WO2019203343A1 - Steel, mechanical component, and connecting rod - Google Patents

Steel, mechanical component, and connecting rod Download PDF

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Publication number
WO2019203343A1
WO2019203343A1 PCT/JP2019/016810 JP2019016810W WO2019203343A1 WO 2019203343 A1 WO2019203343 A1 WO 2019203343A1 JP 2019016810 W JP2019016810 W JP 2019016810W WO 2019203343 A1 WO2019203343 A1 WO 2019203343A1
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Prior art keywords
steel
ferrite
fracture
pearlite
less
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PCT/JP2019/016810
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French (fr)
Japanese (ja)
Inventor
真也 寺本
根石　豊
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日本製鉄株式会社
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Priority to JP2019548087A priority Critical patent/JP6750745B2/en
Publication of WO2019203343A1 publication Critical patent/WO2019203343A1/en

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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
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C7/00—Connecting-rods or like links pivoted at both ends; Construction of connecting-rod heads
    • F16C7/02—Constructions of connecting-rods with constant length

Definitions

  • the present invention relates to steel, machine parts and connecting rods. This application claims priority based on Japanese Patent Application No. 2018-081538 filed in Japan on April 20, 2018, the contents of which are incorporated herein by reference.
  • forming is performed by hot forging, followed by heat treatment such as quenching and tempering (hereinafter, the heat-treated parts are referred to as tempered steel parts), or heat treatment is performed. Without (hereinafter, a part that is not heat-treated is referred to as a non-heat treated steel part), the mechanical properties required for the applied part are obtained. Recently, from the viewpoint of economic efficiency in the manufacturing process, many parts manufactured by omitting heat treatment, that is, non-tempered steel parts are widely used.
  • a connecting rod (hereinafter referred to as a connecting rod).
  • This component is a component that transmits power when the reciprocating motion of the piston is converted into the rotational motion by the crankshaft in the engine.
  • the connecting rod clamps an eccentric portion called a pin portion of the crankshaft sandwiched between the cap portion and the rod portion of the connecting rod, and transmits power by a mechanism in which the pin portion and the connecting portion of the connecting rod rotate and slide.
  • a fracture separation type connecting rod has been widely used.
  • the fracture separation type connecting rod is a steel material formed into a shape in which the cap part and the rod part are integrated by hot forging etc., and then a notch is made in the part corresponding to the boundary between the cap part and the rod part, A method of breaking and separating is adopted.
  • the fracture surfaces separated by breakage at the mating surfaces of the cap portion and the rod portion are fitted together, so that machining of the mating surfaces is unnecessary and processing for alignment is also omitted if necessary. be able to. For this reason, it is possible to greatly reduce the machining process of the parts, and it is possible to greatly improve the economic efficiency when manufacturing the parts.
  • the fracture separation type connecting rod manufactured by such a method requires that the fracture form of the fracture surface is brittle and that the deformation near the fracture surface due to fracture separation is small, that is, the fracture separation property is good. It is done.
  • the DIN standard C70S6 As a steel material to be used for the fracture separation type connecting rod, the DIN standard C70S6 is widely used in Europe and the United States, and contains 0.7% by mass of C.
  • This high carbon non-tempered steel connecting rod has a pearlite structure with low ductility and toughness in order to suppress dimensional changes during fracture separation. Since C70S6 has a small amount of plastic deformation in the vicinity of the fracture surface at the time of fracture, it has excellent fracture separation.
  • Patent Document 1 and Patent Document 2 describe a technique for improving fracture separability by adding a large amount of an embrittlement element such as Si or P to a steel material and reducing the ductility and toughness of the material itself.
  • Patent Documents 3 to 5 describe techniques for improving the fracture separability of steel materials by reducing the ductility and toughness of ferrite by utilizing precipitation strengthening of second phase particles.
  • Patent Documents 6 to 8 describe techniques for improving the fracture separability of steel materials by controlling the form of Mn sulfide.
  • Patent Document 9 describes a technique for improving the fitting property of a fracture surface by controlling the form of Mn sulfide.
  • the present invention provides a machine part and a connecting rod having all of high tensile strength, high yield ratio, excellent fracture separability, and excellent fit of a fracture surface, and such a machine. It is an object of the present invention to provide a steel capable of manufacturing parts and connecting rods.
  • the present inventors have intensively studied a steel suitable for a high strength fracture separation type connecting rod.
  • the gist of the present invention obtained as a result is as follows.
  • the chemical component is unit mass% C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050% and Al: 0.010% or less,
  • the chemical component is unit mass%. Ti: 0.005 to 0.014% and Mo: 0.005 to 0.15% You may contain 1 type or 2 types selected from the group which consists of. [3] In the steel according to [1] or [2], the chemical component is unit mass%, Ca: 0.001 to 0.005%, Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005% You may contain 1 or more types selected from the group which consists of.
  • the chemical component is unit mass%, C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% or less, with the balance being Fe and impurities,
  • the microstructure within 1.0 mm or more from the surface is a ferrite / pearlite structure, and the area fraction of the ferrite / pearlite
  • the chemical component is unit mass%. Ti: 0.005 to 0.014% and Mo: 0.005 to 0.15% You may contain 1 type or 2 types selected from the group which consists of.
  • the chemical component is unit mass%. Ca: 0.001 to 0.005%, Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005% You may contain 1 or more types selected from the group which consists of. [7]
  • the mechanical component according to any one of [4] to [6] may have a tensile strength of 900 MPa or more and a yield ratio of 0.85 or more.
  • the chemical component is unit mass%, C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% or less, with the balance being Fe and impurities,
  • the microstructure within 1.0 mm or more from the surface of the rod part is a ferrite / pearlite structure, and the area fraction of the ferrite
  • the chemical component is unit mass%. Ti: 0.005 to 0.014%, and Mo: 0.005 to 0.15% You may contain 1 type or 2 types selected from the group which consists of. [10] In the connecting rod according to [8] or [9], the chemical component is unit mass%. Ca: 0.001 to 0.005%, Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005% You may contain 1 or more types selected from the group which consists of. [11] The connecting rod according to any one of [8] to [10] may have a tensile strength of 900 MPa or more and a yield ratio of 0.85 or more at the rod portion.
  • steel in this embodiment includes steel used for hot forging (that is, steel for hot forging), which is a material for machine parts and connecting rods. It is a steel bar.
  • the chemical composition is unit mass%, C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070% , Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% It contains the following, and the balance consists of Fe and impurities.
  • the mechanical component according to the present embodiment is made of the above steel, has the above chemical components, the remainder is made of Fe and impurities, and the microstructure inside the surface of 1.0 mm or more from the surface is a ferrite pearlite structure. And the area fraction of the ferrite-pearlite structure is 95% or more.
  • the connecting rod according to the present embodiment is made of the above steel, has the above chemical components, the balance is composed of Fe and impurities, and the microstructure inside the rod portion is 1.0 mm or more from the surface of the ferrite portion.
  • -It is a pearlite structure, and the area fraction of the ferrite-pearlite structure is 95% or more.
  • non-tempered steel parts mechanical parts and connecting rods may be collectively referred to as “non-tempered steel parts”.
  • the non-heat treated steel part is a hot forged product obtained by hot forging the steel according to the present embodiment.
  • the unit “mass%” of the content of the alloy element is described as “%”.
  • the numerical limit ranges described below include the lower limit value and the upper limit value. Numerical values indicated as “exceeding” or “less than” do not include the value in the numerical range.
  • mechanical properties such as tensile strength, yield ratio, fracture separability, and fracture surface fitting properties
  • alloy elements such as tensile strength, yield ratio, fracture separability, and fracture surface fitting properties
  • mechanical properties of steel ie machine parts and connecting rods.
  • the description of the mechanical component according to the present embodiment is also applied to the connecting rod according to the present embodiment unless otherwise specified.
  • C 0.15-0.30%
  • the C content needs to be 0.15% or more.
  • the C content is preferably 0.16% or more, 0.17% or more, or 0.18% or more.
  • the C content is set to 0.30% or less.
  • the C content is preferably 0.29% or less, 0.28% or less, or 0.27% or less.
  • Si 0.40 to 1.30% Si strengthens ferrite by solid solution strengthening and reduces the ductility of non-tempered steel parts, thereby improving fracture separation.
  • the Si content needs to be 0.40% or more.
  • the Si content is preferably 0.45% or more, 0.50% or more, or 0.55% or more.
  • the Si content is 1.30% or less.
  • the Si content is preferably 1.25% or less, 1.20% or less, or 1.15% or less.
  • Mn 0.50 to 1.50% Mn is dissolved in a large amount in cementite and slows the growth rate of pearlite.
  • the delay of the pearlite growth rate has the effect of causing a large amount of alloy carbide such as Nb carbide to precipitate between the pearlite lamellas and significantly reducing the ductility of the non-tempered steel part.
  • Mn combines with S to form Mn sulfide.
  • Mn sulfide reduces the hardenability of non-tempered steel parts by suppressing the coarsening of the austenite structure before ferrite-pearlite transformation. In order to obtain these effects, the Mn content needs to be 0.50% or more.
  • the Mn content is preferably 0.55% or more, 0.60% or more, or 0.65% or more.
  • Mn is contained excessively, the amount of Mn in a solid solution state is increased, and the hardenability of the non-tempered steel part is improved. As a result, not a pearlite structure but a bainite structure is generated, and the amount of Nb carbide precipitated is reduced, so that the ductility of the non-tempered steel part is increased and the fracture separability is significantly reduced. Therefore, the Mn content is 1.50% or less.
  • the Mn content is preferably 1.45% or less, 1.40% or less, or 1.35% or less.
  • P 0.035 to 0.200% P decreases the ductility of ferrite and pearlite, and thus improves the break separability of non-tempered steel parts.
  • the P content needs to be 0.035% or more.
  • the P content is preferably 0.040% or more, 0.045% or more, 0.050% or more, or 0.055% or more.
  • the P content is 0.200% or less.
  • the P content is preferably 0.180% or less, 0.160% or less, or 0.140% or less.
  • S 0.010 to 0.100%
  • Mn sulfide reduces the hardenability of non-tempered steel parts by suppressing the coarsening of the austenite structure before ferrite-pearlite transformation.
  • S has an effect of suppressing the formation of a bainite structure that greatly deteriorates the break separation property of the non-heat treated steel part.
  • the S content is set to 0.010% or more.
  • the S content is preferably 0.015% or more, 0.020% or more, or 0.025% or more.
  • the S content is set to 0.100% or less.
  • the S content is preferably 0.095% or less, 0.090% or less, or 0.085% or less.
  • the Cr content is preferably 0.05% or more.
  • the Cr content is more preferably 0.06% or more, 0.07% or more, or 0.08% or more.
  • the steel and the non-heat treated steel part according to the present embodiment can solve the problem, so the lower limit value of the Cr content is 0%.
  • Cr content shall be 1.00% or less.
  • the Cr content is preferably 0.90% or less, 0.80% or less, or 0.70% or less.
  • Nb 0.010 to 0.20% Nb forms nitrides or carbides in the steel.
  • a large amount of Nb carbide formed during cooling after hot forging precipitates between pro-eutectoid ferrite and / or pearlite lamella, thereby significantly reducing the ductility and improving the fracture separability of non-tempered steel parts.
  • the Nb content needs to be 0.010% or more.
  • the Nb content is more preferably 0.02% or more, 0.03% or more, or 0.04% or more.
  • the Nb content is 0.20% or less.
  • the Nb content is preferably 0.19% or less, 0.18% or less, or 0.17% or less.
  • Ti forms nitrides or carbides.
  • Ti carbide precipitates prior to Nb carbide at the interface between pearlite and austenite in the pearlite transformation process and becomes a nucleus, so that Nb carbide precipitates in a finer amount and in a larger amount than when Nb carbide precipitates alone.
  • the Ti content is preferably 0.005% or more.
  • the steel and non-tempered steel parts according to the present embodiment can solve the problem, so the lower limit of the Ti content is 0%.
  • the Ti content is set to 0.070% or less.
  • the Ti content is preferably 0.065% or less, 0.060% or less, or 0.055% or less.
  • the Ti content is more preferably 0.014% or less.
  • Mo 0 to 0.15% Mo, like Mn and Cr, dissolves much in cementite and slows the growth rate of pearlite.
  • the delay of the pearlite growth rate has an effect of significantly reducing the ductility of the non-tempered steel part by precipitating a large amount of alloy carbide such as Nb carbide between the pearlite lamellae.
  • the Mo content is preferably 0.005% or more.
  • the steel and non-tempered steel parts according to the present embodiment can solve the problem, so the lower limit of the Mo content is 0%.
  • the Mo content is 0.15% or less.
  • the Mo content is preferably 0.13% or less, 0.11% or less, or 0.09% or less.
  • N 0.0010 to 0.0060%
  • N combines with Nb and / or Ti to form a nitride. These nitrides suppress the coarsening of the austenite structure before the ferrite-pearlite transformation and lower the hardenability of the non-tempered steel parts. As a result, N has an effect of suppressing the formation of a bainite structure that significantly deteriorates the fracture separability of the non-heat treated steel part.
  • N content shall be 0.0010% or more.
  • the N content is preferably 0.0015% or more, 0.0020% or more, or 0.0025% or more.
  • the N content is set to 0.0060% or less.
  • the N content is preferably 0.0055% or less, 0.0050% or less, or 0.0045% or less.
  • V 0 to 0.010%
  • V forms nitrides in the steel and promotes transformation into pro-eutectoid ferrite, thus reducing the amount of Nb carbide precipitated between pearlite lamellae. Thereby, ductility becomes high rather, and the fracture separability of a non-heat treated steel part falls. Therefore, the V content is 0.010% or less.
  • the V content is preferably 0.008% or less, 0.006% or less, or 0.004% or less. The smaller the V content, the better, and it may be 0%.
  • the steel and non-heat treated steel parts according to the present embodiment may further include one or more selected from the group consisting of Ca, Zr and Mg in addition to the above-described elements.
  • the steel and non-heat treated steel parts according to this embodiment can solve the problem, so the lower limit of the content of each of Ca, Zr and Mg is 0%.
  • Ca, Zr, and Mg all form oxides in the steel and serve as crystallization nuclei for Mn sulfide, which has the effect of uniformly and finely dispersing Mn sulfide.
  • Mn sulfide When non-tempered steel parts are separated by fracture, cracks propagate along the Mn sulfide elongated in the rolling direction. Therefore, the larger the Mn sulfide, the larger the irregularities of the fractured surface, while the ductility increases and the fracture separability decreases.
  • the content of at least one of Ca, Zr and Mg is preferably 0.001% or more.
  • the contents of Ca, Zr and Mg are set to 0.005% or less.
  • the steel and non-tempered steel parts according to the present embodiment may further include one or more selected from the group consisting of Cu, Ni, Pb and Bi in addition to the elements described above.
  • the steel and non-heat treated steel parts according to this embodiment can solve the problem, so the lower limit of the content of each of Cu, Ni, Pb and Bi is 0. %.
  • Cu 0 to 0.05%
  • Ni 0 to 0.05%
  • Pb 0 to 0.50%
  • Bi 0 to 0.0050%
  • Cu, Ni, and Pb are present alone in the steel, thereby reducing the ductility and toughness of ferrite and pearlite.
  • the reduction in ductility and toughness has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture of the non-heat treated steel part and improving the fracture separability. Therefore, the contents of Cu, Ni, and Pb may each be 0.01% or more, more preferably 0.02% or more. However, if the content of these elements is excessive, hot workability deteriorates and hot rolling becomes difficult.
  • the Cu and Ni contents are 0.05% or less, and the Pb content. Is 0.50% or less.
  • Bi exists as a solid solution state in the steel, thereby reducing the ductility and toughness of ferrite and pearlite.
  • the reduction in ductility and toughness has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture of the non-heat treated steel part and improving the fracture separability. Therefore, the Bi content may be 0.0001% or more. However, if the Bi content is excessive, hot workability deteriorates and hot rolling becomes difficult, so the Bi content is set to 0.0050%.
  • Al 0.010% or less Al may be contained at 0.010% or less in the steel and non-tempered steel parts according to the present embodiment. However, if the Al content exceeds 0.010%, the machinability deteriorates and cannot be applied to automobile engine parts that require high accuracy.
  • the Al content is preferably low, but may be 0.001% or more from the viewpoint of cost reduction required for Al reduction. Even when Al is not included, the steel and non-heat treated steel parts according to the present embodiment can solve the problem, so the lower limit of the Al content may be 0%.
  • the balance of the chemical components of the steel and non-heat treated steel parts according to this embodiment is iron (Fe) and impurities.
  • Impurities are raw materials such as ore or scrap, or components mixed in due to various factors in the production process when industrially producing non-heat treated steel. It means that it is allowed as long as it does not adversely affect the quality steel parts.
  • B, O, etc. are mentioned as an impurity which may be contained in the steel which concerns on this embodiment, and a non-tempered steel component.
  • the B content is not particularly specified, but B that can be contained in the steel and the non-heat treated steel component according to the present embodiment is 3 ppm or less, so the upper limit of the B content may be 3 ppm.
  • the steel and non-tempered steel parts according to the present embodiment can solve the problem, so the lower limit of the B content may be 0%. Moreover, when O is contained as an impurity, the content is 0.0030% or less, for example.
  • the chemical components of the steel and non-heat treated steel parts described above may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).
  • C and S may be measured using a combustion-infrared absorption method, and N may be measured using an inert gas melting-thermal conductivity method.
  • the ferrite and pearlite structure is a structure mainly composed of ferrite and pearlite, and is composed of proeutectoid ferrite and pearlite.
  • the structure mainly composed of ferrite and pearlite means that the area fraction of ferrite and pearlite is 95% or more in the microstructure of non-heat treated steel parts, in other words, the remaining structure other than proeutectoid ferrite and pearlite is 5% or less. It means that there is.
  • the area fraction of pearlite and the area fraction of pro-eutectoid ferrite are approximately the same, or the area fraction of pearlite is pro-eutectoid ferrite.
