JP2006307314A - Method for manufacturing steel strip - Google Patents
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本発明は、表面外観に優れる鋼帯の製造方法に関する。 The present invention relates to a method for producing a steel strip excellent in surface appearance.
近年、鋼帯の製造には連続焼鈍が用いられている。例えば、高強度鋼帯を製造する場合、鋼帯を加熱焼鈍後高速冷却して製造される。高速冷却手法としては、水浸漬法（例えば特許文献１等参照）等が行われている。しかし、この手法で鋼帯を高速冷却すると、鋼帯表面に酸化物が形成され、外観品質が劣化する問題があり、また、冷却時の温度ムラによって鋼帯形状が劣化する等の問題がある。鋼帯形状劣化等の問題は、水噴射ノズルの構造を改善することである程度改善できる（例えば特許文献２〜４等参照）が、外観劣化を防止できる程度に酸化物の生成を抑制することは困難であった。
In recent years, continuous annealing has been used for the production of steel strips. For example, when manufacturing a high-strength steel strip, the steel strip is manufactured by rapid cooling after heating and annealing. As a high-speed cooling method, a water immersion method (see, for example, Patent Document 1) or the like is performed. However, when the steel strip is cooled at a high speed by this method, there is a problem that an oxide is formed on the surface of the steel strip and the appearance quality is deteriorated, and the shape of the steel strip is deteriorated due to temperature unevenness during cooling. . Problems such as steel strip shape deterioration can be improved to some extent by improving the structure of the water injection nozzle (see, for example,
近年、鋼帯の耐食性を向上させるために、焼鈍後の鋼帯に溶融亜鉛めっきを施した高強度溶融亜鉛めっき鋼板も製造されるようになってきた。表面に酸化物が生成した鋼帯に溶融亜鉛めっきを施すと不メッキ等が発生し、表面外観が低下する問題がある。 In recent years, in order to improve the corrosion resistance of steel strips, high-strength hot-dip galvanized steel plates in which hot-dip galvanized steel strips have been applied to the steel strips after annealing have been produced. When hot dip galvanizing is applied to a steel strip on which oxide is formed on the surface, there is a problem that non-plating or the like occurs and the surface appearance deteriorates.
そのため、冷却媒体の水への添加剤を検討することで、酸化物の生成を抑制する技術が開示されている。例えば、特許文献５には、水溶性有機酸と水溶性有機アミンからなる金属冷却剤が記載され、さらに、前記水溶性有機酸は炭素数３以上の水溶性ジカルボン酸であり、マロン酸、コハク酸、グルタール酸、アジピン酸、ピメリン酸等の飽和ジカルボン酸と、マレイン酸、イタコン酸等の不飽和ジカルボン酸と、リンゴ酸、酒石酸等のオキシカルボン酸とが好ましい例としてあげられている。
しかし、前述の特許文献５で開示される技術は、酸化物生成を抑制する作用が安定して発現されず、特に、鋼帯の冷却開始温度が高くなると、酸化物生成を抑制する作用が不十分となりやすい。そのため、冷却後に生成した酸化物を除去するための酸洗処理が行われる。また、冷却開始温度が高くなると冷却時の温度ムラによって鋼帯形状が悪化する等の問題もある。
However, the technique disclosed in
本発明の課題は、前記問題点を解決し、鋼帯冷却開始温度が高い場合であっても、酸化物生成の抑制作用が優れ、また冷却時の温度ムラによる鋼帯形状の劣化を防止できる鋼帯の製造方法を提供することである。 The object of the present invention is to solve the above-mentioned problems, and even when the steel strip cooling start temperature is high, it has an excellent effect of suppressing oxide formation, and can prevent deterioration of the steel strip shape due to temperature unevenness during cooling. It is to provide a method for manufacturing a steel strip.
上記課題を解決する本発明の要旨は次の通りである。 The gist of the present invention for solving the above problems is as follows.
第１発明は、加熱処理工程と、加熱処理後に冷却する冷却工程を含む鋼帯の製造方法であって、前記冷却工程は、アスコルビン酸化合物を含む液体を用いて鋼帯を冷却することを特徴とする鋼帯の製造方法である。 1st invention is a manufacturing method of the steel strip containing a heat treatment process and the cooling process cooled after heat processing, Comprising: The said cooling process cools a steel strip using the liquid containing an ascorbic acid compound, It is characterized by the above-mentioned. It is a manufacturing method of steel strip.
第２発明は、第１発明において、前記液体はさらに、オキシカルボン酸を含むことを特徴とする鋼帯の製造方法である。 A second invention is a method for producing a steel strip according to the first invention, wherein the liquid further contains an oxycarboxylic acid.
第３発明は、第１または第２発明において、前記液体中のアスコルビン酸化合物の含有量は、質量比で０．１％以上２％以下であることを特徴とする鋼帯の製造方法である。 A third invention is a method for producing a steel strip according to the first or second invention, wherein the content of the ascorbic acid compound in the liquid is 0.1% or more and 2% or less by mass ratio. .
第４発明は、第１〜第３発明において、前記液体中のオキシカルボン酸の含有量は、質量比で０．１％以上３％以下であることを特徴とする鋼帯の製造方法である。 4th invention is the manufacturing method of the steel strip characterized by the content of the oxycarboxylic acid in the said liquid in 1st-3rd invention being 0.1% or more and 3% or less by mass ratio. .
