Copper coated steel

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United States Patent Office 3,311,458 Patented Mar. 28, 1967

3,311,458 non-metallic coatings have lower heat transfer coefficients COPPER COATED STEEL than metals and coefficients of thermal expansion which Calvin A. Schunemann, Gates Mills, Ohio, assignor to differ substantially from that of the base metal (so as to Horizons Incorporated, Cleveland, Ohio, a corporation produce mechanical failure of the coating based on such of New Jersey differences) but in many cases the corrosion resistance No Drawing. Filled July 19, 1963, Ser. No. 296,385 under the wide variety of conditions normally encountered 3 Claims. (CI. 29-183.5) in service is poor, even though fully coated by the non metallics in question.

This invention relates to a novel composition of mat In certain installations, pure copper or copper nickel ter involving copper coated steel and to a process for O alloy producing corrosion resistant articles of such materials. tubingtubing composed is utilized since it has been found that the of Such metals or alloys amply with

Ordinary steel, such as the grades normally produced stands the various corrosive conditions encountered in in the basic open hearth process, (e.g. SAE 1020) is one Service. As a consequence, many attempts have been of the most versatile and economical of structural ma made to reduce the cost of manufacture of such structural terials possessing high strength, hot and cold working 5 components, particularly tubing, by applying coatings of properties, and many other properties which make it copper or alloys of copper and nickel to a metallic base suitable for forming into a diversity of useful shapes in material such as steel.

cluding structural beams, angles, sheet, tubs and tubes. Deposition of such metal coatings have been effected by Unfortunately, the corrosion resistance of these articles spraying, electrolysis, dipping and by many other known is mediocre, if not poor, particularly when they are ex 20 coating methods, each of which possesses its own ad posed to specific environments. Pure alpha iron in sheet vantages and disadvantages. In the fabrication of heat form, not normally designated as a steel, exhibits the un exchanger tubes and refrigerator heat exchanger coils, the usual facility for drastic cold working such as deep potential advantages of a suitably prepared copper coat drawing and spinning and thus such type of relatively ing deposited over the base metal have been recognized pure sheet iron possesses a wide utility for the manufac 25 for a long time and certain phenomea which limit the ture of a variety of home appliances. Again, its corro sion resistance is very poor, particularly in the presence the art. The problem coatings usefulness of copper

have also been noted in application of such copper con of moist air.

A most stringent requirement for protection against taining coatings to the inside of small bore tubing aggra vate the limitations of both material and process when corrosion exists in the form of tubular products which may 30 complete corrosion resistance is required. be utilized for hot water systems in the home, for the Two basic processes have been considered most suit manufacture of hot water heaters, for heat exchange able for the application of copper or copper containing tubing involving water or other liquids, for refrigerator alloys to the internal surfaces of a tubular structure, these or dehumidifying purposes, and in the boiler industry being electrolysis and hot dipping in a flux comprising where the water may be required to operate at elevated chiefly temperatures and pressures in the presence of dissolved duction at an elevated temperature. Infollowed a copper containing compound a tube

whose air. In applications such as those just listed the corro length may be considered substantially infinite with re sion problem is aggravated by the conditions of use and spect to its diameter the problems and difficulties inherent by the types of waters utilized in these structures. For in applying a sufficiently thick coating at a sufficiently example, hard water containing significant amounts of 40 high rate of speed to the interior of small bore tubing by dissolved air, chlorides, sulfates, and compounds of alkali electrolysis are obvious. As a matter of fact, the only metals and alkaline earth metals usually as carbonates or electrolytic procedure which appears to have been found bicarbonates is generally more drastic in its corrosive ac practical is the application of a copper plate by elec tion than distilled or chemically pure water. In many trolysis to a flat sheet of steel which is then subsequently cases, chemically pure water at an elevated temperature rolled or otherwise formed into a tube. By virtue of the containing insignificant amounts of dissolved carbon di Subsequent forming procedures required this approach is oxide represents a corrosive agent. All of these actions expensive. In addition, defects are commonly encoun are still further aggravated if these impure waters are utilized in any portion of their cycling in the presence tered such as the presence of pin-holes or other discon tinuities in the copper layer as the result of uneven elec of air. In some situations the rate of corrosion increases 50 by orders of magnitude in the presence of air as com trodeposition

