JPH09271832A - Descaling method of hot rolled ferritic stainless steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a de-scaling method of a hot rolled ferritic stainless steel plate which removes efficiently a scale of a thickness 10 to 20μm level produced in an annealing process and which improves the pickling efficiency in a following pickling process in the production line of a ferritic hot rolled stainless steel plate having a process of annealing in the 800 deg.C to 1050 deg.C and then pickling after hot finish rolling. SOLUTION: A ferritic stainless steel plate of hot rolled in a finish rolling mill is annealed in 800 to 1050 deg.C, then when the surface temperature of this stainless steel plate is lain between 300 to 1050 deg.C, a high pressure water is jetted and collided by >=20kg/cm<2> collision pressure against the same place of the surface of this stainless steel plate so that the collision frequency is made more than two times within five minutes and de-scaling is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when producing a ferritic stainless hot-rolled steel sheet, improves the surface properties of a hot-rolled stainless hot-rolled steel sheet after annealing and before pickling. The present invention relates to a descaling method by jetting high-pressure water.

[0002]

2. Description of the Related Art In the production of a cold rolled stainless steel sheet, generally, a stainless steel slab, which is a stainless material, is heated in a heating furnace and hot rolled by a rough rolling mill, an intermediate rolling mill or a finish rolling mill. , Annealing, pickling, cold rolling,
It is commercialized through processes such as annealing, pickling and skin pass rolling.

After the hot rolled steel sheet is annealed, the scale after hot rolling grows to a thickness of 10 to 20 μm, and the pickling efficiency decreases in the subsequent pickling step. Further, if the pickling is insufficient, it is known that surface defects generated during hot rolling cannot be sufficiently removed and remain as surface defects even after the cold rolling step, which deteriorates the quality of the product. There is.

For this reason, various descaling for removing the generated scale has been conventionally performed in addition to the means for suppressing the scale generation. For example, Japanese Patent Laid-Open No. 6-71330 discloses high pressure water before the finish rolling mill. Descaling by spraying is disclosed.

Here, as a high-pressure water spray condition for austenitic stainless steel, the collision pressure per unit spraying area is 60 g / mm ² or more and 170 g / mm ² or more.
It is specified that the flow rate is ² or less and the flow rate is 0.1 [l / (min · mm ² ) or more and 0.2 [l / (min · mm ² ) or less.

However, even if the descaling is carried out before the hot finish rolling mill, it is 800 to 1050 ° C. after the hot finish rolling.
In the production line of stainless hot-rolled steel sheet having a step of performing pickling by annealing at, scale generation in the annealing step is active, and when pickling is conducted as it is in the pickling step, pickling efficiency is remarkably high. Even if it lowers and goes through the subsequent cold rolling step, it is not possible to obtain a stainless steel sheet having a sufficient surface texture. After annealing, for example, JP-A-6-713.
By applying the descaling by the high pressure water spray for the stainless steel plate, which is disclosed in Japanese Patent No. 30, the impact pressure per unit spraying area is 60 g / mm ² or more and 170 g / mm ² or less as the high pressure water spraying condition. Moreover, the flow rate is 0.1 [l / (min · mm ² ) or more 0.2 [l / (min · mm 2
² ) It is also possible to descale by the following.

However, after hot finish rolling 800-105
In the production line of ferritic stainless hot-rolled steel sheet, which has a step of annealing at 0 ° C and pickling, under these high-pressure water spray conditions, some effect can be expected, but sufficient pickling efficiency in the pickling step It is difficult to remove the scale to such an extent that it is possible to secure the above, and there is still room for improvement when applied to a production line for a ferritic stainless steel hot rolled steel sheet having such annealing and pickling steps.

[0008]

DISCLOSURE OF THE INVENTION The present invention is produced in an annealing step in a production line of a ferritic stainless hot-rolled steel sheet having a step of performing pickling after annealing at 800 to 1050 ° C. after hot rolling. Of a stainless hot-rolled steel sheet rolled in the cold rolling process by efficiently and sufficiently removing scales having a thickness of 10 to 20 μm with high pressure water to improve the pickling efficiency in the subsequent pickling process. It is intended to provide a descaling method for a ferritic stainless hot rolled steel sheet capable of improving surface properties.

