[go: up one dir, main page]

WO2014155341A1 - Procédé de traitement en continu de la surface d'un stratifié en acier inoxydable dans une solution à base d'acide sulfurique - Google Patents

Procédé de traitement en continu de la surface d'un stratifié en acier inoxydable dans une solution à base d'acide sulfurique Download PDF

Info

Publication number
WO2014155341A1
WO2014155341A1 PCT/IB2014/060230 IB2014060230W WO2014155341A1 WO 2014155341 A1 WO2014155341 A1 WO 2014155341A1 IB 2014060230 W IB2014060230 W IB 2014060230W WO 2014155341 A1 WO2014155341 A1 WO 2014155341A1
Authority
WO
WIPO (PCT)
Prior art keywords
laminate
comprised
electrodes
solution
treatment
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/IB2014/060230
Other languages
English (en)
Inventor
Stefano Martines
Giovanni ASTENGO
Stefano Luperi
Luca Lattanzi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tenova SpA
Original Assignee
Tenova SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tenova SpA filed Critical Tenova SpA
Priority to BR112015020701-4A priority Critical patent/BR112015020701B1/pt
Priority to EP14722742.5A priority patent/EP2978879B1/fr
Priority to CN201480018121.7A priority patent/CN105143523B/zh
Publication of WO2014155341A1 publication Critical patent/WO2014155341A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
    • C25F1/02—Pickling; Descaling
    • C25F1/04—Pickling; Descaling in solution
    • C25F1/06—Iron or steel
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating

Definitions

  • the present invention concerns a method for treating in continuous the surface of a laminate made of stainless steel in a solution based on sulfuric acid .
  • the method of the present invention is particularly suitable for treating a laminate made of stainless steel in order to remove the surface oxide layer (so- called "scale") which inevitably forms during the various heat treatments to which the laminate is subjected, including the hot lamination process itself.
  • pickling aims to remove both the outermost surface layer of metal oxide (richer in chrome with respect to the basic composition of steel) and the layer of alloy beneath it that, on the other hand, has a lower chrome content with respect to the base chemical composition of steel (dechromatized layer) .
  • the pickling processes of the prior art generally provide three distinct steps.
  • the first step (descaling) a chemical-physical modification of the scale is induced in order to promote detachment from the laminate.
  • This step is carried out, for example, by immersing the manufactured product in baths of molten oxidizing salts, such as Kolene baths (mixtures of NaOH, NaN0 3 and NaCl) at temperatures around 500 °C ( thermochemical descaling) , or electrolytically (electrolytic descaling) in neutral or acidic aqueous solutions (for example, aqueous solutions of sodium sulfate or sulfuric acid) .
  • molten oxidizing salts such as Kolene baths (mixtures of NaOH, NaN0 3 and NaCl) at temperatures around 500 °C ( thermochemical descaling)
  • electrolytically electrolytic descaling
  • neutral or acidic aqueous solutions for example, aqueous solutions of sodium sulfate or sulfuric acid
  • the descaling step can also be preceded by mechanical scale-removal treatments (so-called “scale-breaking” treatments), like sand-blasting, shotblasting and abrasive brushing.
  • scale-breaking treatments like sand-blasting, shotblasting and abrasive brushing.
  • the residual scale is removed from the surface of the laminate together with the dechromatized layer beneath.
  • This step is generally carried out by immersing the laminates in acid baths with high oxidizing capability, such as the baths of mixtures of mineral acids (e.g. mixtures of HNO 3 and HF, mixtures of H 2 SO 4 , HC1 and H 3 PO 4 , etc.) in the presence of oxidizing compounds, like for example permanganates, persulfates or hydrogen peroxide.
  • acid baths with high oxidizing capability such as the baths of mixtures of mineral acids (e.g. mixtures of HNO 3 and HF, mixtures of H 2 SO 4 , HC1 and H 3 PO 4 , etc.) in the presence of oxidizing compounds, like for example permanganates, persulfates or hydrogen peroxide.
  • the protective layer of chromium oxide forms on the surface of the laminate.
  • This step is generally carried out immersing the manufactured product in baths containing nitric acid or mixtures of mineral acids (generally at lower concentrations with respect to the pickling step and with a lower content of the metal ions making up the steel) .
  • nitric acid or mixtures of mineral acids generally at lower concentrations with respect to the pickling step and with a lower content of the metal ions making up the steel.
  • there is also surface oxidation of the laminate that thus makes the finishing/passivation step superfluous.
  • the pickling processes of the prior art have various drawbacks concerning their potential environmental impact, safety of the work spaces, operative control of the process as well as the equipment costs and the consumption of raw materials.
  • the use of pickling baths of nitric acid and hydrofluoric acid leads to the formation of large quantities of nitrogen oxides (NOx) and waste water contaminated by nitrates and fluorinated compounds, which make it necessary to adopt specific measures to keep down gaseous emissions and to purify the waste water.
  • NOx nitrogen oxides
  • the quantity of contaminating compounds to be treated or disposed of depends on the quantity of material removed from the laminate in the baths containing nitric acid and hydrofluoric acid, a quantity that in turn depends - all other conditions being the same - on the duration of the treatment in these baths.
  • the use of pickling baths based on nitric and hydrofluoric acid is currently considered unavoidable for obtaining high quality products.
  • the quantities of material that are removed using these baths are comprised between 60% and 80% of the material removal overall in the pickling process. Consequently, in industrial plants, the lines for the surface treatment of laminates of stainless steel are of dimensions such as to carry out, at the maximum process speed, the pickling and passivation finishing steps with a minimum duration of no less than 60 s for hot rolled laminates and not less than 30 s for cold rolled laminates.
  • Such durations are typically added to with the time necessary to carry out the chemical descaling in acid solution for the hot rolled strips (30-40 s) and that necessary for the electrolytic descaling in neutral or acid solution for cold annealed laminates (35-45 s) .
  • strips of greater thickness with respect to those of the laminates able to be processed at the maximum speed, being heat treated in the annealing oven for longer times involve proportionally longer descaling and pickling steps.
  • the process described in WO 02/12596 comprises an electrolytic pickling step in alternating current carried out in an aqueous solution of sulfuric acid in the presence of Fe 3+ ions or in the presence of at least one second acid selected from hydrofluoric acid and phosphoric acid.
  • the process described in WO 00/15880 comprises an electrolytic pickling step in continuous current carried out in an aqueous solution of sulfuric acid in the presence of ions Fe 3+ ions.
  • the process can also comprise steps of descaling (in baths of molten salts), chemical pickling (in solutions of H 2 SO and HF in the presence of Fe + and Fe + ions) and/or final passivation (in H 2 S0 4 and H 2 0 2 ) .
  • EP 2102376 Al and JP 5222449 describe processes in which the annealing treatment that precedes the pickling is carried out in temperature and oxygen concentration conditions such as to reduce the amount of oxide that forms overall on the laminates.
  • WO 03/052165 describes an electrolytic descaling process (in continuous current) of the laminates made of stainless steel carried out in a bath of sulfuric acid containing ferric ions, ferrous ions and hydrofluoric acid, followed by a chemical pickling treatment in aqueous solutions of sulfuric acid.
  • the duration of the anode treatment in the electrolytic descaling process is correlated to the current density applied and to two parameters that are experimental in nature .
  • EP 1307609 Al describes an electrolytic pickling process of laminates made of stainless steel carried out in a bath of sulfuric acid with an alternating current of frequency comprised between 40 and 70 Hz and with current density comprised between 10 and 250 A/dm 2 for a duration comprised between 3 s and 60 s.
  • Document WO 02086199 A2 describes an electrolytic descaling process of laminates made of stainless steel carried out with a continuous or alternating current inside an aqueous electrolytic solution of a strong acid (for example hydrochloric acid, sulfuric acid, hydrofluoric acid, etc.), the duration of which is correlated to the current density applied and to two parameters that are experimental in nature.
  • a strong acid for example hydrochloric acid, sulfuric acid, hydrofluoric acid, etc.
  • the main purpose of the present invention is to avoid the drawbacks of the pickling processes of laminates made of stainless steel of the prior art.
