Note: Descriptions are shown in the official language in which they were submitted.
3~ 2
13igh corrosion resistant multi-layer coated steel sheets having
excellent paintability by enahling the prevention of occurrence
of bubble-like ED paint defects, and producing method thereof
TECIINICAL FIELD
The present invention relates to multi-layer coated stéel
sheets having high corrosion resistance excellent in paintability
particularly coated steel sheets suitable to rust proof steel
sheets for automobiles, and relates to a producing metllod thereof.
BACKGROUND OF TIIE T~CI~NIQUE
Aùtomobile bodies are mainly composed of thin steel sheets.
For keeping, therefore, body appearances and safety thereof
due to maintenance of mechanical strength for a long term of
time~ it is indispensable to provide excellent corrosion resist-
ance and paintability for the steel sheets themselves to be
used. To improve the corrosion resistance of the steel sheet,
alloy-electroplated steel sheet such as Zn-Fe, Zn-Ni and otilers
have been conventionally developed. I!ith respect to the paint-
ability, on the other hand, since crater shaped paint defects
appear when zinc or zinc alloy coated steel sheets are subjected
20 to cationic electrodeposition paint, arts for avoiding such defects
are required. As a technique therefor, two-layer coated steel
sheets, which have lower layers of zinc or zinc alloy coating
and upper layers of Fe-Zn alloy coating having compositions
containing not less than 50% Fe thereon, have been developed (Japanese
Patent Publication No.58-15554, same No.57-28754, and Plating
and Surface Finishing, i2 (1985~ No.8, P52). Accordingly, by
using said two-layer coated steel sheets, the high corrosion
~ ~ 3 ~
resistance and the e~cellent paintability may be made compatible.
Ilowever, going with prologation of using terms of the auto-
moiles, :nore excellent corrosion resistance than heretofore
has become necessary. ~s a method of imparting the corrosion
resistance to the steel sheets, it is most preEerable to apply
Zn or Zn alloy coatings having sacrifice protection, talcing
damages at the coated parts into consideration. There are
improvements in the compositions and coating thiclcness as methods
of obtaining tl-e high corrosion resistance in the coatings based
on Zn or Zn alloys. Ilowever, the improvements in the composi-
tions have conventionally been fully investigated, there will
not be many chances of finding out new origins or chemical
compositions exhibiting more excellent properties than the
present ones. Therefore the coating thickening has actually
become the most powerful technique for high corrosion resist-
ance. Since heavily coated materials of course require the paint-
ability, it is necessary to provide, as the upper coated layer,
Fe-Zn alloy coatings or other coatings based on Fe or Fe alloys
containing not less than 50% Fe. However according to the invent
20 ors' investigations, thougll multi-layer thick-coated rust proof
steel sheets which were formed, via the electroplating method,
with the upper layers of Fe-Zn alloy coatings or other coatings
based on Fe or Fe alloys containing not less than 50-~ Fe, might
avoid the crator appearances during the electrodeposition paint,
it was found that the finished outer appearances of the electro-
deposited paint films were considerably de~eriora~ed. Such
coating defects depend upon the electrodepositing or baking
-- 3 --
J
conditions, and were observed as protrudent or depressed rashes
or pepper-and-salt like non-uniformities. Viewin~ through a
scanning type electron microscope, it was found as seen in
photographs of rig.l, that these defects were bubble-like defects
caused in electrodeposited paint. They are quite tlifferent
sorts of paint defects from the crators reported hitherto,
and as later mentioned, when balcing the electrotleposited paint,
absorbed hydrogen is released from the coated layer or the
interior of the steel, and such absorbed hydrogen becomes the
bubbleg in tlle paints. The bubble-lilce paint defects do not
appear in the conventional multi-layer lightly coated steel shcets
performe(l by the electrodeposition paint under the same condit-
ions. Accordingly, the bubble-lilce paint defects may be said
as the defects particular to the multi-layer heavily coated steel
sheets~ The above stated paint defect is not only a pro~lem
from the standpoint of the appearances but also harmful in view
of the corrosion resistance, and is therefore a vital issue
to be solved for putting the multi-layer heavily coated steel
sheets :into practice.
DISCLOSURE OF TIIE INVE,NTION
The inventors made studies on tlle above mentioned paint
defects, and conse(luently cleared up that the cause of the defect
occurrence was a hydrogen absorbed in the multi-layer thick-
coated steel sheets dtlring producing processes, and found that
said paint defects could be avoided by limiting an amount
of the llydrogen absorption to be not more than 300 m~lm~.
