US2819194A - Method of aging titanium base alloys - Google Patents

Description

METHOD OF AGlNG TIT BASE ALLOYS .SchnylerA. l-llerres, Las Vegas, and Thomas K. Redden,

Boulder City, Nev., assignors to Allegheny Ludlum Steel Corporation, Breckenridge, Pa., a corporation of Pennsylvania No Drawing. Original application September 29, 1949,

Serial No. 118,723. Divided and this application 3am!- 'ary15, 1954, Serial No. 404,392

' 3 Claims. (Cl. 148-4130) This invention relates to new and improved procedure for making titanium base alloys, and to alloys produced thereby.

Since titanium is a relatively new metal, the production of its alloys has heretofore been more or less on a laboratory scale. Since it is recognized that titanium has a great afiinity for contaminating materials in the production of its alloys, it has heretofore been the practice to employ relatively pure alloying elements. This has made the production of such alloys almost prohibitive in cost and has limited their field of application.

Pure titanium metal which, itself, is not commercially obtainable, is very soft and ductile. It has been indicated that annealed high purity titanium metal has a tensile strength of about 32,000 p. s. i., a yield strength of about 17,500 p. s. i., 55% elongation, and 73 Brinell hardness. Commercially available titanium sponge metal melted into ingots without appreciable contamination, forged into bars, and annealed at 1500 F. on an average, has a tensile strength of about 70,000 p. s. i., a yield strength of about 60,0000 p. s. i., 30% elongation, and about 160 Brinell hardness. The higher strength and hardness and the lower ductility is accounted for by the impurities, particularly oxygen.

Although a relatively high ductility of metal is required for fabricating cold drawn tubing, and this indicates the use of titanium metal of the highest practical purity, we have determined that for most applications, titanium alloys with strength and hardness much better than those obtained for commercially pure metal are needed. Since the weight of titanium is only about 60% of that of steel, titanium alloys with tensile strengths exceeding 140,000 p. s. i. and having moderate ductility, i. e., about will compare favorably with best alloy steels and aluminum-base alloys for structural uses, such as aircraft engines and frames, turbines, etc. The superior strength per unit weight of titanium alloys together with their excellent corrosion resistance will make it possible to reduce the dead weight of moving parts in transportation and power generating equipment with a resultant substantial increase in operating efficiency.

Additions of nitrogen, oxygen, carbon, iron, tungsten, molybdenum, or chromium as binary alloys with tita- 2,819,194 Patented Jan.,7, 1958 nium gave the following results:formhot-forgedand annealed alloys:

We have determinedthat combinations of oxygen or nitrogen with. the elements chromium, molybednum,:and tungsten or iron, manganese and nickel'provide more beneficial results than the use of any of the single ele ments. Pure chromium, molybdenum, tungsten or manganese are relatively scarce and expensive. 1 Thus, if, as has been the, practice heretofore, relatively pure metals are employed, the expense becomes prohibitive.

In endeavoring to find a solution to the problem'thus presented, we discovered that ferroalloys of these metals which are easily prepared and readily available, are the most economical means of adding alloying metals to titanium. They not only are suitable for making titaniumbase alloys of the desired ternary and higher order, but alsoproduceeven betteralloys than those produced 'by the introduction of pure elements. We have determined that the harder metals, such as chromium, molybdenum, tungsten or manganese. become more readily soluble in molten titanium when they are introduced as ferroalloys, and that thepresence of iron complements and enhances the effects of the chromium, molybdenum, etc. This is believed to be an outsanding development in the art although it is directly contrary to: prior teaching as to the making of titanium-base alloys. 11: not only provides an improved product,-.but a much more economical one.

