JPH02412B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for economically producing a ferritic stainless steel sheet with excellent surface properties and workability, particularly deep drawability. (Conventional technology) Regarding the technology for manufacturing Al-added ferritic stainless steel sheets without hot-rolled sheet annealing,
Already published in JP-A-57-35634 and JP-A-49-17932.
However, it cannot be said that these techniques necessarily satisfy the mechanical properties, values, ridging, and surface properties required of ferritic stainless steel sheets. (Problems to be Solved by the Invention) The present invention provides a technique for inexpensively manufacturing a ferritic stainless steel sheet that is free from surface flaws and has excellent workability, particularly deep drawability. That is, the gist of the present invention is to add Al in the range of 0.08 to 0.5% to ordinary ferritic stainless steel, and to make 1150
After heating at a temperature of ~1250℃, in the later stage of rough rolling
850°C or more, preferably 900°C after rough rolling, which involves rolling with an interpass time of 15 seconds or more at least twice
After finishing hot rolling at a temperature of 700 to 850
After rolling it in the temperature range of ℃, it is descaled and cold rolled into a thin steel plate using a tandem cold rolling mill with a work roll diameter of 300mmφ or more.
The purpose is to perform annealing at a temperature range of ~1000°C for 1 second or more and 60 seconds or less. In addition, in order to obtain a thin ferritic stainless steel sheet with even better surface properties, the same ferritic stainless steel slab as above is subjected to the same hot rolling as above, and after descaling, the work roll diameter is After rolling 60% or more of the total cold rolling amount in a tandem cold rolling mill with a diameter of 300 mmφ or more, the sheet is then rolled into a thin steel sheet in a cold rolling mill with a work roll diameter of 100 mmφ or less, and then rolled in a temperature range of 800 to 1000℃. Annealing may be performed for 1 second or more and 60 seconds or less. The present invention will be explained in detail below. (Means for Solving the Problems) In the present invention, the heating temperature of the ferritic stainless steel slab containing 0.08 to 0.5% (by weight) of Al is set to 1150°C or higher. The temperature of the rolled material during hot rolling decreases,
This is because the rolling load increases, and as a result, flaws occur during hot rolling, and a grinding process is essential to remove these flaws after hot rolling. In particular, in the present invention, the hot rolling winding temperature is 700°C or higher.
In order to perform high-temperature winding of 850℃ or less, 1180℃
A heating temperature higher than that is desirable. On the other hand, in order to prevent the occurrence of defects during hot rolling, the higher the slab heating temperature is, the better; however, excessive temperatures exceeding 1250°C may deteriorate the processing characteristics of the final product due to the following reasons. Since heating requires energy and is uneconomical, the upper limit was set at 1250°C. The reason why processing properties deteriorate when a slab is heated to a temperature of 1250°C or higher is that when the slab is heated to a temperature of 1250°C or higher, precipitates such as MnS, which are preferential nucleation sites for AlN precipitation, dissolve and the hot rolling of time
AlN precipitation is delayed, the deep drawing properties of the product deteriorate, and the yield stress increases. In addition, when heating the slab to 1250℃ or higher, the γ phase generated during solidification completely dissolves into solid solution, which delays the α→γ transformation during rough rolling, and reduces the number of recrystallization nucleation sites in the latter stages of rough rolling, resulting in recrystallization. The progress of this process is delayed, and the ridging properties of the finished product deteriorate. Next, the rough rolling conditions will be described. In the subsequent stage of rough rolling, rough rolling is performed in which rolling with an interpass time of 15 seconds or more is performed at least twice.
