JP4741376B2 - High-strength galvannealed steel sheet with good appearance, manufacturing method and manufacturing equipment thereof - Google Patents

High-strength galvannealed steel sheet with good appearance, manufacturing method and manufacturing equipment thereof Download PDF

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JP4741376B2
JP4741376B2 JP2006021426A JP2006021426A JP4741376B2 JP 4741376 B2 JP4741376 B2 JP 4741376B2 JP 2006021426 A JP2006021426 A JP 2006021426A JP 2006021426 A JP2006021426 A JP 2006021426A JP 4741376 B2 JP4741376 B2 JP 4741376B2
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steel sheet
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JP2006233333A (en
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和彦 本田
鉄生 西山
義広 末宗
健郎 伊藤
幸基 田中
陽一 池松
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Nippon Steel Corp
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Priority to RU2008135330/02A priority patent/RU2418094C2/en
Priority to ES06782398T priority patent/ES2441959T5/en
Priority to CA2640646A priority patent/CA2640646C/en
Priority to PCT/JP2006/315552 priority patent/WO2007086158A1/en
Priority to KR1020087018619A priority patent/KR101016526B1/en
Priority to BRPI0621421A priority patent/BRPI0621421B8/en
Priority to EP06782398.9A priority patent/EP1980638B2/en
Priority to TW095127989A priority patent/TWI354706B/en
Priority to CN200680052096XA priority patent/CN101336308B/en
Priority to PL06782398T priority patent/PL1980638T3/en
Priority to US12/162,739 priority patent/US8592049B2/en
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本発明は、高強度合金化溶融亜鉛めっき鋼板及びその製造方法に係わり、更に詳しくは不めっきや表面疵の無い良好な外観を有し、種々の用途、例えば建材用や自動車用鋼板として適用できるめっき鋼板に関するものである。   The present invention relates to a high-strength galvannealed steel sheet and a method for producing the same, and more specifically, has a good appearance without unplating or surface flaws, and can be applied as a steel sheet for various uses such as building materials and automobiles. The present invention relates to a plated steel sheet.

耐食性の良好なめっき鋼板として合金化溶融亜鉛めっき鋼板がある。この合金化溶融亜鉛めっき鋼板は、通常、鋼板を脱脂後、無酸化炉または直化炉にて予熱し、表面の清浄化および材質確保のために還元炉にて還元焼鈍を行い、溶融亜鉛浴に浸漬し、付着量制御した後合金化を行うことによって製造される。その特徴として、耐食性およびめっき密着性等に優れることから、自動車、建材用途等を中心として広く使用されている。   An alloyed hot-dip galvanized steel sheet is available as a plated steel sheet having good corrosion resistance. This alloyed hot-dip galvanized steel sheet is usually degreased and then preheated in a non-oxidizing furnace or straightening furnace, and subjected to reduction annealing in a reducing furnace to clean the surface and secure the material, It is manufactured by immersing the material in the substrate and controlling the amount of adhesion, followed by alloying. As its feature, it is excellent in corrosion resistance, plating adhesion, etc., it is widely used mainly for automobiles, building materials and the like.

特に近年、自動車分野においては衝突時に乗員を保護するような機能の確保と共に燃費向上を目的とした軽量化を両立させるために、めっき鋼板の高強度化が必要とされてきている。   In recent years, in particular, in the automobile field, it has been necessary to increase the strength of plated steel sheets in order to ensure the function of protecting passengers in the event of a collision and to reduce the weight for the purpose of improving fuel efficiency.

加工性を悪化させずに鋼板を高強度化するためには、ＳｉやＭｎ、Ｐといった元素を添加することが有効であるが、これらの元素の添加は合金化を遅延させるため、軟鋼に比べて高温長時間の合金化を必要とする。この高温長時間の合金化は、鋼板中に残存していたオーステナイトをパーライトに変態させ、加工性を低下させるため、結果として添加元素の効果を相殺することになる。   It is effective to add elements such as Si, Mn, and P to increase the strength of the steel sheet without degrading workability. However, the addition of these elements delays alloying, so compared to mild steel. High temperature and long time alloying is required. This alloying for a long time at a high temperature transforms the austenite remaining in the steel sheet into pearlite and lowers the workability. As a result, the effect of the additive element is offset.

また、ＳｉはＦｅよりも特に酸化し易いことから、Ｓｉを含有した鋼板を通常の溶融亜鉛めっき条件でめっきすると、焼鈍過程で鋼中のＳｉが表面に濃化し、不めっき欠陥の原因となることが知られている。   Moreover, since Si is particularly easier to oxidize than Fe, if a steel sheet containing Si is plated under normal hot dip galvanizing conditions, Si in the steel is concentrated on the surface during the annealing process, causing non-plating defects. It is known.

Ｓｉを含有した鋼板の不めっき欠陥を抑制する技術としては、例えば、特許文献１（特開昭５５−１２２８６５号公報）において、鋼表面に酸化膜の厚みが４００〜１００００Åになるように酸化した後、水素を含む雰囲気中で焼鈍し、めっきする方法が示されている。しかし本技術においては、鉄酸化膜の還元時間の調節は実際上困難であり、還元時間が長すぎればＳｉの表面濃化を引き起こし、短すぎれば鋼表面に鉄の酸化膜が残存するので、結局完全にめっき性不良の解消にはならないという問題点と、表面の鉄酸化膜が厚くなりすぎると、剥離した酸化物がロールに付着し外観疵を発生させるという問題点を有している。   As a technique for suppressing non-plating defects in a steel sheet containing Si, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 55-122865), oxidation is performed on the steel surface so that the thickness of the oxide film is 400 to 10,000 mm. Thereafter, a method of annealing and plating in an atmosphere containing hydrogen is shown. However, in this technique, it is practically difficult to adjust the reduction time of the iron oxide film. If the reduction time is too long, it causes Si surface concentration, and if it is too short, the iron oxide film remains on the steel surface. Eventually, there is a problem that the plating defect is not completely eliminated, and that when the iron oxide film on the surface becomes too thick, the peeled oxide adheres to the roll and causes appearance defects.

上記問題点を改善する目的で、本発明者らは特許文献２（特開２００３−１０５５１６公報）において鋼板表面を酸化させた後に雰囲気を制御した還元炉中で還元することにより、Ｓｉの表面濃化を防止する製造方法を提案した。   For the purpose of improving the above problems, the inventors of the present invention disclosed in Patent Document 2 (Japanese Patent Application Laid-Open No. 2003-105516) that after oxidizing the steel sheet surface, the steel sheet was reduced in a reducing furnace with controlled atmosphere, thereby increasing the surface concentration of Si. A manufacturing method was proposed to prevent crystallization.

また、特許文献３（特開昭５６−３３４６３号公報）及び特許文献４（特開昭５７−７９１６０号公報）には、鋼板表面にＣｒ、Ｎｉ、Ｆｅ等のプレめっきを行うことによって不めっき欠陥を抑制する方法が示されている。更に、特許文献５（特開２００２−１６１３１５号公報）には、連続焼鈍ラインで鋼板の表面直下に内部酸化層を生成させ、同時に生成した表面酸化物を酸洗で除去した後に連続溶融亜鉛めっきラインでめっきを行う方法が示されている。   In Patent Document 3 (Japanese Patent Laid-Open No. Sho 56-33463) and Patent Document 4 (Japanese Patent Laid-Open No. 57-79160), non-plating is performed by pre-plating Cr, Ni, Fe, etc. on the steel sheet surface. A method for suppressing defects is shown. Further, in Patent Document 5 (Japanese Patent Laid-Open No. 2002-161315), an internal oxide layer is formed immediately below the surface of a steel sheet in a continuous annealing line, and the formed surface oxide is removed by pickling at the same time, followed by continuous hot dip galvanization. A method of plating in line is shown.

特開昭５５−１２２８６５号公報JP 55-122865 A 特開２００３−１０５５１６公報JP 2003-105516 A 特開昭５６−３３４６３号公報JP-A-56-33463 特開昭５７−７９１６０号公報JP-A-57-79160 特開２００２−１６１３１５号公報JP 2002-161315 A

しかし、上記及びその他これまで開示された製造技術では、不めっき欠陥を完全に防止することができない。   However, the above and other manufacturing techniques disclosed so far cannot completely prevent non-plating defects.

更に、特許文献３及び特許文献４のようなプレめっき法ではめっき設備が必要となるため、そのスペースがない場合は採用できない。又、プレめっき設備設置により生産コストが上昇する問題も生じる。   Furthermore, since the pre-plating method as in Patent Document 3 and Patent Document 4 requires plating equipment, it cannot be used when there is no space. Moreover, the problem that production cost rises by pre-plating equipment installation also arises.

また、特許文献５のような２回焼鈍も生産コストが上昇する問題が生じる。   Further, the double annealing as in Patent Document 5 causes a problem that the production cost increases.

特にこれまで開示されたＳｉを含有した鋼板の製造技術は、めっき性を確保することに重点が置かれ、成形性や溶接性などめっき鋼板として使用させる際の様々な性能を向上させることまではなされていなかった。   In particular, the manufacturing technology for steel sheets containing Si disclosed so far focuses on ensuring plating properties, and until various performances when used as plated steel plates such as formability and weldability are improved. It wasn't done.

そこで、本発明は上記問題点を解決し、外観が良好で成形性や溶接性に優れた高強度合金化溶融亜鉛めっき鋼板とその製造方法、及びそのための製造設備を提案するものである。   Therefore, the present invention solves the above problems and proposes a high-strength galvannealed steel sheet having a good appearance and excellent formability and weldability, a manufacturing method therefor, and a manufacturing facility therefor.

本発明者らは、高強度鋼板のめっき処理について鋭意研究を重ねた結果、Ｃ、Ｓｉ、Ｍｎが一定量以上添加された鋼を、熱処理条件及びめっき条件を最適化した連続溶融亜鉛めっき設備でめっき処理することにより、Ｓｉ酸化物の種類と位置を制御し、外観が良好で成形性や溶接性に優れた高強度合金化溶融亜鉛めっき鋼板を製造できることを見いだして本発明をなした。   As a result of intensive research on the plating treatment of high-strength steel sheets, the present inventors have conducted continuous hot-dip galvanizing equipment with optimized heat treatment conditions and plating conditions for steel to which a certain amount of C, Si, and Mn has been added. By carrying out the plating treatment, it was found that a high-strength galvannealed steel sheet having a good appearance and excellent formability and weldability can be produced by controlling the type and position of the Si oxide, and the present invention was made.

すなわち、本発明の要旨とするところは、次のとおりである。   That is, the gist of the present invention is as follows.

（１） 質量％で、
Ｃ：０．０５〜０．２５％、
Ｓｉ：０．３〜２．５％、
Ｍｎ：１．５〜２．８％、
Ｐ：０．０３％以下、
Ｓ：０．０２％以下、
Ａｌ：０．００５〜０．５％、
Ｎ：０．００６０％以下を含有し、
残部Ｆｅおよび不可避的不純物からなる高強度鋼板の上に、ＦｅおよびＡｌを含有し、残部がＺｎおよび不可避的不純物からなる合金化溶融亜鉛めっき層を有する鋼板において、前記高強度鋼板と前記めっき層との界面から５μｍ以下の鋼板側の鋼板中の結晶粒界と結晶粒内にＳｉを含む酸化物が平均含有率で０．６〜１０質量％含有されて存在し、かつ、前記めっき層中にＳｉを含む酸化物が平均含有率で０．０５〜１．５質量％含有されて存在し、そして、前記めっき層中及び前記鋼板中に存在するＳｉを含む酸化物がＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉを含む酸化物であることを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板。 (1) In mass%,
C: 0.05 to 0.25%
Si: 0.3 to 2.5%,
Mn: 1.5 to 2.8%,
P: 0.03% or less,
S: 0.02% or less,
Al: 0.005 to 0.5%,
N: 0.0060% or less,
On the steel plate having Fe and Al on the high-strength steel plate made of the remaining Fe and inevitable impurities and having the alloyed hot-dip galvanized layer made of Zn and inevitable impurities, the high-strength steel plate and the plating layer The oxide containing Si is present in an average content of 0.6 to 10% by mass in the crystal grain boundaries and crystal grains in the steel sheet on the steel sheet side of 5 μm or less from the interface with the interface, and in the plating layer The oxide containing Si is present in an average content of 0.05 to 1.5 mass%, and the oxide containing Si present in the plating layer and the steel sheet is FeSiO 3 , Fe 2. A high-strength galvannealed steel sheet having a good appearance, characterized by being an oxide containing one or more kinds of Si selected from SiO 4 , MnSiO 3 and Mn 2 SiO 4 .

（２） さらに、前記鋼板内面側にＳｉＯ2が存在することを特徴とする前記（１）記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板。
 (2) Further, the (1) good appearance according high strength galvannealed steel sheet characterized in that the SiO 2 is present in the steel plate inner surface side.

（３） さらに、前記めっき層の鋼板側及び前記鋼板中にＳｉＯ2が存在することを特徴とする前記（１）記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板。
 (3) In addition, the steel sheet side and the (1) good appearance according high strength galvannealed steel sheet characterized in that the SiO 2 is present in the steel sheet of the plating layer.

（４） 引張強さＦ（ＭＰａ）と伸びＬ（％）の関係が
Ｌ≧５１−０．０３５×Ｆ
を満足することを特徴とする前記（１）乃至（３）のいずれかに記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板。
( 4 ) The relationship between tensile strength F (MPa) and elongation L (%) is L ≧ 51−0.035 × F
The high-strength galvannealed steel sheet having a good appearance according to any one of (1) to (3) , wherein:

（５） 前記（１）に記載の化学成分からなる組成の高強度鋼板に連続的に溶融亜鉛めっきを施す際、還元帯の雰囲気として、Ｈ2を１〜６０体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯ2、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ2 を下記（１）式、（２）式を満足するように
−０．００００３４Ｔ2＋０．１０５Ｔ−０．２〔Ｓｉ％〕2＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ2≦−０．００００３８Ｔ2＋０．１０７Ｔ−９０．４ ・・・（１）
９２３≦Ｔ≦１１７３ ・・・（２）
Ｔ：鋼板の最高到達温度（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
制御した雰囲気で還元を行うことを特徴とする前記（１）乃至（４）のいずれかに記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
 (5) wherein (1) when subjected to continuous hot-dip galvanizing a high strength steel sheet having a composition consisting of chemical ingredients described, as the atmosphere of the reducing zone, and H 2 contains 1 to 60 vol%, the remainder N 2 , H 2 O, O 2 , CO 2 , CO, and inevitable impurities, and the logarithm log PO 2 of the oxygen partial pressure in the atmosphere satisfies the following formulas (1) and (2) -0.000034T 2 + 0.105T-0.2 to [Si%] 2 +2.1 [Si%] - 98.8 ≦ logPO 2 ≦ -0.000038T 2 + 0.107T-90.4 ··· (1)
923 ≦ T ≦ 1173 (2)
T: Maximum temperature of steel sheet (K)
[Si%]: Si content in the steel sheet (mass%)
The method for producing a high-strength galvannealed steel sheet with good appearance according to any one of (1) to (4) , wherein the reduction is performed in a controlled atmosphere.

（６） 前記（５）に記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、還元帯の前に酸化帯において燃焼空気比０．９〜１．２の雰囲気中にて酸化せしめ、その後の還元帯において、還元を行うことを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
( 6 ) In the method for producing a high-strength galvannealed steel sheet described in ( 5 ) above , oxidation is performed in an atmosphere having a combustion air ratio of 0.9 to 1.2 in an oxidation zone before the reduction zone, and thereafter A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by performing reduction in the reduction zone.

（７） 前記（６）に記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、還元帯の前の酸化帯において露点２７３Ｋ以上の雰囲気中にて酸化せしめ、その後の還元帯において、還元を行うことを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
( 7 ) In the method for producing a high-strength galvannealed steel sheet according to ( 6 ), oxidation is performed in an atmosphere having a dew point of 273 K or more in an oxidation zone before the reduction zone, and reduction is performed in the subsequent reduction zone. A method for producing a high-strength alloyed hot-dip galvanized steel sheet having a good appearance, characterized in that:

（８） 前記（１）に記載の化学成分からなる組成のスラブをＡｒ３点以上の温度で仕上圧延を行い、５０〜８５％の冷間圧延を施した後、前記（５）乃至（７）のいずれかに記載の雰囲気の連続溶融亜鉛めっき設備を使用し１０２３Ｋ以上１１５３Ｋ以下のフェライト、オーステナイトの二相共存温度域で焼鈍し、その最高到達温度から９２３Ｋまでを平均冷却速度０．５〜１０度／秒で、引き続いて９２３Ｋから７７３Ｋまでを平均冷却速度３度／秒以上で冷却し、さらに７７３Ｋから平均冷却速度０．５度／秒以上で６９３Ｋ〜７３３Ｋまで冷却し、且つ、７７３Ｋからめっき浴温までを２５秒以上２４０秒以下保持した後、溶融亜鉛めっき処理を行うことによって、前記冷延鋼板の表面上に溶融亜鉛めっき層を形成し、次いで、前記溶融亜鉛めっき層が形成された前記鋼板に対し合金化処理を施すことによって、前記鋼板の表面上に合金化溶融亜鉛めっき層を形成する合金化溶融亜鉛めっき鋼板の製造方法において、前記溶融亜鉛めっき処理を、浴中有効Ａｌ濃度：０．０７〜０．１０５ｍａｓｓ％、残部がＺｎおよび不可避的不純物からなる成分組成の溶融亜鉛めっき浴中で行い、そして、前記合金化処理を、
７２０≦Ｔ≦６９０×ｅｘｐ（１．３５×〔Ａｌ％〕）
但し、〔Ａｌ％〕：亜鉛めっき浴中の浴中有効Ａｌ濃度（ｍａｓｓ％）
を満足する温度Ｔ（Ｋ）において行うことを特徴とする前記（１）乃至（４）のいずれかに記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
( 8 ) The slab having the composition described in the above (1) is finish-rolled at a temperature not lower than the Ar3 point and subjected to cold rolling at 50 to 85%, and then the above ( 5 ) to ( 7 ). Using the continuous hot-dip galvanizing equipment in the atmosphere described in any one of the above, annealing is performed in the two-phase coexistence temperature range of ferrite and austenite of 1023K to 1153K, and the average cooling rate from the highest temperature to 923K is 0.5 to 10 Then, cooling from 923 K to 773 K at an average cooling rate of 3 degrees / second or more, further cooling from 773 K to 693 K to 733 K at an average cooling rate of 0.5 degrees / second or more, and plating from 773 K After maintaining the bath temperature for 25 seconds or more and 240 seconds or less, a hot dip galvanizing treatment is performed to form a hot dip galvanized layer on the surface of the cold-rolled steel sheet. In the method for producing an alloyed hot-dip galvanized steel sheet, an alloyed hot-dip galvanized layer is formed on the surface of the steel sheet by subjecting the steel sheet on which the hot-dip galvanized layer is formed, to the hot-dip galvanized steel sheet. Plating treatment is carried out in a hot dip galvanizing bath having a component composition consisting of an effective Al concentration in the bath of 0.07 to 0.105 mass%, the balance being Zn and inevitable impurities, and the alloying treatment is performed.
720 ≦ T ≦ 690 × exp (1.35 × [Al%])
However, [Al%]: Effective Al concentration in the galvanizing bath (mass%)
The method for producing a high-strength galvannealed steel sheet with good appearance according to any one of (1) to ( 4 ), wherein the method is performed at a temperature T (K) that satisfies the following conditions.

