JPS6054375B2 - Manufacturing method of austenitic stainless steel plate or steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing austenitic stainless steel mainly made of 18%Cr-8%Ni, and in particular, even if hot-rolled plate annealing is omitted, in-plane anisotropy is maintained. The present invention relates to a method by which small and excellent quality cold rolled stainless steel sheets and steel strips can be obtained.

In general, in the manufacturing method of aus4tenitic stainless steel thin sheets mainly made of 18%Cr-8%Ni, the conventional method is to melt and adjust the composition in an electric furnace or converter, then cast, and then hot-roll. I went there and got hot rolled coils.

After that, the hot-rolled sheet was softened and annealed at a high temperature of 1000°C or higher to perform descaling; after that, it was made into a thin sheet by a single-stage cold rolling method or a two-stage cold rolling method with an intermediate annealing, and was then subjected to final annealing and pickling. We have been manufacturing cold-rolled thin steel sheets. The hot rolled sheet annealing process and the descaling process are carried out in a line unique to stainless steel called a ψ line.

One of the main purposes of the hot-rolled sheet annealing process is to achieve uniform mechanical properties, which requires high-temperature heat treatment. Heat treatment consumes a considerable amount of thermal energy, and in many cases, the line speed of ψ is also annealing rate-limiting. Fourth, if the hot rolled sheet annealing process can be omitted, great benefits can be expected in terms of energy savings and productivity improvements.
The present inventors omitted the hot-rolled plate annealing process from the manufacturing process of an austenitic stainless steel sheet mainly made of 18% Cr-8% Ni, and obtained the obtained product by cold rolling with a one-stage cold rolling method and then annealing and pickling. Various studies have been conducted to improve the quality of austenitic stainless steel thin steel sheets.

Particularly in terms of material quality, if hot-rolled sheet annealing is omitted in the normal process, in-plane anisotropy increases at the product stage. If the anisotropy is large, the rolling direction, the direction perpendicular to the rolling direction, and the rolling direction
The characteristics in the stretching direction are different, and when cylindrical deep drawing is performed, for example, earrings are generated to a large extent, causing a significant reduction in material yield. According to research conducted by the present inventors, earrings occur due to the development of a strong texture unique to thin stainless steel sheets, and chemical components, especially C, N, Mn, Ni, and P, contribute to the sharpening of the texture. is large.

As a representative example, the influence of Nl on earrings obtained from SUS3O4 is shown in FIG. 1, and the influence of C is shown in FIG. The earring ratio was calculated according to the following formula, where h1 represents the height measured from the bottom of the cup to the top of the peak at the edge of the cup, and ■ represents the height from the bottom to the trough.

The earring ratio increases almost linearly as the amount of Ni increases.

On the other hand, a similar tendency is observed for C, and its contribution is 0.
．． Although there is a tendency to saturate at 0.7% C or more, the anisotropy increases as the C becomes higher.

Therefore, the smaller the amount of Ni and C, the better the anisotropy.
In particular, the content of C is preferably 0.07% or less. On the other hand, the effects of N1 and C on elongation are shown in FIGS. 3 and 4.

The elongation decreases as the Ni content decreases, and for example, if the Ni content is less than 7.7%, the elongation becomes less than 50%, and the workability is significantly deteriorated.
A similar tendency is observed with respect to C, and the lower the C, the lower the elongation and the worse the workability. Therefore, in order to achieve both low anisotropy and excellent workability, it is necessary to consider the synergistic effects of various elements and determine an appropriate range of ingredients.

Furthermore, the rolling reduction and biting temperature during hot finish rolling also have a significant effect on earrings.

As an example, FIG. 5 shows the effect on earrings of a product sheet when the temperature of hot-finish rolling is changed after rough rolling of SUS3O4 under normal conditions. The earring ratio sharply decreases when the biting temperature in finish rolling becomes 98 degrees Celsius or lower, and shows an almost constant low value when the temperature is between 8259 and 950'C. According to the results of optical microscopic observation of the structure of these hot-rolled sheets, when the finish rolling biting temperature is 1000'C or higher, the structure is fine recrystallized grains, but in the low-temperature biting material, the grain boundary of coarse rolling is The grains remained stretched in the rolling direction.

