JP2008255458A - Thick steel plate having haz toughness and base metal toughness - Google Patents
Thick steel plate having haz toughness and base metal toughness Download PDFInfo
- Publication number
- JP2008255458A JP2008255458A JP2007101944A JP2007101944A JP2008255458A JP 2008255458 A JP2008255458 A JP 2008255458A JP 2007101944 A JP2007101944 A JP 2007101944A JP 2007101944 A JP2007101944 A JP 2007101944A JP 2008255458 A JP2008255458 A JP 2008255458A
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel plate
- thick steel
- toughness
- amount
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
Abstract
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、好ましくは小入熱溶接から超大入熱溶接に至る幅広い入熱量で溶接しても溶接後の熱影響部（Ｈｅａｔ Ａｆｆｅｃｔｅｄ Ｚｏｎｅ、ＨＡＺ）の靭性に優れると共に、母材靭性にも優れた厚鋼板に関する。 The present invention relates to a thick steel plate applied to a welded structure such as a ship and an offshore structure, and preferably a heat-affected zone after welding even if welding is performed with a wide heat input ranging from small heat input welding to super large heat input welding. The present invention relates to a thick steel plate having excellent toughness of (Heat Affected Zone, HAZ) and excellent 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、小入熱溶接時のみならず、入熱量が５０ｋＪ／ｍｍ以上である超大入熱溶接を行ってもＨＡＺ靭性に優れていることが求められる。 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 efficiently weld such a thick steel plate, it is required to have excellent HAZ toughness not only at the time of small heat input welding but also by performing 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靭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, since the HAZ is heated to a high temperature austenite region and then gradually cooled, 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靭性を達成するために、例えば特許文献１は、低Ｃ化、低Ｐ化に加えてＮｂとＢの添加バランスを調節している。また特許文献２では、溶接用鋼中に存在するＴｉＮ系介在物の中に積極的にＮｂを含有させて、粗大フェライトの生成を抑制している。しかしこれら特許文献１〜２では、ＴｉＮが不足しているか、又はＴｉＮが足りている場合にはそのＴｉＮが粗大化しており、さらなるＨＡＺ靭性の改善余地があった。また母材靭性についても考慮されていなかった。 In order to achieve good HAZ toughness by such super-high heat input welding, for example, Patent Document 1 adjusts the addition balance of Nb and B in addition to lowering C and lowering P. In Patent Document 2, Nb is positively contained in TiN inclusions present in the welding steel to suppress the formation of coarse ferrite. However, in these Patent Documents 1 and 2, when TiN is insufficient or TiN is sufficient, TiN is coarsened, and there is room for further improvement of HAZ toughness. In addition, the base material toughness was not taken into consideration.
特許文献３は、鋼材にＮを比較的多量に添加し、かつＴｉとＢの添加バランスを適切に制御すれば、大入熱溶接したときのＨＡＺ靭性を改善できるとしている。しかし特許文献３でも、ＴｉＮやＢＮの析出量が十分でなかったり、微細でなかったり、またはＮｂが不足して焼入性が低いためにフェライトが粗大になったりするため、さらなるＨＡＺ靭性の改善余地がある。また母材靭性についても考慮されていない。
本発明の目的は、小入熱溶接及び超大入熱溶接のいずれであっても優れたＨＡＺ靭性を示すと共に、母材靭性にも優れた厚鋼板を提供することにある。 An object of the present invention is to provide a thick steel plate that exhibits excellent HAZ toughness and excellent base metal toughness in both small heat input welding and super large heat input welding.
前記課題を解決し得た本発明に係るＨＡＺ靭性および母材靭性に優れた厚鋼板は、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：０．００５〜０．０３５％、Ｔｉ：０．０１５〜０．０３％、Ｂ：０．００１０〜０．００３５％、およびＮ：０．００５０〜０．０１％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％以下（０％を含む）を含有し、
残部がＦｅおよび不可避不純物からなる厚鋼板であって、
旧オーステナイト粒の平均円相当径が１２０μｍ以下、島状マルテンサイト（Ｍａｒｔｅｎｓｉｔｅ−Ａｕｓｔｅｎｉｔｅ ｃｏｎｓｔｉｔｕｅｎｔ（ＭＡ））の面積百分率が３％以下、かつ島状マルテンサイト（ＭＡ）のアスペクト比（長径／短径）の個数平均値が３以下であり、
しかも下記式（１）および（２）を満足している点にその要旨を有する。
１．５≦［Ｔｉ］／［Ｎ］≦４ … （１）
４０≦Ｘ値≦１６０ … （２）
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］
（式中、［Ｔｉ］、［Ｎ］、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｎｂ］、［Ｃｕ］、［Ｎｉ］、［Ｃｒ］、［Ｍｏ］、［Ｖ］は鋼板中の各元素の含有量（質量％）を表す）
The thick steel plate excellent in HAZ toughness and base metal toughness according to the present invention that can solve the above problems is C: 0.030 to 0.10% (meaning of mass%, the same applies hereinafter), Si: 1.0% (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: 0.01-0.10%, Nb: 0.005-0.035%, Ti: 0.015-0.03%, B: 0.0010-0.0035%, and N: 0.0050 Contains ~ 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% or less (including 0%),
The balance is a thick steel plate made of Fe and inevitable impurities,
The average equivalent circle diameter of the prior austenite grains is 120 μm or less, the area percentage of island martensite (MA) is 3% or less, and the aspect ratio (major axis / minor axis) of island martensite (MA) The number average value of is 3 or less,
Moreover, it has the gist in that it satisfies the following formulas (1) and (2).
1.5 ≦ [Ti] / [N] ≦ 4 (1)
40 ≦ X value ≦ 160 (2)
X value = 500 [C] +32 [Si] +8 [Mn] -9 [Nb]
+14 [Cu] +17 [Ni] -5 [Cr] -25 [Mo] -34 [V]
(In the formula, [Ti], [N], [C], [Si], [Mn], [Nb], [Cu], [Ni], [Cr], [Mo], [V] are in the steel plate. The content (% by mass) of each element of
本発明の厚鋼板のδ域の温度範囲は、例えば、４０℃以下である。本発明の厚鋼板では、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以下であることが望ましい。 The temperature range of the δ region of the thick steel plate of the present invention is, for example, 40 ° C. or less. In the thick steel plate of the present invention, it is desirable that the average particle diameter of the Ti-based carbonitride is 40 nm or less at a position of depth t / 4 (t = plate thickness).
本発明の厚鋼板は、さらにＣａ：０．００５％以下（０％を含まない）、Ｍｇ：０．００５％以下（０％を含まない）、ＲＥＭ：０．０１％以下（０％を含まない）、Ｚｒ：０．１％以下（０％を含まない）、Ｈｆ：０．０５％以下（０％を含まない）、Ｃｏ：２．５％以下（０％を含まない）、Ｗ：２．５％以下（０％を含まない）などを含有していてもよい。
なお本明細書において「炭窒化物」は、炭化物、窒化物も含む意味で使用する。
The thick steel plate of the present invention is further Ca: 0.005% or less (not including 0%), Mg: 0.005% or less (not including 0%), REM: 0.01% or less (including 0%) Zr: 0.1% or less (not including 0%), Hf: 0.05% or less (not including 0%), Co: 2.5% or less (not including 0%), W: It may contain 2.5% or less (not including 0%).
In the present specification, “carbonitride” is used to include carbides and nitrides.
本発明によれば、各元素の量をそれぞれ単独で制御するだけでなく、Ｘ値、Ｔｉ／Ｎ比などの観点から各元素量の相互の関係を制御しており、しかも旧オーステナイト（γ）粒と島状マルテンサイト（ＭＡ）の大きさ、形態などを制御しているため、小入熱溶接及び超大入熱溶接のいずれであっても優れたＨＡＺ靭性を示し、かつ母材靭性にも優れている厚鋼板を得ることができる。 According to the present invention, not only the amount of each element is controlled independently, but also the mutual relationship between the amounts of each element is controlled from the viewpoint of the X value, Ti / N ratio, etc., and the prior austenite (γ) Since the size and shape of grains and island martensite (MA) are controlled, excellent HAZ toughness is exhibited in both small heat input welding and super large heat input welding, and the base material toughness is also improved. An excellent thick steel plate can be obtained.