~ ~ 3 ~
The present invention is based upon such findings, and
is charactrizetl by a multi-layer coated steel sl-eet having,
on the surface thereof, a coated film based on Zn or Zn
alloys of a coating adheslon amount being not less than 25 g/m',
wllich is a single layer or multi-layer coated film being composed
of one or more than one Icind selected from plated coatillgs
based on Zn alloys or/and composite plated coatings based on
Zn or Zn alloys; or whicll is a multi-layer coated film being
composed of Zn plated coating, and one or more than one kind
10 selected from plated coatings based on Zn alloys or/and
comyosite plated coatings based on Zn or Zn alloys,
F'urther on said coated film basetl on Zn or Zn alloys,
a coated film based on Fe or Fe alloys of a coating adhesion
amount being 1 to 10 g/ml, which is composed of one or more
than one kind selected from Fe plated coating or/and plated
coatings based on Fe alloys containing not less than 50~ Fe,
and wherein a total amount of the absorbed hydrogen in
the coated film and the steel is not more than 300 m~/m~ (per
one side).
Such multi-layer coated steel plates have the excellent
paintabilities and the high degree corrosion resistance, because
of avoiding concurrently occurrences of the craters and the
bubble-lilce paint defects caused by the electrodeposition paint.
~ producing metllod of the present invention may produce
efficiently such coate~ steel sheets. and is characteized by
forming,
on the surface t~ereof, a coated film based on Zn or Zn
?, ~ ~
alloys of a coating adhesion amount bei~g not less than 25 g/m',
which is a single layer or multi-layer coated film being
composed of one or more than one kind selected from plated
coatings based on Zn alloys or/and composite plated coatings
based on Zn or Zn alloys; or wl~ich is a multi-layer coated film
being composed of Zn plated coating, and one or more than one
Icind selected from plated coatings based on Zn alloys or/and
composite plated coatings based on Zn or Zn alloys,
and subsequently forming, on saitl coated film based cn
10 Zn or ~Zn alloys, a coated film based on Fe or Fe alloys of a
coating- adhesion amount being 1 to 10 g/m', whicll is composed
of one or more than one Icind selected from Fe plated coating
or/andi plated coatings based on Fe alloys containing not less
than 50~ Fe,
and heat-treating said rnulti-layered steel plates at a
temperature between 100 and 400C.
In the producing method of the present invention, it is
preferable to carry out the heating treatment of tlle steel plate
after the coating in a continuous line for heightening product~
20 ivity, and in this case, the coated steel sheet is heated at
a temperature of the steel surface between 100 an~ ~iOOC for
not less than one second. In addition, for obtaining a press
formability of high degree, the coated steel plate in an open
coil is heated in a non-oxidizing atmosphere to a temperature
between 100 and 250C.
BRIE~ DESCRIPTION 0~ T}IE DR~INGS
Fig.l is a magnifying microphotograph showing bubble~ e
defects occurring in a cationic electrodeposited paint film;
Figs.2 and 3 show, with respect to an as-coated multi-layer
steel sheets and the multi-layer steel sheets of multi-layers
having removed the absorbed hydrogen by heating after coating,
the results of the quantitative analysis of the concentrations
of the al)sorbed hydrogen therein by an ion micro mass analyzer;
Fie.4 shows the degrees of the relation between the amounts
of the~hydrogen absorption and the bubble-like ED paint defects;
Fig.5 sho~/s the relation betlleen the releasing o the absorbed
hydrogen and the temperature; ~ig.6 sho~s, with respect to the
as-coated multi-layer steel plate and the multi-layer steel
plate having been heat-treated after coating, the results of
the measurement of the hydrogen absorbed therein by a gas
chromatography.
DET~ILED DESCRIPTION OF TIIE I~IVEr~TION
The present invention will be explained in detail.
Tlle multi-layer coated steel sheets of this invention have
the inner layer plated coating, and the outer layer plated
coating,
said inner layer coating being composed of coated films
based on Zn or Zn a]loys having at least the plated coatings
based on Zn alloys or the composite plated coatings based on
Zn or Zn alloys,
and said outer layer plated coa~ing being composed of
2~3~
coated films based on Fe or Fe alloys. The inner layer coating
is to impart the corrosion resistance to the multi-layer coated
steel sheet. The coating adhesion amount of the coated layer is
necessarily not less than 25 g/m2 for securing a desired corrosion
resistance specially in the bodies of automobiles and the like.
As the coated films based on Zn or Zn alloys as an inner
layer coating, there are, for example, coated films of single
layer or multi-layer structure composed of coatings based on
Zn alloys or composite coatings based on Zn or Zn alloys,
or coating films of multi-layer structure composed of
coating based on Zn alloys and composite coating based on Zn
or Zn alloys. Actually, usually assumed are (i) single layer
structure of coating based on Zn alloys, (ii) multilayer
structure composed of the coatings based on Zn alloys of
different kinds (including such a case that contents of alloying
compositions are different. The same will be applied to the
followings), (iii) single layer structure of the composi.te
coating based on Zn or Zn alloys, (iv) multi-layer structure
composed of the composite coatings based on Zn or Zn alloys
of the different kinds, and (v) multi-layer structure composed
of the coatings based on Zn alloys of one or more than one kind,
and composite coatings based on Zn or Zn alloys of one or more
than one kind
The inner layer coating may be structured by mixing the
coating based on Zn alloys or the composite coating based on
Zn or Zn alloys, or the both, with Zn coating respectively.
