EP2000553B1 - Materiau lamine pour bielle a fissure de rupture presentant une excellente capacite de fissure de rupture, element forge a chaud pour bielle présentant une excellente capacité de fissure de rupture et bielle a fissure de rupture - Google Patents

Materiau lamine pour bielle a fissure de rupture presentant une excellente capacite de fissure de rupture, element forge a chaud pour bielle présentant une excellente capacité de fissure de rupture et bielle a fissure de rupture Download PDF

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EP2000553B1
EP2000553B1 EP07738409A EP07738409A EP2000553B1 EP 2000553 B1 EP2000553 B1 EP 2000553B1 EP 07738409 A EP07738409 A EP 07738409A EP 07738409 A EP07738409 A EP 07738409A EP 2000553 B1 EP2000553 B1 EP 2000553B1
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Prior art keywords
fracture
connecting rod
splitting
content
fracture splitting
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German (de)
English (en)
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EP2000553A4 (fr
EP2000553A1 (fr
Inventor
Goro Anan
Keita Shiihashi
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
    • B21K1/00—Making machine elements
    • B21K1/06—Making machine elements axles or shafts
    • B21K1/12—Making machine elements axles or shafts of specially-shaped cross-section
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Definitions

  • the present invention relates to a rolled material for a fracture splitting-type connecting rod with excellent fracture splitting characteristics, a hot-forged part for a fracture splitting-type connecting rod with excellent splitting characteristics, and a fracture splitting-type connecting rod, and more particularly relates to a rolled material suitable for the manufacture of a connecting rod having a through-hole section for assembly with a crankshaft that is fracture split into substantially semicircles, a hot-forged part obtained using this rolled material, and furthermore a fracture splitting-type connecting rod obtained using this hot-forged part.
  • a connecting rod (also known as conrod) constitutes a component part of internal combustion engines including gasoline engines and diesel engines employed for coupling a piston to a crankshaft and transmitting the reciprocal motion of the piston to the crankshaft for conversion to rotational motion.
  • the connecting rod comprises a through-hole (substantially circular) for assembly with the crankshaft and, for ease of assembly and for removal for the purpose of maintenance, it is configured with the through-hole split into two substantially semicircles.
  • the side of the split connecting rod directly coupled with the piston is referred to as a connecting rod main body, while the other side is referred to as a connecting rod cap.
  • connecting rods as described above are manufactured by individual hot forging of the connecting rod main body and connecting rod cap, and then cut-machining of the mating faces thereof, and machining of a knock pin to prevent displacement administered in accordance with need.
  • this kind of machining has the inherent problem of not only lowered material yield but also inflated cost due to the large number of steps necessitated thereby.
  • the material used in Europe for the manufacture of the connecting rod based on the fracture splitting process described above is a DIN standard C70S6 material. Although this material is suitable for the fracture splitting process described above, the problems inherent to this material are its inability to meet the high level of fatigue strength and proof stress demanded and, furthermore, its unsatisfactory machinability. Accordingly, a need exists for a steel for the manufacture of a fracture splitting-type connecting rod of a type that has excellent fatigue strength and proof stress and, furthermore, good machinability.
  • patent document 1 discloses a fracture-splittable high-strength as-rolled steel and an intermediate product thereof.
  • This publication discloses how controlling both the aspect ratio of a sulfide of which MnS is the main constituent and the area ratio of pearlite produces random unevenness on fracture faces and reduces the likelihood of displacement subsequent to a mating thereof.
  • the prescribed area ratio of pearlite is not more than 40% and, where ferrite is the remaining component, the area ratio of ferrite is not less than 60%.
  • the ferrite exists in a soft phase and a large area ratio of ferrite is regarded as a factor in deformation that occurs when the fracture-splitting process is performed.
  • Patent document 2 discloses an as-rolled steel of high strength, low ductility and excellent machinability having a C content of 0.25 to 0.70% and an area ratio of ferrite suppressed to not more than 10%.
  • this technology is based on formation of a hard layer of high pliability and, accordingly, with the increased load required when the fracture splitting process is performed, it is thought that this will lead to increased deformation.
