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
  • 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
  • C23C22/78—Pretreatment of the material to be coated

Definitions

• the present invention relates to a process for forming protective chemical coatings on the surfaces of metallic articles and more particularly relates to processes which are adapted to form phosphate or mixed phosphate-oxide coatings on ferrous surfaces.
• the primary object of the present invention is to provide a process for forming protective chemical coatings on metallic surfaces in a reduced period of time, which coatings exhibit superior corrosion resistance in comparison to that obtained with coatings produced by heretofore conventional procedures.
• Another object of the present invention is to provide a process for forming protective chemical coatings on ferrous surfaces which eliminate the necessity for utilizing conventional acidic pickling procedures prior to the formation of the protective chemical coating.
• Still another object of this invention is to provide a process which enables step-wise deformation operations to be performed on ferrous articles requiring annealing between successive drawing operations, with the minimum of additional steps in the formation of protective chemical coatings after each annealing step.
• the above and related objects may be accomplished by heating the metal article to be coated to a temperature in the range of 100 C. to 400 C. prior to contacting the same with the coating solution, and contacting the article to be coated in its heated con- ICC dition with the aqueous acidic phosphate solution.
• phosphate coating solutions at temperatures ranging from about 100 F. to about 200 F. and to immerse ar ticles to be coated in such solutions for about 5 to 10 minutes, it has been found that superior phosphate coatings may be formed in accordance with the method of the present invention after a contact period of about one minute.
• a low carbon steel having a light oxide coating induced from the atmosphere, was pickled to smoothness with an aqueous sulfuric acid solution (15% by 'volume), rinsed and pre-heated in hot water to C. and then introduced into an aqueous acidic zinc phosphate coating solution at a temperature of 95 C. and allowed to remain therein for 5 minutes.
• a portion of the same steel was heated to 200 C. and immersed in the same zinc phosphate coating solution in its heated condition and allowed to remain in the solution for 5 to 10 seconds.
• Both coated samples were treated with a chromic acid rinse and subjected to a salt spray mist of 3% sodium chloride for 20 hours and observed for rusting.
• the first sample was found to have 60% of its surface covered with a medium thickness of rust.
• the second sample was found to have only 40% of its surface covered with a very light coating of rust.
• the heating of the metallic article to be coated may be done in a mild oxidizing atmosphere if desired and the resultant coating which forms after contacting the oxide coated surface with the phosphate coating solution will evidence the improved corrosion resistance which is characteristic of this invention so long as the oxide coating which is originally induced is relatively thin, tightly adherent, and not the flaky oxide scale which is induced by oxidation for extended periods of time at elevated temperatures.
• oxide coatings may be formed intentionally in atmospheres containing controlled proportions of oxygen or in air, when both the time and temperature are regulated, or may inherently be present from a previous treatment such as a mild annealing or warm-rolling or coiling procedure.
• the article in air or a controlled oxidizing atmosphere, and then subjected to a reducing atmosphere to eliminate the scale and leave the metal surface in a metallicly clean condition, and if the temperature employed for the reducing atmosphere treatment is higher than 400 C., the article should be cooled below 400 C. in an inert atmosphere so that the metallicly clean surface Will be maintained clean.
• the article can then be contacted with the phosphate coating solution while at a temperature of C. to 400 C. to form the superior corrosion-resistant coatings of this invention.
• the particular phosphate coating solution which is selected for use in the process of this invention is not particularly important. Any aqueous acidic phosphate solution which is known to form a protective phosphate coating on metallic surfaces may be used, including zinc phosphate, manganese phosphate, iron phosphate and alkali metal phosphates. One of the most important end uses for the coatings of this invention is for the protection of the metal surface during metal deformation operations,
• a protecting phosphate coating in conjunction with a lubricant, which lubricant usually contains some fatty material.
• the present invention enables the utilization of such fatty material in forming an oxide coating by heating, in a controlled atmosphere where necessary, and eliminates the necessity for solvent removal of the fatty material and conventional pickling procedures prior to the formation of a new protective phosphate coating. All that is necessary is to oxidize the fatty material to a thin, tightly adherent oxide coating and introduce the oxide-coated article at a temperature of between 100 C. and 400 C. in the phosphate solution.
• the contact between the metal to be coated and the coating solution may be made by dipping the article in the solution or by spraying the solution on the article.
• the solution may be cold, at room temperature or preliminarily warmed. It is preferred that the article have a temperature between 200 C. and 300 C. when it is contacted with the phosphate coating solution since these conditions produce the most corrosion resistant coatings in the shortest periods of time.
• Example I Low carbon steel wire was annealed in air at temperatures of 200 C. and 400 C. and while at these temperatures was drawn through an aqueous zinc phosphate solution containing 22 grams/liter P205, 35 grams/liter NO: andl9.5 grams/liter zinc.
• other portions of the same wire were heated in air to 200 C. and 400 C. and allowed to cool.
