Europäisches Patentamt *EP000938593B1* (19) European Patent Office

Office européen des brevets (11) EP 0 938 593 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.7: C22C 19/07, B22F 3/15 of the grant of the patent: 09.10.2002 Bulletin 2002/41 (86) International application number: PCT/US97/20185 (21) Application number: 97948184.3 (87) International publication number: (22) Date of filing: 03.11.1997 WO 98/020177 (14.05.1998 Gazette 1998/19)

(54) POWDER METALLURGY, -BASED ARTICLES HAVING HIGH RESISTANCE TO WEAR AND CORROSION IN SEMI-SOLID METALS PULVERMETALLURGISCHE, AUF KOBALT BASIERTE GEGENSTÄNDE MIT HOHER VERSCHLEISSFESTIGKEIT UND KORROSIONSBESTÄNDIGKEIT IN HALBFESTEN METALLEN ARTICLES A BASE DE COBALT, PRODUITS DE LA METALLURGIE DES POUDRES, PRESENTANT UNE RESISTANCE ELEVEE A L’USURE ET A LA CORROSION DANS DES METAUX SEMI-SOLIDES

(84) Designated Contracting States: (56) References cited: AT BE CH DE DK ES FI FR GB IT LI LU NL SE EP-A- 0 466 401

(30) Priority: 04.11.1996 US 743335 • KUMAR P.: "Properties of P/M Stellite Alloy no. 6" PROG. POWDER METALL., no. 41, 1986, (43) Date of publication of application: pages 415-437, XP002059744 01.09.1999 Bulletin 1999/35 • HAMIUDDIN M: "Development of wear resistant, strong and fully dense stellite by liquid phase (73) Proprietor: Thixomat, Inc. sintering" POWDER METALLURGY Ann Arbor, MI 48104 (US) INTERNATIONAL, 1987, WEST GERMANY, vol. 19, no. 2, ISSN 0048-5012, pages 22-26, (72) Inventors: XP002059745 • KENNETH, E., Pinnow • BETTERIDGE W.: "Cobalt and its Alloys" 1982 , Pittsburgh, PA 15237 (US) ELLIS HORWOOD , GREAT BRITAIN • RAYMOND, F., Decker XP002059746 Pages 119-125 Ann Arbor, MI 48104 (US) • PATENT ABSTRACTS OF JAPAN vol. 096, no. 008, 30 August 1996 & JP 08 109405 A (NIPPON (74) Representative: Patentanwälte Dr. Solf & Zapf STEEL CORP), 30 April 1996, Candidplatz 15 81543 München (DE)

Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 0 938 593 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 0 938 593 B1 2

Description further appreciated, the component construction of the present invention will find applicability as articles, not BACKGROUND AND SUMMARY OF THE INVENTION only in the construction of machines 10 practicing the above method, but also in machines practicing alterna- [0001] The present invention relates to cobalt-base 5 tive variations on the above process and other process- articles having high resistance to wear and corrosion in es. Such machines and articles include, without limita- semi-solid metal environments. More specifically, the in- tion, die casting, metal injection molding, plastic injec- vention relates to fully dense powder metallurgy articles, tion molding machines as well as tools and dies. made from a novel Co-Cr-W-C type alloy being particu- [0004] Because of contact with corrosive semi-solid larly suited for long term use in high wear, high temper- 10 metals (such as magnesium and zinc), the elevated op- ature machinery employing a variant process of semi- erating temperatures, oxidation, and the high wear na- solid metal molding (SSM). ture of the environment (contact between the various [0002] The metallurgical process referred to herein is operating parts of the machine and the semi-solid metal one where metals and metal matrix composites are is an extremely high wear and shock condition), compo- heated and stirred in the solid plus liquid phase region 15 nents of the above machinery are very demanding on and then injected into a mold or die at lower tempera- their materials of construction. Screw velocities, for ex- tures. This process has proven to result in parts having ample, involve acceleration from 0 to 3 meters/sec. and improved material characteristics, previously uncasta- deceleration back down to 0, all in 0.2 seconds. The cho- ble and unobtainable shapes, and reduced post forma- sen materials of construction must be resistant to cor- tion processing steps. Two versions of the above proc- 20 rosive attack by the semi-solid metal being processed, ess, also known as Thixomolding® (Thixomat, Inc., Ann must be highly resistant to wear, and must exhibit suffi- Arbor, Michigan), are generally disclosed in U.S. Patent cient strength and toughness to withstand the stresses Nos. 4,694,881 and 4,694,882, which are herein incor- imposed during long-term exposure at the relevant ele- porated by reference. The process generally involves vated temperatures under these severe thermal cycling the shearing of a semi-solid metal so as to inhibit the 25 and high shock conditions. growth of dendritic solids and to produce nondendritic [0005] From a corrosion standpoint, iron and some solids within a slurry having improved molding charac- cobalt-based alloys have been reported as satisfactory teristics which result in part from its thixotropic proper- for processing semi-solid magnesium-base alloys. Nick- ties (a semi-solid nondendritic material which exhibits a el-base alloys, such as Alloy 718, are of interest as con- viscosity which is proportional to the applied shear rate 30 struction materials because of their good strength at el- and lower than that of the same alloy when in a dendritic evated temperatures and lower cost when compared to state). most cobalt-base alloys. However, because molten [0003] A machine adapted to employ the above type magnesium attacks containing alloys, some SSM of processes and to which the present invention has par- processors have specified that alloys which come into ticular applicability is schematically shown in FIG. 1. The 35 contact with molten magnesium must contain less than construction of the molding machine 10 is, in some re- about three percent nickel. Prior machines avoided this spects, similar to that of a plastic injection molding ma- problem by using Alloy 718 in their barrel constructions chine. In the illustrated machine 10, feed stock is fed via while incorporating a shrink-fitted barrel insert made of a hopper 12 into a heated, reciprocating screw injection a cobalt-base alloy such as Stellite 6 (nominally 28 Cr, system 14 which maintains the feedstock under a pro- 40 4.5W and 1.2C) or Stellite 12 (nominally 30Cr, 8.3W and tective atmosphere 16, such as argon. As the feed stock 1.4C), which are commercially available from the Cabot is moved forward by the rotating motion of a screw 18, Corporation, Kokomo, Indiana. While generally per- it is heated by heaters 20 and stirred and sheared by forming well with respect to corrosion, they are deficient the action of the screw 18. This heating and shearing is in toughness and have exhibited cracking and fracture done to bring the feedstock material into its solid plus 45 in the machines of the above type. Under the high tem- liquid temperature range. The thixotropic slurry formed perature fatigue conditions of the machines, cracks in by this action passes through a nonreturn valve 22 in Stellite liners have been seen to propagate into the Alloy the forward part of the injection system 14 of the ma- 718 barrel resulting in total failure of the barrel assembly. chine 10 into an accumulation chamber 24. Upon accu- This is unsafe and necessitates costly repairs and re- mulation of the needed amount of slurry in the accumu- 50 placements. It has come to be determined that articles lation chamber 24, the injection cycle is initiated by ad- of an alternative material, having greater toughness, vancing the screw 18 with a hydraulic actuator and caus- would be more desirable in that they would provide for ing the mold 26 to fill through a nozzle 28. As opposed longer wearing components. to other methods of semi-solid molding, the above de- [0006] The selection of materials for processing semi- scribed method has the advantage of combining slurry 55 solid aluminum-base alloys is much more complex. This generation and mold filling into a single step. It also min- is particularly true because most iron, cobalt, and nickel- imizes the safety hazards involved in melting and cast- base alloys are readily attacked by aluminum alloys. In ing reactive semi-solid metals. Obviously, and as will be addition to these concerns and those recited in connec-

