JPH0517827A - Annealing and descaling method for stainless steel strip - Google Patents

Abstract

PURPOSE:To provide the annealing and descaling method for a stainless steel strip which does not require a nitrofluoric acid pickling treatment and shot blasting treatment in the descaling stage of the steel strip after hot rolling and does not generate unequal descaling occurring in C warpage. CONSTITUTION:After the hot rolled stainless steel strip S is passed through a device 21 for coating an alkaline earth metal chloride soln., the steel strip is annealed in an annealing furnace 5 and is then passed through a C warpage correcting device 51; thereafter, the steel strip is subjected to the descaling by brushes 32 in an oxide scale removing device 31 The descaling is efficiently executed in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for annealing and descaling a stainless steel strip after hot rolling, and in particular, applying an alkaline earth metal chloride solution to the surface of the hot rolled steel strip and annealing it. The present invention relates to a method for annealing and descaling a stainless steel strip that can be efficiently descaled by performing C warpage correction and then removing oxide scale.

[0002]

2. Description of the Related Art A hot rolled stainless steel strip is continuously annealed and descaled by a continuous annealing pickling line (hereinafter referred to as an AP line). This AP line is divided into an annealing furnace section, a mechanical descaling apparatus section, and a pickling tank section. First, the stainless steel strip is annealed in an annealing furnace. However, since the annealing treatment is performed in a direct flame atmosphere, the oxide scale having a thickness of about 5 μm, which was formed on the surface of the stainless steel strip S during hot rolling, was formed during the annealing. And grows to a dense oxide scale of 10 to 30 μm. Since this oxide scale is extremely difficult to remove, the hot-rolled stainless steel strip is first treated with a powerful mechanical descaling device such as shot blasting to destroy the oxide scale layer,
Then, a descaling method of performing acid cleaning with a strong acid such as sulfuric acid, nitric hydrofluoric acid, or hydrofluoric acid was performed.

However, annealing of such a stainless steel strip
The descaling method has the following drawbacks. It takes time to remove dense and thick oxide scale,
I cannot raise my production capacity. Shot blasting creates irregularities on the surface of the steel strip, increasing the surface roughness. When pickling treatment with nitric hydrofluoric acid is performed, intergranular corrosion becomes severe, and irregularities are formed. If there is unevenness due to intergranular corrosion or shot blasting, this unevenness is crushed in the cold rolling in the next step to form a covered portion, and so-called glitter flaws occur.

Therefore, in order to solve these problems,
The inventors of the present invention first applied an alkaline earth metal chloride solution to the surface of a steel strip in Japanese Patent Application No. 2-324504 and then annealed.
A method of descaling was proposed. According to this method, the mechanical strength of the oxide scale is reduced, so that at least shot blasting or pickling with nitric hydrofluoric acid can be omitted and a grinding brush or an acid having a weaker action can be used.

[0005]

However, in the method of applying an alkaline earth metal chloride solution to the surface of the above-mentioned stainless steel strip and then annealing / descaling, when the shape of the stainless steel strip is bad, the grinding used The load on the brush may increase and scale residue may occur. The case where the shape is bad here refers to the case where the steel strip has "warp". The warp includes a warp in the longitudinal direction of the steel strip (hereinafter referred to as L warp) and a warp in the width direction (hereinafter referred to as C warp). Of these, L warpage does not pose a problem in descaling, but C warpage causes unevenness in the contacting direction of the grinding brush in the steel strip width direction, and as a result, unevenness in descaling occurs. There was a problem that it would occur.

Therefore, the object of the present invention is to solve the above-mentioned conventional problems. After applying an alkaline earth metal chloride solution to the surface of a hot-rolled steel strip and annealing it, C-warp correction is carried out, It is an object of the present invention to provide a method for annealing and descaling a stainless steel strip that does not cause unevenness in descaling due to C warping by removing the oxide scale after that.

[0007]

The present invention is directed to annealing a stainless steel strip which is subjected to an annealing treatment on a hot rolled stainless steel strip and then to a treatment for removing oxide scale on the surface of the steel strip.
In the descaling method, an alkaline earth metal chloride solution is applied to the surface of the steel strip before the annealing treatment, and the descaling treatment after annealing is performed by using a grinding brush equipped with a C-zori straightening device for the steel strip. It is characterized by being used.

[0008]

In the process of introducing the stainless steel strip into the annealing furnace and annealing, the water content of the alkaline earth metal chloride solution that has penetrated into the oxide scale layer on the surface of the steel strip evaporates at 100 ° C.,
The solution becomes solid. This solid is 700-800
It becomes a molten state at around 0 ° C., is densely diffused in the oxide scale layer, and in the temperature rising process during the annealing step, the molten solid matter and the oxide scale cause a solid-liquid reaction. Due to this solid-liquid reaction, a very strong oxide scale having a spinel structure formed on the surface of the stainless steel strip in the hot rolling step is a metal chloride containing an alkaline earth metal of indefinite shape and very weak mechanical strength. It is modified into a thing. The chloride generated on the surface of the steel strip can be easily separated from the surface of the steel strip. On the other hand, it prevents the invasion of oxygen into the inside of the oxide scale to prevent new oxide scale from growing on the surface of the steel strip.

