High corrosion-resistant two-layer plated steel sheet and its production

[Detailed Description of the Invention]

(Field of the Invention) The present invention relates to the two-layer plating steel plate which has the suitable highly corrosion resistant nature for the object for building materials, the object for home electronics, and cars, and its manufacturing method. (PRIOR ART) In recent years, the amount of the surface treatment plate and sheet used in fields of industry, such as construction or a car, is increasing, it is diversified increasingly and demand performance is also becoming severe. If the antirust steel plate for cars is taken for an example, in the North America etc. which sprinkle thaw salt in winter, the surface treatment plate and sheet with high rust prevention is called for. For some time, the antirust steel sheet which carried out electroplating of Zn, a nickel-Zn alloy, the Fe -Zn alloy, etc. as a measure against strengthening of the antirust power of the automobile body in North America etc. is used so much. However, about the antirust steel plate used for the body these days, Although, as for these antirust steel plates that the antirust power of bearing prolonged corrosion, such as a hole-proof vacancy 10 year guarantee, is demanded, and do not have the antirust power in which the above-mentioned antirust steel plate satisfies this demand, the thing of the amount A dawn 2 of plating adhesion of 20~30g is generally used, If it tries to satisfy the demand of a hole-proof vacancy 10 year guarantee by these steel plates, it is said that the amount of adhesion must be carried out more than double. However, since, as for an electroplating steel plate, a cost of production goes up remarkably with the increase in the amount of adhesion, it must be said from a cost side that the application is very difficult -- in addition -- a hole -- it gets damaged, the corrosion of a steel plate advances from a paint defective part, a plating defective part, a portion, the insufficient portion of the surroundings with paint, etc., and pitting corrosion carries out raw [ of the vacancy ], and it refers to the phenomenon which produces penetration corrosion depending on the case. Since it is such, when improving the corrosion resistance of an antirust steel plate, two methods are taken in recent years. The method of one arranging a chromate film and a thin resin coat on zinc or a zinc-alloy-plating steel plate, and using as an organic covering steel plate and another are the methods of thickening the amount of plating adhesion of the alloying hot-dip zinc-coated carbon steel sheet which carried out alloying processing of the hot-dip zinc-coated carbon steel sheet or this which is manufactured in a hot-dipping process. These steel plate itself is comparatively cheap, and also since the rise of the cost of production accompanying the increase in the amount of plating adhesion is also comparatively small, especially the formation of thick eyes of the latter hot-dip zinc-coated carbon steel sheet and an alloying fusion galvanized steel sheet is advantageous in respect of cost. And although there is little quantity which is used for cars from a viewpoint of weldability in the case of a hot-dip zinc-coated carbon steel sheet, in the case of an alloying fusion galvanized steel sheet, also in the remarkable Quantitative use crack Have come circumstances, there is a thing about amount of plating adhesion 45 g/m" from the former. Then, it is although the amount of plating adhesion of this alloying hot-dip zinc-coated carbon steel sheet tends to be formed into thick eyes to a 60g/m" grade and it is going to satisfy the demand of the hole-proof vacancy 10 year guarantee, The alloying fusion galvanized steel sheet is made into material with many difficulties in press-forming nature from the former, and there is a phenomenon in which the plating coat called flaking and powdering at the time of fact fabrication exfoliates from a steel plate. And since this exfoliation becomes remarkable with the increase in the amount of plating adhesion, thick eyes-ization of an alloying hot-dip zinc-coated carbon steel sheet will cause the increase in the trouble in a molding process compared with the former, and spot weldability also eventually makes it fall. 0 [ for this reason, ] as which the method of improving corrosion resistance is proposed variously without thickening especially the amount of plating adhesion of an alloying hot-dip zinc-coated carbon steel sheet -- for example The method which the method of plating with Hot dip galvanizing bath containing Mg plates with Hot dip galvanizing bath which contains 3~22% of aluminum in JP,52-131934,A is indicated by JP,63-48945,A. Although what has corrosion resistance higher than the conventional alloying fusion galvanized steel sheet is obtained by a method given in JP,63-48945,A, the corrosion resistance cannot carry out henchman satisfaction. If a lot of Mg is added to Hot dip galvanizing bath, the processability of a plating coat