本発明の厚鋼板では、ＨＡＺ靭性を改善するために（Ａ）Ｘ値と（Ｂ）Ｔｉ／Ｎ比を制御し、また延性・脆性遷移温度（破面率遷移温度（ｖＴｒｓ）。以下、単に遷移温度という）を下げて母材靭性を改善するために（Ｃ）旧オーステナイト粒と島状マルテンサイト組織（ＭＡ）の大きさや形状を制御している。以下、順に説明する。 In the thick steel sheet of the present invention, (A) the X value and (B) the Ti / N ratio are controlled to improve the HAZ toughness, and the ductility / brittle transition temperature (fracture surface ratio transition temperature (vTrs). (C) The size and shape of prior austenite grains and island martensite structure (MA) are controlled in order to lower the transition temperature and improve the base material toughness. Hereinafter, it demonstrates in order.
（Ａ）Ｘ値
Ｘ値はδ域の温度範囲に関する関数である。ＨＡＺ靭性の改善を試みて、このＸ値に到達した経緯を説明する。まず始めに本発明者らは、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靭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。
(A) X value The X value is a function related to the temperature range of the δ region. An attempt to improve the HAZ toughness and how this X value was reached will be explained. First, the present inventors 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.
前記「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。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。 The “δ region” means a region including 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). In 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。δ域の温度範囲が広いほど、δ鉄が存在する時間が長くなってＴｉの拡散が進むため、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。特定成分を基準にしつつ化学成分量の１つだけを変更しながらＴｈｅｒｍｏ−ｃａｌｃの計算を繰り返すことにより、各化学成分のδ域の温度範囲への影響を調べた。この計算に基づき、δ域の温度範囲と相関関係があり、化学成分組成の関数として表されるＸ値（下記式（３））を定めた：
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］…（３）
（式中、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｎｂ］、［Ｃｕ］、［Ｎｉ］、［Ｃｒ］、［Ｍｏ］、［Ｖ］は鋼板中の各元素の含有量（質量％）を表す。）
In this δ iron, the diffusion rate of Ti is fast. It is considered that the wider the temperature range in the δ region, the longer the time during which δ iron is present and the Ti diffusion proceeds, so that coarse Ti-based carbonitrides are more 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. The influence of each chemical component on the temperature range in the δ region was examined by repeating the calculation of Thermo-calc while changing only one of the chemical component amounts while using the specific component as a reference. Based on this calculation, an X value (formula (3) below), which is 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] (3)
(In the formula, [C], [Si], [Mn], [Nb], [Cu], [Ni], [Cr], [Mo], [V] are the contents (mass of each element in the steel plate). %).)
Ｘ値を定める上記式（３）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域の温度範囲の減少量に対応する。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 (3) for determining the X value corresponds to the amount of decrease 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).
そして様々なＸ値を有する鋼板を製造してそれらの特性を調べたところ、Ｘ値を増大させることによって（δ域の温度範囲を狭くすることによって）、Ｔｉ系炭窒化物が微細化し、かつ小入熱溶接及び超大入熱溶接のいずれであってもＨＡＺ靭性が向上することが判明した。 And when the steel plate which has various X value was manufactured and those characteristics were investigated, Ti system carbonitride refined | miniaturized by increasing X value (by narrowing the temperature range of (delta) area), and It has been found that the HAZ toughness is improved by either the small heat input welding or the super large heat input welding.
従って本発明の厚鋼板では、Ｘ値の値が下記式（２）を満足するようにする。なおＸ値の意味は上記のように解釈されるが、最も重要なのはＸ値と諸特性との間に相関関係がある点であり、解釈の如何に拘わらずＸ値を満足するものは本発明に含まれる。
４０≦Ｘ値≦１６０ … （２）
Therefore, in the thick steel plate of the present invention, the value of X satisfies the following formula (2). The meaning of the X value is interpreted as described above, but the most important point is that there is a correlation between the X value and various characteristics. What satisfies the X value regardless of the interpretation is the present invention. include.
40 ≦ X value ≦ 160 (2)
Ｘ値の範囲は、４０以上、好ましくは４５以上、さらに好ましくは５０以上である。Ｘ値が大きくなるほど、Ｔｉ系炭窒化物が微細化し、ＨＡＺ靭性が良好になる。しかしＸ値が大きくなると、島状マルテンサイト組織（Ｍａｒｔｅｎｓｉｔｅ−Ａｕｓｔｅｎｉｔｅ ｃｏｎｓｔｉｔｕｅｎｔ（ＭＡ））が増大する。従ってＸ値は、１６０以下、好ましくは１００以下、さらに好ましくは７５以下である。 The range of the X value is 40 or more, preferably 45 or more, more preferably 50 or more. As the X value increases, the Ti-based carbonitride becomes finer and the HAZ toughness becomes better. However, as the X value increases, the island-like martensite structure (MA) increases. Therefore, the X value is 160 or less, preferably 100 or less, more preferably 75 or less.
（Ｂ）Ｔｉ／Ｎ比
また本発明の厚鋼板では、Ｔｉ量とＮ量とのバランスをとることによって、ＨＡＺ靭性を改善している。具体的には下記式（１）を満足するようにしている。
１．５≦［Ｔｉ］／［Ｎ］≦４ … （１）
（式中、［Ｔｉ］、［Ｎ］は鋼板中の各元素の含有量（質量％）を表す。）
(B) Ti / N ratio In the thick steel plate of the present invention, the HAZ toughness is improved by balancing the Ti amount and the N amount. Specifically, the following formula (1) is satisfied.
1.5 ≦ [Ti] / [N] ≦ 4 (1)
(In the formula, [Ti] and [N] represent the content (mass%) of each element in the steel sheet.)
［Ｔｉ］／［Ｎ］が４を超えると、Ｔｉ系炭窒化物が粗大になり、ＨＡＺ靭性が低下する。好ましい［Ｔｉ］／［Ｎ］は、３．５以下である。また逆に［Ｔｉ］／［Ｎ］が１．５未満であれば、過剰Ｎの影響で、ＨＡＺ靭性が低下する。好ましい［Ｔｉ］／［Ｎ］は、２．０以上、より好ましくは２．５以上である。 When [Ti] / [N] exceeds 4, the Ti carbonitride becomes coarse and the HAZ toughness decreases. [Ti] / [N] is preferably 3.5 or less. On the other hand, if [Ti] / [N] is less than 1.5, the HAZ toughness decreases due to the influence of excess N. [Ti] / [N] is preferably 2.0 or more, more preferably 2.5 or more.
靭性の観点から、本発明の厚鋼板中のＴｉ系炭窒化物は微細であることが好ましい。本発明の厚鋼板中のＴｉ系炭窒化物は、例えば、４０ｎｍ以下、好ましくは３０ｎｍ以下である。 From the viewpoint of toughness, the Ti-based carbonitride in the thick steel plate of the present invention is preferably fine. The Ti-based carbonitride in the thick steel plate of the present invention is, for example, 40 nm or less, preferably 30 nm or less.
なお本発明におけるＴｉ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（後述する実施例では６万倍）、観察視野２．０×２．０μｍ以上（後述する実施例では２．０×２．０μｍ）、観察箇所５箇所以上（後述する実施例では５箇所）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系炭窒化物の平均粒子径とする。 In addition, the value of the average particle diameter of the Ti-based carbonitride in the present invention is a value measured as follows. First, a position at a depth t / 4 (t = plate thickness) as a portion representing the thermal history of a steel plate is observed with a transmission electron microscope (TEM) at an observation magnification of 60,000 times or more (in the examples described later, 60,000 times). ), An observation visual field of 2.0 × 2.0 μm or more (2.0 × 2.0 μm in the examples described later), and observation sites of 5 or more locations (5 locations in the examples described later). 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. A value obtained by arithmetically averaging (arithmetic mean) the equivalent circle diameters of the carbonitrides is defined as the average particle diameter of the Ti-based carbonitrides in the present invention.
