JPH0559447A - Production of cr-ni stainless steel sheet excellent in surface quality and workability - Google Patents

Abstract

PURPOSE:To obtain the steel sheet by specifying delta-Fecal(%), adding specific amounts of Al, etc., and Y, etc., and specifying manufacturing conditions at the time of producing a Cr-Ni stainless steel sheet by a synchronous continuous casting method. CONSTITUTION:A molten Cr-Ni stainless steel where delta-Fecal (%) defined by delta-Fecal (%)=3(Cr+1.5Si+Mo+2Ti+Nb)-2.8 (Ni+0.5Mn+0.5Cu)-84(C+N)-19.8 (each component is shown by weight percentage) is regulated to 2-10% and also 0.001-1%, independently or in total, of >=0.01% of Al, Ti, Nb, etc., and >=0.001% of Y, Ca, Mg, and B are contained is used. This molten steel is formed into a foil-like cast strip of <=10mm thickness by means of a twin roll continuous caster at >=100 deg.C/sec cooling rate at the time of solidification, cooled down to 1250 deg.C, held at 1250-900 deg.C for <=2min, cooled through the temp. region between 900 and 600 deg.C at >=10 deg.C/sec cooling rate, and coiled. This cast strip is pickled, warm- or cold-rolled, subjected to bright annealing in the annealing and pickling zone, and temper-rolled into a product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention produces a slab of a size close to the product thickness by a so-called synchronous continuous casting process in which there is no relative speed difference between the slab and the inner wall surface of the mold, and the surface quality and workability are improved. The present invention relates to a method for producing an excellent Cr-Ni-based stainless steel sheet.

[0002]

2. Description of the Related Art Conventionally, in order to produce a stainless steel thin plate by a continuous casting method, a casting having a thickness of 100 mm or more is cast while vibrating the casting mold in the casting direction, and the surface of the obtained casting is cleaned. After being heated to 1000 ° C. or higher in a heating furnace, hot rolling was performed by a hot strip mill to obtain a hot strip having a thickness of several mm. After that, the hot rolled sheet was annealed, and the scale on the surface was removed by grinding after the pickling step.

The conventional process requires a large amount of energy for heating and processing the material in a long hot rolling facility, and it is difficult to say that the manufacturing process is excellent in productivity. In addition, the final product has a lot of restrictions in use, such as a texture developed, and it is necessary for the user to take the anisotropy into consideration when applying pressing or the like.

Recently, research has been conducted on a process for obtaining a slab (thin band) having a thickness equal to or close to that of a hot strip in the process of continuous casting. For example, "iron and steel"'
85, A197-A256 and "CAMP ISIJ" v
ol. 1, 1988, pp. 1670-1705, discloses a process for obtaining hot strip directly by continuous casting.

In such a continuous casting process,
The gauge of the slab (strip) to be obtained is 1 to 10 m
When the level is m, the twin drum system is being considered. However, it is said that there is still a problem in the casting stage in these continuous casting processes, and it has not reached the stage where the problems regarding the material and surface quality of the product have been solved.

"CAMP ISIJ" Vol. 1, 1
988, P1670-1705, S cast by twin drum casting, single cold rolling process.
Since the US304 thin plate product has a fine grain structure compared with the conventional process and has a low elongation, as a countermeasure against this, it is stated that the slab is annealed at a high temperature for a long time to eliminate the δ ferrite remaining in the slab. Has been.

Further, "CAMP ISIJ" Vol. 3,
In 1990 and P770, it was reported that orange peel-like surface defects were generated, and as a countermeasure against this, decreasing the γ grain size before cold rolling was reported.

[0008]

In a process which is being developed as a new process and is premised on obtaining a slab (thin strip) having a thickness equal to or close to that of a hot strip by continuous casting. Since the steps from casting to products are simplified, the surface characteristics and workability of stainless steel sheet products are sensitively affected by the slab properties. That is, in order to obtain a product having excellent surface quality and workability, it is necessary to obtain an excellent slab.

The inventors of the present invention have already clarified a method of refining the γ grains of a cast piece for a method of preventing the occurrence of surface defects called the roping phenomenon or the above-mentioned orange peel phenomenon in the above new process, I have applied for. Japanese Patent Application No. 63-221471 Method by slab cooling and hot rolling Japanese Patent Application No. 63-169095 slab cooling and 2CR method Japanese Patent Application No. 63-221472 slab cooling and δ ferrite control Japanese Patent Application No. 63-286680 Slab cooling and δ-ferrite control Japanese Patent Application No. 1-1586 Slab cooling and addition of fine-grained elements However, the elongation and workability of thin plate products, which are the characteristics of Cr-Ni stainless steel, are insufficient only by these methods. It became clear to do.

