JP3702124B2 - Submerged arc welding method for HT590 grade refractory steel - Google Patents

Description

【００１１】
［Ｍｏ］_C ≧０．３２ （２）
ここで、［Ｍｏ］_C ＝α_W ［Ｍｏ］Ｗ＋α_P ［Ｍｏ］Ｐ＋α_F （Ｍｏ）_F
【００１２】
［Ｂ］Ｃ≦０．００１０ （３）
ここで、［Ｂ］_C ＝α_W ［Ｂ］Ｗ＋α_P ［Ｂ］Ｐ＋α_F （Ｂ₂ Ｏ₃ ）_F 、
【００１３】
０．３７≦Ｃｅｑ≦０．４９ （４）
ここで、Ｃｅｑ＝Ｃ＋Ｓｉ／２４＋Ｍｎ／６＋（Ｍｏ＋Ｎｂ）／５＋５Ｂ
【００１４】
但し、（１）式でＣａＯ、ＭｎＯ、ＭｇＯ、ＣａＦ₂ 、ＳｉＯ₂ 、Ａｌ₂ Ｏ₃、ＴｉＯ₂ ：それぞれフラックス中のＣａＯ、ＭｎＯ、ＭｇＯ、ＣａＦ₂ 、ＳｉＯ₂ 、Ａｌ₂ Ｏ₃ 、ＴｉＯ₂ の含有量（重量％）、
（２）、（３）式で［Ｍｏ］_W ：ワイヤ中のＭｏ含有量（重量％）、［Ｍｏ］_P ：母材中のＭｏ含有量（重量％）、（Ｍｏ）_F ：フラックス中のＭｏ含有量（重量％）、［Ｂ］_w ：ワイヤ中 のＢ含有量（重量％）、［Ｂ］_p ：母材中のＢ 含有量（重量％）、（Ｂ₂ Ｏ₃ ）_F ：フラックス中のＢ₂ Ｏ₃ 含有量（重量％）α_w ：ワイヤ中 のＭｏおよびＢの溶接金属中への移行率，α_p ：母材中のＭ ｏおよびＢの溶接金属中への移行率、α_F ：フラックス中のＭｏおよびＢの溶接金属への移行率であり、板厚１９〜２８ｍｍはα_w ＝０．３７、α_p ＝０．４３、α_F ＝０．２０，板厚２８超〜４０ｍｍはα_w＝０．４２、α_p＝０．４８、α_F ＝０．１０、板厚４０超〜５５ｍｍはα_w ＝０．４５、α_p ＝０．５０、α_F＝０．０５、
（４）式でＣ、Ｓｉ、Ｍｎ、Ｍｏ、ＮｂおよびＢはそれぞれ溶接金属中のＣ、Ｓｉ、Ｍｎ、Ｍｏ、ＮｂおよびＢの含有量（重量％）。
【００１５】
【発明の実施の形態】
本発明者らは、前記目的を達成するため種々検討し、適正組成のワイヤおよびフラックスを用い、フラックス、ワイヤおよび鋼板から溶接金属中に移行するＢ量を規制するとともに溶接金属の炭素等量を適正にして高温伸びを確保し、かつ、ワイヤ成分およびフラックス塩基度の適正化により引張強度と靭性を良好に保つ溶接方法を見出したのである。
【００１６】
まず、本発明が対象とする被溶接材の鋼材であるが、Ｍｏ：０．６〜１．２％、Ｎｂ：０．００１〜０．０５％を含有することにより、従来から一般に用いられてきた耐火鋼より強度を向上させたＨＴ５９０級耐火鋼である。この鋼材の全体の成分を上記Ｍｏ、Ｎｂも含めて記載すると、重量％で、Ｃ：０．０５〜０．０９％、Ｓｉ：０．２５〜０．３５％、Ｍｎ：１．２〜１．７％、Ｍｏ：０．６〜１．２％、Ｎｂ：０．００１〜０．０５％、Ｖ：０．０５％以下、Ｔｉ：０．０２％以下、Ｂ：０．００１０％以下を含有し、残部がＦｅ及び不可避不純物からなるものが一般的である。
【００１７】
以前のＨＴ４９０〜ＨＴ５２０級の耐火鋼の溶接では溶接金属の６００℃での耐力を得るため、溶接金属中のＭｏ量の尺度を表す特定式でその値を規定することを提案した。本発明が対象とするＨＴ５９０耐火鋼で考えた場合、通常耐力の規格値４４０Ｎ／ｍｍ² の７０％を６００℃で保証するとすれば、耐力の規格値は３０８Ｎ／ｍｍ² 以上となる。この耐力を得るためには図１のグラフに示す如く溶接金属中のＭｏ量の尺度を示す鋼板、ワイヤおよびフラックスの特定式による［Ｍｏ］_c 値を０．３３以上とすることが必要である。
【００１８】
次に、以前のＨＴ４９０〜ＨＴ５２０の耐火鋼の溶接では溶接金属のミクロ組織において適度の初析フェライトを残すことを提案した。即ち、初析フェライトは６００℃での引張試験における伸びを１８％以上確保するためには残すことが必要であり、一方、良好な靭性を確保するためにはできるだけ仰制することが必要であるので、両立させるためにフラッククス、ワイヤおよび鋼板から溶接金属に移行するＢ量の特定式を規定し、さらにＣｅｑとの関連式で適正範囲を規定した。溶接金属の常温強度は４９０〜６６０Ｎ／ｍｍ² であるので溶接金属に初析フェライトを残すことが比較的容易に出来る。