Quite often or improper cleaning of the base material.

the bond between the electroplate and the pared with the rate of corrosion in the absence of air. base is poor and the variation of thermal expansion is One common expedient used to provide corrosion re sufficient to lift off whole sections of copper plate so as sistance is to alloy the steel with large amounts of nickel to expose the bare poorly corrosion resistant base ma and/or chromium and other expensive metals, to produce 5 5 terials. A single minute pinhole in an entire length of the commonly known stainless steels. Alloying in this tubing permits the possibility for the setting up of a gal manner is a costly procedure and must be carefully con vanic couple and the less noble metal in the pair (such trolled in order to obtain the desired analysis and a specif as the base iron) becomes rapidly eroded, leading to fail ic balancing of properties since some elements which are lure of the article.

beneficial in one or more respects are harmful in other 60 A large number of variations of the second method Ways.

Another commonly practiced art is to place a coating involving dipping of the base article in a molten salt of metal, alloy or non-metallic material over an inex containing copper have been described. This technique would be expected to exhibit the signal advantage over pensive base metal to produce a composite with enhanced electrolysis corrosion resistance as compared with the corrosion re that the interior of small bore tubing may be sistance of the bare base metal. Non-metallic coating coated readily by the method and in addition the dis materials, including resin, paint or other organic or ce continuity and pinhole defect in the original coating com ramic coating materials are undesirable where the end use mon in electrolytically applied coatings would also be ex involves heat transfer through the coated material or pected to be absent. In examination of the articles pro duced in accordance with numerous prior art proposals where the end use involves exposure to temperatures which 70 however, cycle or vary over relatively wide ranges such as may be it was found that though the coatings were uni encountered in a boiler or evaporator. Not only do these form and pinhole free they do not exhibit the desired degree of corrosion resistance. As a matter of fact, in

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some instances the corrosion resistance of the coated ar The corrosion resistance of samples prepared by dipping ticles is actually poorer than the corrosion resistance of with or without subsequent treatment in hydrogen at tem the base metal to which such a coating is applied. peratures above the melting point of copper was some In general, these electrodeless types of copper plating what improved as compared with cemented samples, but utilize variations of a basic approach. In one variation 5 failure of the coating occurred in every instance. Ex an oxide of copper or a halide of copper or mixtures perience with this test indicated that though the purplish thereof are dispersed in organic resin, applied to the sur brown stain developed rapidly in every test without ex faces as paint and then heated to a temperature sufficient ception irrespective of method of application, the time re to remove the organic portions of the compositions and quired for complete destruction of the piece appeared to cement the residual copper to the base steel, either in 0 to be a function of the rate of growth of the grayish the presence or absence of a reducing gas such as hydro brown oxide and its time of emergence so that it would be gen. In another variation, a molten salt bath is pro readily visible. This time of emergence of the grayish vided containing cuprous chloride as the principal con brown oxide varied from a few hours up to about 1 week stituent sometimes diluted with other compatible salts. and generally destructive corrosion was experienced with The steel article is dipped in the molten salt bath and the 5 in about 1 week after the grayish brown oxide was first cementation of copper completed either by retaining the observed.

