JP2008291303A - Ferrittic stainless steel sheet excellent in blanking property for water heater and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferritic stainless steel sheet for a water heater, the ferritic stainless steel assuring low height of burr occurring when the ferritic stainless steel sheet is subjected to blanking, that is, being excellent in blanking property, and to provide a production method therefor. <P>SOLUTION: The ferritic stainless steel sheet excellent in the blanking property for the water heater has the composition comprising by mass% 0.0030-0.012% C, 0.20-0.50% Si, ≤0.25% Mn, ≤0.04% P, ≤0.005% S, 0.02-0.06% Al, 0.0030-0.012% N, 21.0-25.0% Cr, 0.5-1.3% Mo, 0.3-0.5% Nb, 0.02-0.15% Ti and the balance Fe with inevitable impurities, and the ferritic stainless steel sheet is characterized in that ferritic grain diameter is ≤25 μm, complex carbonitride (Nb, Tb)(C, N) having a composition ratio of Nb to Ti [Nb]/[Ti] of 1-10 precipitates in the ferritic grain boundary, and a yield ratio is ≥0.65. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ferritic stainless steel sheet for water heaters, and more particularly to a ferritic stainless steel sheet for water heaters excellent in punching workability and a method for producing the same.

  Ferritic stainless steel sheets are excellent in design and corrosion resistance, and are used in various applications such as buildings, transportation equipment, home appliances, and kitchen appliances. In particular, in recent years, ferritic stainless steel sheets have been used more frequently in heat pump water heater cans in place of austenitic stainless steel sheets that are susceptible to stress corrosion cracking. A structure such as a water heater can body is manufactured through a process of cutting, processing, and joining steel sheets, and in many cases, parts obtained by punching the same steel sheet for reinforcement are joined. However, when a normal ferritic stainless steel sheet is punched, there is a problem that the height of burr (burr) generated during the punching process is large and a gap is formed when joining by welding or the like, resulting in poor welding.

  As a ferritic stainless steel sheet for water heaters, Patent Document 1 includes mass%, C ≦ 0.08%, Si ≦ 0.3%, Mn ≦ 0.3%, 13% ≦ Cr ≦ 26%, N ≦ 0.03%, P <0.015%. , S <0.0010%, 0.02% ≦ Al ≦ 0.20%, and a ferritic stainless steel excellent in use performance mainly composed of corrosion resistance mainly composed of Fe is disclosed.

  Patent Document 2 includes mass%, C ≦ 0.025%, Si ≦ 0.6%, Mn ≦ 1.0%, P ≦ 0.04%, S ≦ 0.01%, Ni ≦ 0.6%, 16% ≦ Cr ≦ 35%, 0.3%. ≦ Mo ≦ 6%, N ≦ 0.025%, 0.01% ≦ Al ≦ 0.5%, 0.1% ≦ Nb ≦ 0.6%, 0.05% ≦ Ti ≦ 0.3%, 0.1% ≦ Cu ≦ 1.0%, and of these components In the mass%, the relationship of C + N ≦ 0.04 and Nb + Ti ≧ 7 (C + N) +0.15 is established, and the following formula, B value = Cr + 3 (Mo + Cu) ≧ 23.5, And the relationship of P value = 5Ti + 20 (Al-0.01) ≧ 1.5 is established, and the ferritic stainless steel is disclosed which is excellent in the corrosion resistance of the welded portion substantially composed of iron and inevitable impurities.

  Patent Document 3 includes mass%, C ≦ 0.003%, 0.1% ≦ Si ≦ 0.4%, Mn ≦ 0.4%, P ≦ 0.04%, S ≦ 0.01%, 16.0% ≦ Cr ≦ 25.0%, 0.8% ≦ Mo. ≦ 2.5%, N ≦ 0.03%, 0.1% ≦ Nb ≦ 0.6%, 0.05% ≦ Ti ≦ 0.3%, 0.01% ≦ Al ≦ 0.5%, and Nb + Ti ≧ Nb between Ti, Ti, C and N 7 (C + N) +0.15 relationship is established, the balance is composed of a ferritic stainless steel plate that is substantially made of Fe, and the body and the upper and lower end panels are caulked and joined together. It is disclosed.

