US3543390A - Fusion-joining coarse-surfaced ferrous metals to metals,using alkaline plating with chelating agents - Google Patents

Description

United States Patent Ofice 3,543,390 Patented Dec. 1, 1970 rm. c1. 323k 31/02 U.S. Cl. 29492 17 Claims ABSTRACT OF THE DISCLOSURE A method of fusion-joining (e.g. welding, soldering or brazing) a fusion-joinable metal part, ordinarily readily fusion-joinable to a low carbon steel, to a coarse-surfaced high carbon ferrous metal such as cast iron, gray iron, malleable iron or wrought iron involving first cleaning from the coarse-surfaced ferrous metal any soil which might prevent electroplating on it an adherent electrodeposit, then electroplating on it a firmly adhering, masking electrod'eposit of iron from an alkaline iron-plating bath having dissolved in it an organic sequestering agent in an amount adequate to hold any iron compound in the bath dissolved in it as the iron chelate, in addition to a sufiicient amount of (a) an alkali metal hyroxide to provide the desired pH and (b) an iron compound 9 to enable electrodeposition from an iron anode.

This application is a division of application Ser. No. 172,117 filed Feb. 9, 1962, now Pat. No. 3,380,151.

This invention concerns the fusion-joining, i.e. by brazing, soldering, or Welding of parts composed of a fusionjoinable metal, and which can be brazed, soldered or welded, to high carbon content ferrous metals which ordinarily have coarse surfaces, such as cast iron as grey cast iron, malleable iron, and wrought iron.

The high carbon content ferrous metals such as cast iron as grey cast iron, and malleable iron and wrought iron ordinarily, that is to say when clean (e.g. free of molding sand or scale) and before being surface ground or polished, have a coarse surface, apparently because of their coarse grain structure as distinguished from that of the low carbon steels which are easily rolled and shaped.

Accordingly, the said coarse-surfaced high carbon ferrous metals, and included among them those which also have high silicon content such as the acid-resistant ferrous metals as the one long known by its trademark Duriron, conveniently can be called ferrous metals ordinarily having a coarse surface or singly an ordinarily coarse-surfaced ferrous metal. The Duriron ferrous metal is a cast ferrous alloy which, in addition to its iron, contains 14.5% silicon, 0.85 carbon, and 0.65% manganese. It is its carbon content which includes it among the high carbon content ferrous metals.

Since such joining operations as brazing, soldering, and welding generally include fusion and subsequent solidification of either a solder or at least part of the base metal along the joint, or fusion of a fluxing agent, these joining operations conveniently are referred to jointly herein as fusion-joining.

Thus, the various metals which can be joined by fusion-joining can be called fusion-joinable metals. When such a metal is fusion-joined to a metal of a different class, such as copper or brass so joined to 'iron, the operation can be called heterogeneous joining.

Then, when a metal such as a ferrous metal is fusionjoined to another part of the same metal as in a repair or to another ferrous metal, the operation can be called homogeneous joining. Where the ferrous metal base and the fusion-joinable metal are joined can be called the fusion junction.

The method of the invention then applies more par ticularly to fusion-joining a fusion-joinable metal to an ordinarily coarse-surfaced ferrous metal, with which such fusion-joining operation heretofore could not be accomplished or at best could be carried out only by undesirable methods involving considerable hazard and expense and yielding only erratic results.

Briefly then, the invention is that of fusion-joining a fusion-joinable metal to an ordinarily coarse-surfaced high carbon content ferrous metal by applying to the latters surface where such joining is to be done, a firmly adhering, substantially continuous, at least masking electrodeposit of iron from an alkalin iron plating bath containing a sufficient amount of an organic sequestering agent, and then fusion-joining the fusion-joinable metal part to the thus iron electroplated surface of said ferrous metal.

In the description firmly adhering, substantially continuous, at least masking for the electrodeposit of iron, the expression firmly adhering means that the deposit adheres to the ferrous base metal Without flaking and is non-peeling in that it cannot be peeled off from the ferrous metal base.

