JP6836969B2 - Ferritic stainless steel sheet - Google Patents

Description

The present invention relates to a ferritic stainless steel sheet, and more particularly to a ferritic stainless steel sheet having excellent formability during molding and surface characteristics after molding.

Austenitic stainless steels such as SUS304 (18Cr-8Ni), which is a representative steel type, are widely used in home appliances, kitchen products, building materials, etc. because they are excellent in corrosion resistance, workability, and beauty. However, it is said that the price of austenitic stainless steel is high because a large amount of Ni, which is expensive and the price fluctuates sharply, is added, and a cheaper one is desired from the viewpoint of economy.
On the other hand, since ferritic stainless steel does not contain Ni or has an extremely low content, the demand for it as a material having excellent cost performance has been increasing in recent years. However, when ferrite-based stainless steel is used for molding, problems are the molding limit and the deterioration of surface characteristics due to the formation of surface irregularities after molding.

First, when comparing the molding limits, the austenitic stainless steel has excellent overhanging property, but the ferritic stainless steel has low overhanging property and cannot be significantly deformed. However, since the deep drawing property can be controlled by adjusting the crystal orientation (organization) in the steel, when ferritic stainless steel is used for molding purposes, a molding method mainly for deep drawing may be used. There are many.

Next, the surface characteristics (surface unevenness) after the molding process 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 these fine irregularities correspond to crystal grains, and the larger the crystal grain size, the more the surface irregularities. Will also be noticeable.
In the case of austenitic stainless steel, a steel sheet having a crystal grain size number of about 10 is manufactured because it has excellent work hardening characteristics and a fine grain structure is relatively easy to form. 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, the fact that the particle size number is small indicates that the crystal particle size is large.
One of the reasons why ferritic stainless steels tend to have coarse grains is that ferritic stainless steels tend to have a large recrystallized grain size, and in particular, like SUS430LX, C and N are reduced to improve workability and formability. Since the high-pure ferritic stainless steels we have planned tend to grow grains easily, the crystal grain size tends to be larger than that of austenitic stainless steels.

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

From the above background, a method for reducing rough skin of high-purity ferritic stainless steel has been disclosed.

Patent Document 1 describes a ferritic stainless steel in which the size and grain size of precipitated particles are controlled by using a high-purity ferritic stainless steel to reduce rough processing and improve formability, and a method for producing the same. It is disclosed. However, in the method described in Patent Document 1, although a steel sheet having a small 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 occurs after molding. There was an easy problem.

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

Patent Document 3 describes a ferritic stainless steel in which deep drawing property, rigging property and rough skin resistance are improved by controlling the grain size of a steel having a component containing Nb and / or Ti before final cold spreading. Is disclosed. However, the crystal grain size of the final product is 15 μm (the crystal grain size number is 8.8), and the rough skin resistance is insufficient.

Further, conventionally, in order to reduce the surface unevenness of high-purity ferritic stainless steel, a method of reducing the surface unevenness by increasing the number of cold spreadings and making the crystal grain size finer when manufacturing the ferrite-based stainless steel sheet. Has also been considered. However, in reality, surface irregularities may be generated on the product plate, and the cause is not always clear, and a technique capable of stably maintaining high quality of the steel sheet surface is desired.

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

R. K. Ray, J. et al. J. Jonas and R. E. Hook: International Materials Reviews. vol. 39, No. 4 (1994), p131. Hotaka Homma, Shuichi Nakamura, Naoki Yoshinaga: Iron and Steel, vol.90, No. 7 (2004), p510-517 "Assembly Organization", edited by Shinichi Nagashima, Maruzen (1984), p23.

As described above, when considering the molding process of ferritic stainless steel, it is very difficult to be able to form a predetermined shape and to satisfy the surface characteristics after molding. For this reason, at present, in the case of ferritic stainless steel with ensured moldability, it is necessary to perform a polishing process in order to remove surface irregularities generated after molding, but polishing takes time, increases manufacturing cost, and polishes. There was also an environmental problem such as a large amount of dust generated in.

The present invention has been made in view of the above problems, and provides a ferritic stainless steel sheet having excellent moldability and surface characteristics after molding.