  • phase interface precipitation in which alloy carbide such as Nb carbide precipitates at the interface between pro-eutectoid ferrite and / or pearlite and austenite can occur.
  • the area fraction of the ferrite / pearlite structure is 95% or more, preferably 96% or more, 97% or more, or 100%.
  • the steel according to the present embodiment is heated to a temperature range of Ac 3 points or higher, hot forged, and cooled to be processed into a non-tempered steel part, the metal structure before being heated is Not specified. This is because the structure of steel before hot forging does not affect the characteristics of machine parts after hot forging.
  • the area fraction of the remaining structure other than the ferrite / pearlite structure contained in the microstructure shall be 0 to 5%.
  • a bainite structure may be included, but when the bainite structure is generated, the yield ratio of the non-tempered steel part is lowered. Therefore, the remaining structure is preferably as small as possible, preferably 4% or less, or 3% or less. More preferably, the balance structure is 0%.
  • the area fraction of the microstructure is measured by the following method.
  • a 10 mm square test piece is cut out from the non-heat treated steel part.
  • the test piece is cut out from a position deeper than 1.0 mm from the surface.
  • the test piece is cut out from an arbitrary position, and in the case of connecting rods, the test piece is cut out from the rod portion.
  • the cut specimen is filled with resin and mirror polished, and then the polished surface is etched with a nital etchant (3% nitric acid alcohol).
  • arbitrary 10 positions are specified by using the surface corroded by etching as an observation surface, and the observation magnification is set to 400 times and observation is performed with an optical microscope.
  • the ferrite and pearlite in the optical micrograph are identified by ordinary means, and the area fraction of these in the photograph is measured by ordinary image analysis. And let the average value of the total area ratio of the ferrite and pearlite in ten places be the area fraction of the ferrite pearlite structure in the microstructure of a non-tempered mechanical part.
  • the area fraction of the ferrite / pearlite structure obtained by the above means is substantially the same as the volume fraction.
  • alloy carbides such as Nb carbides are precipitated not only in pro-eutectoid ferrite but also between pearlite lamellae. Thereby, the ductility of a non-tempered steel part can be reduced and the fracture separability can be improved.
  • the location of the alloy carbide such as Nb carbide can be observed by the following method.
  • a disk having a thickness of 0.5 mm is taken from a position deeper than 1.0 mm from the surface of the non-heat treated steel part.
  • both sides of the disk are ground and polished to a thickness of 50 ⁇ m.
  • a sample having a diameter of 3 mm is taken from the disk.
  • the sample is immersed in a 10% perchloric acid-glacial acetic acid solution, and electropolishing is performed to produce a thin film sample.
  • the obtained thin film sample is observed using an apparatus composed of a transmission electron microscope (TEM) and a high-sensitivity camera.
  • TEM transmission electron microscope
  • the Kikuchi figure is analyzed for the thin film sample, the crystal orientation of the thin film sample is specified, the thin film sample is tilted based on the specified crystal orientation, and the (001) plane can be observed.
  • the observation magnification is 40000 times, and the acceleration voltage is 200 kV.
  • the tensile strength of the non-heat treated steel part according to the present embodiment is, for example, 900 MPa or more and 1250 MPa or less, preferably 925 MPa or more, more preferably 950 MPa or more.
  • the yield ratio of the non-heat treated steel part according to the present embodiment is, for example, 0.85 or more, preferably 0.87 or more, and more preferably 0.90 or more.
  • the non-heat treated steel part according to the present embodiment may have a 0.2% proof stress of 800 MPa or more. If the 0.2% proof stress is 800 MPa or more, the secondary crack at the time of fracture separation becomes short, and it becomes difficult for plastic deformation to occur at the tip of the secondary crack. The fitting property is further improved.
  • the tensile strength, 0.2% proof stress and yield ratio of non-tempered steel parts are measured by the following methods.
  • JIS Z 2241: 2011 is set so that the longitudinal direction of the test piece coincides with the rolling direction, and in the case of a connecting rod, the longitudinal direction of the test piece coincides with the longitudinal direction of the rod part.
  • the described JIS14A test piece is cut out.
  • a test piece is cut out from the inside of a depth of 1.0 mm or more from the surface of a mechanical part or a connecting rod.
  • a connecting rod cut out from the rod.
  • the measurement temperature is 25 ° C. and the strain rate is 5 mm / min.
  • the yield ratio is obtained by dividing the obtained 0.2% yield strength (MPa) by the tensile strength (MPa).
  • the mechanical properties of the steel before hot forging are not particularly limited. As with the metal structure, for example, the mechanical properties of the steel before hot forging performed by heating to a temperature of Ac 3 or higher does not substantially affect the mechanical properties of the steel component mechanical parts after hot forging. It is.
  • the mechanical properties of the steel part machine part after hot forging are determined according to the chemical composition and hot forging conditions. That is, the effect of the steel according to this embodiment is that it can exhibit excellent mechanical properties after being subjected to hot forging.
  • the steel which concerns on this embodiment exhibits the effect excellent when it uses for a hot forging use, the use is not limited to a hot forging.
  • the structure of the steel according to the present embodiment is the same as the non-heat treated steel part machine part, the structure inside 1.0 mm or more from the surface is a ferrite pearlite structure, and the area fraction of the ferrite pearlite structure is It is beneficial to be 95% or more.
  • the steel according to the present embodiment is, for example, a steel bar having a diameter of 20 to 80 mm, but its use is not limited, and its shape is also arbitrary.
  • the steel according to the present embodiment is obtained by casting a steel slab having the above chemical components by continuous casting and, if necessary, through a soaking diffusion process and a block rolling process to obtain a rolled material. Next, the rolled material is heated to 1150 to 1250 ° C., then hot-rolled and then cooled to obtain steel. In the hot rolling, the hot rolling is finished at a temperature of 3 or more points of Ar, and the cooling conditions after the hot rolling need not be particularly limited, and may be cooled or water-cooled. It is not necessary to perform tempering heat treatment such as quenching and tempering after hot rolling.
  • the non-tempered steel part according to the present embodiment is manufactured by heating steel to a temperature of Ac 3 or higher, performing hot forging to form a desired part shape, and then cooling.
  • the cooling conditions after hot forging are not particularly limited as long as the ferrite-pearlite structure can be obtained, and may be cooled or water-cooled.
  • the temperature range of the heating temperature is 1220 ° C. to 1280 ° C.
  • the heating time is 5 min to 15 min.
  • post-processing such as cutting may be performed to adjust the part shape.
  • tempering heat treatment such as quenching and tempering.
  • the use of the steel and machine parts according to the present embodiment is not particularly limited, but has a particularly favorable effect when applied to a machine part used by breaking and separating, for example, a breaking and separating connecting rod.
  • FIG. 1 is an exploded perspective view showing an example of a fracture separation type connecting rod (hereinafter also referred to as a fracture separation type connecting rod) according to the present embodiment.
  • the fracture separation type connecting rod 1 of this example is composed of a semicircular arc-shaped upper-side half-divided body 2 with a rod and a semicircular-arc-shaped lower-side half-divided body 3. Yes. Screw holes 5 having screw grooves for fixing to the lower half half 3 are respectively formed at both ends of the semicircular arc 2A of the upper side half 2. The semicircular arc 3A of the lower side half 3 is formed. Insertion holes 6 for fixing to the upper-side halves 2 are formed on both ends of each.
  • the semicircular arc portion 2A of the upper half halves 2 and the semicircular arc portion 3A of the lower halves 3 are aligned in an annular shape, and the coupling bolts 7 are inserted into the insertion holes 6 and the screw holes 5 on both ends.
  • An annular big end portion 8 is formed by screwing.
  • An annular small end portion 9 is formed on the upper end side of the rod portion 2 ⁇ / b> B of the upper half 2.
  • a piston of an internal combustion engine such as an automobile engine into a rotational motion
  • a small end portion 9 is connected to a piston (not shown).
  • the big end portion 8 is connected to a connecting rod journal (not shown) of the internal combustion engine.
  • the fracture separation type connecting rod 1 is formed of steel having the above-described chemical composition and structure, and the semicircular arc portion 2A of the upper side half body 2 and the semicircular arc portion 3A of the lower side half body 3 are the same.
  • the part which was originally one annular part is formed by brittle fracture.
  • a notch is provided in a part of a hot forged product, and the notch is used as a starting point to break and separate brittlely, so that the butted surface 2a of the semicircular arc portion 2A of the upper half 2 and the lower half
  • the abutting surface 3a of the semicircular arc portion 3A of the body 3 is formed.
  • break-separated connecting rod 1 Since these abutting surfaces 2a and 3a are originally formed by breaking and separating one member, they can be abutted with good alignment accuracy.
  • the break-separated connecting rod 1 having this structure eliminates the need for new processing of the abutting surface and positioning pins, and greatly simplifies the manufacturing process.
  • the fracture separation type connecting rod 1 is C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0% by mass. 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% or less
  • the balance consists of Fe and impurities.
  • a steel having this chemical composition is hot-forged and cooled to obtain a non-tempered steel part, thereby obtaining a break-separated connecting rod having the above-mentione
  • a converter molten steel having the composition shown in Table 1A and Table 1B was manufactured by continuous casting, and if necessary, a rolling raw material of 162 mm square was obtained through a soaking diffusion treatment and a block rolling process. Next, after the rolled material was heated to 1200 ° C., a steel bar having a diameter of 56 mm was obtained by hot rolling. Values underlined in Table 1B indicate values outside the scope of the present invention. Further, the symbol “-” in Table 1A and Table 1B indicates that the element related to the symbol is not added.
  • a test piece corresponding to a connecting rod was produced by hot forging in order to examine the fracture separability, the fracture surface fitting property, the mechanical properties, and the microstructure.
  • a steel bar having a diameter of 56 mm was heated to 1250 ° C. and held for 5 minutes, and then hot forged at 1200 ° C. in a direction perpendicular to the longitudinal direction of the steel bar.
  • the side surface of the steel bar was deformed so as to change from a circular shape to a barrel shape to obtain a forged material having a thickness in the forging direction of 20 mm.
  • the forged material after hot forging was cooled to room temperature by natural cooling (cooling).
  • JIS 14A test piece described in JIS Z 2241: 2011 was produced from the forged material after cooling by cutting.
  • a JIS No. 14A test piece was sampled along the longitudinal direction of the forged material from a position 30 mm from the end surface in the width direction of the forged material and a depth of 10.0 mm in the thickness direction.
  • a tensile test was performed at 25 ° C. at a speed of 5 mm / min in accordance with JIS Z 2241: 2011. From the obtained results, tensile strength, 0.2% proof stress, yield ratio, total elongation and drawing were obtained.
  • the total elongation and the drawing obtained by the tensile test were adopted as indicators of the breaking separation and the fitting property of the fracture surface.
  • the breaking separation property and the fitting property of the fracture surface were evaluated based on the following criteria.
  • Good fracture separation and fractured surface fitting (Good): Total elongation is 1.0-5.0% and drawing is 2.0-8.0% Good fracture separation (Good), but poor fracture surface fitting (Bad) (because the ductility is remarkably low and fracture surface irregularities are small): total elongation is less than 1.0%, and / or Or, the squeezing is less than 2.0% and the fracture separation and the fracture surface fitting property are bad (Bad) (because the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture separation is large): the total elongation exceeds 5.0%, and / Or aperture is over 8.0%
  • bainite contains martensite, it is difficult to distinguish, so it is collectively referred to as bainite in this specification. Therefore, in each field of view, a region other than ferrite and pearlite was identified as bainite. And the average value of the total area ratio of the obtained ferrite and pearlite was made into the area fraction of the ferrite pearlite structure in a microstructure. By subtracting the area fraction of the ferrite / pearlite structure from 100%, the remaining structure other than the ferrite / pearlite structure, that is, the area fraction of bainite was obtained.
  • the position of the alloy carbide such as Nb carbide was observed by the following method.
  • a disc having a thickness of 0.5 mm was taken from a position of 10 mm depth from the surface of the non-heat treated steel part. Both sides of the disk were ground and polished using emery paper, and the thickness of the disk was 50 ⁇ m. Thereafter, a sample having a diameter of 3 mm was collected from the disk. The sample was immersed in a 10% perchloric acid-glacial acetic acid solution and subjected to electropolishing to produce a thin film sample. The obtained thin film sample was observed using an apparatus composed of a transmission electron microscope and a high sensitivity camera.
  • the Kikuchi figure is analyzed for the thin film sample, the crystal orientation of the thin film sample is specified, the thin film sample is tilted based on the specified crystal orientation, and the (001) plane can be observed.
  • a thin film sample was prepared. The observation magnification was 40000 times and the acceleration voltage was 200 kV.
  • Comparative Example AA since Comparative Example AA has a low C content, the precipitation amount of Nb carbides between pearlite lamellas was reduced and the ductility was increased. As a result, the break separation property and the fitting property of the fracture surface became poor. Comparative Examples AB, AD, AH, AM and AN have a large content of C, Si, P, Nb and Ti, respectively. Therefore, the ductility is remarkably low and the fracture separability is good. It became defective.
  • Comparative Examples AC and AG had high ductility due to low Si and P contents, respectively, and the fracture separability and fracture surface fitting properties were poor.
  • Comparative Example AE had a low Mn content, the growth rate of pearlite was high, and alloy carbides such as Nb carbide did not precipitate between pearlite lamellae. As a result, the ductility was high, and the fracture separability and the fitting property of the fracture surface were poor.
  • Comparative Examples AF, AK, and AO have a high content of Mn, Cr, and Mo, respectively, and Comparative Examples AI and AP have a low content of S and N, respectively. Produced, the precipitation amount of Nb carbide between pearlite lamellae was small, and the ductility became high. As a result, the break separation property and the fitting property of the fracture surface became poor.
  • Comparative Example AJ since the content of S was large, the Mn sulfide became coarse, the ductility was high, and the fracture separation property and the fitting property of the fracture surface were poor. Since Comparative Example AL had a low Nb content, and Comparative Examples AQ and AR had a high N and V content, respectively, the precipitation amount of Nb carbide between pearlite lamellas was small, and the ductility was high. As a result, the break separation property and the fitting property of the fracture surface became poor.
  • SYMBOLS 1 Breaking separation type connecting rod (non-heat treated steel part), 2 ... Upper side half split body, 2A ... Semi-arc part, 2B ... Rod part, 2a ... Butting surface, 3 ... Lower side half split body, 3A ... Half arc Part, 3a ... butting surface, 5 ... screw hole, 6 ... insertion hole, 7 ... coupling bolt, 8 ... big end part, 9 ... small end part.

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Abstract

A steel according to an embodiment of the present invention comprises chemical components, by unit mass%, of C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% or less, the remainder comprising Fe and impurities.

Description

鋼、機械部品及びコネクティングロッドSteel, machine parts and connecting rod
　本発明は、鋼、機械部品およびコネクティングロッドに関する。
　本願は、２０１８年４月２０日に、日本に出願された特願２０１８－０８１５３８号に基づき優先権を主張し、その内容をここに援用する。 The present invention relates to steel, machine parts and connecting rods.
This application claims priority based on Japanese Patent Application No. 2018-081538 filed in Japan on April 20, 2018, the contents of which are incorporated herein by reference.
　自動車エンジン用部品および足廻り用部品では、熱間鍛造で成形を行い、次いで焼入れ焼戻しといった熱処理を行うことで（以降、熱処理が行われる部品を調質鋼部品と称する）、または、熱処理を行うことなく（以降、熱処理が行われない部品を非調質鋼部品と称する）、適用する部品に必要な機械特性を得る。最近では、製造工程における経済効率性の観点から、熱処理を省略して製造された部品、すなわち、非調質鋼部品が多く普及している。 In automotive engine parts and undercarriage parts, forming is performed by hot forging, followed by heat treatment such as quenching and tempering (hereinafter, the heat-treated parts are referred to as tempered steel parts), or heat treatment is performed. Without (hereinafter, a part that is not heat-treated is referred to as a non-heat treated steel part), the mechanical properties required for the applied part are obtained. Recently, from the viewpoint of economic efficiency in the manufacturing process, many parts manufactured by omitting heat treatment, that is, non-tempered steel parts are widely used.
　自動車エンジン用部品の一例としてコネクティングロッド（以降、コンロッドと称する）が挙げられる。この部品は、エンジン内でピストンの往復運動をクランクシャフトによる回転運動に変換する際に、動力を伝達する部品である。コンロッドは、クランクシャフトのピン部と称される偏芯部位をコンロッドのキャップ部とロッド部とで挟み込んで締結し、ピン部とコンロッドの締結部とが回転摺動する機構によって動力を伝達する。このキャップ部とロッド部との締結を効率化するために、近年、破断分離型コンロッドが多く採用されている。 An example of a car engine part is a connecting rod (hereinafter referred to as a connecting rod). This component is a component that transmits power when the reciprocating motion of the piston is converted into the rotational motion by the crankshaft in the engine. The connecting rod clamps an eccentric portion called a pin portion of the crankshaft sandwiched between the cap portion and the rod portion of the connecting rod, and transmits power by a mechanism in which the pin portion and the connecting portion of the connecting rod rotate and slide. In order to make the fastening of the cap part and the rod part efficient, in recent years, a fracture separation type connecting rod has been widely used.
