U.S. patent application number 13/638108 was filed with the patent office on 2013-01-17 for ferritic stainless steel sheet excellent in surface gloss and corrosion resistance and method for producing same.
The applicant listed for this patent is Masaharu Hatano, Eiichiro Ishimaru, Shigenori Takahata, Akihito Yamagishi. Invention is credited to Masaharu Hatano, Eiichiro Ishimaru, Shigenori Takahata, Akihito Yamagishi.
Application Number | 20130017116 13/638108 |
Document ID | / |
Family ID | 44712212 |
Filed Date | 2013-01-17 |
United States Patent
Application |
20130017116 |
Kind Code |
A1 |
Hatano; Masaharu ; et
al. |
January 17, 2013 |
FERRITIC STAINLESS STEEL SHEET EXCELLENT IN SURFACE GLOSS AND
CORROSION RESISTANCE AND METHOD FOR PRODUCING SAME
Abstract
The stainless steel sheet according to the present invention is
a ferritic stainless steel which is comprised of, by mass %, C:
0.001 to 0.03%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, P: 0.005 to
0.05%, S: 0.0001 to 0.01%, Cr: 12 to 16%, N: 0.001 to 0.03%, Nb:
0.05 to 0.3%, Ti: 0.03 to 0.15%, Al: 0.005 to 0.5%, Sn: 0.01 to
1.0%, and has the remainder of Fe and unavoidable impurities and
satisfies the relationship of 1.ltoreq.Nb/Ti.ltoreq.3.5. The method
comprises heating a slab of stainless steel which contains the
above steel ingredients, setting the extraction temperature 1080 to
1190.degree. C., and setting the coiling temperature after the end
of hot rolling 500 to 700.degree. C. After hot rolling, the method
comprises annealing the hot rolled sheet, which can be omitted,
cold rolling once or cold rolling twice or more which includes
processing annealing, and finish annealing the steel sheet at 850
to 980.degree. C.
Inventors: |
Hatano; Masaharu;
(Chiyoda-ku, JP) ; Yamagishi; Akihito;
(Chiyoda-ku, JP) ; Takahata; Shigenori;
(Chiyoda-ku, JP) ; Ishimaru; Eiichiro;
(Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hatano; Masaharu
Yamagishi; Akihito
Takahata; Shigenori
Ishimaru; Eiichiro |
Chiyoda-ku
Chiyoda-ku
Chiyoda-ku
Chiyoda-ku |
|
JP
JP
JP
JP |
|
|
Family ID: |
44712212 |
Appl. No.: |
13/638108 |
Filed: |
March 22, 2011 |
PCT Filed: |
March 22, 2011 |
PCT NO: |
PCT/JP2011/057512 |
371 Date: |
September 28, 2012 |
Current U.S.
Class: |
420/36 ; 148/603;
420/41; 420/42; 420/60; 420/62; 420/64; 420/68; 420/70; 72/128 |
Current CPC
Class: |
C21D 8/0205 20130101;
C21D 6/002 20130101; C21D 2211/005 20130101; B21B 3/02 20130101;
C22C 38/26 20130101 |
Class at
Publication: |
420/36 ; 148/603;
420/42; 420/62; 420/70; 420/41; 420/60; 420/64; 420/68; 72/128 |
International
Class: |
C21D 8/02 20060101
C21D008/02; C22C 38/18 20060101 C22C038/18; C22C 38/26 20060101
C22C038/26; C22C 38/30 20060101 C22C038/30; B21B 1/02 20060101
B21B001/02; C22C 38/24 20060101 C22C038/24; C22C 38/20 20060101
C22C038/20; C22C 38/48 20060101 C22C038/48; C22C 38/50 20060101
C22C038/50; C22C 38/28 20060101 C22C038/28; C22C 38/32 20060101
C22C038/32 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2010 |
JP |
2010-076099 |
Oct 26, 2010 |
JP |
2010-239851 |
Claims
1. A ferritic stainless steel sheet which is excellent in surface
gloss and corrosion resistance, comprising: by mass %, C: 0.001 to
0.03%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.5%, P: 0.005 to 0.05%, S:
0.0001 to 0.01%, Cr: 12 to 16%, N: 0.001 to 0.03%, Nb: 0.05 to
0.3%, Ti: 0.03 to 0.15%, Al: 0.005 to 0.5%, and Sn: 0.01 to 1.0%;
the steel sheet having the remainder being Fe and unavoidable
impurities, and satisfying the relationship of
1.ltoreq.Nb/Ti.ltoreq.3.5.
2. The ferritic stainless steel sheet which is excellent in surface
gloss and corrosion resistance as set forth in claim 1, wherein
said stainless steel sheet further contains, by mass %, one element
or more of Ni: 0.01 to 0.5%, Cu: 0.01 to 0.5%, Mo: 0.01 to 0.5%, V:
0.01 to 0.5%, Zr: 0.01 to 0.5%, Co: 0.01 to 0.5%, Mg: 0.0001 to
0.005%, B: 0.0003 to 0.005%, and Ca: 0.0003 to 0.005%.
