JP2019112673A - Ferritic stainless cold rolled steel sheet and manufacturing method thereof - Google Patents

Abstract

To provide a ferritic stainless cold rolled steel sheet having sufficient corrosion resistance and good surface quality with gold dust defect sufficiently suppressed.SOLUTION: A method of manufacturing a ferritic stainless cold rolled steel sheet, in which a steel material having a predetermined composition is subjected to hot rolling to form a hot rolled steel sheet, the hot rolled steel sheet is subjected to hot rolled sheet annealing, shot blasting and pickling in this order, and is subsequently subjected to cold rolling and cold rolled sheet annealing, comprises a heating temperature in the hot rolled sheet annealing being 800 to 900°C, a holding time being 1 to 24 hours, collision energy in the shot blasting being 10 to 40 kJ/m, an average particle size of shot blasting particles used for the shot blasting being 0.2 to 1.0 mm, and a hardness being HV350 to 550 in Vickers hardness.SELECTED DRAWING: None

Description

  The present invention relates to a ferritic stainless cold-rolled steel sheet having sufficient corrosion resistance and good surface beauty and a method of manufacturing the same.

  Japan Industrial Standard: SUS430 (16 to 18 mass% Cr steel) specified in JIS G 4305 is inexpensive and excellent in corrosion resistance among ferritic stainless cold rolled steel sheets, so various construction materials, home appliances, kitchen utensils etc. Used for various purposes.

In addition to the formability which can be processed into a predetermined shape by press forming etc., the steel plate applied to these uses has sufficient corrosion resistance, good surface gloss and surface properties (hereinafter collectively referred to as surface aesthetics It is required to have the
In particular, in recent years, there are many products that make use of the metallic luster of stainless steel as a material, and therefore, a ferritic stainless cold-rolled steel sheet excellent in surface beauty is strongly required.

Here, as a factor to reduce the surface beauty of the ferritic stainless cold-rolled steel sheet, particularly, a gold dust (which may be referred to as glitter) which is a defect of surface exfoliation type may be mentioned.
As a technique for reducing such gold dust, for example, Patent Document 1
“% By weight, C: 0.0010 to 0.30%, N: 0.0010 to 0.050%, Cr: 10.0 to 30.0%, S: not more than 0.010%, P: 0. 04% or less, Mn: 0.01 to 1.0%, Si: 0.01 to 1.0%, Ni: 1.0% or less, O: 0.010% or less, further, Sn: 0.. A ferritic stainless steel excellent in surface properties characterized by containing one or more of 005 to 0.10%, Sb: 0.005 to 0.10%, and the balance being Fe and unavoidable impurities. "
Is disclosed.

Patent Document 2 also includes
"During pickling after hot rolling, soak in a sulfuric acid aqueous solution containing an acid pick accelerator for 100 seconds or more, and that the major axis / minor axis of the steel plate is 2 or more, and the falling defect area rate is 0.1% or less A method of manufacturing a ferritic stainless steel plate characterized by the above.
Is disclosed.

Patent No. 3904683 Patent No. 3878024 gazette

Here, in Patent Document 1, it is considered that the cause of the gold dust is intergranular corrosion (intergranular corrosion) generated at the time of sulfuric acid pickling after hot-rolled sheet annealing caused by grain boundary segregation of P. And in patent document 1, in order to prevent grain boundary segregation of P which arises at the time of hot-rolled sheet annealing etc., 0.5 or 2 times of 1 or more types of Sn or Sb is added to content of P. And
However, when a protective film used for preventing handling wrinkles during steel storage is attached to the ferritic stainless steel described in Patent Document 1, there is a place where a gold dust wrinkle occurs when the protective film is peeled off, and thus gold It can not be said that the dust weir has been sufficiently suppressed.

  Also in Patent Document 2, although the cause of the gold dust is considered as intergranular corrosion (intergranular corrosion) generated during pickling after hot-rolled sheet annealing, it corresponds to SUS 430 manufactured according to the manufacturing method of Patent Document 2 When a protective film used to prevent wrinkles in steel handling is attached to a ferritic stainless cold rolled steel plate, there is a place where a gold dust is generated when the protective film is peeled off, and the gold dust is still sufficient. It could not be said that it was suppressed.

  As described above, simply preventing the intergranular corrosion (intergranular erosion) that occurs during pickling after hot-rolled sheet annealing can not sufficiently suppress the gold dust, and therefore it has sufficient corrosion resistance. At the same time, development of ferritic stainless cold-rolled steel sheet with good surface beauty and suppression of gold dust and its production technology are required at present.

  The present invention has been developed in view of the above-mentioned present situation, and it is advantageous to have a ferritic stainless cold-rolled steel sheet which has sufficient corrosion resistance and good surface beautifulness which sufficiently suppresses gold dust. It aims at providing with the various manufacturing methods.

Here, “sufficient corrosion resistance” means salt water spray cycle test (35 ° C., 5% by mass NaCl, spray time: 2 hours) → drying (60 ° C., relative humidity 40) according to the salt spray cycle test defined in JIS H 8502. %, Retention time: 4 hours → wet (50 ° C., relative humidity 9595%, retention time: 2 hours) as one cycle for 8 cycles of rust area ratio on the steel sheet surface (rust generation on steel sheet surface) The area / total surface area of the surface of the test steel plate) × 100 (%)) means that 25% or less.
Also, "good surface beauty" is
When the surface of the steel sheet is visually observed using a loupe (magnifying glass) with a magnification of 10, there is no oxide scale residue and shot blast residue,
・ Also, surface peeling test, that is, an acrylic adhesive having an adhesive strength of 1.80 N / 20 mm applied to the surface of a steel plate, a width of 100 mm, and a length of 200 mm of polyethylene film (manufactured by Nitto Denko Corporation metal The surface protection material for plate, SPV-363) is pasted so that the film longitudinal direction is perpendicular to the rolling direction of the steel plate, and then the surface peel test is performed to peel the film in the film longitudinal direction. Peeling defects (hereinafter also referred to as surface peeling defects) occurring on the surface are 5 or less per 100 cm ² ,
It means that.
Here, the surface peeling defect means a peeling defect (peeling portion) of 10 μm or more in equivalent circle diameter. The peeling depth is approximately 5 μm. Moreover, although it peels in circular shape in many cases, it may peel in the canyon shape with directivity. Furthermore, the number of spots per 100 cm ^{2 of} surface exfoliation defects is the number of spots of surface exfoliation defects observed by observing the steel sheet surface of the part from which the above-mentioned film was peeled off with a scanning electron microscope at a magnification of 100 × 200. It is calculated from the observation visual field area.
In addition, cold-rolled steel sheet is subjected to cold-rolled sheet annealing after cold rolling, and then the scale formed at the time of cold-rolled sheet annealing is removed by pickling, and further temper rolling is performed if necessary. It also includes steel plates (cold-rolled and acid-washed steel plates) and steel plates (cold-rolled and annealed steel plates) obtained by cold-rolled bright annealing as cold-rolled sheet annealing and further temper rolling as required.