2 3 EP 0 938 593 B1 4 tion with processing magnesium, other important con- ing) of gas atomized prealloyed powders. In general, pri- cerns relate to the availability, cost and manufacturing or studies have shown that PM processing of these ma- characteristics of the construction material. terials produces a material with higher hardness, higher [0007] In the injection molding of magnesium-base al- tensile strength, and higher ductility than is achieved by loys, the maximum operating temperatures within the 5 casting the alloys and that these improvements are still barrel typically range between about 593°C and 649 °C retained at elevated temperature. The abrasive wear re- with the temperatures sometimes ranging to 816 °C. sistance of these PM materials is somewhat lower then Most common AISI iron-base hot work tool steels (such their cast counterparts owing to the smaller sizes of the as H-10 and H-13, and even more highly alloyed hot primary carbides. For the same reasons, their machina- work tool steels such as H-19 and H-21) lose strength, 10 bility has been seen to improve. hardness and wear resistance at these temperatures. [0011] With regard to the properties of the prior Co-Cr- As a result, a number of very specialized materials for W-C-type alloys, it has often been assumed that these machine construction have been used, in particular alloys are at their maximum hardness in the cast or these alloys include Stellite 6 and 12 (mentioned above) welded condition and that their properties cannot be and similar Co-Cr-W-C-type alloys. These alloys have 15 changed by subsequent heat treatment. Similarly, it has been used to form centrifugally-cast barrel liners or weld also been assumed that putting these alloys in service overlays. The use of Co-Cr-W-C-type barrel liners at elevated temperature has little effect on their hard- avoids the corrosion problems that can be encountered ness, toughness, and dimensional stability. Contrary to between molten magnesium and nickel-base alloys. this assumption, some of the published literature for Their use as liners therefore permits the use of the more 20 weld deposits, wrought alloys and PM alloys indicate cost effective nickel-base alloys, such as Alloy 718, for that many of the Co-Cr-W-C-type alloys exhibit an in- barrel construction. Special maraging-type hot work tool crease in hardness due to carbide precipitation when steels, such as Thyssen 1.2888 (nominally 0.2C, 10Cr, heated in the range of 649 to 816 °C. When aged at 2Mo, 5.5W, and 10.00Co) have been used in screws these temperatures, articles of the Co-Cr-W-C-type al- and nonreturn valves. Thyssen 1.2888 reportedly can 25 loys might therefore be subject to a change in size, be used for short times at temperatures as high as strength and toughness and this is not acceptable in all 700°C. applications. The operating temperatures during single [0008] Because of problems related to cost and avail- step, metal injection molding (as generally described ability, as well as in an attempt to upgrade performance, above) approach those at which carbide precipitation the present inventors began a search for a new alloy to 30 may occur in PM Co-Cr-W-C-type alloys. Much of the replace the currently used Co-Cr-W-C-type alloys and work done and resulting in the present invention was Thyssen 1.2888. This search has lead to Alloy 718 bar- based on concerns about the possible effects that high rels HIP-clad with a new, powder metallurgy (PM) co- temperature exposure might have on the mechanical balt-base wear resistant alloy, as well as to the construc- properties and dimensional stability of PM Co-Cr-W-C- tion of various monolithic parts made of the same alloy. 35 type alloys. This research was also conducted to deter- The properties of the present components made from mine what, if any, changes in the alloy composition or PM cobalt-base wear resistant alloys, produced by ni- subsequent heat treatment could be employed to mini- trogen atomization and hot isostatic pressing (HIP), dif- mize the above effects on the resulting articles. fer considerably from the previously seen Co-Cr-W-C- [0012] EP-A-466 401 describes a gear with gear teeth type alloys (produced from powder by conventional 40 formed of a Co-based alloy which has been HIPped. The press and sintering methods). The new alloys exhibit an co-alloy consists in weight% of 10-35% Cr, 0-22% Ni, improved combination of strength, toughness, and di- 0-20% W, 0-20% Fe, 0-10% V, 0-10% Mo, 0-6%Nb, mensional stability and it has been found beneficial to 0-3% Si, 0-3%C, 0-3%B, 0-1% Mn and the balance Co also modify their heat treatment. and inevitable impurities. A specific embodiment fea- [0009] The traditional Co-Cr-W-C-type alloys are qua- 45 tures 26%Cr, 5%W, 1%C, 6%Nb and the balance Co. ternary cobalt-base alloys containing about 27-29% [0013] In view of the above and other limitations of the , a variable amount of (4 to 17%) and prior art, it is a principle object of the present invention (0.9-3.2%). They are widely used in wear resist- to provide fully dense articles made from a novel PM ant applications because of their high strength, corro- Co-Cr-W-C-type alloy which are highly resistant to sion resistance, and ability to retain their hardness at 50 changes in size, hardness, corrosion resistance, elevated temperatures. Because of their limited hot strength and toughness as a result of prolonged expo- workability and machinability, however, most of the high- sure to temperatures in the range of about 649 °Cto er carbon Co-Cr-W-C-type alloys are used in the form 816 °C. of castings, hard facing consumables and powder met- [0014] Another object is to provide a fully dense PM allurgy parts. 55 cobalt-base article which is resistant to corrosion in [0010] Considerable work has been done to explore semi-solid magnesium and zinc. the production of atomized powder metallurgy (PM) [0015] It is also an object of the present invention to Co-Cr-W-C-type alloys by hot isostatic pressing (HIP- provide fully dense PM cobalt-base articles which ex-

