CA1331962C - Process for producing a multilayer-coated steel strip having excellent corrosion resistance and weldability and useful for containers - Google Patents
Process for producing a multilayer-coated steel strip having excellent corrosion resistance and weldability and useful for containersInfo
- Publication number
- CA1331962C CA1331962C CA000532926A CA532926A CA1331962C CA 1331962 C CA1331962 C CA 1331962C CA 000532926 A CA000532926 A CA 000532926A CA 532926 A CA532926 A CA 532926A CA 1331962 C CA1331962 C CA 1331962C
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- Canada
- Prior art keywords
- nickel
- tin
- coating layer
- steel strip
- coating
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/38—Chromatising
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/10—Electroplating with more than one layer of the same or of different metals
- C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/48—After-treatment of electroplated surfaces
- C25D5/50—After-treatment of electroplated surfaces by heat-treatment
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electroplating Methods And Accessories (AREA)
Abstract
PROCESS FOR PRODUCING A MULTILAYER-COATED STEEL STRIP
HAVING EXCELLENT CORROSION RESISTANCE AND
WELDABILITY AND USEFUL FOR CONTAINERS
ABSTRACT OF THE DISCLOSURE
A multilayer-coated steel strip having an excellent corrosion resistance and weldability and useful for cans and containers is produced by a process in which a steel strip substrate is plated with nickel or a nickel-based alloy to form nickel based coating layers each having an average amount of 2 to 10 mg/m2, provided with a number of convex and concave portions thereof, portions of which layers having a coating thickness of 0.001 µm or more have a total area corresponding to 10 to 90% of the entire area of the surfaces of the substrate; the nickel based plated substrate is coated with tin to form tin coating layers on the nickel-based coating layers, each of which tin coating layers has an average amount of 200 to 2000 mg/m2; the resultant precursory coated steel strip is heated at a temperature equal to or higher than the melting point of tin to convert the nickel-based coating layers and the tin coating layers to base coating layers consisting essentially of an Fe-Ni-Sn-based alloy and having a number of convex and concave portions thereof, and intermediate coating layers formed on the base coating layers, consisting essentially of tin and having a number of convex and concave portions thereof; and then an electrolytic chromate treatment is applied onto the intermediate tin coating layers to form surface coating layers consisting of electrolysed chromate.
HAVING EXCELLENT CORROSION RESISTANCE AND
WELDABILITY AND USEFUL FOR CONTAINERS
ABSTRACT OF THE DISCLOSURE
A multilayer-coated steel strip having an excellent corrosion resistance and weldability and useful for cans and containers is produced by a process in which a steel strip substrate is plated with nickel or a nickel-based alloy to form nickel based coating layers each having an average amount of 2 to 10 mg/m2, provided with a number of convex and concave portions thereof, portions of which layers having a coating thickness of 0.001 µm or more have a total area corresponding to 10 to 90% of the entire area of the surfaces of the substrate; the nickel based plated substrate is coated with tin to form tin coating layers on the nickel-based coating layers, each of which tin coating layers has an average amount of 200 to 2000 mg/m2; the resultant precursory coated steel strip is heated at a temperature equal to or higher than the melting point of tin to convert the nickel-based coating layers and the tin coating layers to base coating layers consisting essentially of an Fe-Ni-Sn-based alloy and having a number of convex and concave portions thereof, and intermediate coating layers formed on the base coating layers, consisting essentially of tin and having a number of convex and concave portions thereof; and then an electrolytic chromate treatment is applied onto the intermediate tin coating layers to form surface coating layers consisting of electrolysed chromate.
Description
:.
PROCESS FOR PRODUCING A MULTILAYER-COATED STEEL STRIP
HA~ING EXCELLENT CORROSION RESISTANCE AND
~ = _ ~
WELDABILITY AND USEFUL FOR CONTAINERS
~-","~:.
BACKGROUND OF THE INVENTION ~ -1. Field of the Invention The present invention relates to a process for producing a multilayer-coated steel strip having an ~ ;
excellent corrosion resistance and weldability and useful for producing containers. More particularly, the present invention relates to a process for producing a -~
multilayex-coated steel strip having an excellent ~-corrosion resistance and seam weldability, and thus is useful as a steel material for forming cylindrical portions of cans by a seam welding procedure.
PROCESS FOR PRODUCING A MULTILAYER-COATED STEEL STRIP
HA~ING EXCELLENT CORROSION RESISTANCE AND
~ = _ ~
WELDABILITY AND USEFUL FOR CONTAINERS
~-","~:.
BACKGROUND OF THE INVENTION ~ -1. Field of the Invention The present invention relates to a process for producing a multilayer-coated steel strip having an ~ ;
excellent corrosion resistance and weldability and useful for producing containers. More particularly, the present invention relates to a process for producing a -~
multilayex-coated steel strip having an excellent ~-corrosion resistance and seam weldability, and thus is useful as a steel material for forming cylindrical portions of cans by a seam welding procedure.
2. Description of the Related Art It is known that an electrolytic tin-plate steel strip ~tir.plate), an electrolytic chromate-treated steel strip (TFS-CT), and an electrolytic nickel-plated steel strip (TFS-NT) are usable in the production of three piece cans by soldering, bond-bonding, or seam welding.
Formerly, tinplate was most widely used as a steel material for producing cans, but conventional tinplate is not always satisfactory in view of the price thereof. Therefore, in order to reduce the can-producing cost, attempts have been made to reduce the thickness of the tin coating layer on the steel 25 strip, and to utilize a seam-welding method instead of the conventional soldering method for the tinplate. It has been found, however, that when the thickness of the tin coating layer in the tinplate is reduced to a level of 0.20 ~m or less, the resultant tinplate exhibits a 30 deteriorated paint corrosion resistance and a reduced seam weldability.
; The conventional TFS-NT sometimes used as a ' ~ ~ 2 ~ ~ 3 3 ~
)~ ~teel mat~ri~l for produclng seam-welded can~ u~ually exh~bits a ~ati~factory 8eam weldabillty, but th~s weld~b$1ity is not ~lways sat~factory in prac~cal us~.
. Al~o, the conventional TFS-NT has a satlsfac~ory paint S corrosion resistance in usual use, but the level of th~ :
paint corros~on resis~ance ~s not always sati~factory when brough~ into con~ac~ with a corrosive material, for ex~mple, ~rongly acidic food.
Accordingly, there i8 a strong demand for thé
10 prov~sion of a surface-coated steel ~trip wbich ~8 cheap ~::
and has an excellent paint corrosion resistance and seam weldabil~ty, and thus ~s useful for the production o . ~:
cans and containers.
Japane~e Unexamined Paten~ Publication (~oka~
No. 60-75586 (Nippon Steel Corporation, published 7 April 27, 1985)d$sclose~ a proces~ for producing a coated steel ~trip. ~n thi~ process, a ~teel 6trip is coated with a small amount of nic~el, and the nickel-coated steel strip ls then plated with tin. When the nickel 20 and t~n coated-steel str~p i~ heat treated, and ~he tin coat~ng layer is converted to an Fe-Sn alloy layer,.the ~:
presenc~ of the small amount of nickel coat~ng layar : :
causes the structure of the Fe-Sn alloy layer to exhi~it an enhanced density. There~ore, the xesultant coated 25 steQl strip exhibit~ an improved corrosion re~is~ance.
~180, the presence of the nickel coa~ing layer ~s effective for restxictinq the ~e-Sn alloy-forming reaction ln the heat-treatment) and thus the resultant coated steel exhibits an enhanced ~eam weldability~
30 Further, the inventors o~ the pxesent invention have found that the propertie~, ~or example, seam weldability and corrosion resis~ancet o the coated ~teel ~tr~p usable ~8 a s~eel mater~al for 8eam weldea can6, vary depending on the distriSution of metall~c tin coating 35 over the surface of a s~eel ~trip subs~rate. That i8, it ha~ been ~ound that ~hQ propexties of the coated steel atrlp over which the metallic tin layer i5 unevenly distributed and having an uneven rough ~urface,.are . . .
133~62 - 3 - ~- ~
- -:
better than those of a coated steel strip over which the metallic tin layer is evenly distributed and having a smooth uniform surface.
Namely, the coated steel strip having an uneven thin tin coating layer exhibits a better seam weldability and corrosion resistance than those of a -conventional coated steel strip having an even thin tin coating layer. However, it is very difficult to control the thickness of the unevenness of the thin tin coating layer to a predetermined level, and to produce a coated steel strip having predetermined levels of weldability~-~
and corrosion resistance with a stable reproductivity.
Fujimoto et al, "Iron and Steel~, vol. 72, No. 5, page 39. 1986 discloses that, in order to provide a tin -~ -15 coating layer having an uneven thickness with a stable --reproductivity, it is effective to apply an anodic electrolytic treatment to the steel strip in an alkaline treating liquid before the nickel-plating step. Also, it is known that, when a tin-coated steel strip is subjected to a flux treatment, the unevenness in the thickness of the tin coating iayer is greatly influenced by the conditions of the flux treatment.
However, even if the anionic electrolytic treatment or the flux treatment is utilized, the resultant coated steel strip is unsatisfactory from the viewpoint of corrosion resistance and weldability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing a multilayer-coated steel strip having an excellent corrosion resistance and weldability and useful for producing cans or containers with an improved reproductivity.
The above-mentioned object can be attained by the process of the present invention which comprises the steps of (A) plating a substrate consisting of a steel strip with metallic nickel or a nickel-based alloy to form, on both the upper and lower surfaces of the :
... ~ ' i$
~33~S2 substrate, nickel-~a~e~ coa~ing layer, each of which . ~:
layers $8 coated in ~n aver~ge amoun~ of 2 to 100 mg/m2 and ~8 provided with a number of convex and concave portlons, and in which layer portions thereof having a coa~ing ~hicXness of 0.001 ~m or more have a total area corre~ponding ~o 10% to 95~ oP the entire area of the surface~ of the sub~trate~ IB) ~oating the nickel-based -:
plated ~ubstrate with tin to ~orm tin coa~ng layer~ on the nicXel-ba~ed coating layer~, each o~ which tin coating layers i8 coated ~n an averaqe amount of 200 to 2000 mg/m , to provi~e ~ precur60ry ~oate~ steel str~pS (C~ heating the precursory coated st~el strip at a temperature equal to or higher than the melting point of the tln ~oating layer, to c~u e th~ nic~el-~ased coating layers and the tin coat~ng layer~ to be con~
verted to base ~oating layers, which ar~ ~ormed on ~oth the upper and lower surface~ o~ ~hQ ~u~Btrat~ con- ~ :
8i8ting essentially of an Fe-Ni-Sn-based alloy and ~ :
having a n~mber of convox and concnv~ portions, a~d : :
intermediate coating layers, which arQ located on the base coatinq l~yers, consisting essentlally of t~n And having ~ number o~ convex ~nd concav~ portion~1 an~ tD) ~ :
applying an eleatrolytic ~hromate treatmen~ to th~
lntermediate tin coati~g layer~ to fonm surface coatlng layers, consi8t~ng oi electxoly~ed chromate, on the intermediate tin coating layer.
