Note: Descriptions are shown in the official language in which they were submitted.
`"` ~LO~i~9~3
~ACKGROUND OF THE INVENTION
.
1 Cryo~enic powder making is a relatively new mode
2 for providing a powdered raw material which can be put to use
3 in powder metallurgy techni~ues and other applications. It
4 is promlsing because it appears to provide powdered material
at a significantly lower cost with more useable physical
6 properties, if not enhanced physical properties.
7 According to known technology, cryogenic powder
8 making essentially comprises sub~ecting scrap metal (swarf)
9 or other solid metal starting materials, to a temperature
below the ductile-brittle transition temperature of said
11 metal, such as -(30-40)~ for ferrous based material. The
12 metal becomes 50 brittle at such depressed temperatures
13 that agitation within a conventional hammer mill will reduce
14 the starting material to a powder form over a predetermined
period of time and with typical stress from the hammer
16 eléments. Prior to entering such hammer mill, the swarf may
17 be degreased according to conventional modes (such as by
18 vapor degreasing or by dipping ~n a suitable solvent). The
19 medium most typically utilized to promote ultra-low
temperatures for said ferrous scrap is liquid nitro~en; it
21 can be used in sufficient quantities to assure that the entire
22 mass of said pieces are maintained below said transition
23 temperature.
24 The comminuted particles resulting from a pre-
determined amount of conventional hammer milling under such
26 embrittlement conditions, produces metal particle shapes which
27 are flake-like or irregular, certainly not spherical. The
28 flake-like configuration results from probably two factors:
29 (a) the scrap material was machine turnings which thus have a
-2~
63
1 thin ribbon-like configuration with a large surface-to-
2 volume ratio, and (b~ comminution takes Place b~ fracture
3 insuring irregularity of small broken sections o~ the
4 ribbon resembling flakes. Subsequent to conventional
hammer milling, the prior art employs an independent annealing
6 operation to relieve said partlcles of co~.d work imparted
7 by said hammer milling. The prlor art next may sub,Ject
8 the annealed fragmented particles to a ball milling operation
9 while in the presence of a slurry (promoted b~ the use of
benzene or other organic compounds). Ball milling is carried
11 out by the use of iron elements and for a sufficient time
12 and rate to reduce said fragmented particles to a predetermined
13 powder condition. Subsequent to the ball milling operation3
14 the powdered material is separated from the slurry and
subjected to a drying cycle where it is finally packaged
16 for use in typical powder metallurgy techniques.
17 Such cry~genically produced powder can be processed
18 with conventional po~der metallurgy techniques typically
19 1nvolving heating a desired quantity of powder to a sintering
temperature~ followed by hot forming or forging. Oxidation
21 of such ingredients as manganese or silicon, within such
22 heated metallic powder, will typically take place prior to
23 diffusion and completion of the sintering step. These
24 elements require stringent atmosphere control, more control
than is normally obtainable with current manu~acturin~
26 equipment. Moreover, such powder, when mixed with alloy
27 powders~ demand an uneconomical and inefficient sintering
28 temperature with attendant loss of hardenability. Even with
29 a mixture of only plain carbon powders having carbon contents
at different levels, the kinetlcs of sintering are adversely
63
1 affected by the uncontrollable early diffusion o~ graphite
2 necessitating higher sintering temperatures.
3 SUMMARY OF THE INVENTION
4 A primary ob~ect of this invention is to provide
a single step method of making a cryo~enically produced powder
6 from ferrous based scrap pieces, the powder being suitable
7 for powder metallurgical techniques and particularly
8 improving diffusion kinetics.
9 Another ob~ect of this invention is to provide an
improved method for making cryogenically produced powder,
11 such method combining the operations of ~ragmenting
12 controlled cold working of the fragmented particles, and
13 implanting of a protective metal envelope on each of said
14 fragmented particles to lmprove diffusion kinetics during
sintering, said steps all being carried out preferably and
16 optimally within a continuous single step system.
