EP0453432B1 - A method of forming a zinc-aluminium coating on a steel strip - Google Patents
A method of forming a zinc-aluminium coating on a steel strip Download PDFInfo
- Publication number
- EP0453432B1 EP0453432B1 EP91870059A EP91870059A EP0453432B1 EP 0453432 B1 EP0453432 B1 EP 0453432B1 EP 91870059 A EP91870059 A EP 91870059A EP 91870059 A EP91870059 A EP 91870059A EP 0453432 B1 EP0453432 B1 EP 0453432B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- zinc
- strip
- coating
- steel strip
- thin layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/026—Deposition of sublayers, e.g. adhesion layers or pre-applied alloying elements or corrosion protection
Definitions
- the present invention relates to a method for forming a zinc-aluminum dip coating on a steel strip.
- the dip coating of a continuous steel strip is a technique which has been known and widely applied for many years. Essentially, it consists of running a strip of steel through a bath of molten metal or alloy, then solidifying the coating after adjusting its thickness. Generally, the dip coating operation is preceded by annealing under a reducing atmosphere, in order to rid the surface of the strip of any trace of oxide which may compromise the adhesion of the coating.
- zinc-aluminum alloys are commonly used, typically containing, by weight, in addition to zinc, 55% of aluminum as well as 1.6% of silicon.
- Such alloys combine the high corrosion resistance of aluminum and the cathodic protection provided by zinc.
- the purpose of the addition of silicon is to moderate the reaction between the iron of the steel strip and the aluminum of the coating. In the absence of silicon, this reaction leads in fact to a very significant loss of iron and to a coating completely transformed into Fe-Al which has no adhesion.
- the coatings have a structure, essentially composed of a metastable mixture of two phases which do not solidify simultaneously; thus zones rich in aluminum and zones rich in zinc appear, which have distinct physical properties and are the seat of internal constraints.
- a layer of fragile intermetallic particles is formed at the interface between the steel substrate and the zinc-aluminum coating, which degrades adhesion.
- the silicon added to moderate the reaction between iron and aluminum does not remain entirely in solution; on cooling, it precipitates in the form of needles which are the source of stress concentrations and cause the fragility of the coating.
- the present invention provides a process for forming a zinc-aluminum dip coating on a steel strip which does not give rise to the aforementioned drawbacks and which allows, by simple and economically acceptable means in industrial operation, to give this coating excellent adhesion and ductility properties without altering its corrosion protection power.
- a method for forming a zinc-aluminum dip coating on a steel strip consists of electrolytically depositing on said strip, a thin layer of a metal chosen from nickel, cobalt and chromium, annealing said strip, provided with said thin layer, under a protective atmosphere, and then passing said strip thus coated through a zinc bath having a content of aluminum of about 55% by weight and free of silicon.
- the electrolytic deposition of said thin layer is carried out with a current density of at least 300 A / dm2, and preferably between 350 and 450 A / dm2.
- the thin layer of metal has in particular the effect of slowing down or preventing the exchanges between the steel substrate on the one hand and the zinc-aluminum coating on the other hand. It thus attenuates the reaction between the iron of the substrate and the aluminum of the coating and contributes to improving the adhesion of the latter. In addition, it avoids the presence of silicon in the zinc-aluminum bath; the zinc-aluminum coating therefore no longer contains embrittling silicon precipitates and its ductility is markedly improved.
- nickel was deposited in a thin layer, corresponding to approximately 3 g Ni / m2 in double face, on steel panels.
- An electrolytic solution containing 260 g / l of NiSO4.6H2O and 35 g / l of H3BO3 was used for this purpose, the pH of which was adjusted to 2.5 by addition of sulfuric acid.
- the current density was 330 A / dm2.
- the panels were then annealed at 720 ° C under an atmosphere of N2 - 5% H2 for 3 minutes, then they were coated by immersion in a zinc bath containing 55% by weight of aluminum and no silicon.
- the innermost layers of the reaction zone consist essentially of Fe-Al, with very low percentages of nickel and zinc.
- the actual coating that is to say the outer layer, consists of two main phases, respectively enriched with aluminum and zinc, which still contain traces of iron. In places, the coating also has particles very rich in nickel.
- This structure is very resistant to bending at 180 ° over twice the thickness of the panel, as well as to profiling, without notable cracking or chipping.
