JP3800475B2

JP3800475B2 - Alloyed hot-dip galvanized steel sheet with excellent press formability

Info

Publication number: JP3800475B2
Application number: JP02615099A
Authority: JP
Inventors: 亘江藤林; 洋一飛山; 千昭加藤
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1999-02-03
Filing date: 1999-02-03
Publication date: 2006-07-26
Anticipated expiration: 2019-02-03
Also published as: JP2000226646A

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車用防錆表面処理鋼板として用いられる、プレス成形性に優れる合金化溶融亜鉛めっき鋼板に関するものである。
【０００２】
【従来の技術】
合金化溶融亜鉛めっき鋼板は防錆性に優れ、安価に製造できるため、自動車車体用防錆表面処理鋼板として多用されている。しかし、プレス成形時に、合金化溶融亜鉛めっき鋼板と金型との潤滑が十分でなく、摺動性が不良になる傾向があり、その結果、金型への鋼板の流入が阻害され、プレス割れ等の材料破断の問題が発生する。特に、プレス成形による鋼板の変形に伴うめっき剥離を抑制するために、合金化の程度を抑制し、めっき層中の鉄含有率を比較的低くした合金化溶融亜鉛めっき鋼板の場合は、プレス金型との摺動性がより劣るため、しばしばプレス成形時に材料破断を起こし問題となっていた。かかる問題を回避するために、特開平３−８２７４６号公報に開示されるように、合金化溶融亜鉛めっき上に鉄系合金めっきを施し、めっき層の金型摺動性を改善したり、特開平３−１６２４９２号公報に開示されるように潤滑性に優れた防錆油やプレス油を塗油することにより材料の流入を促進するなどの方法が提案されている。
【０００３】
しかし、合金化溶融亜鉛めっき鋼板の上にさらに鉄系めっきを施しても、それだけではより一層厳しい条件のプレス成形に対応できず、設備の改造および工程の増加に伴う不可避的なコスト上昇を招くという新たな問題もある。また、潤滑油や防錆油の塗布による改善の場合は、塗布むらのためプレス割れを生じたり、脱脂性が劣ることが多く、後工程の作業を煩雑にしたり、また部品によっては工程上、これら潤滑油を使用できない場合があり、必ずしも満足できるものではない。
【０００４】
また後述するように、本願出願人らは、３次元平均表面粗さ（ＳＲａ）を０．７μｍ以上と規定し、かつ本発明で定義する表面粗さの振幅確率密度分布の歪度Ｓを−０．３〜０．１と規定することにより、鋼板に塗布された潤滑油の効果を十分に発揮せしめ、摺動性が改善され、均一で十分な材料流入が確保され、結果的に良好なプレス成形性が得られる合金化溶融亜鉛めっき鋼板を提案した（特許第２７０４０７０号）。この鋼板は相当の改善が認められるが、最近はコスト削減等のため、より大きい鋼板での一体成形化が進み、より一層厳しいプレス成形性が要求されるようになってきた。
【０００５】
【発明が解決しようとする課題】
したがって、材料コストの大きな上昇を避けつつ、合金化溶融亜鉛めっき鋼板のプレス金型との摺動性を改善し、一般の防錆油、洗浄油を用いても、プレス成形時の金型との摺動問題を回避し得るような方策の開発が望まれていた。
