WO2021186375A1 - Procédé de décapage et/ou de passivation d'un acier inoxydable - Google Patents

Procédé de décapage et/ou de passivation d'un acier inoxydable Download PDF

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Publication number
WO2021186375A1
WO2021186375A1 PCT/IB2021/052258 IB2021052258W WO2021186375A1 WO 2021186375 A1 WO2021186375 A1 WO 2021186375A1 IB 2021052258 W IB2021052258 W IB 2021052258W WO 2021186375 A1 WO2021186375 A1 WO 2021186375A1
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Prior art keywords
solution
ions
treatment solution
acid
aqueous
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PCT/IB2021/052258
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English (en)
Inventor
Stefano Martines
Giovanni ASTENGO
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Tenova S.P.A.
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Priority to EP21717527.2A priority Critical patent/EP4121581A1/fr
Publication of WO2021186375A1 publication Critical patent/WO2021186375A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/50—Treatment of iron or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/86—Regeneration of coating baths
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel
    • C23G1/086—Iron or steel solutions containing HF
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/36—Regeneration of waste pickling liquors

Definitions

  • the present invention relates to a process for pickling and/or passivating a stainless steel.
  • a steel is defined as stainless if it is such that it prevents the formation of rust on its surface under normal environmental conditions, for example in the presence of oxygen and atmospheric humidity or in aqueous solutions.
  • Stainless steels are made of iron-based alloys containing at least 10 % by weight of chromium. The formation of chromium oxide on the surface of the material gives stainless steels their characteristic corrosion resistance property.
  • thermal treatments e.g. hot rolling, annealing, etc.
  • a layer of surface oxide is formed on its surface. The removal of the scale is necessary to restore the basic chemical composition of the steel on the surface thereof, so as to give the steel the required corrosion resistance properties.
  • the oxide forming the surface scale in addition to iron oxides, contains oxides of the steel binding elements, for example chromium, nickel, aluminium, titanium or niobium.
  • oxides of the steel binding elements for example chromium, nickel, aluminium, titanium or niobium.
  • chromium oxide takes place in the surface layer.
  • the oxide layer is therefore enriched with chromium instead of iron.
  • the steel layer immediately below the oxide layer is depleted in chromium (so-called "chrome-depleted" layer).
  • a pickling process preferably dissolves the chrome-depleted layer under the oxide layer, so that the surface scale is also completely removed.
  • the passivation treatment can be carried out in treatment solutions similar to the pickling solutions, but having a higher redox potential than the redox potential of the pickling solutions.
  • the passivation treatment forms an optically invisible passivation layer that maintains the surface of the steel polished and rustproof, too.
  • the divalent iron ions are oxidized in the trivalent state by the continuous or discontinuous addition of oxidizing agents, such as for example hydrogen peroxide, perborates, peracids and organic peroxides.
  • the exhausted solution of the pickling processes can be subjected to a regeneration process to recover the acid and the metals present therein, for example by pyrohydrolysis treatments.
  • the regeneration system generally, collects the exhausted treatment solutions coming from the different treatment lines of a same production plant or of several production plants.
  • the regeneration product is an aqueous solution of the acid or acids initially present in the exhausted solutions. This regenerated solution can be recycled in the same process or in other processes.
  • the Applicant has now found that it is possible to achieve the aforesaid object by operating a pickling and/or passivation process in an integrated manner with a process for regenerating the treatment solutions.
  • the integration of the two processes is obtained by carrying out the pickling and/or passivation process under operating conditions that are such to maximise the recovery yield of the acids in the regeneration system of the exhausted treatment solutions and, at the same time, to allow the recycling thereof in the same process that generated it.
  • the aforesaid technical effect is obtained by means of a nitric-free pickling and/or passivation process in which a stainless steel is treated in sequence with at least two treatment solutions, contained in at least a first and a second bath, which are kept at two different redox potential values and wherein the exhausted treatment solution of the first bath is fed to a regeneration treatment to obtain an aqueous solution of regenerated acid having a chemical composition compatible with that of the second bath; in the process, moreover, a part of the treatment solution of the second bath is transferred to the first bath to replace the treatment solution sent for regeneration, while the aqueous solution of regenerated acid is fed to the second bath to replace the part of treatment solution that has been transferred to the first bath.
