US3698055A

US3698055A - Heat resistant alloys of iron, cobalt and/or nickel and articles thereof

Info

Publication number: US3698055A
Application number: US102203A
Authority: US
Inventors: Frederick C Holtz Jr; Hugh Morrow
Original assignee: Crucible Inc
Current assignee: Crucible Materials Corp
Priority date: 1970-12-28
Filing date: 1970-12-28
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17

Abstract

Alloys of iron, cobalt and/or nickel containing from 0.5 to 4.0% carbon and from 5 to 60% tungsten, molybdenum or mixtures thereof characterized by the absence of ''''reactive'''' elements such as Cr, V, Cb, Ta, Ti, Si, Mn and Al. which form hard-to-reduce oxides.

Description

United States Patent Holtz, Jr. et al. [451 Oct. 17, 1972 HEAT RESISTANT ALLOYS OF IRON, [56] References Cited COBALT AND/OR NICKEL AND ARTICLES THEREOF UNITED STATES PATENTS 721 inventors: Frederick c. Holtz, Jr., Evanston, 299L017 8/1937 f X g Ivlol.row Ann Arbor Hams R 5, 3,244,506 4/1966 Reen ..75/o.s

[ Assigneei Crucible, Illc- Primary Examiner-Dewayne Rutledge Assistant Examiner--.l. E. Legru 22 F] d. D 2 1 l 6 BC 8 1970 AttrneyClalr X. Mullen, Jr. 211 Appl. No.: 102,203

Related US. Application Data [57] ABSTRACT Continuation-impart 0f N0 y Alloys of iron, cobalt and/or nickel containing from 1963, abandoned- 0.5 to 4.0% carbon and from to tungsten, molybdenum or mixtures thereof characterized by the 29/l82.5, absence ofreactive elements such as Cr, V, Cb, Ta,

75/12 75/123 75/123 34 Ti, Si, Mn and Al. which form hard-to-reduce oxides.

75/170, 75/176 [5 l] Int. Cl. ....C22c 39/10, C22C 39/36, C220 39/50 [58] Field of Search ..29/] 82.7, 75/l23, 0.5 BC, 7 Claims, No Drawings HEAT RESISTANT ALLOYS OF IRON, COBALT AND/OR NICKEL AND ARTICLES THEREOF This application is a continuation-in-part of application Serial No. 743,92l,f1led July 11, 1968 by the same inventors and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to heat-resistant alloy articles and particularly to an inexpensive heat-resistant alloy which is readily workable and castable. The present invention provides alloys which are not only heat-resistant but have excellent strength and hardening ability and have particular utility in the fabrication of cutting tools, dies and wear parts, or for use as a structural alloy.

2. Description of the Prior Art The development of alloys based on iron, cobalt, and nickel has been characterized by increasing emphasis on the ability of these materials to withstand elevated temperature environments. The structural alloys are used for such applications as turbine buckets, nozzle vanes, rotor discs, combustion liners, and other turbojet engine parts, as well as furnace parts, exhaust manifolds, high pressure steam piping, valves, and other fittings which must sustain loads at high temperatures. In addition, there are numerous tool and die applications which require both strength and wear resistance at elevated temperatures. These include tools for metal cutting and the many metalworking operations such as swaging, forging, rolling, wire drawing, shearing, and extrusion'which are carried out under severe conditions of heat and sliding friction.

These thermal-resistant tool, die, and structural materials may be made by various techniques such as casting directly to shape, forging or rolling, and powder metallurgy. Their major constituent may be iron, nickel, or cobalt, and they are further strengthened by a wide range of alloying elements. However, they have one characteristic in common: all contain additions of reactive metals. A reactive metal is an element characterized by a high negative value for the free energy of formation of its oxide or oxides. Stated in another way, the oxides of reactive metals are increasingly difficult to reduce to the metallic state as the free energy of formation rises to higher negative values. For the purpose of this discussion, a value of -40K cal/gram-atom of oxygen at 1,500 K. represents the dividing line between reactive and non-reactive. Thus M 0 with a value of -32K cal/gram-atom can be reduced by the H or other reductants at comparatively low temperatures, i.e., l,600 F., while A1 0 with a free energy -=95K cal/gram-atom is reducible only at extremely high temperatures.

An examination of compilations of thermal-resistant tool, die and structural alloys of the prior art shows that all conventional compositions contain chromium (-58K cal/gram-atom). A listing of 30 commercial nickel-base high-temperature alloys gives a range of to 27 percent chromium. A similar listing giving compositions of the thermal-resistant cobalt-base tool alloys which have been marketed shows a chromium range of 18.5 to 31 percent. All 29 commercial high speed steels (AlSl designation T and M series) contain 3.75 to 4.25 percent chromium, and the 18 A181 type H hot die steels contain from 2 to 12 percent of this reactive element.

