Classifications

• • 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
  • 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
• • 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
  • C23C22/07—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 containing phosphates
  • C23C22/08—Orthophosphates
  • C23C22/10—Orthophosphates containing oxidants
• • 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

Definitions

• the invention relates to a method for pickling martensitic or ferritic stainless steel (also referred to as “stainless steel”), in particular in the form of wire, tubes or rods.
• martensitic or ferritic stainless steel also referred to as “stainless steel”
• steel in which, under common environmental conditions, such as For example, the presence of atmospheric oxygen and moisture and rust formation in aqueous solutions is prevented.
• Harder corrosion conditions such as acids and salt solutions are resisted by the mostly higher-alloyed so-called corrosion-resistant or acid-resistant steels.
• These steels are collectively referred to as stainless steels , 4th edition, volume 22, pp.
• Stainless steels are iron-based alloys that contain at least 10% chromium. The formation of chromium oxide on the surface of the material gives the stainless steels their corrosion-resistant character.
• Stainless steels can be divided into families: austenitic steels, ferritic steels, martensitic steels, precipitation hardened steels and duplex steels. These groups differ in their physical and mechanical properties as well as in their corrosion resistance, which are caused by the different alloy components.
• the oxide-containing surface layer to be removed differs fundamentally from the oxide layer on low-alloy steels or on carbon steels.
• the surface layer contains oxides of the alloying elements such as chromium, nickel, aluminum, titanium or niobium. When heated, the surface layer accumulates in chromium oxide, since chromium is thermodynamically less noble than iron. This enriches chromium with iron in the oxide layer.
• the surface is chemically activated so that it is covered with an optically disruptive surface layer in the air. This can be prevented by passivating the freshly pickled surfaces after or during pickling. This can be done in treatment solutions similar to the pickling solutions, but a higher redox potential is set for the passivation than for the pickling process.
• the targeted passivation step forms an optically invisible passivation layer on the metal surface. As a result, the steel surface retains its shiny metallic appearance. Whether a treatment solution has a staining or passivating effect on stainless steel mainly depends on the set redox potential.
• Acidic solutions with pH values below about 2.5 have a pickling effect if, owing to the presence of oxidizing agents, they have a redox potential compared to a silver / silver chloride electrode in the range from about 100 to about 350 mV. If the redox potential is increased to values above approximately 350 mV, the treatment solution has a passivating effect, with different minimum values for the potential having to be set depending on the type of stainless steel.
• a possible substitute for the oxidizing effect of nitric acid are Fe (III) ions.
• Their concentration can be maintained, for example, by means of hydrogen peroxide, which is added to the treatment baths continuously or batchwise.
• Such pickling or passivation baths contain about 15 to about 65 g / l of trivalent iron ions.
• trivalent iron ions are reduced to the bivalent stage.
• further divalent iron ions are released from the pickled surface.
• the pickling bath therefore depletes trivalent iron ions during operation, while divalent iron ions accumulate. This shifts the redox potential of the treatment solution so that it finally loses its pickling effect.
• EP-B-505 606 describes a nitric acid-free process for pickling and passivating stainless steel, in which the material to be treated is brought into contact with a bath which has a temperature between 30 and 70 ° C. and at least does so Contains at least 150 g / l sulfuric acid, at least 15 g / l Fe (III) ions and at least 40 g / l HF.
• This bath also contains up to about 1 g / l of additives such as nonionic surfactants and pickling inhibitors.
• Such quantities of hydrogen peroxide are added continuously or discontinuously to the bath that the redox potential is kept in the desired range.
• the other bath components are also added in such a way that their concentration remains in the optimal working range.
• the pickling bath is kept in motion by blowing in air. Movement of the pickling bath is necessary to achieve a uniform pickling result.
• a similar process, which differs from this essentially only in the set redox potential, is described in EP-A-5
• pickling processes work technically satisfactorily and have the ecological advantage of not emitting nitrogen oxides into the environment. They are especially optimized for pickling austinitic stainless steels, which make up around 65 to 85% of the stainless steel market.
• these pickling solutions prove to be too aggressive for objects made of martensitic or ferritic stainless steel, especially if they are in the form of wire, tubes or rods. They attack the base alloy of these steel types too strongly, so that there is a risk of over pickling.
• the pickling process continues in depth at areas already pickled and destroys the surface. Over-pickling creates more divalent iron ions than necessary to maintain the redox potential at the trivalent level must be oxidized.
