JP4499928B2

JP4499928B2 - Immersion member for molten metal plating bath and manufacturing method

Info

Publication number: JP4499928B2
Application number: JP2001001637A
Authority: JP
Inventors: 重治松林; 哲郎野瀬; 芝本　　茂
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-01-09
Filing date: 2001-01-09
Publication date: 2010-07-14
Anticipated expiration: 2021-01-09
Also published as: JP2002206155A

Description

【０００１】
【発明の属する技術分野】
本発明は、鋼板等の連続溶融金属めっき装置における溶融金属めっき浴用浸漬部材及びその製造方法に関する。
【０００２】
【従来の技術】
金属めっき板を得る方法として、図1に示すように、加熱炉で加熱焼鈍された金属板を溶融金属槽に導き、金属板へ溶融金属をめっきし、ポットロール及びガイドロールを介して、これを引上げ連続的に金属めっき板を得る方法が汎用されている。より詳しくは、連続溶融金属めっき装置による金属板へのめっき方法は、金属板として鋼板を用いた場合、前処理として表面を洗浄・活性化した鋼板を溶融金属浴中に挿入して、浴中のポットロールで方向を変えた後、鋼板の幅方向の反りを抑えるために2本のガイドロールの間を通過させる。この後、さらに鋼板を上方に引上げ、めっき浴の直上で鋼板表面に付着した余分の溶融金属を高圧ガスのワイピング等により除去して、所定のめっき量に調整して、溶融金属めっき鋼板を製造するものである。
【０００３】
この溶融金属めっき浴に浸漬されるポットロールの軸受部材及び軸部スリーブ部材には、一般的に、耐食性の良好な24Cr-12Ni系ステンレス鋼が用いられている。ステンレス鋼は、溶融亜鉛、溶融アルミニウム等の溶融金属との反応性が低く、耐食性は良好であるが、耐摩耗性は充分とは言えず、特に、軸受部材は、軸部スリーブ部材と極狭い範囲(上側の半分)で常時接触しているため、摩耗量は軸部スリーブ部材より大きく、寿命は4〜8日程度と短かい。軸受部材の摩耗が進行すると、鋼板にバタツキ等が発生し、良好なめっきが行えないため、該部材を溶融金属めっき浴中から引き上げ、軸受部材を交換しなければならない。そのため、溶融金属めっき浴中に浸漬されているポットロール等の他の部材に異常が無くても、操業を停止し、溶融金属めっき浴中に浸漬されている部品全体を引き上げる必要がある。この際に、浴温から室温へ急激に冷却されるため、熱衝撃破損等のダメージが他の部品に発生することもあり、部品全体を一括交換する場合もあり、生産上の損失は極めて大きい。このため、溶融金属めっき浴中で使用されるロール寿命の延長を図る様々な提案がなされている。
【０００４】
特開平3-253547号公報や特開平5-44002号公報では、溶融亜鉛浴中での軸受部材及び軸部スリーブ部材に、アルミナ又は窒化珪素・サイアロンを用い、回転するポットロールを外部から回転駆動する提案がなされている。しかしながら、該提案では、溶融金属として亜鉛のみを取り上げ、摺動摩耗量及び摩耗係数のみを選定基準としており、耐熱衝撃性や溶融金属との濡れ性等については考慮されていない。さらに、アルミナ又は窒化珪素・サイアロンセラミックスに関しても、組成、焼成条件(密度、組織)、機械的特性、摺動面粗さ等の諸特性についての最適条件の記載はない。
【０００５】
また、モノリシック炭化珪素やジルコニアセラミックスは、窒化珪素やサイアロンより熱衝撃性に劣ることが知られている。比較的耐熱衝撃性に優れる窒化珪素とサイアロンでも軸受け部材のサイズ(φ200ｍｍ以上)や肉厚(ｔ20ｍｍ以上)において、溶融アルミニウム浴温度(660〜680℃)からの急激な空冷に十分耐えうる材質はほとんど見い出されていない。
【０００６】
上記従来技術で開示されている内容に基づき、一般的な焼結助剤であるイットリア、アルミナを用いて、相対密度比９９％まで緻密化した市販の窒化珪素セラミックスで、溶融アルミニウム浴中における摺動及び熱衝撃試験を行った結果、亜鉛浴中の摩耗量を大きく上回り、溶融アルミニウム浴中からの空冷を３回行っただけで破損した。
【０００７】
【発明が解決しようとする課題】
すべり軸受に関する上記技術は、軸受部材及び軸部スリーブ部材の互いに接触する面を、ステンレス鋼に比べれば溶融金属浴中での耐食性が良好で、かつ、高硬度のセラミックスでコーティングしたり、または、サーメット、超硬合金やセラミックス焼結体等とすることで、軸受の長寿命化を図ろうとしたものである。しかし、溶融金属めっき浴用部材にとって、軸受部材と軸部スリーブ部材の最適な組合せは、浴温度(アルミニウムの場合、660〜680℃)からの急激な空冷に十分耐えうることがより必要で、材料の耐熱衝撃性、高靭性、耐酸化性等の特性を考慮することがはるかに重要な選定要素である。数百℃に加熱されたポットロールの引上げ時の空冷に伴う熱衝撃や繰返し熱疲労に対する耐久性を高めることが不可欠である。
【０００８】
また、取り替え作業が迅速に行えれば、操業上の機会損失を低減できるため、当該部材の交換を簡便に行える構造とすることも望まれている。
【０００９】
そこで、本発明の目的は、熱衝撃、繰り返し熱疲労、酸化による剥離現象などに対する耐久性を大幅に向上させ、併せて、摩耗・破損時の交換作業を著しく簡便にした溶融金属めっき浴用浸漬部材及びその製造方法を提供することにある。
【００１０】
【課題を解決するための手段】
本発明は、上記課題を解決して、溶融金属めっき浴中で長時間安定して繰り返し使用でき、めっき浴からロールが出入りする際にも急激な温度変化を抑えるための柄杓がけが不要となり、軸受け部が消耗した後の交換作業時には簡便にセラミックス材を取り替えられる溶融金属めっき浴用浸漬部材を提供することを目的としてなされたものであり、
(1) 溶融金属めっき浴に浸漬されるポットロール装置に付設された浸漬部材であって、該浸漬部材が、該ポットロール設備の少なくともポットロール軸部スリーブ部材と軸受部材の摺動する部分の一部又は全部に嵌合してなる、実質的にβ-Ｓｉ₃Ｎ₄相、Ｓｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相から構成される高耐熱衝撃性、高耐酸化性セラミックス部材であることを特徴とする溶融金属めっき浴用浸漬部材、
(2) 前記浸漬部材が、複数の柱状部材からなる請求項1記載の溶融金属めっき浴用浸漬部材、
(3) 前記柱状部材が、前記軸受部の軸方向に嵌合してなる請求項2記載の溶融金属めっき浴用浸漬部材、
(4) 前記柱状部材の回転方向の摺動面が、平面又は前記ポットロール軸部スリーブ部材の曲率半径以上の円弧状面である請求項3記載の溶融金属めっき浴用浸漬部材、
(5) 前記柱状部材が、前記ポットロール軸部スリーブ部材に軸方向に嵌合してなる請求項2記載の溶融金属めっき浴用浸漬部材、
(6) 前記柱状部材の摺動面が、前記軸受部材の曲率半径以下の円弧状面である請求項5記載の溶融金属めっき浴用浸漬部材、
(7) 前記柱状部材の軸方向の摺動面が、凹凸状及び/又は波形状で、凸部の摺動面高さが軸方向で揃った形状である請求項３又は５に記載の溶融金属めっき浴用浸漬部材、
(8) 前記セラミックス部材が、理論密度の９５％以上の焼結体密度である請求項１〜７に記載の溶融金属めっき浴用浸漬部材、
(9) 前記セラミックス部材の組成が０．１〜３．０質量％のＳｉ₂Ｎ₂Ｏ相、４．９〜１２．０質量％のＹ₂Ｓｉ₂Ｏ₇相及び残部がβ-Ｓｉ₃Ｎ₄相及び不可避的不純物相からなる請求項８記載の溶融金属めっき浴用浸漬部材、
(10) 酸化イットリウム（Ｙ₂Ｏ₃）３〜１０質量％、酸化珪素（ＳｉＯ₂）１〜５質量％および残部が窒化珪素（Ｓｉ₃Ｎ₄）からなる混合粉末を成形し、該成形体を窒素ガス雰囲気中にて１７００〜２０００℃の温度範囲で焼結し、以下の▲１▼〜▲３▼の少なくとも一つの手段により粒界相としてＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相を生成させた焼結体を成形加工することを特徴とする溶融金属めっき浴用浸漬部材の製造方法、
▲１▼焼結の降温過程における降温速度を５℃/分以下とする、
▲２▼焼結の降温過程において、１３５０〜１６５０℃の温度範囲において２時間以上保持する、
▲３▼焼結後、窒素雰囲気中、１３５０〜１６５０℃の温度範囲において２時間以上保持の再加熱処理を行う、
を要旨とするものである。
【００１１】
【発明の実施の形態】
