JP4411196B2 - High tensile alloyed hot-dip galvanized steel sheet with excellent powdering resistance - Google Patents
High tensile alloyed hot-dip galvanized steel sheet with excellent powdering resistance Download PDFInfo
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- 238000000227 grinding Methods 0.000 title claims description 40
- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 12
- 239000008397 galvanized steel Substances 0.000 title claims description 12
- 238000007747 plating Methods 0.000 claims description 54
- 229910000831 Steel Inorganic materials 0.000 claims description 39
- 239000010959 steel Substances 0.000 claims description 39
- 238000000034 method Methods 0.000 claims description 9
- 238000002441 X-ray diffraction Methods 0.000 claims description 4
- 238000005452 bending Methods 0.000 description 13
- 238000005275 alloying Methods 0.000 description 10
- 238000005096 rolling process Methods 0.000 description 6
- 238000005246 galvanizing Methods 0.000 description 5
- 238000012545 processing Methods 0.000 description 5
- 230000035882 stress Effects 0.000 description 4
- 230000003746 surface roughness Effects 0.000 description 4
- 238000001816 cooling Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000005244 galvannealing Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 230000003449 preventive effect Effects 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
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Description
本発明は、耐パウダリング性に優れた高張力の合金化溶融亜鉛めっき鋼板に関するものである。 The present invention relates to a high-tension alloyed hot-dip galvanized steel sheet excellent in powdering resistance.
近年、自動車の軽量化により排ガス低減を図ると共に燃費を向上させて、地球環境を守ろうという動きが活発である。ただ、使用する鋼板を薄くするだけでは衝突安全性を確保できないため、薄くても強度の高い高張力鋼板の使用が進んでいる。また、自動車等に使用されるに当たり、高度な耐食性が必要とされるため、高張力合金化溶融亜鉛めっき鋼板の開発も盛んであるが、自動車等の分野においては、プレス成形時の成形条件が厳しく、曲げ量や絞り量等の変形量が大きいため、素地鋼板は変形に追随できても、めっき層が変形に追随できず、粉状になって剥離してしまうパウダリングが起こることが多い。 In recent years, there has been an active movement to protect the global environment by reducing exhaust gas and reducing fuel consumption by reducing the weight of automobiles. However, collision safety cannot be ensured only by thinning the steel sheet to be used, and the use of high-strength steel sheets with high strength even though they are thin is advancing. In addition, since high corrosion resistance is required for use in automobiles, etc., high-tensile alloyed hot-dip galvanized steel sheets are also being actively developed. Strictly, because the amount of deformation such as bending amount and drawing amount is large, even if the base steel sheet can follow the deformation, the plating layer cannot follow the deformation, and powdering often occurs in a powdery state and peels off. .
耐パウダリング性を改善するには、従来から、めっき層中のＦｅ濃度を低くして、Γ相の平均厚さを薄くする等の手段が広く知られている。また、特許文献１には、ζ相の量を一定範囲に特定すると共に、めっき層の表面粗度を規定して、耐パウダリング性や耐フレーキング性を向上させた発明が開示されており、特許文献２には、プレス成形の際のポンチ側に当接する鋼板面の摩擦係数を一定値以下に調整することで、プレス成形性や耐パウダリング性を高める発明が開示されている。 In order to improve the powdering resistance, means for reducing the Fe concentration in the plating layer and reducing the average thickness of the Γ phase have been widely known. Patent Document 1 discloses an invention in which the amount of ζ phase is specified within a certain range and the surface roughness of the plating layer is defined to improve the powdering resistance and anti-flaking resistance. Patent Document 2 discloses an invention in which press formability and powdering resistance are improved by adjusting the friction coefficient of a steel plate surface that is in contact with the punch side during press forming to a certain value or less.
しかしながら、これらの従来技術による耐パウダリング性の改善効果は充分でなく、昨今の高張力鋼板（強度３４０ＭＰａ以上）はますますパウダリングを起こし易くなっているため、耐パウダリング性に優れた高張力合金化溶融亜鉛めっき鋼板が要求されていた。
本発明は、上記従来技術を考慮して、高張力合金化溶融亜鉛めっき鋼板における耐パウダリング性を向上させることを課題としている。 This invention makes it a subject to improve the powdering resistance in a high-tensile-alloyed hot-dip galvanized steel sheet in consideration of the said prior art.
