EP1167561A2 - Acier pour cémentation et carbonitruration - Google Patents

Acier pour cémentation et carbonitruration Download PDF

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Publication number
EP1167561A2
EP1167561A2 EP00125344A EP00125344A EP1167561A2 EP 1167561 A2 EP1167561 A2 EP 1167561A2 EP 00125344 A EP00125344 A EP 00125344A EP 00125344 A EP00125344 A EP 00125344A EP 1167561 A2 EP1167561 A2 EP 1167561A2
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Prior art keywords
steel
addition
carburizing
impact strength
carburization
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German (de)
English (en)
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EP1167561A3 (fr
Inventor
Tatsuo Fukuzumi
Hideo Ueno
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Mitsubishi Steel Muroran Inc
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Mitsubishi Steel Muroran Inc
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Priority claimed from JP2000193780A external-priority patent/JP3253293B2/ja
Application filed by Mitsubishi Steel Muroran Inc filed Critical Mitsubishi Steel Muroran Inc
Publication of EP1167561A2 publication Critical patent/EP1167561A2/fr
Publication of EP1167561A3 publication Critical patent/EP1167561A3/fr
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/28—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for plain shafts
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/32—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for gear wheels, worm wheels, or the like
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/28—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in one step
    • C23C8/30—Carbo-nitriding
    • C23C8/32—Carbo-nitriding of ferrous surfaces
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working

Definitions

  • the present invention relates to a steel to be subjected to carburizing and carbonitriding for the use in gears and shafts, which are required to have high pitting fatigue strength and high impact strength.
  • Examples of conventional techniques aimed at reducing the grain-boundary oxide phases, which may cause fatigue cracks, in order to achieve higher flexural fatigue strength include those that entail reducing the content of elements more readily oxidizable than Fe (such as Si, Mn, and Cr) and adjusting hardenability and mechanical properties by means of elements less readily oxidizable than Fe (such as Ni and Mo); and those that entail obtaining surface-compression residual stress by employing shot peening to delay the spreading of fatigue cracks. According to some reports, adding Si or V in order to improve pitting fatigue strength has been studied as a promising means because of its ability to improve flexural fatigue strength.
  • Gears and shafts that are more compact and lightweight and are capable of withstanding higher levels of stress loading are currently needed in order to be able to reduce the weight and to increase the engine output of automobiles and industrial machinery. Improved pitting fatigue strength and impact strength are needed as a result. With the conventional techniques, however, it is difficult to achieve both goals at the same time.
  • the means for attaining the stated object resides in improving the temper hardness of the carburized or carbonitrided steel by increasing the Si content thereof, and in improving the fracture toughness of the carburized layer and the core by adding Ni and Mo either singly or in combination thereof.
  • the primary goal of adjusting these chemical components is to improve temper hardness by increasing the Si content and to improve the fracture toughness of the carburized layer and the core by adding Ni and Mo either singly or in combination thereof.
  • temper hardness and carburization impact strength are the most important factors that govern the pitting fatigue and impact strength of carburized gears.
  • Table 1 shows the chemical compositions of inventive and comparative steels used to evaluate these factors.
  • first inventive steel corresponds to the above-prescribed first feature, second feature and third feature, respectively, of the present invention.
  • These types of steel were melted in a highfrequency vacuum melting furnace.
  • the ingots thus obtained were heated to 1250°C, cogged to a diameter of 30 mm, and normalized at 925°C.
  • the blanks were machined, yielding a single test piece, having a shape shown in Fig. 1, for evaluating temper hardness and three test pieces, shaped as shown in Fig. 2, for evaluating impact strength. All these test pieces were carburized, quenched, and tempered under the conditions shown in Fig. 3.
  • the test piece for determining temper hardness shown in Fig. 1 was air-cooled after being kept for 8 hours in an electric furnace heated at 250°C under conditions simulating those under which frictional heat is generated during the rolling of a gear.
  • the air-cooled test pieces were cut perpendicular to the longitudinal direction, hardness was measured every 10 ⁇ m with a Microvickers hardness meter up to a depth of 50 ⁇ m from the surface at two arbitrary locations (at 90° intervals), and the results were averaged. These results are shown in Table 1 above as post-temper hardness values.
