JP4912684B2 - High-strength hot-dip galvanized steel sheet, production apparatus therefor, and method for producing high-strength alloyed hot-dip galvanized steel sheet - Google Patents
High-strength hot-dip galvanized steel sheet, production apparatus therefor, and method for producing high-strength alloyed hot-dip galvanized steel sheet Download PDFInfo
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本発明は、Ｓｉ含有高強度溶融亜鉛めっき鋼板およびその製造装置、ならびに高強度合金化溶融亜鉛めっき鋼板の製造方法に係わるもので、特に優れた耐食性を有し、種々の用途、例えば、建材用、自動車用鋼板等に適用できるめっき鋼板に関する。 The present invention relates to a Si-containing high-strength hot-dip galvanized steel sheet and its production apparatus, and a method for producing a high-strength alloyed hot-dip galvanized steel sheet. The present invention relates to a plated steel sheet that can be applied to steel sheets for automobiles.
近年、溶融亜鉛めっき鋼板の需要は増大し、その用途も多様化しており、特に自動車用に用いられる鋼板に対しては、車体軽量化のため素材の強度、加工性などの機械的性質の向上が要求されている。素材の強度を向上させる方法としては、鋼中にＳｉを添加させることが有効であることは知られているが、Ｓｉを含有する鋼板は、連続式溶融亜鉛めっき設備を用いて溶融亜鉛めっきを施す際に、焼鈍過程で鋼板表面にＳｉ酸化物が濃化し、めっき濡れ性を大幅に低下させるという極めて重大な問題が生じている。これを改善すべく種々の提案がなされている。
例えば、特許文献１には、無酸化炉において鋼表面に厚膜の酸化皮膜を形成した後、水素を含む雰囲気中で焼鈍し、めっきする方法が提案されている。しかし、この方法では、鉄の酸化膜によりＳｉの表面濃化を抑制し、めっき性を阻害するＳｉ酸化物の生成を抑制できるのでめっき密着性を向上させることができるとしているが、無酸化炉における鉄の酸化膜厚生成量が多すぎ、還元炉における鉄の酸化膜の還元が不十分であったり、無酸化炉における酸化膜厚が薄すぎ、めっき性が阻害されるようになったりして、鉄の酸化膜の還元反応を適正に制御できないのが現状である。
In recent years, the demand for hot dip galvanized steel sheets has increased, and their uses have diversified. Especially for steel sheets used in automobiles, mechanical properties such as material strength and workability have been improved to reduce the weight of the car body. Is required. As a method of improving the strength of the material, it is known that adding Si to steel is effective, but a steel sheet containing Si is hot dip galvanized using a continuous hot dip galvanizing facility. During application, Si oxide is concentrated on the surface of the steel sheet during the annealing process, resulting in a very serious problem that the wettability of the plating is greatly reduced. Various proposals have been made to improve this.
For example, Patent Document 1 proposes a method of forming a thick oxide film on a steel surface in a non-oxidizing furnace, and then annealing and plating in an atmosphere containing hydrogen. However, in this method, the iron oxide film suppresses the surface concentration of Si, and the formation of Si oxides that inhibit the plating property can be suppressed, so that the plating adhesion can be improved. The amount of iron oxide film generated in the furnace is too large, the reduction of the iron oxide film in the reduction furnace is insufficient, or the oxide film thickness in the non-oxidation furnace is too thin, which may impair the plating performance. As a result, the reduction reaction of the iron oxide film cannot be properly controlled.
