Ferritic stainless steel and manufacturing method thereof

Abstract

The present invention relates to a ferritic stainless steel and a manufacturing method thereof and, more specifically, to a ferritic stainless steel that contains, in wt%, 0.0030-0.0200% of C, 0.0030-0.0200% of N, 0.05-0.50% of Si, 0.10-1.50% of Mn, 19.0-25.0% of Cr, 0.01-2.00% of Mo, 0.05-1.00% of Nb, and 0.010-0.200% of Ti, with the remainder comprising Fe and inevitable impurities, and satisfies Expression (1). Expression (1): 240.00 ≤ (Cr / Mn)×10(Nb+Mo) ≤ 520.00 (where, Cr, Mn, Nb, and Mo each represent the wt% of the corresponding element)

Description

Ferritic stainless steel and its manufacturing method

[0001] The present invention relates to ferritic stainless steel and a method for manufacturing the same.

[0002] Stainless steel, with its excellent corrosion and oxidation resistance, is used in a wide range of applications, from room temperature to high temperature. Extensive research is being conducted to manufacture stainless steel components, such as separators for fuel cells operating in high-temperature environments.

[0003] To apply stainless steel to high-temperature fuel cells, the scale that forms on the surface of stainless steel in high-temperature, oxidizing environments must not become excessively thick or degrade electrical conductivity. If the scale exceeds a certain thickness, it can peel off and damage the material, and if the electrical conductivity is low, it can reduce fuel cell efficiency.

[0004] When stainless steel oxidizes, chromium oxide (Cr2O3) forms on its surface, and this chromium oxide scale provides corrosion resistance. However, while this scale has excellent corrosion resistance, it has low electrical conductivity.

[0005] In addition, since the durability of the fuel cell deteriorates if excellent strength is not satisfied at high temperatures due to the characteristics of the separator that operates in a high-temperature environment, sufficient strength is required in a high-temperature operating environment.

[0006] Therefore, in order to apply stainless steel as a fuel cell component, it must have excellent strength and conductivity properties at high temperatures.

[0007] In order to solve the above-described problem, the present invention aims to provide a ferritic stainless steel having excellent high-temperature strength characteristics while maintaining high electrical conductivity even in a high-temperature oxidizing environment, and a method for manufacturing the same.

[0008] The technical problems to be achieved in this document are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0009] In order to achieve the above object, a ferritic stainless steel according to one embodiment of the present invention contains, in wt%, C: 0.0030% to 0.0200%, N: 0.0030% to 0.0200%, Si: 0.05% to 0.50%, Mn: 0.10% to 1.50%, Cr: 19.0% to 25.0%, Mo: 0.01% to 2.00%, Nb: 0.05% to 1.00%, Ti: 0.010% to 0.200%, the remainder being Fe and other unavoidable impurities, and can satisfy the following formula (1).

[0010] Equation (1): 240.00 ≤ (Cr / Mn)Х10(Nb+Mo) ≤ 520.00

[0011] (Here, Cr, Mn, Nb and Mo represent the weight percent of each element)

[0012] The above stainless steel can satisfy the following equation (2).

[0013] Formula (2): 35.00 ≤ Cr / Mn ≤ 60.00

[0014] (Here, Cr and Mn represent the weight percent of each element)

[0015] The above stainless steel may have a yield strength (YS) of 30 MPa or more at 800°C.

[0016] The above stainless steel may have a creep rupture time of 100 hrs or more under stress conditions of 700°C and 30 MPa.

[0017] The above stainless steel may have a high temperature interface electrical conductivity of 40 mΩ㎠ or less at 800℃.

[0018] In addition, a method for manufacturing a ferritic stainless steel according to an embodiment of the present invention comprises the steps of: reheating a slab that contains, in wt%, C: 0.0030% to 0.0200%, N: 0.0030% to 0.0200%, Si: 0.05% to 0.50%, Mn: 0.10% to 1.50%, Cr: 19.0% to 25.0%, Mo: 0.01% to 2.00%, Nb: 0.05% to 1.00%, Ti: 0.010% to 0.200%, the remainder Fe and other unavoidable impurities, and satisfying the following formula (1) at 1050 to 1280°C; and after the reheating, hot rolling and hot rolling annealing at 900 to 1150°C to manufacture a hot-rolled material; And it may include a step of cold rolling the hot-rolled material and cold-rolling annealing at 900 to 1150°C.