  • the three test pieces, shown in Fig. 2, for each of different steels for determining carburizing impact were subjected to Charpy impact tests, and average Charpy impact values were calculated. These results are shown in Table 1 above as carburization impact strength values. The data are described in detail below.
  • Fig. 4 shows the relation between temper hardness and Si content. It can be seen in the drawing that when the Si content is 0.40 wt% or higher, the temper hardness is 700 HV or greater, which is higher than the temper hardness of a steel product having an Si content lower than 0.40 wt%. This is because surface hardness can be kept at a high level (even after tempering has been performed under conditions simulating those created when frictional heat is generated during the rolling of a gear) by increasing the Si content, which enhances tempering/softening resistance as previously indicated.
  • Fig. 5 shows the relation between carburization impact strength and Si content. It can be seen that when the combined content of Ni and Mo is less than 0.30 wt%, carburization impact strength decreases with increase in the Si content.
  • Fig. 6 depicts the relation between temper hardness and carburization impact strength. It can be seen that the inventive steel is much more beneficial than a comparative steel, for achieving higher temper hardness and carburization impact strength.
  • the present invention is based on the above-described research results. Described below are the reasons for setting limits to the chemical composition of the present invention.
  • the chemical composition of gear steel is adjusted in a variety of ways with consideration for the factors related to the operating environment, such as gear size, load strength, and carburizing or carbonitriding conditions. It has been confirmed that the present invention provides the above effects in all possible ranges of chemical compositions, and the following compositional ranges are provided.
  • C 0.10 to 0.30 wt%
  • At least 0.10 wt% C must be added in order to provide a gear with the required core strength.
  • An excessive addition however, makes the core unnecessarily hard and adversely affects core toughness.
  • the upper limit must be set to 0.30 wt%.
  • Si is the most important element of the inventive steel. Specifically, Si is an element that reduces softening within a temperature range of 200 to 250°C, which a gear or the like is believed to reach during rolling. To achieve this effect, at least 0.40 wt% must be added. An excessive addition, however, adversely affects not only the toughness of the carburized layer and the core, but also the cold-forging properties or machinability due to inhibited carburization or the excessively high hardness of uncarburized steel materials. To prevent this, the upper limit must be set to 1.00 wt%.
  • Si addition is confined to a range of 0.40 to 1.00 wt%.
  • Mn 0.30 to 1.50 wt%
  • Mn is an element needed to maintain the desired hardenability, and it must be added in an amount of at least 0.30 wt%.
  • An excessive addition however, has an adverse effect on the cold-forging properties or machinability due to the excessively high hardness of uncarburized steel materials.
  • the upper limit must be set to 1.50 wt%.
  • P is an element that lowers toughness or fatigue strength by segregating along austenite grain boundaries and embrittling the grain boundaries. The damage becomes pronounced at a content of greater than 0.035 wt%.
  • the P content is set to 0.035 wt% or lower.
  • Ni is the next most important element of the inventive steel after Si. Specifically, Ni is an element that improves the fracture toughness of the carburized layer and the core in the same manner as Mo does.
  • Ni is an expensive element, however, so adding too much of it is undesirable from the economic standpoint, and such an addition reduces surface hardness by promoting the formation of residual austenite, and has an adverse effect on cold-forging properties or machinability due to the excessively high hardness of uncarburized steel materials.
  • the upper limit must be set to 1.00 wt%.
  • Ni addition is confined to a range of 0.00 to 1.00 wt%.
  • Cr is an element needed to ensure desired hardenability, and it must be added in an amount of at least 0.30 wt%.
  • An excessive addition however, has an adverse effect on the cold-forging properties or machinability due to the excessively high hardness of uncarburized steel materials.
  • the upper limit must be set to 1.50 wt%.
  • Mo is the next most important element of the inventive steel after Si. Specifically, Mo is an element that improves the fracture toughness of the carburized layer and the core in the same manner as Ni does. Consequently, this element must be added in the absence of an Ni addition. Mo is an expensive element, however, so adding too much of it is undesirable from the economic standpoint, and such an addition has an adverse effect on cold-forging properties or machihability due to the excessively high hardness of uncarburized steel materials. To prevent this, the upper limit must be set to 1.00 wt%. Occasionally, the need to add this element may be dispensed with if Ni has been added in the manner described above.
