Classifications

• • 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
  • B22F3/02—Compacting only
• • 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
  • C22C33/0264—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements the maximum content of each alloying element not exceeding 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
  • B22F1/105—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing inorganic lubricating or binding agents, e.g. metal salts
• • 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
  • B22F3/10—Sintering only
• • 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
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • 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

Definitions

• the present invention relates to an iron-based powder mixture including iron-based power mixed with a lubricant, and alloying powder as needed.
• the iron-based powder mixture of the invention is suitable for powder metallurgy, and particularly suitable for compaction in a temperature range from normal temperature to less than 100°C.
• the invention further relates to a powder mixture for powder metallurgy, which is preferable for manufacturing of high-strength sintered parts for automobiles.
• the invention relates to a method of manufacturing an iron-based compacted body using the iron-based powder mixture as a material, and a method of manufacturing an iron-based power sintered-body using the iron-based compacted body as a material.
• the iron-based powder mixture for powder metallurgy is typically manufactured in a way that iron-based powder is added with a lubricant and alloying powder and mixed, and furthermore added with powder of free machining additives and mixed as needed.
• the iron-based powder is a main component of the powder mixture, and iron powder (including pure iron powder), or alloyed steel powder is mainly used as the iron-based powder.
• the alloyed steel powder contains an alloyed element. While steel powder containing no C may be used as the alloyed steel powder, steel powder containing C and iron powder containing no C are generally called alloyed steel powder herein.
• partly diffused alloyed steel powder may be used, in which an alloy element is bonded to pure iron powder or the like by partial diffusion. In the application, the partly diffused alloyed steel powder is assumed to be a type of the alloyed iron powder.
• the lubricant is an additive that is added particularly for facilitating compaction or ejection of a compacted body from a die after compaction. While various substances can be used for the lubricant, the lubricant is selected in consideration of a mixing property with iron-based powder or a decomposition property during sintering. As an example of the lubricant, zinc stearate, aluminum stearate, lead stearate and the like are listed. Various lubricants are exemplified in US Patent No.5,256,185 and the like.
• the alloying powder is added mainly for adjusting a composition and/or a structure of an iron-based compacted body or an iron-based sintered body, and includes graphite powder, copper powder, iron phosphide powder, molybdenum powder, and nickel powder.
• the powder of free machining additives (or free machining elements), such as S or MnS, is added particularly for improving machining performance of the sintered body.
• the warm compaction is a technique that a die and powder are heated to high temperature beforehand, then the iron-based powder mixture is compacted.
• the heating temperature While a range of 70 to 120°C is described in JP-A-2-156002 , heating is substantially preferably performed at 100°C or more as described in JP-B-7-103404 and USP 5,368,630 .
• productivity of sintered parts have been likely reduced.
• the iron-based powder mixture is heated for a long time, resulting in a problem that the iron-based powder mixture is oxidized.
• JP-A-9-104901 (1997 ) or JP-A-10-317001 (1998 ) discloses a technique that an inorganic compound having a layered crystal such as MoS 2 , carbon fluoride, and graphite is used as the lubricant.
• MoS 2 when MoS 2 is used, the MoS 2 may be decomposed during sintering, causing generation of harmful sulfur gas that possibly contaminates a furnace.
• carbon fluoride is used so that the iron-based powder mixture is sintered in a hydrogen atmosphere, there is fear that corrosive hydrogen fluoride may be generated.
• sintered parts When parts of various machines such as automobiles are manufactured by a powder metallurgy technique, a powder mixture for powder metallurgy is filled in a die and compacted, and furthermore sintered. Parts of various machines obtained in this way (hereinafter, called sintered parts) typically have a density of 5.0 to 7.2 g/cm 3 respectively. Moreover, since each of the sintered parts is good in dimension accuracy, a part having a complicated shape can be produced.
• the sintered parts are used for parts of various machines.
