A.
Etched
B . Polished
FIGURE 1. WELDZONE (a)BETWEEN 18-8 (b) AND LESSEXPENSIVE FERROUS MATERIAL (c) PRODUCED BY AN OLDER CLADDING METHOD( X 1000)
FIGURE2.
CONTACT (a)
BETWEEN
AND ELECTROLYTIC IRON (e) BEFORE HEATTREATMENT ( X 500)
18-8 (b)
Cladding of Ferrous Products A New Electrochemical Method RAYMOND R. ROGERS, Columbia University, New York, N. Y.
FIGURE 3. WELDZONE (a) BETWEEN 18-8 ( b ) AND ELECTROLYTIC IRON (cl low r e c o v e r y AFTER HEATING FOR ONE HOUR .4T 9.50 from ingot to C. ( X 750) finished b a r , plate, or sheet. It has been f o u n d t h a t “a stainless or chromium alloy veneer not more than 0.015 inch thick (28 gage) is s u f f i c i e n t to protect the surf a c e of s t e e l against most of the destructive (IS). forces” Hence attempts have been made t o c o v e r ordinary, comparaFIGURE 4. WELD ZONE (a) OF LowCARBONSTEEL(c) CLADWITH 18-8 ( b ) tively cheap, BY ELECTROCHEMICAL METHOD( X 500) ferrous materials with a d h e r e n t veneers of the more expensive iron alloys. I n this way the desired combination of strength with resistance to corrosion or heat may be obtained a t a much more reasonable price. The problem has not been easy to solve, but some progress has already been made in the desired direction.
The demand for clad materials in order to increase the use of the more expensive metals and alloys is discussed. Cladding methods proposed by previous investigators are briefly summarized. A new electrochemical method of cladding ferrous materials with (1) stainless materials, such as 18-8 chromium-nickel steel and low-carbon chromium irons, (2) high-carbon steel, (3) high-speed steel, (4) stellite, and (5) nickel is described. Photomicrographs showing the excellent nature of the clad materials produced by the new method are included.
URING the past twenty-five years many metals and alloys have been produced which exhibit remarkable resistance to corrosion, heat, abrasion, etc. A conception of the important applications of many of these materials in the leading industries, such as those in which dairy products, chemicals, and automobiles are manufactured, may be gained from the recent summary by Thum (1.9). At the present time a wide use of many of these metals and alloys is prevented because of their excessively high price. This is due (1) to the high cost of a number of the elements, such as nickel, chromium, and tungsten, (2) to the high rolling and forging cost which is many times greater than that of ordinary steel, and (3) to the
Historical The art of forge-welding is extremely old and the veneering or cladding of one metal with another was a natural develop783
IXDUSTRIAL AND ENGINEERING CHEMISTRY
784
A
~~
FIGURE 5. A. B.
\VELD ZONES
B
(a)OF STAINLESS I R O N ALLOYS AFTER HEATING .4T 950 ( X 1000)
c.
Between low-carbon, 14 per cent chromium iron ( b ) and electrolytic iron ( e ) . Beta-een low-carbon, 16 per cent chromium iron containing copper and silicon ( b ) and electrolytic iron ( c ) .