Now, the inventors have conducted various studies in order to solve the above-mentioned problems.
as a result,
(1) While limiting the Si content of the component composition to 0.40 mass% or less,
(2) Properly control hot-rolled sheet annealing conditions during production;
(3) Furthermore, shot blasting is performed prior to pickling after hot-rolled sheet annealing, and the processing conditions, particularly the collision energy, are properly controlled.
It is important to obtain a ferritic stainless steel cold rolled steel sheet with good surface aesthetics, with suppressed gold dust,
The findings of the

That is, ferritic stainless cold-rolled steel sheets are generally required in the order of hot rolling, hot rolled sheet annealing, shot blasting, pickling, cold rolling and cold rolled sheet annealing, and also after cold rolled sheet annealing. Accordingly, it is manufactured through the steps of pickling and temper rolling.
As described above, in the prior art represented by Patent Documents 1 and 2, intergranular corrosion (hereinafter also referred to simply as intergranular corrosion) mainly caused by generation of gold dust is mainly generated in pickling after hot-rolled sheet annealing. Was considered to be).
However, when the inventors conducted various experiments, a large number of gold dust may be generated even if intergranular corrosion does not occur, and therefore, the inventors may generate gold dust. It came to think that intergranular corrosion as conventionally considered was not the main cause.

  Therefore, the present inventors repeated many experiments, and under the same conditions as a steel plate in which a large number of gold dust particles were generated, an intermediate material steel plate during production of the steel plate, specifically, pickling after hot-rolled sheet annealing. Steel sheet in the applied stage (hereinafter, also referred to as hot-rolled and acid-washed steel sheet) and steel sheet obtained immediately after cold rolling (cold-rolled steel sheet before cold-rolled sheet annealing), hereinafter, cold-rolled A variety of steel plates were produced, and the detailed metallographic structure of the surface layer portion of the hot-rolled annealed / pickled steel plate and the steel plate as cold-rolled was observed.

as a result,
In the surface layer portion of a hot rolled annealed and pickled steel plate manufactured under the same conditions as a steel plate in which a large number of gold dust defects are generated, micro cracks are generated on some grain boundaries,
・ Also, in the surface layer of the as-cold-rolled steel plate manufactured under the same conditions as the steel plate in which a large number of gold dust defects are generated, cracks on grain boundaries found in the above-described hot-rolled annealed and pickled steel plate develop significantly doing,
-And, if a predetermined protective film is attached to the place where the crack has progressed, and the protective film is peeled off after a certain period of time, a surface peeling defect occurs at the place where the crack develops, which causes gold dust疵 occurs,
I found that.

Therefore, based on the above findings, the inventors believe that the crack on the grain boundary found in the surface layer of the hot rolled annealed / pickled steel sheet is a factor causing the generation of gold dust, and this hot rolled annealing / acidic Various studies were repeated in order to suppress the cracks on grain boundaries found in the surface layer of the steel sheet.
As a result, shot blasting conditions in the production process of a ferritic stainless cold-rolled steel sheet, in particular, the occurrence of cracks on the grain boundary where impact energy was observed in the surface layer portion of hot-rolled annealing and pickling steel sheet, and eventually gold dust It was found to be correlated with the occurrence of epilepsy.

Here, the inventors consider as follows the reason why the condition of shot blasting treatment, in particular the impact energy, is correlated with the generation of gold dust.
That is, the component composition of SUS430 series does not contain an element (hereinafter, also referred to as a stabilization element) that stabilizes C and N, such as Ti and Nb, and so on. It is easy to precipitate a large amount of carbonitrides. For this reason, the toughness of the hot-rolled annealed steel plate in the middle of the production of SUS430 is much lower than that of the hot-rolled annealed steel plate in the middle of the manufacture of a ferritic stainless steel to which a stabilizing element is added.
On the other hand, in the shot blasting process, the counter stress (tensile residual stress generated inside the plate thickness corresponding to the compressive deformation due to the shot blasting) becomes maximum at the depth position from the surface to about several tens to 100 μm .
For this reason, when shot blasting a steel plate with low toughness with high collision energy, it can not withstand the collision energy of shot blasting, and the crystal grain in the depth position from several tens to 100 μm from the surface where the counter stress becomes maximum In the world, micro cracks occur.
Since the crack is generated at a depth position of several tens to 100 μm from the surface, the crack generated particularly at a position deep from the surface remains without being removed even by the subsequent acid washing. Then, the remaining cracks propagate on grain boundaries by shear stress due to subsequent cold rolling, and the expanded cracks also remain on a cold-rolled steel plate to be a final product to generate gold dust.
For these reasons, the present inventors believe that the shot blasting conditions, in particular the impact energy, correlates with the generation of gold dust.

