JP4843973B2 - Hot-dip galvanized steel sheet with excellent clarity after painting - Google Patents
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- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 34
- 239000008397 galvanized steel Substances 0.000 title claims description 34
- 238000010422 painting Methods 0.000 title claims description 16
- 229910000831 Steel Inorganic materials 0.000 claims description 32
- 239000010959 steel Substances 0.000 claims description 32
- 238000005096 rolling process Methods 0.000 claims description 24
- 238000000465 moulding Methods 0.000 claims description 10
- 229910052745 lead Inorganic materials 0.000 claims description 7
- 229910052718 tin Inorganic materials 0.000 claims description 7
- 230000014509 gene expression Effects 0.000 claims description 4
- 238000012545 processing Methods 0.000 description 16
- 230000003746 surface roughness Effects 0.000 description 11
- 239000000463 material Substances 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 239000010960 cold rolled steel Substances 0.000 description 6
- 239000011248 coating agent Substances 0.000 description 5
- 238000000576 coating method Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000005246 galvanizing Methods 0.000 description 4
- 239000003973 paint Substances 0.000 description 4
- 238000007747 plating Methods 0.000 description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 3
- 239000013078 crystal Substances 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000010687 lubricating oil Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229920000298 Cellophane Polymers 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 229910001297 Zn alloy Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000003796 beauty Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
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Description
本発明は、自動車車体の外板等に用いられるプレス成形等の加工後においても塗装後鮮映性に優れる溶融亜鉛めっき鋼板に関するものである。 The present invention relates to a hot-dip galvanized steel sheet that is excellent in post-painting sharpness even after processing such as press forming used for an outer plate of an automobile body.
自動車車体に対する防錆性向上への要求から、溶融亜鉛めっき鋼板(ＧＩ)やそれを合金化処理した合金化溶融亜鉛めっき鋼板(ＧＡ)、電気亜鉛めっき鋼板(ＥＧ)等の表面処理鋼板が使用され始めて久しい。日本および海外の日系自動車メーカーにおいては、従来、自動車車体の外板に用いる表面処理鋼板として、溶接性と加工性に優れる合金化溶融亜鉛めっき鋼板が多く使用されてきた。しかし、近年では、防錆性をさらに向上する観点から、より厚目付けが可能な溶融亜鉛めっき鋼板が使用される傾向にある。 Surface-treated steel sheets such as hot-dip galvanized steel sheets (GI), alloyed hot-dip galvanized steel sheets (GA), and electrogalvanized steel sheets (EG) are used in order to improve the rust resistance of automobile bodies. It's been a long time since it began. In Japanese and overseas Japanese automobile manufacturers, conventionally, alloyed hot-dip galvanized steel sheets that are excellent in weldability and workability have been used as surface-treated steel sheets used for the outer plates of automobile bodies. However, in recent years, from the viewpoint of further improving the rust prevention property, a hot dip galvanized steel sheet that can be thickened tends to be used.
自動車車体の外板に用いられる鋼板には、プレス成形性に優れること、塗装後の鮮映性に優れることが求められる。鋼板の表面粗さが、プレス成形等の加工性に及ぼす影響としては、型かじり性があり、潤滑油を保持し加工性を向上する観点から、表面粗さの指標の１つである算術平均粗さＲaが、ある程度以上の値であることが必要とされている。一方、塗装後鮮映性は、塗膜に写った像の鮮映度を示すもので、自動車外観の美麗性だけでなく、塗装作業性や塗装コストの面からも重要視されている特性である。この塗装後鮮映性は、鋼板の算術平均粗さＲaよりはむしろ、他の表面粗さの指標である表面うねりＷcaと相関があり、塗装後鮮映性を改善するためには、表面うねりＷcaを所定値以下に制御する必要があることが知られている。したがって、自動車車体の外板に用いられる鋼板は、算術平均粗さＲaだけでなく、表面うねりＷcaも適正範囲に制御されたものであることが必要である。 A steel plate used for an outer plate of an automobile body is required to have excellent press formability and excellent sharpness after painting. The influence of the surface roughness of the steel sheet on workability such as press forming is die-squeezing, and is an arithmetic mean that is one of the indices of surface roughness from the viewpoint of maintaining lubricating oil and improving workability. Roughness Ra is required to be a value of a certain level or more. On the other hand, the sharpness after painting indicates the sharpness of the image on the coating film, and is not only the beauty of the appearance of the car, but also the characteristics that are regarded as important in terms of painting workability and painting cost. is there. This sharpness after painting has a correlation with the surface waviness Wca, which is another index of surface roughness, rather than the arithmetic average roughness Ra of the steel sheet. It is known that Wca needs to be controlled below a predetermined value. Therefore, the steel plate used for the outer plate of the automobile body needs to have not only the arithmetic average roughness Ra, but also the surface waviness Wca controlled within an appropriate range.
