JP5196807B2 - Ferritic stainless steel sheet excellent in formability with low roughness of processing surface and method for producing the same - Google Patents

Description

  The present invention relates to a ferritic stainless steel sheet excellent in formability with small roughness of the processed skin and a method for producing the same.

  Ferritic stainless steel sheets are used in a wide range of fields such as kitchen equipment, home appliances, and electronic equipment. However, since the formability is inferior to that of an austenitic stainless steel sheet, the application may be limited.

  In recent years, ferritic stainless steel sheets with improved formability and corrosion resistance have been applied to a wide range of forming applications through the addition of stabilizing elements such as Ti and Nb. is there. This is because ferritic stainless steel has good corrosion resistance in an indoor environment and is more economical than austenitic stainless steel to which a large amount of Ni is added.

  Conventionally, the improvement of formability of ferritic stainless steel sheet has been mainly to improve deep drawability, that is, the r value. For example, in Patent Document 1 and Patent Document 2, the hot rolling conditions are controlled to improve the r value. Manufacturing techniques are disclosed. Moreover, since ferritic stainless steel has low elongation compared to austenitic stainless steel, it has a drawback of being inferior in overhanging property. For example, Patent Literature 3, Patent Literature 4, and Patent Literature 5 disclose component systems that improve the stretchability by improving elongation. In recent years, Patent Document 6 discloses a texture for reducing the in-plane anisotropy of a ferritic stainless steel sheet to which Ti is added with ultra-low carbon, nitrogen, and a manufacturing technique for the same. Has been. However, although these ferritic stainless steel sheets are excellent in formability such as deep drawing and overhanging, the surface quality after processing is not sufficient as compared with austenitic stainless steel sheets.

  Until now, it has been understood that the surface quality of a ferritic stainless steel sheet after processing is significantly degraded by a phenomenon called so-called ridging, that is, fine irregularities generated along the rolling direction when the steel sheet is press-formed. Therefore, many researches and developments have been made on methods for suppressing ridging. For example, Patent Document 7, Patent Document 8, and Patent Document 9 disclose steel components and manufacturing methods that suppress ridging.

  However, even if the ridging resistance of the ferritic stainless steel sheet is improved, roughing of the working surface is more likely to occur in an actual forming application than the austenitic stainless steel sheet, and the surface quality after processing may be regarded as a problem. Patent Literature 10 and Patent Literature 11 disclose a component system and a manufacturing method or a molding method for improving rough processing (orange peel; rough skin due to coarse grains). Patent Document 10 reduces the roughening of the processed skin by expanding the grain refinement region of steel by the combined addition of Ti and Nb. However, these are limited to low Cr ferritic stainless steel plates (Cr <16%), and are not applicable to medium Cr ferritic stainless steel plates (Cr ≧ 16%) that are normally used in kitchen equipment and the like. On the other hand, Patent Document 11 is intended to regulate the amount of forming strain according to the crystal grain size for a ferritic stainless steel sheet to which ultra-low carbon / nitrogenated Ti added similar to Patent Document 6 is added. For this reason, it may be difficult to make full use of excellent formability due to restrictions on rough processing.

  As described above, the medium Cr ferritic stainless steel sheet (Cr ≧ 16%) usually used for kitchen appliances, etc., especially in recent years, making use of the formability of ultra-low carbon, ferritic stainless steel sheet containing Ti and added with Ti There is no one that reduces the roughening of the processed skin. That is, the present situation is that a ferritic stainless steel sheet that does not require strict regulation of the amount of forming strain in a ferritic stainless steel sheet and that has a small rough surface has not yet appeared.

JP 62-77423 A JP-A-7-268485 JP 58-61258 A JP-A-01-77562 JP-A-11-350090 JP 2005-163139 A JP-A-6-81036 JP-A-8-333639 JP-A-10-280046 JP-A-7-292417 JP 2005-139533 A

  The present invention solves the above-mentioned problems by controlling the steel components and texture, more preferably the crystal grain size, within an appropriate range, and a ferritic stainless steel sheet having excellent formability with less rough processing and a method for producing the same. The purpose is to provide.

