JP2980492B2 - Ferritic stainless steel strip with excellent surface properties and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel strip having excellent surface properties, and more particularly to a ferritic stainless steel strip which is free from surface roughening due to rolls in a cold rolling, bright annealing, and temper rolling process. It is about.

[0002]

2. Description of the Related Art As a stainless steel sheet product, JIS
There are BA products, 2B products, and polished products specified in the standards. It is strongly desired that these sheet products have excellent surface properties.

In response to such demands, BA products
Was cold rolled to hot rolled-annealed-pickled steel strip and intermediate plate thickness
The intermediate-annealed pickled steel strip is processed to a specified thickness by a Sendzimir rolling mill.
Cold rolling until ammonia cracking gas
After performing bright annealing (BA) with ambient gas, temper rolling
Has been manufactured. However, most recently N _Two
Or H_TwoHigh-purity gas such as is produced at low cost
The atmosphere gas for bright annealing is H_TwoGas alone
Or N_TwoAnd H_TwoMixing gas is being used
is there. The steel strip that has been subjected to bright annealing with such a gas
When temper rolling is performed in a lubricated state, the work used for the rolling
Roll surface roughening (hereinafter referred to as roll roughening)
And the coil yield of the final product may decrease significantly.
There is. In addition, to ensure surface quality,
The frequency of changing work rolls and the number of work roll polishing increases
Or lower workability and increase manufacturing costs.
You.

On the other hand, as disclosed in, for example, JP-A-58-61220, there is a method of adding a small amount of Nb and controlling the dew point and temperature of a bright annealing furnace to improve rust resistance. . Japanese Patent Application Laid-Open No. 58-197282 discloses a method for improving weather resistance by controlling the dew point and temperature of a bright annealing furnace by focusing on Si in steel. However, these methods are insufficient to prevent roll surface roughness in lubrication-free temper rolling, and require further improvement.

[0005]

It is believed that the cause of roll surface roughness in temper rolling is that the roll surface becomes rough due to non-lubricating rolling, which is transferred to the plate. Therefore, the present inventors have studied a method for effectively and efficiently reducing the roll surface roughness in temper rolling for a ferritic stainless steel strip having excellent surface properties and a manufacturing process for obtaining the same. Was. An object of the present invention is to clarify the surface condition for preventing the roll surface roughness and to present manufacturing conditions for obtaining the surface condition.

[0006]

The present invention has been completed based on the following findings as a result of various studies on the surface condition and manufacturing conditions of a ferritic stainless steel strip before temper rolling. That is, (1) If an oxide film containing 1.0 atomic% or more of Al and having a thickness of 30 ° or more and 350 ° or less is formed on the surface layer of the cold-rolled annealed sheet, roll surface roughening does not occur in subsequent temper rolling. (2) A ferritic stainless steel cold-rolled steel strip having an Al content of more than 0.03% by weight, with a dew point of −35 to −60 ° C.
By performing heat treatment in a reducing atmosphere gas adjusted to a temperature of 800 to 950 ° C. and a residence time of 5 to 100 seconds, an oxide film can be stably obtained. (3) In temper rolling, a work roll having a diameter of 100 mm or more is used in a non-lubricated state and an elongation rate of 2.0 per pass.
% Or less, a ferritic stainless steel strip having particularly excellent surface properties can be stably manufactured.

[0007]

The reason for limiting the present invention will be described below in detail. In order to obtain a ferritic stainless steel strip having excellent surface properties without roughening of the roll in temper rolling, the present inventors used a material having an Al content of more than 0.03% by weight, and performed annealing in a reducing atmosphere. It has been found that it is effective that the steel strip after that, that is, before temper rolling has an oxide film having a thickness of 30 to 350 mm on its surface.

