JPH08291379A - Method for galvannealing p-added high tensile strength steel - Google Patents

Abstract

PURPOSE: To promote the allaying rate after plating in galvannealing a high tensile strength steel plate added with a specified amt. of P and to obtain a plating film excellent in adhesion. CONSTITUTION: A P-added steel plate is subjected, to preoxidation and is thereafter subjected to annealing in such a manner that it is heated at 750 to 900 deg.C and is cooled ate >=750 deg.C, and after the annealing, an oxidized film in which the content of iron oxide expressed in terms of Fe is regulated to 0.05 to 1.0g/m<2> is formed. Next, it is reduced at <750 to >=550 deg.C, is plated in a galvanizing bath having 0.03 to 0.2wt.% Al concn. and is subjected to alloying heat treatment to obtain a galvannealed steel plate. In the case the Al concn. in the plating bath is regulated to 0.12 to 0.2wt.%, the adhesion of the film improves.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明はＰ添加高張力鋼材の改善
された溶融亜鉛めっき方法に関し、特に自動車用鋼板と
して好適な合金化溶融亜鉛めっき鋼板の製造方法に関す
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved hot-dip galvanizing method for P-added high-strength steel materials, and more particularly to a method for producing an alloyed hot-dip galvanized steel sheet suitable as a steel sheet for automobiles.

【０００２】[0002]

【従来の技術】近年、家電、建材、自動車などの産業分
野においては、防錆鋼板として比較的安価に製造できる
溶融亜鉛めっき鋼板が大量に使用されており、とりわけ
経済性とその防錆機能、塗装後の性能の点で、合金化溶
融亜鉛めっき鋼板が広く用いられている。2. Description of the Related Art In recent years, in the industrial fields of home appliances, building materials, automobiles, etc., a large amount of hot dip galvanized steel sheets, which can be manufactured at a relatively low cost, are used as anticorrosion steel sheets. Alloyed hot-dip galvanized steel sheets are widely used in terms of performance after coating.

【０００３】溶融亜鉛めっき鋼板は、適当な脱脂洗浄工
程を経た後、または脱脂洗浄を行うことなく、鋼板を弱
酸化性雰囲気もしくは還元性雰囲気で予熱し、次いで水
素＋窒素の還元性雰囲気（還元炉）で鋼板を焼鈍還元
し、鋼板をめっき温度付近まで冷却した後、溶融亜鉛に
浸漬し、めっき浴出口で付着量を制御する（例、ガスワ
イピングノズルで）という連続溶融亜鉛めっき法により
一般に製造される。めっき付着量は、片面当たり20〜15
0 g/m²の範囲内が普通である。20 g/m² 以下の付着量の
めっき層は通常の溶融亜鉛めっき法では製造が困難であ
る。The hot-dip galvanized steel sheet is preheated in a weakly oxidizing atmosphere or a reducing atmosphere after a suitable degreasing and cleaning step or without degreasing and cleaning, and then in a reducing atmosphere of hydrogen + nitrogen (reduction). In general, a continuous hot dip galvanizing method is used in which the steel plate is annealed and reduced in a furnace), the steel plate is cooled to a temperature near the plating temperature, then immersed in hot dip zinc, and the amount deposited at the plating bath outlet is controlled (eg, with a gas wiping nozzle) Manufactured. Plating coverage is 20 to 15 per side
A range of 0 g / m ² is normal. It is difficult to manufacture a coating layer with an adhesion amount of 20 g / m ² or less by the usual hot dip galvanizing method.

【０００４】溶融亜鉛めっきにおいては、予熱時に鋼板
表面に 80 nm程度の薄い酸化皮膜、即ち、酸化鉄の皮膜
が形成される方が、溶融亜鉛との濡れ性の点で望ましい
とされている。この厚みは、酸化鉄付着量に換算する
と、Fe量として約0.04 g/m² に相当する。しかし、それ
以上の厚さの酸化皮膜の形成は、ドロス発生や溶融めっ
きの密着性の点で悪影響があると考えられてきた。In hot dip galvanizing, it is preferable that a thin oxide film of about 80 nm, that is, an iron oxide film is formed on the surface of the steel sheet during preheating, from the viewpoint of wettability with hot dip zinc. This thickness corresponds to an Fe content of about 0.04 g / m ² when converted to the amount of iron oxide deposited. However, it has been considered that the formation of an oxide film having a thickness larger than that has an adverse effect on the generation of dross and the adhesiveness of hot dip coating.

【０００５】溶融亜鉛めっき層は、めっき／鋼界面での
Fe−Zn合金層の形成によって鉄素地に密着するが、この
合金層は金属間化合物であるため硬くて脆い。従って、
この合金層の形成を抑制して、合金層が必要以上に厚く
なるのを阻止するために、めっき浴中に0.08〜0.14wt％
のAlを存在させる。それにより、皮膜加工性が保持され
ると共に、めっき皮膜の耐パウダリング性が確保され、
製造時のドロスの発生が抑制される。Hot dip galvanized layers are used at the plating / steel interface.
The Fe-Zn alloy layer adheres to the iron substrate, but since this alloy layer is an intermetallic compound, it is hard and brittle. Therefore,
In order to suppress the formation of this alloy layer and prevent the alloy layer from becoming unnecessarily thick, 0.08 to 0.14 wt% in the plating bath
Al is present. As a result, the film processability is maintained and the powdering resistance of the plating film is secured,
Generation of dross during manufacturing is suppressed.

【０００６】合金化溶融亜鉛めっき鋼板は、上記方法で
連続的に溶融亜鉛めっきされた鋼板を、めっき浴から出
た直後に、熱処理炉で 500〜600 ℃程度の材料温度に３
〜60秒加熱することにより、亜鉛めっき層と鋼素地との
間の相互拡散によってめっき層全体をFe−Zn合金化した
ものである。めっき層はFe−Zn金属間化合物となり、一
般にその平均Fe濃度は８〜12wt％である。The alloyed hot-dip galvanized steel sheet is obtained by subjecting the steel sheet hot-dip galvanized continuously by the above method to a material temperature of about 500 to 600 ° C. in a heat treatment furnace immediately after leaving the plating bath.
By heating for ~ 60 seconds, the entire plating layer is Fe-Zn alloyed by mutual diffusion between the zinc plating layer and the steel base. The plated layer is an Fe-Zn intermetallic compound, and generally has an average Fe concentration of 8 to 12 wt%.

【０００７】合金化溶融亜鉛めっき鋼板のめっき付着量
は、通常は片面当たり25〜70 g/m²程度である。付着量
が70g/m²を上回るものは、合金化しためっき層の耐パウ
ダリング性を確保することが困難なため、合金化溶融亜
鉛めっき鋼板においては一般に供給されていない。合金
化溶融亜鉛めっき鋼板の場合も、上記と同様の目的でめ
っき浴にAlを存在させるが、Alは溶融めっき後の合金化
反応についても抑制効果を発揮するので、めっき浴中の
Al濃度は0.08〜0.11wt％と、溶融亜鉛めっきの場合に比
べて低めに抑えるのが普通である。The coating weight of the galvannealed steel sheet is usually about 25 to 70 g / m ² per side. It is difficult to secure the powdering resistance of the alloyed plating layer if the adhesion amount exceeds 70 g / m ^2, and therefore it is not generally supplied in the galvannealed steel sheet. Also in the case of alloyed hot-dip galvanized steel sheet, Al is present in the plating bath for the same purpose as above, but since Al exerts a suppressing effect also on the alloying reaction after hot-dip galvanizing,
The Al concentration is usually 0.08 to 0.11 wt%, which is usually kept low compared to the case of hot dip galvanizing.

【０００８】これらの溶融めっき鋼板の母材は、従来は
低炭素Alキルド鋼板、極低炭素Ti添加鋼板等が主流であ
ったが、自動車材料の高強度化の要求に伴い、延性およ
び靱性に優れた材料を得るため、Ｐ添加鋼が用いられる
ようとしている。Conventionally, the base materials for these hot-dip galvanized steel sheets were low-carbon Al-killed steel sheets and ultra-low-carbon Ti-added steel sheets, but with the demand for higher strength automobile materials, ductility and toughness were In order to obtain an excellent material, P-added steel is being used.

【０００９】しかし、Ｐを添加した鋼材では、Ｐ含有量
が0.02wt％を越えると、溶融亜鉛めっき後の合金化の速
度が著しく遅延し、製造効率が低下することが知られて
いる。同時に、Ｐ含有量が0.02wt％を超えると、めっき
皮膜の密着性が低下することも問題となっており、その
結果、自動車車体に寒冷期に石はねなどが起こると、皮
膜が剥離して、剥離点を起点に錆が発生する原因となっ
ている。However, it is known that in a steel material containing P, when the P content exceeds 0.02 wt%, the alloying rate after hot dip galvanization is significantly delayed and the production efficiency is lowered. At the same time, if the P content exceeds 0.02 wt%, the adhesion of the plating film is also a problem, and as a result, if stones or the like occur on the car body during the cold season, the film will peel off. As a result, rust is generated from the peeling point.

