JP7116064B2 - FERRITIC STAINLESS STEEL EXCELLENT IN RIDGING PROPERTIES AND SURFACE QUALITY AND METHOD FOR MANUFACTURING SAME - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ferritic stainless steel excellent in ridged property and surface quality and a method for producing the same. The present invention relates to a ferritic stainless steel with an improved core structure to improve ridged property and surface quality, and a method for producing the same.

Generally, stainless steels are classified according to their composition system and metallographic structure. Stainless steels are classified into austenitic, ferritic, martensitic, and duplex systems according to metallographic structure. Among these stainless steels, ferritic stainless steels are mainly used for various kitchen appliances, automotive exhaust system parts, building materials, home appliances, etc., because they have excellent corrosion resistance even though they contain few expensive alloying elements. It is a type of steel that requires high-quality surface gloss when used for exterior applications.

However, ferritic stainless steel has a problem that a ridging defect, which is a wrinkle-shaped surface defect parallel to the rolling direction, occurs during forming such as deep drawing. The ridged defects deteriorate the appearance of the product, and when the ridged ridges are severe, a polishing process is added after molding, which increases the manufacturing time and increases the manufacturing cost. Therefore, in order to expand the use of ferritic stainless steel, it is necessary to improve the ridging property and ensure excellent surface quality.

The cause of the occurrence of ridges is fundamentally attributed to the development of columnar crystals in the cast structure. That is, when columnar crystals having a certain orientation remain without being destroyed during rolling or annealing, they appear as ridged defects due to deformation behavior in the width and thickness directions that differs from that of the surrounding recrystallized structure during tensile working. In order to eliminate such ridged defects, various attempts have been made to remove ridge-inducing tissue. Mainly by improving the equiaxed grain ratio and reducing the columnar grain fraction, it is possible to improve the ridging property, and to control process variables such as hot rolling temperature, hot rolling reduction ratio, and annealing temperature during the manufacturing process. Rigging was reduced through the adjustment of

However, at present, there is almost no attempt to improve the texture by subjecting a hot-rolled sheet coiled at a high temperature after hot rolling to symmetrical rolling or asymmetrical rolling before hot rolling annealing, followed by continuous annealing heat treatment. is.

Korean Patent Publication No. 10-2008-0061863 (2008.07.03. Published) Korean Patent Publication No. 10-2014-0080348 (Published on 2014.06.30.)

The present invention provides a ferritic stainless steel with excellent ridged properties and surface quality in the final product by further performing cold rolling before the hot rolling annealing heat treatment of ferritic stainless steel to change the microstructure at the center of the cross section. Kind Code: A1 A stainless steel and method for making the same are provided.

Ferritic stainless steel excellent in ridged property and surface quality according to one embodiment of the present invention has C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0% by weight. .01-1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10-30%, N: 0.005-0.1%, Al: 0.005-0. 2%, the remaining Fe and other unavoidable impurities are included, and the γ _max represented by the following formula (1) is 20% or more and less than 50%.

(1) 420×C+470×N+10×Mn+180-11.5×Cr-11.5×Si-52.0×Al

Here, C, N, Mn, Cr, Si and Al mean the content (% by weight) of each element.

Further, according to an embodiment of the present invention, the stainless steel may have a surface area ratio of microgrooves of 2.0% or less.

Also, according to an embodiment of the present invention, the stainless steel may have a ridge height of 12 μm or less.

Also, according to an embodiment of the present invention, the stainless steel may have an r-bar value of 1.2 or more.

A method for producing ferritic stainless steel excellent in ridged property and surface quality according to an embodiment of the present invention comprises, in weight percent, C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0.01-1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10-30%, N: 0.005-0.1%, Al: 0.005 ~0.2%, the remaining Fe and other unavoidable impurities, producing a slab satisfying γ _max represented by the following formula (1) of 20% or more and less than 50%, and reheating the slab coiling the hot-rolled hot-rolled sheet; and cold-rolling the coiled hot-rolled sheet before hot-rolling annealing heat treatment.

