US3713907A

US3713907A - Graded multiphase materials

Info

Publication number: US3713907A
Application number: US00099366A
Authority: US
Inventors: Thyne R Van; J Rausch
Original assignee: Surface Technology Corp
Current assignee: Surface Technology Corp
Priority date: 1970-12-18
Filing date: 1970-12-18
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30

Abstract

A CARBURIZED, MULTIPHASE MATERIAL FORMED OF AT LEAST ONE METAL OF EACH OF GROUP I, II, AND III. GROUP I IS COLUMBIUM, TANTALUM, AND VANADIUM; GROUP II IS TITANIUM, ZIRCONIUM AND HAFNIUM; AND GROUP III IS MOLYBDENUM TUNGSEN, RHENIUM AND CHROMIUM. HAVE EXCELLENT ABRASION RESISTANCE.

Description

Jan. 30, 1973 R. J VAN THYNE EIAI. 3,113,907

GRADED HULTIPHASE MATERIALS 2 Shobts-Shet' 1 mad Dec. 18,. 1910 SCALE: O.l5 INCHES MIL.

Jan. 30, 1973 J. VAN THYNE FIAL 3,713,907 GRADED MULTIPHASE MATERIALS Filed Dec. 18, 1970 2 Sheets-Sheet 2 SCALEI 0J5 INCHES= l MIL.

3,713,907 GRADED MULTIPHASE MATERIALS Ray J. Van Thyne, Oak Lawn, and John J. Rausch,

Antioch, Ill., assignors to Surface Technology Corporation, Stone Park, Ill.

Filed Dec. 18, 1970, Ser. No. 99,366 Int. Cl. C22c 27/00; C23c 11/14 U.S. Cl. 148-315 17 Claims ABSTRACT OF THE DISCLOSURE A carburized, multiphase material formed of at least one metal of each of Group I, II, and III. Group I is columbium, tantalum, and vanadium; Group II is titanium, zirconium and hafnium; and Group III is molybdenum, tungsten, rhenium and chromium. Have excellent abrasion resistance.

BACKGROUND OF THE INVENTION Our invention is directed particularly to carburized materials of selected alloy compositional ranges which are characterized by a graded microstructure and as having excellent abrasion resistance. Such materials are and must be continuously graded from the surface inwardly in terms of microstructure, hardness and carbide concentration. The alloys required in order to obtain such grading and desired properties are ternary or more complex. The use of refractory metal alloys carburized as hereindescribed results in very substantial abrasion resistance especially as compared with carburized ferrous alloys.

The alloys which we carburized contain certain of the refractory and reactive metals of Group IV-B, V-B, and VIB of the Periodic Table of Elements. We have discovered that when the present alloy systems are carburized there results the surprisingly good properties and related graded microstructure set out below.

In the present specification and claims much usage is given to the terms phase and multiphase. We employ said terms as they are commonly used in good metallurgical practice. By phase we mean a physically homogeneous and distinct portion of a materials system and by multiphase two or more coexisting phases.

We would note obviously that the carburizing of certain metals or alloy systems is not novel and further that certain of the unreacted base alloys which are employed in the present invention are also not novel. Furthermore alloy compositions fairly similar to ours with relatively small carbon additions used principally for strengthening have also been reported. However, nowhere does the prior art show the graded materials with the resulting excellence as are set forth below.

The carbides of the metals of Groups IV-B, VB, and VI-B are known to have high hardness, corrosion and oxidation resistance and high melting points, Methods for utilizing these properties for either wear resistance or strengthening have been studied by numerous investigators over a period of years and such studies have included carburizing, powder processing techniques and the dispersion strengthening of various alloy matrices.

In the dispersion strengthening art, a relatively low volume of fine particles is distributed essentially uniformly throughout an alloy. Carbides have been favorite agents in dispersion strengthening of refractory metal (i.e. Cb,

nited States Patent Ta, V, Mo, W base) alloys particularly for improvement in creep rupture properties. See, for example, U.S. Pats. 2,822,268 and 3,194,697, and Canadian 'Pat. 716,520. Whereas very significant creep strengths can be obtained, the volume of hard phase is low and these dispersion strengthened alloys do not at all compare to the extreme abrasion resistance demonstrated by the materials of the present invention.

