Ferritic stainless steel with excellent ultra-thin rolling properties and its manufacturing method

Abstract

An object of the present invention is to provide a ferritic stainless steel having excellent ultra-thin rollability and a method for producing the same. The present invention provides a ferritic stainless steel with excellent ultra-thin rollability, which is composed of, by weight, 0.001% to 0.1% carbon (C), 0.05% to 0.7% silicon (Si), 0.05% to 1% manganese (Mn), 15% to 19% chromium (Cr), 0.001% to 0.1% nitrogen (N), 0% to 0.01% aluminum (Al), with the remainder being Fe and unavoidable impurities. In a cross section of the cast structure, the total content of Al and Mg exceeds 30% by weight, and the number of inclusions with a length in the thickness direction exceeding 6 μm is 160 mm. 2 It is characterized by having 5 or less pieces per unit.

Description

[Technical Field]

[0001] The present invention relates to a ferritic stainless steel having excellent ultra-thin rollability and a method for producing the same. [Background technology]

[0002] The application of ultra-thin stainless steel is gradually expanding in products that require both flexibility and rigidity, such as flexible solar cells and flexible displays.

[0003] Ultra-thin stainless steel typically has a thickness of 0.01 mm to 0.08 mm. The stainless steel is thinly rolled to increase strength through work hardening while also ensuring flexibility through its thin thickness. In this case, ultra-thin rolled yarn is produced by ultra-thin rolling using cold-rolled coils with a thickness of 0.4 mm or more. However, due to the extremely thin thickness, sheet breakage can occur during the rolling process. Such sheet breakage is believed to be caused by hard, coarse inclusions present inside the coil. To address this issue, conventional methods of preventing sheet breakage have involved multiple low-speed operations, such as reducing the reduction rate and rolling speed, but this has resulted in reduced productivity. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to provide a ferritic stainless steel having excellent ultra-thin rollability and a method for producing the same.

[0005] However, the problems to be solved by the present application are not limited to the above problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0006] The ferritic stainless steel of the present invention, which is excellent in ultra-thin rollability, is composed of, by weight, carbon (C): 0.001% to 0.1%, silicon (Si): 0.05% to 0.7%, manganese (Mn): 0.05% to 1%, chromium (Cr): 15% to 19%, nitrogen (N): 0.001% to 0.1%, aluminum (Al): 0% to 0.01%, with the remainder being Fe and unavoidable impurities, and the total content of Al and Mg exceeds 30% by weight in a cross section of the cast structure, and the number of inclusions having a length in the thickness direction exceeding 6 μm is 160 mm or less. 2 It is characterized by having 5 or less pieces per unit.

[0007] In the ferritic stainless steel of the present invention having excellent ultra-thin rollability, the inclusions may contain silicon-containing oxides or sulfides.

[0008] Furthermore, the ferritic stainless steel of the present invention having excellent ultra-thin rollability may have a ratio of the average grain size at the outer side in the width direction of the stainless steel to the average grain size at the center in the width direction of the stainless steel of 2 or less.

[0009] The method for producing a ferritic stainless steel having excellent ultra-thin rollability of the present invention includes the steps of casting a slab containing, by weight, 0.001% to 0.1% carbon (C), 0.05% to 0.7% silicon (Si), 0.05% to 1% manganese (Mn), 15% to 19% chromium (Cr), 0.001% to 0.1% nitrogen (N), 0% to 0.01% aluminum (Al), with the remainder being Fe and unavoidable impurities; heating the slab at 1150°C to 1250°C; hot-rolling the heated slab to produce a hot-rolled material; hot-rolling annealing the hot-rolled material at 750°C to 880°C; cold-rolling the hot-rolled material to produce a cold-rolled material; and cold-rolling annealing the cold-rolled material at 750°C to 880°C.

[0010] In the method for producing a ferritic stainless steel excellent in ultra-thin rollability of the present invention, the hot rolling may include hot rolling the heated slab to a thickness of 2.5 mm to 5 mm.

[0011] In the method for producing a ferritic stainless steel excellent in ultra-thin rollability of the present invention, the hot rolling may include finish rolling the heated slab at 800°C to 950°C.