In continuous hot rolling, rough rolling ends at a high temperature of 1050° C. or higher, so the structure after rolling becomes coarse crystal grains that have completed recrystallization. However, when several passes of finish rolling are subsequently performed, recrystallization occurs repeatedly during rolling, and the structure of the hot-rolled sheet becomes to have extremely small crystal grains. According to research by the present inventors, when a hot-rolled sheet with a fine grain structure is simply descaled, then cold-rolled and final annealed, recrystallization aggregation occurs because there is a large grain boundary area that serves as a starting point for recrystallization. It promotes preferential growth of the tissue, and the (211) crystallization 11> component increases to an extreme extent, resulting in remarkable anisotropy.

On the other hand, when a steel plate after rough rolling is left on a runout table for a few seconds to lower the temperature and finish rolling is started, the structure of the hot rolled sheet is such that the coarse grain boundaries generated during rough rolling extend in the rolling direction. This results in a so-called elongated grain state, and the area of grain boundaries becomes significantly smaller than under the above conditions. When such a hot-rolled sheet is cold-rolled in the same manner as described above and finally annealed, the resulting product sheet has a random texture and improved anisotropy. That is, if the biting temperature in hot-roll finish rolling is lowered and the hot-rolled sheet structure is made into elongated grains, the anisotropy is improved and the earring ratio is reduced. Furthermore, these behaviors interact additively with the effects of chemical components. Based on the above concept, various austenitic stainless steels were melted, hot-rolled and cold-rolled, and the anisotropy and workability of thin steel sheets were investigated in detail. and (2) by appropriately controlling the reduction rate and biting temperature during hot rolling, an austenitic stainless steel sheet with low anisotropy and excellent workability can be obtained even if hot-rolled sheet annealing is omitted. We have found manufacturing conditions that allow for

That is, in order to achieve such an object, the present invention provides a CO. OO5~0.07%, P
O. O4O% or less, Mn3. 0% or less, Ni6. O~1
1.5%, Crl6-20%, NO. OO5~0.2%
1, including MO4% or less and CU4% or less as necessary.
Contains a total of 0.8% or less of one or more of Ti, Nb, and V, or contains one or two of Ti, Nb, and V with MO of 4% or less and CU of 4% or less.
Contains one or more of 0.8% or less in total, and points A, Bp, Cp, D in Figure 6 according to 2C+N, Mn+Ni and P content (where p is P content × 10-2%
and the points Bp and Cp are respectively determined by the P content), and the steel consisting of the residual V'e and unavoidably mixed impurities is cast, hot rough rolled, and then hot finished. At least one bus, preferably each bus, should be connected to the 7th bus.
The hot-rolled steel plate or steel strip obtained in this way is
It is characterized by descaling without annealing, cold-rolling it to the specified thickness, and then final annealing, which is a breakthrough in that it has low anisotropy, excellent workability, and reduces manufacturing costs. This is a specific manufacturing method.

In the present invention, the increase in anisotropy due to the omission of hot-rolled sheet annealing is achieved by adding an appropriate amount of Mn+Ni within a range that does not impede workability. 2C+N and P
At the same time, the reduction rate and biting temperature of the hot-rolled finish rolling were carried out for at least one bath in the range surrounded by points A, B, C, D, and E in Figure 7, and the structure of the hot-rolled sheet was improved. It was discovered that by doing so, an austenitic stainless steel sheet with low anisotropy and excellent workability can be produced even if hot-rolled sheet annealing is omitted. The present invention has been completed in which the permissible limits for the content of the above elements and the permissible limits for hot rolling and finish rolling have been clarified. In the past, there have been many reports on the omission of hot-rolled sheet annealing, but all of them ignore the fact that the anisotropy increases in the product sheet.

