Ferritic stainless steel sheet and exhaust member

Abstract

A ferritic stainless steel sheet which has a chemical composition comprising, in mass%, 0.001 to 0.030% of C, 0.01 to 1.00% of Si, 0.01 to 0.90% of Mn, 0.010 to 0.100% of P, 0.0001 to 0.0100% of S, 16.0 to 20.0% of Cr, 1.00 to 1.50% of Cu, 0.02 to 0.50% of Mo, 0.050 to 0.300% of Ti, 0.050 to 0.200% of Nb, 0.003 to 0.500% of Al, 0.01 to 0.30% of Ni, 0.0001 to 0.0050% of B, 0.010 to 0.500% of V, 0.001 to 0.020% of N, and the balance of Fe and impurities, satisfies [830 < = 250Cu + 2216Nb + 3083V < = 2000] and [900 < = 1273Nb + 1343Mo + 7257Al <

Description

Technical Field

[0001] The present disclosure relates to a ferritic stainless steel sheet and an exhaust component. Background Art

[0002] Ferritic stainless steel is low-cost and therefore used in exhaust components such as automobiles, which are repeatedly heated and cooled. However, ferritic stainless steel has inferior high-temperature properties compared to austenitic stainless steel. Consequently, ferritic stainless steel containing Nb has been developed. Furthermore, the inclusion of Nb can increase recrystallization temperature, reduce toughness during hot rolling, and sometimes impair manufacturability. Consequently, steel containing Cu, similar to Nb, has been developed to improve high-temperature strength.

[0003] On the other hand, ferritic stainless steels have lower high-temperature properties than austenitic stainless steels. Therefore, to improve high-temperature properties, ferritic stainless steels containing Cu and certain amounts of elements such as Al, Nb, Mo, and Ti have been developed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2015 / 174079

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-240143

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2010-248620 Summary of the Invention

[0009] Technical problem to be solved by the invention

[0010] As discussed in the aforementioned literature, if a certain amount of various expensive elements is contained, manufacturing costs increase. Furthermore, workability may also be reduced. Exhaust components sometimes have very complex shapes, and workability is an important characteristic. Therefore, it is preferable to reduce alloying. On the other hand, in ferritic stainless steel, although it is desirable to reduce alloying by reducing the content of the aforementioned elements, there is the problem of difficulty in achieving both thermal fatigue resistance and workability, which are high-temperature properties, while reducing alloying.

[0011] Based on the above, an object of the present disclosure is to provide a ferritic stainless steel sheet that achieves alloying savings and improves thermal fatigue properties and workability as high-temperature properties.

[0012] Solutions for solving problems

[0013] The present disclosure has been made to solve the above-mentioned problems, and its gist lies in the following ferritic stainless steel sheet and exhaust component.

[0014] (1) A ferritic stainless steel plate having a chemical composition in mass % of

[0015] C: 0.001~0.030%,

[0016] Si: 0.01-1.00%,

[0017] Mn: 0.01~0.90%,

[0018] P: 0.010~0.100%,

[0019] S: 0.0001~0.0100%,

[0020] Cr: 16.0-20.0%,

[0021] Cu: 1.00-1.50%,

[0022] Mo: 0.02~0.50%,

[0023] Ti: 0.050~0.300%,

[0024] Nb: 0.050~0.200%,

[0025] Al: 0.003~0.500%,

[0026] Ni: 0.01~0.30%,

[0027] B: 0.0001~0.0050%,

[0028] V: 0.010~0.500%,

[0029] N: 0.001~0.020%,

[0030] Mg: 0~0.0010%,

[0031] Ca: 0~0.0050%,

[0032] W: 0~3.00%,

[0033] Co: 0-0.30%,

[0034] Zr: 0~0.10%,

[0035] REM: 0~0.10%

[0036] Sn: 0~0.500%,

[0037] Sb: 0-0.50%,

[0038] Ga: 0~0.30%,

[0039] Ta: 0~1.00%,

[0040] Hf: 0~1.00%

[0041] Bi: 0~0.02%,

[0042] Balance: Fe and impurities,

[0043] Satisfying the following equations (i) and (ii),

[0044] The grain size number is 6 to 9,

[0045] 830≤250Cu+2216Nb+3083V≤2000…(i)

[0046] 900≤1273Nb+1343Mo+7257Al≤3800…(ii)

[0047] In the above formula, each element symbol represents the content (mass %) of each element contained in the ferritic stainless steel sheet, and is represented as 0 when not contained.

[0048] (2) The ferritic stainless steel sheet according to (1) above, wherein the grain size number is 6 to 8.

[0049] (3) The ferritic stainless steel sheet according to (1) above, wherein the chemical composition contains, in mass %, selected from

[0050] Mg: 0.0001~0.0010%,

[0051] Ca: 0.0001~0.0050%,

[0052] W: 0.02~3.00%,

[0053] Co: 0.001~0.30%,

[0054] Zr: 0.01~0.10%,

[0055] REM: 0.005~0.10%

[0056] Sn: 0.005~0.500%,

[0057] Sb: 0.005-0.50%,

[0058] Ga: 0.0002~0.30%,

[0059] Ta: 0.001~1.00%,

[0060] Hf: 0.001~1.00%, and

[0061] Bi: 0.001~0.02%

[0062] One or more of the following.

[0063] (4) The ferritic stainless steel sheet according to (1) above, wherein the area ratio of Ti precipitates is 5% or less.

[0064] (5) The ferritic stainless steel sheet according to (2) above, wherein the area ratio of Ti precipitates is 5% or less.

[0065] (6) The ferritic stainless steel sheet according to (1) above, which satisfies the following formula (iii): KAM / HAGB≤0.05 (iii)

[0066] In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary with a relative orientation difference of 15° or more to the total grain boundary length.

[0067] (7) The ferritic stainless steel sheet according to (2) above, which satisfies the following formula (iii): KAM / HAGB≤0.05 (iii)

[0068] In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary with a relative orientation difference of 15° or more to the total grain boundary length.

[0069] (8) The ferritic stainless steel sheet according to (4) above, which satisfies the following formula (iii): KAM / HAGB≤0.05 (iii)

[0070] In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary with a relative orientation difference of 15° or more to the total grain boundary length.

[0071] (9) An exhaust component using the ferritic stainless steel sheet according to any one of (1) to (8) above.

[0072] Effects of the Invention

[0073] According to the present disclosure, it is possible to obtain a ferritic stainless steel sheet that achieves alloying savings and has improved thermal fatigue properties and workability as high-temperature properties. DETAILED DESCRIPTION

[0074] The present inventors conducted various studies and obtained the following findings.

[0075] (a) It is effective to reduce the content of Cu, Nb, V, Mo, Al, and Ti and to keep the content in the steel within an appropriate range. As a result, the precipitation of Ti during production can be suppressed, while precipitation strengthening and solid solution strengthening of Ti are exhibited in the use environment, and a ferritic stainless steel plate with excellent thermal fatigue properties can be obtained.

