JP6410543B2 - Ferritic stainless steel plate excellent in hole expansibility and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ferritic stainless steel plate excellent in hole expansibility and a method for producing the same.

  Ferritic stainless steel has excellent corrosion resistance and is used in many applications. In the case of a ferritic stainless steel thin steel sheet, it is often formed into a desired shape by applying various processes. Processing has modes such as bending, overhanging, deep drawing, and stretch flange, and the metal structure suitable for each processing is controlled.

Above all, stretch flange formability is obtained by investigating the expansion rate (hole expandability) of punch holes opened by processing. In ferritic stainless steels, studies have been made to improve hole expansibility. By optimizing the pressure distribution in the patent document 1, 2 Kaihiyanobe a technique of improving the hole expandability by increasing the r _min values it has been taken. Since the technique of Patent Document 1 is based on the two-time cold rolling method, it cannot be applied to a general one-time cold rolling method.

  A method of improving hole expansibility by controlling precipitates is also known (Patent Document 2 and Patent Document 3). Patent Document 2 and Patent Document 3 disclose a method of improving the hole expandability by controlling the size and density of precipitates by defining intermediate annealing conditions in addition to the components. However, this technique is not necessarily an efficient process because intermediate annealing is essential.

  On the other hand, a technique for adding a small amount of Sn to ferritic stainless steel to improve weather resistance is known (Patent Document 4 and Patent Document 5). In Patent Document 4 and Patent Document 5, a method for defining components and improving weather resistance is described, but there is no description about hole expansibility. Moreover, it is considered that the hole expandability has a large correlation with the metal structure, but no suggestion regarding the metal structure control has been made.

  It is known that hole expansibility correlates qualitatively with the ductility and deep drawability of the material because it corresponds to local deformation, but a technique to improve hole expansibility without adding a process has been established. This is the current situation.

JP-A-4-31518 JP 2003-213376 A JP 2004-360003 A JP 2009-174036 A JP 2010-159487 A

  In view of such a background, an object of the present invention is to provide a ferritic stainless steel excellent in hole expansibility by controlling steel components and metal structure. In particular, it is an object of the present invention to obtain a metal structure that improves hole expansibility by adjusting components and process conditions without passing through a special process on the premise of manufacturing by an existing process.

  In order to solve the above-mentioned problems, the present inventors investigated the influence of components and metal structure on hole expansibility. In particular, focusing on Sn added for improving weather resistance, the relationship between the Sn content and the hole expanding property was thoroughly investigated. As a result, it was found that there is a relationship between the Sn content, the crystal grain size, and the hole expandability. In other words, it has been found that the hole expandability can be maximized by controlling the Sn content and the crystal grain size within a certain range.

  FIG. 1 shows the result of measuring the hole expansion rate using materials having a crystal grain size number (GSN) of 8.0 and 6.3. In the case of the crystal grain size number 6.3, the hole expansion rate hardly changes even when the Sn addition amount is increased. On the other hand, in the case of the crystal grain size number 8.0, the hole expansion rate increases when the Sn addition amount exceeds 0.01%, shows a maximum at Sn: 0.03%, and decreases at an addition amount beyond that.

  Thus, it has been found that there exists an optimum combination of the grain size number and the Sn content. The reason for this is not clear, but since Sn is an element that easily segregates at the grain boundaries, an appropriate amount of Sn segregates at the grain boundaries by combining the grain boundary area (corresponding to the crystal grain size) and the Sn amount. In addition, it is considered that the bondability of the grain boundaries was strengthened to improve the hole expansibility.

