JPH0357539A - Direct production of austenitic stainless steel sheet having excellent acid resistance and deep drawability - Google Patents

Abstract

PURPOSE:To directly produce the stainless steel sheet having excellent acid resistance and deep drawability by subjecting the sheet of a specific sheet thickness which is obtd. by rapidly solidifying the melt of an austenitic stainless steel and has a high equi-axed crystal rate to cold rolling and annealing treatment. CONSTITUTION:The molten steel of the austenitic stainless steel is supplied onto the moving cooling body, such as roll or belt of a continuous casting machine for sheets and is rapidly solidified, by which the sheet is directly produced. The sheet having >=50% equi-axed crystal rate and 0.1 to 20mm thickness is produced by adjusting the casting conditions. The austenitic stainless steel sheet which is small in both of corrosion resistance and earing rate and has the excellent acid resistance and small molding anisotropy is easily obtd. in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for directly producing thin austenitic stainless steel sheets having excellent acid resistance and deep drawability, and particularly relates to a method for directly producing thin austenitic stainless steel sheets from molten stainless steel, by a single roll method or a twin roll method. The present invention relates to a method for continuously and directly producing a thin plate of austenitic stainless steel with excellent acid resistance and deep drawability using a thin plate direct casting machine such as a single-belt method or a double-belt method.

[Conventional technology]

Austenitic stainless steel, represented by SUS304, has excellent corrosion resistance, high strength, and excellent press formability, so it is used in an extremely wide range of applications such as architectural exterior wall panels, interior panels, bathtubs, as well as kitchen utensils and utensils. It is used in

Generally, such thin plates of austenitic stainless steel are produced by first supplying molten steel to a continuous slab casting machine and continuously solidifying it to directly manufacture a slab with a thickness of 200±100 tm from the molten steel, and then hot rolling this slab. After this hot-rolled sheet is made into a hot-rolled sheet, this hot-rolled sheet is subjected to cold rolling treatment and heat treatment according to a conventional method to obtain a steel sheet.

Conventionally, it has been known that among certain chemical agents, Ni and Cu have an effective effect on the acid resistance of such austenitic stainless steels.
This is often dealt with by increasing the amount of i or adding a small amount of Cu.

In addition, conventional austenitic stainless steel sheets manufactured based on such continuous casting slabs are (112
) <111> Tends to form a texture. Especially this (
112) surface is the other low index surface (100), (110)
Compared to the (111) plane, it has poor acid resistance and is therefore unfavorable in terms of overall corrosion resistance. Moreover, it takes (112)
The <111> aggregated ML weave has the disadvantage that large selvages occur during deep drawing.

From this point of view, conventionally, when manufacturing thin plates, efforts have been made to prevent the occurrence of specific textures that often cause problems, and to create a structure with as random crystal orientation as possible. For example, Japanese Patent Publication No. 5811489 and Japanese Patent Publication No. 63-67527 disclose a technique of controlling the temperature during cold rolling as a means to obtain as random an orientation as possible.

[Problem to be solved by the invention]

In the case of the two prior art techniques, the acid resistance of austenitic stainless steel was improved by increasing the amount of Ni and adding a small amount of Cu, but this had the disadvantage of increasing raw material costs. Furthermore, as mentioned above, although there is a technique to control the aggregated Mi texture in order to improve deep drawing properties, there is no consensus on the technique to investigate this texture in order to improve acid resistance. Moreover, even though the texture may be controlled in order to improve deep drawability such as preventing earrings, it is necessary to strictly control the temperature during cold rolling, and the process and work contents are complicated. There was a problem.

[Means to solve the problem]

The present invention solves the above-mentioned problems faced by the prior art, and provides a method for easily producing austenitic stainless steel thin plate strips that exhibit poor acid resistance and deep drawability without increasing raw material costs. , by supplying molten austenitic stainless steel onto the moving cooling body of a continuous thin plate casting machine and rapidly solidifying it, thin plates can be directly produced by adjusting the casting conditions every 6 hours, etc.! lI
η of plate thickness 0.1 to 20-2 with r product ratio of 50% or more -L]
One sheet is cast, and the thin sheet thus obtained is cold rolled.
We propose a direct manufacturing method for austenitic stainless steel thin sheets with excellent acid resistance and deep drawability, which are characterized by annealing.

That is, the present invention is characterized in that it has been realized that it is possible to manufacture a slab that has both acid resistance and deep drawability by simply controlling the equiaxed fraction of the slab.

In the application of the present invention, the moving cooling body of a continuous sheet casting machine refers to a roll or a belt in a single-roll or twin-roll continuous sheet casting machine or a single-belt, double-belt continuous sheet casting machine.

The slab (thin plate) obtained by directly casting the molten steel in a predetermined proportion while continuously supplying it to the cooling surface of the moving cooling body and solidifying it one after another is made from the surface layer toward the inside of the plate thickness. It has an elongated columnar crystal structure and equiaxed crystals that are distorted near the center of the plate thickness.

The ratio of columnar crystals and equiaxed products in this cross-sectional view of the slab is determined by the casting conditions,
In particular, it varies depending on the supply amount of molten steel and solidification conditions such as the moving cooling body speed and cooling intensity. The present invention is a method characterized in that the proportion of equiaxed crystals in the cross-sectional area of the slab is 50% or more.

[For production]

The present inventors cold-rolled and annealed slabs with various changes in the solidification conditions and the proportion of equiaxed crystals, and studied the acid resistance and deep drawability of the slabs.

As a result, they found that an equiaxed product ratio of 50% or more provides both excellent acid resistance and deep drawability.