3. A method of production of a ferritic stainless steel sheet which
is excellent in surface gloss and corrosion resistance, comprising
of: heating a slab of stainless steel which contains the steel
ingredients described in claim 1, taking out the slab from the
heating furnace at an extraction temperature of 1080 to
1190.degree. C., and hot rolling and coiling the steel sheet at a
temperature of 500 to 700.degree. C.
4. The method of production of the ferritic stainless steel sheet
which is excellent in surface gloss and corrosion resistance as set
forth in claim 3, comprising of: coiling the steel sheet in hot
rolling, cold rolling, and finish annealing the steel sheet at 850
to 980.degree. C.
5. The method of production of the ferritic stainless steel sheet
which is excellent in surface gloss and corrosion resistance as set
forth in claim 3, comprising of: coiling the steel sheet in hot
rolling, cold rolling twice or more which includes processing
annealing, and finish annealing the steel sheet at 850 to
980.degree. C.
6. The method of production of the ferritic stainless steel sheet
which is excellent in surface gloss and corrosion resistance as set
forth in claim 4, comprising of: coiling the steel sheet in hot
rolling, and annealing the hot rolled sheet at an annealing
temperature of in the range of the recrystallization temperature to
1050.degree. C. before cold rolling.
Description
TECHNICAL FIELD
[0001] The present invention relates to an alloy-saving type
ferritic stainless steel sheet which is excellent in surface
glossiness and corrosion resistance and a method for producing the
same.
BACKGROUND ART
[0002] A ferritic stainless steel sheet is extensively used in
household electrical appliances, kitchen equipments, and other
fields in which corrosion resistance and surface quality in an
indoor environment are demanded. As examples of such a ferritic
stainless steel sheet, SUS430LX and SUS430J1L in the JIS standard
may be mentioned. Further, NPLT 1 describes representative examples
SUS430LX and SUS430J1L which are excellent in corrosion resistance.
Such a ferritic stainless steel reduces the C and N, contains Cr:
16 to 20%, Nb: 0.3 to 0.6%, and Ti and trace amounts of Cu and Mo
added compositely to prevent deterioration of the surface
properties due to pitting or rusting.
[0003] In the past, the above-mentioned ferritic stainless steel
sheet to which Nb, Ti, etc. have been added, has had the defect of
being inferior in surface glossiness compared with other ferritic
stainless steel sheet (SUS430) in the No. 3D finished or No. 2B
finished products prescribed in JIS G 4305 and G 4307. PLT 1
discloses the method of production of cold rolled steel strip which
is excellent in surface glossiness by the control of the amount of
oxide scale formation in annealing a ferritic stainless steel to
which Ti, Nb, etc. are added. Further, PLT 2 discloses the method
of descaling cold rolled steel strip and the method of production
of stainless cold rolled steel strip which is excellent in
glossiness and corrosion resistance which prescribes the step of
neutral salt electrolysis-nitrate electrolysis. While PLT 3
discloses the method of production of high glossiness stainless
steel strip which controls the roughness of the work roll and
lubrication conditions in cold rolling.
[0004] The above-mentioned ferritic stainless steel sheet is
excellent economically to an austenitic stainless steel sheet which
contains a large amount of Ni--which has remarkably risen in price
in recent years. However, due to the price fluctuations in the
component element Cr of stainless steel and the rising price of the
rare element Nb, it is difficult to say that SUS430LX and SUS430J1L
will also have economically sufficient in the future.
[0005] As a solution to the above problem, the method of improving
the corrosion resistance by utilizing trace elements may be
considered. PLT 4 and PLT 5 disclose a ferritic stainless steel
which proactively adds P so as to improve the weather resistance,
corrosion resistance, and crevice corrosion resistance. PLT 4 is a
high Cr and P ferritic stainless steel which contains Cr: over 20%
to 40% and P: over 0.06% to 0.2%. PLT 5 is a P ferritic stainless
steel which contains Cr: 11% to less than 20% and P: over 0.04% to
0.2%. However, P becomes a factor inhibiting manufacturability,
workability, and weldability.
[0006] The inventors have disclosed a ferritic stainless steel
which is improved in corrosion resistance by utilizing trace
elements--without relying on alloying of Cr or Mo from the
viewpoint of economy. PLT 6 is a ferritic stainless steel which
contains Cr: 13 to 22% and Sn: 0.001 to 1%, reduces the C, N, Si,
Mn, and P, and adds Ti: 0.08 to 0.35% as a stabilizing element.
However, these literatures do not study the effects on the surface
glossiness at all, as explained above.
CITATIONS LIST
Patent Literature
PLT 1: Japanese Unexamined Patent Publication No. 61-288021 A1
PLT 2: Japanese Unexamined Patent Publication No. 4-232297 A1
PLT 3: Japanese Unexamined Patent Publication No. 8-243603 A1
PLT 4: Japanese Unexamined Patent Publication No. 6-172935 A1
PLT 5: Japanese Unexamined Patent Publication No. 7-34205 A1
PLT 6: Japanese Unexamined Patent Publication No. 2009-174036
A1
Non Patent Literature
NPLT 1: Stainless Steel Handbook, 3rd Edition, P532
SUMMARY OF INVENTION
Technical Problem
[0007] As explained above, SUS430LX and SUS430J1L, which contain
16% or more of Cr and have Nb or other stabilizing elements added
to them, have economical problems in the future. On the other hand,
the ferritic stainless steel which utilizes trace elements to
improve the corrosion resistance, has problems from the viewpoint
of manufacturability and surface glossiness. In recent years, in
the stainless steel sheet which is used for household electrical
appliances, kitchen equipments, etc. a demand of the improvement in
surface glossiness increases.
