JPS59226120A - Production of ferritic stainless steel sheet having excellent workability - Google Patents

Abstract

PURPOSE:To produce a ferritic stainless steel sheet having excellent workability by cold rolling a hot-rolled sheet of a ferritic stainless steel contg. specifically composed. Al and subjecting the steel sheet to soaking for short time at an adequate temp. then to finish annealing. CONSTITUTION:A hot-rolled steel sheet of a ferritic stainless steel contg. 0.08- 0.5% Al is subjected to soaking within 60sec in a temp. range of 850-900 deg.C in finish annealing after cold rolling of the hot-rolled sheet without annealing, by which the ferritic stainless sheet having a good (r) value and ridging and mechanical properties is obtd. Good mechanical properties are obtd. by the above-mentioned soaking under the conditions of about 60sec at 850 deg.C and about 20sec soaking at 900 deg.C. The effect is not enough at <=850 deg.C and the soaking at >900 deg.C is undesirable for the (r) value and ridging. If the content of Al is <0.08%, the (r) value is low and if >0.5%, the effect is basically the same and such content is uneconomical.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ferritic stainless steel thin plate with excellent workability, and more specifically, a method for manufacturing a ferritic stainless steel thin plate, typified by 5US430 steel containing 0.08 to 0.5% At. This relates to a manufacturing method.

Ordinary 8US430 type ferritic stainless steel sheet with a ferrite content of 0.08% or less is a hot-rolled sheet with approximately 800~85%
It is generally manufactured by box annealing at a temperature of 0℃ for 2 hours or more, followed by cold rolling, and then annealing for a short time at a temperature of usually 820-850℃, which improves the R value and ridging properties of the product. is known to hardly change depending on the soaking temperature and soaking time. In this hot-rolled sheet annealing process, the α' phase that existed in the hot-rolled sheet changes to a ferrite phase + carbide. However, after hot-rolled sheet annealing, it becomes a ferrite phase and a carbide phase. If such a material is heated after cold rolling, recovery and recrystallization will occur, and the microstructure after recrystallization will be uniformly glazed grains), but the grain size is almost unaffected by the soaking temperature and time. It will not be affected and will remain constant. The temperature at which recrystallization is completed varies slightly depending on the ingredients, hot rolling conditions, and cold rolling reduction ratio, but if the material temperature reaches 800°C or higher, recrystallization will occur regardless of the soaking time; It was found that almost constant r value and ridging characteristics can be obtained regardless of time.

However, when a hot-rolled sheet of 5US430 type ferritic stainless steel containing a large amount of μ is cold-rolled and recrystallized without hot-rolled sheet annealing, the recrystallization temperature is the same as that of the cold-rolled sheet after hot-rolled sheet annealing. Polycrystalline grains that are heated to a higher temperature than those in the case are not mixed grains, and if they are completely recrystallized, the size of the crystal grains is almost unaffected by the soaking temperature and soaking time and remains constant. , r value, and ridging properties vary greatly depending on the soaking temperature and time.In this case, the annealing process that satisfies the r value and ridging properties at the same time is a soaking temperature of 850 to 900°C and a soaking time of 60 seconds. The present invention was completed by confirming that the high-temperature, short-time annealing was within

That is, the gist of the present invention is At O, 08%
After cold rolling a hot-rolled sheet of ferritic stainless steel containing ~0.5 modulus without annealing the hot-rolled sheet, it is necessary to perform finish annealing in a temperature range of 850 to 900°C within 60 seconds. A method for producing a thin ferritic stainless steel plate with excellent workability, which involves heating.

The present invention will be explained in detail below.

In the present invention, a hot-rolled sheet of At-containing ferritic stainless steel, which is the target silver of the present invention, is cold-rolled without hot-rolled sheet annealing, and then subjected to finish annealing. The reason why the temperature and time were limited to 850 to 900°C and within 60 seconds is as follows.

The relationship between the above-mentioned soaking conditions and product r value is as follows: soaking temperature 87
In the range up to 5°C, it improves as the temperature increases over a longer period of time, and when it exceeds 875°C and reaches 900°C, it gradually deteriorates, but it remains at a higher level than in the case of a soaking temperature of 850°C or lower. In addition, the longer the soaking time is, the more remarkable the improvement in r value is, but this is only when the soaking temperature is approximately 875°C or lower;
When the temperature exceeds .degree. C., an improvement in the r value is only observed up to a soaking time of 10 seconds, and even if the soaking time is increased beyond that, the r value is only slightly improved.

