JPWO2019188094A1 - Ferritic stainless steel sheet and its manufacturing method - Google Patents

Abstract

This ferrite-based stainless steel plate has Cr: 11.0 to 30.0%, C: 0.001 to 0.030%, Si: 0.01 to 2.00%, Mn: 0.01 to 2.00%. , P: 0.003 to 0.100%, S: 0.0100% or less, N: 0.030% or less, B: 0 to 0.0025%, Sn: 0 to 0.50%, Ni: 0 to 0 1.00%, Cu: 0 to 1.00%, Mo: 0 to 2.00%, W: 0 to 1.00%, Al: 0 to 1.00%, Co: 0 to 0.50%, V: 0 to 0.50%, Zr: 0 to 0.50%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, Y: 0 to 0.10%, Hf: 0 to 0 .10%, REM: 0 to 0.10%, Sb: 0 to 0.50%, and Ti: 0.40% or less, Nb: 0.50% or less, or both, and the balance Is composed of Fe and impurities, the amount of P existing as a phosphor is 0.003% by mass or more, and the crystal grain size number measured by JIS G 0551 is 9.0 or more.

Description

The present invention relates to a ferritic stainless steel sheet and a method for producing the same, and more particularly to a ferritic stainless steel sheet having excellent formability and rough skin resistance during molding and a method for producing the same.
The present application claims priority based on Japanese Patent Application No. 2018-0697775 filed in Japan on March 30, 2018, the contents of which are incorporated herein by reference.

SUS304 (18Cr-8Ni), which is a representative steel grade of austenitic stainless steel, is widely used in home appliances, kitchen products, building materials, etc. because of its excellent corrosion resistance, workability, and beauty. However, it is said that the price of the steel sheet is high because SUS304 contains a large amount of Ni, which is expensive and the price fluctuates sharply. On the other hand, ferritic stainless steel does not contain Ni or has an extremely low content, so that demand is increasing as a material having excellent cost performance. However, when ferrite-based stainless steel is used for molding, the problems are the molding limit and deterioration of the rough surface resistance due to the formation of surface irregularities after molding.

First, comparing the molding limits, the austenitic stainless steel has excellent overhangability, but the ferrite stainless steel has low overhangability, and the shape cannot be changed significantly. However, since the crystal orientation (organization) can be adjusted to control the deep drawing property, when ferritic stainless steel is used for molding purposes, a molding method mainly for deep drawing is often used.

Next, the surface characteristics after molding, particularly rough processed skin (surface unevenness after molding) will be described. Here, "surface unevenness" refers to fine irregularities (rough skin) that occur on the surface of the steel sheet after processing or molding, and since these fine irregularities correspond to crystal grains, the larger the crystal grain size, the larger the crystal grain size. Surface irregularities also become noticeable.
In the case of austenitic stainless steel, since it is excellent in work hardening characteristics and a fine grain structure is relatively easy to form, a steel sheet having a crystal grain size number of about 10 is manufactured. Therefore, the surface unevenness (rough skin) after the molding process is small, and there is almost no problem. On the other hand, the crystal grain size of ferritic stainless steel is about 9 for SUS430 and about 7 for SUS430LX, which are smaller than those of austenitic stainless steel. Here, a small particle size number indicates a large crystal particle size.
The factors that make ferritic stainless steels more likely to be coarse-grained are that ferritic stainless steels tend to have a large recrystallized particle size and, like SUS430LX, reduce C and N to improve workability and formability. This is because the improved high-purity ferritic stainless steel tends to grow grains. Further, in ferrite stainless steel, even if a product plate having a fine crystal grain size is manufactured by increasing the number of cold spreadings, rough skin may occur, and the cause is not always clear.

When relatively strict formability is required for housings or fixtures of home appliances, high-purity ferritic stainless steel such as SUS430LX is often used as the ferrite stainless steel. Further, in order to ensure the strength after molding, the thickness of the stainless steel sheet used is 0.6 mm or more in most cases, but as described above, the ferritic stainless steel has a large crystal grain size, so after molding. The rough skin is large, and surface irregularities are usually removed by polishing.

From the above background, a method for reducing rough skin of high-purity ferritic stainless steel is disclosed.
Patent Document 1 discloses a ferritic stainless steel having excellent formability with less roughened surface by controlling the size and crystal grain size of precipitated particles using high-purity ferritic stainless steel and a method for producing the same. There is. However, in Patent Document 1, although a steel sheet having a small crystal grain size is obtained, the deep drawing property at the time of molding is not sufficient, and even though the crystal grain size is small, rough skin after molding is likely to occur. There was a problem.

Patent Document 2 describes that ferritic stainless steel containing Ti and Nb is hot-rolled at a low temperature and has a high cold-rolling ratio to make fine particles, and has excellent skin roughness resistance during molding. It discloses the technology for manufacturing stainless steel. Although the stainless steel of Patent Document 2 has a fine grain structure with a crystal grain size number of 9.5 by such a technique, the rough skin after cup drawing molding is not always sufficient.

Patent Document 3 describes a ferritic stainless steel having excellent deep drawing property, rigging property and rough skin resistance by controlling the crystal grain size of a steel having a component composition containing Nb and / or Ti before final cold spreading. Is disclosed. However, in Patent Document 3, the crystal grain size of the final product is 15 μm (crystal grain size number is 9.1), and the rough skin property is insufficient.

As described above, when considering the molding process of ferritic stainless steel, it is currently very difficult to form a predetermined shape and satisfy the surface characteristics after molding. Therefore, when ferritic stainless steel is used for molding, it is necessary to perform a polishing step in order to remove surface irregularities generated after molding. However, in this polishing process, polishing time is required and the manufacturing cost is increased. Further, there is a problem that a large amount of dust generated by polishing is generated.

Japanese Patent No. 4479888 Japanese Unexamined Patent Publication No. 7-292417 Japanese Patent No. 3788311

The present invention has been made in view of the above problems, and provides a ferritic stainless steel sheet having excellent molding processability and rough surface resistance after molding processing, and a method for producing the same.