(1) In mass%, C: 0.001 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.01 to 0.30%, P: 0.005 to 0.035 %, S: 0.0001-0.0100%, Cr: 15-22%, N: 0.001-0.020%, Ti: 0.05-0.35%, Al: 0.005-0. 1%, the balance being Fe and inevitable impurities, the X-ray integrated intensity ratios of the {222} plane, {112} plane, and {002} plane perpendicular to the plate plane are Ia, Ib, and Ic, respectively, in the rolling direction X-ray integration of {222} plane, {112} plane, {002} plane perpendicular to the plate surface after applying 20% elongation strain in three directions of 0 °, 45 °, and 90 ° with 0 ° When the intensity ratios are Ia ′, Ib ′, and Ic ′, the following rough relations are satisfied: Excellent ferritic stainless steel sheet formability are.
<Material> Ia / (Ib + Ic)> 10, Ia> 20
<After giving 20% elongation strain>
0 ° direction Ia ′ / (Ib ′ + Ic ′)> 3, Ia ′> 10
45 ° direction Ia ′ / (Ib ′ + Ic ′)> 5, Ia ′> 10
90 ° direction Ia ′ / (Ib ′ + Ic ′)> 5, Ia ′> 10
(2) The steel is further in mass%, Mg: 0.0050% or less, Nb: 0.6% or less, Mo: 2.0% or less, Ni: 2.0% or less, Cu: 2.0 % Or less, B: 0.005 or less, or a combination of two or more, ferritic stainless steel sheet having excellent formability with less roughened working surface as described in (1).
(3) The crystal grain size of the steel is 20 μm or less, and the surface roughness (expressed in Rz) after giving 20% elongation strain in each of the three directions of 0 °, 45 °, and 90 ° with the rolling direction as 0 °. The ferritic stainless steel sheet having excellent formability with small roughness of the processed surface according to (1) and (2), wherein the ten-point average roughness) is less than 3 μm.
(4) A ferritic stainless steel slab having the steel component described in (1) or (2) is heated to a range of 1050 to 1250 ° C., subjected to rough hot rolling with a total rolling reduction of 80% or more, and then a finish to be performed. In hot rolling, all of the following conditions are satisfied, the steel sheet is wound at a temperature of less than 700 ° C. to obtain a hot rolled sheet, pickled without annealing, and subjected to primary cold rolling with a rolling rate of 40% or more to obtain a cold rolled sheet. The intermediate annealing is performed at 870 to 1000 ° C., the final cold rolling at a rolling rate of 65% or more is performed to obtain the final cold rolled sheet, and the final annealing is performed at 750 to 1000 ° C. (3) to (3 The manufacturing method of the ferritic stainless steel plate excellent in the moldability with the small rough processing surface described in the above .
( I) The total rolling reduction is set to 80 to 95% at 1050 ° C. or lower.
(Ii) The total rolling reduction rate of the final three passes is 40 to 60%, and the time between passes is within 1 second.
(Iii) The start temperature of finish hot rolling is set to 980 to 1030 ° C. , and water cooling is started within 2 seconds after finish rolling.

  Hereinafter, the invention relating to the steel sheets of (1) to (3) and the invention relating to the manufacturing methods of (4) and (5) are referred to as the present invention. The inventions (1) to (5) may be collectively referred to as the present invention.

  As explained above, the ferritic stainless steel sheet of the present invention of (1) to (3) has a strict amount of molding strain by controlling the components and texture, more preferably the crystal grain size, within an appropriate range. The roughness of the processed skin can be reduced without prescribing. This ferritic stainless steel sheet can be produced industrially and stably by the method of the present invention of (4) or (5).

  In order to solve the above-mentioned problems, the present inventors have conducted various studies on the influence of texture and grain size on the roughened working surface generated in a high purity ferritic stainless steel sheet to which Ti has been added. Got.

