JPH04333584A - Continuous annealing and pickling equipment line for stainless steel strip - Google Patents

Abstract

PURPOSE:To provide the above equipment, which can treat all kinds of stainless steel strips of austenitic, ferritic and martenstic series in a simple and compact equipment and low treating cost. CONSTITUTION:The pickling device 7 in the stainless steel strip continuous annealing and pickling equipment, is constituted with a nitrate electrolytic vessel 8 for executing electrolytic treatment by using the steel strip 1 as an anode in neutral salt electrolytic solution containing the nitrate as the main component, a nitric hydrofluoric acid vessel 9 for executing dipping treatment to the steel strip 1 in mixed acid of the nitric acid and the hydrofluoric acid and a cleaning vessel 10 for cleaning this with cleaning rolls 14 while applying force to surface of the steel strip. Then, descale treatment is executed to the ferritic or the martenstic series stainless steel strip only with the nitrate electrolytic vessel 8 and the cleaning vessel 10 and to the austenitic series stainless steel strip with the nitrate electrolytic vessel 8, nitric-hydrofluoric acid vessel 9 and the cleaning vessel 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series of continuous annealing and pickling equipment for stainless steel strip.

0002

[Prior Art] Generally, when producing a strip material by cold rolling a stainless steel strip, the material to be treated that has been work-hardened by the cold rolling is continuously softened and annealed, and then during the softening annealing. Stainless steel strip continuous annealing and pickling equipment is used to continuously remove scale generated on the surface of the treated material.

Conventionally, the pickling equipment used in this continuous annealing and pickling equipment for stainless steel strips has been used for immersion treatment in a molten salt of sodium hydroxide containing sodium nitrate for the purpose of transforming the scale into lower oxides with good solubility. Salt bath, for the purpose of removing scale from austenitic stainless steel, nitric-fluoric acid layer for immersion treatment in a mixed acid of nitric acid and hydrofluoric acid, for the purpose of removing scale from ferritic or martensitic stainless steel, It consists of a nitric acid electrolytic tank for electrolytic treatment in nitric acid, and a cleaning tank.

[0004] In this case, however, the immersion treatment in the molten salt bath is carried out at a high temperature of about 450° C., so there are problems in that the work is dangerous and heating costs are high. Furthermore, regarding the immersion treatment for descaling, separate pickling tanks are required for austenitic and ferritic or martensitic systems, which requires a long installation space and requires a large amount of related equipment costs.

[0005] In addition, as another pickling device,
As disclosed in Japanese Patent No. 12162, a neutral salt electrolytic cell is used in which austenitic stainless steel is electrolytically treated in a neutral salt solution in order to transform scale into lower oxides with good solubility. There is a method consisting of a nitric-fluoric acid tank for immersion descaling in a mixed acid, a nitric acid electrolytic tank for electrolytically descaling ferritic or martensitic stainless steel in nitric acid, and a cleaning tank.

[0006] Even in this case, however, separate pickling tanks are required for austenitic and ferritic or martensitic systems for descaling, and there are problems in that the installation space is long and the associated equipment costs are large. do. On the other hand, as a scale that does not use acids, as disclosed in Japanese Patent Publication No. 57-10200, a scale consisting only of a neutral salt electrolytic cell that undergoes electrolytic treatment in a neutral salt solution containing nitrate as its main component. A removal device is considered. However, in this case, it is possible to descale ferritic or martensitic stainless steel only by electrolytic treatment in the neutral salt solution, but there is a problem in that austenitic stainless steel cannot be completely descaled. be. Furthermore, in the treatment of ferritic or martensitic stainless steel, the current density required for treatment is high and the treatment time is also long, so there is a problem that both equipment costs and treatment costs are high.

[0007]

[Problems to be Solved by the Invention] The present invention overcomes the above-mentioned problems of the conventional stainless steel strip continuous annealing and pickling equipment, and provides a compact device with only one pre-treatment tank and one pickling tank. The objective is to realize continuous annealing and pickling equipment for stainless steel strips that can process all types of stainless steel strips, including austenitic, ferritic, and martensitic, with the same equipment and at low processing costs.

[0008]

[Means for Solving the Problems] The present invention will be explained in detail below based on the embodiment shown in FIGS. 1 and 2. 1 and 2 both show the stainless steel strip continuous annealing and pickling equipment row of the present invention. FIG. 1 shows the processing state of the austenitic stainless steel strip, and FIG. 2 shows the processing state of the ferritic and martensitic stainless steel strip. It is a figure which shows a processing state.

In the series of continuous annealing and pickling equipment for stainless steel strips shown in FIGS. 1 and 2, both the austenitic stainless steel strip and the ferritic and martensitic stainless steel strips are rewound on a payoff reel 2 and then passed through a welding machine. 3
The front and rear steel strips are connected at , and oil or dust adhering to the surface of the steel strip 1 is removed in an annealing furnace front cleaning tank 4 . After that, the steel strip 1 is heated in an annealing furnace 5 at a temperature of about 850°C or higher and 1200°C.
Softening annealing is performed by heating to a high temperature of about °C or less. Next, the steel strip 1 is cooled down to about 100° C. or lower in a cooling device 6, and then sent to a pickling device 7.