第５発明は、第１〜第４発明において、前記冷却工程は、冷却開始温度が５００℃以上８００℃以下であることを特徴とする鋼帯の製造方法である。 5th invention is the manufacturing method of the steel strip characterized by the cooling start temperature being 500 degreeC or more and 800 degrees C or less in the 1st-4th invention.
第６発明は、第１〜第５発明において、冷却工程の後に、溶融亜鉛めっきを行う溶融めっき工程を含むことを特徴とする鋼帯の製造方法である。 6th invention is the manufacturing method of the steel strip characterized by including the hot dipping process which performs hot dip galvanization after a cooling process in 1st-5th invention.
本発明によれば、鋼帯冷却開始温度が高温であっても、鋼帯表面を酸化させないで冷却することが可能である。本発明によれば、冷却後に酸洗を特に行わなくても表面外観にすぐれた鋼帯を得ることができる。また冷却時に鋼帯幅方向の温度ムラが小さくなるため、冷却による形状不良の劣化を防止できる。 According to the present invention, even if the steel strip cooling start temperature is high, it is possible to cool the steel strip without oxidizing it. According to the present invention, a steel strip having an excellent surface appearance can be obtained without particularly performing pickling after cooling. Moreover, since the temperature unevenness in the steel strip width direction is reduced during cooling, it is possible to prevent deterioration of shape defects due to cooling.
本発明者らは、酸化物の生成を抑制できる冷却方法について種々検討調査した結果、水冷の冷媒中（＝水）にアスコルビン酸化合物を含有させると、鋼帯冷却開始温度が高い場合であっても酸化物の生成を抑制する作用が優れ、また鋼帯形状を劣化させる問題点も解消できることを見出した。本発明はこの知見に基づくものである。 As a result of various investigations and investigations on cooling methods that can suppress the formation of oxides, the present inventors have found that when an ascorbic acid compound is contained in a water-cooled refrigerant (= water), the steel strip cooling start temperature is high. It has also been found that it has an excellent effect of suppressing the formation of oxides and can solve the problem of degrading the steel strip shape. The present invention is based on this finding.
本発明で用いられるアスコルビン酸化合物は、例えばアスコルビン酸、アスコルビン酸ナトリウム、アスコルビン酸カリウム、イソアスコルビン酸、イソアスコルビン酸ナトリウム、イソアスコルビン酸カリウムなどである。これらの１種以上を用いる。アスコルビン酸化合物は酸素との反応速度が非常に速いという性質を持つ。水浸漬法により鋼帯を冷却したときの鋼帯表面の酸化は、水中に侵入直後の非常に短い時間で進行すると考えられるが、アスコルビン酸化合物は、酸素との反応速度が非常に速いことから、冷媒にアスコルビン酸化合物を含有させることでこのような表面酸化を効果的に防止でき、また冷媒が蒸発しても酸化物生成が少なくなると考えられる。 Examples of the ascorbic acid compound used in the present invention include ascorbic acid, sodium ascorbate, potassium ascorbate, isoascorbic acid, sodium isoascorbate, and potassium isoascorbate. One or more of these are used. Ascorbic acid compounds have the property of a very fast reaction rate with oxygen. When the steel strip is cooled by the water immersion method, oxidation of the steel strip surface is considered to proceed in a very short time immediately after entering the water, but ascorbic acid compounds have a very fast reaction rate with oxygen. In addition, it is considered that such surface oxidation can be effectively prevented by containing an ascorbic acid compound in the refrigerant, and oxide generation is reduced even when the refrigerant evaporates.
鋼帯温度が３００℃以上になると鋼帯表面が酸化されやすくなる。鋼帯表面の酸化を抑制する作用は冷媒中に含まれるアスコルビン酸化合物の濃度でほぼ決定される。鋼帯表面酸化を抑制するのに必要なアスコルビン酸化合物の濃度は鋼帯冷却開始温度によって異なる。鋼帯冷却開始温度が６００℃未満の鋼帯に対しては、アスコルビン酸化合物を０．１％以上含有させることで鋼帯の表面酸化を抑制する作用が発現される。鋼帯冷却開始温度が６００℃以上では０．２％以上含有させることが必要である。実操業では、鋼帯表面状態のばらつき、その他の操業条件の変動があっても酸化物の生成を安定して抑制できるように、前記濃度＋０１％以上とすることが好ましい。 When the steel strip temperature is 300 ° C. or higher, the steel strip surface is easily oxidized. The action of suppressing the oxidation of the steel strip surface is substantially determined by the concentration of the ascorbic acid compound contained in the refrigerant. The concentration of the ascorbic acid compound necessary for suppressing steel strip surface oxidation varies depending on the steel strip cooling start temperature. For steel strips having a steel strip cooling start temperature of less than 600 ° C., an effect of suppressing surface oxidation of the steel strip is manifested by containing 0.1% or more of an ascorbic acid compound. If the steel strip cooling start temperature is 600 ° C. or higher, it is necessary to contain 0.2% or more. In actual operation, the concentration is preferably + 01% or more so that the formation of oxides can be stably suppressed even when there are variations in the steel strip surface state and other operating conditions.