And when the inventors repeated examinations further,
(1) Limit the Si content to 0.40 mass% or less, and (2) properly control the hot-rolled sheet annealing conditions at the time of production,
In this way, the toughness of the hot-rolled annealed steel sheet is enhanced while the thickness of the oxide scale formed during hot rolling is made as thin as possible.
(3) The conditions of the shot blasting treatment applied to the hot-rolled annealed steel sheet, in particular, the collision energy is controlled in the range of 10 to 40 kJ / m ² ,
By
It is possible to suppress the occurrence of cracks on grain boundaries found in the surface layer of hot rolled annealed / pickled steel sheet while avoiding oxide scale residue and shot blast mark residue in pickling after shot blasting treatment. ,
As a result, it is possible to obtain a ferritic stainless cold-rolled steel sheet having good surface beautifulness, which suppresses gold dust,
The findings of the
The present invention has been completed after further investigation based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. In mass%,
C: 0.015 to 0.050%,
Si: 0.05 to 0.40%,
Mn: 0.45 to 1.00%,
P: 0.04% or less,
S: 0.010% or less,
Cr: 16.0 to 18.0%,
Al: 0.001 to 0.010%,
N: 0.025 to 0.080% and Ni: 0.05 to 0.60%
Is hot rolled to a steel material having a component composition containing the remainder and Fe and incidental impurities to form a hot rolled steel sheet, and the hot rolled steel sheet is subjected to hot rolled sheet annealing, shot blasting and pickling A method for producing a ferritic stainless cold-rolled steel sheet, which is applied in this order to form a hot-rolled annealed / pickled steel sheet and then cold-rolled and cold-rolled sheet annealing is applied to the hot-rolled annealed / pickled steel sheet,
The heating temperature in the hot-rolled sheet annealing is 800 to 900 ° C., and the holding time is 1 to 24 hours,
The collision energy in the shot blasting treatment is 10 to 40 kJ / m ² , and the average particle diameter of shot blasting grains used in the shot blasting treatment is 0.2 to 1.0 mm, and the hardness is HV 350 to 550 in Vickers hardness. A method of manufacturing a ferritic stainless cold rolled steel sheet.
Here, the collision energy in the shot blasting process is defined by the following equation (1).
[Collision energy (kJ / m ² )] = (1/2 × A × B ² ) / 1000 (1)
A: Projection density of shot blasting particles [kg / m ² ]
B: Speed of shot blasting particles at the time of arrival at steel plate [m / s]

2. The method for producing a ferritic stainless cold-rolled steel sheet according to the above 1, wherein the shot blasting grain has a projection density of 25 to 45 kg / m ² and the speed of the shot blasting grain reaching the steel plate of ²⁰ to 45 m / s.

3. The ferritic stainless cold-rolled steel sheet manufactured by the method of producing a ferritic stainless cold-rolled steel sheet according to 1 or 2 above.

4. The ferritic stainless steel cold rolled steel sheet according to the above 3, wherein the surface peeling defect generated when the surface peeling test is performed is 5 or less per 100 cm ² .

  According to the present invention, it is possible to stably manufacture a ferritic stainless cold-rolled steel sheet having sufficient corrosion resistance and good surface beautifulness with sufficiently suppressed gold dust under high productivity. It becomes.

It is an example of the electron micrograph in which the gold dust weir was observed. It is an example of the electron micrograph in which the gold dust weir was observed.

Hereinafter, the present invention will be specifically described.
First, the composition of the ferritic stainless cold-rolled steel sheet of the present invention and the composition of the steel material used in the method of producing the ferritic stainless cold-rolled steel sheet of the present invention will be described. In addition, although the unit in a component composition is all "mass%", unless otherwise indicated, it only shows by "%" unless it refuses.

C: 0.015 to 0.050%
C is an element effective in promoting the formation of an austenite phase during hot rolling and suppressing the occurrence of ridging and roping that impairs surface beauty. From the viewpoint of obtaining such an effect, the C content is made 0.015% or more. However, if the C content exceeds 0.050%, the toughness of the steel decreases and gold dust tends to be generated.
Therefore, the C content is in the range of 0.015 to 0.050%. The lower limit of the C content is preferably 0.025%. The upper limit of the C content is preferably 0.045%.

Si: 0.05 to 0.40%
Si is an element which acts as a deoxidizer at the time of steel melting. From the viewpoint of obtaining such an effect, the Si content is made 0.05% or more. However, if the Si content exceeds 0.40%, the oxide scale mainly formed during hot rolling becomes excessively thick. For this reason, unless the collision energy in shot blasting is increased, sufficient descaling effect can not be obtained by pickling, and as a result, oxidation scale residue and shot blast marks left in pickling after shot blasting are avoided. At the same time, it becomes impossible to obtain good surface beauty that suppresses gold dust.
Therefore, the Si content is in the range of 0.05 to 0.40%. The lower limit of the Si content is preferably 0.10%, more preferably 0.20%. The upper limit of the Si content is preferably 0.35%, more preferably 0.30%.

Mn: 0.45 to 1.00%
Mn, like C, is an element effective in promoting the formation of an austenitic phase during hot rolling and suppressing the occurrence of ridging and roping that impairs the surface beauty. From the viewpoint of obtaining such an effect, the Mn content is set to 0.45% or more. On the other hand, if the Mn content exceeds 1.00%, the steel hardens and the ductility and toughness decrease. In addition, the corrosion resistance may also decrease.
Therefore, the Mn content is in the range of 0.45 to 1.00%. The lower limit of the Mn content is preferably 0.50%, more preferably 0.55%. The upper limit of the Mn content is preferably 0.90%, more preferably 0.80%.

P: 0.04% or less P is an element that promotes intergranular fracture due to intergranular segregation. Therefore, the lower the P content, the better, and the upper limit is made 0.04%. Preferably it is 0.03% or less. More preferably, it is 0.01% or less.

S: 0.010% or less S is an element that is present in the steel as a sulfide-based inclusion such as MnS to reduce ductility, corrosion resistance, and the like. In particular, when the S content exceeds 0.010%, the adverse effect of S becomes large.
Therefore, it is desirable that the S content be as low as possible, and the upper limit of the S content is 0.010%. Preferably it is 0.007% or less. More preferably, it is 0.005% or less.