In accordance with our procedure, oxygen or nitrogen additions may be made as titanium dioxide or titanium nitride compounds which are also commercially available or may be incorporatedwith the ferroalloy. A high nitrogen grade of ferrochromium is commercially obtainable in several analysis ranges, for example, suchas chromium, 33%, iron, and 1.4% nitrogen. The following table is representative of properties obtained in forgediiand annealed titaniumihathas been cooled with proper additions of ferrochromium, ferromolybdenum, ferrotungsten, and ferromanganese, with or without supplementary additions of nitrogen or oxygen:

4 content of the chromium or iron or both of them, a high temperature body-centered cubic lattice structure of titanium is stabilized and retained at room temperature. This Table II Hard- Tensile Yield Elong, Alloy Addition, Percent ness. Strength, Strength, Percent BH p. s. i p. s. i

1 .04 N, 2.0 Cr, 275 120,000 107, 500 22 2 .25 N, 2.0 Cr, 330 153, 500 133, 000 18 3- .25 N, 2.0 Cr. 340 162, 000 148, 000 4- .05 N, 3.4 CI, 330 156, 000 142. 000 16 5- .25 N, 3.4 Ct. 360 172,000 151,000 6. .05 N, 4.2 Cr, 330 154. 000 140. 000 17 7.-- .1 N, 4.1 Cr, 1. 340 160, 000 145. 000 15 8 .2 N, 4.2 Oz, 1. 380 183, 000 174, 000 13 9 .1 N, 5.0 Cr, 2. 388 189, 000 3 10.-.- .2 N, 8.0 Cr, 3. 345 168,000 153, 000 0 11 .2 N, 10.0 C1, F 350 176, 000 163, 000 13 12 .05 N. 14.0 Cr, 9 Fe 360 15 13 .25 N, 3.0 M0, 405 7 14---- .25 N, 2.5 W, 315 15 .25 0, 3.5 0r, 340 19 16 .25 O, 2.5 W, 310 140, 500 H 20 17-- .25 N, 5.0 Fe 420 207, 000 186,000 3 18 .25 N, 5.0 Mn 370 173, 000 160, 000 16 The alloys of Table II may be summarized as follows:

The following table gives percentage analysis ranges for titanium-base alloys of improved characteristics that have been produced in accordance with our procedure: Table III 0= 02-.40 0=.02-.40 A Fe 75-10 A: Fe=4.0-7.0

Or=l.5-l4.0 Gr=8.014.0 N=.05.25 N=.05.20 B Fe=.75-7.0 B: Fe=4.07.0

Cr=1.514.0 1 Cr=8.014.0 N=.02-.25 o=.02-.40 C 0=.02-.40 C N=.02-.25 Cr=1 5-200 2 =4.0-7.0 Fe= 75-100 =s.014.o

o=0.02-0.40 =0.0t r0.40 D Fe=0.53.0 E Fe- .5 =0.02-0.30

Mo=1.0-5.0 Mo=l.0-5.0 =0.5-3.0 =1.0-5.0 0=0.02-0.40 N=0.020.40 =0.02-0.40 G Fe=0.52.0 H Fe=0.52.0 =0.02-0.40

w=1.5-5.0 W=l.5-5.0 =0.5-2.0 =1.55.0 0=0.02-0.40 N=0.02-0.25 =0.02-0.40 .I Fo=0.1-3.0 K Fe= 1-3.0 =0.02-0.a0 Mn=1.07.0 Mn-I 0-7 0 =0.1-5.0

65 i? N=.1- o=.1-.3 {Mn=2.0-6 o {Mn=2.0-6.0 .02-.20

LgllO N=.1.25 0= -3 .0 .0 i Fe=2.5-6.0 l re 02-.20

The alloys of Table III may be used in various conditions of heat treatment depending upon the specific properties desired. Hot working within a temperature range of about 1400" to 1800 F., followed by cooling in air produces desirable properties for most structural uses. A subsequent anneal or stress relief is, however, preferred to obtain uniformity of properties. This is accomplished by reheating to a temperature within the range of about 1200 to 1606 F. and cooling at a suitable rate. Alloys A B C and E to M, inclusive, respond favorably to heat treatment and may be hardened by rapid cooling, as water quenching from temperatures above about 1500 F., or softened by relatively slow cooling from the same temperature.