　破断分離型コンロッドとは、熱間鍛造等でキャップ部とロッド部とが一体となった形状に鋼材を成形した後、キャップ部とロッド部との境界に相当する部分に切欠きを入れて、破断分離する工法を採用したものである。この工法では、キャップ部及びロッド部の合わせ面において破断分離した破断面同士を嵌合させるので、合わせ面の機械加工が不要な上に、位置合わせのために施す加工も必要に応じて省略することができる。そのため、部品の加工工程を大幅に削減することができ、部品製造時の経済効率性を大幅に向上することができる。このような工法で製造される破断分離型コンロッドには、破断面の破壊形態が脆性的であり、破断分離による破断面近傍の変形量が小さいこと、すなわち破断分離性が良好であることが求められる。 The fracture separation type connecting rod is a steel material formed into a shape in which the cap part and the rod part are integrated by hot forging etc., and then a notch is made in the part corresponding to the boundary between the cap part and the rod part, A method of breaking and separating is adopted. In this construction method, the fracture surfaces separated by breakage at the mating surfaces of the cap portion and the rod portion are fitted together, so that machining of the mating surfaces is unnecessary and processing for alignment is also omitted if necessary. be able to. For this reason, it is possible to greatly reduce the machining process of the parts, and it is possible to greatly improve the economic efficiency when manufacturing the parts. The fracture separation type connecting rod manufactured by such a method requires that the fracture form of the fracture surface is brittle and that the deformation near the fracture surface due to fracture separation is small, that is, the fracture separation property is good. It is done.
　破断分離型コンロッドに供する鋼材として、欧米で普及しているのは、ＤＩＮ規格のＣ７０Ｓ６であり、０．７質量％のＣを含む。この高炭素非調質鋼コンロッドは、破断分離時の寸法変化を抑えるために、金属組織を延性及び靱性の低いパーライト組織としたものである。Ｃ７０Ｓ６は、破断時の破断面近傍の塑性変形量が小さいので破断分離性に優れる。一方、現行の中炭素非調質鋼コンロッドのフェライト・パーライト組織に比べて組織が粗大であるので、降伏比（＝０．２％耐力（ＭＰａ）／引張強度（ＭＰａ））が低く、高い座屈強度が要求される高強度コンロッドには適用できないという問題がある。 As a steel material to be used for the fracture separation type connecting rod, the DIN standard C70S6 is widely used in Europe and the United States, and contains 0.7% by mass of C. This high carbon non-tempered steel connecting rod has a pearlite structure with low ductility and toughness in order to suppress dimensional changes during fracture separation. Since C70S6 has a small amount of plastic deformation in the vicinity of the fracture surface at the time of fracture, it has excellent fracture separation. On the other hand, since the structure is coarser than the ferrite / pearlite structure of the current medium carbon non-heat treated steel connecting rod, the yield ratio (= 0.2% proof stress (MPa) / tensile strength (MPa)) is low and high seating. There is a problem that it cannot be applied to a high-strength connecting rod that requires bending strength.
　鋼材の降伏比を高めるためには、炭素量を低減し、フェライト分率を増加させることが必要である。しかしながら、フェライト分率を増加させると鋼材の延性が向上して、破断分離時に塑性変形量が大きくなり、クランクシャフトのピン部に締結されるコンロッド摺動部の形状変形が増大し、コンロッド摺動部の真円度が低下するといった部品性能上の問題が発生する。 In order to increase the yield ratio of steel, it is necessary to reduce the carbon content and increase the ferrite fraction. However, increasing the ferrite fraction improves the ductility of the steel material, increases the amount of plastic deformation during fracture separation, increases the shape deformation of the connecting rod sliding portion fastened to the pin portion of the crankshaft, and connects the connecting rod. There arises a problem in the performance of the parts such as the roundness of the part is lowered.
　高強度の破断分離型コンロッドに好適な鋼材としていくつかの鋼が提案されている。例えば、特許文献１および特許文献２には、鋼材にＳｉまたはＰのような脆化元素を多量に添加し、材料自体の延性および靱性を低下させることによって破断分離性を改善する技術が記載されている。特許文献３～５には、第二相粒子の析出強化を利用してフェライトの延性および靱性を低下させることによって鋼材の破断分離性を改善する技術が記載されている。さらに、特許文献６～８には、Ｍｎ硫化物の形態を制御することによって鋼材の破断分離性を改善する技術が記載されている。 い く つ か Several steels have been proposed as steel materials suitable for high-strength break-away connecting rods. For example, Patent Document 1 and Patent Document 2 describe a technique for improving fracture separability by adding a large amount of an embrittlement element such as Si or P to a steel material and reducing the ductility and toughness of the material itself. ing. Patent Documents 3 to 5 describe techniques for improving the fracture separability of steel materials by reducing the ductility and toughness of ferrite by utilizing precipitation strengthening of second phase particles. Further, Patent Documents 6 to 8 describe techniques for improving the fracture separability of steel materials by controlling the form of Mn sulfide.
　近年は高出力ディーゼルエンジンあるいはターボエンジンの普及によるエンジン出力増大に伴い、コンロッドの高強度化のニーズが高まっている。高強度化手段の一つとして、例えば特許文献１～７に記載の技術では、Ｖを多量に添加し、微細なＶ炭化物による鋼の析出強化が利用されている。合金炭化物を生成する元素の中でもＶは、熱間鍛造前の加熱（１２５０℃前後）で鋼材への固溶量が多く、析出強化の効果が大きい。しかしながら、鋼材においてＶの固溶量には限界があり、Ｖの含有量の増大だけでは、より一層の高強度化は難しい。 In recent years, with the increase in engine output due to the widespread use of high-power diesel engines or turbo engines, the need for higher strength connecting rods has increased. As one of the means for increasing the strength, for example, in the techniques described in Patent Documents 1 to 7, a large amount of V is added, and precipitation precipitation of steel by fine V carbide is used. Among the elements that generate alloy carbides, V has a large amount of solid solution in steel due to heating (around 1250 ° C.) before hot forging, and has a great effect of precipitation strengthening. However, there is a limit to the solid solution amount of V in steel materials, and it is difficult to further increase the strength simply by increasing the V content.
　上述の高強度化手段は、破断分離した部位の変形量を小さくすると同時に、破断面の凹凸を小さくするため、破断面同士を嵌合させた時に位置ずれを生じさせる。例えば、特許文献９には、Ｍｎ硫化物の形態を制御することによって破断面の嵌合性を改善する技術が記載されている。しかしながら、より一層の高強度化において、強度と破断面の嵌合性との両立は現行の工法では実現できなかった。 The above-described high-strength means reduces the amount of deformation at the site where the fracture has been separated, and at the same time reduces the irregularities on the fractured surfaces, thereby causing misalignment when the fractured surfaces are fitted together. For example, Patent Document 9 describes a technique for improving the fitting property of a fracture surface by controlling the form of Mn sulfide. However, in order to further increase the strength, it has been impossible to achieve both the strength and the fitting property of the fracture surface with the current construction method.
　以上のように、近年のコンロッドの高強度化の要求に対応可能な、高い引張強度と、高い降伏比と、優れた破断分離性と、優れた破断面の嵌合性との全てを有する破断分離型コンロッドを製造可能な鋼は、現状では得られていないのが実情である。 As described above, it has a high tensile strength, a high yield ratio, an excellent fracture separability, and an excellent fracture surface fitting ability that can meet the recent demands for increasing the strength of connecting rods. In reality, no steel that can produce separable connecting rods has been obtained.
日本国特許第３６３７３７５号公報Japanese Patent No. 3637375 日本国特許第３７５６３０７号公報Japanese Patent No. 3756307 日本国特許第３３５５１３２号公報Japanese Patent No. 3355132 日本国特許第３９８８６６１号公報Japanese Patent No. 3988661 日本国特許第５３４０２９０号公報Japanese Patent No. 5340290 日本国特許第４３１４８５１号公報Japanese Patent No. 4314851 日本国特許第３６７１６８８号公報Japanese Patent No. 3671688 日本国特許第４２６８１９４号公報Japanese Patent No. 4268194 国際公開第２０１６／１４３８１２号International Publication No. 2016/143812
　本発明は上記の実情に鑑み、高い引張強度と、高い降伏比と、優れた破断分離性と、優れた破断面の嵌合性との全てを有する機械部品およびコネクティングロッド、ならびにこのような機械部品およびコネクティングロッドを製造可能な鋼を提供することを課題とする。 SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a machine part and a connecting rod having all of high tensile strength, high yield ratio, excellent fracture separability, and excellent fit of a fracture surface, and such a machine. It is an object of the present invention to provide a steel capable of manufacturing parts and connecting rods.
　上述の課題を解決するために、本発明者らは高強度の破断分離型コネクティングロッドに好適な鋼について鋭意検討した。その結果得られた本発明の要旨は、次の通りである。
［１］本発明の一態様に係る鋼は、化学成分が、単位質量％で、
Ｃ：０．１５～０．３０％、
Ｓｉ：０．４０～１．３０％、
Ｍｎ：０．５０～１．５０％、
Ｐ：０．０３５～０．２００％、
Ｓ：０．０１０～０．１００％、
Ｃｒ：０～１．００％、
Ｎｂ：０．０１０～０．２０％、
Ｔｉ：０～０．０７０％、
Ｍｏ：０～０．１５％、
Ｎ：０．００１０～０．００６０％、
Ｖ：０～０．０１０％、
Ｃａ：０～０．００５％、
Ｚｒ：０～０．００５％、
Ｍｇ：０～０．００５％、
Ｃｕ：０～０．０５％、
Ｎｉ：０～０．０５％、
Ｐｂ：０～０．５０％、
Ｂｉ：０～０．００５０％、及び
Ａｌ：０．０１０％以下
を含有し、残部がＦｅ及び不純物からなる。
［２］上記［１］に記載の鋼は、前記化学成分が、単位質量％で、
Ｔｉ：０．００５～０．０１４％、及び
Ｍｏ：０．００５～０．１５％
からなる群から選択される１種または２種を含有してもよい。
［３］上記［１］または［２］に記載の鋼は、前記化学成分が、単位質量％で、
Ｃａ：０．００１～０．００５％、
Ｚｒ：０．００１～０．００５％、及び
Ｍｇ：０．００１～０．００５％
からなる群から選択される１種以上を含有してもよい。
［４］本発明の別の態様に係る機械部品は、化学成分が、単位質量％で、
Ｃ：０．１５～０．３０％、
Ｓｉ：０．４０～１．３０％、
Ｍｎ：０．５０～１．５０％、
Ｐ：０．０３５～０．２００％、
Ｓ：０．０１０～０．１００％、
Ｃｒ：０～１．００％、
Ｎｂ：０．０１０～０．２０％、
Ｔｉ：０～０．０７０％、
Ｍｏ：０～０．１５％、
Ｎ：０．００１０～０．００６０％、
Ｖ：０～０．０１０％、
Ｃａ：０～０．００５％、
Ｚｒ：０～０．００５％、
Ｍｇ：０～０．００５％、
Ｃｕ：０～０．０５％、
Ｎｉ：０～０．０５％、
Ｐｂ：０～０．５０％、
Ｂｉ：０～０．００５０％、及び
Ａｌ：０．０１０％以下
を含有し、残部がＦｅ及び不純物からなり、
　表面から１．０ｍｍ以上内部におけるミクロ組織がフェライト・パーライト組織であり、前記フェライト・パーライト組織の面積分率が９５％以上である。
［５］上記［４］に記載の機械部品は、前記化学成分が、単位質量％で、
Ｔｉ：０．００５～０．０１４％、及び
Ｍｏ：０．００５～０．１５％
からなる群から選択される１種または２種を含有してもよい。
［６］上記［４］または［５］に記載の機械部品は、前記化学成分が、単位質量％で、
Ｃａ：０．００１～０．００５％、
Ｚｒ：０．００１～０．００５％、及び
Ｍｇ：０．００１～０．００５％
からなる群から選択される１種以上を含有してもよい。
［７］上記［４］～［６］のいずれか一項に記載の機械部品は、引張強度が９００ＭＰａ以上であり、かつ降伏比が０．８５以上であってもよい。
［８］本発明の別の態様に係るコネクティングロッドは、化学成分が、単位質量％で、
Ｃ：０．１５～０．３０％、
Ｓｉ：０．４０～１．３０％、
Ｍｎ：０．５０～１．５０％、
Ｐ：０．０３５～０．２００％、
Ｓ：０．０１０～０．１００％、
Ｃｒ：０～１．００％、
Ｎｂ：０．０１０～０．２０％、
Ｔｉ：０～０．０７０％、
Ｍｏ：０～０．１５％、
Ｎ：０．００１０～０．００６０％、
Ｖ：０～０．０１０％、
Ｃａ：０～０．００５％、
Ｚｒ：０～０．００５％、
Ｍｇ：０～０．００５％、
Ｃｕ：０～０．０５％、
Ｎｉ：０～０．０５％、
Ｐｂ：０～０．５０％、
Ｂｉ：０～０．００５０％、及び
Ａｌ：０．０１０％以下
を含有し、残部がＦｅ及び不純物からなり、
　ロッド部の表面から１．０ｍｍ以上内部におけるミクロ組織がフェライト・パーライト組織であり、前記フェライト・パーライト組織の面積分率が９５％以上である。
［９］上記［８］に記載のコネクティングロッドは、前記化学成分が、単位質量％で、
　Ｔｉ：０．００５～０．０１４％、及び
　Ｍｏ：０．００５～０．１５％
からなる群から選択される１種または２種を含有してもよい。
［１０］上記［８］または［９］に記載のコネクティングロッドは、前記化学成分が、単位質量％で、
Ｃａ：０．００１～０．００５％、
Ｚｒ：０．００１～０．００５％、及び
Ｍｇ：０．００１～０．００５％
からなる群から選択される１種以上を含有してもよい。
［１１］上記［８］～［１０］のいずれか一項に記載のコネクティングロッドは、前記ロッド部で、引張強度が９００ＭＰａ以上であり、降伏比が０．８５以上であってもよい。 In order to solve the above-mentioned problems, the present inventors have intensively studied a steel suitable for a high strength fracture separation type connecting rod. The gist of the present invention obtained as a result is as follows.
[1] In the steel according to one embodiment of the present invention, the chemical component is unit mass%
C: 0.15 to 0.30%,
Si: 0.40 to 1.30%,
Mn: 0.50 to 1.50%,
P: 0.035 to 0.200%,
S: 0.010 to 0.100%,
Cr: 0 to 1.00%,
Nb: 0.010 to 0.20%,
Ti: 0 to 0.070%,
Mo: 0 to 0.15%,
N: 0.0010 to 0.0060%,
V: 0 to 0.010%,
Ca: 0 to 0.005%,
Zr: 0 to 0.005%,
Mg: 0 to 0.005%,
Cu: 0 to 0.05%,
Ni: 0 to 0.05%,
Pb: 0 to 0.50%,
Bi: 0 to 0.0050% and Al: 0.010% or less, with the balance being Fe and impurities.
[2] In the steel according to [1], the chemical component is unit mass%.
Ti: 0.005 to 0.014% and Mo: 0.005 to 0.15%
You may contain 1 type or 2 types selected from the group which consists of.
[3] In the steel according to [1] or [2], the chemical component is unit mass%,
Ca: 0.001 to 0.005%,
Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005%
You may contain 1 or more types selected from the group which consists of.
[4] In the mechanical component according to another aspect of the present invention, the chemical component is unit mass%,
C: 0.15 to 0.30%,
Si: 0.40 to 1.30%,
Mn: 0.50 to 1.50%,
P: 0.035 to 0.200%,
S: 0.010 to 0.100%,
Cr: 0 to 1.00%,
Nb: 0.010 to 0.20%,
Ti: 0 to 0.070%,
Mo: 0 to 0.15%,
N: 0.0010 to 0.0060%,
V: 0 to 0.010%,
Ca: 0 to 0.005%,
Zr: 0 to 0.005%,
Mg: 0 to 0.005%,
Cu: 0 to 0.05%,
Ni: 0 to 0.05%,
Pb: 0 to 0.50%,
Bi: 0 to 0.0050%, and Al: 0.010% or less, with the balance being Fe and impurities,
The microstructure within 1.0 mm or more from the surface is a ferrite / pearlite structure, and the area fraction of the ferrite / pearlite structure is 95% or more.
[5] In the mechanical component according to [4], the chemical component is unit mass%.
Ti: 0.005 to 0.014% and Mo: 0.005 to 0.15%
You may contain 1 type or 2 types selected from the group which consists of.
[6] In the mechanical component according to [4] or [5], the chemical component is unit mass%.
Ca: 0.001 to 0.005%,
Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005%
You may contain 1 or more types selected from the group which consists of.
[7] The mechanical component according to any one of [4] to [6] may have a tensile strength of 900 MPa or more and a yield ratio of 0.85 or more.
[8] In the connecting rod according to another aspect of the present invention, the chemical component is unit mass%,
C: 0.15 to 0.30%,
Si: 0.40 to 1.30%,
Mn: 0.50 to 1.50%,
P: 0.035 to 0.200%,
S: 0.010 to 0.100%,
Cr: 0 to 1.00%,
Nb: 0.010 to 0.20%,
Ti: 0 to 0.070%,
Mo: 0 to 0.15%,
N: 0.0010 to 0.0060%,
V: 0 to 0.010%,
Ca: 0 to 0.005%,
Zr: 0 to 0.005%,
Mg: 0 to 0.005%,
Cu: 0 to 0.05%,
Ni: 0 to 0.05%,
Pb: 0 to 0.50%,
Bi: 0 to 0.0050%, and Al: 0.010% or less, with the balance being Fe and impurities,
The microstructure within 1.0 mm or more from the surface of the rod part is a ferrite / pearlite structure, and the area fraction of the ferrite / pearlite structure is 95% or more.
[9] In the connecting rod according to [8], the chemical component is unit mass%.
Ti: 0.005 to 0.014%, and Mo: 0.005 to 0.15%
You may contain 1 type or 2 types selected from the group which consists of.
[10] In the connecting rod according to [8] or [9], the chemical component is unit mass%.
Ca: 0.001 to 0.005%,
Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005%
You may contain 1 or more types selected from the group which consists of.
[11] The connecting rod according to any one of [8] to [10] may have a tensile strength of 900 MPa or more and a yield ratio of 0.85 or more at the rod portion.
　本発明に係る上記態様によれば、高い引張強度、高い降伏比、優れた破断分離性及び優れた破断面の嵌合性の全てを有する鋼、機械部品およびコネクティングロッドを提供することができる。 According to the above aspect of the present invention, it is possible to provide a steel, a mechanical part, and a connecting rod that have all of high tensile strength, high yield ratio, excellent fracture separability, and excellent fracture surface fitting properties.
