JP2007169696A - Galvannealed steel superior in appearance quality, and manufacturing method therefor - Google Patents
Galvannealed steel superior in appearance quality, and manufacturing method therefor Download PDFInfo
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本発明は，外観品位に優れる合金化溶融亜鉛めっき鋼およびその製造方法に関するものである。より詳しくは，主として，高強度鋼板を基材とした合金化溶融亜鉛めっき鋼において，そのめっき後の外観が従来の合金化溶融亜鉛めっき鋼板よりも均一美麗で，また，塗装後の外観にも優れ，自動車用等に用いることができる，外観品位に優れる合金化溶融亜鉛めっき鋼とその製造方法に関するものである。 The present invention relates to an alloyed hot-dip galvanized steel excellent in appearance quality and a method for producing the same. More specifically, mainly in alloyed hot-dip galvanized steel based on high-strength steel sheets, the appearance after plating is more uniform and beautiful than that of conventional alloyed hot-dip galvanized steel sheets. The present invention relates to an alloyed hot-dip galvanized steel excellent in appearance quality that can be used for automobiles and the like, and a method for producing the same.
合金化溶融亜鉛めっき鋼は，溶接性や塗装性，塗装後耐食性などに優れることから，自動車，家電製品，建材等に多用されている。この合金化溶融亜鉛めっき鋼は，鋼を溶融亜鉛めっきした後，加熱処理し，鋼中のＦｅとめっき中のＺｎを拡散させ，合金化反応を生じさせることで鋼材表面に鉄−亜鉛合金層を形成させたものである。この合金化反応は，鋼の結晶粒界から優先的に生じると言われるが，粒界に偏析しやすい元素が多く含まれる場合，局所的にＦｅ，Ｚｎの拡散が阻害されるため合金化反応が不均一となり，外観にむらが発生する。このむらは，機械的性質や溶接性などに影響を与えるものではないが，外観不良として拒絶する消費者が多い。特に，近年，鋼の高強度化が進みPを多く含む鋼においてはむらが発生し易く，問題となっている。この原因は，Ｐが鋼加熱時に鋼材表面，粒界に不均一に濃化して，めっき合金化時におけるＦｅとＺｎの拡散を阻害し，局所的なＦｅとＺｎの合金化反応の速度差をもたらすことで，めっき厚み差が生じさせるからと考えられる。 Alloyed hot-dip galvanized steel is widely used in automobiles, home appliances, and building materials because of its excellent weldability, paintability, and post-paint corrosion resistance. This alloyed hot-dip galvanized steel is a hot-dip galvanized steel, which is then heat-treated to diffuse Fe in the steel and Zn in the plating to cause an alloying reaction, thereby causing an iron-zinc alloy layer on the steel surface. Is formed. This alloying reaction is said to occur preferentially from the grain boundaries of the steel, but when there are many segregating elements in the grain boundaries, the diffusion of Fe and Zn is locally inhibited, so the alloying reaction Becomes non-uniform and the appearance is uneven. This unevenness does not affect the mechanical properties or weldability, but many consumers reject it as a poor appearance. In particular, in recent years, the strength of steel has increased and steel containing a large amount of P tends to cause unevenness, which is a problem. This is because P is unevenly concentrated on the steel surface and grain boundaries when the steel is heated, which inhibits the diffusion of Fe and Zn during plating alloying, and the difference in the local alloying reaction rate of Fe and Zn. This is thought to cause a difference in plating thickness.
このため，外観品位に優れる合金化溶融亜鉛めっき鋼が種々検討されている。例えば，(特許文献１）では，焼鈍した鋼板をめっきする前にＦｅ，Ｎｉ，Ｃｏ，Ｃｕなどの金属被覆層を形成する方法が開示されている。また，（特許文献２）では，めっき浴中のＡｌ濃度を鋼中のＰとＴｉの濃度によって規定する方法が開示されている。さらに，（特許文献３）では，冷延焼鈍後の鋼板表面のX線回折からの｛２００}面と｛２２２｝面からの回折X線強度比，I（２００）／I（２２２）を０．１７未満とする鋼が開示されている。
さらにまた，（特許文献４）では，鋼中にＣｕを含ませる方法が開示されている。
For this reason, various types of alloyed hot-dip galvanized steel with excellent appearance quality have been studied. For example, (Patent Document 1) discloses a method of forming a metal coating layer of Fe, Ni, Co, Cu or the like before plating an annealed steel sheet. (Patent Document 2) discloses a method of defining the Al concentration in the plating bath by the concentrations of P and Ti in the steel. Furthermore, in (Patent Document 3), the diffraction X-ray intensity ratio, I (200) / I (222), from the {200} plane and {222} plane from the X-ray diffraction of the steel sheet surface after cold rolling annealing is 0. Steels of less than .17 are disclosed.
Furthermore, in (patent document 4), the method of including Cu in steel is disclosed.
しかし，特許文献１の方法では設備の増加を伴うためにコスト増，工程増となり，実用化は容易ではない。また，特許文献２の方法は,鋼中のＰやＴｉの濃度は鋼種によって異なるため，鋼種に応じて浴中のＡｌ濃度を制御することは困難であり，実現性は低い。さらに特許文献３の鋼は，結晶方位を制御するのは容易でなく，また，対象としている鋼材のＰ含有率が０．０２５％以下であるため，近年のＰを多く含む高強度鋼板には適用できない。さらにまた，特許文献４の方法は，材質への影響が懸念され，汎用的な方法ではない。
However, since the method of
以上のように，外観品位に優れる合金化溶融亜鉛めっき鋼として種々提案されているが，設備導入，工程増などの問題があるため実現が困難で，またＰを多量に含むような高強度鋼に適用できるものでもない。そこで，本発明は，このような設備増や工程増といった問題を解決し，Ｐを多量に含む鋼であっても，外観品位に優れる合金化溶融亜鉛めっき鋼，およびその製造方法を提供することを目的としている。 As described above, various types of alloyed hot-dip galvanized steels with excellent appearance quality have been proposed, but they are difficult to realize due to problems such as equipment installation and increased process, and high-strength steels containing a large amount of P. It is also not applicable to. Accordingly, the present invention provides an alloyed hot-dip galvanized steel excellent in appearance quality even for steel containing a large amount of P, and a method for producing the same, in order to solve the problems such as an increase in equipment and processes. It is an object.
