MXPA99004129A - Powder metallurgy, cobalt-based articles having high resistance to wear and corrosion in semi-solid metals - Google Patents

Abstract

A fully dense powder metal cobalt-base article having high resistance to semi-solid metal wear and corrosion. The article has a constituent composition of C in an amount of about 0.65 to less than about 1%, W in an amount of about 3 to about 5%, Cr in an amount of about 25 to about 30%, Co in an amount principally comprising the balance of the article. The article has a hardness of greater than 42HRC and more preferably 45HRC, a bend fracture strength of greater than 330 ksi and substantial dimensional and mechanical property stability during exposure to temperatures in range of about 1100°F to 1500°F.

Description

ARTICLES BASED ON COBALT, OF POWDER METALLURGY, WHICH HAVE HIGH RESISTANCE TO WEAR AND CORROSION IN SOLID SEMI METALS BACKGROUND AND COMPENDIUM OF THE INVENTION The present invention relates to cobalt-based articles having high resistance to wear and corrosion in semi-solid metal environments. More specifically, the invention relates to fully dense powder metallurgy articles, made from a novel Co-Cr-C type alloy, which is particularly suitable for long-term use in high temperature, high wear machinery, which uses a variant process of molding semi-solid metal (SSM = Semi-Solid Metal Molding). The metallurgical process referred to herein is one in which metals and metal matrix compounds are heated and agitated in the more liquid solid phase reduction and then injected into a mold or matrix at lower temperatures. This process has shown that it results in parts that have improved characteristics of materials, which previously gave non-emptied and non-obtained forms and processing stages with reduced post-formation. Two earlier process versions also known as Thixomolding ™ (Thixomat, Inc., Ann Arbor, Michigan), are generally described in U.S. Pat. Nos. 4,694,881 and 4,694,882, which are hereby incorporated by reference. The process generally involves the shearing of a semi-solid metal to inhibit the growth of dendritic solids and produce non-dendritic solids within a sludge that has improved molding characteristics that result in part from its tisotropic properties (a non-dendritic semi-solid material that exhibits a viscosity that is proportional to the applied shear rate and less than that of the same alloy when it is in a dendritic state). A machine adapted to employ the above type of processes and to which the present invention has particular applicability, is schematically illustrated in Figure 1. The construction of the molding machine 10 in some aspects is similar to that of an injection molding machine. of plastic. In the illustrated machine 10, the feed material is supplied by a hopper 12 in a reciprocating screw injection system before such a state 14 which keeps the feed material under a protective atmosphere 16 such as argon. As the feed material is advanced by the rotary movement of a spindle 18, it is heated by heaters 20 and stirred and sheared by the action of the spindle 18. This heating and shearing are carried out to bring the feed material to its temperature range of solid more liquid. The thixotropic sludge formed by this action passes through a non-return valve 22 at the front of the injection system 14 of the machine 10 to an accumulation chamber 24. Upon accumulation of the required amount of sludge in the accumulation chamber 24 , the injection cycle is started by advancing the spindle 18 with a hydraulic observer and causing the mold 26 to fill through a nozzle 28. As opposed to other semi-solid molding methods, the method described above has the advantage of combining Mud generation and mold filling in a single stage. It also minimizes the safety hazards involved in melting and emptying reactive semi-solid metals. Obviously, as will be appreciated further, the construction of components of the present invention will find applicability as articles, not only in the construction of machines 10 practicing the above method, but also in machines that practice alternate variations in the above process and other processes. These machines and articles include, without limitation, matrix molding, metal injection molding, plastic injection molding machines, as well as tooling and dies. Due to contact with corrosive semi-solid metals (such as magnesium and zinc), the high temperatures of operation, oxidation and the high nature of wear of the environment), the contact between the various operative parts of the machine and the semi-solid metal is an extremely high wear condition and shock (the components of the previous machinery