Note: Descriptions are shown in the official language in which they were submitted.
2 ~
NI~KEL ELECTROPT.ATED COLD-ROLLED STEEL
S~EET EXCELLENT TN PRESS-FORMABILITY
AND PHOSPHATING-TREATABILITY AND METHOD
FOR MANUFACTURING SAME
REFERENCE OF PATENTS, APPLICATIONS AND PUBLICATIONS
PERTINENT TO THE INVENTION
~s far as we know, there are available the
following prior art documents pertinent to the present
invention:
~) Japanese Patent Provisional Publication No. 56-
116,883 dated September 12, 1981;
! 2 ) Japanese Patent Provisional Publication No. 56-
116,887 dated September 12, 1981; and
~3) Japanese Patent Provisional Publication No. 2-
101,200 dated April 12, 1990.
The contents of the prior art disclosed in the
above-mentioned prior art documents will be discussed
hereafter under the heading of the "BACKGROUND OF THE
INVENTION."
BACKGRO~ND OF THE INVENTION
~FIELD OF THE INVENTION)
2 ~ 7 ~
The present invention relates to a nickel
electroplated cold-rolled steel sheet excellent in
press-formability and phosphating-treatability, and a
method for manufacturing same.
! RRIOR ART STAT~MENT)
In general, a cold-rolled steel sheet for
aucomobile or electric appliances is formed into a
prescribed shape by means of a large-capacity press.
With a view to achieving a larger automobile body,
reducing air resistance during running of a car, and
achieving an exterior view of a better style, it is the
present practice to form fenders, dcors and rear quarter
portions into rounded shapes.
From the point of view of economic merits and
environmental protection, on the other hand, efforts
are being made to reduce the weight of an automobile
~ body so as to reduce the fuel consumption. In order to
reduce the weight of the automobile body, it is
necessary to decrease the thickness of a steel sheet
which forms the automobile body, and this is also the case
with a steel sheet such as an exposed panel that should
be subjected to a deep drawing. The steel sheet for an
exposed panel requires a satisfactory dent resistance
-- 2 --
~3~¢~,~75.~
~nd shdpe freezability. It is therefore necessary to
use a high-strength steel having a thin thickness for
the exposed panel. In order to form a thin and
high-strength cold-rolled steel sheet by deep drawing,
it is necessary to previously increase the wrinkle
inhibiting force of the steel sheet by means of a
powerful press so as to prevent wrinkles from producing
on the cold-rolled steel sheet during press forming.
Annealing applied to the cold-rolled steel sheet
for the purpose of recrystallization of crystal grains
subjected to a serious strain during the cold rolling
thereof, is applicable either by a continuous annealing
or a box annealing.
An ordinary low-carbon aluminum-killed steel has
been used as a material for a mild cold-rolled steel
sheet for deep drawing. A low-carbon aluminum-killed
steel containing silicon, manganese and phosphorus has
been used as a material for a high-strength steel sheet
for deep drawing. The box annealing has been applied for
the purpose of annealing the above-mentioned mild
cold-rolled steel sheet for deep drawing and
high-strength steel sheet for deep drawing. The box
annealing is characterized by a long heating time, a
long cooling time, easy growth of crystal grains, and
2 ~ ~J~
the a~7ailability of a cold-rolled steel sheet having a
high Lankford value.
A box-annealed steel sheet is exposed to a
high temperature for a longer period of time than a
5 continuous-annealed steel sheet. As a result, silicon,
manganese and phosphorus contained in the box-annealed
steel sheet are concentrated onto the surface of the
steel sheet in the form of oxides. These oxides
concentrated onto the surface of the steel sheet serve
as a lubricant film during press forming. In addition,
~he box-annealed steel sheet has a high Lankford value
than that of the continuous-annealed steel sheet.
Therefore, troubles such as press cracks hardly occur
in the box-annealed steel sheet.
When the box-annealed steel sheet is
press-formed and then subjected to a phosphating
treatment, the elements contained in the steel sheet
and the elements such as manganese concentrated onto
the surface of steel sheet activate a phosphate film
forming reaction, so that a dense and thin phosphate
film is formed on the surface of the steel sheet. The
phosphate film has a function of improving paint
adhesivity and corrosion resistance after painting of
the steel sheet.
-- 4 --
~-
,
2 ~
Recently, however, it is becoming increasingly
~lsual praciice to anneal a steel sheet by the
continuous annealing for such reasons as the reduction
of manufacturing processes, the improvement of
5 production yield and labor saving. The ~nown
cold-rolled steel sheets suitable for the application
of the continuous annealing treatment, comprise an
extra-low-carbon steel or a steel known as the
inter-sticial free steel (hereinafter referred to as
10 "IF steel").
In order to improve Lankford value serving as
an indicator of press-formability of an
extra-low-carbon steel sheet, the following measure is
taken: degassing the steel during the stee~ma~ing step
to reduce the carbon content to up to 100 ppm, and
minimizing the contents of other impurity elements,
thereby permitting rapid growth of crystal grains of steel.
An if steel is produced by adding at least one of
~ titanium and niobium to an extra-low-carbon steel, and
fixing carbon and nitrogen acting as solid-solution
elements by means of these added elements, thereby
making it possible to obtain a higher Lankford value
with a short continuous annealing.
2~h~
~ince the development of the above-mentioned
extra-low carbon steel and IF steel, it is now possible
to manufacture a cold-rolled steel sheet having a high
Lankford value even by applying the continuous
annealing.
However, the Lankford value of a cold-rolled
steel sheet for deep drawing subjected to the
continuous annealing (hereinafter referred
to as the "continuous-annealed cold-rolled steel
sheet") is equal or even superior to the Lankford value
of a cold-rolled steel sheet for deep drawing subjected
to the conventional box annealing (hereinafter referred
to as the "box-annealed cold-rolled steel sheet").
~owever, the continuous-annealed cold-rolled steel
sheet is easily susceptible to cracks during the press
forming, and when worked into a complicated shape, more
susceptible to the galling than the box-annealed
cold-rolled steel sheet. As a result of various
studies on causes thereof, it was revealed that, as
shown in Table 1, there was a substantial difference in
the value of frictional coefficient of the steel sheet
surface between the continuous-annealed cold-rolled steel
sheet and the box-annealed cold-rolled steel sheet.
Table 1 shows values of frictional coefficient (~) of
the surface, Lankford values (r-value) and limiting
-- 6 --
. ~ . . . - . : . ,. . : . .: : . ,
- . . - . - :: : : . -
.,: . ... . - . . .
- -: . :: :
:, ~
. . .
drawing ratios ~LDR) for the conventional continuous-
annealed and box-annealed cold-rolled steel sheets, and
Table 2 shows chemical compositions of the continuous-
annealed and box-annealed cold-rolled steel sheets used
in these studies.