ment from the forge or smith weld. The methods that were found satisfactory for forge-welding have been adapted to the art of cladding, and a t least as far back as 1882 special methods were being patented. A number of methods of excluding air from the space between cladding and backing materials during the high-temperature treatment rvere patented in that year by Fleitmann ( 3 ) . One of these methods consist* of depositing galvanically (Le., n-ithout the use of an external source of current) from an acid solution, a comparatively noble metal upon the surfaces to be m l d e d . KOattempt is made to remove the oxide or other nonmetallic material already existing on the surface" to be welded before the cladding and backing materials are assembled. The use of pressure during the high-temperature treatment is recommended. There is no doubt that a weld (really brazing) may be produced by this method but the union will contain considerable amounts of oxide or other nonmetallic material. It should be emphasized that the differcnce between brazing and welding, though slight, is important. I n 1894 a patent was granted to Rodig (10) on a process in which two iron plates are placed one upon the other. Then a shell or envelope of copper is cast about the plates. The resulting combination of iron and copper is rolled. "The combined effect of heat and pressure thoroughly unites the plates and shell without, however, causing the metal of the two iron plates to unite." The reduced material is cut into slabs and the edges of the copper sheet are removed either during the rolling of the slabs or by shearing. Each slab thus produces two plates or sheets of iron, each of which is coated on one side with copper. The inventor makes i t clear that other combinations of metals may be used, the only essential being that the coating metal should be the softer of the two. I n 1919 Gillespie (4) was granted a patent on a process in which a billet, bar, plate, or sheet of chromium alloy steel is applied to a billet, bar, plate, or sheet of ordinary mild steel and "melded thereto by hammering. rolling, or pressing under the action of heat." The chromium steel may be applied to one or both sides of the ordinary steel by this process. I n 1934 a patent was reissued to Armstrong ( 1 ) on a process in which two sheets of stable surface material (such as stainless steel) are placed back t o back with, preferably, a layer of asbestos between them. This combination is inserted in an ingot mold, the edges being held in two slots on opposite sides of the mold. Molten ferrous metal is poured into the mold until the stable surface material is surrounded. The resulting ingot may be separated into two parts on the parting piaiie produced by the achestos or other separating layer.
VOL. 27, NO. 7
The parts may be hot-rolled together, the ferrous backings being in contact with each other. This %-illgive a product faced on the exterior with stable surface alloy and having an interior of welded backing material. The parts may be rolled separately, producing a single layer of stable surface material, or the ingot may be rolled as a whole and separated after rolling. Recently, other patents of interest have been issued to Johnson ( 7 ) , Pvlaskrey (Q), and Ingersoll (6). This is by no means a complete survey of the literature or patents on this subject, but it is sufficient to indicate the lines alone: which progress has been made up to th: presenttime, \ve have, therefore, two general classifications for the manufacture Of clad products:
1. The all-assembIy methods, which may be tvpified by the Gillespie process. 2. The special castiig-metho& which may be typified by the Rodig and Armstrong processes,
Clad materials are being manufactured both by all-assembly and by casting methods a t present. I n both the all-assembly and the casting methods great care is taken to remove, by pickling or sand-blast'ing, the oxide scale which has been formed on the corrosion-resist'ant materials during former high-temperature treatments. However, as far as the author is aware, no at'tention has been paid to the film of nonmetallic material-probably oxide--which forms rapidly on the surface of these materials under ordinary atmospheric conditions. This filni is so thin that the metal, when covered by it, may still appear bright to the eye and entirely free from nonmet'allic material. However, it will become thicker and more visible if t'he temperature is raised in the presence of air. I t is to this film that the corrosion-resistant materials owe their resistance to corrosion. On the other hand, the difficulty of welding these materials effectively is increased many fold by its presence. From this discusssion it is to be expected Ohat an extremely thin, continuous film of nonmetallic material will exist between the cladding and backing materials before the rolling takes place in the case of clad products produced by either the all-assembly or the cast'ing methods. This film will prevent the formation of a weld between the unworked materials even a t high temperatures. K h e n rolling takes place, this nonmetallic film will be broken in places and a weld will be produced wherever a break occurs. If this is true, clad materials produced by either of these methods offer two important' disadvantages : 1. No weld will take place when the materials are subjected to high temperatures unless t,heg are rolled or otherwise elongated. 2, The weld, even at best, is not continuous. -4considerable quantity of nonmetallic mat,erial will always be present. This will reduce the strength of the weld and there will be danger of the cladding material separating from the backing material because of strains produced by differences in expansion o r because of mechanical xvork.
The use of a comparatively thick layer of fairly pure iron between cladding and backing materials has been recoinmended by some investigators as an aid in producing a good bond, This does not eliminate the extremely thin film of noninetallic material which forms on the surface of the cladding material under ordinary atmospheric conditions. Furtherniove, the pure iron is weaker than either the cladding or
JULY. 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
backing materials, which means that the weld zone will be the weakest part of the finished product. Samples of commercial clad materials were examined microscopically during the course of the present research. Inclusions of nonmetallic material were clearly visible in the weld zone when a magnification of 1000 diameters was used and when, at the same time, the surface examined was at an angle of 45" or less to the weld. Figure 1 shows typical photomicrographs made during this examination. Both were taken a t a n angle of 45" or less t o the weld and show the junction between the 18-8 cladding material and the less expensive material in contact with it. The black portions which appear a t or near the junction are nonmetallic material. Figure 1A was lightly etched with picric acid; Figure 1B was polished but left unetched to prove beyond a doubt that the black portions are nonmetallic material and not merely etching pits.