  • the first treatment solution contained in the first bath is kept at a redox potential higher than that of the second treatment solution contained in the second bath by suitably regulating the ratio of the Fe III /Fe 11 ions in solution by oxidation.
  • the second treatment solution instead, is not sent for regeneration.
  • the treatment of steel in a first bath having a relatively low redox potential allows a more rational use of the oxidizing compounds since an averagely more concentrated solution of iron ions (Fe tot) and having a relatively high concentration of Fe 11 ions is fed to the process for regenerating the acids.
  • the regeneration of solutions that are relatively more concentrated in iron in particular by means of regeneration processes comprising a heat treatment, is more effective since it allows a significant energy saving compared to the regeneration of diluted solutions, where most of the thermal energy is required to evaporate a higher amount of water.
  • the treatment of the steel in the first bath with lower redox potential allows a more rational regeneration of the exhausted solution, since the maintenance of a lower redox potential value entails a lower consumption of oxidizing additives, since a less forced oxidation of the Fe 11 ions into Fe 111 ions is required.
  • the treatment in a solution having a lower redox potential implies a lower pickling efficiency of the first bath and, consequently, the possibility that the surface of the steel leaving the first bath may still present scale residues and chrome-depleted material.
  • This disadvantage is compensated by the higher efficacy and selectivity of the second treatment solution which is kept at a higher redox potential than the first solution, also due to the recycling of the regenerated acid solution.
  • the high oxidizing capacity of the second solution allows to dissolve the aforesaid scale residues and chrome-depleted material, leaving the layers with the correct chromium content (selective action) untouched and finally to passivate the surface thereof, thus allowing to obtain a final product of high quality.
  • the present invention relates to a process for pickling and/or passivating a stainless steel with an aqueous treatment solution comprising Fe 111 ions which are turned into Fe 11 ions during pickling, comprising the following steps: a. putting said stainless steel (1) in contact with a first aqueous treatment solution (30, 1000), comprising: at least one acid selected from HF and HC1; 10-65 g/1 of Fe 111 ions,
  • step a of the process according to the present invention the treatment of stainless steel is carried out with a first aqueous acid treatment solution comprising at least one mineral acid and iron ions.
  • the acid is selected from: HF, HC1 and H2SO4 and relative mixtures. The selection of the acid depends on various factors, such as the type of steel to be treated (e.g. ferritic, martensitic, austenitic, etc.), the quantity of and degree of adhesion of the scale present, as well as possible pre- and post-treatments of the steel.
  • the concentration thereof in the first treatment solution is in the range 3 - 50 g/1, preferably 5 - 40 g/1.
  • the acid is hydrochloric acid (HC1)
  • the concentration thereof in the first treatment solution is in the range 30 - 60 g/1.
  • the acid present in the first treatment solution is a mixture of HF and H2SO4.
  • the concentration of HF acid in the first treatment solution is in the range 5 - 40 g/ and the concentration of H2SO4is in the range 50-100 g/1.
  • the concentration values of the aforesaid acids refer to the concentration of free acid in the aqueous solution, as measurable, for example, by means of an acid-base, manual or automatic, titration.
  • free acid refers to the acid not yet used to form salts with metal cations, i.e. the acid still available in the bath to form salts with the metal ions just dissolved.
  • the pH of the first treatment solution varies as a function of the type and concentration of the acid present.
  • the pH is preferably less than
  • the pH is preferably less than
  • the pH is preferably less than 1.
  • the first treatment solution contains Fe 111 ions in a concentration in the range 10- 65 g/1.
  • the first treatment solution when the acid is HF, preferably contains Fe 111 ions in a concentration in the range 10-40 g/1 and Fe 11 ions in a concentration in the range 5-40 g/1.
  • the first treatment solution when the acid is HC1, preferably contains Fe 111 ions in a concentration in the range 30-65 g/1 and Fe 11 ions in a concentration in the range 20-60 g/1.
  • Fe III /Fe 11 ion ratio hereinafter also indicated Kl
  • Kl is higher than 1, preferably equal to or higher than 1.1. Except for the process start-up step, where the treatment solution essentially contains Fe 111 ions only, the Kl value under steady operating conditions does not generally exceed the value of 10. In one embodiment, the Kl value is kept in the range 1.1 - 5.