上記課題を解決するために，本発明者らは，Ｐを０．０２％〜０．２％含む鋼を基材とした合金化溶融亜鉛めっき鋼で，外観にむらが発生した鋼，外観にむらが発生しなかった鋼について，その鉄−亜鉛合金被覆中の濃化元素をＧＤＳで詳細に調べた。その結果，外観にむらが発生した鋼はめっき中のＰの濃化が大きいことが分かった。一方，外観にむらが発生しなかった鋼はめっき中のＰの濃化が小さく，さらに，ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度と，鉄−亜鉛合金被覆中のＦｅとＺｎの積分強度の和の比，Ｉ（Ｐ）／Ｉ（Ｆｅ＋Ｚｎ）が０．０２５以下であることを見出し，発明に至った。 In order to solve the above-mentioned problems, the inventors of the present invention are alloyed hot-dip galvanized steel based on steel containing 0.02% to 0.2% P. For the steel with no unevenness, the concentrated elements in the iron-zinc alloy coating were examined in detail by GDS. As a result, it was found that steel with uneven appearance had a large concentration of P during plating. On the other hand, steel with no appearance irregularity has a small P concentration during plating, and further, the integrated strength of P in the iron-zinc alloy coating by GDS, and the Fe and Zn in the iron-zinc alloy coating. It was found that the ratio of the sums of integral intensities, I (P) / I (Fe + Zn), was 0.025 or less, and the present invention was reached.
すなわち，本発明は次の通りである。
（１）質量％で，
Ｃ；０．０１％以下，
Ｓｉ；０．２％以下，
Ｍｎ；２％以下，
Ｐ；０．０２〜０．２％，
Ｓ；０．０３％以下，
Ａｌ；０．００５〜０．１％，
Ｔｉ；０．００１〜０．０５％，
Ｎｂ；０．００１〜０．０５％，
を含有し，残部がＦｅおよび不可避的不純物からなる鋼材の表面に，鉄−亜鉛合金被覆を有する合金化溶融亜鉛めっき鋼において，ＧＤＳによる鉄−亜鉛合金被覆中のＰと（Ｆｅ＋Ｚｎ）の積分強度比，Ｉ（Ｐ）／Ｉ（Ｆｅ＋Ｚｎ）が０．０２５以下であることを特徴とする外観品位に優れる合金化溶融亜鉛めっき鋼。
（２）前記，鉄−亜鉛合金被覆の付着量の偏差が±７ｇ／ｍ２以内であることを特徴とする，（１）に記載の外観品位に優れる合金化溶融亜鉛めっき鋼。
（３）前記，鉄−亜鉛合金被覆のΓ層厚みが１μｍ以下であることを特徴とする，（１）または（２）に記載の外観品位に優れる合金化溶融亜鉛めっき鋼。
（４）質量％で，
Ｃ；０．０１％以下，
Ｓｉ；０．２％以下，
Ｍｎ；２％以下，
Ｐ；０．０２〜０．２％，
Ｓ；０．０３％以下，
Ａｌ；０．００５〜０．１％，
Ｔｉ；０．００１〜０．０５％，
Ｎｂ；０．００１〜０．０５％，
を含有し，残部がＦｅおよび不可避的不純物からなる低炭素鋼スラブを熱間圧延した後，酸洗し，さらに冷間圧延，焼鈍，溶融亜鉛めっき，加熱合金化処理を施して，合金化溶融亜鉛めっき鋼とする合金化溶融亜鉛めっき鋼の製造方法において，熱間圧延後のコイルの捲取温度を７５０℃以上とし，さらにその後，巻き取ったコイルの最外層部の表面温度が５００℃以下となるまで空冷することを特徴とする外観品位に優れる合金化溶融亜鉛めっき鋼の製造方法。
That is, the present invention is as follows.
(1) In mass%,
C; 0.01% or less,
Si: 0.2% or less,
Mn: 2% or less,
P; 0.02 to 0.2%,
S: 0.03% or less,
Al; 0.005 to 0.1%,
Ti; 0.001 to 0.05%,
Nb; 0.001 to 0.05%,
Integral strength of P and (Fe + Zn) in iron-zinc alloy coating by GDS in alloyed hot-dip galvanized steel with iron-zinc alloy coating on the surface of steel material containing Fe and unavoidable impurities An alloyed hot-dip galvanized steel excellent in appearance quality, characterized in that the ratio I (P) / I (Fe + Zn) is 0.025 or less.
(2) The alloyed hot-dip galvanized steel having excellent appearance quality according to (1), wherein the deviation of the adhesion amount of the iron-zinc alloy coating is within ± 7 g / m 2 .
(3) The galvannealed steel having excellent appearance quality according to (1) or (2), wherein the thickness of the Γ layer of the iron-zinc alloy coating is 1 μm or less.
(4) In mass%,
C; 0.01% or less,
Si: 0.2% or less,
Mn: 2% or less,
P; 0.02 to 0.2%,
S: 0.03% or less,
Al; 0.005 to 0.1%,
Ti; 0.001 to 0.05%,
Nb; 0.001 to 0.05%,
Hot-rolled low-carbon steel slab containing Fe and the balance of inevitable impurities, pickling, cold rolling, annealing, hot dip galvanizing, heat alloying treatment, alloying and melting In the manufacturing method of alloyed hot-dip galvanized steel to be galvanized steel, the coiling temperature of the coil after hot rolling is set to 750 ° C. or higher, and then the surface temperature of the outermost layer portion of the coil wound is 500 ° C. or lower. A method for producing an alloyed hot-dip galvanized steel excellent in appearance quality, characterized by air cooling until
本発明の合金化溶融亜鉛めっき鋼，また本発明の製造法を経た合金化溶融亜鉛めっき鋼は，外観品位に優れ，また，摺動性，密着性にも優れる。このため，自動車や家電製品，建材等に用いることができ，産業上の価値は極めて大きい。 The alloyed hot-dip galvanized steel of the present invention and the alloyed hot-dip galvanized steel that has undergone the manufacturing method of the present invention are excellent in appearance quality, slidability, and adhesion. For this reason, it can be used for automobiles, home appliances, building materials, etc., and its industrial value is extremely high.