(1) 420×C+470×N+10×Mn+180-11.5×Cr-11.5×Si-52.0×Al

Here, C, N, Mn, Cr, Si and Al mean the content (% by weight) of each element.

Also, according to an embodiment of the present invention, a coiling temperature in the step of coiling the hot-rolled sheet may be 750° C. or higher.

Also, according to an embodiment of the present invention, the cold rolling may be performed by asymmetric cold rolling.

Also, according to an embodiment of the present invention, the cold rolling or the asymmetric cold rolling may be performed at a rolling reduction of 30% or more.

Further, according to an embodiment of the present invention, the asymmetric cold rolling has a speed ratio (V _h /V _l ) of upper and lower rolling rolls of 1.25 or more and a rolling shape factor (l/d) of 1. .7 or higher.

Also, according to an embodiment of the present invention, the stainless steel manufactured by performing hot rolling annealing, secondary cold rolling and cold rolling annealing after the asymmetric cold rolling has a ridged height of 10 μm or less. good too.

Also, according to an embodiment of the present invention, the step of hot rolling annealing heat treatment after the step of cold rolling may be further included.

Also, according to an embodiment of the present invention, the hot rolling annealing heat treatment can be performed within a temperature range of 550 to 950° C. within 60 minutes.

Further, according to an embodiment of the present invention, after the hot rolling annealing heat treatment, the average aspect ratio of the structure at the center of the thickness of the cross section of the hot rolling annealed material may be 4.0 or less.

In the ferritic stainless steel and its manufacturing method according to the embodiment of the present invention, the aspect ratio of the band structure in the thickness center of the cross section of the steel plate is controlled to be low through cold rolling before hot rolling annealing heat treatment, and the product surface is It is possible to suppress the occurrence of ridged defects.

In addition, the ferritic stainless steel and the method for producing the same according to the embodiments of the present invention have a low area ratio of fine grooves on the surface of the steel sheet, so that they can exhibit excellent surface gloss.

In addition, the ferritic stainless steel and the method for producing the same according to the embodiments of the present invention have excellent ridged property and high r-value, and can reduce the ridged height during molding.

3 is a microstructure photograph of a cross section parallel to the rolling direction of Comparative Example 3 according to an embodiment of the present invention; FIG. 4 is a photograph of the surface of Reference Example 2 according to an embodiment of the present invention taken with an optical microscope; FIG. FIG. 4 is a photograph of the surface of Comparative Example 4 according to the embodiment of the present invention taken with an optical microscope; FIG.

Ferritic stainless steel excellent in ridged property and surface quality according to one embodiment of the present invention has C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0% by weight. .01-1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10-30%, N: 0.005-0.1%, Al: 0.005-0. 2%, the remaining Fe and other unavoidable impurities are included, and the γ _max represented by the following formula (1) is 20% or more and less than 50%.

(1) 420×C+470×N+10×Mn+180-11.5×Cr-11.5×Si-52.0×Al

Here, C, N, Mn, Cr, Si and Al mean the content (% by weight) of each element.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The following examples are presented to fully convey the spirit of the invention to those of ordinary skill in the art to which the invention pertains. This invention is not limited to the embodiments presented herein, but may be embodied in other forms. In order to clarify the present invention, the drawings may omit the illustration of parts that are not related to the description, and may exaggerate the sizes of the components to facilitate understanding.

Ferritic stainless steel excellent in ridged property and surface quality according to one embodiment of the present invention has C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0% by weight. .01-1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10-30%, N: 0.005-0.1%, Al: 0.005-0. 2%, the remaining Fe and other unavoidable impurities are included, and the γ _max satisfies 20% or more and less than 50%.

The role and content of each component contained in the ferritic stainless steel according to the present invention are as follows. % for the following components means % by weight.

The content of C is 0.005% or more and 0.1% or less.

C is an element that greatly affects the strength of the steel. If the content is too high, the strength of the steel is excessively increased and the softness is lowered. However, when the content is low, it is added in an amount of 0.005% or more when the required strength of the steel material is not satisfied.

