U.S. patent application number 11/073769 was filed with the patent office on 2006-09-07 for semisolid metal injection molding machine components.
This patent application is currently assigned to Thixomat, Inc.. Invention is credited to Raymond F. Decker, Ralph E. Vining, Donald M. Walukas.
Application Number | 20060196626 11/073769 |
Document ID | / |
Family ID | 36616931 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060196626 |
Kind Code |
A1 |
Decker; Raymond F. ; et
al. |
September 7, 2006 |
Semisolid metal injection molding machine components
Abstract
The present invention provides an alloy for components of
semi-solid injection molding machinery. In particular, the alloy is
a intermetallic-hardened steel, known as a Maraging steel alloy.
The Maraging steel alloy includes Cr, Co, Mo, and about 0.15% or
less by weight C.
Inventors: |
Decker; Raymond F.; (Ann
Arbor, MI) ; Walukas; Donald M.; (Ann Arbor, MI)
; Vining; Ralph E.; (Brooklyn, MI) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Thixomat, Inc.
|
Family ID: |
36616931 |
Appl. No.: |
11/073769 |
Filed: |
March 7, 2005 |
Current U.S.
Class: |
164/312 ;
164/113; 164/900 |
Current CPC
Class: |
B22D 17/2061 20130101;
B22D 17/10 20130101; B22D 17/007 20130101; B22D 17/2023
20130101 |
Class at
Publication: |
164/312 ;
164/113; 164/900 |
International
Class: |
B22D 17/08 20060101
B22D017/08; B22D 17/10 20060101 B22D017/10 |
Claims
1. A semi-solid injection molding machine, comprising: a plurality
of components defining a flowpath through the machine for a
feedstock, at least one of the plurality of components being
constructed of a martensitic Maraging steel alloy material
Including Cr, Co, Mo, and about 0.15% or less by weight C.
2. The machine of claim 1 wherein the Maraging steel alloy includes
between about 9 and 16% by weight Cr.
3. The machine of claim 2 wherein the Maraging steel alloy includes
between about 12 and 15% by weight Cr.
4. The machine of claim 1 wherein the Maraging steel alloy includes
between 9 and 20% by weight Co.
5. The machine of claim 4 wherein the Maraging steel alloy includes
between about 10 and 14% by weight Co.
6. A semi-solid injection molding machine, comprising: a plurality
of components defining a flowpath through the machine for a
feedstock, at least one of the plurality of components being
constructed of a martensitic Maraging steel alloy material
including Cr, Co, Mo, and about 0.15% or less by weight C. wherein
the Maraging steel alloy includes Mo in the range of about 2.9 and
about 6% by weight Mo.
7. The machine of claim 6 wherein the Maraging steel alloy includes
Mo in the range of about 4 and 5.5% by weight.
8. The machine of claim 1 wherein the Maraging steel alloy has an
austenite state at about 1500-1900 .degree. F.
9. The machine of claim 8 wherein the Maraging steel alloy
martensite ages at between about 900 and 1200.degree. F.
10. The machine of claim 1 wherein the Maraging steel alloy has a
hardness of about 40-50 Rc.
11. A semi-solid injection molding machine comprising: a barrel
which receives feedstock and heats the feedstock; a nozzle from
which feedstock in a semi-solid state is ejected; means for
advancing the feedstock within the barrel; means for subjecting the
feedstock to shear; means for ejecting feedstock from the nozzle;
wherein one of barrel, nozzle, means for advancing, means for
subjecting, and means for ejecting are constructed of a martensitic
Maraging steel alloy material including Cr, Co, Mo, and about 0.15%
or less by weight C.
12. The injection molding machine of claim, 11 wherein the Maraging
steel alloy includes between about 9 and 16% by weight Cr.
13. The Injection molding machine of claim 12 wherein the Maraging
steel alloy includes between about 12 and 15% by weight Cr.
14. The injection molding machine of claim 11 wherein the Maraging
steel alloy includes between 9 and 20% by weight Co.
