JP4616433B2 - Hot-dip aluminized steel sheet with excellent corrosion resistance - Google Patents
Hot-dip aluminized steel sheet with excellent corrosion resistance Download PDFInfo
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- JP4616433B2 JP4616433B2 JP22379499A JP22379499A JP4616433B2 JP 4616433 B2 JP4616433 B2 JP 4616433B2 JP 22379499 A JP22379499 A JP 22379499A JP 22379499 A JP22379499 A JP 22379499A JP 4616433 B2 JP4616433 B2 JP 4616433B2
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- Prior art keywords
- steel sheet
- corrosion resistance
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- excellent corrosion
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Description
【0001】
【発明の属する技術分野】
本発明は、自動車等の排気系部材、ガソリンタンク材、屋根壁等の金属建材、トースター・ストーブ等の家庭用熱器具に使用される耐食性に優れた溶融アルミめっき系鋼板に関する。
【0002】
【従来の技術】
溶融アルミめっき系鋼板は、高い耐食性と耐熱性、美しい外観等から、前記したような自動車部品、建材、家電部品等の鋼板に使用されている。近年の自動車排気系部材の耐食性向上を持たせたものが多数開発されている(特開昭61−231152号公報、特開平3−277761号公報等)。原板としてCr含有鋼のステンレスを使用すると、当然耐食性は向上するが製造コストの増大となり、また加工性は劣化する傾向にある。そこで、めっき浴に耐食性向上元素を添加する検討も種々なされ、特開平2−88754号公報、特開平7−20091号公報等においてCr,Mn添加等が開示されている。
【0003】
一方、最近では、自動車燃料タンクのPbフリー化が検討されつつあり、この用途へのアルミめっき鋼板の適用も進みつつある。この際の課題は、耐食性と加工生、溶接性の高度なバランスである。一般に表面処理鋼板においてめっき付着量が増加するほど耐食性は当然向上するが、加工性、溶接性は低下する傾向にある。この際の溶接性は電極との反応性を意味しアルミは電極材料の銅と容易に反応するため付着量が増大すると電極と反応し易くなり電極寿命の低下を招く。
【0004】
そこで、これらの特性を両立させるべく、やはり多数の発明がなされている(特願平8−201769号公報等)が耐食性、溶接性および加工性を完全に両立できるとは言い難い状況である。また、アルミめっきは特に乾湿繰り返しの腐食環境下では非常に耐食性に優れるが、常時濡れた環境下では溶解が進行し易い傾向にある。特に塩害環境においてはアルミめっきは鋼板を犠牲防食して優先的に溶解するが、常時濡れた環境下ではその速度が大きく短期間でめっきが溶解してしまう可能性がある。
【0005】
【発明が解決しようとする課題】
そこで本発明においてアルミめっき層上にMgおよびCa金属の酸化物もしくは水酸化物を主体とする保護皮膜を形成させる処理を行うことにより(例えばめっき層中にMgおよびCa金属を添加する)めっき鋼板の腐食を抑制し、これにより低付着量でも十分な耐食性を発揮することが可能となり加工性、溶接性をも向上させた溶融アルミめっき系鋼板を提供するものである。
【0006】
【課題を解決するための手段】
本発明者らはめっき鋼板の防食のための詳細な検討を行ったところめっき表面上にMg,Oを主体としたその他Ca,Al,Siを含む皮膜が存在させることによりめっき層の溶解(腐食)を抑制できることを明らかにした。この皮膜が存在すると塩害環境、特に濡れ環境において顕著であるが大気環境、硫酸環境等においても十分な効果を発揮する。
そして、この皮膜を形成させるためにはめっき層中にMgおよびCa金属が必要であり、Mgが最も効果が高い。ただし、めっき浴中にMgを添加するとその高酸化性より表面に大きなシワ模様が発生し外観不良を招く。そこでN2 シールBOXの導入や浴中への微量Ca併用によりシワ発生は抑制可能である。
【0007】
本発明の要旨とするところは以下の通りである。
(1)めっき層中にMgおよびCa金属を含有し、大気開放下での溶融アルミめっき系鋼板のめっき表面において、MgおよびCa金属と酸素を含む皮膜を形成することを特徴とする耐食性に優れた溶融アルミめっき系鋼板。
(2)めっき表面に形成されるMgおよびCa金属と酸素を含む皮膜の厚さが10〜1000Åであることを特徴とする請求項1記載の耐食性に優れた溶融アルミめっき系鋼板にある。
【0008】
次に、本発明の数値の限定理由について説明する。
大気開放下での5%NaCl溶液中で、溶融アルミめっき系鋼板はアルミの安定な酸化物が犯されるためアルミの表面電位が卑になりアルミめっき層が溶解する。その場合、アルミめっき表面上には皮膜は形成されず、72時間経過後もアルミ層が溶解消失してくる。しかし、めっき鋼材表面にMgおよびCa金属の酸化物もしくは水酸化物による10〜1000Åの厚さの皮膜が形成されていると鉄の溶出を抑制し赤錆の発生を防止できることを突き止めた。この皮膜厚みが10Åより薄いとアルミの溶解を抑制するには乏しく、1000Åより厚い皮膜が生成されても鉄の防食効果は変化せず供給するMg量が必要となり不経済であるため1000Å以下が望ましい。また、アルカリ土類金属の中でもMgおよびCaとの併用とする。
