JPH0967617A - Method for annealing and descaling stainless steel strip and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an annealing and descaling method of a stainless steel strip, which can maintain the good quality of a steel strip and the service life of a hearth roll even at high feeding speed of the steel strip at the time of treating it in an annealing furnace by applying descaling solution on the surface of the hot-rolled stainless steel strip, and to provide a device therefor. SOLUTION: At a process preceding to a continuous annealing and pickling equipment of the hot-rolled stainless steel strip in an annealing furnace 5, a coating device 16 for solution used for improving the descaling of the steel strip S is arranged and a drying device 20 for heating and drying the lower surface side of the steel strip coated with the solution is arranged between the coating device 16 and the inlet side of the annealing furnace 5. By this method, after forcedly pre-drying the solution on the steel strip surface, the steel strip S is carried into the annealing furnace 5 and annealed. The defective product surface developed by unevenly scraping out the undried solution with the hearth roll in the furnace can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for annealing and descaling hot-rolled stainless steel strip, and in particular,
Descaling in a continuous annealing pickling line for hot-rolled stainless steel strips where a solution coating device that improves the descaling properties of stainless steel strips was placed in the previous step of the annealing furnace, regardless of the line speed. It was done.

[0002]

2. Description of the Related Art As a conventional technique of this type, there is one disclosed in Japanese Patent Application Laid-Open No. 4-6288 proposed by the present applicant. This product is an AP line (A for continuous annealing / pickling treatment of hot-rolled stainless steel strip.
nnealing and Pickling Lin
e) Improvement of annealing / descaling method for stainless steel strips performed by using equipment called 3rd Edition Steel Handbook III (1), rolling foundation / steel sheet, p.699 to 700, S55.5.15 Maruzen Is.

Generally, the surface of a hot rolled stainless steel strip is
Oxides (called scales) that are more difficult to remove than those of ordinary steel are produced, and descaling is difficult only by pickling with a hydrochloric acid bath like ordinary steel. Therefore, the hot-rolled stainless steel strip is subjected to the annealing treatment and the descaling treatment continuously in the hot-rolled stainless steel strip continuous annealing pickling facility called the AP line. The descaling means in that case is equipped with a stronger one than that of ordinary steel treatment. Mechanical descaling equipment such as mechanical scale breaker, shot blast, grinding brush, sulfuric acid tank, nitric hydrofluoric acid tank, It is usually practiced to use an appropriate combination with a chemical descaling device such as a nitric acid tank.

However, shot blasting has a diameter of 0.3-
A steel ball of about 0.5 mm is made to collide with the surface of the steel strip at a high speed, and if such a strong treatment is performed, a deep dent defect is formed on the surface of the steel strip, and the subsequent cold rolling process is performed. Even after a long time, the flaws remained and contributed to poor surface quality of the product. The applicant's previous proposal (Japanese Patent Laid-Open No. 4-6288)
(Japanese Patent Publication) is intended to solve the problems of such a method of annealing and descaling stainless steel strip, the surface of the hot rolled stainless steel strip before annealing treatment,
A solution (alkaline earth metal chloride solution) that improves the descaling property is applied in advance and allowed to penetrate, and then annealing and pickling are performed.
When the alkaline earth metal chloride solution is applied, the solution penetrates into the oxide scale layer formed on the surface of the steel strip during hot rolling until it reaches the base metal portion of the steel strip by capillary action. When the steel strip was introduced into an annealing furnace and annealed, the water content in the alkaline earth metal chloride solution that had penetrated into the oxide scale layer was reduced to 10%.
Evaporate at 0 ° C. and the solution becomes solid. This solid is in a molten state at around 700 to 800 ° C., diffuses densely in the oxide scale layer, and prevents contact between oxygen and the base metal part of the steel strip during the annealing process, thus preventing the oxide scale on the steel strip surface. Prevent the growth of. Further, in the temperature rising process during the annealing process, the molten chloride and oxide scale undergo a solid-liquid reaction, and a very strong oxidation having a spinel structure formed on the surface of the stainless steel strip during the hot rolling process. scale,
For example, Cr ₂ O ₃ , Fe ₃ O ₄ , FeCr ₂ O _4, etc. are changed to a scale containing chlorides of Cr and Fe containing an amorphous earth metal having an amorphous shape and a very low mechanical strength. This scale can be easily peeled from the surface of the steel strip.