The gist of the present invention is as follows.
[1] In terms of mass%, Cr: 11.0% or more and 25.0% or less, C: 0.001% or more and 0.010% or less, Si: 0.01% or more and 1.0% or less, Mn: 0 .01% or more and 1.0% or less, P: 0.10% or less, S: 0.01% or less, N: 0.002% or more and 0.020% or less, and Ti: 1.0% or less, And Nb: 1 or 2 types of 1.0% or less, the balance is composed of Fe and impurities, and is composed of a ferrite single-phase structure with a crystal grain size number of more than 9.0, with a plate thickness of 1/2 position and a plate. The random intensity ratio of the crystal orientation on the plane parallel to the rolled plane at the thickness 1/10 is I _{{554} <225>} ≧ 7.0, I _{{411} <148>} ≧ 0.9, I _{{211} <} A ferrite-based stainless steel plate having _{011> ≧ 1.0.}
(Note that I _{{hkl} <uvw>} indicates the random intensity ratio of the {hkl} <uvw> orientation)
[2] In terms of mass%, Cr: 11.0% or more and 25.0% or less, C: 0.001% or more and 0.010% or less, Si: 0.01% or more and 1.0% or less, Mn: 0 0.01% or more and 1.0% or less,
P: 0.10% or less, S: 0.0061% or less, and N: 0.002% or more and 0.020% or less, and Ti: 1.0% or less, and Nb: 1.0% or less. 1 or 2 types are included, and further, B: 0.0001% or more and 0.0025% or less, Sn: 0.005% or more and 0.50% or less, Ni: 1.0% or less, Cu: 1.0 % Or less, Mo: 2.0% or less, Al: 1.0% or less, W: 1.0% or less, Co: 0.50% or less, V: 0.50% or less, Zr: 0.50% or less , Ca: 0.0050% or less, Mg: 0.0050% or less, Y: 0.10% or less, Hf: 0.20% or less, REM: 0.10% or less, Sb: 0.50% or less 1 It contains seeds or two or more kinds , and the balance is composed of Fe and impurities, and has a ferrite single-phase structure with a crystal grain size number of more than 9.0. The random intensity ratio of crystal orientations in parallel planes is I _{{554} <225>} ≧ 7.0,
_{I {411} <148> ≧} 0.9, I {211} <011> ≧ 1.0 Der Rukoto you wherein ferrites stainless steel.
[3] The ferrite-based stainless steel sheet according to the above [2], wherein S: 0.0030% or less and Mo: 1.1% or less in mass%.

According to the present invention, it is possible to provide a ferritic stainless steel sheet having excellent moldability and surface characteristics after molding.

Hereinafter, an embodiment of the ferritic stainless steel sheet of the present invention will be described.
The ferritic stainless steel plate according to the present embodiment has Cr: 11.0% or more and 25.0% or less, C: 0.001% or more and 0.010% or less, Si: 0.01% or more and 1 in mass%. .0% or less, Mn: 0.01% or more and 1.0% or less, P: 0.10% or less, S: 0.01% or less, N: 0.002% or more and 0.020% or less, and further It contains one or two types of Ti: 1.0% or less and Nb: 1.0% or less, and the balance consists of Fe and impurities, and consists of a ferritic single-phase structure with a crystal grain size number of more than 9.0. The random intensity ratio of the crystal orientations on the plane parallel to the rolled surface at the plate thickness 1/2 position and the plate thickness 1/10 position is I _{{554} <225>} ≧ 7.0, I _{{411} <148>} ≧ 0. 9.9, I _{{211} <011>} ≧ 1.0.
Each requirement will be described in detail below.

First, the reasons for limiting the components will be described below. The "%" indication of the content of each element means "mass%".

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, excessive addition promotes the formation of an intermetallic compound equivalent to the σ phase (an intermetallic compound of Fe-Cr) and promotes cracking during production, so the upper limit is set to 25.0% or less. From the viewpoint of stable manufacturability (yield, rolling defects, etc.), 14.0% or more and 22.0% or less are desirable. More preferably, it is 16.0% or more and 20.0% or less.

Since C is an element that lowers the moldability (r value), which is important in the present embodiment, it is preferably less, and the upper limit is 0.010% 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 0.008% or less are preferable, and 0.002% or more and 0.006% or less are more preferable.