The present invention has been made for the purpose of providing a simple manufacturing process capable of obtaining an austenitic stainless steel sheet free from surface defects such as roping and orange peel phenomenon and having good elongation and workability. ..

[0011]

The subject matter of the present invention is as follows. (1) δ-Fecal (%) = 3 (Cr + 1.5Si + M
o + 2Ti + Nb) -2.8 (Ni + 0.5Mn + 0.
5Cu) -84 (C + N) -19.8 (each component is wt%)
Δ-Fecal defined by Of -2 to 10%, and further 0.01% or more of Al, Ti, Nb, Zr, La, C
e, Nd or 0.001% or more of Y, Ca, Mg, B
Is used alone or in a total amount of 0.001 to 1% of Cr-Ni-based stainless molten steel by a continuous casting machine in which the mold wall surface moves in synchronization with the slab, and the cooling rate during solidification is 100 ° C. / Sec or more, continuously cast into a strip-shaped slab having a thickness of 10 mm or less, cooled to 1250 ° C., and
Hold for 2 minutes or less in the temperature range between 250 ° C and 900 ° C.
The temperature range between 00 ° C. and 600 ° C. is cooled at a cooling rate of 10 ° C./sec or more and wound, and the slab is pickled, and then subjected to one or two kinds of warm rolling and cold rolling, A method for producing a Cr-Ni-based stainless steel sheet having excellent surface quality and workability, characterized by comprising annealing, pickling or bright annealing and temper rolling to obtain a product.

(2) Manufacture of a Cr-Ni type stainless steel thin plate excellent in surface quality and workability as described in the above item 1, characterized in that the temperature is maintained between 1250 and 900 ° C. in winding, and after cooling, it is annealed. Method.

[0013]

The present invention will be described in detail below. As already described in Japanese Patent Application No. 1-84789, in order to improve the surface quality, it is necessary to reduce the γ grain size of the slab as a measure against roping and orange peel. Therefore, in the present invention, after the cast slab is solidified, it is cooled to 1250 ° C. where the grain growth rate is high, and the molten steel composition is adjusted to obtain δ-Fecal. (%)
Is set to −2 to 10%, and the grain refinement element is further set to 0.00.
The feature is that 1 to 1% is added.

In the present invention, δ-Fecal (%) Is −2 to 10%, the γ ferrite phase is divided into primary crystals, and the γ grains are divided, and fine ferrite is dispersed in the γ grain boundaries, and Al, Ti, Nb, Zr, La, Ce, Nd, Y,
By adding crystal grain refining elements such as Ca, Mg and B,
Fine oxides, nitrides, sulfides, and carbides precipitated in molten steel or during solidification and after solidification are characterized by being uniformly dispersed in γ grains and γ grain boundaries. The growth of γ grains is significantly suppressed.

As a result, the γ grain size of the slab becomes smaller, and the roping of the surface of the cold rolled product is significantly reduced. By the way, the addition of these refined components also suppresses γ grain growth during the final annealing after cold rolling, makes them finer, and deteriorates elongation and the like. Therefore, in order to improve the workability, it is necessary to detoxify these refined elements as oxides, nitrides, sulfides, and carbides between 1250 ° C and 900 ° C, respectively.

FIG. 1 shows the composition of 18Cr-8Ni austenitic stainless steel with δ-Fecal of 4%, Ti 0.06%, Nb (0.03%) + Ce.
Molten steel added with (0.02%) is 3 mm by twin roll method.
After thick casting, cooling to 1250 ° C., holding in the temperature range of 1250 ° C. to 900 ° C., 900 ° C. or less is the result of cold rolling a water-cooled slab and examining the elongation.

When the rapidly cooled slab is cold-rolled, the elongation is poor. However, in the slab cooled by holding at 900 ° C to 1250 ° C, trace addition elements such as MnS are rendered harmless. Growth is improving. Almost the same behavior was observed with addition of 0.06% of Ti and 0.03% of Nb + 0.02% of Ce.

Thus, these refining elements added for refining the γ grains during cooling after solidification are 1250 to 9
By detoxifying between 00 ° C, the product elongation can be greatly improved. As a detoxifying condition, during the cooling of the cast slab, holding at 1250 to 900 ° C. for a short time within 2 minutes or slow cooling, or winding at 1250 to 900 ° C. is also possible. If it exceeds 1250 ° C, the effect is small, while if it is less than 900 ° C, the effect is small. Further, the holding time of 2 minutes is sufficient on the high temperature side, and even if it exceeds 2 minutes, the improvement effect is small. The same effect can be obtained even when the temperature is kept around 1000 ° C.