鋼帯表面酸化を抑制する上で、アスコルビン酸化合物の濃度の上限は規定されないが、コスト面からは２％程度が好ましい。 In order to suppress the steel strip surface oxidation, the upper limit of the concentration of the ascorbic acid compound is not specified, but about 2% is preferable from the viewpoint of cost.
鋼帯表面に生成した酸化物量はレーザーによる反射率測定や、蛍光Ｘ線法などの物理分析、あるいは画像処理法などによって測定できる。したがって、前述の手法等によって鋼帯表面に生成した酸化物量を測定し、測定結果に基づいてアスコルビン酸化合物の濃度を目標酸化物量以下となる濃度に調整してもよい。 The amount of oxide generated on the surface of the steel strip can be measured by laser reflectivity measurement, physical analysis such as fluorescent X-ray method, or image processing method. Therefore, the amount of oxide generated on the steel strip surface by the above-described method or the like may be measured, and the concentration of the ascorbic acid compound may be adjusted to a concentration that is equal to or less than the target oxide amount based on the measurement result.
本発明では、アスコルビン酸化合物添加に加えて、冷媒である水に、さらにオキシカルボン酸を添加することができる。オキシカルボン酸は、例えばクエン酸、酒石酸、リンゴ酸、乳酸、グルコン酸などである。これらの１種以上を用いる。このオキシカルボン酸は、鋼素地の溶解を促進させる作用と、溶解した鉄イオンをキレート作用により可溶性錯体に変化させる作用を有するため、鋼帯表面の酸化物生成防止とともに、鉄イオンの鋼帯への再付着を防止する作用を持ち、また冷却能や酸化防止能力などの冷媒品質を一定に保つ効果に優れる。そのため、冷媒に、アスコルビン酸化合物とオキシカルボン酸とを複合添加することで、より安価に鋼帯表面の酸化物生成を抑制できる。 In the present invention, in addition to the addition of the ascorbic acid compound, oxycarboxylic acid can be further added to water as the refrigerant. Examples of the oxycarboxylic acid include citric acid, tartaric acid, malic acid, lactic acid, and gluconic acid. One or more of these are used. This oxycarboxylic acid has the action of promoting dissolution of the steel base and the action of changing dissolved iron ions into a soluble complex by chelating action. It has the effect of preventing the re-adhesion of the refrigerant, and is excellent in the effect of keeping the refrigerant quality constant such as the cooling ability and the antioxidant ability. Therefore, the composite production | generation of an ascorbic acid compound and oxycarboxylic acid to a refrigerant | coolant can suppress the oxide production | generation of the steel strip surface more cheaply.
アスコルビン酸化合物とオキシカルボン酸を複合添加する場合、オキシカルボン酸の冷媒中の濃度は０．１％以上が好ましい。鋼帯表面酸化を抑制する上で、オキシカルボン酸の濃度の上限は規定されないが、コスト面からは３％以下が好ましい。アスコルビン酸化合物とオキシカルボン酸を複合添加する場合、両者の混合比は鋼帯の冷却開始温度を考慮して決定することが好ましい。すなわち、鋼帯の冷却開始温度が低いと反応速度が小さいので、酸素との反応速度が速いアスコルビン酸化合物よりも、キレート作用があり、かつ比較的安価なオキシカルボン酸の配合比を高める方が液寿命や経済性の点で有利である。逆に鋼帯の冷却開始温度が高い場合、酸化防止の観点で、酸素との反応速度が速いアスコルビン酸化合物の混合比を高める方が有利であり、表面外観を重視する鋼帯の場合は、アスコルビン酸化合物の混合比を高めることが特に有効である。 When the ascorbic acid compound and oxycarboxylic acid are added in combination, the concentration of oxycarboxylic acid in the refrigerant is preferably 0.1% or more. In order to suppress the surface oxidation of the steel strip, the upper limit of the concentration of oxycarboxylic acid is not specified, but 3% or less is preferable from the viewpoint of cost. When the ascorbic acid compound and oxycarboxylic acid are added in combination, the mixing ratio of the two is preferably determined in consideration of the cooling start temperature of the steel strip. That is, since the reaction rate is small when the cooling start temperature of the steel strip is low, it is better to increase the compounding ratio of the oxycarboxylic acid that has a chelating action and is relatively inexpensive than the ascorbic acid compound that has a high reaction rate with oxygen. This is advantageous in terms of liquid life and economy. On the contrary, when the cooling start temperature of the steel strip is high, it is advantageous to increase the mixing ratio of the ascorbic acid compound that has a fast reaction rate with oxygen from the viewpoint of oxidation prevention. It is particularly effective to increase the mixing ratio of the ascorbic acid compound.