Other investigators have also attemped to make multiphase wear products by a variety of powder processing techniques which consist essentially of dispersing carbides in a matrix of refractory metals or alloys. These investigators correctly assume that replacing the cobalt binder used in commercial sintered carbide with a higher melting matrix would enhance wear resistance, but such materials are made only under the most laborious conditions since it is very ditficult to achieve full density. Such wear products may contain a relatively high volume of hard phase uniformly dispersed but they are not produced by external carburizing and are quite different from the materials of our invention. The structures obtained are not graded from the surface inwardly as is the case with our materials.

Patents directed to the carburizing of elemental tantalum metal have issued from at least 1908 (See U.S. 896,705) to the present. See U.S. 3,523,044 of 1970). These inventions disclose the formation of continuous carbide layers at the surface which we specifically reject as having inferior utility and which in no way form a part of the present invention.

The tendency of the carburized layer on elemental metals to crack and delaminate at the carbide-metal interface and spall was reduced by alloying prior to carburizing and resulted in an irregular interlocking interface. (See U.S. Patent 3,163,563.) In this referenced invention the carbide layers are similar to carburized tantalum and an important feature thereof is the formation of a thicker layer of the outer carbide. The patentees objective of a relatively thick outer carbide layer differs quite substantially from our present invention in that the carbide zone in our materials is not continuous. The formation of the irregular serrated boundary between the carbide layer and the substrate may improve adherency somewhat. However, the elimination of a relatively thick continuous carbide layer in favor of a multiphase graded structure as we teach in this present invention results in greatly improved properties in our materials.

Those skilled in the art will recognize that in addition to carbon, boron and nitrogen may also be employed as hardening agents in refractory alloys. In our copending applications, Wear Resistant Materials Ser. No. 755,658 now U.S. Patent 3,549,427 and Wear and Abrasion Resistant Materials Ser. No. 755,662 now U.S. Patent 3,549,429 (counterparts have now issued as French Patents 1,584,635 and 1,596,561) we have disclosed how to prepare graded nitrided materials. These are ternary or higher order alloys and a necessary requirement of thosesystems is the presence of molybdenum and/or tungsten to achieve the desired degree of relative reactivity with nitrogen since both molybdenum and tungsten are essentially inert in nitrogen.

Unlike as in the nitrided systems, molybdenum or tungsten are quite active in a boronizing or carburizing environment and form very hard, stable compounds. We attempted the boronizing of a variety of compositions tha yield useful nitrided materials including alloys of columbium or tantalum with titanium or zirconium, and with up to 20% molybdenum or tungsten. However, in such materials only continuous surface boride layers form thereon. Thus, it was with some considerable surprise that we discovered that similar compositions exhibit the desirable relative reactivity with carbon and form graded multiphase composites with carbide content and hardness lessening as one moves deeper into the material from the surface. Furthermore, we have found that the carburized materials show certain differences and advantages over nitrided materials as demonstrated in the subsequent examples. The physical stability of the carbides is greater than that of the nitrides. The nitrides can exhibit a significant vapor pressure at the reaction temperatures of interest.

In distinction to all of these prior art teachings as will be apparent to those skilled in the art, we have developed a graded, multiphase series of composite structures which are further characterized by excellent wear and abrasion resistant properties.

DESCRIPTION OF THE INVENTION In the preferred embodiments of the present invention certain ternary or higher alloyed systems are carburized. Such alloy systems consist of metals of Groups I, II and III wherein:

Group I is one or more metals of the group columbium,

vanadium and tantalum;

Group II is one or more metals of the group titanium,

zirconium and hafnium; and

Group III is one or more metals of the group molybdenum, tungsten, rhenium and chromium.

A principal object of our invention is to produce a novel group of carburized, multiphase structures consisting of carburized alloys of Groups I, II and III.

Another object of our invention is to provide such novel materials wherein a portion of the carbides are replaced by either nitrides or borides or both.

These and other objects, features, and advantages of our invention will become apparent to those skilled in this particular art from the following detailed disclosure thereof and from the enclosed FIGS. 1 through 6 which are photographs at l50 magnification in which:

FIG. 1 shows Ta-30Ti gas carburized at 3250 F. for 2 hours;

FIG. 2 shows Ta-ZOTi-IOMo gas carburized at 3350 F. for two hours;

FIG. 3 shows unalloyed columbium pack carburized at 3450 F. for two hours;

FIG. 4 shows Cb-70Ti gas carburized at 3250 F. for two hours;

FIG. 5 shows Cb-4OTi gas carburized at 3250 F. for two hours; and

FIG. 6 shows Cb-20Ti-40W gas carburized at 3350 F. for two hours.