17 A more specific ob~ect of this invention is to
18 provide a single step method for conversion of machine scra~
19 turnings into a powder suitable for powder metallurgical
techniques. The ~errous scrap pieces are circulated and
21 sub~ect to impact in one zone of the circulation while the
22~ pieces are at a temperature below the ductile-brittle
23 transition temperature and cold worked in another zone of
24 said circulation while the pieces are allowed to rise
momentarily above sald ductile-brittle transition temperature.
26 Yet still another ob;ect of this invention is to
27 produce a powder derived from a variety of scrap metal pieces
28 traditionally not useable in scrap melting techniques, the
29 powder so produced being completely substitutable for current
.
~ -4-
;,
```\ ~6~g~3
1 commercially made metal powders; an associated ob~ect o~ this
2 in~ention is to upgrade the physical propertles of cr~ogenicall~
3 produced powder and in certain respects to surpass the
4 physical properties of any carbon steel type prior art powder.
SUMMARY OF THE DRAWINGS
6 Figure 1 is a central elevational sectional view
7 of one type Or batch apparatus suitable for use in carrying
8 out the process of this invention;
9 Figure 2 is an end elevational view of the
apparatus of Figure l; and
11 Figure 3 is a central elevational sectional
12 view of an alternative apparatus useful in providing a con-
13 tinuous process for the method o~ this invention.
14 DETAILED DESCRIPTION
A preferred mode ~or carrying out the method
16 aspects of this invention is as follows:
17 (1) Scrap metal, particularly machine turnings,
18 are selected as the starting material. "Machine turnings"
19 is defined herein to mean segments of ribbons of low alloy
steel; they are particularly shavings cut from an alloyed
21 bar. Ferrous based machine turnings include alloying
22 ingredients such as manganese, silicon, chromium, nickel
23 and molybdenum. The turnings should be selected to have a
24 surface-to-volume ratio of at least 60:1, which is characteristic
of machine turnings. The scrap pieces will typically have a
26 size characterized by a width .1-1.1 inch, a thickness of
27 .005_.03 inch, and a length of 1-100 or more inches. Machine
28 turnings are usually not suitable for melting in an electric
-
~6~63
1 furnace because they prevent efficient melt down due to
2 such surface-to-volume ratio.
3 The process herein can be performed with other
4 types or larger pieces of scrap metal, but capital lnvestment
costs will lncrease due to the difficulty of impacting scrap
6 metal sized in pieces bevond .03 inches thick. The scrap
7 pieces should be selected to be generally compatable in
8 chemistry as desired in the final product; this is achieved
9 optimally when the scrap is selected from a common machining
operation ~here the same metal stock was utilized in forming
11 the turnings.
12 (2) Although not critically necessary, it is
13 preferable to degrease the ferrous based pieces by conventional
14 modes which may include vapor degreasing or dippinglthe pieces
I5 in a solvent bath usually containing benzene or meth~l-ethyl-ke~tone.
16 However, with the type of cryogenic processin~ taught herein,
17 it is now possible to remove oil and other organic mat~rials
18 without any separate cleaning. This occurs as a result of
19 allowing the organlc material to freeze upon being sub;ected
to cryogenic temperature levels. The frozen mate~ial can
21 then be removed during or after lmpaction by ball milling
22 elements; the frozen organlc debris can be screened and
23 separated as an lnherent result of this process.
24 (3) A circulating mass of said ferrous based
pieces 10 in a predetermined path 11 is defined. This is con-
26 veniently provided by introducing the scrap pieces to a ball
27 milling drum 14 having an insulating body 14a encased between
28 metal walls 14b and 14c, as specifically shown in Figure 1.