  • Al is an element that combines with N to form AlN and acts to refine the size of austenite crystal grains, contributing through this grain-size refinement to improved toughness for the carburized layer and the core. At least 0.010 wt% of the element must be added to achieve this effect. An excessive addition, however, promotes the formation of Al 2 O 3 inclusions, which have an adverse effect on the fatigue strength. To prevent this, the upper limit must be set to 0.035 wt%.
  • Nb is an element that binds with the C and N in the steel to form carbonitrides, and is effective for reducing the size of austenite crystal grains in the same manner as AlN is.
  • the element improves the toughness of the carburized layer and the core. Addition of the element in an amount of at least 0.01% is needed in order to obtain such effects. However, an excessive addition forms coarse carbonitrides, causes precipitation, and adversely affects the toughness of the carburized layer. To prevent this, the upper limit must be set to 0.050 wt%.
  • O is an element that is present in the steel as oxide-based inclusions and that has an adverse effect on the fatigue strength.
  • the upper limit for O is set to 0.0015 wt% or lower.
  • N 0.0050 to 0.0200 wt%
  • N is an element that combines with Al and Nb to form AlN and NbN and acts to reduce the size of austenite crystal grains, contributing through this gain-size refinement to improved toughness for the carburized layer and the core. At least 0.0050 wt% of the element is needed to achieve this effect. An excessive addition causes foaming on the surface of the steel ingot during solidification and has an adverse effect on the forgeability of steel materials. To prevent this, the upper limit must be set to 0.0200 wt%.
  • Ni and Mo are elements designed to improve the fracture toughness of the carburized layer or the core whose fracture toughness has been reduced by increased Si addition.
  • the parameter expressed as Ni + Mo must be added in an amount of at least 0.30 wt%.
  • Ni and Mo are expensive, however, so adding too much of them is undesirable from the economic standpoint, and such an excessive addition deteriorates the cold-forging properties or machinability due to the excessively high hardness of uncarburized steel materials.
  • the upper limit of the combined amount of these elements must be set to 2.00 wt%.
  • Cu is an element that can be expected to have a precipitation hardening effect at comparatively high temperatures (400 to 600°C). It should therefore be added when rigorous operation conditions are anticipated (such as those resulting from a marked increase in the temperature of a gear or a rolling surface) or when there is a possibility that a high-temperature environment will be created near a jet engine or a turbine, as in an aircraft material. In order to exhibit this effect, addition of at least 0.01% of Cu is needed. However, an excessive addition promotes hot embrittlement and impairs carburization. To prevent this, the upper limit must be set to 0.50 wt%.
  • V is an element that forms carbides even at comparatively low temperatures (near the carburization temperature), and is thus expected to improve hardness and hardenability at the same time.
  • the element should therefore be added in an amount of at least 0.01% in order to obtain such effects.
  • an excessive addition has an adverse effect on the toughness of the carburized layer and is undesirable from the economic standpoint because V is an expensive element.
  • Such an excessive addition also has an adverse effect on cold-forging properties or machinability due to the excessively high hardness of uncarburized steel materials.
  • the upper limit must be set to 0.50 wt%.
  • V addition is confined to a range of 0.01 to 0.50 wt%.
  • Ti is an element added to prevent situations in which the N in the steel binds with B (described below), forming BN and reducing the hardenability improvement effect of B. At least 0.005% addition of the element is therefore needed in order to obtain such an effect. However, adding a large amount may produce coarse TiN, which serves as a starting point for fatigue fracturing. It is therefore necessary to set the upper limit to 0.050 wt%.
  • B is an element that improves the hardenability without adversely affecting the cold-forging properties or machinability of uncarburized steel materials. Addition of the element in an amount of not less than 0.0005 wt% is therefore needed in order to exhibit this effect. However, even when more than 0.0050 wt% is added, the effect reaches saturation and results in reduced hot workability. It is therefore necessary to set the upper limit to 0.0050 wt%.
