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
  • C23G1/088—Iron or steel solutions containing organic acids
• • 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
  • 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
  • C23G1/28—Cleaning or pickling metallic material with solutions or molten salts with molten salts
  • C23G1/32—Heavy metals

Definitions

• the present invention relates to a process for surface treatment of stainless steel (pickling).
• pickling In this process, scale and tarnish in the area of welds and heat-treated surfaces are converted into corrosion-resistant oxide layers.
• the aim of this process is improved corrosion resistance without metal removal taking place.
• the stainless steel surface is treated with an aqueous or pasty solution / mixture.
• the mixture usually comprises a combination of complexing agents and an oxidizing agent.
• Stainless steel which is often referred to as stainless steel, is an iron alloy that can contain other elements such as nickel, molybdenum, titanium, copper and others in addition to iron and chromium.
• the chromium present in the alloy reacts with oxygen from the environment at the surface to form an oxide layer on the surface of the material.
• the resulting chromium oxide can reliably form a dense layer on the surface and thus protects the workpiece from corrosion.
• This protective layer is called a passive layer.
• Such a passive layer is usually about 10 molecule layers thick and contains not only chromium oxide but above all iron oxide in a concentration of 10 - 55 wt .-%. The lower the proportion of iron oxide in the passive layer, the higher its chemical resistance.
• a thermal treatment of stainless steel in an oxidizing atmosphere at temperatures above 200 ° C causes a progressive thermal oxidation of the material to form an oxide layer consisting essentially of oxides of in The alloy existing metals and their ratio to each other substantially corresponds to the ratio of metals in the alloy.
• the thermal oxide layers therefore contain up to about 87% by weight of iron oxides. These oxide layers increase in thickness with increasing temperature and treatment time and lead to discoloration up to black or gray coverings. These are known as tinder and temper colors.
• Such oxide layers which contain significantly more iron oxide than chromium oxide, are not resistant to corrosion, which is why the stainless steel in these areas is not sufficiently resistant to corrosion for general use.
• the iron oxide reacts with water to form iron hydroxide and forms rust.
• the mechanical methods have the disadvantage that the cleaning effect is not complete and sufficient and not reach hard to reach areas such as corners, gaps and cavities. Small and delicate workpieces are easily damaged.
• Electrolytic pickling uses aqueous mixtures of mineral acids which, under the action of direct current, lead to anodic removal of the uppermost metal layer by electrochemical dissolution, wherein the overlying oxide layers are also removed. These methods can only be used with thin oxide layers that are permeable to DC and electrolyte. Furthermore, they require a lot of effort in terms of plant technology. They work with hazardous substances which also waste water containing heavy metals, which must be treated and disposed of consuming.
• Chemical pickling chemically dissolves the oxide layers and the metal of the topmost material layer, creating a metallically clean surface. On top of this, a homogeneous passive layer can be formed which effectively protects the material from corrosion. Chemical pickling allows treatment of the entire surface of workpieces, including hard-to-reach areas. The disadvantage is the fact that the dissolution of the oxides and the Material extremely aggressive and dangerous chemicals are required, which pose a high risk to humans and the environment.
• Hydrofluoric acid or fluorides of salts of hydrofluoric acid, which form hydrofluoric acid in aqueous solution, and also oxidants such as nitric acid or hydrogen peroxide.
• Hydrofluoric acid is extremely poisonous and can lead to death even with relatively little skin contact. Nitric acid releases toxic nitrous gases during pickling, which have a strong lung damaging effect.
• Hydrofluoric acid and nitric acid are gassing acids, which is why the air in the working environment has to be sucked off and treated separately.
• the personnel employed for chemical pickling must wear appropriate protective clothing and, where appropriate, respiratory protection and is subject to constant medical supervision.
• the manufacture, transportation, storage and use of chemicals used for chemical pickling are subject to strict safety regulations.