~L,oG1 963
1 The scrap pieces 10 ~here shown as comrninuted in Figure 1)
2 and milling elements 17 are loaded into the drum 14 prior to
3 closure of cover 14d; liquid nitrogen is added later
4 through conduit 18. The circulating mass is stimulated b~
the rotary movement ~such as in direction 13) of the drum
6 o~ the ball milling machine 12. The circulatory path 11
7 can be selected by the uniform or non-unlform rotary speed
8 of the drum. Llquid nitrogen is introduced to the drum in
9 a predetermined quantity to provide a liquid level 15
slightly below the top surface 16 of the slurry created by
11 the composite of the pieces and liquid nitrogen. As the
12 drum is rotated at a predetermined speed, the liquid nitrogen
13 will be generally retained in a zone A, often assuming a
14 crescent shape silhouette as shown in Figure 2. The ferrous
based scrap pieces will be influenced somewhat differently
16 and will undergo a circulatory movement as indicated in
17 path 11 which rises above the liquid nitrogen in zone B.
18 Thus, for a portion of the circulation along path 11, the
19 ferrous spaced pieces will not be exposed to the liquid
nitrogen. As a result of both the heating (experienced by
21 collision between the ferrous based pieces and the ball
22 milling elements causing a release of energy and the divorce
23 from the liquid nitrogen, the ferrous based particles will
24 experience an increase in temperature in zone B such that they
will be momentarily above the ductile-brittle transition
26 tempera~ure of the particles. Upon return to zone A, of
27 course~ the ferrous based particles will again be contacted by
28 liquid nitrogen to be reduced below the ductile-brittle
29 transition temperature.
--7--
6~9~;3
1 (4) Impaction of said ferrous based pieces or
2 particles is inherently carried out by the circulatory move-
3 ment which collides one particle against the other. ~or the
4 purposes o~ fragmenting the pieces at the sub-brittle
temperatures, milling elements 17 are emploved in the form
6 of balls having a diameter of about .5 inches. Cylindrical
7 rods or segments can also be employed. Such balls are
8 preferably constituted of copper or any other eauivalent
9 protective metal which has a melting temperature below, but
substantially close to the liquidus of said ferrous based
11 particles, said protective metal being completely soluble
12 in the material of which said particles are constituted and
13 said protective metal is relatively easy to abrade and can
14 be abraded at the sub-brittle temperatures of this method.
Thus, in zone A, the impacting elements, preferably in the
16 form of copper balls, will impart a fracturing force to the
17 particles causing them to separate into a classi~iable
18 comminuted condition. At the same time, each of the fragmented
19 particles will receive an infinitesimal portion of the copper
ball upon each collision, which when multiplied by a large
21 number of repeated collisions will form a partial envelope or
22 layer on the outer surface of each particle. Upon the
23 occurrence of a predekermined number of circulatory revolutions,
24 it has been determined that a complete copper envelope or
protective metal envelope is formed upon each particle. The
26 time necessary to achieve such complete envelope is a function
27 of millin~ time and rate which in turn is dependent upon
28 mill volume, mill diameter, size of copper balls, and the
29 speed of drum rotation.
10~9~3
l Iron is brittle at a temperature below 40Celæius
2 and copper is not. Accordin~l~y, the ~errous based machine
3 turnings, introduced into the batch ball milling machlne, will
4 be impacted by elements not brittle at such temperature. A
temperature of 40Celsius or less is achieved by introducing
6 the liquld nitrogen through said feed conduit 18 extending
7 through one end, such as the cover 14d, and substantially
8 coincident with the axis of rotation. Liquified nitrogen
9 is employed, although other mediums which may be used include
dry ice with acetone or other or~an and liquids. A vent is
ll provided in one location of the milling chamber to exhaust
12 gaseous nitrogen as it evaporates.
13 The impaction forces normally required to provide
14 fracture of the pieces should be less than l ft.-lb. and
when impaction is carried out for a sufficient period of time
16 and at a proper rate will reduce such scrap pieces to a
17 powder form.
18 In zone B of the circulatory movement, the ball
l9 milling elements will impart sufficient cold work to the
comminuted particles to generate defect sites in substantially
21 all particles of about 1-4 microns; the ball ~illing operation
22 herein should be carried out for a sufficient time so that
23 substantially each coarse particle has at least one defect
24 site therein.
