Technical Field
[0001] The present invention relates to a method for stably manufacturing a galvanized steel
sheet having a low sliding resistance during press forming and excellent press formability.
Background Art
[0002] The galvanized steel sheet has been widely utilized in wide ranging fields focusing
on the application to automobile bodies. A galvanized steel sheet in such application
is press formed for use. However, the galvanized steel sheet has a disadvantage in
that the press formability is inferior to that of a cold-rolled steel sheet. This
is because the sliding resistance of the galvanized steel sheet in a press die is
higher than that of the cold-rolled steel sheet. More specifically, the galvanized
steel sheet becomes difficult to flow into a press die in a portion where the sliding
resistance between a die and a bead, which easily causes fracture of the steel sheet.
[0003] Here, particularly a galvannealed steel sheet that has been subjected to alloying
treatment after hot dip galvanizing treatment among galvanized steel sheets has more
excellent weldability and coatability than those of a hot-dip zinc-plated steel sheet
that has not been subjected to alloying treatment, and thus has been more preferably
used as automobile bodies.
[0004] The galvannealed steel sheet is one in which an Fe-Zn alloy phase is formed by galvanizing
a steel sheet, and heating the same so that Fe in the steel sheet and Zn in a plating
layer are dispersed to cause an alloying reaction. The Fe-Zn alloy phase is a coating
film generally containing a Γ phase, a δ
1 phase, and a ξ phase and has a tendency that the hardness and the melting point decrease
with a reduction in the Fe concentration, i.e., in the order of Γ phase → δ
1 phase → ξ phase. Therefore, a coating film having a high Fe concentration in which
the hardness is high, the melting point is high, and adhesion is difficult occur is
effective from the viewpoint of slidability. A galvannealed steel sheet in which the
press formability is emphasized is manufactured in such a manner that the average
Fe concentration in the coating film is slightly high.
[0005] However, the coating film having a high Fe concentration has problems in that the
Γ phase that is hard and brittle is easily formed on the plated-steel sheet interface
and a phenomenon of separation from the interface during processing, i.e., a so-called
powdering, is likely to occur.
[0006] As methods for solving the problems, Patent Document 1 and Patent Document 2 disclose
a technique of increasing the weldability and the processability by subjecting the
surface of a galvanized steel sheet to electrolysis treatment, immersion treatment,
coating oxidation treatment, or heat-treatment to form an oxide film mainly containing
ZnO.
[0007] However, when the techniques of Patent Document 1 and Patent Document 2 are applied
to a galvannealed steel sheet, the surface reactivity becomes poor due to the presence
of an Al oxide and an effect of improving the press formability cannot be stably obtained
because the surface irregularities are large. More specifically, since the surface
reactivity is low, it is difficult to form a given film on the surface even when the
electrolysis treatment, immersion treatment, coating oxidation treatment, heat-treatment,
or the like is performed and the film thickness is small in a portion where the reactivity
is low, i.e., a portion in which the number of Al oxides is large. Since the surface
irregularities are large, the surface convex portions directly contact a press die
during press forming. The sliding resistance in contact portions of thin portions
of the convex portions and the die becomes large, and thus an effect of improving
the press formability is not sufficiently obtained.
[0008] Patent Document 3 discloses a technique of forming an oxide layer on a plated surface
layer by hot dip galvanizing a steel sheet, alloying the same by heat treatment, subjecting
the resultant steel sheet to temper rolling, bringing the same into contact with an
acidic solution having pH buffer action, holding the same for 1 to 30 seconds, and
then washing with water.
[0009] Similarly, as a method for uniformly forming an oxide layer on a surface flat portion
of a hot dip galvanized steel sheet that has not been subjected to alloying treatment,
Patent Document 4 discloses a method including bringing a hot dip galvanized steel
sheet after temper rolling into contact with an acidic solution having pH buffer action,
holding the same for a given period of time in a state where a liquid film of the
acidic solution is formed on the surface of the steel sheet, and then washing with
water and drying the same.
[0011] EP 2 014 783 A1 discloses a steel sheet which is coated with a Zn oxide layer by immersion of a steel
plate in an acidic solution containing Zr, Ti, or Sn ions.
[0012] EP 1 288 325 A1 discloses a steel sheet and a method for the production thereof with oxide layer
which is generated by immersion of the galvanized steel sheet in an
acidic solution containing Fe and Zn ions. The Fe ions constitute the main proportion of the ions
contained in the aqueous solution. Thus, an iron zinc oxide formation occurs on the
surface.
[0013] US 2005/0139291 A1 discloses an oxide coated galvanized steel sheet and a method for production thereof.
An acidic solution containing ferrous sulfate heptahydrate is applied on the surface
of the galvanized steel sheet.
[0014] EP 1 666 624 A1 discloses the same method as already discussed for prior art
US 2005/0139291 A1. A galvanized steel sheet is dipped to an iron ion containing acid solution.