【００１０】合金化促進に関しては、プレFeめっきを行
う方法 (特開昭57−79160 号公報)がある。しかし、電
気めっきが加わるため、設備コストおよび生産コストが
大幅に増大するなどの問題があり、実用的ではない。Regarding promotion of alloying, there is a method of performing pre-Fe plating (JP-A-57-79160). However, since electroplating is added, there is a problem that equipment cost and production cost increase significantly, which is not practical.

【００１１】また、同じ問題をかかえるSi添加鋼につい
て、合金化促進のために、無酸化炉で鋼板表面に厚膜の
酸化皮膜を形成するように前酸化した後、還元炉で焼鈍
する方法 (特開昭55−122865号公報) が提案されてい
る。これは、前酸化で生成した鉄酸化物を還元すると、
生成した還元鉄は表面積が著しく大きくなり、反応面積
の増大により合金化時のFe−Zn反応が促進されるという
現象を利用している。Further, for a Si-added steel having the same problem, in order to promote alloying, a method of pre-oxidizing so as to form a thick oxide film on the surface of the steel sheet in a non-oxidizing furnace and then annealing in a reducing furnace ( Japanese Patent Laid-Open No. 55-122865) has been proposed. This is due to the reduction of iron oxide produced by pre-oxidation,
The generated reduced iron has a phenomenon that the surface area becomes remarkably large and the Fe-Zn reaction at the time of alloying is promoted by increasing the reaction area.

【００１２】特開平５−306448号公報には、無酸化炉を
経由していないＰ≧0.03wt％以上の鋼板を、露点の異な
る２ゾーン以上に分割された還元炉内で、酸化皮膜厚み
を第１ゾーンで 100〜1000Åに、第２ゾーンで 200Å以
下に制御するように還元を行う方法が提案されている。
しかし、この方法は制御が難しい。Japanese Unexamined Patent Publication (Kokai) No. 5-306448 discloses that a steel sheet having P ≧ 0.03 wt% or more, which does not pass through an oxidation-free furnace, has an oxide film thickness in a reducing furnace divided into two or more zones having different dew points. A method has been proposed in which the reduction is controlled so that the first zone is controlled to 100 to 1000Å and the second zone is controlled to 200 Å or less.
However, this method is difficult to control.

【００１３】また、以上のいずれの方法も、めっき皮膜
の密着性に関しては改善効果がない。皮膜密着性の改善
は、合金化処理時の条件制御により対処しようと試みら
れているが、十分な効果を上げるには至っていない。Further, none of the above methods has the effect of improving the adhesion of the plating film. Attempts have been made to improve the film adhesion by controlling the conditions during the alloying treatment, but the effect has not been sufficiently enhanced.

【００１４】[0014]

【発明が解決しようとする課題】Ｐ添加鋼の合金化溶融
亜鉛めっきにおいては、合金化を促進して製造を経済的
かつ効率的にすると同時に、めっき皮膜の密着性を高め
ることのできる製造方法が求められている。本発明の目
的は、この要請に応えて、Ｐ添加高張力鋼材の合金化溶
融亜鉛めっき方法を確立することである。具体的には、
Ｐ＞0.02wt％の高張力鋼材の合金化速度を促進させ、同
時に密着性の良好なめっき皮膜を形成することができ
る、Ｐ添加高張力鋼材の合金化溶融亜鉛めっき方法を提
供することである。In the galvannealing of P-added steel, a manufacturing method capable of promoting alloying to make the manufacturing economical and efficient and at the same time enhancing the adhesion of the plating film. Is required. It is an object of the present invention to establish a method for alloying hot dip galvanization of P-added high-strength steel materials in response to this demand. In particular,
It is an object of the present invention to provide an alloying hot-dip galvanizing method for P-added high-strength steel materials, which can accelerate the alloying rate of high-tensile steel materials with P> 0.02 wt% and at the same time form a plating film with good adhesion. .

【００１５】[0015]

【課題を解決するための手段】本発明者らは、Ｐ＞0.02
wt％のＰ添加鋼のめっき前の熱処理が合金化速度に及ぼ
す影響について検討した。The present inventors have established that P> 0.02
The effect of the heat treatment of the wt% P-added steel before plating on the alloying rate was examined.

【００１６】その結果、Fe換算で１g/m²を越える厚膜の
酸化皮膜を形成するように前酸化を行った後、750 ℃以
上で還元すると、合金化速度は促進されることを確認し
た。しかし、このような厚膜の酸化皮膜の形成には還元
炉内での酸化皮膜の剥離という問題がある。一方、前酸
化での酸化鉄量をFe換算で１g/m²未満と小さくして、そ
の後に750 ℃以上で還元を行った場合、合金化速度の促
進効果は小さかった。As a result, it was confirmed that the alloying rate was accelerated by pre-oxidizing so as to form a thick oxide film exceeding 1 g / m ^{2 in} terms of Fe and then reducing at 750 ° C. or higher. . However, the formation of such a thick oxide film has a problem of peeling of the oxide film in the reduction furnace. On the other hand, when the amount of iron oxide in the preoxidation was reduced to less than 1 g / m ^{2 in} terms of Fe and then reduction was performed at 750 ° C. or higher, the effect of promoting the alloying rate was small.

【００１７】酸化鉄量を１g/m²未満に抑えたまま、合金
化速度を促進させることができる方法を検討した結果、
前酸化後の還元温度を550 ℃以上、750 ℃未満と、焼鈍
に必要な再結晶温度より低くすることにより、合金化速
度が促進されることを見出した。しかし、この場合には
再結晶が起こらないため、延性、靱性などの材料特性が
不良となった。予め焼鈍した材料を使用すればこの問題
は解決するが、別に焼鈍工程が必要となり、工程増加に
よるコスト高のため実用的ではない。As a result of studying a method capable of accelerating the alloying rate while suppressing the iron oxide amount to less than 1 g / m ² ,
It was found that the alloying rate was accelerated by reducing the reduction temperature after pre-oxidation to 550 ℃ or more and less than 750 ℃, lower than the recrystallization temperature required for annealing. However, in this case, since recrystallization did not occur, the material properties such as ductility and toughness became poor. This problem can be solved by using a material that has been annealed in advance, but it is not practical because an additional annealing step is required and the cost increases due to the increase in the number of steps.

【００１８】そこで、溶融めっき設備内での焼鈍を検討
した結果、Fe換算で１g/m²未満の前酸化を行った後、酸
化鉄を還元させない雰囲気で再結晶温度に加熱して焼鈍
を行い、この雰囲気中で750 ℃以下に冷却し、550 ℃以
上、750 ℃未満で酸化鉄を還元させると、合金化が促進
されることを究明した。また、めっき皮膜の密着性につ
いては、Al添加量が0.12wt％以上と比較的高い溶融亜鉛
めっき浴を用いることで改善できることを見出した。Therefore, as a result of studying annealing in a hot dip coating facility, after pre-oxidizing less than 1 g / m ^{2 in} terms of Fe, annealing was performed by heating to a recrystallization temperature in an atmosphere that does not reduce iron oxide. It was clarified that alloying is promoted by cooling to 750 ℃ or less in this atmosphere and reducing iron oxide at 550 ℃ or more and less than 750 ℃. Further, it was found that the adhesion of the plating film can be improved by using a relatively high hot-dip galvanizing bath with an Al addition amount of 0.12 wt% or more.

【００１９】ここに、本発明は、Ｐ＞0.020 wt％の高張
力鋼材を、非還元性雰囲気中で再結晶温度以上、900 ℃
以下の温度範囲に加熱した後、750 ℃以下まで冷却し、
この間に鋼板表面にFe換算で0.05 g/m² 以上、1.0 g/m²
以下の酸化皮膜を形成し、次いで750 ℃未満、550 ℃以
上の還元性雰囲気中で還元した後、溶融亜鉛めっきを施
し、合金化熱処理を行うことを特徴とする、Ｐ添加高張
力鋼材の合金化溶融亜鉛めっき方法である。According to the present invention, a high-strength steel material with P> 0.020 wt% is heated at a recrystallization temperature of 900 ° C. or higher in a non-reducing atmosphere.
After heating to the temperature range below, cool to 750 ° C or below,
During this period, 0.05 g / m ² or more, 1.0 g / m ²
An alloy of P-added high-strength steel material, characterized by forming the following oxide film, then reducing in a reducing atmosphere at less than 750 ° C and at least 550 ° C, and then performing hot dip galvanizing and alloying heat treatment. It is a method of chemical galvanizing.

【００２０】この方法によれば、合金化時間を従来より
短縮することができる。好適態様にあっては、溶融亜鉛
めっきを、浴中Al濃度が0.12〜0.20wt％のめっき浴で行
う。それにより、上記のようにめっき密着性が改善され
る。According to this method, the alloying time can be shortened as compared with the conventional case. In a preferred embodiment, hot dip galvanizing is performed in a plating bath having an Al concentration in the bath of 0.12 to 0.20 wt%. Thereby, the plating adhesion is improved as described above.

