CA1213815A - Implantation of certain solid lubricants into certain metallic surfaces by mechanical inclusion - Google Patents

Abstract

Abstract A solid lubricant such as MoS2 is applied to medium to high carbon and stainless steels after surface voids have been produced in the material, as by a final annealing operation, but before a final cold working operation reduces the material to finished size. The latter operation embeds or includes the lubricant into the material and thereby provides a superior lubricated steel for piston ring, shaft, valve stem, spring, stranded wire and the like applications. The technique involved may also employ corrosion inhibiting agents to increase resis-tance to corrosion of the steel as well as to improve its lubricity.

Description

~2i;~

The invention relates to improved techniques of treat-ing certain stee]s with certain solid lubricants to mitigate boundary friction and wear of those steels in sliding contacts and to increase resistance to corrosion.

Molybdenum disulfide (MoS2), for instance, is a well known, versatile solid lubricant having a lattice layer crystal structure. Inherent basal cleavage occurring within its atomic structure results in low lamellar shear strength and contributes to its superior anti-friction or lubricious properties. There is evidence to show that this property is caused by Van der IJaals type bonding between two molecular unit cells on the basal plane connecting the six-fold symmetry of the respective layers com-prising the crystal structure as a whole. It is precisely these chemical bonds, relatively long in physical length, which cause low lamellar shear strength and therefore low dry friction measurement on sliding and rotating contact. Conversely, the chemical bonding occurring in the crystal plane located at right angles to the basal plane is more typical o~ the mono-valent type, shorter in physical length and therefore many times stronger. Recent studies show the hardness for the basal plane as measured on the Vickers Scale to be 32 Kg./mm2 and that for the crystal plane to be 900 Kg./mm2, the latter thus being harder by a multiple of nearly 29. Such a difference in physical measurements within a single unit crystal causes anisotropy, a condition which permits implantation of molybdenum disulfide into metal surfaces to be practical and achievable.
In some motor spring applications an inorganic film containing MoS2 and bonded to the spring material has been utilized to improve the torque consistency of such springs.
Motor springs so treated have proved extremely useful in various mechanical time fuzes and in horological mechanisms of the classic escapement types. Indeed, clocks with such springs have sometimes been operated 300% longer than those w:ithout coated springs before rewinding is required. The increased performance in these instances is a product of the reduction in the kinetic coef~icient of frlction between the spring leaves during the unwinding process, that is to say, a reduction ln the "stick-slip" phenomenon historically associated with main spring applications Application of films of MoS2 to various metallic substrat~s is usual:Ly by spraying or dipping methods and subse-quent drying andJor baking, or even by electroplating the molybdenum directly to the substrate and then heat treating in an atmosphere containing sulfur or sulfide gases. ~hatever the technique, however, it is performed after the material has been processed to finaL or finished size. It has been suggested that transfer oE the MoS2 film to a metallic substrate in these instances is primarily a mechanical process resulting in (a) direct embedding of the solid MoS2 into a softer surface, - tb) deposition of the solid MoS2 into surface depressions generated in the substrate by an "abrasivet' action of the solid MoS2 itself during movement between the substrate and an opposing surface, andlor tc) deposition of ~he solid ~foS2 into the depressions indigenous of the original surface finish and hardness of the substrate. But whatever the case may be, and however satisfactory and lasting these techniques may be for certain applications, the results are not sa~isfactory in the case of items subject to high surface wear. The MoS2 film, essentially still only a surface film, simply does not endure in these environments but is rather quickly removed or destroyed by abrasion. Such high wear items as piston rings, bearings, journals, valve stems, shafts, and ~he like, for instance, are ~3~

composed of various grades of high carbon or stainless steels and though obviously many of them could profit from the low friction characteristics and protection afforded by ~1oS2, especially when other lubrication is at a minimum, no feasible way, so far as is known, has emerged for treating them with MoS2 such that the latter becomes a much more enduring part of the steel itself.
Cold drawrl wire for use in stranded wire constructions, such as wire rope for lifting mechanisms, ship board cable systems, aircraft control cable and the like, and for use in coil springs such as compression, extension and torsion types, is also typically manufactured from various hlgh carbon steel alloysO
The inished wire is furnished to the spring manufacturer, for example, and the springs themselves are ~ormed by various opera-tions including coiling, grinding, secondary forming, stress relieving, plating and, in many instances, special packing.
Likewise, the wire for stranded wire constructions is also shipped to a separate place for manufacture of the rope itself.
The wire for both springs and rope is produced by a combination of cold working, annealing and final tempering operations to a predetermined diameter and shipped on spools, reels or loose wound coils.
Significant improvement in the performance o~ stranded wire cables ought also to be achieved by a solid lubricant such as MoS2 applied to the wire strands in view of earlier work done by the Polymer Corporation of Reading, Pennsylvania, where crane sheaves macle of nylon containing a fine dispersion of MoS2 were manufactured and tested. The lifetime of wire cable passing over the special sheaves was increased, in comparison to that when using standard sheaves. Eventual failure was caused by friction between individual strands in the wire cable.