[0008] Therefore, the present invention has as its theme to obtain
a corrosion resistance which is not different from SUS430LX or
SUS430J1L by an amount of Cr of less than 16% and strikingly
improve the surface glossiness in alloy-saving type ferritic
stainless steel sheet and has as its object the provision of
alloy-saving type ferritic stainless steel sheet and a method for
producing the same which, realize this.
Solution to Problem
[0009] The inventors engaged in in-depth studies to solve the above
problem. As a result, the inventors obtained the following new
findings which are the effect of improvement of corrosion
resistance due to the addition of Sn and, in addition, and the
relationship between the addition of the stabilizing elements Nb
and Ti and the surface glossiness in ferritic stainless steel with
an amount of Cr of less than 16%, and thereby completed the present
invention.
[0010] (a) To realize the effect of improvement of the corrosion
resistance due to addition of a trace amount of Sn, 12% or more of
an amount of Cr is required. In addition, to maintain the soundness
of the passivation film comprised of Cr and a trace amount of Sn,
it is effective to reduce the C, N, Si, Mn, P, and S and add Nb and
Ti which are stabilizing elements.
[0011] (b) Nb is a stabilizing element which is effective for
appearing an action in improving the corrosion resistance and
surface glossiness. In steel to which a trace amount of Sn is
added, that action is appeared from 0.05%. However, if adding Nb
0.3% or more, the rise in the hot rolling heating temperature and
annealing temperature of the steel material leads to a decrease in
the surface gloss due to the oxide scale.
[0012] (c) Ti has an action as a stabilizing element which
immobilizes C and N and, in addition, forms Ti-based carbosulfides
(for example, Ti.sub.4C.sub.2S.sub.2) at the time of heating for
hot rolling and suppresses the formation of MnS or CaS which form
starting points of rust. In steel to which a trace amount of Sn is
added, that action is appeared from 0.03%. However, if, adding Ti
0.15% or more, scabs due to inclusions and concentration of Ti in
the oxide film cause a decrease in surface glossiness.
[0013] (d) It was discovered that the effects of addition of Nb and
Ti in the above steel to which a trace amount of Sn is added,
remarkably appear in composite addition in the range of
1.ltoreq.Nb/Ti.ltoreq.3.5. That is, to improve the corrosion
resistance and surface glossiness of steel to which a trace amount
of Sn is added, it was found that it is effective to add mainly Nb,
which has a large action in improving the surface glossiness, and
compositely add a trace amount of Ti so as to suppress the
formation of starting points of rust and maintain the soundness of
the passivation film.
[0014] (e) The action of improvement of the surface glossiness due
to the addition of Nb is still unclear in many points, but the
cause of the decrease in the surface glossiness, that is, the
internal oxidation and grain boundary oxidation in heating for hot
rolling and annealing, are more suppressed due to the presence of
solute Sn and solute Nb. Therefore, the effect of improvement of
the glossiness due to the addition of Nb is believed to be obtained
due to the superposition with solute Sn.
[0015] (f) The extraction temperature after heating for hot
rolling, from the viewpoint of improvement of the glossiness, is a
temperature for securing the amount of scale formation for removing
inclusions at the cast slab surface layer which induce scabs and
for forming Ti-based carbon sulfides (for example,
Ti.sub.4C.sub.2S.sub.2) to suppress the formation of MnS or CaS
which forms rust. In a steel with an amount of Cr of less than 16%
and to which a trace amount of Sn is added, setting the temperature
1080 to 1190.degree. C. is effective.
[0016] (g) Coiling after hot rolling, from the viewpoint of
improvement of the surface glossiness, suppresses surface defects
at the time of coiling and suppresses internal oxides and grain
boundary oxidation which decrease in glossiness. In a steel with an
amount of Cr of less than 16% and to which a trace amount of Sn is
added, setting the temperature 500 to 700.degree. C. is effective.
Further, it is effective to set the annealing temperature
980.degree. C. or less from the viewpoint of securing
glossiness.
[0017] The gist of the present invention, obtained based on the
above findings (a) to (g), is as follows:
[0018] (1) A ferritic stainless steel sheet which is excellent in
surface glossiness and corrosion resistance comprising: by mass
%,
C: 0.001 to 0.03%,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.5%,
P: 0.005 to 0.05%,
S: 0.0001 to 0.01%,
Cr: 12 to 16%,
N: 0.001 to 0.03%,
Nb: 0.05 to 0.3%,
Ti: 0.03 to 0.15%,
Al: 0.005 to 0.5%, and
Sn: 0.01 to 1.0%; and
[0019] the steel sheet having the remainder being Fe and
unavoidable impurities, and satisfying the relationship of
1.ltoreq.Nb/Ti.ltoreq.3.5.