That is, by applying the alkaline earth metal chloride solution, formation of new oxide scale is prevented, and the mechanical strength of the oxide scale already formed is reduced, resulting in a strong strength such as shot blasting. Descaling treatment can be omitted, and the effect of improving the production capacity and at the same time dramatically improving the surface properties of the product steel strip can be obtained.

[0006]

However, the AP line, which is an equipment for annealing and pickling hot-rolled stainless steel strips,
Generally, a horizontal annealing furnace is often used, and the following problems have arisen accordingly. That is, as shown in FIG. 3, the horizontal annealing furnace 5 is arranged immediately after the coating device 16 of the alkaline earth metal chloride solution as the solution for improving the descaling property (hereinafter referred to as the descaling solution). The stainless steel strip S is the coating rolls 17 and 1 of the coating device 16.
After passing through 8, it is fed into the furnace while being held by the hearth roll 5R in the furnace. In this case, coating roll 1
Steel strips S held by 7, 18 and the hearth roll 5R inevitably move while forming a catenary (catenary line).
When the moving speed of the steel strip S is relatively slow, the descaling solution L applied to the lower surface of the steel strip S is heated to a high temperature existing in the preheat zone 6 in the annealing furnace 5. The sensible heat of the combustion exhaust gas is dried before reaching the first hearth roll 5R [FIG. 3 (a)].

However, when the moving speed of the steel strip S increases, the applied descaling solution L reaches the first hearth roll 5R before it is completely dried [FIG. 3].
(B)]. Then, the undried descaling solution is scraped off unevenly by the hearth roll 5R, and the steel strip S
There is an unsolved problem that a quality defect of a pattern is generated on the surface of the roll and the part of the descaling solution adhering to the surface of the hearth roll is precipitated by drying to shorten the roll life.

The present invention has been made by paying attention to such unsolved problems of the prior art, and when applying a descaling solution to the surface of a hot rolled stainless steel strip and treating it in an annealing furnace. An object of the present invention is to provide a method and an apparatus for annealing and descaling a stainless steel strip which can maintain good quality of the strip and the life of the hearth roll even if the feed rate of the strip is high.

[0009]

In order to achieve the above object, the invention according to claim 1 applies annealing / pickling by applying a solution for improving descaling property to the surface of a hot rolled stainless steel strip in advance. In the method for annealing and descaling a stainless steel strip to be carried out, after drying the solution on the surface of the hot rolled stainless steel strip, the steel strip is conveyed into an annealing furnace and annealed.

The invention according to claim 2 is the method for annealing and descaling a stainless steel strip according to claim 1, wherein the solution applied to the surface of the hot rolled stainless steel strip is dried in an annealing furnace. This is done by utilizing the sensible heat of the combustion exhaust gas. The invention according to claim 3 is the invention of the method for annealing and descaling a stainless steel strip according to claim 1 or 2, wherein the drying of the solution applied to the surface of the hot rolled stainless steel strip is performed in an annealing furnace. Of the combustion exhaust gas, a gas obtained by mixing the exhaust gas with another gas, or a gas that has been heat-exchanged with the combustion exhaust gas in the annealing furnace, is injected onto the surface of the steel strip.

Further, in the invention according to claim 4, a solution coating device for improving the descaling property of the steel strip is provided in the preceding step of the annealing furnace of the continuous annealing / pickling equipment for the hot rolled stainless steel strip. A stainless steel strip annealing / descaling device comprising a drying device for heating and drying the lower surface side of the steel strip coated with the solution between the coating device and the inlet side of the annealing furnace. is there.

The invention according to claim 5 is the invention of the apparatus for annealing and descaling a stainless steel strip according to claim 4, wherein the drying device extracts a part of the high temperature combustion exhaust gas in the annealing furnace. An injection device for spraying the lower surface side of the steel strip coated with the solution is provided.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are diagrams showing an embodiment of the present invention. First, the line configuration of the hot-rolled stainless steel strip continuous annealing pickling equipment shown in FIG. 1 will be described. 1 is a payoff reel, 2 is an inlet side shear, 3 is a welder, and 4 is an inlet side looper. A horizontal annealing furnace 5 is composed of a pre-tropical zone 6, a heating zone 7, a cooling zone 8 and the like. In the heating zone 7, a hearth roll 5R made of asbestos is used for steel strip S.
While supporting and feeding, the heat treatment is continuously performed by an open flame burner. 9 is a scale breaker, 1
Reference numerals 0 and 11 are a plurality of pickling tanks in which a sulfuric acid tank, a nitric hydrofluoric acid tank and the like are appropriately combined, 12 is a cleaning device, 13 is a dryer, 14 is an exit looper, 15 is a dividing shear, and 16 is a tension reel. Normally, it has been considered indispensable in the AP line,
The shot blasting installed between the exit side of the annealing furnace 5 and the pickling tank 10 is omitted to prevent deterioration of the roughness of the steel strip surface.

