Corrosion resistant cobalt-base alloy containing hafnium and a high proportion of chromium and method of making fibers

An alloy suitable for use as a spinner in forming glass fibers, the alloy being cobalt-based and including the following elements in percent by weight: chromium--about 34.0 to about 38.0; nickel--about 10.0 to about 15.0; wolfram--about 4.0 to about 7.0; tantalum--about 2.0 to about 5.0; zirconium--about 0.1 to about 0.4: silicon--present but about 0.15 max; carbon--about 0.65 to about 0.95; boron--about 0.005 to about 0.02; hafnium--about 0.4 to about 1.0; aluminum--0.0 to about 0.2; titanium--0.0 to about 0.2; manganese--0.0 to about 0.5; molybdenum--0.0 toabout 0.1; iron--0.0 to about 2.0; and cobalt--balance; and further that: ##EQU1## said percents of the elements in equation Nos. 1 and 2 each being atom percent.

BACKGROUND OF THE INVENTION 
This invention relates to improved cobalt-base alloys containing hafnium 
and a high proportion of chromium which are particularly suitable for 
high-temperature molten glass enviroments. 
In one of its more specific aspects, the invention relates to articles 
manufactured from the alloys, particularly articles made by casting. 
In certain industrial applications there is a need for alloys which possess 
high rupture strength, high hot corrosion and high oxidation resistance at 
high temperatures. Among such applications are those involved, for 
example, in the glass fiber industry, where filaments are produced by 
passing a molten mineral material, for example, glass, through the 
foraminous walls of a chamber adapted for rotation at high speeds, the 
chamber being known as a spinner, the filaments being emitted through 
fiberizing orifices of the walls due to the centrifugal action to which 
the molten material is subjected upon rotation of the spinner. Such 
spinners are typically operated when spinning glass fibers at temperatures 
of about 2050.degree. F. and rotation speeds of about 2050 RPM. It is 
advantageous, from a production cost standpoint, for the rotation speed to 
be as high as possible to increase the rate at which filaments are emitted 
through the fiberizing orifices. However, high spinner rotational speeds 
result in a reduction in spinner life due to the limited strength and 
corrosion resistance of the prior art alloys used in spinners. Also, cost 
savings are realized by fiberizing lower cost batch formulations such as 
higher viscosity wool glass, but prior art alloys have not had the 
necessary mechanical strength to fiberize at the higher temperatures 
required for higher viscosity wool glass. The stress rupture properties of 
prior art alloys fall off rapidly above 2100.degree. F. 
Conventional commercial materials, prior to the present invention, for use 
in such applications are those defined and claimed in U.S. Pat. No. 
3,933,484 issued Jan. 20, 1976 and U.S. Pat. No. 4,497,771 issued Feb. 5, 
1985, the alloy composition of U.S. Pat. No. 4,497,771 being substantially 
the same as that of U.S. Pat. No. 3,933,484 except that the alloy 
composition of U.S. Pat. No. 4,497,771 has a lower tantalum content. 
The alloy compositions of the present invention have substantially improved 
strength and corrosion resistance compared with the alloy compositions 
disclosed in U.S. Pat. Nos. 3,933,484 and 4,497,771. 
STATEMENT OF THE INVENTION 
Accordingly, an object of this invention is to provide a hafnium and high 
chromium content cobalt-base alloy having superior strength at high 
temperatures and superior corrosion resistance, an alloy which can be 
vacuum-investment cast and which is particularly resistant to corrosion by 
molten glass. 
According to this invention there is provided a cobalt-base alloy 
containing chromium, nickel, wolfram, tantalum, zirconium, silicon, 
carbon, boron and hafnium. The composition may include typical impurity 
elements such as, for example, aluminum, titanium, manganese, molybdenum 
and iron in essentially impurity amounts. The alloys of the present 
invention possess the following approximate composition, the various 
components of this composition being expressed herein on a weight percent 
basis: 
______________________________________ 
Element Approximate Composition, Weight % 
______________________________________ 
Chromium About 34.0 to about 38.0 
Nickel About 10.0 to about 15.0 
Wolfram About 4.0 to about 7.0 
Tantalum About 2.0 to about 5.0 
Zirconium About 0.1 to about 0.4 
Silicon Present but about 0.15 max. 
