JPH0553856B2

JPH0553856B2 -

Info

Publication number: JPH0553856B2
Application number: JP60097385A
Authority: JP
Inventors: Haruo Kaji; Mutsuo Hiromatsu; Toshiaki Suga
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1985-05-07
Filing date: 1985-05-07
Publication date: 1993-08-11
Also published as: JPS61257456A

Description

[Detailed description of the invention]

（産業上の利用分野）本発明は、例えば、橋梁等のような一般の大気
腐食環境において、溶接構造材料として用いるに
適する溶接性及び溶接継手性能にすぐれた高靱性
高リン型耐候性鋼に関する。（従来の技術）Ｐ量0.07〜0.15％のＰ−Cu−Cr系鋼が大気中で
の腐食に対してすぐれた耐候性を有することは既
によく知られている。しかし、この耐候性鋼は、
上記のように、Ｐを多量に含有しているために、
一般溶接構造用鋼に比較して、溶接性、特に、高
温割れ感受性が高く、また、鋼材自体、低温切欠
き靱性に劣ると共に、溶接熱影響部（HAZ）の
脆化が大きい。従つて、上記耐候性鋼は、従来、
主として板厚16mm以下の比較的薄い鋼板として、
溶接性及び低温靱性が厳しく要求されない用途に
のみ用いられている。しかし、近年、橋梁等のように、大気中での腐
食が生じる構造物においても、保守管理不要化の
観点から、耐候性鋼板を裸使用して、無塗装とす
る方式が増加しつつあり、かかる構造物に用いら
れる鋼材には、溶接構造材料としての低温靱性及
び溶接性に加えて、すぐれた耐候性を有すること
が要求される。本発明者らは、かかる鋼体を得るべく、既に特
開昭51−71817号公報において、溶接部の耐高温
割れ性を改善した低Ｃ−高Mn−Ｐ−Cu−Cr系鋼
板を提案している。また、特開昭52−123918号公
報においては、継手部靱性を改善した低Ｃ−Ｐ−
Cu−Ti−Ｎ系鋼板を提案しているが、このよう
な鋼板も−20〜−40℃という寒冷地域で使用され
る場合には、継手部の靱性において尚、改善の余
地が残されている。（発明の目的）そこで、本発明者らは、低温においても良好な
継手部靱性を有する高靱性高Ｐ型耐候性鋼を得る
べく鋭意研究した結果、高Ｐ含有鋼のHAZ靱性
を向上させるためには、炭素当量（Ceq）の低減
と適量のTi又はZrと共にＢ及びＮを複合添加す
ることが極めて有効であることを見出して、本発
明に至つたものである。従つて、本発明は、溶接性及び溶接継手性能に
すぐれた高靱性高リン型耐候性鋼を提供すること
を目的とする。（発明の構成）本発明による溶接性及び溶接継手性能にすぐれ
た高靱性高リン型耐候性鋼は、重量％で (a) Ｃ 0.10％以下、 Si 0.75％以下、 Mn 0.5〜1.2％、Ｐ 0.04〜0.15％、Ｓ 0.007％以下、Ａ 0.005〜0.1％、Ｂ 0.0003〜0.0020％、Ｎ 0.004％を越えて、0.010％以下、 Cu 0.15〜0.6％及び Cr 0.1〜1.0％を含有すると共に、 (b) Ti及びZrよりなる群から選ばれる少なくと
も１種の元素0.002〜0.05％を含有し、且つ、
炭素当量Ceq Ceq＝Ｃ＋Si／24＋Mn／６＋Ni／40＋Cr／５＋Mo／４＋
Ｖ／４が0.35％以下であり、残部鉄及び不可避的不純物よりなることを特徴
とする。以下に本発明について、詳細に説明する。 0.06％Ｃ−0.08％Ｐ−0.3％Cu−0.4％Cr系鋼を
基本成分系鋼とし、これにおいてMn量を種々に
変化させると共に、炭素当量（Ceq）、即ち、 Ceq＝Ｃ＋Si／24＋Mn／６＋Ni／40＋Cr／５＋Mo／４
＋Ｖ／４を0.24〜0.40％の間の範囲に調整してなる鋼から
板厚30mmの鋼板を製造し、これら鋼板について、
入熱量35KJ／cmのサブマージアーク溶接継手部
衝撃試験を行なつた。結果を第１図に示すよう
に、Ceqが減少するにつれて、ボンド部の靱性が
著しく改善されることが見出された。更に、上記
基本鋼に0.010％Ti−10ppmB−50ppmN又は
0.020％Zr−10ppmB−50ppmNを添加した鋼から
鋼板を製作し、同様に入熱量35KJ／cmのサブマ
ージアーク溶接継手部衝撃試験試験を行なつた。
結果を第２図に示すように、いずれの場合もボン
ド部靱性は、前記基本成分系鋼に比較して更に向
上し、Ceq0.35％以下の鋼板においては、脆化破
面率が50％となる遷移温度（vTrs）は−40℃以
下であり、低温においても良好な継手部靱性を有
する高靱性高Ｐ型耐候性鋼を得ることができるこ
とが見出された。このように本発明によれば、Ceqを低減し、且
つ、適量のTi又はZrと共にＢ及びＮを複合添加
することによつて、高Ｐ含有鋼のHAZ靱性を格
段に向上させ得るが、その理由は、Ｐによる
HAZ靱性の脆化が組織のフエライト化を図るこ
とによつて大幅に軽減されること、低Ceq化がマ
トリツクスの焼入れ性を低下させ、HAZ組織の
フエライト化に有効であること、及びTi又はZr
と共にＢ及びＮを複合添加することが、溶接後の
冷却過程において強力なフエライト変態核となる
TiN、ZrN、BNを鋼中に分散析出させ、HAZ組
織のフエライト微細化に大きく寄与することによ
るものとみられる。次に、本発明鋼において化学成分を限定した理
由を説明する。Ｃは、耐高温割れ性及び耐低温われ性、更には
低温靱性にすぐれる特性を付与する点からは、そ
の添加量はできる限り少ない方がよく、添加量の
上限を0.10％とする。 Siは、溶鋼の脱酸及び強度向上に有効な元素で
あるが、0.75％を越えて過多に添加しても、その