オキシカルボン酸とアスコルビン酸化合物の最適な混合比は、鋼帯の侵入板温（冷却開始温度）で異なる。すなわち、鋼帯の侵入板温が５００℃以下の低温ではオキシカルボン酸とアスコルビン酸化合物の混合比を８：２程度にする方が効果的である。これは鋼帯の侵入板温が低温では反応速度が小さいため、酸素との反応速度が速いアスコルビン酸化合物よりも、キレート作用があり、かつ比較的安価なオキシカルボン酸の配合比を高めた方が液寿命や経済性の点で有利であるためである。逆に鋼帯の侵入板温が７００℃以上の高温では、酸化防止の観点で、逆にオキシカルボン酸とアスコルビン酸化合物の混合比を２：８程度にした方が好適であり、表面外観を重視する場合は、特に重要となる。鋼帯の侵入板温が５００〜７００℃程度の中間の温度域では経済性と表面品質の観点から１：１程度が望ましい。また、オキシカルボン酸とアスコルビン酸化合物の混合比は鋼帯の使用用途により変化、すなわち酸化物生成量を低く抑える方が好ましい用途に使用される鋼帯に対しては、アスコルビン酸化合物の割合を高めても良い。 The optimum mixing ratio of oxycarboxylic acid and ascorbic acid compound differs depending on the intrusion plate temperature (cooling start temperature) of the steel strip. That is, it is more effective to set the mixing ratio of the oxycarboxylic acid and the ascorbic acid compound to about 8: 2 at a low temperature where the intrusion plate temperature of the steel strip is 500 ° C. or less. This is because the reaction rate is low when the intrusion plate temperature of the steel strip is low, and the compounding ratio of oxycarboxylic acid, which has a chelating action and is relatively inexpensive, is higher than the ascorbic acid compound, which has a high reaction rate with oxygen. This is because it is advantageous in terms of liquid life and economy. On the contrary, when the intrusion plate temperature of the steel strip is higher than 700 ° C., it is preferable to set the mixing ratio of oxycarboxylic acid and ascorbic acid compound to about 2: 8 from the viewpoint of preventing oxidation. This is especially important when emphasizing. In the intermediate temperature range where the intrusion plate temperature of the steel strip is about 500 to 700 ° C., about 1: 1 is desirable from the viewpoint of economy and surface quality. In addition, the mixing ratio of oxycarboxylic acid and ascorbic acid compound varies depending on the intended use of the steel strip, that is, for steel strips used in applications where it is preferable to keep the oxide production low, the ratio of the ascorbic acid compound is May be raised.
鋼帯冷却時の温度ムラを防止するために必要なオキシカルボン酸濃度、アスコルビン酸化合物濃度は、鋼帯表面の酸化防止のために必要なオキシカルボン酸濃度、アスコルビン酸化合物濃度よりも少ない（後記実施例の図７〜図１１参照）。このことから、鋼帯表面の酸化が抑制される条件であれば、冷却時の温度ムラが防止されることがわかった。アスコルビン酸化合物、オキシカルボン酸の添加で鋼帯冷却時の温度ムラが防止される詳細な理由は不明であるが、冷却の際に酸化物が生成しにくいことや、それによって濡れ性が向上／安定化すること、沸点が上昇しその分蒸気膜が生成しにくくなることなどが考えられる。なお、この温度ムラは、熱応力を発生させるため、鋼帯の反りを誘発し、形状不良を発生させ、さらには材質の不均一性の原因ともなるため、極力抑制させる必要がある。 The oxycarboxylic acid concentration and ascorbic acid compound concentration required to prevent temperature unevenness during cooling of the steel strip are less than the oxycarboxylic acid concentration and ascorbic acid compound concentration required to prevent oxidation on the steel strip surface (see below). (Refer FIG. 7-11 of an Example). From this, it was found that temperature unevenness during cooling can be prevented under the condition that the oxidation of the steel strip surface is suppressed. Although the detailed reason for preventing temperature unevenness during cooling of the steel strip by the addition of ascorbic acid compound and oxycarboxylic acid is unknown, it is difficult to form oxides during cooling, and this improves wettability / Stabilization, the boiling point increases, and the vapor film is less likely to be generated. Since this temperature unevenness generates thermal stress, it induces warpage of the steel strip, causes a shape defect, and further causes non-uniformity of the material, so it needs to be suppressed as much as possible.
本発明において、加熱処理工程は、冷間圧延鋼帯焼鈍炉（連続焼鈍炉）の再結晶焼鈍を行う焼鈍工程であってもよく、また焼鈍炉を備えた連続溶融亜鉛めっき装置の加熱焼鈍工程であってもよい。前記焼鈍炉は、加熱焼鈍工程の後方に過時効処理工程を有していてもよい。 In the present invention, the heat treatment step may be an annealing step for performing recrystallization annealing of a cold-rolled steel strip annealing furnace (continuous annealing furnace), or a heat annealing step of a continuous hot-dip galvanizing apparatus equipped with an annealing furnace. It may be. The annealing furnace may have an overaging treatment step behind the heat annealing step.
本発明において、冷却工程は、再結晶焼鈍後の冷却工程であってもよく、過時効処理後の冷却工程であってもよい。冷却工程の冷却手法は限定されない。水浸漬法、水噴射法、気水噴霧法等で使用される冷媒の水に、アスコルビン酸化合物、またはさらにオキシカルボン酸を含有させることで、冷却時に発生する鋼帯表面の酸化物生成を抑制する効果が奏される。また、酸化物生成が抑制される結果、鋼帯幅方向で冷却速度の変動が低減されることで冷却工程での形状悪化を防止できる。 In the present invention, the cooling step may be a cooling step after recrystallization annealing or a cooling step after overaging treatment. The cooling method of the cooling process is not limited. By containing ascorbic acid compound or further oxycarboxylic acid in the coolant water used in water immersion method, water jetting method, air-water spraying method, etc., the generation of oxide on the surface of the steel strip generated during cooling is suppressed. The effect to do. Moreover, as a result of suppressing oxide production | generation, the deterioration of the shape in a cooling process can be prevented by the fluctuation | variation of a cooling rate being reduced in a steel strip width direction.
