U.S. patent number 3,715,792 [Application Number 05/082,787] was granted by the patent office on 1973-02-13 for powder metallurgy sintered corrosion and wear resistant high chromium refractory carbide alloy.
This patent grant is currently assigned to Chromalloy American Corporation. Invention is credited to Arnold L. Prill, Stuart E. Tarkan.
United States Patent |
3,715,792 |
Prill , et al. |
February 13, 1973 |
POWDER METALLURGY SINTERED CORROSION AND WEAR RESISTANT HIGH
CHROMIUM REFRACTORY CARBIDE ALLOY
Abstract
A corrosion and wear resistant high chromium refractory carbide
alloy is provided by powder metallurgy suitable for use as a
seaming tool in the food canning industry comprising primary
carbide grains of at least one refractory carbide selected from the
group consisting of TiC, CbC, VC and TaC dispersed through a high
chromium alloy matrix consisting essentially by weight of about 14
to 24 percent chromium, about 0.4 to 1.2 percent carbon, up to
about 3 percent nickel, up to about 5 percent molybdenum, and the
balance essentially iron.
Inventors: |
Prill; Arnold L. (Edmond,
OK), Tarkan; Stuart E. (Monsey, NY) |
Assignee: |
Chromalloy American Corporation
(West Nyack, NY)
|
Family
ID: |
22173451 |
Appl.
No.: |
05/082,787 |
Filed: |
October 21, 1970 |
Current U.S.
Class: |
75/236;
419/17 |
Current CPC
Class: |
C22C
38/18 (20130101); C22C 33/0292 (20130101) |
Current International
Class: |
C22C
33/02 (20060101); C22C 38/18 (20060101); C22c
029/00 () |
Field of
Search: |
;75/128R,203,204,200,128W ;29/182.8,182.7 ;148/12.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
clark et al., Physical Metallurgy; Van Nostrand Co., pg. 327, 331
(1962)..
|
Primary Examiner: Quarforth; Carl D.
Assistant Examiner: Schafer; R. E.
Claims
What is claimed is:
1. A powder metallurgy sintered corrosion and wear resistant high
chromium refractory carbide alloy comprising about 30 to 75 percent
by volume of primary grains of at least one refractory carbide
selected from the group consisting of TiC, CbC, VC and TaC
dispersed through a high chromium alloy matrix making up the
balance, said alloy matrix consisting essentially by weight of
about 14 to 24 percent chromium, about 0.4 to 1.2 percent carbon,
up to about 3 percent nickel, up to about 5 percent molybdenum, and
the balance essentially iron.
2. The sintered corrosion and wear resistant high chromium
refractory carbide alloy of claim 1, wherein the refractory carbide
ranges by volume from about 35 to 55 percent TiC, and wherein the
matrix alloy making up substantially the balance consists
essentially by weight of about 16 to 20 percent chromium, about 0.5
to 0.9 percent carbon, and the balance essentially iron.
3. A hardened sintered corrosion and wear resistant tool element
formed of a high chromium refractory carbide alloy comprising about
30 to 75 percent by volume of primary grains of at least one
refractory carbide selected from the group consisting of TiC, CbC,
VC and TaC dispersed through a high chromium alloy matrix
consisting essentially by weight of about 14 to 24 percent
chromium, up to about 3 percent nickel, up to about 5 percent
molybdenum, about 0.4 to 1.2 percent carbon and the balance
essentially iron, the metallographic structure of the alloy matrix
consisting essentially of martensite.
4. The hardened tool element of claim 3, wherein the refractory
carbide ranges by volume from about 35 to 55 percent TiC and
wherein the matrix alloy making up substantially the balance
consists essentially by weight of about 16 to 20 percent chromium,
about 0.5 to 0.9 percent carbon, and the balance essentially iron.
Description
This invention relates to a powder metallurgy sintered corrosion
and wear resistant, high chromium refractory carbide alloy and, in
particular, to a hardened sintered tool element formed of said
alloy.
RELATED U.S. PATENTS
In U.S. Pat. Nos. 2,828,202 dated Mar. 25, 1958 and No. 3,416,976,
dated Dec. 17, 1968 and issued to the same assignee, a tool steel
of high carbon content based on titanium carbide is disclosed in
which the amount of titanium employed by weight is at least 10
percent (U.S. Pat. No. 2,828,202) substantially all combined in the
form of primary carbide grains, the titanium carbide grains being
dispersed through a heat treatable steel matrix.