  • a purpose of the present invention is to provide a method for pickling a laminate made of stainless steel that makes it possible to obtain a high-quality treated product, but with low environmental impact and lower consumption of raw materials, such as mineral acids and additives.
  • Another purpose of the present invention is to provide a method for pickling a laminate made of stainless steel with improved efficacy, so as to reduce the duration of the pickling treatments and the bulk of the plants necessary to carry it out.
  • laminate made of stainless steel hereafter also “laminate” it is meant a semi-worked product made of stainless steel of the type like a plate, a strip, (a wire, a rod iron, a wire rod, a section bar or similar), of indefinite length.
  • laminate made of stainless steel
  • a semi-worked product made of stainless steel of the type like a plate, a strip, (a wire, a rod iron, a wire rod, a section bar or similar), of indefinite length.
  • the method according to the present invention can be applied to effectively remove the layer of metal oxide (scale) from the surface of the laminate and the dechromatized layer beneath, forming a layer of chrome oxide in its place that protects the laminate from corrosion .
  • the method according to the invention can be used to pickle various types of steel, in particular austenite, martensitic and ferritic steels, whether they are obtained through hot and cold lamination processes (hereafter respectively indicated as “hot rolled laminates” and “cold rolled laminates”) .
  • the method according to the invention comprises at least one electrolytic pickling step of the laminate carried out in alternating current (AC) in an aqueous electrolytic solution comprising at least sulfuric acid .
  • AC alternating current
  • the electrolytic pickling in AC is carried out by suitably selecting the frequency of the alternating current applied as a function of the position of the electrodes with respect to the laminate subjected to treatment, as will be illustrated in detail later on.
  • the Applicant has, indeed, found that the efficacy of the electrolytic pickling is greater if, during the crossing path of the electrolytic bath, a given surface portion of the laminate is prevented from being exposed substantially to the same polarization at the pairs of electrodes through which the laminate is made to pass. In this case, indeed, there would be regions of the laminate treated unevenly.
  • the concentration of sulfuric acid in the electrolytic solution is selected in the range 30 g/1 - 300 g/1 according to the type of steel and the type of treatments to which the laminate has been exposed.
  • the concentration of sulfuric acid is more preferably comprised in the ranged 70-300 g/1.
  • the concentration of sulfuric acid is more preferably comprised in the range 40-200 g/1.
  • the concentration of sulfuric acid is more preferably comprised in the range 30-100 g/1.
  • concentration values of sulfuric acid should be taken as in reference to the concentration of the free acid in the aqueous solution, as measurable, for example, through an acid- base titration or conductometric analysis.
  • the electrolytic solution can also comprise variable concentrations of metal ions in solution deriving from the dissolution of steel, such as Fe, Cr, Ni, Mn, Mo, etc.
  • the total content of metals in solution is typically comprised in the range 0 g/1 - 120 g/1.
  • the concentration of dissolved metals depends on the type of steel and on the type of treatments to which the laminate has been subjected. In the case of cold rolled steels, for example, the concentration of dissolved metals is preferably comprised in the range 20-50 g/1. In the case of cold rolled ferritic steels (stabilized and not), the concentration of the dissolved metals is more preferably comprised in the range 30-100 g/1.
  • the concentration of the free acid in the solutions progressively decreases, whereas that of the metal ions, in particular that of the ferrous Fe 2+ ions, increases.
  • the concentration of sulfuric acid can be kept to desired levels through periodic addition of fresh acid or by recycling the aqueous solutions of the acid used in other steps of the method, provided that they have greater concentrations than that desired.
  • the electrolytic pickling is carried out keeping the electrolytic solution at a temperature comprised in the range 30-100°C.
  • the temperature is more preferably comprised in the range 40-95°C, whereas for cold rolled, the temperature is more preferably comprised in the range 30-95°C.
  • the temperature is preferably comprised in the range 40-70°C for steels of the austenitic type, in the range 30-50°C for stabilized ferritic steels and in the range 30-45°C for unstabilized ferritic steels.
  • the alternating current (AC) used in the electrolytic pickling has a density (referring to the unit surface of the laminate) comprised in the range 5- 60 A/dm 2 .
  • the current density is preferably comprised in the range 15-60 A/dm 2 , even more preferably in the range 20-50 A/dm 2 .
  • the current density can preferably be selected as a function of the type of steels, for example, as follows:
  • the frequency of the AC current is comprised in the range 5-150 Hz.
  • the frequency is kept at a constant value during the treatment.
  • it can also be varied as a function of the process requirements, for example to increase the quality of the treatment or to control the pickling speed as a function of the feeding speed of the laminate to the pickling plant.
  • the electrolytic pickling has a duration comprised between 3 and 40 seconds, both for hot rolled laminates and for cold rolled laminates.
  • the duration of the electrolytic pickling is preferably comprised in the range 8-60 seconds, even more preferably in the range 10-50 seconds; in the case of hot rolled austenite steels, the duration is preferably comprised in the range 10-20 seconds.
  • the duration of the electrolytic pickling in AC current can preferably be selected as a function of the type of steels, for example, as follows:
  • the method according to the invention also comprises a finishing and final passivation step (hereafter also just “finishing”) .
  • This step which is generally carried out after having subjected the laminate to careful washing with water to eliminate the residues of sulfuric acid and iron oxides possibly still present on its surface, has the purpose of oxidising the surface of the laminate so as to form a protective layer of chromium oxide.
  • the finishing step can be carried out according to the prior art.
  • the finishing step is carried out by placing the surface of the laminate in contact with an aqueous solution of at least one mineral acid having an oxidation-reduction chemical potential (measured with respect to a reference electrode Ag/AgCl) comprised between 100 and 800 mV, preferably between 200 mV and 600 mV (finishing solution) .
  • an oxidation-reduction potential can be obtained, for example, with aqueous solutions comprising one or more acids selected from nitric acid, or sulfuric acid and Fe 3+ ions possibly in the presence of free hydrofluoric acid.
  • the concentration of Fe 3+ ions in the finishing solution varies in the range 5-50 g/1.
  • the mixture of acids to be used in the finishing solution is concerned, it is selected as a function of the type of steel of the laminate.
  • the mixture of mineral acids used in the finishing step is a mixture of nitric acid and hydrofluoric acid (nitric- hydrofluoric finishing) .