In Patent Document 4, in mass%, 0.001% ≦ C ≦ 0.02%, 0.001% ≦ N ≦ 0.02%, 0.01% ≦ Si ≦ 0.3%, 0.05% ≦ Mn ≦ 1%, P ≦ 0.04%, 0.15% ≦ Including Ni ≦ 3%, 11% ≦ Cr ≦ 22%, 0.01% ≦ Ti ≦ 0.5%, 0.0002% ≦ Mg ≦ 0.002%, 0.5% ≦ Mo ≦ 3.0%, 0.02% ≦ Nb ≦ 0.6%, 0.1% ≦ In the condition of Cu ≦ 1.5%, one or more of Mo, Nb, and Cu are included in a range that satisfies Cr + 3Mo + 6 (Ni + Nb + Cu) ≧ 23, and the balance is Fe and inevitable impurities A ferritic stainless steel having excellent crevice corrosion resistance is disclosed.
JP 58-71356 A Japanese Patent Laid-Open No. 10-81940 JP 2005-15816 JP 2006-257544 A

  However, in any of the ferritic stainless steels described in Patent Documents 1 to 4, the burr height during punching cannot always be reduced.

  The present invention has been made to solve such problems, and provides a ferritic stainless steel sheet for water heaters that can reliably reduce the height of burr at the time of punching, that is, excellent in punching workability, and a method for manufacturing the same. The purpose is to do.

  As a result of detailed investigations on the occurrence of burr at the time of punching of a ferritic stainless steel sheet for water heaters, the present inventors have obtained the following knowledge.

  i) Precipitate a composite carbonitride (Nb, Ti) (C, N) containing Nb and Ti and having a composition ratio [Nb] / [Ti] of 1 to 10 at the ferrite grain boundary This can promote the propagation of cracks during the punching process, and is effective in reducing the burr height during the punching process.

  ii) By reducing the ferrite grain size to 25 μm or less and uniformly dispersing these composite carbonitrides, and further suppressing the significant work hardening by setting the yield ratio to 0.65 or more, the burr height at the time of punching is surely reduced. it can.

  The present invention was made based on such knowledge, and in mass%, 0.0030% ≦ C ≦ 0.012%, 0.20% ≦ Si ≦ 0.50%, Mn ≦ 0.25%, P ≦ 0.04%, S ≦ 0.005%, 0.02% ≦ Al ≦ 0.06%, 0.0030% ≦ N ≦ 0.012%, 21.0% ≦ Cr ≦ 25.0%, 0.5% ≦ Mo ≦ 1.3%, 0.3% ≦ Nb ≦ 0.5%, 0.02% ≦ Ti ≦ 0.15%, A composite carbon having a composition comprising the balance of Fe and inevitable impurities, a ferrite grain size of 25 μm or less, and a Nb / Ti composition ratio [Nb] / [Ti] of 1 to 10 at the ferrite grain boundary Provided is a ferritic stainless steel sheet for water heaters excellent in punching workability, wherein nitride (Nb, Ti) (C, N) is precipitated and the yield ratio is 0.65 or more.

  The ferritic stainless steel sheet of the present invention may further contain at least one element selected from 0.15% ≦ Ni ≦ 0.5% and 0.3% ≦ Cu ≦ 0.6% by mass%.

  The ferritic stainless steel sheet of the present invention is a hot-rolled sheet obtained by heating a steel slab having the above component composition to a temperature of 1000 ° C. or higher and then hot rolling at a finishing temperature of 900 ° C. or higher. Winding at a coiling temperature of 550 ° C to 550 ° C, followed by hot-rolled sheet annealing, cold-rolled into a cold-rolled sheet, and manufactured by a method characterized by recrystallization annealing the cold-rolled sheet it can.

  According to the present invention, the height of the burr at the time of punching can be reliably reduced, and a ferritic stainless steel sheet for water heaters having excellent punchability can be manufactured.

  Below, the ferritic stainless steel plate which is this invention, and its manufacturing method are explained in full detail.

1) Component composition ("%" below represents "% by mass")
0.0030% ≦ C ≦ 0.012%
C precipitates as composite carbonitride (Nb, Ti) (C, N) at the ferrite grain boundary, and reduces the height of burr during punching. For that purpose, the C content needs to be 0.0030% or more. On the other hand, if the C content exceeds 0.012%, the steel hardens, the fracture surface ratio increases at the end face during punching, the height of burr increases, and a large amount of Cr carbide precipitates, resulting in sensitization. Corrosion resistance deteriorates. Therefore, the C content is 0.0030% or more and 0.012% or less.