• parts for automobiles for example, gears
• parts for automobiles for example, gears
• a technique of using a powder mixture for powder metallurgy, which is added with an alloyed element is variously investigated in order to manufacture a sintered part having high strength and high fatigue characteristics.
• JP-B-45-9649 (1970 ) discloses a powder mixture for powder metallurgy, which includes pure Fe powder diffusion-bonded with powder of Ni, Cu, Mo or the like, and is preferable for manufacturing a sintered part having high strength and high fatigue characteristics, and is excellent in compressibility.
• JP-A-61-163239 (1986 ) discloses a powder mixture for powder metallurgy, which includes low alloyed-steel powder, in which C and Mo are contained, and Mn and Cr are substantially not contained, the steel powder being added with Cu powder and/or Ni powder, and furthermore, added with graphite powder.
• JP-A-63-114903 (1988 ) discloses a powder mixture for powder metallurgy, in which Cu powder is diffusion-bonded to alloyed steel powder containing Mo, Mn and C.
• Such degradation in machining performance of a sintered part is caused by a phenomenon that a solid surface intermittently appears in the inside of a work material due to pores within the sintered part, which intermittently give a shock to a tool during cutting, in addition, heat conductivity of the sintered part is thus decreased, and consequently temperature of the sintered part is increased during cutting.
• the machining performance is significantly degraded as strength of a sintered part is increased.
• the powder mixture for powder metallurgy is added with free machining additives, thereby machining performance of a sintered part is improved.
• the free machining additives have an effect of easily breaking chips, or an effect of forming a thin built-up edge on a surface of a cutting tool to improve lubricity of the cutting tool (particularly, on a rake face).
• JP-A-1-255604 (1989 ) discloses a technique that an MgO-SiO 2 composite oxide (for example, anhydrous talc), in which MgO/SiO 2 is 0.5 or more and less than 1.0 in mol ratio, and crystallization water is not contained, is blended to iron-based powder as means of improving machining performance without reducing mechanical properties (for example, strength) of a sintered body.
• an MgO-SiO 2 composite oxide for example, anhydrous talc
• JP-A-64-79302 (1989 ) discloses a technique that free machining additives including a MgO-SiO 2 composite oxide and/or glass powder are contained in reduced iron powder in a configuration that the additives stay inside of each iron powder particle (that is, the additives are added to iron powder raw material before reduction).
• any of the publications describes that the composite oxide is preferably added in a range of 0.1 to 1.5 wt%.
• a lubricant Zinc stearate of 1 wt%) or the like
• an added amount of the composite oxide is increased, an effect of improving machining performance is increased, and particularly large effect is obtained in a range of 0.5 to 1.0 wt%, but on the other hand, mechanical properties are reduced (Table 3 in JP-A-1-255604 , and Figs 6 and 8 in JP-A-64-79302 ). That is, the techniques are not necessarily advantageous in a point of quality of a sintered body.
• the invention advantageously solves the problems, and an object of the invention is to propose an iron-based powder mixture for powder metallurgy, which has no adverse effect on furnace environment during sintering a compact, and provides excellent compaction performance that the powder mixture can be compacted at high density even in a low temperature region of less than 100°C.
• another object of the invention is to provide an iron-based powder mixture for powder metallurgy preferable for machining a sintered part having excellent machining performance, and particularly preferable for machining a high-strength sintered part.
• Still another object of the invention is to propose a method of manufacturing an iron-based compacted body using the iron-based powder mixture as a material, and furthermore, a method of manufacturing an iron-based sintered body using the iron-based compacted body as a material.
• the inventors made earnest investigations on a particular lubricant, by which when an iron-based powder mixture is compacted, furnace environment is not adversely affected, and even if the iron-based powder mixture is compacted at a relatively low heating temperature of the iron-based powder mixture, and preferably even if it is compacted without being heated, a high-density compacted body can be manufactured.
• the invention is designed based on the above findings.