[0076] (b) Specifically, by optimizing the contents of Cu, Nb, V, Mo, and Al, which are elements that affect precipitation strengthening and solid solution strengthening, the thermal fatigue life is extended. Furthermore, by suppressing the precipitation of Ti compounds during manufacturing, Ti compounds that contribute to improving thermal fatigue characteristics can be precipitated during thermal fatigue, thereby more effectively improving thermal fatigue characteristics.

[0077] (c) To exhibit high thermal fatigue properties, it is necessary to obtain a fully recrystallized polycrystalline structure with grain size numbers 6 to 9. This is because if an unrecrystallized structure is formed where recrystallization is not complete, the thermal fatigue properties are likely to deteriorate.

[0078] One embodiment of the present disclosure has been completed based on the above-mentioned findings. Hereinafter, each requirement of the ferritic stainless steel sheet according to the present embodiment will be described in detail.

[0079] 1. Chemical composition

[0080] The reasons for limiting the content of each element are as follows. In the following description, "%" regarding the content means "mass %".

[0081] C: 0.001~0.030%

[0082] Carbon (C) forms carbides, which reduce corrosion resistance and high-temperature strength. Therefore, it is preferable to reduce the C content to 0.030% or less. The C content is preferably 0.015% or less, and more preferably 0.010% or less. However, excessive reduction in C leads to increased refining costs, so the C content is kept at 0.001% or more.

[0083] Si: 0.01~1.00%

[0084] In addition to being used as a deoxidizing element, Si (silicon) also improves high-temperature characteristics and oxidation resistance. Therefore, the Si content is 0.01% or more. In order to suppress abnormal oxidation and scale peeling at 950°C and further improve oxidation resistance, the Si content is preferably 0.05% or more, preferably 0.10% or more, more preferably 0.13% or more, and further preferably 0.15% or more. However, if it contains more than 1.00% Si, the steel plate will harden and the workability and manufacturability of the parts will be reduced. Therefore, the Si content is 1.00% or less. The Si content is preferably 0.80% or less, more preferably 0.50% or less, and further preferably 0.25% or less.

[0085] Mn: 0.01~0.90%

[0086] In addition to being used as a deoxidizing element, Mn (manganese) is also an element that improves high-temperature strength. Furthermore, during long-term use, Mn-based oxides are formed on the surface layer, which helps improve scale adhesion. Therefore, the Mn content is 0.01% or more. To further improve scale adhesion, the Mn content is preferably 0.05% or more, more preferably 0.10% or more, and even more preferably 0.11% or more. However, if the Mn content exceeds 0.90%, in addition to reducing the uniform elongation at room temperature, MnS is formed, resulting in reduced corrosion resistance and oxidation resistance. Therefore, the Mn content is 0.90% or less. Considering high-temperature ductility, suppression of abnormal oxidation, and suppression of oxidation growth, the Mn content is preferably 0.80% or less, more preferably 0.50% or less, and even more preferably 0.30% or less.

[0087] P: 0.010~0.100%

[0088] P (phosphorus) is an element that promotes hot workability and solidification cracking during manufacturing. In addition, FeTiP precipitates in a high-temperature environment, contributing to the improvement of thermal fatigue properties through precipitation strengthening. Therefore, the P content is 0.100% or less. The P content is preferably 0.060% or less, and more preferably 0.050% or less. It is preferable to reduce the P content as much as possible, but excessive reduction of P will increase the refining cost. Therefore, the P content is 0.010% or more. Furthermore, from the perspective of reducing refining costs, the P content is preferably 0.020% or more, and more preferably 0.030% or more.

[0089] S: 0.0001~0.0100%

[0090] Sulfur (S) is an element that reduces hot workability and corrosion resistance. Furthermore, the formation of coarse sulfides (MnS) significantly reduces the inclusion cleanliness of the steel plate. Oxidation resistance is also reduced. Therefore, the S content is set to 0.0100% or less. The S content is more preferably set to 0.0050% or less. However, excessive reduction in S increases refining costs. Therefore, the S content is set to 0.0001% or more. From the perspective of refining costs, the S content is preferably set to 0.0005% or more.

[0091] Cr: 16.0~20.0%

[0092] Cr (chromium) is an element that improves corrosion resistance and oxidation resistance. From the perspective of suppressing abnormal oxidation, salt corrosion, and condensed water corrosion in the exhaust component environment, the Cr content is 16.0% or more. The Cr content is preferably 16.5% or more, and more preferably 17.0% or more. However, excessive Cr content leads to hardening of the raw materials and increased manufacturing costs. Therefore, the Cr content is 20.0% or less. Furthermore, from the perspective of processability, manufacturability, and manufacturing costs, the Cr content is preferably 19.0% or less, and more preferably 18.0% or less.

[0093] Cu: 1.00~1.50%

[0094] Cu (copper) is an element that improves high temperature strength and thermal fatigue properties through precipitation strengthening. These property improvements are due to the precipitation strengthening effect brought about by the precipitation of bcc-Cu and ε-Cu, and are manifested by containing more than 1.00% Cu. Therefore, the Cu content is 1.00% or more. The Cu content is preferably 1.05% or more, more preferably 1.15% or more. However, if Cu is contained in excess, it hardens and reduces the uniform elongation and elongation at break. In addition, the yield strength at room temperature becomes higher, and the manufacturability of components such as stamping formability is reduced. Furthermore, an austenite phase is formed in the high temperature region, the adhesion of the oxide scale is reduced, and abnormal oxidation occurs on the surface. Therefore, the Cu content is 1.50% or less. The Cu content is preferably 1.40% or less, more preferably 1.30% or less.

[0095] Mo: 0.02~0.50%

[0096] Mo (molybdenum) is an element that not only improves corrosion resistance and oxidation resistance, but also improves high-temperature strength and thermal fatigue properties through solid solution strengthening. Therefore, the Mo content is 0.02% or more. The Mo content is preferably 0.11% or more, and more preferably 0.15% or more. However, Mo is expensive and reduces the uniform elongation at room temperature. Therefore, the Mo content is 0.50% or less. Furthermore, from the perspective of inclusion cleanliness, manufacturability, and cost, the Mo content is preferably 0.40% or less, and more preferably 0.30% or less.

[0097] Ti: 0.050~0.300%

[0098] Ti is an element that combines with C, N, and S to improve corrosion resistance and intergranular corrosion resistance. Furthermore, when added in combination with Nb, it improves high-temperature strength and high-temperature ductility, enhancing high-temperature fatigue properties and thermal fatigue characteristics. Furthermore, in high-temperature environments, it precipitates as FeTiP, contributing to improved thermal fatigue properties through precipitation strengthening. Therefore, the Ti content is 0.050% or more. From the perspectives of salt corrosion resistance, condensed water corrosion resistance, high-temperature strength, and intergranular corrosion resistance in welds, the Ti content is preferably 0.080% or more, and more preferably 0.100% or more.

