U.S. patent application number 14/372912 was filed with the patent office on 2015-01-15 for method for prevention of yellowing on surface of steel sheet after pickling.
The applicant listed for this patent is JFE STEEL CORPORATION. Invention is credited to Shigeyuki Aizawa, Satoru Ando, Hiroyuki Masuoka, Kazuki Nakazato, Shoichiro Taira.
Application Number | 20150013716 14/372912 |
Document ID | / |
Family ID | 48799210 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150013716 |
Kind Code |
A1 |
Masuoka; Hiroyuki ; et
al. |
January 15, 2015 |
METHOD FOR PREVENTION OF YELLOWING ON SURFACE OF STEEL SHEET AFTER
PICKLING
Abstract
In a method for prevention of yellowing on a surface of a steel
sheet subjected to re-pickling, washing with water and drying after
a surface of a continuously annealed steel sheet is pickled to
remove Si-containing oxide layer from a surface layer of the steel
sheet, the surface of the steel sheet is held at a wet state
between the pickling and the re-pickling and between the
re-pickling and the washing, and more preferably the washing is
carried out with water having an iron ion concentration decreased
to not more than 20 g/L, whereby the yellowing on the surface of
the steel sheet after the pickling is prevented. Thus, cold rolled
steel sheets being excellent in not only the appearance quality but
also the phosphatability and corrosion resistance after painting
are manufactured stably.
Inventors: |
Masuoka; Hiroyuki;
(Chiyoda-ku, JP) ; Ando; Satoru; (Chiyoda-ku,
JP) ; Aizawa; Shigeyuki; (Chiyoda-ku, JP) ;
Nakazato; Kazuki; (Chiyoda-ku, JP) ; Taira;
Shoichiro; (Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Family ID: |
48799210 |
Appl. No.: |
14/372912 |
Filed: |
January 16, 2013 |
PCT Filed: |
January 16, 2013 |
PCT NO: |
PCT/JP2013/050678 |
371 Date: |
July 17, 2014 |
Current U.S.
Class: |
134/3 |
Current CPC
Class: |
C22C 38/06 20130101;
C23G 1/085 20130101; C23G 1/00 20130101; C23G 1/086 20130101; C22C
38/02 20130101; C23G 1/081 20130101; C22C 38/04 20130101; C21D 8/02
20130101; C23G 1/08 20130101; C21D 9/562 20130101; C21D 8/0278
20130101 |
Class at
Publication: |
134/3 |
International
Class: |
C23G 1/08 20060101
C23G001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2012 |
JP |
2012-007739 |
Claims
1-14. (canceled)
15. A method for prevention of yellowing on a surface of a steel
sheet subjected to re-pickling, washing with water and drying after
a surface of a continuously annealed steel sheet is pickled to
remove Si-containing oxide layer from a surface layer of the steel
sheet, characterized in that the surface of the steel sheet is held
at a wet state between the pickling and the re-pickling and between
the re-pickling and the washing.
16. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the washing is carried out
with washing water having an iron ion concentration decreased to
not more than 20 g/L.
17. The method for prevention of yellowing on a surface of a steel
sheet according to claim 16, wherein the washing water is further
characterized by decreasing a concentration of nitric acid ion to
not more than 10 g/L, a concentration of chloride ion to not more
than 5 g/L, a concentration of fluoride ion to not more than 5 g/L
and a concentration of sulfuric acid ion to not more than 5
g/L.
18. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the washing is conducted by
immersing into washing water at a temperature of not lower than
20.degree. C. for not less than 3 seconds.
19. The method for prevention of yellowing on a surface of a steel
sheet according to claim 16, wherein the washing is conducted by
immersing into washing water at a temperature of not lower than
20.degree. C. for not less than 3 seconds.
20. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the re-pickling is conducted
with a re-pickling solution having an iron ion concentration
decreased to not more than 40 g/L.
21. The method for prevention of yellowing on a surface of a steel
sheet according to claim 20, wherein the re-pickling solution is
further characterized by decreasing a concentration of nitric acid
ion to not more than 20 g/L.
22. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the re-pickling is conducted
with a non-oxidizing acid.
23. The method for prevention of yellowing on a surface of a steel
sheet according to claim 20, wherein the re-pickling is conducted
with a non-oxidizing acid.
24. The method for prevention of yellowing on a surface of a steel
sheet according to claim 22, wherein the non-oxidizing acid is
characterized to be any one of hydrochloric acid, sulfuric acid,
phosphoric acid, pyrophosphoric acid, formic acid, acetic acid,
citric acid, hydrofluoric acid, oxalic acid and a mixture of these
two or more acids.
25. The method for prevention of yellowing on a surface of a steel
sheet according to claim 23, wherein the non-oxidizing acid is
characterized to be any one of hydrochloric acid, sulfuric acid,
phosphoric acid, pyrophosphoric acid, formic acid, acetic acid,
citric acid, hydrofluoric acid, oxalic acid and a mixture of these
two or more acids.
26. The method for prevention of yellowing on a surface of a steel
sheet according to claim 22, wherein the non-oxidizing acid is
hydrochloric acid having a concentration of 0.1-50 g/L, sulfuric
acid having a concentration of 0.1-150 g/L or a mixture of
hydrochloric acid having a concentration of 0.1-20 g/L and sulfuric
acid having a concentration of 0.1-60 g/L.
27. The method for prevention of yellowing on a surface of a steel
sheet according to claim 23, wherein the non-oxidizing acid is
hydrochloric acid having a concentration of 0.1-50 g/L, sulfuric
acid having a concentration of 0.1-150 g/L or a mixture of
hydrochloric acid having a concentration of 0.1-20 g/L and sulfuric
acid having a concentration of 0.1-60 g/L.
28. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the pickling is conducted with
nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid or
a mixture of these two or more acids as a pickling solution.
29. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the pickling is conducted with
a mixture of nitric acid and hydrochloric acid or a mixture of
nitric acid and hydrofluoric acid as a pickling solution.
30. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the steel sheet is a cold
rolled steel sheet containing Si: 1.0-2.0 mass %.
31. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein the steel sheet contains C:
0.01-0.20 mass %, Mn: 1.0-3.0 mass %, P: not more than 0.05 mass %,
S: not more than 0.005 mass % and Al: not more than 0.06 mass % in
addition to Si: 1.0-2.0 mass %.
32. The method for prevention of yellowing on a surface of a steel
sheet according to claim 15, wherein a content ratio (Si/Mn) of Si
to Mn exceeds 0.4.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is the U.S. National Phase application of
PCT/JP2013/050678, filed Jan. 16, 2013, which claims priority to
Japanese Patent Application No. 2012-007739, filed Jan. 18, 2012,
the disclosures of each of these applications being incorporated
herein by reference in their entireties for all purposes.
FIELD OF THE INVENTION
[0002] This invention relates to a technique for the prevention of
yellowing on a pickled surface of a steel sheet.