-- 7 --
- ,
'
7~3
n I ~ I T7
J~. X _ N o o o o o o o o o o _ 0
o G ( r() _ _ _ _ _ _ _ _ ~ _ ~ _ _ O
O _, ~uaT~ ao::) ~ _ _ _ _ _, _ _, _ _ _ _
h~ leuOil ~ [ O O O O O O O O O O O O O S~
'3 _ _ _ ~a
al ~ anleA - ~ _ o _ _ _ ~ o o u~ c~ ~' ~ o O
O (~o) _ _ __ O
æ
u~ ~ 6ul~eaE~ ~ t- oa o~ co oo oo oo c~ ~o co co co
o (O a
o uot~npa~ t- o o u~ ~- o o oo t- o o u~ o ~
U I'paae~6 a~ ~rl U U Q Q Q Q t-:l ~1 ~4 ~1 O
~ ._ _ ~ ~ ~ ~ ~
U~ N N N S ~ ~
~1 rl N
O UQ) ua.) ~o IS . ,.
O O q:~ O ~ O ~ ~r ~ o
~ U~ _ ~
_1. Q ~ CO ~ ~D ~ t- _ Cl~ _. O _ -
,~ o ~uaF::)F~ao~ C~ _ ~N _ c~ ~r c~ c~ _ c~
O ~ I~?uoF~ F~ o o o o o~ o o o o o ~
Ll 3 _ _ o
U~ O U~ U~ O O U~ ~ In ~ U
:~ ~ (.~ ~ 1
m0 F~ ~o ~ t- t-- ~o co t- ~o co ~_ u
UO Fl ~npa>~ _ _ ~
_ laapae~b _ ~: ~: ~: __ _ _ ~: _ __ U
o ~ ~ x~,J ~
~1 ~ ~1 ~1 h O Q ~r ~
u~ O O O 1~5 0 1~ a~ 1~ ~a ~ n5 0
~: o ,q 0 o a) o ~ c) ~1 a) ~ l l
h ~ ~ h ~ I ~ I u~ I O ~1 1::: U1 .C
O u~ n5 U~ 3 ul 3 3 a~ 1~ 0 ~
Q ~ t) ~ -1 C,) 0 ~4 O ~ ~ o ~.C
c~ ~ ~ I c~ l l ~ tn ~
O ~ Id ~ rl 1~ ~ It~ I .,1 ~1
~ rl ~:; $-1 ~; S~ E~ h ~1 I ~ ~ ~ o
3 1 ~ I ~ I ~ I .IJ X t~ ~ O
o o~ ~ ~ X o~ X ~1 X '~ ''~ o u~
~ 1 :~ ~ ~ ~ ~ Z ~ E~ ~1 .C O-r IG
. E- l l 1, ~o t_ I a:~
o O - ~1
~o 00
~ o O~ ~
E~
` Z O O ~ C~ C~ o O
o O O O O O O
¢ U~ ID C~ t- ~ t- O~
._ O o o o o o o .
a~ c~ ' o o o o o o o
~ C~ o o o o o ~o o ~
. _ _ ~n
~ ~ ~r ~ ~ _ ~ o
o o o o o, o o ~,
o o o ~5
C~ ~o ~ o~ ~ ~ ~o ,,
o o o o o o ~ ~
o ~o .~o o o o ~o
_, d o o o o o o
~ .
o ~ ~ - ~ o~ o C~
C~ o o o g o ~o o
. o o o o o o o o~
apel~ ~ m
l~S
_ _
-~
~ . . . - :
2 ~ J ~
Fig. 1 is a graph illustrating the relationship
b~tween a I.ankford value and a limiting drawing ratio
for a continuous-annealed cold-rolled steel sheet and a
box-annealed cold-rolled steel sheet. In Fig. 1, the
mark "o" represents the box-annealed cold-rolled steel
sheet, and the mark "~" represents the continuous-
annealed cold-rolled steel sheet. As shown in Fig. 1,
the differences in the Lankford value and the limiting
drawing ratio between the continuous-annealed and the
box-annealed cold-rolled steel sheets are considered to
be caused by the fact that a high frictional coefficient
of the steel sheet surface as in the continuous-annealed
cold-rolled steel sheet reduces lubricity between the
steel sheet surface and the wrinkle inhibiting jig or
the die, thus impairing smooth flow of the material
in the press die.
Now, the phosphating-treatability of the
continuous-annealed cold-rolled steel sheet is
described. Application of a phosphating treatment to
the press-formed continuous-annealed cold-rolled steel
sheet forms a phosphate film on the surface of the
continuous-annealed cold-rolled steel sheet. Because
the continuous-annealed cold-rolled steel sheet has
only low contents of impurity elements, and the
time of exposure of the steel sheet surface to high
-- 10 --
2 ~ ~ 8 ~
temperatures during annealing is far shorter than that
in the box-annealed steel sheet, there is almost no
concentration of the elements contained in the steel sheet
onto the steel sheet surface. Conse~uently, there are
only a very few cathodes to form precipitation nuclei of
phosphate crystal grains on the surface of the
continuous-annealed cold-rolled steel sheet, so that a
phosphate film formed on the steel sheet surface
comprises rough and coarse crystal grains.
Fig. 5 is an SEM (scanning electron
microscope) micrograph showing the metallurgical
structure of crystals of the phosphate film formed on
the surface of the box-annealed cold-rolled steel
sheet, and Fig. 6 is an SEM micrograph showing the
metallurgical structure of crystals of the phosphate
film formed on the surface of the continuous-annealed
cold-rolled steel sheet. As shown in Fig. 6, the
phosphate film formed on the surface of the
continuous-annealed cold-rolled steel sheet has coarse
and larger crystal grains than those formed on the
surface of the box-annealed cold-rolled steel sheet
shown in Fig. 5. The continuous-annealed cold-rolled
steel sheet is therefore inferior in phosphating-
treatability, paint adhesivity and corrosion resistance
after painting to the box-annealed cold-rolled steel sheet.
. ~ . .
-- 11 --
,
2 ~
The above-mentioned inferiority of the
continuous-annealed cold-rolled steel sheet in
phosphating-treatability is observed when pickling the
steel sheet surface with an inorganic acid not only in
the case of an extra-low-carbon steel but also in the
case of an ordinary low-carbon aluminum-killed steel
and a capped steel.
As a means to solve the problem regarding the
inferior phosphating-treatability of the pickled
continuous-annealed cold-rolled steel sheet,
technologies of forming a plating layer of a metal such
as nickel in a slight amount on the surface of the
cold-rolled steel sheet have been proposed as follows:
(1) A method for improving phosphating-
treatability of a cold-rolled steel sheet, as disclosed
in Japanese Patent Provisional Publication No.
56-116,883 dated September 12, 1981, which comprises
forming a nickel plating layer having a plating weight
within a range of from 0.3 to 10 mg/dm~ on the surface
Of a cold-rolled steel sheet (hereinafter referred to
as the "prior art 1").
(2) A metal plated cold-rolled steel sheet excellent in
phosphating-treatability, as disclosed in Japanese
- 12 -
Patent Provisional Publication No. 56-116,887 dated
~eptember 12, 1981, which comprises:
a cold-rolled steel sheet; and a plating layer
of at least one metal selected from the group
cons.isting of titanium (Ti), manganese (Mn), nickel
(Ni), cobalt (Co), copper (Cu), molybdenum (Mo) and
tungsten (W), having a plating weight within a range of
from l to 500 mg/m2, formed on the surface of said
cold-rolled steel sheet (hereinafter referred to as the
"P t 2")
rlor ar
According to the above-mentioned prior arts l
and 2, it is possible to obtain a nickel electroplated
cold-rolled steel sheet excellent in phosphating-
treatability. This is attributable to the fact that,
because of the metal plating layer of nickel and the
like formed on the surface of the cold-rolled steel
sheet, cathodes activating the phosphate film forming
reaction are formed on the portion where the metal such
as nickel is precipitated.