A~ther ob~ect o~ the invention is to provide a multilaver-coated steel strip having excellent corrosion resistance and weldability, comprising:
(a) a substrate consisting of a steel strip; and -~
(b) a multi-layer coating covering both the upper and lower surfaces of the substrate and comprisinq:
~ 4a - 1 ~ 3 ~ 9 62 (i) a base coating layer deposited on the ~ ~ -substrate surfaces, consisting essentially of a Fe-Ni-Sn-based alloy, the layer having a plurality of convex and concave portions thereof;
S (ii) an intermediate coating layer deposited on the base coating layer to form a ~ ~ :
precursory coated steel strip, consisting essentially :- -of tin deposited in an amount of 200 to 2000 mg/m~, the ~ ~
intermediate coating layer having a plurality of :
10 convex and concave portions thereo~ in contact with ~.
corresponding convex and concave portions of the base coating layer; and :~.
(iii) a chromate coating layer deposited by an electrolytic chromate treatment on the 15 intermediate coating layer in an amount of 3 to 30 mg/m2 in terms of metallic chromium, the base coating ~:~
layer (i) and the intermediate layer (ii) having been formed by: ~ ;
(A) plating the substrate consisting of ~: .
20 a steel strip, with metallic nickel or nickel-based ~ :
alloy consisting of at least 80% by weight of nickel : :
and 20% by weight or less of an additional metal :
element consisting of at least one member selected : :
from zinc, phosphorus, cobalt, copper and chromium, to 25 form a nickel-based coating layer OTI both the upper and lower surfaces o~ the substrate, said nickel-based : ::
coating layers being in an average amount of 2 to 100 mg/m2 and provided with a number of convex portions and . :
concave portions thereof, and wherein said portions 30 thereof having a coating thickness of 0.001 ~m or more ~:
have a total area corresponding to from 10% to 95% of the entire area of the surfaces of the substrate;
(B) coating the resulting nickel-based ;
plated substrate with tin to form tin coating layers 35 on the nickel-based coating layers, each tin coating~ ~:
~ :, ~33~62 - b -layer being in an amount of 200 to 2000 mg/m2, to provide a precursory coated steel strip;
and (C) heating the precursory coated steel S strip at a temperature equal to or higher than the melting point of the tin coating layers, to cause the nickel-based coating layers and the tin coating layers to be converted to the base coating layer and the intermediate coating layer.
,, :' . 15 / : :
/
BRIEF DESCRIPTION 0~ THE DRAWINGS
Figure 1 is a schematic cross-sectional view of an embodiment of the niokel coating layer formed on a steel strip substrate in the first step of the proces~ of the present inventions Fig. 2 i~ a schema~ic cross-sectional view of another embodiment of the nickel coating layer formed on a steel strip ~ubstrate in the first ~tep o~ the process of the pre~ent invent~on~ and, :
Fig. 3A to 3C are ~chematic cross-sectional v~ews ~:
35 of embodiment~ of the produc~s formed re~pectively in ~-" 133~2 the second, third, and fourth steps of the process of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the first step of the present invention, a substrate consisting of a steel strip to be multilayer-coated is plated with nickel or a nickel-based alloy to form nickel-based coating layers on both the upper and lower surfaces of the substrate to an extent such that -the resultant nickel-based coating layers are coated in a small average amount of from 2 to 100 mg/m2, preferably from 5 to 100 mg/m2, per surEace of the substrate and have an uneven thickness distribution, so as to provide a number of convex and concave portions preferably substantially evenly distributed in the layer.
That is, the uneven nickel based coating layer may be, as shown in Fig. 2, in the form of a land having a number of mountains and hills corresponding to the convex portion~ and a number of lakes and valleys corresponding to the concave portions, which mountains, hills, lakes, and valleys are substantially evenly distributed in the land. Some of the lakes and valleys (concave portions) may have bottoms thereof formed by~ ~;
nickel or a nickel-based alloy plated on the substrate surface~. Also, in the bottoms of other lakes and valleyq ~concave portions), portions of the substrate surfaces may be exposed to the outside. That is, the nickel-based coating layer may incompletely cover the surfaces of the substrate.
Alternatively, the uneven nickel-based coating layer may be, as shown in Fig. 2, in the form of a number o islands corresponding to the convex portions, consisting of nickel or the nickel-based alloy and preferably substantially evenly distributed in one or more seas corresponding to the concave portions connected to each other. Some of the island portions may be in the above-mentioned form of a land having a number o mountains, hills, lakes, and valleys. In the bottoms of ,. '.. '.' ~
~ .
',1'.. ~ : ,. ': .; ., ~
6 1~3~962 the sea portions of the nickel-based coating layer, the ', corresponding portions of the substrate surfaces are exposed to the outside~ , Referring to Fig. 1, a surface of a steel strip substrate 1 is coated with an uneven nickel-based coating layer 2 having convex portions 2a and concave portions 2b.
In Fig. 2, a surface of a steel strip substrate 1 is coated with an islands-in-sea type nickel-based coating la~er 2 consisting of a plurality of island~
formed nickel-based coating deposits 2c separated from each other. Portions la of the surface of the substrate 1 are exposed to the outside but not coated with the nickel-based coating deposit.
The coating thicknesses of the convex portions, that is, the heights from the surface of the substrate to the peaks of the convex portions, may be different.
Also, the coating thicknesses of the concave portions, ' that is, the thickness between the surface o the substrate and the bottoms of the concave portions, may be different.
In the formation of the uneven nickel-based coating layers, the total area of portions o the layers having a coating thickness of 0.001 ~m or more must be coated to a level corresponding to 10% to 95~, preferably, 10 to 90%, o the entire area of the surfaces of the substrate to be coated. Also, preferably the convex and concave portions of the resultant nickel-based coating layers satisfy the relationships (1), (2), and (3):
' hmax > 0.002 ~m (1) , hmin > 0 (2) and, hmin > 0, hmax > 2 hmin (31 wherein hmax represents a largest coating thickness of the convex portions and hmin represents a smallest coating thickness of the concave portions of the nickel-based coating layer.
In the first step of the process of the present :':
.~. : . .
~331~2 invention, the steel strip substrate, which has been degreased or surface cleaned by an ordinary method, is subjected to a nickel-plating process. In the surface cleaning procedures, the steel strip substrate may be subjected to an anodic electrolytic treatment in a pickling liquid, for example, a sulfuric acid aqueous solution, or a degreasing liquid, for example, a sodium hydroxide aqueous solution.
The surface cleaned steel strip substrate is unevenly plated with nickel or a nickel-based alloy in an amount of 2 to 100 mg/m2, preferably 5 to 100 mg/m2, per surface of the substrate. The plating process can be carried out in an ordinary nickel plating liquid, for example, a sulfuric acid watt plating liquid. The -composition of the plating liquid, plating current density, plating temperature and time, and other plating conditio~s are determined so that the resultant nickel~
based coating layers are in the above-mentioned specific amount and have the above-mentioned uneven thickness distribution. The plating method is not limited to a specific method and may be an electric plating method or a non-electrolytic plating method, as long as the specific uneven nickel-based coating layers is obtained.
Also, ater the plating operation is completed, the nickel-based pIated substrate may be additionally subjected to an anodic electrolytic treatment. Alter-natively, the nickel-based plated substrate may be ~ ~
subjected to a heat treatment at an elevated tempera- ~ ;
ture, to cause the plated nickel or nickel-based alloy to diffuse into the steel strip substrate.
I the amount of the plated nickel or nickel-based / ¦ alloy is more than 100 mg/m2, the resultant coating ¦ ¦ layer will have a substantially even thickness and it ¦ ¦ will be difficult to provide a coated steel strip having `~
¦~5 a satisfactory corrosion resistance and weldability.
If the amount of the plated nickel or nickel-based alloy is less than 2 mg/m2, it will be difficult to ~L331962 provide a dense Fe-Ni-Sn based base layer having a excellent effect for enhancing the corrosion resistance of the resultant coated steel strip.
As stated above, the limitation in the amount of the nickel-based coating layers to the range of from 2 to 100 mg/m2 per surface of the substrate is very important when causing the resultant nickel-based -coating layers to have an uneven coating thickness distribution and to be provided with a number of convex portions and concave portions thereof. This specific form of the nickel based coating layers is essential when providing a multilayer-coated steel strip having an excellent corrosion resistance ana weldability and useful as a steel matexial for producing cans or con-tainers.
Also, if the total area of the portions of the/¦ nickel-based coating layers having a ~hickness of ¦¦ 0.001 ~m or more is more than 95% or less than 10% of ¦ the entire area of the surfaces of the substrate, the I:20 unevenness in the coating thickness of the nickel-based ¦ coating layers will be unsatisfactory, and thus the ¦ resultant coated steel strip will exhibit an unsatis-factory corrosion resistance and weldability.
The uneven nickel-based coating layer satisfying the above-defined relationships (1), (2), and (3) is very effective for further enhancing the corrasion resistance and weldability of the resultant coated steel strip.
The uneven distribution of the thickness of the 30- nickel~based coating layer can be observed by means of an electron probe micro-analyser or an Auger electron Spectroscopy.
The uneven nickel-based coating layer may consist \ I ¦ of nickel or a nickel-based alloy consisting of at least 80% by weight of nickel and 20% by weight or less o~ an ¦¦ additional metal element consisting of at least one member selected from zinc, phosphorus, cobalt, copper, 13319~2 g .
and chromium. The additional metal element can be alloyed with nickel by the heating treatment and is effective for causing a portion of tin coating layer to remain in the free tin state after the heat treatment.
The remaining free tin forms an intermediate tin coating layer on the base coating layer after the heat-treatment step.
In the second step of the process of the present invention, the nickel-based plated substrate is coated with tin in an average amount of 200 to 2000 mg/m2 per surface of the substrate to provide a precursory coated -steel strip. The tin coating procedures are not limited to a specific method, and can be carried out by any conventional tin plating method. However, the tin coating is preferably carried out by an electric plating method.
The average amount of the tin coating layers formed on the nickel hased plated substrate i limited to a specific range from 200 to 2000 mg/m2 per surface of the substrate to provide a resultant coated steel strip having an excellent corrosion resistance and weldability at a low cost.
If the average amount of the tin coating layers is ~`
l more than 2000 mg/m2, the excess amount of tin over ¦25 2000 mg/m2 has no effect on the enhancing of the ¦ corro~ion reqistance and weldability of the resultant coated steel strip, and undesirably increased the cost of the resultant coated steel strip. Also, an average `~
amount o less than 200 mg/m of the tin coating layer results in an unsatisfactory seam weldability and corrosion resistance of the resultant coated steel strip. -After the tin coating step is completed, the coated -~
steel strip is usually washed with water and, if necessary, is immersed in a flux comprising, as a principal component, phenol sulfonic acid or ammonium chloride, and finally, is dried. The flux may have a ., `` ~331962 concentration corresponding to from 1/2 to 1/~ of that in an ordinary flux for producing a usual tinplate. The necessity for flux treatment and composition and con-centration of the flux can be decided in consideration of the type and constitution of the desired coated steel strip.