15. The injection molding machine of claim 14 wherein the Maraging
steel alloy includes between about 10 and 14% by weight Co.
16. A semi-solid injection molding machine comprising: a barrel
which receives feedstock and heats the feedstock; a nozzle from
which feedstock in a semi-solid state is ejected; means for
advancing the feedstock within the barrel; means for subjecting the
feedstock to shear; means for ejecting feedstock from the nozzle;
wherein one of barrel, nozzle, means for advancing, means for
subjecting, and means for ejecting are constructed of a martensitic
Maraging steel alloy material including Cr, Co, Mo, and about 0.15%
or less bv weight C wherein the Maraging steel alloy includes Mo in
the range of about 2.9 and about 6% by weight.
17. The injection molding machine of claim 16 wherein the Maraging
steel alloy includes Mo in the range of about 4 and about 5.5% by
weight.
18. The Injection molding machine of claim 1 wherein the Maraging
steel alloy has an austenite state at about 1500-1900.degree.
F.
19. The injection molding machine of claim 18 wherein the Maraging
steel alloy martensite ages at between about 900 and 1200.degree.
F.
20. The injection molding machine of claim 1 wherein the components
are formed by all-liquid injection molding.
21. The injection molding machine of claim 1 wherein the components
are formed by die casting.
22. The injection molding machine of claim 1 wherein the components
are heat treated.
23. The injection molding machine of claim 22 wherein the heat
treatment is stabilizing heat treatment.
24. The injection molding machine of claim 22 wherein the heat
treatment is regenerating heat treatment.
25. A semi-solid injection molding machine comprising; a plurality
of components defining a flowpath through the machine for a
feedstock, at least one of the plurality of components being
constructed of a martensitic Maraging steel alloy material
including Cr, Co, Mo, about 0.15% or less by weight C and about 8%
or less by weight Ni.
Description
BACKGROUND
[0001] The present invention relates to alloys for semi-solid and
liquid injection molding and die casting machine components and
components made from such alloys.
[0002] Generally semi-solid metal injection molding is the process
whereby an alloy feedstock is heated, subjected to shearing and
injected under high pressure into a mold cavity. Heating brings the
feedstock into a state where both solid and liquid phases are
present while the application of shearing forces prevents the
formation of dendritic structures in the semi-solid alloy. In this
state, the alloy may exhibit thixotropic properties.
[0003] The feedstock may be received into the barrel of the
semi-solid metal injection molding machinery in one of three forms:
liquid, semi-solid or particulate solid. The former two forms
require additional equipment and special handling precautions to
prevent contamination of the alloy material and therefore increase
costs. The latter form, while being more easily handled, results in
longer cycle times and significant thermal gradients in the first
encountered portions of the barrel and more pronounced thermal
shock to that portion of the barrel.
[0004] More specifically, semi-solid metal injection molding
(SSMIM) involves the feeding of alloy feedstock into the barrel of
the semi-solid metal injection molding machinery. In the barrel,
the alloy feedstock is heated and subjected to shear, often by
rotating a screw or paddles located therein. As a result of heating
and shearing, the temperature of the alloy feedstock is raised so
as to be above its solidus temperature and below its liquidus
temperature. Within this temperature range, the feedstock is
transitioned into semi-molten material having co-existing solid and
liquid phases. In addition to aiding to heating, shearing further
prevents the formation of dendritic structures in the alloy. In
this thixotropic state, the semi-solid alloy material is injected,
either through reciprocation of the screw or transfer and
reciprocation of a plunger to a shot sleeve, into a mold cavity and
solidified to form the desired part.
[0005] Typically, components for the injection molding machine are
formed from conventional carbon-hardened steels. These steels,
however, are not very tough and are not truly weldable. These
steels temper back at service temperatures of about 1200.degree.
F., thus softening. When these steels are formed into components
for an SSMIM machine, such as check rings, they split from the
radial impact fatigue stresses. Many failures have occurred in
other types of components such as screw tips, piston rings, push
rings, flanges, barrels and screws due to this marginal toughness.