【００１９】
しかしながら、本発明が対象とするＨＴ５９０耐火鋼においては鋼板に０.６ 〜１.２％のＭｏが添加されており、この鋼板をボックス柱の角溶接のような大 入熱一層溶接を行えば母材希釈率は４５％程度となり、母材からの希釈だけで０.２７〜０.５７と最大０.６％程度のＭｏが溶接金属へ移行する。溶接金属のＭ ｏが増加するとミクロ組織において粒界の初析フェライトが減少し、０.６％の Ｍｏでは極微の生成になる。このようなＭｏが多量に母材から溶接金属中に移行し初析フェライトが減少しやすい溶接ではＢ量を厳しく仰制するか、さらに溶接金属を高酸素として変態温度を高くして初析フェライトが成長しやすい組成にする必要がある。
【００２０】
ＨＴ５９０鋼の溶接では溶接金属のＢ量はフラックス、ワイヤ、鋼板の不純物から不可避的に入る以外は添加せず、かつ、フラックスでは塩基度を低く設定する。さらに、強度が過大とならないようにＣｅｑは適正範囲に規制することが必要である。
【００２１】
Ｂは鋼板およびワイヤには０.０００６％程度以下、ボンドフラックスでは通常使用するマグネシアクリンカーからＢ₂ Ｏ₃ として０.０３％程度以下がフラ ックスに不可避的に含まれる。溶接金属にＢは意図的に添加せず、さらに溶接金属に移行するＢ量の尺度として特定式の［Ｂ］_c 値を用いて０.００１０以下に 規定する。
【００２２】
さらに、溶接金属に酸素を供給する尺度としてＢｎ＝（０.１０８ＣａＯ＋０.０６８ＭｎＯ＋０.１００ＭｇＯ＋０.０７８ＣａＦ₂ ）／（０．１０５ＳｉＯ₂＋０.００２Ａｌ₂ Ｏ₃ ＋０.０８０ＴｉＯ₂ ）で表される塩基度を０.５５≦Ｂ ｎ≦１.４０とする。それに加えて常温の強度を５９０Ｎ／ｍｍ² 以上を確保す るためにはＣｅｑを０.３７％以上に規制する。
【００２３】
さらに本発明を詳細に説明する。
本発明者らは、まず耐火鋼の溶接金属において［Ｍｏ］_C 量と６００℃の耐力（以下、ＹＰ６００と言う）との関係を求めた。［Ｍｏ］_c 量が大きくなるに従ってＹＰ６００が大きくなることがわかる。［Ｍｏ］_c は溶接金属中のＭｏ量の尺度を示すもので、以前のＨＴ４００〜ＨＴ５２０級耐火鋼では本発明者等は［Ｍｏ］_c として［Ｍｏ］_c =４３［Ｍｏ］_w ＋５５［Ｍｏ］_p +１８（Ｍｏ)_F なる計算値を用いＹＰ６００≧２３５Ｎ／ｍｍ² を確保するために［Ｍｏ］_c ≧８.５とすることを提案した。
【００２４】
本発明が対象するＨＴ５９０級耐火鋼においてはＳＭ５９０鋼の規格ＹＰ≧４４０Ｎ／ｍｍ² に対し耐火鋼としてはＹＰ６００≧３０８（＝４４０×０.７） Ｎ／ｍｍ² が必要である。ここでその尺度として上記式に変え板厚によって差のある母材希釈率を考量した［Ｍｏ］_c 、即ち、特定式［Ｍｏ］_c =α_w ［Ｍｏ］_w＋α_p［Ｍｏ］_p ＋α_F （Ｍｏ）_F を得た。目標値を達成するためには［Ｍｏ］_cが０.３３以上が必要である。
ここで、［Ｍｏ］_W ：ワイヤ中のＭｏ含有量（重量％）、［Ｍｏ］_P ：母材中のＭｏ含有量（重量％）、（Ｍｏ）_F ：フラックス中のＭｏ含有量（重量％）であり、α_w：ワイヤ中 のＭｏの溶接金属中への移行率、α_p：母材中のＭｏの溶 接金属中への移行率、α_F ：フラックス中のＭｏの溶接金属への移行率であり、板厚１９〜２８ｍｍはα_w ＝０．３７、α_p ＝０．４３、α_F ＝０．２０、板厚２８超〜４０ｍｍはα_w ＝０．４２、α_p ＝０．４８、α_F ＝０．１０、板厚４０超〜５５ｍｍはα_w ＝０．４５、α_p ＝０．５０、α_F ＝０．０５である。
【００２５】