In the third step in the process of the present invention, the pxecursory coated steel strip is heat-treated at a temperature equal to or higher than the melting point of the tin coating layer. This heat treatment may be carried out by, for example, an electric resistance-heating method or high-frequency induction heating method. Further, this heat treatment may be effected in an atmosphere consisting of an inert gas, for example, nitrogen or argon gas.
The heat treatment applied to the precursory coated steel strip is effective-for converting the nickel-based coating layers and tin coating layers to base coating layers formed on the two surfaces of the substrate, and consisting essentially of an Fe-Ni-Sn-based alloy and having a number of convex and concave portions, and intermediate coating layers f~rmed on the base coating layers, consisting essentially of tin and having a number of convex and concave portions. ~ ;
Preferably, the heat treatment is controlled to an extent such that the content of tin in the resultant base Fe-Ni-Sn-based alloy coating layers corresponds to about 1/3, that is, from 30% to 35% of the entire weight of the original tin-coating layers.
The heat treatment at a temperature equal to or higher than the melting point of the original tin coating layer results in the conversion of the nickel-based coating layers and the tin coating layers to base Fe-Ni-Sn based alloy coating layers and intermediate tin coating layers, which are effective for imparting an excellent corrosion resistance and weldability to the resultant coated steel strip.
.
~ 33~2 The above-mentioned conversion will be further explained by referring to Figs. 3A to 3C.
Referring to Fig. 3A, a precursory coated steel strip 10 which has been produced by the first and second -steps of the process of the present invention, has a steel strip substr ~ 11, an islands-in-sea type nickel-based coating laye~ 1~ having a number of islands 12a, wherein the--islands 12a are separated from each other, and sea-shaped portions 12b between the islands 12a, and , ' 10 a tin coating layer 13. When the precursory coated ' steel strip is heated at a temperature equal to or higher than the melting poin~ of the tin coating layer, the tin coating layer 13 is melted and the nickel-based coating layer 12 is alloyed with a portion of iron in the steel strip substrate 11 and a portion of tin in the tin coating layer 13.
The alloying rate of nickel or nickel based alloy with the iron and tin is proportional to the concen-tration of nickel or nickel-based alloy in the alloying system. Therefore, each of the nickel-based islands 12a are rapidly converted to a corresponding alloy coating while growing three-dimensionally. Namely, each alloy coating becomes thicker than the corresponding nickel~
based islands and spreads on the substrate surface. The spread alloy coatings are connected to each other and form a continuous alloy coating layer which substantially completely covers the surface of the substrate, as shown in Fig. 3B.
Referring to Figs. 3A and 3B, the resultant alloy coating layer 14 has a number of convex portions 14a corresponding to the nickel-based islands 12a and a number of concave portions 14b corresponding to the sea-shaped portion 12b in the nickel-based coating layer 12 in Fig. 3A.
The tin melt exhibits a larger wetting affinity and a smaller free interface energy to the Fe-Ni-Sn-based alloy layer surface than to the nickel based alloy layer ....
13319~2 surface and to the steel strip surface. Note, the larger the thickness of the Fe-Ni-Sn-based alloy layer, the greater the ~Jetting affinity of the tin melt thereto.
Accordingly, the thickness of the tin melt layer 15 on the Fe-Ni-Sn-based alloy layer 14 corresponds to the thickness of the Fe-Ni-Sn-based alloy layer 14 as shown in Fig. 3B, when the heat-treatment is stopped and the alloy coating layer and tin melt layer are cooled to room temperature, the resultant tin coating layer 15 has a number of convex portions 15a and concave portions 15b thereof respectively corresponding to the convex portions 14a and the concave portions 14b of the alloy coating ~ -layer 14.
If the nickel-based coating layer has an even ~
15 thickness, the conversion of the nickel-based coating ~ ;
layer progresses at an even converting rate throughout -the layer, and the resultant alloy coating layer has a substantially e~ven thickness. Accordingly, the even base alloy coating layer causes the intermediate tin coating layer to have a substantially even thickness.
The even tin coating layer sometimes can be con-verted to an uneven tin coating layer as shown in Fi~, 3B by a flux treatment under a certain condition.
However, the conversion by the flux treatment is not ~
25 always successful. Sometimes, the flux treatment fails `
to convert the even tin coating layer to an uneven tin coating layer. Sometimes, the flux treated tin coating layer contains uneven portions and even portions thereof.
In other ~ords, the flux treatment cannot stably convert 30 the even tin coating layer to an uneven tin coating layer and, therefore, is not valuable for stably pro-ducing the coated steel strip having an enhanced corrosion resistance and weldability.
However, in the process of the present invention, 35 the uneven tin coating layers can be stably produced by utilizing the uneven nickel-based coating l~yers formed ; on the steel strip substrate surfaces. The uneven tin .1,```'~
~ , 1331~62 coating layers are very effective for producing the coated steel strip having an enhanced weldability and corrosion resistance, and therefore, useful for cans and containers.
Preferably, in the intermediate tin coating layers, the convex portions are spaced 1 to 30 ~m apart, and have a coating thickness of 0.20 ~m or more, the concave portions have a coating thickness of 0 to 0.07 ~m, and the average coating thickness of the entire intermediate -tin coating layers is 0.17 ~m or less.
In the fourth step of the process of the present -~
invention, an electrolytic chromate treatment is applied, ~-~
as a final passive state-forming step, to the heat- ~ -treated steel strip to form electrolysed chromate -15 surface coating layers on the intermediate tin coating ~ -~
layers. The resultant surface coating layers have substantially plain surfaces. That is, the thicknesses ~;
of portions of the surface coating layers formed on the convex portions of the intermediate tin coating layers is larger than that of portions of the surface coating layer formed on the concave portions of the intermediate tin coating layer. In other words, referring to Fig. 3C, the surface coating layer 16 has a number of downward convex portions 16a formed on the concave portions 15b 25 of the intermediate tin coating layer 15 and a number of ~;
~ard concave portions 16b formed on the convex portions (15~ of the intermediate tin coating layer 15.
" ~ ~ The upward concave portions 16b of the surface / coating layers having a small coating thickness exhibit / 30 an excellent weldability. Also, the downward convex portions 16a of the surface coating layers having a large coating thickness exhibit a superior corrosion resistance. Therefore, as a whole, the coated steel strip of the present invention exhibits an enhanced weldability and corrosion resistance and is useful for cans and containers. When the coated steel strip having the above-mentioned uneven surface coating layer is .. . .
- 14 - ~33~9~'2 subjected to a seam welding procedure, the concave portions of the uneven surface coating layers having a - small coating thickness serve to stabilize the flow of the electric current, and thus to improve the seam weldability of the coated steel strip. Also, the thick convex portions of the surface coating layers are effective for enhancing the corrosion resistance of the coated steel strip.
The uneven surface coating layers consisting essentially of electrolysed chromate can be produced by a conventional electrolytic chromate-treating method usable for TFS-CT. Usually, the electrolytic chromate treatment is carried out in accordance with a cathodic reduction method in an aqueous solution of chromic -~
anhydride in the presence or absence of anions, for example, sulfuric anions or fluoride anions. Also, any known means for reducing co-depositing anions in the electrolysed chromate layer can be applied to the - ;~
electrolytic chromate treatment. ~ ! ;
The electrolysed chromate surface coating layer may consist essentially of chromium oxide hydrate alone.
The surface coating layer is preferably in an average amount, in terms of metallic chromium, of 3 to 30 mg/m2 / I per surface of the substrate. If the average amount is ¦ 1 25 less than 3 mg/m , the resultant coating steel strip ¦ ¦ sometimes exhlbits an unsatisfactory corrosion resis-¦ ¦ tance and a poor bonding property to paint. Also, if ¦ ¦ the average amount of the surface coating layers is more than 30 mg/m , the resultant coating steel strip 1 30 sometimes exhibits an unsatisfactory weldability.
I The electrolysed chromate surface coating layer may comprise hot alkali-soluble chromium fractions and hot alkali-insoluble chromium fractions.
In the surface coating layers, the proportion in 35 weight of the hot alkali-soluble fractions to the hot alkali-insoluble ~ractions is not limited to a specific level. However, in the concave portions of the surface ;~
, ,.:; ' - 133~962 coating layers, preferably the proportion of the hot alkali-insoluble fractions is larger than that of the hot alkali-insoluble fractions.
The present invention will be further explained by 5 way of specific examples, which, however, are merely ~ ;
representative and do not restrict the scope of the ~-present invention in any way.
In the example, the following tests were carried out. -~
IA) Seam Welding Tes~
A specimen, that is, a piece of a multilayer coated steel strip, was formed into a peripheral portion of a can in which edge portions of the specimen were overlapped to a width of 0.4 mm. The overlapped portion 15 of the specimen was seam welded under a pressure of ~d~
45 hgf at a can-forming rate of 45 mpm. The value of the second order welding current was varied to determine a range of values of the second order welding current, in which range an optimum seam welding was obtained.
The lower limit of the optimum range of the second order welding current corresponded to a second order welding current value at which the resultant welded portion exhibited a lowest value of satisfactory welding strength. Also, the upper limit of the optimum second order welding current value range corresponded to an upper limit of the second order welding current value range in which the seam welding procedure can be carried out without the generation of an undesirable splash phenomenon.
The welding strength of the welded portion was determined by an impact test and a peeling test in which a V-shaped notch was formed in the welded portion of the specimen and the welded two ends of the specimen were peeled from each other by a pair of pincers.
The appearance of the seam welded portion of the specimen was evaluated by naked eye observation in which the generation and intensity of expulsion and - 16 - 1331~62 surface flash on the welded portion were observed.
The specimen to be subjected to the seam welding test was preliminarily heated at a temperature of 210C for 20 minutes in an electric air oven.
(B) Underpaint Rust Resistance Test Two surfaces of a specimen were coated with an ordinary epoxy-phenol coating material for cans, in an amount of 55 mg/dm2 per surface of the specimen, by a roll coating method and the resultant coating layers were heated at a temperature of 205C for 10 minutes and then further heated at a temperature of 190C for 10 minutes. The resultant paint layers were scratched with -a cutting knife and then subjected to an Ericksen "!''~'i.' process at a height of 5 mm by using an Ericksen testing 15 m~chine.
The resultant testing specimen was subjected to a salt water spraying test for one hour, by spraying an aqueous solution of 5% by weight of NaCl. Then the specimen was left in a thermo-hydrostat at a temperature 20 of 25C at a relative humidity of 85% for 14 days. The generation of rust in the scratched portions in the ~ -specimen was observed by the naked eye.
In each example, all of the procedures were repeated twice. The seam welding test and the rust 25 resistance test were applied to both the first product and the second product of each example.