demand Much in its construction materials Spindle speeds for example involve acceleration of 0 to 3 meters / second and deceleration back to 0, all in 0.2 seconds.The selected construction materials must be resistant to corrosive attack by the semi-solid metal that is processed, must be highly resistant to wear, and there must be sufficient strength and tenacity to withstand the stresses imposed during long-term exposure to the relevant elevated temperatures under these severe thermal cycling and high shock conditions from a corrosion point of view. , iron alloys and some based on cobalt have been reported as satisfying for processing semi-solid magnesium base alloys. Nickel-based alloys, such as alloy 718, are of interest as building materials due to their good resistance to high temperatures and lower cost compared to most cobalt-based alloys. However, because molten magnesium attacks alloys containing nickel, some SSM processors have specified that alloys that come in contact with molten magnesium must contain less than about 3% nickel. Previous machines avoid this problem by using alloy 718 in their barrel constructions, while incorporating a barrel insert adapted by shrinkage made of a cobalt base alloy such as Stellite 6 (nominally 28 Cr, 4.5 and 1.2C) or Stellite 12 (not inally 30Cr, 8.3 and 1.4C), which are commercially available from Cabot Corporation, Kokomo. Indiana. While they generally perform well with respect to corrosion, they are deficient in tenacity and have exhibited cracking and fracture in the machines of the previous type. Under conditions of fatigue at high temperature of the machines, it has been seen that cracks in the stellite linings propagate in the alloy barrel 718 resulting in total failure of the barrel structure. This is not safe and requires expensive repairs and replacements. It has come to be determined that articles of an alternative material, which have greater tenacity, would be more convenient since they will provide components of greater wear. The selection of materials to process semi-solid aluminum based alloys is much more complex. This is particularly true because most iron, cobalt and nickel based alloys are easily attacked by aluminum alloys. In addition to these aspects and those described in connection with the magnesium processing, other important aspects are related to the availability, cost and manufacturing characteristics of the construction material. In the injection molding of magnesium-based alloys, the maximum operating temperatures within the barrel are typically in the chamber approximately 593 or 649 ° C (1100 and 1200 ° F), with temperatures sometimes in the range of 816 ° C (1500 ° F). The most common steels for hot work tools based on AISI iron (such as H-10 and H-13, and even more steels for high alloy hot work tools such as H-19 and H-21) lose resistance, hardness and resistance to wear at these temperatures. As a result, a number of highly specialized materials for machine construction have been employed, in particular these alloys include Stellite 6 and 12 (previously mentioned) and alloys of the Co-Cr-W-C type and the like. These alloys have been used to form centrifugal pouring barrel linings or welding coatings. The use of Co-Cr-W-C type barrel linings avoids the corrosion problems that may be found between cast nickel and magnesium based alloys. Its use as liners therefore allows the use of more cost-effective nickel-based alloys such as alloy 718 for barrel construction.

Steels for special hot work tools such as Thyssen 1.2888 (and number) (nominally 0.2C, 12OC, 2Mo, 5.5W and 10.OOCo) have been used in screws and valves without return. Thyssen 1.2888 can supposedly be used for short times at temperatures as high as 700 ° C (1292 ° F). Due to problems regarding cost and availability, as well as in an attempt to improve performance, the present inventors began a search for a new alloy to replace the currently used Co-Cr-W-C-type alloys and Thyssen 1.2888. This search has led to the 718 alloy barrels with HIP-coating with a new wear resistant alloy based on cobalt powder metallurgy (PM) as well as the construction of various monolithic parts made from the same alloy. The properties of the current components made from wear-resistant alloys based on cobalt PM produced by nitrogen atomization and hot isostatic pressure (HIP = Hot Isostatic Pressing) differ considerably from previously mentioned Co-Cr-WC type alloys (produced from powder by conventional sintering and pressing methods). The new alloys exhibit an improved combination of strength, toughness and dimensional stability and it has been found beneficial to also modify their heat