Carbon About 0.65 to about 0.95 
Boron About 0.005 to about 0.02 
Hafnium About 0.4 to about 1.0 
Aluminum 0.0 to about 0.2 
Titanium 0.0 to about 0.2 
Manganese 0.0 to about 0.05 
Molybdenum 0.0 to about 0.1 
Iron 0.0 to about 2.0 
Cobalt Balance 
______________________________________ 
and further that: 
##EQU2## 
said percents of the elements in equation Nos. 1 and 2 each being atom 
percent. 
The percentages of the elements in Equation No. 2 represent the 
concentration of those elements in the matrix of the alloy. These 
percentages are calculated by subtracting from the bulk concentration of 
the elements, the percentages of the elements tied up in carbides or other 
second phases and normalizing the remaining percentages to total 100%. The 
normalized percentages represent the matrix composition of the alloy. 
The weight percent of an element (X) may be converted to the equivalent 
atom percent of the element using the following formula: 
##EQU3## 
wherein Z is the atomic weight of the element and n is the number of 
elements in the composition. Similarly, the atom percent of an element (Y) 
may be converted to the equivalent weight percent of the element using the 
following formula: 
##EQU4## 
wherein Z is the atomic weight of the element and n is the number of 
elements in the composition. 
Silicon is present in the alloy up to a maximum of 0.15%, as indicated 
above. Usually the silicon content of the alloy ranges between 0.05 and 
0.1%, but satisfactory compositions have been produced with 0.01% silicon. 
The alloy compositions of this invention may include, impurities, in 
addition to aluminum, titanium, manganese, molybdenum and iron. However, 
these additional impurities, if present, should be limited to about 0.005 
weight percent sulfur and 0.005 weight percent phosphorous. Also, the 
nitrogen and oxygen gas levels in the compositions should be limited to a 
maximum of 150 ppm and 20 ppm, respectively. 
The preferred composition of this invention is approximately as follows, on 
a weight percent basis: 
______________________________________ 
Element Approximate Composition, Weight % 
______________________________________ 
Chromium About 35.0 to about 36.0 
Nickel About 10.7 to about 11.3 
Wolfram About 5.5 to about 6.1 
Tantalum About 2.2 to about 2.8 
Zirconium About 0.17 to about 0.23 
Silicon Present but about 0.13 max. 
Carbon About 0.70 to about 0.78 
Boron About 0.008 to about 0.012 
Hafnium About 0.60 to about 0.90 
Aluminum 0.0 to about 0.2 
Titanium 0.0 to about 0.2 
Manganese 0.0 to about 0.01 
Molybdenum 0.0 to about 0.1 
Iron 0.0 to about 1.0 
Cobalt Balance 
______________________________________ 
In the above composition, the weight ratio of wolfram to tantalum is within 
the range of from about 2 to about 2.8, and the weight ratio of zirconium 
to boron is within the range of from about 14 to about 29. 
The best mode of practicing the invention is representing by the following 
approximate composition on a weight percent basis: 
______________________________________ 
Element Approximate Composition, Weight % 
______________________________________ 
Chromium About 35.5 
Nickel About 11.0 
Wolfram About 5.8 
Tantalum About 2.5 
Zirconium About 0.20 
Silicon About 0.10 
Carbon About 0.74 
Boron About 0.01 
Hafnium About 0.7 
Aluminum 0.0 to about 0.2 
Titanium 0.0 to about 0.2 
Manganese 0.0 to about 0.01 
Molybdenum 0.0 to about 0.1 
Iron 0.0 to about 1.0 
Cobalt Balance 
______________________________________ 
In the above composition, the weight ratio of wolfram to tantalum is about 
2.3, and the weight ratio of zirconium to boron is about 20. 