【０００６】
プレス成形における鋼板とプレス金型との摺動挙動は、鋼板表面の硬度等の物性と表面形状、および鋼板に塗布されるプレス油、防錆油、洗浄油等の潤滑効果に左右される。そのため、プレス開始から終了までの間、鋼板と金型の間には常に油が存在する状態に維持する必要がある。
【０００７】
油の保持力を高めるためには、めっき鋼板の表面粗さ（Ｒａ）を大きくすること、めっき後の調質圧延によって表面を粗面にすること等が考えられるが、表面粗さを大きくすることにより、プレス時に凸部に局部的な力が加わり、めっき層に欠陥が生じ、型かじりにつながる恐れがある。また粗面にすることによる外観不良の影響も無視できなくなる。
【０００８】
そこで本発明者らは、合金化溶融亜鉛めっき鋼板の表面状態と摺動性との関係を検討した結果、表面の深さ方向のヒストグラムを示す振幅確率密度分布を制御することにより摺動性が改善されることを見いだした。
さらに、本発明者らは、合金化溶融亜鉛めっき鋼板のめっき層中の最表層のζ相（ＦｅＺｎ₁₃）とδ１相のＸ線回折強度比が特定の範囲にある時に、一層摺動性が改善されることを見いだした。
【０００９】
すなわち、本発明者らは、合金化溶融亜鉛めっき鋼板の表面状態を制御することにより、プレス開始から終了までの間、油の保持力を失うことなく、摺動性が十分で、まためっき剥離等の欠陥がなく、めっき密着性が良好であり、結果的にプレス成形性に優れた合金化溶融亜鉛めっき鋼板を見いだした。
【００１０】
【課題を解決するための手段】
本発明は、式（１）で定義される合金化溶融亜鉛めっき鋼板の表面の断面曲線の振幅確率密度分布の歪度Ｓが−１．５以上、−０．３未満であり、式（２）で定義される合金化溶融亜鉛めっき鋼板のめっき層中のζ相とδ１相のＸ線回折強度比Ｄが０．０１以下であることを特徴とするプレス成形性に優れた合金化溶融亜鉛めっき鋼板である。
Ｓ＝μ₃／σ³ （１）
但し μ₃：振幅確率密度の３次モーメント
σ ：振幅確率密度の標準偏差
ζ相｛(-604)+(820)+(-152) ｝面のＸ線回折強度
Ｄ＝───────────────────────── （２）
δ１相(330) 面のＸ線回折強度
【００１２】
好ましい本発明は、溶融亜鉛めっきの上に鉄系電気めっきを施した合金化溶融亜鉛めっき鋼板である。
【００１３】
【発明の実施の形態】
本発明者らは、合金化溶融亜鉛めっき鋼板の表面状態と摺動性との関係を検討した結果、表面の深さ方向のヒストグラムを示す振幅確率密度分布を制御することにより摺動性が改善されることを見いだしたことを根拠にするものである。
深さ方向の振幅確率密度分布とは、合金化溶融亜鉛めっき鋼板の表面の断面曲線をある深さで切ったとき、その直線と断面曲線との交点の数をその深さの頻度とし、それぞれの深さにおける頻度の分布を確率分布とすることにより求めたものである。また深さにおける頻度をヒストグラムに表せば、振幅確率密度分布曲線が得られる。その模式図が図１である。
【００１４】
振幅確率密度分布の歪度Ｓとは、
Ｓ＝μ₃／σ³ （１）
但し μ₃：振幅確率密度の３次モーメント
σ ：振幅確率密度の標準偏差
で定義され、統計学においてヒストグラムの非対称性を示す尺度である。すなわち、Ｎ個の測定点における、Ｘｉなる表面粗さの振幅値を有する試料の出現確率をｆｉ，３次モーメントをＸとする時の標準偏差と３次モーメントは下記式で算出される。
【００１５】
【数１】