base article in the molten bath for a sufficient period of The results of this examination of the teachings of the time or by removing the article from the bath and subse prior art appear to establish that none of the compositions quently reducing the composition with hydrogen. Still of matter and techniques utilized for the applications of further variation involves organic compounds of copper 20 such compositions of matter are adequate for developing utilized in molten form in which the electrodeless depo sufficient corrosion resistance for withstanding prolonged sition was carried out below the decomposition point of exposure to boiling water of commercial or municipal the copper organic mixture. grade in the presence of dissolved air. While the test In order to determine the effectiveness of corrosion re utilized may be considered rigorous it does provide a sistant copper containing coatings on steel structures ca means of evaluation and comparison which relates closely pable of withstanding the rigors of modern requirements to the conditions which may be encountered in the field. involving boiling water containing air, a test procedure To establish that the poor corrosion resistance of the was established for evaluation purposes. A municipal copper plated articles described in the prior art is not a chlorinated potable water was utilized and its hardness function of copper or copper nickel alloys themselves, modified to contain 69 grains of hardness by adding equal 30 similar tests were carried out with pure oxygen free copper amounts of calcium and magnesium carbonate. The re tubing and sheet, and pure Monel tubing and sheet. In Sulting modified municipal water contained the anticipated these tests, neither the purplish discoloration, nor the for impurities considered normal for potable water such as mation of the grayish brown oxide was observed and in calcium, magnesium, sodium and minute amounts of iron, each case both the pure copper specimens and the copper Sulfate, nitrate and chloride. The specimens containing 35 nickel alloy specimens withstood the test for the full 6 their cladding of copper or copper containing alloy were weeks period without any microscopic or macroscopic placed in a flask half filled with such water. Then the evidence of erosion, corrosion or destruction except for flask was connected to a reflux condenser. The system a very slight dulling of the original bright surface. It was brought to boiling and air was bubbled continuously was noted however that if the pure copper contained oxy through the solution in contact with the plated specimen 40 gen the purplish discoloration developed rapidly but the to replace air which might be removed by boiling. The gray brown oxide formation never developed. water was changed every 24 hours. These tests were con It is therefore a primary object of this invention to pro tinued for periods of 6 to 12 weeks and examined criti vide steel or iron tubing in which a thin layer of a metal cally each 24 hours. lic copper or a copper alloy-containing composition is In utilization of such test and applying copper or copper 45 present as a coating on the base metal, in which this alloy coatings to steel sheet stock comprised of SAE 1020 metallic copper or copper alloy composition represents all of the coatings prepared in accordance with prior art a novel composition of matter, and in which the resulti electrolytic or molten salt dipping procedures failed in the ing composite is completely corrosion resistant within corrosion test by exhibiting one or more aspects of ero the context of the test procedures described previously sion or corrosion of destructive character. In every in 50 and possesses the same degree of corrosion resistance stance an unsightly purplish tarnish stain developed on exhibited by chemically pure oxygen free copper metal each of the surfaces irrespective of the method of coating or copper alloys originally designed for corrosion re within the first 2 or 3 hours of submission to the test and sistant purposes.

the amount and thickness of this stain continued to in It is a further object of this invention to supply a proc crease as the test proceeded. In addition, and in the ma 5 5 ess which permits the proper application of the novel jority of cases a grayish brown film, obviously oxidic in coating described in the previous sentence so that small character, continued to grow at a steady rate from the bore tubing whose length may be considered infinite with Surface. In every instance in a period of about a week respect to the diameter of the tubing may be coated either the erosion had proceeded through the copper plating and on the inside or on the outside of the tubing on a con into the base metal and in each case where such an ero 60 tinuous basis in a manner depending on the eventual sion of the coating had been completed, the base material application of the procedure.

was eroded away underneath this area and beyond the It is a further object of this invention to define tech site of initial erosion to the point where it would be con niques whereby strip material in flat form comprised of sidered that an article made of such a composite and steel or alpha iron may be coated with the novel com utilized under similar service conditions would last at position of this invention so that corrosion resistance best 2 to 4 weeks before perforating completely. For under the conditions defined previously is complete for practical purposes.

prior art coatings in which the copper coating was ce It is another object of this invention to define novel mented on to the steel base at temperatures below the products which may be laid over welds in a steel or iron melting point of copper, the cycle of destructive processes structure so that the corrosion resistance over such welds defined in the foregoing was accelerated and in some may be equally as complete as that defined for an un tests the emergence of the grayish brown oxide coating welded structure.

and the purplish brown stain developed simultaneously. It is a principal object of this invention to provide . When this phenomenon occurred rapidly, the final destruc a low cost corrosion proof piping suitable for use in tion of the piece was equally rapid. hot water systems or refrigerator systems whether oper