When these steps are completed, the particles
26 (in powder form) are separated from the slurry, the resultin~
27 powder will have all particles coated with a continuous copper
28 envelope (shell) and each particle (1-4 microns) will be
29 sufficiently stressed so as to have a high degree of compact-
ability. The term "defect site" is defined herein to mean a
~19~3
l defect in local atomic arrangement. The term "copper shell"
2 is defined herein to mean a substantially continuous thin
3 envelope intimately formed on the surface of the particle.
4 Although the shell should preferably be i.mpervious and
continuous about each particle, it is not; critical and that
6 it be absolutely impervious.
7 It has been demonstrated by test examples,
8 performed in connection with reducing this invention to
9 practice, that cold working of the particles predominantly
influences diffusion kinetics when sintering powder of this
11 invention, the copper coating or shell operating to pre-
12 dominantly perform an anti-oxidation barrier during sintering
13 of the powder hereinO
14 (5) The intermediate or resulting product from
the above steps can then be subJected to powder metallurg,v
16 techniques. A predetermined quantity of conditioned powder
17 is compacted by a conventional press to a predetermined
18 density, such as preferably 6.6 grams/cc. This is brought
19 about by the application of forces in the range o~ 30-35 psi.
The presence of the copper envelope about the powder particles
21 improves compressibility. With prior uncoated powders, a
22 density of about 6.4 g./cc is typically obtained using a
23 compressive force of 85,000 psi; with the powder herein,
24 densities of about 6.6 g./cc. are now obtained at the same
force level.
26 The shape into which such powder is com~acted
27 should have an outer configuration sli~htly larger than that
28 desired for the final part. A significant and highly improved
29 shrinkage takes place as the result of the sintering step.
The shrinkage is a predetermined factor and allo~ance can
--10--
1~619~
1 be made ~or it in the compacted shape. 5hrinkage will be
2 in the controlled limits o~ ~.002 inches/inch.
3 (6) The compacted shape is sub~ected to a sintering
4 treatment within a furnace wherein it is heated to a tem~erature
pre~erably in the range o~ 2000-2100F for ~errous based
6 cryogenic powder. The temperature to which each compacts is
7 heated should be at least to the plastic region for the metal
8 constituting the powder. A controlled or protective atmosphere
9 is maintained in the furnace, which may be inert or reducing.
At the sintering temperature, atomic diffusion
11 takes place between particles of the powder3 particularly
12 at solid contact points. Certain atoms o~ one particle are
13 supplied to fill the defects site (absence of certain atoms
14 in the crystal structure o~ the contacted particle) said
de~ect sites being present as a result of cold working.
16 Diffusion is accelerated to such an extent, that an increase
17 oY more than 100 times is obtained. It is theori~ed that at
18 least 60% o~ the improvement in physical properties of the
19 resulting sintered shape is due to the controlled cold working
of the powder. The increased dif~usion is responsible for
21 the increase in shrinkage.
22 The copper envelope on the particles serves to
23 essentially prevent oxidation of certain elements or in~redients
24 within the powder particles, particularly manganese and
silicon. With typical ball milling parameters (physical size
26 of the mill, speed change, and ball size) it can be expected
27 that substantially each particle of the cryogenlc powder will
28 possess an impervious copper shell. However, a totally
29 impervious shell is not absolutely essentially to obtain an
~61963
1 improvement with respect to some of the properties
2 herein.
3 The process of this invention can be carried out
4 continuously, such as by an apparatus shown in Figure 3. The
cylindrical apparatus 20 has rifling or ribs 21 spirally
6 located about the interior 23a of the continuous processing
7 drum 23. Liquid nitrogen is introduced at one end 23b of
8 the drum through a conduit 24 preferably aligned with the
9 axis of the drum. Another conduit 25 is also arranged along
the axis to introduce scrap material in the form of machine
11 turnings or comparable ferrous scrap material. The drum is inclined
12 at an angle to the horizontal preferably in the ran~e of 1 tc 2
13 so that the slurry 26 comprised of liquid nitrogen 28, ball
14 milling elements 27 and the ferrous scrap material 29 will
undergo a transcillatory as well as a rotary movement along
16 the length of the drum 23 and about the diametrical interior
17 f the drum. At the opposite end 23c of the processing drum,
18 an exit opening 30 is provided which is covered by a sieve
19 31 effective to allow exit of processed particles only of a
certain size which rise to the surface of the slurry mixture.
