US20100310405A1 - Ferrous sintered alloy, process for producing ferrous sintered alloy and connecting rod - Google Patents

Ferrous sintered alloy, process for producing ferrous sintered alloy and connecting rod Download PDF

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US20100310405A1
US20100310405A1 US12/794,435 US79443510A US2010310405A1 US 20100310405 A1 US20100310405 A1 US 20100310405A1 US 79443510 A US79443510 A US 79443510A US 2010310405 A1 US2010310405 A1 US 2010310405A1
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mass
powder
sintered alloy
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ferrous sintered
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Mikio Kondoh
Toshitake Miyake
Kimihiko Ando
Hideo HANZAWA
Nobuhiko Matsumoto
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Toyota Motor Corp
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Toyota Motor Corp
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    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C22/00—Alloys based on manganese
    • 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
    • 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%
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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

Definitions

  • the present invention is based on Japanese Patent Application No. 2009-135,668, filed on Jun. 5, 2009, the entire contents of which are incorporated herein by reference.
  • the present invention relates to a ferrous sintered alloy that is made by sintering an iron-system powder, and a process for producing the same.
  • Powder metallurgy methods have been used widely in the manufacture of mechanical component parts, because impurities are less likely to mingle in the course of powder metallurgy methods and because powder metallurgy methods make it feasible to mass-produce products that have complicated configurations with good accuracy.
  • mechanical component parts such as connecting rods and bearing races
  • a connecting rod for instance, is manufactured by hot forging a preform for forging to a desired configuration by means of sinter forging process and then subjecting the hot-forged preform to cutting works that serve as finish processing.
  • a ferrous sintered alloy which is employed on this occasion, is required, not to mention, to be strengthened much further in order to provide connecting rods with higher performance and make them lightweight, but so as to make them exhibit machinability as well.
  • a ferrous powder comprising an Fe-2% by mass Cu-0.6% by mass C alloy has been used generally.
  • the addition of Cu is very effective in enhancing the strength of ferrous sintered alloy, because the circumference where Cu is present in a high concentration is likely to turn into martensite.
  • the fatigue strength of the Fe-2% by mass Cu-0.6% by mass C alloy is improved by increasing the addition amount of copper (Cu) and reducing the addition amount of carbon (C) to the alloy.
  • KKAI Japanese Unexamined Patent Publication
  • 2008-13,818 discloses a ferrous sintered alloy that comprises carbon (C) in an amount of from 0.2 to 0.4% by mass, copper (Cu) in an amount of from 3 to 5% by mass, manganese (Mn) in an amount of 0.5% by mass or less, and the balance being iron (Fe) and inevitable impurities. Moreover, it is possible to enhance the machinability of the Fe-2% by mass Cu-0.6% by mass C alloy by adding a free-cutting component to the alloy.
  • Another ferrous sintered alloy being set forth in Japanese Unexamined Patent Publication (KOKAI) Gazette No.
  • 2008-231,538, for instance, includes the following at least: C in an amount of from 0.4 to 1.0% by mass, molybdenum (Mo) in an amount of from 1.0 to 3.0% by mass, Cu in an amount of from 1.0 to 4.0% by mass, Mn in an amount of from 0.2 to 1.0% by mass, and sulfur (S) in an amount of from 0.05 to 0.3% by mass.
  • C in an amount of from 0.4 to 1.0% by mass
  • Mo molybdenum
  • Cu in an amount of from 1.0 to 4.0% by mass
  • Mn in an amount of from 0.2 to 1.0% by mass
  • sulfur (S) in an amount of from 0.05 to 0.3% by mass.
  • S turns into a compound, manganese sulfide (MnS), and then upgrades the machinability of ferrous sintered alloy.
  • Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2002-20,847 discloses a connecting rod that is made of still another ferrous sintered alloy.
  • This ferrous sintered alloy contains nickel (Ni) in an amount of from 2 to 6% by mass, Cu in an amount of from 0.5 to 2.5% by mass, Mo in an amount of from 0.5 to 1.3% by mass, C in an amount of 0.2 to 0.8% by mass, phosphorous (P) in an amount of from 0.1 to 0.3% by mass, Mn in an amount of from 0.2 to 0.65% by mass, and the balance being made up of Fe and inevitable impurities.
  • Ni nickel
  • Cu in an amount of from 0.5 to 2.5% by mass
  • Mo in an amount of from 0.5 to 1.3% by mass
  • C in an amount of 0.2 to 0.8% by mass
  • phosphorous (P) in an amount of from 0.1 to 0.3% by mass
  • Mn in an amount of from 0.2 to 0.65% by mass
  • Cu is a virtually essential additive element in ferrous sintered alloys from the viewpoint of strengthening the alloys highly.
  • unsolved Cu might bring about cracks in preforms to be hot forged (i.e., hot brittleness). It is possible to inhibit cracks, which result from forging, by heating forging preforms to such a high temperature as 1,190° C. or more or making the heating time longer.
  • the present invention has been developed in view of the aforementioned problematic issues. It is therefore an object of the present invention to provide a ferrous sintered alloy, which is good in terms of machinability while making it keep exhibiting sufficient strength even when including little Cu and furthermore Ni, and a process for producing the same.
  • the inventors of the present invention found out that it is feasible to make ferrous sintered alloys in which strength and machinability are consistent, not by using conventional Fe—Cu—C-system powders, but by using Fe—Cr—Mo-system powders that have been regarded unsuitable for sinter forging. Then, the inventors expanded the achievement to arrive at successfully completing a variety of inventions that are described hereinafter.
  • a ferrous sintered alloy according to the present invention which is good in terms of machinability, comprises:
  • a sintered raw-material powder being made of an Fe—Cr—Mo-system powder, a carbon-system powder and an Mn—Si-system powder before sintering;
  • metallic structure comprising martensite and bainite; metallic structure in which the martensite accounts for an area proportion of 40% or less when the entirety of the metallic structure is taken as 100% by area and the martensite exhibits a particle diameter of 20 ⁇ m or less.
  • the ferrous sintered alloy according to the present invention comprises a sintered raw-material powder.
  • the sintered raw-material powder is made of an Fe—Cr—Mo-system powder, a carbon-system powder, and an Mn—Si-system powder before sintering.
