JP2640565B2 - Continuous production equipment for stainless steel sheets - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the production of stainless steel sheets, and more particularly to an apparatus for continuously producing cold-rolled stainless steel sheets in the same line.

[Conventional technology]

A cold-rolled steel sheet is manufactured through a cold rolling step, an annealing heat treatment step, a descaling step, and a shape correcting step. The annealing heat treatment removes the work hardened layer generated by the cold rolling. The descaling is performed because the oxide scale generated by the annealing heat treatment impairs the commercial value. The shape correction corrects the deformation generated in the stainless steel plate by the annealing heat treatment. In the production of a cold-rolled stainless steel sheet, it is desirable from a viewpoint of productivity and economy that a so-called continuous integrated production process in which the above steps are continuously performed in the same line.

However, conventionally, this has not been realized. It could not be connected to the rolling mill due to the thick scale formed by the annealing heat treatment and the low descaling speed. In the annealing heat treatment, the atmosphere in the annealing furnace has a strong oxidizing property because it is heated by the combustion flame of the gas by the burner, so that a relatively thick scale is generated on the surface of the stainless steel plate. As a method of removing the scale, there is a method of electrolysis in a strong acid such as sulfuric acid, or a method of immersing in a molten alkali salt and then immersing in a mixed solution of nitric hydrofluoric acid. These methods have drawbacks such as a long removal time, a rough surface, and difficulty in handling. As a method of solving these difficulties, a method of electrolysis in a neutral salt aqueous solution and then immersion in a mixed solution of nitric hydrofluoric acid as described in JP-B-38-12162, or described in JP-B-53-13173. As described above, a method has been proposed in which electrolysis is performed in a solution containing nitrate ions after electrolysis in a neutral salt aqueous solution. Further, Japanese Patent Application Laid-Open No. 2-122099 has proposed a method in which electrolysis is carried out in a neutral salt aqueous solution, then electrolysis is carried out in an alkaline aqueous solution, and then electrolysis is carried out in a nitric acid solution or immersed in a nitric / hydrofluoric acid mixed solution.

[Problems to be solved by the invention]

The above prior art focuses on only a partial treatment in the production of a stainless steel sheet, and cannot perform continuous integrated production of a cold-rolled stainless steel sheet.

An object of the present invention is to provide a continuous integrated manufacturing apparatus for cold-rolled stainless steel sheets in the same line.

[Means for solving the problem]

In order to achieve the above object, in the present invention, the steel sheet is directly connected to a cold rolling mill, and the steel sheet is heated and annealed in a non-oxidizing atmosphere, and the annealed steel sheet is cooled while maintaining the non-oxidizing atmosphere. An annealing cooling device, and a descaling device comprising a combination of two or more selected from a neutral salt aqueous solution electrolysis device, an alkaline aqueous solution electrolysis device, a nitric acid aqueous solution electrolysis device or a nitric acid / monofluoric acid mixed aqueous solution immersion device are sequentially provided. In addition, there is provided an apparatus for continuously producing stainless steel sheets, comprising means for maintaining the non-oxidizing atmosphere until the steel sheets are introduced into the solution of the descaling apparatus.

That is, the present invention provides (a) a step of cold-rolling a hot-rolled stainless steel sheet after descaling; (b) a step of annealing heat treatment in a non-oxidizing atmosphere and cooling in the same atmosphere; c) a step of conducting cathodic electrolysis in a neutral salt aqueous solution;
(D) Cathodic electrolysis with an aqueous alkali solution containing an oxidizing agent, and (e) Cathodic electrolysis in a nitric acid solution or immersion in a nitric / hydrofluoric acid mixed solution as a main process, (F) The step of correcting the shape is added.

Cold rolling is performed by a mill having 6 or more steps, whereby thin sheets having excellent shape are continuously produced. The annealing heat treatment is performed by energizing heating in which the atmosphere in the furnace is excluded and Joule heat generated by applying an electric current to a stainless steel sheet in a nitrogen or oxidized gas is applied. This makes it possible to control the amount of current flowing with respect to the volume of the plate, thereby preventing over-annealing. Due to the non-oxidizing atmosphere and the super-annealing control, the scale on the stainless steel plate surface can be controlled to be extremely small, and the descaling of the rear electrode is facilitated. Heating may be performed by means such as laser heating, high-frequency induction heating, or infrared heating.

The annealed stainless steel sheet is cooled in the same atmosphere as the annealing. This atmosphere is maintained until the stainless steel sheet is introduced into the descaling electrolytic solution in the next step. As this means, snout used in continuous hot-dip plating or the like is suitable. By these means, the scale generated on the surface of the stainless steel sheet after annealing is minimized. The scale is descaled at a high speed by sequentially performing the steps (c), (d) and (e).

