WO2020003425A1 - Reinforcing bar for nitriding, and machine component - Google Patents

Reinforcing bar for nitriding, and machine component Download PDF

Info

Publication number
WO2020003425A1
WO2020003425A1 PCT/JP2018/024469 JP2018024469W WO2020003425A1 WO 2020003425 A1 WO2020003425 A1 WO 2020003425A1 JP 2018024469 W JP2018024469 W JP 2018024469W WO 2020003425 A1 WO2020003425 A1 WO 2020003425A1
Authority
WO
WIPO (PCT)
Prior art keywords
steel
nitriding
content
less
hardness
Prior art date
Application number
PCT/JP2018/024469
Other languages
French (fr)
Japanese (ja)
Inventor
将人 祐谷
幹 高須賀
成史 西谷
江頭　誠
秀樹 今高
Original Assignee
日本製鉄株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日本製鉄株式会社 filed Critical 日本製鉄株式会社
Priority to JP2018565897A priority Critical patent/JP6525115B1/en
Priority to PCT/JP2018/024469 priority patent/WO2020003425A1/en
Publication of WO2020003425A1 publication Critical patent/WO2020003425A1/en

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • 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

Definitions

  • the present invention relates to a steel bar for nitriding and a machine component using the same.
  • Machine parts used for automobiles, industrial machines, construction machines, and the like may be subjected to nitriding for the purpose of improving fatigue strength.
  • nitriding is characterized by a very low strain because the processing temperature is low.
  • the nitriding treatment has a disadvantage that the curing depth is shallower than other surface curing methods. This is because Cr contained in ordinary nitrided steel traps nitrogen during nitriding treatment and inhibits diffusion. As the content of Cr increases in order to increase the surface hardness of the nitrided steel, the hardened layer becomes shallower, and depending on the shape of the part, it becomes difficult to sufficiently increase the fatigue strength.
  • Patent Document 1 discloses a technique capable of obtaining a deep hardened layer by a short-time nitriding treatment by nitriding a steel containing Cr and Ti in a complex manner at a high temperature.
  • Patent Literature 2 discloses a technique in which V, Cr, and Mo are contained in a complex manner, and a deep hardened layer can be obtained by precipitating a composite nitride containing an alloy element thereof.
  • Patent Document 1 a large amount of Ti is contained in order to strengthen the nitrided layer. Since a large amount of Ti is contained, S bonds with Ti, and MnS that contributes to machinability and cutability is not generated.
  • the steel bar for nitriding is required to have excellent cold cutting properties from the viewpoint of reducing manufacturing costs. That is, there is a demand for a nitriding steel bar having a low hardness at the steel bar stage and having a desired hardness when it is made into a machine part.
  • Patent Documents 1 and 2 no study has been made on the cutting properties of a steel bar in the cold state (hereinafter, simply referred to as “cutting properties”), and there is room for improvement in the cutting properties of a steel bar.
  • An object of the present invention is to solve the above-mentioned problems, and to provide a nitriding steel bar which is excellent in cuttability as a steel bar and can obtain a mechanical part having a high hardening depth and an excellent fatigue strength. .
  • the present invention has been made to solve the above problems, and has the following steel bars for nitriding and mechanical parts.
  • the chemical composition is expressed in mass% C: 0.09 to 0.30%, Si: 0.01 to 0.50%, Mn: more than 2.20% and not more than 3.50%, P: 0.050% or less, S: 0.001 to 0.100%, Cr: 0.02 to 0.80%, V: 0.10 to 0.40%, Al: 0.001 to 0.080%, N: 0.0250% or less, O: 0.0050% or less, Ti: 0 to 0.050%, Nb: 0 to 0.05%, Mo: 0 to 0.10%, Cu: 0 to 0.30%, Ni: 0 to 0.30%, Bi: 0 to 0.35%, B: 0 to 0.0050%, The balance: Fe and impurities, The metal structure is the average area% of the whole, The total of pro-eutectoid ferrite and pearlite is 35% or more; Steel bars for nitriding.
  • the metal structure is an average area% of the whole, The total of pro-eutectoid ferrite and pearlite is 50% or more;
  • the steel bar is a round bar, and the diameter of the round bar is 70 mm or more;
  • a mechanical part having a hardened layer on its surface The chemical composition in a region excluding the hardened layer is represented by mass%, C: 0.09 to 0.30%, Si: 0.01 to 0.50%, Mn: more than 2.20% and not more than 3.50%, P: 0.050% or less, S: 0.001 to 0.100%, Cr: 0.02 to 0.80%, V: 0.10 to 0.40%, Al: 0.001 to 0.080%, N: 0.0250% or less, O: 0.0050% or less, Ti: 0 to 0.050%, Nb: 0 to 0.05%, Mo: 0 to 0.10%, Cu: 0 to 0.30%, Ni: 0 to 0.30%, Bi: 0 to 0.35%, B: 0 to 0.0050%, The balance: Fe and impurities, In a region excluding the hardened layer up to a position of 2 mm from the surface in the depth direction, and in a region excluding the hardened layer, an average area%, a region in which the hardened
  • the steel bar for nitriding according to the present invention is excellent in cuttability, it is possible to reduce the manufacturing cost.
  • the bar steel for nitriding of the present invention by subjecting the bar steel for nitriding of the present invention to processing and then nitriding, it is possible to obtain a mechanical part having a high hardening depth and excellent fatigue strength.
  • the present inventors have found that, based on steel containing V, various amounts of other nitride-forming elements are changed so that the cutability as a steel bar is excellent, and when a machine part is used, a nitride layer is formed.
  • the method for increasing the hardening depth without lowering the surface hardness of the sample was examined. As a result, the following findings (a) to (f) were obtained.
  • C 0.09 to 0.30%
  • the steel bar according to the present invention has a low hardness at the stage of the steel bar, but has a desired hardness when it is made into a machine part, and therefore contains C in an appropriate range.
  • C forms V carbide together with V in the core portion during the nitriding treatment and precipitates, thereby contributing to an improvement in the hardness of the core portion after forming the mechanical component. Further, the C content affects the area ratio of proeutectoid ferrite and pearlite, which are relatively low hardness structures.
  • a steel having an excessively low C content contains a large amount of ferrite and pearlite at the stage of a steel bar and has low hardness and excellent cutability, but has insufficient hardness at the stage of a machine component.
  • the C content is set to 0.09% or more.
  • steel having an excessively high C content has sufficient hardness at the stage of mechanical parts, but has high hardenability at the stage of steel bars, so that the amount of proeutectoid ferrite and pearlite decreases, resulting in poor cuttability.
  • the C content is limited to 0.30% or less.
  • the C content is preferably at least 0.10%, more preferably at least 0.11%.
  • the C content is preferably 0.27% or less, more preferably 0.25% or less, and further preferably 0.22% or less.
  • Si 0.01 to 0.50% Si is an element required as a steel deoxidizing agent. To obtain this effect, the Si content needs to be 0.01% or more. On the other hand, if the Si content exceeds 0.50%, the hardness of the steel bar becomes too high due to solid solution strengthening, and the cuttability deteriorates. Therefore, the Si content is set to 0.01 to 0.50%.
  • the Si content is preferably at least 0.05%, more preferably at least 0.10%. Further, the Si content is preferably 0.40% or less, more preferably 0.30% or less.
  • Mn more than 2.20% to 3.50% or less
  • Mn is an element that increases the hardness of steel by being contained in steel, and its content needs to be controlled to an appropriate range.
  • Mn forms a composite nitride with V and Cr by nitriding, and contributes to both an increase in surface hardness after nitriding and an increase in hardening depth. In order to properly obtain these effects, the Mn content needs to be more than 2.20%.
  • Mn is an element that enhances the hardenability, and when contained excessively, suppresses the formation of pro-eutectoid ferrite and pearlite, and produces a supercooled structure in the steel bar to increase the hardness.
  • the Mn content is set to more than 2.20% and not more than 3.50%.
  • the Mn content is preferably at least 2.30%. Further, the Mn content is preferably 3.00% or less, more preferably 2.80% or less.
  • P 0.050% or less
  • P is an impurity element. P segregates at crystal grain boundaries, causing grain boundary embrittlement cracking. Therefore, the P content is preferably as low as possible. Therefore, the P content is set to 0.050% or less. The P content is preferably 0.040% or less.
  • S 0.001 to 0.100% S combines with Mn in steel to form MnS and enhances the cuttability and machinability of the steel. In order to obtain this effect, the S content needs to be 0.001% or more. On the other hand, if the S content exceeds 0.100%, coarse MnS is formed, and the fatigue strength deteriorates. Therefore, the S content is set to 0.001 to 0.100%. Note that the S content is preferably 0.005% or more, and more preferably 0.010% or more. Further, the S content is preferably 0.080% or less, and more preferably 0.070% or less.
  • Cr 0.02 to 0.80% Cr forms a composite nitride with Mn and V by nitriding treatment, and contributes to both increase in surface hardness after nitriding and deepening of hardening depth. To obtain this effect, the Cr content needs to be 0.02% or more. On the other hand, if the Cr content is excessive, the effect of inhibiting the diffusion of nitrogen during the nitriding treatment becomes remarkable, and the hardening depth becomes shallow. Furthermore, since Cr is an element that enhances the hardenability, when it is excessively contained, it suppresses the formation of proeutectoid ferrite and pearlite in a steel bar. Therefore, the Cr content is set to 0.02 to 0.80%. The Cr content is preferably at least 0.05%, more preferably at least 0.10%, even more preferably more than 0.15%. Further, the Cr content is preferably 0.60% or less, more preferably 0.50% or less.
  • V 0.10 to 0.40%
  • V exists in a solid solution state before the nitriding treatment, forms and precipitates a fine composite nitride with Mn and Cr by the nitriding treatment, and increases both the surface layer hardness and the hardening depth.
  • V has the effect of increasing the frequency of nucleation of the composite nitride and reducing its size.
  • the V content needs to be 0.10% or more.
  • the V content is set to 0.10 to 0.40%.
  • the V content is preferably 0.13% or more, and more preferably 0.15% or more. Further, the V content is preferably 0.30% or less, more preferably 0.25% or less.
  • Al 0.001 to 0.080%
  • Al is an element used for deoxidizing steel.
  • the Al content is set to 0.001 to 0.080%.
  • the Al content is preferably at least 0.005%, more preferably at least 0.010%. Further, the Al content is preferably 0.060% or less, more preferably 0.050% or less, and even more preferably 0.040% or less.
  • N 0.0250% or less
  • N is an element mixed into steel as an impurity. If the N content is too high, V precipitates as nitride during hot forging, and the amount of solid solution V contributing to hardening during nitriding decreases. Therefore, the N content is set to 0.0250% or less.
  • the N content is preferably 0.0200% or less, more preferably 0.0150% or less, and further preferably less than 0.0080%. Since nitrogen enters from the surface layer by the nitriding treatment, the mechanical component after the nitriding treatment may contain N in the nitrogen compound layer and the nitrogen diffusion layer described later in excess of the upper limit. Also in the mechanical parts, at a position deeper than the hardened layer, the N content becomes 0.0250% or less as in the case of the steel bars.
  • O 0.0050% or less
  • O is an element mixed into steel as an impurity. If the O content is too high, a coarse oxide is formed, and becomes a starting point of fatigue fracture, thereby deteriorating fatigue characteristics. Therefore, the O content is set to 0.0050% or less. Note that the O content is preferably 0.0040% or less, and more preferably 0.0025% or less.
  • Ti 0 to 0.050% Ti combines with N in the base material to form TiN, and suppresses coarsening of crystal grains during hot forging. For this reason, you may make it contain as needed. However, when the Ti content is excessive, TiC is generated, and the variation in hardness of the steel increases. Therefore, the Ti content is set to 0.050% or less.
  • the Ti content is preferably at most 0.040%, more preferably at most 0.030%. In order to obtain the above effect, the Ti content is preferably 0.005% or more, and more preferably 0.010% or more.
  • Nb 0 to 0.05% Nb combines with N in the base material to form NbN, delays recrystallization during hot forging, and suppresses coarsening of crystal grains. For this reason, you may make it contain as needed.
  • the Nb content is set to 0.05% or less.
  • the Nb content is preferably at most 0.04%, more preferably at most 0.03%. In order to obtain the above effect, the Nb content is preferably at least 0.01%, more preferably at least 0.02%.
  • Mo 0 to 0.10% Mo enhances the hardenability of the steel to increase the strength and fatigue strength of the steel. For this reason, you may make it contain as needed. However, when the Mo content is excessive, the production cost of steel increases. Therefore, the Mo content is set to 0.10% or less.
  • the Mo content is preferably 0.09% or less, and more preferably 0.08% or less. In order to obtain the above effect, the Mo content is preferably 0.02% or more, and more preferably 0.03% or more.
  • Cu 0 to 0.30%
  • Cu forms a solid solution in ferrite and increases the strength and fatigue strength of steel. For this reason, you may make it contain as needed.
  • the Cu content is set to 0.30% or less.
  • the Cu content is preferably at most 0.25%, more preferably at most 0.20%. In order to obtain the above effects, the Cu content is preferably at least 0.05%, more preferably at least 0.10%.
  • Ni 0 to 0.30%
  • Ni forms a solid solution in ferrite to increase the strength and fatigue strength of the steel.
  • Ni further has an effect of suppressing hot cracking caused by Cu when the steel contains Cu. For this reason, you may make it contain as needed.
  • the Ni content is set to 0.30% or less.
  • the Ni content is preferably at most 0.25%, more preferably at most 0.20%. In order to obtain the above effect, the Ni content is preferably at least 0.05%, more preferably at least 0.10%.
  • Bi 0 to 0.35%
  • Bi has the effect of reducing cutting resistance and extending tool life. For this reason, you may make it contain as needed. However, if the Bi content is excessive, cracks and flaws are likely to occur during hot rolling. Therefore, the Bi content is set to 0.35% or less.
  • the Bi content is preferably at most 0.30%, more preferably at most 0.25%. In order to obtain the above effects, the Bi content is preferably at least 0.03%, more preferably at least 0.05%.
  • B 0 to 0.0050% B has the effect of reducing the area ratio of ferrite and pearlite in the structure of the mechanical part. For this reason, you may make it contain as needed. However, when the B content is excessive, the area ratio of ferrite and pearlite in the structure in the state of the steel bar cannot be increased. Therefore, the B content is set to 0.0050% or less.
  • the B content is preferably at most 0.0040%, more preferably at most 0.0030%. In order to obtain the above effects, the B content is preferably 0.0005% or more, and more preferably 0.0010% or more.
  • the balance is Fe and impurities.
  • the impurities are those that are mixed from the ore, scrap, or the production environment as raw materials when the steel is industrially manufactured, and within a range that does not adversely affect the bar for nitriding of the present invention. Means acceptable.
  • elements that can be mixed into steel as impurities include, for example, Pb, Ca, Mg, W, Sb, Co, Ta, and REM. Even when these elements are contained, their contents are respectively Pb: 0.10% or less, Ca: 0.001% or less, Mg: 0.001% or less, W: 0.10% or less, If Sb: 0.005% or less, Co: 0.10% or less, Ta: 0.10% or less, and REM: 0.001% or less, the present invention can be practiced without any problem.
  • the steel bar according to the present invention contains a large amount of Mn and Cr, which are elements that enhance hardenability, bainite cannot be avoided.
  • Mn and Cr which are elements that enhance hardenability, bainite cannot be avoided.
  • the total area ratio of proeutectoid ferrite and pearlite contained in the metal structure of the steel bar must be 35% or more. In order to further improve the cutting properties, the total area ratio is preferably 50% or more.