treatment. The traditional Co-Cr-W-C type alloys are cobalt-quaternary base alloys containing approximately 27-29% chromium, a variable amount of tugstene (4 to 17%) and carbon (0.9-3.2%). They are widely used in wear resistance applications due to their high strength, corrosion resistance and ability to retain their hardness at elevated temperatures. Due to its limited hot workability and machinability, however, most Co-Cr-W-C alloys of higher carbon content are used in the form of molded parts, hard front consumables and powder metallurgy parts. Considerable work has been done to explore the production of type (PM) alloys Co-Cr-W-C (powder metallurgy atomized by isostatic pressing (HIPing) of prealloyed powders atomized with gas. In general, previous studies have shown that PM processing of these materials produces a material with higher hardness, superior tensile strength and superior ductility than what is achieved when molding the alloys and that these improvements are still retained at high temperature. The abrasive wear resistance of these PM materials is somewhat lower than their cast or molded counterparts due to the smaller sizes of the primary carbides. For the same reasons, its machinability has been improved. With respect to the properties of the prior Co-Cr-W-C type alloys, it has often been estimated that these alloys are at their maximum hardness in the emptied or welded condition and that their properties can not be changed by subsequent heat treatment. Similarly, it has also been considered that putting these alloys into service at elevated temperature has little effect on their hardness, toughness and dimensional stability. Contrary to this consideration, some of the literature published for weld deposits, forged alloys and PM alloys, indicates that many that Co-Cr-WC alloys exhibit an increase in hardness due to carbide precipitation, when heated in the range of 649 to 816 ° C (1200 to 1500 ° F). When they are aged at these temperatures, articles of the Co-Cr-W-C type alloys can therefore undergo a change in size, strength and toughness and this is not acceptable in all applications. Operating temperatures during single-shot metal injection molding (as described generally above) approximate those in which carbide precipitation may occur in PM-type alloys Co-Cr-W-C. Much of the work carried out and which results in the present invention is based on aspects related to the possible effects that high-temperature exposure may have on the mechanical properties and dimensional stability of PM-Co-Cr-W-C type alloys. This investigation is also carried out to determine that, if there are changes in the alloy composition or subsequent thermal treatment, they can be used to minimize the previous effects in the resulting articles. In view of the foregoing and other limitations of the prior art, it is a primary object of the present invention to provide fully dense articles made from a novel Co-Cr-WC PM-type alloy which are highly resistant to change and size, hardness , corrosion resistance, strength and tenacity, as a result of prolonged exposure to temperatures in the range of approximately 649 to 816 ° C (1200 to 1500 ° F). Another objective is to provide a fully dense cobalt PM base article that is resistant to corrosion in semi-solid magnesium and zinc. It is also an object of the present invention to provide fully dense cobalt PM-based articles that exhibit adequate hardness without a decrease in toughness. A still further objective of this invention is to provide totally dense PM cobalt-based articles exhibiting increased toughness against articles and alloys of the prior art, thereby resulting in longer lasting components and increased safety. Exceptional benefits and advantages of the present invention will be apparent those with desires in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, which are taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a machine to which the present invention will have particular applicability; Figure 2 is a table of the chemical decompositions of some PM alloys mainly investigated, including the alloy of the present invention, as well as an alloy cast of the same general variety. Figure 3a-3c are microphotographs (lOOOx amplification); ammonium persulfate as mordant (from the PM alloys presented in the table of Figure 1); Figures 4a and 4b with microphotographs (amplification 400x and lOOOx, respectively); ammonium persulfate as mordant (from the cast alloy 12 presented in the table of Figure 1); Figure 5 is a table of comparative hardness for some of the alloys investigated in the discovery of the present invention; Figure 6 is a table of the