The objective is to reduce the ridging of the final product plate, improve its value, lower the yield stress, and prevent surface defects from occurring. Ridging can be done by reducing the size of colonies with preferential textures (especially {111} and {100}) in the finished sheet, but according to research by the present inventors, it is possible to cause recrystallization during rough rolling and reduce finishing heat. It has been found that by making the crystal grains as fine as possible and randomizing the crystal orientation as much as possible immediately before the start of inter-rolling, the ridging of the product can be reduced. The present inventors conducted a detailed investigation on this recrystallization during rough rolling, and found that the slab heating temperature was set to 1250°C or lower, preferably 1200°C or lower, to prevent the γ phase generated during solidification from becoming a complete solid solution. By starting rough rolling and performing rolling with an inter-pass time of 15 seconds or more at least twice in the subsequent stage of rough rolling, recrystallization during rough rolling progresses and the temperature immediately before finishing hot rolling is started. After hot rolling, the grains are refined and randomized.
It has been found that the final product has extremely good ridging properties even when rolled at high temperatures of 700°C or higher and 850°C or lower. Next, we will discuss the values and yield stress. The value can be determined by developing the {111} texture in the final annealing process.
According to the research of the present inventors, the amount of local shear deformation during cold rolling is reduced by reducing the α′ phase before cold rolling. Precipitating nitrides before cold rolling to reduce the amount of residual solid solution N.
Well developed in some cases. The rough rolling process contributes to the value in the case of , which will be explained here and will be described later. The effect of this on ordinary steel thin plates is
Corresponds to the scavenging effect, but in the case of ferritic stainless steels, it is a strong carbide-forming element
Since it contains a large amount of Cr, there is usually almost no solid solute C present before cold rolling, and only solid solute N poses a problem. In the case of the steel of the present invention, there are mainly two types of nitrides precipitated to reduce this solid solution N before cold rolling, and they are AlN and Cr ₂ N. Simply reducing solid solution N is the same no matter which nitride is precipitated, but as a result of detailed research by the present inventors, AlN
It has been found that precipitating is more advantageous in terms of value and is also advantageous in lowering yield stress. The reason for this is that in the case of the steel of the present invention, Cr ₂ N decomposes in the final annealing step at 800° C. or higher and 1000° C. or lower, but AlN does not decompose at all. i.e. before cold rolling
If a large amount of Cr ₂ N is precipitated, Cr ₂ N decomposes in the final annealing process and solid solution N increases compared to when AlN is precipitated, resulting in a higher yield stress and a lower value because it inhibits grain growth. It is considered to be. Therefore, it was concluded that it would be better to precipitate a large amount of nitrides and increase the amount of AlN precipitated before cold rolling. Therefore, we investigated the precipitation behavior of nitrides during the rough rolling process and found that Cr ₂ N precipitates mainly in the first stage of rough rolling, and AlN precipitates in the second stage, and AlN precipitation is accelerated under the following conditions. I discovered that. That is, the slab heating temperature is 1250
By performing rolling with an interpass time of 15 seconds or more and 60 seconds or less at least twice in the subsequent stage of rough rolling at a temperature below ℃, AlN precipitation during rough rolling is promoted, improving the value and lowering the yield point. was found to be promoted. Next, the surface texture and rough rolling conditions will be described. Conventionally, it has been thought that when the time between passes is increased or the rolling reduction is increased in the rough rolling process, the rolling reaction force increases and rolling defects called scale (b) are more likely to occur. However, as a result of detailed research by the inventors, we found that
It has been found that the deformation resistance of the plate is lowered when the interpass time is on the order of seconds or less. The reasons for this are the reduction in dislocation density due to static recovery and recrystallization, and the purification of the parent phase by concentrating C and N into the γ phase (C, N
This is thought to be due to softening due to The reasons for limiting the rough rolling conditions will be described below, summarizing what has been stated above. According to the present invention, the rolling with specified inter-pass time and rolling reduction ratio is limited to the latter stage of rough rolling. Prioritize and
This is because Cr ₂ N precipitation takes precedence over AlN precipitation.