次に、６００℃の引張試験の伸びを確保するための尺度としてＨＴ４００〜ＨＴ５２０級耐火鋼では本発明者等はまず溶接金属中のＢ量の尺度として［Ｂ］c＝４３００［Ｂ］_w ＋５５００［Ｂ］_p ＋１２０（Ｂ₂ Ｏ₃ ）_F を提案したがＨＴ５９０鋼では上記式に換え板厚によって差のある母材希釈率を考慮した［Ｂ］_c 、即ち、［Ｂ］_c ＝α_w ［Ｂ］_w ＋α_p［Ｂ］_p ＋α_F （Ｂ₂ Ｏ₃ ）_F を用い、［Ｂ］_c ≦０.００１０が必要であることを見出した。［Ｂ］_w ：ワイヤ中のＢ含有量（重量％）、［Ｂ］_p ：母材中のＢ含有量（重量％）、（Ｂ₂ Ｏ₃ ）_F：フラックス中のＢ₂ Ｏ₃ 含有量（重量％）、α_w ：ワイヤ中 のＢの溶接金属中への移行率、α_p ：母材中のＢの溶接金属中への移行率、α_F ：フラックス中のＢの溶接金属への移行率であり、板厚１９〜２８ｍｍはα_w ＝０．３７、α_p＝０．４３、α_F ＝０．２０、板厚２８超〜４０ｍｍはα_w ＝０．４２、α_p ＝０．４８、α_F ＝０．１０、板厚４０超〜５５ｍｍはα_w ＝０．４５、α_p ＝０．５０、α_F ＝０．０５である。
【００２６】
さらに、６００℃の引張試験の伸びを確保するため粒界の初析フェライトが生成するためにはフラックスの塩基度を小さくすることが必要である。フラックスの塩基度は溶接金属中への酸素量の尺度である。即ち、塩基度が小さくなるほど溶接金属中の酸素量が増加し、粒界の初析フェライトが生成して６００℃の引張試験の伸びが向上する。いま塩基度としてＢｎ＝（０.１０８ＣａＯ＋０.０６８ＭｎＯ＋０.１００ＭｇＯ＋０.０７８ＣａＦ₂ ）／（０.１０５ＳｉＯ₂ ＋０.００２Ａｌ₂ Ｏ₃ ＋０.０８０ＴｉＯ₂ ）を用いるとして、６００℃の引張試験で 良好な伸びを確保するためにはＢｎ≦１.４０が必要である。一方、Ｂｎが０.５５未満となると靭性が劣化する。即ち、０.５５≦Ｂｎ≦１.４０となる。
【００２７】
また、常温での引張強度（以下ＴＳ_RTと言う）を適正範囲に保つには焼き入れの尺度の制限が必要である。即ち、Ｃｅｑ≦０.４９％であることが必要である。また、５９０Ｎ／ｍｍ² 以上にするにはＣｅｑ≧０.３７％である。即ち、 ０.３７≦Ｃｅｑ≦０.４９％である。
【００２８】
以下に本発明で使用するサブマージアーク溶接用ワイヤの成分について説明する。
Ｃは常温強度の確保ならびにＭｏ、Ｎｂの添加効果を発揮させるために必要であり０．０１％が下限である。また、０．１３％を越えると高温割れ感受性が増加するとともに靭性が劣化する。
【００２９】
Ｓｉは脱酸元素として０．００５％以上の添加が必要であるが０．１５％を越えると溶接金属の靭性を劣化させる。
Ｍｎは強度および靭性を確保するために不可欠であり１．２％以上の添加が必要であるが、２．２％を越えると、高温割れ感受性が増加するとともに靭性が劣化する。
【００３０】
ＭｏおよびＮｂは十分な高温耐力を確保するために必要であるが、フラックスからも添加が可能であるから特に下限は規定しない。一方、Ｍｏ、Ｎｂが過多になると、常温強度が高くなりすぎ靭性が劣化するので、添加量はＭｏは０．６０％以下、Ｎｂは０．０５％以下にする必要がある。
【００３１】
Ｖは常温強度の確保に必要であるが、ワイヤとしては０．０２％を越えると靭性が劣化する。
Ｔｉは脱酸元素であり、且つ、靭性確保に重要な元素であり０.００１％以上の添加が望ましいが、過剰に添加すると溶接金属の高温伸びを劣化させるので０.０３％以下にする必要がある。
【００３２】
Ｂは６００℃の高温引張の伸びの確保に重要であり、意図的に添加せず０.０ ００５％以下と不純物から不可避的に入る量に規制する必要がある。
また、本発明ワイヤには以上規定した成分以外としては、Ｎｉを１％以下、Ｃｒを０.５％以下、Ｃｕをメッキも含め０.５％以下、Ｐを０.０２５％以下、Ｓ を０.０１５％以下を許容できる。その他残部はＦｅおよび不可避的不純物である。
【００３３】
【実施例】
以下実施例により、本発明の効果をさらに具体的に示す。
鋼板は表１に示すＰ１〜Ｐ４の４種類、ワイヤは表２に示すＷ１〜Ｗ３の３種類の組成のものを用いた。フラックスは表３のＦ１〜Ｆ６の６種類のボンドフラックスを作製した。このうちＦ１〜Ｆ４は本発明例のフラックス、Ｆ５、Ｆ６は本発明の効果を明確にするための比較例のフラックスである。
【００３４】
【表１】

