JPH05195053A - Production of polished ferritic stainless steel sheet excellent in oxidation resistance - Google Patents

Abstract

PURPOSE:To inexpensively mass-produce a polished ferritic stainless steel sheet having attractive metallic luster and excellent in oxidation resistance. CONSTITUTION:The polished steel sheet can be produced by subjecting a ferritic stainless steel having a composition consisting of, by weight, 16-35% Cr, <=0.020% C, <=0.030% N, 0.01-3.0% Si, one or more kinds among 0.01-3.0% Mo, 0.01-1.0% Cu, 0.01-1.0% Nb, 0.01-1.0% Ti, and 0.01-7.0% Al, and the balance essentially Fe with inevitable impurities to rolling, to finish annealing and pickling or to temper rolling, and then to surface polishing. In the above process, polishing is done at 150-300 deg.C, or, after the completion of polishing the steel sheet is held in the air at <=300 deg.C for >=48hr until the thickness of a passivating film reaches >=2.5nm.

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 ferritic stainless steel sheet which has been surface-polished so as to have a beautiful metallic luster on the surface thereof so as to improve its oxidation resistance.

[0002]

2. Description of the Related Art Steel plates used for parts exposed to high temperatures, such as the inner and outer cylinders of oil stoves and parts of gas stoves, do not have to have only heat resistance, but have a beautiful metallic luster on the surface. In many cases, a stainless steel plate with a polished finish is used because it is desired to have a material with a ferritic stainless steel. There is. Conventionally, ferritic stainless steels used for these applications usually have a weight ratio of Cr: 1.
0 to 35 wt%, C: 0.020 wt% or less, N: 0.
030 wt% or less, Si: 0.01 to 3.0 wt%, Mo: 0.01 to 3.0 wt%, Cu: 0.01 to
1.0 wt%, Nb: 0.01 to 1.0 wt%, Ti:
0.01-1.0 wt%, Al: 0.01-7.0 wt
%, And the balance consists essentially of Fe and inevitable impurities. Such stainless steel has good heat resistance, and the steel plate can be polished to have a beautiful metallic luster on its surface.

[0003]

However, the oxidation resistance of ferritic stainless steel is inferior to that of a polished finish compared to that of a pickled finish with an oxidizing acid ("Corrosion Protection Society, 32nd Annual Meeting"). Proceedings of the "Corrosion and Anti-corrosion Debate", pages 310 to 312), so it is desired that the oxidation resistance be sufficiently large even in the case of polishing finish. In the case of pickling finish with the above-mentioned oxidizing acid, a thick passivation film is formed on the surface of stainless steel, but it is often used on the polished surface due to its designability. It is considered that the oxidation resistance is lowered because the oxide film is almost removed. If it is desired to maintain the oxidation resistance even with such a polishing finish, it is possible to add a larger amount of elements such as Cr, Al, and Si to the stainless steel. There is a drawback that it leads to deterioration of the physical properties. An object of the present invention is to solve these drawbacks and to establish a method for mass-producing an abrasive-finished ferritic stainless steel sheet excellent in oxidation resistance at low cost.

[0004]