21 Here again, the ferrous particles will undergo a circulatory
22 movement along a path 32 which includes a zone A when the
23 particles are immersed in the li~uid nitrogen(with their
24 temperature below the ductile-brittle transition point) and a
zone B when the particles are lifted momentarily out of the
26 slurry as a result of the rotary action. During this momentar~
27 exposure, the ~errous based particles will experience an
28 increase in temperature to above the ductile-brittle transition
29 temperature (but below ambient temperature conditions) to permit
-12-
~61963
1 imparting cold work to the particles. The exlt openin~ 30
2 permits discharge of gasified nitrogen as well as a small
3 portion of the liquid nitrogen. It has been found that
4 regulation of the opening shape between wires of the
screen is important as well as the mesh size of the screen.
6 To this end, -30 mesh has been found pre~erably to achieve
7 a type of powder which has optimum sinterability and
8 compaction characteristics. The sieve opening shape should
9 be pre~erably square shaped.
I claim:
-13-
6196i3
SUPPLEMENTARY DISCLOSURE
In the principal disclosure there is described
a method of improving the sinterability ,and compactability
of ferrous scrap converted to powder by a continuous
operation in which there are circulated the metallic scrap
particles having a volume-to-surface ratio of at least 60:1
and a temperature below the ductile-brittle transition
temperature in at least one phase of its circulation. The
particles are simultaneously impacted to fracture during
one phase and coated by impact transfer with a protective
metal.
The protective metal is one having a melting
temperature below but substantially about the liquidus of
the particles, completely soluble in the metal of the
particles and relatively easy to abrade,
In a preferred embodiment, the metallic scrap
particles are allowed to rise in temperature abo~e the
ductile-brittle temperature but below ambient during
another phase of the circulation and during the elevated
temperature condition the particles are additionally
impacted to impart a degree of cold work to the surface
of the fragmented particles. The protective metal is used
for the cold working.
The operation of the principal disclosure
preferably is carried out using elements laden with the
protective metal and having a transverse dimension of at
least 50 times the shortest dimension of any of the
particles, such as cylindrical or spheric~l elements
consisting essentially of the protective metal in a cylindrical
rotatable mill chamber~ The mill chamber is defined with a
maximum control dimension extending across a central cross-
- 14 -
,
~ .. . .
10~i196;~
section of the chamber. The elements have their smallest
dimension no greater than 10% of~the control dimension.
The spherical elements generally are solid spheres of the
protective metal having a diameter of at least 0.1 inch.
This Supplementary Disclosure also provides
additional sintering test data supplementing that of the
principal disclosure.
The problem of prevention of oxidation of alloying
elements dissolved in the iron powder is a kin~tic one
involving diffusion through the coating material to the particle
surface. If diffusion is slow, chemical potentials of the
metallics can be kept low enough at the outer surface of the
coated particle, where oxygen potentials are the highest,
to avoid oxidation. For the times and temperatures involved
in formation of initial sinter bonds this is probably the
case; at least for most substitutional elements soluble in
iron. However, the fact that the diffusion process, as well
as the process of solution o~ the coating material, is going
on continuously during sintering implies that oxidation will
2Q occur to some extent after formation of the initial sinter
bonds. However, once these bonds are formed they can continue
to grow independently of the state of oxidation of the free
particle surfaces. Further oxidation, therefore, is important
only if subsequent operations require that inner pore surfaces
be oxide free.
Selection of a coating that will not oxidize in
endothermic gas atmospheres, or at least not have a stable
form at sintering temperatures, may be made from equilibrium
thermodynamic data for metal-oxide reactions. Figure ~
accompanying this Supplementary Disclosure is a plot of this
type of data for metals of interest here. With the natural
logarithm of the equilibrium oxygen pressure of the atmosphere
. -- 15 --
; ~ .
