JP6439654B2 - Method for producing hot-dip galvanized steel sheet - Google Patents

Method for producing hot-dip galvanized steel sheet

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JP6439654B2
JP6439654B2 JP2015211121A JP2015211121A JP6439654B2 JP 6439654 B2 JP6439654 B2 JP 6439654B2 JP 2015211121 A JP2015211121 A JP 2015211121A JP 2015211121 A JP2015211121 A JP 2015211121A JP 6439654 B2 JP6439654 B2 JP 6439654B2
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zone
gas
soaking zone
steel strip
dew point
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JP2017082278A (en
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玄太郎 武田
玄太郎 武田
高橋　秀行
秀行 高橋
洋一 牧水
洋一 牧水
鈴木　克一
克一 鈴木
善正 姫井
善正 姫井
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JFE Steel Corp
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JFE Steel Corp
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Priority to JP2015211121A priority Critical patent/JP6439654B2/en
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Priority to PCT/JP2016/003631 priority patent/WO2017072989A1/en
Priority to EP16859230.1A priority patent/EP3369836B1/en
Priority to MX2018005073A priority patent/MX2018005073A/en
Priority to KR1020187013015A priority patent/KR102072560B1/en
Priority to CN201680060387.7A priority patent/CN108138297B/en
Priority to US15/753,260 priority patent/US20180237896A1/en
Publication of JP2017082278A publication Critical patent/JP2017082278A/en
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Publication of JP6439654B2 publication Critical patent/JP6439654B2/en
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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Description

本発明は、加熱帯、均熱帯及び冷却帯がこの順に並置された焼鈍炉と、前記冷却帯に隣接した溶融亜鉛めっき設備と、を有する連続溶融亜鉛めっき装置を用いた溶融亜鉛めっき鋼板の製造方法に関する。   The present invention provides a hot-dip galvanized steel sheet using a continuous hot-dip galvanizing apparatus having an annealing furnace in which a heating zone, a soaking zone and a cooling zone are juxtaposed in this order, and a hot-dip galvanizing facility adjacent to the cooling zone Regarding the method.

近年、自動車、家電、建材等の分野において、構造物の軽量化等に寄与する高張力鋼板（ハイテン鋼板）の需要が高まっている。ハイテン鋼材としては、例えば、鋼中にＳｉを含有することにより穴広げ性の良好な鋼板や、ＳｉやＡｌを含有することにより残留γが形成しやすく延性の良好な鋼板が製造できることがわかっている。   In recent years, in the fields of automobiles, home appliances, building materials, etc., there is an increasing demand for high-tensile steel plates (high-tensile steel plates) that contribute to weight reduction of structures. As a high-tensile steel material, for example, it has been found that a steel plate with good hole expansibility by containing Si in the steel, and a steel plate with good ductility can be produced by easily containing residual γ by containing Si or Al. Yes.

しかし、Ｓｉを多量に（特に０．２質量％以上）含有する高張力鋼板を母材として合金化溶融亜鉛めっき鋼板を製造する場合、以下の問題がある。合金化溶融亜鉛めっき鋼板は、還元雰囲気又は非酸化性雰囲気中で６００〜９００℃程度の温度で母材の鋼板を加熱焼鈍した後に、該鋼板に溶融亜鉛めっき処理を行い、さらに亜鉛めっきを加熱合金化することによって、製造される。   However, when an alloyed hot-dip galvanized steel sheet is produced using a high-tensile steel sheet containing a large amount of Si (particularly 0.2% by mass or more) as a base material, there are the following problems. An alloyed hot-dip galvanized steel sheet is obtained by subjecting a base steel sheet to heat annealing at a temperature of about 600 to 900 ° C. in a reducing atmosphere or a non-oxidizing atmosphere, and then subjecting the steel sheet to hot-dip galvanization and further heating the galvanizing. Manufactured by alloying.

ここで、鋼中のＳｉは易酸化性元素であり、一般的に用いられる還元雰囲気又は非酸化性雰囲気中でも選択酸化されて、鋼板の表面に濃化し、酸化物を形成する。この酸化物は、めっき処理時の溶融亜鉛との濡れ性を低下させて、不めっきを生じさせる。そのため、鋼中Ｓｉ濃度の増加と共に、濡れ性が急激に低下して不めっきが多発する。また、不めっきに至らなかった場合でも、めっき密着性に劣るという問題がある。さらに、鋼中のＳｉが選択酸化されて鋼板の表面に濃化すると、溶融亜鉛めっき後の合金化過程において著しい合金化遅延が生じ、生産性を著しく阻害するという問題もある。   Here, Si in steel is an easily oxidizable element, and is selectively oxidized in a generally used reducing atmosphere or non-oxidizing atmosphere to concentrate on the surface of the steel sheet to form an oxide. This oxide reduces wettability with molten zinc during the plating process and causes non-plating. Therefore, as the Si concentration in the steel increases, the wettability decreases sharply and non-plating occurs frequently. In addition, even when non-plating does not occur, there is a problem that the plating adhesion is poor. Further, when Si in the steel is selectively oxidized and concentrated on the surface of the steel sheet, there is a problem that a remarkable alloying delay occurs in the alloying process after hot dip galvanizing, and the productivity is remarkably hindered.

このような問題に対して、例えば、特許文献１には、直火型加熱炉（ＤＦＦ）を用いて、鋼板の表面を一旦酸化させた後、還元雰囲気下で鋼板を焼鈍することで、Ｓｉを内部酸化させ、鋼板の表面にＳｉが濃化するのを抑制し、溶融亜鉛めっきの濡れ性および密着性を向上させる方法が記載されている。加熱後の還元焼鈍については常法（露点−３０〜−４０℃）でよいと記載されている。   For such a problem, for example, Patent Document 1 discloses that by directly oxidizing the surface of the steel sheet using a direct-fired heating furnace (DFF), the steel sheet is annealed in a reducing atmosphere, thereby obtaining Si. Has been described, which suppresses the concentration of Si on the surface of the steel sheet and improves the wettability and adhesion of hot dip galvanizing. It is described that reduction annealing after heating may be performed by a conventional method (dew point of −30 to −40 ° C.).

特許文献２には、順に加熱帯前段、加熱帯後段、保熱帯及び冷却帯を有する焼鈍炉と溶融めっき浴とを用いた連続焼鈍溶融めっき方法において、鋼板温度が少なくとも３００℃以上の領域の鋼板の加熱または保熱を間接加熱とし、各帯の炉内雰囲気を水素１〜１０体積％、残部が窒素及び不可避的不純物よりなる雰囲気とし、前記加熱帯前段で加熱中の鋼板到達温度を５５０℃以上７５０℃以下とし、かつ、露点を−２５℃未満とし、これに続く前記加熱帯後段及び前記保熱帯の露点を−３０℃以上０℃以下とし、前記冷却帯の露点を−２５℃未満とする条件で焼鈍を行うことにより、Ｓｉを内部酸化させ、鋼板の表面にＳｉが濃化するのを抑制する技術が記載されている。また、加熱帯後段及び／又は保熱帯に、窒素と水素の混合ガスを加湿して導入することも記載されている。   Patent Document 2 discloses a steel plate in a region where the steel plate temperature is at least 300 ° C. in a continuous annealing hot dipping method using an annealing furnace and a hot dipping bath having a heating zone first stage, a heating zone latter stage, a heat retention zone, and a cooling zone in this order. The in-furnace atmosphere of each zone is 1 to 10% by volume of hydrogen, the balance is nitrogen and inevitable impurities, and the temperature reached by the steel sheet during heating in the preceding stage of the heating zone is 550 ° C. More than 750 ° C., and dew point is less than −25 ° C., and the subsequent dew point of the heating zone and the retentive zone is −30 ° C. to 0 ° C., and the dew point of the cooling zone is less than −25 ° C. The technique which suppresses that Si is internally oxidized by performing annealing on the conditions to make it concentrate on the surface of a steel plate. In addition, it is also described that a mixed gas of nitrogen and hydrogen is introduced after humidification into the latter stage of the heating zone and / or the tropical zone.

特許文献３には、炉内ガスの露点を測定しながら、その測定値に応じて、炉内ガスの供給及び排出の位置を変化させることによって、還元炉内ガスの露点を−３０℃超０℃以下の範囲内になるように制御して、鋼板の表面にＳｉが濃化するのを抑制する技術が記載されている。加熱炉についてはＤＦＦ（直火加熱炉）、ＮＯＦ（無酸化炉）、ラジアントチューブタイプのいずれでもよいが、ラジアントチューブタイプで顕著に発明効果が発現できるので好ましいとの記載がある。   In Patent Document 3, while measuring the dew point of the in-furnace gas, the position of the supply and discharge of the in-furnace gas is changed according to the measured value, so that the dew point of the in-reduction furnace gas exceeds 0 to -30 ° C. A technique is described in which Si is concentrated on the surface of a steel sheet by controlling the temperature to be within a range of ° C or less. The heating furnace may be any of DFF (direct flame heating furnace), NOF (non-oxidation furnace), and radiant tube type, but there is a description that it is preferable because the invention effect can be remarkably exhibited in the radiant tube type.

