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(11) | EP 0 419 678 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | HIGHLY CORROSION-RESISTANT, DOUBLE-COATED STEEL SHEET EXCELLENT IN COATABILITY AND PREVENTED FROM BLISTERING IN ELECRODEPOSITION COATING AND PROCESS FOR PRODUCING THE SAME |
| (57) A double-coated steel sheet having a zinc-base coating containing at least a zinc
alloy coating or a zinc composite coating and having a coating weight of 25 g/m² or
above, formed on a steel sheet, and an iron-base coating containing at least an iron
coating or an iron alloy coating of an iron content of 50% or above and having a coating
weight of 1 to 10 g/m², formed on the zinc-base coating, wherein the total hydrogen
occlusion of the coating and the steel is limited to 300 ml/m² or below (per sheet
face). This sheet has such an excellent coatability that it is prevented from both
cratering and blistering in electrodeposition coating and is especially suitable as
a rust-preventive steel sheet for automobiles. This steel sheet is produced by applying
the aforementioned double-coating on a steel sheet and heat-treating the coated sheet
at 100 to 400°C. |
TECHNICAL FIELD
[0001] The present invention relates to multi-layer coated steel sheets having high corrosion resistance excellent in paintability particularly coated steel sheets suitable to rust proof steel sheets for automobiles, and relates to a producing method thereof,
BACKGROUND OF THE TECHNIQUE
[0002] Automobile bodies are mainly composed of thin steel sheets. For keeping, therefore, body appearances and safety thereof due to maintenance of mechanical strength for a long term of time, it is indispensable to provide excellent corrosion resistance and paintability for the steel sheets themselves to be used. To improve the corrosion resistance of the steel sheet, alloy-electroplated steel sheet such as Zn-Fe, Zn-Ni and others have been conventionally developed. With respect to the paintability, on the other hand, since crater shaped paint defects appear when zinc or zinc alloy coated steel sheets are subjected to cationic electrodeposition paint, arts for avoiding such defects are required. As a technique therefor, two-layer coated steel sheets, which have lower layers of zinc or zinc alloy coating and upper layers of Fe-Zn alloy coating having compositions containing not less than 50% Fe thereon, have been developed (Japanese Patent Publication No.58-15554, same No.57-28754, and Plating and Surface Finishing, 72 (1985) No.8, P52). Accordingly, by using said two-layer coated steel sheets, the high corrosion resistance and the excellent paintability may be made compatible.
[0003] However, going with prologation of using terms of the automoiles, more excellent corrosion resistance than heretofore has become necessary. As a method of imparting the corrosion resistance to the steel sheets, it is most preferable to apply Zn or Zn alloy coatings having sacrifice protection, taking damages at the coated parts into consideration. There are improvements in the compositions and coating thickness as methods of obtaining the high corrosion resistance in the coatings based on Zn or Zn alloys. However, the improvements in the compositions have conventionally been fully investigated, there will not be many chances of finding out new origins or chemical compositions exhibiting more excellent properties than the present ones. Therefore the coating thickening has actually become the most powerful technique for high corrosion resistance. Since heavily coated materials of course require the paintability, it is necessary to provide, as the upper coated layer, Fe-Zn alloy coatings or other coatings based on Fe or Fe alloys containing not less than 50% Fe. However according to the inventors' investigations, though multi-layer thick-coated rust proof steel sheets which were formed, via the electroplating method, with the upper layers of Fe-Zn alloy coatings or other coatings based on Fe or Fe alloys containing not less than 50% Fe, might avoid the crator appearances during the electrodeposition paint, it was found that the finished outer appearances of the electrodeposited paint films were considerably deteriorated. Such coating defects depend upon the electrodepositing or baking conditions, and were observed as protrudent or depressed rashes or pepper-and-salt like non-uniformities. Viewing through a scanning type electron microscope, it was found as seen in photographs of Fig.1, that these defects were bubble-like defects caused in electrodeposited paint. They are quite different sorts of paint defects from the crators reported hitherto, and as later mentioned, when baking the electrodeposited paint, absorbed hydrogen is released from the coated layer or the interior of the steel, and such absorbed hydrogen becomes the bubbles in the paints. The bubble-like paint defects do not appear in the conventional multi-layer lightly coated steel sheets performed by the electrodeposition paint under the same conditions. Accordingly, the bubble-like paint defects may be said as the defects particular to the multi-layer heavily coated steel sheets. The above stated paint defect is not only a problem from the standpoint of the appearances but also harmful in view of the corrosion resistance, and is therefore a vital issue to be solved for putting the multi-layer heavily coated steel sheets into practice.
