JPH06158173A - Production of cr-ni stainless steel thin sheet excellent in surface quality - Google Patents

Abstract

PURPOSE:To produce a stainless steel thin sheet having good surface quality by specifying Cr-Ni stainless steel components, subjecting a slab to cold rolling and thereafter executing annealing at a specified temp. rising rate in a specified temp. range. CONSTITUTION:Cr-Ni stainless steel is cast into a thin slab of <=10mm and is subjected to cold rolling and annealing into a thin sheet product. The Md 30 (shown in the formula I) of the Cr-Ni stainless steel components is regulated to 30 to 50 deg.C. Simultaneously, after the cold rolling of the ingot, at the time of annealing it at 1000 to 1200 deg.C, the temp. rising rate is regulated to >=40 deg.C/sec. Furthermore, the rolling ratio of the cold rolling is regulated to >=60%. In this way, high effect can be produced from the viewpoints of energy conservation and reduction in production cost.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin plate product obtained by casting a Cr-Ni type stainless steel represented by 18Cr-8Ni steel into a thin cast piece having a plate thickness of 10 mm or less, and cold rolling the thin cast piece. , Which has excellent surface quality
The present invention relates to a method for producing an i-type stainless steel thin plate. recent years,
A technique for directly obtaining a thin strip having a thickness of 10 mm or less from molten steel by casting has been developed and industrial production has been achieved. According to this new technology, the step of hot-rolling the slab into a ribbon can be omitted, and a great effect can be brought about in terms of energy saving and manufacturing cost reduction. Hereinafter, in the present invention, a process of directly casting a thin slab having a thickness of 10 mm or less from molten steel by casting, and cold-rolling and annealing the slab to produce a thin plate product is referred to as an STC (Strip Casting) process, A process of hot rolling a slab into a hot rolled steel strip, and cold rolling and annealing the hot rolled steel strip to obtain a thin plate product is referred to as a current hot rolling process.

[0002]

2. Description of the Related Art Conventionally, when a Cr-Ni type stainless steel thin plate product represented by 18% Cr-8% Ni steel is manufactured by the STC process, the surface of the product is roughened (called orange peel or roping). It was a problem.

For example, "Nisshin Steel Making Technique", No. 62 (19)
90) In p62 to 78, the roping is that the γ grain of the thin cast piece is coarser than that of the current hot rolled annealed sheet, and the difference in deformability between the crystal grains appears on the surface of the cold rolled sheet. As a preventive measure, it is stated that rolling is carried out at an appropriate temperature and rolling rate, and then annealing is performed to reduce the γ grain size of the slab to 40 μm or less, followed by cold rolling. However, performing the rolling in two steps has a problem of increasing the production cost, and there is a problem that it is necessary to build a dedicated hot rolling equipment in order to perform the hot rolling. It was not a preferable improvement measure.

The inventors of the present invention improved roping by reducing the difference in deformability between crystal grains during cold rolling as a method for producing a Cr-Ni type stainless steel thin plate having excellent surface quality by the STC process. Thinking, Cr
-Md30 of Ni-based stainless steel is 30 to 50 ° C.
Has been applied so that the martensitic transformation during cold rolling occurs in most of the crystal grains of the slab and the deformability of each crystal grain is made uniform. The present invention is characterized in that roping can be reduced even if the crystal grain size of the slab is large.

[0005]

The inventors of the present invention manufactured Cr-Ni type stainless steel thin plates according to the above invention in an actual production facility. However, the roping varies depending on the production line, and the thin plates are stable and free from roping. I couldn't manufacture the product. Therefore, there has been a need for a technology for stably manufacturing thin plate products without roping. The present invention aims to provide such a technique.

[0006]

The present invention has the following constitution in order to achieve the above object. That is, a feature of the present invention is that a thin-walled slab having a plate thickness of 10 mm or less is cast from a Cr-Ni-based stainless steel, the thin-walled slab is cold-rolled, and annealed to obtain a thin-plate product. In the manufacturing method of, the Cr-Ni-based stainless steel component Md30 is 3
After setting the temperature to 0 to 50 ° C. and cold rolling the slab (if necessary, cold rolling at a rolling rate of 60% or more), 100
When annealing in the temperature range of 0 to 1200 ° C, the temperature rising rate is 40
C / sec or more, and the above-mentioned Cr-N
In the method for producing an i-based stainless steel thin plate, Cr-Ni
The Md30 of the system stainless steel component is set to 30 to 50 ° C., and the rolling ratio of cold rolling is set to 60% or more. However, Md30 = 413-462 (C + N) -9.2Si
-8.1Mn-13.7Cr-18.5Mo-9.1
(Ni + Cu) (component is wt%)

[0007]

Function: Cr-N whose component Md30 is 30 to 50 ° C
Although the i-type stainless steel thin slab does not undergo roping during cold rolling, rough skin may occur when the cold rolled sheet is annealed. This phenomenon is considered to be a result of volume change caused by the reverse transformation of the work-induced martensite structure generated by cold rolling to austenite in the annealing process, resulting in surface irregularities. In the conventional hot rolling process, since the crystal grains were small, the volume change due to the reverse transformation occurred in small units and was not conspicuous. Also, in the STC process, it is considered that when Md30 was small, the crystal grains were large but the amount of reverse transformation was small, so that it was not noticeable.