効果が飽和し、却つて溶接性や靱性を劣化させる
ので、添加量の上限を0.75％とする。 Mnは、その添加量が0.5％よりも少ないとき
は、耐高温割れ性の改善及び母材強度の確保が困
難である。また、後述するように、本発明鋼にお
いては、Ｓ量を0.007％以下に抑えているので、
このような極低Ｓ鋼においては、1.2％を越えて
多量に添加しても、上記効果が飽和し、逆に
HAZ靱性を劣化させるので、Mnの添加量を0.5
〜1.2％の範囲とする。Ｐは、大気中での耐候性の向上のために添加さ
れる。この効果を有効に発現させるためには、少
なくとも0.04％の添加を必要とする。しかし、
0.15％を越えて多量に添加しても、耐候性改善の
効果が飽和するのみならず、却つて溶接性及び低
温靱性を劣化させるので、本発明鋼においては、
Ｐは0.04〜0.15％の範囲で添加する。Ｓは、溶接部の高温割れに有害な元素である
が、含有量が多いときは、高温割れを防止するた
めに併せて多量のMnを必要とし、Mnを過多に
添加するときは、前述したように、鋼板のHAZ
靱性を低下させる。従つて、本発明においては、
Ｓの含有量の上限を0.007％とする。 Cuは、Ｐと共に耐候性の向上に有効な元素で
あり、この効果を有効に得るために、少なくとも
0.15％を添加することが必要である。しかし、
0.6％を越えて多量に添加しても、上記効果が飽
和するのみならず、却つて時効性及び熱間圧延時
に表面ひび割れ等が生じるので、添加量は0.15〜
0.6％の範囲とする。 Crは、耐候性を向上させるのに効果的な元素
である。本発明においてはかかる効果を有効に発
現させるために、少なくとも0.1％を添加するこ
とが必要である。しかし、1.0％を越えて過多に
添加するときは、溶接性を著しく劣化させるの
で、上限を1.0％とする。Ｂは、溶接後の冷却過程でオーステナイト粒内
にBNを形成し、オーステナイト粒内の組織のフ
エライト化を促進すると共に、靱性に有害な鋼中
の固溶Ｎを低減させ、HAZ靱性を向上させる効
果を有する。しかし、添加量が0.0003％よりも少
ないときは、かかる効果に乏しく、一方、0.0020
％を越えて過多に添加するときは、Ｂ化合物が増
加し、HAZ靱性のみならず、母材靱性をも著し
く劣化させるので、その上限を0.0020％とする。Ａは、脱酸及び結晶粒の調整元素として必要
不可欠の元素である。しかし、添加量が0.005％
よりも少ないときは、かかる効果に乏しく、ま
た、0.1％を越える多量であるときは、その効果
が飽和するのみならず、砂疵等の欠陥を発生させ
る原因となるので、Ａの添加量は0.005〜0.1％
の範囲とする。Ｎは、本発明鋼を構成するための主要な元素で
あり、フエライト変態核として、HAZ組織のフ
エライト化に寄与するTiN，ZrN及びBNを有効
量確保するうえで、0.004％を越えて含有するこ
とが必要である。しかし、Ｎを0.010％を越えて
過多に含有する場合は、溶接金属部の靱性を著し
く劣化させる。従つて、本発明においては、Ｎ含
有量は0.004％を越えて、0.010％以下の範囲とす
る。特に、好ましくは、0.004％を越えて、0.007
％以下の範囲である。本発明鋼は、上記した元素に加えて、更にTi
及びZrから選ばれる少なくとも１種の元素を含
有する。これら元素はHAZ靱性を改善する効果
を有し、本発明においては、これら元素の少なく
とも１種又は２種を総量にて0.002％を添加する
ことが必要である。しかし、0.05％を越えるとき
は、Ti又はZrの非金属介在物の増加と共に大き
い窒化物が析出し、HAZ靱性が劣化するばかり
でなく、母材靱性も低下する。従つて、本発明に
おいては、Ti又はZrの添加量は、総量にて0.002
〜0.05％の範囲とする。本発明においては、鋼は上記したような化学組
成を有すると共に、Ceq、即ち、 Ceq＝Ｃ＋Si／24 ＋Mn／６＋Ni／40＋Cr／５＋Mo／４＋Ｖ／４が0.35％以下であることを要する。前述したように、Ceqの低減は、高Ｐ型耐候性
鋼のHAZ靱性向上に極めて有効であり、Ceqが
0.35％を越えるときは、Ti又はZrと共にＢ又はＮ
を所定量添加しても、−40℃においてすぐれた
HAZ靱性を安定に確保することができないから
である。本発明による高Ｐ型耐候性鋼は、上記した元素
に加えて、更に、Ca及びCeよりなる群から選ば
れる少なくとも１種の元素を含有することができ
る。これら元素は、酸硫化物形成元素であるの
で、これらを添加することにより、介在物の性質
及び形状を改善し、溶接部の高温割れ感受性、母
材のＺ方向特性、及び母材とHAZの靱性を一層
向上させることができる。 Caは、例えば、Ca−Si，Ca（CN）₂、CaC₂等の
ような合金化合物の形態で溶鋼中に0.5〜20／溶
鋼トン程度投入することにより、通常、得られる
鋼中にCaが0.004％以下の含有量にて残留する。
上記したように、介在物の性質及び形状を制御す
るためには、上記量を越えて多量に添加する必要
がないので、Caの添加量の上限は0.004％とする。 Ceは、その添加量が0.001％よりも少ないとき
は、上記したような介在物制御効果が乏しく、他
方、0.1％を越えて多量に添加するときは、鋼塊
の底部にCeS等の大型介在物が集積し、鋼板の超
音波探傷欠陥の原因となるので、添加量は0.001
〜0.1％の範囲とする。更に、本発明鋼は、上記した元素とは別に、又
は上記した元素と共に、Ni，Mo，Ｖ及びNbよ
りなる群から選ばれる少なくとも１種の元素を
HAZ靱性を損なわない程度に含有することがで
きる。 Niは、耐候性、母材強度、母材切欠き靱性及
びHAZ靱性向上に効果を有するので、これら要
求に応じて広範囲にその添加量を変化させて利用
される。上記効果を有効に得るためには、少なく
とも0.005％以上を添加する必要があるが、しか
し、余りに多量に添加しても、その効果が飽和
し、また、経済性の点からも好ましくないので、