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able at atmospheric pressures or above, in the presence a comparable cobalt salt. The application of nickel of commercial and potable waters and in contact with and/or cobalt flashing on the surface results in the im

provement of corrosion resistance of the overall coating

These and other objects are achieved by the practice but is not alsoluetly necessary, nor is the drastic pickling of this invention as defined in the following description. procedure followed by wire brushing necessary, although The invention comprises a novel composition of matter it too is preferred.

preferably in the form of a coating which is corrosion Whether or not the steel or iron surface has been pro proof against boiling hot water in the presence of air, vided with an electrodeless coating of nickel or a com said composition comprising a combination of metallic bination of nickel and cobalt and whether or not the copper, cuprous oxide, metallic nickel and/or metallic O surface has been previously cleaned by the drastic hydro cobalt and metallic iron; such coating being at least .3 chloric acid treatment described above, the articles are mill in thickness. then immersed for 1 minute in a molten salt bath in Another aspect of the invention comprises a fused air, said molten salt bath being maintained at 450° C. coating bath consisting essentially of cuprous chloride A mixture of air and steam may be bubbled through the and containing up to 10% cuprous oxide, with or with Salt bath. After the specified immersion the article is out the addition of 2 to 10% of a hydrated chloride removed and allowed to air cool. A suitable salt bath selected from the group consisting of hydrated nickelic consisted of a mixture containing 2.5% cuprous oxide, chloride (NiCl3.6H2O) and hydrated cobaltic chloride 5.0% of hydrated nickelic chloride, and the balance (CoCl3.6H2O) and mixtures thereof. cuprous chloride. The cuprous oxide content may be The process in which said coating and said bath are 20 varied between 2 and 10% and the hydrated nickel utilized comprises the following sequence of steps: chloride content may be varied between 2 and 10%. (a) Surface preparation (optional) e.g. cleaning (de The lower percentages in the ranges are preferred. Under grease, pickle, wash, dry). conditions where purplish discoloration is not considered (b) Undercoating with metallic nickel or cobalt (op a disadvantage, the nickel salts may be omitted from the tional) e.g. by immersion of iron or steel article in dilute 25 salt bath. The hydrated nickel chloride may be replaced solution of nickel borosulfate at pH 4.5-5.5. in whole or in part by the equivalent cobalt salt, namely, (c) Salt bath coating by dipping into molten salt cobalt chloride hexahydrate and equivalent results are bath at 450° C. for fraction of a minute. achieved.

(d) Heating in hydrogen atmosphere at about 1100 The coating of small pieces may be accomplished simply C. with controlled preheating and subsequent heating. 30 by dipping. In the coating of tube stock where it is In summary, a coating consisting chiefly of metallic desired to coat only the interior, the steel tube stock is copper is applied to a base iron or steel surface from a initially heated in air to a temperature of 450° C. and molten salt bath containing halides and oxides of copper the molten salt also at a temperature of 450° C. is poured with or without hydrated salts of nickel and cobalt; there into the tube and the tube allowed to drain. In the case after the article containing the fused salt coating is heat where both the interior and exterior of the tube is to be treated in hydrogen at a temperature above the melting coated, the tube stock is pulled through a bath of the point of copper for a brief period of time for cementa molten salt at a temperature of 450° C. so that both the tion purposes; the heat treatment is continued at tem interior and exterior surface of the tube are completely peratures below the eutectic temperature of copper and bathed in the molten salt and reeled in such a manner iron which latter is of the order of 835° C. such heat 40 that complete drainage is achieved. On a continuous treatment being carried out in the presence of hydrogen; basis such tube stock is then maintained at a temperature whereby the base is coated with a coating of at least 0.3 of 1100 C. in an atmosphere of flowing clean hydrogen mil in cross section, the exterior of which is oxygen-free in a conventional atmosphere controlled furnace, and as a consequence of the hydrogen treatment below the each portion of the strip or tube is retained at this tem eutectic temperature of the copper iron alloy preliminarily perature in the atmosphere of clean hydrogen for a formed; and the material at the base of the coating, at period of 1 minute. The normal time required to heat tached to the iron, contains Sufficient oxygen to provide the tube or strip stock to the treatment temperature of an oxygen content of at least 0.1% and preferably in the 1100° C. is 15 seconds. Thereafter, and while still in the range of 0.2 to 0.6%; and wherein the resulting article flowing hydrogen atmosphere, the tube or strip is passed may or may not have nickel or an alloy of nickel and 50 into a Zone maintained at 700° C. and retained therein cobalt as a binding layer between the copper contain for a period of 2 minutes after which the tube or strip ing coating and iron or steel base. is allowed to cool to room temperature in a hydrogen In a preferred procedure, the iron or steel articles are atmosphere for an additional 3 minutes and finally re first pickled in a 1 to 1 hydrochloric acid solution at moved from the furnace.