  • Patent document 3 discloses a technology to ensure machinability and low ductility of a hot forged steel for the manufacture of a connecting rod with a C content of 0.5% to 0.7% and an area ratio of ferrite of 5 to 15%.
  • patent document 4 discloses a steel of a C content of 0.2 to 0.6% in which the fracture splitting characteristics are ensured by the addition of V or Ti.
  • patent documents 5 to 7 disclose steels for a fracture splitting-type connecting rod in which both the C content and the ferrite fraction are suppressed to ensure machinability and mateability.
  • Patent document 8 discloses a hot as-rolled steel in which the fracture splitting characteristics are improved with the aspect ratio of the sulfide-based inclusion being not more than 10.
  • the MnS is formed in a spherical shape, it is thought that a large number of voids originating in the MnS will be generated in the fracture-splitting process when the S content is comparatively large. Because, as a result, ductile fracture of the ferrite portion attributable thereto is more likely to occur and the fracture faces of the connecting rod cap and the connecting rod main body cannot be mated, an apparent greater deformation is thought to occur in the fracture-splitting process.
  • the present invention was made in view of the above circumstances it is an object of the invention to provide a rolled material ideal for manufacturing a connecting rod in which a through-hole section for assembly with a crankshaft is fracture split in substantially semicircles, a hot-forged part obtained using this rolled material and, furthermore, a fracture splitting-type connecting rod obtained using this hot-forged part.
  • the rolled material for a fracture splitting-type connecting rod having excellent fracture splitting characteristics pertaining to the present invention is characterized in that a chemical composition comprises, by mass% (hereinafter the same for each component),
  • the rolled material may further comprise, as an additional element, Se: 0.0010 to 0.1% and/or Bi and Pb: 0.01 to 0.2% in total.
  • the present invention includes a hot-forged part for a fracture splitting-type connecting rod with excellent splitting characteristics, obtained by hot forging a rolled material and, furthermore, a fracture splitting-type connecting rod obtained using this hot-forged part.
  • the average aspect ratio of the sulfide-based inclusion refers to a value measured by a method indicated in the later-described examples.
  • a rolled material for a connecting rod in which the costs of the splitting processing can be reduced because the through-hole section of the connecting rod can be satisfactorily fracture split into substantially semicircles and, in addition, that exhibits a higher strength and better machinability than the C70S6 material used in the USA, as well as a hot-forged part obtained using this rolled material and, furthermore, a fracture splitting-type connecting rod obtained using this hot-forged part, can be actualized.
  • the inventors conducted earnest research of steel materials of low C content and increased S content which ensures a workability (in particular, machinability) in order to obtain a rolled material for a connecting rod in which fracture splitting can be satisfactorily implemented when a through-hole section for assembly with a crankshaft is split into two substantially semicircles.
  • machinability workability
  • the inventors discovered a specific method for actualizing a connecting rod material for a connecting rod having excellent machinability and adequately improved fracture splitting characteristics based on the concept of controlling the relationship between the ferrite fraction and the C content and, in addition, controlling the aspect ratio of the sulfide-based inclusion thereof.
  • the present invention will be hereinafter described in detail.
  • FIG. 1 is a graph showing the relationship between Pc and distortion (splitting distortion) generated in the fracture splitting process that depicts the test results of later-described examples (aspect ratio of sulfide-based inclusion in each case within a prescribed range) (notably, the line drawn in FIG. 1 represents the trend at C content 0.33%). It is clear from FIG. 1 that the splitting distortion can be reliably controlled by not only controlling the sulfide-based inclusion within a later-described prescribed range but by controlling the Pc.
  • the minimum splitting distortion when fracture splitting is performed occurs in the range close to Pc 0.5, and that to suppress the splitting distortion to not more than 200 ⁇ m (the maximum splitting distortion of the C70S6 material is of the order of 200 ⁇ m and, accordingly, a figure of not more than 200 ⁇ m is targeted) the lower limit of Pc must be 0.41.
  • the Pc should be not less than 0.45.
  • the upper limit of the Pc should be 0.75. In order to minimize the splitting distortion to not more than 100 ⁇ m, the Pc should be between 0.47 and 0.60.