添加量の上限を1.0％とする。 Moは、少量の添加にて母材強度を著しく向上
させるので、厚物の強度確保に有効な元素であ
る。この効果を有効に得るためには、少なくとも
0.005％以上を添加する必要があるが、しかし、
余りに多量に添加するときは、HAZ靱性が劣化
するので、添加量の上限は0.5％とする。Ｖ及びNbは、共に窒化物を形成して、溶接部
の軟化防止、母材強度の向上、更には低Ceq化に
よる耐溶接割れ性の向上を図ることができる。か
かる効果を有効に発現させるためには、それぞれ
少なくとも0.01％を添加することが必要である
が、他方、それぞれ0.15％を越えて過多に添加し
ても、母材強度の向上効果が顕著には増大せず、
却つて溶接性の劣化やHAZ靱性の低下を招く。
従つて、本発明鋼においては、Nb及びＶはそれ
ぞれ0.01〜0.15％の範囲で添加する。以上のような本発明鋼は、溶接性及び溶接継手
性能のすぐれた高靱性高Ｐ型耐候性鋼であつて、
通常の製鋼、分解、圧延又は圧延後加速冷却（直
接焼入れを含む。）によつて製造することができ、
引張強さ40〜60Kgｆ／mm²級の強度を有する。（発明の効果）以上のように、本発明鋼は、Ｐ−Cu−Cr系耐
候性鋼板において、低Ｃ、極低Ｓ化すると共に低
Ceq化し、且つ、Ti又はZrと共に適量のＢ及びＮ
を複合添加することによつて、HAZの低温切欠
き靱性を著しく改善してなる高Ｐ型耐候性鋼であ
つて、特に、耐候性や溶接性の要求が厳しい寒冷
地域における橋梁、建築、鉄塔等の構造物への使
用に適する。勿論、厚さ16mm以上の厚板としてか
かる用途に好適に用いることができる。（実施例）以下に本発明を実施例によつて説明するが、本
発明はこれら実施例によつて何ら制限されるもの
ではない。実施例１第１表に本発明鋼板１〜１３、従来鋼板１４、
及び比較鋼板１５〜１７の化学組成、板厚、炭素
当量及び溶接性を示す。溶接性は、JIS規格に制
定されているＣ型ジグ拘束突合せ溶接割れ試験
（高温割れ試験）及び斜めＹ型拘束突合せ溶接割
れ試験（低温割れ試験）によつた。この試験結果によれば、従来鋼１４の高温割れ
率が10％であるのに対して、本発明鋼の場合はす
べて０％である。また、比較鋼１５，１６及び１
７（板厚30mm）は、低温割れ防止予熱温度とし
て、50〜125℃を必要とするのに対して、本発明
鋼１〜８，１０，１２及び１３は、50℃以下でよ
く、すぐれた耐高温割れ性及び耐低温割れ性を有
していることが明らかである。次に、第１表に示す鋼板について調べた機械的
性質、入熱量35KJ／cm及び60KJ／cmのサブマー
ジアーク溶接継手ボンド部の−40℃における吸収
エネルギー、即ち、vE_-40及び発露型腐食試験に
よる腐食度を第２表に示す。 (Field of Industrial Application) The present invention relates to a high-toughness, high-phosphorous weathering steel with excellent weldability and welded joint performance suitable for use as a welded structural material in general atmospheric corrosive environments such as bridges, etc. . (Prior Art) It is already well known that P-Cu-Cr steel with a P content of 0.07 to 0.15% has excellent weather resistance against corrosion in the atmosphere. However, this weathering steel
As mentioned above, because it contains a large amount of P,
Compared to general welded structural steels, it has high weldability, especially susceptibility to hot cracking, and the steel itself has poor low-temperature notch toughness, and the weld heat-affected zone (HAZ) is highly embrittled. Therefore, the weathering steel mentioned above is conventionally
Mainly as a relatively thin steel plate with a thickness of 16 mm or less,
It is used only in applications where weldability and low temperature toughness are not strictly required. However, in recent years, even in structures where corrosion occurs in the atmosphere, such as bridges, there has been an increase in the use of bare weathering steel plates and unpainted structures from the perspective of eliminating the need for maintenance management. Steel materials used in such structures are required to have excellent weather