JP7241545B2 - Ferritic stainless steel sheet and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ferritic stainless steel sheet and a method for producing the same.

When a ferritic stainless steel sheet is formed, a striped pattern called ridging may occur on the surface of the formed product. It is also known that adding Al or Ti to a ferritic stainless steel sheet can improve bending workability. Reduces surface texture. These are problems in appearance quality of the ferritic stainless steel sheet.

Patent Document 1 discloses a technique of adding Si and Mo instead of Al in order to improve the bending workability of a ferritic stainless steel sheet. Further, the ferritic stainless steel sheet disclosed in Patent Document 2 has improved bending workability by adding Al and Ti, and also improves ridging resistance by not performing hot-rolled sheet annealing.

Further, Patent Document 3 discloses a technique for randomizing the orientation of ferrite crystal grains in order to improve the bending workability of ferritic stainless steel sheets by adding Al and Ti and to improve the resistance to ridging. ing.

JP-A-2002-80941 JP-A-10-280047 JP 2018-80386 A

However, the addition of Si and Mo as in Patent Document 1 increases the manufacturing cost of the ferritic stainless steel sheet. In addition, it does not propose a technique capable of improving the ridging resistance in the ferritic stainless steel sheet of such a composition system. In addition, Patent Documents 2 and 3 disclose techniques for improving the bending workability and ridging resistance of ferritic stainless steel sheets, but do not disclose techniques for realizing good surface properties in addition to these. .

An object of one aspect of the present invention is to provide a ferritic stainless steel sheet containing Al and Ti, which has three points of good bending workability, surface properties, and ridging resistance.

In order to solve the above-mentioned problems, a ferritic stainless steel sheet according to an aspect of the present invention has, in mass %, C: 0.020 to 0.120%, Si: 0.10 to 1.00%, Mn: 0.10-1.00%, Ni: 0.01-0.60%, Cr: 14.00-19.00%, N: 0.010-0.050%, Al: 0-0.050% , Ti: 0 to 0.050%, Mo: 0 to 0.50%, Cu: 0 to 0.50%, Co: 0 to 0.10%, V: 0 to 0.20%, of which Al: 0.005 to 0.030%, Ti: contains one or more selected from the group of 0.005 to 0.030%, the balance being Fe and unavoidable impurities, determined by the following formula (1) A ferritic stainless steel sheet having a chemical composition with a γmax value of 30 to 55, a 20-degree specular gloss of the steel sheet surface of 900 or more, and a breaking elongation in the rolling direction of 28.0% or more.

γmax=420C-11.5Si+7Mn+23Ni-11.5Cr-12Mo+9Cu-49Ti-52Al+470N+189 (1)
Here, the content of the element represented by mass % is substituted for the symbol of the element in the formula (1), and 0 (zero) is substituted for the non-additive element.

The ferritic stainless steel sheet according to one aspect of the present invention may contain Al: 0.005 to 0.030%.

A ferritic stainless steel sheet according to an aspect of the present invention may contain Ti: 0.005 to 0.030%.

In the ferritic stainless steel sheet according to one aspect of the present invention, the sum of the Al content and the Ti content may be 0.065% or less by mass.

In order to solve the above-mentioned problems, a method for producing a ferritic stainless steel sheet according to one aspect of the present invention comprises C: 0.020 to 0.120% and Si: 0.10 to 1.00% , Mn: 0.10 to 1.00%, Ni: 0.01 to 0.60%, Cr: 14.00 to 19.00%, N: 0.010 to 0.050%, Al: 0 to 0 .050%, Ti: 0-0.050%, Mo: 0-0.50%, Cu: 0-0.50%, Co: 0-0.10%, V: 0-0.20% , Of which, Al: 0.005 to 0.030%, Ti: 0.005 to 0.030%, containing one or more selected from the group, the balance consisting of Fe and unavoidable impurities, the following (1) formula A method for producing a ferritic stainless steel sheet having a chemical composition with a γmax value of 30 or more and 55 or less determined by a rough hot rolling process in which the rolling reduction per pass in the latter three passes including the final pass is 40% or more and a finish hot rolling step in which the temperature during rolling is held at Ac ₁ point + 30 to 70 ° C. of the stainless steel plate, and a finish cold rolling step in which the rolling rate is 63% or more in this order, and the finishing No hot-rolled sheet annealing is performed between the hot-rolling process and the finish cold-rolling process.