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
- Electroplating Methods And Accessories (AREA)
- Coating With Molten Metal (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
La présente invention concerne un procédé pour former un revêtement au trempé de zinc-aluminium sur une bande d'acier.The present invention relates to a method for forming a zinc-aluminum dip coating on a steel strip.
Le revêtement au trempé d'une bande d'acier en continu est une technique qui est connue et largement appliquée depuis de nombreuses années. Pour l'essentiel, elle consiste à faire défiler une bande d'acier dans un bain de métal ou d'alliage fondu, puis à solidifier le revêtement après avoir réglé son épaisseur. Généralement, l'opération de revêtement au trempé est précédée d'un recuit sous une atmosphère réductrice, afin de débarrasser la surface de la bande de toute trace d'oxyde pouvant compromettre l'adhérence du revêtement.The dip coating of a continuous steel strip is a technique which has been known and widely applied for many years. Essentially, it consists of running a strip of steel through a bath of molten metal or alloy, then solidifying the coating after adjusting its thickness. Generally, the dip coating operation is preceded by annealing under a reducing atmosphere, in order to rid the surface of the strip of any trace of oxide which may compromise the adhesion of the coating.
Un procédé de ce type est connu par le document JP-A-61-44168.A process of this type is known from document JP-A-61-44168.
On utilise couramment dans ce cadre, des alliages de zinc-aluminium, contenant typiquement, en poids, outre le zinc, 55 % d'aluminium ainsi que 1,6 % de silicium. De tels alliages combinent la haute résistance à la corrosion de l'aluminium et la protection cathodique assurée par le zinc. L'addition de silicium a pour but de modérer la réaction entre le fer de la bande d'acier et l'aluminium du revêtement. En l'absence de silicium, cette réaction conduit en effet à une très importante perte en fer et à un revêtement complètement transformé en Fe-Al qui ne présente aucune adhérence.In this context, zinc-aluminum alloys are commonly used, typically containing, by weight, in addition to zinc, 55% of aluminum as well as 1.6% of silicon. Such alloys combine the high corrosion resistance of aluminum and the cathodic protection provided by zinc. The purpose of the addition of silicon is to moderate the reaction between the iron of the steel strip and the aluminum of the coating. In the absence of silicon, this reaction leads in fact to a very significant loss of iron and to a coating completely transformed into Fe-Al which has no adhesion.
Il est cependant apparu que ces revêtements de Zn-Al-Si présentent de graves défauts d'adhérence et de ductilité lorsque les articles revêtus sont soumis à des opérations de pliage ou de profilage, par exemple lors de la fabrication de panneaux destinés à la construction. Ces défauts conduisent à la fissuration du revêtement, les fissures formées pouvant quelquefois mener à l'écaillage et même à la pelade du revêtement.However, it has appeared that these Zn-Al-Si coatings have serious adhesion and ductility defects when the coated articles are subjected to bending or profiling operations, for example during the manufacture of panels intended for construction. . These defects lead to cracking of the coating, the cracks formed can sometimes lead to chipping and even to the coating of the coating.
La fragilité et le manque d'adhérence de ces revêtements semblent provenir de trois causes principales. En premier lieu, les revêtements présentent une structure, composée essentiellement d'un mélange métastable de deux phases qui ne se solidifient pas simultanément; il apparaît ainsi des zones riches en aluminium et des zones riches en zinc, qui présentent des propriétés physiques distinctes et sont le siège de contraintes internes. De plus, il se forme à l'interface entre le substrat en acier et le revêtement de zinc-aluminium, une couche de particules intermétalliques fragiles qui dégradent l'adhérence. Enfin, le silicium ajouté pour modérer la réaction entre le fer et l'aluminium ne reste pas entièrement en solution; au refroidissement, il précipite sous forme d'aiguilles qui sont à l'origine de concentrations de contraintes et entraînent la fragilité du revêtement.The fragility and lack of adhesion of these coatings appear to stem from three main causes. Firstly, the coatings have a structure, essentially composed of a metastable mixture of two phases which do not solidify simultaneously; thus zones rich in aluminum and zones rich in zinc appear, which have distinct physical properties and are the seat of internal constraints. In addition, a layer of fragile intermetallic particles is formed at the interface between the steel substrate and the zinc-aluminum coating, which degrades adhesion. Finally, the silicon added to moderate the reaction between iron and aluminum does not remain entirely in solution; on cooling, it precipitates in the form of needles which are the source of stress concentrations and cause the fragility of the coating.