Crystal grain size and strain amount are known as factors that affect the roughened surface of ferrite stainless steel. However, as described above, roughened processed skin may occur even if the crystal grain size and the amount of strain are increased by controlling the cold spreading conditions and the like, and in recent years, steel capable of more stably suppressing the occurrence of roughened processed skin has been desired. It was.
Therefore, the present inventors investigated the relationship between the rough processed surface and the metallographic structure in ferritic stainless steel. For the first time, it was found that not only the conventionally known crystal grain size and strain amount but also the precipitation amount of precipitates in steel affect the roughened processed surface. Further, it was clarified that in order to control the precipitation amount within an appropriate range, it is necessary to control the heat treatment temperature before and after cold rolling, and further, rapid heating is required in the heat treatment after cold rolling.

The gist of one aspect of the present invention is as follows.
[1] By mass%
Cr: 11.0% or more and 30.0% or less,
C: 0.001% or more and 0.030% or less,
Si: 0.01% or more and 2.00% or less,
Mn: 0.01% or more and 2.00% or less,
P: 0.003% or more and 0.100% or less,
S: 0.0100% or less,
N: 0.030% or less,
B: 0% or more and 0.0025% or less,
Sn: 0% or more and 0.50% or less,
Ni: 0% or more and 1.00% or less,
Cu: 0% or more and 1.00% or less,
Mo: 0% or more and 2.00% or less,
W: 0% or more and 1.00% or less,
Al: 0% or more and 1.00% or less,
Co: 0% or more and 0.50% or less,
V: 0% or more and 0.50% or less,
Zr: 0% or more and 0.50% or less,
Ca: 0% or more and 0.0050% or less,
Mg: 0% or more and 0.0050% or less,
Y: 0% or more and 0.10% or less,
Hf: 0% or more and 0.10% or less,
REM: 0% or more and 0.10% or less,
Sb: Contains 0% or more and 0.50% or less, and further
Ti: 0.40% or less, Nb: 0.50% or less, one or both of them are contained, and the balance is composed of Fe and impurities.
The amount of P present as a phosphide is 0.003% by mass or more,
A ferritic stainless steel sheet having a crystal grain size number of 9.0 or more as measured by JIS G 0551.
[2] By mass%, further
B: 0.0001% or more and 0.0025% or less,
Sn: 0.005% or more and 0.50% or less,
Ni: 0.05% or more and 1.00% or less,
Cu: 0.05% or more and 1.00% or less,
Mo: 0.05% or more and 2.00% or less,
W: 0.05% or more and 1.00% or less,
Al: 0.05% or more and 1.00% or less,
Co: 0.05% or more and 0.50% or less,
V: 0.05% or more and 0.50% or less,
Zr: 0.05% or more and 0.50% or less,
Ca: 0.0001% or more and 0.0050% or less,
Mg: 0.0001% or more and 0.0050% or less,
Y: 0.001% or more and 0.10% or less,
Hf: 0.001% or more and 0.10% or less,
REM: 0.001% or more and 0.10% or less,
Sb: The ferrite-based stainless steel sheet according to the above [1], which contains one or more of 0.005% or more and 0.50% or less.

[3] A hot rolling step of hot rolling a steel having the component according to the above [1] or [2], and heat of heat treatment at a temperature of 850 ° C. or higher and 900 ° C. or lower after the hot rolling step. A rolled plate annealing step, a cold rolling step of rolling with a rolling ratio of 75% or more and 90% or less after the hot rolled plate annealing step, and a cold rolled plate annealing step performed following the cold rolling step are provided. In the cold-rolled plate annealing step, the average heating rate in the temperature range of 400 ° C. to 800 ° C. in the temperature raising process is 80 ° C./s or more, and the maximum temperature reached of the plate temperature is 880 ° C. or more and 980 ° C. or less. The present invention is characterized in that cooling is started within 5 seconds after reaching the maximum reached temperature, and the average cooling rate in the temperature range from the maximum reached temperature to 700 ° C. is 50 ° C./s or more. The method for producing a ferrite-based stainless steel sheet according to [2].
[4] After the hot rolling step of hot rolling the steel having the component according to the above [1] or [2] and the hot rolling step, heat treatment is performed at a temperature of 850 ° C. or higher and 900 ° C. or lower. A hot-rolled plate annealing step in which the amount of P present as a phospholide is 0.003% by mass or more, and a cold rolling step in which the rolling ratio is 75% or more and 90% or less after the hot-rolled plate annealing step. A cold-rolled sheet annealing step performed following the cold-rolled step is provided, and in the cold-rolled sheet annealing step, the average heating rate in the temperature range of 400 ° C. to 800 ° C. is 80 ° C./s. As described above, the maximum reached temperature of the plate temperature is 880 ° C. or higher and 980 ° C. or lower, cooling is started within 5 seconds after reaching the maximum reached temperature, and the average cooling rate in the temperature range from the highest reached temperature to 700 ° C. is 50. The method for producing a ferrite-based stainless steel sheet according to the above [1] or [2], which comprises cooling at ° C./s or higher.

According to one aspect of the present invention, it is possible to provide a ferritic stainless steel sheet having excellent moldability and rough surface resistance after molding.

It is a TEM observation result (TEM photograph) of the recrystallized structure of the ferritic stainless steel sheet which concerns on this embodiment. It is a figure which shows the relationship between the crystal particle size number and the precipitation amount (Pp) of P which concerns on this Example.

Hereinafter, each requirement of the ferritic stainless steel sheet according to the embodiment of the present invention will be described in detail. In addition, "%" display of the content of each element means "mass%".

The reason for limiting the component (I) will be described below.

Cr is an element that improves corrosion resistance, which is a basic property of stainless steel. If it is less than 11.0%, sufficient corrosion resistance cannot be obtained, so the lower limit is set to 11.0% or more. On the other hand, if an excessive amount of Cr is contained, the formation of an intermetallic compound equivalent to the σ phase (Fe-Cr intermetallic compound) is promoted and cracking during production is promoted, so the upper limit is 30.0% or less. To do. From the viewpoint of stable manufacturability (yield, rolling defects, etc.), 14.0% or more and 25.0% or less are desirable. More preferably, it is 16.0% or more and 20.0% or less.

Since C is an element that reduces moldability, which is important in the present embodiment, it is preferably less, and the upper limit is 0.030% or less. However, since excessive reduction causes an increase in refining cost, the lower limit is set to 0.001% or more. Considering both refining cost and moldability, 0.002% or more and 0.020% or less are preferable.

