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%
  • C22C33/0285—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 Cr, Co, or Ni having a minimum content higher than 5%
• • 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
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F5/007—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of moulds
• • 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
  • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
  • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
• • 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
  • C22C33/0207—Using a mixture of prealloyed powders or a master alloy
• • 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

Definitions

• the invention relates to a method of producing a steel moulding using a sinter powder with a base of iron which contains at least one non-ferrous metal selected from a group comprising manganese, chromium, silicium, molybdenum, cobalt, vanadium, boron, beryllium, nickel and aluminium, the rest being iron with the inevitable impurities resulting from the manufacturing process, comprising the steps of preparing the sinter powder, compacting the sinter powder to form a green compact in a mould, sintering the green compact under a reducing atmosphere and then cooling and hardening it, as well as a sintered moulding with a moulding body, at least part of which is made from a sinter powder with a base or iron containing at least one non-ferrous metal selected from a group comprising manganese, chromium, silicium, molybdenum, cobalt, vanadium, boron, beryllium, nickel and aluminium, the rest being iron
• patent specification DE 11 2004 001 875 T5 proposes a method of producing a thin individual component, comprising the steps of heating the thin individual component, followed by subjecting the thin individual component to a quenching and isothermal process using pressing moulds as a means of cooling the thin individual component. This is preferably used to produce steel components containing at least 0.4% by weight of carbon. The isothermal conditions cause a reaction which converts the pattern structure into a bainitic structure.
• the steel used is an S53C steel containing nickel and a steel based on a composition with an improved quenching property and which enables adequate hardness to be obtained by slow cooling, and this steel contains 0.7% by weight of carbon, 1% by weight silicium, 0.6% by weight manganese, 1.5% by weight chromium and 0.3% by weight molybdenum.
• This DE-T5 also describes a process of producing martensite based on continuous quenching, but which is followed by a step of heating at 150° C. for 120 minutes.
• the bainite structure is preferred because shorter quenching is needed according to the explanations given in this DE-T5, which results in the required toughness without having to run a heating step and which prevents any secular change in dimension.
• the disadvantage of the method described in the DE-T5 is that either the pressing moulds have to be air-cooled for a longer period once the components have hardened or it is necessary to heat the actual mould, thereby incurring extra expense to produce the mould and work with it.
• the proportion of non-ferrous metals in the sinter powder is selected from a range with a lower limit of 1% by weight and an upper limit of 60% by weight and the sinter powder is sintered almost completely to an austenitic structure, and hardening take place by subjecting the steel moulding to mechanical pressure to at least partially transform it from an austenitic to a martensitic structure, and, independently of this by the sintered moulding, for which the total proportion of the at least one non-ferrous metal in the sinter powder is selected from a range with a lower limit of 1% by weight and an upper limit of 60% by weight, and the moulding body has a martensitic structure at least in the surface or in the regions close to the surface or in the surface regions obtained by a reaction induced by high pressure.
• the process of producing high-precision sintered components normally includes a finishing step which does not involve the removal of material, for example calibration. To this end, these sintered components are placed in a calibrating die and processed under pressure to obtain the final shape.
• the method proposed by the invention offers an advantage in this respect in that surface hardening takes place at the same time as this mechanical transformation during this calibration process, thereby obviating the need for an additional hardening step in the processing sequence. It is also of advantage if the component is additionally subjected to temperature during the hardening step, thereby preventing the undesired occurrence of re-crystallisation. An additional cost advantage can also be obtained as a result due to the shorter cycle times on the one hand and due to reduced processing at temperature on the other hand.
• the total proportion of the at least one non-ferrous metal in the iron-based sinter powder may also be selected from a range with a lower limit of 5% by weight and an upper limit of 55% by weight or may be selected from a range with a lower limit of 18% by weight and an upper limit of 27% by weight.
• mechanical load may be applied by operating at a pressure corresponding to the range of ⁇ 10% of the pressure threshold and the maximum resistance to pressure of the respective material (measured in accordance with DIN 50106) and/or at a temperature selected from a range with a lower limit of 20° C. (room temperature) and an upper limit of 180° C. if the sintered mouldings are subjected to pressure in the cold state, or which is selected from a range with a lower limit of 180° C. and an upper limit of 550° C. if the sintered mouldings are subjected to pressure accompanied by heat. This further reduces the cycle time and thus increases productivity.
