JPS61163216A - Manufacture of ferritic stainless steel sheet superior in surface property and workability - Google Patents

Abstract

PURPOSE:To manufacture inexpensively the titled steel sheet having no surface flaw and superior deep drawability, by applying heating, rough rolling, finishing hot rolling, winding, cold rolling, final annealing in order under specified conditions to ferritic stainless steel slab contg. a specified quantity of Al. CONSTITUTION:Ferritic stainless steel slab contg. 0.08-0.5wt% Al is heated to 1,150-1,250 deg.C range. Next, said slab is rolled roughly, by performing >=2 times rollings having >=15sec-<=60sec pass time in latter step thereof, then finishing hot rolled at >=850 deg.C, favorably at >=900 deg.C at hot rolling. Rolled steel plate is wound at 700-850 deg.C range, then descaled, and cold rolled by continuous cold rolling mill having >=300mmphi work roll diameter. Further, said sheet is annealed finally at 800-1,000 deg.C range for >=1sec-<=60sec.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for economically producing a ferritic stainless steel sheet with excellent surface texture and workability, particularly deep drawability.

(Prior art) A technology for manufacturing At-added ferritic stainless steel sheets without hot-rolled sheet annealing has already been disclosed in JP-A No. 5.
These techniques are introduced in Japanese Patent Publication No. 7-35634 and Japanese Patent Publication No. 17932/1982, but these techniques do not necessarily satisfy the mechanical properties, T value, ridging, and surface properties required for ferritic stainless steel sheets. I can't take it lightly.

(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 At in the range of 0.08 to 0.5% to ordinary ferritic stainless steel, and to
After heating at a temperature of 1250°C, 15
After rough rolling at least twice with an i4 interval time of seconds or more, finish hot rolling at a temperature of 850°C or higher, preferably 900°C or higher, and then winding at a temperature range of 700 to 850°C; Mainly descaling is carried out by pickling mainly with acids other than nitric-fluoric acid without annealing the hot-rolled sheet, and 60 inches or more of fully cold-rolled I is rolled in a tandem cold rolling mill with a work roll diameter of 300 mm or more. After that, continue to work roll diameter 10
After rolling into a thin steel plate using a cold rolling mill with a diameter of 0 mm or less,
The purpose is to perform annealing at a temperature range of 00 to 1000°C for 1 second or more and 60 seconds or less.

The present invention will be explained in detail below.

(Means for solving the problem) In the present invention, the heating temperature of a slab of sulferite stainless steel containing 0.08 to 0.5% (by weight) of At is set to 1.
The reason for setting the temperature to 150°C or higher is that when heating below this temperature,
The temperature of the material to be rolled during hot rolling decreases, 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. It is from.

In particular, in the present invention, in order to perform high-temperature winding at a hot rolling winding temperature of 700°C or higher and 850°C or lower,
A heating temperature of ℃ or higher is desirable. On the other hand, in order to prevent the occurrence of defects during hot rolling, it is preferable that the slab heating temperature be as high as possible; however, excessive temperatures exceeding 1250°C may deteriorate the processing characteristics of the final product for the following reasons. , as 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 1,250°C or higher is that when the slab is heated to a temperature of 1,250°C or higher, 8% Mn precipitates, which are preferential nucleation sites for AtN precipitation, dissolve and AtN precipitation during rolling is delayed, the deep drawing properties of the finished product deteriorate, and the yield stress also increases. In addition, when heating the slab at 1250°C 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 stage of rough rolling, resulting in recrystallization. progress is delayed, and the properties of the finished product are deteriorated.

Next, the rough rolling conditions will be described. After the rough rolling, rolling with an interpass time of 15 seconds or more is performed at least twice.
The purpose of carrying out rough rolling more than once is to reduce the final product plate's glue song, improve the r value, lower the yield stress, and prevent surface defects from occurring. Linong is the preferential texture (% (111) and (100)) in the finished board.
However, according to the research of the present inventors, it is necessary to cause recrystallization during rough rolling, to make the crystal grains as fine as possible just before the start of finishing hot rolling, and to randomize the crystal orientation as much as possible. It was found that the linong of the product becomes smaller. The present inventors conducted a detailed investigation on recrystallization during rough rolling, and as mentioned above, the slab heating temperature was set to 1250°C or lower, preferably 120.0°C or lower, to completely dissolve the γ phase generated during solidification. By starting rough rolling without rolling and performing rolling with an interpass time of 15 seconds or more at least twice in the subsequent stage of rough rolling, recrystallization during rough rolling progresses and the finish hot rolling is completed. - It has been found that even when the immediately preceding crystal grains are made fine and randomized, and the product is rolled up at a high temperature of 700°C or more and 850°C or less, the bending properties of the most P-product are extremely good.

Next, we will discuss the 7 value and yield stress. The r value can be determined by developing a (111) texture in the final annealing process, and according to the research of the present inventors, it is possible to - Reducing the amount of deformation, ■ Reducing macroscopic shear deformation as plastic deformation during the cold rolling process, ■ Reducing the amount of residual solid solution N by precipitating nitrides before cold rolling. do. The rough rolling process contributes to the r value in the case of (2), and here, (2) will be explained.

The effects of (1) and (2) correspond to the scavanging effect in ordinary steel sheets, but in the case of ferritic stainless steels, they contain a large amount of Cr, a strong carbide-forming element, so they are usually hardened before cold rolling. There is almost no dissolved C, and only solid solute N is a problem.

In the case of the steel of the present invention, there are two types of nitrides, A and A.
tN and Cr2N. Precipitating any nitride is the same in order to simply reduce solid solution N, but as a result of detailed research by the present inventors, precipitating AtN is more advantageous in terms of 7 value, and further reduces yield. It has been found that this method is also advantageous in reducing stress. The reason for this is that in the case of the steel of the present invention, Cr2N is decomposed in the final annealing step at 800° C. or more and 1000° C. or less, but AtN is not decomposed at all. That is, if a large amount of Cr2N is precipitated before cold rolling, Cr2N will decompose in the final annealing process compared to when AtN is precipitated, solute N will increase, yield stress will increase, and grain growth will be inhibited.
It is thought that the value will also be lower. Therefore, it was concluded that it would be better to precipitate a large amount of nitrides and increase the amount of AtN precipitated before cold rolling. Therefore, when we investigated the precipitation behavior of nitrides in the rough rolling process, we found that Cr2N mainly precipitates in the first stage of rough rolling, and AtN precipitates in the second stage, and we found that AtN precipitation is promoted under the following conditions. I found it.

That is, by setting the slab heating temperature to 1250° C. or lower and performing rolling at least twice with an interval time of 15 seconds or more and 60 seconds or less in the subsequent stage of rough rolling, AtN precipitation during rough rolling is promoted, and T It has been found that this helps improve the value and lower the yield point.