However, the prior arts 1 and 2 have the
following problems.
In order to improve phosphating-treatability
- 13 -
~ ~3 ~ 7'~
of the cold-rolled steel sheet, it is particularly
important to adjust the number of precipitation
neuclei of phosphate to a certain distribution density.
According to the prior arts 1 and 2, however, the range
of the plating weight of the plating layer of nickel
and the like is so wide as from 1 to 500 mg/m2. When
the plating weight of the plating layer of nickel and
the like is large beyond the necessary level, or when
particles of nickel and the like are not distributed at
a certain distribution density, a crystal grain size
suitable for forming a thin and dense phosphate film is
not available, thus making it impossible to obtain an
excellent paint adhesivity and an excellent corrosion
resistance after painting. When the plating weight of
the plating layer of nickel and the like is too slight,
on the contrary, the number of precipitation nuclei of
phosphate is insufficient with a coarse and thick
phosphate film, and a sufficient reducing effect of
frictional coefficient of the steel sheet surface is
not available.
Even when the plating weight of the plating
layer of nickel and the like is within a prescribed
range, if the oxide film of nickel and the like is not
existent on the plating layer., or when the oxide film,
if any, is very thin the frictional coefficient of the
- 14 -
s~rface of the cold-rolled steel sheet increases, this
causing decrease in press-formability of the steel
sheet. In order to prevent press-formability from
decreasing, it is required to bring the plating weight
of the metal plating layer closer to the upper limit of
the amount disclosed in the prior arts 1 and 2. This
however in turn causes deterioration of
phosphating-treatability of the steel sheet.
As a technology for improving phosphating-
treatability and corrosion resistance of the
cold-rolled steel sheet, the following cold-rolled
steel sheet is proposed;
A nickel pla~ed c~ld-rolled ~te~l s-heet excellent in
phosphating-treatability and corrosion resistance,
disclosed in Japanese Patent Provisional Publication
No. 2-101,200 dated April 12, 1990, which comprises: a
cold-rolled steel sheet; and a nickel plating layer,
formed on the surface of said cold-rolled steel sheet,
in which layer nickel particles are precipitated at a
distribution density within a range of from 1 x 1012 to
5 x 1014/m~, the plating weight of said nickel plating
layer being within a range of from 1 to S0 mg/m2 per
surface of said cold-rolled steel sheet, each of said
nickel particles comprising metallic nickel and
non-metallic nickel, having a thickness within a range
- 15 -
2~ 7
of from 3.0G09 to 0.03 ~m, adhering to the surface of
said metallic nickel, and said nickel particles having
particle size within a range of from 0.001 to 0.3 ~m
(hereinafter referred to as the "prior art 3").
According to the above-mentioned prior art 3,
it is possible to form a dense and uniform phosphate
film having a crystal grain size within a certain
range, thereby making it possible to obtain a
cold-rolled steel sheet excellent in
phosphating-treatability and corrosion resistance. In
addition, the prior art 3 permits reduction of
frictional coefficient of the surface of the
continuous-annealed cold-rolled steel sheet.
However, our detailed studies revealed that
the prior art 3 had the following problems.
In the prior art 3, when the plating weight of
the nickel plating layer is under 5 mg/m2, a cold-
rolled steel sheet excellent in phosphating-treatability
is unavailable. The reason is as follows. More
specifically, the number of initially precipitated
nuclei of phosphate, which is required for forming a
dense and uniform phosphate film and giving a crystal
grain size within a certain range by means of the
phosphating treatment, is within a range of from 1 x
- 16 -
2 ~
101 to 5 x 10 1~m2 in terms of the distribution
density.
In order to limit the distribution density of
nickel particles in the nickel plating layer within the
range of from 1 x 101~ to 5 x 1014/m2 as described
above, however, the plating weight of the nickel
plating layer must be at least 5 mg/m2. According to
the prior art 3, however, the plating weight of the
nickel plating layer is disclosed to be within a range
of from 1 to 50 mg/m2. Accordingly, when the plating
weight of the nickel plating layer is under 5 mg/m2, it
is impossible to achieve a distribution density of the
nickel particles of at least 1 x 1012/m2. Therefore,
the number of initially precipitated nuclei of
phosphate cannot in some cases be kept within a desired
range described above by the prior art 3, in which case
an excellent phosphating-treatability of the steel
sheet is unavailable.
In the prior art, 3 furthermore, improvement
of phosphat.ing-treatability and reduction of frictional
coefficient of the surface of the cold-rolled steel
sheet are attempted by forming a non-metallic nickel
film on the surface of the nickel plating layer.
However, non-metallic nickel is basically a metal
oxide, and as disclosed in the examples of the prior
art 3, when forming a non-metallic nickel oxide film
having an average thickness of at least 0.005 ~m on the
steel sheet surface by subjecting the steel sheet to an
anodic electrolytic treatment in an alkaline bath,
non-metallic nickel oxide film having an average
thickness larger than the above is formed on a portion
of the steel sheet surface not having a nickel plating
layer. Consequently, although press-formability is
improved, the phosphate film contains more portions
with a small deposited weight, thus resulting in a
lower paint adhesivity and a poorer corrosion
resistance after painting.
~hen manufacturing a cold-rolled steel sheet
for deep drawing by using a mild steel sheet as the
material and subjecting same to a continuous annealing
treatment, it is necessary to solve simultaneously the
two problems of a decrease in phosphating-treatability
as well as in press-formability.
Under such circumstances, there is a strong
demand for the development of a nickel electroplated
cold-rolled steel sheet for deep drawing excellent in
press-formability and phosphating-treatability,
suitable for the application: of the continuous annealing
- 18 -
2 ~ 7 5~
treatment, but such a cold-rolled steel sheet and a
method for manufacturing same have not as yet been
proposed.
SUMMARY OF THE INVENTION
An object of the present invention is therefore
to provide a nickel electroplated cold-rolled steel
sheet for deep drawing excellent in press-formability
and phosphating-treatability, suitable for the
application of the continuous annealing treatment.
In accordance with one of the features of the
present invention, there is provided a nickel
electroplated cold-rolled steel sheet excellent in
press-formability and phosphating-treatability, which
comprises:
a cold-rolled steel sheet consisting
essentially of:
carbon (C) : up to 0.06 wt.%,
silicon ~Si) : up to 0.5 wt.%,
manganese (Mn) : up to 2.5 wt.%,
phosphorus (P) : up to 0.1 wt.%,
sulfur (S) : up to 0.025 wt.%,
soluble aluminum (Sol.~l)
: up to 0.10 wt.%,
-- 19 --
2~.3
nitrogen iN) : up to 0.005 wt.%,
and
the balance being iron (Fe) and incidental
impurities;
a nickel electroplating layer, formed on at
least one surface of said cold-rolled steel sheet, in
which layer nickel particles are precipitated at a
distribution density of at least 1 x 1012/m2, the
~lating weight of said nickel electroplating layer being
within a range of from 5 to 60 mg/m2 per surface of
said cold-rolled steel sheet; and
a nickel oxide film, formed on the surface of
said nickel electroplating layer, having an average
thickness within a range of from 0.0005 to 0.003 ~m.