• Each of the content of an alloyed element (including Mo or Mn) in the iron-based powder, the amount of alloying powder (including Cu powder and graphite powder) to be added, and the added amount of talc or steatite refers to percentage of mass of the iron-based powder mixture.
• materials of the iron-based powder mixture of the invention are described.
• the content of each of alloyed elements in the iron-based powder, and the blending amount of each of the materials (alloying powder, lubricant and the like) are expressed in a weight percent of mass (100 mass%) of an iron-based powder mixture obtained by mixing those, that is, the weight percent is expressed using a numerical value included in a numerical value of the mass of the powder mixture.
• a weight percent is not significantly different in numerical value from that in the case that the alloy content (including the amount of partly diffused alloy) and the like in the iron-based powder is expressed in a weight percent of mass of the iron-based powder.
• the iron-based powder pure iron powder such as atomized iron powder or reduced iron powder, or alloyed steel powder is exemplified.
• alloyed steel powder partly-diffused alloyed steel powder and prealloyed steel powder (in which alloyed elements are already contained when melted) are exemplified, and furthermore, hybrid steel powder is exemplified, in which alloyed elements are partly diffused in the prealloyed steel powder.
• the content of impurities in the iron-based powder may be about 3 mass% or less in total.
• the content of each of typical impurities is as follows: C is 0.05 mass% or less, Si is 0.10 mass% or less, Mn (in the case that Mn is not added as an alloy element) is 0.50 mass% or less, P is 0.03 mass% or less, S is 0.03 mass% or less, O is 0.30 mass% or less, and N is 0.1 mass% or less.
• alloyed steel powder Cr, Mn, Ni, Mo, V, Ti, Cu, Nb and the like can be alloyed.
• Ti, Ni, Mo, Cu and the like can be added even by diffusion bonding. If the precondition as the iron-based powder (Fe content is 50 mass% or more) is satisfied, other alloy elements are not particularly limited in content.
• Average particle diameter of the iron-based powder is preferably adjusted to be in a typically used range for powder metallurgy, that is, in a range of about 70 to 100 ⁇ m.
• the particle diameter of the powder is shown as a measurement value by a sieving method according to JIS Z 2510, unless otherwise specified.
• prealloyed steel powder is preferably shown, which contains Mo of 0.3 to 0.5 mass%, Mn of 0.1 to 0.25 mass%, and the remainder being Fe and inevitable impurities.
• the steel powder is preferably water-atomized alloyed steel powder, which is manufactured by water-atomizing the steel having the above composition.
• Mo is an element that increases strength of a sintered part by solution hardening or improvement in hardenability (quench hardenability) of alloyed steel powder.
• Mo content is less than 0.3 mass%, an effect of increasing strength of the sintered part by Mo is not obtained.
• the content is more than 0.5 mass%, since the effect of increasing strength of the sintered part is saturated, machining performance is unnecessarily reduced. Therefore, Mo content is preferably adjusted to be in a range of 0.3 to 0.5 mass%.
• Mn is an element that increases strength of a sintered part by solution hardening or improvement in hardenability of water-atomized alloyed steel powder.
• Mn content is less than 0.1 mass%, an effect of increasing strength of the sintered part by Mn is not obtained.
• Mn content is preferably adjusted to be in a range of 0.1 to 0.25 mass%.
• the rest of the powder other than the above components preferably is Fe and inevitable impurities.
• the inevitable impurities inevitably gets into the steel in a stage that an ingot being a material of the water-atomized alloyed steel powder is produced, or in a stage that water-atomized alloyed steel powder is manufactured from the ingot.
• a preferable method of manufacturing the water-atomized alloyed steel powder is described, the method being preferably used in the invention.
• An ingot containing a predetermined composition that is, the above composition
• the ingot is formed into powder by a water atomizing method.
• the obtained powder is subjected to finish reduction and crushing (or pulverizing) thereby obtaining water-atomized alloyed steel powder.