γmax=420C-11.5Si+7Mn+23Ni-11.5Cr-12Mo+9Cu-49Ti-52Al+470N+189 (1)
Here, the content of the element represented by mass % is substituted for the symbol of the element in the formula (1), and 0 (zero) is substituted for the non-additive element.

According to one aspect of the present invention, it is possible to provide a ferritic stainless steel sheet containing Al and Ti, which has three points of good bending workability, surface properties, and ridging resistance.

BRIEF DESCRIPTION OF THE DRAWINGS It is process drawing which shows the manufacturing method of the ferritic stainless steel plate which concerns on one Embodiment. FIG. 4 is a diagram schematically showing a contact bending method for evaluating workability of a ferritic stainless steel sheet according to one embodiment. FIG. 4 is a diagram schematically showing a method for evaluating a ridging index in a ferritic stainless steel sheet according to one embodiment. FIG. 2 is a diagram showing chemical compositions of ferritic stainless steel sheets according to examples of the present invention and comparative examples. FIG. 2 is a diagram showing the relationship between the method of manufacturing ferritic stainless steel sheets according to the invention example and the comparative example, and the characteristic evaluation results of each steel sheet. FIG. 3 is a diagram showing evaluation results of workability of ferritic stainless steel sheets according to examples of the present invention and comparative examples.

An embodiment of the present invention will be described in detail below with reference to the drawings. The following description is for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less".

[Chemical composition]
Hereinafter, "%" relating to the chemical composition of steel means "% by mass" unless otherwise specified.

C is an austenite forming element and is effective for preventing coarsening of ferrite grains during hot rolling. As a result of examination, the present embodiment requires a C content of 0.020% or more. However, if the C content is too high, workability is lowered. C content is limited to 0.120% or less. More preferably less than 0.100%.

Si is an element having a deoxidizing effect, but when contained in a large amount, the workability and toughness are lowered. On the other hand, excessive Si reduction leads to an increase in refining cost. The Si content should be 0.10 to 1.00%. It may be managed within the range of 0.20 to 0.70%.

Mn is an austenite forming element and is effective for preventing coarsening of ferrite grains during hot rolling, ensuring a Mn content of 0.10% or more. More preferably 0.25% or more. However, the Mn content is limited to 1.00% or less because a large amount of Mn content causes deterioration of workability and corrosion resistance.

Ni is an austenite forming element and is effective for preventing coarsening of ferrite grains during hot rolling. It is also effective in improving toughness and corrosion resistance. A Ni content of 0.010% or more is ensured in order to exhibit these effects. More preferably 0.050% or more. However, since an excessive Ni content leads to an increase in raw material costs, the Ni content is made 0.60% or less. You may manage in the range of 0.30% or less.

Cr ensures a content of 14.00% or more from the viewpoint of corrosion resistance. However, since a large amount of Cr content causes a decrease in workability, a decrease in toughness, and an increase in cost, the Cr content is made in the range of 19.00% or less.

N is an austenite-forming element, is effective for preventing coarsening of ferrite grains during hot rolling, and ensures an N content of 0.010% or more. However, the N content is limited to 0.050% or less because the workability tends to decrease when the N content increases. It is more preferably 0.035% or less.

Al has a great effect of reducing the austenite phase formation temperature range and increasing the temperature at which the austenite phase is stabilized. This action enables hot rolling at a higher temperature when performing hot rolling in a temperature range where the austenite phase cannot stably exist, thereby promoting the decomposition reaction from the austenite phase to the ferrite phase and carbides. Sufficient progress of this decomposition reaction during hot rolling brings about improvement in workability. In addition, Al has the action of fixing N and contributes to high purity. However, Al is a strong ferrite-forming element, and excessive addition will unnecessarily reduce the amount of austenite phase produced at high temperatures, causing the surface properties of the steel sheet to deteriorate, so the Al content is 0.050%. Limited to: It is more preferably 0.030% or less.