[0009]

According to the present invention, after hot-rolled ferritic stainless steel sheet is annealed at 800 to 1050 ° C. and before pickling, the steel sheet surface in a temperature range of 300 to 1050 ° C. , High pressure water, collision pressure 20kg / cm
² above, injection and collide as the number of collisions for the same location of the surface of the steel sheet is more than 2 times within 5 seconds, descaling ferritic stainless hot-rolled steel sheet which is characterized in that the descaling Is the way.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to FIG. The production line of a ferritic stainless hot rolled steel sheet (hereinafter simply referred to as "stainless hot rolled steel sheet") to which the present invention is applied is generally configured as follows. As shown in FIG. 1 (a), a stainless steel slab 1 s is introduced into a heating furnace 2 and heated to 1100 to 1200 ° C. to be a hot rolling mill including a rough rolling mill 3, an intermediate rolling mill 4, and a finish rolling mill 5. At 1000 to 1150 ° C., after being cooled by the cooling device 6, the obtained stainless hot-rolled steel sheet 1a is wound by the winder 7 to form the hot-rolled coil c1. As shown in FIG. 1 (b), the hot rolled coil c1 is unwound and the stainless hot rolled steel sheet 1a is heated in the annealing furnace 8 at 800
Annealing is performed at 1050 ° C., descaling is performed by the descaling device 9, and after cooling, pickling is performed by the pickling device 10, and the obtained hot-rolled stainless steel plate 1b is wound by the winder 11 and primary pickling is performed. Use coil c2. As shown in FIG. 1 (c), the primary pickling coil c2 is cold rolled by the reverse rolling mill 12 to form a cold rolled coil c3. As shown in FIG. 1 (d), the cold rolled coil c3 is unwound, annealed in the annealing furnace 13 at 800 to 1050 ° C., cooled, and then secondary pickled by the pickling device 14 and adjusted by the skin pass rolling machine 15. The product is rolled into a product coil as a hot rolled stainless steel plate 1p.

In the present invention, a high-pressure water injection device 9w is arranged as a descaling device 9 on the outlet side of the annealing furnace 8 for annealing the hot rolled stainless steel sheet 1a unwound from the hot rolled coil c1 in the step of The injection hole of the injection nozzle 16 of the injection device 9w is arranged so that the distance h can be adjusted with respect to the surface of the hot-rolled stainless steel plate 1a from the annealing furnace 8, and the supply source 17 via the high-pressure pump 18 Descaling is performed by jetting high-pressure water w onto the surface of the hot-rolled stainless steel plate 1a immediately after annealing at a predetermined collision pressure for a predetermined number of collisions within a predetermined time.

The collision pressure P here can be obtained by using, for example, an estimation formula of a collision force derived from the law of conservation of momentum and the law of conservation of mass (continuous equation). It is also possible to obtain the value by actually measuring with a load cell or the like and substituting the operating condition satisfying this. P = {ρ ^0.5 * C ₃ * / (2 * 2 ^0.5 * tan α * tan β)} * P ₀ ^0.5 * Q * H ^-2 * sin ² γ ... ... (1) P: Collision pressure (kg / cm ² ) ρ: Fluid density (kg / m ³ ) C ₃ : C ₃ = C ₁ * C ₂ = 0.9 C ₁ : Pressure in the nozzle Velocity coefficient due to loss (0.95 <C ₁ <1.0) C ₂ : Jet deceleration coefficient due to air resistance (0.9 <C ₂ <1.0) α: Spread angle in jet width direction (degrees) → ( (See Fig. 3-a) β: Spread angle in the jet thickness direction (degrees) → (See Fig. 3-b) γ: Nozzle orientation angle (°) → (See Fig. 3-c) P ₀ : Header pressure (kgf / cm) ² ) Q: Liquid flow rate of the nozzle (liter / min) H: Distance between the tip of the nozzle and the surface of the material to be descaled (mm) where C ₃ = 0.9 and β is considered to be about 1 degree Then P Equal to or less than the as. P = 30.4 * P ₀ ^0.5 * Q * sin ² γ / (H ⁻² tan α) (2) The collision force P can also be obtained by actually measuring with a load cell or the like.

In the present invention, the collision pressure when the high pressure water is jetted and collided with the surface of the hot rolled stainless steel plate 1a is determined and set as described above, and the collision pressure of the jetted high pressure water w on the surface of the steel plate 1a is set. Is 20 kg / cm ² or more, high-pressure water is jetted from the jet nozzle 16 to jet and collide with the surface of the hot-rolled stainless steel sheet 1a. In this case, the number of collisions with the same place on the surface of the steel sheet is within 5 seconds. It is an injection / collision that is performed twice or more. So, in this example,
The injection nozzle 16 of the high-pressure water injection device 9w is, for example, as shown in FIG.
As shown in (a) and FIG. 2 (b), a plurality of slit-shaped injection holes 16a, 16b are provided, and the plurality of rows are arranged in the width direction and the running direction of the hot rolled stainless steel plate 1a. By using the high-pressure water having a predetermined collision pressure, the high-pressure water is stably jetted and collided with the hot-rolled stainless steel sheet with a predetermined number of collisions.