• An apparatus for obtaining powder from an ingot by the water atomizing method is not limited to a particular type, and any previously known apparatus may be used as the apparatus.
• alloying powder graphite powder, metal powder of such as Cu, Mo and Ni, boron powder, cuprous oxide powder and the like are exemplified. Such alloying powder is mixed to the iron-based powder, so that strength of a sintered body can be increased.
• the blending amount of the alloying powder is preferably adjusted to be about 0.1 to 10 mass% in the iron-based powder mixture.
• the reason for this is that the alloying powder is blended by 0.1 mass% or more, so that strength of an obtained sintered body is advantageously improved, on the other hand, when it is blended by more than 10 mass%, dimension accuracy of the sintered body is reduced.
• iron-based powder example 1 particularly Cu powder of 1 to 3 mass% and graphite powder of 0.5 to 1.0 mass% are preferably added.
• C being a main component of graphite powder is an element that increases strength of a sintered part by solution hardening or improvement in hardenability of water-atomized alloyed steel powder.
• the added amount of graphite powder is less than 0.5 mass%, a desired effect is not sufficiently obtained in the iron-based powder example 1.
• the content is more than 1.0 mass%, strength of the sintered part is increased beyond necessity, and consequently machining performance is unnecessarily reduced. Therefore, the content of graphite powder is adjusted to be in a range of 0.5 to 1.0 mass%.
• Cu is an element that increases strength of a sintered part by solution hardening or improvement in hardenability of alloyed steel powder. Moreover, Cu powder is melted during sintering and thus changed into a liquid phase, causing adhesion of particles of the alloyed steel powder to one another. When the added amount of Cu powder is less than 1 mass%, a desired effect is not sufficiently obtained in the iron-based powder example 1. On the other hand, when the amount is more than 3 mass%, since the effect of increasing strength of the sintered part is saturated, machining performance is unnecessarily reduced. Therefore, the content of Cu powder is adjusted to be in a range of 1 to 3 mass%.
• an adding method may be a method where alloyed steel powder is added with Cu powder and then simply mixed, or a method of adhering Cu powder on a surface of water-atomized alloyed steel powder via a binder.
• the alloyed steel powder and the Cu powder are mixed and subjected to heat treatment, so that the Cu powder is diffusion-bonded on a surface of the alloyed steel powder so as to be formed into partly-diffused alloyed steel powder (or hybrid alloyed steel powder).
• talc 3MgO-4SiO 2
• steatite is sometimes called fired talc, and contains enstatite (MgO-SiO 2 ) as a main component.
• talc or steatite When talc or steatite is added together with fatty acid amide, it exhibits a particularly large effect as a lubricant. Moreover, while talc or steatite is one of MgO-SiO 2 composite oxides known as free machining additives, if talc or steatite is further added together with metallic soap, it exhibits a particularly large effect even as a free machining additive.
• the talc or steatite is blended as the lubricant, thereby compressibility of a compacted body is improved, in addition, ejection force in compaction process is reduced, so that compaction performance is remarkably improved.
• the reason for this is considered as follows.
• the iron-based powder mixture is not necessarily heated, and the effects effectively contribute to increasing density of an iron-based compacted body in compaction even at normal temperature. Moreover, when the iron-based powder is heated, since plastic deformation resistance of the iron-based powder is decreased during compaction, higher density of a compacted body can be obtained. Therefore, while heating temperature of the iron-based powder can be appropriately set depending on a required density of a compacted body, sufficient heating temperature is less than 100°C. More preferably, the heating temperature is 80°C or less.
• a sintered part manufactured by using the powder mixture for powder metallurgy of the invention may have high strength similar to that of a usual high-strength sintered part, and in addition, may have extremely excellent machining performance.
• the blending amount of the talc or steatite is preferably adjusted to be about 0.01 to 0.5 mass% in total in the iron-based powder mixture.