[0015] A further method performing a zinc oxide film on a surface of a galvanized steel
sheet is known from the post-published document
EP 2 186 925 A1. Said document discloses an improved method forming a zinc oxide film on the surface
of a galvanized steel sheet. Therefore, sulfate heptahydrate is added to an aqueous
solution with a pH value of about 5.2 to 5.6 such that the zinc ion concentration
is in the range between 4.5 and 11.4 g/l.
[0016] Further from
WO 00/15878 there is known a steel plate coated with a metal layer based on zinc and zinc hydroxysulphate
layer, whereof the surface density of the surface is more than 0.5 mg/m
2. In the most example disclosed in said document, a so-called anodic polarizing is
used to cause the polarization current to circulate. There is disclosed one example,
wherein instead of a basic solution an acidic solution between 5 and 7 pH is used.
[0017] A further surface treatment with a solution containing sulfate ions is disclosed
in
WO 2005/071140 A1.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 53-60332
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2-190483
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2003-306781
Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-3004
[0018] When the techniques disclosed in Patent Document 3 and Patent Document 4 are applied,
favorable press formability can be obtained under former manufacturing conditions.
However, in recent years, the development of a manufacturing method for generating
a thicker oxide film in a shorter period of time has been demanded in order to increase
the productivity. When performed under such conditions, a sufficient oxide film is
not formed and favorable press formability is not obtained in some cases in the techniques
disclosed in Patent Document 3 and Patent Document 4.
[0019] In view of such circumstance, it is an object of the present invention to provide
a method capable of stably manufacturing a galvanized steel sheet having excellent
press formability even in a short time and a galvanized steel sheet having excellent
press formability.
Disclosure of Invention
[0020] The present inventors have repeatedly conducted extensive research in order to solve
the problems. As a result, the following findings have been obtained.
[0021] The acidic solution for use in the techniques of Patent Document 3 and Patent Document
4 has pH buffer action in order to promote the dissolution of zinc. Therefore, it
is considered that an increase in the pH is delayed, and thus the formation of an
oxide layer is delayed. In order to compensate zinc for forming an oxide layer with
zinc eluting from a plated coating film, an elution time of zinc is included in a
generation time of the oxide film. As a result, it is considered that generating a
thick oxide film in a short time becomes difficult.
[0022] Then, the present inventors have devised a technique of generating an oxide film
in a shorter time by omitting an elution time of zinc by blending zinc ion in an aqueous
solution for generating an oxide film beforehand. However, the formation of an oxide
film has not been promoted merely by blending zinc ion in an aqueous solution beforehand.
Particularly in the case where the pH is 2 described in Examples of Patent Document
3 and Patent Document 4, even when zinc is blended in a treatment liquid, the formation
of an oxide film has not been promoted.
[0023] This is considered to be because, according to the techniques of Patent Document
3 and Patent Document 4, an environment is established in which a zinc oxide is likely
to generate because the pH near the surface increases due to the reduction of hydrogen
ion occurring simultaneously with the elution of zinc, but the pH near the surface
does not increase merely by blending zinc ion in an aqueous solution, and thus an
environment is not established in which a zinc oxide is likely to generate.
[0024] Then, the present inventors have devised a technique of setting the pH of an aqueous
solution to 4 to 6, the pH at which a zinc oxide is likely to generate. Then, the
present inventors have found that, by setting the pH of a treatment liquid to 4 to
6, zinc is generated as a hydroxide due to a slight increase in the surface pH caused
by slight elution of zinc of a plated coating film.
[0025] In view of the aforementioned findings, the present invention provides a method for
manufacturing a galvanized steel sheet having the features defined in claim 1. Further
preferred embodiments of the method are defined in dependent claims 2 and 3.
[0026] In the invention, the galvanized steel sheet is a plated steel sheet having a coating
film containing zinc as the main component formed on the surface and includes a hot
dip galvanized steel sheet (abbreviated as a GI steel sheet), a galvannealed Steel
Sheet (abbreviated as a GA steel sheet), an electrogalvanized steel sheet (abbreviated
as an EG steel sheet), a vapor deposition galvanized steel sheet, an alloy galvanized
steel sheet containing an alloy element of Fe, Al, Ni, MgCo, or the like, etc.
Brief Description of Drawings
[0027]
Fig. 1 is a view of a principal part of an oxide layer formation treatment facility
used in Examples.
Fig. 2 is a schematic front view showing a friction coefficient measuring device.
Fig. 3 is a schematic perspective view showing the shape and the size of a bead in
Fig. 2.
Fig. 4 is a schematic perspective view showing the shape and the size of the bead
in Fig. 2.
Fig. 5 is a view showing influence of the zinc ion concentration on the oxide film
thickness.