  • S is an element that is present in the steel primarily as sulfide-based inclusions and that is effective for improving the machinability where the steel is used for components shaped by cutting, such as gears. For this effect, at least 0.005 wt% of the element should therefore be added. An excessive addition, however, results in lower fatigue strength. To prevent this, the upper limit must be set to 0.050 wt%.
  • Pb is an element that further improves the machinability as compared with the case of adding S alone. For this effect, at least 0.01 wt% addition of the element is therefore needed. An excessive addition of this element, however, results in lower fatigue strength. At over 0.10 wt%, the handling of Pb is subject to legal restrictions in terms of dust collection equipment, processes, and the like. To prevent this, the upper limit must be set to 0.09 wt%.
  • Bi is an element that further improves the machinability as compared with the case of adding S alone. For this effect, at least 0.04 wt% addition of the element is therefore needed. An excessive addition of this element, however, results in lower toughness. To prevent this, the upper limit must be set to 0.20 wt%.
  • Te is an element that further improves the machinability as compared with the case of adding S alone. For this effect, at least 0.002 wt% of the element should therefore be added. An excessive addition of this element, however, brings about hot brittleness. To prevent this, the upper limit must be set to 0.050 wt%.
  • Te addition is confined to a range of 0.002 to 0.050 wt%.
  • Zr 0.01 to 0.20 wt%
  • Zr is an element that further improves the machinability as compared with the case of adding S alone. For this effect, at least 0.01 wt% of the element should therefore be added. An excessive addition of this element results in lower toughness, however. To prevent this, the upper limit must be set to 0.20 wt%.
  • Ca is an element that further improves the machinability as compared with the case of adding S alone. For this effect, at least 0.0001 wt% of the element should therefore be added. An excessive addition of this element results in lower toughness, however. To prevent this, the upper limit must be set to 0.0100 wt%.
  • the Ca addition is confined to a range of 0.0001 to 0.0100 wt%.
  • Table 2 shows the chemical compositions of inventive steels obtained in actual furnaces on the basis of the above-described data, as well as chemical compositions of comparative steels used for comparison purposes.
  • Inventive Steel A is a boron-free steel
  • Inventive Steel B is a boron-containing steel
  • Comparative Steel I is SNCM420H specified in Japanese Industrial Standard (JIS)
  • Comparative Steel H is a steel based on SCM420H (JIS) and obtained by increasing the Si content.
  • Fig. 7 is a schematic of the roller/pitting fatigue tester used.
  • 1 is a test piece
  • 2 is a loading roller
  • 3 and 4 are meshing gears
  • 5 is a bearing
  • 6 is a coupling
  • 7 is a transmission belt
  • 8 is a motor.
  • Fig. 8 depicts the shape of the roller/pitting fatigue test piece
  • Fig. 9 depicts the shape of the loading roller for the roller/pitting fatigue tester.
  • inventive and comparative steels were first hot-forged to a diameter of 30 mm and were then normalized, yielding five roller/pitting fatigue test pieces such as the one shown in Fig. 8, and five carburization impact test pieces such as the one shown in Fig. 2. These test pieces were subsequently carburized, quenched, and tempered under the conditions shown in Fig. 3.
  • roller/pitting fatigue test pieces were subjected to the roller pitting fatigue test under the conditions shown in Table 3, and their pitting fatigue life was determined.
  • the carburization impact test pieces were subjected to a Charpy impact test, and their carburization impact strength was determined. The results are shown in Table 4. In the roller/pitting fatigue test, 20.00 ⁇ 10 6 rolling cycles were performed, and the test was completed if no pitting had occurred. The results shown in Table 4 are summarized in Fig. 10. Items Specifics Maximum Hertzian Stress 2940 MPa Slip rate -40% Rotational speed 1000 r.p.m.
  • Inventive Steels A and B have a pitting fatigue life of 20.00 ⁇ 10 6 or greater, and a carburization impact strength of 30 J/cm 2 or greater.
  • Comparative Steel I has a carburization impact strength of 30 J/cm 2 or greater but possesses a short pitting fatigue life.
  • Comparative Steel H has an adequate pitting fatigue life but possesses low carburization impact strength.