Some of the failures of check rings and push rings appear to be
aggravated by the heat affected zone under weld deposits. These
steels are also susceptible to embrittlement during "torching" when
operators tend to overheat the components by gas torches, causing
components such as nozzles to fail by a brittle mode at the flange,
as well as by bulging and splitting longitudinally.
[0006] Thus, welding of these carbon hardened alloys is prone to
variation in the skill of the welder. Careful pre-and post-heating
is required to prevent cracking in the heat-affected zone of the
steel. Even with good practice, however, the toughness of the heat
affected weld zone appears to be quite inferior to the base
steel.
[0007] As seen from the above, there exists a need for an improved
material for components of an SSIMM machine and component made of
such material.
SUMMARY
[0008] In satisfying the above need, as well as overcoming the
enumerated drawbacks and other limitations of the related art, the
present invention provides an alloy for components of semi-solid
injection molding machinery. In particular, the alloy is a
intermetallic-hardened steel, known as a Maraging steel alloy. The
Maraging steel alloy includes Cr, Co, Mo, and about 0.15% or less
by weight C.
[0009] Since during welding of these alloys, the heat-affected zone
is both soft and tough, these maraging steels are very weldable.
This heat-affected zone can be returned to the hardness and
toughness of the base alloy by simple post-weld aging, thus
avoiding the three-stage temper treatment cycle commonly employed
for conventional carbon hardened steels. To save heat treating
costs, the aging can be accomplished in start up of a machine.
[0010] Further features and advantages of this invention will
become readily apparent to persons skilled in the art after a
review of the following description, with reference to the drawings
and claims that are appended to and form a part of this
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic illustration of one version of a
semi-solid metal injection molding machine with which the present
invention may be utilized;
DETAILED DESCRIPTION
[0012] Referring now to the drawings, seen in FIG. 1 is an
apparatus/machine 10 used for semi-solid metal injection molding
(SSMIM). The construction of the machine 10 is, in some respects,
similar to that of a plastic injection molding machine.
[0013] The machine 10 includes a feed hopper 11 for the
accommodation of a supply of pellets, chips, or powder of a
suitable metal alloy at room temperature. For purposes of
describing the salient features of the subject invention, magnesium
alloys will be referred to as examples of suitable metal alloys
that may be used in practicing the invention. Al and Zn are other
such alloys.
[0014] A suitable form of feeder 12 is in communication with the
bottom of the hopper 11 to receive pellets therefrom by gravity.
The feeder 12 includes an auger (not shown) which functions to
advance pellets at a uniform rate from the feeder 12. The feeder 12
is in communication with a feed throat 13 of a barrel 14 through a
vertical conduit 15 which delivers a quantity of pellets into the
barrel 14 at a rate determined by the speed of the feeder auger. An
atmosphere of inert gas is maintained in the conduit 15 and barrel
14 during feeding of the pellets so as to prevent oxidation
thereof. A suitable inert gas is Argon and its supply is effected
in a conventional manner.
[0015] As is conventional in a thermoplastic injection molding
machine, barrel 14 accommodates a reciprocable and rotatable screw
16 provided with a helical flight or vane 17. Adjacent the
discharge end of the barrel, the screw has a non-return valve
assembly 18 and terminates in a screw tip 19. The discharge end of
barrel 14 is provided with a nozzle 20 having a tip 20a received
and aligned by a sprue bushing mounted in a suitable two-part mold
22 having a stationary half 23 fixed to a stationary platen 24. The
mold half 23 cooperates with a movable mold half 25 carried by a
movable platen 26. The mold halves define a suitable cavity 27 in
communication with the nozzle. Mold 22 may be of any suitable
design including a runner spreader 28 in communication with the
cavity 27 and through which the semi-solid material may flow to the
cavity in the mold. Although not shown in the drawings, suitable
and conventional mold heating and/or chilling means may be supplied
if required.