The content of Si is 0.01% or more and 2.0% or less.

Si is an element added for deoxidizing molten steel and stabilizing ferrite during steelmaking, and is added in an amount of 0.01% or more in the present invention. However, if the content is too high, the material is hardened and the softness of the steel is lowered, so the content is limited to 2.0% or less.

The content of Mn is 0.01% or more and 1.5% or less.

Mn is an element effective for improving corrosion resistance, and in the present invention, it is added in an amount of 0.01% or more, preferably 0.2% or more. However, if the content is too large, Mn-based fumes are rapidly generated during welding, resulting in poor weldability and excessive formation of MnS precipitates, which reduces the softness of the steel. , more preferably 1.0% or less.

The content of P is 0 to 0.05%.

P is an unavoidable impurity contained in steel, and is an element that causes intergranular corrosion during pickling and impairs hot workability, so its content should be controlled as low as possible. is preferred. In the present invention, the upper limit of the P content is controlled at 0.05%.

The content of S is 0 to 0.005%.

S is an impurity that is unavoidably contained in steel and is an element that segregates at grain boundaries and is the main cause of impairing hot workability. Therefore, it is preferable to control the content of S as low as possible. In the present invention, the upper limit of the S content is controlled at 0.005%.

The Cr content is 10% or more and 30% or less.

Cr is an element effective in improving the corrosion resistance of steel, and is added in an amount of 10% or more in the present invention. However, if the content is too high, there is a problem that the production cost rises sharply, so it is limited to 30% or less.

The content of N is 0.005% or more and 0.03% or less.

N is an element that forms nitrides and exists as an interstitial type, so if it is excessively contained, it causes a decrease in impact toughness and formability, so it is limited to 0.03% or less.

The content of Al is 0.005% or more and 0.2% or less.

Al is a strong deoxidizing agent and plays a role in reducing the oxygen content in molten steel. However, if the content is too high, the increase in non-metallic inclusions causes sleeve defects in the cold-rolled strip and deteriorates the weldability. Limited to:

γ _max is a well-known austenite stability index corresponding to the maximum amount of austenite at high temperatures. γ _max is calculated by the following formula (1). In the present invention, the γ _max value satisfies 20% or more and less than 50%.

(1) 420×C+470×N+10×Mn+180-11.5×Cr-11.5×Si-52.0×Al

If γ _max is less than 20%, sufficient deformation of the ferrite phase is not accumulated by the austenite phase during hot rolling, and recrystallization of the ferrite band is not promoted, resulting in no improvement in the ridged property. On the other hand, in order to increase γ _max , the content of austenite-forming elements such as C, N, Mn and Ni can be controlled to be high, but these lead to hardening of the steel material and an increase in cost _. should be less than 50%.

In the case of a ferritic stainless steel satisfying the above compositional system and γ _max range, the accumulation of deformation energy for recrystallization is sufficient before the hot rolling annealing heat treatment, so the texture is favorable for ridged property and formability. can be formed.

For example, the ferritic stainless steel according to one embodiment of the present invention may have a ridged height of 12 μm or less and an r-bar value of 1.2 or more.

In addition, the ferritic stainless steel according to an embodiment of the present invention may have an area ratio of microgrooves on the steel surface of 2.0% or less. The area ratio of the fine grooves on the surface has a correlation with the glossiness, and the lower the area ratio of the fine grooves, the higher the glossiness. The ferritic stainless steel according to the present invention has an area ratio of fine grooves on the surface of the steel of 2.0% or less, and can exhibit a beautiful surface.

Next, a method for producing ferritic stainless steel with excellent ridged property and surface quality will be described.

In order to improve the ridged property and surface quality of ferritic stainless steel, it is necessary to promote the formation of a texture favorable to formability and remove the band structure that induces ridges. In order to form the texture and remove the band structure, it is important to promote recrystallization during the annealing heat treatment of the hot-rolled sheet. is necessary. Attempts have been made to lower the hot-rolling finish temperature in order to accumulate deformation energy in the hot-rolled sheet, but the accumulation of deformation energy was insufficient. Accordingly, in the present invention, in order to promote recrystallization due to accumulation of deformation energy, cold rolling is performed before hot rolling annealing heat treatment to form a texture advantageous for formability.