DISCLOSURE OF THE INVENTION
[0004] The inventors made studies on the above mentioned paint defects, and consequently cleared up that the cause of the defect occurrence was a hydrogen absorbed in the multi-layer thick-coated steel sheets during producing processes, and found that said paint defects could be avoided by limiting an amount of the hydrogen absorption to be not more than 300 mℓ/m².
[0005] The present invention is based upon such findings, and is charactrized by a multi-layer coated steel sheet having,
[0006] on the surface thereof, a coated film based on Zn or Zn alloys of a coating adhesion amount being not less than 25 g/m², which is a single layer or multi-layer coated film being composed of one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys; or which is a multi-layer coated film being composed of Zn plated coating, and one or more than one kind s selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys,
[0007] Further on said coated film based on Zn or Zn alloys, a coated film based on Fe or Fe alloys of a coating adhesion amount being 1 to 10 g/m²', which is composed of one or more than one kinds selected from Fe plated coating or/and plated coatings based on Fe alloys containing not less than 50% Fe,
[0008] and wherein a total amount of the absorbed hydrogen in the coated film and the steel is not more than 300 mℓ/m² (per one side).
[0009] Such multi-layer coated steel plates have the excellent paintabilities and the high degree corrosion resistance, because of avoiding concurrently occurrences of the craters and the bubble-like paint defects caused by the electrodeposition paint.
[0010] A producing method of the present invention may produce efficiently such coated steel sheets, and is characteized by forming,
[0011] on the surface thereof, a coated film based on Zn or Zn alloys of a coating adhesion amount being not less than 25 g/m², which is a single layer or multi-layer coated film being composed of one or more than one kind s selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys; or which is a multi-layer coated film being composed of Zn plated coating, and one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys,
[0012] and subsequently forming, on said coated film based on Zn or Zn alloys, a coated film based on Fe or Fe alloys of a coating adhesion amount being 1 to 10 g/m², which is composed of one or more than one kinds selected from Fe plated coating or/and plated coatings based on Fe alloys containing not less than 50% Fe,
[0014] In the producing method of the present invention, it is preferable to carry out the heating treatment of the steel plate after the coating in a continuous line for heightening productivity, and in this case, the coated steel sheet is heated at a temperature of the steel surface between 100 and 400°C for not less than one second. In addition, for obtaining a press formability of high degree, the coated steel plate in an open coil is heated in a non-oxidizing atmosphere to a temperature between 100 and 250°C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Fig.1 is a magnifying microphotograph showing bubble-like defects occurring in a cationic electrodeposited paint film; Figs.2 and 3 show, with respect to an as-coated multi-layer steel sheets and the multi-layer steel sheets of multi-layers having removed the absorbed hydrogen by heating after coating, the results of the quantitative analysis of the concentrations of the absorbed hydrogen therein by an ion micro mass analyzer; Fig.4 shows the degrees of the relation between the amounts of the hydrogen absorption and the bubble-like ED paint defects; Fig.5 shows the relation between the releasing of the absorbed hydrogen and the temperature; Fig.6 shows, with respect to the as-coated multi-layer steel plate and the multi-layer steel plate having been heat-treated after coating, the results of the measurement of the hydrogen absorbed therein by a gas chromatography.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The multi-layer coated steel sheets of this invention have the inner layer plated coating, and the outer layer plated coating,
[0018] said inner layer coating being composed of coated films based on Zn or Zn alloys having at least the plated coatings based on Zn alloys or the composite plated coatings based on Zn or Zn alloys,
[0019] and said outer layer plated coating being composed of coated films based on Fe or Fe alloys. The inner layer coating is to impart the corrosion resistance to the multi-layer coated steel sheet. The coating adhesion amount of the coated layer is necessarily not less than 25 g/m² for securing a desired corrosion resistance specially in the bodies of automobiles and the like.