本発明者らは、特開平3-253547号公報や特開平5-44402号公報で提案された溶融亜鉛浴中ロール軸受けを見直し、鋭意検討を行った結果、亜鉛(mp=430℃)に比べ高融点の溶融アルミニウム(mp=660℃)浴中にも適用可能にすることを前提としている。ロールを溶融アルミニウム浴から出し入れする場合に起きる急激な温度変化に備え、柄杓で該溶融金属をロールに浴びせ掛けながら、急加熱や急冷却が起こらないように配慮していた。本発明によって、その必要がない軸受け材質と構造を提唱することができた。同時に、従来技術では困難であった摺動摩耗及び熱疲労部周囲のチッピングや割れ等の欠損を抑えることができた。これらのチッピングや割れ等の欠損は、熱衝撃及び機械的衝撃により生成、進展するものであり、部材に空孔が多い場合、低強度、低靭性、低熱伝導、低耐熱衝撃、摺動面が粗い場合、等に顕著であることが見い出された。一方で、摺動摩耗は、摺動部位が曲面ではなく、線接触もしく点接触である場合等に顕著に抑制されることを確認した。
【００１２】
本発明の溶融金属めっき浴用浸漬部材は、溶融金属めっき浴に浸漬されるポットロール装置に付設された浸漬部材であって、該浸漬部材が該ポットロール設備の少なくともポットロール軸部スリーブ部材または軸受部材の摺動する部分の一部又は全部に嵌合してなる、実質的にβ-Ｓｉ₃Ｎ₄相、Ｓｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相から構成される高耐熱衝撃性、高耐酸化性セラミックス部材である。また、浸漬部材の取扱い易さの観点から、柱状部材を複数嵌合することが好ましい。埋め込み形状について、ポットロールと直接摺動する面が平面またはポットロール軸部スリーブ部材の曲率半径以上の上に凸な円弧状面が好ましいが、特に限定するものではなく、軸に垂直方向の断面形状が四角形以上の多角形や半円形、円形でも良い。回転方向に柱状部材を配置することは好適ではない。圧縮応力負荷に限定するために、回転方向と同じ方向に線接触ならびに点接触させる配置を推奨する。また、ポットロール軸部スリーブ部材の曲率半径以下の上に凸な円弧状面もしくは曲率半径以上の凹な円弧状面では埋め込み材に圧縮応力以外が負荷され、圧縮に比べて破損の確率が高くなることが予想される。好ましくは、下辺が上辺に比べて長い等脚台形を断面とするセラミックス製軸受け片を使用すれば、楔(くさび)や接着剤等を使用せず、位置決めすることが容易であり、圧縮応力のみを負荷させることが可能である。さらに、図2の iii)〜iv)に示したように柱状の埋め込み材の回転軸と平行な方向に凹凸または波形を順次付与することにより、線接触から点接触にすることが可能であり、めっき浴の流動を促進することが可能になることから回転が円滑なものになることが想定される。隣接する埋め込み材との凹凸または波形パターンを逆相にするか同相にするかはめっき浴の流動性やポットロールの回転数によって対応すべきである。このような形状にすることにより、軸受け部での溶融金属溜りができにくくなり、補修作業等の作業効率を改善できる。
【００１３】
また、ポットロールの回転軸部材の摺動部について、軸受け部材と同じセラミックス材または超硬(＝ＷＣ)粒子を結合金属(＝銅、チタン、亜鉛、クロム等のバインダー)中に分散させたものでも構わない。この場合も、上記と同様に軸の曲率より軸受け側の曲率が大きくなければ、軸受け部材に押し広げようとする引っ張り応力が印加されることとなり、全く不適である。平面もしくは円弧状であれば加工が容易であり、曲率が大きい場合はポットロール側の回転軸の安定性が僅かながら高まることが容易に予想される。また、回転軸に嵌合する場合は軸受けの曲率より回転軸側の埋め込み材の曲率が大きくなれば、埋め込み材の形状が極端に大きくなるか、薄過ぎることになるため好適ではない。
【００１４】
そして、この部材を上記形状とすることにより、該部材を嵌合される金属製部材との熱膨張係数差によって生じる浴中および空冷時の伸縮差の絶対値を小さくでき、セラミックス側に加わる圧縮または引張応力を低減することに加え、該セラミックス部材を製造する上での緻密化を容易にする効用をもたらす。嵌合する部材の形状は肉厚が5ｍｍ以上２０ｍｍ以下で、２本以上の柱状部材を用いることが好ましい。５ｍｍ未満では、セラミックス部材の圧縮強度も低く、使用後に摺動面に生じた摩耗痕を研磨し、リサイクル利用するときにもトータル寿命が短くなり好適ではない。２本未満即ち1本の柱状部材では回転時の安定性が全く得られず相応しくない。また、ロールアームをハンドリングする時の機械的衝撃に対する強度付与の点からも５〜２０ｍｍ厚みの範囲が好ましい。幅については、ポットロール径の大小や柱状部材の嵌合せ本数に依存するが１０〜３０ｍｍが好適である。さらに柱状部材の長さは該部材を嵌合される金属製部材のスリーブ長さによって一義的に求められる。一般的には、８０〜２００ｍｍ程度がよく用いられている。
【００１５】
図３に示したように、セラミックス製軸受けを保持するために用いる金属製リング部材との間隙に噛み込まれた溶融金属との熱膨張係数差に起因する圧縮または引張応力を軽減するため、セラミックス部材と金属部材との嵌合部の間隙は1ｍｍ以下にすることが好ましい。
【００１６】
上記とは全く逆に、軸受け部が円形の一体品で構成され、軸受けの曲率以下の上に凸な円弧状面を有する柱状部材をポットロール軸部スリーブに嵌合することも可能である。但し、軸受け部に埋め込む際に十分な固定強度が得られるように配慮が必要で、軸受け部の接触時の摩擦抵抗を軽減するためには摺動部は平面ではなく軸受け部の内径より曲率の小なる円弧状曲面が最も好適である。さらに、半周以上に渡って嵌合することが必要であり、２本以上ではなく、少なくとも３本以上、より好ましくは５本以上で安定した回転が得られる。３本以上でなければ、柱状部材以外の部分で摺動する機会が増え、金属製の軸部スリーブ材が柱状部材より選択的に摩耗し、寿命の延長は望めなくなる。
【００１７】
高耐熱衝撃、耐摩耗、耐酸化などの特性を同時に向上させる方法としては、各種結晶相より構成される複合組成焼結体を作製し、その特性を評価した。従来の低融点ガラス相を有する窒化珪素や炭化珪素焼結体では、高温下における耐酸化性、耐熱衝撃性に劣る。特性評価の結果、β-Ｓｉ₃Ｎ₄相および粒界相としてＳｉ₂Ｎ₂Ｏ相、Ｙ₂Ｓｉ₂Ｏ₇相から構成される緻密なセラミックス焼結体が優れた特性を有することを見出した。また、埋め込み材の柱状部材形状(図２)が、単純な平面もしくは円弧面さらには長手方向に凹凸もしくは波形の単純研削で付与可能なことから、焼結体の仕上げ加工コストを高めることなく、溶融金属めっき浴用部材の長寿命化を実現することができる。
【００１８】
本発明の溶融金属めっき浴用部材は、耐熱衝撃性、耐酸化性に優れ、使用環境下で部材中に生じる温度勾配に起因する静的な疲労特性、また浴中から引上げられる時の急激な冷却に伴う熱応力破壊抵抗特性を高めるなどの特徴を有する。粒界相としてＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相を結晶化させるためには、焼結の降温過程で５℃/分以下の降温速度で冷却するか、降温過程で１３５０〜１６５０℃、２時間以上保持の熱処理するか、あるいは焼結後窒素雰囲気中にて1１３５０〜１６５０℃、２時間以上保持の再加熱処理の少なくとも一つを行うようにする。２時間以上の保持について、より好ましくは１２時間以上２４時間以下が好ましい。２時間から１２時間までにもＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相の結晶化が少しずつ促進されるが、焼成物の肉厚に応じてその処理時間を延長する必要があり、セラミックス部材の肉厚として汎用的な１００ｍｍ以下では２４時間が適当と考えられる。降温過程でＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相を析出させる場合の降温速度は５℃/分以下が好ましいが、より望ましくは０．１℃／分以上２℃/分以下である。０．１℃／分未満では製造効率上長時間の熱処理が必要となるため好ましくない。降温速度が５℃/分より速い場合はＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相が十分生成しない。また、降温過程の際の保持温度、および、再加熱処理の際の保持温度が１３５０℃未満、１６５０℃超の場合も同様にＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相が十分に生成しない。また、各々の保持時間が２時間未満の場合もＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相は生成しない。Ｓｉ₂Ｎ₂Ｏ相とＹ₂Ｓｉ₂Ｏ₇相がそれぞれ質量比で０．１、４．９％未満では焼結体中の気孔率が高くなり好ましくなく、それぞれ３、１２％を越えるとβ-Ｓｉ₃Ｎ₄結晶粒が十分に絡み合わず強度や靭性が低下し好ましくない。また、Ｓｉ₂Ｎ₂Ｏ相とＹ₂Ｓｉ₂Ｏ₇相に関し、Ｓｉ₂Ｎ₂Ｏ相の質量比が全体の０．