will fall. If the plating coat surface after alloying becomes coarse, it plates with a method given in JP,52-131934,A by Hot dip galvanizing bath which cannot bear practical use and containing such a lot of aluminum and alloying processing is performed, Advance of alloying takes place very unevenly and it presents unevenness with the remarkable surface of the plating coat after alloying processing. (Object of the Invention) There is RB of the present invention in improving the corrosion resistance of an alloying fusion galvanized steel sheet, without increasing the amount of plating adhesion. It aims at providing the two-layer plating steel plate excellent in the hole-proof vacancy nature, the blister-proof nature, processability, and surface quality after the paint which is specifically an amount of plating adhesion 40~45g/m" grade of alloying hot-dip-galvanizing #4 board, and its manufacturing method. (Means for solving problem) Above-mentioned Mg and aluminum raise corrosion resistance. Mg or aluminum in a plating coat condenses on a plating surface in the alloying process after hot dipping, and this is presumed to be formation dried cuttlefish and the thing which has controlled advance of corrosion in aluminum103 or the stable corrosion product of MgO in corrosion environment, respectively. However, when an alloying hot-dip zinc-coated carbon steel sheet is manufactured using Hot dip galvanizing bath which contains a lot of aluminum like before, The plating coat surface quality after alloying gets remarkably bad, and if an alloying hot-dip zinc-coated carbon steel sheet is manufactured using Hot dip galvanizing bath containing a lot of Mg, it will become a plating coat inferior to processability. However, these artificers have the comparatively low degree of Alfi, and it plates a steel plate with the usual Hot dip galvanizing bath which does not contain Mg, If the alloy of aluminum and ?1g is covered with the ion plating method or other methods on this alloying hot-dip zinc-coated carbon steel sheet after carrying out alloying processing of this, surface quality is not spoiled -- the amount of plating adhesion of an alloying hot-dip zinc-coated carbon steel sheet -- thin (it found out becoming what The also has sufficient corrosion resistance and is excellent in processability.) The present invention makes a gist following (1) and (2). (1) To the steel sheet surface, as the 1st layer, Fe is 7~20 % of the weight, and aluminum is 0.05~0.5 % of the weight, The highly corrosion resistant two-layer plating steel plate whose amount of adhesion of a Mg-aluminum alloy plating layer the remainder has an alloying hot-dip-galvanizing layer which consists of Zn and inescapable impurities, the content of Mg has a Mg-aluminum alloy plating layer which is 0.1~80 % of the weight as the 2nd layer, and is 0.1~30g/m." (2) The remainder plates the steel plate after a pretreatment with Hot dip galvanizing bath which consists of Zn and inescapable impurities including 0.05~0.3% of the weight of aluminum, A manufacturing method of the highly corrosion resistant two-layer plating steel plate of the above-mentioned (1) statement characterized by forming a Mg-aluminum alloy plating layer by the ion plating method on an alloying hot-dip-galvanizing layer after carrying out alloying processing. (OPERATION) Hereinafter, the present invention is explained in detail. First, the reason which limits each coat composition of the two-layer plating steel plate of the 1st invention of this application and the amount of adhesion of the 2nd layer as mentioned above is explained. Fe in a layer [ 1st ] alloying hot-dip-galvanizing layer is Fe which flows from steel plate foundation by the counter diffusion of a steel plate and a plating layer in the alloying processing after hot dipping. Weldability and the blister-proof nature after paint fall that this Fe is less than 7 % of the weight, if it exceeds 20 % of the weight, hole-proof vacancy nature will fall remarkably, and also powdering-proof nature falls, and it becomes easy to produce exfoliation of a plating coat at the time of press processing. aluminum similarly contained in a layer [ 1st ] alloying hot-dip-galvanizing layer is aluminum added in Hot dip galvanizing bath, in order to suppress Dros's generating in hot dipping. Making aluminum in a coat low with less than 0.05 % of the weight is lessening extremely the amount of aluminum in a fusion zinc bath. Not only operability falls, but if it does so, a reaction of a steel plate and Molten metal will become intense, Dros's yield increases, and a plating coat after alloying is inferior to processability. Although it is made better [ to include many aluminum in improving the corrosion resistance of a plating coat ], if aluminum in a coat exceeds 0.5 % of the weight, alloying speed will fall remarkably, operability falls, and also unevenness on the surface of a coat after alloying becomes intense, and paintwork falls. Therefore, aluminum in a coat is good to make 0.5 % of the weight into a