JPH0263650A - Production of austenitic stainless strip - Google Patents

Abstract

PURPOSE:To obtain a steel strip having good balance to high strength and elongation by pressure-welding solidified shells of steel mutually to each other at narrow gap part between twin rolls under the prescribed pressure-welding load, continuously producing the steel strip having the specific range of thickness, cold-rolling the obtd. steel strip to the aimed value and annealing. CONSTITUTION:The solidified shells of the stainless steel formed on circumference of the twin rolls 3, 3' are mutually pressure-welded to each other at the narrow gap part between the twin rolls under pressure-welding of 1-40kgf per 1mm of the width as the pressure-welding load to continuously produce the steel strip having 0.2-5.0mm thickness. The load applied to load cells 8, 8' fitted to roll bearing 7 show the pressure-welding load of the solidified shells 6, 6'. The steel strip is cold-rolled to the aimed thickness and if necessary, annealing is executed, to continuously produce the steel strip of the normal austenitic stainless steel. By this method, the steel produced under the suitable range of casting condition has a little anisotropy and fine crystal grains and the grains are difficult to grow and the steel strip having good balance to the strength and elongation can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an austenitic stainless steel strip having a good balance between strength and ductility and having small anisotropy.

[Conventional technology]

As is well known, austenitic stainless steel has good corrosion resistance and workability, and is widely used for processing such as press forming. 3113304 is a typical material. Typical applications include household items such as kitchens and bathtubs, construction materials such as interior and exterior materials, and various electrical appliances and parts.

The conventional manufacturing method for these austenitic stainless steel strips and sheets is continuous casting, which produces steel strips and sheets with a thickness of 100 to 2
It was common practice to cast into a 0'Omm slab, which was then subjected to a combination of hot and cold rolling and annealing and pickling to form a thin steel strip or steel plate.

Steel sheets manufactured in this way have large in-plane anisotropy,
The mechanical properties, especially the directionality of elongation, increase depending on the direction, and when processing such as deep drawing is performed, earrings are produced, leading to a decrease in material yield. It is generally believed that the cause of in-plane anisotropy is the influence of the texture produced by rolling in a certain direction, and various methods have been proposed as countermeasures. It is no exaggeration to say that all of these involved regulating the number of cold rolling and annealing times, cold rolling rate, and annealing temperature in the cold rolling process.

For example, according to ``Method for producing austenitic stainless steel strip or steel plate with low in-plane anisotropy'' in JP-A-56-72125, after annealing a hot-rolled steel strip or steel plate,
- In a manufacturing method in which cold rolling is performed, annealing is performed, and then final cold rolling is performed to the thickness of the product, and final annealing is performed, a method is disclosed in which the final cold rolling is performed at a rolling rate of 30 to 50%. . Furthermore, according to ``Method for manufacturing austenitic thin stainless steel sheet for deep drawing of rectangular cylinders'' in Japanese Patent Application Laid-open No. 5228424, it is known that hot-rolled steel strips or steel sheets can be used as they are, or at most
A method of cold rolling after heat treatment at a temperature of up to 30°C.

Alternatively, a method is described in which rolling is carried out while maintaining the first pass rolling temperature at 20° C. or lower during cold rolling. Further, ``Method for producing austenitic stainless steel strip with small in-plane anisotropy of plastic strain ratio'' in JP-A-52-104416.
According to the above, after annealing a hot-rolled steel strip, the annealing temperature is 1150 to 125 when rolled to the product thickness in one cold rolling and finish annealed.
0°C, or the temperature during cold rolling is 35-2
A method of setting the temperature to 50°C is shown.

[Problem that the invention seeks to solve]

Conventional means to solve the in-plane anisotropy of austenitic stainless steel include conditions such as annealing conditions after hot rolling, rolling temperature during cold rolling, reduction ratio, and number of times of cold rolling, final annealing temperature and number of times, etc. and is extremely complex. Depending on how you look at it, it is inefficient and worsens manufacturability.

Furthermore, if attempts are made to suppress earrings using conventional techniques, the good balance between strength and elongation, which is the most characteristic feature of austenitic stainless steel, may be sacrificed. Whether or not the austenitic stainless steel is used for deep drawing, a good balance between strength and elongation is often emphasized as a material characteristic. However, in order to obtain high elongation, it is necessary to perform annealing at a high temperature, and coarsening of crystal grains is inevitable. This causes a decrease in strength and causes roughness during processing. At present, there is no known effective method for preventing crystal grain growth during annealing.