上記観点から、塗装後鮮映性に優れた溶融亜鉛めっき鋼板の製造技術が幾つか提案されている。例えば、特許文献１には、溶融亜鉛めっき鋼板の調質圧延におけるワークロールの平均粗さＲaおよびうねりＷcaを制御することによって、プレス成形性および鮮映性に優れた溶融亜鉛めっき鋼板を得る方法が開示されている。また、特許文献２には、溶融亜鉛めっき鋼板の表面に、固体粒子を混合した液体を噴射して、鋼板表面の平均粗さＲa、ＰＰＩおよびうねりＷcaを制御することにより、塗装後の鮮映性に優れる亜鉛めっき鋼板の製造方法が開示されている。また、特許文献３には、めっき素材の表面粗さＲz、亜鉛めっき浴中のAl濃度およびガスワイピング条件あるいはめっき後の冷却条件を制御することによりプレス成形性と外観に優れた溶融亜鉛めっき鋼板の製造方法が開示されている。
ところで、一般冷延鋼板や合金化溶融亜鉛めっき鋼板(ＧＡ)の場合には、鋼板表面の表面うねりＷcaが、プレス成形等の加工を施す前の素材段階で所定の基準を満たしていれば、加工後もその傾向が引き継がれて、塗装後鮮映性が優れているのが一般的である。しかしながら、自動車用外板に、溶融亜鉛めっき鋼板(ＧＩ)を使用するようになると、ＧＩは、加工前の素材段階で表面うねりＷcaが基準を満たしていても、プレス成形後にはＷcaが基準を外れて塗装後鮮映性が大きく劣化することがあり、加工に伴う鮮映性の変化挙動が、一般冷延鋼板やＧＡとは異なることが次第に明らかとなってきた。 By the way, in the case of a general cold-rolled steel sheet or an alloyed hot-dip galvanized steel sheet (GA), if the surface waviness Wca of the steel sheet surface satisfies a predetermined standard at the material stage before processing such as press molding, In general, the tendency is inherited even after processing, and the sharpness after painting is excellent. However, when hot-dip galvanized steel sheets (GI) are used for automotive outer panels, GI has a standard for Wca after press forming even if surface waviness Wca meets the standard at the material stage before processing. It has become clear that the sharpness after painting may be greatly deteriorated, and the change behavior of the sharpness due to processing is different from that of general cold-rolled steel sheets and GA.
しかしながら、上記特許文献１〜３の従来技術においては、このような加工に伴う溶融亜鉛めっき鋼板の塗装後鮮映性の変化については、何らの考慮もされておらず、未解決の問題として残されていた。そのため、ＧＩを自動車用外板として安定して用いるためには、上記鮮映性の改善が強く望まれていた。 However, in the prior arts of Patent Documents 1 to 3 above, no consideration is given to the change in the sharpness after coating of the hot dip galvanized steel sheet due to such processing, and it remains as an unsolved problem. It had been. Therefore, in order to stably use GI as an automobile outer plate, improvement of the above-described sharpness has been strongly desired.
そこで、本発明の目的は、プレス成形等の加工後においても鋼板の表面うねりＷcaが小さく、塗装後鮮映性に優れる溶融亜鉛めっき鋼板を提供することにある。 Accordingly, an object of the present invention is to provide a hot-dip galvanized steel sheet that has a small surface waviness Wca of the steel sheet even after processing such as press forming and has excellent post-painting clarity.
