US2780542A - Wear-resistant alloy - Google Patents

Description

United States Patent WEAR-RESISTANT ALLOY 'Clarence E. Cormack, Buffalo, N. Y., assignor to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Application December 8, 1953,

Serial No. 397,009

7 Claims. (Cl. 75-134) Alloys of the type containing one or more metals of the tungsten-molybdenum-chromium group and cobalt or .nickel or both have been known and widely used for :many years because of their extremely useful property of resistance to wear. There are certain applications in industry in which it is desired to use materials having even greater resistance to wear than the conventional a1- loys of this type which are available commercially, for instance, applications where there is sliding, metal-tometal contact. Although it was suggested many years ago that the wear resistance of alloys of this type may 'be increased if they are so treated as to convert a portion of their carbon content to flake graphite, it has been the general experience of the art that alloys containing flake graphite are usually weaker than similar alloys free of flake graphite. Graphitic alloys of the above-mentioned type have not been commercially accepted. The problem therefore presented is one of producing graphitic alloys of the above type but that combine both wear-resistance and strength. The solution to this problem demands the presence of graphite but in a form that will not weaken the inherent strength of the component metals, yet these very metals that lend strength to the alloy are jealous of the presence of free carbon and the problem thus faced requires a solution that will at once both provide free carbon in company with metals that seize upon free carbon to form carbides and the free carbon must not be substantially present in flake form.

It is the principal object of this invention to provide :alloys of tungsten-molybdchum-chromium group metal .and iron-cobalt-nickel group metal materials having :superior wear resistance and good strength.

This object is achieved by the present invention which is based on the discovery that the resistance to wear of :alloys of the type in question in which the carbon is normally present as carbides may be quite markedly increased if the carbon content of the alloys is increased beyond the normal range and the alloys are treated so :as to produce, in substantially uniform distribution, .zgraphite in spheroidal or nodular form. The invention, accordingly, comprises alloys containing 10% to 65% in the aggregate of at least one metal selected from the group consisting of chromium, molybdenum and tungsten; the chromium content of the alloys not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25%; 2% to 7% carbon; the remainder being metal selected from the group consisting of iron, cobalt and nickel together with incidental impurities, the iron content not exceeding 15%. The alloys also contain a small proportion of a graphite nodularizing agent, selected from the group consisting of cerium, mischmetal and magnesium, effective to convert at least a substantial portion of the carbon content of the alloys to the form of ice nodular graphite substantially uniformly distributed. A preferred upper limit for the aggregate of chromium, molybdenum and tungsten is 50%, chromium not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25%.

Alloys having the composition above disclosed and containing nodular graphite in substantially uniform distribution may be simply prepared. To promote the formation of nodular graphite, it is necessary that the alloys contain a relatively high proportion of carbon and that they be treated in the molten condition with a graphite nodularizing agent, selected from the group consisting of cerium, mischmetal and magnesium. One convenient method of producing a desired alloy Within the invention is to form a molten bath of a high carbon cobalt or nickel metal and then to add the desired alloy elements to the bath. Up to 1 /z% silicon may be added to the alloy, improving its fiuidity in the molten condition, but the presence of silicon is not essential to the formation of nodular graphite. The graphite nodularizing agent may then be placed in the pouring ladle and the molten metal tapped into the ladle. The molten alloy is then cast in conventional manner into molds. Although the mold used may be of any conventional mold material, for instance sand or other refractory material, generally more nodular graphite is retained if the mold does not chill the metal too severely.

To attain the desired nodularization of graphite in the alloys of the invention, it is necessary that there be a small proportion of the selected nodularizing agent retained in the composition. Because of losses due to volatilization or splashing or oxidation or other causes it is desirable to add to the alloys substantially more of the selected agent than the minimum quantity required. In a series of tests in which difierent quantities of nodularizing agents were added to an alloy containing 15% chromium, 5% tungsten, 1.5% silicon, 4% carbon, remainder cobalt, effective nodularization of graphite was attained with additions of a 50% cerium mischmetal ranging from 0.25% to 1%. The cerium retained in the alloys varied from about 0.08% to 0.4%. Similar tests of the same alloy to which were added diiterent proportions of magnesium showed that efiective nodularization of graphite was attained with magnesium additions rang ing from 0.125% to 1%, retained magnesium ranging from about 0.05% to 0.23%. Because of analytical difficulties, it is not possible to state a precise lower limit for retained quantities of nodularizing agent, but the best evidence indicates that at least 0.05 of such agent should be present in the alloys of the invention in the cast con dition. To assure the retention of this minimum quantity, it is recommended that when cerium is used about 0.075% to 0.5% be added and that when magnesium is used about 0.075 to 1% be added.