（９） 前記（５）乃至（８）のいずれかに記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、溶融めっき後６７３Ｋ以下の温度に冷却されるまでの時間を３０秒以上１２０秒以下とすることを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
( 9 ) In the method for producing a high-strength galvannealed steel sheet according to any one of ( 5 ) to ( 8 ), the time until cooling to a temperature of 673 K or less after hot dipping is 30 seconds to 120 seconds. A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized in that:

（１０） 前記（５）乃至（９）のいずれかに記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、焼鈍後６７３Ｋ以上７２３Ｋ以下まで冷却した後、７０３Ｋ以上７４３Ｋ以下まで再加熱を行い、溶融亜鉛めっき処理を行うことを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
(10) In the method for producing a high-strength galvannealed steel sheet according to any one of ( 5 ) to ( 9 ), after annealing, the steel sheet is cooled to 673K to 723K and then reheated to 703K and 743K. A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by performing a galvanizing treatment.

（１１） 無酸化炉又は直火炉を有し、鋼板に連続的に溶融亜鉛めっきを施す前記（５）記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、ＣＯ2を１〜１００体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯおよび不可避的不純物からからなる気体を導入する装置を還元炉に配設し、還元帯の雰囲気を、Ｈ 2 を１〜６０体積％含有し、残部Ｎ 2 、Ｈ 2 Ｏ、Ｏ 2 、ＣＯ 2 、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ 2 を下記（１）式、（２）式を満足するように
−０．００００３４Ｔ 2 ＋０．１０５Ｔ−０．２〔Ｓｉ％〕 2 ＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ 2 ≦−０．００００３８Ｔ 2 ＋０．１０７Ｔ−９０．４・・・・・（１）
９２３≦Ｔ≦１１７３・・・・・（２）
Ｔ：鋼板の最高到達温度（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
制御することを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
(11) In the method for producing a high-strength galvannealed steel sheet according to the above (5) , which has a non-oxidizing furnace or a direct-fired furnace and continuously galvanizes the steel sheet, 1 to 100% by volume of CO 2 And a device for introducing a gas composed of the balance N 2 , H 2 O, O 2 , CO and inevitable impurities is disposed in the reduction furnace, and the atmosphere of the reduction zone contains 1 to 60% by volume of H 2 And the balance N 2 , H 2 O, O 2 , CO 2 , CO 2 or more and unavoidable impurities, and the logarithmic log PO 2 of the oxygen partial pressure in the atmosphere is expressed by the following formula (1): 2) To satisfy the equation
−0.000034T 2 + 0.105T−0.2 [Si%] 2 +2.1 [Si%] − 98.8 ≦ log PO 2 ≦ −0.000038 T 2 + 0.107T−90.4 1)
923 ≦ T ≦ 1173 (2)
T: Maximum temperature of steel sheet (K)
[Si%]: Si content in the steel sheet (mass%)
A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by being controlled.

（１２） 無酸化炉又は直火炉を有し、鋼板に連続的に溶融亜鉛めっきを施す前記（５）記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、還元炉中でＣＯまたは炭化水素を燃焼させ、ＣＯ2を１〜１００体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯおよび不可避的不純物からからなる気体を発生させる装置を配設し、
還元帯の雰囲気を、Ｈ 2 を１〜６０体積％含有し、残部Ｎ 2 、Ｈ 2 Ｏ、Ｏ 2 、ＣＯ 2 、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ 2 を下記（１）式、（２）式を満足するように
−０．００００３４Ｔ 2 ＋０．１０５Ｔ−０．２〔Ｓｉ％〕 2 ＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ 2 ≦−０．００００３８Ｔ 2 ＋０．１０７Ｔ−９０．４ ・・・（１）
９２３≦Ｔ≦１１７３ ・・・（２）
Ｔ：鋼板の最高到達温度（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
制御することを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
(12) In the method for producing a high-strength galvannealed steel sheet according to the above (5) , which has a non-oxidation furnace or a direct-fired furnace and continuously galvanizes the steel sheet, CO or hydrocarbons in the reduction furnace And a device for generating a gas comprising 1 to 100% by volume of CO 2 and the balance N 2 , H 2 O, O 2 , CO and unavoidable impurities ,
The atmosphere in the reduction zone contains 1 to 60% by volume of H 2 , and the balance is composed of one or more of N 2 , H 2 O, O 2 , CO 2 , CO, and unavoidable impurities. Logarithm log PO 2 of oxygen partial pressure so that the following formulas (1) and (2) are satisfied
−0.000034T 2 + 0.105T−0.2 [Si%] 2 +2.1 [Si%] − 98.8 ≦ log PO 2 ≦ −0.000038 T 2 + 0.107T-90.4 (1)
923 ≦ T ≦ 1173 (2)
T: Maximum temperature of steel sheet (K)
[Si%]: Si content in the steel sheet (mass%)
A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by being controlled.

以上述べたように、外観に優れる高強度合金化溶融亜鉛めっき鋼板とその製造方法及びその装置を提供することを可能としたものであり、産業の発展に貢献するところが極めて大である．   As described above, it is possible to provide a high-strength galvannealed steel sheet with excellent appearance, a method for manufacturing the same, and an apparatus therefor, which greatly contributes to industrial development.

以下に本発明を詳細に説明する。   The present invention is described in detail below.

まず、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎの数値限定理由について述べる．Ｃはマルテンサイトや残留オーステナイトによる組織強化で鋼板を高強度化しようとする場合に必須の元素である．Ｃの含有量を０．０５％以上とする理由は、Ｃが０．０５％未満ではミストや噴流水を冷却媒体として焼鈍温度から急速冷却することが困難な溶融亜鉛めっきラインにおいてセメンタイトやパーライトが生成しやすく、必要とする引張強さの確保が困難であるためである．一方、Ｃの含有量を０．２５％以下とする理由は、Ｃが０．２５％を超えると、スポット溶接で健全な溶接部を形成することが困難となると同時にＣの偏析が顕著となり加工性が劣化するためである。   First, the reasons for limiting the numerical values of C, Si, Mn, P, S, Al, and N will be described. C is an essential element for increasing the strength of steel sheets by strengthening the structure with martensite and retained austenite. The reason why the C content is 0.05% or more is that when C is less than 0.05%, cementite and pearlite are not easily formed in a hot dip galvanizing line where mist or jet water is difficult to rapidly cool from the annealing temperature. This is because it is easy to form and it is difficult to secure the required tensile strength. On the other hand, the reason why the C content is 0.25% or less is that when C exceeds 0.25%, it becomes difficult to form a sound weld by spot welding, and at the same time, segregation of C becomes prominent. This is because the property deteriorates.

Ｓｉは鋼板の加工性、特に伸びを大きく損なうことなく強度を増す元素として０．３〜２．５％添加する．Ｓｉの含有量を０．３％以上とする理由は、Ｓｉが０．３％未満では必要とする引張強さの確保が困難であるためであり、Ｓｉの含有量を２．５％以下とする理由は、Ｓｉが２．５％を超えると強度を増す効果が飽和すると共に延性の低下が起こるためである．望ましくは、Ｃ含有量の４倍以上の質量％とすることで、めっき直後に行う合金化処理のための再加熱でパーライトおよびベイナイト変態の進行を著しく遅滞させ、室温まで冷却後にも体積率で３〜２０％のマルテンサイトおよび残留オーステナイトがフェライト中に混在する金属組織とすることができる。   Si is added in an amount of 0.3 to 2.5% as an element that increases the strength without significantly detracting from the workability of the steel sheet, particularly the elongation. The reason why the Si content is 0.3% or more is that it is difficult to ensure the required tensile strength when Si is less than 0.3%, and the Si content is 2.5% or less. The reason for this is that when Si exceeds 2.5%, the effect of increasing the strength is saturated and the ductility is lowered. Desirably, by setting the mass to 4% or more by mass of the C content, the progress of pearlite and bainite transformation is significantly delayed by reheating for alloying performed immediately after plating, and even after cooling to room temperature, the volume ratio A metal structure in which 3 to 20% of martensite and retained austenite are mixed in the ferrite can be obtained.

ＭｎはＣとともにオーステナイトの自由エネルギーを下げるため、めっき浴に鋼帯を浸漬するまでの間にオーステナイトを安定化する目的で１．５％以上添加する．また、Ｃ含有量の１２倍以上の質量％を添加することにより、めっき直後に行う合金化処理のための再加熱でパーライトおよびベイナイト変態の進行を著しく遅滞させ、室温まで冷却後にも体積率で３〜２０％のマルテンサイトおよび残留オーステナイトがフェライト中に混在する金属組織とできる．しかし添加量が過大になるとスラブに割れが生じやすく、またスポット溶接性も劣化するため、２．８％を上限とする。   In order to lower the free energy of austenite together with C, Mn is added in an amount of 1.5% or more for the purpose of stabilizing the austenite until the steel strip is immersed in the plating bath. In addition, by adding a mass% of 12 times or more of the C content, the progress of pearlite and bainite transformation is significantly delayed by reheating for alloying performed immediately after plating, and in volume ratio after cooling to room temperature. A metal structure in which 3 to 20% of martensite and retained austenite are mixed in the ferrite can be formed. However, if the amount added is excessive, cracks are likely to occur in the slab and spot weldability deteriorates, so the upper limit is 2.8%.

Ｐは一般に不可避的不純物として鋼に含まれるが、その量が０．０３％を超えるとスポット溶接性の劣化が著しいうえ、本発明におけるような引張強さが４９０ＭＰａを超すような高強度鋼板では靭性とともに冷間圧延性も著しく劣化するため、その含有量は０．０３％以下とする．Ｓも一般に不可避的不純物として鋼に含まれるが、その量が０．０２％を超えると、圧延方向に伸張したＭｎＳの存在が顕著となり、鋼板の曲げ性に悪影響をおよぼすため、その含有量は０．０２％以下とする。   P is generally contained in steel as an unavoidable impurity. However, when its amount exceeds 0.03%, the spot weldability is significantly deteriorated, and in a high-strength steel sheet having a tensile strength exceeding 490 MPa as in the present invention. The cold-rollability as well as toughness deteriorates significantly, so the content is 0.03% or less. S is also generally contained in steel as an unavoidable impurity. However, if the amount exceeds 0.02%, the presence of MnS stretched in the rolling direction becomes significant, which adversely affects the bendability of the steel sheet. 0.02% or less.

Ａｌは鋼の脱酸元素として、またＡｌＮによる熱延素材の細粒化、および一連の熱処理工程における結晶粒の粗大化を抑制し材質を改善するために０．００５％以上添加する必要がある．ただし、０．５％を超えるとコスト高となるばかりか、表面性状を劣化させるため、その含有量は０．５％以下とする．Ｎもまた一般に不可避的不純物として鋼に含まれるが、その量が０．００６％を超えると、伸びとともに脆性も劣化するため、その含有量は０．００６％以下とする。   Al is a deoxidizing element for steel, and it is necessary to add 0.005% or more in order to improve the material by suppressing the grain refinement of the hot rolled material by AlN and the coarsening of crystal grains in a series of heat treatment steps. . However, if it exceeds 0.5%, not only the cost increases, but also the surface properties deteriorate, so the content is made 0.5% or less. N is also generally contained in steel as an unavoidable impurity, but if its amount exceeds 0.006%, the brittleness deteriorates with elongation, so its content is made 0.006% or less.

また、これらを主成分とする鋼にＮｂ、Ｔｉ、Ｂ、Ｍｏ、Ｃｕ、Ｎｉ、Ｓｎ、Ｚｎ、Ｚｒ、Ｗ、Ｃｏ、Ｃａ、希土類元素（Ｙを含む）、Ｖ、Ｔａ、Ｈｆ、Ｐｂ、Ｍｇ、Ａｓ、Ｓｂ、Ｂｉを合計で１％以下含有しても本発明の効果を損なわず、その量によっては耐食性や加工性が改善される等好ましい場合もある。   In addition, Nb, Ti, B, Mo, Cu, Ni, Sn, Zn, Zr, W, Co, Ca, rare earth elements (including Y), V, Ta, Hf, Pb, Even if Mg, As, Sb, and Bi are contained in a total amount of 1% or less, the effects of the present invention are not impaired, and depending on the amount, it may be preferable such as improvement in corrosion resistance and workability.

次に、合金化溶融亜鉛めっき層について述べる．本発明において、合金化溶融亜鉛めっき層とは、合金化反応によってＺｎめっき中に鋼中のＦｅが拡散しできたＦｅ−Ｚｎ合金を主体としためっき層のことである．Ｆｅの含有率は特に限定しないが、めっき中のＦｅ含有率７質量％未満ではめっき表面に柔らかいＺｎ−Ｆｅ合金が形成されプレス成形性を劣化させ、Ｆｅ含有率１５質量％を超えると地鉄界面に脆い合金層が発達し過ぎてめっき密着性が劣化するため、７〜１５質量％が適切である。   Next, the alloyed hot-dip galvanized layer is described. In the present invention, the alloyed hot-dip galvanized layer is a plated layer mainly composed of an Fe-Zn alloy in which Fe in steel can diffuse during Zn plating by an alloying reaction. The Fe content is not particularly limited, but if the Fe content in the plating is less than 7% by mass, a soft Zn—Fe alloy is formed on the plating surface to deteriorate the press formability. Since a brittle alloy layer develops too much at the interface and plating adhesion deteriorates, 7 to 15% by mass is appropriate.

また、一般に連続的に溶融亜鉛めっきを施す際、めっき浴中での合金化反応を制御する目的でめっき浴にＡｌを添加するため、めっき中には０．０５〜０．５質量％のＡｌが含まれる．また、合金化の過程ではＦｅの拡散と同時に鋼中に添加した元素も拡散するため、めっき中にはこれらの元素も含まれる。   In general, when continuously hot dip galvanizing is performed, Al is added to the plating bath for the purpose of controlling the alloying reaction in the plating bath. Is included. In addition, during the alloying process, the elements added to the steel diffuse simultaneously with the diffusion of Fe, so these elements are also included in the plating.

本発明鋼板は、溶融亜鉛めっき浴中あるいは亜鉛めっき中にＰｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｍｇ、Ｍｎ、Ｎｉ、Ｃｒ、Ｃｏ、Ｃａ、Ｃｕ、Ｌｉ、Ｔｉ、Ｂｅ、Ｂｉ、希土類元素の１種または２種以上を含有、あるいは混入してあっても本発明の効果を損なわず、その量によっては耐食性や加工性が改善される等好ましい場合もある．合金化溶融亜鉛めっきの付着量については特に制約は設けないが、耐食性の観点から２０ｇ／ｍ2以上、経済性の観点から１５０ｇ／ｍ2以下で有ることが望ましい。 The steel sheet of the present invention is one of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and rare earth elements during hot dip galvanizing bath or galvanizing. Alternatively, even if two or more kinds are contained or mixed, the effects of the present invention are not impaired, and depending on the amount, the corrosion resistance and workability may be improved. There are no particular restrictions on the amount of galvannealed coating, but it is preferably 20 g / m 2 or more from the viewpoint of corrosion resistance and 150 g / m 2 or less from the viewpoint of economy.

本発明において加工性の優れた高強度合金化溶融亜鉛めっき鋼板とは、引張強さが４９０ＭＰａ以上で、引張強さＦ（ＭＰａ）と伸びＬ（％）の関係が、
Ｌ≧５１−０．０３５×Ｆ
を満足する性能を持つ鋼板である。 In the present invention, the high-strength galvannealed steel sheet having excellent workability has a tensile strength of 490 MPa or more, and the relationship between tensile strength F (MPa) and elongation L (%) is
L ≧ 51−0.035 × F
It is a steel plate with performance that satisfies

伸びＬを［５１−０．０３５×Ｆ］％以上と限定した理由は、Ｌが［５１−０．０３５×Ｆ］より低い場合、深絞り等の厳しい加工のときに破断する等加工性が不十分であるためである。   The reason why the elongation L is limited to [51-0.035 × F]% or more is that, when L is lower than [51-0.035 × F], the workability such as breaking when severe processing such as deep drawing is performed. This is because it is insufficient.

本発明の高強度合金化溶融亜鉛めっき鋼板は、高強度鋼板とめっき層との界面から５μｍ以下の鋼板側の結晶粒界と結晶粒内にＳｉを含む酸化物が平均含有率０．６〜１０質量％で存在し、めっき層中にＳｉを含む酸化物が平均含有率０．０５〜１．５質量％で存在することにより不めっき欠陥を無くすことが可能となる．高強度鋼板の結晶粒界と結晶粒内にＳｉを含む酸化物が存在すると不めっき欠陥を無くすことが可能となる理由は、焼鈍過程で鋼板内にＳｉを含む酸化物が生成することによって、鋼板表面に不めっき欠陥の原因となるＳｉを含む酸化膜が生成しなくなるためであると考えられる。   The high strength alloyed hot dip galvanized steel sheet of the present invention has an average content of 0.6 to 0.5% from the interface between the high strength steel sheet and the plating layer and a grain boundary on the steel sheet side of 5 μm or less and an oxide containing Si in the crystal grains. The presence of 10% by mass and the presence of an oxide containing Si in the plating layer with an average content of 0.05 to 1.5% by mass makes it possible to eliminate non-plating defects. The reason why it is possible to eliminate non-plating defects when there is an oxide containing Si in the crystal grain boundaries and crystal grains of the high-strength steel sheet is that the oxide containing Si is generated in the steel sheet during the annealing process. This is considered to be because an oxide film containing Si that causes non-plating defects is not generated on the steel plate surface.

また、めっき層中の酸化物は焼鈍過程で鋼板内に生成したＳｉを含む酸化物が合金化過程でめっき中に拡散したものであると考えられる。   Further, the oxide in the plating layer is considered to be an oxide containing Si produced in the steel plate during the annealing process and diffused during the alloying process during the plating.