[0016] The opposite end of injection molding machine 10 includes a
known form of high speed injection apparatus A including an
accumulator 29 and a cylinder 30 supported by stationary supports
31 on a suitable support surface S. Downstream from the cylinder 30
a shot or injection ram 32 projects into a thrust bearing and
coupler 33 for operational connection in known manner with a drive
shaft 34 for the rotary and reciprocable screw 16. Thrust bearing
and coupler 33 may separate the shot ram 32 from drive shaft 34 so
that shot ram 32 may merely reciprocate and not rotate when
desired. Drive shaft 34 extends through a conventional form of
rotary drive mechanism 35 which is splined to drive shaft 34 to
permit horizontal reciprocation of drive shaft 34 in response to
reciprocation of shot ram 32 while the drive shaft 34 rotates. This
shaft is in turn coupled with the screw 16 through a drive coupling
36 of known type to transmit rotation to the screw 16 as well as
high speed axial movement within barrel 14 in response to operation
of high speed injection apparatus A. It will be understood that
suitable and conventional hydraulic control circuits will be used
in the conventional manner to control the operation of injection
molding machine 10.
[0017] Typically, operation of injection molding machine 10
involves rotation of the screw 16 within the barrel 14 to advance
and continuously shear the feed stock supplied through feed throat
13 to a material accumulation chamber C between the screw tip 19
and the nozzle. Suitable heating means of a type to be described
supply heat to barrel 14 to establish a temperature profile which
results in conversion of the feed stock to a slushy or semi-solid
state at a temperature that is above its solidus temperature and
below its liquidus temperature. In this semi-solid state the
material is subjected to shearing action by the screw 16 and such
material is continuously advanced toward the discharge end of the
barrel to pass the non-return valve 18 in sufficient accumulated
volume ultimately to permit high speed forward movement of the
screw 16 to accomplish a mold filling injection or shot. High speed
injection apparatus A functions at the appropriate time (in a
manner to be explained) to move shot ram 32 forwardly, or toward
the discharge end of the barrel 14, which results in forward
movement of the thrust bearing 33 and drive shaft 34. Since drive
shaft 34 is coupled to the shaft of the screw 16 through coupling
36, extrude screw 16 moves forward quickly to accomplish the mold
filling shot. Non-return valve assembly 18 prevents the return or
backward movement of the semi-solid metal accumulated in the
chamber C during the mold filling shot.
[0018] As opposed to other methods of semi-solid molding, the above
described method has the advantage of combining slurry generation
and mold filling into a single step. It also minimizes safety
hazards which occur when separately melting and casting reactive
semi-solid metal alloys. Obviously, and as will be further
appreciated, the alloy of the present invention will have utility
with machines other than the one of the illustrated variety. By way
of illustration and not of limitation, such other variety machines
and apparatus include two stage machines and plastic injection
molding machines, similar to die casting machines, where slurry
generation and injection molding occur in separate portions of the
apparatus, and non-horizontally oriented machines. Additionally, it
will be understood by those skilled in the art that other
mechanisms could be used to advance the material in the barrel
(including gravity), that other mechanisms could be used to induce
shear (such as rotating paddles, fins or electromagnetic fields)
and that other mechanisms could be used to eject the material from
the machine (such as a plunger of a shot sleeve). Furthermore,
alloys of this invention can be applied to all-liquid injection
molding and die casting.
[0019] The barrel 14 of the machine 10 is divided along its length
into a series of different heating zones, with the exact number of
zones being, to a certain extent, a matter of design choice.
Proceeding from the end of the barrel 14 where the feedstock is
received, the respective heating zones are increasingly hotter
until leveling out in the latter half of the barrel 14. The barrel
temperatures may be measured by a thermocouple positioned
approximately three-quarters of the way through the barrel (towards
the interior of the barrel).
[0020] The feedstock may be designed to exhibit a gradual melting
reaction to match the desired temperature profile along the barrel
14. In this manner, processing of the feedstock material is done
while imparting vigorous shear to the semi-solid, avoiding plugs,
reducing thermal shock and stress on the barrel and while being
able to precisely fix the fraction solids in the subsequently
molded part.