maximum. Under corrosion environment, a layer [ 2nd ] Mg-aluminum alloy plating layer forms aluminum20. and the stable corrosion product of MgO, and controls the corrosion of a layer [ 1st ] alloying hot-dip-galvanizing layer. Since the amount of formation of uzos will become insufficient if Mg in this Mg-aluminum alloy plating layer becomes insufficient [ the amount of formation of MgO ] for it to be less than 0.1 superposition % and exceeds 80 % of the weight, The amount of adhesion of a layer [ 2nd ] ?1g-^1-go gilding layer with corrosion-resistant small improvement in which aluminum and a 21-g synergistic effect do not show up, Since the corrosion-resistant improvement effect will be saturated even if sufficient corrosion resistance is not acquired but it plates thickly too much if small, when as for the amount of adhesion 0.1~30g7m" processes good press-forming etc. and is used, since powdering-proof nature will fall if a plating layer is thick -- 10g/s" -- it is desirable to use the following amounts of adhesion. The two-layer plating steel plate of the 1st above-mentioned invention of this application can be manufactured by the method of the 2nd invention of this application. Namely, the steel plate pretreated by general methods, such as the Zenjima method and a flux method, After the remainder plates with Hot dip galvanizing bath which consists of Zn and inescapable impurities and carries out alloying processing including 0.05~0.3% of the weight of aluminum, a Mg-aluminum alloy plating layer is formed by the ion plating method on an alloying fusion galvanization layer. In the manufacturing method of this 2nd invention, it is because Dros's yield increases that it is less than 0.05 % of the weight which made aluminum concentration in Hot dip galvanizing bath into 0.05 % of the weight or more, and operability falls and also the processability of a coat also falls. On the other hand, since the amount of aluminum in a coat will exceed 0.5 % of the weight if aluminum concentration in Hot dip galvanizing bath exceeds 0.3% of the weight, unevenness on the surface of a coat after alloying becomes remarkable. aluminum in Hot dip galvanizing bath has the character in which the content condenses in a coat at 1.0 % of the weight or less. Therefore, if more aluminum than 0.3 % of the weight is added in Hot dip galvanizing bath, aluminum in a coat will increase more than 0.5 % of the weight. The alloying furnace in a plating line may perform alloying processing after hot dipping, and an off-line batch type furnace may perform. At an alloying furnace, it is good to alloy with the material temperature of 500~600 degreeC. Carrying out alloying processing with the low material temperature of 350~380 degreeC cuts with a batch type furnace. 7~20% of the weight of Fe is made to flow into a hot-dip-galvanizing layer by this alloying processing. After alloying, it is on an alloying hot-dip zinc-coated carbon steel sheet by the ion plating method, The vapor deposition crucible which inserted the Mg-aluminum alloy in 0, for example, the vacuum interior of a room, which vapor-deposit the Mg-aluminum alloy whose PIg is 0.1~80 % of the weight so that it may become the amount of adhesion of 0.1~30g / ■2 is arranged, It is made to evaporate according to electron beam cancer, and the amount of MgO(s) may adjust like and may make it vapor-deposit 0.1~80% of the weight. When the light dress crucible which inserted Mg in the vacuum interior of a room, and the vapor deposition crucible which inserted in aluminum are arranged, irradiation of electron beam cancer is separately controlled by aluminum and Mg, and the quantity of PIg may adjust like and may make it vapor-deposit 0.1~80% of the weight, the vacuum interior of a room is good to consider it as a degree of vacuum higher than 10-'torr. The two-layer plating steel plate of the 1st invention of this application can be manufactured also by methods other than the manufacturing method of the 2nd invention. That is, it plates with the same Hot dip galvanizing bath as the above, and forms a Mg-aluminum alloy plating layer by the hot-dipping method or a thermal-spraying method on the alloying hot-dip zinc-coated carbon steel sheet which carried out alloying processing. Or it can obtain also by the method which the galvanization layer after carrying out hot dip galvanizing sprays the end of Mg-aluminum alloyed powder between molten states, and carries out alloying processing after that. (EXAMPLE) C: 0.002 % of the weight, Si : 0.01 % of the weight, Mn : 0.25 % of the weight, P : 0.011 % of the weight, S : 0.012 % of the weight, Sol, aluminum : 0.025 % of the weight, Ti : From the full hard material of super-low C-IF steel (Interstttiai Free steel) containing 0.024 % of the weight, Two or more sample offering material of Looms X 250m- is started, and solvent washing of these sample offering material is carried out, After carrying out electrolytic degreasing in NagCOs+NaOH solution, using the hot-dipping simulator, reduction annealing was performed