As pointed out in the aforementioned patents, the composition is
formed by employing titanium and carbon together in the combined
form as primary grains of titanium carbide as an alloying
ingredient together with a steel matrix which reacts with the
carbide to a certain extent in producing the desired composition.
The steel employed in forming the matrix contains at least about 60
percent iron by weight of the steel matrix composition.
Powder metallurgy is employed as the preferred method in producing
the desired composition which comprises broadly mixing powdered
steel-forming ingredients and forming a compact by pressing the
mixture in a mold, followed by subjecting the compact to liquid
phase sintering under non-oxidizing conditions, such as in vacuum.
A steel matrix found particularly useful in combination with
titanium carbide is one containing about 0.5 percent carbon, about
3 percent chromium, about 3 percent molybdenum and the balance
iron.
In producing a titanium carbide tool steel composition containing
for example 33 percent by weight of TiC (approximately 45 volume
percent) and substantially the balance the aforementioned steel
matrix, about 500 grams of powdered TiC (of about 5 to 7 microns in
average size) are mixed with about 1,000 grams of steel-forming
ingredients in a mill half filled with stainless steel balls. To
the powder ingredients is added one gram of paraffin wax for 100
grams of mix. The milling is conducted for about 40 hours using
hexane as a vehicle.
After completion of the milling, the mix is removed and dried and
compacts of a desired shape pressed at about 15 t.s.i. and the
compacts then subjected to liquid phase sintering in vacuum at a
temperature of about 2,640.degree.F (1,450.degree.C) for about
one-half hour at a vacuum corresponding to 20 microns of mercury or
better. After completion of the sintering, the compacts are cooled
and then annealed by heating to 900.degree.C for 2 hours followed
by cooling at a rate of about 60.degree.F (33.degree.C or
35.degree.C) per hour to about 1,000.degree.F (538.degree.C) and
thereafter furnace cooled to room temperature to produce an
annealed structure containing spheroidite. The annealed hardness is
in the neighborhood of about 45 R.sub.c and the high carbon tool
steel is capable of being machined and/or ground into a desired
tool shape or machine part prior to hardening.
The hardening treatment employed comprises heating the machined
piece to an austenitizing temperature of about 1,750.degree.F
(about 955.degree.C) for about one-quarter hour followed by
quenching in oil to produce a hardness in the neighborhood of about
70 R.sub.c.
THE PROBLEM CONFRONTING THE ART
The aforementioned titanium carbide tool steel containing by volume
about 45 percent titanium carbide and the balance a low
chromium-molybdenum steel containing by weight of about 0.3 to 0.8
percent C, 1 to 6 percent Cr, 0.3 to 6 percent Mo and the balance
essentially iron has been found very useful in the manufacture of
tools, dies and many wear parts; particularly for use under
generally normal environmental conditions.
However, in certain special environments, such as prevail in the
food canning industry, among others, including corrosive media, the
foregoing composition presents certain problems, insofar as tool
life and overall tool efficiency are concerned. For example, where
the tool is a pair of seaming rolls or hammers employed in the
manufacture of cans involving the use of chloride soldering fluxes
(for example, a mixture of ammonium and zinc chlorides), the tool
does not exhibit adequate corrosion resistance to the fluxes,
whereby the steel matrix relative to the titanium carbide grains is
selectively corroded. When this occurs, titanium carbide grains are
dislodged due to the lack of support in the matrix. This leads to
an accelerated wearing of the seaming rolls, which results in a
loss in tool life and tool efficiency. Similarly, where the
aforementioned tool composition is employed as a tool or wear part
in food canning apparatus, the acid media which normally prevail in
the canning of foods, such as, by way of example, citric acid,
carbonic acid and the like, will generally have a corrosive effect
on the tool or wear part and, as described hereinabove, adversely
affect the life of the tool or wear resistant part.
It would be desirable to provide a corrosion and wear resistant
composition capable of being heat treated to a substantially high
hardness and which will provide a long life under conditions of use
ranging from room temperature up to as high as 800.degree.F
(427.degree.C).