0.20% ≦ Si ≦ 0.50%
Si is an element necessary as a deoxidizer and an element effective for improving the corrosion resistance of the weld. In particular, it is oxidized at the heat-affected zone during welding to form a dense film, and prevents deterioration of the corrosion resistance of the base material in a solution containing residual chlorine such as a water heater. For that purpose, the Si amount needs to be 0.02% or more, preferably 0.35% or more. On the other hand, Si is a solid solution strengthening element, and when its amount exceeds 0.50%, the steel becomes hard and ductile. Therefore, the Si content is 0.02% or more, preferably 0.35% or more and 0.50% or less.

Mn ≦ 0.25%
If the Mn content exceeds 0.25%, it is an element that degrades the corrosion resistance, and precipitates as MnS at the ferrite grain boundary, increasing the burr height during punching. For this reason, the amount of Mn is made 0.25% or less.

P ≦ 0.04%
If the P content exceeds 0.04%, the steel is strengthened by solid solution and embrittled. Therefore, the P content is 0.04% or less.

S ≦ 0.005%
When the amount of S exceeds 0.005%, it precipitates as MnS at the ferrite grain boundary, which deteriorates the corrosion resistance and increases the burr height during punching. Therefore, the S content is 0.005% or less.

0.02% ≦ Al ≦ 0.06%
Al is a deoxidizer, and positive addition is desired to improve the cleanliness of steel. Further, like Si, it is oxidized at the heat affected zone during welding to form a dense film, and prevents deterioration of the corrosion resistance of the base material in a solution containing residual chlorine such as a water heater. In order to obtain such an effect, the Al content needs to be 0.02% or more. On the other hand, when the Al content exceeds 0.06%, AlN and fine oxides are generated, and the burr height during punching is increased. Therefore, the Al content is 0.02% or more and 0.06% or less.

0.0030% ≦ N ≦ 0.012%
N, like C, precipitates as composite carbonitrides (Nb, Ti) (C, N) at the ferrite grain boundaries, and reduces the burr height during punching. For that purpose, the N amount needs to be 0.0030% or more. On the other hand, if the N content exceeds 0.012%, the amount of composite carbonitride increases, the steel becomes hard, the fracture surface ratio increases at the end face during stamping, and the burr height increases. Therefore, the N content is 0.0030% or more and 0.012% or less.

21.0% ≦ Cr ≦ 25.0%
Cr is an element that forms a passive film on the surface of stainless steel and improves corrosion resistance. A typical ferritic stainless steel sheet contains 18% Cr, as represented by SUS430. Gas shield is not enough in TIG welding etc. in water heater can manufacturing, and an oxide film called temper color containing Cr is generated in the bead part etc., lowering the Cr concentration of the base material and deteriorating the corrosion resistance of the welded part Let In particular, the oxide film generated at 1000 ° C. or higher contains a large amount of Cr selectively, which extremely deteriorates the corrosion resistance of the weld in hot water. Therefore, the present inventors examined the amount of Cr causing such extreme deterioration of corrosion resistance.When the amount of Cr is less than 21.0%, even when Mo or other elements are added, the corrosion resistance in warm water becomes unstable. It became clear that pitting corrosion was caused in the gaps. On the other hand, when the Cr content exceeds 25.0%, the workability is significantly reduced. Therefore, the Cr content is 21.0% or more and 25.0% or less, preferably 22.0% or more and 24.0% or less.

0.5% ≦ Mo ≦ 1.3%
When the Mo content is 0.5% or more, the corrosion resistance is remarkably improved. However, when it exceeds 1.3%, the toughness is remarkably lowered within the range of the Cr content of the present invention. Therefore, the Mo content is 0.5% or more and 1.3% or less, preferably 0.8% or more and 1.2% or less.

0.3% ≦ Nb ≦ 0.5%
Nb is a heavy element in the present invention, and is precipitated as a composite carbonitride (Nb, Ti) (C, N) at the ferrite grain boundary, effectively reducing the height of burr during punching. If the Nb content is less than 0.3%, the precipitation amount of (Nb, Ti) (C, N) decreases, and not only these effects can be obtained, but Cr carbide is liable to precipitate, and the corrosion resistance of the weld zone deteriorates. To do. On the other hand, if the amount of Nb exceeds 0.5%, NbC is complex-precipitated on coarse TiN in the ferrite grains, and the effect of reducing the burr height during punching is lost. Therefore, the Nb amount is set to 0.3% to 0.5%.