  • the present ferrous sintered alloy is highly strengthened because it contains C, Mn and Si in a proper amount, respectively. Consequently, it is not necessary for the present ferrous sintered alloy to include Cu that has been considered essential in order to strengthen ferrous sintered alloys. Moreover, it is possible to procure Mn and Si more inexpensively than to procure Cu comparatively. In addition, it is possible to make the present ferrous sintered alloy using Mn and Si in smaller quantities relatively. That is, the present ferrous sintered alloy also makes it feasible to reduce the raw-material cost.
  • the ferrous sintered alloy according to the present invention exhibits remarkably enhanced quench hardenability, because an Mn—Si-system powder is used as an element of the raw-material powder together with an Fe—Cr—Mo-system powder. In other words, martensite structures are likely to arise in the present ferrous sintered alloy.
  • the ferrous sintered alloy according to the present invention exhibits a density of 7.4 g/cm 3 or more.
  • the present ferrous sintered alloy's density is 7.4 g/cm 3 or more
  • the present ferrous sintered alloy not only shows high strength but also good machinability.
  • the term, “high strength,” means that the present ferrous sintered alloy can exhibit 960 MPa or more, or further 1,000 MPa, by tensile strength preferably.
  • the ferrous sintered alloy according to the present invention has a metallic structure that comprises martensite and bainite.
  • a ferrous sintered alloy has a metallic structure that is made of bainite independently, or when it has a composite metallic structure that is made of bainite and pearlite, the alloy is soft. Accordingly, chips, which occur while performing cutting to such an alloy, namely, a workpiece to be cut, are likely to become continuous so that adhesion might occur between a cutting tool and the workpiece.
  • the present ferrous sintered alloy that is made up of martensite and bainite is hard comparatively. Consequently, chips that arise when cutting the present ferrous sintered alloy are likely to be segmented or separated from each other.
  • the present ferrous sintered alloy it is possible to inhibit a cutting tool and a workpiece to be cut, namely, the present ferrous sintered alloy, from adhering each other. Moreover, the greater the presence proportion of martensite a ferrous sintered alloy exhibits the harder the alloy becomes. However, ferrous sintered alloys that are hard excessively are not suitable for cutting works, because they are hard excessively so that they become brittle. On the contrarily, the present ferrous sintered alloy shows excellent machinability, because it exhibits a martensite proportion of 40% or less by area ratio.
  • the martensite exhibits a particle diameter of 20 ⁇ m or less. Even when a martensite proportion is kept down to 40% or less as described above, if ferrous sintered alloys, which include martensite whose particle diameter is large, are subjected to cutting work, there arises such an adverse affect that a cutting tool might be chipped or worn out during the work. When the particle diameter of martensite is set to 20 ⁇ m or less, the hardness of martensite particles themselves lowers. Therefore, it is possible to inhibit cutting tools from getting chipped and wearing off in the course of processing the present ferrous sintered alloy by cutting.
  • the martensite particles separate or segment the resulting chips from each other favorably because the particulate martensite exists to disperse within the alloy's matrix.
  • the martensite particles inhibit a cutting tool and a workpiece to be cut, namely, the present ferrous sintered alloy, from adhering each other.
  • a raw-material powder which comprises an Fe—Mn—Si-system powder that is classified to have a particle diameter of 5 ⁇ m or less, is employed in producing the ferrous sintered alloy according to the present invention, it is possible to keep a particle diameter of the resultant martensite down to 20 ⁇ m or less in the metallic structure.
  • the present ferrous sintered alloy involves not only simple sintered bodies but also sintered and forged bodies that are obtained by forging the simple sintered bodies. That is, in the present specification, the sintered and forged bodies as well as the simple sintered bodies are collectively referred to as “ferrous sintered alloys” regardless of being forged or not being forged in the course of their production processes.
  • FIG. 1 is a chart for showing the Vickers hardness of ferrous sintered alloys that were made by sintering later-described raw-material powder Nos. 1 through 30.
  • FIG. 2 is a chart for showing the proportions of phases that were included in the metallic structure of ferrous sintered alloys that were made by sintering later-described raw-material powder Nos. 1 through 30, and photographs that substitute for drawings for illustrating the metallic structures of the ferrous sintered alloys that were made of sintered raw-material powders Nos. 2, 12 and 22.
  • FIG. 3 is a graph for illustrating the relationships between a particle diameter “d” of Fe—Mn—Si-system powder and a particle diameter of martensite “D,” in the case of ferrous sintered alloys that were made by sintering later-described raw-material powder Nos. 12, 31, 34 and 35.
  • FIG. 4 is an explanatory diagram for illustrating a cutting test.
  • FIG. 5 is a graph for illustrating the wear amounts of cutting tool with respect to the number of working paths.
  • FIG. 6 is a photograph that substitutes for a drawing for illustrating the state of wear on the flank of chip after a cutting test was performed onto a test specimen that was made of a ferrous sintered alloy according to a comparative example, and that substitutes for another drawing for illustrating the appearance of chips that the test specimen produced when being cut.
  • FIG. 7 is a photograph that substitutes for a drawing for illustrating the state of wear on the flank of chip after a cutting test was performed onto a test specimen that was made of a ferrous sintered alloy according to the present invention, and that substitutes for another drawing for illustrating the appearance of chips that the test specimen produced when being cut.
  • FIG. 8 is a photograph that substitutes for a drawing for illustrating the state of wear on the flank of chip after a cutting test was performed onto a test specimen that was made of another ferrous sintered alloy according to the present invention, and that substitutes for another drawing for illustrating the appearance of chips that the test specimen produced when being cut.
  • FIG. 9 is a diagram for illustrating an automotive connecting rod schematically.
  • preferable modes which not only embody a ferrous sintered alloy according to the present invention and a process for producing the same but also a connecting rod comprising the present ferrous sintered alloy.
  • the numerical designations namely, “from ‘x’ to ‘y’” as set forth in the present specification, involve the lower limit, “x,” and the upper limit, “y,” within the ranges unless otherwise specified.
  • a ferrous sintered alloy according to the present invention comprises chromium (Cr), molybdenum (Mo), silicon (Si), manganese (Mn), carbon (C), and the balance being iron (Fe) and inevitable impurities.
  • the present ferrous sintered alloy has a metallic structure that is made up of martensite and bainite.