In accordance with another one of the features
; of the present invention, there is provided a method for
manufacturing a nickel electroplated cold-rolled steel
sheet excellent in press-formability and
phosphating-treatability, which comprises the steps of:
preparing a steel ingot consisting essentially
of:
carbon (C) : up to 0.06 wt.%,
silicon ~Si) : up to 0.5 wt.%,
- 20 -
2 ~
manganese (Mn) : up to 2.5 wt.%,
phosphorus (P) : up to 0.1 wt.%,
sulfur (S) : up to 0.025 wt.%,
soluble aluminum (Sol.Al)
: up to 0.10 wt.%,
nitrogen (N) : up to 0.005 wt.%,
and
the balance being iron (Fe) and incidental
impurities; then
hot-rolling said steel ingot to prepare a
hot-rolled steel sheet; then
cold-rolling said hot-rolled steel sheet at a
reduction ratio within a range of from 60 to 85% to
prepare a cold-rolled steel sheet; then
subjecting said cold-rolled steel sheet to a
continuous annealing treatment which comprises heating
said cold-rolled steel sheet to a recrystallization
temperature and then slowly cooling same; then
subjecting said continuously annealed
cold-tolled steel sheet to a continuous nickel electro-
plating treatment in an acidic electroplating bath to
form a nickel electroplating layer, in which layer
nickel particles are precipitated at a distribution
- , .
- :
2~ 3rJ7
density OI at leasl l x 10l2/m2, on at least one
surface of said cold-rolled steel sheet, said nickel
electroplating layer having a plating weight within a
range of from 5 to 60 mg/m2 per surface o said
cold-rolled steel sheet; and then
immersing said cold-rolled steel sheet having
said nickel electroplating layer on said at least one
surface thereof into a neutral bath or an alkaline bath
to form a nickel oxide film having an average thickness
within a range of from 0.0005 to 0.003 ~m on said
nickel electroplating layer.
; In the above-mentioned nickel electroplated
cold-rolled steel sheet and manufacturing method
therefor, said cold-rolled steel sheet may additionally
contain any one of the following element(s):
(1) Titanium (Ti) in an amount of up to 0.15 wt.%;
(2) Niobium (Nb) in an amount of up to 0.15 wt.%;
(3) Titanium (Ti) in an amount of up to 0.15 wt.%
and niobium (Nb) in an amount of up to 0.15 wt.~;
(~) Titanium (Ti) in an amount of up to 0.15 wt.%
and boron (B) in an amount of up to 0.003 wt.%;
- 22 -
~3 ~ !3
(5) Niobium (Nb) in an amount of up to 0.15 wt.%
and boron (B) in an amount of up to 0.003 wt.%; or
(6) Titanium (Ti) in an amount of up to 0.15 wt.%,
niobium (Nb) in an amount of up to 0.15 wt.% and
boron (B) in an amount of up to 0.003 wt.%.
BRIEF DESCRIPTION OF THE DRAWINGS
~ ig. 1 is a graph illustrating the
relationship between the Lankford value and the
limiting drawing ratio, for the conventional
continuous-annealed cold-rolled steel sheet and the
conventional box-annealed cold-rolled steel sheet, both
without plating;
Fig. 2 is a graph illustrating the effect of the
plating weight of the nickel electroplating layer on
the number of initially precipitated nuclei of
phosphate, the distribution density of nickel
particles, frictional coefficient and the grain size of
crystals of the phosphate, film, for the examples of
the present invention and the examples for comparison
outside the scope of the present invention;
Fig. 3 is a graph illustrating the
relationship between the Lankford value and the
limiting drawing ratio, for the examples of the present
invention and the examples for comparison outside the
scope of the present invention;
Fig. 4 is a graph illustrating the effect of
the average thickness of the nickel oxide film on the
grain size of crystals of the phosphate film and the
frictional coefficient, for the examples of the
present invention and the examples for comparison
outside the scope of the preset invention;
Fig. 5 is an SEM micrograph showing the
metallurgical structure of crystals of the phosphate
film formed on the surface of the box-annealed
cold-rolled steel sheet;
Fig. 6 is an SEM micrograph showing the
metallurgical structure of crystals of the phosphate
film formed on the surface of the continuous-annealed
cold-rolled steel sheet;
Fig. 7 is an SEM micrograph showing the
metallurgical structure of crystals of the phosphate
film formed on the surface of the sample of the
invention No. 7, which has a nickel electroplating
layer having a plating weight of 23 mg/m and a nickel
oxide film having an average thickness of 17 A; and
- 24 -
r ig . ~ is an SEM micrograph showing the
metallurgical structure of crystals of the phosphate
film formed on the surface of the sample for comparison
No. 10 outside the sc~pe of the present invention,
which has a nickel plating layer having a plating
weight of 23 mg/m2 and a nickel oxide film having an
average thickness of 75 A.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
From the above-mentioned point of view,
extensive studies were carried out to develop a nickel
electroplated cold-rolled steel sheet excellent in
press-formability and phosphating-treatability and a
method for manufacturing same. As a result, the
following findings were obtained: -
By forming a nickel electroplating layer
having a prescribed plating weight, in which layer
nickel particles are precipitated at a prescribed
distribution density, on the surface of a
continuous-annealed cold-rolled steel sheet having a
specific chemical composition, then forming a nickel
oxide film having a prescribed average thickness on the
surface of the nickel electroplating layer, and then
subjecting the cold-rolled steel sheet to a phosphating
treatment to form a phosphate film on the surface of
- 25 -
2~
the nickel oxide film, the phosphate film becomes
denser, and paint adhesivity and corrosion resistance
after painting are further improved.
The present invention was made on the basis of
the above-mentioned findings. Now, the nickel
electroplated cold-rolled steel sheet excellent in
press-formability and phosphating-treatability of the
present invention and the method for manufacturing same
are described further in detail.
The chemical composition of the cold-rolled
steel sheet of the present invention is limited within
the above-mentioned range for the following reasons.
(l) Carbon:
A carbon content of over 0.06 wt.% seriously
impairs ductility of the cold-rolled steel sheet, thus
leading to a poorer workability. A carbon content of
under 0.0005 wt.% results, on the other hand, in a
longer refining time of steel, which is economically
unfavorable.
(2~ Silicon and manganese:
Silicon and manganese are added to a
high-strength steel sheet required to have a high
- 26 -
~ ~3 ~
press-formability. Silicon and manganese are e]ements
which strengthen the solid-solution. Addition of
silicon and manganese improves strength of the
cold-rolled steel sheet without seriously impairing
workability thereof. However, because of the easy
oxidation of these elements, a silicon content of over
0.5 w~.% or a mangane.se content of over 2.5 wt.~ causes
oxidation of the steel sheet surface, thus impairing
the surface appearance unique to the cold-rolled steel
sheet. A silicon content of under 0.005 wt.~ or a
manganese content of under 0.05 wt.% results on the
other hand in a longer refining time of steel, which is
economically unfavorable.