Next, the surface texture and rough rolling conditions will be described. Conventionally, in the rough rolling process, No.J? It has been thought that when the rolling time is increased or the rolling reduction rate is increased, the rolling reaction force increases and rolling flaws called scale (b) are more likely to occur. However, as a result of detailed research by the present inventors, the deformation resistance of the plate is lower when the f-s time is between 15 seconds and 60 seconds, rather than the normal f-s time of about 10 seconds. I discovered that. The reasons for this are: ■ Decrease in dislocation density due to static recovery and recrystallization; ■ Purification of the parent phase by concentrating C and N into the γ phase (C+
This is thought to be due to softening due to N, etc.).

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 interpass time and rolling reduction ratio is limited to the latter stage of rough rolling.
This is because →γ transformation takes priority and Cr2N precipitation takes priority over AtN 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 precipitation of γ phase, which becomes the preferential nucleation site for recrystallization in the second stage, will occur. This has the advantage of encouraging Also, the reason why the lower limit of the inter-flash time was set to 15 seconds or more is that this is the minimum time required for recrystallization and AtN precipitation to occur effectively, and the reason why the upper limit was set to 60 seconds or less. Although it depends on the plate thickness, the i4
During the rolling time, the deformation resistance increases significantly due to the decrease in sheet temperature, which exceeds the effect of decreasing deformation resistance due to recovery, recrystallization, and concentration of C9N into the γ phase, making rolling defects more likely to occur.
This is because the effect of improving the material quality due to progress of recrystallization and AAN precipitation is saturated, and this is not preferable from the viewpoint of productivity.

Further, the reason why the rolling process having the desired deformation time is limited to two or more times is because if the number of times is less than this, the effect of improving the material quality will be insufficient. Note that the technology of the present invention, which improves the material quality of the finished plate by increasing the time between passes in rough rolling, promotes recrystallization and AtN precipitation, and is closely related to the rolling reduction rate in the rough rolling process, and is maintained. It is advantageous that the immediate rolling reduction rate is at least 20% or more, and it goes without saying that the higher the rolling reduction rate, the more effective it is.

However, from the viewpoint of surface quality, the lower the reduction rate, the more desirable it is.
Even considering the reduction in deformation resistance due to high-temperature slab heating of 1150° C. or higher and the time between passes, it is desirable that the rolling reduction ratio be 50% or less.

In addition, the reason why the finishing rolling temperature was limited to 850°C or higher was as follows.
This is because the T value decreases at a finishing temperature of less than 850°C. In particular, since the present invention deals with ferritic stainless steel sheets having excellent deep drawability, it is desirable that the finishing temperature be 900° C. or higher. On the other hand, the finish rolling end temperature is preferably at a high temperature, but in consideration of the upper limit of the slab heating temperature in the present invention, it is preferably set to 1000° C. or less. The reason why the T value deteriorates as the finish rolling end temperature becomes lower than 850°C is that shear deformation bands occur inside the steel sheet, making it difficult for the (111) texture, which is advantageous for deep drawability, to develop in the final annealing. It is.

Next, we will discuss the hot-rolled red material. Winding temperature is 700℃
The reason for limiting the temperature to 850° C. or lower is to improve the T value, lower the yield stress, increase the total elongation value, and prevent the ridging properties from deteriorating and surface defects from occurring. Regarding T value, yield stress and total elongation, see Japanese Patent Publication No. 58-3221.
As shown in the prior art disclosed in Publication No. 7, the excavation temperature is
Characteristics are improved by increasing the temperature to 50°C or higher. But usually
As the winding temperature increases, the ridging deteriorates, and the grain boundary cracking phenomenon after pickling also becomes more severe, resulting in a significant deterioration of the surface quality of the finished sheet. It is not possible to manufacture a ferritic stainless steel sheet with excellent properties. Also, special public service in 1977-
As shown in the prior art described in Publication No. 17932, the ridging characteristics are improved by setting the winding temperature to 600°C or less, but
7 value and mechanical properties are deteriorated, and problems such as ear cracking are likely to occur during the subsequent cold rolling process.

The greatest feature of the present invention is that it is possible to solve the above-mentioned inconsistency in various property changes related to the winding temperature' by satisfying all the properties and manufacturing economically by using the above-mentioned rough rolling conditions and the below-mentioned cold rolling method. It's about to become possible.

The reason is explained below. The biggest reason why the above characteristics change depending on the winding temperature (especially the T value song) is
According to the research conducted by the present inventors, this is caused by the amount of α' phase present after hot rolling and winding.

In other words, when the winding temperature is low and the amount of α' phase increases, shear deformation occurs around the α' phase, which is harder than the parent phase, during the cold rolling process, randomizing the cold rolling texture and increasing the final Although it improves the adhesive and song characteristics of the finished product, at the same time the T value deteriorates significantly. The reason for the deterioration of the T value is that the nucleation of (111) grains is inhibited during the final annealing due to the randomization of the cold rolling texture, and the α' phase decomposes during the final annealing process, resulting in 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 increased the yield stress and the total elongation value. This is thought to cause a decrease in Conversely, in order to reduce the deterioration of the T value and mechanical properties due to the α' phase, it has conventionally been necessary to reduce the α' phase by winding at a high temperature of 850° C. or higher. However, according to the method of the present invention, by first adding ■A/-, 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 7-value and mechanical properties is lowered. 700
It can be reduced to about ℃. ■By adding At, N'l1-
It can be fixed with AtN. As mentioned above, AtN is effective in improving the V value and lowering the yield stress, and its precipitation steps are 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 detailed investigation by the present inventors, in the case of the steel of the present invention, 7
Below 00°C, Cr2N mainly precipitates, and the ratio of the amount of N in all nitrides to the amount of N contained is almost 100% above 700°C.
It was also found that AtN precipitation is promoted at temperatures above 700°C (see Figure 1).

That is, in the present invention, by containing At, r→α
The transformation rate is accelerated and the lower limit scraping temperature at which the negative effects of the α' phase are removed and the lower limit coiling temperature at which total N becomes nitrides are lowered, and the precipitation of AtN is promoted in the rough rolling process. The AtN0 ratio in the nitride can be increased.

Therefore, in the method of the present invention, it has become possible to reduce the winding temperature of 850'C or higher, which was conventionally necessary to improve the S-coupling, T value and mechanical properties, to 700C or higher.

In addition, in the conventional method, ridging deteriorates at a rolling temperature of 700°C 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, The upper limit of the winding temperature for ridging is set to 85
It became possible to raise the temperature to 0℃ (see Figure 2).
.

Next, we will discuss the surface properties. As mentioned above, when winding is carried out at a high temperature of 850° C. or higher, the grain boundary cracking phenomenon 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 portions and sagging portions 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 is not as noticeable when the hot rolling winding temperature is 850'C or less. However, even within the winding temperature range of 700°C to 850°C according to the present invention,
(80°C or higher), some intergranular cracking phenomenon occurs. 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 α required to obtain a material with high workability is
Since metallurgical phenomena such as the decomposition of the ' phase and the precipitation of AtN require time, a finished sheet with high workability cannot be obtained if water cooling is carried out at the hot rolling winding temperature point. In research to date, 800
When a hot-rolled coil wound at ℃ is left to cool for 30 minutes and then cooled, and when a hot-rolled coil wound at 750℃ is left to cool for 60 minutes and then water-cooled, the material quality of the finished sheet is satisfied and after pickling. It has been found that almost no intergranular cracking occurs and a finished plate with extremely good surface properties can be obtained. Examples of elements that prevent such grain boundary cracking include Sb, Sn, Cu, and B.