また、MgおよびCa金属の供給に関してはMgおよびCa金属単独、もしくは化合物としてめっき層中に存在させる方法がある。
【0009】
次に、実施例で本発明を詳細に説明する。
【実施例】
冷延鋼板を連続焼鈍し以下のA,B浴中に鋼板を浸漬し約30g/m2 の付着量のサンプルを作製した。
浴組成 A:Al−10wt%Si
B:Al−10wt%Si−6wt%Mg+0.01wt%Ca
そして、大気開放下中でめっき表面の後処理皮膜や有機皮膜をペーパー研磨で取り除きめっき金属を露出させる。次に水洗して表面の削り粉を除去した後乾燥させる。そのサンプルを、XPSによる皮膜分析およびスパッタ法による膜厚測定を行う。膜厚は酸素の強度がピーク強度の1/3になった時間を別途シリコン膜でのスパッタ速度測定結果をもとに換算した。その結果を表1に示す。
【0010】
【表1】
【0011】
また、寸法70×150mmの試料に対してJIS Z 2371に準拠した塩水噴霧試験を90日行い、腐食生成物を剥離して腐食減量を測定した。この腐食減量の表示はめっき片面に対しての値である。
〔評価基準〕
◎:腐食減量5g/m2 以下
〇:腐食減量10g/m2 未満
△:腐食減量10〜25g/m2
×:腐食減量25g/m2 超
【0012】
【発明の効果】
以上述べたように、本発明による溶融アルミめっき系鋼板表面においてアルカリ土類金属を主体とした皮膜を形成させることにより耐食性の優れた溶融アルミめっき系鋼板を得ることができる、極めて優れた効果を奏するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot-dip aluminum plated steel sheet having excellent corrosion resistance, which is used for exhaust system members such as automobiles, gasoline tank materials, metal building materials such as roof walls, and household heat appliances such as toasters and stoves.
[0002]
[Prior art]
Hot-dip aluminum-plated steel sheets are used in steel sheets such as automobile parts, building materials, and home appliance parts as described above because of their high corrosion resistance, heat resistance, beautiful appearance, and the like. A number of recent automobile exhaust system members having improved corrosion resistance have been developed (Japanese Patent Laid-Open Nos. 61-231152, 3-27761, etc.). When stainless steel of Cr-containing steel is used as the original plate, the corrosion resistance is naturally improved, but the manufacturing cost is increased, and the workability tends to deteriorate. Accordingly, various studies have been made to add an element for improving the corrosion resistance to the plating bath, and addition of Cr, Mn and the like are disclosed in JP-A-2-88754 and JP-A-7-20091.
[0003]
On the other hand, recently, Pb-free automobile fuel tanks are being studied, and application of aluminum-plated steel sheets for this application is also progressing. The problem at this time is a high balance between corrosion resistance, workability and weldability. In general, the corrosion resistance naturally improves as the coating amount increases in the surface-treated steel sheet, but the workability and weldability tend to decrease. The weldability at this time means the reactivity with the electrode, and aluminum easily reacts with the copper of the electrode material. Therefore, when the amount of adhesion increases, it reacts easily with the electrode, leading to a decrease in the electrode life.