On a déjà cherché à remédier à ces inconvénients au moyen de traitements thermiques spécifiques. On a notamment proposé d'effectuer un réchauffage de la bande revêtue à 300 - 350°C pendant 3 minutes, ou encore un recuit en bobine à 150°C pendant 24 heures. Ces traitements se sont avérés techniquement satisfaisants, mais non viables sur le plan économique en raison des charges qu'ils imposent.We have already sought to remedy these drawbacks by means of specific heat treatments. In particular, it has been proposed to reheat the coated strip at 300-350 ° C for 3 minutes, or even coil annealing at 150 ° C for 24 hours. These treatments have proven to be technically satisfactory, but not economically viable because of the costs they impose.
La présente invention propose un procédé pour former un revêtement au trempé de zinc-aluminium sur une bande d'acier qui ne donne pas lieu aux inconvénients précités et qui permet, par des moyens simples et économiquement acceptables en fonctionnement industriel, de conférer à ce revêtement d'excellentes propriétés d'adhérence et de ductilité sans altérer son pouvoir de protection contre la corrosion.The present invention provides a process for forming a zinc-aluminum dip coating on a steel strip which does not give rise to the aforementioned drawbacks and which allows, by simple and economically acceptable means in industrial operation, to give this coating excellent adhesion and ductility properties without altering its corrosion protection power.
Conformément à la présente invention, un procédé pour former un revêtement au trempé de zinc-aluminium sur une bande d'acier consiste à déposer par voie électrolytique sur ladite bande, une couche mince d'un métal choisi parmi le nickel, le cobalt et le chrome, à recuire ladite bande, munie de ladite couche mince, sous une atmosphère protectrice, et à faire ensuite passer ladite bande ainsi revêtue à travers un bain de zinc présentant une teneur en aluminium d'environ 55 % en poids et exempt de silicium.According to the present invention, a method for forming a zinc-aluminum dip coating on a steel strip consists of electrolytically depositing on said strip, a thin layer of a metal chosen from nickel, cobalt and chromium, annealing said strip, provided with said thin layer, under a protective atmosphere, and then passing said strip thus coated through a zinc bath having a content of aluminum of about 55% by weight and free of silicon.
Suivant une caractéristique supplémentaire du procédé de l'invention, on opère le dépôt électrolytique de ladite couche mince avec une densité de courant d'au moins 300 A/dm², et de préférence comprise entre 350 et 450 A/dm².According to an additional characteristic of the method of the invention, the electrolytic deposition of said thin layer is carried out with a current density of at least 300 A / dm², and preferably between 350 and 450 A / dm².
La couche mince de métal a notamment pour effet de freiner ou d'empêcher les échanges entre le substrat en acier d'une part et le revêtement de zinc-aluminium d'autre part. Elle atténue ainsi la réaction entre le fer du substrat et l'aluminium du revêtement et contribue à améliorer l'adhérence de ce dernier. En outre, elle permet d'éviter la présence de silicium dans le bain de zinc-aluminium; le revêtement de zinc-aluminium ne comporte donc plus de précipités de silicium fragilisants et sa ductilité s'en trouve nettement améliorée.The thin layer of metal has in particular the effect of slowing down or preventing the exchanges between the steel substrate on the one hand and the zinc-aluminum coating on the other hand. It thus attenuates the reaction between the iron of the substrate and the aluminum of the coating and contributes to improving the adhesion of the latter. In addition, it avoids the presence of silicon in the zinc-aluminum bath; the zinc-aluminum coating therefore no longer contains embrittling silicon precipitates and its ductility is markedly improved.
A titre d'exemple, on a déposé du nickel en couche mince, correspondant à environ 3 g Ni/m² en double face, sur des panneaux en acier. On a utilisé à cet effet une solution électrolytique à 260 g/l de NiSO₄.6H₂O et 35 g/l de H₃BO₃, dont le pH a été ajusté à 2,5 par addition d'acide sulfurique. La densité de courant était de 330 A/dm². Les panneaux ont ensuite subi un recuit à 720°C sous une atmosphère de N₂ - 5 % H₂ pendant 3 minutes, puis ils ont été revêtus par immersion dans un bain de zinc contenant 55 % en poids d'aluminium et pas de silicium.For example, nickel was deposited in a thin layer, corresponding to approximately 3 g Ni / m² in double face, on steel panels. An electrolytic solution containing 260 g / l of NiSO₄.6H₂O and 35 g / l of H₃BO₃ was used for this purpose, the pH of which was adjusted to 2.5 by addition of sulfuric acid. The current density was 330 A / dm². The panels were then annealed at 720 ° C under an atmosphere of N₂ - 5% H₂ for 3 minutes, then they were coated by immersion in a zinc bath containing 55% by weight of aluminum and no silicon.