[0020] As the coated films based on Zn or Zn alloys as an inner layer coating, there are, for example, coated films of single layer or multi-layer structure composed of coatings based on Zn alloys or composite coatings based on Zn or Zn alloys,
[0021] or coating films of multi-layer structure composed of coating based on Zn alloys and composite coating based on Zn or Zn alloys. Actually, usually assumed are (i) single layer structure of coating based on Zn alloys, (ii) multilayer structure composed of the coatings based on Zn alloys of different kinds (including such a case that contents of alloying compositions are different. The same will be applied to the followings), (iii) single layer structure of the composite coating based on Zn or Zn alloys, (iv) multi-layer structure composed of the composite coatings based on Zn or Zn alloys of the different kinds, and (v) multi-layer structure composed of the coatings based on Zn alloys of one or more than one kinds, and composite coatings based on Zn or Zn alloys of one or more than one kinds.
[0022] The inner layer coating may be structured by mixing the coating based on Zn alloys or the composite coating based on Zn or Zn alloys, or the both, with Zn coating respectively. Also in this case, as the coating based on Zn alloys and the composite coating based on Zn or Zn alloys, the coatings of one or more than one kinds being different may be mixed.
[0023] The coatings based on Zn alloys are Zn-Fe, Zn-Ni, Zn-Mn, Zn-Co alloyed coatings, or said alloyed coatings thereof, each of which is contained with one or more than one kinds of elements as Ti, Cr, Mo, W, etc.
[0024] As a means for producing these coatings based on Zn alloys, there are a method of thermally alloying the hot dipping Zn platings,or electrogalvanized platings, an electroplating method, a vacuum evaporating method, and an ion plating method.
[0025] As the composite coating based on Zn or Zn alloys, one or more than one kinds of Al₂O₃, Cr₂O₃, SiO₂, BaCrO₄, etc. are Co deposited in the Zn coating or the above mentioned coatings based on Zn alloys.
[0026] The coating based on Fe or Fe alloys as the outer layer coatings are composed of an Fe coating or the coating based on Fe alloys containing not less than 50% Fe, or the multi-layer coatings of these coatings, and have a coating adhesion amount of 1 to 10 g/m². For preventing the occurrences of the craters during the electrodeposition paint, it is necessary to form the coating based on Fe or Fe alloys in the uppermost layer. In the case of the coating based on Fe alloys, the Fe content of less than 50% is not sufficient to prevent the crater occurrence.
[0027] The coated film based on Fe or Fe alloys is usually composed of the single layer structure of Fe alloyed coating or Fe coating but, as the case may be, this film may be, for example, composed of the multi-layer structure of Fe coating and Fe alloyed coating, or the multi-layer structure, etc. of more than one kinds of the coatings based on Fe alloys containing different Fe contents.
[0028] Herein, if the coating weight of the outer layer coating is less than 1g/m², the surface coverage is low, and the crater occurrence cannot be exactly prevented. On the other hand; if the coating amount exceeds 10 g/m², the adhering property of the coated layer is lowered.
[0029] The outer layer coating is formed by an electro-plating. At the present, as an industrial method for forming closely and uniformly a thin coated layer over a strip of large width, the electro-plating method is the only way.
[0030] The coatings based on Fe alloys are coatings containing, in Fe, one or more than one kinds of, e.g., Zn, Ni, Co, Mn, Cr, Mo, W, P and B.
[0031] In the present invention, the total amount of the absorbed hydrogen in the coated film and in the steel sheet is limited to be not more than 300mℓ/m² per one side of the steel sheet (which is the absorbed amount under the normal conditions of 1 atm and 25°C) in producing the above mentioned multi-layer coated structures.
[0032] If the coated film based on Fe alloys or the Fe coated film is formed as the outer layer by means of the electro-plating, the hydrogen is generated on surface of the inner layer in great volume, and a part thereof is absorbed in the coated layers and the steel.