特開２０１０−２０２９５９号公報JP 2010-202959 A ＷＯ２００７／０４３２７３号公報WO2007 / 043273 特開２００９−２０９３９７号公報JP 2009-209397 A

しかし、特許文献１に記載の方法では、還元後のめっき密着性は良好であるものの、Ｓｉの内部酸化量が不足しやすく、鋼中のＳｉの影響で合金化温度が通常よりも３０〜５０℃高温になってしまい、その結果鋼板の引張強度が低下する問題があった。十分な内部酸化量を確保するために酸化量を増加させると、焼鈍炉内のロールに酸化スケールが付着し鋼板に押し疵、いわゆるピックアップ欠陥が発生する。このため、酸化量を単に増加させる手段は取れない。   However, in the method described in Patent Document 1, although the plating adhesion after reduction is good, the amount of internal oxidation of Si tends to be insufficient, and the alloying temperature is 30 to 50 higher than usual due to the influence of Si in steel. As a result, there was a problem that the tensile strength of the steel sheet was lowered. If the amount of oxidation is increased in order to ensure a sufficient amount of internal oxidation, the oxide scale adheres to the roll in the annealing furnace and the steel sheet is pressed, so-called pickup defects occur. For this reason, there is no way to simply increase the oxidation amount.

特許文献２に記載の方法では、加熱帯前段、加熱帯後段、保熱帯の加熱・保温を間接加熱としているため、特許文献１の直火加熱の場合のような鋼板表面の酸化が起こりにくく、特許文献１と比較してもＳｉの内部酸化が不十分であり、合金化温度が高くなるという問題がより顕著である。更に、外気温変動や鋼板の種類によって炉内に持ち込まれる水分量が変化することに加え、混合ガス露点も外気温変動によって変動しやすく、安定して最適露点範囲に制御することが困難であった。このように露点変動が大きいことで、上記露点範囲や温度範囲であっても、不めっき等の表面欠陥が発生し、安定した製品を製造するは困難であった。   In the method described in Patent Document 2, since the heating zone and the heating zone are the indirect heating, the oxidation of the steel sheet surface is unlikely to occur as in the case of the direct flame heating in Patent Literature 1, Even when compared with Patent Document 1, the problem that the internal oxidation of Si is insufficient and the alloying temperature becomes higher is more remarkable. Furthermore, in addition to changes in the amount of moisture brought into the furnace due to fluctuations in the outside air temperature and the type of steel sheet, the dew point of the mixed gas tends to fluctuate due to fluctuations in the outside air temperature, making it difficult to stably control the optimum dew point range. It was. Thus, since the dew point variation is large, surface defects such as non-plating occur even in the above dew point range and temperature range, and it is difficult to manufacture a stable product.

特許文献３に記載の方法では、加熱炉にＤＦＦを使用すれば鋼板表面の酸化は起こりえるが、焼鈍炉に積極的に加湿ガスを供給しないので、露点を制御範囲の中でも高露点領域の−２０〜０℃で安定的に制御することが困難である。また、仮に露点が上昇した場合には炉上部の露点が高くなりやすく、炉下部の露点計で０℃となったときには、炉上部では＋１０℃以上の高露点雰囲気となる場合があり、そのまま長期間操業するとピックアップ欠陥が発生することがわかった。   In the method described in Patent Document 3, oxidation of the steel sheet surface can occur if DFF is used for the heating furnace, but since the humidifying gas is not actively supplied to the annealing furnace, the dew point is − It is difficult to control stably at 20 to 0 ° C. Also, if the dew point rises, the dew point at the top of the furnace tends to be high, and when the dew point meter at the bottom of the furnace reaches 0 ° C, a high dew point atmosphere of + 10 ° C or more may be formed at the top of the furnace. It was found that pick-up defects occurred during the operation.

そこで本発明は、上記課題に鑑み、Ｓｉを０．２質量％以上含む鋼帯に溶融亜鉛めっきを施した場合でも、めっき密着性が高く良好なめっき外観を得ることが可能な溶融亜鉛めっき鋼板の製造方法を提供することを目的とする。   Therefore, in view of the above problems, the present invention provides a hot dip galvanized steel sheet that has a high plating adhesion and can provide a good plating appearance even when hot dip galvanizing is applied to a steel strip containing 0.2 mass% or more of Si. It aims at providing the manufacturing method of.

本発明の要旨構成は以下のとおりである。
［１］加熱帯と、均熱帯と、冷却帯とがこの順に並置された焼鈍炉と、前記冷却帯に隣接した溶融亜鉛めっき設備と、を有する連続溶融亜鉛めっき装置を用いた溶融亜鉛めっき鋼板の製造方法であって、
鋼帯を前記焼鈍炉の内部で、前記加熱帯、前記均熱帯及び前記冷却帯の順に搬送して、前記鋼帯に対して焼鈍を行う工程と、
前記溶融亜鉛めっき設備を用いて、前記冷却帯から排出される鋼帯に溶融亜鉛めっきを施す工程と、
を有し、
前記均熱帯に供給される還元性ガス又は非酸化性ガスは、加湿装置により加湿された加湿ガス、及び前記加湿装置により加湿されていない乾燥ガスであり、
前記均熱帯を通過する鋼帯の幅及び通板速度が一定である間は、前記乾燥ガスの流量を調節することで前記焼鈍炉内の圧力の変動を抑制するのに対して、前記加湿ガスによって前記均熱帯に供給される水分量の変動幅を20％以下とすることを特徴とする溶融亜鉛めっき鋼板の製造方法。 The gist of the present invention is as follows.
[1] A hot-dip galvanized steel sheet using a continuous hot-dip galvanizing apparatus having an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order, and a hot-dip galvanizing facility adjacent to the cooling zone A manufacturing method of
Conveying the steel strip in the annealing furnace in the order of the heating zone, the soaking zone, and the cooling zone, and annealing the steel strip; and
Using the hot dip galvanizing equipment, applying hot dip galvanizing to the steel strip discharged from the cooling zone;
Have
The reducing gas or non-oxidizing gas supplied to the soaking zone is a humidified gas humidified by a humidifier, and a dry gas not humidified by the humidifier,
While the width of the steel strip passing through the soaking zone and the plate passing speed are constant, the humidified gas is controlled against the fluctuation of the pressure in the annealing furnace by adjusting the flow rate of the dry gas. The method for producing a hot-dip galvanized steel sheet, characterized in that the fluctuation range of the amount of water supplied to the soaking zone is 20% or less.

［２］前記加湿ガスによって前記均熱帯に供給される水分量M（g/min）が、以下の式（１）を満たすように、前記加湿ガスの流量及び露点を設定する、上記［１］に記載の溶融亜鉛めっき鋼板の製造方法。
40＋Vf（W−0.9）（S＋4）／90 ＜ Ｍ ＜ 60＋Vf（W−0.9）（S＋4）／90 ・・・（１）
ここで、Vfは前記均熱帯の容積（m3）、Wは前記均熱帯を通過する鋼帯の幅（m）、Sは前記鋼帯の通板速度（m/s）である。 [2] The flow rate and dew point of the humidified gas are set so that the amount of moisture M (g / min) supplied to the soaking zone by the humidified gas satisfies the following formula (1): [1] The manufacturing method of the hot-dip galvanized steel sheet as described in 2.
40 + Vf (W−0.9) (S + 4) / 90 <M <60 + Vf (W−0.9) (S + 4) / 90 (1)
Here, Vf is the soaking zone volume (m 3 ), W is the width (m) of the steel strip that passes through the soaking zone, and S is the plate passing speed (m / s) of the steel strip.

［３］前記均熱帯を通過する鋼帯の幅及び通板速度の少なくとも一方が変動したとき、前記水分量M（g/min）が前記式（１）を満たすように、前記加湿ガスの流量及び露点を変更する、上記［２］に記載の溶融亜鉛めっき鋼板の製造方法。   [3] The flow rate of the humidified gas so that the water content M (g / min) satisfies the formula (1) when at least one of the width of the steel strip passing through the soaking zone and the plate passing speed fluctuates. And the manufacturing method of the hot dip galvanized steel plate as described in said [2] which changes a dew point.

［４］前記均熱帯の高さ方向の上部１／２の領域内で、前記均熱帯に設けられた前記加湿ガスの供給口の位置から１ｍ以上離れた位置で、かつ、前記供給口に対向する前記均熱帯の内壁位置から１ｍ以上離れた位置で、前記均熱帯に設けられた露点測定口において測定される前記均熱帯内の露点を−２５℃以上０℃以下に制御する、上記［１］〜［３］のいずれか一項に記載の溶融亜鉛めっき鋼板の製造方法。   [4] Within a region of the upper half in the height direction of the soaking zone, at a position 1 m or more away from the position of the humidifying gas feeding port provided in the soaking zone, and facing the feeding port The dew point in the soaking zone measured at a dew point measuring port provided in the soaking zone is controlled to -25 ° C. or more and 0 ° C. or less at a position 1 m or more away from the inner wall position of the soaking zone. ] The manufacturing method of the hot dip galvanized steel plate as described in any one of [3].

