JP4032319B2 - Method for removing scale from chromium-containing alloy iron - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention contains chromium Alloy iron The present invention relates to an acid descaling method. More specifically, it contains hot-rolled or annealed chromium. Alloy iron The top oxide is an alloy that is dipped in an inorganic acid and then pickled. The Aqueous solution containing hydrogen peroxide Contact with Is removed.
[0002]
[Prior art]
One of the biggest environmental problems in steel production is pickling the steel to remove oxides or scales formed during heat treatments such as rolling in a hot strip mill or annealing. Most low carbon steels are descaled in hydrochloric acid at high speed. However, the scale on stainless steel has a very fine structure and is firmly attached, and shot blasting, rolling bending or straightening of the steel strip to loosen (loose) the scale before pickling Such mechanical scale cracking is usually required. Also, stainless steel pickling acids such as hydrofluoric acid, sulfuric acid, nitric acid or mixtures thereof must generally be stronger than those required for low carbon steels. The immersion time required for stainless steel is much longer than that required for low carbon steel, and electrical assistance is required to help remove scales and the like. The major motivation to improve the descaling method is the environmental waste costs and capital associated with pickling. A major disadvantage of chemical descaling with hydrochloric acid and nitric acid is an environmental problem with respect to its waste.
[0003]
It is known to use acid mixtures containing hydrogen peroxide to pickle and clean stainless steel. For example, US Pat. No. 5,154,774 describes the addition of oxidizing agents such as hydrogen peroxide, potassium permanganate or air to stainless steel pickling hydrofluoric acid to convert ferrous ions to ferric ions. Is taught. U.S. Pat.No. 5,164,016 describes adding organic acids such as formic acid, acetic acid, propionic acid, lactic acid, benzoic acid, phthalic acid and naphthoic acid to hydrogen peroxide for pickling stainless steel. Taught. Hydrogen peroxide is added to the acid with the ratio of ferrous / ferric ions adjusted to the range of 10/90 to 40/60. Japanese Patent Application Laid-Open No. 63-20494 discloses a method for chemically removing scale from the surface of stainless steel by adding an adhesive to a solution containing hydrogen peroxide, phosphoric acid and hydrogen fluoride. . The pressure-sensitive adhesive is not decomposed by hydrogen peroxide but gives viscosity to the cleaning liquid to form a paste-like liquid. JP-A-60-243289 discloses reducing smut on steel using an acid bath containing hydrofluoric acid, hydrogen peroxide and hydrochloric acid or sulfuric acid. JP 54-64022 discloses providing a viscous pickling agent for removing stain and scale from steel. Abrasive particles such as alumina, Cr oxide, silicon carbide or silica are added to an acidic solution containing hydrogen peroxide, sulfuric acid, hydrochloric acid and a surfactant. Japanese Patent Application Laid-Open No. 58-110682 discloses pickling hot rolled stainless steel with a solution containing sulfamic acid, nitric acid, hydrofluoric acid and hydrogen peroxide.
[0004]
Although these acids are effective in removing scale from stainless steel, the use of the acids creates certain undesirable problems and has limited use. For example, the use of sulfuric acid alone to remove scale from stainless steel is undesirable because the acid leaves a black smut on the pickled steel. The use of hydrochloric acid alone results in a shiny stainless steel surface, but is undesirable because it reacts slowly with the scales that are firmly attached. More severe acids such as nitric acid and hydrofluoric acid to remove scale from stainless steel, when used, aroma mitigation device for treating aroma from pickling tank, special device for storing acid Is undesirable, and requires special treatment of the by-product by pickling and is costly to dispose of. Other disadvantages are the safety and health risks from chronic exposure to these acids and the limitations on nitrates and fluorides that can be discarded into the treated wastewater stream. Organic acids are undesirable because they are not useful for stainless steel descaling.
[0005]
[Problems to be solved by the invention]
Therefore, it does not contain nitric acid, hydrofluoric acid or fluoride, it contains chromium Alloy iron A method of pickling is necessary. In addition, it contains chromium, which does not cause expensive environmental disposal problems of waste by-products due to pickling Alloy iron This pickling method is necessary. Another need is to eliminate the need for expensive pollution management and wastewater treatment facilities associated with the use of nitric acid, hydrofluoric acid or fluoride.