更に、特許文献２には、Ｓｉ：０．２〜２質量％を含有する鋼板を無酸化炉を有する連続式溶融亜鉛めっき設備で溶融亜鉛めっきする際に、無酸化炉の燃焼空気比と還元炉の雰囲気の露点を調整して鋼板表面の酸化膜厚を制御する方法や、特許文献３には、同量のＳｉを含有する鋼板を無酸化炉を有しない連続式溶融亜鉛めっき設備で溶融亜鉛めっきする際に、還元炉を２ゾーン以上に分割し各ゾーンの雰囲気の露点を調整して同様の効果を得る提案がなされている。更に、特許文献４には、Ｓｉ：０．４〜２質量％を含有する鋼板を連続式溶融亜鉛めっき設備で溶融亜鉛めっきする際に、酸化帯で燃焼空気比０．９〜１．２の雰囲気中で酸化させた後、還元帯で水分圧と水素分圧を特定の関係式を満たす雰囲気で還元する方法が提案されている。 Furthermore, in Patent Document 2, when hot-dip galvanizing a steel sheet containing Si: 0.2-2 mass% with a continuous hot dip galvanizing facility having a non-oxidation furnace, the combustion air ratio and reduction of the non-oxidation furnace A method of adjusting the dew point of the furnace atmosphere to control the oxide film thickness on the steel sheet surface, and Patent Document 3 describes melting a steel sheet containing the same amount of Si in a continuous hot dip galvanizing facility that does not have a non-oxidizing furnace. When galvanizing, a reduction furnace is divided into two or more zones, and the dew point of the atmosphere in each zone is adjusted to obtain the same effect. Furthermore, Patent Document 4 discloses that when a steel sheet containing Si: 0.4-2 mass% is hot dip galvanized with a continuous hot dip galvanizing facility, the combustion air ratio is 0.9-1.2 in the oxidation zone. There has been proposed a method in which after oxidation in the atmosphere, the moisture pressure and the hydrogen partial pressure are reduced in an atmosphere satisfying a specific relational expression in the reduction zone.
しかしながら、これら特許文献1〜3では、上述したような鉄の酸化膜の還元反応を適正に制御すること、およびＳｉの表面濃化を解消することはできず、依然としてめっきの濡れ性は改善されていない。また、特許文献4では酸化帯の酸化膜厚みがやや大きくなりすぎ炉内ロール疵の原因となりやすい等の問題がある。 However, in these patent documents 1 to 3, it is not possible to properly control the reduction reaction of the iron oxide film as described above, and it is not possible to eliminate the surface concentration of Si, and the wettability of the plating is still improved. Not. Further, in Patent Document 4, there is a problem that the oxide film thickness of the oxidation zone becomes too large and tends to cause in-furnace rolls.
本発明は、めっき性が良好で耐食性に優れた高Ｓｉを含有する高強度溶融亜鉛めっき鋼板およびその製造装置ならびに高強度合金化溶融亜鉛めっき鋼板の製造方法を提供する。 The present invention provides a high-strength hot-dip galvanized steel sheet containing high Si that has good plating properties and excellent corrosion resistance, a manufacturing apparatus therefor, and a method for manufacturing a high-strength galvannealed steel sheet.
（１）Ｓｉ含有量：０．４〜２．０質量％を含む高強度鋼板に連続溶融亜鉛めっきを施す際に、鋼板を予熱し、次いで、直火還元炉で直火還元バーナーの空気比を０．６以上０．９未満とした還元雰囲気で鋼板を還元し、その後、水素還元を行う間接加熱炉で水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が下式（１）を満たす雰囲気で鋼板を還元し、間接加熱炉からめっき設備入側のスナウト部まで間では下式（２）を満たす雰囲気として還元及び冷却を行い、連続溶融亜鉛めっきを施すことを特徴とする高強度溶融亜鉛めっき鋼板の製造方法。
−１．６≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．５ ・・・ （１）
ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−１．５ ・・・ （２）
（２）（１）に記載のめっき鋼板の製造方法において、合金化処理を施すこと
を特徴とする耐食性の良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
（３）Ｓｉ含有量：０．４〜２．０質量％、Ｍｎ含有量：１．０〜３．０質量％を含み、残部Ｆｅおよび不可避的不純物からなる高強度鋼板に連続溶融亜鉛めっきを施す際に、鋼板を予熱し、次いで、直火還元炉で直火還元バーナーの空気比を０．６以上０．９未満とした還元雰囲気で鋼板を還元し、その後、水素還元を行う間接加熱炉で水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が下式（３）を満たす雰囲気で鋼板を還元し、連続溶融亜鉛めっきを施すことを特徴とする高強度溶融亜鉛めっき鋼板の製造方法。
ｌｏｇ（α１×T2.56×（Csi/100-28/（2×54）×α２×Cmn/100）2.24）
≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．５ ・・・ （３）
α１=4.04×10(-5)
α２=0.7〜0.9（直火還元炉内でのMn酸化分）
ここで、Csiは、鋼板中のＳｉ含有質量％
Cmnは、鋼板中のＭｎ含有質量％
（４）（３）記載のめっき鋼板の製造方法において、合金化処理を施すことを特徴とする耐食性の良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
（５）前記間接加熱炉の還元帯に水蒸気を含む加湿ガスを吹き込むことを特徴とする（１）又は（３）に記載の耐食性の良好な高強度溶融亜鉛めっき鋼板の製造方法。
（６）前記間接加熱炉の還元帯に水蒸気を含む加湿ガスを吹き込むことを特徴とする（２）又は（４）に記載の耐食性の良好な高強度合金化溶融亜鉛めっき鋼板の製造方法。
（７）前記直火還元炉を含む焼鈍炉外において、水蒸気を含む加湿ガス発生装置の出側配管に加温装置を設け、該配管が２箇所以上の焼鈍炉内へ連結されていることを特徴とする（１）又は（３）記載の高強度溶融亜鉛めっき鋼板の製造装置。