【００１６】
【数２】

【００１７】
合金化溶融亜鉛めっき鋼板の表面状態と振幅確率密度分布曲線と歪度Ｓとの関係を模式的に図２に示した。図２から明らかなように、Ｓが０未満の場合は、めっき鋼板の表面状態が凹部に比べ、比較的平坦な凸部が多く存在することが分かる。一方、Ｓが０超の場合は、平坦な凹部が多く存在することが分かる。本発明は、歪度Ｓが−１．５以上、−０．３未満であることを特徴とするが、これは合金化溶融亜鉛めっき鋼板の表面に、平坦な凸部が多く存在することを意味する。
【００１８】
歪度Ｓが０または０超の場合は、凹部の容積が大きいため、プレス成形時の油の保持は可能であるが、プレス成形時に鋼板と金型とが接する凸部の面積が小さいため、プレス成形時の面圧がその凸部に集中することになる。そのため、凸部における、めっきの欠落による型かじりが起こりやすくなり、摺動性を劣化させる原因になる。
【００１９】
一方、比較的平坦な凸部が多く存在する合金化溶融亜鉛めっき鋼板では、鋼板と金型とが接する面積が大きくなり、プレス成形時に局所的な面圧の上昇は起こらず、歪度Ｓは−０．３が限界であることが分かった。またＳが−１．５未満では、凹部の容積が小さく、防錆油等の油の保持力が小さいため、潤滑が劣化し、摺動性は改善されない。好ましい歪度Ｓは−０．５〜１．５である。
【００２０】
一般的に合金化溶融亜鉛めっき鋼板のめっき層は、鉄含有率の高い方からΓ相、δ１相、ζ相と命名される。鉄含有率の低いζ相は比較的柔らかいため、プレス成形時には摩擦係数が高くなり、摺動性の劣化を引き起こす。そのため、式（２）で定義されるζ相とδ１相のＸ線回折強度比Ｄが０．０１以下であることが望まれる。要するに、合金化溶融亜鉛めっき鋼板表面の歪度Ｓに加えて、さらに鋼板のめっき層の相構造を制御することで、めっき密着性と摺動性が改善される。好ましいＸ線回折強度比Ｄは０．００６以下である。

【００２１】
これは、溶融亜鉛めっき層を加熱合金化する際に、鋼板表面の結晶粒界等が局所的に早く合金化する場合があり、その局所部分はδ１相にあり、体積膨張および近傍の亜鉛の吸収により、凸部になり易い。一方合金化の遅い部分は、摺動性を劣化させるζ相が多く存在し、凹部となり易い。しかし、強度比Ｄが０．０１超の場合は、ζ相が凹部のみならず、凸部にも存在するようになる。そのため、プレス成形時に金型とζ相が接触する部分が増大し、摩擦係数が上昇して、摺動性が劣化するものと推測される。
【００２２】
また、表面状態やめっき層構造を制御した合金化溶融亜鉛めっき鋼板のめっき層の上に、Ｆｅ−Ｚｎ，Ｆｅ−Ｐのような鉄系の上層めっきを施せば、さらに摺動性を改善することができる。
【００２３】
【実施例】
板厚０．８ｍｍの極低炭素鋼板を、連続溶融亜鉛めっきラインにおいて、溶融亜鉛めっきおよび合金化を行い、めっき付着量が表裏とも４５ｇ／ｍ²の合金化溶融亜鉛めっき鋼板を得た。合金化温度と合金化パターンの制御により、ζ相とδ１相との比率、したがって強度比を変化させた。
その後、得られた合金化溶融亜鉛めっき鋼板を、調質圧延し、プレス成形用鋼板を製造した。調質圧延の際のロールの表面粗さと調質圧延時の荷重を制御することにより、振幅確率密度の歪度Ｓを変化させた。得られたプレス成形用鋼板について、鋼板表面粗さの振幅確率密度分布、めっき層中のζ相とδ１相のＸ線回折強度を測定し、振幅確率密度分布の歪度ＳとＸ線回折強度比Ｄを算出した。歪度Ｓと強度比Ｄを表１に示した。
【００２４】
合金化溶融亜鉛めっき鋼板のプレス成形性は、限界絞り比と摩擦係数で示し、限界絞り比が２．１以下、摩擦擦係数が０．１３５以上の場合を成形性不良と判定した。また鋼板の機械的強度（引張強度、曲げ強度、伸び）も測定し、限界絞り比と摩擦係数とともに表１に示した。
【００２５】
振幅確率密度分布は、３次元粗さ測定器（明伸工機（株）製ＳＡＳ２００２）を用い、接触式触針（先端径５μｍ）により、測定面積１０ｍｍ×５ｍｍ、測定ピッチ（ｘ軸方向１０μｍ、ｙ軸方向５μｍ）で測定した。
Ｘ線回折強度は、理学電機（株）製のＲＩＮＴ１５００を用い、管球銅、管電圧５０ｋｖ、管電流２５０ｍＡ、スキャン速度４．００度／分、走査軸２θ／θの条件で、ζ相｛（−６０４）＋（８２０）＋（−１５２）｝面は、面間隔１．２６０Åのピーク、δ１相（３３０）面は面間隔２．１３５Åのピークの強度を測定した。
【００２６】
限界絞り比は、ポンチ径３３ｍｍの平底円筒絞り試験機を用い、しわ押さえ圧０．７ｔで前記鋼板を絞り成形して測定した。潤滑剤としては一般の防錆油（パーカー興産（株）製ノックスラスト^R５５０ＫＨ）を用いた。
摩擦係数は、前記鋼板から切り出した幅２０ｃｍの試験片を、プレス金型と同一の材料で作成した平坦部長さ１２ｍｍの平金型に挟み、２０ｍｍ／秒の速度で、長さ５０ｍｍだけ引き抜く時の力を測定した結果より求めた。潤滑剤として一般の防錆油（パーカー興産（株）製ノックスラスト^R５５０ＫＨ）を用いた。
【００２７】
【表１】