Si is an element that improves oxidation resistance, but if an excessive amount of Si is contained, the moldability is lowered, so the upper limit is set to 2.00% or less. From the viewpoint of moldability, it is preferable that the amount of Si is low, but since an excessive decrease causes an increase in raw material cost, the lower limit is set to 0.01% or more. From the viewpoint of manufacturability, the desirable range is 0.05% or more and 1.00% or less, and more preferably 0.05% or more and 0.30% or less.

Similar to Si, Mn causes a decrease in moldability when a large amount of Mn is contained, so the upper limit is set to 2.00% or less. From the viewpoint of moldability, it is preferable that the amount of Mn is low, but an excessive decrease causes an increase in raw material cost, so the lower limit is set to 0.01% or more. From the viewpoint of manufacturability, the desirable range is 0.05% or more and 1.00% or less, and more preferably 0.05% or more and 0.30% or less.

P is an important element that contributes to the improvement of roughened skin resistance by precipitating as a phosphide in the steel sheet of the present embodiment. The amount of P is set to 0.003% or more in order to secure the amount of phosphide precipitated and improve the resistance to rough skin. However, since P is an element that lowers moldability, the upper limit is set to 0.100% or less. It should be noted that an excessive reduction in the amount of P brings about an increase in raw material cost, and when both moldability and rough skin resistance are taken into consideration, the preferable ranges are 0.010% or more, 0.050% or less, more preferably. Is 0.020% or more and 0.040% or less.

Since S is an impurity element and promotes cracking during production, a lower value is preferable, and the upper limit is 0.0100% or less. The lower the amount of S, the more preferable, and 0.0030% or less is desirable. On the other hand, it is desirable that the lower limit is 0.0003% or more because an excessive decrease causes an increase in refining cost. From the viewpoint of manufacturability and cost, the preferable ranges are 0.0004% or more and 0.0020% or less.

Like C, N is an element that lowers moldability, and the upper limit is 0.030% or less. However, since excessive reduction leads to an increase in refining cost, the lower limit is preferably 0.002% or more. From the viewpoint of moldability and manufacturability, the preferable range is 0.005% or more and 0.015% or less.

One or both of Ti and Nb are contained as follows.
Ti binds to C and N, fixes C and N as precipitates of TiC, TiN and the like, and brings about improvement in r value and product elongation through high purification. In order to obtain these effects, when Ti is contained, the lower limit is preferably 0.03% or more. On the other hand, if it is contained excessively, the alloy cost increases and the recrystallization temperature increases, resulting in a decrease in manufacturability. Therefore, the upper limit is set to 0.40% or less. From the viewpoint of moldability and manufacturability, the preferable range is 0.05% or more and 0.30% or less. Further, the preferable range for positively utilizing the above-mentioned effect of Ti is 0.10% or more and 0.20% or less.

Like Ti, Nb is also a stabilizing element that fixes C and N, and through this action, the purity of steel is improved, and the r value and product elongation are improved. In order to obtain these effects, when Nb is contained, the lower limit is preferably 0.03% or more. On the other hand, if it is contained excessively, it leads to an increase in alloy cost and a decrease in manufacturability due to an increase in recrystallization temperature, so the upper limit is set to 0.50% or less. From the viewpoint of alloy cost and manufacturability, the preferable ranges are 0.03% or more and 0.30% or less. Further, the preferable range for positively utilizing the above-mentioned effect of Nb is 0.04% or more and 0.15% or less. More preferably, it is 0.06 to 0.10%.

The ferritic stainless steel sheet of the present embodiment is composed of Fe and impurities other than the elements described above (the balance), but in the present embodiment, in addition to the above basic composition, one of the following element groups or Two or more kinds may be selectively contained. That is, the lower limit of the content of B, Sn, Ni, Cu, Mo, W, Al, Co, V, Zr, Ca, Mg, Y, Hf, REM, and Sb is 0% or more.
The "impurities" in the present embodiment are components that are mixed due to various factors in the manufacturing process, including raw materials such as ores and scraps, when steel is industrially manufactured, and are inevitably mixed. Also includes ingredients.

B is an element that improves the secondary processability. Since 0.0001% or more is required to exert the effect, this is set as the lower limit. On the other hand, if it is contained excessively, the manufacturability, particularly the castability, is deteriorated, so the upper limit is 0.0025% or less. The preferred range is 0.0003% or more and 0.0012% or less.

Since Sn is an element having an effect of improving corrosion resistance, it may be contained depending on the corrosive environment at room temperature. Since the effect is exhibited at 0.005% or more, this is set as the lower limit. On the other hand, if it is contained in a large amount, the manufacturability is deteriorated, so the upper limit is 0.50% or less. In consideration of manufacturability, the preferable range is 0.02% or more and 0.10% or less.

Ni, Cu, Mo, Al, W, Co, V, and Zr are elements effective for enhancing corrosion resistance or oxidation resistance, and may be contained as necessary. The effect is exhibited by setting the content of each of Ni, Cu, Mo, Al, W, Co, V, and Zr to 0.05% or more. However, if it is contained in an excessive amount, not only the moldability is lowered, but also the alloy cost is increased and the manufacturability is hindered. Therefore, the upper limit of Ni, Cu, Al, and W is set to 1.00% or less. The upper limit of Ni, Cu, Al, and W is preferably 0.50% or less. Since Mo causes a decrease in manufacturability, the upper limit is set to 2.00% or less. The upper limit of Mo is preferably 1.00% or less. The upper limit of Co, V, and Zr is 0.50% or less in consideration of the development of the effect of improving corrosion resistance or oxidation resistance. The lower limit of the more preferable content of any of the elements Ni, Cu, Mo, Al, W, Co, V and Zr is 0.10% or more.

Ca and Mg are elements that improve hot workability and secondary workability, and may be contained as necessary. However, if it is contained in an excessive amount, it will hinder the manufacturability, so the upper limit of Ca and Mg is set to 0.0050% or less. The preferred lower limit is 0.0001% or more for both. Considering the manufacturability and hot workability, the preferable ranges are 0.0002% or more and 0.0010% or less for both Ca and Mg.

Y, Hf, and REM are elements effective for improving hot workability, steel cleanliness, and oxidation resistance, and may be contained as necessary. When it is contained, the upper limit is 0.10% or less. The preferable lower limit is 0.001% or more for all of Y, Hf, and REM. Here, the "REM" in the present embodiment is composed of one or more selected from the element group (lanthanoid) belonging to atomic numbers 57 to 71, and is, for example, La, Ce, Pr, Nd, etc. Is. The content of "REM" in the present embodiment is the total amount of lanthanoids.

