JP5354156B2 - Method for producing galvannealed steel sheet - Google Patents
Method for producing galvannealed steel sheet Download PDFInfo
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- JP5354156B2 JP5354156B2 JP2008225611A JP2008225611A JP5354156B2 JP 5354156 B2 JP5354156 B2 JP 5354156B2 JP 2008225611 A JP2008225611 A JP 2008225611A JP 2008225611 A JP2008225611 A JP 2008225611A JP 5354156 B2 JP5354156 B2 JP 5354156B2
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 76
- 239000010959 steel Substances 0.000 title claims abstract description 76
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 13
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 25
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 25
- 239000001301 oxygen Substances 0.000 claims abstract description 25
- 230000003647 oxidation Effects 0.000 claims abstract description 23
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 23
- 238000000137 annealing Methods 0.000 claims abstract description 16
- 230000009467 reduction Effects 0.000 claims abstract description 14
- 238000005246 galvanizing Methods 0.000 claims abstract description 7
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 17
- 239000008397 galvanized steel Substances 0.000 claims description 17
- 238000005275 alloying Methods 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 11
- 230000008569 process Effects 0.000 claims description 7
- 239000000463 material Substances 0.000 claims description 6
- 238000007747 plating Methods 0.000 abstract description 39
- 239000011248 coating agent Substances 0.000 abstract description 7
- 238000000576 coating method Methods 0.000 abstract description 7
- 230000001105 regulatory effect Effects 0.000 abstract description 2
- 238000005244 galvannealing Methods 0.000 abstract 2
- 238000010438 heat treatment Methods 0.000 description 20
- 239000012298 atmosphere Substances 0.000 description 10
- 230000007547 defect Effects 0.000 description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 230000002829 reductive effect Effects 0.000 description 5
- 238000005554 pickling Methods 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 229910000905 alloy phase Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000005238 degreasing Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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Abstract
Description
本発明は、めっき表面の均一性に優れる合金化溶融亜鉛めっき鋼板の製造方法に関する。 The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet that is excellent in plating surface uniformity.
自動車、家電、建材等の分野において素材鋼板に防錆性を付与した表面処理鋼板、中でも安価に製造できかつ防錆性に優れた合金化溶融亜鉛めっき鋼板が使用されている。 In the fields of automobiles, home appliances, building materials, etc., surface-treated steel sheets imparted with rust prevention properties to raw steel sheets, especially alloyed hot-dip galvanized steel sheets that can be manufactured at low cost and have excellent rust prevention properties are used.
一般的に、合金化溶融亜鉛めっき鋼板は、スラブを熱延、冷延あるいはさらに熱処理した薄鋼板を母材鋼板として用い、連続式溶融亜鉛めっきライン等において、母材鋼板を前処理工程にて脱脂および／または酸洗して洗浄するか、あるいは前処理工程を省略して予熱炉内で母材鋼板表面の油分を燃焼除去した後、非酸化性雰囲気中あるいは還元性雰囲気中で６００〜９００℃程度の温度域に加熱して再結晶焼鈍し、その後、非酸化性雰囲気中あるいは還元性雰囲気中で鋼板をめっきに適した温度まで冷却して大気に触れることなく０．１〜０．２質量％程度のＡｌを添加した溶融亜鉛浴に浸漬して溶融亜鉛めっきし、引き続いて合金化炉内でめっき層を合金化処理して製造する。 In general, alloyed hot-dip galvanized steel sheets use thin steel sheets that are hot-rolled, cold-rolled or further heat-treated as slabs as base material steel sheets. After degreasing and / or pickling and washing, or by omitting the pretreatment process and burning off the oil on the surface of the base steel plate in the preheating furnace, it is 600 to 900 in a non-oxidizing atmosphere or a reducing atmosphere. Recrystallization annealing is performed by heating to a temperature range of about 0 ° C., and then the steel sheet is cooled to a temperature suitable for plating in a non-oxidizing atmosphere or a reducing atmosphere without touching the atmosphere. It is manufactured by dipping in a hot dip galvanizing bath to which about 1% by mass of Al is added and hot dip galvanizing, and then alloying the plating layer in an alloying furnace.