【００２１】[0021]

【作用】以下、本発明についてさらに詳しく説明する。
なお、以下の説明において、％は特に指定のない限りwt
％であるが、ガス組成に関する％は vol％である。ま
た、以下の説明では、めっき母材が鋼板である場合につ
いて説明するが、本発明の方法は原理的には鋼板の合金
化溶融亜鉛めっきに限定されるものではなく、管、棒、
異形材などの他の鋼材についても適用可能であることは
いうまでもない。The present invention will be described in more detail below.
In the following explanation,% is wt unless otherwise specified.
%, But% related to gas composition is vol%. Further, in the following description, the case where the plating base material is a steel plate will be described, but the method of the present invention is not limited to alloying hot dip galvanizing of a steel plate in principle, and a pipe, a rod,
It goes without saying that it is also applicable to other steel materials such as profile materials.

【００２２】本発明の方法に従ってＰ添加鋼板の溶融め
っき前の熱処理を行うと、めっき後の合金化が促進され
る理由は完全には解明されていないが、次のように推測
される。The reason why the alloying after plating is promoted by heat treatment of the P-added steel sheet before hot dipping according to the method of the present invention has not been completely clarified, but it is presumed as follows.

【００２３】Ｐ添加鋼を前酸化すると、Ｐも同時に酸化
され、生成した酸化皮膜は鉄酸化物とともに微量のＰ酸
化物を含有する。その後、従来のように750 ℃以上で還
元焼鈍を施すと、鉄酸化物が還元されて還元鉄になると
同時に、共存する微量のＰ酸化物も一緒に還元される。
還元されたＰは合金化時のFe−Zn反応に関与し、この反
応を著しく遅延させる。従って、この場合、還元鉄の生
成に伴う有効表面積の増加によるFe−Zn反応の活性化は
得られるものの、この活性化が還元Ｐによる反応阻害に
よって相殺されることになり、合金化促進効果が小さく
なる。When P-added steel is pre-oxidized, P is also oxidized at the same time, and the resulting oxide film contains iron oxide and a trace amount of P oxide. Then, when reduction annealing is performed at 750 ° C. or higher as in the conventional case, the iron oxide is reduced to reduced iron and, at the same time, a small amount of coexisting P oxide is also reduced.
The reduced P participates in the Fe-Zn reaction during alloying and significantly delays this reaction. Therefore, in this case, although the activation of the Fe-Zn reaction can be obtained by the increase of the effective surface area due to the generation of reduced iron, this activation is offset by the reaction inhibition by the reduced P, and the alloying promotion effect is Get smaller.

【００２４】これに対して、本発明の方法のように還元
を750 ℃未満の比較的低温で行うと、鉄酸化物は還元さ
れて還元鉄になるが、Ｐ酸化物は還元されない。従っ
て、還元鉄の組成は、鉄と微量のＰ酸化物とを含有する
ことになる。Ｐ酸化物は、還元Ｐとは異なり、合金化時
のFe−Zn反応に関与しないため、鋼板表面は純鉄に近い
ような高い反応性を有する。そのため、還元鉄による有
効表面積の増大の効果が十分に発揮され、合金化速度が
飛躍的に向上するものと考えられる。しかし、酸化鉄量
が１g/m²を超えると、比較的低温での還元であるため酸
化物が残る、または酸化物が炉内で剥離するといった問
題が起こる。On the other hand, when the reduction is carried out at a relatively low temperature of less than 750 ° C. as in the method of the present invention, iron oxide is reduced to reduced iron, but P oxide is not reduced. Therefore, the composition of reduced iron contains iron and a trace amount of P oxide. Unlike reduced P, P oxide does not participate in the Fe-Zn reaction during alloying, so the surface of the steel sheet has a high reactivity similar to that of pure iron. Therefore, it is considered that the effect of increasing the effective surface area by the reduced iron is sufficiently exerted and the alloying rate is dramatically improved. However, when the amount of iron oxide exceeds 1 g / m ² , there is a problem that the oxide remains because it is reduced at a relatively low temperature, or the oxide peels off in the furnace.

【００２５】浴中Al濃度を高くすることによってめっき
皮膜の密着性が向上する理由も完全には解明されていな
いが、現状では次のように推測される。還元鉄からなる
被めっき表面は活性が高く、浴中Al濃度が高いと、めっ
き時には界面にFe−Al合金層が多量に生産される。この
Fe−Al合金層は、合金化時のFe−Zn反応を抑制するた
め、合金化熱処理の昇温時にはFe−Zn反応が起こり難
く、高温でFe−Al合金層が破壊されて合金化が進行す
る。高温での反応は、Fe−Al合金層を不均一に破壊する
ため、皮膜界面に凹凸を形成する。この凹凸が密着性向
上につながっているものと考えられる。The reason why the adhesion of the plating film is improved by increasing the Al concentration in the bath has not been completely clarified, but it is presumed as follows at present. The plated surface made of reduced iron has high activity, and if the Al concentration in the bath is high, a large amount of Fe-Al alloy layer is produced at the interface during plating. this
The Fe-Al alloy layer suppresses the Fe-Zn reaction during alloying, so the Fe-Zn reaction does not easily occur at the temperature rise during the alloying heat treatment, and the Fe-Al alloy layer is destroyed at high temperature and alloying proceeds. To do. The reaction at a high temperature destroys the Fe-Al alloy layer non-uniformly, so that unevenness is formed at the film interface. It is considered that these irregularities lead to improvement in adhesion.

【００２６】本発明のめっき方法におけるめっき母材
は、主として連続溶融亜鉛めっき装置においてライン内
還元焼鈍を必要とする鋼板 (例、冷延鋼板) であるが、
本発明方法の熱処理過程での機械的特性の変化を特に問
題としなければ、熱延鋼板等のライン外焼鈍を行う鋼板
についても適用可能である。The plating base material in the plating method of the present invention is a steel plate (eg, cold rolled steel plate) which requires in-line reduction annealing mainly in a continuous hot-dip galvanizing apparatus.
If the change in mechanical properties during the heat treatment process of the method of the present invention is not a particular problem, the present invention can be applied to a steel sheet such as a hot rolled steel sheet that is subjected to out-of-line annealing.

【００２７】本発明方法で対象とする鋼種はＰ添加高張
力鋼である。Ｐ含有量が0.020 ％より大の時に合金化速
度の遅延とめっき密着性の低下が問題となるので、Ｐ含
有量が0.020 ％超の鋼に本発明方法を適用する。Ｐ添加
量の上限は特に限定されないが、熱間および冷間圧延で
鋼板に割れなどが入らない領域として0.2 ％程度が上限
となる。The steel type targeted by the method of the present invention is P-added high-strength steel. When the P content is more than 0.020%, the alloying rate is delayed and the plating adhesion is deteriorated. Therefore, the method of the present invention is applied to the steel having a P content of more than 0.020%. The upper limit of the amount of P added is not particularly limited, but the upper limit is about 0.2% as a region where cracks do not occur in the steel sheet during hot rolling and cold rolling.

【００２８】母材鋼板のその他の成分は特に制限され
ず、Feと不可避不純物以外に、Ｃ、Ｓ、Si、Mn、Ti、M
g、Cr、Ni、Cu、Nb、Ta、Alなどの１種もしくは２種以
上の元素を含有することができる。高張力鋼板の機械的
特性を低下させないため、これらの元素は、次に示す鋼
中濃度とすることが好ましい。Si＜0.05％、Ｃ＜0.2
％、Ｓ＜0.03％、Mn＜2.0 ％、Ti＜0.1 ％、Mg＜1.0
％、Cr＜2.0 ％、Ni＜2.0 ％、Cu＜2.0 ％、Nb＜0.1
％、Ta＜0.1 ％、Al＜0.1 ％。その他の元素について
は、各元素につき0.01％未満で、合計で2.0 ％以下まで
とすることが好ましい。Other components of the base steel sheet are not particularly limited, and in addition to Fe and unavoidable impurities, C, S, Si, Mn, Ti, M
One or more elements such as g, Cr, Ni, Cu, Nb, Ta and Al can be contained. In order not to deteriorate the mechanical properties of the high-strength steel sheet, it is preferable that these elements have the following concentrations in steel. Si <0.05%, C <0.2
%, S <0.03%, Mn <2.0%, Ti <0.1%, Mg <1.0
%, Cr <2.0%, Ni <2.0%, Cu <2.0%, Nb <0.1
%, Ta <0.1%, Al <0.1%. With respect to other elements, it is preferable that the content of each element is less than 0.01% and the total content is 2.0% or less.

【００２９】図１に、本発明の方法を連続的に実施する
のに利用できる合金化溶融亜鉛めっき鋼板製造装置 (合
金化熱処理炉を備えた連続溶融亜鉛めっきライン) の１
例を示す。この図を参照しながら、以下、本発明方法を
工程順に説明する。FIG. 1 shows an apparatus for producing an alloyed hot-dip galvanized steel sheet (continuous hot-dip galvanizing line equipped with an alloying heat treatment furnace) which can be used for continuously carrying out the method of the present invention.
Here is an example. With reference to this figure, the method of the present invention will be described below in the order of steps.