冷却工程の後で溶融亜鉛めっきを行う場合、冷却工程は、めっき浴温より低い温度まで冷却し、その後加熱装置で鋼帯をめっき浴に浸漬させるのに適した温度、例えば４５０〜５００℃程度の温度まで再加熱した後めっき浴に浸漬してもよい。また、冷却工程は、冷却終了温度を、鋼帯をめっき浴に浸漬させるのに適した温度まで冷却してめっき浴に浸漬させてもよい。溶融亜鉛めっき後、必要に応じて合金化処理を行ってもよい。 When hot dip galvanization is performed after the cooling step, the cooling step is a temperature suitable for cooling to a temperature lower than the plating bath temperature and then immersing the steel strip in the plating bath with a heating device, for example, about 450 to 500 ° C. It may be immersed in a plating bath after being reheated to the above temperature. In the cooling step, the cooling end temperature may be cooled to a temperature suitable for immersing the steel strip in the plating bath and immersed in the plating bath. After hot dip galvanization, an alloying treatment may be performed as necessary.
前述のアスコルビン酸化合物、オキシカルボン酸は、そのほとんどが食品添加を認められているなど安全性が極めて高く、生分解性に優れているため、特別な排水処理設備が不要であり、また酸洗やリンス工程などの後処理が不要であるため、設備コスト、ランニングコストの点からも有利である。 Most of the aforementioned ascorbic acid compounds and oxycarboxylic acids are extremely safe and have excellent biodegradability, including the addition of food, so no special wastewater treatment equipment is required. Since post-processing such as a rinsing process or a rinsing process is unnecessary, it is advantageous in terms of equipment cost and running cost.
以上述べたごとく、本発明によれば、冷却時の鋼帯表面酸化の問題や冷却温度ムラに起因する鋼帯形状不良を防止して、急速冷却可能となる。 As described above, according to the present invention, it is possible to prevent the steel strip surface oxidation problem during cooling and the steel strip shape defect due to the uneven cooling temperature, thereby enabling rapid cooling.
前述の方法で製造された鋼帯に溶融亜鉛めっきを施すと、表面酸化物が多いことに起因して発生する不メッキ等を防止して表面外観に優れる溶融亜鉛めっき鋼帯を得ることができる。
また冷媒に含有されるアスコルビン酸化合物、オキシカルボン酸を処理するための特別の排水処理設備等が不要であり、また、特段の後処理も不要であるため、設備費やランニングコストを抑制することが可能である。
When hot dip galvanizing is applied to the steel strip manufactured by the above-described method, a hot dip galvanized steel strip excellent in surface appearance can be obtained by preventing unplating and the like caused by a large amount of surface oxide. .
In addition, special waste water treatment equipment for treating ascorbic acid compounds and oxycarboxylic acids contained in the refrigerant is not required, and no special post-treatment is required, thereby reducing equipment costs and running costs. Is possible.
窒素９５％＋水素５％の雰囲気（露点：−４０℃）中で、８５０℃で１分加熱した鋼帯に対して、種々のオキシカルボン酸、アスコルビン酸化合物を添加した冷媒（水）を用いて浸漬法による冷却試験（焼入れ試験）を実施した。使用した鋼帯サンプル（板厚１．２ｍｍ×長さ３００ｍｍ×幅１５０ｍｍ）の成分組成を表１に示す。
Refrigerant (water) with various oxycarboxylic acids and ascorbic acid compounds added to steel strip heated at 850 ° C for 1 minute in an atmosphere of 95% nitrogen + 5% hydrogen (dew point: -40 ° C) Then, a cooling test (quenching test) by an immersion method was performed. Table 1 shows the component composition of the steel strip sample used (plate thickness 1.2 mm ×
温度はＣＡ熱電対で測定し、焼入れ開始温度（冷却開始温度）は４００℃〜８００℃とし、冷媒温度（常温程度）まで冷却した。その際、３００℃まで冷却されたときの各点の時間差で面内の冷却ムラを評価した（測定箇所は図１参照。３０ｍｍ間隔で５点測定）。冷却後の酸化物厚さの評価をＧＤＳ（グロー放電発光分析）で行った。各条件における酸化量（酸化物量）を図２〜図６に示す。冷却ムラの評価結果を図７〜図１１に示す。 The temperature was measured with a CA thermocouple, the quenching start temperature (cooling start temperature) was set to 400 ° C. to 800 ° C., and the coolant was cooled to the refrigerant temperature (about room temperature). At that time, the in-plane cooling unevenness was evaluated by the time difference of each point when it was cooled to 300 ° C. (refer to FIG. 1 for measurement points. Measurement at 5 points at intervals of 30 mm). The oxide thickness after cooling was evaluated by GDS (glow discharge emission analysis). The oxidation amount (oxide amount) under each condition is shown in FIGS. The evaluation results of the uneven cooling are shown in FIGS.