Examples 1 to 5 and Comparative Examples 1 to 3 In each o Examples 1 to 5 and Comparative Examples 1 to 3, two surfaces of a substrate consisting 30 of a steel strip, which had been surface cleaned by an ordinary cleaning method, were plated with nickel in a ~
plating aqueous solution containing 200 g/l of ~ ;
NiSO4-7H2O, 60 g/l of NiC12 6H2O, and 50 g/l of ~3PO3 at the temperature of 50C at the pH selected 35 from the range of from 1.8 to 4.0 and at the cathodic current density selected from the range of from 5 to ~ i 50 A/dm2 as shown in Table 1. The resultant nickel ~ ;;
' '.., ~:' ~ 133196~ :
coating layers consisted of the plated nickel in an -amount in the range of from 2 to 120 mg/m2 per surface of the substrate, as shown in Table l. The resultant ;
nickel coating layers were in the form as indicated in Table l and had the largest coating thickness (hmax) and the percentage RA of the total area portions of the nickel coating layers having a coating thickness f -0.001 ~m or more based on the entire area of the surfaces of the su~strate, as shown in Table l.
The form and thickness of the nickel coating layers were determined by AES and EPMA analyses.
In Examples l to 5 in accordance with the process of the present invention, the largest thickness (hmax) of the nickel coating layers was 0.002 ~m or more and the percentage RA of the portions of the nickel coating layers having a coating thickness of 0.001 ~m or more was in the range of from 10% to 95%.
The nickel-coated steel strip was plated with tin in a tin plating aqueous liquid containing 25 g/l of tin sulfate, 30 ~/l of phenol sulfonic acid, and 2 g/l of ethoxylated a-naphthol sulfonic acid at a temperature in the range of from 40 to 50C at a cathodic current density of 20 A/dm2. The average amount of the resultant tin coating layers was in the range of from 800 to 1000 mg/m per surface of the substrate, as shown in Table l.
The resultant precursory coated steel strip was immersed in an aqueous flux solution containing 1 to 2 g/l of phenol sulfonic acid at a temperature of 45C~
and then dried.
The flux-treated precursory coated steel strip was heat-treated by an electric resistance heating method at a temperature of from 240C to 280C for 2 seconds to 6 seconds in the air atmosphere. The heating tempera~
ture and time were decided so that the resultant Fe-Ni-Sn alloy base layer contained tin in an amount corresponding to about 1/3 of the entire amount of tin 1 3 3 1 .9 ~ 2 plated on the substrate.
The heat-treated steel strip was subjected to an electrolytic chromate treatment in an aqueous treating solution containing 2 to 100 g/l of CrO3 , 0.1 to 1.0 g/l of H2SO4 and 0 to 3 g/l of Na2SiF6 at a temperature of from 40C to 60C at a cathodic current density in the range of from 5 to 90 A/dm2 so as to form electrolysed chromate surface coating layers in an average amount of 12 to 17 mg/m2, in terms of metallic chromium, per surface of the substrate.
The distribution of the electrolysed chromate in the surface coating layers was determined from the characteristic X-ray intensity of chromium measured by EPMA analysis.
In Table 1, the term "even distribution" refers to a distribution of thickness of the intermediate tin coating layers in such a manner that the ratio of the average thickn~.ss TV of the downward convex portions to the average thickness TC of the upward concave portions of the surface coating layers is 1 or more and less than 1.2. Also the term "uneven distribution"
refers to a distribution of thickness of the inter-mediate tin coating layers in such a mannex that the ratio o~ the average thickness TV of the downwaxd convex portions to the average thickness TC of the upward concave portions of the surface coating layers is ~
1.2 or more. ;
Preferably, the surface coating layers have an uneven thickness distribution.
The results of the seam welding test and the rust resistance test in the examples and comparative examples are shown in Table 1. ~ ~
Examples 6 and 7 ~`
In each of Examples 6 and 7, the same procedures as those described in Example 1 were carried out with the following exception.
The nickel-plating step was carried out so that the ~ ,. , :::
~33~
.
resultant nickel coating layers were as indicated in Table 1.
The tin-coating step was carried out in an aqueous plating solution containing 75 g/l of stannous chloride, 25 g/l of sodium fluoride, 50 g/l of potassium hydrogen fluoride, and 45 g/l of sodium chloride at a temperature in the range of from 40 to 50C and at a cathodic :
current density in the range of from 20 to 40 A/dm2, so that the resultant tin coating layers had the average amount as indicated in Table 1~
No flux treatment was applied to the tin-coated steel strip. The tin-coated steel strip was washed with water and then subjected to the heat treatment.
The results of the tests are shown in Table 1.
Comparative Examples 4 and 5 In each of Comparative Examples 4 and 5, the same procedures as those mentioned in Example 1 were carried out except that. the nickel plating step was omitted, and in Comparative Example 5, the average amount of the tin coating layer was 1100 mg/m per surface of the substrate.
The results of the tests are indicated in Table 1~ . . .
Referential Example :
., An ordinary tinplate #25 having tin coating layers in an amount of 2800 mg/m2 per surface of the tinplate was subjected to the same electrolytic chromate treatment and tests as those mentioned above. ~
The results are shown in Table 1. ~:
- ~3~
~ 3 ;~3 ~3~ 3 3~
3;~ ~3~1 ~3 ~ ;
N ~O O ~ ~ ~ ~ ¦
. ~ ~1 U') ~ O O N cCI
~ ~ ~ ~ ~ ,' ~-~ ~ ~ I I I I I ~ ~ I I I
_~ ~ ~ co _I r ~ ~ o . ~ .
~1 ~= ~ ~ ~ ~ L
~ 5 Y~ ~ ~ ~ o o o o o o o oo o ,~Y~ o 'r~ u~ ' . ,~ , . ~ In o~~ o ~O
;~ ~1 ~ ~ ~
O ~I N ~'1 ~1 ~ t`l ~7 117 ~D t"
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-~3 . ~ ~ o o ~ ~
.~ ~ . ~ ~n N n ,~
~ _ ~ ~ 1. 1. 1. .~ .
g ~ ~ ~ ~. ~ ~ ' ' '.
.~ ~ , .~ ~ ~ ' ''~.'~,',;.
~3 ~ ~ a ,~ en~ O g `-E~ 5! nl E ~1 o~ n ~,~ n ~ ~I ~ 'I ~ N ' ~ .
3 ~ --~ ~ ~ A
,~ ~ lll i~
.~ _ ~ , ~o '' ~ ~ l l l ~ ~ ~ '',''`'''~"~ ;' . S!; _ .
' . 3~ ~ l l l . ~p Ul .
.....
:`'~.. ` ,:, ' . . ,., .. . : , .. ~ , . .
In Examples 1, 2, 3 and 6, the resultant multilayer coated steel strips exhibited excellent seam weldability and corrosion resistance compatible with those of the ordinary tinplate, although the amounts of the tin coating layers in Examples 1, 2, 3 and 6 are in a low level of from 800 or 1000 mg/m2, whereas the ordinary tinplate had a large amount of tin coating layers of 2800 mg/m2.
Also, from Examples 1 to 7 in comparison with Comparative Examples 1 to 5, it is clear that the presence of the uneven nickel coating layers on the substrate surfaces is very effective for enhancing the seam weldability and corrosion resistance of the resultant coated steel strip.
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Formerly, tinplate was most widely used as a steel material for producing cans, but conventional tinplate is not always satisfactory in view of the price thereof. Therefore, in order to reduce the can-producing cost, attempts have been made to reduce the thickness of the tin coating layer on the steel 25 strip, and to utilize a seam-welding method instead of the conventional soldering method for the tinplate. It has been found, however, that when the thickness of the tin coating layer in the tinplate is reduced to a level of 0.20 ~m or less, the resultant tinplate exhibits a 30 deteriorated paint corrosion resistance and a reduced seam weldability.
; The conventional TFS-NT sometimes used as a ' ~ ~ 2 ~ ~ 3 3 ~
)~ ~teel mat~ri~l for produclng seam-welded can~ u~ually exh~bits a ~ati~factory 8eam weldabillty, but th~s weld~b$1ity is not ~lways sat~factory in prac~cal us~.
. Al~o, the conventional TFS-NT has a satlsfac~ory paint S corrosion resistance in usual use, but the level of th~ :
paint corros~on resis~ance ~s not always sati~factory when brough~ into con~ac~ with a corrosive material, for ex~mple, ~rongly acidic food.
Accordingly, there i8 a strong demand for thé
10 prov~sion of a surface-coated steel ~trip wbich ~8 cheap ~::
and has an excellent paint corrosion resistance and seam weldabil~ty, and thus ~s useful for the production o . ~:
cans and containers.
Japane~e Unexamined Paten~ Publication (~oka~
No. 60-75586 (Nippon Steel Corporation, published 7 April 27, 1985)d$sclose~ a proces~ for producing a coated steel ~trip. ~n thi~ process, a ~teel 6trip is coated with a small amount of nic~el, and the nickel-coated steel strip ls then plated with tin. When the nickel 20 and t~n coated-steel str~p i~ heat treated, and ~he tin coat~ng layer is converted to an Fe-Sn alloy layer,.the ~:
presenc~ of the small amount of nickel coat~ng layar : :
causes the structure of the Fe-Sn alloy layer to exhi~it an enhanced density. There~ore, the xesultant coated 25 steQl strip exhibit~ an improved corrosion re~is~ance.
~180, the presence of the nickel coa~ing layer ~s effective for restxictinq the ~e-Sn alloy-forming reaction ln the heat-treatment) and thus the resultant coated steel exhibits an enhanced ~eam weldability~
30 Further, the inventors o~ the pxesent invention have found that the propertie~, ~or example, seam weldability and corrosion resis~ancet o the coated ~teel ~tr~p usable ~8 a s~eel mater~al for 8eam weldea can6, vary depending on the distriSution of metall~c tin coating 35 over the surface of a s~eel ~trip subs~rate. That i8, it ha~ been ~ound that ~hQ propexties of the coated steel atrlp over which the metallic tin layer i5 unevenly distributed and having an uneven rough ~urface,.are . . .
133~62 - 3 - ~- ~
- -:
better than those of a coated steel strip over which the metallic tin layer is evenly distributed and having a smooth uniform surface.
Namely, the coated steel strip having an uneven thin tin coating layer exhibits a better seam weldability and corrosion resistance than those of a -conventional coated steel strip having an even thin tin coating layer. However, it is very difficult to control the thickness of the unevenness of the thin tin coating layer to a predetermined level, and to produce a coated steel strip having predetermined levels of weldability~-~
and corrosion resistance with a stable reproductivity.
Fujimoto et al, "Iron and Steel~, vol. 72, No. 5, page 39. 1986 discloses that, in order to provide a tin -~ -15 coating layer having an uneven thickness with a stable --reproductivity, it is effective to apply an anodic electrolytic treatment to the steel strip in an alkaline treating liquid before the nickel-plating step. Also, it is known that, when a tin-coated steel strip is subjected to a flux treatment, the unevenness in the thickness of the tin coating iayer is greatly influenced by the conditions of the flux treatment.