This eliminates the need for shot blasting for breaking and peeling the oxide scale, and most of the oxide scale reformate can be removed by a grinding brush.
However, if the grinding brush is used after the C warp of the steel strip is corrected by the C-zori straightening device, the contact of the grinding brush in the width direction of the steel strip does not become uneven, so that efficient descaling can be performed. it can.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows an example of an AP line used in the steel strip annealing / descaling method of the present invention. The steel strip S after hot rolling is wound around the payoff reel 1. The stainless steel strip S is unwound and cut at the leading end or the trailing end by the entrance shear 2, and then welded to the leading coil or trailing coil in the welder 3. Then, via the inlet looper 4, the alkaline earth metal chloride solution coating device 2
1 is transported. In the alkaline earth metal chloride solution coating device 21, as shown in FIG. 2, the steel strip S guided by the roll 25 is immersed in the alkaline earth metal chloride aqueous solution 23 in the solution tank 22, The alkaline earth metal chloride aqueous solution 23 is uniformly applied to the surface of the steel strip S. After that, the steel strip S is pressed by the pressure roll 24, and the alkaline earth metal chloride aqueous solution 23 is permeated into the oxide scale 50 of the steel strip S until the base iron portion of the steel strip S is reached as shown in FIG. Let

In FIG. 3, the alkaline earth metal chloride aqueous solution 23 is formed in the layer of the oxide scale 50 formed on the surface of the stainless steel strip S through the cracks 52 existing in the oxide scale 50 of the stainless steel strip S. 3 shows a state in which the dull portion 51 has penetrated due to the capillary phenomenon. Then, the stainless steel strip S was sent to the heating part 6 which comprises the annealing furnace 5 through the roll 25, and heat-processed at a predetermined temperature. Here, the alkaline earth metal chloride aqueous solution 23 that has penetrated into the oxide scale 50 becomes a solid state due to the evaporation of water, then becomes a molten state, and diffuses densely into the oxide scale 50. A solid-liquid reaction proceeds between the metal chloride aqueous solution 23 and the oxide scale 50. Then, the stainless steel strip S is sent to the cooling part 7 which comprises the annealing furnace 5, and is cooled at a predetermined temperature.

Thereafter, the stainless steel strip S is provided with a C warpage straightening device.
C warpage is corrected in place 51 and then oxide scale
It is sent to the removal device 31 and adheres to the surface of the stainless steel strip S.
Reaction of Alkaline Earth Metal Chloride with Oxide Scale
The reaction product 33 is removed. FIG. 4 shows a C warp straightening device 51.
FIG. 3 is an enlarged view of an oxide scale removing device 31 and C warpage.
The straightening device 51 sandwiches the stainless steel strip S from the front and back sides.
It consists of multiple roles. That is, in FIG.
A placed above and below the stainless steel strip S as shown₁~ A₃
Rolls and B correspondingly arranged above and below₁
~ B₃It is equipped with a roll group and each roll is rotatable
Is. Also, each roll depends on the shape of the stainless steel strip S.
It can be moved up and down. For example, C
The warp is upward (concave shape with the center recessed in Fig. 5)
Roll A as shown_1,A_2,A₃The
Pressed against the steel strip S, the C warp is downward (Fig. 5)
If the center is a convex shape protruding upwards,
Recessed roll B_1,B_2,B ₃To the stainless steel strip S
Straighten and correct the C sled.

The oxide scale removing device 31 has two sets of upper and lower grinding brushes 32 in series in order to remove a reaction product 33 of the alkaline earth metal chloride adhering to the surface of the stainless steel strip S and the oxide scale. Are opposed to each other. The reaction force 3 from the stainless steel strip S is generated from the stainless steel strip S by the grinding force of the grinding brush 32 generated by the grinding brush 32 rotating in opposition to the traveling direction of the stainless steel strip S.
Remove 3. At this time, since the C-warp of the stainless steel strip S has been already removed and corrected by the C-warp straightening device 51, there is no unevenness in the contact of the grinding brush 32 with the steel strip surface in the steel strip width direction. Reaction product 3 removed
3 is washed away by the water spray nozzle 34 and discharged from a discharge pipe 35 provided at the lower end of the oxide scale removing device 31. As described above, since the reaction product 33 can be easily removed from the stainless steel strip S by the grinding force of the grinding brush 32, shot blasting is not necessary. Moreover, even if the stainless steel strip S has a C warp, the stainless steel strip S is straightened by the C warp straightening device 51 and no unevenness occurs on the grinding brush 32 in the oxide scale removing device 31. 33 can be removed evenly.