However, when rolling is performed according to the present invention, if the inter-pass time is set between 15 seconds and 60 seconds even in the first stage of rough rolling, the γ phase, which becomes a preferential nucleation site for recrystallization in the second stage, can be used. This has the advantage of promoting the precipitation of. The reason why the lower limit of the inter-pass time was set to 15 seconds or more is that this is the minimum time necessary for recrystallization and AlN precipitation to occur effectively, and the reason why the upper limit was set to 60 seconds or more is because the plate thickness Although it varies depending on the pass time, if the interpass time is longer than this, the deformation resistance increases significantly due to the decrease in plate temperature, which exceeds the effect of deformation resistance due to recovery, recrystallization, and concentration of C and N in the γ phase. This is because rolling defects are likely to occur, and the effect of improving the material quality due to progress of recrystallization and precipitation of AlN is saturated, and this is not preferable from the viewpoint of productivity. Further, the reason why the rolling with the desired interpass time is limited to two or more times is because the effect of improving the material quality becomes insufficient if the number of times is less than this. In addition, recrystallization and
The technology of the present invention, which promotes AlN precipitation and improves the material quality of the finished sheet, is closely related to the reduction rate in the rough rolling process, and it is advantageous to set the reduction rate immediately before holding to at least 20%. , it is natural that the higher the value, the more effective it is. However, from the viewpoint of surface properties, the lower the rolling reduction ratio is, the more desirable it is, and even considering the reduction in deformation resistance due to high-temperature slab heating of 1150° C. or higher and the time between passes, the rolling reduction ratio is preferably 50% or less. Further, the reason why the finish rolling finishing temperature is limited to 850°C or higher is that the value decreases at a finishing temperature lower than 850°C. In particular, the present invention targets ferritic stainless steel sheets with excellent deep drawability.
A finishing temperature of 900℃ or higher is desirable. On the other hand, the finish rolling end temperature is preferably as high as possible, but in consideration of the upper limit of the slab heating temperature in the present invention, it is preferably 1000°C or less. The reason why the value deteriorates as the finish rolling end temperature becomes lower than 850℃ is that shear deformation bands occur inside the steel sheet, making it difficult to develop the {111} texture, which is advantageous for deep drawability, in the final annealing. be. Next, the hot-rolling conditions will be described. Winding temperature
The reason for limiting the temperature to 700°C or higher and 850°C or lower is to improve the value, lower the yield stress, increase the total elongation value, and avoid deteriorating the ridging properties and causing surface defects. As for values, yield stress, and total elongation, the properties are improved by increasing the winding temperature to 850° C. or higher, as shown in the prior art disclosed in Japanese Patent Publication No. 58-32217. However, normally, the higher the winding temperature, the more the ridging deteriorates, the grain boundary cracking phenomenon after pickling becomes more severe, and the surface quality of the finished sheet deteriorates significantly. It is not possible to manufacture a ferritic stainless steel sheet with excellent surface properties and workability. Furthermore, as shown in the prior art described in Japanese Patent Publication No. 49-17932, the ridging properties are improved by lowering the winding temperature to 600°C or less, but the value and mechanical properties are deteriorated, and in the subsequent cold rolling process. This causes problems such as ear cracking. The greatest feature of the present invention is that it solves the above-mentioned contradiction of various property changes related to the winding temperature by satisfying all the properties and economically by using the addition of Al, the above-mentioned rough rolling conditions, and the cold rolling method described below. This is because we have made it possible to manufacture these products. The reason is explained below. According to the research conducted by the present inventors, the main reason for the above-mentioned changes in properties (especially value and ridging) depending on the winding temperature is the amount of α' phase present after hot rolling. caused by. In other words, when the winding temperature is low and the amount of α′ phase is large,
During the cold rolling process, shear deformation occurs around the α′ phase, which is harder than the parent phase, randomizing the cold rolling texture and improving the ridging properties of the final product, but at the same time the values are significantly degraded. . The reason for the deterioration of the value is that the nucleation of {111} grains is inhibited during final annealing due to the randomization of the cold rolling texture;
During the final annealing process, the α′ phase decomposes to form solid solution C,
This is thought to be due to the inhibition of grain growth due to the formation of N, carbides, and nitrides, and the solid solution C, N, carbides, and nitrides generated by the decomposition of the α' phase increase the yield stress and increase the total This is thought to cause a decrease in elongation value. Conversely, in order to reduce the deterioration of the values and mechanical properties due to the above α' phase, it has conventionally been necessary to reduce the α' phase by high-temperature winding at 850° C. or higher. However, according to the method of the present invention, by first adding Al, the γ → α transformation rate during the winding process is increased, and the lower limit of the winding temperature that reduces the deterioration of the value and mechanical properties can be lowered.