The influence of the final annealing cycle on the ridging properties is complex, but when annealing is performed at various temperatures with a constant soaking time, the least glue song is shown at a certain soaking temperature, and when it is lower than that temperature. There is a tendency that the optimal temperature shifts to the higher temperature side as the soaking time is shorter, and the optimal temperature range is narrower, and the reduction in ridging is greater. For example, when the soaking time is as long as 60 seconds, the relative value of ridging is relatively large, 850 to 87
It shows a nearly constant value in the range of 5℃, and on the contrary, the ridging tends to deteriorate at temperatures exceeding 875℃ or below 850℃, and when the soaking time is as short as 10 seconds, the soaking temperature is 875℃. In a relatively narrow temperature range of ~900°C, the ridging shows a low value, and this absolute value is lower than the soaking time of 6
This is better than the ridging value obtained by annealing at the optimum temperature for a long time of 0 seconds.

In the case of a thin sheet obtained by cold rolling a 5US430 type ferritic stainless steel hot-rolled sheet containing AA without hot-rolled sheet annealing, the r value and the The reason why the ridging characteristics change drastically is considered as follows. 5US430 type ferritic stainless steel containing At has less hard phases such as martensite phase and bainite phase in the as-hot-rolled state compared to normal 5US430 type ferritic stainless steel that does not contain At. However, there are about 10 coefficients. This hard phase is elongated in the rolling direction in the subsequent cold rolling process, and decomposed in the final annealing process to form a ferrite phase and carbide), and this ferrite phase also recrystallizes at a temperature higher than the recrystallization temperature. First, the reason why the r value improves with high-temperature annealing is that the carbides separated from the hard phase and the fine carbides that were already present aggregate, and these carbides interfere with the activity of dislocations that become active during plastic deformation. This is because the plastic deformation becomes easier due to the loss of the
It is thought that the r value is improved due to the precipitation of N. When hot-rolled sheets are annealed, the size and dispersion of carbides are determined during the hot-rolled sheet annealing process, and solid solution N is also fixed by Cr nitride and a small amount of At, etc. In the process, the dispersion state of these precipitates does not change depending on the annealing method, so once recrystallization is completed, the r value does not change regardless of the annealing conditions. When the hot-rolled sheet annealing temperature exceeds 875°C, the r-value gradually deteriorates because the grains begin to dissolve into solid solution again, and the carbides begin to dissolve into solid solution again.
This is because the particles become fine again, and (ma) the amount of solid solution C and N in the IJ wax increases.

Next, regarding the ridging property, the steel subject to the present invention deteriorates when the annealing temperature is low. ? q
precipitates and the recrystallization completion temperature becomes high, so complete recrystallization does not occur and the randomization of the texture is insufficient. Furthermore, as the temperature rises, the aging properties tend to deteriorate because the fine carbides re-dissolve into solid solution, and the fine grains that existed at the grain boundaries of the ferrite phase disappear, and the adjacent grains disappear. Since the elongated ferrite phase is often composed of low-angle grain boundaries, it essentially acts in the same way as coarsened core crystals, deteriorating the ridging properties. In addition, the M of the target steel of the present invention is set to 0.08% or more because 0.08%
If the temperature is less than
Furthermore, surface defects called sparkling scratches are likely to appear.The reason why the content was limited to 0.5% or less is that even if it is contained in a larger amount, the actual effect will not change and it is not economical. . The reason why the soaking time is limited to 60 seconds or less is because the r value and ridging properties do not improve even if heated for a longer period of time, and if the temperature is high, they will deteriorate.

The present invention will be specifically described below according to examples.