近年、合金化溶融亜鉛めっき鋼板は自動車外板に多用されるようになってきた。この用途では、合金化溶融亜鉛めっき鋼板は塗装して使用され、塗装後に外観ムラが発生しない均一なめっき表面が求められている。しかしながら、溶融亜鉛めっき後にめっき層の合金化処理を行う合金化溶融亜鉛めっき鋼板では、母材鋼板の外観が均一であっても、鋼板表面の僅かな化学組成の違いによって、溶融亜鉛めっきの際のめっき付着性、合金化処理の際の合金相の成長が異なるため、合金化処理後のめっき表面が不均一になり、めっき外観が劣るだけでなく、塗装後に外観ムラになる。 In recent years, alloyed hot-dip galvanized steel sheets have been widely used for automobile outer panels. In this application, the alloyed hot-dip galvanized steel sheet is used after being coated, and a uniform plated surface that does not cause uneven appearance after coating is required. However, in the galvannealed steel sheet in which the plating layer is alloyed after hot dip galvanization, even if the appearance of the base steel sheet is uniform, there is a slight difference in the chemical composition of the steel sheet surface. Since the plating adhesion and the growth of the alloy phase during the alloying process are different, the plated surface after the alloying process is not uniform, and the plating appearance is not only inferior, but also the appearance is uneven after coating.
めっき表面が不均一になる要因の一つに、めっき前鋼板表面のスケール（鉄を主体とする酸化物）残存がある。めっき前鋼板表面にスケールが残存すると、スケールがあるところとスケールが無いところでめっき付着性が異なり、また、合金化処理の際に素地鋼との反応性が異なることから、合金化処理後の皮膜組成、皮膜付着量が異なり、めっき表面が不均一になる。 One of the factors that make the plating surface uneven is the remaining scale (oxide mainly composed of iron) on the surface of the steel plate before plating. If scale remains on the surface of the steel plate before plating, the plating adhesion will be different between where the scale is present and where there is no scale, and the reactivity with the base steel will be different during the alloying treatment. The composition and the amount of coating are different and the plating surface becomes non-uniform.
めっき表面外観の改善のための技術として、例えば、特許文献１に、めっきに先立ち、鋼板表層を０．１μｍ以上除去することが記載されている。このような技術によっても、ここで問題としているスケール残存による欠陥も改善することが期待できる。しかしながら、鋼板表層を均一除去することは容易ではなく、除去のため、例えば砥石を使用すれば砥石でできた傷により、外観の均一性が損なわれるといった弊害を起こすことに繋がる。
本発明は、かかる事情に鑑みてなされたものであって、めっき前鋼板表面のスケール残存に起因して合金化処理後のめっき表面が不均一になるのを防止し、良好なめっき外観を有し、塗装後も外観ムラが発生しない合金化溶融亜鉛めっき鋼板の製造方法を提供することを課題とする。 The present invention has been made in view of such circumstances, and prevents the plating surface after alloying from becoming non-uniform due to the remaining scale on the surface of the steel sheet before plating, and has a good plating appearance. It is another object of the present invention to provide a method for producing an alloyed hot-dip galvanized steel sheet that does not cause uneven appearance after coating.
上記課題を解決する本発明の手段は、母材鋼板を還元焼鈍した後、溶融亜鉛めっきし、さらに合金化処理を行う合金化溶融亜鉛めっき鋼板の製造方法において、
母材鋼板の表面酸素量Ｙを１５０ｍｇ／ｍ２以下に規定し、この母材鋼板を加熱酸化し酸化後の母材鋼板表面の酸素量Ｘが２５〜５００ｍｇ／ｍ２の範囲内で、かつＸとＹが式（１）を満足するようする酸化処理を行い、その後還元焼鈍処理することを特徴とする合金化溶融亜鉛めっき鋼板の製造方法である。
Ｙ×２．５≦Ｘ ・・・（１）
The means of the present invention for solving the above-mentioned problems is a method for producing an alloyed hot-dip galvanized steel sheet in which a base steel sheet is subjected to reduction annealing, followed by hot-dip galvanizing and further alloying treatment.
The surface oxygen amount Y of the base steel plate is specified to be 150 mg / m 2 or less, the base material steel plate is heated and oxidized, and the oxygen amount X on the base steel plate surface after oxidation is in the range of 25 to 500 mg / m 2 , and An oxidation galvanized steel sheet manufacturing method characterized in that an oxidation treatment is performed so that X and Y satisfy formula (1), followed by a reduction annealing treatment.