The present invention has been made based on this finding, and the gist thereof is as follows.
(1)
% By weight
C: 0.0005 to 0.020%,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%
P: less than 0.050%,
S: less than 0.010%,
Cr: 10.0-15.0%,
N: 0.0005 to 0.020%,
Sn: 0.010 to 0.050%
Ti: 0.03-0.25%,
Nb: less than 0.030%,
The balance is substantially iron and inevitable impurities, and the crystal grain size number of the crystal grains is 7.0 or more and 9.5 or less. Ferritic stainless steel sheet.
(2)
% By mass
Al: 0.003-0.5%
The ferritic stainless steel sheet having excellent hole expansibility as described in (1).
(3)
% By mass
Ni: 0.01 to 0.50%,
Cu: 0.01 to 0.50%,
Mo: 0.01 to 0.50%
Sb: 0.001 to 0.30%,
Zr: 0.005 to 0.5%,
Co: 0.005 to 0.50%,
W: 0.002 to 0.50%,
V: 0.02 to 0.50%,
Ga: Ferritic stainless steel sheet excellent in hole expansibility according to (1) or (2), characterized by containing one or more of 0.001 to 0.10%.
(4)
% By mass
B: 0.0003 to 0.0025%,
Mg: 0.0001 to 0.0030%,
Ca: 0.0003 to 0.0030%
REM (rare earth metal): 0.002 to 0.20%
Zn: 0.002-0.10%
Ta: 0.002 to 0.50%
Hf: 0.002 to 0.50%
As: 0.001 to 0.20%
Bi: 0.001 to 0.30%
Pb: 0.001 to 0.10%
Se: 0.001 to 0.10%
The ferritic stainless steel sheet having excellent hole expansibility according to any one of (1) to (3), wherein the ferritic stainless steel sheet contains one or more of them.
(5)
(1) to (4) the steel having any one of the components was hot-rolled at a total rolling reduction in hot rolling of 97% or more and a final finishing rolling temperature of 950 ° C. or less. Then, after performing a winding process at a temperature of less than 700 ° C., heat treatment is performed by heating to a temperature of 875 ° C. or more and 950 ° C. or less. performed between rolling, it has rows heating heat treated so that the range of eight hundred and twenty to nine hundred ° C. in a subsequent heat treatment step, spread hole grain size number of crystal grains, characterized in that 7.0 to 9.5 Of ferritic stainless steel sheet with excellent properties.

  According to the present invention, by controlling each component of the steel component system and the manufacturing process, it is possible to apply existing manufacturing equipment and provide a ferritic stainless steel sheet having excellent hole expandability without going through a special process. it can.

It is a figure which shows the relationship between Sn content and a hole expansion rate. It is a figure which shows the relationship between the crystal grain size and the hole expansion rate in the stainless steel containing about 0.03% of Sn.

The present invention will be described below.
The inventors made 13% Cr stainless steel as a basic component, and produced steel ingots having different sizes by changing the addition amount of various elements. After the steel ingot was hot-rolled under various conditions, a steel plate having a thickness of 1.0 mm was produced by a combination of cold rolling and heat treatment. The crystal grain size was adjusted by adjusting the final annealing temperature. A 90 mm square steel plate was cut out from the obtained steel plate and subjected to a hole expansion test. The hole expansion test is performed when a circular hole with a diameter of 10 mm is punched out so that the clearance becomes 12.5%, and then pressed by a 60 ° conical punch, and the hole edge crack penetrates the plate thickness. Stopped. The hole expansion ratio λ was obtained from the following equation (1) from the hole diameter after the test and the hole diameter before the test.

Hole expansion ratio λ (%) = ((hole diameter after test−hole diameter before test) / hole diameter before test) × 100 (1)

  As a result, it was found that there is an amount of Sn that maximizes the hole expandability when the crystal grain size is controlled within a certain range. FIG. 1 shows the result of measuring the hole expansion rate using materials having a crystal grain size number (GSN) of 8.0 and 6.3. In the case of the particle size number 6.3, the hole expansion rate hardly changes even when the Sn addition amount is increased. On the other hand, in the case of the particle size number 8.0, the hole expansion rate increases when the Sn addition amount exceeds 0.01%, shows a maximum at Sn: 0.03%, and decreases at an addition amount beyond that. Thus, it was found that the effect of Sn addition on the hole expansibility differs depending on the crystal grain size.

  Next, the reasons for limiting the constituent elements of the ferritic stainless steel sheet according to the present invention and the reasons for limiting the manufacturing conditions will be described. In addition, the description of% about a composition means the mass% unless there is particular notice.

<C: 0.0005 to 0.020%>
When C is added in a large amount, the workability is deteriorated. Moreover, since the corrosion resistance by the sensitization of a welded part may be caused, less is preferable. However, excessive reduction leads to an increase in cost at the steelmaking stage, so the lower limit is made 0.0005%. From the viewpoint of stable productivity, the content is preferably 0.0015% or more. The upper limit is 0.020% from the viewpoint of corrosion resistance. In consideration of deep drawability, bendability, etc., it is preferably 0.0080% or less, more preferably 0.0060% or less.

