Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
  • C22C33/0292—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with more than 5% preformed carbides, nitrides or borides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J9/00—Piston-rings, e.g. non-metallic piston-rings, seats therefor; Ring sealings of similar construction
  • F16J9/26—Piston-rings, e.g. non-metallic piston-rings, seats therefor; Ring sealings of similar construction characterised by the use of particular materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2241/00—Treatments in a special environment
  • C21D2241/01—Treatments in a special environment under pressure
  • C21D2241/02—Hot isostatic pressing
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races

Definitions

• the present invention relates to a metallic composite material that is particularly intended for piston rings, and to a method of manufacturing said metal matrix-composite material, according to which a composite powder is produced by mixing two different powder materials, whereupon said powder mixture is exposed to pressure and heat .
• the first powder material is a metal powder
• the second powder material is a ceramics powder for producing a material, which at least partly exhibit a network of ceramics material throughout the matrix structure.
• the invention also concerns a piston ring, particularly a piston ring intended for marine diesel engines .
• piston rings that are intended for use m for instance marine diesel engines, particularly as concerns strength, antI-corrosive properties, wear strength, and material resilience.
• the piston ring is intended to abut on the one hand against an associated piston groove, on the other against an engine cylinder-bore . Consequently, the ring must be wear-resistant, particularly at the interface towards the cylinder bore, where high friction is generated when the engine is m operation. It therefore also must: Dossess an inherent tension or resilience, whereby the piston ring will constantly be forced outwards, into abutment against the cylinder bore.
• the piston ring is urged with considerable force radially outwards, into abutment against the cylinder bore, with consequential increase of stress.
• the piston ring is also exposed to high temperatures, to considerable temperature differences, and to the effects of a highly corrosive environment.
• the piston ring In order to withstand the effects of these stress-inducing causes, the piston ring therefore also must exhibit considerable wear strength, ductility and toughness.
• ductility is to be understood herein the maximum possible deformation of the material before dislocations occur and cracking begins.
• toughness is to be understood herein the maximum possible deformation of the material from the instance of incipient cracking until a fracture occurs m the material.
• piston rings generally are manufactured from a cast-iron blank, which meets the requirements imposed on the material as regards strength and resilience but not on wear resistance on the surface thereof that faces the cylinder bore. Cast iron does not either possess the required toughness.
• a cast-iron piston ring blank therefore usually is provided with a wear-resistant wear layer on the surfaces most exposed to wear.
• the wear layer which usually is formed by a chromium-compound material, generally is applied to the piston ring blank in an electrolysis process as described e.g. m EP Patent Specification 0 668 375.
• the piston ring blank (substrate) is given a hard chromium layer m an electrolysis process .
• the object of the present invention is to provide a material, particularly intended for piston rings, that meets the requirements necessary m piston rings as regards wear resistance, resilience, anti-corrosiveness , hardness, toughness, and ductility.
• Another object of the invention is to provide a method of producing the material, and a piston ring, which does not suffer from the above drawbacks found in the prior art .
• the first object of the present invention is achieved by means of a metallic composite material as described in the introduction, the pressure and heat treatments of the production method being simultaneous and the metallic powder materials, after mixture of the two powders, including from 2.1 to 2.8 percent by weight of C.
• the second object of the present invention is achieved by means of a method as set forth in the introduction, according to which method the pressure and heat treatments are simultaneous and are carried out until the austenitic temperature has been reached, whereupon the material is cooled to form a martensitic matrix structure, followed by annealing, when the material has formed a martensitic structure.
• the composite powder comprises from 2.1 to 2.8 percent by weight of C.
• the third object of the present invention is to provide a piston ring manufactured from such a material .
• the object is to produce a steel that is able to withstand severe abrasion, a capacity necessary in e.g. tools that are used to crush stone.
• the disclosed material is formed essentially from two components, the first one being an austenitic powder, more precisely a so called Hadfield manganese steel powder, and the second one an iron-based, essentially martensitic powder which, when transformed, produces segregated particles in the material .
• the martensitic powder comprises a total of at least 0.8 percent by weight of C and N, and at least 8% of alloying elements which form the segregated particles in the finished material .