[0033] With respect to the multi-layer coated steel sheets formed with the coating of Fe-Zn alloy containing 80% Fe on the hot dipping alloyed Zn coating, and the multi-layer steel sheets where said coated steel sheets are heated after coating to remove the absorbed hydrogen, Figs.2 and 3 show the results of the quantitative analysis of the concentration of the absorbed hydrogen therein by an ion micro mass analyzer (IMA). If a comparison is made between the case having removed the absorbed hydrogen by heating and the case not having done, it is found that the hydrogen is considerably absorbed in as-coated steel sheets.
[0034] The hydrogen was released by heating in an Ar atmosphere the multi-layer coated steel plates as mentioned above, and the hydrogen amount was measured with a gas chromatograph method, and the amount of the absorbed hydrogen in the coated steel sheets was measured. Then the relation between the amount of the absorbed hydrogen and an occurring degree of bubble-like paint defects was obtained. Fig.4 shows the results. A test sample used herein was the multi-layer coated steel sheet with the inner layer being the hot dipping alloyed zinc coating of the coating amount of 38 g/m² and the outer layer being the 80% Fe-Zn alloyed electro-plated coating of the coating amount of 5 g/m². The amount of the absorbed hydrogen in the coated steel sheet was adjusted by a preheating treatment prior to the electro-painting. As seen from Fig .4, it is a necessary condition that the amount of the absorbed hydrogen is to be not more than 300 mℓ/m² for preventing the occurrence of the bubble-like defects.
[0035] It is apparent from the above mentioned result that the hydrogen absorbed in the coated layers and in the steel sheet apparently has a close relation with the bubble-like paint defect. The bubble-like paint defect is assumed to be generated due to a mechanism as follows. Namely, if the electrodeposition paint is performed on the steel sheet where the hydrogen of more than a determined amount is absorbed in the coated layer and in the steel, the surface of the electrodeposited paint film is solidified before the hydrogen is fully released in a baking process, and a thin film is formed on the outside thereof. Since the hydrogen which is not released at the beginning of the baking process and remains therein, is enclosed within the coated film, the hydrogen gathers, and further is expanded by the heating and turns out the bubbles to cause the defects in the electrodeposited paint film. The baking temperature of the electrodeposited paint is generally 170 to 180°C, and this is a temperature range where the absorbed hydrogen is released at a high transmisson rate, as seen in Fig.5, that is, a temperature condition where the absorbed hydrogen is easily released, and accordingly the bubble is easily generated.
[0036] For controlling the amount of the absorbed hydrogen, there are methods of (1) heating, after coating the outer layer, the coated steel sheet; (2) selecting conditions difficult to cause the hydrogen absorption, as the condition of coating the outer layer; (3) employing steel kinds which are low in the hydrogen absorption, or difficult to release the hydrogen if absorbing it, or methods of combining them.
[0037] A further reference will be made to a producing method of the invention, a subject of which is to release the absorbed hydrogen by heating.
[0038] The producing method of the invention, as said above, comprises forming, on the steel surface, the inner layer coating composed of the coated film based on Zn or Zn alloys having at least the coating based on Zn alloys or the composite coating based on Zn or Zn alloys, and further forming, on said inner layer coating, the outer layer coating composed of the coated film based on Fe or Fe alloys, and heating the steel sheet at a temperature of 100 to 400°C after having formed said films. If the heating temperature is less than 100°C, the bubble-like paint defects cannot be sufficiently avoided, and if it exceeds 400°C, the inner layer coating and the steel plate make a thermal diffusion, and an alloyed layer is formed where the coating adhesion is deteriorated. For these reasons, the heating temperature is set to be 100 to 400°C.
[0039] The heating procedure is performed in a continuous line, aiming at a high productivity for not less than one second at said temperature (steel surface temperature). If the heating temperature is less than one second, it is diffuclt to avoid the bubble-like paint defects even at said temperature range. A maximum heating time is not especially limited, as far as the inner layer coating and the steel sheet do not create an alloying reaction. Heating manners are a high frequency induction heating system, and electric heating system and others, not especially limiting. A heating atmosphere is sufficient with the atmosphere containing no hydrogen or hydrogen of a degree actually not causing the hydrogen absorption, such as a nitrogen, or an air atmosphere, not yet especially limiting. If heating for a long period of time in the atmosphere, the outer layer coating is oxidized, and consequently a modifying treatment is hindered. Therefore, a time is limited to the heating in the atmosphere.