Chromium is added to these alloys primarily because of its beneficial effect upon oxidation resistance and, in the case of tool steels, its ability to give a moderate increase in the depth of hardening. lts primary drawback is the fact that its oxides are extremely difficult to remove by chemical means. Other reactive elements are also-added to nearly all of the iron, cobalt and nickel thermal-resistant alloys. These elements include AL, Cb, Mn, Si, Ta, Ti, V, Zr, etc. These elements generally promote alloy strengthening or wear resistance but, as in the case of chromium, their oxides are also very difficult to reduce. Alloys containing reactive metals suffer an additional limitation in that during melting, the reactive elements present require additional protection from the atmosphere and they also react with common refractory crucible materials such as alumina, magnesia, silica, etc. This means that inert atmospheres such as argon or a vacuum and extremely inert crucible materials (beryllia, thoria, zirconia) be used or else melting must be done by arc-melting in a water-cooled copper crucible. There are obvious economic drawbacks in using these special melting methods.

SUMMARY OF THE INVENTION The present invention provides a thermal-resistant alloy free of reactive elements such as chromium and vanadium, consisting essentially of about 0.5 percent to 4.0 percent carbon, about 5 percent to 60 percent of a carbide-former selected from the group consisting of nonreactive elements, such as tungsten, molybdenum and mixtures thereof, and the balance being M with usual impurities in ordinary amounts, wherein M is base metal selected from the group consisting of iron, cobalt, nickel and mixtures of two or more of these elements. Such alloys exhibit increased cutting speed capabilities and wear resistance by providing structures free from embrittling oxides, thereby permitting higher carbide volumes and larger contents of refractory metal alloying elements such as tungsten and molybdenum which appreciably improve the elevated-temperature strength properties. These alloys are harder than any heretofore known cast or wrought tool or die alloys based on iron, nickel or cobalt, and they gave cutting performance far superior to the conventional tool steels which were tested for comparison purposes. Further, such alloys have been found to have excellent high temperature strength, very high transverse-rupture bending strength, exceptional response to heat treatments, very high fabricability, and the ability to be produced from very low cost powders.

Also provided by the present invention are structural alloys for use in applications where great strength at high temperature is required. Such alloys are prepared by reducing the carbon content of the alloy composition set forth above to lower the hardness of the alloy to Rc or below and increase the toughness. The solidsolution strengthening provided by the high tungsten and molybdenum levels results in alloys which are capable of withstanding severe mechanical stress at elevated temperatures above about 700 F. for prolonged periods of time. Moreover, these new tool and structural alloys, can be produced with an ultrafine Oxides Formed by Free Energy Reactive" Elements of Formation (l500K) V 0, 48 0,0, 58 mp, 62 MnO --66 T3203 *67 z -72 Tao -80 mp, 95

Oxides Formed by Free Ener Nonreactive" Elements Of Formal-I011 NiO 27 C00 27 MoO -32 W0: 38 F9304 -38 DESCRIPTION OF THE PREFERRED EMBODIMENTS The broad composition of alloys within the present invention is as follows:

About 0.5 4.0 percent carbon About 5 60 percent of a non-reactive element whose oxides are easily reduced at low temperatures, and the remainder being M with usual impu rities in ordinary amounts, wherein M is iron, cobalt, nickel or a mixture of two or more of these elements. All of the alloys are characterized by the complete absence of reactive elements such as Cr, V, Cb, Ta, Ti, Si, Mn and Al.

Molybdenum and tungsten are non-reactive elements which are carbide formers. Each may be absent altogether or present up to a maximum of 60 percent. Accordingly, the outside limits of such use in accordance with the present invention are:

Mo about 0 60% W about 0 60% Mo W about 5 60% The invention will be better understood by a consideration of the examples wherein the various embodiments will be brought out in detail. Several different compositions of material were melted to form an alloy according to this invention. Illustrative compositions of these materials are given in Table I.

TABLE I Alloy Compositions, Weight Percent alloy Fe Co Ni W Mo A76 45 47.25 5 2.75 A81 62.5 10 25 2.5 A82 37.510 45 s 2.5 A83 42.5 20 10 25 2.5 A91 37.5 10 35 is 2.5 106 57.5 40 2.5 A113 56.5 40 3.5 A136. 58.7 20 20 1.3 M37 38740 20 1.3 A138 53.7 20 25 1.3

A146 28.1 50 20 1.3 A147 38.7 40 1o 10 1.3 A151 38.7 40 20 1.3 A152 38.9 39.9 19.9 1.3 A163 39.2 40 20 0.8 A164 38.33 40 20 1.67 A165 39.2 40 20 0.8 A169 34 34.7 30 1.3 A170 34 34.7 30 13 A171 34 34.710 20 1.3 A172 34 34.710 20 1.3

articles made therefrom can be produced free of deleterious oxides by chemical deoxidation procedures.