However, even if the anionic electrolytic treatment or the flux treatment is utilized, the resultant coated steel strip is unsatisfactory from the viewpoint of corrosion resistance and weldability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing a multilayer-coated steel strip having an excellent corrosion resistance and weldability and useful for producing cans or containers with an improved reproductivity.
The above-mentioned object can be attained by the process of the present invention which comprises the steps of (A) plating a substrate consisting of a steel strip with metallic nickel or a nickel-based alloy to form, on both the upper and lower surfaces of the :
... ~ ' i$
~33~S2 substrate, nickel-~a~e~ coa~ing layer, each of which . ~:
layers $8 coated in ~n aver~ge amoun~ of 2 to 100 mg/m2 and ~8 provided with a number of convex and concave portlons, and in which layer portions thereof having a coa~ing ~hicXness of 0.001 ~m or more have a total area corre~ponding ~o 10% to 95~ oP the entire area of the surface~ of the sub~trate~ IB) ~oating the nickel-based -:
plated ~ubstrate with tin to ~orm tin coa~ng layer~ on the nicXel-ba~ed coating layer~, each o~ which tin coating layers i8 coated ~n an averaqe amount of 200 to 2000 mg/m , to provi~e ~ precur60ry ~oate~ steel str~pS (C~ heating the precursory coated st~el strip at a temperature equal to or higher than the melting point of the tln ~oating layer, to c~u e th~ nic~el-~ased coating layers and the tin coat~ng layer~ to be con~
verted to base ~oating layers, which ar~ ~ormed on ~oth the upper and lower surface~ o~ ~hQ ~u~Btrat~ con- ~ :
8i8ting essentially of an Fe-Ni-Sn-based alloy and ~ :
having a n~mber of convox and concnv~ portions, a~d : :
intermediate coating layers, which arQ located on the base coatinq l~yers, consisting essentlally of t~n And having ~ number o~ convex ~nd concav~ portion~1 an~ tD) ~ :
applying an eleatrolytic ~hromate treatmen~ to th~
lntermediate tin coati~g layer~ to fonm surface coatlng layers, consi8t~ng oi electxoly~ed chromate, on the intermediate tin coating layer.
A~ther ob~ect o~ the invention is to provide a multilaver-coated steel strip having excellent corrosion resistance and weldability, comprising:
(a) a substrate consisting of a steel strip; and -~
(b) a multi-layer coating covering both the upper and lower surfaces of the substrate and comprisinq:
~ 4a - 1 ~ 3 ~ 9 62 (i) a base coating layer deposited on the ~ ~ -substrate surfaces, consisting essentially of a Fe-Ni-Sn-based alloy, the layer having a plurality of convex and concave portions thereof;
S (ii) an intermediate coating layer deposited on the base coating layer to form a ~ ~ :
precursory coated steel strip, consisting essentially :- -of tin deposited in an amount of 200 to 2000 mg/m~, the ~ ~
intermediate coating layer having a plurality of :
10 convex and concave portions thereo~ in contact with ~.
corresponding convex and concave portions of the base coating layer; and :~.
(iii) a chromate coating layer deposited by an electrolytic chromate treatment on the 15 intermediate coating layer in an amount of 3 to 30 mg/m2 in terms of metallic chromium, the base coating ~:~
layer (i) and the intermediate layer (ii) having been formed by: ~ ;
(A) plating the substrate consisting of ~: .
20 a steel strip, with metallic nickel or nickel-based ~ :
alloy consisting of at least 80% by weight of nickel : :
and 20% by weight or less of an additional metal :
element consisting of at least one member selected : :
from zinc, phosphorus, cobalt, copper and chromium, to 25 form a nickel-based coating layer OTI both the upper and lower surfaces o~ the substrate, said nickel-based : ::
coating layers being in an average amount of 2 to 100 mg/m2 and provided with a number of convex portions and . :
concave portions thereof, and wherein said portions 30 thereof having a coating thickness of 0.001 ~m or more ~:
have a total area corresponding to from 10% to 95% of the entire area of the surfaces of the substrate;
(B) coating the resulting nickel-based ;
plated substrate with tin to form tin coating layers 35 on the nickel-based coating layers, each tin coating~ ~:
~ :, ~33~62 - b -layer being in an amount of 200 to 2000 mg/m2, to provide a precursory coated steel strip;
and (C) heating the precursory coated steel S strip at a temperature equal to or higher than the melting point of the tin coating layers, to cause the nickel-based coating layers and the tin coating layers to be converted to the base coating layer and the intermediate coating layer.
,, :' . 15 / : :
/
BRIEF DESCRIPTION 0~ THE DRAWINGS
Figure 1 is a schematic cross-sectional view of an embodiment of the niokel coating layer formed on a steel strip substrate in the first step of the proces~ of the present inventions Fig. 2 i~ a schema~ic cross-sectional view of another embodiment of the nickel coating layer formed on a steel strip ~ubstrate in the first ~tep o~ the process of the pre~ent invent~on~ and, :
Fig. 3A to 3C are ~chematic cross-sectional v~ews ~:
35 of embodiment~ of the produc~s formed re~pectively in ~-" 133~2 the second, third, and fourth steps of the process of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the first step of the present invention, a substrate consisting of a steel strip to be multilayer-coated is plated with nickel or a nickel-based alloy to form nickel-based coating layers on both the upper and lower surfaces of the substrate to an extent such that -the resultant nickel-based coating layers are coated in a small average amount of from 2 to 100 mg/m2, preferably from 5 to 100 mg/m2, per surEace of the substrate and have an uneven thickness distribution, so as to provide a number of convex and concave portions preferably substantially evenly distributed in the layer.
That is, the uneven nickel based coating layer may be, as shown in Fig. 2, in the form of a land having a number of mountains and hills corresponding to the convex portion~ and a number of lakes and valleys corresponding to the concave portions, which mountains, hills, lakes, and valleys are substantially evenly distributed in the land. Some of the lakes and valleys (concave portions) may have bottoms thereof formed by~ ~;
nickel or a nickel-based alloy plated on the substrate surface~. Also, in the bottoms of other lakes and valleyq ~concave portions), portions of the substrate surfaces may be exposed to the outside. That is, the nickel-based coating layer may incompletely cover the surfaces of the substrate.
Alternatively, the uneven nickel-based coating layer may be, as shown in Fig. 2, in the form of a number o islands corresponding to the convex portions, consisting of nickel or the nickel-based alloy and preferably substantially evenly distributed in one or more seas corresponding to the concave portions connected to each other. Some of the island portions may be in the above-mentioned form of a land having a number o mountains, hills, lakes, and valleys. In the bottoms of ,. '.. '.' ~
~ .
',1'.. ~ : ,. ': .; ., ~
6 1~3~962 the sea portions of the nickel-based coating layer, the ', corresponding portions of the substrate surfaces are exposed to the outside~ , Referring to Fig. 1, a surface of a steel strip substrate 1 is coated with an uneven nickel-based coating layer 2 having convex portions 2a and concave portions 2b.
In Fig. 2, a surface of a steel strip substrate 1 is coated with an islands-in-sea type nickel-based coating la~er 2 consisting of a plurality of island~
formed nickel-based coating deposits 2c separated from each other. Portions la of the surface of the substrate 1 are exposed to the outside but not coated with the nickel-based coating deposit.
The coating thicknesses of the convex portions, that is, the heights from the surface of the substrate to the peaks of the convex portions, may be different.
Also, the coating thicknesses of the concave portions, ' that is, the thickness between the surface o the substrate and the bottoms of the concave portions, may be different.
In the formation of the uneven nickel-based coating layers, the total area of portions o the layers having a coating thickness of 0.001 ~m or more must be coated to a level corresponding to 10% to 95~, preferably, 10 to 90%, o the entire area of the surfaces of the substrate to be coated. Also, preferably the convex and concave portions of the resultant nickel-based coating layers satisfy the relationships (1), (2), and (3):
' hmax > 0.002 ~m (1) , hmin > 0 (2) and, hmin > 0, hmax > 2 hmin (31 wherein hmax represents a largest coating thickness of the convex portions and hmin represents a smallest coating thickness of the concave portions of the nickel-based coating layer.
In the first step of the process of the present :':
.~. : . .
~331~2 invention, the steel strip substrate, which has been degreased or surface cleaned by an ordinary method, is subjected to a nickel-plating process. In the surface cleaning procedures, the steel strip substrate may be subjected to an anodic electrolytic treatment in a pickling liquid, for example, a sulfuric acid aqueous solution, or a degreasing liquid, for example, a sodium hydroxide aqueous solution.
The surface cleaned steel strip substrate is unevenly plated with nickel or a nickel-based alloy in an amount of 2 to 100 mg/m2, preferably 5 to 100 mg/m2, per surface of the substrate. The plating process can be carried out in an ordinary nickel plating liquid, for example, a sulfuric acid watt plating liquid. The -composition of the plating liquid, plating current density, plating temperature and time, and other plating conditio~s are determined so that the resultant nickel~
based coating layers are in the above-mentioned specific amount and have the above-mentioned uneven thickness distribution. The plating method is not limited to a specific method and may be an electric plating method or a non-electrolytic plating method, as long as the specific uneven nickel-based coating layers is obtained.
Also, ater the plating operation is completed, the nickel-based pIated substrate may be additionally subjected to an anodic electrolytic treatment. Alter-natively, the nickel-based plated substrate may be ~ ~
subjected to a heat treatment at an elevated tempera- ~ ;
ture, to cause the plated nickel or nickel-based alloy to diffuse into the steel strip substrate.
I the amount of the plated nickel or nickel-based / ¦ alloy is more than 100 mg/m2, the resultant coating ¦ ¦ layer will have a substantially even thickness and it ¦ ¦ will be difficult to provide a coated steel strip having `~
¦~5 a satisfactory corrosion resistance and weldability.
If the amount of the plated nickel or nickel-based alloy is less than 2 mg/m2, it will be difficult to ~L331962 provide a dense Fe-Ni-Sn based base layer having a excellent effect for enhancing the corrosion resistance of the resultant coated steel strip.
As stated above, the limitation in the amount of the nickel-based coating layers to the range of from 2 to 100 mg/m2 per surface of the substrate is very important when causing the resultant nickel-based -coating layers to have an uneven coating thickness distribution and to be provided with a number of convex portions and concave portions thereof. This specific form of the nickel based coating layers is essential when providing a multilayer-coated steel strip having an excellent corrosion resistance ana weldability and useful as a steel matexial for producing cans or con-tainers.
Also, if the total area of the portions of the/¦ nickel-based coating layers having a ~hickness of ¦¦ 0.001 ~m or more is more than 95% or less than 10% of ¦ the entire area of the surfaces of the substrate, the I:20 unevenness in the coating thickness of the nickel-based ¦ coating layers will be unsatisfactory, and thus the ¦ resultant coated steel strip will exhibit an unsatis-factory corrosion resistance and weldability.