BACKGROUND OF THE INVENTION
[0003] Recently, it is strongly demanded to improve fuel
consumption of an automobile from a viewpoint of protecting the
global environment. Also, the improvement in the safety of the
automobile is strongly demanded from a viewpoint of ensuring
occupants' safety at the time of impact. In order to meet these
demands, it is necessary to simultaneously attain weight saving and
high strengthening of an automobile body. In this connection,
thinning through the high strengthening is positively proceeding in
cold rolled steel sheets as a raw material for members of the
automobile. However, many members for the automobile are
manufactured by shape forming of steel sheets, so that these steel
sheets are required to have an excellent formability in addition to
the high strength.
[0004] There are various methods for increasing the strength of the
cold rolled steel sheet. As one of methods capable of attaining
high strength without largely damaging the formability is mentioned
a solid-solution strengthening method based on the addition of Si
or Mn. However, when a greater amount of Si or Mn, particularly not
less than 0.5 mass % of Si is added in the cold rolled steel sheet,
it is known that Si-containing oxides such as SiO.sub.2, Si--Mn
composite oxide and the like are formed on the surface of the steel
sheet in the slab heating or in the annealing after hot rolling or
cold rolling. Since the Si-containing oxide deteriorates the
phosphatability remarkably, there is a problem that the
high-strength cold rolled steel sheets containing a greater amount
of Si are poor in not only the phosphatability but also the
corrosion resistance after painting because they are liable to
cause peeling of the coating as compared with ordinary steel sheets
when they are exposed to severer corrosion environments such as an
immersion test in hot salt water and a composite cycle corrosion
test repeating wetting-drying after electrodeposition coating.
[0005] As a measure to this problem, Patent Document 1 proposes a
high-strength cold rolled steel sheet wherein Si concentration is
decreased on the surface of the steel sheet by heating a slab at a
temperature of not lower than 1200.degree. C. in the hot rolling,
descaling under a high pressure, grinding the surface of the hot
rolled steel sheet with an abrasive-containing nylon brush before
pickling and immersing in a 9% hydrochloric acid tank twice to
conduct pickling. Also, Patent Document 2 proposes a high-strength
cold rolled steel sheet having an improved corrosion resistance by
making a line width of a linear Si-containing oxide, which is
observed from the surface of the steel sheet to a depth of 1-10
.mu.m thereof, to not more than 300 nm.
[0006] In the high-strength cold rolled steel sheet disclosed in
Patent Document 1, however, the improvement of the corrosion
resistance after painting is not obtained even if the Si
concentration is decreased on the surface of the steel sheet before
the cold rolling because the Si-containing oxide is formed on the
surface of the steel sheet by annealing after the cold rolling. In
the high-strength cold rolled steel sheet disclosed in Patent
Document 2, the corrosion resistance does not come into question
under corrosion environment such as salt water spraying test
defined in JIS Z2371, but sufficient corrosion resistance after
painting is not obtained under severer corrosion environment such
as an immersion test in hot salt water or a composite cycle
corrosion test. That is, high-strength cold rolled steel sheets
having an excellent corrosion resistance after painting cannot be
obtained only by decreasing Si concentration on the surface of the
steel sheet after hot rolling or by decreasing the Si-containing
linear oxide.
[0007] As a technique of solving the above problems, Patent
Document 3 discloses a technique of improving the phosphatability
wherein the Si-containing oxide enriched on the surface of the
steel sheet at an annealing step or the like is removed by pickling
and further a S-based compound is applied onto the surface to
enhance reactivity with a phosphating solution. Patent Document 4
discloses a technique wherein a P-based compound is applied instead
of the S-based compound in the aforementioned technique.
[0008] On the other hand, the lowering of the temperature in the
phosphating solution is recently proceeding for the purpose of
decreasing industrial waste (suppressing formation of sludge) and
reducing the running cost, and hence the reactivity of the
phosphating solution to the steel sheet largely decreases as
compared with the conventional phosphate coating condition. The
lowering of the temperature in the phosphating solution does not
become problematic by improvement of surface adjustment technique
prior to phosphating or the like in the plain steel sheets with a
less alloy addition used from the past. In the high-strength cold
rolled steel sheets containing a greater amount of Si, however, the
reactivity with the phosphating solution is considerably
deteriorated by an influence of the Si-containing oxide formed on
the surface layer of the steel sheet at the annealing step, so that
it is necessary to enhance the reactivity from the side of the
steel sheet in some way. However, the techniques disclosed in
Patent Documents 3 and 4 are effective for the conventional plain
steel sheets, but have a problem that sufficient improving effects
capable of coping with the lowering of the temperature in the
phosphating solution cannot be expected in the high-strength cold
rolled steel sheets containing a greater amount of Si.
[0009] Now, the inventors have developed a production technique of
cold rolled steel sheets being excellent in not only the
phosphatability but also the corrosion resistance after painting by
pickling the surface of the steel sheet continuously annealed after
cold rolling with a strong acid to remove the Si-containing oxide
layer formed on the surface layer of the steel sheet during
annealing together with iron matrix and also by removing iron-based
oxide produced on the surface of the steel sheet after the above
pickling through re-pickling, which was filed as Japanese Patent
Application No. 2011-177861.
[0010] In the cold rolled steel sheet obtained by subjecting the
continuously annealed steel sheet to pickling, re-pickling, washing
with water (rinsing) and drying, however, the color in the surface
of the steel sheet may be sometimes changed into yellow to
considerably damage the appearance quality.
[0011] As a technique of preventing the above yellowing are made
some proposals. For example, Patent Document 5 proposes a technique
of preventing tarnish of a steel band by blowing a mixture of a
rinsing solution containing a yellowing-control agent and a
nitrogen gas to the steel band at a rinsing step for pickling
treatment of pickling the steel band, and Patent Document 6
proposes a technique of preventing tarnish of a steel band by
starting spray of a tarnish-preventing agent just before the stop
of a line in a cleaning step of spraying the tarnish-preventing
agent to the pickled steel sheet and then stopping spray of washing
water and thereafter passing the sheet over a given distance and
sequentially conducting stop of sheet passing and stop of spraying
the tarnish-preventing agent. Furthermore, Patent Documents 7 and 8
propose a technique of preventing tarnish by conducting spray of
hydrochloric acid between pickling and rinsing steps to hold pH of
a liquid film on the steel sheet at a low state.
PATENT DOCUMENTS
[0012] Patent Document 1: JP-A-2004-204350
[0013] Patent Document 2: JP-A-2004-244698
[0014] Patent Document 3: JP-A-2007-217743
[0015] Patent Document 4: JP-A-2007-246951
[0016] Patent Document 5: JP-A-2000-178775
[0017] Patent Document 6: JP-A-2006-131924
[0018] Patent Document 7: JP-A-2003-193275
[0019] Patent Document 8: JP-A-H02-270977
SUMMARY OF THE INVENTION
[0020] When a strong oxidative acid such as nitric acid is used as
a pickling solution even in the application of the techniques
disclosed in Patent Documents 5-8, it is difficult to prevent the
tarnish on the surface of the steel sheet completely. Also, in case
of spraying the yellowing-preventive agent of a high concentration
or hydrochloric acid, the yellowing-preventive agent or
hydrochloric acid flows into subsequent rinsing step, and hence
there are problems that the phosphatability is rather deteriorated
and the sufficient corrosion resistance cannot be obtained under
severer corrosion test after painting such as immersion test in hot
salt water or composite cycle corrosion test.