［５］前記加熱帯は直火型加熱炉を含み、前記連続溶融亜鉛めっき装置は前記溶融亜鉛めっき設備に隣接した合金化設備を有し、
前記合金化設備を用いて、前記鋼帯に施された亜鉛めっきを加熱合金化する工程をさらに有する、上記［１］〜［４］のいずれか一項に記載の溶融亜鉛めっき鋼板の製造方法。 [5] The heating zone includes a direct-fired heating furnace, and the continuous hot dip galvanizing apparatus has an alloying equipment adjacent to the hot dip galvanizing equipment,
The method for producing a hot-dip galvanized steel sheet according to any one of the above [1] to [4], further comprising a step of heat-alloying the zinc plating applied to the steel strip using the alloying equipment. .

本発明の溶融亜鉛めっき鋼板の製造方法によれば、Ｓｉを０．２質量％以上含む鋼帯に溶融亜鉛めっきを施した場合でも、めっき密着性が高く良好なめっき外観を得ることが可能である。   According to the method for manufacturing a hot dip galvanized steel sheet of the present invention, even when hot dip galvanizing is applied to a steel strip containing 0.2 mass% or more of Si, it is possible to obtain a good plating appearance with high plating adhesion. is there.

本発明の一実施形態による連続溶融亜鉛めっき装置１００の構成を示す模式図である。It is a schematic diagram which shows the structure of the continuous hot dip galvanizing apparatus 100 by one Embodiment of this invention. 図１における均熱帯１２への加湿ガス及び乾燥ガスの供給系を示す模式図である。It is a schematic diagram which shows the supply system of the humidification gas and dry gas to the soaking zone 12 in FIG.

まず、本発明の一実施形態による溶融亜鉛めっき鋼板の製造方法に用いる連続溶融亜鉛めっき装置１００の構成を、図１を参照して説明する。連続溶融亜鉛めっき装置１００は、加熱帯１０、均熱帯１２及び冷却帯１４，１６がこの順に並置された焼鈍炉２０と、冷却帯１６に隣接した溶融亜鉛めっき設備としての溶融亜鉛めっき浴２２と、この溶融亜鉛めっき浴２２と隣接した合金化設備２３と、を有する。本実施形態において加熱帯１０は、第１加熱帯１０Ａ（加熱帯前段）及び第２加熱帯１０Ｂ（加熱帯後段）を含む。冷却帯は、第１冷却帯１４（急冷帯）及び第２冷却帯１６（除冷帯）を含む。第２冷却帯１６と連結したスナウト１８は、先端が溶融亜鉛めっき浴２２に浸漬しており、焼鈍炉２０と溶融亜鉛めっき浴２２とが接続されている。   First, the structure of the continuous hot dip galvanizing apparatus 100 used for the manufacturing method of the hot dip galvanized steel sheet by one Embodiment of this invention is demonstrated with reference to FIG. The continuous hot dip galvanizing apparatus 100 includes an annealing furnace 20 in which a heating zone 10, a soaking zone 12, and cooling zones 14 and 16 are arranged in this order, and a hot dip galvanizing bath 22 as a hot dip galvanizing facility adjacent to the cooling zone 16. The hot-dip galvanizing bath 22 and the adjacent alloying equipment 23 are provided. In the present embodiment, the heating zone 10 includes a first heating zone 10A (a heating zone upstream) and a second heating zone 10B (a heating zone downstream). The cooling zone includes a first cooling zone 14 (quenching zone) and a second cooling zone 16 (cooling zone). The tip of the snout 18 connected to the second cooling zone 16 is immersed in a hot dip galvanizing bath 22, and the annealing furnace 20 and the hot dip galvanizing bath 22 are connected.

鋼帯Ｐは、第１加熱帯１０Ａの下部の鋼帯導入口から第１加熱帯１０Ａ内に導入される。各帯１０，１２，１４，１６には、上部及び下部に１つ以上のハースロールが配置される。ハースロールを起点に鋼帯Ｐが１８０度折り返される場合、鋼帯Ｐは焼鈍炉２０の所定の帯の内部で上下方向に複数回搬送され、複数パスを形成する。図１においては、均熱帯１２で１０パス、第１冷却帯１４で２パス、第２冷却帯１６で２パスの例を示したが、パス数はこれに限定されず、処理条件に応じて適宜設定可能である。また、一部のハースロールでは、鋼帯Ｐを折り返すことなく直角に方向転換させて、鋼帯Ｐを次の帯へと移動させる。このようにして、鋼帯Ｐを焼鈍炉２０の内部で、加熱帯１０、均熱帯１２及び冷却帯１４，１６の順に搬送して、鋼帯Ｐに対して焼鈍を行うことができる。   The steel strip P is introduced into the first heating zone 10A from the steel strip inlet at the bottom of the first heating zone 10A. In each of the bands 10, 12, 14, and 16, one or more hearth rolls are disposed at the upper and lower portions. When the steel strip P is folded back 180 degrees starting from the hearth roll, the steel strip P is conveyed a plurality of times in the vertical direction inside a predetermined strip of the annealing furnace 20 to form a plurality of passes. In FIG. 1, an example of 10 passes in the soaking zone 12, 2 passes in the first cooling zone 14, and 2 passes in the second cooling zone 16 is shown. However, the number of passes is not limited to this, and it depends on the processing conditions. It can be set as appropriate. Further, in some hearth rolls, the steel strip P is changed to a right angle without turning back, and the steel strip P is moved to the next strip. In this way, the steel strip P can be transported in the annealing furnace 20 in the order of the heating zone 10, the soaking zone 12, and the cooling zones 14 and 16, and the steel strip P can be annealed.

焼鈍炉２０において、隣接する帯は、それぞれの帯の上部同士または下部同士を接続する連通部を介して連通している。本実施形態では、第１加熱帯１０Ａと第２加熱帯１０Ｂとは、それぞれの帯の上部同士を接続するスロート（絞り部）を介して連通する。第２加熱帯１０Ｂと均熱帯１２とは、それぞれの帯の下部同士を接続するスロートを介して連通する。均熱帯１２と第１冷却帯１４とは、それぞれの帯の下部同士を接続するスロートを介して連通する。第１冷却帯１４と第２冷却帯１６とは、それぞれの帯の下部同士を接続するスロートを介して連通する。各スロートの高さは適宜設定すればよいが、各帯の雰囲気の独立性を高める観点から、各スロートの高さはなるべく低いことが好ましい。焼鈍炉２０内のガスは、炉の下流から上流に流れ、第１加熱帯１０Ａの下部の鋼帯導入口から排出される。   In the annealing furnace 20, the adjacent bands communicate with each other via a communication portion that connects the upper parts or the lower parts of the respective bands. In the present embodiment, the first heating zone 10 </ b> A and the second heating zone 10 </ b> B communicate with each other via a throat (throttle portion) that connects the upper portions of the respective zones. The second heating zone 10B and the soaking zone 12 communicate with each other via a throat that connects the lower portions of each zone. The soaking zone 12 and the first cooling zone 14 communicate with each other via a throat connecting the lower portions of the respective zones. The 1st cooling zone 14 and the 2nd cooling zone 16 are connected via the throat which connects the lower parts of each zone. The height of each throat may be set as appropriate, but it is preferable that the height of each throat is as low as possible from the viewpoint of increasing the independence of the atmosphere of each band. The gas in the annealing furnace 20 flows from the downstream to the upstream of the furnace and is discharged from the steel strip inlet at the bottom of the first heating zone 10A.

（加熱帯）
本実施形態において、第２加熱帯１０Ｂは、直火型加熱炉（ＤＦＦ）である。ＤＦＦは公知のものを用いることができる。図１においては図示しないが、第２加熱帯１０Ｂにおける直火型加熱炉の内壁には、複数のバーナが鋼帯Ｐに対向して分散配置される。複数のバーナは複数のグループに分けられ、グループごとに燃料率及び空気比を独立に制御可能とすることが好ましい。第１加熱帯１０Ａの内部には、第２加熱帯１０Ｂの燃焼排ガスが供給され、その熱で鋼帯Ｐを予熱する。 (Heating zone)
In the present embodiment, the second heating zone 10B is a direct-fired heating furnace (DFF). A well-known DFF can be used. Although not shown in FIG. 1, a plurality of burners are arranged in a distributed manner facing the steel strip P on the inner wall of the direct-fired heating furnace in the second heating zone 10B. The plurality of burners are preferably divided into a plurality of groups, and the fuel ratio and the air ratio can be independently controlled for each group. The combustion exhaust gas from the second heating zone 10B is supplied into the first heating zone 10A, and the steel strip P is preheated by the heat.

燃焼率は、実際にバーナに導入した燃料ガス量を、最大燃焼負荷時のバーナの燃料ガス量で割った値である。バーナを最大燃焼負荷で燃焼したときが燃焼率１００％である。バーナは、燃焼負荷が低くなると安定した燃焼状態が得られなくなる。よって、燃焼率は通常３０％以上とすることが好ましい。   The combustion rate is a value obtained by dividing the amount of fuel gas actually introduced into the burner by the amount of fuel gas in the burner at the maximum combustion load. When the burner is burned at the maximum combustion load, the burning rate is 100%. The burner cannot obtain a stable combustion state when the combustion load becomes low. Therefore, it is preferable that the combustion rate is usually 30% or more.