Also in this case, as the coating based on Zn alloys and the
~3~3~ ~ ~
composite coating based on Zn or Zn alloys, the coatings of
one or more than one kind being different may be mixed.
Tlle coatings based on Zn alloys are Zn-Fe, Zn-Ni, Zn-~ln,
Zn-Co alloyed coatings, or said alloyed coatings thereof, each
of ~hich is contained with one or more than one kind of elements
as Ti, Cr, ~to, 1~, etc.
~ s a means for producing these coatings based on Zn alloys,
there are a metllod of thermally alloying the hot dipping Zn
platings,or electrogalvanized platings, an electroplating method,
10 a vacuum evaporating method, and an ion plating method.
~ s the composite coating based on Zn or Zn alloys, one
or more than one kind of A1203, Cr2O3, SiO2, BaCrO4, etc. are
Co deposited in the Zn coating or the above mentioned coatings
based on Zn alloys.
The coating based on Fe or Fe alloys as the outer layer
coatings are composed of an Fe coating or the coating ~ased
on Fe alloys containing not less than 50~ Fe, or the multi-layer
coatings of these coatings, and have a coating adhesion amount
of 1 to lO g/m~. ~or preventing the occurrences of the craters
20 during the electrodeposition paint, it is necessary to form
the coating based on Fe or Fe alloys in the uppermost layer.
In the case of the coating based on Fe alloys, the Fe content
of less than 50% is not sufficient to prevent the crater occurr-
ence.
The coated film based on Fe or Fe alloys is usually composed
of the single layer structure of Fe alloyed coating or Fe coating
but, as the case may be, this film may be, for example, composed
c~
of tlle multi-layer structure of Fe coating and Fe alloyed
coating, or the multi-layer structure, etc. of more than one
Icind of the coatin~s based on Fe alloys containing different
~e contents.
Ilerein, if the coating weight of the outer layer coating
is less than lg/m~, the surface coverage is low, and the crater
occurrence cannot be exactly prevented. On the other hand,
i~ the coating amount is more than 10 g/m , the adhering property
of the coated layer is lowered.
Tlle outer layer coating is formed by an electro-plating.
At the present, as an industrial method ~or forming closely
and uniformly a thin coated layer over a strip of lar~e width,
the electro-plating method is the only way.
The coatings based on Fe alloys are coatings containin~,
in Fe, one or more than one kind of, e.g., Zn, Ni, Co, Mn,
Cr, Mo, W, P and B.
In the present invention, the total amount of the absorbed
hydrogen in the coated film and in the steel sheet is limited to
be not more than 300 m~/m per one side of the steel sheet
20 (which is the absor~ed amount under the normal conditions of
1 atm and 25C) in producing the above mentioned multi-layer
coated structures.
If the coated film based on Fe alloys or the Fe coated
film is formed as the outer layer by means of the electro-plating
the hydrogen is generated on surface of the inner layer in great
volume, and a part thereof is absorbed in ~he coated layers
and the steel.
_ 10 -
?J !~J ~ J
With respect to the multi-layer coated steel sheets formed
with the coating of Fe-Zn alloy containing 80% ~e on the hot
dipping alloyed Zn coating, and the multi-layer steel sheets
wllere said coate~d steel sheets are heated after coating to remove
the absorbed hydrogen, Figs.2 and 3 sho~Y the results of the
quantitative analysis oE the ccncentration of tl1e absorbed hydro-
gen therein by an ion micro mass analyzer (I~IA). If a comparison
is made between the case having removed the absorbed hydrogen
by heating and the case not having done, it is found that the
hydrogt~n is considerably absorbed in as-coated steel sheets.
The hydrogen was released by heating in an Ar atmosphere
the multi-layer coated steel plates as mentioned above, and
the hydrogen amount was measured with a gas chromatograpl1 method,
and the amount of the absorbed hydrogen in the coated steel
sheets was measured. Then the relation between the amount of
the absorbed l~ydrogen and an occurring degree of bubble-lilce
paint defects ~Yas obtained. Fip,.4 shows the results. A test
sample used herein was the multi-layer coated steel sheet with
the inner layer being the hot dipping alloyed zinc coating
of the coating amount of 38 g/ml and the outer layer being the
80~ Fe-Zn alloyed electro-plated coating of the coating amount
of 5 g/m2. The amount of the absorbed hydrogen in the coated
steel sheet was adjusted by a preheating treatment prior to
the electro-painting. As seen from Fig.4t it is a necessary
condition that the amount of the absorbed hydrogen is to be
not more than 300 mQ/ml for preventing the occurrence of the
bubble-lilce defects.