~21:~8~5 Aircraft carrier arresting cables represent another area of utility for a solid lubricant such as MoS2. Current practice is to reduce friction and corrosion of such cables by repeated applications of a barrier film, such as grease ~ut _he grease is gradually removed from the cable during use. and causes the flight deck to become slippery in critical places~ In adfll~
tion, the grease, being flammable, is a fire hazard, and ~ts elimination would thus provide safer operating condi~ions.
Another carrier-related problem is corrosion of internal aircra~t con~rol cables by sal~ air, and those too ought to ~e i~ipro-~red both in longevity and corrosion resistance by such a lubric1nt.
In short, a wide range of products formed from medium to high carbon and stainless steels ought to benefit greatly from treatment by a solid lubricant such as MoS2 if only the endur-ance of the treatment could be increased by making the lubricant more a part of the steel itself. Not only would friction be reduced but corrosion resistance increased as well in those applications where corrosion is a problem that must be reckoned with. These are thus the chief objects of the present invention.
The invention takes advantage of certain properties of medium to high carbon and stainless steels when they are cold worked in ordcr to bring them down to a predetermined finished size. Here and in the appended claims by "cold working" is meant operations such as drawing, forging, rolling and other standard methods of cold working metal, and by "medium to high carbon and stainless steels" are meant carbon steels, such as AISI-SAE Nos.
1035 to 1095 and AISI-SAE stainless Types 301, 302, 304, 316, 316L, 416, and the like, all of which ar~ "interstitial" in nature or structure and typically used for high surface wear applications. I~hen such steels are cold worked they tend, as is well known, to "work hardened", whereupon they must be annealed ~%~

in order to relieve the dislocation of their crystal lattice which the cold working has produced, the annealing being done at each metal's "recrystallization" temperature. After annealing the metal is then suitable for further cold working. Hence, in many appllcations the cold working process involves a succession of cold workings interspersed by a succession of annealings, the number of each and their arrangement depending upon the extent to which the metal must be reduced in cross sectional size, some-times re~erred to as "breaking down" of the metal to ~inished si2e.
A byproduct of the annealing operation is a phenomenon called "carbide precipitation" owing to the interstitial nature of the metals concerned. During cold working the metal substrate forms macro~molecu]ar carbon clusters between asperities on the metal's surface from which the heat of the annealing process removes the carbon and thereby creates decarbonized voids on the surface of the metal. These voids, not surprisingly, are more pronounced in siæe at -the end of an annealing operation than they are at the end of a subsequent cold working operation.
The essence of the invention, therefore, is the appli-cation of a solid lubricant such as MoS2, for instance/ to the metal after the final annealing operation but before the final cold working operation, the final annealing operation in this case in effect constituting a preparation of the metal for deposit of the MoS2. At that time the surface hardness of the metal is less than it is after final cold working and tempering.
Hence the final cold working, owing to the extreme pressure under which it occurs, will effectively embed the MoS2 into the micro-structure of the metal substrate. Furthermore, the anisotrophlc properties of the MoS2 allow the latter better to penetrate the voids than is possible when the MoS~ is applied to the metal substrate after final cold working when the sub-strate possesses a higher superficial hardness.
Typically, Mo is in micro-powder form which is sul-onatecl to obtaln MoS2, also a powder. That is then sometimes mixed with graphite in a liquid carrier such as perchlorethylene, the graphite being added to improve lubricity at lower loads.
I~hen one form o~ the invention is practiced the MoS2 in the foregoing state is further mixed ~ith an inorganic binding agent such as sodium silicate. After the final annealing operation the steel is coated, ln the manner hereafter described, with the Eoregoing mixture and the perchlorethylene "flash evaporated"
before the final cold working operation. Where corrosion is not a problem this manner o~ practicing the invention is satis-factory. But in environments where the steel is open to corro-sion when employec7 in various finished products, the graphite tends to accelerate corrosion rather than to decrease it even though the surface of the steel is somewhat decarburized by the final annealing. In order to avoid that effect the invention is practiced in another form in which graphite is omitted and an organic based synthetic resin system is used as the binding agent in place of sodium silicate. The system includes a corrosion inhibiter in the form of a "redox" resin.
The latter are synthetic polymers having a highly cross-linked hydro-carbon matrix with inherent reversible func-tional groups attached, such as quinone-hydro-quinone, which are al~ernately oxidi7.ed and reduced. In terms of corrosion inhibit-ing these resins can be referred to as "election exchangers", "redox ion exchangers" or simply redox resins. In fact rapidly reacting MoS2 bonded films containing organic based binding systems including redox resins have only comparatively re-cently become commercially available. The corrosion inhibiting principle is based UpOIl the slowing of the reaction rate in which corrosion occurs. In the oxidation phase, as metallic components ionize they attract anions and form a soluble salt or oxides, causing erosion o~ ~he base metal. In the reduction phase metallic cations are attracted toward cathodic cells that are created or become present owing to the ambient environment. The latter type of corrosion is typically termed galvanic corrosion.
I~hen redox resins are present and in intimate contact within the surface interface, they act as solid electrolytes facilitating an electrical balance, chemically speaking, and cause the rate at which the various reactions occur to be slowed. Corrosion pro-tection is af~orded the base alloy even in the absence of a sacrificial ad~ition of anodic protection.