本発明の耐パウダリングに優れた高張力合金化溶融亜鉛めっき鋼板は、めっき層の面方向のうちの少なくともいずれか一方向に延びるクラックが、平均間隔１５μｍ以下でめっき層中に多数存在するところに要旨を有する。この高張力合金化溶融亜鉛めっき鋼板は、垂直荷重２９．４Ｎ／ｍｍ2で測定しためっき層表面の動摩擦係数が０．１３０以下であることが好ましい。また、めっき層表面の中心線平均粗さＲａ７５が０．８μｍ以下であり、Ｘ線回折法を用いて測定されためっき層中のζ相の回折強度Ｉζとδ１相の回折強度Ｉδ1との比Ｉζ／Ｉδ1が０．１以下であることも、本発明の好ましい実施態様である。 The high-tensile alloyed hot-dip galvanized steel sheet excellent in powdering resistance according to the present invention has a large number of cracks extending in at least one of the plane directions of the plating layer in the plating layer with an average interval of 15 μm or less. Has a summary. This high-tensile alloyed hot-dip galvanized steel sheet preferably has a dynamic friction coefficient of 0.130 or less on the surface of the plating layer measured at a vertical load of 29.4 N / mm 2 . The center line average roughness Ra75 of the plating layer surface is 0.8 μm or less, and the diffraction intensity Iζ of the ζ phase and the diffraction intensity Iδ 1 of the δ1 phase in the plating layer measured using the X-ray diffraction method. It is also a preferred embodiment of the present invention that the ratio Iζ / Iδ 1 is 0.1 or less.
本発明により、耐パウダリング性に優れた高張力合金化溶融亜鉛めっき鋼板を提供することができた。 According to the present invention, a high-tensile galvannealed steel sheet having excellent powdering resistance can be provided.
本発明の鋼板では、合金化溶融亜鉛めっき層にクラックが入っており、その平均間隔が１５μｍ以下でなければならない。このクラックは、めっき層の面方向に延びるクラックであり、本発明においては、深さがめっき層の厚みの１／２以上である亀裂をクラックとする。深さがめっき層の厚みの１／２以上でないクラックは、耐パウダリング性の向上に寄与しにくい。この点で、素地鋼板まで達しているクラックが望ましい。なおクラックの長さは、特に限定されない。 In the steel sheet of the present invention, the alloyed hot-dip galvanized layer has cracks, and the average interval must be 15 μm or less. This crack is a crack extending in the surface direction of the plating layer. In the present invention, a crack having a depth that is 1/2 or more of the thickness of the plating layer is defined as a crack. Cracks whose depth is not ½ or more of the thickness of the plating layer are unlikely to contribute to the improvement of powdering resistance. In this respect, a crack reaching the base steel plate is desirable. The length of the crack is not particularly limited.
このクラックは、めっき層断面を光学顕微鏡やＳＥＭ等で観察することで認識することができる。本発明のめっき層には、めっき層の面方向のうち少なくともいずれか一方向に延びる多数のクラックが存在しているので、めっき層断面においては、深さ方向に延びるクラックが間隔を空けて並列した状態を観察することができる。そして、本発明ではこの間隔の平均値が１５μｍ以下であることを必須要件としている。 This crack can be recognized by observing the cross section of the plating layer with an optical microscope or SEM. In the plating layer of the present invention, since there are a large number of cracks extending in at least one of the surface directions of the plating layer, in the plating layer section, cracks extending in the depth direction are arranged in parallel at intervals. The observed state can be observed. In the present invention, it is an essential requirement that the average value of the interval is 15 μm or less.
クラックが平均間隔１５μｍ以下で並列していることによって耐パウダリング性が改善されるメカニズムは明確ではないが、プレス加工の際にめっき層の伸び量が変形量に追随できなくなると、めっき層／素地鋼板界面に亀裂が発生し、この亀裂が面方向へ伝播してめっき層が剥離してしまうが、めっき層にクラックがあることでこのクラックが楔となって、亀裂の伝播を止めることができるのではないかと考えられる。また、加工の際にめっき層内に発生する応力が、クラックによって緩和されることも、耐パウダリング性の向上に役立つと考えられる。 The mechanism by which the powdering resistance is improved by the parallel arrangement of cracks with an average interval of 15 μm or less is not clear. However, if the elongation of the plating layer cannot follow the deformation during the press working, A crack occurs at the base steel plate interface, and this crack propagates in the surface direction and the plating layer is peeled off. However, if there is a crack in the plating layer, this crack becomes a wedge and stops propagation of the crack. It may be possible. In addition, it is considered that the stress generated in the plating layer during processing is alleviated by cracks, which is useful for improving the powdering resistance.