• the reason for this is that such a lubricant blended by 0.01 mass% or more, thereby density of a compacted body can be adequately increased during compaction, and ejection force can be adequately decreased during ejecting the compacted body.
• the lubricant is preferably added by 0.01 mass% or more, too.
• the added amount of talc and/or steatite is preferably adjusted to be 0.05 mass% or more in total.
• an upper limit of the blending amount is 0.3 mass%, and the upper limit is preferably adjusted to be 0.2 mass% or less to substantially eliminate influence on mechanical properties of the sintered body.
• talc has a monoclinic or triclinic crystal structure
• steatite has a monoclinic crystal structure
• boron nitride has a hexagonal crystal structure.
• Size of talc or steatite is preferably about 1 to 10 ⁇ m in particle diameter.
• At least one of fatty acid amides is blended as a lubricant.
• the fatty acid amide at least one selected from fatty acid monoamide (such as stearic acid monoamide), and fatty acid bisamide (such as ethylene-bis-stearoamide and methylene-bis-stearoamide) is preferably used.
• Each of them acts as not only a lubricant, but also a binder. Therefore, by using each of them, segregation or dusting of the relevant iron-based powder mixture is effectively prevented, and flowability and compaction performance can be further improved. While a fatty acid is sometimes mixed in fatty acid amide, this is not particularly prohibited.
• the blending amount of the fatty acid amide is preferably adjusted to be about 0.01 to 0.5 mass% in the iron-based powder mixture.
• the reason for this is that when the blending amount is less than 0.01 mass%, the adding effect is poor, and on the other hand, when the blending amount is more than 0.5 mass%, strength of a compacted body (or green compact) is decreased.
• a lower limit of the blending amount is more preferably 0.03 mass% in the case that the iron-based powder is pure iron powder, and 0.05 mass% in the case that it is alloyed steel powder.
• An upper limit of the blending amount is more preferably 0.4 mass%, and in the case that the iron-based powder is pure iron powder, 0.3 mass% is further more preferable as the upper limit.
• metallic soap can be further blended. According to a previous common idea, the metallic soap is also counted as a lubricant.
• the metallic soap zinc stearate, lithium stearate, calcium stearate and the like are listed. Among them, the zinc stearate and the lithium stearate are particularly preferable.
• the blending amount of the metallic soap is preferably adjusted to be about 0.01 to 0.5 mass% in the iron-based powder mixture.
• the reason for this is that when the blending amount is less than 0.01 mass%, the adding effect is poor, and on the other hand, when the blending amount is more than 0.5 mass%, strength of a compacted body is decreased.
• a lower limit of the blending amount is more preferably 0.05 mass% or more, and an upper limit thereof is more preferably 0.3 mass%.
• the added amount of the fatty acid amide and the metallic soap in total is preferably adjusted to be 0.1 mass% to 1.0 mass%.
• the lower limit is more preferably 0.2 mass%, and the upper limit is more preferably 0.6 mass%.
• the blending amount of the talc/steatite, the fatty acid amide, and the metallic soap in total is preferably adjusted to be about 0.01 to 2.0 mass% in the iron-based powder mixture.
• the lower limit is more preferably 0.15 mass%, and the upper limit is more preferably 0.8 mass%.
• a known additive such as surface modification agent (including siloxanes) may be further added by about 0.5 mass% or less.
• Iron-based powder is added with the respective materials (such as talc, steatite, fatty acid amide, metallic soap, and alloying powder), and then subjected to primary mixing. Then, a mixture after primary mixing is agitated while it is heated to a melting point or higher of at least one of the fatty acid amide and metallic soap, and then the mixture is gradually cooled while being mixed. As a result, the alloying powder or other material powder is adhered on the iron-based powder by an effect of the melted material.
• the respective materials such as talc, steatite, fatty acid amide, metallic soap, and alloying powder
• the material which is melted and used for adhesion, acts even as a binder.