180° C. for 1 minute. To obtain the best cleaning the In order for the surface to exhibit the desired total acid pickled material is wire brushed and repickled for corrosion resistance equivalent to that of pure metallic 1 minute at 180° F. after which the articles are rinsed in copper, the thickness of coating on the base steel must hot water, then dipped in alcohol and then dried at be a minimum of 0.3 mill and not thicker than 0.6 mil. room temeprature. This complicated pickling proce It has been established that the presence of between dure is required only if a nickel or nickel-cobalt flash is 60 2 and 10% of cuprous oxide in the salt bath is an essential applied to the surface prior to the application of the requirement for achieving this thickness. In the absence copper containing coating. of cuprous oxide from the bath the effect of nickel in the The nickel flash which is placed on the iron or steel coating is somewhat minimal.

surface by electrodeless techniques is deposited simply by The gray brown oxide coating which develops on dipping the articles in a solution containing nickel and/or 65 corrosion testing in the water defined previously is more cobalt salts buffered with boric acid at a suitable pH properly designated as "iron breakthrough.” This iron for specific times and temperatures. In one instance, breakthrough represents a certain aspect of destruction. the Solution consisted of one gallon of water plus eight The combination of hydrogen reduction below the first ounces of hydrated nickelous chloride of composition eutectic temperature plus the presence of nickel prevents NiCl2.6H2O, plus boric acid. The plating solution is 70 not only the formation of the purplish overcast but also maintained at a temperature of 160 F. The wire-brushed prevents the initiation of iron breakthrough. acid-pickled articles are immersed in such a bath for 1% The complete elimination of all evidences of corrosion minutes, water rinsed and alcohol rinsed and air dried. Was achieved only when nickel chloride or cobalt chloride Nickel sulfates may be used in place of nickel chloride was added to the mixture of cuprous chloride and cuprous and a portion of the nickel chloride may be replaced with oxide. In the presence of the cuprous oxide and in ac

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cordance with the preferred process a coating thickness water in contact with the specimen. At the end of 6 weeks the bright original surface was still retained with of 0.4 to 0.5 mill was regularly obtained, no purple tarnish no evidence of corrosion or tarnish. was ever observed, and the iron breakthrough was elimi nated entirely. For all practical purposes, the corrosion EXAMPLE II resistance under the boiling water aerated test appeared The compositions and techniques defined in Example I to be permanent. A slight dulling of the surface did were again utilized except that the welded specimen was develop after 6 weeks. When the combination of cuprous given no treatment whatsoever prior to immersion in the chloride, cuprous oxide and post reduction at 700 C. molten cuprous chloride-cuprous oxide-nickel chloride for 2 minutes to remove exposed cuprous oxide was salt bath at 450° C. After the treatment was complete utilized even this dulling was eliminated. O it was found that the copper coating had flowed under the