[0006]
The main object of the present invention is to use a chrome-containing surface with a bright, oxide-free surface, using a pickling solution of hydrochloric acid or sulfuric acid by-products that do not cause environmental disposal problems. Alloy iron Is to provide. Another object of the present invention is to contain chromium with a bright, oxide-free surface without the use of nitric acid, hydrofluoric acid or fluoride. Alloy iron Is to provide. Another object of the present invention includes the provision of pickling methods with hydrochloric acid or sulfuric acid where the cost of the chemical is not higher than that required for nitric acid, hydrofluoric acid or fluoride. Another object of the present invention is to contain chromium. Alloy iron Pickling the strip at a speed of at least 30 m / min.
[0007]
[Means for Solving the Problems]
The present invention contains chromium that has been hot rolled or annealed Alloy iron It relates to descaling the strip with acid. Hot rolled or annealed Alloy iron The strip is pretreated to crack the scale and then immersed in at least one pickling tank containing an inorganic acid selected from the group consisting of hydrochloric acid and sulfuric acid to remove the cracked scale. Then an aqueous solution containing hydrogen peroxide In , Pickled alloy strip Contact , Wherein the aqueous solution further contains an inorganic acid or the pickled strip is further contacted with a second aqueous solution containing an inorganic acid; The remaining scale is then activated by the peroxide. And Residual scale due to inorganic acid But Removal Being Clean chrome Alloy iron A strip is provided.
[0008]
Another feature of the invention is that the aqueous solution contains at least about 10 g / l of hydrogen peroxide.
Another feature of the present invention is that the aqueous solution contains an inorganic acid for removal of the remaining scale.
Another feature of the invention is that the aqueous solution contains at least about 5 g / l of an inorganic acid.
Another feature of the present invention is that the aqueous solution is used in a pickling tank. Another feature of the invention is that the pickling tank contains at least 50 g / l of inorganic acid.
Another feature of the invention is that the acid in the pickling tank has a temperature of at least about 60 ° C.
[0009]
The advantage of the present invention is that it contains chromium. Alloy iron Rather than using nitric acid, hydrofluoric acid or fluoride to remove hot rolling mill scale or annealing scale from the strip, it is to use hydrochloric acid or sulfuric acid. Another advantage of the present invention is that the pickling speed can be increased without the use of nitric acid, hydrofluoric acid or fluoride. Another advantage is that there is little environmental concern, the waste water containing peroxide is compatible with hydrochloric acid or sulfuric acid waste by-products, resulting in a smut-free chromium alloy strip, and electrical removal for scale removal. The need for mechanical assistance has been eliminated, and pickling is highly corrosion resistant iron A chromium alloy surface is obtained. The above and other objects, features and advantages of the present invention will become apparent upon consideration of the detailed description and accompanying drawings.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes chromium-containing, such as ferritic stainless steel strips. Alloy iron Relates to a method of using an inorganic acid for descaling. In particular, hot-rolled or annealed chromium content Alloy iron The oxide or scale above (hereinafter referred to as scale) is used to treat the alloy with hydrochloric acid (HCl) or sulfuric acid (H ₂ SO ₄ ) And then pickling the pickled strip with hydrogen peroxide (H ₂ O ₂ ) Is removed by rinsing with an aqueous solution. The scale remaining in the strip is activated by hydrogen peroxide contained in the rinsing aqueous solution and then removed by inorganic hydrochloric acid or sulfuric acid. The inorganic acid to remove the remaining scale is sprayed onto the strip after activation with hydrogen peroxide, and the activated strip contains the inorganic acid, preferably the inorganic acid contains the hydrogen peroxide rinse. It can be immersed in a tank contained in an aqueous solution.
[0011]
Activation of the remaining scale with a solution containing hydrogen peroxide, containing chromium during fast pickling Alloy iron The use of nitric acid or hydrofluoric acid and / or fluorine-containing compounds for the proper removal of scale from water becomes unnecessary. Without being bound by theory, the meaning of activating the scale is that hydrogen peroxide reacts with the base metal of the steel to loosen and / or decompose the scale firmly attached thereto, which is caused by inorganic acids. It is believed to aid in removing the remainder of the scale from the substrate.