[0020] (2) The ferritic stainless steel sheet which is excellent in
surface glossiness and corrosion resistance as set forth in (1),
wherein the stainless steel sheet further contains, by mass %, one
element or more of
Ni: 0.01 to 0.5%,
Cu: 0.01 to 0.5%,
Mo: 0.01 to 0.5%,
V: 0.01 to 0.5%,
Zr: 0.01 to 0.5%,
Co: 0.01 to 0.5%,
Mg: 0.0001 to 0.005%,
B: 0.0003 to 0.005%, and
Ca: 0.0003 to 0.005%.
[0021] (3) A method of production of a ferritic stainless steel
sheet which is excellent in surface glossiness and corrosion
resistance, comprising of: heating a slab of stainless steel which
contains the steel ingredients described in the above (1) or (2),
taking out the slab from the heating furnace at an extraction
temperature of 1080 to 1190.degree. C., and hot rolling and coiling
the steel sheet at a temperature of 500 to 700.degree. C.
[0022] (4) The method of production of ferritic stainless steel
sheet which is excellent in surface glossiness and corrosion
resistance as set forth in (3), comprising of: coiling the steel
sheet in hot rolling, cold rolling and finish annealing the steel
sheet at 850 to 980.degree. C.
[0023] (5) The method of production of the ferritic stainless steel
sheet which is excellent in surface glossiness and corrosion
resistance as set forth in (3), comprising of: coiling the steel
sheet in hot rolling, cold rolling twice or more which includes
processing annealing, and finish annealing the steel sheet at 850
to 980.degree. C.
[0024] (6) The method of production of the ferritic stainless steel
sheet which is excellent in surface glossiness and corrosion
resistance as set forth in (4) or (5), comprising of: coiling the
steel sheet in hot rolling, and annealing the hot rolled sheet at
an annealing temperature of in the range of the recrystallization
temperature to 1050.degree. C. before cold rolling.
Advantageous Effects of Invention
[0025] According to the present invention, the remarkable effect is
exhibited of obtaining an alloy saving type ferritic stainless
steel sheet which is excellent in surface glossiness and corrosion
resistance which does not rise in alloy cost or manufacturing cost
and therefore is excellent in economy. The steel sheet has a
corrosion resistance no different from SUS430LX and SUS430J1L, and
remarkably improves the surface glossiness.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 shows the relationship between the Nb/Ti amount and
surface glossiness Ga45.degree. (0.degree.).
[0027] FIG. 2 shows the relationship between the Nb/Ti amount and
surface glossiness Ga45.degree. (90.degree.).
DESCRIPTION OF EMBODIMENTS
[0028] The requirements of the present invention will be explained
in detail. Note that the "%" of content of the elements means "mass
%".
[0029] [1] The reasons limitation of the ingredients will be
explained below.
Because C degrades the corrosion resistance, the upper limit of its
content is 0.03%. From the viewpoint of the corrosion resistance,
the less the content of C is, the better characteristics are
presented. The upper limit is preferably 0.02%, more preferably
0.01%, still more preferably 0.005%. Further, excessive reduction
leads to an increase in the refining cost, so the lower limit of
the content is 0.001%. Considering the corrosion resistance or
manufacturing cost, the lower limit is preferably 0.002%.
[0030] Si is sometimes added as a deoxidizing element. However, Si
is a solution strengthening element. From the viewpoint of the
suppression of the decrease in the workability, the upper limit is
1.0%. From the viewpoint of the workability, the less the content
of Si is, the better characteristics are presented. The upper limit
is preferably 0.6%, more preferably 0.3%, still more preferably
0.2%. Further, because an excessive reduction leads to an increase
in the refining cost, the lower limit of the Si content is 0.01%.
If considering the workability and manufacturing cost, the lower
limit is preferably 0.05%.
[0031] Since Mn is an element which forms MnS, the starting point
of rust, and inhibits the corrosion resistance, so content should
be as little as possible. From the viewpoint of suppression of the
decrease in the corrosion resistance, the upper limit of the
content is 1.5%. From the viewpoint of the corrosion resistance,
the less the content of Mn is, the better characteristics are
presented. The upper limit is preferably 1.0%, more preferably
0.3%, still more preferably 0.2%. Further, excessive reduction
leads to an increase in the refining cost, so the lower limit of
the content of Mn is 0.01%. Preferably, considering the corrosion
resistance and the manufacturing cost, the lower limit should be
0.05%.
[0032] Because P is an element which inhibits manufacturability and
weldability, the less the content of P is, the better
characteristics are presented. From the viewpoint of suppression of
the decrease in manufacturability and weldability, the upper limit
of the content is 0.05%. From the viewpoint of the
manufacturability and weldability, the less the content of P is,
the better characteristics are presented. The upper limit is
preferably 0.04%, more preferably 0.03%. Further, an excessive
reduction leads to an increase in the refining costs, so the lower
limit of the content of P is 0.005%. More preferably, considering
the manufacturing cost, it should be 0.01%.