  • the total concentration of iron ions hereinafter also referred to as Fe tot (a), is preferably in the range 30 - 100 g/1.
  • the concentration Fe tot (a) is in the range 30 - 70 g/1.
  • the concentration Fe tot (a) is in the range 40- 100 g/1.
  • Said concentration Fe tot (a) is kept at a value higher than the concentration of Fe tot in the treatment solution used in step b, hereinafter also referred to as Fe tot (b).
  • the ratio Fe tot ( a)/Fe tot (b), is equal to or higher than 1.1, more preferably equal to or higher than 1.2.
  • the aforesaid ratio in general, is less than 10, preferably less than 7. In particular, in the case of ferritic steels, the aforesaid ratio is preferably higher than 1.5.
  • the ratio Fe tot (a)/Fe tot (b) is selected on the basis of the type of steel treated and the type and mass of scale to be removed. In general, the value of the aforesaid ratio is kept in the range 1.2 - 7.
  • Step a is carried out by keeping the treatment solution at a temperature in the range 45-65°C.
  • step b the steel that has undergone the treatment of step a is placed in contact with a second acid treatment solution comprising at least one mineral acid and iron ions.
  • the second treatment solution the same acid or mixture of acids as the first treatment solution is used. In this way, when the first exhausted treatment solution is sent for regeneration, at least part of the second solution can be transferred to the first bath to replace the first exhausted solution.
  • the concentration thereof in the second treatment solution is in the range 3-50 g/1, preferably 4 - 40 g/1.
  • the concentration thereof in the second treatment solution is in the range 60 - 100 g/1.
  • the concentration of HF acid in the second treatment solution is in the range 4 - 40 g/ and the concentration of H 2 SO 4 is in the range 60-110 g/1.
  • the pH of the treatment solution in step b varies as a function of the type and concentration of the acid present. If the acid is HC1, the pH is preferably less than
  • the pH is preferably less than
  • the pH is preferably less than 1.
  • the second treatment solution contains Fe 111 ions in a concentration in the range 10- 50 g/1 and Fe 11 ions in a concentration in the range 0- 40 g/1.
  • the second treatment solution when the acid is HF, preferably contains Fe 111 ions in a concentration in the range 10-40 g/1 and Fe 11 ions in a concentration in the range 0-30 g/1.
  • the second treatment solution when the acid is HC1, preferably contains Fe 111 ions in a concentration in the range 30-50 g/1 and Fe 11 ions in a concentration in the range 0-40 g/1.
  • the Fe III /Fe 11 ion ratio hereinafter also referred to as K2
  • K2 is higher than 1, preferably higher than 1.1.
  • the K2 value may tend to infinity if a treatment solution with a high redox potential and therefore substantially free of Fe 11 ions or with a very low concentration of these ions is used.
  • This treatment solution can be advantageously used, for example, when the steel is ferritic (AISI 430, 409, 441, etc.).
  • the concentration of Fe 11 ions in the second treatment solution can be kept in the range 1-30 g/1, more preferably 1-20 g/1.
  • the value of the ratio K corresponding to the ratio between the K2 value and the K1 value, under steady operating conditions does not exceed the value of 6, especially of 5.
  • the K value is kept in the range 1.1-2.
  • the K value can however tend to infinity if K2 tends to infinity, for example under the aforesaid described operating conditions.
  • the total concentration of iron ions hereinafter also referred to as Fe tot (b), is preferably in the range 10 - 60 g/1.
  • Analytical methods for determining the concentration of Fe 111 and Fe 11 ions, acids and the pH in treatment solutions are known in the art, for example acid-base titrations, conductometric methods and density measurements.
  • Step b is carried out by keeping the treatment solution at a temperature in the range of 40-65°C.
  • the ratio between the Fe III /Fe 11 ions in the treatment solutions is adjusted by one or more of the following operations:
  • the oxidizing reagent may be selected for example from: hydrogen peroxide, compounds releasing hydrogen peroxide, oxygenated acids of the chlorine, permanganate salts, persulphate salts and relative mixtures.
  • the oxidizing reagent is fed into the first and/or second treatment solution by means of a venturi-type mixer.
  • the oxidation of the treatment solutions can be carried out in a continuous or discontinuous way.