[0099] However, excessive Ti content can easily lead to the formation of coarse Ti carbonitrides, which can become the starting point of fatigue fracture, and can also easily cause nozzle clogging during the casting process, significantly reducing manufacturability. Therefore, the Ti content is set to 0.300% or less. Furthermore, from the perspective of manufacturing costs, the Ti content is preferably 0.250% or less, and more preferably 0.190% or less.

[0100] Nb: 0.050~0.200%

[0101] Nb (niobium) is an element that improves high-temperature strength and thermal fatigue properties through solid solution strengthening. Nb precipitates finely as a Laves phase (primarily Fe2Nb) at approximately 750°C, thereby improving high-temperature strength and thermal fatigue properties. Furthermore, like Ti, it combines with C and N to improve corrosion resistance, such as salt corrosion resistance and condensed water corrosion resistance, as well as intergranular corrosion resistance in welds. Therefore, the Nb content is set to 0.050% or more. The Nb content is preferably 0.080% or more, and more preferably 0.100% or more.

[0102] However, excessive Nb content significantly reduces hot workability and increases the recrystallization temperature. This results in reduced manufacturability and increased manufacturing costs. Therefore, the Nb content is limited to 0.200% or less. The Nb content is preferably 0.180% or less, and more preferably 0.160% or less.

[0103] Al: 0.003~0.500%

[0104] Al (aluminum) acts as a deoxidizing element and improves the cleanliness of inclusions. In addition, it improves high-temperature strength and thermal fatigue properties through solid solution strengthening. Therefore, the Al content is 0.003% or more. The Al content is preferably 0.010% or more, and more preferably 0.020% or more. However, if Al is contained in excess, the pickling property decreases and the surface roughness increases. Furthermore, the amount of inclusions increases, thus becoming the starting point of fatigue cracking, and the fatigue strength decreases. In addition, hot workability also decreases. Therefore, the Al content is 0.500% or less. It should be noted that from the perspective of refining cost and surface properties, the Al content is preferably 0.300% or less. Furthermore, from the perspective of hot workability, the Al content is preferably 0.150% or less, and more preferably 0.090% or less.

[0105] Ni: 0.01~0.30%

[0106] Ni (nickel) is an element that not only improves the toughness of ferritic stainless steel sheets, but also suppresses brittle cracking during forming. Therefore, the Ni content is 0.01% or more. The Ni content is preferably 0.05% or more, more preferably 0.07% or more, and even more preferably 0.10% or more. However, if Ni is contained excessively, abnormal oxidation is induced due to the precipitation of the austenite phase, and thermal fatigue properties are reduced. Therefore, the Ni content is 0.30% or less. From the perspective of manufacturability, abnormal oxidation suppression, thermal fatigue properties, salt corrosion resistance, and condensed water corrosion resistance, the Ni content is preferably 0.20% or less, and more preferably 0.15% or less.

[0107] B: 0.0001~0.0050%

[0108] B (boron) is an element that not only improves hot workability but also suppresses work hardening and secondary work cracking at room temperature. In addition, it also has the effect of improving ductility. Therefore, the B content is 0.0001% or more. From the perspective of ductility, the B content is preferably 0.0002% or more, more preferably 0.0003% or more. However, if B is contained in excess, boron carbide is formed, and the inclusion cleanliness and intergranular corrosion resistance of the steel plate are reduced. Therefore, the B content is 0.0050% or less. From the perspective of refining costs, the B content is preferably 0.0030% or less, more preferably 0.0020% or less, and further preferably 0.0010% or less.

[0109] V: 0.010~0.500%

[0110] V (vanadium) is an element that improves corrosion resistance. In addition, V forms carbides and nitrides, improving high-temperature strength and thermal fatigue properties. Therefore, the V content is 0.010% or more. In order to improve thermal fatigue properties, the V content is preferably 0.020% or more, and more preferably 0.025% or more. However, if V is contained excessively, in addition to increasing manufacturing costs, the abnormal oxidation limit temperature is also lowered. Therefore, the V content is 0.500% or less. From the perspective of manufacturability, the V content is preferably 0.300% or less, more preferably 0.150% or less, more preferably 0.100% or less, and more preferably 0.050% or less.

[0111] N: 0.001~0.020%

[0112] Like C, N (nitrogen) reduces corrosion resistance and high-temperature strength. Therefore, the N content is 0.020% or less. It is preferably 0.015% or less, and more preferably 0.013% or less. While it is desirable to minimize the N content, excessive reduction increases refining costs. Therefore, the N content is 0.001% or more. It is preferably 0.003% or more, more preferably 0.004% or more, and even more preferably 0.005% or more.

[0113] In addition to the above elements, one or more selected from Mg, Ca, W, Co, Zr, REM, Sn, Sb, Ga, Ta, Hf, and Bi may be further contained within the ranges shown below. The reasons for limiting each element are explained below.

[0114] Mg: 0~0.0010%

[0115] Mg (magnesium) acts as a deoxidizing element, improving inclusion cleanliness and corrosion resistance. Therefore, it may be contained as needed. However, excessive Mg content can reduce weldability and corrosion resistance. Therefore, the Mg content is set to 0.0010% or less. From the perspective of weldability, the Mg content is preferably 0.0008% or less, and more preferably 0.0005% or less. On the other hand, to achieve the above-mentioned effects, the Mg content is preferably 0.0001% or more. From the perspective of corrosion resistance, particularly condensed water corrosion resistance, the Mg content is more preferably 0.00015% or more.

[0116] Ca: 0~0.0050%

[0117] Ca (calcium) has the effect of acting on desulfurization to improve the cleanliness of inclusions and improve corrosion resistance. Therefore, it can also be contained as needed. However, if more than 0.0050% of Ca is contained, water-soluble inclusions CaS are formed. As a result, the inclusion cleanliness (surface properties) and corrosion resistance of the steel plate are significantly reduced. Therefore, the Ca content is 0.0050% or less. From the perspective of manufacturability and surface properties, the Ca content is preferably 0.0030% or less, more preferably 0.0020% or less. On the other hand, in order to obtain the above-mentioned effects, the Ca content is preferably 0.0001% or more, preferably 0.0003% or more, more preferably 0.0005% or more, and further preferably 0.0007% or more.

[0118] W: 0~3.00%

[0119] W (tungsten), like Mo, has the effect of improving high-temperature strength through solid solution strengthening. In addition, it also has the effect of improving corrosion resistance. Therefore, it can also be contained as needed. However, if more than 3.00% of W is contained, the raw material will be hardened, the toughness will deteriorate during manufacturing, and the manufacturing cost will increase. Therefore, the W content is 3.00% or less. Furthermore, from the perspective of manufacturability and refining cost, the W content is preferably 2.00% or less, more preferably 1.50% or less, and even more preferably 1.00% or less. On the other hand, in order to obtain the above-mentioned effect, the W content is preferably 0.02% or more, more preferably 0.10% or more.