[0012] In the method for producing a ferritic stainless steel having excellent ultra-thin rollability of the present invention, the cold rolling may include first cold rolling the hot-rolled material to a thickness of 0.4 mm to 1 mm, and then second cold rolling to a thickness of 0.01 mm to 0.2 mm.

[0013] The method for producing a ferritic stainless steel excellent in ultra-thin rollability according to the present invention is characterized in that the total content of Al and Mg in a cross section of the cast structure is more than 30% by weight, and the number of inclusions exceeding 6 μm in length in the thickness direction is 160 mm. 2 There can be five or fewer per prize.

[0014] In the method for producing a ferritic stainless steel having excellent ultra-thin rollability of the present invention, the ratio of the average grain size at the outer sides in the width direction of the stainless steel to the average grain size at the center in the width direction of the stainless steel may be 2 or less. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a ferritic stainless steel having excellent ultra-thin rollability that can prevent sheet breakage during thin cold rolling, and a method for producing the same.

[0016] The effects that can be obtained in this specification are not limited to the effects described above, and other effects not mentioned here will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0017] [Figure 1] This is a photograph of an inclusion that has the properties to induce sheet fracture during ultra-thin rolling. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes preferred embodiments of the present invention. However, the embodiments of the present invention can be modified into various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. The terms used in this application are merely used to describe specific examples. Thus, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Note that the terms "comprise" or "include" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not intended to preclude the presence of other features, steps, functions, components, or combinations thereof.

[0019] On the other hand, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Therefore, unless clearly defined herein, specific terms should not be interpreted in an overly ideal or formal sense. For example, the singular expression in this specification includes the plural expression unless there is a clear exception in the context.

[0020] Furthermore, in this specification, the terms "about," "substantially," and the like are used to mean from or near a numerical value when manufacturing and material tolerances inherent in the stated meaning are given, and are used to prevent unscrupulous infringers from unfairly taking advantage of disclosures in which precise or absolute numerical values ​​are stated to aid in the understanding of the present invention.

[0021] A ferritic stainless steel with excellent ultra-thin rollability according to one example of the present invention can consist, in weight percent, of carbon (C): 0.001% to 0.1%, silicon (Si): 0.05% to 0.7%, manganese (Mn): 0.05% to 1%, chromium (Cr): 15% to 19%, nitrogen (N): 0.001% to 0.1%, aluminum (Al): 0% to 0.01%, with the remainder being Fe and unavoidable impurities.

[0022] The reasons for limiting the range of each alloy element will be explained below. Unless otherwise specified, the units are % by weight.

[0023] The carbon (C) content may be 0.001% to 0.1%.

[0024] C is an element necessary for ensuring the strength of the steel grade. In consideration of this, the lower limit of the carbon content is set to 0.001% or more, preferably 0.01% or more. However, if the carbon content exceeds 0.1%, a hard martensite phase is formed after cold rolling annealing and cooling, which may cause sheet fracture during ultra-thin rolling. Therefore, the upper limit of the carbon content is set to 0.1% or less, preferably 0.07% or less.

[0025] The silicon (Si) content may be 0.05% to 0.7%.

[0026] Silicon (Si) is an element that can ensure strength and improve corrosion resistance. Taking this into consideration, the lower limit of the silicon content is set to 0.05% or more, preferably 0.11% or more. However, excessive silicon content can cause brittleness and lead to sheet breakage during ultra-thin rolling. Furthermore, silicon (Si) is an element that can react with oxygen (O) or sulfur (S) to form oxide or sulfide inclusions. However, silicon (Si) inclusions are relatively prone to elongation during rolling. However, because silicon (Si) inclusions can act as nuclei for aluminum (Al) or magnesium (Mg) inclusions, the upper limit of the silicon content is set to 0.7% or less, preferably 0.61% or less.

[0027] The manganese (Mn) content may be 0.05% to 1%.