Cr: 16.0 to 18.0%
Cr is an element having the effect of forming a passive film on the surface of the steel sheet to improve the corrosion resistance. From the viewpoint of obtaining such an effect, the Cr content is made 16.0% or more. However, if the Cr content exceeds 18.0%, the amount of austenitic phase formed during hot rolling may be reduced to reduce the ridging resistance.
Therefore, the Cr content is in the range of 16.0 to 18.0%. The upper limit of the Cr content is preferably 17.0%, more preferably 16.5%.

Al: 0.001 to 0.010%
Al, like Si, is an element that acts as a deoxidizer. From the viewpoint of obtaining such an effect, the Al content is made 0.001% or more. However, if the Al content exceeds 0.010%, Al-based inclusions such as Al ₂ O ₃ increase and it tends to cause deterioration of the surface properties.
Therefore, the Al content is in the range of 0.001 to 0.010%. The lower limit of the Al content is preferably 0.002%. The upper limit of the Al content is preferably 0.007%, more preferably 0.005%.

N: 0.025 to 0.080%
N, like C and Mn, is an element effective in promoting the formation of an austenite phase during hot rolling and suppressing the occurrence of ridging and roping that impairs surface beauty. From the viewpoint of obtaining such an effect, the N content is set to 0.025% or more. However, if the N content exceeds 0.080%, the toughness of the steel sheet is significantly reduced and gold dust tends to be generated.
Therefore, the N content is in the range of 0.025 to 0.080%. The lower limit of the N content is preferably 0.040%. The upper limit of the N content is preferably 0.060%, more preferably 0.055%.

Ni: 0.05 to 0.60%
Like C, N and Mn, Ni is an element effective in promoting the formation of an austenite phase during hot rolling and suppressing the occurrence of ridging and roping which impairs the surface beauty. In addition, Ni is an element effective for improving the corrosion resistance. From the viewpoint of obtaining such an effect, the Ni content is made 0.05% or more. However, if the Ni content exceeds 0.60%, the steel is excessively hardened and the formability is reduced. Therefore, the Ni content is in the range of 0.05 to 0.60%. The lower limit of the Ni content is preferably 0.10%. The upper limit of the Ni content is preferably 0.50%, more preferably 0.30%.

  The components other than the above are Fe and unavoidable impurities.

Next, the manufacturing conditions of the method for manufacturing the ferritic stainless steel cold rolled steel sheet of the present invention will be described.
The method for producing a ferritic stainless cold rolled steel sheet according to the present invention comprises subjecting a steel material having the above-described composition to hot rolling to form a hot rolled steel sheet, hot rolled steel sheet, hot rolled sheet annealing, shot blasting and Pickling is applied in this order to form a hot-rolled annealing / pickling steel plate, and then the hot-rolled annealing / pickling steel plate is subjected to cold rolling and cold-rolled sheet annealing. Yes,
The heating temperature in the hot-rolled sheet annealing is 800 to 900 ° C., the holding time is 1 to 24 hours, the collision energy in the shot blasting is 10 to 40 kJ / m ² , and the shot blasting is used. The average particle diameter of shot blasting particles is 0.2 to 1.0 mm, and the hardness is HV 350 to 550 in Vickers hardness.

That is, molten steel having the above-described component composition is melted by a known method such as a converter, an electric furnace, a vacuum melting furnace, etc., and made into a steel material (slab) by a continuous casting method or an ingot-slump method.
Then, the obtained steel material is suitably heated at 1100 to 1250 ° C. for 1 to 24 hours, or a high temperature steel material is directly heated, and then the steel material is subjected to hot rolling to obtain a hot rolled steel sheet I assume. The hot rolling conditions may be in accordance with a conventional method.
Next, hot rolled sheet annealing is performed on the obtained hot rolled steel sheet under the following conditions.

<Heating temperature of hot rolled sheet annealing: 800 to 900 ° C.>
If the heating temperature is less than 800 ° C., recrystallization does not occur sufficiently, so that the machined structure generated at the time of hot rolling remains, and the effect of improving formability can not be obtained.
On the other hand, when the heating temperature exceeds 900 ° C., the oxide scale formed during the hot rolling is increased. For this reason, a sufficient descaling effect can not be obtained by pickling unless the collision energy in shot blasting is increased. On the other hand, since the crystal grains are coarsened and the toughness of the steel plate is significantly reduced, when the collision energy in the shot blasting treatment is increased, cracks occur on the grain boundaries of the hot-rolled annealed steel plate to attract gold dust. Do. Therefore, it is not possible to obtain good surface beauty with reduced gold dust while avoiding oxide scale residue and shot blast trace residue in pickling after shot blasting.
Therefore, the heating temperature of hot-rolled sheet annealing shall be 800-900 ° C. The preferable lower limit of the heating temperature of hot-rolled sheet annealing is 820 ° C. Moreover, the preferable upper limit of the heating temperature of hot-rolled sheet annealing is 880 degreeC.

<Holding time of hot-rolled sheet annealing: 1 to 24 hours>
In addition, when the holding time at the above heating temperature is less than 1 hour, recrystallization does not occur sufficiently, so that the processed structure generated in the hot rolling remains, and the necessary formability can not be obtained. On the other hand, when the holding time exceeds 24 hours, an increase in the scale of oxide formed during hot rolling is caused. For this reason, unless the collision energy in shot blasting is increased, sufficient descaling effect can not be obtained by pickling, and as a result, oxidation scale residue and shot blast marks left in pickling after shot blasting are avoided. At the same time, it becomes impossible to obtain good surface beauty that suppresses gold dust.
Therefore, the holding time of hot-rolled sheet annealing is 1 to 24 hours. The preferable lower limit of the holding time of hot-rolled sheet annealing is 6 hours. Moreover, the suitable upper limit of the holding time of hot-rolled sheet annealing is 18 hours.

In order to prevent the oxide scale increases, the hot-rolled sheet annealing is preferably performed at 75 vol% N ₂ -25 vol% H ₂ and in a reducing atmosphere such as 100 vol% H ₂ Further, the hot-rolled sheet There is no limitation in particular in the method of annealing, It may carry out by either box annealing (batch annealing) and continuous annealing. The conditions other than the above are not particularly limited, and may be in accordance with the ordinary method.