Then the expression at least masking means that the deposit is at least thick enough at least to mask the generally overall finely spotted or matted surface of the ordinary coarse surface of the high carbon content ferrous metal to the extent that the finely spotted or matted appearance is replaced by a substanially uniform apparenly silvery-grey clean iron surface color,

Heretofore, considerable difiiculty was encountered in trying to accomplish practical fusion-joining with an ordinarily coarse-surfaced ferrous metal. For example, it has been substantially impossible dependably to fusionjoin a metal, except to a limited extent and under special conditions, to such ordinarily coarse-surfaced ferrous metal, especially cast iron such as grey cast iron.

To a limited extent, for example, brazing has been carried out with some high carbon content ferrous metals. However, such operation required first subjecting the such ferrous metal base article to a special p-re-treatrnent in one of a few proprietary molten inorganic cleaning and descaling baths. That involved initially preparing the surfaces of the metal products for the fusion-joining operation by immersing them, for example, in a catalyzed molten salt reduction bath (having a melting point of about 500 F.) and at an operating range of 850-950 F., and passing a direct current from an anode through the molten bath to a cathode.

Not only is such a procedure overly costly due to the energy required to maintain the bath molten, but also it is highly hazardous to the operators working about such bath, for example, from dragout on the articles leaving such hot bath; yet, in addition the results were inadequate. Thus, there appears to be a lack of uniformity in the treatment, for the percentage of rejects is undesirably too high for general practical operation; and'all too often the resulting brazed joints are inadequate as manifested, for example, by a high percentage of leaks.

The foregoing disadvantages and others are overcome by the process of the invention, which is a significantly less costly, relatively quicker, and considerably safer method of fusion-joining, and provides a resulting more regularly and uniformly dependable product.

Considered broadly, the process of the invention is a method of fusion-joining a fusion-joinable metal to an ordinarily coarse-surfaced high carbon content ferrous metal, which comprises removing from at least the portion of the surface of said ferrous metal which will be included in the fusion-junction any soil and/or rust which initially should be removed, depositing on at least said portion of the surface of the ordinarily coarse-surfaced ferrous metal a firmly adhering, substantially continuous, at least masking electrodeposit of iron from an alkaline iron plating bath containing a sufficient amount of an organic sequestering agent to hold the iron of any iron derivative in the bath dissolved therein as its iron chelate; and thereafter fusion-joining a fusion-joinable metal to at least that thus iron electrodeposit masked portion of said ferrous metal. The masking electrodeposit is essentially pure carbon-free iron.

Where necessary, the removal of any soil and/or rust can be done separately by any of the respectively suitable available methods, depending On the nature and extent of the soil. In many cases, wherein the residual molding sand or oil or grease, or rust are not extraordinarily excessive, such soil can be removed in the same alkaline bath in which the iron electrodeposition is to be carried out.

The firmly adhering electrodeposit of iron can be deposited from any suitable aqueous alkaline iron plating bath which can be operated to give such firmly adhering masking deposit, and having dissolved therein various effective amounts of one or more sequestering agents which form water-soluble chelates with iron whether ferrous or ferric under the alkaline conditions, along with an effective concentration of an alkali metal hydroxide, such as sodium or potassium hydroxide or ammonium hydroxide.

Applicable sequestering agents include the polyalkylene polyamine polyacetic acid compounds and their monoand divalent metal salts, for example, diethylenetriamine pentaacetic acid and any of its alkali metal and ammonium salts or even any of its alkaline earth salts as its calcium or magnesium salts, and any of the mono-hydroxyethyl-tetra-carboxymethyl diethylenetriamines or dihydroxy-ethyl-tricarboxymethyl diethylenetriamines, and any of the corresponding same salts of any of them, as well as any of the free acid and salt form sequestering agents disclosed in US. Letters Patent 2,831,885; 2,848,469; 2,859,104; and 2,906,762.