It can be reduced to around 700℃. N by adding Al
Can be fixed with AlN. As mentioned above, AlN is effective in improving the value and lowering the yield stress, and its precipitation process is in the subsequent stages of rough rolling, winding, and final annealing. Since the precipitation behavior of nitrides in the rough rolling process has already been described, the behavior in the winding process will be explained here. According to a detailed investigation by the present inventors, in the case of the steel of the present invention, Cr ₂ N mainly precipitates at temperatures below 700°C, and the ratio of the amount of N in the total nitrides to the amount of N contained is approximately 100 at temperatures above 700°C. % and that AlN precipitation is promoted at temperatures above 700°C (see Figure 1). That is, in the present invention, by containing Al, γ→
The lower limit winding temperature at which the α transformation rate accelerates and removes the adverse effects of the α' phase and the lower limit winding temperature at which all N becomes nitrides are lower, and the rough rolling process promotes AlN precipitation, so total nitrides are reduced. The ratio of AlN in the material can be increased. Therefore, in the case of the method of the present invention, it has become possible to reduce the winding temperature of 850°C or higher, which was necessary to improve conventional values and mechanical properties, to 700°C or higher. In addition, in the conventional method, ridging deteriorates at a winding temperature of 700℃ or higher, but as explained in the rough rolling process, due to the effect of recrystallization during rough rolling, which refines and randomizes the crystal grains, It has become possible to raise the upper limit of the winding temperature for ridging to 850°C (see Figure 2). It goes without saying that, after winding the hot-rolled coil, if it is not left to cool but is slowly cooled or kept at that temperature, the appropriate winding temperature range will shift to a lower temperature range of 700 to 850°C. Next, we will discuss the surface properties. As mentioned above
If high-temperature winding is carried out at temperatures above 850°C, the phenomenon of intergranular cracking after pickling becomes severe. This grain boundary cracking phenomenon occurs during winding in the pickling process or during the cold rolling process, and the grain boundaries open. When cold rolling is performed in this state, the grain boundary openings collapse in the rolling direction, and some overlap or tear. Such overlapping parts and torn parts remain even after the final annealing, resulting in serious surface defects in the finished sheet. The grain boundary cracking phenomenon that causes such surface defects occurs when the hot rolling winding temperature is 850°C.