[0040] For imparting a press formability of high degree to the steel sheet, the heating treatment is carried out in the open coil heating. In this open coil heating, the steel sheet is heated at the temperature between 100 and 250°C in the non-oxidizing atmosphere. The lower limit thereof is as referred to above. In such heating system taking a long time from the heating to the cooling as the open coil heating, if heating at the temperature range exceeding 250°C, the inner layer coating and the steel plate are effected with a thermal diffusion to form an alloyed layer of the coating adhesion being deteriorated. Therefore, the upper limit of the heating temperature is set at 250°C. Further, the heating atmosphere is determined to be non-oxidizing for the following reasons. If heating in the oxidizing atmosphere, the coating based on Fe or Fe alloys of the outer layer is oxidized on the surface during heating and cooling, and subsequently a phosphate film is not normally formed which is required as an undercoated treatment for painting. However, if using a gas bearing the hydrogen, though the non-oxidizing atmosphere, the hydrogen concentration thereof should be made to an extent that the hydrogen is not absorbed in the coated layer and in the steel sheet while performing the heating. The heating time is sufficient with not less than one second in total at the steel temperature of not less than 100°C. If the heating time is less than one second, it is not possible to prevent the occurrence of the bubble-like ED paint defects even in said temperature range. The upper limit of the heating time in said temperature range is not especially limited, and is enough with about 30 minutes, taking the productivity into consideration.
[0041] With respect to the multi-layer coated steel sheet formed with Fe-Zn alloy coating of 80% Fe on the hot dipping alloyed zinc coating, and the multi-layer coated steel plate heated after having coated said steel sheet, Fig.6 shows the results that the hydrogen absorption amount in the coated steel sheet was measured with the gas chromatograph in the both cases. When the hydrogen absorption amounts are compared between the cases heated and non-heated, it is found that the hydrogen is considerably absorbed in an as-coated steel sheet, and the hydrogen concentration is lowered after heating.
[0042] The bubble-like paint defects generated in the electrodeposition paint can be prevented by the heating as above mentioned, because the hydrogen which has been absorbed while coating the outer layer, is removed by said heating, and in addition to such a factor, there is a possibility that it also influences thereto that Fe enriched contents of the outer layer are diffused, so that a closer outer coated layer is formed. In other words, as another reason why the bubble-like paint defect is generated other than the reason of the hydrogen absorption caused at coating of the outer layer, the following consideration may be taken. That is, an electric current is concentrated at the inner layer coating exposed microscopically when depositing the outer layer, and as a result, the hydrogen gas bubbles are locally concentrated. These gas bubbles are not completely released from the coated layer during the baking process but remain therein, and it is assumed that such bubbles expanded become the bubble-like paint defects. By heating them at the high temperature, the coated state of the outer layer which is, if being as-coated, incomplete microscopically, is improved due to the thermal diffusion thereby, and it is also assumed that the microscopic defects of the outer layer are repaired consequently. Therefore, the above mentioned matters will possibly contribute to the prevention of the occurrence of the bubble-like paint defects.
[0043] If the producing object of this invention is BH steel sheets, it is preferable to perform the heating treatment at a temperature as low as practicable. A temper rolling can be performed after coating the inner layer, coating the outer layer or the heating treatment, but it is desirable to carry out the temper rolling after the heating treatment for providing the high degree press formability or in a case of outer panels of the automobiles.
[0044] Depending upon the present invention, it is possible to supply the multi-layer coated steel sheets having the high corrosion resistance and without causing the crators and the bubble-like paint defects at the cation electrodepositing paint and accordingly with the excellent paintability. Thus, the high corrosion resistance and the beautification of the automobile bodies and others are compatible.