tensile properties of the PM 12 alloy that was investigated in the discovery of the present invention; Figure 7 is a table of the aging response of some PM alloys and a cast alloy which is investigated in the discovery of the present invention; Figure 8 is a table of the dimensional stability of the PM 12 alloy when heat treated for a period of 48 hours; Figure 9 is a table of the bending fracture properties of the PM alloys and the cast alloy presented in Figure 7. DETAILED DESCRIPTION OF THE PREFERRED MODALITY The chemical compositions of some of the Co-Cr-WC type alloys evaluated in this investigation as potential building materials for the machine 10 (see Figure 1) are given in Figure 2. Included in the table are three alloys of type PM Co-Cr-WC and an alloy of Cr-Co-W type cast in Centrifugal form. The compositions of the alloys PM 6 and 12 are similar to those commonly used for alloys of Stellite 6 and Stellite 12, respectively. The sample of the cast alloy 12 is taken from a Stellite 12 centrifugally cast barrel liner which is produced commercially for a machine 10 of the above variety and which fails and breaks in service. As seen in Figure 2, the nominal composition of the PM 0.8 C alloy was 0.80 C, 27.81 Cr and 4.11 W and the rest mainly Co with 0.066 N; for the alloy PM 6 these constituents are 1.11 C, 29.34 Cr and 4.60 W and the rest mainly Co; for the PM12 alloy these constituents are 1.41 C, 28.79 Cr, 8.68 W and the rest mainly Co; and for the cast alloy 12, these constituents are 1.31 C, 28.79 Cr, 8.23 W, the rest mainly Co. The nickel content in each of the above was respectively 2. 15, 0.13, 1.57 and 2.80. Numerous samples for further analysis were created by hot isostatic pressure (HIPing) of PM materials. As discussed further below, the PM 0.8C alloy intentionally melted at a lower than normal carbon and tungsten content. PM 0.8C alloy powders were prepared not by ordinary argon atomization techniques but by atomization with nitrogen. The nitrogen dissolved in the resulting alloy during this process seems to increase its resistance and response to aging. When using nitrogen atomization to produce the alloy, thermal induced porosity that is often found in atomized argon alloys is substantially non-existent. Figures 3a-3c and 4a and 4b show the microstructures of the Co-Cr-WC type alloys of Figure 2. As those Figures are seen, the Co-Cr-WC PM type alloys in the condition as they were subjected to Hot isostatic pressure (HIPed) contain a substantially random dispersion of small carbides, the amount of which size increases with the carbon content of the alloy. The primary carbides in the Co-Cr-W-C alloy centrifugally emptied have the expected dendritic distribution of voided material. Accordingly, these latter carbides are much larger than those in the Co-Cr-W-C PM type alloys, and in particular with respect to the PM 12 alloy which has a similar composition. As a result of the larger carbides, it is anticipated and supported by proof that the material will have less tenacity than the others. Hardness measurements for various alloys at various temperatures are presented in the table in Figure 5. These data are obtained in some cases from published literature that is provided by the commercial supplier of the material. In those cases, the provider is placed at the bottom of the table. Regarding the sources for the data in those samples, Stellite 6B (Haynes Wrought Wear-Resistant Alloys, 1976, Cabot Corporation Stellite Division, Kokomo, Indiana); Stellite cast in sand mold 6 and 12 (Thermadyne Stellite Coatings, Goshen, Indiana); and steel for tool H-13 and steel for tool H-19 (Crisol CPM, data sheets 9V, 1987, Crucible Materials Corporation, Pittsburg, Pennsylvania). Of the three PM12 alloy samples one was from a sleeve or insert of a composite barrel construction as described above in connection with machine 10. The other two samples were taken from a test ring made by hot isostatic pressure coating (HIP) alloy PM12 to a hollow cylinder made of conventional alloy 718. Because most of the HIP coating barrels of the 718 alloy will likely age after HIP coating, one of these latter samples is given the standard aged double hardening treatment for alloy 718 (718 ° C (1325 ° F) / 8 hours / FC at 621 ° C (1150 ° F) / 8 hours / AC) before it is tested. The other sample coated with HIP is tested in a condition such as under hot isostatic pressure (HIPed). For PM 0.8C alloy, a sample is tested as it was subjected to hot isostatic pressure (HIPed) and a sample as recoated at 1199 ° C (2190 ° F) before testing. Allowing some dispersion in the data, it is clear that the hot hardness of the PM12 alloy