3 5 EP 0 938 593 B1 6 hibits adequate hardness without a decrease in tough- lite 6 and Stellite 12 respectively. The cast alloy 12 sam- ness. ple was taken from a Stellite 12 centrifugally cast barrel [0016] A still further object of this invention is to pro- liner commercially produced for a machine 10 of the vide fully dense PM cobalt base articles exhibiting in- above variety and which failed, cracked, in service. As creased toughness over prior art articles and alloys 5 seen in FIG. 2, the nominal composition of PM Alloy thereby resulting in components of longer life and in- 0.8C was 0.80C, 27.81Cr and 4.11W and the balance creased safety. principally Co with 0.066N; for PM Alloy 6 these constit- [0017] Additional benefits and advantages of the uents were 1.11C, 29.34Cr and 4.60W and the balance present invention will become apparent to those skilled principally Co; for PM Alloy 12 these constituents were in the art to which the present invention relates from the 10 1.41C, 28.90Cr, 8.68W and the balance principally Co; subsequent description of the preferred embodiment and for Cast Alloy 12 these constituents were 1.31C, and the appended claims, taken in conjunction with the 28.79Cr, 8.23W and the balance principally Co. The accompanying drawings. nickel content in each of the above was respectively 2.15, 0.13, 1.57 and 2.80. Numerous samples for further BRIEF DESCRIPTION OF THE DRAWINGS 15 analysis were created by HIPing the PM materials. As further discussed below, PM Alloy 0.8C was intention- [0018] ally melted to a lower than normal carbon and tungsten content. The powders of PM alloy 0.8C were prepared FIG. 1 is a schematic illustration of a machine to not by common argon atomization techniques, but by which the present invention will have particular ap- 20 nitrogen atomization. The nitrogen dissolving into the re- plicability; sulting alloy during this process appears to increase its FIG. 2 is a table of the chemical compositions of strength and aging response. By using nitrogen atomi- some of the PM alloys principally investigated, in- zation for producing the alloy, thermal induced porosity, cluding the alloy of the present invention, as well as which is often encountered in argon atomized alloys, a cast alloy of the same general variety; 25 was found to be substantially non-existent. FIGs. 3a-3c are micrographs (1000x magnification; [0020] FIGs. 3a-3c and 4a and 4b, show the micro- ammonium persulfate as etchant) of the PM alloys structures of the Co-Cr-W-C-type alloys of FIG. 2. As presented in the table of FIG. 1; seen in those figures, the PM Co-Cr-W-C-type alloys in FIGs. 4a and 4b are micrographs (400x and 1000x the as-HIPed condition contain a fairly random disper- magnification, respectively; ammonium persuifate 30 sion of small carbides, the amount and size of which in- as etchant) of the cast alloy 12 presented in the ta- crease with the carbon content of the alloy. The primary ble of FIG. 1; carbides in the centrifugally cast Co-Cr-W-C-type alloy FIG. 5 is a comparative hardness table for some of have the dendritic distribution expected of cast material. the alloys investigated in the discovery of the Accordingly, these latter carbides are very much larger present invention; 35 than those in the PM Co-Cr-W-C-type alloys, and in par- FIG. 6 is a table of the tensile properties of PM Alloy ticular with respect to PM Alloy 12 which has a similar 12 which was investigated in the discovery of the composition. As a result of the larger carbides, it is an- present invention; ticipated and borne out by testing that the material would FIG. 7 is a table of the aging response of some PM be less tough than the others. alloys and one cast alloy investigated in the discov- 40 [0021] Hardness measurements for various alloys at ery of the present invention; various temperatures are presented in the table of FIG. FIG. 8 is a table of the dimensional stability of PM 5. This data was obtained in some instances from pub- Alloy 12 when heat treated for a period of forty-eight lished literature provided by the commercial supplier of hours; and the material. In those instances the supplier is footnoted FIG. 9 is a table of the bend fracture properties of 45 in the table. Regarding the sources for the data on those the PM alloys and cast alloy presented in FIG. 7. samples, Stellite® 6B (Haynes Wrought Wear-Resistant Alloys, 1976, Cabot Corporation Stellite Division, Koko- DETAILED DESCRIPTION OF THE PREFERRED mo, Indiana); sand cast Stellite® 6 and 12 (Thermadyne EMBODIMENT Stellite Coatings, Goshen, Indiana); and H-13 Tool Steel 50 and H-19 Tool Steel (Crucible CPM, 9V data sheet, [0019] The chemical compositions of some of the 1987, Crucible Materials Corporation, Pittsburgh, Penn- Co-Cr-W-C-type alloys evaluated in this investigation as sylvania). Of the three PM Alloy 12 samples, one was potential construction materials for the machine 10 from a sleeve or insert for a composite barrel construc- (seen in FIG. 1) are given in FIG. 2. Included in the table tion as described above in connection with machine 10. are three PM Co-Cr-W-C-type alloys and one centrifu- 55 The other two samples were taken from a test ring made gally cast Cr-Co-W-C-type alloy. The compositions of by HIP-cladding PM Alloy 12 to a hollow cylinder made the PM Alloys 6 and 12 are similar to those commonly of conventional Alloy 718. Because most HIP-clad bar- used for cast Co-Cr-W-C-type alloys, in particular Stel- rels of Alloy 718 will probably be aged after HIP-clad-