１％未満では機械的強度に寄与する効果が少なく、３％を越えるとβ-Ｓｉ₃Ｎ₄結晶粒が十分に絡み合わず強度や靭性が低下するため好ましくない。同様にＹ₂Ｓｉ₂Ｏ₇相の質量比が全体の４．９％未満ではＳｉ₃Ｎ₄のα→β転移時の液相が少なく相転移を円滑に進行させず、１２％を越えるとβ-Ｓｉ₃Ｎ₄結晶粒が十分に絡み合わず強度や靭性が低下するため好ましくない。本発明により得られる窒化珪素質焼結体は、 β-Ｓｉ₃Ｎ₄の平均結晶粒径が１〜３μｍ程度、アスペクト比が１．５〜１０程度と大きく、かつβ-Ｓｉ₃Ｎ₄の柱状結晶粒が絡み合った組織を呈し、また粒界に高融点のＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相が析出しているため、高温まで高い強度を維持したまま高い靭性を有し、抗折強さが大気中１４００℃にて５００ＭPa以上の高強度でかつ靭性値Ｋ_ICが５ＭPaｍ^1/2の高靭性を有するため、高温環境下での特性を要求される浴用部材に好適に用いることができる。ここで、Ｓｉ₂Ｎ₂Ｏ相は粉末Ｘ線回折法により同定されるＳｉ₂Ｎ₂Ｏ結晶と同じ型のＸ線回折パターンを持ち、Ｓｉ₃Ｎ₄とＳｉＯ₂とからなる化合物の中で高温酸化雰囲気中にて最も安定な化合物である。同様に、Ｙ₂Ｓｉ₂Ｏ₇結晶相は粉末Ｘ線回折法により同定されるＹ₂Ｓｉ₂Ｏ₇結晶と同じ型のＸ線回折パターンを持ち、Ｙ₂Ｏ₃とＳｉＯ₂とからなる化合物の中で高温酸化雰囲気中にて最も安定な化合物である。また、β-Ｓｉ₃Ｎ₄結晶相は、ＪＣＰＤＳカード３３−１１６０で示されるβ-Ｓｉ₃Ｎ₄結晶と同じ型のＸ線回折パターンを持つ。さらに、前記β-Ｓｉ₃Ｎ₄相、Ｓｉ₂Ｎ₂Ｏ相、Ｙ₂Ｓｉ₂Ｏ₇相及び不可避的不純物相により構成される窒化珪素質焼結体の相対密度は理論密度に対して９５％以上であることが望ましい。相対密度が９５％未満では、熱的安定性、機械的安定性が不充分になり易く、長期耐久性の向上効果が見られない恐れが高くなる。
【００１９】
本発明において使用される窒化珪素粉末は、α型の結晶構造をもつＳｉ₃Ｎ₄粉末が焼結性の点から好適であるが、β型あるいは非晶質Ｓｉ₃Ｎ₄粉末が含まれていても構わない。焼結時に十分に高い密度とするためには、平均粒径1μｍ以下の微粒子であることが望ましい。
【００２０】
窒化珪素は共有結合性の強い物質であり、単独では焼結が困難であることが多いため、一般に緻密化するために焼結助剤を添加する。本発明においては、焼結助剤としては、酸化珪素、酸化イットリウムを用いる。ここで、酸化イットリウムはＳｉ₃Ｎ₄の焼結時にα-Ｓｉ₃Ｎ₄相からβ-Ｓｉ₃Ｎ₄相への結晶相転移をその融液中で促進させる機能を持ち、さらにβ-Ｓｉ₃Ｎ₄の柱状相の成長を助長することにより、高温強度および靭性を向上させることが知られている。それぞれの添加量は、酸化珪素が１〜５質量％、酸化イットリウムが３〜１０質量％が好ましい。酸化珪素が1質量％未満の場合、焼結昇温時の液相生成温度が高くなり十分緻密な焼結体が得られず、またＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相が形成されない。５質量％を越えるとＹ₂Ｓｉ₂Ｏ₇相が形成されず比較的低融点のＳｉＯ₂相が形成され高温での機械的強度が低下するため好ましくない。酸化イットリウムの添加量が３質量％より少ないと融液形成が不十分で相対密度が９５％未満となり緻密化が進行しない。酸化イットリウムの添加量が１０質量％を超えるとＹ₂Ｓｉ₂Ｏ₇相が形成されず比較的低融点のＹ₂ＳｉＯ₅相が形成され、得られた焼結体の高温での機械的強度および耐酸化性が低下する。酸化珪素も酸化イットリウムも均質かつ高密度の焼結体を得るためには平均粒径が２μｍ以下の微粒子であることが好ましい。焼結助剤として用いるこれら原料粉末は比較的安価であり、水中での混合工程での変質せず安定なセラミックス粉末である。
【００２１】
焼結方法としては、窒素ガスを含む雰囲気にて、例えば無加圧焼結法、ガス圧焼結法、熱間静水圧プレス焼結法、ホットプレス焼結法、等の各種焼結法を用いることができ、さらにこれらの焼結法を複数組合せても良い。窒素ガスを含む雰囲気で焼結するのは、焼結中でのＳｉ₃Ｎ₄の分解を抑制するためである。Ｓｉ₃Ｎ₄は窒素ガス1気圧下では約１８５０℃以上で分解が生じるため、１８５０℃以上にて焼結を行う場合は、窒素ガス圧を焼結温度におけるＳｉ₃Ｎ₄の臨界分解圧力以上に設定するようにする。また、大型厚肉形状のバタフライ弁を製造する場合には、十分な緻密化を図るために、無加圧焼結後に、さらに窒素ガス雰囲気中での熱間静水圧プレス焼結を行うことがより好ましい。無加圧及び熱間静水圧プレス焼結条件としては、焼結温度が１７００〜２０００℃であることが望ましい。１７００℃未満では、緻密な焼結体が得られず、固溶体粒子近傍に残留応力を十分に発生させることが困難となり、高靭性の焼結体とすることができない。一方、２０００℃を越える高温では、β-Ｓｉ₃Ｎ₄結晶粒が粗大化し強度低下を起こし、高硬度と耐熱衝撃性が得られない。また、保持時間が８時間未満では成形体の肉厚にも依存するが緻密化が十分に進行しない。
【００２２】
【実施例】
次に、本発明の実施例を比較例と共に説明する。
【００２３】
（実施例１〜３）
窒化珪素（Ｓｉ₃Ｎ₄）粉末（α化率９７％以上、純度９９．７％、平均粒径０．３μｍ）に酸化イットリウム（Ｙ₂Ｏ₃）粉末（平均粒径１．５μｍ）、酸化珪素（ＳｉＯ₂）粉末（平均粒径０．３μｍ）を表１に示す所定量（質量％）添加し、分散媒として精製水またはアセトンを用い、炭化珪素セラミックスを内貼りしたボールミルで２４時間混練した。精製水またはアセトンの添加量は、セラミックス全粉末原料１００ｇに対し１２０ｇとした。
【００２４】
次いで、得られた混合粉末を成形後焼結した。成形条件としては冷間静水圧による加圧１５０ＭPaとし、１００ｍｍ角、高さ２２ｍｍの板状成形体を得た。焼結条件としては、窒素ガス流通中にて、表１中に示す各温度で４〜１６時間保持の無加圧焼結を行った。
【００２５】
得られた焼結体から、１５ｍｍ×２０ｍｍ×長さ８０ｍｍの固定側軸受けテスト材を研削加工し、溶融アルミニウム浴中軸受け試験（図４）に供した。
【００２６】
板状焼結体から該１５ｍｍ×２０ｍｍ×長さ８０ｍｍテスト材を切り出す際の残材から機械的性質評価用の試験片を切り出し、その特性を評価した。硬さは、押込荷重１０ｋｇにてビッカース硬さとして測定した。靭性についてはＪＩＳＲ１６０７のＳＥＰＢ法により室温にて破壊靭性値Ｋ_ICを測定した。また、耐熱衝撃性としては、曲げ試験片を大気中にて所定の温度に加熱後、水中急冷し、抗折強さの劣化が始まる急冷温度差ΔＴで評価した。焼結体密度は、アルキメデス法により相対密度として測定した。濡れ性は、通常の溶融液滴と水平板状態の接触角で測定した。
【００２７】
得られた各焼結体のアルキメデス密度、機械的性質、並びに図４に示したアルミニウム浴中軸受け評価結果を各配合系ごとに表２に示す。アルミニウム浴中試験は、以下の条件にて行った。
【００２８】
（１）回転側軸受けテスト材：超硬リング材φ９０ｍｍ×高さ６０ｍｍ
（２）固定側軸受けテスト材：セラミックス試験材１５ｍｍ×２０ｍｍ×長さ８０ｍｍを３本
（３）溶融アルミニウム温度：６８０℃
（４）押し当て力：３０〜５０Ｎ
（５）すべり速度：２〜３ｍ／秒
（６）摺り合わせ時間：浸漬後、１０時間
（７）テスト前の仕上げ面粗さ：Ｒmax.＝０．２μｍ（△△△△程度、JIS-B0031参照）
（８）繰り返し熱疲労試験：１時間浴中に漬けた後、浴から引き上げ３０分間空冷を繰り返す。
【００２９】
上記（１）〜（７）の条件にて摩耗量を求める方法として、回転側、固定側にそれぞれ発生した摩耗痕跡の深さｈr、ｈｓを表面粗さ計にて測定した。また、摩耗痕跡周囲の損傷有無、チッピング深さ、および割れ深さを蛍光探傷法および断面研磨面の光学顕微鏡観察により評価した。再利用に当たっての軸受け摺り合わせ面の必要研削量は、摩耗痕跡周囲に割れ・チッピングの損傷が観察されない場合は摩耗痕跡深さｈの１．２倍、チッピングが生じている場合はチッピング深さの１．２倍、そして割れが生じている場合は割れ深さの１．２倍として表２中に示した。
【００３０】
（比較例４〜９）
比較例４〜５は実施例１〜３と同一原料を用い同じく精製水またはアセトンで調製したが、それぞれ降温時の焼結条件が不適で相対密度が９５％を下回った場合（比較例４）、焼結助剤（Ｙ₂Ｏ₃）の添加割合が不適で相対密度が９５％を下回った場合（比較例５）の各比較例である。
【００３１】
比較例６〜９は、一般市販のサイアロンを用いた場合（比較例６）、市販の安価な窒化珪素セラミックスを用いた場合（比較例７）、市販の比較的高価な窒化珪素セラミックスを用いた場合（比較例８）、公知の炭化珪素を用いた場合（比較例９）の各比較例である。これら比較例の材料も実施例１〜３と同様の条件で溶融アルミニウム浴中試験を行い、その結果を表２に示した。
【００３２】
【表１】