It goes without saying that it is effective to add 0.1% or less of a grain boundary segregation type element such as Mo.

Next, explain the reason for limiting the descaling conditions. In the present invention, the hot-rolled ferritic stainless steel sheet is descaled in the as-hot-rolled state, so the properties of the scale are different from the normal hot-rolled sheet descaling process in which the hot-rolled sheet is annealed and descaled. It is easy to descale, but in order to descale more effectively, mechanical descaling such as light reduction of 10 inches or less, shot blasting, or spraying of iron sand powder with high pressure water, and acid solution are recommended. It is effective to perform this in combination with descaling. When pickling is carried out with an acid solution mainly composed of HNO3/4 (FJPH2S04 or HCl), grain boundary corrosion does not occur after pickling and the degree of unevenness is small, so there is no need to polish after pickling. In the present invention, the pickling used for descaling is limited because surface defects are less likely to occur.

Next, the conditions for cold rolling will be described. The reason why cold rolling is carried out using large-diameter rolls in the first stage and small-diameter rolls in the second stage is to improve the T value, reduce ridging, and prevent surface defects from occurring. The T value can be determined by developing a (111) texture in the final annealing process, but according to the inventors' research,
Among the three effects mentioned above, we found that in the cold rolling process in particular, by reducing macroscopic shear deformation as plastic deformation during cold rolling, the (m) texture develops in the final annealing process. The 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 fiφ or more improves rolling by about 10 to 30 on a 7-value basis compared to rolling with a cold rolling mill with a work roll diameter of 50 mφ %
A degree of improvement was observed. This 7 value improvement effect can be achieved by rolling 60% or more of the total amount of cold rolling with large-diameter rolls with a roll diameter of 300wφ or more, and the effect will not change even if the remaining reduction amount is rolled with small-diameter rolls. Therefore, 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 (100) texture that exists in the as-hot-rolled state is reduced. Even after cold rolling and annealing, a large proportion of steel remains in that form without recrystallizing, resulting in poor ridging properties.

This (1001 texture) is the final stable orientation of cold rolling and recrystallization, and when the roll diameter is larger and the cold rolling rate is higher, conversely, the orientation is faster than when cold rolling with small diameter rolls. A stable orientation will be reached, and conversely (100
) The degree of accumulation of texture is higher than in the case of small-diameter roll rolling9, resulting in deterioration of ridging properties.

That is, the degree of accumulation of the (100) texture that deteriorates ridging properties has a correlation between the cold rolling rate and the roll diameter, and first decreases as the cold rolling rate and roll diameter increase. , and again shows an increasing phenomenon. In the end (10
0) There is a cold rolling rate and a roll diameter that give the minimum value of the degree of accumulation of texture. On the other hand, the cold rolling rate and roll diameter at which the degree of accumulation of the (100) texture becomes the minimum value also differ depending on the state 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 accumulation of (100) texture than annealed material, so the degree of accumulation of (10) texture after finish 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, but by using a roll with a maximum diameter of about 700 Wφ,
Even when rolled at a high rolling reduction of about 90%, no deterioration in ridging property occurs.

In the present invention, the first stage of cold rolling is 300wnφ or more and 700wnφ
The reason for stipulating that cold rolling be carried out at a rolling ratio of 60 or more on a rolling mill with a roll diameter of From this point of view, it means that the entire rolling amount only needs to be cold rolled once in a tandem cold rolling mill. However, considering the surface properties, it is advantageous to use a large-diameter roll in the first stage and a small-diameter roll in the second stage. The reason is as follows. First, if the first stage is cold rolled with a large diameter roll of 300 mm or more, even if irregularities occur on the steel plate surface during the pickling process as described above, if the irregularities are not extremely large, then cold rolling with small diameter rolls will result. In comparison, the shear deformation in the surface layer is small, so the convex parts collapse into the four parts, and surface defects due to overlapping parts do not occur, so the polishing process to smooth out the uneven parts before cold rolling is unnecessary. It becomes necessary. 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 is thick, υ, and the oil present in the recesses on the surface of the steel sheet, which depends on the viscosity of the lubricating oil. This is because depressions called pits 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, it is possible to obtain the shape and surface properties of stainless steel, but it is not economical to change the conditions each time stainless steel rolling is performed. 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 100wφ or less, 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 used as is. At the same time, the oil bit is repaired and a stainless steel plate with excellent gloss and low surface roughness can be obtained.

By rolling 60% or more of the total rolling amount using large-diameter rolls before cold rolling, the unevenness during pickling is shallow.)
Furthermore, since work hardening of the surface layer progresses, even if small diameter roll rolling is performed thereafter, the above-mentioned heavy wrinkles will not occur.
No surface defects due to heavy scratches were observed. In addition, by using small diameter rolls, the contact area between the roll and the rolled material is reduced, which prevents oil film breakage and oil bits from occurring, so if the roll surface roughness is made fine, the surface gloss can be improved. It can be a thin steel plate. In this case, the smaller the diameter of the roll, the better, but since the effect can be exhibited if it is 100-φ or less, it is limited to 1001EI11φ or less of the small-diameter roll following cold rolling with the large-diameter roll. The larger the amount of cold rolling with rolls of 100 m + φ or less, the more it becomes possible to improve oil bits caused by large diameter roll rolling, surface roughness (when the roll surface roughness is large in the case of large diameter roll rolling), etc. 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.

Cold rolling according to the method of the present invention is performed at a factory that produces both ordinary steel sheets and stainless steel sheets, that is, ordinary rolling.
At a factory where stainless steel thin plates are rolled using a tandem mill and a special Sendzimir cold rolling mill, the stainless steel is rolled using the same tandem cold rolling mill used for regular rolling, and then rolled using the Sendzimir cold rolling mill. Compared to the conventional process where the entire cold rolling process is rolled using a Sendzimir cold rolling mill, not only is the productivity of the cold rolling process significantly improved, but the workability (r value, ridging It can be said that this cold rolling technology is extremely superior in terms of both quality and cost. As described above, the cold rolling mill that can achieve the object of the present invention may be a combination of an existing tandem cold rolling mill and a Sendzimir cold rolling mill, or a roll on a stand at the rear stage of the tandem cold rolling mill. A cold rolling mill with small diameter rolls may be used.

Next, the reason why the final annealing is specified to be within 60 seconds at a temperature range of 800 to 1000°C is to particularly lower the yield point and improve workability. In the case of the method of the present invention,
Although AtN precipitation is promoted in the rough rolling process and hot rolling winding process (see Figure 1), about half of the total N amount is C.
r2N.

Therefore, when final annealing is performed for a short time within 10 seconds, part of the Cr2N decomposes, and the α' phase remaining during the hot-rolling process decomposes to form solid solution N, making it difficult to lower the yield point. It doesn't happen. However, as shown in the table, when the final annealing is carried out at a temperature of 800°C to 1000°C for 1 second to 60 seconds according to the present invention, solid solution N
is fixed as AtN, and a low yield point can be achieved.