Si is an element for improving oxidation resistance, but excessive addition causes deterioration of moldability, so the upper limit is 1.0% or less. From the viewpoint of moldability, it is preferable that the Si content is low, but an excessive decrease causes an increase in raw material cost, so the lower limit is 0.01% or more. From the viewpoint of manufacturability, the desirable ranges are 0.05% or more and 0.60% or less, and more preferably 0.05% or more and 0.30% or less.

As with Si, the upper limit of Mn is set to 1.0% or less because the addition of a large amount causes deterioration of moldability. From the viewpoint of moldability, it is preferable that the Mn content is low, but an excessive decrease causes an increase in raw material cost, so the lower limit is 0.01% or more. From the viewpoint of manufacturability, the desirable ranges are 0.05% or more and 0.40% or less, and more preferably 0.05% or more and 0.30% or less.

Since P is an element that lowers moldability (r value and product elongation), it is preferably low, and the upper limit is limited to 0.10% or less. However, since excessive reduction brings about an increase in raw material cost, the lower limit is preferably 0.005% or more. Considering both moldability and manufacturing cost, the preferable range is 0.007% or more and 0.030% or less, and more preferably 0.010% or more and 0.025% or less.

S is an unavoidable impurity element, and it is preferably low because it promotes cracking during production, and the upper limit is limited to 0.01% or less. The lower the amount of S, the more preferably 0.0030% or less. 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 0.002% or less.

Like C, N is an element that lowers moldability (r value), and the upper limit is 0.020% or less. However, since excessive reduction leads to an increase in refining cost, the lower limit is set to 0.002% or more. From the viewpoint of moldability and manufacturability, the preferable ranges are 0.005% or more and 0.015% or less.

It contains one or two of Ti and Nb as follows.
Ti binds to C and N and fixes C and N as precipitates of TiC, TiN and the like (purification), thereby improving moldability (r value) and product elongation. In order to obtain these effects, the lower limit is preferably 0.01% or more. On the other hand, excessive addition causes an increase in alloy cost and a decrease in manufacturability due to an increase in recrystallization temperature, so the upper limit is set to 1.0% or less. From the viewpoint of moldability and manufacturability, the preferable range is 0.05% or more and 0.50% or less. Further, the preferable range for positively utilizing the above-mentioned effect of Ti is 0.10% or more and 0.30% or less.

Nb is also a stabilizing element that fixes C and N like Ti, and brings about improvement in formability (r value) and product elongation through high purification of steel by this action. In order to obtain these effects, the lower limit is preferably 0.01% or more. On the other hand, excessive addition causes an increase in alloy cost and a decrease in manufacturability due to an increase in recrystallization temperature, so the upper limit is set to 1.0% or less. From the viewpoint of alloy cost and manufacturability, the preferable ranges are 0.02% 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. Even more preferably, it is 0.06% or more and 0.10% or less.

The ferrite-based stainless steel sheet of the present embodiment may selectively contain one or more of the following element groups in addition to the above basic composition.

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, excessive addition causes deterioration of manufacturability, particularly castability, so the upper limit is 0.0025% or less. The preferred range is 0.0002 to 0.0020%, more preferably 0.0003 to 0.0012%.

Since Sn is an element having an effect of improving corrosion resistance, it may be added 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, since a large amount of addition causes deterioration of manufacturability, the upper limit is 0.50% or less. In consideration of manufacturability, the preferred range is 0.01 to 0.20%, more preferably 0.02 to 0.10%.

Ni, Cu, Mo, Al, W, Co, V, and Zr are elements effective for enhancing corrosion resistance or oxidation resistance, and are added as necessary. However, excessive addition of these elements may not only reduce the moldability but also increase the alloy cost and hinder the manufacturability. Therefore, the upper limit of Ni, Cu, Al, and W is 1.0% or less. Since Mo causes a decrease in manufacturability, the upper limit is set to 2.0% or less. The upper limit of Co, V, and Zr is 0.50% or less. The lower limit of the more preferable content of each element is 0.10% or more.

Ca and Mg are elements that improve hot workability and secondary workability, and are added as necessary. However, since excessive addition of these elements leads to inhibition of manufacturability, the upper limit of Ca and Mg is set to 0.0050% or less. The preferable lower limit is 0.0001% or more. Considering the manufacturability and hot workability, the preferable range is 0.0002 to 0.0020% for both Ca and Mg, and the more preferable range is 0.0002 to 0.0010%.