（８）前記直火還元炉を含む焼鈍炉外において、水蒸気を含む加湿ガス発生装置の出側配管に加温装置を設け、該配管が２箇所以上の焼鈍炉内へ連結されていることを特徴とする（２）又は（４）記載の高強度合金化溶融亜鉛めっき鋼板の製造装置。
(1) Si content: When continuous hot-dip galvanizing is applied to a high-strength steel sheet containing 0.4 to 2.0 mass%, the steel sheet is preheated, and then the air ratio of the direct-fire reduction burner in a direct-fire reduction furnace The steel sheet is reduced in a reducing atmosphere with a value of 0.6 or more and less than 0.9, and then the logarithm log (PH 2 O / PH 2 ) of the water pressure and the hydrogen partial pressure in the indirect heating furnace that performs hydrogen reduction is expressed by the following formula ( 1) The steel sheet is reduced in an atmosphere satisfying 1), and the space between the indirect heating furnace and the snout section on the plating equipment entry side is reduced and cooled as an atmosphere satisfying the following formula (2), and is subjected to continuous hot dip galvanization. A method for producing a high-strength hot-dip galvanized steel sheet.
−1.6 ≦ log (PH 2 O / PH 2 ) ≦ −0.5 (1)
log (PH 2 O / PH 2 ) ≦ −1.5 (2)
(2) A method for producing a high-strength galvannealed steel sheet with good corrosion resistance, characterized in that alloying treatment is performed in the method for producing a plated steel sheet according to (1) .
(3) Continuous hot-dip galvanizing is applied to high-strength steel sheets containing Si content: 0.4 to 2.0 mass%, Mn content: 1.0 to 3.0 mass%, and the balance Fe and inevitable impurities. When performing, indirect heating is performed by preheating the steel sheet, then reducing the steel sheet in a reducing atmosphere in which the air ratio of the direct fire reduction burner is 0.6 or more and less than 0.9 in a direct flame reduction furnace, and then performing hydrogen reduction A high-strength hot-dip galvanizing characterized in that the steel sheet is reduced and subjected to continuous hot-dip galvanizing in an atmosphere where the logarithm log (PH 2 O / PH 2 ) of moisture pressure and hydrogen partial pressure satisfies the following formula (3) A method of manufacturing a steel sheet.
log (α1 × T 2.56 × (Csi / 100-28 / (2 × 54) × α2 × Cmn / 100) 2.24 )
≦ log (PH 2 O / PH 2 ) ≦ −0.5 (3)
α1 = 4.04 × 10 (-5)
α2 = 0.7 to 0.9 (Mn oxidation content in direct flame reduction furnace)
Here, Csi is the Si content mass% in the steel sheet.
Cmn is the Mn content mass% in the steel sheet
(4) A method for producing a high-strength galvannealed steel sheet with good corrosion resistance, characterized in that in the method for producing a plated steel sheet according to ( 3) , an alloying treatment is performed.
(5) The method for producing a high-strength hot-dip galvanized steel sheet with good corrosion resistance according to ( 1) or (3) , wherein a humidified gas containing water vapor is blown into the reduction zone of the indirect heating furnace.
(6) The method for producing a high-strength galvannealed steel sheet with good corrosion resistance according to ( 2) or (4), wherein a humidified gas containing water vapor is blown into the reduction zone of the indirect heating furnace.
(7) Outside the annealing furnace including the direct-fire reduction furnace, a heating device is provided on the outlet side piping of the humidified gas generator including water vapor, and the piping is connected to two or more annealing furnaces. An apparatus for producing a high-strength hot-dip galvanized steel sheet according to ( 1) or (3) .
(8) Outside the annealing furnace including the direct-fire reduction furnace, a heating device is provided in the outlet side piping of the humidified gas generator including water vapor, and the piping is connected to two or more annealing furnaces. An apparatus for producing a high-strength galvannealed steel sheet according to ( 2) or (4), which is characterized.