° As a basic component of the steel of the present invention, kl is o, oss ~ 0
．． The reasons for containing At less than 0.08% are as follows: 1) cold rollability decreases, leading to edge cracking, breakage, etc. in the cold rolling process, making stable cold rolling impossible; )
During pickling, the surface irregularities become larger, and these irregularities overlap during cold rolling, or the overlapped and thinner parts break off, resulting in surface defects on the final product.i! This is because defects such as a decrease in the r value, i) a marked increase in the yield point, and a decrease in elongation occur. , these defects can be prevented. The higher the amount of At added, the better.
．． Even if it is added in excess of 5%, the effect is slight, but it becomes almost saturated, so the upper limit was set at 0.5%.

(Example) The present invention will be explained in detail below according to examples.

Example A 250 m thick ferritic stainless steel slab with the ingredients shown in Table 1 was heated to a temperature of 1190°C, and then hot rolled as shown in Table 2 to obtain a hot rolled slab with a thickness of 3.0 mm. I made it into a coil. After shot blasting 6 coils (■ to ■) of these hot-rolled coils, they were subjected to shot blasting at a temperature of 90°C with a H2SO4 concentration of 30011/l for 40 seconds, and then with HN of 15011/l.
Descaling was performed at a temperature of 50°C for 40 seconds at an O3 concentration. Next, it was cold rolled to a thickness of 1 mm in a 5-stand tandem cold rolling mill with a work roll diameter of 500 wφ, and then
Cold rolling was carried out in 4 passes to a thickness of 0.24 mm using a Sendzimir cold rolling mill having a roll diameter of wφ. Then 875
Annealing was carried out at a temperature of 30 seconds.

Furthermore, for comparison, hot-rolled coil 0 was prepared using the conventional method (8401:
After hot-rolled sheet annealing for 4 hours, the sheet was processed into a 0.4-thick thin steel sheet using a Sendzimir cold rolling mill alone.

The r value, ridging property, yield stress, cutting rollability, etc. of the thin steel sheets produced in this manner are summarized in Table 3. Third
Compared to the properties of the ■coil manufactured by the conventional manufacturing method, the coil manufactured by the method of the present invention has high ridging characteristics and r value, and is found to be sufficiently usable as steel for deep drawing applications. It will be done. In addition, due to the manufacturing conditions of the present invention, the coil has a low winding temperature, has good ridging properties, but has a low r value as a material for deep drawing, and the inter-pass time in the rough rolling process is short. In this case, the 7 value is high but the ridging property is poor, and in the case of a coil with a low At content, the cold rollability is poor, the surface quality is poor, and the yield stress is high, and the ridging property and 7 value also meet the conditions for deep drawing steel. I know that it is not satisfied.

(Effects of the Invention) As detailed above, according to the present invention, it is possible to omit 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. We provide ferritic stainless steel sheets with no surface defects and excellent workability, especially deep drawing properties, using an extremely economical manufacturing method in which the main cold rolling is performed using a highly productive tandem cold rolling mill. It is extremely useful for industrial purposes because it is a valuable product.

[Brief explanation of drawings]