OBJECTS OF THE INVENTION
It is thus an object of this invention to provide a corrosion and
wear resistant high chromium refractory carbide alloy.
Another object is to provide a hardened sintered corrosion and wear
resistant tool element formed of a high chromium refractory carbide
alloy.
These and other objects will more clearly appear from the following
disclosure and the appended claims.
STATEMENT OF THE INVENTION
Broadly stated, the invention is directed to a powder metallurgy
sintered corrosion and wear resistant high chromium containing
refractory carbide alloy comprising primary grains of at least one
refractory carbide selected from the group consisting of TiC, CbC,
VC and TaC dispersed or distributed through a high chromium alloy
matrix consisting essentially by weight of about 14 to 24 percent
chromium, about 0.4 to 1.2 percent carbon and the balance
essentially iron. The term "balance essentially iron" does not
exclude the presence of other elements in amounts which do not
adversely affect the basic characteristics of the matrix alloy.
Thus, the high chromium ferrous matrix may contain other elements,
such as small amounts of one or more of the elements silicon,
manganese, vanadium, molybdenum, and the like.
A composition range which is particularly advantageous is one in
which the refractory carbide ranges by volume from about 30 to 75
percent, with the balance substantially the aforementioned high
chromium matrix alloy.
A more advantageous composition is one in which the refractory
carbide (e.g. TiC) ranges by volume from about 35 to 55 percent,
and wherein the matrix alloy making up substantially the balance
consists essentially by weight of about 16 to 20 percent chromium,
about 0.5 to 0.9 percent carbon, and the balance essentially
iron.
The foregoing composite refractory carbide alloy is capable of
being annealed to a hardness as low as 50 R.sub.c and hardened to
as high as 69 R.sub.c to provide markedly improved resistance to
wear and corrosion. By controlling the carbon content of the matrix
alloy over the broad range of 0.4 to 1.2 percent by weight of the
matrix and, more preferably, over the range of about 0.5 to 0.9
percent, a substantially martensitic matrix is assured by heat
treatment, including a dispersion in the matrix of a secondary
carbide containing chromium, probably an iron-chromium carbide. The
secondary carbide together with the primary carbide provides
improved wear resistance while the chromium dissolved in the matrix
assures resistance to corrosion.
DETAIL ASPECTS OF THE INVENTION
As illustrative of the various embodiments of the invention, the
following examples are given:
EXAMPLE 1
A heat treatable high chromium refractory carbide alloy comprised
of titanium carbide and a matrix of a high chromium ferrous alloy
was produced with the following composition:
Primary Carbide about 45 vol.% TiC Matrix about 55 vol.%
The matrix metal had the following nominal composition by
weight:
Percent Carbon 0.8 Chromium 20.0 Iron.sup.1 balance 1. The balance
iron may include the presence of amounts of other ingredients which
do not adversely affect the basic characteristics of the alloy.
In producing the composition, 500 grams of TiC powder (about 45
vol. percent) of average particle size of about 3 to 7 microns are
mixed with 1,000 grams of powdered steel-forming ingredients
corresponding to the aforementioned matrix metal composition. The
1,000 grams of steel-forming ingredients include 200 grams of minus
100 mesh high purity electrolytic chromium powder, an amount of
carbon equivalent to 8 grams (0.8 percent) taking into account any
free carbon available through titanium carbide and the balance
about 792 grams of iron powder of approximately 20 microns average
size. The powder mixture (TiC and the steel-forming ingredients)
also contains 1 gram of paraffin (1 percent) for each 100 grams of
mix. The mix is placed in a stainless steel ball mill half filled
with stainless steel balls, using hexane as the vehicle. The
milling is conducted for about 40 hours.