[0120] Co: 0-0.30%

[0121] Co (cobalt) has the effect of improving corrosion resistance and high-temperature strength. Therefore, it can also be contained as needed. However, if more than 0.30% of Co is contained, it will lead to hardening of the steel plate, reduction of toughness during manufacturing, and increase in manufacturing costs. Therefore, the Co content is 0.30% or less. Taking into account manufacturability and refining costs, the Co content is preferably 0.20% or less, more preferably 0.10% or less. On the other hand, in order to obtain the above-mentioned effects, the Co content is preferably 0.001% or more. From the perspective of improving salt corrosion resistance and condensed water corrosion resistance in corrosion resistance, and improving high-temperature strength, the Co content is preferably 0.005% or more, more preferably 0.010% or more.

[0122] Zr: 0~0.10%

[0123] Zr (zirconium), like Ti and Nb, combines with C or N to form carbides or nitrides, improving high-temperature strength, oxidation resistance, and intergranular corrosion resistance of welds. Therefore, it may be contained as needed. However, if Zr is contained in an amount exceeding 0.10%, manufacturability is significantly reduced, and manufacturing costs increase. Therefore, the Zr content is set to 0.10% or less. From the perspective of manufacturability and refining costs, the Zr content is preferably 0.08% or less. On the other hand, to achieve the above-mentioned effects, the Zr content is preferably 0.01% or more, and more preferably 0.03% or more.

[0124] REM: 0~0.10%

[0125] REM (rare earth elements) have the effect of improving oxidation resistance. Therefore, they may be contained as needed. However, if REM is contained in excess, oxides containing REM may form on the nozzles that flow the molten steel during casting, causing nozzle clogging, or sulfides containing REM may form, reducing corrosion resistance. Therefore, the REM content is set to 0.10% or less. The REM content is more preferably 0.07% or less, and even more preferably 0.05% or less. On the other hand, to achieve the above-mentioned effects, the REM content is preferably 0.005% or more, and more preferably 0.010% or more.

[0126] REM refers to a total of 17 elements including Sc, Y, and lanthanoids. The above REM content refers to the total content of these elements. REM is often added in the form of mixed rare earth metals in industry.

[0127] Sn: 0~0.500%

[0128] Sn (tin) improves corrosion resistance and high-temperature strength. Therefore, it may be contained as needed. However, if Sn exceeds 0.500%, slab cracking may occur during manufacturing. Therefore, the Sn content is set to 0.500% or less. Furthermore, from the perspectives of manufacturability and refining costs, the Sn content is preferably 0.300% or less. On the other hand, to achieve the above-mentioned effects, the Sn content is preferably 0.005% or more, and more preferably 0.030% or more.

[0129] Sb: 0~0.50%

[0130] Sb (antimony) segregates at grain boundaries, improving high-temperature properties. Therefore, it may be contained as needed. However, if Sb exceeds 0.50%, segregation occurs, leading to cracking during welding. Therefore, the Sb content is preferably 0.50% or less. Furthermore, considering toughness and manufacturing costs, the Sb content is preferably 0.30% or less. On the other hand, to achieve the aforementioned effects, the Sb content is preferably 0.005% or more. To further improve high-temperature properties, the Sb content is more preferably 0.030% or more.

[0131] Ga: 0~0.30%

[0132] Gallium (Ga) improves corrosion resistance and suppresses hydrogen embrittlement. Therefore, it may be contained as needed. However, if Ga is contained in an amount exceeding 0.30%, coarse sulfides will form, reducing component workability. Therefore, the Ga content is set to 0.30% or less. From the perspective of manufacturability and manufacturing costs, the Ga content is preferably 0.20% or less, more preferably 0.10% or less. On the other hand, to achieve the above-mentioned effects, the Ga content is preferably 0.0002% or more, more preferably 0.0020% or more.

[0133] Ta: 0~1.00%

[0134] Hf: 0~1.00%

[0135] Bi: 0~0.02%

[0136] Ta (tantalum) has the effect of improving high-temperature strength. Therefore, it may be contained as needed. However, excessive Ta content increases manufacturing costs. Therefore, the Ta content is set to 1.00% or less. The Ta content is preferably 0.50% or less, and more preferably 0.20% or less. On the other hand, to achieve the above-mentioned effect, the Ta content is preferably 0.001% or more. Furthermore, to further improve strength, the Ta content is more preferably 0.010% or more.

[0137] For the same reason, Hf may be contained as needed. However, excessive Hf content increases manufacturing costs. Therefore, the Hf content is also limited to 1.00% or less. The Hf content is preferably 0.50% or less, and more preferably 0.20% or less. Furthermore, for the same reason, the Hf content is preferably 0.001% or more, and more preferably 0.010% or more.

[0138] Bi can also be included as needed for the same reasons. However, excessive Bi content increases manufacturing costs. Therefore, the Bi content is 0.02% or less. The Bi content is preferably 0.015%, and more preferably 0.01% or less. On the other hand, to achieve the same effects as described above, the Bi content is preferably 0.001% or more, and more preferably 0.005% or more.

[0139] In the chemical composition of this embodiment, the balance is Fe and impurities. Here, "impurities" refer to components that are mixed into the ferritic stainless steel sheet during industrial production due to various reasons, such as raw materials such as ores and scrap, and the manufacturing process, and are allowed within the range that does not adversely affect this embodiment.

[0140] (i)Formula

[0141] In the ferritic stainless steel sheet of this embodiment, the contents of Cu, Nb, and V, which affect precipitation strengthening, need to satisfy the following formula (i). Cu precipitates finely as bcc-Cu or ε-Cu, Nb as Fe2Nb (Laves phase), and V as carbonitride, thereby improving thermal fatigue properties.

[0142] 830≤250Cu+2216Nb+3083V≤2000…(i)

[0143] In the above formula, each element symbol represents the content (mass %) of each element contained in the ferritic stainless steel sheet, and is represented as 0 when not contained.

[0144] When the value of 250Cu+2216Nb+3083V as the middle term of formula (i) is less than 830, the thermal fatigue characteristics cannot be improved. Therefore, the value of the middle term of formula (i) is 830 or more. The value of the middle term of formula (i) is preferably 850 or more, more preferably 870 or more, and further preferably 900 or more. On the other hand, if the value of the middle term of formula (i) exceeds 2000, hardening may occur and the workability of the component is reduced. Therefore, the value of the middle term of formula (i) is 2000 or less. The value of the middle term of formula (i) is preferably 1900 or less, more preferably 1800 or less, and further preferably 1500 or less.

[0145] Formula (ii)

[0146] In the ferritic stainless steel sheet of the present embodiment, the contents of Nb, Mo, and Al, which affect solid solution strengthening, need to satisfy the following formula (ii).

[0147] 900≤1273Nb+1343Mo+7257Al≤3800…(ii)

[0148] In the above formula, each element symbol represents the content (mass %) of each element contained in the ferritic stainless steel sheet, and is represented as 0 when not contained.

[0149] When the value of 1273Nb+1343Mo+7257Al as the middle term of formula (ii) is less than 900, it is difficult to improve the thermal fatigue characteristics. Therefore, the value of the middle term of formula (ii) is 900 or more. The value of the middle term of formula (ii) is preferably 1000 or more, more preferably 1100 or more, and further preferably 1300 or more. On the other hand, when the value of the middle term of formula (ii) exceeds 3800, hardening may occur and the workability of the component may be reduced. Therefore, the value of the middle term of formula (ii) is 3800 or less. The value of the middle term of formula (ii) is more preferably 3500 or less, further preferably 3000 or less, and further preferably 2700 or less.