空気比は、実際のバーナに導入した空気量を、燃料ガスを完全燃焼するために必要な空気量で割った値である。本実施形態では、第２加熱帯１０Ｂの加熱用バーナを４つの群（＃１〜＃４）に分割し、鋼板移動方向上流側の３つの群（＃１〜＃３）は酸化用バーナ、最終ゾーン（＃４）は還元用バーナとし、酸化用バーナ及び還元用バーナの空気比を個別に制御可能とした。酸化用バーナでは、空気比を０．９５以上１．５以下とすることが好ましい。還元用バーナでは、空気比を０．５以上０．９５未満とすることが好ましい。また、第２加熱帯１０Ｂの内部の温度は、８００〜１２００℃とすることが好ましい。   The air ratio is a value obtained by dividing the amount of air introduced into the actual burner by the amount of air necessary for complete combustion of the fuel gas. In the present embodiment, the heating burner of the second heating zone 10B is divided into four groups (# 1 to # 4), and the three groups (# 1 to # 3) on the upstream side in the steel plate moving direction are oxidation burners, The final zone (# 4) is a reduction burner, and the air ratio of the oxidation burner and the reduction burner can be individually controlled. In the oxidation burner, the air ratio is preferably 0.95 or more and 1.5 or less. In the reduction burner, the air ratio is preferably 0.5 or more and less than 0.95. Moreover, it is preferable that the temperature inside the 2nd heating zone 10B shall be 800-1200 degreeC.

（均熱帯）
本実施形態において均熱帯１２では、加熱手段としてラジアントチューブ（ＲＴ）（図示せず）を用いて、鋼帯Ｐを間接加熱することができる。均熱帯１２の内部の平均温度Tr（℃）は、均熱帯内に熱電対を挿入することによりにより測定されるが、７００〜９００℃とすることが好ましい。 (Soaking)
In this embodiment, in the soaking zone 12, the steel strip P can be indirectly heated using a radiant tube (RT) (not shown) as a heating means. The average temperature Tr (° C.) inside the soaking zone 12 is measured by inserting a thermocouple into the soaking zone, but is preferably 700 to 900 ° C.

均熱帯１２には還元性ガス又は非酸化性ガスが供給される。還元性ガスとしては、通常Ｈ2−Ｎ2混合ガスが用いられ、例えばＨ2：１〜２０体積％、残部がＮ2および不可避的不純物からなる組成を有するガス（露点：−６０℃程度）が挙げられる。また、非酸化性ガスとしては、Ｎ2および不可避的不純物からなる組成を有するガス（露点：−６０℃程度）が挙げられる。 The soaking zone 12 is supplied with reducing gas or non-oxidizing gas. As the reducing gas, a mixed gas of H 2 —N 2 is usually used, for example, H 2 : 1 to 20% by volume, and the balance is composed of N 2 and inevitable impurities (dew point: about −60 ° C.) Is mentioned. Examples of the non-oxidizing gas include a gas (dew point: about −60 ° C.) having a composition composed of N 2 and inevitable impurities.

本実施形態では、均熱帯１２に供給される還元性ガス又は非酸化性ガスは、加湿ガス及び乾燥ガスの二形態である。ここで、「乾燥ガス」とは、露点が−６０℃〜−５０℃程度の上記還元性ガス又は非酸化性ガスであって、加湿装置により加湿されていないものである。一方、「加湿ガス」とは、加湿装置により露点が０〜３０℃に加湿されたガスである。   In the present embodiment, the reducing gas or non-oxidizing gas supplied to the soaking zone 12 is in two forms, a humidified gas and a dry gas. Here, the “dry gas” is the reducing gas or non-oxidizing gas having a dew point of about −60 ° C. to −50 ° C., and is not humidified by a humidifier. On the other hand, “humidified gas” is a gas whose dew point is humidified to 0 to 30 ° C. by a humidifier.

例えば、Ｓｉを０．２質量％以上含有する成分組成を有する高張力鋼板の製造時には、均熱帯内の露点を上昇させるために、乾燥ガスに加えて、加湿ガスを均熱帯１２に供給することが好ましい。これに対し、例えば普通鋼板（引張強度２７０ＭＰａ程度）の製造時には、乾燥ガスのみを均熱帯１２に供給し、混合ガスは供給しないことが好ましい。   For example, when producing a high-tensile steel sheet having a component composition containing Si by 0.2% by mass or more, in order to increase the dew point in the soaking zone, a humidified gas is supplied to the soaking zone 12 in addition to the dry gas. Is preferred. On the other hand, it is preferable to supply only the dry gas to the soaking zone 12 and not to supply the mixed gas, for example, when producing a plain steel plate (tensile strength of about 270 MPa).

図２は、均熱帯１２への加湿ガス及び乾燥ガスの供給系を示す模式図である。加湿ガスは、加湿ガス供給口４２Ａ，４２Ｂ，４２Ｃと、加湿ガス供給口４４Ａ，４４Ｂ，４４Ｃと、加湿ガス供給口４６Ａ，４６Ｂ，４６Ｃの三系統で供給される。図２において、上記還元性ガス又は非酸化性ガス（乾燥ガス）は、ガス分配装置２４によって、一部は加湿装置２６へと送られ、残部は乾燥ガスのまま乾燥ガス用配管３２を通過して、乾燥ガス供給口４８Ａ，４８Ｂ，４８Ｃ，４８Ｄを介して均熱帯１２内に供給される。   FIG. 2 is a schematic diagram showing a supply system of humidified gas and dry gas to the soaking zone 12. The humidified gas is supplied in three systems: humidified gas supply ports 42A, 42B, 42C, humidified gas supply ports 44A, 44B, 44C, and humidified gas supply ports 46A, 46B, 46C. In FIG. 2, the reducing gas or non-oxidizing gas (dry gas) is partly sent to the humidifier 26 by the gas distribution device 24, and the remainder passes through the dry gas pipe 32 with the dry gas remaining. Then, it is supplied into the soaking zone 12 through the dry gas supply ports 48A, 48B, 48C, 48D.

乾燥ガス供給口の位置及び数は特に限定されず、種々の条件を考慮して適宜決めればよい。しかし、乾燥ガス供給口は、同じ高さ位置に複数配置されることが好ましく、鋼帯進行方向に均等に配置されることが好ましい。   The position and number of the drying gas supply ports are not particularly limited, and may be appropriately determined in consideration of various conditions. However, it is preferable that a plurality of the drying gas supply ports be arranged at the same height position, and it is preferable that the drying gas supply ports are arranged uniformly in the steel strip traveling direction.

加湿装置２６で加湿されたガスは、加湿ガス分配装置３０で上記三系統に分配され、各々の加湿ガス用配管３６を経由して、加湿ガス供給口４２Ａ，４２Ｂ，４２Ｃと、加湿ガス供給口４４Ａ，４４Ｂ，４４Ｃと、加湿ガス供給口４６Ａ，４６Ｂ，４６Ｃを介して均熱帯１２内に供給される。   The gas humidified by the humidifying device 26 is distributed to the three systems by the humidifying gas distribution device 30 and is supplied to the humidified gas supply ports 42A, 42B, 42C and the humidified gas supply ports via the humidified gas pipes 36, respectively. 44A, 44B, 44C and humidified gas supply ports 46A, 46B, 46C are supplied into the soaking zone 12.

加湿ガス供給口の位置及び数は特に限定されず、種々の条件を考慮して適宜決めればよい。しかし、加湿ガス供給口は、均熱帯１２の上下方向に２分割、入出方向に２分割した計４区域にそれぞれ１ヶ所以上設けることが好ましい。これにより、均熱帯１２全体を均一に露点制御できるからである。符号３８は加湿ガス用流量計、符号４０は加湿ガス用露点計である。加湿ガスの露点は、加湿ガス用配管３４，３６内のわずかな結露等で変化することがあるので、露点計４０は、加湿ガス供給口４２，４４，４６の直前に設置することが望ましい。   The position and number of the humidified gas supply ports are not particularly limited, and may be appropriately determined in consideration of various conditions. However, it is preferable to provide one or more humidified gas supply ports in each of the four zones divided into two in the vertical direction of the soaking zone 12 and two in the entrance / exit direction. This is because the dew point can be uniformly controlled throughout the soaking zone 12. Reference numeral 38 denotes a humidified gas flow meter, and reference numeral 40 denotes a humidified gas dew point meter. Since the dew point of the humidified gas may change due to slight dew condensation in the humidified gas pipes 34, 36, the dew point meter 40 is desirably installed immediately before the humidified gas supply ports 42, 44, 46.