In other words, an austenitic stainless steel with low anisotropy and excellent workability as in the present invention. There is no known method for manufacturing steel sheets (TM strips). Hereinafter, the reason for limiting the content of each element and the basis for limiting the hot rolling finish rolling conditions in the present invention will be explained.

The anisotropy and workability of austenitic stainless steel sheets without hot-rolled sheet annealing are extremely influenced by the chemical composition of the steel and hot-rolling finish rolling. These two effects act additively with each other, and by appropriately combining the regulation of steel composition, the reduction rate and biting temperature in hot rolling finish rolling, an austenitic stainless steel with low anisotropy and particularly excellent workability can be produced. You can get thin plates. Next, each component will be explained in detail.

C: C is a factor that has the greatest effect on improving the anisotropy of an austenitic stainless steel thin sheet obtained by omitting hot-rolled sheet annealing, and its effect is exhibited at 0.07% or less, and a lower value is preferable.

However, it is industrially difficult to reduce the concentration to 0.005% or less, and if we dare to do so, the price will be high, so we set the lower limit to 0.005%.
It was set at 5%. Si: Si is a strong deoxidizer and is effective in removing oxygen that is harmful to workability, but if it becomes too high, it inhibits hot workability, so it is set to 1.0% or less.

P: Like C, a lower P value improves anisotropy. The anisotropy is improved by lowering P in Mn+Ni, . In relation to 2C+N, the permissible range of these components is expanded within the range shown in FIG. 6, and this has an advantageous effect on improving elongation and Erichsen value. Therefore, it is preferable that the content be lower, but it is set to 0.04% or less, which can be reduced industrially and economically. Mn: Mn exhibits the same effect as Ni on anisotropy, and the lower the Mn, the better the anisotropy.

The effect becomes noticeable below 3.0%, so the upper limit is set to 3.0%.
．． It was set to 0%. Ni:N1 is an element effective in reducing anisotropy, and the lower the content, the better the anisotropy, but the higher it is in terms of elongation, the more desirable it is.

Therefore, if it is too low, the processability will be inhibited, and if it is too high, it will increase the anisotropy. ．． 2C
+N and P. In the present invention, Nl is set to 6.0 to 11.5% in relation to the above components. Cr: Cr does not have much influence on anisotropy and workability, but 16% is necessary to maintain corrosion resistance.
The above is necessary.

However, when it exceeds 20%, the amount of ferrite increases and hot workability deteriorates. Ru. For this reason, the range of Cr is 16 to 20.
%. N:N<:) Similar to C, Mn, Nl and P, the lower the anisotropy, the better, 0.2% or less, and industrially and economically it is desirable to be as low as possible.
However, it is industrially difficult to reduce the content to 0.005% or less, and the N range is set to 0.005 to 0.2%. In addition to the above-mentioned addition ranges, the above-mentioned components include, in particular, C, N, Mn, Ni,
Regarding P, set the range surrounded by points A, Bp, Cp, and D in Figure 6 (however, p indicates P content x 10-2%, and points Bp and Cp are each determined by the P content). That is,
This is an essential condition for improving anisotropy and processability.

In FIG. 6, the line ABpCp is the limit regulated by anisotropy, and in the range above this, the earring rate increases rapidly and the quality of the product board deteriorates. The wire dove indicates the lower limit of the amount of Mn+Ni, but if the amount of Mn+Ni is lower than this, the austenite phase becomes too unstable and elongation deteriorates.
What is the line CpD? It indicates the lower limit l of the amount of +N, ? If the amount of +N is lower than this, the manufacturing cost will increase rapidly and it will be less economical.
Therefore, C, N, Mn, Ni, and P are all 6th.
It must satisfy the range surrounded by points A, Bp, Cp, and D in the figure. Furthermore, in addition to the above chemical components, MO4. 0% or less, CU4% or less, or both.

MO is an effective component for improving corrosion resistance, and especially when it is necessary to improve the corrosion resistance of hot-rolled sheets or cold-rolled sheets, the upper limit should be set to 4.
Add as 0%. Cu exhibits the same behavior as Ni as an austenite-forming element.