Comparing the alloy compositions of the present invention with the alloy 
compositions disclosed and claimed in U.S. Pat. Nos. 3,933,484 and 
4,497,771, the alloy compositions of the present invention: have a higher 
tantalum content, which results in the formation of more MC carbides 
(where M are suitable carbide formers, as for example, zirconium and 
tantalum) enhancing the strength of the alloys; have a higher zirconium 
content to also form more MC carbides which partition to the grain 
boundaries reducing grain boundary sliding and thereby enhancing the 
strength of the alloys; have a higher chromium content to substantially 
improve glass corrosion resistance; and contain hafnium which, like the 
tantalum, enhances the strength of the alloys and, in addition, 
substantially reduces the glass corrosion rate of the alloys. Stronger 
alloy castings are produced using vacuum-casting techniques rather than 
air-casting techniques provided that the silicon content of the alloys is 
maintained low. Accordingly, the silicon content of the alloys of the 
present invention is relatively low to permit the formation of higher 
strength castings by vacuum-casting techniques. 
Comparing the alloy compositions of the present invention with the alloy 
compositions disclosed and claimed in copending parent application Ser. 
No. 746,158 filed June 18, 1985, the alloy compositions of the present 
invention are more resistant to the formation of a sigma phase, which 
causes embrittlement of the alloy at high temperatures, e.g. 
1500.degree.-1700.degree. F., even though there may not be a significant 
problem at higher temperatures. A problem of spinners comprising some of 
such alloy compositions has been that when the spinners or portions 
thereof are operated in the temperature range of 1500.degree.-1700.degree. 
F. the portions of the spinners operated in that temperature range tend to 
become brittle and cracks may form. This is believed due to the fact that 
the sigma phase is precipitated in the alloys on casting and when 
operating in the 1500.degree.-1700.degree. F. range causing the hardness 
of the alloys to increase substantially and the ductility of the alloys to 
decrease substantially. 
Spinners comprising the improved alloys of the present invention are phase 
stable throughout that operating temperature range and higher without loss 
of impact strength or ductility of the alloy. Reliability and longevity of 
spinners comprising the alloys of the present invention are substantially 
improved.

DETAILED DESCRIPTION OF THE INVENTION 
The compositions of this invention can be prepared by vacuum-melting and 
vacuum-casting according to recognized melt procedures for cobalt-base 
alloys, sometimes known as superalloys. 
In the preferred method of producing the alloys, the original melt formed 
in the crucible will consist principally of chromium and cobalt. 
Thereafter, the remainder of the elements required can be introduced into 
the original melt in any order when the melt temperature is within the 
range from about 2700.degree. F. to about 2800.degree. F. As an alternate, 
however, all components of the composition can be introduced into the 
crucible with the cobalt and chromium. Inasmuch as zirconium and boron are 
contained in the composition in minimal amounts and certain weight ratios 
have been indicated desirable, it is preferred that the zirconium, boron 
and tantalum be introduced into the melt immediately prior to pouring in 
order to prevent either the oxidation of these latter materials or their 
loss from the crucible. Hafnium is added last to minimize oxidation and 
volatilization. After the addition of these latter materials, the melt is 
heated to a temperature within the range of from about 2800.degree. F. to 
about 3025.degree. F. to produce a uniform composition. The temperature of 
the melt is reduced to 2600.degree. F. to 2750.degree. F. and poured into 
a heated investment mold. The mold temperature is between 1600.degree. F. 
and 1900.degree. F. with 1800.degree. F. being optimum. The investment 
mold is produced by the lost wax process. A wax pattern of the casting is 
invested in a series of ceramic slurries which are cured. The wax is 
removed in a steam autoclave and the finished mold is heated in a suitable 
high-temperature furnace. Preferably, the resulting cast alloy is heated 
at 2000.degree. F. for 3 hours and air-cooled. 
Castings made from the alloys of the present invention are produced by the 
vacuum investment cast process which allows the introduction of the 
reactive element, hafnium, and the introduction of higher levels of other 
reactive elements such as zirconium and tantalum than can be used with the 
prior art alloys of U.S. Pat. No. 3,933,484. The vacuum investment cast 
process is described in The Superalloys by Sims and Hagel, John Wiley & 
Sons, Inc., 1972, pages 383-391 and 403-425. Castings of the prior art 
alloys are produced via an air-melt process requiring the presence of a 
high level of silicon in the alloys to increase the fluidity of the melt. 
Fluidity is not a problem with the vacuum investment cast process, and 
therefore the silicon content in the alloys of the present invention is 
kept at a low level. Furthermore, the use of high silicon content alloys 
in vacuum investment cast processes should be avoided as castings formed 
by this process are susceptible to a defect known as shrinkage porosity. 