発明者らは、従来技術が抱える上記問題点の改善を目的として、溶融亜鉛めっき鋼板の製造条件に着目して鋭意検討を重ねた。その結果、プレス成形等の加工後の塗装後鮮映性を良好に維持する、すなわち、加工による表面うねりの変動ΔＷcaを小さく抑制するには、めっき後に行われる調質圧延(スキンパス)に、放電ダル加工を施したをロールを用いること、さらには、溶融亜鉛めっき層中に含まれる不純物成分を制御してスパングルを小さく制御することが有効であることを知見し、本発明を完成させた。 The inventors have made extensive studies focusing on the production conditions of the hot dip galvanized steel sheet for the purpose of improving the above-mentioned problems of the prior art. As a result, in order to maintain good post-paint clarity after processing such as press molding, that is, to suppress the fluctuation of surface waviness ΔWca due to processing, discharge to temper rolling (skin pass) performed after plating. It has been found that it is effective to use rolls that have been subjected to dull processing, and further to control the impurity components contained in the hot-dip galvanized layer to reduce spangles, thereby completing the present invention.
すなわち、本発明は、溶融亜鉛めっき後、放電ダル加工ロールを用いて調質圧延した溶融亜鉛めっき鋼板であって、該鋼板は、調質圧延後の表面うねりＷｃａが０．２５〜０．５μｍ、圧延方向に４％のプレス成形歪を付与したときの表面うねりの変動ΔＷｃａが０．１μｍ以下であり、亜鉛めっき層中のＰｂおよびＳｎが、
Ｐｂ≦６ｍａｓｓｐｐｍかつ（２Ｐｂ＋５Ｓｎ）≦２０ｍａｓｓｐｐｍ
の関係式を満たすよう含有することを特徴とする成形後の塗装後鮮映性に優れる溶融亜鉛めっき鋼板である。
That is, the present invention is a hot dip galvanized steel sheet tempered and rolled using a discharge dull processing roll after galvanizing, and the steel sheet has a surface waviness Wca after temper rolling of 0.25 to 0.5 μm. The surface waviness fluctuation ΔWca when a press molding strain of 4% is applied in the rolling direction is 0.1 μm or less, and Pb and Sn in the galvanized layer are
Pb ≦ 6 massppm and (2Pb + 5Sn) ≦ 20 massppm
The hot-dip galvanized steel sheet is excellent in post-painting sharpness after forming, which is contained so as to satisfy the relational expression of
本発明によれば、プレス成形後においても優れた塗装後鮮映性を有する溶融亜鉛めっき鋼板を提供することができるので、防錆性と美麗性が強く求められる自動車車体の外板にも好適に用いることができる。 According to the present invention, it is possible to provide a hot-dip galvanized steel sheet having excellent post-painting sharpness even after press molding. Therefore, it is also suitable for an outer panel of an automobile body that strongly requires rust prevention and aesthetics. Can be used.
本発明を開発する契機となった実験について説明する。
Ｃ：0.0008〜0.0022mass％の極低炭素Ti，Nb，Ｂ添加鋼の鋼スラブを素材とし、通常公知の方法で熱間圧延、酸洗した後、冷間圧延して板厚：0.7mmの冷延鋼帯とした。その後、連続溶融亜鉛めっきライン(ＣＧＬ)に通板して、目付量が(100ｇ/m2／100ｇ/m2)と(60ｇ/m2／60ｇ/m2)の２種の溶融亜鉛めっきを施した後、それぞれについてショットダル(ＳＤロール：目標Ｒa 0.7μm)と放電ダル加工したロール(ＥＤＴロール：目標Ｒa 2.3μm)の２種のロールを用いて、圧下率1.0％の調質圧延を行い、溶融亜鉛めっき鋼板を製造した。この溶融亜鉛めっき鋼板から供試材を採取し、そのままの原板と、その供試材に対して、圧延方向に４％、圧延方向に直角方向に２％のプレス歪を付与した後の鋼板について、算術平均粗さＲaおよび表面うねりＷcaを測定した。また、比較材として、目付量(45ｇ/m2／45ｇ/m2)の合金化溶融亜鉛めっき鋼板に、ショットダル(ＳＤロール：目標Ｒa 2.3μm)で圧下率1.0％の調質圧延を行った鋼板についても同様の調査を行った。
An experiment that triggered the development of the present invention will be described.