[0004]
Therefore, many inventions have been made in order to achieve both of these characteristics (Japanese Patent Application No. 8-201769), but it is difficult to say that corrosion resistance, weldability, and workability can be completely achieved. In addition, aluminum plating is extremely excellent in corrosion resistance especially in a corrosive environment of repeated wet and dry conditions, but dissolution tends to proceed easily in an always wet environment. In particular, in a salt damage environment, aluminum plating preferentially dissolves by sacrificial corrosion protection of the steel sheet. However, in a constantly wet environment, the speed is large and the plating may be dissolved in a short period of time.
[0005]
[Problems to be solved by the invention]
Accordingly, in the present invention, a plated steel sheet is formed by performing a treatment for forming a protective film mainly composed of an oxide or hydroxide of Mg and Ca metal on the aluminum plating layer (for example, adding Mg and Ca metal to the plating layer). Accordingly, the present invention provides a hot-dip aluminum-plated steel sheet that can exhibit sufficient corrosion resistance even with a low adhesion amount, and has improved workability and weldability.
[0006]
[Means for Solving the Problems]
The present inventors have conducted a detailed study for corrosion protection of the plated steel sheet. As a result, the coating layer is dissolved (corrosion) by the presence of a coating containing Ca , Al, and Si mainly composed of Mg and O on the plating surface. ) Can be suppressed. The presence of this film is remarkable in a salt damage environment, particularly a wet environment, but exhibits a sufficient effect even in an air environment, a sulfuric acid environment, and the like.
And in order to form this membrane | film | coat, Mg and Ca metal are required in a plating layer, and Mg is the most effective. However, when Mg is added to the plating bath, a large wrinkle pattern is generated on the surface due to its high oxidation property, resulting in poor appearance. Therefore, the generation of wrinkles can be suppressed by introducing an N 2 seal BOX or using a trace amount of Ca in the bath.
[0007]
The gist of the present invention is as follows.
(1) containing Mg and Ca metal in the plating layer excellent in corrosion resistance to the plating surface of the molten aluminum plating system steel sheet under air opening, and forming a film containing Mg and Ca metal and oxygen Hot-dip aluminized steel sheet.
(2) The thickness of the coating film containing Mg and Ca metal and oxygen formed on the plating surface is 10 to 1000 mm.
[0008]
Next, the reason for limiting the numerical values of the present invention will be described.
In a 5% NaCl solution in the open atmosphere, the molten aluminum plated steel sheet is violated by a stable oxide of aluminum, so that the surface potential of the aluminum becomes base and the aluminum plating layer dissolves. In that case, no film is formed on the aluminum plating surface, and the aluminum layer dissolves and disappears after 72 hours. However, they found that the occurrence of the thickness of the film of 10~1000Å an oxide or hydroxide of Mg and Ca metals plated steel material surface is formed to suppress the elution of iron rust can be prevented. If this film thickness is less than 10 mm, it is not enough to suppress the dissolution of aluminum, and even if a film thicker than 1000 mm is formed, the anticorrosion effect of iron does not change and it is uneconomical because it requires an amount of Mg to be supplied. desirable. Further, among alkaline earth metals, it is used in combination with Mg and Ca.
Further, with respect to the supply of Mg and Ca metals there is a method to present in the plating layer as Mg and Ca metals alone or compound.
[0009]
Next, an Example demonstrates this invention in detail.
【Example】
The cold-rolled steel sheet was continuously annealed, and the steel sheet was immersed in the following A and B baths to prepare a sample having an adhesion amount of about 30 g / m 2 .
Bath composition A: Al-10 wt% Si
B : Al-10 wt% Si-6 wt% Mg + 0.01 wt% Ca
Then, the post-treatment film and the organic film on the plating surface are removed by paper polishing in the open atmosphere to expose the plating metal. Next, it is washed with water to remove the surface shavings and then dried. The sample is subjected to film analysis by XPS and film thickness measurement by sputtering. The film thickness was converted based on the result of the sputtering rate measurement on the silicon film separately for the time when the oxygen intensity became 1/3 of the peak intensity. The results are shown in Table 1.