resistance in addition to low-temperature toughness and weldability as welded structural materials. In order to obtain such a steel body, the present inventors have already proposed a low C-high Mn-P-Cu-Cr steel sheet with improved hot cracking resistance of welded parts in Japanese Patent Application Laid-Open No. 71817/1983. ing. Furthermore, in Japanese Patent Application Laid-open No. 52-123918, a low C-P-
Although we have proposed Cu-Ti-N steel sheets, there is still room for improvement in the toughness of joints when such steel sheets are used in cold regions of -20 to -40°C. There is. (Purpose of the Invention) Therefore, as a result of intensive research to obtain a high-toughness, high-P type weathering steel that has good joint toughness even at low temperatures, the present inventors have found that the HAZ toughness of high-P-containing steel can be improved. The present invention was developed based on the discovery that it is extremely effective to reduce the carbon equivalent (Ceq) and add B and N in combination with an appropriate amount of Ti or Zr. Therefore, an object of the present invention is to provide a high-toughness, high-phosphorus type weathering steel with excellent weldability and weld joint performance. (Structure of the Invention) The high-toughness, high-phosphorus type weathering steel with excellent weldability and weld joint performance according to the present invention has (a) C 0.10% or less, Si 0.75% or less, Mn 0.5-1.2%, P in weight percentages. Contains 0.04-0.15%, S 0.007% or less, A 0.005-0.1%, B 0.0003-0.0020%, N exceeding 0.004% and 0.010% or less, Cu 0.15-0.6%, and Cr 0.1-1.0%, and ( b) Contains 0.002 to 0.05% of at least one element selected from the group consisting of Ti and Zr, and
Carbon equivalent Ceq Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+
It is characterized by having a V/4 of 0.35% or less, with the remainder consisting of iron and unavoidable impurities. The present invention will be explained in detail below. The basic composition steel is 0.06%C-0.08%P-0.3%Cu-0.4%Cr steel, in which the amount of Mn is varied variously, and the carbon equivalent (Ceq), that is, Ceq=C+Si/24+Mn/6+Ni /40+Cr/5+Mo/4
Steel plates with a thickness of 30 mm are manufactured from steel with +V/4 adjusted to a range of 0.24 to 0.40%, and for these steel plates,
An impact test was conducted on a submerged arc welded joint with a heat input of 35 KJ/cm. As the results are shown in FIG. 1, it was found that as Ceq decreased, the toughness of the bond portion was significantly improved. Furthermore, 0.010%Ti-10ppmB-50ppmN or