Best Modes for Carrying Out the Invention
[0028] In the invention, when forming an oxide layer on the surface of a steel sheet by
galvanizing a steel sheet, bringing the steel sheet into contact with an aqueous solution,
holding the steel sheet for 1 to 60 seconds after the termination of the contact treatment,
and then washing with water and drying the steel sheet, the aqueous solution contains
zinc ion in the range of 50 to 100 g/l as the zinc ion concentration, the pH is 4
to 6, and the liquid temperature is 20 to 70°C. To prepare an aqueous solution containing
zinc ion in a given concentration and having a specified pH and a specified liquid
temperature as described above as the aqueous solution for use in the contact treatment
of the steel sheet is an important requirement and a feature in the invention. Thus,
an oxide layer sufficient for securing favorable press formability can be formed in
a short time.
[0029] The "after the termination of the contact treatment" refers to "after the termination
of an immersion process" in the case of immersion treatment, "after the termination
of a spraying process" in the case of spraying treatment, and "after the termination
of a coating process" in the case of roll coating.
[0030] The use of an aqueous solution containing zinc ion as the aqueous solution for use
in the contact treatment of the steel sheet allows omission of an elution time of
zinc. When the zinc ion concentration exceeds 100 g/l, the concentration of sulfuric
acid contained in the oxide layer to be formed becomes high, resulting in concern
about contamination of a treatment liquid when the oxide dissolves in chemical conversion
treatment to be carried out thereafter.
[0031] In particular, the present invention provides an aqueous solution, wherein the zinc
ion concentration is in the range of 50 to 100 g/l.
[0032] In order to form a stable zinc compound as an oxide layer, it is preferable to add
zinc ion as a sulfate. It is considered that when zinc ion is added as a sulfate,
sulfuric acid ion is taken into an oxide layer to be formed to thereby produce an
effect of stabilizing the oxide layer.
[0033] As described above, the formation of an oxide film is not promoted merely by blending
zinc ion in a treatment liquid beforehand. Then, in the invention, the pH needs to
be set to 4 to 6, at which a zinc oxide easily generates. When the pH of a treatment
liquid is set to 4 to 6, zinc generates as a hydroxide due to a slight increase in
the surface pH caused by slight elution of zinc of a plated coating film. As a result
thereof, the zinc elution time can be omitted and the generation of a zinc oxide can
be achieved. When the pH exceeds 6, zinc ion precipitates in the aqueous solution
(formation of a hydroxide) and is not formed as an oxide on the surface of the steel
sheet. When the pH is lower than 4, the formation of the oxide layer is hindered due
to the delay of an increase in the pH as described above.
[0034] The temperature of the aqueous solution is 20 to 70°C. Since the oxide layer formation
reaction occurs when holding the steel sheet in a given period of time after contacting
the aqueous solution, it is effective to control the sheet temperature during holding
in the range of 20 to 70°C. When the sheet temperature is lower than 20°C, a long
period of time is required for the oxide layer generation reaction, resulting in a
reduction in the productivity. In contrast, when the sheet temperature exceeds 70°C,
a reaction relatively quickly proceeds but treatment unevenness is likely to occur
on the surface of the steel sheet.
[0035] The aqueous solution used in Patent Document 3 and Patent Document 4 has a feature
in that the aqueous solution is acidic and has pH buffer action. In the invention,
however, since an aqueous solution containing zinc ion is used, a sufficient oxide
layer can be formed even when the dissolution of zinc is not caused by increasing
the pH of the aqueous solution. A prompt increase in the pH is considered to be advantageous
for the formation of an oxide. Therefore, the pH buffer action is not necessarily
indispensable.
[0036] In the invention, an oxide layer excellent in slidability can be stably formed when
zinc is contained in the aqueous solution contacting the surface of the steel sheet.
Therefore, even when other metal ions, inorganic compounds, and the like are contained
as impurities or intentionally contained in the aqueous solution, the effects of the
invention are not impaired. Even when N, P, B, Cl, Na, Mn, Ca, Mg, Ba, Sr, Si, and
the like are taken into the oxide layer, it can be applied insofar as the effects
of the invention are not impaired.
[0037] Preferably, after bringing a galvanized steel sheet into contact with the aqueous
solution containing the above, the aqueous solution is present on the surface of the
steel sheet in the form of a thin liquid film. This is because when the amount of
the aqueous solution present on the surface of the steel sheet is large, the pH of
the aqueous solution is hard to increase even when the dissolution of zinc occurs,
and a long period of time is required for the formation of the oxide layer. From this
viewpoint, it is preferable and effective to adjust the amount of an aqueous solution
film to be formed on the surface of the steel sheet to 30 g/m
2 or lower. In order to prevent the liquid film from drying, the amount of the liquid
film of 5 g/m
2 or more is suitable. As described above, the liquid film to be formed on the surface
of the steel sheet after contacting the aqueous solution is preferably 5 to 30 g/m
2. The adjustment of the amount of the aqueous solution film can be performed by a
squeeze roll, air wiping, or the like.