この結果から、アスコルビン酸化合物は高温焼入れでもその酸化防止効果は非常に大きいこと、オキシカルボン酸は、高温焼入れでは酸化防止効果は小さいが、低温では十分大きいことが分かる。酸化量は鋼帯用途にもよるが１００ｍｇ／ｍ２以上になると外観上問題になる場合が多い。この酸化量を基準に考えるとアスコルビン酸化合物濃度は６００℃以上の高温焼入れでは０．２％以上、６００℃未満の低温焼入れでは０．１％以上で酸化物の生成を抑制する効果が十分であることが分かる。ただし、実際の操業では焼入れ開始温度が種々あるのが普通であるので、このような場合は、アスコルビン酸化合物濃度は、前記濃度＋０．１％以上の濃度に調整することが好ましい。 From this result, it can be seen that the ascorbic acid compound has a very high antioxidant effect even at high temperature quenching, and oxycarboxylic acid has a small antioxidant effect at high temperature quenching but is sufficiently large at low temperature. Although the oxidation amount depends on the steel strip application, when it is 100 mg / m 2 or more, it often causes a problem in appearance. Considering this amount of oxidation as a standard, the concentration of ascorbic acid compound is 0.2% or higher for high-temperature quenching at 600 ° C. or higher, and 0.1% or higher for low-temperature quenching at less than 600 ° C., which is sufficient to suppress the formation of oxides. I understand that there is. However, since there are usually various quenching start temperatures in actual operation, in such a case, it is preferable to adjust the concentration of the ascorbic acid compound to the concentration + 0.1% or more.
オキシカルボン酸単独でも酸化量生成を抑制する作用がある。しかし、その作用はアスコルビン酸化合物に比べて劣るため冷却開始温度が５００℃超になると、鋼帯酸化物生成量を安定して１００ｍｇ／ｍ２以下にできない。 Even oxycarboxylic acid alone has the effect of suppressing oxidation amount generation. However, since its action is inferior to that of an ascorbic acid compound, when the cooling start temperature exceeds 500 ° C., the production amount of steel strip oxide cannot be stably reduced to 100 mg / m 2 or less.
アスコルビン酸化合物とオキシカルボン酸を複合添加したものは、アスコルビン酸化合物単独添加の場合に比べて酸化量が僅かに増加するだけで低温域ではほぼ同程度の酸化量である。オキシカルボン酸はキレート効果をもつため、鋼帯面へのスラジ等の再付着を防止する効果を持つ。その効果はオキシカルボン酸濃度が高いほど長時間保持できる。冷媒中に、アスコルビン酸化合物とオキシカルボン酸を複合添加することで、より効果的に酸化物生成を抑制できる。 A compound in which an ascorbic acid compound and an oxycarboxylic acid are added in combination has an oxidation amount that is substantially the same in a low temperature range, with only a slight increase in the amount of oxidation compared to the case of adding an ascorbic acid compound alone. Since oxycarboxylic acid has a chelating effect, it has the effect of preventing redeposition of sludge and the like on the steel strip surface. The effect can be maintained for a longer time as the oxycarboxylic acid concentration is higher. Oxide formation can be more effectively suppressed by adding a complex of an ascorbic acid compound and oxycarboxylic acid to the refrigerant.
なお、いずれの例でも、水のみの冷却の場合に比べて、鋼帯幅方向の冷却ムラは少なく、問題のないレベルであった。 In any of the examples, the cooling unevenness in the width direction of the steel strip was small as compared with the case of cooling only with water, and the level was satisfactory.
供試材として、実施例１で作製した冷却後の鋼帯サンプルのうち、冷却水に、イソアスコルビン酸、クエン酸及びイソアスコルビン酸、クエン酸を各々０．５％添加した冷却水を用いたもの、及び、実施例１と同様の成分組成を有する鋼板をイソアスコルビン酸とクエン酸を各々０．３％添加した冷却水を用いて実施例１と同様の方法で浸漬法による冷却試験（焼入れ試験）を実施して作製した冷却後の鋼帯サンプルを準備した。 As the test material, among the steel strip samples after cooling produced in Example 1, cooling water in which 0.5% each of isoascorbic acid, citric acid, isoascorbic acid, and citric acid was added to the cooling water was used. And a steel plate having the same composition as in Example 1 using a cooling water to which 0.3% each of isoascorbic acid and citric acid were added, and a cooling test by quenching (quenching) in the same manner as in Example 1. A steel strip sample after cooling prepared by performing (Test) was prepared.
溶融亜鉛めっき試験装置を用いて、準備した供試材を、窒素９５％＋水素５％雰囲気（露点：−４０℃）中で５５０℃まで加熱後、浴温：４６０℃、浴中Ａｌ濃度：０．１３質量％の亜鉛浴に浸漬して、片面あたり亜鉛めっき量：４０ｇ／ｍ２の溶融亜鉛めっきを施して溶融亜鉛めっき鋼板を作製した。 The prepared test material was heated to 550 ° C. in a 95% nitrogen + 5% hydrogen atmosphere (dew point: −40 ° C.) using a hot dip galvanizing test apparatus, bath temperature: 460 ° C., Al concentration in the bath: It was immersed in a 0.13% by mass zinc bath and subjected to hot dip galvanization with a galvanization amount of 40 g / m 2 per side to produce a hot dip galvanized steel sheet.