That is, FIG. 1 shows the (112) strength ratio (I/[0) of austenitic stainless steel based on the above test results,
5%}1250, is a diagram showing the relationship between corrosion values. As can be seen from this figure, the (112) intensity ratio (1/I.) is 2.
If it exceeds 1, 5%H. S.O. Corrosion value increases rapidly.

Therefore, in order to obtain excellent acid resistance, it is necessary to have a small intensity ratio (11.2), that is, I/I. It can be seen that the condition of ≦2.1 is required. Note that T0 is (112) of the random sample.
Strength, ■ indicates the (112) strength of the sample material.

Figure 2 shows that the thin plates with different equiaxed crystal ratios obtained as described above were subjected to 50% cold rolling and then rolled at 1100°C for 30 minutes.
(112) intensity ratio 1/I. This figure shows the results of investigating the relationship between the columnar crystal ratio and the columnar crystal ratio of the thin plate.

As can be seen from this figure, the (112) intensity ratio 1/I. indicates a large value. However, in the case of a ribbon with an equiaxed product ratio of 50% or more, the strength ratio of 1/10 decreases rapidly.

Therefore, to obtain excellent acid resistance, the equiaxed crystallinity should be 50
It can be said that a material with a small strength ratio I/Io made of slabs exceeding % is effective.

Moreover, FIG. 3 shows the results of Fit l with different equiaxed crystallinity for the continuous cast slabs obtained as described above.
This figure shows the results of investigating the relationship between the earring ratio during deep drawing and the equiaxed crystallinity of the thin plate after cold rolling 50% and heat treating at 1100° C. for 3 minutes. As can be seen from this figure, there is a clear tendency for the earring ratio after cold rolling and annealing to decrease as the equiaxed product ratio of the thin plate increases.

As explained above, at least for thin sheets manufactured by continuous thin sheet casting machines, increasing the equiaxed crystallinity alone improves both the acid resistance and deep drawability of the product after cold rolling and annealing. It is clear that the
In particular, this effect becomes remarkable when the equiaxed product ratio becomes 50% or more.

In addition, as a method to increase the equiaxed product rate of cast thin plates to 50% or more, the casting speed based on the composition of the molten steel to be cast,
This is done by selecting the casting temperature, casting plate thickness, etc. In particular, the yield of the cast structure, ie, the equiaxed crystal, is influenced to some extent by the Mi and casting temperature. First, regarding the strength composition, it is sufficient to add elements that do not easily produce δ ferrite 1 or elements that easily generate solidification heat.On the other hand, regarding the casting temperature, it is possible to control the temperature at a lower temperature. It is valid.

As explained above, the equiaxed product ratio can be controlled by various methods, but if the control is unsuccessful, the equiaxed crystal ratio of the slab will be about 40%, which will not achieve the purpose of the present invention. I can't.

〔Example〕

In this example, molten steel of SUS304 steel and SOS 3105 steel of Kaibungumi shown in Table 1 is melted in a 10 kg atmospheric induction furnace, and then fed to a twin-roll continuous thin plate casting machine with an inclined plate, where it is rapidly solidified. In this way, a thin plate with a predetermined thickness was manufactured. This thin plate was cast under solidification conditions such that at least 50% of the vertical cross-sectional area at the approximate center of the slab had equiaxed crystallinity. ~llh8), 5%11. S0
4 Corrosion test and deep drawing test were conducted to measure the corrosivity and earring rate, and confirm the respective effects. The results are shown in Table 2.

On the other hand, as a conventional method, after refining molten steel of the same type in an AOD furnace, it is cast in a normal continuous slab casting machine to a thickness of 14 mm.
A 5D slab was prepared, and this slab was hot-rolled using a planetary wheel to form a hot-rolled plate having a thickness of 5.51 mm, and a product plate was obtained under the same conditions shown in Table 2. Then, for these product plates, the corrosion value obtained by a corrosion test at 60°C, 5% 112sO, and the ear height of the deep drawing cup obtained by a deep drawing 9 test were measured, and the earring ratio was determined. These measurement results are shown in Table 2. 9
．． They are collectively shown as 10.

Table 1 (1%) 10 1 1 As is clear from Table 2 showing the experimental results, according to the method of the present invention, both the corrosiveness and the earring rate were lower for each test material than those made using the conventional method. It turned out that.

〔Effect of the invention〕

As explained above, according to the present invention, corrosion resistance can be reduced simply by controlling the equiaxed crystallinity of the slab. Since a product with a small earring ratio can be obtained, it is possible to easily produce an austenitic stainless steel thin plate having excellent acid resistance and small anisotropy.

[Brief explanation of drawings]

Figure 1 shows the (112) strength ratio of SUS304 and 5%ll.
2so, a graph showing the relationship with the corrosion value. Figure 2 is a graph showing the relationship between the equiaxed grain rate and (112) strength ratio of SUS304. Figure 3 is the graph showing the relationship between the equiaxed crystal rate and the earring rate of SUS304. It is a graph showing the relationship between. 12 ("q・BUv53)H'fi'lJI 'O'E"H
%9. ln09? Scoop ■■■ (gTT)

Claims (1)

[Claims] 1. By supplying molten austenitic stainless steel onto the moving cooling body of a continuous thin plate casting machine and rapidly solidifying it, the equiaxed crystal ratio of 50 can be achieved by adjusting the casting conditions when directly manufacturing thin plates. Plate thickness 0.1~ with % or more
A method for directly producing an austenitic stainless steel thin plate having excellent acid resistance and deep drawability, which comprises casting a 20 mm thin plate, cold rolling the thin plate thus obtained, and annealing the thin plate.