[0019] Equation (1): 240.00 ≤ (Cr / Mn)Х10(Nb+Mo) ≤ 520.00

[0020] (Here, Cr, Mn, Nb and Mo represent the weight percent of each element)

[0021] The stainless steel according to one embodiment of the present invention can satisfy the following equation (2).

[0022] Formula (2): 35.00 ≤ Cr / Mn ≤ 60.00

[0023] (Here, Cr and Mn represent the weight percent of each element)

[0024] According to one embodiment of the present invention, the finishing rolling temperature during hot rolling may be 700 to 950°C.

[0025] According to one embodiment of the present invention, a ferritic stainless steel having excellent high-temperature strength characteristics while maintaining high electrical conductivity even in a high-temperature oxidizing environment can be provided.

[0026] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the spirit of the present invention to those skilled in the art. The present invention is not limited to the embodiments presented herein and may be embodied in other forms. To clarify the present invention, the drawings may omit portions irrelevant to the description, and the sizes of components may be slightly exaggerated to facilitate understanding.

[0028] Additionally, when a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0029] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0030] In the present invention, by controlling the ratio of Nb and Mo in consideration of the correlation with high temperature strength, it is intended to manufacture a ferritic stainless steel that exhibits excellent electrical conductivity characteristics at high temperatures and at the same time exhibits excellent strength characteristics at high temperatures.

[0031] A ferritic stainless steel according to one embodiment of the present invention contains, in wt%, C: 0.0030% to 0.0200%, N: 0.0030% to 0.0200%, Si: 0.05% to 0.50%, Mn: 0.10% to 1.50%, Cr: 19.0% to 25.0%, Mo: 0.01% to 2.00%, Nb: 0.05% to 1.00%, Ti: 0.010% to 0.200%, the remainder being Fe and other unavoidable impurities.

[0032] Below, the reasons for limiting the composition of the above lecture are explained in detail. Unless otherwise specified, the composition of the above lecture lecture refers to weight %.

[0033] The carbon (C) content can be from 0.0030% to 0.0200%.

[0034] Carbon (C) is an essential element in the stainless steel manufacturing process. Excessive C content can lead to the formation of precipitates such as chromium carbides, which can adversely affect the composition and oxidation characteristics of the base metal. Considering this, the upper limit of C is recommended to be 0.0200%. However, controlling the C content to extremely low levels can lead to excessive cost increases. Therefore, the lower limit of C is recommended to be 0.0030%.

[0035] The nitrogen (N) content can be 0.0030% to 0.0200%.

[0036] Excessive nitrogen content can negatively impact quality by precipitating various nitrides or creating pores. Considering this, it is desirable to limit the upper limit of nitrogen to 0.0200%. However, controlling the nitrogen content to extremely low levels can lead to excessive cost increases. Therefore, it is desirable to limit the lower limit of nitrogen to 0.0030%.

[0037] The silicon (Si) content can be 0.05% to 0.50%.

[0038] Silicon (Si) is an element that must be strictly controlled because it forms a film-like precipitate at the interface between the scale and the base material when exposed to high temperatures, forming an insulating layer. Considering this, the upper limit for Si is preferably set at 0.50%. However, reducing the Si content below 0.05% requires expensive processes such as vacuum melting. Therefore, the lower limit for Si is preferably set at 0.05%.

[0039] The manganese (Mn) content can be from 0.10% to 1.50%.

[0040] When stainless steel oxidizes at high temperatures, manganese rapidly diffuses, forming dense manganese / chromium oxides on the outer layer of the scale. Considering this, the lower limit of manganese is recommended to be 0.10%. However, excessive manganese addition may excessively promote scale growth and potentially lead to scale exfoliation. Therefore, the upper limit of manganese is recommended to be 1.50%.

[0041] The chromium (Cr) content may be 19.0% to 25.0%.

[0042] Chromium (Cr) is an essential element for ensuring the corrosion resistance of stainless steel. It is crucial to prevent Cr depletion due to prolonged oxidation in high-temperature, oxidizing environments. Considering this, the lower limit for Cr is recommended to be 19.0%. However, to prevent increased manufacturing costs and the precipitation of chromium carbides and intermetallic compounds, the upper limit for Cr is recommended to be 25.0%.