  • the martensite accounts for 40% or less with respect to the entirety of the metallic structure being taken as 100% by area. It is preferable that the martensite proportion can fall in a range of from 4 to 40%, more preferably from 4 to 25%, with respect to the entire metallic structure being taken as 100% by area.
  • the martensite proportion can be found in the following manner: a cross section of ferrous sintered alloy is observed with a microscope, and then an image analysis is carried out to calculate how much an area that results from martensite occupies or accounts for the entire area of the obtained image.
  • the existence of martensite makes the present ferrous sintered alloy harder, and accordingly the present ferrous sintered alloy can be cut or machined satisfactorily.
  • the martensite proportion exceeds 40%, the resultant ferrous sintered alloys have become likely to embrittle because they are too hard, and have adversely showed declining machinability.
  • the ferrous sintered alloy according to the present invention comprises martensite whose particle diameter is 20 ⁇ m or less.
  • the particle diameter of martensite can fall in range of from 2 to 20 ⁇ m, more preferably from 5 to 20 ⁇ m.
  • the particle diameter of martensite can be a value that is obtained by observing a cross-sectional face of ferrous sintered alloy and then measuring a maximum diameter of crystalline particles in the obtained image, for instance.
  • the “maximum diameter” herein means the maximum value of intervals between two parallel lines when the crystalline particles are held between the parallel lines.
  • the ferrous sintered alloy according to the present invention exhibits a density of 7.4 g/cm 3 or more.
  • the present ferrous sintered alloy's density can preferably be 7.5 g/cm 3 or more. It is more preferable that the density can fall in a range of from 7.4 or more to 7.9 g/cm 3 or less, much more preferably from 7.5 or more to 7.9 g/cm 3 or less.
  • the density of the present ferrous sintered alloy is set as described herein, because it is difficult to expect that ferrous sintered alloys with lower densities can be highly strengthened and their machinability can be enhanced even when the alloys include the aforementioned alloying elements and have the above-described metallic structure.
  • the ferrous sintered alloy according to the present invention can preferably exhibit a Vickers hardness of from 300 Hv or more to 400 Hv or less, and can preferably exhibit a tensile strength of 960 MPa or more.
  • the Vickers hardness herein was obtained by applying a force, which fell in a range of from 5 to 20 kgf, to a unit surface area of test specimen (i.e., mm 2 ). It is more preferable that the Vickers hardness can fall in a range of from 320 Hv to 370 Hv, and that the tensile strength can fall in a range of from 960 to 1,500 MPa, much more preferably from 1,000 to 1,210 MPa.
  • the present ferrous sintered alloy which is composed of alloying elements as set forth above and which comprises a metallic structure as described above, can demonstrate a Vickers hardness and tensile strength that definitely fall in the aforementioned ranges, respectively.
  • the present ferrous sintered alloy whose Vickers hardness falls in the range of from 300 Hv to 400 Hv is much better in terms of machinability. Meanwhile, it is possible to say that the present ferrous sintered alloy exhibiting a tensile strength of 960 MPa or more, or further exhibiting 1,000 MPa or more, possesses sufficient strength as a material for applications to mechanical component parts, such as connecting rods.
  • the ferrous sintered alloy according to the present invention which is made of the aforementioned metallic structure and which is further provided with the above-described physical properties, can be made by sintering a raw-material powder that comprises an Fe—Cr—Mo-system powder, a carbon-system powder and an Mn—Si-system powder.
  • the Fe—Cr—Mo-system powder makes the major component.
  • the carbon-system powder and Mn—Si-system powder serve as a strengthening powder, respectively.
  • the Fe—Cr—Mo-system powder comprises chromium (Cr), molybdenum (Mo), and the balance being Fe and inevitable impurities.
  • Cr and Mo are elements that are effective in strengthening ferrous sintered alloy. It is suitable to set the Cr content so as to fall in a range of from 0.5 to 3.5% by mass, or further from 1 to 2% by mass, when the entire Fe—Cr—Mo-system powder is taken as 100% by mass.
  • the Cr content is 0.5% by mass or more, it is possible to provide the resulting ferrous sintered alloys with sufficient strength.
  • the Cr content exceeding 3.5% is not preferable because the compressibility of the raw-material powder has lowered.
  • the Mo content so as to fall in a range of from 0.1 to 2% by mass, or from 0.1 to 0.6% by mass, or further from 0.1 to 0.3% by mass, when the entire Fe—Cr—Mo-system powder is taken as 100% by mass.
  • the Mo content being 0.1% by mass or more enables the resulting ferrous sintered alloys to exhibit sufficient strength.
  • the Fe—Cr—Mo-system powder can further comprise silicon (Si) or manganese (Mn) as an additive element, if needed.
  • Si silicon
  • Mn manganese
  • the Mn—Si-system powder serves as a strengthening powder for enhancing the mechanical strengths of ferrous sintered alloy.
  • the Mn—Si-system powder can preferably comprise an alloy or intermetallic compound of Mn, Si and Fe, which makes the major component of the ferrous sintered alloy according to the present invention.
  • Such an alloy powder or intermetallic-compound powder can be procured with ease, because it can be produced inexpensively relatively by means of pulverizing an Fe—Mn—Si-system alloy ingot that has been available commercially.
  • the resulting Fe—Mn—Si-system powder can comprise Mn in an amount of from 40 to 70% by mass, Si in an amount of from 10 to 40% by mass, and the balance of Fe and inevitable impurities when the entire Fe—Mn—Si-system powder is taken as 100% by mass. Too little Mn and Si make iron alloys with ductility, and accordingly it is difficult to pulverize the resultant iron alloys to a fine powder. Moreover, too much Mn and Si are not preferable because costs have gone up due to their compositional adjustments.
  • Mn and Si contents can be from 40 to 70% by mass for Mn, and from 15 to 35% by mass for Si, when the entire Fe—Mn—Si-system powder is taken as 100% by mass; and that a sum of the Mn and Si contents can fall in a range of from 75 to 85% by mass, or from 80 to 85% by mass.
  • a compositional ratio between Mn and Si in the Mn—Si-system powder does not matter, it is preferable that a compositional ratio of Mn to Si (or Mn/Si) can preferably fall in a range of from 0.5 to 4 by mass, or more preferably from 1.5 to 4 by mass. This is because it is likely to produce the present ferrous sintered alloy, which is good and well balanced in all of strength, ductility and dimensional stability, in such a preferable setting.