Additional eifective sequestering agents are the various monohydroxy or polyhydroxy, monoor polycarboxy lower aliphatic acids having from two through seven carbon atoms such as citric acid, tartaric acid, gluconic acid, glucoheptonic acid, and its isomers galactoheptonic acid, fructoheptonic acid, and the mixed hexahydroxyheptonic acids, and saccharic acid, or an amino, polyhydroxy lower aliphatic acid such as 3-amino-2,4,5,6,7-pentahydroxyheptoic acid, as well as the alkali metal and ammonium salts of any of those acids and the alkaline earth (including magnesium with them) salts of any of those polycarboxylic acids. 1

While individual baths can be prepared using any one of the foregoing and other effective sequestering agents along with a suitable amount of alkali metal hydroxide to give an effective pH value over 7, more than one of any applicable sequestering agents can be used. There can be included various amounts of ethylene-diamine tetraacetic acid or of any of its monoto tetra-alkali metal or ammonium salts as well as any of its alkaline earth metal salts (including magnesium among them), and generally to the extent of no more than about one-half the amount of the other sequestering agent, or of a lower alkanolamine such as mono-, di, or triethanolamine and like propanolamines.

Also any of the various six or seven carbon atom polyhydroxy acids or any of the sugar acids can be admixed with one another or with any of the other sequestering agents, and advantageously with from about one-third to three times its quantity of a hexitol as sorbitol or mannitol.

Obviously, the amount of alkali metal hydroxide used will be greater when any organic sequestering agent is to be added to the bath in its free acid form, for in such case the amount of such hydroxide used must be sufiicient to neutralize the acidity of any such organic agent and to provide the needed pH over 7.

Any of these applicable aqueous alkaline baths can include also an inorganic sequestering agent such as any of the sequestering phosphates such as the alkali metal hexametaphosphates, or other alkaline phosphate such as a di-(alkali metal or ammonium) hydrogen phosphate as disodium or dipotassium hydrogen phosphate.

The aqueous alkaline baths can be used at any suitable pH above 7 depending on the sequestering agent and the nature of any other alkaline agent included, and up to about pH 13.8 and possibly somewhat higher. The alkaline baths are advantageous in exhibiting better throwing power, and serve more effectively in the preliminary cleaning of soil and/or rust as referred to above and discussed in some detail below.

When the preliminary cleaning is not going to be conducted in the plating bath, it is desirable that it contain in solution at least some small amount of a compatible iron salt or chelate, which is soluble at the pH of the aqueous alkaline plating bath. It is advantageous also to use some suitable iron-bearing anode. Thus generally, the starting composition of the bath need contain only very little of the water-soluble iron compound such as an iron salt or chelate, if the bath will not be used to clean the coarse-surfaced ferrous metal which is to be given the iron electrodeposit.

To provide then the initial iron content of the bath, it can contain a very small amount such as one-tenth percent or even less of such water-soluble iron salt as a ferrous or a ferric salt, soluble at the pH of the bath, such as ferrous or a ferric sulphate, chloride, acetate or nitrate, as well as any of the iron chelates of any of the applicable sequestering agents and soluble at the pH of the bath at least and to the extent merely sufiicient to initiate therein electrodeposition of iron.

As already indicated, initial content of such iron salt or chelate can be avoided when the alkaline plating bath is to be used for the preliminary cleaning of the coarsesurfaced ferrous metal which is to receive the iron electrodeposit. That is so because such preliminary cleaning conducted by direct current from iron-containing anodes, and beneficially by periodic reverse current procedure, to affect such preliminary cleaning, results in providing an adequate initial amount of dissolved iron in the bath sufficient to enable electrodeposition of iron on the cathode to progress by continued dissolution of iron from the particular iron-containing anode used to enable depositing the necessary firmly adhering, at least masking electrodeposit of iron on the originally coarse-surfaced ferrous metal cathode.

Where such cathode initially is clean and an iron salt or chelate soluble in the bath is not available or will not be used for some reason, a suitable amount of scrap iron can be suspended or immersed in the bath to be acted on by the bath under direct, and beneficially by periodic reverse, current thereby to enable dissolving into the bath sufiicient iron necessary to permit electrodeposition of iron on the cathode thereafter to continue with accompanying dissolution of iron from the iron containing anode.

For regularly dependable deposition of iron, the total dissolved solids in the bath can range from about one to about five pounds per gallon (i.e. about to about 600 grams per liter). A generally good practical concentration, bearing in mind such factors as conductivity, plating rate, and dragout is in the neighborhood of two pounds per gallon. However, for higher conductivity with certain solutions, it is more desirable to Work with solutions of about four pounds per gallon.

An advantage provided by using an alkaline bath is that an acid-resistant tank is not needed.