本実施形態に係る機械部品の一例である破断分離型のコネクティングロッドを示す分解斜視図である。It is a disassembled perspective view which shows the fracture | rupture isolation | separation type connecting rod which is an example of the machine component which concerns on this embodiment.
　本発明者らは、高い引張強度、高い降伏比、優れた破断分離性及び優れた破断面の嵌合性の全てを実現する鋼、機械部品およびコネクティングロッドについて鋭意検討した結果、以下の（ａ）～（ｃ）の知見を得た。 As a result of diligent research on steels, mechanical parts, and connecting rods that achieve all of high tensile strength, high yield ratio, excellent fracture separability, and excellent fracture surface fitting properties, the following (a ) To (c) were obtained.
（ａ）本発明者らは、鋼中のＮｂ含有量を調整することによって、フェライト・パーライト組織中の初析フェライトにＮｂ炭化物を析出させるだけでなく、パーライトラメラ間のフェライトにもＮｂ炭化物を析出させることができ、著しく鋼の延性を低下させ、破断分離性を向上できることを見出した。これは、Ｎｂ炭化物の析出量が増えるだけでなく、初析フェライト中よりパーライトラメラ間で析出させた方が、微細かつ多量にＮｂ炭化物が析出するためであると推測される。 (A) By adjusting the Nb content in the steel, the present inventors not only precipitate Nb carbide in the pro-eutectoid ferrite in the ferrite-pearlite structure, but also add Nb carbide in the ferrite between the pearlite lamellae. It has been found that the steel can be precipitated, the ductility of the steel can be significantly reduced, and the break separation can be improved. This is presumed to be because not only the precipitation amount of Nb carbide increases, but also that Nb carbide precipitates between pearlite lamellae in the pro-eutectoid ferrite in a fine and large amount.
（ｂ）本発明者らは、Ｎｂ炭化物等の合金炭化物をより微細かつ多量に析出させる手段について検討を重ねた。その結果、Ｎｂに加えて微量のＴｉを鋼中に含有させることによって、より延性を低下させ、破断分離性をより向上できることを見出した。これは、微量のＴｉを鋼中に含有させることで、Ｔｉ炭化物がＮｂ炭化物よりも先に析出し、Ｔｉ炭化物がＮｂ炭化物の核となることで、単独でＮｂ炭化物を析出させるよりも、より微細かつ多量にＮｂ炭化物が析出するためと推測される。 (B) The inventors of the present invention have repeatedly studied a means for depositing alloy carbides such as Nb carbides in a finer amount and in a large amount. As a result, it has been found that by containing a small amount of Ti in addition to Nb in the steel, the ductility can be further reduced and the fracture separability can be further improved. This is because, by containing a small amount of Ti in the steel, Ti carbide precipitates before Nb carbide, and Ti carbide becomes the core of Nb carbide, so that it is more than the precipitation of Nb carbide alone. It is presumed that Nb carbide precipitates finely and in large quantities.
（ｃ）本発明者らは、Ｎｂに加えてＶを鋼中に含有させることによって、かえって延性が高くなり、破断分離性が低下することを見出した。これは、Ｖが窒化物を形成し、初析フェライトへの変態を促進させるため、パーライトラメラ間におけるＮｂ炭化物の析出量が減少するためと推測される。 (C) The present inventors have found that inclusion of V in steel in addition to Nb increases ductility and lowers break separation. This is presumably because V forms nitrides and promotes transformation into pro-eutectoid ferrite, so that the amount of Nb carbide precipitated between pearlite lamellae decreases.
　以下、本実施形態に係る鋼、機械部品およびコネクティングロッドについて説明する。なお、鋼とは、本実施形態における「鋼」とは、機械部品及びコネクティングロッドの素材となる、熱間鍛造に供される鋼（即ち熱間鍛造用鋼）を含むものであり、例えば、棒鋼である。
　本実施形態に係る鋼は、化学成分が、単位質量％で、Ｃ：０．１５～０．３０％、Ｓｉ：０．４０～１．３０％、Ｍｎ：０．５０～１．５０％、Ｐ：０．０３５～０．２００％、Ｓ：０．０１０～０．１００％、Ｃｒ：０～１．００％、Ｎｂ：０．０１０～０．２０％、Ｔｉ：０～０．０７０％、Ｍｏ：０～０．１５％、Ｎ：０．００１０～０．００６０％、Ｖ：０～０．０１０％、Ｃａ：０～０．００５％、Ｚｒ：０～０．００５％、Ｍｇ：０～０．００５％、Ｃｕ：０～０．０５％、Ｎｉ：０～０．０５％、Ｐｂ：０～０．５０％、Ｂｉ：０～０．００５０％、及びＡｌ：０．０１０％以下を含有し、残部がＦｅ及び不純物からなる。 Hereinafter, the steel, the machine part, and the connecting rod according to the present embodiment will be described. Note that “steel” in this embodiment includes steel used for hot forging (that is, steel for hot forging), which is a material for machine parts and connecting rods. It is a steel bar.
In the steel according to this embodiment, the chemical composition is unit mass%, C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070% , Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% It contains the following, and the balance consists of Fe and impurities.
　本実施形態に係る機械部品は、上記鋼を素材とするものであって、上記化学成分を有し、残部がＦｅ及び不純物からなり、表面から１．０ｍｍ以上内部におけるミクロ組織がフェライト・パーライト組織であり、前記フェライト・パーライト組織の面積分率が９５％以上である。
　本実施形態に係る機械部品は、圧延方向と平行に採取した丸棒試験片（１４Ａ号）をＪＩＳ　Ｚ　２２４１：２０１１に準拠して測定した引張強度が９００ＭＰａ以上であり、かつ降伏比（＝０．２％耐力（ＭＰａ）／引張強度（ＭＰａ））が０．８５以上であることが好ましい。 The mechanical component according to the present embodiment is made of the above steel, has the above chemical components, the remainder is made of Fe and impurities, and the microstructure inside the surface of 1.0 mm or more from the surface is a ferrite pearlite structure. And the area fraction of the ferrite-pearlite structure is 95% or more.
The mechanical component according to this embodiment has a tensile strength of a round bar test piece (14A) collected in parallel with the rolling direction measured according to JIS Z 2241: 2011 and 900 MPa or more, and a yield ratio (= 0) .2% yield strength (MPa) / tensile strength (MPa) is preferably 0.85 or more.
　本実施形態に係るコネクティングロッドは、上記鋼を素材とするものであって、上記化学成分を有し、残部がＦｅ及び不純物からなり、ロッド部の表面から１．０ｍｍ以上内部におけるミクロ組織がフェライト・パーライト組織であり、前記フェライト・パーライト組織の面積分率が９５％以上である。
　本実施形態に係るコネクティングロッドは、ロッド部から長手方向と平行に採取した丸棒試験片（１４Ａ号）をＪＩＳ　Ｚ　２２４１：２０１１に準拠して測定した引張強度が９００ＭＰａ以上であり、降伏比（＝０．２％耐力（ＭＰａ）／引張強度（ＭＰａ））が０．８５以上であることが好ましい。 The connecting rod according to the present embodiment is made of the above steel, has the above chemical components, the balance is composed of Fe and impurities, and the microstructure inside the rod portion is 1.0 mm or more from the surface of the ferrite portion. -It is a pearlite structure, and the area fraction of the ferrite-pearlite structure is 95% or more.
The connecting rod according to the present embodiment has a tensile strength of 900 MPa or more when a round bar specimen (No. 14A) taken from the rod portion in parallel with the longitudinal direction is measured according to JIS Z 2241: 2011, and has a yield ratio ( = 0.2% yield strength (MPa) / tensile strength (MPa)) is preferably 0.85 or more.
＜化学成分＞
　以下、本実施形態に係る鋼、機械部品およびコネクティングロッドの化学成分について説明する。なお、以下の説明において、機械部品およびコネクティングロッドを総称して「非調質鋼部品」と言う場合がある。非調質鋼部品とは、本実施形態に係る鋼を熱間鍛造等することによって得られる熱間鍛造品である。また、以下の説明において、合金元素の含有量の単位「質量％」は「％」と記載する。以下に記載する数値限定範囲には、下限値および上限値がその範囲に含まれる。「超」、「未満」と示す数値には、その値が数値範囲に含まれない。また、以下の説明において、合金元素の作用効果として機械特性（引張強さ、降伏比、破断分離性、及び破断面の嵌合性など）を挙げることがあるが、これらは熱間鍛造後の鋼（即ち機械部品及びコンロッド）の機械特性を意味する。さらに以下の説明において、本実施形態に係る機械部品についての説明は、特に断りがない限り、本実施形態に係るコンロッドにも適用される。 <Chemical component>
Hereinafter, the chemical components of the steel, the machine part, and the connecting rod according to the present embodiment will be described. In the following description, mechanical parts and connecting rods may be collectively referred to as “non-tempered steel parts”. The non-heat treated steel part is a hot forged product obtained by hot forging the steel according to the present embodiment. In the following description, the unit “mass%” of the content of the alloy element is described as “%”. The numerical limit ranges described below include the lower limit value and the upper limit value. Numerical values indicated as “exceeding” or “less than” do not include the value in the numerical range. In the following explanation, mechanical properties (such as tensile strength, yield ratio, fracture separability, and fracture surface fitting properties) may be mentioned as the effects of alloy elements. It refers to the mechanical properties of steel (ie machine parts and connecting rods). Further, in the following description, the description of the mechanical component according to the present embodiment is also applied to the connecting rod according to the present embodiment unless otherwise specified.
Ｃ：０．１５～０．３０％
　Ｃは非調質鋼部品の強度を確保する効果を有する。所望の引張強度を得るためには、Ｃ含有量を０．１５％以上にする必要がある。Ｃ含有量は、０．１６％以上、０．１７％以上、または０．１８％以上が好ましい。
　一方、Ｃを過剰に含有すると、延性が顕著に低くなり、破断面の凹凸が小さくなり、非調質鋼部品の破断面の嵌合性が低下する。そのため、Ｃ含有量は０．３０％以下とする。Ｃ含有量は、０．２９％以下、０．２８％以下、または０．２７％以下が好ましい。 C: 0.15-0.30%
C has the effect of ensuring the strength of the non-heat treated steel part. In order to obtain a desired tensile strength, the C content needs to be 0.15% or more. The C content is preferably 0.16% or more, 0.17% or more, or 0.18% or more.
On the other hand, when C is contained excessively, the ductility is remarkably lowered, the unevenness of the fracture surface is reduced, and the fitting property of the fracture surface of the non-heat treated steel part is lowered. Therefore, the C content is set to 0.30% or less. The C content is preferably 0.29% or less, 0.28% or less, or 0.27% or less.
Ｓｉ：０．４０～１．３０％
　Ｓｉは、固溶強化によってフェライトを強化し、非調質鋼部品の延性を低下させることで、破断分離性を向上させる。この効果を得るためには、Ｓｉ含有量は０．４０％以上にする必要がある。Ｓｉ含有量は、０．４５％以上、０．５０％以上、または０．５５％以上が好ましい。
　一方、Ｓｉを過剰に含有すると、延性が顕著に低くなり、破断面の凹凸が小さくなるため、非調質鋼部品の破断面の嵌合性が低下する。そのため、Ｓｉ含有量は１．３０％以下とする。Ｓｉ含有量は、１．２５％以下、１．２０％以下、または１．１５％以下が好ましい。 Si: 0.40 to 1.30%
Si strengthens ferrite by solid solution strengthening and reduces the ductility of non-tempered steel parts, thereby improving fracture separation. In order to obtain this effect, the Si content needs to be 0.40% or more. The Si content is preferably 0.45% or more, 0.50% or more, or 0.55% or more.
On the other hand, when Si is contained excessively, the ductility is remarkably lowered and the unevenness of the fracture surface is reduced, so that the fitting property of the fracture surface of the non-heat treated steel part is lowered. Therefore, the Si content is 1.30% or less. The Si content is preferably 1.25% or less, 1.20% or less, or 1.15% or less.
Ｍｎ：０．５０～１．５０％
　Ｍｎは、セメンタイトに多く固溶してパーライトの成長速度を遅くする。パーライトの成長速度の遅延は、パーライトラメラ間でＮｂ炭化物等の合金炭化物を多量に析出させ、非調質鋼部品の延性を顕著に低下させる効果がある。また、Ｍｎは、Ｓと結合してＭｎ硫化物を形成する。Ｍｎ硫化物はフェライト・パーライト変態前のオーステナイト組織の粗大化を抑制することで、非調質鋼部品の焼入れ性を低下させる。これらの効果を得るためには、Ｍｎ含有量を０．５０％以上にする必要がある。Ｍｎ含有量は、０．５５％以上、０．６０％以上、または０．６５％以上が好ましい。
　一方、Ｍｎを過剰に含有すると、固溶状態のＭｎ量が増加し、かえって非調質鋼部品の焼入れ性が向上する。これによりパーライト組織ではなくベイナイト組織が生成し、Ｎｂ炭化物の析出量が減少するため、非調質鋼部品の延性が高くなり破断分離性が顕著に低下する。したがって、Ｍｎ含有量は１．５０％以下とする。Ｍｎ含有量は、１．４５％以下、１．４０％以下、または１．３５％以下が好ましい。 Mn: 0.50 to 1.50%
Mn is dissolved in a large amount in cementite and slows the growth rate of pearlite. The delay of the pearlite growth rate has the effect of causing a large amount of alloy carbide such as Nb carbide to precipitate between the pearlite lamellas and significantly reducing the ductility of the non-tempered steel part. Mn combines with S to form Mn sulfide. Mn sulfide reduces the hardenability of non-tempered steel parts by suppressing the coarsening of the austenite structure before ferrite-pearlite transformation. In order to obtain these effects, the Mn content needs to be 0.50% or more. The Mn content is preferably 0.55% or more, 0.60% or more, or 0.65% or more.
On the other hand, when Mn is contained excessively, the amount of Mn in a solid solution state is increased, and the hardenability of the non-tempered steel part is improved. As a result, not a pearlite structure but a bainite structure is generated, and the amount of Nb carbide precipitated is reduced, so that the ductility of the non-tempered steel part is increased and the fracture separability is significantly reduced. Therefore, the Mn content is 1.50% or less. The Mn content is preferably 1.45% or less, 1.40% or less, or 1.35% or less.
Ｐ：０．０３５～０．２００％
　Ｐは、フェライト及びパーライトの延性を低下させるため、非調質鋼部品の破断分離性を向上させる。この効果を得るためには、Ｐ含有量を０．０３５％以上にする必要がある。Ｐ含有量は、０．０４０％以上、０．０４５％以上、０．０５０％以上、または０．０５５％以上が好ましい。一方、Ｐを過剰に含有すると、延性が顕著に低くなり、破断面の凹凸が小さくなるため、非調質鋼部品の破断面の嵌合性が低下する。そのため、Ｐ含有量は０．２００％以下とする。Ｐ含有量は、０．１８０％以下、０．１６０％以下、または０．１４０％以下が好ましい。 P: 0.035 to 0.200%
P decreases the ductility of ferrite and pearlite, and thus improves the break separability of non-tempered steel parts. In order to obtain this effect, the P content needs to be 0.035% or more. The P content is preferably 0.040% or more, 0.045% or more, 0.050% or more, or 0.055% or more. On the other hand, when P is contained excessively, the ductility is remarkably lowered and the unevenness of the fracture surface is reduced, so that the fitting property of the fracture surface of the non-heat treated steel part is lowered. Therefore, the P content is 0.200% or less. The P content is preferably 0.180% or less, 0.160% or less, or 0.140% or less.
Ｓ：０．０１０～０．１００％
　Ｓは、Ｍｎと結合してＭｎ硫化物を形成する。Ｍｎ硫化物はフェライト・パーライト変態前のオーステナイト組織の粗大化を抑制することで、非調質鋼部品の焼入れ性を低下させる。これによりＳには、非調質鋼部品の破断分離性を大幅に劣化させるベイナイト組織の生成を抑制する効果がある。この効果を得るために、Ｓ含有量を０．０１０％以上とする。Ｓ含有量は、０．０１５％以上、０．０２０％以上、または０．０２５％以上が好ましい。
　一方、Ｓを過剰に含有すると、Ｍｎ硫化物が粗大となり、非調質鋼部品の破断分離性が顕著に低下するため、Ｓ含有量は０．１００％以下とする。Ｓ含有量は、０．０９５％以下、０．０９０％以下、または０．０８５％以下が好ましい。 S: 0.010 to 0.100%
S combines with Mn to form Mn sulfide. Mn sulfide reduces the hardenability of non-tempered steel parts by suppressing the coarsening of the austenite structure before ferrite-pearlite transformation. Thereby, S has an effect of suppressing the formation of a bainite structure that greatly deteriorates the break separation property of the non-heat treated steel part. In order to obtain this effect, the S content is set to 0.010% or more. The S content is preferably 0.015% or more, 0.020% or more, or 0.025% or more.
On the other hand, when S is contained excessively, the Mn sulfide becomes coarse, and the fracture separability of the non-tempered steel parts is remarkably lowered. Therefore, the S content is set to 0.100% or less. The S content is preferably 0.095% or less, 0.090% or less, or 0.085% or less.