4 7 EP 0 938 593 B1 8 ding, one of these latter samples was given the standard highest hardness value after seventy-two hours. Solu- double age hardening treatment for Alloy 718 (728,3°C/ tion annealing the PM Co-Cr-W-C-type alloys at 1199°C 8hr/FC to 621 °C /8hr/AC) before it was tested. The oth- for two hours prior to aging at 649°C F appeared to re- er HIP-clad sample was tested in the as-HIPed condi- duce aging response, both in terms of the magnitude of tion. For PM Alloy 0.8C, one sample was tested as HI- 5 the hardness increase and the maximum hardness Ped and one sample as annealed at 1198,8°C prior to achieved. These hardnesses, however, were still at ac- testing. ceptable levels. Regarding aging of the as-cast sample [0022] Allowing for some scatter in the data, it is clear of Stellite 12 at 649 °C for 72 hours, only a small change the hot hardness of PM Alloy 12 is greater than that of in hardness of about 1.5HRC was produced. the wrought alloy, Stellite 6B, cast Stellite 6 and sand 10 [0026] The size change data in FIG. 8 indicates that cast Stellite 12, at both room and at elevated tempera- as-HIPed PM Alloy 12 shrinks slightly (0.0001 inches) tures. The results also indicate that a double aging heat after being heated at 1200° F for 48 hours. No size treatment increased the hardness of Alloy 718 over the change measurements have been made on specimens non-aged sample at both room and elevated tempera- of PM Alloy 12 heated for longer times at 649 °C. As tures. The same also appears to be true to, but to a less- 15 further discussed below, in at least one instance of ac- er extent, for the double aged sample of PM Alloy 12. tual use, severe shrinkage occurred in a PM Alloy 12 As expected, the hot hardness of all the Co-Cr-W-C- barrel liner. The cause of that shrinkage has not yet been type materials, except possibly for the wrought alloy of identified. Stellite 6B, are significantly higher than those of the list- [0027] With the PM alloys all exhibiting good hard- ed two conventional hot work tool steels. 20 ness, the bend fracture strength or toughness, another [0023] In that PM Alloy 12 showed a hardness in- critical property for the intended application, of the PM crease when double aged, an investigation into its ten- Co-Cr-W-C-type alloys and of centrifugally cast Stellite sile properties was conducted. The results of these in- 12 were respectively determined for specimens in the vestigations are summarized in the table of FIG. 6 where as-HIPed or as-cast conditions and in a variety of aged data for Stellite 6 and 12 are presented for comparison. 25 or heat treated conditions. The specimens were tested The results show that the tensile strength levels of PM using a standard three point bend test fixture and during Alloy 12 (as HIPed) are quite high both at room and el- the tests, the deflection of the specimens was recorded evated temperature. Both proved to be higher than that at 400 pound load intervals and at the time of fracture. reported in the literature for sand cast Stellite 6 and St- The table of FIG. 9 gives the bend fracture strength and ellite 12 at room temperature. The heat treating of PM 30 the deflection at the time of fracture for each of the test Alloy 12 using a standard Alloy 718 double aging treat- specimens (two specimens each for PM Alloy 0.8C). ment did not significantly change the tensile properties [0028] For the PM Alloy 0.8C and PM Alloy 6, which at either room temperature or 649 °C. have similar base compositions other than their carbon [0024] The long term structural stability of the PM contents, the average as-HIPed results indicate that Co-Cr-W-C-type alloys when used at elevated temper- 35 lowering the carbon content from 1.11 to 0.80% produc- atures was investigated by measuring the room temper- es a notable increase in bend ductility. Solution anneal- ature hardness of specimens after the specimens had ing these two alloys at 1199°C also improved the bend been heated for various lengths of time at 649 to 760°C. ductility of these materials both with and without aging These results are presented in the table of FIG. 7. Size at 1200° F. Solution annealing the PM Alloy 12 material change measurements on a cylindrical sample of as-HI- 40 at 1199°C for 2 hours also sightly improved the bend Ped PM Alloy 12, which had been heated in a vacuum ductility of PM Alloy 12, both with and without aging at for 48 hours at 649 °C, are presented in the table of FIG. 649°C. The results for the specimens of as-cast Alloy 8. 12 indicate that the bend fracture strength and bend [0025] Referring to FIG. 7, all three PM Co-Cr-W-C- ductility of this material is significantly lower than those type alloys in the as-HIPed condition exhibited signifi- 45 of the PM Alloy 12, which is of similar composition. The cant hardening after being heated to 649 or 760°C and large differences in the bend ductility of these two ma- aged. The magnitude of the hardness increase pro- terials most probably relates to the pronounced differ- duced after aging at 649 °C for 72 hours varied with a ences in the amount, size and distribution of the primary given alloy with the low carbon PM Alloy 0.8C increasing carbides, as previously illustrated in FIGs, 3 and 4. 6HRC, PM Alloy 6 increasing 7HRC and PM Alloy 12 50 [0029] The results of the above tests generally indi- increasing 3.5HRC. Surprisingly, the low carbon PM Al- cate that PM Co-Cr-W-C-type alloys produce materials loy 0.8C increased in hardness to 48HRC, well above with higher hardness, higher tensile strength, and great- the preferred hardness of 42HRC and the more pre- er ductility than is achieved by casting alloys of the same ferred hardness of 45HRC for the intended application composition. They also show that the PM alloys in the in the machine 10 described above. However, the max- 55 as-HIPed condition exhibit an increase in hardness with imum hardness achieved after the aging treatment at only a very small change in dimensions (for PM Alloy 649 °C increased generally in relation to the carbon con- 12) when aged at temperatures between 649°C and tent of the PM alloys with PM Alloy 12 exhibiting the 760°C. Solution annealing at 1199°C F of the as-HIPed

5 9 EP 0 938 593 B1 10 materials appears to reduce, but does not entirely elim- chipped at the seal area during seal maintenance after inate, the aging response of these PM alloys when heat- 320 hours of service. Another barrel liner exhibited a ed at these temperatures. crack in the cast alloy 12 liner after nine cycles (one [0030] From the test results, it has also been seen hour) of service in a 400 ton magnesium processing unit. that, surprisingly, both the toughness and ductility of the 5 Suddenly, after 200,000 cycles, this crack propagated PM Co-Cr-W-C-type alloys can be significantly im- into the Alloy 718 barrel to a length of eighteen inches, proved by lowering their carbon contents below the lev- resulting in failure of the barrel and leakage of high pres- els customarily used for Stellite 6 and 12 or PM Alloys sure magnesium. While the size change data of FIG. 8 6 and 12 while still retaining high hardness values, val- indicates minor shrinkage for PM Alloy 12, severe ues in excess of 42HRC. These carbon contents below 10 shrinkage occurred in a PM alloy 12 liner for a 400 ton 1.0% are preferred and more preferably below 0.88%. unit during the first hours of service, opening up to a Lower carbon contents, below 0.65%, are expected to 0.015" gap at the seal and resulting in dangerous mag- be too soft and not capable of resisting wear at the nesium blow-by. The cause of this shrinkage has not yet 1200°F operating temperature. It is believed that, be- been determined. While extensive service time on a PM cause of the finer grain structure, fine carbide size and 15 alloy 0.8C liner has yet to be fully completed, it is noted uniform carbide distribution which is obtained in articles that fabrication of a new barrel for a 600 ton unit pro- of the present lower carbon PM Co-Cr-W-C-type alloy, ceeded without incident and without shrinkage. articles out of the present alloy exhibits higher tough- [0034] In testing nozzles, it was noted that standard ness and strength than cast or PM Co-Cr-W-C-type al- alloy steel (e.g. DIN 1.2885 and 1.2888) nozzles have loys of higher carbon content. The same benefit of fine 20 oxidized rapidly and softened to < 10Rc. One alloy steel grain size will be seen in high temperature fatigue re- nozzle lost 1/8" from its surface after only 500 hours of sistance of liner and barrel components as well as other service in processing magnesium. This softening also articles. As seen in FIG. 9, the toughness of the low car- led to bending of the nozzle. A PM alloy 0.8C nozzle bon PM alloy, when solution annealed and aged, exhib- was found not to have oxidized or softened in service. ited a three fold increase over similarly treated PM Alloy 25 Its thermal properties were found to be better than alloy 12 and a 30% increase over similarly treated PM Alloy steel in that it held temperature better and thereby eased 6 while providing substantially the same hardness. For temperature control at the nozzle. this reason, it is concluded that articles of the lower car- [0035] Regarding piston and sliding rings, PM alloy 6 bon Co-Cr-W-C-type alloys, such as PM Alloy 0.8C, pro- piston rings were put into service and were found to vide significant advantages as high stress components 30 have fractured from low toughness. This occurred both (such as nozzles, adapter rings, sliding rings, non-return during mounting and after only 200 shots in 4 hours. PM valves and other monolithic parts as well as barrel liners alloy 0.8C piston rings have lasted 25,000 shots, without and lined barrels) in SSM machines 10. It is also be- failure. A PM alloy 6 sliding ring failed in 75 shots under lieved that this lower carbon content, and at least down the high shock conditions seen by these parts. PM alloy to 0.65C, for the PM Co-Cr-W-C-type alloys would fur- 35 0.8C sliding rings have been fabricated and, based on ther reduce any dimensional changes in articles result- the above results, service life is expected to be 60,000 ing from service at the relevant elevated temperatures. shots or more. Alloy steel piston and sliding rings were [0031] The aging response and mechanical proper- further found to have softened, leading to high wear, in ties of the PM Co-Cr-W-C-type alloys are dependent on a few hours in processing semi-solid magnesium. This composition, particularly carbon content, and on heat 40 opened up a very significant bypass of slurry through treatment. For these reasons PM Co-Cr-W-C-type al- the non-return valve. This, in turn, decreased the effec- loys in general are good candidates for SSM machine tiveness of the high pressure and velocity of the forward 10 construction. In particular, the PM low carbon modi- shot and led to poor filling of the parts and to abnormal fication, containing 0.65%-0.88% carbon, is believed to porosity in the parts. be the best candidate for the SSM machine 10 compo- 45 nents as a result of its significantly enhanced toughness as well as good wear (hardness) and oxidation resist- Claims ance at elevated temperatures. [0032] To further substantiate the conclusions pre- 1. A powder, fully dense metal cobalt-base article hav- sented above, tests were conducted on various compo- 50 ing been hot isostatically pressed and heat treated, nents for various ones of the above materials. The com- said article having high wear and corrosion resist- ponents included barrel liners, nozzles, piston rings and ance to semi-solid metal and being characterized sliding rings. by: [0033] Regarding tests on barrel liners, a cast alloy 12 liner put into service in a 400 ton Thixomolder® was 55 C in an amount of 0.6 to less than 1%; found to have cracked after only 100 hours of service in W in an amount of 3 to 5%; processing semi-solid magnesium. Another cast alloy Cr in an amount of 25 to 30%; 12 liner in a 400 ton Thixomolder® was found to have Co in an amount principally comprising the bal-