[0012]
Contains chromium Alloy iron Means an alloy of iron and chromium, such as chromium alloyed steel, stainless steel, with a chromium content of at least about 5%, preferably at least 10% to about 30%. The alloy comprises up to about 0.5% Al; up to about 0.3% C; up to about 1% of one or more of Si, Ti, Nb, Zr; up to about 5% Ni and / or Ferritic stainless steel containing Mo; and up to about 1.5% Mn is preferred. All percentages are by weight. These alloys can also contain one or more of Ta, Ca, Cu, B, N, etc. as the intended adduct.
[0013]
Shot blasting or rolling after a scale is formed during a heat treatment such as rolling in a hot strip mill or continuous annealing furnace and then cut into continuous stainless steel strip or foil or plate length (hereinafter referred to as strip) A mechanical cracking process such as bending is applied to loosen the scale. Then, it is immersed in a pickling tank containing an inorganic acid to remove the cracked scale. In the present invention, the inorganic acid is defined to include both sulfuric acid and hydrochloric acid. An important feature of the present invention is that after that an aqueous solution containing hydrogen peroxide is applied to the pickled strip so that the remaining scale, smut, dust, etc. are activated by the hydrogen peroxide. It is. Preferably, the aqueous solution contains an inorganic acid, and the remaining activated scale is simultaneously removed by the inorganic acid in the aqueous solution containing hydrogen peroxide. The pickling tank preferably contains the same inorganic acid used for removing the remaining scale. This remaining scale is then removed when the strip is rinsed with a solution containing an inorganic acid and hydrogen peroxide and then when the strip is brushed and rinsed with water.
[0014]
Since the pickling tank preferably contains the same inorganic acid as that used to remove the remaining scale, it is used in the pickling tank after using the used hydrogen peroxide and aqueous solution containing inorganic acid for activation. Can help and remove the remaining scale of the strip. It should be considered to prepare the solution in a pickling tank since it will evaporate if the acid is hot. The aqueous solution is advantageously sent to the pickling tank as part of what is needed for its preparation.
[0015]
When iron is removed from the steel strip and becomes soluble in the hydrogen peroxide-containing solution, the hydrogen peroxide immediately becomes ferrous (Fe ⁺² ) And ferric iron (Fe ⁺³ ) The reason is that the hydrogen peroxide of the present invention is preferably dissolved directly in hydrochloric acid or sulfuric acid and applied directly to the surface of the strip rather than accumulating in a dip tank. If the peroxide is dissolved in the inorganic acid accumulated in the dip tank, it becomes ineffective after a relatively short period of time and the scale remaining on the pickled strip is no longer activated. Ferrous ion dissolved in inorganic acid (Fe ⁺² ) Is oxidized to ferric ions (Fe ⁺³ ), Hydrogen peroxide is consumed.
[0016]
Astonishment The Should be fully activated by hydrogen peroxide In In order to do so, it has been found that it is advantageous to contact the remaining scale with an aqueous solution containing hydrogen peroxide for a very short time, whereby the scale is easily removed by the inorganic acid. When an inorganic acid is contained in the aqueous solution, the remaining scale is removed simultaneously with the acid. Simultaneous removal of the remaining scale from the strip means an activation time of about 1 second, preferably at least about 3 seconds, more preferably 10 seconds or less. A great advantage of the present invention is that it is not necessary to apply an inorganic acid, apart from hydrogen peroxide, to the steel strip to remove the remaining scale.