It is apparent from the above mentioned result that the
hydrogen absorbed in the coated layers and in the steel sheet
apparently has a close relation with the bubble~ e paint
defect. 'lhe bubble-lilce paint defect is assumed to be generated
due to a mechanism as follo~s. Namely, if the electrodeposition
paint is performed on the steel sheet where the llydrogen of
more than a determined amount is absorbed in the coated layer
and in the steel, the surface of the electrodeposited paint
film is solidified before the hydrogen is fully released in
a baking process, and a thin film is formed on the outside
thereof. Since the hydrogen wllich is not rele~sed at the
beginning of tlle baking process and remains therein, is enclosed
within the coated film, the llydrogen gathers, and further is
expanded by the heating and turns out the bubbles to cause the
defects in the electrodeposited paint film. The bal~ing tempera-
ture of the electrodeposited paint is generally 170 to 1~0C,
and this is a temperature range ~here the absorbed hy(lrogen
is released at a high transmisson rate, as seen in Fig.5, that
is, a temperature condition ~here the absorbed hydro~en is easily
released, and accordingly the bubble is easily generated.
~ or controlling the amount of the absorbed llydrogen, there
are methods of ~1) heating, after coating the outer layer, the
coated steel sheet; (2) selecting conditions diEficult to cause
the hydrogen absorption, as the condition of coating the outer
layer; (3) employing steel kinds which are low in the hydrogen
absorption, or difficlllt to release the hydrogen if absorbing
it, or methods of combining them.
- 12 -
~ J~r~)
A furtl1er reEerence will be made to a producing method
of the invention, a subject of wllich is to release the absorl7ed
hydrogen by heating.
The producing method of the invention, as said above,
comprises forming, on the steel surface, the inner layer coating
composed of the coated filrn based on Zn or Zn alloys having
at least the coating based on Zn alloys or the composite coating
based on Zn or Zn alloys, and lurther forming, on said inner
layer coating, the outer layer coating composed of the coated
film ~ased on Fe or Fe alloys, and heating the steel sheet at
a temperature oE lO0 to 400C after having formed said f~lms.
If the heating temperature is less than 100C, the bubble-lilce
paint defects cannot be sufficiently avoided, and if it exceeds
400C, the inner layer coating and the steel plate malce a thermal
diffusion, and an alloyed layer is formed where the coating
adhesion is deteriorated. For these reasons, the heating
temperature is set to be lO0 to 400C.
The heating procedure is performed in a continuous line,
aiming at a hlgh productivity for not less than one second at said
20 temperature ~steel surface temperature). If the heating tempera-
ture is less tl1al1 one second, it is diffuclt to avoid the bubble-
like paint defects even at said temperature range. A maximum
heating time is not especially limited, as far as the inner
layer coating and the steel sheet do not create an ailoying
reaction. Ileatil1g manners are a high frequency induction heating
system, and electric heating system and others, not especially
limiting. ~ heating atmosphere is sufficient with the atmosphere
2~3 ~
containing no hydrogen or hydrogen of a degree actually not
causing the hydrogen absorption, such as a nitrogen, or an air
atmosphere, not yet especially limiting. If heating for a long
period of time in the atmosphere, the outer layer coating is
oxidized, and consequently a modifying treatment is hindered.
Therefore, a time is limited to the heating in the at~osphere.
~ or imparting a press formability of lligh degree to the
steel sheet, the heating treatment is carried out in the open
coil heating. In this open coil heating, the steel sheet is
10 heated' at the temperature between 100 and 25aoc in the
non-oxidizing atmosphere. The lower limit thereof is as referred
to above. In SUCII heating system taking a long time from the
heating to the cooling as the open coil heating, if heating
at ~he temperature range exceeding 250C, the inner layer coating
and the steel plate are effected with a thermal diffusion to
form an alloyed layer of the coating adhesion being deteriorated.
Therefore, the upper limit of tlle heating temperature is set
at 250C. Further, the heating atmosphere is determine(l to
be non-oxidizing for the following reasons. If heating in the
20 oxidizing atmosphere, the coating based on ~e or Fe alloys of
the outer layer is oxidized on the surface during heating and
cooling, and subsequently a phospllate film is not normally formed
which is required as an undercoated treatment for painting.