[0043] The content of molybdenum (Mo) can be from 0.01% to 2.00%.

[0044] Molybdenum (Mo) is an element that can increase the strength of materials in high-temperature environments. Therefore, it is desirable to limit the lower limit of Mo to 0.01%. However, because Mo is an expensive element, it is necessary to suppress increased manufacturing costs. Therefore, it is desirable to limit the upper limit of Mo to 2.00%.

[0045] The content of niobium (Nb) can be 0.05% to 1.00%.

[0046] Niobium (Nb) oxidizes at the scale / base material interface, forming oxides. This inhibits the formation of insulating silicon oxide and contributes to improving the strength of the material. Considering this, the lower limit of Nb is recommended to be 0.05%. However, excessive Nb addition impairs hot workability and increases manufacturing costs. Therefore, the upper limit of Nb should be set at 1.00%.

[0047] The titanium (Ti) content can be from 0.010% to 0.200%.

[0048] Titanium (Ti) is an element that increases the strength of materials by forming internal oxides near the surface of the base metal, just below the interface between the base metal and the scale at high temperatures. Considering this, the lower limit of Ti is preferably set at 0.010%. However, excessive Ti addition increases manufacturing costs and forms titanium oxide outside the scale. Therefore, the upper limit of Ti is preferably set at 0.200%.

[0049] The remaining component is iron (Fe). However, during the normal manufacturing process, unintended impurities from raw materials or the surrounding environment may inevitably be mixed in, and thus cannot be excluded. Since these impurities are readily apparent to anyone skilled in the normal manufacturing process, their full details are not specifically mentioned in this specification.

[0050] Among the alloying components of the present invention, Nb and Mo play a role in improving the strength of the material at high temperatures. Accordingly, the present invention derives the following relationship by considering the correlation between the ratio of Nb and Mo and high-temperature strength, thereby manufacturing stainless steel having both excellent high-temperature strength characteristics and excellent electrical conductivity characteristics.

[0051] The ferritic stainless steel according to one embodiment of the present invention can satisfy the following equation (1).

[0052] Equation (1): 240.00 ≤ (Cr / Mn)Х10(Nb+Mo) ≤ 520.00

[0053] In the above formula (1), Cr, Mn, Nb, and Mo represent the weight% of each element.

[0054] In the above formula (1), if the value of (Cr / Mn)Х10(Nb+Mo) is too low or too high, the strength at high temperatures and the high temperature creep strength may decrease, or the high temperature interface electrical conductivity may become poor, and the manufacturability may become poor due to the decrease in hot workability. Therefore, in order to obtain a material with excellent high temperature strength, it is preferable that the value of (Cr / Mn)Х10(Nb+Mo) satisfies the range of 240.00 or more and 520.00 or less, more preferably satisfies the range of 240.00 or more and 500.00 or less, and most preferably satisfies the range of 250.00 or more and 480.00 or less.

[0055] According to one embodiment of the present invention, the ferritic stainless steel may have a yield strength (YS) of 30 MPa or more at 800°C and a creep rupture time of 100 hrs or more under stress conditions of 700°C and 30 MPa.

[0056] If the yield strength at 800℃ is less than 30MPa or the creep rupture time is less than 100hrs under stress conditions of 700℃ and 30MPa, it may be impossible to manufacture a material with excellent strength in a high-temperature oxidizing environment.

[0057] That is, in the present invention, in order to obtain stainless steel having improved strength characteristics at high temperatures, the ratio of Nb and Mo, which are related to the high-temperature strength of the material among alloying elements, is controlled to the value of the above formula (1) to be 240.00 or more and 520.00 or less, thereby manufacturing a ferritic stainless steel having a yield strength of 30 MPa or more at 800°C and a creep rupture time of 100 hrs or more under stress conditions of 700°C and 30 MPa.

[0058] In addition, a ferritic stainless steel according to one embodiment of the present invention can satisfy the following equation (2).

[0059] Formula (2): 35.00 ≤ Cr / Mn ≤ 60.00

[0060] In the above formula (2), Cr and Mn represent the weight% of each element.

