JPH0366370B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for manufacturing a ferritic stainless thin steel sheet with excellent workability, and particularly to a method for manufacturing a ferritic stainless steel sheet with excellent workability that can simplify the manufacturing process. <Conventional technology> Conventionally, the manufacturing method of ferritic stainless steel is as follows:
The material is hot-rolled into a hot-rolled steel strip, and then subjected to a hot-rolled plate annealing treatment for several days, including raising the temperature to 800-850℃ in a batch annealing furnace, holding it, and cooling it, followed by one cold rolling. Alternatively, after performing two or more cold rollings with intermediate annealing in between, the product is subjected to final annealing. In the conventional manufacturing method as described above, the annealing treatment performed before cold rolling requires a long time, resulting in poor productivity and high manufacturing costs. In order to eliminate the above drawbacks, conventionally, for example,
- In Publication No. 17932, after hot rolling, the steel is immediately cooled and rolled at 600℃ or below, cold rolled without annealing the hot rolled sheet, and final annealed to produce ferritic stainless steel with good ridging properties. It shows what can be done. However, when the hot rolling winding temperature is set to 600° C. or lower, although the ridging properties are improved, problems arise such as poor deep drawing properties and increased yield stress. In addition, Japanese Patent Publication No. 58-32217 discloses that by increasing the hot-rolling temperature to a high temperature of 850 to 950°C, the yield stress, total elongation, and deep drawability are comparable to those of conventional batch annealed materials. It shows. However, this method has the disadvantage that the ridging characteristics deteriorate. <Problems to be Solved by the Invention> The purpose of the present invention is to improve the low productivity of the prior art and to provide a method for manufacturing ferritic stainless steel with excellent mechanical properties, deep drawability, and ridging properties. It is something to do. <Means for Solving the Problems> In order to solve the above problems, the present invention specifies the rolling conditions of the hot rolling process. When cold rolling and final annealing are performed to produce a steel plate with a desired finished thickness, the logarithmic strain under hot rolling is calculated from the rough hot rolling finished plate thickness t _B of the above hot rolling process and the final hot rolling finished plate thickness t _H. Calculate ε _H (=logt _H /t _{B )} and calculate the cold rolling logarithmic strain ε _C (=logt _{C /} t _H ), the ratio k of both rolling logarithmic strains: ε _H /ε _C is set in the range of 1 to 3, and hot rolling is completed within the range of the rolling logarithmic strain ratio k. In particular, ferritic stainless steel is hot-rolled and then subsequently pickled, cold-rolled, and finally annealed, or after hot-rolled, it is
The effects of the present invention become clear in a manufacturing method in which continuous annealing is carried out within minutes, pickling, cold rolling, and final annealing. In addition, in the method of this invention, usually 10 to 30% Cr,
The target is ferritic stainless steel containing up to 0.1% C, up to 1% Si, and up to 1% Mn.
If necessary, alloying elements such as Al, Ti, Zr, B, and Nb may be contained. In particular, when Al is added to the target material, more favorable results can be obtained. Al is a useful element that improves the deep drawability of ferritic stainless steel and also improves mechanical properties such as lowering yield stress, and its effect is sufficient at 0.06% or more, and the upper limit is the above. Due to reduction in material quality improvement effect, deterioration of ridging properties, economic reasons, etc., it is set to 0.5% or less. In addition, the material quality improvement effect of Al can be partially enhanced by other nitride-forming elements, e.g.
It can be replaced with elements such as Ti, B, Nb, V, and Zr, and the amount of Al added can be reduced accordingly. In other words, by adding one or more of the alloying elements listed below, the lower limit of the amount of Al added can be lowered.
It can be reduced to 0.04%. Note B: 0.0002~0.005% by weight Ti: 0.005~0.4 〃 Nb: 0.005~0.4 〃 V: 0.005~0.4 〃 Zr: 0.005~0.4 〃 If a ferritic stainless steel sheet is manufactured according to the present invention, the Even if the hot-rolled plate annealing step is omitted or the annealing time is shortened, a product with workability equivalent to or better than that of the conventional method can be obtained, and manufacturing costs can be lowered by improving production efficiency. The features of the present invention will be further explained below. In general, α-stainless steel does not undergo complete transformation like ordinary steel, and is also less likely to undergo dynamic recrystallization.
Therefore, in the hot rolling process, under normal rough rolling conditions, static recrystallization occurs partially and the grains become fine, but under normal finishing hot rolling conditions, recrystallization does not occur and the crystal grains are expanded. only. That is, the finish hot rolling of a ferritic stainless steel sheet can be said to have more of a cold rolling element than the finish hot rolling of ordinary steel in that it merely stretches the crystal grains. This tendency is particularly strong when the hot rolled sheet annealing process is omitted.
Therefore, the present inventors investigated in detail the relationship between finish hot rolling and cold rolling of ferritic stainless steel, and found that there is an optimal reduction distribution between finish hot rolling and cold rolling. It has also been found that the above-mentioned k value is a good parameter to express the optimum reduction distribution. Now, let the plate thickness at the end of rough hot rolling be t _B , and the plate thickness at the end of finish hot rolling be t _H , and if the rolling strain ε _H due to finish hot rolling is expressed as a logarithmic strain, ε _H = logt _H /t _B
