JP5729008B2 - Method for producing hot-dip galvanized steel sheet - Google Patents
Method for producing hot-dip galvanized steel sheet Download PDFInfo
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- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 21
- 239000008397 galvanized steel Substances 0.000 title claims description 21
- 238000004519 manufacturing process Methods 0.000 title claims description 15
- 238000010438 heat treatment Methods 0.000 claims description 44
- 229910000831 Steel Inorganic materials 0.000 claims description 39
- 239000010959 steel Substances 0.000 claims description 39
- 230000001603 reducing effect Effects 0.000 claims description 11
- 238000005246 galvanizing Methods 0.000 claims description 8
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- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 238000007747 plating Methods 0.000 description 23
- 239000007789 gas Substances 0.000 description 14
- 238000000137 annealing Methods 0.000 description 11
- 238000002485 combustion reaction Methods 0.000 description 7
- 230000007423 decrease Effects 0.000 description 6
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- 230000000052 comparative effect Effects 0.000 description 5
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- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 238000009864 tensile test Methods 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
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- 239000002737 fuel gas Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 208000023514 Barrett esophagus Diseases 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 230000032683 aging Effects 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 239000000567 combustion gas Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
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- 239000000446 fuel Substances 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 210000004894 snout Anatomy 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
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- 229910052751 metal Inorganic materials 0.000 description 1
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- 239000010731 rolling oil Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
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- Coating With Molten Metal (AREA)
Description
本発明は、めっき性及び伸び特性に優れた溶融亜鉛めっき鋼板の製造方法に関するものであり、詳しくは、直火加熱方式の直火帯と還元帯を備える焼鈍炉で熱処理したのち溶融亜鉛めっき処理を施して製造する溶融亜鉛めっき鋼板の製造方法に関するものである。 The present invention relates to a method for producing a hot dip galvanized steel sheet having excellent plating properties and elongation characteristics, and more specifically, hot dip galvanizing treatment after heat treatment in an annealing furnace having a direct fire heating type direct fire zone and a reduction zone. The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet manufactured by applying the above.
溶融亜鉛めっき鋼板は、自動車、家電、建材等の分野において広く用いられている金属材料である。溶融亜鉛めっき鋼板は、直火加熱方式の直火帯と還元帯を備える焼鈍炉で熱処理したのち溶融亜鉛めっき処理を施すことで製造される。 A hot dip galvanized steel sheet is a metal material widely used in fields such as automobiles, home appliances, and building materials. The hot dip galvanized steel sheet is manufactured by performing a hot dip galvanizing process after heat treatment in an annealing furnace having a direct fire heating type direct fire zone and a reduction zone.
特許文献１には、Ｓｉ濃度及びＭｎ濃度が高い鋼板を加熱焼鈍したのち溶融亜鉛めっき処理を施して高強度溶融亜鉛めっき鋼板を製造する際に、めっき性不良の発生を防止することを目的として、還元帯内の還元性ガスの流れの方向が鋼板の進行方向と逆方向になるような流路を構成し、竪型還元帯では、少なくとも入側領域において雰囲気ガスを鋼板進行方向と逆方向に流す方法が開示されている。 Patent Document 1 aims to prevent the occurrence of poor plating properties when a high-strength hot-dip galvanized steel sheet is manufactured by heat-annealing a steel sheet having a high Si concentration and Mn concentration and then performing hot-dip galvanizing treatment. The flow path of the reducing gas in the reduction zone is configured to be opposite to the traveling direction of the steel plate, and in the vertical reduction zone, the atmosphere gas is directed in the direction opposite to the steel plate traveling direction at least in the inlet side region. A method of flowing in is disclosed.
特許文献２には、直火帯と還元帯の連接部またはその近傍から炉内のガスを排気することで、直火加熱帯で形成された酸化皮膜が続く還元帯で十分に還元され、溶融亜鉛めっき時のめっき不良の発生を防止する方法が開示されている。 In Patent Document 2, the gas in the furnace is exhausted from or near the joint between the direct fire zone and the reduction zone, so that the oxide film formed in the direct fire heating zone is sufficiently reduced and melted. A method for preventing the occurrence of defective plating during zinc plating is disclosed.
しかしながら、上記従来技術では、めっき性は改善されるものの、鋼板の伸びが不足する問題がある。 However, although the above-described prior art improves the plating property, there is a problem that the elongation of the steel sheet is insufficient.
