定した。この実施例では、引張強度が４９０ＭＰａ以上のものを合格とした。
[Tensile strength]
Tensile strength was measured by collecting a JIS No. 4 test piece at a position of depth t / 4 (t = plate thickness) and conducting a tensile test. In this example, those having a tensile strength of 490 MPa or more were regarded as acceptable.
［低温靱性］
深さｔ／４の位置（ｔ＝板厚）でＪＩＳ４号試験片を採取し、−６０℃でシャルピー衝撃試験を行い、吸収エネルギー（ｖＥ-60）を測定した。この実施例では、引張強度が１５０Ｊ以上のものを合格とした。
[Low temperature toughness]
A JIS No. 4 test piece was sampled at a position of depth t / 4 (t = plate thickness), subjected to a Charpy impact test at −60 ° C., and the absorbed energy (vE −60 ) was measured. In this example, those having a tensile strength of 150 J or more were regarded as acceptable.
［ＨＡＺ靭性］
入熱５０ｋＪ／ｍｍで溶接（エレクトロガスアーク溶接）を行い、図１に示す部位からＪＩＳ４号試験片を採取し（ノッチ位置は、ボンドから０．５ｍｍＨＡＺ側）、−４０℃でシャルピー衝撃試験を行い、吸収エネルギー（ｖＥ-40）を測定した。この実施例では、引張強度が２００Ｊ以上のものを合格とした。
[HAZ toughness]
Perform welding (electrogas arc welding) at a heat input of 50 kJ / mm, extract a JIS No. 4 specimen from the site shown in FIG. 1 (notch position is 0.5 mm HAZ side from the bond), and perform a Charpy impact test at -40 ° C. The absorbed energy (vE- 40 ) was measured. In this example, those having a tensile strength of 200 J or more were regarded as acceptable.
鋼板Ｎｏ．１〜２４は、本発明の各化学成分量の要件を満たすものである。また鋼板Ｎｏ．２５および２６は、Ｃ量は本発明で規定する下限未満であるが、その他の成分量の要件は満たすものである。これら鋼板Ｎｏ．１〜２６のＸ値とδ域の温度範囲との関係、Ｘ値とＴｉ系炭窒化物の平均粒子径との関係、およびＸ値とＮｂ系炭窒化物の平均粒子径との関係を図２〜４に示す。図２から分かるように、Ｘ値とδ域の温度範囲とは、良好な相関関係（具体的にはほぼ反比例の関係）にある。また図３および４から分かるように、Ｘ値が増大するにつれ、炭窒化物の平均粒子径が減少している。 Steel plate No. 1-24 satisfy | fill the requirements of each chemical component amount of this invention. Steel plate No. In Nos. 25 and 26, the amount of C is less than the lower limit specified in the present invention, but the requirements for the other component amounts are satisfied. These steel plates No. The relationship between the X value of 1 to 26 and the temperature range of the δ region, the relationship between the X value and the average particle size of the Ti-based carbonitride, and the relationship between the X value and the average particle size of the Nb-based carbonitride are illustrated. 2-4. As can be seen from FIG. 2, the X value and the temperature range in the δ region have a good correlation (specifically, a substantially inversely proportional relationship). As can be seen from FIGS. 3 and 4, the average particle size of carbonitrides decreases as the X value increases.
鋼板Ｎｏ．１〜２６のＸ値とＨＡＺ靱性（ｖＥ-40）との関係、Ｘ値と低温靱性（ｖＥ-60）との関係、δ域の温度範囲とＨＡＺ靱性（ｖＥ-40）との関係、およびδ域の温度範囲と低温靱性（ｖＥ-60）との関係を、図５〜８に示す。これらの図から分かるように、Ｘ値が増大するにつれ、即ちδ域の温度範囲が減少するにつれ、鋼板のＨＡＺ靱性および低温靱性が向上している。そしてＸ値が４０以上である鋼板（δ域の温度範囲が４０℃以下である鋼板）は、そのｖＥ-40が２００Ｊ以上であり、ｖＥ-60が１５０Ｊ以上であり、良好なＨＡＺ靱性および低温靱性を有している。これは、Ｘ値が４０以上となるように化学成分組成を調整することにより、δ域の温度範囲が狭くなる結果、Ｔｉの拡散が抑制されて、Ｔｉ系炭窒化物およびＮｂ系炭窒化物の平均粒子径が抑制されたためであると考えられる。 Steel plate No. Relationship between X value of 1 to 26 and HAZ toughness (vE -40 ), relationship between X value and low temperature toughness (vE -60 ), relationship between temperature range of δ region and HAZ toughness (vE -40 ), and The relationship between the temperature range of the δ region and the low temperature toughness (vE- 60 ) is shown in FIGS. As can be seen from these figures, as the X value increases, that is, as the temperature range in the δ region decreases, the HAZ toughness and low temperature toughness of the steel sheet are improved. A steel plate having an X value of 40 or more (a steel plate having a temperature range in the δ region of 40 ° C. or less) has a vE -40 of 200 J or more, a vE -60 of 150 J or more, good HAZ toughness and low temperature. Has toughness. This is because, by adjusting the chemical composition so that the X value is 40 or more, the temperature range in the δ region is narrowed. As a result, Ti diffusion is suppressed, and Ti-based carbonitride and Nb-based carbonitride This is considered to be because the average particle size of the particles was suppressed.