【００２８】
【表２】

【００２９】
【発明の効果】
合金化溶融亜鉛めっき鋼板の表面状態を制御することにより、プレス成形時の鋼板表面の油の保持と圧力の分散を可能にし、鋼板と金型との潤滑を改善し、良好なプレス成形性、特に連続プレス成形性を有する合金化溶融亜鉛めっき鋼板が得られる。また表面状態の制御が既存の製造ラインで、めっきおよび合金化条件と調質圧延条件を調整すれば可能であることからコストアップすることなく実現できる。さらに、上層に鉄系の電気めっきを施したり、特別の潤滑処理を施す場合にも、コストアップに見合う以上の効果を顕現せしめることができるので、工業的な利用範囲は広く、その意義は大きい。
【図面の簡単な説明】
【図１】合金化溶融亜鉛めっき鋼板における、鋼板の表面状態と振幅確率密度分布との関係を示す模式図。
【図２】合金化溶融亜鉛めっき鋼板における、表面状態と振幅確率密度分布と振幅確率密度分布の歪度との関係を示す模式図。
【符号の説明】
１基板（地鉄）
２合金化溶融亜鉛めっき
３合金化溶融亜鉛めっき鋼板の表面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alloyed hot-dip galvanized steel sheet having excellent press formability, which is used as a rust-proof surface-treated steel sheet for automobiles.
[0002]
[Prior art]
Alloyed hot-dip galvanized steel sheets are widely used as rust-proof surface-treated steel sheets for automobile bodies because they are excellent in rust prevention and can be manufactured at low cost. However, during press forming, the alloyed hot-dip galvanized steel sheet and the mold are not sufficiently lubricated, and the slidability tends to be poor. As a result, the flow of the steel sheet into the mold is hindered, and the press cracks. The problem of material breakage occurs. In particular, in the case of an alloyed hot-dip galvanized steel sheet in which the degree of alloying is suppressed and the iron content in the plating layer is relatively low in order to suppress plating peeling due to deformation of the steel sheet due to press forming, press gold Since the slidability with the mold is inferior, the material often breaks during press molding, which is a problem. In order to avoid such a problem, as disclosed in Japanese Patent Laid-Open No. 3-82746, iron-based alloy plating is performed on the alloyed hot dip galvanizing to improve the mold slidability of the plating layer. As disclosed in Japanese Laid-Open Patent Publication No. 3-162492, there has been proposed a method of promoting the inflow of materials by applying a rust preventive oil or a press oil excellent in lubricity.
[0003]
However, even if iron-based plating is further applied to the alloyed hot-dip galvanized steel sheet, it alone cannot cope with press forming under even more severe conditions, leading to inevitable cost increase due to modification of equipment and increase in processes. There is also a new problem. In addition, in the case of improvement by application of lubricating oil or rust preventive oil, press cracks occur due to uneven application, and degreasing is often inferior, making the work of the post process complicated, and depending on the part, on the process, These lubricating oils may not be used and are not always satisfactory.
[0004]
Further, as will be described later, the applicants of the present application specify the three-dimensional average surface roughness (SRa) as 0.7 μm or more, and the skewness S of the amplitude probability density distribution of the surface roughness defined in the present invention − By defining it as 0.3 to 0.1, the effect of the lubricating oil applied to the steel plate is fully exerted, the slidability is improved, the uniform and sufficient material inflow is ensured, and the result is good An alloyed hot-dip galvanized steel sheet capable of achieving press formability was proposed (Japanese Patent No. 2704070). Although this steel plate is considerably improved, recently, in order to reduce costs, integration with a larger steel plate has progressed, and more severe press formability has been required.
[0005]
[Problems to be solved by the invention]
Therefore, while avoiding a significant increase in material costs, the slidability of the alloyed hot-dip galvanized steel sheet with the press mold is improved, and even when using general rust preventive oil and cleaning oil, Development of measures that can avoid the sliding problem is desired.
[0006]
The sliding behavior between the steel sheet and the press die in press molding depends on the physical properties such as hardness of the steel sheet surface and the surface shape, and the lubricating effect of press oil, rust preventive oil, cleaning oil, etc. applied to the steel sheet. Therefore, it is necessary to maintain a state where oil always exists between the steel plate and the mold from the start to the end of pressing.