New Method of Cladding The purpose of this paper is to describe a new method, involving electrochemical processes, by which comparatively cheap, ferrous products may be clad with expensive iron alloys, with nickel, or with stellite. Clad materials produced by this new method possess the following advantages: 1. The weld between the cladding and backing materials takes place under the influence of high temperature alone. Rolling or other methods of elongation are not necessary, although it is probable that working strengthens the weld still further. 2. The weld between the cladding and backing material is continuous. Nonmetallic materials are entirely absent. 3. There is no abrupt change in composition at the weld. A very thin layer of pure iron is introduced (by electrolytic means) between cladding and backing materials. An excellent diffusion takes place between each of these materials and the thin layer of iron. Hence, a t the end of the process the weld zone consists of an alloy gradually varying in composition from that of the cladding material on the one side t o that of the backing material on the other.
I n working out t h e details of this method, 18-8 chromium nickel steel was used as the cladding material. Then later the method was used, with certain modifications in some cases, for cladding with other materials.
785
results, i t was considered undesirable because of its slowness and because 12 N hydrochloric acid is an unpleasant and corrosive material to use. Hence a search was made for some other process which would give equally good results and would be less undesirable. It was found that an anodic pickle in more dilute hydrochloric acid is much quicker and also gives excellent results. The chemical method was therefore replaced by the electrochemical one. Hydrochloric acid solutions as dilute as 3 N gave satisfactory results. However, as these solutions could be used only for a limited length of time, i t was considered preferable to use a 6 N bath. I n such a n anodic process the rate of pickling depends upon the current density which may be varied between wide limits. The anodic pickling process is as follows: 1. The exposed surfaces of the welded 18-8 plates are pickled at ordinary temperature at a current density of 60 amperes per square foot until, on scrubbing, a clean surface, entirely free from nonmetallic material, is produced. Surfaces which are in fairly good condition to begin with, require about 10 minutes a t this current density. 2. The plates areremovedfrom the bath, rinsed, and thoroughly scrubbed. 3. The plates are replaced in the bath and anodically pickled long enough to remove any nonmetallic material formed on the surface during the scrubbing. Ordinarily 30 seconds are sufficient. 4. The plates are placed immediately in the iron electroplating bath without removing the adhering acid. The electroplating is begun at once. The fact that the acid remains on the plates during the transfer from pickling tank to plating tank is important because it insures that no nonmetallic film will be formed on the surface during the transfer.
ELECTRODEPOSITION OF IRON.Iron is now electrodeposited upon these 18-8 surfaces which are still entirely free from nonmetallic material. After considerable experimentation with different iron-plating baths described in the literature, it was decided that the Fischer-Langbein chloride bath mentioned by Hughes (5) and by Blum and Hogaboom (2) would be best for the present purpose. The composition of this bath is: Ferrous chloride (FeClz.4HzOj Calcium chloride (CaC12) Hydrochloric acld
300 grams/liter (40 oz./gal.) 335 grams/liter (46 oz./gal.)
Just enough to prevent formation of ppt. in bath
Cladding with 18-8 Chromium-Nickel Steel The new electrochemical method of cladding may be summarized as follows: 1. Two plates of 18-8 are placed back to back with a thin separating layer of talc or magnesia in sodium silicate between them. These plates are welded together around the edges. 2. All nonmetallic material is removed from the exposed s u r f a c e s of the 18-8 plates. 3. Before a new nonmetallic film can be formed, a layer of iron is electrodeposited upon the clean surfaces of the 18-8 plates. 4. A weld is produced between the 18-8 and the electrolytic iron. 5 . The c o m p o s i t e t h u s produced is given a backing of ordinary, comparatively c h e a p , ferrous material by rolling (the electrol tic iron being between the 18-8 and the baczing material).