なおＴｉ系炭窒化物であるかの判別は、各炭窒化物粒子の主体となる成分によって定まる。すなわちＴｉ系炭窒化物とは、炭素および窒素を除いた残りの元素の合計質量を１００％としたとき、Ｔｉの割合が５０質量％以上になるものをいう。元素の量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、円相当径が５ｎｍ以上のものに限定する。 In addition, discrimination | determination whether it is Ti type carbonitride is decided by the component used as the main body of each carbonitride particle | grain. That is, the Ti-based carbonitride refers to a material in which the ratio of Ti is 50% by mass or more when the total mass of the remaining elements excluding carbon and nitrogen is 100%. The amount of element can be determined by an energy dispersive X-ray detector (EDX). In addition, since an extremely fine carbonitride cannot be measured, the carbonitride in the present invention is limited to those having an equivalent circle diameter of 5 nm or more.
（Ｃ）旧オーステナイト粒と島状マルテンサイト組織（ＭＡ）
さらに本発明の厚鋼板では、組織制御もされており、具体的には旧オーステナイト粒の平均円相当径が１２０μｍ以下、島状マルテンサイト（ＭＡ）の面積百分率が３％以下、かつ島状マルテンサイト（ＭＡ）のアスペクト比（長径／短径）の個数平均値が３以下である。組織制御することによって、遷移温度（ｖＴｒｓ）を下げることができる。なお本発明の厚鋼板の組織は、ベイナイトを主体とする組織、又はフェライトとベイナイトを主体と組織である。主体とは面積率で７０％以上であることをいい、残りの組織には、前述の島状マルテンサイト（ＭＡ）の他、パーライト、マルテンサイト、残留オーステナイト、セメンタイトなどの１種又は２種以上が含まれる。
(C) Old austenite grain and island martensite structure (MA)
Furthermore, in the thick steel plate of the present invention, the structure is controlled. Specifically, the average equivalent circle diameter of the prior austenite grains is 120 μm or less, the area percentage of island martensite (MA) is 3% or less, and the island martensite. The number average value of the aspect ratio (major axis / minor axis) of the site (MA) is 3 or less. By controlling the tissue, the transition temperature (vTrs) can be lowered. The structure of the thick steel plate of the present invention is a structure mainly composed of bainite or a structure mainly composed of ferrite and bainite. The main body means an area ratio of 70% or more, and the remaining structure includes one or more of martensite (MA), pearlite, martensite, retained austenite, cementite, etc. Is included.
ところで旧オーステナイト粒を微細化することによって母材靭性を改善すること自体は知られている。旧オーステナイト粒を微細化するためには、一般に、低温圧延が行われている。しかし、低温圧延すると、変態後に伸長した（アスペクト比の大きな）島状マルテンサイト（ＭＡ）が生成する。島状マルテンサイト（ＭＡ）のアスペクト比が大きいと、衝撃が加わったときに先端部分に応力が集中し、靭性が劣化する。一方、島状マルテンサイト（ＭＡ）のアスペクト比を小さくするには、高温で圧延することが考えられる。しかし、高温圧延すると、今度は旧オーステナイト粒が粗大化してしまい、母材靭性が劣化する。これらのため、これまで旧オーステナイト粒の微細化と島状マルテンサイト（ＭＡ）の球状化を両立されることは困難であった。本発明では、後述する特定の熱間圧延方法を採用しているため、旧オーステナイト粒の微細化と島状マルテンサイト（ＭＡ）の球状化を両立できている。 By the way, it is known to improve the base material toughness by refining the prior austenite grains. In order to refine the prior austenite grains, low temperature rolling is generally performed. However, when rolling at a low temperature, island-shaped martensite (MA) that is elongated after transformation (high aspect ratio) is generated. When the aspect ratio of island martensite (MA) is large, stress is concentrated at the tip portion when an impact is applied, and toughness deteriorates. On the other hand, in order to reduce the aspect ratio of island martensite (MA), rolling at a high temperature is considered. However, when high-temperature rolling is performed, the prior austenite grains are coarsened and the base material toughness is deteriorated. For these reasons, it has been difficult to achieve both the refinement of prior austenite grains and the spheroidization of island martensite (MA). In this invention, since the specific hot rolling method mentioned later is employ | adopted, refinement | miniaturization of a prior austenite grain and spheroidization of island-like martensite (MA) can be made compatible.
旧オーステナイト粒の平均円相当径は、好ましくは１１０μｍ以下、さらに好ましくは１００μｍ以下である。なお平均円相当径の下限を設定する必要はないが、容易に達成できる範囲が望ましく、例えば、３０μｍ以上、好ましくは６０μｍ以上であってもよい。 The average equivalent circle diameter of the prior austenite grains is preferably 110 μm or less, more preferably 100 μm or less. Although it is not necessary to set the lower limit of the average equivalent circle diameter, a range that can be easily achieved is desirable, and may be, for example, 30 μm or more, preferably 60 μm or more.
なお旧オーステナイト粒の平均円相当径の測定法は以下の通りである。鋼板を圧延方向に沿って切断し、この切断面のｔ／４（ｔ＝板厚）位置をナイタール腐食した後、光学顕微鏡写真（観察倍率：１００倍、観察視野：６００×８００μｍ）を撮影する（ｎ数＝１０）。撮影した写真を画像解析装置（Ｍｅｄｉａ Ｃｙｂｅｒｎｅｔｉｃｓ製、Ｉｍａｇｅ−Ｐｒｏ Ｐｌｕｓ）で処理することよって、平均円相当径（μｍ）が求まる。 The measuring method of the average equivalent circle diameter of the prior austenite grains is as follows. The steel plate is cut along the rolling direction, and the t / 4 (t = plate thickness) position of the cut surface is subjected to nital corrosion, and then an optical micrograph (observation magnification: 100 times, observation field of view: 600 × 800 μm) is taken. (N number = 10). The average equivalent circle diameter (μm) is obtained by processing the photographed image with an image analysis apparatus (Image Cyber Pro, manufactured by Media Cybernetics).
また島状マルテンサイト（ＭＡ）の面積百分率は、好ましくは２．８％以下、さらに好ましくは２．５％以下であり、最も優れている場合には２．０％以下（特に１．５％以下）にすることも可能である。面積百分率の下限を設定する必要はないが、容易に達成できる範囲が望ましく、例えば、０以上、好ましくは０．５以上であってもよい。 The area percentage of island martensite (MA) is preferably 2.8% or less, more preferably 2.5% or less, and 2.0% or less (especially 1.5% or less) in the best case. It is also possible to Although it is not necessary to set the lower limit of the area percentage, a range that can be easily achieved is desirable, and may be, for example, 0 or more, preferably 0.5 or more.
島状マルテンサイト（ＭＡ）のアスペクト比は、好ましくは２．９以下であり、最も優れている場合には２．５以下（特に２．０以下）にすることも可能である。アスペクト比の下限を設定する必要はないが、容易に達成できる範囲が望ましく、例えば、１以上、好ましくは１．５以上であってもよい。 The aspect ratio of the island martensite (MA) is preferably 2.9 or less, and in the best case, it can be 2.5 or less (particularly 2.0 or less). Although it is not necessary to set the lower limit of the aspect ratio, a range that can be easily achieved is desirable, and may be, for example, 1 or more, preferably 1.5 or more.
島状マルテンサイト（ＭＡ）の面積百分率及びアスペクト比（個数平均値）の測定法は、次の通りである。鋼板のｔ／４（ｔ＝板厚）位置をナイタール腐食した後、光学顕微鏡写真（観察倍率：１０００倍、観察視野：６０×８０μｍ）を撮影する（ｎ数＝１０）。撮影した写真を画像解析装置（Ｍｅｄｉａ Ｃｙｂｅｒｎｅｔｉｃｓ製、Ｉｍａｇｅ−Ｐｒｏ Ｐｌｕｓ）で処理することよって、面積百分率とアスペクト比（個数平均値）が求まる。 The method for measuring the area percentage and aspect ratio (number average value) of island-like martensite (MA) is as follows. After n / 4 corrosion at the t / 4 (t = plate thickness) position of the steel plate, an optical micrograph (observation magnification: 1000 times, observation field of view: 60 × 80 μm) is taken (n number = 10). By processing the photographed image with an image analysis device (Image-Pro Plus, manufactured by Media Cybernetics), the area percentage and the aspect ratio (number average value) can be obtained.