  • step c a part of the first treatment solution is taken and fed to a regeneration process to obtain a regenerated aqueous solution of the acid or mixture of acids used.
  • the treatment solution to be regenerated is preferably taken when the solution is exhausted: this condition occurs when an excessive quantity of iron ions accumulates in the treatment solution due to the progressive dissolution of the scale and of the dechromised layer.
  • the total iron concentration (Fetot) at which a solution can be considered exhausted varies as a function of the composition of the treatment solution, the type of steel treated, the composition of the scale, the number of treatment baths present as a whole, the temperature and other parameters. In general, the value of Fetot is known to those skilled in the art or it can be determined, case by case, by experimental tests.
  • the first treatment solution is considered exhausted when the concentration Fetot is higher than a value comprised in the range 40 - 100 g/1.
  • the acid is HF the first treatment solution is considered exhausted when the concentration Fetot is higher than a value in the range 40 - 70 g/1.
  • the first treatment solution is considered exhausted when the concentration Fetot is higher than a value in the range 70 - 100 g/1.
  • the regeneration can be carried out by pyrohydrolysis.
  • the process of regeneration by pyrohydrolysis comprises the following steps: i. spray-drying at least a portion of the aqueous treatment solution by means of a gaseous heating fluid having a temperature within the range 180-500°C, preferably 300-400°C, to obtain in gaseous form the acid contained in said solution and dried metal salts; ii. absorbing said acid in gaseous form obtained in said step i. in water to form a regenerated aqueous solution of said acid.
  • the aforesaid regeneration process can further comprise the steps: iii. pyrolizing the dried metal salts leaving step ii, for example at a temperature in the range 400-900°C, to obtain metal oxides and further acid in gaseous form; iv. absorbing said further acid in gaseous form in water to form a further regenerated aqueous solution of said acid.
  • the yield of the regeneration process of an exhausted treatment solution can reach values higher than 95% by weight, said percentage being referred to the total content of anions of the acid present in the solution fed for regeneration.
  • the regeneration process also enables the metals extracted from the solution, in particular chromium, nickel and molybdenum, to be recovered, which can be recycled effectively in the context of the processes made in a steel manufacturing plant.
  • step d a part of the second treatment solution used in step b is taken and transferred into the bath containing the first treatment solution of step a, so as to partially or totally replace the volume of the first treatment solution fed for regeneration. Since the redox potential K2 of the second treatment solution is higher than the redox potential K1 of the first treatment solution, the transfer of the second solution contributes to controlling the K1 value in the first solution.
  • the transfer of the second treatment solution into the bath containing the first solution can be carried out continuously or discontinuously.
  • step e the aqueous solution of the regenerated acid obtained in step c is recycled at least in part in the bath containing the second treatment solution, so as to partially or totally replace the volume of the second treatment solution transferred to the first bath.
  • the composition of the regenerated aqueous solution of acid (hereinafter also referred to as "regenerated acid"), in particular the concentration of the acid or mixture of acids used, is compatible with that of the second treatment solution and therefore it is recycled at least to it.
  • the term "compatible" means that the concentration of acid in the regenerated solution is equal to or higher than the concentration of the acid expected in the second treatment solution.
  • the regenerated acid if compatible with the first treatment solution or with other treatment solutions used in the process, can also be recycled in the baths containing the aforesaid treatment solutions.
  • the treatment solutions if necessary, can be maintained under the desired acid and iron ion concentration conditions through the periodic or continuous addition of fresh (i.e., non-regenerated) acids, water and oxidizing compounds.
  • the process according to the present invention is based on the use of at least two separate treatment solutions, in step a and in step b, to treat a stainless steel.
  • other intermediate treatment solutions comprising the same acid or mixture of acids as the solutions of steps a and b together with iron ions can also be used.
  • the number of the intermediate treatment solutions could be 1, 2, 3 or more.
  • the intermediate treatment solutions have chemical composition and redox potential in the ranges described above for the treatment solutions of steps a and b.
  • the chemical composition and the redox potential of the intermediate treatment solutions are selected so as to allow the transfer of each of them to the treatment solution preceding it in the sequence, so as to create a reverse cascade treatment solution flow, i.e.