It is not so noticeable at temperatures below ℃. However, even within the winding temperature range of 700°C to 850°C according to the present invention, some intergranular cracking phenomenon occurs on the high temperature side (800°C or higher). Although the cause of this grain boundary cracking phenomenon is not necessarily clear at present, research by the present inventors has revealed that it can be prevented by cooling the hot rolled coil with water after winding. However, as mentioned above, the metallurgical phenomena such as the decomposition of the α' phase and the precipitation of AlN, which are necessary to obtain a material with high workability, require time. I can't get a finished product board. Research to date has shown that when a hot-rolled coil wound at 800°C is left to cool for 30 minutes and then water-cooled, and when a hot-rolled coil wound at 750°C is left to cool for 60 minutes and then water-cooled, the material of the finished sheet changes. It has been found that it is possible to obtain a finished plate with satisfactory surface properties, with almost no intergranular cracking occurring after pickling. It goes without saying that the hot-rolled coil may not be left to cool but may be slowly cooled or cooled with water after heat retention. It goes without saying that it is effective to add 0.1% or less of grain boundary segregation type elements such as Sb, Sn, Cu, B, and Mo to prevent such grain boundary cracking. Next, the reason for limiting the descaling conditions will be explained. In the present invention, since hot-rolled ferritic stainless steel sheets are descaled in the as-hot-rolled state, the properties of the scale are different from those in the case of normal hot-rolled sheet descaling in which hot-rolled sheets are descaled after hot-rolled sheet annealing. It is easy to scale, but to make descaling more effective, mechanical descaling such as light reduction of 10% or less, shot blasting, or spraying of iron sand powder with high pressure water, and descaling with acid solution are recommended. It is effective to use them in combination. When pickling is carried out using an acid solution mainly containing HNO ₃ /HF, H ₂ SO ₄ or HCl, grain boundary corrosion does not occur after pickling, the degree of unevenness is small, and polishing is possible after pickling. Even if it is not done, surface defects are less likely to occur. Next, the conditions for cold rolling will be described. The purpose of performing cold rolling with large diameter rolls, or with large diameter rolls in the first stage and small diameter rolls in the second stage, is to improve the value, reduce ridging, and prevent surface defects. The value can be determined by developing {111} texture in the final annealing process, but according to the research of the inventors, among the three effects mentioned above, in the cold rolling process in particular, the macroscopic plastic deformation due to cold rolling is {111} in the final annealing process by reducing shear deformation.
It was found that a texture develops, and furthermore, this macroscopic shear deformation can be reduced by increasing the diameter of the cold rolling rolls. According to a detailed investigation by the present inventors, rolling with a cold rolling mill with a work roll diameter of 300 mmφ or more reduces the value by approximately 10 to 30% compared to rolling with a cold rolling mill with a work roll diameter of 50 mmφ.
A degree of improvement was observed. This value improvement effect is
At least 60% of the total rolling amount to be cold rolled is
As long as the roll is rolled with a large diameter roll of 300 mmφ or more, the effect will not change even if the remaining rolling reduction is rolled with a small diameter roll, so the large diameter roll cold rolling ratio is set to 60% or more. Next, let's consider ridging. When hot-rolled material is rolled with small-diameter rolls, the deformation in the central region of the sheet thickness is relatively small compared to when rolled with large-diameter rolls, so the hot-rolled material remains in the as-hot-rolled state {100}
Even after cold rolling and annealing, a large proportion of the texture remains in that form without recrystallizing, resulting in deterioration of ridging properties. This {100} texture is the final stable orientation of cold rolling and recrystallization, and conversely, when the roll diameter is larger and the cold rolling rate is higher, the texture is faster than when cold rolling with small diameter rolls. A stable orientation is reached, and conversely, the degree of accumulation of {100} texture becomes higher than in the case of small-diameter roll rolling, and the ridging property deteriorates. In other words, there is a correlation between the cold rolling rate and the roll diameter, and the degree of accumulation of the {100} texture that deteriorates ridging properties increases as the cold rolling rate and roll diameter increase. It first decreases and then increases again. After all, there is a cold rolling rate and a roll diameter at which the degree of accumulation of the {100} texture becomes the minimum value. On the other hand, the cold rolling rate and roll diameter at which the degree of accumulation of {100} texture becomes the minimum value also differ depending on the condition of the material to be rolled. As in the present invention, a hot rolled sheet material that has not been annealed has a higher degree of {100} texture accumulation than annealed material, so the {100} texture concentration degree after final annealing shows the lowest value. The cold rolling rate and roll diameter shift to the larger side. In this way, in the present invention, the roll diameter is determined by confirming the range in which the ridging property does not deteriorate even if the roll diameter is moved to the larger diameter side. Even when rolled at a high reduction rate, the ridging property does not deteriorate. In the present invention, the first stage of cold rolling is 300mmφ or more and 700mmφ