  • the average area ratio in the whole tissue is determined by the following procedure. First, a cross section perpendicular to the longitudinal direction of the steel is cut out and then corroded with nital to reveal a structure.
  • the steel bar has a round bar shape and the radius of the round bar is R
  • the center position of the round bar and the distance in the radial direction from the center of the round bar are (3/4) ⁇ R
  • a total of four observation test pieces are collected around the positions of (2/4) ⁇ R and (1/4) ⁇ R.
  • an optical micrograph (magnification: 210 ⁇ m ⁇ 160 ⁇ m) is photographed at a magnification of 500 times using each observation test piece, and the total area ratio of proeutectoid ferrite and pearlite is determined from image analysis. Then, the arithmetic average of the total area ratios of pro-eutectoid ferrite and pearlite individually obtained from the photographs taken from the above four locations is defined as the average area ratio of the total of pro-eutectoid ferrite and pearlite in the entire steel bar.
  • ⁇ Bars include round steel having a circular cross section, square steel having a square cross section, flat steel having a rectangular cross section, hexagonal steel having a hexagonal cross section, and octagon steel having an octagonal cross section.
  • the radius of the cross section perpendicular to the longitudinal direction of the round bars is R.
  • the bar includes round steel, square steel, flat steel, hexagonal steel, octagonal steel, and the like.
  • the machine component manufactured using the bar steel for nitriding according to the present invention as a raw material is used for industrial machines, construction machines, and the like. Therefore, it is desirable that the diameter or thickness of the nitriding bar is larger than a predetermined value.
  • the diameter or thickness of the bar for nitriding is preferably 70 mm or more, and more preferably 75 mm or more.
  • the ratio of the long side to the short side of the cross section is preferably more than 1.0 and not more than 2.5.
  • Machine Parts obtained from the above-mentioned bar for nitriding have a hardened layer composed of a nitrogen compound layer and a nitrogen diffusion layer on the surface.
  • the nitrogen compound layer is a layer formed by nitriding treatment and mainly composed of iron nitride (Fe 3 N or Fe 4 N) with a thickness of about several ⁇ m.
  • the nitrogen diffusion layer refers to a layer reinforced by the nitrogen element in which the base material has penetrated.
  • a nitrogen compound layer is formed on the surface of the mechanical component by the nitriding treatment, and a nitrogen diffusion layer is formed at a position deeper than the nitrogen compound layer.
  • the chemical composition of the mechanical component according to the embodiment of the present invention in the region other than the hardened layer is the same as that of the above-described bar for nitriding, and thus the description is omitted.
  • the total area ratio of pro-eutectoid ferrite and pearlite is 40% on average from the surface where high stress is applied during use to a position 2 mm in the depth direction and excluding the hardened layer. It has the following areas: The area ratio is preferably 30% or less, more preferably 20% or less.
  • the above-mentioned region for measuring the total area ratio of proeutectoid ferrite and pearlite preferably has an area of at least 210 ⁇ m ⁇ 160 ⁇ m.
  • the total area ratio of proeutectoid ferrite and pearlite is 40% or less and 30% or less on average in a region from the surface to a position of 2 mm in the depth direction and excluding the hardened layer. Or less, or 20% or less.
  • the average area ratio of proeutectoid ferrite and pearlite in a region from the surface to a position of 2 mm in the depth direction and excluding the hardened layer is determined by the following procedure.
  • a test piece is cut out so that a position of 1 mm in the depth direction from the surface of the machine component becomes the center of the test surface, and the cross section is corroded with nital to reveal a structure.
  • four different visual fields were randomly selected from a range of ⁇ 2.0 mm from the center of the test surface so as not to include the cured layer, and an optical microscope photograph (visual field: 210 ⁇ m ⁇ 160 ⁇ m) with a magnification of 500 ⁇ was taken.
  • the total area ratio of proeutectoid ferrite and pearlite is determined from image analysis.
  • the arithmetic mean of the total of pro-eutectoid ferrite and pearlite individually obtained from the photographs taken from the above four places was calculated from the surface up to a position of 2 mm in the depth direction and in the region excluding the hardened layer. And the average area ratio of the total of pearlite.
  • the machined parts after nitriding have a hardening depth of more than 0.26 mm.
  • the curing depth is preferably at least 0.30 mm.
  • a hardened layer is formed on the surface of the mechanical component of the present invention by nitrogen entering from the surface layer by nitriding.
  • the hardened layer indicates a region where nitrogen has entered from the surface layer by the nitriding treatment.
  • the hardening depth refers to a distance from the surface layer to a depth where sufficient hardness is formed in the hardened layer.
  • the cure depth of a mechanical part is measured by the following procedure. First, a machine component after nitriding is cut perpendicular to the nitriding surface, and embedded in a resin so that the cut surface including the nitriding surface can be observed, to prepare a sample for hardness measurement.
  • the Vickers hardness is measured at a pitch of 0.05 mm from the surface (nitrided surface) of the manufactured sample at a pitch of 0.05 mm according to JIS ⁇ Z ⁇ 2244.
  • the test force shall be 2.94N.
  • the test is performed three times at each measurement depth position, and the average value of the three obtained Vickers hardnesses is defined as the hardness at that depth position. It is assumed that the hardness between the measurement points is on a straight line connecting the hardness of the two measurement points sandwiching the depth position.
  • the hardness near the center of the sample is measured at five points at a test force of 2.94 N, and the average value of the obtained five Vickers hardnesses is defined as the core hardness after nitriding. Further, in the nitrided layer, the distance from the surface to the point where the hardness becomes 50 HV higher than the core hardness is defined as the hardened depth.
  • the method for manufacturing the bar for nitriding is not particularly limited.
  • the bar can be manufactured by the following method.
  • the produced molten steel is made into a slab (slab, bloom) by a casting method or an ingot by an ingot-making method. Further, if necessary, the cast slab or the ingot is subjected to hot working to produce a billet. Then, a hot-rolling is applied to the slab, ingot, or billet to produce a bar for nitriding.
  • the conditions in the above hot rolling are not particularly limited, but in order to make the total area ratio of proeutectoid ferrite and pearlite contained in the metal structure of the steel bar equal to or more than a predetermined amount, 500 ° C. after hot rolling.
  • a predetermined amount 500 ° C. after hot rolling.
  • the average cooling rate up to 0.40 ° C./sec. If the average cooling rate is more than 0.40 ° C./sec, the amount of proeutectoid ferrite cannot be sufficiently secured, and the cutting properties of the steel bar may be deteriorated.
  • the bar for nitriding manufactured by the above manufacturing process has low hardness and excellent cutability.
  • Hot working step The manufactured steel bar is heated. If the heating temperature is too low, an excessive load is applied to the hot working device. On the other hand, if the heating temperature is too high, the scale loss is large. Therefore, the heating temperature is preferably set to 1000 to 1300 ° C. Further, the holding time at the heating temperature is preferably 30 to 1000 minutes.
  • Hot work is performed on the steel bar after heating.
  • the hot working is, for example, hot forging.
  • the hot working in this step will be described as hot forging.
  • the preferred finishing temperature for hot forging is 900 ° C or higher. If the finishing temperature is too low, the load on the mold of the hot forging device increases. On the other hand, a preferable upper limit of the finishing temperature is 1250 ° C.
  • a heat treatment of maintaining the temperature in a temperature range of 400 to 700 ° C. for 30 to 300 minutes and then allowing it to cool may be performed.
  • Nitriding treatment is performed on the cut and shaped material.
  • a known nitriding process is employed.
  • the nitriding treatment is, for example, gas nitriding, salt bath nitriding, ion nitriding, or the like.
  • Gas introduced into the furnace during nitridation it may be only NH 3, and NH 3, or may be a mixed gas containing a N 2 and / or H 2. Further, a nitrocarburizing treatment may be performed by containing a carburizing gas in these gases. Therefore, the term “nitriding” in this specification includes “soft nitriding”.
  • the soaking temperature is set to 550 to 620 ° C. in an atmosphere in which an endothermic transformation gas (RX gas) and ammonia gas are mixed at a ratio of 1: 1 for 1 to 3 hours. do it.
  • RX gas endothermic transformation gas
  • ammonia gas ammonia gas
  • test material having a diameter of 75 mm were used. In No. 27, a test material having a diameter of 50 mm was used. Table 2 shows the average cooling rate to 500 ° C. after hot rolling.
  • each test material was cut, and the cutting property was evaluated by measuring the current value when cutting with a band saw.
  • the feed rate of the saw blade was fixed so that each round bar could be cut in about 200 seconds, and a normalizing material of the same diameter, SCr420, was cut as a comparative material, and the maximum power value at that time was recorded.
  • SCr420 a normalizing material of the same diameter
  • the cutability is particularly excellent, and the cut power exceeds 1.3 times and exceeds 1.5 times. If the ratio is not more than twice, the cutting performance is excellent, and if it exceeds 1.5 times, it is considered that the cutting performance is inferior, and the test was interrupted to cut at a reduced cutting speed.
  • Particularly excellent cutability was evaluated as A, excellent cutability was evaluated as B, and poor cutability was evaluated as C. Subsequent tests were not performed on test materials that resulted in poor cuttability.
  • each test material was heated to 1250 ° C., hot forged into a smaller round bar under the condition that the finishing temperature was about 1000 ° C., and the area reduction rate was 51 to 56%, and allowed to cool to room temperature. .
  • a test material having a diameter of 75 mm was hot forged into a round bar having a diameter of 50 mm.
  • the test material having a diameter of 50 mm was to be hot-forged into a round bar having a diameter of 35 mm.
  • the cooling rate during cooling was 0.60 ° C./s for a round bar having a diameter of 50 mm.
  • Ono-type rotating bending fatigue test pieces A shown in FIG. 1 were collected from each test material.
  • the diameter of the smooth portion at the center of the test piece was 10 mm, and a notch having a depth of 1 mm and a radius of curvature of 3 mm was provided at the center in the length direction.
  • the fatigue test piece A was sampled by cutting such that the rotation axis was within 1.0 mm from the position of R / 2 in the original test material.
  • Ono-type rotating bending fatigue test pieces B shown in FIG. 2 were collected from each test material.
  • the diameter of the smooth part at the center of the test piece was 8 mm.
  • the fatigue test piece B was also sampled by cutting so that the rotation axis was within 1.0 mm from the position of R / 2 in the original test material.
  • ⁇ ⁇ Nitriding treatment was performed at 600 ° C. for 2 hours on the collected test pieces for hardness measurement and the Ono-type rotating bending fatigue test pieces having two types of shapes.
  • the nitriding treatment was performed by introducing ammonia gas and RX gas into the furnace at a flow rate of 1: 1. After the holding time at 600 ° C. was 2 hours, the test piece was taken out of the heat treatment furnace and quenched with 100 ° C. oil.
  • the hardness near the center of each embedded sample was measured at five points at a test force of 2.94 N, and the average value of the five Vickers hardness values was defined as the core hardness after nitriding. Further, in the nitrided layer, the distance from the surface to the point at which the hardness becomes 50 HV higher than the core hardness was defined as the cured depth, and the cured depth was determined.
  • the sample after hardness measurement was corroded with nital to reveal the structure.
  • Four different visual fields were randomly selected from a range of ⁇ 2.0 mm from the center of the test surface (that is, the position of R / 2 of the ⁇ 50 round bar after hot forging), and an optical microscope photograph with a magnification of 500 times (visual field: 210 ⁇ m ⁇ 160 ⁇ m), and the total area ratio of pro-eutectoid ferrite and pearlite was determined from image analysis.
  • the arithmetic mean of the total area ratio of proeutectoid ferrite and pearlite individually obtained from the photographs taken from the above four places was calculated from the surface up to a position of 2 mm in the depth direction and in the region excluding the hardened layer. And the average area ratio of the total of pearlite.
  • the field of view used for the structure observation is near the position of 12.5 mm depth from the surface in the cross section of the round bar after forging. Even if the surface of the round bar is shaved by 5 mm to simulate the cutting process, the field of view used for the above-described structure observation is in the vicinity of a position 7.5 mm deep from the surface.
  • the structure of the field of view used for the above structure observation has a lower cooling rate during cooling after forging than the structure closer to the surface layer than the field of view, so the area ratio of ferrite and pearlite of the structure closer to the surface layer than the field of view is smaller. Is smaller than the tissue in the visual field used for the above-described tissue observation.
  • the center axis is located near the R / 2 position in the original test material. Therefore, in each of the fatigue test pieces, there is a region in the surface layer where the total area ratio of pro-eutectoid ferrite and pearlite is smaller than the R / 2 position in the original test material.
  • Ono-type rotating bending fatigue test was performed using two types of Ono-type rotary bending fatigue test pieces subjected to the nitriding treatment described above.
  • a rotary bending fatigue test based on JIS Z 2274 (1978) was performed in an air atmosphere at room temperature (25 ° C.). The test was performed under a double swing condition at a rotation speed of 3000 rpm. Among the test pieces that did not break until the number of repetitions of 1.0 ⁇ 10 7 times, the highest stress was defined as the fatigue strength (MPa) of the test number. In the test using two types of test pieces, when the fatigue strength was 600 MPa or more, it was determined that the fatigue strength was excellent.
  • “Fatigue strength A” in Table 2 means the fatigue strength (MPa) obtained by a test using Ono-type rotating bending fatigue test piece A, and “Fatigue strength B” is Ono-type rotating bending fatigue. It means the fatigue strength (MPa) obtained in the test using the test piece B.
  • test no. Nos. 1 to 18 are examples of the present invention in which the chemical composition and metal structure of the steel bar satisfy the requirements. Therefore, these steels have good cutting properties. Also, after nitriding, the curing depth exceeded 0.26 mm. As a result, since the fatigue strength A is 620 MPa or more and the fatigue strength B is 610 MPa or more, it can be expected that high fatigue strength can be obtained even for components having various stress gradient shapes.
  • Test No. Steel W used in No. 25 corresponds to SCM420 which is a general low alloy steel. Since V was not contained and the Mn content was lower than the specified range of the present invention and the Cr content was higher than the specified range of the present invention, the core hardness after nitriding was low and the hardening depth was shallow. Therefore, the fatigue strength B was reduced to 490 MPa.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