As pointed out previously, drastic acid pickling and oxide coating covering the steel and the Weld and that nickel flashing represents an advantage but these are not the oxide coating adhered to the outer surface of the cop required to produce commercially acceptable results. The per. Wire brushing removed the oxide coating exposing coating bath itself in the low temperature immersion stage a bright shiny surface again and corrosion testing of such evidently is a drastic pickling operation and the effective 5 bright exposed surface under the conditions previously ness of its utility is evidenced by the fact that it works defined demonstrated that protection was complete. In equally well across flat surfaces as it does across weld a variation of this example the oxide coating was not ments. In order to establish the effectiveness of the addition of nickel and cobalt to the coating itself samples removed by a wire brushing but was found to be substan of pure copper which contained proportions of cuprous tially all removed by the turbulent action of the boiling oxide in its composition were subjected to the boiling water in the corrosion test.

water test and again the purplish discoloration previously EXAMPLE III described was obtained. The effect of the addition of A sheet of SAE 1020 steel was pickled in 1 to 1 hydro nickel on the elimination of such purplish discoloration chloric acid at 180° F. for 1 minute, after which the was dramatic. specimen was water rinsed, alcohol dipped and dried at In order to establish the chemical composition of the room temperature. A nickel flash was then applied by coating which defines one aspect of this invention an immersing such pickled and clean sample in a bath con immersion was made in a bath containing 92.5% cuprous taining 8 oz. per gallon of nickel chloride hexahydrate chloride, 5.0% nickelic chloride hexahydrate and 2.5% cuprous oxide. After treatment in hydrogen through the 30 and 160 5% oz. per gallon of boric acid at a temperature of

F. for 90 seconds after which it was water rinsed, preferred temperature cycling an analysis of this coating alcohol rinsed and air dried. This specimen was then showed that it contained 1.43% nickel, 3.26% iron and immersed in a molten salt bath comprising 92.5 parts of 0.38% oxygen, the balance being copper. anhydrous cuprous chloride, 2.5 parts of red copper oxide It was found that in order to achieve the desired thick and maintained at a temperature of 450° C. in air for a ness of coating through the addition of cuprous oxide in period of 1 minute and then allowed to air cool. There the first immersion bath that the final coating must con after, the specimen was treated in a hydrogen atmosphere tain an average of at least 0.1% oxygen and preferably through the 1100° C. and 700° C. cycle previously de from 0.2 to 0.6% oxygen in order to produce the desired scribed. Corrosion testing showed no evidence of iron results while still maintaining a useful degree of flexibility for working the finished product without delamination 40 breakthrough the coating and no purple tarnish and measurement of thickness indicated that a coating of the order of the coating from the surface. of 0.4 to 0.5 mill had been achieved. After the corrosion The following specific examples will serve to illustrate testing was carried out for a period of 12 weeks the for the invention and are not intended to be taken as limita mation of purple tarnish started to become evident. tive.

EXAMPLE I EXAMPLE IV

A steel specimen comprising two sections joined to The same as in Example III except the iron base in the gether by a weldment was first immersed in a 1 to 1 preliminarily pickled condition was utilized without the hydrochloric acid solution for 2 minutes at 180° F. and nickel immersion coating. Again, the sample withstood then wire brushed to remove any oxide not removed by 50 the corrosion test conditions without any major defect except for the emergence of purple tarnish in the 4th the acid pickle. After water washing and alcohol rinsing Week of corrosion testing.