  Roughness of the processed surface is a case where surface irregularities generated by processing with an elongation strain of 20% in each of three directions of 0 °, 45 °, and 90 ° with a rolling direction of 0 ° are evaluated by a ten-point average roughness Rz defined in JISB0601. Will be described as an example.

(A) Roughness of the processed surface is obtained by sharpening a texture called γ-fiber from {111} <112> to {111} <110> as a material, and {111} <110 after processing in any of the three directions. It has been found that it is reduced by increasing the accumulation in>.

(B) In the ferritic stainless steel which is a body-centered cubic metal polycrystal, {111} <110> can be a stable orientation after processing. However, when the roughened surface becomes large, in addition to {111} <110> after processing, there is a feature that the abundance of orientations called α-fibers of {112} <110> and {001} <110> also increases. did.

(C) The texture of the material in which the abundance of α-fiber increases after processing is the following (i) or (ii), or a combination of (i) and (ii).
(I) Strongly accumulated in {111} <112> and {554} <225>.
(Ii) The abundance of {112} <110> and {001} <110> is large.

(D) When the texture described in (c) is formed, the roughened processed skin is not sufficiently reduced even if the crystal grain size is reduced.

(E) From (a) to (d), the result of judging that the involvement of the texture in addition to the crystal grain size was large as an influencing factor on the roughened processing skin was obtained. That is, it is considered effective to reduce the roughness of the processed skin by suppressing α-fiber appearing by processing and smoothing the crystal rotation in the {111} plane.

(F) The effect of reducing the roughness of the processed skin due to the texture described in (e) is remarkably exhibited when the crystal grain size is 20 μm or less.

(G) When the texture described in (a) is provided and the crystal grain size is 20 μm or less, the surface roughness Rz after processing in any of the three directions is less than 3 μm. This is comparable to the case of austenitic stainless steel, such as SUS304, at which the roughened working surface is at a level where practical problems are not regarded as a problem.

(H) In order to sharpen the γ-fiber as described in (a) without forming the texture described in (i) of (c), two cold operations omitting hot-rolled sheet annealing It is preferable to use a rolling process.

(I) When the crystal grain size is 20 μm or less in addition to (h), it is preferable to increase the final cold rolling rate and lower the final annealing temperature.

(J) In order to reduce the abundance of the orientation described in (ii) of (c), it is effective to develop γ-fiber in the hot rolling stage. For this purpose, in addition to the above (h), manufacturing conditions directed to the following (iii) and (iv) are more preferable.
(Iii) Increase the rolling ratio of rough hot rolling to promote recrystallization after rough hot rolling.
(Iv) While increasing the rolling reduction of the finish hot rolling, the finish hot rolling and the coiling temperature are lowered to obtain a processed structure in which strain is accumulated while suppressing recrystallization.

  The texture described above can be analyzed by obtaining a crystallite orientation distribution function (referred to as ODF) using X-ray diffraction or EBSP (Electron Back-Scatter Diffraction Pattern). . The abundance of the {222} plane, {112} plane, and {002} plane can be quantified by the X-ray integral intensity ratio.

  The present inventions (1) to (5) have been completed based on the findings (a) to (i).

  Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" display of the content of each element means "mass%".

  (A) The reason for limitation of a component is demonstrated below.

  Since C deteriorates moldability and corrosion resistance, the lower the content, the better. Therefore, the upper limit is made 0.015%. However, excessive reduction leads to an increase in refining costs, so the lower limit is made 0.001%. Preferably, it is 0.002 to 0.005% in consideration of corrosion resistance and manufacturing cost.

  Si may be added as a deoxidizing element. However, since it is a solid solution strengthening element and its content is preferably as small as possible from the suppression of elongation reduction, the upper limit is made 0.60%. However, excessive reduction leads to an increase in refining costs, so the lower limit is made 0.01%. Preferably, considering the workability and manufacturing cost, 0.03 to 0.30%.

  Since Mn is a solid solution strengthening element like Si, the smaller the content, the better. The upper limit is made 0.30% in order to suppress the decrease in elongation. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.01%. Preferably, considering the workability and the manufacturing cost, 0.03 to 0.15%.