Provided is a reinforcing bar for nitriding having the following chemical composition, in percentage by mass: 0.09-0.30% C; 0.01-0.50% Si; more than 2.20% but not more than 3.50% Mn; not more than 0.050% P; 0.001-0.100% S; 0.02-0.80% Cr; 0.10-0.40% V; 0.001-0.080% Al; not more than 0.0250% N; not more than 0.0050% O, 0-0.050% Ti; 0-0.05% Nb; 0-0.10% Mo; 0-0.30% Cu; 0-0.30% Ni; 0-0.35% Bi; 0-0.0050% B; with the remainder being made up of Fe and unavoidable impurities. The total of pro-eutectoid ferrite and pearlite makes up at least 35% of the average surface area of the entire metal structure.

Description

窒化用棒鋼および機械部品Steel bars and machine parts for nitriding
　本発明は、窒化用棒鋼およびそれを用いた機械部品に関する。 The present invention relates to a steel bar for nitriding and a machine component using the same.
　自動車、産業機械および建設機械などに用いられる機械部品には、疲労強度を向上させる目的で、窒化処理が施されることがある。窒化処理は、他の表面硬化手法である浸炭処理または高周波焼入れ処理と比較すると、処理温度が低温であるため、ひずみが極めて小さいという特徴がある。 (4) Machine parts used for automobiles, industrial machines, construction machines, and the like may be subjected to nitriding for the purpose of improving fatigue strength. Compared with other surface hardening methods such as carburizing or induction hardening, nitriding is characterized by a very low strain because the processing temperature is low.
　一方、窒化処理は、他の表面硬化手法と比較して、硬化深さが浅いという欠点がある。これは、通常の窒化鋼に含まれるＣｒが窒化処理時に窒素をトラップして拡散を阻害するためである。窒化鋼の表層硬さを高めるためにＣｒの含有量を増やせば増やすほど、硬化層は浅くなるため、部品の形状によっては、疲労強度を十分に高くすることが困難になる。 On the other hand, the nitriding treatment has a disadvantage that the curing depth is shallower than other surface curing methods. This is because Cr contained in ordinary nitrided steel traps nitrogen during nitriding treatment and inhibits diffusion. As the content of Cr increases in order to increase the surface hardness of the nitrided steel, the hardened layer becomes shallower, and depending on the shape of the part, it becomes difficult to sufficiently increase the fatigue strength.
　そこで、Ｃｒを含む鋼に、窒素との相互作用の強いＴｉおよびＶを複合的に含有させることで、窒化後の表層硬さと硬化深さとを両立する種々の技術が開発されている。 Therefore, various techniques have been developed to allow both the surface hardness after nitriding and the hardening depth to be achieved by compounding Ti and V, which have a strong interaction with nitrogen, in a steel containing Cr.
　特許文献１では、ＣｒおよびＴｉを複合的に含有させた鋼を高温で窒化することで、短時間の窒化処理で深い硬化層を得ることができる技術が開示されている。 Patent Document 1 discloses a technique capable of obtaining a deep hardened layer by a short-time nitriding treatment by nitriding a steel containing Cr and Ti in a complex manner at a high temperature.
　特許文献２では、Ｖ、ＣｒおよびＭｏを複合的に含有させ、それらの合金元素を含む複合窒化物を析出させることで、深い硬化層を得ることができる技術が開示されている。 Patent Literature 2 discloses a technique in which V, Cr, and Mo are contained in a complex manner, and a deep hardened layer can be obtained by precipitating a composite nitride containing an alloy element thereof.
特開２００８－１３８０７号公報JP 2008-13807 A 特開２００６－２２３５０号公報JP 2006-22350A
　特許文献１では、窒化層を強化するために多量のＴｉが含有されている。多量のＴｉが含まれているため、ＳはＴｉと結合することになり、被削性、切断性に寄与するＭｎＳが生成しない。 で は In Patent Document 1, a large amount of Ti is contained in order to strengthen the nitrided layer. Since a large amount of Ti is contained, S bonds with Ti, and MnS that contributes to machinability and cutability is not generated.
　特許文献２が開示するように、Ｃｒ，Ｔｉ，Ｖ，Ｍｏといった元素を含有させた場合、これらの合金元素が含まれることによって鋼の硬さが高まる。さらに、これらの元素は焼入れ性を高める元素であるため、これらの元素を多く含有する鋼ではフェライトまたはパーライトといった柔らかい組織の形成が阻害され、硬い過冷組織（ベイナイト、マルテンサイト等）が形成されやすい。 場合 As disclosed in Patent Document 2, when elements such as Cr, Ti, V, and Mo are contained, the hardness of steel is increased by including these alloy elements. Furthermore, since these elements are elements that enhance hardenability, the formation of soft structures such as ferrite or pearlite is inhibited in steels containing a large amount of these elements, and hard undercooled structures (bainite, martensite, etc.) are formed. Cheap.
　窒化処理を施す前の窒化用棒鋼には、製造コスト低減の観点から、冷間での優れた切断性が要求される。すなわち、棒鋼の段階では硬さが低く、その後、機械部品とした際に所望の硬さとなる窒化用棒鋼が求められている。特許文献１および２では、棒鋼の冷間での切断性（以下、単に「切断性」という。）については一切検討がなされておらず、棒鋼の切断性には改善の余地があった。 棒 Before performing the nitriding treatment, the steel bar for nitriding is required to have excellent cold cutting properties from the viewpoint of reducing manufacturing costs. That is, there is a demand for a nitriding steel bar having a low hardness at the steel bar stage and having a desired hardness when it is made into a machine part. In Patent Documents 1 and 2, no study has been made on the cutting properties of a steel bar in the cold state (hereinafter, simply referred to as “cutting properties”), and there is room for improvement in the cutting properties of a steel bar.
　本発明は、上記課題を解決し、棒鋼としての切断性に優れ、かつ、高い硬化深さおよび優れた疲労強度を有する機械部品を得ることが可能な窒化用棒鋼を提供することを目的とする。 An object of the present invention is to solve the above-mentioned problems, and to provide a nitriding steel bar which is excellent in cuttability as a steel bar and can obtain a mechanical part having a high hardening depth and an excellent fatigue strength. .
　本発明は、上記の課題を解決するためになされたものであり、下記の窒化用棒鋼および機械部品を要旨とする。 The present invention has been made to solve the above problems, and has the following steel bars for nitriding and mechanical parts.
　（１）化学組成が、質量％で、
　Ｃ：０．０９～０．３０％、
　Ｓｉ：０．０１～０．５０％、
　Ｍｎ：２．２０％を超えて３．５０％以下、
　Ｐ：０．０５０％以下、
　Ｓ：０．００１～０．１００％、
　Ｃｒ：０．０２～０．８０％、
　Ｖ：０．１０～０．４０％、
　Ａｌ：０．００１～０．０８０％、
　Ｎ：０．０２５０％以下、
　Ｏ：０．００５０％以下、
　Ｔｉ：０～０．０５０％、
　Ｎｂ：０～０．０５％、
　Ｍｏ：０～０．１０％、
　Ｃｕ：０～０．３０％、
　Ｎｉ：０～０．３０％、
　Ｂｉ：０～０．３５％、
　Ｂ：０～０．００５０％、
　残部：Ｆｅおよび不純物であり、
　金属組織が、全体の平均面積％で、
　初析フェライトおよびパーライトの合計が３５％以上である、
　窒化用棒鋼。 (1) The chemical composition is expressed in mass%
C: 0.09 to 0.30%,
Si: 0.01 to 0.50%,
Mn: more than 2.20% and not more than 3.50%,
P: 0.050% or less,
S: 0.001 to 0.100%,
Cr: 0.02 to 0.80%,
V: 0.10 to 0.40%,
Al: 0.001 to 0.080%,
N: 0.0250% or less,
O: 0.0050% or less,
Ti: 0 to 0.050%,
Nb: 0 to 0.05%,
Mo: 0 to 0.10%,
Cu: 0 to 0.30%,
Ni: 0 to 0.30%,
Bi: 0 to 0.35%,
B: 0 to 0.0050%,
The balance: Fe and impurities,
The metal structure is the average area% of the whole,
The total of pro-eutectoid ferrite and pearlite is 35% or more;
Steel bars for nitriding.
　（２）前記金属組織が、全体の平均面積％で、
　初析フェライトおよびパーライトの合計が５０％以上である、
　上記（１）に記載の窒化用棒鋼。 (2) The metal structure is an average area% of the whole,
The total of pro-eutectoid ferrite and pearlite is 50% or more;
The steel bar for nitriding according to the above (1).
　（３）前記棒鋼が丸鋼であり、当該丸鋼の直径が７０ｍｍ以上である、
　上記（１）または（２）に記載の窒化用棒鋼。 (3) the steel bar is a round bar, and the diameter of the round bar is 70 mm or more;
The steel bar for nitriding according to the above (1) or (2).
　（４）表面に硬化層を有する機械部品であって、
　前記硬化層を除く領域における化学組成が、質量％で、
　Ｃ：０．０９～０．３０％、
　Ｓｉ：０．０１～０．５０％、
　Ｍｎ：２．２０％を超えて３．５０％以下、
　Ｐ：０．０５０％以下、
　Ｓ：０．００１～０．１００％、
　Ｃｒ：０．０２～０．８０％、
　Ｖ：０．１０～０．４０％、
　Ａｌ：０．００１～０．０８０％、
　Ｎ：０．０２５０％以下、
　Ｏ：０．００５０％以下、
　Ｔｉ：０～０．０５０％、
　Ｎｂ：０～０．０５％、
　Ｍｏ：０～０．１０％、
　Ｃｕ：０～０．３０％、
　Ｎｉ：０～０．３０％、
　Ｂｉ：０～０．３５％、
　Ｂ：０～０．００５０％、
　残部：Ｆｅおよび不純物であり、
　前記表面から深さ方向に２ｍｍの位置までで、かつ前記硬化層を除く領域に、平均面積％で、初析フェライトおよびパーライトの合計が４０％以下となる領域を有し、
　硬化深さが０．２６ｍｍ超である、
　機械部品。 (4) A mechanical part having a hardened layer on its surface,
The chemical composition in a region excluding the hardened layer is represented by mass%,
C: 0.09 to 0.30%,
Si: 0.01 to 0.50%,
Mn: more than 2.20% and not more than 3.50%,
P: 0.050% or less,
S: 0.001 to 0.100%,
Cr: 0.02 to 0.80%,
V: 0.10 to 0.40%,
Al: 0.001 to 0.080%,
N: 0.0250% or less,
O: 0.0050% or less,
Ti: 0 to 0.050%,
Nb: 0 to 0.05%,
Mo: 0 to 0.10%,
Cu: 0 to 0.30%,
Ni: 0 to 0.30%,
Bi: 0 to 0.35%,
B: 0 to 0.0050%,
The balance: Fe and impurities,
In a region excluding the hardened layer up to a position of 2 mm from the surface in the depth direction, and in a region excluding the hardened layer, an average area%, a region in which the total of proeutectoid ferrite and pearlite is 40% or less,
The curing depth is more than 0.26 mm,
Mechanical parts.
　本発明に係る窒化用棒鋼は、切断性に優れるため、製造コストを低減することが可能になる。加えて、本発明の窒化用棒鋼に加工を施してから窒化処理を施すことによって、高い硬化深さおよび優れた疲労強度を有する機械部品を得ることが可能になる。 窒 化 Since the steel bar for nitriding according to the present invention is excellent in cuttability, it is possible to reduce the manufacturing cost. In addition, by subjecting the bar steel for nitriding of the present invention to processing and then nitriding, it is possible to obtain a mechanical part having a high hardening depth and excellent fatigue strength.
小野式回転曲げ疲労試験片Ａの形状を示す図である。It is a figure which shows the shape of the Ono-type rotating bending fatigue test piece A. 小野式回転曲げ疲労試験片Ｂの形状を示す図である。It is a figure which shows the shape of the Ono-type rotary bending fatigue test piece B.
　本発明者らは、Ｖを含有させた鋼をベースに、他の窒化物形成元素量を種々に変化させることによって、棒鋼としての切断性に優れ、かつ、機械部品とした際に、窒化層の表層硬さを低下させることなく、硬化深さを増大させる方法について検討を行った。その結果、下記（ａ）～（ｆ）の知見を得た。 The present inventors have found that, based on steel containing V, various amounts of other nitride-forming elements are changed so that the cutability as a steel bar is excellent, and when a machine part is used, a nitride layer is formed. The method for increasing the hardening depth without lowering the surface hardness of the sample was examined. As a result, the following findings (a) to (f) were obtained.
　（ａ）Ｃｒ、ＴｉおよびＡｌをＶと複合的に含有させると、表層硬さが増加する。しかし、十分に高い表層硬さを得るために、多量のＣｒ、ＴｉおよびＡｌを加えると、窒素の拡散が阻害され、機械部品における硬化深さを十分に深くすることが困難になる。 (A) When Cr, Ti and Al are combined with V, the surface hardness increases. However, when a large amount of Cr, Ti, and Al are added to obtain a sufficiently high surface hardness, diffusion of nitrogen is hindered, and it is difficult to sufficiently deepen the hardening depth in a mechanical part.
　（ｂ）Ｍｎは窒素との結合力が比較的弱いため、Ｍｎを単独で鋼に含有させても、窒化物の形成駆動力が小さく、十分に窒化層を強化できない。しかし、窒化物形成の駆動力が大きなＶと複合的に含有させると、生成する窒化物のサイズが微細化し、Ｍｎによる強化能が大きくなる。 (B) Since Mn has a relatively weak bonding force with nitrogen, even if Mn is contained alone in steel, the driving force for forming nitrides is small and the nitrided layer cannot be sufficiently strengthened. However, when V and V, which have a large driving force for forming a nitride, are combined with V, the size of the generated nitride becomes finer, and the strengthening ability by Mn increases.
　（ｃ）Ｍｎは窒素との結合力が比較的弱いため、窒素の拡散を阻害しにくい。Ｖのみで表層硬さを高めた鋼と、Ｖの一部をＭｎで置換した鋼を比較すると、後者の方が窒化時の硬化深さは大きくなる。 Since (c) Mn has a relatively weak binding force with nitrogen, it is difficult to inhibit the diffusion of nitrogen. Comparing a steel in which the surface hardness is increased only with V and a steel in which a part of V is replaced with Mn, the latter has a greater hardening depth during nitriding.
　（ｄ）Ｖを含む鋼にＭｎを複合的に含有させた場合の表層硬さの上昇量には、Ｍｎの含有量および、他の窒化物形成元素の含有量が影響する。 (D) The increase in surface hardness when Mn is compounded into steel containing V is affected by the content of Mn and the content of other nitride-forming elements.
　（ｅ）ＭｎおよびＶの複合添加により表層硬さが大きく増大するための条件の一つは、Ｍｎ含有量を一定量以上とすることである。通常の機械構造用炭素鋼に含有される程度の量のＭｎを含有させても、窒化層の硬さへの影響は小さい。 (E) One of the conditions for greatly increasing the surface hardness by the combined addition of Mn and V is that the Mn content be a certain amount or more. Even if Mn is contained in such an amount as to be contained in ordinary carbon steel for machine structural use, the effect on the hardness of the nitrided layer is small.
　（ｆ）ＭｎおよびＶの複合添加により表層硬さが大きく増大するための条件のもう一つは、Ｖ以外の窒化物形成元素の含有量が多すぎないことである。例えば、１．５％Ｃｒと０．５％Ｖとを共に含む鋼にＭｎを含有させても表層の硬さの変化量は小さい。 Ｆ (f) Another condition for greatly increasing the surface hardness by the combined addition of Mn and V is that the content of nitride-forming elements other than V is not too large. For example, even if steel containing both 1.5% Cr and 0.5% V contains Mn, the change in hardness of the surface layer is small.
　（ｇ）表層硬さを増大させるため焼入れ性を過度に高めると、棒鋼段階での切断性が劣化する。切断性を確保するためには、棒鋼の金属組織中に含まれる初析フェライトおよびパーライトの合計面積率を所定量以上とする必要がある。 (G) If the hardenability is excessively increased in order to increase the surface layer hardness, the cuttability at the steel bar stage deteriorates. In order to ensure the cuttability, the total area ratio of proeutectoid ferrite and pearlite contained in the metal structure of the steel bar must be equal to or more than a predetermined amount.
　（ｈ）棒鋼の硬さを低減させ切断性を向上させた場合であっても、上述のようにＭｎおよびＶの複合添加により、窒化後には高い表層硬さが得られる。加えて、十分な量のＶを固溶させておくことによって、窒化時に窒素が拡散しない芯部においてＶ炭化物が析出し、芯部硬さを高めることができる。 (H) Even when the hardness of the steel bar is reduced to improve cutability, a high surface hardness is obtained after nitriding by the combined addition of Mn and V as described above. In addition, by dissolving a sufficient amount of V in solid solution, V carbide is precipitated in the core where nitrogen does not diffuse during nitriding, and the hardness of the core can be increased.
　本発明は上記の知見に基づいてなされたものである。以下、本発明の各要件について詳しく説明する。 The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.
　１．化学組成
　本発明に係る棒鋼において、各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「％」は、「質量％」を意味する。 1. Chemical Composition In the steel bar according to the present invention, the reasons for limiting each element are as follows. In the following description, “%” for the content means “% by mass”.