  Then, the hot-rolled annealed steel sheet obtained by the above-described hot-rolled sheet annealing is subjected to a shot blasting treatment under the following conditions.

<Collision energy: 10 to 40 kJ / m ² >
The hot rolled annealed steel sheet is subjected to shot blasting prior to pickling in order to provide sufficient strain and / or crack to the oxide scale formed during hot rolled sheet annealing to effectively remove the oxide scale. .
Here, when the collision energy exceeds 40 kJ / m ² , it can not withstand the collision energy of shot blasting, and it is minute on the grain boundary at a depth position of about several 10 to 100 μm from the surface where the counter stress becomes maximum. Cracks often occur. Since the crack is generated at a depth position of several tens to 100 μm from the surface, the crack generated particularly at a position deep from the surface remains without being removed even by the subsequent acid washing. Then, the remaining cracks propagate on grain boundaries by shear stress due to subsequent cold rolling, and the expanded cracks also remain on the cold rolled steel sheet as the final product to generate many gold dust deposits. . In addition, there is a possibility that shot blast marks may be left.
On the other hand, when the collision energy is less than 10 kJ / m ² , a sufficient descaling effect can not be obtained by pickling, resulting in oxidation scale residue in pickling after shot blasting.
Therefore, the collision energy in the shot blasting treatment is 10 to 40 kJ / m ² . Preferably it is 20 kJ / m ² or more. Moreover, Preferably it is 35 kJ / m < ² > or less. More preferably, it is 33 kJ / m ² or less, still more preferably 32 kJ / m ² or less.
Furthermore, in particular, when the Si content is 0.30% or more, the oxide scale formed by hot-rolled sheet annealing becomes thick, and the descaling property is reduced. For this reason, when the Si content is 0.30% or more, it is more preferable to set the collision energy in the shot blasting process to 30 kJ / m ² or more.

Here, the collision energy in the shot blasting process is defined by the following equation (1).
[Collision energy (kJ / m2)] = (1/2 × A × B ² ) / 1000 (1)
A: Projection density of shot blasting particles [kg / m ² ]
B: Speed of shot blasting particles at the time of arrival at steel plate [m / s]

<Projected density of shot blasting particles: 25 to 45 kg / m ² >
As described above, in order to suppress the generation of cracks on grain boundaries in the hot-rolled annealed steel sheet in the shot blasting treatment while avoiding the oxidation scale residue and shot blast mark residue in pickling after the shot blasting treatment, It is important to control the collision energy to an appropriate range, and in order to obtain this effect more advantageously, the shot blast particle projection density is preferably 25 to 45 kg / m ² . More preferably, it is 30 to 40 kg / m ² .

<Speed at the time of shot blast grain arrival to steel plate: 20 to 45 m / s>
As described above, in order to suppress the generation of cracks on grain boundaries in the hot-rolled annealed steel sheet in the shot blasting treatment while avoiding the oxidation scale residue and shot blast mark residue in pickling after the shot blasting treatment, It is important to control the collision energy in an appropriate range, and in order to obtain this effect more advantageously, the velocity of the shot blasting particles when they reach the steel plate is preferably 20 to 45 m / s. More preferably, it is 25 to 40 m / s.

In addition, the shot blasting apparatus should just use the apparatus generally used.
However, if the distance from the nozzle tip of the shot blasting apparatus to the steel plate which is the material to be treated is too short, the projected area that can be covered by a single nozzle becomes small, and the number of nozzles required to cover the entire steel plate is small. To increase. In that case, the apparatus becomes large and / or complicated, which is not preferable in terms of manufacture.
On the other hand, when the distance from the nozzle tip of the shot blasting apparatus to the steel plate which is the material to be treated is too long, the nozzle of the shot blasting apparatus to obtain necessary collision energy and suitable shot blasting particle speed upon reaching the steel plate. It is necessary to increase the projection speed (initial speed) from the above, and it is necessary to enlarge the shot blasting apparatus. Moreover, there is a possibility that the effect of shot blasting may fall by interference between shot blasting particles projected from each nozzle.
Therefore, it is preferable to make the distance from the nozzle tip of a shot blasting apparatus to the steel plate which is a to-be-treated material into the range of 200-1000 mm. More preferably, it is 300-800 mm.

<Average particle size of shot blasting particles: 0.2 to 1.0 mm>
When the average particle size of the shot blasting particles used for the shot blasting treatment is less than 0.2 mm, the individual collision energy of the shot blasting particles becomes small, and sufficient strain and / or crack is not introduced to the oxide scale, and the shot is Descaling in pickling after blasting becomes difficult. On the other hand, when the average particle size of the shot blasting particles exceeds 1.0 mm, the collision energy of each shot blasting particle becomes excessively large, and gold dust is generated. In addition, since the number of shot blast particles to be projected is reduced, the contact of the shot blast particles to the steel plate to be treated becomes uneven, which may cause uneven gloss in the cold rolled steel plate of the final product. .
Therefore, the average particle size of shot blasting particles is 0.2 to 1.0 mm. Preferably it is 0.3-0.6 mm.
Here, the average particle diameter of the shot blasting particles means a mass average particle diameter (sometimes called a median diameter), and can be specifically determined by the following method.
First, based on JIS Z 8801, nominal openings: 2000, 1700, 1400, 1180, 1000, 850, 710, 600, 500, 425, 355, 300, 250, 212, 180, 150, 125, 106, 90. Using the 75 μm, 63 μm and 53 μm sieves, the shot blasting particles are sieved in order from the sieve with the largest nominal opening, and the cumulative amount of residual on the net of the sieve with each nominal opening (hereinafter, Measure the cumulative residual amount).
Next, the accumulated residual amount for each nominal opening obtained is plotted against the nominal opening, and by interpolation, the cumulative residual amount is 50% by mass (the mass percentage referred to here is shot-blasted particles subjected to sieving classification) Determine the nominal aperture, which is relative to the total mass of), and let this be the mass average particle size.