本発明は、かかる事情に鑑み、めっき性及び伸び特性に優れた溶融亜鉛めっき鋼板を製造する方法を提供することを目的とする。 In view of such circumstances, an object of the present invention is to provide a method for producing a hot dip galvanized steel sheet having excellent plating properties and elongation characteristics.
上記課題を解決するための本発明の要旨構成は次のとおりである。 The gist configuration of the present invention for solving the above-described problems is as follows.
質量％で、C：0.04％以下、Si：0.05％以下、Mn：0.05〜0.5％、S：0.01％以下、P：0.05％以下、sol.Al：0.08％以下、N：0.01％以下を含有する成分組成を有する鋼板に対して、直火加熱方式の直火帯で加熱し、さらに、還元帯において還元雰囲気中で表面の還元と焼鈍を行ったのち、溶融亜鉛めっき浴に浸漬させて亜鉛めっき処理を行う溶融亜鉛めっき鋼板の製造方法において、前記直火帯を入側から第１〜第４の４つのゾーンに分け、各々のゾーンの空気比を以下のようにすることを特徴とする溶融亜鉛めっき鋼板の製造方法。
第１ゾーンの空気比：0.70〜0.90
第２ゾーンの空気比：0.70〜0.90
第３ゾーンの空気比：0.70〜0.90
第４ゾーンの空気比：0.70〜0.85
なお、本明細書において、鋼の成分を示す％は、すべて質量％である。
In mass%, C: 0.04% or less, Si: 0.05% or less, Mn: 0.05 to 0.5%, S: 0.01% or less, P: 0.05% or less, sol.Al: 0.08% or less, N: 0.01% or less The steel sheet having the component composition to be heated is heated in a direct-fired heating zone, and after reducing and annealing the surface in a reducing atmosphere in the reducing zone, it is immersed in a hot dip galvanizing bath and zinc In the manufacturing method of the hot dip galvanized steel sheet that performs the plating treatment, the direct fire zone is divided into first to fourth zones from the entrance side, and the air ratio of each zone is as follows: Manufacturing method of hot dip galvanized steel sheet.
Air ratio of the first zone: 0.70-0.90
Second zone air ratio: 0.70-0.90
Air ratio in the third zone: 0.70-0.90
In addition, in this specification,% which shows the component of steel is mass% altogether.
本発明によれば、めっき性及び伸び特性に優れた溶融亜鉛めっき鋼板が得られる。めっき性及び伸び特性に優れるので、自動車用途での高加工プレス材に適用することが可能となる。 According to the present invention, a hot-dip galvanized steel sheet having excellent plating properties and elongation characteristics can be obtained. Since it has excellent plating properties and elongation properties, it can be applied to high-working press materials for automotive applications.
以下、本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described.
従来の直火加熱方式の直火帯と還元帯を備える溶融亜鉛めっき設備（焼鈍炉）での焼鈍の考え方は、以下の通りである。スケールがあるとめっき性は低下することは知られているため、前段の直火帯のゾーンで鋼板表面を酸化させ、後段の還元帯のゾーンの不完全燃焼（未燃焼）領域でスケールの最表面のみを還元して、めっき性を改善するというものである。このように、従来は、前段の直火帯のゾーンは、完全燃焼である。しかしながら、直火加熱方式の直火帯と還元帯を備える溶融亜鉛めっきラインで、種々製造条件を変えて機械的性質を検討する実験を行い、伸び特性が劣る原因を調査したところ、直火帯のゾーンで完全燃焼し鋼板表面を酸化させることで、粒界酸化が起こり、酸化したところが引張試験時の破壊の起点となり、伸び特性が劣ることがわかった。 The concept of annealing in a hot dip galvanizing facility (annealing furnace) having a direct flame zone and a reduction zone of a conventional direct fire heating method is as follows. It is known that if there is a scale, the plateability deteriorates. Therefore, the surface of the steel plate is oxidized in the zone of the direct flame zone in the preceding stage, and the scale reaches the maximum in the incomplete combustion (unburned) region in the zone of the downstream zone. Only the surface is reduced to improve the plating property. Thus, conventionally, the zone in the preceding stage of the direct flame is complete combustion. However, in a hot dip galvanizing line equipped with a direct flame heating type direct flame zone and a reduction zone, experiments were conducted to investigate the mechanical properties under various production conditions and the cause of poor elongation characteristics was investigated. It was found that when the steel sheet surface was completely burned in this zone and the steel plate surface was oxidized, grain boundary oxidation occurred, and the oxidized portion became the starting point of fracture during the tensile test, resulting in poor elongation characteristics.