作製した溶融亜鉛めっき鋼板の外観を目視観察し、不メッキの有無およびその程度に基いてめっき性の評価を行った。評点は１〜５で、評点が高いほど、めっき性が良好であることを示す。実用面からの合格レベルは評点４点以上である。めっき性の評価結果を図１２に示す。 The appearance of the produced hot-dip galvanized steel sheet was visually observed, and the plating property was evaluated based on the presence or absence and the degree of non-plating. The score is 1 to 5, and the higher the score, the better the plating property. The practically acceptable level is 4 or more. The evaluation result of the plating property is shown in FIG.
図１２によると、めっき性は、実施例１に示した酸化膜の生成量とほぼ同じような傾向、すなわち、アスコルビン酸化合物を添加した冷却水を用いた場合はオキシカルボン酸を添加した冷却水を用いた場合よりもめっき性に優れ、アスコルビン酸化合物とオキシカルボン酸を複合添加した冷却水を用いたものは、めっき性がより優れることがわかる。ただし、アスコルビン酸化合物を添加した冷却水を用いたもの、及びオキシカルボン酸を添加した冷却水を用いたものでは、焼入れ開始温度は６００℃がもっともめっき性が良好であった。これは、次の理由によると考えられる。 According to FIG. 12, the plating property tends to be almost the same as the amount of the oxide film shown in Example 1, that is, when the cooling water to which the ascorbic acid compound is added is used, the cooling water to which the oxycarboxylic acid is added. It can be seen that the plating property is superior to that of the case of using the cooling water, and that using the cooling water to which the ascorbic acid compound and the oxycarboxylic acid are added in combination is more excellent in the plating property. However, in the case of using the cooling water to which the ascorbic acid compound was added and the case of using the cooling water to which the oxycarboxylic acid was added, the quenching start temperature was 600 ° C., and the plating property was the best. This is considered to be due to the following reason.
不メッキの原因には、（１）鉄の酸化膜の過多が原因で発生するものと、（２）鋼中のＳｉ、Ｍｎ等が鋼板表面に濃化して、鋼板表面にＳｉ、Ｍｎ等の酸化物が生成し、これによって不メッキが発生するもの、とがあり、（２）のＳｉ、Ｍｎ等の表面濃化は焼鈍中に起こる現象で、高Ｓｉ、高Ｍｎ鋼であるほど顕著に発生する。高温焼入れの場合、水冷却時に鉄の酸化膜が多く生成し、そのために不メッキが発生しやすくなる。一方、低温焼入れの場合、水冷却時に鉄の酸化膜の生成量は少ないが、冷却液の還元性が低いため、焼鈍中に生成しているＳｉ、Ｍｎ等の酸化物を除去できないため、不メッキが発生する。 Causes of non-plating are (1) those caused by excessive iron oxide film, and (2) Si, Mn, etc. in the steel are concentrated on the steel plate surface, and Si, Mn, etc. are concentrated on the steel plate surface. Oxide is generated, which causes non-plating. (2) Surface enrichment of Si, Mn, etc. is a phenomenon that occurs during annealing. The higher the Si, the higher the Mn steel, the more pronounced it is. appear. In the case of high-temperature quenching, a large amount of iron oxide film is generated during water cooling, and thus non-plating is likely to occur. On the other hand, in the case of low-temperature quenching, the amount of iron oxide film formed during water cooling is small, but the reducibility of the cooling liquid is low, so that oxides such as Si and Mn generated during annealing cannot be removed. Plating occurs.
以上の結果から、溶融亜鉛めっきを行う場合は、アスコルビン酸化合物の濃度は０．３％以上が好ましく、０．５％以上がより好ましい。また焼入れ開始温度は６００〜７００℃程度が最適であると考えられる。 From the above results, when performing hot dip galvanization, the concentration of the ascorbic acid compound is preferably 0.3% or more, and more preferably 0.5% or more. Further, it is considered that the quenching start temperature is optimally about 600 to 700 ° C.
表１の成分組成で厚さ１．２ｍｍ×幅１０００ｍｍの冷間圧延鋼帯を、連続焼鈍ライン（ＣＡＬ）に装入して、窒素９５％＋水素５％の雰囲気（露点：−４０℃）中で、８５０℃で１分加熱焼鈍後、冷媒（水）中に添加されるイソアスコルビン酸、クエン酸濃度を種々変えた冷却設備（冷却槽）に浸漬冷却し、冷却後の鋼帯の酸化膜厚さ及び反り量を評価した。冷却開始時の鋼帯温度は多重反射型放射温度計で測定し、焼入れ開始温度は４００℃〜８００℃とした。 A cold rolled steel strip having a thickness of 1.2 mm and a width of 1000 mm with the composition shown in Table 1 was charged into a continuous annealing line (CAL), and an atmosphere of 95% nitrogen + 5% hydrogen (dew point: −40 ° C.) Inside, after annealing at 850 ° C. for 1 minute, the steel strip is cooled by immersion in a cooling facility (cooling tank) with various concentrations of isoascorbic acid and citric acid added to the refrigerant (water). The film thickness and warpage amount were evaluated. The steel strip temperature at the start of cooling was measured with a multiple reflection type radiation thermometer, and the quenching start temperature was set to 400 ° C to 800 ° C.
