JP2001026818A - Method and apparatus for continuously annealing stainless steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve descaling property after annealing process by annealing under state of not lower than a specific value of H2O concn. in the atmosphere in a direct firing type annealing furnace and changing the distribution of the produced oxidized scale in the sheet thickness direction. SOLUTION: The direct firing type annealing furnace 1 is provided with a burner 3 for heating the inside of the annealing furnace 1 by burning fuel with pure oxygen and a device 4 for adjusting the H2O concn. in the atmosphere by blowing H2O into the atmosphere in the annealing furnace 1. The stainless steel sheet 2 fed into the annealing furnace 1, is fed out to the outside of the annealing furnace 1 after annealing while supporting and conveying with rolls 11 in the annealing furnace 1. At this time, the inner part of the annealing furnace 1, is heated with the burner 3 and the atmosphere having high H2O concn. of >=30 vol.% is made with this heating. Temporarily, in the case of being the H2O concn. at lower than 30 vol.% the H2O concn. is adjusted by blowing H2O gas into the annealing furnace 1 with the device 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous annealing method and apparatus for a stainless steel strip, and more particularly to a continuous annealing method for a stainless steel strip for improving descalability after annealing in a continuous annealing pickling line. And an apparatus.

[0002]

BACKGROUND OF THE INVENTION Stainless steel strip is annealed after hot rolling.
It is generally manufactured in the order of pickling, cold rolling, annealing, pickling, and temper rolling. Both the hot-rolled steel strip and the cold-rolled steel strip are annealed and pickled.
A continuous annealing and pickling line called a line (Annealing and Pickling Line) for continuously performing an annealing step and a pickling step is used. Both the hot-rolled steel strip and the cold-rolled steel strip are annealed in a horizontal or vertical direct-fired annealing furnace in a continuous annealing and pickling facility, and grow on the steel strip surface during the annealing process. The scale generated during hot rolling grows, and in the case of a cold-rolled steel strip, newly formed oxide scale) is removed in the next pickling step. The reason why the oxide scale is removed is that the oxide scale on the surface of the steel strip not only impairs the inherent corrosion resistance and aesthetics of stainless steel, but also has an adverse effect on processing such as pressing. In order to improve the descaling property in this pickling step, a pickling method has been conventionally studied.

On the other hand, oxide scale grows in the annealing step
Therefore, the annealing conditions including the annealing atmosphere depend on the amount of scale
In this case, the descaling property is affected and the annealing conditions are not appropriate.
In such cases, the pickling equipment in the pickling process must be lengthened or pickled.
This leads to prolonged time, which reduces equipment and acid solution costs.
There were problems such as soaring. About these problems
Various, various solutions have been proposed, for example,
JP-A-5-222558 discloses an austenitic system.
Continuous annealing of cold rolled stainless steel strip and subsequent descaling
In doing so, O in the annealing atmosphere in the annealing furnace _TwoDark
Anneal to a degree of 1% or more and 10% or less, and then continue
Mixed acid composed of nitric acid and hydrofluoric acid with a composition that satisfies the concentration relationship
Austenitic stainless steel descaled using
A method for producing a rolled steel strip has been proposed. This is an annealing atmosphere
Not the concept of air to air ratio but O_TwoMeasure the concentration directly
To a positive specific range and a mixed acid in a specific composition range.
Good descaling properties can be obtained by pickling.
It is something that has been done.

[0004]

However, in this conventional method for manufacturing austenitic stainless steel cold-rolled steel strip, in the annealing step, the O ₂ concentration in the annealing atmosphere is regulated to an appropriate specific range. The thickness of the oxide scale generated on the band surface is limited to a predetermined thickness or less, thereby obtaining a good descaling property after the annealing step. It does not change the distribution in the thickness direction, and the descalability after the annealing step is not sufficient.

On the other hand, an improved pickling apparatus has been disclosed in Japanese Patent Application Laid-Open No. 5-222.
It is also important to improve the descalability by improving the acid solution described in JP-A-558. However, there is a limit to the improvement of the descalability by the improvement of the pickling process. Therefore, the present invention solves these conventional problems, and changes the distribution in the thickness direction of the oxide scale composition generated by setting the atmosphere in the annealing furnace to a specific composition. It is an object of the present invention to provide a continuous annealing method and apparatus for a stainless steel strip which improves the descaling property in the pickling process of the present invention.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, a first aspect of the present invention is directed to annealing at an H ₂ O concentration of 30 vol% or more in an atmosphere in a direct-fired annealing furnace. Features. That is, the stainless steel strip is continuously annealed when the H ₂ O concentration in the atmosphere in the direct-fired annealing furnace is 30% by volume or more.