  • the Mn—Si-system powder can further comprise carbon (C) in an amount of from 2.5% by mass or less, or from 1.5 to 2% by mass, when the entire Mn—Si-system powder with C added is taken as 100% by mass.
  • the carbon-system powder introduces C into the ferrous sintered alloy according to the present invention.
  • the Mn—Si-system powder strengthens the present ferrous sintered alloy
  • using the carbon-system powder further intends to strengthen the present ferrous sintered alloy furthermore highly.
  • Fe-C alloy powders and various carbide powders it is preferable to use a graphite powder in which C accounts for 100% virtually.
  • the raw-material powder can comprise the carbon-system powder in an amount of from 0.3 to 0.7% by mass, or from 0.5 to 0.7% by mass, and the Mn—Si-system powder in an amount of from 0.4 to 1% by mass, or from 0.5 to 0.8% by mass, when the entire raw-material powder is taken as 100% by mass.
  • the Fe—Cr—Mo-system powder makes the balance mainly.
  • metallic structures being composed of martensite are less likely to be obtainable. The more the contents of the carbon-system powder and Mn—Si-system powder increase, the more the martensite proportion enlarges.
  • the raw-material powder can preferably comprise the carbon-system powder and Mn—Si-system powder in predetermined proportions, and the Fe—Cr-Mn-system powder making the balance mainly, it is permissible that the raw-material powder can further comprise a free-cutting component, such as an MnS powder and a BN powder. It is affordable that the raw-material powder can further comprise a free-cutting component in an amount of 0.6% by mass or less, 0.3% by mass or less, or from 0.1 to 0.3% by mass, when the entire raw-material powder including the free-cutting component is taken as 100% by mass.
  • the ferrous sintered alloy according to the present invention can be specified so as to comprise Cr in an amount of from 0.5 to 3.5% by mass, Mo in an amount of from 0.1 to 0.6% by mass, Si in an amount of from 0.04 to 0.4% by mass, Mn in an amount of from 0.1 to 0.7% by mass, C in an amount of from 0.3 to 0.9% by mass, and the balance of Fe and inevitable impurities.
  • Mo and Cr are elements that enhance the quench hardenability of ferrous sintered alloy. It is not possible to identify suitable contents of Mo and Cr typically, because such contents depend on addition amounts of C and the other constituent elements. However, it is preferable that the ferrous sintered alloy according to the present invention can contain Cr in an amount of from 0.5 to 3.5% by mass, more preferably from 1.3 to 1.7% by mass, and Mo in an amount of from 0.1 to 0.6% by mass, more preferably from 0.1 to 0.3% by mass, for instance, when the entire present ferrous sintered alloy is taken as 100% by mass.
  • the ferrous sintered alloy according to the present invention comprises both of Mn and Si in an appropriate amount, respectively, it exhibits greatly enhanced mechanical strength, and additionally is good in terms of dimensional stability as well.
  • Mn is an element that is effective in enhancing the strength of ferrous sintered alloy especially.
  • a preferable Mn content can be from 0.1 to 0.7% by mass, more preferably from 0.16 to 0.7% by mass, much more preferably from 0.2 to 0.6% by mass. Too little Mn addition produces the advantage poorly.
  • Mn is added excessively, not only the elongation of resulting ferrous sintered alloys decreases to decline the toughness, but also the dimension of resultant sintered products changes increasingly to disturb the dimensional-stability improvement.
  • the ferrous sintered alloy according to the present invention can preferably comprise Si in an amount of from 0.04 to 0.4% by mass, more preferably from 0.1 to 0.3% by mass, when the entire ferrous sintered alloy is taken as 100% by mass. Too little Si content is not preferable, because the resulting ferrous sintered alloys are poor in terms of the dimensional stability. Too much Si content is not preferable either, because the resultant ferrous sintered alloys show greater amount of dimensional shrinkage.
  • C is one of important strengthening elements for ferrous sintered alloy. Not to mention that C diffusing during sintering makes ferrous sintered alloys by means of solid-solution strengthening or hardening, but including C in an adequate amount makes it possible to subject ferrous sintered alloys to heat treatments, such as quenching and tempering. Thus, it becomes possible to enhance the mechanical characteristics of ferrous sintered alloys much more greatly.
  • a preferable C content can be from 0.3 to 0.9% by mass, or more preferably from 0.3 to 0.7% by mass.
  • C is added to little, the resulting ferrous sintered alloys cannot enjoy the advantages fully. An excessive C addition results in a ferrous sintered alloy with lower ductility.
  • the ferrous sintered alloy according to the present invention can preferably make a Cu-free ferrous sintered alloy that does not include any copper (Cu) virtually, or an Ni-free ferrous sintered alloy that does not include any nickel (Ni) virtually.
  • the present ferrous sintered alloy is of high strength without ever containing Cu or Ni.
  • the present ferrous sintered alloy exhibits enhanced recyclability so as to become a preferable material in view of environmental measure.
  • the present ferrous sintered alloy when the present ferrous sintered alloy is free from Cu, it is possible to avoid the hot shortness or brittleness of ferrous sintered alloy that results from Cu.
  • the present ferrous sintered alloy does not exclude the inclusion of Cu and Ni at all. That is, the present ferrous sintered alloy, which comprises Cu or Ni in an appropriate amount in addition to the above-described alloying elements, falls within the scope of the present invention.
  • the content when specifying a content of Cu or Ni daringly, the content can preferably be 2% by mass or less, or more preferably 1% by mass or less, with respect to the entire present ferrous sintered alloy with Cu or Ni included being taken as 100% by mass.
  • ferrous sintered alloy according to the present invention constitutes a broader concept that involves ferrous-sintered-alloy members, which comprise the present ferrous sintered alloy, throughout the entire present specification.
  • ferrous-sintered-alloy members which comprise the present ferrous sintered alloy
  • suitable forms for producing a ferrous sintered alloy or ferrous-sintered-alloy member according to the present invention will be described.
  • a process for producing ferrous sintered alloy according to the present invention comprises a classifying step, a raw-material-powder mixing step, a compacting step, and a sintering step.
  • the constituent steps will be hereinafter described in detail, respectively. Note that the compositions and compounding proportions of an Fe—Cr—Mo-system powder, Mn—Si-system powder and carbon-system powder are identical with those having been indicated as above already.