[0033] S is an impurity element. It inhibits corrosion resistance
and hot workability. The less the content of S is, the better
characteristics are presented. To secure the corrosion resistance
and hot workability, the upper limit of the content of S is 0.01%.
From the viewpoint of the corrosion resistance or hot workability,
the less the content of S is, the better characteristics are
presented. The upper limit is preferably 0.005%, more preferably
0.003%, still more preferably 0.002%. Further, since an excessive
reduction leads to an increase in the refining cost, preferably the
lower limit of the content is 0.0001%. More preferably, considering
the corrosion resistance and manufacturing cost, the lower limit
should be 0.0002%.
[0034] Cr is an element of ferritic stainless steel. It is also an
essential element for securing the corrosion resistance. To secure
the corrosion resistance of the present invention, the lower limit
is 12%. The upper limit is 16% from the viewpoint of economy
compared with SUS430LX. Considering the corrosion resistance and
the amount of addition of Sn, it is preferably 13 to 15%.
[0035] N, as well as C, degrades the corrosion resistance, so the
smaller the content, the better, therefore the upper limit is
0.03%. From the viewpoint of the corrosion resistance, the less the
content of N, the better characteristics are presented. The upper
limit is preferably 0.02%, more preferably 0.012%. Further,
excessive reduction leads to an increase in the refining cost, so
preferably the lower limit is 0.001%. More preferably, considering
the corrosion resistance and manufacturing cost, the content should
be 0.005%.
[0036] Nb is an essential element for improving the corrosion
resistance and, in addition, improving the surface gloss in the
trace Sn steel of the present invention. The above effect is
expressed from 0.05% or more. However, excessive addition raises
the recrystallization temperature of the steel and conversely
causes a decrease in the surface glossiness. Therefore, the upper
limit is 0.3%. Preferably, considering the corrosion resistance,
surface glossiness, and manufacturability, the content is 0.1 to
0.2%.
[0037] Ti functions as a stabilizing element which immobilizes the
C and N and also is an essential element for improvement of the
corrosion resistance. The above effect is expressed from 0.03%.
However, excessive addition leads to a decrease in the surface
glossiness due to scabs caused by inclusions and concentration of
Ti in the oxide film. Therefore, the upper limit is 0.15%.
Preferably, considering the corrosion resistance, surface gloss,
and manufacturability, the content is 0.05 to 0.1%.
[0038] Because Al is an element which is effective as a deoxidizing
element, the lower limit of the content is 0.005%. However, since
excessive addition causes deterioration of the workability or
toughness and weldability, the upper limit of the content of Al is
0.5%. From the viewpoint of the workability, toughness, and
weldability, the less the content of Al is, the better
characteristics are presented. The upper limit is preferably 0.1%,
more preferably 0.05%, still more preferably 0.03%. Further,
considering the refining cost, the lower limit of the content is
more preferably 0.01%.
[0039] Sn is an essential element for securing the corrosion
resistance which is targeted by the present invention without
relying on alloying of Cr and No and addition of the rare elements
Ni, Co, etc. To obtain the corrosion resistance which is targeted
by the present invention, the lower limit of the content of Sn is
0.01%. To secure the better corrosion resistance, the content is
preferably 0.05% or more, more preferably 0.1% or more. However,
excessive addition leads to a decrease in the surface gloss or
manufacturability. The effect of improvement of the corrosion
resistance also becomes saturated. For this reason, the upper limit
is 1.0%. Considering the corrosion resistance and the surface
glossiness, the upper limit of the content is 0.5% or less, more
preferably 0.3%, still more preferably 0.2%.
[0040] Nb and Ti are added in the above ranges. The amounts of
addition should satisfy 1.ltoreq.Nb/Ti.ltoreq.3.5 to obtain the
corrosion resistance and the surface glossiness which are targeted
by the present invention. When Nb/Ti<1, surface gloss due to the
Ti-based inclusions or Ti-based oxides decreases. On the other
hand, when 3.5<Nb/Ti, surface gloss due to the internal
oxidation or grain boundary oxidation caused by the rise of the hot
rolling heating temperature and annealing temperature decreases.
The more preferable range is 1.5.ltoreq.Nb/Ti.ltoreq.3 considering
the corrosion resistance and surface glossiness which are targeted
by the present invention.
[0041] Ni, Cu, Mo, V, Zr, and Co are elements which improve the
corrosion resistance due to a synergistic effect with Sn and may be
added in accordance with need. When added, the contents are the
0.01% or more where this effect is exhibited, preferably 0.02% or
more. More preferably, the contents are 0.05% where the effect is
more remarkable. However, if over 0.5%, a rise in the material cost
or a decrease in the surface glossiness occurs, so the upper limits
of the contents are 0.5%. Since these elements are rare, in case of
adding these elements, the preferable ranges of Ni and Cu are 0.1
to 0.4%, while the preferable range of Mo is 0.1 to 0.3%. The
preferable ranges of V, Zr, and Co are 0.02 to 0.3%.