The concentration of the sequestering agent, whether a single one or a mixture of them, can vary widely, generally from about two to about one hundred percent of the total solids content, and beneficially from about five to about ninety-five percent of it, depending on providing the required pH value or range.

Grey cast iron, or black iron or other cast iron is very satisfactory for anodes of the ferrous material to replenish iron to the bath as it is plated out to provide a consistently uniform iron electrodeposit on the initially coarsesurfaced ferrous metal cathode. Electrolytic iron anodes also are suitable and at times even cold rolled steel anodes can be used. To avoid interference with the quality of the iron deposit by suspended carbon particles released from a high carbon ferrous metal anode over continued use, it is desirable to enclose such anodes in Orlon or other suitable anode bags, as preferable over filtration of the bath.

Consideration should be given to the relationship of anode area to that of the articles being plated and thus serving as cathodes. Generally, it is advisable that the anode area be significantly greater than that of the part to be plated, and even up to double its area particularly if the cathode part has deep hollows.

The bath may be operated over a wide temperature range, for example, from as low as ambient (-i.e. room) temperature. However, the plating rate then is very slow (e.g. at about 80 F.) and the voltage needed for suitable current density is excessive, being from 12 to 15 volts, or even more. A presently indicated most practical tempera ture range is from about 140 to about 180 F., although there is no discernible difference in the adhesion and generally desirable character of the iron electrodeposit even at the lower temperatures. Where conditions permit, very satisfactory practical results are obtained even at 200 F. and can be obtained also at possibly even a. higher point. It appears generally advisable, of course, to work safely below the boiling point.

Current density, for generally good results, should range from about 200 to about 80 amperes per square foot, and under many conditions can be as high as 100 amperes per square foot. However, for cathode articles having sharp points or projections, it may be advisable to operate somewhat under 80 amperes per square foot to avoid burning.

Thus, the maxi-mum current density for any particular bath should be just under that at which the electrodeposit would begin to show signs of burning. However, the current density generally would have to be well over 100 amperes per square foot before any indications of burning or other undesirable injury can occur to the iron deposit on the coarse-surfaced high carbon content ferrous metal article cathode, or produce a flaky (and thus undesirable) electrodeposit.

The method of the invention is operable readily in quantity production scale. Quite regularly the alkaline bath used in the method of the invention can be relied on for the preliminary treatment to remove the average ordinary amounts of soil, grease and oil, and rust encountered on the general run of articles which will need to be given the plating treatment in the bath. As already indicated, such soil can be removed by subjecting the articles to preliminary electrolytic treatment, including periodic reverse current, for a time sufficient to remove soil and rust. That will depend on the type and extent of soil and rust, the bath, and the treatment.

For some combinations of these conditions, including mild soil and/or rust, two or three minutes of reverse current treatment may be adequate. Slightly heavy soil and rust, possibly may need from about ten to almost fi-fteen minutes. For heavy soil, oil or grease and/or rust conditions, up to about thirty minutes or so may be required.

For such preliminary cleaning treatment in an alkaline bath, and possibly more so for organic soils, it may be helpful to include an alkali metal carbonate in an amount below that at which its concentration could interfere with the quality of the iron electrodeposit. Excess such carbonate even can prevent entirely the iron deposition. Present indications are that such carbonate content be restricted to no more than about ten percent of the total dissolved solids in the bath.

For some soils, perhaps more so with oil and grease, it can help to include a small percent, generally under onehalf percent and possibly more often about half of that or less, of a synthetic detergent, nonionic or anionic and at times even cationic, or a mixture of any of them, as specific conditions may dictate.

As stated above, the iron electrodeposit need be merely sufiicient to mask the coarse, generally grainy surface appearance. Because of the generally rough and irregular surface of the base coarse-surfaced ferrous metal base, in that his not flat and smooth as in the case of low carbon steel, no specific numerical minimum thickness can be stated. Thus, with cast iron or any other coarsesurfaced ferrous metal, the deposit thickness appears to be adequate when the original (cleaned) surface is covered with the iron electrodeposit to the extent that the plated surface, at least over the area which will be in the fusion junction, appears to be covered by an overall substantially continuous electrodeposit of iron.