6 11 EP 0 938 593 B1 12

ance of said article; and 17. The article as set forth in Claim 1 characterized by said article having a hardness of greater than hardness being greater than 45HRC. 42HRC, a bend fracture strength of greater than 2285MPa and substantial dimensional 18. A method of manufacturing a wear and corrosion and mechanical property stability during expo- 5 resistant, powder metallurgy, fully dense Co-Cr- sure to temperatures in range of about 316° C W-C-type article, said method characterized by to 816° C. the steps of:

2. The article as set forth in Claim 1 characterized by providing a powder metal constituent composi- C in an amount of 0.65 to 0.88%. 10 tion of C in an amount of 0.65 to 0.88%, W in an amount of 3 to 5%, Cr in an amount of 27 to 3. The article as set forth in Claim 1 characterized by 30%, and Co in an amount principally compris- C in an amount of 0.8%. ing a balance of said composition; consolidating said constituent composition by 4. The article as set forth in Claim 1 characterized by 15 a hot isostatic pressure process; W in an amount of 4%. heat treating said article and said article having a hardness of greater than 42HRC, a bend frac- 5. The article as set forth in Claim 1 characterized by ture strength of greater than 2285MPa, and Cr in an amount of 27 to 28%. substantial dimensional and mechanical prop- 20 erty stability during exposure to temperatures 6. The article as set forth in Claim 1 containing N in an in the range of 593° C to 816° C. amount of less than 0.1%. 19. The method of manufacture as set forth in Claim 18 7. The article as set forth in Claim 6 characterized by characterized by C being provided in an amount N in an amount of 0.066%. 25 of 0.8%.

8. The article as set forth in Claim 1 further character- 20. The method of manufacture as set forth in Claim 18 izing an amount of N and C amounting to less than characterized by W being provided in an amount 1% in total. of 4%. 30 9. The article as set forth in Claim 1 further character- 21. The method of manufacture as set forth in Claim 18 izing an amount of N and C amounting to greater characterized by Cr being provided in an amount than 0.65% in total. of 27 to 28%.

10. The article as set forth in Claim 1 characterized by 35 22. The method of manufacture as set forth in Claim 18 bend fracture strength being greater than 2492 MPa characterized by Cr being provided in an amount of 27.8%. 11. The article as set forth in Claim 1 characterized by said article being heated treated by aging. 23. The method of manufacture as set forth in Claim 18 40 characterized by constituent composition being 12. The article as set forth in Claim 1 characterized by provided with N in an amount of less than 0.1%. said article being heat treated by solution anneal- ing. 24. The method of manufacture as set forth in Claim 18 characterized by constituent composition being 13. The article as set forth in Claim 12 characterized 45 provided with N in an amount of 0.066%. by said article being also heat treated by aging. 25. The method of manufacture as set forth in Claim 18 14. The article as set forth in Claim 1 characterized by characterized by constituent composition being said article having an average bend deflection of provided with N and C in an amount of less than 1% greater than 0.254 cm . 50 in total.

15. The article as set forth in Claim 1 characterized by 26. The method of manufacture as set forth in Claim 18 said article exhibiting a service life of greater than characterized by constituent composition being 60,000 cycles at temperatures of 649° C when in- provided with N and C in an amount of greater than jection molding semi-solid magnesium. 55 0.65% in total.

16. The article as set forth in Claim 1 characterized by 27. The method of manufacture as set forth in Claim 18 hardness being greater than 44HRC. characterized by heat treating step including an-

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nealing at a temperature greater than 1093° C. 38. An apparatus as set forth in Claim 35 character- ized by Cr in an amount of 27 to 28%. 28. The method of manufacture as set forth in Claim 18 characterized by heat treating step including an- 39. An apparatus as set forth in Claim 35 character- nealing at a temperature of greater than 1149° C. 5 ized by Cr in an amount of 27.8%.

29. The method of manufacture as set forth in Claim 18 40. An apparatus as set forth in Claim 35 character- characterized by heat treating step including aging ized by component being a heat treated compo- at a temperature of at least 593° C for 72 hours. nent. 10 30. The method of manufacture as set forth in Claim 18 41. An apparatus as set forth in Claim 40 character- characterized by heat treating step including aging ized by component being annealed at a tempera- at a temperature of about 649° C for 72 hours. ture greater than 1093° C.

31. The method of manufacture as set forth in Claim 18 15 42. An apparatus as set forth in Claim 40 character- characterized by method further comprising the ized by component being aged at a temperature of step of preparing said powder metal constituent at least 593° C for 72 hours. composition by a nitrogen atomization process. 43. An apparatus as set forth in Claim 35 character- 32. The method of manufacture as set forth in Claim 31 20 ized by component being a nozzle. characterized by preparing step including dissolv- ing nitrogen into said powder metal. 44. An apparatus as set forth in Claim 35 character- ized by component being a barrel. 33. The method of manufacture as set forth in Claim 18 characterized by hardness being greater than 25 45. An apparatus as set forth in Claim 35 character- 44HRC. ized by component being a liner for a barrel.