Figure 1 shows a slab of 5US430 steel containing 0.13% At, heated at 1200°C, hot rolled to a thickness of 3.0 m, and the precipitation behavior of nitrides in a hot rolled coil. This is a diagram showing the relationship between the total precipitates of Ni and A.
The amount of N precipitated as tN is expressed as the ratio to the total amount of N contained (
%), the single line in the figure shows the hot rolled coil manufactured by the hot rolling method of the present invention, and the broken line shows the case of the hot rolled coil produced by the hot rolling method of the present invention (the interpass time of rough rolling). 15 seconds or less) is shown. Figure 2 shows At 0.1
A slab of 5U8430 steel containing 3% was heated at 1200°C and then hot rolled.3. The OwO hot rolled coil was then pickled and cold rolled to obtain a 0.4 m cold rolled coil.
This is a diagram showing the song height and F value of a product board manufactured by annealing at 875°C for 25 seconds, with respect to the hot rolling winding temperature. The case of manufacturing by the cold rolling method of the present invention is shown, and the broken line shows the case of manufacturing by the normal hot rolling method (interpass time of rough rolling process 15 seconds or less) and the cold rolling method of the present invention, The one-dot chain line indicates the normal hot rolling method and the normal cold rolling method (work roll diameter 10
The case where 7 ICs are manufactured with 7 ICs is shown. Figure 1 Rolling temperature ('C) Procedural amendment (voluntary) March 20, 1985 Mr. Manabu Shiga, Commissioner of the Patent Office ■, Incident indication 1985 Patent application No. 003882 2, Name of invention Surface properties and Manufacturing method of ferritic stainless steel sheet with excellent workability 3, relationship with the amended case Patent applicant: 2-chome Otemachi, Chiyoda-ku, Tokyo [6-3 (665) New 1]
4 Takeshi, representative of Wooden Steel Co., Ltd. 1) Yutaka 5, Date of amendment order 1920, month, day 6 Detailed explanation of the invention in the specification subject to amendment 7, Contents of the amendment (1) Specification 3 pages 6-8 700-850 after
After winding in the temperature range of ℃, descaling is performed and the workpiece opening is corrected. (2) On page 4, line 12, "The processing characteristics are different when heated" is corrected to "The processing characteristics are different when heated." (3) Page 4, line 13 “When implemented” “When implemented”
Correct to. (4) Same page 7 line 11 r CrzN decomposes and solid solution [N increases j k r Cr2N decomposes and solid solution N increases,'' is corrected. (5) "Recovery and recrystallization" on page 9, line 13 is amended to "recovery and recrystallization." (6) Page 12, line 1, “Contradiction, as mentioned above”; “Contradiction money, A.
t addition and the above-mentioned correction. (Competence page 14, line 13 "(See Figure 2)." is replaced with "(See Figure 2)." In addition, after winding up the hot-rolled coil, do not leave it to cool but slowly cool it or keep it at that temperature. , the appropriate winding temperature range is 7
Needless to say, the temperature shifts to a lower temperature range of 00 to 850°C. ”. (8) Replace “(780°C or higher)” in line 6 on page 15 with r(800°C).
℃ or higher)”. (9) At the end of page 15, “Heading. Like this” was changed to “
I'm finding out. 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 will be corrected to ``like this again''. 04, page 17, line 3, "hot-rolled hot-rolled sheet" is corrected to "hot-rolled hot-rolled sheet." αη force, page 7, line 6, ``Su, descaling'' is corrected to ``ri descaling.'' α2, page 17, line 7, "To perform light reduction rolling of 10% or less," should be corrected to "to perform light reduction, rolling of 10% or less." (To) Page 17, lines 14-16: “Because it becomes less likely to occur,
・・・・・・・・・・・・It is limited. ” will be corrected to “It will be less likely to occur.” CI4 Same page 24, 2 lines from the bottom, within rlo seconds, Jkr, within 1 second.'' (G) Correct "7 value is high" to "7 value is good" in lines 5 and 6 of page 27. α, page 27, line 9, “7 The problem is that the value is low,” is corrected to “The problem is that the r value is somewhat low, and the winding temperature is high.” αη force 7 value r1.05Jkr with code ■ in Table 3 on page 9
1.01i, sign climbing height ``26'''1r2
4J, the ridging height "3o" of code ■ is corrected to "26", respectively. Procedural amendment (voluntary) July 8, 1985 Michibu Uga, Director General of the Office of the Chief Justice, 1, Indication of the case, Patent Application No. 003882, filed in 1985, 2, Name of the invention: Ferritic type with excellent surface texture and workability Stainless Steel Sheet Manufacturing Method 3, Relationship with the Amendment Case Patent Applicant 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Nippon Steel Corporation Representative Takeshi 1) Toyota 4, Agent Tokyo 2-4-1-6 Marunouchi, Chiyoda-ku, Tokyo, Specification subject to amendment 1, Name of the invention, Method for manufacturing ferritic stainless steel sheet with excellent surface texture and workability 2, Claims (1) AtO, 08 A slab of ferritic stainless steel containing ~0.5% by weight of 1150-1250
After heating to a temperature range of °C, hot rolling is performed by a rough rolling mill and a continuous finishing rolling mill.
After performing rough rolling at least once, finish hot rolling is performed at a finishing temperature of 850°C or higher, and after winding at a temperature range of 700 to 850°C, descaling is performed, and then the work roll diameter is 300 mrtdz or higher. Cold rolling is performed in a continuous cold rolling mill consisting of a cold rolling mill, and then
A method for producing a ferritic stainless steel sheet with excellent surface texture and workability, characterized by carrying out final annealing in a temperature range of 0.000C for 1 to 60 seconds. (2) A slab of ferritic [1] stainless steel containing 08 to 0.5% by weight of klO is heated to a temperature range of 1150 to 1250°C, and then heated by a rough rolling mill and a continuous finishing rolling mill. In the stage of rough rolling, 1
After performing rough rolling in which rolling with an interpass time of 5 seconds or more and less than 60 seconds is performed two or more times, finishing hot rolling is performed at a finishing temperature of 850°C or higher, and rolling is performed at a temperature range of 700 to 850°C. After that, descaling is performed, and then the work roll diameter is 3
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 diameter of 100mmφ or more, and then the remainder is rolled by a cold rolling machine with a work roll diameter of 100mmφ or less. Roll the reduction amount, then 800-10
A method for producing a ferritic stainless steel sheet with excellent surface texture and workability, characterized by carrying out final annealing at a temperature range of 00°C for 1 to 60 seconds. 3. Detailed description of the invention (industrial application field)
The present invention relates to an economical method for manufacturing ferritic stainless steel sheets. (Prior art) A technology for manufacturing At-added ferritic stainless steel sheets without hot-rolled sheet annealing has already been disclosed in JP-A No. 5.
Although introduced in Japanese Patent Publication No. 7-35634 and Japanese Patent Publication No. 49-17932, these techniques do not necessarily satisfy the mechanical properties, T value, ridging, and surface properties required for ferritic stainless steel sheets. I can't say that it is. (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 drawing properties. That is, the gist of the present invention is to add kt in the range of 0.08 to 0.5% to ordinary ferritic stainless steel, and to
After heating at a temperature of 1250°C, 15
74 seconds or more? After rough rolling at least twice with a hot rolling time, finish hot rolling is performed at a temperature of 850°C or higher, preferably 900°C or higher, and after rolling at a temperature range of 700 to 850°C, descaling is performed. The steel sheet is then cold-rolled in a tandem cold rolling mill with a work roll diameter of 300 mm or more to obtain a thin steel plate, and then annealed at a temperature range of 800 to 1000° C. for 1 second to 60 seconds. 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 300. After rolling 60% or more of the total cold rolling amount in a tandem cold rolling mill with a diameter of 10 mm or more, the sheet is then rolled into a thin steel sheet in a cold rolling mill with a work roll diameter of 100 mm or less, and then rolled at 800 to 1000 °C. Annealing may be performed within a temperature range of 1 second or more and 60 seconds or less. The present invention will be explained in detail below. (Another means to solve the problem) In the present invention, the heating temperature of a slab of ferritic stainless steel containing 08 to 0.5% of AAo (overlapping) is set to 1.
The reason for setting the temperature to 150°C or higher is that when heating below this temperature,
During hot rolling, the temperature of the rolled material decreases and the rolling load increases, resulting in flaws occurring during hot rolling, and a grinding process is essential to remove these flaws after hot rolling. Because it will be. In particular, in the present invention, a heating temperature of 1180° C. or higher is desirable in order to perform high-temperature winding at a hot rolling winding temperature of 700° C. or higher and 850° C. or lower. On the other hand, in order to prevent the occurrence of defects during hot rolling, it is preferable that the slab heating temperature be as high as possible; however, excessive temperatures exceeding 1250°C will deteriorate the processing characteristics of the final product due to the following reasons. Moreover, since energy is required for heating and it is cine-economical, the upper limit was set at 1250°C. 1250℃