Like Al, Ti has a large effect of narrowing the austenite phase formation temperature range and increasing the temperature at which the austenite phase is stabilized. As described above, this action works favorably in advancing the decomposition reaction from the austenite phase to the ferrite phase and carbides during hot rolling, and contributes to the improvement of workability. In addition, Ti fixes N and C and contributes to high purity. However, excessive addition of Ti unnecessarily reduces the amount of austenite phase generated at high temperatures, which is a factor in lowering workability and also a factor in deteriorating the surface properties of the steel sheet. % or less. It is more preferably 0.030% or less.

In addition, since Al and Ti exert similar actions as described above, either Al or Ti is contained in an amount of 0.005% or more in the present embodiment. Also, in order to maintain good surface properties of the steel sheet, the content of either Al or Ti is limited to 0.030% or less. Also, the sum of the Al content and the Ti content is preferably 0.065% or less by mass.

Mo is effective in improving the corrosion resistance of Cr-containing steel, and can be added as necessary. It is more effective to ensure a Mo content of 0.010% or more. However, since excessive Mo content causes a decrease in workability and an increase in cost, when adding Mo, it is desirable to do it in the range of 0.50% or less, and it may be controlled in the range of 0.15% or less. .

Cu is an austenite forming element and is effective for preventing coarsening of ferrite grains during hot rolling, so it can be added as necessary. It is more effective to ensure a Cu content of 0.010% or more. However, since excessive Cu content causes deterioration of corrosion resistance and workability, when Cu is added, it is desirable to do it in the range of 0.50% or less, and it may be controlled in the range of 0.15% or less. .

V is effective for fixing C in the steel and increasing its purity, as well as increasing the _Ac1 value described later. One or more of these elements can be added as necessary. However, if these elements are excessively added, the cost increases and workability deteriorates due to hardening. desirable.

The balance is Fe and unavoidable impurities. Regarding P and S, which are included as unavoidable impurities, there is no problem if the content is within the range of P: 0.050% or less and S: 0.030% or less, as in conventional general ferritic stainless steels.

That is, the ferritic stainless steel sheet according to the present embodiment has, in mass %, C: 0.020 to 0.120%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00% Ni: 0.01-0.60%, Cr: 14.00-19.00%, N: 0.010-0.050%, Al: 0-0.050%, Ti: 0-0.050% , Mo: 0 to 0.50%, Cu: 0 to 0.50%, Co: 0 to 0.10%, V: 0 to 0.20%, of which Al: 0.005 to 0.030 %, Ti: 0.005 to 0.030%, and the balance is Fe and unavoidable impurities.

(γmax value)
The γmax value determined by the following formula (1) is an index for estimating the amount of austenite (% by volume) in the case of isothermal holding at 1100° C. and reaching an equilibrium state from the component composition. If the γmax value is 100 or more, the maximum austenite content of the steel is assumed to be 100%.

γmax=420C-11.5Si+7Mn+23Ni-11.5Cr-12Mo+9Cu-49Ti-52Al+470N+189 (1)
Here, the content of the element represented by mass % is substituted for the symbol of the element in the formula (1), and 0 (zero) is substituted for the non-additive element.

In this embodiment, a steel in which the content of each component element is adjusted so that the γmax value falls within the range of 30-55 is used. According to the studies of the inventors, promoting the introduction of rolling strain into the ferrite phase and advancing the pulverization of ferrite colonies during hot rolling leads to a marked improvement in ridging resistance. It is considered that this is because the crystal orientation in the metal structure of the steel sheet is randomized.

In the case of steel with a γmax value of less than 30, the amount of austenite phase generated at high temperatures is small, so the aforementioned colony crushing effect may not be sufficiently enjoyed. On the other hand, if the γmax value exceeds 55, the amount of austenite phase produced increases, and although the effect of pulverizing ferrite colonies increases, the austenite phase may remain more than necessary during hot rolling. If the amount of austenite phase that cannot be decomposed by annealing after cold rolling remains, the hard martensite phase will remain in the steel sheet and cause a decrease in workability. it becomes difficult to

〔Production method〕
A method for manufacturing a ferritic stainless steel sheet according to the present embodiment will be described below with reference to FIG. FIG. 1 is a process drawing showing the manufacturing method.

As shown in FIG. 1, the manufacturing method can be divided into a steelmaking process, a hot rolling process, and a cold rolling process. In order to obtain a ferritic stainless steel sheet having good workability, surface properties and ridging resistance, it is necessary to devise the hot rolling process and the cold rolling process. For other steps, conventional general conditions may be applied. The hot rolling process and the cold rolling process are described below.