is shown. Similarly, when the plate thickness at the end of cold rolling is t _C and the rolling strain ε _C due to cold rolling is expressed as logarithmic strain, ε _C = logt _C /
t becomes _H. The ratio of ε _H and ε _C is set as k. k is expressed by the following formula. k=ε _H /ε _C = logt _H /t _B /logt _C /t _H That is, the present inventors investigated the processing characteristics of the finished plate when t _B , t _H , and t _C were variously changed, and t _C When fixed, k
It has been found that when t _B and t _H are selected so that the values are 1 or more and 3 or less, the processing characteristics of the finished plate are improved. An example of the results is shown in FIG. Figure 1 shows Al at 0.14
After hot rolling, the SUS430 steel containing SUS430 steel with a weight% content of FIG. For reference, ordinary SUS430 steel was manufactured using the conventional manufacturing method, that is, after hot rolling (t _H = 3.8 mm), box annealing at 840℃ for 4 hours, and then cold rolling (t _C = 0.6 mm). The material level when manufactured according to the manufacturing method of final annealing is indicated by an arrow in the margin of the figure. As is clear from the figure, the total elongation value and value are 1 when the k value is 1.
It shows maximum in the area of 3 or less, which is normal SUS430
This value is higher than when manufactured using steel and conventional manufacturing methods. Also, the yield stress and ridging height are k
It decreases as the value increases, which is better than the material level of the conventional method. The reason why the processing characteristics change depending on the k value when the hot rolled sheet annealing process is omitted as described above is considered to be as follows. Changing the k value when manufacturing a ferritic stainless steel sheet with a certain product thickness _tC means changing the reduction distribution between finish hot rolling and cold rolling, which increases the amount of strain accumulated (dislocation density) before final annealing. will change. That is, the higher the k value, the smaller the amount of strain accumulation before final annealing, the fewer recrystallization nucleation sites during final annealing, and the larger the recrystallized grain size after final annealing. This is considered to be the reason why the higher the k value, the lower the yield stress. Furthermore, having large recrystallized grains is advantageous in improving the total elongation value. Furthermore, when the k value changes, the recrystallization nucleation sites during final annealing also change. In general, recrystallization nucleation sites are mainly grain boundaries and deformation zones within grains, and it is thought that {111} grains recrystallize from grain boundaries, and {110} grains recrystallize from deformation zones. There is. As mentioned above, in the case of ferritic stainless steel, almost no recrystallization occurs during finish hot rolling, and the grains are simply stretched, so the grain boundary density at the end of rough hot rolling is Even if the k value is changed to the same extent, if t _C remains the same, the grain boundary density after cold rolling is considered to be almost the same. On the other hand, in the deformation zone within the grain, the larger the k value, the smaller the amount of accumulated strain, and therefore the density of the deformation zone becomes smaller. That is, the larger the k value, the higher the frequency of occurrence of {111} grains that recrystallize from grain boundaries, and the larger the grain size. Therefore, it is considered that the larger the k value, the higher the value. However, k
If the value is extremely large (for example, if the k value is infinite (i.e., cold rolling rate 0%)), the amount of strain required for recrystallization is insufficient, or the {111} grains are separated from the grain boundaries. It is thought that the value decreases for reasons such as the fact that multiple sliding near the grain boundaries, which is necessary for the occurrence of grain boundaries, becomes less likely to occur. Hot rolling and cold rolling have different textures formed due to differences in friction coefficient, temperature, etc. In particular, in hot rolling, the shear deformation caused by the rolls is large and the number of {110} grains increases. In general, ferritic stainless steels do not undergo complete transformation, so the solidified structure is not destroyed by hot rolling or cold rolling, and the steel is drawn to the center of the plate thickness.{100}
It is believed that a large amount of grains are formed and this causes ridging. However, as in the present invention, when the k value is increased and the finish hot rolling ratio is increased, the penetrance of shear deformation increases accordingly, and {100}
This reduces grain formation, which in turn increases {110} grains and improves ridging properties. Furthermore, increasing the k value and decreasing the cold rolling rate also greatly contributes to improving the ridging properties. Regarding the value, it is somewhat advantageous to decrease the formation of {100} grains and increase the formation of {110} grains. However, cold rolling is considered to be more advantageous than hot rolling for the development of {111} grains, which are particularly advantageous for the k value, and when the k value is further increased, the cold rolling rate decreases and {111}
It is thought that the grains do not develop much and the value decreases. Furthermore, regarding the texture, it is also possible to increase the k value and decrease the final hot-rolled plate thickness _tH .