Ｃｒ：０～１．００％
　Ｃｒは、セメンタイトに多く固溶してパーライトの成長速度を遅くする。パーライトの成長速度の遅延は、パーライトラメラ間でＮｂ炭化物等の合金炭化物を多量に析出させ、非調質鋼部品の延性を顕著に低下させる効果がある。この効果を確実に得るためには、Ｃｒ含有量を０．０５％以上にすることが好ましい。Ｃｒ含有量は、０．０６％以上、０．０７％以上、または０．０８％以上がより好ましい。ただし、Ｃｒが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ｃｒ含有量の下限値は０％である。
　一方、Ｃｒを過剰に含有すると、パーライト組織ではなくベイナイト組織が生成し、Ｎｂ炭化物の析出量が減少するため、かえって非調質鋼部品の延性が高くなる。これにより、非調質鋼部品の破断分離性が顕著に低下するため、Ｃｒ含有量は１．００％以下とする。Ｃｒ含有量は、０．９０％以下、０．８０％以下、または０．７０％以下が好ましい。 Cr: 0 to 1.00%
A large amount of Cr dissolves in cementite and slows the growth rate of pearlite. The delay of the pearlite growth rate has the effect of causing a large amount of alloy carbide such as Nb carbide to precipitate between the pearlite lamellas and significantly reducing the ductility of the non-tempered steel part. In order to obtain this effect reliably, the Cr content is preferably 0.05% or more. The Cr content is more preferably 0.06% or more, 0.07% or more, or 0.08% or more. However, even when Cr is not included, the steel and the non-heat treated steel part according to the present embodiment can solve the problem, so the lower limit value of the Cr content is 0%.
On the other hand, when Cr is excessively contained, a bainite structure is generated instead of a pearlite structure, and the amount of Nb carbide precipitated is reduced, so that the ductility of the non-tempered steel part is increased. Thereby, since the fracture separability of a non-tempered steel part falls remarkably, Cr content shall be 1.00% or less. The Cr content is preferably 0.90% or less, 0.80% or less, or 0.70% or less.
Ｎｂ：０．０１０～０．２０％
　Ｎｂは、鋼中に窒化物又は炭化物を形成する。熱間鍛造後の冷却時に形成するＮｂ炭化物が初析フェライトおよび／またはパーライトラメラ間に多量に析出することで、延性を顕著に低下させ、非調質鋼部品の破断分離性を向上させる。この効果を確実に得るためには、Ｎｂ含有量を０．０１０％以上にする必要がある。Ｎｂ含有量は、０．０２％以上、０．０３％以上、または０．０４％以上がより好ましい。
　一方、Ｎｂを過剰に含有すると、延性が著しく低くなるため、破断面の凹凸が小さくなり、非調質鋼部品の破断面の嵌合性が低下する。そのため、Ｎｂ含有量は０．２０％以下とする。Ｎｂ含有量は、０．１９％以下、０．１８％以下、または０．１７％以下が好ましい。 Nb: 0.010 to 0.20%
Nb forms nitrides or carbides in the steel. A large amount of Nb carbide formed during cooling after hot forging precipitates between pro-eutectoid ferrite and / or pearlite lamella, thereby significantly reducing the ductility and improving the fracture separability of non-tempered steel parts. In order to reliably obtain this effect, the Nb content needs to be 0.010% or more. The Nb content is more preferably 0.02% or more, 0.03% or more, or 0.04% or more.
On the other hand, when Nb is contained excessively, the ductility is remarkably lowered, so that the unevenness of the fracture surface is reduced, and the fitting property of the fracture surface of the non-heat treated steel part is lowered. Therefore, the Nb content is 0.20% or less. The Nb content is preferably 0.19% or less, 0.18% or less, or 0.17% or less.
Ｔｉ：０～０．０７０％
　Ｔｉは、窒化物又は炭化物を形成する。Ｔｉ炭化物はパーライト変態過程においてパーライトとオーステナイトとの界面でＮｂ炭化物より先に析出し、核となることで、単独でＮｂ炭化物が析出するより微細かつ多量にＮｂ炭化物が析出する。これにより、単独でＮｂ炭化物が析出するよりもより延性を低下させ、非調質鋼部品の破断分離性をより向上させることができる。この効果を確実に得るためには、Ｔｉ含有量は０．００５％以上が好ましい。ただし、Ｔｉが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ｔｉの含有量の下限値は０％である。
　一方、Ｔｉを過剰に含有すると、延性が顕著に低くなり、破断面の凹凸が小さくなるため、非調質鋼部品の破断面の嵌合性が低下する。そのため、Ｔｉ含有量は０．０７０％以下とする。Ｔｉ含有量は、０．０６５％以下、０．０６０％以下、または０．０５５％以下が好ましい。Ｔｉ含有量は、０．０１４％以下がより好ましい。 Ti: 0 to 0.070%
Ti forms nitrides or carbides. Ti carbide precipitates prior to Nb carbide at the interface between pearlite and austenite in the pearlite transformation process and becomes a nucleus, so that Nb carbide precipitates in a finer amount and in a larger amount than when Nb carbide precipitates alone. Thereby, ductility can be lowered more than the precipitation of Nb carbide alone, and the fracture separability of non-tempered steel parts can be further improved. In order to reliably obtain this effect, the Ti content is preferably 0.005% or more. However, even when Ti is not included, the steel and non-tempered steel parts according to the present embodiment can solve the problem, so the lower limit of the Ti content is 0%.
On the other hand, when Ti is contained excessively, the ductility is remarkably reduced and the unevenness of the fracture surface is reduced, so that the fitting property of the fracture surface of the non-heat treated steel part is lowered. Therefore, the Ti content is set to 0.070% or less. The Ti content is preferably 0.065% or less, 0.060% or less, or 0.055% or less. The Ti content is more preferably 0.014% or less.
Ｍｏ：０～０．１５％
　Ｍｏは、ＭｎやＣｒと同様に、セメンタイトに多く固溶してパーライトの成長速度を遅くする。パーライトの成長速度の遅延はパーライトラメラ間でＮｂ炭化物等の合金炭化物を多量に析出させ、非調質鋼部品の延性を顕著に低下させる効果がある。この効果を確実に得るためには、Ｍｏ含有量は０．００５％以上が好ましい。ただし、Ｍｏが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ｍｏ含有量の下限値は０％である。
　一方、Ｍｏを過剰に含有すると、パーライト組織ではなくベイナイト組織が生成し、Ｎｂ炭化物の析出量が減少するため、かえって非調質鋼部品の延性が高くなる。これにより非調質鋼部品の破断分離性が顕著に低下するため、Ｍｏ含有量は０．１５％以下とする。Ｍｏ含有量は、０．１３％以下、０．１１％以下、または０．０９％以下が好ましい。 Mo: 0 to 0.15%
Mo, like Mn and Cr, dissolves much in cementite and slows the growth rate of pearlite. The delay of the pearlite growth rate has an effect of significantly reducing the ductility of the non-tempered steel part by precipitating a large amount of alloy carbide such as Nb carbide between the pearlite lamellae. In order to reliably obtain this effect, the Mo content is preferably 0.005% or more. However, even when Mo is not included, the steel and non-tempered steel parts according to the present embodiment can solve the problem, so the lower limit of the Mo content is 0%.
On the other hand, when Mo is contained excessively, not a pearlite structure but a bainite structure is generated, and the amount of precipitation of Nb carbides is reduced, so that the ductility of the non-tempered steel part is increased. As a result, the fracture separability of the non-tempered steel part is significantly reduced, so the Mo content is 0.15% or less. The Mo content is preferably 0.13% or less, 0.11% or less, or 0.09% or less.
Ｎ：０．００１０～０．００６０％
　Ｎは、Ｎｂおよび／またはＴｉと結合して窒化物を形成する。これらの窒化物はフェライト・パーライト変態前のオーステナイト組織の粗大化を抑制して非調質鋼部品の焼入れ性を低下させる。これによりＮには、非調質鋼部品の破断分離性を大幅に劣化させるベイナイト組織の生成を抑制する効果がある。この効果を得るために、Ｎ含有量を０．００１０％以上とする。Ｎ含有量は、０．００１５％以上、０．００２０％以上、または０．００２５％以上が好ましい。
　一方、Ｎを過剰に含有すると、窒化物が増大し、熱間鍛造後の冷却時に生成するＮｂ炭化物等の合金炭化物の析出量が減少するため、かえって非調質鋼部品の延性が高くなる。これにより非調質鋼部品の破断分離性が顕著に低下するため、Ｎ含有量は０．００６０％以下とする。Ｎ含有量は、０．００５５％以下、０．００５０％以下、または０．００４５％以下が好ましい。 N: 0.0010 to 0.0060%
N combines with Nb and / or Ti to form a nitride. These nitrides suppress the coarsening of the austenite structure before the ferrite-pearlite transformation and lower the hardenability of the non-tempered steel parts. As a result, N has an effect of suppressing the formation of a bainite structure that significantly deteriorates the fracture separability of the non-heat treated steel part. In order to acquire this effect, N content shall be 0.0010% or more. The N content is preferably 0.0015% or more, 0.0020% or more, or 0.0025% or more.
On the other hand, when N is contained excessively, nitrides increase, and the precipitation amount of alloy carbides such as Nb carbides generated during cooling after hot forging decreases, so that the ductility of the non-tempered steel parts is increased. As a result, the fracture separability of the non-heat treated steel parts is significantly reduced, so the N content is set to 0.0060% or less. The N content is preferably 0.0055% or less, 0.0050% or less, or 0.0045% or less.
Ｖ：０～０．０１０％
　Ｖは、鋼中に窒化物を形成し、初析フェライトへの変態を促進させるため、パーライトラメラ間におけるＮｂ炭化物の析出量を減少させる。これにより、かえって延性が高くなり、非調質鋼部品の破断分離性が低下する。そのため、Ｖ含有量は０．０１０％以下とする。Ｖ含有量は、０．００８％以下、０．００６％以下、または０．００４％以下が好ましい。Ｖ含有量は少ないほど好ましく、０％であってもよい。 V: 0 to 0.010%
V forms nitrides in the steel and promotes transformation into pro-eutectoid ferrite, thus reducing the amount of Nb carbide precipitated between pearlite lamellae. Thereby, ductility becomes high rather, and the fracture separability of a non-heat treated steel part falls. Therefore, the V content is 0.010% or less. The V content is preferably 0.008% or less, 0.006% or less, or 0.004% or less. The smaller the V content, the better, and it may be 0%.
　本実施形態に係る鋼及び非調質鋼部品は、上述の元素に加えてさらに、Ｃａ、Ｚｒ及びＭｇからなる群から選択される１種以上を含んでも良い。ただし、Ｃａ、Ｚｒ及びＭｇが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ｃａ、Ｚｒ及びＭｇそれぞれの含有量の下限は０％である。 The steel and non-heat treated steel parts according to the present embodiment may further include one or more selected from the group consisting of Ca, Zr and Mg in addition to the above-described elements. However, even when Ca, Zr and Mg are not included, the steel and non-heat treated steel parts according to this embodiment can solve the problem, so the lower limit of the content of each of Ca, Zr and Mg is 0%.
Ｃａ：０～０．００５％
Ｚｒ：０～０．００５％
Ｍｇ：０～０．００５％
　Ｃａ、ＺｒおよびＭｇはいずれも鋼中に酸化物を形成し、Ｍｎ硫化物の晶出核となりＭｎ硫化物を均一に微細分散させる効果がある。非調質鋼部品を破断分離させる際には、圧延方向に伸長したＭｎ硫化物に沿ってき裂が伝播する。そのため、Ｍｎ硫化物が大きいほど破断面の凹凸が大きくなる一方で、延性が高くなり、破断分離性が低くなる。Ｍｎ硫化物を微細分散することにより、き裂進展方向にき裂が伝播しやすくなり、非調質鋼部品の破断分離性がより向上する。この効果を確実に得るためには、Ｃａ、ＺｒおよびＭｇのいずれか１種以上の含有量は０．００１％以上が好ましい。一方、いずれか１種でもその含有量が０．００５％を超えると、鋼の熱間加工性が劣化し、熱間圧延が困難となる。そのため、Ｃａ、ＺｒおよびＭｇの含有量は、０．００５％以下とする。 Ca: 0 to 0.005%
Zr: 0 to 0.005%
Mg: 0 to 0.005%
Ca, Zr, and Mg all form oxides in the steel and serve as crystallization nuclei for Mn sulfide, which has the effect of uniformly and finely dispersing Mn sulfide. When non-tempered steel parts are separated by fracture, cracks propagate along the Mn sulfide elongated in the rolling direction. Therefore, the larger the Mn sulfide, the larger the irregularities of the fractured surface, while the ductility increases and the fracture separability decreases. By finely dispersing Mn sulfide, cracks are easily propagated in the direction of crack propagation, and the fracture separation of non-tempered steel parts is further improved. In order to surely obtain this effect, the content of at least one of Ca, Zr and Mg is preferably 0.001% or more. On the other hand, if the content of any one of them exceeds 0.005%, the hot workability of the steel deteriorates and hot rolling becomes difficult. Therefore, the contents of Ca, Zr and Mg are set to 0.005% or less.
　本実施形態に係る鋼及び非調質鋼部品は、上述の元素に加えてさらに、Ｃｕ、Ｎｉ、ＰｂおよびＢｉからなる群から選択される１種以上を含んでも良い。ただし、Ｃｕ、Ｎｉ、Ｐｂ及びＢｉが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ｃｕ、Ｎｉ、Ｐｂ及びＢｉそれぞれの含有量の下限は０％である。 The steel and non-tempered steel parts according to the present embodiment may further include one or more selected from the group consisting of Cu, Ni, Pb and Bi in addition to the elements described above. However, even when Cu, Ni, Pb and Bi are not included, the steel and non-heat treated steel parts according to this embodiment can solve the problem, so the lower limit of the content of each of Cu, Ni, Pb and Bi is 0. %.
Ｃｕ：０～０．０５％
Ｎｉ：０～０．０５％
Ｐｂ：０～０．５０％
Ｂｉ：０～０．００５０％
　Ｃｕ、ＮｉおよびＰｂは、鋼中に単独で存在することにより、フェライト及びパーライトの延性及び靭性を低下させる。延性及び靱性の低下は、非調質鋼部品の破断時の破断面近傍の塑性変形量を小さくし、破断分離性を向上させる効果がある。したがって、Ｃｕ、ＮｉおよびＰｂの含有量はそれぞれ０．０１％以上、より好ましくは０．０２％以上としてもよい。しかしながら、これらの元素の含有量が過剰であると、熱間加工性が劣化し、熱間圧延が困難となることから、Ｃｕ及びＮｉの含有量はそれぞれ０．０５％以下、Ｐｂの含有量は０．５０％以下とする。
　また、Ｂｉは鋼中に固溶状態として存在することにより、フェライト及びパーライトの延性及び靱性を低下させる。延性及び靱性の低下は、非調質鋼部品の破断時の破断面近傍の塑性変形量を小さくし、破断分離性を向上させる効果がある。したがって、Ｂｉの含有量を０．０００１％以上としてもよい。しかしながら、Ｂｉの含有量が過剰であると、熱間加工性が劣化し、熱間圧延が困難となることから、Ｂｉの含有量は０．００５０％とする。 Cu: 0 to 0.05%
Ni: 0 to 0.05%
Pb: 0 to 0.50%
Bi: 0 to 0.0050%
Cu, Ni, and Pb are present alone in the steel, thereby reducing the ductility and toughness of ferrite and pearlite. The reduction in ductility and toughness has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture of the non-heat treated steel part and improving the fracture separability. Therefore, the contents of Cu, Ni, and Pb may each be 0.01% or more, more preferably 0.02% or more. However, if the content of these elements is excessive, hot workability deteriorates and hot rolling becomes difficult. Therefore, the Cu and Ni contents are 0.05% or less, and the Pb content. Is 0.50% or less.
Further, Bi exists as a solid solution state in the steel, thereby reducing the ductility and toughness of ferrite and pearlite. The reduction in ductility and toughness has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture of the non-heat treated steel part and improving the fracture separability. Therefore, the Bi content may be 0.0001% or more. However, if the Bi content is excessive, hot workability deteriorates and hot rolling becomes difficult, so the Bi content is set to 0.0050%.
Ａｌ：０．０１０％以下
　本実施形態に係る鋼及び非調質鋼部品は、Ａｌが０．０１０％以下で含まれていてもよい。しかし、Ａｌ含有量が０．０１０％を超えると、被削性が劣化し、高精度が要求される自動車エンジン用部品に適用することができない。Ａｌ含有量は低い方が好ましいが、Ａｌ低減に要するコスト低減の観点から、０．００１％以上としてもよい。Ａｌが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ａｌ含有量の下限は０％としてもよい。 Al: 0.010% or less Al may be contained at 0.010% or less in the steel and non-tempered steel parts according to the present embodiment. However, if the Al content exceeds 0.010%, the machinability deteriorates and cannot be applied to automobile engine parts that require high accuracy. The Al content is preferably low, but may be 0.001% or more from the viewpoint of cost reduction required for Al reduction. Even when Al is not included, the steel and non-heat treated steel parts according to the present embodiment can solve the problem, so the lower limit of the Al content may be 0%.
　本実施形態に係る鋼及び非調質鋼部品の化学成分の残部は鉄（Ｆｅ）及び不純物である。不純物とは、非調質鋼を工業的に製造する際に、鉱石もしくはスクラップ等のような原料、又は製造工程の種々の要因によって混入する成分であって、本実施形態に係る鋼及び非調質鋼部品に悪影響を与えない範囲で許容されるものを意味する。
　なお、本実施形態に係る鋼及び非調質鋼部品に含有され得る不純物として、ＢやＯなどが挙げられる。Ｂ含有量はとくに規定しないが、本実施形態に係る鋼および非調質鋼部品に含まれ得るＢは３ｐｐｍ以下であるため、Ｂ含有量の上限を３ｐｐｍとしてもよい。Ｂが含まれない場合でも本実施形態に係る鋼及び非調質鋼部品はその課題を解決できるので、Ｂ含有量の下限は０％としてもよい。また、Ｏが不純物として含まれる場合、例えば、その含有量は０．００３０％以下である。 The balance of the chemical components of the steel and non-heat treated steel parts according to this embodiment is iron (Fe) and impurities. Impurities are raw materials such as ore or scrap, or components mixed in due to various factors in the production process when industrially producing non-heat treated steel. It means that it is allowed as long as it does not adversely affect the quality steel parts.
In addition, B, O, etc. are mentioned as an impurity which may be contained in the steel which concerns on this embodiment, and a non-tempered steel component. The B content is not particularly specified, but B that can be contained in the steel and the non-heat treated steel component according to the present embodiment is 3 ppm or less, so the upper limit of the B content may be 3 ppm. Even when B is not included, the steel and non-tempered steel parts according to the present embodiment can solve the problem, so the lower limit of the B content may be 0%. Moreover, when O is contained as an impurity, the content is 0.0030% or less, for example.