Y × 2.5 ≦ X (1)
本発明によれば、めっき前鋼板表面のスケール残存に起因して合金化処理後にめっき表面が不均一になるのを防止し、良好なめっき外観を有する合金化溶融亜鉛めっき鋼板を製造できる。本発明法で製造された合金化溶融亜鉛めっき鋼板は、塗装後も外観ムラが発生しない。 ADVANTAGE OF THE INVENTION According to this invention, it can prevent that the plating surface becomes non-uniform | heterogenous after alloying processing resulting from the scale remaining on the steel plate surface before plating, and can manufacture the galvannealed steel plate which has a favorable plating external appearance. The alloyed hot-dip galvanized steel sheet produced by the method of the present invention does not cause uneven appearance even after coating.
本発明者らは、めっき前鋼板表面に存在するスケール（鉄を主体とする酸化物）に起因する合金化溶融亜鉛めっき鋼板のめっき表面の不均一の改善、解消について検討を行った。その結果、めっき前の還元焼鈍に先立って、鋼板表面を酸化させ、その後、酸化物を還元することにより、合金化処理後のめっき表面の不均一が改善され、良好なめっき外観を有する合金化溶融亜鉛めっき鋼板を製造できるようになることを見出した。本発明はこの知見に基づくものである。 The present inventors examined improvement and elimination of non-uniformity of the plating surface of the galvannealed steel sheet caused by the scale (oxide mainly composed of iron) existing on the surface of the steel sheet before plating. As a result, prior to the reduction annealing before plating, the surface of the steel sheet is oxidized, and then the oxide is reduced, thereby improving the non-uniformity of the plating surface after the alloying treatment and alloying with a good plating appearance. It has been found that hot-dip galvanized steel sheets can be manufactured. The present invention is based on this finding.
以下、本発明について詳しく説明する。なお、本発明では、鋼板表面のスケール量（鉄を主体とする酸化物の量）を、鋼板表面の酸素量で規定する。 The present invention will be described in detail below. In the present invention, the amount of scale on the surface of the steel sheet (the amount of oxide mainly composed of iron) is defined by the amount of oxygen on the surface of the steel sheet.
本発明では、母材鋼板を還元焼鈍する前に、加熱炉で母材鋼板を加熱して酸化する酸化処理を行う。酸化処理を行った後母材鋼板を還元焼鈍し、その後溶融亜鉛めっきし、さらに合金化処理を行い、合金化溶融亜鉛めっき鋼板を製造する。 In this invention, before carrying out reduction annealing of a base material steel plate, the oxidation process which heats and oxidizes a base material steel plate with a heating furnace is performed. After performing the oxidation treatment, the base steel plate is subjected to reduction annealing, then hot dip galvanized, and further subjected to alloying treatment to produce an alloyed hot dip galvanized steel plate.
母材鋼板は、表面の酸素量Ｙを１５０ｍｇ／ｍ２以下に規定する。母材鋼板表面の酸化物量が酸素量で評価したときに１５０ｍｇ／ｍ２超になると、加熱炉で鋼板表面を酸化させた後還元しても、もともとの母材鋼板表面のスケールによる表面の不均一は解消されず、スケールが多く残存した領域が還元後も残存し、合金化処理後にスケールに起因するめっき表面の不均一が発生するためである。 The base steel sheet has a surface oxygen content Y of 150 mg / m 2 or less. If the amount of oxide on the surface of the base steel plate exceeds 150 mg / m 2 when the oxygen content is evaluated, the surface of the base steel plate surface will not be damaged due to the scale of the original base steel plate surface even if the steel plate surface is oxidized and then reduced. This is because the uniformity is not eliminated, and a region where a large amount of scale remains is left even after reduction, and unevenness of the plating surface due to the scale occurs after the alloying treatment.
母材鋼板表面の酸素量Ｙを１５０ｍｇ／ｍ２以下にすることは、熱延によるスケールの噛み込みを抑制するため、熱延時のデスケーリングの強化を行うことにより、また、熱延後行う酸洗工程における酸洗時間の延長、酸洗温度を上げることなど、酸洗条件の適正化により、達成される。 Setting the amount of oxygen Y on the surface of the base steel sheet to 150 mg / m 2 or less is to suppress the biting of the scale due to hot rolling, and by strengthening descaling during hot rolling, This is achieved by optimizing the pickling conditions such as extending the pickling time in the washing step and raising the pickling temperature.