• the temperature may also be specifically selected from a range with a lower limit of 40° C. and an upper limit of 150° C. or a lower limit of 60° C. and an upper limit of 100° C.
• the temperature may be selected from a range with a lower limit of 200° C. and an upper limit of 500° C. or from a range with a lower limit of 250° C. and an upper limit of 350° C.
• a carburizing gas is added to the reducing atmosphere for the sintering process or a carburizing gas is used as the reducing atmosphere. This enables the carbon content in at least the superficial regions of the green compact to be increased during sintering, which is conducive to the subsequent formation of martensite.
• pre-sintering which takes place at a temperature below the temperature of the second sintering step, followed by what is referred to as high-temperature sintering.
• pre-sintering which takes place at a temperature below the temperature of the second sintering step
• high-temperature sintering This enables higher carbon contents to be obtained without the risk of brittle cracking during the hardening reaction, thereby generally enabling greater strength to be imparted to the sintered component.
• the temperature applied during pre-sintering may be selected from a range with a lower limit of 60% and an upper limit of 80% of the temperature of the second sintering step for example.
• pre-sintering may be run at a temperature selected from a range with a lower limit of 600° C. and an upper limit of 1000° C. and the high-temperature sintering may be run at a temperature selected from a range with a lower limit of 1100° C. and an upper limit of 1450° C.
• the steel moulding is produced with a density of max. 7.3 g/cm 3 , at least at the core. This enables the properties of the steel moulding to be optimised in that there is a certain residual elasticity at the core, whilst an appropriate mechanical strength is imparted to superficial areas due to the hardening reaction. Furthermore, the weight of the steel moulding can be reduced. By superficial regions is meant those regions which extend to a component depth of 0.5 mm.
• the proportion of graphite may also be selected from a range with a lower limit of 0.1% by weight and an upper limit of 3% by weight or from a range with a lower limit of 0.5% by weight and an upper limit of 2% by weight.
• the proportion of pressing agent may be specifically selected so that it is also up to a max. 2.5% by weight or up to a max. 1.5% by weight and the proportion of binding agent may be up to a max. of 0.75% by weight or a max. 0.5% by weight.
• the method may be operated in such a way that an additional sinter powder is placed in the mould and this is compacted jointly with the iron-based sinter powder, or, in another variant of the method, a semi-finished moulding is produced in a first step, this is placed in the pressing mould and at least certain areas of it are coated with the steel powder with an iron base, e.g.
• a semi-finished moulding is made from the iron-based sinter powder in a first step and the semi-finished moulding is joined to another finished moulding made from a sinter powder that is different from the sinter powder of the first semi-finished moulding in another step.
• those surfaces which will be subjected to higher loads in the application for which the sintered component will be used can be selectively coated with the iron-based sinter powder and then hardened by a martensite reaction, in other words specific properties can be obtained to suit the intended application.
• the invention relates to the manufacture of components of sintered steel made from an austenitic material which forms martensite during moulding and thus hardens.
• the surface may be compacted or alternatively, components which do not undergo any surface compaction can be produced, or the surface density may also be reduced. By preference, however, the surface is compacted.
• the method proposed by the invention offers new possibilities for moulding high-precision sintered components which are able to withstand high stress. To this end, there are several variants of the method used to produce the compact.
• whole components may be pressed from sinter powder with a base of iron.
• the pressing die may be filled with at least two or more different sinter powder mixtures which are then jointly compacted or a component composite is made by a multi-stage powder pressing process, whereby a semi-finished component is pressed, and optionally also sintered, from a sinter powder that is different from the iron-based sinter powder and the iron-based sinter powder is pressed onto it in another pressing step, after which they are sintered jointly.