[0021] Such a feedstock enables faster cycle times while decreasing
thermal shock and stress on the machine 10. A preferred feedstock
exhibits a mild on-setting of melting or a spreading of the
eutectic reaction over a larger temperature range when initially
introduced into the barrel. This decreases the thermal shock in the
initial portion of the barrel, and, further, upon the on-set of
melting and the introduction of the liquid phase in the feedstock,
thermal transfer is enhanced and further melting is activated.
[0022] In accordance with the invention, various components of the
machinery 10 are made of intermetallic-hardened steels, referred to
as Maraging steels formed by martensite aging, rather than
conventional carbide-hardened steels. These alloys are hardened by
nano-sized intermetallic precipitates within a soft and tough
martensite matrix, rather than coarse carbide phases that form a
brittle martensite matrix that occurs in conventional steels. The
intermetallic precipitates are more resistant to softening than
carbides at barrel temperatures of 1100 to 1200.degree. F.
[0023] Components formed of Maraging type steels are very weldable
in that the heat-affected zone is both soft and tough. This zone
can be returned to the hardness and toughness level of the base
alloy by simple post-weld aging at, for example, about 900.degree.
F. for about 3 hours, thereby avoiding the long and rigorous quench
and three stage temper treatment cycle associated with conventional
steels. Furthermore, dimensional changes that occur during aging
are minimal, such that final machining can be done in the soft
annealed state before hardening and aging may be accomplished in
machine start-up. These steels are also designed with sufficient Cr
to resist oxidation at the service temperatures of the molding
machine 10, while also resisting liquid Mg attack.
[0024] Shown below in Table 1 is a comparison of conventional
carbon hardened steels (first four entries), referred to
hereinafter as C steels, with Maraging steels (next nine entries):
TABLE-US-00001 TABLE 1 Composition (wgt. %) Steel Type C Cr Co Mo W
Ni Other H-11 C .40 5.0 -- 1.3 -- -- 0.5V H-13 C .40 5.2 -- 1.3 --
-- 1.0V T-2888 C .20 9.5 10.0 2.0 5.5 -- -- Volvic 10 C .18 10.0
10.0 -- 6.5 -- -- T-30 Maraging + C .14 14.7 13.0 5.0 -- -- 0.3V
T-31 Maraging .03 14.0 12.0 5.0 -- 4.0 -- X14N4K14M3T Maraging .02
14.0 13.0 3.0 -- 4.0 0.3Ti Russian Maraging .02 12.0 14.0 5.0 --
5.0 -- AFC-260 Maraging + C .08 15.5 13.0 4.3 -- 2.0 0.14Nb D.70
Maraging <.03 12.0 14.5 4.0 -- 4.3 Ti, Nb, Al, B, Zr Pyromer
X-15 Maraging <.01 15.0 20.0 2.9 -- -- -- Pyromer X-23 Maraging
<.03 10.0 10.0 5.5 -- 7.0 -- Ultrafort 403 Maraging <.02 11.0
9.0 4.5 -- 7.7 0.4Ti, 0.15Al Preferred Range <.03 12-15 10-14
4-5.5 -- 0-5 0-.5Ti, 0-.2Al, 0-.5V, 0-.2Nb Broad Range <.03-.15
9-16 9-20 2.9-6 -- 0-8 0-.5Ti, 0-.2Al, 0-.5V, 0-.2Nb
[0025] In general, Maraging types of steel employ a Co/Mo hardening
mechanism. As to hardening precipitates, the T-30 composition, for
example, uses carbides of M.sub.23C.sub.6 that precipitate at about
900.degree. F.; but overage, however, at about 1200.degree. F. The
T-31 composition is precipitation hardened by the more stable
Laves, R and Chi phases (Fe,Cr,Co,Mo intermetallics) which
precipitate at about 1200.degree. F. in fine arrays that are most
resistant to overaging and softening.
[0026] The T-31 composition has soft and ductile martensite matrix
which forms near room temperature upon cooling from the austenite
matrix that exists during solution treatment at about 1900.degree.