It is a feature of this invention that metal and metal powders of the defined composition characterized by the absence of the "reactive elements chromium, vanadium, columbium, tantalum, titanium, silicon, manganese and aluminum, are easily reduced chemically and oxides removed, e.g., by using carbon present in the alloy composition as a reducing agent. In this process, an alloy powder is jacketed in a thin-walled container, and the canned powder heated to a temperature in the range of about l,700 to 2,l00 F. A small vent can be provided for escaping gases of CO and C0,. However, it is not necessary that a vent be provided or that the container be evacuated. 100 percent dense, oxide-free alloy stock is produced by extruding the self-cleaned powder into a bar and removing the jacketing material. Alternatively, the heated canned powder can be consolidated by hot pressing followed by forging, rolling and removal of the cladding.

It has also been found that it is not necessary to jacket the powders in order to remove oxide films from powders which have low softening temperatures. For example, in the case of the tool steel powders, cobalt and nickel structural alloy powders, and some cobalt base tool alloy powders, which can be softened by annealing in the temperature range of about l,400 to l,700 F the alloy powders can be cleaned and softened in one step by heating them to such temperature in a reducing atmosphere of hydrogen, cracked ammonia, a hydrocarbon gas, such as methane, a mixture of CO and CO or the like. After annealing the powder by slow cooling, it can be cold pressed at room temperature to form an easily handled billet. Subsequently, the billet of material is heated to about 2,000 F. in a protective atmosphere such as nitrogen, argon or the like, and extruded into 100 percent bar stock.

As a specific example of the process for making an oxide-free alloy in accordance with the present invention, the production of alloy A 138 of the foregoing Table I will be considered in detail. In this example the alloy is made by powder metallurgy process, although it is to be understood that other methods of producing a1- loys can also be used.

An appropriate alloy charge, e.g., 5 pounds, of the desired composition (C0 20W 25Mo 1.3C) was weighed out, melted in an induction furnace (or other suitable melting device), and atomizedl. quenched using a conventional atomizer. Suitable apparatus is disclosed in copending application Ser. No. 435,733, entitled Alloy Composition and Process filed Feb. 26, 1965, by the present inventor. The molten stream was broken up into fine particles which were quickly quenched by the high pressure inert gas stream and by the water utilized asa collection medium. The oxygen content of dried alloy powderproduced in this manner was in the order of about 500 1,000 part per million.

The atomized alloy powder was then consolidated into solid stock by the following process. The powder was first enclosed in a sealed Inconel can without evacuation and with no provision for venting gas formed during subsequent heating. The welded can was heated to a temperature of approximately 2,050 F.

prior to open-die, upset hammer forging on a 250 pound capacity mechanical forge unit. Forging was used to produce pancake ingots approximately one-half inch thick. After forging, the canned billets were hot rolled to approximately 0.22 to 0.24 inches using a percent reduction per pass, this representing a total reduction in thickness of 90 to 92 percent of the original billet thickness. The cladding material was then removed and the rolled plate stock sectioned for metallurgical examination and mechanical property evaluations. Visual examination of photo-micrographs of the consolidated powder showed that the alloy stock was free of oxides and exhibited an ultrafine microstructure. Additional properties demonstrating that adequate hardness and thermal stability had been achieved were apparent from the following measurements:

Hardness, as-rolled Re 60.6 Hardness, aged at 1300F. Re 66.6 coarsening temperature 2350F.

By lowering the carbon content of alloy A 138 (e.g., to 0.5 percent carbon) the hardness falls to a level below Rc 56 permitting use as a structural alloy. The alloy is readily hot-workable and has the ability to withstand severe mechanical stress at elevated temperatures above 700 F. for prolonged periods of time due to the so1id-solution strengthening provided by the high tungsten and molybdenum levels.

The alloys of the present invention were tested for hardness and bend tests were conducted at room temperature to ascertain transverse rupture strengths. Data illustrating the test results are given for exemplary alloys in Table 11.

TABLE 11 Alloy Properties The foregoing test results demonstrate that the tool alloys of the present invention possess excellent strength and are capable of exhibiting high hardness levels.