上述したように本発明では、（Ａ）Ｘ値、（Ｂ）Ｔｉ／Ｎ比、（Ｃ）旧オーステナイト粒と島状マルテンサイト組織（ＭＡ）などを制御することによって、ＨＡＺ靭性を改善し、遷移温度（ｖＴｒｓ）を下げている。しかし、これらの効果を有効に発揮させるためには、鋼板の成分組成も重要である。本発明の鋼板の成分組成及びその限定理由は、以下の通りである。 As described above, in the present invention, by controlling (A) X value, (B) Ti / N ratio, (C) prior austenite grains and island martensite structure (MA), etc., HAZ toughness is improved, The transition temperature (vTrs) is lowered. However, in order to effectively exhibit these effects, the component composition of the steel sheet is also important. The component composition of the steel sheet of the present invention and the reasons for limitation are as follows.
［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相組織（ＭＡ）が多くなりすぎて、母材靭性、遷移温度（ｖＴｒｓ）およびＨＡＺ靭性が劣化する。そこでＣ量を０．０３０〜０．１０％と定めた。Ｃ量の好ましい下限は０．０４％以上、さらに好ましくは０．０５％以上である。またＣ量の好ましい上限は０．０９％以下、さらに好ましくは０．０７％以下である。
[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 structure (MA) increases too much, and the base material toughness, transition temperature (vTrs) and HAZ toughness deteriorate. Therefore, the C amount is determined to be 0.030 to 0.10%. The minimum with preferable C amount is 0.04% or more, More preferably, it is 0.05% or more. Moreover, the upper limit with preferable C amount is 0.09% or less, More preferably, it is 0.07% or less.
［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、０．０１％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、母材靭性および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量の好ましい下限は、０．０５％以上、さらに好ましくは０．１％以上である。Ｓｉの好ましい上限は０．８％以下であり、より好ましくは０．５％以下である。
[Si: 1.0% or less (excluding 0%)]
Si is an effective element for ensuring the strength of the steel sheet, and for that purpose, it is preferable to add 0.01% or more. However, if Si is added excessively, a large amount of MA structure is generated, and the base metal toughness and the HAZ toughness are lowered. Therefore, the upper limit must be made 1.0%. The preferable lower limit of the amount of Si is 0.05% or more, more preferably 0.1% or more. The upper limit with preferable Si is 0.8% or less, More preferably, it is 0.5% 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、母材靭性および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１．０％以上であり、より好ましくは１．２％以上である。一方、Ｍｎ量の好ましい上限は１．８％以下、より好ましくは１．６％以下である。
[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 1.0% or more, More preferably, it is 1.2% or more. On the other hand, the preferable upper limit of the amount of Mn is 1.8% or less, more preferably 1.6% or less.
［Ｐ：０．０３％以下（０％を含まない）］
不純物元素であるＰは、母材靭性および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０．０２％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 0.02%. 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靭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、かえって母材靭性およびＨＡＺ靭性が低下するため、上限を０．１０％とする。Ａｌ量の好ましい下限は０．０２％以上である。一方、その好ましい上限は０．０６％以下であり、より好ましくは０．０４％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 0.02% or more. On the other hand, the preferable upper limit is 0.06% or less, and more preferably 0.04% or less.
［Ｎｂ：０．００５〜０．０３５％］
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０．００５％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、母材靭性および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０．０１０％以上であり、好ましくは０．０２５％以下、より好ましくは０．０２０％以下である。
[Nb: 0.005 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 0.005% or more. However, if Nb is added excessively, the base metal toughness and the HAZ toughness are lowered, so the upper limit was set to 0.035%. The Nb amount is preferably 0.010% or more, preferably 0.025% or less, more preferably 0.020% 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により）、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０．０１７％以上（特に０．０２０％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 coarsening of austenite grains of HAZ during welding (due to a 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 0.017% or more (particularly 0.020% or more) and 0.025% or less.
［Ｂ：０．００１０〜０．００３５％］
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、０．００１０％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靭性が劣化する。そのためＢ量の上限を０．００３５％と定めた。Ｂ量は、好ましくは０．００１５％以上（特に０．００２０％以上）、０．００３０％以下（特に０．００２５％以下）である。
[B: 0.0010 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, 0.0010% 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 0.0015% or more (particularly 0.0020% or more) and 0.0030% or less (particularly 0.0025% or less).
［Ｎ：０．００５０〜０．０１％］
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０．００５０％以上に定めた。一方、Ｎ量が過剰であると、母材靭性および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０．００６％以上であり、より好ましくは０．００７％以上である。またＮ量の好ましい上限は０．００９％以下であり、より好ましくは０．００８％以下である。
[N: 0.0050 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 0.0050% or more. 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 0.006% or more, More preferably, it is 0.007% or more. Moreover, the upper limit with preferable N amount is 0.009% or less, More preferably, it is 0.008% or less.
本発明の厚鋼板は、上記各成分を必須成分として含有するが、必要に応じてさらに追加の成分を含有していてもよい。例えば、本発明の厚鋼板は、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖなどの第１の追加成分を、下記に示す範囲で含有していてもよい。なお任意成分であるため、下限値は０％に設定しているが、積極添加する場合には下限値は０％超になる。またこれらＣｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖなどは、単独で添加してもよく、２種以上を組み合わせて添加してもよい。 The thick steel plate of the present invention contains the above components as essential components, but may further contain additional components as necessary. For example, the thick steel plate of the present invention may contain a first additional component such as Cu, Ni, Cr, Mo, and V in the range shown below. In addition, since it is an arbitrary component, the lower limit value is set to 0%, but when it is actively added, the lower limit value exceeds 0%. Moreover, these Cu, Ni, Cr, Mo, V, etc. may be added independently and may be added in combination of 2 or more type.
［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０．１％以上、より好ましくは０．２％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、母材靭性およびＨＡＺ靭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、さらに好ましくは０．５％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 an effect, it is recommended that the amount of Cu is preferably 0.1% or more, more preferably 0.2% 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, more preferably 0.5% 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０．２％以上、より好ましくは０．３％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、母材靭性およびＨＡＺ靭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、さらに好ましくは０．５％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 0.2% or more, more preferably 0.3% 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, more preferably 0.5% 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０．２％以上、より好ましくは０．４％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、母材靭性およびＨＡＺ靭性が低下するので、その上限を１％と定めた。Ｃｒ量の好ましい上限は０．８％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 0.2% or more, more preferably 0.4% or more. However, if the amount of Cr is excessive, the base metal toughness and the HAZ toughness are lowered, so the upper limit was set to 1%. The upper limit with preferable Cr amount is 0.8%.
［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、母材靭性および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０．３％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 Mo amount is excessive, the base metal toughness and the HAZ toughness deteriorate, so the upper limit was set to 0.5%. The amount of Mo is preferably 0.3% 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、母材靭性および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.
本発明の厚鋼板では、さらに必要に応じて第２の追加の成分を含有していてもよい。第２の追加の成分を添加する場合、それらの組み合わせ及び添加量は、以下の通りである。
（イ）Ｃａ：０．００５％以下（０％を含まない）、Ｍｇ：０．００５％以下（０％を含まない）、及びＲＥＭ：０．０１％以下（０％を含まない）から選択される少なくとも１種、
（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）、
（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）。
The thick steel plate of the present invention may further contain a second additional component as necessary. When adding a 2nd additional component, those combinations and addition amount are as follows.
(I) Ca: 0.005% or less (not including 0%), Mg: 0.005% or less (not including 0%), and REM: 0.01% or less (not including 0%) At least one of
(B) Zr: 0.1% or less (not including 0%) and / or Hf: 0.05% or less (not including 0%),
(C) Co: 2.5% or less (not including 0%) and / or W: 2.5% or less (not including 0%).
なお前記（イ）、（ロ）、（ハ）は、いずれか一つを実施してもよく、二つ以上を組み合わせて実施してもよい。以下、（イ）、（ロ）、（ハ）の詳細を説明する。 In addition, said (I), (B), (C) may implement any one, and may implement it in combination of 2 or more. Details of (A), (B), and (C) will be described below.
