Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/38—Chromatising
• • 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
  • C23C22/24—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 hexavalent chromium compounds
• • 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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F17/00—Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25

Definitions

• the stainless steel is immersed inan aqueous solution of chromic acid which also contains sulphuric acid and," in the latter of these patents, also containing manganous sulfate.
• the coloring bath may contain CrO in an amount between 50 and 1,000 g/l. (grams per liter) of water, and canbe further acidified with sulfuric acid in amounts up to 600 g/l.
• a preferred ratio of the weights of Cr(), to sul-' fate ion added as sulfuric acid is from' about 100:1 to about 1:1, although in'some cases the ratiocan extend to 1:2.
• the bath temperature should be in the range from about room temperature up to about 100C., e.g.,
• a so-called terminal gold color can be. produced by immersion in the above-described solutions, e.g., a chromic acidsulfuric acid bath at a temperature of 65 to 75C. containing 520 g/l. to 580 g/l. of CrO, and a Cro -sulfate ion ratio of from 3:1 to 7 :1, which color is not changed by increasing the period of immersion. It is possible, however, to obtain. blue to red colored films from such terminal gold film by heat treating in air at a temperature of from 300 to 7000C.,
• the corrosion resistance of stainless steel is well known but nevertheless susceptible of improvement.
• Our main object in the invention is to improve this resistance.
• Another object is to improve the resistance of colored stainless steel to both corrosion and abrasion.
• a film is produced on the surface of stainless steel by treatment with an aqueous solution of chromic acid with or without other constitubred and uncolored (that is-to say, natural colored) steels are rendered more resistant to corrosion by the application of the'cathodic treatment and the resistance to abrasion of colored steels is muchimproved.
• Coloring may preferablybe achieved by'immersing the-stainless steel in a hot aqueous solution containing chromicand sulphuric acids, thecomposition and temperature range being as follows:
• the cathodic treatment of the film-bearing stainless steel is most advantageously carried out in an electrolyte containing 250 g/l. CrO, and 2.5 g/l. sulfuric acid at a temperature of 40C.
• the most advantageous current density is from 2.4 to 4.8 amp/dm.
• the period of treatment will then normally be from 4 to 15 minutes, e.g., from 7 to 10 minutes.
• the concentration of CrO is at least 25 gll.,' preferably from 100 to 750 g/l.
• sulfuric acid is broadly 0.1 to 100 g/l'., preferablyfrom l to 10 g/L
• the temperature may vary from 10 to about 100C., e.g., from 20 to C.
• the current density may be in the range 0.3 to 30 ampldm., preferably 0.6 to 10 amp/dm., e.g., from about 1 to 5 amp/dm.
• Both the coloring and hardening treatments can be carried out in lead-lined tanks heated by steam jackets, of the type used for conventional chromium plating. It is desirable to stir the coloring solution gently so as to maintain uniformity of temperature throughout it, but not to agitate either solution.
• the resistance to corrosion can be tested by the CASS test described in BS 4601/1970, Appendedix G, and various test panels have been subjected to this test.
• Panels of an l 8/8 chromium-nickel stainless steel polished to a mirror finish were colored blue by immersion in an aqueous solution containing 300 g/l. of CrO and 550 g/l. of sulfuric acid at 70C for 8 minutes. The blue films thus formed were removed from some of these after from 2 to 4 rubs.
• the other panels were then given cathodic hardening treatment in aqueous solutions containing various amounts of chromic acid under various conditions of temperature, time of exposure and current density. The color of the test panels was virtually unaffected by this treatment.
• the colored and hardened panels were then rubbed, the tests being stopped after 200 rubs. The results are shown in Table 3 below in which 200+ means that the coating had not failed at this stage.
• mechanically abraded steel surfaces preferably are employed to obtain an even color.
• the treated material can be bent, deep drawn and rigidized without cracking the film or reducing the color intensity of the deformed areas.
• the colored and hardened material has been bent through 90 without cracking or flaking the colored films orreducing the color intensity at the bent portion. Further, the material has been deep drawn to form a cup 35 mm. in diameter by 20 mm. deep without damaging the colored film. Colored and hardened panels have also been rigidized, by deforming them in a diamond pattern without cracking the film or reducing its color intensity.
• a process for improving the corrosion resistance of stainless steel and the abrasion resistance of an immersion coating thereon which comprises forming a coating on the steel surface by immersion in chromic acid and then electrolytically treating the coated stainless steel as a cathode in a chromic acid bath for 21 period of time not of sufficient duration to produce a visible chromium deposit on the surface, but of sufficient duration to harden the immersion coating.
• a process according to claim 1 wherein said electrolytic treatment comprises immersing the coated stainless steel as a cathode in a bath containing from about 25 to about 750 g/l. of chromic acid and 0.1 to 100 g/l. of sulfuric acid, maintaining the bath temperature from about 10 to about 100C., and passing current through the bath at a current density of from about 0.6 to about 10 A/dm for a period of at least one-half minute.
• the concentration of chromic acid is at least l00 g/l.
• the concentration of sulfuric acid is about 1 to 10 g/L
• the bath temperature is in the range from about 20 to about 80C.
• the current density is from about 1 to about 5 A/dm
• the time of treatment is from about 2 to about 30 minutes.
• the immersion coating is produced by immersion in an aqueous solution containing about 200 to about 400 g/l. chromic acid, about 350 to about 700 g/l. sulfuric acid, at atemperature of about 65 to about 80C. for a time of at least about 5 minutes.
• said aqueous solution contains about 300 g/l. chromic acid, about 550 g/l sulfuric acid and is used at a temperature of about C.
• a process according to claim 1 wherein the immersion coating is produced in an aqueous solution containing 50 to 1 ,000 g/l. chromic acid, up to 600 g/l. sulfuric acid and up to 50 g/l. manganous sulfate.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Mechanical Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Treatment Of Metals (AREA)
• Electroplating Methods And Accessories (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (2)

Family Applications After (1)

Country Status (13)

Cited By (4)

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Citations (11)

Family Cites Families (1)

• 1970
  • 1970-05-26 GB GB2521570A patent/GB1305636A/en not_active Expired
• 1971
  • 1971-02-10 US US00114357A patent/US3755117A/en not_active Expired - Lifetime
  • 1971-05-11 CA CA112,732A patent/CA1009605A/en not_active Expired
  • 1971-05-24 ES ES391488A patent/ES391488A1/es not_active Expired
  • 1971-05-25 FR FR7118913A patent/FR2090295B1/fr not_active Expired
  • 1971-05-25 NL NL717107126A patent/NL149556B/xx not_active IP Right Cessation
  • 1971-05-25 DK DK251971AA patent/DK135855B/da not_active IP Right Cessation
  • 1971-05-25 SE SE7106713A patent/SE382079B/xx unknown
  • 1971-05-25 NO NO01963/71A patent/NO130239B/no unknown
  • 1971-05-25 CH CH761771A patent/CH525287A/fr not_active IP Right Cessation
  • 1971-05-26 AT AT452471A patent/AT304986B/de not_active IP Right Cessation
  • 1971-05-26 BE BE767691A patent/BE767691A/fr not_active IP Right Cessation
  • 1971-05-26 JP JP3559871A patent/JPS5331817B1/ja active Pending
• 1972
  • 1972-05-11 US US00252459A patent/US3766023A/en not_active Expired - Lifetime
  • 1972-05-12 CA CA142,020A patent/CA1008401A/en not_active Expired

Patent Citations (11)

Non-Patent Citations (3)

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