  • the concentration of nitric acid in the finishing solution is preferably comprised in the range 50-150 g/1, whereas that of the free hydrofluoric acid is preferably comprised in the range 5-45 g/1.
  • the concentration of nitric acid is more preferably comprised in the range 100-150 g/1, whereas that of free hydrofluoric acid is preferably comprised in the range 20-35 g/1.
  • the concentration of nitric acid is more preferably comprised in the range 75-130 g/1, whereas that of free hydrofluoric acid is preferably comprised in the range 5-20 g/1.
  • the concentration of Fe 3+ ions in the finishing solution is preferably comprised in the range 5-35 g/1.
  • the concentration of nitric acid is more preferably comprised in the range 60-150 g/1, whereas that of hydrofluoric acid is preferably comprised in the range 10-30 g/1.
  • the concentration of nitric acid is more preferably comprised in the range 50-130 g/1, whereas that of hydrofluoric acid is preferably comprised in the range 10-25 g/1.
  • the mixture of mineral acids used in the finishing step is an aqueous solution of sulfuric acid containing, possibly, also free hydrofluoric acid (sulphuric or sulphuric- hydrofluoric finishing) comprising Fe 3+ and Fe 2+ ions.
  • the concentration of sulfuric acid in the finishing solution is preferably comprised in the range 20-150 g/1, whereas that of the possible free hydrofluoric acid is preferably comprised in the range 5-30 g/1.
  • the concentration of Fe 3+ ions is preferably comprised in the range 5-80 g/1, whereas the concentration of Fe 2+ ions is preferably comprised in the range 5-20 g/1.
  • the concentration of sulfuric acid is more preferably comprised in the range 60-150 g/1, whereas that of the possible free hydrofluoric acid is preferably comprised in the range 10-30 g/1.
  • the concentration of sulfuric acid is more preferably comprised in the range 40-100 g/1, whereas that of the possible free hydrofluoric acid is preferably comprised in the range 5-25 g/1.
  • the concentration of sulfuric acid is more preferably comprised in the range 40-150 g/1, whereas that of the possible free hydrofluoric acid is preferably comprised in the range 5-30 g/1.
  • the concentration of sulfuric acid is more preferably comprised in the range 30-150 g/1, whereas that of the possible free hydrofluoric acid is preferably comprised in the range 5-25 g/1.
  • the concentration of Fe 3+ ions is more preferably comprised in the range 45-90 g/1, whereas the concentration of Fe 2+ ions is more preferably comprised in the range 5-40 g/1.
  • the concentration of Fe 3+ ions is more preferably comprised in the range 35-80 g/1, whereas the concentration of Fe 2+ ions is more preferably comprised in the range 5-40 g/1.
  • the concentration of Fe 3+ ions is preferably comprised in the range 25-80 g/1, whereas the concentration of Fe 2+ ions is preferably comprised in the range 5-20 g/1.
  • the concentration of Fe 3+ ions is preferably comprised in the range 20-70 g/1, whereas the concentration of Fe 2+ ions is preferably comprised in the range 5-25 g/1.
  • the finishing solution comprises an aqueous solution of nitric acid, as single acid, also comprising Fe 3+ ions.
  • concentration of nitric acid in the finishing solution is preferably comprised in the range 20-100 g/1, whereas that of the Fe 3+ ions is on the other hand comprised in the range 20-50 g/1.
  • This finishing solution is particularly preferred in the case of ferritic cold rolled laminates.
  • a further preferred finishing solution comprises nitric acid in a concentration comprised in the range 40-100 g/1 and dissolved metals in a concentration comprised in the range 0-10 g/1 (substantially in the absence of Fe 3+ ions) .
  • finishing solutions that are particularly preferred are those that do not comprise nitric acid, since they allow the environmental impact of the process to be reduced in terms of emissions of polluting gases (NOx) and nitrate and fluorinated compounds in the waste water.
  • NOx polluting gases
  • the finishing solution is kept at a temperature that can vary from 25°C to 65°C.
  • the duration of the finishing treatment varies from 10 seconds to 60 seconds.
  • the finishing step of the pickled laminate can be carried out by placing the laminate in contact with one or more of the aforementioned finishing solutions as a function of the type of steel, of the lamination process undergone and of the previous pickling steps.
  • the finishing step can comprise a first treatment with a sulphuric-hydrofluoric solution followed by a second treatment with a nitric- hydrofluoric solution.
  • This embodiment of the finishing step is particularly suitable in the case of cold rolled laminates.
  • the composition of the scale depends strictly on the type of lamination undergone - hot or cold - and on possible annealing heat treatments to which the laminate has been subjected.
  • the method according to the invention can comprise one or more further treatment steps.
  • the treatment method can advantageously also comprise a chemical descaling step to promote the removal of scale in the subsequent electrolytic pickling step.
  • the chemical descaling step is carried out by placing the laminate in contact with an aqueous solution comprising sulfuric acid and possibly metal ions (descaling solution) .
  • the concentration of sulfuric acid in the descaling solution is selected in the range 150 g/1 - 300 g/1, preferably in the range 200 g/1 - 250 g/1, according to the type of steel and the type of treatments to which the laminate has been subjected.
  • the concentration of dissolved metals is typically comprised in the range 0-120 g/1.
  • the descaling solution comprises 200-280 g/1 of sulfuric acid and 30-50 g/l of dissolved metals.
  • the duration of the chemical descaling treatment is typically comprised in the range 15-60 seconds, preferably 25-50 seconds.
  • the temperature of the descaling solution is preferably kept in the range 70-98°C.
  • the chemical descaling step although possible, is generally omitted, since it is unnecessary.
  • the quality of the pickled surfaces can be improved by also subjecting the laminate to at least one electrolytic treatment in continuous current (DC) , using an electrolytic solution having the same composition as the solution used in the treatment in AC current or similar composition.
  • DC continuous current
  • the electrolytic treatment in DC current is carried out by applying a DC current of density comprised in the range 4-14 A/dm 2 .
  • the current density DC is preferably comprised in the range 5-12 A/dm 2 .
  • the duration of the treatment in DC current is comprised between 3 and 35 seconds, such a duration referring to the period in which a given surface portion of the laminate is anodically polarized.
  • the duration of the electrolytic pickling in DC current can vary as a function of the type of steels in the following way:
  • the treatment in DC current can be carried out before or after the treatment in AC current, preferably before.
  • the treatment stages in AC and DC current can be carried out in the same tank or in separate tanks, arranged in series in the pickling plant.
  • AC current and the duration of the anodic polarization obtained with the DC treatment is generally comprised between 0.15 and 1, preferably between 0.20 and 0.50.
  • the concentration of sulfuric acid and that of dissolved metals varies over time as the treatment of the laminates proceeds. Also in these cases, the concentrations of the different species can be restored through the discharge of the spent solutions, the addition (periodic or in continuous) of fresh reactants, water and for the metals through the addition of oxidants such as hydrogen peroxide, organic and/or inorganic peracids and/or their salts.