0.02% ≦ Ti ≦ 0.15%
Ti, like Nb, is a heavy element in the present invention, and precipitates at the ferrite grain boundary as composite carbonitride (Nb, Ti) (C, N), effectively increasing the burr height during punching. Make it smaller. If the Ti content is less than 0.02%, the amount of (Nb, Ti) (C, N) deposited decreases and such an effect cannot be obtained. On the other hand, if the Ti content exceeds 0.15%, a large amount of TiC precipitates, the steel hardens, the fracture surface ratio during punching increases, and the burr height increases. Therefore, the Ti content is 0.02% or more and 0.15% or less.

  The balance is Fe and unavoidable impurities, but for the following reason, at least one element selected from 0.15% ≦ Ni ≦ 0.5% and 0.3% ≦ Cu ≦ 0.6% is further added by mass%. It can be included.

0.15% ≦ Ni ≦ 0.5%
When the Ni content is 0.15% or more, there is an effect of improving the corrosion resistance, in particular, the corrosion resistance against crevice corrosion. On the other hand, if the amount exceeds 0.5%, the steel is made hard and ductile. Therefore, the Ni content is 0.15% or more and 0.5% or less.

0.3% ≦ Cu ≦ 0.6%
Cu has a function of improving the corrosion resistance, particularly the resistance to crevice corrosion, for ferritic stainless steel having a Cr content of 21.0% or more like the steel of the present invention. For that purpose, it is necessary to make the amount of Cu 0.3% or more, but when it exceeds 0.6%, CuS is precipitated, and the burr height at the time of punching is increased. Therefore, the Cu content is 0.3% or more and 0.6% or less, preferably 0.5% or less.

  The effects of the present invention can be obtained even if B ≦ 0.001%, V ≦ 0.05%, Mg ≦ 0.01%, Ca ≦ 0.01%, etc. are mixed as inevitable impurities, but the smaller the number of these elements, the better.

2) Ferrite grain size: 25 μm or less If the ferrite grain size exceeds 25 μm, composite carbonitride (Nb, Ti) (C, N) is dispersed unevenly or deformation of each ferrite grain during punching The amount increases and the height of the burr increases. For this reason, the ferrite grain size is set to 25 μm or less.

3) Composite carbonitrides (Nb, Ti) (C, N) on ferrite grain boundaries
Cracks at the time of punching occur at the interface between precipitates and ferrite grains present in the ferrite grain boundary, coalesce with propagation, and cause destruction of the material. The height of burr is determined by the amount of plastic deformation up to the point where the material breaks. When composite carbonitride (Nb, Ti) (C, N) with a composition ratio [Nb] / [Ti] of Nb and Ti of 1 to 10 is used as the precipitate, cracking is promoted and The height becomes smaller. The reason for this is not necessarily clear, but it is presumed that the lattice constant and the lattice defects of the precipitates change depending on the composition ratio [Nb] / [Ti], and cracks are likely to occur at the ferrite interface.

4) Yield ratio: 0.65 or more If the yield ratio is less than 0.65, it is easy to work harden, so the ferrite grains are easily deformed, and the amount of deformation of each ferrite grain increases during punching, resulting in high burr height. Becomes larger. For this reason, the yield ratio is 0.65 or more.

5) Manufacturing conditions As described above, the ferritic stainless steel sheet of the present invention is, for example, hot rolled at a finishing temperature of 900 ° C. or higher after heating a steel slab having the above component composition to a temperature of 1000 ° C. or higher. A hot-rolled sheet is obtained, the hot-rolled sheet is wound at a coiling temperature of 400 ° C. or higher and 550 ° C. or lower, and then subjected to hot-rolled sheet annealing, and then cold-rolled to obtain a cold-rolled sheet. It can be manufactured by a method characterized by crystal annealing.