A steel plate was made from steel to which 0.020% Zr-10ppmB-50ppmN was added, and a submerged arc welding joint impact test was similarly conducted with a heat input of 35KJ/cm.
As the results are shown in Figure 2, in both cases, the bond toughness is further improved compared to the above-mentioned basic composition steel, and the embrittlement fracture rate is 50% in steel plates with Ceq of 0.35% or less. It has been found that the transition temperature (vTrs) at which the transition temperature becomes -40°C or lower, and that it is possible to obtain a high-toughness, high-P type weathering steel that has good joint toughness even at low temperatures. As described above, according to the present invention, the HAZ toughness of high P-containing steel can be significantly improved by reducing Ceq and adding B and N together with an appropriate amount of Ti or Zr. The reason is due to P.
Embrittlement of HAZ toughness can be significantly reduced by converting the structure to ferrite, lowering Ceq reduces the hardenability of the matrix and is effective in converting the HAZ structure to ferrite, and Ti or Zr
In addition, the combined addition of B and N forms a strong ferrite transformation nucleus during the cooling process after welding.
This appears to be due to TiN, ZrN, and BN being dispersed and precipitated in the steel, which greatly contributes to the refinement of ferrite in the HAZ structure. Next, the reason for limiting the chemical components in the steel of the present invention will be explained. From the viewpoint of imparting excellent properties in hot cracking resistance, low temperature cracking resistance, and furthermore low temperature toughness, the amount of C added should be as small as possible, and the upper limit of the amount added is set at 0.10%. Si is an effective element for deoxidizing molten steel and improving its strength, but if it is added in excess of 0.75%, its effect will be saturated and it will actually deteriorate weldability and toughness, so the amount of Si added should be limited. The upper limit is set at 0.75%. When the amount of Mn added is less than 0.5%, it is difficult to improve hot cracking resistance and ensure base material strength. In addition, as will be described later, in the steel of the present invention, the amount of S is suppressed to 0.007% or less, so
In such ultra-low S steel, even if the addition exceeds 1.2%, the above effect will be saturated, and on the contrary,
Since it deteriorates the HAZ toughness, the amount of Mn added is reduced to 0.5.
