Ferritic stainless steel with excellent ultra-thin rollability and methods for producing it.

Abstract

Invention details;

Description

Ferritic stainless steel with excellent ultra-thin rollability and method for manufacturing the same

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

[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 is usually 0.01 to 0.08 mm thick. Rolling the stainless steel thinly increases strength through work hardening while also ensuring flexibility due to its thin thickness. In this case, ultra-thin rolling mills use cold-rolled coils with a thickness of 0.4 mm or more to perform ultra-thin rolling. However, the significantly thinner coil thickness can cause sheet fracture during the rolling process. This sheet fracture is believed to be due to hard, coarse inclusions within the coil. To prevent sheet fracture, reduction ratios and rolling speeds were reduced, and multiple, low-speed operations were performed. However, this resulted in a decrease in productivity.

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

[0005] However, the problems that the present invention seeks to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0006] According to one embodiment of the present invention, a ferritic stainless steel having excellent ultra-thin rollability comprises, in wt%, 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, and a total content of Al and Mg exceeding 30 wt% in a cross-section within a cast structure, and inclusions exceeding 6 ㎛ in length in the thickness direction are 160 mm. 2 There may be less than 5 per party.

[0007] In addition, the ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention may include a silicon-containing oxide or sulfide as the inclusion.

[0008] In addition, the ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention may have a ratio of the average grain size on the outer side in the width direction of the stainless steel to the average grain size on the central side in the width direction of 2 or less.

[0009] A method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention comprises the steps of: casting a slab containing, in wt%, 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 Fe and unavoidable impurities; heating the slab at 1150°C to 1250°C; hot-rolling the heated slab to manufacture a hot-rolled material; hot-rolling and annealing the hot-rolled material at 750°C to 880°C; cold-rolling the hot-rolled material to manufacture a cold-rolled material; and forming a cold-rolled material by heating the cold-rolled material. It may include a step of cold rolling annealing at 750°C to 880°C.

[0010] A method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention may include hot rolling the heated slab to a thickness of 2.5 mm to 5 mm.

[0011] A method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention may include the hot rolling including finishing rolling the heated slab at 800°C to 950°C.

[0012] A method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention 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.

[0013] A method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to one embodiment of the present invention is characterized in that the stainless steel has a total content of Al and Mg exceeding 30 wt% in a cross-section within a cast structure, and an inclusion exceeding 6 ㎛ in length in the thickness direction is 160 mm. 2 There may be less than 5 per party.

[0014] According to one embodiment of the present invention, a method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability may be provided in which the stainless steel has a ratio of an average grain size on the outer side in the width direction to an average grain size on the central side in the width direction of 2 or less.

[0015] According to an embodiment of the present invention, a ferritic stainless steel having excellent ultra-thin rollability capable of preventing sheet fracture during cold rolling and a method for manufacturing the same can be provided.

[0016] The effects that can be obtained from this invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art to which the present invention pertains from the description below.

[0017] Figure 1 is a photograph of an inclusion that has the characteristics of causing plate fracture during ultra-thin rolling.

[0018] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, 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 fully explain the present invention to those of ordinary skill in the art.

[0019] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" 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 used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0020] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, unless explicitly defined herein, specific terms should not be interpreted in an overly idealistic or formal sense. For example, singular expressions herein include plural expressions unless the context clearly indicates otherwise.

[0021] In addition, the terms "about", "substantially", etc. in this specification are used in the sense of or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure contents in which exact or absolute numerical values ​​are mentioned to aid in the understanding of the present invention.

[0022] A ferritic stainless steel having excellent ultra-thin rollability according to an example of the present invention may include, in wt%, 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%, and the remainder of iron and unavoidable impurities.

[0023] Below, the reasons for limiting the composition range of each alloy element are explained. Unless otherwise specified, the unit is weight percent.

[0024] The carbon (C) content can be 0.001% to 0.1%.

[0025] Carbon is an element necessary for securing the strength of steel. Considering this, the lower limit of the carbon content is limited 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 lower limit of the carbon content is limited to 0.1% or less, preferably 0.07% or less.

[0026] The silicon (Si) content may be 0.05% to 0.7%.