[0028] Mn can refine the structure during hot rolling and reduce the grain size ratio in the width direction. In consideration of this, the lower limit of the manganese content is set to 0.05% or more, preferably 0.26% or more. However, if the manganese content exceeds 1%, a martensite phase may be formed after cold rolling annealing, so the upper limit of the manganese content is set to 1% or less, preferably 0.85% or less.

[0029] The chromium (Cr) content may be 15% to 19%.

[0030] Cr is an element that improves corrosion resistance. If the chromium content is less than 15%, a martensite phase may be formed in the cold rolling annealing zone, so the lower limit of the chromium content is set to 15% or more, preferably 15.1% or more. However, if the chromium content exceeds 19%, the steel may become excessively hard. Therefore, the upper limit of the chromium content is set to 19% or less, preferably 18.7% or less.

[0031] The nitrogen (N) content may be 0.001% to 0.1%.

[0032] N is an element necessary for ensuring the strength of steel grades. In consideration of this, the lower limit of the nitrogen content is set to 0.001% or more, preferably 0.01% or more. However, if the nitrogen content exceeds 0.1%, a hard martensite phase is formed after cold rolling annealing and cooling, which may cause sheet fracture during ultra-thin rolling. Therefore, the upper limit of the nitrogen content is set to 0.1% or less, preferably 0.07% or less.

[0033] The aluminum (Al) content may be 0% to 0.01%.

[0034] Al can react with oxygen (O) to form oxide inclusions. Taking this into consideration, the aluminum content is controlled to 0.01% or less.

[0035] The remaining component is iron (Fe). However, in normal manufacturing processes, unintentional impurities may inevitably be mixed in from raw materials or the surrounding environment, making it difficult to eliminate them. Since these impurities are known to anyone skilled in normal manufacturing processes, not all of their contents will be specifically mentioned in this specification. In one embodiment, the ferritic stainless steel has a total content of Al and Mg exceeding 30 wt % in a cross section of the cast structure, and the number of inclusions exceeding 6 μm in length in the thickness direction is 160 mm. 2 There can be five or fewer per prize. Furthermore, the inclusions may include oxides or sulfides with a high silicon content that tend to elongate during rolling, and it is preferable that inclusions that maintain a large size without thinning or breaking during rolling, such as oxides or sulfides with a high aluminum or magnesium content, are minimized.

[0036] Ferritic stainless steel contains inclusions formed during casting. These are oxides or sulfides primarily composed of Al, Mg, Si, and Mn. In typical stainless steel manufacturing processes, the thickness of the coil is reduced through hot rolling and cold rolling, and the inclusions also become thinner or are destroyed internally. Assuming a cold-rolled coil thickness of 0.5 mm, the size of conventional inclusions is on the order of several to several tens of micrometers. Since the size of the inclusions is small relative to the coil thickness, they do not pose a significant problem during rolling. However, in ultra-thin rolling, where the thickness of the cold-rolled coil is on the order of 0.01 mm to 0.1 mm, the size of these inclusions is not relatively small relative to the overall coil thickness.

[0037] Furthermore, inclusions that remain without being significantly thinned or destroyed during ultra-thin rolling can cause sheet breakage during rolling. For example, FIG. 1 shows an electron microscope image of 5 μm-sized inclusions observed in a 0.03 mm-thick cold-rolled coil. These inclusions remain at a size of about one-third of the total coil thickness and can cause sheet breakage. According to one embodiment of the present invention, sheet breakage during ultra-thin rolling can be prevented by preventing inclusions that remain during ultra-thin rolling from being present in the cold-rolled coil.

[0038] Therefore, among the components of inclusions, inclusions with a total Al and Mg content exceeding 30% must be limited. This is because inclusions with a total Al and Mg content exceeding 30% by weight become hard and may remain even after ultra-thin rolling. On the other hand, inclusions with a total Al and Mg content of 30% or less may reduce in size due to elongation or fracture during rolling, and may not affect sheet fracture.