~1.2% range. P is added to improve weather resistance in the atmosphere. In order to effectively express this effect, it is necessary to add at least 0.04%. but,
Even if it is added in a large amount exceeding 0.15%, the effect of improving weather resistance will not only be saturated, but it will also deteriorate weldability and low-temperature toughness, so in the steel of the present invention,
P is added in a range of 0.04 to 0.15%. S is an element that is harmful to hot cracking in welds, but when the content is high, a large amount of Mn is also required to prevent hot cracking, and when adding too much Mn, the above-mentioned As in, HAZ of steel plate
Decreases toughness. Therefore, in the present invention,
The upper limit of the S content is 0.007%. Cu is an element that is effective in improving weather resistance together with P, and in order to effectively obtain this effect, at least
It is necessary to add 0.15%. but,
Even if it is added in a large amount exceeding 0.6%, the above effects will not only be saturated, but also aging properties and surface cracks will occur during hot rolling, so the addition amount should be 0.15~
The range shall be 0.6%. Cr is an effective element for improving weather resistance. In the present invention, in order to effectively exhibit such effects, it is necessary to add at least 0.1%. However, when added in excess of 1.0%, weldability is significantly deteriorated, so the upper limit is set at 1.0%. B forms BN within the austenite grains during the cooling process after welding, promotes the formation of ferrite in the structure within the austenite grains, reduces solid solution N in the steel that is harmful to toughness, and improves HAZ toughness. have an effect. However, when the amount added is less than 0.0003%, this effect is poor;
If it is added in excess of 0.0%, the B compound will increase and will significantly deteriorate not only the HAZ toughness but also the base material toughness, so the upper limit is set at 0.0020%. A is an essential element as a deoxidizing and crystal grain adjusting element. However, the amount added is 0.005%
If the amount is less than 0.1%, the effect will be poor, and if the amount exceeds 0.1%, the effect will not only be saturated, but also cause defects such as sand spots. 0.005~0.1%
The range shall be . N is a main element constituting the steel of the present invention, and is contained in an amount exceeding 0.004% in order to secure an effective amount of TiN, ZrN, and BN, which contribute to ferrite formation of the HAZ structure, as ferrite transformation nuclei. It is necessary. However, when N is contained in an excessive amount exceeding 0.010%, the toughness of the weld metal part is significantly deteriorated. Therefore, in the present invention, the N content is in the range of more than 0.004% and less than 0.010%. Particularly preferably more than 0.004% and 0.007
% or less. In addition to the above-mentioned elements, the steel of the present invention further contains Ti.
and Zr. These elements have the effect of improving HAZ toughness, and in the present invention, it is necessary to add at least one or two of these elements in a total amount of 0.002%. However, when it exceeds 0.05%, large nitrides precipitate as non-metallic inclusions of Ti or Zr increase, and not only the HAZ toughness deteriorates, but also the base metal toughness. Therefore, in the present invention, the total amount of Ti or Zr added is 0.002
The range shall be ~0.05%. In the present invention, the steel is required to have the chemical composition as described above, and Ceq, that is, Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V/4, is 0.35% or less. As mentioned above, reducing Ceq is extremely effective in improving the HAZ toughness of high P type weathering steel, and Ceq
When it exceeds 0.35%, B or N is added together with Ti or Zr.
Even with the addition of a specified amount of
This is because HAZ toughness cannot be stably ensured. The high P type weathering steel according to the present invention can further contain at least one element selected from the group consisting of Ca and Ce in addition to the above-mentioned elements. These elements are oxysulfide forming elements, so their addition improves the properties and shape of inclusions, improves the hot cracking susceptibility of the weld, the Z-direction properties of the base metal, and the relationship between the base metal and HAZ. Toughness can be further improved. Ca is usually added to molten steel in the form of an alloy compound such as Ca-Si, Ca(CN) ₂ , CaC ₂ , etc. at a rate of 0.5 to 20/ton of molten steel. Remains at a content of 0.004% or less.
As mentioned above, in order to control the properties and shapes of inclusions, it is not necessary to add more than the above amount, so the upper limit of the amount of Ca added is set at 0.004%. When the amount of Ce added is less than 0.001%, the above-mentioned inclusion control effect is poor, and on the other hand, when it is added in a large amount exceeding 0.1%, large inclusions such as CeS etc. occur at the bottom of the steel ingot. The amount of addition is 0.001, as it may accumulate and cause defects in ultrasonic inspection of steel plates.
The range should be ~0.1%. Furthermore, the steel of the present invention contains at least one element selected from the group consisting of Ni, Mo, V, and Nb, in addition to or together with the above-mentioned elements.
It can be contained to an extent that does not impair HAZ toughness. Since Ni has the effect of improving weather resistance, base material strength, base material notch toughness, and HAZ toughness, it is used by varying the amount added over a wide range depending on these requirements. In order to effectively obtain the above effect, it is necessary to add at least 0.005% or more, but if too much is added, the effect will be saturated and it is also unfavorable from an economic point of view.