  • the method of the invention can also comprise the conventional steps (intermediate or preliminary) of washing and degreasing the surface of the laminate with suitable aqueous solutions containing surfactants or other additives.
  • the washing steps (which can be carried out by immersion, spraying with water jets and possibly with the help of metallic brushes) have the purpose of eliminating the residues of the previous treatments from the surface and avoiding contamination of the solutions used in the subsequent steps of the method.
  • the electrolytic pickling step in particular, can be carried out in a tank of the type described in patent application WO 2011/039596.
  • Figure 1 schematically represents a possible embodiment of an apparatus in which it is possible to carry out the electrolytic pickling step according to the method of the invention.
  • the apparatus wholly indicated with 10, comprises a treatment tank 12 suitable for containing the electrolytic solution SE and inside which the laminate 11 is made to pass in continuous along a direction and in the advancing sense indicated by the arrow F.
  • the position of the laminate inside the treatment tank 12 is determined by the rollers 20 and 21 and by the pull applied on the strip.
  • the apparatus 10 also comprises at least two pairs of electrodes 14 that are opposite one another and between which the laminate 11 is made to pass in continuous .
  • Each pair of electrodes 14 comprises at least one first electrode 15 facing one of the two faces of the laminate 11 and at least one second electrode 17 facing the other of the two faces of the laminate 11.
  • the electrodes 15, 17, are also substantially equidistant from the laminate 11, each of them being at a distance Lc from the laminate in general comprised between 50 and 250 mm.
  • the electrodes 15, 17 are arranged in a direction substantially parallel to the faces of the laminate along the path in the tank 12 and they extend substantially for the entire width La of the laminate (the width La is not shown in the figures) .
  • the two electrodes 15, 17 of a pair of electrodes 14 are separated by a distance Lg preferably comprised between 100 and 500 mm.
  • Each of the electrodes 15, 17 has a length Le , measured along the movement direction of the laminate, preferably comprised between 300 mm and 2200 mm.
  • Each pair of electrodes 14 is a distance Lx from the next pair, in the movement direction of the laminate, in general comprised between 100 and 800 mm.
  • the electrodes 15, 17 of each pair of electrodes 14 are immersed in the electrolytic solution SE and can be associated with an electric power supply group (not shown in the figures) capable of delivering a continuous current DC or an alternating current AC at variable frequency.
  • an electric power supply group capable of delivering a continuous current DC or an alternating current AC at variable frequency.
  • a first preferred configuration is that for which the AC current is supplied to the electrodes 15, 17 so that the two electrodes of each pair 14 are with voltage in phase between them, so as to have, at a given moment, on both of the electrodes, a polarization of the same sign.
  • there is at least one separator element made of an insulating material for example in the form of an immersing roller coated in plastic material or of a static separator made from plastic material (not shown in the figures) .
  • the separators made from insulating material allow the formation of dispersed currents between electrodes of adjacent pairs that have opposite polarization to be reduced .
  • a second preferred configuration provides that the electrodes 15 and 17 facing each other are connected to two different phases of the alternating current; in this case it is preferable for successive pairs of electrodes 14, if adjacent and not separated by immersing rollers and other insulating separators, to be connected to the same phases; pairs of electrodes separated by appropriate distance and by immersing rollers and insulating separators, on the other hand, will be connected to different phases so as to minimise the dispersed currents and, at the same time, avoid unbalanced loads on the power supply network.
  • the resulting electric field has current lines that are substantially vertical and orthogonal to the surface of the laminate, which is thus passed through by the current along the thickness.
  • the electrolytic pickling treatment is carried out by applying to the electrodes 15, 17 an alternating current of frequency f , variable from 5 Hz to 150 Hz, said frequency f being correlated to the forward speed v (expressed in m/s) of the laminate and to the length L e (expressed in metres) of the electrodes 15, 17 by the relation (1)
  • A is a rational number greater than 1, preferably greater than 2. Generally, A does not exceed the value 300.
  • the solution indicated above to improve the efficiency of treatment of the laminate can also be applied to the case in which the apparatus for carrying out the electrolytic treatment comprises electrodes consisting of a plurality of elements (for example plates of the type described in WO 2011/039596) .
  • This configuration schematically illustrated in figure 2, has the advantage of avoiding the accumulation of electrolysis gases and of solid residues (essentially metal oxides) that detach from the surface during the electrolytic process, thus improving the efficiency of the treatment.
  • the apparatus of figure 2 comprises pairs of electrodes 140 consisting of two groups 150, 170 of elements 160, 180.
  • the elements 160, 180 extend for the entire width of the laminate and have a length Lb (measured in the forward direction of the laminate) .
  • the elements 160, 180 are arranged substantially parallel with respect to the laminate 11.
  • the distance between two adjacent elements 160, 180 is indicated in figure 2 with reference La.
  • Each element 160, 180, in the apparatus 10 performs the function of electrode in the same way as the electrodes 17, 15 of the apparatus 10 described in figure 1.
  • the electrolytic treatment of the laminate 11 could not be uniform over the entire surface for particular geometric arrangements of the electrodes 150, 170, of the elements 160, 180 and of the laminate 11.
  • non-uniform treatments can be encountered when the distance La between two adjacent elements is close to or greater than the distance L c between the element 160, 180 and the laminate 11.
  • this drawback can be overcome in the case of an apparatus of the type illustrated in figure 2 by applying to the electrodes an alternating current of frequency f , comprised in the range 5 Hz - 150 Hz, said frequency f being correlated to the forward speed v (expressed in m/s) of the laminate and to the length Lb (expressed in metres) of the element 160, 180 by the relation (2)
  • A' is a rational number greater than 1, preferably comprised between 1 and 25, more preferably comprised between 1 and 10.
  • the frequency f when the ratio between the distance L g between the opposite electrodes 150, 170 and the distance La of the elements 160, 180 that form said opposite electrodes 150, 170 is greater than 4, it is preferable for the frequency f to respect at least the relation (1) .
  • the aforementioned ratio L g /Ld is equal to or less than 4, it is preferable for the frequency f to respect at least the relation (2) .
  • the method according to the present invention makes it possible to overcome or at least lessen the drawbacks highlighted by the state of the art in the field of pickling treatments of laminates made of stainless steel.