<Si: 0.01 to 1.0%>
Si may be used as a deoxidizing element or may be actively added to improve oxidation resistance. However, since the extremely low Si causes an increase in cost, the lower limit is set to 0.01%. From the viewpoint of deoxidation, it is preferably 0.03% or more. Moreover, since addition of a large amount may cause a decrease in hole expansibility due to hardening of the material, the upper limit is preferably set to 1.0%. In view of workability and stable productivity, the content is preferably 0.30% or less, and more preferably 0.20% or less. Furthermore, it is desirable to make it 0.15% or less in order to ensure workability and stable manufacturability.

<Mn: 0.01 to 1.0%>
Mn may also be used as a deoxidizing element like Si, but excessive reduction of Mn causes an increase in cost, so the lower limit is made 0.01%. In addition, it is preferable to set it as 0.03% or more from the point of refining cost, More preferably, it is 0.07% or more. Moreover, since a large amount of Mn may cause hardening of the material, the upper limit is preferably set to 1.0%. In view of workability and stable productivity, the content is preferably 0.30% or less, and more preferably 0.25% or less. Furthermore, it is desirable to make it 0.15% or less in order to ensure workability and stable manufacturability.

<P: less than 0.050%>
P is an inevitable impurity. Although it may be mixed from the raw material as an impurity element, the smaller the content, the better. If P is present in a large amount, the secondary workability is deteriorated. Therefore, although it is an unavoidable impurity, the upper limit is limited to less than 0.050%. In addition, from a viewpoint of suppression of workability deterioration, it is preferable to set it as 0.035% or less, More preferably, it is less than 0.030%. On the other hand, it is not necessary to determine the lower limit of the amount of P. However, excessive reduction leads to an increase in raw material and steelmaking costs. From this point, 0.005% may be the lower limit, and further 0.010% or more Also good.

<S: less than 0.010%>
S is an inevitable impurity. In some cases, it is mixed as an impurity element from the raw material. Since it is an element that degrades corrosion resistance and its content is preferably as small as possible, the upper limit is limited to less than 0.010% although it is an unavoidable impurity. Moreover, since corrosion resistance is so favorable that content is low, Preferably it is less than 0.0030%. More preferably, it is less than 0.0010%. On the other hand, since excessive reduction leads to an increase in refining costs, the lower limit may be set to 0.0002%, and further may be set to 0.0005% or more.

<Cr: 10.0 to 15.0%>
Cr is an extremely important element for ensuring corrosion resistance, and forms a passive film to exhibit stable corrosion resistance. In order to obtain this effect, 10.0% or more is necessary. In addition, it is preferable to set it as 12.0% or more from a viewpoint of corrosion resistance and stable productivity.
On the other hand, addition of a large amount causes toughness deterioration during production, so the upper limit is made 15.0%. In addition, it is preferable to set it as 14.0% or less from the point of hole expansibility. More preferably, it is 13.5% or less.

<N: 0.0005 to 0.020%>
N, like C, is an element that causes a decrease in workability and the generation of stretcher strains, so a smaller amount is preferable. However, since excessive reduction causes an increase in cost at the steelmaking stage, the lower limit value may be 0.0005%. From the viewpoint of stable productivity, the content is preferably 0.0015% or more, and more preferably 0.0030% or more. In addition to the decrease in N workability, the corrosion resistance of the welded portion decreases, so the upper limit is made 0.020%. In addition, from the viewpoint of workability, it is preferably 0.015% or less, and more preferably 0.010% or less.

<Sn: 0.010 to 0.05%>
Sn is an important element in the present invention, and is an element that maximizes hole expansibility in combination with the crystal grain size. Since the addition amount of 0.010% or more is necessary to exhibit the effect, this is the lower limit. In addition, in order to ensure the said effect more stably, it is preferable to set it as 0.015% or more. More preferably, it may be 0.020% or more. Moreover, even if it adds exceeding 0.050%, since the effect of a hole expansion improvement is not exhibited, this is made an upper limit. In addition, it is preferable to set it as 0.040% from a viewpoint of hole expansibility and raw material cost, It is good to set it as 0.035% or less more preferably.
Further, Sn contributes to improvement of weather resistance as described in Patent Document 4 and Patent Document 5. If the Sn content is within the above range, the effect of improving weather resistance can also be obtained.

<Ti: 0.03-0.25%>
Ti is an important element for improving deep drawability by fixing C and N as precipitates, and is also effective for improving workability. In order to exert the effect, 0.03% or more must be added, so this is the lower limit. In consideration of deep drawability, addition of 0.06% or more is preferable. More preferably, the content is 0.1% or more. On the other hand, addition of a large amount leads to ductility deterioration of the product, and also causes generation of rolling wrinkles during production. For this reason, the upper limit is made 0.25%. In consideration of raw material cost and production stability, the upper limit is preferably 0.20%.