【００３５】
【表２】

【００３６】
【表３】

【００３７】
図２に示す（ａ）の開先形状はＹ型開先、（ｂ）はレ型開先であって、（ａ）の開先形状のθ₁ は開先角度３５゜、Ｔ₁ は板厚４０ｍｍ又は４５ｍｍ、ｒ₁ はルートフェース２ｍｍ、ｔ₁ は裏当金２５ｍｍである。また、（ｂ）の開先形状のθ₂ は開先角度４０゜、Ｔ₂ は板厚２５ｍｍ、ｒ₂ はルートフェース２ｍｍ、ｔ₂ は裏当金２５ｍｍである。以上の３種類の試験体を用い、表４に示す溶接条件Ｃ１〜Ｃ３の条件で、予熱を行わずに２電極によるサブマージアーク溶接を実施した。
【００３８】
【表４】

【００３９】
溶接終了後、板表面１０ｍｍ下の溶接部よりＪＩＳ Ａ１号引張試験片を１個、ＪＩＳ４号Ｖノッチシャルピー試験片を３個、高温引張試験片（６ｍｍ径）１個および分析試料ををそれぞれ採取して供試した。その結果を表５、表６および表７に示す。表６の中で記号１〜１２は本発明の実施例、記号１３〜２１は本発明の効果を明確にするための比較例である。これらの結果、本発明の実施例１〜１２はＴＳ_RT、ＹＰ600、Ｅｌ600およびｖＥ_-5℃のいずれも良好な値を示し問題はなかった。
【００４０】
【表５】

【００４１】
【表６】

【００４２】
【表７】

【００４３】
比較例のうち１３は式（１）の値の下限を割ったため靭性が劣化した。また比較例のうち１４は式（１）の値の上限を超えたためＥｌ600が劣化した。また比 較例のうち１５は（３）値の上限を越えたためＥｌ600が劣化し、式（２）の値 の下限を割ったためＹＰ600が劣化した。
【００４４】
比較例のうち１６は式（４）の値の下限を割ったため強度不足及び（２）値の下限を割ったためＹＰ600が劣化した。また比較例のうち１７は式（２）の値が 下限を割ったためＹＰ600が劣化した。また比較例のうち１８は式（２）の値が 下限を割ったためＹＰ600が劣化した。
【００４５】
比較例のうち１９は式（３）の値が上限を越えたためＥｌ600が劣化した。ま た比較例のうち２０は式（３）の値が上限を越えたためＥｌ600が劣化した。ま た比較例のうち２１は式（４）の値の上限を越えたためＴＳ_RTが過大となった。
【００４６】
【発明の効果】
以上説明したごとく本発明を用いれば、実施例にも示した通りＨＴ５９０級耐火鋼のサブマージアーク溶接方法において、溶接入熱１０〜４０ｋＪ／ｍｍで一層溶接した場合、６００℃での耐力および高温伸びに優れ、且つ、靭性も良好な溶接部が得られ、大型構造物の溶接に貢献するところ大である。
【図面の簡単な説明】
【図１】溶接金属の［Ｍｏ］_cと６００℃の耐力（ＹＰ600）との関係を示したグラフ
【図２】（ａ）、（ｂ）はそれぞれ実施例で用いた溶接試験板の開先形状を示す断面図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a submerged arc welding method of HT590 grade steel plate (hereinafter referred to as HT590 grade refractory steel) having excellent fire resistance for use in various structures in the building and bridge fields, and more specifically, corner joint welding of box columns using refractory steel. In this case, when one layer welding is performed at a welding heat input of 10 to 50 kJ / mm, it relates to a submerged arc welding method which is excellent in yield strength at 600 ° C. and high temperature elongation and obtains good toughness.
[0002]
[Prior art]
Conventionally, HT400 grade, HT490 grade, HT520 grade refractory steel and weather resistant refractory steel having a normal temperature strength of 400 to 520 N / mm ² have been put to practical use as fireproof steel, and various welding materials used therefor have been put into practical use. As submerged arc welding, for example, Japanese Patent Publication No. 5-025598 proposes a submerged arc welding wire and flux for refractory steel, and has obtained high-temperature proof stress, proper normal-temperature strength, and good toughness in the weld metal. Japanese Patent Laid-Open No. 3-174978 discloses a fire-resistant steel and a weather-resistant fire-resistant steel having excellent toughness and high-temperature ductility and improved creep rupture life without impairing properties such as high-temperature proof stress at 600 ° C. and weather resistance at ordinary temperature. Submerged arc welding methods have been proposed.
[0003]
In addition, in the Japanese Patent Application No. 8-58246, the present inventors used a flux with an appropriate basicity as a submerged arc welding method that can be shared by Al-B and Mo-Nb refractory steels as a new steel plate component. , Propose a submerged arc welding method that optimizes the amount of Mo and B transferred from the wire and steel plate into the weld metal, the carbon content of the weld metal, etc., ensures high-temperature proof stress and elongation, and keeps the tensile strength and toughness properly. did.
[0004]
[Problems to be solved by the invention]