Furthermore, it is more preferable to use shot blasting particles that satisfy the following conditions 1 or 2 when shaking using sieves having various nominal openings.
Condition 1:
a. Nominal opening: Remaining amount on the net (remaining amount on sieve) when shaken with a sieve of 710 μm is 0% by mass (note that% by mass as referred to here is based on the total mass of shot-blasted particles subjected to sieving) And the same applies to b to f)
b. Nominal opening of shot blasting particles under the sieve of a: Remaining amount on the net of at most 20% by mass when shaken with a sieve of 600 μm c. Nominal opening of shot blasting particles under the screen of b: Remaining amount on the net of 40% by mass or less when shaken with a screen of 500 μm d. Nominal opening of shot blasting particles under the sieve of c: 30% or more by mass on the net when shaken with a 425 μm sieve e. Nominal opening of shot blasting particles under the screen of d: The total amount of residual on the net when shaken with a 355 μm sieve and the residual on the net of a to d is 90% by mass or more f. Nominal opening of shot blasting particles under the sieve of e: Shot blasting particles under the sieve of 5% by mass or less when shaken with a sieve of 300 μm condition 2
a. Nominal opening: Remaining amount on the net (remaining amount on sieve) when shaken with a sieve of 630 μm is 0% by mass (note that the mass% mentioned here is relative to the total mass of shot blasting particles subjected to sieving) And the same applies to b to g)
b. Nominal opening of shot blasting particles under the sieve of a: Remaining amount on the net of at most 20% by mass when shaken with a sieve of 560 μm c. Nominal opening of shot blasting particles under the screen of b: Remaining amount on the net of 40% by mass or less when shaken with a screen of 500 μm d. Nominal opening of shot blasting particles under the sieve of c: 30% or more by mass on the net when shaken with a sieve of 400 μm e. Nominal opening of shot blasting particles under the screen of d: The total amount of residual on the net when shaken with a sieve of 315 μm and the residual on the net of a to d is 70% by mass or more f. Nominal opening of shot-blasted particles under the sieve e): Remaining amount on the net of at most 20% by mass when shaken with a sieve of 200 μm g. Nominal opening of shot blasting particles under the sieve of f: less than 5% by mass of shot blasting particles under the sieve when shaken with a 180 μm sieve

<Hardness of shot blasting grain: HV350 to 550 in Vickers hardness>
Moreover, it is suitable for the hardness of a shot blasting grain to be HV350-550 by Vickers hardness. Here, when the hardness of the shot blasting particles is less than HV350 in Vickers hardness, sufficient strain and / or crack is not introduced to the oxide scale, and it becomes difficult to descaling in pickling after shot blasting treatment. On the other hand, when the hardness of shot blasting grains exceeds HV550 in Vickers hardness, it causes the generation of cracks on grain boundaries in the hot-rolled and annealed steel sheet.
For this reason, the hardness of shot blasting particles is set to HV 350 to 550 in Vickers hardness. Preferably it is HV380-520.

After the above-mentioned shot blasting treatment is performed, the hot-rolled annealed steel sheet is pickled to obtain a hot-rolled annealed / pickled steel sheet.
Here, the pickling method is not particularly limited, and may be in accordance with a conventional pickling method such as an acid immersion method or an electrolytic pickling method.
As an example of the pickling, there is a method of combining immersion in a sulfuric acid aqueous solution and immersion in a nitric hydrofluoric acid aqueous solution. Alternatively, a combination of immersion in a sulfuric acid aqueous solution and immersion in a nitric acid aqueous solution or a combination of immersion in a hydrochloric acid aqueous solution and immersion in a nitric acid aqueous solution may be used.

The hot rolled annealed and pickled steel sheet thus obtained is subjected to cold rolling and cold rolled sheet annealing.
Here, the cold rolling conditions may be in accordance with the usual method, but it is preferable to set the rolling reduction to 50% or more from the viewpoint of extensibility, bendability, shape correction and the like.
In addition, cold-rolled sheet annealing may be performed according to a conventional method, but the surface finish No. 2B or No. 2 having a surface finish defined by JIS G 0203 is also acceptable. In the case of 2D finishing, it is preferable to set the heating temperature to 800 to 950 ° C. and the holding time at the heating temperature to 5 to 300 seconds from the viewpoint of obtaining good mechanical properties and pickling properties. Furthermore, from the viewpoint of formability, the heating temperature is more preferably set to a temperature below the austenite transformation point.
The austenite transformation point can be determined by the following method.
First, the steel sheet as cold rolled having a predetermined component composition is heated to various heat treatment temperatures, held at the heat treatment temperature for 180 seconds, and then subjected to heat treatment of water cooling. Next, test pieces for cross-sectional observation are prepared from the heat-treated steel plate, subjected to an etching treatment with a picric acid saturated hydrochloric acid solution, and then observed with an optical microscope at a magnification of 100 times. A distinction is made between the phases (the austenitic phase is transformed and formed during water cooling) and the ferrite phase. Then, among the heat treatment temperatures of the steel plate after heat treatment in which the martensitic phase is recognized, the lowest temperature is taken as the austenite transformation point.
Furthermore, in order to obtain more gloss, bright annealing (BA annealing) may be performed as cold-rolled sheet annealing. When performing bright annealing, the annealing atmosphere was a mixed atmosphere of a reducing atmosphere H ₂ or H ₂ and N ₂ (e.g. 75 vol% H ₂ -25 vol% N _2), the heating temperature was 800 to 950 ° C. Moreover, it is preferable to make holding time in this heating temperature into 5 to 300 seconds. High glossiness is obtained in the steel plate subjected to bright annealing.
The above-mentioned cold rolling and cold rolled sheet annealing may be repeated twice or more, respectively.

Moreover, after cold-rolled sheet annealing, you may perform pickling and temper rolling as needed.
Here, the pickling method and the temper rolling conditions are not particularly limited, and may be in accordance with a conventional method. In the case of bright annealing (BA annealing), since no oxide scale is generated on the surface, pickling after cold-rolled sheet annealing is basically unnecessary.
Furthermore, from the viewpoint of further improving the surface properties, grinding or polishing may be further performed after cold-rolled sheet annealing.