The reason for stipulating that cold rolling be carried out at a rolling reduction of 60% or more using a rolling mill with a roll diameter of , the entire rolling amount only needs to be cold rolled once in a tandem cold rolling mill. However, considering the surface texture,
It is advantageous for the first stage to be a large-diameter roll and the latter stage to be a small-diameter roll. The reason is as follows. First, if the first stage is cold-rolled with large-diameter rolls of 300 mmφ or more, even if the surface of the steel plate is uneven during the pickling process, as mentioned above, if the unevenness is not extremely large, it will be more effective than cold-rolling with small-diameter rolls. Since the shear deformation of the surface layer is small, the convex parts collapse into the concave parts, and surface defects due to overlapping parts do not occur, so a polishing process to smooth out the uneven parts before cold rolling is unnecessary. Become. If the purpose is only to prevent surface defects caused by such unevenness, the entire cold rolling process can be carried out using a tandem cold rolling mill equipped with large-diameter rolls; When rolling the entire process using a tandem cold rolling mill, there is a drawback that the surface gloss required for the stainless steel sheet cannot be obtained. The reason for this is that when high-speed cold rolling is performed using large-diameter rolls, the lubricating oil film thickness at the roll bite becomes thicker, although it depends on the viscosity of the lubricating oil. This is because so-called dents tend to form and the surface gloss tends to deteriorate. Furthermore, when using a tandem cold rolling mill that is normally used for rolling ordinary steel as it is for cold rolling stainless steel, the rolling oil, roll surface roughness, crown, etc. must be adjusted to be suitable for rolling ordinary steel. By changing these conditions to conditions suitable for stainless steel rolling, the shape and surface properties of stainless steel can be almost obtained, but it is not economical to change the conditions each time stainless steel rolling is performed, and it is unconventional. Therefore, it is not preferable from an economic point of view to roll the entire process using a tandem cold rolling mill. Therefore, if additional cold rolling is performed by using small diameter rolls of 100 mmφ or less and using lubricating oil suitable for stainless steel, adjusting the roll surface roughness and performing additional cold rolling up to the final gauge in the latter stage of cold rolling, the conditions for rolling ordinary steel can be maintained. The oil pits can be repaired, the surface roughness can be reduced, and a stainless steel plate with excellent gloss can be obtained. By rolling 60% or more of the total rolling amount with large-diameter rolls before cold rolling, the unevenness during pickling becomes shallower, and work hardening of the surface layer progresses.
Even when rolling with small diameter rolls is carried out thereafter, the above-mentioned overlap does not occur, and no surface defects due to the overlap are observed. Also, by using small diameter rolls,
Since the contact area between the roll and the rolled material becomes smaller,
Since the occurrence of oil film breakage and oil pits can be prevented, if the surface roughness of the roll is made fine, a thin steel sheet with good surface gloss can be obtained. In this case, the smaller the diameter of the roll, the better, but since the effect can be exhibited if it is 100 mmφ or less, the roll diameter is limited to 100 mmφ or less, which is followed by cold rolling with a large diameter roll. The larger the amount of cold rolling with rolls of 100mmφ or less, the more it is possible to improve oil pits and surface roughness caused by large-diameter roll rolling (if the roll surface roughness is large in the case of large-diameter roll rolling). However, the amount of reduction by the small diameter rolls can be improved by rolling at least 1% or more of the sheet thickness before cold rolling. The cold rolling according to the method of the present invention is carried out in a factory that produces both ordinary steel thin plates and stainless steel thin plates, that is, ordinary steel rolling is carried out in a tandem mill, and stainless steel thin plates are carried out in a special Sendzimir cold rolling mill. At our factory, stainless steel is rolled as it is in the tandem cold rolling mill used for rolling ordinary steel, and then rolled in the Sendzimir cold rolling mill. Compared to rolling with a rolling mill, the productivity of the cold rolling process is not only significantly improved, but also
Processability (value, ridging property) is improved, and after pickling,
This cold rolling technology is extremely superior in terms of both quality and cost, as it eliminates the need for a special polishing process to reduce unevenness on the plate surface.