It is considered that the value in terms of cold rolling texture formation is advantageous for ridging. It is conventionally known that increasing the diameter of the cold rolling roll improves the value and ridging, but in the present invention, even if the diameter of the cold rolling roll is the same, by increasing the k value and decreasing _tH . , it is thought that the effect is similar to that of relatively increasing the roll diameter. In other words, when cold rolling is performed with the same number of passes regardless of the size of t _H (for example, cold rolling with a continuous cold rolling mill)
It seems that the smaller _tH is, the lower the rolling reduction per pass is, and the less shear deformation caused by the cold roll, which is similar to the effect of increasing the diameter of the cold roll. . For the above reasons, it is thought that a finished plate with good material properties can be obtained when the k value is set to 1 or more and 3 or less. In addition, as mentioned in the section, the cold rolling rate is required to be at least a certain level, and it is desirable that ε _C be 0.7 or more. Furthermore, as described in JP-A No. 59-13026, if the method of the present invention is combined with the method of increasing the inter-pass time to 15 seconds or more in the rough hot rolling process, the ridging properties and values can be further improved. Needless to say. Now, the effects of the k value described above are all related to manufacturing processes that omit the hot-rolled plate annealing process, but basically they also apply when hot-rolled plates are continuously annealed for less than 10 minutes at a temperature range of 800 to 1000℃. The above effects are the same, and if the k value is further increased and ε _H is increased, the amount of strain accumulated in the hot rolled sheet will be larger, recrystallization during continuous annealing will be promoted, and processing of the finished sheet will be easier. Improves sex. For the same reason as in the case of continuous annealing described above, the effect of the k value still exists even if conventional box annealing hot rolled sheet annealing is performed. However, in conventional hot-rolled sheet annealing (box annealing), the dependence of values and mechanical properties on the k value becomes small. Figure 2 shows the results. Figure 2 shows SUS430 steel containing 0.14% by weight of Al, which was hot rolled, annealed at 840°C for 4 hours, and then cold rolled to 0.6mm using a cold rolling mill with a work roll diameter of 150mm.
The material properties of a thick cold-rolled plate and final annealing are as follows:
It is a figure shown with respect to k value. Compared to FIG. 1, the dependence of values and mechanical properties on the k value is smaller, but a clear dependence on ridging is recognized. The reason for this is thought to be as follows. In general, ferritic stainless steel has a slower transformation rate than ordinary steel, and the γ phase generated during hot rolling cannot be completely decomposed into the α phase and carbides and remains in the hot rolled sheet or becomes martensite. These prior γ phase parts have a higher amount of solute C and N than the parent α phase, and are hard, so if they are cold rolled as they are, they will inhibit the development of the cold rolling texture, and the ridging properties of the finished sheet will deteriorate. However, it degrades the value and mechanical properties. However, when hot-rolled sheets are annealed for a long time as in the conventional method, this prior γ phase completely decomposes into α phase, carbides, nitrides, etc., and is sufficiently recrystallized, resulting in a decrease in values and mechanical properties. is considered to be sufficiently improved and the dependence on the k value to be reduced. but,
In the case of ridging, the effect of inhibiting the development of the cold rolling texture due to the prior γ phase disappears, so it is thought that the overall deterioration occurs and the dependence on the k value becomes clear. In addition, in Figures 1 and 2, Al was added.
The results are shown for SUS430 steel, but the results are basically the same for the case without Al addition. The effect of adding Al is due to (i) coarsening of coagulated grains, (ii) precipitation of AlN, (iii) increase in decomposition rate of γ phase, (iv) reduction of γ phase loop, etc., and changes in mechanical properties. These include improvement and deterioration of ridging properties, and the above are basically different from the effect of the k value, and it is thought that each characteristic value shifts almost in parallel due to the addition or non-addition of Al. (Example) Examples of the present invention will be described below. Example 1 Ferritic stainless steel with the components shown in Table 1 was melted according to the usual melting method to form a slab with a thickness of 250 mm.
mm, length 250mm, heated to 1200℃, then subjected to 7 passes of rough hot rolling and 6 passes of finish hot rolling, while the temperature of the hot rolled sheet does not drop (within 40 seconds after finish hot rolling) First, the hot-rolled sheet was charged into an electric furnace maintained at 700°C, held for 40 minutes, and then taken out and air-cooled. After pickling, these hot-rolled plates were subsequently cold-rolled in a cold rolling mill with a work roll diameter of 150 mm to obtain cold-rolled plates with a thickness of 0.4 mm, and annealed at 875° C. for 30 seconds to obtain finished plates.
In the above manufacturing process, the rough hot-rolled finished plate thickness t _B , finished hot-rolled finished plate thickness t _H , finished hot-rolled reduction ratio ε _H , cold rolling reduction ε _C and k value (=ε _H /ε _C ), etc. The results are shown in Table 2, and the values of the finished plate, ridging, yield stress, and total elongation are shown in Figure 1 against the k value. In addition, the finishing hot rolling reduction ratio and cold rolling ratio in Table 2 are expressed as absolute values of logarithmic strain expression (the following formula). ε _H = logt _H /t _B , ε _C = logt _C /t _H