　上述した鋼及び非調質鋼部品の化学成分は、ＩＣＰ－ＡＥＳ（Ｉｎｄｕｃｔｉｖｅｌｙ　Ｃｏｕｐｌｅｄ　Ｐｌａｓｍａ－Ａｔｏｍｉｃ　Ｅｍｉｓｓｉｏｎ　Ｓｐｅｃｔｒｏｍｅｔｒｙ）を用いて測定すればよい。なお、ＣおよびＳは燃焼－赤外線吸収法を用い、Ｎは不活性ガス融解－熱伝導度法を用いて測定すればよい。 The chemical components of the steel and non-heat treated steel parts described above may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). C and S may be measured using a combustion-infrared absorption method, and N may be measured using an inert gas melting-thermal conductivity method.
＜非調質鋼部品のミクロ組織＞
フェライト・パーライト組織
　フェライト・パーライト組織とは、フェライト・パーライトを主体とする組織であり、初析フェライトとパーライトとからなる組織である。ここで、フェライト・パーライト主体の組織とは、非調質鋼部品のミクロ組織において、フェライト・パーライトの面積分率が９５％以上、換言すると初析フェライトおよびパーライト以外の残部組織が５％以下であることを意味する。なお、本実施形態に係る非調質鋼部品のフェライト・パーライト組織では、パーライトの面積分率と初析フェライトの面積分率とが同程度であるか、またはパーライトの面積分率が初析フェライトの面積分率より少ない。
　フェライト・パーライト組織では、初析フェライトおよびパーライトの成長時に、初析フェライトおよび／またはパーライトとオーステナイトとの界面で、Ｎｂ炭化物等の合金炭化物が析出する相界面析出が起こりうる。つまり、熱間鍛造後の冷却過程で、オーステナイトから初析フェライトおよび／またはパーライトへの変態と、Ｎｂ炭化物等の合金炭化物の析出とが同時に起こりうる。一方、ベイナイト組織およびマルテンサイト組織では、オーステナイトから変態した後、Ｎｂ炭化物等の合金炭化物を析出させるために、これらの合金炭化物が析出する温度に再加熱する必要がある。したがって、非調質鋼部品においてＮｂ炭化物等の合金炭化物を多量に析出させるために、非調質鋼部品の表面から１．０ｍｍ以上内部におけるミクロ組織はフェライト・パーライト組織とする。フェライト・パーライト組織の面積分率は、９５％以上であり、好ましくは、９６％以上、９７％以上、または１００％である。
　なお、本実施形態に係る鋼は、Ａｃ３点以上の温度域まで加熱されて熱間鍛造され、冷却されることで非調質鋼部品に加工されるため、加熱される前の金属組織は特に規定しない。熱間鍛造前の鋼の組織は、熱間鍛造後の機械部品の特性に何ら影響を及ぼさないからである。 <Microstructure of non-heat treated steel parts>
Ferrite and pearlite structure The ferrite and pearlite structure is a structure mainly composed of ferrite and pearlite, and is composed of proeutectoid ferrite and pearlite. Here, the structure mainly composed of ferrite and pearlite means that the area fraction of ferrite and pearlite is 95% or more in the microstructure of non-heat treated steel parts, in other words, the remaining structure other than proeutectoid ferrite and pearlite is 5% or less. It means that there is. In the ferrite-pearlite structure of the non-heat treated steel part according to the present embodiment, the area fraction of pearlite and the area fraction of pro-eutectoid ferrite are approximately the same, or the area fraction of pearlite is pro-eutectoid ferrite. Less than the area fraction of
In the ferrite-pearlite structure, during the growth of pro-eutectoid ferrite and pearlite, phase interface precipitation in which alloy carbide such as Nb carbide precipitates at the interface between pro-eutectoid ferrite and / or pearlite and austenite can occur. That is, in the cooling process after hot forging, transformation from austenite to pro-eutectoid ferrite and / or pearlite and precipitation of alloy carbide such as Nb carbide can occur simultaneously. On the other hand, in the bainite structure and martensite structure, in order to precipitate alloy carbides such as Nb carbide after transformation from austenite, it is necessary to reheat to a temperature at which these alloy carbides precipitate. Therefore, in order to precipitate a large amount of alloy carbide such as Nb carbide in the non-tempered steel part, the microstructure within 1.0 mm or more from the surface of the non-tempered steel part is a ferrite / pearlite structure. The area fraction of the ferrite / pearlite structure is 95% or more, preferably 96% or more, 97% or more, or 100%.
In addition, since the steel according to the present embodiment is heated to a temperature range of Ac 3 points or higher, hot forged, and cooled to be processed into a non-tempered steel part, the metal structure before being heated is Not specified. This is because the structure of steel before hot forging does not affect the characteristics of machine parts after hot forging.
　ミクロ組織に含まれるフェライト・パーライト組織以外の残部組織の面積分率は、０～５％とする。残部組織としては例えばベイナイト組織が含まれ得るが、ベイナイト組織が生成すると非調質鋼部品の降伏比が低下する。そのため、残部組織は極力少ないことが好ましく、４％以下、または３％以下が好ましい。より好ましくは、残部組織は０％である。 The area fraction of the remaining structure other than the ferrite / pearlite structure contained in the microstructure shall be 0 to 5%. As the remaining structure, for example, a bainite structure may be included, but when the bainite structure is generated, the yield ratio of the non-tempered steel part is lowered. Therefore, the remaining structure is preferably as small as possible, preferably 4% or less, or 3% or less. More preferably, the balance structure is 0%.
　ミクロ組織の面積分率は、以下の方法により測定する。
　非調質鋼部品から１０ｍｍ角のサイズの試験片を切り出す。試験片は、表面から１．０ｍｍより深い位置から切り出す。なお、機械部品の場合は、任意の位置から、コネクティングロッドの場合はロッド部から、試験片を切り出す。切り出した試験片を樹脂埋めし、鏡面研磨仕上げした後、ナイタール腐食液（３％硝酸アルコール）で研磨面をエッチングする。そして、エッチングにより腐食した面を観察面として任意の１０箇所を特定し、観察倍率を４００倍とし光学顕微鏡で観察する。光学顕微鏡写真におけるフェライト及びパーライトを通常の手段により特定し、これらが写真に占める面積分率を通常の画像解析により測定する。そして、１０か所におけるフェライト及びパーライトの合計面積率の平均値を、非調質機械部品のミクロ組織におけるフェライト・パーライト組織の面積分率とする。なお、上記手段によって得られたフェライト・パーライト組織の面積分率は、その体積分率と実質的に同一である。 The area fraction of the microstructure is measured by the following method.
A 10 mm square test piece is cut out from the non-heat treated steel part. The test piece is cut out from a position deeper than 1.0 mm from the surface. In the case of mechanical parts, the test piece is cut out from an arbitrary position, and in the case of connecting rods, the test piece is cut out from the rod portion. The cut specimen is filled with resin and mirror polished, and then the polished surface is etched with a nital etchant (3% nitric acid alcohol). Then, arbitrary 10 positions are specified by using the surface corroded by etching as an observation surface, and the observation magnification is set to 400 times and observation is performed with an optical microscope. The ferrite and pearlite in the optical micrograph are identified by ordinary means, and the area fraction of these in the photograph is measured by ordinary image analysis. And let the average value of the total area ratio of the ferrite and pearlite in ten places be the area fraction of the ferrite pearlite structure in the microstructure of a non-tempered mechanical part. The area fraction of the ferrite / pearlite structure obtained by the above means is substantially the same as the volume fraction.
　本実施形態に係る非調質鋼部品は、Ｎｂ炭化物等の合金炭化物が初析フェライト析出しているだけでなく、パーライトラメラ間にも析出している。これにより、非調質鋼部品の延性を低下させ、破断分離性を向上することができる。 In the non-tempered steel part according to this embodiment, alloy carbides such as Nb carbides are precipitated not only in pro-eutectoid ferrite but also between pearlite lamellae. Thereby, the ductility of a non-tempered steel part can be reduced and the fracture separability can be improved.
　Ｎｂ炭化物等の合金炭化物の存在位置は、以下の方法により観察できる。
　非調質鋼部品の表面から１．０ｍｍ以上深い位置から、厚さ０．５ｍｍの円板を採取する。エメリー紙を用いて円板の両面を研削研磨し、円板の厚さを５０μｍとする。その後、円板から直径３ｍｍのサンプルを採取する。サンプルを１０％過塩素酸－氷酢酸溶液中に浸漬して、電解研磨を実施して、薄膜試料を作製する。透過型電子顕微鏡（ＴＥＭ：Ｔｒａｎｓｍｉｓｓｉｏｎ　Ｅｌｅｃｔｒｏｎ　Ｍｉｃｒｏｓｃｏｐｅ）と高感度カメラとで構成された装置を用いて、得られた薄膜試料を観察する。具体的には、薄膜試料に対して菊池図形を解析して、薄膜試料の結晶方位を特定し、特定した結晶方位に基づいて薄膜試料を傾斜させて、（００１）面を観察できるように、薄膜試料を調整する。観察倍率は４００００倍とし、加速電圧は２００ｋＶとする。 The location of the alloy carbide such as Nb carbide can be observed by the following method.
A disk having a thickness of 0.5 mm is taken from a position deeper than 1.0 mm from the surface of the non-heat treated steel part. Using emery paper, both sides of the disk are ground and polished to a thickness of 50 μm. Thereafter, a sample having a diameter of 3 mm is taken from the disk. The sample is immersed in a 10% perchloric acid-glacial acetic acid solution, and electropolishing is performed to produce a thin film sample. The obtained thin film sample is observed using an apparatus composed of a transmission electron microscope (TEM) and a high-sensitivity camera. Specifically, the Kikuchi figure is analyzed for the thin film sample, the crystal orientation of the thin film sample is specified, the thin film sample is tilted based on the specified crystal orientation, and the (001) plane can be observed. Prepare a thin film sample. The observation magnification is 40000 times, and the acceleration voltage is 200 kV.
＜非調質鋼部品の機械特性＞
　引張強度が９００ＭＰａ以上、かつ降伏比が０．８５以上
　引張強度が９００ＭＰａ以上であれば、コネクティングロッドとして使用された場合でも十分な強度を確保することができる。また、降伏比が０．８５以上であれば、破断分離時の二次き裂が短くなり、二次き裂の先端で塑性変形が生じにくく、非調質鋼部品の破断分離性及び破断面の嵌合性が向上する。よって、本実施形態に係る非調質鋼部品の引張強度は、例えば、９００ＭＰａ以上、１２５０ＭＰａ以下であり、好ましくは９２５ＭＰａ以上、より好ましくは９５０ＭＰａ以上である。また、本実施形態に係る非調質鋼部品の降伏比は、例えば、０．８５以上であり、好ましくは０．８７以上であり、より好ましくは０．９０以上である。なお、本実施形態における降伏比は、単位ＭＰａの０．２％耐力を単位ＭＰａの引張強度で除した値（降伏比＝０．２％耐力（ＭＰａ）／引張強度（ＭＰａ））である。 <Mechanical properties of non-tempered steel parts>
When the tensile strength is 900 MPa or more and the yield ratio is 0.85 or more, if the tensile strength is 900 MPa or more, sufficient strength can be ensured even when used as a connecting rod. Moreover, if the yield ratio is 0.85 or more, the secondary crack at the time of fracture separation is shortened, plastic deformation is unlikely to occur at the tip of the secondary crack, and the fracture separability and fracture surface of non-heat treated steel parts The fitting property is improved. Therefore, the tensile strength of the non-heat treated steel part according to the present embodiment is, for example, 900 MPa or more and 1250 MPa or less, preferably 925 MPa or more, more preferably 950 MPa or more. Moreover, the yield ratio of the non-heat treated steel part according to the present embodiment is, for example, 0.85 or more, preferably 0.87 or more, and more preferably 0.90 or more. The yield ratio in the present embodiment is a value obtained by dividing the 0.2% yield strength of unit MPa by the tensile strength of unit MPa (yield ratio = 0.2% yield strength (MPa) / tensile strength (MPa)).
　本実施形態に係る非調質鋼部品は、０．２％耐力が８００ＭＰａ以上であってもよい。０．２％耐力が８００ＭＰａ以上であれば、破断分離時の二次き裂が短くなり、二次き裂の先端で塑性変形が生じにくくなり、非調質鋼部品の破断分離性及び破断面の嵌合性がより向上する。 The non-heat treated steel part according to the present embodiment may have a 0.2% proof stress of 800 MPa or more. If the 0.2% proof stress is 800 MPa or more, the secondary crack at the time of fracture separation becomes short, and it becomes difficult for plastic deformation to occur at the tip of the secondary crack. The fitting property is further improved.
　非調質鋼部品の引張強度、０．２％耐力及び降伏比は以下の方法で測定する。機械部品の場合は、試験片の長手方向が圧延方向と一致するように、またコネクティングロッドの場合は、試験片の長手方向がロッド部の長手方向と一致するように、ＪＩＳ　Ｚ　２２４１：２０１１に記載のＪＩＳ１４Ａ号試験片を切り出す。試験片は、機械部品またはコネクティングロッドの表面から深さ１．０ｍｍ以上内部から切り出す。また、コネクティングロッドの場合はロッド部から切り出す。切り出した試験片を用いて、ＪＩＳ　Ｚ　２２４１：２０１１に準拠して引張強度及び０．２％耐力を測定する。測定温度は２５℃とし、ひずみ速度は５ｍｍ／ｍｉｎとする。得られた０．２％耐力（ＭＰａ）を引張強度（ＭＰａ）で除することで、降伏比を得る。 The tensile strength, 0.2% proof stress and yield ratio of non-tempered steel parts are measured by the following methods. In the case of mechanical parts, JIS Z 2241: 2011 is set so that the longitudinal direction of the test piece coincides with the rolling direction, and in the case of a connecting rod, the longitudinal direction of the test piece coincides with the longitudinal direction of the rod part. The described JIS14A test piece is cut out. A test piece is cut out from the inside of a depth of 1.0 mm or more from the surface of a mechanical part or a connecting rod. In the case of a connecting rod, cut out from the rod. Using the cut-out test piece, the tensile strength and the 0.2% proof stress are measured according to JIS Z 2241: 2011. The measurement temperature is 25 ° C. and the strain rate is 5 mm / min. The yield ratio is obtained by dividing the obtained 0.2% yield strength (MPa) by the tensile strength (MPa).
　なお、熱間鍛造前の鋼の機械特性は特に限定されない。金属組織と同様に、例えばＡｃ３点以上の温度に加熱して行われる熱間鍛造より前の鋼の機械特性は、熱間鍛造後の鋼部品機械部品の機械特性に実質的に影響しないからである。熱間鍛造後の鋼部品機械部品の機械特性は、化学成分及び熱間鍛造条件に応じて定まることとなる。即ち、本実施形態に係る鋼の作用効果は、熱間鍛造に供した後に優れた機械特性を発揮しうるという点にある。
　ただし、本実施形態に係る鋼は、熱間鍛造用途に用いた場合に優れた効果を発揮するものの、その用途は熱間鍛造に限定されない。例えば、本実施形態に係る鋼を冷間加工することによって、高い強度、高い降伏比、優れた破断分離性、及び、優れた破断面の嵌合性を有する機械部品を製造することも可能である。この場合、本実施形態に係る鋼の組織を、非調質鋼部品機械部品と同様に、表面から１．０ｍｍ以上内部の組織がフェライト・パーライト組織であり、フェライト・パーライト組織の面積分率が９５％以上であるものとすることは有益である。さらに本実施形態に係る鋼は、例えば、直径２０～８０ｍｍの棒鋼であるが、用途が限定されないので、その形状も任意である。 The mechanical properties of the steel before hot forging are not particularly limited. As with the metal structure, for example, the mechanical properties of the steel before hot forging performed by heating to a temperature of Ac 3 or higher does not substantially affect the mechanical properties of the steel component mechanical parts after hot forging. It is. The mechanical properties of the steel part machine part after hot forging are determined according to the chemical composition and hot forging conditions. That is, the effect of the steel according to this embodiment is that it can exhibit excellent mechanical properties after being subjected to hot forging.
However, although the steel which concerns on this embodiment exhibits the effect excellent when it uses for a hot forging use, the use is not limited to a hot forging. For example, by cold working the steel according to the present embodiment, it is also possible to produce a mechanical component having high strength, high yield ratio, excellent fracture separation, and excellent fracture surface fitting. is there. In this case, the structure of the steel according to the present embodiment is the same as the non-heat treated steel part machine part, the structure inside 1.0 mm or more from the surface is a ferrite pearlite structure, and the area fraction of the ferrite pearlite structure is It is beneficial to be 95% or more. Furthermore, the steel according to the present embodiment is, for example, a steel bar having a diameter of 20 to 80 mm, but its use is not limited, and its shape is also arbitrary.
＜鋼及び非調質鋼部品の製法＞
　本実施形態に係る鋼は、上記の化学成分を有する鋼片を連続鋳造により鋳造し、必要に応じて、均熱拡散処理、分塊圧延工程を経て圧延素材とする。次に、圧延素材を１１５０～１２５０℃に加熱した後、熱間圧延してから冷却することで、鋼を得る。熱間圧延はＡｒ３点以上の温度で熱間圧延を終了し、熱間圧延後の冷却条件は特に限定する必要はなく、放冷でも水冷でもよい。熱間圧延後は焼入れ焼戻し等の調質熱処理を行う必要はない。 <Production method of steel and non-heat treated steel parts>
The steel according to the present embodiment is obtained by casting a steel slab having the above chemical components by continuous casting and, if necessary, through a soaking diffusion process and a block rolling process to obtain a rolled material. Next, the rolled material is heated to 1150 to 1250 ° C., then hot-rolled and then cooled to obtain steel. In the hot rolling, the hot rolling is finished at a temperature of 3 or more points of Ar, and the cooling conditions after the hot rolling need not be particularly limited, and may be cooled or water-cooled. It is not necessary to perform tempering heat treatment such as quenching and tempering after hot rolling.