[0027] Silicon (Si) is an element that can secure strength and improve corrosion resistance. Considering this, the lower limit of the silicon content is limited to 0.05% or more, preferably 0.11% or more. However, if the silicon content is excessive, it can cause brittleness and cause plate fracture during ultra-thin rolling. In addition, Si is an element that can react with oxygen (O) or sulfur (S) to form oxide or sulfide inclusions. However, silicon (Si) inclusions have the characteristic of being relatively elongated during rolling. However, since silicon (Si) inclusions can become nuclei for aluminum (Al) or magnesium (Mg) inclusions, the upper limit of the silicon content is limited to 0.7% or less, preferably 0.61% or less.

[0028] The manganese (Mn) content may be 0.05% to 1%.

[0029] Manganese can refine the structure during hot rolling, thereby reducing the ratio of grain sizes in the width direction. Considering this, the lower limit of the manganese content is limited to 0.05% or more, preferably 0.26% or more. However, if the manganese content exceeds 1%, a martensite phase may form after cold rolling and annealing, so the upper limit of the manganese content is limited to 1% or less, preferably 0.85% or less.

[0030] The chromium (Cr) content may be between 15% and 19%.

[0031] Cr is an element that improves corrosion resistance. If the chromium content is less than 15%, martensite phase may form during the cold rolling annealing section, so the lower limit of the chromium content is limited to 15% or more, preferably 15.1% or more. However, if the chromium content exceeds 19%, the steel may become excessively hardened, so the upper limit of the chromium content is limited to 19% or less, preferably 18.7% or less.

[0032] The nitrogen (N) content can be 0.001% to 0.1%.

[0033] Nitrogen is an element necessary for securing the strength of steel. Considering this, the lower limit of the nitrogen content is limited 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 limited to 0.1% or less, preferably 0.07% or less.

[0034] The content of aluminum (Al) can be 0% to 0.01%.

[0035] Al can react with oxygen (O) to form oxide inclusions. Considering this, the aluminum content is controlled to be 0% or less.

[0036] The remaining component is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment can inevitably be mixed in during the normal manufacturing process, this cannot be ruled out. Since these impurities are readily apparent to anyone skilled in the normal manufacturing process, their full details are not specifically mentioned in this specification.

[0037] According to one embodiment, a ferritic stainless steel has a total content of Al and Mg exceeding 30 wt% in a cross-section within a cast structure, and an inclusion exceeding 6 ㎛ in length in the thickness direction is 160 mm. 2 There may be less than 5 per party.

[0038] In addition, the above inclusions may include oxides or sulfides with a high silicon content that are easily elongated during rolling, and inclusions that maintain a large size without thinning or breaking during rolling, for example, oxides or sulfides with a high aluminum or magnesium content, are preferably minimized.

[0039] Ferritic stainless steels contain inclusions that form internally during casting. These are mainly oxides or sulfides composed of Al, Mg, Si, and Mn. In the typical stainless steel manufacturing process, as the coil thickness decreases during hot and cold rolling, 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, which is relatively small compared to the coil thickness, so it does not pose a major problem during rolling. However, in ultra-thin rolling where the cold-rolled coil thickness is on the order of 0.01 mm to 0.1 mm, the size of these inclusions is relatively large compared to the entire coil thickness.

[0040] In addition, there are inclusions that remain without being significantly thinned or destroyed during ultra-thin rolling, which may cause plate breakage during rolling. For example, Fig. 1 is an electron microscope photograph of a 5㎛-sized inclusion observed in a cold-rolled coil having a thickness of 0.03mm. Such inclusions remain at a size of about 1 / 3 of the total thickness of the coil, which may cause plate breakage. According to one embodiment of the present invention, plate breakage during ultra-thin rolling can be prevented by preventing the presence of inclusions that remain in the cold-rolled coil during ultra-thin rolling.

[0041] Therefore, inclusions whose combined aluminum and magnesium content exceeds 30% should be restricted. This is because inclusions with a combined aluminum and magnesium content exceeding 30 wt% may harden and remain even after ultra-thin rolling. On the other hand, inclusions with a combined aluminum and magnesium content of 30 wt% or less may not affect plate fracture due to reduction in size during rolling due to elongation or fracture.