【００３０】脱脂工程 冷延または熱延を受けた母材鋼板は、まず、必要に応じ
て脱脂される。脱脂は、例えば、約60℃の２〜３％水酸
化ナトリウム水溶液中に10〜300 秒間浸漬することによ
り行われる。或いは、トリクレン、シンナーなどの有機
溶剤脱脂、オルソ珪酸ソーダ水溶液中での電解脱脂など
も可能である。 Degreasing Step The base steel sheet that has been cold-rolled or hot-rolled is first degreased if necessary. Degreasing is performed by, for example, immersing in a 2-3% aqueous sodium hydroxide solution at about 60 ° C. for 10-300 seconds. Alternatively, organic solvent degreasing such as trichlene and thinner, and electrolytic degreasing in an aqueous solution of sodium orthosilicate are also possible.

【００３１】前酸化および焼鈍工程 必要により脱脂された鋼板は、十分水洗され、ドライヤ
ーにおいて熱風などで乾燥した後、加熱炉に送って、非
還元性雰囲気中で再結晶温度以上、900 ℃以下の温度範
囲に加熱した後、750 ℃以下まで冷却することによっ
て、前酸化と焼鈍を行う。 Pre-oxidation and annealing steps The steel sheet degreased as necessary is thoroughly washed with water, dried in a dryer with hot air or the like, and then sent to a heating furnace to be heated to a recrystallization temperature or higher and 900 ° C. or lower in a non-reducing atmosphere. After being heated to the temperature range, it is cooled down to 750 ° C or lower to perform preoxidation and annealing.

【００３２】この前酸化により鋼板表面に形成される酸
化皮膜は、上記の加熱と冷却を行った後のFe換算での酸
化鉄量が、0.05 g/m² 以上、1.0 g/m²以下となるように
する。酸化鉄量が0.05 g/m² より少ないと、酸化物の被
覆が少なく、次の還元工程で還元鉄が生成しても、合金
化促進効果が十分に得られない。また、1.0 g/m²より酸
化鉄量が多いと、炉内に酸化鉄のピックアップなどが起
こり、表面欠陥の原因となる。The oxide film formed on the surface of the steel sheet by this pre-oxidation has an iron oxide amount of 0.05 g / m ² or more and 1.0 g / m ² or less in terms of Fe after the above heating and cooling. To be When the amount of iron oxide is less than 0.05 g / m ² , the oxide coating is small, and even if reduced iron is produced in the subsequent reduction step, the alloying promotion effect cannot be sufficiently obtained. If the amount of iron oxide is more than 1.0 g / m ² , iron oxide may be picked up in the furnace, causing surface defects.

【００３３】前酸化は、鋼板を常温から上記温度範囲ま
で加熱する間のどの温度領域で行ってもよいが、酸化鉄
量が1.0 g/m²以下と少ないので、酸化反応の速度や制御
の容易さを考慮すると、酸化初期の 500〜750 ℃の温度
領域で酸化を主に進行させることが好ましい。750 ℃以
上の高温では、酸化反応が速いので、酸化鉄量の制御が
より困難となる。The pre-oxidation may be performed in any temperature range during the heating of the steel sheet from room temperature to the above temperature range. However, since the amount of iron oxide is as small as 1.0 g / m ² or less, the rate and control of the oxidation reaction are controlled. Considering the easiness, it is preferable to proceed the oxidation mainly in the temperature range of 500 to 750 ° C. at the initial stage of the oxidation. At a high temperature of 750 ° C or higher, the oxidation reaction is fast, so that it becomes more difficult to control the amount of iron oxide.

【００３４】その場合、図示のように、非還元性雰囲気
の加熱炉内を、予備加熱炉と焼鈍炉に区分し、最初の予
備加熱炉で 500〜750 ℃の温度領域の加熱を行う間に、
必要な酸化の大半を行う。次の焼鈍炉を通過する間に、
再結晶温度 (約750 ℃) 以上、900 ℃以下に昇温させ、
再結晶させる。この焼鈍炉内の非還元性雰囲気は、予備
加熱炉内の雰囲気より酸化性を弱くし、酸化皮膜の還元
を生じないが、それ以上の酸化もあまり起こらないよう
にする。その後、還元炉の前に設けた冷却帯において非
還元性雰囲気中で750 ℃以下まで冷却する。それによ
り、酸化鉄量をほとんど増大させずに焼鈍を行うことが
できる。このように酸化を主に 500〜750℃の温度領域
で行うことで、焼鈍後 (冷却後) の酸化鉄量を0.05〜1.
0 g/m²の範囲内に容易に制御することができる。In that case, as shown in the drawing, the inside of the heating furnace in the non-reducing atmosphere is divided into a preheating furnace and an annealing furnace, and while heating in the temperature range of 500 to 750 ° C. in the first preheating furnace. ,
Performs most of the required oxidation. While passing through the next annealing furnace,
Raise the temperature above the recrystallization temperature (about 750 ℃) and below 900 ℃,
Recrystallize. The non-reducing atmosphere in the annealing furnace has a weaker oxidizing property than the atmosphere in the preheating furnace and does not cause the reduction of the oxide film, but prevents further oxidation. Then, it is cooled to 750 ° C or lower in a non-reducing atmosphere in a cooling zone provided in front of the reduction furnace. Thereby, annealing can be performed without increasing the amount of iron oxide. In this way, the oxidation is performed mainly in the temperature range of 500 to 750 ° C, so that the amount of iron oxide after annealing (after cooling) is 0.05 to 1.
It can be easily controlled within the range of 0 g / m ² .

【００３５】予備加熱炉では、バーナー加熱、通電加
熱、誘導加熱、赤外加熱などの加熱方式によって、酸化
に必要な 500〜750 ℃の温度領域まで昇温させる。炉内
雰囲気は、1.0 g/m²以下の必要な前酸化が起こるような
弱酸化性雰囲気とする。好ましいう雰囲気は、酸素(O₂)
を５〜20,000 ppm含み、残りが不活性ガス (N₂が安価で
好ましい) からなる酸化性雰囲気である。O₂のかわりに
H₂O(露点０〜＋40℃) を、N₂の代わりにAr、He等の希ガ
スを使用してもよい。バーナー加熱方式の場合には、空
気と燃料ガスの混合比 (空燃比) を1.0 以上とすること
により、酸化させることも可能である。In the preheating furnace, the temperature is raised to a temperature range of 500 to 750 ° C. necessary for oxidation by a heating method such as burner heating, electric heating, induction heating, infrared heating or the like. The atmosphere in the furnace should be a weakly oxidizing atmosphere in which the required preoxidation of 1.0 g / m ² or less occurs. The preferred atmosphere is oxygen (O ₂ )
Is an oxidative atmosphere containing 5 to 20,000 ppm of hydrogen and the balance of an inert gas (N ₂ is inexpensive and preferable). Instead of O ₂
H ₂ O (dew point 0 to + 40 ° C.) may be used, and a rare gas such as Ar or He may be used instead of N ₂ . In the case of the burner heating method, it is also possible to oxidize by setting the mixing ratio of air and fuel gas (air-fuel ratio) to 1.0 or more.

【００３６】予備加熱炉で酸化した鋼板を、次いで焼鈍
炉内で 750〜900 ℃の温度領域内の到達温度まで昇温さ
せ、この温度に短時間保持した後、冷却帯にて冷却し、
焼鈍を行う。焼鈍は、圧延、特に冷間圧延中に生じた歪
みを除去し、適正な材料特性(延性、靱性など) を得る
ために必要である。Ｐ添加鋼の再結晶には750 ℃以上の
温度が一般に必要となる。900 ℃が上限となるのは、そ
れより高い温度で焼鈍すると、母材結晶粒が粗大とな
り、材料特性が劣化するばかりでなく、鋼板が軟化して
板の形状が保持できず、破断の危険性もあるからであ
る。The steel sheet oxidized in the preheating furnace is then heated in the annealing furnace to the ultimate temperature in the temperature range of 750 to 900 ° C., held at this temperature for a short time, and then cooled in the cooling zone.
Anneal. Annealing is necessary to remove the strain generated during rolling, especially cold rolling, and to obtain appropriate material properties (ductility, toughness, etc.). Recrystallization of P-added steel generally requires temperatures above 750 ° C. The upper limit of 900 ℃ is that not only the base material crystal grains become coarse and the material properties deteriorate when annealed at a higher temperature, but also the steel sheet softens and the shape of the sheet cannot be maintained, and there is a risk of fracture. Because there is also a nature.