上記結果を受けて、本発明では、前段の直火帯のゾーンでは完全燃焼せず、不完全燃焼(未燃焼を含む)とし、鋼板表面が酸化するのを防止することとする。鋼板表面が酸化するのを防止することで引張試験の破壊の起点となる粒界酸化を防止する。その結果、伸び特性の低下を抑えることができる。さらに、直火帯のゾーンで不完全燃焼とした場合でも、めっき性が劣化しないように、本発明では、成分組成の範囲を規定することとする。このように、めっき性が劣化しない成分組成とした上で、直火帯のゾーンで不完全燃焼とすることで、めっき性及び伸び特性に優れた溶融亜鉛めっき鋼板が得られることになる。 In view of the above results, in the present invention, it is assumed that incomplete zone combustion (including unburned) is not performed in the zone of the direct flame zone in the previous stage, and oxidation of the steel sheet surface is prevented. By preventing oxidation of the steel sheet surface, grain boundary oxidation, which is the starting point of fracture in the tensile test, is prevented. As a result, a decrease in elongation characteristics can be suppressed. Further, in the present invention, the range of the component composition is defined so that the plating property does not deteriorate even when incomplete combustion is performed in the zone of the direct fire zone. As described above, a hot-dip galvanized steel sheet having excellent plating properties and elongation characteristics can be obtained by setting the component composition so that the plating properties do not deteriorate and performing incomplete combustion in the zone of the direct flame zone.
図1は、直火加熱方式の直火帯と還元帯を備える焼鈍炉で熱処理をした後、亜鉛めっきを行う溶融亜鉛めっき鋼板の製造設備の要部構成例を示す概略側面図である。 FIG. 1 is a schematic side view showing a configuration example of a main part of a manufacturing facility for a hot-dip galvanized steel sheet that is subjected to galvanization after heat treatment in an annealing furnace including a direct-fired heating zone and a reduction zone.
図1において、１は鋼板、２は直火加熱方式の直火帯（以下、単に「直火加熱帯」とも記載する。）、３は還元帯（竪型還元帯）、４は冷却帯、５はスナウト、６は溶融めっき槽、７はガスワイピング装置である。直火加熱帯２と竪型還元帯３が連接されている。溶融めっき槽６にはめっき金属である溶融亜鉛が保持されている。
In FIG. 1, 1 is a steel plate, 2 is a direct-fired heating zone (hereinafter also simply referred to as “direct-fired heating zone”), 3 is a reduction zone (a vertical reduction zone), 4 is a cooling zone, 5 is a snout, 6 is a hot dipping bath, and 7 is a gas wiping device. The direct fire heating zone 2 and the
直火加熱帯は、（Ａ）加熱速度が速い、（Ｂ）鋼板温度が低くても、燃焼ガス温度が高く、燃焼ガス中のラジカルが鋼板に達して鋼板との反応に関与するので反応速度が速く、空気比が高ければ酸化膜が早く形成され、空気比が低く還元が早く行われる直火還元帯を設ければ還元も行える、などの特徴がある。 The direct-fired heating zone is (A) fast heating rate, (B) even if the steel plate temperature is low, the combustion gas temperature is high, and the radicals in the combustion gas reach the steel plate and participate in the reaction with the steel plate, so the reaction rate However, there is a feature that if the air ratio is high and the air ratio is high, the oxide film is formed earlier, and if a direct flame reduction zone is provided in which the air ratio is low and reduction is performed quickly, reduction can be performed.