However, the submerged arc welding method proposed in Japanese Patent Publication No. 5-025598 for a refractory steel uses a flux and a submerged arc welding method. Is not considered enough.
[0005]
Japanese Patent Laid-Open No. 3-174978 proposes a submerged arc welding method for refractory steel and weatherproof refractory steel in consideration of elongation in addition to proof stress at high temperatures. The refractory steel in this case is a 400 to 520 N / mm ² class refractory steel added with Mo or Nb, and the weather resistant refractory steel is further added with Ni and Cu. The welding material with respect to this has restrict | limited B and Ti and acquired the favorable performance.
[0006]
Furthermore, in Japanese Patent Application No. Hei 8-58246, Mo and Nb are reduced, Al and B are increased, and as a welding material corresponding to a boron-treated steel sheet, the present inventors describe the amount of Mo in the welding material and the Ceq of the welding metal. The basicity of the flux is specified to obtain good high-temperature elongation and toughness, but this is for HT400 to HT520 grade refractory steel, and the room temperature strength is about 660 N / mm ^{2 at the} maximum and more Strength is not considered. However, HT590N / mm ² refractory steel containing Mo or Mo and Nb was developed as a refractory steel with higher strength, and this high heat input single layer submerged arc welding method is disclosed in Japanese Patent Laid-Open No. 3-174978. In the welded material, good high-temperature tensile properties cannot always be obtained in welding with a large base material dilution rate such as box column corner welding.
[0007]
In addition, the welding material proposed in Japanese Patent Application No. 8-58246 is not necessarily good for a high strength weld metal such as HT590 N / mm ^{2 in} welding with a large base metal dilution rate such as box column corner welding. Characteristics are not obtained. That is, in the high heat input single layer submerged arc welding method, the base material dilution rate is about 40 to 60%, and among the metal components transferred from the base material into the weld metal, high temperature proof stress such as Mo, Mn, Si, normal temperature strength, high temperature It was difficult to satisfy all the characteristics because the elements affecting the elongation and toughness deviated from the appropriate values.
[0008]
Accordingly, there is an urgent need to develop a high heat input single layer submerged arc welding material such as a box column corner joint used for the newly developed HT590N / mm ² refractory steel and a welding method.
[0009]
[Means for Solving the Problems]
The present inventors solve the above-mentioned problems, and are a submerged for welding HT590 grade refractory steel containing Mo: 0.6 to 1.2% and Nb: 0.001 to 0.05%. An arc welding method that satisfies the following formulas (1), (2), (3), and (4), and also satisfies the following formulas (2), (3), and (4). And C: 0.01 to 0.13%, Si: 0.005 to 0.15%, Mn: 1.2 to 2.2%, Mo: 0.60% or less, Nb: 0.05 %: V: 0.02% or less, Ti: 0.03% or less, B: 0.0005% or less, and the balance is performed in combination with a wire for submerged arc welding consisting of Fe and inevitable impurities. A featured submerged arc welding method.
[0010]