That is, in the neutral salt aqueous solution electrolysis, anodic electrolysis and cathodic electrolysis are repeated by indirect energization in a Na ₂ SO ₄ aqueous solution, and finally anodic electrolysis is performed. This dissolves the Cr oxide in the scale. Finally, the anodic electrolysis is performed so that the eluted material is not reprecipitated.

In alkaline aqueous solution electrolysis, anodic electrolysis and cathodic electrolysis are repeated by indirect energization, and finally anodic electrolysis is performed using an aqueous solution comprising at least one of an alkali metal hydroxide, an alkali metal oxide and an alkali metal peroxide and an oxide. NaOH is preferable as the alkali metal hydroxide, and nitrate is preferable as the oxidizing agent. However, it goes without saying that the purpose can be achieved even by using other strong alkaline substances or oxidizing agents other than nitrates.

The nitric acid electrolysis is applied when the stainless steel sheet is ferritic, and dissolves the Fe oxide remaining on the stainless steel sheet surface. Again, anodic electrolysis and cathodic electrolysis are repeated by indirect energization, but it is important to perform cathodic electrolysis last and to increase the time ratio of cathodic electrolysis.

The nitric hydrofluoric acid solution immersion is applied when the stainless steel plate is austenitic, and also chemically dissolves the remaining Fe oxide.

After removing the scale by the steps (c) to (e),
The shape change due to elongation of the steel sheet caused by the annealing heat treatment is corrected. This is done at high speed by a skin pass mill and a tension leveler. As described above, by connecting the cold rolling mill of (a) to the tension leveler for correcting the shape of (f), a stainless steel cold-rolled thin steel plate can be continuously and continuously produced in the same line at high speed.

[Operation] The cold rolling mill in the cold rolling step performs an operation of continuously rolling down a hot-rolled stainless steel sheet with a work roll to form a thin plate.

Annealing heat treatment is performed when the cold-rolled stainless steel sheet is subjected to work hardening,
At the temperature of 10 minutes within a short time heating to restore the effect. The non-oxidizing atmosphere has an effect of reducing the amount of scale generated on the surface when the stainless steel sheet is heated to a high temperature. That is, oxidation of the stainless steel surface is suppressed by lowering the oxygen partial pressure in the atmosphere. The direct energization in the heating means utilizes the electrical resistance of stainless steel and performs heat treatment by Joule heat. Laser,
Infrared and high-frequency induction heating also employs heat treatment using radiant heat or heat generated by resistance to eliminate work hardening caused by cold rolling. Since these heating means do not involve gas combustion, annealing can be performed without increasing the partial pressure of water vapor in the atmosphere while suppressing oxidation of the stainless steel surface.

Cooling after annealing is performed in the same non-oxidizing atmosphere, and the cooling temperature is set at a temperature slightly higher than the temperature of the electrolytic solution. As a result, the liquid temperature can be maintained.

By suppressing this oxidation, the speed of descaling can be increased to 100 m / min or more, so that the integrated production of cold rolling and descaling becomes possible.

The neutral salt aqueous solution electrolysis dissolves and removes the Cr oxide in the outermost layer of the scale. That is, the insoluble Cr ₂ O ₃ is dissolved as soluble hexavalent Cr by anodic electrolysis in an aqueous solution of Na ₂ SO ₄ . Cathodic electrolysis does not act on scale dissolution, but is inevitably performed due to the nature of indirect electrolysis.

In alkaline aqueous solution electrolysis, a mixed aqueous solution of an alkali metal hydroxide such as NaOH and an oxidizing agent such as sodium nitrate is practical. The effect here is to dissolve the Cr oxide similar to the neutral salt electrolysis and dissolve the Cr oxide containing Mn and Fe, to expose the Fe oxide near the stainless steel surface and to activate the surface. . This facilitates the dissolution of the Fe oxide in the subsequent nitric acid electrolysis. Also in alkaline aqueous solution electrolysis,
Anodic electrolysis does not directly affect the dissolution of scale, but anodic electrolysis shows an effect.

In nitric acid electrolysis, after removing Cr oxide and Mn, Fe, Cr composite oxide in the scale by neutral salt aqueous solution electrolysis and alkaline aqueous solution electrolysis, the Fe oxide remaining on the stainless steel surface is dissolved. In this case, unlike the former two, cathodic electrolysis exhibits a scale dissolving action. That is, the Fe oxide in the scale is
Fe ₃ O ₄ , where trivalent Fe and divalent Fe are mixed, and the dissolution rate in an acid solution is Fe (II)> Fe (III). In cathodic electrolysis, Fe (II) is dissolved in nitric acid by the action of reducing and dissolving electrons in the scale. In this nitric acid electrolysis, stainless steel is used for ferrite, and a beautiful surface with high gloss can be obtained.