Next, in the case where the reaction product 33 remains on the surface even after the brushing with the grinding brush 32, the stainless steel strip S is removed by an acid other than hydrofluoric acid such as sulfuric acid or hydrochloric acid in order to remove it. Etc. to the pickling tank 41.
At this time, since pickling with nitric hydrofluoric acid is not performed, the crystal grain boundaries are not corroded. Then, a passivation treatment is performed in the nitric acid tank 42 as a final pickling.

Next, after passing through the cleaning device 12 and the dryer 13, the stainless steel strip S is cut into a predetermined size by the split shear 15 through the exit side looper 14, and the tension reel 1 is cut.
Take up to 6. Of course, if there is no residue or if there is a little residue, only nitric acid tank 42 should be used, and if there is no residue at all and no passivation treatment is required. Can bypass these pickling tanks.

[0016]

Example 1 With respect to the stainless steel strip after hot rolling, the stainless steel strip was annealed and descaled under the conditions shown in Table 1 by the AP line of the present invention (see FIG. 1) described in the above example, The adhesion state of oxide scale was investigated.

[0017]

[Table 1]

The thickness of the oxide scale before application of the aqueous solution of calcium chloride was 5 μm, and it was 5 μm on the exit side of the annealing furnace 5, and the oxide scale did not grow. And, when the C warpage straightening device 51 was not used, the oxide scale residual rate on the output side of the oxide scale removing device 31 was 5%, but when the acid C warpage straightening device 51 was used, the oxide scale residual rate was up to 1%. It was possible to reduce.

Of course, no oxide scale remained after pickling with nitric acid.

[0020]

[Embodiment 2] Using the AP line shown in FIG. 1 and under substantially the same method and conditions as in the above embodiment, except that one stand or two stands are used for the grinding brush 32 and the C warp straightening device 51 is used. The scale residual rate (%) of the stainless steel strip S after passing through the grinding brush 32 was investigated for the case of not using and the case of not using.

The results are shown in Table 2.

[0022]

[Table 2]

The evaluations in Table 2 are as follows. ⊚: No oxide scale remains, which is good. Δ: Some oxide scale remains. As is clear from the results shown in Table 2, C warpage straightening device 5
When 1 is not used, it is necessary to pass the grinding brush in two passes in order to completely remove the oxide scale.
By using the warp straightening device 51 together, the oxide scale could be almost completely removed by making one pass through the grinding brush.

As described above, in the descaling method of the present invention, it is possible to effectively perform descaling by using the C warp straightening device. Table 3 shows the results of evaluating the surface quality of the stainless steel strip S thus treated.

[0025]

[Table 3]

By using the C warpage straightening device, it is possible to reduce the pressing pressure of the grinding brush, and as a result, the surface roughness is reduced to about 1 μm in R _Z value, and the smoothness of the steel strip surface is reduced. Could be realized.

[0027]

As described above, according to the present invention,
In the annealing / descaling method of a stainless steel strip, where the stainless steel strip after hot rolling is annealed, and then the oxide scale on the surface of the steel strip is removed, an alkaline earth metal is applied to the surface of the steel strip before the annealing treatment. The metal chloride solution was applied, and the descaling treatment after annealing was carried out by using a grinding brush equipped with a C-bending straightening device for steel strips. Therefore, the strong oxide scale is modified into a metal chloride containing an alkaline earth metal having a weak mechanical strength, and it can be removed by a grinding brush instead of shot blasting. Since the grinding brush is used after being straightened, the contact of the grinding brush in the width direction of the steel strip becomes uniform, and the effect of efficient descaling can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a line configuration of an example of an AP line to which the annealing / descaling method for a steel strip according to the present invention is applied.

FIG. 2 is an enlarged cross-sectional view of the alkaline earth metal chloride solution coating device in FIG.

FIG. 3 is a schematic cross-sectional view of a steel strip surface for explaining the permeation action of the alkaline earth metal chloride solution into the oxide scale layer formed on the surface of the stainless steel strip.

FIG. 4 is an enlarged cross-sectional view of the oxide scale removing device in FIG.

5 is a cross-sectional view taken along the line VV of FIG.

[Explanation of symbols] S Stainless steel strip 5 Annealing furnace 21 Alkaline earth metal chloride solution coating device 31 Oxide scale removing device 32 Grinding brush 51 C Warp straightening device

Front page continuation (72) Inventor Kuniaki Sato 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Hiroyuki Kakiuchi 1-Kawasaki-Chiba, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (1)

Claim: What is claimed is: 1. A method for annealing and descaling a stainless steel strip, comprising: subjecting a stainless steel strip after hot rolling to an annealing treatment, and then removing a scale of oxide scale on the surface of the steel strip. Before the treatment, the alkaline earth metal chloride solution is applied to the surface of the steel strip, and the descaling treatment after annealing is characterized by using a grinding brush equipped with a C-zori straightening device for the steel strip. Annealing and descaling method for stainless steel strip.