本発明によるＳｉ含有高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板は、優れた耐食性とめっき性を有するため、特に建材用、自動車用鋼板等の種々の用途に適用することができる。 The Si-containing high-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet according to the present invention have excellent corrosion resistance and plating properties, and therefore can be applied to various applications such as steel for construction materials and automobiles. .
以下に本発明について詳細に説明する。 The present invention is described in detail below.
先ず、本発明によるＳｉ含有高強度溶融亜鉛めっき鋼板を製造するための連続溶融亜鉛めっき設備は、予熱帯、均熱帯を含む直火還元炉、急冷帯、スナウト部、溶融亜鉛めっきポットの構成からなり、特に、直火還元炉を含む焼鈍炉外において、水蒸気を含む加湿ガス発生装置の出側配管に加温装置を設け、該配管が２箇所以上の焼鈍炉内へ連結されている高強度溶融亜鉛めっき鋼板の製造装置である。また、合金化溶融亜鉛めっき鋼板を得る場合には、これらの設備列に加え合金化処理炉を設けている。 First, the continuous hot dip galvanizing equipment for producing the Si-containing high-strength hot dip galvanized steel sheet according to the present invention is composed of a direct-fire reduction furnace including a pre-tropical zone, a soaking zone, a quench zone, a snout part, and a hot dip galvanizing pot. In particular, outside the annealing furnace including the direct-fire reduction furnace, a heating device is provided on the outlet side piping of the humidified gas generator including water vapor, and the piping is connected to two or more annealing furnaces. It is a manufacturing apparatus of a hot-dip galvanized steel sheet. In addition, in order to obtain an alloyed hot-dip galvanized steel sheet, an alloying furnace is provided in addition to these equipment rows.
めっき不良の原因は焼鈍中に還元炉内で鋼板表面に生成するＳｉ酸化物（ＳｉＯ2）である。特に、この現象は鋼中Ｓｉ量の増加に伴ってめっき不良が著しくなる。しかし、鋼板強度を確保する上ではＳｉは有効な元素であるため多量添加が望ましいが、上記Ｓｉ酸化物の生成を抑制できるＳｉ濃度は２質量％が限界である。一方、Ｓｉ濃度が０．４質量％未満では必要な鋼板強度を確保できなくなる。 The cause of the plating failure is Si oxide (SiO 2 ) generated on the steel sheet surface in the reduction furnace during annealing. In particular, this phenomenon causes significant plating defects as the amount of Si in the steel increases. However, since Si is an effective element in securing the steel sheet strength, it is desirable to add a large amount, but the Si concentration that can suppress the formation of the Si oxide is limited to 2% by mass. On the other hand, if the Si concentration is less than 0.4% by mass, the required steel sheet strength cannot be secured.
本発明者は、鋼板表面に生成するＳｉ酸化物の生成と鉄の酸化膜の還元反応について鋭意検討したところ、連続溶融亜鉛めっきを施す際に、焼鈍炉における直火帯での空気比制御および還元帯での水分圧と水素分圧の比が上記２つの現象にとって最も重要な要素であることが多くの実験により判明した。
すなわち、まず直火炉において直火還元バーナーの空気比を０．６以上０．９未満で鋼板を還元する。直火炉で直火還元バーナーを使用する理由は、Ｓｉを含有する鋼板では直火還元バーナーを使用することで無酸化炉よりもＳｉ酸化膜を薄くコントロールすることが可能となる。次いで還元帯で加湿した気体を炉内に吹き込むことで、鋼板表面のＳｉ濃化を防ぎ、鋼中にSi酸化物を生成させ、めっきの濡れ性を向上させることができ、合金化処理を行なう場合には合金化速度も向上させることができる。すなわち、従来のように、無酸化炉で空気比を上げると、鋼板表面には先ず鉄酸化物が生成され、その後、鉄酸化膜のバリアを通って、鋼中にＳｉ酸化物が生成され、酸素が移動するために時間がかかるためにＳｉ酸化物生成量が小さくなるものと考えられる。そのため、従来は、空気比：０．９以上必要となる。その結果、表面酸化膜量が増加し、無酸化炉内のハースロールビルドアップ等の問題が発生し易くなり、一方、上記空気比を下げ過ぎるとＳｉ酸化物が生成しにくくなり操業条件の範囲が極めて狭まってくるという問題がある。
The present inventor has intensively studied the generation of Si oxide and the reduction reaction of the iron oxide film generated on the steel sheet surface. When performing continuous hot dip galvanization, the air ratio control in the direct flame zone in the annealing furnace and Many experiments have shown that the ratio of water pressure to hydrogen partial pressure in the reduction zone is the most important factor for the above two phenomena.