• the iron-based powder is added with only some of the materials, and subjected to primary mixing, and then further added with the rest of the materials, and subjected to secondary mixing.
• the material subjected to secondary mixing exists in the powder mixture in a free state.
• a method is given, in which at least part of the metallic soap is supplied for the secondary mixing, and the rest of the materials is supplied for the primary mixing, and fatty acid amide, or a co-melt of the fatty acid amide with the metallic soap is used for the binder. According to the method, the added amount of each material to be blended to the iron-based powder can be minimized.
• Mixing means of the iron-based powder and each material is not particularly limited, and any of previously known mixers can be used.
• a high-speed mixer, counter current mixer, plough share mixer, and conical mixer in each of which the material powders being easily heated, are particularly advantageously suited.
• the iron-based powder mixture of the invention can be made into a compacted body by a typical compaction method.
• the iron-based powder mixture is filled into a die, and furthermore subjected to compaction.
• pressing force is preferably adjusted to be 400 to 1000 MPa.
• the die may be heated to 50 to 70°C.
• the powder mixture for powder metallurgy and the die may be heated to 80 to 130°C.
• the iron-based powder mixture of the invention can be adequately compacted in high density even at normal temperature, and preferably compacted at normal temperature in the light of productivity.
• the iron-based powder mixture or the die may be advantageously heated, and the die may be advantageously coated with a lubricant.
• temperature of the iron-based powder mixture or temperature of the die is preferably adjusted to be less than 100°C.
• the reason for this is that since the iron-based powder mixture according to the invention is high in compressibility, the powder mixture exhibits excellent compaction performance even at a temperature of less than 100°C, and when the temperature is more than 100°C, there is fear that the powder mixture may be degraded due to oxidation. More preferably, the temperature is 80°C or less.
• the high density, iron-based compacted body obtained in the above way is ejected from the die, then subjected to sintering so as to be formed into a high-density sintered body.
• a sintering method is not particularly limited, and any of previously known sintering methods can be preferably used. In the sintering, preferably, heating temperature is 1100 to 1600°C, and heating time is 10 to 60 min.
• a sintered part After sintering, a sintered part can be subjected to heat treatment such as carburizing and quenching (gas carburizing heat treatment), bright hardening, induction hardening, and carbonitriding heat treatment, so that strength of the (high strength) sintered part can be further increased. Furthermore, tempering may be performed.
• heat treatment such as carburizing and quenching (gas carburizing heat treatment), bright hardening, induction hardening, and carbonitriding heat treatment, so that strength of the (high strength) sintered part can be further increased.
• tempering may be performed.
• Table 1 shows various types of iron powder for powder metallurgy (each having an average particle diameter of about 80 ⁇ m) used as the iron-based powder in examples 1 to 4. Particularly, in the case of alloyed steel powder, whether the alloyed steel powder is prealloyed steel powder, partly alloyed steel powder, or hybrid steel powder in which the prealloyed steel powder is partly diffused with an alloyed element is distinctively shown.
• the added amount (part by mass) of a lubricant is expressed in percentage of total mass of 100% of the iron-base powder, natural graphite powder, and copper powder. While the percentage is expressed using a numerical value being not included in that of the total mass, the percentage is approximately the same as in the case that it is expressed using a numerical value being included in that of the total mass. Average particle diameter of the talc powder and average particle diameter of the steatite powder were 6 ⁇ m and 4 ⁇ m respectively.
• powder mixtures were prepared (refer to Table 3) in a way that various types of powder having the same components as the above, each including the iron-based powder, and natural graphite powder and/or copper powder, were added with zinc stearate of 0.8 mass%, then the powder was mixed by a V-container-turning mixer.
• Each of the comparative materials has a composition typically used in normal compaction.
• each of the obtained iron-based powder mixtures was filled in a superhard tablet-shaped die having an inner diameter of 11 mm, and compacted at 490 MPa and 686 MPa.