  Since P is a solid solution strengthening element like Si and Mn, the smaller the content, the better. The upper limit is made 0.035% in order to suppress the decrease in elongation. However, excessive reduction leads to an increase in refining costs, so the lower limit is made 0.005%. Preferably, considering the manufacturing cost and workability, the content is made 0.010 to 0.020%.

  S is an impurity element and inhibits hot workability and corrosion resistance, so the smaller the content, the better. Therefore, the upper limit is made 0.010%. However, excessive reduction leads to an increase in refining costs, so the lower limit is made 0.0001. Preferably, considering the corrosion resistance and the manufacturing cost, the content is made 0.0010 to 0.0050%.

  Cr is an essential element for ensuring corrosion resistance, and its lower limit is 15%. However, addition over 22% impairs manufacturability due to a decrease in toughness and degrades elongation. Therefore, the upper limit of Cr is 22%. Preferably, considering the corrosion resistance and manufacturability and workability, the content is made 16 to 19%.

  N, like C, deteriorates moldability and corrosion resistance, so the lower the content, the better. Therefore, the upper limit is made 0.020%. However, excessive reduction may cause TiN which becomes the nucleus of ferrite grain formation at the time of solidification, the solidified structure becomes columnar crystals, and the ridging resistance at the time of product plate forming may be deteriorated. Moreover, when N is added excessively, since the reduction | decrease of elongation is brought about by solid solution N, a minimum is made into 0.001%. Preferably, considering the manufacturing cost and the corrosion resistance, the content is made 0.005 to 0.012%.

  Ti combines with C, N, S, and P to improve corrosion resistance, intergranular corrosion resistance and formability, and contributes to refinement of the solidified structure, so the lower limit is made 0.05%. However, Ti is also a solid solution strengthening element, and excessive addition leads to a decrease in elongation, so the upper limit is made 0.35%. Preferably, considering the intergranular corrosion property and formability of the welded portion, it is made 0.10 to 0.20%.

  Since Al is an effective element as a deoxidizing element, the lower limit is made 0.005%. However, excessive addition causes deterioration of formability, weldability and surface quality, so the upper limit is made 0.1%. Preferably, considering the refining cost, 0.01 to 0.05%.

  Mg forms Mg oxide with Al in molten steel and acts as a deoxidizer, and also acts as a crystallization nucleus of TiN. TiN becomes a solidification nucleus of the ferrite phase in the solidification process, and by facilitating crystallization of TiN, the ferrite phase can be finely formed during solidification. By refining the solidified structure, orientation grains derived from coarse solidified structures such as product ridging and roughened processed skin of the present invention can be reduced, and the moldability is improved. Therefore, when adding, it is 0.005% or less. If it exceeds 0.0050%, the weldability deteriorates. Aggressive formation in the molten steel of Mg oxide, which becomes a crystallization nucleus of TiN, appears stably from 0.0001%. More preferably, considering the refining cost, the content is made 0.0002 to 0.0020%.

  Nb is an element that improves moldability and corrosion resistance. When Nb is added, the Nb content is 0.6% or less. If it exceeds 0.6%, the material strength is increased and ductility is reduced. The effect appears stably from 0.01%. More preferably, it is 0.05 to 0.3% in consideration of manufacturability, moldability and corrosion resistance.

  Mo, Ni, and Cu are elements that improve the corrosion resistance, and when added, the content is made 2.0% or less. If it exceeds 2.0%, the moldability, particularly the ductility, is lowered. The effect appears stably from 0.1%. More preferably, it is 0.3 to 1.5% in consideration of manufacturability and ductility.

  B is an element that improves secondary workability, and addition to Ti-added steel is effective. When added, the content is 0.005% or less. If it exceeds 0.005%, the ductility is lowered. The effect appears stably from 0.0001%. More preferably, considering the refining cost and ductility, the content is made 0.0003 to 0.0030%.

  (B) The reason for limitation regarding the texture will be described below.

  The ferritic stainless steel sheet of the present invention has the components described in the item (A), and defines the texture and preferably the crystal grain size in order to reduce the roughened working surface.