The rough skin due to such reverse transformation is generated during the temperature rise in the annealing process, and is considered to occur because the temperature range in which the reverse transformation occurs varies depending on the driving force of the reverse transformation. Therefore, it was considered that rough heating is improved by rapid heating in the annealing process and reverse transformation in the same temperature range. Therefore, the present inventors investigated the annealing conditions of cold-rolled sheet and the roping of the cold-rolled annealed sheet, and as a result, found that the annealing rate and the cold rolling rate greatly affect the roping of the cold-rolled annealed sheet, Completed the invention. The roping of a Cr-Ni-based stainless steel thin cast piece after cold rolling is greatly affected by the components as shown in FIG. 1, and when the Md30 is 30 ° C. or higher, the cold rolling sheet becomes almost inconspicuous. Therefore, the component is Md30 30
It is desirable to set the temperature above ℃. However, Md30 is 50
If the temperature exceeds ℃, the product becomes more susceptible to age cracking, so Md30 must be 50 ℃ or less.

The roping of a thin slab cast with Md 30 of 30 ° C. to 50 ° C. after cold rolling annealing is greatly affected by the temperature rising rate during annealing, and as shown in FIG.
If it is less than a second, the roping of the cold-rolled annealed sheet is larger than the roping of the cold-rolled sheet. Further, this phenomenon remarkably occurs when a cold rolled sheet having a low cold rolling rate is annealed (see FIG. 3). Therefore, it is necessary to set the temperature rising rate to 40 ° C./sec or more, and the upper limit is 200 ° C./s due to the capacity limitation of the heating equipment. In this way, if the temperature rising rate is set to 40 ° C./second or more,
Although roping can be passed at a normal cold rolling rate (30% or more), the rate of temperature increase is a normal rate (20 ° C).
/ Sec), the target roping level can be obtained by setting the cold rolling rate to 60% or more. The heating rate is 40
A better roping level can be obtained by setting the cold rolling rate to 60 ° C./sec or more and the cold rolling rate to 60% or more. However, the annealing temperature at this time is the annealing temperature used for the cold rolled sheet in the current hot rolling process. That is, if the temperature is lower than 1000 ° C, recovery and recrystallization do not proceed sufficiently, so the temperature is set to 1000 ° C or higher.
If the annealing temperature is higher than 1200 ° C, the crystal grain size after annealing becomes coarse, and roughening occurs when the product is processed.
It was set to 200 ° C. or lower.

[0010]

[Examples] Cr-Ni stainless steel containing 18% Cr-8% Ni as a main component shown in Table 1 was melted and cast into a thin cast piece having a thickness of 3 mm by a twin drum type thin plate continuous casting machine. . The slab was subjected to solution heat treatment under the conditions as shown in Table 2 or descaling without heat treatment, cold rolled at various reduction ratios, and annealed at 1100 ° C. The heating rate at this time was such that the average heating rate from room temperature to 1100 ° C. was 40 to 200 ° C./sec. The roping of the cold rolled annealed plate was measured with a two-dimensional roughness meter. As a comparative example, a thin cast piece was cast from a Cr—Ni-based stainless steel having the composition shown in Table 3 to obtain a cold rolled annealed plate under the conditions shown in Table 2. Table 2 and FIG. 3 summarize the roping of the cold rolled annealed sheets of Examples of the present invention and Comparative Examples. The cold-rolled and annealed sheet produced by the method of the present invention has a small roping, and in particular, the cold-rolling rate is 60.
% Or more, the roping became smaller. The cold-rolled annealed sheet produced by the comparative method had large roping, and the surface quality was at an unacceptable level.

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

[Table 3]

[0014]

According to the present invention, the STC process can produce a Cr-Ni-based stainless steel sheet having good surface quality. Therefore, the technical effect is extremely large in terms of economy.

[Brief description of drawings]

FIG. 1 is a diagram showing an influence of Md30 on a roping height of a cold rolled sheet.

FIG. 2 is a diagram showing the influence of the temperature rising rate during cold rolling annealing on the roping of a cold rolled annealed sheet.

FIG. 3 is a diagram showing influences of a cold rolling ratio and a heating rate during annealing of the cold rolled sheet on the roping of the cold rolled sheet.

Front page continuation (72) Inventor Shuichi Inoue 3434 Shimada, Hikari City, Yamaguchi Prefecture Shin Nippon Steel Co., Ltd.

Claims (3)

[Claims] 1. A Cr-Ni stainless steel plate having a thickness of 10 mm.
In the method for producing a Cr-Ni-based stainless steel thin plate, which is cast into the following thin-walled slab, cold-rolled the thin-wall slab, and annealed to obtain a thin plate product, M of a Cr-Ni-based stainless steel component is used.
Excellent surface quality characterized by setting d30 to 30 to 50 ° C. and setting the temperature rising rate to 40 ° C./second or more when annealing the slab after cold rolling in the temperature range of 1000 to 1200 ° C. Method for producing a Cr-Ni-based stainless steel thin plate. However, Md30 = 413-462 (C + N) -9.2S
i-8.1Mn-13.7Cr-18.5Mo-9.1
(Ni + Cu) (component is wt%) 2. A plate thickness of Cr-Ni stainless steel is 10 mm.
In the method for producing a Cr-Ni-based stainless steel thin plate which is cast into the following thin-walled slab, cold-rolled the thin-walled slab and annealed to obtain a thin plate product, M of a Cr-Ni-based stainless steel component is used.
A method for producing a Cr-Ni-based stainless steel thin plate having excellent surface quality, characterized in that d30 is set to 30 to 50 ° C and a rolling ratio of the cold rolling is set to 60% or more. 3. The method for producing a Cr—Ni-based stainless steel sheet according to claim 1, wherein the cold rolling reduction rate is 60% or more.