The upper limit of the amount added is 1.0%. Mo can significantly improve the strength of the base material when added in a small amount, so it is an effective element for ensuring the strength of thick materials. In order to effectively obtain this effect, at least
It is necessary to add 0.005% or more, but,
If added in too large a quantity, the HAZ toughness will deteriorate, so the upper limit of the amount added is 0.5%. V and Nb together form nitrides, which can prevent softening of the weld zone, improve base metal strength, and further improve weld cracking resistance by lowering Ceq. In order to effectively express such effects, it is necessary to add at least 0.01% of each of them, but on the other hand, even if they are added in excess of 0.15%, the effect of improving the strength of the base material will not be noticeable. does not increase,
On the contrary, it leads to deterioration of weldability and a decrease in HAZ toughness.
Therefore, in the steel of the present invention, Nb and V are each added in a range of 0.01 to 0.15%. The steel of the present invention as described above is a high-toughness, high-P type weathering steel with excellent weldability and welded joint performance, and
Can be produced by ordinary steel manufacturing, decomposition, rolling or accelerated cooling after rolling (including direct quenching),
Tensile strength: 40-60Kgf/mm, class ² strength. (Effects of the invention) As described above, the steel of the present invention has low C and extremely low S as well as low C and extremely low S in P-Cu-Cr weathering steel sheets.
Ceq and appropriate amount of B and N along with Ti or Zr
It is a high-P type weathering steel that has significantly improved the low-temperature notch toughness of HAZ by adding a combination of Suitable for use in structures such as Of course, a thick plate with a thickness of 16 mm or more can be suitably used for such purposes. (Examples) The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 Table 1 shows steel plates 1 to 13 of the present invention, conventional steel plate 14,
The chemical composition, plate thickness, carbon equivalent, and weldability of comparative steel plates 15 to 17 are also shown. Weldability was determined by a C-shaped jig restraint butt weld cracking test (hot cracking test) and an oblique Y-shape restraint butt weld cracking test (cold cracking test) established in JIS standards. According to the test results, the hot cracking rate of conventional steel 14 is 10%, whereas it is 0% in all cases of the steel of the present invention. In addition, comparative steels 15, 16 and 1
Steel No. 7 (thickness: 30 mm) requires a preheating temperature of 50 to 125°C to prevent cold cracking, whereas steels 1 to 8, 10, 12, and 13 of the present invention require a preheating temperature of 50°C or less and have excellent properties. It is clear that it has hot cracking resistance and cold cracking resistance. Next, we investigated the mechanical properties of the steel plates shown in Table 1, the absorbed energy at -40°C of the submerged arc welding joint bond part with heat inputs of 35 KJ/cm and 60 KJ/cm, that is, vE _-40 , and the dew corrosion test. Table 2 shows the degree of corrosion.

【表】【table】

【表】機械的性質については、本発明鋼板は圧延のま
まで40Kgｆ／mm²級、加速度冷却を適用することに
よつて50Kgｆ／mm²級或いは60Kgｆ／mm²級の強度を
得ることができる。また、サブマージアーク溶接
継手ボンド部の衝撃特性については、従来鋼及び
比較鋼に比べて、本発明鋼板が格段にすぐれた
HAZ靱性を有していることが明らかである。比
較鋼１５は、本発明鋼に比べて高Mn、高Ｓであ
り、且つ、Ti及びＮを含有するが、Ｂを含有し
ないので、溶接性は本発明鋼板とほぼ同等であつ
ても、低温衝撃特性が著しく劣る。更に、発露型
腐食試験機を用いて、海洋工業地帯を想定した条
件下で行なつた試験期間６週間の促進試験結果
も、本発明鋼板が従来の高耐候性鋼と同等以上の
耐候性を有することを示している。特に、本発明
鋼板は、比較鋼１６及び１７に比べれば、それら
の２〜３倍のすぐれた耐候性を有している。[Table] Regarding mechanical properties, the steel plate of the present invention can obtain strength of 40Kgf/mm ^2nd class as it is rolled, and 50Kgf/mm ^2nd class or 60Kgf/mm ^2nd class strength by applying accelerated cooling. . In addition, regarding the impact properties of submerged arc welded joint bond parts, the steel plate of the present invention was significantly superior to conventional steel and comparative steel.