[0150] Thermal fatigue is a phenomenon in which fatigue failure occurs in an environment where heating and cooling are repeated continuously from a low temperature of about 200°C to a high temperature of about 900°C. Therefore, it is necessary to strengthen the material at various temperatures. In the ferritic stainless steel plate of this embodiment, the cycle of fatigue crack penetration under the condition of a thermal cycle test with a minimum temperature of 200°C and a maximum temperature of 850°C was studied as the thermal fatigue life. As a result, the above-mentioned formulas (i) and (ii) were derived experimentally. In order to ensure the thermal fatigue properties of components that can be used as automobile exhaust parts, both formulas (i) and (ii) need to be satisfied. If either or both are not satisfied, the thermal fatigue properties are reduced.

[0151] 2. Grain size number

[0152] The grain size number of the ferritic stainless steel plate of this embodiment is in the range of 6 to 9. If the grain size number is less than 6, the grains become too coarse, resulting in a decrease in material strength or structural changes caused by strain due to heating and cooling during thermal fatigue. Therefore, thermal fatigue properties are sometimes reduced. Therefore, the grain size number is 6 or more. If the grain size number is 6 or more, in addition to improving the strength, structural changes caused by strain due to heating and cooling during thermal fatigue can also be suppressed. As a result, sufficient thermal fatigue properties can be ensured. On the other hand, if the grain size number exceeds 9, the grains become too fine, and workability is reduced. In addition, recrystallization is sometimes not completed. Therefore, the grain size number is 9 or less. The grain size number is preferably 9.0 or less, preferably 8.9 or less, and preferably 8 or less. The grain size number is preferably in the range of 6 to 8.

[0153] It should be noted that the grain size number of ferritic stainless steel plate can be measured by the following steps. The cross section (L cross section) parallel to the rolling direction and the plate thickness direction is used as the observation surface and embedded in thermosetting resin for observation. The measurement range is the range from the center of the plate thickness to the area of ​​1 / 4 of the plate thickness. 5 fields of view are observed at 100-200 times. The grain size number is obtained based on the total observation field of view using the cutting method specified in Appendix JB of JIS G0551:2020.

[0154] 3. Area ratio of Ti precipitates

[0155] To further improve thermal fatigue properties, the ferritic stainless steel sheet of this embodiment preferably controls the area ratio of Ti precipitates. Specifically, the area ratio of Ti precipitates is preferably 5% or less. This is to minimize the amount of Ti present as precipitates in the steel sheet at room temperature, allowing fine Ti precipitation in the operating environment to form FeTiP, which contributes to precipitation strengthening. Therefore, to ensure a sufficient amount of Ti precipitates in high-temperature operating environments, the area ratio of Ti precipitates is preferably 5% or less at room temperature. The area ratio of Ti precipitates is preferably set to 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. From the perspective of improving thermal fatigue properties, the area ratio of Ti precipitates is preferably as low as possible, with a lower limit of 0%. However, achieving a 0% area ratio of Ti precipitates is difficult in manufacturing, so the area ratio of Ti precipitates is preferably 0.1% or more, more preferably 0.2% or more, and even more preferably 0.3% or more.

[0156] The area ratio of Ti precipitates can be determined by the following steps. A cross section (L cross section) parallel to the rolling direction and the plate thickness direction is used as the observation surface, embedded in a thermosetting resin, and mirror-polished by mechanical grinding. Then, a scanning electron microscope (hereinafter referred to as "SEM") equipped with an energy dispersive X-ray spectrometer (hereinafter referred to as "EDS") is used for observation and analysis to calculate the area ratio of the precipitates. The measurement range is the range of the area from the center of the plate thickness to 1 / 4 of the plate thickness. 10 fields of view are observed at 1000 times. The average value of the area of ​​the precipitates containing Ti in each field of view obtained by image analysis is divided by the field of view area of ​​1 field of view to obtain the area ratio of each field of view, and the average value of the area ratio is used as the area ratio of Ti precipitates. Here, the precipitates containing Ti contain more than 1.0wt% of Ti, and the equivalent circle diameter is more than 3μm.

[0157] 4. Formula (iii)

[0158] In order to further improve thermal fatigue properties, the ferritic stainless steel sheet of the present embodiment preferably satisfies the following formula (iii).

[0159] KAM / HAGB≤0.05…(iii)

[0160] In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary with a relative orientation difference of 15° or more to the total grain boundary length.

[0161] Formula (iii) above indicates that the strain within the grains of a ferritic stainless steel sheet having a polycrystalline structure is low. In other words, this indicates that a fully recrystallized structure with low residual strain within the grains is obtained by properly manufacturing the steel sheet. It is believed that in the case of a poorly recrystallized structure with residual strain within the grains, structural changes occur during heating during thermal fatigue, resulting in a decrease in thermal fatigue properties.

[0162] Furthermore, if the value of the left-hand side term of formula (iii), i.e., KAM / HAGB, is 0.05 or less, thermal fatigue properties are more easily improved. Therefore, the value of the left-hand side term of formula (iii) is preferably 0.05 or less, more preferably 0.03 or less, even more preferably 0.01 or less, and even more preferably 0.005 or less. It should be noted that the lower limit of the value of the left-hand side term of formula (iii) is not particularly limited; a smaller value is more preferred, and the most preferred value of the left-hand side term of formula (iii) is 0.

[0163] KAM and HAGB can be measured according to the following steps. The cross section (L cross section) parallel to the rolling direction and the thickness direction is used as the observation surface, and mechanical grinding and mechanical chemical grinding using a colloidal silica suspension are performed to remove surface strain. After such grinding is performed to obtain a mirror-like observation surface, a field emission scanning electron microscope (JEOL, hereinafter referred to as "FE-SEM") equipped with an EBSD (also known as "Electron Back-Scattering Difraction pattern") measuring device is used for observation and measurement. Then, it is analyzed and obtained by OIM (TSL, also known as "Orientation Imaging Microscopy"). In addition, the software can use "OIM Annalysis".

[0164] The measurement range is from the center of the plate to 1 / 4 of the plate thickness, which is set to 19mm. 2 The measurement was carried out in 10 fields of view at a measurement magnification of 1000 times and a measurement interval of 0.5 μm. The KAM value generally refers to the average value of the crystal orientation difference between the measurement point being the object and the measurement points around it. In this application, it is the ratio of the measurement points with an average value of the above-mentioned crystal orientation difference of 1 to 2 degrees to all the measurement points. HAGB is the proportion of high-angle grain boundaries, which is calculated by dividing the length of grain boundaries with a relative orientation difference of 15 degrees or more by the total grain boundary length, that is, by dividing the length of grain boundaries with a relative orientation difference of 2 degrees or more.