（イ）Ｃａ：０．００５％以下、Ｍｇ：０．００５％以下、及びＲＥＭ：０．０１％以下から選択される少なくとも一種について
Ｃａ、Ｍｇ、およびＲＥＭ（希土類元素）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およびＲＥＭは、ＭｎＳの球状化効果、言い換えれば介在物の形態制御による異方性の低減作用があり、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は０．０００５％以上、Ｍｇは０．０００１％以上、ＲＥＭは０．０００５％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、かえって母材靭性およびＨＡＺ靭性を劣化させるので、Ｃａは０．００５％以下、Ｍｇは０．００５％以下、ＲＥＭは０．０１％以下と定めた。好ましくはＣａが０．００３％以下、Ｍｇが０．００３５％以下、ＲＥＭが０．００７％以下である。
(B) At least one selected from Ca: 0.005% or less, Mg: 0.005% or less, and REM: 0.01% or less Ca, Mg, and REM (rare earth elements) improve HAZ toughness. It is an element which has the effect to make. Specifically, Ca and REM have a spheroidizing effect of MnS, in other words, an effect of reducing anisotropy by shape control of inclusions, and improve HAZ toughness. 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, it is preferable to contain 0.0005% or more of Ca, 0.0001% or more of Mg, and 0.0005% or more of REM in the steel sheet. However, if these amounts are excessive, the base metal toughness and the HAZ toughness are deteriorated. Therefore, Ca is set to 0.005% or less, Mg is set to 0.005% or less, and REM is set to 0.01% or less. Preferably, Ca is 0.003% or less, Mg is 0.0035% or less, and REM is 0.007% or less.
（ロ）Ｚｒ：０．１％以下および／またはＨｆ：０．０５％以下について
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０．０００５％以上、Ｈｆ量は、好ましくは０．００１％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、かえって母材靭性および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。
(B) Zr: 0.1% or less and / or Hf: 0.05% or less Zr and Hf form nitrides similarly to Ti, and suppress coarsening of austenite grains of HAZ during welding. , An element effective in improving HAZ toughness. In order to sufficiently exhibit such effects, it is recommended that the Zr amount is preferably 0.0005% or more, and the Hf amount is preferably 0.001% 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%. .
（ハ）Ｃｏ：２．５％以下および／またはＷ：２．５％以下について
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０．１％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、母材靭性および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。
(C) 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 at 0.1% 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%.
本発明の厚鋼板では、残部は、Ｆｅおよび不可避不純物であってもよい。 In the thick steel plate of the present invention, the balance may be Fe and inevitable impurities.
本発明の厚鋼板は、概略、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、通常の条件で加熱した後、後述する所定の方法で熱間圧延し、さらに圧延後は加速冷却することによって製造できる。なお冷却後の鋼板は、必要により、焼戻しする。 The thick steel plate of the present invention is generally prepared by melting a steel satisfying the above-mentioned chemical component amounts, [Ti] / [N] and X value by an ordinary melting method, and cooling the molten steel into a slab. After heating under the above conditions, it can be manufactured by hot rolling by a predetermined method to be described later, and further by accelerated cooling after rolling. In addition, the steel plate after cooling is tempered if necessary.
まず溶鋼の冷却について詳述すると、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しているので、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）してスラブを形成しても、Ｔｉ系炭窒化物を十分に小さくできる。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して、凝固時の冷却速度を向上させることが好ましい。 First, the cooling of the molten steel will be described in detail. 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.). Even if the slab is formed by cooling at a cooling rate of 0.1 to 2.0 ° C./second), the Ti-based carbonitride can be made sufficiently small. However, in order to form a finer carbonitride, it is preferable to improve the cooling rate during solidification by changing the cooling water amount and cooling method of the casting machine.
そして本発明の厚鋼板の製造工程で最も重要なのは、熱間圧延条件及びその後の冷却条件である。本発明の熱間圧延では、温度８５０〜８００℃の圧下率を４０％以上（例えば、４０〜８０％程度）にし、かつ８５０〜８００℃での各パス間時間を５〜１０秒に制御する。温度８５０〜８００℃で実質的な圧延を行うことにすれば、温度８００℃未満での圧延負荷を低減でき（例えば、圧下率を５％未満にでき）、島状マルテンサイト（ＭＡ）の伸長を防ぐことができる。また８５０〜８００℃で実質的な圧延を行うと、通常であれば旧オーステナイト粒が粗大化してしまうが、本発明では各パス間時間を制御しているため、旧オーステナイト粒を微細化できる。パス間時間が短すぎても長すぎても、旧オーステナイト粒が粗大化する。なおパス間時間とは、前パスの進行方向後端の圧延時と、本パスの進行方向後端の圧延時との間の時間差のことをいう。また前記製造工程では、温度８５０℃超での圧下率は特に限定されず、例えば、０〜８０％程度の範囲で適宜設定できる。 And the most important thing in the manufacturing process of the thick steel plate of this invention is hot rolling conditions and subsequent cooling conditions. In the hot rolling of the present invention, the rolling reduction at a temperature of 850 to 800 ° C. is set to 40% or more (for example, about 40 to 80%), and the time between passes at 850 to 800 ° C. is controlled to 5 to 10 seconds. . If substantial rolling is performed at a temperature of 850 to 800 ° C., the rolling load at a temperature of less than 800 ° C. can be reduced (for example, the rolling reduction can be reduced to less than 5%), and island martensite (MA) is elongated. Can be prevented. Further, when substantial rolling is performed at 850 to 800 ° C., the old austenite grains are usually coarsened. However, since the time between passes is controlled in the present invention, the old austenite grains can be refined. If the time between passes is too short or too long, the prior austenite grains become coarse. The time between passes refers to the time difference between the rolling at the rear end in the traveling direction of the previous pass and the rolling at the rear end in the traveling direction of the main pass. Moreover, in the said manufacturing process, the rolling reduction in temperature over 850 degreeC is not specifically limited, For example, it can set suitably in the range of about 0 to 80%.
熱間圧延後は、加速冷却する。加速冷却することによって島状マルテンサイトの粗大化を防止し、面積百分率を所定の範囲内に抑えることができる。冷却速度は、Ｃ量などに応じて適宜設定できるが、例えば、圧延終了後の７００〜５００℃の範囲を、平均速度を５℃／秒以上で冷却することが推奨される。 After hot rolling, accelerated cooling is performed. By accelerating cooling, the island-shaped martensite can be prevented from becoming coarse, and the area percentage can be kept within a predetermined range. Although a cooling rate can be suitably set according to C amount etc., for example, it is recommended to cool the range of 700-500 degreeC after completion | finish of rolling at an average rate of 5 degree-C / sec or more.
本発明の厚鋼板は、ＪＩＳの厚鋼板の定義に従い、板厚が３．０ｍｍ以上であるが、好ましくは１０ｋＪ／ｍｍ以上の入熱（特に超大入熱）の溶接が求められるような厚さを有する。１０ｋＪ／ｍｍ以上の入熱（特に超大入熱）が求められる板厚は、例えば、２０ｍｍ以上、さらに好ましくは４０ｍｍ以上、特に６０ｍｍ以上である。本発明によれば、１０ｋＪ／ｍｍ程度の入熱量から超大入熱量に至る幅広い入熱量の溶接で良好なＨＡＺ靭性を示すため、板厚を厚くしても、ＨＡＺ靭性を低下することなく溶接できる。 The thick steel plate of the present invention has a thickness of 3.0 mm or more according to the definition of JIS thick steel plate, but preferably has a thickness that requires welding with a heat input of 10 kJ / mm or more (especially a very large heat input). Have The plate thickness for which a heat input of 10 kJ / mm or more (particularly ultra-high heat input) is required is, for example, 20 mm or more, more preferably 40 mm or more, particularly 60 mm or more. According to the present invention, since excellent HAZ toughness is exhibited by welding with a wide heat input amount ranging from a heat input amount of about 10 kJ / mm to an extremely large heat input amount, welding can be performed without decreasing the HAZ toughness even if the plate thickness is increased. .
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記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, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.