　Ｃ：０．０９～０．３０％
　Ｃは、鋼に含まれることで鋼の硬度を高めるため、棒鋼および機械部品の硬さを制御するうえで重要な元素である。本発明に係る棒鋼は、棒鋼の段階では硬さが低く、一方で機械部品とした際に所望の硬さとなるために、Ｃを適切な範囲で含む。Ｃは、窒化処理の際に、芯部ではＶとともにＶ炭化物を形成して析出することで、機械部品となった後の芯部硬さの向上にも寄与する。また、Ｃ含有量は、比較的硬さの低い組織である初析フェライトおよびパーライトの面積率に影響を与える。すなわち、Ｃ含有量が過少である鋼は、棒鋼の段階ではフェライトおよびパーライトを多く含み、硬さが低く切断性に優れるが、機械部品の段階では硬度が不十分となる。このような観点から、本発明ではＣ含有量を０．０９％以上とする。反面、Ｃ含有量が過大である鋼は、機械部品の段階では十分な硬度を有するが、棒鋼の段階では焼入れ性が高いために初析フェライトおよびパーライトが少なくなり、切断性が悪くなる。このような観点から、Ｃ含有量を０．３０％以下に限定する。Ｃ含有量は０．１０％以上であることが好ましく、０．１１％以上であることがより好ましい。また、Ｃ含有量は、０．２７％以下であることが好ましく、０．２５％以下であることがより好ましく、０．２２％以下であることがさらに好ましい。 C: 0.09 to 0.30%
C is an element that is important in controlling the hardness of steel bars and mechanical parts because it is included in steel to increase the hardness of the steel. The steel bar according to the present invention has a low hardness at the stage of the steel bar, but has a desired hardness when it is made into a machine part, and therefore contains C in an appropriate range. C forms V carbide together with V in the core portion during the nitriding treatment and precipitates, thereby contributing to an improvement in the hardness of the core portion after forming the mechanical component. Further, the C content affects the area ratio of proeutectoid ferrite and pearlite, which are relatively low hardness structures. That is, a steel having an excessively low C content contains a large amount of ferrite and pearlite at the stage of a steel bar and has low hardness and excellent cutability, but has insufficient hardness at the stage of a machine component. From such a viewpoint, in the present invention, the C content is set to 0.09% or more. On the other hand, steel having an excessively high C content has sufficient hardness at the stage of mechanical parts, but has high hardenability at the stage of steel bars, so that the amount of proeutectoid ferrite and pearlite decreases, resulting in poor cuttability. From such a viewpoint, the C content is limited to 0.30% or less. The C content is preferably at least 0.10%, more preferably at least 0.11%. Further, the C content is preferably 0.27% or less, more preferably 0.25% or less, and further preferably 0.22% or less.
　Ｓｉ：０．０１～０．５０％
　Ｓｉは、鋼の脱酸剤として必要な元素である。この効果を得るためには、Ｓｉ含有量を０．０１％以上とする必要がある。一方、Ｓｉ含有量が０．５０％を超えると、固溶強化により棒鋼での硬さが高くなりすぎ、切断性が劣化する。したがって、Ｓｉ含有量は０．０１～０．５０％とする。Ｓｉ含有量は０．０５％以上であることが好ましく、０．１０％以上であることがより好ましい。また、Ｓｉ含有量は、０．４０％以下であることが好ましく、０．３０％以下であることがより好ましい。 Si: 0.01 to 0.50%
Si is an element required as a steel deoxidizing agent. To obtain this effect, the Si content needs to be 0.01% or more. On the other hand, if the Si content exceeds 0.50%, the hardness of the steel bar becomes too high due to solid solution strengthening, and the cuttability deteriorates. Therefore, the Si content is set to 0.01 to 0.50%. The Si content is preferably at least 0.05%, more preferably at least 0.10%. Further, the Si content is preferably 0.40% or less, more preferably 0.30% or less.
　Ｍｎ：２．２０％を超えて３．５０％以下
　Ｍｎは、鋼に含まれることで鋼の硬度を高める元素であり、含有量が適切な範囲に制御されることが必要である。またＭｎは、窒化処理によってＶおよびＣｒと複合窒化物を形成し、窒化後の表層硬さの増大と硬化深さの深化との両立に寄与する。これらの効果を適切に得るためには、Ｍｎ含有量を２．２０％超とする必要がある。反面、Ｍｎは焼入れ性を高める元素であり、過度に含有された場合には初析フェライトおよびパーライトの生成を抑制し、棒鋼において過冷組織を生じて硬さを高める。すなわち、Ｍｎ含有量が３．５０％を超えると、棒鋼の切断性を劣化させる。したがって、Ｍｎ含有量は２．２０％を超えて３．５０％以下とする。Ｍｎ含有量は２．３０％以上であることが好ましい。また、Ｍｎ含有量は、３．００％以下であることが好ましく、２．８０％以下であることがより好ましい。 Mn: more than 2.20% to 3.50% or less Mn is an element that increases the hardness of steel by being contained in steel, and its content needs to be controlled to an appropriate range. In addition, Mn forms a composite nitride with V and Cr by nitriding, and contributes to both an increase in surface hardness after nitriding and an increase in hardening depth. In order to properly obtain these effects, the Mn content needs to be more than 2.20%. On the other hand, Mn is an element that enhances the hardenability, and when contained excessively, suppresses the formation of pro-eutectoid ferrite and pearlite, and produces a supercooled structure in the steel bar to increase the hardness. That is, when the Mn content exceeds 3.50%, the cuttability of the steel bar is deteriorated. Therefore, the Mn content is set to more than 2.20% and not more than 3.50%. The Mn content is preferably at least 2.30%. Further, the Mn content is preferably 3.00% or less, more preferably 2.80% or less.
　Ｐ：０．０５０％以下
　Ｐは、不純物元素である。Ｐは結晶粒界に偏析し、粒界脆化割れを引き起こす。したがって、Ｐ含有量はなるべく低い方がよい。そのため、Ｐ含有量は０．０５０％以下とする。Ｐ含有量は０．０４０％以下であるのが好ましい。 P: 0.050% or less P is an impurity element. P segregates at crystal grain boundaries, causing grain boundary embrittlement cracking. Therefore, the P content is preferably as low as possible. Therefore, the P content is set to 0.050% or less. The P content is preferably 0.040% or less.
　Ｓ：０．００１～０．１００％
　Ｓは、鋼中でＭｎと結合してＭｎＳを形成し、鋼の切断性および被削性を高める。この効果を得るためには、Ｓ含有量を０．００１％以上とする必要がある。一方、Ｓ含有量が０．１００％を超えると、粗大なＭｎＳが形成され、疲労強度が劣化する。したがって、Ｓ含有量は０．００１～０．１００％とする。なお、Ｓ含有量は０．００５％以上であることが好ましく、０．０１０％以上であることがより好ましい。また、Ｓ含有量は、０．０８０％以下であることが好ましく、０．０７０％以下であることがより好ましい。 S: 0.001 to 0.100%
S combines with Mn in steel to form MnS and enhances the cuttability and machinability of the steel. In order to obtain this effect, the S content needs to be 0.001% or more. On the other hand, if the S content exceeds 0.100%, coarse MnS is formed, and the fatigue strength deteriorates. Therefore, the S content is set to 0.001 to 0.100%. Note that the S content is preferably 0.005% or more, and more preferably 0.010% or more. Further, the S content is preferably 0.080% or less, and more preferably 0.070% or less.
　Ｃｒ：０．０２～０．８０％
　Ｃｒは、窒化処理によってＭｎおよびＶと複合窒化物を形成し、窒化後の表層硬さの増大と硬化深さの深化の両立に寄与する。この効果を得るためには、Ｃｒ含有量を０．０２％以上とする必要がある。一方、Ｃｒ含有量が過度であると、窒化処理の際に窒素の拡散を阻害する作用が顕著になり、硬化深さが浅くなる。さらに、Ｃｒは焼入れ性を高める元素であるため、過度に含有された場合には棒鋼での初析フェライトおよびパーライトの生成を抑制する。したがって、Ｃｒ含有量は０．０２～０．８０％とする。Ｃｒ含有量は、０．０５％以上であることが好ましく、０．１０％以上であることがより好ましく、０．１５％を超えることがさらに好ましい。また、Ｃｒ含有量は、０．６０％以下であることが好ましく、０．５０％以下であることがより好ましい。 Cr: 0.02 to 0.80%
Cr forms a composite nitride with Mn and V by nitriding treatment, and contributes to both increase in surface hardness after nitriding and deepening of hardening depth. To obtain this effect, the Cr content needs to be 0.02% or more. On the other hand, if the Cr content is excessive, the effect of inhibiting the diffusion of nitrogen during the nitriding treatment becomes remarkable, and the hardening depth becomes shallow. Furthermore, since Cr is an element that enhances the hardenability, when it is excessively contained, it suppresses the formation of proeutectoid ferrite and pearlite in a steel bar. Therefore, the Cr content is set to 0.02 to 0.80%. The Cr content is preferably at least 0.05%, more preferably at least 0.10%, even more preferably more than 0.15%. Further, the Cr content is preferably 0.60% or less, more preferably 0.50% or less.
　Ｖ：０．１０～０．４０％
　Ｖは、窒化処理前の時点では固溶の状態で存在し、窒化処理によってＭｎおよびＣｒと微細な複合窒化物を形成して析出し、表層硬さの増大と硬化深さの深化との両方に寄与する。また、Ｖは、複合窒化物の核生成頻度を高め、そのサイズを微細化させる効果を有する。さらに、窒化処理による窒素の侵入が届かない深部においても、窒化処理による加熱によってＣと結合してＶ炭化物を形成し、芯部硬さを増大させる効果も有する。この効果を得るためには、Ｖ含有量を０．１０％以上とする必要がある。一方、Ｖ含有量が０．４０％を超えると、合金コストが上昇し、経済性が劣化する。したがって、Ｖ含有量は０．１０～０．４０％とする。なお、Ｖ含有量は０．１３％以上であるのが好ましく、０．１５％以上であることがより好ましい。また、Ｖ含有量は、０．３０％以下であることが好ましく、０．２５％以下であることがより好ましい。 V: 0.10 to 0.40%
V exists in a solid solution state before the nitriding treatment, forms and precipitates a fine composite nitride with Mn and Cr by the nitriding treatment, and increases both the surface layer hardness and the hardening depth. To contribute. V has the effect of increasing the frequency of nucleation of the composite nitride and reducing its size. In addition, even in a deep part where the intrusion of nitrogen by the nitriding treatment does not reach, there is also an effect of forming V carbide by combining with C by heating by the nitriding treatment and increasing the core hardness. To obtain this effect, the V content needs to be 0.10% or more. On the other hand, if the V content exceeds 0.40%, the alloy cost increases and the economic efficiency deteriorates. Therefore, the V content is set to 0.10 to 0.40%. Note that the V content is preferably 0.13% or more, and more preferably 0.15% or more. Further, the V content is preferably 0.30% or less, more preferably 0.25% or less.
　Ａｌ：０．００１～０．０８０％
　Ａｌは、鋼の脱酸に用いられる元素である。一方、Ａｌ含有量が高すぎると、窒素の拡散が阻害され、硬化深さが浅くなる。したがって、Ａｌ含有量は０．００１～０．０８０％とする。Ａｌ含有量は０．００５％以上であるのが好ましく、０．０１０％以上であるのがより好ましい。また、Ａｌ含有量は０．０６０％以下であるのが好ましく、０．０５０％以下であるのがより好ましく、０．０４０％以下であるのがさらに好ましい。 Al: 0.001 to 0.080%
Al is an element used for deoxidizing steel. On the other hand, if the Al content is too high, diffusion of nitrogen is hindered, and the curing depth becomes shallow. Therefore, the Al content is set to 0.001 to 0.080%. The Al content is preferably at least 0.005%, more preferably at least 0.010%. Further, the Al content is preferably 0.060% or less, more preferably 0.050% or less, and even more preferably 0.040% or less.
　Ｎ：０．０２５０％以下
　Ｎは、不純物として鋼に混入する元素である。Ｎ含有量が高すぎれば、熱間鍛造中にＶが窒化物として析出し、窒化時の硬化に寄与する固溶Ｖが減少する。したがって、Ｎ含有量は０．０２５０％以下とする。なお、Ｎ含有量は０．０２００％以下であることが好ましく、０．０１５０％以下であることがより好ましく、０．００８０％未満であることがさらに好ましい。なお、窒化処理によって窒素が表層から侵入するため、窒化処理がなされた後の機械部品は、後述する窒素化合物層および窒素拡散層において上記上限以上のＮを含有しうる。機械部品においても、硬化層よりも深い位置においては、棒鋼と同様にＮ含有量は０．０２５０％以下となる。 N: 0.0250% or less N is an element mixed into steel as an impurity. If the N content is too high, V precipitates as nitride during hot forging, and the amount of solid solution V contributing to hardening during nitriding decreases. Therefore, the N content is set to 0.0250% or less. The N content is preferably 0.0200% or less, more preferably 0.0150% or less, and further preferably less than 0.0080%. Since nitrogen enters from the surface layer by the nitriding treatment, the mechanical component after the nitriding treatment may contain N in the nitrogen compound layer and the nitrogen diffusion layer described later in excess of the upper limit. Also in the mechanical parts, at a position deeper than the hardened layer, the N content becomes 0.0250% or less as in the case of the steel bars.
　Ｏ：０．００５０％以下
　Ｏは、不純物として鋼に混入する元素である。Ｏ含有量が高すぎれば、粗大な酸化物が形成され、疲労破壊の起点となることで疲労特性が劣化する。したがって、Ｏ含有量は０．００５０％以下とする。なお、Ｏ含有量は０．００４０％以下であることが好ましく、０．００２５％以下であることがより好ましい。 O: 0.0050% or less O is an element mixed into steel as an impurity. If the O content is too high, a coarse oxide is formed, and becomes a starting point of fatigue fracture, thereby deteriorating fatigue characteristics. Therefore, the O content is set to 0.0050% or less. Note that the O content is preferably 0.0040% or less, and more preferably 0.0025% or less.
　Ｔｉ：０～０．０５０％
　Ｔｉは、母材中のＮと結合してＴｉＮを形成し、熱間鍛造時の結晶粒の粗大化を抑制する。このため、必要に応じて含有させてもよい。しかしながら、Ｔｉ含有量が過剰になると、ＴｉＣが生成して鋼の硬さのばらつきが大きくなる。したがって、Ｔｉ含有量は０．０５０％以下とする。Ｔｉ含有量は、０．０４０％以下であるのが好ましく、０．０３０％以下であるのがより好ましい。なお、上記効果を得るためには、Ｔｉ含有量は０．００５％以上であるのが好ましく、０．０１０％以上であるのがより好ましい。 Ti: 0 to 0.050%
Ti combines with N in the base material to form TiN, and suppresses coarsening of crystal grains during hot forging. For this reason, you may make it contain as needed. However, when the Ti content is excessive, TiC is generated, and the variation in hardness of the steel increases. Therefore, the Ti content is set to 0.050% or less. The Ti content is preferably at most 0.040%, more preferably at most 0.030%. In order to obtain the above effect, the Ti content is preferably 0.005% or more, and more preferably 0.010% or more.
　Ｎｂ：０～０．０５％
　Ｎｂは母材中のＮと結合してＮｂＮを形成し、熱間鍛造時の再結晶を遅滞させ、結晶粒の粗大化を抑制する。このため、必要に応じて含有させてもよい。しかしながら、Ｎｂ含有量が過剰になると、ＮｂＣが生成して鋼の硬さのばらつきが大きくなる。したがって、Ｎｂ含有量は０．０５％以下とする。Ｎｂ含有量は０．０４％以下であるのが好ましく、０．０３％以下であるのがより好ましい。なお、上記効果を得るためには、Ｎｂ含有量は０．０１％以上であるのが好ましく、０．０２％以上であるのがより好ましい。 Nb: 0 to 0.05%
Nb combines with N in the base material to form NbN, delays recrystallization during hot forging, and suppresses coarsening of crystal grains. For this reason, you may make it contain as needed. However, when the Nb content is excessive, NbC is generated and the hardness of the steel varies widely. Therefore, the Nb content is set to 0.05% or less. The Nb content is preferably at most 0.04%, more preferably at most 0.03%. In order to obtain the above effect, the Nb content is preferably at least 0.01%, more preferably at least 0.02%.
　Ｍｏ：０～０．１０％
　Ｍｏは鋼の焼入れ性を高めて鋼の強度および疲労強度を高める。このため、必要に応じて含有させてもよい。しかしながら、Ｍｏ含有量が過剰になると、鋼の製造コストが増加する。したがって、Ｍｏ含有量は０．１０％以下とする。Ｍｏ含有量は０．０９％以下であるのが好ましく、０．０８％以下であるのがより好ましい。なお、上記効果を得るためには、Ｍｏ含有量は０．０２％以上であるのが好ましく、０．０３％以上であるのがより好ましい。 Mo: 0 to 0.10%
Mo enhances the hardenability of the steel to increase the strength and fatigue strength of the steel. For this reason, you may make it contain as needed. However, when the Mo content is excessive, the production cost of steel increases. Therefore, the Mo content is set to 0.10% or less. The Mo content is preferably 0.09% or less, and more preferably 0.08% or less. In order to obtain the above effect, the Mo content is preferably 0.02% or more, and more preferably 0.03% or more.