上記結晶粒界と結晶粒内に存在するＳｉを含む酸化物は、顕微鏡観察において明瞭に区別できる。高強度鋼板とめっき層との界面から５μｍ以下の鋼板側の結晶粒界と結晶粒内にＳｉを含む酸化物の一例として、断面観察結果を図１に示す。図１は、不めっきが発生しなかった高強度合金化溶融亜鉛めっき鋼板の断面を１０度に傾斜させて埋め込み研磨を行い、ＳＥＭ像で観察した結果である。この図からも解るように、高強度鋼板の結晶粒界に存在するＳｉを含む酸化物４ｂと結晶粒内に存在するＳｉを含む酸化物４ａは顕微鏡観察によって明瞭に区別できる。
The crystal grain boundary and the oxide containing Si existing in the crystal grain can be clearly distinguished by microscopic observation. A cross-sectional observation result is shown in FIG. 1 as an example of a crystal grain boundary on the steel plate side of 5 μm or less from the interface between the high-strength steel plate and the plating layer and an oxide containing Si in the crystal grains. FIG. 1 shows the result of observing an SEM image by embedding and polishing the cross-section of a high-strength galvannealed steel sheet in which no unplating occurred at an angle of 10 degrees. As can be seen from this figure, the oxide 4b containing Si present in the crystal grain boundaries of the high-strength steel sheet and the oxide 4a containing Si present in the crystal grains can be clearly distinguished by microscopic observation.

また、高強度鋼板２のめっき層１中に存在するＳｉを含む酸化物５、内部酸化層３も顕微鏡観察において明瞭に区別できる。   Further, the Si-containing oxide 5 and the internal oxide layer 3 present in the plating layer 1 of the high-strength steel plate 2 can also be clearly distinguished by microscopic observation.

さらに、これら結晶粒界と結晶粒内の酸化物４ａ、４ｂ、及びめっき層中の酸化物５をＥＤＸにより分析するとＳｉ、Ｍｎ、Ｆｅ、Ｏのピークが観察されることから、観察される酸化物はＳｉＯ2、ＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4であると考えられる。 Furthermore, when these crystal grain boundaries, oxides 4a and 4b in the crystal grains, and oxide 5 in the plating layer are analyzed by EDX, peaks of Si, Mn, Fe, and O are observed, and thus the observed oxidation. The product is considered to be SiO 2 , FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , Mn 2 SiO 4 .

本発明において、Ｓｉを含む酸化物を含有する鋼層とは、顕微鏡観察において上記酸化物が観察される層である。また、Ｓｉを含む酸化物の平均含有率とは、この鋼層中に含まれる酸化物の含有率の算術平均を示し、Ｓｉを含む酸化物を含有する鋼層の厚みとは、鋼板表面からこれら酸化物が観察される部分までの幅を示す。 In the present invention, a steel layer containing an oxide containing Si is a layer in which the oxide is observed in a microscope. Moreover, the average content rate of the oxide containing Si shows the arithmetic average of the content rate of the oxide contained in this steel layer, and the thickness of the steel layer containing the oxide containing Si is from the steel sheet surface. The width to the part where these oxides are observed is shown.

Ｓｉを含む酸化物の含有率の測定は、酸化物の質量％が測定できればどの様な方法でも構わないが、Ｓｉを含む酸化物を含有する層を酸で溶解し、Ｓｉを含む酸化物を分離させた後、重量を測定する方法が確実である．また、Ｓｉを含む酸化物を含有する鋼層の厚みの測定方法も特に規定しないが、断面から顕微鏡観察で測定する方法が確実である。   The content of the oxide containing Si can be measured by any method as long as the mass% of the oxide can be measured, but the layer containing the oxide containing Si is dissolved with an acid, and the oxide containing Si is obtained. After separation, there is a reliable way to measure the weight. Moreover, although the measuring method of the thickness of the steel layer containing the oxide containing Si is not prescribed | regulated in particular, the method of measuring with a microscope observation from a cross section is certain.

本発明において、Ｓｉを含む酸化物の平均含有率を０．６〜１０質量％に限定した理由は、０．６質量％未満では外部酸化膜の抑制が不十分で不めっき欠陥を防止する効果がみられないためであり、１０質量％を超えると不めっき欠陥を防止する効果が飽和するためである。   In the present invention, the reason why the average content of the oxide containing Si is limited to 0.6 to 10% by mass is that if the amount is less than 0.6% by mass, the suppression of the external oxide film is insufficient and the effect of preventing non-plating defects is achieved. This is because the effect of preventing non-plating defects is saturated when the content exceeds 10% by mass.

また、Ｓｉを含む酸化物を含有する鋼層の厚みを５μｍ以下に限定した理由は、５μｍを超えるとめっき密着性を向上させる効果が飽和するためである。   Moreover, the reason which limited the thickness of the steel layer containing the oxide containing Si to 5 micrometers or less is because the effect which improves plating adhesiveness will be saturated when it exceeds 5 micrometers.

また、めっき層中にＳｉを含む酸化物を平均含有率０．０５〜１．５質量％に限定した理由は、０．０５質量％未満では外部酸化膜の抑制が不十分で不めっき欠陥を防止する効果がみられないためであり、１．５質量％を超えると不めっき欠陥を防止する効果が飽和するためである。   The reason why the oxide containing Si in the plating layer is limited to an average content of 0.05 to 1.5% by mass is that if it is less than 0.05% by mass, the suppression of the external oxide film is insufficient and non-plating defects are caused. This is because the effect of preventing is not observed, and when it exceeds 1.5% by mass, the effect of preventing non-plating defects is saturated.

めっき層中のＳｉを含む酸化物の含有率の測定も、酸化物の質量％が測定できればどの様な方法でも構わないが、めっき層のみを酸で溶解し、Ｓｉを含む酸化物を分離させた後、質量を測定する方法が確実である。   The content ratio of the oxide containing Si in the plating layer may be any method as long as the mass% of the oxide can be measured, but only the plating layer is dissolved with an acid, and the oxide containing Si is separated. After that, the method of measuring the mass is reliable.

次に、製造条件の限定理由について述べる．本発明において、Ｓｉを含む酸化物を含有する鋼層を積極的に生成させるためには、連続式溶融めっきラインの焼鈍過程でＳｉを含む酸化物の内部酸化させる方法が有効である。   Next, the reasons for limiting the manufacturing conditions are described. In the present invention, in order to actively produce a steel layer containing an oxide containing Si, a method of internally oxidizing the oxide containing Si in the annealing process of the continuous hot dip plating line is effective.

ここで、Ｓｉを含む酸化物の内部酸化とは鋼板内に拡散した酸素が合金の表層付近でＳｉと反応して酸化物を析出する現象である．内部酸化現象は、酸素の内方への拡散速度がＳｉの外方への拡散速度よりはるかに早い場合、即ち雰囲気中の酸素ポテンシャルが比較的高いかもしくはＳｉの濃度が低い場合に起こる．このときＳｉはほとんど動かずその場で酸化されるため、めっき密着性低下の原因である鋼板表面へのＳｉの酸化物の濃化を防ぐことができる。   Here, the internal oxidation of the oxide containing Si is a phenomenon in which oxygen diffused in the steel plate reacts with Si in the vicinity of the surface layer of the alloy to precipitate the oxide. The internal oxidation phenomenon occurs when the inward diffusion rate of oxygen is much faster than the outward diffusion rate of Si, that is, when the oxygen potential in the atmosphere is relatively high or the concentration of Si is low. At this time, since Si hardly oxidizes and is oxidized in-situ, it is possible to prevent the concentration of Si oxide on the steel sheet surface, which is the cause of the decrease in plating adhesion.

ただし、内部酸化法で調整された鋼板であっても、Ｓｉ酸化物の種類とその位置関係によって、その後のめっき性に差が出るため、Ｓｉの酸化物は、鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が存在し、鋼板内面側にＳｉＯ2が存在する状態とする。これは、ＳｉＯ2が内部酸化状態であっても、鋼板表面に存在するとめっき性を低下させるためである。 However, even a steel plate prepared by an internal oxidation method has a difference in the subsequent plating properties depending on the type of Si oxide and its positional relationship. Therefore, the oxide of Si is FeSiO 3 on the steel plate surface or surface side. One or more Si oxides selected from Fe 2 SiO 4 , MnSiO 3 and Mn 2 SiO 4 are present, and SiO 2 is present on the inner surface side of the steel sheet. This is because even if SiO 2 is in the internal oxidation state, if it is present on the surface of the steel sheet, the plating property is lowered.

ＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4は、ＳｉＯ2よりも酸素ポテンシャルが高い領域で安定なため、鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が存在し、鋼板内面側にＳｉＯ2が存在する状態とするためには、ＳｉＯ2が単独で内部酸化する酸素ポテンシャルより大きくする必要がある。 Since FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , and Mn 2 SiO 4 are stable in a region where the oxygen potential is higher than that of SiO 2 , FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , Mn 2 is formed on the steel sheet surface or surface side. In order to obtain a state in which one or more Si oxides selected from SiO 4 are present and SiO 2 is present on the inner surface side of the steel sheet, it is necessary to make it larger than the oxygen potential at which SiO 2 is independently oxidized.

鋼中の酸素ポテンシャルは鋼板表面から内部に向かって減少するため、鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が生成する酸素ポテンシャルに鋼板表面を制御すると、鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が生成し、酸素ポテンシャルが減少した鋼板内面側にＳｉＯ2が生成する。 Since the oxygen potential in steel decreases from the steel sheet surface toward the inside, one or more Si oxides selected from FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 and Mn 2 SiO 4 are present on the steel sheet surface or surface side. When the surface of the steel sheet is controlled to the generated oxygen potential, one or more Si oxides selected from FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , Mn 2 SiO 4 are generated on the steel sheet surface or surface side, and the oxygen potential is increased. SiO 2 is generated on the inner surface side of the reduced steel plate.

上記のようなＳｉ酸化物の種類とその位置関係とすることにより、次の溶融亜鉛めっき浴への浸漬過程においてＳｉＯ2による不めっき欠陥を防止することが可能となる。 By setting the kind of Si oxide and the positional relationship as described above, it is possible to prevent non-plating defects due to SiO 2 in the subsequent immersion process in the hot dip galvanizing bath.

また、こうして作製した鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が生成した鋼板に亜鉛めっきを行い、合金化することによって、めっき層中へＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物の拡散が起こる。 Further, the steel plate produced in this manner is galvanized and alloyed on the steel plate on which one or more Si oxides selected from FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , and Mn 2 SiO 4 are formed. This causes diffusion of one or more Si oxides selected from FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , and Mn 2 SiO 4 into the plating layer.

Ｓｉの酸化状態は雰囲気中の酸素ポテンシャルで決まるため、本発明で規定した酸化物を所望の条件で生成させるためには雰囲気中のＰＯ2を直接管理する必要がある。 Since the oxidation state of Si is determined by the oxygen potential in the atmosphere, it is necessary to directly control the PO 2 in the atmosphere in order to produce the oxide defined in the present invention under the desired conditions.

雰囲気中のガスがＨ2、Ｈ2Ｏ、Ｏ2、残部Ｎ2の場合、下記平衡反応が起こると考えられ、ＰＨ2Ｏ／ＰＨ2はＰＯ2の１／２乗と平衡定数１／Ｋ１に比例する。
Ｈ２Ｏ＝Ｈ２＋１／２Ｏ２：Ｋ１＝Ｐ（Ｈ２）・Ｐ（Ｏ２）１／２／Ｐ（Ｈ２Ｏ）
ただし、平衡定数Ｋ１は温度に依存する変数であるため、温度が変化した場合、ＰＨ2Ｏ／ＰＨ2とＰＯ2は別々に変化する．即ち、ある温度域でＳｉの内部酸化領域の酸素ポテンシャルにあたる水分圧と水素分圧の比の領域であっても、別の温度域では鉄が酸化する領域の酸素ポテンシャルに対応したり、Ｓｉの外部酸化領域の酸素ポテンシャルに対応したりするためである。 When the gas in the atmosphere is H 2 , H 2 O, O 2 , and the balance N 2 , the following equilibrium reaction is considered to occur, and PH 2 O / PH 2 is the 1/2 power of PO 2 and the equilibrium constant 1 / K1. Is proportional to
H 2 O = H 2 + 1 / 2O 2 : K1 = P (H 2 ) · P (O 2 ) 1/2 / P (H 2 O)
However, since the equilibrium constant K1 is a variable depending on temperature, when the temperature changes, PH 2 O / PH 2 and PO 2 change separately. That is, even in a region where the ratio of moisture pressure and hydrogen partial pressure, which corresponds to the oxygen potential of the internal oxidation region of Si at a certain temperature range, corresponds to the oxygen potential of the region where iron is oxidized at another temperature range, This is to cope with the oxygen potential of the external oxidation region.

従って、ＰＨ2Ｏ／ＰＨ2を管理しても本発明で規定した酸化物を生成させることができない。 Therefore, even if PH 2 O / PH 2 is controlled, the oxide defined in the present invention cannot be generated.

また、雰囲気中のガスがＨ2、ＣＯ2、ＣＯ、Ｏ2、残部Ｎ2の場合、下記平衡反応が起こると考えられ、ＰＣＯ2／ＰＣＯがＰＯ2の１／２乗と平衡定数１／Ｋ２に比例する。
ＣＯ2＝ＣＯ＋１／２Ｏ2 ： Ｋ２＝Ｐ（ＣＯ）・Ｐ（Ｏ2）1/2／Ｐ（ＣＯ2）
また、同時に下記平衡反応が起こるため、雰囲気中にＨ2Ｏが発生すると考えられる。
ＣＯ2＋Ｈ2＝ＣＯ＋Ｈ2Ｏ ： Ｋ３＝Ｐ（ＣＯ）・Ｐ（Ｈ2Ｏ）／Ｐ（ＣＯ2）・Ｐ（Ｈ2）
従って、ＰＯ2は、ＰＨ2Ｏ、ＰＨ2、ＰＣＯ2、ＰＣＯと温度が決まらないと決まらないため、本発明で規定した酸化物を生成させるためには、ＰＯ2を規定するか、上記値を全て規定するかのどちらかを行う必要がある。 Further, when the gas in the atmosphere is H 2 , CO 2 , CO, O 2 , and the balance N 2 , it is considered that the following equilibrium reaction takes place, and PCO 2 / PCO is the second power of PO 2 and the equilibrium constant 1 / Proportional to K2.
CO 2 = CO + 1 / 2O 2 : K2 = P (CO) · P (O 2 ) 1/2 / P (CO 2 )
It is also contemplated that simultaneously for the following equilibrium reaction occurs, H 2 O is generated in the atmosphere.
CO 2 + H 2 = CO + H 2 O: K3 = P (CO) · P (H 2 O) / P (CO 2 ) · P (H 2 )
Therefore, since PO 2 is not determined unless the temperature is determined as PH 2 O, PH 2 , PCO 2 , and PCO, in order to produce the oxide defined in the present invention, PO 2 must be defined or the above value. It is necessary to do either one of the above.

具体的には、還元帯において鉄を還元しながらＳｉの外部酸化を抑制し、鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物を生成させる目的で、還元帯の雰囲気としてＨ2を１〜６０体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯ2、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ2を
−０．００００３４Ｔ2＋０．１０５Ｔ−０．２〔Ｓｉ％〕2＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ2≦−０．００００３８Ｔ2＋０．１０７Ｔ−９０．４・・・（１）
９２３≦Ｔ≦１１７３ ・・・（２）
Ｔ：鋼板の最高到達板温（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
に制御した雰囲気で還元を行う。 Specifically, the external oxidation of Si is suppressed while reducing iron in the reduction zone, and at least one selected from FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , and Mn 2 SiO 4 on the steel sheet surface or surface side. For the purpose of generating Si oxide, 1 to 60% by volume of H 2 is contained as the reducing zone atmosphere, and the balance is one or more of N 2 , H 2 O, O 2 , CO 2 , CO, and unavoidable. It is made of impurities, and the logarithmic log PO 2 of the oxygen partial pressure in the atmosphere is −0.000034T 2 + 0.105T−0.2 [Si%] 2 +2.1 [Si%] − 98.8 ≦ log PO 2 ≦ −0 .000038T 2 + 0.107T-90.4 (1)
923 ≦ T ≦ 1173 (2)
T: Maximum steel sheet temperature (K)
[Si%]: Si content in the steel sheet (mass%)
Reduction is performed in a controlled atmosphere.

ここで、本発明においては、対数は全て常用対数で示す。   Here, in this invention, all logarithms are shown by a common logarithm.

Ｈ2を１〜６０体積％に限定する理由は、１％未満では鋼板表面に生成した酸化膜を十分還元できず、めっき濡れ性が確保できないためであり、６０％を超えると、還元作用の向上が見られず、コストが増加するためである。 The reason for limiting H 2 to 1 to 60% by volume is that if it is less than 1%, the oxide film formed on the steel sheet surface cannot be sufficiently reduced, and plating wettability cannot be ensured. This is because there is no improvement and costs increase.

ｌｏｇＰＯ2を−０．００００３８Ｔ2＋０．１０７Ｔ−９０．４以下に限定する理由は、還元帯において鉄の酸化物を還元するためである。ｌｏｇＰＯ2が−０．００００３８Ｔ２＋０．１０７Ｔ−９０．４を超えると鉄の酸化領域にはいるため、鋼板表面に鉄の酸化膜が生成し、ブルーイングとなる。 The reason for limiting the LogPO 2 below -0.000038T 2 + 0.107T-90.4 is to reduce oxides of iron in the reduction zone. If logPO 2 exceeds -0.000038T2 + 0.107T-90.4, it enters the iron oxidation region, so that an iron oxide film is formed on the steel plate surface, resulting in bluing.

ｌｏｇＰＯ2を−０．００００３４Ｔ2＋０．１０５Ｔ−０．２〔Ｓｉ％〕２＋２．１〔Ｓｉ％〕−９８．８以上に限定する理由は、ｌｏｇＰＯ２が−０．００００３４Ｔ２＋０．１０５Ｔ−０．２〔Ｓｉ％〕２＋２．１〔Ｓｉ％〕−９８．８未満ではＳｉの酸化物ＳｉＯ2が表面に露出し、めっき密着性を低下させるためである。 The reason why the logPO 2 is limited to −0.000034T 2 + 0.105T−0.2 [Si%] 2 + 2.1 [Si%] − 98.8 or more is that the log PO 2 is −0.000034T2 + 0.105T−0.2 [ If the Si content is less than 2 + 2.1 [Si%] − 98.8, the Si oxide SiO 2 is exposed on the surface and the plating adhesion is lowered.