  • the classifying step is a step of classifying (or sieving) the Mn—Si-system powder to particles that have a particle diameter of 5 ⁇ m or less at the maximum.
  • Making use of the Mn—Si-system powder being sorted out to have a particle diameter of 5 ⁇ m or less makes it possible to keep a particle diameter of martensite from being more than 20 ⁇ m in the metallic structure of the resulting ferrous sintered alloy.
  • FIG. 3 illustrates a relationship between particle diameters of Mn—Si-system powder and particle diameters of martensite in ferrous sintered alloys.
  • the ferrous sintered alloys were made by sintering raw-material powders that comprised the Mn—Si-system powders with various particle diameters and a set of the Fe—Cr—Mo-system powder and carbon-system powder.
  • the horizontal axis being designated as “FeMS ⁇ 's Particle Diameter “d” specifies the particle diameters of the Mn—Si-system powders
  • the vertical axis being designated as “Martensite's Diameter “D”” specifies the particles diameters of martensite.
  • the resulting martensite's particle diameters are about twice as large as the Mn—Si-system powders' particle diameters.
  • the Mn—Si-system powder being categorized to particles with particle diameters of 5 ⁇ m or less.
  • Fe—Cr—Mo-system powders have particle diameters that are employable as the constituent element of the raw-material powder. For example, later-described “AstaloyCrL” whose maximum particle diameter is 212 ⁇ m can be used as the Fe—Cr—Mo-system powder in the raw-material powder.
  • Fe—Cr—Mo-system powder When making use of such a commercially available Fe—Cr—Mo-system powder, it is permissible to sort out the Fe—Cr—Mo-system powder to particles with a maximum particle diameter of 212 ⁇ m or less, 180 ⁇ m or less, or 150 ⁇ m or less. Especially, when using the Fe—Cr—Mo-system powder that is categorized to particles having a particles diameter of 150 ⁇ m or less at the maximum, it becomes likely to obtain a homogenous ferrous sintered alloy, which is less likely to suffer from componential variations or segregations, and accordingly the resulting raw-material powder makes powder compacts that exhibit enhanced powder-compact density ratios and sintered-body density ratios between the density and the theoretical density. However, it is not desirable to use the Fe—Cr—Mo-system powder that is classified to particles with 63- ⁇ m-or-less particle diameters, because the resultant raw-material powder shows lowered compactibility.
  • the raw-material-powder mixing step is a step of preparing a raw-material powder that comprises the Fe—Cr—Mo-system powder, the carbon-system powder, and the Mn—Si-system powder.
  • a raw-material powder is made so that the carbon-system powder accounts for from 0.3 to 0.7% by mass, or from 0.5 to 0.7% by mass, the Mn—Si-system powder accounts for from 0.4 to 1% by mass, or from 0.5 to 0.8% by mass, and the Fe—Cr—Mo-system powder accounts for the balance, when the entire raw-material powder is taken as 100% by mass.
  • the ferrous sintered alloy according to the present invention that comprises the above-described metallic structure is more likely to be obtainable by preparing the respective powders, which have compositions falling in the predetermined ranges as mentioned previously, and then mixing them in the predetermined compounding proportions as above.
  • the constituent powders can be mixed to make the raw-material powder by means of ordinary methods.
  • a lubricant agent can be further added to the raw-material powder in the raw-material-powder mixing step when the sintering step following the compacting step is a sinter forging step. That is, the Fe—Cr—Mo-system powder, the carbon-system powder, the Mn—Si-system powder and a lubricant agent are mixed in the raw-material-powder mixing step. It is allowable that a content of the lubricant agent can be 1% by mass or less, or from 0.4 to 0.8% by mass, when the raw-material powder including the lubricant agent is taken as 100% by mass.
  • the lubricant agent zinc stearate; lithium stearate; and waxy lubricant agents, for instance, like “ACRAWAX C” (trademark) produced by LONZA JAPAN Co., Ltd., “AMIDE WAX” (trademark) produced by NIHON YUSHI Co., Ltd., and “KENOLUBE” (trademark) produced by HOEGANAES Corp. It is permissible to select one of the lubricant agents to use independently, or to select and then mix two or more of them to use.
  • the compacting step is a step of compacting the raw-material powder to turn it into a powder compact whose density is 7.4 g/cm 3 or more.
  • density 7.4 g/cm 3 or more.
  • the clause, “density is 7.4 g/cm 3 or more” indicates high-density powder compacts, which exhibit a powder-compact ratio, namely, a ratio of apparent powder-compact density to theoretical powder-compact density, that is 95% or more. It is possible to name a compacting method for powder compact that is disclosed in Japanese Patent Publication Gazette No. 3,309,970 (or U.S. Pat. No. 7,083,760), as an example that makes such high-density powder compacts producible.
  • the compacting method will be hereinafter referred to as “die-lubricating warm pressurized compacting method” wherever appropriate.
  • the die-lubricating warm pressurized compacting method makes it possible to perform super high-pressure compacting at industrial levels, super high-pressure compacting which is carried out at a compacting pressure of 1,000 MPa or more, 1,200 MPa or more, 1,500 MPa or more, or 2,000 MPa or more that transcends conventional levels.
  • the die-lubricating warm pressurized compacting method results in producing powder compacts whose density can reach 96% or more, 97% or more, 98% or more, or even up to 99%.
  • the powder compact can exhibit a density of 7.4 g/cm 3 or more when completing the sinter forging process.
  • the powder compact can have a density of 6.5 g/cm 3 at least, 6.8 g/cm 3 or more, or 7.0 g/cm 3 or more, when completing the compacting process. Therefore, it is not required necessarily to use the aforementioned die-lubricating warm pressurized compacting method in the compacting step. That is, it is permissible to compact the raw-material powder to make a powder compact by a commonly-used method. It should be noted herein that powder compacts made by commonly-used methods can make the claimed simple powder compact (or green compact).
  • the resultant powder compact whose density is 7.4 g/cm 3 or more is subjected to the sintering step.
  • the sintering step comprises a heating sub-step, and a cooling sub-step.
  • the heating sub-step the powder compact is heated.
  • the cooling sub-step the powder compact, which has undergone the heating sub-step, is cooled to make a sintered body that has the metallic structure comprising martensite and bainite.