  • excellent fracture splitting characteristics can be ensured in the present invention by controlling the morphology of the later-described sulfide-based inclusion to promote development of the fracture faces in the fracture splitting process, and controlling the relationship between the ferrite fraction and the C content. Furthermore, because voids proximal to notches that are generated when the sulfide-based inclusion content is increased can be suppressed, excellent machinability can also be ensured.
  • Sulfide-based inclusions of large aspect ratio created by an expanding step in the manufacturing process inhibit the development of cracks in the fracture splitting process.
  • the deformation (distortion) occurring in the fracture splitting process increases.
  • FIG. 2 is a graph showing the relationship between the distortion (splitting distortion) generated in the fracture splitting process and the average aspect ratio (L/W) of the sulfide-based inclusion (the Pc in each case falls within the prescribed range).
  • the average aspect ratio of the sulfide-based inclusion must be not more than 10.0.
  • the aspect ratio be not more than 9.5.
  • sulfide-based inclusion principally implies MnS, it incorporates other sulfides apart from Mn including Zr, Ti, Mg, Ca, Se, Te and REM, as well as composite sulfides thereof, and composite compounds of these sulfides and composite sulfides with an oxide nucleus.
  • Veq V + Ti / 2 + Si / 20 ⁇ [In Equation (2), V, Ti and Si represent the content of each element in steel (mass %) ⁇ > Irrespective of whether or not an inclusion such as MnS or the like is present, voids are caused and ductility fractures are induced when the fracture splitting process is performed. The origin thereof is thought to be attributable to insufficient ferrite hardness. Thereupon, subsequent to an examination carried out to determine those elements affecting ferrite hardness, the inventors discovered that the elements effecting ferrite hardness were V, Ti and Si and, through various tests, discovered that a correlation exists between the Veq described above containing V, Ti and Si, and ferrite hardness.
  • FIG. 3 is a graph that shows the relationship between Veq and distortion (splitting distortion) generated in the fracture splitting process which depicts the test results of the later-described examples. It is clear from FIG. 3 that to suppress the splitting distortion to not more than 200 ⁇ m and to ensure excellent fracture splitting characteristics, the Veq must be not less than 0.18 mass%. More preferably, this is not less than 0.22 mass%. As the effect thereof is saturated when the Veq is 0.40 mass% or more, from the viewpoint of cost the Veq is preferably not more than 0.40 mass%.
  • Ceq C + 0.28 ⁇ Mn - 1.0 ⁇ S + 0.32 ⁇ Cr + 1.7 ⁇ V + 1.3 ⁇ Ti ⁇ In Equation (3), C, Mn, S, Cr, V and Ti represent the content of each element in steel (mass%) ⁇ > Ceq constitutes a correlation parameter of the hardness of the steel material.
  • the Ceq should be controlled to not less than 0.80 mass% (more preferably not less than 0.90 mass%) to ensure a strength of the steel material that facilitates the use thereof as a connecting rod.
  • the upper limit thereof is preferably 1.50 mass%.
  • PM 554 ⁇ C + 71 ⁇ Mn - 262 ⁇ S + 82 ⁇ Cr + 429 ⁇ V ⁇ In Equation (4), C, Mn, S, Cr and V represent the content of each element in steel (mass%) ⁇ > PM constitutes a correlation parameter of machinability.
  • PM should be not more than 500 mass% (more preferably not more than 400 mass%).
  • the C is an element necessary for ensuring strength and reducing distortion in the fracture splitting process. It has the additional effect of facilitating the formation of a pearlite system or the like for controlling the generation in the ferrite portion of voids having a sulfide-based inclusion nucleus. Accordingly, the C content must be not less than 0.25%. More preferably, this is not less than 0.30%. However, because of the deterioration in machinability that occurs when the C content is excessive, the content thereof should be not more than 0.60%. More preferably, this is not more than 0.55%.
  • the Mn content increases the strength of the steel material and, in addition, improves the quenching characteristics thereof and, when the carbon content is high, it facilitates the generation of a fragile heat-affected layer in a laser-processed notch base portion that improves the ease of fracture splitting.
  • the Mn content is preferably not less than 0.5%.
  • bainite is generated following forging that, in turn, results in an increase in hardness and lowering of machinability.
  • the Mn content in the present invention is not more than 2%. More preferably, it is not more than 1.5%.