【００３３】
【表２】

【００３４】
表２に示すように、本発明の実施例によるものは、耐熱衝撃性(=ΔT/℃)が比較例のほぼ２倍と大きい上に、摩耗痕跡深さが固定側・回転側の何れも２５μｍ以下と非常に少なく、かつ摩耗痕跡周囲には割れ・チッピングの欠損が何れの場合も認められず、耐摩耗性、耐欠損性共に優れる。これに対し、比較例の各軸受けは本発明の実施例に比べて、摩耗痕跡深さ５０μｍ以上と大きく、かつ割れ・チッピングのいずれかが発生しており、耐摩耗性、耐欠損性ともに未達成であることが確認された。必要研削量も実施例の３０μｍ以下に比べ、比較例では６０μｍ以上と著しく大きいことが判明した。
【００３５】
表３に、各材料ごとの耐酸化試験(大気中、1200℃、保持100h)を行った際の重量増加ならびにアルミニウム浴中軸受け評価の試験条件（８）に基づいた耐久試験結果を示す。
【００３６】
【表３】

【００３７】
軸受けに繰り返し熱疲労を負荷した場合も、本発明によるものは表２の耐熱衝撃性、ならびに表３の耐酸化性が効果を発現し、繰返し３６０回使用可能であるのに対し、比較例の各材料では摩耗が進んでいない場合でも熱衝撃による大きな亀裂が発生し５〜２５回と１桁以上少ないという結果が得られた。加えて熱衝撃で破損が起こる前に、摺動摩耗によって高さの不均衡が生じた場合、摺動部の再研磨を行い高さを調節することも必要になり、その際のセラミックス加工費を加えたリサイクル性を考慮した総寿命による費用対効果まで考慮した結果でも、本発明の焼結体による軸受け材は比較例の軸受け材より極めて有利であることが確認された。高温のアルミニウム浴中での評価結果から、より低温の亜鉛浴中の耐熱衝撃性も満たすことが容易に想定されるため、本発明は、より広い溶融温度範囲の溶融金属めっき浴用部材への適用が可能と判断できる。
【００３８】
【発明の効果】
本発明により、連続溶融金属めっき装置における軸受部材の寿命が大幅に延長できる。このことにより、長時間安定して金属めっき鋼板の生産が可能となり、その工業的有用性は非常に大きい。
【図面の簡単な説明】
【図１】溶融めっき浴の装置断面模式図
【図２】埋め込み部材の長手方向断面図
【図３】軸受け部の組み付け構造図
【図４】本発明の実施例による軸受け損耗評価時の装置断面図
【符号の説明】
１：めっき処理ラインで通板中の鋼板
２：ポットロール
３：ガイドロール
４：加熱機能付き浴槽
５：回転側軸受けテスト材：φ９０ｍｍ×高さ５０ｍｍ
６：固定側軸受けテスト材：１５ｍｍ×２０ｍｍ×長さ８０ｍｍ
７：溶融アルミニウム浴（６８０℃）
８：保護管付き熱電対[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an immersion member for a molten metal plating bath in a continuous molten metal plating apparatus such as a steel plate and a method for manufacturing the immersion member.
[0002]
[Prior art]
As shown in FIG. 1, as a method of obtaining a metal plating plate, a metal plate heated and annealed in a heating furnace is led to a molten metal tank, the molten metal is plated on the metal plate, and this is passed through a pot roll and a guide roll. A method of continuously obtaining a metal plating plate by pulling up the plate is widely used. More specifically, in the case of using a steel plate as the metal plate, the plating method on the metal plate by the continuous molten metal plating apparatus inserts the steel plate whose surface has been cleaned and activated as a pretreatment into the molten metal bath, After changing the direction with a pot roll, the sheet is passed between two guide rolls in order to suppress warpage in the width direction of the steel sheet. After this, the steel plate is further lifted upward, and excess molten metal adhering to the steel plate surface is removed immediately above the plating bath by high-pressure gas wiping, etc., and adjusted to a predetermined plating amount to produce a molten metal-plated steel plate. To do.
[0003]
Generally, 24Cr-12Ni stainless steel having good corrosion resistance is used for the bearing member and the shaft sleeve member of the pot roll immersed in the molten metal plating bath. Stainless steel has low reactivity with molten metals such as molten zinc and molten aluminum, and has good corrosion resistance, but it cannot be said to have sufficient wear resistance. In particular, the bearing member is extremely narrow compared to the shaft sleeve member. Since the contact is always made in the range (the upper half), the wear amount is larger than that of the shaft sleeve member, and the life is as short as about 4 to 8 days. As wear of the bearing member progresses, fluttering or the like occurs on the steel sheet, and satisfactory plating cannot be performed. Therefore, the member must be lifted from the molten metal plating bath and the bearing member must be replaced. Therefore, even if there is no abnormality in other members such as a pot roll immersed in the molten metal plating bath, it is necessary to stop the operation and pull up the entire component immersed in the molten metal plating bath. At this time, since it is cooled rapidly from the bath temperature to room temperature, damage such as thermal shock breakage may occur in other parts, and the entire part may be replaced in a lump, and production loss is extremely large. . For this reason, various proposals have been made to extend the life of rolls used in a molten metal plating bath.
[0004]
In JP-A-3-253547 and JP-A-5-44002, alumina or silicon nitride sialon is used for a bearing member and a shaft sleeve member in a molten zinc bath, and a rotating pot roll is driven to rotate from the outside. Proposals have been made. However, in this proposal, only zinc is taken as the molten metal, and only the sliding wear amount and the wear coefficient are used as selection criteria, and the thermal shock resistance and wettability with the molten metal are not considered. Furthermore, regarding alumina or silicon nitride / sialon ceramics, there is no description of optimum conditions for various properties such as composition, firing conditions (density, structure), mechanical properties, and sliding surface roughness.
[0005]
Monolithic silicon carbide and zirconia ceramics are known to be inferior in thermal shock properties to silicon nitride and sialon. Silicon nitride and sialon, which are relatively excellent in thermal shock resistance, can withstand abrupt air cooling from the molten aluminum bath temperature (660 to 680 ° C) at the bearing member size (φ200mm or more) and wall thickness (t20mm or more). Almost not found.
[0006]
Based on the contents disclosed in the above prior art, commercially available silicon nitride ceramics that have been densified to a relative density ratio of 99% using yttria and alumina, which are general sintering aids, in a molten aluminum bath. As a result of the dynamic and thermal shock tests, the amount of wear in the zinc bath was greatly exceeded, and it was damaged only by performing air cooling from the molten aluminum bath three times.
[0007]
[Problems to be solved by the invention]
The above-mentioned technology relating to the sliding bearing is such that the surfaces of the bearing member and the shaft sleeve member that are in contact with each other have better corrosion resistance in a molten metal bath than stainless steel, and are coated with a high-hardness ceramic, or By using cermet, cemented carbide, ceramic sintered body, etc., it is intended to extend the life of the bearing. However, for a member for a molten metal plating bath, the optimal combination of a bearing member and a shaft sleeve member is more necessary to sufficiently withstand abrupt air cooling from the bath temperature (660 to 680 ° C. in the case of aluminum). Considering characteristics such as thermal shock resistance, high toughness, and oxidation resistance is a much more important selection factor. It is essential to increase the durability against thermal shock and repeated thermal fatigue associated with air cooling when the pot roll heated to several hundred degrees Celsius is pulled up.
[0008]
Moreover, since the opportunity loss in operation can be reduced if the replacement operation can be performed quickly, it is also desired that the member can be replaced easily.
[0009]
Accordingly, the object of the present invention is to greatly improve the durability against thermal shock, repeated thermal fatigue, detachment due to oxidation, etc., and at the same time, a dipping member for a molten metal plating bath that makes the replacement work at the time of wear / breakage extremely simple. And a manufacturing method thereof.
[0010]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems, can be used stably and repeatedly for a long time in a molten metal plating bath, and it is not necessary to handle a handle for suppressing a rapid temperature change even when a roll enters and leaves the plating bath. It was made for the purpose of providing a dipping member for a molten metal plating bath in which the ceramic material can be easily replaced at the time of replacement work after the bearing portion is consumed,
(1) An immersion member attached to a pot roll apparatus immersed in a molten metal plating bath, wherein the immersion member is at least a portion of the pot roll equipment where the pot roll shaft sleeve member and the bearing member slide. High thermal shock resistance and high oxidation resistance ceramics substantially composed of β-Si ₃ N ₄ phase, Si ₂ N ₂ O phase and Y ₂ Si ₂ O ₇ phase, which are partly or entirely fitted Immersion member for hot metal plating bath characterized by being a member,
(2) The immersion member for a molten metal plating bath according to claim 1, wherein the immersion member comprises a plurality of columnar members,
(3) The immersion member for a molten metal plating bath according to claim 2, wherein the columnar member is fitted in the axial direction of the bearing portion,
(4) The immersion member for a molten metal plating bath according to claim 3, wherein the sliding surface in the rotation direction of the columnar member is a flat surface or an arcuate surface having a radius of curvature of the pot roll shaft sleeve member, or more.
(5) The immersion member for a molten metal plating bath according to claim 2, wherein the columnar member is fitted to the pot roll shaft sleeve member in the axial direction.
(6) The immersion member for a molten metal plating bath according to claim 5, wherein the sliding surface of the columnar member is an arcuate surface having a radius of curvature of the bearing member or less.
(7) The melting according to claim 3 or 5, wherein the sliding surface in the axial direction of the columnar member has a concavo-convex shape and / or a wave shape, and the sliding surface height of the convex portion is aligned in the axial direction. Immersion member for metal plating bath,
(8) The immersion member for a molten metal plating bath according to any one of claims 1 to 7, wherein the ceramic member has a sintered body density of 95% or more of a theoretical density.
(9) Si ₂ N ₂ O phase with 0.1 to 3.0% by mass of the ceramic member, 4.9 to 12.0% by mass of Y ₂ Si ₂ O ₇ phase and the balance being β-Si ₃ The immersion member for a molten metal plating bath according to claim 8, comprising an N ₄ phase and an inevitable impurity phase,
(10) A molded powder comprising _{3 to} 10% by mass of yttrium oxide (Y ₂ O ₃ ), 1 to 5% by mass of silicon oxide (SiO ₂ ), and the balance being silicon nitride (Si ₃ N ₄ ), and Is sintered in a nitrogen gas atmosphere at a temperature range of 1700 to 2000 ° C., and Si ₂ N ₂ O phase and Y ₂ Si ₂ O are used as grain boundary phases by at least one of the following means (1) to (3). _A method for producing a dipping member for a molten metal plating bath, characterized by forming a sintered body that has generated _seven phases,
(1) The cooling rate in the sintering cooling process is 5 ° C./min or less.
(2) Hold for 2 hours or more in the temperature range of 1350 to 1650 ° C. in the temperature lowering process of sintering.
(3) After sintering, reheating treatment is performed for 2 hours or more in a temperature range of 1350 to 1650 ° C. in a nitrogen atmosphere.
Is a summary.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors reviewed the roll bearing in the molten zinc bath proposed in Japanese Patent Laid-Open No. 3-253547 and Japanese Patent Laid-Open No. 5-44402, and as a result of intensive studies, compared with zinc (mp = 430 ° C.) It is assumed that it can be applied to a high melting point molten aluminum (mp = 660 ° C.) bath. In preparation for the rapid temperature change that occurs when the roll is taken in and out of the molten aluminum bath, consideration has been given so that rapid heating and rapid cooling do not occur while the molten metal is bathed on the roll with a handle. According to the present invention, bearing materials and structures that do not need to be proposed. At the same time, it was possible to suppress sliding wear and chipping and cracking around the thermally fatigued portion, which were difficult with the prior art. These defects such as chipping and cracking are generated and propagated by thermal shock and mechanical shock, and when there are many holes in the member, low strength, low toughness, low thermal conductivity, low thermal shock, sliding surface is It was found to be prominent in the coarse case. On the other hand, it was confirmed that the sliding wear was remarkably suppressed when the sliding part was not a curved surface but a line contact or a point contact.