Ilowever, if using a gas bearing the hydrogen, though the
non-oxidizing atmosphere, the hydrogen concentration thereof
should be made to an extent that the hydrogen is not absorbed
in the coated layer and in the steel sheet while performing
_ 14 -
3 $ ~ ~3
the heating. The heating time is suf~iclent with not less thall
one second in total at the steel temperature of not less than
100C. If tlle heating time is less than one secon~, it is not
possible to prevent the occurrence of the bubble-lilce ED paint
defects even in said temperature range. The upper limit of
the heating time in said temperature range is not especially
limited, and is enough with about 30 minutes, talcing the
productivity into consideration.
With respect to the multi-layer coated steel sheet ~ormed
10 ~itil Fç-Zn alloy coating of 80% Fe on the hot dippin~ alloyed
zinc c`oating, and the multi-layer coated steel plate heated
after having coated said steel sheet, Fig.6 shows the results
that the hydrogen absorption amount in the coated steel sheet
was measured with the gas chromato~raph in the both cases.
Ilhen the hydrogen absorption amounts are compared between the
cases heated and non-heated, it is found that the hydrogen is
considerably absorbed in an as-coated steel sheet, and tlle
hydrogen concentratioll is lowered after heating.
Tlle bubble-like paint (lefects generated in the electro-
20 deposition paint can be prevented by the heating as abovementioned, because the hydrogen which has been absorbed while
coating the outer layer, is removed by said heating, and in
addition to such a factor, there is a possibility that it also
influences thereto that Fe enriched contents of tlle outer layer
are diffused, so that a closer outer coated layer is forrned.
In other words, as another reason why the bubble-lilce paint
defect is generated other than the reason of the hydrogen
_ 15 -
absorption caused at coating of the outer layer, the following
consideration may be talcen. That is, an electric current is
concentrated at the inner layer coatin~ exposed microscopic-
ally when depositing the outer layer, and as a result, the
hydrogen gas bubl)les are locally concentrated. These gas bubbles
are not completely released from the coated layer during the
baking process but remain therein, and it is assumed that such
bubbles expanded become the bubble-lilce paint defects. By
heating them at the higl1 temperature, the coated state of the
outer layer which is, if heing as-coated, incomplete microscop-
ically, is improved due to the thermal diffusion thereby, and
it is also assumed that the microscopic defects of the outer
layer are repaired consequently. Therefore, the above mentioned
matters will possibly contribute to the prevention oE the
occurrence of the bubble-like paint defects.
If the producing object of this invention is Bll steel
sheets, it is preferable to perform the heating treatment at
a temperature as low as practicahle. A temper rolling can be
performed after coating the inner layer, coating the outer
layer or the heating treatment, but it is desirable to carry
out the temper rolling after the heating treatment for providing
the high degree press formability or in a case of outer panels
of the automobiles.
Depending upon the present invention, it is possible to
supply the multi~layer coated steel sheets having the high corro-
sion resistance and without causing the crators and the bubble-
like paint defects at the cation electrodepositing paint and
- 16 -
2 ~ 3 ~ 2
accordingly with the excellent paintability. Thus, the high
corrosion resistance and the beautification of the automobile
bodies and others are compatible.
EXA~IPL~S
Example I
The cold rolled coils of the compositions of Table l were
successively subjected, as blank coils, to the hot dipping
zinc plating in the continuous plating line of the non-oxidiæing
furnace system, the alloying treatment, the temper rolling,
and Fe~Zn electric plating, whereby the multi-layer coated steel
sheets were produced. The hy~rogen absorption amounts were
adjusted by changing the Fe-Zn coating amounts, continuously
l1eat-treating the multi-layer coated steel sheets at the tempera-
ture of not less than lOO C in the induction heating sys-tem~ or
heat-treating the open coils. The Fe-Zn electric platings
for the outer layers were practised under following conditions:-
(l) Plating bath
Composition
FeSO~.7~1,0 ~
~ - 350 - 500 g/~,
ZnSO4.7ll20 -
CH,COOt~la.3fl~0 20 g/~
Na2SO4 30 ~/e
pll 1.8 to 2.0
(2) Plating conditions
Bath temperature 50C
Flowing rate 2 m/s
.
- 17 -
~urrent density 30 to 120 A/dm~ 2
The Fe contents in the films of the Fe-Zn by electric
platings adjusted by mainly changing Fe salt ratio ( = FeS04.
7H,0/[FeS04.7H20+ZnS04.7H~0]) and the current density, and the
adhesion amounts were adjusted by changing the coating time
and the current density. Table 2 shows the appreciating results
of the outer appearances of the coated films and the corrosion
resistances after the electrodeposition paint and the process-
abilities. It is seen from the same that the multi-layer coated
10 steel plates where the releasing amounts of the absorbed hydrogen
were not more than 300 m /m , are superior in all properties.