34. The method of manufacture as set forth in Claim 18 46. An apparatus as set forth in Claim 35 character- characterized by hardness being greater than ized by component being a piston ring. 45HRC. 30 47. An apparatus as set forth in Claim 35 character- 35. An apparatus for semi-solid processing of a metal ized by component having a hardness of greater by heating the metal into a liquid plus solid phase than 44HRC. at a temperature in the range of 316° C to 816° C while stirring the metal to inhibit the formation of 35 48. An apparatus as set forth in Claim 35 character- dendrites in the semi-solid metal and injecting the ized by component having a hardness of greater semi-solid metal into a mold to form a molded arti- than 45HRC. cle, said apparatus characterized by a component being at least partially formed from a fully dense powder metal Co-Cr-W-C-type article with said ar- 40 Patentansprüche ticle defining a surface for contacting the semi-solid metal, said article having a constituent composition 1. Auf Kobalt basierender, vollmassiver Pulvergegen- of C in an amount of 0.65 to 0.88%, W in an amount stand, der isostatisch gepresst und wärmebehan- of 3 to 5%, Cr in an amount of 27 to 30%, and Co delt worden ist, wobei der Gegenstand gegenüber in an amount principally comprising a balance of 45 halbmassivem Metall hohe Verschleiß- und Korro- said composition, said article having a hardness of sionsbeständigkeit aufweist gekennzeichnet greater than 42HRC, a bend fracture strength of durch: greater than 2285MPa, and substantial dimension- al and mechanical property stability during expo- C mit einem Anteil von 0,6 bis weniger als 1%, sure to temperatures in the range of 593° C to 816° 50 W mit einem Anteil von 3 bis 5%, C , and said article being formed to at least a near Cr mit einem Anteil von 25 bis 30%, net shape by a hot isostatic pressure process. Co mit einem Anteil, der im wesentlichem dem Rest des Gegenstands entspricht, und 36. An apparatus as set forth in Claim 35 character- ized by C in an amount of 0.8%. 55 wobei der Gegenstand eine Härte größer als 42 HRC, eine Biegebruchfestigkeit größer als 2285 37. An apparatus as set forth in Claim 35 character- MPa und im wesentlichen abmessungsmäßige und ized by W in an amount of 4%. mechanische Stabilität aufweist, wenn er Tempera-

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turen im Bereich von etwa 316 °C bis 816 °C aus- durch eine Härte größer als 45 HRC. gesetzt ist. 18. Verfahren zum Herstellen eines verschleiß- und 2. Gegenstand nach Anspruch 1, gekennzeichnet korrosionsbeständigen, vollmassiven Pulvermetall- durch C mit einem Anteil von 0,65 bis 0,88%. 5 urgie-Co-Cr-W-C-Gegenstands, wobei das Verfah- ren durch die Schritte gekennzeichnet ist: 3. Gegenstand nach Anspruch 1, gekennzeichnet durch C mit einem Anteil von 0,8%. Bereitstellen einer Pulvermetallbestandteilszu- sammensetzung aus C mit einem Anteil von 4. Gegenstand nach Anspruch 1, gekennzeichnet 10 0,65 bis 0,88%, W mit einem Anteil von 3 bis durch W mit einem Anteil von 4%. 5%, Cr mit einem Anteil von 27 bis 30% und Co mit einem Anteil, der im wesentlichen dem Rest 5. Gegenstand nach Anspruch 1, gekennzeichnet der Zusammensetzung entspricht, durch Cr mit einem Anteil von 27 bis 28%. Verfestigen der Bestandteilszusammenset- 15 zung durch einen Wärmeprozess unter isosta- 6. Gegenstand nach Anspruch 1, enthaltend M mit ei- tischem Druck, nem Anteil von weniger als 0,1%. Wärmebehandeln des Gegenstands, der eine Härte größer als 42 HRC, eine Biegebruchfe- 7. Gegenstand nach Anspruch 6, gekennzeichnet stigkeit größer als 2285 MPa und im Wesentli- durch N mit einem Anteil von 0,066%. 20 chen einen abmessungsmäßige und mechani- sche Stabilität aufweist, während er Tempera- 8. Gegenstand nach Anspruch 1, außerdem gekenn- turen im Bereich von 593 °C bis 816 °C ausge- zeichnet durch einen Anteil von N und C, der we- setzt wird. niger als insgesamt 1% beträgt. 25 19. Herstellungsverfahren nach Anspruch 18, dadurch 9. Gegenstand nach Anspruch 1, außerdem gekenn- gekennzeichnet, dass C mit einem Anteil von zeichnet durch einen Anteil von N und C, der mehr 0,8% vorgesehen wird. als insgesamt 0,65% beträgt. 20. Herstellungsverfahren nach Anspruch 18, dadurch 10. Gegenstand nach Anspruch 1, gekennzeichnet 30 gekennzeichnet, dass W mit einem Anteil von 4% durch eine Biegebruchfestigkeit, die größer als vorgesehen wird. 2492 MPa ist. 21. Herstellungsverfahren nach Anspruch 18, dadurch 11. Gegenstand nach Anspruch 1, dadurch gekenn- gekennzeichnet, dass Cr mit einem Anteil von 27 zeichnet, dass er durch Altern wärmebehandelt ist. 35 bis 28% vorgesehen wird.

12. Gegenstand nach Anspruch 1, dadurch gekenn- 22. Herstellungsverfahren nach Anspruch 18, dadurch zeichnet, dass er durch Lösungsglühen wärmebe- gekennzeichnet, dass Cr mit einem Anteil von handelt ist. 27,8% vorgesehen wird. 40 13. Gegenstand nach Anspruch 12, dadurch gekenn- 23. Herstellungsverfahren nach Anspruch 18, gekenn- zeichnet, dass er außerdem durch Altern wärme- zeichnet durch eine Bestandteilszusammenset- behandelt ist. zung mit N mit einem Anteil von weniger als 0,1%.

14. Gegenstand nach Anspruch 1, dadurch gekenn- 45 24. Herstellungsverfahren nach Anspruch 18, gekenn- zeichnet, dass er einen mittleren Biegepfeil größer zeichnet durch eine Bestandteilszusammenset- als 0,254 cm aufweist. zung mit N mit einem Anteil von weniger als 0,066%. 15. Gegenstand nach Anspruch 1, dadurch gekenn- zeichnet, dass er aus halbmassivem Magnesium 50 25. Herstellungsverfahren nach Anspruch 18, gekenn- spritzgegossen eine Lebensdauer größer als zeichnet durch eine Bestandteilszusammenset- 60.000 Zyklen bei einer Temperatur von 649 °C auf- zung mit N und C mit einem Anteil von weniger als weist. insgesamt 1%.

16. Gegenstand nach Anspruch 1, gekennzeichnet 55 26. Herstellungsverfahren nach Anspruch 18, gekenn- durch eine Härte größer als 44 HRC. zeichnet durch eine Bestandteilszusammenset- zung, die mit N und C mit einem Anteil größer als 17. Gegenstand nach Anspruch 1, gekennzeichnet insgesamt 0,65% vorgesehen ist.

