JPH0617514B2 - Method for producing cold rolled steel strip or steel sheet of austenitic stainless steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a cold rolled steel strip or steel sheet of austenitic stainless steel. More specifically, the present invention relates to a method for producing an austenitic stainless steel strip or steel sheet that can obtain a cold-rolled steel strip or steel sheet with little plastic anisotropy even if the annealing of the hot-rolled sheet is omitted.

[Conventional technology]

BACKGROUND ART Conventionally, when manufacturing a cold-rolled steel sheet or strip of austenitic stainless steel (these may be collectively referred to as cold-rolled sheet in this specification), a hot-rolled steel sheet or strip obtained by hot rolling is used. (Also called hot rolling) was annealed, pickled, cold rolled, and finally annealed. In other words, hot rolled austenitic stainless steel is
Since it has an unrecrystallized austenite structure and is in a sensitized state in which carbide is precipitated in the austenite grain boundaries and deformation zones, it is annealed at a temperature near 1100 ° C to complete recrystallization and soften and carbide. Has been carried out to improve the corrosion resistance. In recent years,
It has been proposed to omit this hot-rolled sheet annealing to save equipment and energy.

Japanese Patent Application Laid-Open No. 55-70404, which is filed by the same applicant, discloses a technique capable of omitting hot-rolled sheet annealing of this austenitic stainless steel by appropriately controlling hot-rolling conditions.

Japanese Unexamined Patent Publication No. 59-129731 also discloses a technique that makes it possible to omit hot-rolled sheet annealing of austenitic stainless steel by appropriately setting hot-rolling conditions and pickling conditions.

[Problems to be solved by the invention]

When a cold-rolled steel sheet or strip of austenitic stainless steel is manufactured by omitting hot-rolled sheet annealing, the problem of plastic anisotropy is accompanied. That is, there is a difference in mechanical properties between the rolling direction, the direction perpendicular to the rolling direction, and the 45 ° rolling direction, and, for example, earring occurs when this thin plate is deep-cylindrically processed.

According to the invention method described in the above-mentioned JP-A-55-70404,
Since the recrystallization of the hot rolled sheet is completed and the sensitization is suppressed, the hot rolled sheet annealing can be omitted, but the problem of plastic anisotropy remains unsolved.

On the other hand, Japanese Patent Laid-Open No. 59-129731 teaches hot rolling conditions in which the structure of the hot rolled sheet is an unrecrystallized structure in order to reduce plastic anisotropy. In this case, the hot rolled sheet becomes hard. There are restrictions on cold rolling, and because sensitization is not completely suppressed, there are restrictions on pickling conditions.

The present invention is intended to solve the problem of plastic anisotropy when hot-rolled sheet annealing is omitted in the subsequent cold rolling and final annealing steps.

[Means for solving problems]

The present invention is to manufacture a cold-rolled steel sheet or strip of austenitic stainless steel through a hot rolling process, a cold rolling process and a final annealing process, in which the heat treatment between the hot rolling process and the cold rolling process is performed. Omit the annealing process of the rolled sheet and cold-roll to the product sheet thickness without intermediate annealing in the cold-rolling process. Set the total cold-rolling rate in the cold-rolling process within the range of 40 to less than 70%. , And the final annealing process is carried out by continuous annealing.
The temperature shall be soaked in the range of temperature and time enclosed by the points AGBCEJF in the figure. [However, in Fig. 1, the temperature on the vertical axis is ° C, and the time on the horizontal axis is the seconds on a logarithmic scale. Point AGBCEJF
The coordinates (time, temperature) of A (1,1000), G (10,1020), B (9
0,900), C (300,900), E (300,1000), J (100,1080), F (1,1
The present invention provides a method for producing an austenitic stainless cold-rolled steel sheet or steel strip having less plastic anisotropy, which is characterized in [200].

The present invention also provides a hot-rolling process, a cold-rolling process, and a final annealing process for producing a cold-rolled steel sheet or strip of austenitic stainless steel, which is performed between the hot-rolling process and the cold-rolling process. Eliminate the annealing process of hot-rolled sheet, and cold-roll to the product sheet thickness without intermediate annealing in the cold-rolling step, and set the total cold-rolling rate in the cold-rolling step within the range of 70 to 95%. , And the final annealing process is carried out by continuous annealing.
The temperature shall be soaked in the temperature and time range enclosed by the points AGBCHID in the figure. [However, in Fig. 1, the temperature on the vertical axis is ° C and the time on the horizontal axis is the seconds expressed in logarithmic scale.
The coordinates (time, temperature) of A (1,1000), G (10,1020), B (9
0,900), C (300,900), H (100,1000), I (10,1080), D (1,11
30)] is provided, the method for producing an austenitic stainless cold-rolled steel sheet or steel strip having little plastic anisotropy is provided.

