JPS62185832A - Manufacture of cold rolled steel strip or sheet of austenitic stainless steel - Google Patents

Abstract

PURPOSE:To obtain the titled steel sheet or strip having a low plastic anisotropy, by omitting annealing treatment of hot rolled plate between hot and cold rolling processes and applying cold rolling thereafter under a suitable condition. CONSTITUTION:Cold rolled steel sheet or strip of austenitic stainless steel is manufactured through hot and cold rolling processes and final annealing process. The hot rolling process is carried out under a condition in which hot rolled plate having recrystallization structure is obtd., and annealing treatment of hot rolled plate between hot and cold rolling processes is omitted. The plate is cold rolled to product sheet thickness without applying intermediate annealing in cold rolling process. Further, total cold rolling draft therein is regulated to <40%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a cold-rolled austenitic stainless steel strip or steel plate. More specifically, the present invention relates to a method for producing an austenitic stainless steel strip or steel plate that can produce a cold-rolled steel strip or steel plate with low plastic anisotropy even if the annealing of the hot-rolled steel sheet is omitted.

[Conventional technology]

Conventionally, when producing cold-rolled steel sheets or steel strips of austenitic stainless steel (these may be collectively referred to as cold-rolled sheets in the specification of this application), hot-rolled steel sheets or copper strips obtained by hot rolling are used. (also sometimes referred to as a hot rolled sheet) was annealed, pickled, cold rolled, and final annealed.

In other words, a hot-rolled austenitic stainless steel sheet has 1
Under normal hot rolling conditions, it exhibits an unrecrystallized austenite Mi texture and is in a sensitized state with carbide precipitated at austenite grain boundaries and deformation zones, so it is annealed at a temperature around 1100°C. The treatment completes recrystallization, softens the material, and converts carbide into a solid solution to improve corrosion resistance. In recent years, it has been proposed to omit this hot-rolled sheet annealing to save equipment and energy.

JP-A-55-70404, filed by the same applicant, discloses a technique that makes it possible to omit hot-rolled sheet annealing of austenitic stainless steel by appropriately controlling hot-rolling conditions.

JP-A-59-129731 also discloses a technique that makes it possible to omit hot-rolled sheet annealing of austenitic stainless steel by optimizing hot-rolling conditions and pickling conditions.

[Problem that the invention seeks to solve]

When cold-rolled steel sheets or strips of austenitic stainless steel are manufactured by omitting hot-rolled sheet annealing, the problem of plastic anisotropy occurs. In other words, there are differences in mechanical properties in the same rolling direction, in the direction perpendicular to the rolling direction, and in the 45° direction to the rolling direction.
For example, earrings are generated when this thin plate is deep drawn into a cylinder.

According to the invention method described in JP-A No. 55-70404, the recrystallization of the hot-rolled sheet is completed and sensitization is suppressed, so hot-rolled sheet annealing can be omitted, but the plastic anisotropy is The issue remains unresolved.

On the other hand, JP-A-59-129731 teaches hot rolling conditions in which the &[l weave of the hot rolled sheet is made into an unrecrystallized structure in order to reduce plastic anisotropy. Since the steel becomes hard, cold rolling is restricted, and sensitization is not completely suppressed, so pickling conditions are restricted.

Conventionally, the problem of plastic anisotropy when hot-rolled sheet annealing is omitted has not been solved in the subsequent cold rolling process or annealing process.The present invention omit hot-rolled sheet annealing. The objective is to solve the problem of plastic anisotropy in this case by appropriately performing the subsequent cold rolling process.

[Means to solve problems]

The present invention is for producing cold-rolled steel plates or steel strips of austenitic stainless steel through a hot rolling process, a cold rolling process, and a final annealing process.

To omit annealing treatment of a hot rolled sheet between a hot rolling process and a cold rolling process, and to cold roll the sheet to a product thickness without performing intermediate annealing in the cold rolling process.

The total cold rolling rate in the cold rolling process should be less than 40%.

The present invention provides a method for producing an austenitic stainless steel cold-rolled steel sheet or a toning strip characterized by low plastic anisotropy.