[0038] The time (retention time before washing with water) before washing with water after
immersion in the aqueous solution is 1 to 60 seconds. When the time before washing
with water is lower than 1 second, the aqueous solution is washed away before a sufficient
oxide layer is formed, and thus an effect of improving the slidability is not obtained.
In contrast, when the time before washing with water exceeds 60 seconds, the productivity
decreases. Since the object of the invention is to stably manufacture a galvanized
steel sheet even in a short time, the retention time is 60 seconds or lower for sufficiently
demonstrating the effects of the invention.
[0039] As described above, on the surface of the plated steel sheet of the invention, an
oxide layer mainly containing zinc as a metal component and having an average thickness
of 10 nm or more is obtained.
[0040] The "mainly containing zinc" refers to containing zinc in a proportion of 50% by
mass or more as a metal component.
[0041] The above mentioned oxide layer refers to a layer containing an oxide and/or a hydroxide
mainly containing zinc as a metal component. The average thickness of the oxide layer
is required to be 10 nm or more. When the average thickness of the oxide layer is
small, e.g., lower than 10 nm, an effect of reducing sliding resistance becomes insufficient.
In contrast, when the average thickness of the oxide layer containing zinc as an essential
ingredient exceeds 100 nm, there is a tendency that the coating film breaks during
press processing, the sliding resistance increases, and the weldability decreases.
Thus, such a thickness is not preferable.
[0042] Methods for bringing the galvanized steel sheet into contact with the aqueous solution
containing zinc are not particularly limited. For example, a method for immersing
the plated steel sheet in the aqueous solution, a method for spraying the aqueous
solution to the plated steel sheet, a method for applying the aqueous solution to
the plated steel sheet with a coating roll, and the like are mentioned. It is preferable
for the aqueous solution to be finally present on the surface of the steel sheet in
the form of a thin liquid film.
[0043] For manufacturing the galvannealed steel sheet according to the invention, Al needs
to be added into a plating bath but additional element ingredients other than Al are
not particularly limited. More specifically, even when Pb, Sb, Si, Sn, Mg, Mn, Ni,
Ti, Li, Cu, and the like other than Al are contained or added, the plating bath can
be applied insofar as the effects of the invention are not impaired.
EXAMPLES
[0044] Next, the invention will be described in more detail with reference to Examples.
[0045] A GI steel sheet was produced by performing hot dip galvanizing in which the deposit
amount per surface was 45 g/m
2 and the Al concentration was 0.20% by mass on a cold-rolled steel sheet having a
sheet thickness of 0.8 mm, and then performing temper rolling. A GA steel sheet was
obtained by forming a plated coating film in which the deposit amount per surface
was 45 g/m
2, the Fe concentration was 10% by mass, and the Al concentration was 0.20% by mass
on a cold-rolled steel sheet having a sheet thickness of 0.8 mm by a standard galvannealing
method, and further performing temper rolling. An EG steel sheet was produced by having
a plated coating film having a deposit amount per surface of 30 g/m
2 on a cold-rolled steel sheet having a sheet thickness of 0.8 mm by a standard electrogalvanizing
method.
[0046] Subsequently, an oxide layer was formed using a treatment facility having a structure
shown in Fig. 1. First, steel sheets S, such as the GI steel sheet, the GA steel sheet,
and the EG steel sheet obtained above were immersed in aqueous solutions in which
the treatment liquid composition, the temperature, and the pH were different from
each other as shown in Tables 1-1 and 1-2 in a solution bath 2. Subsequently, the
amount of liquid films on the surface of the steel sheets was adjusted with a squeeze
roll 3. The adjustment of the amount of liquid films was performed by changing the
pressure of the squeeze roll. Subsequently, the steel sheets were made to pass through
a washing bath 5 and a washing bath 6 without being treated, hot water of 50°C was
sprayed to the steel sheets in a washing bath 7 for washing, and the steel sheets
were dried with a drier 8, so that an oxide layer is formed on the plated surface.
A washing bath 1 can be provided before the solution bath 2.
[0047] As the aqueous solution for use in the immersion treatment in the solution bath 2,
an aqueous solution was used to which a given amount of zinc sulfate heptahydrate
was added in order to add zinc ion. For comparison, a solution containing 20 g/L of
sodium acetate whose pH was adjusted with sulfuric acid was also used in some cases.
[0048] The retention time before washing with water was the time before washing in the washing
bath 7 was started after adjusting the amount of liquid films with the squeeze roll
3 and was adjusted by changing the line speed. Some of the steel sheets were produced
by washing immediately after squeezing using a shower washing device 4 at the exit
side of the squeeze roll 3.
[0049] Next, the steel sheets produced as described above were judged whether or not they
have an appearance sufficient as an exterior panel for automobiles, and also the measurement
of a friction coefficient as a method for simply evaluating the press formability
and a spherical head bulging test was carried out in order to simulate the actual
formability in detail were carried out. The measurement methods are as follows.