• Another option for producing component composites is to shape a green compact to close to the final contour from another sinter powder by pressing the powder in a mould and optionally also sintering it, and then applying the sinter powder with an iron base to at least those regions of the steel component or sintered moulding which will be subjected to higher loads during the service life of the component by coating or spraying methods known from the prior art, after which this coated and optionally sintered green compact is then sintered. It goes without out saying that in this case, it would also be possible to coat the entire surface of the green compact with the iron-based powder. Instead of using a green compact shaped close to the final contour, however, it would also be possible to produce a semi-finished part from a solid material which is not manufactured by a sintering process but is made using a casting or punching process.
• Another option would be to join two or more components pressed in separate work steps using a known method, e.g. sinter joining or sintering and brazing or similar.
• sinter joining it is possible to join two green compacts or two sintered parts to one another or to join one sintered component to a green compact, in which case it would also be possible to join more than two parts and the enumeration of options for two parts is then adapted accordingly.
• at least one of the two or more parts to be joined is at least partially contains the sinter powder with an iron base or is made from it.
• the other sinter powder may also be a sinter powder with a base of iron but if this is the case, it is based on a different composition.
• a sinter powder known from the prior art as the other sinter powder for example with a base of Cu, e.g. bronze.
• a structure is produced in some regions of the iron-based sinter powder which becomes harder under mechanical load.
• the ability to harden is achieved due to the fact that a soft, primarily austenitic structure is obtained after the sintering process, which then reacts when subjected to mechanical load, in particular pressure, and the reaction brings about a transformation to a martensitic structure. This structural transformation results in hardening in the moulded region.
• Moulding may be achieved in various ways, for example by cross-compaction (transverse rollers) or by axial compaction (axial rollers) or by a multi-stage final pressing (e.g. calibration).
• iron-based powder mixtures may be used with a total of up to 10% by weight of metallic non-ferrous alloying elements, optionally up to 5% by weight of graphite and/or optionally up to 3% by weight of pressing agents and optionally up to 0.5% by weight of organic binders.
• These mixtures are produced in a conventional manner from pure iron powder or pre-alloyed or alloyed-on iron powders serving as the base material, to which alloying elements and optionally other agents are added.
• a so-called master mixture in a highly concentrated form is pre-mixed, possibly at a temperature and/or using solvents, and then admixed with iron powder or individual elements are mixed in by adding them directly to the iron powder.
• the binding agents used may include resins, silanes, oils, polymers or adhesives.
• the pressing agents which may be used are waxes, stearates, silanes, amides and polymers, for example.
• the properties of such sintered components made from an iron-based powder can be improved accordingly, in a manner already known from the prior art.
• an alloy with molybdenum will prevent brittleness during tempering in the case of chromium steels.
• the hardening capacity and toughness are improved as a result.
• resistance to creep at higher temperatures can be increased.
• Adding nickel will improve moulding ability under cold conditions.
• Manganese can increase tensile strength and yield strength.
• Silicium will prevent the precipitation of cementite from the martensite during tempering.
• the proportion of non-ferrous alloying elements may also be selected from a range with a lower limit of 0.2% by weight and an upper limit of 8% by weight, in particular from a range with a lower limit of 1% by weight and an upper limit of 6% by weight.
• the proportion of copper used may be selected from a range with a lower limit of 0% by weight and an upper limit of 6% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 4% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 2% by weight.
• the proportion of chromium may be selected from a range with a lower limit of 0% by weight and an upper limit of 5% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 4% by weight, preferably from a range with an upper limit of 0.2% by weight and an upper limit of 3% by weight.
• the proportion of nickel may be selected from a range with a lower limit of 0% by weight and an upper limit of 8% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 4% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 2% by weight.
• the proportion of manganese may be selected from a range with a lower limit of 0% by weight and an upper limit of 10% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 5% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 2% by weight.
• the proportion of molybdenum may be selected from a range with a lower limit of 0% by weight and an upper limit of 3% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 1.5% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 0.85% by weight.
• the proportion of silicium may be selected from a range with a lower limit of 0% by weight and an upper limit of 5% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 2% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 0.5% by weight.
• the proportion of vanadium may be selected from a range with a lower limit of 0% by weight and an upper limit of 8% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 2% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 0.5% by weight.
• the proportion of graphite may also be selected from a range with a lower limit of 0% by weight and an upper limit of 2% by weight, in particular from a range with a lower limit of 0.1% by weight and an upper limit of 1.5% by weight, preferably from a range with a lower limit of 0.2% by weight and an upper limit of 0.8% by weight.