963
gas plotted versus temperature, each of the equilibrium lines
shown describes the temperature and oxygen pressure conditions
required to cause dissociation of the metal oxide into metal +
oxygen gas. Thus atmospheres with greater oxygen pressures
or potentials than the dissociation pressure of an oxide lie
above the equilibrium line and are in the region of oxide
stability. ~tmospheres with oxygen pressures less than the
dissociation pressure lie below the equilibrium line and
avour reduction of the oxide to pure metal. The cross-hatched
areas shown in Figure 4 represent the operational ranges of
endothermic gas generators and dissociated ammonia atmospheres.
Note that the data shown here indicates why the
common alloying elements in steel, other than copper, nickel
and molybdenum, are not particularly well suited for iron
sintering furnace atmospheres. Because of this the choice
of coating materials from the-elements shown reduces to
copper, nickel, molybdenum or iron itself. Copper was
chosen for initial trials because of the variety of coating
methods available, both chemical and mechanical. Since
copper melts at 1083C (1981F), it offers the additional
advantages of being liquid at sintering temperatures and
thus potentially promoting the rate of sintering ~ia the
action of capillary forces.
A number of additional powders were examined.
Some of these powders, their nominal chemistry and screen
analyses are listed in Table I appended to and forming part
of this Supplementary Disclosure. The first three powders
originated from steel machining swarf and the fourth from
cast iron machining swarf. The steels, S~E 1050 (Cryo 314,
3Q Cryo 319) and 8620, (Cryo 138) were comminuted at cryogenic
temperatures to avoid excessive plastic deformation. This
was accomplished after preliminary cleaning and shredding
- 16 -
963
by immersion in liquid nitrogen followed by hammer milling,
a process subjecting the chips to high impact loads at
temperatures below their ductile~to-ductile fract~lre transi-
tion. The combination of high impact loading and low
temperature seemed to reduce the powder shape characteristics
associated with mechanical comminution of ductile materials
considerably. These ma~erials, after comminution, were
given a decarburizing anneal to reduce carbon levels below
0.1~ by weight.
The 314 powder, supposedly from the same scrap
source as the 319, illustrates a problem which must be
contended with in dealing with the processing of scrap of
this sort. The combination of abnormally high carbon and
silicon of the 314, compared to the 319, suggested that the
apparently "segregated" scrap did contain some cast iron
swarf also. Thus, after decarburization, the 314 and 319
dif~ered inadvertently in silicon concentration as well as in
the intended particle size distribution.
The cast iron swarf powder (Iron 139) was
comminuted by ordinary grinding procedures since it was
inherently brittle. It was used in the ferritized condition
to enhance compressibility properties. Some silicon carbide
was noted in the powder; probably carried over from the
grinding operation. The cast iron powder was not given a
decarburizing anneal. Decarburization was accomplished during
sintering by additions of Fe~O3 powder to the po~der mix.
All powders were coated for varying lengths of
time to determine the effect of thickness and continuity
of the coating on the sintered properties. Once coated,
processing of the coated powders was the same as for uncoated
powders. Powders were blended with 1% zinc stearate and
17 -
.,~ ,.: .
9~3
sufficient graphite to achieve a final combined carbon concen-
tration of 0.6-0.8~. In the case of the cast iron~ the
stoichiometric amount of iron oxide required to reduce
carbon to this level was substituted for the graphite.
Powders were compacted into M.P.I.F. transverse rupture bars
or tensile bars. Pressures used were kept constant at 414
MPa (30 tsi~ and green densities were recorded as a measure
of compressibility. Sintering was accomplished in endothermic
gas atmosphere using a thermal cycle of 30 minutes at 788C
(1450F) for burnoff of l~bricant and 20 minutes at 1121C
(2050F) for sintering, followed by a controlled cool to
room temperature.