  • MnS sulfide
  • S generates a sulfide (MnS) with Mn and is an element effective for improving machinability.
  • this effect is exhibited in an S content not less than 0.05%. More preferably, this is not less than 0.08% and desirably not less than 0.10%.
  • MnS formed in the manufacturing process in a long and narrow stretched shape by rolling or the like interferes with the development of the fracture faces when the fracture splitting process is performed.
  • the S content is not more than 0.2%. More preferably, it is not more than 0.12%.
  • Si is useful as a deoxidizing element in the molten steel manufacture process and is also effective for, by solid dissolving in ferrite, improving the strength of the soft phase (ferrite) which constitutes the main cause of the plasticity deformation that occurs when the fracture splitting process is performed, and for improving the proof stress and fatigue strength of the steel.
  • it is effective for suppressing deformation (roundness change) when the fracture splitting process is performed, and for improving the mateability of the fracture faces.
  • V has the effect of suppressing deformation when the fracture splitting process is performed by increasing the strength of the ferrite in the same way as Si.
  • the V content is preferably not less than 0.05%.
  • the upper limit thereof is 0.3%.
  • the P in the present invention is effective for controlling deformation in the fracture-splitting process and improving the mateability of the fracture faces. In order to exhibit this effect, it may be actively contained in an amount not less than 0.010%. More preferably, this is not less than 0.02%. However, because P constitutes an element that increases the likelihood of defects being formed in a continuous forging process, the content thereof is not more than 0.15% (and more preferably not more than 0.08%).
  • Al is an element that exhibits a deoxidizing effect in the manufacture of molten steel. Because the sulfide-based inclusion can more easily be formed in a spherical shape as a result of a lowered oxygen concentration in the molten steel, it contributes to the sulfide-based inclusion being formed in a spherical shape. For these effects to be exhibited it is preferably contained in an amount not less than 0.0010%. More preferably, this is not less than 0.010%. However, the effect thereof is saturated if the Al content and so on is excessive, and formation of the sulfide-based inclusion in a spherical shape is prevented if the oxygen concentration in the molten steel is too low. Accordingly, the Al content is not more than 0.06% (and more preferably not more than 0.020%).
  • N is an element that is unavoidably contained in the steel. Because it is a cause of forging defects if contained in a large amount, the content thereof is suppressed to not more than 0.03% (and more preferably not more than 0.02%).
  • the strength of the steel material is increased and the quenching characteristics are improved in the same way as Mn described above.
  • the carbon content is high, it facilitates the generation of a fragile heat-affected layer in a laser-processed notch base portion that improves ease of fracture splitting. In order to exhibit this effect it is preferably contained in an amount not less than 0.1% (and more preferably not less than 0.15%).
  • Cr is contained in a large amount bainite is generated following forging with a resultant increase in hardness and lowering of machinability.
  • bainite contains many movable dislocations, a lowering of the proof stress, which constitutes an essential characteristic of the connecting rod, occurs. Accordingly, the Cr content in the present invention is not more than 2% (and more preferably not more than 1.0%).
  • ⁇ At least one type selected from a group consisting of:
  • Ti contributes to the formation of the sulfide-based inclusion in a spherical shape and, in addition, has the effect of suppressing deformation of the sulfide-based inclusion and increasing the strength of the ferrite in the same way as Si and V.
  • the Ti is preferably contained in an amount not less than 0.005%. More preferably, this is not less than 0.05%.
  • the upper limit thereof is 0.1%. More preferably, this upper limit is not more than 0.08%.
  • Ca has the effect of affording formation of the sulfide-based inclusion in a spherical shape.
  • the Ca is contained in an amount not less than 0.0005%.
  • Al or the like is added directly prior to the addition of Ca to reduce the oxygen content in the molten steel after which the Ca is added.
  • the Ca content should be not more than 0.01% (and more preferably not more than 0.0030%).
  • Te is another element that has the effect of forming the sulfide-based inclusion as a spherical shape. In order that this effect is exhibited, it is preferably contained in an amount not less than 0.0010%. However, because of the deterioration in heat deformation behavior that occurs when it is contained in a large amount, it should be contained in an amount not more than 0.1% (and preferably not more than 0.01%).