[0061] Even if the (Cr / Mn) Х10(Nb+Mo) value of the above formula (1) is satisfied as 240.00 or more and 520.00 or less, if the Cr / Mn value of the formula (2) is not satisfied, it may be difficult to secure the high-temperature interface electrical conductivity targeted by the present invention. That is, the ferritic stainless steel of the present invention must satisfy the value of the above formula (1) and the value of the formula (2) as 35.00 or more and 60.00 or less to secure excellent high-temperature electrical conductivity of 40 mΩ㎠ or less at 800℃. Therefore, the Cr / Mn value of the above formula (2) is preferably satisfied in the range of 35.00 or more and 60.00 or less, more preferably 35.00 or more and 55.00 or less, and most preferably 37.00 or more and 54.00 or less.

[0062] That is, in the present invention, by controlling the ratio of Nb and Mo, excellent strength characteristics can be satisfied in a high-temperature oxidation environment, and at the same time, excellent electrical conductivity at high temperatures can be secured by controlling the ratio of Cr and Mn.

[0063] When the ferritic stainless steel according to the present invention is exposed to an oxidizing environment of 300 to 900°C, manganese / chromium oxides containing Cr and Mn can be formed on the surface of the ferritic stainless steel. When the manganese / chromium oxides are formed uniformly, excellent electrical conductivity can be secured. At this time, when the alloy composition of the ferritic stainless steel falls within the scope of the present invention, and Cr / MnХ10(Nb+Mo) of formula (1) satisfies the range of 240.00 or more and 520.00 or less, and Cr / Mn of formula (2) satisfies the range of 35.00 or more and 60.00 or less, fine and uniform manganese / chromium oxides are formed on the surface, thereby exhibiting excellent electrical conductivity characteristics at high temperatures and expressing excellent strength characteristics at high temperatures.

[0064] Next, a method for manufacturing ferritic stainless steel according to one embodiment of the present invention will be described.

[0065] A method for manufacturing a ferritic stainless steel according to one embodiment of the present invention may include the steps of: reheating a slab containing, in wt%, C: 0.0030% to 0.0200%, N: 0.0030% to 0.0200%, Si: 0.05% to 0.50%, Mn: 0.10% to 1.50%, Cr: 19.0% to 25.0%, Mo: 0.01% to 2.00%, Nb: 0.05% to 1.00%, Ti: 0.010% to 0.200%, the remainder Fe and other unavoidable impurities, and satisfying the following formula (1); hot-rolling and hot-rolling annealing after the reheating to manufacture a hot-rolled material; and cold-rolling and cold-rolling annealing the hot-rolled material.

[0066] The reason for limiting the composition range of each alloy element is as described above, and each manufacturing step is described in more detail below.

[0067] After manufacturing a slab that satisfies the above alloy composition, it can undergo a series of processes including reheating, hot rolling, hot annealing, cold rolling, and cold annealing.

[0068] First, the above slab can be reheated at 1050°C to 1280°C, and then hot-rolled and hot-annealed to produce a hot-rolled material.

[0069] The above reheating temperature may be 1050℃ or higher to reduce hot rolling load, and may be limited to 1280℃ or lower to prevent internal grain coarsening.

[0070] The finishing rolling temperature during the above hot rolling may be 700 to 950°C, and the thickness of the hot-rolled material thus hot-rolled may be 2 to 6 mm.

[0071] If the finishing rolling temperature during the above hot rolling is less than 700℃, the rolling load may increase and shape defects may increase, which may lower productivity. If it exceeds 950℃, the surface quality may deteriorate due to an increase in oxides caused by excessive high-temperature work.

[0072] The hot rolling annealing temperature of the above hot rolled material can be 900 to 1150°C.

[0073] If the above hot rolling annealing temperature is less than 900℃, recrystallization may not occur and thus a grain structure may not be formed. If it exceeds 1150℃, the grains may become coarser and the strength of the material may be weakened.

[0074] The above hot-rolled and annealed hot-rolled material can be cold-rolled and cold-rolled and annealed.

[0075] The above cold rolling annealing can be performed at 900 to 1150°C, and the thickness of the final cold rolled product can be 0.05 to 2 mm.