The sintered transverse rupture strengths (T.R.S.)
of each powder were used as measures of the "~uality" of
sintering. The problems associated with the oxi-dation of
silicon, manganese, and other alloying elements are reflected
in significantly lower strengths than normally obtained with
commercial iron powder mixes. As a reference, an iron - O.7%
carbon sintered alloy at a density of 6.7 g/cc will have a
T.R.S. of the order of 550 MPa (80 ksi), while the same
alloy with 1.5% copper, admixed can attain a T.R.S. of 786
MPa (110 ksi).
Most of the initial test work was performed on
Cryo-138 because of its high alloy concentration and because
a plentiful supply of comminuted powder was available.
These results are summarized in Table II appended to and
forming part of this Supplementary Disclosure. The first
five entries represent attempts at sintering without prior
coating. The data demonstrates the difficulty encountered
in attaining acceptable property levels with ordinary wrought
steel chemistry. The best situation~ sintering at 1150C
- 18 -
~L~)6~963
for 40 minutes in dissociated ammonia produces transverse
rupture strengths only 73% of that possible with commercial
iron powder a~ lower sintering temperatures and shorter
times. The coated samples on the other hand, all possessed
significantly higher transverse rupture strengths after
sintering. The data presented for coated samples in Table
II descxi~es only the effects of coating variables. The code
indicated in the Table has coating treatment indicated by
the letter prefix and coating time or thickness by the
number. With the exception of the B treatment r the values
selected for the Table were optimum treatments for highest
strength. Although it is not evident from the sintered
densities shown, the B4 sample differed from the B3 in the
amount of shrinkage which occurred during sintering; the
B4 having shrunk significantly more.
The marked effect of coating ~as observed to be
highly reproducible and relatively independent of the
nature of the starting material itself. The coating
treatmenk variations examined were primarily designed to
2~ vary the rate of copper plating and the adherence of the
coating. From the data in Table II it is evident that B4,
C2, and D5 treatments all provide properties equivalent to
or better than the best commercial iron powder with 1.5%
copper admixed. Copper analysis of the Cryo-138 powder
indicates,about 1% Cu present in samples with the thicker
,coatings.
Table III appended to and forming part of this
Supplementary Disclosure contains the data obtainecl from
powder produced from essentially a plain carbon steel swarf.
Cryo-314 is the finest particle size distribution examined
from this material, Cryo-319, the coarsest. Once again the
- 19 -
~0~63
effect of coating is quite marked although the properties
are not as high as for the Cryo-138. The Cryo-314 i9,
however, within the range of commercial iron powders without
copper additions. The Cryo-319 is obviously too coarse and
thus has too few interparticle contacts to provide adequate
strength. The contacts existing did, however, sinter
satisfactorily as indicated by the data. The abnormally high
silicon in Cryo-314 did not appear to have influenced the
sintering process.
Table IV appended to and forming part of this
Supplementary Disclosure lists the results obtained from
Iron 139 coating experiments. The coating procedure not
only improved the sintered strength but increased the
sintered density also. With green densities in all of
these materials of the order of 5.0 g/cc, the large shrinkage
during sintering is probably associated primarily with the
high concentration of "fines" in the comminuted scrap. The
coating schedule A4a represents the same coating conditions
as A4 except that Fe2O3 was not added tc the initial powder
2Q mixture for A4a samples. The higher combined carbon appears
to have been responsible ~or the lower density.
Finally, the results obtained from coated and
uncoated commercial iron powders, atomized and sponge, are
shown in Table V appended to and forming part of this
Supplementary Disclosure. With no alloying elements present
;` to cause oxidation problems during sintering, no effect would
be expected. The unusual results obtained prompted examina-
tion of tensile properties as well. These too are shown in
Table V. A definite improvementt albeit small compared to
the mechanically comminuted powders, is present in both
transverse rupture and tensile strengths for atomized iron.
Sponge iron, however, shows a definite deterioration of
20 -
3L~6~63
transverse strength and little or no effect on tensile
strength comparing coated to uncoated forms. The coating
treatments were short time or thin coatings, to be sure,
and coatings may not have been continuous but the dramatic
difference in effect between atomi~ed and sponge is real.
Other atomized powders and regularly shaped powders, like
car~onyl iron, were coated and sintered also with similar
results i.e., a small but perceptible effect on sintered
properties.