The austenitic stainless steel strip is electrolytically treated in a pickling device 7 as shown in FIG. 1 in an electrolytic solution containing nitrate as a main component at least once using a DC power supply with the steel strip 1 serving as an anode. A nitrate electrolytic bath 8, a nitric-fluoric acid bath 9, where the steel strip 1 is immersed in a mixed acid of nitric acid and hydrofluoric acid for descaling using a dipping roll 13, and a cleaning bath 10 where the steel strip 1 is washed with a cleaning roll 14. Continuously guided and descaled.

On the other hand, the ferritic and martensitic stainless steel strips are treated in a pickling device 7 as shown in FIG.
After being descaled in a nitrate electrolytic tank 8 in which the steel strip 1 is electrolyzed at least once with a DC power supply as an anode in an electrolytic solution mainly composed of nitrates, the steel strip 1 is descaled in a nitrofluoric acid tank as a bypass mechanism for threading. By raising the dipping roll 13 above the liquid level of the nitric-fluoric acid tank 9, the liquid passes through the nitric-fluoric acid tank 9,
Thereafter, the steel strip 1 is guided to a cleaning tank 10 where it is rubbed with cleaning rolls 14 and washed with cleaning water, where it is subjected to scale removal treatment.

After this scale removal treatment, both the ferritic and martensitic stainless steel strips and the austenitic stainless steel strips are cut into arbitrary lengths by a cutting machine 11 and wound up by a tension reel 12.

In addition, in the descaling treatment of any austenitic, ferritic or martensitic stainless steel strip, an intermediate cleaning tank 15 is installed between the nitrate electrolytic tank 8 and the nitrofluoric acid tank 9 as shown in FIG. It is more preferable that the band 1 is subjected to an intermediate cleaning treatment using a cleaning roll 16.

[0014]

[Function] In the stainless steel strip continuous annealing and pickling equipment array of the present invention constructed as described above, descaling of the austenitic stainless steel strip is carried out in the pickling device 7 by the nitrate electrolytic bath 8, nitrofluoric acid bath 9, It is processed in a cleaning tank 10. The austenitic stainless steel strip 1 is first electrolytically treated in a nitrate electrolytic cell 8 with the steel strip 1 as an anode, so that the scale is easily dissolved, as described in Japanese Patent Publication No. 38-12162. It transforms into lower oxides and is eluted into the electrolyte as chromate ions Cr2O7 2- or iron ions Fe3+.

However, the electrolytic treatment in the nitrate electrolytic bath 8 alone does not completely remove the scale, and the scale remaining on the surface of the austenitic stainless steel strip 1 is removed by the cleaning treatment in the cleaning bath 10. cannot be completely removed.

Therefore, in the case of an austenitic stainless steel strip, it is led to a nitrate electrolytic cell 8 and then to a nitrofluoric acid bath 9. By immersing the steel strip 1 in the nitric-fluoric acid tank 9, the scale remaining on the surface of the steel strip 1 is eluted into the acid solution and the base material is removed. A portion also dissolves into the acid solution. Additionally, a healthy passive film is formed on the surface of the steel strip 1. Subsequently, the austenitic stainless steel strip 1 is led to a cleaning tank 10, and the acid solution adhering to the surface of the steel strip 1 is removed by a cleaning roll 14 and cleaning water. This completes the scale removal treatment of the austenitic stainless steel strip.

On the other hand, the descaling treatment of ferritic or martensitic stainless steel strip is carried out in a nitrate electrolytic bath 8.
and processed in the cleaning tank 10. The ferritic or martensitic stainless steel strip 1 is first electrolytically treated in a nitrate electrolytic cell 8 with the steel strip 1 as an anode, thereby removing chromium oxide, Cr, which is a hardly soluble component in the scale.
2 O3 is eluted into the electrolyte as chromate ion Cr2 O7 2-. In addition, on the surface of the steel strip 1, which is the anode, nitrate ions NO3 − dissociated in the electrolyte
Nitric acid HNO3 is generated from the steel strip 1, and the nitric acid HNO3 removes iron oxide FeO remaining on the surface of the steel strip 1.

[0018] Some nitrates are also peroxonitrate N
aNO4, but this peroxo nitrate NaNO4
Since it has strong oxidizing ability, it forms a healthy passive film on the surface of the steel strip 1. However, on the other hand, iron oxide Fe
The iron hydroxide Fe(OH
)3 has poor solubility in the electrolytic solution, so it becomes a solid and precipitates, and a part of it adheres to the surface of the steel strip 1.

Iron hydroxide Fe(O
H)3 is gradually removed by gas generated by continuing electrolysis, but removal of the iron hydroxide Fe(OH)3 only by electrolytic treatment requires high current density and long processing time.