EXAMPLES
Example I
[0045] The cold rolled coils of the compositions of Table 1 were successively subjected, as blank coils, to the hot dipping zinc plating in the continuous plating line of the non-oxidizing furnace system, the alloying treatment, the temper rolling, and Fe-Zn electric plating, whereby the multi-layer coated steel sheets were produced. The hydrogen absorption amounts were adjusted by changing the Fe-Zn coating amounts, continuously heat-treating the multi-layer coated steel sheets at the temperature of not less than 100°C in the induction heating system, or heat-treating the open coils. The Fe-Zn electric platings for the outer layers were practised under following conditions:-
[0046] The Fe contents in the films of the Fe-Zn by electric platings adjusted by mainly changing Fe salt ratio ( = FeSO₄. 7H₂O/[FeSO₄.7H₂O+ZnSO₄.7H₂O]) and the current density, and the adhesion amounts were adjusted by changing the coating time and the current density. Table 2 shows the appreciating results of the outer appearances of the coated films and the corrosion resistances after the electrodeposition paint and the processabilities. It is seen from the same that the multi-layer coated steel plates where the releasing amounts of the absorbed hydrogen were not more than 300 m / m², are superior in all properties.
Example II
[0047] The multi-layer coated steel sheets were produced from the cold rolled coils shown in the Table 1 which have passed the annealings and temper rollings, by alkaline degreasing, sulfuric acid picklings, Zn-Fe alloy electroplating and Fe-Zn alloying electroplatings in the electrogalvanizing line. The hydrogen absorption amounts were adjusted by the amounts of the outer layer coatings and by the continuous heating treatment or batch-heating treatment at the temperature of not less than than 100°C after having been coated. The inner and outer layer coatings of this Example were practised under the same conditions as the outer layer Fe-Zn electric platings of Example I. The Fe contents and the coating weight of Fe-Zn and Zn-Fe electroplated films were also adjusted under the same manners as Example I. The results of the evaluation of the properties are shwon in Table 3. It is seen from the same that the multi-layer coated steel sheets where the releasing amounts of the absorbed hydrogen were not more than 300 m / m², are superior in all properties.
Example III
[0048] The cold rolled coils of the compositions of Table 1 were successively subjected, as blank coils, to the hot dipping zinc plating in the continuous plating line of the non-oxidizing furnace system, the alloying treatment, the temper rolling, and Fe-Zn electroplating, and were successively subjected to the heating treatment under the atmospheric conditions via the induction heating system. With respect to the thus produced multi-layer coated steel sheets, Table 4 the shows results of the evaluation of the outer appearances of the coated films and the corrosion resistances after the electro-deposition paint and the coating adhesion together with the producing conditions. According to the above table, the multi-layer coated steel sheets heat-treated at the temperature from 100 to 400°C are superior in all properties.
Example IV
[0049] The multi-layer coated steel plates were produced from the cold rolled coils shown in the Table 1 which have passed the annealings and temper rollings, by alkaline degreasing, sulfuric acid picklings, Zn-Fe alloying electroplating and Fe-Zn alloying electroplatings, and were successively subjected to the heating treatmetns under the nitrogen atmosphere via the induction heating system. With respect to the thus produced multi-layer coated steel sheets, Table 5 shows the results of the evaluation of the outer appearances of the coated films and the corrosion resistances after the electro-deposition paint and the coating adhesion together with the producing conditions. It is seen from the same that the multi-layer coated steel sheets which have been heat-treated at the temperature between 100 and 400°C, are superior in all properties.
Example V
[0050] The cold rolled coils of the compositions of Table 1 were successively subjected, as blank coils, to the hot dipping zinc plating in the continuous plating line of the non-oxidizing furnace system, the alloying treatment, the temper rolling, and Fe-Zn electroplating, whereby the multi-layer coated steel sheets were produced. Thereafter, these coated steel plates were subjected to the open coil heating with a cover type annealing furnace under the nitrogen gas bearing atmosphere. With respect to the thus produced multi-layer coated steel sheets, Table 6 shows the results of the evaluation of the outer appearances of the coated films and the corrosion resistances after the electro-deposition paints and the coating adhesion together with the producing conditions. It is seen from the same that the multi-layer coated steel plates of open coils which have been heat-treated at the temperature between 100 and 250°C, are superior in all properties.
INDUSTRIAL APPLICABILITY
1. High corrosion resistant multi-layer coated steel sheet having excellent paintability,
enabling the prevention of occurence of bubble-like ED paint defects, having, on the
surface thereof,
a coated film based on Zn or Zn alloys of a coating weight being not less than 25 g/m², which is a single layer or multi-layer coated film being composed of one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys; or which is a multi-layer coated, film being composed of Zn plated coating, and one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys,
on said coated film based on Zn or Zn alloys, a coated film based on Fe or Fe alloys of a coating weight being 1 to 10 g/m², which is composed of one or more than one kinds selected from Fe plated coating or/and plated coatings based on Fe alloys containing not less than 50% Fe,
and wherein a total amount of the absorbed bydrogen in the coated film and the steel is not more than 300 m /m² (per one side).