このような作用効果を発現させるためには、クラックの平均間隔は１５μｍ以下でなければならない。従来から、合金化溶融亜鉛めっき鋼板のめっき層には、めっき層形成時および形成後の加熱−冷却過程での熱応力によってクラックが発生することが知られているが、これらのクラックは平均間隔が大きいため、耐パウダリング性は改善されない。しかし、本発明者等の知見によれば、平均間隔１５μｍ以下のクラックは耐パウダリング性の向上に有効に寄与するので、後述する方法で、平均間隔１５μｍ以下のクラックを多数形成することが好ましい。クラックの平均間隔は１２μｍ以下が好ましく、１０μｍ以下がさらに好ましい。 In order to exhibit such an effect, the average interval between cracks must be 15 μm or less. Conventionally, it has been known that cracks are generated in the plating layer of the alloyed hot-dip galvanized steel sheet due to thermal stresses during the heating and cooling processes during and after the formation of the plating layer. Therefore, the powdering resistance is not improved. However, according to the knowledge of the present inventors, cracks with an average interval of 15 μm or less contribute effectively to the improvement of powdering resistance. Therefore, it is preferable to form many cracks with an average interval of 15 μm or less by the method described later. . The average interval between cracks is preferably 12 μm or less, and more preferably 10 μm or less.
クラックは、めっき層の面方向の少なくとも一方向（例えば、鋼板の長手方向）に延びるものであればよい。これは、めっき層は一定の面積をもって剥離しようとするので、広がっていこうとする剥離部分がそのいずれかの方向においてクラックと出会えば、前記したように亀裂の伝播が止まると考えられるため、鋼板に加工が施される方向にかかわらず、少なくとも一方向に延びるクラックが存在していればよいのである。なお、後述する方法においてめっき層にクラックを形成する場合は、鋼板長手方向（Ｌ方向）に平均間隔１５μｍ以下のクラックが多数形成され、幅方向（Ｃ方向）には平均間隔が１５μｍを超えるクラックが形成されるが、このような場合ももちろん、一方向（Ｌ方向）において平均間隔１５μｍ以下のクラックが形成されている以上、本発明に含まれる。なお、クラックは、めっき層の全面に形成されていることが望ましい。鋼板の状態では、加工部位がどこに位置するかがわからないからである。 The crack should just extend in at least one direction (for example, the longitudinal direction of the steel sheet) in the surface direction of the plating layer. This is because the plating layer tries to peel off with a certain area, so if the peeled part that is going to spread encounters a crack in either direction, the propagation of cracks is considered to stop as described above. Regardless of the direction in which the material is processed, it is sufficient that there is a crack extending in at least one direction. When cracks are formed in the plating layer in the method described later, many cracks having an average interval of 15 μm or less are formed in the longitudinal direction (L direction) of the steel sheet, and cracks having an average interval exceeding 15 μm in the width direction (C direction). Of course, such a case is included in the present invention as long as cracks having an average interval of 15 μm or less are formed in one direction (L direction). Note that the crack is desirably formed on the entire surface of the plating layer. This is because in the state of the steel plate, it is not possible to know where the processing site is located.
本発明の鋼板においては、上記クラックの要件に加えて、鋼板のめっき層の摩擦係数を一定値以下にすることでより一層耐パウダリング性を高めることができるため、垂直荷重２９．４Ｎ／ｍｍ2で測定したときのめっき層表面の動摩擦係数を０．１３０以下にすることが好ましい。プレス成形時には、めっき層が金型からの摺動抵抗を受け、剪断応力によってめっき層が損傷してパウダリングを起こす。特に、高張力鋼板は素地鋼板の変形抵抗が大きいため、プレス加工部での剪断応力が大きくなってパウダリングを起こし易い。しかし、垂直荷重を２９．４Ｎ／ｍｍ2と高めに設定したときの動摩擦係数は、耐パウダリング性と高い相関が得られることが見出され、このときの動摩擦係数が０．１３０以下であれば、剪断応力をかなり低減させることができ、高レベルな耐パウダリング性を示すことがわかった。上記垂直荷重の摺動条件が、プレス加工時の表面摺動条件に近いためと考えられる。動摩擦係数は、０．１２７以下がより好ましい。動摩擦係数は、例えば、摺動試験装置を用いて測定することができる。具体的には、鋼板のめっき層の上に適宜防錆油を塗布してから１８ｍｍ×１８ｍｍの平面治具を置き、２９．４Ｎ／ｍｍ2の垂直荷重（加圧力）を治具に加え、摺動速度３００ｍｍ／分で治具の下から鋼板を引き抜いたときの引き抜き荷重を測定することにより、動摩擦係数を算出することができる。 