【table】

[Table] For comparison, we also use the conventional method, that is, SUS430, which contains only an impurity level of Al (0.04wt%).
After finishing hot rolling steel from 20mm thickness to 3.8mm thickness, 840
Manufacturing method: annealing at ℃ for 4 hours, pickling, cold rolling to 0.6 mm thickness, and annealing at 850℃ for 30 seconds (k = 0.90)
The material level obtained in the above is indicated by an arrow in the margin of Fig. 1. In addition, the above hot-rolled sheet was annealed at 840°C for 4 hours, pickled, and then cold-rolled in a cold rolling mill with a work roll diameter of 150mm to form a cold-rolled sheet with a thickness of 0.6mm and annealed at 850°C for 30 seconds. Figure 2 shows the material properties with respect to the k value when a finished plate is made. As is clear from FIG. 1, when the k value is 1 or more and 3 or less, the deep drawability, ridging properties, and mechanical properties are good, and are better than the material quality level obtained by the conventional method. Furthermore, as is clear from Figure 2, when conventional hot-rolled sheet annealing (box annealing) is performed, the value, yield stress,
Although it is recognized that the total elongation value is dependent on the k value, the degree of the effect is small. However, its effect on ridging properties is clearly recognized. Example 2 Ferritic stainless steel with the components shown in Table 3 was melted according to the usual melting method to form a slab with a thickness of 250 mm. After heating these slabs to 1180°C,
A rough bar with a thickness of 21 mm (t _B ) was obtained by rough hot rolling for 7 passes, and a hot rolled coil having a thickness (t _H ) shown in Table 4 was obtained by finishing hot rolling for 6 passes in a continuous hot rolling mill. And so. Table 4 shows the hot rolling results. The finishing reduction rate (ε _H ) in the table is the absolute value of the logarithmic strain display (logt _B /t _H )
It was shown in

【table】

[Table] After hot rolling, the manufacturing method is roughly divided into (i) hot rolling followed by pickling, cold rolling, and final annealing at 875℃ for 30 seconds, and (ii) continuous annealing furnace after hot rolling. After hot-rolled sheet annealing at 100° C., pickling, cold rolling, and final annealing at 850° C. for 30 seconds were used to produce finished sheets. Table 5 shows the results of manufacturing using the manufacturing method (i), and Table 6 shows the results of manufacturing using the manufacturing method (ii).