[0007] In the present invention, a second aspect of the present invention is to provide an apparatus for injecting H ₂ O gas into an atmosphere in a direct-fired annealing furnace to thereby adjust the H ₂ O concentration in the atmosphere. Features. Furthermore, claim 3 of the present invention is:
Cracks are formed in the scale on the hot-rolled stainless steel strip by mechanical means.
₂ O concentration is characterized by annealing at 30 vol% or more.

In the present invention, a mechanical means for cracking a scale on a hot-rolled stainless steel strip is provided upstream of the direct-fired annealing furnace, and the mechanical means for cracking the atmosphere of the annealing furnace is provided. A device for adjusting the H ₂ O concentration by blowing H ₂ O gas into the device is provided.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic view of an embodiment of a direct-fired annealing furnace used in a continuous annealing method and apparatus for a stainless steel strip according to the present invention. In FIG. 1, a direct-fired annealing furnace 1 includes a burner 3 that burns fuel (fuel) with pure oxygen (O ₂ ) to heat the inside of the annealing furnace 1, and an H ₂ gas in the atmosphere in the annealing furnace 1. A device 4 for blowing O gas to adjust the H ₂ O concentration in the atmosphere is provided. The stainless steel strip 2 sent into the annealing furnace 1 is supported by rolls 11 in the annealing furnace 1, annealed while being conveyed, and then sent out of the annealing furnace 1. At this time, the annealing furnace 1
The inside is heated by a burner 3 which burns fuel with pure oxygen, and this heating causes an atmosphere having a high H ₂ O concentration, that is, H _2.
An atmosphere having an O concentration of 30% by volume or more is created. If, when the H ₂ O concentration is lower than 30% by volume, H ₂ O gas is blown into the annealing furnace 1 by the device 4 with H ₂ O
The density is adjusted. For this reason, the stainless steel strip 2 is annealed when the H ₂ O concentration in the atmosphere is 30% by volume or more. Further, in the annealing furnace 1, an H ₂ O concentration detecting means for detecting the H ₂ O concentration in the atmosphere, for example, a cell type dew point meter A is provided. The detection result detected by the cell type dew point meter A is sent to the control device B. The control device B automatically controls the H ₂ O concentration in the atmosphere by the device 4 based on the detection result. The cell type dew point meter A and the control device B
Need not necessarily be provided.

Next, FIG. 2 is a schematic view showing another embodiment of a direct-fired annealing furnace used in the continuous annealing method and apparatus for stainless steel strip according to the present invention. In FIG. 2, a direct-fired annealing furnace 1 is supplied with fuel (F) by air (Air).
burner 3 for heating the inside of the annealing furnace 1 by burning
And an apparatus 4 for blowing H ₂ O gas into the gas atmosphere in the annealing furnace 1 to thereby adjust the H ₂ O concentration in the atmosphere.
Are provided. The stainless steel strip 2 sent into the annealing furnace 1 is supported by rolls 11 in the annealing furnace 1, annealed while being conveyed, and then sent out of the annealing furnace 1. At this time, the inside of the annealing furnace 1 is different from the inside of the annealing furnace 1 shown in FIG.
By being heated, since H ₂ O concentration is low in the atmosphere (lower than H ₂ O concentration of 30% by volume in the atmosphere), the device 4 H ₂ O gas actively blown into the annealing furnace 1,
The H ₂ O concentration is adjusted to 30% by volume or more. For this reason, the stainless steel strip 2 is annealed when the H ₂ O concentration in the gas atmosphere is 30% by volume or more. Further, in the annealing furnace 1, an H ₂ O concentration detecting means for detecting the H ₂ O concentration in the atmosphere, for example, a cell type dew point meter A is provided. The detection result detected by the cell type dew point meter A is sent to the control device B. The control device B automatically controls the H ₂ O concentration in the atmosphere by the device 4 based on the detection result. The cell type dew point meter A and the control device B may not be necessarily provided.