加湿装置２６内には、フッ素系もしくはポリイミド系の中空糸膜又は平膜等を有する加湿モジュールがあり、膜の内側には乾燥ガスを流し、膜の外側には循環恒温水槽２８で所定温度に調整された純水を循環させる。フッ素系もしくはポリイミド系の中空糸膜又は平膜とは、水分子との親和力を有するイオン交換膜の一種である。中空糸膜の内側と外側に水分濃度差が生じると、その濃度差を均等にしようとする力が発生し、水分はその力をドライビングフォースとして低い水分濃度の方へ膜を透過し移動する。乾燥ガス温度は、季節や１日の気温変化にしたがって変化するが、この加湿装置では、水蒸気透過膜を介したガスと水の接触面積を十分に取ることで熱交換も行えるため、乾燥ガス温度が循環水温より高くても低くても、乾燥ガスは設定水温と同じ露点まで加湿されたガスとなり、高精度な露点制御が可能となる。加湿ガスの露点は５〜５０℃の範囲で任意に制御可能である。加湿ガスの露点が配管温度よりも高いと配管内で結露してしまい、結露した水が直接炉内に浸入する可能性があるので、加湿ガス用の配管は加湿ガス露点以上かつ外気温以上に加熱・保熱されている。   In the humidifier 26, there is a humidification module having a fluorine-based or polyimide-based hollow fiber membrane or a flat membrane, and a dry gas is allowed to flow inside the membrane, and the outside of the membrane is brought to a predetermined temperature in a circulating constant temperature water bath 28. Circulate adjusted pure water. A fluorine-based or polyimide-based hollow fiber membrane or a flat membrane is a kind of ion exchange membrane having an affinity for water molecules. When a difference in moisture concentration occurs between the inside and outside of the hollow fiber membrane, a force is generated to make the concentration difference uniform, and the moisture permeates through the membrane toward a lower moisture concentration using the force as a driving force. The dry gas temperature changes according to the season and daily temperature change, but this humidifier can also exchange heat by taking sufficient contact area between the gas and water through the water vapor permeable membrane. Regardless of whether the temperature is higher or lower than the circulating water temperature, the dry gas becomes a gas humidified to the same dew point as the set water temperature, and high-precision dew point control is possible. The dew point of the humidified gas can be arbitrarily controlled in the range of 5 to 50 ° C. If the dew point of the humidified gas is higher than the piping temperature, condensation may occur in the piping, and the condensed water may directly enter the furnace.Therefore, the humidifying gas piping should be above the humidifying gas dew point and above the ambient temperature. It is heated and insulated.

加湿ガスを均熱帯１２に供給しているか否かに関わらず、焼鈍炉内の圧力は、加熱帯１０の燃焼条件や冷却帯１４，１６での冷却ファンの運転条件によって随時変動する。ここで、炉内圧が高すぎると、炉壁に過剰な力が加わるため焼鈍炉を傷めることがあり、逆に炉内圧が低すぎると、均熱帯１２内に焼鈍炉外の酸素が混入したり、加熱帯１０の燃焼ガスが流入したりして鋼板品質に悪影響を及ぼす。そのため一般的には、炉内圧の変動を抑制する、好ましくは炉内圧を一定に保つように、均熱帯１２に供給するガス流量を増減する制御を行う。従って、均熱帯１２に加湿ガスと乾燥ガスの両方を供給する操業を行うとき、従来の制御方法では、乾燥ガスの流量のみならず、加湿ガスの流量も変動させており、そのため加湿ガスによって均熱帯に供給される水分量も変動していた。   Regardless of whether or not the humidified gas is supplied to the soaking zone 12, the pressure in the annealing furnace varies depending on the combustion conditions of the heating zone 10 and the operating conditions of the cooling fans in the cooling zones 14 and 16. Here, if the furnace pressure is too high, an excessive force is applied to the furnace wall, which may damage the annealing furnace. Conversely, if the furnace pressure is too low, oxygen outside the annealing furnace may be mixed in the soaking zone 12. The combustion gas in the heating zone 10 may flow in and adversely affect the steel plate quality. Therefore, in general, control is performed to increase or decrease the gas flow rate supplied to the soaking zone 12 so as to suppress fluctuations in the furnace pressure, and preferably keep the furnace pressure constant. Therefore, when an operation for supplying both humidified gas and dry gas to the soaking zone 12 is performed, the conventional control method varies not only the flow rate of the dry gas but also the flow rate of the humidified gas. The amount of water supplied to the tropics also fluctuated.

しかし、均熱帯１２には、鋼帯中のＳｉやＭｎを内部酸化させるという観点から必要な水分量を常に供給する必要がある。炉内圧の変動を抑制するために加湿ガスの流量を減少させると、均熱帯１２に供給される水分量が不足して、均熱帯１２内の露点が適正範囲の下限を下回り、その結果、部分的な不めっきが生じ、めっき外観が劣化することがあった。また、合金化処理も行う操業では、合金化温度が上昇し、その結果、所望の引張強度が得られないことがあった。あるいは炉内圧の変動を抑制するために加湿ガスの流量を増加させると、均熱帯１２に供給される水分量が過剰になり、その結果ロールピックアップが発生し、鋼帯表面にもロールピックアップに起因する疵が発生し、めっき外観が劣化することがあった。   However, it is necessary to always supply the soaking zone 12 with a necessary amount of water from the viewpoint of internally oxidizing Si and Mn in the steel strip. When the flow rate of the humidified gas is decreased to suppress fluctuations in the furnace pressure, the amount of water supplied to the soaking zone 12 is insufficient, and the dew point in the soaking zone 12 falls below the lower limit of the appropriate range, resulting in partial Non-plating occurred, and the appearance of plating sometimes deteriorated. Further, in an operation in which alloying treatment is also performed, the alloying temperature increases, and as a result, a desired tensile strength may not be obtained. Alternatively, if the flow rate of the humidifying gas is increased in order to suppress fluctuations in the furnace pressure, the amount of water supplied to the soaking zone 12 becomes excessive, resulting in roll pick-up, and the steel strip surface is also caused by the roll pick-up. In some cases, the plating appearance deteriorates and the plating appearance deteriorates.

そこで本実施形態では、均熱帯１２を通過する鋼帯の幅及び通板速度が一定である間（以下、「同一操業条件下」とも称する。）は、乾燥ガスの流量を調節することで焼鈍炉内の圧力の変動を抑制するのに対して、加湿ガスによって均熱帯１２に供給される水分量は極力一定とすること、具体的には水分量の変動幅を20％以下にすることが肝要である。これにより、良好なめっき外観を得ることができ、合金化処理も行う操業では、合金化温度を下げることで引張強度の低下を抑制することができる。ここで、均熱帯に供給される「水分量の変動幅」は、同一操業条件下での水分量の最大をMmax、最小をMminとしたとき、（Mmax−Mmin）／Mmaxで定義される。水分量は、後述の式（２）により算出できる。 Therefore, in this embodiment, while the width of the steel strip passing through the soaking zone 12 and the plate passing speed are constant (hereinafter also referred to as “same operating conditions”), annealing is performed by adjusting the flow rate of the dry gas. While suppressing fluctuations in the pressure in the furnace, the amount of water supplied to the soaking zone 12 by the humidified gas should be kept as constant as possible, specifically, the fluctuation range of the moisture amount should be 20% or less. It is essential. Thereby, a favorable plating appearance can be obtained, and in an operation in which alloying treatment is also performed, a decrease in tensile strength can be suppressed by lowering the alloying temperature. Here, the “variation range of the amount of water” supplied to the soaking zone is (M max −M min ) / M max where the maximum amount of water under the same operating conditions is M max and the minimum is M min. Defined by The amount of water can be calculated by the following formula (2).

水分量の変動幅を20％以下に抑制する態様は特に限定されない。一態様として、加湿ガスの露点を一定とし、流量の変動幅を20％以下に制御することが挙げられる。なお、本実施形態のように複数の加湿ガス供給口が設けられる場合、各供給口からの加湿ガス流量も、合計の加湿ガス流量も、極力一定（具体的には20％以下）とすることが好ましい。   The aspect which suppresses the fluctuation | variation range of a moisture content to 20% or less is not specifically limited. As one aspect, the dew point of the humidified gas is made constant and the fluctuation range of the flow rate is controlled to 20% or less. When a plurality of humidified gas supply ports are provided as in this embodiment, the humidified gas flow rate from each supply port and the total humidified gas flow rate should be as constant as possible (specifically, 20% or less). Is preferred.

加湿ガスによって均熱帯１２に投入される水分量M（g/min）は、均熱帯の容積、均熱帯１２を通過する鋼帯Ｐの幅及び通板速度によって調整する必要がある。発明者らは鋭意検討した結果、加湿ガスによって均熱帯１２に供給される水分量M（g/min）が、以下の式（１）を満たすように、加湿ガスの流量及び露点を設定することが、良好なめっき外観を得るために有効であることを見出した。
40＋Vf（W−0.9）（S＋4）／90 ＜ Ｍ ＜ 60＋Vf（W−0.9）（S＋4）／90 ・・・（１）
ここで、Vfは均熱帯１２の容積（m3）、Wは均熱帯１２を通過する鋼帯Ｐの幅（m）、Sは鋼帯Ｐの通板速度（m/s）である。 The amount of water M (g / min) introduced into the soaking zone 12 by the humidified gas needs to be adjusted by the soaking zone volume, the width of the steel strip P passing through the soaking zone 12, and the plate passing speed. As a result of intensive studies, the inventors set the flow rate and dew point of the humidified gas so that the amount of water M (g / min) supplied to the soaking zone 12 by the humidified gas satisfies the following formula (1). Has been found to be effective for obtaining a good plating appearance.
40 + Vf (W−0.9) (S + 4) / 90 <M <60 + Vf (W−0.9) (S + 4) / 90 (1)
Here, Vf is the volume of the soaking zone 12 (m 3 ), W is the width (m) of the steel strip P passing through the soaking zone 12, and S is the plate speed (m / s) of the steel strip P.