Such minimum deposit then being suflicient to resist being destroyed or burned away by oxidation under the flame used in the joining operation, as a single such simple test if needed can show, is adequate to enable dependable fusion-joining then to be accomplished with the particular coarse-surfaced ferrous metal.

Ordinarily, the electrodeposit thickness does not have to be much more than that just described above, even though the thus plated surface then may not be entirely flat. A slightly thicker deposit even below 0.0001 inch could be more practical. However, it is difficult also to set a numerical maximum thickness applicable to all surfaces of the various coarse-surfaced ferrous metals. While up to about 0.0001 inch thick might be more than enough for most conditions, yet, where particularly desired, it could be as much as up to about 0.0002 inch thick. Generally, there does not appear to be any particular need to plate a deposit thicker than that.

While the method of the invention is applicable to fusion-joining of any coarsely-surfaced ferrous metal, it is applicable particularly to fusion-joining to cast iron such as grey cast iron. Accordingly, the invention will be more fully illustrated below, but is not intended to be restricted, by a description of details of its application to fusion-joining to grey cast iron. It applies equally to fusion-joining with any other coarse-surfaced high carbon content ferrous metal.

Cast iron castings, for example, of a manifold (5 inches long by 5 inches high by 2.5 inches wide) for a liquid heat exchanger were cleaned of any adhering loose mold sand, in customary manner. One end has an opening to be threaded to receive a one inch outside diameter threaded input line. In one side at the other end, there were counterbored three non-threaded holes around each of which there is to be fusion-joined a one-half inch outside diameter copper outlet line. 7

These manifolds then were suspended suitably spaced from one another by inserting a hanger hook of a cathode rack into the one inch bore at one end of each of them respectively. As thus suspended, they were immersed, properly spaced from grey iron anodes (of about double the cathode area), in an aqueous alkaline iron plating bath held at 200 F. and containing per liter grams of sodium hydroxide, 60 grams of sodium gluconate, and 9.5 grams of sodium carbonate.

Since these cast manifolds were oily and dirty, and rusted in areas, they were subjected in this bath for fifteen minutes to periodic reverse current of five seconds direct current to the cathode, and ten seconds the reverse, to

clean them. Without removing them from this bath, direct current (set to deliver 100 amperes per square foot of cathode area) then was passed from the anodes to these manifolds as cathodes to deposit iron on them for fifteen minutes. The castings then were removed, rinsed adequately with hot water and allowed to air dry. They showed a continuous and uniform electrodeposit of iron completely masking the original spotted cast grey iron surface.

Then a clean end of each of the three one-half inch O.D. copper tubes was dipped in flux and brazed to the counter-bored opening for it in the manifold, by placing a silver solder ring (with half inch CD.) at each such counter-bored hole, inserting the fluxed end of the copper tube in the silver solder ring, and flame-fusing it around the junction in the usual manner.

Such completed manifold tested under high water pressure shows no leaks in any part of the fusion-joint around any of the copper tubes thus fusion-joined to the cast grey iron manifold.

Splitting the copper tube by sawing down through its axis and also likewise through its counter-bore in the casting and then separately gripping the copper of each half near its fusion junction and pulling it, towards its axis, away from its part of the casting, exposed an adhering continuous (unbroken) semi-circular portion of the solder outside that end of each half of the copper tube and in its half of the counter-bore. Thus, the absence of any break in each such residual semi-circular portion, which otherwise would expose an originally solder covered area where no fusion-joining occurred, shows that with the applied iron electrodeposit the brazing took hold around that entire counter-bore.

Any of the various reverse current cleaning and combined bath operating conditions in the foregoing more fully described illustrative operation can be changed at least within the ranges disclosed ahead of that description, to be practical. So also the same bath at any combination of suitable operating conditions can be used to clean and plate a corresponding iron electrodeposit on any other such castings of the same or any other coarse-surfaced high carbon ferrous metal of the type disclosed herein.

As already stated above, the already described electrodeposition of iron can be carried out in any suitable aqueous alkaline iron plating bath, illustrated by, but not restricted to, the following:

ALKALINE BATHS Grams per liter Sodium glucoheptonate 45 Sodium hydroxide 185 Sodium carbonate This bath shows pH 13.8. Its sodium carbonate content can be reduced or even omitted for it is not essential to obtaining a good iron electrodeposit. In a mixture of the dry ingredients, the sodium carbonate included serves to prevent caking of the mixture.