The alloys which were carburized were melted under an inert atmosphere in a non-consumable arc furnace using a water-cooled hearth. The alloy specimens were gas carburized in an atmosphere of either methane-hydrogen or methane-argon using high purity gases with a methane content under 10% or pack carburized by embedding in chunk carbon and heating in an atmosphere consisting of 95% argon-5% hydrogen. Gas carburizing results in a smoother surface, particularly at the higher titanium compositions.

Many ternary alloys were carburized and then evaluated metallographically. A number of examples of compositions falling within our invention are presented in Table I. All of said compositions have a multiphase, graded composite structure essentially to the surface and because of a high volume of hard phase near the surface demonstrate good abrasion resistance. For efiective wear resistance, materials of the present invention should contain at least by volume of hard phase at the surface. Our carburized materials contain substantially more than 25 hard phase at the surface. The multiphase structure minimizes chipping and by imparting toughness contributes to high performance.

In the present specification and claims all compositions are given in weight percent.

TABLE I Carburization fomposition (W/O) F. Hours Type 1 (b 20Ii-20M0 3, 450 2 G Cb 'Ii-10Mo 3,350 2 G Cb-30Ti 20Mo 3,350 2 G (b-4OTi-30Mo 3, 450 2 G C li-30'Ii-20W t 3, 350 2 G C hlOTi-IOW 3, 350 2 G (h-10TH 0M0. 3, 250 7 P Cb-l7Ti- 0W 3, 250 6 P C D-lTTl-IZO 3, 450 2 P Cb-30Ti-20W 3, 250 8 P Ch-2U'Ii-40W 3, 250 7 P 'Ia-20Ti-l0lll0. 3, 350 2 G 'Ia-30Ti-20Mo 3,350 2 G Ta-'Ii-35Mo. 3,350 2 G Ta 20Ti-20W l 450 2 G 3, 450 2 G 3. 250 6 P 3, 250 6 P 3, 250 (i P 3, 450 2 P l l 2, 950 2. 5 G

l G: Gas carburized using methane-hydrogen or metlianeargon;

P=Pack carburized using chunk carbon and A5% Hz.

FIG. 1 shows a carburized binary alloy, Ta-30Ti, with a thick continuous carbide layer similar to that formed on carburized tantalum and obviously is excluded from our invention. The resulting difference in carburizing of a ternary alloy, Ta-20Ti-10Mo is shown in FIG. 2-an improved structure that is included in our invention. A thick surface carbide is illustrated for unalloyed columbium and Cb-Ti in FIGS. 3 and 4, respectively. After carburizing a range of Cb-Ti compositions, We find that at a composition of Cb-40Ti a coarse two-phase structure is formed under the continuous surface carbide (FIG. 5). The significant modification in structure achieved by addition of a ternary constituent prior to carburizing is seen in FIG. 6, representing Cb-20Ti-40W. Other microstructural forms are seen in other carburized materials within our invention but in all examples such structures are multiphase and grade inwardly. The precipitated phases shown in FIGS. 2 and 6 form from single phase solid solutions during carburizing. Preferential segregation of carbon and titanium into the precipitated hard phases was shown by microprobe analyses of carburized Ta-lZTi- 15W.

By the term graded as used regarding carbide formation in the present specification and claims we mean that there is a lessening of metal carbide formation and thus concentration as one moves inwardly from the surface. Such grading is shown in FIGS. 2 and 6.

The good grading in our carburized materials is also demonstrated by microhardness (DPN) readings on the flat surfaces of metallographically polished cross sections. For 4; inch thick materials falling within our invention the 25 gram load hardness measured on a cross sectional traverse in a zone between the surface and a depth of 0.5 mil is at least 800 DPN and the hardness grades inwardly in a mostly continuous fashion. Selected data using a 50 gram load at 0.5 mil and a 200 gram load at 1 to 8 mils from the surface are given in Table II.

TABLE II 6 Cb-Ti-15Hf-2OW. We find that hafnium tends to promote the formation of a continuous carbide surface layer, especially at external corners where carburization is Carburization Mierohardness at depth (mils) N ates-C Cracking; M Hardness in matrix.