Cutting tests were performed using exemplary alloys of the present invention by operating the tools in comparison with what is believed to be the best prior art alloy for the service indicated, The tool life tests were obtained on Inconel 718 which is a commercial superalloy widely used in jet engines and considered among the most difficult-to-machine materials in existence. .Tool alloys of the presentinvention were compared with the commercial high speed steel known as M43 having the following composition:

Fe 8.7 Mo- 1.8W 3.75 Cr- 2.0V 8.2 Co 1.23C.

Each of the tools, ground to the same geometry, was used to cut the test bar of Income] 718 on a machinabliity lathe at 25 surface feet per minute, 0.0625 inch depth of cut, 0.005 inch/rev. feed, using a conventional coolant. A wear land of about 0.030 inch on the tool was used as the end point of the test. The results of these tests are shown in Table 111.

TABLE I11 Lathe Turning Test Data On Inconel 718, BHN 375 1000F., 2 hr 2 hr oil quenched The above results demonstrate that excellent tool life has been obtained on difficult-to-machine commercial alloys using novel alloy materials produced according to the present invention.

Alloys A 136 and A 137 are capable of being annealed so that cold pressing of their powders can be accomplished. Bar stock prepared by forging and rolling was found to be of excellent quality. Alloy A 136 was found to have a coarsening temperature of 2,325 F. and an even higher coarsening temperature was noted for alloy A 137. The ultrafine carbide particle size of this latter alloy was unchanged after 1 hour at 2,3 50 F. Both alloys responded to quench and temper" hardening treatments similar to those given high sped steel. In the case of A 137, a maximum hardness of Ra 88 (Re 72) was obtained. This value is higher than the hardness of any commercial high speed steel or cobalt base tool alloy known, and is in the range of hardness encounted in sintered carbides.

While there have been described and disclosed certain preferred embodiments of the invention in the foregoing specification, it will be understood that this invention may be otherwise embodied within the spirit and scope of the following claims.

What is claimed is:

l. A readily workable, oxide-free, thermal-resistant, alloy stock material consisting essentially be weight of about 0.5 4.0 percent of carbon, about 60 percent of tungsten, about 0 60 percent of molybdenum, wherein the total amount of tungsten plus molybdenum is in the range of about 60 percent, and the balance being base metal with usual impurities in ordinary amounts selected form the group consisting of iron, colbalt, nickel and mixtures thereof, wherein the amount in said alloy of any element capable of forming an oxide having a negative free energy of formation value higher than 40 cal/gram-atom of oxygen at l,500 K. does not exceed the amount of such element usually present with said base metal as an ordinary impurity.

2. An alloy according to claim 1 suitable for use as a tool alloy, wherein said alloy has a hardness above Re 56 and the ability to hold a cutting edge under high temperatures generated during metal cutting and to resist softening at temperatures of l,000 F. and above.

3. An alloy according to claim 1 suitable for use as a structural material, wherein said alloy has a hardness below 'Re 56 and the ability to withstand severe mechanical stress at elevated temperatures above 700 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3,698,055 Dated October 17, 1972 lnvamorfifl Frederick C. Holtz, Jr. and Hugh Morrow, III

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 51; change "M 0 to "MbO Column 1, line 54, change'-CZ95K" to "-95K"1 Signed and sealed this 15th day of May 1973;

(SEAL) Attest: V

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM 0-1050 (10-69) -pc 60375-p69 .5. GOVERNMENT PRINTING OFFICE: I959 0-365-334 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,698 ,055 Dated OctQber 1972 Inventor) Frederick C. Holtz, Jr. and Hugh Morrow, III

Column 1, line 51, change "M 0 to "M00 Column 1, line 54, change "-CZ 95K" to -95K"L Signed and sealed this 15th day of May 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents F ORM PTO-1050 (10-69) USCOMM-DC 60376-F'59 U.S GOVERNMENT PRINTING OFFICE: 1989 0-366-334

Claims

2. An alloy according to claim 1 suitable for use as a tool alloy, wherein said alloy has a hardness above Rc 56 and the ability to hold a cutting edge under high temperatures generated during metal cutting and to resist softening at temperatures of 1,000* F. and above.
3. An alloy according to claim 1 suitable for use as a structural material, wherein said alloy has a hardness below Rc 56 and the ability to withstand severe mechanical stress at elevated temperatures above 700* F. for prolonged periods of time.
4. An alloy in accordance with claim 1, in which the alloy contains about 0 - 90 percent cobalt.
5. An alloy in accordance with claim 1, in which the alloy contains about 0 - 90 percent nickel.
6. An alloy in accordance with claim 1, in which the alloy contains about 0 - 90 percent iron.
7. A fully dense, consolidated powder article of the alloy of claim 1.