<Nb: less than 0.030%>
Since Nb causes the material to harden when added, Nb is preferably low. However, since it may be contained in steel as impurities, the upper limit was made 0.030%. The lower one is preferable, and the upper limit is preferably less than 0.020%.

<Grain size number is 7.0 to 9.5>
The present invention is based on the fact that the size of crystal grains (crystal grain size number), the amount of Sn added, and the hole expansion rate are closely related, and the crystal grain size number is an important requirement. The crystal grains referred to in the present invention are ferrite crystal grains. The crystal grain size number conforms to JIS G 0552. As shown in FIG. 1, when the crystal grain size number is 6.3, the hole expandability hardly changes regardless of the Sn content. On the other hand, when the crystal grain size number is 8.0, it has been found that the hole expansion ratio changes when the Sn content is in the range of 0.01% to 0.05%. At this time, the Sn content is 0.03%, and the hole expansion rate shows a maximum.

  FIG. 2 shows the relationship between the crystal grain size and the hole expandability when the Sn content is about 0.03% (0.028% to 0.031%). It can be seen that the crystal grain size is about 8.0 to 8.5. Here, it is understood that the crystal grain size is about 7 to 9.5 when the range of the hole expansion ratio λ = 100 is considered as a standard for good hole expansion performance. In the present invention, it was confirmed that the hole expandability was good within this range, so the crystal grains were defined as 7 to 9.5 in terms of crystal grain size number.

  On the other hand, when the crystal grain size number is small, rough skin is likely to occur during molding, so 7.0 is set as the lower limit. Since rough skin is less likely to occur as the particle size number is larger, it is preferably 7.5 or more. On the other hand, when the crystal grain size number exceeds 9.5, the strength increases, but the ductility and hole expansibility decrease. For this reason, the upper limit of the crystal grain size number is set to 9.5. Moreover, it is preferable to set it as 9.0 or less from a viewpoint of stable productivity.

In the present embodiment, in addition to the above elements, Al: 0.003 to 1.0% may be added.
Since Al is sometimes used as a deoxidizing element and is known to improve oxidation resistance, it may be added as necessary. The effective amount for deoxidation is 0.003%, which is preferably the lower limit, and in order to obtain a certain degree of deoxidation effect, the lower limit is preferably 0.005%. Further, when the addition amount exceeds 1.0%, the increase in strength is increased, and the moldability may be deteriorated. Therefore, this is preferably set as the upper limit. More preferably, the upper limit is 0.15% in order not to greatly reduce the moldability.

In this embodiment, in addition to the above elements, Ni: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Mo: 0.01 to 0.50%, Sb: 0.0. 001 to 0.30%, Zr: 0.005 to 0.50%, Co: 0.005 to 0.50%, W: 0.002 to 0.50%, V: 0.02 to 0.50% , Ga: 0.001 to 0.10%
It is preferable to add one or more of these.

  Ni, Cu, and Mo are elements that improve the corrosion resistance, and may be added as necessary. In any case, since the effect is exhibited by addition of 0.01% or more, it is preferable to set the lower limit. Moreover, since addition of a large amount causes hardening of a material and deterioration of ductility, about Ni, Cu and Mo, it is preferable to make 0.50% an upper limit. Desirably, it is 0.01 to 0.10%.

  Sb, Zr, Co, and W can also be added as necessary to improve the corrosion resistance. These are important elements for suppressing the corrosion rate, but excessive addition deteriorates manufacturability and cost, so the range of Sb is 0.001 to 0.30%, and the range of Zr and Co is 0.00. The range of 005 to 0.50% and W was 0.002 to 0.50%. More desirably, it is 0.01 to 0.2%.

  V improves crevice corrosion resistance and can be added as necessary. However, excessive addition of V lowers workability and also saturates the effect of improving corrosion resistance, so the lower limit of V is 0.02% and the upper limit is 0.50%. More desirably, it is 0.05 to 0.30%.

  Ga: Ga is an element contributing to corrosion resistance and workability improvement, and can be contained in a range of 0.001 to 0.10%. More preferably, it is 0.002 to 0.05%.

  In this embodiment, in addition to the above elements, one or two of B: 0.0003 to 0.0025%, Mg: 0.0001 to 0.0030%, Ca: 0.0003 to 0.0030% More seeds can be added.