First, the stainless steel shown in FIGS.
On the operation of the present invention when the belt 2 is a cold-rolled steel strip
explain. Conventional low H_TwoO atmosphere (H_TwoO concentration is 10
Volume% to 25 volume%), the surface of the cold rolled steel strip
The structure of the oxide scale that grows and grows on the outer layer
Tight (Fe_TwoO_Three), Spinel (FeCr_TwoO_Four),
The innermost layer is corundum (Cr _TwoO_Four). this house,
Spinel reduces descalability in pickling process
It is known.

On the other hand, the present inventors have conducted research and found that when annealing a cold-rolled steel strip in a high H ₂ O atmosphere (H ₂ O concentration is 30% by volume or more), H ₂ O on the surface of the cold-rolled steel strip is reduced. It has been found that, due to rapid oxidation by gas, an oxide film grows before receiving a sufficient supply of Cr from the base iron, so that Fe-rich hematite is formed in the outermost layer. Since hematite is excellent in descaling property as compared with spinel, descaling property in the next pickling step is improved.

Next, the stainless steel shown in FIGS.
On the operation of the present invention when the belt 2 is a hot-rolled steel strip
explain. For hot rolled steel strip, it is different from that for cold rolled steel strip.
Scale already formed during hot rolling before annealing
are doing. H_TwoWhen the O concentration is high as in the range of the present invention
(H _TwoO concentration of 30% by volume or more)
The mechanism above is not fully understood. However
However, the inventors' research shows that descaling
It was found to improve. For the reason,_TwoO
Decomposes into H, penetrates into the scale, combines with O,
And H again_TwoIt becomes O and decomposes again.
It is estimated that the scale changes and hematite
I have. It is presumed that this effect is greater at the surface layer.
In addition, descaling property should be measured beforehand on the hot rolled steel strip before annealing.
If you apply mechanical force to the
It was also found that it improved. The reason is from crack
H_TwoIt is presumed that O easily penetrates into scale
ing.

FIG. 3 shows a continuous annealing pickling line (HAP: Hot coil Annealing and Pickling Line) of a hot rolled stainless steel strip incorporating the direct fire type annealing furnace shown in FIG. 1 or FIG.
FIG. In FIG. 3, a continuous annealing pickling line for a hot-rolled stainless steel strip is used to perform annealing of the pay-off reel 5 on which the hot-rolled hot-rolled stainless steel strip 2a is unwound and the hot-rolled stainless steel strip 2a. The same annealing furnace 1 as shown in FIG. 2, a tension leveler 9 for extending the stainless steel strip 2a after annealing, and a pickling apparatus 7 for pickling the stainless hot rolled steel strip 2a extended by the tension leveler 9
And a tension reel 8 for winding the hot-rolled stainless steel strip 2a. Then, the stainless steel hot rolled steel strip 2a unwound from the payoff reel 5 is annealed in the annealing furnace 1 by the above-described method, and further, the tension leveler 9
After the elongation, it is pickled by the pickling device 7 to be descaled. The reason for extending the hot-rolled stainless steel strip 2a by the tension leveler 9 after the annealing is to promote descaling in the pickling process, and there is a conventional method in which a mechanical force is applied after the annealing to crack the scale. Is the way.

FIG. 4 is a schematic view of another continuous pickling line for hot rolled stainless steel strip incorporating the annealing furnace shown in FIG. 1 or FIG. In FIG. 4, a continuous annealing pickling line for a hot-rolled stainless steel strip comprises a pay-off reel 5 on which a hot-rolled stainless steel strip 2a is unwound and a stainless steel hot-rolled strip 2a cooled at a predetermined rolling reduction. Rolling mill 6 for cold rolling
And the same annealing furnace 1 as shown in FIG. 1 or 2 for annealing the cold-rolled hot-rolled stainless steel strip 2a, and a pickling apparatus 7 for pickling the annealed stainless steel strip 2a. And a tension reel 8 for winding the hot-rolled stainless steel strip 2a. Then, the hot-rolled stainless steel strip 2a unwound from the pay-off reel 5 is cold-rolled by the rolling mill 6, and
Thereafter, the steel sheet is annealed in the annealing furnace 1 by the above-described method, and further, is pickled by the pickling apparatus 7 to be descaled. FIG.
In the continuous annealing and pickling line for hot rolled stainless steel strip in
Unlike the continuous annealing and pickling line of hot rolled stainless steel strip of
The hot-rolled stainless steel strip 2a is cold-rolled by a rolling mill 6 to crack the scale on the hot-rolled stainless steel strip 2a, and then annealed in an annealing furnace 1. Thereby, the descaling property in the pickling process by the pickling apparatus 7 is further improved as compared with the continuous annealing pickling line of the hot-rolled stainless steel strip in FIG. The method of cracking the scale on the hot-rolled stainless steel strip 2a is not limited to the cold rolling of the hot-rolled stainless steel strip 2a, but may be performed by other mechanical means such as a tension leveler or a brush. Is also good.