[0011]
[Mo] _C ≧ 0.32 (2)
Here, [Mo] _C = α _W [Mo] W + α _P [Mo] P + α _F (Mo) _F
[0012]
[B] C ≦ 0.0010 (3)
Here, [B] _C = α _W [B] W + α _P [B] P + α _F (B ₂ O ₃ ) _F ,
[0013]
0.37 ≦ Ceq ≦ 0.49 (4)
Here, Ceq = C + Si / 24 + Mn / 6 + (Mo + Nb) / 5 + 5B
[0014]
However, (1) CaO in _{formula, MnO, MgO, CaF 2,} SiO 2, Al 2 O 3, TiO 2: CaO respectively in the _{flux, MnO, MgO, CaF 2,} SiO 2, Al 2 O 3, TiO 2 Content (% by weight),
In the formulas (2) and (3), [Mo] _W : Mo content (wt%) in the wire, [Mo] _P : Mo content (wt%) in the base material, (Mo) _F : In the flux Mo content (wt%), [B] _w : B content (wt%) in wire, [B] _p : B content (wt%) in base material, (B ₂ O ₃ ) _F : Flux the content of B ₂ O ₃ in (wt%) α _w: migration rate to the weld metal of Mo and B in the wire, alpha _p: migration rate to the weld metal of M o and B in the matrix, α _F : Transfer rate of Mo and B in the flux to the weld metal, plate thickness 19 to 28 mm is α _w = 0.37, α _p = 0.43, α _F = 0.20, plate thickness over 28 ~40mm is _{α w = 0.42, α p =} 0.48, α F = 0.10, thickness 40 super ~55mm is _{α w = 0.45, α p =} 0.50, α F = 0. 05,
In the formula (4), C, Si, Mn, Mo, Nb and B are the contents (% by weight) of C, Si, Mn, Mo, Nb and B in the weld metal, respectively.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have made various studies in order to achieve the above object, and use wires and fluxes of appropriate composition to regulate the amount of B transferred from the flux, wire and steel plate into the weld metal, and to determine the carbon equivalent of the weld metal. The inventors have found a welding method that appropriately ensures high-temperature elongation and maintains good tensile strength and toughness by optimizing wire components and flux basicity.
[0016]
First, although it is the steel material of the to-be-welded material which this invention makes object, it has been generally used conventionally by containing Mo: 0.6-1.2% and Nb: 0.001-0.05%. HT590 grade refractory steel with improved strength over refractory steel. When the entire components of this steel material are described including Mo and Nb, C: 0.05 to 0.09%, Si: 0.25 to 0.35%, and Mn: 1.2 to 1 in weight percent. 0.7%, Mo: 0.6-1.2%, Nb: 0.001-0.05%, V: 0.05% or less, Ti: 0.02% or less, B: 0.0010% or less It is common to contain it, with the balance being Fe and inevitable impurities.
[0017]
In the previous welding of HT490 to HT520 grade refractory steels, it was proposed that the value be specified by a specific formula representing a measure of the amount of Mo in the weld metal in order to obtain the proof strength of the weld metal at 600 ° C. Considering the HT590 refractory steel targeted by the present invention, if 70% of the standard value 440 N / mm ² of normal proof is guaranteed at 600 ° C., the standard value of proof strength is 308 N / mm ² or more. In order to obtain this proof stress, it is necessary to set the [Mo] _c value to 0.33 or more according to the specific formula of steel plate, wire and flux indicating the scale of the amount of Mo in the weld metal as shown in the graph of FIG. .
[0018]
Next, it was proposed to leave moderate proeutectoid ferrite in the microstructure of the weld metal in the previous welding of HT490-HT520 refractory steel. That is, the pro-eutectoid ferrite needs to be left in order to ensure an elongation of 18% or more in a tensile test at 600 ° C., while it needs to be as high as possible in order to ensure good toughness. Therefore, in order to achieve both, a specific formula for the amount of B transferred from the flux, the wire, and the steel plate to the weld metal is defined, and an appropriate range is defined by a related formula with Ceq. Since the normal temperature strength of the weld metal is 490 to 660 N / mm ² , it is relatively easy to leave pro-eutectoid ferrite in the weld metal.
[0019]
However, in the HT590 refractory steel targeted by the present invention, 0.6 to 1.2% of Mo is added to the steel plate, and if this steel plate is subjected to high heat input single-layer welding such as box column corner welding. The base material dilution rate is about 45%, and Mo of about 0.2% to 0.57 at the maximum is transferred to the weld metal only by dilution from the base material. When the Mo of the weld metal increases, the proeutectoid ferrite at the grain boundaries decreases in the microstructure, and a very small amount of Mo is formed at 0.6% Mo. In welding where such Mo moves from the base metal to the weld metal and the pro-eutectoid ferrite tends to decrease, the amount of B is severely controlled, or the weld metal is made high oxygen and the transformation temperature is raised to increase the pro-eutectoid ferrite. It is necessary to make the composition easy to grow.
[0020]
In the welding of HT590 steel, the B amount of the weld metal is not added except that it inevitably enters from impurities in the flux, wire, and steel plate, and the basicity is set low in the flux. Furthermore, Ceq needs to be regulated within an appropriate range so that the strength is not excessive.
[0021]
About 0.5% or less of B is unavoidably contained in the flux in steel sheets and wires, and about 0.03% or less as B ₂ O ₃ from the magnesia clinker usually used in bond flux. B is not intentionally added to the weld metal, and is specified to be 0.0010 or less using the [B] _c value of the specific formula as a measure of the amount of B transferred to the weld metal.
[0022]
Furthermore, the basicity represented by Bn = (0.108CaO + 0.068MnO + 0.100MgO + 0.078CaF ₂ ) / (0.105SiO ₂ + 0.002Al ₂ O ₃ + 0.080TiO ₂ ) as a scale for supplying oxygen to the weld metal is 0. .55 ≦ B n ≦ 1.40. In addition, Ceq is regulated to 0.37% or more in order to ensure the strength at room temperature of 590 N / mm ² or more.
[0023]
Further, the present invention will be described in detail.