2. The steel sheet as claimed in claim 1, wherein the coating based on Zn alloys is Zn-Fe,
Zn-Ni, Zn-Mn or Zn-Co alloyed coatings, or said alloyed coatings, each of which is
contained with one or more than one kinds of elements as Ti, Cr, Mo, W, etc.
3. The steel sheet as claimed in claim 1, wherein the composite coating based on Zn or
Zn alloys is that one or more than one kinds of Al₂O₃, Cr₂O₃, SiO₂, and BaCrO₄ are
Co deposited in the Zn coating or the coating based on Zn alloys.
4. The steel sheet as claimed in claim 1, wherein the coating based on Fe alloys contains
one or more than one kinds of the elements as Zn, Ni, Co, Mn, Cr, Mo, W, P and B.
5. A method of producing the multi-layer coated steel sheet as claimed in claim 1, characterized
by forming, on the surface thereof,
a coated film based on Zn or Zn alloys of a coating weight being not less than 25 g/m², which is a single layer or multilayer coated film being composed of one of more than one kinds selected from of plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys; or which is a multi-layer coated film being composed of Zn plated coating, and one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys,
and subsequently forming, on said coated film based on Zn or Zn alloys, a coated film based on Fe or Fe alloys of a coating weight being 1 to 10 g/m², which is composed of one or more than one kinds selected from Fe plated coating or/and plated coatings based on Fe alloys containing not less than 50% Fe,
and heat-treating said multi-layer steel plates at a temperature between 100 and 400°C.
6. The method as claimed in claim 5, wherein th heating treatment is carried out in a
continuous line, and the coated steel sheet is heated for not less than one second
at a steel surface temperature of 100 to 400°C.
7. The method as claimed in claim 5, wherein the heating treatment is carried out in
an open coil in a non-oxidizing atmosphere and the coated steel sheet is heated to
a temperature of 100 to 250°C.
8. The method as claimed in claim 5, wherein the heating treatment is carried out in
an atmosphere containing no hydrogen or in an atmosphere of such a hydrogen concentration
to an extent that the hydrogen is not absorbed in the steel sheet practically.
9. The method as claimed in claim 5, wherein the heating treatment is carried out in
an atmosphere containing no hydrogen or an atmosphere of such a hydrogen concentration
that the hydrogen is not absorbed in the steel sheet practically, and the coated steel
sheet is heated for not less than one second at a steel surface temperature of 100
to 400°C.
10. The method as claimed in claim 5 wherein the heating treat ment is carried out in
an open coil in a non-oxidizing atmosphere containing no hydrogen or in a non-oxidizing
atmosphere of such a hydrogen concentration that the hydrogen is not absorbed in the
steel sheet practically, and the coated steel sheet is heated for more than one second
at a steel surface temperature of 100 to 250°C.
11. The method as claimed in claim 5, wherein the coating based on Zn alloys is Zn-Fe,
Zn-Ni, Zn-Mn or Zn-Co alloyed coatings, or said alloyed coatings, each of which is
contained with one or more than one kinds of elements as Ti, Cr, Mo, W, etc.
12. The method as claimed in claim 5, wherein the composite coating based on Zn or Zn
alloys is that one or more than one kinds of Al₂O₃, Cr₂O₃, SiO₂, and BaCrO₄ are Co
deposited in the Zn coating or the coating based on Zn alloys.
13. The method as claimed in claim 5, wherein the coating based on Fe alloys contains
one or more than one kinds the elements as of Zn, Ni, Co, Mn, Cr, Mo, W, P and B.
Amended claims in accordance with Rule 86(2) EPC.