is higher than that of the forged alloy Stellite 6B, Stellite cast 6 and Stellite cast in sand mold 12, both at room temperature and at elevated temperature . The results also indicate that an aged double heat treatment increases the hardness of alloy 718 on the non-aged sample both at ambient and selected temperatures. The same seems to be true, but in a smaller proportion, for the double-aged sample of PM12 alloy. As expected, the hot hardness of all Co-Cr-W-C type materials except possibly for the forged alloy of Stellite 6B, are significantly higher than those of the two steels for conventional hot processing tools. Because the PM 12 alloy shows an increase in hardness when bending stale, an investigation into its attractive properties was performed. The results of these investigations are summarized in the table of Figure 6, where data for Stellite 6 and 12 are presented for comparison. The results show that the levels of tensile strength of the PM 12 alloy (as it was subjected to pressure hot isostatic (HIPed), are quite high as at room temperature as well as at elevated temperature.They proved to be superior to those reported in the literature for Stellite casting in sand mold 6 and Stellite 12 at room temperature.The heat treatment of PM12 alloy uses a double-aging treatment of standard 718 alloys does not significantly change the properties of the attraction either at room temperature or at 649 ° C (1200 ° F) The long-term structural stability of Co-Cr-WC PM-type alloys , when used at elevated temperatures, it is investigated by measuring the hardness at room temperature of specimens after the specimens have been heated. or for various times at 649-760 ° C (1200 to 1400 ° F). These results are presented in the table of Figure 7. Measurements change and size a cylindrical sample of PM 12 alloy as it was subjected to hot isostatic pressure (HIPed), which has been heated under vacuum for 48 hours at 649 ° F ( 1200 ° F) is presented in the table of Figure 8. With reference to Figure 7, all three Co-Cr-WC PM type alloys in the condition as being subjected to hot isostatic pressure (HIPed) exhibit significant hardening after heating of 649 or 760 ° C (1200 or 1400 ° F) and aging. The magnitude of the increase in hardness produced after aging at 649 ° C (1200 ° F) for 72 hours, varies with an alloy determined with the PM 0.8C alloy of low carbon content that increases 6 HRC, alloy PM 6 increases 7 HRC and alloy PM 12 increases 3.5 HRC. Surprisingly, the PM 0.8C alloy of low carbon content increases in hardness to 48 HRC, well above the preferred hardness of 42 HRC and the most preferred hardness of 45 HRC for the intended application in the machine 10 described above. However, the maximum hardness achieved after the aging treatment at 649 ° C (1200 ° F) is generally increased in relation to the carbon content of the PM alloys with the PM 12 alloy which exhibits the highest hardness value after 72 hours. Solution annealing of Co-Cr-WC PM alloys at 1199 ° C (2190 ° F) for two hours before aging at 649 ° C (1200 ° F) appears to reduce the aging response, both in terms of magnitude of the increase in hardness as the maximum hardness achieved. These hardnesses, however, were still at acceptable levels. Regarding aging of the sample as it was emptied of Stellite 12 at 649 ° C (1200 ° F) for 72 hours, only a small hardness change of about 1.5 HRC is produced. The size change data in Figure 8 indicate that the PM12 alloy, as it was subjected to hot isostatic pressure (HIPed), shrinks slightly .00254 cm (.0001 inch) after heating at 649 ° C (1200 ° F). ) for 48 hours. No size change measurements have been made on PM12 alloy specimens heated for times greater than 649 ° C (1200 ° F). As discussed further below, at least in a current use case, severe shrinkage occurs in an alloy PM12 barrel liner. The cause of that shrinkage has not yet been identified. With PM alloys that all exhibit good hardness, strength or fracture toughness by bending, another critical property for the intended application of the Co-Cr-WC PM and Stellite centrifugally casting 12 alloys, were determined respectively for specimens in the condition as it was emptied or as it was-subjected to hot isostatic pressure (HIPed), and in a variety of aged or heat-treated conditions. The spens were tested using the standard three-point bend test attachment and during testing, the spen deviation is recorded at load intervals of 181.6 kg (400 pounds) and at the time of fracture. The table in Figure 9 gives the resistance of the bending fracture and the deviation at the time of fracture for each of the test spens (two spens each for PM 0.8C alloy).