If magnesium is used as the nodularizing agent, it is convenient to employ it in the form of an alloy, for in stance of nickel and magnesium. However, it is preferred to use either cerium or mischmetal as the nodularizing agent as magnesium tends to produce a violent action.

In accordance with the invention, many alloys have been prepared, which contained, in addition to carbon and cobalt or nickel, one or more of the metals chromium, molybdenum, tungsten and iron. Table 1 lists as examples of the invention several of these alloys. To each of these alloys had been added 0.5% mischmetal as nodularizing agent. The mischmetal contained 50% cerium.

3 T able 1 COlWPOSlTION-REMAINDER COBALT, 1.5% SILICON AND INCIDENTAL IhlPURITlES COMPOSITION-RF1WAINDER NICKEL, 1.5% SllllCON AND INCIDENTAL IMPURIlIlTS l lcrcent i Percent; Percent Percent Or I C filo ll 40 l Nll lNll l 4 Nil 15 1 4 )5 Nil 15 l 4 l2. 5 l2. 5 Nil i Nil I 1 Microscopic examination of each of the alloys listed in Table l has shown them to contain nodular graphite substantially uniformly distributed throughout the alloys. Generally, the major proportion of the free carbon appears to he in the form of nodular graphite. Mechanical tests or these alloys have shown that they are generally strong as the alloys 0t conventional composition containing no graphite and are significantly stronger than similar alloys containing flake graphite.

For instance. indicative of the strength of alloys containing noduntr graphite as compared with substantially identical alloys containing flake graphite, the following data are cited. Two alloys containing about 23% chromium, 5% tungsten, 5% carbon, 1.5% silicon, remainder cobalt, were melted and cast in the form of /2-inch square bars in four-print sand molds. One alloy (alloy A) was treated with 0.5% mischmetal as a nodularizing agent, and the other (alloy B) was not. Otherwise, both alloys were made and treated identically. Each of the bars was broken on four-inch centers with a load applied at the center. Results of these tests are set forth in Table II.

Table 11 Percent Composition-Remainder Co Transverse Strength, Lbs.

Alloy Cr W C 1st Bar 2nd Bar 3rd Bar 4th Bar *Treated with mischrnet-al.

Microscopic examination of samples of alloys A and B showed both to contain free carbon as graphite, but in alloy A the graphite was nodular in form and in alloy B was in the form of flakes. The greater strength of alloy A is evident from the data in Table ll.

The Wear resistance of the alloys of the invention is generally at least equal to that of the conventional chromium-cobalt-tungsten alloys well known to industry and is superior in some cases, particularly in the case where one article is in sliding contact with another. It is believed that the improved wear resistance may be due to the fact that the material containing nodular graphite has minute pits on its surfaces in the areas where the nodular graphite exists, and that these pits provide sites for the retention of lubricant. Whether or not this explanation is correct, however, it is a fact that the alloys of the invention have superior wear resistance under the conditions specified above to alloys of similar composition in which the carbon is not present as nodular graphite. For this reason, the alloys of the invention are particularly suited for use in such applications as hearings, or other parts subjected to either continuous or intermittent motion in contact with another article of the same or other composition.

The alloy may be cast into welding rods from which hard faci deposits may be produced in a conventional manner, example, as by fusion-deposition, the Weld deposit retaining nodular graphite.

What is claimed is:

1. An alloy containing 10% to 65% in the aggregate of at least one metal selected from the group consisting of. chromium, molybdenum and tungsten, the chromium not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25%; 2% to 7% carbon; up to l5% iron; at least one graphite nodularizing agent selected from the group consisting of cerium, mischmetal and magnesium in a proportion suilicient to promote the formation of nodular graphite in said alloy; the remainder at least one metal elected from the group consisting of cobalt and nickel, together with incidental impurities; at least a substantial. portion of the carbon content of said alloy being present in the form of nodular graphite substantially uniformly distributed throughout said alloy.

2. An alloy containing 10% to 50% in the aggregate of at least one metal selected from the group consisting chromium, nolybdenum and tungsten, the chromium not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25%; 2% to 7% carbon; upto l5% iron; about 0.05 to 0.4% in the aggregate of at least one graphite nodularizing agent selected from the group consisting of cerium, mischmetal and magnesium; the remainder at least one metal selected from the group consisting of cobalt and nickel, together with incidental impurities; at least the greater portion of the carbon content of said alloy being present in the form of nodular graphite substantially uniformly distributed throughout said alloy.