(3) Phosphorus:
Phosphorus has a function of improving
strength of the cold-rolled steel sheet. A phosphorus
content of over 0.1 wt.% causes however, longitudinal
cracks during the deep drawing of the cold-rolled steel
sheet. A phosphorus content of under 0.001 wt.%
results on the other hand in a longer refining time of
steel, which is economically unfavorable.
~4) Sulfur and nitrogen:
A lower sulfur content or a lower nitrogen
content brings about an improved press-formability of
- 27 -
~he ,old-rolled steel sheet. A sulfur content of over
0.025 wt.% or a nitrogen content of over 0.005 wt.~
is however economically unfavorahle. A sulfur content
of under 0.005 wt.% or a nitrogen content of under
0.0005 wt.% results on the other hand in a longer
refining time of steel, which is economically
unfavorable.
(5) Soluble aluminum:
Soluble aluminum is contained in steel as a
residue of aluminum (Al) used as a deoxidizing agent.
When a hot-rolled coil is prepared in the hot-rolling
process at a coiling temperature of at least 640C,
soluble aluminum has functions of fixing nitrogen and
improving formability. By adjusting a soluble aluminum
content to at least 0.01 wt.%, it is possible to obtain
a stably deoxidized aluminum-killed steel. With a
soluble aluminum content of over 0.1 wt.%, however, the
above-mentioned effects are saturated.
~6) Titanium and niobium:
Titanium and niobium are additionally added as
required in cases where a very high formability is
required to the cold-rolled steel sheet. Titanium and
niobium have a function of fixing carbon and nitrogen,
thus making it possible to manufacture IF steel by
- 2~ -
-
adding titaniwm and/or niobium to steel. The contents
of titanium and niobium are dependent on the contents
of carbon and nitrogen. With the contents of titanium
and nitrogen of over 0.15 wt.%, respectively, a desired
effect of fixing carbGn and nitrogen is unavailable and
economic demerits are encountered. When the contents
of titanium and niobium are under 0.001 wt.%,
respectively, the effect as described above is
unavailable.
(7) Boron:
Boron has a function of preventing longitudinal
cracks inevitably occurring in a cold-rolled steel
sheet which comprises IF steel containing titanium
and/or niobium. Addition of boron improves
deep-drawability of the cold-rolled steel sheet.
Therefore, boron is additionally added as required
together with titanium and/or niobium. A boron content
of over 0.003 wt.% leads however to a lower ductility
of the cold-rolled steel sheet. With a boron content
of under 0.0002 wt.%, on the other hand, a desired
effect as described above is unavailable.
In the present invention, a nickel
electroplating layer is formed on the surface of the
continuous-annealed cold-rolled steel sheet having the
above-mentioned chemical composition. Nickel particles
- 29 -
~ ~ ~3 ~ 3
are precipitated in the nickel electroplating layer at
a distribution density of at least 1 x 101~/m2, and the
nickel electroplating layer has a plating weight within
a range of from 5 to 60 mg/m2. The reason is as
~ollows.
In order to improve phosphating-treatability
of the continuous-annealed cold-rolled steel sheet, it
.is necessary that cathodes serving as precipitation
nuclei for the precipitation of hopeite (Zn3(PO4)2) and
phosphophyllite (Zn2Fe(PO4)2), which are phosphate
cr~stals, are distributed at a certain density on the
surface of the continuous-annealed cold-rolled steel
sheet to form initially precipitated nuclei of
phosphate known as local cells. The number of cathodes
distributed on the surface of the steel sheet is equal
to the number of local cells formed under the effect of
the difference in potential which is produced by
elements concentrated on the steel sheet surface and
nickel particles precipitated in the nickel
electroplating layer formed on the steel sheet surface.
In order to ensure an excellent paint
adhesivity and, an excellent corrosion resistance after
painting, the crystal grains of the phosphate film
- 3~ -
,
.~hould have a grain size within a certain range, and
for this purpose, ihe number of initially precipitated
nuclei of phosphate should have a distribution density
within a range of from 1 x 10 to 5 x lO /m . In
order for the number of initially precipitated nuclei
of phosphate to achieve a distribution density within
the above-mentioned range, the nickel particles
precipitated in the nickel electroplating layer should
have a distribution density within a range of from l x
10l2 to 5 x 10l4/m2. Furthermore, to achieve a
distribution density of the precipitated nickel
particles within the above-mentioned range, it is
necessary to limit the plating weight of the nickel
electroplating layer within a range of from 5 mg/m2 to
lS 60 mg/m2 per surface of the cold-rolled steel sheet.
By limiting the plating weight of the nickel
electroplating layer within the above-mentioned range,
it is possible to adjust the distribution density of
the nickel particles precipitated in the nickel
electroplating layer to at least 1 x 10l2/m2, and
hence, to ensure the number of initially precipitated
nuclei of phosphate necessary for the phosphating
treatment. thereby reducing frictional coefficient.
The average grain size of phosphate crystals
thus made available by limiting the plating weight of
- 31 -
the nickel electroplating layer and the distribution
density of the precipitated nickel particles is within
a range of from 1 to 3 ~m, which is equal to that of
the phosphate crystals formed on the surface of the
box-annealed cold-rolled steel sheet. This permits
achievement of satisfactory paint adhesivity and
corrosion resistance after painting.
With a plating weight of the nickel
electroplating layer of under 5 mg/m2 per surface of
the cold-rolled steel sheet, however, it is impossible
to adjust the distribution density of the nickel
particles to at least 1 x 1012/m2, thus making it
impossible to ensure the number of initially
precipitated nuclei necessary for the phosphating
treatment. In addition, a desired effect of reducing
frictional coefficient of the steel sheet surface is
unavailable. With a plating weight of the nickel
electroplating layer of over 60 mgJm2, on the other
hand, the above-mentioned effect reaches saturation,
and the resultant consumption is only uneconomical. A
plating weight of the nickel electroplating layer of
over 60 mg/m2, furthermore, leads to a decreasing
tendency of the number of initially precipitated nuclei
of phosphate, which is an adverse effect.
~ 3~.3
In ~he present invention, a nickel oxide film
having an average thickness within a range of from
0.0005 to 0.003 ~m is formed on the surface of the
nickel electroplating layer. The reason is as follows.
When forming the nickel electroplating layer
on the surface of the continuous-annealed cold-rolled
steel sheet, hardness of the steel sheet surface
becomes relatively low. In order to increase hardness
of the steel sheet surface, it is necessary to increase
the plating weight of the nickel electroplating layer.
However, when increasing the plating weight of the
nickel electroplating layer, it becomes impossible to
keep the distribution density of the nickel particles
precipitated therein within an appropriate range. In
the present invention, therefore, the plating weight of
the nickel electroplating layer is not increased, but a
nickel oxide film having an average thickness within a
range of from 0.0005 to 0.003 ~m, or more preferably,
within a range of from 0.001 to 0.002 ~m is formed on
the surface of the nickel electroplating layer so as to
increase lubricity of the steel sheet surface. This
permits reduction of frictional coefficient of the steel
sheet surface. An average thickness of the nickel oxide
film of under 0.0005 ~m cannot provide a desired effect
of reducing frictional coefficient.
h ~ ?