(Hot rolling process)
The hot rolling process can be performed using a rough rolling mill and a finishing rolling mill. The finish rolling mill is a hot rolling mill capable of reducing the thickness of the hot-rolled steel sheet to the final target thickness. Hereinafter, the process performed by the rough rolling mill is referred to as "rough hot rolling process", and the process performed by the finish rolling mill is referred to as "finish hot rolling process".

The rough hot rolling process is a process for producing a steel sheet rolled to such an extent that it can be subjected to the finish hot rolling process from the steel obtained in the steelmaking process as a pretreatment for the finish hot rolling process. The number of rolling passes in the rough hot rolling step can be, for example, 5 to 9 passes. Here, the rolling reduction per pass (once) in the latter three passes including the final pass is preferably 40% or more. With such a rolling reduction, strain can be efficiently generated in the ferrite phase of the steel sheet, so that the crystal orientation in the metal structure of the steel sheet can be efficiently randomized. Therefore, a ferritic stainless steel sheet having good ridging resistance can be obtained.

In the finish hot rolling process, the temperature during rolling is maintained in the ferrite-austenite transformation point (Ac ₁ point) +30 to 70 ° C. estimated from the following formula (2), thereby improving workability and ridging resistance. to improve For this purpose, it is extremely effective to use a Steckel hot rolling mill equipped with strip heat-retaining furnaces on the front and rear surfaces of the rolling stand, and to heat the strip within the above temperature range between each hot rolling pass.

The Ac ₁ value determined by the following formula (2) is an index for estimating the Ac ₁ point (°C) when the temperature is raised from the ferrite phase to the temperature range where the austenite phase begins to form from the composition.

Ac ₁ =-250C+73Si-66Mn-115Ni+35Cr+60Mo-18Cu+620Ti+750Al-280N+310 (2)
Here, the content of the element represented by mass % is substituted for the symbol of the element in the formula (2), and 0 (zero) is substituted for the non-additive element.

According to the temperature range of Ac ₁ point +30 to 70°C, it is possible to allow the austenite phase to remain in the steel sheet while promoting the transformation from the austenite phase to the ferrite phase during the finishing hot rolling process. The austenite phase remaining in the steel sheet turns into a hard martensite phase and strains the ferrite phase, so that the crystal orientation in the metal structure of the steel sheet can be randomized. Therefore, a ferritic stainless steel sheet having good ridging resistance can be obtained.

Moreover, according to the above temperature range, the amount of austenite phase (martensite phase) remaining in the steel sheet can be limited to an amount that can be completely eliminated by cold-rolled sheet annealing, which will be described later. Therefore, since no hard martensite phase remains in the steel sheet after cold-rolled sheet annealing, a ferritic stainless steel sheet having good workability can be obtained.

The total rolling reduction in the finish hot rolling step can be, for example, 55 to 90%, and the number of rolling passes can be, for example, 5 to 7 passes. Further, the time required from the start of the first pass to the end of the final pass in the finishing hot rolling process is preferably in the range of, for example, 5 to 15 minutes, including the holding time for heating between passes. The thickness of the steel sheet after the finish hot rolling process may be adjusted, for example, within the range of 2.0 to 8.0 mm.

Such a finish hot rolling process is realized by using a Steckel hot rolling machine. In a general finish hot rolling process using a tandem hot rolling mill, it is difficult to finely adjust the heating temperature and heating time during the finish hot rolling as described above.

The coiling of the steel sheet after the finish hot rolling step is preferably performed after the steel sheet is cooled to a temperature of Ac ₁ point or less. As a result, a small amount of the undecomposed γ phase remaining in the steel sheet after coiling transforms into a hard martensite phase after cooling, and rolling strain is introduced into the ferrite phase in the finishing cold rolling process described later, and the crystal orientation changes. More randomization is encouraged. Examples of the cooling method include, but are not limited to, water cooling.

(Cold rolling process)
As shown in FIG. 1, the cold rolling process includes a first pickling process, a finish cold rolling process, a cold rolled sheet annealing process, and a second pickling process in this order. Conventional general conditions may be applied to the first and second pickling processes and the cold-rolled sheet annealing process in the cold rolling process.