Sb is an element having an effect of improving corrosion resistance like Sn, and may be contained if necessary. However, if it is contained in a large amount, the manufacturability is deteriorated, so the upper limit is 0.50% or less. On the other hand, since the effect of improving corrosion resistance is exhibited at 0.005% or more, this is set as the lower limit.

The ferrite-based stainless steel plate of the present embodiment is composed of Fe and impurities (including unavoidable impurities) other than the elements described above, but the effects of the present embodiment are not impaired in addition to the elements described above. It can be contained in a range. In the present embodiment, for example, Bi, Pb, Se, H, Ta and the like may be contained, but in that case, it is preferable to reduce as much as possible. On the other hand, the content ratio of these elements is controlled to the extent that the problem of the present embodiment is solved, and Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, H ≦ 100 ppm, Ta ≦ 500 ppm, if necessary. It may contain one or more kinds.

(II) Next, the metal structure will be described.
The ferritic stainless steel plate of the present embodiment has a ferrite single-phase structure having a crystal grain size number of 9.0 or more.
The crystal grain size number shall be 9.0 or more. Rough processing after molding is less likely to occur as the crystal grain size number is larger, that is, as the grain size of ferrite crystal grains is smaller, and this is set as the lower limit. In order to further suppress rough skin, it is preferably more than 9.5, more preferably more than 10.0. However, if the grain size of the crystal grains becomes excessively small, the strength may increase and the press moldability may decrease. Therefore, the crystal particle size number is preferably 12 or less.

The crystal grain size number can be obtained by the line segment method of JIS G 0551 (2013). Note that "grain size number: 9" corresponds to an average line segment length of 14.1 μm per crystal grain crossing the inside of the crystal grain, and "grain size number: 10" corresponds to one crystal crossing the inside of the crystal grain. This corresponds to an average line segment length of 10.0 μm per grain. In the measurement of the crystal grain size, the number of crystal grains crossed per sample is set to 500 or more from the optical microstructure photograph of the cross section of the test piece. The etching solution is preferably aqua regia or reverse aqua regia, but other solutions may be used as long as the grain boundaries can be determined. Further, depending on the orientation relationship of adjacent crystal grains, the grain boundaries may not be clearly visible, so it is preferable to perform deep etching. In addition, when measuring the grain boundaries, the twin grain boundaries are not measured.

Further, the metal structure of the ferritic stainless steel sheet of the present embodiment has a ferrite single-phase structure, and a precipitate (phosphide) of P described later is formed. This means that it does not contain the austenite phase or the martensite structure. This is because it is relatively easy to make the crystal grain size finer when it contains an austenite phase or a martensite structure. Furthermore, the austenite phase exhibits high moldability due to the TRIP effect. However, in addition to the high raw material cost, a decrease in yield such as ear cracking is likely to occur during production, so the metal structure is a ferrite single-phase structure. In addition to phosphide, precipitates such as carbonitride may be present in the steel, but these do not significantly affect the effect of this embodiment, and the above is the main phase. Describes the organization.

(III) Next, the amount of P precipitated will be described.
Generally, it is considered that the content of P in a ferritic stainless steel sheet should be reduced because it lowers the formability (r value and product elongation). However, as a result of the studies by the present inventors, it was found for the first time that the amount of phosphide precipitated in steel affects the roughened processed skin. From this, it is clear that in the present embodiment, by controlling the amount of P existing as a phosphide, that is, the amount of precipitation Pp of P, in addition to controlling the crystal grain size, it is possible to further stably further suppress the roughened processed skin. It is characterized in that the precipitation amount Pp of P is defined.

As described above, since the phosphide in the steel greatly contributes to the suppression of roughened processed skin, it is necessary to secure the amount of P precipitated. For this reason, in the present embodiment, the amount of P existing as a phosphide (precipitation amount of P Pp) is set to 0.003% by mass or more. It is preferably 0.004% by mass or more, and more preferably 0.005% by mass or more. The upper limit of the precipitation amount Pp of P is not particularly limited, but since the upper limit of the P content of the steel sheet is 0.100% or less, the upper limit of the precipitation amount Pp of P may be 0.100% or less in the same manner. The phosphide referred to in this embodiment includes, for example, Fe phosphide, Mn phosphide, Ti phosphide, Nb phosphide, Al phosphide, and the like, but the type and composition are not particularly limited. That is, in the present embodiment, it is important that the amount of P existing as the phosphide (precipitation amount Pp of P) is within the above range regardless of the specific composition and existence form of the phosphide.

The details of the method for controlling the precipitation amount Pp of P within the above range will be described later, but the treatment temperature of the heat treatment (hot-rolled sheet annealing and finish annealing) performed before and after the cold rolling step is controlled, and cold rolling is performed. It can be controlled by rapidly performing the heating process in the subsequent heat treatment.

The reason why the precipitated phosphide contributes to the suppression of rough processed skin is under intensive investigation, but at present, it is considered as follows.
In general, since the precipitates are likely to be precipitated on the grain boundaries, it is considered that most of the phosphides precipitated by hot-rolled plate annealing are also precipitated on the grain boundaries. After that, as the metallographic structure is crushed by cold rolling and stretches in the rolling direction, it is considered that the phosphide deposited on the grain boundaries are arranged substantially parallel to the rolling direction. From that state, if finish annealing such as rapid heating, short-time holding, and rapid cooling is performed to recrystallize the phosphide, a recrystallized structure of the metal structure can be obtained with almost no change in the precipitation state of the phosphide. That is, by rapidly heating, holding for a short time, and rapidly cooling the finish annealing, a recrystallized structure in which the phosphide is maintained parallel to the rolling direction is obtained.
In fact, the present inventors observed the thin film TEM of the product plate manufactured by such a manufacturing method (within the manufacturing method range of the present embodiment described later), in which the phosphide in the crystal grains of the recrystallized structure was parallel to the rolling direction. You can see how they are lined up in. FIG. 1 shows a TEM observation result of a recrystallized structure in a steel sheet manufactured under the conditions satisfying the present embodiment described later. As is clear from FIG. 1, it can be confirmed that P-forms are precipitated along the rolling direction in the crystal grains of the recrystallized structure. Whether or not the precipitate deposited in the crystal grains was a P compound was identified by EDS analysis and electron diffraction pattern analysis.
When a stainless steel sheet having a phosphide in such a precipitated state is processed and strained, the movement of dislocations is hindered by the phosphides arranged in parallel with each other. As a result, it is considered that this phosphide showed the same action and effect as the grain boundaries and contributed to the suppression of rough processed skin.