?n the other hand, because the nickel oxide
fLlm is an electric insulator, an average thickness
thereof of over 0.003 ~m hinders smooth flow of
electric current for causing precipitation of phosphate
crystals. Therefore, when a nickel oxide film is
formed through an anodic electrolytic treatment in a
neutral or alkaline bath, if a bath concentration is
high or an electric current is large, a thick nickel
oxide film is formed, not only on the surface of the
nickel electroplating layer, but also on the surface
portions of the steel sheet not covered with the nickel
electroplating layer. This reduces the number of
lnitially precipitated nuclei of phosphate, leading to
coarser crystal grains of phosphate, thus preventing
formation of a dense phosphate film. For this reason,
the average thickness of the nickel oxide film should be
limited within a range of from 0.0005 to 0.003 ~m, or
more preferably, from 0.001 to 0.002 ym.
The above-mentioned nickel electroplated
cold-rolled steel sheet of the present invention is
manufactured as follows.
A steel ingot having a chemical composition
within the above~mentioned range of the present
invention is prepared. Then, the steel ingot is
hot-rolled to prepare a hot-rolled steel sheet.
- 34 -
,J
Then che hot-rolled steel sheet is cold-rolled
at a reduction ratio within a range of form 60 to 85%
to prepare a cold-rolled steel sheet. The reduction
ratio in the cold-rolling should be limited within the
range of from 60 to 85%. With a reduction ratio of
under 60% or over 85% in the cold-rolling, a sufficient
deep-drawability of the cold-rolled steel sheet is
unavaialble.
Then, the thus prepared cold-rolled steel
sheet is subjected to a continuous annealing treatment
which comprises heating the cold-rolled steel sheet to
a recrystallization temperature and then slowly cooling
same.
An exemplification of the continuous annealing
lS treatment in the present invention is described. More
specifically, the cold-rolled steel sheet is heated to
a recrystallization temperature, and held at this
temperature for a period of time within a range of from
three to ten minutes. Then, the thus heated
cold-rolled steel sheet is slowly cooled to a
temperature of about 50C at a cooling rate of up to
5C/sec appropriately selected depending upon the grade
of steel.
Another exemplification of the continuous
annealing treatment in the present invention is as
follows. The cold-rolled steel sheet is heated to a
recrystallization temperature, and held at this
temperature for a period of time within a range of from
three to ten minutes. Then, thus heated cold-rolled
steel sheet is rapidly cooled to a temperature of up to
~50C at a cooling rate of at least 10C/sec. Then,the
steel sheet is subjected to an overaging treatment at a
temperature within a range of from 250 to 400C for a
period of time within a range of from one to three
minutes. Then, the steel sheet is cooled to a
temperature of up to 50C.
The cold-rolled steel sheet is thus subjected
to the continuous annealing treatment because of the
possibility of reducing the operation time, the
availability of uniformity in quality, and the
potential improvement of product yield and
productivity.
Subsequently, the thus continuous-annealed
cold-rolled steel sheet is subjected to a continuous
nickel electroplating treatment in an acidic
electroplating bath to form, on at least one surface of
the cold-rolled steel sheet, a nickel electroplating
layer having a plating weight within a range of from 5
- 36 -
~.3(.~ t~
'o 50 mg1m~ per surface of the cold-rolled steel sheet,
in which layer nickel particles are precipitated at a
distribution density of at least 1 x 1012/m2.
The nickel particles may be precipitated on
the surface of the cold-rolled steel sheet by a
substitution method which comprises immersing the
cold-rolled steel sheet in an acidic plating bath, but
in order to cause stable precipitation of the nickel
particles at a constant distribution density, the
10 electroplating treatment should by employed.
Then, the cold-rolled steel sheet on at least
one surface of which the nickel electroplating layer
has thus been formed, is immersed into a neutral bath
or an alkaline bath, or is subjected to an anodic
elec.trolytic treatment in the neutral bath or the
alkaline bath. A nickel oxide film having an average
thickness within a range of from 0.0005 to 0.003 ~m is
.thus formed on the surface of the nickel electroplating
layer. An aqueous solution of 10 g/l sodium carbonate
(Na2CO3) is applicable as an alkaline bath.
Prior to the continuous nickel electroplating
.reatment, the surface of the cold-rolled steel sheet
is cleaned by a pickling as required. The pickling is
applied because a continuous annealing equipment is
2 ~
in manv cases provided with a direct heating furnace on
tne entry side and a rapid cooling apparatus such as a
water coiling device and an air/water cooling device in
a rapid cooling zone in the middle so that the increase
in the dew point of the atmospheric gas during the
heating produces an iron oxide film on the steel sheet
surface, and this may prevent the nickel particles from
being precipitated in a desirable state. While the
immersion method in a hydrochloric acid bath is adopted
for pickling in these exemplifications, use of the
immersion method in a sulfuric acid bath or an
electrolytic treatment in a diluted sulfuric acid bath
for the pickling does not impair the essence of the
present invention.
Now, the present invention is described
further in detail by means of examples while comparing
with examples for comparison.
EXAMPLE
Steels B to G each having a chemical
composition as shown in Table 2 were refined, and then
slabs were prepared from the respective steels B to G
by the continuous casting method. Then, the thus
prepared slabs were hot-rolled to prepare respective
hot-rolled steel sheets having a prescribed thickness.
- 38 -
The finishing temperature of each of the hot-rolled
steel sheets was a temperature of at least the Ar3
transformation point of each of the steels, and the
coiling temperature in the hot-rolling was 730C for
the steels B to E and G, and 560C for the steel F.
Then, the hot-rolled steel sheets were subjected to the
pickling by the hydrochloric acid pickling method to
remove scale from the surfaces of the hot-rolled steel
sheets.
Then, the pickled hot-rolled steel sheets were
cold-rolled under the conditions as shown in Table 4 to
prepare respective cold-rolled steel sheets having a
thickness within a range of from 0.8 to 1.0 mm. Then,
the cold-rolled steel sheets were subjected to a
continuous annealing treatment under the conditions as
shown in Table 4. Then, the thus continuous-annealed
cold-rolled steel sheets were immersed in an acidic
bath comprising hydrochloric acid as shown in Table 3
to apply a pickling under the conditions as shown in
Table 3.
Then, each of the pickled cold-rolled steel
sheets was subjected to a continuous nickel
electroplating treatment in a nickel electroplating
bath as shown in Table 3 under the conditions as shown
also in Table 3. Then, the cold-rolled steel sheet
- 39 -
2 ~ ,,3 ~
having the nickel electroplating layer formed thereon
was subjected to an anodic electrolyti.c treatment in an
aqueous solution of sodium hydrogencarbonate (NaHCO3)
under the conditions as shown in Table 3 to form a
nickel oxide film on the surface of the nickel
electroplating layer. The cold-rolled steel sheets on
each of which the nickel electroplating layer and.the
nickel oxide film had been formed, were subjected to a
temper rolling with an elongation ratio of about 1.0%
10 to prepare samples of the nickel electroplated
cold-rolled steel sheet within the scope of the present
invention ~hereinafter referred to as the "samples of
the invention") Nos. 1 to 12.
~or comparison purposes, samples of the nickel
15 electroplated steel sheet outside the scope of the
present invention (hereinafter referred to as the
"samples for comparison") Nos. 1 to 13 were prepared by
the use of the steels D and E each having a chemical
composition within the scope of the present invention
20 as shown in Table 2. The samples for comparison Nos. 1
to 13 had a plating weight of the nickel electroplating
layer outside the scope of the present invention or an
average thickness of the nickel oxide film outside the
scope of the present invention as shown in Table 5.