For PM 0.8C alloy and alloy 6, which have similar base compositions different from their carbon contents, the results as outside-subjected to average hot isostatic pressure (HIPed) indicate that the reduction of carbon content from 1.11 to 0.80 % produces a remarkable increase in bending ductility. The recosido of solution of these two alloys to 1199 ° C (2190 ° F) also improves the ductility of bending of these materials both with and without aging at 1199 ° C (1200 ° F). Solution annealing of PM12 alloy material at 1190 ° C (2190 ° F) for two hours also slightly improves the ductility of PM12 alloy bending both with and without aging at 1199 ° C (1200 ° F). The results for the alloy 12 specimens as cast out indicate that the bending fracture and bending ductility strength of this material is significantly less than those of the PM 12 alloy which is of similar composition. The large differences in bending ductility of these two materials are more likely related to the pronounced differences in the quantity, size and distribution of the primary carbides as previously illustrated in Figures 3 and 4. The results of the above tests generally indicate that the alloys of type PM Co-Cr-WC produces materials with superior hardness, superior resistance to the traction and greater ductility that the one that obtains when emptying alloys of the same composition. All samples that PM alloys in the condition as it was subjected to hot isostatic pressure (HIPed), exhibit an increase in hardness with only very small change in dimensions (for alloy PMl 2) when aged at temperatures between 649/760 ° C (1200/1400 ° F). The annealing in solution at 1199 ° C (2190 ° F) of the materials as they were subjected to hot isostatic pressure (HIPed), seems to reduce, but not completely eliminate the aging response of these PM alloys, when heated at these temperatures . From the test results, it has also been seen that surprisingly both the toughness and ductility of the Co-Cr-WC PM type alloys can be significantly improved by reducing their carbon contents below the levels usually used for Stellite 6 and 12 or PM 6 and 12 alloys while some have high hardness values, values that exceed 42 HRC. These carbon contents less than 1.0% are preferred and more preferably lower by .88%. Lower carbon contents below 0.65%, are expected to be too soft and are not able to withstand wear at the operating temperature of 649 ° C (1200 ° F). It is considered that due to the finer grain structure, finer carbide size and uniform distribution of carbides that is obtained in articles of the present alloy of Co-Cr-WC PM type of lower carbon content, articles of the present alloy they exhibit superior tenacity and strength than cast-type Co-Cr-WC PM alloys of higher carbon content. The same benefit of fine grain size will be seen in high temperature fatigue resistance of barrel and liner components, as well as other items. As seen in Figure 9, the toughness of the low carbon PM alloy, when annealed in solution and stale, exhibits a threefold increase over similarly treated PM 12 alloy and a 30% increase over PM 6 alloy. similarly treated, while providing substantially the same hardness. For this reason, it is concluded that articles of Co-Cr-WC type alloys of lower carbon content, such as alloy PM 0.08C, provide significant advantages as high stress components (such as nozzles, adapter rings, slip rings, non-return valves and other monolithic parts as well as barrel liners and lined barrels) in SSM 10 machines. This lower carbon content is also considered., and at least until descending to 0.65C, for the Co-Cr-W-C PM type alloys further reduces any dimensional changes in articles resulting from service at the relevant elevated temperatures. The response to aging and mechanical properties of the Co-Cr-W-C PM type alloys depends on the composition, particularly carbon content, and heat treatment. For these reasons, Co-Cr-WC PM type alloys in general are good candidates for the construction of SSM 10 machine. In particular, the modification of low carbon PM content containing 0.65% -0.88% carbon, is considered to be It is the best candidate for the SSM 10 machine components as a result of its significantly improved toughness, as well as good resistance to wear (hardness) and oxidation at elevated temperatures. To further substantiate the conclusions presented above, tests were performed on various components for various of the above materials. Components include drum liners, nozzles, piston rings, and slip rings. Regarding tests on casing liners, a cast alloy liner 12 put into service on a 400 ton Thixomolder ™ was found to have cracked after only 100 hours of service when processing semi-solid magnesium. Another alloy liner based on a 400 ton Thixomolder ™ is found to have fragmented in the seal area during seal maintenance after 320 service hours. Another barrel liner exhibits a fissure in the cast alloy liner 12 after 9 cycles (one hour of service) in a 400 ton magnesium processing unit. Suddenly, after 200,000 cycles, this crack propagates in the alloy barrel 718 to a length of 45.72 cm (18 inches) resulting in barrel failure and magnesium leak at high pressure. While the size change data in Figure 8 indicate less shrinkage for PM alloy 12, severe shrinkage occurred in a PM alloy liner 12 for a unit of 400 tons during the first hours of service, with a space of 0.381 cm (0.15 inch) on the seal and resulting in a dangerous magnesium leak. The cause of this shrinkage has not yet been determined. While extensive service time in an PM 0.8C alloy lining has yet to be fully completed, it is noted that the manufacture of a new barrel for a 600 ton unit proceeded without incident and without shrinkage. When testing nozzles, it was noted that standard alloy steel nozzles (e.g. DIN 1.2885 and 1.2888) oxidized rapidly and softened to < 10Rc. An alloy steel nozzle lost .3175 cm (an eighth of an inch) of its surface only after 500 hours of service in processing magnesium. This softening also leads to bending of the nozzle. An PM 0.8C alloy nozzle is found that was not oxidized or softened in service. Its thermal properties were better than in alloy alloys since it maintained at a better temperature and thus facilitated temperature control in the nozzle. With respect to pistons and slip rings, PM6 alloy piston rings were put into service and found to fracture due to low tenacity. This happened both during assembly and after only 200 loads in 4 hours. PM 0.8C alloy piston rings lasted 25,000 loads, without failure. A PM6 alloy slip ring failed at 75 loads under the high shock conditions seen in these parts. PM 0.8C alloy slip rings have been manufactured and based on the above results, the service life is expected to be 60,000 loads or more. Pistons and slip rings made of alloy steel have been additionally found to soften, leading to high wear in a few hours when processing semi-solid magnesium. This opened up a very significant derivation of sludge through the non-return valve. This in turn decreases the effectiveness of the high pressure and speed of the feed load and leads to poor filling of the parts and abnormal porosity in parts or parts. While the foregoing description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modifications, variations and changes without departing from the appropriate scope and fair meaning of the appended claims.