以下，本発明を詳細に説明する。
まず，本発明の要点である，鉄−亜鉛合金被覆中のＰ含有率について説明する。Ｐは鋼の強度増加を目的に鋼中に添加される。また，Ｐは合金化加熱時にめっき中に拡散，濃化するが，このめっき中のＰ自体も外観に影響を与える元素である。発明者らが，合金化加熱後のめっき中のＰ量とめっき外観との関係を詳細に調査した結果，ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度Ｉ（Ｐ）が，（Ｆｅ＋Ｚｎ）の積分強度Ｉ（Ｆｅ＋Ｚｎ）の０．０２５以下である場合，外観が良好で，一方，ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度Ｉ（Ｐ）が，（Ｆｅ＋Ｚｎ）の積分強度Ｉ（Ｆｅ＋Ｚｎ）の０．０２５より大きい場合，外観が不良となることを見出した。この理由は定かではないが，ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度Ｉ（Ｐ）が，（Ｆｅ＋Ｚｎ）の積分強度Ｉ（Ｆｅ＋Ｚｎ）の０．０２５以下である場合，めっき中のＰがＺｎ，Ｆｅの合金化反応速度を均一化させる効果があると考えられる。好ましくは，ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度Ｉ（Ｐ）が，（Ｆｅ＋Ｚｎ）の積分強度Ｉ（Ｆｅ＋Ｚｎ）の０．０２０以下，より好ましくは，０．０１５以下である。なお，ここで言う，ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度Ｉ（Ｐ）とは，株式会社リガク製ＧＤＳ（高周波グロー放電発光分析装置），ＧＤＡ７５０を用い，分析径２．５ｍｍで鉄−亜鉛合金被覆深さ方向の元素分布を測定した際の，鉄−亜鉛合金被覆中のＰの強度を積分した値である。また，ここで言う鉄−亜鉛合金被覆とは，ＧＤＳによる測定でＦｅの強度が増加しなくなった深さまでと定義する。ＧＤＳによる鉄−亜鉛合金被覆中のＰの積分強度Ｉ（Ｐ）を，（Ｆｅ＋Ｚｎ）の積分強度Ｉ（Ｆｅ＋Ｚｎ）の０．０２５以下とするには，めっき前の表面のＰ濃度を低減させておくことが望ましい。このためには，熱延時の捲取温度を高くする，また巻き取ったコイルを空冷する，めっき前の鋼を酸洗する，あるいは鋼材表面を研削する等の処理が有効である。
The present invention will be described in detail below.
First, the P content in the iron-zinc alloy coating, which is the main point of the present invention, will be described. P is added to the steel for the purpose of increasing the strength of the steel. P diffuses and concentrates during plating during alloying heating, and P itself during plating is an element that affects the appearance. As a result of detailed investigations by the inventors on the relationship between the amount of P in the plating after the alloying heating and the plating appearance, the integrated strength I (P) of P in the iron-zinc alloy coating by GDS is (Fe + Zn). When the integrated strength I (Fe + Zn) is 0.025 or less, the appearance is good. On the other hand, the integrated strength I (P) of P in the iron-zinc alloy coating by GDS is the integrated strength I of (Fe + Zn) ( It has been found that the appearance is poor when it is larger than 0.025 of (Fe + Zn). The reason for this is not clear, but when the integral strength I (P) of P in the iron-zinc alloy coating by GDS is 0.025 or less of the integral strength I (Fe + Zn) of (Fe + Zn), P Is considered to have the effect of uniforming the alloying reaction rate of Zn and Fe. Preferably, the integrated intensity I (P) of P in the iron-zinc alloy coating by GDS is 0.020 or less, more preferably 0.015 or less of the integrated intensity I (Fe + Zn) of (Fe + Zn). The integral intensity I (P) of P in the iron-zinc alloy coating by GDS is GDS (High Frequency Glow Discharge Emission Analyzer), GDA750 manufactured by Rigaku Corporation, and the analysis diameter is 2.5 mm. It is a value obtained by integrating the strength of P in the iron-zinc alloy coating when the element distribution in the depth direction of the iron-zinc alloy coating is measured. Further, the iron-zinc alloy coating referred to here is defined as the depth at which the strength of Fe does not increase as measured by GDS. In order to make the integral strength I (P) of P in the iron-zinc alloy coating by GDS 0.025 or less of the integral strength I (Fe + Zn) of (Fe + Zn), the P concentration on the surface before plating is reduced. It is desirable to keep it. For this purpose, it is effective to increase the coiling temperature during hot rolling, to cool the coiled coil, to pickle the steel before plating, or to grind the steel surface.
次に，本発明の合金化溶融亜鉛めっき鋼の鋼成分の限定理由について説明する。なお，各鋼成分において％は何れも質量％である。
Ｃ；０．０１％以下
Ｃは鋼の強化に必要な元素である。しかし，Ｃ量が０．０１％を超えると脆化しやすくなるため，Ｃ量は０．０１％以下とする。
Ｓｉ；０．２％以下
Ｓｉは鋼の強化，脱酸の効果を有する元素である。しかし，過剰に添加すると脆化しやすくなる。また，溶融亜鉛めっき時にめっきの濡れ性を阻害し，まためっき密着性も劣化させる。このため，Ｓｉは０．２％以下とする。
Ｍｎ；２％以下
Ｍｎも鋼の強化，脱酸の効果を有する元素である。しかし，過剰に添加すると脆化しやすくなる。また，溶融亜鉛めっき時にめっきの濡れ性を阻害し，まためっき密着性も劣化させる。このため，Ｍｎは２％以下とする。
Ｐ；０．０２〜０．２％
Ｐは鋼の強化に必要な元素である。しかし，過剰に添加すると脆化しやすくなる。また，溶融亜鉛めっき後の合金化処理性を劣化させる。このため，Ｐは，０．０２〜０．２％とする。尚，鋼板の強度と脆化のバランスを考慮すると，Ｐは，０．０３〜０．０５％とすることが好ましい。
Ｓ；０．０３％以下
Ｓは不純物であり，加工性や熱間脆性を劣化させるため少ないほうが望ましい。このためＳは０．０３％以下とする。
Ａｌ；０．００５〜０．１％
Ａｌは鋼中のＮとの親和力が強く，固溶しているＮを析出物として固定し加工性を向上させる効果がある。また，脱酸の効果がある。しかし，多すぎると逆に加工性を劣化させる。このためＡｌは０．００５〜０．１％とする。
Ｔｉ；０．００１〜０．０５％
ＴｉはＣ，Ｎを固定し，鋼の加工性を向上させる効果がある。しかし，多すぎると逆に加工性を劣化させる。このため，Ｔｉは０．００１〜０．０５％とする。
Ｎｂ；０．００１〜０．０５％
ＮｂはＣを固定し，鋼の加工性を向上させる効果がある。しかし，多すぎると逆に加工性を劣化させる。このため，Ｎｂは０．００１〜０．０５％とする。
Next, the reasons for limiting the steel components of the galvannealed steel of the present invention will be described. In each steel component,% is mass%.