• a material is obtained having a microstructure consisting of a ductile austenitic steel in combination with a martensitic structure comprising hard segregated particles.
• the martensitic structure and the associated segregated particles are the cause of the abrasive effect aimed at for stone-crushing applications.
• the austenitic structure is tougher than the martensitic and essentially forms a matrix around the harder and more brittle martensitic areas. In this way the toughness and the ductility of the material are increased, and cracking of the material is prevented.
• a material of the kind described in EP-0 785 289 is, however, too abrasive to be used in piston rings.
• a piston ring made from such a material would, in operation of the engine, risk tearing of the associated cylinder-lining material.
• the ductility and the toughness are not sufficient to make the material adequate for use for piston rings and consequently, hard particles would risk being torn away from the surface of the ring, which would increase further the abrasive friction against the rest of the ring when the engine is in operation.
• the ceramics material is found to form a protective network around the steel matrix.
• the material thus produced has been found to possess satisfactory abrasiveness , which is required from cutting tools but which also makes the material unfit for use m the manufacture of piston rings.
• the material does not possess sufficient ductility to serve as a material for a piston ring used in e.g. diesel engines.
• the present invention therefore suggests a metallic powder material, which is particularly intended for piston rings and which is produced by mixing two different powder materials and transforming said materials into an essentially compact material by means of pressure and heat, one of said powders being a metallic powder and the other one a ceramics powder chosen to ensure that after transformation of the material a ceramics -material network completely or partly extends through a metal matrix likewise formed in the transformation.
• the pressure and heat treatments are simultaneous and after mixing of the two powders, the metallic powder material contains from 2.1 to 2.8 percent by weight of C.
• the transformation of this material comprises austenisation, cooling to form a martensitic phase, and annealing.
• the material has a microstructure similar to that of an annealed martensitic steel structure through which extends a ceramics-material network.
• the piston ring when properly lubricated, does not wear out piston grooves or lining materials.
• the hardness of the material is of a nature making it superfluous to provide the piston ring with further external wear layers.
• the piston ring may be manufactured throughout from one single material as disclosed above .
• the finally formed compact material m accordance with the invention has the structure of an annealed martensite with the ceramics material forming a cohesive/bonding network structure m the martensite.
• the martensite which is hard but brittle, thus is protected by the ceramics-material network, which acts as reinforcement of the martensite.
• the discrete ceramics-material particles form hard, in themselves abrasive particles.
• the ceramics-material to be chosen as a reinforcement material should exhibit tendencies to form microstructures in the form of networks and useful diffusion with the matrix without the formation of new powder-material phases caused by chemical reactions.
• the reinforcing ceramics material consists of a carbide material, and preferably of Cr 3 C 2 .
• This material has proved to possess suitable properties inasmuch as it forms networks in the material in the HIP process but does not subsequently diffuse further in the material. In this manner a network is formed throughout the entire material and not only e.g. on one surface thereof. It is likely that this affects also the elasticity and the strength of the material.
• Another suitable ceramics material is Cr 2 C 3 , which possesses the advantage of being thermally stable.
• the metal powder could consist of e.g. a hard chrome steel .
• the powder materials obtained when the two powders are mixed comprise the following substances in the proportions indicated, viz.: 2.1- 2.8 percent by weight of C, 0.7-1 percent by weight of Si, 0.1-0.5 percent by weight of Mn, 20-24 percent by weight of Cr, 1-3 percent by weight of Mo, and 2-4 percent by weight of V.
• the inventive material preferably exhibits a
• the elasticity module preferably amounts to at least 200 000 N/mm2.
• the tensile strength advantageously exceeds 700 N/mm2 , and preferably exceeds 1 100 N/mm2.
• the elongation should exceed
• the invention also provides a method of producing a metal matrix composite material of the kind referred, according to which a composite powder is formed by mixing two different powder materials, whereafter the powder mixture thus obtained is subjected to pressure and heat until it reaches an austenitic temperature, and then it is cooled to form a martensitic matrix structure.