　Ｃｕ：０～０．３０％
　Ｃｕはフェライトに固溶して鋼の強度および疲労強度を高める。このため、必要に応じて含有させてもよい。しかしながら、Ｃｕ含有量が過剰になると、熱間鍛造時に鋼の粒界に偏析して熱間割れを誘起する。したがって、Ｃｕ含有量は０．３０％以下とする。Ｃｕ含有量は０．２５％以下であるのが好ましく、０．２０％以下であるのがより好ましい。なお、上記効果を得るためには、Ｃｕ含有量は０．０５％以上であるのが好ましく、０．１０％以上であるのがより好ましい。 Cu: 0 to 0.30%
Cu forms a solid solution in ferrite and increases the strength and fatigue strength of steel. For this reason, you may make it contain as needed. However, when the Cu content is excessive, it segregates at the grain boundaries of the steel during hot forging and induces hot cracking. Therefore, the Cu content is set to 0.30% or less. The Cu content is preferably at most 0.25%, more preferably at most 0.20%. In order to obtain the above effects, the Cu content is preferably at least 0.05%, more preferably at least 0.10%.
　Ｎｉ：０～０．３０％
　Ｎｉはフェライトに固溶して鋼の強度および疲労強度を高める。Ｎｉはさらに、鋼がＣｕを含有する場合に、Ｃｕに起因する熱間割れを抑制する効果を有する。このため、必要に応じて含有させてもよい。しかしながら、Ｎｉ含有量が過剰になると、その効果が飽和し、製造コストが高くなる。したがって、Ｎｉ含有量は０．３０％以下とする。Ｎｉ含有量は０．２５％以下であるのが好ましく、０．２０％以下であるのがより好ましい。なお、上記効果を得るためには、Ｎｉ含有量は０．０５％以上であるのが好ましく、０．１０％以上であるのがより好ましい。 Ni: 0 to 0.30%
Ni forms a solid solution in ferrite to increase the strength and fatigue strength of the steel. Ni further has an effect of suppressing hot cracking caused by Cu when the steel contains Cu. For this reason, you may make it contain as needed. However, when the Ni content is excessive, the effect is saturated and the production cost is increased. Therefore, the Ni content is set to 0.30% or less. The Ni content is preferably at most 0.25%, more preferably at most 0.20%. In order to obtain the above effect, the Ni content is preferably at least 0.05%, more preferably at least 0.10%.
　Ｂｉ：０～０．３５％
　Ｂｉは、切削抵抗を低下させ工具寿命を長寿命化させる作用を有する。このため、必要に応じて含有させてもよい。しかしながら、Ｂｉ含有量が過剰になると、熱間圧延時に割れや疵が生じやすくなる。したがって、Ｂｉ含有量は０．３５％以下とする。Ｂｉ含有量は０．３０％以下であるのが好ましく、０．２５％以下であるのがより好ましい。なお、上記効果を得るためには、Ｂｉ含有量は０．０３％以上であるのが好ましく、０．０５％以上であるのがより好ましい。 Bi: 0 to 0.35%
Bi has the effect of reducing cutting resistance and extending tool life. For this reason, you may make it contain as needed. However, if the Bi content is excessive, cracks and flaws are likely to occur during hot rolling. Therefore, the Bi content is set to 0.35% or less. The Bi content is preferably at most 0.30%, more preferably at most 0.25%. In order to obtain the above effects, the Bi content is preferably at least 0.03%, more preferably at least 0.05%.
　Ｂ：０～０．００５０％
　Ｂは、機械部品の組織のフェライトおよびパーライトの面積率を低下させる作用を有する。このため、必要に応じて含有させてもよい。しかしながら、Ｂ含有量が過剰になると、棒鋼の状態における組織のフェライトおよびパーライトの面積率を大きくすることができない。したがって、Ｂ含有量は０．００５０％以下とする。Ｂ含有量は０．００４０％以下であるのが好ましく、０．００３０％以下であるのがより好ましい。なお、上記効果を得るためには、Ｂ含有量は０．０００５％以上であるのが好ましく、０．００１０％以上であるのがより好ましい。 B: 0 to 0.0050%
B has the effect of reducing the area ratio of ferrite and pearlite in the structure of the mechanical part. For this reason, you may make it contain as needed. However, when the B content is excessive, the area ratio of ferrite and pearlite in the structure in the state of the steel bar cannot be increased. Therefore, the B content is set to 0.0050% or less. The B content is preferably at most 0.0040%, more preferably at most 0.0030%. In order to obtain the above effects, the B content is preferably 0.0005% or more, and more preferably 0.0010% or more.
　本発明の化学組成において、残部はＦｅおよび不純物である。ここで、不純物とは、鋼を工業的に製造する際に、原料としての鉱石、スクラップ、または製造環境などから混入されるものであって、本発明の窒化用棒鋼に悪影響を与えない範囲で許容されるものを意味する。 に お い て In the chemical composition of the present invention, the balance is Fe and impurities. Here, the impurities are those that are mixed from the ore, scrap, or the production environment as raw materials when the steel is industrially manufactured, and within a range that does not adversely affect the bar for nitriding of the present invention. Means acceptable.
　なお、不純物として鋼中に混入しうる元素として、例えば、Ｐｂ、Ｃａ、Ｍｇ、Ｗ、Ｓｂ、Ｃｏ、ＴａおよびＲＥＭが挙げられる。これらの元素を含む場合であっても、その含有量が、それぞれ、Ｐｂ：０．１０％以下、Ｃａ：０．００１％以下、Ｍｇ：０．００１％以下、Ｗ：０．１０％以下、Ｓｂ：０．００５％以下、Ｃｏ：０．１０％以下、Ｔａ：０．１０％以下、およびＲＥＭ：０．００１％以下であれば、問題なく本発明を実施することができる。 元素 Note that elements that can be mixed into steel as impurities include, for example, Pb, Ca, Mg, W, Sb, Co, Ta, and REM. Even when these elements are contained, their contents are respectively Pb: 0.10% or less, Ca: 0.001% or less, Mg: 0.001% or less, W: 0.10% or less, If Sb: 0.005% or less, Co: 0.10% or less, Ta: 0.10% or less, and REM: 0.001% or less, the present invention can be practiced without any problem.
　２．窒化用棒鋼の金属組織
　本発明に係る棒鋼は、焼入れ性を高める元素であるＭｎおよびＣｒを多く含むため、ベイナイトの生成は避けられない。しかしながら、棒鋼段階での切断性を確保するためには、棒鋼の金属組織を適切に制御する必要がある。具体的には、棒鋼の金属組織中に含まれる初析フェライトおよびパーライトの合計面積率を３５％以上とする必要がある。切断性のさらなる改善のためには、上記の合計面積率は５０％以上であることが好ましい。 2. Metal Structure of Bar Steel for Nitriding Since the steel bar according to the present invention contains a large amount of Mn and Cr, which are elements that enhance hardenability, bainite cannot be avoided. However, it is necessary to appropriately control the metallographic structure of the steel bar in order to ensure the cutting properties at the steel bar stage. Specifically, the total area ratio of proeutectoid ferrite and pearlite contained in the metal structure of the steel bar must be 35% or more. In order to further improve the cutting properties, the total area ratio is preferably 50% or more.
　なお、本発明において、組織全体での平均面積率は、以下の手順により求めるものとする。まず、鋼の長手方向に垂直な断面を切り出した後、ナイタルで腐食し、組織を現出させる。そして、棒鋼が、丸棒状の場合には、丸棒の半径をＲとした場合に、丸棒の中心位置、ならびに、丸棒の中心から半径方向の距離が、（３／４）×Ｒ、（２／４）×Ｒ、および（１／４）×Ｒとなる位置を中心として、観察用試験片を合計４つ採取する。 In the present invention, the average area ratio in the whole tissue is determined by the following procedure. First, a cross section perpendicular to the longitudinal direction of the steel is cut out and then corroded with nital to reveal a structure. When the steel bar has a round bar shape and the radius of the round bar is R, the center position of the round bar and the distance in the radial direction from the center of the round bar are (3/4) × R, A total of four observation test pieces are collected around the positions of (2/4) × R and (1/4) × R.
　また、棒鋼が、角棒状の場合には、角棒の厚さをｔとした場合に、角棒の厚さ方向中心位置、ならびに、（１／８）×ｔ、（２／８）×ｔ、および（３／８）×ｔとなる位置を中心として、観察用試験片を合計４つ採取する。 Further, when the steel bar is in the shape of a square bar, when the thickness of the square bar is t, the center position in the thickness direction of the square bar, and (1/8) × t, (2/8) × t , And (3/8) × t, and a total of four observation test pieces are collected.
　その後、それぞれの観察用試験片を用いて倍率５００倍の光学顕微鏡写真（視野：２１０μｍ×１６０μｍ）を撮影し、画像解析から初析フェライトおよびパーライトの合計面積率を求める。そして、上記の４箇所から撮影した写真から個々に求めた初析フェライトおよびパーライトの合計面積率の算術平均を、その棒鋼全体における初析フェライトおよびパーライトの合計の平均面積率とする。 Thereafter, an optical micrograph (magnification: 210 μm × 160 μm) is photographed at a magnification of 500 times using each observation test piece, and the total area ratio of proeutectoid ferrite and pearlite is determined from image analysis. Then, the arithmetic average of the total area ratios of pro-eutectoid ferrite and pearlite individually obtained from the photographs taken from the above four locations is defined as the average area ratio of the total of pro-eutectoid ferrite and pearlite in the entire steel bar.
　なお、棒鋼には、断面が円形の丸鋼、断面が正方形状の角鋼、断面が長方形状の平鋼、断面が六角形の六角鋼、断面が八角形の八角鋼などが含まれる。丸鋼の場合には、丸鋼の長手方向に垂直な断面の半径がＲである。一方、角鋼の場合には断面の一辺の長さ、平鋼の場合には断面の短辺の長さ、六角鋼または八角鋼の場合には断面の対辺の距離を、それぞれ棒鋼の厚さｔとする。 棒 Bars include round steel having a circular cross section, square steel having a square cross section, flat steel having a rectangular cross section, hexagonal steel having a hexagonal cross section, and octagon steel having an octagonal cross section. In the case of round bars, the radius of the cross section perpendicular to the longitudinal direction of the round bars is R. On the other hand, in the case of square steel, the length of one side of the cross section, in the case of flat steel, the length of the short side of the cross section, in the case of hexagonal steel or octagon steel, the distance between the opposite sides of the cross section, the thickness t of the steel bar, respectively. And
　３．窒化用棒鋼の寸法
　上述のように、棒鋼には、丸鋼、角鋼、平鋼、六角鋼、八角鋼などが含まれる。本発明に係る窒化用棒鋼を素材として製造される機械部品は、産業機械および建設機械などに用いられる。そのため、窒化用棒鋼の直径または厚さは所定の値より大きいことが望ましい。具体的には、窒化用棒鋼の直径または厚さは、７０ｍｍ以上であることが好ましく、７５ｍｍ以上であることが好ましい。また、平鋼の場合には、断面の短辺に対する長辺の比が１．０を超えて２．５以下であることが好ましい。 3. Dimensions of Bar for Nitriding As described above, the bar includes round steel, square steel, flat steel, hexagonal steel, octagonal steel, and the like. The machine component manufactured using the bar steel for nitriding according to the present invention as a raw material is used for industrial machines, construction machines, and the like. Therefore, it is desirable that the diameter or thickness of the nitriding bar is larger than a predetermined value. Specifically, the diameter or thickness of the bar for nitriding is preferably 70 mm or more, and more preferably 75 mm or more. In the case of flat steel, the ratio of the long side to the short side of the cross section is preferably more than 1.0 and not more than 2.5.
　４．機械部品
　上記の窒化用棒鋼から得られる機械部品は、表面に窒素化合物層および窒素拡散層からなる硬化層を有する。窒素化合物層とは、窒化処理により形成された、鉄窒化物（Ｆｅ３ＮまたはＦｅ４Ｎ等）を主体とする厚さ数μｍ程度の層のことである。窒素拡散層とは、母材が侵入した窒素元素により強化された層のことを指す。なお一般に、窒化処理によって機械部品の表面に窒素化合物層が形成され、窒素化合物層よりも深い位置に窒素拡散層が形成される。また、本発明の一実施形態に係る機械部品の、硬化層を除く領域における化学組成については、上記の窒化用棒鋼と同じであるため、説明は省略する。 4. Machine Parts Machine parts obtained from the above-mentioned bar for nitriding have a hardened layer composed of a nitrogen compound layer and a nitrogen diffusion layer on the surface. The nitrogen compound layer is a layer formed by nitriding treatment and mainly composed of iron nitride (Fe 3 N or Fe 4 N) with a thickness of about several μm. The nitrogen diffusion layer refers to a layer reinforced by the nitrogen element in which the base material has penetrated. In general, a nitrogen compound layer is formed on the surface of the mechanical component by the nitriding treatment, and a nitrogen diffusion layer is formed at a position deeper than the nitrogen compound layer. In addition, the chemical composition of the mechanical component according to the embodiment of the present invention in the region other than the hardened layer is the same as that of the above-described bar for nitriding, and thus the description is omitted.
　また、機械部品の組織においては、高い表層硬さを確保するため、表層部における組織を制御する必要がある。具体的には、使用時に高い応力が負荷される部位である表面から深さ方向に２ｍｍの位置までで、かつ硬化層を除く領域において、初析フェライトおよびパーライトの合計面積率が平均で４０％以下である領域を有する。上記面積率は、３０％以下であるのが好ましく、２０％以下であるのがより好ましい。 In the structure of mechanical parts, it is necessary to control the structure of the surface layer in order to ensure high surface hardness. Specifically, the total area ratio of pro-eutectoid ferrite and pearlite is 40% on average from the surface where high stress is applied during use to a position 2 mm in the depth direction and excluding the hardened layer. It has the following areas: The area ratio is preferably 30% or less, more preferably 20% or less.
　なお、初析フェライトおよびパーライトの合計面積率を測定する上記の領域は、少なくとも２１０μｍ×１６０μｍの面積を有することが好ましい。また、本実施形態に係る機械部品においては、表面から深さ方向に２ｍｍの位置までで、かつ硬化層を除く領域において、初析フェライトおよびパーライトの合計面積率を平均で４０％以下、３０％以下、または２０％以下としてもよい。 The above-mentioned region for measuring the total area ratio of proeutectoid ferrite and pearlite preferably has an area of at least 210 μm × 160 μm. In the mechanical component according to the present embodiment, the total area ratio of proeutectoid ferrite and pearlite is 40% or less and 30% or less on average in a region from the surface to a position of 2 mm in the depth direction and excluding the hardened layer. Or less, or 20% or less.
　本発明において、表面から深さ方向に２ｍｍの位置までで、かつ硬化層を除く領域での初析フェライトおよびパーライトの平均面積率は、以下の手順により求めるものとする。 に お い て In the present invention, the average area ratio of proeutectoid ferrite and pearlite in a region from the surface to a position of 2 mm in the depth direction and excluding the hardened layer is determined by the following procedure.
　まず、機械部品の表面から深さ方向に１ｍｍの位置が被検面の中心になるように試験片を切り出し、断面をナイタルで腐食し、組織を現出させる。その後、上記被検面の中心からφ２．０ｍｍの範囲から、硬化層を含まないように異なる視野をランダムに４箇所選び、倍率５００倍の光学顕微鏡写真（視野：２１０μｍ×１６０μｍ）を撮影し、画像解析から初析フェライトおよびパーライトの合計面積率を求める。そして、初析フェライトおよびパーライトの合計面積率が所定値以下である領域が少なくとも１箇所存在する場合に、初析フェライトおよびパーライトの合計面積率が所定値以下である領域を有すると判断する。 (1) First, a test piece is cut out so that a position of 1 mm in the depth direction from the surface of the machine component becomes the center of the test surface, and the cross section is corroded with nital to reveal a structure. Thereafter, four different visual fields were randomly selected from a range of φ2.0 mm from the center of the test surface so as not to include the cured layer, and an optical microscope photograph (visual field: 210 μm × 160 μm) with a magnification of 500 × was taken. The total area ratio of proeutectoid ferrite and pearlite is determined from image analysis. Then, when there is at least one region where the total area ratio of proeutectoid ferrite and pearlite is equal to or less than a predetermined value, it is determined that there is a region where the total area ratio of proeutectoid ferrite and pearlite is equal to or less than a predetermined value.