C: 0.01% or less C is an element necessary for strengthening steel. However, if the C content exceeds 0.01%, embrittlement tends to occur, so the C content is set to 0.01% or less.
Si: 0.2% or less Si is an element having the effect of strengthening and deoxidizing steel. However, it becomes brittle when added in excess. In addition, the wettability of the plating is hindered during hot dip galvanizing, and the plating adhesion is also deteriorated. For this reason, Si is made 0.2% or less.
Mn: 2% or less Mn is an element having the effect of strengthening and deoxidizing steel. However, it becomes brittle when added in excess. In addition, the wettability of the plating is hindered during hot dip galvanizing, and the plating adhesion is also deteriorated. For this reason, Mn is made 2% or less.
P: 0.02 to 0.2%
P is an element necessary for strengthening steel. However, it becomes brittle when added in excess. In addition, the alloying processability after hot dip galvanizing is deteriorated. For this reason, P is made 0.02 to 0.2%. In consideration of the balance between strength and embrittlement of the steel sheet, P is preferably 0.03 to 0.05%.
S: 0.03% or less S is an impurity, and it is desirable that S is less because it degrades workability and hot brittleness. For this reason, S is made 0.03% or less.
Al; 0.005 to 0.1%
Al has a strong affinity with N in the steel, and has an effect of improving the workability by fixing the dissolved N as a precipitate. It also has a deoxidizing effect. However, if the amount is too large, the workability is deteriorated. For this reason, Al is made 0.005 to 0.1%.
Ti; 0.001 to 0.05%
Ti has the effect of fixing C and N and improving the workability of steel. However, if the amount is too large, the workability is deteriorated. For this reason, Ti is made 0.001 to 0.05%.
Nb; 0.001 to 0.05%
Nb has the effect of fixing C and improving the workability of steel. However, if the amount is too large, the workability is deteriorated. For this reason, Nb is made 0.001 to 0.05%.
次に鉄−亜鉛合金被覆について説明する。鉄−亜鉛合金被覆の付着量の偏差は±７ｇ／ｍ２以内であることが望ましい。標準偏差が±７ｇ／ｍ２の範囲を超える場合，外観上の濃淡が助長されて，外観不良となりやすい。鉄−亜鉛合金被覆の付着量は特に規定するものではないが，耐食性および加工性の観点から，２０〜１５０ｇ／ｍ２であることが望ましい。 Next, the iron-zinc alloy coating will be described. The deviation in the amount of iron-zinc alloy coating is preferably within ± 7 g / m 2 . When the standard deviation exceeds the range of ± 7 g / m 2 , the shade on the appearance is promoted and the appearance is liable to be poor. The adhesion amount of the iron-zinc alloy coating is not particularly specified, but is preferably 20 to 150 g / m 2 from the viewpoint of corrosion resistance and workability.
また，鉄−亜鉛合金被覆のΓ（ガンマ）層の平均厚みは１μｍ以下であることが望ましい。１μｍを超える場合，めっき密着性に劣るため，プレスした際にめっきが剥離しやすくなる。 The average thickness of the Γ (gamma) layer of the iron-zinc alloy coating is preferably 1 μm or less. When the thickness exceeds 1 μm, the plating adhesion is inferior, so that the plating easily peels off when pressed.
鉄−亜鉛合金被覆中のＦｅ含有率は，質量％で，７〜１１％であることが望ましい。７％未満であれば，めっき外観が不均一となりやすい。一方，１１％を超える場合，外観は良好であるが，めっきが過合金となり密着性に劣る。 The Fe content in the iron-zinc alloy coating is preferably 7 to 11% by mass. If it is less than 7%, the plating appearance tends to be uneven. On the other hand, if it exceeds 11%, the appearance is good, but the plating becomes overalloyed and the adhesion is poor.
本発明の合金化溶融亜鉛めっき鋼は，低炭素鋼スラブを熱間圧延した後，酸洗し，さらに冷間圧延，焼鈍，溶融亜鉛めっき，加熱合金化処理を施して，製造する。スラブ加熱温度や熱間圧延条件は，特に規定するものでなく，一般的な鋼を製造する条件であればなんら問題ないが，仕上げ圧延後の捲取温度は７５０℃以上とする必要がある。高温で巻き取るほど鋼中のＰが酸化され，その後の酸洗工程でそのＰの酸化層が除去される。この表面のＰ濃化が小さい鋼を溶融亜鉛めっき，加熱合金化処理することで，本発明の外観品位に優れる合金化溶融亜鉛めっき鋼を製造できる。捲取温度が７５０℃よりも小さい場合は，Ｐの酸化が不十分であるため，めっき前の鋼板表面のＰ濃度も大きく，これを溶融亜鉛めっき，加熱合金化処理すると外観品位に劣る合金化溶融亜鉛めっきとなる。このため，熱間圧延後の鋼の捲取温度は７５０℃以上とする必要がある。一方，巻取温度が高すぎるとスケールが厚く成長し，その後の酸洗工程に負荷がかかるため，巻取温度の上限は８１０℃とすることが望ましい。好ましい巻取温度範囲は，７６０℃以上８００℃以下，より好ましくは７７０℃以上７９０度以下である。 The alloyed hot dip galvanized steel of the present invention is manufactured by hot rolling a low carbon steel slab and then pickling, and further performing cold rolling, annealing, hot dip galvanizing, and heat alloying treatment. The slab heating temperature and hot rolling conditions are not particularly specified and there is no problem as long as they are conditions for producing general steel, but the cutting temperature after finish rolling needs to be 750 ° C. or higher. As the steel is wound at a higher temperature, P in the steel is oxidized, and the oxidized layer of P is removed in the subsequent pickling process. By galvanizing and heat-alloying the steel having a small P concentration on the surface, an alloyed galvanized steel excellent in appearance quality of the present invention can be produced. When the cutting temperature is lower than 750 ° C, the oxidation of P is insufficient, so the P concentration on the surface of the steel plate before plating is also large. If this is hot-dip galvanized and heat-alloyed, it is inferior in appearance quality. It becomes hot dip galvanizing. For this reason, the steel cutting temperature after hot rolling needs to be 750 ° C. or higher. On the other hand, if the coiling temperature is too high, the scale grows thick and a load is applied to the subsequent pickling process, so the upper limit of the coiling temperature is preferably 810 ° C. A preferable winding temperature range is 760 ° C. or higher and 800 ° C. or lower, more preferably 770 ° C. or higher and 790 ° C. or lower.