The uneven nickel-based coating layer satisfying the above-defined relationships (1), (2), and (3) is very effective for further enhancing the corrasion resistance and weldability of the resultant coated steel strip.
The uneven distribution of the thickness of the 30- nickel~based coating layer can be observed by means of an electron probe micro-analyser or an Auger electron Spectroscopy.
The uneven nickel-based coating layer may consist \ I ¦ of nickel or a nickel-based alloy consisting of at least 80% by weight of nickel and 20% by weight or less o~ an ¦¦ additional metal element consisting of at least one member selected from zinc, phosphorus, cobalt, copper, 13319~2 g .
and chromium. The additional metal element can be alloyed with nickel by the heating treatment and is effective for causing a portion of tin coating layer to remain in the free tin state after the heat treatment.
The remaining free tin forms an intermediate tin coating layer on the base coating layer after the heat-treatment step.
In the second step of the process of the present invention, the nickel-based plated substrate is coated with tin in an average amount of 200 to 2000 mg/m2 per surface of the substrate to provide a precursory coated -steel strip. The tin coating procedures are not limited to a specific method, and can be carried out by any conventional tin plating method. However, the tin coating is preferably carried out by an electric plating method.
The average amount of the tin coating layers formed on the nickel hased plated substrate i limited to a specific range from 200 to 2000 mg/m2 per surface of the substrate to provide a resultant coated steel strip having an excellent corrosion resistance and weldability at a low cost.
If the average amount of the tin coating layers is ~`
l more than 2000 mg/m2, the excess amount of tin over ¦25 2000 mg/m2 has no effect on the enhancing of the ¦ corro~ion reqistance and weldability of the resultant coated steel strip, and undesirably increased the cost of the resultant coated steel strip. Also, an average `~
amount o less than 200 mg/m of the tin coating layer results in an unsatisfactory seam weldability and corrosion resistance of the resultant coated steel strip. -After the tin coating step is completed, the coated -~
steel strip is usually washed with water and, if necessary, is immersed in a flux comprising, as a principal component, phenol sulfonic acid or ammonium chloride, and finally, is dried. The flux may have a ., `` ~331962 concentration corresponding to from 1/2 to 1/~ of that in an ordinary flux for producing a usual tinplate. The necessity for flux treatment and composition and con-centration of the flux can be decided in consideration of the type and constitution of the desired coated steel strip.
In the third step in the process of the present invention, the pxecursory coated steel strip is heat-treated at a temperature equal to or higher than the melting point of the tin coating layer. This heat treatment may be carried out by, for example, an electric resistance-heating method or high-frequency induction heating method. Further, this heat treatment may be effected in an atmosphere consisting of an inert gas, for example, nitrogen or argon gas.
The heat treatment applied to the precursory coated steel strip is effective-for converting the nickel-based coating layers and tin coating layers to base coating layers formed on the two surfaces of the substrate, and consisting essentially of an Fe-Ni-Sn-based alloy and having a number of convex and concave portions, and intermediate coating layers f~rmed on the base coating layers, consisting essentially of tin and having a number of convex and concave portions. ~ ;
Preferably, the heat treatment is controlled to an extent such that the content of tin in the resultant base Fe-Ni-Sn-based alloy coating layers corresponds to about 1/3, that is, from 30% to 35% of the entire weight of the original tin-coating layers.
The heat treatment at a temperature equal to or higher than the melting point of the original tin coating layer results in the conversion of the nickel-based coating layers and the tin coating layers to base Fe-Ni-Sn based alloy coating layers and intermediate tin coating layers, which are effective for imparting an excellent corrosion resistance and weldability to the resultant coated steel strip.
.
~ 33~2 The above-mentioned conversion will be further explained by referring to Figs. 3A to 3C.
Referring to Fig. 3A, a precursory coated steel strip 10 which has been produced by the first and second -steps of the process of the present invention, has a steel strip substr ~ 11, an islands-in-sea type nickel-based coating laye~ 1~ having a number of islands 12a, wherein the--islands 12a are separated from each other, and sea-shaped portions 12b between the islands 12a, and , ' 10 a tin coating layer 13. When the precursory coated ' steel strip is heated at a temperature equal to or higher than the melting poin~ of the tin coating layer, the tin coating layer 13 is melted and the nickel-based coating layer 12 is alloyed with a portion of iron in the steel strip substrate 11 and a portion of tin in the tin coating layer 13.
The alloying rate of nickel or nickel based alloy with the iron and tin is proportional to the concen-tration of nickel or nickel-based alloy in the alloying system. Therefore, each of the nickel-based islands 12a are rapidly converted to a corresponding alloy coating while growing three-dimensionally. Namely, each alloy coating becomes thicker than the corresponding nickel~
based islands and spreads on the substrate surface. The spread alloy coatings are connected to each other and form a continuous alloy coating layer which substantially completely covers the surface of the substrate, as shown in Fig. 3B.
Referring to Figs. 3A and 3B, the resultant alloy coating layer 14 has a number of convex portions 14a corresponding to the nickel-based islands 12a and a number of concave portions 14b corresponding to the sea-shaped portion 12b in the nickel-based coating layer 12 in Fig. 3A.
The tin melt exhibits a larger wetting affinity and a smaller free interface energy to the Fe-Ni-Sn-based alloy layer surface than to the nickel based alloy layer ....
13319~2 surface and to the steel strip surface. Note, the larger the thickness of the Fe-Ni-Sn-based alloy layer, the greater the ~Jetting affinity of the tin melt thereto.
Accordingly, the thickness of the tin melt layer 15 on the Fe-Ni-Sn-based alloy layer 14 corresponds to the thickness of the Fe-Ni-Sn-based alloy layer 14 as shown in Fig. 3B, when the heat-treatment is stopped and the alloy coating layer and tin melt layer are cooled to room temperature, the resultant tin coating layer 15 has a number of convex portions 15a and concave portions 15b thereof respectively corresponding to the convex portions 14a and the concave portions 14b of the alloy coating ~ -layer 14.
If the nickel-based coating layer has an even ~
15 thickness, the conversion of the nickel-based coating ~ ;
layer progresses at an even converting rate throughout -the layer, and the resultant alloy coating layer has a substantially e~ven thickness. Accordingly, the even base alloy coating layer causes the intermediate tin coating layer to have a substantially even thickness.
The even tin coating layer sometimes can be con-verted to an uneven tin coating layer as shown in Fi~, 3B by a flux treatment under a certain condition.
However, the conversion by the flux treatment is not ~
25 always successful. Sometimes, the flux treatment fails `
to convert the even tin coating layer to an uneven tin coating layer. Sometimes, the flux treated tin coating layer contains uneven portions and even portions thereof.
In other ~ords, the flux treatment cannot stably convert 30 the even tin coating layer to an uneven tin coating layer and, therefore, is not valuable for stably pro-ducing the coated steel strip having an enhanced corrosion resistance and weldability.
However, in the process of the present invention, 35 the uneven tin coating layers can be stably produced by utilizing the uneven nickel-based coating l~yers formed ; on the steel strip substrate surfaces. The uneven tin .1,```'~
~ , 1331~62 coating layers are very effective for producing the coated steel strip having an enhanced weldability and corrosion resistance, and therefore, useful for cans and containers.
Preferably, in the intermediate tin coating layers, the convex portions are spaced 1 to 30 ~m apart, and have a coating thickness of 0.20 ~m or more, the concave portions have a coating thickness of 0 to 0.07 ~m, and the average coating thickness of the entire intermediate -tin coating layers is 0.17 ~m or less.
In the fourth step of the process of the present -~
invention, an electrolytic chromate treatment is applied, ~-~
as a final passive state-forming step, to the heat- ~ -treated steel strip to form electrolysed chromate -15 surface coating layers on the intermediate tin coating ~ -~
layers. The resultant surface coating layers have substantially plain surfaces. That is, the thicknesses ~;
of portions of the surface coating layers formed on the convex portions of the intermediate tin coating layers is larger than that of portions of the surface coating layer formed on the concave portions of the intermediate tin coating layer. In other words, referring to Fig. 3C, the surface coating layer 16 has a number of downward convex portions 16a formed on the concave portions 15b 25 of the intermediate tin coating layer 15 and a number of ~;
~ard concave portions 16b formed on the convex portions (15~ of the intermediate tin coating layer 15.
" ~ ~ The upward concave portions 16b of the surface / coating layers having a small coating thickness exhibit / 30 an excellent weldability. Also, the downward convex portions 16a of the surface coating layers having a large coating thickness exhibit a superior corrosion resistance. Therefore, as a whole, the coated steel strip of the present invention exhibits an enhanced weldability and corrosion resistance and is useful for cans and containers. When the coated steel strip having the above-mentioned uneven surface coating layer is .. . .
- 14 - ~33~9~'2 subjected to a seam welding procedure, the concave portions of the uneven surface coating layers having a - small coating thickness serve to stabilize the flow of the electric current, and thus to improve the seam weldability of the coated steel strip. Also, the thick convex portions of the surface coating layers are effective for enhancing the corrosion resistance of the coated steel strip.
The uneven surface coating layers consisting essentially of electrolysed chromate can be produced by a conventional electrolytic chromate-treating method usable for TFS-CT. Usually, the electrolytic chromate treatment is carried out in accordance with a cathodic reduction method in an aqueous solution of chromic -~
anhydride in the presence or absence of anions, for example, sulfuric anions or fluoride anions. Also, any known means for reducing co-depositing anions in the electrolysed chromate layer can be applied to the - ;~
electrolytic chromate treatment. ~ ! ;
The electrolysed chromate surface coating layer may consist essentially of chromium oxide hydrate alone.
The surface coating layer is preferably in an average amount, in terms of metallic chromium, of 3 to 30 mg/m2 / I per surface of the substrate. If the average amount is ¦ 1 25 less than 3 mg/m , the resultant coating steel strip ¦ ¦ sometimes exhlbits an unsatisfactory corrosion resis-¦ ¦ tance and a poor bonding property to paint. Also, if ¦ ¦ the average amount of the surface coating layers is more than 30 mg/m , the resultant coating steel strip 1 30 sometimes exhibits an unsatisfactory weldability.
I The electrolysed chromate surface coating layer may comprise hot alkali-soluble chromium fractions and hot alkali-insoluble chromium fractions.
In the surface coating layers, the proportion in 35 weight of the hot alkali-soluble fractions to the hot alkali-insoluble ~ractions is not limited to a specific level. However, in the concave portions of the surface ;~
, ,.:; ' - 133~962 coating layers, preferably the proportion of the hot alkali-insoluble fractions is larger than that of the hot alkali-insoluble fractions.
The present invention will be further explained by 5 way of specific examples, which, however, are merely ~ ;
representative and do not restrict the scope of the ~-present invention in any way.