[0039] In addition, the ferritic stainless steel according to one embodiment of the present invention has a thickness of 160 mm or less and a thickness of 160 mm or less. 2 The number of inclusions with a length in the thickness direction of 6 μm or less can be limited to 5 or less per 160 mm. Inclusions with a length in the thickness direction of 6 μm or less have already been reduced in size through elongation and destruction, and are relatively small compared to the ultra-thin rolled thickness, so their effect on sheet fracture can be minimal. That is, the number of inclusions with a length in the thickness direction of more than 6 μm can be limited to 5 or less per 160 mm. 2 When the number of defects per unit area is controlled to 5 or less, the number of sites at which stress concentrates during ultra-thin rolling is reduced, making it possible to prevent sheet breakage during ultra-thin rolling.

[0040] Furthermore, in a ferritic stainless steel according to one embodiment of the present invention, the ratio of the average grain size at the outer side in the width direction of the stainless steel to the average grain size at the center in the width direction may be no more than 2. If there is a large difference in grain size in the width direction, stress may be concentrated on one side during ultra-thin rolling, so the ratio of the average grain sizes is limited to no more than 2, preferably no more than 1.9.

[0041] Next, a method for producing a ferritic stainless steel having excellent ultra-thin rollability according to an embodiment of the present invention will be described.

[0042] A method for producing a ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention includes the steps of casting a slab containing, by weight, 0.001% to 0.1% carbon (C), 0.05% to 0.7% silicon (Si), 0.05% to 1% manganese (Mn), 15% to 19% chromium (Cr), 0.001% to 0.1% nitrogen (N), 0% to 0.01% aluminum (Al), with the remainder being Fe and unavoidable impurities; heating the slab at 1150°C to 1250°C; hot-rolling the heated slab to produce a hot-rolled material; hot-rolling annealing the hot-rolled material at 750°C to 880°C; cold-rolling the hot-rolled material to produce a cold-rolled material; and cold-rolling annealing the cold-rolled material at 750°C to 880°C.

[0043] The reasons for limiting the ranges of the numerical values ​​of the components of each alloy composition are as described above, and each manufacturing step will be described in more detail below.

[0044] First, a slab satisfying the above alloy composition is produced, and then the slab can undergo a series of steps including reheating, hot rolling, hot rolling annealing, cold rolling, and cold rolling annealing.

[0045] First, the slab is heated to a temperature of 1150°C to 1250°C in a hot rolling furnace, and then hot rolled to a thickness of 2.5mm to 5mm to produce a hot-rolled steel sheet. If the heating temperature is too high, the internal crystal grains may become too coarse, causing severe surface oxidation and inducing surface defects, resulting in non-uniform distribution in the width direction, making it difficult to control the crystal grain size in the width direction after hot rolling. Also, if the temperature is too low, it becomes difficult to reabsorb inclusions during heating, so the heating temperature can be limited to 1150°C to 1250°C, preferably 1181°C to 1245°C.

[0046] Furthermore, if the hot-rolled thickness is greater than 5 mm, the remaining thickness must be thinned by cold rolling. In this case, however, inclusions that should be elongated in the longitudinal direction may break instead of being elongated. In other words, the inclusions must be elongated more easily at high temperatures. If they break, they will not be reabsorbed into the base metal during the annealing process described below, remaining thick and potentially causing sheet breakage. On the other hand, if the thickness is less than 2.5 mm, the hot-rolled thickness is limited as described above because the hot-rolling load becomes too large.

[0047] In the hot rolling, the finish rolling can be carried out at 800°C to 950°C. If the finish rolling temperature is too low, sticking may occur on the surface of the slab during hot rolling, and inclusions may not be fully reabsorbed during hot rolling. However, if the finish rolling temperature is too high, coarse ferrite grains may be formed, so the finish rolling temperature can be limited as described above.

[0048] The hot-rolled material can be hot-rolled and annealed at a temperature of 750°C to 880°C.

[0049] If the hot rolling annealing temperature is low, the stress formed during hot rolling may not be sufficiently removed, resulting in reduced workability and insufficient reabsorption of inclusions. However, if the hot rolling annealing temperature is too high, the edges in the width direction may be overheated, resulting in a large difference in grain size in the width direction. Therefore, the hot rolling annealing temperature of the hot rolled material can be limited to 750°C to 880°C, preferably 760°C to 865°C.