また、直火加熱帯は複数の加熱ゾーンに分割され、各々の加熱ゾーンには直火加熱バーナ１０３が配置され、燃料供給系統１０１から燃料ガス、空気供給系統１０２から燃焼用空気が供給される。各加熱ゾーンの燃料ガス流量、燃焼用空気流量及びその流量比は独立に制御可能である。
The direct fire heating zone is divided into a plurality of heating zones, and a direct
還元帯３は、炉内の上部及び下部に所定の高さをもって配設された炉内ロールが所定間隔で複数設けられている。還元帯３内を走行する鋼板１は、上部炉内ロールと下部炉内ロールで支持されて鉛直方向に走行する複数の縦パスが存在し、縦パス間に鋼板に面してラジアントチューブバーナ８が配設されている。
The
通常は、図示されていない鋼板送り出し装置から送り出された鋼板は、直火加熱帯２で燃料ガスを用いて直火加熱され、鋼板表面の圧延油が除去されるとともに、鋼板表面にＦｅ酸化物（酸化皮膜）を形成する。直火加熱帯の前段は、空気比を高くして鋼板を加熱し、鋼板表面に酸化膜を形成し、次いで直火加熱帯の後段（以下、直火還元帯とも記載する。）は、前段より空気比を低くして前段で形成した酸化膜を還元する。直火還元帯だけでは還元が不十分であるので、次の還元帯でさらに酸化膜の還元が行われる。 Normally, a steel sheet fed from a steel sheet feeding device (not shown) is directly heated by using a fuel gas in the direct fire heating zone 2 to remove rolling oil on the surface of the steel sheet and to remove Fe oxide on the surface of the steel sheet. (Oxide film) is formed. The front stage of the direct fire heating zone heats the steel sheet by increasing the air ratio, forms an oxide film on the surface of the steel sheet, and then the latter stage of the direct fire heating zone (hereinafter also referred to as the direct fire reduction zone). The oxide film formed in the previous stage is reduced by lowering the air ratio. Since the reduction is insufficient only with the direct reduction zone, the oxide film is further reduced in the next reduction zone.
次に鋼板は還元帯３に通板される。通常、還元性ガスとして、水素濃度が数％〜数十％（ｖｏｌ％）の水素と窒素の混合ガスがガス供給配管１０４から冷却帯４及び還元帯３の複数箇所に供給され、供給されたガスは還元帯３入側に流れ、直火加熱帯２と還元帯３の連接部９を通って直火加熱帯２に流出する。このガスによって、還元帯３の雰囲気は還元性に保持される。鋼板は、還元帯３を通板される間に、高温のラジアントチューブ８によって所定温度で所定時間に加熱焼鈍され、同時に鋼板表面の酸化皮膜が還元される。還元の進行は、炉内の温度パターンや通板速度、炉内ガスの水素濃度と供給量で決まる。還元帯で鋼板の還元が完了するように適宜の条件が設定される。還元帯３に供給された還元性ガスは還元帯３と直火加熱帯２の連接部９を通って直火加熱帯２へ流れる。
Next, the steel plate is passed through the
酸化皮膜が還元された鋼板１は、冷却帯４で溶融めっき槽６に浸漬させるのに適した鋼板温度に調整されたのち溶融めっき槽６に浸漬めっきされ、溶融めっき浴槽６から引き上げられてガスワイピング装置７で所要のめっき付着量に調整され、さらにスパングル調整あるいは合金化処理が施された後冷却され、あるいは前記処理を施すことなく冷却され、所要の溶融亜鉛めっき鋼板となる。
The steel plate 1 with the reduced oxide film is adjusted to a steel plate temperature suitable for being immersed in the hot dipping
ここで、本発明においては、直火加熱帯のゾーンにおいて、空気比を低く制御して、鋼板表面を不完全燃焼とし、鋼板表面が酸化するのを防止する。その結果、伸び特性の向上が図られる。通常は、直火加熱帯の前段は、空気比を高くして鋼板を加熱し、鋼板表面に酸化膜を形成し、次いで直火加熱帯の後段（以下、直火還元帯とも記載する。）は、前段より空気比を低くして前段で形成した酸化膜を還元する。これに対して、本発明では、直火加熱帯を入側（鋼板送り出し装置側）から第１〜第４の４つのゾーンに分け、各々のゾーンの空気比を以下のようにする。
第１ゾーンの空気比：0.70〜0.90
第２ゾーンの空気比：0.70〜0.90
第３ゾーンの空気比：0.70〜0.90
第４ゾーンの空気比：0.70〜0.85
いわゆる直火加熱帯の前後である第１、第2ゾーンを含む第１〜３ゾーンの空気比が0.90、第４ゾーンの空気比が0.85を超えると、伸び特性が低下する。一方、第１〜４ゾーンの空気比が0.70未満では、原単位が極端に低下して生産コスト高となり、また、アフターバーニングによる設備トラブルの原因となる場合がある。
Here, in the present invention, in the zone of the direct-fired heating zone, the air ratio is controlled to be low so that the steel sheet surface is incompletely burned and the steel sheet surface is prevented from being oxidized. As a result, the elongation characteristics can be improved. Usually, the front stage of the direct fire heating zone heats the steel sheet by increasing the air ratio, forms an oxide film on the surface of the steel sheet, and then the latter stage of the direct fire heating zone (hereinafter also referred to as the direct fire reduction zone). Reduces the oxide film formed in the previous stage by lowering the air ratio than in the previous stage. On the other hand, in this invention, a direct-fired heating zone is divided into the 1st-4th four zones from an entrance side (steel plate delivery device side), and the air ratio of each zone is made as follows.