  • the pickling treatments carried out with the method according to the invention have an improved efficacy, making it possible to obtain high- quality pickled surfaces with an overall duration of the treatment that is short.
  • the method according to the invention also contemplating carrying out a final finishing and passivation step of the laminates in mixtures containing nitric and hydrofluoric acid, determines a reduction in the environmental impact with respect to that typically observed in the processes of the prior art.
  • the pickling carried out according to the present invention is able to remove - in certain cases - up to 80% by weight of the overall mass of scale and dechromatized steel, thus making it sufficient to have a finishing step in nitric-hydrofluoric acid that is even very short and, consequently, significantly limiting the formation of polluting residues to be disposed of (nitrate, fluorinated compounds and emissions of NOx) .
  • the improved efficacy of the treatment method according to the present invention makes it possible to treat the laminates in plants of smaller dimensions with respect to the state of the art, being able to provide for shorter residency times of the laminate in contact with the pickling baths.
  • a further advantage of the method according to the present invention is the fact that, since at least one electrolytic pickling step is provided, it is possible to adjust the overall speed of the pickling process by acting on the current intensity applied in this step. In the case of slowing down of the pickling line, for example, it is possible to temporarily attenuate the pickling action of the sulfuric acid (decreasing the intensity of the current applied) , thus avoiding phenomena of excessive dissolving erosion of the laminate .
  • EXAMPLES The method according to the present invention was applied to treat strips of stainless steel of different chemical composition, obtained through hot or cold rolling processes, possibly accompanied by annealing treatments.
  • the production and treatment plant comprised the following sections: continuous annealing section, of overall length equal to 90 m, capable of heating the strip up to the temperature of 1120°C with a maximum productivity equal to about 133 t/h with strips of width up to 1550 mm;
  • cooling section of overall length equal to 45 m, equipped with cooling means consisting of air blades combined with jets of nebulised water and capable of cooling the laminate up to about 80°C; scale-breaker roller for stretch levelling the strip with elongation up to 1% of its original length;
  • sandblasting section consisting of 3 cabins equipped with 4 turbines each capable of homogeneously projecting, on both surfaces of the strip, spherical shots of type S110 at speed comprised between 50 m/s and 80 m/s, with flow rate of shots for each turbine comprised between 500 and 1300 kg/min;
  • chemical descaling section consisting of 2 immersion tanks of length equal to 15 m each;
  • - electrolytic pickling section consisting of 2 tanks of length equal to 16 m each, each tank being equipped with a series of electrodes arranged above and below the strip, in a position substantially parallel to its surface, the overall length of which (taken as the sum of the lengths Le of all of the electrodes arranged on the same side with respect to the laminate) is equal to 15 m; the electrodes are connected to 5 transformers capable of delivering a current up to 110 kA; the electrolytic section is made according to what is described in document WO 2011/039596 and has the following geometric parameters (with reference to figure 2 ) :
  • finishing and passivation section consisting of 2 tanks of length equal to 14 m each where the strip is immersed in the solution that is continually renewed through a recirculation system having an overall flow rate equal to 800 m 3 /h.
  • washing, final brushing and drying section equipped with high pressure pumps and non-abrasive brushes .
  • LAMINATES L1-L4 Four different laminates of stainless steel (AISI 304 (LI), AISI 430 (L2), AISI 441 (L3), AISI 409 (L4)) .
  • the concentrations of the different species in the aqueous solutions and the operative conditions adopted in each step of the process together with the dimensional parameters of the laminates L1-L4 are given in Table 3.
  • the efficacy of the method was evaluated by calculating the percentage amount of metal removed from the laminate and/or dissolved during each step with respect to the amount of metal removed and/or dissolved overall .
  • the method according to the invention applied to the hot rolled laminates, has resulted in a significant reduction of the polluting substances to be treated.
  • the production and treatment plant comprised the following sections :
  • continuous annealing section of overall length equal to 120 m, capable of heating the strip up to the temperature of 1120°C with a maximum productivity equal to about 133 t/h with strips of width up to 1550 mm;
  • cooling section of overall length equal to 65 m, equipped with cooling means consisting of air blades combined with jets of water that intervene on the strip when it reaches temperatures below 200 °C up to a temperature of about 70°C;
  • electrolytic pickling section comprising 1 tank of length equal to 55 m to carry out the treatment in DC and AC current; for the treatment in DC current the tank is equipped with a series of horizontal electrodes arranged above and below the strip, in a position substantially parallel to its surface; the overall length of the electrodes that anodically polarize the strip for the DC treatment (taken as the sum of the lengths of all of the electrodes that anodically polarize arranged on the same side with respect to the laminate) is equal to 24 m; the electrodes are connected to 8 current rectifiers capable of delivering a DC current up to 10 kA (max 40 V) each; for the AC treatment, the tank is equipped with a series of horizontal electrodes, arranged above and below the strip, in a position substantially parallel to its surface, the overall length of which (taken as the sum of the lengths of the electrodes arranged on the same side with respect to the laminate) is equal to 9 m; the electrodes are connected to 3 transformers capable of delivering an AC current up to 10 kA
  • washing section equipped with 100 bar pumps
  • finishing section consisting of 2 tanks of overall length equal to 35 m.
  • the same pickling treatment was applied to a fifth laminate (AISI 304 (L9) ) obtained through a hot rolling and annealing process.
  • the efficacy of the method was evaluated by calculating the percentage amount of metal removed from the laminate and/or dissolved during each step with respect to the amount of metal removed and/or dissolved overall.
  • the finishing treatments carried out in the conditions given in Table 4 proved sufficient to obtain a uniformly passivated surface.
  • Such a treatment generated a significantly small amount of polluting products to be disposed of (muds containing nitrate, fluorinated compounds and emissions of NO x ) , since the amount of metal removed and/or dissolved in the finishing step is reduced to values of 20% by weight (L9) of the mass of steel removed and/or dissolved overall in the entire treatment.
  • L9 20% by weight
  • the amount of metal removed and/or dissolved in the nitric and/or hydrofluoric acid baths can reach 80% by weight of the amount pickled overall.
  • the method according to the invention applied to cold rolled laminates, obtained a significant reduction in polluting substances to be treated.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • ing And Chemical Polishing (AREA)
  • Chemical Treatment Of Metals (AREA)