These jet nozzles 16 may be arranged in a plurality of rows in the width direction and the running direction, and it is not essential to make the jetting condition of the high-pressure water from the jet nozzles 16 constant. The strength may be set in the width direction and the length direction for each injection hole unit or each injection hole row unit. In addition to the above-mentioned jet nozzle, a rotary jet nozzle is also suitable as the jet nozzle used here. Further, in the case of performing descaling by injecting and colliding high-pressure water with the stainless hot-rolled steel sheet in a stationary state, an injection nozzle or the like having a pulsating structure is suitable.

In the present invention, as described above, the high pressure water w jetted from the jet nozzle 16 of the high pressure water jetting device 9w.
The collision pressure and the number of collisions are controlled (or set) within a predetermined range, and therefore, the output control of the high-pressure pump 18 that controls the supply amount and the supply pressure of the high-pressure water w that influences the collision pressure. A device 19 and a height control device 20 for the injection nozzle are provided, and a collision number control device (not shown) that can control (set) the number of collisions is provided.

Each of these control devices operates on the basis of information from the line speed measuring instrument 21, the annealing furnace outlet thermometer 22, the height measuring instrument 23 of the injection nozzle 16 and the setting information.
8 output, the height of the injection nozzle 16, and the collision number condition are controlled by the arithmetic unit 24. These controls are not essential, and may be fixed under initial setting conditions. The present invention can be implemented by using the descaling device configured as described above.

In the present invention, the hot-rolled stainless steel sheet 1a hot-rolled by the finish rolling mill 5 is 800-1 in the annealing furnace 8.
It is premised on annealing at 050 ° C., and the surface temperature of the steres hot-rolled steel sheet 1a immediately after this annealing is 300 to 105.
When it is at 0 ° C, the injection nozzle 16 of the high pressure water injection device 9w
Descaling is performed by injecting and colliding high-pressure water w with a collision pressure of 20 kg / cm ² or more onto the same place on the surface of the hot-rolled stainless steel plate 1a so that the number of collisions is two or more within 5 seconds. I do.

The surface temperature of the hot rolled stainless steel sheet 1a is 30
If the temperature is lower than 0 ° C., the descaling effect of the scale is insufficient because the scale peeling action is insufficient even if the injection conditions of high-pressure water are changed. The surface temperature of the stainless hot rolled steel sheet 1a is 1050 ° C.
In the above cases, the rolling temperature and the annealing temperature are exceeded, the mechanical properties (for example, toughness) of the stainless hot rolled steel sheet deteriorate, and the amount of scale formation also increases. In addition, a cooling process is required because it interferes with the subsequent pickling process, and there is a problem that the stainless hot-rolled steel plate is cut at a temperature near the melting temperature, which hinders the operation. No scale removal effect is found to compensate for these problems.

As a condition for injecting and colliding high-pressure water with the surface of the hot rolled stainless steel sheet, the collision pressure is 20 to 40 kg /
It is preferable to select a condition in which the number of collisions within 5 seconds with respect to the same place on the surface of the steel sheet is 2 to 3 times in cm ² . When the collision pressure is less than 20 kg / cm ² , the descaling effect is not sufficient. Also, the collision pressure is 40 kg
If it exceeds / cm ² , the descaling effect slightly increases, but the descaling cost increases remarkably, which is not preferable.

Regarding the number of collisions, when a time of 5 seconds or more elapses between the first collision and the second collision, a new scale is generated during this time and a high pressure is applied to the original scale that is in close contact with the metal surface. Since the water impinges on the collision pressure and interferes with the scale peeling effect, the high pressure water is applied to the same place on the surface of the hot-rolled stainless steel plate 1a more than twice within 5 seconds. Descaling by injecting and colliding with. If this condition is satisfied, 92% or more of the scale joined to the base steel can be removed. If the second collision is 5 seconds or more, only 66 to 83% of the scale joined to the base steel can be removed.

FIG. 4 shows the surface of a stainless hot-rolled steel sheet (steel type A in Table 1) 1a immediately after annealing in an annealing furnace 8 using a descaling device with a high-pressure water jet device 9w as shown in FIGS. 1 and 2. In the temperature range of 800 ° C., the collision pressure of high-pressure water w and the number of collisions are controlled to perform descaling, and the effect is expressed by the pickling treatment time ratio in the subsequent pickling apparatus 10. Here, when the current pickling treatment time is set to 100%, it means how much the pickling treatment time is shortened, and it is shown that the smaller the pickling treatment time ratio, the greater the descaling effect.