The grain growth suppressing effect of δ-ferrite and precipitates depends on its amount. If δ-Fecal (%) is less than -2%, the effect of δ solidification is insufficient, and δ-Fecal The larger (%) is, the more effective it is, but when it exceeds 10%, the effect is saturated. As grain refinement elements, Al, Ti, Nb, Z
r, La, Ce, Nd, Y, Mg, Ca, B and the like are effective, and the grain growth is remarkably suppressed by the oxides, nitrides, sulfides, and carbides of the above elements finely precipitated in the cast piece. The larger the amount of the crystal grain refining element added, the greater the refinement effect, but it becomes harmful to render it harmless and improve elongation, and the total amount of addition must be 1% or less.

[0020]

EXAMPLES Austenitic stainless steels having various components based on 18Cr-8Ni steel shown in Tables 1 and 2 were melted. δ-Fecal (%) Is changed in the range of −2 to 10%, and as a grain refinement element, 0.01% or more of Al, Ti, Nb, Zr, La, Ce, Nd or 0.
001% or more of Y, Mg, Ca, and B was added in the range of 0.001 to 0.9% in a total amount of one or two or more.

These molten steels are continuously cast into a slab having a thickness of 1 to 6 mm and a width of 1000 mm by an internal water-cooling twin-roll continuous casting machine, and the slab solidified from the twin roll outlet is rapidly cooled by a method of pressing it on a water-cooling drum. did. In this case 125
The average cooling rate up to 0 ° C was 50 ° C / sec or more. The retention between 1250 ° C and 900 ° C was carried out under three conditions. (A) Air-cooled after 1100 ° C. for 20 seconds, water-cooled at 900 ° C. or lower and wound at 550 ° C. (b) Air-cooled after 1050 ° C. × 100 seconds and water-cooled at 900 ° C. or lower, wound at 550 ° C. (c) 1000 ° C. The obtained product was slowly cooled, solution heat treated at 1100 ° C., pickled, and cold rolled to obtain a 2B product and a BA product according to a usual method. These results are shown in Table 3 together with the conditions for producing the slab.
The results are shown in Table 4.

According to the method of the present invention for a slab which utilizes δ solidification and contains refined elements, and the retention conditions of the detoxification step of the refined elements are maintained during the cooling of the slab, the elongation of the product is significantly increased. Improved and roping was good. In the comparative method, the element was not refined, or the δ solidification was not utilized, and the slab retention conditions were not satisfied, so the elongation was poor and the roping was inferior.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

According to the present invention, an austenitic stainless steel sheet excellent in surface quality and workability is obtained by a simple process of continuously producing a strip-shaped slab having a thickness close to the product thickness by direct casting-direct cold rolling. Can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between retention conditions and product elongation in a slab cooling process.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication C22C 38/50 (72) Inventor Hideki Oka 3434 Shimada, Hikari City, Yamaguchi Prefecture Nippon Steel Corporation Inside the Hikari Steel Works (72) Inventor Yuji Yoshimura 3434 Shimada, Hikari City, Yamaguchi Prefecture Nippon Steel Works Hikari Steel Works Co., Ltd.

Claims (2)

[Claims] 1. δ-Fecal (%) = 3 (Cr + 1.5)
Si + Mo + 2Ti + Nb) -2.8 (Ni + 0.5M
δ-Fecal defined by (n + 0.5Cu) -84 (C + N) -19.8 (each component is wt%) Of −2 to 10%, and 0.01% or more of Al, Ti, Nb, Zr,
La, Ce, Nd or 0.001% or more of Y, Ca,
Mg and B alone or in a total amount of 0.001 to 1
% Of Cr-Ni system stainless steel molten steel in the range of the component range by a continuous casting machine in which the mold wall surface moves in synchronization with the slab.
Thickness 1 with cooling rate at solidification of 100 ° C / sec or more
Continuously cast into strip-shaped slabs of 0 mm or less, cooled to 1250 ° C, and held in the temperature range between 1250 ° C and 900 ° C for 2 minutes or less, and the temperature range between 900 ° C and 600 ° C is 10 ° C / s.
After cooling at a cooling rate of ec or more and winding, the slab is pickled, and then subjected to one or two kinds of warm rolling, cold rolling, annealing / pickling or bright annealing, and temper rolling. A method for producing a Cr-Ni-based stainless steel thin plate having excellent surface quality and workability, which is characterized by being manufactured as a product. 2. The production of a Cr—Ni-based stainless steel thin plate excellent in surface quality and workability according to claim 1, characterized in that holding between 1250 and 900 ° C. is performed in winding, cooling is followed by annealing. Method.