[0021] The present invention is made in view of the aforementioned
problems of the conventional techniques and is to propose a method
wherein yellowing is prevented on the surface of the steel sheet
after pickling and hence cold rolled steel sheets being excellent
in not only the appearance quality but also the phosphatability and
corrosion resistance after painting are manufactured stably.
[0022] The inventors have made various studies on the method for
preventing the yellowing on the surface of the steel sheet in order
to solve the above problems. As a result, it has been found out
that when cold rolled steel sheets are manufactured by pickling the
surface of the steel sheet and further re-pickling it, and
thereafter washing with water and drying, the surface of the steel
sheet is always held at a wet state over the above whole process
and more preferably concentrations of various contamination
components introduced into the water used for the above washing,
particularly concentration of iron ion are controlled, which are
very effective for preventing the yellowing on the surface of the
steel sheet, and the invention has been accomplished.
[0023] The invention includes a method for prevention of yellowing
on a surface of a steel sheet subjected to re-pickling, washing
with water and drying after a surface of a continuously annealed
steel sheet is pickled to remove Si-containing oxide layer from a
surface layer of the steel sheet, wherein the surface of the steel
sheet is held at a wet state between the pickling and the
re-pickling and between the re-pickling and the washing.
[0024] The method for prevention of yellowing on the surface of the
steel sheet according to an embodiment of the invention includes
washing carried out with water having an iron ion concentration
decreased to not more than 20 g/L.
[0025] In the method for prevention of yellowing on the surface of
the steel sheet according to an embodiment of the invention, the
washing water can be further characterized by decreasing a
concentration of nitric acid ion to not more than 10 g/L, a
concentration of chloride ion to not more than 5 g/L, a
concentration of fluoride ion to not more than 5 g/L and a
concentration of sulfuric acid ion to not more than 5 g/L.
[0026] The method for prevention of yellowing on the surface of the
steel sheet according to an embodiment of the invention can be
characterized in that the washing is conducted by immersing into
water at a temperature of not lower than 20.degree. C. for not less
than 3 seconds.
[0027] Also, the method for prevention of yellowing on the surface
of the steel sheet according to an embodiment of the invention can
be characterized in that the re-pickling is conducted with a
re-pickling solution having an iron ion concentration decreased to
not more than 40 g/L.
[0028] Further, the re-pickling solution according to an embodiment
of the invention can be characterized by decreasing a concentration
of nitric acid ion to not more than 20 g/L.
[0029] The method for prevention of yellowing on the surface of the
steel sheet according to an embodiment of the invention can be
characterized in that the re-pickling is conducted with a
non-oxidizing acid.
[0030] The non-oxidizing acid according to an embodiment of the
invention can be characterized to be any one of hydrochloric acid,
sulfuric acid, phosphoric acid, pyrophosphoric acid, formic acid,
acetic acid, citric acid, hydrofluoric acid, oxalic acid and a
mixture of these two or more acids.
[0031] Also, the non-oxidizing acid according to an embodiment of
the invention can be characterized to be hydrochloric acid having a
concentration of 0.1-50 g/L, sulfuric acid having a concentration
of 0.1-150 g/L or a mixture of hydrochloric acid having a
concentration of 0.1-20 g/L and sulfuric acid having a
concentration of 0.1-60 g/L.
[0032] Furthermore, the method for prevention of yellowing on the
surface of the steel sheet according to an embodiment of the
invention can be characterized in that the pickling is conducted
with nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric
acid or a mixture of these two or more acids as a pickling
solution.
[0033] Also, the method for prevention of yellowing on the surface
of the steel sheet according to an embodiment of the invention can
be characterized in that the pickling is conducted with a mixture
of nitric acid and hydrochloric acid or a mixture of nitric acid
and hydrofluoric acid as a pickling solution.
[0034] The steel sheet in the method for prevention of yellowing on
the surface of the steel sheet according to an embodiment of the
invention can be characterized to be a cold rolled steel sheet
containing Si: 1.0-2.0 mass %.
[0035] Also, the steel sheet in the method for prevention of
yellowing on the surface of the steel sheet according to an
embodiment of the invention can be further characterized to contain
C: 0.01-0.20 mass %, Mn: 1.0-3.0 mass %, P: not more than 0.05 mass
%, S: not more than 0.005 mass % and Al: not more than 0.06 mass %
in addition to Si: 1.0-2.0 mass %.
[0036] Moreover, the steel sheet in the method for prevention of
yellowing on the surface of the steel sheet according to an
embodiment of the invention can be characterized in that a content
ratio (Si/Mn) of Si to Mn exceeds 0.4.
[0037] According to the invention, the yellowing on the surface of
the steel sheet after the pickling can be prevented, so that it is
possible to stably manufacture cold rolled steel sheets being
excellent in not only the appearance quality but also the
phosphatability and corrosion resistance after painting.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0038] At first, a basic technical aspect of the invention will be
described.
[0039] Recently, high-strength cold rolled steel sheets are
frequently manufactured by recrystallizing the steel sheet after
cold rolling and simultaneously subjecting to finish annealing in a
continuous annealing furnace for providing desirable strength and
workability. In the continuous annealing furnace, a non-oxidizing
or reducing gas is usually used as an atmosphere gas, so that a dew
point is severely controlled. Even if the component or dew point of
the atmosphere gas in the annealing is severely controlled,
however, elements such as Si, Mn and the like, which are
easy-oxidizable as compared with Fe, form a Si-containing oxide
layer such as Si oxide (SiO.sub.2), Si--Mn composite oxide or the
like on the surface of the steel sheet. Among them, the Si--Mn
composite oxide is easily dissolved in an acid, but SiO.sub.2 is
formed not only on the surface of the steel sheet but also in the
inside of iron matrix because it is hardly soluble in an acid.
Therefore, it is known that the latter obstructs the etching
property of the steel sheet surface in the phosphating subjected as
an underground treatment for electrodeposition (phosphate
treatment) and badly affects the formation of sound phosphate
coating.
[0040] Now, the inventors have examined a method of improving the
phosphatability of the aforementioned steel sheet and found out
that it is effective to remove Si-containing oxide layer formed on
the surface of the steel sheet through continuous annealing or the
like together with iron matrix by pickling the surface of the cold
rolled steel sheet after the continuous annealing with a strong
acid such as nitric acid or the like. The term "Si-containing
oxide" means SiO.sub.2 or Si-Mn composite oxide formed on the
surface of the steel sheet or along crystal grain boundaries inside
the steel sheet in the annealing after slab heating or hot rolling
or cold rolling. The range existing these Si-containing oxides
varies depending upon the components of the steel sheet, annealing
conditions (temperature, time, and atmosphere) or the like, but is
said to be usually about 1 .mu.m from the surface of the steel
sheet.