さらに鋼板Ｎｏ．１〜２６のＴｉ系炭窒化物の平均粒子径とＨＡＺ靱性（ｖＥ-40）との関係、およびＮｂ系炭窒化物の平均粒子径と低温靱性（ｖＥ-60）との関係を、図９および１０に示す。これらの図から炭窒化物の平均粒子径が小さくなるにつれ、ＨＡＺ靱性および低温靱性は向上することが分かる。殊に図９から、Ｔｉ系炭窒化物の平均粒子径が４０ｎｍ以下であれば、２００Ｊ以上のｖＥ-40が達成されることが示され、図１０からＮｂ系炭窒化物の平均粒子径が６０ｎｍ以下であれば、１５０Ｊ以上のｖＥ-60が達成されることが示される。 Furthermore, steel plate No. FIG. 9 shows the relationship between the average particle size of 1 to 26 Ti-based carbonitrides and the HAZ toughness (vE- 40 ), and the relationship between the average particle size of Nb-based carbonitrides and the low-temperature toughness (vE- 60 ). And 10. From these figures, it can be seen that the HAZ toughness and the low temperature toughness are improved as the average particle size of the carbonitride is reduced. In particular, FIG. 9 shows that if the average particle size of the Ti-based carbonitride is 40 nm or less, vE- 40 of 200 J or more is achieved, and FIG. 10 shows that the average particle size of the Nb-based carbonitride is If it is 60 nm or less, it shows that vE- 60 of 150 J or more is achieved.
表にまとめた結果から、本発明の各化学成分量、［Ｔｉ］／［Ｎ］およびＸ値の要件を満たす鋼板Ｎｏ．１〜２３は、引張強度、低温靱性およびＨＡＺ靱性に優れていることが分かる。これに対して、基本的に本発明の各化学成分量の要件を満たすが、４０≦Ｘ値の要件を満たさない鋼板Ｎｏ．２４〜２６は、低温靱性、または低温およびＨＡＺ靱性の両方が不充分である。さらに鋼板Ｎｏ．２５および２６は、Ｃ量が０．０３０％未満であり、引張強度も不充分である。 From the results summarized in the table, the steel plate No. satisfying the requirements of the amount of each chemical component, [Ti] / [N] and X value of the present invention. 1 to 23 are found to be excellent in tensile strength, low temperature toughness and HAZ toughness. On the other hand, the steel plate No. which basically satisfies the requirements of each chemical component amount of the present invention but does not satisfy the requirement of 40 ≦ X value. 24-26 are insufficient in low temperature toughness, or both low temperature and HAZ toughness. Furthermore, steel plate No. Nos. 25 and 26 have a C content of less than 0.030% and insufficient tensile strength.
本発明で規定する化学成分量の上限値の要件のいずれかを満たさない鋼板Ｎｏ．２７〜３３、３５、３７および４０は、化学成分のいずれかを過剰に含有するため、低温靱性およびＨＡＺ靱性の両方とも不充分である。逆に本発明で規定する各化学成分量の下限値の要件のいずれかを満たさない鋼板も、靱性が不充分である。具体的にはＴｉまたはＮを下限値未満でしか含有しない鋼板Ｎｏ．３４または３８は、Ｔｉ系炭窒化物が充分に形成されないため、ＨＡＺ靱性が不充分である。同様にＢを下限値未満でしか含有しない鋼板Ｎｏ．３６は、ＢＮが充分に形成されないため、ＨＡＺ靱性が不充分である。さらに鋼板Ｎｏ．３９は、［Ｔｉ］／［Ｎ］が２未満であり、過剰Ｎの影響で靱性が不充分である。 Steel plate No. which does not satisfy any of the requirements for the upper limit value of the chemical component amount defined in the present invention. 27-33, 35, 37 and 40 contain either of the chemical components in excess, so both low temperature toughness and HAZ toughness are insufficient. Conversely, a steel sheet that does not meet any of the requirements for the lower limit value of each chemical component defined in the present invention is also insufficient in toughness. Specifically, steel plate No. containing Ti or N only below the lower limit value. No. 34 or 38 has insufficient HAZ toughness because Ti-based carbonitrides are not sufficiently formed. Similarly, a steel plate No. containing only B below the lower limit value. No. 36 has insufficient HAZ toughness because BN is not sufficiently formed. Furthermore, steel plate No. In No. 39, [Ti] / [N] is less than 2, and the toughness is insufficient due to the influence of excess N.
Claims (7)
２≦［Ｔｉ］／［Ｎ］≦４ ・・・ （１）
４０≦Ｘ値 ・・・ （２）
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］
（式中、［ ］は各元素の含有量（質量％）を表す。） C: 0.030 to 0.080% (meaning of mass%, the same shall apply hereinafter), Si: 1.0% or less (not including 0%), Mn: 0.8 to 2.0%, P: 0.0. 03% or less (not including 0%), S: 0.01% or less (not including 0%), Al: 0.01 to 0.10%, Nb: 0.015 to 0.035%, Ti: 0.015 to 0.03%, B: 0.0015 to 0.0035%, and N: 0.0055 to 0.01%, further Cu: 2.0% or less (including 0%), Ni: 2.0% or less (including 0%), Cr: 1% or less (including 0%), Mo: 0.5% or less (including 0%), and V: 0.1% or less (0%) HAZ toughness and low-temperature base material toughness characterized in that the balance consists of Fe and inevitable impurities, and satisfies the following formulas (1) and (2): Excellent thick steel plate.
2 ≦ [Ti] / [N] ≦ 4 (1)
40 ≦ X value (2)
X value = 500 [C] +32 [Si] +8 [Mn] -9 [Nb]
+14 [Cu] +17 [Ni] -5 [Cr] -25 [Mo] -34 [V]
(In the formula, [] represents the content (% by mass) of each element.)
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| JPS62174323A (en) * | 1986-01-24 | 1987-07-31 | Kobe Steel Ltd | Manufacture of nontempered thick steel plate having 50kgf/mm2 yield strength or more and superior weldability |
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