Claims (48)

1. CLAIMS 1. - An article based on cobalt of totally dense pulverulent metal that has not been pressed isostatically in hot and heat-treated, the article has high resistance to wear and corrosion to semi-solid metal and that is characterized by: C in an amount of 0.6 less than 1%; W in an amount of 3 to 5%; Cr in an amount of 25 to 30%; Co in a quantity mainly comprising the remainder of the article; and the article has a hardness greater than 42 HRC, a resistance to bending fracture greater than 331 ksi and substantial dimensional stability and stability of mechanical properties during exposure to temperature in a range of 316 to 816 ° C (600 to 1500 ° F) .
2. 2. The article according to claim 1, characterized in that C is an amount of 0.65 to 0.88%.
3. 3. The article according to claim 1, characterized in that C is an amount of 0.8%.
4. 4. The article according to claim 1, characterized in that W is in an amount of 0.4%.
5. 5. - The article according to claim 1, characterized in that Cr is in an amount of 25 to 28%.
6. 6. - The article according to claim 1, characterized in that N in an amount less than 0.1%.
7. 7. - The article according to claim 1, characterized in that N in an amount of 0.066%.
8. 8. - The article according to claim 1, further characterized by an amount of N and C that represents less than 1% in total.
9. 9. - The article according to claim 1, further characterized by an amount of N and C that represents more than 0.65% in total.
10. 10. The article according to claim 1, characterized in that the resistance to bending fracture is greater than 360 ksi.
11. 11. The article according to claim 1, characterized in that the article is heat-treated by aging.
12. 12. The article according to claim 1, characterized in that the article is heat-treated by annealing in solution.
13. 13. - The article according to claim 1, characterized in that the article is also heat-treated by aging.
14. 14. - The article according to claim 1, characterized in that the article has an average bending deflection greater than 0.254 cm (0.101 inch).
15. 15. The article according to claim 1, characterized in that the article exhibits a service life greater than 60,000 cycles at a temperature of 649 ° C (1200 ° F) when semi-solid magnesium injection is molded.
16. 16. - The article according to claim 1, characterized in that the hardness is greater than 44 RHC.
17. 17. The article according to claim 1, characterized in that the hardness is greater than 45 HRC.
18. 18. Method for manufacturing a fully dense Co-Cr-WC type article, powder metallurgy, wear and corrosion resistance, the method is characterized by the steps of: providing a composition of metallic powder constituents of C in an amount from 0. 65 to 0.88%, W in an amount of 3 to 5%, Cr in an amount of 27 to 30%, and Co in a quantity mainly comprising the remainder of the composition; consolidate the constituent composition by a hot isostatic pressure process; heat-treating the article and the article having a hardness greater than 42 HRC, a resistance to bending fracture greater than 330 ksi, and substantial dimensional stability and mechanical properties during exposure to temperatures in the range of 593 to 816 ° C (1100 a 1500 ° F).
19. 19. Manufacturing method according to claim 18, characterized in that C is provided in an amount of 0.8%.