The reason why the processing properties deteriorate when the slab is heated at temperatures above 1250°C is that when the slab is heated above 1250°C, precipitates such as Mn8, which are the preferential nucleation sites for AtN precipitation, are dissolved, and during hot rolling. AtN precipitation is delayed, the deep drawing properties of the product deteriorate, and the yield stress also increases. Also, 1250
When heating the slab at temperatures above ℃, the γ phase generated during solidification completely dissolves into solid solution, which delays the α→γ transformation during rough rolling, resulting in fewer recrystallization nucleation sites in the later stage of rough rolling. delay, and the properties of the finished product deteriorate. Next, the rough rolling conditions will be described. After the rough rolling, rolling with an interpass time of 15 seconds or more is performed at least twice.
The purpose of carrying out rough rolling more than once is to reduce the final product plate's adhesive ginder, improve the Lr value, lower the yield stress, and prevent surface defects from occurring. Rigging can be achieved by reducing the size of colonies with preferential textures (Special K (111) and (100)) in the finished sheet, but according to research by the present inventors, it is possible to cause recrystallization during rough rolling. It has been found that product glue song can be reduced by making the crystal grains as fine as possible and making the crystal orientation as random as possible just before the start of finish hot rolling. The present inventors conducted a detailed investigation on recrystallization during rough rolling, and as mentioned above, the slab heating temperature was set to 1250°C or lower, preferably 1200°C or lower, so that the γ phase generated during solidification was not completely dissolved. By starting rough rolling at , and performing rolling with an interpass time of 15 seconds or more at least twice in the subsequent stage of rough rolling, recrystallization during rough rolling progresses and the finish hot rolling (6) It was found that the final product has extremely good adhesive properties even when the crystal grains immediately before the start are refined and randomized, and the final product is rolled at a high temperature of 700°C or more and 850°C or less after hot rolling. 7 value and yield stress.The T value can be determined by developing the final annealing (111) texture.According to the research of the present inventors, ■Reducing the amount of local shear deformation during rolling, ■Reducing macroscopic shear deformation as plastic deformation in the cold rolling process, ■Precipitating nitrides before cold rolling to reduce the amount of residual solid solution N. The rough rolling process contributes to the 7 value in the case of ■, and here we will explain ■, and ■ and ■ will be discussed later. saavengi
However, in the case of ferritic stainless steel, since it contains a large amount of Cr, which is a strong carbide-forming element, there is usually almost no solid solute C and no solid solute N before cold rolling. only is 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: AtN and Cr2N. Simply precipitating nitrides in solid solution to reduce the solid solution N is the same, but as a result of detailed research by the present inventors, precipitating AtN is more advantageous for the 7 value. Furthermore, it has been found that it is advantageous in reducing yield stress. The reason for this is that in the case of the steel of the present invention, Cr
This is because 2N decomposes, but AtN Fi does not decompose at all. In other words, if a large amount of Cr2N is precipitated before cold rolling, Cr2N will be reduced in the final annealing process compared to when AtN is precipitated.
It is thought that N decomposes, solid solution N increases, yield stress becomes high, and rounding 7 value, which inhibits grain growth, also decreases. Therefore, it was concluded that it would be better to precipitate a large amount of nitrides and increase the amount of ktN precipitated before cold rolling. Therefore,
When we investigated the precipitation behavior of nitrides during the rough rolling process, we found that
It has been found that Cr2N is mainly precipitated in the first stage of rough rolling, and AtN is precipitated in the second stage, and that AtN precipitation is promoted under the following conditions. That is, by performing rolling at least twice or more with an interpass time of 15 seconds or more and 60 seconds or less in the subsequent stage of rough rolling at a slab heating temperature of 1250° C. or less, the AtN during rough rolling is
Precipitation is promoted, improving the 7 value and lowering the yield point rL
I discovered that. Next, the surface texture and rough rolling conditions will be described. Conventionally, it has been thought that when the time between passes is lengthened or the rolling reduction is increased in the rough rolling process, the rolling reaction force increases and rolling needles called scale (b) are more likely to occur. However, as a result of detailed research by the present inventors, we found that the deformation resistance of the plate is lower when the pass time is between 15 seconds and 60 seconds, compared to the normal pass time of about 10 seconds. Ta. The reason for this is ■ Decrease in dislocation density due to static recovery and recrystallization, ■
It is thought that the softening is due to the purification of the parent phase (C, N, etc.) due to the concentration of C and N into the γ phase. The reasons for limiting the rough rolling conditions will be described below, summarizing what has been stated above. According to the present invention, the reason why the rolling with the defined spacing time and reduction ratio is limited to the latter stage of the rough rolling is that in the first stage of the rough rolling following the heating temperature of the slab, the α→r transformation is not caused by recrystallization after rolling. This is because Cr2N precipitation has priority over AtN 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 precipitation of γ phase, which becomes the preferential nucleation site for recrystallization in the second stage, will occur. This has the advantage of promoting Also, the reason why the lower limit of the Al space gap was set to 15 seconds or more was because this was the minimum time required for recrystallization and AtN precipitation to occur effectively, and the reason why the upper limit was set to 60 seconds or less was because Although it varies depending on the plate thickness, if the time between the plates is longer than this, the deformation resistance increases significantly due to the decrease in plate temperature, and the effect of reducing the deformation resistance due to recovery, recrystallization, and concentration of C and H in the γ phase is overridden. This is because deformation and rolling needles are more likely to occur, and because the effect of improving the material quality due to progress of recrystallization and AtN precipitation is saturated, and it is also unfavorable 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. The technology of the present invention improves the material quality of finished sheets by promoting recrystallization and AtN precipitation (lO) by increasing the time between passes during rough rolling.
It is closely related to the rolling reduction rate in the rough rolling process, and it is advantageous that the rolling reduction rate immediately before holding is at least 20% or more, and it goes without saying that the higher the rolling reduction rate, the more effective it is. However, from the viewpoint of surface quality, the lower the rolling reduction is, the more desirable it is.
Even taking into consideration the reduction in deformation resistance due to high-temperature slab heating of ℃ or higher and the time between milling, it is desirable that the reduction ratio is 1j50% or less.The reason why the finish rolling end temperature was limited to 850℃ or higher is as follows.
This is because the V value decreases at a finishing temperature of less than 850°C. In particular, since the present invention deals with ferritic stainless steel sheets having excellent deep drawing properties, it is desirable that the finishing temperature be 900° C. or higher. - The finishing temperature of force rolling is preferably a high temperature phase, but considering the upper limit of the slab heating temperature in the present invention, 100
The temperature is preferably 0°C or lower. Finish rolling end temperature is 85
The reason why the T value deteriorates as the temperature becomes lower than 0° C. is that shear deformation bands occur inside the steel sheet, making it difficult for the (111) texture, which is advantageous for deep drawing properties, to develop in the final annealing. Next, the hot-rolling conditions will be described. Winding temperature is 700℃
The reason for limiting the temperature to 850°C or less is to improve the r value, lower the yield stress, increase the total elongation value, and prevent the ridging properties from deteriorating and surface defects from occurring. Regarding r value, yield stress and total elongation, see Japanese Patent Publication No. 58-3221.
As shown in the prior art disclosed in Publication No. 7, the winding temperature (i