【table】

【table】

[Table] The hot-rolled coil of the steel type is divided into two parts, and one of the hot-rolled coils is pickled after hot rolling, and the roll diameter is
It was cold rolled to a thickness of 0.4 mm using a 50 mm Sendzimir cold rolling mill (hereinafter referred to as Z mill) and annealed at 875° C. for 30 seconds to obtain a finished plate. The remaining hot-rolled coil was heated to 980℃ in a continuous annealing furnace and then cooled to 800℃ for 2 minutes.
After water cooling from 800℃ (hereinafter referred to as continuous annealing), it was pickled, cold rolled to a thickness of 0.4mm using a Z mill, and then heated to 850℃ for 30 minutes.
It was annealed for seconds to produce a finished plate. All hot-rolled steel coils were also divided into two. , , one of the hot-rolled coils was subsequently pickled and then cold-rolled to a thickness of 1.0 mm using a Z mill.
The finished plate was annealed at 875°C for 30 seconds. Also,
The remaining hot-rolled coils were then pickled and then processed in a Z mill.
It was cold rolled to a thickness of 0.4 mm and annealed at 875°C for 30 seconds. In addition, one of the hot-rolled coils was pickled, then cold-rolled to a thickness of 1.0mm in a four-layer continuous cold rolling mill (hereinafter referred to as T-mill) with a roll diameter of 400mm, and then cold-rolled to a thickness of 0.4mm in a Z-mill. Rolled at 875℃ for 30
It was annealed for seconds to obtain a finished plate. The remaining hot-rolled coils of , , were subjected to continuous annealing, pickled, cold-rolled in a Z mill to a thickness of 0.4 mm, and annealed at 850°C for 30 seconds to produce finished sheets. The hot-rolled coil of the steel type was then pickled and then cold rolled in a T mill to a thickness of 1.0 mm, followed by cold rolling in a Z mill to a thickness of 0.4 mm, and annealed at 875° C. for 30 seconds to obtain a finished plate. Hot-rolled coils of steel are hot-rolled, then pickled, and then cold-rolled in a Z mill to a thickness of 0.4mm.
It was annealed at ℃ for 30 seconds to obtain a finished plate. The cold rolling reduction ratio (ε _C ) in Tables 5 and 6 is expressed as an absolute value in logarithmic strain. Also, the k value is 1 or more and 3
The following methods are the methods of the present invention, and the others are comparative methods. The value of the finished board manufactured as above, ridging,
The yield stress and total elongation values were investigated, and Table 7 shows the results obtained by omitting the hot-rolled sheet annealing process, and Table 8 shows the results obtained by annealing hot-rolled sheets in a continuous annealing furnace.

【table】

[Table] The present invention compared to the comparative method in both cases where the hot-rolled sheet annealing process was omitted (Table 7-, -) and when hot-rolled sheet annealing was carried out by continuous annealing (Table 8-,-). The processing properties of the finished plate produced by this method are better, with a value of 0.8 or higher, which satisfies normal flat plate applications, and the ridging is also extremely good at about 10 μm. However, the yield stress is slightly higher in the hot-rolled plate without annealing (-). Therefore, it is fully expected that for steel types, if the method of the present invention is used in the step of annealing hot rolled sheets by continuous annealing, it will be possible to produce flat plate materials. In the above example, the method of the present invention has better processing characteristics in all cases, but this is because the k value of the comparative method is 1 or less. Table 7 for finished product thickness 1.0mm by steel type -, -,
In -, the value, ridging, yield stress, and total elongation value of - of the present invention method are all better than - with a k value of 1 or less, but when compared with - with a k value of 3 or more, the value, The total elongation value is good, and the ridging and yield stress are somewhat high. The effect of adding Al is shown in -, - and -, - in Table 7 in the hot-rolled sheet annealing process, and in Table 8 in the case where hot-rolled sheet annealing is carried out by continuous annealing.
It is clear from comparing -, - and -, - in the table that the value and yield stress are greatly improved by adding Al. In addition, the effects of the present invention on Al additive materials are - and - and -, -
It is clear if you compare and -. In particular, in cases of - and -, which combine the effects of Al addition and the present invention, the value is as high as about 1.2, and the ridging is also about 15 μm, which fully satisfies deep drawing applications. Also, the effect of the difference in cold rolling roll diameter is −,
It is clear when comparing - and -, - that the values and ridging are better in - and - which were cold rolled in a continuous cold rolling mill with a larger roll diameter. The effect of the present invention is also recognized in large-diameter roll cold-rolled materials, and the - material fully satisfies deep drawing applications. It goes without saying that the use of a continuous cold rolling mill improves productivity over the conventional single-stand Sendzimir cold rolling mill. The steel type (−, −) is a composite additive of Al and Ti, and the value is the Al additive (−, −)
It becomes even higher. The effect of the present invention is recognized even in this steel type, and in particular, the - material has a value as high as about 1.4 and can be expected to be used as a material for ultra-deep drawing. In addition, the effect of hot rolling is also recognized in low Cr ferritic stainless steel materials such as steel (-
,-). (Effects of the Invention) As explained above, the effects of the present invention are that when producing a ferritic stainless steel sheet with a predetermined finished product thickness, by setting the k value defined in the present invention to 1 to 3, deep drawing The objective is to improve properties, rigidity, and mechanical properties. As a result of this effect, it is possible to omit or shorten the process of heating, holding, and cooling the hot-rolled coil over several days in the past, and it is possible to significantly reduce manufacturing costs. Furthermore, if ferritic stainless steel containing Al or ferritic stainless steel containing Al and one or more of Ti, B, Zr, V, and Nb is manufactured according to the manufacturing method of the present invention, deep drawing is possible. It is also possible to manufacture steel for industrial use.