[0165] 5. Purpose

[0166] The ferritic stainless steel plate of this embodiment can be suitably used as exhaust components of automobiles and components used in exhaust components. It is particularly suitable for components used in an environment exposed to exhaust gas at about 600 to 900°C. Specifically, it can be suitably used as components used in exhaust manifolds, center pipes, front pipes, converter peripheral components, mufflers, exhaust gas purification components, turbocharger housings and internal components. This is because the components used in the above-mentioned parts are prone to thermal fatigue in an environment of repeated heating and cooling. In addition, in the above-mentioned uses, it is preferred that the condensed water corrosion resistance is good. Here, the condensed water corrosion resistance refers to the resistance to corrosion caused by moisture after the exhaust gas components are condensed.

[0167] 6. Manufacturing Method

[0168] The ferritic stainless steel sheet of this embodiment can be stably produced, for example, using the following production method. The ferritic stainless steel sheet of this embodiment is preferably produced through a process of steelmaking - hot rolling - annealing / pickling - cold rolling - annealing / pickling, or steelmaking - hot rolling - pickling - cold rolling - annealing / pickling. Each process is described in detail below.

[0169] 6-1. Steelmaking process

[0170] A preferred method is to melt the steel having the above chemical composition in an electric furnace or converter, followed by secondary refining. The smelted steel is then formed into slabs using known casting methods (e.g., continuous casting). To prevent excessive inclusions during continuous casting, it is effective to provide a settling time before continuous casting. Preferably, the settling time is set to at least one minute before continuous casting.

[0171] 6-2. Hot rolling process

[0172] The slabs obtained in the steelmaking process are then hot-rolled by continuous rolling to form hot-rolled sheets. Hot-rolling conditions are not particularly limited, except for the cooling conditions described below. The slab thickness and the reduction ratio during hot rolling can be appropriately selected. For example, the heating temperature of the slab is preferably set within the range of 1030-1200°C.

[0173] After hot rolling, the hot-rolled sheet is coiled and cooled. It is preferable to suppress the precipitation of V carbonitrides, Ti(C,N), or Ti compounds such as FeTiP during the cooling process from coiling to post-coiling, and to increase the cooling rate. This is to keep the area fraction of Ti precipitates to 5% or less.

[0174] Therefore, the cooling rate after hot rolling is preferably set to 40°C / s or more within the range of the hot rolling temperature to 450°C. Taking into account manufacturability, the cooling rate after the above-mentioned hot rolling is more preferably 70°C / s or more. In order to promote recrystallization after hot rolling, annealing can be performed as needed. When annealing is performed, it is performed in the range of 900-1200°C and 10-200s. After hot rolling (after annealing when annealing is performed), the steel plate is usually pickled. It should be noted that it is sufficient to cool to room temperature after hot rolling.

[0175] 6-3. Cold rolling and annealing process

[0176] Next, the sheet is cold rolled to a predetermined thickness. It should be noted that the cold rolling reduction can be appropriately selected. Furthermore, the roll diameter of the cold rolling mill can be appropriately selected. After cold rolling, the sheet is annealed and pickled. The ferritic stainless steel sheet of this embodiment contains a small amount of Nb to lower the recrystallization temperature. Therefore, the annealing temperature is set at 800-980°C to obtain a recrystallized structure. Furthermore, the annealing time is preferably set within the range of 1-240 seconds.

[0177] Here, in the production of the ferritic stainless steel sheet of this embodiment, in order to ensure high thermal fatigue properties, recrystallization is preferably performed in a manner that does not retain strain within the grains. In other words, the annealing conditions are controlled to satisfy equation (iii) and obtain a relatively fine-grained structure with grain size numbers 6 to 9. Specifically, the time for the steel sheet to reach a temperature of 880°C or higher is preferably 15 seconds or longer. It should be noted that if the cooling rate after hot rolling is slow and the time to reach 880°C or higher is less than 15 seconds, recrystallization and grain growth are difficult to proceed, and the grain size number may become too large.

[0178] Annealing of cold-rolled sheets can be performed between cold-rolling passes, and can be either intermittent or continuous. The heating and cooling of annealing after cold rolling can cause the formation of precipitates, such as Cu particles, Laves phases containing Nb, and FeTiP containing Ti, that affect high-temperature strength. By minimizing the amount of these precipitates in the steel sheet and allowing them to precipitate in the operating environment, high-temperature strength and thermal fatigue properties can be effectively improved.

[0179] In the final annealing of the ferritic stainless steel sheet of this embodiment, the heating rate from 350°C to the annealing temperature is preferably 2.0°C / s or higher. This is because a heating rate of 2.0°C / s or higher in this temperature range reduces strain, making it easier to satisfy equation (iii). The heating rate in this temperature range is more preferably 10.0°C / s or higher. The upper limit of the heating rate in this temperature range is not particularly limited, but is, for example, 150.0°C / s.

[0180] Therefore, regarding cooling after final annealing after cold rolling, the cooling rate in the temperature range of 800°C to 350°C, where the above-mentioned precipitates are likely to precipitate, is preferably set to 5°C / s or higher. If the cooling rate in the temperature range of 800°C to 350°C is less than 5°C / s, a large amount of precipitates may precipitate, and heat resistance and workability may be easily reduced.

[0181] After annealing and cooling, pickling is preferably performed. Pickling can remove scale formed on the steel surface during annealing. The pickling method can be any chemical descaling method, such as sulfuric acid, nitric acid-hydrofluoric acid, or nitric acid electrolysis. Molten salt alkali immersion can be performed as a pretreatment. The temperature and duration of the molten salt alkali immersion can be appropriately adjusted depending on the desired properties of the steel sheet. After cold rolling, annealing, and pickling, the steel sheet can be subjected to skin-pass rolling and grinding.

[0182] Hereinafter, the ferritic stainless steel sheet of the present disclosure will be described in more detail with reference to examples, but the present embodiment is not limited to these examples.

[0183] Example

[0184] After the steel having the chemical composition shown in Table 1 was cast in a flat 17 kg mold, the following process was performed to obtain a steel plate. Specifically, hot rolling was performed at 1050°C to form a 5 mm thickness, and the hot rolled plate was cooled from 1050°C to 450°C at a cooling rate of 5.3 to 75°C / s and pickled. Then, cold rolling was performed, the temperature was raised to 920°C as the annealing temperature at a heating rate of 0.8 to 20.3°C / s, and annealed at 920°C for 120 seconds. After cooling from 800°C to 350°C at a cooling rate of 3.1 to 11.2°C / s, pickling was performed to form a 2.0 mm thick steel plate (hereinafter also referred to as "product plate"). It should be noted that the time to reach above 880°C in the annealing after cold rolling is between 5 and 180 seconds as shown in Table 2.

[0185] [Table 1]

[0186]

[0187] [Table 2]

[0188] Table 2

[0189]

[0190] Underline: Indicates a departure from the requirements of this embodiment.

[0191] Double underline: Indicates deviation from the preferred or more preferred production conditions of this embodiment.