　また、上記の４箇所から撮影した写真から個々に求めた初析フェライトおよびパーライトの合計の算術平均を、表面から深さ方向に２ｍｍの位置までで、かつ硬化層を除く領域での初析フェライトおよびパーライトの合計での平均面積率とする。 The arithmetic mean of the total of pro-eutectoid ferrite and pearlite individually obtained from the photographs taken from the above four places was calculated from the surface up to a position of 2 mm in the depth direction and in the region excluding the hardened layer. And the average area ratio of the total of pearlite.
　さらに、窒化後の機械部品は、０．２６ｍｍを超える硬化深さを有する。上述のように、棒鋼中のＣｒ含有量を所定値以下に制限するとともに、ＭｎおよびＶを複合添加することにより、深い硬化深さを確保することが可能となる。硬化深さは０．３０ｍｍ以上であるのが好ましい。 Furthermore, the machined parts after nitriding have a hardening depth of more than 0.26 mm. As described above, by limiting the Cr content in the steel bar to a predetermined value or less and adding Mn and V in combination, it is possible to secure a deep hardening depth. The curing depth is preferably at least 0.30 mm.
　なお、前述したとおり、本発明の機械部品の表面には、窒化処理により表層から侵入した窒素により硬化層が形成される。言い換えると、硬化層は窒化処理によって窒素が表層から侵入した領域を指す。硬化深さとは、表層から、硬化層内部のうち、十分な硬さが形成された深さまでの距離を指す。 As described above, a hardened layer is formed on the surface of the mechanical component of the present invention by nitrogen entering from the surface layer by nitriding. In other words, the hardened layer indicates a region where nitrogen has entered from the surface layer by the nitriding treatment. The hardening depth refers to a distance from the surface layer to a depth where sufficient hardness is formed in the hardened layer.
　より具体的には、機械部品の硬化深さは、以下の手順により測定する。まず、窒化後の機械部品を窒化処理面と垂直に切断し、当該窒化処理面を含む切断面を観察できるように樹脂に埋め込み、硬さ測定用のサンプルを作製する。 More specifically, the cure depth of a mechanical part is measured by the following procedure. First, a machine component after nitriding is cut perpendicular to the nitriding surface, and embedded in a resin so that the cut surface including the nitriding surface can be observed, to prepare a sample for hardness measurement.
　続いて、作製したサンプルの表面（窒化処理面）から深さ方向に、０．０５ｍｍピッチでＪＩＳ　Ｚ　２２４４に基づくビッカース硬さの測定を行う。試験力は２．９４Ｎとする。測定深さ位置ごとに試験を３回行い、得られた３つのビッカース硬さの平均値を、その深さ位置の硬さと定義する。測定点間の硬さは、その深さ位置を挟む二つの測定点の硬さを結ぶ直線上に乗ると仮定する。 Next, the Vickers hardness is measured at a pitch of 0.05 mm from the surface (nitrided surface) of the manufactured sample at a pitch of 0.05 mm according to JIS {Z} 2244. The test force shall be 2.94N. The test is performed three times at each measurement depth position, and the average value of the three obtained Vickers hardnesses is defined as the hardness at that depth position. It is assumed that the hardness between the measurement points is on a straight line connecting the hardness of the two measurement points sandwiching the depth position.
　また、サンプルの中央付近の硬さを試験力２．９４Ｎで各５点測定し、得られた５つのビッカース硬さの平均値を、窒化後の芯部硬さと定義する。さらに、窒化層のうち、その硬さが芯部硬さよりも５０ＨＶ高くなる点までの、表面からの距離を硬化深さと定義する。 Furthermore, the hardness near the center of the sample is measured at five points at a test force of 2.94 N, and the average value of the obtained five Vickers hardnesses is defined as the core hardness after nitriding. Further, in the nitrided layer, the distance from the surface to the point where the hardness becomes 50 HV higher than the core hardness is defined as the hardened depth.
　５．窒化用棒鋼の製造方法
　窒化用棒鋼の製造方法については特に制限は設けないが、例えば、以下の方法により製造が可能である。 5. Method for Manufacturing Bar for Nitriding The method for manufacturing the bar for nitriding is not particularly limited. For example, the bar can be manufactured by the following method.
　上述の化学組成を満たす溶鋼を製造する。そして、製造された溶鋼を、鋳造法により鋳片（スラブ、ブルーム）にするか、または、造塊法によりインゴットにする。さらに必要に応じて、上記の鋳片またはインゴットに熱間加工を施して、ビレットを製造する。そして、上記の鋳片もしくはインゴット、またはビレットに熱間圧延を加えることにより、窒化用棒鋼を作製する。 製造 Manufacturing molten steel that satisfies the above chemical composition. Then, the produced molten steel is made into a slab (slab, bloom) by a casting method or an ingot by an ingot-making method. Further, if necessary, the cast slab or the ingot is subjected to hot working to produce a billet. Then, a hot-rolling is applied to the slab, ingot, or billet to produce a bar for nitriding.
　上記の熱間圧延における条件について、特に制限は設けないが、棒鋼の金属組織中に含まれる初析フェライトおよびパーライトの合計面積率を所定量以上とするためには、熱間圧延後の５００℃までの平均冷却速度を０．４０℃／秒以下とすることが好ましい。平均冷却速度が０．４０℃／秒超では、初析フェライトの量を十分に確保することができなくなり、棒鋼の切断性が劣化するおそれがある。 The conditions in the above hot rolling are not particularly limited, but in order to make the total area ratio of proeutectoid ferrite and pearlite contained in the metal structure of the steel bar equal to or more than a predetermined amount, 500 ° C. after hot rolling. Preferably, the average cooling rate up to 0.40 ° C./sec. If the average cooling rate is more than 0.40 ° C./sec, the amount of proeutectoid ferrite cannot be sufficiently secured, and the cutting properties of the steel bar may be deteriorated.
　以上の製造工程により製造された窒化用棒鋼は、硬さが低く切断性に優れる。 窒 化 The bar for nitriding manufactured by the above manufacturing process has low hardness and excellent cutability.
　６．機械部品の製造方法
　機械部品の製造方法についても特に制限は設けないが、例えば、上記の窒化用棒鋼に対して、熱間加工および切削加工を施し、素形材とした後に窒化処理を行うことで製造することができる。以下、それぞれの工程について説明する。 6. There is no particular limitation on the method of manufacturing the mechanical parts. For example, the above-described steel bar for nitriding is subjected to hot working and cutting, and then subjected to nitriding after forming a shaped material. Can be manufactured. Hereinafter, each step will be described.
　６－１．熱間加工工程
　製造された上記棒鋼を加熱する。加熱温度が低すぎれば、熱間加工装置に過度の負荷がかかる。一方、加熱温度が高すぎれば、スケールロスが大きい。したがって、加熱温度は１０００～１３００℃とするのが好ましい。また、上記加熱温度での保持時間は、３０～１０００分とするのが好ましい。 6-1. Hot working step The manufactured steel bar is heated. If the heating temperature is too low, an excessive load is applied to the hot working device. On the other hand, if the heating temperature is too high, the scale loss is large. Therefore, the heating temperature is preferably set to 1000 to 1300 ° C. Further, the holding time at the heating temperature is preferably 30 to 1000 minutes.
　加熱後の上記棒鋼に対して、熱間加工を実施する。熱間加工は例えば、熱間鍛造である。以下、本工程での熱間加工を熱間鍛造として説明を続ける。 熱 Hot work is performed on the steel bar after heating. The hot working is, for example, hot forging. Hereinafter, the hot working in this step will be described as hot forging.
　熱間鍛造の好ましい仕上げ温度は９００℃以上である。仕上げ温度が低すぎれば、熱間鍛造装置の金型への負担が大きくなるためである。一方、仕上げ温度の好ましい上限は、１２５０℃である。 好 ま し い The preferred finishing temperature for hot forging is 900 ° C or higher. If the finishing temperature is too low, the load on the mold of the hot forging device increases. On the other hand, a preferable upper limit of the finishing temperature is 1250 ° C.
　熱間鍛造後に、組織の均質化を図るため、例えば、４００～７００℃の温度域で３０～３００分保持した後、放冷する熱処理を行ってもよい。 (4) After the hot forging, in order to homogenize the structure, for example, a heat treatment of maintaining the temperature in a temperature range of 400 to 700 ° C. for 30 to 300 minutes and then allowing it to cool may be performed.
　６－２．切削加工
　上述の熱間加工後の棒鋼に対して、切削加工を実施して所定の形状の素形材にする。 6-2. Cutting The above-mentioned hot-rolled steel bar is subjected to cutting to obtain a shaped material having a predetermined shape.
　６－３．窒化処理
　切削加工された素形材に対して、窒化処理を実施する。本実施形態では、周知の窒化処理が採用される。窒化処理は例えば、ガス窒化、塩浴窒化、イオン窒化等である。窒化中に炉内に導入するガスは、ＮＨ３のみであってもよいし、ＮＨ３と、Ｎ２および／またはＨ２とを含有する混合気体であってもよい。また、これらのガスに、浸炭性のガスを含有して、軟窒化処理を実施してもよい。したがって、本明細書にいう「窒化」とは「軟窒化」も含む。 6-3. Nitriding treatment Nitriding treatment is performed on the cut and shaped material. In the present embodiment, a known nitriding process is employed. The nitriding treatment is, for example, gas nitriding, salt bath nitriding, ion nitriding, or the like. Gas introduced into the furnace during nitridation, it may be only NH 3, and NH 3, or may be a mixed gas containing a N 2 and / or H 2. Further, a nitrocarburizing treatment may be performed by containing a carburizing gas in these gases. Therefore, the term “nitriding” in this specification includes “soft nitriding”.
　ガス軟窒化処理を実施する場合、例えば、吸熱型変成ガス（ＲＸガス）とアンモニアガスとを１：１に混合した雰囲気中で、均熱温度を５５０～６２０℃にして１～３時間均熱すればよい。 When performing the gas nitrocarburizing treatment, for example, the soaking temperature is set to 550 to 620 ° C. in an atmosphere in which an endothermic transformation gas (RX gas) and ammonia gas are mixed at a ratio of 1: 1 for 1 to 3 hours. do it.
　以上の製造工程により製造された機械部品は、優れた疲労強度を有する。 機械 Machine parts manufactured by the above manufacturing processes have excellent fatigue strength.
　以下、実施例によって本発明をより具体的に説明するが、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
　まず、表１に示す化学組成を有する鋼種のインゴットを作製した。 First, steel ingots having the chemical compositions shown in Table 1 were produced.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　そして、上記インゴットを１２５０℃に加熱してから熱間圧延を施して、円形の断面を持つ丸棒を製造し、試験材とした。試験Ｎｏ．１～２６では、直径７５ｍｍの試験材とし、試験Ｎｏ．２７では、直径５０ｍｍの試験材とした。熱間圧延後の５００℃までの平均冷却速度を表２に示す。 Then, the ingot was heated to 1250 ° C. and then subjected to hot rolling to produce a round bar having a circular cross section, which was used as a test material. Test No. In Nos. 1 to 26, test materials having a diameter of 75 mm were used. In No. 27, a test material having a diameter of 50 mm was used. Table 2 shows the average cooling rate to 500 ° C. after hot rolling.
　次に、各試験材を用いて、金属組織観察および切断性評価試験を実施した。まず、各試験材の長手方向に垂直な断面を切り出した後、ナイタルで腐食し、組織を現出させた。そして、丸棒状の試験材の半径をＲとした場合に、丸棒の中心位置、ならびに、丸棒の中心から半径方向の距離が、（３／４）×Ｒ、（２／４）×Ｒ、および（１／４）×Ｒとなる位置を中心として、観察用試験片（計４か所）を採取した。その後、それぞれの観察用試験片を用いて倍率５００倍の光学顕微鏡写真（視野：２１０μｍ×１６０μｍ）を撮影し、画像解析から初析フェライトおよびパーライトの合計面積率を求め、平均値を算出した。 Next, using each test material, a metallographic structure observation and cutability evaluation test were performed. First, a cross section perpendicular to the longitudinal direction of each test material was cut out, and then corroded with nital to reveal a structure. When the radius of the round bar-shaped test material is R, the center position of the round bar and the radial distance from the center of the round bar are (3/4) × R and (2/4) × R , And (１ ／) × R, the test specimens for observation (4 places in total) were collected. Thereafter, an optical microscope photograph (magnification: 210 μm × 160 μm) was photographed at a magnification of 500 times using each observation specimen, and the total area ratio of proeutectoid ferrite and pearlite was determined from image analysis, and the average value was calculated.
　続いて、各試験材を切断し、バンドソーによる切断時の電流値を測定することで、切断性を評価した。各丸棒を約２００秒で切断できるように鋸刃の送り速度を一定に定め、比較材として同径のＳＣｒ４２０の焼きならし材を切断し、その際の最大の電力値を記録した。各試験材を同じ条件で切断し、最大の電力値がＳＣｒ４２０を切断した際の最大の電力値の１．３倍以下である場合、切断性が特に優れ、１．３倍を超え１．５倍以下である場合、切断性が優れ、１．５倍を超える場合、切断性に劣るとみなし、試験を中断して、切削速度を落として切断した。切断性が特に優れるものを評価Ａ、切断性が優れるものを評価Ｂ、切断性が劣るものを評価Ｃとした。切断性が劣る結果となった試験材については、以降の試験を行わなかった。 Subsequently, each test material was cut, and the cutting property was evaluated by measuring the current value when cutting with a band saw. The feed rate of the saw blade was fixed so that each round bar could be cut in about 200 seconds, and a normalizing material of the same diameter, SCr420, was cut as a comparative material, and the maximum power value at that time was recorded. When each test material is cut under the same conditions and the maximum power value is 1.3 times or less of the maximum power value when the SCr420 is cut, the cutability is particularly excellent, and the cut power exceeds 1.3 times and exceeds 1.5 times. If the ratio is not more than twice, the cutting performance is excellent, and if it exceeds 1.5 times, it is considered that the cutting performance is inferior, and the test was interrupted to cut at a reduced cutting speed. Particularly excellent cutability was evaluated as A, excellent cutability was evaluated as B, and poor cutability was evaluated as C. Subsequent tests were not performed on test materials that resulted in poor cuttability.
　その後、各試験材を１２５０℃に加熱し、仕上げ温度がおよそ１０００℃程度となる条件で、減面率５１～５６％となる条件でより小さい丸棒に熱間鍛造し、室温まで放冷した。具体的には、直径７５ｍｍの試験材は直径５０ｍｍの丸棒に熱間鍛造した。直径５０ｍｍの試験材は直径３５ｍｍの丸棒に熱間鍛造する予定であったが、上述の通り直径５０ｍｍの試験材は切断性が劣る結果となったため、熱間鍛造は行わなかった。なお、放冷時の冷却速度は、直径５０ｍｍの丸棒の場合は０．６０℃／ｓとなった。 Thereafter, each test material was heated to 1250 ° C., hot forged into a smaller round bar under the condition that the finishing temperature was about 1000 ° C., and the area reduction rate was 51 to 56%, and allowed to cool to room temperature. . Specifically, a test material having a diameter of 75 mm was hot forged into a round bar having a diameter of 50 mm. The test material having a diameter of 50 mm was to be hot-forged into a round bar having a diameter of 35 mm. However, as described above, the test material having a diameter of 50 mm resulted in inferior cutability, and thus hot forging was not performed. The cooling rate during cooling was 0.60 ° C./s for a round bar having a diameter of 50 mm.