Alloys A B C and D respond favorably to heat treatment of a different type from the above groups. On heating to a temperature above about 1500 F. and cooling at a rate that may be slower, the higher the provides a softer, more ductile metal than is obtained if the same alloy is cooled sufiiciently slowly to alloy the titanium and transform it to its normal hexagonal close packed lattice structure.

All of the alloys of Table III may be hardened somewhat following moderately rapid cooling from a temperature above about 1200 F., by an aging or precipitation hardening mechanism on reheating and holding for various periods in the temperature range of about 700 to 1200 F. The time of holding is less, the higher the aging temperature in this range and the effect is reversible, so that the alloy may be softened again by reheating to a higher temperature. All the alloys may also be hardened by cold working, i. e. mechanical reduction in crosssectional area at temperatures below about 1200 F. and may be softened again by heating to temperatures above about 1200 F. for various periods, the temperature and time employed in the softening operation will depend on the degree of cold work accomplished.

All of the alloys and commercially pure titanium may be surface hardened by heating in air or atmospheres, mixtures, or fused baths that provide nitrogen or oxygen for combination with the titanium. It has been found, for example, that titanium heated in the presence of oxygen for about one hour at 1900 F. is hardened for a depth of .050 of an inch below the surface with a maximum surface hardness of 400 Brinell. Similar surface hardening effects are produced by heating titanium or the alloys in nitrogen-rich atmospheres, such as ammonia gas at temperatures as low as 950 F. The depth and degree of hardness produced is controlled by the time and temperature of exposure as Well as the composition of the atmosphere or bath used.

In accordance with our preferred procedure, all elements are made from commercially available titanium metal, such as produced by the reaction of chemically pure titanium tetrachloride with magnesium metal and which contains approximately .02% nitrogen, .1% oxygen, and .l% iron as the principal impurities. We prefer to produce our titanium alloys in accordance with the Herres arc-melting procedure (see application filed September 13, 1949, Serial No. 115,454, now abandoned) which is carried out in a Water-cooled copper crucible and in an atmosphere that is non-contaminating of the titanium. Also, the alloys may be prepared by any melting or powder metallurgy technique that will produce metal of the desired chemical composition. In accordance with our procedure, ferromctal, and particularly, ferrocompounds of one or more of the elements chromium, molybdenum, tungsten, or manganese are added to the titanium While it is in a molten state and while an ambient atmosphere is maintained that is non-contaminating of the titanium. Such additions may be eifected through an air lock into an enclosed furnace or crucible While a titanium halide is being reduced therein.

In accordance with such procedure, the titanium halide or compound upon reduction is immediately converted to molten metal to which the alloying additions may be made. A proportionate amount of nitrogen and oxygen or a combination of them may be made to obtain the desired ultimate content of the alloy as indicated by the tables.

Our heat treatment as set forth herein, although specifically worked out from the standpoint of titanium-base alloys of a ternary or high order, and particularly, ternary or higher alloys containing iron, may be used where applicable to other titanium alloys as indicated herein.

In Table III A, B, and C represent broader ranges of the alloys within their representative groups, while alloys A A B B and C and C are preferred ranges within the specified broader ranges.

Alloys M, M, N, and 0 when made by the additions of ferromanganese, may contain a small amount of iron and oxygen as impurities, for example, about .1% or less, each, relatively small percentages of such impurities do not appear to have deleterious elfects in these managanese alloys, although they can be substantially removed by well known procedure.

It should be noted that the specific alloys 17, 18 (P' and M) of column 3 and M to R, inclusive, of column 3 are, in themselves, the sole invention of Thomas K. Redden, and that their disclosure herein is made (Without prejudice to his rights therein) to show that iron or ferro additions are beneficial, and to better or more completely illustrate the procedure for making and conditioning titanium-base alloys which with the other alloys (except those above specifically listed) constitute our joint invention or inventions.