The present invention aims to solve the problems of the prior art, and can fully exhibit the characteristics inherent in austenitic stainless steel. The aim is to provide a manufacturing method that is different from conventional methods.

[Means for solving problems]

The inventors of the present invention have continued various experimental studies with the intention of reviewing and developing the entire manufacturing technology of austenitic stainless steel in order to solve the above-mentioned problems, but the conventional manufacturing method of austenitic stainless steel If we omit the necessary hot rolling from a slab and directly produce a thin plate from molten austenitic stainless steel by rapidly solidifying it under appropriate conditions and then cold rolling it, the above purpose can be achieved. I have found that it is quite achievable.

That is, in the present invention, molten austenitic stainless steel is continuously poured into a twin-roll continuous casting machine having a pair of internal cooling rolls that rotate in opposite directions and are disposed opposite each other, and the molten metal is poured onto the circumferential surface of each of the rolls. The solidified shells of the cough steel formed in the narrow gap between the twin rolls
The thickness is 0.2 to 5.0 when crimped under a crimping load of gf.
In-plane anisotropy is achieved by continuously manufacturing a steel strip of 1.0 mm in thickness, cold-rolling the obtained steel strip with or without annealing to a target thickness, and annealing as necessary. The present invention provides a method for producing an austenitic stainless steel strip with high strength and good workability.

In the present invention, the conventional hot rolling from a slab is not performed, but molten austenitic stainless steel is rolled onto the surface of two cooling rolls, cold-solidified to form a solidified shell, and then rolled between two rolls in an appropriate manner. Manufacture steel strip by crimping under certain conditions,
This results in a steel strip with a special solidification structure that is different from the conventional hot-rolled structure, which is then cold-rolled.
As a result, a material with low in-plane anisotropy was obtained.

Furthermore, the steel strip has been industrially obtained, which suppresses the coarsening of crystal grains even during annealing and has the characteristics inherent to austenitic stainless steel with a good balance between high strength and elongation.

[Detailed description of the invention]

Figures 1 and 2 show the main parts of a double-mouth continuous caster to which the method of the present invention is applied.As shown in Figure 1, the molten steel of austenitic stainless steel (
(hereinafter simply referred to as molten steel) 1 is continuously poured from the opening of the kundish into a pool 4 formed on the circumferential surface of internal water-cooled twin rolls 3, 3, which rotate in opposite directions. Injected. As shown in Fig. 2, the molten steel injected into the pool is rapidly solidified on the circumferential surface of the twin rolls 3, 3'' to form a thin solidified shell 6.6'', which As the twin rolls rotate, they are crimped and rolled together at the narrowest gap to produce a continuous steel strip 5. At this time, the load applied to the load cells 8, 8° attached to the roll bearings 7 is the crimping load of the solidified shell 6.6°. As the solidification progresses at a low roll rotation speed, the crimping load increases, and conversely, as the rotation speed increases, the crimping load decreases.Such a twin-roll continuous casting machine is disclosed in Japanese Patent Application No. 1983-1985 filed by the same applicant. 84555 and Japanese Patent Application No. 63-42805 and the drawings.

The present inventors manufactured a large number of thin plates of austenitic stainless steel using the twin-roll continuous caster. Figure 3 shows the properties of the plates at the time, using a load cell for an example of 5US316 steel. The results are organized according to the relationship between the crimp load and plate thickness shown in Figures 8 and 8'.As seen in the results in Figure 3, when the crimp load is less than 1 kgf/mm, internal defects (
Porosity, etc.) occur frequently, and when the pressure exceeds 40 kgf/mm, surface defects such as vertical cracks and horizontal cracks occur on the surface of the steel strip. Further, if the plate thickness is less than 0.5 mm, wrinkling occurs in the wakame shape and the plate width becomes uneven. Further, if the plate thickness exceeds 5.0 mm, a breakout occurs in which the unsolidified portion leaks to the outside. However, the crimping load is 1 to 40 kgf/m.
Normal austenitic stainless steel can be obtained by plating 6.6" resolidified shells using a roll gap (by pressing the resolidified shells together) so that the plate thickness is in the range of 0.2 to 5.0 mm. It was found that steel strips can be manufactured continuously.And when the steel strips manufactured under the appropriate range of casting conditions are cold rolled and annealed, as shown in the following example, It was found that the steel strip has little anisotropy, has fine crystal grains, is difficult to grow, and has a good balance of strength and ductility.