(1) Press formability evaluation test (Friction coefficient measurement test)
[0050] In order to evaluate the press formability, the friction coefficient of each test
piece was measured as follows.
[0051] Fig. 2 is a schematic front view showing a friction coefficient measuring device.
As shown in Fig. 2, a friction coefficient measuring sample 11 extracted from the
test piece is fixed to a sample stand 12. The sample stand 12 is fixed to the upper
surface of a horizontally movable slide table 13. On the lower surface of the slide
table 13, a vertically movable slide table support stand 15 having a roller 14 contacting
the lower surface of the slide table 13. By pressing up the same, a first load cell
17 for measuring a pressing load N to the friction coefficient measuring sample 11
by a bead 16 is attached to the slide table support stand 15. In order to measure
a sliding resistance F for horizontally moving the slide table 13 along a rail 19
in the state where the pressing force was made to act, a second load cell 18 is attached
to one end of the slide table 13. As a lubricant, a cleaning oil for pressing, Preton
R352L manufactured by Sugimura Chemical Industrial Co., Ltd., was applied onto the
surface of the friction coefficient measuring sample 11, and thus a test was carried
out.
[0052] Figs. 3 and 4 are schematic perspective view showing the shape and the size of the
used bead. The bead 16 slides while the lower surface of the bead 16 being pressed
against the surface of the sample 11. In the bead 16 shown in FIG. 3, the width is
10 mm, the length in the sliding direction of the sample is 12 mm, and each end in
the sliding direction of the lower surface of the bead 16 is curved with a curvature
of 4.5 mmR. The lower surface of the bead 16 against which the sample is pressed has
a plane with a width of 10 mm and a length in the sliding direction of 3 mm. In the
bead 16 shown in FIG. 4, the width is 10 mm, the length in the sliding direction of
the sample is 69 mm, and each end in the sliding direction of the lower surface of
the bead 16 is curved with a curvature of 4.5 mmR. The lower surface of the bead 16
against which the sample is pressed has a plane with a width of 10 mm and a length
in the sliding direction of 60 mm.
[0053] The friction coefficient measurement test was carried out under two conditions shown
below.
[Condition 1]
[0054] The bead shown in Fig. 3 was used, the pressing load N was 400 kgf, and the sample
drawing rate (horizontal movement rate of the slide table 13) was 100 cm/min.
[Condition 2]
[0055] The bead shown in Fig. 4 was used, the pressing load N was 400 kgf, and the sample
drawing rate (horizontal movement rate of the slide table 13) was 20 cm/min.
[0056] The friction coefficient between the test piece and the bead was calculated based
on Equation: µ = F/N.
(2) Spherical head bulging test
[0057] A test piece having a size of 200 × 200 mm was subjected to bulge forming using a
150 mmφ punch by a liquid pressure bulge testing machine. Then, the maximum forming
height when the test piece was broken was measured. During the test, a wrinkle pressing
force of 100 Ton was applied in order to prevent inflow of materials, and a lubricating
oil was applied only to the surface which the punch contacted. The used lubricating
oil is the same as that of the friction coefficient measurement test described above.
(3) Measurement of thickness of oxide layer (oxide film thickness)
[0058] An Si wafer on which a thermal oxidation SiO
2 film having a film thickness of 96 nm was formed was used as a reference substance,
and the average thickness of the oxide layer in terms of SiO
2 was determined by measuring the O·Kα·X rays by an x-ray fluorescence spectrometer.
The analysis area is 30 mmφ.
[0059] The test results obtained in the above are shown in Tables 1-1 and 1-2.