C: 0.0008-0.0022 mass% steel slab of extra low carbon Ti, Nb, B added steel as a raw material, after hot rolling and pickling by a generally known method, cold rolling and sheet thickness: 0.7 mm A cold-rolled steel strip was used. Then Tsuban a continuous galvanizing line (CGL), basis weight of 2 kinds of molten zinc plating (100g / m 2 / 100g / m 2) and (60g / m 2 / 60g / m 2) After application, temper rolling with a rolling reduction of 1.0% was performed using two types of rolls: shot dull (SD roll: target Ra 0.7 μm) and discharge dull processed roll (EDT roll: target Ra 2.3 μm). A hot dip galvanized steel sheet was manufactured. About the steel sheet after collecting the specimen from this hot dip galvanized steel sheet and applying the press strain of 4% in the rolling direction and 2% in the direction perpendicular to the rolling direction to the raw original sheet and the specimen. The arithmetic average roughness Ra and the surface waviness Wca were measured. Further, as a comparative material, the galvannealed steel sheet having a basis weight (45g / m 2 / 45g / m 2), shot dull: performing (SD roll target Ra 2.3 .mu.m) reduction ratio of 1.0% of temper rolling with A similar investigation was conducted on the steel plates.
結果を、図１に示した。図１から、溶融亜鉛めっき鋼板(ＧＩ)の場合には、調質圧延ロールの種類により、プレス歪付与による算術平均粗さＲaおよび表面うねりＷcaの変化挙動が異なり、ＳＤロールを用いた場合には、算術平均粗さＲa、表面うねりＷcaとも増大し、特に、表面うねりＷcaが大きく増加する傾向がある。これに対して、ＥＤＴロールを用いた場合には、いずれも変動が小さく、特に表面うねりＷcaの変動ΔＷcaは0.1μm以下に抑えられていることがわかる。一方、合金化溶融亜鉛めっき鋼板(ＧＡ)では、歪付与による表面粗さＲa、表面うねりＷcaはほとんど認められず、従来の知見があらためて確認された。 The results are shown in FIG. From FIG. 1, in the case of hot-dip galvanized steel sheet (GI), the change behavior of arithmetic average roughness Ra and surface waviness Wca due to the application of press strain differs depending on the type of temper rolling roll. The arithmetic mean roughness Ra and the surface waviness Wca increase, and in particular, the surface waviness Wca tends to increase greatly. On the other hand, when the EDT roll is used, it can be seen that the fluctuation is small, and especially the fluctuation ΔWca of the surface waviness Wca is suppressed to 0.1 μm or less. On the other hand, in the alloyed hot-dip galvanized steel sheet (GA), the surface roughness Ra and the surface waviness Wca due to the strain were hardly recognized, and the conventional knowledge was reconfirmed.
上記の結果から、成形後の塗装後鮮映性に優れる溶融亜鉛めっき鋼板(ＧＩ)を製造するためには、調質圧延ロールとして、放電ダル加工したＥＤＴロールを用いる必要があることがわかった。ＥＤＴロールを用いることにより、成形歪付与による表面うねりＷcaの増大が抑制される原因については、まだ、十分に解明されているわけではないが、ＥＤＴロール特有のロール面全体の均一な粗さ(ロール面の微視的山および谷)の実現により、鋼板に転写されるテクスチャ(山および谷)が均一となり、その結果、プレス成形が施されても、鋼板表面の均一なテクスチャが維持されるためと考えられる。つまり、ＳＤロールの場合は、鋼板に転写されるテクスチャが不均一であるため、プレス成形されると山と谷の落差がより拡大し、Ｗcaの増大に繋がるものと考えられる。また、成形歪付与によるＧＩとＧＡの表面粗さ変化の違いは、ＧＡは、鋼板表面に存在するFe−Zn合金層が硬質で脆弱であるため、歪が付与された場合には、合金層に多数のミクロクラックが導入される結果、表面粗さの変化が小さく抑えられるのに対して、ＧＩでは、鋼板表面に存在するZn層が軟質でかつ厚いため、歪付与によって、Zn層が塑性流動を起こす結果、算術平均粗さＲa、表面うねりＷcaがともに増大するものと考えている。 From the above results, it was found that in order to produce a hot-dip galvanized steel sheet (GI) having excellent post-painting clarity after forming, it is necessary to use an EDT roll that has been subjected to discharge dull processing as a temper rolling roll. . Although the cause of the increase in surface waviness Wca due to the application of molding strain by using the EDT roll is not yet fully elucidated, the uniform roughness of the entire roll surface unique to the EDT roll ( By realizing microscopic peaks and valleys on the roll surface, the texture (peaks and valleys) transferred to the steel sheet becomes uniform, and as a result, the uniform texture of the steel sheet surface is maintained even when press forming is performed. This is probably because of this. In other words, in the case of the SD roll, the texture transferred to the steel sheet is non-uniform, so that when the press roll is formed, the drop between the peaks and valleys is further expanded, leading to an increase in Wca. In addition, the difference in surface roughness between GI and GA due to forming strain is that GA is an alloy layer when strain is applied because the Fe-Zn alloy layer existing on the steel sheet surface is hard and brittle. As a result of the introduction of a large number of microcracks, the change in surface roughness is suppressed to a small level, whereas in GI, the Zn layer present on the steel sheet surface is soft and thick. As a result of the flow, both the arithmetic average roughness Ra and the surface waviness Wca are considered to increase.
