JP3026232B2 - Manufacturing method of thin stainless steel slab with excellent corrosion resistance and workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin slab of stainless steel, particularly a thin slab of stainless steel having excellent corrosion resistance and workability. In recent years, molten steel
Techniques for directly producing thin slabs of 0 mm or less have been developed and are already being implemented on an industrial scale. This new technology has been attracting attention because it eliminates the hot rolling step and is a process that can be greatly expected in terms of energy saving and cost saving.

[0002]

2. Description of the Related Art Conventionally, in a method of manufacturing a thin slab, F
An austenitic stainless steel containing e-18% Cr-8% Ni as a main component has a problem of roping that occurs on the surface of a cold-rolled sheet when the slab is cold-rolled due to coarse slab grains. On the other hand, for ferritic stainless steel containing Fe-17% Cr as a main component, ridging occurs due to coarse slab grains when processing a thin product sheet obtained by cold rolling and annealing a slab. There is a problem.

In order to solve these problems, Ti, Nb
However, there is no study on the workability and corrosion resistance of stainless steel thin slabs containing Ti, Nb and the like. For example, CA
In MP ISIJ Vol.1 (1988) -1702, the relationship between the slab grain size of chromium-based stainless steel thin slabs added with Ti and Nb and the ridging of cold-rolled annealed sheets has been studied. In No. 1586, a technique of adding Ti and Nb to refine γ grains in austenitic stainless steel thin slabs is studied, but no mention is made of workability and corrosion resistance of the stainless steel thin slabs. That is, at present, no study has been made on the workability and rust resistance of such stainless steel slabs containing Ti and Nb.

[0004]

SUMMARY OF THE INVENTION Ti,
By adding Nb, C and N in steel are fixed and corrosion resistance is improved.
In order to improve workability, it is often performed in a conventional hot rolling process. SUS43 is a common steel type.
Ti such as 0LX, SUS304N, SUS321
There are steel types containing Nb.

In the conventional slab continuous casting, slab heating, hot rolling and cold rolling annealing processes, Ti and Nb form carbides and nitrides during slab heating, and fix C and N of the base material. However, in the process of casting a thin slab in the casting step, the slab heating and hot rolling steps are eliminated, so that Ti, Nb
Does not have time to precipitate carbides and nitrides, so that C and N in the matrix are not sufficiently fixed. Therefore, the corrosion resistance and workability of the cast slab are lower than that of the hot rolled process material.
Furthermore, the corrosion resistance of the thin plate obtained by cold rolling and annealing the slab,
Workability is also lower than that of hot rolled process materials.

[0006] An object of the present invention is to provide a method of manufacturing a thin stainless steel slab which can solve such problems of the prior art.

[0007]

The above objects are achieved by the present invention. That is, the gist of the present invention is as follows.

[0008] By weight, C ≦ 0.1%, Si ≦ 5%, Mn
≦ 2%, Cr: 9-35%, Ni ≦ 18%, Al ≦ 7
%, Mo ≦ 7%, one or both of Ti and Nb in a total amount of 0.05 to 2.0%, N ≦ 0.04%, and a balance of steel having a thickness of 6 mm or less including Fe and unavoidable impurities. After continuous casting into a thin ribbon, it is wound in a temperature range of 1200 to 750 ° C., and is kept in a temperature range of 1200 to 750 ° C.
A method for producing a thin stainless steel slab excellent in corrosion resistance and workability, characterized by being immersed in water within 0 to 60 minutes and cooled to 600 ° C. or less.

[0009]

Next, the reason why the composition of steel in the present invention is numerically limited as described above will be described. C, Si, Mn, C
r, Ni, Al and Mo are the amounts that have been conventionally adjusted as the basic components of stainless steel.

Regarding Ti and Nb Ti and Nb are effective elements that form carbides and nitrides with C and N, thereby preventing grain boundary precipitation of Cr carbonitride and improving corrosion resistance and workability. However, if added in excess, large precipitates and inclusions are formed to deteriorate castability, and rusting occurs at the starting point of inclusions and precipitates.
0% or less. The same effect can be obtained by adding one kind or two kinds of composites.

Next, the reason for specifying the winding temperature of the slab in the present invention will be described. In the slab continuous casting-slab heating-hot rolling process, it was possible to easily control the precipitate of the slab in each step. However, in the thin continuous casting process, there is no step of applying heat to the slab, and the slab is only cooled after solidification. Therefore, when a stainless steel containing 0.03% or more of Ti and Nb is produced by a thin-wall continuous casting process, precipitation of carbides and nitrides is insufficient. Lower. Therefore, the present inventors have studied a method for controlling precipitates in thin slabs.However, after casting, a process of reheating and precipitating slabs cooled to room temperature, a process of cold-rolling slabs and then reannealing the slabs. It was found that in the process of precipitation during crystallization, carbides and nitrides were not sufficiently precipitated. Even when the slab and the cold-rolled annealed plate were heated and heated for a long time to precipitate, the precipitates were deposited very finely, which hindered the growth of recrystallized grains and had adverse effects on the product.