In the steel sheet of the present invention, in addition to the above-mentioned crack requirements, the powdering resistance can be further improved by making the friction coefficient of the plated layer of the steel sheet not more than a certain value, so that the vertical load is 29.4 N / mm. The dynamic friction coefficient of the plating layer surface as measured in 2 is preferably 0.130 or less. At the time of press molding, the plating layer receives sliding resistance from the mold, and the plating layer is damaged by the shear stress and causes powdering. In particular, since the high-tensile steel plate has a large deformation resistance of the base steel plate, the shear stress in the press-worked portion is increased and powdering is likely to occur. However, it has been found that the dynamic friction coefficient when the vertical load is set as high as 29.4 N / mm 2 is highly correlated with the powdering resistance, and the dynamic friction coefficient at this time is 0.130 or less. As a result, it was found that the shear stress can be considerably reduced and a high level of powdering resistance is exhibited. This is probably because the sliding condition of the vertical load is close to the surface sliding condition during press working. The dynamic friction coefficient is more preferably 0.127 or less. The dynamic friction coefficient can be measured using, for example, a sliding test apparatus. Specifically, after appropriately applying a rust preventive oil on the plated layer of the steel plate, a flat jig of 18 mm × 18 mm is placed, a vertical load (pressing force) of 29.4 N / mm 2 is applied to the jig, The dynamic friction coefficient can be calculated by measuring the pulling load when the steel plate is pulled out from under the jig at a sliding speed of 300 mm / min.
動摩擦係数とめっき層の表面粗さとは相関があるので、本発明の鋼板は、中心線平均粗さＲａ７５（１９９４年のＪＩＳ Ｂ０６０１に基づく）が０．８μｍ以下であることが好ましい。より好ましくは０．６μｍ以下である。また、動摩擦係数とζ相の量にも相関があるので、本発明の鋼板は、Ｘ線回折法を用いて測定されためっき層中のζ相の回折強度をＩζとし、δ１相の回折強度をＩδ1としたときの両者のの比「Ｉζ／Ｉδ1」が０．１以下であることが好ましい。めっき層中のζ相が少ないと動摩擦係数は小さくなることが知られているが、Ｒａ７５が０．８μｍ以下でなければ、動摩擦係数を好ましい範囲に低減させることができず、高レベルな耐パウダリング性を発現させることはできない。Ｒａ７５を０．８μｍ以下にし、かつＩζ／Ｉδ1を０．１以下にすることで、高レベルな耐パウダリング性を達成することができる。なお、Ｉζの回折ピーク位置２θは７３．９°であり、Ｉδ1の回折ピーク位置２θは７５．４°である。 Since there is a correlation between the dynamic friction coefficient and the surface roughness of the plating layer, it is preferable that the steel sheet of the present invention has a center line average roughness Ra75 (based on 1994 JIS B0601) of 0.8 μm or less. More preferably, it is 0.6 μm or less. In addition, since there is a correlation between the dynamic friction coefficient and the amount of ζ phase, the steel sheet of the present invention has the diffraction intensity of the ζ phase in the plating layer measured using the X-ray diffraction method as Iζ, and the diffraction intensity of the δ1 phase. that is preferable ratio of the both when the i? 1 "Iζ / Iδ 1" is 0.1 or less. It is known that the dynamic friction coefficient is small when the ζ phase in the plating layer is small. Ring property cannot be expressed. The Ra75 to 0.8μm or less, and Iζ / Iδ 1 to be to 0.1 or less, it is possible to achieve a high level of powdering resistance. The diffraction peak position 2θ of Iζ is 73.9 °, and the diffraction peak position 2θ of Iδ 1 is 75.4 °.
本発明の鋼板における合金化溶融亜鉛めっき層の付着量は、３０〜６０ｇ／ｍ2が好ましい。３０〜６０ｇ／ｍ2より少ないと耐食性が不充分となりがちであり、６０ｇ／ｍ2を超えるとめっき付着量が多すぎるためにパウダリングが起こりやすくなるからである。なお、合金化溶融亜鉛めっき層におけるＦｅ量は、７〜１５質量％とすることが好ましい。７質量％未満では、合金化ムラが残存して均一な表面外観が得られにくい。１５質量％を超えると、めっき層が硬くて脆くなっていくので、耐パウダリング性が低下するおそれがある。 As for the adhesion amount of the galvannealing layer in the steel plate of this invention, 30-60 g / m < 2 > is preferable. Tend to be less than 30 to 60 g / m 2 and insufficient corrosion resistance, because powdering is likely to occur because the coating weight exceeds 60 g / m 2 is too large. In addition, it is preferable that the amount of Fe in an alloying hot-dip galvanization layer shall be 7-15 mass%. If it is less than 7% by mass, uneven alloying remains and it is difficult to obtain a uniform surface appearance. If it exceeds 15% by mass, the plating layer becomes hard and brittle, so that the powdering resistance may be lowered.