[0012]
The immersion member for a molten metal plating bath of the present invention is an immersion member attached to a pot roll apparatus immersed in a molten metal plating bath, and the immersion member is at least a pot roll shaft sleeve member or a bearing of the pot roll equipment. High thermal shock composed substantially of β-Si ₃ N ₄ phase, Si ₂ N ₂ O phase and Y ₂ Si ₂ O ₇ phase, fitted to part or all of the sliding part of the member And high oxidation resistance ceramic member. Moreover, it is preferable to fit a plurality of columnar members from the viewpoint of easy handling of the immersion member. As for the embedded shape, the surface that slides directly with the pot roll is preferably a flat surface or an arcuate surface that is convex above the radius of curvature of the pot roll shaft sleeve member, but there is no particular limitation, and the cross section is perpendicular to the axis. The shape may be a polygon more than a quadrangle, a semicircle, or a circle. It is not preferable to arrange the columnar members in the rotation direction. In order to limit the compressive stress load, it is recommended to arrange line contact and point contact in the same direction as the rotation direction. In addition, an arcuate surface that is convex upward or less than the radius of curvature of the pot roll shaft sleeve member or a concave arcuate surface that is greater than or equal to the radius of curvature loads the embedded material other than compressive stress, and has a higher probability of failure than compression. It is expected to be. Preferably, if a ceramic bearing piece having an isosceles trapezoidal cross section whose lower side is longer than the upper side is used, positioning is easy without using wedges or adhesives, and only compressive stress is used. Can be loaded. Furthermore, as shown in iii) to iv) of FIG. 2, it is possible to change from line contact to point contact by sequentially providing irregularities or corrugations in a direction parallel to the rotation axis of the columnar embedding material, Since the flow of the plating bath can be promoted, it is assumed that the rotation becomes smooth. Whether the unevenness or corrugated pattern with the adjacent embedding material should be reversed or in phase should correspond to the flowability of the plating bath and the number of rotations of the pot roll. By adopting such a shape, it becomes difficult to collect molten metal at the bearing portion, and work efficiency such as repair work can be improved.
[0013]
Also, for the sliding part of the rotating shaft member of the pot roll, the same ceramic material or carbide (= WC) particles as the bearing member are dispersed in a binding metal (= binder of copper, titanium, zinc, chromium, etc.) It doesn't matter. Also in this case, if the curvature on the bearing side is not larger than the curvature of the shaft, as described above, a tensile stress to be applied to the bearing member is applied, which is completely inappropriate. If it is flat or arcuate, processing is easy, and if the curvature is large, it is easily expected that the stability of the rotating shaft on the pot roll side will slightly increase. Further, when fitting to the rotating shaft, if the curvature of the embedded material on the rotating shaft side is larger than the curvature of the bearing, the shape of the embedded material becomes extremely large or too thin, which is not preferable.
[0014]
And by making this member into the above-mentioned shape, the absolute value of the expansion / contraction difference in the bath and air cooling caused by the difference in thermal expansion coefficient with the metal member fitted to the member can be reduced, and compression applied to the ceramic side Or, in addition to reducing the tensile stress, it has the effect of facilitating densification in manufacturing the ceramic member. The member to be fitted has a thickness of 5 mm or more and 20 mm or less, and preferably two or more columnar members are used. When the thickness is less than 5 mm, the compressive strength of the ceramic member is low, and the wear mark generated on the sliding surface after use is polished, and the total life is shortened when recycled, which is not preferable. Less than two, that is, one columnar member is not suitable because it does not provide any stability during rotation. Moreover, the range of 5-20 mm thickness is preferable also from the point of intensity | strength provision with respect to the mechanical impact at the time of handling a roll arm. About width, although depending on the size of the pot roll diameter and the number of the fitted columnar members, 10 to 30 mm is preferable. Further, the length of the columnar member is uniquely determined by the sleeve length of the metal member into which the member is fitted. Generally, a thickness of about 80 to 200 mm is often used.
[0015]
As shown in FIG. 3, in order to reduce the compressive or tensile stress caused by the difference in thermal expansion coefficient from the molten metal caught in the gap between the metal ring member used to hold the ceramic bearing, The gap between the fitting part between the member and the metal member is preferably 1 mm or less.
[0016]
Contrary to the above, it is also possible to fit a columnar member having a circular arc-shaped surface having a bearing portion which is a circular integral part and having a convexity lower than the curvature of the bearing to the pot roll shaft portion sleeve. However, care must be taken to ensure that sufficient fixing strength is obtained when embedding in the bearing part.In order to reduce the frictional resistance when the bearing part comes into contact, the sliding part is not a flat surface but has a curvature larger than the inner diameter of the bearing part. A small arcuate curved surface is most preferred. Furthermore, it is necessary to fit over half a circle or more, and stable rotation is obtained with at least three, more preferably five or more, not two or more. If it is not three or more, the chances of sliding at a portion other than the columnar member will increase, and the metal shaft sleeve material will be selectively worn away from the columnar member, making it impossible to extend the life.
[0017]
As a method for simultaneously improving characteristics such as high thermal shock resistance, abrasion resistance, and oxidation resistance, composite composite sintered bodies composed of various crystal phases were prepared and the characteristics were evaluated. Conventional silicon nitride and silicon carbide sintered bodies having a low-melting glass phase are inferior in oxidation resistance and thermal shock resistance at high temperatures. As a result of characteristic evaluation, it was found that a dense ceramic sintered body composed of a β-Si ₃ N ₄ phase and a Si ₂ N ₂ O phase and a Y ₂ Si ₂ O ₇ phase as grain boundary phases has excellent characteristics. It was. Moreover, since the columnar member shape of the embedding material (FIG. 2) can be imparted by simple grinding of corrugations or corrugations in a simple plane or arcuate surface or in the longitudinal direction, without increasing the cost of finishing the sintered body, It is possible to extend the life of the member for a molten metal plating bath.
[0018]
The molten metal plating bath member of the present invention has excellent thermal shock resistance and oxidation resistance, static fatigue characteristics due to temperature gradients occurring in the member under the usage environment, and rapid cooling when pulled up from the bath It has the characteristics such as enhancing the thermal stress fracture resistance characteristics associated with. In order to crystallize the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase as the grain boundary phase, cooling is performed at a temperature lowering rate of 5 ° C./min or lower during the temperature lowering process of sintering, Heat treatment is performed at 1650 ° C. for 2 hours or more, or at least one of reheating treatment at 1135 to 1650 ° C. for 2 hours or more in a nitrogen atmosphere after sintering. About holding | maintenance for 2 hours or more, More preferably, 12 hours or more and 24 hours or less are preferable. Although the crystallization of the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase is gradually promoted from 2 hours to 12 hours, it is necessary to extend the treatment time depending on the thickness of the fired product. It is considered that 24 hours is appropriate when the thickness of the ceramic member is 100 mm or less, which is a general purpose. When the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase are precipitated in the temperature lowering process, the temperature decreasing rate is preferably 5 ° C./min or less, more preferably 0.1 ° C./min to 2 ° C./min. is there. If it is less than 0.1 ° C./minute, it is not preferable because a long heat treatment is required for production efficiency. When the temperature lowering rate is faster than 5 ° C./min, the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase are not sufficiently formed. In addition, when the holding temperature during the temperature lowering process and the holding temperature during the reheating process are less than 1350 ° C. or higher than 1650 ° C., the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase are also sufficient. Do not generate. Further, even when each holding time is less than 2 hours, the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase are not generated. If the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase are less than 0.1 and 4.9% in mass ratio, respectively, the porosity in the sintered body becomes high, which is not preferable. The β-Si ₃ N ₄ crystal grains are not sufficiently entangled and the strength and toughness are lowered, which is not preferable. Further, regarding the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase, if the mass ratio of the Si ₂ N ₂ O phase is less than 0.1% of the whole, the effect of contributing to the mechanical strength is small and exceeds 3%. And β-Si ₃ N ₄ crystal grains are not sufficiently entangled and the strength and toughness are lowered. Similarly, if the mass ratio of the Y ₂ Si ₂ O ₇ phase is less than 4.9% of the total, the liquid phase during the α → β transition of Si ₃ N ₄ is small and the phase transition does not proceed smoothly. Since β-Si ₃ N ₄ crystal grains are not sufficiently entangled, strength and toughness are lowered, which is not preferable. The silicon nitride sintered body obtained by the present invention has an average crystal grain size of β-Si ₃ N ₄ of about 1 to ₃ μm, an aspect ratio of about 1.5 to 10 and a β-Si ₃ N ₄ It has a structure in which columnar crystal grains are intertwined, and high melting point Si ₂ N ₂ O phase and Y ₂ Si ₂ O ₇ phase are precipitated at the grain boundary, so it has high toughness while maintaining high strength up to high temperature. In addition, the bending strength is high strength of 500 MPa or higher at 1400 ° C. in the atmosphere and the toughness value K _IC is high toughness of 5 MPam ^1/2 , so it is suitable for a bath member that requires characteristics in a high temperature environment. Can be used. Here, the Si ₂ N ₂ O phase has the same type of X-ray diffraction pattern as the Si ₂ N ₂ O crystal identified by the powder X-ray diffraction method, and among the compounds composed of Si ₃ N ₄ and SiO ₂ It is the most stable compound in a high-temperature oxidizing atmosphere. Similarly, the Y ₂ Si ₂ O ₇ crystal phase has the same type of X-ray diffraction pattern as the Y ₂ Si ₂ O ₇ crystal identified by the powder X-ray diffraction method, and is a compound comprising Y ₂ O ₃ and SiO ₂ Among them, it is the most stable compound in a high-temperature oxidizing atmosphere. The β-Si ₃ N ₄ crystal phase has the same type of X-ray diffraction pattern as the β-Si ₃ N ₄ crystal shown by the JCPDS card 33-1160. Furthermore, the relative density of the silicon nitride sintered body composed of the β-Si ₃ N ₄ phase, Si ₂ N ₂ O phase, Y ₂ Si ₂ O ₇ phase and inevitable impurity phase is 95% of the theoretical density. % Or more is desirable. If the relative density is less than 95%, the thermal stability and mechanical stability tend to be insufficient, and there is a high possibility that the effect of improving long-term durability will not be seen.