REMOVALOF KONMETALLIC MATERIAL 18-8 SURFACE.After a thorough preliminary cleaning to remove grease, the exposed surfaces of the 18-8 plates are given an acid pickle. A t first an ordinary chemical pickle in 12 N hydrochloric acid was used for this purpose. Although this procedure gave excellent
It is interesting to note that Kern (8) used a similar bath as early as 1908. The bath is operated at or near 90" C. (194' F.) with a cathode current density of 60 amperes per square foot. Iron anodes are used. I n cases where a smooth deposit is required,
FROM
A
B
FIGURE 6. WELDZONES (a) BETWEEN HIGH-CARBON HIGH-CHROMIUM STEEL(b) AND ELECTROLYTIC IRON(c) NOTSHOWN IN B A . After heating for one hour at 950' C. and then 10 per cent reduction by forging ( X 1000). E . -4iter further iorging and annealing ( X 500).
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INDUSTRIAL AND EKGIKEERING CHEMISTRY
these anodes are placed behind porous alundum plates. The best anode and cathode efficiencies are obtained when the acidity of the bath is just high enough to prevent the formation of precipitate but not sufficiently high to produce considerable hydrogen evolution a t the anodes. The desired p H is in the neighborhood of 2 as measured by the quinhydrone electrode. Additions of hydrochloric acid must be made a t
1
VOE. 27, YO. 7
placed in an ingot mold and surrounded by molten backing material. The resulting combination is rolled down, the edges are sheared, and two plates or sheets, each clad on one side with 18-8, are again the result. For the production of very thin sheets of clad material, it is preferable to use the welding process resembling the allassembly methods rather than that resembling the casting methods because a smaller assembly may be used, thus requiring less reduction. If a weld absolutely free from nonmetallic material is essential, it is safer to use the process resembling the all-assembly methods because the surface of the electrolytic iron is sure to be oxidized to a certain extent during the casting process. This oxide will remain between the electrolytic iron and the backing material permanently, unless it is dissolved, preferably by a slag of low melting point. I n any case, the weld produced by casting the backing material against the film of electrolytic iron will be superior to that which would be obtained if the molten backing A B material were cast directly against the surface* FIGUREi . WELDZOYES (a) OF LOW-CARBON STEEL(c) C L ~ WITH D HIGH-CIRBO\ 'Figure 3, taken at an angle of 48" or STEEL( b ) BY ELECTROCHEMICAL METHOD less to the weld, shows the weld produced A . After 10 per cent reduction by hot-forging ( X 200), B. After forging and annealing ( X 500). between 18-8 and electrolytic iron, by heating for one hour a t 950" C. The diffusion zone is entirely free from nonmetallic material. The diffusion apparently takes place at intervals. Since the anode efficiency is greater than the cathode efficiency, the iron concentration of the bath tends to inthe greatest rate along the grain boundaries. The large size of crease. Hence, the bath must be "bled" from time t o time. the iron grains is due to the high temperatures to which the Under the conditions described, iron is deposited a t the rate material was subjected, If there had been a film of nonmetallic material between the 18-8 and the electrolytic iron, of about 0.003 inch per hour. The rate of deposition may be greatly increased by increasing the cathode current density. there would have been no diffusion and the iron grains would A deposit of electrolytic iron on a sheet of 18-8, which is have been uniform in size even t o the edge of the 18-8. There 0.025 inch in thickness, adheres perfectly even when the comis good reason to believe that this diffusion will take place a t posite is bent backward and forward until i t breaks. This is temperatures much lower than 950" C. However, a t the a good indication that no nonmetallic material exists between lower temperatures the rate is much slower. Figure 4, taken a t 45" or less to the meld, shows a sample of the iron and the 18-8. It has been found that, if the plating current 1s interrupted, even for a short length of time, the iron clad material which was produced by the welding process redeposited after the interruption is fairly readily separated sembling the all-assembly methods. This sample had been rolled a t 1160" C. (2100' F.). It was then cooled and refrom that which mas deposited previous to the