On the other hand, a mixed aqueous solution of nitric hydrofluoric acid is used for austenitic stainless steel, and has an effect of removing Cr oxide and Mn, Fe, Cr composite oxide and dissolving Fe oxide remaining on the surface. In austenitic stainless steel, a Cr-deficient layer is formed near the surface of the base material due to annealing, which hinders corrosion resistance. Therefore, it is necessary to dissolve to the vicinity of the base surface and remove the Cr-depleted layer.) You.

After annealing in a non-oxidizing atmosphere as described above, the scale can be dissolved at high speed by electrolysis of a neutral salt solution, electrolysis of an alkali solution, electrolysis of nitric acid, or immersion in a mixed solution of nitric hydrofluoric acid. In the alkaline aqueous solution electrolysis, a combination of NaOH and NaNO ₃ is described, but other alkali metal hydroxides, alkali metals, alkali metal oxides, alkali metal peroxides and perchlorates other than nitrates, The purpose can also be achieved by using an oxidizing agent such as manganate.

The shape correction serves to correct deformation due to partial elongation generated when the material is softened by being heated with tension applied during annealing. That is, light rolling is performed by a skin pass mill, bending elongation is performed by a tension leveler, and partial elongation is corrected to obtain a stainless steel sheet having high flatness.

Although not described in the description, it is obvious in the continuous production of stainless steel plates that means such as washing and drying are used between each step.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Example 1 FIG. 1 shows an apparatus which is an embodiment of a continuous integrated production method of a stainless steel sheet according to the present invention.

The ferritic stainless steel strip 1 which has been hot-rolled and whose scale has been removed is continuously fed from a pay-off reel 2 and enters a cold rolling mill 3 where it is rolled to a predetermined thickness. The rolled and hardened stainless steel sheet 1 is introduced into an annealing furnace 4 and subjected to heat treatment. The inside of the annealing furnace 4 is filled with a nitrogen atmosphere to maintain the non-oxidizing property. The conveying direction of the stainless steel strip 1 is changed by an energizing roller and a turn roller 5, 6, and the roller 5 becomes a positive electrode and the roller 6 becomes a negative electrode. It is arranged so that it is energized. As a result, an electric current flows in the stainless steel strip 1 to generate Joule heat, and the stainless steel strip 1 is heated and annealed. Next, it passes through the cooling furnace 7 and is cooled to a predetermined temperature by low-temperature nitrogen gas.
The cooling furnace 7 is provided with a snout 8 to keep the non-oxidizing atmosphere until the stainless steel strip 1 is introduced into the aqueous neutral salt solution.

Next, the stainless steel strip 1 is introduced into a neutral salt aqueous solution electrolytic cell 9. The neutral salt aqueous solution electrolyzer 9 has a pH of 20%
It is filled with an aqueous solution of Na ₂ SO _{4 at} 6.5 and 80 ° C. A pair of positive electrodes 10 is provided above and below the stainless steel strip 1, and a positive voltage is applied.
10 'is provided and current flows from the positive electrode 10 through the stainless steel strip 1 to the negative electrode 10'. With this current, the Cr oxide in the scale becomes Cr ₂ O ₇ ²⁻ and dissolves. Next, the stainless steel strip 1 is washed with Na ₂ SO ₄ remaining on the surface in a washing tank 11, and then the washing water is squeezed out with a ringer roller 12.

Next, the stainless steel strip 1 is placed in the alkaline aqueous solution electrolytic bath 13.
Will be introduced. In the alkaline aqueous solution electrolysis tank 13, 30 ° C.
A pair of upper and lower positive electrodes, which are filled with an aqueous solution of NaOH at a concentration of 10% and an aqueous solution of NaNO _{3 at a} concentration of 10%
A positive voltage is applied by 14 and current flows through the stainless steel strip 1 to the negative electrode 14 '. Due to the current flowing at this time, Cr oxide and Mn, Fe, Cr composite oxide in the scale
Dissolves as O ₄ ²⁻ , MnO ₄ ²⁻ , FeO ₄ ²⁻ etc. As a result, Fe oxide in the scale remains on the surface of the stainless steel strip 1. Next, the stainless steel strip 1 is washed in the washing tank 15,
The alkali remaining on the surface is removed, and then the washing water is squeezed out by the ringer roller 16.

Next, the stainless steel strip 1 is introduced into the nitric acid electrolytic cell 17. The nitric acid electrolytic cell 17 is filled with nitric acid at 50 ° C. and 10% concentration, and the positive electrode 18 and the negative electrode 18 ′ are opposed to the stainless steel strip 1.
Is provided. A positive voltage is applied to the positive electrode 18,
Current flows through the stainless steel strip 1 to the negative electrode 18 '.
Since the stainless steel strip 1 is polarized to the cathode, the Fe oxide is reduced and dissolved, and as described above, Fe (III) becomes Fe (II) and elutes as Fe ²⁺ in nitric acid.