[0017]
FIG. 1 illustrates one embodiment of a pickling line incorporating the method of the present invention. More particularly, reference numeral 10 contains chromium, such as stainless steel covered with scale, from a rolling or hot strip mill. Alloy iron Is schematically described. The scale on the strip 10 is cracked by passing it through a shot blasting machine or a roll straightening machine (not shown). The stainless steel scale is loosened to promote the descaling effect even when nitric acid, hydrofluoric acid and / or fluoride are not used. The strip is then immersed in sulfuric acid or hydrochloric acid in one or more pickling tanks such as tanks 12 and 14. When the pickling line of the present invention has a plurality of pickling tanks, the acid in the pickling tank should be counter-current such that it flows through the pipe 15 leading to the tank in the direction opposite to the traveling direction of the strip. Is preferred. Thereafter, the strip typically has the remaining tightly attached scale 11. This tightly adhered remaining scale is activated by contact with an aqueous solution containing hydrogen peroxide and then removed with hydrochloric acid or sulfuric acid. This aqueous solution is like a spray header 16 located at the top of the strip and extending completely across the strip and another spray header 18 located at the bottom of the strip and extending completely across the strip. Is sprayed on the strip. It is preferred to provide another set of spray headers 24 and 26 that extend completely across the strip. The use of two upper and lower spray headers increases the activation time of the remaining scale with the strip firmly attached by hydrogen peroxide. Contains chromium with a very clean surface Alloy iron Is pickled at a speed of at least 30 m / min. Peroxide spray droplets from the strip are collected in collection pan 30 and flow to tank 28. If it is desired to apply hydrochloric acid or sulfuric acid to the strip separately from the aqueous solution, another set of spray headers can be placed slightly downstream of the spray headers 24 and 26. The hydrochloric acid or sulfuric acid spray droplets from the strip are then collected in the collection pan 30 and flow to the tank 28. After rinsing with hydrogen peroxide, the pickled steel strip is preferably polished with one or more brushes 20 and 22. These brushes are composed of a grit impregnated polymer. The strip is rinsed with water. If the acid in tanks 12 and 14 is sulfuric acid, black smut remains on the surface of the strip coming out of tank 14. This smut is easily removed by the inorganic acid contained in the hydrogen peroxide solution and the cleanliness of the cleaned strip 42 is improved.
[0018]
If tanks 12 and 14 contain hydrochloric acid, tank 34 is passed through pipes 32 and 33, respectively, to collect liquid sprayed hydrogen peroxide solution containing hydrochloric acid to compensate for the liquid lost to evaporation. And 35. The used acidic hydrogen peroxide solution can flow by gravity through lines 37 to tanks 34 and 35 by opening valve 44. After the acid is saturated with iron, the acid is exchanged for new acid. Spent acid is periodically withdrawn from tanks 34 and 35 through line 50 and sent to an acid recovery plant (not shown). Fresh acid is pumped from the tank 34 to the pickling tank 14 along with the used aqueous hydrogen peroxide solution.
[0019]
FIG. 2 illustrates another embodiment of the pickling line in which the method of the present invention is combined. In this aspect, it has many components similar to the aspect described in FIG. Scale 11 on strip 10 is very stuck The If so, and / or if high speed pickling is desired, the strip must be pickled again by passing the pickled strip through another tank 38 containing an inorganic acid. Thereafter, if the strip still has the remaining scale 11, it is located at the top of the strip and extends completely across the strip and the spray headers 52, 54 at the bottom of the strip and the strip completely The remaining scale can be reactivated by an aqueous solution containing inorganic acid and hydrogen peroxide sprayed onto the strip from a second set of spray headers 56, 58 extending across the surface. By using a second set of spray headers above and below the strip, the activation time of the remaining scale with hydrogen peroxide is about twice that of FIG. 1, ensuring a very bright strip 42. Because it contains chromium Alloy iron Can be pickled on a very clean surface at a speed of 60 m / min or more. Peroxide spray droplets from the second set of spray headers are collected in collection pan 60 and flow to tank 62. Thereafter, the pickled steel strip is polished by brushes 20 and 22 and rinsed with water. The used peroxide solution flows by gravity from tank 62 to tank 36 by opening valve 68. Also, the spent peroxide solution can be pumped through line 64 to waste water storage tank 66 by opening valve 70. The wastewater in storage tank 66 is then sent through line 46 to a wastewater treatment plant (not shown). The acid solution in tank 38 can be pumped through line 40 to an acid recovery plant.
[0020]
In the embodiment of FIG. 2, the aqueous solution containing spent hydrogen peroxide collected in tank 28 flows through line 17 to acid tank 14 and is used. Since the inorganic acid in the pickling tank 14 contains dissolved iron, hydrogen peroxide remaining in the aqueous solution is decomposed by water and oxygen.