[0019]
The silicon nitride powder used in the present invention is preferably an Si ₃ N ₄ powder having an α-type crystal structure from the viewpoint of sinterability, but includes a β-type or amorphous Si ₃ N ₄ powder. It doesn't matter. In order to obtain a sufficiently high density during sintering, fine particles having an average particle diameter of 1 μm or less are desirable.
[0020]
Since silicon nitride is a substance having strong covalent bonding and is often difficult to sinter alone, generally a sintering aid is added for densification. In the present invention, silicon oxide and yttrium oxide are used as the sintering aid. Here, yttrium oxide has a function of accelerating the crystal phase transition from alpha-Si ₃ N ₄ phase during sintering of Si ₃ N ₄ beta-Si to ₃ N ₄ phase in its molten in further beta-Si It is known to improve high temperature strength and toughness by promoting the growth of ₃ N ₄ columnar phase. The addition amount of silicon oxide is preferably 1 to 5% by mass and yttrium oxide is preferably 3 to 10% by mass. When silicon oxide is less than 1% by mass, the liquid phase formation temperature at the time of sintering temperature rise becomes high and a sufficiently dense sintered body cannot be obtained, and the Si ₂ N ₂ O phase and the Y ₂ Si ₂ O ₇ phase Not formed. If it exceeds 5% by mass, the Y ₂ Si ₂ O ₇ phase is not formed, and a relatively low melting point SiO ₂ phase is formed, resulting in a decrease in mechanical strength at high temperatures. If the amount of yttrium oxide added is less than 3% by mass, melt formation is insufficient, the relative density is less than 95%, and densification does not proceed. If the amount of yttrium oxide added exceeds 10% by mass, the Y ₂ Si ₂ O ₇ phase is not formed, and a relatively low melting point Y ₂ SiO ₅ phase is formed. The mechanical strength of the obtained sintered body at high temperature And the oxidation resistance decreases. Both silicon oxide and yttrium oxide are preferably fine particles having an average particle diameter of 2 μm or less in order to obtain a homogeneous and high-density sintered body. These raw material powders used as sintering aids are relatively inexpensive, and are stable ceramic powders that do not deteriorate during the mixing process in water.
[0021]
As a sintering method, various sintering methods such as a pressureless sintering method, a gas pressure sintering method, a hot isostatic pressing sintering method, a hot pressing sintering method, etc. are performed in an atmosphere containing nitrogen gas. A plurality of these sintering methods may be combined. The reason why sintering is performed in an atmosphere containing nitrogen gas is to suppress the decomposition of Si ₃ N ₄ during sintering. Since Si ₃ N ₄ decomposes at about 1850 ° C. or higher under 1 atmosphere of nitrogen gas, when sintering at 1850 ° C. or higher, the nitrogen gas pressure is higher than the critical decomposition pressure of Si ₃ N _{4 at} the sintering temperature. Set to. In addition, when manufacturing a large butterfly-shaped butterfly valve, it is possible to perform hot isostatic pressing in a nitrogen gas atmosphere after pressureless sintering in order to achieve sufficient densification. More preferred. As pressureless and hot isostatic pressing sintering conditions, the sintering temperature is desirably 1700 to 2000 ° C. If the temperature is less than 1700 ° C., a dense sintered body cannot be obtained, and it becomes difficult to generate sufficient residual stress in the vicinity of the solid solution particles, so that a highly tough sintered body cannot be obtained. On the other hand, at a high temperature exceeding 2000 ° C., the β-Si ₃ N ₄ crystal grains become coarse and the strength is lowered, and high hardness and thermal shock resistance cannot be obtained. Further, if the holding time is less than 8 hours, the densification does not proceed sufficiently although it depends on the thickness of the molded body.
[0022]
【Example】
Next, examples of the present invention will be described together with comparative examples.
[0023]
(Examples 1-3)
Silicon nitride (Si ₃ N ₄ ) powder (alpha conversion 97% or more, purity 99.7%, average particle size 0.3 μm), yttrium oxide (Y ₂ O ₃ ) powder (average particle size 1.5 μm), oxidized A predetermined amount (mass%) of silicon (SiO ₂ ) powder (average particle size 0.3 μm) is added as shown in Table 1, purified water or acetone is used as a dispersion medium, and kneaded for 24 hours in a ball mill with silicon carbide ceramics attached inside. did. The amount of purified water or acetone added was 120 g with respect to 100 g of all ceramic powder raw materials.
[0024]
Next, the obtained mixed powder was molded and then sintered. As the molding conditions, a pressure of 150 MPa was applied by cold isostatic pressure, and a plate-like molded body having a 100 mm square and a height of 22 mm was obtained. As sintering conditions, pressureless sintering was performed for 4 to 16 hours at each temperature shown in Table 1 in a nitrogen gas flow.
[0025]
From the obtained sintered body, a fixed-side bearing test material of 15 mm × 20 mm × length 80 mm was ground and subjected to a bearing test in a molten aluminum bath (FIG. 4).
[0026]
A test piece for mechanical property evaluation was cut out from the remaining material when the test material of 15 mm × 20 mm × length 80 mm was cut out from the plate-like sintered body, and its characteristics were evaluated. The hardness was measured as Vickers hardness at an indentation load of 10 kg. For toughness, the fracture toughness value K _IC was measured at room temperature by the SEPB method of JIS R1607. The thermal shock resistance was evaluated based on a rapid cooling temperature difference ΔT at which a bending test piece was heated to a predetermined temperature in the air and then rapidly cooled in water, and the bending strength began to deteriorate. The sintered body density was measured as a relative density by the Archimedes method. The wettability was measured by the contact angle between a normal molten droplet and a horizontal plate.
[0027]
Table 2 shows the Archimedes density, mechanical properties, and bearing evaluation results in the aluminum bath shown in FIG. 4 for each blended system. The test in the aluminum bath was performed under the following conditions.
[0028]
(1) Rotating side bearing test material: Carbide ring material φ90mm x Height 60mm
(2) Fixed side bearing test material: 3 ceramic test materials 15 mm × 20 mm × 80 mm length (3) Molten aluminum temperature: 680 ° C.
(4) Pushing force: 30-50N
(5) Sliding speed: 2 to 3 m / sec (6) Sliding time: 10 hours after immersion (7) Finished surface roughness before test: Rmax. = 0.2 μm (about Δ △ Δ △, JIS-B0031 reference)
(8) Repeated thermal fatigue test: After being immersed in a bath for 1 hour, it is lifted from the bath and repeatedly air-cooled for 30 minutes.
[0029]
As a method for obtaining the wear amount under the above conditions (1) to (7), the depths hr and hs of the wear traces generated on the rotating side and the fixed side were measured with a surface roughness meter. In addition, the presence or absence of damage around the wear trace, the chipping depth, and the crack depth were evaluated by fluorescent flaw detection and observation of the cross-section polished surface with an optical microscope. The amount of grinding required for the bearing-to-bearing surfaces for reuse is 1.2 times the wear trace depth h if no cracking or chipping damage is observed around the wear trace, and the chipping depth of the chip when chipping occurs. If the crack is 1.2 times, it is shown in Table 2 as 1.2 times the crack depth.
[0030]
(Comparative Examples 4 to 9)
In Comparative Examples 4 to 5, the same raw materials as in Examples 1 to 3 were used and prepared in the same manner with purified water or acetone. However, when the temperature was lowered, the sintering conditions were inappropriate and the relative density was less than 95% (Comparative Example 4). These are comparative examples when the addition ratio of the sintering aid (Y ₂ O ₃ ) is unsuitable and the relative density falls below 95% (Comparative Example 5).
[0031]
In Comparative Examples 6 to 9, when a commercially available sialon was used (Comparative Example 6), a commercially available inexpensive silicon nitride ceramic was used (Comparative Example 7), a commercially available relatively expensive silicon nitride ceramic was used. It is each comparative example when the case (comparative example 8) and the known silicon carbide are used (comparative example 9). The materials of these comparative examples were also tested in a molten aluminum bath under the same conditions as in Examples 1 to 3, and the results are shown in Table 2.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
As shown in Table 2, the thermal shock resistance (= ΔT / ° C.) of the example of the present invention is almost twice as large as that of the comparative example, and the wear trace depth is both on the fixed side and the rotating side. It is very small at 25 μm or less, and no cracks or chipping defects are observed around the wear trace, and both wear resistance and chip resistance are excellent. On the other hand, each bearing of the comparative example has a wear trace depth of 50 μm or more larger than that of the embodiment of the present invention, and either cracking or chipping has occurred. It was confirmed that this was achieved. The required amount of grinding was found to be remarkably large at 60 μm or more in the comparative example as compared to 30 μm or less in the example.
[0035]
Table 3 shows the results of endurance tests based on the test results (8) for the weight increase and the evaluation of bearings in the aluminum bath when an oxidation resistance test (in the atmosphere, 1200 ° C., holding time 100 h) is performed for each material.
[0036]
[Table 3]

