JP2007046118A - Method for producing austenitic stainless steel sheet having excellent surface quality - Google Patents
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本発明は、表面均一性に優れたオーステナイト系ステンレス鋼熱間圧延鋼材の製造方法に関わるものであり、特に、熱間圧延後に実施される熱処理の雰囲気および鋼材の化学組成に関するものである。 The present invention relates to a method for producing an austenitic stainless steel hot-rolled steel material having excellent surface uniformity, and particularly relates to an atmosphere of heat treatment performed after hot rolling and a chemical composition of the steel material.
ステンレス鋼の薄鋼板の製造方法は、一般に、連続鋳造後に熱間圧延したコイルを、焼鈍→脱スケール→冷間圧延→焼鈍→脱スケール→調質圧延、の順に実施される。
この工程における、熱間圧延後の焼鈍では、熱間圧延後の緩冷却時に析出したＣｒ炭化物の母相への固溶化、および熱間圧延後に残留した歪みを除去することを目的としており、その焼鈍はＪＩＳ Ｇ４３０４に規定されるように、オーステナイト系ステンレス鋼の代表鋼種のＳＵＳ３０４では一般に１０１０〜１１５０℃の範囲で焼鈍後急冷処理することが規定されている。
A method for producing a stainless steel sheet is generally performed in the order of annealing, descaling, cold rolling, annealing, descaling, temper rolling of a coil that has been hot rolled after continuous casting.
In this process, the annealing after hot rolling is aimed at solidifying the Cr carbide precipitated during slow cooling after hot rolling into the matrix and removing the residual strain after hot rolling. As specified in JIS G4304, annealing is generally specified in SUS304, which is a representative steel type of austenitic stainless steel, to be rapidly cooled after annealing in the range of 1010 to 1150 ° C.
更に、引き続き実施される熱間圧延後の脱スケール工程では、スケールが数〜十ミクロン程度の厚さがあるため、ショットブラストやベンダーなどの機械的脱スケール処理を実施してから、硫酸や硝ふっ酸等の酸洗液中に浸漬して、素地を熔解することで脱スケール処理される。オーステナイト系ステンレス鋼では、これらの焼鈍・脱スケール工程は、双方が連続的に実施される連続焼鈍酸洗ライン（ＡＰＬ）において処理される。 Furthermore, in the subsequent descaling process after hot rolling, the scale has a thickness of several to tens of microns. Therefore, after carrying out mechanical descaling treatment such as shot blasting or bender, sulfuric acid or glass is used. It is descaled by immersing it in a pickling solution such as hydrofluoric acid and melting the substrate. In austenitic stainless steel, these annealing and descaling processes are performed in a continuous annealing pickling line (APL) in which both are carried out continuously.
ステンレス鋼板はその特性上、表面の均一性・美麗性が重視される場合が多い。熱延板焼鈍酸洗後の表面に微小な疵やむらが発生した場合、冷間圧延以降の工程を経ても消失しない場合が多く、その場合には冷間圧延前にコイル研削工程を追加して表面を研削除去しなければならないため、コスト的・納期的に問題となる。また、ＢＡ材のように特に高光沢が要求される場合は、熱延板焼鈍酸洗後で生じる粒界浸食溝も光沢の妨げになるため、疵が無くても上記コイル研削工程が必須となる。従って、焼鈍酸洗のみを施した表面肌を如何に平滑・均一化するか従来より検討されてきた。 Stainless steel sheets often place importance on surface uniformity and beauty due to their characteristics. When fine wrinkles and unevenness occur on the surface after hot-rolled sheet annealing and pickling, it often does not disappear even after the cold rolling process.In that case, a coil grinding process is added before cold rolling. Since the surface has to be ground and removed, there is a problem in terms of cost and delivery time. In addition, when a particularly high gloss is required, such as BA material, the grain boundary erosion grooves that occur after hot-rolled sheet annealing pickling also interfere with the gloss, so the coil grinding process is essential even without wrinkles. Become. Therefore, it has been conventionally studied how to smooth and uniform the surface skin that has been subjected to only the annealing pickling.