Air ratio of the first zone: 0.70-0.90
Second zone air ratio: 0.70-0.90
Air ratio in the third zone: 0.70-0.90
When the air ratio of the first to third zones including the first and second zones before and after the so-called direct fire heating zone exceeds 0.90 and the air ratio of the fourth zone exceeds 0.85, the elongation characteristics are deteriorated. On the other hand, if the air ratio in the first to fourth zones is less than 0.70, the basic unit is extremely reduced, resulting in high production costs, and may cause equipment troubles due to afterburning.
次に本発明の溶融亜鉛めっき鋼板の成分組成について説明する。 Next, the component composition of the hot dip galvanized steel sheet of the present invention will be described.
Ｃ：0.04％以下
Ｃは、過剰に含有すると伸び特性の低下をもたらすため、0.04％以下とする。好ましくは0.03％以下である。
C: 0.04% or less C is contained in an amount of 0.04% or less because excessive elongation causes a decrease in elongation characteristics. Preferably it is 0.03% or less.
Si：0.05％以下
Siは、めっき性に悪影響を及ぼし、鋼板表面に濃化して不めっきの原因となるため、0.05％以下とする。
Si: 0.05% or less
Si has an adverse effect on the plating properties and concentrates on the surface of the steel sheet to cause non-plating, so 0.05% or less.
Mn：0.05％以上0.5％以下
Mnは、Ｓによる熱間割れを抑制する働きがあるので0.05％以上とする。一方、過剰に含有すると、耐食性を低下させるため、0.5％以下とする。
Mn: 0.05% or more and 0.5% or less
Mn has a function of suppressing hot cracking due to S, so is 0.05% or more. On the other hand, if excessively contained, the corrosion resistance is lowered, so the content is made 0.5% or less.
Ｓ：0.01％以下
Ｓは、Mnと結合してMnＳを形成し、耐食性を低下させるため、0.01％以下とする。
S: 0.01% or less S is combined with Mn to form MnS and lowers the corrosion resistance, so 0.01% or less.
Ｐ：0.05％以下
Ｐは、伸び特性の低下をもたらすため、低いほど望ましいが、0.05％以下であれば伸び特性を著しく低下させることはない。このため、0.05％以下とする。
P: 0.05% or less P is preferable as it is low because it causes a decrease in elongation characteristics. However, if it is 0.05% or less, the elongation characteristics are not significantly decreased. For this reason, it is 0.05% or less.
Sol.Al： 0.08％以下
Alは、脱酸に用いられる元素であるが、過剰に含有されると伸び特性の低下をもたらすため、Sol.Al で0.08％以下とする。なお、Alは固溶Ｎを固定して耐常温時効性を向上させる作用効果もあるため、鋼板中のsol.Alは0.001%以上とすることが好ましい。
Sol.Al: 0.08% or less
Al is an element used for deoxidation, but if it is excessively contained, the elongation characteristics are deteriorated. Therefore, the content of Sol.Al is 0.08% or less. In addition, since Al has the effect of fixing solid solution N and improving the normal temperature aging resistance, sol.Al in the steel sheet is preferably 0.001% or more.
Ｎ： 0.01％以下
Ｎは、多量に含有すると、伸びが低下するとともに、耐常温時効性が低下するため、0.01％以下とする。Ｎは低いほど好ましいが、0.0001％未満とするには生産コストが著しく大きくなるため、下限は0.0001％程度とすることが好ましい。
N: 0.01% or less N is contained in an amount of 0.01% or less because, if contained in a large amount, elongation decreases and room temperature aging resistance decreases. N is preferably as low as possible. However, if it is less than 0.0001%, the production cost becomes remarkably high, so the lower limit is preferably about 0.0001%.