  • the treatment solution which is sent for regeneration when exhausted is at least the treatment solution of step a, that is, the first of the sequence, and the regenerated acid is recycled at least in the bath containing the treatment solution of step b, that is the last of the sequence.
  • the treatment solutions used in the process according to the invention can also comprise the additives typically used in pickling and passivation baths known in the art, such as compounds having the function of improving the wettability of the steel surface, brighteners, accelerating agents or inhibitors of pickling reactions.
  • the process according to the present invention is generally a sub-step of a treatment sequence of a stainless steel.
  • the treatment sequence may comprise one or more further steps of steel surface treatment, which are carried out before and/or after the process according to the present invention. Examples of preliminary treatments are the removal of the scale by mechanical methods, such as sandblasting or shot blasting and/or chemical and electrochemical methods.
  • the process according to the invention may optionally comprise at least one final finishing/passivation treatment step dedicated to particular materials or finishing grades, which is carried out after step b.
  • the process according to the invention may further comprise conventional steps of washing the surface of the laminate with water or aqueous solutions optionally containing surfactants or other additives. In particular, the washing steps, which can be carried out by immersion, spraying with water jets and possibly with the aid of metal brushes, aim at eliminating the residues of the previous treatments from the surface and avoiding contamination of the treatment solutions.
  • a system for pickling and/or passivating a stainless steel for example in the form of a strip of a steel laminate, comprises a series of treatment solutions 10, 20, 30 and 40, each contained in a corresponding tank, inside which the strip 1 is made to advance along a direction and in the advancement direction indicated by the arrow F.
  • the position of the strip 1 in the treatment solutions 10, 20, 30 and 40 is determined by the rollers 81 and 82, any other intermediate rollers positioned between the tanks or inside the tanks themselves (not shown in the figures) and by the pull applied to the strip.
  • the treatment solutions are made to circulate inside each bath, for example by means of recirculation pumps (not shown in the figures).
  • the strip 1 is subjected to a preliminary chemical or electrochemical descaling treatment.
  • the strip 1 leaving the treatment solution 10 is then subjected to a rinsing treatment with water in the treatment solution 20 in order to eliminate the residues of the treatment solution 10 which may be present on the surface.
  • the strip 1 can also be subjected to brushing.
  • the strip 1 is placed in contact with a first treatment solution 30 comprising HF and iron ions.
  • the strip 1 is placed in contact with a second treatment solution 40 also comprising HF and iron ions.
  • the first 30 and second 40 treatment solution have chemical composition, redox potential and pH according to the present invention.
  • the regeneration system 90 comprises a spray-drying unit 50, a water absorption unit 60 and a pyrolysis unit 70.
  • the solution to be regenerated 32 is fed to the spray-drying unit 50 to obtain HF in gaseous form 55 and dried metal salts 56.
  • the gaseous HF 55 is separated from the dried metal salts 56 and sent to the absorption unit 60 (e.g. a water absorption column) where a regenerated aqueous solution of HF 34 is produced.
  • the dried metal salts 56 are fed to the pyrolysis unit 70 to obtain metal oxides 75 and further acid in gaseous form 76, which can be sent to the absorption unit 60 to produce further regenerated solution of HF 34.
  • a portion 35 of the second treatment solution 40 is transferred to the tank containing the first treatment solution 30, where it is mixed with the remaining portion of the first treatment solution 30.
  • This can be achieved through at least one duct in hydraulic communication between the two baths, for example by gravity or through active means, such as pumps and/or bleeding from the recirculation systems of the treatment solution.
  • the regenerated aqueous solution of HF 34 is recycled to the tank containing the treatment solution 40 to restore or maintain the desired operating conditions for the second treatment solution 40.
  • a part 36 of the regenerated aqueous solution of HF can also be sent to the tank containing the treatment solution 30 to maintain or restore the HF and iron ion concentration conditions in this first solution.
  • a second embodiment of the process according to the present invention is exemplified in Figure 2. This embodiment is particularly suitable for treating steel laminates obtained by hot rolling.
  • the strip 1 is subjected to a preliminary descaling treatment.
  • the descaling treatment can be advantageously carried out in an aqueous treatment solution 1000 comprising HC1 and iron ions (descaling solution).
  • the descaling solution 1000 comprises: - at least 30 g/1 of free HC1,
  • the descaling solution 1000 has a pH less than or equal to 1.