Therefore, by adding Cu, it is possible to reduce the amount of Ni by a corresponding amount and the manufacturing cost can be reduced, so it is added when necessary. However, Cu is 4.0
% or more, hot workability is significantly impaired and edge cracking occurs during hot rolling. Therefore, the upper limit of Cu was set to 4.0%. Further, by including one or more of Ti, Nb, and V (7) as necessary, carbide precipitation is suppressed and the surface texture after pickling is improved. Therefore, it is added when the cooling rate after hot rolling is insufficient and there is a concern that carbide precipitation may occur. However, when these elements are added in excess, Tl generates many inclusions, and Nb and V cause problems in hot workability and cause edge cracks during hot rolling. Therefore, the upper limit of the total amount of Ti, Nb, and V added was set at 0.8%. In addition to the above-mentioned chemical components, hot rolling and finish rolling have a large influence on the reduction of anisotropy, and act additively to the effects of the above-mentioned components.

That is, after performing normal rough rolling with a continuous hot rolling mill,
The hot-rolling finish rolling must be carried out in at least one bath or more, preferably each bath at a rolling reduction rate and biting temperature within the ABCDEA range shown in FIG.

The conditions in the ABCDEA range shown in FIG. 7 indicate rolling conditions in which recrystallization does not occur, that is, the crystal grains after rough rolling are simply expanded into grains, and the grain boundary area can be kept to a minimum.

In Figure 7, the upper limit of the biting temperature is line AB and line ? However, if finish rolling is started at a higher temperature than this,
Recrystallization occurs during finish rolling, and the structure becomes fine grained.

Furthermore, when the biting temperature falls below the line DE, deformation resistance increases, surface flaws rapidly occur, and productivity is inhibited.

If the rolling reduction ratio is greater than the line CD, surface flaws increase and at the same time, edge cracks begin to occur. If the rolling reduction rate is lower than the line EA, the finished plate thickness will become extremely thick, or the number of baths will increase, resulting in a decrease in rolling efficiency. Therefore, the finish rolling conditions must be a reduction rate and a biting temperature within the shaded range of ABCDEA shown in FIG. The present invention will be specifically explained below using examples. Austenitic stainless steel having the components shown in Table 1 was melted using an electric furnace-AOD method to obtain a continuously cast slab with a thickness of 16 hours.

After that, after heating to 1250℃ in a heating furnace and performing rough hot rolling,
Finish hot rolling was carried out under the conditions shown in Table 2. These hot-rolled sheets were not subjected to solution heat treatment, but were immediately descaled and subjected to cold rolling at room temperature. The cold rolling was performed using a Sendzimir mill to a thickness of 0.7 Tfn. The final annealing was performed by rapid cooling in a furnace at 1100°C five times to obtain a product plate.

Material tests on the product plates were conducted for 0.2% yield strength, tensile strength, elongation, and earring ratio. Table 3 shows the results of these measurements. The material properties of austenitic stainless steel sheets produced under manufacturing conditions in which the chemical composition and hot rolling conditions satisfy the conditions shown in Figures 6 and 7, respectively, show that the earring ratio is small even if hot rolled sheet annealing is omitted. It can be seen that the anisotropy is improved and at the same time the elongation is large, indicating excellent workability.

In other words, the present invention can omit the annealing of hot-rolled austenitic stainless steel sheets, thereby reducing manufacturing costs.At the same time, the product sheets manufactured through the same process have fewer earrings generated by deep drawing and are less likely to be cut off after pressing. This is an innovative manufacturing method that can significantly improve yields by reducing the amount of blanks or reducing the size of the blank before deep drawing.

[Brief explanation of drawings]

Figures 1 and 2 show SUS3O4-based steel with different Ni and C content, finish hot-rolled at a biting temperature of 940'C and a reduction rate of 22% per bath, and then cold-rolled without hot-rolled plate annealing. Figures 3 and 4 are diagrams showing the elongation of the annealed product plate, Figure 5 is a diagram showing the elongation of the product plate, and Figure 5 is a diagram showing the earring ratio of the annealed product plate.
Figure 6 shows the relationship between the earring ratio and the biting temperature in a product sheet that was cold-rolled and annealed by omitting the hot-rolled plate annealing after changing the biting temperature during hot-rolling finish rolling using US3O4. h+Ni amount in invention? It is a figure showing the relationship between +N amount and P amount.