  B, Mg and Ca are elements having an effect of improving secondary workability and ridging resistance. Since the effect is exhibited at B: 0.0003%, Mg: 0.0001%, Ca: 0.0003% or more, it is preferable to set this as the lower limit. On the other hand, since a large amount of decrease may cause a decrease in yield during production, the upper limit is preferably set to B: 0.0025%, Mg and Ca: 0.0030%. In addition, a more preferable addition range is B and Ca: 0.0003-0.0010%, Mg: 0.0002-0.0008%.

  In this embodiment, in addition to the above elements, REM (rare earth metal): 0.002 to 0.20%, Zn: 0.002 to 0.10%, Ta: 0.002 to 0.50%, Hf: 0.002 to 0.50%, As: 0.001 to 0.20%, Bi: 0.001 to 0.30%, Pb: 0.001 to 0.10%, Se: 0.001 One or two or more of 0.10% can be contained. These elements are elements that act to ensure strength, improve corrosion resistance, and the like. If it is within the above range, it works effectively, so this was made the upper and lower limit range.

Next, manufacturing conditions will be described.
The present invention is novel in that it has found an optimum value of grain size number and components, particularly Sn content. The grain size is greatly affected by the final heat treatment temperature and the amount of strain before that.
Therefore, the total rolling reduction in hot rolling is set to 97% or more. The total rolling reduction in hot rolling greatly affects the recrystallized grain size and recrystallized texture in the subsequent heat treatment. If the total rolling reduction is less than 97%, the crystal grain size after hot rolling becomes coarse, and a predetermined crystal grain size cannot be obtained under the cold rolling and heat treatment conditions described later. The upper limit of the total rolling reduction is not particularly required, but is preferably 99% in consideration of the load on the rolling mill. The total rolling reduction in hot rolling has the following relationship, where t ₀ is the slab thickness (sheet thickness) before hot rolling, and t _f is the thickness after hot rolling. Therefore, theoretically, the total reduction ratio in the hot rolling does not become 100% or more.

Total rolling reduction = (t ₀ −t _f ) / t ₀ = 1−t _f / t ₀

  The rolling finishing temperature of the final pass in hot rolling is set to 950 ° C. or lower. This is because if the rolling finishing temperature exceeds 950 ° C., a predetermined crystal grain size cannot be obtained after the final heat treatment. The lower limit of the rolling finishing temperature is preferably 700 ° C. in consideration of the load on the rolling mill and the suppression of rolling wrinkles.

  The coiling temperature after hot rolling is less than 700 ° C. This is because if the coiling temperature is 700 ° C. or higher, the crystal grains are coarsened in the subsequent heat treatment, and a predetermined crystal grain size cannot be finally obtained.

  The maximum temperature in the heat treatment after hot rolling is set to 875 ° C. or higher. This is because below this range, an unrecrystallized structure remains, and the ridging property and hole expansibility of the product deteriorate. The upper limit of the heat treatment temperature is 950 ° C. If it exceeds this, the crystal grains become coarse, and the crystal grain diameter after the final heat treatment becomes coarse and the hole expandability deteriorates, so this was made the upper limit.

  The rolling reduction of the cold rolling before the final heat treatment is 50% or more and less than 85%. The cold rolling reduction ratio greatly affects the subsequent recrystallized grain size. When the rolling reduction of cold rolling is less than 50%, the recrystallization driving force is small, so there may be an unrecrystallized structure. Even if recrystallization occurs, the crystal grain size becomes large, and the crystal grain size number is Since it was less than 7.0, this was made into the minimum. The higher the rolling reduction in cold rolling, the finer the recrystallized grain size, so 60% or more is preferable if possible. Further, the higher the cold rolling reduction ratio, the greater the load on the cold rolling mill, so the upper limit was set to 85%. In consideration of stability during cold rolling (plate thickness, shape, etc.), it is preferably 80% or less. As for the conditions of cold rolling, even if the roll roughness of the work roll used, roll diameter, rolling oil, number of rolling passes, rolling speed, rolling temperature are changed, the metal structure obtained after heat treatment does not change significantly. These conditions are not specified.

  The maximum temperature in the final heat treatment step after cold rolling is set to 820 ° C. or higher. If the temperature is lower than 820 ° C., the material becomes hard due to insufficient recrystallization, and the hole expansibility decreases. In order to ensure recrystallization, the lower limit is preferably set to 850 ° C. At 900 ° C. or higher, the grain size number becomes less than 7.0 due to grain growth, so this is the upper limit. Preferably it is 880 degrees C or less.