The ferritic stainless cold-rolled steel sheet having sufficient corrosion resistance and good surface beautifulness with sufficiently suppressed gold dust by the above-mentioned manufacturing method, in particular, surface peeling that occurs when the surface peeling test is performed A ferritic stainless cold-rolled steel sheet having five or less defects per 100 cm ² is obtained.

Molten steels of the components shown in Table 1 (the balance is Fe and unavoidable impurities) are melted by refining using a converter with a capacity of 150 tons and vacuum oxygen decarburization (VOD) method, and then by continuous casting It was set as the slab of width: 1000 mm and thickness: 200 mm.
After heating the slab at 1200 ° C. for 1 hour, hot rolling was performed using a 7-pass rough rolling using a reverse rolling mill consisting of three stands and a one-way rolling mill consisting of seven stands A finish rolling consisting of 7 passes was performed, and a winding process was performed at about 750 ° C. to obtain a hot-rolled steel plate having a plate thickness of about 5.0 mm.
Next, these hot rolled steel sheets are subjected to hot rolled sheet annealing using a box annealing method under the conditions shown in Table 2 to form hot rolled annealed steel sheets, and then the conditions shown in Table 2 on the surface of the hot rolled annealed steel sheets. Shot blasting treatment. In addition, hot-rolled sheet annealing is No. Except for 4 carried out in a 75 vol% N ₂ -25 vol% H ₂ atmosphere, No. 4 was performed in an atmosphere of 100% by volume H ₂ .
In the shot blasting process, an impeller type shot blasting apparatus was used. The apparatus was installed above the steel plate to be treated such that the distance between the surface of the steel plate and the projection nozzle of the shot blasting particle of the shot blasting apparatus was 500 mm, and the shot blasting treatment was performed.
Moreover, the shot blasting particle which becomes hardness (distribution) HV400-500 is used for all as a shot blasting particle. Also, no. No. 1-2, no. 4 to 7, No. 12-16, and No. In No. 19 to No. 20, shot blasting particles satisfying the above-mentioned condition 1 are No. 1 3, No. In 10 to 11, shot blasting particles satisfying the above-mentioned condition 2 were used.

After the above-described shot blasting treatment, the hot-rolled annealed steel sheet is pickled and descaled to obtain a hot-rolled annealing / pickled steel sheet.
Here, the pickling was performed by immersing in a 25% by mass aqueous sulfuric acid solution (temperature: 80 ° C.) for 120 seconds and then soaking in a mixed acid aqueous solution of 10% by mass nitric acid and 2% by mass hydrofluoric acid (temperature: 60 ° C.) It did by doing.
The obtained hot-rolled annealed / pickled steel sheet was cold-rolled to a plate thickness of 1.0 mm and cold-rolled sheet annealing was performed at 830 ° C. for 60 seconds to obtain a cold-rolled annealed steel sheet. Then, the cold-rolled annealed steel sheet is subjected to electrolytic pickling at a current density of 40 C / dm ² in an 18% by mass sodium sulfate aqueous solution at 80 ° C. to descaling to obtain a cold-rolled annealed / pickled steel sheet.
Also, for some hot-rolled annealed, pickled steel sheet (No.1 and 5), sheet thickness: after cold rolling 1.0 mm, as cold-rolled sheet annealing, 75 vol% H ₂ -25 vol% Bright annealing was performed at 830 ° C. for 60 seconds in an atmosphere of N ₂ to obtain a cold rolled annealed steel sheet.

  The steel sheets thus obtained were subjected to (1) evaluation of surface appearance, (2) evaluation of gold dust and (3) evaluation of corrosion resistance by the following method. The evaluation results are shown in Table 2.

(1) Evaluation of Surface Appearance From the obtained steel plate, test specimens of 50 mm × 50 mm are collected from 10 arbitrary locations, and the surface of the test specimen is visually observed using a loupe with a magnification of 10 × to obtain oxidation. The presence of scale residue and shot blast marks was investigated, and the surface appearance was evaluated according to the following criteria.
○ (pass): When neither oxide scale residue nor shot blast residue is recognized × (fail): When either oxide scale residue or shot blast residue is recognized

(2) Evaluation of Gold Dust Gasket A surface of the obtained steel plate was coated with an acrylic adhesive having an adhesive strength of 1.80 N / 20 mm Width: 100 mm, length: 200 mm polyethylene film (Nitto Denko Corporation The surface protective material for metal plate, SPV-363) was attached so that the film longitudinal direction was perpendicular to the rolling direction of the steel plate, and the film was peeled (immediately) in the film longitudinal direction.
And the steel plate surface of the part which peeled off the film was observed 200 fields of vision by 100 times with a scanning electron microscope, and the number of places of 10 micrometers or more of surface exfoliation defects was counted by the circle equivalent diameter observed. Here, the partial surface peeling defects as shown in FIG. 1 were also counted. And the number of places per 100 cm ^{2 of the} surface peeling defect was calculated from the number of the portion of the surface peeling defect and the observation visual field area, and the evaluation of the gold dust was performed according to the following criteria.
((Pass, particularly excellent): surface peeling defect is ² or less per 100 cm ² ○ (pass): surface peeling defect is ² or more and 5 or less per 100 cm ² x (reject): surface peeling defect is 100 cm ² More than 5 per region For reference, an example (No. 13 and 16) of an electron micrograph in which a gold dust glaze is observed in a surface peeling test is shown in FIG. 1 and FIG. However, FIGS. 1 and 2 are electron micrographs taken at a magnification of 1000 to clearly show the characteristics of the gold dust glaze.