[0041] Since nitric acid is strong oxidizable, however, when the
pickling is carried out with nitric acid, the Si-containing oxide
in the surface layer of the steel sheet can be removed, but an
iron-based oxide is newly formed and deposited on the surface of
the steel sheet after the pickling. As the surface coating ratio of
such an iron-based oxide becomes higher, the phosphatability and
the corrosion resistance after painting are rather deteriorated.
The inventors developed a technique of dissolving and removing such
an iron-based oxide by re-pickling with a non-oxidizing acid and
filed as aforementioned Japanese Patent Application No.
2011-177861.
[0042] The phosphatability is largely improved by applying the
above technique wherein the surface of the steel sheet after
continuous annealing is strongly pickled with nitric acid to remove
the Si-containing oxide layer existing on the surface layer and
further the iron-based oxide produced by the strong pickling is
removed with the non-oxidizing acid.
[0043] In the case of conducting the strong pickling as mentioned
above, however, the surface of the steel sheet may be changed into
yellow at moments (also referred to as "yellowing" hereinafter).
Also, when the phosphatability and the corrosion resistance after
painting are examined on such a yellowed steel sheet, they become
clear to be largely poor as compared with the steel sheet not
tarnished.
[0044] The inventors have ascertained causes of the yellowing and
found that the yellowing is caused when the steel sheet taken out
from a pickling tank is dried prior to the entering into a next
re-pickling tank or further when the steel sheet taken out from the
re-pickling tank is dried prior to the entering into a next washing
tank and that once the yellowing is caused, it retains without
easily removed even by the re-pickling or washing with water and
badly affects the subsequent phosphatability and the corrosion
resistance after painting.
[0045] Now, the inventors have made further examination on the
method for prevention of yellowing on the surface of the steel
sheet, and found that it is preferably to always hold the surface
of the steel sheet at a wet state (water wetting state) and more
preferably it is advantageous to limit the concentration of
contaminant ingredient, particularly iron ion contained in water
used in the washing or a re-pickling solution used in the
re-pickling.
[0046] Although the causes of the yellowing become not clear
sufficiently, the inventors believe as follows:
[0047] In the case of the strong pickling with nitric acid, the
Si-containing oxide layer is removed from the surface layer of the
steel sheet, but a film of the pickling solution containing nitric
acid ingredient with a strong oxidation force retains on the
surface of the steel sheet until washing with water. As a result,
the film of the pickling solution is dried on the surface of the
steel sheet during the drying process to concentrate the pickling
solution, and iron dissolving reaction is continuously proceeding
in the film of the pickling solution to simultaneously generate
iron ion (Fe.sup.2+, Fe.sup.3+ or the like) and hydrogen to thereby
raise pH, and hence the iron ion is deposited on the surface of the
steel sheet as an iron-based hydroxide. Also, since a greater
amount of the iron ion produced in the pickling solution through
pickling is introduced at a state of attaching to the steel sheet
into the washing water or the re-pickling solution and present
therein, it is also deposited on the surface of the steel sheet as
an iron-based hydroxide. Further, nitric acid ion, fluoride ion and
the like introduced by the same pickling solution are included in
the washing water or the re-pickling solution. If the concentration
of these ions is high, iron dissolving reaction is proceeding on
the surface of the steel sheet to produce iron ion, which further
increases the iron-based hydroxide. The iron-based hydroxide is
removed by subsequent washing with water as it is at a water
wetting state. However, if the iron-based hydroxide is adhered to
the surface of the steel sheet as an iron-based oxide by taking out
water molecule from the hydroxide once the surface of the steel
sheet is dried, such an oxide cannot be easily removed by
subsequent washing or re-pickling and is thought to cause the
yellowing on the surface of the steel sheet.
[0048] The steel sheet prior to the pickling according to an
embodiment of the invention is a steel sheet continuously annealed
after cold rolling, which is preferable to have the following
chemical composition.
[0049] Si: 1.0-2.0 mass %
[0050] Si is an element effective for attaining the increase of the
strength in steel because it is large in the solid-solution
strengthening capacity and increases the strength of the steel
without largely damaging the workability. When it is added as a way
for attaining high strength, the addition of not less than 1.0 mass
% is preferable. Si is also an element badly exerting on the
phosphatability and the corrosion resistance after painting, but
when it is less than 1.0 mass %, the influence due to the
deterioration of phosphating conditions is small. Also, when the
addition amount of Si is not more than 2.0 mass %, the bad
influence upon the productivity due to the deterioration of the hot
rolling or cold rolling property is small, and there is no
deterioration of the ductility in a steel sheet product. Therefore,
the addition of Si is preferably within a range of 1.0-2.0 mass %,
more preferably within a range of 1.0-1.6 mass %.
[0051] Also, the steel sheet of the invention is preferable to have
the following chemical composition in addition to Si when it is
applied to a high-strength cold rolled steel sheet used in an
automobile body and having a tensile strength TS of not less than
590 MPa.
[0052] C: 0.01-0.20 mass %
[0053] C is an element effective for increasing the strength of
steel and is further effective for producing residual austenite
having a TRIP (Transformation induced plasticity) effect, or
bainite and martensite. When C is not less than 0.01 mass %, the
above effect is obtained. Also, when C is not more than 0.20 mass
%, there is caused no deterioration of the weldability. Therefore,
C is added preferably within a range of 0.01-0.20 mass %, more
preferably, within a range of 0.10-0.20 mass %.
[0054] Mn: 1.0-3.0 mass %
[0055] Mn is an element for solid-solution strengthening the steel
to increase the strength and enhance the hardenability and having
an action promoting the formation of residual austenite or bainite
and martensite. Such effects are developed by the addition of not
less than 1.0 mass %. On the other hand, when Mn is not more than
3.0 mass %, the effects can be obtained without increasing the
cost. Therefore, Mn is added preferably within a range of 1.0-3.0
mass %, more preferably within a range of 1.0-2.8 mass %.
[0056] P: not more than 0.05 mass %
[0057] P is an element not damaging the drawability though the
solid-solution strengthening capacity is large, and is also an
element effective for attaining the high strength. Therefore, it is
preferable to be included in an amount of not less than 0.005 mass
%. Although P is an element damaging the spot weldability, there is
caused no problem when it is not more than 0.05 mass %. Therefore,
P is preferably not more than 0.05 mass %, more preferably not more
than 0.03 mass %.
[0058] S: not more than 0.005 mass %
[0059] Si is an impurity element inevitably incorporated into
steel, and is a harmful ingredient precipitating as MnS to
deteriorate the elongation and flange formability of the steel
sheet. In order not to deteriorate the elongation and flange
formability, S is preferable to be limited to not more than 0.005
mass %. More preferably, it is not more than 0.003 mass %.
[0060] Al: not more than 0.06 mass %
[0061] Al is an element added as a deoxidizer at a steel-making
step, and is also an element effective for separating a non-metal
inclusion, which degrades the elongation and flange formability, as
a slug. Therefore, it is preferable to be included in an amount of
not less than 0.01 mass %. On the other hand, when the addition
amount of Al is not more than 0.06 mass %, the above effect can be
obtained without bringing about the increase of the raw material
cost, so that the upper limit is preferable to be 0.06 mass %. More
preferably, it is a range of 0.02-0.04 mass %.