Claims (1)

[Claims] 1. 0.005 to 0.07% by weight, Si
1.0% or less, P 0.040% or less, Mn 3.0% or less, Ni 6.0 to 11.5%, Cr 16 to 20%, N0.
005 to 0.2% and 2C+N to Mn+Ni and P content according to points A, Bp, Cp, D in Figure 6 (however, p indicates P content x 10^-^2%, and point Bp , Cp are respectively determined by the P content), and the steel consisting of the remainder Fe and unavoidably mixed impurities is cast, rough hot rolled, and then hot finished rolled at least one pass or more. is carried out at the rolling reduction rate and biting temperature in the range surrounded by points A, B, C, D, and E in Fig. 7, and the hot-rolled steel plate or steel strip thus obtained is descaled without annealing. A method for manufacturing an austenitic stainless steel plate or steel strip, which comprises cold rolling to a predetermined thickness and then final annealing. 2 C0.005-0.07% by weight, Si
1.0% or less, P 0.040% or less, Mn 3.0% or less, Ni 6.0 to 11.5%, Cr 16 to 20%, N0.
005~0.2% plus Mo4% or less or Cu4%
Contains one or two of the following, and 2C+N is Mn+Ni
and points A, Bp, Cp, D (
However, p indicates P content x 10^-^2%, and the points Bp,C
p is determined by the P content), and the steel consisting of the balance Fe and unavoidably mixed impurities is cast, and after hot rough rolling, the hot finished rolling is at least 1
The above steps are carried out at the rolling reduction rate and biting temperature within the range surrounded by points A, B, C, D, and E in Fig. 7, and the hot-rolled steel plate or steel strip thus obtained is descaled without annealing. After that,
A method for producing an austenitic stainless steel plate or steel strip, which comprises cold rolling to a predetermined thickness and then final annealing. 3 C0.005-0.07% by weight, Si
1.0% or less, P 0.040% or less, Mn 3.0% or less, Ni 6.0 to 11.5%, Cr 16 to 20%, N0.
005 to 0.2% plus one or two of Ti, Nb, and V
Contains 0.8% or less of species or more in total, and 2C+N is M
Points A, Bp, C in Figure 6 depending on n+Ni and P content
p, D (however, p indicates P content x 10^-^2%, points Bp and Cp are each determined by the P content), and the remainder is Fe and unavoidably mixed impurities. After casting the steel and hot rough rolling, hot finish rolling is performed at least one pass or more at a rolling reduction rate and biting temperature within the range surrounded by points A, B, C, D, and E in Figure 7. An austenitic stainless steel plate or steel, characterized in that the thus obtained hot rolled steel plate or steel strip is descaled without annealing, then cold rolled to a predetermined thickness, and then final annealed. How to make obi. 4 C0.005-0.07% by weight, Si
1.0% or less, P 0.040% or less, Mn 3.0% or less, Ni 6.0 to 11.5%, Cr 16 to 20%, N0.
In addition to 0.005 to 0.2%, one or two of Mo4% or less, Cu4% or less, and one or two of Ti, Nb, and V
Contains 0.8% or less of species or more in total, and 2C+N is M
Points A, Bp, C in Figure 6 depending on n+Ni and P content
p, D (where p indicates P content x 10^-^2%, points Bp and Cp are each determined by the P content), and the remainder is Fe and unavoidably mixed impurities. After casting the steel and hot rough rolling, hot finish rolling is performed at least one pass or more at a rolling reduction rate and biting temperature within the range surrounded by points A, B, C, D, and E in Figure 7. An austenitic stainless steel plate or steel, characterized in that the thus obtained hot rolled steel plate or steel strip is descaled without annealing, then cold rolled to a predetermined thickness, and then final annealed. How to make obi.