3. An alloy containing 10% to 50% in the aggregate of at least one metal selected from the group consisting of chromium, molybdenum and tungsten, the chromium not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25%; 2% to 7% carbon; up to 15% iron; about 0.05% to 0.4% cerium; the remainder at least one metal selected from the group consisting of cobalt and nickel, together with incidental impurities; at least the greater portion of the carbon content of said alloy being present in the form of nodular graphite substantially uniformly distributed throughout said alloy.

4. An article required in its normal use to withstand wear, at least the surface portions of said article exposed to Wear being composed of an alloy containing 10% to 50% in the aggregate of at least one metal selected from the group consisting of. chromium, molybdenum and tungsten, the chromium not exceeding 40% and the ag gregate of molybdenum and tungsten not exceeding 25%; 2% 7% carbon; up to 15% iron; about 0.05% to 0.4% in the aggregate of at least one graphite nodularizing agent selected from the group consisting of cerium, mischmetal and magnesium; the remainder at least one metal selected from the group consisting of cobalt and nickel, together with incidental impurities; at least the greater portion of the carbon content of said alloy being present in the form of nodular graphite substantially uniformly distributed throughout said alloy.

5. An article required in its normal use to withstand wear, at least the surface portions of said article exposed to wear being fushion-depositcd, said surface portion being composed of an alloy containing 10% to 50% in the aggregate of at least one metal selected from the group consisting of chromium, molybdenum and tungsten, the chromium not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25%; 2% to 7% carbon; up to 15% iron; about 0.05% to 0.4% in the aggregate of at least one graphite nodularizing agent selected from the group consisting cf cerium, mischmetal and magnesium; the remainder at least one metal selected from the group consisiting of cobalt and nickel, together With incidental impurities; at least the greater portion of the carbon content of said alloy being present in the form of nodular graphite substantially uniformly distributed throughout said alloy.

6. A welding electrode having the composition 10% to 50% in the aggregate of at least one metal selected from the group consisting of chromium, molybdenum and tungsten, the chromium not exceeding 40% and the aggregate of molybdenum and tungsten not exceeding 25% 2% to 7% carbon; up to 15% iron; about 0.05% to 0.4% in the aggregate of at least one graphite nodularizing agent selected from the group consisting of cerium, mischmetal and magnesium; the remainder at least one metal selected from the group consisting of cobalt and nickel, together with incidental impurities; at leastrthe greater portion of the carbon content of said alloy being present in the tungsten, the chromium not exceeding 40% and the agform of nodular graphite substantially uniformly distributed throughout said alloy.

gregate of molybdenum and tungsten not exceeding 25%; 2% t0 7% carbon; up to 15% iron; about 0.05% to 0.4% in the aggregate of at least one graphite nodularizing agent selected from the group consisting of cerium, mischmetal and magnesium; the remainder at least one metal selected from the group consisting of cobalt and nickel, together with incidental impurities; at least the greater portion of the carbon content of said alloy being present in the form of nodular graphite substantially uniformly distributed throughout said alloy.

References Cited in the file of this patent Stahl und Eisen, December 18, 1924, page 1719.

The Institute of British Foundrymen, Paper No. 875, pages 8 to 10. Paper prepared for presentation at the 44th annual meeting, June 17 to 20, 1947.

Claims (1)

1. AN ALLOY CONTAINING 10% TO 65% IN THE AGGREGATE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM, MOLYBDENUM AND TUNGSTEN, THE CHROMIUM NOT EXCEEDING 40% AND THE AGGREGATE TO MOLYBDENUM AND TUNGSTEN NOT EXCEEDING 25%; 2% TO 7% CARBON; UP TO 15% IRON; AT LEAST ONE GRAPHITE NODULARIZING AGENT SELECTED FROM THE GROUP CONSISTING OF CERIUM, MISCHMETAL AND MAGNEISUM IN A PROPORTION SUFFICIENT TO PROMOTE THE FORMATION OF NODULAR GRAPHITE IN SAID ALLOY; THE RAMAINDER AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF COBALT AND NICKEL, TOGETHER WITH INCIDENTAL IMPURITIES; AT LEAST A SUBSTANTIAL PORTION OF THE CARBON CONTENT OF SAID ALLOY BEING PRESENT IN THE FORM OF NODULAR GRAPHITE SUBSTANTIALLY UNIFORMLY DISTRIBUTED THROUGHOUT SAID ALLOY.