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27. Herstellungsverfahren nach Anspruch 18, dadurch genstand eine Härte größer als 42 HRC, eine Bie- gekennzeichnet, dass der Wärmebehandlungs- gebruchfestigkeit größer als 2285 MPa und im we- schritt Glühen bei einer Temperatur größer als 1093 sentlichen eine abmessungsmäßige und mechani- °C enthält. sche Stabilität aufweist, während er Temperaturen 5 im Bereich von 593 °C bis 816 °C ausgesetzt ist, 28. Herstellungsverfahren nach Anspruch 18, dadurch und wobei der Gegenstand zumindest im wesentli- gekennzeichnet, dass der Wärmebehandlungs- chen auf die endgültige Form durch einen heißen schritt Glühen bei einer Temperatur größer als 1149 Prozess unter isostatischem Druck gebildet ist. °C enthält. 10 36. Vorrichtung nach Anspruch 35, gekennzeichnet 29. Herstellungsverfahren nach Anspruch 18, dadurch durch C mit einem Anteil von 0,8%. gekennzeichnet, dass der Wärmebehandlungs- schritt Altern bei einer Temperatur von zumindest 37. Vorrichtung nach Anspruch 35, gekennzeichnet 593 °C für 72 Stunden enthält. durch W mit einem Anteil von 4%. 15 30. Herstellungsverfahren nach Anspruch 18, dadurch 38. Vorrichtung nach Anspruch 35, gekennzeichnet gekennzeichnet, dass der Wärmebehandlungs- durch Cr mit einem Anteil von 27 bis 28%. schritt Altern bei einer Temperatur von etwa 649 °C für 72 Stunden enthält. 39. Vorrichtung nach Anspruch 35, gekennzeichnet 20 durch Cr mit einem Anteil von 27,8%. 31. Herstellungsverfahren nach Anspruch 18, dadurch gekennzeichnet, dass zusätzlich der Schritt vor- 40. Vorrichtung nach Anspruch 35, dadurch gekenn- gesehen ist, die Pulvermetallbestandteilszusam- zeichnet, dass es sich bei der Komponente um ei- mensetzung durch einen Stickstoffzerstäubungs- ne wärmebehandelte Komponente handelt. prozess zuzubereiten. 25 41. Vorrichtung nach Anspruch 40, dadurch gekenn- 32. Herstellungsverfahren nach Anspruch 31, dadurch zeichnet, dass die Komponente bei einer Tempe- gekennzeichnet, dass der Zubereitungsschritt ratur größer als 1093 °C geglüht ist. das Lösen von Stickstoff in dem Pulvermetall ent- hält. 30 42. Vorrichtung nach Anspruch 40, dadurch gekenn- zeichnet, dass die Komponente bei einer Tempe- 33. Herstellungsverfahren nach Anspruch 18, dadurch ratur von zumindest 593 °C für 72 Stunden gealtert gekennzeichnet, dass die Härte größer als 44 ist. HRC ist. 35 43. Vorrichtung nach Anspruch 35, dadurch gekenn- 34. Herstellungsverfahren nach Anspruch 18, dadurch zeichnet, dass die Komponente eine Düse bildet. gekennzeichnet, dass die Härte größer als 45 HRC ist. 44. Vorrichtung nach Anspruch 35, dadurch gekenn- zeichnet, dass es sich bei der Komponente um ein 35. Vorrichtung zur halbmassiven Verarbeitung von 40 Fass handelt. Metall durch Erwärmen des Metalls auf eine flüssi- ge und eine feste Phase bei einer Temperatur im 45. Vorrichtung nach Anspruch 35, dadurch gekenn- Bereich von 316 °C bis 816 °C, während das Metall zeichnet, dass es sich bei der Komponente um ei- umgerührt wird, um die Ausbildung von Dentriten in ne Auskleidung für ein Fass handelt. dem halbfesten Metall zu unterbinden und während 45 das halbfeste Metall in eine Form eingespritzt wird, 46. Vorrichtung nach Anspruch 35, dadurch gekenn- um einen geformten Gegenstand zu bilden, wobei zeichnet, dass es sich bei der Komponente um ei- die Vorrichtung dadurch gekennzeichnet ist, nen Kolbenring handelt. dass eine Komponente zumindest teilweise aus ei- nemvollmassivenPulvermetall-CO-Cr-W-C-Gegen- 50 47. Vorrichtung nach Anspruch 35, dadurch gekenn- stand gebildet ist, wobei der Gegenstand eine zeichnet, dass die Komponente eine Härte größer Oberfläche zur Kontaktierung des halbfesten Me- als 44 HRC aufweist. talls festlegt, wobei der Gegenstand eine Bestand- teilszusammensetzung aus C mit einem Anteil von 48. Vorrichtung nach Anspruch 35, dadurch gekenn- 0,65 bis 0,88%, W mit einem Anteil von 3 bis 5%, 55 zeichnet, dass die Komponente eine Härte größer Cr mit einem Anteil von 27 bis 30% und Co mit ei- als 45 HRC aufweist. nem Anteil enthält, der im wesentlichen dem Rest der Zusammensetzung entspricht, wobei der Ge-

10 19 EP 0 938 593 B1 20

Revendications dans une solution.

1. Article à base de cobalt, métallique, à densité totale, 13. Article selon la revendication 12, caractérisé en ce en poudre, ayant subi une compression isostatique que ledit article est également traité thermiquement à chaud et traité thermiquement, ledit article ayant 5 par vieillissement. une résistance à l'usure et à la corrosion élevée pour un métal semi-solide et étant caractérisé par : 14. Article selon la revendication 1, caractérisé en ce que ledit article présente une déformation à la du C en une quantité comprise entre 0,6 et flexion moyenne supérieure à 0,254 cm. moins de 1 % ; 10 du W en une quantité comprise entre 3 et 5 % ; 15. Article selon la revendication 1, caractérisé en ce du Cr en une quantité comprise entre 25 et 30 que ledit article présente une durée de vie supé- %; rieure à 60.000 cycles à des températures de 649°C du Co en une quantité correspondant principa- lors du moulage par injection de magnésium semi- lement à la partie restante dudit article ; et 15 solide. ledit article ayant une dureté supérieure à 42HRC, une résistance à la rupture par flexion 16. Article selon la revendication 1, caractérisé en ce supérieure à 2285 MPa et une stabilité des pro- que la dureté est supérieure à 44HRC. priétés dimensionnelles et mécaniques impor- tante pendant l'exposition à des températures 20 17. Article selon la revendication 1, caractérisé en ce dans une plage d'environ 316°C à 816°C. que la dureté est supérieure à 45HRC.