  • the REM (rare earth elements; for example, a mish metal) have an effect comparable to that of Mg for forming the sulfide-based inclusion as a fine structure and contributing to improved mechanical characteristics.
  • the amount of REM that may be added with the anticipation of this effect in mind is not less than 0.0005%. More preferably, this amount should be not less than 0.0010%. However, when added in an excessive amount a large amount of oxides are formed and a loss of mechanical characteristics occurs. Accordingly, the REM should be contained in an amount not more than 0.3% (more preferably not more than 0.010%).
  • the present invention contains the prescribed elements noted above, the balance thereof is made up of iron and unavoidable impurities, these unavoidable impurities being allowable as infiltrated elements introduced according to conditions such as the raw materials, materials and manufacturing equipment conditions and so on.
  • these elements can be acceptably contained within a prescribed range that facilitates further improvement of the fracture splitting characteristics.
  • ⁇ Se 0.0010 to 0.1%
  • Each of the elements Se, Bi and Pb has the effect of improving machinability. In order for this effect to be exhibited, it is preferable that Se is contained in an amount not less than 0.0010%. In addition, if the elements Bi and/or Pb are contained, it is preferable that they are contained in an amount not less than 0.01%. However, because of the deterioration in hot deformation behavior that occurs when Se is contained in a large amount, it is preferable that it is contained in an amount not more than 0.1% (and more preferably not more than 0.03%).
  • the Bi and/or Pb contained in a large amount are a catalyst of forging defects in the steel material and faults during the rolling thereof, the Bi and/or Pb should be contained in a total amount of not more than 0.2% (and more preferably not more than 0.15$).
  • the rolling material of the present invention is a 2-phase ferrite and pearlite system in which the total area ratio of the ferrite and pearlite is 95% or more of the whole.
  • Other systems apart from the ferrite and pearlite may allowably occupy not more than 5% of the area ratio.
  • a heating temperature for the hot forging of not less than 950°C is preferred.
  • the temperature is preferably not more than 1200°C.
  • the ferrite fraction can be adjusted by well-known means such as adjustment of the rolled material temperature directly following forging, adjustment of the cooling speed directly following forging, or adjustment of alloy elements other than C. More specifically, the following method may be employed. That is to say, with the forging being implemented under suitable conditions, the ferrite fraction is measured and the Pc calculated. When the Pc does not fall within the prescribed range, adjustments to establish the Pc within the prescribed range based on lowering of the ferrite fraction include lowering the cooling speed, lowering the steel material temperature directly following forging, and lowering of the alloy components such as Mn within a prescribed range are implemented. The Pc can be constantly adjusted by repeating this trial and error process in this way until the Pc is of the order of 0.5.
  • the rolling material of the present invention is an as-rolled steel that in the manufacture of a hot forged component that uses this rolling material can be used unaltered in the cooled state without need for a heat treatment such as quenching or baking to be implemented to ensure the mechanical characteristics following forging.
  • a heat treatment such as quenching or baking to be implemented to ensure the mechanical characteristics following forging.
  • the shape of the rolled material is rod-shape, there are no particular restrictions to the size thereof, the diameter thereof being normally of the order of 25 to 50mm.
  • the hot-forged part of the fracture splitting-type connecting rod of the present invention is obtained using this rolling material to form the external shape of the connecting rod by hot forging with a well-known method.
  • production of this fracture splitting-type connecting rod involves implementation of a processing such as mold processing of the forged component part to form a through-hole for assembly with a crankshaft, and then fracture splitting of this through-hole section into two substantially semicircles.
  • Samples were taken from a cross-section parallel to the longitudinal direction to allow for observation of a D/4 section of the produced bar steel (see FIG. 4 ) and, following mirror-surface polishing of the surface thereof, test pieces were prepared for system observation by corrosion of the samples with Nital.
  • the samples were observed in 1-visual field with a 100x magnification optical microscope (1-visual field photographic size: 9cm x 7cm), and an image analysis of the obtained photos was carried out. This measurement was carried out in the same way using a desired 3-visual field of the sample surface, the average value thereof being taken as the ferrite fraction (area ratio%).
  • the total area ratio of the ferrite and the pearlite was determined on the basis of this image analysis.