interruption. I n bending tests it has been found that such an iron-to-iron heated to 980" C, (1800" F - j for 2 hours. The backing bond is considerably weaker than a bond between iron and material was low-carbon steel. The nature of both the electro18-8, produced by the method described. lytic iron to 18-8 weld and the electrolytic iron to lowcarbon Figure 2, taken a t a n angle of 45" or less to the weld, shows steel weld is nicely shonn. I n fact, because of the long period electrolytic iron as it appeared after having been deposited of heating, the diffusion has gone completely across the elecupon a sample of 18-8. S o nonmetallic material is visible a t trolytic iron zone and into the backing material. There is or near the interface. The 18-8 was given a n exceptionally no evidence whatever of nonmetallic material between the iron and the 18-8. long acid pickle previous to plating. I n this sample interIt should be emphasized that the layer of metal next to the granular corrosion is apparent. The corrosion cavities are 18-8 is no longer pure iron. The layer is an alloy whose coinfilled with the electrolytic iron. This process may be somewhat simiWELDING PROCESS. position varies gradually from that of the cladding material lar to the process used in either the all-assembly methods or on the one side to that of the backing material on the other. the casting methods. This condition will always exist when a proper combination I n the first case the two welded plates of 18-8, whose exof electrolytic iron film thickness, temperature of heat treatposed surfaces have been pickled and plated with iron, are ment, and length of heat treatment has been used. placed between two slabs of backing material such as low.Not only is it possible to form sheets of comparatively carbon steel, and the four are seam-welded around the edges. cheap ferrous material, such as low-carbon steel clad on one The combination is heated for an hour at about 950" C. side with 18-8, but also sheets clad on both sides with 18-8 (1750" F.), to produce a diffusion weld between the electromay be produced. It is necessary only to roll together two lytic iron and the 18-8. It is then heated to about 1150" C. sheets which have been clad on one side (low-carbon steel to (2100° F.) and rolled. Finally, the welded edges are sheared lowcarbon steel). off and two plates or sheets, each clad on one side with 18-8, Rods of ordinary steel clad with 18-8 have also been produced by the electrochemical method. The inner surfaces of are the result. I n the second case the two plates of 18-8, whose exposed 18-8 tubes [1.25 and 1.5 inches (3.2 and 3.8 em.) inside dlsurfaces have been pickled and plated with iron, may be ameter] were pickled and plated with iron in the usual ~ v a y .
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INDUSTRIAL AND ENGINEERING CHEMISTRY
781
Another high-chromium alloy steel high in carbon (1.57 Freshly ground bars of low-carbon steel were then inserted, per cent carbon, 11.82 chromium, 0.18 vanadium, 0.68 no attempt being made to obtain a driving fit. The tubes molybdenum, 0.25 manganese, 0.19 per cent silicon) also gave were welded to the bars a t the ends and the resulting combinaexcellent results as a cladding material for low-carbon steel, tions were heated to 950" C. (1750" F.) for onehour, and then as shown in Figure 6A and B, taken a t 45" or less to the weld. raised to 1100" C. (2000" F.) and rolled down to bars 0.5 Figure 6A shows the sample after plating and heating for an inch (1.27 cm.) square. These bars were cut a t an angle of hour a t 950" C. It was then given about 10 per cent reducabout 30°, and the weld zone was carefully examined under tion by forging. The unetched band is the diffusion zone the microscope. No oxide was observed a t or near the conwhich is quite free from entrapped nonmetallic material. tact between 18-8 and electrolytic iron, and apparently there was not sufficient oxide present a t or near the contact between the electrolytic iron and low-carbon steel to show any inclusions. The welds were considered perfect. When the bars were given a prolonged annealing, the diffusion reached from one side of the electrolytic iron to the other. The weld was very strong, and, although repeated attempts were made, no fracture could be produced in or adjacent to the weld. So far, only cases have been discussed in which considerable reduction by rolling, etc., is p e r m i s s i b l e . By using a modification of the process already