表面の酸素量が上記範囲内にある母材鋼板を、加熱炉で酸化する。その際、酸化後の母材鋼板表面の酸素量Ｘが２５〜５００ｍｇ／ｍ２の範囲内で、かつ酸化後の表面の酸素量Ｘと酸化前の表面の酸素量Ｙが式（１）を満足するようにする。
Ｙ×２．５≦Ｘ （１）
A base steel plate having a surface oxygen amount within the above range is oxidized in a heating furnace. At that time, the amount of oxygen X on the surface of the base steel plate after oxidation is in the range of 25 to 500 mg / m 2 , and the amount of oxygen X on the surface after oxidation and the amount of oxygen Y on the surface before oxidation are expressed by the formula (1). Try to be satisfied.
Y × 2.5 ≦ X (1)
加熱炉で酸化後の鋼板表面の酸素量Ｘを２５ｍｇ／ｍ２以上５００ｍｇ／ｍ２以下に規定するのは次の理由による。２５ｍｇ／ｍ２未満では酸素量が少ないため、母材鋼板表面に不均一に存在していたスケールを均一化できず、スケールが多く残存した領域が残存し、還元焼鈍後もスケールが部分的に多く残存してしまうために、めっき付着性が異なり、合金化処理後に均一な外観が得られなくなる。５００ｍｇ／ｍ２超ではスケール量が多過ぎるためその後の還元焼鈍工程においてスケールを十分に還元することができず、スケールが還元されている部分とスケールが残存する部分が共存するようになり、合金化処理後に均一なめっき外観が得られなくなる。 The oxygen amount X on the steel sheet surface after oxidation in the heating furnace is regulated to 25 mg / m 2 or more and 500 mg / m 2 or less for the following reason. If the amount is less than 25 mg / m 2 , the amount of oxygen is small, so the scale that has existed unevenly on the surface of the base steel sheet cannot be made uniform, and there remains a large amount of remaining scale. Since much remains, plating adhesion is different and a uniform appearance cannot be obtained after alloying treatment. If the amount exceeds 500 mg / m 2 , the scale amount is too large, so that the scale cannot be sufficiently reduced in the subsequent reduction annealing process, and the portion where the scale is reduced and the portion where the scale remains coexist. A uniform plating appearance cannot be obtained after the crystallization treatment.
酸化後の母材鋼板表面の酸素量Ｘを、酸化前の母材鋼板表面の酸素量Ｙに対して、Ｙ×２．５≦Ｘを満足するように規定するのは次の理由により。ＸがＹとの差が小さいと母材鋼板表面に不均一に存在していたスケールを均一にできない。母材鋼板表面のスケールの不均一性を解消して酸化処理後にスケールを均一に存在せしめるには、酸化処理後に初期酸化物量の２．５倍以上の酸化物を存在せしめる必要がある。 The oxygen amount X on the base steel plate surface after oxidation is defined to satisfy Y × 2.5 ≦ X with respect to the oxygen amount Y on the base steel plate surface before oxidation for the following reason. If the difference between X and Y is small, the scale that was unevenly present on the surface of the base steel sheet cannot be made uniform. In order to eliminate the non-uniformity of the scale on the surface of the base steel plate and make the scale uniformly exist after the oxidation treatment, it is necessary to make the oxide more than 2.5 times the initial oxide amount after the oxidation treatment.
鋼板を酸化する加熱炉には、鋼板に直接火炎を当てて加熱する直火タイプと、ラジアントチューブを備えた加熱炉内の雰囲気温度を高くして加熱するラジアントタイプの、主に二つのタイプがある。加熱炉内で鋼板表面の酸素量を上記関係を満足するように酸化させることができれば、加熱炉のタイプは問わないが、短時間に効率よく酸化させることを考慮すると、直火タイプの方が好ましい。 There are two main types of furnaces that oxidize steel sheets: a direct fire type that directly heats the steel sheet with a flame, and a radiant type that heats the atmosphere in the furnace equipped with a radiant tube at a high temperature. is there. If the amount of oxygen on the surface of the steel sheet can be oxidized so as to satisfy the above relationship in the heating furnace, the type of the heating furnace will not matter, but considering that it can be oxidized efficiently in a short time, the direct fire type is better preferable.
直火タイプの加熱炉の場合は、加熱炉バーナーに供給する空気と燃料の比である空気比を適宜制御することで鋼板表面の酸素量が上記を満足するように鋼板を酸化させることができる。例えば、空気比を増加させ１に近づけていくことにより酸化量を増加させることができ、さらに１以上にすることで酸化量をさらに増加させることができる。 In the case of a direct-fired type heating furnace, the steel sheet can be oxidized so that the amount of oxygen on the steel sheet surface satisfies the above by appropriately controlling the air ratio that is the ratio of air to fuel supplied to the heating furnace burner. . For example, the amount of oxidation can be increased by increasing the air ratio and approaching 1, and the amount of oxidation can be further increased by increasing the air ratio to 1 or more.