In particular, the present invention uses the method described in JP-A No. 55-70404, that is, the total rolling reduction of the finishing rolling mill group and the finishing rolling temperature of the copper strip as shown in Fig. 1 of JP-A-55-70404. The toning strip flowing on the hot run table from the finishing mill to the winding machine is controlled so that it falls within the shaded area shown, and is air-cooled for 3 to 10 seconds and then rapidly cooled to 40 ml.
A hot-rolled sheet with complete recrystallization and suppressed sensitization in the hot rolling process is manufactured according to a method of controlling the line so that it can be wound in a temperature range of 0 to 600°C, and this hot-rolled sheet is used in subsequent processes. Preferably, it is subjected to cold rolling according to the invention.

In the method of the present invention, even if hot-rolled sheet annealing is omitted, cold-rolled steel sheets or strips of austenitic stainless steel with low plastic anisotropy are obtained by performing subsequent cold rolling under appropriate conditions. In the hot rolling process, the above-mentioned JP-A-55-7
Regardless of whether the method described in Publication No. 0404 is followed or not, it is preferable to control the hot rolling finishing temperature in the range of 850 to 1030°C and the drawing temperature in the range of 400 to 600°C.

The present inventors conducted a hot-rolled sheet obtained under the above-mentioned hot-rolling conditions for 5O3304, which is a representative steel type of austenitic stainless steel, without annealing (one-time cold rolling (cold rolling without intermediate annealing). ) and final annealing, and the total cold rolling rate and final annealing conditions were varied over a wide range to investigate the plastic anisotropy of the cold rolled sheet. Plastic anisotropy was evaluated according to the following formula using a cylindrical cup test. According to earring rate (χ).

(Hmax+Hn+in)'X'AHtaax
: Flange peak height Hsin s Flange valley height When we investigated how the cold rolling rate and final annealing conditions (annealing temperature and annealing time) were related to the earring rate, we found that hot rolled sheet annealing Even if this is omitted, if a cold rolled sheet is produced by one cold rolling with a cold rolling ratio of less than 40%, the final annealing after cold rolling will be profitable even if the conditions are not particularly regulated. It has been found that the earring ratio of the cold-rolled sheet obtained by this method is reduced to the same level as when hot-rolled sheet annealing is performed, and that the problem of plastic anisotropy that occurs when hot-rolled sheet annealing is omitted can be substantially solved.

An example of this test result is shown in FIGS. 1 and 2. FIG. 1 shows the relationship between the cold rolling rate, the final annealing temperature, and the earring rate. The test that yielded the relationship shown in Figure 1 was conducted under the following conditions. Namely.

The composition of the steel tested was: C: 0.071%, S
i: 0.56%, Mn: 1.10%, Ni: 8.58%
, Cr: 18.15%.

Ni: 0.026%, the hot rolling conditions were hot rolling at a finishing temperature of 980°C and a coiling temperature of 460°C, and then pickling without annealing the hot rolled sheet, which was carried out once. A thin plate was produced by cold rolling by varying the cold rolling rate, and the annealing time was varied while the final annealing time was kept constant at 30 seconds, and the earring ratio of the obtained cold rolled plate was determined using the above formula.

From the results shown in FIG. 1, it can be seen that the lower the cold rolling rate, the lower the earring ratio, and the lower the annealing temperature, the lower the earring ratio. It can be seen that when the cold rolling rate is less than 40%, the earring rate is 7% or less in the normal final annealing temperature range of 1000 to 1200°C. This level of earring ratio of 7% or less is the level of a cold-rolled sheet obtained by a conventional method in which a hot-rolled austenitic stainless steel sheet is annealed in accordance with a conventional method, followed by cold rolling and final annealing. Therefore, even if hot-rolled sheet annealing is omitted, in the case of the method of the present invention, a cold-rolled sheet with less plastic anisotropy equivalent to that obtained when hot-rolled sheet annealing is performed is obtained.

