JP2792737B2 - Method for producing thin Cr-Ni stainless steel sheet with excellent workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a so-called synchronous continuous casting method in which there is no relative speed difference between a slab and the inner wall surface of a mold. The present invention relates to a method for producing a steel sheet, and more particularly to a method for producing a Cr-Ni-based stainless steel sheet having good workability by suppressing the precipitation of fine sulfides in the process of cooling a slab.

[0002]

2. Description of the Related Art Conventionally, in order to manufacture a stainless steel thin plate using a continuous casting method, a mold is cast into a slab having a thickness of 100 mm or more while vibrating a mold in a casting direction. After heating in a heating furnace to 1000 ° C or more,
Hot rolling was performed by a hot strip mill consisting of a rough rolling mill and a finishing rolling mill to form a hot strip having a thickness of several mm.

When the hot strip thus obtained is cold-rolled, the hot strip that has been subjected to strong hot working is softened in order to secure the shape (flatness), material and surface properties required for the final product. In addition to performing hot-rolled sheet annealing for performing the heat treatment, scale and the like on the surface were removed by grinding after the pickling step. In this conventional process, a large amount of energy is required for heating and processing the material in a long hot rolling facility, and it is difficult to say that the production process is excellent in terms of productivity. In addition, the final product has a lot of restrictions on its use, for example, the texture has developed and it is necessary to take into account the anisotropy when the user presses or the like.

In order to solve the problem of requiring a long hot rolling equipment and a large amount of energy and rolling power in order to roll a slab having a thickness of 100 mm or more into a hot strip, continuous casting has recently been carried out. In this process, researches on a process for obtaining a slab (thin strip) having a thickness equal to or close to that of a hot strip have been conducted. For example, "iron and steel"'8
5, a paper featured in A197-A256 discloses a process for obtaining hot strip directly by continuous casting. In such a continuous casting process,
When the gauge of the slab to be obtained is at the level of 1 to 10 mm, the twin drum system is studied, and when the gauge of the slab is at the level of 20 to 50 mm, the twin belt system is studied.

[0005]

It is known that a sheet product manufactured by a continuous casting process of this type has a fine grain structure and a lower elongation than a sheet product manufactured by a conventional process. For example, "CAMP ISIJ" vol.1 198
8, 1670-1705, it is reported that the slab is annealed to eliminate δ-ferrite remaining in the slab as a countermeasure.

In the current process, the cooling rate of the slab after solidification is about 0.5 ° C./sec.
Sulfides such as MnS and Cu ₂ S are coarsely precipitated to about several μm. The coarse sulfide is harmless and does not inhibit the growth of grains in the process of hot rolling, hot rolling annealing, cold rolling and then cold rolling annealing the cast slab. However, in the continuous strip casting process (hereinafter referred to as the strip continuous casting process), even when the slab is air-cooled, the slab cools at about 50 to 20 ° C./sec, so that precipitation of S as sulfide is suppressed and the amount of solid solution S increases. . Therefore, it precipitates finely during cold rolling annealing and inhibits grain growth. Furthermore, when the cast slab is secondarily cooled to perform low-temperature winding in order to prevent sensitization during winding of the slab, the amount of dissolved S further increases depending on the secondary cooling start temperature. As a result, the cold rolled annealed sheet manufactured from the continuous cast slab has a fine-grained structure and low ductility.

[0007] Such a phenomenon of reducing the grain size and reducing the ductility of the cold-rolled annealed sheet is a phenomenon peculiar to the SUS304 strip continuous casting process. The present inventors have developed a Cr-Ni by strip continuous casting.
Study of the stainless steel sheet manufacturing process in detail reveals the existence of δ ferrite, inclusions, and fine precipitates remaining in the slab as factors that suppress the growth of recrystallized grains during cold rolling and annealing. became.