  As described above, the texture is analyzed by obtaining a crystallite orientation distribution function (referred to as ODF) using an X-ray diffraction method or EBSP (Electron Back-Scatter Diffraction Pattern). be able to. This function is described in, for example, light metals; Hiroshi Inoue, Vol. 42, no. 6, 358 to 367, there are three variables (ψ1, φ, ψ2) that uniquely specify the crystal grain orientation with respect to the material coordinate system. By obtaining this function, it is possible to know the abundance of crystal grains having Euler angles (ψ1, φ, ψ2).

  Specifically, (ψ1, φ) on the ψ2 = 45 ° cross section as shown in FIG. 1 is {111} <112> is (30 °, 54.7 °) and (90 °, 54.7 °). ), {111} <110> are (0 °, 54.7 °) and (60 °, 54.7 °), {112} <110> is (0 °, 34.7 °), {001} < 110> can know its abundance by the intensity of (0 °, 0 °) and (90 °, 0 °).

  Further, the abundance of the {111} plane, {112} plane, and {001} plane can be easily quantified by the X-ray integral intensity. For example, when a Mo tube is used as the X-ray source, the 2θ measurement position of the MoKα ray is 50.8 ° for the {222} plane, 35.3 ° for the {112} plane, and 28.7 for the {002} plane. °. The strength of {111} plane and {001} plane is reflected in the strength of {222} plane and {002} plane. Therefore, the abundance of the {111} plane, {112} plane, and {001} plane can be quantified by measuring the integrated intensity of the {222} plane, {112} plane, and {002} plane. As the X-ray integral intensity ratio of each measurement surface, a value obtained by normalizing the integral intensity measurement value with the integral intensity measurement value of the random sample of α-Fe is used.

  The sample used for the ODF or integral intensity measurement described above is a surface (ND surface) parallel to the material and the plate surface at the center of the plate thickness after processing.

  The texture of the material sharpens the γ-fiber from {111} <211> to {111} <110> in order to reduce roughness of the processed skin. Therefore, when the X-ray integrated intensity ratios of the {222} plane, {112} plane, and {002} plane perpendicular to the plate plane are Ia, Ib, and Ic, respectively, Ia / (Ib + Ic)> 10, Ia> 20 And In the case of Ia / (Ib + Ic) <10, Ia <20, after processing, the accumulation in {111} <110> is weakened, and the roughening of the processed skin is increased due to the appearance of an orientation derived from α-fiber. Preferably, Ia / (Ib + Ic)> 15, Ia> 40, and further, Ib <2, Ic <2 in order to maintain the accumulation in {111} <110> and reduce the roughness of the processed skin after processing. .

However, if the material has a large accumulation in {111} <211> or {554} <225> belonging to the above-described γ-fiber, the appearance of the orientation derived from α-fiber after processing increases, and the processing surface becomes rough. Become. Therefore, all the following conditions shall be satisfied also about the texture after processing.
0 ° direction Ia ′ / (Ib ′ + Ic ′)> 3, Ia ′> 10
45 ° direction Ia ′ / (Ib ′ + Ic ′)> 5, Ia ′> 10
90 ° direction Ia ′ / (Ib ′ + Ic ′)> 5, Ia ′> 10
Here, Ia ′, Ib ′, and Ic ′ are X-ray integrated intensity ratios after applying 20% elongation strain in three directions of 0 °, 45 °, and 90 ° with the rolling direction as 0 °, and Ia ′, Ib ′ and Ic ′ mean {222} plane, {112} plane, and {002} plane perpendicular to the plate surface, respectively. Preferably, Ia ′ / (Ib ′ + Ic ′) is 4 or more in the 0 ° direction, 6 or more in the 45 ° direction, and 7 or more in the 90 ° direction in order to reduce the appearance of α-fiber and reduce the roughness of the processed skin. And Ib ′ <3, Ic ′ <2.