Abstract

L'invention concerne un procédé permettant de traiter en continu la surface d'un stratifié en acide inoxydable qui comprend au moins les étapes consistant à : (a) faire passer ledit stratifié (11) en continu dans un réservoir (12) contenant une solution électrolytique aqueuse (SE) d'acide sulfurique, ledit stratifié (11) passant entre au moins deux électrodes (150, 170) immergées dans ladite solution électrolytique (SE) et disposées en une direction sensiblement parallèle à la direction du mouvement du stratifié (11) et ayant une longueur Le mesurée le long de ladite direction, lesdites électrodes (150, 170) faisant face aux faces opposées dudit stratifié (11) et étant disposées dans une position face l'une à l'autre, (b) soumettre ledit stratifié (11) à un traitement de décapage électrolytique en appliquant un courant alternatif d'une fréquence f comprise entre 5 Hz et 150 Hz, ladite fréquence f étant corrélée à ladite vitesse v du stratifié (11) et à ladite longueur Le desdites électrodes (150, 170) selon la relation F ≥ (A*v)/Le, A étant un nombre rationnel supérieur à 1, de préférence supérieur à 2 ; (c) soumettre ledit stratifié décapé par voie électrolytique (11) à une finition et à un traitement de passivation de surface.
PCT/IB2014/060230 2013-03-29 2014-03-27 Procédé de traitement en continu de la surface d'un stratifié en acier inoxydable dans une solution à base d'acide sulfurique Ceased WO2014155341A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
BR112015020701-4A BR112015020701B1 (pt) 2013-03-29 2014-03-27 Método para o tratamento em continuidade da superfície de um laminado feito de aço inoxidável em uma solução baseada em ácido sulfúrico
EP14722742.5A EP2978879B1 (fr) 2013-03-29 2014-03-27 Procédé de traitement en continu de la surface d'un stratifié en acier inoxydable dans une solution à base d'acide sulfurique
CN201480018121.7A CN105143523B (zh) 2013-03-29 2014-03-27 在基于硫酸的溶液中连续处理不锈钢制成的层压制件的表面的方法

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITMI2013A000493 2013-03-29
IT000493A ITMI20130493A1 (it) 2013-03-29 2013-03-29 Metodo per trattare in continuo la superficie di un laminato di acciaio inossidabile in una soluzione a base di acido solforico

Publications (1)

Publication Number Publication Date
WO2014155341A1 true WO2014155341A1 (fr) 2014-10-02

Family

ID=48444515

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2014/060230 Ceased WO2014155341A1 (fr) 2013-03-29 2014-03-27 Procédé de traitement en continu de la surface d'un stratifié en acier inoxydable dans une solution à base d'acide sulfurique

Country Status (5)

Country Link
EP (1) EP2978879B1 (fr)
CN (1) CN105143523B (fr)
BR (1) BR112015020701B1 (fr)
IT (1) ITMI20130493A1 (fr)
WO (1) WO2014155341A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105040088A (zh) * 2015-08-11 2015-11-11 佛山市环宇新型材料有限公司 一种带钢电解除污装置
EP4044299A4 (fr) * 2019-11-11 2023-09-13 Posco Procédé de fabrication d'acier inoxydable pour séparateur de pile à combustible polymère
EP4253591A4 (fr) * 2020-11-25 2024-05-01 POSCO Co., Ltd Acier inoxydable austénitique pour séparateur de pile à combustible présentant une résistance de contact améliorée et son procédé de fabrication

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107653485A (zh) * 2017-10-11 2018-02-02 徐州中泰能源科技有限公司 一种绿色环保的铁制品除锈方法
BE1026906B1 (nl) * 2018-12-20 2020-07-22 Aperam Stainless Belgium Werkwijze voor het produceren van op ten minste drie verschillende manieren afgewerkt roestvast plaatstaal
BE1026907B1 (nl) * 2018-12-20 2020-07-22 Aperam Stainless Belgium Werkwijze voor het produceren van op ten minste drie verschillende manieren afgewerkt roestvast plaatstaal
CN113337875B (zh) * 2021-04-02 2023-03-28 无锡透平叶片有限公司 一种铁基变形高温合金锻件低倍流线腐蚀液及其腐蚀方法

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4713153A (en) * 1985-07-12 1987-12-15 N. V. Bekaert S. A. Process and apparatus for cleaning by electrochemical pickling with alternating current of specified frequency
WO2000015880A1 (fr) 1998-09-11 2000-03-23 Henkel Kommanditgesellschaft Auf Aktien Procede de decapage electrolytique a l'aide de solutions exemptes d'acide nitrique
WO2002012596A2 (fr) 2000-08-10 2002-02-14 Centro Sviluppo Materiali S.P.A. Procede de decapage electrolytique continu pour produits metalliques utilisant des cellules alimentees en courant alternatif
WO2002086199A2 (fr) 2001-04-24 2002-10-31 Centro Sviluppo Materiali S.P.A. Procede electrolytique continu realise dans une solution acide pour decalaminer des aciers inoxydables, en presence d'effets indirects d'un flux de courant
WO2003052165A1 (fr) 2001-12-19 2003-06-26 Centro Sviluppo Materiali S.P.A. Procede, et installation a cet effet, permettant de decalaminer, decaper et de proceder au finissage et/ou a la passivation de bandes d'acier inoxydable et bandes ainsi obtenues
EP2102376A1 (fr) 2006-11-14 2009-09-23 DANIELI & C. OFFICINE MECCANICHE S.p.A. Procédé de recuit et de décapage chimique
WO2010055145A1 (fr) * 2008-11-13 2010-05-20 Voestalpine Stahl Gmbh Procédé de fabrication d'une tôle d'acier à haute résistance zinguée électrolytiquement
WO2011039596A1 (fr) 2009-09-30 2011-04-07 Tenova S.P.A. Unité de préparation de surfaces pour lignes de transformation de bandes métalliques
JP5222449B2 (ja) 2008-12-26 2013-06-26 三菱伸銅株式会社 めっき付銅条材のスリット方法及びめっき付銅条材のスリット装置

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002050344A1 (fr) * 2000-12-18 2002-06-27 Centro Sviluppo Materiali S.P.A. Decapage et decalaminage par voie electrolytique continue de l'acier au carbone et de l'acier inoxydable