Y, Hf, and REM are elements effective for improving hot workability, cleanliness of steel, and improving oxidation resistance, and may be added as necessary. When added, the upper limit is 0.10% or less for Y and REM, and 0.20% or less for Hf, respectively. The preferable lower limit is 0.001% or more for all of Y, Hf, and REM. Here, "REM" in the present embodiment refers to an element (lanthanoid) belonging to atomic numbers 57 to 71, and is, for example, Ce, Pr, Nd, or the like.

Sb is an element having an effect of improving corrosion resistance like Sn, and may be contained if necessary. However, since the addition of a large amount of Sb causes deterioration of manufacturability, 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 ferritic stainless steel plate of the present embodiment is composed of Fe and impurities (including unavoidable impurities) other than the elements described above, but in addition to the above-mentioned elements, the effect of the present invention is not impaired. Can be contained in. 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 invention is solved, and if necessary, 1 of Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, H ≦ 100 ppm, Ta ≦ 500 ppm. It may contain more than a seed.

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 more than 9.0.
The crystal grain size number shall be over 9.0. Since the surface unevenness after molding is less likely to occur as the crystal grain size number is larger, that is, the smaller the grain size of the ferrite crystal grains is, this is set as the lower limit. In order to further suppress the surface unevenness, it is preferably more than 9.5, more preferably more than 10.0.
The method for measuring the crystal grain size number can be obtained by the line segment method of JIS G 0551 (2013). The particle size number: 9 corresponds to the average line segment length of 14.1 μm per crystal grain that crosses the inside of the crystal grain, and the particle size number: 10 corresponds to the average line segment length of 10.0 μm per crystal grain that crosses the inside of the crystal grain. Equivalent to. In the crystal grain size measurement, the number of crystal grains crossed per sample is 500 or more based on 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, the twin grain boundaries are not measured when measuring the grain boundaries.

Normally, it is known that the crystal orientation has a good correlation with the formability (r value), but in the present embodiment, the texture is defined as follows based on the new findings obtained by the present inventors. I decided to. That is, based on the new finding that the crystal orientation has a great influence on the surface unevenness after molding. At each of the plate thickness 1/2 position and the plate thickness 1/10 position, the random intensity ratio of the crystal orientation in the plane parallel to the rolled surface is set as follows.
I _{{554} <225>} ≧ 7.0
I _{{411} <148>} ≧ 0.9
I _{{211} <011>} ≧ 1.0
Note that I _{{hkl} <uvw>} indicates the random intensity ratio of the {hkl} <uvw> orientation.

It is known that the {554} <225> orientation is formed as a recrystallization orientation of high-purity ferritic stainless steel and has good moldability (Non-Patent Document 1). Therefore, it is required to increase the {554} <225> orientation when performing the molding process centering on the drawing. On the other hand, the {411} <148> orientation is generated when the cold rolling ratio is increased (for example, Non-Patent Document 2), but it is not preferable for moldability. Further, the {211} <011> orientation is the orientation formed by rolling (Non-Patent Document 3), but since it is the orientation that is eclipsed at the time of recrystallization, it hardly remains after the completion of recrystallization. Therefore, conventionally, in order to ensure moldability, it is necessary to increase the degree of integration (random intensity ratio) of the {554} <225> orientation and decrease the degree of integration of the {411} <148> orientation and the {211} <011> orientation. It has been considered effective and controlled.