described, it is possible to produce clad maA B terials with little or no reduction. Instead of merely electrodepositing a thin OF NICKEL (b) AND ELECTROLYTIC IRON(e) ( X 1000) FIGURE 8. COMBINATIONS film of iron on the cladding m a t e r i a l A . Contact ( a ) before heat treatment. B . Weld zone (a) after heating for one hour a t 950' C. and then giving it a backing of ordin a r y steel b y rolling, t h e plating process mag be continued until the layer Figure 6B shows the same sample after further forging and of electrolytic iron is sufficiently thick to act as the backing annealing. The etching is much lighter. The light area material. Then, as before, heating the combination at 950" containing large quantities of carbides is the high-carbon, C. will produce the weld between the cladding material and high-chromium cladding material, and the pearlite-laden the electrolytic iron. area is the electrolytic iron which has been diffused with both Tubes of electrolytic iron clad either inside or outside with chromium and carbon. Since there is no entrapped nonexpensive material such as 18-8 may be produced by this metallic material present, and since a great deal of diffusion method. has taken place, the weld is very strong. This material is Cladding with Stainless-Iron Alloys an expensive die steel, very hard and very durable when heattreated. To work a solid piece of this material into the reLowcarbon stainless irons are becoming increasingly imquired die shape is expensive. Since only about 20 to 25 portant because of their excellent resistance to many kinds of per cent of the actual thickness of the die block or die proper corrosion and other desirable properties. Samples of lowis actually used for cutting purposes, a backing of comparacarbon stainless iron of the following types were used as cladtively cheap, low-carbon steel might well be applied by the ding materials by the same method as that just outlined for new cladding process. 18-8 chromium-nickel steel: (1) 14 per cent chromium, (2) 16 per cent chromium, and (3) 16 per cent chromium, 1.25 per cent copper, 1.25 per cent silicon. The excellent nature Cladding with High-Carbon Steel of the diffusion welds produced between cladding materials The importance of high-carbon steel in ploughs, shears, and electrolytic iron in the first and last cases is shown in dies, etc., is well recognized. Hence, the possibility of cladFigure 5A and B, respectively, taken a t an angle of 45" or less ding with high-carbon steel by the new electrochemical procto the weld. No nonmetallic material can be seen in these ess was investigated. Figure 7 A , taken a t 90" to the weld, welds. Just as good results were obtained in the case of the shows the excellent diffusion meld obtained. In this case, 16 per cent chromium iron, the weld resembling closely that after heating a t 950" C. for one hour, the sample was given obtained in the case of the 14 per cent chromium iron. about 10 per cent reduction by hot-forging. Figure 'iB At first it was difficult to obtain good adherence between shows a similar sample which was given further heat treatthe electrolytic iron and the first two stainless irons menment and forging. The carbon from the high-carbon cladtioned, before heat treatment. It was finally learned that the ding material has diffused completely across the electrolytic trouble lay in the straight chemical pickling procedure which iron zone and into the backing material. Hence, the weld was being used a t that time. Much better results were obzone varies gradually in composition from that of the cladtained when the material was left in the pickling bath (12 N ding material to that of the backing material. N o entrapped hydrochloric acid) until a uniform evolution of hydrogen was nonmetallic material is to be found, and it is difficult to locate produced and then for 15 or 20 minutes longer. This may the junction between the high-carbon facing and the carbonhave been because the extremely thin nonmetallic film on the ized backing. This junction is actually along a horizontal metal surface did not dissolve uniformly, or it may have been line through the center of the photomicrograph. The analymerely because the surface became rougher when pickled for sis of the particular material used was 1.08 per cent carbon, a longer time. 0.30 per cent silicon, 0.35 per cent manganese, and 0.06 per The anodic pickling procedure, when it was adopted, was found to work well in all of these cases. cent chromium.