ｌｏｇＰＯ2を−０．００００３４Ｔ２＋０．１０５Ｔ−０．２〔Ｓｉ％〕２＋２．１〔Ｓｉ％〕−９８．８以上とすることで鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が存在し、鋼板内面側にＳｉＯ2が存在する酸化状態が得られるようになる。 By setting logPO 2 to −0.000034T2 + 0.105T−0.2 [Si%] 2 + 2.1 [Si%] − 98.8 or more, FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , One or more Si oxides selected from Mn 2 SiO 4 are present, and an oxidized state in which SiO 2 is present on the inner surface side of the steel sheet can be obtained.

また、ｌｏｇＰＯ2がさらに小さい雰囲気では、Ｓｉの外部酸化領域にはいるため、めっき密着性は著しく低下する。 Further, in an atmosphere where logPO 2 is smaller, the plating adhesion is remarkably lowered because it enters the external oxidation region of Si.

本発明において、雰囲気中の酸素分圧の対数ｌｏｇＰＯ2を規定する鋼板の最高到達板温Ｔは９２３Ｋ以上、１１７３Ｋ以下とする。 In the present invention, the maximum reached sheet temperature T of the steel sheet that defines the logarithmic log PO 2 of the oxygen partial pressure in the atmosphere is set to 923K or more and 1173K or less.

Ｔを９２３Ｋ以上に限定する理由は、Ｔが９２３Ｋ未満ではＳｉが外部酸化する酸素ポテンシャルが小さく、工業的に操業できる範囲の酸素ポテンシャルでは鉄の酸化域となるため、鋼板表面にＳｉＯ2が生成し塗装後耐食性を劣化させることがないためである。一方、Ｔを１１７３Ｋ以下に限定する理由は、１１７３Ｋを超える温度で焼鈍するのは多大のエネルギーを要して不経済であるためである．鋼板の機械特性を得る目的であれば、後に記すように最高到達板温は１１５３Ｋ以下で十分である。 The reason for limiting the T above 923K may, T is small the oxygen potential Si to external oxidation is less than 923K, to become an oxidation zone of the iron in the oxygen potential range that can be industrially operated, SiO 2 is produced on the surface of the steel sheet This is because the corrosion resistance does not deteriorate after painting. On the other hand, the reason for limiting T to 1173K or less is that annealing at a temperature exceeding 1173K requires a lot of energy and is uneconomical. For the purpose of obtaining the mechanical properties of the steel sheet, it is sufficient that the maximum reached plate temperature is 1153 K or less as described later.

また、炉内の雰囲気温度は高いほど鋼板の板温を上げ易くなるため有利であるが、雰囲気温度が高すぎると炉内の耐火物の寿命が短くなり、コストがかかるため１２７３Ｋ以下が望ましい。   Further, the higher the atmospheric temperature in the furnace, the easier it is to raise the plate temperature of the steel sheet. However, if the atmospheric temperature is too high, the life of the refractory in the furnace is shortened and the cost is increased.

本発明において、ＰＯ2はＨ2Ｏ、Ｏ2、ＣＯ2、ＣＯの１種または２種以上を導入することにより操作する。前述した平衡反応式において、温度が決まれば平衡定数が決定し、その平衡定数に基づいて酸素分圧、即ち酸素ポテンシャルが決定する．雰囲気温度７７３Ｋから１２７３Ｋにおいては、気体の反応は短時間で平衡状態に達するため、ＰＯ2は炉内のＰＨ2、ＰＨ2Ｏ、ＰＣＯ2、ＰＣＯと雰囲気温度が決まると決定する。 In the present invention, PO 2 is operated by introducing one or more of H 2 O, O 2 , CO 2 and CO. In the equilibrium reaction equation described above, the equilibrium constant is determined when the temperature is determined, and the oxygen partial pressure, that is, the oxygen potential is determined based on the equilibrium constant. At atmospheric temperatures from 773 K to 1273 K, the gas reaction reaches an equilibrium state in a short time, so that PO 2 is determined to determine the atmospheric temperature of PH 2 , PH 2 O, PCO 2 and PCO in the furnace.

Ｏ2とＣＯは意識的に導入する必要はないが、本焼鈍温度でＨ2を１体積％以上含有する炉内にＨ2Ｏ、ＣＯ2を導入した場合、その一部とＨ２との平衡反応により、Ｏ2、ＣＯが生成する。Ｈ2Ｏ、ＣＯ2は必要な量導入できればよく、その導入方法は特に限定しないが、例えば、ＣＯとＨ2を混合した気体を燃焼させ、発生したＨ2Ｏ、ＣＯ2を導入する方法や、ＣＨ4、Ｃ2Ｈ6、Ｃ3Ｈ8等の炭化水素の気体や、ＬＮＧ等の炭化水素の混合物を燃焼させ、発生したＨ2Ｏ、ＣＯ2を導入する方法、ガソリンや軽油、重油等、液体の炭化水素の混合物を燃焼させ、発生したＨ2Ｏ、ＣＯ2を導入する方法、ＣＨ3ＯＨ、Ｃ2Ｈ5ＯＨ等のアルコール類やその混合物、各種の有機溶剤を燃焼させ、発生したＨ2Ｏ、ＣＯ2を導入する方法等が上げられる。 O 2 and CO do not need to be consciously introduced, but when H 2 O and CO 2 are introduced into a furnace containing 1% by volume or more of H 2 at the main annealing temperature, some of them and the equilibrium of H 2 O 2 and CO are produced by the reaction. The introduction method of H 2 O and CO 2 is not particularly limited as long as a necessary amount can be introduced. For example, a method in which a gas in which CO and H 2 are mixed is burned and the generated H 2 O and CO 2 are introduced. , CH 4 , C 2 H 6 , C 3 H 8 and other hydrocarbon gases, and a mixture of hydrocarbons such as LNG, and the generated H 2 O and CO 2 are introduced, gasoline, light oil, heavy oil Such as burning a mixture of liquid hydrocarbons and introducing the generated H 2 O, CO 2 , burning alcohols such as CH 3 OH, C 2 H 5 OH and mixtures thereof, various organic solvents, A method of introducing the generated H 2 O and CO 2 is raised.

ＣＯのみ燃焼させ、発生したＣＯ2を導入する方法も考えられるが、本焼鈍温度、雰囲気の炉内にＣＯ2を導入した場合、その一部がＨ2により還元され、ＣＯとＨ2Ｏが生成するため、Ｈ2Ｏ、ＣＯ2を導入した場合と本質的に差はない。 CO only burned, but also conceivable to introduce CO 2 generated, the annealing temperature, if CO 2 was introduced into the furnace atmosphere, part is reduced by H 2, CO and H 2 O is Therefore, there is essentially no difference from the case where H 2 O and CO 2 are introduced.

また、燃焼させ、発生したＨ2Ｏ、ＣＯ2を導入する方法以外にも、ＣＯとＨ2を混合した気体、ＣＨ4、Ｃ2Ｈ6、Ｃ3Ｈ8等の炭化水素の気体や、ＬＮＧ等の炭化水素の混合物、ガソリンや軽油、重油等、液体の炭化水素の混合物、ＣＨ3ＯＨ、Ｃ2Ｈ5ＯＨ等のアルコール類やその混合物、各種の有機溶剤等を酸素と同時に焼鈍炉内に導入し、炉内で燃焼させてＨ2Ｏ、ＣＯ2を発生させる方法も使用できる。 In addition to the method of introducing H 2 O and CO 2 generated by combustion, a gas containing a mixture of CO and H 2 , a hydrocarbon gas such as CH 4 , C 2 H 6 , C 3 H 8 , LNG and other hydrocarbon mixtures, gasoline, light oil, heavy oil, liquid hydrocarbon mixtures, CH 3 OH, C 2 H 5 OH and other alcohols and mixtures, various organic solvents, etc. A method of introducing H 2 O and CO 2 by introducing the gas into the furnace and burning it in a furnace can also be used.

こうした方法は、水蒸気を飽和させたＮ2や露点を上げたＮ2を利用して水蒸気を供給する方法に比べ、簡便で制御性が優れる．また、配管内で結露したりする心配もないため、配管の断熱を行う手間なども省くことができる。 Such method utilizes N 2 raising the N 2 and dew point saturated with water vapor compared to the method of supplying steam, simple and the control is excellent. In addition, since there is no fear of condensation in the pipe, it is possible to save the trouble of heat insulation of the pipe.

本発明において、請求項に規定したＰＯ2と温度における還元時間は特に規定しないが、望ましくは１０秒以上３分以下である．還元炉内においてＰＯ2を大きくすると、昇温過程において、ｌｏｇＰＯ2が−０．００００３８Ｔ２＋０．１０７Ｔ−９０．４を超える領域を通過した後、−０．００００３８Ｔ２＋０．１０７Ｔ−９０．４以下の領域で還元されるため、最初に生成した鉄の酸化膜を還元し、目的とした鋼板表面または表面側にＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉ酸化物が存在し、鋼板内面側にＳｉＯ2が存在する鋼板を得るためには、１０秒以上保持することが望ましい．ただし、３分を超えて保持してもエネルギーの無駄となるばかりか連続ラインでの生産性低下を引き起こすため好ましくない。 In the present invention, the reduction time at the PO 2 and temperature specified in the claims is not particularly specified, but is preferably 10 seconds or more and 3 minutes or less. Increasing the PO 2 in the reducing furnace, the Atsushi Nobori process, after the LogPO 2 has passed the region exceeding -0.000038T2 + 0.107T-90.4, -0.000038T2 + 0.107T-90.4 in the following areas In order to be reduced, the iron oxide film formed first is reduced, and one or more kinds of Si selected from FeSiO 3 , Fe 2 SiO 4 , MnSiO 3 , and Mn 2 SiO 4 are formed on the target steel sheet surface or surface side. In order to obtain a steel plate in which oxide is present and SiO 2 is present on the inner surface side of the steel plate, it is desirable to hold for 10 seconds or more. However, holding for more than 3 minutes is not preferable because it not only wastes energy but also reduces productivity in a continuous line.

また、還元雰囲気のＰＯ2と温度が本発明範囲内であれば、通常の無酸化炉方式の溶融めっき法やオールラジアントチューブ方式の焼鈍炉を使用した溶融めっき法を使用できる。特開昭５５−１２２８６５号公報に記されたように予め鋼板表面に酸化膜を生成させた後、焼鈍及び前記鉄酸化膜の還元を行う方法も使用可能である。 If the PO 2 and temperature in the reducing atmosphere are within the range of the present invention, a normal non-oxidizing furnace type hot dipping method or a hot dipping method using an all radiant tube type annealing furnace can be used. As described in JP-A-55-122865, a method of forming an oxide film on the surface of a steel plate in advance and then annealing and reducing the iron oxide film can be used.

鉄酸化膜を形成せしめる方法としては、例えば酸化帯において燃焼空気比を０．９〜１．２に制御し鉄酸化膜を形成させる方法や酸化帯の露点を２７３Ｋ以上に制御し鉄酸化膜を形成させる方法が使用できる。   As a method of forming the iron oxide film, for example, a method of forming an iron oxide film by controlling the combustion air ratio in the oxidation zone to 0.9 to 1.2, or a dew point of the oxidation zone is controlled to 273 K or more and the iron oxide film is formed. Any method of forming can be used.

燃焼空気比を０．９〜１．２の範囲に調節する理由は、Ｓｉの外部酸化を抑制するのに十分な鉄酸化膜を生成するために０．９以上の燃焼空気比が必要であり、０．９未満の場合は十分な鉄酸化膜を形成せしめることができないためである．又、燃焼空気比が１．２を超えると酸化帯内で形成される鉄酸化膜厚が厚すぎて、剥離した酸化物がロールに付着し外観疵を発生させるためである。   The reason for adjusting the combustion air ratio in the range of 0.9 to 1.2 is that a combustion air ratio of 0.9 or more is necessary to generate an iron oxide film sufficient to suppress external oxidation of Si. If it is less than 0.9, a sufficient iron oxide film cannot be formed. Further, when the combustion air ratio exceeds 1.2, the iron oxide film formed in the oxidation zone is too thick, and the peeled oxide adheres to the roll and generates appearance defects.

また、酸化帯の露点を２７３Ｋ以上に制御する理由は、Ｓｉの外部酸化を抑制するのに十分な鉄酸化膜を生成するために２７３Ｋ以上の露点が必要であり、２７３Ｋ未満の場合は十分な鉄酸化膜を形成せしめることができないためである．露点の上限は特に規定しないが、設備の劣化などへの影響を考慮し、３７３Ｋ以下が望ましい。   The reason for controlling the dew point of the oxidation band to 273K or more is that a dew point of 273K or more is necessary to generate an iron oxide film sufficient to suppress external oxidation of Si, and the dew point is less than 273K. This is because an iron oxide film cannot be formed. The upper limit of the dew point is not specified, but it is preferably 373K or less in consideration of the influence on the deterioration of the equipment.

酸化膜の厚みは、燃焼空気比、露点のみではなく、ライン速度、到達板温等も影響するため、これらを適切に制御し、酸化膜の厚みが２００〜２０００Åになるような条件で通板することが望ましい。   The thickness of the oxide film affects not only the combustion air ratio and the dew point, but also the line speed, the reaching plate temperature, etc., so these are controlled appropriately, and the plate is passed under the condition that the thickness of the oxide film is 200 to 2000 mm. It is desirable to do.

ただし、生成した鉄の酸化膜の還元を終了させるため、請求項に規定したＰＯ2と温度における還元時間は、２０秒以上とすることが望ましい。 However, in order to finish the reduction of the generated iron oxide film, the reduction time at PO 2 and temperature specified in the claims is preferably 20 seconds or more.

上記製造方法は，連続溶融めっき設備に，ＣＯ2を１〜１００体積％含有し，残部Ｎ2，Ｈ2Ｏ，Ｏ2，ＣＯおよび不可避的不純物からからなる気体を導入する装置を還元炉に配設することや，還元炉中でＣＯまたは炭化水素を燃焼させ，ＣＯ2を１〜１００体積％含有し，残部Ｎ2，Ｈ2Ｏ，Ｏ2，ＣＯおよび不可避的不純物からからなる気体を発生させる装置を配設することにより可能となる．具体的な製造設備の例を図２，図３に示す．図２に示す例は、鋼板進行方向１１から鋼板６を焼鈍炉の加熱帯７、焼鈍炉の均熱帯８、焼鈍炉の冷却帯９を通過させて、焼鈍し、スナウト１４を通して溶融亜鉛１３の入った溶融亜鉛めっき層１２に浸漬し、シンクロール１５を介して引き上げ、ガスワイピングノズル１６で付着量を調整し、合金化炉１７で合金化処理する装置である。焼鈍炉の均熱帯８には、燃料ガス配管２４からの燃料ガスと空気配管２６からの空気とを燃焼装置２１で燃焼させた燃焼ガスを燃焼ガス配管２２を通じて配給される。また、焼鈍炉の均熱帯８及び焼鈍炉の冷却帯９には、還元ガス配管１９を通じて還元ガスが還元性ガス流れ方向（矢印２０で示す）から供給される。 In the above manufacturing method, the apparatus for introducing a gas containing 1 to 100% by volume of CO 2 into the continuous hot dipping equipment and the balance N 2 , H 2 O, O 2 , CO and unavoidable impurities is used as a reduction furnace. be arranged and the CO or hydrocarbon is combusted in a reducing furnace, the CO 2 containing 1 to 100% by volume, balance N 2, H 2 O, a gas consisting of O 2, CO and unavoidable impurities This can be done by installing a generating device. Examples of specific manufacturing facilities are shown in Figs. In the example shown in FIG. 2, the steel sheet 6 is annealed by passing through the heating zone 7 of the annealing furnace, the soaking zone 8 of the annealing furnace, and the cooling zone 9 of the annealing furnace from the steel plate traveling direction 11, and the molten zinc 13 passes through the snout 14. It is an apparatus that is immersed in the hot dip galvanized layer 12 and pulled up through a sink roll 15, the amount of adhesion is adjusted by a gas wiping nozzle 16, and alloying treatment is performed by an alloying furnace 17. In the soaking zone 8 of the annealing furnace, the combustion gas obtained by burning the fuel gas from the fuel gas pipe 24 and the air from the air pipe 26 by the combustion device 21 is distributed through the combustion gas pipe 22. Further, the reducing gas is supplied from the reducing gas flow direction (indicated by the arrow 20) to the soaking zone 8 of the annealing furnace and the cooling zone 9 of the annealing furnace through the reducing gas pipe 19.

また、図３に示す例は、図２と基本的構造は同じであるが、燃焼炉の均熱帯８内に炉内に設置された燃焼装置２８を備えていて、燃料ガス配管２４からの燃料と空気配管２６からの空気とを燃焼装置２８で燃焼させることが異なっているものである。   The example shown in FIG. 3 has the same basic structure as FIG. 2, but includes a combustion device 28 installed in the soaking zone 8 of the combustion furnace, and fuel from the fuel gas pipe 24. And the air from the air pipe 26 are burned by the combustion device 28.

このように，ＣＯ2を１〜１００体積％含有し，残部Ｎ2，Ｈ2Ｏ，Ｏ2，ＣＯおよび不可避的不純物からからなる気体を導入する装置を還元炉に配設することや，還元炉中でＣＯまたは炭化水素を燃焼させ，ＣＯ2を１〜１００体積％含有し，残部Ｎ2，Ｈ2Ｏ，Ｏ2，ＣＯおよび不可避的不純物からからなる気体を発生させる装置を配設することにより，目的とした酸化層を得られる雰囲気に還元炉を制御することが可能となる。 Thus, a device for introducing a gas containing 1 to 100% by volume of CO 2 and the balance N 2 , H 2 O, O 2 , CO and unavoidable impurities is disposed in the reduction furnace, An apparatus for combusting CO or hydrocarbons in a furnace and containing 1 to 100% by volume of CO 2 and generating a gas composed of the balance N 2 , H 2 O, O 2 , CO and inevitable impurities is provided. As a result, the reduction furnace can be controlled to an atmosphere in which a target oxide layer can be obtained.