The presence of high amounts of silicon in the alloys increases the 
freezing range of the alloys giving rise to casting integrity problems. 
One of the benefits of using the vacuum investment cast process is the 
ability to produce near net shape castings. The alloys of the present 
invention are ideal for vacuum investment cast processes compared with the 
prior art alloys containing a high silicon content. 
Even if a good quality casting of a prior art alloy of U.S. Pat. No. 
3,833,484 is made by the vacuum investment cast process, the casting will 
not possess the mechanical performance of the alloys of the present 
invention. For example, a casting consisting of a prior art alloy of U.S. 
Pat. No. 3,933,484 may have a rupture life of only 31 hours compared with 
the same alloy which has been subjected to a vacuum melting process which 
may have a rupture life of 93 hours. However, even though the rupture life 
is increased by the vacuum melting process, the creep rate is too high for 
dimensional stability. The creep rate may increase from 
6.8.times.10.sup.-4 in./in./hr. to 3.7.times.10.sup.-3 in./in./hr. at 
2100.degree. F. and 3000 psi. Thus, the mechanical performance of the 
prior art alloys even when subjected to a vacuum investment cast process 
is not as good as the alloys of the present invention when subjected to 
the vacuum investment cast process. 
The cobalt-base alloys of the present invention are more stable at 
temperatures in the range of 1500.degree. F. to 1700.degree. F. than the 
alloys disclosed and claimed in applicant's copending application Ser. No. 
746,158 and continuation application Ser. No. 827,135 filed Feb. 7, 1986. 
This stability is attributable to the fact that the alloy matrix is 
primarily in the preferred gamma phase. The formation of undesirable 
phases, and particularly the sigma phase, at these temperatures is 
avoided. The sigma phase has a composition which can be approximated as 
(Co,Ni).sub.x (W,Cr).sub.y. This phase forms if the chromium content is 
above a predetermined level. The alloys of the present invention maintain 
a high chromium content close to the gamma phase boundary, which is 
necessary for glass corrosion resistance, while at the same time the 
chromium content is maintained low enough to avoid formation of the sigma 
phase. Sigma phase formation is prevented by (1) increasing the nickel 
concent to stabilize the matrix and (2) removing chromium from the matrix 
as a carbide by reducing the tantalum and zirconium content and increasing 
the carbon content. This has been accomplished without loss of stress 
rupture performance. 
The composition of the gamma phase stable alloys of the present invention 
is defined by a "Phacomp" computation, the theory and calculations of 
which are described generally in The Superalloys, supra, pages 259-284. 
"Phacomp" is an acronym for "phase computation". This computation serves 
to define the concentration limits of the various components of phase 
stable austenitic alloys. Phacomp computations are based on the electron 
hole theory. The electron hole number for each element is based on the 
number of electrons needed to fill the third orbital in combination with 
the amount of pairing that occurs. 
A Phacomp number is determined for the cobalt-base alloy, the number being 
an indicator of the stability of the gamma phase. The lower the number, 
the more stable the gamma phase. It has been determined that for 
cobalt-base alloys the critical Phacomp number is 2.74 (the first number 
appearing in equation No. 2), above which the alloy composition will 
develop several undesirable phases, most notably the sigma phase, which 
result in an unstable alloy. 
Sigma is known as an electron compound, and therefore the formation of 
sigma increases as the electron hole number, and accordingly the Phacomp 
number, increases. Consequently, it is essential for the cobalt-base 
alloys of the present invention that the alloys contain elements in the 
gamma phase, or matrix, with low electron hole numbers. Different elements 
of the alloy have a greater or lesser effect on the Phacomp number. 
Chromium and tungsten, for example, have the most adverse effect by 
increasing the Phacomp number. Thus, the matrix content of chromium and 
tungsten in the alloys is maintained as low as possible to gain a more 
stable alloy composition, but chromium levels must be high for corrosion 
resistance. 