Both carburized columbium and Cb-70Ti show cracking around the hardness impressions in the hard continuous carbide layer and an abrupt change in hardness between the outer carbide layer and the substrate whereas grading and support of the hardened surface is evident in the three materials in Table II included in our invention. Our materials can exhibit very high hardness near the surface. The 50 gram microhardness at a depth of 0.3 mil from the surface was 4350 DPN for carburized Ta-18Ti-25W. Carburized tantalum exhibits a soft (195 DPN) substrate immediately beneath the outer compounds. Carburizing of Ta-Ti at 3250 F. for six hours results in the formation of a 2 mil thick carbide layer and a sharp transition in hardness at this boundary is noted. The 50 gram microhardness through the carbide is 1890, 1480 and 1560 DPN at a depth of 0.5, 1, and 1.8 mils, respectively, and 370 DPN at a depth of 2.2 mils just below the carbide layer. Carburizing of molybdenum and tungsten also result in the formation of continuous carbide layers several mils thick.

Some examples of other carburized compositions that fall outside our invention because a multiphase structure existing essentially to the surface is not present are:

Cb-2Ti-2Mo pack carburized at 3250 F. for seven hours; Ta-lOHf pack carburized at 3250" F. for six hours; Ta-lOW pack carburized at 3250 F. for six hours; Ta-70Ti gas carburized at 3250 F. for two hours; Ta-80Ti-10W pack carburized at 2850 F. for six hours; V-8OTi-10Mo pack carburized at 2850 F. for six hours; Cb-85Mo pack carburized at 3250 F. for seven hours; Cb-10Ti-75W pack carburized at 3450 F. for two hours.

Carburized Cb-2Ti-2Mo shows some limited reaction below a continuous 1.5 mil thick outer carbide layer but such materials differ from the materials of the present invention. US. Pat. 3,163,563 teaches the formation of continuous carbide layers and Ta-10Hf and Ta-lOW carburized at 4170 and 4530 F. were two of the examples used in that specification. Temperature may be expected to play a role in microstructural relationships. Accordingly, we carburized these two compositions at a lower temperature (3250 F.) but confirmed that a continuous outer carbide layer still forms. The three carburized compositions containing 70 or 80% titanium all show structures similar to FIG. 4. Carburized Cb-85% Mo results in a 12 mil layer with serious cracking and carburized Cb-l0Ti-70W showed a 3 mil outer carbide layer that was chipping off in some areas. All of these materials are excluded from our invention.

The numerous carburized materials given in Table I falling within our invention should be considerd as a series of examples and are presented in tabular form for brevity. Although graded multiphase structures extending essentially to the surface are observed for all, the morphology of the precipitated carbide phase varies and different microstructures are seen for some compositions. For example, vanadium-titanium materials containing molybdenum and tungsten generally show fine carbide platelets rather than the structure of FIGS. 2 and 6. Zirconium may be substituted for titanium in our materials. Hafniurn additions have been made both in a ternary material, Cb-Hf-15W, and a quaternary material,

greatest. This tendency is reduced when the titanium and/or zirconium content is at least equal to the hafnium content.

Rhenium and chromium have been substituted for molybdenum and tungsten in some of the examples shown. Restricted amounts of other metallic or metalloid elements may be added and certain limited amounts of impurities may be present. Of the up-to-ten metals in our alloyed materials, rhenium is the only element that does not form a stable carbide. It may thus be expected that compositrons higher in rhenium may be carburized without the formation of a continuous carbide layer. Carburized Cb-20Ti-25Cr shows a lower volume of hard carbide phase than the corresponding compositions with molybdenum, tungsten, or rhenium. Chromium additions in some cases may be limited because of this and because of the embrlttling effect of high chromium additions to alloys.

These various metals hereof readily interalloy and carburized multiphase materials may be produced from alloys containing four or more metallic components. Restricted amounts of metallic or metalloid elements may also be added and certain limited amounts of impurities may be present. Our materials are required to be ternary or more complex. In such materials of this invention:

Group I content is 20% to 90%; Group II content is 2% to 45%; and Group III content is 2% to 55%.