次に、その他の製造条件の限定理由について述べる．その目的はマルテンサイトおよび残留オーステナイトを３〜２０％含む金属組織とし、高強度とプレス加工性が良いことが両立させることにある．マルテンサイトおよび残留オーステナイトの体積率が３％未満の場合には高強度とならない．一方、マルテンサイトおよび残留オーステナイトの体積率が２０％を超えると、高強度ではあるものの鋼板の加工性が劣化し、本発明の目的が達成されない。   Next, the reasons for limiting other manufacturing conditions are described. The purpose is to make the metal structure 3 to 20% martensite and retained austenite, and to achieve both high strength and good press workability. When the volume ratio of martensite and retained austenite is less than 3%, the strength is not high. On the other hand, if the volume ratio of martensite and retained austenite exceeds 20%, the workability of the steel sheet is deteriorated although it is high in strength, and the object of the present invention is not achieved.

熱間圧延に供するスラブは特に限定するものではなく、連続鋳造スラブや薄スラブキャスター等で製造したものであればよい．また鋳造後直ちに熱間圧延を行う連続鋳造−直送圧延（ＣＣ−ＤＲ）のようなプロセスにも適合する。   The slab to be used for hot rolling is not particularly limited as long as it is manufactured with a continuously cast slab or a thin slab caster. It is also compatible with processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.

熱間圧延の仕上温度は鋼板のプレス成形性を確保するという観点からＡｒ３点以上とする必要がある．熱延後の冷却条件や巻取温度は特に限定しないが、巻取温度はコイル両端部での材質ばらつきが大ききなることを避け、またスケール厚の増加による酸洗性の劣化を避けるためには１０２３Ｋ以下とし、また部分的にベイナイトやマルテンサイトが生成すると冷間圧延時に耳割れを生じやすく、極端な場合には板破断することもあるため８２３Ｋ以上とすることが望ましい．冷間圧延は通常の条件でよく、フェライトが加工硬化しやすいようにマルテンサイトおよび残留オーステナイトを微細に分散させ、加工性の向上を最大限に得る目的からその圧延率は５０％以上とする．一方、８５％を超す圧延率で冷間圧延を行うことは多大の冷延負荷が必要となるため現実的ではない。   The hot rolling finishing temperature must be at least Ar3 from the viewpoint of ensuring the press formability of the steel sheet. The cooling conditions and coiling temperature after hot rolling are not particularly limited, but the coiling temperature is to avoid large material variations at both ends of the coil and to avoid pickling deterioration due to increased scale thickness. Is 1023K or less, and when bainite or martensite is partially formed, ear cracks are likely to occur during cold rolling, and in extreme cases, the plate may be broken. Cold rolling may be performed under normal conditions, and the rolling rate should be 50% or more in order to finely disperse martensite and retained austenite so that the ferrite is easy to work harden and maximize workability. On the other hand, it is not realistic to perform cold rolling at a rolling rate exceeding 85% because a large cold rolling load is required.

ライン内焼鈍方式の連続溶融亜鉛めっき設備で焼鈍する際、その焼鈍温度は１０２３Ｋ以上１１５３Ｋ以下のフェライト、オーステナイト二相共存域とする．焼鈍温度が１０２３Ｋ未満では再結晶が不十分であり、鋼板に必要なプレス加工性を具備できない．１１５３Ｋを超すような温度で焼鈍することは生産コストが上昇すると共に設備の劣化が早くなるため好ましくない．また引き続きめっき浴へ浸漬し、冷却する過程で、９２３Ｋまでを緩冷却しても十分な体積率のフェライトが成長せず、９２３Ｋからめっき浴までの冷却途上でオーステナイトがマルテンサイトに変態し、その後合金化処理のための再加熱でマルテンサイトが焼き戻されてセメンタイトが析出するため高強度とプレス加工性の良いことの両立が困難となる。   When annealing in a continuous hot-dip galvanizing facility using an in-line annealing method, the annealing temperature is in the range of 1023K or more and 1153K or less of ferrite and austenite. If the annealing temperature is less than 1023K, recrystallization is insufficient and the press workability required for the steel sheet cannot be achieved. Annealing at a temperature exceeding 1153 K is not preferable because the production cost increases and the equipment deteriorates quickly. Further, in the process of immersing and cooling in the plating bath, ferrite with sufficient volume fraction does not grow even if it is slowly cooled to 923K, and austenite is transformed into martensite during the cooling from 923K to the plating bath. Martensite is tempered by reheating for alloying treatment, and cementite is precipitated, so that it is difficult to achieve both high strength and good press workability.

鋼帯は焼鈍後、引き続きめっき浴へ浸漬する過程で冷却されるが、この場合の冷却速度は、その最高到達温度から９２３Ｋまでを平均０．５〜１０度／秒で、引き続いて９２３Ｋから７７３Ｋまでを平均冷却速度３度／秒以上で冷却し、さらに７７３Ｋから平均冷却速度０．５度／秒以上で６９３Ｋ〜７３３Ｋまで冷却し、且つ、７７３Ｋからめっき浴までを２５秒以上２４０秒以下保持する。   The steel strip is cooled in the process of being subsequently immersed in the plating bath after annealing. In this case, the cooling rate is 0.5 to 10 degrees / second on average from its maximum temperature to 923 K, and subsequently from 923 K to 773 K. Is cooled at an average cooling rate of 3 degrees / second or more, further cooled from 773 K to 693 K to 733 K at an average cooling speed of 0.5 degrees / second or more, and maintained from 773 K to the plating bath for 25 seconds or more and 240 seconds or less. To do.

９２３Ｋまでを平均０．５〜１０度／秒とするのは加工性を改善するためにフェライトの体積率を増すと同時に、オーステナイトのＣ濃度を増すことにより、その生成自由エネルギーを下げ、マルテンサイト変態の開始する温度をめっき浴温度以下とすることを目的とする．９２３Ｋまでの平均冷却速度を０．５度／秒未満とするためには連続溶融亜鉛めっき設備のライン長を長くする必要がありコスト高となるため、９２３Ｋまでの平均冷却速度は０．５度／秒以上とする。   The average of 0.5 to 10 degrees / second up to 923K is to increase the volume fraction of ferrite in order to improve workability, and at the same time, to increase the C concentration of austenite, thereby lowering the free energy of formation, and martensite The purpose is to keep the temperature at which transformation starts below the bath temperature. In order to make the average cooling rate up to 923K less than 0.5 degree / second, it is necessary to lengthen the line length of the continuous hot dip galvanizing equipment, resulting in high cost, so the average cooling rate up to 923K is 0.5 degree / Second or more.

９２３Ｋまでの平均冷却速度を０．５度／秒未満とするためには、最高到達温度を下げ、オーステナイトの体積率が小さい温度で焼鈍することも考えられるが、その場合には実際の操業で許容すべき温度範囲に比べて適切な温度範囲が狭く、僅かでも焼鈍温度が低いとオーステナイトが形成されず目的を達しない。   In order to make the average cooling rate up to 923 K less than 0.5 degrees / second, it is conceivable to lower the maximum temperature and anneal at a temperature at which the volume fraction of austenite is small, but in that case, in actual operation If the appropriate temperature range is narrower than the allowable temperature range and the annealing temperature is low even a little, austenite is not formed and the purpose is not achieved.

一方、９２３Ｋまでの平均冷却速度を１０度／秒を超えるようにすると、フェライトの体積率の増加が十分でないばかりか、オーステナイト中Ｃ濃度の増加も少ないため、鋼帯がめっき浴に浸漬される前にその一部がマルテンサイト変態し、その後合金化処理のための加熱でマルテンサイトが焼き戻されてセメンタイトとして析出するため高強度と加工性の良いことの両立が困難となる。   On the other hand, when the average cooling rate up to 923 K is made to exceed 10 degrees / second, not only the volume fraction of ferrite is not increased sufficiently, but also the increase in C concentration in austenite is small, so the steel strip is immersed in the plating bath. A part of it is transformed into martensite before, and then martensite is tempered by heating for alloying treatment and precipitates as cementite. Therefore, it is difficult to achieve both high strength and good workability.

９２３Ｋから７７３Ｋまでの平均冷却速度を３度／秒以上とするのは、その冷却途上でオーステナイトがパーライトに変態するのを避けるためであり、その冷却速度が３度／秒未満では本発明で規定する温度で焼鈍し、また９２３Ｋまで冷却したとしてもパーライトの生成を避けられない。平均冷却速度の上限は特に規定しないが、平均冷却速度２０度／秒を超えるように鋼帯を冷却することはドライな雰囲気では困難である。   The reason why the average cooling rate from 923 K to 773 K is set to 3 degrees / second or more is to avoid the transformation of austenite to pearlite during the cooling, and is specified by the present invention when the cooling rate is less than 3 degrees / second. Even if it is annealed at a temperature to cool to 923K, the formation of pearlite is inevitable. The upper limit of the average cooling rate is not particularly defined, but it is difficult to cool the steel strip so that the average cooling rate exceeds 20 degrees / second in a dry atmosphere.

７７３Ｋからの平均冷却速度を０．５度／秒以上とするのは、その冷却途上でオーステナイトがパーライトに変態するのを避けるためであり、その冷却速度が０．５度／秒未満では本発明で規定する温度で焼鈍し、また７７３Ｋまで冷却したとしてもパーライトの生成を避けられない。平均冷却速度の上限は特に規定しないが、平均冷却速度２０度／秒を超えるように鋼帯を冷却することはドライな雰囲気では困難である。また、冷却終了温度を６９３Ｋ〜７３３Ｋとするのは、オーステナイト中へのＣの濃化が促進され加工性の優れた高強度合金化溶融亜鉛めっきが得られるためである。   The reason why the average cooling rate from 773 K is 0.5 degrees / second or more is to avoid the transformation of austenite to pearlite during the cooling, and if the cooling rate is less than 0.5 degrees / second, the present invention. Even if it is annealed at a temperature specified in (1) and cooled to 773K, the formation of pearlite is inevitable. The upper limit of the average cooling rate is not particularly defined, but it is difficult to cool the steel strip so that the average cooling rate exceeds 20 degrees / second in a dry atmosphere. Moreover, the reason why the cooling end temperature is set to 693 K to 733 K is that concentration of C in austenite is promoted and high strength alloyed hot dip galvanizing excellent in workability is obtained.

７７３Ｋからめっき浴までを２５秒以上２４０秒以下保持する理由は、２５秒未満ではオーステナイト中へのＣの濃化が不十分となり、オーステナイト中のＣ濃度が、室温でのオーステナイトの残留を可能とする水準まで到達しないためであり、２４０秒を超えると、ベイナイト変態が進行し過ぎて、オーステナイト量が少なくなり、十分な量の残留オーステナイトを生成できないためである。   The reason why the temperature from 773K to the plating bath is maintained for 25 seconds or more and 240 seconds or less is that if less than 25 seconds, the concentration of C in the austenite becomes insufficient, and the C concentration in the austenite allows austenite to remain at room temperature. This is because when the time exceeds 240 seconds, the bainite transformation proceeds excessively, the amount of austenite decreases, and a sufficient amount of retained austenite cannot be generated.

さらにこの７７３Ｋからめっき浴まで保持する間、一度６７３Ｋ〜７２３Ｋの温度まで冷却し、保持するとオーステナイト中へのＣの濃化が促進され加工性の優れた高強度合金化溶融亜鉛めっきが得られる。ただし、７０３Ｋ以下でめっき浴中へ板を浸漬させ続けるとめっき浴が冷却され凝固するため、７０３〜７４３Ｋの温度まで再加熱を行った後、溶融亜鉛めっき処理を行う必要がある。   Further, while holding from 773K to the plating bath, once cooling to 673K to 723K and holding, concentration of C in the austenite is promoted and high strength alloyed hot dip galvanizing excellent in workability is obtained. However, if the plate is continuously immersed in the plating bath at 703K or less, the plating bath is cooled and solidified, and thus it is necessary to perform hot dip galvanizing after reheating to a temperature of 703 to 743K.

本発明の合金化溶融亜鉛めっき鋼板の製造において、用いる溶融亜鉛めっき浴はＡｌ濃度が浴中有効Ａｌ濃度Ｃで０．０７〜０．１０５ｍａｓｓ％に調整する．ここでめっき浴中の有効Ａｌ濃度とは、浴中Ａｌ濃度から浴中Ｆｅ濃度を差し引いた値である。   In the production of the alloyed hot dip galvanized steel sheet of the present invention, the hot dip galvanizing bath used is adjusted so that the Al concentration is 0.07 to 0.105 mass% in terms of the effective Al concentration C in the bath. Here, the effective Al concentration in the plating bath is a value obtained by subtracting the Fe concentration in the bath from the Al concentration in the bath.

有効Ａｌ濃度を０．０７〜０．１０５ｍａｓｓ％に限定する理由は、有効Ａｌ濃度が０．０７％よりも低い場合には、めっき初期の合金化バリアとなるＦｅ−Ａｌ−Ｚｎ相の形成が不十分であってめっき処理時にめっき鋼板界面に脆いΓ相が厚くできるため、加工時のめっき皮膜密着力が劣る合金化溶融亜鉛めっき鋼板しか得られないためである．一方、有効Ａｌ濃度が０．１０５％よりも高い場合には、高温長時間の合金化が必要となり、鋼中に残存していたオーステナイトがパーライトに変態するため、高強度と加工性の良いことの両立が困難となる．望ましくは０．０９９ｍａｓｓ％以下である。   The reason for limiting the effective Al concentration to 0.07 to 0.105 mass% is that when the effective Al concentration is lower than 0.07%, the formation of an Fe—Al—Zn phase that becomes an alloying barrier at the initial stage of plating is performed. This is because it is insufficient and the brittle Γ phase can be thickened at the surface of the plated steel sheet during the plating process, so that only an alloyed hot-dip galvanized steel sheet with poor plating film adhesion during processing can be obtained. On the other hand, when the effective Al concentration is higher than 0.105%, alloying for a long time at high temperature is required, and austenite remaining in the steel is transformed into pearlite, so that high strength and workability are good. It becomes difficult to achieve both. Desirably, it is 0.099 mass% or less.

更に、本発明において合金化処理時の合金化温度を
７２０≦Ｔ≦６９０×ｅｘｐ（１．３５×〔Ａｌ％〕）
但し、〔Ａｌ％〕：亜鉛めっき浴中の浴中有効Ａｌ濃度（ｍａｓｓ％）
を満足する温度Ｔ（Ｋ）において行うことが望ましい。 Furthermore, in the present invention, the alloying temperature during the alloying treatment is 720 ≦ T ≦ 690 × exp (1.35 × [Al%]).
However, [Al%]: Effective Al concentration in the galvanizing bath (mass%)
It is desirable to carry out at a temperature T (K) that satisfies the above.

合金化温度Ｔを７２０Ｋ以上、６９０×ｅｘｐ（１．３５×〔Ａｌ％〕）℃以下に限定した理由は、合金化温度Ｔが７２０Ｋよりも低いと合金化が進行しないか、或いは合金化の進行が不十分で合金化未処理となりめっき表層が成形性の劣るη相に覆われるためである．また、Ｔが６９０×ｅｘｐ（１．３５×〔Ａｌ％〕）℃よりも高いと、合金化が進み過ぎてめっき鋼板界面に脆いΓ相が厚くできるため、加工時のめっき密着力が低下するためである。   The reason why the alloying temperature T is limited to 720K or more and 690 × exp (1.35 × [Al%]) ° C. or less is that the alloying does not proceed when the alloying temperature T is lower than 720K, or the alloying temperature T This is because the progress is insufficient, the alloying is untreated, and the plating surface layer is covered with the η phase with poor formability. Moreover, when T is higher than 690 × exp (1.35 × [Al%]) ° C., alloying proceeds too much, and a brittle Γ phase can be formed at the plated steel plate interface, so that the plating adhesion during processing is reduced. Because.

溶融めっき後６７３Ｋ以下の温度に冷却されるまでの時間を３０秒以上１２０秒以下に限定する理由は、３０秒未満では合金化が不十分で合金化未処理となりめっき表層が成形性の劣るη相に覆われるためであり、１２０秒を越えると、ベイナイト変態が進行し過ぎて、オーステナイト量が少なくなり、十分な量の残留オーステナイトを生成できないためである。   The reason for limiting the time until cooling to a temperature of 673 K or less after hot dipping to 30 seconds or more and 120 seconds or less is that if less than 30 seconds, alloying is insufficient and alloying is untreated, and the plating surface layer has poor formability. This is because the phase is covered by the phase, and if it exceeds 120 seconds, the bainite transformation proceeds too much, the amount of austenite decreases, and a sufficient amount of retained austenite cannot be generated.

本発明において合金化炉加熱方式については特に限定するものではなく、本発明の温度が確保できれば、通常のガス炉による輻射加熱でも、高周波誘導加熱でもかまわない．また、合金化加熱後の最高到達板温度から冷却する方法も、問うものではなく、合金化後、エアーシール等により、熱を遮断すれば、開放放置でも十分であり、より急速に冷却するガスクーリング等でも問題ない。   In the present invention, the alloying furnace heating method is not particularly limited. If the temperature of the present invention can be secured, radiation heating by a normal gas furnace or high frequency induction heating may be used. In addition, the method of cooling from the highest plate temperature after alloying heating is not questioned. If the heat is shut off by air seal etc. after alloying, it is sufficient to leave open, and the gas that cools more rapidly There is no problem with cooling.

以下、実施例により本発明を具体的に説明する。   Hereinafter, the present invention will be described specifically by way of examples.

表１の組成からなるスラブを１４２３Ｋに加熱し、仕上温度１１８３〜１２０３Ｋで４．５ｍｍの熱間圧延鋼帯とし、８５３〜９５３Ｋで巻き取った．酸洗後、冷間圧延を施して１．６ｍｍの冷間圧延鋼帯とした後、ライン内焼鈍方式の連続溶融亜鉛めっき設備を用いて表２に示すような条件のめっきを行い、合金化溶融亜鉛めっき鋼板を製造した．連続溶融亜鉛めっき設備は、無酸化炉による加熱後、還元帯で還元・焼鈍を行う方式を使用した．無酸化炉の燃焼空気比は１．０に調節し、酸化帯として使用した．還元帯はＣＯとＨ2を混合した気体を燃焼させ発生したＨ2Ｏ、ＣＯ2を導入する装置を取り付け、Ｈ2を１０体積％含むＮ2ガスにＨ2ＯとＣＯ2を導入した。 A slab having the composition shown in Table 1 was heated to 1423K to form a 4.5 mm hot-rolled steel strip at a finishing temperature of 1183 to 1203K, and wound at 853 to 953K. After pickling, cold rolling to obtain a 1.6 mm cold rolled steel strip, followed by plating under the conditions shown in Table 2 using an in-line annealing method of continuous hot dip galvanizing equipment, and alloying A hot-dip galvanized steel sheet was manufactured. The continuous hot-dip galvanizing equipment used a method of reducing and annealing in the reduction zone after heating in a non-oxidizing furnace. The combustion air ratio of the non-oxidizing furnace was adjusted to 1.0 and used as the oxidation zone. Reduction zone is CO and H 2 The mixed gas by burning generated H 2 O, fitted with a device for introducing the CO 2, introducing H 2 O and CO 2 and H 2 in N 2 gas containing 10 vol%.