On the other hand, in front of the entrance side of the annealing furnace 5, a coating device 16 for the alkaline earth metal chloride aqueous solution which is a descaling solution is installed, and between the coating device 16 and the annealing furnace 5. A drying device 20 for drying the lower surface of the steel strip S is provided. The coating device 16 has a roll 17 for coating the upper surface of the steel strip S and a roll 18 for coating the lower surface, and can coat the upper and lower surfaces of the steel strip S with the alkaline earth metal chloride aqueous solution.

As shown in detail in FIG. 2, the drying device 20 of this embodiment is composed of a pipe 21, a mixing adjusting valve 22, a blower 23, and a nozzle 24 which is an injection device for blowing combustion exhaust gas to the lower surface of the steel strip. ing. The pipe 21 is an annealing furnace 5.
Connected to the wall surface of the pre-tropical zone 6, and part of the high temperature combustion exhaust gas generated by the combustion of the direct-burning burner in the heating zone 7 is extracted from the pre-tropical zone 6 by the blower 23 through the pipe 21 and injected from the nozzle 24. It is supposed to be done. The mixing control valve 22 is connected to the branch line of the pipe 21 and is connected to the annealing furnace 5
The amount of diluting air for adjusting the temperature of the combustion exhaust gas taken out from is adjusted. An exhaust blower 27 is connected to the upper surface of the pre-heat zone 6 of the annealing furnace 5 via a flue 25 and a heat exchanger 26, and the combustion exhaust gas generated in the heating zone 7 is pre-heated by the exhaust blower 27. The heat is sucked toward the tropical zone 6 as indicated by the arrow 28, passes through the flue 25 to exchange heat with the combustion air in the heat exchanger 26, and is then discharged to the outside. The drying apparatus 20 of the present embodiment extracts a part of the combustion exhaust gas and uses sensible heat to dry the alkaline earth metal chloride aqueous solution applied to the lower surface side of the steel strip.

Next, the operation of this embodiment will be described. The steel strip S after hot rolling is wound around the payoff reel 1.
This stainless steel strip S is rewound and the leading end or the rear end is cut by the entrance side shear 2, and then the welder 3
At the front coil or the trailing coil. Then, it is conveyed to the alkaline earth metal chloride solution coating device 16 through the entrance looper 4. In this alkaline earth metal chloride solution coating device 16, a top surface coating roll 17
The surface of the steel strip S (upper and lower surfaces) is evenly coated with the aqueous solution of the alkaline earth metal chloride in the solution tank by the lower surface coating roll 18. The aqueous solution is hot rolled stainless steel strip S
It penetrates into the oxide scale formed during hot rolling on the surface of the steel sheet and reaches the base iron portion of the steel strip S.

Next, the steel strip S passes over the nozzle 24 of the drying device 20. At that time, the high temperature combustion exhaust gas ejected from the nozzle 24 is sprayed on the lower surface of the steel strip to preliminarily dry the applied alkaline earth metal chloride aqueous solution. The aqueous solution of the alkaline earth metal chloride becomes solid by evaporation of water. After that, the steel strip S is sent to the annealing furnace 5 and reaches the heating zone 7 while being preheated in the preheat zone 6 and annealed at a predetermined temperature. The steel strip S supported by the upper and lower rolls 17 and 18 of the coating device 16 reaches the first hearth roll 5R installed at the entrance of the heating zone 7 without a catenary (suspension line) without contacting anything. Nonetheless supported. The alkaline earth metal chloride aqueous solution applied to the surface of the steel strip has already evaporated, and its components have solidified while permeating inside the scale, and the surface is dry. When it comes into contact with the hearth roll 5R, solid alkaline earth metal chlorides will be discharged into the hearth roll 5R.
There is no uneven scraping with R. Therefore, unlike the conventional case, the undried alkaline earth metal chloride is not unevenly scraped off on the hearth roll 5R to cause a pattern-like quality defect on the product surface. Further, there is no phenomenon such that a part of the alkaline earth metal chloride aqueous solution adhered to the surface of the hearth roll 5R is deposited by drying and the roll life is shortened.