Grams per liter Citric acid 45 Sodium hydroxide 195 In this aqueous bath, obviously part of the sodium hydroxide neutralizes the citric acid so that the actual composition of the solution is equivalent in grams per liter to about 60 of sodium citrate and 165 of sodium hydroxide. It shows pH 13.6.

Grams per liter Sodium diethylenetriamine pentaacetate 68 Sodium hydroxide 40 The sodium diethylenetriamine pentaacetate used in making up this bath (whose pH is 13.6) was obtained and used as a 34% aqueous solution.

Grams Sodium glucoheptonate 0.3 Sorbitol 0.1 Sodium hydroxide 15 Water 84.6

The free alkali in any of the alkaline baths can be replaced by the equivalent or other amount of any other herein indicated applicable alkaline agent. The quantity of any alkali in any of the foregoing baths, or any modifications of them, can be varied by reasonable increase or decrease so long as the pH is above 7.

Likewise, the sequestering agent in any of those alkaline baths can be replaced in part or as a whole by the same or other quantity of any other herein indicated to be applicable sequestering agents and within the indicated range so long as the bath still has a pH over 7.

The sodium citrate resulting from the neutralization in bath (b) can be added directly as sodium, or can be replaced by and added as some other alkali metal or ammonium, citrate without any noticeable difference, or even by a compatible amine salt of it as indicated in the preceding paragraph.

The sodium diethylenetriamine pentaacetate can be replaced in whole or part by its corresponding salt of any other alkali metal or its ammonium or above indicated amine salt, or by the corresponding tetra-, tri-, di-, or mono-acetate, or even of ethylenediamine pentaacetic acid itself or by any other sequestering agent sufficiently soluble in water for the pH of the bath to be within the above disclosed range.

The alkaline bath in the hereinabove more fully described illustrative operation, showing the overall treatment of cast manifolds, can be replaced in that complete operation by any other alkaline bath respectively specifically identified in any of the foregoing specific baths or any above explained possible modifications of them. The method of the invention similarly can be carried out even in a bath of above pH 7 just as earlier above set forth.

However, where it is possible to conduct the electrolytic cleaning in the same bath from which the iron deposit is to be plated out, th bath should be high enough on the alkaline side to enable a practical rate of such cleaning to occur.

The method of the invention works also with the low carbon ferrous metals such as the low carbon steels which can be cold rolled and shaped by such operations as forging and spinning. However, ordinarily such low carbon ferrous metals readily can be brazed, soldered, or welded.

Thus, the method of the invention is beneficial primarily with those ferrous metals and alloys, with which some difficulty or disadvantage is met in attempts to braze, solder or weld them, so that they generally cannot be brazed, soldered or welded readily or require some special preliminary treatment more difiicult, hazardous, and/ or costly than merely preliminary electrodeposition of Herein and in the appended claims, the expression ferrous metal is to be broadly construed as including the ordinary commercial forms of the various irons as well as its common alloys composed highly predominately of iron.

Similarly, the expression metal material in the longer expression metal material which ordinarily can be fusion-joined readily to a low carbon steel is to be broadly construed to include not only a different metal such as copper or an alloy of it such as brass or bronze, but also a ferrous metal, whether it is an independently formed piece to be fusion-joined, for example, to a casting, or is merely another part of the same ferrous metal which is to be fusion-joined at a crack or seam (as in a butt or lap joint).

While the invention has been explained more extensively by detailed description of certain specific illustrative embodiments of it, it is understood that various modifications and substitutions can be made in any of the thus described embodiments within the scope of the appended claim which are intended also to include equivalents of any such embodiments.