F. Moreover, using the T-31 composition avoids the delta phase
during annealing. In contrast to carbon hardened steels, severe
quenching is not be needed after solution treatment of the T-31
composition. That is, air cooling may suffice to transform the
alloy to martensite. In some implementations, to obtain complete
transformation of austenite to martensite, refrigeration can be
used. The transformation defects in the martensite help nucleate
nanometer precipitates upon Maraging (martensite aging) between
about 900 and 1200.degree. F. The soft martensite (having a
hardness of about 30 Rc) can be formed, welded and machined before
final aging which provides a hardness up to about 67 Rc.
Dimensional changes that occur during final aging are less than
0.0001 in/in compared to +0.0006 in/in for C steels.
[0027] During subsequent heating at 10000 to 1250.degree. F.,
martensite reverts to austenite in a time dependent mode. Some
reverted austenite of about 5 to 15% improves the toughness. This
reverted austenite is of nanometer dimensions but still contains
the fine precipitates and is still strong while acting as a tough
crack stopper. Note, however, that more reversion softens the
steel. Thus, to obtain sufficient life spans for the machine
components, the Maraging steels are alloyed to obtain the proper
amount of reverted austenite. In accordance with the invention,
preferred ranges for the composition of the various alloying
elements are listed as the fourteenth entry of Table 1, and broad
ranges are listed in the last entry of the table. It is
advantageous to stabilize the alloy at 1250.degree. F. before
service. It is feasible to rejuvenate used components to extend
their life, by re-annealing at 1500 to 1900.degree. F. followed by
aging/stabilizing at 1100 to 1250.degree. F.
[0028] The alloying elements in the Maraging steels provide at
least the following benefits: [0029] a. Cr imparts oxidation
resistance and participates in the hardening intermetallic and
carbides. For example, raising Cr from 5 to 15% diminishes
oxidation in 300 hrs at 1200.degree. F. from 3.81 to 0.32 mg/cm2.
[0030] b. Cobalt prevents embrittling delta formation, maintains
martensite transformation above room temperature, speeds the aging
reactions, participates in the intermetallic hardening phases, and
slows formation of too much austenite at 1200.degree. F. [0031] c.
Mo, in synergism with Co, participates in the intermetallic
hardening phases. Moreover, Mo in synergy with Cr enhances the
stability of the carbide phase. [0032] d. C provides for hard,
brittle martensite and introduces the delta phase. Thus, the delta
phase increase as the amount of C increases. [0033] e. Ni toughens
the martensite phase. Note, however, too much Ni depresses the
martensite transformation temperature and the austenite reversion
temperature.
[0034] Heat treatment, for example, stabilizing heat treatment or
regenerating heat treatment, of molding machine components made of
the Maraging steels offers flexibility in obtaining a desired life
span of the components. Solution temperature can be from
1500.degree. F. to about 1900.degree. F. The higher temperatures
dissolve the coarse precipitates and minimize the delta phase.
Aging temperature and time can be designed to provide fine
precipitates along with 5 to 15% reverted austenite. A pre-service
aging treatment at about 1200.degree. F. serves to stabilize the
age hardening reaction to prevent over-hardening or softening at
lower service temperatures. For example, aging at 1200.degree. F.
in one grade provides components with a hardness of about 40 Rc,
which does not change during service times of 200 hrs at
1200.degree. F.
[0035] Surface treatment also provides certain benefits to Maraging
steels. For example, gas nitriding in NH.sub.3 increased surface
hardness by 20-30%, while boosting fatigue life, rolling contact
life and wear resistance. Ion nitriding may improve wear resistance
by 100-150%. In contrast, such nitriding treatments may embrittle
the marginally tough C steels, so that such treatments may not be
useful on these alloys.