焼鈍は、最高到達温度を表２に示す値となるよう調節し、均熱温度（最高到達温度−２０度から最高到達温度までの範囲）に入っている均熱時間を６０秒とした後、その最高到達温度から９２３Ｋまでを平均冷却速度１度／秒で、引き続いて９２３Ｋから７７３Ｋまでを平均冷却速度４度／秒で冷却し、さらに７７３Ｋから平均冷却速度１．７度／秒以上で７２３Ｋまで冷却し、且つめっき浴まで７２３Ｋで保持し、７７３Ｋからめっき浴までを３０秒確保した後、溶融亜鉛めっきを行い７７３Ｋで合金化処理を行った。   Annealing is adjusted so that the maximum reached temperature becomes the value shown in Table 2, and the soaking time in the soaking temperature (the range from the maximum attainable temperature minus 20 degrees to the maximum attainable temperature) is set to 60 seconds. From the maximum temperature reached 923K at an average cooling rate of 1 degree / second, subsequently from 923K to 773K at an average cooling rate of 4 degrees / second, and further from 773K at an average cooling rate of 1.7 degrees / second or more at 723K. After cooling to 723 K and holding at 723 K until 30 seconds from 773 K to the plating bath, hot dip galvanization was performed and alloying was performed at 773 K.

還元炉内のＰＯ2は、炉内の水素濃度、水蒸気濃度、ＣＯ2濃度、ＣＯ濃度、雰囲気温度の測定値と平衡反応
Ｈ2Ｏ＝Ｈ2＋１／２Ｏ2
ＣＯ2＝ＣＯ＋１／２Ｏ2
の平衡定数Ｋ１、Ｋ２を使用して求めた。 The PO 2 in the reduction furnace is the measured value of the hydrogen concentration, water vapor concentration, CO 2 concentration, CO concentration, atmospheric temperature in the furnace and the equilibrium reaction H 2 O = H 2 + 1 / 2O 2.
CO 2 = CO + 1 / 2O 2
Using the equilibrium constants K1 and K2.

引張強さ（ＴＳ）、伸び（Ｅｌ）は、各鋼板からＪＩＳ５号試験片を切り出し、常温での引張試験を行うことにより求めた。   Tensile strength (TS) and elongation (El) were determined by cutting out a JIS No. 5 test piece from each steel plate and conducting a tensile test at room temperature.

めっきの付着量は、めっきをインヒビター入りの塩酸で溶解し、重量法により測定した．めっき中のＦｅ％は、めっきをインヒビター入りの塩酸で溶解し、ＩＣＰにより測定して求めた。   The amount of plating adhered was measured by the gravimetric method after dissolving the plating with hydrochloric acid containing an inhibitor. The Fe% during plating was obtained by dissolving the plating with hydrochloric acid containing an inhibitor and measuring by ICP.

鋼板の結晶粒界と結晶粒内に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．内部酸化層の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物が結晶粒界と結晶粒内に観察されたものを○、観察されなかったものを×とした．内部酸化層の厚みは、同様にＳＥＭ像で観察し、鋼板とめっき層との界面から結晶粒界と結晶粒内に酸化物が観察される部分の厚さを測定した．内部酸化層の組成は、ＳＥＭに取り付けたＥＤＸを使用して解析し、Ｓｉ、Ｏのピークが観察されたものを○、観察されなかったものを×とした。   The oxides containing Si present in the grain boundaries and in the crystal grains of the steel sheet were evaluated by observing the embedded and polished plated steel sheet from the cross section with an SEM image. The state of the internal oxide layer was observed with an SEM image, where an oxide containing Si was observed in the crystal grain boundary and in the crystal grain, and x was not observed. Similarly, the thickness of the internal oxide layer was observed by an SEM image, and the thickness of the portion where the oxide was observed in the crystal grain boundary and in the crystal grain from the interface between the steel sheet and the plating layer was measured. The composition of the internal oxide layer was analyzed using EDX attached to the SEM, and the case where the Si and O peaks were observed was evaluated as ◯, and the case where the Si and O peaks were not observed as ×.

鋼板内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解した後の鋼板を使用し、Ｓｉを含む酸化物を含有する層を酸で溶解してＳｉを含む酸化物を分離させた後、その質量を測定して求めた。   Measurement of the content ratio of oxides containing Si in the steel sheet uses the steel sheet after the plating is dissolved with hydrochloric acid containing an inhibitor, and the oxide-containing layer is oxidized by dissolving the layer containing the oxide containing Si with an acid. After separating the object, its mass was measured and determined.

ＦｅＯの有無は、鋼板表面からＸＲＤ測定を行い、ＦｅＯの回折ピークが観察されなかったものを○、回折ピークが観察されたものを×とした。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4、ＳｉＯ2の位置は、埋め込み研磨しためっき鋼板を断面からＳｉを含む酸化物をＣＭＡ像で観察し、以下の基準で評価した。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4の位置
○：ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が鋼板表面に観察されるもの
×：ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が観察されないもの
ＳｉＯ2の位置
○：Ｓｉ、Ｏが同じ位置に観察される酸化物が鋼板の内側に観察されるもの
×：Ｓｉ、Ｏが同じ位置に観察される酸化物が鋼板の内側に観察されないもの
めっき層に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．酸化物の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物がめっき層内に観察されたものを○、観察されなかったものを×とした。 The presence or absence of FeO was measured by XRD from the surface of the steel sheet. The case where the diffraction peak of FeO was not observed was evaluated as ◯, and the case where the diffraction peak was observed was evaluated as ×.
The positions of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 , and SiO 2 were evaluated on the basis of the following criteria by observing an oxide containing Si from a cross-section of the embedded and polished plated steel sheet using a CMA image.
Position of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 ○: Fe or Mn and Si, O observed at the same position Oxide observed on steel sheet surface ×: Fe or Mn Oxides observed at the same position of Si and O are not observed SiO 2 position ○: Oxides observed at the same position of Si and O are observed inside the steel plate ×: Si and O are the same Oxides observed in position are not observed inside the steel plate The oxides containing Si present in the plating layer were evaluated by observing the embedded and polished plated steel plate from the cross section with an SEM image. The state of the oxide was observed with an SEM image, where the oxide containing Si was observed in the plating layer was marked with ◯, and the oxide was not observed with x.

めっき層内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解させた後、Ｓｉを含む酸化物を分離させた後、その重量を測定して求めた。   The content ratio of the oxide containing Si in the plating layer was obtained by dissolving the plating with hydrochloric acid containing an inhibitor, separating the oxide containing Si, and measuring the weight thereof.

（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4、ＳｉＯ2の位置は、埋め込み研磨しためっき鋼板を断面からＳｉを含む酸化物をＣＭＡ像で観察し、ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が鋼板表面に観察されるものを○、ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が観察されないものを×とした。 The positions of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 , SiO 2 are obtained by observing an oxide containing Si from a cross-section of the embedded and polished plated steel sheet with a CMA image. Is observed when the oxide observed at the same position is observed on the surface of the steel sheet, and when the oxide observed when Fe or Mn and Si and O are observed at the same position is not evaluated as x.

めっき外観は通板したコイル全長を目視で観察し、不めっき面積率を以下に示す評点づけで判定した．評点は３以上を合格とした。
４：不めっき面積率１％未満、
３：不めっき面積率１％以上５％未満、
２：不めっき面積率５％以上１０％未満、
１：不めっき面積率１０％以上
評価結果は表２に示す通りである．番号５、９、１２、１５、１７、２０、２３、２６、３０、３２、３５、３８、４２、４５は炉内のｌｏｇＰＯ2が本発明の範囲外であるため鋼板表面にＳｉ酸化物が濃化し、不めっきが発生したため外観が不合格となった。番号６、８、１１、１４、１８、２１、２４、２７、２９、３３、３６、３９、４１、４４は炉内のｌｏｇＰＯ2が本発明の範囲外であるため鋼板表面のＦｅの酸化物を還元できず不めっきが発生したため、外観が不合格となった。これら以外の本発明方法で作製した鋼板は、外観が優れた高強度合金化溶融亜鉛めっき鋼板であった。 The plating appearance was judged by visually observing the entire length of the passed coil and by rating the unplated area ratio as shown below. A score of 3 or more was accepted.
4: Non-plating area ratio is less than 1%,
3: Non-plating area ratio 1% or more and less than 5%,
2: Non-plating area ratio 5% or more and less than 10%,
1: Unplated area ratio of 10% or more The evaluation results are as shown in Table 2. Nos. 5, 9, 12, 15, 17, 20 , 23, 26, 30, 32, 35, 38, 42, and 45 indicate that the log PO 2 in the furnace is outside the scope of the present invention, so Si oxide is present on the steel plate surface. Thickening and non-plating occurred and the appearance was rejected. Nos. 6, 8, 11, 14, 18, 21, 24, 27, 29, 33, 36, 39, 41, 44 are oxides of Fe on the steel sheet surface because log PO 2 in the furnace is outside the scope of the present invention. Since the film could not be reduced and non-plating occurred, the appearance was rejected. The steel plate produced by the method of the present invention other than these was a high-strength galvannealed steel plate having an excellent appearance.

Figure 0004741376
Figure 0004741376

Figure 0004741376
Figure 0004741376

表１の組成からなるスラブを１４２３Ｋに加熱し、仕上温度１１８３〜１２０３Ｋで４．５ｍｍの熱間圧延鋼帯とし、８５３〜９５３Ｋで巻き取った．酸洗後、冷間圧延を施して１．６ｍｍの冷間圧延鋼帯とした後、ライン内焼鈍方式の連続溶融亜鉛めっき設備を用いて表３に示すような条件のめっきを行い、合金化溶融亜鉛めっき鋼板を製造した．連続溶融亜鉛めっき設備は、無酸化炉による加熱後、還元帯で還元・焼鈍を行う方式を使用した．無酸化炉及びその廃熱を利用して昇温させるゾーンの露点は２８３Ｋに調節し、酸化帯として使用した．還元帯はＣＯとＨ2を混合した気体を燃焼させ発生したＨ2Ｏ、ＣＯ2を導入する装置を取り付け、Ｈ2を１０体積％含むＮ2ガスにＨ2ＯとＣＯ2を導入した．
焼鈍は、最高到達温度を表３に示す値となるよう調節し、均熱温度（最高到達温度−２０度から最高到達温度までの範囲）に入っている均熱時間を６０秒とした後、その最高到達温度から９２３Ｋまでを平均冷却速度１度／秒で、引き続いて９２３Ｋから７７３Ｋまでを平均冷却速度４度／秒で冷却し、さらに７７３Ｋから平均冷却速度１．７度／秒以上で７２３Ｋまで冷却し、且つめっき浴まで７２３Ｋで保持し、７７３Ｋからめっき浴までを３０秒確保した後、溶融亜鉛めっきを行い７７３Ｋで合金化処理を行った。 A slab having the composition shown in Table 1 was heated to 1423K to form a 4.5 mm hot-rolled steel strip at a finishing temperature of 1183 to 1203K, and wound at 853 to 953K. After pickling, cold rolling to obtain a 1.6 mm cold rolled steel strip, followed by plating under the conditions shown in Table 3 using an in-line annealing method of continuous hot dip galvanizing equipment, and alloying A hot-dip galvanized steel sheet was manufactured. The continuous hot-dip galvanizing equipment used a method of reducing and annealing in the reduction zone after heating in a non-oxidizing furnace. The dew point of the non-oxidizing furnace and the zone where the temperature was raised using the waste heat was adjusted to 283K and used as the oxidation zone. Reduction zone is CO and H 2 The mixed gas by burning generated H 2 O, fitted with a device for introducing the CO 2, introducing H 2 O and CO 2 and H 2 in N 2 gas containing 10 vol%.
The annealing was adjusted so that the maximum temperature reached the value shown in Table 3, and the soaking time in the soaking temperature (the range from the maximum temperature to -20 degrees to the maximum temperature) was set to 60 seconds. From the maximum temperature reached 923K at an average cooling rate of 1 degree / second, subsequently from 923K to 773K at an average cooling rate of 4 degrees / second, and further from 773K at an average cooling rate of 1.7 degrees / second or more at 723K. After cooling to 723 K and holding at 723 K until 30 seconds from 773 K to the plating bath, hot dip galvanization was performed and alloying was performed at 773 K.

還元炉内のＰＯ2は、炉内の水素濃度、水蒸気濃度、ＣＯ2濃度、ＣＯ濃度、雰囲気温度の測定値と平衡反応
Ｈ2Ｏ＝Ｈ2＋１／２Ｏ2
ＣＯ2＝ＣＯ＋１／２Ｏ2
の平衡定数Ｋ１、Ｋ２を使用して求めた。 The PO 2 in the reduction furnace is the measured value of the hydrogen concentration, water vapor concentration, CO 2 concentration, CO concentration, atmospheric temperature in the furnace and the equilibrium reaction H 2 O = H 2 + 1 / 2O 2.
CO 2 = CO + 1 / 2O 2
Using the equilibrium constants K1 and K2.

引張強さ（ＴＳ）、伸び（Ｅｌ）は、各鋼板からＪＩＳ５号試験片を切り出し、常温での引張試験を行うことにより求めた。   Tensile strength (TS) and elongation (El) were determined by cutting out a JIS No. 5 test piece from each steel plate and conducting a tensile test at room temperature.

めっきの付着量は、めっきをインヒビター入りの塩酸で溶解し、重量法により測定した．めっき中のＦｅ％は、めっきをインヒビター入りの塩酸で溶解し、ＩＣＰにより測定して求めた。   The amount of plating adhered was measured by the gravimetric method after dissolving the plating with hydrochloric acid containing an inhibitor. The Fe% during plating was obtained by dissolving the plating with hydrochloric acid containing an inhibitor and measuring by ICP.

鋼板の結晶粒界と結晶粒内に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．内部酸化層の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物が結晶粒界と結晶粒内に観察されたものを○、観察されなかったものを×とした．内部酸化層の厚みは、同様にＳＥＭ像で観察し、鋼板とめっき層との界面から結晶粒界と結晶粒内に酸化物が観察される部分の厚さを測定した．内部酸化層の組成は、ＳＥＭに取り付けたＥＤＸを使用して解析し、Ｓｉ、Ｏのピークが観察されたものを○、観察されなかったものを×とした。   The oxides containing Si present in the grain boundaries and in the crystal grains of the steel sheet were evaluated by observing the embedded and polished plated steel sheet from the cross section with an SEM image. The state of the internal oxide layer was observed with an SEM image, where an oxide containing Si was observed in the crystal grain boundary and in the crystal grain, and x was not observed. Similarly, the thickness of the internal oxide layer was observed by an SEM image, and the thickness of the portion where the oxide was observed in the crystal grain boundary and in the crystal grain from the interface between the steel sheet and the plating layer was measured. The composition of the internal oxide layer was analyzed using EDX attached to the SEM, and the case where the Si and O peaks were observed was evaluated as ◯, and the case where the Si and O peaks were not observed as ×.

鋼板内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解した後の鋼板を使用し、Ｓｉを含む酸化物を含有する層を酸で溶解してＳｉを含む酸化物を分離させた後、その重量を測定して求めた。   Measurement of the content ratio of oxides containing Si in the steel sheet uses the steel sheet after the plating is dissolved with hydrochloric acid containing an inhibitor, and the oxide-containing layer is oxidized by dissolving the layer containing the oxide containing Si with an acid. After separating the object, its weight was measured and determined.

ＦｅＯの有無は、鋼板表面からＸＲＤ測定を行い、ＦｅＯの回折ピークが観察されなかったものを○、回折ピークが観察されたものを×とした。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4、ＳｉＯ2の位置は、埋め込み研磨しためっき鋼板を断面からＳｉを含む酸化物をＣＭＡ像で観察し、以下の基準で評価した。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4の位置
○：ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が鋼板表面に観察されるもの
×：ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が観察されないもの
ＳｉＯ2の位置
○：Ｓｉ、Ｏが同じ位置に観察される酸化物が鋼板の内側に観察されるもの
×：Ｓｉ、Ｏが同じ位置に観察される酸化物が鋼板の内側に観察されないもの
めっき層に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．酸化物の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物がめっき層内に観察されたものを○、観察されなかったものを×とした。
めっき層内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解させた後、Ｓｉを含む酸化物を分離させた後、その質量を測定して求めた。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4、ＳｉＯ2の位置は、埋め込み研磨しためっき鋼板を断面からＳｉを含む酸化物をＣＭＡ像で観察し、ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が鋼板表面に観察されるものを○、ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が観察されないものを×とした。 The presence or absence of FeO was measured by XRD from the surface of the steel sheet. The case where the diffraction peak of FeO was not observed was evaluated as ◯, and the case where the diffraction peak was observed was evaluated as ×.
The positions of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 , and SiO 2 were evaluated on the basis of the following criteria by observing an oxide containing Si from a cross-section of the embedded and polished plated steel sheet using a CMA image.
Position of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 ○: Fe or Mn and Si, O observed at the same position Oxide observed on steel sheet surface ×: Fe or Mn Oxides observed at the same position of Si and O are not observed SiO 2 position ○: Oxides observed at the same position of Si and O are observed inside the steel plate ×: Si and O are the same Oxides observed in position are not observed inside the steel plate The oxides containing Si present in the plating layer were evaluated by observing the embedded and polished plated steel plate from the cross section with an SEM image. The state of the oxide was observed with an SEM image, where the oxide containing Si was observed in the plating layer was marked with ◯, and the oxide was not observed with x.
The content ratio of the oxide containing Si in the plating layer was obtained by dissolving the plating with hydrochloric acid containing an inhibitor, separating the oxide containing Si, and then measuring the mass thereof.
The positions of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 , SiO 2 are obtained by observing an oxide containing Si from a cross-section of the embedded and polished plated steel sheet with a CMA image. Is observed when the oxide observed at the same position is observed on the surface of the steel sheet, and when the oxide observed when Fe or Mn and Si and O are observed at the same position is not evaluated as x.