Here, the cold rolling process preferably does not include the hot-rolled sheet annealing process. In other words, in the present embodiment, the steel sheet is preferably not subjected to hot-rolled sheet annealing between the finish hot-rolling process and the finish cold-rolling process, which will be described later. That is, the steel sheet after the hot rolling process is directly subjected to the finish cold rolling process after the first pickling process.

When the hot-rolled sheet is annealed, it becomes difficult to remove the oxide layer formed on the surface of the steel sheet. This is because the surface of a hot-rolled steel sheet is usually covered with an oxide layer consisting of a plurality of layers. By annealing the hot-rolled steel sheet, Si, Al and Ti An enriched layer in which is concentrated develops locally. When the annealed steel sheet is pickled, unevenness appears on the surface of the steel sheet due to the difference in pickling properties between the areas where the thickened layer is formed and the areas where the thickened layer is not formed, and the surface properties are deteriorated. In addition, since the thickened layer containing Al and Ti is very hard compared to the surrounding steel sheet base, scabs may appear on the steel sheet surface. In addition, this concentrated layer tends to occur remarkably particularly in steel containing a large amount of Al and Ti. That is, in the present embodiment, by not performing hot-rolled sheet annealing, a ferritic stainless steel sheet having good surface properties can be obtained. Also, by omitting the hot-rolled sheet annealing step, the manufacturing cost of the ferritic stainless steel sheet can be reduced.

The total rolling reduction in the finish cold rolling step immediately before reaching the product target thickness is preferably 63% or more. According to such a rolling reduction, it is possible to realize a ferritic stainless steel sheet having excellent surface properties with little finish unevenness and scab marks after cold-rolled sheet annealing. The number of rolling passes in the finish cold rolling process can be set to 7 to 13 passes, for example.

[Characteristics of steel plate]
(workability)
As described above, the ferritic stainless steel sheet according to the present embodiment contains Al and Ti, albeit in very small amounts, so that inclusions such as alumina and titanium nitride are formed at points in the matrix composed of recrystallized ferrite grains. It exhibits good workability because it exhibits a metallographic structure that is dispersed in a regular shape. For example, the breaking elongation (JIS Z2241:2011) in the rolling direction of a JIS 13B tensile test piece obtained from the ferritic stainless steel sheet according to the present embodiment after cold-rolled sheet annealing is 28.0% or more.

(Surface texture)
As described above, in the ferritic stainless steel sheet according to the present embodiment, the contents of Al and Ti are each set to a very small amount of 0.050% or less, the hot-rolled sheet annealing process is omitted, and the rolling reduction in cold rolling is set to 63%. % or more, the surface of the steel sheet exhibits good surface properties such that the 20-degree specular gloss (JIS Z8741: 1997) is 900 or more.

(Ridging resistance)
FIG. 3 is a diagram schematically showing the evaluation method of the ridging index. The ferritic stainless steel sheet according to the present embodiment has excellent ridging resistance, which is evaluated according to strict criteria considering both the height of the surface unevenness and the wavelength. A ridging index “Wa×WSm value” can be adopted as a specific evaluation index. A method of calculating the ridging index “Wa×WSm value” will be described below with reference to FIG.

Using a JIS No. 5 tensile test piece sampled so that the longitudinal direction L is the rolling direction, tensile strain is applied until the elongation rate in the parallel part becomes 20%, and then unloaded. Five measurement lines in the direction perpendicular to the rolling direction are set on the parallel portion at intervals of 5 mm, and a surface profile with a reference length of 20 mm is measured on each measurement line according to JIS B0601:2013.

Next, the upper limit of the wavelength component is 8.0 mm, the lower limit is 0.5 mm, and the cutoff value is determined to determine the undulation curve of the wavelength component of 0.5 to 8.0 mm. The average waviness height Wa (μm) and the average wavelength WSm (μm) of the waviness curve element are obtained from the waviness curve for each of the five measurement lines, and the addition average value Wa _(AVE) of Wa on each measurement line The product of WSm and the addition average value WSm _(AVE) , Wa _(AVE) .times.WSm _(AVE), is calculated. This test is performed on three test pieces, and the addition average value of the Wa _(AVE) × WSm _(AVE) values of a total of six (three test pieces x both sides) is taken as the ridging index of the steel plate, “Wa × WSm value.