Since tungsten disulfide (WS2) and graphite (C) are also solid lubricants, having lattice layer crystal structures similar to ~loS2, it is believed and forecast that they too could advantageously be included using the process of the in-vention though to date no tests have yet been conducted to that end. Furthermore, it is contemplated that antimony thioanti-monate (Sb-SbS4) might be added to the MoS2, WS2 or C.
This is because recent studies have shown that certain complex chalcogenides used in combination with solid lubricants, such as ~foS2, WS2 and C, have improved the wear properties of steel in counter-conformal sliding contact under partial hydrodynamic conditions in the presence of certain greases having those lubricants as addi~ives. Among these chalcogenides are arsenic thioantimonate and antimony thioantimonate. The first 9 unlike the second, is suspected of being toxic and is therefore not deemed suitable.
30Hence in its broad aspect the invention contemplates a process of providing a lubricious sur~ace for medium to high carbon and stainless steels for high wear applications wherein a length of the steel is reduced from an initlal larger to a final smaller cross-sectional size by one or more cold working operations. A process of providiny a lubricious surface for medium to high carbon and stainless steels for hi~h wear applications wherein a length of the steel is reduced from an initial larger to a final smaller cross-sectional size by one or more cold workings. The process is carried out by preparing the surface of the steel including annealing the steel in order to form voids on the surface thereof, then covering the surface of the steel by coating the same with micrometer sized particles of at least one inorganic solid lubricant, and then subsequently cold working the steel after the coating to reduce the same to the final cross-sectional size, the temperatures during -the coating and subsequent cold working being below the oxidation temperature of the lubricant.
The invention will first be set forth in terms of a partially predicted application of a solid lubricant to the manufac-ture of piston ring material for internal combustion en~ines.
Piston rings for that purpose are typically fabricated from various high carbon steel alloys.
Vsually the material is furnished the ring manufacturer in the form of flat strips of cross-sectional dimensions, for example, of .61 mm by 2.70 mm in the case of material for oil control rings, produced by a combination of cold working, annealing and final tempering operations. The invention, of course, would be practiced by the manufacturer of the strips before the latter are shipped to the ring maker. Assume, for example, a strip of the above dimensions in finished size whose cross sectional area is thus 1.665 mm2. Assume further that the interim cross-sectional area of the strip after the penultimate cold working operation and the ultimate annealing operation but before the final or ultimate cold working operation is 4.645 mm2 whereby the latter operation accom-plishes about a 65~ reduction in cross-sectional area.
Essentia]ly the invention may be practic~d in this instance by coiling an interim size strip, after preparation by final annealing, on a take-off drum providing a low back tension on the strip and then recoiled on a suitable take-up drum spaced from the former drum in a sometimes called "coil-to-coil" opera-tion. Between the two drums i5 disposed a tank, which may be open to the atmosphere, of perhaps 84 litre capacity and equipped with a suitable stiring device. Into the tank is placed a mix-ture of solid, micro-meter sized particles of the lubricant, e.~, MoS2, graphite, a liquid carrier such as perchlorethylene and an inorganic bonding agent such as sodium silicate, all more or less at room temperature. Between the tank and the take-~lp drum is placed a thermostatically controlled oven or furnace capable of maintaining a temperature of about 260 C over a distance of 2 linear metres. The strip from the take-off drum is then led by suitable well known means through the mixture in the tank~ which is agitated by the stirring device in order to keep the MoS2 in suspension, from which i~ emerges "we~", and then through the oven where the perchlorethylene is "flash evaporated"
in order to produce a dry bonded film of MoS2 on the strip, the latter being finally recoiled on the takeup drum, all at the rate of about 3.65 linear metres per minute. A 34 litre mi~ture con-taining 3275 cc of solid MoS2, sodium silicate, and graphi~e in the proportions of 71, 22 and 8, respectively, the balance being perchlorethylene should result in ~ dry bonded film of MoS2 on the strip of between .0025 and .005 mm thickness. The strip from the take-up drum is next finally cold worked to its finished cross-sectional dimension in the us~al manner and then tempered 12131~S