  • the sequence of Figure 2 differs mainly in that it provides for a step of regeneration of the exhausted descaling solution 1000 and for recycling the regenerated acid to the same solution, in addition to the regeneration of the treatment solution 30 containing HF and iron ions and relative recycling to the treatment solution 40.
  • a part 320 of said solution 1000 is fed to a regeneration system 94 to produce a regenerated aqueous solution of HC1 340.
  • the regeneration system 94 comprises a spray drying unit 500, a water absorption unit 600 and a pyrolysis unit 700.
  • the solution to be regenerated 320 is fed to the spray-drying unit 500 to obtain HC1 in gaseous form 550 and dried metal salts 560.
  • the gaseous HC1 550 is separated from the dried metal salts 560 and sent to the absorption unit 600 (e.g.
  • a water absorption column where a regenerated aqueous solution of HC1 340 is produced.
  • the dried metal salts 560 are fed to the pyrolysis unit 700 to obtain metal oxides 750 and further acid in gaseous form 760, which can be sent to the absorption unit 600 to produce further aqueous solution of HC1.
  • the regenerated aqueous solution of HC1 340 is recycled to the treatment solution 1000.
  • said descaling solution is preferably regenerated with a batch process.
  • the strip 1 leaving the descaling treatment in the treatment solution 1000 is sent to the successive tanks containing the treatment solutions 20, 30 and 40, where it undergoes the treatments previously described with reference to Figure 1.
  • a third embodiment of the process according to the present invention is exemplified in Figure 3.
  • the sequence of Figure 3 differs mainly in that it provides for carrying out a preliminary descaling step in which at least two treatment solutions 1000 and 1001 are used in sequence, each containing HC1 and iron ions, operating under ion concentration conditions and redox potential selected in accordance with the present invention.
  • the chemical descaling step comprises a first treatment of the strip 1 in the descaling solution 1000 (step al) and a second treatment in the subsequent descaling solution 1001 (step bl).
  • the first descaling solution 1000 comprises:
  • the second descaling solution 1001 comprises:
  • the aforesaid steps al and bl are carried out by keeping the weight ratio between the Fe III /Fe 11 ions of the second descaling solution 1001 at a value higher than the ratio between the Fe III /Fe 11 ions in the aforesaid first descaling solution 1000.
  • the first descaling solution 1000 is exhausted, for example when the total concentration of Fe 111 and Fe 11 ions is higher than 70 g/1, a part 320 of said solution is taken and fed to a regeneration system 94 to obtain a regenerated aqueous solution of HC1 340.
  • the regeneration system 94 can be substantially the same system described above with reference to Figure 2.
  • a part 350 of the second descaling solution 1001 present in the bath 1001 is taken and transferred to the descaling solution 1000 to replace the part 320 of said first descaling solution sent for regeneration.
  • a part 360 of the regenerated aqueous solution of HC1 can also be sent to the descaling solution 1000 to maintain or restore the HC1 and iron ion concentration conditions in this solution.
  • the strip 1 leaving the descaling treatment in the treatment solutions 1000 and 1001 is sent to the successive treatment solutions 20, 30 and 40, where it undergoes the treatments previously described with reference to Figure 1.
  • the embodiments illustrated with reference to Figures 1 - 3 can also be used in plants which process cold rolled products or combined plants which process both hot rolled and cold rolled products.
  • the preliminary descaling treatment in the treatment solution 1000 can be advantageously carried out, according to the prior art, by electrolytic treatment in an aqueous treatment solution comprising sulphuric acid at low concentration (for cold rolled products, the sulphuric acid concentration is preferably in the range 40-100 g/1; for hot-rolled products, the sulphuric acid concentration is preferably in the range 100-250 g/1) at a controlled temperature (40-80 °C).
  • the pH of the aforesaid descaling solution is kept at a value equal to or less than 3.
  • the aforesaid concentration and pH conditions of the electrolytic descaling solution favour turning the hexavalent chromium dissolved by the scale of the treated material into trivalent chromium.
  • the descaling solution 1000 containing sulphuric acid and iron ions, when exhausted, can also be subjected to regeneration and the regenerated acid solution can be recycled to the same descaling step.