• This object is achieved by a method for pickling martensitic or ferritic stainless steel, the stainless steel being brought into contact with a pickling solution which contains Fe (III) ions, sulfuric acid and HF, characterized in that the
• Pickling solution has a temperature in the range of 15 to 29 ° C and
• the concentrations of the individual components of this pickling bath are each in a range which is known per se in the prior art. However, the concentrations are coordinated with one another in such a way that no pickling of the martensitic or ferritic substrates occurs.
• An essential parameter for avoiding over pickling is the temperature, which according to the invention is set in the range between 15 and 29 ° C. It is preferably between 20 and 29 ° C. and in particular between 23 and 28.5 ° C. If the temperature exceeds 30 ° C, there is an increasing risk of over pickling.
• the time for the pickling process depends on the selected temperature, the set concentrations of free acid and the pretreatment of the objects before the actual pickling process.
• the pickling time is in the range of about 5 minutes for blasted substrates, 10 to 15 minutes for substrates treated in a molten salt and 10 to 25 minutes for pretreatment with a strongly alkaline solution of potassium permanganate. To achieve complete pickling success, it may be necessary to repeat the pretreatment and pickling steps. The pickling times mentioned then apply to the individual steps.
• the minimum concentration of free sulfuric acid depends on which pickling time is considered acceptable.
• the concentration of free HF is preferably at least 10 g / l in order to achieve the abovementioned pickling times. In practice, the maximum concentration can be between about 25 and about 30 g / l. If particularly short pickling times are desired, the maximum concentration can be set to around 35 g / l. The pickling process is still manageable even with an upper limit of 40 g / l free HF. At higher concentrations, however, the risk of over pickling increases.
• the minimum concentration of free sulfuric acid is preferably set between 55 and 60 g / l, the upper limit between 70 and 100 g / l.
• the pickling solution can contain 55 to 75 g / l of free sulfuric acid.
• the concentration of Fe (III) ions decreases in the course of the pickling process, since these are reduced to the bivalent stage by the redox reaction with the elemental iron of the steel surface.
• the concentration of Fe (III) ions is preferably regulated in such a way that the pickling solution, when incorporated, contains between about 10 and about 25 g / l of these ions. This is preferably done by oxidizing the resulting Fe (II) ions to the corresponding degree to the trivalent stage. Depending on the quantitative ratio between divalent and trivalent iron ions in the pickling solution, this has a certain redox potential.
• the pickling solution can therefore also be controlled via the measured redox potential.
• the pickling solution in the incorporated state preferably has a redox potential, measured at 25 ° C. with a platinum electrode relative to an Ag / AgCl reference electrode, of 100 to 240 mV, in particular 150 to 235 mV.
• a redox potential measured at 25 ° C. with a platinum electrode relative to an Ag / AgCl reference electrode, of 100 to 240 mV, in particular 150 to 235 mV.
• a strong oxidizing agent such as hydrogen peroxide or with a substance that releases hydrogen peroxide is possible.
• Such substances are, for example, inorganic or organic peracids or peroxo acids.
• peroxosulfuric acid or peroxodisulfuric acid is suitable.
• Oxidizing halogen acids such as chloric acid or perchloric acid are also possible, but are less preferred for practical reasons.
• the divalent iron can be oxidized to the trivalent stage by catalytic oxidation with an oxygen-containing gas, preferably air, using a homogeneous or heterogeneous oxidation catalyst.
• Copper ions for example, can be used as a homogeneous oxidation catalyst, as described in German patent application DE-A-197 55 350. If you want to avoid the presence of copper ions in the pickling solution, the divalent iron can be catalytically oxidized to the trivalent stage in an external fixed bed reactor with oxygen or air. Such a method is known from EP-A-795 628.
• the divalent iron can be directly or indirectly oxidized to the trivalent stage by electrochemical oxidation. Such a method is described, for example, in WO 00/15880 and in the literature cited there.
• the concentration of Fe (II) ions in the pickling solution depends on the operating state of the pickling solution. This concentration can be 0 for a freshly prepared pickling solution. It increases in the course of the pickling process, the increase being controlled by the oxidation of Fe (II) to Fe (III).
• the concentration of Fe (II) can increase up to 70 to 80 g / l. In practical tests with the pickling process according to the invention, Fe (II) concentrations in the range between 40 and 60 g / l were observed after one week of operation.
• the concentration of divalent and trivalent iron ions exceeds a limit value to be specified, which can be, for example, in the range from 90 to 110 g / l, it is advisable to drain part, for example 2/3, of the pickling solution and through fresh pickling solution which does not contain Fe ( ll) contains ion to replace. It is sufficient to add only the acids, since sufficient amounts of Fe (III) ions usually still remain in the solution. If necessary, some of the remaining Fe (II) ions can also be oxidized to Fe (III). As a result, the concentration of Fe (II) ions drops again, for example to a value in the range of 20 g / l.