[0042] Mg forms Mg oxides in the molten steel together with Al and
acts as a deoxidant and also acts as nuclei for precipitation of
TiN. TiN forms the nuclei for solidification of the ferrite phase
in the solidification process. By promoting the crystallization of
TiN, it is possible to cause the fine formation of the ferrite
phase at the time of solidification. By refining the solidified
structure, it is possible to prevent surface defects due to ridging
or roping or other coarse solidified structures of the product. In
addition, it causes improvement of the workability. Therefore, it
may be added as needed. When added, the content is 0.0001% or more
for realizing these effects. However, if over 0.005%, the
manufacturability deteriorates, so the upper limit is 0.005%.
Preferably, considering the manufacturability, the content is
0.0003 to 0.002%.
[0043] B is an element which improves the hot workability and the
secondary workability. Addition to ferritic stainless steel is
effective, so it may be added as needed. When added, the content is
0.0003% or more for realizing these effects. However, excessive
addition leads to a decrease in the elongation, so the upper limit
is 0.005%. Preferably, considering the material cost and
workability, the content is 0.0005 to 0.002%.
[0044] Ca is an element which improves the hot workability and the
cleanliness of the steel and may be added as needed. When added,
the content is 0.0003% or more for realizing these effects.
However, excessive addition leads to a decrease in the
manufacturability or a decrease in the corrosion resistance due to
CaS and other water soluble inclusions, so the upper limit is
0.005%. Preferably, considering the manufacturability and corrosion
resistance, the content is 0.0003 to 0.0015%.
[0045] [II] The reasons for limitation of the production method
will be explained below.
One example of the production method which is required for
obtaining sheets which have the ingredients shown in the above
section [I] and which have the same corrosion resistances as
SUS430LX and SUS430J1L and surface gloss superior to SUS430LX and
SUS430J1L, will be shown.
[0046] A slab of steel which has the ingredients which are shown in
the above section [I] was inserted in a hot rolling heating furnace
and heated. The extraction temperature of the slab from the hot
rolling heating furnace was 1080.degree. C. or more so as to secure
an amount of scale formation for removing inclusions at the surface
layer of the cast slab which would lead to scabs. The amount of
scale formation should be, converted to scale thickness, 0.2 mm or
more. Further, the upper limit of the extraction temperature was
1190.degree. C. to suppress the formation of MnS or CaS which form
starting points of rust and stabilize Ti-based carbon sulfides (for
example Ti.sub.4C.sub.2S.sub.2). If considering securing the
corrosion resistance and the surface gloss which are targeted by
the present invention, the extraction temperature is preferably
1140 to 1180.degree. C.
[0047] The coiling temperature after hot rolling is 500.degree. C.
or more so as to suppress surface defects during coiling. If the
coiling temperature is less than 500.degree. C., the spraying of
water after hot rolling causes shape defects in the hot rolled
steel strip and induces surface defects at the time of uncoiling or
running operations. The coiling temperature is 700.degree. C. or
less so as to suppress the growth of internal oxides or grain
boundary oxidation which leads to a decrease in gloss. Over
700.degree. C., precipitates which contain Ti or P easily form and
are liable to lead to a decrease in corrosion resistance. If
considering securing the surface gloss and corrosion resistance
which are targeted by the present invention, the coiling
temperature is preferably 550 to 650.degree. C.
[0048] After coiling in hot rolling, the sheet is cold rolled. At
this time, before the cold rolling, the hot rolled sheet may also
be annealed. Further, the cold rolling may be performed once, or
twice or more. However, when cold rolling twice or more, process
annealing is performed between the cold rolling operations. When
annealing the hot rolled sheet, to suppress the growth of internal
oxides or grain boundary oxidation which is caused to a decrease in
gloss, the annealing temperature is preferably 1050.degree. C. or
less. Further, the lower limit of the annealing temperature is
preferably the recrystallization temperature of the steel
(850.degree. C. or so). Here, the "recrystallization temperature"
means the temperature where new strain-free crystal grains are
formed from the rolled worked structure. In the case of performing
process annealing between the cold rolling operations, it is
preferable to use a similar temperature range.
[0049] The conditions of the cold rolling are not particularly
limited. The finish annealing after the cold rolling is preferably
performed at 980.degree. C. or less by considering the surface
gloss. As explained above, the lower the annealing temperature, the
more the internal oxidation and grain boundary oxidation are
suppressed. It is advantageous for improvement of the surface
gloss. Therefore, the lower limit is preferably the
recrystallization temperature of 850.degree. C. The pickling method
is not particularly limited. There is no problem even if performed
by a method which is commonly used industrially. For example, there
are dipping in an alkali salt bath+electrolytic pickling+dipping in
nitrofluoric acid and dipping in an alkali salt bath+electrolytic
pickling. The electrolytic pickling may be performed by neutral
salt electrolysis, nitric acid electrolysis, etc.
EXAMPLES
[0050] Examples of the present invention will be explained as
follows.
[0051] A ferritic stainless steel which has the ingredients of
Table 1 was smelted, hot rolled by an extraction temperature of
1150 to 1220.degree. C., and coiled by a coiling temperature of 480
to 750.degree. C. to obtain hot rolled steel sheet of a thickness
of 4.0 to 6.0 mm. The hot rolled steel sheet was annealed, or not,
and was cold rolled once or twice interspaced by process annealing
to produce 0.4 to 1.0 mm thick cold rolled steel sheet. The
obtained cold rolled steel sheet was treated by finish annealing at
a temperature of completion of recrystallization of 870 to
1020.degree. C. and was treated by ordinary pickling to obtain the
No. 2B product in surface specifications prescribed in JIS G 4307.