The amount of P deposited, Pp, is measured by the following electrolytic extraction residue method.
A test piece having a size of about 30 mm square is cut out from the center of the stainless steel sheet in the width direction, and the entire surface of the test piece corresponding to the surface of the steel sheet is wet-polished with water-resistant abrasive paper of number # 600. After polishing, the test piece base material (stainless steel base material) is dissolved by electrolysis at a constant potential of -100 mV in a methanol solution containing 10% maleic anhydride and 2% tetramethylammonium chloride. After electrolysis, the residue (precipitate) remaining in the solution without being dissolved is captured using a 200 nm mesh filter. The captured precipitate is washed and dried with pure water. Next, the precipitate is dissolved with aqua regia and perchloric acid, and elemental analysis is performed using ICP emission spectroscopy in accordance with JIS G 1258 to determine the mass of P in the precipitate. The amount of P obtained is divided by the amount of change in the mass of the test piece due to electrolysis (“mass of the test piece before electrolysis”-“mass of the test piece after electrolysis”) and displayed as a percentage, which is expressed as “P”. Precipitation amount Pp ”(mass%).

(IV) Next, a method for manufacturing the ferritic stainless steel sheet of the present embodiment will be described.
The method for producing a ferritic stainless steel sheet according to the present embodiment is to combine hot rolling, hot rolling plate annealing, cold rolling and cold rolling plate annealing (finish annealing), and if necessary, pickling as appropriate. I will do it. That is, as an example of the manufacturing method, for example, a manufacturing method including each step of steelmaking-hot rolling-hot-rolled sheet annealing-cold rolling-cold-rolled sheet annealing (finish annealing) can be adopted.
The conditions to be controlled in order to satisfy both the crystal grain size and the precipitation state of the phosphonic acid, which are important in the present embodiment, are the conditions of heat treatment (annealing of hot-rolled sheet) after hot rolling and cold rolling. The conditions are the rate and heat treatment after cold rolling (annealing of cold rolled plate), and there are no particular restrictions on other processes and conditions.

After hot rolling, heat treatment (hot rolling plate annealing) is performed at a temperature of 850 ° C. or higher and 900 ° C. or lower to secure the precipitation amount Pp of the phosphide after the heat treatment. If the heat treatment temperature is less than 850 ° C., recrystallization defects may occur in the central portion of the plate thickness, which may cause deterioration of moldability due to a decrease in r value and deterioration of polishing characteristics after processing due to rigging. Therefore, the lower limit of the heat treatment temperature for hot-rolled sheet annealing is set to 850 ° C. or higher. Desirably, it is 860 ° C. or higher. Further, if the heat treatment temperature exceeds 900 ° C., the amount of phosphide precipitated is insufficient, and the above-mentioned amount of precipitation Pp cannot be secured. Therefore, the upper limit of the heat treatment temperature for hot-rolled sheet annealing is set to 900 ° C. or lower. It is preferably 880 ° C. or lower, and more preferably less than 870 ° C. In addition, since the precipitation state is hardly changed by annealing after cold stretching (finish annealing), it is important to control the precipitation amount Pp of P at this stage. By hot-rolled plate annealing, the amount of P present as a phosphide (precipitation amount Pp of P) is preferably 0.003% by mass or more at the stage after hot-rolled plate annealing.

The rolling ratio in the subsequent cold rolling is 75% or more and 90% or less.
In order to make the recrystallized grain size finer by the heat treatment performed after cold rolling, it is necessary to increase the introduced strain amount. Recrystallization starts from the part where a lot of strain is introduced. That is, the larger the amount of processing (the larger the rolling ratio), the larger the portion (nucleus) that becomes the starting point of recrystallization, so that the recrystallization grain size becomes smaller. From these facts, in order to increase the crystal grain size number (decrease the crystal grain size), the rolling ratio should be high. If the rolling ratio is less than 75%, these effects cannot be obtained, and the r value may decrease, resulting in a decrease in moldability. Therefore, in the present embodiment, the rolling ratio is 75% or more. Further, the higher the rolling ratio, the higher the r value, so that the rolling ratio is preferably 80% or more. On the other hand, if the rolling ratio exceeds 90%, the r value may decrease, resulting in a decrease in moldability. Therefore, the rolling ratio is in the range of 90% or less.

After cold rolling, heat treatment (cold-rolled sheet annealing) is subsequently performed, and this embodiment is characterized in that this heat treatment is performed rapidly. Specifically, in the cold-rolled plate annealing, the average heating rate in the temperature range of 400 ° C. to 800 ° C. in the temperature raising process is set to 80 ° C./s or more. The maximum temperature reached is 880 ° C or higher and 980 ° C or lower. Cooling is started within 5 seconds after reaching the maximum temperature, and the average cooling rate in the temperature range from the maximum temperature to 700 ° C. is set to 50 ° C./s or more.
The "average temperature rise rate in the temperature range of 400 ° C. to 800 ° C." in the present embodiment means the time required for raising the temperature of the steel sheet in the temperature range (400 ° C.). The value is divided by. "Average cooling rate in the temperature range from the maximum temperature reached to 700 ° C" means that the temperature drop width of the steel sheet from the maximum temperature to 700 ° C is from the time when the maximum temperature is reached to the time when it reaches 700 ° C. The value is divided by the required time. In addition, all the temperatures (° C) in the following description refer to the temperature of the steel sheet.

As described above, in the present embodiment, the phosphide precipitated by hot-rolled sheet annealing is crushed by cold rolling to obtain a precipitated state in which the phosphide is arranged parallel to the cold-rolled direction, and recrystallization is performed while maintaining this precipitated state. And get the product board. Then, even if the product plate containing the phosphide in the above-mentioned precipitated state is formed and strained, the movement of dislocations can be hindered by the phosphide, so that roughened processed skin can be suppressed.
For this reason, it is important that the cold rolled sheet annealing is carried out under conditions that allow recrystallization while maintaining the precipitation state after cold rolling.