On the other hand, casting conditions outside this range will result in a non-uniform metal structure, resulting in a decrease in elongation during a tensile test and cracking during processing.

Two typical examples of the present invention will be given below to specifically demonstrate the effects of the present invention.

[Example 1] Twin roll continuous casting machine described in the main text (patent application 1984-845)
The belt was manufactured directly from molten steel of 5IIS316 using a thin plate continuous caster described in No. 55 and Japanese Patent Application No. 63-42805 and the drawings. Table 1 shows the relationship between the plate thickness, pressure bonding load, and defects at that time.

Table 1 [Example 2] Molten steels of austenitic stainless steels A and B whose chemical composition values are shown in Table 2 were made into steel strips using the same twin-roll continuous caster as in Example 1. At that time, a steel strip having a plate thickness of 2 mm was cast with a compression load of 20 kgf/mm (an example of the present invention). In addition, as a comparative example, the same steel strip with a thickness of 2 mm was crimped with a crimping load of 0.3 kg.
f/mm and 45 kgf/mm (comparative example).

The obtained toning zones are all 1150° (: x 3 m
After carrying out the solution treatment in, cold rolling to a plate thickness of 0.6 mm and annealing at 1050'CX 1 min were carried out.

On the other hand, thin steel strips were manufactured from austenitic stainless steel@C whose chemical composition values are shown in Table 2 according to conventional manufacturing methods (conventional example). The manufacturing conditions are as follows. That is, a slab with a thickness of 200 mm is manufactured by continuous casting, a hot-rolled steel strip with a thickness of 4.0 mm is produced by hot rolling, and after solution treatment at 1150° C. It was used as a material. In addition, some parts are cold rolled to a thickness of 1.0mm and then rolled at 1150°C
After performing intermediate annealing for 1 min, it was made into a cold-rolled material with a plate thickness of 0.6 mm. All of these cold-rolled materials are 1150°CX
Annealing was carried out for l min.

Samples were taken from the cold-rolled materials obtained in the inventive examples, comparative examples, and conventional examples.
Mechanical tests were conducted in three directions (90°), yield strength,
Tensile strength and elongation were measured.

The results are summarized in Table 3.

As seen from the results in Table 3, although the anisotropy of the materials manufactured by the conventional method was improved by performing intermediate annealing, the anisotropy was still large. In contrast, the material produced by the method of the present invention has extremely small anisotropy. In addition, the tensile strength x average elongation is higher than that of conventional materials, and the balance between strength and elongation is good.

Note that stable material properties were not obtained with the comparative material in which the 2-press bonding load was 0.3.45 kgf/mm 2 .

[Example 3] The materials of the present invention example and the conventional example obtained by cold rolling to a plate thickness of 0.6 m11 in Example 2 were annealed by varying the annealing temperature and time, and the annealed materials obtained were The crystal grain size (crystal grain size number: G, S, No.) and hardness (Hv) were measured. The results are shown in Figure 4.

From Figure 4, the crystal grains of the steel strip produced by the conventional method rapidly become coarser and soften as the annealing temperature increases, but 2
It is clear that the steel strip produced by the method of the present invention is less likely to undergo softening as the crystal grains become coarser.

Similarly, the cold-rolled materials of the present invention example and the conventional example were annealed at a temperature of 1.
Annealing was carried out by changing the annealing time at a constant temperature of 050°C, and the crystal grain size of the obtained annealed material (crystal grain size number 2G, S, No.
) was investigated. The results are shown in Figure 5.

From FIG. 5, it can be seen that the grains of the steel strip produced by the conventional method become coarser over time.

It is clear that the crystal grain size of the ribbon produced by the method of the present invention hardly changes and two-grain growth is difficult.

[Example 4] 5US301 whose chemical composition values are shown in Table 4. 81F
4 was made into a steel strip using the same twin-roll continuous caster as in Example 1.

At this time, the crimping load was divided into 0.5 kgf/mm and 20 kgf/mm for casting into a steel strip having a thickness of 3.0 mm. The obtained steel strip was immediately cold-rolled to a thickness of 0.6 mm without annealing, and then rolled to a thickness of 1100'CX.
Annealing was performed for 3 min.