上記知見から、調質圧延ロールとして、ＥＤＴロールを用いれば、成形加工による表面うねりＷcaの変動を小さく抑制できることが判明した。しかし、目標とする塗装後鮮映性を達成するためには、表面うねりＷca自体をも小さくする制御する必要がある。そこで、表面うねりＷcaの値を小さくする方策について検討した結果、亜鉛めっき層の結晶粒の大きさ、いわゆるスパングルを小さく制御することが有効であり、そのためには、不純物として溶融亜鉛めっき層中に含まれるPbおよびSnの含有量を、適正範囲に制御する必要があることを見出した。本発明は、上記知見に基き開発したものである。 From the above findings, it has been found that if an EDT roll is used as the temper rolling roll, the fluctuation of the surface waviness Wca due to the forming process can be reduced. However, in order to achieve the target post-paint clarity, it is necessary to control to reduce the surface waviness Wca itself. Therefore, as a result of examining measures to reduce the value of the surface waviness Wca, it is effective to control the size of crystal grains of the galvanized layer, that is, so-called spangles. It was found that the contents of contained Pb and Sn need to be controlled within an appropriate range. The present invention has been developed based on the above findings.
次に、本発明の鋼板について説明する。
本発明に係る溶融亜鉛めっき鋼板は、溶融亜鉛めっき後、放電ダル加工ロール(ＥＤＴロール)を用いて調質圧延を施したものであることが必要である。上記に説明したように、従来のショットダルロール(ＳＤロール)では、成形加工後の表面うねりＷcaが増大し、良好な塗装後鮮映性を確保できないのに対して、放電ダル加工ロールを用いて調質圧延を施した場合には、成形加工後の表面うねりの変動ΔＷcaを0.1μm以下に抑制することができるからである。なお、本発明の溶融亜鉛めっき鋼板の原板となる冷延鋼板は、通常公知の方法で製造されたものであればよく、成分組成や製造条件については問わない。
Next, the steel plate of the present invention will be described.
The hot dip galvanized steel sheet according to the present invention needs to be subjected to temper rolling using a discharge dull processing roll (EDT roll) after hot dip galvanization. As explained above, in the conventional shot dull roll (SD roll), the surface waviness Wca after the molding process is increased, and a good post-painting clarity cannot be ensured. This is because when the temper rolling is performed, the fluctuation ΔWca of the surface waviness after the forming process can be suppressed to 0.1 μm or less. In addition, the cold-rolled steel plate used as the original plate of the hot dip galvanized steel plate of the present invention may be any material as long as it is produced by a generally known method, and the component composition and production conditions are not questioned.
調質圧延を施した後の溶融亜鉛めっき鋼板は、表面うねりＷcaが0.25〜0.5μmの範囲に制御されたものであることが必要である。それは、塗装後鮮映性が良好であるためには、表面うねりＷcaが0.6μm以下であることが好ましく、上述した成形歪による表面うねりの変動ΔＷca(≦0.1μm)を考慮した場合には、成形前の素材の段階で、Ｗca：0.5μm以下であることが必要となる。一方、表面うねりＷcaを小さくするには、使用する調質圧延ロールの表面粗さを低減させる必要があり、そのためには、放電ダル加工速度を低くする必要があり、ロール加工時間が長時間化する。一方、たとえそのロールを実現したとしても、ＣＧＬの調質圧延に適用した場合には、比較的早期に鋼板表面の平均粗さが低下し、自動車外板として所望されるＲaスペックの下限割れを起こすため、ロール寿命が短くなる。すなわち、ロール加工時間の長時間化とロール寿命の短時間化という両方のデメリットがある。これらの問題を回避するためには、現実的に得られる鋼板うねりＷcaは、0.25μm以上であること必要である。好ましくは、Ｗcaは、0.3〜0.45μmの範囲である。 The hot-dip galvanized steel sheet after temper rolling needs to have a surface waviness Wca controlled in the range of 0.25 to 0.5 μm. It is preferable that the surface waviness Wca is 0.6 μm or less in order to have good post-painting sharpness. In consideration of the above-described surface waviness variation ΔWca (≦ 0.1 μm) due to molding distortion, At the material stage before molding, Wca: 0.5 μm or less is required. On the other hand, in order to reduce the surface waviness Wca, it is necessary to reduce the surface roughness of the temper rolling roll to be used. For that purpose, it is necessary to reduce the discharge dull processing speed, and the roll processing time is prolonged. To do. On the other hand, even if the roll is realized, when applied to temper rolling of CGL, the average roughness of the steel sheet surface decreases relatively early, and the lower limit crack of the Ra spec desired as an automobile outer sheet is reduced. This causes the roll life to be shortened. That is, there are disadvantages of both a long roll processing time and a short roll life. In order to avoid these problems, the steel sheet waviness Wca that can be actually obtained needs to be 0.25 μm or more. Preferably, Wca is in the range of 0.3 to 0.45 μm.