The method of the present invention is to obtain a cold-rolled steel sheet or strip of austenitic stainless steel with less plastic anisotropy by performing subsequent cold rolling and annealing under appropriate conditions even if hot-rolled sheet annealing is omitted. However, in the hot rolling process,
It is preferable to control the temperature in the range of 850 to 1030 ° C and the winding temperature in the range of 400 to 600 ° C.

In the practice of the present invention, it is not always necessary to obtain a hot-rolled sheet having a recrystallized structure that has been recrystallized in the hot rolling process, but a hot-rolled sheet having a recrystallized structure is sufficiently softened so that it is cold. This is preferable in that the rolling load is reduced. Therefore, it is particularly preferable to apply the hot rolling conditions described in JP-A-55-70404 to the present invention to obtain a hot rolled sheet in which recrystallization is completed and sensitization is suppressed.

The present inventors performed a single cold rolling (cold rolling without intermediate annealing) of a hot rolled sheet obtained by subjecting SUS304, which is a typical austenitic stainless steel type, to the hot rolling conditions described above without annealing. The final cold rolling and the final annealing were performed, and the plastic anisotropy of the cold-rolled sheet was investigated by varying the total cold rolling rate and the final annealing conditions in a wide range. The evaluation of plastic anisotropy was based on the earring rate (%) according to the following formula by the cylindrical cup test.

Then, we investigated how the cold rolling rate and final annealing conditions (annealing temperature and annealing time) affect the earring rate. Even when hot-rolled sheet annealing was omitted, cold rolling rate and final annealing If the conditions of 1) are appropriate, the earring rate decreases to the same level as that when hot-rolled sheet annealing is performed, and the problem of plastic anisotropy that occurs when hot-rolled sheet annealing is omitted is substantially We have found that it can be solved regardless of the above. That is, in the case of a cold-rolled sheet obtained by the conventional method in which a hot-rolled sheet of austenitic stainless steel is annealed according to the conventional method, then cold-rolled and finally annealed, the earring rate is below 7%. The cold rolling rate at which the earring rate is 7% or less, which is equal to this level, and the conditions for the final annealing are arranged from the results of the wide range of tests described above to obtain the relationship shown in FIG.

FIG. 2 shows an example of the experimental results that lead to the relationship shown in FIG. The test of Fig. 2 shows that C: 0.074%, Si: 0.61%,
Mn: 1.04%, Ni: 8.63%, Cr: 18.30%, N: 0.0
22% steel with the balance being Fe and inevitable impurities,
Hot rolling was performed at a finishing temperature of 980 ° C and a coiling temperature of 460 ° C, pickling was performed without annealing the hot-rolled sheet, and this was cold-rolled once by intermediate rolling without annealing to produce a thin sheet. By varying the final annealing temperature and the soaking time over a wide range, the earring rate of the cold-rolled annealed sheet obtained was obtained by the above equation, and this earring rate was arranged and plotted by the cold rolling rate and the annealing conditions. It is a thing. The subscript R in FIG. 2 indicates the total cold rolling rate (%), and the subscript E indicates the earring rate (%). In Fig. 2, △ indicates unrecrystallized after annealing, ○ indicates total cold rolling rate of 40 to less than 70%, and earring rate is 7% or less, and ● indicates. Indicates that the total cold rolling rate is 40 to less than 70% and the earring rate exceeds 7%. The mark □ indicates that the total cold rolling rate is 70 to 95% and the earring rate is 7% or less. The total cold rolling rate is 70 to 95% and the earring rate exceeds 7%.

As shown in the result of Fig. 2, when the total cold rolling rate in the cold rolling process is set in the range of 40 to less than 70%,
If the final annealing is soaked at a temperature and time within the range enclosed by the points AGBCEJF in Fig. 1, and if the total cold rolling rate in the cold rolling process is in the range of 70 to 95%, the final annealing is shown in Fig. 1. Point If soaking is performed at a temperature and time within the range surrounded by AGBCHID, a cold-rolled sheet with less plastic anisotropy with an earring ratio of 7% or less can be obtained.

That is, when the total cold rolling rate is 70 to 95%, the CHID line in Fig. 1 is the upper limit, and when the total cold rolling rate is 40 to less than 70%, the EJF line is in the upper limit. Even if the strip annealing is omitted, the same low earring rate as in the case where it is not omitted is achieved. On the other hand, in the region exceeding these upper limits, the recrystallization texture develops and the earring rate decreases. Further, in the region below the AGB line in Fig. 1, recrystallization does not occur sufficiently and workability deteriorates significantly, so the lower limit of annealing conditions is this AGB line.

In Fig. 1, the temperature on the vertical axis is ° C, the time on the horizontal axis is seconds expressed in logarithmic scale, and the coordinates (time, temperature) of each point AGBCEJF are A (1,1000), B (90,900), C (300,900), D
(1,1130), E (300,1000), F (1,1200), G (10,1020), H (10
0,1000), I (10,1080), J (100,1080).