[0008] Using SUS430 cold rolled steel strip, N
Bright Annealing in Mixing Gases of ₂ and H ₂ , followed by Non-lubricating Temper Rolling, Roller Surface Roughness Due to Temper Rolling and Al Content of Material on Surface Gloss after Temper Rolling FIG. 1 shows the results of investigating the influence of the thickness of the surface oxide film before temper rolling. Here, the roll surface roughness was evaluated in four ranks. "D: remarkable" occurs when it occurs clearly over the entire length of the coil, "C: present" occurs when it occurs only slightly over the entire length of the coil, and "B: slightly" occurs when it is slightly observed over part of the coil. , "A: None" was defined as the case where no occurrence occurred over the entire length of the coil. The thickness of the surface oxide film was measured using an Auger electron spectrometer.
The surface glossiness was measured based on JIS Z8741. As is clear from FIG. 1, in the case of a material having an Al content of more than 0.03% by weight, the thickness of the surface oxide film is 30%.
From the above, it can be seen that the occurrence of roll surface roughening is about "B: slightly", and that when the surface becomes 50 ° or more, roll surface roughening does not occur. In addition, in the case of a material having an Al content exceeding 0.03% by weight, the surface glossiness begins to decrease when the surface oxide film is 200 ° or more, and the glossiness is remarkably reduced at 350 ° C or more. Therefore, a preferable range of the oxide film thickness is 30 to 350 °. More preferably, the thickness of the oxide film is set to 50 to 200 °.

In order to obtain a ferritic stainless steel strip having excellent surface properties, the present inventors have set annealing conditions as follows:
In a reducing atmosphere gas whose dew point is adjusted to −35 to −60 ° C., the residence time in a temperature range of 800 to 950 ° C. is 5 to 1
Heat treatment for 100 seconds, followed by 100 mm diameter
It has been found that it is only necessary to perform temper rolling at an elongation of 2.0% or less per pass without using a work roll having a diameter of at least 2.0 mm.

SU having an Al content exceeding 0.03% by weight
With cold-rolled steel strip S430, N ₂ and H surface oxide film thickness and temper rolling before surface properties when subjected to bright annealing in ₂ mixing gas and dew point and 800-9
FIG. 2 shows the result of investigation of the relationship of the residence time in the temperature range of 50 ° C. In addition, the alphabetic character in a figure shows a roll rough surface rank, and a number shows glossiness. As is clear from FIG. 2, the dew point was adjusted to −35 to −60 ° C. and 800 to 950 ° C.
When the residence time in the temperature range of 5 to 100 sec is 5 to 100 sec, the thickness of the surface oxide film becomes 30 to 350 °, the sheet surface after temper rolling has no roll surface roughness, and the surface glossiness is 8
It turns out that it becomes 00 or more. Further, in order to make the thickness of the surface oxide film 50 to 200 °, the dew point should be -35 to -50 ° C.
And the residence time in the temperature range of 800 to 950 ° C. is preferably in the range of 10 to 30 sec. Here, when the plate temperature is lower than 800 ° C., the Al content is 0.03.
If it exceeds 950 ° C., recrystallization of the ferritic stainless steel is inadequate.
→ γ transformation occurs and deteriorates workability after annealing.

SU having an Al content exceeding 0.03% by weight
In S430, bright annealing is performed in a mixing gas of N ₂ and H ₂ , and using a steel strip having a surface oxide film thickness of 50 to 80 °, the occurrence of roll surface roughening due to temper rolling and the work roll diameter and per work pass FIG. 3 shows the result of investigation of the relationship between the elongation percentages of the two. As is clear from FIG.
It can be seen that when the temper rolling is performed using a work roll having a diameter of 100 mm or more at an elongation of 2.0% or less per pass, roll surface roughness can be prevented. Here, as the material of the work roll, it is preferable to use a steel material having a surface hardness of 600 or more in Hv such as semi-high-speed steel or high-speed steel from the viewpoint of abrasion resistance. Further, from the viewpoint of improving the surface gloss, the elongation rate per pass is preferably set to 0.3% or more.

The action and mechanism relating to the prevention of roll surface roughness in temper rolling are not always clear, but are presumed as follows. By forming a surface oxide film before temper rolling, a kind of lubricating film is formed between the work roll and the plate, which reduces the coefficient of friction during rolling and damages the roll surface due to plastic deformation of the surface layer of the plate Is considered to be prevented. The lubricating effect of the oxide film on the plate surface is considered to be related to the composition in the film in addition to the film thickness. FIG. 4 shows the result of examining the relationship between the Al content of the material and the Al content in the coating. As can be seen from the figure, when the Al content exceeds 0.03% by weight, Al is present in the oxide film in an amount of 1.0 atomic% or more. Thus, it is presumed that the Al-based oxide strengthens the oxide film, and a lubricating effect can be obtained even with a thin film thickness as compared with the Al-free material. It is presumed that the increase in the diameter of the work roll and the upper limit of the elongation rate per pass in the temper rolling effectively act in the direction of relaxing the pressure on the oxide film and maintaining the effect as a lubricating film. . The above lubrication effect is
The same applies to ferritic stainless steel strips in which one or more of i, Mo, Nb, Cu, V and the like are added in a slight amount to about 3.0% by weight.