Materials within the above ranges with higher titanium (greater than 35%) and lower columbium (lower than 40%) form coarser carburized structures. Also, we find that in some cases the amount of Group III additions must be limited to 40%. A more preferred range is:

Group I content is 40% to 90%; Group II content is 2% to 35%; and Group III content is 2% to 40%.

Furthermore, we find that it is preferred to have at least 5% of both Group II and III additions rather than the minimum 2% and that it is desirable to decrease Group I content from the maximum of 90% to We find enhanced microstructures and properties by so doing.

The direct forming of the materials to shape prior to hardening is one of the advantages of this invention. Restricting metals of Group II such that the ratio Group II/Group III is greater than one results in more fabricable alloys prior to carburizing. Thus, a fabricable, more preferred range hereof is given by:

Group I content is 40% to 85%; Group II content is 7.5% to 35%; Group III content is 5% to 30%; and

Group II Rat/10 of m is greater than one 7 angle is measured between the test specimen surface and particle stream. Results are shown in Table 111:

Carburized Cb-30Ti-20Mo falling within our invention shows a much higher abrasion resistance than carburized Cb-70Ti having a continuous carbide layer. Our carburized Cb-30Ti-20Mo shows excellent erosion resistance compared to a commercial wear resistant material Stellite 6B (3Ni-2Si-3Fe-2Mn-30Cr-1.5Mo-4.5W-0.9-1.4C Balance Co).

The excellent abrasion resistance of the carburized materials was confirmed by employing the materials as lathe cutting tool inserts for machining type 4340 steel of hardness Re 44. A standard negative rake tool holder was used, the feed and depth were 0.005 inch per revolution and 0.050 inch, the speed was 750 surface feet per minute (s.f.m.), and two cubic inches of workpiece was removed. The following materials falling within our invention cut at 750 s.f.m.:

Cb-30Ti-20Mo gas carburized at 3350" for two hours;

Cb-l7Ti-30W gas carburized at 3350 F. for two hours;

Cb-l7Ti-20W pack carburized at 3350 F. for six hours;

Cb-30Ti-2OW pack carburized at 3350 F. for eight hours;

Ta-lZTi-ISW pack carburized at 3350 F. for seven hours.

Cb-70Ti gas carburized at 3350 F. for two hours and Ta10W pack carburized at 3250 F. for seven hours were also tested at 750 s.f.m. but failed immediately in testing. As noted above, both of these materials have continuous outer carbide layers and are excluded from our invention.

Metal cutting is a severe test that represents a complex interrelationship of adhesion and abrasion. For similar alloy compositions the carburized materials show different performance and offer certain advantages over nitrided materials. For example in cutting nodular iron, Cb-l7Ti-20W and Cb-17Ti-30W pack carburized at 3250" F. showed greater tool life at speeds up to 600 s.f.m. as compared to Cb-17Ti-20W nitrided at 3585 F.

Our carburized materials having excellent abrasion resistance and utility as cutting tools must possess all of the following characteristics to be included in the present invention:

(a) graded, as above described (b) the microstructure is multiphase essentially to the surface (c) carbon pick-up is at least 0.1 milligram per square centimeter of surface area ((1) the 25 gram load hardness measured on a cross sectional traverse in a zone between the surface and a depth of 0.5 mil is at least 800 DPN (e) the composition must contain at least one metal from each of three groups wherein:

Group I is 20% to 90% columbium, tantalum, and

vanadium; Group II is 2% to titanium, zirconium and hafnium; Group III is 2% to molybdenum, tungsten,

rhenium and chromium.

In addition to carburizing we have combined carburizing plus nitriding treatments as shown in Table IV. Substantial weight pick-up occurred for all treatments and the desired multiphase structure is obtained. The relative weight pick-up of the secondary treatment is dependent upon the extent of reaction in the primary treatment. Microstructures are basically similar to those resulting from the primary treatment. The structure of Cb-30-Ti-20W was coarser when carburized at 3250" F. compared to nitriding at the same temperature. A finer structure was obtained by nitriding prior to carburizing as compared with carburizing alone. A combined concurrent treatment in which the relative quantity of reactants may be varied and controlled can also be used. Therefore, carbur-nitriding treatments as used herein means carburizing followed by nitriding, nitriding followed by carburizing, or a combined concurrent treatment. A substantial portion of the carbon may be replaced by nitrogen.