That is, first, the steel sheet is reduced in an direct furnace with an air ratio of the direct fire reduction burner of 0.6 or more and less than 0.9. The reason why the direct flame reduction burner is used in the direct flame furnace is that the Si oxide film can be controlled thinner than the non-oxidation furnace by using the direct flame reduction burner in the steel plate containing Si. Next, by blowing the gas humidified in the reduction zone into the furnace, Si concentration on the steel sheet surface can be prevented, Si oxide can be generated in the steel, and the wettability of the plating can be improved. In some cases, the alloying rate can also be improved. That is, as in the prior art, when the air ratio is increased in a non-oxidizing furnace, iron oxide is first generated on the steel sheet surface, then, through the barrier of the iron oxide film, Si oxide is generated in the steel, Since it takes time for oxygen to move, it is considered that the amount of Si oxide generated becomes small. Therefore, conventionally, an air ratio of 0.9 or more is required. As a result, the amount of surface oxide film increases and problems such as hearth roll buildup in a non-oxidizing furnace are likely to occur. On the other hand, if the air ratio is too low, Si oxides are less likely to be produced and the range of operating conditions There is a problem that becomes very narrow.
そこで、本発明では、直火還元バーナーを用いることで、鋼板表面の酸化皮膜を過剰に生成させることなくＳｉ酸化物を多量に生成させる必要があり、この目的のために、本発明では直火炉における直火還元バーナーの空気比を０．６以上０．９未満に限定した。この直火還元バーナーの空気比が０．９以上では鋼板表面酸化膜が約800Å以上成長し、炉内のハースロールビルドアップ等の問題が多発するため上限を０．９とした。一方、下限の０．６は直火還元バーナーの還元能力が低下する限界値である。 Therefore, in the present invention, it is necessary to generate a large amount of Si oxide without excessively forming an oxide film on the surface of the steel sheet by using a direct flame reduction burner. The air ratio of the direct fire reduction burner in was limited to 0.6 or more and less than 0.9. When the air ratio of this direct fire reduction burner is 0.9 or more, the steel plate surface oxide film grows about 800 mm or more, and problems such as hearth roll buildup in the furnace occur frequently, so the upper limit was set to 0.9. On the other hand, the lower limit of 0.6 is a limit value at which the reducing ability of the direct flame reduction burner is reduced.
更に、水素還元を行う間接加熱炉の還元帯では、水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が下式（１）を満たす雰囲気で鋼板を還元
−１．６≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．５ ・・・ （１）
することにより、めっきの濡れ性および合金化速度を向上させることができる。ここでは、Ｈ2：２〜１０％及びを含むＮ2を雰囲気ガスとして用いて還元する。重要なことはこの上記雰囲気ガスの水分圧と水素分圧を上記（１）式で制御する必要がある。水分圧と水素分圧（ＰＨ2Ｏ／ＰＨ2）は、炉内に水蒸気を含む加湿ガスを吹き込むことにより制御する。ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）を−１．６以上とした理由は、−１．６未満では直火炉における直火還元バーナーの空気比０．９以上としなければ、鋼板表面のSi濃化が生じるためである。またｌｏｇ（ＰＨ2Ｏ／ＰＨ2）を−０．５以下とした理由は、−０．５より大きいと直火炉で生成した鉄の酸化膜を還元できないためであり、さらに、炉内構造物の耐酸化性が悪化するためである。この理由は、予熱帯および直火炉で生成した鉄の酸化物を還元し、鋼板表面に生成する外部Ｓｉ酸化物（ＳｉＯ2）の生成を防止し、鋼板中にＳｉ酸化物（ＳｉＯ2）を生成させ、更に鋼板表面に生成した鉄酸化物を還元して鋼板表面にＦｅのみを残すためである。また、Ｍｎが存在する場合はめっき性に対して無害なＳｉ，Ｍｎの酸化物（Ｍｎ2ＳｉＯ4）を生成し見かけ上のＳｉ濃度が低くなる。鋼板中に酸化物を生成する水分圧と水素分圧の比は鋼板に含有されるＳｉ、Ｍｎ量と相関関係があり、以下のような式（３）の元で制御する。
ｌｏｇ（α１×T2.56×（Csi/100-28/（2×54）×α２×Cmn/100）2.24）
≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．５ ・・・ （３）
α１=4.04×10(-5)
α２=0.7〜0.9（直火還元炉内でのMn酸化分）
ここで、Csiは、鋼板中のＳｉ含有質量％
Cmnは、鋼板中のＭｎ含有質量％
上記ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）の制御のために水蒸気を含む加湿ガスの吹き込みは、間接加熱炉の出側に加湿ガス吹き込み装置を設け、一定の圧力下で加湿ガス吹き込みを行うことが好ましい。