次に、めっき層にクラックを形成する方法を説明する。最も簡便な方法は、合金化溶融亜鉛めっき後に、鋼板にスキンパス圧延を施す方法である。スキンパス圧延においては、トータルの伸び率が１．３％以上になるように、２回以上行うことが好ましい。より好ましい伸び率は１．７％以上、さらに好ましくは２．０％以上である。スキンパス圧延の際の鋼板の張力は１７６〜７８４ＭＰａ、圧下荷重は９８０〜２９４０Ｎ／ｍｍが好ましい。 Next, a method for forming a crack in the plating layer will be described. The simplest method is a method of subjecting the steel sheet to skin pass rolling after galvannealing. The skin pass rolling is preferably performed twice or more so that the total elongation is 1.3% or more. A more preferable elongation is 1.7% or more, and more preferably 2.0% or more. The tension of the steel plate during skin pass rolling is preferably 176 to 784 MPa, and the rolling load is preferably 980 to 2940 N / mm.
また、スキンパス圧延で、めっき層表面の中心線平均粗さＲａ７５を０．８μｍ以下に調整するためには、表面粗度の小さいロールを使用することが望ましい。特に、めっき層のＲａ７５を０．６μｍ以下にするには、ロール表面の中心線平均粗さＲａ７５が０．５μｍ以下のブライトロールを用いるとよい。なお、最終のスキンパスロールのみをブライトロールにしてもよい。また、溶融亜鉛めっき層を合金化した後、鋼板をミスト冷却で急冷（冷却速度３０℃／秒以上）することによっても、多数のクラックをめっき層に形成することができる。 In order to adjust the center line average roughness Ra75 of the plating layer surface to 0.8 μm or less by skin pass rolling, it is desirable to use a roll having a small surface roughness. In particular, in order to make Ra75 of the plating layer 0.6 μm or less, it is preferable to use a bright roll having a roll surface centerline average roughness Ra75 of 0.5 μm or less. Only the final skin pass roll may be a bright roll. Also, after alloying the hot dip galvanized layer, many cracks can be formed in the plated layer by quenching the steel sheet with mist cooling (cooling rate of 30 ° C./second or more).
一層高レベルな耐パウダリング性を得るためにＩζ／Ｉδ1を０．１以下にする必要があるときは、溶融亜鉛めっき浴のＡｌ濃度は０．１０％以上に高めることが好ましい。また、例えば、直火バーナー加熱方式の合金化炉であれば、複数段ある直火バーナーのうちの加熱炉の入口側のバーナーを用いて溶融亜鉛めっき浴から取り出された鋼板を急速に加熱して、ζ相の包晶温度である５００℃以上（より好ましくは５３０℃程度）に速やかに到達させることが好ましい。なお、Ｉζ／Ｉδ1を０．１以下にする必要がないとき（高レベルな耐パウダリング性が要求されない場合）は、公知の合金化処理条件（浴中Ａｌ濃度０．０８％以上、合金化温度４６０℃以上）で合金化を行えばよい。 When Iζ / Iδ 1 needs to be 0.1 or less in order to obtain a higher level of powdering resistance, the Al concentration of the hot dip galvanizing bath is preferably increased to 0.10% or more. Also, for example, in the case of a direct-fired burner heating type alloying furnace, the steel sheet taken out from the hot dip galvanizing bath is rapidly heated using a burner on the inlet side of the heating furnace among a plurality of direct-fired burners. Thus, it is preferable to quickly reach the peritectic temperature of the ζ phase of 500 ° C. or higher (more preferably about 530 ° C.). When Iζ / Iδ 1 does not need to be 0.1 or less (when high level of powdering resistance is not required), known alloying treatment conditions (Al concentration in the bath of 0.08% or more, alloy) Alloying may be performed at a temperature of 460 ° C. or higher.