[0036] Table II below illustrates the hardness stability of the
T-31 alloy as compared to conventional C steel (H-13):
TABLE-US-00002 TABLE II LOSS OF HARDNESS DURING SERVICE Hardness
After Original 25,000 cycles to Alloy Hardness, Rc 1250.degree. F.,
Rc .DELTA.Hardness, Rc H-13 46 31 15 T-31 48 43 5
[0037] Thus, H-13 as well as H-11 are not strong enough for the
rigorous wear, impact and fatigue exposure of certain machine
components. Furthermore, they soften and oxidize very quickly at
1200.degree. F.
[0038] As for the T-2888 and Volvic 10 alloys, these suffer from
low toughness, as measured by Charpy v-notch (CVN) impact energy
tests, and softening. Thus, components such as screws 16, barrels
14 or sections thereof, nozzles 20, nozzle flanges, screw tips,
screw adaptor, check rings, piston rings and push rings made of
Volvic 10 may experience failures at undesirable rates. For
example, check rings and piston rings made of Volvic 10 may require
replacement after 40,000 to 50,000 cycles of machine operation. Not
only are replacement parts costly, but the down time associated
with replacing the parts raises the production costs very
significantly.
[0039] Examples of semi-solid injection molding machinery
components made of Maraging steels in accordance with the invention
have been tested without failing include: [0040] A. Nozzle made of
T-30: After 5000 cycles, the nozzle retained its original hardness
at 40 Rc, bulged a slight 1.5% and did not oxidize significantly.
This compares to the conventional carbon hardened steel Volvic 10
which softened from the original 45 Rc to 20 to 35 Rc and bulged 1%
in 3000 cycles. [0041] B. Piston rings made of T-30: After 5000
cycles, the rings retained a hardness at 47 Rc and were ductile
enough to be removed. In contrast, Volvic 10 rings embrittle in
service and then fracture upon removal. [0042] C. Check rings made
of T-31: After 7000 cycles, no distress was observed; hardness
retained at 40 Rc; some pitting on seal face observed. [0043] D.
Push ring made of T-31: After 3000 cycles, no distress was
observed, hardness retained at 47 Rc.
[0044] Thus, in accordance with the invention, the Maraging and
Maraging +C alloys are useful for machine components such as hot
runners, hot sprues, nozzles, nozzle retaining flanges, barrel end
caps, barrels, barrel liners, screw tips, check rings, piston
rings, push rings, screw extensions and screws.
[0045] Referring now to Table III, the mechanical properties of the
conventional carbon hardened steels (first three entries) are
compared with that of some of the Maraging steels (last five
entries): TABLE-US-00003 TABLE III MECHANICAL PROPERTIES Aging UTS,
YS, UTS @ R.S, 100 hr @ Temp, 1000 1000 RA CVN, 1100 F. 1100 F.
Alloy F. psi psi El, % % ft-lb KIC Rc KSI KSI H-13 10 50 T- 1200
223 180 5 49 124 2888 Volvic 1200 260 190 5 48 130 10 T-30 1100 290
214 10 32 9 23 53 176 80-90 700 255 200 17 52 18 50 50 T-31 960 215
33 49 AFC260 1000 254 228 14 44 61 140 60 800 224 188 20 56 92
Pyromet 900-1050 258 237 15 58 18 70 50 <140 X-23 Ultrafort 895
245 242 10 60 25 49-61 120 403
where UTS is the ultimate tensile strength, YS is the yield
strength, El is the elongation, RA is reduction in area, CVN is the
Charpy v-notch impact energy, Kic is the fracture toughness, Rc is
the Rockwell hardness, and R.S. indicates the rupture strength.
[0046] Of particular note is that with a hardness between 48-50 Rc,
the room temperature toughness of Maraging steel is the highest at
33 ft-lb (CVN impact energy), with Maraging plus C being lower at
18 ft-lb, and conventional C hardened T2888 and Volvic 10 being
even lower at 5 ft-lb.
[0047] As a person skilled in the art will readily appreciate, the
above description is meant as an illustration of implementations of
the principles of this invention. This description is not intended
to limit the scope or application of this invention in that the
invention is susceptible to modification, variation and change,
without departing from spirit of this invention, as defined in the
following claims.
* * * * *