• any other standard compositions used in the sintering industry may also be used.
• the iron-based sinter powder which hardens during moulding or the corresponding alloys are mixed using conventional mixing techniques.
• the properties of the highly alloyed powder in particular the fact that the materials are substances which are very hard and not readily compressible or not compressible at all.
• aqueous, gaseous or oil-sprayed iron-based powders in which case higher contents of one or more elements from the group comprising Mn, Cr, Si, Mo, Co, V, B, Be, Ni and Al are added.
• the total content of this non-ferrous metal in the sinter powder with a base of iron may also be specifically selected from a range with a lower limit of 15% by weight and an upper limit of 55% by weight, in particular from a range with a lower limit of 20% by weight and an upper limit of 50% by weight or from a range with a lower limit of 25% by weight and an upper limit of 40% by weight.
• the proportion of manganese in the sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 35% by weight, in particular from a range with a lower limit of 5% by weight and an upper limit of 25% by weight or from a range with a lower limit of 10% by weight and an upper limit of 15% by weight.
• the proportion of chromium in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 20% by weight, in particular from a range with a lower limit of 4% by weight and an upper limit of 15% by weight or from a range with a lower limit of 7% by weight and an upper limit of 12% by weight.
• the proportion of silicium in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 10% by weight, in particular from a range with a lower limit of 1% by weight and an upper limit of 8% by weight or from a range with a lower limit of 3% by weight and an upper limit of 6% by weight.
• the proportion of molybdenum in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 10% by weight, in particular from a range with a lower limit of 2% by weight and an upper limit of 8% by weight or from a range with a lower limit of 4% by weight and an upper limit of 6% by weight.
• the proportion of cobalt in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 10% by weight, in particular from a range with a lower limit of 1% by weight and an upper limit of 7% by weight or from a range with a lower limit of 2.5% by weight and an upper limit of 5% by weight.
• the proportion of vanadium in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 10% by weight, in particular from a range with a lower limit of 2.4% by weight and an upper limit of 8.1% by weight or from a range with a lower limit of 3.2% by weight and an upper limit of 6.5% by weight.
• the proportion of boron in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 5% by weight, in particular from a range with a lower limit of 1% by weight and an upper limit of 4% by weight or from a range with a lower limit of 2% by weight and an upper limit of 3 by weight.
• the proportion of beryllium in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 5% by weight, in particular from a range with a lower limit of 1.5% by weight and an upper limit of 4.3% by weight or from a range with a lower limit of 2.3% by weight and an upper limit of 3.8% by weight.
• the proportion of nickel in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 35% by weight, in particular from a range with a lower limit of 5% by weight and an upper limit of 25% by weight or from a range with a lower limit of 10% by weight and an upper limit of 15% by weight.
• the proportion of aluminium in the finished sinter powder mixture with a base of iron when ready for moulding may be selected from a range with a lower limit of 0% by weight and an upper limit of 10% by weight, in particular from a range with a lower limit of 2% by weight and an upper limit of 7.8% by weight or from a range with a lower limit of 3.9% by weight and an upper limit of 6.2% by weight.
• mixtures are made up and homogenised using appropriate mixing methods known from powder metallurgy. It is also possible to use techniques known from the prior art for processing binding agents or the known process of diffusion alloying used to obtain a uniform distribution, especially in the case of fine powders.
• the iron powder mixtures produced by the methods described above are compacted and shaped by means of coaxial pressing methods. In this respect, care should be taken to ensure that allowance is already made for the changes in shape and design which occur during the process of producing the pressing die. Depending on the pouring density and theoretical density of the powder mixtures, pressing pressures of 600 Mpa to 1200 Mpa are used.
• the compacts obtained by these different methods are the starting point for the subsequent pressing steps.
• the compacts may also be pre-sintered using a heat treatment involving an atmosphere based on gases which produce at least partial carburization.
• reducing atmospheres are obtained using nitrogen-hydrogen mixtures with hydrogen in a proportion of up to 50% by volume.
• the proportion of hydrogen may also be 0% by vol to 100% by vol or 1% by vol to 60% by vol or 2% by vol to 40% by vol.