以上、本発明の特徴的な点につき説明したが、これら以外の条件、例えば、溶融亜鉛めっき条件は特に限定されず、通常のＡｌ濃度のめっき浴を用いて公知の条件で行えばよい。また、鋼板原板としては、公知の高張力鋼板を用いることができる。 Although the characteristic points of the present invention have been described above, conditions other than these, for example, hot dip galvanizing conditions are not particularly limited, and may be performed under known conditions using a normal Al concentration plating bath. Moreover, a well-known high tension steel plate can be used as a steel plate original plate.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することは可能であり、それらはいずれも本発明の技術的範囲に包含される。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is possible to carry out and they are all included in the technical scope of the present invention.
実験例１（Ｎｏ．１〜６）
板厚：１．２ｍｍ、強度：７８０ＭＰａ、溶融亜鉛めっき付着量：４５ｇ／ｍ2、めっき層中のＦｅ濃度：１１質量％である合金化溶融亜鉛めっき鋼板を用いて、スキンパス条件を変え、クラックの間隔と耐パウダリング性の関連について検討した。１回目のスキンパスは、連続溶融亜鉛めっき設備内で行い、２回目以降はオフラインで行った。なお、スキンパス圧延の際の鋼板の張力は３９２ＭＰａとし、圧下荷重は９８０〜２９４０Ｎ／ｍｍの範囲で適宜調整して、トータル伸び率を制御した。
Experimental Example 1 (Nos. 1 to 6)
Thickness: 1.2 mm, strength: 780 MPa, galvanized coating weight: 45 g / m 2 , Fe concentration in the plating layer: 11% by mass An alloyed galvanized steel sheet was used to change the skin pass conditions and crack We investigated the relationship between the interval between the two and powdering resistance. The first skin pass was performed in a continuous hot dip galvanizing facility, and the second and subsequent times were performed offline. In addition, the tension of the steel plate at the time of skin pass rolling was set to 392 MPa, and the reduction load was appropriately adjusted in the range of 980 to 2940 N / mm to control the total elongation.
クラックの間隔は、ＳＥＭを用いて、めっき層断面（鋼板の長手方向断面と幅方向断面の両方）を長さ７００μｍに亘って観察し、確認できた全てのクラックの間隔の平均値を平均間隔（μｍ）とした。 For the crack interval, the SEM was used to observe the cross section of the plating layer (both the longitudinal cross section and the cross section in the width direction of the steel sheet) over a length of 700 μm, and the average value of all the crack intervals that could be confirmed was the average interval. (Μm).
この実験例１では、耐パウダリング性をＶ曲げ加工で評価した。Ｖ曲げ加工性は、先端曲率半径０．５ｍｍのポンチを使用して鋼板を６０°にＶ曲げし、加工部にテープを貼って剥がした後、剥離した（テープに付着した）めっき層を塩酸に溶解させて、ＩＣＰ（発光分光装置）で定量して、下記基準で評価した。
加工部５０ｍｍ長さ当たり、剥離量２．０ｍｇ未満…◎
剥離量２．０ｍｇ以上〜２．５ｍｇ未満…○
剥離量２．５ｍｇ以上〜３．０ｍｇ未満…△
剥離量３．０ｍｇ以上…×
スキンパスにおけるトータル伸び率とパス回数、クラック間隔およびＶ曲げ加工による耐パウダリング性評価結果を表１に示した。
In Experimental Example 1, the powdering resistance was evaluated by V-bending. V bending workability is determined by bending the steel sheet to 60 ° using a punch with a radius of curvature of 0.5 mm at the tip, attaching the tape to the processed part and peeling it off, and then removing the plating layer attached to the tape (hydrochloric acid). And was quantified with an ICP (Emission Spectrometer) and evaluated according to the following criteria.
Peeling amount less than 2.0mg per 50mm length of processed part ... ◎
Stripping amount 2.0 mg to less than 2.5 mg ... ○
Stripping amount 2.5 mg to less than 3.0 mg ... △
Peeling amount 3.0mg or more ... ×
Table 1 shows the total elongation in the skin pass, the number of passes, the crack interval, and the powdering resistance evaluation result by V-bending.
表１から明らかなように、スキンパスのトータル伸び率が１．２％以下では、クラック間隔が１５μｍ以下とならず、Ｖ曲げ加工時の耐パウダリング性が劣っているが、トータル伸び率が１．７％を超えると、鋼板長手方向のクラックは間隔が１２μｍ以下となって、Ｖ曲げ加工時の耐パウダリング性が改善された。スキンパスでのトータル伸び率が２％を超えると、鋼板長手方向のクラックの間隔が１０μｍ以下となって、Ｖ曲げ加工時の耐パウダリング性が非常に良好となった。 As is apparent from Table 1, when the total elongation of the skin pass is 1.2% or less, the crack interval is not 15 μm or less, and the powdering resistance at the time of V-bending is inferior, but the total elongation is 1 When it exceeded 0.7%, the cracks in the longitudinal direction of the steel sheet became 12 μm or less, and the powdering resistance at the time of V bending was improved. When the total elongation percentage in the skin pass exceeded 2%, the crack interval in the longitudinal direction of the steel sheet was 10 μm or less, and the powdering resistance at the time of V bending was very good.