Referring to equation No. 1 above, it has been determined that the chromium 
in the cobalt-base alloys, because of its affect on alloy stability and 
glass corrosion resistance, must be no more than 32 a/o (note: atom 
percent is indicated "a/o" and weight percent is indicated "%") in the 
alloy matrix. A chromium content of more than 32 a/o will substantially 
reduce the stability of the alloy. Since chromium is in both the matrix 
and in carbides, the total chromium content of the alloy will depend upon 
the amount of carbide-forming elements present. Thus: 
EQU Maximum Cr content=32 a/o+Cr in M.sub.23 C.sub.6 carbides. (5) 
For calculation purposes, the formula for M.sub.23 C.sub.6 carbide is 
Cr.sub.21 W.sub.2 C.sub.6. Thus, the Cr-to-C ratio in the carbide is 21/6, 
or 3.5. Substituting in equation No. 5 we obtain: 
EQU Maximum Cr=32 a/o+(C in M.sub.23 C.sub.6).times.3.5 (6) 
All of the carbon is in two forms, MC or M.sub.23 C.sub.6. The total carbon 
content is limited to 0.95% or 4.5 a/o to avoid problems with casting and 
handling of the alloy. To maximize the chromium content the amount of 
carbon tied up in the MC carbides must first be calculated: 
EQU C.sub.inMC =Ta+Hf+Ti+Zr=1.52 a/o (7) 
The hafnium range is selected for corrosion resistance and therefore cannot 
cover a very broad range. The atom percent of hafnium, tantalum, titanium 
and zirconium can float as long as the combined total is less than or 
equal to 1.52. This number may be higher only if there is excess carbon 
available and if the chromium is below 32 a/o. The MC carbide information 
must be substituted to determine the carbon available for the M.sub.23 
C.sub.6 carbides: 
EQU Maximum C.sub.M.sbsb.23.sub.C.sbsb.6 =4.5-1.52=2.98 a/o of C (8) 
Since the chromium-to-carbon ratio if the M.sub.23 C.sub.6 carbide is 3.5, 
then 10.43 a/o of the chromium is tied up in the carbides. This value is 
substituted into equation No. 5 yielding: 
EQU Maximum Cr=32+10.43=42.43 a/o=38% (9) 
Thus, 38% (weight) chromium can be used in the alloy with the composition 
being phase stable. 
If the above equations are combined, one can see the dependence that the 
elements have on one another: 
EQU 32.gtoreq.a/oCr-3.5[a/oC-(a/oTa+a/oZr+a/oHf+a/oTi)] (10) 
It is important to note that this equation only defines the relationship 
that the major carbide formers have with each other. A second equation is 
needed to further define the alloy. As stated earlier, the prime objective 
of the Phacomp computation is to obtain the matrix composition of the 
alloy. A Phacomp number, which is a measure of alloy stability, is 
obtained from the following equation: 
##EQU5## 
where N.sub.v is the average electron hole number, or Phacomp number, for 
the alloy, m.sub.i is the atomic fraction of that particular element, 
N.sub.v is the individual electron-hole number of a particular element, 
and n is the number of elements in the matrix. In the case of the alloys 
of the present invention, N.sub.v must be less than or equal to 2.74. 
Therefore, an equation governing the possible alloy compositions is: 
##EQU6## 
where the different elemental values are given as the atom percent in the 
matrix. 
The combination of equation Nos. 10 and 12 define the possible variations 
in applicant's alloy composition. Of course, equation Nos. 3 and 4 above 
are required to convert from weight percent to atom percent and vice 
versa. 
As previously indicated, alloys of this invention are particularly suited 
for use in manufacture of spinners. A combination of stress rupture and 
metal corrosion by molten glass limit the service life of spinners in 
operation. 
Referring to FIGS. 1 and 2, in which like numerals represent like parts, 
there is shown a rotary or centrifugal fiber-forming system including a 
rotor or spinner 50 fabricated in its entirety of the alloy of this 
invention. 
As shown in FIG. 1, rotary or centrifugal fiber-forming system 40 is 
comprised of a flow means or channel 42 having a body of molten inorganic 
material 43, such as glass, therein. A stream of molten glass 46 is 
supplied to the rotor or spinner 50 from channel 42, as is known in the 
art. 
Spinner 50 (shown in detail in FIG. 2), which is adapted to be rotated at 
high speeds, is comprised of a quill 52 and a circumferential 
stream-defining or working wall 54 having a plurality of orifices or 
apertures 55 therethrough to supply a plurality of pre-filament or primary 
streams of molten and inorganic material, such as glass, to be fiberized. 