• Carburizing gases (endo-gas, methane, propane and similar) may optionally also be used.
• the temperature for pre-sintering may be between 600° C. and 1050° C., for example, and the pre-sintering time may be between 10 minutes and 2 hours for example.
• Pre-sintering causes organic binding agents and lubricants to be burned off and makes it easier to produce a bond between the particles.
• a lower hardness level can be achieved due to incomplete dissolution of individual alloying elements.
• the hardness of the sintered component may be adjusted so that a high degree of moulding is obtained during the subsequent compaction process (calibration) with an excess of up to 30%. Especially in the case where hardness is less than 140 HB 2.5/62.5, a surprisingly high degree of moulding ability was observed.
• Alloying elements involving oxygen in particular are difficult to process during pre-sintering.
• a massive build-up of oxygen can be at least largely prevented during pre-sintering so that this does not have a negative effect on moulding ability.
• Cr—Mo pre-alloyed powders are also easier to calibrate.
• the powder grains are sintered to only a limited degree, resulting in a somewhat weak sintered bond.
• the graphite is only incompletely diffused into the iron matrix material.
• the temperatures applied during the actual sintering process are typically between 1100° C. and 1350° C. or higher depending on the alloying system used and the sintering time is between 10 minutes and 2 hours, in particular between 29 minutes and 60 minutes.
• the sintered component is cooled, to which end it is preferable to set a cooling rate selected from a range with a lower limit of 10° C./minute and an upper limit of 250° C./minute, in particular selected from a range with a lower limit of 30° C./minute and an upper limit of 200° C./minute, for example selected from a range with a lower limit of 50° C./minute and an upper limit of 150° C./minute.
• the moulding process is set up so that the predominantly austenitic structure (present in at least the peripheral regions) is transformed at least partially to produce martensite, preferably up to at least 99%.
• the mechanically applied pressure may be a pressure selected from one of the ranges specified above.
• Moulding may optionally also take place at an increased temperature.
• the temperature for cold or warm moulding may be selected from the ranges specified above.
• the sintered component may be heated prior to moulding for this purpose and/or may be processed using a tempered mould.
• Another option is one whereby the sintered component is not cooled to room temperature after moulding and instead is moulded at this temperature, in which case there is no need for additional tempering of the component or mould.
• heat treatment with a view to further optimising the properties (e.g. baking or tempering).
• the components are often thermally de-greased beforehand. If sinter-hardened materials are used for component composites, a non-carburizing process may be used, such as inductive hardening.
• Composition of the sinter powder 18% by weight Mn+3.5% Si+2.5% by weight Al+0.5% by weight V+0.3% by weight B+1% by weight pressing agent, the rest being Fe
• composition of the reducing atmosphere N2/H2 (60% by vol/40% by vol)
• the finished sintered gear exhibited better durability properties than sintered gears with the same geometry made from conventional sinter powder and dynamically hardened following surface compaction.
• a coating of sinter powder which can be hardened during moulding was sprayed onto the functional surface of a compact made from conventional sinter powder and a composite component produced by sintering which was then partially compacted and thus moulded and hardened.
• Composition of the sinter powder for the base component 2% by weight Cu+0.7% by weight C+0.8% by weight pressing agent, the rest being Fe
• composition of the sinter powder for the functional surface 14% by weight Mn+5% by weight Ni+3% by weight Al+3% by weight Si+6% by weight pressing agent+2% by weight binding agent, the rest being Fe
• Coating density of the sinter powder for the functional surface after sintering 0.5 mm
• the finished composite sprocket wheel exhibited significantly better wear resistance than conventionally produced sprocket wheels.

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• 2009
  • 2009-02-05 AT AT0020009A patent/AT507836B1/de not_active IP Right Cessation
• 2010
  • 2010-01-25 DE DE102010000186A patent/DE102010000186A1/de not_active Withdrawn
  • 2010-01-29 FR FR1050641A patent/FR2941637A1/fr active Pending
  • 2010-01-29 US US12/657,921 patent/US20100196188A1/en not_active Abandoned
  • 2010-02-05 CN CN201010113651A patent/CN101829783A/zh active Pending

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