and drying the steel specimen containing the weldment was immersed in a molten salt bath comprising a mixture EXAMPLE V of 92.5 parts of anhydrous cuprous chloride, 2.5 parts A pure iron base without nickel flashing was utilized of red cuprous oxide, and 5.0 parts of nickel chloride and the molten salt bath was comprised of 90 parts of hexahydrate melted and maintained at 450° C. Im 55 anhydrous cuprous chloride, 5 parts of red copper oxide mersion was for a period of 1 minute after which the and 5 parts of nickelic chloride hexahydrate. By fol specimen was removed and allowed to cool to room lowing the heat treatment and immersion described in temperature. The specimens were then suspended verti Example I, a coating thickness of 0.5 mill was attained. cally in a hydrogen atmosphere and brought to a tem The specimen was subjected to corrosion testing and no perature of 1100° C. over a time period of 15 seconds and 60 maintained at this temperature for 1 minute. The tem evidence of either iron breakthrough or purplish tarnish perature was thereafter lowered to 700 C. by reducing was obtained after 12 weeks of corrosion testing. the power input to the induction heater. The specimens EXAMPLE VI were maintained at this temperature while still in the A pure iron base was deliberately oxidized by heat atmosphere of hydrogen for 2 minutes, after which the treating in air at 600 C. prior to the application of the power was shut off completely and the specimen cooled dip bath. The evenly oxidized iron base without nickel to room temperature in 3 minutes while still surrounded flashing was treated in a bath comprised of 95 parts of by the hydrogen atmosphere. anhydrous cuprous chloride and 5 parts of red cuprous Using municipal water containing 69 grains of hard 70 oxide. Again, the appearance of the coat and adhesion ness as the result of the deliberate addition of equivalent of the coat to the base was excellent and a thickness in amounts of calcium and magnesium carbonates, the speci the range of 0.4 to 0.5 mill of coating was obtained. In men was corrosion tested in the solution at the boiling the water test, no evidence of water breakthrough was point under reflux conditions for a period of 6 weeks. obtained and while a slight development of purplish coat During the test air was bubbled continuously through the 75 ing was produced after about 6 weeks, all further cor

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rosion appeared purplish coating.

to cease after the emergence of this tion of coating adjacent to the coated surface of the fer

EXAMPLE VII

rous article and virtually no oxygen in the outer surface portion of the coating.

A pickled steel specimen was immersed in a molten 2. A ferrous article having on its surface a tightly ad bath containing 94% anhydrous cuprous chloride, 2% tin 5 herent copper coating at least about 0.3 mil and not as stannous chloride and 4% manganese as manganous more than about 0.6 mil in thickness and containing chloride. The resistance to the boiling water test was oxygen in amounts between 0.3% and 0.6% in the por poor showing both the purplish overcast and the iron tion of coating adjacent to the coated surface of said fer breakthrough and the thickness of the coating achieved rous article and virtually no oxygen in the outer surface in accordance with the schedule given in Example I was 10 portion of the coating, and containing an effective amount 0.1 to 0.15 mill. up to 3% by weight of a metal selected from the group EXAMPLE VIII consisting of nickel and cobalt and an effective amount To the dipping composition given in Example VIII, 5 up3.to Aabout 5% by weight of iron. ferrous article having on its surface a tightly ad parts of red cuprous oxide was added. In this case the herent copper coating at least about 0.3 mil and not corrosion resistance was good except for the delayed more than about 0.6 mill emergence of the thin purplish coating. The thickness oxygen in amounts between in0.3% thickness and containing and 0.6% in the por of the coating was in the range of 0.4 to 0.5 mil and after tion of coating adjacent to the coated surface of said 12 weeks of corrosion testing, no further development of ferrous article and virtually no oxygen in the outer sur corrosion beyond the initial emergence of the thin pur 20 face portion of the coating, and containing an effective plish surface was evident. amount up to 3% by weight of a metal selected from the In order to form alloys with the copper coating, the group consisting of nickel and cobalt and an effective fused salt bath may be modified by the addition thereto amount up to about 5% by weight of iron and containing of suitable amounts, e.g. 2-5% by weight of stannous an effective amount up to 5% of at least one metal which chloride, zinc chloride, manganous chloride, chromous alloys chloride and mixtures thereof, provided sufficient cuprous of tin, with copper and selected from the group consisting manganese, Zinc and chromium.

oxide is present to yield the necessary coating thickness.

In the above description and examples, all parts are by References Cited by the Examiner weight unless otherwise indicated. UNITED STATES PATENTS

1. A ferrous article having on its surface a tightly ad 2,036,667 4/1936 Williams ----------- 29-196.3 herent copper coating at least about 0.3 mil and not 2,514,873 7/1950 Keene ------------- 29-196.3 more than about 0.6 mill in thickness and containing HYLAND BIZOT, Primary Examiner. oxygen in amounts between 0.3% and 0.6% in the por