[0062] Si/Mn: more than 0.4
[0063] In the steel sheet of the invention, it is preferable that a
content ratio of Si to Mn (Si/Mn) is more than 0.4. When (Si/Mn)
exceeds 0.4, the high strength of not less than 590 MPa and the
excellent workability can be easily established simultaneously.
More preferably, it is more than 0.6.
[0064] The remainder other than the above components in the steel
sheet of an embodiment of the invention is Fe and inevitable
impurities. However, the other components may be added when they
are included in the chemical composition of the usual cold rolled
steel sheet and within a range not damaging the action and effect
of the invention.
[0065] The production method of the cold rolled steel sheet
according to an embodiment of the invention will be described
below.
[0066] The production method of the cold rolled steel sheet
according to an embodiment of the invention comprises the steps of
heating a steel raw material (slab) containing components such as
Si, Mn and the like, which are easily oxidizable as compared with
Fe, hot rolling, hot band annealing after hot rolling, if
necessary, pickling, cold rolling, continuously annealing to
provide desired strength and workability, pickling with a strongly
oxidizable acid such as nitric acid or the like as a pickling
solution to remove Si-containing oxide layer on a surface layer of
a steel sheet together with iron matrix, re-pickling with a
non-oxidizing acid to remove an iron-based oxide formed on the
surface of the steel sheet through the above pickling, washing with
water to remove the pickling solution or re-pickling solution
adhered to the surface of the steel sheet and reaction products
produced by the pickling or re-pickling, and then drying.
[0067] In the above production method, the procedure up to the
continuous annealing step may be conducted according to the
conventionally known usual manner and is not particularly limited.
However, the subsequent pickling and later steps are preferable to
be carried out under conditions mentioned below. In the invention,
it is particularly preferred that the surface of the steel sheet is
always kept at a wet state (water wetting state) without drying
over a period from the pickling to the re-pickling and a period
from the re-pickling to the washing with water and more preferably
that the concentration of iron ion in water used for the washing
and the re-pickling solution used for the re-pickling is reduced to
not more than a given value.
[0068] Next, the conditions of the pickling and subsequent steps
will be described concretely.
<Pickling>
[0069] On the surface layer of the steel sheet after the continuous
annealing containing more than 0.5 mass % of easy-oxidizing
components such as Si, Mn and the like are formed a greater amount
of Si-containing oxides such as SiO.sub.2, Si--Mn based composite
oxide and the like, so that the phosphatability and the corrosion
resistance after painting are considerably deteriorated. Therefore,
it is preferred that the Si-containing oxides in the surface layer
of the steel sheet after the continuous annealing are removed by
pickling with any acid such as nitric acid, hydrochloric acid,
hydrofluoric acid, sulfuric acid or a mixture of these acids.
[0070] Since SiO.sub.2 is hardly soluble in the acid, in order to
remove it through pickling, it is desirable to remove together with
iron matrix of the steel sheet with a strong acid such as nitric
acid or hydrofluoric acid. However, since nitric acid is
strong-oxidizable, Fe eluted by pickling is oxidized to produce
iron-based oxide covering the surface of the steel sheet, which
adversely exerts on the subsequent phosphatability and the
corrosion resistance after painting. In case of using nitric acid,
therefore, the concentration of nitric acid is preferable to be a
range of 100-200 g/L for suppressing the above adverse effect. When
it is not less than 100 g/L, the pickling force is sufficient.
While when it is not more than 200 g/L, the amount of the
iron-based oxide formed does not increase. More preferably, it is a
range of 110-150 g/L.
[0071] However, when the concentration of nitric acid is merely
limited to the above range, it is difficult to suppress the
formation of the iron-based oxide produced on the surface of the
steel sheet. In order to more surely suppress the formation of the
iron-based oxide on the surface of the steel sheet after the
pickling, it is preferable to conduct the pickling with such a
mixed acid that a concentration ratio R of hydrochloric acid having
an effect of breaking an oxide film to nitric acid (HCl/HNO.sub.3)
is within a range of 0.01-0.25 in addition to the limitation of
nitric acid concentration to the aforementioned range. When the
ratio R is not less than 0.01, the effect of suppressing the
formation of the iron-based oxide is obtained sufficiently. While,
when it is not more than 0.25, the dissolving amount of the steel
sheet does not decrease and the Si-containing oxide layer can be
removed easily.
[0072] Alternatively, when hydrofluoric acid is used instead of the
mixed acid of nitric acid and hydrochloric acid, the concentration
is preferable to be a range of 30-70 g/L. Further, in case of using
a mixed acid of nitric acid and hydrofluoric acid, it is preferable
to conduct the pickling with such a mixed acid that the
concentration ratio R (HF/HNO.sub.3) to nitric acid is within a
range of 0.01-0.25. When the ratio R is not less than 0.01, the
effect of suppressing the formation of the iron-based oxide is
obtained sufficiently. While, when it is not more than 0.25, the
dissolving amount of the steel sheet does not decrease and the
Si-containing oxide layer can be removed easily.
[0073] Moreover, the pickling is preferably conducted under
conditions that a temperature of the pickling solution is
20-70.degree. C. and a pickling time is 3-30 seconds even in the
use of any pickling solutions. Particularly, it is preferable to
use a mixed acid of nitric acid and hydrochloric acid or a mixed
acid of nitric acid and hydrofluoric acid because the excellent
effect of suppressing the formation of the iron-based oxide and the
effect of removing the Si-containing oxide layer are obtained. It
is more preferable to use a mixed acid of nitric acid and
hydrochloric acid.
<Re-Pickling>
[0074] In the steel sheet after the pickling, it is preferred to
conduct re-pickling for subsequently dissolving and removing the
iron-based oxide produced on the surface of the steel sheet through
the pickling. As an acid used in the re-pickling, it is preferable
to use a non-oxidizing acid, particularly any one of hydrochloric
acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, formic
acid, acetic acid, citric acid, hydrofluoric acid, oxalic acid and
a mixed acid of two or more. For example, when hydrochloric acid is
used as an acid for re-pickling, the concentration of hydrochloric
acid is preferably 0.1-50 g/L. Also, when sulfuric acid is used,
the concentration of sulfuric acid is preferably 0.1-150 g/L, while
when the mixed acid of hydrochloric acid and sulfuric acid is used
in the re-pickling, it is preferable that the concentration of
hydrochloric acid in the mixed acid is 0.1-20 g/L and the
concentration of sulfuric acid is 0.1-60 g/L. Further, in case of
using phosphoric acid, pyrophosphoric acid, formic acid, acetic
acid, citric acid, hydrofluoric acid or oxalic acid, it is
preferable that the concentration is 0.1-130 g/L in phosphoric
acid, 0.1-240 g/L in pyrophosphoric acid, 0.1-60 g/L in formic
acid, 0.1-80 g/L in acetic acid, 0.1-260 g/L in citric acid, 0.1-30
g/L in hydrofluoric acid and 0.1-120 g/L in oxalic acid,
respectively.