[0021]
Another means of applying an aqueous solution containing hydrogen peroxide to pickled steel is the use of an abrasive contact roll or laminar flow that contacts each side of the steel strip. FIG. 3 illustrates an embodiment in which a laminar flow is used to apply a peroxide-containing aqueous solution to pickled steel. The pickled strip is passed through apparatus 72 for laminar flow of the aqueous solution. The laminar flow device 72 has a pair of parallel panels 74 and 76 that sealably connect to the strip inlet end 78 and the strip outlet end 80. The ends 78 and 80 are equipped with squeegee type wipers for sealing the end of the applicator. The aqueous solution containing hydrogen peroxide is pumped through line 82 to laminar flow device 72. The steel strip is immersed in the aqueous solution. The spent aqueous solution is continuously withdrawn from the laminar flow device 72 through line 84 for disposal in one of the acid tanks to avoid the accumulation of dissolved iron.
[0022]
An important feature of the present invention is that the aqueous solution containing hydrogen peroxide is metered into the pickled strip using a contact roll or by spray header or laminar flow, rather than contained in a dip tank. It is to be applied while. Hydrogen peroxide easily oxidizes ferrous iron to ferric iron. When the pickled steel strip is continuously immersed in a tank containing an aqueous peroxide solution, the solution continuously dissolves iron from the steel and consumes hydrogen peroxide continuously. This is a very inefficient use of hydrogen peroxide and is wasteful. It is important that the hydrogen peroxide-containing aqueous solution is not contaminated with iron, such as ferrous ions, before it is applied to the pickled steel strip. Therefore, it is important that the hydrogen peroxide-containing aqueous solution be free of ferrous ions before it is applied to the pickled steel strip.
[0023]
Another important feature of the present invention is that the spent hydrogen peroxide-containing aqueous solution and the wastewater containing inorganic acids do not contain free hydrogen peroxide. When hydrogen peroxide is present and the pH of the solution is at least equal to about 7, trivalent chromium, ie Cr ⁺³ Is easily dangerous hexavalent, ie Cr ⁺⁶ Oxidized to chromium. Trivalent chromium precipitates as environmentally safe insoluble chromium hydroxide, but dangerous hexavalent chromium remains soluble and cannot be safely disposed of like unsafe landfills. Therefore, an aqueous solution containing spent inorganic acid and hydrogen peroxide is mixed with wastewater containing dissolved ferrous ions or used inorganic acid containing dissolved ferrous ions to obtain a spent solution. Hydrogen oxide is decomposed with water and oxygen.
[0024]
The strip is first pickled in tanks 12, 14, and 38 with a hot inorganic acid, such as hydrochloric acid or sulfuric acid, maintained at a temperature of at least 60 ° C. The strip is preferably pickled with hydrochloric acid in pickling tanks 12, 14 and 38 at a temperature of at least 77 ° C, preferably at least 82 ° C, and most preferably at least 88 ° C. It is preferred to maintain hydrochloric acid at least 50 g / l, more preferably at least 75 g / l, most preferably at least 100-200 g / l.
[0025]
The concentration of hydrochloric acid in the aqueous solution should be at least 10 g / l. When the concentration is not at least 10 g / l, the peroxide does not effectively activate the stainless steel scale. The concentration of hydrogen peroxide in the aqueous solution is at least 25 g / l, more preferably at least 30 g / l, most preferably at least 40 g / l. Hydrogen peroxide is preferably dissolved in an aqueous solution containing at least 5 g / l inorganic acid. The aqueous solution preferably contains at least 20 g / l, more preferably at least 40 g / l, most preferably at least 50 g / l of inorganic acid.
[0026]
【Example】
Example 1
409 grade stainless steel was hot rolled in a continuous strip mill and then shot blasted. The steel strip was then cut into coupons and pickled at 99 ° C. in a solution containing 280 g / l sulfuric acid and then pickled at 88 ° C. in 150 g / l hydrochloric acid. The coupon was then removed from the acid, washed with water, brushed and dried. The coupon had a small amount of scale and a large amount of smut. The dry appearance of the coupon was an unacceptable steel for many exposed applications.