As a cold rolling mill that can achieve the object of the present invention,
As mentioned above, an existing tandem cold rolling mill and a Sendzimir cold rolling mill may be combined, or a cold rolling mill may be used in which the roll diameter of the stand after the tandem cold rolling mill is small. . Next, the final annealing was specified to be within 60 seconds at a temperature range of 800 to 1000°C, especially with the aim of lowering the yield point and improving workability. In the case of the method of the present invention, in the rough rolling process and the hot rolling winding process.
Although AlN precipitation is promoted (see Figure 1), about half of the total N amount is Cr ₂ N. For this reason, if a short final annealing of less than 1 second is performed,
Part of the Cr ₂ N decomposes, and the α' phase remaining during the hot-rolling process decomposes to form solid solution N, making it impossible to lower the yield point. However, when the final annealing is performed at a temperature of 800°C to 1000°C for 1 second to 60 seconds according to the present invention, the solid solution N generated by decomposition of Cr ₂ N and α' phase is fixed as AlN. A lower yield point can be achieved. The basic component of the steel of the present invention is 0.08% to 0.5% Al.
The reason why Al is contained within the range of 0.08% is that (i) cold rollability decreases, leading to edge cracking in the cold rolling process,
Fractures occur, making stable cold rolling impossible; (ii) The surface becomes more uneven during pickling, and these uneven areas overlap or become thinner during cold rolling. This is because defects such as tearing and surface flaws on the final product, (iii) a decrease in value, and (iv) a significantly higher yield point and less elongation occur. Preferably, these defects can be prevented by adding 0.1% or more. The higher the amount of Al added, the better; however, even if it is added in excess of 0.5%, the effect is still slight, but almost saturated, so the upper limit was set at 0.5%. (Examples) The present invention will be described in detail below based on Examples. Example After heating a 250 mm thick ferritic stainless steel slab to a temperature of 1190°C with the ingredients shown in Table 1,
The hot rolling shown in Table 2 was carried out to obtain a hot rolled coil with a thickness of 3.0 mm. After shot blasting 6 of these hot-rolled coils, they were shot blasted at a temperature of 90°C with _a concentration of 300g/ _H2SO4 for 40 seconds.
Descaling was carried out at a temperature of 50° C. for 40 seconds at a HNO ₃ concentration of 150 g/HNO 3 . Next, the work roll diameter
1 with a 500mmφ 5-stand tandem cold rolling mill
After cold rolling to a thickness of 0.4mm, it was rolled in 4 passes on a Sendzimir cold rolling mill with a roll diameter of 55mmφ to a thickness of 0.4mm.
Cold rolling was carried out until then. Then 30 at a temperature of 875℃
Annealing was performed for seconds. Furthermore, for comparison, hot-rolled coils were prepared using the conventional method (840
After hot-rolled sheet annealing for 4 hours at ℃, the product is processed using a Sendzimir cold rolling mill to produce a product with a temperature of 0.4 ℃.
A thin steel plate with a thickness of mm was used. Table 3 summarizes the values, ridging properties, yield stress, cold rollability, etc. of the thin steel sheets produced in this manner. From Table 3, it can be seen that the coils manufactured by the method of the present invention have good ridging characteristics and values, and can be used satisfactorily as steel for deep drawing purposes, compared to the characteristics of coils manufactured by the conventional manufacturing method. In addition, due to the manufacturing conditions of the present invention, a coil with a low winding temperature has good ridging properties, but the value is somewhat low as a material for deep drawing. In the case of a short coil, the value is high but the ridging property is poor, and in the case of a coil with a low Al content, the cold rollability is poor, the surface quality is poor, and the yield stress is high, and the ridging property and value are also the conditions for deep drawing steel. It can be seen that the following is not satisfied.