[0075] Moreover, the re-pickling is preferable to be conducted
under conditions that the temperature of the re-pickling solution
is 20-70.degree. C. and the treating time is 1-30 seconds even in
the use of any re-pickling solutions.
<Washing with Water, Drying>
[0076] The steel sheet after the re-pickling is subsequently
subjected to a step of washing with water by immersing in the
washing water or by spraying or brushing the washing water to
remove the pickling solution or re-pickling solution adhered to the
surface of the steel sheet and the reaction product produced on the
surface of the steel sheet through the pickling or re-pickling, and
then rapidly dried so as not to cause drying unevenness to thereby
provide a product sheet.
<Keep Wet>
[0077] In the production procedure of the invention comprising the
above pickling, re-pickling, washing and drying steps, it is
preferred that the surface of the steel sheet is always kept at a
wet state (water wetting state) without drying the surface of the
steel sheet over a period from the completion of the pickling to
the start of the subsequent re-pickling step and over a period from
the completion of the re-pickling to the start of the subsequent
washing step for preventing yellowing of the steel sheet. On the
surface of the steel sheet after the pickling and the re-pickling
is existent the iron-based oxide produced by pickling, while
greater amounts of iron ion included in the pickling solution or
the re-pickling solution or iron ion generated by dissolution
reaction of nitric acid ion or the like adhered to the surface of
the steel sheet is adhered as an iron-based hydroxide. These
iron-based oxide and iron-based hydroxide are modified upon drying
to cause yellowing.
[0078] Moreover, the method of keeping the surface of the steel
sheet at the wet state is not particularly limited. For example, a
method of spraying or mist-spraying water onto the surface of the
steel sheet, a method of increasing humidity to suppress drying, or
the like can be carried out between the pickling and the
re-pickling and between the re-pickling and the washing with water.
Moreover, water to be sprayed onto the surface of the steel sheet
is preferable to be fresh water. Especially, fresh water with pH 6
is preferable between the re-pickling and the washing with water,
and fresh water with pH: 6-7 is further preferable. However, the
re-pickling solution may be used between the pickling and the
re-pickling.
<Washing Water, Re-Pickling Solution>
[0079] By always keeping the surface of the steel sheet at the wet
state as mentioned above can be prevented the yellowing caused due
to the modification of the iron-based oxide or iron-based hydroxide
adhered to the surface of the steel sheet to a certain extent.
However, the iron-based hydroxide causing the yellowing is not
reduced, so that the sufficient effect may not be obtained. In the
invention, therefore, it is preferable that the concentration of
iron ion included in water used in the washing is limited to not
more than 20 g/L in order to prevent the adhesion of iron ion
causing the iron-based hydroxide onto the surface of the steel
sheet. More preferably, it is not more than 10 g/L.
[0080] In addition to the iron ion, the washing water contains a
greater amount of nitric acid ion, chloride ion, hydrofluoric acid
ion, sulfuric acid ion and the like, which are introduced from the
pickling solution or re-pickling solution into the steel sheet.
There is a fear that when these ions adhere to the surface of the
steel sheet, they dissolve iron matrix to increase the
concentration of iron ion on the surface of the steel sheet and
hence the iron-based hydroxide is produced and deposited onto the
surface of the steel sheet. Therefore, it is desirable to reduce
the concentration of these ions. Concretely, it is preferable to
limit the concentration to nitric acid ion: not more than 10 g/L,
chloride ion: not more than 5 g/L, fluoride ion: not more than 5
g/L and sulfuric acid ion: not more than 5 g/L, respectively. More
preferably, it is nitric acid ion: not more than 5 g/L, chloride
ion: 2.5 g/L, fluoride ion: not more than 2.5 g/L and sulfuric acid
ion: not more than 2.5 g/L.
[0081] Moreover, the aforementioned iron ion, nitric acid ion and
the like in the washing water are mainly introduced due to adhesion
of contaminant components in the re-pickling solution at the
re-pickling step to the surface of the steel sheet. In order to
reduce the iron ion or nitric acid ion in the washing water,
therefore, it is also desirable to set an upper limit on that the
concentration of iron ion or nitric acid ion in the re-pickling
solution. In the invention, it is preferable to limit the
concentrations of iron ion and nitric acid ion in the re-pickling
solution to not more than 40 g/L and not more than 20 g/L,
respectively. More preferably, iron ion is not more than 20 g/L and
nitric acid ion is not more than 10 g/L.
[0082] Moreover, it is preferable that the washing with water is
conducted by immersing in water at a temperature of not lower than
20.degree. C. for 3 seconds or more. When the temperature of the
washing water is not lower than 20.degree. C. and the washing time
is not less than 3 seconds, the surface of the steel sheet can be
washed sufficiently. On the other hand, when the temperature of the
washing water is not higher than 70.degree. C., there is no
increase of energy cost. Also, when the washing time is not more
than 30 seconds, it is not required to make equipment length long
or slow down the sheet passing rate. More preferably, the
temperature of the washing water is 30-50.degree. C., and the
immersion time is 4-20 seconds.
EXAMPLES
[0083] Steel raw materials A-F containing greater amounts of Si and
Mn as shown in Table 1 are subjected to hot rolling, pickling, cold
rolling and continuous annealing, and thereafter pickled,
re-pickled, washed with water and dried under various conditions
shown in Table 2 to provide high-strength cold rolled steel sheets
having various strengths. Then, a sample is taken out from each of
the above high-strength cold rolled steel sheets to evaluate the
degree of yellowing on the surface of the steel sheet by the
following method, while the sample is subjected to phosphating and
painting treatments under the following conditions and then
subjected to three corrosion tests of immersion test in hot salt
water, salt water spraying test and composite cycle corrosion test
to evaluate the corrosion resistance after painting.
[0084] (1) Evaluation of Yellowing
[0085] A test piece of 70 mm.times.150 mm is cut out from the
sample of the high-strength cold rolled steel sheet and an area
ratio of a yellowed portion are visually measured.
[0086] (2) Evaluation of Corrosion Resistance after Painting
a. Phosphating Conditions
[0087] Each of the test pieces used for the evaluation of the
yellowing is subjected to phosphating with a degreasing agent:
FC-E2011, a surface adjusting agent: PL-X and a phosphating agent:
Palbond PB-L3065 made by Japan Perkalizing Co., Ltd. so that an
amount of a phosphated film adhered is 1.7-3.0 g/m.sup.2 under the
following standard condition and comparative condition of lowering
a temperature of a phosphating solution.
<Standard Condition>
[0088] Degreasing step; treating temperature: 40.degree. C.,
treating time: 120 seconds [0089] Spray degreasing, surface
adjusting step; pH: 9.5, treating temperature: room temperature,
treating time: 20 seconds [0090] Phosphating step; temperature of
phosphating solution: 35.degree. C., treating time: 120 seconds
<Condition of Lowering Temperature>
[0091] Condition of lowering the temperature of the phosphating
solution in the above standard condition to 33.degree. C.
b. Corrosion Test
[0092] The surface of the test piece subjected to the phosphating
is subjected to electrodeposition with an electrodepositing paint
V-50 made by Nippon Paint Co., Ltd. so as to provide a film
thickness of 25 .mu.m and then subjected to the following three
corrosion tests.