[0027]
Example 2
The hot rolled stainless steel of Example 1 was treated according to the present invention. Samples were processed in a manner similar to that described in Example 1 except as noted below. After pickling in hot sulfuric acid, the coupon is washed with 20 g / l sulfuric acid and 40 g / l H. ₂ O ₂ Was immersed for 5 seconds at 88 ° C. The coupon was removed from the aqueous solution, washed with water, brushed, and then re-immersed in hydrochloric acid at 88 ° C. The coupon was then removed from the second acid, washed, brushed and dried. Unlike the coupon of Example 1, the coupon had no scale or smut. These samples treated according to the present invention had a very shiny appearance and were acceptable steel for all exposure applications. This demonstrates that adding hydrogen peroxide to the aqueous solution is important to obtain a clean surface without smut or scale.
[0028]
Example 3
409 grade stainless steel was hot rolled with a continuous strip mill and then pretreated with a shot blasting machine. The treatment according to the invention was then carried out by pickling the steel strip in a solution containing 150 g / l hydrochloric acid heated to 82 ° C. at a rate of 20 m / min. After pickling in hot hydrochloric acid, the strip is subjected to 50 g / l hydrochloric acid and 50 g / l H. ₂ O ₂ An aqueous solution containing was sprayed for about 2 seconds. The activated strip was then brushed and rinsed with water. The strip had no visible scale or smut. The strip treated according to the present invention had a very brilliant appearance and was an acceptable steel for all exposure applications. This example demonstrates that it is important to add hydrogen peroxide to aqueous hydrochloric acid to obtain a clean surface without smut or scale. This test demonstrates that the line speed can be increased to 60 m / min if the acid strip is pickled using three acid tanks instead of one acid tank.
[0029]
Example 4
409 grade stainless steel was hot rolled with a continuous strip mill and then pretreated with a shot blasting machine. The treatment according to the invention was then carried out in which the steel strip was pickled at a rate of 40 m / min in two acid tanks each containing 250 g / l sulfuric acid heated to 112 ° C. After pickling in hot sulfuric acid, the strip is subjected to 40 g / l sulfuric acid and 40 g / l H ₂ O ₂ An aqueous solution containing was sprayed for about 2 seconds. The activated strip was then brushed and rinsed with water. The strip had no visible scale or smut. The strip treated according to the present invention had a very brilliant appearance and was an acceptable steel for all exposure applications.
[0030]
Example 5
409 grade stainless steel was hot rolled with a continuous strip mill and then pretreated with a shot blasting machine. The treatment according to the invention was then carried out in which the steel strip was pickled at a rate of 40 m / min in two acid tanks each containing 250 g / l sulfuric acid heated to 112 ° C. After pickling in hot sulfuric acid, the strip is subjected to 40 g / l sulfuric acid and 40 g / l H ₂ O ₂ An aqueous solution containing was sprayed for about 2 seconds. The activated strip was then brushed and rinsed with water, after which the strip was again immersed in an acid tank containing 150 g / l hydrochloric acid heated to 82 ° C. After pickling with hot hydrochloric acid, the strip is again applied with 40 g / l sulfuric acid and 40 g / l H. ₂ O ₂ An aqueous solution containing was sprayed for about 2 seconds. The strip had no visible scale or smut. The strips treated according to the present invention were completely descaled, smutless, had a very brilliant appearance and were acceptable steel for all exposure applications.
[0031]
It should be understood that various modifications can be made to the present invention without departing from the spirit and scope of the invention. Accordingly, the limits of the invention should be determined based on the claims.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a pickling line in which the method of the present invention is combined.
FIG. 2 is a schematic explanatory view showing another embodiment of the pickling line combined with the method of the present invention.
FIG. 3 shows that the inorganic acid solution containing hydrogen peroxide according to the present invention contains pickled chromium. Alloy iron It is a schematic explanatory drawing which shows the other aspect of the means for applying to a strip.