However, the present inventors not only increase the degree of integration of the {554} <225> orientation, which is a preferable orientation for moldability, but also the {411} <148> orientation, which is not preferable for moldability, and are unlikely to remain after recrystallization. It has been found that by increasing the degree of integration of {211} <011> and controlling it in combination with the crystal grain size (crystal grain size), surface unevenness (rough skin) after molding can be stably suppressed.
That is, in the present embodiment, the {554} <225> orientation has a random strength ratio of 7.0 or more in consideration of forming the steel sheet into various shapes. As described above, it is preferable that the random intensity ratio of the {554} <225> orientation is higher in order to raise the molding limit, and therefore it is preferably 8.0 or more.
The {411} <148> orientation is an important orientation for suppressing surface irregularities, and the random intensity ratio is 0.9 or more. It is preferably 1.0 or more. When a ferrite-based stainless steel sheet is manufactured by a conventional method, it is generally less than 0.7. Therefore, in the present embodiment, in order to increase the {411} <148> orientation, it is necessary to control the manufacturing method as described later.
The degree of integration of the {211} <011> orientation is 1.0 or more. As described above, the {211} <011> orientation is unlikely to remain after the completion of recrystallization, and the orientation is generally 0.8 or less when the ferritic stainless steel sheet is manufactured by a conventional method. Therefore, it is necessary to devise the manufacturing conditions as well as the control of the {411} <148> direction.

A method for measuring the random intensity ratio of the crystal orientation will be described.
X-ray diffraction is performed on a surface parallel to the rolled surface of the steel sheet at a position of 1/2 of the plate thickness and a position of 1/10 of the plate thickness. The 1/2 position often indicates the average texture of the steel material and can be an index of formability. Further, since surface unevenness (rough skin) after molding occurs on the surface, the crystal orientation distribution near the surface is important, so the 1/10 position is also measured.
A three-dimensional orientation analysis is performed from the obtained data. As the analysis method, the widely known "Bunge" method can be used. From the crystal orientation distribution map, read the random intensity ratio in the corresponding orientation. It is also possible to use local orientation analysis by EBSD, but in that case, it is necessary to investigate the region where the number of crystal grains is 1000 or more and be careful so that average information on the texture can be obtained. Become.

The reason why both the moldability and the surface unevenness (rough skin) after molding are improved by the above-mentioned regulations of the texture is under intensive investigation, but at present, it is presumed as follows.
When forming a steel material, each crystal grain is deformed according to each crystal orientation. The slip system that is active at that time is considered to be different for each crystal orientation. Generally, the direction in which the r value is high and the direction in which the r value is low have different active slip systems (directions). Therefore, when a crystal grain having a high r value and a crystal grain having a low r value are adjacent to each other on the surface of the steel material, the surface change (concave or convex) caused by the slip of one grain is caused by the adjacent crystal. It is thought that the surface changes (convex or concave) of different grains cancel each other out, and as a result, the surface unevenness is suppressed. However, since there are a huge number of combinations of adjacent crystal grain orientations on the surface of steel materials, further studies are required to elucidate this mechanism.

The metal structure of the ferritic stainless steel sheet of the present embodiment has a ferrite single-phase structure. This means that it does not contain the austenite phase or the martensite structure. When an austenite phase or a martensite structure is contained, the crystal grain size can be made finer, and the austenite phase exhibits high moldability due to the TRIP effect, but in addition to the high raw material cost. The metal structure is a ferrite single-phase structure because the yield such as cracks in the ears is likely to decrease during manufacturing. Although precipitates such as carbonitride are present in the steel, they are not considered because they do not greatly affect the effect of the present invention, and the structure of the main phase is described above.

The thickness of the ferrite-based 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 the plate thickness in consideration of the size and shape of the parts to be manufactured, the load capacity, and the like.

Next, in the method for producing a ferritic stainless steel sheet of the present embodiment described above, hot rolling, cold rolling and each heat treatment (annealing) are combined, and pickling is appropriately performed as necessary. 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 can be adopted.
The points to be controlled in order to satisfy both the crystal grain size and the crystal orientation (organization), which are important in the present embodiment, as described above are the heat treatment conditions after hot rolling, the cold rolling ratio, and after cold rolling. It is a heat treatment condition, and there are no particular restrictions on other processes and conditions.

In the heat treatment after hot rolling (annealing of hot rolled plate), the recrystallization temperature T ₁ (° C) of the hot rolled plate differs depending on the plate thickness and composition, and the reduction rate of hot rolling, but the maximum temperature reached is T ₁ to 1. It is necessary to control in the range of (T _{1 +35) (° C.).} This is because if the maximum temperature reached for hot-rolled sheet annealing _{is less than T 1} ° C., unrecrystallized grains remain and the rigging characteristics and moldability of the product become poor. On the other hand, when the maximum temperature reached exceeds T ₁ + 35 ° C., the crystal grains become coarse due to grain growth, and the crystal grain size after cold-rolled and cold-rolled plate annealing becomes coarse, or after cold-rolled and cold-rolled plate annealing, This is because the above-mentioned crystal orientation, which is important for rough skin, cannot be obtained.