In general, the deformation state of a plate during rolling deformation can be represented by two factors: shear deformation and planar deformation. In conventional symmetrical rolling, shear deformation acts on the surface layer of the plate material, and the shear deformation rate decreases toward the central layer due to the symmetry that is an essential characteristic. The rate is always 0. That is, plane deformation always acts on the central layer of the plate material. In the present invention, asymmetric rolling can be applied to apply shear deformation to the thickness center of the plate material. When asymmetric rolling is applied, there are many rolling variables, and only if these variables are optimized will an appropriate shear deformation rate act in all thickness layers to activate recrystallization and improve the microstructure. The variation can reduce the ridge height which is critical to the surface quality of the final cold rolled product.

A method for producing ferritic stainless steel according to an embodiment of the present invention comprises, in weight percent, C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0.01 to 1.0%. 5%, P: 0.05% or less, S: 0.005% or less, Cr: 10-30%, N: 0.005-0.1%, Al: 0.005-0.2%, the rest producing a slab containing Fe and other inevitable impurities and having a γ _max of 20% or more and less than 50%; reheating and hot rolling the slab; and cold-rolling the rolled hot-rolled sheet prior to hot-rolling annealing heat treatment.

By further cold rolling the hot-rolled hot-rolled sheet before the hot-rolling annealing heat treatment, deformation energy for promoting recrystallization can be accumulated.

Prior to said cold rolling, the produced slab is reheated and hot rolled. A hot-rolled hot-rolled sheet is coiled at a high temperature (black coil) by a winder. , 750° C. or higher.

On the other hand, in the method of manufacturing ferritic stainless steel according to an embodiment of the present invention, in the step of cold-rolling the coiled hot-rolled sheet before the hot-rolling annealing heat treatment, the cold-rolling is performed by asymmetric cold-rolling. can be implemented in

As described above, in the present invention, asymmetric rolling can be applied to cause shear deformation at the center of the thickness of the plate material. Appropriate shear deformation at the center of the thickness activates recrystallization to change the microstructure, thereby reducing the ridge height, which is important for the surface quality of the final cold-rolled product.

Asymmetric cold rolling is carried out under rolling conditions in which the reduction ratio is 30% or more, the speed ratio ( _Vh /Vl) of the upper and lower rolling rolls is 1.25 or more, and the rolling shape factor ( _l /d) is 1.7 or more. can do.

In asymmetric cold rolling, the speed ratio (V _h /V _l ) of the upper and lower rolling rolls must be 1.25 or more in order to cause shear deformation to the thickness center. If it is less than 1.25, shear deformation may not be imparted to the central portion of the thickness. where _Vh means the speed of the fast roll and _Vl means the speed of the slow roll.

The rolling shape factor (l/d) is also required to be 1.7 or more in order to cause shear deformation up to the central part of the thickness. If it is less than that, the shear deformation may not be imparted to the central part of the thickness. The rolling shape factor related to the size of the rolling roll and the rolling reduction is a scale for adding shear deformation during rolling, and is defined by the following formula (2).

Here, l is the projected length of the contact arc between the roll and the plate in the roll bight, d is the average thickness of the plate (d = (h ₀ + h) / 2), r is the radius of the rolling roll , h ₀ means the initial thickness of the plate and h the final thickness of the plate.

The present invention is the result of investigating the correlation between rolling variables during asymmetric rolling and ridged property, formability and surface quality when cold rolling is performed before hot rolling annealing heat treatment. It is characterized by adjusting rolling reduction and rolling shape factor (l/d) to improve ridgeability and surface quality.