Further, FIG. 5 shows a continuous annealing and pickling line (CAP) of a cold-rolled stainless steel strip incorporating the annealing furnace shown in FIG. 1 or FIG.
FIG. In FIG. 5, the continuous cold-rolled stainless steel strip pickling line is used to perform annealing of the cold-rolled stainless steel strip 2b and the pay-off reel 5 on which the cold-rolled stainless steel strip 2b is unwound. The same annealing furnace 1 as shown in FIG. 2, a pickling apparatus 7 for pickling the cold-rolled stainless steel strip 2b after annealing, a temper rolling mill 10, and a tension for winding the cold-rolled stainless steel strip 2b. And a reel 8. Then, the cold-rolled stainless steel strip 2b unwound from the payoff reel 5 is annealed in the annealing furnace 1 by the above-described method, and thereafter, is pickled by the pickling device 7 to be descaled.

[0017]

EXAMPLE Next, the effect of the present invention will be verified with an example using the continuous annealing pickling line shown in FIGS. 3, 4 and 5. FIG. (Example 1) In Example 1, a continuous annealing and pickling line for a hot rolled stainless steel strip shown in FIG.
A 500 mm SUS304 hot-rolled steel strip is annealed in an annealing furnace 1 under the following conditions, an annealing plate temperature of 1,100 ° C. × 10 seconds, and a tension leveler 9 reduces the SUS304 hot-rolled steel strip to 1%. After elongation, neutral pickling and pickling were continued in the pickling device 7. Although not shown, the pickling apparatus 7 is divided into two and is divided into a neutral salt tank and a pickling tank. Neutral salt electrolysis is 200 g / l Na
_{In a 2} SO ₄ aqueous solution at a liquid temperature of 80 ° C., 40 coulombs / dm ²
At the charge density of The pickling was performed at 60 ° C. in a mixed acid of 135 g / l nitric acid and 25 g / l hydrofluoric acid.

The atmosphere in the annealing furnace 1 is as shown in Table 1 below.

[0019]

[Table 1]

In the "Level 1" and "Level 2" in Table 1, the H ₂ O concentration in the gas atmosphere was 57% by volume and 30% by volume, respectively, and annealing was performed by burning propane gas with pure oxygen by a burner. The furnace 1 is being heated. "Level 3" in Table 1 is added for comparison, the H ₂ O concentration in the atmosphere is 20% by volume, and the inside of the annealing furnace 1 is heated by burning butane gas with air by a burner. . Note that despite being burned with pure oxygen instead of air in the "Level 2", why the N ₂ is present, there is a penetration of air from outside of the furnace. This can be adjusted by controlling the atmosphere pressure of the furnace to be positive or negative compared to the atmospheric pressure by a device (not shown) so that air entering from outside the furnace can be introduced or not.

FIG. 6 shows the effect of improving the descalability in the first embodiment. Here, “evaluation of descaling” in FIG. 6 is performed on the number of remaining scales after pickling, and the number of scales per 1 dm ² is 5, 5, 1 is 4, and 1 to 2 is 3, 3, Two cases were defined as four cases and one case was defined as four or more cases.
And evaluation 3 or more judged that descaling property was favorable.

As is clear from FIG. 6, when the H ₂ O concentration in the atmosphere corresponding to level 1 is 57% by volume, the descaling evaluation is 4, and the H ₂ O concentration in the atmosphere corresponding to level 2 is 30.
In the case of volume%, the descaling evaluation was 3 or 4. When the H ₂ O concentration in the atmosphere was 30 volume% or more, good descaling property could be obtained. On the other hand, when the H ₂ O concentration in the atmosphere corresponding to level 3 was 20% by volume, the descaling evaluation was 1, and good descaling properties were not obtained.