Example 1 5US4 containing At with a thickness of 2.70w shown in Table 1
A hot-rolled sheet (4) of Type 30 ferritic stainless steel was reduced to a thickness of 1.3 mm without annealing the hot-rolled sheet. Owts and 0.4m
It was made into a cold-rolled sheet. These cold-rolled sheets were heat-treated in a salt bath, and after the heat treatment, the r value and ridging were measured. For comparison, hot-rolled sheet (B) of 5US430 type ferritic stainless steel containing a small amount of ht was heated at 840°C x 4
After annealing the hot-rolled sheet for hr, a cold-rolled sheet with a thickness of i and 0.4 m was subjected to the same heat treatment, and the r value and ridging height were measured. The measurement results of the ridging height and r value are shown in Table 2, and when the target steel of the present invention is heat treated within a temperature range of 850 to 900°C for 60 seconds or less, both the r value and the ridging property are good. I understand.

Table 1 Procedural amendment (voluntary) for the main chemical components (wt%) of the sample material March 10, 1980 Kazuo Wakasugi, Commissioner of the Patent Office1, Indication of the case, Patent Application No. 098512, 1982, Invention Name of Manufacturing Method for Ferritic Stainless Steel Thin Plate with Excellent Workability 3, Relationship with the Amendment Case Patent Applicant: Tokyo Group 5, No. 1-16-3, Otemachi 2-chome, Chiyogawa-ku (665)
New 1" Takeshi, Representative of Honshu Steel Co., Ltd. 1) Yutaka 4, Agent Address: 2-4-1-6, Marunouchi 2-4, Chiyoda-ku, Tokyo 100, Japan, Full text of the amended lighting specification and drawings (2) Figure 1 and Figure 2 is supplemented as shown in the attached sheet.

Description 1. Name of the invention. Method for manufacturing a ferritic stainless steel sheet with excellent workability. 2. Claims: A hot-rolled sheet of ferritic stainless steel containing AtO, 08% to 0.5%. A method for manufacturing a ferritic stainless steel sheet with excellent workability, characterized in that after cold rolling without annealing, soaking is performed within 60 seconds in a temperature range of 850 to 900° C. during final annealing.

3. Detailed Description of the Invention The present invention relates to a method for manufacturing a thin ferritic stainless steel plate with excellent workability, and more specifically, a method for manufacturing a thin plate of ferritic stainless steel such as SUS 430 containing 0.08 to 0.5 inches of ALf. It concerns the manufacturing method.

Normal SUS 430 type ferritic stainless steel sheet with AA content of 0.08% or less has a hot-rolled sheet size of 800~
It is generally manufactured by box annealing at a temperature of 850℃ for 2 hours or more, followed by cold rolling, and then annealing for a short time at a temperature of usually 820~850℃.The r value and ridging properties of the product are It is known that the soaking temperature and soaking time hardly change.

In this hot-rolled sheet annealing step, the α' phase present in the hot-rolled sheet changes to a ferrite phase decacarbide, and becomes a ferrite phase and a carbide phase after the hot-rolled sheet annealing. If such a material is heated after cold rolling, recovery and recrystallization will occur.The microstructure after recrystallization becomes uniformly glazed grains, and the crystal grain size is almost unaffected by soaking temperature and time and remains constant. becomes. The temperature at which recrystallization is completed varies slightly depending on the ingredients, hot rolling conditions, and cold rolling reduction ratio, but if the material temperature reaches 800°C or higher, recrystallization will occur regardless of the soaking time, and if crystallization occurs, soaking will begin. It was found that almost constant r value and ridging characteristics were obtained regardless of temperature and time. Furthermore, it has been found that mechanical properties such as yield strength, yield point elongation, tensile strength, total elongation, and uniform elongation can be kept almost constant by recrystallization.

However, hot-rolled sheets of SUS 430 type 7 elite stainless steel containing a large amount of At, hot-rolled and calcined,
/ The recrystallization temperature when cold rolling without dulling and recrystallization annealing is lower than that when cold rolling is performed after hot-rolled plate annealing.The crystal grains also become mixed grains. The r value and ridging properties change significantly depending on the soaking temperature and time.The annealing condition that satisfies the r value and ridging properties at the same time is a soaking temperature of 8.
The present invention was completed by confirming that high-temperature, short-time annealing was performed at 50 to 900°C and soaking time was within 60 seconds. Furthermore, even after recrystallization is completed, the mechanical properties change significantly depending on the soaking temperature and time.
It was discovered that the higher the temperature in the temperature range of ~900°C, and the longer the soaking time is 60 seconds or less, the more effective it is, and the present invention was completed.