[0007]
In order to increase the oil holding power, it is conceivable to increase the surface roughness (Ra) of the plated steel sheet, or to roughen the surface by temper rolling after plating, but increase the surface roughness. As a result, a local force is applied to the convex portion during pressing, and the plating layer may be defective, leading to mold galling. In addition, the influence of the appearance defect due to the rough surface cannot be ignored.
[0008]
Therefore, as a result of examining the relationship between the surface state of the galvannealed steel sheet and the slidability, the present inventors have determined that the slidability is controlled by controlling the amplitude probability density distribution indicating a histogram in the depth direction of the surface. I found it improved.
Further, the present inventors have further improved slidability when the X-ray diffraction intensity ratio of the outermost layer ζ phase (FeZn ₁₃ ) and δ1 phase in the coating layer of the galvannealed steel sheet is in a specific range. I found it improved.
[0009]
That is, by controlling the surface state of the galvannealed steel sheet, the present inventors have sufficient slidability without losing the oil holding force from the start to the end of the press, and the plating peeling. As a result, an alloyed hot-dip galvanized steel sheet having good plating adhesion and excellent press formability was found.
[0010]
[Means for Solving the Problems]
In the present invention, the skewness S of the amplitude probability density distribution of the cross-sectional curve of the surface of the alloyed hot-dip galvanized steel sheet defined by the formula (1) is −1.5 or more and less than −0.3, and the formula (2 An alloyed hot dip zinc excellent in press formability, characterized in that the X-ray diffraction intensity ratio D between the ζ phase and the δ1 phase in the coating layer of the galvannealed steel sheet defined by It is a plated steel sheet.
S = μ ₃ / σ ³ (1)
Where μ _{3 is} the third moment of amplitude probability density
σ: Standard deviation of amplitude probability density
X-ray diffraction intensity of the ζ phase {(-604) + (820) + (-152)} plane D = ───────────────────────── (2)
X-ray diffraction intensity of the δ1 phase (330) surface
A preferred present invention is an alloyed hot-dip galvanized steel sheet in which iron-based electroplating is performed on hot-dip galvanizing.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As a result of examining the relationship between the surface state of the galvannealed steel sheet and the slidability, the present inventors have improved the slidability by controlling the amplitude probability density distribution showing a histogram in the depth direction of the surface. It is based on having found what is done.
The amplitude probability density distribution in the depth direction means that when the cross-sectional curve of the surface of the alloyed hot-dip galvanized steel sheet is cut at a certain depth, the number of intersections between the straight line and the cross-sectional curve is the frequency of the depth, The frequency distribution at the depth is determined as a probability distribution. An amplitude probability density distribution curve can be obtained by expressing the frequency at the depth in a histogram. The schematic diagram is shown in FIG.
[0014]
The skewness S of the amplitude probability density distribution is
S = μ ₃ / σ ³ (1)
Where μ _{3 is} the third moment of the amplitude probability density σ is defined by the standard deviation of the amplitude probability density, and is a measure of the asymmetry of the histogram in statistics. That is, at N measurement points, the standard deviation and the third moment when the appearance probability of a sample having the amplitude value of the surface roughness Xi is fi and the third moment is X are calculated by the following equations.
[0015]
[Expression 1]