[0037]
Even when the bearing is subjected to repeated thermal fatigue, the thermal shock resistance shown in Table 2 and the oxidation resistance shown in Table 3 are effective in the bearing according to the present invention and can be used repeatedly 360 times. Even if the wear did not progress in each material, a large crack was generated by thermal shock, and the result was obtained that it was 5 to 25 times less than one digit. In addition, if there is an imbalance in height due to sliding wear before damage occurs due to thermal shock, it is also necessary to adjust the height by re-grinding the sliding part. As a result of considering the cost-effectiveness of the total life in consideration of the recyclability including the above, it was confirmed that the bearing material by the sintered body of the present invention is extremely advantageous than the bearing material of the comparative example. Since it is easily assumed that the thermal shock resistance in a lower temperature zinc bath is also satisfied from the evaluation results in a high temperature aluminum bath, the present invention is applied to a member for a molten metal plating bath having a wider melting temperature range. Can be determined to be possible.
[0038]
【The invention's effect】
By this invention, the lifetime of the bearing member in a continuous molten metal plating apparatus can be extended significantly. This makes it possible to produce a metal-plated steel sheet stably for a long time, and its industrial utility is very large.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an apparatus of a hot dipping bath. FIG. 2 is a longitudinal cross-sectional view of an embedded member. FIG. 3 is an assembly structure diagram of a bearing. Figure [Explanation of symbols]
1: Steel plate passing through plating line 2: Pot roll 3: Guide roll 4: Bath with heating function 5: Rotating side bearing test material: φ90 mm × Height 50 mm
6: Fixed side bearing test material: 15 mm × 20 mm × length 80 mm
7: Molten aluminum bath (680 ° C.)
8: Thermocouple with protective tube