• a compacted body was ejected from the die, ejection force was measured, and green density of each of obtained compacted bodies was measured.
• the obtained iron-based powder mixtures were subj ected to compaction for preparing test pieces for a machining test (outer diameter of 60 mm, inner diameter of 20 mm, and length of 30 mm).
• pressing force was 590 MPa.
• Sintering was performed in an RX gas atmosphere, wherein heating temperature was 1130°C, and heating time was 20 min.
• a machining test was performed with cutting speed of 200 m/min, feed of 0.1 mm per unit, depth of cut of 0.3 mm, and a cutting distance of 1000 m, and flank wear width of the cutting tool was measured. Smaller flank wear width of the cutting tool shows more excellent machining performance of a sintered body.
• the lubricants according to the invention are used as lubricants, thereby a high-density compacted body can be obtained without significantly increasing ejection force even in the case of normal temperature compaction, and furthermore, machining performance is remarkably improved.
• powder mixtures were prepared in a way that various types of powder having the same components as the above, each including the iron-based powder, and natural graphite powder and/or copper powder, were added with ethylene-bis-stearoamide of 0.6 mass%, then the powder was mixed by a V-container-turning mixer (comparative materials).
• each of the obtained iron-based powder mixtures was filled in a superhard tablet-shaped die having an inner diameter of 11 mm, which was heated beforehand such that temperature of a cavity wall surface was increased to 80°C, and then the powder mixture was compacted at 490 MPa and 686 MPa.
• a compacted body was ejected from the die, ejection force was measured, and green density of each of the obtained compacted bodies was measured.
• each of the comparative materials was compacted at a typical compaction condition of warm compaction, that is, the comparative material was heated to 120°C, then filled into a superhard tablet-shaped die having an inner diameter of 11 mm and which was heated to 130°C, and then compacted at 490 MPa and 686 MPa.
• a typical compaction condition of warm compaction that is, the comparative material was heated to 120°C, then filled into a superhard tablet-shaped die having an inner diameter of 11 mm and which was heated to 130°C, and then compacted at 490 MPa and 686 MPa.
• test pieces for a machining test were prepared by compaction as in the example 1, so that machining performance was examined.
• the primary and secondary additives of the invention were added as lubricants, thereby the die was simply heated to a relatively low temperature of less than 100°C, so that even if the powder mixture was not heated, a compacted body having high density, which was similar to that of a typical warm compacted body, was able to be obtained without causing increase in ejection force.
• Flank wear width (mm) of each inventive example was reduced to about 20 to 40% of that of a comparative example in the same grouping (number), showing remarkable improvement even in machining performance.
• powder mixtures were prepared in a way that each of various types of powder was added with ethylene-bis-stearoamide having a respective weight, then mixed by a V-container-turning mixer.
• each of the obtained iron-based powder mixtures was heated to 60°C, then filled in a superhard tablet-shaped die having an inner diameter of 11 mm, which was heated beforehand such that temperature of a cavity wall surface was increased to 80°C, and furthermore coated with lithium stearate powder on its wall surface, and then the powder mixture was compacted at 490 MPa and 686 MPa.
• a compacted body was ejected from the die, ejection force was measured, and green density of each of the obtained compacted bodies was measured.
• each of the comparative materials was compacted at a typical compaction condition of warm compaction, that is, the comparative material was heated to 120°C, then filled into a superhard tablet-shaped die having an inner diameter of 11 mm and which was heated to 130°C, and then compacted at 490 MPa and 686 MPa.
• a typical compaction condition of warm compaction that is, the comparative material was heated to 120°C, then filled into a superhard tablet-shaped die having an inner diameter of 11 mm and which was heated to 130°C, and then compacted at 490 MPa and 686 MPa.
• test pieces for a machining test were prepared by compaction as in the example 1, so that machining performance was examined.