【００３７】この焼鈍は、焼鈍中に還元を生じさせない
ように、非還元性雰囲気中で行う。焼鈍中に還元が起こ
ると、前述したように酸化皮膜中に含まれる微量のＰ酸
化物の還元が起こり、合金化速度の促進効果が著しく低
下する。また、焼鈍は高温で行うため、雰囲気の酸化性
が強いと酸化がさらに著しく進行し、焼鈍炉内で酸化鉄
のピックアップが起こるだけでなく、次の還元工程で酸
化鉄を還元しきれず、不めっきが発生することもある。
そのため、焼鈍雰囲気は、予備加熱炉の雰囲気より酸化
性が著しく弱い、微酸化性または実質的に不活性の雰囲
気とすることが好ましい。This annealing is performed in a non-reducing atmosphere so as not to cause reduction during annealing. When reduction occurs during annealing, a small amount of P oxide contained in the oxide film is reduced as described above, and the effect of promoting the alloying rate is significantly reduced. Further, since the annealing is performed at a high temperature, if the oxidizing property of the atmosphere is strong, the oxidation further progresses, and not only iron oxide is picked up in the annealing furnace, but also the iron oxide cannot be completely reduced in the next reduction step, resulting Plating may occur.
Therefore, it is preferable that the annealing atmosphere is a slightly oxidizing or substantially inert atmosphere in which the oxidizing property is significantly weaker than that in the preheating furnace.

【００３８】焼鈍に適した実質的に不活性または微酸化
性の雰囲気ガスガスとしては、(a)O₂を１〜500 ppm 含
み、残りがN₂からなるN₂-0₂ ガス、及び(b) 0.4 ≦Ｐ(H
₂O)/Ｐ(H₂)≦ 1.0程度のH₂O-H₂-N₂ ガスが挙げられる。
前酸化の雰囲気と同様に、N₂の代わりにAr、He等の希ガ
スを使用してもよい。これらのガスのO₂またはH₂O 濃度
の下限は、Feの還元を生じさせない最小濃度であり、上
限は高温の焼鈍炉内での鉄の酸化を著しく促進しないよ
うな濃度である。As the substantially inert or slightly oxidizing atmospheric gas gas suitable for annealing, (a) N ₂ -0 ₂ gas containing ₁ to 500 ppm of O ₂ and the balance of N ₂ and (b) ) 0.4 ≤ P (H
₂ O) / P (H ₂ ) ≦ 1.0 H ₂ OH ₂ —N ₂ gas may be mentioned.
As with the preoxidation atmosphere, a rare gas such as Ar or He may be used instead of N ₂ . The lower limit of the O ₂ or H ₂ O concentration of these gases is the minimum concentration that does not cause the reduction of Fe, and the upper limit is the concentration that does not significantly accelerate the oxidation of iron in the high temperature annealing furnace.

【００３９】焼鈍炉内のガス雰囲気を上記のように保持
するには、予備加熱炉と焼鈍炉の間の雰囲気を遮断する
ことが好ましい。この雰囲気の遮断は、予備加熱炉と焼
鈍炉の間に、シールロールやスロートを設けるか、また
はエアーカーテンなどのガスシールドにより達成され
る。予備加熱炉内の酸化性がより高いガスが、より高温
の焼鈍炉に侵入すると、焼鈍炉内で酸化が促進されす
ぎ、上記のような問題が起こることがある。In order to maintain the gas atmosphere in the annealing furnace as described above, it is preferable to shut off the atmosphere between the preheating furnace and the annealing furnace. This shutoff of the atmosphere is achieved by providing a seal roll or throat between the preheating furnace and the annealing furnace, or by using a gas shield such as an air curtain. When a gas having a higher oxidizing property in the preheating furnace enters the higher temperature annealing furnace, the oxidation may be excessively promoted in the annealing furnace, and the above problems may occur.

【００４０】焼鈍炉での鋼板の昇温は、誘導加熱、通電
加熱、ラジアントチューブ、赤外加熱などの加熱方式で
達成することができる。焼鈍が目的であるため、焼鈍炉
内での昇温速度は特に制限されないが、生産効率から急
速加熱が好ましい。実際には、上記のガス雰囲気であれ
ば、10℃/s以上、特に10〜100 ℃/sの昇温速度で十分で
ある。また、焼鈍温度 (到達温度) での保持時間は、再
結晶に必要な時間であるが、材料特性が良好であれば１
秒程度で十分である。加熱方式やその制御方法にも依存
するが、実際の保持時間は10〜100 秒程度となろう。The temperature rise of the steel sheet in the annealing furnace can be achieved by a heating method such as induction heating, electric heating, radiant tube, infrared heating or the like. Since the purpose is annealing, the heating rate in the annealing furnace is not particularly limited, but rapid heating is preferable from the viewpoint of production efficiency. In fact, in the above gas atmosphere, a heating rate of 10 ° C./s or more, particularly 10 to 100 ° C./s is sufficient. Also, the holding time at the annealing temperature (reaching temperature) is the time required for recrystallization, but if the material properties are good, it is 1
Seconds are enough. The actual holding time will be about 10 to 100 seconds, depending on the heating method and its control method.

【００４１】焼鈍温度の鋼板を次の還元炉に直ちに送る
と、750 ℃以上の高温で鋼板表面の酸化鉄皮膜が還元を
受け、Ｐ酸化物の還元が起こるため、還元炉に送る前に
鋼板温度が750 ℃以下に下がるように、焼鈍炉内または
還元炉への移送中の冷却帯において、鋼板を焼鈍と同様
の雰囲気中で冷却する。この時の冷却速度は特に制限さ
れないが、５〜20℃/sが好ましい。When the steel sheet at the annealing temperature is immediately sent to the next reduction furnace, the iron oxide film on the surface of the steel sheet is reduced at a high temperature of 750 ° C. or higher to reduce the P oxide. The steel sheet is cooled in an atmosphere similar to that used for annealing in the annealing zone or in the cooling zone during transfer to the reduction furnace so that the temperature falls to 750 ° C or lower. The cooling rate at this time is not particularly limited, but is preferably 5 to 20 ° C./s.

【００４２】なお、上記のように予備加熱炉と焼鈍炉に
分けて加熱を行うことが、酸化鉄量の制御が容易で好ま
しいが、これは必ずしも必須ではない。酸化鉄量の制御
はより難しくなるが、焼鈍炉の酸化性をやや高くして、
焼鈍炉内での 750〜900 ℃への加熱だけで前酸化と焼鈍
の両方の目的を達成することができる。要は、焼鈍が終
了して750 ℃以下に冷却された鋼板が、酸化後に実質的
に還元を受けておらず、かつ酸化鉄量が0.05〜1.0 g/m²
の範囲内にあればよい。It is preferable to separately heat the preheating furnace and the annealing furnace as described above because the amount of iron oxide can be easily controlled, but this is not always essential. It becomes more difficult to control the amount of iron oxide, but the oxidizability of the annealing furnace is made slightly higher,
Only heating to 750 to 900 ° C in the annealing furnace can achieve both the purpose of preoxidation and annealing. In short, the steel sheet that has been annealed and cooled to 750 ° C or less has not been substantially reduced after oxidation and the iron oxide content is 0.05 to 1.0 g / m ²
Within the range of.

【００４３】還元工程 上記のように、還元を伴わずに焼鈍した鋼板を次いで還
元炉内に送る。この還元炉を通過する間に、鋼板を750
℃未満、550 ℃以上の温度で還元して、鋼板表面の鉄酸
化物を還元鉄にする。しかし、還元温度が750 ℃未満で
あるため、鉄酸化物中に存在する微量のＰ酸化物は還元
を受けず、酸化物の状態にとどまる。そして、このＰ酸
化物は、前述したように、めっき後の合金化工程におい
て不活性であり、Fe−Zn反応の遅延を生じないため、還
元鉄による合金化促進効果が十分に発揮され、合金化速
度が著しく高くなる。 Reduction Step As described above, the steel sheet annealed without reduction is then fed into a reduction furnace. While passing through this reduction furnace, the steel plate was
It is reduced at temperatures below ℃ and above 550 ℃ to convert iron oxides on the surface of steel sheet to reduced iron. However, since the reduction temperature is less than 750 ° C., the trace amount of P oxide present in the iron oxide does not undergo reduction and remains in the oxide state. As described above, this P oxide is inactive in the alloying process after plating and does not delay the Fe-Zn reaction, so that the alloying promotion effect of reduced iron is sufficiently exerted, The rate of conversion becomes extremely high.

【００４４】還元温度が550 ℃未満では還元速度が遅
く、鋼板表面に鉄酸化物が残存して、不めっきの原因と
なる恐れがある。還元温度が750 ℃以上になると、酸化
鉄中のＰ酸化物も一緒に還元され、還元鉄は母材と同等
の濃度で還元Ｐを含むことになり、これがFe−Zn反応に
関与して、反応を遅延させるため、合金化促進効果が低
くなる。If the reduction temperature is less than 550 ° C., the reduction rate is slow and iron oxide may remain on the surface of the steel sheet, which may cause non-plating. When the reduction temperature is 750 ° C. or higher, the P oxide in iron oxide is also reduced, and the reduced iron contains reduced P at a concentration equivalent to that of the base material, which participates in the Fe-Zn reaction, Since the reaction is delayed, the alloying promotion effect becomes low.