<Immersion Test in Hot Salt Water>
[0093] After a cross cut flaw of 45 mm in length is formed on the
surface of the test piece subjected to the phosphating and
electrodeposition by means of a cutter, the test piece is immersed
in a solution of 5 mass % NaCl (60.degree. C.) for 240 hours,
washed with water and then dried and thereafter a tape peeling test
of adhering an adhesive tape onto a cut flaw portion and peeling
off therefrom is conducted to measure a maximum peeling full width
ranging from right to left of the cut flaw portion. When the
maximum peeling full width is not more than 5.0 mm, the corrosion
resistance in the immersion test in hot salt water can be evaluated
to be good.
[0094] <Salt Water Spraying Test (SST)>
[0095] After a cross cut flaw of 45 mm in length is provided on the
surface of the test piece subjected to the phosphating and
electrodeposition by means of a cutter, the test piece is subjected
to a salt water spraying test with an aqueous solution of 5 mass %
NaCl for 1000 hours according to a neutral salt water spraying test
defined in JIS Z2371:2000, and then a tape peeling test is
conducted on the cross cut flaw portion to measure a maximum
peeling full width ranging from right to left of the cut flaw
portion. When the maximum peeling full width is not more than 4.0
mm, the corrosion resistance in the salt water spraying test can be
evaluated to be good.
<Composite Cycle Corrosion Test (CCT)>.
[0096] After a cross cut flaw of 45 mm in length is provided on the
surface of the test piece subjected to the phosphating and
electrodeposition by means of a cutter, the test piece is subjected
to a corrosion test of 90 cycles repeating a cycle of salt water
spraying (aqueous solution of 5 mass % NaCl: 35.degree. C.,
relative humidity: 98%).times.2 hours.fwdarw.drying (60.degree. C.,
relative humidity: 30%).times.2 hours.fwdarw.wetting (50.degree.
C., relative humidity: 95%).times.2 hours and then washed with
water and dried, and thereafter a tape peeling test is conducted on
the cross cut flaw portion to measure a maximum peeling full width
ranging from right to left of the cut flaw portion. When the
maximum peeling full width is not more than 6.0 mm, the corrosion
resistance in the composite cycle corrosion test can be evaluated
to be good.
[0097] The results of the above tests are also shown in Table 2. As
seen from these results, the steel sheets of the invention, which
are obtained by pickling, re-pickling and washing with water under
conditions adaptable for the invention after the continuous
annealing, are small in not only the degree of yellowing but also
the maximum peeling full width in the all of the hot salt water
immersion test, salt water spraying test and composite cycle
corrosion test, and indicate good corrosion resistance after
painting. On the contrary, the steel sheets of the comparative
examples not satisfying the pickling conditions of the invention
cause yellowing or are poor in the corrosion resistance after
painting.
TABLE-US-00001 TABLE 1 Chemical composition (mass %) Steel symbol C
Si Mn P S Al Si/Mn Remarks A 0.04 1.4 2.2 0.025 0.003 0.04 0.64 590
grade high tensile strength B 0.12 1.1 1.4 0.030 0.002 0.03 0.79
590 grade high tensile strength C 0.12 1.6 1.3 0.028 0.003 0.03
1.23 590 grade high tensile strength D 0.17 1.2 2.0 0.015 0.002
0.04 0.60 780 grade high tensile strength E 0.18 1.5 2.6 0.010
0.003 0.03 0.58 1180 grade high tensile strength F 0.13 1.5 2.8
0.020 0.003 0.03 0.54 1180 grade high tensile strength
TABLE-US-00002 TABLE 2 Re-pickling conditions Keep wet conditions
ion Keep wet consitions presence concentration presence Pickling
conditions or Wet solution (g/L) or wet solution composition of
absence spray tem- composition of tem- nitric absence spray tem-
Test Steel pickling solution temperature time of or perature
pickling solution perature time iron acid of or perature No. symbol
(g/L) (.degree. C.) (s) keep wet mist kind (.degree. C.) pH (g/L)
(.degree. C.) (s) ion ion keep wet mist kind (.degree. C.) pH
Remarks 1 A nitric acid: 100 + 45 10 presence spray fresh 25 6.6
hydrochloric acid: 10 45 4 5.3 3.8 presence spray fresh 25 6.9
Invention hydrochloric acid: 10 water water Example 2 B nitric
acid: 100 + 45 10 presence spray fresh 25 6.7 hydrochloric acid: 10
45 4 4.9 3.9 presence spray fresh 25 6.8 Invention hydrochloric
acid: 10 water water Example 3 C nitric acid: 100 + 45 10 presence
spray fresh 25 6.7 hydrochloric acid: 10 45 4 5.2 4.2 presence
spray fresh 25 6.9 Invention hydrochloric acid: 10 water water
Example 4 D nitric acid: 100 + 45 10 presence spray fresh 25 6.7
hydrochloric acid: 10 45 4 5.1 4.4 presence spray fresh 25 6.9
Invention hydrochloric acid: 10 water water Example 5 E nitric
acid: 100 + 45 10 presence spray fresh 25 7 hydrochloric acid: 10
45 4 4.8 4.1 presence spray fresh 25 7.1 Invention hydrochloric
acid: 10 water water Example 6 F nitric acid: 100 + 45 10 presence
spray fresh 25 6.9 hydrochloric acid: 10 45 4 5.2 3.6 presence
spray fresh 25 6.8 Invention hydrochloric acid: 10 water water
Example 7 A nitric acid: 100 + 45 10 presence spray fresh 25 6.7
hydrochloric acid: 10 45 4 4.9 25.4 presence spray fresh 25 6.7
Invention hydrochloric acid: 10 water water Example 8 A nitric
acid: 100 + 45 10 presence spray fresh 25 6.8 hydrochloric acid: 10
45 4 5.1 9.5 presence spray fresh 25 6.7 Invention hydrochloric
acid: 25 water water Example 9 A nitric acid: 100 + 45 10 presence
spray fresh 25 6.8 hydrochloric acid: 10 45 4 5.2 8.2 presence
spray fresh 25 6.8 Invention hydrochloric acid: 15 water water