The cold rolling ratio shall be 93% or more. In the conventional method, the cold rolling ratio is generally set to about 90% at the maximum, but in the present embodiment, it is necessary to increase the introduced strain amount in order to make the recrystallized particle size after cold rolling finer. There is. Recrystallization starts from the part where a lot of strain is introduced. That is, the larger the amount of processing (the higher the rolling ratio), the smaller the recrystallization grain size because there are more parts (nuclei) where recrystallization starts, and in addition, it is important for rough skin after recrystallization, {554}. It is also important to control the <225> orientation, the {411} <148> orientation, and the {211} <011> orientation within the above range, and in order to increase these orientations, it is necessary to increase the rolling ratio. From these facts, in this embodiment, it is important that the reduction rate is 93% or more. The upper limit of the rolling ratio is not particularly limited, but may be 97% or less from the viewpoint of the capacity of the rolling mill.
In addition, other rolling conditions for cold rolling of the present embodiment may be appropriately selected and set.

Heat treatment after cold rolling (cold-rolled sheet annealing, final annealing) maximum temperature is in, when the recrystallization temperature of the cold-rolled sheet and _{T 2 (℃) (T 2} -10) ~ (T 2 +30) of ° C. It is necessary to control the range. Peak temperature range (T 2 _-10) is less than the material occurs easily molding cracks and hardening formability of the cold-rolled sheet annealing is due to the possibility of degradation. On the other hand, if the maximum temperature reached exceeds (T ₂ +30), the crystal grain size becomes large and a specified crystal grain size number cannot be obtained, or a predetermined crystal orientation cannot be obtained, and rough skin occurs after molding.

In the present embodiment, intermediate annealing may be performed during cold rolling. That is, the cold rolling of the present embodiment may be one-time rolling or two-time or more rolling with intermediate annealing sandwiched between them. The intermediate and final 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 recrystallization temperatures T ₁ and T ₂ can be determined from the observation of the metallographic structure after heat treatment at different temperatures using a hot-rolled plate or a cold-rolled plate.

The ferrite-based stainless steel sheet according to the present embodiment can be obtained by the manufacturing method described above.

Next, examples of the present invention will be shown. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is used in the following examples. It is not limited to the conditions. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
The underlined lines in the table below indicate those outside the scope of the present invention.

Stainless steel having the composition shown in Table 1 was melted and cast into a slab, and the slab was rolled by hot rolling. 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-No. 28 was manufactured. Each process condition was changed as shown in Table 2. The annealing time (holding time) in the hot-rolled plate annealing and the cold-rolled plate annealing was within the range of 1 to 60 seconds, respectively, and the intermediate annealing was omitted in this example.

Next, the obtained stainless steel plate No. 1-No. The crystal grain size number (GSN) of 28 was measured according to JIS G 0551 (2013).
In addition, stainless steel plate No. 1-No. The textures of the 28 plate thickness centers (1 / 2t position) and 1 / 10t position were measured by X-ray diffraction, which is the method described above, and the {554} <225> orientation, {411} <148> orientation, { _{The random intensity ratios I {554} <225>} , I _{{411} <148>} , and I _{{211} <011>} of the 211} <011> orientations were obtained.

Furthermore, the stainless steel plate No. 1-No. A sample having a diameter of 100 mm was cut out from 28, and a cup forming test with a limit drawing ratio of 2.0 was performed by a hydraulic forming tester. It is known that the limit drawing ratio has a great influence on the surface roughness after cup molding, but other molding conditions have no influence. The cup forming test conditions carried out this time were a punch diameter of 50 mm, a punch shoulder R of 5 mm, a die diameter of 53 mm, a die shoulder R of 8 mm, a wrinkle pressing pressure of 10 tons, and as a lubricant between the sample and the punch. , Apply the rust preventive oil "Daphne Oil Coat Z3 (registered trademark)" manufactured by Idemitsu Kosan Co., Ltd., and then attach the lubricating sheet "Nachias Co., Ltd. Naflon Tape TOMBO9001" to protect the surface of the steel plate after molding. It was.