　本実施形態に係る非調質鋼部品は、鋼をＡｃ３点以上の温度に加熱し、熱間鍛造を行って所望の部品形状に加工し、その後、冷却することにより製造する。熱間鍛造後の冷却条件は、フェライト・パーライト組織が得られる条件であれば特に限定する必要はなく、放冷でも水冷でもよい。例えば、加熱温度の温度範囲は１２２０℃～１２８０℃とし、加熱時間は５ｍｉｎ～１５ｍｉｎとする。また、熱間鍛造後に更に切削等の後加工を行って部品形状を調整してもよい。熱間鍛造後は焼入れ焼戻し等の調質熱処理を行う必要はない。 The non-tempered steel part according to the present embodiment is manufactured by heating steel to a temperature of Ac 3 or higher, performing hot forging to form a desired part shape, and then cooling. The cooling conditions after hot forging are not particularly limited as long as the ferrite-pearlite structure can be obtained, and may be cooled or water-cooled. For example, the temperature range of the heating temperature is 1220 ° C. to 1280 ° C., and the heating time is 5 min to 15 min. Further, after hot forging, post-processing such as cutting may be performed to adjust the part shape. After hot forging, it is not necessary to perform tempering heat treatment such as quenching and tempering.
　本実施形態に係る鋼及び機械部品の用途は特に限定されないが、破断分離して用いられる機械部品、例えば破断分離型のコネクティングロッドに適用された場合に、特に好適な効果を奏する。 The use of the steel and machine parts according to the present embodiment is not particularly limited, but has a particularly favorable effect when applied to a machine part used by breaking and separating, for example, a breaking and separating connecting rod.
　図１は、本実施形態に係る破断分離型のコネクティングロッド（以下、破断分離型コンロッドと言う場合がある）の一例を示す分解斜視図である。この例の破断分離型コンロッド１は、図１に示すように上下に分割されたロッド付半円弧状のアッパ側半割体２と、半円弧状のロア側半割体３とから構成されている。アッパ側半割体２の半円弧部２Ａの両端側にはそれぞれロア側半割体３に固定するためのねじ溝を有するねじ孔５が形成され、ロア側半割体３の半円弧部３Ａの両端側にはそれぞれアッパ側半割体２に固定するための挿通孔６が形成されている。 FIG. 1 is an exploded perspective view showing an example of a fracture separation type connecting rod (hereinafter also referred to as a fracture separation type connecting rod) according to the present embodiment. As shown in FIG. 1, the fracture separation type connecting rod 1 of this example is composed of a semicircular arc-shaped upper-side half-divided body 2 with a rod and a semicircular-arc-shaped lower-side half-divided body 3. Yes. Screw holes 5 having screw grooves for fixing to the lower half half 3 are respectively formed at both ends of the semicircular arc 2A of the upper side half 2. The semicircular arc 3A of the lower side half 3 is formed. Insertion holes 6 for fixing to the upper-side halves 2 are formed on both ends of each.
　アッパ側半割体２の半円弧部２Ａとロア側半割体３の半円弧部３Ａとを円環状に合わせて相互の両端側の挿通孔６とねじ孔５に結合ボルト７を挿通し、螺合することで円環状のビッグエンド部８が構成されている。アッパ側半割体２のロッド部２Ｂの上端側には円環状のスモールエンド部９が形成されている。 The semicircular arc portion 2A of the upper half halves 2 and the semicircular arc portion 3A of the lower halves 3 are aligned in an annular shape, and the coupling bolts 7 are inserted into the insertion holes 6 and the screw holes 5 on both ends. An annular big end portion 8 is formed by screwing. An annular small end portion 9 is formed on the upper end side of the rod portion 2 </ b> B of the upper half 2.
　図１に示す構造の破断分離型コンロッド１は、自動車エンジン等の内燃機関のピストンの往復運動を回転運動に変換するために内燃機関に組み込まれ、スモールエンド部９が図示略のピストンに接続され、ビッグエンド部８が内燃機関のコネクティングロッドジャーナル（図示略）に接続される。 1 is incorporated in an internal combustion engine to convert a reciprocating motion of a piston of an internal combustion engine such as an automobile engine into a rotational motion, and a small end portion 9 is connected to a piston (not shown). The big end portion 8 is connected to a connecting rod journal (not shown) of the internal combustion engine.
　本実施形態に係る破断分離型コンロッド１は上述された化学成分、組織を備える鋼から形成され、アッパ側半割体２の半円弧部２Ａとロア側半割体３の半円弧部３Ａとは、元々１つの円環状部品であった部分を脆性破断して形成される。一例として、熱間鍛造品の一部に切欠きを設けてその切欠きを起点として脆性的に破断分離して、アッパ側半割体２の半円弧部２Ａの突き合わせ面２ａとロア側半割体３の半円弧部３Ａの突き合わせ面３ａとを形成する。これらの突き合わせ面２ａ、３ａは元々１つの部材を破断分離して形成しているので、良好な位置合わせ精度で突き合わせが可能となる。
　この構造の破断分離型コンロッド１は突き合わせ面の新たな加工や位置決めピンが不要となり、大幅な製造工程の簡略化がなされる。 The fracture separation type connecting rod 1 according to the present embodiment is formed of steel having the above-described chemical composition and structure, and the semicircular arc portion 2A of the upper side half body 2 and the semicircular arc portion 3A of the lower side half body 3 are the same. The part which was originally one annular part is formed by brittle fracture. As an example, a notch is provided in a part of a hot forged product, and the notch is used as a starting point to break and separate brittlely, so that the butted surface 2a of the semicircular arc portion 2A of the upper half 2 and the lower half The abutting surface 3a of the semicircular arc portion 3A of the body 3 is formed. Since these abutting surfaces 2a and 3a are originally formed by breaking and separating one member, they can be abutted with good alignment accuracy.
The break-separated connecting rod 1 having this structure eliminates the need for new processing of the abutting surface and positioning pins, and greatly simplifies the manufacturing process.
　破断分離型コンロッド１は、一例として、質量％で、Ｃ：０．１５～０．３０％、Ｓｉ：０．４０～１．３０％、Ｍｎ：０．５０～１．５０％、Ｐ：０．０３５～０．２００％、Ｓ：０．０１０～０．１００％、Ｃｒ：０～１．００％、Ｎｂ：０．０１０～０．２０％、Ｔｉ：０～０．０７０％、Ｍｏ：０～０．１５％、Ｎ：０．００１０～０．００６０％、Ｖ：０～０．０１０％、Ｃａ：０～０．００５％、Ｚｒ：０～０．００５％、Ｍｇ：０～０．００５％、Ｃｕ：０～０．０５％、Ｎｉ：０～０．０５％、Ｐｂ：０～０．５０％、Ｂｉ：０～０．００５０％およびＡｌ：０．０１０％以下を含有し、残部がＦｅ及び不純物からなる。この化学組成を有する鋼を熱間鍛造して冷却し、非調質鋼部品とすることで、上述の特性を有する破断分離型のコンロッドが得られる。 As an example, the fracture separation type connecting rod 1 is C: 0.15 to 0.30%, Si: 0.40 to 1.30%, Mn: 0.50 to 1.50%, P: 0% by mass. 0.035 to 0.200%, S: 0.010 to 0.100%, Cr: 0 to 1.00%, Nb: 0.010 to 0.20%, Ti: 0 to 0.070%, Mo: 0 to 0.15%, N: 0.0010 to 0.0060%, V: 0 to 0.010%, Ca: 0 to 0.005%, Zr: 0 to 0.005%, Mg: 0 to 0 0.005%, Cu: 0 to 0.05%, Ni: 0 to 0.05%, Pb: 0 to 0.50%, Bi: 0 to 0.0050%, and Al: 0.010% or less The balance consists of Fe and impurities. A steel having this chemical composition is hot-forged and cooled to obtain a non-tempered steel part, thereby obtaining a break-separated connecting rod having the above-mentioned characteristics.
　本発明を実施例によって以下に詳述する。なお、これら実施例は本発明の技術的意義、効果を説明するためのものであり、本発明の範囲を限定するものではない。 The present invention will be described in detail below by examples. These examples are for explaining the technical significance and effects of the present invention, and do not limit the scope of the present invention.
　表１Ａおよび表１Ｂに示す組成を有する転炉溶製鋼を連続鋳造により製造し、必要に応じて、均熱拡散処理、分塊圧延工程を経て１６２ｍｍ角の圧延素材とした。次に、圧延素材を１２００℃に加熱した後、熱間圧延によって、直径が５６ｍｍの棒鋼を得た。表１Ｂの下線が付された値は、本発明の範囲外の値であることを示す。また、表１Ａおよび表１Ｂの記号「－」は、その記号に係る元素が添加されていないことを示す。 A converter molten steel having the composition shown in Table 1A and Table 1B was manufactured by continuous casting, and if necessary, a rolling raw material of 162 mm square was obtained through a soaking diffusion treatment and a block rolling process. Next, after the rolled material was heated to 1200 ° C., a steel bar having a diameter of 56 mm was obtained by hot rolling. Values underlined in Table 1B indicate values outside the scope of the present invention. Further, the symbol “-” in Table 1A and Table 1B indicates that the element related to the symbol is not added.
　得られた棒鋼について、破断分離性及び破断面の嵌合性、機械特性、ミクロ組織を調べるため、コンロッド相当の試験片を熱間鍛造により作製した。具体的には、直径５６ｍｍの棒鋼を１２５０℃に加熱し５分間保持した後、１２００℃で、棒鋼の長手方向に対して垂直方向に熱間鍛造した。棒鋼の長手方向に垂直な方向から見たときに、棒鋼側面が円形から樽型になるように変形させて、鍛造方向の厚さが２０ｍｍである鍛造材を得た。熱間鍛造後の鍛造材を自然放冷（放冷）によって室温まで冷却した。 For the obtained steel bar, a test piece corresponding to a connecting rod was produced by hot forging in order to examine the fracture separability, the fracture surface fitting property, the mechanical properties, and the microstructure. Specifically, a steel bar having a diameter of 56 mm was heated to 1250 ° C. and held for 5 minutes, and then hot forged at 1200 ° C. in a direction perpendicular to the longitudinal direction of the steel bar. When viewed from the direction perpendicular to the longitudinal direction of the steel bar, the side surface of the steel bar was deformed so as to change from a circular shape to a barrel shape to obtain a forged material having a thickness in the forging direction of 20 mm. The forged material after hot forging was cooled to room temperature by natural cooling (cooling).
　冷却後の鍛造材から、切削加工により、ＪＩＳ　Ｚ　２２４１：２０１１に記載のＪＩＳ１４Ａ号試験片を作製した。ＪＩＳ１４Ａ号試験片は、鍛造材の幅方向端面から３０ｍｍの位置、且つ厚さ方向１０．０ｍｍ深さの位置から、鍛造材の長手方向に沿って採取した。該試験片を用いて、ＪＩＳ　Ｚ　２２４１：２０１１に準拠して、２５℃で５ｍｍ／ｍｉｎの速度にて引張試験を実施した。得られた結果から、引張強度、０．２％耐力、降伏比、全伸びおよび絞りを得た。 JIS 14A test piece described in JIS Z 2241: 2011 was produced from the forged material after cooling by cutting. A JIS No. 14A test piece was sampled along the longitudinal direction of the forged material from a position 30 mm from the end surface in the width direction of the forged material and a depth of 10.0 mm in the thickness direction. Using the test piece, a tensile test was performed at 25 ° C. at a speed of 5 mm / min in accordance with JIS Z 2241: 2011. From the obtained results, tensile strength, 0.2% proof stress, yield ratio, total elongation and drawing were obtained.
　破断分離性及び破断面の嵌合性の指標として、引張試験によって得られた全伸びおよび絞りを採用した。破断分離性及び破断面の嵌合性は、以下の基準に基づいて評価した。
破断分離性及び破断面の嵌合性が良好（Ｇｏｏｄ）：全伸びが１．０～５．０％、かつ絞りが２．０～８．０％
破断分離性は良好（Ｇｏｏｄ）であるが、破断面の嵌合性が不良（Ｂａｄ）（延性が顕著に低く、破断面の凹凸が小さいため）：全伸びが１．０％未満、および／または絞りが２．０％未満
破断分離性及び破断面の嵌合性が不良（Ｂａｄ）（破断分離時の破断面近傍の塑性変形量が大きいため）：全伸びが５．０％超、および／または絞りが８．０％超 The total elongation and the drawing obtained by the tensile test were adopted as indicators of the breaking separation and the fitting property of the fracture surface. The breaking separation property and the fitting property of the fracture surface were evaluated based on the following criteria.
Good fracture separation and fractured surface fitting (Good): Total elongation is 1.0-5.0% and drawing is 2.0-8.0%
Good fracture separation (Good), but poor fracture surface fitting (Bad) (because the ductility is remarkably low and fracture surface irregularities are small): total elongation is less than 1.0%, and / or Or, the squeezing is less than 2.0% and the fracture separation and the fracture surface fitting property are bad (Bad) (because the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture separation is large): the total elongation exceeds 5.0%, and / Or aperture is over 8.0%
　引張強度が９００ＭＰａ以上の場合および降伏比（＝０．２％耐力（ＭＰａ）／引張強度（ＭＰａ））が、小数点以下第３位で四捨五入して０．８５以上となる場合、本発明で所望される引張強度および降伏比を有しているとして合格と判定した。一方、引張強度が９００ＭＰａ未満の場合および／または降伏比が、小数点以下第３位で四捨五入して０．８５未満となる場合、不合格と判定した。 Desirable in the present invention when the tensile strength is 900 MPa or more and the yield ratio (= 0.2% proof stress (MPa) / tensile strength (MPa)) is rounded off to the second decimal place to be 0.85 or more. It was determined to be acceptable as having a tensile strength and a yield ratio. On the other hand, when the tensile strength was less than 900 MPa and / or when the yield ratio was rounded off to the second decimal place and less than 0.85, it was determined to be unacceptable.
　また、鍛造材の幅方向端面から３０ｍｍの位置、且つ厚さ方向１０．０ｍｍ深さの位置から、１０ｍｍ角サンプルを２個切り出し、ミクロ組織を観察した。切り出したサンプルを樹脂埋めし、観察面を鏡面研磨仕上げした後、ナイタール腐食液（３％硝酸アルコール）で観察面をエッチングした。その後、エッチングされた観察面を４００倍の光学顕微鏡で観察し、任意の１０視野の写真画像を得た。フェライト、パーライト、およびベイナイトの各相は、相ごとにコントラストが異なるため、組織観察では、コントラストに基づいて各相を特定し、その面積分率を求めた。ここでは、フェライト・パーライト以外の残部組織をベイナイトと定義する。ベイナイトにはマルテンサイトを含むが、区別が困難であるため、本明細書では総称してベイナイトという。したがって、各視野において、フェライト及びパーライト以外の領域を、ベイナイトと特定した。そして、得られたフェライトおよびパーライトの合計面積率の平均値をミクロ組織におけるフェライト・パーライト組織の面積分率とした。１００％からフェライト・パーライト組織の面積分率を差し引くことで、フェライト・パーライト組織以外の残部組織、すなわちベイナイトの面積分率を得た。表２Ａおよび表２Ｂ中、ミクロ組織の欄に「Ｆ／Ｐ」と記載した例は、ミクロ組織が実質的にフェライトおよびパーライトのみからなる、すなわちフェライトおよびパーライトの合計面積率が１００％の組織であったことを示す。「Ｆ／Ｐ／Ｂ」と記載した例は、ミクロ組織がフェライト、パーライト、並びに、フェライトおよびパーライト以外の残部組織（ベイナイト）からなる組織であったことを示す。 Further, two 10 mm square samples were cut out from a position 30 mm from the end surface in the width direction of the forged material and a depth of 10.0 mm in the thickness direction, and the microstructure was observed. The cut out sample was filled with resin, and the observation surface was mirror-polished, and then the observation surface was etched with a nital corrosive solution (3% nitric acid alcohol). Thereafter, the etched observation surface was observed with a 400 × optical microscope to obtain photographic images of arbitrary 10 fields of view. Since each phase of ferrite, pearlite, and bainite has a different contrast for each phase, in the structure observation, each phase was specified based on the contrast, and the area fraction was obtained. Here, the remaining structure other than ferrite and pearlite is defined as bainite. Although bainite contains martensite, it is difficult to distinguish, so it is collectively referred to as bainite in this specification. Therefore, in each field of view, a region other than ferrite and pearlite was identified as bainite. And the average value of the total area ratio of the obtained ferrite and pearlite was made into the area fraction of the ferrite pearlite structure in a microstructure. By subtracting the area fraction of the ferrite / pearlite structure from 100%, the remaining structure other than the ferrite / pearlite structure, that is, the area fraction of bainite was obtained. In Table 2A and Table 2B, the example in which “F / P” is described in the microstructure column is a structure in which the microstructure is substantially composed of only ferrite and pearlite, that is, the total area ratio of ferrite and pearlite is 100%. Indicates that there was. The example described as “F / P / B” indicates that the microstructure was composed of ferrite, pearlite, and the remaining structure (bainite) other than ferrite and pearlite.