Example 10 A nitric acid: 100 45 10 presence spray fresh 25 6.5
hydrochloric acid: 10 45 10 5.3 7.8 presence spray fresh 25 6.6
Invention water water Example 11 A nitric acid: 100 + 45 10
presence mist fresh 25 6.2 hydrochloric acid: 10 45 4 7.8 4.9
presence mist fresh 25 6.1 Invention hydrochloric acid: 10 water
water Example 12 A nitric acid: 100 + 45 10 presence spray fresh 25
6.5 hydrochloric acid: 10 + 45 4 6.3 6.3 presence spray fresh 25
6.8 Invention hydrochloric acid: 10 water sulfuric acid: 30 water
Example 13 A nitric acid: 100 + 45 10 presence spray fresh 25 6.7
hydrochloric acid: 60 45 4 2.9 5.5 presence spray fresh 25 6.7
Invention hydrochloric acid: 10 water water Example 14 A nitric
acid: 100 + 45 10 presence spray fresh 25 6.7 sulfuric acid: 200 45
4 10.1 9.1 presence spray fresh 25 6.5 Invention hydrochloric acid:
10 water water Example 15 A nitric acid: 100 + 45 10 presence spray
fresh 25 6.7 hydrochloric acid: 30 + 45 4 5.3 8.2 presence spray
fresh 25 6.7 Invention hydrochloric acid: 10 water sulfuric acid:
70 water Example 16 A nitric acid: 100 + 45 10 presence spray fresh
25 6.8 hydrochloric acid: 10 45 4 7.2 4.3 presence spray fresh 25
6.6 Invention hydrochloric acid: 10 water water Example 17 A nitric
acid: 100 + 45 10 presence spray fresh 25 6.1 hydrochloric acid: 10
45 4 6.1 5.1 presence spray fresh 25 6.7 Invention hydrofluoric
acid: 10 water water Example 18 A nitric acid: 100 + 45 10 presence
mist fresh 25 6.9 hydrochloric acid: 10 45 4 41.2 2.1 presence mist
fresh 25 6.3 Invention hydrochloric acid: 10 water water Example 19
A nitric acid: 100 + 45 10 presence spray fresh 25 6.8 hydrochloric
acid: 10 45 4 5.8 3.3 presence spray fresh 25 6.5 Invention
hydrochloric acid: 10 water water Example 20 A nitric acid: 100 +
45 10 presence spray fresh 25 6.8 hydrochloric acid: 10 45 4 3.3
2.8 presence spray fresh 25 6.4 Invention hydrochloric acid: 10
water water Example 21 A nitric acid: 100 + 45 10 presence spray
fresh 25 6.8 hydrochloric acid: 10 45 4 7.6 3.4 presence spray
fresh 25 6.8 Invention hydrofluoric acid: 10 water water Example 22
A nitric acid: 100 + 45 10 presence spray fresh 25 6.7 hydrochloric
acid: 10 + 45 4 7.7 11.5 presence spray fresh 25 6.8 Invention
hydrochloric acid: 10 water sulfuric acid: 30 water Example 23 A
nitric acid: 100 + 45 10 presence spray fresh 25 6.3 hydrochloric
acid: 10 45 4 5.3 3.9 presence spray fresh 25 6.7 Invention
hydrochloric acid: 10 water water Example 24 A nitric acid: 100 +
45 10 absence -- -- -- -- hydrochloric acid: 10 45 4 4.9 12.8
absence -- -- -- -- Comparative hydrochloric acid: 10 Example 25 A
nitric acid: 100 + 45 10 absence -- -- -- -- hydrochloric acid: 10
45 4 4.5 10.1 presence spray fresh 25 6.7 Comparative hydrochloric
acid: 10 water Example 26 A nitric acid: 100 + 45 10 absence -- --
-- -- hydrochloric acid: 10 45 4 5.3 10.9 presence spray fresh 25
6.7 Comparative hydrochloric acid: 10 water Example Maximum peeling
full width Water washing condition after corrosion test (mm) ion
concentration in washing water (g/L) Ratio of temperature of
phosphating solution: 35.degree. C. 33.degree. C. immersion nitric
sulfuric yellowing hot composite Test Steel or temperature time
iron acid chloride fluoride acid after pickling salt water salt
water cycle No. No. spray (.degree. C.) (s) ion ion ion ion ion (%)
immersion test spray test corrosion test Remarks 1 A immersion 60 4
3.2 1.1 2.3 -- -- 0 4.0 2.9 5.1 5.2 Invention Example 2 B immersion
60 4 3.1 1.5 3.3 -- -- 0 4.1 3.1 5.0 5.3 Invention Example 3 C
immersion 60 4 3.5 1.5 3.2 -- -- 0 4.0 3.0 5.2 5.0 Invention
Example 4 D immersion 60 4 3.9 2.1 2.9 -- -- 0 4.0 3.1 5.1 5.2
Invention Example 5 E immersion 60 4 3.4 1.6 2.4 -- -- 0 4.1 3.2
5.2 5.3 Invention Example 6 F immersion 60 4 3.2 2.3 1.8 -- -- 0
4.1 3.1 5.1 5.4 Invention Example 7 A immersion 60 4 2.9 5.3 1.5 --
-- 0 4.4 3.4 5.4 5.6 Invention Example 8 A immersion 60 4 3.1 3.8
1.8 -- -- 0 4.3 3.5 5.3 5.5 Invention Example 9 A immersion 60 4
3.0 4.2 1.5 -- -- 0 4.4 3.4 5.4 5.7 Invention Example 10 A
immersion 60 4 2.9 4.5 2.1 -- -- 15 4.9 4.0 5.7 6.1 Invention
Example 11 A immersion 60 4 4.3 3.9 1.4 -- -- 0 4.5 3.5 5.3 5.9
Invention Example 12 A immersion 60 4 11.5 4.2 3.2 -- 1.5 0 4.6 3.7
5.3 5.8 Invention Example 13 A immersion 60 4 8.2 5.1 2.9 -- -- 0
4.3 3.6 5.5 5.7 Invention Example 14 A immersion 60 4 2.1 2.9 4.5
-- 4.8 0 4.5 3.7 5.5 5.7 Invention Example 15 A immersion 60 4 1.6
5.8 4.8 -- 1.5 0 4.5 3.5 5.4 5.8 Invention Example 16 A immersion
60 4 3.6 6.2 3.2 -- -- 0 4.6 3.6 5.5 5.8 Invention Example 17 A
immersion 60 4 7.1 6.9 4.9 1.2 -- 0 4.3 3.7 5.4 5.8 Invention
Example 18 A spray 60 4 5.5 2.3 2.1 -- -- 5 4.6 3.8 5.7 5.8
Invention Example 19 A immersion 60 4 4.3 12.1 0.9 -- -- 10 4.8 3.9
5.9 5.9 Invention Example 20 A immersion 60 4 3.8 4.2 5.1 -- -- 10
4.9 3.8 5.8 5.9 Invention Example 21 A immersion 60 4 9.2 3.5 1.5
5.5 -- 10 4.7 3.9 5.8 6.0 Invention Example 22 A immersion 60 4
13.9 4.6 2.1 -- 5.2 10 4.8 3.9 5.9 5.8 Invention Example 23 A
immersion 60 4 21.9 7.2 0.4 -- -- 10 4.8 3.8 5.8 5.9 Invention
Example 24 A immersion 60 4 4.2 5.8 1.5 -- -- 90 6.3 5.9 7.2 8.1
Comparative Example 25 A immersion 60 4 4.1 5.6 2.3 -- -- 65 4.9
4.0 5.9 6.3 Comparative Example 26 A immersion 60 4 20.4 5.6 2.3 --
-- 75 5.0 4.5 6.2 6.9 Comparative Example
[0098] The technique of the invention is not limited to
high-strength cold rolled steel sheets containing a greater amount
of Si or Mn and is applicable to all steel sheets for manufacturing
products by pickling.
* * * * *