[0042] In addition, the ferritic stainless steel according to one embodiment of the present invention has a number of inclusions exceeding 6 ㎛ in the thickness direction of 160 mm. 2The number of inclusions can be limited to 5 or less per sheet. Inclusions with a length of 6 ㎛ or less in the thickness direction have already been reduced due to elongation and destruction, and thus have a relatively small size compared to the ultra-thin rolled thickness, so their effect on sheet fracture may be minimal. In other words, the number of inclusions exceeding 6 ㎛ in the thickness direction is limited to 160 mm. 2 When the number of plates is controlled to 5 or less, the site where stress is concentrated during ultra-thin rolling is reduced, which can prevent plate breakage during ultra-thin rolling.

[0043] In addition, the ferritic stainless steel according to one embodiment of the present invention may have a ratio of the average grain size on the outer side in the width direction of the stainless steel to the average grain size on the center side in the width direction of 2 or less. If the difference in grain size in the width direction is large, stress may be concentrated on one side during ultra-thin rolling, so the ratio of the average grain size is limited to 2 or less, preferably 1.9 or less.

[0044] Next, a method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to an example of the present invention will be described.

[0045] A method for manufacturing a ferritic stainless steel having excellent ultra-thin rollability according to an example of the present invention comprises the steps of: casting a slab containing, in wt%, 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 Fe and unavoidable impurities; heating the slab at 1150°C to 1250°C; hot-rolling the heated slab to manufacture a hot-rolled material; hot-rolling and annealing the hot-rolled material at 750°C to 880°C; cold-rolling the hot-rolled material to manufacture a cold-rolled material; and forming a cold-rolled material by heating the cold-rolled material. It may include a step of cold rolling annealing at 750°C to 880°C.

[0046] The reason for limiting the component range values ​​of each alloy composition is as described above, and each manufacturing step is described in more detail below.

[0047] First, a slab satisfying the above alloy composition is manufactured, and then a series of reheating, hot rolling, hot annealing, cold rolling, and cold annealing processes can be performed.

[0048] First, the slab is heated in a hot rolling furnace at a temperature of 1150°C to 1250°C, and then hot-rolled to a thickness of 2.5 mm to 5 mm to produce a hot-rolled steel sheet. If the heating temperature is too high, the internal grains may become too coarse, surface oxidation may occur severely, causing surface defects, and the distribution in the width direction may become uneven, making it difficult to control the grain size in the width direction after hot rolling later. In addition, if the temperature is too low, it becomes difficult to reabsorb inclusions during heating, and therefore the heating temperature may be limited to 1150°C to 1250°C, preferably 1181°C to 1245°C.

[0049] In addition, if the hot-rolled thickness is thicker than 5 mm, the remaining thickness must be processed thinly by cold rolling. In this case, the inclusions that should be elongated in the longitudinal direction may be segmented instead of elongated. In other words, the inclusions must be made to be more easily elongated at high temperatures. If they are segmented, they will not be reabsorbed into the base metal during the annealing process described later and will remain thick, which may cause plate fracture. On the other hand, if the thickness is thinner than 2.5 mm, the hot-rolling load increases, so the hot-rolled thickness is limited as mentioned above.

[0050] In the above hot rolling, finishing rolling can be performed at 800°C to 950°C.

[0051] If the finishing rolling temperature is too low, sticking bonds may occur on the slab surface during hot rolling, and inclusion reabsorption may be insufficient during hot rolling. However, if the finishing rolling temperature is too high, coarse ferrite grains may form, so the finishing rolling temperature can be limited as described above.

[0052] Additionally, hot-rolled material can be hot-rolled and annealed at a temperature of 750°C to 880°C.

[0053] If the hot rolling annealing temperature is low, the stress formed during hot rolling may not be sufficiently removed, resulting in poor workability and insufficient reabsorption of inclusions. However, if the hot rolling annealing temperature is too high, the widthwise edge portion may be overheated, resulting in a large difference in grain size in the widthwise direction. Therefore, the hot rolling annealing temperature of the hot-rolled material may be limited to 750°C to 880°C, preferably 760°C to 865°C.