ラジアントタイプの加熱炉の場合、加熱炉内の雰囲気を制御して鋼板表面の酸素量が上記を満足するように鋼板を酸化させる。例えば加熱炉中の酸素濃度を制御し、その濃度を上げることにより酸化量を増加させることができる。 In the case of a radiant type heating furnace, the atmosphere in the heating furnace is controlled to oxidize the steel sheet so that the oxygen content on the steel sheet surface satisfies the above. For example, the amount of oxidation can be increased by controlling the oxygen concentration in the heating furnace and increasing the concentration.
上記のようにして加熱炉で加熱して酸化した鋼板を還元焼鈍する。還元焼鈍は還元雰囲気で行い鋼板表面の酸化物を還元する。還元雰囲気は通常採用される還元雰囲気でよい。また、還元焼鈍では、鋼板を６００〜９００℃の温度域に加熱して再結晶焼鈍する。 The steel sheet heated and oxidized in the heating furnace as described above is subjected to reduction annealing. Reduction annealing is performed in a reducing atmosphere to reduce oxides on the surface of the steel sheet. The reducing atmosphere may be a normally used reducing atmosphere. In reduction annealing, the steel sheet is heated to a temperature range of 600 to 900 ° C. and recrystallized.
還元焼鈍後、冷却、溶融亜鉛めっきを順次施し、その後合金化処理を施すことで、めっき表面が不均一になるのが防止され、めっき外観が良好で、塗装後も外観ムラの発生しない合金化溶融亜鉛めっき鋼板を得ることができる。 After reductive annealing, cooling, hot dip galvanizing, and alloying treatment are performed in order to prevent the plating surface from becoming non-uniform, and the appearance of plating is good. A hot-dip galvanized steel sheet can be obtained.
以下、本発明を、実施例に基づいて具体的に説明する。 Hereinafter, the present invention will be specifically described based on examples.
本発明の効果を確認するために、直火タイプの加熱炉を備える連続式溶融亜鉛めっき設備で以下の製造実験を行った。 In order to confirm the effect of the present invention, the following production experiment was conducted in a continuous hot dip galvanizing facility equipped with a direct-fire type heating furnace.
母材鋼板として、板厚０．７５ｍｍ、板巾１５００ｍｍで、表面スケール量の異なる冷延鋼板を準備した。この母材鋼板を直火タイプの加熱炉で加熱して酸化する酸化処理を行った後、引き続き還元焼鈍（Ｈ２：４ｖｏｌ％−Ｎ２雰囲気中で鋼板を６００℃まで６０秒で昇温し、その後６００〜８５０℃の温度域を１００秒で昇温し、８５０℃で２０秒保持。）、冷却を経てめっき浴中Ａｌ濃度０．１４質量％、浴温４６０℃のＡｌ含有Ｚｎ浴に浸漬し、めっき付着量を片面あたり４５〜５５ｇ／ｍ２に調整し、さらに合金化処理を５２０℃で行い、めっき皮膜中のＦｅ％が９〜１１質量％の範囲になるようにして、合金化溶融亜鉛めっき鋼板を作製した。 Cold rolled steel sheets having a plate thickness of 0.75 mm and a plate width of 1500 mm and having different surface scale amounts were prepared as base steel sheets. The base steel sheet was heated in a direct-fired heating furnace to oxidize, and then the steel sheet was heated to 600 ° C. in 60 seconds in a reduction annealing (H 2 : 4 vol% -N 2 atmosphere). Then, the temperature range of 600 to 850 ° C. is raised in 100 seconds and held at 850 ° C. for 20 seconds.) After cooling, the Al concentration in the plating bath is 0.14% by mass and the bath temperature is 460 ° C. Dipping, adjusting the plating adhesion to 45 to 55 g / m 2 per side, further alloying treatment at 520 ° C., so that the Fe% in the plating film is in the range of 9 to 11% by mass. A galvannealed steel sheet was prepared.