According to the manufacturing method according to the present embodiment, a ferritic stainless steel sheet having anti-ridging properties such that the Wa×WSm value is 8200 or less can be realized. Such a steel sheet can be evaluated as having excellent ridging resistance under strict standards that consider both the height of the surface irregularities and the wavelength.

〔Example〕
The results of evaluating steel sheets according to examples of the present invention (examples of the present invention) and comparative examples are shown below with reference to FIGS. 4 to 6. FIG. FIG. 4 is a diagram showing chemical compositions of ferritic stainless steel sheets according to examples of the present invention and comparative examples. FIG. 5 is a diagram showing the relationship between the method of manufacturing ferritic stainless steel sheets according to the present invention example and the comparative example and the characteristic evaluation results of each steel sheet.

Using the steel having the chemical composition shown in FIG. 4, steel sheets were manufactured under the hot-rolling process conditions and the cold-rolling process conditions shown in FIG. The workability, surface properties, and ridging resistance of each steel sheet thus obtained were evaluated. Items underlined in FIGS. 4 and 5 are items outside the scope of the chemical composition and manufacturing method of the steel sheet according to the present embodiment.

(workability)
With respect to workability, each steel plate was subjected to close contact bending, which will be described later, five times. The evaluation results are shown in the "bending" column in FIG. In addition, the breaking elongation (JIS Z2241: 2011) in the rolling direction using a JIS 13B tensile test piece obtained from each steel plate is evaluated, and if the breaking elongation is 28.0% or more, ○ (pass), less than 28.0% In the case of , it was evaluated as × (failed). The evaluation results are shown in "elongation at break (%)" in FIG.

FIG. 2 is a diagram schematically showing a contact bending method for evaluating workability of a steel sheet. As shown in FIG. 2, first, in order to impart a certain degree of bending angle to the steel plate, a load was applied so as to bend an arbitrary straight portion of the steel plate to form a straight bend in the steel plate. Next, a load is applied to both ends of the steel plate, which are substantially parallel to the linear bending, in a direction in which the inner surfaces of the bent steel plate approach each other, and the steel plate is bent until the inner surfaces are in close contact with each other, thereby performing contact bending. formed.

In order to evaluate the workability of the steel sheet, the bending ridgeline of the contact bending was observed from the direction shown as "observation direction" in FIG. 2, and the presence or absence of cracks on the bending ridgeline was evaluated.

For the surface properties, the 20-degree specular gloss (JIS Z8741: 1997) of each steel plate surface was measured using a handy gloss meter. When the 20-degree specular glossiness of the steel sheet surface was 900 or more, it was evaluated as ◯ (accepted), and when it was less than 900, it was evaluated as x (failed). The evaluation results are shown in "Glossiness" in FIG.

Ridging resistance was evaluated by calculating the above-described Wa×WSm value for each steel plate, and evaluating Wa×WSm value of 8200 or less as ◯ (accepted), and when larger than 8200 as x (failed). The evaluation results are shown in "Ridging resistance" in FIG.

(Evaluation results)
If any one of the chemical composition and manufacturing method of the steel sheet is out of the range according to the present embodiment, that is, if even one item is underlined in FIG. At least one of the properties, surface properties, and ridging resistance was rejected (see Comparative Example Nos. B1 to B23). On the other hand, all of the ferritic stainless steel sheets satisfying the chemical composition and manufacturing method of the steel sheet according to the present embodiment had good workability, surface properties, and ridging resistance (Example No. A1 of the present invention). to A4).

FIG. 6 is a diagram showing evaluation results of workability of ferritic stainless steel sheets according to examples of the present invention and comparative examples. These steel plates were subjected to the above-described contact bending, and the presence or absence of cracks on the bending ridge was evaluated. In addition, the shapes of inclusions formed by alumina, titanium nitride, etc., contained in these steel sheets were also observed.

According to the invention sample A1 containing 0.012% of Al and not containing Ti, no cracks are observed on the bending ridge line. This is similar to Comparative Example B9, which contains 0.117% Al, and Comparative Example B10, which contains 0.104% Ti. In addition, the shape of inclusions in Inventive Example A1 is observed as a point-like shape, as in Comparative Examples B9 and B10.