Therefore, the present inventors have
As a result of earnest research to achieve the above objective, (a)
When manufacturing a polished finished surface mainly by dry method, the polishing temperature is
The oxidation resistance is improved by performing the treatment within a certain range as compared with a normal polishing finish surface. (B) Further, when the polishing finish surface is manufactured mainly by a wet method, the surface passivation film after polishing is The present invention has been completed based on the new finding that the oxidation resistance is improved by holding for a long time at room temperature or in a heated atmosphere. That is, the present invention has achieved the above object by the following method. (1) Cr: 16 to 35 wt% and C: 0.
020 wt% or less, N: 0.030 wt% or less, Si:
Other than 0.01 to 3.0 wt%, Mo: 0.01 to 3.0
wt%, Cu: 0.01 to 1.0 wt%, Nb: 0.0
1 to 1.0 wt%, Ti: 0.01 to 1.0 wt%, A
1: 0.01 to 7.0 wt% of one or more kinds, and the balance is substantially ferritic stainless steel consisting essentially of Fe and unavoidable impurities, and after rolling, finish annealing, pickling, or temper rolling, A method for producing a polished finished ferritic stainless steel sheet having excellent oxidation resistance, which comprises performing polishing at 150 to 300 ° C. in the method for producing a polished finished steel sheet for surface polishing. (2) Cr: 16-35 wt% and C: 0.
020 wt% or less, N: 0.030 wt% or less, Si:
Other than 0.01 to 3.0 wt%, Mo: 0.01 to 3.0
wt%, Cu: 0.01 to 1.0 wt%, Nb: 0.0
1 to 1.0 wt%, Ti: 0.01 to 1.0 wt%, A
1: 0.01 to 7.0 wt% of one or more kinds, and the balance is substantially ferritic stainless steel consisting essentially of Fe and unavoidable impurities, and after rolling, finish annealing, pickling, or temper rolling, In the method for producing a polished steel sheet for surface polishing, the steel sheet has a passivation film thickness of 2.5 n after polishing.
A method for producing a polished finish ferritic stainless steel sheet having excellent oxidation resistance, which is characterized by holding in an atmosphere of 300 ° C. or less for 48 hours or more until it becomes m or more.

The composition of the material steel of the ferritic stainless steel sheet to which the present invention is applied is as described above. Some ferritic stainless steels are wider than the above composition range. It can be processed appropriately. The reason for limiting the composition will be described in the section "Action". The steps of rolling, finish annealing, pickling, or temper rolling the ferritic stainless steel in this manufacturing method are performed in exactly the same manner as the conventional steps. Further, the surface polishing is performed by the same means as the conventional one. When the polishing is performed at 150 to 300 ° C., the polishing may be performed in a state of being exposed to air, and thus the polishing may be performed by a dry method or a wet method. The polishing can be performed, for example, by rubbing a cloth having an abrasive attached thereto with a moving steel plate.

When the above-mentioned polishing is carried out at room temperature, if exposed to air thereafter, an oxide film is formed on the surface, and if the oxide film has a thickness of 2.5 nm or more, sufficient oxidation resistance is obtained. Until it reaches the thickness of 3
It is kept in the atmosphere at 00 ° C or lower. The time is required to be 48 hours or more in a heated state, and the oxidation reaction is promoted when heated, so that a longer time is required when kept at room temperature.

[0007]

Next, the method of producing the polished ferritic stainless steel sheet according to the present invention and the component composition of the stainless steel will be described in detail together with the action and the reason for the limitation. As described above, the present inventors, in the polishing finish ferritic stainless steel, by performing the polishing step at a relatively high temperature within the range that does not deteriorate the corrosion resistance at room temperature, or when the temperature such as wet polishing does not rise, It was found that, by holding the film in the air or heated air for a long time after the completion of polishing to increase the thickness of the passivation film, the oxidation resistance is improved as compared with a normal polished surface. Then, as a result of diligent research on the conditions under which such a phenomenon is obtained, after a steel sheet having reduced C and N in the steel is obtained by rolling, finish annealing / pickling, or temper rolling, the polishing temperature is 150 to It has been found that it is necessary to carry out the polishing at 300 ° C., or to hold the surface passivation film thickness at 2.5 nm or more by holding it in the atmosphere at 300 ° C. or less for 48 hours or more after the polishing. The present inventors have conducted the following various studies in order to consider the reason why the oxidation resistance is improved in this way.
The pickled surface before polishing usually has a passivation film with a thickness of 2.5 nm or more on the surface, but this film is once removed when polishing is performed. Immediately after the polishing is completed, a film starts to be formed again by the oxygen in the atmosphere, but it is difficult to recover the thickness to the level of the pickled surface. However,
The present inventors have found that there is a close correlation between the oxidation resistance and the passivation film thickness as shown in FIG. 1, and based on this finding, the polishing treatment temperature and the retention in the atmosphere after polishing are completed. The relationship between time and passivation film thickness was investigated. This Figure 1
After polishing 17.5Cr-1Mo-0.3Ti steel, 1
It is a graph showing the relationship between the pre-test surface passivation film thickness and the oxidation increase when an atmospheric continuous oxidation test is performed at 050 ° C. for 200 hours. From FIG. 1, it can be seen that the smaller the pre-test surface passivation film thickness, the greater the increase in oxidation, that is, the poorer the oxidation resistance.