【００４５】還元は鋼板表面の鉄酸化物が還元鉄に還元
されるまで行う。好ましい還元時間は30〜120 秒の範囲
内である。30秒未満では鉄酸化物を完全に還元すること
ができず、不めっきが生じる。また、120 秒以上では、
ライン長を長くする、またはライン速度を低下させるな
どの処置が必要となり、設備または生産などのコストが
かかる。温度保持を行うため、還元炉内でも加熱設備が
一般に必要となる。加熱方式は、誘導加熱、通電加熱、
ラジアントチューブ方式、赤外加熱方式などが可能であ
る。The reduction is performed until the iron oxide on the surface of the steel sheet is reduced to reduced iron. The preferred reduction time is within the range of 30 to 120 seconds. If it is less than 30 seconds, the iron oxide cannot be completely reduced, and non-plating occurs. Also, over 120 seconds,
It is necessary to take measures such as lengthening the line length or reducing the line speed, which requires equipment or production costs. In order to maintain the temperature, heating equipment is generally required even in the reduction furnace. The heating method is induction heating, electric heating,
Radiant tube method, infrared heating method, etc. are possible.

【００４６】前工程が鉄酸化が起こりうる非還元性雰囲
気であるので、前工程と還元工程との間の雰囲気の遮断
が必要である。この遮断には、シールロール、スロー
ト、エアーシールドなどを使用することができる。Since the previous step is a non-reducing atmosphere where iron oxidation can occur, it is necessary to shut off the atmosphere between the previous step and the reducing step. A seal roll, throat, air shield, or the like can be used for this interruption.

【００４７】還元雰囲気は、上記温度範囲で鉄酸化物は
還元されるが、Ｐ酸化物は還元されないように設定す
る。具体的には、水素濃度が２〜25％で、露点が−60℃
〜０℃であれば、このような条件となる。露点が低く、
水素濃度が高いほど酸化鉄を還元し易いので、ライン速
度を速くすることができ、生産性が向上する。しかし、
還元温度が 700℃以上、750 ℃未満と本発明の範囲内で
比較的高い場合には、還元雰囲気のO₂(H₂O) ポテンシャ
ルの低い状態で還元すると、先に述べたＰ酸化物の還元
が起こって改善効果が小さくなる可能性があるので、露
点を−30℃以上とし、還元時間を30〜90秒とすることが
好ましい。The reducing atmosphere is set so that iron oxide is reduced but P oxide is not reduced in the above temperature range. Specifically, the hydrogen concentration is 2 to 25%, and the dew point is -60 ° C.
If the temperature is up to 0 ° C, such a condition will be obtained. Low dew point,
The higher the hydrogen concentration, the easier it is to reduce iron oxide, so that the line speed can be increased and the productivity is improved. But,
When the reduction temperature is 700 ° C. or higher and lower than 750 ° C., which is relatively high within the scope of the present invention, when the reduction is carried out in a state where the O ₂ (H ₂ O) potential is low, the P oxide Since reduction may occur and the improvement effect may be reduced, it is preferable to set the dew point to −30 ° C. or higher and the reduction time to 30 to 90 seconds.

【００４８】溶融亜鉛めっき工程 以上の条件下で酸化焼鈍工程、および還元工程を経た
後、鋼板を通常はめっき浴温度まで冷却してから、めっ
き浴中の溶融亜鉛に浸漬して溶融亜鉛めっきを行う。こ
のめっき工程自体は、従来と同様の条件下で行えばよ
く、本発明においては特に条件を設定しない。 Hot-dip galvanizing step After the oxidative annealing step and the reducing step under the above conditions, the steel sheet is usually cooled to the plating bath temperature and then dipped in hot-dip zinc in the plating bath to perform hot-dip galvanizing. To do. The plating step itself may be performed under the same conditions as the conventional one, and the conditions are not particularly set in the present invention.

【００４９】めっき浴は主としてZnとAlで構成されてい
る。Al濃度は0.03〜0.2 ％の範囲内が好ましく、Al濃度
がこの範囲内であれば、本発明のよる合金化促進効果が
十分に期待できる。即ち、本発明では、合金化溶融亜鉛
めっきに従来用いられてきた0.08〜0.11％のAl濃度に比
べて、Al濃度の幅を広くすることができる。これは、従
来はAlが合金化の抑制効果を示すため、濃度を制限して
きたのに対し、本発明では上記のように合金化促進効果
が発揮されるため、Al濃度が高くなっても、合金化の遅
延が起こらないためである。The plating bath is mainly composed of Zn and Al. The Al concentration is preferably in the range of 0.03 to 0.2%, and if the Al concentration is in this range, the alloying promoting effect of the present invention can be expected sufficiently. That is, in the present invention, the width of the Al concentration can be widened as compared with the Al concentration of 0.08 to 0.11% conventionally used for galvannealing. This is because Al conventionally exhibits an alloying suppressing effect, so that the concentration has been limited, whereas in the present invention, since the alloying promoting effect is exhibited as described above, even if the Al concentration is high, This is because there is no delay in alloying.

【００５０】Al濃度の下限はドロス生成によるもので、
0.03％未満ではドロス発生が多く、操業が困難である。
Al濃度の上限は、本発明の対象製品が主に自動車用鋼板
であって、Zn−Al合金めっき鋼板は対象外であるためで
ある。従って、0.2 ％以上のAl濃度でめっきすることは
ほとんどない。The lower limit of the Al concentration is due to the generation of dross,
If it is less than 0.03%, dross is often generated and operation is difficult.
The upper limit of the Al concentration is because the target products of the present invention are mainly steel plates for automobiles, and Zn-Al alloy-plated steel plates are not. Therefore, plating with an Al concentration of 0.2% or more is rare.

【００５１】前述したように、めっき浴中のAl濃度が0.
12〜0.2 ％と、上記範囲内で高めの場合には、合金化後
のめっき密着性の向上が顕著に起こる。従って、合金化
溶融亜鉛めっき製品のうち、外板に使用するものなど特
に密着性を必要とするものについては、0.12〜0.2 ％の
Alを含有するめっき浴中でめっきを行うことが好まし
い。As described above, the Al concentration in the plating bath is 0.
When it is as high as 12 to 0.2% within the above range, the plating adhesion after alloying is remarkably improved. Therefore, among alloyed hot-dip galvanized products, those that require particularly good adhesion, such as those used for outer plates, should be 0.12-0.2%.
It is preferable to perform the plating in a plating bath containing Al.

【００５２】めっき浴成分としては、他に鋼板の溶出に
よるFeの混入などがあるが、Fe濃度が0.05％以下 (ドロ
スを含まない) であれば影響はない。その他、不可避不
純物としてNi、Co、Cr、Cu、Si、Ti、Li、Nb、Mo、Ta、
Ca、Mg、Mn、Ｋ、Na、Pb、Sn、Ｗなどの金属が１種以上
混入していても、各元素当たりの濃度が0.02％以下で合
計の濃度が0.5 ％以下であれば、影響はほとんどない。Other components of the plating bath include mixing of Fe due to elution of the steel sheet, but if the Fe concentration is 0.05% or less (does not include dross), there is no effect. Other unavoidable impurities include Ni, Co, Cr, Cu, Si, Ti, Li, Nb, Mo, Ta,
Even if one or more metals such as Ca, Mg, Mn, K, Na, Pb, Sn, and W are mixed, if the concentration of each element is 0.02% or less and the total concentration is 0.5% or less, the effect Almost never.

【００５３】めっき浴の温度は、通常は 420〜520 ℃の
範囲である。420 ℃未満では凝固点近傍であるため浴が
凝固することがあり操業が困難となり、520 ℃より高温
ではFe溶出量が増加し、ドロス発生が顕著になる。めっ
き浴の温度上昇を避けるため、めっき浴侵入時の鋼板温
度も 420〜520 ℃の範囲内のめっき浴温度になるべく近
い温度にする。The temperature of the plating bath is usually in the range of 420 to 520 ° C. At temperatures below 420 ° C, the bath may solidify because it is near the freezing point, making operation difficult, and at temperatures above 520 ° C, the amount of Fe elution increases and dross generation becomes noticeable. In order to prevent the temperature of the plating bath from rising, the temperature of the steel sheet when entering the plating bath should be as close as possible to the temperature of the plating bath within the range of 420 to 520 ° C.

【００５４】めっき付着量は、従来と同様、片面当たり
25〜70 g/m² 程度が普通である。このめっき付着量は、
めっき浴の上部に設けた付着量制御手段 (例、ガスワイ
ピングノズル) によって行われる。The amount of plating applied is the same as the conventional one
25 to 70 g / m ² is normal. This coating weight is
It is carried out by a deposit amount control means (eg, gas wiping nozzle) provided on the upper part of the plating bath.

【００５５】合金化熱処理工程 めっき浴を出た溶融亜鉛めっき鋼板を、めっき浴のすぐ
下流に設けた熱処理炉で加熱して、Znめっき層をZn−Fe
合金層に変える。この合金化熱処理も従来と同様に実施
すればよく、本発明では特に条件を設定しない。 Alloying heat treatment step The hot-dip galvanized steel sheet that has left the plating bath is heated in a heat treatment furnace provided immediately downstream of the plating bath to form a Zn-plated layer of Zn-Fe.
Change to alloy layer. This alloying heat treatment may be carried out in the same manner as the conventional one, and no particular conditions are set in the present invention.