Therefore, it is necessary to precipitate Ti and Nb as carbides and nitrides in the process of cooling the slab to room temperature. As a method thereof, it is desirable to use the heat of the slab to precipitate the slab during winding. The control of the slab precipitate by controlling the slab winding temperature is a key technology in the thin-wall continuous casting process, and is a unique technology of the present inventors.

Since the temperature of the wound slab except for the coil ends is small, the slab is heated at a temperature close to the wound temperature for several tens of minutes to several hours. Therefore, the winding temperature becomes the heat retention temperature of the slab. According to the study of the present inventors, Ti and Nb of the slab were carbonized.
Heat retention temperature for depositing as a product or nitride is 1200
~ 750 ° C is effective. FIG. 1 shows the relationship between the winding temperature of the slab and the corrosion resistance of the slab. It can be seen that the corrosion resistance is improved by setting the slab winding temperature to 750 ° C. or higher.

FIG. 2 shows the relationship between the coiling temperature of the slab and the elongation of the sheet product obtained by cold rolling and annealing the slab. The slab winding temperature is 80
It is understood that the elongation of the product is lower at 0 ° C. or lower. FIG. 3 shows the relationship between the coiling temperature of the slab and the roughening (roping) of the cold-rolled sheet that occurs when the slab is cold-rolled. Although the precipitation of carbonitride is promoted by the high-temperature winding, roping occurs on the surface of the cold-rolled sheet because the grains of the slab grow. 1 grain growth
The temperature rapidly advances at more than 200 ° C., and as a result, the roping becomes large, thereby deteriorating the surface properties of the cold-rolled sheet. Therefore,
From the viewpoint of roping, the winding temperature needs to be 1200 ° C. or less.

However, since the cast slab wound at a temperature of 750 ° C. or more is slowly cooled in a temperature range of 700 to 600 ° C., which is a precipitation region of Cr carbide, carbide is precipitated. Steel types with low matrix toughness, such as high Cr stainless steel and high Al stainless steel, have a further reduced toughness due to the precipitation of Cr carbide, so it is necessary to prevent the precipitation of Cr carbide. After I wound up at 1200 to 750 ° C. As the method,
It is necessary to keep the temperature at 1200 to 750 ° C and to cool it to 600 ° C or less by water cooling within 10 to 60 minutes.

Accordingly, a thin stainless steel slab having excellent workability and corrosion resistance can be manufactured by controlling the component composition and the winding temperature as described above.

[0017]

EXAMPLE In a high-frequency induction furnace, 10 tons of molten stainless steel having the composition shown in Table 1 were melted, and a thin cast piece having a width of 800 mm and a thickness of 2 mm was cast by a twin-roll caster and wound under the conditions shown in Table 2. After performing a corrosion resistance test (pitting potential measurement) on the slab, pickling the slab and performing cold rolling of 80%, the ferritic stainless steel was heated at 950 ° C. for 60 seconds, and the austenitic stainless steel was Annealed at 1100 ° C for 60 seconds to make a thin plate product,
A tensile test was performed.

As shown in Table 2, the steel subject to the present invention has excellent corrosion resistance of cast slabs and good workability of thin plate products, while the comparative steel has poor corrosion resistance of cast slabs and low workability of thin plate products. I understood.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As described above, the stainless steel thin slab produced according to the present invention has good corrosion resistance as cast, and also has good workability of cold rolled and annealed sheet products. Therefore, the field of application as a thin slab is significantly expanded.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the casting temperature of a slab and the corrosion resistance of the slab.

FIG. 2 is a diagram showing the relationship between the winding temperature of a slab and the elongation of a cold-rolled annealed sheet.

FIG. 3 is a view showing the relationship between the winding temperature of a slab and the surface roughness (roping) of a cold rolled sheet.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI C22C 38/00 302 C22C 38/00 302Z 38/58 38/58 (58) Field surveyed (Int.Cl. ⁷ , DB name) B22D 11/00 B22D 11/12 B22D 11/124 B21C 47/26 C21D 9/46 C22C 38/00 C22C 38/58

Claims (1)

(57) [Claims] 1. By weight, C ≦ 0.1%, Si ≦ 5%, M
n ≦ 2%, Cr: 9 to 35%, Ni ≦ 18%, Al ≦ 7
%, Mo ≦ 7%, one or both of Ti and Nb in a total amount of 0.05 to 2.0%, N ≦ 0.04%, and a balance of steel having a thickness of 6 mm or less including Fe and unavoidable impurities. After continuous casting into a thin ribbon, it is wound in a temperature range of 1200 to 750 ° C., and is kept in a temperature range of 1200 to 750 ° C.
A method for producing a thin stainless steel slab excellent in corrosion resistance and workability, characterized by being immersed in water within 0 to 60 minutes and cooled to 600 ° C. or less.