巻き取ってコイル状としたコイルは，そのコイルの最外層部の鋼板表面温度が５００℃以下となるまで空冷する必要がある。５００℃以下となるまで空冷することで鋼板中のＰが十分に酸化され，その後の酸洗工程でＰの濃化層が除去されるため，外観品位に優れる合金化溶融亜鉛めっき鋼を製造できる。一方，捲取後，直ちに水冷するなど，コイルの最外層部の鋼板表面温度が５００℃よりも高温で急冷した場合，Ｐの酸化が不十分なため，外観品位に劣る合金化溶融亜鉛めっき鋼を生み出す原因となる。このため，巻き取ったコイルはその最外層部の表面温度が５００℃以下となるまで空冷する必要がある。但し，巻き取ったコイルを，その最外層部の表面温度が極めて低温になるまで空冷した場合は，生産性を落とすことに繋がる。このため，空冷終了までの好ましい温度範囲は１００℃以上５００℃以下，より好ましい範囲は２００℃以上４００℃とする。 The coil that has been wound up into a coil shape needs to be air-cooled until the surface temperature of the steel plate at the outermost layer of the coil becomes 500 ° C. or lower. By cooling to 500 ° C. or less, P in the steel plate is sufficiently oxidized, and the concentrated layer of P is removed in the subsequent pickling process, so that an alloyed hot-dip galvanized steel with excellent appearance quality can be produced. . On the other hand, when the steel sheet surface temperature at the outermost layer of the coil is rapidly cooled to a temperature higher than 500 ° C, such as immediately after cooling, when the steel sheet surface temperature is higher than 500 ° C, the oxidation of galvannealed steel is inferior in appearance due to insufficient oxidation It becomes a cause to produce. For this reason, the wound coil needs to be air-cooled until the surface temperature of the outermost layer becomes 500 ° C. or lower. However, if the wound coil is air-cooled until the surface temperature of the outermost layer becomes extremely low, productivity will be reduced. For this reason, the preferable temperature range until the air cooling end is 100 ° C. or more and 500 ° C. or less, and the more preferable range is 200 ° C. or more and 400 ° C.
熱間圧延後は酸洗，冷間圧延をするが，これらの方法は従来から行われている方法で実施すればよい。例えば，酸洗では５０℃以上の塩酸中に鋼を浸漬，冷間圧延は圧下率５０〜９０％で行えばよい。なお，酸洗に際しては，Ｐの濃化層をできるだけ除去するために，塩酸温度は高く，また鋼の塩酸中の浸漬時間は長い方が好ましい。酸洗前に熱間圧延材の表面にショットブラスト，サンドブラストなどを行うことはなお望ましい。 After hot rolling, pickling and cold rolling are performed, but these methods may be carried out by conventional methods. For example, in pickling, steel may be immersed in hydrochloric acid at 50 ° C. or higher, and cold rolling may be performed at a reduction rate of 50 to 90%. In pickling, in order to remove the concentrated layer of P as much as possible, it is preferable that the hydrochloric acid temperature is high and the immersion time of steel in hydrochloric acid is long. It is still desirable to perform shot blasting, sand blasting, etc. on the surface of the hot rolled material before pickling.
冷間圧延後は再結晶焼鈍を行う。これは連続式溶融亜鉛めっき設備（ＣＧＬ）の前段に設置された焼鈍設備で行う。一般的な鋼を製造する条件であれば，焼鈍条件はなんら規定するものはないが，焼鈍温度が高すぎる場合は再結晶粒が粗大化し加工後の肌荒れの原因となるため，焼鈍温度は８８０℃以下とすることが望ましい。 After cold rolling, recrystallization annealing is performed. This is performed by an annealing facility installed in the preceding stage of the continuous hot dip galvanizing facility (CGL). As long as the conditions for producing general steel, there are no specific annealing conditions, but if the annealing temperature is too high, the recrystallized grains become coarse and cause rough skin after processing, so the annealing temperature is 880. It is desirable that the temperature is not higher than ° C.
再結晶焼鈍後は溶融亜鉛めっき，加熱合金化処理を行う。亜鉛めっき浴の温度は４４５℃〜５００℃，加熱合金化温度は４５０〜５８０℃とすることが望ましい。 After recrystallization annealing, hot dip galvanizing and heat alloying are performed. The temperature of the galvanizing bath is preferably 445 ° C to 500 ° C, and the heating alloying temperature is preferably 450 to 580 ° C.
以下に実施例に基づき本発明について説明する。表１に示す組成の鋼を転炉で溶製し，連続鋳造してスラブとした。そのスラブを１２００℃で１時間加熱後，熱間圧延して板厚５ｍｍの熱延鋼板とした。熱延時の仕上げ温度は９００℃，捲取温度は７２５℃〜７８５℃である。また捲取後の冷却は，コイルの最外層部が５００℃以下となるまで空冷した場合と，コイルの最外層部が５００℃以上の状態で水冷した場合との２水準実施した。得られた熱延鋼板を１０％塩酸中で酸洗した後，冷間圧延して板厚１ｍｍの冷延鋼板とした。その冷延鋼板を，連続溶融めっき設備を用い，均熱温度８００℃，均熱時間２０秒で焼鈍し，冷却速度２０℃／秒で４６５℃まで冷却した後，浴温４６０℃のＺｎ−０．１３％Ａｌめっき浴に３秒間浸漬し，ワイピングで付着量が４５ｇ／ｍ２となるように調整し，その後，温度５４０℃〜５８０℃で加熱合金化処理し，合金化溶融亜鉛めっき鋼を製造した。
作製した合金化溶融亜鉛めっき鋼の外観は下記の評価をした。
The present invention will be described below based on examples. Steel having the composition shown in Table 1 was melted in a converter and continuously cast into a slab. The slab was heated at 1200 ° C. for 1 hour and hot-rolled to obtain a hot-rolled steel sheet having a thickness of 5 mm. The finishing temperature at the time of hot rolling is 900 ° C, and the cutting temperature is 725 ° C to 785 ° C. In addition, the cooling after scraping was carried out in two levels: when the coil was air-cooled until the outermost layer of the coil was 500 ° C. or less, and when cooled with the outermost layer of the coil being 500 ° C. or higher. The obtained hot-rolled steel sheet was pickled in 10% hydrochloric acid and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1 mm. The cold-rolled steel sheet was annealed at a soaking temperature of 800 ° C. and a soaking time of 20 seconds using a continuous hot dipping equipment, cooled to 465 ° C. at a cooling rate of 20 ° C./second, and then Zn-0 having a bath temperature of 460 ° C. .Immerse in a 13% Al plating bath for 3 seconds, adjust the adhesion amount to 45 g / m 2 by wiping, then heat alloy at a temperature of 540 ° C. to 580 ° C. Manufactured.