これまでのラボ試験結果から、冷却後の鋼帯外観と酸化膜厚は非常に良い相関があることが分かっているので、酸化膜厚さの評価は、浸漬冷却後の供試鋼帯の外観を目視観察して評価した。具体的には、予め準備した酸化膜厚が既知で酸化膜厚の異なる鋼帯と外観を比較して供試鋼板の酸化膜厚を評価し、酸化膜厚２００ｍｇ／ｍ２以上は×、１００ｍｇ／ｍ２以上２００ｍｇ／ｍ２未満は△、５０ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満は○、５０ｍｇ／ｍ２以下は◎とした。 From the laboratory test results so far, it is known that the steel strip appearance after cooling and the oxide film thickness have a very good correlation, so the evaluation of the oxide film thickness is the appearance of the test steel strip after immersion cooling. Was visually observed and evaluated. Specifically, the oxide film thickness of the test steel sheet is evaluated by comparing the appearance with a steel strip having a known oxide film thickness that is prepared in advance and having a different oxide film thickness, and the oxide film thickness of 200 mg / m 2 or more is x, 100 mg. / M 2 or more and less than 200 mg / m 2 is indicated by Δ, 50 mg / m 2 or more and less than 100 mg / m 2 is indicated by ◯, and 50 mg / m 2 or less is indicated by ◎.
また、反り測定は、冷却試験後の鋼帯をそれぞれ１ｍ切り出して、その板の凹凸をレーザー変位計で測定し、反り量に換算し求めた。 In addition, the warp measurement was performed by cutting 1 m of each steel strip after the cooling test, measuring the unevenness of the plate with a laser displacement meter, and converting to a warp amount.
調査結果を表２に記載する。 The survey results are listed in Table 2.
焼き入れ開始温度が６００℃以上の高温焼入れでは、イソアスコルビン酸濃度が０．２％以上で酸化量が１００ｍｇ／ｍ２未満であり、外観上問題となる酸化物の生成を抑制するのに必要な十分な効果が得られている。これに対してクエン酸を添加した試験Ｎｏ．２〜５は、イソアスコルビン酸を添加した試験Ｎｏ．６〜１０に比べて酸化物量が多く、焼き入れ開始温度が６００℃超では酸化量が１００ｍｇ／ｍ２未満のものが安定して得られていない。焼き入れ開始温度が６００℃未満の低温焼入れでも、イソアスコルビン濃度が０．１％以上でクエン酸単独添加の場合に比べて酸化物の生成を抑制する効果が十分に認められる。 In high-temperature quenching where the quenching start temperature is 600 ° C. or higher, the isoascorbic acid concentration is 0.2% or more and the oxidation amount is less than 100 mg / m 2, which is necessary to suppress the formation of oxides that are problematic in appearance. A sufficient effect is obtained. On the other hand, test no. Nos. 2 to 5 are test Nos. To which isoascorbic acid was added. Compared with 6 to 10, the amount of oxide is large, and when the quenching start temperature exceeds 600 ° C., the amount of oxidation less than 100 mg / m 2 is not stably obtained. Even at a low temperature quenching at a quenching start temperature of less than 600 ° C., the effect of suppressing the formation of oxides is sufficiently recognized as compared with the case where isoascorbine concentration is 0.1% or more and citric acid alone is added.
イソアスコルビン酸とクエン酸を複合添加した試験Ｎｏ．１１は、イソアスコルビン酸を単独添加した試験Ｎｏ．９とほぼ同程度の酸化量である。クエン酸のキレート効果によって鋼帯面へのスラジ等の再付着を防止する効果を持つので、イソアスコルビン酸化合物とクエン酸を複合添加することで、より効果的に酸化物生成を抑制できるようになる。 Test No. in which isoascorbic acid and citric acid were added in combination. No. 11 is a test No. 1 with isoascorbic acid added alone. The amount of oxidation is almost the same as 9. The chelate effect of citric acid has the effect of preventing redeposition of sludge and the like on the steel strip surface. By adding a combination of isoascorbic acid compound and citric acid, the generation of oxide can be suppressed more effectively. Become.
冷媒中に、イソアスコルビン酸及びクエン酸の少なくとも一方を添加した試験Ｎｏ．２〜１１は、これらを添加してない試験Ｎｏ．１に比べて反り発生量が顕著に少なく、反り発生を防止する効果が優れている。 Test No. 1 in which at least one of isoascorbic acid and citric acid was added to the refrigerant. Nos. 2 to 11 are test Nos. In which these were not added. Compared with 1, the amount of warpage is remarkably small, and the effect of preventing warpage is excellent.
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Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4894174B2 (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS52138013A (en) * | 1976-05-14 | 1977-11-17 | Nippon Kokan Kk <Nkk> | Continuous annealing equipment |
| JPS52156710A (en) * | 1976-06-23 | 1977-12-27 | Centre Rech Metallurgique | Continuous process for heat treatment of rolled sheet steel |
-
2005
- 2005-06-17 JP JP2005177165A patent/JP4894174B2/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS52138013A (en) * | 1976-05-14 | 1977-11-17 | Nippon Kokan Kk <Nkk> | Continuous annealing equipment |
| JPS52156710A (en) * | 1976-06-23 | 1977-12-27 | Centre Rech Metallurgique | Continuous process for heat treatment of rolled sheet steel |
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| Publication number | Publication date |
|---|---|
| JP4894174B2 (en) | 2012-03-14 |
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