実験例２（Ｎｏ．７〜１４）
実験例１と同様の原板を用い、めっき層中のＦｅ量（質量％）、合金化処理条件、スキンパス条件を変えることで、めっき層の摩擦係数、中心線平均粗さＲａ７５、Ｉζ／Ｉδ1を種々変化させ、耐パウダリング性との関連について検討した。Ｆｅ量とスキンパス条件は表２に示した。なお、ロール表面の中心線平均粗さＲａ７５とめっき層のＲａ７５は、非接触型表面粗さ計（「サーフコム１４００」：東京精密社製）を用いて、１９９４年制定のＪＩＳ Ｂ０６０１に基づいて測定した値である。
Experimental Example 2 (No. 7 to 14)
Using the same original plate as in Experimental Example 1 and changing the amount of Fe (mass%) in the plating layer, alloying treatment conditions, and skin pass conditions, the friction coefficient, centerline average roughness Ra75, Iζ / Iδ 1 of the plating layer The relationship between anti-powdering resistance was investigated. The Fe amount and skin pass conditions are shown in Table 2. The roll surface centerline average roughness Ra75 and the plating layer Ra75 were measured based on JIS B0601 established in 1994 using a non-contact type surface roughness meter ("Surfcom 1400" manufactured by Tokyo Seimitsu Co., Ltd.). It is the value.
Ｎｏ．７〜９、１２〜１４では、溶融亜鉛めっき浴中のＡｌ濃度を０．０９％とし、めっき層を形成した後、３段の直火バーナーを備えた合金化炉で、これらの３段の直火バーナーを均等に加熱し、炉温から判断して板温（直接測定不能）が大体４６０〜５００℃程度になるように調整して合金化処理を行い、Ｎｏ．１０〜１１は、浴中のＡｌ濃度を０．１０％とし、合金化炉で板温が速やかに５００℃以上になるように前段の直火バーナーで鋼板を急速に加熱して合金化処理を行って、めっき層のＦｅ量とＩζ／Ｉδ1を変えた。なお、Ｉζ／Ｉδ1は、Ｘ線回折法により、ターゲットにはＣｕを用いて、ζ相（回折ピーク位置２θ＝７３．９゜）とδ１相（回折ピーク位置２θ＝７５．４°）のそれぞれの回折強度ＩζおよびＩδ1を求めて算出した。 No. 7-9 and 12-14, the Al concentration in the hot dip galvanizing bath was 0.09%, and after forming the plating layer, these three-stages were formed in an alloying furnace equipped with three-stage direct-fired burners. The direct flame burner is heated evenly, and the alloying treatment is performed by adjusting the plate temperature (not directly measurable) to about 460 to 500 ° C. as judged from the furnace temperature. Nos. 10 to 11 have an Al concentration in the bath of 0.10%, and the steel plate is rapidly heated with the direct flame burner in the previous stage so that the plate temperature quickly becomes 500 ° C. or higher in the alloying furnace. Then, the Fe amount of the plating layer and Iζ / Iδ 1 were changed. Note that Iζ / Iδ 1 is obtained by X-ray diffraction, using Cu as a target, and ζ phase (diffraction peak position 2θ = 73.9 °) and δ1 phase (diffraction peak position 2θ = 75.4 °). The respective diffraction intensities Iζ and Iδ 1 were obtained and calculated.
めっき層の動摩擦係数は、摺動試験装置（「オートグラフＤＣＳ−５０００」：島津社製）を用いて測定した。鋼板のめっき層の上に、防錆油（「ノックスラスト５５０ＨＮ」；パーカー興産製）を塗布してから１８ｍｍ×１８ｍｍの平面治具を置き、２９．４Ｎ／ｍｍ2の垂直荷重（加圧力）を治具に加え、摺動速度３００ｍｍ／分で治具の下から鋼板を引き抜いたときの引き抜き荷重を測定して、摩擦係数を求めた。 The dynamic friction coefficient of the plating layer was measured using a sliding test device (“Autograph DCS-5000” manufactured by Shimadzu Corporation). After applying a rust preventive oil (“Knox Last 550HN”; manufactured by Parker Kosan Co., Ltd.) on the plated layer of the steel plate, a flat jig of 18 mm × 18 mm is placed and a vertical load (pressing force) of 29.4 N / mm 2 Was added to the jig, and the pulling load when the steel sheet was pulled out from under the jig at a sliding speed of 300 mm / min was measured to obtain the friction coefficient.