そして、均熱帯１２を通過する鋼帯Ｐの幅W及び通板速度Sの少なくとも一方が変動したとき、前記水分量M（g/min）が式（１）を満たすように、加湿ガスの流量及び露点を変更することが有効である。   Then, when at least one of the width W and the sheet passing speed S of the steel strip P passing through the soaking zone 12 fluctuates, the flow rate of the humidified gas so that the water content M (g / min) satisfies the formula (1). It is also effective to change the dew point.

均熱帯１２の容積Vfは、実質的には定数となる。均熱帯１２を通過する鋼帯Ｐの幅W及び通板速度Sが増加する場合、あるいは幅W及び通板速度Sの片方が一定で他方が増加する場合、単位時間当たりに均熱帯１２内のガスに接触する鋼帯面積が増大するため、式（１）に基づいて、加湿ガスによる水分量を増加させる。均熱帯１２を通過する鋼帯Ｐの幅W及び通板速度Sが減少する場合、あるいは幅W及び通板速度Sの片方が一定で他方が減少する場合は逆に、式（１）に基づいて加湿ガスによる水分量は減少させる必要がある。幅W及び通板速度Sの片方が増加し、他方が減少する場合でも、式（１）に基づいて、加湿ガスによる水分量を調整する。いずれにしても、操業条件変化に伴う均熱帯１２内の露点の変化を待たずに、式（１）を満たすように加湿ガスの流量及び露点を調整することが望ましい。   The volume Vf of the soaking zone 12 is substantially a constant. When the width W of the steel strip P passing through the soaking zone 12 and the passing plate speed S increase, or when one of the width W and the passing plate speed S is constant and the other increases, the inside of the soaking zone 12 per unit time. Since the steel strip area in contact with the gas increases, the amount of moisture by the humidified gas is increased based on the formula (1). When the width W and the sheet passing speed S of the steel strip P passing through the soaking zone 12 decrease, or when one of the width W and the sheet passing speed S is constant and the other decreases, on the contrary, based on the formula (1) Therefore, it is necessary to reduce the amount of moisture by the humidified gas. Even when one of the width W and the sheet passing speed S increases and the other decreases, the amount of moisture by the humidified gas is adjusted based on the formula (1). In any case, it is desirable to adjust the flow rate of the humidified gas and the dew point so as to satisfy the formula (1) without waiting for the dew point change in the soaking zone 12 due to the change in the operating conditions.

水分量M（g/min）は、加湿ガスの露点Tw（℃）と合計流量Vm（Nm3/hr）から、式（２）で算出することができる。

Figure 0006439654
The amount of moisture M (g / min) can be calculated by the formula (2) from the dew point Tw (° C.) of the humidified gas and the total flow rate Vm (Nm 3 / hr).
Figure 0006439654

均熱帯１２内に供給される加湿ガスの流量Vmは、上記のように制御される限り特に限定されないが、概ね１００〜４００（Nm3/hr）の範囲内に維持される。また、均熱帯１２内に供給される乾燥ガスの流量は、特に限定されないが、概ね１０〜３００（Nm3/hr）の範囲内に維持される。 The flow rate Vm of the humidified gas supplied into the soaking zone 12 is not particularly limited as long as it is controlled as described above, but is generally maintained within a range of 100 to 400 (Nm 3 / hr). Further, the flow rate of the dry gas supplied into the soaking zone 12 is not particularly limited, but is generally maintained within a range of 10 to 300 (Nm 3 / hr).

均熱帯１２内において、水蒸気は窒素ガスよりも比重が軽いため、上部に溜まりやすい。したがって、露点測定口５０は、均熱帯１２の高さ方向の上部１／２の領域内に配置する。また、加湿ガス供給口の近傍は、局所的に高露点となるため、露点測定には不向きな領域である。そこで、露点測定口５０は、各々の加湿ガス供給口の位置から１ｍ以上離れた位置で、かつ、各々の供給口に対向する均熱帯の内壁位置から１ｍ以上離れた位置に配置することが好ましい。そして、露点測定口５０において測定される均熱帯１２内の露点が−２５℃以上０℃以下に維持されるように、加湿ガスの流量を制御することが好ましい。これにより、良好なめっき外観を得ることができ、合金化処理も行う操業では、合金化温度を下げることで引張強度の低下を抑制することができる。   In the soaking zone 12, water vapor has a lighter specific gravity than nitrogen gas, so it tends to accumulate at the top. Therefore, the dew point measuring port 50 is arranged in the upper half region in the height direction of the soaking zone 12. Moreover, since the vicinity of the humidified gas supply port has a locally high dew point, it is an unsuitable region for dew point measurement. Therefore, the dew point measurement port 50 is preferably disposed at a position 1 m or more away from the position of each humidified gas supply port, and at a position 1 m or more away from the inner wall position of the soaking zone facing each supply port. . And it is preferable to control the flow rate of humidified gas so that the dew point in the soaking zone 12 measured at the dew point measuring port 50 is maintained at -25 ° C or higher and 0 ° C or lower. Thereby, a favorable plating appearance can be obtained, and in an operation in which alloying treatment is also performed, a decrease in tensile strength can be suppressed by lowering the alloying temperature.

（冷却帯）
本実施形態において冷却帯１４，１６では、鋼帯Ｐが冷却される。鋼帯Ｐは、第１冷却帯１４では４８０〜５３０℃程度にまで冷却され、第２冷却帯１６では４７０〜５００℃程度にまで冷却される。 (Cooling zone)
In the present embodiment, the steel strip P is cooled in the cooling zones 14 and 16. The steel strip P is cooled to about 480 to 530 ° C. in the first cooling zone 14 and is cooled to about 470 to 500 ° C. in the second cooling zone 16.

冷却帯１４，１６にも、上記還元性ガス又は非酸化性ガスが供給されるが、ここでは、乾燥ガスのみが供給される。冷却帯１４，１６への乾燥ガスの供給は特に限定されないが、冷却帯内に均等に投入されるように、高さ方向２ヶ所以上、長手方向２ヶ所以上の投入口から供給することが好ましい。冷却帯１４，１６に供給される乾燥ガスの合計ガス流量Qcdは、配管に設けられたガス流量計（図示せず）により測定され、特に限定されないが、２００〜１０００（Nm3/hr）程度とする。焼鈍炉内の圧力の変動を抑制することは、均熱帯に供給される乾燥ガスの流量のみを調節することで行ってもよいが、冷却帯に供給される乾燥ガスの流量をも調節して行うことが好ましい。 Although the reducing gas or non-oxidizing gas is also supplied to the cooling zones 14 and 16, only the dry gas is supplied here. The supply of the drying gas to the cooling zones 14 and 16 is not particularly limited, but it is preferable to supply the drying gas from two or more inlets in the height direction and two or more inlets in the longitudinal direction so as to be uniformly introduced into the cooling zone. . The total gas flow rate Qcd of the dry gas supplied to the cooling zones 14 and 16 is measured by a gas flow meter (not shown) provided in the pipe, and is not particularly limited, but is about 200 to 1000 (Nm 3 / hr). And The pressure fluctuation in the annealing furnace may be suppressed by adjusting only the flow rate of the dry gas supplied to the soaking zone, but also adjusting the flow rate of the dry gas supplied to the cooling zone. Preferably it is done.

（溶融亜鉛めっき浴）
溶融亜鉛めっき浴２２を用いて、第２冷却帯１６から排出される鋼帯Ｐに溶融亜鉛めっきを施すことができる。溶融亜鉛めっきは定法に従って行えばよい。 (Hot galvanizing bath)
Using the hot dip galvanizing bath 22, hot dip galvanization can be performed on the steel strip P discharged from the second cooling zone 16. Hot dip galvanization may be performed according to a conventional method.

（合金化設備）
合金化設備２４を用いて、鋼帯Ｐに施された亜鉛めっきを加熱合金化することができる。合金化処理は定法に従って行えばよい。本実施形態によれば、合金化温度が高温にならないため、製造された合金化溶融亜鉛めっき鋼板の引張強度の低下を抑制することができる。ただし、本発明において合金化設備２４や、それによる合金化処理は必須ではない。良好なめっき外観を得るとの効果は、合金化処理をしない場合にも得ることができるからである。 (Alloying equipment)
Using the alloying equipment 24, the galvanization applied to the steel strip P can be heated and alloyed. The alloying process may be performed according to a conventional method. According to this embodiment, since alloying temperature does not become high temperature, the fall of the tensile strength of the manufactured galvannealed steel plate can be suppressed. However, in the present invention, the alloying equipment 24 and the alloying treatment using it are not essential. This is because the effect of obtaining a good plating appearance can be obtained even when the alloying treatment is not performed.

焼鈍及び溶融亜鉛めっき処理の対象とする鋼帯Ｐは特に限定されないが、Ｓｉを０．２質量％以上含有する成分組成の鋼帯、すなわち高張力鋼の場合、本発明の効果を有利に得ることができる。   The steel strip P to be subjected to annealing and hot dip galvanizing treatment is not particularly limited, but in the case of a steel strip having a component composition containing 0.2% by mass or more of Si, that is, a high-strength steel, the effect of the present invention is advantageously obtained. be able to.