[0008] It is necessary to improve the ductility by facilitating grain growth by eliminating these factors inhibiting grain growth when manufacturing a thin sheet product having good workability in the present process. An object of the present invention is to control fine precipitates and improve ductility.

[0009]

The gist of the present invention is as follows. In the process of casting a thin Cr-Ni stainless steel slab by the continuous strip casting method and cold-rolling the slab to produce a thin sheet product, δ ferrite and inclusions remaining in the slab and precipitate during cold rolling annealing Fine sulfide
The growth of recrystallized grains is suppressed in the annealing step after cold rolling.

Among them, in order to prevent the precipitation of fine sulfides (MnS, Cu ₂ S) having a particularly large effect of inhibiting the grain growth by the precipitates, the content of Mn, Cu, S in the steel is expressed as Adjust the components to satisfy. The contents of the elements described below are all by weight. S × (Mn + Cu) ≦ 10 ^{−3 By} this component adjustment, fine precipitation of MnS during annealing of the cold-rolled sheet is suppressed regardless of the cooling speed of the slab. Therefore, after cooling the slab to 800 ° C. or less after casting, the slab can be wound up.

[0011]

FIG. 1 simply shows the effect of the present invention. It is. SUS304 thin cast pieces (thickness: 2.2 mm _t ) were cast by changing the amount of S in steel in various ways, and after casting, air-cooled to 1000 ° C at an average cooling rate of 40 ° C / sec, and then water-cooled. The film was wound at a temperature of 400 ° C. or less. After descaling the slab, the slab was cold-rolled 70%, and the cold-rolled sheet was annealed at 1100 ° C for 20 seconds, and the grain size and L-direction elongation of the cold-rolled annealed sheet were measured.

The grain size of the cold-rolled annealed sheet increases as the amount of S decreases, and when it is 10 ppm or less, it becomes almost the same as that of the current process material. It can be seen that as the grain size increases, the elongation also increases, and elongation comparable to that of the current material can be obtained.

[0013]

EXAMPLES Austenitic stainless steels of various components based on 18% Cr-8% Ni steel shown in Table 1 were melted and desulfurized with Ca, REM, etc. to determine the amounts of S, Mn and Cu according to the present invention. Range. This molten steel was continuously cast into a slab having a thickness of 3 mm and a width of 100 mm by an internal water-cooled twin-drum continuous caster, and the slab was subjected to secondary cooling and wound at 400 ° C., followed by pickling.
After cold rolling to 0.6 mm, annealing, pickling, and temper rolling were performed to obtain a thin sheet product.

As a comparative example, a thin slab was cast from a molten steel containing Mn, Cu, and S outside the scope of the present invention in the same manner without using a desulfurizing material to produce a thin plate product. As shown in Table 2, the thin plate produced by the present invention had excellent ductility and good workability. The thin plate manufactured in the comparative example had low ductility and poor workability.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

According to the present invention, an austenitic stainless steel sheet excellent in workability can be obtained by a simple process of continuously casting a strip-shaped slab having a thickness close to the product thickness to a product by direct cold rolling. it can. Therefore, the effect is extremely large in terms of economy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between S × (Mn + Cu) and elongation of a cold-rolled annealed sheet.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C21D 9/46-9/48 C21D 8/02-8/04 B22D 11/00 B22D 11/06 330

Claims (1)

(57) [Claims] 1. Cr represented by 18% Cr-8Ni steel
-Mn, Cr and S in Ni-based stainless steel
× (Mn + Cu) ≦ 10 ⁻³ The molten steel whose composition was adjusted to the range of −10 ⁻³ was continuously cast into a strip-shaped slab having a thickness of 6 mm or less by continuous casting in which the mold wall surface moved in synchronization with the slab. After winding the slab at a temperature of 800 ° C. or less, pickling,
Cold rolling, then annealing-pickling or bright annealing,
A method for producing a Cr-Ni-based stainless steel sheet, wherein temper rolling is performed thereafter to obtain a sheet product.