After the average temperature rise rate in the temperature range of 400 ° C to 800 ° C in the temperature rise process is set to 80 ° C / s or more and the maximum temperature is reached, in order to maintain the precipitation state after cold rolling and obtain the processing rough surface effect. Start cooling within 5 seconds. That is, the temperature range of 400 ° C. to 800 ° C. is rapidly heated at an average temperature rise rate of 80 ° C./s or more, heated to the maximum temperature reached (880 ° C. or more and 980 ° C. or less), and the holding time at the maximum temperature reached. Start cooling within 5 seconds. In the present embodiment, the temperature may be kept constant when the temperature is maintained at the maximum temperature, but within the range of the maximum temperature ± 10 ° C (maximum temperature −10 ° C to maximum temperature + 10 ° C). If there is, it is permissible even if the holding temperature fluctuates. However, when the holding temperature fluctuates within the above range, it is necessary to control so as not to deviate from the appropriate range of the maximum reached temperature (880 ° C. or higher and 980 ° C. or lower).

If the average heating rate in the temperature range of 400 ° C. to 800 ° C. is less than 80 ° C./s or the holding time is more than 5 seconds, the phosphide may dissolve and the amount of precipitation as a product may not be secured. Further, the rapid temperature rise in the temperature range of 400 ° C. to 800 ° C. also has an effect of refining the recrystallized particle size, and is effective in suppressing roughened processed skin. Further, when the temperature is rapidly raised in the presence of precipitates, the grain growth is suppressed by the pinning effect of the precipitates, so that the product particle size is further refined and the processed skin roughness is further suppressed. From this point of view, the average temperature rise rate in the temperature range of 400 ° C. to 800 ° C. is preferably 150 ° C./s or more.
Further, from the viewpoint of maintaining the precipitated state of the phosphide, it is desirable that the holding time at the maximum temperature reached is 2 seconds or less. Cooling may be started as soon as the holding time reaches 0 seconds, that is, the maximum temperature reached.

In the present embodiment, since the heating process is performed by rapid heating, the time required for heating is shortened. In order to complete recrystallization in this short time, the maximum temperature reached is 880 ° C. or higher. If the maximum temperature reached is less than 880 ° C., recrystallization may be insufficient and workability may be deteriorated due to a decrease in elongation. Therefore, in the present embodiment, the maximum temperature reached is 880 ° C. or higher, preferably 900 ° C. or higher. On the other hand, if the grain growth progresses after the completion of recrystallization, the maximum temperature reached is 980 ° C or lower because the roughened skin resistance may deteriorate due to the coarsening of the crystal grains and the insufficient precipitation amount due to the solid solution of the phosphide. Is the upper limit. It is preferably 950 ° C. or lower.

If crystal grain growth or solid solution of phosphide progresses in the cooling process, the rough surface resistance to processing deteriorates. Therefore, the lower limit of the average cooling rate in the temperature range from the maximum temperature reached to 700 ° C. is set to 50 ° C./s or more. Desirably, it is 100 ° C./s or higher. The upper limit of the average cooling rate in the temperature range from the maximum temperature reached to 700 ° C. is preferably 500 ° C./s or less.

In cold-rolled plate annealing, it is possible to secure a phosphide and obtain a recrystallized structure by heat-treating for a longer time in a lower temperature range than the above conditions, but the crystal grain size becomes large and the skin roughness resistance is obtained. Deteriorates. Further, the effect of suppressing the roughening of the processed skin is exhibited only when the precipitation state of the phosphide in the grain is arranged parallel to the rolling direction. Therefore, even if a phosphide is precipitated in the process of annealing a cold-rolled plate, it does not exert the effect. That is, it is important to perform cold rolled sheet annealing under the above conditions in which the precipitation state of the phosphide can be controlled by cold rolling and the precipitation state can be maintained.

The ferrite-based stainless steel sheet according to the present embodiment can be manufactured by the manufacturing method described above.
In the present embodiment, the hot-rolled plate annealing and the cold-rolled plate annealing may be batch annealing or continuous annealing. Further, each annealing may be bright annealing, which is annealed in a non-oxidizing atmosphere such as hydrogen gas or nitrogen gas, if necessary, or may be annealed in the atmosphere.

The thickness applied to the ferritic stainless steel sheet of the present embodiment is not particularly limited, but is preferably 0.5 mm or more, preferably 0.6 mm or more from the viewpoint of ensuring strength. This is because if the plate thickness is thin, the strength of the molded part may be insufficient. It is necessary to design in consideration of the size and shape of the parts to be manufactured, the load capacity, etc.

As described above, according to the present embodiment, it is possible to provide a ferritic stainless steel sheet having excellent molding processability and rough surface resistance after molding. Further, since the ferrite-based stainless steel sheet of the present embodiment has excellent resistance to rough skin, it is particularly suitable for applications that require polishing to remove surface irregularities (rough skin) after molding.

Next, an example of the present invention will be shown. The conditions in this example are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to the conditions used in the following examples. In the present invention, various conditions can be adopted as long as the object of the present invention is achieved without departing from the requirements of the present invention.
The underlined lines in the table below indicate those outside the scope of the present embodiment.

Stainless steel having the composition shown in Table 1 was melted and cast into a slab, and the slab was hot-rolled to a predetermined plate thickness. After that, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing were performed to obtain a 0.6 mm thick stainless steel sheet (product plate) No. 1-44 were manufactured. Heat treatment temperature (annealing temperature) of hot-rolled plate annealing, cold spreading rate, average temperature rise rate between 400 and 800 ° C. in cold-rolled plate annealing, maximum temperature reached, time required to start cooling (holding time), and maximum reached The average cooling rate in the temperature range from temperature to 700 ° C. was changed as shown in Tables 2 to 4. The annealing time (holding time) in the hot-rolled plate annealing was within the range of 40 to 60 seconds.

Next, the obtained stainless steel plate No. 1-No. A test piece was cut out from the vicinity of the center of the width of 44, and the crystal grain size number (GSN) was measured by the line segment method according to JIS G 0551 (2013). When measuring the crystal grain size, the number of crystal grains crossed per sample was set to 500 or more from the optical microscope microstructure photograph of the cross section of the test piece.