Claims

溶融金属めっき浴に浸漬されるポットロール装置に付設された浸漬部材であって、該浸漬部材が、該ポットロール設備の少なくともポットロール軸部スリーブ部材と軸受部材の摺動する部分の一部又は全部に嵌合してなる、実質的にβ−Ｓｉ₃Ｎ₄相、Ｓｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相から構成される高耐熱衝撃性、高耐酸化性セラミックス部材であることを特徴とする溶融金属めっき浴用浸漬部材。An immersion member attached to a pot roll apparatus immersed in a molten metal plating bath, wherein the immersion member is a part of a sliding portion of at least a pot roll shaft sleeve member and a bearing member of the pot roll equipment or It is a ceramic member with high thermal shock resistance and high oxidation resistance which is composed of a β-Si ₃ N ₄ phase, a Si ₂ N ₂ O phase and a Y ₂ Si ₂ O ₇ phase. An immersion member for a molten metal plating bath.

前記浸漬部材が、複数の柱状部材からなる請求項１記載の溶融金属めっき浴用浸漬部材。The immersion member for a molten metal plating bath according to claim 1, wherein the immersion member includes a plurality of columnar members.

前記柱状部材が、前記軸受部の軸方向に嵌合してなる請求項２記載の溶融金属めっき浴用浸漬部材。The immersion member for a molten metal plating bath according to claim 2, wherein the columnar member is fitted in the axial direction of the bearing portion.

前記柱状部材の回転方向の摺動面が、平面又は前記ポットロール軸部スリーブ部材の曲率半径以上の円弧状面である請求項３記載の溶融金属めっき浴用浸漬部材。The immersion member for a molten metal plating bath according to claim 3, wherein the sliding surface in the rotation direction of the columnar member is a flat surface or an arcuate surface having a radius of curvature of the pot roll shaft sleeve member.

前記柱状部材が、前記ポットロール軸部スリーブ部材に軸方向に嵌合してなる請求項２記載の溶融金属めっき浴用浸漬部材。The immersion member for a molten metal plating bath according to claim 2, wherein the columnar member is fitted to the pot roll shaft sleeve member in the axial direction.

前記柱状部材の摺動面が、前記軸受部材の曲率半径以下の円弧状面である請求項５記載の溶融金属めっき浴用浸漬部材。The immersion member for a molten metal plating bath according to claim 5, wherein the sliding surface of the columnar member is an arcuate surface having a radius of curvature of the bearing member.

前記柱状部材の軸方向の摺動面が、凹凸状及び／又は波形状で、凸部の摺動面高さが軸方向で揃った形状である請求項３又は５に記載の溶融金属めっき浴用浸漬部材。6. The molten metal plating bath according to claim 3, wherein the sliding surface in the axial direction of the columnar member has an uneven shape and / or a wave shape, and the sliding surface height of the convex portion is aligned in the axial direction. Immersion member.

前記セラミックス部材が、理論密度の９５％以上の焼結体密度である請求項１〜７に記載の溶融金属めっき浴用浸漬部材。The immersion member for a molten metal plating bath according to claim 1, wherein the ceramic member has a sintered body density of 95% or more of a theoretical density.

前記セラミックス部材の組成が０．１〜３．０質量％のＳｉ₂Ｎ₂Ｏ相、４．９〜１２．０質量％のＹ₂Ｓｉ₂Ｏ₇相及び残部がβ−Ｓｉ₃Ｎ₄相及び不可避的不純物相からなる請求項８記載の溶融金属めっき浴用浸漬部材。The ceramic member has a composition of 0.1 to 3.0% by mass of Si ₂ N ₂ O phase, 4.9 to 12.0% by mass of Y ₂ Si ₂ O ₇ phase, and the balance is β-Si ₃ N ₄ phase. The immersion member for a molten metal plating bath according to claim 8, comprising an unavoidable impurity phase.

酸化イットリウム（Ｙ₂Ｏ₃）３〜１０質量％、酸化珪素（ＳｉＯ₂）１〜５質量％および残部が窒化珪素（Ｓｉ₃Ｎ₄）からなる混合粉末を成形し、該成形体を窒素ガス雰囲気中にて１７００〜２０００℃の温度範囲で焼結し、以下の▲１▼〜▲３▼の少なくとも一つの手段により粒界相としてＳｉ₂Ｎ₂Ｏ相及びＹ₂Ｓｉ₂Ｏ₇相を生成させた焼結体を成形加工することを特徴とする溶融金属めっき浴用浸漬部材の製造方法。
▲１▼焼結の降温過程における降温速度を５℃／分以下とする。
▲２▼焼結の降温過程において、１３５０〜１６５０℃の温度範囲において２時間以上保持する。
▲３▼焼結後、窒素雰囲気中、１３５０〜１６５０℃の温度範囲において２時間以上保持の再加熱処理を行う。A mixed powder composed of _{3 to} 10% by mass of yttrium oxide (Y ₂ O ₃ ), 1 to 5% by mass of silicon oxide (SiO ₂ ) and the balance of silicon nitride (Si ₃ N ₄ ) is molded, and the molded product is converted into nitrogen gas. Sintering is performed in an atmosphere at a temperature range of 1700 to 2000 ° C., and Si ₂ N ₂ O phase and Y ₂ Si ₂ O ₇ phase are formed as grain boundary phases by at least one of the following methods (1) to (3). A method for producing an immersion member for a molten metal plating bath, wherein the formed sintered body is molded.
(1) The temperature decreasing rate in the temperature decreasing process of sintering is set to 5 ° C./min or less.
(2) Hold for 2 hours or more in a temperature range of 1350 to 1650 ° C. in the temperature lowering process of sintering.
{Circle around (3)} After sintering, reheating treatment is performed for 2 hours or more in a temperature range of 1350 to 1650 ° C. in a nitrogen atmosphere.