[0013]

EXAMPLES Tables 1 to 4 show examples of the present invention, comparative examples and conventional examples. SUS430 type as steel type, 0.3 as plate thickness
Performed using materials in the range of 〜2.0 mm. Tables 1 and 3 show the components of the present invention and comparative examples and conventional examples, and Table 2 and Table 2 show the atmosphere annealing conditions, surface conditions after annealing, and temper rolling conditions of the present invention and comparative examples and conventional examples. The results are shown in Table 4. Before mixing the pure gas such as N ₂ or H ₂ , the dew point of the annealing furnace was controlled by passing a part of the gas through a water tank so as to contain water. With respect to the surface of the temper-rolled material, the roll surface roughness, glossiness, and image clarity were evaluated. Here, the image clarity was measured based on JIS H8686. It can be seen that the examples of the present invention have no surface roughness such as glossiness and image clarity, and have excellent surface properties as compared with the comparative example and the conventional example. Further, it can be seen that the temper rolling speed of the example of the present invention is significantly improved as compared with the conventional example.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

As is apparent from the above, according to the present invention, a BA-finished ferritic stainless steel strip excellent in surface properties without the occurrence of roll surface roughness in temper rolling can be obtained. Furthermore, the manufacturing method according to the present invention enables the temper rolling operation to be performed with extremely high efficiency as compared with the conventional method, and enables the manufacturing cost to be reduced by improving the yield.

[Brief description of the drawings]

FIG. 1 shows the appearance of roll surface roughening due to temper rolling when bright annealing is performed in a N ₂ and H ₂ mixing gas using a SUS430 cold-rolled steel strip, followed by lubrication-free temper rolling. Of Al on surface glossiness after tempering and temper rolling
It is a figure which shows the influence of content and the thickness of the surface oxide film before temper rolling.

FIG. 2 SUS4 having an Al content exceeding 0.03% by weight
With cold-rolled steel strip 30, N ₂ and when subjected to bright annealing in the mixing gas of H _2, the surface the surface properties of the oxide film thickness and temper after rolling and dew point and 800-95
Diagram showing the relationship between residence time in a temperature range of 0 ° C. (English letters: roll rough surface rank, numbers: gloss / GS45 ° C.)
It is.

FIG. 3 SUS4 having an Al content exceeding 0.03% by weight
At 30, bright annealing was performed in a mixing gas of N ₂ and H ₂ , and using a steel strip having a surface oxide film thickness of 50 to 80 °, the occurrence of roll surface roughening due to temper rolling and the work roll diameter and per work pass It is a figure which shows the relationship of the elongation rate.

FIG. 4 is a diagram showing the result of examining the relationship between the Al content of a material and the amount of Al present in a film.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C21D 8/02 C21D 8/02 D 9/46 9/46 R C22C 38/00 302 C22C 38/00 302Z C23C 8/18 C23C 8 / 18 (72) Inventor Tsutomu Ito 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Nippon Steel Corporation Hikari Works (72) Inventor Kazuo Muraoka 3434 Shimada, Hikari-shi, Hikari-shi Yamaguchi Prefecture Nippon Steel Corporation Hikari Inside the ironworks (72) Inventor Kazuhiro Yanai 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Inside the Nippon Steel Corporation Hikari Works (56) References JP-A-1-47880 (JP, A) JP-A-2-192801 ( JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 26/00

Claims (4)

(57) [Claims] 1. A cold-rolled annealed steel strip of ferritic stainless steel, characterized in that a surface layer has an oxide film containing 1.0 atomic% or more of Al and having a thickness of 30 to 350 °. 2. The cold-rolled annealed steel strip of ferritic stainless steel according to claim 1, wherein the ferritic stainless steel has an Al content of more than 0.03% by weight. 3. A cold-rolled steel strip of ferritic stainless steel having an Al content exceeding 0.03% by weight having a dew point of −35 to −35.
800 to 9 in a reducing atmosphere gas adjusted to -60 ° C.
A method for producing a ferritic stainless steel strip having excellent surface properties, wherein a heat treatment is performed so that the residence time in a temperature range of 50 ° C. is 5 to 100 sec. 4. A surface texture characterized by subjecting the heat treatment according to claim 3 to temper rolling with a work roll having a diameter of 100 mm or more without lubrication and an elongation of 2.0% or less per pass. Method for producing ferritic stainless steel strip with excellent properties.