Further, in the reduction zone of the indirect heating furnace that performs hydrogen reduction, the steel sheet is reduced in an atmosphere in which the logarithm log of the water pressure and the hydrogen partial pressure (PH 2 O / PH 2 ) satisfies the following formula (1): −1.6 ≦ log (PH 2 O / PH 2 ) ≦ −0.5 (1)
By doing so, the wettability of plating and the alloying speed can be improved. Here, reduction is performed using N 2 containing 2 to 10% of H 2 as an atmospheric gas. What is important is that the moisture pressure and hydrogen partial pressure of the atmospheric gas must be controlled by the above equation (1). The water pressure and the hydrogen partial pressure (PH 2 O / PH 2 ) are controlled by blowing a humidified gas containing water vapor into the furnace. The reason why the log (PH 2 O / PH 2 ) is −1.6 or more is that if it is less than −1.6, unless the air ratio of the direct-fire reduction burner in the direct-fired furnace is 0.9 or more, Si concentration on the steel sheet surface This is because. The reason why the log (PH 2 O / PH 2 ) is −0.5 or less is that if it is larger than −0.5, the iron oxide film generated in the direct-fired furnace cannot be reduced. This is because the oxidation resistance of the deteriorates. The reason for this is that iron oxides generated in the pre-tropical and direct-fired furnaces are reduced to prevent the formation of external Si oxide (SiO 2 ) generated on the steel sheet surface, and Si oxide (SiO 2 ) is added to the steel sheet. This is because the iron oxide generated and further reduced on the steel sheet surface leaves only Fe on the steel sheet surface. Further, when Mn is present, an oxide of Si and Mn (Mn 2 SiO 4 ) that is harmless to plating properties is generated, and the apparent Si concentration is lowered. The ratio of the water pressure and the hydrogen partial pressure that generate oxides in the steel sheet correlates with the amounts of Si and Mn contained in the steel sheet, and is controlled based on the following equation (3).
log (α1 × T 2.56 × (Csi / 100-28 / (2 × 54) × α2 × Cmn / 100) 2.24 )
≦ log (PH 2 O / PH 2 ) ≦ −0.5 (3)
α1 = 4.04 × 10 (-5)
α2 = 0.7 to 0.9 (Mn oxidation content in direct flame reduction furnace)
Here, Csi is the Si content mass% in the steel sheet.
Cmn is the Mn content mass% in the steel sheet
In order to control the log (PH 2 O / PH 2 ), the humidified gas containing water vapor is blown by providing a humidified gas blowing device on the outlet side of the indirect heating furnace and blowing the humidified gas under a constant pressure. preferable.
更に、間接加熱炉からめっき設備入側のスナウト部まで間では下式（２）を満たす雰囲気として還元及び冷却を行う。
ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−１．５ ・・・ （２）
ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）を−１．５以下とした理由は、スナウト部において−１．５を超える雰囲気ではスナウト浴面での亜鉛の酸化が促進されて亜鉛ヒュームが発生し、これが鋼板に付着することでメッキ欠陥を生じるためである。
Furthermore, reduction and cooling are performed as an atmosphere satisfying the following expression (2) between the indirect heating furnace and the snout portion on the plating equipment entry side.
log (PH 2 O / PH 2 ) ≦ −1.5 (2)
The reason why the log (PH 2 O / PH 2 ) is set to −1.5 or less is that in the atmosphere exceeding −1.5 in the snout part, the oxidation of zinc on the surface of the snout bath is promoted to generate zinc fume. This is because plating defects are caused by adhering to the steel plate.