The hot-rolled sheet subjected to the cold rolling or asymmetric cold rolling can be subsequently subjected to hot rolling annealing heat treatment. The hot rolling annealing heat treatment can be performed within 60 minutes at a temperature range of 550 to 950°C. The hot-rolling annealing heat treatment is a process performed to improve the softness of the hot-rolled hot-rolled sheet, and can induce precipitation and recrystallization of carbonitrides through this process. For this purpose, it is necessary to carry out the annealing at a temperature of 550° C. or higher. However, if the annealing temperature exceeds 950° C. or the annealing time exceeds 60 minutes, the crystal grains are coarsened, possibly deteriorating formability and ridging properties. On the other hand, the lower limit of the annealing time does not have to be set in particular, but in order to obtain a sufficient effect, it is preferable to carry out the annealing for 30 seconds or longer.

The heat-treated hot-rolled and annealed sheet may have an average aspect ratio of 4.0 or less in the structure at the center of the thickness of the cross section in the direction parallel to the rolling direction. The aspect ratio is the ratio of the ferrite grain size in the rolling direction to the ferrite grain size in the plate thickness direction (grain size in the rolling direction/grain size in the plate thickness direction). If the average aspect ratio exceeds 4.0, cold workability may be degraded due to the ferrite structure expanded in the rolling direction. In addition, if a band structure elongated in the rolling direction remains in the hot-rolled annealed sheet at the center of the thickness, uneven deformation due to the band structure during cold rolling will cause unevenness on the surface and reduce the surface glossiness. Therefore, the average aspect ratio is limited to 4.0 or less.

Except for the case where the method for producing ferritic stainless steel excellent in ridged property and surface quality according to the present invention is controlled as described above, the conditions are not particularly limited, and can be carried out in accordance with the usual method for producing ferritic stainless steel. . Also, the hot-rolled and annealed sheet can be cold-rolled and cold-rolled and annealed to produce a cold-rolled steel sheet.

Hereinafter, the present invention will be described in more detail through preferred embodiments.

Example A slab was produced by continuously casting molten steel having the composition shown in Table 1 below, and after reheating the slab and hot rolling, a hot-rolled sheet having an initial thickness of 3 to 7 mm was produced before the hot rolling annealing heat treatment. First cold rolling was carried out.

The primary cold rolling was normal cold rolling or asymmetric cold rolling at a rolling reduction of 20 to 50%. Secondary cold rolling is performed at a reduction rate of 50 to 85% after subjecting the primary cold-rolled hot-rolled sheet to hot rolling annealing heat treatment and pickling, and a test piece is obtained after cold rolling annealing heat treatment and pickling. made.

Tensile test pieces were processed in the directions of 0°, 45°, and 90° with respect to the rolling direction of the test piece, and the r value (Lankford value) was measured after a 15% tensile test. The r-bar value (r-bar=(r ₀ +r ₉₀ +2*r ₄₅ )/4) was calculated from the r-values (r ₀ , r ₄₅ , r ₉₀ ) measured in each direction. Moreover, the ridged height was measured by processing the test piece and measuring the surface roughness after a 15% tensile test. Table 2 below shows the measurement results of r-bar and ridged height (Wt) depending on the rolling conditions of the ferritic stainless steel used in this example.

Comparative Examples 3 to 7, in which normal rolling was performed, had an r-bar value of 1 or less and a high ridged height of 14 μm or more. In Comparative Examples 1 and 2 in which primary cold rolling was performed prior to hot rolling annealing heat treatment after hot rolling, the reduction rate was less than 30% and the r-bar value was 1.2 or less. It was found that the moldability was disadvantageous. As in Reference Examples 1 to 3, when the primary cold rolling is performed before the hot rolling annealing heat treatment and the reduction rate is 30% or more, an r-bar value of 1.2 or more can be obtained, which is visible to the naked eye. Therefore, it was possible to achieve a ridged height of 12 μm or less, which is a level that does not deteriorate the appearance characteristics of the processed product.

In Examples 4 to 6, the remaining conditions were the same except that the primary cold rolling was performed by asymmetric rolling instead of symmetric rolling in Reference Examples 1 to 3, and Comparative Examples 8 and 9 were also the same. , Except that the primary cold rolling in Comparative Examples 1 and 2 was not symmetrical but asymmetrical, the remaining conditions were
are identical.