（実験条件）
図１及び図２に示す連続溶融亜鉛めっき装置を用いて、表１に示す成分組成の鋼帯を表２に示す各種焼鈍条件で焼鈍し、その後溶融亜鉛めっき及び合金化処理を施した。鋼種Ａ、鋼種Ｂともに高張力鋼である。表２に記載の「時間」は操業開始からの経過時間を意味し、時間の経過とともに、表２のとおりに通板する鋼帯の種類、板厚、板幅、及び連続溶融亜鉛めっき装置の操業条件を変更した。 (Experimental conditions)
Using the continuous hot dip galvanizing apparatus shown in FIGS. 1 and 2, the steel strip having the composition shown in Table 1 was annealed under various annealing conditions shown in Table 2, and then hot dip galvanized and alloyed. Both steel types A and B are high-tensile steels. “Time” shown in Table 2 means the elapsed time from the start of operation, and with the passage of time, the type, thickness, width, and continuous hot-dip galvanizing device The operating conditions were changed.

第２加熱帯はＤＦＦとした。加熱用バーナを４つの群（＃１〜＃４）に分割し、鋼板移動方向上流側の３つの群（＃１〜＃３）は酸化用バーナ、最終ゾーン（＃４）は還元用バーナとし、酸化用バーナ及び還元用バーナの空気比を表２に示す値に設定した。なお、各群の鋼板搬送方向の長さは４ｍである。   The second heating zone was DFF. The heating burner is divided into four groups (# 1 to # 4), and the three groups (# 1 to # 3) on the upstream side in the steel plate moving direction are oxidation burners, and the final zone (# 4) is a reduction burner. The air ratio of the oxidation burner and the reduction burner was set to the values shown in Table 2. In addition, the length of the steel plate conveyance direction of each group is 4 m.

均熱帯は、容積Vfが700m3のＲＴ炉とした。均熱帯の内部の平均温度Trは表２に示すものに設定した。乾燥ガスとしては、１５体積％のＨ2で残部がＮ2および不可避的不純物からなる組成を有するガス（露点：−５０℃）を用いた。この乾燥ガスの一部を、１０台の中空糸膜式加湿モジュールを有する加湿装置により加湿して、加湿ガスを調製した。各モジュールに最大500L/minの乾燥ガスと、最大20L/minの循環水を流した。循環恒温水槽は各モジュールで共通とし、計200L/minの純水を供給可能である。乾燥ガス供給口及び加湿ガス供給口は、図２に示す位置に配置した。 The soaking zone was an RT furnace with a volume Vf of 700 m 3 . The average temperature Tr in the soaking zone was set as shown in Table 2. As the drying gas, a gas (dew point: −50 ° C.) having a composition composed of 15% by volume of H 2 and the balance of N 2 and inevitable impurities was used. Part of this dry gas was humidified by a humidifier having 10 hollow fiber membrane humidification modules to prepare a humidified gas. Each module was supplied with a maximum of 500 L / min of dry gas and a maximum of 20 L / min of circulating water. The circulating water bath is common to each module and can supply a total of 200 L / min of pure water. The dry gas supply port and the humidified gas supply port were arranged at the positions shown in FIG.

表２に示すように、鋼種、板厚、及び板幅のいずれかが互いに異なる８種類の鋼帯を通板した。前半（時間0：00から0：55まで）は比較例、鋼板（時間0：55から1：50まで）は発明例である。すなわち、前半の通板では、均熱帯に供給される乾燥ガスの流量及び加湿ガスの流量並びに冷却帯に供給される乾燥ガスの流量を表２に示すように変動させて、炉内圧を一定に保つようにした。後半の通板では、表２に示すように、均熱帯を通過する鋼帯の種類、幅及び通板速度が一定である間は、加湿ガスの露点は一定にし、加湿ガスの流量の変動幅は20％以下にした。そして、均熱帯及び冷却帯に供給される乾燥ガスの流量を調節することで炉内圧を一定に保つようにした。   As shown in Table 2, 8 types of steel strips with different steel types, plate thicknesses, and plate widths were passed through. The first half (time 0:00 to 0:55) is a comparative example, and the steel plate (time 0:55 to 1:50) is an invention example. That is, in the first half plate, the flow rate of the dry gas supplied to the soaking zone, the flow rate of the humidified gas, and the flow rate of the dry gas supplied to the cooling zone are varied as shown in Table 2 to keep the furnace pressure constant. I tried to keep it. As shown in Table 2, in the second half of the plate, the dew point of the humidifying gas is constant and the fluctuation range of the flow rate of the humidifying gas is constant while the type, width, and plate passing speed of the steel strip passing through the soaking zone are constant. Was less than 20%. And the furnace pressure was kept constant by adjusting the flow rate of the dry gas supplied to the soaking zone and the cooling zone.

表２中均熱帯の「露点」の欄には、図２の露点測定口５０の位置で測定した測定された均熱帯内の露点を示した。また、「加湿ガス供給口近傍露点」は、図２の加湿ガス供給口４０Ｂから８０ｃｍ離れた位置で測定した均熱帯内の露点を示した。「加湿ガス露点」は、図２の加湿ガス用露点計４０で測定した露点を示した。   In the column of “dew point” of the soaking tropics in Table 2, the dew point in the soaking tropics measured at the position of the dew point measuring port 50 in FIG. 2 is shown. The “dew point near the humidified gas supply port” indicates the dew point in the soaking zone measured at a position 80 cm away from the humidified gas supply port 40B in FIG. The “humidified gas dew point” indicates the dew point measured by the humidified gas dew point meter 40 of FIG.

第１冷却帯及び第２冷却帯には、各帯の最下部から上記乾燥ガス（露点：−５０℃）を表２に示す流量で供給した。   The dry gas (dew point: −50 ° C.) was supplied to the first cooling zone and the second cooling zone from the bottom of each zone at the flow rates shown in Table 2.

めっき浴温は４６０℃、めっき浴中Ａｌ濃度０．１３０％、付着量はガスワイピングにより片面当り５０ｇ／ｍ2に調節した。なお、ライン速度は板厚の変化に伴って１．０〜２．０ｍ／ｓとした。また、溶融亜鉛めっきを施した後に、皮膜合金化度（Fe含有率）が１０〜１３％内となるように、誘導加熱式合金化炉にて合金化処理を行った。その際の合金化温度は表２に示す。 The plating bath temperature was 460 ° C., the Al concentration in the plating bath was 0.130%, and the adhesion amount was adjusted to 50 g / m 2 per side by gas wiping. The line speed was set to 1.0 to 2.0 m / s with the change of the plate thickness. In addition, after hot dip galvanization, alloying treatment was performed in an induction heating type alloying furnace so that the degree of film alloying (Fe content) was within 10 to 13%. The alloying temperature at that time is shown in Table 2.

（評価方法）
めっき外観の評価は、光学式の表面欠陥計による検査（φ０．５以上の不めっき欠陥やロールピックアップによる疵を検出）および目視による合金化ムラ判定を行い、全ての項目が合格で○、軽度の合金化ムラがある場合は△、一つでも不合格があれば×とした。結果を表２に示す。 (Evaluation method)
The appearance of the plating is evaluated by optical surface defect meter inspection (detection of unplating defects of φ0.5 or more and wrinkles by roll pick-up) and visual judgment of alloying unevenness. △ when there was an alloying unevenness, and × if there was any failure. The results are shown in Table 2.

また、各種条件で製造した合金化溶融亜鉛めっき鋼板の引張強度を測定した。高張力鋼の鋼種Ａは５９０ＭＰａ以上、高張力鋼の鋼種Ｂは９８０ＭＰａ以上を合格とした。結果を表２に示す。   Moreover, the tensile strength of the galvannealed steel plate manufactured on various conditions was measured. The steel type A of high-tensile steel passed 590 MPa or more, and the steel type B of high-tensile steel passed 980 MPa or more. The results are shown in Table 2.

（評価結果）
比較例では、均熱帯内の露点が−２５℃を下回った場合は、部分的な不めっきによりめっき外観が劣化し、また、合金化温度の上昇に伴って引張強度が不合格となった。また、均熱帯露点が０℃を上回った場合には、ロールピックアップが発生し、鋼帯表面にもロールピックアップに起因する疵が発生した結果、めっき外観が劣化した。また、0：20、0：35、0：45の時間帯では、水分量も式（１）を満たしていたが、前後の時間帯との水分量の変動が大きく、露点も−２５〜０℃の範囲に入っていなかったため、軽度の合金化ムラが見られた。 (Evaluation results)
In the comparative example, when the dew point in the soaking zone was lower than −25 ° C., the plating appearance was deteriorated due to partial non-plating, and the tensile strength was rejected as the alloying temperature increased. Moreover, when the soaking zone dew point exceeded 0 degreeC, roll pick-up generate | occur | produced and the plating external appearance deteriorated as a result of the wrinkles resulting from roll pick-up also having occurred on the steel strip surface. Moreover, in the time zone of 0:20, 0:35, 0:45, the water content also satisfied the formula (1), but the fluctuation of the water content with the previous and subsequent time zones was large, and the dew point was also −25 to 0. Since it was not in the range of ° C., mild uneven alloying was observed.