Example II
The multi-layer coated steel sheets were produced from
the cold rolled coils shown in the Table 1 which have passed
the annealings and temper rollings, by alkaline degreasing,
sulfuric acid picklings, Zn-Fe alloy electroplating and Fe-Zn
alloying electroplatings in the electrogalvanizing line. The
hydrogen absorption amounts were adjusted by the amounts of
the outer layer coatings and by the continuous heating treat-
20 men-t or batch-heating treatment at the temperature of no-t less
than 100C after having been coated. The inner and outer layer
coatings of this Example were practised under the same conditions
as the outer layer Fe-Zn electric platings of Example Io The
Fe contents and the coating weight of Fe-Zn and Zn-Fe electro-
plated films were also adjusted under the same manners as Example
I. The results of the evaluation of the properties are shwon
.
- 1 0 - 2 ~
n Table 3. It is seen from the same that the multi-layer coated
steel sheets where the releasing amounts of the absorbed hydrogen
were not more th~n 300 m /m2, are superior in all properties.
Example III
The cold rolled coils of the compositions of Table 1 were
successively subjected, as blank coils, to the hot dipping zinc
plating in the continuous plating line of the non-oxidizing
furnace system, the alloying treatment, the temper rolling,
and Fe-Zn electroplating, and were successively subjected to
the heating treatment under the atmospheric conditions via
the induction heating system. With respect to the thus produced
multi-layer coated steel sheets, Table 4 the shows results
of the evaluation of the outer appearances of the coated ~ilms
and the corrosion resistances after the electro-deposition paint
and the coating adhesion together with the producing conditions.
According to the above table, the multi-layer coated sceel sheets
heat-treated at the temperature from 100 to 400C are superior
in all properties.
Example IV
The multi-layer coated steel plates were produced from
the cold rolled coils shown in the Table 1 which have passed
the annealings and temper rollings, by alkaline degreasing,
sulfuric acid picklings, Zn-Fe alloying electroplating and
Fe-Zn alloying electroplatings, and were successively subjected
to the heating treatmetns under the nitrogen at~osphere via
2~3 ~.2
~he induction heating system. With respect to the thus produced
multi-layer c`oated steel sheets, Table 5 shows the results
of the evaluation of the outer appearances of the coated films
and the corrosion resistances after the electro-deposition paint
and the coating adhesion together with the producing conditions,
It is seen from the sarne that the multi-layer coated steel sheets
which have been heat-treated at the temperature between 100
and 400C, are superior in all properties.
Example V
The cold rolled coils of the compositions of Table 1 ~ere
successively subjected, as blank coils, to the hot dipping zinc
plating in the continuous plating line of the non-oxidizing
furnace system, the alloying treatment, the temper rolling,
and Fe-Zn electroplating, whereby the multi-layer coated steel
sheets were produced. Thereafter, these coated steel plates
were subjected to the open coil heating with a cover type
annealing furnace under the nitrogen gas bearing atmosphere.
~ith respect to the thus produced multi-layer coated steel
sheets, Table 6 shows the results of the evaluation of the
outer appearances of the coated films and the corrosion
resistances after the electro-deposition paints and the coating
adhesion together with the producing conditions. It is seen
from the same that the multi-layer coated steel plates of open
coils which have been heat-treated at the temperature between
100 and 250C, are superior in all properties.
:, . : .
- 20 -
INDUSTRIAL APPLICABILITY
The present invention is especially useEul as the coated
steel plates to be painted witll a cationic electrodeposition for
bodies of automol)iles, and as a pro~ucing method thereof.
Table 1 (~t~)
. _
Cbils C Si Mn P S Sol.Al N Others
_ _ I
. A 0.0028 0.01 0.17 0.0090.008 0.032 0,0035 Ti:0,072
I I I
U 0.0024 0.17 0.58 0.0250.006 0.05~ 0.0025 Nb:0.013
C 0.0012 0.01 0,023 1 0.010 0.011 0.0~5 0.0042
D 0.0~2 0.01 0.023 ¦ 0.010 0.011 0.0~5 0.00~2
E 0.020 0.01 0.015 0.012 ~0.010 0.0~0 0.0025
~ c ~
~ ~ 9 o 3 ~ . ~ 2
~c~5 ~G~
e'~
~ ~ ~ ~ ~ ~ ~ ~ T ~ ~
* ¢ ¢ ¢ ~ ¢ ¢ ¢ r ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ : : E - O x
O ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ r ¢ r ¢ ¢ ¢ r ¢ ¢ ¢ ¢ ~ ~ ¢ E E ~, E
i Z * ¢ r r L ¢ i ¢ ¢ L l ¢ ¢ ¢ r ¢ ¢ ¢ ¢ l ¢ ¢ ¢ ¢ ~ E C P- E ..