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4713153A (en) * 1985-07-12 1987-12-15 N. V. Bekaert S. A. Process and apparatus for cleaning by electrochemical pickling with alternating current of specified frequency
WO2000015880A1 (fr) 1998-09-11 2000-03-23 Henkel Kommanditgesellschaft Auf Aktien Procede de decapage electrolytique a l'aide de solutions exemptes d'acide nitrique
WO2002012596A2 (fr) 2000-08-10 2002-02-14 Centro Sviluppo Materiali S.P.A. Procede de decapage electrolytique continu pour produits metalliques utilisant des cellules alimentees en courant alternatif
EP1307609A2 (fr) 2000-08-10 2003-05-07 CENTRO SVILUPPO MATERIALI S.p.A. Procede de decapage electrolytique continu pour produits metalliques utilisant des cellules alimentees en courant alternatif
WO2002086199A2 (fr) 2001-04-24 2002-10-31 Centro Sviluppo Materiali S.P.A. Procede electrolytique continu realise dans une solution acide pour decalaminer des aciers inoxydables, en presence d'effets indirects d'un flux de courant
WO2003052165A1 (fr) 2001-12-19 2003-06-26 Centro Sviluppo Materiali S.P.A. Procede, et installation a cet effet, permettant de decalaminer, decaper et de proceder au finissage et/ou a la passivation de bandes d'acier inoxydable et bandes ainsi obtenues
EP2102376A1 (fr) 2006-11-14 2009-09-23 DANIELI & C. OFFICINE MECCANICHE S.p.A. Procédé de recuit et de décapage chimique
WO2010055145A1 (fr) * 2008-11-13 2010-05-20 Voestalpine Stahl Gmbh Procédé de fabrication d'une tôle d'acier à haute résistance zinguée électrolytiquement
JP5222449B2 (ja) 2008-12-26 2013-06-26 三菱伸銅株式会社 めっき付銅条材のスリット方法及びめっき付銅条材のスリット装置
WO2011039596A1 (fr) 2009-09-30 2011-04-07 Tenova S.P.A. Unité de préparation de surfaces pour lignes de transformation de bandes métalliques

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105040088A (zh) * 2015-08-11 2015-11-11 佛山市环宇新型材料有限公司 一种带钢电解除污装置
EP4044299A4 (fr) * 2019-11-11 2023-09-13 Posco Procédé de fabrication d'acier inoxydable pour séparateur de pile à combustible polymère
EP4253591A4 (fr) * 2020-11-25 2024-05-01 POSCO Co., Ltd Acier inoxydable austénitique pour séparateur de pile à combustible présentant une résistance de contact améliorée et son procédé de fabrication

Also Published As

Publication number Publication date
ITMI20130493A1 (it) 2014-09-30
CN105143523B (zh) 2018-06-19
BR112015020701B1 (pt) 2021-08-24
EP2978879A1 (fr) 2016-02-03
BR112015020701A2 (pt) 2017-07-18
CN105143523A (zh) 2015-12-09
EP2978879B1 (fr) 2017-11-08

Similar Documents

Publication Publication Date Title
EP2978879B1 (fr) Procédé de traitement en continu de la surface d'un stratifié en acier inoxydable dans une solution à base d'acide sulfurique
KR100934303B1 (ko) 스테인레스 스틸 스트립의 디스케일링, 피클링 및 마감처리/페시베이팅 방법 및 플랜트, 및 이에 의해 제조된 스트립
KR101289147B1 (ko) 표면품질이 우수한 저크롬 페라이트계 스테인리스 냉연강판을 제조하기 위한 친환경 고속 산세 프로세스
CN1318652C (zh) 使用交流电源电解池的用于金属产品的连续电解酸洗方法
CA2849304C (fr) Decapage d'acier inoxydable dans un bain acide electrolytique, oxydant
KR20010089247A (ko) 무질산 용액을 사용한 전해 산세척 방법
KR101228730B1 (ko) 고크롬 페라이트계 스테인리스강 산세 방법
KR20170089919A (ko) 스테인리스강 스트립의 처리, 특히 피클링 처리를 위한 방법 및 시스템
JPH09137300A (ja) ステンレス鋼からなる帯板製品を製造するための方法及び設備
CN105431574B (zh) 酸洗高铬铁素体不锈钢的方法
KR101359098B1 (ko) 오스테나이트계 스테인리스 냉연강판을 제조하기 위한 고속 산세 프로세스
EP4056737A1 (fr) Liquide ionique pour décapage d'acier inoxydable et procédé de décapage d'acier inoxydable en utilisant celui-ci
JP6031606B2 (ja) オーステナイト系ステンレス冷延鋼板を製造するための高速酸洗プロセス
EP2978878B1 (fr) Procédé de traitement continu de la surface d'un stratifié fait d'acier inoxydable dans une solution à base d'acide chlorhydrique
KR100696850B1 (ko) 저크롬 페라이트계 스테인레스강의 고속산세방법
JP3792335B2 (ja) ステンレス鋼帯の脱スケールにおける仕上げ電解酸洗方法
KR101382934B1 (ko) 내식성 향상을 위한 오스테나이트계 스테인리스 냉연강판의 고속 산세 프로세스
Hudson Pickling and descaling
Covino et al. Pickling of Stainless Steels--a Review
JP2517353B2 (ja) ステンレス鋼帯の脱スケ―ル方法
KR101353856B1 (ko) 오스테나이트계 스테인리스 냉연강판을 제조하기 위한 저온 고속 산세 프로세스
KR101242990B1 (ko) 표면 품질 개선을 위한 페라이트계 스테인리스 냉연강판의 산세공정
JPH09296285A (ja) オーステナイト系ステンレス熱延鋼帯の酸洗方法

Legal Events

Date Code Title Description
WWE Wipo information: entry into national phase

Ref document number: 201480018121.7

Country of ref document: CN

121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14722742

Country of ref document: EP

Kind code of ref document: A1

REEP Request for entry into the european phase

Ref document number: 2014722742

Country of ref document: EP

WWE Wipo information: entry into national phase

Ref document number: 2014722742

Country of ref document: EP

NENP Non-entry into the national phase

Ref country code: DE

REG Reference to national code

Ref country code: BR

Ref legal event code: B01A

Ref document number: 112015020701

Country of ref document: BR

ENP Entry into the national phase

Ref document number: 112015020701

Country of ref document: BR

Kind code of ref document: A2

Effective date: 20150827