Heating temperature of steel slab: 1000 ° C or more If the heating temperature of steel slab is less than 1000 ° C, Nb and Ti carbonitride existing in the slab cannot be dissolved before heating, and composite carbonitriding in the subsequent process It becomes difficult to control the precipitation state of the product (Nb, Ti) (C, N). For this reason, the heating temperature of a steel slab shall be 1000 degreeC or more.

Hot rolling finishing temperature: 900 ° C or higher If the hot rolling finishing temperature is less than 900 ° C, an unrecrystallized structure remains after hot rolling, resulting in 25 μm of ferrite grains after cold rolling and recrystallization annealing. Expanded coarse particles with a particle size exceeding. For this reason, the finishing temperature of hot rolling shall be 900 degreeC or more.

Winding temperature: 400 ° C or more and 550 ° C or less If the winding temperature after hot rolling is less than 400 ° C, composite carbonitride (Nb, Ti) (C, N) does not precipitate during winding, and the hot rolling continues. At the time of sheet annealing, it precipitates only at the grain boundaries along the rolling direction, and as a result, the ferrite grains after the hot-rolled sheet annealing become coarse grains expanded in the rolling direction. The ferrite grains remain after the subsequent recrystallization annealing and become expanded coarse grains, so that the burr height at the time of punching increases. On the other hand, when the coiling temperature exceeds 550 ° C, the composite carbonitride (Nb, Ti) (C, N) precipitates as coarse precipitates with coarse TiN in the ferrite grains as the core, and cold rolling, re- Even after the crystal annealing, it is present in the ferrite grains, and the effect of the present invention cannot be obtained. Therefore, the coiling temperature is set to 400 ° C. or more and 550 ° C. or less.

  The Nb, Ti, C, N content and the coiling temperature depend on the composite carbonitride (Nb, Ti) (C) with a composition ratio [Nb] / [Ti] of Nb to Ti of 1 to 10. , N) is formed. This composite carbonitride does not change during subsequent hot-rolled sheet annealing or recrystallization annealing, and suppresses grain growth during recrystallization annealing to reduce the ferrite grain size to 25 μm or less, and remains at the ferrite grain boundary for punching. Workability will be improved.

  The hot-rolled sheet after winding is subjected to hot-rolled sheet annealing, the scale is removed by pickling, the sheet is cold-rolled by cold rolling, and subjected to recrystallization annealing. These conditions are the same as those of a normal ferritic stainless steel sheet. Further, after recrystallization annealing, it is preferable to perform skin pass rolling with an elongation of 0.5% or more and 1.5% or less.

  The method for producing the steel before hot rolling is not particularly limited, but the steel having the component composition within the scope of the present invention is melted in a converter, an electric furnace, etc., and then secondary by strong stirring vacuum oxygen decarburization treatment or the like. Refining and slab by continuous casting method.

  Steel Nos. 1 to 26 of the chemical composition shown in Table 1 are melted in a 50 kg small vacuum melting furnace to form a steel ingot, and then hot rolled in the laboratory under the hot rolling conditions shown in Tables 2 and 3. After that, it was placed in a heat insulation box and subjected to a heat treatment equivalent to winding to obtain a hot rolled sheet having a thickness of 3 mm. This hot-rolled sheet was annealed by hot-rolled sheet annealing shown in Tables 2 and 3, pickled, cold-rolled to form a cold-rolled sheet having a thickness of 0.8 mm, and recrystallized at the annealing temperatures shown in Tables 2 and 3 It annealed and produced steel plate No. 1-30. And with respect to the produced steel plates No. 1 to 30, the ferrite grain size, the composition ratio of Nb and Ti in the composite carbonitride (Nb, Ti) (C, N) [Nb] / [Ti ], Mechanical properties, burr height, and pitting potential were measured.

  Ferrite grain size: Thickness section cut from steel sheet along rolling direction is polished, etched with thin aqua regia (nitric acid: hydrochloric acid = 1: 3), observed with optical microscope, and average grain size is measured did.

  Composition ratio [Nb] / [Ti] of Nb and Ti in composite carbonitride (Nb, Ti) (C, N): A thin film is prepared by the twin jet method from the center of the plate thickness of the steel plate, and a transmission electron microscope The average of the composition ratio [Nb] / [Ti] of Nb and Ti in the observed composite carbonitride (Nb, Ti) (C, N) was determined from the analytical strength by EDX.