for 30 seconds at the temperature of 840 degreeC in the atmosphere of 25%Hz+Nt, and hot dipping was carried out by Plating bath of predetermined Bath composition. After hot dipping adjusted the amount of adhesion, and formed the Mg-aluminum alloy layer on this galvanization layer. a Mg-aluminum alloy layer -- the steel plate after hot dip galvanizing -- 25%Hz -- after carrying out alloying processing at the temperature of 500 degreeC under +N x atmosphere, it formed by the ion plating method, the hot-dipping method, and the thermal-spraying method. Or when a hot-dip-galvanizing layer was a molten state, the end of Mg-aluminum alloyed powder was sprayed, and after that, under 25%Hz+Nz atmosphere, at the temperature of 500'C, alloying processing was carried out and it formed. The crucible which inserted aluminum and PIg in the vacuum room maintained at the degree of vacuum of 10-'torr separately was arranged, the output of electron beam cancer was made into - 30, and the ion plating method covered the Mg-aluminum alloy layer by adjusting the distribution with which the crucible of aluminum and Mg is irradiated. Mg-aluminum alloy Plating bath 30~70 superposition % Containing a season was used, and the Mg-aluminum alloy layer was covered with the hot-dipping method. After adjusting the pressure of acetylene, oxygen, and air to 1.5kg/cm", 3kg/cm", and 4 kg/cm" in a thermal-spraying method using a gas type line type thermal-spraying machine, respectively, Thermal spraying of the Mg-aluminum alloy wire rod which adjusted Mg to 0.1~80% of the weight was sent out and carried out from the center of a nozzle, and Mg-^1 alloy layer was covered. The spraying in the end of Mg-aluminum alloyed powder used N2 of 5 kg/cm" for carrier gas by 400"C, sprayed the end of Mg-aluminum alloyed powder particle diameter 5~20micro-0Mg powder is included 0.1~80% of the weight on the hot-dip-galvanizing surface, and carried out it. In this way, about each produced two-layer plating steel plate, powdering-proof nature, corrosion resistance, and appearance were investigated. These results are shown in the 1st table with the 1st layer and 2nd-layer coat composition and the amount of adhesion. After powdering-proof nature pierced the coupon of 60-Ugliness phi from each two-layer plating copper plate and did the cylinder iris diaphragm examination of diameter of punch 3 * Zen -, and dice shoulder radius 3R, it performed tape exfoliation of the outside cylinder part, and evaluated the exfoliation grade by viewing. x to which evaluation is performed in four steps, O is inferior to which in good and O is usually inferior to which in delta a little is inferior -- it comes out. Appearance carried out visual observation of phosphate conversion treatment and the surface after doing the cation Electricity r7I paint of on condition of the following, and evaluated each two-layer plating copper plate. O is good and x is poor. [Phosphate conversion treatment conditions] It processes for 120 seconds by 43 degrees of solution temperature C using the immersion type phosphate conversion treatment liquid for cars (Japanese bar power rising company make: PBL3080). [Paint conditions] The usual cationic electrodeposition paint for cars (Nippon Paint [ Co., Ltd. ] make: U-80) is painted in voltage 200■, and electrodeposited time 3 minutes, and it carries out with a paint glow by 180 degreeC for 30 minutes. Film thickness is 20micro Rin. Corrosion resistance attaches a scratch crack to phosphate conversion treatment and the two-layer plating steel plate after carrying out cathodic electrodeposition coating on the above-mentioned conditions, After this was immersed in NaC1 solution 5% for 1 hour, the dryness-and-moisture cyclic test which repeats by turns the process dried by the hot wind of 60 degreeC for 1 hour was done on the 200th, and the maximum corrosion depth of the steel plate in the portion which attached the crack was measured and evaluated. (Hereinafter, space) the 1st table -- the two-layer plating steel plate of the example of the present invention (lt16~A patient 37) -- each -- corrosion resistance, processability, and surface quality -- Being trained -- things are understood. On the other hand, the two-layer plating steel plate of a comparative example (Nlll-Unexpected 15) detached from the range specified by the present invention is inferior to one of the above-mentioned characteristics. Although Nu 37 is the conventional alloying hot-dip zinc-coated carbon steel sheet which formed into thick eyes the amount of plating adhesion which does not have a Mg-aluminum alloy plating layer to 60 g/at", it is inferior to powdering-proof nature and corrosion resistance in this thing. (EFFECT OF THE INVENTION) As shown in the example, although the two-layer plating steel plate of the present invention is half-closed-eyes attachment, it has the outstanding corrosion resistance and, moreover, processability and its surface quality are also better than the conventional alloying hot-dip zinc-coated carbon steel sheet.