The inventors first determined the relationship between the [Mo] _C content and the 600 ° C. yield strength (hereinafter referred to as YP600) in the weld metal of refractory steel. It can be seen that YP600 increases as the amount of [Mo] _c increases. [Mo] _c is a measure of the amount of Mo in the weld metal. In the previous HT400 to HT520 grade refractory steels, the inventors have set [Mo] _c as [Mo] _c = 43 [Mo] _w +55 [Mo It was proposed that [Mo] _c ≧ 8.5 in order to secure YP600 ≧ 235 N / mm ² using the calculated value of _p + 18 (Mo) _F.
[0024]
In the HT590 grade refractory steel to which the present invention is applied, YP600 ≧ 308 (= 440 × 0.7) N / mm ² is required as the refractory steel in contrast to the standard YP ≧ 440 N / mm ² of SM590 steel. Here, the scale is changed to the above formula, and [Mo] _c taking into account the base material dilution rate that varies depending on the plate thickness, that is, the specific formula [Mo] _c = α _w [Mo] _w + α _p [Mo] _p + α _F (Mo) _F was obtained. In order to achieve the target value, [Mo] _c needs to be 0.33 or more.
Here, [Mo] _W : Mo content (wt%) in the wire, [Mo] _P : Mo content (wt%) in the base material, (Mo) _F : Mo content (wt%) in the flux Α _w : Mo transfer rate in the wire into the weld metal, α _p : Mo transfer rate in the base metal into the weld metal, α _F : Mo in the flux to the weld metal It is a transition rate, α _w = 0.37, α _p = 0.43, α _F = 0.20, and plate thickness 28 to 40 mm are α _w = 0.42 and α _p = 0. .48, α _F = 0.10, plate thickness over 40 to 55 mm are α _w = 0.45, α _p = 0.50, α _F = 0.05.
[0025]
Next, in the HT400 to HT520 grade refractory steel as a measure for securing the elongation at 600 ° C., the inventors first set [B] c = 4300 [B] _w +5500 as a measure of the amount of B in the weld metal. [B] _p +120 (B ₂ O ₃ ) _F was proposed, but in the case of HT590 steel, [B] _c , ie, [B] _c = α _w taking into account the base material dilution rate that differs depending on the plate thickness, instead of the above formula. Using [B] _w + α _p [B] _p + α _F (B ₂ O ₃ ) _F , it was found that [B] _c ≦ 0.0010 is required. [B] _w : B content (% by weight) in the wire, [B] _p : B content (% by weight) in the base material, (B ₂ O ₃ ) _F : B ₂ O ₃ content in the flux (Wt%), α _w : transfer rate of B in the wire into the weld metal, α _p : transfer rate of B in the base metal into the weld metal, α _F : transfer of B in the flux to the weld metal It is a transition rate, α _w = 0.37, α _p = 0.43, α _F = 0.20, and plate thickness 28 to 40 mm are α _w = 0.42 and α _p = 0. .48, α _F = 0.10, plate thickness over 40 to 55 mm are α _w = 0.45, α _p = 0.50, α _F = 0.05.
[0026]
Furthermore, it is necessary to reduce the basicity of the flux in order to produce proeutectoid ferrite at the grain boundaries in order to ensure the elongation of the tensile test at 600 ° C. The basicity of the flux is a measure of the amount of oxygen in the weld metal. That is, as the basicity decreases, the amount of oxygen in the weld metal increases, proeutectoid ferrite at the grain boundaries is generated, and the elongation at 600 ° C. in the tensile test is improved. Assuming that Bn = (0.108CaO + 0.068MnO + 0.100MgO + 0.078CaF ₂ ) / (0.105SiO ₂ + 0.002Al ₂ O ₃ + 0.080TiO ₂ ) is used as the basicity, good elongation is secured in a 600 ° C. tensile test. In order to achieve this, Bn ≦ 1.40 is required. On the other hand, when Bn is less than 0.55, toughness deteriorates. That is, 0.55 ≦ Bn ≦ 1.40.
[0027]
Further, in order to keep the tensile strength at normal temperature (hereinafter referred to as TS _RT ) within an appropriate range, it is necessary to limit the scale of quenching. That is, it is necessary that Ceq ≦ 0.49%. In order to obtain 590 N / mm ² or more, Ceq ≧ 0.37%. That is, 0.37 ≦ Ceq ≦ 0.49%.
[0028]
The components of the submerged arc welding wire used in the present invention will be described below.
C is necessary for securing the strength at room temperature and exhibiting the effect of adding Mo and Nb, and 0.01% is the lower limit. On the other hand, if it exceeds 0.13%, the hot cracking susceptibility increases and the toughness deteriorates.
[0029]
Si needs to be added in an amount of 0.005% or more as a deoxidizing element, but if it exceeds 0.15%, the toughness of the weld metal is deteriorated.
Mn is indispensable for securing strength and toughness, and addition of 1.2% or more is necessary. However, if it exceeds 2.2%, hot cracking susceptibility increases and toughness deteriorates.
[0030]
Mo and Nb are necessary to ensure a sufficient high-temperature proof stress, but no particular lower limit is specified because they can be added from the flux. On the other hand, if Mo and Nb are excessive, the room temperature strength becomes too high and the toughness deteriorates, so the addition amount must be 0.60% or less for Mo and 0.05% or less for Nb.
[0031]
V is necessary for securing the room temperature strength, but if the wire exceeds 0.02%, the toughness deteriorates.
Ti is a deoxidizing element and is an element important for securing toughness, and is preferably added in an amount of 0.001% or more. However, if excessively added, the high temperature elongation of the weld metal is deteriorated, so 0.03% or less is necessary. There is.
[0032]
B is important for securing the high temperature tensile elongation at 600 ° C., and is not intentionally added, and it is necessary to regulate it to 0.0005% or less so that it is inevitable from impurities.
In addition to the components specified above, the wire of the present invention includes Ni of 1% or less, Cr of 0.5% or less, Cu including plating including 0.5% or less, P of 0.025% or less, and S 2. 0.015% or less is acceptable. The other balance is Fe and inevitable impurities.
[0033]
【Example】
The effects of the present invention will be described more specifically with reference to the following examples.
The steel plates used were four types P1 to P4 shown in Table 1, and the wires used were three types of compositions W1 to W3 shown in Table 2. Six types of bond fluxes F1 to F6 in Table 3 were prepared. Among these, F1 to F4 are fluxes of the present invention example, and F5 and F6 are fluxes of comparative examples for clarifying the effects of the present invention.
[0034]
[Table 1]