That is, the gist of the present invention is At0.08%~
After cold rolling a hot-rolled sheet of ferritic stainless steel containing 0.5%'e without annealing the hot-rolled sheet, soaking is carried out within 60 seconds at a temperature range of 850 to 900°C for finish annealing. We will introduce a manufacturing method for ferritic stainless steel thin sheets with excellent special workability.

The present invention will be explained in detail below.

In the present invention, a hot-rolled sheet of At-containing ferritic stainless steel, which is the target steel of the present invention, is inter-rolled without hot-rolled sheet annealing, and then finish annealed at K, the soaking temperature of finish annealing, and The reason why the time i was limited to 850 to 900°C and within 60 seconds is as follows.

The relationship between the above-mentioned soaking conditions and product r value is as follows: soaking temperature 87
In the range of up to 5°C, high temperature and long-time annealing is performed, and in temperatures exceeding 875°C and up to 900'C, deterioration occurs slowly, but at a higher level than in the case of soaking temperatures of 850°C or lower. In addition, the longer the soaking time is, the more remarkable the improvement in r value is, but this is only when the soaking temperature is approximately 875°C or lower;
When the temperature exceeds 5℃, the r value improves after soaking time 10.
Even if the soaking time is increased by up to seconds, the r value will only improve slightly.

The effect of the final annealing cycle on the ridging properties is complex, but when annealing is performed at various temperatures with a constant soaking time, a certain soaking temperature exhibits the least glue zinc, and lower temperatures There is a tendency that the optimal temperature shifts to the higher temperature side as the soaking time is shorter, and the optimal temperature range is narrower, and the reduction in ridging is greater. For example, when the soaking time is as long as 60 seconds, the relative value of ridging is relatively large, 850 to 87
It shows a nearly constant value in the range of 5℃, and on the contrary, the ridging tends to deteriorate at temperatures exceeding 875℃ or below 850℃, and when the soaking time is as short as 10 seconds, the soaking temperature is 875℃. In a relatively narrow temperature range of ~900°C, the ridging shows a low value, and this absolute value is lower than the soaking time of 6
This is better than the ridging value obtained by annealing at the optimum temperature for a long time of 0 seconds.

The relationship between the soaking conditions for the steel of the present invention and the mechanical properties of the product is as follows. Figure 1 schematically shows the typical relationship between soaking time, soaking temperature, and yield strength. The comparative product in the figure is a material obtained by box annealing and then rolling annealing a hot rolled sheet of ordinary 430 steel with an At content of 0.08% or less. As is clear from the figure, the influence of soaking time and temperature is small for the comparative product, but in the case of non-inventive steel, it can be seen that there is an optimum combination of soaking time and temperature in order to obtain a low yield strength. The optimum combination conditions also vary depending on the hot rolling conditions, particularly the slab heating temperature and winding conditions.

In other words, when the slab heating temperature is 1150°C or lower, the optimum soaking conditions are lower and lower than when the slab is heated to a high temperature of 1200°C or higher.
It changes to the short time side, and the influence of soaking temperature conditions becomes smaller, showing behavior similar to the comparative product. Although the influence of the winding temperature is not as remarkable as that of the slab heating temperature, increasing the winding temperature has the same effect as lowering the slab heating temperature. The effect is even smaller b, but the rate of temperature rise and cooling at the neck that reaches the soaking temperature also has an effect, and slow heating and cooling speeds have the same effect as lengthening the soaking time. .

As mentioned above, the optimal combination of temperature and time to lower the yield strength varies depending on the previous history of the material, but the highest temperature and long-term annealing is considered to be high-temperature slab heating of 1200°C or higher, and 600°C. In order to obtain a low yield strength of 35 kIf/m+n2 or less when using a hot-rolled sheet that has undergone all the following low-temperature rolling as a starting material and rapidly raising the temperature by salt bath heating, etc., at a soaking temperature of 825°C, it is necessary to more than seconds, 8
30 seconds to 60 seconds or more at 50℃ to 875℃, 900℃ to
At 925° C., a soaking time of 20 seconds or more is sufficient. 95
At 0°C, soaking for about 10 seconds lowers the yield point, but if the soaking time is longer than this, the yield point increases again, which is not preferable. This is due to r-phase precipitation.