• the first material powder is a metal powder
• the second material powder is a ceramics powder
• the material is annealed to form a material that completely or partly exhibits a network of a ceramics material throughout the essentially martensitic matrix structure.
• the pressure and heat treatments are effected simultaneously, and the metallic powder material resulting from the mixture of the two powders contains 2.1-2.8 percent by weight of C.
• the treatment involving subjecting the material simultaneously to pressure and heat employs the so called HIP (Hot Isostatic Pressing) technique.
• HIP Het Isostatic Pressing
• the material is annealed to reduce the hardness to a desired value.
• Annealing advantageously is performed by repetition of the annealing process at least once.
• the material in accordance with the invention likewise makes possible the manufacture of a serviceable piston ring in accordance with the invention, wherein the material is a metallic composite material, which forms a steel matrix and a reinforcement structure from a reinforcement material .
• a piston ring of this nature meets the demands on strength, anti- corrosiveness, wear resistance and resilience, thus obviating the problems caused by separation on or wear of a separate wear layer.
• the material is not so hard that, when the piston cylinder system is lubricated, it damages the piston groove or the cylinder bore.
• Fig 1 is a diagram showing the rate of wear relative to pressure-exposure in tests of a previously known material, vis-a-vis an alloy known as tark alloy.
• Fig 2 is a diagram showing the rate of wear relative to pressure-exposure in tests of a material in accordance with one embodiment of the invention vis-a-vis an alloy known as tark alloy.
• Fig 3a is an OM picture shown in 25x magnification, of a material in accordance with the invention that has been etched to make the microstructure appear more clearly.
• Fig 3b is an OM picture shown in 500x magnification, of the material in Fig 3a.
• Fig 3c is an OM picture shown in 1300x magnification, of the material in Fig 3a.
• Fig 3d is an OM picture shown in 3000x magnification, of the material of Fig 3a.
• Fig 4 shown one embodiment of a piston ring in accordance with the invention.
• Fig 5 is a partial view of two piston rings fitted into their respective piston groove in a piston-cylinder unit.
• a material is produced using the HIP method, which material comprises a high-chrome steel matrix reinforced with 1-10 percent by weight of Cr 3 C 2 .
• the grain size of Cr 3 C 2 is 20-100 micrometers.
• the matrix material is used a powder material comprising the following substances in the proportions indicated, viz.: 1.7 percent by weight of C, 0.8 percent by weight of Si, 0.3 percent by weight of Mn, 18 percent by weight of Cr, 1.0 percent by weight of Mo, 3.0 percent by weight of V, the balance of the material essentially consisting of Fe .
• the powder material used should be of a very pure quality.
• Cr 3 C 2 was chosen as the reinforcement material on account of its tendency to form microstructures in the form of networks and its useful diffusion with the matrix without new phases of the powder materials being formed through chemical reactions.
• the mixture of metal and composite powders was effected in a conventional Turbula mixer, initially in a dry state and subsequently using a conventional tacking agent, in order to prevent particles having different densities from separating during the handling of the powder mixture. After mixing, the powders were put in a steel container and were dried for 18 hours. The containers were sealed, evacuated and introduced into conventional HIP equipment for transformation.
• the transformation parameters were the following, viz.: a temperature of 1180-1215°C, a pressure of 100 MPa, and a heat-holding period of 3 hours.
• the HIP-treatment was followed by a heat treatment involving slow heating up to 850°C for 45 minutes and quick heating to 1050°C for 40 minutes, followed by rapid cooling to 500°C and finally cooling in air at room temperature. After this procedure, the material exhibit an essentially martensitic structure, with a comparatively high degree of hardness.
• the annealing process consisted of double annealing, at 600°C and thereafter at 650°C, each for a length of 2 hours. The annealing process serves to reduce the abrasiveness and hardness of the material to values that make the material suitable for piston rings.
• the resulting material possesses excellent workability and resistance against wear and abrasive wear, and it possesses excellent strength in combination with high elasticity.
• the Brinell hardness is between 270 and 350 and the elasticity module is 200 kN/mm2.