  The above elongation strain of 20% substantially corresponds to the uniform elongation range of ferritic stainless steel. For this reason, if an elongation strain greater than this is applied, local elongation, that is, necking may occur, and roughening of the processed skin cannot be evaluated correctly. Accordingly, rough processing is evaluated with an elongation strain of 20% as the upper limit.

  The crystal grain size is preferably 20 μm or less. More preferably, it is 5 to 15 μm. Setting the crystal grain size to less than 5 μm is practically difficult in the case of steel having the components described in the item (A).

  The surface roughness Rz (ten-point average roughness) defined in the present invention represents the degree of roughness of the processed skin after the application of 20% elongation strain. If the rolling direction is 0 ° and Rz is less than 3 μm in three directions of 0 °, 45 °, and 90 °, an austenitic stainless steel that is practically visually or tactilely not subject to rough processing, such as, for example, The roughness of the processed skin is reduced without any discomfort from SUS304. More preferably, Rz is less than 2.5 μm.

(C) Manufacturing method In the ferritic stainless steel having the component described in the item (A), in order to obtain the texture and the crystal grain size described in the item (B) after the material and processing, the following manufacturing conditions are used. Is preferred.

  In order to form the texture of the present invention, it is preferable to perform two cold rolling steps in which hot-rolled sheet annealing is omitted. Intermediate annealing is performed between the primary cold rolling and the final cold rolling.

  The rolling ratio of primary cold rolling is set to 40% or more in order to promote recrystallization in the subsequent intermediate annealing. Preferably it is 45% or more. When the rolling ratio of the primary cold rolling is increased, the thickness of the hot rolled sheet and the final cold rolling ratio are restricted, so 60% or less is preferable. Intermediate annealing is performed at 850 ° C. or higher in order to promote recrystallization. In order to prevent coarsening of the crystal grain size, the upper limit of the annealing temperature is set to 1000 ° C.

  The rolling ratio of the final cold rolling is set to 65% or more in order to develop the texture of the present invention. Preferably it is 70% or more. More preferably, it is 75% or more. The final annealing is performed at a recrystallization lower limit temperature of 750 ° C. or higher and 1000 ° C. or lower in order to prevent coarsening. In order to develop the texture of the present invention so that the crystal grain size is 20 μm or less, the final annealing temperature is preferably 800 to 850 ° C.

  Cold rolling may be performed by a reversible 20-stage Sendzimir mill, 6-stage or 12-stage mill, or a tandem mill that continuously rolls a plurality of passes. In order to form the texture of the present invention, the work roll diameter is preferably large. Therefore, the work roll diameter is preferably 200 mm or more. Such large diameter roll rolling is preferably performed at the time of primary cold rolling.

  The product sheet thickness after the final cold rolling is not particularly specified. However, when it is intended to be used for forming the steel of the present invention, the product plate thickness is preferably 0.5 mm or more.

  In order to suppress the α-fiber appearing by processing and reduce the roughness of the processed skin, it is preferable to increase the rolling ratio of the rough hot rolling and the finishing hot rolling and lower the finishing hot rolling and the winding temperature.

  The heating temperature for hot rolling is preferably 1050 ° C. or more and 1250 ° C. or less. When the temperature is lower than 1050 ° C., the hot deformation resistance increases, the hot rolling load increases, and seizure flaws may occur. When it exceeds 1250 ° C., the crystal grain size becomes coarse. In order to promote recrystallization after rough hot rolling, the temperature is more preferably 1100 to 1200 ° C. In the rough hot rolling, the total rolling reduction is preferably 80% or more in order to pulverize and subdivide {001} oriented grains derived from the solidified structure to promote recrystallization after the rough hot rolling.

In order to form a texture in which γ-fiber is developed at the hot-rolled sheet stage, the finish hot rolling is preferably a processed structure in which strain is sufficiently accumulated by suppressing recrystallization. Therefore, it is preferable that the following conditions (i) to (iii) are all satisfied and the winding is performed at less than 700 ° C.
(I) The total rolling reduction is set to 80 to 95% at 1050 ° C. or lower.
(Ii) The total rolling reduction rate of the final three passes is 40 to 60%, and the time between passes is within 1 second.
(Iii) Due to the development of γ-fiber, the finishing temperature is set to 800 ° C. or more and 950 ° C. or less for the purpose of suppressing recrystallization during rolling, and water cooling is started within 2 seconds after finishing rolling.