- 40 -
2 ~
For eacn of the thus prepared samples of the
invention Nos. 1 to 12 and the samples for comparison
Nos. 1 to 13, a frictional coefficient (~) of the steel
sheet surface, a limiting drawing ratio (LDR), a
Lankford value (r-value), phosphating-treatability, a
distribution density of the nickel particles in the
nickel electroplating layer, and an average thi¢kness
of the nickel oxide film were investigated. The
results are shown in Tables 4 and 5.
- 10 Test method of frictional coefficient of steel sheet
surface:
A test piece having a size of 30 mm x 200 mm
was cut out from each of the samples of the invention
Nos. 1 to 12 and the samples for comparison Nos. 1 to
13. The test piece was placed on guide rollers, and
then a pressing member having a size of 3 mm x 10 mm
was pressed under a pressure of 400 kg-F from above
onto the surface of the test piece. Then, in this
state, the test piece was withdrawn at a speed of 1,000
m/minute to determine the withdrawing force F (kg-f) at
this moment, and the frictional coefficient ~ = 400/F
was calculated from the thus determined withdrawing
force F. The surface roughness was imparted to the
bottom surface of the pressing mem~er in the direction
at right angles to the sliding direction by means of
~ 3 !~
diamond particles having a particle size of about 3 ~m.
Test method of limiting drawing ratio:
A plurality of disks having various diameters
were cut out from each of the samples of the invention
Nos. 1 to 12 and the samples for comparison Nos. 1 to
13. Then, these disks were drawn by means of a punch
having a diameter of 50 mm. The ratio of the maximum
disks diameter, in which cracks had not been produced
on the disk, to the punch diameter was determined as a
limiting drawing ratio. When measuring the limiting
drawing ratio, a commercially available anticorrosive
oil was smeared as a lubricant on the disk and the punch.
Test method of Lankford value:
For each of the samples of the invention Nos.
1 to 12 and the samples for comparison Nos. 1 to 13, a
Lankford value was measured by a known method prior to
forming the nickel electroplating layer.
Test method of phosphating-treatability:
Each of the samples of the invention Nos. 1 to
12 and the samples for comparison Nos. 1 to 13 was
immersed for 15 seconds in a phosphating treatment
- 42 -
'
solution (manufactured by Japan Perkerizing Co., Ltd.;
PB-3030), then rinsed and dried. The surface of each
of the samples of the invention and the samples for
comparison thus immersed in the phosphating treatment
solution was observed by means of a scanning type
electron microscope to measure the number of initially
precipitated nuclei of phosphate. In addition, each of
the samples of the invention and the samples for
comparison was immersed in the above-mentioned
phosphating treatment solution for 120 seconds to form
a phosphate film completely on the surface of the steel
sheet, and was observed by means of a scanning type
electron microscope to measure the grain size of
phosphate crystal grains and the appearance of the
phosphate film. The appearance of the phosphate slim
was evaluated in accordance with the following
criteria:
: the phosphate crystal grain has a grain size
within a range of from 1.5 to 2.5 ~m, and the
deposited amount of the phosphate film is
sufficient;
o : the phosphate crystal grain has a grain size
within a range of from 1.0 to under 1.5 ym or
from over 2.5 ~m to 3.0 ~m, and the deposited
amount of the phosphate film is sufficient;
7 ~
: the phosphate crystal grain has a grain size
of over 3.0 ~m, and the deposited amount of
the phosphate film is sufficient,
x : the phosphate crystal grain has a grain size
of over 3.0 ~m, and the deposited amount of
~he phosphate film is insufficient.
The phosphate film was peeled off by the
reverse electrolysis to determine the deposited amount
of the phosphate film from the difference in weight
between before and after peeloff.
Measuring methods of the distribution density of nickel
particles in the nickel electroplating layer and the
average thickness of the nickel oxide film:
The distribution density of nickel particles
was measured by extracting nickel precipitated on the
steel sheet surface by the application of the extraction
replica method, and then observing by means of a
transmission type electron microscope. Measurement of
the average thickness of the nickel oxide film was
conducted by the application of the Anger electron
spectroscopic method.
- 44 -
2 ~
~abl~ 3
~rocess Bath composition Temperature Electric
current
density
. _ l ~
Pickling HCl 50 g/Q 50+5C
NiSo4-6H2O 240 g/Q
Ni NiCQ2-6H ~ 4S g/Q 40~5C -1.0-3.0
plating A/dm2
. H3BO3 30 g/Q
pH 2.5-3.5
Ni oxide
film NaHCO320 gJQ 25~5C 0.1-1.0
~orming A/dm2
~ ~ _
2 ,~ ~J ~ r,,i, ,~
aaueleadd~ ¦ O _ O _ _ ~ ~) ~) _ ~) _ O
~ (ulr()
.~az I s ulelfj o o t- ~o u~ u~ o o o~ c~ o c.
e~s,SI~ ~ _ c~ _ _ c~i c~ ~ _ c~ _ o~
a~(zu~ ~ad) _ _ _ _ _ _ _ _ _ _ _ O
alonu o o o o o o o o o o o -o
~liei~FUF X X X X X X X X X X X X
~::~F O I aqumN ~ ~ ~ ~r o~ t-- ~ r- _ ~ cc,
~ _ _ _ . _ _
~o (zUI/6UI) C`l o ID a~ _ ~ u~ co t- ~ ~ cr,
a I s oda c~ ~ c~i ~ c~ ~ c~ c~ c i t~i ~ c~i
.P ~ ~ _ _ _ __ _ _
~r ~r co co a~ c~ _ ~ ~r ~ co o
~1 ~ O O O O O _ _ _ _ _ O~
~ ~ c~ c~i c~ c~i c~ ~ ~ ~ c~ c~ _ c~
u~ ~(r~) a~ ~ ~ o~ o~ ~ c~ C~ ~ co ~ t-
~o~uaF::)F~ao::) o o o o o c~ o o o o o o
P. ~leuOF~FI~
(O , _
~r UIIF~ aPFXO _ _ _ _ _ _ _ _ _ co _ t-
D ~
E- J~( zUI lad) wO _ O 0 0 O ~0 0 -o ~0 ~0 O
sal~F~Ied IN _ _ _ _ _ _ _ _ _ _ _ _
~o ~1 Fsuap X X X X X X X X X X X X
uoF~nqFI~ sFa c~c~ _~ NC~ _ 0~ D _ a~ ~ N
.~ _ _ __
( zW/61J~) 1~Ir~ Ir~ N1~ O~ CO O t-- CO ID L~
1 u6 F aM _ ~r ~u~ _ N ~ N
6uF~ela _
lS~ O O Ir~ 1~ O O U~ 1~ 1~ O ls~
anleA - l ~ ~ ~ x oo o - - - N _ N
_ _ _ _ _ N N N N N _ N
~(~o) _ __ .
s::6uF~eaH o o o o o o o o o o o o
~ _
g ~(O
o ~au O F ~ O n p a~ ~ o ~_ o ~ ~ ou~ ~ o o o
8apel6 laa~s m m c~ c~ o
_ _
Z _ N O~ ~r U~l ~D t-- oo a~ _ _ N
_ _
uoF~uaAul au~ ~o aldUleS
.