  • FIG. 5(a) shows an upper surface view of a test piece and (b) shows a side view of a test piece, a denoting a notch, b denoting a bolthole, and the arrow c denoting the direction of rolling in each of the drawings.
  • the test pieces were of a plate shape of 65mm x 65m x 22mm thickness, a ⁇ 40mm cylinder shape being bored in the center thereof. A notch was provided in the end part of the bored portion.
  • a bolthole b ( ⁇ 8.3mm) was provided along the direction of rolling of the test pieces.
  • a fracture splitting of the test pieces involving the setting thereof in a press setter (1600t press, press speed: 270mm/s [speed at time of jig contact (jig height 110mm), and, because the wedge angle between the wedge 4 and wedge 5 is 30°, a TP fracture speed of approximately 150mm/s]) was implemented.
  • the hole diameter difference before and after fracture splitting (L2-L1) was measured as the splitting distortion, and the splitting characteristics were evaluated as excellent if the splitting distortion was 200mm or less.
  • b01 to b03 constitute examples in which the average aspect ratio of the sulfide-based inclusion is controlled by altering the steel material temperature directly prior to rolling and altering the steel material temperature directly following forging.
  • the aspect ratio does not necessarily fall within the prescribed range even if an element such as Ca for facilitating the formation of the sulfide-based inclusion in a spherical shape is added and, in addition, it is affected by the steel material temperature directly prior to rolling and the steel material temperature directly following forging. Because the splitting distortion exceeds 200 ⁇ m (maximum fracture distortion of the C70S6 material is exceeded) when the aspect ratio exceeds 10.0 as in b03, excellent fracture splitting characteristics cannot be ensured.
  • the comparatively small Mn content in e01 promotes the generation of ferrite and results in the Pc exceeding the prescribed range.
  • the comparatively large Mn content in e04 generates an insignificant amount of ferrite and, accordingly, the Pc is below the prescribed range. For this reason, the fracture splitting characteristics of e01 and e04 are poor.
  • i01 to i04 constitute examples in which the V content is varied, and while in i01 the average aspect ratio of the sulfide-based inclusion is suppressed to not more than 10.0 and the ferrite fraction lies within the prescribed range, voids are generated and the fracture splitting characteristics is poor because of the low Veq.
  • m01 to m16 constitute examples in which a socalled selective element such as Ti and Zr or the like has been added, voids are generated and the fracture splitting characteristics of m01 is poor because of the low Veq in the same ways as i01.
  • m04 constitutes an example to which B has been added, it is clear that the addition of B in this way has no undesirable effect on the fracture splitting characteristics.
  • the Ca is comparatively small and the addition of other elements and the manufacturing conditions for forming the sulfide-based inclusion in a spherical shape are not controlled, the average aspect ratio of the sulfide-based inclusion is increased and the splitting distortion is increased.
  • the rolling material satisfying the conditions of the present invention and having a splitting distortion not more than the 200 ⁇ m maximum distortion range of the C70S6 material used in Europe is suitable for the manufacture of a fracture splitting-type connecting rod. More particularly, because the C content thereof is less than in the C70S6 material and the S content can be added in a sufficient amount, this rolling material also has excellent machinability.
  • the steel of the chemical compositions a01 to 07 of Table 1 was melted and forged in accordance with a method for manufacturing molten steel, and then bloomed and rolled (steel material temperature directly prior to rolling 950°C) to produce a 32mm ⁇ bar steel. This was then hot forged at the conditions shown in Table 5 and, by further mechanical processing, a hot-forged part (thickness 18mm) having the external shape of a connecting rod was manufactured.
  • the hot-forged part has an integrated morphology of a connecting rod main body part having a coupling axis with a piston and a semi-circular portion for assembly with a crankshaft, and a connecting rod cap portion having a semi-circular portion for forming a through-hole together with the connecting rod main body part, the coupling axis being formed along the direction of rolling.
  • the hot-forged part is split into the connecting rod main body portion and the connecting rod cap portion by creation of a notch therein using a laser and the action of a mechanical force causing it to fracture.
  • the notch is formed so that the fracture faces are orthogonal to the direction of rolling.