As a result, as shown in FIGS. 2 and 3, the polishing temperature is 150 ° C. or higher, and the polishing temperature is low. For example, even in the case of wet polishing, by holding at room temperature or in a heated atmosphere for 48 hours or more, It was revealed that a passivation film thickness equal to or greater than that of the pickled surface can be obtained. Figure 2
Is a graph showing the relationship between the polishing execution temperature and the oxidation weight gain when the same 17.5Cr-1Mo-0.3Ti steel was polished at a temperature higher than room temperature and then subjected to an atmospheric continuous oxidation test at 1050 ° C. for 200 hours. FIG. 3 is a graph showing the relationship between the atmospheric holding time before the polishing test and the increase in the amount of oxidation when the same steel was polished at room temperature and then subjected to an atmospheric continuous oxidation test at 1050 ° C. for 200 hours. However, in the case of FIG. 2, when the polishing temperature is 300 ° C. or higher, a colored film called a so-called temper color is formed on the surface, and general corrosion resistance is extremely deteriorated. For this reason, polishing is carried out at a polishing temperature of 150 to 300 ° C., or after completion of polishing, the film is held in the atmosphere at 300 ° C. or lower for 48 hours or more to limit the passivation film thickness to 2.5 nm or more. did.

After the completion of polishing, when it is held in the atmosphere of over 300 ° C., the temper color is formed as described above, and the corrosion resistance is deteriorated. Next, regarding the composition of the ferritic stainless steel according to the present invention, its action and the reason for limitation will be described. Cr is extremely effective as an element for improving the oxidation resistance of the steel, but if it is 16 wt% or less, the oxidation resistance is insufficient, and if it is 35 wt% or more, it becomes extremely difficult to manufacture a steel sheet. For this reason, the Cr content is limited to 16 to 35 wt%. C and N are elements that combine with Cr in the steel to reduce the amount of effective Cr and deteriorate the oxidation resistance. Therefore, the lower the content, the better. However, there is an industrial limit, so C is 0. 0.020 wt%
Hereinafter, N is 0.030 wt% or less.

Although Si is an element effective for oxidation resistance,
If it is less than 0.01%, the effect is not obtained, and if it is 3.0% by weight, it becomes difficult to manufacture a steel sheet and the formability is extremely deteriorated. For this reason, the Si content is 0.01 to
It was limited to 3.0 wt%. Mo is an element that improves the oxidation resistance and the corrosion resistance, but if it is 0.01 wt% or less, it has no effect, and if it is 3.0 wt% or more, the peel resistance of the oxide scale deteriorates. Moreover, the addition of a large amount of expensive Mo impairs the economical efficiency of the steel material. For this reason, the Mo content is set to 0.1.
It was limited to ˜3.0 wt%. Cu is an element effective for corrosion resistance, but if it is 0.01 wt% or less, it has no effect.
If the content is 1.0 wt% or more, the hardness increases and the formability deteriorates. For this reason, the Cu content is 0.01 to 1.0 w.
Limited to t%. Nb and Ti are elements that fix C and N in the steel and do not reduce the amount of effective Cr in the steel, and are themselves effective in improving the oxidation resistance.
If it is less than wt%, the effect is not present, and if it is more than 1.0 wt%, the effect is saturated, and at the same time, the hardness is increased and the formability is deteriorated. Limited to%. Al is extremely effective for oxidation resistance, but if it is 0.01 wt% or less, it is not effective, and if it is 7.0 wt% or more, not only is it difficult to manufacture a steel sheet, but also formability is deteriorated. For this reason Al
Content was limited to 0.01 to 7.0 wt%.

[0011]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Example A cold-rolled stainless steel plate having the chemical composition shown in Table 1 was used.
After processing by the polishing method according to the present invention and the polishing method not according to the present invention to produce a polished finished steel plate, 20 mm × 2
Cut out to 5 mm, 1 for high Al and high Cr content steel
An atmospheric continuous oxidation test at 150 ° C. for 100 hours was performed, and an atmospheric continuous test at 950 ° C. for 100 hours was performed for other steels, and the increase in oxidation was measured and compared. Further, in order to investigate the corrosion resistance of the obtained steel sheet, the pitting potential measurement specified in JIS G0577 was carried out.