Figure 2 schematically shows the typical relationship between soaking time, soaking temperature, and elongation at yield point. It can be seen from the figure that the behavior of yield point elongation is almost similar to that of yield point. hot rolling conditions,
The effects of temperature rise and cooling rate also do not reach the yield point and almost correspond to the effects. In Figure 2, when the soaking temperature is high, the yield point elongation disappears in both the comparative product and the inventive product due to r-phase precipitation.In this case, the yield strength increases to 9 and the elongation decreases. So I don't like it.

Total elongation, uniform elongation, and tensile strength are all affected by soaking temperature conditions very little for conventional products, but for the steel of the present invention, the soaking temperature and time have a large effect, and it can be annealed at high temperatures for a long time compared to conventional annealing. It is improved by doing this.

Specifically, taking into consideration the previous history of the material, we will
If soaked for up to 60 seconds at a temperature below 00℃,
It is possible to obtain good values on the same level as conventional products.

In the case of a thin plate obtained by cold rolling an SO8430 type ferritic stainless steel hot-rolled plate containing Atwo without hot-rolled plate annealing, the r value, ridging properties, and mechanical properties are significantly improved even after recrystallization. The reason for the change is thought to be as follows. A
In SO8430 type ferritic stainless steel containing Atf, ordinary SUS 43 which does not contain Atf
Compared to type 0 ferritic stainless steel, hard phases such as martensitic phase and bainite phase are present in the as-hot-rolled state, although there are fewer hard phases such as martensite phase and bainite phase. This hard phase is elongated in the rolling direction in the subsequent cold rolling process, and decomposed in the final annealing process to form a ferrite phase and carbide, and this ferrite phase also recrystallizes at a temperature higher than the recrystallization temperature. First, the reason why the r value improves with high-temperature annealing is that carbides separated from such hard phases and fine carbides that were already present aggregate, and these carbides hinder the activity of dislocations that become active during plastic deformation. It is thought that the r value is improved because this action is eliminated and plastic deformation becomes easier, and because AtN is precipitated during annealing. When hot-rolled sheet annealing is performed, the size and dispersion of carbides are determined in the hot-rolled sheet annealing process, and solid solution N is also fixed by nitriding Or or a small amount of At, etc., resulting in poor finishing. In the annealing process, the dispersion state of these precipitates does not change depending on the annealing method, so once recrystallization is completed, the r value does not change regardless of the annealing conditions. When the hot-rolled sheet annealing temperature exceeds 7b x 875°C, the r value gradually deteriorates because AtN begins to dissolve completely again, carbides re-dissolve, become finer again, and the amount of solute C and N in the matrix decreases. This is because it becomes expensive.

Next, regarding ridging properties, the reason for deterioration when the annealing temperature is low is that in the case of the target steel of the present invention, AtN precipitates during annealing, and the recrystallization completion temperature becomes high, so complete recrystallization does not occur. First, this is due to insufficient randomization of the texture.

Furthermore, as the temperature rises, the aging properties tend to deteriorate.As the fine carbides re-dissolve, the fine grains existing at the grain boundaries of the old ferrite phase disappear, and the adjacent elongated ferrite phase Since they are often composed of small-angle grain boundaries, they act essentially in the same way as if coarse crystals have become coarser, and the ridging properties deteriorate.

Next, the reason why the mechanical properties of the steel of the present invention vary significantly depending on the annealing conditions will be explained. The main metallurgical changes in the final annealing process of the steel of the present invention are: (1) recrystallization, (2) separation from α' phase to α decacarbide and the associated release of free N, and (2) Cr.
2. Release of free N due to decomposition of N, etc.; ■■, ■Precipitation of AtH due to reaction of At with the N released in ■■ and free N that was in supersaturated solid solution before main annealing; ■ Ferrite matrix. Solubility change of solid solution C and N, ■ Agglomeration or re-solid solution of micro carbides, ■ Precipitation of γ phase (when the annealing temperature is high)
This is thought to be due to the transformation of the γ phase to the α′ phase with cooling.