For the ordinary pickling, for example, dipping in an alkali salt
bath (430.degree. C.), then treatment by neutral salt electrolysis
(50.degree. C., Na.sub.2SO.sub.4) may be used.
For the ingredients of the steel, both of the ranges prescribed by
the present invention and other ranges were used. For the
manufacturing conditions, both of the conditions prescribed by the
present invention and other conditions were used. For the
comparative steel, SUS430LX (17% Cr--0.3% Ti) was used.
[0052] The surface gloss was evaluated by measuring the gloss
45.degree. Gloss value (Gs45.degree.) in the rolling direction of
the steel sheet (0.degree.) and in the direction perpendicular to
the rolling (90.degree.) prescribed in JIS Z 8741. The corrosion
resistance was evaluated by preparing samples of steel sheets
(thickness.times.100 mm square) of No. 2B surfaces and #600
polished surfaces and running tests dipping them in a 80.degree.
C., 0.5% NaCl aqueous solution for 168 hr and salt spray tests
based on JIS Z 2371 (168 hr continuous spray test). The extent of
rusting was evaluated compared with SUS430LX as "Very good" in the
case of a good level with no stains or spot rusting, as "Good" in
the case of an equivalent level and no difference, and as "Poor" in
the case of rust streaks or other inferior level. Table 2 shows the
test results.
TABLE-US-00001 TABLE 1 C Si Mn P S Cr N Nb Ti Al Sn Nb/Ti Others
Remarks A 0.003 0.11 0.09 0.021 0.001 12.2 0.012 0.21 0.09 0.028
0.31 2.3 Inv. steel B 0.003 0.09 0.1 0.014 0.001 15.7 0.011 0.15
0.07 0.035 0.05 2.1 Inv. steel C 0.009 0.07 0.08 0.02 0.001 13.8
0.008 0.14 0.04 0.04 0.18 3.5 Ca: 0.003, B: 0.003 Inv. steel D
0.002 0.05 0.28 0.022 8E-04 14.6 0.009 0.15 0.07 0.02 0.12 2.1 Inv.
steel E 0.003 0.05 0.05 0.015 0.002 15.2 0.009 0.16 0.06 0.032 0.13
2.7 Inv. steel F 0.003 0.11 0.12 0.022 0.002 14.8 0.017 0.12 0.07
0.022 0.15 1.7 Inv. steel G 0.004 0.11 0.09 0.012 0.001 12.5 0.016
0.27 0.13 0.03 0.25 2.1 Inv. steel H 0.004 0.09 0.11 0.021 9E-04
14.6 0.009 0.06 0.05 0.016 0.15 1.2 Ni: 0.1, Cu: 0.1 Inv. steel I
0.005 0.11 0.08 0.015 8E-04 14.4 0.008 0.12 0.08 0.035 0.11 1.5 Mo:
0.2, Mg: 0.005 Inv. steel J 0.018 0.05 0.28 0.022 8E-04 14.1 0.009
0.17 0.08 0.02 0.12 2.1 V: 0.2 Inv. steel K 0.001 0.8 0.03 0.022
7E-04 14.8 0.006 0.16 0.09 0.02 0.13 1.8 Co: 0.05, Zr: 0.05 Inv.
steel L 0.002 0.01 0.8 0.022 5E-04 14.5 0.005 0.13 0.09 0.02 0.12
1.4 V: 0.02, Co: 0.015, Zr: 0.015 Inv. steel M 0.002 0.12 0.15
0.022 0.001 14.4 0.011 0.12 0.08 0.085 0.11 1.5 Inv. steel N 0.005
0.08 0.08 0.02 0.001 14.2 0.009 0.13 0.1 0.042 0.11 1.30 B: 7 ppm,
Ca: 3 ppm Inv. steel O 0.034 0.09 0.12 0.022 0.002 13.2 0.012 0.14
0.06 0.04 0.09 2.3 Comp. steel P 0.003 0.11 1.55 0.023 0.002 13.3
0.013 0.15 0.05 0.045 0.11 3.0 Comp. steel Q 0.007 0.12 0.13 0.023
0.011 13.1 0.012 0.15 0.06 0.042 0.12 2.5 Comp. steel R 0.005 0.11
0.11 0.021 0.001 11.7 0.013 0.14 0.07 0.045 0.11 2.0 Comp. steel S
0.006 0.11 0.12 0.023 0.001 13.3 0.011 0.32 0.09 0.05 0.11 3.6
Comp. steel T 0.004 0.11 0.11 0.021 9E-04 13.3 0.012 0.04 0.05 0.05
0.09 0.8 Comp. steel U 0.004 0.11 0.09 0.023 0.002 13.2 0.011 0.12
0.17 0.05 0.11 0.7 Comp. steel V 0.003 0.11 0.11 0.023 0.002 13.2
0.011 0.09 0.02 0.05 0.11 4.5 Comp. steel
TABLE-US-00002 TABLE 2 Gloss Corrosion resistance Annealing Times
of Final Gs45.degree. Dipping in Spraying of Hot rolling (.degree.