In the example, the following tests were carried out. -~
IA) Seam Welding Tes~
A specimen, that is, a piece of a multilayer coated steel strip, was formed into a peripheral portion of a can in which edge portions of the specimen were overlapped to a width of 0.4 mm. The overlapped portion 15 of the specimen was seam welded under a pressure of ~d~
45 hgf at a can-forming rate of 45 mpm. The value of the second order welding current was varied to determine a range of values of the second order welding current, in which range an optimum seam welding was obtained.
The lower limit of the optimum range of the second order welding current corresponded to a second order welding current value at which the resultant welded portion exhibited a lowest value of satisfactory welding strength. Also, the upper limit of the optimum second order welding current value range corresponded to an upper limit of the second order welding current value range in which the seam welding procedure can be carried out without the generation of an undesirable splash phenomenon.
The welding strength of the welded portion was determined by an impact test and a peeling test in which a V-shaped notch was formed in the welded portion of the specimen and the welded two ends of the specimen were peeled from each other by a pair of pincers.
The appearance of the seam welded portion of the specimen was evaluated by naked eye observation in which the generation and intensity of expulsion and - 16 - 1331~62 surface flash on the welded portion were observed.
The specimen to be subjected to the seam welding test was preliminarily heated at a temperature of 210C for 20 minutes in an electric air oven.
(B) Underpaint Rust Resistance Test Two surfaces of a specimen were coated with an ordinary epoxy-phenol coating material for cans, in an amount of 55 mg/dm2 per surface of the specimen, by a roll coating method and the resultant coating layers were heated at a temperature of 205C for 10 minutes and then further heated at a temperature of 190C for 10 minutes. The resultant paint layers were scratched with -a cutting knife and then subjected to an Ericksen "!''~'i.' process at a height of 5 mm by using an Ericksen testing 15 m~chine.
The resultant testing specimen was subjected to a salt water spraying test for one hour, by spraying an aqueous solution of 5% by weight of NaCl. Then the specimen was left in a thermo-hydrostat at a temperature 20 of 25C at a relative humidity of 85% for 14 days. The generation of rust in the scratched portions in the ~ -specimen was observed by the naked eye.
In each example, all of the procedures were repeated twice. The seam welding test and the rust 25 resistance test were applied to both the first product and the second product of each example.
Examples 1 to 5 and Comparative Examples 1 to 3 In each o Examples 1 to 5 and Comparative Examples 1 to 3, two surfaces of a substrate consisting 30 of a steel strip, which had been surface cleaned by an ordinary cleaning method, were plated with nickel in a ~
plating aqueous solution containing 200 g/l of ~ ;
NiSO4-7H2O, 60 g/l of NiC12 6H2O, and 50 g/l of ~3PO3 at the temperature of 50C at the pH selected 35 from the range of from 1.8 to 4.0 and at the cathodic current density selected from the range of from 5 to ~ i 50 A/dm2 as shown in Table 1. The resultant nickel ~ ;;
' '.., ~:' ~ 133196~ :
coating layers consisted of the plated nickel in an -amount in the range of from 2 to 120 mg/m2 per surface of the substrate, as shown in Table l. The resultant ;
nickel coating layers were in the form as indicated in Table l and had the largest coating thickness (hmax) and the percentage RA of the total area portions of the nickel coating layers having a coating thickness f -0.001 ~m or more based on the entire area of the surfaces of the su~strate, as shown in Table l.
The form and thickness of the nickel coating layers were determined by AES and EPMA analyses.
In Examples l to 5 in accordance with the process of the present invention, the largest thickness (hmax) of the nickel coating layers was 0.002 ~m or more and the percentage RA of the portions of the nickel coating layers having a coating thickness of 0.001 ~m or more was in the range of from 10% to 95%.
The nickel-coated steel strip was plated with tin in a tin plating aqueous liquid containing 25 g/l of tin sulfate, 30 ~/l of phenol sulfonic acid, and 2 g/l of ethoxylated a-naphthol sulfonic acid at a temperature in the range of from 40 to 50C at a cathodic current density of 20 A/dm2. The average amount of the resultant tin coating layers was in the range of from 800 to 1000 mg/m per surface of the substrate, as shown in Table l.
The resultant precursory coated steel strip was immersed in an aqueous flux solution containing 1 to 2 g/l of phenol sulfonic acid at a temperature of 45C~
and then dried.
The flux-treated precursory coated steel strip was heat-treated by an electric resistance heating method at a temperature of from 240C to 280C for 2 seconds to 6 seconds in the air atmosphere. The heating tempera~
ture and time were decided so that the resultant Fe-Ni-Sn alloy base layer contained tin in an amount corresponding to about 1/3 of the entire amount of tin 1 3 3 1 .9 ~ 2 plated on the substrate.
The heat-treated steel strip was subjected to an electrolytic chromate treatment in an aqueous treating solution containing 2 to 100 g/l of CrO3 , 0.1 to 1.0 g/l of H2SO4 and 0 to 3 g/l of Na2SiF6 at a temperature of from 40C to 60C at a cathodic current density in the range of from 5 to 90 A/dm2 so as to form electrolysed chromate surface coating layers in an average amount of 12 to 17 mg/m2, in terms of metallic chromium, per surface of the substrate.
The distribution of the electrolysed chromate in the surface coating layers was determined from the characteristic X-ray intensity of chromium measured by EPMA analysis.
In Table 1, the term "even distribution" refers to a distribution of thickness of the intermediate tin coating layers in such a manner that the ratio of the average thickn~.ss TV of the downward convex portions to the average thickness TC of the upward concave portions of the surface coating layers is 1 or more and less than 1.2. Also the term "uneven distribution"
refers to a distribution of thickness of the inter-mediate tin coating layers in such a mannex that the ratio o~ the average thickness TV of the downwaxd convex portions to the average thickness TC of the upward concave portions of the surface coating layers is ~
1.2 or more. ;
Preferably, the surface coating layers have an uneven thickness distribution.
The results of the seam welding test and the rust resistance test in the examples and comparative examples are shown in Table 1. ~ ~
Examples 6 and 7 ~`
In each of Examples 6 and 7, the same procedures as those described in Example 1 were carried out with the following exception.
The nickel-plating step was carried out so that the ~ ,. , :::
~33~
.
resultant nickel coating layers were as indicated in Table 1.
The tin-coating step was carried out in an aqueous plating solution containing 75 g/l of stannous chloride, 25 g/l of sodium fluoride, 50 g/l of potassium hydrogen fluoride, and 45 g/l of sodium chloride at a temperature in the range of from 40 to 50C and at a cathodic :
current density in the range of from 20 to 40 A/dm2, so that the resultant tin coating layers had the average amount as indicated in Table 1~
No flux treatment was applied to the tin-coated steel strip. The tin-coated steel strip was washed with water and then subjected to the heat treatment.
The results of the tests are shown in Table 1.
Comparative Examples 4 and 5 In each of Comparative Examples 4 and 5, the same procedures as those mentioned in Example 1 were carried out except that. the nickel plating step was omitted, and in Comparative Example 5, the average amount of the tin coating layer was 1100 mg/m per surface of the substrate.
The results of the tests are indicated in Table 1~ . . .
Referential Example :
., An ordinary tinplate #25 having tin coating layers in an amount of 2800 mg/m2 per surface of the tinplate was subjected to the same electrolytic chromate treatment and tests as those mentioned above. ~
The results are shown in Table 1. ~:
- ~3~
~ 3 ;~3 ~3~ 3 3~
3;~ ~3~1 ~3 ~ ;
N ~O O ~ ~ ~ ~ ¦
. ~ ~1 U') ~ O O N cCI
~ ~ ~ ~ ~ ,' ~-~ ~ ~ I I I I I ~ ~ I I I
_~ ~ ~ co _I r ~ ~ o . ~ .
~1 ~= ~ ~ ~ ~ L
~ 5 Y~ ~ ~ ~ o o o o o o o oo o ,~Y~ o 'r~ u~ ' . ,~ , . ~ In o~~ o ~O
;~ ~1 ~ ~ ~
O ~I N ~'1 ~1 ~ t`l ~7 117 ~D t"
.':' ' ,' '. ~':
-~3 . ~ ~ o o ~ ~
.~ ~ . ~ ~n N n ,~
~ _ ~ ~ 1. 1. 1. .~ .
g ~ ~ ~ ~. ~ ~ ' ' '.
.~ ~ , .~ ~ ~ ' ''~.'~,',;.
~3 ~ ~ a ,~ en~ O g `-E~ 5! nl E ~1 o~ n ~,~ n ~ ~I ~ 'I ~ N ' ~ .
3 ~ --~ ~ ~ A
,~ ~ lll i~
.~ _ ~ , ~o '' ~ ~ l l l ~ ~ ~ '',''`'''~"~ ;' . S!; _ .
' . 3~ ~ l l l . ~p Ul .
.....
:`'~.. ` ,:, ' . . ,., .. . : , .. ~ , . .
In Examples 1, 2, 3 and 6, the resultant multilayer coated steel strips exhibited excellent seam weldability and corrosion resistance compatible with those of the ordinary tinplate, although the amounts of the tin coating layers in Examples 1, 2, 3 and 6 are in a low level of from 800 or 1000 mg/m2, whereas the ordinary tinplate had a large amount of tin coating layers of 2800 mg/m2.
Also, from Examples 1 to 7 in comparison with Comparative Examples 1 to 5, it is clear that the presence of the uneven nickel coating layers on the substrate surfaces is very effective for enhancing the seam weldability and corrosion resistance of the resultant coated steel strip.
' ;.' ~
", -., .' '~ ' ... . . . .
...: . ~.
. .
: :"
.
; ~
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.
.
, `.': ~ : : . :
Claims (5)
1. A process for producing a multilayer-coated steel strip having an excellent corrosion resistance and weldability and useful for containers, comprising the steps of:
(A) plating a substrate consisting of a steel strip, with metallic nickel or nickel-based alloy consisting of at least 80% by weight of nickel and 20% by weight or less of an additional metal element consisting of at least one member selected from zinc, phosphorus, cobalt, copper and chromium, to form a nickel-based coating layer on both the upper and lower surfaces of the substrate, said nickel-based coating layers being in an average amount of 2 to 100 mg/m2 and provided with a number of convex portions and concave portions thereof, and wherein said portions thereof having a coating thickness of 0.001 µm or more have a total area corresponding to 10-95% of the entire area of the surfaces of the substrate;
(B) coating the resulting nickel-based plated substrate with tin to form tin coating layers on the nickel based coating layers, each tin coating layer being in an amount of 200 to 2000 mg/m2, to provide a precursory coated steel strip;
(C) heating the precursory coated steel strip at a temperature equal to or higher than the melting point of the tin coating layers, to cause the nickel-based coating layers and the tin coating layers to be converted to a base coating layer which is formed on both the upper and lower surfaces of the substrate, consisting essentially of an Fe-Ni-Sn-based alloy and having a number of convex portions and concave portions thereof, and an intermediate coating layer which is formed on the base coating layer, consisting essentially of tin and having a number of convex portions and concave portions thereof corresponding to the convex portions and the concave portions of the base coating layer, respectively; and (D) applying an electrolytic chromate treatment onto the intermediate tin coating layer to form a chromate surface coating layer in an average amount of 3 to 30 mg/m2 in terms of metallic chromium, consisting of electrolysed chromate, on the intermediate layer.