First, the relationship between changes in yield strength, these metallurgical changes, and changes in annealing conditions will be explained. When the annealing temperature is low (
For example, 775℃~800℃, Fig. 1 (-) Osho),
The yield point is significantly higher than that of conventional products, and as the annealing time increases, the yield point decreases mainly due to ■
This is related to the recrystallization behavior of the steel, and while the conventional steel completely recrystallizes even after such low-temperature annealing, the steel of the present invention
This is because recrystallization is insufficient when the annealing temperature is low because the recrystallization temperature is high, and the reason why the recrystallization rate decreases as the soaking time increases is because the recrystallization rate increases. When the annealing temperature is slightly high (e.g. 850°C to 875°C, the first
(corresponding to figure (b)) is mainly ■.

This corresponds to the change in solid solution N in the ferrite matrix due to (1) and (2). In the conventional product, due to long-time box annealing in the ferrite region of the hot-rolled sheet, the α' phase has disappeared, and most of the N is fixed in the form of AtN and Cr2N, and solid solution C,
N is a constant low value (the amount of C, N, and phase drawn is almost in equilibrium with the box annealing temperature (middle 840°C)), and Cr2N decomposes slightly under such annealing temperature conditions. Although tree N is released, since the number is a little small, the increase in solid solution N is small, and it is thought that the increase in yield strength is proportionally small. In the case of the steel of the present invention, free N increases in the ferrite matrix due to the release of free N due to the decomposition of the α' phase and the release of 7 LiN due to the decomposition of Cr2N, and as a result, free N increases in proportion to the soaking time. yield strength increases. As the soaking time increases further, the yield strength decreases because the solid solution N in the ferrite matrix is fixed as AtN by transforming from α' phase to α phase.
The main cause is thought to be due to a decrease in the strength of the steel, and a further decrease in strength due to agglomeration of fine carbides.

When the annealing temperature is higher (e.g. 90°C to 925°C,
(corresponding to Fig. 1 (c)) are also mainly ■ and ■.

This corresponds to the change in solid solution N in the ferrite matrix (2). In this case, if the soaking time is longer than a certain level,
A reversal phenomenon occurs in which the product of the present invention has a lower yield strength than the comparative product. This is because the conventional product has a low At content.
, the free N released by the decomposition of Cr2N is At
Since N is small at 0.08% or less, it is not fixed in the form of AtN, so the solid solution N in the matrix increases and the yield strength increases.
The N released by the decomposition of N is mostly At-containing rats, and A
Since this is the temperature range in which tH is likely to precipitate, it is fixed as AtN, and the solid solution N in the matrix δ is lower than that of the conventional product, resulting in a reverse phenomenon in which the yield strength is lower than that of the conventional product. In this case, the reason why the yield strength decreases as the soaking time increases is due to the decomposition of the α' phase and the precipitation of ALN.
This is thought to be because the longer the soaking time is, the more the amount increases.

When the annealing temperature is extremely high (e.g. 950°C to 1000°C)
℃ or higher (corresponding to FIG. 1(d)), the longer the soaking time, the higher the yield strength of both the conventional product and the product of the present invention. This is because, in addition to the aforementioned ■→■, ■→■ is also involved. That is, γ
Even in the temperature range below phase precipitation, C, N
When the solubility of C and N increases, C and N become solid solutions again, and when the cooling rate is fast (above air cooling), the supersaturation of C and N in the ferrite matrix increases, the precipitation of fine carbide phases occurs during the cooling process, and yielding occurs. The strength increases. Furthermore, at higher temperatures, the γ phase precipitates and the α' phase is lost during the cooling process, resulting in an increase in yield strength mainly due to the α' phase.

Like the yield strength, the yield point elongation also changes mainly based on the change in solid solution N in the ferrite matrix, and can be summarized using the same metallurgy as the yield strength.

In other words, the reason why no yield point elongation is observed when the annealing temperature is low is mainly due to the unrecrystallized portion, and the reason why there is no yield point elongation even when the annealing temperature is extremely high is due to the γ during annealing.
This is due to the formation of an α' phase shadow due to the precipitation of the phase, and the subtle changes in yield point elongation depending on the annealing conditions in the intermediate temperature range are due to the decomposition of the α' phase and Cr2N formed during hot rolling. This is determined by the relationship between the increase in Schiffly N and the decrease in free N due to the precipitation of AtN.