  Examples of ferritic stainless steel sheets having the texture and crystal grain size of the present invention by carrying out the production method of the present invention will be described below.

  A ferritic stainless steel slab having a thickness of 250 mm having the components shown in Table 1 was melted and hot-rolled to obtain a hot-rolled steel plate having a thickness of 3 to 6 mm. In all the examples, the time between final rolling final passes was in the range of 0.3 to 0.6 seconds, and the water cooling start time after the final pass was in the range of 0.8 to 1.6 seconds. The hot-rolled steel sheet was subjected to primary cold rolling, intermediate annealing, final cold rolling, and final annealing after pickling to obtain a product having a thickness of 0.6 to 0.9 mm. The surface specification of the product is 2B or 2D. Manufacture of products from hot-rolled and hot-rolled steel sheets was carried out in the range specified in the present invention and other conditions.

  Table 2 shows the thickness and manufacturing conditions during the manufacturing. Production No. 4 and 5 have shown performing hot-rolled sheet annealing. Production No. 5 represents manufacturing in one cold rolling process. These production Nos. Nos. 4 and 5 are regular manufacturing methods for carrying out hot-rolled sheet annealing, and were used for comparison of rough processing.

  The crystal grain size of the obtained steel sheet was determined by the ferrite grain size measuring method specified in JISG0552. The texture at the center of the plate thickness was quantified by X-ray integral intensity measurement. The X-ray source is MoKα ray, the integrated intensity of {222} plane, {112} plane, {002} plane is measured, normalized with the integrated intensity measurement value of a random sample of α-Fe, and Ia, Ib, The value of Ic was determined.

  Roughness of the processed surface is 10-point average surface roughness Rz specified in JISB0601, after taking JIS No. 5 tensile test pieces from 3 directions of 0 °, 45 ° and 90 ° with the rolling direction as 0 ° and applying 20% elongation strain. (Hereinafter, Rz) was measured and evaluated. Further, a SUS304 steel plate / 2B specification having a plate thickness of 0.8 mm was used as a comparative example of rough processing.

  For the texture after processing, a sample was taken from a JIS No. 5 tensile parallel portion, and the X-ray integrated intensity at the central portion of the plate thickness was measured. The measurement plane was {222} plane, {112} plane, and {002} plane, and the values standardized with random samples were Ia ′, Ib ′, and Ic ′.

  The results are shown in Table 3.

  Production No. Although 4-7 and 10-12 have the component of this invention, they do not satisfy | fill the texture prescribed | regulated by this invention. Production No. Nos. 4 and 5 do not satisfy the texture defined in the present invention even though the crystal grain size is as small as 20 μm or less, so that the roughness of the processed skin is not reduced. Hereinafter, the above is referred to as a comparative example.

  Production No. 1-3, 8, and 9 have the components and texture defined in the present invention, Rz is smaller than that of the comparative example, and the roughness of the processed skin is reduced. Production No. with a crystal grain size exceeding 20 μm. Nos. 3, 8, and 9 are conventional production Nos. Having a crystal grain size of 20 μm or less. Compared with 4,5, the processed skin is less rough. Further, in the case of production no. It can also be seen that the surface roughness 1 and 2 is reduced to a level comparable to SUS304.

  The result of investigating the relationship between the surface roughness Rz and the crystal grain size is shown in FIG. In order to reduce Rz, the crystal grain size may be reduced by having the texture of the present invention. In order to obtain Rz <3 μm, it can be confirmed that the crystal grain size should be 20 μm or less.

  The result of investigating the relationship between the material and the texture after processing is shown in FIG. In order to maintain the accumulation on the {111} plane even after processing by increasing the A ′ value, the A value of the material may be increased. Here, it is assumed that A value = Ia / (Ib + Ic) and A ′ value = Ia ′ / (Ib ′ + Ic ′).