[0010]
[Table 1]
[0011]
Further, a salt spray test based on JIS Z 2371 was performed on a sample having a size of 70 × 150 mm for 90 days, and the corrosion products were peeled off to measure the weight loss. This indication of corrosion weight loss is a value for the plated surface.
〔Evaluation criteria〕
◎: Corrosion weight loss 5 g / m 2 or less ○: Corrosion weight loss less than 10 g / m 2 Δ: Corrosion weight loss 10-25 g / m 2
×: Corrosion weight loss over 25 g / m 2
【The invention's effect】
As described above, by forming a coating mainly composed of alkaline earth metal on the surface of the hot-dip aluminum plated steel sheet according to the present invention, a hot-dip aluminum plated steel sheet having excellent corrosion resistance can be obtained. It is what you play.
Claims (2)
Priority Applications (1)
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JP22379499A JP4616433B2 (en) | 1999-08-06 | 1999-08-06 | Hot-dip aluminized steel sheet with excellent corrosion resistance |
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JP22379499A JP4616433B2 (en) | 1999-08-06 | 1999-08-06 | Hot-dip aluminized steel sheet with excellent corrosion resistance |
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JP2001049416A JP2001049416A (en) | 2001-02-20 |
JP4616433B2 true JP4616433B2 (en) | 2011-01-19 |
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JP22379499A Expired - Fee Related JP4616433B2 (en) | 1999-08-06 | 1999-08-06 | Hot-dip aluminized steel sheet with excellent corrosion resistance |
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Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
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JP4267184B2 (en) * | 1999-06-29 | 2009-05-27 | 新日本製鐵株式会社 | Hot-dip aluminized steel sheet with excellent corrosion resistance and appearance and manufacturing method thereof |
JP2004244655A (en) * | 2003-02-12 | 2004-09-02 | Nippon Steel Corp | HOT DIP Al BASED PLATED STEEL SHEET HAVING EXCELLENT CORROSION RESISTANCE, AND PRODUCTION METHOD THEREFOR |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5273138A (en) * | 1975-12-16 | 1977-06-18 | Nippon Steel Corp | Process for sealing aluminum plated steel sheet |
JPS56127762A (en) * | 1980-03-06 | 1981-10-06 | Nippon Steel Corp | Preparation of aluminum alloy plated steel plate with excellent corrosion resistance and processability |
JPS58181855A (en) * | 1982-04-15 | 1983-10-24 | Nisshin Steel Co Ltd | Production of steel plate hot-dipped in aluminum base composite |
JPH11279734A (en) * | 1998-03-27 | 1999-10-12 | Nisshin Steel Co Ltd | Aluminum-silicon-magnesium series hot dip aluminum base plated steel sheet excellent in surface property |
JP2000319786A (en) * | 1999-04-30 | 2000-11-21 | Nkk Corp | Surface treated steel sheet excellent in corrosion resistance |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH01263256A (en) * | 1988-04-15 | 1989-10-19 | Nippon Steel Corp | Aluminized steel sheet |
JPH0611906B2 (en) * | 1988-09-27 | 1994-02-16 | 新日本製鐵株式会社 | Hot-dip aluminum plated steel sheet with excellent corrosion resistance |
-
1999
- 1999-08-06 JP JP22379499A patent/JP4616433B2/en not_active Expired - Fee Related
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5273138A (en) * | 1975-12-16 | 1977-06-18 | Nippon Steel Corp | Process for sealing aluminum plated steel sheet |
JPS56127762A (en) * | 1980-03-06 | 1981-10-06 | Nippon Steel Corp | Preparation of aluminum alloy plated steel plate with excellent corrosion resistance and processability |
JPS58181855A (en) * | 1982-04-15 | 1983-10-24 | Nisshin Steel Co Ltd | Production of steel plate hot-dipped in aluminum base composite |
JPH11279734A (en) * | 1998-03-27 | 1999-10-12 | Nisshin Steel Co Ltd | Aluminum-silicon-magnesium series hot dip aluminum base plated steel sheet excellent in surface property |
JP2000319786A (en) * | 1999-04-30 | 2000-11-21 | Nkk Corp | Surface treated steel sheet excellent in corrosion resistance |
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