Changes in tensile strength, total elongation, and uniform elongation are mainly due to the decomposition of α' phase → ferrite + carbide. The longer the temperature and longer time, the more the ferrite matrix is cleaned and the carbides aggregate and coarsen, resulting in an increase in elongation. , the tensile strength will decrease. However, it goes without saying that if the annealing temperature is too high, the elongation decreases and the tensile strength increases due to the formation of the α' phase based on the redecipitation of the γ phase. The above metallurgy
As is obvious from the explanation, the lower the slab heating temperature is, the more AtN is already precipitated in the slab heating state, and the lower the slab heating temperature is about 1150°C or lower, the more the γ phase that exists during the slab heating. As a result, the α' phase decreases in the as-hot-rolled state, and a hot-rolled sheet hot-rolled in such a state has an A/1.
It is fixed in the shape of N, and the N should be fixed in the final annealing process.
Since the amount of α′ phase is small and it is easy to transform the α′ phase into ferrite + carbide, the soaking temperature required to obtain good mechanical properties is lower than that of high-temperature slab heating materials. This means that the soaking time can be much shorter. The longer the time from extraction after heating the slab until hot rolling and winding, and the higher the winding temperature, the more precipitation of ALN will be promoted.
Since the phases are also reduced, lower soaking temperatures and shorter soaking times are required to obtain good mechanical properties.

If the rough rolled piece is kept warm in a coil box or the like at the start of finish rolling after rough rolling, it will reach 60
It goes without saying that if so-called delay rolling, such as a period of time longer than 2 seconds, is performed, the γ→α transformation will be promoted in this step, and the precipitation of ktN will also proceed, so that the annealing conditions in the final annealing step can be relaxed. Although the hot rolling conditions are not particularly important, the slower the heating and cooling rate during final annealing, especially the speed from 800°C or higher to the soaking temperature, the lower the soaking temperature, and even if the soaking time is short, it is good. It becomes possible to obtain mechanical properties. The reason why the Alt of the target steel of the present invention is set to 0.08% or more is because if the Alt content is less than O.OS*, the mechanical properties of the product, especially the yield point, will become high regardless of the annealing temperature and time selected. , the r value is low regardless of the heat treatment conditions, and surface defects called sparkling scratches are more likely to occur1).The reason for limiting the content to 0.5 tres or less is that if the content is higher than this, This is because the actual effect remains the same and it is not economical.

As mentioned above, the mechanical properties of the product, especially the yield strength, elongation at yield point, total elongation, uniform elongation, etc., vary depending on the hot rolling conditions, especially the slab heating temperature and winding temperature conditions, but the optimal annealing conditions also change. , even under the most severe hot rolling conditions (high-temperature slab heating, low-temperature rolling), 850℃ for about 60 seconds, 900℃
If the temperature is about 20 degrees Celsius, or 950 degrees Celsius, good mechanical properties can be obtained by soaking for less than 10 seconds. When the hot rolling conditions are severe like this, the heat treatment conditions that yield the best mechanical properties are shifted toward higher temperatures and longer times than the heat treatment conditions that yield the best r value and ridging.

If we focus only on mechanical properties, it is sufficient to anneal for a short time even if the soaking temperature is 950°C, but in this case, it is not preferable for the r value and ridging. In the present invention, the soaking temperature was limited to 900°C or lower in consideration of this point, and the soaking temperature was set at 850°C or higher in consideration of three points: r value, ridging, and mechanical properties. . The reason for setting the soaking time to within 60 seconds is that if the soaking temperature is appropriately selected according to the previous history of the material, the mechanical properties can be satisfied, and as mentioned above, the r value and ridging can also be maintained within the soaking time of 60 seconds.
This is because even if it is longer than seconds, the effect is small and it is economical.

As explained above, SUS 430 copper containing 0.08% or more and 0.5% or less of At can be cold-rolled to the final thickness in one cold rolling without the usual hot-rolled sheet annealing. , It is necessary to perform the finishing baking process, it is necessary to soak the needle within 60 seconds in the temperature range of 850 to 900 ° C, processability,
That is, it can provide good r value, ridging, and mechanical properties.