Table 1-1
No. |
Test piece |
Used solution |
pH |
Solution Temperature |
Liquid film amount (g/m2) |
Time before water Washing (second) |
Oxide film thickness (nm) |
Friction coefficient |
Maxium forming height (mm) |
Steel sheet appearance |
Remarks |
pH buffer |
Zn concentratio |
Condition 1 |
Condition 2 |
1 |
GA |
- |
- |
- |
- |
- |
- |
8 |
0.180 |
0.223 |
35.0 |
○ |
Comparative example 1 |
2 |
|
Sodium acetate (20g/L) |
- |
2.0 sulfuric acid added |
35°C |
10 |
10 |
15 |
0.149 |
0.190 |
36.5 |
○ |
Comparative example 2 |
3 |
|
10 |
30 |
30 |
0.128 |
0.165 |
38.1 |
○ |
Comparative example 3 |
4 |
|
10 |
60 |
42 |
0.120 |
0.163 |
39.3 |
○ |
Comparative example 4 |
5 |
|
- |
5.0 sulfuric add added |
35°C |
10 |
10 |
8 |
0.183 |
0.219 |
35.6 |
○ |
Comparative example 5 |
6 |
|
10 |
30 |
8 |
0.179 |
0.221 |
35.9 |
○ |
Comparative example 6 |
7 |
|
10 |
60 |
8 |
0.180 |
0.217 |
35.9 |
○ |
Comparative example 7 |
8 |
|
- |
2.5g/l |
5.6 |
35°C |
10 |
10 |
12 |
0.148 |
0.200 |
36.5 |
○ |
Comparative example 8 |
9 |
|
|
10 |
30 |
25 |
0.140 |
0.174 |
37.9 |
○ |
Comparative example 9 |
10 |
|
|
10 |
60 |
32 |
0.132 |
0.163 |
38.9 |
○ |
Comparative example 10 |
11 |
|
|
5g/l |
5.5 |
35°C |
10 |
10 |
18 |
0.138 |
0.187 |
37.6 |
○ |
Comparative example 40 |
12 |
|
|
10 |
30 |
32 |
0.123 |
0.166 |
39.1 |
○ |
Comparative example 41 |
13 |
|
|
10 |
60 |
43 |
0.122 |
0.163 |
39.5 |
○ |
Comparative example 42 |
14 |
|
|
10g/l |
5.2 |
35°C |
10 |
10 |
25 |
0.134 |
0.174 |
39.0 |
○ |
Comparative example 43 |
15 |
|
|
10 |
30 |
35 |
0.128 |
0.164 |
39.4 |
○ |
Comparative example 44 |
16 |
|
|
10 |
60 |
45 |
0.124 |
0.163 |
40.1 |
○ |
Comparative example 45 |
17 |
|
|
50g/l |
5.0 |
35°C |
10 |
0 |
12 |
0.160 |
0.205 |
37.2 |
○ |
Comparative example 11 |
18 |
|
|
|
|
10 |
1 |
15 |
0.145 |
0.200 |
38.1 |
○ |
Example of present invention 7 |
19 |
|
|
|
|
10 |
5 |
24 |
0.137 |
0.173 |
39.0 |
○ |
Example of present invention 8 |
20 |
|
|
|
|
10 |
10 |
32 |
0.127 |
0.165 |
38.9 |
○ |
Example of present invention 9 |
21 |
|
|
|
|
10 |
30 |
40 |
0.127 |
0.159 |
39.9 |
○ |
Example of present invention 10 |
22 |
|
|
|
|
10 |
60 |
50 |
0.125 |
0.160 |
40.8 |
○ |
Example of present invention 11 |
23 |
|
|
|
|
15°C |
10 |
10 |
14 |
0.145 |
0.198 |
37.1 |
○ |
Comparative example 12 |
24 |
|
|
|
|
10 |
30 |
27 |
0.134 |
0.169 |
38.1 |
○ |
Comparative example 13 |
25 |
|
|
|
|
10 |
60 |
37 |
0.125 |
0.166 |
39.2 |
○ |
Comparative example 14 |
26 |
|
|
|
|
25°C |
10 |
10 |
19 |
0.138 |
0.189 |
38.5 |
○ |
Example of present invention 12 |
27 |
|
|
|
|
10 |
30 |
32 |
0.129 |
0.166 |
40.3 |
○ |
Example of present invention 13 |
28 |
|
|
|
|
10 |
60 |
43 |
0.127 |
0.162 |
40.0 |
○ |
Example of present invention 14 |
29 |
|
|
|
|
65°C |
10 |
10 |
35 |
0.128 |
0.164 |
40.5 |
○ |
Example of present invention 15 |
30 |
|
|
|
|
10 |
30 |
44 |
0.125 |
0.162 |
41.6 |
○ |
Example of present invention 16 |
31 |
|
|
|
|
10 |
60 |
51 |
0.123 |
0.160 |
41.8 |
○ |
Example of present invention 17 |
32 |
|
|
|
|
75°C |
10 |
10 |
35 |
0.124 |
0.161 |
40.6 |
× |
Comparative example 15 |
33 |
|
|
|
|
10 |
30 |
45 |
0.120 |
0.163 |
40.5 |
× |
Comparative example 16 |
34 |
|
|
|
|
10 |
60 |
52 |
0.121 |
0.158 |
41.0 |
× |
Comparative example 17 |
35 |
|
|
|
|
35°C |
30 |
10 |
20 |
0.143 |
0.185 |
38.5 |
○ |
Example of present invention 18 |
36 |
|
|
|
|
30 |
30 |
34 |
0.128 |
0.163 |
39.1 |
○ |
Example of present invention 19 |
37 |
|
|
|
|
30 |
60 |
49 |
0.127 |
0.161 |
40.4 |
○ |
Example of present invention 20 |
No. |
Test piece |
Used solution |
pH |
Solution Temperature |
Liquid film amount (g/m2 ) |
Time before water Washing (second) |