＜実施例１＞
Ｓｉ：０．４〜１．５質量％を含有する低炭素高強度鋼板を常法により熱延、冷延した板厚０．８ｍｍの鋼板を、脱油・酸洗後、連続溶融亜鉛めっきを施すに当たり、連続式円焼鈍炉にて４５０〜８００℃に短時間予熱し、次いでＣガス、ＬＰＧ、天然ガス等を熱源とする直火還元バーナーの空気比を０．６、０．８、０．９の３段階で燃焼させ、炉内をＣＯ−ＣＯ2−Ｈ2−Ｈ2Ｏの雰囲気とし、１０００〜１３００℃の高温に保持後、水素還元を行う間接加熱炉での雰囲気ガスを水素を５％含む窒素ガスを加湿し水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が−２及び−１になるように調節し鋼板を還元した。次いで、鋼板を溶融亜鉛めっき出側のスナウト部から還元帯の間の水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）を−２、−１になるよう調整した雰囲気内を通板して板温を調整し、約４５０℃に維持された溶融亜鉛めっき浴に鋼板を浸漬して溶融亜鉛めっきを施した。その後、めっき層全体をＦｅ−Ｚｎ合金とする合金化処理を行った。その結果を表１に示した。表１から分かるように、直火還元炉における直火還元バーナーの空気比を本発明範囲内の０．６〜０．９、還元炉内の水分圧と水素分圧の対数を本発明範囲内の−１．６〜−０．５、およびスナウト部から還元帯の間の水分圧と水素分圧の対数を−１．５以下とした場合にはめっき性が良好な高強度合金化亜鉛めっき鋼板を得ることができた。
Ｓｉ：０．２質量％、１．５質量％、２．０質量％、Ｍｎ：１．５質量％の３水準を含有する低炭素高強度鋼板を常法により熱延、冷延した板厚０．８ｍｍの鋼板を、脱油・酸洗後、連続溶融亜鉛めっきを施すに当たり、連続式焼鈍炉にて４５０〜８００℃に短時間予熱し、次いで直火還元バーナーの空気比を０．８で燃焼させ、水素還元を行う間接加熱炉では炉温：９００℃、８００℃、７００℃の３水準とし、雰囲気ガスを水素を５％含む窒素ガスを加湿し水分圧と水素分圧の対数を請求項３に規定した式に基づいて算出した値、−２．６、−１．３、−１、−０．６の４水準に調整した雰囲気内として通板し、その後、約４５０℃に維持された溶融亜鉛めっき浴に鋼板を浸漬して溶融亜鉛めっきを施した。その後、めっき層全体をＦｅ−Ｚｎ合金とする合金化処理を行った。その結果を表２に示した。表２から分かるように、直火還元炉における直火還元バーナーの空気比を本発明範囲内の０．６〜０．９、還元炉内の水分圧と水素分圧の対数を本発明範囲内で規定した式（１）の値、およびスナウト部から還元帯の間の水分圧と水素分圧の対数を−１．５以下とした場合には、めっき性良好な高強度合金化亜鉛めっき鋼板を得ることができた。
Si: A low-carbon high-strength steel sheet containing 0.4 to 1.5 mass% is hot-rolled and cold-rolled by a conventional method, and a 0.8 mm-thick steel sheet is deoiled and pickled, followed by continuous hot-dip galvanizing. For application, it is preheated to 450-800 ° C. for a short time in a continuous circular annealing furnace, and then the air ratio of the direct flame reduction burner using C gas, LPG, natural gas or the like as the heat source is 0.6, 0.8, 0. .9 is burned in three stages, the inside of the furnace is made an atmosphere of CO—CO 2 —H 2 —H 2 O, and the atmosphere gas in the indirect heating furnace that performs hydrogen reduction is maintained after maintaining at a high temperature of 1000 to 1300 ° C. The steel sheet was reduced by humidifying nitrogen gas containing 5% and adjusting the logarithm log (PH 2 O / PH 2 ) of water pressure and hydrogen partial pressure to −2 and −1. Next, the steel sheet was passed through an atmosphere in which the logarithm log (PH 2 O / PH 2 ) of the water pressure and the hydrogen partial pressure between the snout portion on the galvanizing outlet side and the reduction zone was −2 and −1. The steel sheet was adjusted to a plate temperature, and the steel sheet was immersed in a hot dip galvanizing bath maintained at about 450 ° C. to perform hot dip galvanizing. Then, the alloying process which makes the whole plating layer the Fe-Zn alloy was performed. The results are shown in Table 1. As can be seen from Table 1, the air ratio of the direct flame reduction burner in the direct flame reduction furnace is 0.6 to 0.9 within the range of the present invention, and the logarithm of the moisture pressure and hydrogen partial pressure within the reduction furnace is within the range of the present invention. High-strength galvanized plating with good plating properties when the logarithm of -1.6 to -0.5 and the logarithm of the water pressure between the snout portion and the reduction zone and the hydrogen partial pressure are -1.5 or less A steel plate could be obtained.