  The effect of the present invention can be obtained by performing the final heat treatment after the cold rolling twice and the third cold rolling, but it is preferable to manufacture by the single cold rolling method in view of production efficiency.

The holding time in the heat treatment after the hot rolling and the heat treatment after the cold rolling is not particularly specified, but is preferably 1 second or more from the viewpoint of stable productivity of the crystal grain size. In addition, if the holding time is long, the manufacturability deteriorates, so the maximum holding time is preferably 100 seconds. More preferably, it may be within 60 seconds. If the cooling rate after the heat treatment is too slow, the grain size is affected, so 1 ° C./second is the lower limit. The upper limit of the cooling rate is preferably 100 ° C./second so as not to significantly increase the manufacturing cost. Forced air cooling, mist spraying, water cooling, etc. satisfy the above range.
By going through the above manufacturing process, a stainless steel plate having a grain size number of 7.0 to 9.5 can be obtained.

  The effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.

  Steel having the component composition (% by mass) shown in Table 1 was melted. Next, the steel ingot obtained from the steel ingot was cut and collected into a steel piece having a thickness of 90 mm, and hot rolled, hot rolled sheet annealed, and cold rolled were performed under various conditions to produce a 1.0 mm thick cold rolled steel sheet . Thereafter, heat treatment was performed at various temperatures. After the heat treatment, the metal structure was observed and the crystal grain size number was measured. The measurement of the grain size number was based on JIS Z 0552. The hole expansion rate was measured from the obtained annealed plate. As described above, a 90 mm square steel plate was cut out, a circular hole having a diameter of 10 mm was punched out so that the clearance would be 12.5%, and the measurement was performed by pressing with a 60 ° conical punch. The hole expansion test was performed with n = 5, and an average value was used.

  Table 2 lists the properties obtained. The steel sheet obtained by the present invention has a hole expansion rate of 100% or more. On the other hand, in the comparative steel (comparative method), the hole expansion rate is less than 100%.

  ADVANTAGE OF THE INVENTION According to this invention, the ferritic stainless steel plate excellent in hole expansibility can be obtained, and it can utilize in all industrial fields.

Claims (5)

% By weight
C: 0.0005 to 0.020%,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%
P: less than 0.050%,
S: less than 0.010%,
Cr: 10.0-15.0%,
N: 0.0005 to 0.020%,
Sn: 0.010 to 0.050%
Ti: 0.03-0.25%,
Nb: less than 0.030%,
Ferritic stainless steel with excellent hole-expandability, characterized in that it has a steel composition in which the balance is iron and inevitable impurities, and the crystal grain size number is 7.0 or more and 9.5 or less steel sheet. % By mass
Al: 0.003-0.5%
The ferritic stainless steel sheet having excellent hole expandability according to claim 1. % By mass
Ni: 0.01 to 0.50%,
Cu: 0.01 to 0.50%,
Mo: 0.01 to 0.50%
Sb: 0.001 to 0.30%,
Zr: 0.005 to 0.50%,
Co: 0.005 to 0.50%,
W: 0.002 to 0.50%,
V: 0.02 to 0.50%,
Ga: 0.001 to 0.10%
The ferritic stainless steel sheet excellent in hole expansibility according to claim 1 or 2, wherein one or more of them are contained. % By mass
B: 0.0003 to 0.0025%,
Mg: 0.0001 to 0.0030%,
Ca: 0.0003 to 0.0030%
REM (rare earth metal): 0.002 to 0.20%
Zn: 0.002-0.10%
Ta: 0.002 to 0.50%
Hf: 0.002 to 0.50%
As: 0.001 to 0.20%
Bi: 0.001 to 0.30%
Pb: 0.001 to 0.10%
Se: 0.001 to 0.10%
The ferritic stainless steel sheet excellent in hole expansibility according to any one of claims 1 to 3, wherein one or more of them are contained. The steel having the component according to any one of claims 1 to 4 is hot-rolled with a total rolling reduction in hot rolling of 97% or more and a final finish rolling temperature of 950 ° C or less, and less than 700 ° C. After performing the winding process at a temperature of 875 ° C. or higher, heat treatment is performed at a temperature of 875 ° C. or higher and 950 ° C. or lower. There line heat treatment method superior ferritic stainless steel sheet hole expansion, wherein the grain size number of the crystal grains is 7.0 to 9.5.

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