L'analyse des revêtements obtenus montre que le nickel ne joue pas uniquement un rôle de barrière entre l'acier et le revêtement. Les couches les plus intérieures de la zone de réaction, c'est-à-dire du côté de l'acier, sont essentiellement constituées de Fe-Al, avec de très faibles pourcentages de nickel et de zinc. En se déplaçant vers l'extérieur, on rencontre alors des couches à base d'aluminium enrichies en nickel et en zinc, avec une teneur en fer très faible.Analysis of the coatings obtained shows that nickel does not only act as a barrier between the steel and the coating. The innermost layers of the reaction zone, that is to say on the steel side, consist essentially of Fe-Al, with very low percentages of nickel and zinc. By moving outwards, we then come across aluminum-based layers enriched in nickel and zinc, with a very low iron content.
Le revêtement proprement dit, c'est-à-dire la couche extérieure, est constitué deux phases principales, respectivement enrichies en aluminium et en zinc, qui contiennent encore des traces de fer. Par endroits, le revêtement présente en outre des particules très riches en nickel.The actual coating, that is to say the outer layer, consists of two main phases, respectively enriched with aluminum and zinc, which still contain traces of iron. In places, the coating also has particles very rich in nickel.
Cette structure résiste très bien à la flexion à 180° sur deux fois l'épaisseur du panneau, ainsi qu'au profilage, sans fissuration notable ni écaillage.This structure is very resistant to bending at 180 ° over twice the thickness of the panel, as well as to profiling, without notable cracking or chipping.
Claims (2)
- Process for forming an adherent coating of zinc-aluminium on a steel strip, in which a thin layer of a metal chosen from nickel, cobalt and chromium is deposited electrolytically on a steel strip, the strip provided with the said thin layer is annealed under a protective atmosphere and is then passed through a bath of zinc which has an aluminium content of approximately 55 % by weight and is free from silicon.
- Process according to Claim 1, characterized in that the electrolytic deposition of the said thin layer is performed with a current density of at least 300 A/dm².
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE9000428A BE1004079A6 (en) | 1990-04-17 | 1990-04-17 | Process for forming a coating zinc-aluminum strip steel. |
| BE9000428 | 1990-04-17 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0453432A1 EP0453432A1 (en) | 1991-10-23 |
| EP0453432B1 true EP0453432B1 (en) | 1994-11-30 |
Family
ID=3884763
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP91870059A Expired - Lifetime EP0453432B1 (en) | 1990-04-17 | 1991-04-12 | A method of forming a zinc-aluminium coating on a steel strip |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0453432B1 (en) |
| JP (1) | JPH0726357A (en) |
| AT (1) | ATE114739T1 (en) |
| BE (1) | BE1004079A6 (en) |
| DE (1) | DE69105340D1 (en) |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1521824A (en) * | 1966-05-04 | 1968-04-19 | M & T Chemicals Inc | Process for depositing chromium on metal strips |
| SE393403B (en) * | 1972-08-09 | 1977-05-09 | Bethlehem Steel Corp | WAY TO COVER THE SURFACE OF AN IRON STRING WITH AN AL-ZN ALLOY |
| SE378118B (en) * | 1974-03-14 | 1975-08-18 | Nordstjernan Rederi Ab |
-
1990
- 1990-04-17 BE BE9000428A patent/BE1004079A6/en not_active IP Right Cessation
-
1991
- 1991-04-12 EP EP91870059A patent/EP0453432B1/en not_active Expired - Lifetime
- 1991-04-12 DE DE69105340T patent/DE69105340D1/en not_active Expired - Lifetime
- 1991-04-12 AT AT91870059T patent/ATE114739T1/en not_active IP Right Cessation
- 1991-04-15 JP JP3176277A patent/JPH0726357A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0453432A1 (en) | 1991-10-23 |
| ATE114739T1 (en) | 1994-12-15 |
| DE69105340D1 (en) | 1995-01-12 |
| JPH0726357A (en) | 1995-01-27 |
| BE1004079A6 (en) | 1992-09-22 |
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