  • the average aspect ratio of the sulfide-based inclusion and the ferrite fraction of the obtained fracture splitting-type connecting rod were measured in the same way as described above.
  • the hole difference diameter (L2-L1) of the through-hole prior to and following fracture splitting was measured as the splitting distortion.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Shafts, Cranks, Connecting Bars, And Related Bearings (AREA)

Claims (5)

  1. Matériau laminé pour une bielle à tête divisée caractérisé en ce que la composition chimique comprend, en % massique applicable à chaque composant,
    C : 0,25 à 0,60%,
    Mn : 0,5 à 2%,
    S : 0,05 à 0,2%,
    Si : 0,05 à 1,5%,
    V : 0,05 à 0,3%,
    P : 0,010 à 0,15%,
    Al : 0,0010 à 0,06%,
    N : 0,03% ou moins et
    Cr : 0,1 à 2%,
    et comprend en outre au moins un type de composant choisi d'un groupe constitué de
    Zr : 0,005 à 0,2%,
    Ti : 0,005 à 0,1%,
    Ca : 0,0005 à 0,01%,
    Te : 0,0010 à 0,1%, et
    REM : 0,0005 à 0,3%,
    et le reste est constitué du fer et d'impuretés inévitables,
    la ferrite et la perlite occupent au total un rapport de surface par rapport à la surface totale d'au moins 95%,
    un rapport moyen hauteur/largeur d'une inclusion à base de sulfure ne dépasse pas 10,0 lorsqu'on regarde dans une partie correspondant à D/4, D étant le diamètre du matériau laminé, dans une section transversale parallèle à une direction longitudinale d'un matériau laminé en forme de tige, et
    un rapport Pc indiqué dans l'équation (1) ci-dessous se trouve entre 0,41 et 0,75 et un rapport Veq indiqué dans l'équation (2) ci-dessous est d'au moins 0,18% en masse Pc = C / 1 - α / 100
    Figure imgb0033
    dans l'équation (1), C représente une teneur en carbone dans l'acier (en % massique) et α représente une fraction de ferrite (rapport de surface en %) Veq = V + Ti / 2 + Si / 20
    Figure imgb0034
    dans l'équation (2), V, Ti et Si représentent la teneur de chaque élément en acier (en % massique).
  2. Matériau laminé pour une bielle à tête divisée selon la revendication 1, comprenant en outre un rapport Ceq d'au moins 0,80% en masse comme indiqué dans l'équation (3) ci-dessous et un rapport PM d'au plus 500% en masse comme indiqué dans l'équation (4) ci-dessous Ceq = C + 0 , 28 ⁢ Mn - 1 , 0 ⁢ S + 0 , 32 ⁢ Cr + 1 , 7 ⁢ V + 1 , 3 ⁢ Ti
    Figure imgb0035
     PM = 554 ⁢ C + 71 ⁢ Mn - 262 ⁢ S + 82 ⁢ Cr + 429 ⁢ V
    Figure imgb0036
    dans les équations (3) et (4), C, Mn, S, Cr, V et Ti représentent la teneur de chaque élément en acier (en % massique).
  3. Matériau laminé pour une bielle à tête divisée selon la revendication 1, comprenant en outre au moins un type de composant choisi du groupe constitué de
    Se : 0,0010 à 0,1 %, et
    Bi et Pb : 0,01 à 0,2 % au total.
  4. Pièce forgée à chaud pour bielle à tête divisée avec d'excellentes caractéristiques de division par fractionnement, obtenue par forgeage à chaud du matériau laminé pour une bielle à tête divisée selon l'une quelconque des revendications 1 à 3.
  5. Bielle à tête divisée, obtenue en utilisant la pièce forgée à chaud selon la revendication 4.
EP07738409A 2006-03-15 2007-03-13 Materiau lamine pour bielle a fissure de rupture presentant une excellente capacite de fissure de rupture, element forge a chaud pour bielle présentant une excellente capacité de fissure de rupture et bielle a fissure de rupture Active EP2000553B1 (fr)

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KR101054198B1 (ko) 2011-08-03
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KR20080097457A (ko) 2008-11-05
US20090047169A1 (en) 2009-02-19
CN101405418B (zh) 2012-07-11

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