at about 200 C. The temperatures of the strip during the deposit of the MoS2, the riddance of the carrier liquid and the final cold working and tempering operations, should be kept below the oxidation temperature of the MoS2 which is about 425-480 C Even so, the oxidation rate of MoS2 to MoO3 is quite slow and studies have shown that MoS2 does not lose its lubricity at those temperatures until 30% or so has been oxidized.

As a result the MoS2 is mechanically embedded or "included" in the working surfaces of the piston ring material to a greater extent than would be the case were the MoS2 applied in the usual manner as a film after cold working to finished size. This is borne out by a quantity of piston ring high carbon compression ring steel, AlSl-SAE-C1075, in the form of cold rolled strip 1.78 mm thick and sub-critically annealed for 5 hours at 649C in an argon atmosphere. The material was divided into three specimens: the first was left without treatment; the second had a .0051 mm thick film of MoS2 applied to it using sodium silicate as a bonding agent; the third was given a brief anneal in air at 649C and then a bonded film of MoS2 as in the second specimen. The extra annealing or decarburization of the third specimen before treatment was done in order to determine what effect that would have on depth penetration with respect to implantation of MoS2 into the micro-9tructure of the substrate.
All specimens were then returned to the mill and cold rolled to .60 mm thickness, a reduction in cross-sectional area of about 65%.
Upon their return from the mill the second and third specimens were then cut lengthwise at right angles to the direc-tion of rolling or grain elongation to determine the amount of MoS2 inclusion within the micro-structure of the substrate.
Observation of the cut specimens showed partial and total mechanical inclusion of MoS2 in unusually large deposits. The depth of the inclusion in the case of the second specimen was .02 mm while that of the third or decarburized specimen was .02~ mm.
Tlence it appeare(i that the clepth of the inclusion is ~ f~lnc~ion o ~he depth oi lhe respective decarbur{zed zone9; that is to say, the clegree of inclusion appears constant at about 55-60% of the starting dep~h of the zones concerned for a given amount of cold working. It was also concluded that annealing of the steel before treatment produces a relatively soft ferritic transforma-tion near the surface compared with the underlying pearlite and therefore that ferritic layer Oll the surface of the substrate lends itself to substrate embodiment by the implantation process of the invention.
Friction tests performed on the first and third speci-mens showed a reduction in friction by approximately 25~ in the case of the third specimen compared with the first. This was determined, briefly speaking, by mounting each specimen and two strain gauges intermediate the ends of a lever pivoted at one end and loaded by a weight at the other. Each specimen pressed upon the peripheral surface of a disk of AlSl 4340 steel 73 mm in diameter and 7.2 mm thick revolving at a constant 100 rpm. No fluid lubrication was used between the specimens and the disc.
Output of the strain gauges were led through an amplifier to a Brush Mark 220 strip chart recorder.
Wear tests were also conducted on the second and third specimens using the above test apparatus by weighing the speci-mens before and after in order to determine the loss of welght of the specimens during the tests. The following results were obtained, the weight loss values being averages of three to five tests:

3~

Reduction of wear Weight on specimen Average weight loss (mg) of specimen 3 vs.
(kg) Specimen 2 Specimen 3 specimen 2 (%~

2.5 2.1 1.5 29 ~:lO m.irl. ) 2.0 1.1 1.05 5 (10 min.) 1.25 1.15 0.77 33 (20 min.) 1.0 0.85 0.7~ $
(20 min.) The data shows that the third specimen (that having the e~tra ann~aling and hence decarb~lrization and thus a deeper implanta-tion of MoS2) compar~d with the second specimen (that having only the initial annealing) had 'less material loss for each of the applied loads. The cumulative average material loss for the third specimen was 19~ less than that for the second.
In another test, two plain carbon steel strips, AlSl-1078, were annealed in air. One was then coated with a mix-ture f M~2 and a bonding agent, sodium silicate in a liquidcarrier, dried, and reduced by cold working to.3.28 mm width and .61 mm thickness. The other strip was cold worked to the same dimension before being coated with the foregoing mixture. Both strips were then mounted in epoxy so that their cross-sections were visible and ground and polished using .05 micron alumina powder. Precautions were taken to minimize edge rounding during the polishing. Both samples were then viewed with incident light in a metallurgical microscope at magnifications up to l,000x.
The first sample showed numerous inclusions of dark material into the surface to typical depths of .0025 mm, while the second sample showed no such inclusions.
Further wear tests were conducted using C1075 steel specimens to compare untreated steel (I~plain steel"), steel ~L2~3~

coated with MoS2 hy spraying as in the prior art ("sprayed steel"), ancl steel treated by the process of the invention in-clllding the extra anneallng ("Badger steel"). Each specimen had undergone a Einal cold working whlch reduced its cross-sectional area by 65~, the cold worki.ng of the sprayed steel having been done beEore app]:icat:ion of the MoS2 and that of the Badger steel after the two annealings and the application of the MoS2.
Essentially the same test apparatus described above was used and the surEaces of the specimens were loaded onto the steel disc sufficiently to guarantee that boundary lubrication conditions were present, producing a value of PV of equal to aro~md 80,000 lb-in. 2 ft min 1 This quantity represents a measure of how much energy per urlit time (or power) is being absorbed by the spccimen surfaces ln a counter-conforming mode of sliding contact with the disc. The quantity P is the load per projected area, and the quantity V is the relative velocity of the two surfaces.
This value of PV has been found to cause significant wear of un-treated surfaces under boundary lubrication conditions. For each test five examples of eac'n of the three specimens were fabricated and were each weighed on a chemical balance capable of discrimi-nation to four places of decimals of a gram. The test apparatus was then run in each case at 100 rev/min, a direct load of 2.5 kg was applied together with the requisite number of oil drops per hour. The following table gives the weight of material removed by wear as well as the rate of lubrication of the contacting surfaces:

Type of Final Weight Surface Initial After After After After And Oi.l ~eight 1 hr 2 hr 3 hr 4 hr Rate gms gms gms gms gms ___ __ ___ ___ __ _ l'lain _teel 8 drops/hr 0.46~5 0.~670 0.4585 0.4584 Sprayed Steel 60 drops/hr 0.4824 0.4757 8 drops/hr 0.4735 0.4714 0.4668 0.4507 Badger Steel 6n drops/hr 0.4799 0.4793 8 drops/hr 0.4917 0.4915 0.4914 0.49150.4915 Rate of Revolution = lOO rev/min Surace Direct Load = 24.5 newton Approximate Value of PV = 80,000 lb-in 2 ft min 1 No of Samples for Each Test = 5 It is clear from the table that under conditions of boundary lubrication the wear rate of the Badger steel is sub-stantially zero after the first hour's run, and its actual wear rate is only one-tenth that of the sprayed steel. In addition, in the case of the sprayed steel, wear appears to continue after the first hour and its rate is approximately 50% greater than that of the plain steel after 1 hour's run. After two hours run-ning, the rate of wear increases and thence the sprayed steel has approximately twice the wear rate of the plain steel~ Another remarkable aspect is that the at the beginning of the runs the width of the contact area between the specimens and the steel L3~