[0076] If the above cold rolling annealing temperature is lower than 900℃, the stress formed during rolling may not be sufficiently removed, which may result in reduced workability. If it exceeds 1150℃, the grains may become coarser and plate breakage may occur.

[0077] Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is intended only to illustrate the implementation of the present invention and is not intended to limit the present invention. This is because the scope of the present invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0078] Example

[0079] Slabs were manufactured to satisfy various alloy compositions shown in Table 1 below.

[0080] The manufactured ingot was reheated to a temperature of 1250℃, hot-rolled so that the finishing rolling temperature became 900℃, and then hot-rolled and annealed at a temperature of 1050℃ to manufacture a hot-rolled product having a thickness of 5.0㎜. The hot-rolled product was cold-rolled to a thickness of 1.0㎜, cold-rolled and annealed at a temperature of 1050℃, and a 15㎜Х15㎜ sample was manufactured to manufacture a ferritic stainless steel specimen.

[0081] The units in Table 1 below are weight%.

[0082] Classification CSiMnCrMoTiNbN(Cr / Mn)×10(Nb+Mo)Cr / MnExample 10.00600.110.4622.40.200.0480.500.0072340.8748.70Example 20.00500.140.4921.50.200.0690.510.0060311.5343.88Example 30.00530.130.5321.90.010.0530.710.0058297.5141.32Comparative Example 10.00600.120.2921.60.200.0350.5 00.0049521.3874.48Comparative Example 20.00500.110.6622.50.200.0500.490.0056235.2334.09Comparative Example 30.00500.130.6721.50.0010.0430.510.0060163.9832.09Comparative Example 40.00690.130.3622.70.210.0670.0010.0102133.0563.06Comparative Example 50.00510.130.4721.60.200.0480.0020.005792.8345.96

[0083] Table 2 below shows the high-temperature strength, creep rupture time, and high-temperature interfacial electrical conductivity of the ferritic stainless steel manufactured above. The high-temperature strength was measured by sampling and testing according to the KS D 0026 standard. The manufactured samples were mounted on a tensile tester and subjected to tensile testing at 800°C until fracture, thereby measuring the yield strength.

[0084] Creep rupture time was measured by producing samples and conducting experiments according to the ASTM E139 standard, and applying a stress of 30 MPa at a temperature of 700℃.

[0085] High-temperature interfacial electrical conductivity was measured by applying Pt paste to both sides of a high-temperature oxidized specimen, pre-drying at 200°C, and sintering at 800°C for 3 hours. The prepared specimen with Pt sintered on both sides was laminated with Pt mesh on both sides, and a load of 15 g was applied. Then, a Pt wire was withdrawn through four terminals and placed in a furnace. After the temperature was increased to 800°C, the resistance was measured at 500 hours using the DC 4-point probe method to calculate the resistance value.

[0086] ClassificationHigh-temperature strength (MPa)Creep rupture time (hrs)High-temperature interfacial electrical conductivity (mΩ㎠)Example 142.0133.99.33Example 240.7125.75.66Example 331.5103.38.72Comparative example 138.5101.849.2Comparative example 239.8112.540.9Comparative example 321.071.850.8Comparative example 427.351.841.8Comparative example 527.647.76.25

[0087] As shown in Table 2 above, in the case of Examples 1 to 3 that satisfy the alloy composition and formula (1) presented in the present invention, the yield strength (YS) at 800°C was 30 MPa or more, and the creep rupture time was 100 hrs or more under stress conditions of 700°C and 30 MPa, confirming that the strength characteristics at high temperatures were excellent. In addition, it was confirmed that Examples 1 to 3, which satisfy the Cr / Mn of Formula (2) of 35.00 or more and 60.00 or less, exhibit excellent electrical conductivity characteristics at high temperatures with a high temperature interface electrical conductivity of 40 mΩ㎠ or less. On the other hand, Comparative Example 1, which satisfies the alloy composition suggested in the present invention but has a value of Formula (1) exceeding 520.00 and a value of Formula (2) exceeding 60, and Comparative Example 2, which satisfies the alloy composition suggested in the present invention but has a value of Formula (1) less than 240.00 and a value of Formula (2) less than 35, has a high content of Nb and Mo alloy elements that affect high temperature strength, so that the yield strength at 800℃ is 38.5 MPa and 39.8 MPa, and the creep rupture time at 700℃, 30 MPa stress condition is 101.8 hrs and 112.5 hrs, which are limited by the present invention. Although it showed a tendency close to the numerical value, it was confirmed that the high-temperature interface electrical conductivity was inferior because the value of equation (2) was not satisfied.