After completion of the milling, the mix is removed and vacuum
dried. A proportion of the mixed product is compressed in a die at
15 tons/sq. inch to the desired shape. The shape is liquid phase
sintered at a temperature of about 1,350.degree.C for one-half hour
(after reaching the temperature) at a vacuum corresponding to 20
microns or better. After completion of sintering, the shape is
cooled and then annealed by heating to 900.degree.C for 2 hours
followed by cooling at a rate of about 25.degree.C/hour to about
550.degree.C and thereafter furnace cooled to room temperature to
produce an annealed microstructure containing mainly sphereoidite,
the hardness being about 50 R.sub.c. The sintered shape is then
machined into a tool element, e.g., seaming rolls or hammers for
the canning industry, and thereafter hardened by heating to an
austenitizing temperature of about 1,875.degree.F (about
1,025.degree.C) for about one-quarter hour at temperature and then
air or oil quenched to form a hard microstructure consisting
essentially of martensite. Following hardening, the tool element is
tempered at a temperature within the range of about 400.degree.F
(205.degree.C) to 800.degree.F (427.degree.C) for about 1 to 2
hours and thereafter cooled in air. The final hardness is in the
neighborhood of about 68 R.sub.c. Following hardening, the tool
element which is slightly oversize is then precision ground.
EXAMPLE 2
Primary carbide about 30 vol.% CbC Matrix about 70 vol.%
The nominal composition of the matrix by weight is as follows:
Percent Carbon 0.6 Chromium 16.0 Iron balance
The method of formulation, the sintering procedure and the heat
treatment are similar to those described for Example 1.
Similar procedures are employed in the following examples.
EXAMPLE 3
Primary carbide about 40 vol.% VC Matrix about 60 vol.%
The nominal composition of the matrix by weight is as follows:
Percent Carbon 1.0 Chromium 18.0 Iron balance
EXAMPLE 4
Primary Carbide about 55 vol.% Tac Matrix about 45 vol.%
The nominal composition by weight of the matrix is as follows:
Percent Carbon 1.1 Chromium 22.0 Nickel 1.0 Iron balance
EXAMPLE 5
Primary Carbide about 65 vol.% TiC Matrix about 35 vol.%
The nominal composition of the matrix by weight is as follows:
Percent Carbon 1.2 Chromium 23.0 Nickel 1.5 Iron balance
EXAMPLE 6
Primary carbide about 70 vol.% TiC Matrix about 30 vol.%
The nominal composition of the matrix by weight is as follows:
Percent Carbon 0.5 Chromium 15.0 Molybdenum 2.0 Iron balance
Broadly, in producing the various compositions by powder
metallurgy, the appropriate amount of steel-forming ingredients is
mixed with an appropriate amount of primary carbide in a ball mill.
The mixture may be shaped a variety of ways. It is preferred to
press the mixture to a density of at least about 50 percent of true
density by pressing over the range of about 10 t.s.i. to 75 t.s.i.,
preferably 15 t.s.i. to 50 t.s.i., followed by sintering under
substantially inert conditions, e.g., in a vacuum or an inert
atmosphere. Advantageously, the temperature employed is above the
melting point of the chromium steel matrix, for example, at a
temperature up to about 100.degree.C above the melting point for a
time sufficient for the primary carbide and the matrix to reach
equilibrium and to obtain substantially complete densification, for
example, for about one minute to six hours.
When the liquid phase sintering is completed, the product is
allowed to furnace cool to room temperature. If necessary, the
as-sintered product is subjected to mechanical cleaning. If the
as-sintered product requires annealing, it is heated to a
temperature of about 1,550.degree.F (845.degree.C) to
1,700.degree.F (926.degree.C) for about 2 to 5 hours and then
slowly cooled at a rate not exceeding 25.degree.C/hour.
For hardening, the austenitizing temperature may range from about
1,700.degree.F (926.degree.C) to 2,000.degree.F (1,093.degree.C)
for about 30 minutes to 2 hours followed by air cooling.
Thereafter, the hardened composition may be tempered at a
temperature ranging from about 400.degree.F (205.degree.C) to
800.degree.F (427.degree.C) for about 1 to 2 hours. For the
compositions given hereinbefore, the hardness after tempering may
range from about 65 R.sub.c to 71 R.sub.c.
Corrosion studies have indicated that the alloy compositions of the
invention exhibit good resistance to corrosion in such acid media
as concentrated nitric acid and dilute (about 10 vol. percent)
sulfuric acid.
Although the present invention has been described in conjunction
with preferred embodiments, it is to be understood that
modifications and variations may be resorted to without departing
from the spirit and scope of the invention as those skilled in the
art will readily understand. Such modifications and variations are
considered to be within the purview and scope of the invention and
the appended claims.
* * * * *