20. 20. Manufacturing method according to claim 18, characterized in that the amount of 4% is provided.
21. 21. Manufacturing method according to claim 18, characterized in that Cr provides an amount of 27 to 28%.
22. 22. - Manufacturing method according to claim 18, characterized in that Cr is an amount of 27.8%.
23. 23. Manufacturing method according to claim 18, characterized in that the constituent composition is provided with N in an amount lower than 0.1%.
24. 24. - Manufacturing method according to claim 18, characterized in that the constituent composition is provided with N in an amount of 0.066%.
25. 25. Method of manufacturing according to claim 18, characterized in that the constituent composition is provided with N and C in an amount less than 1% in total.
26. 26. Method of manufacturing according to claim 18, characterized in that the constituent composition is provided with N and C in an amount greater than 0.65% in total.
27. 27. Method of manufacturing according to claim 18, characterized in that the heat treatment step includes annealing at a temperature greater than 1093 ° C (2000 ° F).
28. 28. Method of manufacturing according to claim 18, characterized in that the heat-treating step includes annealing at a temperature greater than 1149 ° C (2100 ° F).
29. 29. Method of manufacturing according to claim 18, characterized in that the heat treatment step includes aging a temperature of at least 593 ° C (1100 ° F) for 72 hours.
30. 30. - Manufacturing method according to claim 18, characterized in that the heat treatment step includes aging at a temperature of approximately 649 ° C (1200 ° F) for 72 hours.
31. 31.- Manufacturing method according to claim 18, characterized in that the method further comprises the step of preparing the constituent composition of powdered metal by a process of atomization with nitrogen.
32. 32. Method of manufacturing according to claim 31, characterized in that the preparation step includes dissolving nitrogen in the powdery metal.
33. 33. Method of manufacturing according to claim 18, characterized in that the hardness is greater than 44HRC.
34. 34. - Manufacturing method according to claim 18, characterized in that the hardness is greater than 45 HRC.
35. 35.- An apparatus for semi-solid processing of a metal, by heating the metal in a more solid liquid phase at a temperature in the range of 316 to 816 ° C (600 to 1500 ° F) while stirring the metal to inhibit the formation of dendrites in the semi-solid metal and injecting semi-solid metal into a mold to form a molded article, the apparatus is characterized by a component that is at least partially formed from a Co-Cr-WC type article of pulverulent metal completely dense, with the article defining a surface for contacting the semi-solid metal, the article has a constituent composition of C in an amount of 0.65 to 0.88%, W an amount of 3 to 5%, Cr in an amount of 27 to 30 %, and Co in a quantity mainly comprising a remainder of the composition, the article has a hardness greater than 42 HRC, a resistance to bending fracture greater than 330 ksi and substantial dimensional stability and mechanical properties during ex position at temperatures in the range of 593 to 816 ° C (1100 to 1500 ° F) and the article is formed at least to an almost net shape by a hot isostatic pressing process.
36. 36.- An apparatus according to claim 35, characterized in that C is in an amount of 0.8%.
37. 37.- An apparatus according to claim 35, characterized in that W is in an amount of 4%.
38. 38.- An apparatus according to claim 35, characterized in that Cr is in an amount of 27 to 28%.
39. 39. - An apparatus according to claim 35, characterized in that Cr is in an amount of 27.8%.
40. 40.- An apparatus according to claim 35, characterized in that the component is a heat-treated component.
41. 41. - An apparatus according to claim 35, characterized by the component annealed at a temperature greater than 1093 ° C (2000 ° F).
42. 42. - An apparatus according to claim 35, characterized in that the component is aged at a temperature of at least 593 ° C (1100 ° F) for 72 hours.
43. 43. - An apparatus according to claim 35, characterized in that the component is a nozzle.
44. 44. - An apparatus according to claim 35, characterized in that the component is a barrel.
45. 45.- An apparatus according to claim 35, characterized in that the component is a liner for a barrel.
46. 46.- An apparatus according to claim 35, characterized by the component is a piston ring.
47. 47. - An apparatus according to claim 35, characterized in that the component has a hardness greater than 44 HRC.
48. 48. An apparatus according to claim 35, characterized in that the component has a hardness greater than 45 HRC.