• the same phosphate solution was heated to 95 C. and the cooled sections immersed therein for 5 minutes and withdrawn.
• the wires were then coated with the same rust resisting oil coating. All of the sections of wire were subjected to identical salt spray tests in 3% sodium chloride mist for hours and checked for corrosion.
• the wires treated in accordance with the method of this invention showed trace quantities of rust on about 40% of their surface.
• the wire sections treated by immersion for 5 minutes showed light rust over the entire surface and much heavier rust over about 40% of the surface.
• Example II Low carbon sheet steel having some fatty material on its surface was cleaned with trichloroethylene and dried.
• An aqueous zinc phosphate solution was prepared having 11.5 grams/liter Zinc, 14 grams/liter nitrate and 13 grams/liter P205 and the temperature of the solution was raised to 100 C. and the cleaned metal immersed in the heated solution for 5 minutes and withdrawn, the phosphate coated surface being then treated with oil.
• Another. portion of the same sheet metal was first wiped with trichloroethylene, then heated to above 450 C. in a controlled atmosphere furnace which contained a mild oxidizing atmosphere, and the oxidized surface was then treated in a reducing atmosphere of hydrogen at 450 C. until the surface became clean.
• the metal was then transferred to an inert atmosphere cooling chamber where the temperature was decreased to approximately 400 C. and the article was then immersed in the same aqueous phosphate solution as used before for one minute and withdrawn.
• the coated metal was then oiled in a manner similar to the oiling procedure used in connection with the article resulting from the 5 minute immersion. Both articles were then subjected to a salt spray test of 92 hours duration in a chamber employing a 3% sodium chloride fog spray for 15 minutes out of each hour.
• Example III An aqueous zinc phosphate solution was prepared containing 10 grams/liter P205, 27 grams/liter zinc and 6 grams/liter chlorate. Low carbon steel preliminarily degreased was immersed in this aqueous zinc phosphate solution at 100 C. for 5 minutes and withdrawn. Another portion of the same sheet steel was heated to 400 C. m a mild oxidizing atmosphere and at this temperature 1mmersed in the same solution for one minute and withdrawn. Without applying oil or otherwise treating the coating for the enhancement of the corrosion resistance, both portions of the coated steel were subjected to a 3% sodium chloride fog spray for a 3 hour period. At the end of this time, the immersion process portion of the sheet steel was found to be completely covered with a medium thickness layer of rust. The portion of the steel treated in accordance with the method of this invention was found to have 20% of its surface completely free of rust and the other covered with only a very light layer of rust.
• a method for forming a chemical protective coating on metallic surfaces which comprises the steps of heating the metallic surface in an oxidizing atmosphere to a temperature above 400 C. to form an oxide coating thereon, heating the oxide coated surface in a reducing atmosphere to remove the said oxide coating and form a metallicly clean surface, cooling said surface to a temperature in the range of C. to 400 C. in an inert atmosphere, and contacting the said article in heated condition with a phosphate coating solution for a time suiiicient to form a phosphate coating on said surface.
• a method for forming a chemical protective coating on ferrous surfaces which comprises the steps of heating the ferrous surface in an oxidizing atmosphere to a temperature above 400 C. to form an oxide coating thereon, heating the oxide coated surface in a reducing atmosphere to remove the said oxide coating and form a metallicly clean surface, cooling said surface to a temperature in the range of 200 C. to 300 C. in an inert atmosphere, and contacting the said article in heated condition with a phosphate coating solution for a time suflicient to form a phosphate coating on said surface.
• a method for forming a protective chemical coating on metallic surfaces which have previously been mechanically deformed which comprises the steps of heating the said surface to a temperature above 400 C. slowly cooling said surface in an oxidizing atmosphere to a temperature in the range of 100 C. to 400 C., and contacting the said surface while in the heated condition with an aqueous acidic phosphate solution for a time sufficient to form on said surface a coating which is at least partially a phosphate coating, and thereafter mechanically deforming said surface.
• a method for forming a protective chemical coating on ferrous surfaces which have previously been mechanically deformed which comprises the steps of heating the said surface to a temperature above 400 C. slowly cooling said surface in an oxidizing atmosphere to a temperature in the range of 200 C. to 300 C., and contacting the said surface while in the heated condition with an aqueous acidic phosphate solution for a time sufiicient to form on said surface a coating which is at least partially a phosphate coating, and thereafter mechanically deforming said surface.
• a method for forming a protective chemical coating on ferrous surfaces which comprises the steps of forming a phosphate coating on said surface, contacting said phosphate coated surface with a lubricant containing fatty material, mechanically deforming said surface, heating said mechanically deformed surface in an oxidizing atmosphere, and contacting the said re-heated surface with an aqueous acidic phosphate solution for a time suflicient to form on said surface a coating which is at least par tially a phosphate coating.

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• Chemical & Material Sciences (AREA)
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• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)

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• 1952
  • 1952-12-17 DE DEM16706A patent/DE1147819B/de active Pending
• 1953
  • 1953-12-11 US US397778A patent/US2813813A/en not_active Expired - Lifetime
  • 1953-12-16 FR FR64944D patent/FR64944E/fr not_active Expired

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