In addition to carburizing or carbur-nitriding alone, our reacted materials can be further modified by combining such treatments with a modest amount of boronizing. For example, we have pack carburized Ta-l2Ti-15W at 3250 F. for seven hours followed by boronizing at 2550 F. for six hours thus producing additional hardening.

l C=Pack carburizing using chunk carbon and A-5% Hz. N=Nitriding using nitrogen.

for three hours or Cb-l7Ti-30W nitrided at 3500 F. for two hours.

The carbon pick-up is in excess of 1 mg per square centimeter for all of the examples shown in Table I. However, the amount of carbon required for an equivalent surface hardness is substantially reduced when the material is used as a thin blade edge or sheet or as a thin coating or cladding. Also, such materials may be used for a wide variety of applications requiring Wear and abrasion resistance where the requirement for surface hardness or depth of hardening may be less than that required for metal cutting. Thus, for certain applications the carbon pick-up might be 0.1 to 1 mg. per sq. cm. of surface area.

The amount of reaction due to boronizing must be limited to 25% of the total weight pick-up. Such duplex treatments cannot be performed in reverse order since continuous outer borides would then be produced.

The present useful alloys may be produced by powder processing techniques in addition to the treatment of solid metal stock as described above. Furthermore, such alloys may be employed on another metal or alloy as a surface coating or cladding. Spraying and/or fusing the desired alloy onto the surface are included in the various coating methods available. Small other additions may be made to our alloys to enhance the coatability. A variety of direct deposition methods may be employed or alternate layers could be deposited followed by a diffusion annealing treatment. The reacted material can be used as a mechanically locked insert or it can be boned or joined by brazing, for example, to a substrate.

Since our carburized and carbur-nitrided materials are in a thermodynamically metastable condition, those skilled in the art will realize that a variety of heat treatments, including multiple and sequential treatments, can be used to modify the reaction product and resulting properties whether performed as part of the over-all hardening reaction or as separate treatments. The materials can also be reacted at higher temperatures (and times) that normally would produce some embrittlement and then subsequently annealed in inert gas or various partial pressures of the reactive gas as a tempering or drawing operation to improve toughness.

We have also observed the excellent corrosion resistance of both the alloys and the carburized materials in strong acids, and these materials could effectively be employed for applications requiring both corrosion and abrasion resistance. The materials can be employed for applications involving Wear resistance and structural properties (hardness, strength, stiffness, toughness) at room and elevated temperatures. Other useful properties of the carburized materials include good electrical and thermal conductivity, high melting temperature, and thermal shock resistance.

Although the alloys receptive to carburizing can be produced by coating or surface alloying techniques, many uses involve the forming and machining of a homogeneous alloy. One of the advantages in utility of these materials is our ability to form the metallic alloys by cold or hot working and/or to machine (or bone) to shape in the relatively soft condition prior to final carburizing. Only minimal distortion occurs during carburizing and replication of the starting shape and surface finish is excellent. The final surface is reproducible and is controlled by original surface condition, alloy composition, and carburizing treatment. For some applications, the utility would be enhanced by lapping, polishing, or other finishing operations after carburization. The carburized surface is quite hard but only a small amount of material removal is required to produce a highly finished surface.

The excellent cutting properties and wear resistance of the carburized and carbur-nitrided materials can be effectively employed with the other useful properties of the alloys and reacted materials to produce a wide range of products. Some of these are: single point cutting tools, multiple point cutting tools (including rotary burrs, files, routers and saws), drills, taps, punches, dies for extrusion, drawing, and other forming operations, armor, gun barrel liners, impeller or fan blades, EDM (Electrical Discharge Machining) electrodes, spinnerets, guides (thread, wire, and other), knives, razor blades, scrapers, slitters, shears, forming tools, grinding media, pulverizing hammers and rolls, capstans, needles, gages (thread, plug, and ring), bearings and bushings, nozzles, cylinder liners, tire studs, pumps parts, mechanical seals such as rotary seals and valve components engine components, brake plates, screens, feed screws, sprockets and chains, specialized electrical contacts, protection tubes, crucibles, molds and casting dies, and a variety of parts used in corrosion-abrasion environments in the paper-making or petrochemical industries, for example.

It will be understood that various modifications and variations may be affected without departing from the spirit or scope of the novel concepts of our invention.