実験例２では、Ｖ曲げ加工による耐パウダリング性の評価に加え、さらに高レベルな耐パウダリング性（摺動を伴う高加工時の耐パウダリング性）を評価することのできるビード付きＵ曲げ加工を行った。しわ押さえ圧（ＢＨＦ）を１トンに設定して、クランクプレスでＵ曲げ成形し（Ｕ字高さは６５ｍｍ、Ｕ字底辺は５０ｍｍ、幅４０ｍｍ、ビード部は半径５ｍｍ）た。成形後の試料の側壁の外側のめっき層にテープを貼付した後、剥離して、Ｖ曲げのときと同様に、めっきの剥離量の定量を行って、下記基準で評価した。
剥離量が３ｇ／ｍ2未満…○
剥離量が３ｇ／ｍ2以上６ｇ／ｍ2未満…△
剥離量が６ｇ／ｍ2以上…×
In Experimental Example 2, in addition to the evaluation of powdering resistance by V-bending, a higher level of powdering resistance (powdering resistance during high processing with sliding) can be evaluated. Processing was performed. The wrinkle holding pressure (BHF) was set to 1 ton, and U-bending was performed with a crank press (the U-shaped height was 65 mm, the U-shaped base was 50 mm, the width was 40 mm, and the bead portion had a radius of 5 mm). The tape was affixed to the plating layer outside the side wall of the molded sample, and then peeled off. The amount of plating peeling was quantified in the same manner as in the case of V-bending, and the following criteria were evaluated.
Peeling amount is less than 3 g / m 2 ... ○
Peeling amount is 3g / m 2 or more and less than 6g / m 2 ... △
Peeling amount is 6g / m 2 or more… ×
表２から、Ｎｏ．７〜１４では、めっき層の鋼板長手方向のクラック間隔がいずれも１５μｍ以下であり、Ｖ曲げによる耐パウダリング性は良好であったが、より過酷なレベルでのＵ曲げの場合は、めっき層のＩζ／Ｉδ1が０．１以下、動摩擦係数０．１３０以下、Ｒａ７５が０．８μｍ以下でなければ、○にはならないことがわかった。 From Table 2, no. In Nos. 7 to 14, the crack interval in the longitudinal direction of the steel sheet of the plating layer was 15 μm or less, and the powdering resistance by V bending was good, but in the case of U bending at a more severe level, the plating layer When Iζ / Iδ 1 is 0.1 or less, the coefficient of dynamic friction is 0.130 or less, and Ra75 is 0.8 μm or less, it was found that it was not good.
本発明の合金化溶融亜鉛めっき鋼板は、耐パウダリング性に優れているので、種々の加工が施される自動車用の高張力鋼板として、有用である。
Since the alloyed hot-dip galvanized steel sheet of the present invention is excellent in powdering resistance, it is useful as a high-tensile steel sheet for automobiles subjected to various processing.
Claims (3)
垂直荷重２９．４Ｎ／ｍｍ 2 で測定しためっき層表面の動摩擦係数が０．１３０以下であるとともに、
めっき層表面の中心線平均粗さＲａ７５が０．８μｍ以下であり、
さらに、Ｘ線回折法を用いて測定されためっき層中のζ相の回折強度Ｉζとδ１相の回折強度Ｉδ 1 との比であるＩζ／Ｉδ 1 が０．１以下であることを特徴とする耐パウダリングに優れた高張力合金化溶融亜鉛めっき鋼板。 A number of cracks extending in at least one of the plane directions of the plating layer are present in the plating layer with an average interval of 15 μm or less ,
The dynamic friction coefficient of the plating layer surface measured at a vertical load of 29.4 N / mm 2 is 0.130 or less,
The center line average roughness Ra75 of the plating layer surface is 0.8 μm or less,
Furthermore, Iζ / Iδ 1, which is a ratio of the diffraction intensity Iζ of the ζ phase and the diffraction intensity Iδ 1 of the δ1 phase in the plating layer measured using the X-ray diffraction method, is 0.1 or less. High tensile alloyed hot dip galvanized steel sheet with excellent powdering resistance.
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