2. Article selon la revendication 1, caractérisé par du 18. Procédé de fabrication d'un article du type Co-Cr- C en une quantité comprise entre 0,65 et 0,88 %. W-C, totalement dense, par la métallurgie des pou- 25 dres, résistant à l'usure et à la corrosion, ledit pro- 3. Article selon la revendication 1, caractérisé par du cédé étant caractérise par les étapes consistant à : C en une quantité de 0,8 %. prévoir une composition constitutive de poudre 4. Article selon la revendication 1, caractérisé par du métallique comprenant du C en une quantité W en une quantité de 4 %. 30 comprise entre 0,65 et 0,88 %, du W en une quantité comprise entre 3 et 5 %, du Cr en une 5. Article selon la revendication 1, caractérisé par du quantité comprise entre 27 et 30 % et du Co en Cr en une quantité comprise entre 27 et 28 %. une quantité correspond principalement à la partie restante de ladite composition ; 6. Article selon la revendication 1, contenant du N en 35 consolider ladite composition constitutive par une quantité inférieure à 0,1 %. une opération de pression isostatique à chaud ; traiter thermiquement ledit article, ledit article 7. Article selon la revendication 6, caractérisé par du ayant une dureté supérieure à 42HRC, une ré- N en une quantité de 0,066 %. sistance à la rupture par flexion supérieure à 40 2285 MPa et une stabilité des propriétés di- 8. Article selon la revendication 1, caractérisé en mensionnelles et mécaniques importante pen- outre par une quantité de N et de C s'élevant à dant l'exposition à des températures dans la moins de 1 % au total. plage de 593°C à 816°C.

9. Article selon la revendication 1, caractérisé en 45 19. Procédé de fabrication selon la revendication 18, outre par une quantité de N et de C s'élevant à plus caractérisé en ce que le C est prévu en une quan- de 0,65 % au total. tité de 0,8 %.

10. Article selon la revendication 1, caractérisé en ce 20. Procédé de fabrication selon la revendication 18, que la résistance à la rupture par flexion est supé- 50 caractérisé en ce que le W est prévu en une quan- rieure à 2492 MPa. tité de 4 %.

11. Article selon la revendication 1, caractérisé en ce 21. Procédé de fabrication selon la revendication 18, que ledit article est traité thermiquement par vieillis- caractérisé en ce que le Cr est prévu en une quan- sement. 55 tité comprise entre 27 et 28 %.

12. Article selon la revendication 1, caractérisé en ce 22. Procédé de fabrication selon la revendication 18, que ledit article est traité thermiquement par recuit caractérisé en ce que le Cr est prévu en une quan-

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tité de 27,8 %. 35. Dispositif pour le traitement d'un métal semi-solide par chauffage du métal dans une phase liquide plus 23. Procédé de fabrication selon la revendication 18, solide à une température dans la plage de 316°Cà caractérisé en ce que la composition constitutive 816°C tout en agitant le métal afin d'empêcher la comprend du N en une quantité inférieure à 0,1 %. 5 formation de dendrites dans le métal semi-solide et en injectant le métal semi-solide dans un moule afin 24. Procédé de fabrication selon la revendication 18, de former un article moulé, ledit dispositif étant ca- caractérisé en ce que la composition constitutive ractérisé par un composant au moins partiellement comprend du N en une quantité de 0,066 %. formé à partir d'un article du type Co-Cr-W-C mé- 10 tallique, en poudre, de densité totale, ledit article 25. Procédé de fabrication selon la revendication 18, définissant une surface de contact avec le métal caractérisé en ce que la composition constitutive semi-solide, ledit article ayant une composition comprend du N et du C en une quantité inférieure comprenant du C en une quantité comprise entre à 1 % au total. 0,65 % et 0,88 %, du W en une quantité comprise 15 entre 3 % et 5 %, du Cr en une quantité comprise 26. Procédé de fabrication selon la revendication 18, entre 27 % et 30 % et du Co en une quantité cor- caractérisé en ce que la composition constitutive respondant principalement à la partie restante de comprend du N et du C en une quantité supérieure ladite composition, ledit article ayant une dureté su- à 0,65 % au total. périeure à 42HRC, une résistance à la rupture par 20 flexion supérieure à 2285 MPa et une stabilité des 27. Procédé de fabrication selon la revendication 18, propriétés dimensionnelles et mécaniques impor- caractérisé en ce que l'étape de traitement ther- tante pendant l'exposition à des températures dans mique comprend un recuit à une température supé- la plage de 593°C à 816°C, et ledit article étant réa- rieure à 1093°C. lisé au moins en une forme presque nette par une 25 opération de pression isostatique à chaud. 28. Procédé de fabrication selon la revendication 18, caractérisé en ce que l'étape de traitement ther- 36. Dispositif selon la revendication 35, caractérisé mique comprend un recuit à une température supé- par du C en une quantité de 0,8 %. rieure à 1149°C. 30 37. Dispositif selon la revendication 35, caractérisé 29. Procédé de fabrication selon la revendication 18, par du W en une quantité de 4 %. caractérisé en ce que l'étape de traitement ther- mique comprend un vieillissement à une tempéra- 38. Dispositif selon la revendication 35, caractérisé ture d'au moins 593°C pendant 72 heures. par du Cr en une quantité comprise entre 27 et 28 35 %. 30. Procédé de fabrication selon la revendication 18, caractérisé en ce que l'étape de traitement ther- 39. Dispositif selon la revendication 35, caractérisé mique comprend un vieillissement à une tempéra- par du Cr en une quantité de 27,8 %. ture d'environ 649°C pendant 72 heures. 40 40. Dispositif selon la revendication 35, caractérisé en 31. Procédé de fabrication selon la revendication 18, ce qu'un composant consiste en un composant trai- caractérisé en ce que le procédé comprend en té thermiquement. outre l'étape de préparation de ladite composition constitutive métallique en poudre par une opération 41. Dispositif selon la revendication 40, caractérisé en d'atomisation sous azote. 45 ce qu'un composant est recuit à une température supérieure à 1093°C. 32. Procédé de fabrication selon la revendication 31, caractérisé en ce que l'étape de préparation com- 42. Dispositif selon la revendication 40, caractérisé en prend la dissolution d'azote dans ledit métal en pou- ce qu'un composant est vieilli à une température dre. 50 d'au moins 593°C pendant 72 heures.

33. Procédé de fabrication selon la revendication 18, 43. Dispositif selon la revendication 35, caractérisé en caractérisé en ce que la dureté est supérieure à ce qu'un composant est un ajutage. 44HRC. 55 44. Dispositif selon la revendication 35, caractérisé en 34. Procédé de fabrication selon la revendication 18, ce qu'un composant est une cuve. caractérisé en ce que la dureté est supérieure à 45HRC. 45. Dispositif selon la revendication 35, caractérisé en

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ce qu'un composant est une chemise pour une cu- ve.

46. Dispositif selon la revendication 35, caractérisé en ce qu'un composant est un segment de piston. 5

47. Dispositif selon la revendication 35, caractérisé en ce qu'un composant a une dureté supérieure à 44HRC. 10 48. Dispositif selon la revendication 35, caractérisé en ce qu'un composant a une dureté supérieure à 45HRC.

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