Therefore, in the pickling apparatus 7 according to the present invention, the steel strip 1 is transferred from the nitrate electrolytic bath 8 to the nitrofluoric acid bath 9 when scale elution and passive film formation by the electrolytic treatment are completed.
is transferred to the cleaning tank 10 through a bypass. Cleaning tank 10
Inside, iron hydroxide Fe(OH) adhered to the surface of steel strip 1.
3 is removed by washing the surface of the steel strip 1 with a cleaning liquid while rubbing it with a cleaning roll such as a nylon or cloth brush roll. As a result, the scale removal treatment of the ferritic or martensitic stainless steel strip is completed with only a low current density and short time electrolytic treatment.

In addition, in any descaling process for austenitic, ferritic, or martensitic stainless steel strips, an intermediate cleaning tank 15 is installed between the nitrate electrolytic tank 8 and the nitrofluoric acid tank 9 as shown in FIG. The nitrate electrolyte and iron hydroxide Fe(O
By removing a portion of H)3 by washing with water using the washing roll 16, the load on the subsequent nitric-fluoric acid tank 9 and washing tank 10 is reduced, and descaling can be completed more easily.

[0022]

[Example] SUS, an austenitic stainless steel
430 cold-rolled steel strip with a thickness of 1.0 mm was heated in an annealing furnace 5.
After annealing at 00° C., the material was introduced into a pickling device 7. In this case, the sodium nitrate concentration in the nitrate electrolytic cell 8 is 200g/
1. After electrolytic treatment for 10 seconds at a current density of 0.04 A/cm2 using the steel strip 1 as an anode in an electrolytic solution with a liquid temperature of 80°C, the fluorocarbon By immersing the steel strip 1 in an acid solution with an acid concentration of 35 g/l and a liquid temperature of 50°C for 15 seconds, and then rinsing it with water in the cleaning tank 10, the scale is completely removed and the condition is maintained. We were able to produce a steel strip with an excellent surface gloss and a passive film.

[0023] SUS4, which is ferritic stainless steel
30 cold rolled steel strips with a thickness of 1.0 mm were heated to 850 mm in an annealing furnace 5.
After annealing at ℃, the sample was introduced into a pickling device 7. In this case, the sodium nitrate concentration in the nitrate electrolytic cell 8 is 200 g/l,
After electrolytic treatment was performed for 10 seconds at a current density of 0.1 A/cm2 using the steel strip 1 as an anode in an electrolytic solution with a liquid temperature of 80°C,
By washing with water using a brush roll in the washing tank 10, it was possible to completely remove scale and produce a steel strip with a healthy passive film and excellent surface gloss.

[0024]

Effects of the Invention: By using the stainless steel strip continuous annealing and pickling equipment array of the present invention, the number of pretreatment tanks and pickling tanks is one each.
All types of stainless steel strips, including austenitic, ferritic, and martensitic, can be treated with compact equipment consisting only of a tank, low processing costs, and short processing time.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 Steel strip 2 Payoff reel 3 Welding machine 4　　　Furnace cleaning tank 5 Annealing furnace 6 Cooling zone 7 Pickling equipment 8 Nitrate electrolytic cell 9 Nitrofluoric acid tank 10　Cleaning tank 11 Cutting machine 12 Tension reel 13 Nitrofluoric acid tank immersion roll 14 Washing roll 15 Intermediate cleaning tank 16 Washing roll

Claims (3)

[Claims] Claim 1: A series of continuous annealing and pickling equipment for stainless steel strips, which comprises a steel strip unwinding device, a cleaning device, an annealing furnace, a pickling device, a winding device, and their auxiliary devices. A nitrate electrolytic cell, in which the steel strip is electrolytically treated at least once in a neutral salt electrolyte containing nitrate as an anode, and a nitric-fluoric acid bath, in which the steel strip is immersed in a mixed acid solution of nitric acid and hydrofluoric acid. A series of continuous annealing and pickling equipment for stainless steel strips characterized by comprising a cleaning tank and a cleaning tank in which the surface of the stainless steel strip is rubbed with cleaning rolls and washed with cleaning water. 2. A series of continuous annealing and pickling equipment for stainless steel strips consisting of a steel strip unwinding device, a cleaning device, an annealing furnace, a pickling device, a winding device, and their auxiliary devices, wherein the pickling device The equipment includes a nitrate electrolytic cell in which a steel strip is electrolytically treated at least once as an anode in a neutral salt electrolyte containing nitrate as a main component, and a nitrate electrolytic bath in which a steel strip is electrolyzed in a mixed acid solution of nitric acid and hydrofluoric acid, which is equipped with a bypass mechanism for threading. 2. The continuous stainless steel strip according to claim 1, comprising a nitric-fluoric acid bath for immersing the strip and a cleaning bath for washing the stainless steel strip with washing water while rubbing the surface of the stainless steel strip with a cleaning roll. Annealing and pickling equipment row. 3. The continuous annealing and pickling equipment array for stainless steel strips according to claim 1 or 2, further comprising an intermediate cleaning tank between the nitrate electrolytic tank and the nitrofluoric acid tank.