We claim as our invention:

1. An article of manufacture consisting essentially of a graded, carbur-nitrided material with the carbon and nitrogen concentration lessening inwardly from the surface having excellent abrasion resistance, said material being formed of an alloy consisting essentially of at least one metal of each of Groups I, H, and III and wherein:

(a) Group I is columbium, tantalum, and vanadium and is present in amounts ranging from 20% to 90%;

(b) Group II is titanium, zirconium and hafnium and is present in amounts ranging from 2% to 45%;

(c) Group III is molybdenum, tungsten, rhenium and chromium and is present in amounts ranging from 2% to 55%;

(d) the pick-up of carbon and nitrogen is at least 0.1

milligram per square centimeter of surface area;

(e) the microhardness in the zone between the surface and up to 0.5 mil below the surface is at least 800 diamond pyramid numerals;

(f) the multiphase structure of said material extends substantially to the surface thereof; and wherein (g) said material has at least 25% by volume of carbur-nitn'ded, hard phase at the surface thereof.

2. An article as defined in claim 1 wherein said article is first nitrided and then carburized.

3. An article as defined in claim 1 wherein up to 25 of the carbon and nitrogen are replaced by boron.

4. An article as defined in claim 1 wherein the carbon and nitrogen pick-up is at least one milligram per square centimeter of surface area.

5. The article as defined in claim 1 wherein Group II is titanium.

6. The article as defined in claim 1 wherein Group II is zirconium.

7. An article of manufacture consisting essentially of a graded, carbur-nitrided material with the carbon and nitrogen concentration lessening inwardly from the surface having excellent abrasion resistance, said material being formed of an alloy consisting essentially of at least one metal of each of Groups I, II and III and wherein:

(a) Group I is columbium, tantalum, and vanadium and is present in amounts ranging from 40% to 90%;

(b) Group II is titanium, zirconium and hafnium, and

is present in amounts ranging from 2% to 35 (c) Group III is molybdenum, tungsten, rhenium and chromium and is present in amounts ranging from 2% to 40%;

(d) the pick-up of carbon and nitrogen is at least 0.1

milligram per square centimeter of surface area;

(e) the microhardness in the zone between the surface and up to 0.5 mil below surface is at least 800 diamond pyramid numerals;

(f) the multiphase structure of said material extends substantially to the surface thereof; and wherein (g) said material has at least 25 by volume of carbur-nitrided, hard phase at the surface thereof. 8. An article as defined in claim 7 wherein said article is first nitrided and then carburized.

9. An article as defined in claim 7 wherein:

Group II is titanium and zirconium; and

Group III is molybdenum, tungsten and rhenium.

10. An article as defined in claim 9 wherein the carbon and nitrogen pick-up is at least one milligram per square centimeter of surface area.

11. An article as defined in claim 9 wherein said article is first nitrided and then carburized.

12. An article as defined in claim 9 wherein Group I is columbium and Group II is titanium.

13. An article as defined in claim 12 wherein said article is first nitrided and then carburized.

14. An article as defined in claim 12 wherein up to 25 of the carbon and nitrogen are replaced by boron.

15. An article as defined in claim 7 wherein:

Group I content ranges from 40% to Group II content ranges from 7.5% to 35%;

Group HI content ranges from 5% to 30%; and

The ratio of Group II to Group III is greater than one.

16. An article as defined in claim 15 wherein:

Group I is columbium;

Group II is titanium and zirconium; and

Group III is molybdenum, tungsten and rhenium.

11 12 17. An article as defined in claim 16 wherein said OTHER REFERENCES article is first nitrided and then carburized. DMIOMetalWOrking, olofson et a1 May 22, 1968,

3 pages (1-3 and 4). References Clted Acta Metallurgical, vol. 17, December 1969, pp. 1483- 5 1499. UNITED STATES PATENTS IIT Research Inst.-Holtz, IR-718-7 (III), Develop- 3,163,563 12/1964 Do l et 75 174 X ment of Improved Cutting Tool Materials, 1967, pp. 51- 3,492,100 1/1970 Roubin et a1. 23-315 60, 65 and 3523044 8/1970 Johanscn 148*203 X 10 CHARLES N. LOVELL, Primary Examiner FOREIGN PATENTS US' CL X.R

6,812,592 3/1969 Netherlands 148-315 29182.2, 182.5; 148-20.3