After forming the body of the rotor by any suitable process, such as 
casting, thousands of holes are formed in the circumferential wall. 
In conjunction with rotor 50, a shroud 56 and circumferential blower or 
fluid attenuation means 57 are adapted to assist in the attenuation of the 
streams of molten material into fibers or filaments 60. A binder material 
or coating may be applied to the fibers 60 by means of binder applicators 
58 as is known in the art. The fibers then may be collected as a pack or 
mat to produce "wool" type glass fiber insulation. 
The following example demonstrates the improved properties of the alloys of 
the present invention as compared with those alloys defined in U.S. Pat. 
No. 3,933,484. Tests were conducted to compare the relative strengths and 
corrosion resistances of an alloy of the present invention with a prior 
art alloy of U.S. Pat. No. 3,933,484. 
The alloy of the present invention had the following composition on a 
weight percent basis: 
______________________________________ 
Chromium About 35.5 
Nickel About 11.0 
Wolfram About 5.8 
Tantalum About 2.5 
Zirconium About 0.20 
Silicon About 0.10 
Carbon About 0.74 
Boron About 0.01 
Hafnium About 0.7 
Aluminum About 0.11 
Titanium About 0.14 
Manganese About 0.01 
Molybdenum About 0.05 
Iron About 0.14 
Cobalt Balance 
______________________________________ 
The prior art alloy, which was hafnium free, contained the following on a 
weight percent basis: 
______________________________________ 
Chromium About 31.2 
Nickel About 11.7 
Wolfram About 7.4 
Tantalum About 1.8 
Zirconium About 0.025 
Silicon About 0.63 
Carbon About 0.59 
Boron About 0.038 
Aluminum About 0.02 
Titanium About 0.025 
Manganese About 0.012 
Molybdenum About 0.3 
Iron About 1.13 
Cobalt Balance 
______________________________________ 
Both the alloy of the present invention and the prior art alloy were 
heat-treated at 2000.degree. F. for 3 hours and then air-cooled. 
The following exemplifies the application of equation Nos. 1 and 2 to the 
above alloys of the present invention and prior art. 
Considering first the alloy of the present invention, the alloy composition 
must be expressed as atomic percent (a/o) rather than weight percent: 
______________________________________ 
Element Atomic Percent (a/o) 
______________________________________ 
Cr 39.51 
Ni 10.85 
W 1.82 
Ta 0.80 
Zr 0.13 
Si 0.21 
C 3.57 
B 0.05 
Hf 0.23 
Al 0.24 
Ti 0.17 
Mo 0.03 
Mn 0.01 
Fe 0.15 
Co 42.21 
______________________________________ 
Equation No. 1 is satisfied using the above atomic percent figures: 
EQU 32.gtoreq.39.51-3.5[3.57-(0.80+0.13+0.23+0.17)]32.gtoreq.31.67 
As stated above cobalt-base alloys of the type with which the present 
invention is concerned comprise a combination of the matrix and second 
phases. In order to apply equation No. 2, the amount of second phases must 
be first determined before the composition of the matrix can be 
determined. The second phases are carbides of the nature MC and M.sub.23 
C.sub.6, the latter in this case obviously being Cr.sub.21 (W,Mo).sub.2 
C.sub.6. The M of MC thus becomes 1.33 which is the sum of the atom 
percent of Hf, Ta, Zr and Ti. Up to one-half of the total C can be used to 
form MC carbides. To form the MC carbides, an amount of C equivalent to 
the total of the Hf, Ta, Zr and Ti, 1.33 a/o, is used leaving 2.24 a/o C 
(3.57-1.33) to form Cr.sub.21 (W,Mo).sub.2 C.sub.6. The amount of Cr tied 
up in Cr.sub.21 (W,Mo).sub.2 C.sub.6 is 2.24.times.(21/6), or 7.84 a/o. 