Thickness obtained by hot-rolling and cold-rolling a low-carbon high-strength steel sheet containing three levels of Si: 0.2% by mass, 1.5% by mass, 2.0% by mass, and Mn: 1.5% by mass by a conventional method. In performing continuous hot-dip galvanization after deoiling and pickling a 0.8 mm steel plate, preheat it to 450-800 ° C in a continuous annealing furnace for a short time, and then set the air ratio of the direct flame reduction burner to 0.8 In an indirect heating furnace that burns with hydrogen and performs hydrogen reduction, the furnace temperature is set to three levels of 900 ° C., 800 ° C., and 700 ° C., and the atmosphere gas is humidified with nitrogen gas containing 5% of hydrogen, and the logarithm of water pressure and hydrogen partial pressure is set. Passing through the atmosphere adjusted to four levels of -2.6, -1.3, -1, and -0.6, calculated based on the formula defined in claim 3, and then about 450 ° C The steel sheet was immersed in a maintained hot dip galvanizing bath and hot dip galvanized. Then, the alloying process which makes the whole plating layer the Fe-Zn alloy was performed. The results are shown in Table 2. As can be seen from Table 2, the air ratio of the direct flame reduction burner in the direct flame reduction furnace is 0.6 to 0.9 within the range of the present invention, and the logarithm of the moisture pressure and hydrogen partial pressure within the reduction furnace is within the range of the present invention. When the logarithm of the water pressure and hydrogen partial pressure between the snout part and the reduction zone is −1.5 or less, the high strength galvanized steel sheet with good plating properties Could get.
Claims (8)
−１．６≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．５ ・・・ （１）
ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−１．５ ・・・ （２） When continuous hot-dip galvanizing is performed on a high-strength steel sheet containing Si content: 0.4 to 2.0 mass%, the steel sheet is preheated, and then the air ratio of the direct-fire reduction burner is set to 0. 0 in a direct-fire reduction furnace. The logarithm log (PH 2 O / PH 2 ) of the water pressure and the hydrogen partial pressure is expressed by the following equation (1) in an indirect heating furnace in which the steel sheet is reduced in a reducing atmosphere of 6 or more and less than 0.9. High strength , characterized by reducing the steel sheet in a satisfying atmosphere and reducing and cooling to an atmosphere that satisfies the following formula (2) between the indirect heating furnace and the snout part on the entry side of the plating equipment, and performing continuous hot dip galvanizing Manufacturing method of hot dip galvanized steel sheet.
−1.6 ≦ log (PH 2 O / PH 2 ) ≦ −0.5 (1)
log (PH 2 O / PH 2 ) ≦ −1.5 (2)
を特徴とする耐食性の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 with good corrosion resistance according to claim 1, wherein alloying treatment is performed.
ｌｏｇ（α１×T2.56×（Csi/100-28/（2×54）×α２×Cmn/100）2.24）
≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．５ ・・・ （３）
α１=4.04×10(-5)
α２=0.7〜0.9（直火還元炉内でのMn酸化分）
ここで、Csiは、鋼板中のＳｉ含有質量％
Cmnは、鋼板中のＭｎ含有質量％ When continuous hot-dip galvanizing is applied to a high-strength steel sheet containing Si content: 0.4 to 2.0 mass%, Mn content: 1.0 to 3.0 mass%, and the balance Fe and inevitable impurities Then, preheat the steel plate, then reduce the steel plate in a reducing atmosphere in which the air ratio of the direct fire reduction burner is 0.6 or more and less than 0.9 in a direct flame reduction furnace, and then moisture in an indirect heating furnace that performs hydrogen reduction Production of a high strength hot dip galvanized steel sheet characterized by reducing the steel sheet in an atmosphere where the logarithm log (PH 2 O / PH 2 ) of the pressure and the hydrogen partial pressure satisfies the following formula (3) and performing continuous hot dip galvanizing Method.
log (α1 × T 2.56 × (Csi / 100-28 / (2 × 54) × α2 × Cmn / 100) 2.24 )
≦ log (PH 2 O / PH 2 ) ≦ −0.5 (3)
α1 = 4.04 × 10 (-5)
α2 = 0.7 to 0.9 (Mn oxidation content in direct flame reduction furnace)
Here, Csi is the Si content mass% in the steel sheet.
Cmn is the Mn content mass% in the steel sheet
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