Characteristics are improved by increasing the temperature to 1-850°C or higher. However, normally, as the winding temperature increases, the nongloss deteriorates and the grain boundary cracking phenomenon after pickling is also severe, resulting in a significant deterioration of the surface quality of the sheet product. It is not possible to manufacture a ferritic stainless steel sheet with excellent surface quality and workability by using only this method. Furthermore, as shown in the prior art described in Japanese Patent Publication No. 49-17932, the ridging properties are improved by setting the winding temperature to 600°C or less, but the 7 value and mechanical properties are deteriorated, and the subsequent cold rolling process This can cause 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, and can be manufactured economically while satisfying all properties by adding At, the above-mentioned rough rolling conditions, and the cold rolling method described below. This is because we have made it possible to do so. The reason is explained below. The biggest reason why the above characteristics change depending on the winding temperature (especially in r-value songs) is
According to the research conducted by the present inventors, this is caused by the amount of α' phase present after hot rolling and winding. That is, when the winding temperature is low and the amount of α' phase increases, shear deformation occurs around the α' phase, which is harder than the matrix, during the cold rolling process, randomizing the cold rolled aggregated ml weave. Although the adhesive properties of the final product are improved, at the same time the 7 value is significantly degraded. The reason why the r value deteriorates is that the nucleation of (Ill) grains is inhibited during the final annealing due to the randomization of the cold rolling texture, and the α' phase decomposes during the final annealing process, causing 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 increased the yield stress and the total elongation value. This is thought to cause a decrease in Conversely, in order to reduce the deterioration of the r value and mechanical properties due to the α' phase mentioned above, it was conventionally necessary to reduce the α' phase by high-temperature winding at 850°C or higher. . However, according to the method of the present invention, firstly, by adding At, the γ→α transformation rate during the winding process is increased, and the lower limit of the winding temperature is set to reduce the deterioration of the 7-value and mechanical properties. 700
It can be reduced to about ℃. (2) By adding At, N can be fixed with AtN. As mentioned above, AtN is effective in improving the r 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 detailed investigation by the present inventors, in the case of the steel of the present invention, 7
At temperatures below 00°C, Cr2N mainly precipitates, and at temperatures above 700°C, the ratio between the amount of N in the total nitrides and the amount of N contained is nearly 100%), and above 700°C, AtN' precipitation is promoted. Heading fc (see Figure 1). That is, in the present invention, by possessing At, r→α
The transformation rate is faster and the lower limit winding temperature is lower to remove the negative influence of the α' phase, and the lower limit winding temperature is lower at which all N becomes nitride.Also, the rough rolling process promotes AtN precipitation, so total nitridation is possible. The ratio of AtN in the material can be increased. Therefore, in the case of the method of the present invention, the winding temperature of 850°C or higher, which was conventionally necessary to improve the r value and mechanical properties, is reduced to 70°C.
It became possible to reduce the temperature to 0°C or higher. In addition, in the conventional method, ridging deteriorates at a winding temperature of 700°C or higher, but as explained in the rough rolling process, the recrystallization during rough rolling makes the crystal grains finer and more random. It became possible to raise the upper limit of the winding temperature for ridging to 850°C (see Figure 2). still,
After winding a hot-rolled coil, if it is not left to cool but is gradually cooled or kept at that temperature, the appropriate winding temperature range is 700 to 850.
It goes without saying that the lateral pressure shifts from ℃ to ℃. Next, we will discuss the surface properties. As mentioned above, when winding is carried out at a high temperature of 850° C. or higher, the grain boundary cracking phenomenon 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 overlapped parts and torn parts remain even after the final annealing, resulting in serious surface defects in the finished board. The intergranular cracking phenomenon that causes such surface defects is not so remarkable when the hot rolling winding temperature is 850° C. or lower. However, 700 according to the invention
Even within the winding temperature range of ℃ to 850℃, the high temperature side (800℃
(above), some grain boundary cracking phenomenon occurs. 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 α required to obtain a material with high workability is
Since metallurgical phenomena such as the decomposition of the ' phase and the precipitation of AtN require time, a finished sheet with high workability cannot be obtained if water cooling is carried out at the hot rolling winding temperature point. In research to date, 800
When a hot-rolled coil wound at ℃ was left to cool for 30 minutes and then cooled, and when a hot-rolled coil wound at 750℃ was left to cool for 60 minutes and then water-cooled, the material quality of the finished sheet was not satisfied. It has been found that almost no intergranular cracking occurs and a finished plate with extremely good surface properties can be obtained. 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 scales are different from those in the case of normal hot-rolled sheet descaling in which hot-rolled sheets are annealed and descaled. Descaling is easy, but for more effective descaling, mechanical descaling such as light reduction of 10 inches 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. As a pickling solution)
IINO3/HF-? When pickling is performed with an acid solution mainly containing H2SO4 or HCl, grain boundary corrosion does not occur after pickling, the degree of unevenness is small, and surface defects are less likely to occur even if polishing is not performed after pickling. 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 r value, reduce ridging, and prevent surface defects. 7 value can be obtained by developing a (111) texture in the final annealing process, but according to the research of the inventors, among the three effects mentioned above, in the special cold rolling process, the plastic deformation due to cold rolling is It has been found that by reducing macroscopic shear deformation, a (111) texture develops in the final annealing step, and further, this macroscopic shear deformation can be reduced by increasing the cold rolling roll diameter. According to detailed research by the present inventors, rolling with a cold rolling mill with a work roll diameter of 300i+i+φ or more has an r value of approximately 10 to 30 % improvement was observed. This V value improvement effect accounts for 60% of the total rolling amount to be cold rolled.
If the above is rolled with a large-diameter roll with a roll diameter of 300, - or more, the effect will not change even if the reduction amount of the remaining material is rolled with a small-diameter roll, so the large-diameter roll cold rolling ratio should be set to 60% or more. This is what I did. 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 (100) texture that exists in the as-hot-rolled state is reduced. Even after cold rolling and annealing, a large proportion of steel remains in that form without recrystallizing, resulting in poor ridging properties. This (100) texture is the final stable orientation of cold rolling and recrystallization, and conversely, when the roll diameter is large and the cold rolling rate is high, it is cold rolled with small diameter rolls. It is important to reach a stable direction as soon as possible, reverse K (100
) The degree of accumulation of texture becomes higher in the case of small-diameter roll rolling, and the ridging property deteriorates. That is, the degree of accumulation of the (100) texture that deteriorates ridging property has a correlation between the cold rolling rate and the roll diameter.
As the diameter of the roll increases, 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 the (100) texture becomes the minimum value also differ depending on the state 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 accumulation of (1oO) texture than annealed material, so the degree of accumulation of (100) texture after finish 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, but rolls with a maximum diameter of about 700 mm are used,
Even when rolled at a high rolling reduction of about 90%, no deterioration in ridging property occurs. In the present invention, the first stage of cold rolling is 300mmφ or more and 700myφ
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 properties, it is advantageous to use a large-diameter roll in the first stage and a small-diameter roll in the second stage. The reason is as follows. First, if the first stage is cold rolled with a large diameter roll of 300 m or more, even if unevenness occurs on the steel plate surface during the pickling process as described above,
If the irregularities are not extremely large, the shearing deformation of the surface layer is smaller than in the case of cold rolling with small diameter rolls, so the convex parts collapse into the four parts, causing surface defects due to the occurrence of overlapping parts. This eliminates the need for a polishing step to smooth out uneven portions before cold rolling. 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,