(Example 2) In Example 2, a continuous annealing pickling line for a hot rolled stainless steel strip shown in FIG.
mm (2.7mm after entering side rolling), SUS with 1,200mm width
After cold rolling the 304 hot-rolled steel strip with the rolling mill 6, the annealing furnace 1
Atmosphere under the following conditions, annealing plate temperature 1,100 ° C
X Annealed under the condition of 10 seconds, and thereafter, neutral pickling and pickling were continued in the pickling device 7. Although not shown, the pickling apparatus 7 is divided into two and is divided into a neutral salt tank and a pickling tank. Neutral salt electrolysis was carried out in a 200 g / l Na ₂ SO ₄ aqueous solution at a liquid temperature of 80 ° C. and a charge density of 40 coulombs / dm ² . The pickling was performed in a mixed acid of 135 g / l of nitric acid and 25 g / l of hydrofluoric acid at 60 ° C. The atmosphere in the annealing furnace 1 is as shown in Table 2 below.

[0024]

[Table 2]

The “Level 1” and “Level 2” in Table 2 indicate that the H ₂ O concentration in the atmosphere is 57% by volume and 43% by volume, respectively, and that the propane gas is burned with pure oxygen by a burner to perform the annealing. 1 is being heated. "Level 3" in Table 2 is an additional value for comparison,
_{The 2} O concentration is 20% by volume, and the inside of the annealing furnace 1 is heated by burning butane gas with air by a burner.

FIG. 6 shows the effect of improving descalability in Example 2. As is clear from FIG. 6, when the H ₂ O concentration in the atmosphere corresponding to the level 1 is 57% by volume, the descaling evaluation is 5, and when the H ₂ O concentration in the atmosphere corresponding to the level 2 is 43% by volume, the descaling is evaluated. The evaluation was 4,5, and when the H ₂ O concentration in the atmosphere was 43% by volume or more, good descaling properties could be obtained. On the other hand, when the H ₂ O concentration in the atmosphere corresponding to level 3 was 20% by volume, the descaling evaluation was 2, 2.5, and good descaling properties were not obtained.

The descalability in Example 2 is as follows:
As is evident from FIG. 6, it can be seen that in any of the levels 1, 2, and 3, the descalability in Example 1 was exceeded. This is because in Example 2, the SUS304 hot-rolled steel strip was cold-rolled by the rolling mill 6 to crack the scale on the steel strip, and then the annealing furnace 1
This is due to the fact that annealing has been performed.

Example 3 In Example 3, a continuous annealing and pickling line for a cold rolled stainless steel strip shown in FIG.
SUS304 cold-rolled steel strip having a width of 1,000 mm and a width of 1,000 mm was placed in an annealing furnace 1 under the following conditions, at an annealing plate temperature of 1,100
Annealing was carried out at a temperature of 10 ° C. for 10 seconds, and thereafter, neutral pickling and pickling were continued in a pickling apparatus 7. Although not shown, the pickling apparatus 7 is divided into two and is divided into a neutral salt tank and a pickling tank. Neutral salt electrolysis was carried out in a 200 g / l Na ₂ SO ₄ aqueous solution at a liquid temperature of 80 ° C. and a charge density of 40 coulombs / dm ² . Pickling: 135g / l nitric acid, 25g / l hydrofluoric acid
The atmosphere in the annealing furnace 1 performed at 60 ° C. in the mixed acid is as shown in Table 3 below.

[0029]

[Table 3]

The "Level 1" and "Level 2" in Table 3 indicate that the H ₂ O concentration in the atmosphere was 57% by volume and 43% by volume, respectively, and that the propane gas was burned with pure oxygen by a burner to perform annealing. 1 is being heated. “Level 3” in Table 3 is an additional value for comparison,
_{The 2} O concentration is 20% by volume, and the inside of the annealing furnace 1 is heated by burning butane gas with air by a burner.

FIG. 6 shows the effect of improving the descalability in Example 3. As is clear from FIG. 6, when the H ₂ O concentration in the atmosphere corresponding to level 1 was 57% by volume, the descaling evaluation was 4, 5, and the H ₂ O concentration in the atmosphere corresponding to level 2 was 4%.
In the case of 3% by volume, the descaling evaluation was 4, and when the H ₂ O concentration in the atmosphere was 43% by volume or more, good descaling properties could be obtained. On the other hand, when the H ₂ O concentration in the atmosphere corresponding to level 3 was 20% by volume, the descaling evaluation was 2, and good descaling properties were not obtained.