The appearance of the produced alloyed hot-dip galvanized steel was evaluated as follows.
（１）外観
目視観察し，外観むらの程度に応じてグレード１から６まで，０．５刻みで１１段階に分類した。３．５以上が合格である。
（２）鉄−亜鉛合金層中のＰ濃化量
ＧＤＳで鉄−亜鉛合金被覆層の深さ方向の元素分布を測定し，鉄−亜鉛合金被覆層中のＰの積分強度，ＦｅとＺｎの積分強度の和を求めた。用いたＧＤＳは，リガク製高周波グロー放電発光分析装置，ＧＤＡ７５０であり，分析径は２．５ｍｍである。
（３）鉄−亜鉛合金被覆層の付着量
鉄−亜鉛合金被覆の付着量を求め，その偏差および組成を測定した。測定は，板幅方向，長手方向の任意の位置から数箇所選び，インヒビターを添加した塩酸で鉄−亜鉛合金被覆を溶解し，ＩＣＰで分析して行った。
（４）Γ層厚み
板幅中央，長手方向の任意の位置から２５×１０ｍｍの大きさに切り出し，ＳＥＭ（走査型電子顕微鏡）でその断面組織を観察し，Γ層の厚みを測定した。用いたＳＥＭは，日立製Ｓ−２４６０Ｎである。
（５）鉄−亜鉛合金被覆層の密着性
密着性を６０度Ｖ曲げ後のテープ剥離試験で評価した。これは，Ｖ曲げ部に貼り付けたテープに付着した鉄−亜鉛合金の付着量（付着した部分の長さ）を測定する方法で，付着した部分の長さが６ｍｍ以下であれば合格，それよりも大きければ不合格とした。
(1) Appearance Visually observed,
(2) The element distribution in the depth direction of the iron-zinc alloy coating layer is measured by the P enrichment amount GDS in the iron-zinc alloy layer, the integrated strength of P in the iron-zinc alloy coating layer, Fe and Zn The sum of integral intensities was obtained. The GDS used was a Rigaku high-frequency glow discharge emission spectrometer, GDA750, and the analysis diameter was 2.5 mm.
(3) Amount of iron-zinc alloy coating layer The amount of iron-zinc alloy coating was determined, and the deviation and composition were measured. The measurement was performed by selecting several points from arbitrary positions in the plate width direction and longitudinal direction, dissolving the iron-zinc alloy coating with hydrochloric acid to which an inhibitor was added, and analyzing by ICP.
(4) Gamma Layer Thickness The width of the Γ layer was measured by slicing it to a size of 25 × 10 mm from an arbitrary position in the longitudinal center of the plate width and observing its cross-sectional structure with a SEM (scanning electron microscope). The SEM used is Hitachi S-2460N.
(5) Adhesiveness of the iron-zinc alloy coating layer The tape adhesion test after 60 degree V-bending was evaluated. This is a method of measuring the amount of iron-zinc alloy adhering to the tape affixed to the V-bend (the length of the adhering part). If the adhering part is 6 mm or less in length, it passes, If it was larger than that, it was rejected.
各評価結果を表２および表３に示す。Ｎｏ．１〜４は，鋼Ａを種々の温度で捲取り，鉄−亜鉛合金被覆中のＰ濃化量を変化させた場合である。捲取温度が低く，鉄−亜鉛合金被覆中のＰと（ＦｅとＺｎ）の積分強度比が０．０２５を超える場合（Ｎｏ．４），外観グレードは５．５であり，外観品位に劣る。Ｎｏ．５〜８は，鋼Ｂを種々の温度で捲取り，鉄−亜鉛合金被覆中のＰ濃化量を変化させた場合である。捲取温度が低く，鉄−亜鉛合金被覆中のＰと（ＦｅとＺｎ）の積分強度比が０．０２５を超える場合（Ｎｏ．８），外観グレードは５．０であり，外観品位に劣る。Ｎｏ．９〜１２は，鋼Ｃを種々の温度で捲取り，鉄−亜鉛合金被覆中のＰ濃化量を変化させた場合である。捲取温度が低く，鉄−亜鉛合金被覆中のＰと（ＦｅとＺｎ）の積分強度比が０．０２５を超える場合（Ｎｏ．１１および１２），外観グレードは４．０および５．０であり，外観品位に劣る。Ｎｏ．１３〜１５は，鋼Ｄを種々の温度で捲取り，鉄−亜鉛合金被覆中のＰ濃化量を変化させた場合である。捲取温度が低く，鉄−亜鉛合金被覆中のＰと（ＦｅとＺｎ）の積分強度比が０．０２５を超える場合（Ｎｏ．１４および１５），外観グレードは４．５および５．５であり，外観品位に劣る。なお，Ｎｏ．１〜１５の鋼はいずれもコイルに巻き取った後の冷却はコイル最外層部の鋼表面温度が５００℃以下となるまで空冷した。
The evaluation results are shown in Table 2 and Table 3. No. 1-4 are the cases where the steel A is scraped at various temperatures and the P concentration in the iron-zinc alloy coating is changed. When the ironing temperature is low and the integrated strength ratio of P and (Fe and Zn) in the iron-zinc alloy coating exceeds 0.025 (No. 4), the appearance grade is 5.5, which is inferior in appearance quality. . No. 5 to 8 are cases where steel B is scraped at various temperatures and the P concentration in the iron-zinc alloy coating is changed. When the ironing temperature is low and the integrated strength ratio of P and (Fe and Zn) in the iron-zinc alloy coating exceeds 0.025 (No. 8), the appearance grade is 5.0, which is inferior in appearance quality. . No. 9 to 12 are cases where the steel C was scraped at various temperatures and the P concentration in the iron-zinc alloy coating was changed. When the ironing temperature is low and the integrated strength ratio of P and (Fe and Zn) in the iron-zinc alloy coating exceeds 0.025 (No. 11 and 12), the appearance grade is 4.0 and 5.0. Yes, inferior in appearance. No. 13 to 15 are cases where the steel D was scraped at various temperatures and the P concentration in the iron-zinc alloy coating was changed. When the ironing temperature is low and the integrated strength ratio of P and (Fe and Zn) in the iron-zinc alloy coating exceeds 0.025 (No. 14 and 15), the appearance grade is 4.5 and 5.5 Yes, inferior in appearance. No. All the
Ｎｏ．１６〜２３は，鋼Ａ〜Dを種々の温度で捲取り，さらにコイルに巻き取った後の冷却をコイル最外層部の鋼表面温度が５００℃より高温の状態で水冷し，鉄−亜鉛合金被覆中のＰ濃化量を変化させた場合である。このようにして製造したＮｏ．１６〜２３の鋼は，いずれもめっき後の外観グレードが４．０以上であり，外観品位に劣る。 No. Nos. 16 to 23 are steels A to D which are wound at various temperatures, and further cooled after being wound on a coil by water cooling with the steel surface temperature of the coil outermost layer being higher than 500 ° C. This is a case where the P concentration amount in the coating is changed. No. manufactured in this way. All the steels of Nos. 16 to 23 have an appearance grade after plating of 4.0 or more, and are inferior in appearance quality.