[0192] The resulting product sheets were measured for grain size, area ratio of Ti precipitates, KAM, and HAGB. Furthermore, thermal fatigue testing, condensed water corrosion resistance testing, and tensile testing were performed to evaluate the various properties.

[0193] (Grain size number)

[0194] The grain size number is determined using the following procedure. A cross section (L-section) parallel to the rolling direction and the thickness direction is used as the observation surface and embedded in thermosetting resin for observation. The measurement range is from the center of the plate thickness to 1 / 4 of the plate thickness. Five fields of view are observed at 100-200x magnification. The grain size number is determined based on the total field of view using the sectioning method specified in Appendix JB of JIS G 0551:2020.

[0195] (Area ratio of Ti precipitates)

[0196] The area ratio of Ti precipitates is determined according to the following steps. A cross section (L cross section) parallel to the rolling direction and the plate thickness direction is used as the observation surface, embedded in a thermosetting resin, and mirror-polished by mechanical grinding. Then, an SEM equipped with EDS is used for observation, analysis, and calculation. The measurement range is the range of the area from the center of the plate thickness to 1 / 4 of the plate thickness. 10 fields of view are observed at 1000 times. The average value of the area of ​​the precipitates containing Ti in each field of view obtained by image analysis is divided by the field of view area of ​​1 field of view to obtain the area ratio of each field of view, and the average value of the area ratio is used as the area ratio of Ti precipitates. Here, the precipitates containing Ti contain more than 1.0wt% Ti, and the equivalent circle diameter is more than 3μm.

[0197] (KAM and HAGB)

[0198] KAM and HAGB are measured using the following procedures. A cross section (L-section) parallel to the rolling direction and the thickness direction is used as the observation surface. Mechanical polishing and mechanochemical polishing using a colloidal silica suspension, for example, are performed to remove surface strain. After polishing to obtain a mirror-finished observation surface, observation and measurement are performed using a FE-SEM equipped with an EBSD analyzer. These values ​​are determined using OIM analysis. The software used is "OIM Annalysis."

[0199] The measurement range is from the center of the plate to 1 / 4 of the plate thickness, which is set to 19mm. 2 The measurement was performed over 10 fields of view at a measurement magnification of 1000x and a measurement interval of 0.5 μm within a range of 1000×. The KAM value is the ratio of measurement points with an average crystal orientation difference of 1 to 2 degrees relative to all measurement points. The HAGB is the proportion of high-angle grain boundaries, which is calculated by dividing the length of grain boundaries with a relative orientation difference of 15 degrees or more by the length of grain boundaries with a relative orientation difference of 2 degrees or more.

[0200] (Thermal fatigue test)

[0201] The thermal fatigue test is carried out according to the following steps. A tubular test piece with a diameter of 38.1 mm and a test plate thickness of 1.5 mm is used. The electric hydraulic servo fatigue testing machine and the high-frequency induction heating device are controlled in such a way that the maximum temperature is 850°C, the minimum temperature is 200°C, the holding time at the maximum temperature is 120s, and the constraint rate is 30%. The test is carried out by continuously repeating heating and cooling. The thermal fatigue life is defined as the number of cycles in which cracks are generated through the pipe. The thermal fatigue life of more than 1300 cycles is marked as A, more than 1100 cycles and less than 1300 cycles is marked as B, more than 1000 cycles and less than 1100 cycles is marked as C, and less than 1000 cycles is marked as D.

[0202] (Tensile test)

[0203] Tensile testing was conducted according to the following procedure. JIS 13B test pieces were prepared from the product sheets with their longitudinal sides parallel to the rolling direction. The tensile test was conducted to measure the total elongation (elongation at break) at room temperature. A total elongation of 30% or greater at room temperature was considered good formability and designated B. On the other hand, a total elongation of less than 30% was considered poor formability and designated D.

[0204] (Condensation water corrosion test)

[0205] The condensation water corrosion test was conducted according to the following procedure. The product plate was cut into pieces of 100 mm (parallel to the long side) x 25 mm (parallel to the short side) in size, and the entire surface was finished with #600 wet grinding. Using this test piece, after a preheat treatment at 400°C for 8 hours in the atmosphere, a condensation water corrosion test was conducted according to JASO M611-92 A method (temperature: 80°C, time: 600 hours). After the test piece after the condensation water corrosion test was descaled, the maximum corrosion depth of the test piece was determined using the microscope depth of focus method. The maximum corrosion depth was evaluated as the average value of the maximum corrosion depth of each test piece (n=2). In order to ensure condensation water corrosion resistance suitable for exhaust components, a maximum corrosion depth of 800 μm or less was marked as B, and a depth deeper than 800 μm was marked as D. It should be noted that, in the table, when comprehensively evaluating the characteristics of exhaust components based on various characteristics, good exhaust component performance was marked as B, poorer than B but better was marked as C, and poor performance was marked as D. The results are summarized in Table 3 below.

[0206] [Table 3]

[0207] Table 3

[0208]

[0209] Underline: Indicates a departure from the requirements of this embodiment.

[0210] Double underline: Indicates deviation from the preferred elements of this embodiment.

[0211] The chemical composition of the examples of the present invention meets the requirements of this embodiment, and the manufacturing conditions are within the preferred range, so the thermal fatigue characteristics and workability are good. In addition, the maximum corrosion depth after the condensation water corrosion test is also good. In the examples of the present invention, No. 9 and No. 10 have a high area ratio of Ti precipitates due to the slow cooling rate after hot rolling, and the amount of Ti that contributes to precipitation strengthening is small, so the thermal fatigue characteristics are reduced. As a result, the results are slightly worse as characteristics of automobile exhaust components. In addition, No. 11 has a short holding time above 880°C during annealing, so it does not meet formula (iii), and the thermal fatigue characteristics are slightly reduced. As a result, the results are slightly worse as characteristics of automobile exhaust components. No. 15 has a slow heating rate during annealing, so it does not meet formula (iii), and the thermal fatigue characteristics are slightly reduced.

[0212] On the other hand, No. 17 has low Nb content, resulting in reduced thermal fatigue properties. No. 18, due to its low Cr content and the resulting low Cu precipitation that contributes to precipitation strengthening, has reduced thermal fatigue properties. Furthermore, its condensed water corrosion resistance is also reduced. No. 19 has low Cu content, resulting in reduced thermal fatigue properties. No. 20 has low Mo content, resulting in reduced thermal fatigue properties. Furthermore, its condensed water corrosion resistance is also reduced. No. 21 has low Al content, resulting in reduced thermal fatigue properties.

[0213] No.22 has a low V content, so the thermal fatigue characteristics are reduced. In addition, the condensed water corrosion resistance is also reduced. No.23 Although the content of each element is within the scope of the present invention, it does not satisfy the formulas (i) and (ii), so the thermal fatigue characteristics are reduced. No.24 Although the content of each element is within the scope of this embodiment, it does not satisfy the formulas (i) and (ii), so the workability is reduced. The steel composition of No.25 is A1 as No.1, the cooling rate after hot rolling is slow, and the heating rate during annealing after cold rolling is also low, and the holding time above 880°C is short. In addition, the cooling rate at 800-350°C is also low. As a result, the area ratio of Ti precipitates is high, and the amount of Ti that contributes to improving the thermal fatigue characteristics in the form of Ti precipitates is small. Moreover, since it is a poorly recrystallized structure, residual strain remains in the grains, and the thermal fatigue characteristics and workability are reduced. In addition, the condensed water corrosion resistance is reduced.