　Ｎｂ炭化物等の合金炭化物の存在位置は、以下の方法により観察した。非調質鋼部品の表面から深さ１０ｍｍ位置から、厚さ０．５ｍｍの円板を採取した。エメリー紙を用いて円板の両面を研削研磨し、円板の厚さを５０μｍとした。その後、円板から直径３ｍｍのサンプルを採取した。サンプルを１０％過塩素酸－氷酢酸溶液中に浸漬して、電解研磨を実施して、薄膜試料を作製した。透過型電子顕微鏡と高感度カメラとで構成された装置を用いて、得られた薄膜試料を観察した。具体的には、薄膜試料に対して菊池図形を解析して、薄膜試料の結晶方位を特定し、特定した結晶方位に基づいて薄膜試料を傾斜させて、（００１）面を観察できるように、薄膜試料を調整した。観察倍率は４００００倍とし、加速電圧は２００ｋＶとした。 The position of the alloy carbide such as Nb carbide was observed by the following method. A disc having a thickness of 0.5 mm was taken from a position of 10 mm depth from the surface of the non-heat treated steel part. Both sides of the disk were ground and polished using emery paper, and the thickness of the disk was 50 μm. Thereafter, a sample having a diameter of 3 mm was collected from the disk. The sample was immersed in a 10% perchloric acid-glacial acetic acid solution and subjected to electropolishing to produce a thin film sample. The obtained thin film sample was observed using an apparatus composed of a transmission electron microscope and a high sensitivity camera. Specifically, the Kikuchi figure is analyzed for the thin film sample, the crystal orientation of the thin film sample is specified, the thin film sample is tilted based on the specified crystal orientation, and the (001) plane can be observed. A thin film sample was prepared. The observation magnification was 40000 times and the acceleration voltage was 200 kV.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　表１Ａにおいて、鋼Ｎｏ．Ａ～ｄの本発明例は、いずれも化学成分が本発明の規定範囲内とされたものである。これら本発明例Ａ～ｄは、Ｎｂ炭化物等の合金炭化物が、初析フェライトだけでなくパーライトラメラ間にも微細かつ多量に観察された。このため、表２Ａに示すように、引張強度が９００ＭＰａ以上となり、降伏比が０．８５以上となった。また、０．２％耐力も８００ＭＰａ以上となった。更に、全伸びが１．０％以上、５．０％以下、かつ絞りが２．０％以上、８．０％以下となり、破断分離性が良好であり、破断面の嵌合性も良好だった。本発明例Ａ～ｄを非調質鋼部品とした場合には、高い引張強度及び降伏比を有し、更には、破断分離性及び破断面の嵌合性に優れた非調質鋼部品が得られる。 In Table 1A, steel No. In all of the examples of the present invention A to d, the chemical components are within the specified range of the present invention. In these inventive examples A to d, alloy carbides such as Nb carbide were observed in fine and large amounts not only in the pro-eutectoid ferrite but also between the pearlite lamellae. For this reason, as shown in Table 2A, the tensile strength was 900 MPa or more, and the yield ratio was 0.85 or more. Further, the 0.2% proof stress was 800 MPa or more. Furthermore, the total elongation is 1.0% or more and 5.0% or less, the drawing is 2.0% or more and 8.0% or less, and the fracture separation property is good, and the fitting property of the fracture surface is also good. It was. In the case where the inventive examples A to d are non-heat treated steel parts, non-heat treated steel parts having high tensile strength and yield ratio and excellent fracture separation and fracture surface fitting properties are obtained. can get.
　これに対して、表１Ｂ及び表２Ｂに示すように、比較例ＡＡは、Ｃの含有量が少ないため、パーライトラメラ間のＮｂ炭化物の析出量が少なくなり、延性が高くなった。これにより破断分離性及び破断面の嵌合性は不良となった。
　比較例ＡＢ、ＡＤ、ＡＨ、ＡＭおよびＡＮは、それぞれＣ、Ｓｉ、Ｐ、ＮｂおよびＴｉの含有量が多いため、延性が顕著に低く破断分離性は良好なものの、破断面の嵌合性は不良となった。 On the other hand, as shown in Table 1B and Table 2B, since Comparative Example AA has a low C content, the precipitation amount of Nb carbides between pearlite lamellas was reduced and the ductility was increased. As a result, the break separation property and the fitting property of the fracture surface became poor.
Comparative Examples AB, AD, AH, AM and AN have a large content of C, Si, P, Nb and Ti, respectively. Therefore, the ductility is remarkably low and the fracture separability is good. It became defective.
　比較例ＡＣおよびＡＧは、それぞれＳｉおよびＰの含有量が少ないため、延性が高く、破断分離性及び破断面の嵌合性は不良となった。 Comparative Examples AC and AG had high ductility due to low Si and P contents, respectively, and the fracture separability and fracture surface fitting properties were poor.
　比較例ＡＥは、Ｍｎ含有量が少ないため、パーライトの成長速度が速く、Ｎｂ炭化物等の合金炭化物がパーライトラメラ間で析出しなかった。これにより延性が高く、破断分離性及び破断面の嵌合性は不良となった。
　比較例ＡＦ、ＡＫおよびＡＯは、それぞれＭｎ、ＣｒおよびＭｏの含有量が多いため、また比較例ＡＩおよびＡＰは、それぞれＳおよびＮの含有量が少ないため、フェライト・パーライト組織の他にベイナイト組織が生成し、パーライトラメラ間のＮｂ炭化物の析出量が少なく、延性が高くなった。これにより破断分離性及び破断面の嵌合性は不良となった。 Since Comparative Example AE had a low Mn content, the growth rate of pearlite was high, and alloy carbides such as Nb carbide did not precipitate between pearlite lamellae. As a result, the ductility was high, and the fracture separability and the fitting property of the fracture surface were poor.
Comparative Examples AF, AK, and AO have a high content of Mn, Cr, and Mo, respectively, and Comparative Examples AI and AP have a low content of S and N, respectively. Produced, the precipitation amount of Nb carbide between pearlite lamellae was small, and the ductility became high. As a result, the break separation property and the fitting property of the fracture surface became poor.
　比較例ＡＪは、Ｓの含有量が多いため、Ｍｎ硫化物が粗大となり、延性が高く、破断分離性及び破断面の嵌合性は不良となった。
　比較例ＡＬは、Ｎｂ含有量が少ないため、また比較例ＡＱおよびＡＲは、それぞれＮおよびＶの含有量が多いため、パーライトラメラ間のＮｂ炭化物の析出量が少なく、延性が高くなった。これにより破断分離性及び破断面の嵌合性が不良となった。 In Comparative Example AJ, since the content of S was large, the Mn sulfide became coarse, the ductility was high, and the fracture separation property and the fitting property of the fracture surface were poor.
Since Comparative Example AL had a low Nb content, and Comparative Examples AQ and AR had a high N and V content, respectively, the precipitation amount of Nb carbide between pearlite lamellas was small, and the ductility was high. As a result, the break separation property and the fitting property of the fracture surface became poor.
１…破断分離型コンロッド（非調質鋼部品）、２…アッパ側半割体、２Ａ…半円弧部、２Ｂ…ロッド部、２ａ…突き合わせ面、３…ロア側半割体、３Ａ…半円弧部、３ａ…突き合わせ面、５…ねじ孔、６…挿通孔、７…結合ボルト、８…ビッグエンド部、９…スモールエンド部。 DESCRIPTION OF SYMBOLS 1 ... Breaking separation type connecting rod (non-heat treated steel part), 2 ... Upper side half split body, 2A ... Semi-arc part, 2B ... Rod part, 2a ... Butting surface, 3 ... Lower side half split body, 3A ... Half arc Part, 3a ... butting surface, 5 ... screw hole, 6 ... insertion hole, 7 ... coupling bolt, 8 ... big end part, 9 ... small end part.
　本発明に係る上記一態様によれば、高い引張強度、高い降伏比、優れた破断分離性及び優れた破断面の嵌合性の全てを有する鋼、機械部品およびコネクティングロッドを提供することができる。 According to the above-described aspect of the present invention, it is possible to provide a steel, a machine part, and a connecting rod that have all of high tensile strength, high yield ratio, excellent breaking separation property, and excellent fracture surface fitting property. .

Claims (11)

  1. 　化学成分が、単位質量％で、
    Ｃ：０．１５～０．３０％、
    Ｓｉ：０．４０～１．３０％、
    Ｍｎ：０．５０～１．５０％、
    Ｐ：０．０３５～０．２００％、
    Ｓ：０．０１０～０．１００％、
    Ｃｒ：０～１．００％、
    Ｎｂ：０．０１０～０．２０％、
    Ｔｉ：０～０．０７０％、
    Ｍｏ：０～０．１５％、
    Ｎ：０．００１０～０．００６０％、
    Ｖ：０～０．０１０％、
    Ｃａ：０～０．００５％、
    Ｚｒ：０～０．００５％、
    Ｍｇ：０～０．００５％、
    Ｃｕ：０～０．０５％、
    Ｎｉ：０～０．０５％、
    Ｐｂ：０～０．５０％、
    Ｂｉ：０～０．００５０％、及び
    Ａｌ：０．０１０％以下
    を含有し、残部がＦｅ及び不純物からなることを特徴とする鋼。     Chemical component is unit mass%,
    C: 0.15 to 0.30%,
    Si: 0.40 to 1.30%,
    Mn: 0.50 to 1.50%,
    P: 0.035 to 0.200%,
    S: 0.010 to 0.100%,
    Cr: 0 to 1.00%,
    Nb: 0.010 to 0.20%,
    Ti: 0 to 0.070%,
    Mo: 0 to 0.15%,
    N: 0.0010 to 0.0060%,
    V: 0 to 0.010%,
    Ca: 0 to 0.005%,
    Zr: 0 to 0.005%,
    Mg: 0 to 0.005%,
    Cu: 0 to 0.05%,
    Ni: 0 to 0.05%,
    Pb: 0 to 0.50%,
    Steel containing Bi: 0 to 0.0050% and Al: 0.010% or less, with the balance being Fe and impurities.
  2. 　前記化学成分が、単位質量％で、
    Ｔｉ：０．００５～０．０１４％、及び
    Ｍｏ：０．００５～０．１５％
    からなる群から選択される１種または２種を含有することを特徴とする請求項１に記載の鋼。     The chemical component is unit mass%,
    Ti: 0.005 to 0.014% and Mo: 0.005 to 0.15%
    The steel according to claim 1, comprising one or two selected from the group consisting of:
  3. 　前記化学成分が、単位質量％で、
    Ｃａ：０．００１～０．００５％、
    Ｚｒ：０．００１～０．００５％、及び
    Ｍｇ：０．００１～０．００５％
    からなる群から選択される１種以上を含有することを特徴とする請求項１または請求項２に記載の鋼。     The chemical component is unit mass%,
    Ca: 0.001 to 0.005%,
    Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005%
    The steel according to claim 1, comprising at least one selected from the group consisting of:
  4. 　化学成分が、単位質量％で、
    Ｃ：０．１５～０．３０％、
    Ｓｉ：０．４０～１．３０％、
    Ｍｎ：０．５０～１．５０％、
    Ｐ：０．０３５～０．２００％、
    Ｓ：０．０１０～０．１００％、
    Ｃｒ：０～１．００％、
    Ｎｂ：０．０１０～０．２０％、
    Ｔｉ：０～０．０７０％、
    Ｍｏ：０～０．１５％、
    Ｎ：０．００１０～０．００６０％、
    Ｖ：０～０．０１０％、
    Ｃａ：０～０．００５％、
    Ｚｒ：０～０．００５％、
    Ｍｇ：０～０．００５％、
    Ｃｕ：０～０．０５％、
    Ｎｉ：０～０．０５％、
    Ｐｂ：０～０．５０％、
    Ｂｉ：０～０．００５０％、及び
    Ａｌ：０．０１０％以下
    を含有し、残部がＦｅ及び不純物からなり、
    　表面から１．０ｍｍ以上内部におけるミクロ組織がフェライト・パーライト組織であり、前記フェライト・パーライト組織の面積分率が９５％以上であることを特徴とする機械部品。     Chemical component is unit mass%,
    C: 0.15 to 0.30%,
    Si: 0.40 to 1.30%,
    Mn: 0.50 to 1.50%,
    P: 0.035 to 0.200%,
    S: 0.010 to 0.100%,
    Cr: 0 to 1.00%,
    Nb: 0.010 to 0.20%,
    Ti: 0 to 0.070%,
    Mo: 0 to 0.15%,
    N: 0.0010 to 0.0060%,
    V: 0 to 0.010%,
    Ca: 0 to 0.005%,
    Zr: 0 to 0.005%,
    Mg: 0 to 0.005%,
    Cu: 0 to 0.05%,
    Ni: 0 to 0.05%,
    Pb: 0 to 0.50%,
    Bi: 0 to 0.0050%, and Al: 0.010% or less, with the balance being Fe and impurities,
    A mechanical part characterized in that the microstructure inside the surface of 1.0 mm or more from the surface is a ferrite / pearlite structure, and the area fraction of the ferrite / pearlite structure is 95% or more.
  5. 　前記化学成分が、単位質量％で、
    Ｔｉ：０．００５～０．０１４％、及び
    Ｍｏ：０．００５～０．１５％
    からなる群から選択される１種または２種を含有することを特徴とする請求項４に記載の機械部品。     The chemical component is unit mass%,
    Ti: 0.005 to 0.014% and Mo: 0.005 to 0.15%
    The machine part according to claim 4, comprising one or two selected from the group consisting of:
  6. 　前記化学成分が、単位質量％で、
    Ｃａ：０．００１～０．００５％、
    Ｚｒ：０．００１～０．００５％、及び
    Ｍｇ：０．００１～０．００５％
    からなる群から選択される１種以上を含有することを特徴とする請求項４または請求項５に記載の機械部品。     The chemical component is unit mass%,
    Ca: 0.001 to 0.005%,
    Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005%
    The machine part according to claim 4, comprising at least one selected from the group consisting of:
  7. 　引張強度が９００ＭＰａ以上であり、かつ降伏比が０．８５以上であることを特徴とする請求項４～６の何れか一項に記載の機械部品。 The mechanical component according to any one of claims 4 to 6, wherein the tensile strength is 900 MPa or more and the yield ratio is 0.85 or more.
  8. 　化学成分が、単位質量％で、
    Ｃ：０．１５～０．３０％、
    Ｓｉ：０．４０～１．３０％、
    Ｍｎ：０．５０～１．５０％、
    Ｐ：０．０３５～０．２００％、
    Ｓ：０．０１０～０．１００％、
    Ｃｒ：０～１．００％、
    Ｎｂ：０．０１０～０．２０％、
    Ｔｉ：０～０．０７０％、
    Ｍｏ：０～０．１５％、
    Ｎ：０．００１０～０．００６０％、
    Ｖ：０～０．０１０％、
    Ｃａ：０～０．００５％、
    Ｚｒ：０～０．００５％、
    Ｍｇ：０～０．００５％、
    Ｃｕ：０～０．０５％、
    Ｎｉ：０～０．０５％、
    Ｐｂ：０～０．５０％、
    Ｂｉ：０～０．００５０％、及び
    Ａｌ：０．０１０％以下
    を含有し、残部がＦｅ及び不純物からなるコネクティングロッドであって、
    　ロッド部の表面から１．０ｍｍ以上内部におけるミクロ組織がフェライト・パーライト組織であり、前記フェライト・パーライト組織の面積分率が９５％以上であることを特徴とするコネクティングロッド。     Chemical component is unit mass%,
    C: 0.15 to 0.30%,
    Si: 0.40 to 1.30%,
    Mn: 0.50 to 1.50%,
    P: 0.035 to 0.200%,
    S: 0.010 to 0.100%,
    Cr: 0 to 1.00%,
    Nb: 0.010 to 0.20%,
    Ti: 0 to 0.070%,
    Mo: 0 to 0.15%,
    N: 0.0010 to 0.0060%,
    V: 0 to 0.010%,
    Ca: 0 to 0.005%,
    Zr: 0 to 0.005%,
    Mg: 0 to 0.005%,
    Cu: 0 to 0.05%,
    Ni: 0 to 0.05%,
    Pb: 0 to 0.50%,
    A connecting rod containing Bi: 0 to 0.0050% and Al: 0.010% or less, with the balance being Fe and impurities,
    A connecting rod characterized in that a microstructure within 1.0 mm or more from the surface of the rod part is a ferrite / pearlite structure, and an area fraction of the ferrite / pearlite structure is 95% or more.
  9. 　前記化学成分が、単位質量％で、
    　Ｔｉ：０．００５～０．０１４％、及び
    　Ｍｏ：０．００５～０．１５％
    からなる群から選択される１種または２種を含有することを特徴とする請求項８に記載のコネクティングロッド。     The chemical component is unit mass%,
    Ti: 0.005 to 0.014%, and Mo: 0.005 to 0.15%
    The connecting rod according to claim 8, comprising one or two selected from the group consisting of:
  10. 　前記化学成分が、単位質量％で、
    Ｃａ：０．００１～０．００５％、
    Ｚｒ：０．００１～０．００５％、及び
    Ｍｇ：０．００１～０．００５％
    からなる群から選択される１種以上を含有することを特徴とする請求項８または請求項９に記載のコネクティングロッド。     The chemical component is unit mass%,
    Ca: 0.001 to 0.005%,
    Zr: 0.001 to 0.005%, and Mg: 0.001 to 0.005%
    The connecting rod according to claim 8 or 9, comprising at least one selected from the group consisting of:
  11. 　前記ロッド部で、引張強度が９００ＭＰａ以上であり、降伏比が０．８５以上であることを特徴とする請求項８～１０の何れか一項に記載のコネクティングロッド。 The connecting rod according to any one of claims 8 to 10, wherein the rod portion has a tensile strength of 900 MPa or more and a yield ratio of 0.85 or more.
PCT/JP2019/016810 2018-04-20 2019-04-19 Steel, mechanical component, and connecting rod WO2019203343A1 (en)

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Publication number Priority date Publication date Assignee Title
JP2004286196A (en) * 2003-03-25 2004-10-14 Nissan Motor Co Ltd High-strength connecting rod and its manufacturing method
JP2012077371A (en) * 2010-10-06 2012-04-19 Sumitomo Metal Ind Ltd Rolled steel for hot forging, and method for production thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004286196A (en) * 2003-03-25 2004-10-14 Nissan Motor Co Ltd High-strength connecting rod and its manufacturing method
JP2012077371A (en) * 2010-10-06 2012-04-19 Sumitomo Metal Ind Ltd Rolled steel for hot forging, and method for production thereof

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