　表２に示すように、熱間鍛造後の丸棒の一部には、組織の均質化を図るために、５５０～６２０℃で６０分保持して、その後に室温まで放冷する熱処理を施した。試験Ｎｏ．２６のみは、上記工程のとおり丸棒に鍛造した後、室温まで冷却する際にセラミックスシートをかぶせて冷却速度が遅い状態で室温まで冷却した。この時の冷却速度は、０．２５℃／ｓとなった。 As shown in Table 2, a part of the round bar after hot forging was subjected to a heat treatment of maintaining the temperature at 550 to 620 ° C. for 60 minutes and then cooling to room temperature in order to homogenize the structure. did. Test No. For only 26, after forging into a round bar as in the above process, when cooling to room temperature, it was covered with a ceramic sheet and cooled to room temperature at a low cooling rate. The cooling rate at this time was 0.25 ° C./s.
　＜硬さ測定用試験片、小野式回転曲げ疲労試験片の作製＞
　φ５０の各試験材の丸棒から、元の丸棒の中心と表面とを結ぶ直線の中点を中心とした１辺の長さが１３ｍｍの正方形の断面を持つ、長さ１００ｍｍの硬さ測定用の試験片を切削加工により作製した。すなわち、硬さ測定用の試験片（正方形）の中心は、元のφ５０の試験材である丸棒において、中心と表面との中間地点、すなわちＲ／２の位置に対応する。 <Preparation of hardness test specimen and Ono-type rotary bending fatigue test specimen>
From a round bar of each test material of φ50, hardness measurement of 100 mm length with a 13 mm square cross section with a side of 13 mm centered on the midpoint of a straight line connecting the center of the original round bar and the surface Test specimens were prepared by cutting. That is, the center of the test piece (square) for hardness measurement corresponds to the middle point between the center and the surface, that is, the position of R / 2, in the original round bar of φ50 test material.
　さらに、各試験材から、図１に示す小野式回転曲げ疲労試験片Ａを複数採取した。試験片中央部の平滑部の直径は１０ｍｍであり、長さ方向の中心には、深さ１ｍｍ、曲率半径３ｍｍの切欠きを設けた。疲労試験片Ａは、その回転軸が、元の試験材におけるＲ／２の位置から１．０ｍｍ以内の位置となるように、切削加工により採取した。 Furthermore, a plurality of Ono-type rotating bending fatigue test pieces A shown in FIG. 1 were collected from each test material. The diameter of the smooth portion at the center of the test piece was 10 mm, and a notch having a depth of 1 mm and a radius of curvature of 3 mm was provided at the center in the length direction. The fatigue test piece A was sampled by cutting such that the rotation axis was within 1.0 mm from the position of R / 2 in the original test material.
　さらに、各試験材から、図２に示す小野式回転曲げ疲労試験片Ｂを複数採取した。試験片中央部の平滑部の直径は８ｍｍであった。疲労試験片Ｂも、その回転軸が、元の試験材におけるＲ／２の位置から１．０ｍｍ以内の位置となるように、切削加工により採取した。 Furthermore, a plurality of Ono-type rotating bending fatigue test pieces B shown in FIG. 2 were collected from each test material. The diameter of the smooth part at the center of the test piece was 8 mm. The fatigue test piece B was also sampled by cutting so that the rotation axis was within 1.0 mm from the position of R / 2 in the original test material.
　採取された硬さ測定用の試験片、および２種類の形状の小野式回転曲げ疲労試験片に対して、６００℃で２時間の窒化処理を実施した。窒化処理は、アンモニアガスおよびＲＸガスを流量が１：１になるようにして炉内に導入することで行った。６００℃での保持時間が２時間となった後、試験片を熱処理炉から取り出し、１００℃の油で急冷した。 窒 化 Nitriding treatment was performed at 600 ° C. for 2 hours on the collected test pieces for hardness measurement and the Ono-type rotating bending fatigue test pieces having two types of shapes. The nitriding treatment was performed by introducing ammonia gas and RX gas into the furnace at a flow rate of 1: 1. After the holding time at 600 ° C. was 2 hours, the test piece was taken out of the heat treatment furnace and quenched with 100 ° C. oil.
　＜窒化後の硬さ測定および組織観察＞
　窒化後の硬さ測定用の試験片の端部から１０ｍｍ位置を切断し、切断面を観察できるように樹脂に埋め込み、硬さ測定用のサンプルを作製した。作製したサンプルの表面から０．０５ｍｍピッチでＪＩＳ　Ｚ　２２４４に基づくビッカース硬さの測定を行った。試験力は２．９４Ｎとした。測定深さ位置ごとに試験を３回行い、得られた３つのビッカース硬さの平均値を、その深さ位置の硬さと定義した。測定点間の硬さは、その深さ位置を挟む二つの測定点の硬さを結ぶ直線上に乗ると仮定した。そして、表面から０．０５ｍｍ深さ位置の硬さを窒化後の表層硬さと定義した。 <Hardness measurement and structure observation after nitriding>
A 10 mm position was cut from the end of the test specimen for hardness measurement after nitriding, and embedded in resin so that the cut surface could be observed to prepare a sample for hardness measurement. Vickers hardness was measured at a pitch of 0.05 mm from the surface of the manufactured sample based on JIS Z 2244. The test force was 2.94N. The test was performed three times at each measurement depth position, and the average value of the obtained three Vickers hardness values was defined as the hardness at that depth position. The hardness between the measurement points was assumed to be on a straight line connecting the hardness of the two measurement points sandwiching the depth position. The hardness at a depth of 0.05 mm from the surface was defined as the surface hardness after nitriding.
　また、各埋め込みサンプルの中央付近の硬さを試験力２．９４Ｎで各５点測定し、得られた５つのビッカース硬さの平均値を、窒化後の芯部硬さと定義した。さらに、窒化層のうち、その硬さが芯部硬さよりも５０ＨＶ高くなる点までの、表面からの距離を硬化深さと定義し、硬化深さを求めた。 Furthermore, the hardness near the center of each embedded sample was measured at five points at a test force of 2.94 N, and the average value of the five Vickers hardness values was defined as the core hardness after nitriding. Further, in the nitrided layer, the distance from the surface to the point at which the hardness becomes 50 HV higher than the core hardness was defined as the cured depth, and the cured depth was determined.
　続いて、硬さ測定後のサンプルをナイタルで腐食し、組織を現出させた。被検面の中心（すなわち、熱間鍛造後のφ５０丸棒のＲ／２の位置）からφ２．０ｍｍの範囲から、異なる視野をランダムに４箇所選び、倍率５００倍の光学顕微鏡写真（視野：２１０μｍ×１６０μｍ）を撮影し、画像解析から初析フェライトおよびパーライトの合計面積率を求めた。上記の４箇所から撮影した写真から個々に求めた初析フェライトおよびパーライトの合計面積率の算術平均を、表面から深さ方向に２ｍｍの位置までで、かつ硬化層を除く領域での初析フェライトおよびパーライトの合計での平均面積率とした。 Subsequently, the sample after hardness measurement was corroded with nital to reveal the structure. Four different visual fields were randomly selected from a range of φ2.0 mm from the center of the test surface (that is, the position of R / 2 of the φ50 round bar after hot forging), and an optical microscope photograph with a magnification of 500 times (visual field: 210 μm × 160 μm), and the total area ratio of pro-eutectoid ferrite and pearlite was determined from image analysis. The arithmetic mean of the total area ratio of proeutectoid ferrite and pearlite individually obtained from the photographs taken from the above four places was calculated from the surface up to a position of 2 mm in the depth direction and in the region excluding the hardened layer. And the average area ratio of the total of pearlite.
　なお、組織観察に用いた視野は、鍛造後の丸棒の横断面において、表面から１２．５ｍｍ深さ位置付近である。切削加工を模擬して丸棒の表面を５ｍｍ削ったとしても、上記組織観察に用いた視野は、表面から７．５ｍｍ深さ位置付近となる。上記組織観察に用いた視野の組織は、その視野よりも表層に近い組織と比べて鍛造後の冷却時の冷却速度が遅いため、その視野よりも表層に近い組織のフェライトおよびパーライトの面積率は、上記組織観察に用いた視野の組織よりも小さい。また、疲労試験片Ａおよび疲労試験Ｂにおいても、その中心軸が元の試験材におけるＲ／２位置付近に位置する。そのため、いずれの疲労試験片にも、表層に、元の試験材におけるＲ／２位置よりも初析フェライトおよびパーライトの面積率の合計が少ない領域が存在する。 視野 The field of view used for the structure observation is near the position of 12.5 mm depth from the surface in the cross section of the round bar after forging. Even if the surface of the round bar is shaved by 5 mm to simulate the cutting process, the field of view used for the above-described structure observation is in the vicinity of a position 7.5 mm deep from the surface. The structure of the field of view used for the above structure observation has a lower cooling rate during cooling after forging than the structure closer to the surface layer than the field of view, so the area ratio of ferrite and pearlite of the structure closer to the surface layer than the field of view is smaller. Is smaller than the tissue in the visual field used for the above-described tissue observation. Also, in the fatigue test pieces A and B, the center axis is located near the R / 2 position in the original test material. Therefore, in each of the fatigue test pieces, there is a region in the surface layer where the total area ratio of pro-eutectoid ferrite and pearlite is smaller than the R / 2 position in the original test material.
　＜小野式回転曲げ疲労試験＞
　上述の窒化処理がされた２種類の形状の小野式回転曲げ疲労試験片を用いて、小野式回転曲げ疲労試験を実施した。ＪＩＳ　Ｚ　２２７４（１９７８）に準拠した回転曲げ疲労試験を室温（２５℃）の大気雰囲気中において実施した。試験は、回転数３０００ｒｐｍの両振り条件で実施した。繰り返し数１．０×１０７回まで破断しなかった試験片のうち、最も高い応力を、その試験番号の疲労強度（ＭＰａ）と定義した。２種類の試験片を用いた試験において、疲労強度がいずれも６００ＭＰａ以上である場合、疲労強度に優れると判断した。 <Ono-type rotating bending fatigue test>
An Ono-type rotary bending fatigue test was performed using two types of Ono-type rotary bending fatigue test pieces subjected to the nitriding treatment described above. A rotary bending fatigue test based on JIS Z 2274 (1978) was performed in an air atmosphere at room temperature (25 ° C.). The test was performed under a double swing condition at a rotation speed of 3000 rpm. Among the test pieces that did not break until the number of repetitions of 1.0 × 10 7 times, the highest stress was defined as the fatigue strength (MPa) of the test number. In the test using two types of test pieces, when the fatigue strength was 600 MPa or more, it was determined that the fatigue strength was excellent.
　表２に試験結果を示す。 Table 2 shows the test results.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　なお、表２中の「疲労強度Ａ」は小野式回転曲げ疲労試験片Ａを用いて行った試験で得られた疲労強度（ＭＰａ）を意味し、「疲労強度Ｂ」は小野式回転曲げ疲労試験片Ｂを用いて行った試験で得られた疲労強度（ＭＰａ）を意味する。 "Fatigue strength A" in Table 2 means the fatigue strength (MPa) obtained by a test using Ono-type rotating bending fatigue test piece A, and "Fatigue strength B" is Ono-type rotating bending fatigue. It means the fatigue strength (MPa) obtained in the test using the test piece B.
　表２を参照して、試験Ｎｏ．１～１８は、棒鋼の化学組成および金属組織が規定を満足する本発明例である。そのため、これらの鋼は、良好な切断性を有する。また、窒化後には、硬化深さが０．２６ｍｍを超えていた。その結果、疲労強度Ａが６２０ＭＰａ以上であり、疲労強度Ｂが６１０ＭＰａ以上であるため、種々の応力勾配形状の部品となっても高い疲労強度を得ることが期待できる。 試 験 Referring to Table 2, test no. Nos. 1 to 18 are examples of the present invention in which the chemical composition and metal structure of the steel bar satisfy the requirements. Therefore, these steels have good cutting properties. Also, after nitriding, the curing depth exceeded 0.26 mm. As a result, since the fatigue strength A is 620 MPa or more and the fatigue strength B is 610 MPa or more, it can be expected that high fatigue strength can be obtained even for components having various stress gradient shapes.
　これに対して、本発明の規定から外れた試験Ｎｏ．１９～２７の比較例の場合には、目標とする性能が得られていない。 に 対 し て On the other hand, test Nos. In the case of Comparative Examples 19 to 27, the target performance was not obtained.
　試験Ｎｏ．１９では、Ｍｎ含有量が本発明の規定範囲よりも低いため、窒化後の芯部硬さおよび表層硬さが低かった。そのため、疲労強度Ａが５５５ＭＰａ、疲労強度Ｂが５７０ＭＰａと低くなった。 Test No. In No. 19, since the Mn content was lower than the specified range of the present invention, the core hardness and the surface hardness after nitriding were low. Therefore, the fatigue strength A was reduced to 555 MPa, and the fatigue strength B was reduced to 570 MPa.
　試験Ｎｏ．２０では、Ｍｎ含有量が本発明の規定範囲よりも高いため、棒鋼中に初析フェライトおよびパーライトが含まれず、切断性が劣る結果となった。 Test No. In No. 20, since the Mn content was higher than the specified range of the present invention, the bar steel did not contain pro-eutectoid ferrite and pearlite, resulting in poor cuttability.
　試験Ｎｏ．２１では、Ｃ含有量が本発明の規定範囲よりも低いため、窒化後の芯部硬さが低かった。そのため、硬化深さは深いものの内部破壊を抑制できず、疲労強度Ｂが５９０ＭＰａと低くなった。 Test No. In No. 21, the core content after nitriding was low because the C content was lower than the specified range of the present invention. Therefore, although the hardening depth was deep, internal destruction could not be suppressed, and the fatigue strength B was low at 590 MPa.
　試験Ｎｏ．２２では、Ｃ含有量が本発明の規定範囲よりも高いため、棒鋼中に初析フェライトおよびパーライトの合計面積率が低くなり、切断性が劣る結果となった。 Test No. In No. 22, since the C content was higher than the specified range of the present invention, the total area ratio of proeutectoid ferrite and pearlite in the steel bar was low, resulting in poor cuttability.
　試験Ｎｏ．２３では、Ｖ含有量が本発明の規定範囲よりも低いため、窒化後の芯部硬さと表層硬さが低かった。そのため、疲労強度Ａが５６０ＭＰａ、疲労強度Ｂが５５０ＭＰａと低くなった。 Test No. In No. 23, since the V content was lower than the specified range of the present invention, the core hardness and the surface hardness after nitriding were low. Therefore, the fatigue strength A was reduced to 560 MPa, and the fatigue strength B was reduced to 550 MPa.
　試験Ｎｏ．２４では、Ｃｒ含有量が本発明の規定範囲よりも高いため、硬化深さが浅かった。そのため、内部破壊が抑制できず疲労強度Ｂが５６０ＭＰａと低くなった。 Test No. In No. 24, the hardening depth was shallow because the Cr content was higher than the specified range of the present invention. Therefore, internal fracture could not be suppressed, and the fatigue strength B was low at 560 MPa.
　試験Ｎｏ．２５で用いた鋼Ｗは、一般的な低合金鋼であるＳＣＭ４２０に相当するものである。Ｖを含まず、Ｍｎ含有量が本発明の規定範囲よりも低く、さらに、Ｃｒ含有量が本発明の規定範囲よりも高いため、窒化後の芯部硬さが低く、硬化深さも浅かった。そのため、疲労強度Ｂが４９０ＭＰａと低くなった。 Test No. Steel W used in No. 25 corresponds to SCM420 which is a general low alloy steel. Since V was not contained and the Mn content was lower than the specified range of the present invention and the Cr content was higher than the specified range of the present invention, the core hardness after nitriding was low and the hardening depth was shallow. Therefore, the fatigue strength B was reduced to 490 MPa.
　試験Ｎｏ．２６では、鋼Ａを用いており、化学組成は本発明の規定範囲内であるが、窒化処理後の金属組織中のフェライトおよびパーライトの合計面積率が高いため、Ｖが有効に作用せず、表層硬さが低く、硬化深さも浅かった。そのため、疲労強度Ａが５３０ＭＰａと低くなった。 Test No. In No. 26, steel A was used, and the chemical composition was within the range specified by the present invention. However, since the total area ratio of ferrite and pearlite in the metal structure after the nitriding treatment was high, V did not act effectively, The surface hardness was low and the hardening depth was shallow. Therefore, the fatigue strength A was reduced to 530 MPa.
　試験Ｎｏ．２７では、棒鋼製造時における熱間鍛造後の平均冷却速度が０．４℃／秒を超えているため、棒鋼中に初析フェライトおよびパーライトが含まれず、切断性が劣る結果となった。