  • the powder compact is needed to be heated to the A 1 transformation temperature (i.e., about 730° C). or more and then to undergo austenitizing process in the heating sub-step of the sintering step.
  • sintering has been usually done at a temperature of 1,050° C. or more, or 1,100° C. or more.
  • a much higher sintering temperature like 1,200° C. or more, 1,250° C. or more, 1,300° C. or more, or 1,350° C. or more, has been selected.
  • the sintering step can preferably be provided with a heating sub-step in which the powder compact is heated in an inert gas atmosphere at a temperature of from 1,100° C. or more to 1,370° C. or less, or from 1,100° C. or more to 1,180° C. or less, for instance.
  • the powder compact in such a heating sub-step, can desirably be retained in such a predetermined temperature range for a time period of from 1 minute or more, or 5 minutes or more. Still, it is allowable to set the retaining time to 60 minutes or less, or 30 minutes or less.
  • the cooling sub-step of the sintering step is done in succession to the aforementioned heating sub-step, and is a step of lowering the resultant ferrous sintered alloy's temperature from the sintering temperature to and around room temperature.
  • the cooling sub-step makes a step in which a temperature of the resulting ferrous sintered alloy is lowered from the sintering temperature to the M s point or less. It is possible to reliably carry out quenching onto the resultant ferrous sintered alloy by means of increasing the cooling rate in the cooling sub-step. Accordingly, it is preferable to set the cooling rate to 5° C./second or more, or 10° C./second or more, for instance.
  • the process for producing ferrous sintered alloy with good machinability according to the present invention comprising the sintering step, which is provided with the above-described heating and cooling sub-steps, enables producers of ferrous sintered alloys to produce a sintered body, namely, the ferrous sintered alloy according to the present invention, which has the metallic structure that is composed of martensite and bainite as aforementioned, after completing the sintering step. That is, it is feasible to intend to reduce the costs in producing high-strength ferrous alloys, because it is possible to even complete the quenching of the resulting ferrous sintered alloy simultaneously with finishing the sintering step. Besides, not only the present ferrous-sintered-alloy production process does not require to be provided with any additional rapid-cooling facilities separately, but also can be put into practical uses on industrial scale.
  • the process for producing ferrous sintered alloy with good machinability according to the present invention can further comprise a step of heat treating the resultant sintered alloy in order to control the strength or toughness after finishing the sintering step, if needed.
  • a step of heat treating the resultant sintered alloy in order to control the strength or toughness after finishing the sintering step, if needed.
  • the present ferrous-sintered-alloy production process is not necessarily required to be further provided with any heat treatment, though the quenching of ferrous sintered alloys has been done commonly by doing extra heat treatments to the ferrous sintered alloys additionally.
  • the present ferrous-sintered-alloy production process makes it possible to carry out the quenching by means of making use of the heating sub-step and subsequent cooling sub-step, which are done in the course of the sintering step.
  • a powder compact which comprises the raw-material powder including a lubricant agent
  • another sintering step that comprises the following sub-steps: a sub-step of heating the powder compact; a sub-step of hot forging the powder compact, which has undergone the heating sub-step, to make a density of the powder compact 7.4 g/cm 3 or more; and a sub-step of cooling the powder compact, which has undergone the hot-forging sub-step, to yield the sintered body.
  • the hot-forging sub-step alone will be hereinafter described, because the heating sub-step and cooling sub-step that make another modified sintering step are the same as those that have been described in paragraphs [0056] and [0057] above.
  • the hot-forging sub-step is done following the heating sub-step, and is a step in which the powder compact is hot forged to make the density 7.4 g/cm 3 or more.
  • Hot forging is usually a process for forming workpiece to be processed as desirable configurations after heating the workpiece to such a high temperature as the raw material's recrystallization temperature or more.
  • the powder compact which is retained at a predetermined temperature for a prescribed time in the above-described heating sub-step, to a hot-forging process as it is.
  • a hot-forging process it is possible to name repressing (or coining), roll forging, and upset coining.
  • the hot-forging sub-step is followed by the cooling sub-step that is done successively.
  • a connecting rod is a member for connecting a piston with a crankshaft.
  • FIG. 9 illustrates an example of the connecting rod.
  • a connecting rod 70 comprises a minor end 71 at one of the opposite ends, and a major end 72 at the other one of the opposite ends.
  • the minor end 71 is provided with a through hole 71 h into which a piston pin is fitted.
  • the major end 72 is provided with a through hole 72 h into which a crankshaft's pin is fitted.
  • such a connecting rod can be manufactured in the following manner: forming a raw workpiece with a predetermined configuration by means of the process for producing ferrous sintered alloy with good machinability according to the present invention; and then providing the resulting raw workpiece with the through holes 71 h and 72 h , which are required in order to connect a piston with a crankshaft securely, by means of cutting work.
  • the following powders were prepared: an Fe-1.5Cr-0.2Mo alloy powder, and a graphite (hereinafter abbreviated to as “Gr”) powder.
  • the Fe-1.5Cr-0.2Mo alloy powder was “AstaloyCrL” (trademark) that was produced by HOEGANAES Corp. and had particle diameters of from 20 to 212 ⁇ m.
  • the “Gr” powder was “JCPB” (trademark) that was produced by NIHON KOKUEN Co., Ltd., and had particle diameters of 45 ⁇ m or less.
  • an Fe-50Mn-30Si ingot was pulverized with a vibration milling machine for 30 minutes, thereby turning the ingot into another powder alloy.
  • the ingot was produced by NIHON DENKO Corp.
  • the vibration milling machine was manufactured by CHUO KAKOKI Co., Ltd. These three powders were sieved to particles with particle diameters of 5 ⁇ m or less, particles with particle diameters of 10 ⁇ m or less, particles with particle diameters of 25 ⁇ m or less, and particles with particle diameters of 45 ⁇ m or less, respectively.
  • a silicon-manganese ingot was likewise pulverized to a powder with the vibration milling machine for 30 minutes, and then the resulting powder was classified to particles with particle diameters of 5 ⁇ m or less, namely, to particle-size-5 ⁇ m particles.
  • the silicon-manganese ingot was type #1 according to JIS (i.e., Japanese Industrial Standards). Note that Fe-50Mn-30Si alloy powder, and the silicon-manganese alloy powder will be hereinafter designated as “FeMS ⁇ ,” and “FeMSC,” respectively. Moreover, the two powders will be hereinafter referred to as “FeMS” collectively. Table 1 below shows the compositions of “FeMS ⁇ ” and “FeMS.”