Oxide film thickness (nm) |
Friction coefficient |
Maxium forming height (mm) |
Steel sheet appearance |
Remarks |
pH buffer |
Zn concentratio |
Condition 1 |
Condition 2 |
38 |
|
|
|
|
35° C |
40 |
10 |
13 |
0.155 |
0.202 |
37.4 |
○ |
Example of present invention 21 |
39 |
|
|
|
|
40 |
30 |
28 |
0.132 |
0.167 |
39.0 |
○ |
Example of present invention 22 |
40 |
|
|
|
|
40 |
60 |
42 |
0.127 |
0.163 |
39.7 |
○ |
Example of present invention 23 |
41 |
|
|
|
3.5 sulfuric acid added |
35°C |
10 |
10 |
14 |
0.149 |
0.201 |
36.0 |
○ |
Comparative example 18 |
42 |
|
|
|
|
10 |
30 |
27 |
0.130 |
0.165 |
39.2 |
○ |
Comparative example 19 |
43 |
|
|
|
|
10 |
60 |
40 |
0.124 |
0.162 |
41.0 |
○ |
Comparative example 20 |
44 |
|
|
100g/l |
4.9 |
35°C |
10 |
10 |
34 |
0.125 |
0.166 |
40.5 |
○ |
Example of present invention 24 |
45 |
|
|
|
|
10 |
30 |
41 |
0.123 |
0.164 |
40.9 |
○ |
Example of present invention 25 |
46 |
|
|
|
|
10 |
60 |
50 |
0.121 |
0.163 |
40.8 |
○ |
Example of present invention 26 |
Table 2-1
No |
Test piece |
Used solution |
pH |
Solution Temperature |
Liquid film amount (g/m2 ) |
Time before water washing (second) |
Oxide film thickness (nm) |
Friction coefficient |
Maxium forming height (mm) |
Steel sheet appearance |
Remarks |
pH buffer |
Zn concentration |
Condition 1 |
Condition 2 |
47 |
GI |
- |
- |
- |
- |
- |
- |
7 |
0.175 |
0.215 |
35.7 |
○ |
Comparative example 21 |
48 |
|
Sodium acetate (20 g/L) |
- |
2.0 sulfuric acid added |
35°C |
10 |
10 |
13 |
0.147 |
0.187 |
36.7 |
○ |
Comparative example 22 |
49 |
|
10 |
30 |
27 |
0.125 |
0.164 |
38.6 |
○ |
Comparative example 23 |
50 |
|
10 |
60 |
39 |
0.119 |
0.160 |
39.6 |
○ |
Comparative example 24 |
51 |
|
- |
2.5g/l |
5.6 |
35°C |
10 |
10 |
11 |
0.161 |
0.198 |
36.3 |
○ |
Comparative example 25 |
52 |
|
10 |
30 |
24 |
0.13 |
0.168 |
38 |
○ |
Comparative example 26 |
53 |
|
10 |
60 |
34 |
0.121 |
0.163 |
39.1 |
○ |
Comparative example 27 |
54 |
|
10g/l |
5.2 |
35°C |
10 |
10 |
19 |
0.138 |
0.177 |
37.1 |
○ |
Comparative example 46 |
55 |
|
10 |
30 |
32 |
0.124 |
0.161 |
38.5 |
○ |
Comparative example 47 |
56 |
|
10 |
60 |
42 |
0.121 |
0.161 |
39.5 |
○ |
Comparative example 48 |
57 |
|
50g/l |
5.0 |
35°C |
10 |
10 |
26 |
0.127 |
0.166 |
38.4 |
○ |
Example of present invention 30 |
58 |
|
10 |
30 |
36 |
0.122 |
0.163 |
39 |
○ |
Example of present invention 31 |
59 |
|
10 |
60 |
45 |
0.12 |
0.159 |
39.7 |
○ |
Example of present invention 32 |
60 |
EG |
- |
- |
- |
- |
- |
- |
9 |
0.146 |
0.289 |
33.7 |
○ |
Comparative example 28 |
61 |
|
Sodium acetate (20g/L) |
- |
2.0 sulfuric acid added |
35°C |
10 |
10 |
11 |
0.136 |
0.241 |
34.0 |
○ |
Comparative example 29 |
62 |
|
10 |
30 |
23 |
0.135 |
0.195 |
36.6 |
○ |
Comparative example 30 |
63 |
|
10 |
60 |
36 |
0.128 |
0.173 |
37.9 |
○ |
Comparative example 31 |
64 |
|
- |
2.5g/l |
5.6 |
35°C |
10 |
10 |
12 |
0.140 |
0.199 |
37.0 |
○ |
Comparative example 32 |
65 |
|
10 |
30 |
23 |
0.131 |
0.181 |
37.2 |
○ |
Comparative example 33 |
66 |
|
10 |
60 |
31 |
0.131 |
0.159 |
37.5 |
○ |
Comparative example 34 |
67 |
|
10g/l |
5.2 |
35°C |
10 |
10 |
20 |
0.139 |
0.221 |
35.4 |
○ |
Comparative example 49 |
68 |
|
10 |
30 |
35 |
0.132 |
0.195 |
36.9 |
○ |
Comparative example 50 |
69 |
|
10 |
60 |
45 |
0.129 |
0.160 |
37.6 |
○ |
Comparative example 51 |
70 |
|
50g/l |
5.0 |
35°C |
10 |
10 |
22 |
0.136 |
0.192 |
37.6 |
○ |
Example of present invention 36 |
71 |
|
10 |
30 |
37 |
0.131 |
0.153 |
39.3 |
○ |
Example of present invention 37 |
72 |
|
10 |
60 |
46 |
0.125 |
0.156 |
38.9 |
○ |
Example of present invention 38 |
[0060] The following items were clarified from the test results shown in Tables 1-1 and
1-2.