[0054] Hot-rolled steel sheets can be manufactured by cold-rolling and then cold-annealing hot-rolled steel sheets. At this time, the cold-rolling annealing can be performed at a temperature of 750℃ to 880℃. If the cold-rolling annealing temperature is too low, the stress formed during cold rolling is not sufficiently removed, which may result in poor workability for ultra-thin rolling and insufficient reabsorption of inclusions. If the cold-rolling annealing temperature is too high, the width-wise edge portion may be overheated, which may increase the difference in grain size in the width-wise direction. Therefore, the cold-rolling annealing temperature may be limited to 750℃ to 880℃, preferably 755℃ to 871℃.

[0055] In the above cold rolling, after the hot-rolled material is first cold rolled to a thickness of 0.4 mm to 1 mm, a second cold rolling can be further performed to a thickness of 0.01 to 0.2 mm to manufacture an ultra-thin cold-rolled coil.

[0056] The reduction ratio in the first cold rolling may be 60% to 92%, and the rolling speed may be 50mpm to 700mpm. In addition, the reduction ratio in the second cold rolling may be 50% to 88%, and the rolling speed may be 50mpm to 700mpm.

[0057] A ferritic stainless steel according to one embodiment of the present invention can prevent plate breakage without reducing the reduction ratio and rolling speed, thereby improving the productivity of cold-rolled coils.

[0058] A method for manufacturing a ferritic stainless steel according to one embodiment of the present invention 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.

[0059] A method for manufacturing a ferritic stainless steel according to one embodiment of the present invention is a method for manufacturing a ferritic stainless steel, wherein the stainless steel has a total content of Al and Mg exceeding 30 wt% in a cross-section within a cast structure, and an inclusion exceeding 6 ㎛ in length in the thickness direction is 160 mm. 2 There may be less than 5 per party.

[0060] According to one embodiment of the present invention, a method for manufacturing a ferritic stainless steel is provided, wherein the stainless steel has a ratio of an average grain size on the outer side in the width direction to an average grain size on the central side in the width direction, and is preferably 2 or less and 1.1 to 1.9.

[0061] Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to further illustrate the present invention, and the scope of the present invention is not limited by the following examples.

[0062] {Example}

[0063] A slab having an alloy composition according to Table 1 below was cast to a thickness of 220 mm. The cast slab was heated under the manufacturing conditions shown in Table 1 below, hot-rolled to 3 mm, and then hot-rolled and annealed. The hot-rolled and annealed material was cold-rolled to 0.5 mm, then cold-rolled and annealed, and then cold-rolled a second time to 0.1 mm, and then cold-rolled and annealed at approximately 820°C. Ultra-thin rolling was performed to a thickness of 0.05 mm.

[0064] For the cold-rolled coil specimen manufactured above, the total content of Al and Mg exceeding 30 wt% in the cross-section of the cast structure, the number per unit area of ​​inclusions exceeding 6 ㎛ in the thickness direction, the ratio of the average grain size on the outer side in the width direction of the stainless steel to the average grain size on the center side in the width direction, and whether plate fracture occurred are shown in Table 1 below.

[0065] In the present invention, inclusions existing inside a cold rolled coil used for ultra-thin rolling and inclusions remaining after ultra-thin rolling were compared to analyze the type of inclusions that do not remain, i.e., do not become thin or destroyed during rolling and maintain a large size.

[0066] The analysis of inclusions was performed using an Energy Dispersive X-ray Spectrometer in a scanning electron microscope. A random 160 mm section of the cold-rolled coil was taken. 2 The area was observed with an electron microscope, and the number, size, and composition of inclusions containing more than 1% oxygen were measured, and 160 mm 2 The number of inclusions in which the total content of Al and Mg exceeds 30 wt% in the cross-section of the casting structure per area and the length in the thickness direction exceeds 6 ㎛ is shown in Table 1. Here, the size of the inclusion means the length in the thickness direction.

[0067] The crystal grain size ratio was measured by observing the average crystal grain size when observing the cross-section from the outer and central sides in the width direction of the cold-rolled coil, and then the ratio was calculated. At this time, the observation area was 2500㎛, which includes all thickness layers in the thickness direction. 2 As described above, the observation method can be an optical microscope or a scanning electron microscope, and the unit is ㎛. Alternatively, the grain size number can be obtained by measuring using the method defined in ASTM E112 and then converted to ㎛. The outer side in the width direction is the area from 0 to 100 mm from the edge, and the center side in the width direction is the area ±100 mm from the center of the entire width of the coil.