C.) after hot cold annealing No. Steel 0.degree. 90.degree. 0.5%
NaCl 3.5% NaCl Extraction Coiling rolling rolling (.degree. C.)
Remarks Inv. ing. 1 A 680 620 Good Good 1140 580 Yes 1 870 Inv. ex.
2 B 720 680 Very good Very good 1180 600 Yes 1 950 Inv. ex. 3 C 800
750 Good Good 1160 590 Yes 1 940 Inv. ex. 4 D 780 730 Very good
Very good 1180 610 Yes 1 930 Inv. ex. 5 E 820 780 Very good Very
good 1180 680 Yes 1 945 Inv. ex. 6 F 790 730 Very good Good 1180
550 Yes 1 950 Inv. ex. 7 850 800 Very good Very good 1160 600 No 2
950 Inv. ex. 8 630 550 Good Good 1050 480 No 1 950 Inv. ex. 9 630
550 Good Good 1180 620 Yes 1 1020 Inv. ex. 10 G 690 630 Good Good
1150 600 Yes 1 880 Inv. ex. 11 H 720 670 Good Very good 1160 600
Yes 1 930 Inv. ex. 12 I 800 750 Very good Very good 1180 680 Yes 1
940 Inv. ex. 13 850 820 Very good Very good 1160 550 Yes 2 930 Inv.
ex. 14 840 810 Very good Very good 1160 650 No 2 940 Inv. ex. 15
640 550 Good Good 1220 750 Yes 1 960 Inv. ex. 16 680 600 Good Good
1160 650 Yes 1 990 Inv. ex. 17 J 720 650 Good Good 1180 650 Yes 1
940 Inv. ex. 18 K 680 630 Good Good 1180 550 Yes 1 950 Inv. ex. 19
L 650 620 Good Good 1180 650 Yes 1 950 Inv. ex. 20 M 640 620 Good
Good 1180 550 Yes 1 960 Inv. ex. 21 N 790 760 Good Good 1150 580
Yes 1 910 Inv. ex. Comp. ing. 22 O 750 700 Poor Good 1180 600 Yes 1
930 Comp. ex. 23 P 700 650 Poor Poor 1180 600 Yes 1 930 Comp. ex.
24 Q 680 650 Poor Poor 1180 620 Yes 1 930 Comp. ex. 25 R 700 650
Poor Poor 1160 600 Yes 1 890 Comp. ex. 26 S 580 550 Good Good 1180
620 Yes 1 1000 Comp. ex. 27 T 590 500 Good Good 1180 630 Yes 1 870
Comp. ex. 28 U 600 510 Good Good 1180 600 Yes 1 940 Comp. ex. 29 V
610 520 Poor Poor 1180 600 Yes 1 870 Comp. ex. SUS430LX 610 520
Reference Reference (spot 1200 650 Yes 1 920 Conv. ex. (stains)
rusting) (Note 1) Evaluation of corrosion resistance/Compared with
SUS430LX, Very good: Excellent (no stains or spot rusting) Good: No
difference (equal) Poor: Inferior (streaks of rust)
[0053] From Table 2, Test No. 1 to 21 are ferritic stainless steel
which satisfies all of the ingredients which are limited in the
present invention. It was found that these steel sheets have higher
surface gloss compared with SUS430LX (gloss of SUS430LX at
Ga45.degree. (0.degree.)=610 or more and gloss at Ga45.degree.
(90.degree.)=520 or more) and have corrosion resistance which is
higher than or the same quality as SUS430LX.
[0054] Test No. 8, 9, 15, and 16 have the ingredients which are
prescribed in the present invention, but deviate from the method of
production according to the present invention (extraction
temperature and coiling temperature). These steel sheets satisfy
the corrosion resistance or gloss which is targeted by the present
invention, but the gloss is inferior to other examples of the
present invention.
[0055] Test No. 22 to 29 are the production method which is
prescribed in the present invention, but using ingredients are
deviated from that of the present invention. These steel sheets
cannot give both the surface gloss and corrosion resistance which
are targeted in the present invention.
[0056] FIG. 1 and FIG. 2 show the relationship between the amounts
of Nb/Ti and the surface gloss in the examples. To obtain the
surface gloss which is targeted by the present invention, that is,
Gs45.degree. (0.degree.) of 610 or more and) Gs45.degree.
(90.degree.) of 520 or more corresponding to SUS430LX, it is
important to obtain the ranges of ingredients according to the
present invention being 1.ltoreq.Nb/Ti.ltoreq.3.5.
INDUSTRIAL APPLICABILITY
[0057] According to the present invention, it is possible to obtain
an alloy-saving type ferritic stainless steel excellent in surface
gloss and corrosion resistance, which is economically excellent
without rising in alloy cost or manufacturing cost, has a corrosion
resistance of SUS430LX or SUS430J1L, and is strikingly improved in
surface gloss.
* * * * *