この連続ラインで実施される熱延板焼鈍酸洗後の表面品質の問題として、酸洗後に斑点状または筋状に光沢むらが観察される場合がある。これは焼鈍前の熱間圧延コイルに存在しているスケールが焼鈍中に不均一剥離することに起因している。不均一剥離の原因としては、熱間圧延時および巻き取り時の冷却のむら、およびコイル保管時の水濡れ等が考えられており、これが焼鈍時のスケール成長と相まって剥離が促進されると推定されている。この光沢むらは、そのままでは冷間圧延しても消えない場合が多いため、冷間圧延前に前述のコイル研削工程を追加しなければならない。 As a problem of surface quality after hot-rolled sheet annealing pickling performed in this continuous line, uneven gloss may be observed in the form of spots or streaks after pickling. This is because the scale existing in the hot rolled coil before annealing peels off unevenly during annealing. Possible causes of non-uniform exfoliation include uneven cooling during hot rolling and coiling, water wetting during coil storage, etc., and this is considered to promote exfoliation in combination with scale growth during annealing. ing. Since this uneven luster often does not disappear even if it is cold-rolled as it is, the above-described coil grinding step must be added before cold rolling.
この熱延板の焼鈍酸洗後に生じる鋼板表面の光沢むらについて、その改善策として種々の提案がなされている。例えば特開平７−４８６２８号公報（特許文献１）では、焼鈍前に熱延板へ機械的脱スケール処理を実施することで、スケール起因のむらを軽減させる方法が提案されている。また、特開２００１−２６８１８号公報（特許文献２）では、焼鈍前の機械的脱スケール処理と合わせて、引き続き実施される焼鈍雰囲気中のＨ2 Ｏ濃度を３０ｖｏｌ％以上とすることでスケール厚を制御する方法が提案されている。さらに、特開平１１−１４０５４５号公報（特許文献３）では、熱間圧延の巻き取り温度を７００℃以下とし焼鈍工程での昇降温速度を１０℃／ｓ以上と規定することで、粒界起因の表面凹凸を低減する方法が提案されている。 Various proposals have been made as measures for improving the uneven glossiness of the steel sheet surface that occurs after annealing and pickling of hot-rolled sheets. For example, Japanese Patent Laid-Open No. 7-48628 (Patent Document 1) proposes a method of reducing unevenness due to scale by performing a mechanical descaling process on a hot-rolled sheet before annealing. Further, in JP 2001-26818 (Patent Document 2), in conjunction with the mechanical descaling prior to annealing, scale thickness of H 2 O concentration in the annealing atmosphere continue to be carried out by a 30 vol% or more A method for controlling the above has been proposed. Furthermore, in JP-A-11-140545 (Patent Document 3), the coiling temperature of hot rolling is set to 700 ° C. or lower, and the temperature raising / lowering rate in the annealing step is defined as 10 ° C./s or higher, thereby causing grain boundaries. A method for reducing the surface roughness of the surface has been proposed.
しかし、焼鈍前の機械的脱スケール処理を実施するには、既存の設備では新たに機械的脱スケール装置を設置しなければならず、また、新設の場合でも焼鈍前のほか後にも必要なため、設備費、設置場所とも膨大になる懸念がある。また、昇降温速度の向上では、Ｃｒの拡散抑制による粒界起因の凹凸は低減できても、スケール剥離に伴う光沢むら低減には効果は得られない。 However, in order to perform mechanical descaling before annealing, a new mechanical descaling device must be installed in existing facilities, and even in the case of new installations, it is necessary both before and after annealing. There is a concern that the equipment cost and installation location will be enormous. In addition, in the improvement of the temperature raising / lowering speed, the unevenness due to the grain boundary due to the diffusion suppression of Cr can be reduced, but no effect is obtained in reducing the uneven gloss due to scale peeling.