残部は、Feおよび不可避的不純物であることが好ましい。不可避的不純物としては、Ni、Cu、Cr、O（酸素）などがあるが、例えば、Ni、Cu、Crは各々0.05％程度以下、O（酸素）は、0.02％程度以下とすることが好ましい。
以上、必須成分について説明したが、本発明では、その他にも以下に述べる元素を適宜含有させることができる。
The balance is preferably Fe and inevitable impurities. Inevitable impurities include Ni, Cu, Cr, and O (oxygen). For example, Ni, Cu, and Cr are each preferably about 0.05% or less, and O (oxygen) is preferably about 0.02% or less. .
Although the essential components have been described above, in the present invention, other elements described below can be appropriately contained.
B：0.0030％以下（好適元素）
Bは、組織を微細化し、幅方向の組織を均一化するのに有効元素であり、この効果を得るためには、0.0005％以上含有させることが好ましい。一方、0.0030％を超えて含有すると再結晶温度が高くなり、伸びが低下しやすくなるので、上限は0.0030％とすることが好ましい。より好ましくは0.0020％以下である。
B: 0.0030% or less (preferred element)
B is an effective element for refining the structure and making the structure in the width direction uniform. In order to obtain this effect, B is preferably contained in an amount of 0.0005% or more. On the other hand, if the content exceeds 0.0030%, the recrystallization temperature becomes high and the elongation tends to decrease, so the upper limit is preferably made 0.0030%. More preferably, it is 0.0020% or less.
実施例１
表1に示す化学組成からなる1.2ｍｍの冷延鋼板を、表2に示す条件にて直火加熱方式の直火帯で加熱し、さらに、還元帯において還元雰囲気中で表面の還元と焼鈍（焼鈍温度：760℃）を行ったのち、溶融亜鉛めっき浴に浸漬させて亜鉛めっき処理を行い、溶融亜鉛めっき鋼板を製造した。なお、炉の雰囲気（還元条件）は、水素ガス：5vol％、窒素ガス：95 vol％であり、露点（Ｄ.Ｐ）：−30℃である。めっき処理は両面に施し、片面あたりの目付量は45g/m2であった。また、直火加熱方式の直火帯を有する焼鈍炉の代わりに、加熱手段の全てをラジアントチューブとした、オールラジアントチューブ炉を用いて酸化を抑制した状態で熱処理および焼鈍を行い、その他は本発明例と同様の条件にて行った参考例も準備した。なお、参考例および直火帯での加熱時の空気比が本発明範囲外の比較例については、本発明例１と同様の冷延鋼板を用いた。
以上により得られた溶融亜鉛めっき鋼板に対して、伸び特性およびめっき性を評価した。各測定方法および評価基準は以下の通りである。
Example 1
A 1.2 mm cold-rolled steel sheet having the chemical composition shown in Table 1 is heated in a direct-fired heating zone under the conditions shown in Table 2, and further reduction and annealing of the surface in a reducing atmosphere in the reducing zone ( (Annealing temperature: 760 ° C.) was immersed in a hot dip galvanizing bath and galvanized to produce a hot dip galvanized steel sheet. The furnace atmosphere (reduction conditions) is hydrogen gas: 5 vol%, nitrogen gas: 95 vol%, and dew point (DP): −30 ° C. The plating treatment was performed on both sides, and the basis weight per side was 45 g / m 2 . Also, instead of an annealing furnace having a direct flame heating type direct heating zone, all the heating means are radiant tubes, and all radiant tube furnaces are used for heat treatment and annealing while suppressing oxidation, and the others are A reference example carried out under the same conditions as the invention example was also prepared. In addition, the cold-rolled steel plate similar to Example 1 of the present invention was used for the reference example and the comparative example in which the air ratio during heating in the open flame zone was outside the range of the present invention.
With respect to the hot-dip galvanized steel sheet obtained as described above, the elongation characteristics and the plating properties were evaluated. Each measuring method and evaluation criteria are as follows.