  • compositions are expressed in “% by mass” in the present specification. Moreover, the expression will mean the same hereinafter unless otherwise specified.
  • LiSt lithium stearate
  • each of the raw-material powders was compacted to a cylinder-shaped powder compact with a size of ⁇ 23 mm in diameter and 12 mm in length.
  • the resulting powder compacts were sintered respectively in a 1,150-° C. nitrogen-gas atmosphere using a fast-cooling sintering furnace, thereby making sintered bodies (i.e., ferrous sintered alloys).
  • the used fast-cooling sintering furnace was produced by SHIMADZU CORPORATION, and could provide variable atmospheres. Note that the powder compacts were retained at 1,150° C. for 10 minutes, and were then cooled at a cooling rate of 70° C./minute after sintering. Thereafter, tempering was carried out onto the resultant sintered bodies in air at 200° C. for 60 minutes.
  • the powder compacts and sintered bodies which were made in accordance with the above-described procedures, were measured for the densities.
  • the densities were computed from the volumes of the powder compacts and sintered bodies, and their masses.
  • the volumes were calculated from the outside diameters and heights of the cylinder-shaped powder compacts and sintered bodies that were measured using a micrometer.
  • the masses of the powder compacts and sintered bodies were weighed separately. Table 2 above shows the computed results. Note that the designations, “G. D.” and “S. D.” in Table 2, specify the densities of the powder compacts and the densities of the sintered bodies, respectively.
  • the hardness of each of the sintered bodies was measured while applying a testing load of 30 kgf to the cross-sectional surface using a Vickers hardness meter. Table 2 recites the measured results, and FIG. 1 illustrates them.
  • the content proportions of the respective elements that the sintered bodies included were substantially equal to those values that were calculated from the compositions and blended proportions of the respective raw-material powders. In some of the sintered bodies, however, their C content alone decreased slightly.
  • the cross-sectional surface to be observed was prepared by subjecting each of the sintered bodies' cut cross-sectional face to an etching treatment using nital after grinding the face.
  • An area proportion of martensite i.e., a martensite proportion
  • the martensite proportion was determined by calculating an area of martensite how much it accounted for in the entire area of the thus obtained image by means of image analysis.
  • FIG. 2 illustrates the martensite proportions that were calculated in this manner.
  • “M” designates martensite
  • “UB” designates upper bainite
  • “FP” designates micro-fine pearlite, respectively.
  • a maximum diameter “D” of martensitic crystalline particles, and a maximum diameter “d” of FeMS ⁇ particles were determined in the resulting image of each of the sintered bodies. Note that the maximum diameter “D” of martensitic crystalline particles herein means the maximum value of intervals being exhibited by two parallel lines that hold the martensitic crystalline particles between them.
  • the maximum diameter “d” of FeMS ⁇ particles herein means an interval being exhibited by two parallel lines that hold an FeMS ⁇ particle between them, FeMS ⁇ particle which is visible at the central part of a martensitic crystalline particle that is labeled as having the maximum diameter “D” as described herein.
  • the graph shown in FIG. 3 gives individual maximum diameters “D” and “d” of the respective martensitic crystalline particles and FeMS ⁇ particles that were found in some of the photographed images of the sintered bodies.
  • the upper left of FIG. 3 schematically illustrates how to measure the maximum diameter “D” of a martensitic crystalline particle and the maximum diameter “d” of an FeMS ⁇ particle in the martensitic crystalline particle.
  • FIG. 2 shows not only the martensite proportions in the resulting sintered bodies but also outcomes of the microscopic observations on the cross-sectional faces of the sintered bodies that Raw-material Powder Nos. 2, 12 and 22 yielded.
  • FIG. 1 shows a relationship between Vickers hardness, varying addition amount of FeMS ⁇ powder with particle-size-5 ⁇ m, and varying addition amount of “Gr” powder.
  • the table in FIG. 2 gives another relationship between structural proportion, varying addition amount of “FeMS ⁇ ” powder with particle-size-5 ⁇ m, and varying addition amount of “Gr” powder. It was understood that controlling the proportions of “Gr” powder and “FeMS ⁇ ” powder that occupy in the raw-material powder makes it possible to yield a ferrous sintered alloy, which has a metallic structure that is composed of martensite and bainite, and that exhibits a martensite proportion of 40% or less by area.
  • a ferrous sintered alloy having such a noble metallic structure can be readily available by setting the content of “FeMS ⁇ ” powder so as to fall in a range of from 0.5 to 1% approximately, and setting the content of “Gr” powder to 0.7% or less, with respect to the entire raw-material powder. Moreover, it was ascertained that a ferrous sintered alloy being composed of the unprecedented metallic structure comes to demonstrate a Vickers hardness of from 300 to 400 Hv approximately.
  • FIG. 3 is a graph for illustrating a relationship between the maximum particle diameter “d” of “FeM ⁇ ” particles, which raw-material powder included, and the maximum particle diameter “D” of martensitic crystalline particles in resultant sintered body.
  • the values, which lie in a range where the maximum particle diameter “d” is from 25 to 45 ⁇ m, are derived from the cross-sectional photomicrographs on the sintered bodies that were fabricated using Raw-material No. 31; the values, which lie in a range where the maximum particle diameter “d” is from 10 to 25 ⁇ m, are derived from the cross-sectional photomicrographs on the sintered bodies that were fabricated using Raw-material No.
  • the maximum particle diameter “D” of martensitic crystalline particles was about twice as large as the maximum particle diameter “d” of “FeMS ⁇ ” particles.
  • employing the “FeMS ⁇ ” powder whose particle size was 5 ⁇ m or less enabled the resulting martensitic crystalline particles to exhibit a maximum particle diameter “D” of 20 ⁇ m or less.
  • measuring the Vickers hardness of martensitic crystalline particles revealed that martensitic crystalline particles whose particle diameters were 20 ⁇ m or less exhibited a hardness of from 400 to 500 Hv approximately. Meanwhile, martensitic crystalline particles having particle diameters of more than 20 ⁇ m exhibited a hardness that surpassed 500 Hv.
  • Cylinder-shaped powder compacts were made of the above given raw-material powders with a common die-compacting apparatus.