disc of the test apparatus was .254 mm while at the conclusion of the runs that widt~h in the case of the plain steel was 1.52l~ mm but only .762 mm in the case of the Badger steel. ~lence the con~.act area of the plain steel was twice that of the Badger steel so that tlle pressure upon the latter was twice that upon the former. There~ole the greatly improved wear rate of the Bad~er steel was obtained even though the pressure upon it rose to twice that upon the plain steel.
No essential change in the steel itsel~, from the standpoints of hardness, strength, and the like, seems to occur when treated by the process of the invention. The steel can thereafter be fashioned into piston rings, for instance, in the conventional manner but the typical operation of chrome plating of the finished ring would be omitted. The customary differen-tial is superficial hardness between the chrome plated ring and the cylinder wall is thus reduced and thereby wear on the wall itself is also diminished. At the same time wear on the ring is reduced because its inherent lubrication supplements normal liquid or hydrodynamic lubrication between the ring and the cylinder wall. The lubricated ring better withstands high operating loads, better operates for short periods with boundary lubrication, better distributes local loads, and betters the wear characteristics of the mating surfaces. This is especially important adjacent top and bottom dead centers since the greatest wear of a cylinder wall in an internal combustion engine has been found to occur where piston direction changes and where the oil film is unable to accumulate sufficient thickness to separate the two opposing surfaces. This is because the zero velocity of the piston at those two points means that the hydrodynamic require-ment of relative velocity between opposing surfaces is not met atthese precise locations. The lubricated rings, on the other ~2~L3~

hand 9 provides supplemental lubrication at these points at these crucial times, somethlng a chrome plated ring cannot do, as well as over the ent:lre cylincler wall during the critical breakin period of a new engitle.
The invention will next be set forth in terms of a pre-dicted application o~ a solid lubricant to the manufacture of cold drawn wire for use in springs and stranded wire con-structions.
~ ssume, for example, wire having a finished diameter of .71 mm or a cross-sectional area of .40 mm2, and that the in~erim diameter of the wire after the penultimate cold working operation and the ultimate annealing but `before the ultimate cold working operation is about 1.90 mm or a cros~-sectional area of 2.84 mm2, whereby the latter operation accomplishes about an 85% reduction in cross- sectional area. Also assume that the foregoing annealing was accomplished in the usual mamler in a non-oxidizing atmosphere to achieve recrystalization and that a subsequent anneallng operation is performed in a strand type annealer at about 650 C for a flash type decarburiæation of between 40 and 60 seconds duration, the latter operation broaden-ing the decarburlzed zone to about .045 mm and thus optimizing the surface for mechanical inclusion pursuant to the invention.
As before, the wire a~ter the latter annealing opera-tion, may be coiled on a pay-off reel with which is appropriately associated a take-up reel for a coil to-coil coating operation.
Between the two reels is disposed a refrigerated tank of perhaps 70 to 80 litre capacity into which is placed a mixture of solid, micro-meter sized lubricant, e.g., MoS2, organic based binding agents, such as phenolic-vinyl-resin or epoxy-vinyl-resin, together with redox resins to act as corrosion inhibiting agents, and a guick drying composite solvent or liquid carrier consisting of 60% cellulose acetate, 30% xylene, and 10% methyl ethyl ketone. The refrigeration of the tank is regulated to keep the mixture at a tempcrature between 0 and 5 C owing to the vola-tili~y of the solvent. Between the tank and the take-up reel is also disposed a thermostatically controlled oven or Eurnace capable of maintailling a temperature of 260 C over a distance of 2 linear metres. The wire from the pay-off reel is then led by well known means through the mixture in the tank which is agi-tflted by a suitable stirring device in order to keep the MoS2 in suspension. The wire then emerges from the tank "wet" and into the oven where the solvent is "flash evaporated" in order to leave a dry bonded film of MoS2 on the wire. The latter is recoiled on the take-up reel at the rate of 3 to 3-1/2 linear metres per minute, the rapid rate of reaction of the resins con-cerned being essentlal because of the relatively immediate recoiling of the wire after it has passed through the tank.
Finally, the wire is transferred to a suitable wire drawing in-stallation and reduced in cross-sectional area, that is to say, cold worked, to its previously mentioned finished diameter. Such cold working in this case should be kept at temperatures below about 315 C because the resins involved tend to decompose above that point.
Wire so treated would have several advantages. For instance, when used to manufacture coil springs, expensive post-plating for corro.sion protection would become unnecessary, thus eliminating the inherent problems of hydrogen embrittlement, tangling of springs, and the absence of pla~ing between the close-wound coils of extension springs. Furthermore, the wire would retain improved duc~ility and toughness compared to hot dipped galvanized wire because the brittle alloy between the zinc and the steel interface would be eliminated. The same or similar ~3~