伸び特性
JIS5号試験片とし、JIS Z 2241に準拠して引張試験を行った。引張試験は、幅方向ミドル1箇所から測定した。
Elongation characteristics
A tensile test was conducted in accordance with JIS Z 2241 using JIS No. 5 test pieces. The tensile test was measured from one position in the middle in the width direction.
めっき性
めっき性は、パウダリング試験を行い評価した。
パウダリング試験は、まず、試験片幅方向3カ所（両側および中央部）の表、裏面について９０°曲げを行う。折り曲げ後、曲げ部内面にセロテープ（登録商標）を強く貼り付け、次いで、引き剥がす。セロテープ（登録商標）に付着しためっき皮膜の量を目視で観察し、パウダリング性を評価した。パウンダリング性の結果は、本発明例、比較例とも、皮膜剥離に大きな差はなく、パウダリング性は良好であった。
Plating ability Plating ability was evaluated by conducting a powdering test.
In the powdering test, first, the front and back surfaces of three places (both sides and center portion) in the width direction of the test piece are bent by 90 °. After bending, a cello tape (registered trademark) is firmly attached to the inner surface of the bent portion, and then peeled off. The amount of the plating film adhered to the cello tape (registered trademark) was visually observed to evaluate the powdering property. As a result of the powdering property, there was no significant difference in film peeling between the inventive example and the comparative example, and the powdering property was good.
以上により得られた結果を図２に示す。 The results obtained as described above are shown in FIG.
図２より、本発明例では、直火帯での空気比を制御することで、比較例に比べて、伸び特性が約２％改善され、オールラジアントチューブ炉を用いた参考例と同等の伸び特性を得ることができた。
また、上記したように、パウンダリング試験の結果も良好でめっき性にも優れていた。
一方、比較例では伸び特性が劣っている。
From FIG. 2, in the present invention example, by controlling the air ratio in the direct flame zone, the elongation characteristics are improved by about 2% compared to the comparative example, and the elongation equivalent to that of the reference example using the all radiant tube furnace is obtained. The characteristics could be obtained.
In addition, as described above, the result of the powdering test was good and the plating property was also excellent.
On the other hand, the elongation characteristic is inferior in the comparative example.
１ 鋼板
２ 直火加熱方式の直火帯（直火加熱帯）
３ 竪型還元帯（還元帯）
４ 冷却帯
５ スナウト
６ 溶融めっき槽
７ ガスワイピング装置
８ ラジアントチューブバーナ
９ 直火加熱帯と還元帯の連接部
１０１ 燃料供給系統
１０２ 空気供給系統
１０３ 直火加熱バーナ
１０４ ガス供給配管
1 Steel plate 2 Direct flame heating type (direct flame heating zone)
3 Vertical type reduction zone (reduction zone)
Claims (3)
直火加熱方式の直火帯で加熱し、さらに、還元帯において還元雰囲気中で表面の還元と焼鈍を行ったのち、溶融亜鉛めっき浴に浸漬させて亜鉛めっき処理を行う溶融亜鉛めっき鋼板の製造方法において、
前記直火帯を入側から第１〜第４の４つのゾーンに分け、各々のゾーンの空気比を以下のようにすることを特徴とする溶融亜鉛めっき鋼板の製造方法。
第１ゾーンの空気比：０．７０〜０．９０
第２ゾーンの空気比：０．７０〜０．９０
第３ゾーンの空気比：０．７０〜０．９０
第４ゾーンの空気比：０．７０〜０．８５ In mass%, C: 0.04% or less, Si: 0.05% or less, Mn: 0.05 to 0.5%, S: 0.01% or less, P: 0.05% or less, sol. For steel sheets containing Al: 0.08% or less, N: 0.01% or less, with the balance being composed of Fe and inevitable impurities ,
Manufacture of hot dip galvanized steel sheet that is heated in a direct fire zone of the direct fire heating system, and further reduced and annealed in a reducing atmosphere in the reduction zone, and then immersed in a hot dip galvanizing bath and galvanized. In the method
A method for producing a hot-dip galvanized steel sheet, wherein the direct fire zone is divided into first to fourth zones from the entrance side, and the air ratio of each zone is as follows.
First zone air ratio: 0.70-0.90
Second zone air ratio: 0.70-0.90
Third zone air ratio: 0.70-0.90
Air ratio of the fourth zone: 0.70 to 0.85
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