本発明は上記の熱延板焼鈍酸洗後に生じる光沢むらを防止することを目的に、焼鈍時の雰囲気と化学組成との関連を検討した結果、以下の方法を知見したのである。
本発明は、熱間圧延したオーステナイト系ステンレス鋼材の製造方法において、熱間圧延後に実施される熱処理時の雰囲気を酸素濃度３．５ｖｏｌ％以上１０ｖｏｌ％以下、水蒸気濃度２０ｖｏｌ％以下の雰囲気で処理することを特徴とする、表面均一性に優れかつ脱スケールが容易となるオーステナイト系ステンレス鋼の製造方法である。
また、上記のオーステナイト系ステンレス鋼の化学組成が、Ｓ：≧０．００５％を含有することを特徴とするＳＵＳ３０４系ステンレス鋼であることを特徴とする製造方法である。
The present invention has found the following method as a result of investigating the relationship between the atmosphere during annealing and the chemical composition for the purpose of preventing the uneven glossiness that occurs after the hot-rolled sheet annealing pickling.
The present invention is a method for producing a hot-rolled austenitic stainless steel material, wherein the atmosphere during heat treatment performed after hot rolling is treated in an atmosphere having an oxygen concentration of 3.5 vol% or more and 10 vol% or less and a water vapor concentration of 20 vol% or less. This is a method for producing an austenitic stainless steel that is excellent in surface uniformity and that can be easily descaled.
Moreover, the chemical composition of the austenitic stainless steel is a SUS304 stainless steel characterized by containing S: ≧ 0.005%.
以上述べたように、 本発明によれば、膨大な設備投資の必要が無く、焼鈍雰囲気の制御と化学組成との組み合わせにより、光沢むらのない平滑美麗な熱延鋼板が得られるため、コイル研削工程の削減等、歩留まり、工程上のメリットが大きい。また、通常の熱延板コイル全てが平滑となり表面品質が向上でき、さらにＢＡ材で必須であったコイル研削工程も省略可能となり、オーステナイト系ステンレス鋼生産に大きく寄与できる。 As described above, according to the present invention, there is no need for enormous capital investment, and a smooth and beautiful hot-rolled steel sheet having no gloss unevenness can be obtained by combining the control of the annealing atmosphere and the chemical composition. There are significant advantages in yield and process, such as process reduction. Moreover, all the normal hot-rolled coil coils can be made smooth and the surface quality can be improved. Further, the coil grinding step essential for the BA material can be omitted, which can greatly contribute to the production of austenitic stainless steel.
先ず、オーステナイト系ステンレス鋼板の熱延板焼鈍酸洗後に生じた光沢むらを詳細に調査した結果、光沢むら部は正常部に比較して光沢度が高いこと、また、ミクロ観察より光沢むら部は正常部より、結晶粒界の浸食溝が浅く、かつ粒内凹凸がほとんど無く平滑な表面となっていることが判明した。製品の特性上としては、光沢むら内部で見られる粒界浸食溝の浅い、平滑な表面の方が望ましいため、光沢むら内部の表面がコイル表面全体で均一に得られれば、従来の熱延焼鈍酸洗板よりも平滑で均一な表面が得られる可能性がある。このような考えのもとに、熱延板焼鈍中にスケールを均一剥離する技術を種々検討した結果、熱延板焼鈍雰囲気制御ならびに化学組成の組合せにより、本技術を知見した。 First, as a result of investigating the uneven luster generated after hot-rolled plate annealing pickling of an austenitic stainless steel plate in detail, the uneven luster part has a higher gloss than the normal part, and the uneven luster part from the micro observation is From the normal part, it was found that the erosion groove of the crystal grain boundary is shallow, and there is almost no intragranular unevenness, resulting in a smooth surface. From the standpoint of product characteristics, it is desirable to have a smooth surface with shallow grain boundary erosion grooves seen inside the uneven luster. There is a possibility of obtaining a smoother and more uniform surface than the pickled plate. Based on these ideas, as a result of various studies on techniques for uniformly peeling the scale during hot-rolled sheet annealing, the present technique was discovered through a combination of hot-rolled sheet annealing atmosphere control and chemical composition.