The present invention will be specifically described below according to examples.

Example 1 5 containing At with a thickness of 2.70 tan shown in Table 1
US430 type 6 ferritic stainless steel hot rolled plate (4
), the plate thickness is 1.0 and 0.4 without annealing the hot rolled plate.
It was made into a cold-rolled sheet of m. These cold-rolled sheets were heat-treated in a salt bath, and after the heat treatment, the r value and ridging were measured. For comparison, the hot rolled sheet (B) of SUS 430 type ferritic stainless steel containing a small amount of At was 840'
After cX 4 hr hot rolled sheet annealing, sheet thickness 1. Ottrm and 0.4 tra cold-rolled sheets were subjected to similar heat treatment, and the r value and ridging height were measured. The measurement results of the ridging height and r value are shown in Table 2, and when the target steel of the present invention is heat treated within a temperature range of 850 to 900°C for 60 seconds or less, both the r value and the ridging property are good. I understand.

Table 1 Main temporary chemical components (wt%) of test materials Example 2 A 5US430 type ferritic stainless steel slab with a thickness of 200 cm and the chemical components shown in Table 3 was heated at a temperature of 1220°C.
After heating for a period of time, it was roughly rolled to a thickness of 20 cavities with 6 nogs, and then rolled with 6 passes to form a hot-rolled coil with a thickness of 2.3 mm. The temperature when finished to 2.3 degrees was 900°C, and immediately after finishing hot rolling, it was rapidly cooled and rolled up at a low temperature of 600°C. Regarding the conventional low At element side of the hot-rolled coil manufactured in this way,
After box annealing at 840°C for 4 hours, 0 after one cold rolling.
．． It was cold rolled to 4 wn.

The steel of the present invention containing AA was cold rolled at 0.4 rran't in one cold rolling without hot-rolled plate annealing. These cold-rolled sheets were then heated at various temperatures from 775° C. to 1000° C. while changing the soaking time from 0 seconds to a maximum of 2 minutes, and then air-cooled. Table 3 shows the mechanical properties of the thus heat-treated materials. As is clear from Table 4, the mechanical properties of the conventional material show good mechanical properties under any heat treatment conditions.
In the case of the steel of the present invention, even when the hot rolled sheet is not annealed, it is necessary to apply soaking time of 30 seconds to 60 seconds at a temperature of 850°C or higher and 900°C, as shown in the claims of the present invention. It can be seen that good mechanical properties equivalent to or better than conventional products can be imparted.

Table 3 Main chemical components of test materials (wt%) Example 3 SUS 430 type ferrite stainless steel slab containing At shown in Table 5 (thickness 250 mm) 12
After heating at a temperature of 50° C. for 2 hours, rough rolling was performed in 7 passes to a thickness of 20 mm. The rough rolling completion temperature was 1150°C. Then, finish rolling was performed at 6/'1' speed to obtain a hot rolled sheet with a thickness of 3.0 mm. The finishing temperature of finish rolling was 920°C.

The hot-rolled sheet thus rolled was immediately quenched and rolled at a temperature of 630°C, cooled to room temperature, and cold-rolled to a thickness of 1.0 without annealing the hot-rolled sheet. The heat treatment conditions shown in the claims and the conventional 430 for comparison.
Heat treatment was performed under heat treatment conditions commonly used for steel, and mechanical properties were measured and are shown in Table 6. As shown in Table 6, good mechanical properties can be obtained by treating the steel of the present invention under the heat treatment conditions specified in the present invention.

Table 5 Main chemical components of sample materials (overlapping %) CSt
Mn Cr At FeO
, 0470, 150, 1516, 80, 14 Residue 4, Brief explanation of the drawings Figure 1 is a schematic diagram showing the relationship between the yield strength, soaking time, and temperature of the steel of the present invention. A schematic diagram showing the relationship between yield point elongation, soaking time, and temperature.

Claims (1)

[Claims] When a hot-rolled sheet of ferritic stainless steel containing 0.08% to 0.5% At is cold-rolled without hot-rolled sheet annealing and then finish annealed, in a temperature range of 850 to 900°C. A method for producing a thin ferritic stainless steel plate with excellent workability, characterized by soaking within 60 seconds.