The drawback is that the surface gloss required for stainless steel sheets cannot be obtained. The reason for this is that when high-speed cold rolling is performed using large-diameter rolls, the lubricating oil film at the roll bite is thicker, depending on the viscosity of the lubricating oil, and the oil existing in the recesses on the surface of the steel sheet increases. This is because depressions called so-called oil bits tend to occur 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, it is possible to obtain the shape and surface properties of stainless steel, but it is not economical to change the conditions each time stainless steel rolling is performed. 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 with a small diameter roll of 100 mφ or less and a lubricating oil suitable for cystine-less steel, and the roll surface roughness is adjusted to the final r-ge of the cold rolling ridge stage, it is possible to roll ordinary steel. In addition to being able to use the same conditions as they are, the oil bits are repaired and the surface roughness is reduced, making it possible to obtain a stainless steel plate with excellent gloss. 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, so rolling with small-diameter rolls is performed afterward. Even if this is done, the above-mentioned overlap υ does not occur, and no surface defects due to overlap are observed. In addition, by using small diameter rolls, the contact area between the roll and the rolled material is reduced, which prevents the occurrence of oil film breakage and oil bits.If the roll surface roughness is made fine, the surface gloss can be reduced. It can be made of good thin steel plate. In this case, the smaller the diameter of the roll, the better, but since the effect can be exhibited if it is 100 mφ or less, it is limited to 100+w+φ or less of the small diameter roll following cold rolling with the large diameter roll. 1
The larger the amount to be cold-rolled with rolls of 00■φ or less, the rougher the oil bits produced by large-diameter roll rolling.
However, the amount of reduction by the small diameter rolls can be improved by rolling at least 1 inch thicker than the sheet thickness before cold rolling. The cold rolling according to the method of the present invention is carried out at a factory that produces both ordinary steel thin plates and stainless steel thin plates, that is, ordinary rolling is carried out in a tandem mill, and stainless steel thin plates are carried out in a dedicated Sendzimir cold rolling mill. At the factory, the stainless steel is rolled as it is in the tandem cold rolling mill used for regular rolling, and then rolled in the Sendzimir cold rolling mill. Compared to rolling with an inter-rolling mill, not only is the productivity of the cold rolling process significantly improved, but the workability (〒 value,
This improves quality, such as improving the ridging property and eliminating the need for a special polishing process to reduce unevenness on the board surface after pickling.
It can be said that this cold rolling technology is extremely superior in terms of both cost and cost. The cold rolling mill that can achieve the object of the present invention may be a combination of the existing tandem cold rolling mill described above and a Sendzimir cold rolling mill, or a roll on a stand at the rear stage of the tandem cold rolling mill. A cold rolling mill with small diameter rolls may be used. Next, the reason why the final annealing is specified to be within 60 seconds at a temperature range of 800 to 1000°C is to particularly lower the yield point and improve workability. In the case of the method of the present invention, A in the rough rolling process and the hot rolling winding process.
Although tN precipitation is promoted (see Figure 1), about half of the total N amount is Cr 2N. For this reason, 1
When final annealing is carried out for a short period of time within seconds, part of the Cr2N decomposes, and the α' phase remaining during the hot-rolling process decomposes to form solid solution N, resulting in a lower yield point. . However, according to the present invention, final annealing is performed at 800°C or higher and 1000°C.
When annealing is performed at the following temperature for 1 second to 60 seconds,
Solid solution N generated by decomposition of Cr2N and α' phase is fixed as AtN, and a low yield point can be achieved. The basic component of the steel of the present invention is At from 0.08% to 0.5%.
The reason why AtO is contained in the range of 0.08% is that (i) cold rollability decreases, leading to edge cracking, breakage, etc. in the cold rolling process, making stable cold rolling impossible; The surface irregularities during pickling become larger, and as if these irregularities were overlapped during cold rolling, the overlapped and thinner parts could be torn off, resulting in surface flaws on the final product. 1ii) The r value decreased. 1v) This is because defects such as a significantly high yield point and a decrease in elongation occur.
Preferably, these defects can be prevented by adding 0.1 or more. The higher the amount of At added, the better, but 0.5
Even if it is added in excess of 0.5%, the effect is slight, but it becomes almost saturated, so the upper limit was set at 0.5%. (Examples) The present invention will be described in detail below according to examples. Example A 250 m thick ferritic stainless steel slab with the ingredients shown in Table 1 was heated to a temperature of 1190°C, and then hot rolled as shown in Table 2 to obtain a 3.0-thick hot rolled slab. I made it into a coil. After shot blasting 6 coils of these hot-rolled coils, 300gAL:D at a temperature of 90°C.
40 seconds at H2SO4 concentration followed by 1509/l HNO
Descaling was carried out at a temperature of 50°C for 40 seconds at a concentration of . Then, after cold rolling to 1-thickness in a 5-stand tandem cold rolling mill with a work roll diameter of 500+w+φ,
4 on a Sendzimir cold rolling mill with a roll diameter of 5wIφ.
Cold rolling was performed to a thickness of 26) 0.4 mm in passes. Then, annealing was performed at a temperature of 875° C. for 30 seconds. Furthermore, for comparison, hot-rolled coil ■ was prepared using the conventional method (840℃
After annealing the hot-rolled sheet for 1 hour, the sheet was processed into a thin steel sheet with a thickness of 0.4 hours using a Sendzimir cold rolling mill alone. Table 3 summarizes the values, ridging properties, yield stress, cold rollability, etc. of the thin steel sheets produced in this manner. Third
From the table, compared to the characteristics of the ■ coil manufactured by the conventional manufacturing method, the ■, ■, ■ coil manufactured by the method of the present invention has better ridging characteristics and 1 value, and can be used as deep drawing υ application steel. What you can do is recognized. Furthermore, from the manufacturing conditions of the present invention,
The winding temperature is low ■ In the case of coils, the ridging properties are good, but as a material for deep drawing, there is a problem that the 1 value is slightly low.
The winding temperature is high, but the time between passes in the rough rolling process is short.■ Coils have a high r value, but have poor ridging properties and low At content. ■ Coils have poor cold rollability and poor surface texture. It can be seen that the yield stress is also high, and the ridging properties and 〒 values do not satisfy the conditions for steel for deep drawing applications. (Effects of the Invention) As detailed above, according to the present invention, it is possible to omit 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. This is because it is possible to provide a ferritic stainless steel sheet with no surface defects and excellent workability, especially deep drawability, through an extremely economical manufacturing method in which the main cold rolling is performed using a highly productive tandem cold rolling mill. The industrial benefits are extremely large. 4. Brief explanation of the drawings Figure 1 shows a slab of 5US430 steel containing 0.13% At, heated at 1200°C and then hot rolled to a thickness of 3.0mm. This is a diagram showing precipitation behavior with respect to hot rolling winding temperature, and shows the amount of N in total precipitates and At
This is a diagram showing the amount of N precipitated as N as a ratio (A) to the total amount of N contained. The solid line in the diagram shows the case of the hot rolled coil manufactured by the hot rolling method of the present invention, and the broken line shows the case of the hot rolled coil manufactured by the hot rolling method of the present invention. The case of a hot-rolled coil (a, +) manufactured by the hot rolling method (rough rolling) with a 4-strip time of 15 seconds or less is shown. Figure 2 shows 5U containing 0.13% At.
3. A slab of 8430 steel was heated at 1200°C and then hot rolled. A hot-rolled coil with a weight of 0.4 wg was prepared, followed by pickling and cold rolling to obtain a cold-rolled coil with a weight of 0.4 wg.
This is a diagram showing the rolling height and r value of a product sheet manufactured by annealing for 5 seconds against the hot rolling winding temperature. The dashed line indicates the case produced by the normal hot rolling method (rough rolling process with a rolling time of 15 seconds or less) and the cold rolling method of the present invention. is the normal hot rolling method and the normal cold rolling method (work roll diameter 100 was
φ or less).

Claims (1)

[Claims] 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. 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, finishing hot rolling is performed at a finishing temperature of 850°C or higher, and rolling is performed at a temperature range of 700 to 850°C. After removing the material, descaling is performed, and then the work roll diameter is 300 m.
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 diameter of mφ or more, and then the remaining rolling amount is rolled by a cold rolling machine with a work roll diameter of 100 mmφ or less. Rolled, then 800-1000
A method for producing a ferritic stainless steel sheet with excellent surface texture and workability, characterized by carrying out final annealing in a temperature range of 1 to 60 seconds at a temperature of 1 to 60 seconds.