[0214] (Note)

[0215] (1) A ferritic stainless steel plate having a chemical composition in mass % of

[0216] C: 0.001~0.030%,

[0217] Si:0.01~1.00%、

[0218] Mn:0.01~0.90%、

[0219] P:0.010~0.100%、

[0220] S:0.0001~0.0100%、

[0221] Cr:16.0~20.0%、

[0222] Cu:1.00~1.50%、

[0223] Mo:0.02~0.50%、

[0224] Ti:0.050~0.300%、

[0225] Nb:0.050~0.200%、

[0226] Al:0.003~0.500%、

[0227] Ni:0.01~0.30%、

[0228] B:0.0001~0.0050%、

[0229] V:0.010~0.500%、

[0230] N:0.001~0.020%、

[0231] Mg:0~0.0010%、

[0232] Ca:0~0.0050%、

[0233] W:0~3.00%、

[0234] Co:0~0.30%、

[0235] Zr:0~0.10%、

[0236] REM:0~0.10%、

[0237] Sn:0~0.500%、

[0238] Sb:0~0.50%、

[0239] Ga:0~0.30%、

[0240] Ta:0~1.00%、

[0241] Hf:0~1.00%、

[0242] Bi: 0~0.02%,

[0243] Balance: Fe and impurities,

[0244] Satisfying the following equations (i) and (ii),

[0245] The grain size number is 6 to 9,

[0246] 830≤250Cu+2216Nb+3083V≤2000…(i)

[0247] 900≤1273Nb+1343Mo+7257Al≤3800…(ii)

[0248] In the above formula, each element symbol represents the content (mass %) of each element contained in the ferritic stainless steel sheet, and is represented as 0 when not contained.

[0249] (2) The ferritic stainless steel sheet according to (1) above, wherein the grain size number is 6 to 8.

[0250] (3) The ferritic stainless steel sheet according to (1) or (2) above, wherein the chemical composition contains, in mass %,

[0251] Mg: 0.0001~0.0010%,

[0252] Ca: 0.0001~0.0050%,

[0253] W: 0.02~3.00%,

[0254] Co: 0.001~0.30%,

[0255] Zr: 0.01~0.10%,

[0256] REM: 0.005~0.10%

[0257] Sn: 0.005~0.500%,

[0258] Sb: 0.005-0.50%,

[0259] Ga: 0.0002~0.30%,

[0260] Ta: 0.001~1.00%,

[0261] Hf: 0.001~1.00%, and

[0262] Bi: 0.001~0.02%

[0263] One or more of the following.

[0264] (4) The ferritic stainless steel sheet according to any one of (1) to (3) above, wherein the area ratio of Ti precipitates is 5% or less.

[0265] (5) The ferritic stainless steel sheet according to any one of (1) to (4) above, which satisfies the following formula (iii):

[0266] KAM / HAGB≤0.05…(iii)

[0267] In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary with a relative orientation difference of 15° or more to the total grain boundary length.

[0268] (6) An exhaust component using the ferritic stainless steel sheet according to any one of (1) to (5) above.

[0269] Industrial applicability

[0270] According to the present disclosure, a ferritic stainless steel sheet can be provided that achieves excellent thermal fatigue resistance at temperatures between 200°C and 850°C while achieving alloy savings. This ferritic stainless steel sheet can be used to provide components that meet automotive exhaust gas environmental requirements, achieve lightweighting, conserve resources, and improve fuel efficiency. Furthermore, this material is not limited to exhaust components for automobiles and motorcycles but can also be used in various boilers, fuel cell systems, heat exchangers, and other components used in high-temperature environments and exposed to condensed water corrosion or salt corrosion.

Claims

1. A ferritic stainless steel plate having a chemical composition of C: 0.001-0.030% by mass, Si: 0.01-1.00%, Mn: 0.01~0.90%, P：0.010～0.100％、 S：0.0001～0.0100％、 Cr：16.0～20.0％、 Cu: 1.00-1.50%, Mo: 0.02~0.50%, Ti: 0.050~0.300%, Nb: 0.050~0.200%, Al：0.003～0.500％、 Ni: 0.01~0.30%, B：0.0001～0.0050％、 V：0.010～0.500％、 N：0.001～0.020％、 Mg: 0~0.0010%, Ca: 0~0.0050%, W：0～3.00％、 Co: 0-0.30%, Zr：0～0.10％、 REM: 0~0.10% Sn: 0~0.500%, Sb: 0-0.50%, Ga: 0~0.30%, Ta: 0~1.00%, Hf: 0~1.00% Bi: 0~0.02%, Balance: Fe and impurities, Satisfying the following equations (i) and (ii), The grain size number is 6 to 9, 830≤250Cu+2216Nb+3083V≤2000…(i) 900≤1273Nb+1343Mo+7257Al≤3800…(ii) in, The symbols of the elements in the above formula represent the content of the elements in the ferritic stainless steel sheet in mass %, and when the elements are not contained, they are expressed as 0.

2. The ferritic stainless steel plate according to claim 1, wherein the grain size number is 6 to 8.

3. The ferritic stainless steel sheet according to claim 1, wherein The chemical composition contains, in mass%, Mg: 0.0001~0.0010%, Ca: 0.0001~0.0050%, W：0.02～3.00％、 Co: 0.001~0.30%, Zr：0.01～0.10％、 REM: 0.005~0.10% Sn: 0.005~0.500%, Sb: 0.005-0.50%, Ga: 0.0002~0.30%, Ta: 0.001~1.00%, Hf: 0.001~1.00%, and Bi: 0.001~0.02% One or more of the following.

4. The ferritic stainless steel sheet according to claim 1, wherein The area ratio of Ti precipitates is 5% or less.

5. The ferritic stainless steel sheet according to claim 2, wherein The area ratio of Ti precipitates is 5% or less.

6. The ferritic stainless steel sheet according to claim 1, which satisfies the following formula (iii): KAM / HAGB≤0.05…(iii) in, In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary having a relative orientation difference of 15° or more to the total grain boundary length.

7. The ferritic stainless steel sheet according to claim 2, which satisfies the following formula (iii): KAM / HAGB≤0.05…(iii) in, In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary having a relative orientation difference of 15° or more to the total grain boundary length.

8. The ferritic stainless steel sheet according to claim 4, which satisfies the following formula (iii): KAM / HAGB≤0.05…(iii) in, In the above formula, KAM represents the KAM value, and HAGB represents the ratio of the length of the grain boundary having a relative orientation difference of 15° or more to the total grain boundary length. 9 . An exhaust component using the ferritic stainless steel sheet according to claim 1 .

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