  The result of investigating the relationship between the texture after processing and the surface roughness Rz is shown in FIG. In the case of having a texture defined by the present invention, it can be confirmed that in order to obtain Rz <3 μm, A ′ value> 3,445 ° in the 0 ° direction and A ′ value> 5 in the 90 ° direction. The plot of the present invention in which Rz exceeds 3 μm is when the crystal grain size is as large as 35 μm.

  According to the present invention, while making use of the excellent formability of a ferritic stainless steel sheet, it is possible to reduce the rough working surface that is practically satisfactory, and the ferritic stainless steel is more economical than an austenitic stainless steel sheet. It can be applied to steel plate processing applications.

ψ2 = existence position of crystal orientation in 45 ° cross section Relationship between surface roughness Rz and crystal grain size Relationship between material and texture after processing Relationship between texture after processing and surface roughness Rz

Claims (4)

In mass%, C: 0.001 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.01 to 0.30%, P: 0.005 to 0.035%, S : 0.0001 to 0.0100%, Cr: 15 to 22%, N: 0.001 to 0.020%, Ti: 0.05 to 0.35%, Al: 0.005 to 0.1%, The balance consists of Fe and inevitable impurities, and the X-ray integrated intensity ratios of the {222} plane, {112} plane, and {002} plane perpendicular to the plate plane are Ia, Ib, and Ic, respectively, and the rolling direction is 0 ° X-ray integrated intensity ratio of {222} plane, {112} plane, {002} plane perpendicular to the plate surface after applying 20% elongation strain in three directions of 0 °, 45 °, and 90 ° as In the case of Ia ′, Ib ′, and Ic ′, respectively, it is possible to reduce the roughness of the processed skin characterized by satisfying all of the following relationships. Excellent ferritic stainless steel sheet to sex.
<Material> Ia / (Ib + Ic)> 10, Ia> 20
<After giving 20% elongation strain>
0 ° direction Ia ′ / (Ib ′ + Ic ′)> 3, Ia ′> 10
45 ° direction Ia ′ / (Ib ′ + Ic ′)> 5, Ia ′> 10
90 ° direction Ia ′ / (Ib ′ + Ic ′)> 5, Ia ′> 10   The steel is further in mass%, Mg: 0.0050% or less, Nb: 0.6% or less, Mo: 2% or less, Ni: 2% or less, Cu: 2% or less, B: 0.005% The ferritic stainless steel sheet excellent in formability with small roughness of the processed skin according to claim 1, comprising one or more of the following.   The crystal grain size of the steel is 20 μm or less, and the surface roughness after adding 20% elongation strain in three directions of 0 °, 45 °, and 90 ° with the rolling direction as 0 ° (represented by Rz). 3. The ferritic stainless steel sheet excellent in formability with a small roughened working surface according to claim 1, wherein the point average roughness is less than 3 μm. The ferritic stainless steel slab having the steel component according to claim 1 or 2 is heated to a range of 1050 to 1250 ° C., subjected to rough hot rolling with a total rolling reduction of 80% or more, and then in the finishing hot rolling to be performed, the following All the conditions are satisfied, and it is wound at a temperature of less than 700 ° C. to obtain a hot rolled sheet, pickled without annealing, and subjected to primary cold rolling with a rolling rate of 40% or more to obtain a cold rolled sheet, 870 to 1000 ° C. The intermediate annealing is carried out, and the final cold rolling with a rolling rate of 65% or more is performed to obtain a final cold rolled sheet, and the final annealing is performed at 750 to 1000 ° C. A method for producing a ferritic stainless steel sheet having excellent formability with less rough processing.
(I) The total rolling reduction is set to 80 to 95% at 1050 ° C. or lower.
(Ii) The total rolling reduction rate of the final three passes is 40 to 60%, and the time between passes is within 1 second.
(Iii) The start temperature of finish hot rolling is set to 980 to 1030 ° C. , and water cooling is started within 2 seconds after finish rolling.

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