実験Ｎｏ．１〜６０
表１〜３に示す組成の鋼を、通常の溶製法によって溶製し、この溶鋼を冷却（１５００℃から１１００℃までの冷却速度：０．１〜２．０℃／秒）し、スラブを得た（スラブ厚＝２７０ｍｍ）。このスラブを温度１１００℃に加熱した後、仕上圧延温度：８００℃（実験Ｎｏ．１〜５５及び５９〜６０の場合）又は仕上げ圧延温度：８００℃未満（実験Ｎｏ．５６〜５８の場合）で、厚さ６０ｍｍまで熱間圧延した。またこの熱間圧延では、８５０〜８００℃の範囲の各パス間時間を表４〜５に示す通りにした。なおＮｏ．５６〜５８の例では、８００℃未満の範囲でも熱間圧延し、この温度範囲での圧下率は、５％（Ｎｏ．５６）、２０％（Ｎｏ．５７）、又は３０％（Ｎｏ．５８）にした。熱間圧延終了後、直ちに２００℃以下まで加速冷却した。温度７００〜５００℃の間の冷却速度は、表４〜５に示した通りである。
Experiment No. 1-60
Steels having the compositions shown in Tables 1 to 3 were melted by an ordinary melting method, the molten steel was cooled (cooling rate from 1500 ° C. to 1100 ° C .: 0.1 to 2.0 ° C./second), and the slab was Obtained (slab thickness = 270 mm). After heating this slab to a temperature of 1100 ° C., finish rolling temperature: 800 ° C. (in the case of Experiment Nos. 1 to 55 and 59 to 60) or finish rolling temperature: less than 800 ° C. (in the case of Experiment No. 56 to 58) And hot rolled to a thickness of 60 mm. In this hot rolling, the time between passes in the range of 850 to 800 ° C. was as shown in Tables 4 to 5. No. In the example of 56-58, it hot-rolls also in the range below 800 degreeC, and the reduction rate in this temperature range is 5% (No. 56), 20% (No. 57), or 30% (No. 58). ) Immediately after the hot rolling, accelerated cooling was performed to 200 ° C. or lower. The cooling rate between temperatures 700-500 ° C is as shown in Tables 4-5.
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１〜３に示す。 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) are shown in Tables 1-3. Shown in
また上記のようにして製造した鋼板について、前述した要領で、旧オーステナイト粒径、島状マルテンサイト（ＭＡ）の面積百分率及びアスペクト比、並びにＴｉ系炭窒化物の平均粒径を調べた。また下記要領で、鋼板の引張強さ、遷移温度（ｖＴｒｓ）、およびＨＡＺ靭性を測定した。これらの結果を表４〜５に示す。 Further, with respect to the steel sheets produced as described above, the prior austenite grain size, the area percentage and aspect ratio of island martensite (MA), and the average grain size of Ti-based carbonitride were examined in the manner described above. Further, the tensile strength, transition temperature (vTrs), and HAZ toughness of the steel sheet were measured in the following manner. These results are shown in Tables 4-5.
［引張強さ］
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。引張強さが４４０ＭＰａ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. Those having a tensile strength of 440 MPa or more were regarded as acceptable.
［遷移温度（ｖＴｒｓ）］
深さｔ／４の位置（ｔ＝板厚）でＪＩＳ Ｚ ２２４２に規定するＶノッチ標準試験片を採取し、測定温度を変えてシャルピー衝撃試験（衝撃刃半径２ｍｍ）を行い、脆性破面率が５０％以下になる温度（ｖＴｒｓ）を調べた。遷移温度（ｖＴｒｓ）が−６０℃以下のものを合格とした。
[Transition temperature (vTrs)]
Take a V-notch standard test piece specified in JIS Z 2242 at a depth of t / 4 (t = plate thickness), perform a Charpy impact test (impact blade radius 2 mm) at different measurement temperatures, and measure the brittle fracture surface ratio. The temperature (vTrs) at which is 50% or less was examined. One having a transition temperature (vTrs) of −60 ° C. or lower was regarded as acceptable.
［ＨＡＺ靭性］
１）入熱量５０ｋＪ／ｍｍの場合
板厚６０ｍｍの鋼板に対して入熱５０ｋＪ／ｍｍでセガーク（ＳＥＧＡＲＣ）溶接を行った。図１に示すｔ／２部（ｔ＝板厚）からＪＩＳ Ｚ ２２４２に規定するＶノッチ標準試験片を採取し（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（衝撃刃半径２ｍｍ）を行い、吸収エネルギー（ｖＥ-40）を測定した。吸収エネルギーが２００Ｊ以上のものを合格とした。
[HAZ toughness]
1) In case of heat input of 50 kJ / mm SEGARC welding was performed on a steel plate having a thickness of 60 mm at a heat input of 50 kJ / mm. A V-notch standard test piece specified in JIS Z 2242 is taken from t / 2 part (t = plate thickness) shown in FIG. 1 (the notch position is 0.5 mm HAZ side from the bond), and a Charpy impact test at −40 ° C. ( Impact blade radius was 2 mm), and the absorbed energy (vE -40 ) was measured. The absorbed energy was 200 J or more.
２）入熱量１５ｋＪ／ｍｍの場合
８５０℃超の圧下率を高くして、得られる鋼板の板厚を２０ｍｍにする以外は、実験Ｎｏ．１〜６０と同様にした。すなわち８５０℃以下の圧延条件及び冷却条件は、実験Ｎｏ．１〜６０と同じである。このようにして得られた板厚２０ｍｍの鋼板も、前記板厚６０ｍｍの鋼板と同じＮｏ．を付して説明する。この板厚２０ｍｍの鋼板に対して入熱１５ｋＪ／ｍｍでエレクトロガスアーク溶接を行った。ｔ／２部（ｔ＝板厚）からＪＩＳ Ｚ ２２４２に規定するＶノッチ標準試験片を採取し（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（衝撃刃半径２ｍｍ）を行い、吸収エネルギー（ｖＥ-40）を測定した。吸収エネルギーが２００Ｊ以上のものを合格とした。
2) In case of heat input of 15 kJ / mm Experiment No. 1 was conducted except that the reduction rate was over 850 ° C. and the thickness of the resulting steel sheet was 20 mm. Same as 1-60. That is, the rolling conditions and cooling conditions below 850 ° C. It is the same as 1-60. The steel plate having a thickness of 20 mm obtained in this way is also the same as the steel plate having a thickness of 60 mm. Will be described. Electrogas arc welding was performed on the steel plate having a thickness of 20 mm at a heat input of 15 kJ / mm. A V-notch standard test piece specified in JIS Z 2242 was taken from t / 2 part (t = plate thickness) (notch position is 0.5 mm HAZ side from bond), and Charpy impact test at −40 ° C. (impact blade radius 2 mm) ) And the absorbed energy (vE -40 ) was measured. The absorbed energy was 200 J or more.
また本発明の成分範囲を満足する実験Ｎｏ．１〜３６の結果に基づき、Ｘ値、Ｔｉ系炭窒化物の平均粒径、入熱量５０ｋＪ／ｍｍのときのＨＡＺ靭性（ｖＥ-40）、入熱量１５ｋＪ／ｍｍのときのＨＡＺ靭性（ｖＥ-40）の関係を整理した。結果を図２〜４に示す。 Experiment No. 1 satisfying the component range of the present invention. Based on the results of 1-36, the X value, the average particle size of the Ti-based carbonitride, the HAZ toughness (vE -40 ) when the heat input is 50 kJ / mm, the HAZ toughness (vE − when the heat input is 15 kJ / mm) 40 ) Organized the relationship. The results are shown in FIGS.
図２〜４から明らかなように、Ｘ値を大きくすることで、Ｔｉ系炭窒化物の平均粒径を小さくでき、入熱量５０ｋＪ／ｍｍのときのＨＡＺ靭性（ｖＥ-40）を改善でき、かつ入熱量１５ｋＪ／ｍｍのときのＨＡＺ靭性（ｖＥ-40）も改善できる。また表４のＮｏ．１〜３５に示されるように、さらに旧オーステナイト粒径を微細にすると共に、島状マルテンサイト（ＭＡ）を小さくかつ丸くすることで、遷移温度を下げることもできる。 As apparent from FIGS. 2 to 4, by increasing the X value, the average particle size of the Ti-based carbonitride can be reduced, and the HAZ toughness (vE -40 ) when the heat input is 50 kJ / mm can be improved. Moreover, the HAZ toughness (vE- 40 ) when the heat input is 15 kJ / mm can be improved. In Table 4, No. 1 to 35, the transition temperature can be lowered by further reducing the prior austenite grain size and making the island martensite (MA) small and round.