It is clear that it has HAZ toughness. Comparative Steel 15 has higher Mn and higher S than the inventive steel, and contains Ti and N, but does not contain B, so even though the weldability is almost the same as the inventive steel sheet, it has a high weldability at low temperatures. Impact properties are significantly inferior. Furthermore, the results of an accelerated test conducted over a 6-week period using a dew-type corrosion tester under conditions simulating a marine industrial zone also showed that the steel sheet of the present invention has weather resistance equal to or higher than that of conventional high weathering steel. It shows that it has. In particular, the steel sheet of the present invention has weather resistance that is two to three times better than Comparative Steels 16 and 17.

[Brief explanation of drawings]

第１図は、0.06％Ｃ−0.08％Ｐ−0.3％Cu−0.4
％Cr鋼板の入熱量35KJ／cmのサブマージアーク
溶接継手ボンド部のvTrsとCeqとの関係を示すグ
ラフ、第２図は、第１図に示す基本成分鋼板に更
にTi又はZrと共にＢとＮを複合添加した鋼板の
入熱量35KJ／cmのサブマージアーク溶接継手ボ
ンド部のvTrsとCeqとの関係を示すグラフであ
る。 Figure 1 shows 0.06%C-0.08%P-0.3%Cu-0.4
%Cr A graph showing the relationship between vTrs and Ceq of a submerged arc welded joint bond part with a heat input of 35 KJ/cm for a steel plate. Figure 2 is a graph showing the relationship between vTrs and Ceq of a submerged arc welding joint bond part with a heat input of 35 KJ/cm for a steel plate with the basic components shown in Figure 1. It is a graph showing the relationship between vTrs and Ceq of a submerged arc welded joint bond part with a heat input of 35 KJ/cm of a steel plate with composite addition.

Claims

[Claims] 1% by weight: (a) C 0.10% or less, Si 0.75% or less, Mn 0.5-1.2%, P 0.04-0.15%, S 0.007% or less, A 0.005-0.1%, B 0.0003-0.0020 %, N exceeding 0.004% and 0.010% or less, Cu 0.15-0.6% and Cr 0.1-1.0%, and (b) 0.002-0.05% of at least one element selected from the group consisting of Ti and Zr. contains, and
Carbon equivalent Ceq Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+
A high-toughness, high-phosphorous weathering steel with excellent weldability and weld joint performance, characterized by having a V/4 of 0.35% or less and consisting of the remainder iron and unavoidable impurities. 2 Weight%: (a) C 0.10% or less, Si 0.75% or less, Mn 0.5-1.2%, P 0.04-0.15%, S 0.007% or less, A 0.005-0.1%, B 0.0003-0.0020%, N 0.004%. (b) 0.002-0.05% of at least one element selected from the group consisting of Ti and Zr; and (c) Ce. 0.001 to 0.1% and at least one element selected from the group consisting of Ca 0.004% or less, and carbon equivalent Ceq Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 +
A high-toughness, high-phosphorous weathering steel with excellent weldability and weld joint performance, characterized by having a V/4 of 0.35% or less and consisting of the remainder iron and unavoidable impurities. 3 Weight%: (a) C 0.10% or less, Si 0.75% or less, Mn 0.5-1.2%, P 0.04-0.15%, S 0.007% or less, A 0.005-0.1%, B 0.0003-0.0020%, N 0.004%. (b) 0.002-0.05% of at least one element selected from the group consisting of Ti and Zr; (c) Ni 0.05 to 1.0%, Mo 0.05 to 0.5%, V 0.01 to 0.15%, and at least one element selected from the group consisting of Nb 0.01 to 0.15%, and carbon equivalent Ceq Ceq = C + Si / 24 + Mn / 6 + Ni /40+Cr/5+Mo/4+
A high-toughness, high-phosphorous weathering steel with excellent weldability and weld joint performance, characterized by having a V/4 of 0.35% or less and consisting of the remainder iron and unavoidable impurities. 4 Weight%: (a) C 0.10% or less, Si 0.75% or less, Mn 0.5-1.2%, P 0.04-0.15%, S 0.007% or less, A 0.005-0.1%, B 0.0003-0.0020%, N 0.004%. (b) contains 0.002-0.05% of at least one element selected from the group consisting of Ti and Zr; ) at least one element selected from the group consisting of Ce 0.001-0.1% and Ca 0.004% or less; (d) Ni 0.05-1.0% or less, Mo 0.05-0.5% or less, V 0.01-0.15% and Nb 0.01- 0.15% and at least one element selected from the group consisting of carbon equivalent Ceq Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+
A high-toughness, high-phosphorous type weathering steel with excellent weldability and weld joint performance, characterized by having V/4 of 0.35% or less and consisting of the remainder iron and unavoidable impurities.