As shown in FIG. 4, high-pressure water is sprayed onto the same place on the surface of the hot-rolled stainless steel sheet twice per second.
In case of collision, the collision pressure of high pressure water w is 20kg / cm
^{When the value is 2} , the pickling treatment time ratio sharply decreases, and as the high-pressure water collision pressure increases, the pickling treatment time ratio gradually decreases. This indicates that the pickling treatment time can be shortened to the current 30% level.

On the other hand, when high-pressure water is sprayed and made to collide with the same place on the surface of the hot-rolled stainless steel sheet once per second, the collision pressure of the high-pressure water w is 20 kg / cm ^2. If so, the pickling treatment time ratio will be somewhat smaller, and as the high-pressure water collision pressure increases, the pickling treatment time ratio will gradually decrease, but the pickling treatment time can only be shortened to the current 80% level. Is shown.

The temperature of the surface of the hot rolled stainless steel sheet after annealing is 800 ° C. in FIG.
In the 300 ° C. region, the shortening rate of the pickling treatment time is 5 to 10% lower than the shortening rate of the pickling treatment time in FIG. 4, but high pressure water is applied to the same place on the surface of the stainless hot-rolled steel sheet. 1
When the injection / collision is performed twice per second, the pickling time can be significantly shortened as compared with the case where the injection / collision is performed once per second.

When the temperature of the surface of the stainless steel sheet after annealing is in the range of 800 to 1050 ° C., the reduction rate of the pickling treatment time is, for example, 2 times per second or 1 time per second. The reduction rate of the pickling treatment time in FIG. 4 is improved by several percent, but it is difficult to say that the reduction rate of the pickling treatment time is sufficient when the number of collisions is once per second.

The present invention is not limited to the descaling of the ferritic stainless hot rolled steel sheets of the A steel type and the B steel type of Table 1, and can be applied to the descaling of other ferritic stainless hot rolled steel sheets. . Further, the high-pressure water injection device for carrying out the present invention is not limited to those shown in FIGS. 1 and 2, and, for example, types of injection nozzle, pulsation device, high-pressure pump, etc., structure and control mechanism. The injection conditions and the like are changed according to the standard, size, and manufacturing conditions (for example, hot rolling, annealing, pickling, cold rolling, etc.) of the hot-rolled stainless steel sheet to be applied.

[0027]

Embodiments A descaling device as shown in FIGS. 1 and 2 is used, and after finishing rolling by a finish rolling mill 5, a cooling zone 6 is provided.
The coiled ferritic stainless steel hot rolled steel sheet (the composition of which is shown in Table 1 for A steel type and B steel type is shown in Table 1) is rewound and guided to the annealing furnace 8.
In the case of annealing at 00 to 1050 ° C. and immediately after this annealing, after performing the descaling method by high-pressure water injection of the present invention and pickling with the pickling apparatus 10, the execution conditions, the execution results and the evaluation results are shown in the present invention. The results are shown in Tables 2 and 3 together with those of the comparative examples outside the condition range. In addition, the evaluation here was performed by the pickling time ratio with respect to the pickling time at the time of performing descaling by shot blasting at room temperature and then pickling.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

Table 2 shows the case of steel type A,
Immediately after annealing, high-pressure water is sprayed onto the same location on the surface of the hot-rolled stainless steel sheet in the temperature range of 300 to 950 ° C at a collision pressure of 20 kg / cm ² or more and two collisions per second. -Examples (2, 3, 4, 12, 13, 14, which satisfy the conditions of the descaling method of the present invention, which are caused to collide with each other.
As for the pickling treatment time ratio of 15), when the pickling treatment time in Comparative Example (1) when descaling by shot blasting at room temperature is 100%, the pickling treatment time is significantly reduced to 16 to 27%. It was possible and satisfactory.

On the other hand, the pickling treatment time ratios in Comparative Examples (5 to 11) satisfying some of the conditions of the present invention but not all of them were descaled by shot blasting at room temperature. In case (1), the pickling time is 100
%, It was possible to shorten the pickling treatment time to 57 to 90%, but this was not sufficiently satisfactory. Further, Table 3 shows the case of the B steel type having a slightly different composition from the A steel type, and examples (2, 3, 4, 12, 13, which satisfy the conditions of the descaling method of the present invention. 1
The pickling treatment time ratio of 4 and 15) is almost the same as that of the A steel type, and can be greatly shortened to 18 to 29% of the pickling treatment time.
It was very satisfying.