It has been found that the ridge height is reduced by about 20% or more when primary cold rolling is performed with asymmetric rolling compared to symmetric rolling. In particular, Examples 4 to 6 were able to achieve a ridged height of 10 μm or less. Through this, it was found that the band structure can be sufficiently refined by shear deformation during asymmetric rolling rather than symmetric rolling, and the ridged property is improved.

In the case of Comparative Examples 8 and 9 in which primary cold rolling was carried out prior to hot rolling annealing heat treatment after hot rolling, even if carried out by asymmetric rolling, the rolling reduction was carried out at less than 30%, r The -bar value appeared to be 1.2 or less, indicating that moldability was disadvantageous.

That is, as in Examples 4 to 6, when asymmetric cold rolling is performed before hot rolling annealing heat treatment and the total rolling reduction is 30% or more, an r-bar value of 1.2 or more can be obtained. , it was found that a ridged height of 12 μm or less, which is a degree that does not deteriorate the appearance characteristics of the processed product because it is difficult to observe with the naked eye, can be achieved.

On the other hand, Table 3 below shows the average aspect ratios of the hot-rolled annealed material manufactured by the conventional manufacturing method in which cold rolling is not performed before hot-rolling annealing and the hot-rolled annealed material manufactured by the present invention. Table 3 below also shows the area ratio of the fine grooves of the cold-rolled and annealed material which has been subsequently cold-rolled and cold-rolled and annealed.

The average aspect ratio is obtained by photographing the cross-sectional fine structure of the hot-rolled and annealed material parallel to the rolling direction using an optical microscope, and then measuring the grain size in the rolling direction and the plate thickness direction of the band structure. The average aspect ratio of 5 grains is shown. FIG. 1 shows a microstructure photograph of a cross section parallel to the rolling direction of Comparative Example 3. FIG. As shown in FIG. 1, the length and thickness of the band structure elongated in the rolling direction were measured from the microstructure photograph of the cross section, and then the average aspect ratio was calculated.

The area ratio of the fine grooves was evaluated by photographing the surface of the cold-rolled and annealed material with an optical microscope at a maximum light source, increasing the exposure time at a magnification of 50, and then measuring the area ratio with an Image Analyzer. Representative measurement results are shown in FIGS.

2 shows the surface of Reference Example 2, and FIG. 3 shows the surface of Comparative Example 4. FIG. In the drawings, the area of the fine grooves indicates the portion expressed with a deep hue. It was found that the area ratio of the fine grooves of Reference Example 2 according to the present invention shown in FIG. 2 was significantly reduced compared to Comparative Example 4 of FIG.

Comparative Example 1 in which the primary cold rolling was performed by normal rolling with a rolling reduction of less than 30% has a high average aspect ratio of 6 or more, and Comparative Examples 3 and 4 produced by a conventional manufacturing method have an average aspect ratio. Compared to Comparative Example 1 in which the primary cold rolling was performed, the tensile strength increased nearly three times. On the other hand, after hot rolling, prior to the hot rolling annealing heat treatment, the primary cold rolling was performed by normal rolling with a rolling reduction of 30% or more, and the primary cold rolling was performed with a rolling reduction of 30% or more. In Examples 5 and 6, which were asymmetrically rolled, the average aspect ratio of the hot-rolled and annealed material was as low as 3 or less.

In addition, in Comparative Examples 1, 3, and 4 in which the primary cold rolling was performed by normal rolling, the area ratio of fine grooves in the cold-rolled annealed material was as high as 2.2% or more. In the case of Reference Examples 2 and 3 in which the primary cold rolling was performed prior to the spread annealing heat treatment and Examples 5 and 6 in which the primary cold rolling was performed by asymmetric rolling, the area ratio of the fine grooves was 1.8. % appeared low.