[0068] CSiMnCrNAl slab heating temperature (℃) hot rolling annealing temperature (℃) cold rolling annealing temperature (℃) number of inclusions in the cross section within the cast structure (units / 160mm) 2)Critical fracture occurrence by grain size Example 10.040.310.5216.10.030.003118184085031.6Good Example 20.040.250.8518.70.030.004118983585131.9Good Example 30.010.610.5215.10.070.002120584284541.3Good Example 40.070.310.6216.20.010.003120484585231.4Good Example 50.060.350.8116.10.040.002122983983521.3 Good embodiment 60.010.110.2615.90.010.001124583583211.2 Good embodiment 70.040.310.5216.10.030.008120581579941.1 Good embodiment 80.030.310.5216.20.030.006120484085031.5 Good embodiment 90.040.310.6216.10.020.003122983984521.5 Good embodiment 100.040.280.5216.30.030.003124586587101.5 Good Example 110.040.310.4516.10.030.009118276075551.1 Good Comparative Example 10.110.550.2918.50.030.005122283584421.1 Fracture Comparative Example 20.030.480.3319.10.110.009121884184431.1 Fracture Comparative Example 30.040.310.5516.30.030.03121582283581.3 Fracture Comparative Example 40.030.280.4515.80.020.111218826811121.4Fracture comparison example 50.040.80.6117.20.030.005121683382291.3Fracture comparison example 60.050.331.2216.90.020.003121883382181.1Fracture comparison example 70.040.280.5516.30.030.002125586087052.2Fracture comparison example 80.050.330.4516.10.020.001122589090052.5Fracture comparison example 90.040.320.4816.20.020.001114582083071.6 Fracture comparison example 100.050.330.4916.10.030.002118974074571.5 Fracture comparison example 110.040.330.5216.20.030.001114074276581.1 Break.

[0069] Referring to Table 1, in the case of Examples 1 to 11 that 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 inclusions having a length in the thickness direction exceeding 6 ㎛ are 160 mm. 2 It was confirmed that inclusions less than 5 μm in diameter remained even after ultra-thin rolling, and the inclusions satisfying the above range were reduced in size due to elongation and destruction during rolling, and became a size that did not affect plate fracture. In other words, inclusions smaller than 6 μm in size had already become smaller due to elongation and destruction, and were relatively small compared to the ultra-thin rolling thickness, so they had a minimal effect on plate fracture. In addition, it was confirmed that the ratio of the average grain size on the outer side in the width direction to the average grain size on the center side in the width direction was 2 or less, and the difference in grain size in the width direction was not large, so fracture did not occur. On the other hand, in the case of Comparative Example 1, which did not satisfy the alloy composition of the present invention, the carbon content was 0.11%, so that a hard martensite phase was formed after cold rolling annealing and cooling, resulting in plate fracture during ultra-thin rolling. In the case of Comparative Example 2, not only was the steel excessively hardened due to the chromium content of 19.1%, but it was also confirmed that the nitrogen content was 0.11%, so that a hard martensite phase was formed after cold rolling annealing and cooling, resulting in plate fracture during ultra-thin rolling. In addition, in the case of Comparative Examples 3 and 4, the aluminum contents were 0.03% and 0.11%, respectively, which induced the formation of oxide inclusions, so that the total content of Al and Mg in the cross-section within the cast structure exceeded 30 wt%, and inclusions exceeding 6 ㎛ in the thickness direction were 160 mm. 2 We were able to confirm that the plate breakage occurred by taking 8 or 12 pieces.

[0070] And in the case of Comparative Example 5, the silicon content was 0.8%, which was excessive, causing brittleness, and silicon (Si) inclusions became the nuclei of aluminum (Al) or magnesium (Mg) inclusions, so that the total content of Al and Mg in the cross-section of the cast structure exceeded 30 wt%, and inclusions exceeding 6 ㎛ in length in the thickness direction were 160 mm. 2 It was confirmed that there were 9 of them and that this caused the plate to break.