これらに対して、実験Ｎｏ．３６、５１、５２はＸ値が小さすぎる例であり、ＨＡＺ靭性が悪化する。Ｎｏ．５０はＸ値が大きすぎ、島状マルテンサイト（ＭＡ）が増えすぎたため、遷移温度が高くなり、かつＨＡＺ靭性も悪化した。Ｎｏ．３７〜４９は、成分範囲やＴｉ／Ｎ比が不適切であるため、ＨＡＺ靭性が劣化した。 In contrast, Experiment No. 36, 51 and 52 are examples in which the X value is too small, and the HAZ toughness deteriorates. No. No. 50 had an X value that was too large and island martensite (MA) increased too much, so the transition temperature increased and the HAZ toughness also deteriorated. No. As for 37-49, since the component range and Ti / N ratio were inadequate, HAZ toughness deteriorated.
Ｎｏ．５３〜５５は、熱間圧延後の冷却速度が遅く、島状マルテンサイト（ＭＡ）が増えすぎたため、遷移温度が高くなった。Ｎｏ．５６〜５８は、８５０〜８００℃の圧下率を小さくした結果、８００℃未満での圧下量が大きくなってしまい、島状マルテンサイト（ＭＡ）が伸長し、遷移温度が高くなった。Ｎｏ．５９と６０は、８５０〜８００℃の間を圧延するときのパス間時間が不適切であって旧オーステナイト粒が粗大化したため、遷移温度が高くなった。 No. In 53 to 55, the cooling rate after hot rolling was slow, and the island-like martensite (MA) increased too much, so the transition temperature was high. No. As for 56-58, as a result of reducing the rolling reduction of 850-800 degreeC, the amount of rolling below 800 degreeC became large, the island-like martensite (MA) expanded, and the transition temperature became high. No. In Nos. 59 and 60, the transition temperature was high because the time between passes when rolling between 850 and 800 ° C. was inappropriate and the prior austenite grains became coarse.
本発明の厚鋼板の引張強度クラスは、例えば、４４０ＭＰａ以上、好ましくは４９０ＭＰａ以上であり、さらに好ましくは５４０ＭＰａ以上であり、最も好ましい場合には５９０ＭＰａ以上の厚鋼板も提供できる。本発明の厚鋼板は、例えば、船舶および海洋構造物などの溶接構造物に適用でき、特に引張強度の優れた高張力鋼板は、大型のコンテナ船等の製造に適している。 The tensile strength class of the thick steel plate of the present invention is, for example, 440 MPa or more, preferably 490 MPa or more, more preferably 540 MPa or more, and most preferably 590 MPa or more. The thick steel plate of the present invention can be applied to, for example, welded structures such as ships and offshore structures. Particularly, a high-tensile steel plate having excellent tensile strength is suitable for manufacturing a large container ship or the like.
Claims (6)
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％以下（０％を含む）を含有し、
残部がＦｅおよび不可避不純物からなる厚鋼板であって、
旧オーステナイト粒の平均円相当径が１２０μｍ以下、島状マルテンサイト（ＭＡ）の面積百分率が３％以下、かつ島状マルテンサイト（ＭＡ）のアスペクト比（長径／短径）の個数平均値が３以下であり、
しかも下記式（１）および（２）を満足することを特徴とするＨＡＺ靭性および母材靭性に優れた厚鋼板。
１．５≦［Ｔｉ］／［Ｎ］≦４ … （１）
４０≦Ｘ値≦１６０ … （２）
Ｘ値＝５００［Ｃ］＋３２［Ｓｉ］＋８［Ｍｎ］−９［Ｎｂ］
＋１４［Ｃｕ］＋１７［Ｎｉ］−５［Ｃｒ］−２５［Ｍｏ］−３４［Ｖ］
（式中、［Ｔｉ］、［Ｎ］、［Ｃ］、［Ｓｉ］、［Ｍｎ］、［Ｎｂ］、［Ｃｕ］、［Ｎｉ］、［Ｃｒ］、［Ｍｏ］、［Ｖ］は鋼板中の各元素の含有量（質量％）を表す） C: 0.030 to 0.10% (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: 0.005 to 0.035%, Ti: 0.015 to 0.03%, B: 0.0010 to 0.0035%, and N: 0.0050 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 (0 %) And V: 0.1% or less (including 0%),
The balance is a thick steel plate made of Fe and inevitable impurities,
The average equivalent circle diameter of the prior austenite grains is 120 μm or less, the area percentage of the island martensite (MA) is 3% or less, and the number average value of the aspect ratio (major axis / minor axis) of the island martensite (MA) is 3. And
And the thick steel plate excellent in HAZ toughness and base-material toughness characterized by satisfying following formula (1) and (2).
1.5 ≦ [Ti] / [N] ≦ 4 (1)
40 ≦ X value ≦ 160 (2)
X value = 500 [C] +32 [Si] +8 [Mn] -9 [Nb]
+14 [Cu] +17 [Ni] -5 [Cr] -25 [Mo] -34 [V]
(In the formula, [Ti], [N], [C], [Si], [Mn], [Nb], [Cu], [Ni], [Cr], [Mo], [V] are in the steel plate. The content (% by mass) of each element of
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2007101944A JP4976905B2 (en) | 2007-04-09 | 2007-04-09 | Thick steel plate with excellent HAZ toughness and base metal toughness |
| CN2008100903864A CN101285150B (en) | 2007-04-09 | 2008-04-01 | Heavy plate excellent in haz toughness and mother plate toughness |
| KR1020080032411A KR100954041B1 (en) | 2007-04-09 | 2008-04-08 | Thick steel plate having excellent toughness of weld heat-affected zone and excellent base material toughness |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2007101944A JP4976905B2 (en) | 2007-04-09 | 2007-04-09 | Thick steel plate with excellent HAZ toughness and base metal toughness |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2008255458A true JP2008255458A (en) | 2008-10-23 |
| JP4976905B2 JP4976905B2 (en) | 2012-07-18 |
Family
ID=39979333
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2007101944A Active JP4976905B2 (en) | 2007-04-09 | 2007-04-09 | Thick steel plate with excellent HAZ toughness and base metal toughness |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JP4976905B2 (en) |
| KR (1) | KR100954041B1 (en) |
| CN (1) | CN101285150B (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010134220A1 (en) * | 2009-05-22 | 2010-11-25 | Ｊｆｅスチール株式会社 | Steel material for high heat input welding |
| JP2011074403A (en) * | 2009-09-16 | 2011-04-14 | Jfe Steel Corp | Steel for high heat input welding |
| JP2011074446A (en) * | 2009-09-30 | 2011-04-14 | Jfe Steel Corp | Steel for high heat input welding |
| JP2012246520A (en) * | 2011-05-26 | 2012-12-13 | Sumitomo Metal Ind Ltd | Steel material excellent in fatigue-crack propagation resistance and low-temperature toughness at weld heat-affected zone, and method for production thereof |
| JP2013117055A (en) * | 2011-12-05 | 2013-06-13 | Jfe Steel Corp | Steel material for large heat-input welding and method for manufacturing the same |
| CN103866199A (en) * | 2014-03-24 | 2014-06-18 | 济钢集团有限公司 | Steel plate used for ocean energy equipment and preparation process of steel plate |
| EP2806042A4 (en) * | 2012-01-18 | 2015-06-03 | Jfe Steel Corp | Process for producing tapered plate |
| KR101608239B1 (en) | 2011-12-14 | 2016-04-01 | 제이에프이 스틸 가부시키가이샤 | Steel material for high-heat-input welding |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101724780B (en) * | 2008-10-20 | 2012-01-04 | 株式会社神户制钢所 | Thick steel plate |
| KR101091306B1 (en) * | 2008-12-26 | 2011-12-07 | 주식회사 포스코 | High Strength Steel Plate for Containment Vessel of Atomic Plant and Manufacturing Method Thereof |
| CN101701326B (en) * | 2009-10-28 | 2011-07-20 | 南京钢铁股份有限公司 | High strength and high toughness ship plate steel with thick specification and production method thereof |
| TWI551387B (en) * | 2012-03-01 | 2016-10-01 | Jfe Steel Corp | Large heat into the welding steel |
| KR20160078650A (en) | 2014-12-24 | 2016-07-05 | 주식회사 포스코 | The steel sheet having excellent toughness and ductility of butt weld joint and method for manufacturing the same |
| JP6881616B2 (en) * | 2018-09-10 | 2021-06-02 | Ｊｆｅスチール株式会社 | Manufacturing method of vertical narrow groove welded joint and vertical narrow groove welded joint |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05163527A (en) * | 1991-12-13 | 1993-06-29 | Nippon Steel Corp | Manufacture of high tension steel superior in weldability |
| JP2004300567A (en) * | 2003-03-19 | 2004-10-28 | Kobe Steel Ltd | High tensile steel sheet and its manufacturing method |
| JP2007051321A (en) * | 2005-08-17 | 2007-03-01 | Nippon Steel Corp | 490 MPa CLASS THICK HIGH-TENSILE STRENGTH FIRE-RESISTANT STEEL FOR WELDED STRUCTURE HAVING EXCELLENT WELDABILITY AND GAS CUTTING PROPERTY, AND ITS MANUFACTURING METHOD |