That is, as is clear from the results of Reference Examples 2 and 3 and Examples 5 and 6, the lower the average aspect ratio of the hot-rolled and annealed material, the lower the area ratio of the fine grooves of the cold-rolled and annealed material. Therefore, by satisfying the average aspect ratio of 4.0 or less and the area ratio of the fine grooves of 2.0% or less as in Examples, a cold-rolled steel sheet having excellent surface quality was obtained.

While illustrative embodiments of the invention have been described above, the invention is not so limited and a person of ordinary skill in the art will appreciate the following claims which follow. It can be understood that various modifications and variations are possible without departing from the concept and scope.

Since the ferritic stainless steel according to the embodiment of the present invention is excellent in surface quality and gloss of the steel sheet, it can be used for various kitchen utensils, automobile exhaust system parts, building materials, home electric appliances, and the like.

Claims (3)

% by weight, C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0.01 to 1.5%, P: 0.05% or less, S: 0.005 % or less, Cr: 10 to 30%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, the rest consisting of Fe and other inevitable impurities,
γmax, which is an index of austenite stability calculated by the following formula (1), is 20% or more and less than 50%,
The average aspect ratio of the band structure at the center of the thickness of the cross section of the material that has been annealed after cold rolling is 4.0 or less,
The area ratio of fine grooves on the surface photographed with an optical microscope is 2.0% or less,
The r-bar value calculated from the r value measured after the 15% tensile test is 1.2 or more,
A ferritic stainless steel sheet having excellent ridged property and surface quality, characterized by having a ridged height of 12 μm or less as determined by surface roughness measurement.
Formula (1) 420×C+470×N+10×Mn+180−11.5×Cr−11.5×Si−52.0×Al
Here, C, N, Mn, Cr, Si and Al mean the content (% by weight) of each element. % by weight, C: 0.005 to 0.1%, Si: 0.01 to 2.0%, Mn: 0.01 to 1.5%, P: 0.05% or less, S: 0.005 % or less, Cr: 10 to 30%, N: 0.005 to 0.1%, Al: 0.005 to 0.2%, the remaining Fe and other inevitable impurities, represented by the following formula (1) producing a slab satisfying γmax of 20% or more and less than 50%;
reheating and hot rolling the slab;
winding the hot-rolled sheet;
Asymmetric cold rolling at a rolling reduction of 30% or more without subjecting the wound hot-rolled sheet to hot-rolling annealing ;
Annealing the cold rolled sheet ,
The asymmetric cold rolling is performed under rolling conditions in which the speed ratio (Vh/Vl) of the upper and lower rolling rolls is 1.25 or more and the rolling shape factor (l/d) is 1.7 or more,
The cold-rolled sheet is annealed within a temperature range of 550 to 950° C. within 60 minutes. The ratio (grain size in the rolling direction/grain size in the plate thickness direction) is 4.0 or less ,
The area ratio of fine grooves on the surface photographed with an optical microscope is 2.0% or less,
The r-bar value calculated from the r value measured after the 15% tensile test is 1.2 or more,
A method for producing a ferritic stainless steel sheet having excellent ridged property and surface quality, characterized in that the ridged height ascertained by surface roughness measurement is 12 μm or less .
Formula (1) 420×C+470×N+10×Mn+180−11.5×Cr−
11.5×Si-52.0×Al
In formula (1), C, N, Mn, Cr, Si and Al mean the content (% by weight) of each element.
In the speed ratio (Vh/Vl) of the upper and lower rolling rolls, Vh indicates a high roll speed and Vl indicates a low roll speed.
The rolling shape factor (l / d) is a value obtained by formula (2),

The meanings of the symbols in formula (2) are as follows.
l: Projected length of the contact arc between the roll and the plate material in the rolling roll bite d: Average thickness of the plate material d=(h ₀ +h)/2
r: radius of rolling roll _h0 : initial thickness of plate material h: final thickness of plate material 3. The method for producing a ferritic stainless steel sheet excellent in ridged property and surface quality according to claim 2, wherein the coiling temperature in the step of coiling the hot-rolled sheet is 750[deg.] C. or higher.

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