• the wastewater produced by chemical pickling contains in a high concentration the acids contained in the pickle as well as the heavy metals contained in the alloy such as chromium, iron, nickel and molybdenum. For disposal, they must be chemically treated and the resulting solids disposed of as hazardous waste. Used pickling solutions are to be disposed of as hazardous waste.
• the subject of the present invention is a chemical pickling process for stainless steel which is harmless to humans and the environment and in terms of achievable corrosion resistance of the method according to the prior art at least equivalent, but in many cases clearly superior.
• the present invention selects a new, previously unused path to solve the problem:
• the invention is based on the idea that it is basically not necessary to eliminate the existing thermal oxide layers. Instead, it is also sufficient to reduce the concentration of iron oxides in the thermal oxide layers so far that the thermal oxide layers result in a concentration ratio of chromium oxides to iron oxides, which corresponds at least to that of intact passive layers.
• an agent is needed whose chemical affinity is more selective to iron than the affinity of iron for oxygen. This makes it possible that the iron oxides are split. The iron can then be selectively removed from the thermal oxide layers.
• an aqueous solution having a specific combination of organic complexing agents in combination with an oxidizing agent has these sought-after properties.
• the process according to the invention makes it possible selectively to remove the iron from all oxidation states of the iron, with the exception of hematite.
• hematite is chemically sufficiently stable even under corrosive conditions so that residual hematite residues have no negative impact on the corrosion resistance of stainless steel.
• the invention thus provides a process for surface treatment of stainless steel, in which the thermal oxide layers are brought into contact with a composition which causes a selective dissolution of iron ions from the oxide layer.
• Thermal oxide layers in the context of the invention are scale and tarnish as they usually occur in thermal treatment or in the welding of stainless steels. These surface layers are regularly recognized by the fact that they lead to a discoloration of the surface. The surface may then have a straw-yellow coloration, but may, depending on the duration and intensity of the thermal treatment of the surface, even in brown and blue shades.
• tempering in the case of high-alloyed steels, the following tempering colors and layer thicknesses are regularly observed at a tempering (elevated temperature) of about 350 ° C. to> 1200 ° C.
• the chemical composition of the solution or mixture used according to the invention is now selected such that on the one hand there is no measurable erosion of the surface, but on the other hand a dissolution of the iron ions takes place from the surface.
• the method according to the invention thus behaves like a pickling method, wherein, in contrast to pickling according to the prior art, the thermal oxide layers are not detached. Therefore, it is also possible according to the invention to use such mixtures which do not entail the disadvantages of the pickling baths used in the prior art.
• the dissolution of the iron ions from the surface preferably takes place selectively.
• selective herein is meant that the complexing agent for iron has a stronger affinity (that is, stronger complex formation) than the other components in the thermal oxide layers (eg, chromium or nickel).
• the solutions / mixtures according to the invention comprise a combination of a complexing agent for iron and an oxidizing agent.
• the complexing agent is usually such a compound that can complex iron ions in aqueous solution.
• hydroxycarboxylic acids, phosphonic acids and organic nitrosulfonic acids can be used as complexing agents.
• the preferred complexing agents are multidentate complexing agents. These multidentate complexing agents can form chelate complexes with iron ions. This makes it possible to increase the ratio of chromium oxide to iron oxide in the thermal oxide layers.
• suitable complexing agents furthermore include hydroxycarboxylic acid, which have 1, 2 or 3 hydroxyl groups and 1, 2 or 3 carboxyl groups or their salts.
• a particularly suitable hydroxycarboxylic acid is citric acid.
• Another suitable complexing agent is the phosphonic acid having the general formula R'-PO (OH) 2 , where R 'is a monovalent alkyl, hydroxyalkyl or aminoalkyl radical.
• Diphosphonic acid of the general formula R "[- PO (OH) 2 ] 2 can also be used according to the invention, where R" is a divalent alkyl, hydroxyalkyl or aminoalkyl radical.
• phosphonic acids and / or diphosphonic acids it is also possible to use one or more salts of these phosphonic acids or diphosphonic acids.
• a particularly preferred example of such an acid is 1-hydroxyethane-1,1-diphosphonic acid (HEDP) or its salt.
• HEDP 1-hydroxyethane-1,1-diphosphonic acid