On the other hand, the pickling treatment time ratios in Comparative Examples (5 to 11) satisfying some of the conditions of the present invention but not all of them were descaled by shot blasting at room temperature. In case (1), the pickling time is 100
%, The pickling time could be shortened to 60 to 95%, but this was not sufficiently satisfactory.

[0034]

In the present invention, the surface temperature of the hot-rolled ferritic stainless hot-rolled steel sheet is 300 to 105 after the annealing that causes the active formation of scale.
When the temperature is 0 ° C, high-pressure water is sprayed on the surface of the stainless steel plate to effectively perform de-scaling by mechanical impact of high-pressure water and thermal impact.
Pre-pickling cooling can be performed at the same time, and in subsequent processes such as pickling and cold rolling, deterioration of product quality due to residual scale can be prevented, and the pickling treatment time can be greatly shortened. As a result, productivity can be improved and production cost can be reduced.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional side view outline explanatory view showing an example of equipment arrangement and an example of arrangement of a descaling device in a production line of a stainless hot-rolled steel sheet for carrying out the present invention.

FIG. 2 is a schematic bottom view showing an arrangement example of injection holes of the injection nozzle in FIG.

FIG. 3 is an explanatory diagram of each angle (α, β, γ) and distance (H) of the injection nozzle in the theoretical formula for determining the impact pressure of high-pressure water.

FIG. 4 is an explanatory diagram showing the relationship between the collision pressure of high-pressure water, the number of collisions, and the pickling treatment time ratio for evaluating the effect of the present invention.

[Explanation of symbols]

 1s Stainless steel slab 1a, 1b, 1p Stainless hot rolled steel sheet 2 Heating furnace 3 Rough rolling mill 4 Intermediate rolling mill 5 Finishing rolling mill 6 Cooling zone 7 Winder furnace 8 Annealing furnace 9 Descaling device 9w High pressure water injection device 10 Acid Washing device 11 Winder 12 Reverse rolling mill 13 Annealing furnace 14 Pickling device 15 Skin pass rolling machine 16 Injection nozzles 16a, 16b Injection holes 17 (Water) supply source 18 High pressure pump 19 Output control device 20 Injection nozzle height control device 21 Line speed meter 22 Annealing furnace exit side thermometer 23 Injection nozzle height gauge 24 Computing device w High pressure water

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[Procedure amendment]

[Submission date] June 28, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

The collision pressure P here can be obtained by using, for example, an estimation formula of a collision force derived from the law of conservation of momentum and the law of conservation of mass (continuous equation). It is also possible to obtain the value by actually measuring with a load cell or the like and substituting the operating condition satisfying this. P = {ρ ^0.5 * C ₃ / (2 * 2 ^0.5 * tan α * tan β)} * P ₀ ^0.5 * Q * H ⁻² * sin ² γ ... (1) P: Impact pressure (kg / cm ² ) ρ: Fluid density (kg / m ³ ) C ₃ : C ₃ = C ₁ * C ₂ = 0.9 C ₁ : Pressure loss in the nozzle Velocity coefficient (0.95 <C ₁ <1.0) C ₂ : jet deceleration coefficient due to air resistance (0.9 <C ₂ <1.0) α: jet width direction spreading angle (degrees) → (Fig. 3-a) β: Spread angle in jet thickness direction (degree) → (see Fig. 3-b) γ: Nozzle orientation angle (deg) → (see Fig. 3-c) P ₀ : Header pressure (kgf / cm ² ) Q: Liquid flow rate of the nozzle (liter / min) H: Distance between the tip of the nozzle and the surface of the material to be descaled (mm) where C ₃ = 0.9 and β is considered to be about 1 degree. , P is It becomes as follows. P = 30.4 * P ₀ ^0.5 * Q * sin ² γ / (H ⁻² tan α) (2) The collision force P can also be obtained by actually measuring with a load cell or the like.

Claims (1)

[Claims] 1. A hot rolled ferritic stainless steel sheet is annealed at 800 to 1050 ° C. and before pickling, 300 times.
High-pressure water is applied to the surface of the steel sheet in the temperature range of 1050 ° C. so that the collision pressure is 20 kg / cm ² or more, and the number of collisions with the same place on the surface of the steel sheet is 2 or more times within 5 seconds. Descaling method for hot-rolled ferritic stainless steel sheet, characterized by performing descaling by injecting and colliding with.