• the pickling solution In the method according to the invention it can be preferred to move the pickling solution relative to the substrate surface, preferably by pumping around, stirring or blowing in air. This is particularly the case when the objects to be pickled are bundled or rolled up into bundles. Moving the pickling solution makes it easier to replace the pickling solution in narrow spaces between the surfaces to be pickled and thus leads to a uniform pickling result. This is particularly the case when the martensitic or ferritic stainless steel is in the form of wire, tubes or rods. The method according to the invention is particularly suitable for such substrates.
• the pickling solution can contain further auxiliaries or additives.
• auxiliaries or additives for example, in the case of oxidation with hydrogen peroxide, it is customary to add this in the form of a stabilized aqueous solution.
• stabilizer for H 2 O 2 gets into the pickling bath.
• This is known, for example, from the cited EP-A-582 121, where 8-hydroxyquinoline, sodium stannate, phosphoric acid, salicylic acid, pyridinecarboxylic acid and in particular phenacetin are mentioned as stabilizers.
• a particularly preferred stabilizer for H 2 O 2 is a mixture of phosphoric acid and glycol ether, as described for example in WO 01/49899.
• the pickling solution contains surface-active substances, in particular those of the nonionic type.
• examples include fatty alcohol ethoxylates or fatty alcohol ethoxylates / propoxylates.
• the C chain length of the fatty alcohols is preferably in the range between 8 and 22, in particular between 12 and 18.
• the pickling process according to the invention usually represents a partial step in the entire surface treatment sequence of the objects mentioned.
• This treatment sequence comprises a pre-treatment before the pickling that breaks up oxide deposits and a passivating after-treatment after the pickling step in order to keep the surfaces shiny metallic.
• the present invention also encompasses a process sequence for the surface treatment of martensitic or ferritic stainless steel, preferably objects in the form of wire, tubes or rods, the stainless steel being subjected to at least a) a treatment which breaks down oxidic deposits, preferably sand or shot blasting, one Treatment with a molten salt or treatment with an aqueous permanganate / alkali hydroxide solution, b) with the method according to one or more of claims 1 to 6, c) aftertreated with a passivation solution.
• steps a) and b) a pickling with a solution which contains one or more acids (HCl, H 2 SO 4 , HF).
• a solution which contains one or more acids HCl, H 2 SO 4 , HF.
• rinsing and / or neutralization steps are preferably provided between the individual treatment steps, which, however, can also be omitted immediately after radiation.
• Treatment a) which breaks up oxide coatings is common in the prior art prior to pickling treatment.
• the permanganate / alkali hydroxide solution mentioned is preferably a solution which contains 5 to 20% by weight of NaOH and 5 to 20% by weight of potassium permanganate. This solution preferably has a temperature in the range from 95 to 100.degree. If alkaline products are used for step a), neutralization is preferably provided before step b), for example by treating the substrate with dilute sulfuric acid. This can also be useful after radiation.
• the passivation solution for sub-step c) must have a redox potential which (under the same measurement conditions) is above the potential set in step b), for example in the range from about 600 to about 800 mV.
• a solution containing nitric acid, for example, is suitable for this purpose, but is less preferred for reasons of environmental protection.
• a passivation solution containing sulfuric acid and hydrogen peroxide can be used.
• the passivation solution preferably additionally contains a stabilizer for H 2 O 2 , for example a mixture of phosphoric acid and glycol ether according to WO 01/49899.
• the passivation solutions can additionally have low HF contents, for example in the range of 5 g / l.
• dark deposits that can form in the pickling step b) are simultaneously removed on the substrate surface.
• a sequence of processes according to the invention may look as follows: 1. Pretreatment with an aqueous solution, each containing 10 wt .-% NaOH and KMnO 4 and having a temperature of 95 ° C, for a treatment period of 20 minutes.
• Water rinse preferably as a high pressure spray rinse.
• Water rinse preferably as a spray rinse.
• suitable substrates can first be blasted in sub-step a).
• the pickling treatment is then carried out in sub-step b) at 28 ° C. for a period in the range from 5 to 10 minutes, followed by a water rinse and the passivation step c) as above under 9.

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

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• 2001
  • 2001-12-07 DE DE10160318A patent/DE10160318A1/de not_active Withdrawn
• 2002
  • 2002-11-28 ES ES02785414T patent/ES2367424T3/es not_active Expired - Lifetime
  • 2002-11-28 PT PT02785414T patent/PT1472388E/pt unknown
  • 2002-11-28 AT AT02785414T patent/ATE516386T1/de active
  • 2002-11-28 WO PCT/EP2002/013415 patent/WO2003048418A2/fr not_active Application Discontinuation
  • 2002-11-28 KR KR1020047008715A patent/KR100926924B1/ko not_active IP Right Cessation
  • 2002-11-28 EP EP02785414A patent/EP1472388B1/fr not_active Expired - Lifetime
• 2004
  • 2004-06-04 US US10/860,911 patent/US7229506B2/en not_active Expired - Fee Related

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