(A) plating a substrate consisting of a steel strip, with metallic nickel or nickel-based alloy consisting of at least 80% by weight of nickel and 20% by weight or less of an additional metal element consisting of at least one member selected from zinc, phosphorus, cobalt, copper and chromium, to form a nickel-based coating layer on both the upper and lower surfaces of the substrate, said nickel-based coating layers being in an average amount of 2 to 100 mg/m2 and provided with a number of convex portions and concave portions thereof, and wherein said portions thereof having a coating thickness of 0.001 µm or more have a total area corresponding to 10-95% of the entire area of the surfaces of the substrate;
(B) coating the resulting nickel-based plated substrate with tin to form tin coating layers on the nickel based coating layers, each tin coating layer being in an amount of 200 to 2000 mg/m2, to provide a precursory coated steel strip;
(C) heating the precursory coated steel strip at a temperature equal to or higher than the melting point of the tin coating layers, to cause the nickel-based coating layers and the tin coating layers to be converted to a base coating layer which is formed on both the upper and lower surfaces of the substrate, consisting essentially of an Fe-Ni-Sn-based alloy and having a number of convex portions and concave portions thereof, and an intermediate coating layer which is formed on the base coating layer, consisting essentially of tin and having a number of convex portions and concave portions thereof corresponding to the convex portions and the concave portions of the base coating layer, respectively; and (D) applying an electrolytic chromate treatment onto the intermediate tin coating layer to form a chromate surface coating layer in an average amount of 3 to 30 mg/m2 in terms of metallic chromium, consisting of electrolysed chromate, on the intermediate layer.
2. The process as claimed in claim 1, wherein the convex and concave portions in the nickel-based coating layer satisfy the relationships (1), (2) and (3):
(1) hmax ? 0.002 µm (2) hmin ? 0 and (3) where hmin >0, hmax 2 ? hmin wherein hmax represents the largest coating thickness of the convex portions, and hmin represents the smallest coating thickness of the concave portions in the nickel-based coating layer.
(1) hmax ? 0.002 µm (2) hmin ? 0 and (3) where hmin >0, hmax 2 ? hmin wherein hmax represents the largest coating thickness of the convex portions, and hmin represents the smallest coating thickness of the concave portions in the nickel-based coating layer.
3. The process as claimed in claim 1, wherein in the intermediate tin coating layer, a number of the convex portions are spaced apart in the range of from 1 to 30 µm, the coating thickness of the concave portions is 0.07 µm or less, the coating thickness of the convex portions is 0.20 µm or more and the average coating thickness of the entire tin coating layer is 0.17 µm or less.
4. The process as claimed in claim 1, wherein the electrolysed chromate surface coating layer has substantially plane surfaces thereof.
5. A multilayer-coated steel strip having excellent corrosion resistance and weldability, comprising:
(a) a substrate consisting of a steel strip; and (b) a multi-layer coating covering both the upper and lower surfaces of the substrate and comprising:
(i) a base coating layer deposited on the substrate surfaces, consisting essentially of a Fe-Ni-Sn-based alloy, the layer having a plurality of convex and concave portions thereof;
(ii) an intermediate coating layer deposited on the base coating layer to form a precursory coated steel strip, consisting essentially of tin deposited in an amount of 200 to 2000 mg/m2, the intermediate coating layer having a plurality of convex and concave portions thereof in contact with corresponding convex and concave portions of the base coating layer; and (iii) a chromate coating layer deposited by an electrolytic chromate treatment on the intermediate coating layer in an amount of 3 to 30 mg/m2 in terms of metallic chromium, the base coating layer (i) and the intermediate layer (ii) having been formed by:
(A) plating the substrate consisting of a steel strip, with metallic nickel or nickel-based alloy consisting of at least 80% by weight of nickel and 20% by weight or less of an additional metal element consisting of at least one member selected from zinc, phosphorus, cobalt, copper and chromium, to form a nickel-based coating layer on both the upper and lower surfaces of the substrate, said nickel-based coating layers being in an average amount of 2 to 100 mg/m2 and provided with a number of convex portions and concave portions thereof, and wherein said portions thereof having a coating thickness of 0.001 µm or more have a total area corresponding to from 10% to 95% of the entire area of the surfaces of the substrate;
(B) coating the resulting nickel-based plated substrate with tin to form tin coating layers on the nickel-based coating layers, each tin coating layer being in an amount of 200 to 2000 mg/m2, to provide a precursory coated steel strip;
and (C) heating the precursory coated steel strip at a temperature equal to or higher than the melting point of the tin coating layers, to cause the nickel-based coating layers and the tin coating layers to be converted to the base coating layer and the intermediate coating layer.
(a) a substrate consisting of a steel strip; and (b) a multi-layer coating covering both the upper and lower surfaces of the substrate and comprising:
(i) a base coating layer deposited on the substrate surfaces, consisting essentially of a Fe-Ni-Sn-based alloy, the layer having a plurality of convex and concave portions thereof;
(ii) an intermediate coating layer deposited on the base coating layer to form a precursory coated steel strip, consisting essentially of tin deposited in an amount of 200 to 2000 mg/m2, the intermediate coating layer having a plurality of convex and concave portions thereof in contact with corresponding convex and concave portions of the base coating layer; and (iii) a chromate coating layer deposited by an electrolytic chromate treatment on the intermediate coating layer in an amount of 3 to 30 mg/m2 in terms of metallic chromium, the base coating layer (i) and the intermediate layer (ii) having been formed by:
(A) plating the substrate consisting of a steel strip, with metallic nickel or nickel-based alloy consisting of at least 80% by weight of nickel and 20% by weight or less of an additional metal element consisting of at least one member selected from zinc, phosphorus, cobalt, copper and chromium, to form a nickel-based coating layer on both the upper and lower surfaces of the substrate, said nickel-based coating layers being in an average amount of 2 to 100 mg/m2 and provided with a number of convex portions and concave portions thereof, and wherein said portions thereof having a coating thickness of 0.001 µm or more have a total area corresponding to from 10% to 95% of the entire area of the surfaces of the substrate;
(B) coating the resulting nickel-based plated substrate with tin to form tin coating layers on the nickel-based coating layers, each tin coating layer being in an amount of 200 to 2000 mg/m2, to provide a precursory coated steel strip;
and (C) heating the precursory coated steel strip at a temperature equal to or higher than the melting point of the tin coating layers, to cause the nickel-based coating layers and the tin coating layers to be converted to the base coating layer and the intermediate coating layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61-220521 | 1986-09-18 | ||
| JP61220521A JPS6376896A (en) | 1986-09-18 | 1986-09-18 | Production of surface-treated steel sheet having excellent seam weldability and corrosion resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1331962C true CA1331962C (en) | 1994-09-13 |
Family
ID=16752317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000532926A Expired - Lifetime CA1331962C (en) | 1986-09-18 | 1987-03-25 | Process for producing a multilayer-coated steel strip having excellent corrosion resistance and weldability and useful for containers |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0260374B1 (en) |
| JP (1) | JPS6376896A (en) |
| AU (1) | AU573122B2 (en) |
| CA (1) | CA1331962C (en) |
| DE (1) | DE3788178T2 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0660434B2 (en) * | 1987-04-01 | 1994-08-10 | 日本鋼管株式会社 | Method for manufacturing surface-treated steel sheet |
| JP2580923B2 (en) * | 1991-12-27 | 1997-02-12 | 日本鋼管株式会社 | Laminated steel sheet for welding can and method for producing the same |
| US5993994A (en) * | 1993-10-22 | 1999-11-30 | Toyo Kohan Co., Ltd. | Surface treated steel sheet for battery containers, a battery container, and a battery produced thereof |
| JP4742641B2 (en) * | 2005-03-28 | 2011-08-10 | Ｊｆｅスチール株式会社 | Manufacturing method of tinned steel sheet for welding can |
| CN104790002B (en) * | 2015-03-13 | 2017-04-12 | 武汉钢铁(集团)公司 | Production method of wear-resistant double composite plated tie for packaging hardware products |
| CN105177641A (en) * | 2015-10-27 | 2015-12-23 | 姜少群 | Nickel-plated steel shell |
| CN115175466B (en) * | 2022-07-04 | 2023-06-06 | 江苏富乐华半导体科技股份有限公司 | Welding method for improving electroplated tin-nickel alloy on surface of ceramic copper-clad substrate |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54142135A (en) * | 1978-04-28 | 1979-11-06 | Nippon Kokan Kk <Nkk> | Tin-plated steel plate and its manufacture |
| JPS56130487A (en) * | 1980-03-18 | 1981-10-13 | Toyo Kohan Co Ltd | After-treatment for extra-thin tin-plated steel sheet for welding |
| GB2079319B (en) * | 1980-06-03 | 1983-11-16 | Nippon Steel Corp | Hydrated chromium oxide-coated steel strip for welded cans and other containers |
| JPS5828356B2 (en) * | 1980-12-29 | 1983-06-15 | 新日本製鐵株式会社 | Chrome-plated steel sheet with excellent weldability |
| CA1187660A (en) * | 1981-04-23 | 1985-05-28 | Takao Saito | Steel strip having differentiated multilayer coatings and being useful for manufacture of cans |
| GB2157319A (en) * | 1984-04-13 | 1985-10-23 | Toyo Kohan Co Ltd | Tin free steel and its production |
| JPS60258499A (en) * | 1984-06-04 | 1985-12-20 | Kawasaki Steel Corp | Manufacture of surface-treated steel plate for resistance welding |
| JPS61130500A (en) * | 1984-11-29 | 1986-06-18 | Kawasaki Steel Corp | Production of sn/cr two-layered plated steel plate |
-
1986
- 1986-09-18 JP JP61220521A patent/JPS6376896A/en active Granted
-
1987
- 1987-03-23 DE DE87104231T patent/DE3788178T2/en not_active Expired - Lifetime
- 1987-03-23 EP EP87104231A patent/EP0260374B1/en not_active Expired - Lifetime
- 1987-03-25 CA CA000532926A patent/CA1331962C/en not_active Expired - Lifetime
- 1987-03-27 AU AU70712/87A patent/AU573122B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU573122B2 (en) | 1988-05-26 |
| DE3788178D1 (en) | 1993-12-23 |
| DE3788178T2 (en) | 1994-03-10 |
| AU7071287A (en) | 1988-03-24 |
| JPS6376896A (en) | 1988-04-07 |
| EP0260374A2 (en) | 1988-03-23 |
| EP0260374A3 (en) | 1989-09-06 |
| JPH0214438B2 (en) | 1990-04-09 |
| EP0260374B1 (en) | 1993-11-18 |
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