加熱炉バーナーの空気比を変えることで、加熱炉で酸化後の鋼板表面の酸化物量を調整した。例えば、比較例２３は直火炉の空気比を０．９３とした。加熱炉で酸化後の鋼板表面の酸化物量（酸素量）は、加熱炉直後のオンライン赤外線干渉型酸化物計で測定を行った。 By changing the air ratio of the heating furnace burner, the amount of oxide on the steel sheet surface after oxidation in the heating furnace was adjusted. For example, in Comparative Example 23, the air ratio of the direct furnace was set to 0.93. The oxide amount (oxygen amount) on the surface of the steel sheet after oxidation in the heating furnace was measured with an on-line infrared interference type oxide meter immediately after the heating furnace.
作製した合金化溶融亜鉛めっき鋼板のめっき外観を評価した。めっき外観の評価は、板巾×長さ１０００ｍｍのサンプルを採取して目視で以下の基準により評価した。なお、軽微な欠陥とは、周囲との境界が不明瞭で欠陥のサイズがコイル長手方向に５ｍｍ以下のものをいい、これよりも長いもの若しくは周囲との境界が明瞭で目立つものを重度の欠陥とした。
◎：外観良好（欠陥がまったく観察されない）
○：外観良好（軽微な欠陥が片面当り３個以下観察される）
△：外観不良（軽微な欠陥が片面当り３個超観察される）
×：外観不良（重度の欠陥が１個でも観察される）
The plating appearance of the produced galvannealed steel sheet was evaluated. For the evaluation of the plating appearance, a sample having a plate width × length of 1000 mm was collected and visually evaluated according to the following criteria. Minor defects are those in which the boundary with the surrounding is unclear and the size of the defect is 5 mm or less in the longitudinal direction of the coil, and those that are longer than this or that have a clear and conspicuous boundary with the surrounding are severe defects. It was.
A: Appearance is good (no defects are observed)
○: Appearance is good (less than 3 minor defects are observed per side)
Δ: poor appearance (more than 3 minor defects are observed per side)
X: Appearance defect (even one severe defect is observed)
その製造実験の条件と実験材の評価結果をまとめて表１に示す。 Table 1 summarizes the conditions of the manufacturing experiment and the evaluation results of the experimental materials.
表１から明らかなように、加熱炉で酸化前の鋼板表面の酸素量Ｙおよび加熱炉で酸化処理後の鋼板表面の酸素量Ｘが本発明範囲内である発明例では、外観評価が良好で、良好なめっき外観を有する合金化溶融亜鉛めっき鋼板が得られている。めっき外観が良好なものは、塗装後の外観はムラの発生はなく、良好であった。 As apparent from Table 1, in the invention examples in which the oxygen amount Y on the surface of the steel sheet before oxidation in the heating furnace and the oxygen amount X on the surface of the steel sheet after oxidation treatment in the heating furnace are within the scope of the present invention, the appearance evaluation is good. An alloyed hot-dip galvanized steel sheet having a good plating appearance has been obtained. Those with a good plating appearance were good with no unevenness in the appearance after coating.
本発明は、良好なめっき外観を有する合金化溶融亜鉛めっき鋼板を製造する方法として利用できる。本発明法で製造された合金化溶融亜鉛めっき鋼板は、塗装後も外観ムラがないので、自動車外板用途に使用する合金化溶融亜鉛めっき鋼板として利用することができる。 The present invention can be used as a method for producing an alloyed hot-dip galvanized steel sheet having a good plating appearance. Since the alloyed hot-dip galvanized steel sheet produced by the method of the present invention has no uneven appearance even after painting, it can be used as an alloyed hot-dip galvanized steel sheet used for automobile outer plate applications.
Claims (1)
母材鋼板の表面酸素量Ｙを１５０ｍｇ／ｍ２以下に規定し、この母材鋼板を加熱酸化し酸化後の母材鋼板表面の酸素量Ｘが２５〜５００ｍｇ／ｍ２の範囲内で、かつＸとＹが式（１）を満足するようする酸化処理を行い、その後還元焼鈍処理することを特徴とする合金化溶融亜鉛めっき鋼板の製造方法。
Ｙ×２．５≦Ｘ ・・・（１） In the manufacturing method of the alloyed hot-dip galvanized steel sheet, after subjecting the base steel sheet to reduction annealing, galvanizing and further alloying,
The surface oxygen amount Y of the base steel plate is specified to be 150 mg / m 2 or less, the base material steel plate is heated and oxidized, and the oxygen amount X on the base steel plate surface after oxidation is in the range of 25 to 500 mg / m 2 , and The manufacturing method of the galvannealed steel plate characterized by performing the oxidation process which makes X and Y satisfy Formula (1), and performing a reduction annealing process after that.
Y × 2.5 ≦ X (1)
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