1. High corrosion resistant multi-layer coated steel sheet having excellent paintability,
enabling the prevention of occurence of bubble-like ED paint defects, having, on the
surface thereof,
a coated film based on Zn or Zn alloys of a coating weight being not less than 35 g/m², which is a single layer or multi-layer coated film being composed of one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys; or which is a multi-layer coated film being composed of Zn plated coating, and one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys,
on said coated film based on Zn or Zn alloys, a coated film based on Fe or Fe alloys of a coating weight being 1 to 10 g/m², which is composed of one or more than one kinds selected from Fe plated coating or/and plated coatings based on Fe alloys containing not less than 50% Fe,
and wherein a total amount of the absorbed bydrogen in the coated film and the steel is not more than 300 m /m² (per one side).
2. The steel sheet as claimed in claim 1, wherein the coating based on Zn alloys is Zn-Fe,
Zn-Ni, Zn-Mn or Zn-Co alloyed coatings, or said alloyed coatings, each of which is
contained with one or more than one kinds of elements as Ti, Cr, Mo, W, etc.
3. The steel sheet as claimed in claim 1, wherein the composite coating based on Zn or
Zn alloys is that one or more than one kinds of Al₂O₃, Cr₂O₃, SiO₂, and BaCrO₄ are
Co deposited in the Zn coating or the coating based on Zn alloys.
4. The steel sheet as claimed in claim 1, wherein the coating based on Fe alloys contains
one or more than one kinds of the elements as Zn, Ni, Co, Mn, Cr, Mo, W, P and B.
5. A method of producing the multi-layer coated steel sheet as claimed in claim 1, characterized
by forming, on the surface thereof,
a coated film based on Zn or Zn alloys of a coating weight being not less than 35 g/m², which is a single layer or multilayer coated film being composed of one of more than one kinds selected from of plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys; or which is a multi-layer coated film being composed of Zn plated coating, and one or more than one kinds selected from plated coatings based on Zn alloys or/and composite plated coatings based on Zn or Zn alloys,
and subsequently forming, on said coated film based on Zn or Zn alloys, a coated film based on Fe or Fe alloys of a coating weight being 1 to 10 g/m², which is composed of one or more than one kinds selected from Fe plated coating or/and plated coatings based on Fe alloys containing not less than 50% Fe,
and heat-treating said multi-layer steel plates at a temperature between 100 and 400°C.
6. The method as claimed in claim 5, wherein th heating treatment is carried out in a
continuous line, and the coated steel sheet is heated for not less than one second
at a stell surface temperature of 100 to 400°C.
7. The method as claimed in claim 5, wherein the heating treatment is carried out in
an open coil in a non-oxidizing atmosphere and the coated steel sheet is heated to
a temperature of 100 to 250°C.
8. The method as claimed in claim 5, wherein the heating treatment is carried out in
an atmosphere containing no hydrogen or in an atmosphere of such a hydrogen concentration
to an extent that the hydrogen is not absorbed in the steel sheet practically.
9. The method as claimed in claim 5, wherein the heating treatment is carried out in
an atmosphere containing no hydrogen or an atmosphere of such a hydrogen concentration
that the hydrogen is not absorbed in the steel sheet practically, and the coated steel
sheet is heated for not less than one second at a steel surface temperature of 100
to 400°C.
10. The method as claimed in claim 5 wherein the heating treat ment is carried out in
an open coil in a non-oxidizing atmosphere containing no hydrogen or in a non-oxidizing
atmosphere of such a hydrogen concentration that the hydrogen is not absorbed in the
steel sheet practically, and the coated steel sheet is heated for more than one second
at a steel surface temperature of 100 to 250°C,
11. The method as claimed in claim 5, wherein the coating based on Zn alloys is Zn-Fe,
Zn-Ni, Zn-Mn or Zn-Co alloyed coatings, or said alloyed coatings, each of which is
contained with one or more than one kinds of elements as Ti, Cr, Mo, W, etc.
12. The method as claimed in claim 5, wherein the composite coating based on Zn or Zn
alloys is that one or more than one kinds of Al₂O₃, Cr₂O₃, SiO₂, and BaCrO₄ are Co
deposited in the Zn coating or the coating based on Zn alloys.
13. The method as claimed in claim 5, wherein the coating based on Fe alloys contains
one or more than one kinds the elements as of Zn, Ni, Co, Mn, Cr, Mo, W, P and B.