めっき外観は通板したコイル全長を目視で観察し、不めっき面積率を以下に示す評点づけで判定した．評点は３以上を合格とした。
４：不めっき面積率１％未満、
３：不めっき面積率１％以上５％未満、
２：不めっき面積率５％以上１０％未満、
１：不めっき面積率１０％以上
評価結果は表３に示す通りである．番号５、９、１２、１５、１７、２０、２３、２６、３０、３２、３５、３８、４２、４５は炉内のｌｏｇＰＯ2が本発明の範囲外であるため鋼板表面にＳｉ酸化物が濃化し、不めっきが発生したため外観が不合格となった。番号６、８、１１、１４、１８、２１、２４、２７、２９、３３、３６、３９、４１、４４は炉内のｌｏｇＰＯ2が本発明の範囲外であるため鋼板表面のＦｅの酸化物を還元できず不めっきが発生したため、外観が不合格となった。これら以外の本発明方法で作製した鋼板は、外観が優れた高強度合金化溶融亜鉛めっき鋼板であった。 The plating appearance was judged by visually observing the entire length of the passed coil and by rating the unplated area ratio as shown below. A score of 3 or more was accepted.
4: Non-plating area ratio is less than 1%,
3: Non-plating area ratio 1% or more and less than 5%,
2: Non-plating area ratio 5% or more and less than 10%,
1: Unplated area ratio of 10% or more The evaluation results are as shown in Table 3. Nos. 5, 9, 12, 15, 17, 20 , 23, 26, 30, 32, 35, 38, 42, and 45 indicate that the log PO 2 in the furnace is outside the scope of the present invention, so Si oxide is present on the steel plate surface. Thickening and non-plating occurred and the appearance was rejected. Nos. 6, 8, 11, 14, 18, 21, 24, 27, 29, 33, 36, 39, 41, 44 are oxides of Fe on the steel sheet surface because log PO 2 in the furnace is outside the scope of the present invention. Since the film could not be reduced and non-plating occurred, the appearance was rejected. The steel plate produced by the method of the present invention other than these was a high-strength galvannealed steel plate having an excellent appearance.

Figure 0004741376
Figure 0004741376

表１に示す組成からなるスラブを１４２３Ｋに加熱し、仕上温度１１８３〜１２０３Ｋで４．５ｍｍの熱間圧延鋼帯とし、８５３〜９５３Ｋで巻き取った．酸洗後、冷間圧延を施して１．６ｍｍの冷間圧延鋼帯とした後、ライン内焼鈍方式の連続溶融亜鉛めっき設備を用いて表４に示すような条件のめっきを行い、合金化溶融亜鉛めっき鋼板を製造した．連続溶融亜鉛めっき設備は、無酸化炉による加熱後、還元帯で還元・焼鈍を行う方式を使用した．無酸化炉及びその廃熱を利用して昇温させるゾーンの露点は２８３Ｋに調節し、還元帯はＣＯとＨ2を混合した気体を燃焼させ発生したＨ2Ｏ、ＣＯ2を導入する装置を取り付け、Ｈ2を１０体積％含むＮ2ガスにＨ2ＯとＣＯ2を導入し、炉内の酸素ポテンシャルの対数ｌｏｇＰＯ2が表４に示す値となるように調節した。 A slab having the composition shown in Table 1 was heated to 1423K, and a 4.5 mm hot rolled steel strip was formed at a finishing temperature of 1183 to 1203K, and wound at 853 to 953K. After pickling, cold rolling to obtain a 1.6 mm cold rolled steel strip, followed by plating under the conditions shown in Table 4 using an in-line annealing method of continuous hot dip galvanizing equipment, and alloying A hot-dip galvanized steel sheet was manufactured. The continuous hot-dip galvanizing equipment used a method of reducing and annealing in the reduction zone after heating in a non-oxidizing furnace. The dew point of the non-oxidizing furnace and the zone where the temperature is raised using the waste heat is adjusted to 283K, and the reduction zone is a device that introduces H 2 O and CO 2 generated by burning a mixed gas of CO and H 2. Mounting, H 2 O and CO 2 were introduced into N 2 gas containing 10% by volume of H 2, and the logarithm log PO 2 of the oxygen potential in the furnace was adjusted to the value shown in Table 4.

焼鈍は、最高到達温度を表４に示す値となるよう調節し、均熱温度（最高到達温度−２０度から最高到達温度までの範囲）に入っている均熱時間を６０秒とした。
還元炉内のＰＯ2は、炉内の水素濃度、水蒸気濃度、ＣＯ2濃度、ＣＯ濃度、雰囲気温度の測定値と平衡反応
Ｈ2Ｏ＝Ｈ2＋１／２Ｏ2
ＣＯ2＝ＣＯ＋１／２Ｏ2
の平衡定数Ｋ１、Ｋ２を使用して求めた。 The annealing was adjusted so that the maximum temperature reached the value shown in Table 4, and the soaking time in the soaking temperature (the range from the maximum temperature to -20 degrees to the maximum temperature) was 60 seconds.
The PO 2 in the reduction furnace is the measured value of the hydrogen concentration, water vapor concentration, CO 2 concentration, CO concentration, atmospheric temperature in the furnace and the equilibrium reaction H 2 O = H 2 + 1 / 2O 2.
CO 2 = CO + 1 / 2O 2
Using the equilibrium constants K1 and K2.

引張強さ（ＴＳ）、伸び（Ｅｌ）は、各鋼板からＪＩＳ５号試験片を切り出し、常温での引張試験を行うことにより求めた。   Tensile strength (TS) and elongation (El) were determined by cutting out a JIS No. 5 test piece from each steel plate and conducting a tensile test at room temperature.

めっきの付着量は、皮膜をインヒビター入りの塩酸で溶解し、重量法により測定した。
めっき中のＦｅ％は、めっきをインヒビター入りの塩酸で溶解し、ＩＣＰにより測定して求めた。 The adhesion amount of plating was measured by a gravimetric method after dissolving the film with hydrochloric acid containing an inhibitor.
The Fe% during plating was obtained by dissolving the plating with hydrochloric acid containing an inhibitor and measuring by ICP.

鋼板の結晶粒界と結晶粒内に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．内部酸化層の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物が結晶粒界と結晶粒内に観察されたものを○、観察されなかったものを×とした．内部酸化層の厚みは、同様にＳＥＭ像で観察し、鋼板とめっき層との界面から結晶粒界と結晶粒内に酸化物が観察される部分の厚さを測定した．内部酸化層の組成は、ＳＥＭに取り付けたＥＤＸを使用して解析し、Ｓｉ、Ｏのピークが観察されたものを○、観察されなかったものを×とした。   The oxides containing Si present in the grain boundaries and in the crystal grains of the steel sheet were evaluated by observing the embedded and polished plated steel sheet from the cross section with an SEM image. The state of the internal oxide layer was observed with an SEM image, where an oxide containing Si was observed in the crystal grain boundary and in the crystal grain, and x was not observed. Similarly, the thickness of the internal oxide layer was observed by an SEM image, and the thickness of the portion where the oxide was observed in the crystal grain boundary and in the crystal grain from the interface between the steel sheet and the plating layer was measured. The composition of the internal oxide layer was analyzed using EDX attached to the SEM, and the case where the Si and O peaks were observed was evaluated as ◯, and the case where the Si and O peaks were not observed as ×.

鋼板内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解した後の鋼板を使用し、Ｓｉを含む酸化物を含有する層を酸で溶解してＳｉを含む酸化物を分離させた後、その重量を測定して求めた。   Measurement of the content ratio of oxides containing Si in the steel sheet uses the steel sheet after the plating is dissolved with hydrochloric acid containing an inhibitor, and the oxide-containing layer is oxidized by dissolving the layer containing the oxide containing Si with an acid. After separating the object, its weight was measured and determined.

めっき層に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．酸化物の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物がめっき層内に観察されたものを○、観察されなかったものを×とした。   The oxide containing Si present in the plating layer was evaluated by observing the embedded and polished plated steel sheet with a SEM image from the cross section. The state of the oxide was observed with an SEM image, where the oxide containing Si was observed in the plating layer was marked with ◯, and the oxide was not observed with x.

めっき層内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解させた後、Ｓｉを含む酸化物を分離させた後、その質量を測定して求めた。   The content ratio of the oxide containing Si in the plating layer was obtained by dissolving the plating with hydrochloric acid containing an inhibitor, separating the oxide containing Si, and then measuring the mass thereof.

めっき外観は通板したコイルの不めっき面積率を以下に示す評点づけで判定した．評点は３以上を合格とした。
４：不めっき面積率１％未満、
３：不めっき面積率１％以上５％未満、
２：不めっき面積率５％以上１０％未満、
１：不めっき面積率１０％以上
評価結果は表４に示す通りである．本発明方法により、めっき濡れ性が優れた高強度合金化溶融亜鉛めっき鋼板が製造可能となった。 The plating appearance was judged by the following rating of the unplated area ratio of the passed coil. A score of 3 or more was accepted.
4: Non-plating area ratio is less than 1%,
3: Non-plating area ratio 1% or more and less than 5%,
2: Non-plating area ratio 5% or more and less than 10%,
1: Unplated area ratio of 10% or more The evaluation results are as shown in Table 4. By the method of the present invention, a high-strength galvannealed steel sheet having excellent plating wettability can be produced.

特に、番号１、２、３、４、６、７、９、１０、１１、１２、１５、１６、１７、１８、１９、２０、２４、２５、２６、２８、２９、３０に示す製造方法は、焼鈍炉内での冷却速度、溶融亜鉛めっき浴中の有効Ａｌ濃度、合金化処理温度が適切であるため、加工性の良好な高強度合金化溶融亜鉛めっき鋼板を製造することが可能となった。   In particular, the manufacturing methods indicated by numbers 1, 2, 3, 4, 6, 7, 9, 10, 11, 12, 15, 16, 17, 18, 19, 20, 24, 25, 26, 28, 29, 30 Is suitable for the cooling rate in the annealing furnace, the effective Al concentration in the hot dip galvanizing bath, and the alloying treatment temperature, making it possible to produce high strength alloyed hot dip galvanized steel sheets with good workability. became.

Figure 0004741376
Figure 0004741376

表１のＥに示す組成からなるスラブを１４２３Ｋに加熱し、仕上温度１１８３〜１２０３Ｋで４．５ｍｍの熱間圧延鋼帯とし、８５３〜９５３Ｋで巻き取った．酸洗後、冷間圧延を施して１．６ｍｍの冷間圧延鋼帯とした後、オールラジアントチューブ方式の焼鈍炉を使用した連続溶融亜鉛めっき設備を用いて表５に示すような条件のめっきを行い、合金化溶融亜鉛めっき鋼板を製造した．還元炉はＣＯとＨ2を混合した気体を燃焼させ発生したＨ2Ｏ、ＣＯ2を導入する装置を取り付け、Ｈ2を１０体積％含むＮ2ガスにＨ2ＯとＣＯ2を導入した。 A slab having the composition shown in E of Table 1 was heated to 1423K, and a 4.5 mm hot rolled steel strip was formed at a finishing temperature of 1183 to 1203K, and wound at 853 to 953K. After pickling and cold rolling to obtain a 1.6 mm cold rolled steel strip, plating under conditions as shown in Table 5 using a continuous hot dip galvanizing facility using an all radiant tube type annealing furnace The alloyed hot-dip galvanized steel sheet was manufactured. Reducing furnace is fitted with a device for introducing of H 2 O, CO 2 generated by burning gas of a mixture of CO and H 2, introducing H 2 O and CO 2 and H 2 in N 2 gas containing 10 vol%.

焼鈍は、最高到達温度を表５に示す値となるよう調節し、均熱温度（最高到達温度−２０度から最高到達温度までの範囲）に入っている均熱時間を６０秒とした後、その最高到達温度から９２３Ｋまでを平均冷却速度１度／秒で、引き続いて９２３Ｋから７７３Ｋまでを平均冷却速度４度／秒で冷却し、さらに７７３Ｋから平均冷却速度１．７度／秒以上で７２３Ｋまで冷却し、且つめっき浴まで７２３Ｋで保持し、７７３Ｋからめっき浴までを３０秒確保した後、溶融亜鉛めっきを行い７７３Ｋで合金化処理を行った。   Annealing is adjusted so that the maximum reached temperature becomes the value shown in Table 5, and the soaking time in the soaking temperature (the range from the maximum attainable temperature −20 degrees to the maximum attainable temperature) is set to 60 seconds, From the maximum temperature reached 923K at an average cooling rate of 1 degree / second, subsequently from 923K to 773K at an average cooling rate of 4 degrees / second, and further from 773K at an average cooling rate of 1.7 degrees / second or more at 723K. After cooling to 723 K and holding at 723 K until 30 seconds from 773 K to the plating bath, hot dip galvanization was performed and alloying was performed at 773 K.

還元炉内のＰＯ2は、炉内の水素濃度、水蒸気濃度、ＣＯ2濃度、ＣＯ濃度、雰囲気温度の測定値と平衡反応
Ｈ2Ｏ＝Ｈ2＋１／２Ｏ2
ＣＯ2＝ＣＯ＋１／２Ｏ2
の平衡定数Ｋ１、Ｋ２を使用して求めた。 The PO 2 in the reduction furnace is the measured value of the hydrogen concentration, water vapor concentration, CO 2 concentration, CO concentration, atmospheric temperature in the furnace and the equilibrium reaction H 2 O = H 2 + 1 / 2O 2.
CO 2 = CO + 1 / 2O 2
Using the equilibrium constants K1 and K2.

引張強さ（ＴＳ）、伸び（Ｅｌ）は、各鋼板からＪＩＳ５号試験片を切り出し、常温での引張試験を行うことにより求めた。   Tensile strength (TS) and elongation (El) were determined by cutting out a JIS No. 5 test piece from each steel plate and conducting a tensile test at room temperature.

めっきの付着量は、めっきをインヒビター入りの塩酸で溶解し、重量法により測定した．めっき中のＦｅ％は、めっきをインヒビター入りの塩酸で溶解し、ＩＣＰにより測定して求めた。   The amount of plating adhered was measured by the gravimetric method after dissolving the plating with hydrochloric acid containing an inhibitor. The Fe% during plating was obtained by dissolving the plating with hydrochloric acid containing an inhibitor and measuring by ICP.

鋼板の結晶粒界と結晶粒内に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．内部酸化層の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物が結晶粒界と結晶粒内に観察されたものを○、観察されなかったものを×とした．内部酸化層の厚みは、同様にＳＥＭ像で観察し、鋼板とめっき層との界面から結晶粒界と結晶粒内に酸化物が観察される部分の厚さを測定した．内部酸化層の組成は、ＳＥＭに取り付けたＥＤＸを使用して解析し、Ｓｉ、Ｏのピークが観察されたものを○、観察されなかったものを×とした。   The oxides containing Si present in the grain boundaries and in the crystal grains of the steel sheet were evaluated by observing the embedded and polished plated steel sheet from the cross section with an SEM image. The state of the internal oxide layer was observed with an SEM image, where an oxide containing Si was observed in the crystal grain boundary and in the crystal grain, and x was not observed. Similarly, the thickness of the internal oxide layer was observed by an SEM image, and the thickness of the portion where the oxide was observed in the crystal grain boundary and in the crystal grain from the interface between the steel sheet and the plating layer was measured. The composition of the internal oxide layer was analyzed using EDX attached to the SEM, and the case where the Si and O peaks were observed was evaluated as ◯, and the case where the Si and O peaks were not observed as ×.

鋼板内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解した後の鋼板を使用し、Ｓｉを含む酸化物を含有する層を酸で溶解してＳｉを含む酸化物を分離させた後、その重量を測定して求めた。   Measurement of the content ratio of oxides containing Si in the steel sheet uses the steel sheet after the plating is dissolved with hydrochloric acid containing an inhibitor, and the oxide-containing layer is oxidized by dissolving the layer containing the oxide containing Si with an acid. After separating the object, its weight was measured and determined.

ＦｅＯの有無は、鋼板表面からＸＲＤ測定を行い、ＦｅＯの回折ピークが観察されなかったものを○、回折ピークが観察されたものを×とした。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4、ＳｉＯ2の位置は、埋め込み研磨しためっき鋼板を断面からＳｉを含む酸化物をＣＭＡ像で観察し、以下の基準で評価した。
（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4の位置
○：ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が鋼板表面に観察されるもの
×：ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が観察されないもの
ＳｉＯ2の位置
○：Ｓｉ、Ｏが同じ位置に観察される酸化物が鋼板の内側に観察されるもの
×：Ｓｉ、Ｏが同じ位置に観察される酸化物が鋼板の内側に観察されないもの
めっき層に存在するＳｉを含む酸化物は、埋め込み研磨しためっき鋼板を断面からＳＥＭ像で観察して評価した．酸化物の状態は、ＳＥＭ像で観察し、Ｓｉを含む酸化物がめっき層内に観察されたものを○、観察されなかったものを×とした。 The presence or absence of FeO was measured by XRD from the surface of the steel sheet. The case where the diffraction peak of FeO was not observed was evaluated as ◯, and the case where the diffraction peak was observed was evaluated as ×.
The positions of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 , and SiO 2 were evaluated on the basis of the following criteria by observing an oxide containing Si from a cross-section of the embedded and polished plated steel sheet using a CMA image.
Position of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 ○: Fe or Mn and Si, O observed at the same position Oxide observed on steel sheet surface ×: Fe or Mn Oxides observed at the same position of Si and O are not observed SiO 2 position ○: Oxides observed at the same position of Si and O are observed inside the steel plate ×: Si and O are the same Oxides observed in position are not observed inside the steel plate The oxides containing Si present in the plating layer were evaluated by observing the embedded and polished plated steel plate from the cross section with an SEM image. The state of the oxide was observed with an SEM image, where the oxide containing Si was observed in the plating layer was marked with ◯, and the oxide was not observed with x.

めっき層内のＳｉを含む酸化物の含有率の測定は、めっきをインヒビター入りの塩酸で溶解させた後、Ｓｉを含む酸化物を分離させた後、その質量を測定して求めた。   The content ratio of the oxide containing Si in the plating layer was obtained by dissolving the plating with hydrochloric acid containing an inhibitor, separating the oxide containing Si, and then measuring the mass thereof.

（Ｆｅ、Ｍｎ）ＳｉＯ3、（Ｆｅ、Ｍｎ）2ＳｉＯ4、ＳｉＯ2の位置は、埋め込み研磨しためっき鋼板を断面からＳｉを含む酸化物をＣＭＡ像で観察し、ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が鋼板表面に観察されるものを○、ＦｅまたはＭｎとＳｉ、Ｏが同じ位置に観察される酸化物が観察されないものを×とした。 The positions of (Fe, Mn) SiO 3 , (Fe, Mn) 2 SiO 4 , SiO 2 are obtained by observing an oxide containing Si from a cross-section of the embedded and polished plated steel sheet with a CMA image. Is observed when the oxide observed at the same position is observed on the surface of the steel sheet, and when the oxide observed when Fe or Mn and Si and O are observed at the same position is not evaluated as x.