  Test No. In No. 27, since the average cooling rate after hot forging during the production of the bar exceeded 0.4 ° C./sec, the bar did not contain pro-eutectoid ferrite and pearlite, resulting in inferior cuttability.

Claims (4)

  1. 　化学組成が、質量％で、
    　Ｃ：０．０９～０．３０％、
    　Ｓｉ：０．０１～０．５０％、
    　Ｍｎ：２．２０％を超えて３．５０％以下、
    　Ｐ：０．０５０％以下、
    　Ｓ：０．００１～０．１００％、
    　Ｃｒ：０．０２～０．８０％、
    　Ｖ：０．１０～０．４０％、
    　Ａｌ：０．００１～０．０８０％、
    　Ｎ：０．０２５０％以下、
    　Ｏ：０．００５０％以下、
    　Ｔｉ：０～０．０５０％、
    　Ｎｂ：０～０．０５％、
    　Ｍｏ：０～０．１０％、
    　Ｃｕ：０～０．３０％、
    　Ｎｉ：０～０．３０％、
    　Ｂｉ：０～０．３５％、
    　Ｂ：０～０．００５０％、
    　残部：Ｆｅおよび不純物であり、
    　金属組織が、全体の平均面積％で、
    　初析フェライトおよびパーライトの合計が３５％以上である、
    　窒化用棒鋼。     Chemical composition in mass%
    C: 0.09 to 0.30%,
    Si: 0.01 to 0.50%,
    Mn: more than 2.20% and not more than 3.50%,
    P: 0.050% or less,
    S: 0.001 to 0.100%,
    Cr: 0.02 to 0.80%,
    V: 0.10 to 0.40%,
    Al: 0.001 to 0.080%,
    N: 0.0250% or less,
    O: 0.0050% or less,
    Ti: 0 to 0.050%,
    Nb: 0 to 0.05%,
    Mo: 0 to 0.10%,
    Cu: 0 to 0.30%,
    Ni: 0 to 0.30%,
    Bi: 0 to 0.35%,
    B: 0 to 0.0050%,
    The balance: Fe and impurities,
    The metal structure is the average area% of the whole,
    The total of pro-eutectoid ferrite and pearlite is 35% or more;
    Steel bars for nitriding.
  2. 　前記金属組織が、全体の平均面積％で、
    　初析フェライトおよびパーライトの合計が５０％以上である、
    　請求項１に記載の窒化用棒鋼。     The metal structure is an average area% of the whole,
    The total of pro-eutectoid ferrite and pearlite is 50% or more;
    The bar steel for nitriding according to claim 1.
  3. 　前記棒鋼が丸鋼であり、当該丸鋼の直径が７０ｍｍ以上である、
    　請求項１または請求項２に記載の窒化用棒鋼。     The steel bar is a round bar, the diameter of the round bar is 70 mm or more,
    The steel bar for nitriding according to claim 1 or 2.
  4. 　表面に硬化層を有する機械部品であって、
    　前記硬化層を除く領域における化学組成が、質量％で、
    　Ｃ：０．０９～０．３０％、
    　Ｓｉ：０．０１～０．５０％、
    　Ｍｎ：２．２０％を超えて３．５０％以下、
    　Ｐ：０．０５０％以下、
    　Ｓ：０．００１～０．１００％、
    　Ｃｒ：０．０２～０．８０％、
    　Ｖ：０．１０～０．４０％、
    　Ａｌ：０．００１～０．０８０％、
    　Ｎ：０．０２５０％以下、
    　Ｏ：０．００５０％以下、
    　Ｔｉ：０～０．０５０％、
    　Ｎｂ：０～０．０５％、
    　Ｍｏ：０～０．１０％、
    　Ｃｕ：０～０．３０％、
    　Ｎｉ：０～０．３０％、
    　Ｂｉ：０～０．３５％、
    　Ｂ：０～０．００５０％、
    　残部：Ｆｅおよび不純物であり、
    　前記表面から深さ方向に２ｍｍの位置までで、かつ前記硬化層を除く領域に、平均面積％で、初析フェライトおよびパーライトの合計が４０％以下となる領域を有し、
    　硬化深さが０．２６ｍｍ超である、
    　機械部品。
     

          A machine component having a hardened layer on its surface,
    The chemical composition in a region excluding the hardened layer is represented by mass%,
    C: 0.09 to 0.30%,
    Si: 0.01 to 0.50%,
    Mn: more than 2.20% and not more than 3.50%,
    P: 0.050% or less,
    S: 0.001 to 0.100%,
    Cr: 0.02 to 0.80%,
    V: 0.10 to 0.40%,
    Al: 0.001 to 0.080%,
    N: 0.0250% or less,
    O: 0.0050% or less,
    Ti: 0 to 0.050%,
    Nb: 0 to 0.05%,
    Mo: 0 to 0.10%,
    Cu: 0 to 0.30%,
    Ni: 0 to 0.30%,
    Bi: 0 to 0.35%,
    B: 0 to 0.0050%,
    The balance: Fe and impurities,
    In a region up to a position of 2 mm in the depth direction from the surface, and in a region excluding the hardened layer, an average area% has a region in which the total of proeutectoid ferrite and pearlite is 40% or less,
    The curing depth is more than 0.26 mm,
    Mechanical parts.


PCT/JP2018/024469 2018-06-27 2018-06-27 Reinforcing bar for nitriding, and machine component WO2020003425A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP2018565897A JP6525115B1 (en) 2018-06-27 2018-06-27 Nitriding bars and machine parts
PCT/JP2018/024469 WO2020003425A1 (en) 2018-06-27 2018-06-27 Reinforcing bar for nitriding, and machine component

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2018/024469 WO2020003425A1 (en) 2018-06-27 2018-06-27 Reinforcing bar for nitriding, and machine component

Publications (1)

Publication Number Publication Date
WO2020003425A1 true WO2020003425A1 (en) 2020-01-02

Family

ID=66730609

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2018/024469 WO2020003425A1 (en) 2018-06-27 2018-06-27 Reinforcing bar for nitriding, and machine component

Country Status (2)

Country Link
JP (1) JP6525115B1 (en)
WO (1) WO2020003425A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112239842A (en) * 2020-10-12 2021-01-19 山东大学 Surface layer tellurium infiltration weakening auxiliary processing method for nickel and chromium alloy cutting
WO2022124274A1 (en) * 2020-12-08 2022-06-16 大同特殊鋼株式会社 Ferrite-based stainless steel welding wire

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000063935A (en) * 1998-08-20 2000-02-29 Mitsubishi Seiko Muroran Tokushuko Kk Production of nitrided part
EP1700925A1 (en) * 2005-03-09 2006-09-13 Imatra Steel Oy Ab High-strength air cooled steel alloy, manufacturing method and hot worked product
WO2010070958A1 (en) * 2008-12-19 2010-06-24 新日本製鐵株式会社 Hardfacing steel for machine structure, and steel component for machine structure
JP2014043609A (en) * 2012-08-27 2014-03-13 Nippon Steel & Sumitomo Metal Age hardening type steel for soft nitriding
JP2016056450A (en) * 2014-09-05 2016-04-21 Ｊｆｅスチール株式会社 Steel and component for soft nitriding and manufacturing method therefor
WO2016098143A1 (en) * 2014-12-18 2016-06-23 新日鐵住金株式会社 Method for manufacturing nitrided component and steel for nitriding

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000063935A (en) * 1998-08-20 2000-02-29 Mitsubishi Seiko Muroran Tokushuko Kk Production of nitrided part
EP1700925A1 (en) * 2005-03-09 2006-09-13 Imatra Steel Oy Ab High-strength air cooled steel alloy, manufacturing method and hot worked product
WO2010070958A1 (en) * 2008-12-19 2010-06-24 新日本製鐵株式会社 Hardfacing steel for machine structure, and steel component for machine structure
JP2014043609A (en) * 2012-08-27 2014-03-13 Nippon Steel & Sumitomo Metal Age hardening type steel for soft nitriding
JP2016056450A (en) * 2014-09-05 2016-04-21 Ｊｆｅスチール株式会社 Steel and component for soft nitriding and manufacturing method therefor
WO2016098143A1 (en) * 2014-12-18 2016-06-23 新日鐵住金株式会社 Method for manufacturing nitrided component and steel for nitriding

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112239842A (en) * 2020-10-12 2021-01-19 山东大学 Surface layer tellurium infiltration weakening auxiliary processing method for nickel and chromium alloy cutting
WO2022124274A1 (en) * 2020-12-08 2022-06-16 大同特殊鋼株式会社 Ferrite-based stainless steel welding wire

Also Published As

Publication number Publication date
JP6525115B1 (en) 2019-06-05
JPWO2020003425A1 (en) 2020-07-02

Similar Documents

Publication Publication Date Title
EP2514847B1 (en) Surface layer-hardened steel part and method of manufacturing the same
JP4956146B2 (en) Case-hardened steel excellent in forgeability and prevention of grain coarsening, its manufacturing method, and carburized parts
JP4888277B2 (en) Hot rolled steel bar or wire rod
KR101617985B1 (en) Case hardening steel material with little heat-treatment strain
JP4729135B2 (en) Nitriding steel and nitriding parts
JP5333682B2 (en) Rolled steel bar or wire rod for hot forging
WO2015125915A1 (en) Steel material for induction hardening
US20060225814A1 (en) Crankshaft and method for manufacturing same
WO2017090738A1 (en) Steel, carburized steel component, and carburized steel component production method
WO2017090731A1 (en) Steel, carburized steel component, and carburized steel component production method
JP5630523B2 (en) Steel sheet for nitriding treatment and method for producing the same
JP4609585B2 (en) Soft nitriding steel, soft nitriding steel and crankshaft
JP6525115B1 (en) Nitriding bars and machine parts
JP6911606B2 (en) Nitriding parts and nitriding method
JPH10306343A (en) Steel for soft-nitriding, excellent in cold forgeability and pitting resistance
JP6477904B2 (en) Crankshaft rough profile, nitrided crankshaft, and method of manufacturing the same
JP4464861B2 (en) Case hardening steel with excellent grain coarsening resistance and cold workability
JP2009167505A (en) Rough shaped article for quenched and tempered nitrocarburized crankshaft and quenched and tempered nitrocarburized crankshaft
JP4488228B2 (en) Induction hardening steel
JP2003193128A (en) Method of producing carburized and quenched member, and carburized and quenched member
JP2012077333A (en) Nitriding steel excellent in machinability, and nitrided part
JP5768734B2 (en) Rolled steel for cold forging and nitriding
JP5582296B2 (en) Iron-based material and manufacturing method thereof
JP7436826B2 (en) Nitrided parts and manufacturing method of nitrided parts
JP2007002292A (en) Non-heat-treated steel to be nitrocarburized

Legal Events

Date Code Title Description
ENP Entry into the national phase

Ref document number: 2018565897

Country of ref document: JP

Kind code of ref document: A

121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 18924886

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 18924886

Country of ref document: EP

Kind code of ref document: A1