[0016]
[Expression 2]

[0017]
The relationship between the surface state of the galvannealed steel sheet, the amplitude probability density distribution curve, and the degree of distortion S is schematically shown in FIG. As can be seen from FIG. 2, when S is less than 0, the surface state of the plated steel sheet has many relatively flat convex portions as compared to the concave portions. On the other hand, when S is more than 0, it can be seen that many flat concave portions exist. The present invention is characterized in that the skewness S is -1.5 or more and less than -0.3, which means that there are many flat protrusions on the surface of the galvannealed steel sheet. means.
[0018]
When the degree of distortion S is 0 or more than 0, the volume of the concave portion is large, so it is possible to retain oil during press molding, but the area of the convex portion where the steel plate and the mold come into contact during press molding is small, The surface pressure at the time of press molding is concentrated on the convex portion. For this reason, mold galling due to lack of plating tends to occur at the convex portion, which causes deterioration of slidability.
[0019]
On the other hand, in an alloyed hot-dip galvanized steel sheet having many relatively flat protrusions, the area where the steel sheet and the mold are in contact with each other increases, and the local surface pressure does not increase during press forming, and the degree of distortion S is -0.3 was found to be the limit. On the other hand, when S is less than −1.5, the volume of the concave portion is small and the holding power of oil such as rust preventive oil is small, so that the lubrication is deteriorated and the slidability is not improved. The preferred skewness S is -0.5 to 1.5.
[0020]
Generally, the plated layer of the alloyed hot-dip galvanized steel sheet is named as Γ phase, δ1 phase, and ζ phase from the higher iron content. Since the ζ phase with a low iron content is relatively soft, the friction coefficient becomes high during press molding, causing deterioration of the slidability. Therefore, it is desirable that the X-ray diffraction intensity ratio D between the ζ phase and the δ1 phase defined by the formula (2) is 0.01 or less. In short, in addition to the degree of distortion S on the surface of the galvannealed steel sheet, the plating adhesion and slidability are improved by further controlling the phase structure of the plating layer of the steel sheet. A preferable X-ray diffraction intensity ratio D is 0.006 or less.