図１は，Ｎｏ．１〜２３の鋼における鉄−亜鉛合金被覆中のＰと，（ＦｅとＺｎ）の積分強度比Ｉ（Ｐ）／Ｉ（Ｆｅ＋Ｚｎ）に対する外観グレードの関係である。鉄−亜鉛合金被覆中のＰと（ＦｅとＺｎ）の積分強度比Ｉ（Ｐ）／Ｉ（Ｆｅ＋Ｚｎ）は，外観グレードと線形関係にあり，積分強度比Ｉ（Ｐ）／Ｉ（Ｆｅ＋Ｚｎ）が０．０２５以下であると外観グレードは３以下であり，良好な外観を有する。
FIG. It is the relationship of the appearance grade with respect to P in the iron-zinc alloy coating in
表１に示すＡの組成の鋼を転炉で溶製し，連続鋳造してスラブとした。そのスラブを１２００℃で１時間加熱後，熱間圧延して板厚５ｍｍの熱延鋼板とした。熱延時の仕上げ温度は９００℃，捲取温度は７８０℃であり，捲取後はコイルの最外層部が５００℃以下となるまで空冷した。作製した熱延鋼板を１０％塩酸中で酸洗した後，冷間圧延して板厚１ｍｍの冷延鋼板とした。その冷延鋼板を，連続溶融めっき設備を用い，均熱温度８００℃，均熱時間２０秒で焼鈍し，冷却速度２０℃／秒で４６５℃まで冷却した後，浴温４６０℃のＺｎ−０．１３％Ａｌめっき浴に３秒浸漬し，ワイピングで付着量が４０〜５０ｇ／ｍ２となるように調整し，その後，加熱温度４８０〜５６０℃で合金化処理した。作製した合金化溶融亜鉛めっき鋼は，実施例１と同様の方法で各種評価した。評価結果を表４に示す。 Steel of composition A shown in Table 1 was melted in a converter and continuously cast into a slab. The slab was heated at 1200 ° C. for 1 hour and hot-rolled to obtain a hot-rolled steel sheet having a thickness of 5 mm. The finishing temperature at the time of hot rolling was 900 ° C. and the cutting temperature was 780 ° C. After the cutting, the coil was air-cooled until the outermost layer portion of the coil was 500 ° C. or less. The produced hot-rolled steel sheet was pickled in 10% hydrochloric acid and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1 mm. The cold-rolled steel sheet was annealed at a soaking temperature of 800 ° C. and a soaking time of 20 seconds using a continuous hot dipping equipment, cooled to 465 ° C. at a cooling rate of 20 ° C./second, and then Zn-0 having a bath temperature of 460 ° C. .Immersion in a 13% Al plating bath for 3 seconds and wiping to adjust the adhesion amount to 40 to 50 g / m 2 , followed by alloying at a heating temperature of 480 to 560 ° C. The produced alloyed hot-dip galvanized steel was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 4.
Ｎｏ．２４とＮｏ．２５は，鉄−亜鉛合金層付着量の偏差が異なる場合である。偏差が７ｇ・ｍ-2以下であるＮｏ．２４は，偏差が８ｇ・ｍ-2のＮｏ．２５よりも外観グレードに勝る。また，Ｎｏ．２４とＮｏ．２６，Ｎｏ．２７はＦｅ含有率，Γ層厚みの違いである。Ｆｅ含有率，Γ層厚みが最も小さいＮｏ．２４は，Ｎｏ．２６，Ｎｏ．２７より外観グレード，密着性に優れる。また，Ｎｏ．２６とＮｏ．２７の比較では，Ｆｅ含有率，Γ層厚みがより小さいＮｏ．２６の方が外観グレード，密着性に優れる。 No. 24 and no. 25 is a case where the deviation of the iron-zinc alloy layer adhesion amount is different. The deviation is 7 g · m −2 or less. No. 24 has a deviation of 8 g · m −2 . The appearance grade is better than 25. No. 24 and no. 26, no. 27 is the difference in Fe content and Γ layer thickness. No. with the smallest Fe content and Γ layer thickness. 24 is No. 24. 26, no. Excellent appearance grade and adhesion than 27. No. 26 and no. In the comparison of No. 27, the Fe content and the Γ layer thickness are smaller. 26 is superior in appearance grade and adhesion.