以下、本発明について詳細に説明する。
焼鈍処理は、通常連続式の直下熱処理炉でＬＮＧを燃料として加熱処理される。この時の雰囲気を、Ｏ2 が３．５ｖｏｌ％以上、好ましくは５ｖｏｌ％以上で、かつＨ2 Ｏ：２０％以下とすることによりスケール剥離性が向上する。この作用の詳細は明らかになっていないが、高Ｏ2 でかつ高Ｈ2 Ｏの雰囲気下では、スケールが、より剥離しやすいヘマタイトＦｅ2 Ｏ3 への変質が促進されたためと推定される。Ｏ2 濃度は高くても問題はないが、空燃比を上げるか、またはＯ2 を強制的に吹き込むかが必要になるため、高すぎると燃焼効率が低下する。そのため１０％程度が上限として望ましい。
Hereinafter, the present invention will be described in detail.
In the annealing treatment, heat treatment is usually performed using LNG as fuel in a continuous direct heat treatment furnace. When the atmosphere at this time is O 2 of 3.5 vol% or more, preferably 5 vol% or more and H 2 O: 20% or less, the scale peelability is improved. Although the details of this action have not been clarified, it is presumed that in an atmosphere of high O 2 and high H 2 O, the scale was promoted to be transformed into hematite Fe 2 O 3 which is more easily peeled off. Even if the O 2 concentration is high, there is no problem, but it is necessary to raise the air-fuel ratio or forcibly blow in O 2. Therefore, if it is too high, the combustion efficiency is lowered. Therefore, about 10% is desirable as the upper limit.
Ｈ2 Ｏは低くても問題はないが、通常のＬＮＧ燃焼雰囲気では十数％程度となるため、特に問題はない。Ｈ2 Ｏが２０％以上となる場合は、水蒸気酸化によりスケールが厚く生成するため好ましくない。焼鈍温度は、ＪＩＳで規定された１０１０〜１１５０℃の範囲でよく、昇温速度も通常の設備で実施可能な速度で十分である。焼鈍に引き続き実施される機械的脱スケール処理および酸洗処理も通常のオーステナイト系ステンレス鋼で実施される条件で問題がない。ただし、本発明では焼鈍後にスケールの大部分が剥離除去されているので、機械的脱スケール処理および酸洗処理とも軽減できる期待がある。特に酸洗については、従来の半分以下の時間で脱スケールが完了できる可能性もある。 Although there is no problem even if H 2 O is low, there is no particular problem because it is about 10% or more in a normal LNG combustion atmosphere. When H 2 O is 20% or more, a thick scale is generated by steam oxidation, which is not preferable. The annealing temperature may be in the range of 1010 to 1150 ° C. defined by JIS, and the rate of temperature rise is sufficient at a rate that can be implemented with ordinary equipment. The mechanical descaling treatment and pickling treatment carried out following the annealing are not problematic under the conditions carried out with ordinary austenitic stainless steel. However, in the present invention, since most of the scale is peeled and removed after annealing, there is an expectation that both mechanical descaling and pickling can be reduced. Especially for pickling, descaling may be completed in less than half of the conventional time.
化学組成については、Ｓ含有率を０．００５質量％以上とする必要がある。Ｓは従来よりスケール密着性を低下させる元素の１つとして上げられており、スケールと母材の界面に濃縮してその結合を弱めるためにスケールの密着性を低減させると言われている。本発明も同様の効果と推測されるが、Ｓ含有量のみを増加させても、スケールは均一には剥離しない。先の焼鈍雰囲気制御との組み合わせにより、全面で均一なスケール剥離が得られる。Ｓ含有量は多い方がスケール剥離が促進されるが、多すぎるとＭｎＳが多く析出して、耐食性の劣化を引き起こすため、０．０１質量％程度を上限とするのが望ましい。 About a chemical composition, it is necessary to make S content into 0.005 mass% or more. S is conventionally raised as one of the elements that lowers the adhesion of the scale, and is said to reduce the adhesion of the scale in order to concentrate at the interface between the scale and the base material and weaken the bond. The present invention is presumed to have the same effect, but even if only the S content is increased, the scale does not peel uniformly. By combining with the previous annealing atmosphere control, uniform scale peeling can be obtained on the entire surface. When the S content is large, scale peeling is promoted. However, if the content is too large, MnS is precipitated in a large amount, causing deterioration of corrosion resistance. Therefore, it is desirable that the upper limit is about 0.01% by mass.