Thus, the steel strip S is passed through the first hearth roll 5R while keeping the alkaline earth metal chloride on the surface dry and in a good state, and is heat-treated in the heating zone 7. here,
The alkaline earth metal chloride that has penetrated into the oxide scale becomes a molten state and diffuses densely into the oxide scale, and a solid-liquid reaction proceeds with the oxide scale. By this solid-liquid reaction, as described above, a very strong oxide scale having a spinel structure formed in the hot rolling step is amorphous, and Cr containing an alkaline earth metal of weak mechanical strength, It changes to a scale containing Fe and easily comes off from the surface of the steel strip.

Further, the molten alkaline earth metal chloride solid is densely diffused in the oxide scale layer of the steel strip during the annealing step and contained in the combustion gas used during the annealing step. Oxygen generated is prevented from entering the base metal portion of the steel strip, so that no additional oxide scale grows on the surface of the steel strip during the heat treatment in the annealing furnace 5. Subsequently, the stainless steel strip S is sent to the cooling zone 8 of the annealing furnace 5 and cooled to a predetermined temperature.

Then, the stainless steel strip S is mechanically descaled by a scale breaker 9, and then chemically descaled in a sulfuric acid bath 10 and a nitric hydrofluoric acid bath 11 and passivated. After the surface is cleaned by the cleaning device 12 and dried by the dryer 13,
After being cut into a predetermined length by the dividing shear 15 via the exit side looper 14, it is wound on the tension reel 16.

According to this embodiment, the hot air obtained by using the high-temperature combustion exhaust gas discharged from the annealing furnace 5 is used for the steel strip S.
Since the alkaline earth metal chloride aqueous solution applied to the surface of the steel strip S is dried by being sprayed from the nozzle 24 of the drying device 20 to the lower surface of the conventional annealing furnace in the horizontal annealing furnace. Hearth Roll 5 was a problem
It is possible to prevent the occurrence of pattern defects on the lower surface side of the steel strip which comes into contact with R. Further, since the sensible heat of the combustion exhaust gas is used, the above-described action and effect can be obtained without further needing another heating source.

Below, the effects of the present invention will be verified by examples using the equipment shown in FIGS. (Example) Steel strip: SUS304 hot-rolled stainless steel strip, thickness 4.0 m
m Descaling solution: 2% calcium chloride aqueous solution Application amount: 20 g / m ² per one side of steel strip Steel strip moving speed: 30, 40, 50 m / min Sprayed from nozzle 24 of drying device 20 under the above conditions A comparative experiment was performed between the case (with drying) and the case without spraying (without drying).

Hot air temperature: 350 ° C. (the amount of dilution air was adjusted by the mixing adjustment valve 22) Hot air ejection speed: 30 m / sec The evaluation item was the presence or absence of pattern defects on the surface of the steel strip after the descaling treatment. The results are shown in Table 1.

[0024]

[Table 1]

The column of "dry state" in Table 1 shows the state of the coating material on the surface of the steel strip when the sample steel strip comes into contact with the first hearth roll 5R of the annealing furnace. Represents undried. In the column of "Result", the presence or absence of pattern defects on the surface of the product steel strip is shown, where "O" indicates no pattern defects and "X" indicates the occurrence of defects. As is clear from the table, when the moving speed of the steel strip was 30 m / min, there were no pattern defects and good surface quality could be obtained both with and without drying.

When the moving speed of the steel strip was 40 m / min or more, pattern defects occurred without drying, whereas with drying, pattern defects did not occur up to 50 m / min. However,
In this experiment, when the moving speed of the steel strip was increased to 60 m / min, the occurrence of pattern defects was recognized, but in that case as well, the hot air temperature and hot air jet speed were made larger than the above conditions to enhance the drying action. If so, the occurrence of pattern defects can be prevented.