めっき外観は通板したコイル全長を目視で観察し、不めっき面積率を以下に示す評点づけで判定した．評点は３以上を合格とした。
４：不めっき面積率１％未満、
３：不めっき面積率１％以上５％未満、
２：不めっき面積率５％以上１０％未満、
１：不めっき面積率１０％以上
評価結果は表５に示す通りである．番号５は炉内のｌｏｇＰＯ2が本発明の範囲外であるため鋼板表面にＳｉ酸化物が濃化し、不めっきが発生したため外観が不合格となった。番号６は炉内のｌｏｇＰＯ2が本発明の範囲外であるため鋼板表面にＦｅの酸化物が生成し不めっきが発生したため、外観が不合格となった。これら以外の本発明方法で作製した鋼板は、外観が優れた高強度合金化溶融亜鉛めっき鋼板であった。 The plating appearance was judged by visually observing the entire length of the passed coil and by rating the unplated area ratio as shown below. A score of 3 or more was accepted.
4: Non-plating area ratio is less than 1%,
3: Non-plating area ratio 1% or more and less than 5%,
2: Non-plating area ratio 5% or more and less than 10%,
1: Non-plating area ratio of 10% or more The evaluation results are as shown in Table 5. In No. 5, the log PO 2 in the furnace was outside the scope of the present invention, so that the Si oxide was concentrated on the steel sheet surface and non-plating occurred, so the appearance was rejected. In No. 6, since the log PO 2 in the furnace was outside the range of the present invention, an oxide of Fe was generated on the steel sheet surface and non-plating occurred, so that the appearance was rejected. The steel plate produced by the method of the present invention other than these was a high-strength galvannealed steel plate having an excellent appearance.

Figure 0004741376
Figure 0004741376

鋼板側の結晶粒界と結晶粒内に存在するＳｉを含む酸化物の一例を示す図である。It is a figure which shows an example of the oxide containing Si which exists in the crystal grain boundary on the steel plate side, and a crystal grain. 本発明に係わる溶融亜鉛めっき鋼板の製造設備の一例を示す側面図である。It is a side view which shows an example of the manufacturing equipment of the hot dip galvanized steel plate concerning this invention. 本発明に係わる溶融亜鉛めっき鋼板の製造設備の一例を示す側面図である。It is a side view which shows an example of the manufacturing equipment of the hot dip galvanized steel plate concerning this invention.

符号の説明Explanation of symbols

１ めっき層
２ 高強度鋼板
３ 内部酸化層
４ａ 結晶粒内に存在するＳｉを含む酸化物
４ｂ 結晶粒界に存在するＳｉを含む酸化物
５ めっき層内に存在するＳｉを含む酸化物
６ 高強度鋼板
７ 焼鈍炉の加熱帯
８ 焼鈍炉の均熱帯
９ 焼鈍炉の冷却帯
１０ 炉内ロール
１１ 鋼板進行方向
１２ 溶融亜鉛めっき槽
１３ 溶融亜鉛
１４ スナウト
１５ シンクロール
１６ ガスワイピングノズル
１７ 合金化炉
１８ ガス流量調整弁
１９ 還元性ガス配管
２０ 還元性ガス流れ方向
２１ 燃焼装置
２２ 燃焼ガス配管
２３ 燃焼ガス流れ方向
２４ 燃料ガス配管
２５ 燃料ガス流れ方向
２６ 空気配管
２７ 空気流れ方向
２８ 炉内に設置された燃焼装置 DESCRIPTION OF SYMBOLS 1 Plating layer 2 High-strength steel plate 3 Internal oxide layer 4a Oxide containing Si existing in crystal grains 4b Oxide containing Si existing in crystal grain boundaries 5 Oxide containing Si existing in plating layers 6 High strength Steel plate 7 Annealing furnace heating zone 8 Annealing furnace soaking zone 9 Annealing furnace cooling zone 10 In-furnace roll 11 Steel plate traveling direction 12 Hot-dip galvanizing tank 13 Hot-zinc 14 Snout 15 Sink roll 16 Gas wiping nozzle 17 Alloying furnace 18 Gas Flow control valve 19 Reducing gas pipe 20 Reducing gas flow direction 21 Combustion device 22 Combustion gas pipe 23 Combustion gas flow direction 24 Fuel gas pipe 25 Fuel gas flow direction 26 Air pipe 27 Air flow direction 28 Combustion installed in the furnace apparatus

Claims (12)

質量％で、
Ｃ：０．０５〜０．２５％、
Ｓｉ：０．３〜２．５％、
Ｍｎ：１．５〜２．８％、
Ｐ：０．０３％以下、
Ｓ：０．０２％以下、
Ａｌ：０．００５〜０．５％、
Ｎ：０．００６０％以下を含有し、
残部Ｆｅおよび不可避的不純物からなる高強度鋼板の上に、ＦｅおよびＡｌを含有し、残部がＺｎおよび不可避的不純物からなる合金化溶融亜鉛めっき層を有する鋼板において、前記高強度鋼板と前記めっき層との界面から５μｍ以下の鋼板側の鋼板中の結晶粒界と結晶粒内にＳｉを含む酸化物が平均含有率で０．６〜１０質量％含有されて存在し、かつ、前記めっき層中にＳｉを含む酸化物が平均含有率で０．０５〜１．５質量％含有されて存在し、そして、前記めっき層中及び前記鋼板中に存在するＳｉを含む酸化物がＦｅＳｉＯ3、Ｆｅ2ＳｉＯ4、ＭｎＳｉＯ3、Ｍｎ2ＳｉＯ4から選ばれた１種以上のＳｉを含む酸化物であることを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板。
% By mass
C: 0.05 to 0.25%
Si: 0.3 to 2.5%,
Mn: 1.5 to 2.8%,
P: 0.03% or less,
S: 0.02% or less,
Al: 0.005 to 0.5%,
N: 0.0060% or less,
On the steel plate having Fe and Al on the high-strength steel plate made of the remaining Fe and inevitable impurities and having the alloyed hot-dip galvanized layer made of Zn and inevitable impurities, the high-strength steel plate and the plating layer The oxide containing Si is present in an average content of 0.6 to 10% by mass in the crystal grain boundaries and crystal grains in the steel sheet on the steel sheet side of 5 μm or less from the interface with the interface, and in the plating layer The oxide containing Si is present in an average content of 0.05 to 1.5 mass%, and the oxide containing Si present in the plating layer and the steel sheet is FeSiO 3 , Fe 2. A high-strength galvannealed steel sheet having a good appearance, characterized by being an oxide containing one or more kinds of Si selected from SiO 4 , MnSiO 3 and Mn 2 SiO 4 .
さらに、前記鋼板内面側にＳｉＯ2が存在することを特徴とする請求項１記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板。 The high strength alloyed hot-dip galvanized steel sheet with good appearance according to claim 1 , wherein SiO 2 is present on the inner surface side of the steel sheet. さらに、前記めっき層の鋼板側及び前記鋼板中にＳｉＯ2が存在することを特徴とする請求項１記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板。 Further, the steel plate side and the high strength galvannealed steel sheet appearance of claim 1 wherein is good, wherein the SiO 2 is present in the steel sheet of the plating layer. 引張強さＦ（ＭＰａ）と伸びＬ（％）の関係が
Ｌ≧５１−０．０３５×Ｆ
を満足することを特徴とする請求項１乃至請求項３のいずれかに記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板。 The relationship between tensile strength F (MPa) and elongation L (%) is L ≧ 51−0.035 × F
The high-strength galvannealed steel sheet having a good appearance according to any one of claims 1 to 3 , wherein: 請求項１に記載の化学成分からなる組成の高強度鋼板に連続的に溶融亜鉛めっきを施す際、還元帯の雰囲気として、Ｈ2を１〜６０体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯ2、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ2を下記（１）式、（２）式を満足するように
−０．００００３４Ｔ2＋０．１０５Ｔ−０．２〔Ｓｉ％〕2＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ2≦−０．００００３８Ｔ2＋０．１０７Ｔ−９０．４ ・・・（１）
９２３≦Ｔ≦１１７３ ・・・（２）
Ｔ：鋼板の最高到達温度（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
制御した雰囲気で還元を行うことを特徴とする請求項１乃至請求項４のいずれかに記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 When continuously hot-dip galvanizing the high strength steel plate having the composition of the chemical component according to claim 1, the atmosphere of the reduction zone contains 1 to 60% by volume of H 2 , and the balance is N 2 and H 2 O. , O 2 , CO 2 , CO, and inevitable impurities, and the logarithm log PO 2 of the oxygen partial pressure in the atmosphere satisfies the following formulas (1) and (2) − 0.000034T 2 + 0.105T−0.2 [Si%] 2 +2.1 [Si%] − 98.8 ≦ log PO 2 ≦ −0.000038 T 2 + 0.107T-90.4 (1)
923 ≦ T ≦ 1173 (2)
T: Maximum temperature of steel sheet (K)
[Si%]: Si content in the steel sheet (mass%)
The method for producing a high-strength galvannealed steel sheet having a good appearance according to any one of claims 1 to 4 , wherein the reduction is performed in a controlled atmosphere. 請求項５に記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、還元帯の前に酸化帯において燃焼空気比０．９〜１．２の雰囲気中にて酸化せしめ、その後の還元帯において、還元を行うことを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 In the manufacturing method of the high intensity | strength galvannealed steel plate of Claim 5 , it oxidized in the atmosphere of combustion air ratio 0.9-1.2 in the oxidation zone before the reduction zone, and in the reduction zone after that A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by performing reduction. 請求項６に記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、還元帯の前の酸化帯において露点２７３Ｋ以上の雰囲気中にて酸化せしめ、その後の還元帯において、還元を行うことを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 The method for producing a high-strength galvannealed steel sheet according to claim 6 , wherein oxidation is performed in an atmosphere having a dew point of 273 K or more in an oxidation zone before the reduction zone, and reduction is performed in the subsequent reduction zone. A method for producing a high-strength galvannealed steel sheet having a good appearance. 請求項１に記載の化学成分からなる組成のスラブをＡｒ３点以上の温度で仕上圧延を行い、５０〜８５％の冷間圧延を施した後、請求項５乃至請求項７のいずれかに記載の雰囲気の連続溶融亜鉛めっき設備を使用し１０２３Ｋ以上１１５３Ｋ以下のフェライト、オーステナイトの二相共存温度域で焼鈍し、その最高到達温度から９２３Ｋまでを平均冷却速度０．５〜１０度／秒で、引き続いて９２３Ｋから７７３Ｋまでを平均冷却速度３度／秒以上で冷却し、さらに７７３Ｋから平均冷却速度０．５度／秒以上で６９３Ｋ〜７３３Ｋまで冷却し、且つ、７７３Ｋからめっき浴温までを２５秒以上２４０秒以下保持した後、溶融亜鉛めっき処理を行うことによって、前記冷延鋼板の表面上に溶融亜鉛めっき層を形成し、次いで、前記溶融亜鉛めっき層が形成された前記鋼板に対し合金化処理を施すことによって、前記鋼板の表面上に合金化溶融亜鉛めっき層を形成する合金化溶融亜鉛めっき鋼板の製造方法において、前記溶融亜鉛めっき処理を、浴中有効Ａｌ濃度：０．０７〜０．１０５ｍａｓｓ％、残部がＺｎおよび不可避的不純物からなる成分組成の溶融亜鉛めっき浴中で行い、そして、前記合金化処理を、
７２０≦Ｔ≦６９０×ｅｘｐ（１．３５×〔Ａｌ％〕）
但し、〔Ａｌ％〕：亜鉛めっき浴中の浴中有効Ａｌ濃度（ｍａｓｓ％）
を満足する温度Ｔ（Ｋ）において行うことを特徴とする請求項１乃至請求項４のいずれかに記載の外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 The slab having the composition of the chemical component according to claim 1 is finish-rolled at a temperature equal to or higher than an Ar3 point and cold-rolled by 50 to 85%, and then subjected to any of claims 5 to 7. Using a continuous hot-dip galvanizing facility with an atmosphere of 1023K to 1153K in the two-phase coexistence temperature range of ferrite and austenite, from the highest temperature to 923K at an average cooling rate of 0.5 to 10 degrees / second, Subsequently, 923K to 773K were cooled at an average cooling rate of 3 degrees / second or more, further cooled from 773 K to 693 K to 733 K at an average cooling rate of 0.5 degrees / second or more, and from 773K to the plating bath temperature was 25. After holding for at least 240 seconds and not more than 240 seconds, a hot dip galvanizing treatment is performed to form a hot dip galvanized layer on the surface of the cold-rolled steel sheet, In the method for producing an alloyed hot-dip galvanized steel sheet, in which an alloyed hot-dip galvanized layer is formed on the surface of the steel sheet by subjecting the steel sheet on which the coating layer has been formed, The effective Al concentration in the bath is 0.07 to 0.105 mass%, the balance is made in a hot dip galvanizing bath having a component composition consisting of Zn and inevitable impurities, and the alloying treatment is performed.
720 ≦ T ≦ 690 × exp (1.35 × [Al%])
However, [Al%]: Effective Al concentration in the galvanizing bath (mass%)
The method for producing a high-strength galvannealed steel sheet having a good appearance according to any one of claims 1 to 4 , wherein the method is performed at a temperature T (K) that satisfies the following conditions. 請求項５及至請求項８のいずれかに記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、溶融めっき後６７３Ｋ以下の温度に冷却されるまでの時間を３０秒以上１２０秒以下とすることを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 The method for producing a high-strength galvannealed steel sheet according to any one of claims 5 to 8 , wherein the time until cooling to a temperature of 673 K or less after hot dipping is 30 seconds or more and 120 seconds or less. A method for producing a high-strength alloyed hot-dip galvanized steel sheet having a good external appearance. 請求項５及至請求項９のいずれかに記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、焼鈍後６７３Ｋ以上７２３Ｋ以下まで冷却した後、７０３Ｋ以上７４３Ｋ以下まで再加熱を行い、溶融亜鉛めっき処理を行うことを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 In the manufacturing method of the high intensity | strength galvannealed steel plate in any one of Claim 5 to 9 , after cooling to 673K or more and 723K or less after annealing, it reheats to 703K or more and 743K or less, and galvanized. A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by performing a treatment. 無酸化炉又は直火炉を有し、鋼板に連続的に溶融亜鉛めっきを施す請求項５記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、ＣＯ2を１〜１００体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯおよび不可避的不純物からからなる気体を導入する装置を還元炉に配設し、還元帯の雰囲気を、Ｈ 2 を１〜６０体積％含有し、残部Ｎ 2 、Ｈ 2 Ｏ、Ｏ 2 、ＣＯ 2 、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ 2 を下記（１）式、（２）式を満足するように
−０．００００３４Ｔ 2 ＋０．１０５Ｔ−０．２〔Ｓｉ％〕 2 ＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ 2 ≦−０．００００３８Ｔ 2 ＋０．１０７Ｔ−９０．４ ・・・（１）
９２３≦Ｔ≦１１７３ ・・・（２）
Ｔ：鋼板の最高到達温度（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
制御することを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 Has a non-oxidizing furnace or direct fired furnace, the method of producing a high strength galvannealed steel sheet according to claim 5, wherein performing continuous molten zinc plating steel sheet, the CO 2 containing 1 to 100% by volume, the balance An apparatus for introducing a gas composed of N 2 , H 2 O, O 2 , CO and unavoidable impurities is disposed in the reduction furnace, the atmosphere in the reduction zone contains 1 to 60% by volume of H 2 , and the balance N 2 , one or more of H 2 O, O 2 , CO 2 , CO and unavoidable impurities, and the logarithm log PO 2 of the oxygen partial pressure in the atmosphere is expressed by the following equations (1) and (2) To be satisfied
−0.000034T 2 + 0.105T−0.2 [Si%] 2 +2.1 [Si%] − 98.8 ≦ log PO 2 ≦ −0.000038 T 2 + 0.107T-90.4 (1)
923 ≦ T ≦ 1173 (2)
T: Maximum temperature of steel sheet (K)
[Si%]: Si content in the steel sheet (mass%)
A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by being controlled. 無酸化炉又は直火炉を有し、鋼板に連続的に溶融亜鉛めっきを施す請求項５記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、還元炉中でＣＯまたは炭化水素を燃焼させ、ＣＯ2を１〜１００体積％含有し、残部Ｎ2、Ｈ2Ｏ、Ｏ2、ＣＯおよび不可避的不純物からからなる気体を発生させる装置を配設し、
還元帯の雰囲気を、Ｈ 2 を１〜６０体積％含有し、残部Ｎ 2 、Ｈ 2 Ｏ、Ｏ 2 、ＣＯ 2 、ＣＯの１種又は２種以上および不可避的不純物からなり、その雰囲気中の酸素分圧の対数ｌｏｇＰＯ 2 を下記（１）式、（２）式を満足するように
−０．００００３４Ｔ 2 ＋０．１０５Ｔ−０．２〔Ｓｉ％〕 2 ＋２．１〔Ｓｉ％〕−９８．８≦ｌｏｇＰＯ 2 ≦−０．００００３８Ｔ 2 ＋０．１０７Ｔ−９０．４ ・・・（１）
９２３≦Ｔ≦１１７３ ・・・（２）
Ｔ：鋼板の最高到達温度（Ｋ）
〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
制御することを特徴とする外観が良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。 The method for producing a high-strength alloyed hot-dip galvanized steel sheet according to claim 5, wherein the hot-dip galvanized steel sheet is subjected to continuous hot-dip galvanizing on the steel sheet, and CO or hydrocarbons are burned in a reduction furnace. An apparatus for generating a gas containing CO 2 in an amount of 1 to 100% by volume and comprising the balance N 2 , H 2 O, O 2 , CO and unavoidable impurities is provided ,
The atmosphere in the reduction zone contains 1 to 60% by volume of H 2 , and the balance is composed of one or more of N 2 , H 2 O, O 2 , CO 2 , CO, and unavoidable impurities. Logarithm log PO 2 of oxygen partial pressure so that the following formulas (1) and (2) are satisfied
−0.000034T 2 + 0.105T−0.2 [Si%] 2 +2.1 [Si%] − 98.8 ≦ log PO 2 ≦ −0.000038 T 2 + 0.107T-90.4 (1)
923 ≦ T ≦ 1173 (2)
T: Maximum temperature of steel sheet (K)
[Si%]: Si content in the steel sheet (mass%)
A method for producing a high-strength galvannealed steel sheet having a good appearance, characterized by being controlled.
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