Furthermore, the stainless steel plate No. 1-No. A sample having a diameter of 110 mm was cut out from 44, and a cup forming test with a drawing ratio of 2.2 was carried out by a hydraulic forming tester. It is known that the drawing ratio has a great influence on the rough skin after cup molding, but other molding conditions have no influence. The cup forming test conditions carried out this time are: punch diameter 50 mm, punch shoulder R 5 mm, die diameter 52 mm, die shoulder R 5 mm, wrinkle pressing pressure 1 ton, clearance 1.67 t on one side (t is a plate). Thick). Further, as a lubricant between the sample and the punch, a rust preventive oil "Daphne Oil Coat Z3 (registered trademark)" manufactured by Idemitsu Kosan Co., Ltd. was applied. After that, a lubricating sheet "Nachias Corporation Naflon Tape TOMBO9001" was attached to protect the surface of the steel sheet after molding.

For the sample that could be molded with a drawing ratio of 2.2, the surface roughness after cup molding was measured to evaluate the processed skin roughness.
Here, when the degree and variation of the surface roughness of each part of the sample (molded product) after cup molding was investigated, it was found that there was a variation between the inside and the outside of the vertical wall portion. The survey results will be described in detail.
The present inventors investigated the surface roughness of each part of the sample after cup molding. Rough processing after cup molding is not simply proportional to the crystal grain size and the amount of strain as is generally known, and the formation of irregularities on the surface of the molded product is suppressed by contact with the mold during molding. Therefore, it was found that the surface roughness becomes small. In particular, in the outer wall of the vertical wall portion of the molded product, the force of being pressed against the mold during molding is strong, and the generation of unevenness during molding and the suppression of unevenness due to contact with the mold compete with each other. It was found that the roughness of was greatly varied depending on the measurement position. Therefore, it was considered inappropriate to evaluate the rough texture of the processed skin after cup molding on the outer wall of the vertical wall.
Therefore, the surface roughness of the inner wall of the vertical wall portion where the force pressed by the mold is relatively small was measured. As a result, it was found that the surface roughness after cup molding can be measured with high accuracy. Further, since the surface roughness of the inner wall is larger than that of the outer wall, the inner wall having a large roughness takes the longest polishing time in the polishing process after molding. Therefore, it is considered appropriate to measure the surface roughness assuming polishing after molding (evaluation of processed skin roughness) on the inner wall of the vertical wall portion of the molded product. If the evaluation of the roughened skin is good on the inner wall of the vertical wall portion of the molded product, it can be judged that the outer wall is also good.

The surface according to JIS B 0601 using a two-dimensional contact type surface roughness measuring machine for a length of 5 mm parallel to the height direction at the center of the height inside the vertical wall portion of the sample after cup forming. Roughness measurement was performed and the arithmetic mean roughness Ra was calculated. Based on the arithmetic mean roughness Ra 1.00 μm, if Ra is less than 1.00 μm, the processed skin roughness evaluation is judged to be good (“○”), and if Ra is 1.00 μm or more, the processed skin roughness evaluation is poor (““ ○ ”). × ”) was judged.

Further, in the same manner as described above, the precipitation amount Pp of P on the product plate was measured by the electrolytic extraction residue method.
First, a test piece having a size of about 30 mm square was cut out from the center of the stainless steel sheet in the width direction, and the entire surface of the test piece corresponding to the surface of the steel sheet was wet-polished with water-resistant abrasive paper of number # 600. After polishing, the test piece base material (stainless steel base material) was dissolved by electrolysis at a constant potential of -100 mV in a methanol solution containing 10% maleic anhydride and 2% tetramethylammonium chloride. After electrolysis, the residue (precipitate) remaining in the solution without being dissolved was captured using a 200 nm mesh filter. The captured precipitate was washed with pure water and dried. Next, the precipitate was dissolved with aqua regia and perchloric acid, and elemental analysis was performed using ICP emission spectroscopy in accordance with JIS G 1258 to determine the mass of P in the precipitate. The amount of P obtained is divided by the amount of change in the mass of the test piece due to electrolysis (“mass of the test piece before electrolysis”-“mass of the test piece after electrolysis”) and displayed as a percentage, which is expressed as “P”. Precipitation amount Pp ”(mass%).
The precipitation amount Pp of P in the hot-rolled annealed sheet before cold rolling was also measured by the same method.
The measurement results and evaluation results are shown in Tables 5 to 7.

As shown in Tables 2 to 7, according to the present embodiment, by controlling the precipitation amount of the phosphide by optimizing the annealing conditions and rolling conditions, the rough skin after processing is excellent and the moldability is excellent. It was found that a ferritic stainless steel sheet can be obtained.
In the example of the present invention, Ra <1.00 μm, and rough processed skin was suppressed.

On the other hand, No. in Tables 2 to 7. Examples 25 and 26 are examples in which the component composition is out of the range. In each case, although the precipitation amount Pp of P and the crystal particle size number are within the range of the embodiment, the moldability is deteriorated and it cannot be squeezed out. It was. In addition, No. Both 27 and 28 are examples of using steel L to which Ti and Nb are not added, but the immobilization of P is insufficient, the precipitation amount Pp of P is less than 0.001%, and the moldability deteriorates. I couldn't squeeze it out.
No. In Nos. 3 and 22, the average rate of temperature rise during annealing of the cold-rolled plate was too low, so that the solid solution of the phosphide proceeded and the amount of P deposited Pp was insufficient. Further, the crystal grain size number became smaller, and the roughened surface was deteriorated.
No. In Nos. 5, 10, 12, and 24, the retention time was too long, so that the solid solution of the phosphide progressed and the amount of P deposited Pp was insufficient. Further, the crystal grain size number was also reduced, and the roughened surface was deteriorated.
No. In Nos. 6 and 15, the annealing temperature at the time of annealing the hot-rolled plate was low and the average heating rate was too low, so that the crystal grain size number became small and the roughened surface was deteriorated.
No. In No. 7, since the cold spreading ratio was small and the maximum temperature reached was too high, the grain growth progressed, the crystal grain size number became small, and the processed skin roughness deteriorated.
No. In No. 9, since the annealing temperature at the time of annealing the hot-rolled plate was too high, the precipitation amount Pp of P could not be secured and the roughened surface of the processed surface deteriorated.
No. In No. 16, since the maximum temperature reached was too high, the crystal grain size number became small and the processed skin roughness deteriorated.
No. In No. 19, the average rate of temperature rise during annealing of the cold-rolled plate was low, and the holding time was too long, so that the solid solution of the phosphide progressed and the amount of P deposited Pp was insufficient. Further, the crystal grain size number was also reduced, and the roughened surface was deteriorated.
No. In No. 20, the crystal grain size number became small because the cold spreading ratio was too small. As a result, the rough texture of the processed skin deteriorated.
No. In No. 21, the annealing temperature at the time of annealing the hot-rolled plate was too high, so that the precipitation amount Pp of P could not be secured and the roughened surface of the processed surface deteriorated.
No. In No. 14, since the maximum temperature reached was too high, the grain growth progressed, the crystal grain size number became small, and the processed skin roughness deteriorated.
No. In No. 31, since the average cooling rate at the time of annealing the cold-rolled plate was low, the solid solution of the phosphide progressed, the precipitation amount Pp of P was insufficient, the crystal grain size number was also small, and the roughened texture was deteriorated.
No. In No. 32, since the average cooling rate at the time of annealing the cold-rolled plate was low, the solid solution of the phosphide progressed, the amount of P deposited Pp was insufficient, and the roughened skin was deteriorated.
No. In No. 36, the annealing temperature at the time of annealing the hot-rolled plate was too high, so that the precipitation amount Pp of P could not be secured and the roughened surface of the processed skin deteriorated.
No. In No. 38, the average rate of temperature rise during annealing of the cold-rolled plate was low, and the maximum temperature reached was too high, so that grain growth progressed, the crystal grain size number became smaller, and the roughened surface of the processed material deteriorated.