[0050] The hot-rolled material that has been hot-rolled and annealed can be cold-rolled and then cold-rolled and annealed to produce a cold-rolled steel sheet. Cold-rolling and annealing can be performed at a temperature of 750°C to 880°C. If the cold-rolling and annealing temperature is too low, the stress formed during cold rolling is not sufficiently removed, resulting in reduced workability for ultra-thin rolling and insufficient reabsorption of inclusions. If the cold-rolling and annealing temperature is too high, the edges in the width direction may be overheated, resulting in a large difference in grain size in the width direction. Therefore, the cold-rolling and annealing temperature can be limited to 750°C to 880°C, preferably 755°C to 871°C.

[0051] In the cold rolling, the hot rolled material is first cold rolled to a thickness of 0.4 mm to 1 mm, and then second cold rolled to a thickness of 0.01 to 0.2 mm to manufacture an ultra-thin cold rolled coil.

[0052] The reduction rate during the first cold rolling may be 60% to 92%, and the rolling speed may be 50 mpm to 700 mpm, and the reduction rate during the second cold rolling may be 50% to 88%, and the rolling speed may be 50 mpm to 700 mpm.

[0053] The ferritic stainless steel according to one embodiment of the present invention can prevent sheet breakage without reducing the reduction rate and rolling speed, thereby improving the productivity of cold-rolled coils.

[0054] In the method for producing a ferritic stainless steel according to one embodiment of the present invention, the cold rolling may include first cold rolling the hot-rolled material to a thickness of 0.4 mm to 1 mm, and then second cold rolling the hot-rolled material to a thickness of 0.01 mm to 0.2 mm.

[0055] In one embodiment of the present invention, a method for producing a ferritic stainless steel is provided, wherein the stainless steel has a total content of Al and Mg exceeding 30% by weight in a cross section of a cast structure, and the number of inclusions exceeding 6 μm in length in the thickness direction is 160 mm. 2 There may be five or fewer per prize.

[0056] In one embodiment of the present invention, in a method for producing a ferritic stainless steel, the stainless steel may have a ratio of the average grain size at the outer side in the width direction to the average grain size at the center side in the width direction of 2 or less, preferably 1.1 to 1.9.

[0057] The present invention will be described in more detail below with reference to examples. However, the following examples are intended to more specifically explain the present invention, and the scope of the present invention is not limited to the following examples. [Example]

[0058] Slabs having the alloy composition shown in Table 1 below were cast to a thickness of 220 mm. The cast slabs were heated under the manufacturing conditions shown in Table 1 below, and the heated slabs were hot rolled to 3 mm and then hot rolled and annealed. The hot rolled and annealed material was cold rolled to 0.5 mm, cold rolled and annealed, and then secondarily cold rolled to 0.1 mm and cold rolled and annealed at approximately 820°C. Ultra-thin rolling was performed to 0.05 mm.

[0059] For the cold-rolled coil test pieces manufactured as described above, the number of inclusions per unit area in the cross section of the cast structure in which the total content of Al and Mg exceeded 30 wt % and the length in the thickness direction exceeded 6 μm, the ratio of the average crystal grain size at the outer side in the width direction of the stainless steel to the average crystal grain size at the center in the width direction, and whether or not sheet fracture occurred are shown in Table 1 below.

[0060] In the present invention, the types of inclusions that do not remain, i.e., that do not become thin or are destroyed during rolling and maintain their large size, were analyzed by comparing inclusions present inside the cold-rolled coil used in ultra-thin rolling with inclusions that remain after ultra-thin rolling. The inclusions were analyzed using a scanning electron microscope and an Energy Dispersive X-ray Spectrometer. 2 The area was observed under an electron microscope, and the number, size, and composition of inclusions containing 1% or more oxygen were measured. 2The number of inclusions with a total content of Al and Mg exceeding 30 wt % and a length in the thickness direction exceeding 6 μm in a cross section of the cast structure per area is shown in Table 1. Here, the size of an inclusion means the length in the thickness direction.