表１に示す化学組成のオーステナイト系ステンレス鋼を熱間圧延して熱延コイルを製造した。これらを表２の条件で焼鈍・脱スケール処理した。焼鈍条件としてはＬＮＧバーナーを用いた熱処理炉で、１１００℃に１分間処理した。脱スケール処理は、機械的脱スケール処理としてショットブラストを、酸洗処理として、１０％硝酸と２％ふっ酸の混酸を６０℃に６０秒浸漬処理した。剥離性評価は、○が両面均一剥離を、△は部分的な剥離を、×は全面スケール密着を示す。光沢評価は、○は光沢むらもなく均一美麗な場合を、×は光沢むらが発生した場合、△は光沢むらはないものの黒っぽくミクログルーブも深い場合を示している。この結果を表２に示す。これより、Ｓ含有率が０．００３質量％の場合には、焼鈍雰囲気を変更させても、スケールの部分的な剥離は見られるが、全面剥離は生じない。一方、Ｓ含有量が０．００５質量％および０．００９質量％の場合には、Ｏ2 が５％以上でかつＨ2 Ｏが２０％以下の条件では、いずれもスケールは全面均一剥離した。その他の条件では部分的にはスケールは剥離するが、全面には至らず、また、低Ｏ2 濃度では全面スケール密着となった。 Hot rolled coils were manufactured by hot rolling austenitic stainless steel having the chemical composition shown in Table 1. These were annealed and descaled under the conditions shown in Table 2. As annealing conditions, the heat treatment was performed at 1100 ° C. for 1 minute in a heat treatment furnace using an LNG burner. In descaling, shot blasting was performed as mechanical descaling, and mixed acid of 10% nitric acid and 2% hydrofluoric acid was immersed in 60 ° C. for 60 seconds as pickling. In the peelability evaluation, ○ indicates uniform peeling on both sides, Δ indicates partial peeling, and × indicates full-scale adhesion. In the gloss evaluation, ◯ indicates a case where the gloss is uniform and beautiful, x indicates a case where gloss unevenness occurs, and Δ indicates a case where there is no gloss unevenness but blackness and deep microgrooves. The results are shown in Table 2. From this, when S content is 0.003 mass%, even if it changes annealing atmosphere, although partial peeling of a scale is seen, peeling of the whole surface does not arise. On the other hand, when the S content was 0.005% by mass and 0.009% by mass, the scale was peeled uniformly over the entire surface under the conditions of O 2 of 5% or more and H 2 O of 20% or less. Under other conditions, the scale partially peeled off, but did not reach the entire surface, and the entire surface was in close contact with the low O 2 concentration.
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| JP2011528751A (en) * | 2008-03-21 | 2011-11-24 | アルセロールミタル−ステンレス・フランス | Method for producing austenitic stainless steel sheet having high mechanical properties and steel sheet thus obtained |
| JP2010162575A (en) * | 2009-01-15 | 2010-07-29 | Kobe Steel Ltd | Method of manufacturing solid wire for welding excellent in pickling property |
| JP2010184294A (en) * | 2009-01-15 | 2010-08-26 | Kobe Steel Ltd | Steel wire rod for solid wire showing excellent acid pickling property, and method of manufacturing the same |
| JP2012515843A (en) * | 2009-01-22 | 2012-07-12 | エスエムエス・ジーマーク・アクチエンゲゼルシャフト | Method and apparatus for removing scale by annealing stainless steel strip |
| WO2018011934A1 (en) * | 2016-07-14 | 2018-01-18 | 新日鐵住金株式会社 | Method for manufacturing cladded molded body and method for manufacturing heat-resistant gasket |
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