  • the powder compacts had a size of ⁇ 61 mm in diameter and 27 mm in thickness. Note that the compacting operation was carried out so as to make the resulting powder compacts exhibit a density of 7.0 g/cm 3 .
  • the resultant powder compacts were heated in a 1,150-° C. nitrogen-gas atmosphere for 10 minutes using an ambient-heating furnace (or Erema furnace).
  • the heated powder compacts were forged by means of coining by a facing pressure of 10 ton/cm 2 and were then cooled at a cooling rate of 70° C./min., thereby producing sintered forged bodies (or ferrous sintered alloys).
  • the sintered forged bodies which were fabricated using Raw-material Powder Nos. 2c, 11e through 13e, 22e and 12e + , were labeled in this order as Sintered Forged Body Nos. C2, E11 through E13, E22 and E12 + .
  • the sintered forged bodies which were made through the above-described fabrication steps, were examined for the hardness, respectively.
  • the hardness was measured following the method of measuring hardness that has been described already in paragraph [0070].
  • each of the sintered forged bodies was tested for the tensile strength and elongation. Note that the tensile strength and elongation were found by means of procedures that conformed to “Z 2241” according to JIS (i.e., Japanese Industrial Standards).
  • Test specimens were prepared by removing mill scales from the sintered forged bodies that were produced following the above-described procedures.
  • the thus prepared test specimens had a size of ⁇ 61 mm in diameter and 23 mm in thickness.
  • the test specimens were subjected to a cutting test in which a computer numerical controlled (or CNC) lathe was used. After chucking a test specimen “P” with a soft jaw 41 as illustrated in FIG. 4 , an outside-diameter cutting process by turning was carried out with a cutting tool 42 for processing outside diameter. Note that the cutting tool 42 was fitted with a bit 42t.
  • the used bit 42 t was a carbide bit “SPP-321S-CG05” produced by SUMITOMO DENKO Co., Ltd.
  • the cutting conditions were set up as follows: the cutting speed: 195 m/min.; the feed: 0.12 mm/revolution; and the cut depth: 0.05 mm.
  • the outer circumference of the test specimens was cut by turning by 12 mm in outside diameter for every operation of the processing paths (or for every processing path), and the test specimens were subjected to the turning operation up to 150 processing paths (e.g., 30 processing paths ⁇ 5 times).
  • the finished surface of the test specimens that had undergone 30 processing paths, and the finished surface of the test specimens that had undergone 150 processing paths were measured for the 10-point average roughness Rz (as per JIS), respectively, with a surface roughness meter.
  • bit 42 t was examined with a stereomicroscope for the wear amount (or wear depth) every time the test specimens had undergone processing paths.
  • Table 4 shows the resulting finished-surface roughness of the test specimens.
  • FIG. 5 illustrates the resultant wear amounts of the bit 42 t .
  • Sintered Body No. C2 was a comparative example, which was made using Raw-material Powder No. 2c that was free from “FeMS ⁇ .” As a result, Sintered Body No. C2 did not contain any martensite in the metallic structure, and accordingly exhibited insufficient hardness and tensile strength. Consequently, Sintered Body No. C2 suffered from chipping that occurred when it underwent the processing only up to 90 processing paths only during the cutting test, and thereby could not complete the test.
  • Sintered Body Nos. E11 through E13, E22 and E12 + could go through the processing of the cutting test up to 150 processing paths.
  • Sintered Body Nos. E11 through E13, E22 and E12 + had a metallic structure that comprised martensite and bainite, and whose martensite proportion fell in a range of from 5 to 40% by area, respectively.
  • Sintered Body Nos. E11 through E13, E22 and E12 + exhibited a Vickers hardness that came in a range of from 300 to 400 Hv; showed a tensile strength of 1,000 MPa approximately; and exhibited an elongation of from 6 to 10%. According to the results of the cutting test, Sintered Body Nos.
  • E11 through E13, E22 and E12 + demonstrated a remarkable finished-surface roughness, respectively. That is, the finished-surface roughness, which they exhibited after they underwent the processing of the cutting test up to 150 processing paths, was virtually unchanged from that they showed after they experienced 30 processing paths in the course of the cutting test. Note that the values of the surface roughness, which Sintered Body Nos. E11 through E13, E22 and E12 + exhibited, were equivalent to that of a ferrous sintered alloy (i.e., an Fe—Cu—C—MnS material whose Vickers hardness is 270 Hv) that has been put into practical use so far. In addition, Sintered Body Nos. E12 and E12 + differed in that they contained the MnS powder or not. Despite the presence or absence of the MnS powder, the two sintered bodies demonstrated good characteristics regarding both of the strength and machinability.
  • a ferrous sintered alloy i.e., an Fe—Cu—C—MnS material whose Vickers hardness is 270
  • FIGS. 6 , 7 and 8 show wear states that appeared on the flank of the bit 42 t after finish cutting Sintered Body Nos. C2, E12 and E12 + in the cutting test, respectively, and appearances of chips that occurred during the test.
  • FIG. 6 the surface of the bit 42t, which machined Sintered Body No. C2 by turning, was abraded considerably, and continuous chips occurred.
  • FIGS. 7 and 8 no visible wear arose on the surface of each of the bits 42 t , which machined Sintered Body Nos. E12 and E12 + by turning, and the resulting chips were divided or segmented into pieces.
  • FIG. 8 the surface of the bit 42 t , which machined Sintered Body No. E12 + by turning, was worn less, as well as the resultant chips were fractured apart favorably.
  • the ferrous sintered alloys according to the present invention produced high strength of 1,000 MPa approximately, and simultaneously exhibited good machinability, which was on par with that of Fe—Cu—C material that has been made use of at present, without ever adding any free-cutting component like the MnS powder.
  • a raw-material powder which comprises an Mn—Si-system powder in an amount of 0.5% by mass, a carbon-system powder in an amount of from 0.5 to 0.7% by mass, a free-cutting component, if needed, in an amount of 0.6% by mass or less, and the balance of an Fe—Cr—Mo-system powder, yields a ferrous sintered alloy that not only demonstrates high strength but also is superb in terms of machinability.
  • the compositional proportion of an Mn—Sn-system powder which comes in a range of from 0.4 to 0.6% by mass, for instance, fall within the error range of the measurement.

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