Further, in the region where the particle size number is 9.0 or more and the amount of precipitated P is less than 0.003% in FIG. Therefore, it is inferior in processing rough skin resistance as compared with the example of the present invention in which the particle size number is the same and the amount of precipitated P is large.

For steel components with P of less than 0.003%, refer to No. 1 in Tables 2 to 7. When manufactured in the same manner as in No. 4, the amount of precipitated P was 0.003% or less, and Ra after the molding test was 1.00 μm or more. Regarding the steel composition in which P exceeds 0.1%, No. 1 in Tables 2 to 7. When it was manufactured in the same manner as in No. 4, the moldability was inferior and it could not be molded.

According to the present embodiment, it is possible to provide a ferritic stainless steel sheet having excellent molding processability and rough surface resistance after molding processing, and a method for producing the same. Therefore, the ferritic stainless steel sheet of the present embodiment is suitably applied to molding applications.

Claims (4)

By mass%
Cr: 11.0% or more and 30.0% or less,
C: 0.001% or more and 0.030% or less,
Si: 0.01% or more and 2.00% or less,
Mn: 0.01% or more and 2.00% or less,
P: 0.003% or more and 0.100% or less,
S: 0.0100% or less,
N: 0.030% or less,
B: 0% or more and 0.0025% or less,
Sn: 0% or more and 0.50% or less,
Ni: 0% or more and 1.00% or less,
Cu: 0% or more and 1.00% or less,
Mo: 0% or more and 2.00% or less,
W: 0% or more and 1.00% or less,
Al: 0% or more and 1.00% or less,
Co: 0% or more and 0.50% or less,
V: 0% or more and 0.50% or less,
Zr: 0% or more and 0.50% or less,
Ca: 0% or more and 0.0050% or less,
Mg: 0% or more and 0.0050% or less,
Y: 0% or more and 0.10% or less,
Hf: 0% or more and 0.10% or less,
REM: 0% or more and 0.10% or less,
Sb: Contains 0% or more and 0.50% or less, and further
Ti: 0.40% or less, Nb: 0.50% or less, one or both of them are contained, and the balance is composed of Fe and impurities.
The amount of P present as a phosphide is 0.003% by mass or more,
A ferritic stainless steel sheet having a crystal grain size number of 9.0 or more as measured by JIS G 0551. In% by mass,
B: 0.0001% or more and 0.0025% or less,
Sn: 0.005% or more and 0.50% or less,
Ni: 0.05% or more and 1.00% or less,
Cu: 0.05% or more and 1.00% or less,
Mo: 0.05% or more and 2.00% or less,
W: 0.05% or more and 1.00% or less,
Al: 0.05% or more and 1.00% or less,
Co: 0.05% or more and 0.50% or less,
V: 0.05% or more and 0.50% or less,
Zr: 0.05% or more and 0.50% or less,
Ca: 0.0001% or more and 0.0050% or less,
Mg: 0.0001% or more and 0.0050% or less,
Y: 0.001% or more and 0.10% or less,
Hf: 0.001% or more and 0.10% or less,
REM: 0.001% or more and 0.10% or less,
Sb: The ferrite-based stainless steel sheet according to claim 1, wherein it contains one or more of 0.005% or more and 0.50% or less. A hot rolling step of hot rolling a steel having the component according to claim 1 or 2.
After the hot rolling step, a hot rolled sheet annealing step of performing heat treatment at a temperature of 850 ° C. or higher and 900 ° C. or lower,
After the hot-rolled sheet annealing step, a cold rolling step of rolling with a rolling ratio of 75% or more and 90% or less, and a cold rolling step.
It is provided with a cold rolled sheet annealing step that is performed following the cold rolling step.
In the cold-rolled plate annealing step, the average temperature rise rate in the temperature range of 400 ° C. to 800 ° C. is 80 ° C./s or more, and the maximum temperature reached is 880 ° C. or higher and 980 ° C. or lower. According to claim 1 or 2, cooling is started within 5 seconds after reaching the maximum temperature, and the average cooling rate in the temperature range from the maximum temperature to 700 ° C is 50 ° C / s or more. The method for manufacturing a ferrite-based stainless steel sheet according to the description. A hot rolling step of hot rolling a steel having the component according to claim 1 or 2.
After the hot rolling step, heat treatment is performed at a temperature of 850 ° C. or higher and 900 ° C. or lower to bring the amount of P present as a phosphide to 0.003% by mass or more, and a hot rolling plate annealing step.
After the hot-rolled sheet annealing step, a cold rolling step of rolling with a rolling ratio of 75% or more and 90% or less, and a cold rolling step.
It is provided with a cold rolled sheet annealing step that is performed following the cold rolling step.
In the cold-rolled plate annealing step, the average temperature rise rate in the temperature range of 400 ° C. to 800 ° C. in the temperature rise process is 80 ° C./s or more, and the maximum temperature reached is 880 ° C. or higher and 980 ° C. or lower. According to claim 1 or 2, cooling is started within 5 seconds after reaching the maximum temperature, and the average cooling rate in the temperature range from the maximum temperature to 700 ° C is 50 ° C / s or more. The method for manufacturing a ferrite-based stainless steel sheet according to the description.