【table】

【table】

[Table] (Effects of the Invention) As detailed above, according to the present invention, the hot-rolled plate annealing process and the surface polishing process after pickling, which were indispensable in the production of conventional ferritic stainless steel plates, are omitted. A ferritic stainless steel sheet with no surface defects and excellent workability, especially deep drawability, can be provided by an extremely economical manufacturing method in which the main cold rolling is performed using a tandem cold rolling mill, which is highly efficient and highly productive. Therefore, the industrial benefits are extremely large.

[Brief explanation of drawings]

Figure 1 shows the precipitation behavior of nitrides in a hot-rolled coil in which a slab of SUS430 steel containing 0.13% Al was heated to 1200℃ and then hot-rolled to a thickness of 3.0mm, as a function of the hot-rolling winding temperature. This is a diagram showing the amount of N in total precipitates and the amount of N precipitated as AlN as a ratio (%) to the total amount of N contained. The case of a manufactured hot rolled coil is shown, and the broken line shows the case of a hot rolled coil manufactured by a normal hot rolling method (rough rolling pass time is 15 seconds or less). Figure 2 contains 0.13% Al.
A slab of SUS430 steel was heated at 1200℃ and then hot-rolled into a 3.0mm hot-rolled coil, which was then pickled and cold-rolled into a 0.4mm cold-rolled coil.
This is a diagram showing the ridging height and r value of a product sheet manufactured by second-second annealing with respect to the hot rolling winding temperature, and the solid line in the diagram is the result of the hot rolling method of the present invention and the cold rolling method of the present invention. The dashed line shows the case produced by the normal hot rolling method (pass time of 15 seconds or less in the rough rolling process) and the cold rolling method of the present invention, and the dashed line shows the case produced by the normal hot rolling method. This shows the case of manufacturing by hot rolling method and normal cold rolling method (work roll diameter 100 mmφ or less).

Claims (1)

[Claims] 1 A slab of ferritic stainless steel containing 0.08 to 0.5% by weight of Al is heated to a temperature range of 1150 to 1250°C, and then hot-rolled by a rough rolling mill and a continuous finishing mill. In rolling, after performing rough rolling in which rolling with an interpass time of 15 seconds or more and less than 60 seconds is performed twice or more in the latter stage of rough rolling, finish hot rolling is performed at a finishing temperature of 850 ° C or higher, and After rolling in a temperature range of 850℃, descaling is performed, and then cold rolling is performed in a continuous cold rolling mill consisting of a cold rolling mill with a work roll diameter of 300 mmφ or more, and then a temperature range of 800 to 1000℃ is performed. A method for producing a ferritic stainless steel sheet with excellent surface texture and workability, characterized by carrying out final annealing for 1 second to 60 seconds. 2 A slab of ferritic stainless steel containing 0.08 to 0.5% by weight of Al is heated to a temperature range of 1150 to 1250°C and then hot rolled by a rough rolling mill and a continuous finishing mill. In the latter stage, after rough rolling is performed two or more times with an interpass time of 15 seconds or more and less than 60 seconds, finish hot rolling is performed at a finishing temperature of 850°C or higher, and the rolling process is performed at a temperature range of 700 to 850°C. After winding, descaling is performed, and then 60% or more of the total reduction to be cold rolled is rolled by a continuous cold rolling mill consisting of a cold rolling mill with a work roll diameter of 300 mmφ or more, and then A surface texture characterized by rolling the remaining reduction amount using a cold rolling mill with a work roll diameter of 100 mmφ or less, and then final annealing at a temperature range of 800 to 1000°C for 1 second to 60 seconds. A method for producing a ferritic stainless steel sheet with excellent workability.