By the above three electrolytic treatments, the scale on the stainless steel strip 1 is removed at a high speed. The stainless steel strip 1 is cleaned of residues on the surface in a washing tank 22 and then dried in a dryer 23. The stainless steel strip 1 from which the scale on the surface was removed and washed was lightly rolled by a skin pass mill 24, and then passed through a tension leveler to correct the shape such as ear extension.
A flat stainless steel strip is wound around the tension reel 26 in a coil shape.

The above is the stainless steel sheet (ferrite type) according to the present invention.
Has been described.

Example 2 An example of an austenitic stainless steel sheet will be described with reference to FIG.

The austenitic stainless steel strip 1 was treated in the same manner as in Example 1 and subjected to alkaline aqueous solution electrolysis to remove Cr oxide, Mn, Fe, and Cr composite oxide in the scale, and Fe oxide remained on the surface. In this state, it is introduced into the nitric acid electrolysis tank 17, but without electrolysis here, it is simply immersed in a nitric acid solution and introduced into the next nitric hydrofluoric acid mixed solution tank 21, or the nitric acid is extracted from the tank, The stainless steel strip 1 is directly introduced into the nitric hydrofluoric acid mixed solution. 60 ° C in the nitric / hydrofluoric acid mixed solution tank 21
Is filled with 10% nitric acid and 1% hydrofluoric acid, and the stainless steel strip 1 is immersed in the
The oxide is dissolved and removed chemically. Next, the surface of the stainless steel strip 1 is washed and removed in a washing tank 22, and the stainless steel strip 1 is dried.
Dry at 23. Next, the shape is corrected by a skin pass mill and a tension leveler in the same manner as in the first embodiment, and the product is wound on a tension reel 26 as a product.

In both cases of Example 1 and Example 2, either an insoluble electrode or a soluble electrode can be used as the electrode of the electrolytic cell, but the insoluble electrode is practical from the viewpoint of productivity and economy. The number of electrodes can be arbitrarily changed depending on the production capacity.

〔The invention's effect〕

As described above, continuous and consistent production of stainless steel sheets in the same line can be performed by scale suppression during annealing and high-speed descaling.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a continuous continuous manufacturing method of a stainless steel sheet according to the present invention. 1 ... Stainless steel strip, 2 ... Pay-off reel, 3 ...
Cold rolling mill, 4 ... annealing furnace, 5, 6 ... energizing roller, 7 ...
... cooling furnace, 8 ... snout, 9 ... neutral salt aqueous solution electrolytic cell, 10 ... positive electrode, 10 '... negative electrode, 11 ... washing tank, 12
... Ringer roller, 13 ... alkaline aqueous electrolytic cell, 14 ...
... Positive electrode, 14 '... Negative electrode, 15 ... Rinse bath, 16 ... Linger roller, 17 ... Nitric acid electrolytic bath, 18 ... Positive electrode, 18' ...
Negative electrode, 19: Washing tank, 20: Ringer roller, 21: Nitric hydrofluoric acid mixed solution tank, 22: Washing tank, 23: Dryer, 24 ...
… Skin pass mill, 25 …… Tension leveler, 26 ……
Tension reel

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masakiyo Izumaya 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. Hitachi, Ltd. Hitachi Plant (56) References JP-A-52-41106 (JP, A) JP-A-59-157288 (JP, A) JP-B-44-19122 (JP, B1)

Claims (3)

(57) [Claims] 1. An annealing cooling device directly connected to a cold rolling mill for heating and annealing a steel sheet in a non-oxidizing atmosphere, and for cooling the annealed steel sheet while maintaining the non-oxidizing atmosphere. Salt solution electrolysis device, alkali solution electrolysis device,
A descaling device comprising a combination of two or more selected from a nitric acid aqueous solution electrolysis device or a nitric acid / hydrofluoric acid mixed aqueous solution immersion device, and until the steel sheet is introduced into the solution of the descaling device. An apparatus for continuously producing stainless steel sheets, comprising: means for maintaining the non-oxidizing atmosphere. 2. The continuous integrated stainless steel sheet manufacturing apparatus according to claim 1, wherein said heating means in said annealing cooling device uses any one of electric heating, laser heating, high frequency induction heating and infrared heating. . 3. The electrolysis apparatus according to claim 1, wherein the electrolysis apparatus comprises an indirect or direct energization in an aqueous solution in which at least one of an alkali metal oxide, an alkali metal peroxide and an alkali metal hydroxide is dissolved with an oxidizing agent. 2. The continuous continuous production apparatus for stainless steel sheets according to claim 1, further comprising means.