- (1) Since Nos. 1, 47, and 60 were not treated with a solution, an oxide film sufficient
for increasing the slidability was not formed on the flat portion. Thus, the friction
coefficient is high.
- (2) Nos. 2 to 4, Nos. 48 to 50, and Nos. 61 to 63 are comparative examples using an
acidic solution having pH buffer action. In the case of the treatment of 30 seconds
or more, the friction coefficient is low and the maximum forming height is large but
in the case of the treatment of 10 seconds, a sufficient reduction in the friction
coefficient and an increase in the maximum forming height are not satisfied.
- (3) Nos. 5 to 7 are comparative examples using an acidic solution having pH buffer
action. High friction coefficients are exhibited.
- (4) Nos. 8 to 10, Nos. 51 to 53, and Nos. 64 to 66 are comparative examples in which
zinc ion is contained but the amount is smaller than the range of the invention. In
the case of the treatment of 30 seconds or more, the friction coefficient is low and
the maximum forming height is large but in the case of the treatment of 10 seconds,
a sufficient reduction in the friction coefficient and an increase in the maximum
forming height are not satisfied.
- (5) Nos. 11 to 13, Nos. 54 to 56, Nos. 67 to 69, and Nos. 14 to 16 are comparative
examples, wherein the zinc ion concentration is outside the claimed range. The comparative
examples were treated with a solution containing zinc ion. In the comparative examples
the friction coefficient decreases and also the maximum forming height increases.
- (6) Nos. 44 to 46 are examples of the invention in which the treatment conditions
were the same as those of Nos. 11 to 13 and the zinc ion concentration in the liquid
was increased. The friction coefficient becomes stable at lower levels and also the
maximum forming height further increases. Similarly, Nos. 57 to 59 and Nos. 70 to
72 are examples of the invention in which the treatment conditions were the same as
those of Nos. 54 to 56 and the zinc ion concentration in the liquid was increased.
The friction coefficient becomes stable at lower levels and also the maximum forming
height further increases.
- (7) Nos. 17 to 22 are examples in which a solution film was formed on the surface
of the steel sheets and the time until washing with water was carried out was changed.
In No. 17 which was washed with water without being held, the friction coefficient
merely slightly decreases. In contrast, in Nos. 18 to 22 in which the retention time
was 1 second or more, the friction coefficient decreases and also the bulging properties
stably increase.
- (8) Nos. 23 to 40 are examples in which the treatment liquid temperature was changed.
In Nos. 23 to 25 having a low treatment liquid temperature, effects of improving the
friction coefficient and the maximum forming height are not sufficient as compared
with the other examples. In contrast, Nos. 32 to 34 are examples having a high treatment
liquid temperature and effects of improving the friction coefficient or the maximum
forming height were sufficient but treatment unevenness was observed in many portions
and thus the appearance was not favorable as an exterior panel for automobiles.
- (9) Nos. 35 to 40 are examples of the invention in which the liquid film formation
amount was changed relative to Nos. 20 to 22. A comparison between the samples in
which the retention time until washing with water was carried out is the same shows
that when the liquid film amount was large, a sufficient reduction in the friction
coefficient and an increase in the maximum forming height are achieved but the friction
coefficient was slightly high and also the maximum forming height was small as compared
with the samples in which the liquid film amount was small.
- (10) Nos. 41 to 43 are comparative examples using a treatment liquid in which pH is
lower than the range of the invention. The effect of reducing the friction coefficient
is not observed and also an increase in the maximum forming height is not observed
as compared with Nos. 20 to 22.
[0061] Fig. 5 is a view showing the influence of the zinc ion concentration on the oxide
film thickness using Nos. 8 to 22 and Nos. 44 to 46 of Tables 1-1 and 1-2.
[0062] According to the present invention, a galvanized steel sheet having a low sliding
resistance during press forming and excellent press formability can be stably manufactured
at a saved space even under short-time manufacturing conditions. For example, even
when a high strength galvanized steel sheet which has a high forming load and is likely
to cause die galling, the sliding resistance during press forming is low and excellent
press formability can be achieved. Since the press formability is excellent, the invention
can be applied to wide ranging fields focusing on the application to automobile bodies.