advantages would also accrue to such wire when employed in various stranded wire construction, as previously mentioned. To the extent the fi.nal cold working diminishes some of the corro-si.on inhibiting ploperties achievecl by the invention, for added protecti.on the w:i.re can be recoated with MoS2 by the previously described prior art methocls after final colcl working.
The invention is also believed applicable to other high wear components previously mentioned, such as bearings, journals, shafts and so forth, on which it would be practiced in manners analogous to those described in the cases of piston rings and wire.

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process of providing a lubricious surface for medium to high carbon and stainless steels for high wear applica-tions wherein a length of the steel is reduced from an initial larger to a final smaller cross-sectional size by one or more cold working operations, characterized by: forming voids in the surface of the steel by a preparatory operation including anneal-ing the steel after a penultimate cold working operation; then covering the surface of the steel by a coating operation with a mixture containing micrometer sized particles of a solid lubri-cant selected from the group consisting of molybdenum disulfide, tungsten disulfide and graphite, plus a bonding agent in a liquid carrier; then removing the liquid carrier by a drying operation;
and then performing an ultimate cold working operation upon the steel to reduce the same to said final crosssectional size, the temperatures during said coating drying and ultimate working operation being below the oxidation temperature of the lubricant.

2. The process of claim 1 further characterized by again annealing the steel to decarburize the surface thereof before said coating operation.

3. The process of claim 2 further characterized by the addition of antimony thioantimonate to said mixture.

4. The process of claim 1 further characterized by the lubricant being molybdenum disulfide.

5. The process of claim 4 further characterized by again annealing the steel to decarburize the surface thereof before said coating operation.

6. The process of claim 5 further characterized by the addition of antimony thioantimonate to said mixture.

7. The process of claim 5 further characterized by the liquid carrier being perchlorethylene and the bonding agent being sodium silicate.

8. The process of claim 5 further characterized by the bonding agent being an organic based synthetic resin and the liquid carrier being a composite solvent.

9. The process of claim 8 further characterized by the bonding agent also including a redox resin.

10. The process of claim 9 further characterized by coating the steel with a mixture of micro-meter sized molybdenum disulfide and a bonding agent in a liquid carrier after said ultimate cold working operation.

11. A process of providing a lubricious surface for medium to high carbon and stainless steels for high wear applications wherein a length of the steel is reduced from an initial larger to a final smaller cross-sectional size by one or more cold workings, characterized by:
preparing the surface of the steel including annealing the steel in order to form voids on the surface thereof;
covering the surface of the steel by coating the same with micrometer sized particles of at least one inorganic solid lubricant; and subsequently cold working the steel after said coating to reduce the same to said final cross-sectional size, the temperatures during said coating and subsequent cold working being below the oxidation temperature of the lubricant.

12. The process of claim 11 further characterized by the steel having been cold worked prior to said annealing.

13. The process of claim 12 further characterized by said annealing comprising successive anneals to recrystallize the steel and then to decarburize the surface thereof before said coating.

14. The process of claim 13 further characterized by the addition of antimony thioantimonate to the lubricant.

15. The process of claim 11 further characterized by the lubricant being selected from the group consisting of molybdenum disulfide, tungsten disulfide, and graphite.

16. The process of claim 15 further characterized by the steel having been cold worked prior to said annealing.

17. The process of claim 16 further characterized by said annealing comprising successive anneals to recrystalize the steel and then to decarburize the surface thereof before said coating.

18. The process of claim 17 further characterized by coating the steel with a mixture of said lubricant and a bonding agent in a liquid carrier after said subsequent cold working.

19. The process of claim 17 wherein said coating is further characterized by covering the surface of the steel with a mixture of said lubricant and a bonding agent in a liquid carrier and then removing the liquid carrier by drying before said subse-quent cold working.

20. The process of claim 19 further characterized by the addition of antimony thioantimonate to the lubricant.

21. The process of claim 19 further characterized by the liquid carrier being perchlorethylene and the bonding agent being sodium silicate.

22. The process of claim 19 further characterized by the bonding agent being an organic based synthetic resin and the liquid carrier being a composite solvent.

23. The process of claim 22 further characterized by the bonding agent also including a redox resin.