  • the regeneration can be carried out by pyrolysis, with systems known in the art similar to those illustrated above.
  • at least the recovery of the free acid from the exhausted solution can be carried out, for example by means of ion-delayed resin systems, optionally preceded by scale decantation systems.
  • the strip 1 leaving the descaling treatment in the treatment solution 1000 is sent to the successive tanks containing the treatment solutions 20, 30 and 40, where it undergoes the treatments previously described with reference to Figure 1.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Abstract

La présente invention concerne un procédé de décapage et/ou de passivation d'un acier inoxydable par des solutions de traitement aqueuses acides comprenant des ions de FeIII et des ions de FeII, au moins une première et une deuxième solution de traitement étant utilisées en séquence, le potentiel redox de la deuxième solution étant maintenu à une valeur supérieure au potentiel redox de la première solution ; la concentration totale en ions de fer dans la première solution de traitement étant maintenue à une valeur supérieure à celle de la concentration totale des ions de fer dans la deuxième solution de traitement ; la première solution, lorsqu'elle est épuisée, étant soumise à une régénération pour obtenir de l'acide régénéré, qui est recyclé vers la deuxième solution ; une partie de la deuxième solution étant transférée à la première solution pour compenser l'élimination de la première solution épuisée.
PCT/IB2021/052258 2020-03-19 2021-03-18 Procédé de décapage et/ou de passivation d'un acier inoxydable WO2021186375A1 (fr)

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Citations (5)

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Publication number Priority date Publication date Assignee Title
WO1998038353A1 (fr) * 1997-02-25 1998-09-03 Centro Sviluppo Materiali S.P.A. Montures de lunettes inalterables a differentes temperatures et leur procede de fabrication
US6250314B1 (en) * 1998-07-15 2001-06-26 Andritz-Patentverwaltungs-Gesellschaft M.B.H. Process of pickling stainless steel
WO2001049901A1 (fr) * 2000-01-05 2001-07-12 United States Filter Corporation Regeneration de liqueur de decapage usee
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
EP2352861A2 (fr) * 2008-11-14 2011-08-10 Ak Steel Properties, Inc. Décapage ferrique d acier au silicium

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FR2587369B1 (fr) 1985-09-19 1993-01-29 Ugine Gueugnon Sa Procede de decapage acide de produits en acier inoxydable
FR2673200A1 (fr) 1991-02-25 1992-08-28 Ugine Aciers Procede de surdecapage de materiaux en acier tels que les aciers inoxydables et les aciers allies.
IT1255655B (it) 1992-08-06 1995-11-09 Processo di decapaggio e passivazione di acciaio inossidabile senza impiego di acido nitrico
IT1276955B1 (it) 1995-10-18 1997-11-03 Novamax Itb S R L Processo di decapaggio e passivazione di acciaio inossidabile senza impiego di acido nitrico
FR2745301B1 (fr) 1996-02-27 1998-04-03 Usinor Sacilor Procede de decapage d'une piece en acier et notamment d'une bande de tole en acier inoxydable
DE69612957T2 (de) 1996-03-14 2001-09-06 Condoroil Impianti S R L Beizen von rostfreien Stahlen mit kontinuierliche katalytische Oxidation der Beizlösung
AU2002333772A1 (en) 2002-08-30 2004-03-19 Henkel Kommanditgesellschaft Auf Aktien An economic method for restoring the oxidation potential of a pickling solution
AT508774B1 (de) 2010-04-20 2011-04-15 Key Technologies Ind Gmbh Verfahren zur gewinnung bzw. rückgewinnung von salpetersäure und flusssäure aus lösungen von edelstahlbeizanlagen

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998038353A1 (fr) * 1997-02-25 1998-09-03 Centro Sviluppo Materiali S.P.A. Montures de lunettes inalterables a differentes temperatures et leur procede de fabrication
US6250314B1 (en) * 1998-07-15 2001-06-26 Andritz-Patentverwaltungs-Gesellschaft M.B.H. Process of pickling stainless steel
WO2001049901A1 (fr) * 2000-01-05 2001-07-12 United States Filter Corporation Regeneration de liqueur de decapage usee
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
EP2352861A2 (fr) * 2008-11-14 2011-08-10 Ak Steel Properties, Inc. Décapage ferrique d acier au silicium

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