[0088] In addition, it was confirmed that in the case of comparative examples 3 and 4, which did not satisfy the alloy composition suggested in the present invention and did not satisfy the values ​​of equations (1) and (2), the yield strength, creep rupture time, and high-temperature interface electrical conductivity were all inferior.

[0089] Meanwhile, in the case of Comparative Example 5, which does not satisfy the alloy composition and equation (1) presented in the present invention but satisfies the value of equation (2), it was confirmed that the yield strength and creep rupture time were inferior, but the high-temperature interface electrical conductivity was good.

[0090] From these results, it was found that only when the alloy composition suggested in the present invention and equations (1) and (2) for controlling the ratio of Nb and Mo are simultaneously satisfied, a ferritic stainless steel satisfying not only excellent electrical conductivity at high temperatures but also high-temperature strength characteristics can be manufactured, and that such a ferritic stainless steel can be efficiently applied to a fuel cell operating in a high-temperature environment.

[0091] Although the embodiments of the invention disclosed above have been illustrated and described, the disclosed invention is not limited to the specific embodiments described above, and various modifications may be implemented by a person having ordinary skill in the art to which the disclosed invention pertains without departing from the gist claimed in the claims.

Claims

1. Containing, by weight%, C: 0.0030% to 0.0200%, N: 0.0030% to 0.0200%, Si: 0.05% to 0.50%, Mn: 0.10% to 1.50%, Cr: 19.0% to 25.0%, Mo: 0.01% to 2.00%, Nb: 0.05% to 1.00%, Ti: 0.010% to 0.200%, the remainder being Fe and other unavoidable impurities, Ferritic stainless steel satisfying the following equation (1). Equation (1): 240.00 ≤ (Cr / Mn)×10(Nb+Mo) ≤ 520.00 (Here, Cr, Mn, Nb and Mo represent the weight% of each element) 2. In paragraph 1, The above stainless steel is a ferritic stainless steel satisfying the following formula (2). Formula (2): 35.00 ≤ Cr / Mn ≤ 60.00 (Here, Cr and Mn represent the weight% of each element) 3. In paragraph 1, The above stainless steel is a ferritic stainless steel having a yield strength (YS) of 30 MPa or more at 800°C.

4. In paragraph 1, The above stainless steel is a ferritic stainless steel having a creep rupture time of 100 hrs or more under stress conditions of 700°C and 30 MPa.

5. In paragraph 1, The above stainless steel is a ferritic stainless steel having a high temperature interface electrical conductivity of 40 mΩ㎠ or less at 800℃.

6. A step of reheating a slab containing C: 0.0030% to 0.0200%, N: 0.0030% to 0.0200%, Si: 0.05% to 0.50%, Mn: 0.10% to 1.50%, Cr: 19.0% to 25.0%, Mo: 0.01% to 2.00%, Nb: 0.05% to 1.00%, Ti: 0.010% to 0.200%, the remainder being Fe and other unavoidable impurities, and satisfying the following formula (1) at 1050 to 1280°C; A step of manufacturing a hot-rolled material by hot-rolling and hot-annealing at 900 to 1150°C after the above reheating; and A step of cold rolling the above hot-rolled material and cold annealing at 900 to 1150°C; A method for manufacturing a ferritic stainless steel comprising: Equation (1): 240.00 ≤ (Cr / Mn)×10(Nb+Mo) ≤ 520.00 (Here, Cr, Mn, Nb and Mo represent the weight% of each element) 7. In paragraph 6, The above stainless steel is a method for manufacturing a ferritic stainless steel satisfying the following formula (2). Formula (2): 35.00 ≤ Cr / Mn ≤ 60.00 (Here, Cr and Mn represent the weight% of each element) 8. In paragraph 6, A method for manufacturing ferritic stainless steel in which the finishing rolling temperature during the above hot rolling is 700 to 950°C.