The results in Figure 2 show the relationship with the earring ratio when the same test as in Figure 1 was conducted, except that the final annealing temperature was kept constant at 1100°C and the annealing time was varied. . In this case as well, it can be seen that when the cold rolling rate is less than 40%, the earring rate is 7% or less within the normal soaking time range of continuous annealing.

Therefore, 1. When the cold rolling ratio is set to less than 40% according to the present invention, the final annealing conditions are not particularly limited; 9. It is sufficient to carry out the final continuous annealing within the range of the final continuous annealing conditions for ordinary austenitic stainless steels. .

In carrying out the present invention, cold rolling is carried out by one interval rolling (however, the number of passes is arbitrary). In other words, the relationships shown in Figures 1 and 2 are suitable for continuous annealing, in which cold rolling is not performed multiple times with intermediate annealing, but the plate is rolled down to the desired thickness by one interval rolling, and then final annealing is performed. The conditions are as follows.

According to the invention, the final annealing can be carried out by continuous annealing. By setting the cold rolling ratio to less than 40%, even if hot-rolled sheet annealing is omitted or intermediate annealing in the cold rolling process is omitted, the plastic anisotropy remains the same as when hot-rolled sheet annealing is performed. It is clear that the production process can be reduced to the level of The present invention provides an advantageous manufacturing method.

Example C: 0.072%, Si: 0.60%, Mn:
1.04%.

Ni: 8.62%, Cr: 18.18%, N
: 0.027%, 5tlS304 (7) A continuous cast slab (thickness: 200111I) was heated for 1230 tons and rough rolled, and hot rolled plates with a thickness of 1.6 to 3.41 were obtained by changing the hot rolling finishing temperature. was manufactured. The winding temperature at that time was all 50.
The temperature was below 0°C. Then, the hot rolled sheet was pickled without being annealed, cold rolled once to a thickness of 1.0 to 1.4 mm, and then final annealed. Table 1 shows each hot rolling condition, cold rolling rate, and final annealing condition. Table 1 also lists the measurement results of the presence or absence of recrystallization of the hot-rolled sheets, the hardness (Hv) of the hot-rolled sheets, and the earring ratio (%) of each obtained cold-rolled sheet by the cylindrical cup test.

From the results in Table 1, if the cold rolling ratio is set to 40% or less according to the present invention, even if hot-rolled sheet annealing is omitted, the earring ratio will decrease regardless of the presence or absence of recrystallization of the hot-rolled sheet, and the plasticity It can be seen that a cold-rolled austenitic stainless steel sheet with low anisotropy can be obtained.

In particular, it can be seen that the plastic anisotropy of the cold-rolled sheet is significantly reduced when the hot-rolled sheet is recrystallized. Therefore, if the present invention is carried out using a hot-rolled sheet that has been recrystallized by the method described in JP-A-55-70404, for example, the hot-rolled sheet will become softer and the plastic anisotropy will be reduced. can be realized at the same time.

[Brief explanation of drawings]

, Figure 1 shows the relationship between cold rolling rate, final annealing temperature, and earring rate when hot-rolled sheet annealing of 5US304 steel is omitted and cold rolling and final annealing are performed, and Figure 2 shows the relationship between cold rolling rate, final annealing temperature, and earring rate. FIG. 3 is a diagram showing the relationship between elongation, final annealing time, and earring ratio. Figure 1 1000 1050. 1100 1150
1200 Final annealing degree ('C) Figure 2 Soaking time during final annealing (seconds)

Claims (2)

[Claims] (1) In producing cold rolled steel plates or steel strips of austenitic stainless steel through a hot rolling process, a cold rolling process and a final annealing process, hot rolling between the hot rolling process and the cold rolling process. To omit the annealing treatment of the plate, and to cold-roll the plate to the product plate thickness without performing intermediate annealing in the cold rolling process, and to make the total cold rolling rate in the cold rolling process less than 40%. A method for producing cold-rolled austenitic stainless steel sheets or steel strips with low plastic anisotropy, characterized by: (2) The manufacturing method according to claim 1, wherein the hot rolling step is carried out under conditions that allow a hot rolled sheet having a recrystallized structure to be obtained.