I claim:

1. The method of fusion-joining to a coarse-surfaced high carbon content ferrous metal object, a part composed of a fusion-joinable metal which ordinarily can be fusion-joined readily to a low carbon steel, but which may be fusion-joined to a coarse-surfaced high carbon content ferrous metal ordinarily in only a limited way and under specially different conditions; which method comprise cleaning from at least the portion of said ferrous metal object, which will be in the fusion junction, any soil which could prevent electroplating on such portion an adherent electrodeposit of iron; thereafter electroplating on at least such portion of said object a firmly adherent at least masking electrodeposit of iron while said at least cleaned portion of said metal object is im mersed as a cathode in an aqueous iron-plating bath containing dissolved therein as its essential iron-plating-enabling constituents (a) an amount of a dissolved iron compound sufiicient to enable electrodepositing iron on passing an electric current through an iron anode immersed in said bath, through the bath and to said cathode, (b) an organic sequestering agent in an amount substantially sufiicient to hold the iron of any iron compound in the bath dissolved therein as the iron chelate of said agent, and (c) an alkali metal hydroxide in an amount sufiicient for the bath to have a pH from at least above 7 to below that at which iron will precipitate out, said iron compound being a water-soluble salt or chelate; removing the thus iron-plated ferrous metal object from said bath and any plating solution adhering to it; and then fusion-joining said fusion-joinable metal to the said object at its said iron-plated portion and by any simpler fusion-joining method generally readily applicable to fu sion-joining to a low carbon steel.

2. A method as claimed in claim 1, wherein the sequestering agent is a hydroxy-substituted lower aliphatic compound soluble in the bath, which compound includes at least one group COOR wherein R is a cation which can be replaced by iron at whichever valence it exists in the bath and for it to form a chelate with the ligand portion of the sequestering agent.

3. A method as claimed in claim 2, wherein the hydroxy-substituted lower aliphatic sequestering agent is polyhydroxy.

4. A method as claimed in claim 3, wherein the polyhydroxy-substituted aliphatic sequestering agent has from 6 to 7 carbons.

5. A method as claimed in claim 4, wherein said bath also contains a hexitol dissolved therein in an amount from about one-third of to three times the weight of said sequestering agent.

6. A method as claimed in claim 5, wherein the sequestering agent is sodium glucoheptonate and the hexitol is sorbitol.

7. A method as claimed in claim 2, wherein the sequestering agent content of the bath comprises and R is defined as in claim 2.

8. A method as claimed in claim 7, wherein about half of the sequestering agent content of the bath is an alkali metal glucoheptonate.

9. A method as claimed in claim 8, wherein the alkali metal is sodium.

10. A method as claimed in claim 8, wherein the maximum pH of the bath is about 14.

11. A method as claimed in claim 10, wherein the bath contains also another sequestering agent which is a hydroxy lower aliphatic carboxylic acid having from two to seven carbon atoms, from one to six hydroxyl groups, from one to three carboxyl groups, and is only hydroxy and carboxy substituted.

12. A method as claimed in claim 2, wherein the sequestering agent content of the bath comprises wherein R is defined as in claim 2.

13. A method as claimed in claim 12, wherein the maximum pH of the bath is about 14.

14. A method as claimed in claim 13, wherein the sequestering agent content consists essentially of an alkali metal citrate.

15. A method as claimed in claim 2, wherein prior to direct current deposition of iron on the ferrous metal object, soil is removed from it by subjecting it to the effect of periodic reverse current in the bath for a time sufficient to remove any soil from at least the portion of its surface, which is to be in the fusion junction; and then subjecting the thus cleaned ferrous metal object as a cathode while in the same bath to direct current to electroplate on it said electrodeposit of iron.

16. A method as claimed in claim 15, wherein the maximum pH of the bath is about 14.

17. The method as claimed in claim 2, wherein the coarse-surfaced high carbon content ferrous metal object is cast iron and the fusion-joinable metal is a member of the class consisting of copper, brass and bronze, and the sequestering agent is citric acid.

References Cited UNITED STATES PATENTS 1,651,403 12/1927 Mougey 29504 X 1,997,538 4/ 1935 Armstrong 29492 X 2,714,089 7/ 1955 Meyer 20448 OTHER REFERENCES The Condensed Chemical Dictionary, 6th ed., copyright 1961 by Reinhold Publishing 00., p. 1013.

Industrial and Engineering Chemistry, vol. 45, No. 12, December 1953, pp. 2782-2784.

JOHN F. CAMPBELL, Primary Examiner R. J. SHORE, Assistant Examiner US. Cl. X.R.