• suitable complexing agents are the organic nitrosulfonic acids, for example nitroalkylsulfonic acids, nitroarylsulfonic acids or salts thereof.
• a particularly preferred nitroarylsulfonic acid is meta-nitrobenzenesulfonic acid.
• the substituted or unsubstituted alkyl or aryl radicals used should be selected such that the acid or salt has sufficient solubility in the aqueous solution / mixture. Therefore, a hydrocarbon chain preferably has not more than twelve carbon atoms.
• compositions of the invention may additionally contain oxidizing agents.
• Suitable oxidizing agents are, for example, nitrates, peroxo compounds, iodates and cerium (IV) compounds in the form of the respective acids or water-soluble salts.
• peroxo compounds are peroxides, persulfates, perborates or percarboxylates such as peracetate.
• the oxidizing agents may be used alone or in the form of mixtures.
• an iron alloy containing a considerable proportion for example, about 13 wt .-% and more chromium.
• the solutions / mixtures according to the invention may additionally comprise one or more wetting agents which reduce the surface tension of the aqueous compositions.
• suitable wetting agents are already around nitroalkyl or nitroarylsulfonic acids described in connection with complexing agents, or also alkylglycols of the general formula H- (O-CHR-CH 2 ) n -OH, where R is hydrogen or an alkyl radical having 1, 2 or 3 carbon atoms, and n is preferably is an integer between 1 and 5, for example 2 or 3.
• compositions may be added in these compositions in a concentration between 0.02 and 2.0% by weight, preferably between 0.05 and 1.0% by weight.
• these compositions may optionally contain one or more thickening agents. Suitable thickeners are, for example, methyl cellulose and kieselguhr. Such a thickener serves to increase the viscosity of the mixture.
• the inventive method is carried out regularly at a temperature between room temperature and 95 ° C. But there are also other temperatures conceivable, while it must always be ensured that there is no significant removal of the treated thermal oxide layers.
• the surface treatment according to the invention is usually carried out over a period of time which can be between 1 and 7 hours.
• the stainless steel surface is rinsed regularly, usually with deionized water rinse.
• the pickling process can be carried out as a liquid by spraying, trickling, wiping or - slightly thickened by a suitable thickener (methylcellulose) - as spreadable paste in the dipping bath or by applying to the surfaces to be cleaned.
• a suitable thickener methylcellulose
• the application temperature is in the immersion bath. preferably 50 ° C to 95 ° C, preferably 50 ° C to 70 ° C.
• the pickling time is 3 to 5 hours depending on the degree of scaling, the alloying and the applied temperature. At lower temperatures, the exposure time may be longer. Temperatures below 50 ° C are only used in applications outside the bath. The temperature of the immersion baths should at least be permanently 50 ° C in order to avoid biological degradation of the pickling liquid.
• the present invention therefore also relates to the use of a complexing agent for iron-containing composition which is substantially free of hydrofluoric acid and / or fluoride ions and other halide ions and mineral acids for surface treatment of a stainless steel workpiece, this surface having thermal oxide layers ,
• the other constituents of the composition and the procedure for the surface treatment the prerequisites and features previously established and specified for the method apply.
• substantially free of hydrofluoric acid and / or fluoride ions means that the composition contains, for example, not hydrofluoric acid in a proportion as it is present in conventional mordants. Preferably, however, the composition is completely free of hydrofluoric acid. Usually, the composition also contains virtually no mineral acids.

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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)
• Chemical Treatment Of Metals (AREA)

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• 2008
  • 2008-10-29 EP EP08018874A patent/EP2182095A1/fr not_active Withdrawn
• 2009
  • 2009-10-15 US US13/126,827 patent/US9115433B2/en not_active Expired - Fee Related
  • 2009-10-15 AU AU2009310094A patent/AU2009310094A1/en not_active Abandoned
  • 2009-10-15 JP JP2011533578A patent/JP5586614B2/ja not_active Expired - Fee Related
  • 2009-10-15 WO PCT/EP2009/007402 patent/WO2010049065A1/fr active Application Filing
  • 2009-10-15 CA CA2741704A patent/CA2741704A1/fr not_active Abandoned
  • 2009-10-15 EP EP09737363.3A patent/EP2352860B1/fr not_active Not-in-force
  • 2009-10-15 ES ES09737363.3T patent/ES2559387T3/es active Active
  • 2009-10-15 HU HUE09737363A patent/HUE026531T2/en unknown

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