The metallographic Mi texture of the obtained annealed material is shown in FIGS. 6 and 7. FIG. 6 shows the case where the rolling load is 20 kgf/mm, and FIG. 7 shows the case where the rolling load is 0.5 kgf/mm. The one in FIG. 6 shows a uniform metal structure, but in the case of the rolling load Q of 5 kgf/mm in FIG. 7, the crystal grain size is irregular and the metal structure is non-uniform.

Therefore, it is clear from the viewpoint of the metallographic structure that it is important to compress the solidified shell with an appropriate compression load in order to obtain a good cold-rolled annealed material.

Table 4 [Example 5] Deep drawing was performed using each annealed material obtained in Example 2.

The processing was carried out by punching a blank with a diameter of 29 mm using a type 13 punch specified in JIS-Z-2249.

The height of the ear after squeezing was measured at 4 points on the high side and 4 points on the low side, and the average value of the difference was evaluated as the earring height. The results are shown in Table 5.

As seen in the results in Table 5, the earring height of the steel strip produced by the conventional method is considerably higher than the earring height of the steel strip produced by the method of the present invention.9 How small is the anisotropy of the steel strip produced by the method of the present invention? is clear.

As is clear from the results of the examples shown in Table 5 and above, compared to the conventional method for manufacturing austenitic stainless steel strip, which involves manufacturing slabs and performing hot rolling, the method of the present invention is more effective than the conventional method for manufacturing austenitic stainless steel strip. It is possible to obtain a steel strip with an excellent balance between high strength and elongation. In addition, the problem of in-plane anisotropy in steel sheets, which was difficult to suppress with conventional methods, is solved by the method of the present invention, and even when applied to deep drawing applications, the material has fewer earrings, improving product yield and saving money. By improving manufacturability through processes, it is possible to provide the market with materials that are inexpensive, have high strength, and have good workability.

Such an effect has also been proven from a metallurgical point of view, in that the method of the present invention produces a metal structure in which crystal grains are less likely to become coarse compared to the conventional method.

The method of the present invention provides a technique useful in the production of austenitic stainless steel strip and sheet.

The steel type to which the method of the present invention can be applied is 5US301S.
US304.5US316.5US310S, 5US
302.5US302B, 5US301LSLIS3
04L, 5US316L, 5US321, 5US
Not only austenitic stainless steels such as 347.5US201, but also austenitic/ferritic stainless steels such as 5US329JI, and precipitation hardened stainless steels such as 5US630SUS631 can be used. In addition, the method of the present invention can exhibit properties not found in conventional materials not only for annealed materials, but also for as-cold-rolled materials, materials whose shape is modified by temper rolling or tension reshaping after annealing, and even materials that are polished. It is.

[Brief explanation of the drawing]

1M is a schematic cross-sectional view showing the main parts of a twin-roll continuous casting machine to which the method of the present invention is applied, FIG. 2 is a schematic cross-sectional view showing the state during casting by the twin-roll continuous casting machine, and FIG. is a diagram showing the relationship between crimp load and plate thickness on plate quality when 5US316 steel strip is manufactured using a twin-roll continuous caster according to the present invention;
Figure 4 shows the relationship between the annealing temperature, hardness, and grain size number of the cold-rolled material manufactured according to the present invention in comparison with comparative materials and conventional materials. A diagram showing the relationship between the holding time and the grain size number when the material is annealed at an annealing temperature of 1050 ° C compared to the conventional material,
FIGS. 6 and 7 are metallurgical micrographs showing the metallographic structures of cold-rolled annealed materials when the pressure applied by the twin-roll continuous caster was varied. 1. Molten steel, 2. Tundish, 3. Internally cooled twin rolls, 4. Pool section, 5. Adjustment zone,
6. Solidified shell 7. Roll chock, 8
・・Load cell. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1050°cx Time (min) Figure 6 Figure 7 100μ

Claims (1)

[Claims] Molten austenitic stainless steel is continuously poured into a twin-roll continuous caster, and the solidified shells of the steel formed on the circumferential surface of each roll are mixed together in the narrow gap of the twin rolls per 1 mm of sheet width. Steel strips with a thickness of 0.2 to 5.0 mm are continuously produced by crimping under a crimping load of 1 to 40 kgf, and the obtained steel strips are annealed or not to achieve the target thickness. A method for producing a high-strength, good-formability austenitic stainless steel strip with little in-plane anisotropy, which comprises cold-rolling and annealing the steel strip.