[0021]
This is because when the hot dip galvanized layer is heat-alloyed, the grain boundaries on the surface of the steel sheet may be alloyed locally quickly, and the local part is in the δ1 phase, and the volume expansion and the nearby zinc Due to absorption, it tends to be convex. On the other hand, in the slow-alloying portion, there are many ζ phases that deteriorate the slidability, and it tends to be a recess. However, when the intensity ratio D is more than 0.01, the ζ phase is present not only in the concave portion but also in the convex portion. For this reason, it is presumed that the portion where the mold and the ζ phase contact during press molding increases, the friction coefficient increases, and the slidability deteriorates.
[0022]
Moreover, if iron-based upper layer plating such as Fe-Zn and Fe-P is applied on the plated layer of the alloyed hot-dip galvanized steel sheet whose surface state and plated layer structure are controlled, the slidability is further improved. be able to.
[0023]
【Example】
An ultra-low carbon steel sheet having a thickness of 0.8 mm was subjected to hot dip galvanization and alloying in a continuous hot dip galvanizing line to obtain an alloyed hot dip galvanized steel sheet having an adhesion amount of 45 g / m ^{2 on} both sides. By controlling the alloying temperature and the alloying pattern, the ratio between the ζ phase and the δ1 phase, and hence the strength ratio, was changed.
Thereafter, the obtained galvannealed steel sheet was temper-rolled to produce a press forming steel sheet. By controlling the surface roughness of the roll during temper rolling and the load during temper rolling, the skewness S of the amplitude probability density was changed. For the obtained steel sheet for press forming, the amplitude probability density distribution of the surface roughness of the steel sheet, the X-ray diffraction intensity of the ζ phase and the δ1 phase in the plating layer, and the skewness S and the X-ray diffraction intensity of the amplitude probability density distribution are measured. The ratio D was calculated. The skewness S and the strength ratio D are shown in Table 1.
[0024]
The press formability of the alloyed hot-dip galvanized steel sheet is indicated by a limit drawing ratio and a friction coefficient. When the limit drawing ratio is 2.1 or less and the friction friction coefficient is 0.135 or more, it is determined that the formability is poor. The mechanical strength (tensile strength, bending strength, elongation) of the steel sheet was also measured and shown in Table 1 together with the limit drawing ratio and friction coefficient.
[0025]
The amplitude probability density distribution was measured using a three-dimensional roughness measuring instrument (SAS2002 manufactured by Meishin Koki Co., Ltd.), with a contact stylus (tip diameter 5 μm), measurement area 10 mm × 5 mm, measurement pitch (x-axis direction 10 μm, Measurement was performed in the y-axis direction (5 μm).
The X-ray diffraction intensity was measured using a RINT 1500 manufactured by Rigaku Corporation with the following conditions: tube copper, tube voltage 50 kv, tube current 250 mA, scan speed 4.00 ° / min, scan axis 2θ / θ. The (−604) + (820) + (− 152)} plane was measured for the peak intensity of 1.260 ピーク, and the δ1 phase (330) plane was measured for the peak intensity of 2.135 Å.
[0026]
The limit drawing ratio was measured by drawing the steel sheet with a wrinkle holding pressure of 0.7 t using a flat bottom cylindrical drawing tester having a punch diameter of 33 mm. As the lubricant, a general rust preventive oil (Knoxlast ^R 550KH manufactured by Parker Kosan Co., Ltd.) was used.
The friction coefficient is obtained when a test piece having a width of 20 cm cut out from the steel plate is sandwiched between a flat die having a flat portion length of 12 mm made of the same material as the press die and pulled out by a length of 50 mm at a speed of 20 mm / second. It was obtained from the result of measuring the force of. A general rust preventive oil (Knoxlast ^R 550KH manufactured by Parker Kosan Co., Ltd.) was used as a lubricant.
[0027]
[Table 1]

[0028]
[Table 2]

[0029]
【The invention's effect】
By controlling the surface condition of the alloyed hot-dip galvanized steel sheet, it is possible to retain oil on the steel sheet surface during press forming and disperse the pressure, improve the lubrication between the steel sheet and the mold, In particular, an alloyed hot-dip galvanized steel sheet having continuous press formability is obtained. Further, since the surface state can be controlled by adjusting the plating and alloying conditions and the temper rolling conditions on an existing production line, it can be realized without increasing the cost. Furthermore, even when iron-based electroplating is applied to the upper layer or special lubrication treatment is performed, an effect beyond the cost increase can be manifested, so the industrial application range is wide, and its significance is great. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the relationship between the surface state of a steel sheet and the amplitude probability density distribution in an alloyed hot-dip galvanized steel sheet.
FIG. 2 is a schematic diagram showing the relationship among the surface state, amplitude probability density distribution, and skewness of the amplitude probability density distribution in an alloyed hot-dip galvanized steel sheet.
[Explanation of symbols]
1 Substrate (Ground iron)
2 Alloyed galvanized steel 3 Surface of alloyed galvanized steel sheet

Claims

The skewness S of the amplitude probability density distribution of the cross-sectional curve of the surface of the alloyed hot-dip galvanized steel sheet defined by the formula (1) is −1.5 or more and less than −0.3, and is defined by the formula (2) An alloyed hot-dip galvanized steel sheet excellent in press formability, characterized in that the X-ray diffraction intensity ratio D between the ζ phase and the δ1 phase in the plated layer of the alloyed hot-dip galvanized steel sheet is 0.01 or less.
S = μ ₃ / σ ³ (1)
Where μ _{3 is} the third moment of amplitude probability density
σ: Standard deviation of amplitude probability density X-ray diffraction intensity of the ζ phase {(-604) + (820) + (-152)} face D = ───────────────── ──────── (2)
X-ray diffraction intensity of δ1 phase (330) plane

The galvannealed steel sheet according to claim 1, wherein iron-based electroplating is performed on the hot dip galvanizing.