On the other hand, according to Comparative Example B11 containing neither Al nor Ti, cracks are observed on the bending ridgeline. In addition, the shape of inclusions in Comparative Example B11 was observed as a linear shape, which is clearly different from that of Inventive Example A1. That is, according to the present invention, it was shown that a ferritic stainless steel sheet exhibiting good workability similar to that of a steel sheet containing about 0.10% of Al or Ti can be realized with a small amount of Al and Ti added. .

Moreover, Example A4, in which the total content of Al and Ti was 0.078%, had good workability, surface texture, and ridging resistance. However, compared with Example A3 in which the total content of Al and Ti was 0.061%, the glossiness was inferior. That is, it was shown that a ferritic stainless steel sheet exhibiting better surface properties can be realized when the total content of Al and Ti is 0.065% or less.

[Additional notes]
The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.

L Longitudinal direction Wa Average swell height WSm Average wave height

Claims (5)

% by mass, C: 0.020 to 0.120%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, Ni: 0.01 to 0.60%, Cr: 14.00-19.00%, N: 0.010-0.050%, Al: 0-0.050%, Ti: 0-0.050%, Mo: 0-0.50%, Cu: 0 ~0.50%, Co: 0-0.10%, V: 0-0.20%, of which Al: 0.005-0.030%, Ti: 0.005-0.030% A ferritic stainless steel sheet having a chemical composition containing one or more selected from the group, the balance being Fe and unavoidable impurities, and having a γmax value of 30 to 55 determined by the following formula (1),
The 20 degree specular glossiness of the steel plate surface is 900 or more,
The breaking elongation in the rolling direction is 28.0% or more,
A ferritic stainless steel sheet having a ridging index Wa×WSm value defined in (A) below of 8200 or less .
γmax=420C-11.5Si+7Mn+23Ni-11.5Cr-12Mo+9Cu-49Ti-52Al+470N+189 (1)
Here, the content of the element represented by mass % is substituted for the symbol of the element in the formula (1), and 0 (zero) is substituted for the non-additive element.
(A) Using a JIS No. 5 tensile test piece sampled so that the longitudinal direction is the rolling direction, tensile strain is applied until the elongation in the parallel part becomes 20%, and then unloaded. Five measurement lines in the direction perpendicular to the rolling direction are set on the parallel portion of the test piece at intervals of 5 mm, and a surface profile with a reference length of 20 mm is measured on each measurement line according to JIS B0601:2013. Next, the upper limit of the wavelength component is 8.0 mm, the lower limit is 0.5 mm, and the cutoff value is determined to determine the undulation curve of the wavelength component of 0.5 to 8.0 mm. The average waviness height Wa (μm) and the average wavelength WSm (μm) of the waviness curve element are obtained from the waviness curve for each of the five measurement lines, and the addition average value Wa (AVE) of Wa on each measurement _line The product of WSm and the addition average value WSm _(AVE) , Wa _(AVE) .times.WSm _(AVE), is calculated. This test is performed on the three test pieces, and the addition average value of the Wa _(AVE) × WSm _(AVE) values of a total of six pieces (three test pieces x both sides) is taken as the ridging index of the steel sheet, “Wa x WSm value”. The ferritic stainless steel sheet according to claim 1, containing Al: 0.005 to 0.030%. The ferritic stainless steel sheet according to claim 1 or 2, containing Ti: 0.005 to 0.030%. The ferritic stainless steel sheet according to any one of claims 1 to 3, wherein the sum of the Al content and the Ti content is 0.065% by mass or less. A method for manufacturing a ferritic stainless steel sheet according to claim 1 ,
A rough hot rolling step in which the rolling rate per pass in the latter three passes including the final pass is 40% or more;
A finishing hot rolling step in which the temperature during rolling is held at Ac ₁ point + 30 to 70 ° C. of the steel sheet,
A first pickling step of pickling the steel sheet after the finish hot rolling step;
A finish cold rolling step in which the rolling reduction is 63% or more;
A cold-rolled sheet annealing step of annealing the steel sheet after the finish cold-rolling step;
a second pickling step of pickling the steel plate after the cold-rolled steel annealing step, in this order;
A method for producing a ferritic stainless steel sheet, wherein hot-rolled sheet annealing is not performed between the finish hot rolling process and the finish cold rolling process .

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