【００５６】通常は、温度 480〜600 ℃程度で３〜60秒
間程度の加熱を行うことで、皮膜中Fe濃度を８〜12％程
度に調整したZn−Fe合金層を形成する。加熱方法につい
ては、誘導加熱、直接通電、バーナー、赤外線による加
熱などが可能である。加熱雰囲気は大気中が普通であ
る。熱処理炉を出た合金化溶融亜鉛めっき鋼板は、適当
な冷却手段 (例、水冷および／または空冷) で冷却し、
通常は歪取りのためにスキンパス圧延を受けてから、巻
き取られる。Usually, heating is performed at a temperature of about 480 to 600 ° C. for about 3 to 60 seconds to form a Zn—Fe alloy layer in which the Fe concentration in the film is adjusted to about 8 to 12%. As a heating method, induction heating, direct energization, a burner, heating with infrared rays, or the like is possible. The heating atmosphere is usually in the air. The alloyed hot-dip galvanized steel sheet leaving the heat treatment furnace is cooled by an appropriate cooling means (eg, water cooling and / or air cooling),
Usually, it is subjected to skin pass rolling for strain relief and then wound.

【００５７】[0057]

【実施例】実施例１ めっき母材として、表１に示す組成を持った、Ｐ添加量
の異なる下記Ａ〜Ｆの６種類の炭素鋼冷延鋼板の未焼鈍
材 (板厚0.8 mm) を、 250×100 mmに裁断して使用し
た。 Example 1 As a plating base material, unannealed materials (plate thickness 0.8 mm) of 6 types of carbon steel cold-rolled steel sheets having the compositions shown in Table 1 and different P addition amounts from the following A to F were used. , 250 × 100 mm, and cut.

【００５８】[0058]

【表１】 [Table 1]

【００５９】上記の各鋼板を、予め10％NaOH水溶液で脱
脂した後、所定雰囲気での熱処理が可能で、かつ還元雰
囲気から直接溶融めっきすることが可能な、実験用竪型
溶融めっき装置 (レスカ社製) を用いて、次に述べるよ
うにして(1) 前酸化、(2) 焼鈍、(3) 還元の各工程と
(4) 溶融めっきを行った。装置内での各加熱時の絶対圧
はいずれも１気圧であった。An experimental vertical hot dip galvanizing apparatus (less scaler) capable of performing heat treatment in a predetermined atmosphere after degreasing each of the above steel sheets with a 10% NaOH aqueous solution in advance and performing hot dip plating directly from a reducing atmosphere (1) pre-oxidation, (2) annealing, and (3) reduction steps as described below.
(4) Hot dip plating was performed. The absolute pressure during each heating in the device was 1 atm.

【００６０】(1) 前酸化 脱脂した鋼板は、上記めっき装置の熱処理炉内で、表２
のａ〜ｅに示す、O₂濃度５〜5000 ppmのO₂-N₂ 混合ガス
中または大気中で、表２に示す条件下で、 500〜700 ℃
の温度に予備加熱して鋼板表面を酸化し、酸化皮膜を形
成した。鋼板表面の酸化鉄量を溶液分析法により測定し
た。測定結果をFe換算量として表４に示す。(1) The pre-oxidized and degreased steel sheet was placed in Table 2 in the heat treatment furnace of the above plating apparatus.
500 to 700 ° C. under the conditions shown in Table 2 in an O ₂ —N ₂ mixed gas having an O ₂ concentration of 5 to 5000 ppm shown in a to e of Table 1 or in the atmosphere.
The surface of the steel sheet was oxidized by preheating to the temperature of 1 to form an oxide film. The amount of iron oxide on the surface of the steel sheet was measured by the solution analysis method. The measurement results are shown in Table 4 as the Fe conversion amount.

【００６１】[0061]

【表２】 [Table 2]

【００６２】(2) 焼鈍 上記のように予備加熱して前酸化した後、鋼板を上記雰
囲気中で一旦200 ℃まで冷却し、次いで雰囲気ガスを表
３に示す〜のいずれかの非還元性 (微酸化性または
実質的に不活性) ガスに置換し、このガス雰囲気中で、
昇温速度20℃/sで750 ℃以上、900 ℃以下の到達温度ま
で昇温させ、この温度に10〜90秒間保持した後、冷却速
度10℃/sで、750 ℃未満の還元温度まで冷却することに
よって、焼鈍を行った。この焼鈍後の酸化鉄量も上記と
同様に測定した。焼鈍工程での到達温度と保持時間およ
び還元温度、ならびに焼鈍後の酸化鉄量は表４に示す。(2) Annealing After pre-heating and pre-oxidizing as described above, the steel sheet is once cooled to 200 ° C. in the above atmosphere, and then the atmosphere gas is shown in Table 3 as one of non-reducing properties ( (Slightly oxidizing or substantially inert) gas, and in this gas atmosphere,
The temperature is raised at a temperature rise rate of 20 ° C / s to a temperature of 750 ° C or higher and 900 ° C or lower, held at this temperature for 10 to 90 seconds, and then cooled at a cooling rate of 10 ° C / s to a reduction temperature of less than 750 ° C. By doing so, annealing was performed. The amount of iron oxide after this annealing was also measured in the same manner as above. Table 4 shows the ultimate temperature, the holding time, the reduction temperature, and the amount of iron oxide after annealing in the annealing process.

【００６３】[0063]

【表３】 [Table 3]

【００６４】(3) 還元 焼鈍雰囲気中で還元温度まで冷却した後、雰囲気ガスを
露点が−60℃〜０℃、H₂濃度が５〜30％のN₂-H₂ 混合ガ
スに置換し、この鉄還元性雰囲気中で 550℃以上、750
℃未満の表４に示す還元温度に20〜90秒保持して還元を
行った。還元温度と保持時間は表４に示す。比較のため
に、還元温度が本発明の範囲外 (550 ℃未満か、750 ℃
以上) であるか、或いは雰囲気ガスが還元性雰囲気では
ない (即ち、露点が０℃超) 条件下で同様に還元を行っ
た。この時の条件も表４に示す。(3) Reduction After cooling to the reduction temperature in an annealing atmosphere, the atmosphere gas was replaced with a N ₂ —H ₂ mixed gas having a dew point of −60 ° C. to 0 ° C. and an H ₂ concentration of 5 to 30%, 550 ℃ or more, 750
The reduction was carried out by holding the reduction temperature shown in Table 4 below 20 ° C. for 20 to 90 seconds. The reduction temperature and the holding time are shown in Table 4. For comparison, the reduction temperature is outside the range of the invention (less than 550 ° C or 750 ° C).
Or more) or the atmosphere gas is not a reducing atmosphere (that is, the dew point is higher than 0 ° C.), and the reduction is similarly performed. The conditions at this time are also shown in Table 4.

【００６５】(4) 溶融亜鉛めっき 還元工程での温度保持が終了した後、この還元性雰囲気
で鋼板温度が約460 ℃になるまで冷却した。冷却した鋼
板を、次いでAl濃度0.03％以上、0.2 ％以下、残部Znか
らなる、浴温460 ℃の溶融亜鉛浴中に浸漬して両面溶融
めっきを行った。めっき浴浸漬時間は２秒であり、ガス
ワイパーによりZn付着量を約60 g/m²(片面当たり) に調
整した。(4) Hot-dip galvanizing After the temperature was maintained in the reducing step, the steel sheet was cooled in this reducing atmosphere until the temperature of the steel sheet reached about 460 ° C. The cooled steel sheet was then immersed in a hot dip zinc bath having an Al concentration of 0.03% or more and 0.2% or less and the balance Zn and having a bath temperature of 460 ° C. to perform double-sided hot dip plating. The immersion time in the plating bath was 2 seconds, and the Zn adhesion amount was adjusted to about 60 g / m ² (per surface) with a gas wiper.

【００６６】(5) 合金化熱処理 めっき後、500 ℃の塩浴で合金化熱処理し、皮膜中Fe濃
度が９〜11％になった時間を合金化完了時間として測定
した。合金化時間が20秒以下を○、20〜40秒を△、40秒
以上を×と判定した。この合金化の評価も表４に併せて
示す。(5) Alloying heat treatment After plating, alloying heat treatment was carried out in a salt bath at 500 ° C., and the time when the Fe concentration in the coating became 9 to 11% was measured as the alloying completion time. An alloying time of 20 seconds or less was evaluated as O, 20 to 40 seconds was evaluated as Δ, and 40 seconds or more was evaluated as x. Evaluation of this alloying is also shown in Table 4.