  Mechanical properties: JIS 13B tensile test specimens were taken from the steel sheet so that the tensile direction was parallel to the rolling direction, and a tensile test was performed at a strain rate of 10 mm / min. Tensile strength TS, elongation El, yield ratio ( Yield strength / tensile strength).

  Height of burr: A 100 mm square sample was cut out from a steel sheet, a 10 mmφ hole was punched in the center, and the burr height was measured. When the height of the burr thus obtained is 50 μm or less, it can be said that the punching workability is excellent.

Pitting potential: Specimen taken from steel plate, electrode: 1.6mm tungsten electrode, welding voltage: 10V, welding current: 60-100A, welding speed: 600mm / min, front bead side shielding gas: Ar (20L / min) The bead-on-plate TIG welding was performed on the test piece so that the back bead width was 2 mm or more under the condition of back bead side shielding gas: Ar + 5% O ₂ (20 L / min). Then, based on JIS G 0577 “Method for measuring pitting corrosion potential of stainless steel”, the back bead surface of the welded part and the part (material) away from the welded part in a 85 ppm 200 ppm NaCl solution that simulates the water heater environment. Pitting potential was measured. In addition, the potential was measured immediately without polishing the test piece before the test and without leaving it for 10 minutes after the solution was immersed. The pitting corrosion potential is evaluated by the potential Vc10 (mV vs SCE) at which the melting current value is 10 μA / cm ² for the non-welded part and the potential Vc100 (mV vs SCE) at which the melting current value is 100 μA / cm ² for the welded part. did. If the pitting potential (Vc100) of the welded portion thus obtained is 100 mV or more, it can be said that the welded portion has excellent corrosion resistance and is not problematic for a water heater.

  The results are shown in Tables 2 and 3. A composite carbonitride (Nb, Ti) having the composition of the present invention, having a ferrite grain size of 25 μm or less, and a ferrite grain boundary having a composition ratio [Nb] / [Ti] of Nb to Ti of 1 to 10. Steel plates No. 2-4, 7-9, 12-14, 17-19, 21, 22, 28, 29 where (C, N) is precipitated and the yield ratio is 0.65 or more It can be seen that the height is 50 μm or less and the pitting potential is 100 mV or more, which is excellent in punching workability and corrosion resistance of the weld. Incidentally, even when the ferrite grain size, the composition ratio of Nb and Ti [Nb] / [Ti], and the yield ratio are within the range of the present invention, the amount of Si, Cr, Mo is less than the range of the present invention. In 25, a burr height of 50 μm or less is obtained, but the pitting corrosion potential of the welded portion is remarkably low, and the corrosion resistance of the welded portion is inferior.

Claims (3)

  % By mass, 0.0030% ≦ C ≦ 0.012%, 0.20% ≦ Si ≦ 0.50%, Mn ≦ 0.25%, P ≦ 0.04%, S ≦ 0.005%, 0.02% ≦ Al ≦ 0.06%, 0.0030% ≦ N ≦ 0.012% 21.0% ≦ Cr ≦ 25.0%, 0.5% ≦ Mo ≦ 1.3%, 0.3% ≦ Nb ≦ 0.5%, 0.02% ≦ Ti ≦ 0.15%, with the balance being composed of Fe and inevitable impurities, Composite carbonitride (Nb, Ti) (C, N) with a ferrite grain size of 25 μm or less and a composition ratio [Nb] / [Ti] of Nb and Ti of 1 to 10 is precipitated at the ferrite grain boundary. A ferritic stainless steel sheet for water heaters with excellent punchability, characterized by having a yield ratio of 0.65 or higher.   The punching according to claim 1, further comprising a component composition containing at least one element selected from 0.15% ≦ Ni ≦ 0.5% and 0.3% ≦ Cu ≦ 0.6% by mass%. Ferritic stainless steel sheet for water heaters with excellent workability.   A steel slab having the component composition according to claim 1 or 2 is heated to a temperature of 1000 ° C or higher and then hot-rolled at a finishing temperature of 900 ° C or higher to form a hot rolled plate, and the hot rolled plate is 400 ° C or higher to 550 ° C. Hot water with excellent punchability, characterized by winding at a coiling temperature of ℃ or less and then performing hot-rolled sheet annealing, followed by cold rolling to form a cold-rolled sheet and recrystallizing the cold-rolled sheet Manufacturing method for ferritic stainless steel sheet