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INDUSTRIIL AND ENGINEERING CHEMISTRY
YOL. 27, NO. 7
a t 90" to the weld, shows a sample in which the cladding process has been completed by giving the combination of highspeed steel and electrolytic iron a backing of Ion--carbon steel. The sample was forged to produce about 10 per cent reduction and then annealed, The carbon from the high-speed steel has migrated most of the may across the electrolytic iron zone. Further heat treatment would have entirely o b l i t e r a t e d t h i s z o n e . Figure 11, taken at 90" to the meld, is a highly magnified picture of the weld zone between high-speed steel and electrolytic iron. The excellent diffusion of B A the elements present in the high-speed steel may be seen. This diffusion and F I G U R E 9. C O & i B I S 4 T I O Y S O F HIGH-SPEED S T E E L ( b ) AVD ELECTROLYTIC l R O 3 (C) ( x 1000) the absence of nonmetallic m a t e r i a l s insure a weld zone of great strength. A Contact (a)before heat treatment B. Weld zone (a)after heating for one hour at Q50' C. The cladding of high-speed steel with iron is also nossible bv this nrocess and should prove of benefit to manufacturers of high-speed steel products. Ordinarily there is a considerCladding with Nickel able loss of valuable material due to the oxidation and crackOther materials besides alloys of iron may be applied as ing which occur a t the surface of the high-speed steel during cladding materials by the new electrochemical process. high-temperature treatment. This loss may be largely, if Sickel gives excellent results, as is shown by Figure 8, taken not entirely, eliminated if the well-annealed ingot is first a t &'or less to the weld. The oxide-free nature of the nickelpickled and plated, as already described, with a layer of iron electrolytic iron interface before heat treatment is seen in inch or more in thickness and then heated for an hour a t Figure 8 8 , and the excellent nature of the weld produced by 950" C. (1750" F.) to produce a perfect weld between the one hour of heating a t 950" C. in Figure 8B. This is much iron and the high-speed steel. The ingot, thus protected by superior to the weld produced by ordinary cladding methods. a comparatively cheap layer of electrolytic iron, is then ready for high-temperature forging treatment. The iron layer Cladding with High-speed Steel must be thick enough so that it will not have scaled away completely by the time the high-temperature treatment is High-speed steel is used for cutting tools such as shear completed. A good weld between the iron envelope and the blades and milling cutters. Shear blades of lom--carbon steel ingot is essential. Otherwise the envelope will merely be clad with high-speed steel should be highly acceptable. Millelongated and vill not serve as a protection t o the ingot, ing cutters may be produced from clad materials as follows: Similar processes may be used in the production of other A bar of lo-iv-carbon steel is clad with high-speed steel in a expensive alloy materials. way similar to that mentioned for bars clad mith 18-8. The teeth of the cutter are cut in the high-speed steel veneer. Cladding with SteUite With such applications as these in mind, the problem of Stellite, another expensive alloy material, has earned a n cladding with high-speed steel was investigated. It was enviable reputation for itself because of its corrosion resistfound that for best results the process described for cladding ance, red hardness, and low coefficient of friction. Having mith 18-8 should be considerably modified. High-speed met with success in cladding with so many other materials steel of the following type was used in the experiments: by the new method, the application of the process to clad17.80 per cent tungsten, 4.13 chromium, 1.07 vanadium, 0.68 ding with stellite was attempted. Here again success was carbon, 0.25 silicon, 0.29 per cent manganese. The high-speed steel is pickled by an alkaline anodic process, the details of which have already been published by the author (11). The last step in the pickling process consists of a short dip in hydrochloric acid. The high-speed steel parts are removed from this dip. still covered with acid, and immediately placed in the iron-plating bath. From this point the procedure for cladding with high-speed steel is the same as that for 18-8. Figure 9 8 , taken at 45" or less to the weld, shows the oxide-free nature of the contact between high-speed steel and electrolytic iron before heat treatment. Figure 9B, taken a t 45" or less t o the FIGURE 11 NELDZONE (a) JJCTWCCN weld, shows the excellent nature of the HIGH-SPEED S r E m ( 6 ) * N O ELECTROFIGLRE 10. WELDZOUE (a) OF Lowdiffusion weld produced between theic CARBONSTEEL( c ) CLAD WITH NIGM- LYTlC l R O V ( N O T SHOWN) AFTER COYtwo materials by heating the sample for STDER ZBLE HEAT TRCAT\fIF\T 4RD S P E E D STEEL ( 6 ) BY ELECTROCHEMICAL FORGlVG ( x 500) PROCESS ( x 100) one hour a t 950' C. Figure 10, taken
JULY, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
achieved. Stellite containing approximately 65 per cent cobalt, 30 per cent chromium, and 15 per cent tungsten was used in the experiments. The following procedure was found to give good results: The stellite, after a preliminary cleaning to remove grease, is treated anodically in 12 N hydrochloric acid a t room temperature and a current density of about 60 amperes per square foot. This continues until the stellite is covered by a dark blue material (vhich cannot be removed with a scrub brush). After rinsing, the stellite is pickled by the alkaline anodic treatment already mentioned (11). As a final step in the alkaline pickling, the stellite is given a short hydrochloric acid dip which dissolves the nonmetallic material formed on the surface. A fresh, metallic surface is thus produced. Still covered with acid, the stellite is immediately transferred to the iron-plating bath. When the plating is completed, the stellite-electrolytic iron composite is seam-welded to a piece of backing material such as lowcarbon steel. The combination is heated for some time a t about 950” C., and the stellitJe and backing material are pressed together. No photomicrographs of the stellite-electrolytic iron weld were taken. However, t o test its effciency, one corner of the sample was treated with nitric acid until the iron a t that point was completely removed. The surface was considerably changed in appearance. Many vain attempts were made t o separate the remaining iron from the stellite. This would indicate an excellent weld between cladding and backing materials.