[0035]
[Table 2]

[0036]
[Table 3]

[0037]
2A, the groove shape of (a) is a Y-shaped groove, (b) is a lave-shaped groove, and θ ₁ of the groove shape of (a) is a groove angle of 35 °, and T ₁ is a plate. The thickness is 40 mm or 45 mm, r ₁ is the root face 2 mm, and t ₁ is the backing metal 25 mm. Further, in the groove shape of (b), θ ₂ has a groove angle of 40 °, T ₂ has a plate thickness of 25 mm, r ₂ has a root face of 2 mm, and t ₂ has a backing metal of 25 mm. Using the above three types of specimens, submerged arc welding with two electrodes was performed under the conditions of welding conditions C1 to C3 shown in Table 4 without performing preheating.
[0038]
[Table 4]

[0039]
After welding, one JIS A1 tensile test piece, three JIS4 V-notch Charpy test pieces, one high-temperature tensile test piece (6 mm diameter) and an analytical sample were collected from the welded part 10 mm below the plate surface. I tried it. The results are shown in Table 5, Table 6, and Table 7. In Table 6, symbols 1 to 12 are examples of the present invention, and symbols 13 to 21 are comparative examples for clarifying the effects of the present invention. As a result, Examples 1 to 12 of the present invention showed good values for TS _RT , YP600, El600, and vE- ₅ ° C., and there was no problem.
[0040]
[Table 5]

[0041]
[Table 6]

[0042]
[Table 7]

[0043]
Since 13 of the comparative examples divided the lower limit of the value of the formula (1), the toughness deteriorated. In Comparative Example 14, El600 deteriorated because it exceeded the upper limit of the value of the formula (1). In Comparative Example 15, El600 deteriorated because the upper limit of (3) value was exceeded, and YP600 deteriorated because the lower limit of the value of Equation (2) was divided.
[0044]
Of the comparative examples, 16 divided the lower limit of the value of equation (4), so that the strength was insufficient, and (2) the lower limit of the value was divided, so that YP600 deteriorated. In Comparative Example 17, YP600 deteriorated because the value of Equation (2) divided the lower limit. In Comparative Example 18, YP600 deteriorated because the value of Equation (2) divided the lower limit.
[0045]
In Comparative Example 19, El600 deteriorated because the value of Equation (3) exceeded the upper limit. In Comparative Example 20, El600 deteriorated because the value of Equation (3) exceeded the upper limit. In addition, 21 of the comparative examples exceeded the upper limit of the value of equation (4), and thus the TS _RT was excessive.
[0046]
【The invention's effect】
As described above, when the present invention is used, in the submerged arc welding method of HT590 grade refractory steel as shown in the examples, when further welding is performed at a welding heat input of 10 to 40 kJ / mm, the proof stress and the high temperature elongation at 600 ° C. In addition, it is possible to obtain a welded portion which is excellent in toughness and excellent in toughness and contributes to welding of a large structure.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between [Mo] _{c of} weld metal and 600 ° C. yield strength (YP600). FIG. 2 (a) and (b) are the groove of the weld test plate used in the examples. Cross section showing shape

Claims (1)

A submerged arc welding method for welding HT590 grade refractory steel containing Mo: 0.6 to 1.2% and Nb: 0.001 to 0.05%, which includes the following formulas (1) and (2) , (3) and (4) satisfy the following submerged arc welding flux, and satisfy the following formulas (2), (3) and (4), and C: 0.01 to 0.13%, Si : 0.005 to 0.15%, Mn: 1.2 to 2.2%, Mo: 0.60% or less, Nb: 0.05% or less, V: 0.02% or less, Ti: 0.03 %, B: 0.0005% or less, and the balance is performed in combination with a wire for submerged arc welding consisting of Fe and inevitable impurities.

[Mo] _C ≧ 0.32 (2)
Here, [Mo] _C = α _W [Mo] _W + α _P [Mo] _P + α _F (Mo) _F
[B] C ≦ 0.0010 (3)
Here, [B] _C = α _W [B] _W + α _P [B] _P + α _F (B ₂ O ₃ ) _F ,
0.37 ≦ Ceq ≦ 0.49 (4)
Here, Ceq = C + Si / 24 + Mn / 6 + (Mo + Nb) / 5 + 5B
However, (1) CaO in _{formula, MnO, MgO, CaF 2,} SiO 2, Al 2 O 3, TiO 2: CaO respectively in the _{flux, MnO, MgO, CaF 2,} SiO 2, Al 2 O 3, TiO 2 Content (% by weight),
In the formulas (2) and (3), [Mo] _W : Mo content (wt%) in the wire, [Mo] _P : Mo content (wt%) in the base material, (Mo) _F : In the flux Mo content (wt%), [B] _w : B content (wt%) in wire, [B] _p : B content (wt%) in base material, (B ₂ O ₃ ) _F : Flux the content of B ₂ O ₃ in (wt%) α _w: migration rate to the weld metal of Mo and B in the wire, alpha _p: migration rate to the weld metal of M o and B in the matrix, α _F : Transfer rate of Mo and B in the flux to the weld metal, plate thickness 19 to 28 mm is α _w = 0.37, α _p = 0.43, α _F = 0.20, plate thickness over 28 ~40mm is _{α w = 0.42, α p =} 0.48, α F = 0.10, thickness 40 super ~55mm is _{α w = 0.45, α p =} 0.50, α F = 0. 05,
In the formula (4), C, Si, Mn, Mo, Nb and B are the contents (% by weight) of C, Si, Mn, Mo, Nb and B in the weld metal, respectively.

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