[0061] The grain size ratio was calculated by observing and measuring the average grain size when observing the cross section of the cold-rolled coil at the outer and central sides in the width direction. The observation area was 2500 μm2, including all thickness layers in the thickness direction. 2 Observation can be performed using an optical microscope or a scanning electron microscope, with units of μm. Alternatively, measurements can be performed using the method defined in ASTM E112 to obtain the grain size number, which can then be converted to μm. The outer side in the width direction is the region 0 to 100 mm from the edge, and the center side in the width direction is the region ±100 mm from the center of the entire coil width.

[0062] [Table 1]

[0063] As shown in Table 1, in Examples 1 to 11, which satisfy the alloy composition and manufacturing conditions of the present invention, the total content of Al and Mg in the cross section of the cast structure among the components of the inclusions exceeds 30 wt % and the number of inclusions with a length in the thickness direction exceeding 6 μm is 160 mm. 2 Since the number of inclusions per sheet was 5 or less, it was confirmed that the inclusions became hard and remained even after ultra-thin rolling. Inclusions satisfying the above range were reduced in size by elongation, fracture, etc. during rolling, and reached a size that did not affect sheet breakage.

[0064] That is, inclusions smaller than 6 μm in size have already been reduced in size through elongation and fracture, and are relatively small compared to the ultra-thin rolled thickness, so their effect on sheet fracture is minimal.It was confirmed that fractures do not occur because the ratio of the average grain size at the outer side in the width direction to the average grain size at the center in the width direction is 2 or less, so the difference in grain size in the width direction is not large.

[0065] On the other hand, in Comparative Example 1, which did not satisfy the alloy composition of the present invention, the carbon content was 0.11%, and a hard martensite phase was formed after cold rolling annealing and cooling, causing sheet fracture during ultra-thin rolling.In Comparative Example 2, the chromium content was 19.1%, and not only was the steel excessively hardened, but the nitrogen content was 0.11%, and a hard martensite phase was formed after cold rolling annealing and cooling, causing sheet fracture during ultra-thin rolling.

[0066] In addition, in the case of Comparative Examples 3 and 4, the aluminum content was 0.03% and 0.11%, respectively, which induced the formation of oxide inclusions, and in the cross section of the cast structure, the total content of Al and Mg exceeded 30 wt % and the inclusions with a length in the thickness direction exceeding 6 μm were found to be 160 mm. 2 It was confirmed that there were 8 and 12 pieces per hole, and plate fractures occurred.

[0067] In the case of Comparative Example 5, the silicon content was 0.8%, which was excessive, causing embrittlement. Silicon (Si) inclusions became the nuclei of aluminum (Al) or magnesium (Mg) inclusions. In the cross section of the cast structure, the total content of Al and Mg exceeded 30% by weight, and inclusions with a length in the thickness direction exceeding 6 μm were found to be 160 mm. 2 It was confirmed that there were nine hits, which caused the plate to break.

[0068] In addition, in the case of Comparative Example 6, the manganese content was 1.22%, and a martensite phase was formed after cold rolling and annealing. In the cross section of the cast structure, the total content of Al and Mg exceeded 30 wt %, and the number of inclusions exceeding 6 μm in the thickness direction was 160 mm. 2 It was confirmed that there were eight pieces per impact, which caused the plate to break.

[0069] Furthermore, in the case of Comparative Examples 7 and 8, the cold rolling annealing temperatures were 870°C and 900°C, respectively, which are outside the range of the present invention. As a result, the widthwise edges were overheated, which increased the difference in grain size in the widthwise direction. As a result, stress was concentrated on one side during ultra-thin rolling, and the ratios of the average grain size at the outer side in the widthwise direction to the average grain size at the center side in the widthwise direction were 2.2 and 2.5, respectively, and it was confirmed that sheet fracture occurred.