(3) Evaluation of Corrosion Resistance A test piece of 60 × 100 mm was taken from the obtained steel plate, and the surface was polished and finished with # 600 emery paper. Thereafter, the end face of the test piece was sealed and subjected to a salt spray cycle test specified in JIS H8502.
Here, the salt spray cycle test is salt spray (35 ° C., 5% by mass NaCl, spray time: 2 hours) → drying (60 ° C., relative humidity 40%, holding time: 4 hours) → wetting (50 ° C., relative 8 cycles were performed, with humidity サ イ ク ル 95%, retention time: 2 hours) as one cycle.
The surface of the test piece after the salt spray cycle test is photographed, the rusted area of the surface of the test piece is measured by image analysis, and the rusted area ratio (( The rust area / total area of the surface of the test piece) × 100 (%)) was calculated. And corrosion resistance was evaluated by the following criteria.
○ (pass): Rusted area rate is 25% or less × (failed): Rusted area rate is more than 25%

  From Table 2, in all of the invention examples, the surface appearance was good, and the generation of gold dust was sufficiently suppressed, and good surface beauty was obtained. Moreover, corrosion resistance was also favorable.

On the other hand, No. 1 which is a comparative example. In No. 12 (Steel B1), an excessively thick oxide scale was formed during hot rolling because the Si content exceeded the appropriate range. For this reason, descaling in pickling after hot-rolled sheet annealing becomes inadequate, an oxide scale remainder arises, and the favorable surface appearance was not obtained.
In addition, about evaluation of the gold dust, since a large amount of oxide scale remainder had arisen on the surface of the steel plate finally obtained, it was not able to evaluate.

Also, no. In No. 13 (Steel B1), since the Si content exceeds the appropriate range, the toughness of the hot-rolled annealed steel sheet is lowered. For this reason, the said hot-rolled annealing steel plate can not stand the collision energy in shot blasting processing, many micro cracks arose on the grain boundary, and many gold dust wrinkles generate | occur | produced.
No. In No. 14 (Steel B2), since the C content exceeds the appropriate range, a large amount of carbides precipitate at the time of hot-rolled sheet annealing, and the toughness of the hot-rolled annealed steel sheet decreases. For this reason, the said hot-rolled annealing steel plate can not stand the collision energy in shot blasting processing, many micro cracks arose on the grain boundary, and many gold dust wrinkles generate | occur | produced.
No. In No. 15, since the impact energy of shot blasting was below the appropriate range, descaling by pickling after hot-rolled sheet annealing was insufficient, oxide scale residue was generated, and a good surface appearance was not obtained.
No. In No. 16, since the impact energy of shot blasting exceeds the appropriate range, the hot-rolled annealed steel sheet can not withstand the impact energy in shot blasting treatment, many fine cracks are generated on grain boundaries, and many gold dust defects are generated. did.
No. In No. 17, since the average particle size of the shot blasting particles is below the appropriate range, descaling by pickling after hot-rolled sheet annealing becomes insufficient, oxide scale residue occurs, and a good surface appearance is not obtained. The
No. In No. 18, since the average particle size of the shot blasting particles exceeded the appropriate range, the collision energy of the shot blasting particles became excessively large, and many gold dust particles were generated. In addition, the shot blast particle hit became uneven, and the descaling by pickling after hot-rolled sheet annealing became insufficient at the portion where the shot blast particle did not hit, and an oxide scale residue was generated. In addition, shot blast marks also remained, and a good surface appearance was not obtained.
No. In No. 19, since the heating temperature of hot-rolled sheet annealing exceeds an appropriate range, the crystal grain in the structure | tissue of a hot-rolled annealing steel plate coarsened, and toughness fell. For this reason, the said hot-rolled annealing steel plate can not stand the collision energy in shot blasting processing, many micro cracks arose on the grain boundary, and many gold dust wrinkles generate | occur | produced. Moreover, the descaling in pickling after hot-rolled sheet annealing became inadequate, the oxide scale remainder produced, and the favorable surface appearance was not obtained.
No. In No. 20, since the holding time of hot-rolled sheet annealing exceeded the appropriate range, the oxide scale increased at the time of hot-rolled sheet annealing. For this reason, descaling in pickling after hot-rolled sheet annealing becomes inadequate, an oxide scale remainder arises, and the favorable surface appearance was not obtained.

  The ferritic stainless cold rolled steel sheet of the present invention is particularly suitable for applications requiring high surface beauty, such as kitchen appliances and dishes.

Claims (4)

In mass%,
C: 0.015 to 0.050%,
Si: 0.05 to 0.40%,
Mn: 0.45 to 1.00%,
P: 0.04% or less,
S: 0.010% or less,
Cr: 16.0 to 18.0%,
Al: 0.001 to 0.010%,
N: 0.025 to 0.080% and Ni: 0.05 to 0.60%
Is hot rolled to a steel material having a component composition containing the remainder and Fe and incidental impurities to form a hot rolled steel sheet, and the hot rolled steel sheet is subjected to hot rolled sheet annealing, shot blasting and pickling A method for producing a ferritic stainless cold-rolled steel sheet, which is applied in this order to form a hot-rolled annealed / pickled steel sheet and then cold-rolled and cold-rolled sheet annealing is applied to the hot-rolled annealed / pickled steel sheet,
The heating temperature in the hot-rolled sheet annealing is 800 to 900 ° C., and the holding time is 1 to 24 hours,
The collision energy in the shot blasting treatment is 10 to 40 kJ / m ² , and the average particle diameter of shot blasting grains used in the shot blasting treatment is 0.2 to 1.0 mm, and the hardness is HV 350 to 550 in Vickers hardness. A method of manufacturing a ferritic stainless cold rolled steel sheet.
Here, the collision energy in the shot blasting process is defined by the following equation (1).
[Collision energy (kJ / m ² )] = (1/2 × A × B ² ) / 1000 (1)
A: Projection density of shot blasting particles [kg / m ² ]
B: Speed of shot blasting particles at the time of arrival at steel plate [m / s] The method for producing a ferritic stainless cold-rolled steel sheet according to claim 1, wherein a shot density of the shot blasting particles is 25 to 45 kg / m ² and a speed of the shot blasting particles at the time of reaching the steel plate is 20 to 45 m / s.   The ferritic stainless cold-rolled steel plate manufactured by the manufacturing method of the ferritic stainless cold-rolled steel plate according to claim 1 or 2. The ferritic stainless steel cold rolled steel sheet according to claim 3, wherein the surface peeling defect generated when the surface peeling test is performed is 5 or less per 100 cm ² .