表１に示すＡの組成の鋼を転炉で溶製し，連続鋳造してスラブとした。そのスラブを１２００℃で１時間加熱後，熱間圧延して板厚５ｍｍの熱延鋼板とした。熱延時の仕上げ温度は９００℃，捲取温度は７８０℃である。捲取後はコイルの最外層部が，所定の温度となるまで空冷し，その後水冷した。所定の温度は，約１００℃，２５０℃，３５０℃，４５０℃，６００℃の５水準実施した。作製した熱延鋼板を１０％塩酸中で酸洗した後，冷間圧延して板厚１ｍｍの冷延鋼板とした。その冷延鋼板を，連続溶融めっき設備を用い，均熱温度８００℃，均熱時間２０秒で焼鈍し，冷却速度２０℃／秒で４６５℃まで冷却した後，浴温４６０℃のＺｎ−０．１３％Ａｌめっき浴に３秒浸漬し，ワイピングで付着量が４０〜５０ｇ／ｍ２となるように調整し，その後，加熱温度５４０℃で合金化処理した。作製した合金化溶融亜鉛めっき鋼は，実施例１と同様の方法で各種評価した。評価結果を表５に示す。 Steel of composition A shown in Table 1 was melted in a converter and continuously cast into a slab. The slab was heated at 1200 ° C. for 1 hour and hot-rolled to obtain a hot-rolled steel sheet having a thickness of 5 mm. The finishing temperature at the time of hot rolling is 900 ° C., and the cutting temperature is 780 ° C. After coiling, the outermost layer of the coil was air cooled until it reached a predetermined temperature, and then water cooled. Predetermined temperatures were implemented at five levels of about 100 ° C, 250 ° C, 350 ° C, 450 ° C, and 600 ° C. The produced hot-rolled steel sheet was pickled in 10% hydrochloric acid and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1 mm. The cold-rolled steel sheet was annealed at a soaking temperature of 800 ° C. and a soaking time of 20 seconds using a continuous hot dipping equipment, cooled to 465 ° C. at a cooling rate of 20 ° C./second, and then Zn-0 having a bath temperature of 460 ° C. .Immersion in a 13% Al plating bath for 3 seconds and wiping to adjust the adhesion amount to 40 to 50 g / m 2 , followed by alloying at a heating temperature of 540 ° C. The produced alloyed hot-dip galvanized steel was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 5.
Ｎｏ．２８〜Ｎｏ．３１は，捲取後にコイルの最外層部が５００℃以下となるまで空冷した場合で，いずれも外観品位に優れる。低温になるまで空冷した方が外観グレードに優れる傾向にあるが，約１００℃まで空冷した場合（Ｎｏ．２８）は，その温度になるまで４８時間かかり，生産性を大きく落とすことに繋がる。一方，約２５０℃と約３５０℃となるまで空冷した場合（それぞれ，Ｎｏ．２９，Ｎｏ．３０）は，その温度になるまでに要する時間も２４時間以内であり，外観品位も良好で，バランスに優れる。また，約６００℃となるまで空冷し，その後水冷した場合（Ｎｏ．３２）は，外観品位に劣る。 No. 28-No. No. 31 is a case where the outermost layer portion of the coil is air-cooled until it reaches 500 ° C. or less after the cutting, and all have excellent appearance quality. Air cooling to a low temperature tends to be superior in appearance grade, but when air cooling to about 100 ° C. (No. 28), it takes 48 hours to reach that temperature, leading to a significant reduction in productivity. On the other hand, when air-cooled to about 250 ° C and about 350 ° C (No. 29 and No. 30 respectively), the time required to reach that temperature is within 24 hours, the appearance quality is good, and the balance Excellent. In addition, when air-cooled to about 600 ° C. and then water-cooled (No. 32), the appearance quality is inferior.
本発明は，例えば自動車，家電製品，建材等に用いられる合金化溶融亜鉛めっき鋼板に適用できる。 The present invention can be applied to alloyed hot-dip galvanized steel sheets used for automobiles, home appliances, building materials, and the like.
Claims (4)
Ｃ；０．０１％以下，
Ｓｉ；０．２％以下，
Ｍｎ；２％以下，
Ｐ；０．０２〜０．２％，
Ｓ；０．０３％以下，
Ａｌ；０．００５〜０．１％，
Ｔｉ；０．００１〜０．０５％，
Ｎｂ；０．００１〜０．０５％，
を含有し，残部がＦｅおよび不可避的不純物からなる鋼材の表面に，鉄−亜鉛合金被覆を有する合金化溶融亜鉛めっき鋼において，ＧＤＳによる鉄−亜鉛合金被覆中のＰと（Ｆｅ＋Ｚｎ）の積分強度比，Ｉ（Ｐ）／Ｉ（Ｆｅ＋Ｚｎ）が０．０２５以下であることを特徴とする外観品位に優れる合金化溶融亜鉛めっき鋼。 % By mass
C; 0.01% or less,
Si: 0.2% or less,
Mn: 2% or less,
P; 0.02 to 0.2%,
S: 0.03% or less,
Al; 0.005 to 0.1%,
Ti; 0.001 to 0.05%,
Nb; 0.001 to 0.05%,
Integral strength of P and (Fe + Zn) in iron-zinc alloy coating by GDS in alloyed hot-dip galvanized steel with iron-zinc alloy coating on the surface of steel material containing Fe and unavoidable impurities An alloyed hot-dip galvanized steel excellent in appearance quality, characterized in that the ratio I (P) / I (Fe + Zn) is 0.025 or less.
Ｃ；０．０１％以下，
Ｓｉ；０．２％以下，
Ｍｎ；２％以下，
Ｐ；０．０２〜０．２％，
Ｓ；０．０３％以下，
Ａｌ；０．００５〜０．１％，
Ｔｉ；０．００１〜０．０５％，
Ｎｂ；０．００１〜０．０５％，
を含有し，残部がＦｅおよび不可避的不純物からなる低炭素鋼スラブを熱間圧延した後，酸洗し，さらに冷間圧延，焼鈍，溶融亜鉛めっき，加熱合金化処理を施して，合金化溶融亜鉛めっき鋼とする合金化溶融亜鉛めっき鋼の製造方法において，熱間圧延後のコイルの捲取温度を７５０℃以上とし，さらにその後，巻き取ったコイルの最外層部の表面温度が５００℃以下となるまで空冷することを特徴とする外観品位に優れる合金化溶融亜鉛めっき鋼の製造方法。 % By mass
C; 0.01% or less,
Si: 0.2% or less,
Mn: 2% or less,
P; 0.02 to 0.2%,
S: 0.03% or less,
Al; 0.005 to 0.1%,
Ti; 0.001 to 0.05%,
Nb; 0.001 to 0.05%,
Hot-rolled low-carbon steel slab containing Fe and the balance of inevitable impurities, pickling, cold rolling, annealing, hot dip galvanizing, heat alloying treatment, alloying and melting In the manufacturing method of alloyed hot-dip galvanized steel to be galvanized steel, the coiling temperature of the coil after hot rolling is set to 750 ° C. or higher, and then the surface temperature of the outermost layer portion of the wound coil is 500 ° C. or lower. A method for producing an alloyed hot-dip galvanized steel excellent in appearance quality, characterized by air cooling until
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| JPH03243751A (en) * | 1990-02-21 | 1991-10-30 | Nippon Steel Corp | Production of alloyed galvanized steel sheet |
| JPH06336666A (en) * | 1993-05-31 | 1994-12-06 | Sumitomo Metal Ind Ltd | Manufacture of galvannealed steel sheet having excellent surface characteristic |
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