~ ~ ~ ~ ~ ~ ~ a
O ~ c i r r ~ ~ r r r r r O z ~ ~ h ~ E a
~ ~ ~ L~ L~ U~ U~ ~:1 Il~ C~l O U~ Lr~ cr ~r ~ c~ c~ ,~ n u~ t~ c~ u~ O ~ : E ~ ~a ~`
~ O f O L O r--r r--l O I o r~ O O O O O O O l ~ v ~ ~ c
H X ~ oo oO oO oo oo o0 cO j~a L LL L ~ L L Lq~ ~ L L ~ ~ ~ O j~ O H h ~: V
~* ~ 1- ~ 1 1 ~ ~ ~ ._ ~ c~ L~ L~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
- ~ I¢ I¢ - _ L¢ _ L¢ L~ _ _ L ¢ ~ i ~ 1~ ~ ~ ¢ ¢ 1~ ¢ ~ 1l o ~ c
_ ~ L~ 1~ L~ ~ 1~ ~ L~ 1~ ~ ~ ~ ~ ~ r 0l ~ ~ Ln I ~c
~ . . Examples I I 1
-- 22 --
~_ . ...... - - ~'J
e~
K '`~,~'
O
O ¢ ¢ ¢ ¢ ¢ L ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ r ¢ ¢ ¢ ¢ _ ¢ ~ a o
z * ¢ ¢ ~ ~ ¢ ~ ¢ ¢ r ¢ ¢ ¢ r ¢ ¢ r ~ ¢ ¢ ¢ ¢ a
7. ,~ Vl 1~ 1~ ~ ~ v L o L ~ ~ O ~ r O L~ O r ~ r ~` ~ o E
, :~ o o u : : : æ C ~ ~ o o o z ~7 7 ~ o
r ~ l :~~
~ol~ 3 W L ~L
~ i~ ~ i~ ~ ~ f~ 7~r~'`
_ ,_ ,_ _ ~ _ ~ l ~ ~ ~ c~l _ _ ~ ~ ~r ~ _ ~r ~ ~r _ , O ^ ~ ~ ~ . .
~ _ _ ¢ i~ 1~ j¢ ~ ¢ ¢ ¢ ~ ~ ~ ¢ ~q ~ i~ ~ ¦~ r r ¢ r ¢ i Yc~
o ~ L~ ~ ~ L ~ ~ i~ ~ ~ c~ ~ ~ ~ r- Oo l~ ~ C~ ~ m ,~
~Z Exampl e s I I Comp .
_
-- 23 ~
,, . , _
~, 1, ~ ~ ~3 ~.3
~o~ .~, C~,
P~ f~5 ~Ga
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~ ~ . ~ u
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~ x ~ _ ~ _ _ i ~ ~ _ _ r ¢ ~ i~ ~ ~L r ~ ~ ~ _ E ~ J- . r
_ I_ æ O ~ ~ ~ ~ 1~ ~ ~ _ ~ ~ ~ ~ u~ O O O ~ ~ ~ --~¦ ` ~ ~ ~ h rl O O' ~J O
H E ~ ~ ~ ~ ~ ~ ; ~ ~ ~ ~ i i O ;~ r ~ ~ O ~ i C ~ ~ E E - ~
_ ~æ ~ ~ ~ ~ ~ ¦~ ~ ~ - ~ - ~ ~ o ~ - ~ ~ ~ :~ ~ ~ v v
t~ --r ~1~ ~L E~ll P :5 I I e~ E E
~T ;- ~ r j~:
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~ ~ I¢ ~ ` 1 ~ ` i ~ ` ~ ~
Y o ¢ ~ ~ t ~ ~ ~ ~ ~ ~ ~ ~ 1~ ~ ¢ ~ ~ ¢ l) ¢ ~ c
* æ ¢~ ~ r 1 ~ :~ :: :~ : :~ - ::: :~ - ::: ~ m ~ I¢ ~ ¢ ~ ~ ~ fi o o
s ~ o~c tc I o ¦o ~ ~ o o o o o o o o o o o ~ c o ~i~ o o o ~a rl fi
I t t t--t~ ~ a ~
E ~_
O ~ ~ ~ ~ _ r O O rr~ _ i _ ~ ~ ~ ~ :~ E ~ o o ~ ~ h v o~ I
C~ ~,r~ U~O 1~ r,~ O ,r~1 ~ O ~ O ~ ~ ~ ~ ~ ~ ~ ~ :C 1 O~0 r~l r~l ~ ~
~ ~ ~ _~__ _ _ _ ~ _ _ ~_;__ ~ ~ _ _ _ ~ ~`1 h a v
~ 1 ~ ~
~ c ¦ ~ ~ ~: r. ~ ~ cr) o ~ ~ :~ ~ ` ~ 1 ` ~ ¦ ` ¦ ` ~ --~ ¦ - Q
~ ~ ~ _ I I ~ I I I ~ ? U) a Q)
(I~ r~ ¦ ~ ~ ~--~ _ _ ~_ ~ ~ ~D O 0 ~L~1 ` _ ~ _ ~ U 0~ 00 Q~ E
: ~ L~L ~L ; ~ L o ~L~ ~ 2 ~ _; H ~ ~ Q~ ?
u~ I ¦ ¦ ¦ ¦ ¦ ~ ~ ~ ~ ~ ~ ~ ~ ~ o ~L- ~1~ ~ ~ Q H ~ I ~a a
a) I I ~1~ ~ l c ~ ~ ~ ~ ~ ¦m¦~ ~1¢1~ 1~--i ~ ~ 3 E~
n~ c~ ~1~ _ _ o _ c~ r~ ~1~ _ _ ~ --~ C~l ¦~------.~ ~ Q~
~ I Ex~mple IV ¦ Comp.