[0032]

As described above, according to the method for continuously annealing stainless steel strip according to the first aspect of the present invention, annealing is performed at an H ₂ O concentration of 30 vol% or more in the atmosphere in the annealing furnace. Therefore, the descalability in the pickling step after annealing can be improved by changing the distribution of the scale composition that grows on the surface of the stainless steel strip in the thickness direction.
For this reason, in the continuous annealing pickling line of the stainless steel strip, it is possible to perform the annealing pickling process without quality defects due to scale residue. Thereby, the length of the pickling apparatus provided for the pickling step can be minimized, and the equipment cost can be significantly reduced. Further, the amount of the acid solution used in the pickling step can be reduced, and the cost of the acid solution can be greatly reduced.

The stainless steel according to claim 2 of the present invention.
According to the continuous annealing apparatus for steel strip, H
_TwoO gas is blown, whereby H_TwoO
Since a device for adjusting the concentration is provided,
H_TwoEven if the O concentration is low,
H_TwoO gas is blown into the annealing furnace, and H _Two
O concentration can be made high.

Further, according to the continuous annealing method for a stainless steel strip according to the third aspect of the present invention, a crack is formed on the scale on the stainless steel hot-rolled steel strip by mechanical means, and the stainless steel hot-rolled steel strip is annealed. After being sent into the furnace, the H ₂ O concentration in the atmosphere is annealed at 30% by volume or more, so that the distribution of the scale composition that grows on the surface of the hot-rolled stainless steel strip in the thickness direction can be changed, and the annealing can be performed. The descalability in the subsequent pickling step is further improved.

According to the continuous annealing apparatus for a stainless steel strip according to claim 4 of the present invention, mechanical means for cracking a scale on the hot-rolled stainless steel strip is provided upstream of the annealing furnace, Since a device for blowing H ₂ O into the atmosphere and adjusting the H ₂ O concentration in the atmosphere is provided, it is possible to change the distribution in the thickness direction of the scale composition that grows on the surface of the hot-rolled stainless steel strip. The descaling property in the subsequent pickling step is further improved, and H
_Even when the concentration of ₂ O is low, H ₂ O
The concentration can be actively adjusted to increase the H ₂ O concentration.

[Brief description of the drawings]

FIG. 1 is a schematic view of an embodiment of an annealing furnace used for a method and an apparatus for annealing a stainless steel strip according to the present invention.

FIG. 2 is a schematic view of another embodiment of an annealing furnace used in the method and apparatus for annealing a stainless steel strip according to the present invention.

FIG. 3 is a schematic diagram of a continuous annealing pickling line for a hot-rolled stainless steel strip incorporating the annealing furnace shown in FIG. 1 or FIG.

FIG. 4 is a schematic view of a continuous annealing pickling line for another stainless hot-rolled steel strip incorporating the annealing furnace shown in FIG. 1 or FIG.

FIG. 5 is a schematic view of a continuous annealing pickling line for a cold rolled stainless steel strip incorporating the annealing furnace shown in FIG. 1 or FIG.

FIG. 6 is a graph showing the relationship between the H ₂ O concentration in the annealing furnace and the descaling evaluation in each example.

[Explanation of symbols]

 1 is an annealing furnace 2 is a stainless steel strip 2a is a hot rolled stainless steel strip 2b is a cold rolled stainless steel strip 3 is a burner 4 is a device 5 is a payoff reel 6 is a rolling mill 7 is a pickling device 8 is a tension reel 9 is a tension leveler 10 is a temper rolling mill 11 is a roll A is a cell type dew point meter B is a control device

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yukio Ida 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Kawasaki Steel Corporation (72) Inventor Kyushu Furukawa 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Kawa Saki Steel Corporation

Claims (4)

[Claims] 1. A continuous annealing method for a stainless steel strip, wherein annealing is performed at an H ₂ O concentration of 30% by volume or more in an atmosphere in a direct-fired annealing furnace. 2. A continuous annealing of stainless steel strip, characterized in that a device for adjusting the H ₂ O concentration in the atmosphere by blowing H ₂ O gas into an atmosphere in a direct-fired annealing furnace is provided. apparatus. 3. A scale on a hot-rolled stainless steel strip is cracked by mechanical means, and thereafter, annealing is performed when the H ₂ O concentration in the atmosphere in a direct-fired annealing furnace is 30% by volume or more. Continuous annealing method for stainless steel strip. 4. A mechanical means for cracking a scale on a hot-rolled stainless steel strip is provided upstream of the direct-fired annealing furnace, and H ₂ O gas is blown into the atmosphere of the annealing furnace. continuous annealing apparatus of a stainless steel strip, characterized in that a device for adjusting the ₂ O concentration.