The principal disclosure discloses the application
of the treatment process to ferrous based metal particles,
mainly machine scrap turnings. In accordance with this
Supplementary Disclosure, the invention may be used in
connection with hypoeutectoid steel or hypoeutectoid
alloy steel which is normally ductile. Such material is
first subjected to heat treatment embrittlement procedures,
as described in detail and claimed in our copending
application Serial No.agV, IY~ filed concurrently with this
Supplementary Disclosure. The embrittlement procedure
involves providing particles having a substantially
martensite structure, preferably at least 80% SO, and
according to this Supplementary ~isclosure, the invention
is also applicable to particles having a predominantly
martensite str~cture.
,~,
~,~1j963
A. Nominal Chemical Analyses
(weight percent)
Powder C Mn Si P S N.i Cr Mo Cu
Cryo 138 0.20 0.42 0.330.03 0.03 0.44 0.58 0.14 0.26
Cryo 314 1.12 0.74 0.860.02 0.01 0.01 0.03 0.05 0.04
Cryo 319 0.53 0.80 0.250.02 0.02 0.01 0.03 0.05 0.01
Iron 139 1.57 0.62 2.300.03 0.15 0.03 0.04 0.05 0.31
Sponge 0.110.74 0.86 0.010.01 -- 0.03 0.04 0.04
Atomized 0.01 0.27 0.040.01 0.03 0.04 0.04 0.04 0.14
B. Sieve Analyses
(weight percent)
Powder Mesh Size
+60 ~100+140~200 +325 -325
Cryo 138 60.5 17.0 5.4 7.2 5.0 5.0
Cryo 314 S9.0 17.310.2 8.6 4.4 0.6
Cryo 319 80.4 10.6 4.0 4.5 0.5
: : Iron 139 -- 26.831.1 21.5 14.6 6.0
Sponge -- 6.225.5 39.2 21.0 8.1
Atomized -- 7.327.0 37.4 20.4 7.9
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! .
~t ~
~6~L~63
TABLE II: CRYO 138 RESULTS
Sintering Conditions Final
Type Time Temp. Density T.R.S
Coa ~ (min.) (C) Atm.(g/cc) (MPa)
No Coating 40 1150 D.A.*6.9 399.2
No Coating 20 1121 Endo**6.8 121.4
No Coating 20 1121 Endo**5.5 113.8
No Coating 20 1135 Endo**6.5 141.3
No Coating 20 1149 Endo**6.6 151.7
10A4 20 1121 Endo**6.7 648.1
B3 20 1121 Endo**6.5 655.0
B4 20 1121 Endo**6.4 931.8
C2 20 1121 Endo**6.8 742.3
D5 20 1121 Endo**6.4 813.6
* Dissociated Ammonia
** Endothermic Generator Gas (Dew Point = 7C)
- 23
~61963
TABLE III: CRYO 31A AND CRYO 319 RESULTS
Sintered 20 min. at 1121~C in Endothermic
Gas (Dew Point 7C)
FinalTrans. Rupture
Density Strength
Coating (g/cc) (MPa)
None 6.8 144.8
314
D2 6.7 586.1
None 6.7 17.2
319 D2 6.5 103.4
TABLE IV: IRON 139 RESULTS
Sintered 20 min. at 1121VC in Endothermic
Gas (Dew Point 7C)
FinalTrans. Rupture
Density Strength
Coating (g/cc) (MPa)
None 4.7 50. 3
A3 5.8 562.7
A4 6.5 666.7
.
A4a 6. 3 647.4
.
TABLE V: ATOMIZED AND SPONGE IRON RESULTS
Sintered 20 min. at 1121C ln Endothermic
Gas (Dew Point 7F)
Trans. Rupture Tensile
Density Strength Strength
Coating (g/cc) (MPa) _(MPa)
None 6.6557.8 248.2
Atomized
Dl 6.4587.4 303.4
None 6.3724.0 243.4
Sponge
Dl 6.2558.5 262.0
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