• the tensile strength is less that of the non-annealed material but still exceeds
• the material exhibits sufficient toughness to be used for the manufacture of piston rings. If the same procedure is used with 10 percent by weight of Cr 3 C 2 instead of 4 percent, a Brinell hardness of 360-440 is obtained, and an elasticity module of 200 kN/mm2 , a tensile strength of mores than 1100 N/mm2 , and a breaking strength exceeding 1%. Also this material is useable for piston rings.
• Figs 1 and 2 show the unique properties of the inventive material as found in another comparison.
• the diagrams of Figs 1 and 2 show the results of the rate of pressure- induced wear found in tests carried out vis-a-vis so called tark alloy, which is a commonly used cylinder-bore material.
• Fig 1 shows a commercially available cast material.
• the rate of wear is about 100 mm/lOOOkm (totally) at pressures between 5 and 10 MPa.
• the rate of wear rises drastically, causing scuffing of the material, and the figure shows the functional-strength limit of the material .
• the corresponding diagram with respect to the inventive material shows a completely different pattern.
• the rate of wear increases very slowly, and not even at a pressure of 22 MPa does it attain the lOOmm/lOOOkm (totally) that the cast material exhibits at pressures between 5 and 10 MPa. There is no scuffing.
• Fig 3a is an OM picture, shown in a 25 times magnification, of an inventive material, which has been etched to make the microstructure of the material appear more clearly.
• the ceramics-material particles are clearly visible against the background of a metal matrix. These particles contribute strongly to the excellent wear resistance of the material .
• Fig 3c shows the same material as Fig 3a but magnified 1300 times. Also from this figure does appear the bonding ceramics-material network, which extends at least partly through the metal matrix. The ceramics-material network contributes to retaining the larger ceramics-material particles, preventing the latter from separating from the matrix and in consequence thereof form discrete, strongly abrasive particles.
• Fig 3d finally, is shown the ceramics- material network of Fig 3c, magnified 3000 times. This figure also shows the structure of the small particles of the ceramics network that have aggregated during the manufacturing process so as to form a network.
• Figs 4 and 5 are part of the present description in order to explain in more detail the appearance and function of the piston ring proper.
• Figs 4 and 5 show a piston ring (1) intended for marine diesel engines of a conventional nature.
• the shape of the piston ring (1) is not completely round, and the ring (1) proper is provided with a through-slit (2) to allow the ring to be compressed when being mounted in the associated piston groove
• the piston ring (1) When the piston ring (1) is received in the piston groove (3) its inherent resilience will force it slightly outwards, into abutment against the cylinder bore (5) . During operation of the diesel engine, the piston ring (1) is exposed to wear primarily at the surface thereof that abuts against the cylinder bore (5) but also at the surfaces (4) that face the piston groove (3) .
• the present invention is not limited to the embodiment described herein.
• further substances may be added to the powder material in order to modify its properties in some respect .
• a lubricant could for instance be added to the powder mixture in order to produce a material that is suitable for the manufacture of a so called self-lubricating ring.
• the ceramics material used as a reinforcing material could be e.g. Al 2 0 3 , Cr 2 0 3 or any other ceramics material possessing the necessary network- forming properties.
• Different ceramics materials could also be used simultaneously, such as for example one ceramics material could make up the larger- size granules having the abrasive effect whereas another ceramics material could be the one that forms the essentially thinner network structure.
• these ceramics materials should form a stable network capable of reinforcing the martensite structure and of retaining the larger ceramics-material particles.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Pistons, Piston Rings, And Cylinders (AREA)

Applications Claiming Priority (3)

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• 1999
  • 1999-05-04 SE SE9901593A patent/SE514167C2/sv not_active IP Right Cessation
• 2000
  • 2000-05-02 AU AU44470/00A patent/AU4447000A/en not_active Abandoned
  • 2000-05-02 WO PCT/SE2000/000845 patent/WO2000066797A1/en not_active Ceased
  • 2000-05-02 JP JP2000615419A patent/JP2002543287A/ja active Pending
  • 2000-05-02 EP EP00925843A patent/EP1206586A1/de not_active Withdrawn

Non-Patent Citations (1)

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