[0070] In Comparative Example 9, the slab heating temperature was 1145°C, and it became difficult to reabsorb the inclusions during heating. In the cross section of the cast structure, the total content of Al and Mg exceeded 30 wt % and the inclusions with a length in the thickness direction exceeding 6 μm were 160 mm 2 In Comparative Example 10, the hot rolling annealing temperature was 740°C and the cold rolling annealing temperature was 745°C, so the stress formed during hot rolling was not sufficiently removed, which reduced workability and resulted in insufficient reabsorption of inclusions. In addition, the stress formed during cold rolling was not sufficiently removed, which reduced workability for ultra-thin rolling. In addition, due to insufficient reabsorption of inclusions, the total content of Al and Mg exceeded 30 wt% in the cross section of the cast structure, and inclusions with a length in the thickness direction exceeding 6 μm were found in 160 mm 2 In the case of Comparative Example 11, the slab heating temperature was 1140°C and the hot rolling annealing temperature was 742°C, making it difficult to reabsorb the inclusions, and the stress formed during hot rolling was not sufficiently removed, resulting in a decrease in workability. In the cross section of the cast structure, the total content of Al and Mg exceeded 30 wt % and inclusions with a length in the thickness direction exceeding 6 μm were found to be 160 mm thick. 2 It was confirmed that eight cracks were formed per crack, causing plate fracture.

[0071] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and it will be understood by those skilled in the art that various changes and modifications can be made without departing from the concept and scope of the claims set forth below.

Claims

1. In weight percent, carbon (C): 0.001% to 0.1%, silicon (Si): 0.05% to 0.7%, manganese (Mn): 0.05% to 1%, chromium (Cr): 15% to 19%, nitrogen (N): 0.001% to 0.1%, aluminum (Al): 0% to 0.01%, the remainder being Fe and unavoidable impurities, In the cross section of the cast structure, the total content of Al and Mg exceeds 30 wt % and the number of inclusions exceeding 6 μm in the thickness direction is 160 mm. ２ A ferritic stainless steel having excellent ultra-thin rollability, characterized in that the number of defects per one defect is 5 or less.

2. 2. The ferritic stainless steel having excellent ductility in ultra-thin film rolling according to claim 1, wherein the inclusions include silicon-containing oxides or sulfides.

3. A ferritic stainless steel with excellent ultra-thin rollability as described in claim 1, characterized in that the ratio of the average crystal grain size on the outer side in the width direction of the stainless steel to the average crystal grain size on the center side in the width direction is 2 or less.

4. Casting a slab consisting of, by weight, 0.001% to 0.1% carbon (C), 0.05% to 0.7% silicon (Si), 0.05% to 1% manganese (Mn), 15% to 19% chromium (Cr), 0.001% to 0.1% nitrogen (N), 0% to 0.01% aluminum (Al), with the remainder being Fe and unavoidable impurities; heating the slab to 1150°C to 1250°C; hot rolling the heated slab to produce a hot rolled material; hot rolling annealing the hot rolled material at 750°C to 880°C; cold rolling the hot rolled material to produce a cold rolled material; and cold-rolling and annealing the cold-rolled material at 750°C to 880°C.

5. 5. The method for producing a ferritic stainless steel having excellent ultra-thin rollability according to claim 4, wherein the hot rolling comprises hot rolling the heated slab to a thickness of 2.5 mm to 5 mm.

6. 5. The method for producing a ferritic stainless steel having excellent ultra-thin rollability according to claim 4, wherein the hot rolling includes finish rolling the heated slab at 800°C to 950°C.

7. 5. The method for producing a ferritic stainless steel with excellent ultra-thin rollability according to claim 4, wherein the cold rolling comprises first cold rolling the hot-rolled material to a thickness of 0.4 mm to 1 mm, and then second cold rolling the hot-rolled material to a thickness of 0.01 mm to 0.2 mm.

8. The stainless steel has a cross section in the cast structure in which the total content of Al and Mg exceeds 30 wt % and the number of inclusions exceeding 6 μm in length in the thickness direction is 160 mm ２ 5. The method for producing a ferritic stainless steel having excellent ultra-thin rollability according to claim 4, wherein the number of defects is 5 or less per one.

9. A method for producing a ferritic stainless steel with excellent ultra-thin rollability as described in claim 4, characterized in that the ratio of the average crystal grain size at the outer sides of the stainless steel in the width direction to the average crystal grain size at the center of the width direction is 2 or less.

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