[Explanation of symbols]
10 strips
11 scale
12, 14, 38 Pickling tank
16, 18, 24, 26 Spray header
20, 22, brush
28, 62 tanks
30, 60 Spray droplet collecting pan
34, 35, 36 tanks
42 Beautiful strip
72 Laminar flow device
74, 76 parallel panels
82 Aqueous solution supply line
84 Aqueous solution extraction line

Claims (20)

Prepare a chromium-containing alloy iron strip covered with scale;
Pre-treating the strip to crack the scale;
Immersing the pretreated strip in at least one pickling tank containing an inorganic acid selected from the group consisting of hydrochloric acid and sulfuric acid to remove cracked scale;
The pickled strip is contacted with an aqueous solution containing hydrogen peroxide, wherein, if the aqueous solution further contains an inorganic acid, or even contact the pickled strip with a second aqueous solution containing an inorganic acid is allowed, how the time remaining scale on the strip is removed by and inorganic acids are activated by the hydrogen peroxide to remove scale from the chromium-containing ferroalloy, wherein a clean strip is formed. The process according to claim 1 , wherein the aqueous solution contains at least 10 g / l of hydrogen peroxide. The method of claim 1 , wherein the aqueous solution contains an inorganic acid to remove the remaining scale. 4. A process according to claim 3 , wherein the aqueous solution contains at least 5 g / l of an inorganic acid. 4. The method of claim 3 , wherein the aqueous solution contains at least 20 g / l inorganic acid and at least 25 g / l hydrogen peroxide. 6. The method of claim 5 , wherein the aqueous solution after activating the strip is used in the pickling tank. 6. A process according to claim 5 , wherein the pickling tank contains at least 50 g / l of inorganic acid at a temperature of at least 60 [deg.] C. The method according to claim 1 , wherein the pickling tank contains 100 to 200 g / l of an inorganic acid. There are two said pickling tank, the method according to claim 1 second pickling tank is at a temperature of at least 60 ° C., containing an inorganic acid of at least 50 g / l. The method according to claim 9 , wherein the second tank contains 100 to 200 g / l of inorganic acid and has a temperature of at least 70 ° C. The method according to claim 10 , wherein the acid in the pickling tank is countercurrent flowing in a direction opposite to the direction of travel of the strip. The method of claim 1 comprising the additional step of immersing the activated strip to another tank containing inorganic acid. The method of claim 12 , wherein the tank contains hydrogen peroxide. The process according to claim 1 , wherein the aqueous solution after activation of the strip is mixed with waste water containing dissolved ferrous iron to decompose free hydrogen peroxide. The process according to claim 1 , wherein the aqueous solution after activation of the strip is mixed with an inorganic acid containing dissolved ferrous iron to decompose free hydrogen peroxide. The method of claim 1 wherein the pickled strip by brushing, to remove the remaining scale not removed by acid. The method of claim 1 , wherein the strip is hot rolled or annealed ferritic stainless steel. The method of claim 1 , wherein the pretreatment is shot blasting. Prepare a chromium-containing alloy iron strip covered with scale;
Pre-treating the strip to crack the scale;
Immersing the treated strip in at least one tank containing an inorganic acid selected from the group consisting of hydrochloric acid and sulfuric acid to remove cracked scale;
The pickled strip, is contacted with an aqueous solution containing an inorganic acid hydrogen peroxide and at least 5 g / l of at least 20 g / l, the remaining scale is activated by the hydrogen peroxide and simultaneously an aqueous solution on the time the strip A method of removing scale from chromium-containing alloy iron , characterized in that it is removed by inorganic acids contained therein to form a clean strip. Prepare a stainless steel strip covered with scale;
Pre-treating the strip to crack the scale;
Immersing the treated strip in at least one pickling tank containing at least 50 g / l inorganic acid at a temperature of at least 77 ° C. to remove cracked scale;
Activating the remaining scale on the strip by contacting with an aqueous solution containing at least 20 g / l hydrogen peroxide and at least 20 g / l inorganic acid;
Immersing the activated strip in another pickling tank containing at least 50 g / l of inorganic acid at a temperature of 77 ° C. to remove the remaining activated scale;
At least 20 g / l hydrogen peroxide and contacting the strip is activated in an aqueous solution containing an inorganic acid of at least 20 g / l, its time remaining scale on the strip is activated by the hydrogen peroxide and simultaneously an aqueous solution A method for removing scale from chromium-containing alloy iron , characterized in that a clean strip is formed by removal with an inorganic acid contained in the steel .

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