.
-- 46 --
3 ~ ?
;3~uele~d,d~ __ __ _ X X -- X ¦ X ¦ X ¦ <~
~z 1 5 u relfj oo u~ C~l c~ o u~ oo a~ c~ u~ c~ co
.~ 'le~sA~::, c~ c~ c~ C`J C`~ C" ~ C`~ ~r u~ e- ~ er
( zw lad) , O _ _ _ O O O O , ., O O~
al::)nu o o o o o o o o o o o o o
~p~e~ldloald ._ _ _ _ _ _ _ _ _ _ _ _
.~Aliel~FuF X X X X X X X X X X X X X
~~0 l~3qwn~ _ ~r ~ o~ ID _ _ C'~ ~ t- ~ _ t-
o (zw/~w) _ ~ ~ c~ c~ u~ t- ~ ~ c~l o ~ t-
1 unowe _ _ _ _ _ c~ _ _ _ _ _ ~ ~
~ ~; o o ~ co c~ o~ ~ c~ ~ _ c~ c~l
~ ~ _ _ _ o _ _ _ _ _ _ _ _ ~
,~ ~ ._ c~ ~ c~ ~ ~ c~ ~i c~ c~ ~i c~i ~ c~
I ~ (1~) t- cc, U~ Ir~ ~ C~ C~ C~ C'~ C`J _ O'~ C'~
h ~ leuol~ o O O O O O O O O O O O O
_ (-O- __ _ _ _
I F~ ~ ~ .~ ~ c~ ~ o~ ~ u~ Lt~ o ~ t-
aplxo ~ u~ c~ ~r ~_ m _ _
~s:: _ _ _ _ _
E-JJ ( zW .lad) -o o ~o O O ~0 wO ~oo ~0 _ ~oo -o -o
}0 A~rs uap X X X X X X X X X X X X X
Uol~nqFl~sla _ t- o~ _. _~ _ ~ ~ _ _ u~ _ C~l
Z ( Z~W/fiFWa~ ~ ~ c~ co oo _ u~ t- ~ o~ u~ o o
~ela _ _ _ _ _ c~,
o o u~ o u~ o ~ o u~ o u~ o u~
o s anleA - I _4 _, _ ~ ~ _ _ c~ c~ _ _ _ C`J
o aln~eladwa~ o o o o o o o o o o o o o
6uF~ea~ __ co co co _ co oo __ ~ co co
,1~o (%) o o o o o o o o o o o o o
~ ~ oF~el co co co oo oo c~ oo oo c~ oo oo ~ oo
o uoF~onpa~ __ __ _
ape~6 laa~s a a ~ a ~3 a 1i3 ~ _ _ ~ ~ ~
Z _ c~ CO ~ ID CO ~ CO ~n o _ __
UoF~uaAuF a~ F aldwes
_ .
:-- 47 ~
2 ~ j r~
As shown in Tables ~ and 5, the samples of the
invention Nos. 1 to 12, of which the plating weight of
the nickel electroplating layer, the distribution
density of nickel particles and the avera~e thickness
of the nickel oxide film were within the scope of the
present invention, showed satisfactory results of tests
and were excellent in press-formability and
phosphating-treatability.
~he sample for comparison No. 1, in contrast,
having a low plating weight of the nickel
electroplating layer outside the scope of the present
invention and a low distribution density of nickel
particles outside the scope of the present invention,
showed a high frictional coefficient and a large grain
size of phosphate crystal grains resulting in inferior
press-formability and phosphating-treatability.
The samples for comparison Nos. 2 to 5, of
which the average thickness of the nickel oxide film
was low outside the scope of the present invention,
showed a high frictional coefficient and an
insufficient limiting drawing ratio, thus resulting in
an inferior press-formability.
In the samples for comparison Nos. 6 to 11, of
- 48 -
$~3' 8
~hich the average thickness of the nickel oxide film
was large outside the scope of the present invention,
the grain size of phosphate crystal grains was large,
with an insufficient deposited amount of the phosphate
film, resulting in an inferior
phosphating-treatability.
The samples for comparison Nos. 12 and 13,
having a large plating weight of the nickel
electroplating layer outside the scope of the present
invention and a low distribution density of nickel
particles outside the scope of the present invention,
showed a large grain size of phosphate crystal grains,
hence an inferior phosphating-treatability.
Fig. 2 is a graph illustrating the effect of
the plating weight of the nickel electroplating layer
; on the number of initially precipitated nuclei of
phosphate, the distribution density of nickel
particles, frictional coefficient and the grain size of
crystals of the phosphate film, for the examples of the
present invention and the examples for comparison
outside the scope of the present invention. In Fig. 2,
the mark "o" represents the sample of the invention,
and the mark "o" represents the sample for comparison.
In Fig. 2, the range of the grain size of crystals of
_ ,~9 _
$
~he phosphate film formed on the surface of the nickel
electroplated cold-rolled steel sheet prepared from the
steel H and the range of the frictional coefficient are
indicated by the arrows. It is understood from fig. 2,
that, with a plating weight of the nickel
electroplating layer within the scope of the present
invention, the number of initially precipitated nuclei
of phosp~te, the distribution density of nickel
particles, the frictional coefficient and the grain
size of phosphate crystal grains are as satisfactory as
the results available in the box-annealed cold-rolled
steel sheet.
Fig. 3 is a graph illustrating the
relationship between the Lankford value and the
limiting drawing ratio, for the examples of the present
invention and the examples for comparison outside the
scope of the present invention. In Fig. 3, the mark
"o" represents the sample of the invention, the mark
"o" represents the sample for comparison, and the mark
"~" represents a continuous-annealed cold-rolled steel
sheet not nickel-electroplated. It is understood from
Fig. 3 that there are differences in the Lankfrod value
and the limiting drawing ratio between the examples of
the invention and the examples for comparison.
- 50 -
J ~
Fig. 4 is a graph illustrating the effect of
~e average thickness of the nickel oxide film on the
grain size of crystals of the phosphate film and the
frictional coefficient, for the examples of the present
invention and the examples for comparisor. outside the
scope of the present invention. In Fig. 4, the mark
"O`' represents the sample of the invention, and the
mark "e" represents the sample for comparison. In Fig.
4, the range of the grain size of crystals of the
phosphate film formed on the surface of the nickel
electroplated cold-rolled steel prepared from the steel
F and the range of the frictional coefficient are
indicated by the arrows. It is understood from fig. 4
that, even with a plating weight of the nickel
electroplating layer within the scope of the present
invention, if the average thickness of the nickel oxide
film is low outside the scope of the present invention,
the frictional coefficient becomes higher. With a low
average thickness of the nickel oxide film outside the
scope of the present invention, on the other hand, the
grain size of phosphate crystal grains becomes larger,
thus resulting in an inferior phosphating-treatability.
.
According to the present invention, as
described above in detail, it is possible to obtain a
nickel electroplated cold-rolled steel sheet for deep
2 ~ ' Y.i ~,
drawing excellent in press-formability and
phosphating-treatability, suitable for the application
of the continuous annealing treatment and a method for
manufacturing same, thus providing industrially useful
effects.
- 52 -
.