Table 2 shows the measurement results. According to Tables 1 and 2, each of the steels having the steel components included in the present invention and subjected to the polishing treatment according to the present invention has a lower oxidation gain than the comparative steels and also has poor corrosion resistance. Absent. Therefore, the steel plate having the components included in the present invention is 150 to
Polishing at 300 ℃ or 300 after polishing
It was found that a polished finish ferritic stainless steel sheet having excellent oxidation resistance can be produced by keeping the passivation film at a thickness of 2.5 nm or more by keeping it in the air at a temperature of ℃ or less for 48 hours or more.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

According to the present invention, when polishing a ferritic stainless steel sheet having the above-mentioned specific composition,
The polishing temperature is controlled to 150 to 300 ° C., or the passivation film thickness after the polishing is completed is 300 nm until it becomes 2.5 nm or more.
By holding it in the atmosphere at ℃ or below, a polished ferritic stainless steel sheet with a passivation film having a thickness of 2.5 nm or more can be obtained. This steel sheet has excellent oxidation resistance and a beautiful metallic luster. It has, and is suitable for use as an exterior member for high temperature.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the pre-test surface passivation film thickness and the increase in oxidation when a 17.5Cr-1Mo-0.3Ti steel was polished and subjected to an atmospheric continuous oxidation test at 1050 ° C. for 200 hours. Indicates.

FIG. 2 shows the relationship between the temperature at which polishing is carried out and the amount of oxidation increase when a 17.5Cr-1Mo-0.3Ti steel is polished at a temperature higher than room temperature and then subjected to an atmospheric continuous oxidation test at 1050 ° C. for 200 hours. A graph is shown.

FIG. 3 is a graph showing the relationship between the holding time in the atmosphere after polishing and the amount of increase in oxidation when a 17.5Cr-1Mo-0.3Ti steel was polished at room temperature and then subjected to an atmospheric continuous oxidation test at 1050 ° C. for 200 hours. The graph showing is shown.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location // C22C 38/00 302 Z 7217-4K 38/34 (72) Inventor Yu Kobayashi Kawasaki City, Kanagawa Prefecture Kawasaki-ku Kojimacho 4-2 Nihon Metallurgical Industry Co., Ltd.

Claims (2)

[Claims] 1. A weight ratio of Cr: 16 to 35 wt%,
C: 0.020 wt% or less, N: 0.030 wt% or less, Si: 0.01 to 3.0 wt%, Mo: 0.0
1 to 3.0 wt%, Cu: 0.01 to 1.0 wt%, N
b: 0.01 to 1.0 wt%, Ti: 0.01 to 1.0
wt%, Al: 0.01 to 7.0 wt% of one or more kinds, and the balance is substantially ferritic stainless steel consisting of Fe and unavoidable impurities, rolled, finish-annealed, pickled, or tempered. A method for producing a polished finished ferritic stainless steel sheet having excellent oxidation resistance, which comprises performing polishing at 150 to 300 ° C. in a method for producing a polished finished steel sheet which is subjected to surface polishing after rolling. 2. A weight ratio of Cr: 16 to 35 wt%,
C: 0.020 wt% or less, N: 0.030 wt% or less, Si: 0.01 to 3.0 wt%, Mo: 0.0
1 to 3.0 wt%, Cu: 0.01 to 1.0 wt%, N
b: 0.01 to 1.0 wt%, Ti: 0.01 to 1.0
wt%, Al: 0.01 to 7.0 wt% of one or more kinds, and the balance is substantially ferritic stainless steel consisting of Fe and unavoidable impurities, rolled, finish-annealed, pickled, or tempered. In the method for producing a polished steel sheet, which is subjected to surface polishing after rolling, the steel sheet is kept in the atmosphere of 300 ° C. or less for 48 hours or more after polishing until the passivation film thickness becomes 2.5 nm or more. A method for producing a polished ferritic stainless steel sheet having excellent oxidation resistance.