• the primary and secondary additives of the invention were added as lubricants, thereby the die and the powder were simply heated to a relatively low temperature of less than 100°C, so that a compacted body having high density, which was similar to that of a typical warm compacted body, was able to be obtained with an extremely low ejection force.
• Flank wear width (mm) of each inventive example was reduced to about 25 to 35% of that of a comparative example in the same grouping (number), showing remarkable improvement even in machining performance.
• each of the obtained iron-based powder mixtures was filled in a superhard tablet-shaped die having an inner diameter of 11 mm, and compacted at 490 MPa and 686 MPa.
• a compacted body was ejected from the die, ejection force was measured, and green density of each of obtained compacted bodies was measured.
• the obtained iron-based powder mixtures were subjected to compaction for preparing tensile test pieces according to Japan Powder Metallurgy Association JPMA M04-1992, and test pieces for a machining test (outer diameter of 60 mm, inner diameter of 20 mm, and length of 30 mm).
• compaction pressing force was 590 MPa.
• Sintering was performed in an RX gas atmosphere, wherein heating temperature was 1130°C, and heating time was 20 min.
• An evaluation method of machining performance was the same as in the example 1.
• fatty acid amide and the like need to be added with steatite and the like to obtain a high-density compacted body without increasing ejection force. Moreover, it is known that metallic soap is further added, thereby machining performance of a sintered body can be remarkably improved.
• Water-atomized alloyed steel powder having a composition shown in Table 11 was manufactured by a water-atomizing method. The rest of the powder other than Mn and Mo is Fe and inevitable impurities. The water-atomized alloyed steel powder was added with Cu powder, graphite powder, talc, and steatite in a ratio as shown in the Table 11. Each of Mo content and Mn content (mass%) in the water-atomized steel powder, or each of the added amount (mass%) of the Cu powder, graphite powder, talc, and steatite to be added to the water-atomized steel powder is shown in percentage of mass of a powder mixture for powder metallurgy, the percentage being expressed using a numerical value included in a numerical value of mass of the powder mixture.
• a lubricant was added in a ratio as shown in Table 11.
• the added amount (part by mass) of the lubricant is shown in percentage of mass (100 part by mass) of a powder mixture for powder metallurgy obtained by mixing the water-atomized alloyed steel powder and additives, the percentage being expressed using a numerical value being not included in a numerical value of moss of the powder mixture (but, the percentage is approximately the same as in the case that it is expressed using a numerical value included therein).
• inventive examples use a powder mixture for powder metallurgy that satisfies the scope of the invention
• comparative examples use a powder mixture for powder metallurgy that departs from the scope of the invention.
• a powder mixture for powder metallurgy using Fe-4Ni-1.5Cu-0.5Mo water-atomized alloyed steel powder which is previously practically used, is blended with a conventional lubricant.
• Numerical values added to respective alloy elements of No. 22 are expressed in mass%.
• any of sintered bodies obtained from the powder mixtures for powder metallurgy of the inventive examples are excellent in mechanical properties and machining performance.
• the prior-art example is particularly significantly bad in machining performance of a sintered body.
• the water-atomized alloyed steel powder contains Mo of 0.3 to 0.5 mass% and Mn of 0.1 to 0.25 mass%, and the powder mixture contains Cu powder of 1 to 3 mass% and graphite powder of 0.5 to 1.0 mass%, a sintered body can be obtained, which has a tensile strength of 500 MPa or more, and is excellent in machining performance.
• an iron-based powder mixture can be obtained, which gives high compaction density and small ejection force even if the powder mixture is compacted at low temperature of about room temperature.
• a powder mixture for powder metallurgy can be obtained, which is preferable for machining a sintered part having excellent machining performance, particularly, preferable for machining a high-strength sintered part.
• the iron-based powder mixture is used as a material, thereby an iron-based compacted body having high compaction density can be obtained, and furthermore, an iron-based sintered body can be obtained, which has high sintering density, or has further excellent machining performance.

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