なお、本発明の溶融亜鉛めっき鋼板は、表面うねりＷcaのほかに、成形性を確保するために、算術平均粗さＲaを適正な範囲に制御することが好ましく、例えば、Ｒa：0.4〜1.4μm程度に規制することが好ましい。算術平均粗さＲaが0.4μm未満では、成形に用いる潤滑油の保油性が小さいため型かじりが発生しやすく、また、鋼板どうしの摩擦により表面疵が発生し易いからである。一方、算術平均粗さＲaが1.4μmを超えると、Ｒaそのものが高いために、塗装面の荒れが目立ち、自動車外板に用いる素材鋼板として適さなくなるからである。より好ましい表面粗さＲaの範囲は、0.5〜1.2μmである。 In addition to the surface waviness Wca, the hot dip galvanized steel sheet of the present invention preferably has an arithmetic average roughness Ra controlled within an appropriate range in order to ensure formability. For example, Ra: 0.4 to 1.4 μm It is preferable to regulate to the extent. When the arithmetic average roughness Ra is less than 0.4 μm, the lubricating oil used for forming has a small oil retaining property, so that mold galling is likely to occur, and surface flaws are likely to occur due to friction between the steel plates. On the other hand, when the arithmetic average roughness Ra exceeds 1.4 μm, Ra itself is high, so that the roughness of the painted surface is conspicuous and it is not suitable as a material steel plate used for an automobile outer plate. A more preferable range of the surface roughness Ra is 0.5 to 1.2 μm.
本発明の鋼板は、上述したように、調質圧延後の表面うねりＷcaを小さく制御する必要があり、そのためには、亜鉛めっき層の結晶粒の大きさ(スパングル)を小さく制御することが好ましい。特に、表面うねりＷcaの値を0.5μm以下とするためには、スパングルの大きさは1.2mm以下、さらにＷcaの値を0.3μm以下とするためには、スパングルの大きさは1.0mm以下に制御することが好ましい。 As described above, the steel sheet of the present invention needs to control the surface waviness Wca after temper rolling to be small, and for that purpose, it is preferable to control the crystal grain size (spangle) of the galvanized layer to be small. . In particular, to reduce the surface waviness Wca value to 0.5 μm or less, the spangle size is controlled to 1.2 mm or less. To further reduce the Wca value to 0.3 μm or less, the spangle size is controlled to 1.0 mm or less. It is preferable to do.
上述したように、スパングルの大きさは、亜鉛めっき層中に不純物として含まれるPbおよびSnによって大きく影響され、上記1.0mm以下のスパングルを得るためには、亜鉛めっき層中に含まれるPbおよびSnは、Pb≦６massppm以下かつ(２Pb＋５Sn)≦20massppmの関係式を満たすよう含有することが好ましい。というのは、上記関係式のいずれかを満たさない場合には、スパングルが粗大化し、表面うねりＷcaの値を0.3μm以下に制御することができなくなる虞があるからである。なお、亜鉛めっき層中のPbおよびSnの含有量を、上記範囲に制御するためには、溶融亜鉛めっき浴中のPbおよびSnの濃度を、それぞれPb：10massppm以下、Sn：５massppm以下に管理することが好ましい。 As described above, the size of spangle is greatly influenced by Pb and Sn contained as impurities in the galvanized layer, and in order to obtain the spangle of 1.0 mm or less, Pb and Sn contained in the galvanized layer are used. Is preferably contained so as to satisfy the relational expression of Pb ≦ 6 massppm or less and (2Pb + 5Sn) ≦ 20 massppm. This is because if one of the above relational expressions is not satisfied, the spangle becomes coarse and the value of the surface waviness Wca cannot be controlled to 0.3 μm or less. In order to control the contents of Pb and Sn in the galvanized layer to the above ranges, the concentrations of Pb and Sn in the hot dip galvanizing bath are respectively controlled to Pb: 10 massppm or less and Sn: 5 massppm or less. It is preferable.