This leaves 31.67 a/o Cr in the matrix (39.51-7.84). Both W and Mo are 
also used in the M.sub.23 C.sub.6 carbide in amounts equivalent to their 
relative atom percents (W/Mo ratio=1.82/0.03). The amount of W tied up in 
Cr.sub.21 (W, Mo).sub.2 C.sub.6 is 
##EQU7## 
or 0.73 a/o. This leaves 1.09 a/o W (1.82-0.73) in the matrix. The amount 
of Mo tied up in M.sub.23 C.sub.6 carbides equals 
##EQU8## 
or 0.01 a/o, leaving 0.02 a/o (0.03-0.01) in the matrix. The total atomic 
percent of elements tied up in the second phases is 13.48 a/o [1.33 a/o 
for M in MC, 3.57 a/o for total C, 7.84 a/o for Cr in Cr.sub.21 
(W,Mo).sub.2 C.sub.6, 0.73 a/o for W in Cr.sub.21 (W,Mo).sub.2 C.sub.6 and 
0.01 a/o for Mo in Cr.sub.21 (W, Mo).sub.2 C.sub.6 ]. Thus, the matrix is 
86.52 a/o of the alloy which when normalized to a 100 a/o basis results in 
a multiplying factor of 1.156. Thus, the concentrations of the elements 
remaining for the matrix must be multiplied by this factor: 
Cr=31.67(1.156)=36.61 
Ni=10.85(1.156)=12.54 
W=1.09(1.156)=1.26 
Si=0.21(1.156)=0.24 
Ti=0.0(1.156)=0.0 
Mo=0.2(1.156)=0.023 
Fe=0.15(1.156)=0.17 
Mn=0.01(1.156)=0.011 
Al=0.24(1.156)=0.28 
Co=42.21(1.156)=48.79 
Equation No. 2 is satisfied as follows: 
##EQU9## 
With regard to the prior art alloy, its composition on an atom percent 
basis is as follows: 
______________________________________ 
Element Atom Percent a/o 
______________________________________ 
Cr 34.97 
Ni 11.62 
W 2.35 
Ta .58 
Zr .02 
Si 1.31 
C 2.86 
B .20 
Al .04 
Ti .02 
Mn .01 
Mo .182 
Fe 1.18 
Co 44.65 
______________________________________ 
Equation No. 1 is satisfied using the above atomic percent figures: 
##EQU10## 
Equation No. 2 is satisfied as follows: 
##EQU11## 
The relative strengths of the above alloys of the present invention and 
prior art were determined by a standard stress-rupture test (American 
National Standard/ASTM E-139-70 (reapproved 1978)). Average stress rupture 
performance under the conditions set forth demonstrates the markedly 
improved average life of the alloy of the present invention compared with 
the prior art alloy: 
______________________________________ 
Test Conditions Average Average 
Pressure Life Creep Rate 
Temp. (.degree.F.) 
(psi) (Hours) (in./in./hr.) 
______________________________________ 
Alloy of 
2100 3000 274.0 1.3 .times. 10.sup.-4 
present 
invention 
Prior art 
2100 3000 31-32 6.8 .times. 10.sup.-4 
alloy 
______________________________________ 
The relative corrosion rates of the alloys were determined by a spinner 
coupon test. In this test holes are countersunk into the top inside of the 
spinner face of a spinner of the type described above which is cast from 
one of the two alloys. Samples or coupons composed of the other alloy are 
press-fit into the holes after which the spinner blanks are drilled. Thus, 
the samples or coupons become an integral part of the spinner wall, and a 
direct comparison can be made between the alloy of the present invention 
and the prior art alloy under identical process conditions. 
The compositions of the prior art alloy and the alloy of the present 
invention were the same as in the above-described stress-rupture test. The 
following test data demonstrates under a variety of test conditions that 
the average corrosion rate of the alloy of the present invention 
containing hafnium and a higher proportion of chromium is substantially 
lower than the average corrosion rate of the prior art alloy: 
______________________________________ 
Corrosion Rate 
Alloy (mil/200 hr.) 
______________________________________ 
Alloy of the present invention 
8.89 
Prior art alloy 12.70 
Alloy of present invention 
7.20 
Prior art alloy 10.17 
______________________________________ 
The above comparative stress-rupture and corrosion data demonstrate that 
the alloys of the present invention have a markedly improved average life 
and corrosion rate compared with the prior art alloys. 
It will be evident from the foregoing that various modifications can be 
made to this invention; such, however, are within the scope of the 
invention.