[0071] In addition, in the case of Comparative Example 6, the manganese content was 1.22%, and a martensite phase was formed after cold rolling annealing, so that the total content of Al and Mg in the cross section of the cast structure exceeded 30 wt%, and inclusions exceeding 6 ㎛ in length in the thickness direction were 160 mm. 2 It was confirmed that there were 8 of them and that this caused the plate to break.

[0072] In addition, in the case of Comparative Examples 7 and 8, the cold rolling annealing temperatures were 870°C and 900°C, respectively, which were outside the scope of the present invention, and as a result, the edge portion in the width direction was overheated, and the difference in grain size in the width direction increased, so that stress was concentrated on one side during ultra-thin rolling, and the ratio of the average grain size on the outer side in the width direction to the average grain size on the center side in the width direction was 2.2 and 2.5, respectively, which confirmed that plate fracture occurred.

[0073] In addition, Comparative Example 9 had a slab heating temperature of 1145°C, making it difficult to reabsorb inclusions during heating, so the total content of Al and Mg in the cross-section of the cast structure exceeded 30 wt%, and inclusions exceeding 6 ㎛ in length in the thickness direction were 160 mm. 2Comparative Example 10 has 7, and the hot rolling annealing temperature is 740℃ and the cold rolling annealing temperature is 745℃, so the stress formed during hot rolling is not sufficiently removed, which may result in poor workability, and not only is there insufficient reabsorption of inclusions, but the stress formed during cold rolling is not sufficiently removed, which may result in poor workability for ultra-thin rolling, and there is insufficient reabsorption of inclusions, so that the total content of Al and Mg in the cross section of the cast structure exceeds 30 wt%, and inclusions exceeding 6㎛ in length in the thickness direction are 160 mm. 2 It was confirmed that 7 inclusions were formed and plate fracture occurred, and in the case of Comparative Example 11, the slab heating temperature was 1140℃ and the hot rolling annealing temperature was 742℃, making it difficult to reabsorb inclusions, and the stress formed during hot rolling was not sufficiently removed, resulting in poor workability, with the total content of Al and Mg exceeding 30 wt% in the cross section of the cast structure, and inclusions exceeding 6㎛ in length in the thickness direction were 160mm. 2 It was confirmed that 8 sugars were formed and a plate fracture occurred.

[0074] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the claims set forth below.

Claims

DEPCT6915 / 09 / 25681. Ferritic stainless steel with excellent ultra-thin rollability, composed of the following elements in percentages by weight (% 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%, and the remainder being Iron (Fe) and unavoidable impurities, where in the cross-section of the ferritic stainless steel casting structure, the total inclusion of Al and Mg exceeds 30%.

1. Ferritic stainless steel with excellent ultra-thin rollability according to claim 1, where the inclusions include silicon oxides or silicon sulfides.

3. Ferritic stainless steel with excellent ultra-thin rollability according to claim 1, where the ratio of average grain size in the outer width region to the average grain size in the center width region of the stainless steel is 2 or less. 4.The method for producing exceptionally thin, rollable ferritic stainless steel involves casting flat billets containing the following elements in percentages by weight (% 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%, and the remainder being iron (Fe) and unavoidable impurities; heating the billets to 1150°C to 1250°C; hot rolling; and finally...

5. Method under claim 4 where hot rolling includes hot rolling of flat bars heated to a thickness of 2.5 mm to 5 mm.

6. Method under claim 4 where hot rolling includes surface finishing rolling of flat bars heated to 800 mm to 950 mm. 7.Claims 4 method where cold rolling includes a first cold rolling operation on hot-rolled material to a thickness of 0.4 mm to 1 mm and then a second cold rolling operation on hot-rolled material to a thickness of 0.01 mm to 0.2 mm.

8. Claims 4 method where in the cross-section of the ferritic stainless steel casting structure, the number of inclusions with a total Al and Mg content exceeding 30% by weight and a length exceeding 6 micrometers in the thickness direction is 5 points or less per 160 square millimeters.

9. Claims 4 method where the ratio of the average grain size in the outer region along the width to the average grain size in the center region along the width of the stainless steel is 2 or less.

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