According to the above-mentioned embodiment, since the descaling solution applied on the surface of the steel strip is dried, the steel strip is conveyed to the heating furnace. Therefore, when the steel strip is heat-treated while being moved at high speed. However, it is possible to maintain uniform surface quality. In the above embodiment, the sensible heat of the combustion exhaust gas was used as the heat source of the drying device in the relationship intended for the direct-fired annealing furnace, but not limited to this, other energy sources such as steam and electric power are used. The same effect can be obtained even with such a drying device.

Further, particularly in the case of a steel strip which does not like jetting of hot air, a radiation heat transfer type drying device utilizing sensible heat of exhaust gas may be used. Further, the description has been given of the case where the descaling solution coating device is arranged immediately before the annealing furnace, but by installing the drying device of the present invention on both upper and lower surfaces, the coating device can be arranged at any position before the annealing furnace. Will be possible.

[0029]

As described above, according to the first aspect of the present invention.
According to the invention of the method according to, since the descaling solution applied to the surface of the hot-rolled stainless steel strip is dried and then conveyed to the annealing furnace for annealing, the descaling is performed even if heat treatment is performed at high speed. It is possible to prevent the inconvenience that the solution is not dried and is unevenly scraped by the hearth roll in the furnace to cause pattern defects on the product surface, and the surface quality can be maintained.

According to the second aspect of the invention, since the applied descaling solution is dried by utilizing the sensible heat of the combustion exhaust gas in the annealing furnace, a separate heat source is not required and it is economical. The effect is high. According to the third aspect of the invention, the applied solution is dried by injecting high temperature gas using combustion exhaust gas onto the surface of the steel strip, so that the drying speed can be increased and the steel strip can be conveyed at high speed. While performing the annealing treatment, there is an effect that a product with good surface quality can be manufactured.

According to the invention of the apparatus according to claim 4, since the forced drying apparatus is arranged on the lower surface side of the steel strip between the coating apparatus for the descaling solution and the inlet side of the annealing furnace, the solution is dried. In this state, it is possible to reach the hearth roll in the furnace, and it is possible to achieve high-speed annealing treatment with good surface quality without shot blasting. According to the apparatus of the fifth aspect of the present invention, the effect that the combustion exhaust gas in the annealing furnace can be effectively used as the heat source of the drying apparatus and the thermal efficiency can be improved is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a line configuration of a hot-rolled stainless steel strip continuous annealing pickling equipment of the present invention.

FIG. 2 is a schematic diagram showing an example of an embodiment of a device for drying a descaling solution in the equipment of FIG.

FIG. 3 is a schematic diagram for explaining a difference in a dried state of a coating descaling solution depending on a steel strip transportation speed, in which (a) shows a high speed and (b) shows a slow speed.

[Explanation of symbols]

 S Steel strip 5 Annealing furnace 5R Hearth roll 16 (Descaling solution) coating device 20 Drying device 24 Injection device

Claims (5)

[Claims] 1. A method for annealing and descaling a stainless steel strip, which comprises applying a solution for improving descaling property to the surface of the hot rolled stainless steel strip and annealing and pickling the solution beforehand. A method for annealing and descaling a stainless steel strip, which comprises drying the solution and then transporting the steel strip into an annealing furnace for annealing. 2. The annealing of the stainless steel strip according to claim 1, wherein the solution applied to the surface of the hot rolled stainless steel strip is dried by utilizing the sensible heat of the combustion exhaust gas in the annealing furnace. Descaling method. 3. The solution applied to the surface of the hot-rolled stainless steel strip is dried by exchanging heat with the combustion exhaust gas in the annealing furnace, a gas obtained by mixing the exhaust gas with another gas, and the combustion exhaust gas in the annealing furnace. The method for annealing / descaling a stainless steel strip according to claim 1 or 2, wherein a high temperature gas made of any of the above gases is jetted onto the surface of the steel strip. 4. A continuous annealing of hot-rolled stainless steel strip / annealing of a stainless steel strip comprising a solution coating device for improving the descaling property of the steel strip in the preceding step of an annealing furnace of pickling equipment. In the descaling device, an annealing device for a stainless steel strip, comprising a drying device for heating and drying the lower surface side of the steel strip coated with the solution between the coating device and the inlet side of the annealing furnace.・ Descaling device. 5. The drying device is provided with an injection device for extracting a part of the high temperature combustion exhaust gas in the annealing furnace and spraying it onto the lower surface side of the steel strip coated with the solution. Item 4. A stainless steel strip annealing / descaling device according to item 4.