[Brief explanation of drawings]

Figure 1 shows SUS430 steel containing 0.14% by weight of Al, which was hot-rolled with varying thicknesses at the end of rough hot rolling (t _B ) and at the end of finishing hot rolling (t _H ), and then pickled and rolled into work rolls. The material properties of the finished plate are shown when the plate is cold-rolled to a thickness of 0.6 mm using a cold rolling mill with a diameter of 150 mm, and then annealed at 875°C for 30 seconds to produce a finished plate. Also, the arrows on the outside of Figure 1 indicate normal
After hot rolling SUS430 steel (t _B = 20mm, t _H = 3.8mm)
After box annealing at 840°C for 4 hours and pickling, it was cold rolled to a thickness of 0.6 mm using a Sendzimir cold rolling mill.
This shows the material quality when manufactured using the conventional manufacturing method of annealing at 850℃ for 30 seconds. Figure 2 shows Al content of 0.14% by weight.
After hot rolling the SUS430 steel containing SUS430 steel with varying rough hot-rolled end thickness (t _B ) and finished hot-rolled end thickness (t _H ), annealed at 840°C for 4 hours and pickled, The material properties of the finished plate were then cold-rolled using a cold rolling mill with a work roll diameter of 150 mm to form a cold-rolled plate with a thickness of 0.4 mm and annealed at 850°C for 30 seconds.

Claims (1)

[Scope of Claims] 1. When ferritic stainless steel is hot-rolled, pickled, cold-rolled, and finally annealed to produce a steel plate with a desired thickness, the crude heat of the hot-rolling process is The final hot-rolling logarithmic strain ε _H (=logt _H /t _B ) is determined from the finished plate thickness t _B and the final hot-rolled plate thickness t _H , and the final hot-rolled plate thickness t H and the cold-rolled plate thickness t _H are In the rolling process, the cold rolling end plate thickness t _C and the cold rolling logarithmic strain ε _C (=logt _C /t _H )
Find the ratio of rolling logarithmic strain k: ε _H /ε _C to 1 or more,
A method for producing a ferritic stainless steel sheet with excellent workability, characterized in that hot rolling is completed within the range of the rolling logarithmic strain ratio k of 3 or less. 2. The manufacturing method according to claim 1, wherein the ferritic stainless steel is hot-rolled and then pickled without annealing the hot-rolled sheet. 3 After hot rolling ferritic stainless steel,
The manufacturing method according to claim 1, wherein continuous annealing is carried out at a temperature range of 800 to 1000°C for up to 10 minutes and pickling is performed. 4. The manufacturing method according to claim 1, characterized in that ferritic stainless steel containing 0.06 to 0.5% by weight of Al is used. 5. The manufacturing method according to claim 1, characterized in that ferritic stainless steel containing 0.04 to 0.5% by weight of Al and one or more of the following alloying elements is used. Note B: 0.0002-0.005% by weight Ti: 0.005-0.4 〃 Nb: 0.005-0.4 〃 V: 0.005-0.4 〃 Zr: 0.005-0.4 〃