【００６７】[0067]

【表４】 [Table 4]

【００６８】表４からわかるように、本発明に従って、
前酸化でFe換算量で0.05〜１．０ ｇ／ｍ^２となるよう
に鋼板表面を酸化した後、非還元性雰囲気中で酸化鉄量
が１．０ ｇ／ｍ^２を超えないように焼鈍し、次いで75
0 ℃未満で還元するという工程順でめっき前処理を行う
ことにより、Ｐ添加鋼の溶融亜鉛めっき後の合金化が促
進され、短時間で合金化処理を完了することができた。
一方、比較例のように、還元条件が本発明の範囲外で
は、合金化促進効果は得られなかった。As can be seen from Table 4, according to the present invention,
After oxidizing the steel sheet surface such that 0.05 to 1.0 g / m ² in terms of Fe content in the pre-oxidation annealing as iron oxide content in a non-reducing atmosphere does not exceed 1.0 g / m ² Then 75
By performing the pretreatment for plating in the order of the steps of reduction at less than 0 ° C., the alloying of the P-added steel after the hot dip galvanization was promoted, and the alloying treatment could be completed in a short time.
On the other hand, as in the comparative example, when the reducing condition was outside the range of the present invention, the alloying promoting effect was not obtained.

【００６９】実施例２ 実施例１と同様に合金化溶融亜鉛めっき鋼板を作製し
た。ただし、溶融亜鉛めっき時の浴中Al濃度を0.12％以
上とし、次の合金化熱処理を皮膜中のFe濃度が９〜11％
になるまで行った。得られた合金化溶融亜鉛めっき鋼板
について、次の２種類の試験方法でめっき皮膜の密着性
を評価した。 Example 2 A galvannealed steel sheet was prepared in the same manner as in Example 1. However, the concentration of Al in the bath during hot dip galvanizing is 0.12% or more, and the Fe concentration in the film is 9 to 11% during the next alloying heat treatment.
I went to. With respect to the obtained galvannealed steel sheet, the adhesion of the plating film was evaluated by the following two test methods.

【００７０】カップ絞り後の皮膜剥離試験：直径60 m
m の円板状に打ち抜いた合金化溶融亜鉛めっき鋼板の試
験片を、常温でポンチ直径30 mm 、ダイス肩半径３Ｒの
円筒絞りにより剪断を付与した後、外側円筒部のテープ
剥離を行い、剥離重量を測定し、次の基準で評価した。 ○：25mg未満 (良好) 、 △：25mg以上、35mg未満 (通常) 、 ×：35mg以上 (不良) 。Film peeling test after cup drawing: diameter 60 m
A test piece of an alloyed hot-dip galvanized steel sheet punched out in a disk shape of m is sheared by a cylindrical squeeze with a punch diameter of 30 mm and a die shoulder radius of 3R at room temperature, and then the tape is peeled off from the outer cylindrical portion. The weight was measured and evaluated according to the following criteria. ◯: Less than 25 mg (good), Δ: 25 mg or more, less than 35 mg (normal), ×: 35 mg or more (poor).

【００７１】塗装後の低温衝撃試験： 150×70mmの寸
法に切り出した合金化溶融亜鉛めっき鋼板の試験片を、
市販の浸漬式リン酸塩処理液で化成処理した後、カチオ
ン型電着塗料による下塗り→中塗り→上塗りの３コート
塗装 (合計膜厚：100 μｍ)を施した。得られた塗装鋼
板を−20℃に冷却保持し、グラベロ試験機において直径
４〜６mmの砂利石 (玄武岩) 10個を空気圧2.0 kg/cm²、
衝突速度100 〜150km/hrの条件で衝突させ、各衝突点で
の塗装の剥離径を測定した。この剥離径の平均(平均剥
離径) により、次の基準で評価した。 ○：4.0mm 以下 (良好) 、 ×：4.0mm 超 (不良) 。Low temperature impact test after coating: A test piece of an alloyed hot-dip galvanized steel sheet cut into a size of 150 × 70 mm was
After chemical conversion treatment with a commercially available immersion type phosphating solution, three-coat coating (total film thickness: 100 μm) of cationic type electrodeposition coating of undercoating → intermediate coating → topcoating was applied. The coated steel sheet thus obtained was cooled and kept at -20 ° C, and 10 pieces of gravel stone (basalt) with a diameter of 4 to 6 mm were air-pressure 2.0 kg / cm ² in a gravure tester.
Collisions were made at a collision speed of 100 to 150 km / hr, and the paint peeling diameter at each collision point was measured. The average of the peeled diameters (average peeled diameter) was used for evaluation according to the following criteria. ◯: 4.0 mm or less (good), ×: more than 4.0 mm (poor).

【００７２】この密着性試験の結果を、母材の鋼種およ
び各処理条件と一緒に表５にまとめて示す。表５におい
て、各記号の意味は実施例１と同じである。比較のため
に、浴中Al濃度が0.12％未満の例、ならびにその他の条
件が本発明の範囲外の例の結果も、比較例として示す。The results of this adhesion test are summarized in Table 5 together with the steel type of the base material and each processing condition. In Table 5, each symbol has the same meaning as in Example 1. For comparison, the results of the examples in which the Al concentration in the bath is less than 0.12% and the examples in which other conditions are outside the scope of the present invention are also shown as comparative examples.

【００７３】[0073]

【表５】 [Table 5]

【００７４】表５からわかるように、めっき浴中のAl濃
度が0.12％以上と高いと、合金化処理後のめっき皮膜の
密着性が向上し、密着性試験で剪断付与後の剥離が少
なく、密着性試験の低温衝撃にも十分に耐える、密着
性に優れためっき皮膜が得られるので、自動車外板など
の用途に特に好適となる。しかし、浴中Al濃度が0.12％
以上であっても、還元条件が本発明の範囲外になると、
めっき密着性の改善は得られない。即ち、このめっき密
着性改善効果は、めっき前の処理条件が本発明の範囲内
であって、かつ浴中Al濃度が0.12％以上の時に得られる
のである。As can be seen from Table 5, when the Al concentration in the plating bath is as high as 0.12% or more, the adhesion of the plating film after the alloying treatment is improved, and the peeling after shearing is small in the adhesion test, Since a plating film having excellent adhesiveness that sufficiently withstands low-temperature impact in the adhesiveness test can be obtained, it is particularly suitable for applications such as automobile outer panels. However, the Al concentration in the bath is 0.12%
Even above, if the reducing conditions are outside the scope of the present invention,
No improvement in plating adhesion can be obtained. That is, this plating adhesion improving effect is obtained when the treatment conditions before plating are within the range of the present invention and the Al concentration in the bath is 0.12% or more.

【００７５】[0075]

【発明の効果】以上に説明した通り、本発明によれば、
Ｐ添加高張力鋼板の合金化溶融亜鉛めっきにおいて、従
来に比べて合金化速度を著しく高めることができ、合金
化溶融亜鉛めっき鋼板を効率的かつ経済的に製造するこ
とができる。また、めっき浴のAl濃度を調整すること
で、合金化後のめっき皮膜の密着性を高めることができ
る。本発明の方法で製造されためっき鋼板は、自動車用
材料、特に外板材料として使用可能な高性能を示すが、
比較的安価に製造できるため、家電製品や建材などの他
の用途にも有用である。As described above, according to the present invention,
In alloying hot-dip galvanizing of a P-added high-strength steel sheet, the alloying rate can be remarkably increased as compared with the conventional case, and the alloyed hot-dip galvanized steel sheet can be manufactured efficiently and economically. Further, by adjusting the Al concentration of the plating bath, the adhesion of the plated film after alloying can be enhanced. The plated steel sheet produced by the method of the present invention shows high performance that can be used as a material for automobiles, particularly as an outer plate material,
Since it can be manufactured relatively inexpensively, it is also useful for other applications such as home appliances and building materials.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明の方法を実施するのに適した溶融亜鉛め
っきラインの模式図である。1 is a schematic view of a hot dip galvanizing line suitable for carrying out the method of the present invention.

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】 Ｐ＞0.020 wt％の高張力鋼材を、非還元
性雰囲気中で再結晶温度以上、900 ℃以下の温度範囲に
加熱した後、750 ℃以下まで冷却し、この間に鋼板表面
にFe換算で0.05 g/m² 以上、1.0 g/m²以下の酸化皮膜を
形成し、次いで750 ℃未満、550 ℃以上の還元性雰囲気
中で還元した後、溶融亜鉛めっきを施し、合金化熱処理
を行うことを特徴とする、Ｐ添加高張力鋼材の合金化溶
融亜鉛めっき方法。1. A high-strength steel material with P> 0.020 wt% is heated in a non-reducing atmosphere to a temperature range not lower than the recrystallization temperature but not higher than 900 ° C. and then cooled to not higher than 750 ° C. An oxide film of 0.05 g / m ² or more and 1.0 g / m ² or less in terms of Fe is formed, which is then reduced in a reducing atmosphere at less than 750 ° C and 550 ° C or more, and then hot dip galvanizing is applied, and alloying heat treatment A method of alloying hot-dip galvanizing a P-added high-strength steel material, the method comprising: 【請求項２】 前記溶融亜鉛めっきを、浴中Al濃度が0.
12〜0.20wt％のめっき浴で行う、請求項１記載の方法。2. The hot dip galvanizing process has an Al concentration of 0.
The method according to claim 1, which is carried out in a plating bath of 12 to 0.20 wt%.