表１に示す成分組成を有する鋼スラブを連続鋳造して製造し、その後、通常公知の方法で熱間圧延、酸洗した後、冷間圧延して板厚：0.7mmの冷延鋼帯とした。この冷延鋼帯を、表２に示す条件で、溶融亜鉛めっきした後、調質圧延を行い、各種の溶融亜鉛めっき鋼板を製造した。これらの溶融亜鉛めっき鋼板から供試材を採取して、調質圧延ままの状態における表面粗さ(算術平均粗さＲa、表面うねりＷca)を測定した。さらに、上記供試材に圧延方向に対して４％、圧延直角方向に２％のプレス成形を行って歪を付与した後、再度、表面粗さ(算術平均粗さＲa、表面うねりＷca)を測定すると共に、Ｗcaの成形歪付与前後の変動(ΔＷca)を求めた。また、上記プレス成形歪を付与した後の鋼板に、ＥＤ塗装を行い、この鋼板上にセロハンテープを貼り付けた後、テープ上から鮮明度光沢度計(ＰＧＤ計、日本色彩研究所製)を用いて、塗装後鮮映性を評価し、ＰＧＤ測定値が0.3以上を「合格」、0.3未満を「不合格」とした。 A steel slab having the composition shown in Table 1 is continuously cast and manufactured. Thereafter, the steel slab is usually hot-rolled and pickled by a known method, and then cold-rolled to obtain a cold-rolled steel strip having a thickness of 0.7 mm. did. The cold-rolled steel strip was hot-dip galvanized under the conditions shown in Table 2, and then temper-rolled to produce various hot-dip galvanized steel sheets. Sample materials were collected from these hot-dip galvanized steel sheets, and the surface roughness (arithmetic average roughness Ra, surface waviness Wca) in the state of temper rolling was measured. Further, after applying strain to the above-mentioned specimen by press forming at 4% with respect to the rolling direction and 2% in the direction perpendicular to the rolling direction, surface roughness (arithmetic average roughness Ra, surface waviness Wca) is again applied. While measuring, the fluctuation | variation ((DELTA) Wca) before and behind the shaping | molding distortion provision of Wca was calculated | required. In addition, ED coating is applied to the steel plate after the press-forming strain is applied, and a cellophane tape is applied onto the steel plate, and then a sharpness gloss meter (PGD meter, manufactured by Nippon Color Research Laboratory) is applied from above the tape. Using this, the sharpness after coating was evaluated, and a PGD measurement value of 0.3 or more was determined to be “pass”, and less than 0.3 was determined to be “fail”.
上記測定の結果を、表２中に併記して示した。この結果から、本発明に適合する溶融亜鉛めっき鋼板は、プレス成形後においても、優れた塗装後鮮映性を維持していることがわかる。 The results of the above measurements are shown together in Table 2. From this result, it can be seen that the hot-dip galvanized steel sheet suitable for the present invention maintains excellent post-paint clarity even after press forming.
Claims (1)
Ｐｂ≦６ｍａｓｓｐｐｍかつ（２Ｐｂ＋５Ｓｎ）≦２０ｍａｓｓｐｐｍ
の関係式を満たすよう含有することを特徴とする成形後の塗装後鮮映性に優れる溶融亜鉛めっき鋼板。 A hot-dip galvanized steel sheet that has been temper- rolled using an electric discharge dulling roll after hot-dip galvanization, the steel sheet having a surface waviness Wca after temper rolling of 0.25 to 0.5 μm, and 4% in the rolling direction. The fluctuation ΔWca of the surface waviness when the press molding strain is applied is 0.1 μm or less, and Pb and Sn in the galvanized layer are
Pb ≦ 6 massppm and (2Pb + 5Sn) ≦ 20 massppm
A hot-dip galvanized steel sheet having excellent post-painting sharpness after forming, which is contained so as to satisfy the relational expression:
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