| JP2007332402A (en) * | 2006-06-13 | 2007-12-27 | Jfe Steel Kk | Steel material superior in fatigue-crack propagation resistance and manufacturing method therefor |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5798004A (en) * | 1995-01-26 | 1998-08-25 | Nippon Steel Corporation | Weldable high strength steel having excellent low temperature toughness |
| JPH11229077A (en) | 1998-02-12 | 1999-08-24 | Nippon Steel Corp | Steel plate excellent in ctod characteristic in multi layer weld zone and its production |
| JP4213833B2 (en) | 1999-10-21 | 2009-01-21 | 新日本製鐵株式会社 | High toughness and high strength steel with excellent weld toughness and manufacturing method thereof |
| JP3895687B2 (en) * | 2000-12-14 | 2007-03-22 | ポスコ | Steel plate for depositing TiN + ZrN for welded structure, method for producing the same, and welded structure using the same |
| CA2415573C (en) * | 2003-01-02 | 2007-11-13 | Sumitomo Metal Industries, Ltd. | High strength steel weld having improved resistance to cold cracking and a welding method |
| US7520943B2 (en) * | 2003-06-12 | 2009-04-21 | Jfe Steel Corporation | Steel plate and welded steel tube exhibiting low yield ratio, high strength and high toughness |
| JP4279231B2 (en) * | 2004-10-22 | 2009-06-17 | 株式会社神戸製鋼所 | High-strength steel material with excellent toughness in weld heat affected zone |
| JP4283757B2 (en) * | 2004-11-05 | 2009-06-24 | 株式会社神戸製鋼所 | Thick steel plate and manufacturing method thereof |
-
2007
- 2007-04-09 JP JP2007101944A patent/JP4976905B2/en active Active
-
2008
- 2008-04-01 CN CN2008100903864A patent/CN101285150B/en not_active Expired - Fee Related
- 2008-04-08 KR KR1020080032411A patent/KR100954041B1/en active IP Right Grant
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05163527A (en) * | 1991-12-13 | 1993-06-29 | Nippon Steel Corp | Manufacture of high tension steel superior in weldability |
| JP2004300567A (en) * | 2003-03-19 | 2004-10-28 | Kobe Steel Ltd | High tensile steel sheet and its manufacturing method |
| JP2007051321A (en) * | 2005-08-17 | 2007-03-01 | Nippon Steel Corp | 490 MPa CLASS THICK HIGH-TENSILE STRENGTH FIRE-RESISTANT STEEL FOR WELDED STRUCTURE HAVING EXCELLENT WELDABILITY AND GAS CUTTING PROPERTY, AND ITS MANUFACTURING METHOD |
| JP2007332402A (en) * | 2006-06-13 | 2007-12-27 | Jfe Steel Kk | Steel material superior in fatigue-crack propagation resistance and manufacturing method therefor |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010134220A1 (en) * | 2009-05-22 | 2010-11-25 | Ｊｆｅスチール株式会社 | Steel material for high heat input welding |
| JP2011006772A (en) * | 2009-05-22 | 2011-01-13 | Jfe Steel Corp | Steel material for high heat input welding |
| KR101386042B1 (en) * | 2009-05-22 | 2014-04-16 | 제이에프이 스틸 가부시키가이샤 | Steel material for high heat input welding |
| TWI478785B (en) * | 2009-05-22 | 2015-04-01 | Jfe Steel Corp | High heat input welding steel |
| JP2011074403A (en) * | 2009-09-16 | 2011-04-14 | Jfe Steel Corp | Steel for high heat input welding |
| JP2011074446A (en) * | 2009-09-30 | 2011-04-14 | Jfe Steel Corp | Steel for high heat input welding |
| JP2012246520A (en) * | 2011-05-26 | 2012-12-13 | Sumitomo Metal Ind Ltd | Steel material excellent in fatigue-crack propagation resistance and low-temperature toughness at weld heat-affected zone, and method for production thereof |
| JP2013117055A (en) * | 2011-12-05 | 2013-06-13 | Jfe Steel Corp | Steel material for large heat-input welding and method for manufacturing the same |
| KR101608239B1 (en) | 2011-12-14 | 2016-04-01 | 제이에프이 스틸 가부시키가이샤 | Steel material for high-heat-input welding |
| EP2806042A4 (en) * | 2012-01-18 | 2015-06-03 | Jfe Steel Corp | Process for producing tapered plate |
| CN103866199A (en) * | 2014-03-24 | 2014-06-18 | 济钢集团有限公司 | Steel plate used for ocean energy equipment and preparation process of steel plate |
Also Published As
| Publication number | Publication date |
|---|---|
| KR20080091716A (en) | 2008-10-14 |
| CN101285150A (en) | 2008-10-15 |
| JP4976905B2 (en) | 2012-07-18 |
| CN101285150B (en) | 2010-09-08 |
| KR100954041B1 (en) | 2010-04-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4976905B2 (en) | Thick steel plate with excellent HAZ toughness and base metal toughness | |
| JP4844687B2 (en) | Low yield ratio high strength high toughness steel sheet and method for producing the same | |
| JP5110989B2 (en) | Large steel plate for high heat input welding with excellent brittle crack propagation stopping characteristics | |
| JP4976906B2 (en) | Thick steel plate with excellent HAZ toughness, base material toughness, elongation, and strength-elongation balance | |
| JP5821173B2 (en) | Low yield ratio high strength high uniform stretch steel sheet and method for producing the same | |
| KR101846759B1 (en) | Steel plate and method for manufacturing same | |
| JP5037744B2 (en) | High strength steel plate and manufacturing method thereof | |
| JP4914783B2 (en) | Large steel plate for high heat input welding with excellent shearability | |
| JP4547944B2 (en) | Manufacturing method of high strength and high toughness thick steel plate | |
| JP4507745B2 (en) | Low yield ratio high strength high toughness steel pipe excellent in strain aging resistance and manufacturing method thereof | |
| JP6301805B2 (en) | Thick steel plate for tanks with excellent toughness of weld heat affected zone | |
| WO2016060141A1 (en) | Steel for high-energy-input welding | |
| JP4412098B2 (en) | Low yield ratio high strength steel sheet with excellent weld heat affected zone toughness and method for producing the same | |
| JP2009521601A (en) | Extremely thick steel plate for welded structure with excellent strength and toughness at the center of thickness and little material deviation, and method for manufacturing the same | |
| JP4768526B2 (en) | Thick steel plate with excellent high heat input HAZ toughness and low temperature base metal toughness | |
| JP5520105B2 (en) | Steel material excellent in toughness of weld heat-affected zone and method for producing the same | |
| KR100954042B1 (en) | Thick steel plate having excellent haz toughness | |
| JP4964007B2 (en) | Thick steel plate with little material anisotropy and excellent HAZ toughness and low temperature base metal toughness | |
| JP2003293079A (en) | Sour resistant steel for high energy density welding and steel structure | |
| JP6237681B2 (en) | Low yield ratio high strength steel plate with excellent weld heat affected zone toughness | |
| JP4586080B2 (en) | High-strength steel sheet with excellent stress-relieving annealing characteristics and low-temperature toughness | |
| JP2006089830A (en) | Steel plate having low yield ratio and excellent toughness and welded joint toughness, and its manufacturing method | |
| JP2018016890A (en) | Thick steel sheet for tank excellent in toughness of hot affected zone | |
| JP6447253B2 (en) | High strength steel for welding | |
| JP2004218010A (en) | Steel for welding |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20090929 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20111116 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20120131 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20120321 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20120410 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20120413 |
|
| R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150420 Year of fee payment: 3 |