Effectiveness of New Method To test further the effectiveness of this new method of cladding, samples of low-carbon steel clad with high-carbon steel, high-speed steel, and the steel shown in Figure 6B were forged with the welded surfaces in a vertical position. Even under this rigorous treatment no separation of the welded materials took place. I n certain cases it mny be considered desirable to have a film of some other metal such as nickel between the cladding and backing materials in order to prevent the migration of carbon from one material to the other. Such a film may be electrodeposited upon the cladding material by a method similar t o that described in the case of the film of electrolytic iron, care being taken to eliminate all nonmetallic material as before. Electrolytic iron will then be deposited upon the nickel, and the cladding procedure will be continued as already described. The backing material used in most cases will probably be ordinary low-carbon steel. However, by this electrochemical method of cladding, it is possible to use any desired backing material. Difficulty may be encountered in producing, by rolling alone, a good weld between some backing materials and the film of electrolytic iron on the cladding material. This difficulty may be avoided by pickling and iron-plating the backing material in such a way as to eliminate all non-
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metallic material. Then a weld is produced between the backing and its coating of electrolytic iron in the usual manner. Finally the cladding and backing materials are brought together with their electrolytic iron surfaces in contact, and a good weld may be produced between these surfaces by rolling alone. The purpose of this paper is rather to outline the principles involved in this new electrochemical cladding process than to give a n exhaustive list of possible applications. However, the applications are almost without limit. The procedure recommended as a result of small-scale work in the laboratory has been adopted in the large-scale plant with practically no change.
Photomicrographs The photomicrographs presented demonstrate the excellence of the diffusion welds produced by the electrochemical method of cladding. It was found in working with commercially available clad materials that, when the surface examined was a t a n angle of 90” to the weld area, frequently not enough of the weld area was exposed t o develop properly the entrapped oxide. Samples in which the surface examined was a t an angle of 45” or less gave much better results. It was found that, except in the case of one of the nickeliron combinations (Figure 8B) the weld area was best resolved by a 5 per cent solution of picric acid in alcohol. I n the case of Figure 8B the best etching agent was found to be a solution of nitric and acetic acids, 1 t o 1 by volume. In all cases the etching was quite light and continued just long enough to resolve the weld area.
Aclcno wledgment The author wishes to express his gratitude to P. A. E. Armstrong for permission to publish the results of this research and for supplying the photomicrographs.
Literature Cited Armstrong, P. A. E., U. S. Patent Reissue 19,058 (Jan. 23, 1934), original patent applied for Oct. 21, 1925. Blum, W., and Hogaboom, G. B., “Principles of Electroplating and Electroforming,” p. 284, New York, McGraw-Hill Book Co., 1930. Fleitmann, Th., German Patent 23,500 (Nov. 17, 1882). Gillespie, 9. E., U. S. Patent 1,306,690 (June 17, 1919). Hughes, W. E., Trans. Electrochem. Soe., 40,200 (1921). Ingersoll, S. L., U. S.Patent 1,868,749(July26, 1932). Johnson, W. C., Ibid., 1,886,615(Nov. 8, 1932). Kern, E. F., Trans. Electrochem. Soc., 13,109 (1908). Maskrey, A. E., U. S. Patent 1,896,411(Feb. 7,1933). Rodig, A., Ibid., 530,719 (Dec. 11, 1894). Rogers, R . R., Trans. Electrochem. Soc., 65, 357 (1934). Thum, E. E., “Book of Stainless Steels,” Cleveland, Am. SOC. Steel Treating, 1933. Ibid., p. 201. RECEIVED JANUARY17,1935.
S U R F A C E P L A N T AND VILLAGE OF A PENNSYLVANIA
BITUMIXOUS C O A L MINE