'~ ~ 3)~2
- 1~ 1~ 1~ 1~ ~ 1 ~ I 1~
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
V~ ¢ _ :~ ~ _ :: ::: r. :~ _ :: :~ ::: :~ :~ : 2 :~ ¢ 2 _ _ _ ~q
* ¢ :~ :~ ~ ~ _ ~ ~ ~ ~; ¦ ~ ~ _ ~ ¢ ~ C 5~:
* e ¢ __ ~ O ~ ~ _ ~ _ ~ __ ~ O ~ O __ m ~ _ _ ~ C~
O O O O O O O O O O O O O O O O O O O OI O O ~ C
~: ~ ~D Il~ c~l ~ _ oo C~ ~ tD r~l Ll~ Il~ Il ~ I_ _ Ir~ u~ Il~ Il~ ~ ~ ~ ¦ ~ O ~ Q ~J r u
_. E O t o o o o _ + o ~ ~ o
V ~; 1 ~ ~ l 2 ~ ~
~ a ~I r ~ ~1 ~ ~ ~ r ~ --
~ I L ~ I z I . . z h ~ r-l 0 ~ r~ ~~
_I_ I I _ _ _ I I _ Tr __ ~ O ~ cn
_ ~ ~ ::: ¦ ~ ~; ~ ~: ~ cr~ O ~ ~ :: ~: U ) ::~ ~ t~) a.) ~ rl (~ _
+ ¦ + ¦ +1 + _ ~1-- a) rl ~ S~ r-l
I c~ ~ I - - I ~ ~ - ~ - I ~ ~ u~ 10~ 1 - I - I - ~ ~ ~ I ~ ? I ~ I ~ o ~ ~ o
t ~ ~ T--_ _ t I I _I I I I _ _ ~ t~ _
~ ~ r-l 1: ~ r~
.` H ¦oo I - ~ I ~ ~ ~ ~ I :c ~ ~ 1 1 l co I - ~ ~ o O ~ a) h ~ O O
II t _ _ _ ~ I II I I I I I I I I _ u~ o
~D I ~ ~ ~ ::: -- --~ ~¦~ C ~ -- ~ :::~ .
c~ ~ ¢ I ~ ~ I ~ ~ ~ I ~ c I ~ I - ~ I ~ I - I m I O ~1~1 ¢ I ~ ~ I ~ I - ~ ~ o ~ c~
r-l I t _ _ _ t --I t +l I I_ I I I I I _
~ z ~1~ ~ _ _ _ ~1~ ~1~ ~ I ~r I ~ ~ ~ C~ o
Exampl~s V ¦ Comp.
- 26 -
~ ~ 3 ~
Table 7
Test method and evaluating references
Testing items Testing methods Evafluating
re erences
_
Immersion type
phosphate
treatment
. (PAL BOND 3080)
. l
Cationic electro B : Occurrence of
Bubble-like painting defects
paint defects (ELECTRON 9410) A : No occurrence of
. l defects
, ~ .
After baking,
observing
outer
appearance
Immersion type .
phosphate A: The number of
treatment crators, not more
. (PAL BOND 3080) than 10/40 mm~
~ . .
Cation electro- B: The number of
depositing crators, more than
Crators (ELECTRON 9410 10 - less than 50/
Distance between 40 mm~
cathode and anode,
1:1
Momentary conduc-
tivity, 280V, 3min)
l' C: The number of
Evaluating outer crators, not less
appearance than 50/40 mm~
.
Immersion type
phosphate .
treatment
(PAL BOND 3080)
Cationic electro-
Corrosion painting A: Not more than 0.1 mm
resistance (ELECTRON 9410)
s,,,,~
Scribing
. 1~
Cyclic corrosion .
tests .
Corrosion (Combination of
resistance SST, HCTj Salt B: Not less than
water immersion 0.3 mm
and drying)
3 months
After removing
coating paint films
and corrosion product s
measuring maximum
corrosion depth
_
. Draw bead test A: No delamination
. I of plated films
Coating ~'
Adhesion Taping B: P~emarkable
delamination of .
plated f.ilms