As to alloys A B C and D, it has been found that with normal impurities of about .02% nitrogen, about .1% oxygen, and .1% iron, a chromium addition will retain the body-centered structure on water quenching, but not on air cooling, while a chromium addition will retain it on air cooling. An alloy of 4.8% iron and 10% chromium with .2% nitrogen, and .1% oxygen as impurities, will retain the body-centered cubic structure on air cooling. It thus appears that the combination of iron and chromium definitely favors retention of such structure. Small amounts of oxygen or nitrogen appear beneficial in improving the properties of the bodycentered structure alloys, but in general, appear to have a non-controlling influence as to the body-centered lattice structure. In any event, a body-centered lattice structure is assured by water-quenching alloys containing about 4% iron and 8% chromium through the upper limit of about 7% iron and 14% chromium.

This application is a division of application Ser. No. 118,723, filed September 29, 1949, now abandoned.

What we claim is:

1. A method of conditioning a ternary and higher titanium base alloy which is responsive to the following defined treatment and which consists essentially of an alloying gas selected from the group consisting of nitrogen and oxygen with a range of .02 to .40% each, an alloying metal selected from the group consisting of and within the specified ranges of about .1 to 10% iron, 1.5 to 20% chromium, 1 to 5% molybdenum, 1.5 to 5% tungsten, and 1 to 10% manganese, and the remainder titanium which comprises, aging and precipitation hardening the alloy by heating and holding it within a temperature range of about 700 to 1200 F.

2. A method as defined in claim 2 wherein the alloying gas is introduced into the titanium base alloy by ferroalloy additions to a molten titanium melt.

3. A method of conditioning as defined in claim 2 wherein the alloy is preliminarily hardened by heating it to a temperature above about 1200" F. and is moderately rapidly cooled from such temperature before the alloy is aged and precipitation hardened.

References Cited in the file of this patent UNITED STATES PATENTS 1,674,959 Dean June 26, 1928 2,169,193 Comstock Aug. 8, 1939 2,317,979 Dean et a1 May 4, 1943 2,520,753 Ball et al Aug. 29, 1950 2,554,031 Jafiee et al. May 22, 1951 2,588,007 Jafiee Mar. 4, 1952 OTHER REFERENCES Preparation and Evaluation of Titanium Alloys, Summary Report; Part III covering the period May 18, 1948,

to July 30, 1949.

Patent No. 2,819,194

U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION January '7, 1958 Schuyler A Herres et a1,

appears in the printed specification I It is hereby certified that error correction and that the said Letters of the above numbered patent requiring Patent should read as corrected below.

read 60,000 column 3,, in the Column 1, line 35,, for "60,0000" summary of Table II, second column thereof, last line for "Fe: 050" read Fe=5.,0 column 6, lines 23 and 26 for the claim reference numeral '2', each occurrence, read l Signed and sealed this 1st day of April 1958 (SEAL) Attest: I

KARL mAXLINE ROBERT c. WATSON C'omnissioner of Patents Attesting Officer

Claims (1)

1. A METHOD OF CONDITIONING A TERNARY AND HIGHER TITANIUM BASE ALLOY WHICH IS RESPONSIVE TO THE FOLLOWING DEFINED TREATMENT AND WHICH CONSISTS ESSENTIALLY OF AN ALLOYING GAS SELECTED FROM THE GROUP CONSISTING OF NITROGEN AND OXYGEN WITH A RANGE OF .02 TO .04% EACH, AND ALLOYING METAL SELECTED FROM THE GROUP CONSISTING OF AND WITHIN THE SPECIFIED RANGES OF ABOUT .1 TO 10% IRON, 1.5 TO 20% CHROMIUM, 1 TO 5% MOLYBENUM, 1.5 TO 5% TUNGSTEN, AND 1 TO 10% MANGANESE, AND THE REMAINDER TITANIUM WHICH COMPRISES, AGING AND PRECIPITATION HARDENING THE ALLOY BY HEATING AND HOLDING IT WITHIN A TEMPERATURE RANGE OF ABOUT 700* TO 1200*F.