In the practice of the present invention, in the continuous annealing step, it is economically desirable that the striping time is as short as possible, and soaking at less than 900 ° C requires long-term holding, which is economically problematic. Not only occurs, but the undissolved carbides are also a concern, so the lower limit of the final annealing temperature should be 900 ° C. In addition, the manufacturing cost increases rapidly as the final annealing time increases, so the upper limit of the soaking time is set to 300 seconds. If the total cold rolling rate is less than 40%, the practical value will be reduced in relation to the manufacturable thickness and the thickness of the cold rolled steel sheet. Therefore, the cold rolling rate is 40% or more. Cold rolling manufacturability is a problem, and plastic anisotropy is not a problem for ultra-thin products in many cases, so the cold rolling rate is 95%.
The upper limit is

Further, in carrying out the present invention, cold rolling is performed by one cold rolling (however, the number of passes is arbitrary).
That is, the cold rolling is not performed many times with the intermediate annealing sandwiched between them, but the cold rolling is performed once to reduce the thickness to a desired sheet thickness, and then the final annealing is performed. The relationship in FIG. 1 is a condition suitable for continuous annealing, and according to the present invention, the final annealing can be performed by continuous annealing. Even if the hot-rolled sheet annealing is omitted or the intermediate annealing in the cold rolling process is omitted, the plastic anisotropy is limited only by limiting the final annealing condition to the range shown in Fig. 1 in relation to the cold rolling rate. It is obvious that the manufacturing process can be simplified and the energy for annealing can be saved because it can be reduced to the same level as that in the case of performing hot-rolled sheet annealing. In this respect, the method of the present invention is applicable to the austenitic stainless steel. The present invention provides a method for economically advantageous production of the cold-rolled steel sheet or steel strip.

Example C: 0.074%, Si: 0.58%, Mn: 1.13, Ni: 8.64
%, Cr: 18.21%, N: 0.024%, continuous cast slab (thickness 200 mm) of SUS304 is heated to 1230 ° C for rough rolling, and hot-rolling of 2.3 ~ 8.0 mm thickness is performed by changing the hot rolling finishing temperature. A board was manufactured. The winding temperature is 50 at that time.
It was set to 0 ° C. or less. Then, it was pickled without annealing the hot rolled sheet, cold-rolled once to a sheet thickness of 0.8 to 1.0 mm, and then finally annealed. Table 1 shows each hot rolling condition, cold rolling ratio, and final annealing condition. Then, the earring ratio (%) of each of the obtained cold-rolled sheets was measured by a cylindrical cup test. The results are also shown in Table 1.

From the results shown in Table 1, when the cold rolling rate and the final annealing conditions according to the present invention are satisfied, the earring rate is reduced and the austenite system with a small plastic anisotropy is obtained even if the hot-rolled sheet annealing is omitted. It can be seen that a cold rolled steel sheet or strip of stainless steel is obtained.

[Brief description of drawings]

Figure 1 shows the relationship between the annealing temperature and the annealing time of the final annealing, which shows the range where the earring rate is 7% or less when the cold rolling and the final annealing are performed without the hot-rolled sheet annealing of SUS304 steel. FIG. 2 and FIG. 2 are diagrams showing an example of the test results which led to the relationship of FIG.

Claims (2)

[Claims] 1. When manufacturing a cold-rolled steel sheet or strip of austenitic stainless steel through a hot rolling step, a cold rolling step and a final annealing step, a hot rolling step and a cold rolling step are performed. Annealing treatment of hot-rolled sheet is omitted, and cold-rolled to the product sheet thickness without intermediate annealing in the cold-rolling process, and the total cold-rolling ratio in the cold-rolling process is in the range of 40 to less than 70%. Then, the final annealing process was performed by continuous annealing, and the first
The temperature shall be soaked in the temperature and time range enclosed by the points AGBCEJF in the figure. [However, in Fig. 1, the temperature on the vertical axis is ° C and the time on the horizontal axis is the seconds in logarithmic scale.
The coordinates (time, temperature) are A (1,1000), G (10,1020), B (9
0,900), C (300,900), E (300,1000), J (100,1080), F (1,1
200)], which is a method for producing an austenitic stainless cold-rolled steel sheet or strip having a small plastic anisotropy. 2. When manufacturing a cold-rolled steel sheet or strip of austenitic stainless steel through a hot rolling step, a cold rolling step and a final annealing step, a hot rolling step and a cold rolling step are performed. Eliminate the annealing process of hot-rolled sheet, and cold-roll to the product sheet thickness without intermediate annealing in the cold-rolling step, and set the total cold-rolling rate in the cold-rolling step within the range of 70 to 95%. , And the final annealing process is carried out by continuous annealing.
The temperature shall be soaked in the range of temperature and time enclosed by points AGBCHID in the figure. [However, in Fig. 1, the temperature on the vertical axis is ° C and the time on the horizontal axis is the seconds expressed in logarithmic scale.
The coordinates (time, temperature) are A (1,1000), G (10,1020), B (9
0,900), C (300,900), H (100,1000), I (10,1080), D (1,113
0)], which is a method for producing an austenitic stainless cold-rolled steel sheet or strip having a small plastic anisotropy.