一方、発明例においては、均熱帯の全体のガス流量が変化しても、所定水分量を安定的に供給できたので、コイル全長全幅に亘って良好な表面外観となり、所望の引張特性を得ることもできた。水分量の変動を20％以内にし、かつ式（１）を満足して露点を−２５〜０℃に制御した1:20〜2:00の時間帯で、引張強度と表面外観が特に高位で安定した。   On the other hand, in the example of the invention, even if the gas flow of the entire tropical zone changes, the predetermined moisture amount can be stably supplied, so that a good surface appearance is obtained over the entire length of the coil, and desired tensile characteristics are obtained. I was also able to. The tensile strength and surface appearance are particularly high in the time range of 1:20 to 2:00 when the fluctuation of the water content is within 20% and the dew point is controlled to −25 to 0 ° C. satisfying the formula (1). Stable.

Figure 0006439654
Figure 0006439654

Figure 0006439654
Figure 0006439654

本発明の溶融亜鉛めっき鋼板の製造方法によれば、Ｓｉを０．２質量％以上含む鋼帯に溶融亜鉛めっきを施した場合でも、めっき密着性が高く良好なめっき外観を得ることが可能である。また、本発明の溶融亜鉛めっきの製造方法によれば、さらに合金化処理をする際に、合金化温度が高温にならないため、製造された合金化溶融亜鉛めっき鋼板の引張強度の低下を抑制することができる。   According to the method for manufacturing a hot dip galvanized steel sheet of the present invention, even when hot dip galvanizing is applied to a steel strip containing 0.2 mass% or more of Si, it is possible to obtain a good plating appearance with high plating adhesion. is there. Moreover, according to the manufacturing method of the hot dip galvanizing of the present invention, when the alloying process is further performed, the alloying temperature does not become high, so that the decrease in the tensile strength of the manufactured hot galvanized steel sheet is suppressed. be able to.

１００ 連続溶融亜鉛めっき装置
１０ 加熱帯
１０Ａ 第１加熱帯（前段）
１０Ｂ 第２加熱帯（後段、直火型加熱炉）
１２ 均熱帯
１４ 第１冷却帯（急冷帯）
１６ 第２冷却帯（除冷帯）
１８ スナウト
２０ 焼鈍炉
２２ 溶融亜鉛めっき浴
２３ 合金化設備
２４ 乾燥ガス分配装置
２６ 加湿装置
２８ 循環恒温水槽
３０ 加湿ガス分配装置
３２ 乾燥ガス用配管
３４，３６ 加湿ガス用配管
３８ 加湿ガス用流量計
４０ 加湿ガス用露点計
４２Ａ，４２Ｂ，４２Ｃ 加湿ガス供給口
４４Ａ，４４Ｂ，４４Ｃ 加湿ガス供給口
４６Ａ，４６Ｂ，４６Ｃ 加湿ガス供給口
４８Ａ，４８Ｂ，４８Ｃ，４８Ｄ 乾燥ガス供給口
５０ 露点測定口
５２Ａ 上部ハースロール
５２Ｂ 下部ハースロール
Ｐ 鋼帯 100 Continuous hot dip galvanizing equipment 10 Heating zone 10A First heating zone (previous stage)
10B Second heating zone (later, direct-fired heating furnace)
12 Soaking zone 14 First cooling zone (quenching zone)
16 Second cooling zone (cooling zone)
18 Snout 20 Annealing furnace 22 Hot dip galvanizing bath 23 Alloying equipment 24 Drying gas distribution device 26 Humidification device 28 Circulating thermostatic water tank 30 Humidification gas distribution device 32 Drying gas piping 34, 36 Humidification gas piping 38 Humidification gas flow meter 40 Humidification gas dew point meter 42A, 42B, 42C Humidification gas supply port 44A, 44B, 44C Humidification gas supply port 46A, 46B, 46C Humidification gas supply port 48A, 48B, 48C, 48D Dry gas supply port 50 Dew point measurement port 52A Upper hearth Roll 52B Lower Hearth Roll P Steel strip

Claims (4)

加熱帯と、均熱帯と、冷却帯とがこの順に並置された焼鈍炉と、前記冷却帯に隣接した溶融亜鉛めっき設備と、を有する連続溶融亜鉛めっき装置を用いた溶融亜鉛めっき鋼板の製造方法であって、
Ｓｉを０．２質量％以上含む鋼帯を前記焼鈍炉の内部で、前記加熱帯、前記均熱帯及び前記冷却帯の順に搬送して、前記鋼帯に対して焼鈍を行う工程と、
前記溶融亜鉛めっき設備を用いて、前記冷却帯から排出される鋼帯に溶融亜鉛めっきを施す工程と、
を有し、
前記均熱帯に供給される還元性ガス又は非酸化性ガスは、加湿装置により加湿された加湿ガス、及び前記加湿装置により加湿されていない乾燥ガスであり、
前記均熱帯を通過する鋼帯の幅及び通板速度が一定である間は、前記乾燥ガスの流量を調節することで前記焼鈍炉内の圧力の変動を抑制するのに対して、前記加湿ガスによって前記均熱帯に供給される水分量の変動幅を20％以下とし、
前記加湿ガスによって前記均熱帯に供給される水分量M（g/min）が、以下の式（１）を満たすように、前記加湿ガスの流量及び露点を設定することを特徴とする溶融亜鉛めっき鋼板の製造方法。
40＋Vf（W−0.9）（S＋4）／90 ＜ Ｍ ＜ 60＋Vf（W−0.9）（S＋4）／90 ・・・（１）
ここで、Vfは前記均熱帯の容積（m 3 ）、Wは前記均熱帯を通過する鋼帯の幅（m）、Sは前記鋼帯の通板速度（m/s）である。 A method for producing a hot-dip galvanized steel sheet using a continuous hot-dip galvanizing apparatus, comprising: an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are arranged in this order; and a hot-dip galvanizing facility adjacent to the cooling zone Because
A step of annealing the steel strip by conveying a steel strip containing 0.2 mass% or more of Si in the annealing furnace in the order of the heating zone, the soaking zone, and the cooling zone;
Using the hot dip galvanizing equipment, applying hot dip galvanizing to the steel strip discharged from the cooling zone;
Have
The reducing gas or non-oxidizing gas supplied to the soaking zone is a humidified gas humidified by a humidifier, and a dry gas not humidified by the humidifier,
While the width of the steel strip passing through the soaking zone and the plate passing speed are constant, the humidified gas is controlled against the fluctuation of the pressure in the annealing furnace by adjusting the flow rate of the dry gas. The fluctuation range of the amount of water supplied to the soaking zone is set to 20% or less by
The hot dip galvanizing is characterized in that the flow rate and dew point of the humidified gas are set so that the amount of water M (g / min) supplied to the soaking zone by the humidified gas satisfies the following formula (1): A method of manufacturing a steel sheet.
40 + Vf (W−0.9) (S + 4) / 90 <M <60 + Vf (W−0.9) (S + 4) / 90 (1)
Here, Vf is the soaking zone volume (m 3 ), W is the width (m) of the steel strip that passes through the soaking zone, and S is the plate passing speed (m / s) of the steel strip. 前記均熱帯を通過する鋼帯の幅及び通板速度の少なくとも一方が変動したとき、前記水分量M（g/min）が前記式（１）を満たすように、前記加湿ガスの流量及び露点を変更する、請求項１に記載の溶融亜鉛めっき鋼板の製造方法。 When at least one of the width of the steel strip passing through the soaking zone and the plate passing speed fluctuates, the flow rate and dew point of the humidified gas are set so that the water content M (g / min) satisfies the equation (1). The manufacturing method of the hot dip galvanized steel plate of Claim 1 to change. 前記均熱帯の高さ方向の上部１／２の領域内で、前記均熱帯に設けられた前記加湿ガスの供給口の位置から１ｍ以上離れた位置で、かつ、前記供給口に対向する前記均熱帯の内壁位置から１ｍ以上離れた位置で、前記均熱帯に設けられた露点測定口において測定される前記均熱帯内の露点を−２５℃以上０℃以下に制御する、請求項１又は２に記載の溶融亜鉛めっき鋼板の製造方法。 Within the upper half area of the soaking zone, the soaking zone facing the feeding port at a position 1 m or more away from the humidifying gas feeding port provided in the soaking zone. at a distance above 1m from the inner wall position of tropical the controls to -25 ° C. or higher 0 ℃ below the dew point in the soaking zone as measured in dewpoint measurement port provided in the soaking zone, to claim 1 or 2 The manufacturing method of the hot-dip galvanized steel sheet of description. 前記加熱帯は直火型加熱炉を含み、前記連続溶融亜鉛めっき装置は前記溶融亜鉛めっき設備に隣接した合金化設備を有し、
前記合金化設備を用いて、前記鋼帯に施された亜鉛めっきを加熱合金化する工程をさらに有する、請求項１〜３のいずれか一項に記載の溶融亜鉛めっき鋼板の製造方法。 The heating zone includes a direct-fired heating furnace, and the continuous hot dip galvanizing apparatus has an alloying equipment adjacent to the hot dip galvanizing equipment,
The manufacturing method of the hot dip galvanized steel sheet as described in any one of Claims 1-3 which further has the process of heat-alloying the galvanization performed to the said steel strip using the said alloying equipment.
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