For the samples that could be molded with the limit drawing ratio of 2.0, the rough skin after cup molding was evaluated. Specifically, the surface roughness was measured 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 of the vertical wall portion of the sample after cup molding. .. The arithmetic average roughness Ra described in JIS B 0031 (2003) is based on 2.0 μm, and when it is less than that, the surface roughness evaluation is good (“○”), and when Ra is more than 2.0 μm, the surface roughness is rough. The evaluation was judged to be defective (“x”).
Table 2 shows the stainless steel sheet No. 1-No. The result of the above-mentioned characteristic evaluation of 28 is shown. The stainless steel sheets of the examples of the present invention were all ferrite single phases (excluding the austenite phase and the martensite structure).

As shown in Table 2, according to the example of the present invention, the crystal grain size number and the texture were controlled, and a ferritic stainless steel sheet having excellent rough skin resistance and moldability could be obtained.
In the case of the comparative example in which Ra exceeds 2.0 μm, the surface unevenness is remarkable, and the unevenness is finally removed by polishing, so that the evaluation is inferior in terms of manufacturing cost.

According to the present invention, it is possible to provide a ferritic stainless steel sheet having excellent molding processability and surface characteristics after molding. Further, since the ferritic stainless steel sheet according to the present invention has excellent surface characteristics after molding, the polishing step after molding for the purpose of removing surface irregularities, which has been conventionally performed, can be omitted. You can fully enjoy the effect in terms of cost.

Claims (3)

By mass%
Cr: 11.0% or more and 25.0% or less,
C: 0.001% or more and 0.010% or less,
Si: 0.01% or more and 1.0% or less,
Mn: 0.01% or more and 1.0% or less,
P: 0.10% or less,
S: 0.01% or less,
N: Including 0.002% or more and 0.020% or less
Further, it contains one or two kinds of Ti: 1.0% or less and Nb: 1.0% or less, and the balance is composed of Fe and impurities.
It consists of a ferrite single-phase structure with a crystal grain size number of more than 9.0, and the random intensity ratio of the crystal orientation on the plane parallel to the rolled surface at the plate thickness 1/2 position and the plate thickness 1/10 position is
I _{{554} <225>} ≧ 7.0,
I _{{411} <148>} ≧ 0.9,
I _{{211} <011>} ≧ 1.0
Ferritic stainless steel sheet characterized by being.
(Note that I _{{hkl} <uvw>} indicates the random intensity ratio of the {hkl} <uvw> orientation) By mass%
Cr: 11.0% or more and 25.0% or less,
C: 0.001% or more and 0.010% or less,
Si: 0.01% or more and 1.0% or less,
Mn: 0.01% or more and 1.0% or less,
P: 0.10% or less,
S: 0.0061% or less, and
N: Including 0.002% or more and 0.020% or less
Further, one or two kinds of Ti: 1.0% or less and Nb: 1.0% or less are included.
Furthermore,
B: 0.0001% or more and 0.0025% or less, Sn: 0.005% or more and 0.50% or less, Ni: 1.0% or less, Cu: 1.0% or less, Mo: 2.0% or less, Al: 1.0% or less, W: 1.0% or less, Co: 0.50% or less, V: 0.50% or less, Zr: 0.50% or less, Ca: 0.0050% or less, Mg: Contains one or more of 0.0050% or less, Y: 0.10% or less, Hf: 0.20% or less, REM: 0.10% or less, Sb: 0.50% or less , and the balance is Consists of Fe and impurities
It consists of a ferrite single-phase structure with a crystal grain size number of more than 9.0, and the random intensity ratio of the crystal orientation on the plane parallel to the rolled surface at the plate thickness 1/2 position and the plate thickness 1/10 position is
I _{{554} <225>} ≧ 7.0,
I _{{411} <148>} ≧ 0.9,
I _{{211} <011>} ≧ 1.0
Ferrites stainless steel you characterized der Rukoto.
(Note that I _{{hkl} <uvw>} indicates the random intensity ratio of the {hkl} <uvw> orientation) By mass%
S: 0.0030% or less,
Mo: 1.1% or less
The ferrite-based stainless steel sheet according to claim 2, wherein the ferritic stainless steel sheet is characterized by the above.