  • the inventive steel has high pitting fatigue strength and improved impact strength.
  • the present invention allows both pitting fatigue strength and impact strength to be improved merely by adjusting the chemical composition of steel, allowing the stated object to be attained.
  • the present invention is effective for reducing the size and weight of carburized gears in current manufacturing processes and in achieving higher outputs with the same sizes and shapes, greatly contributing to reduced costs and improved reliability in gear-related industrial applications.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Articles (AREA)
EP00125344A 2000-06-28 2000-11-30 Acier pour cémentation et carbonitruration Withdrawn EP1167561A3 (fr)

Applications Claiming Priority (2)

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JP2000193780 2000-06-28
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FR2868083A1 (fr) * 2004-03-24 2005-09-30 Ascometal Sa Acier pour pieces mecaniques, procede de fabrication de pieces mecaniques l'utilisant et pieces mecaniques ainsi realisees
EP1757711A3 (fr) * 2005-08-24 2008-04-23 Daido Steel Co.,Ltd. Portions de machines carburées
EP2058560A1 (fr) * 2006-08-30 2009-05-13 Kabushiki Kaisha Kobe Seiko Sho Poulie pour une transmission à variation continue
CN101298645B (zh) * 2007-05-02 2011-03-30 株式会社神户制钢所 耐点蚀性优异的钢板及其制造方法
US20140251507A1 (en) * 2009-01-16 2014-09-11 Nippon Steel & Sumitomo Metal Corporation Steel for surface hardening for machine structural use and part for machine structural use
EP2816128A4 (fr) * 2012-02-15 2015-05-20 Jfe Bars & Shapes Corp Acier à nitruration modérée et matière d'acier utilisant un composant à nitruration modérée
US10272960B2 (en) 2015-11-05 2019-04-30 Caterpillar Inc. Nitrided track pin for track chain assembly of machine
US10745772B2 (en) 2014-03-05 2020-08-18 Daido Steel Co., Ltd. Age hardening non-heat treated bainitic steel
WO2020178854A3 (fr) * 2019-03-04 2020-10-15 Bharat Forge Limited Acier pour carburation à haute température et son procédé de préparation

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JPH05263183A (ja) * 1992-03-19 1993-10-12 Sumitomo Metal Ind Ltd 耐遅れ破壊性に優れた浸炭肌焼鋼
JPH06240409A (ja) * 1993-02-16 1994-08-30 Sumitomo Metal Ind Ltd 耐火性に優れたボルトおよびナット用鋼
JPH07126803A (ja) * 1993-11-08 1995-05-16 Daido Steel Co Ltd 浸炭歯車用鋼
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2868083A1 (fr) * 2004-03-24 2005-09-30 Ascometal Sa Acier pour pieces mecaniques, procede de fabrication de pieces mecaniques l'utilisant et pieces mecaniques ainsi realisees
WO2005098070A2 (fr) * 2004-03-24 2005-10-20 Ascometal Acier pour pieces mecaniques, procede de fabrication de pieces mecaniques l'utilisant et pieces mecaniques ainsi realisees
WO2005098070A3 (fr) * 2004-03-24 2006-10-05 Ascometal Sa Acier pour pieces mecaniques, procede de fabrication de pieces mecaniques l'utilisant et pieces mecaniques ainsi realisees
CN101033536B (zh) * 2005-08-24 2010-11-10 大同特殊钢株式会社 经渗碳处理的机器零件
EP1757711A3 (fr) * 2005-08-24 2008-04-23 Daido Steel Co.,Ltd. Portions de machines carburées
EP2058560A1 (fr) * 2006-08-30 2009-05-13 Kabushiki Kaisha Kobe Seiko Sho Poulie pour une transmission à variation continue
EP2058560A4 (fr) * 2006-08-30 2010-03-31 Kobe Steel Ltd Poulie pour une transmission à variation continue
US8523722B2 (en) 2006-08-30 2013-09-03 Kobe Steel, Ltd. Pulley for continuously variable transmission
CN101298645B (zh) * 2007-05-02 2011-03-30 株式会社神户制钢所 耐点蚀性优异的钢板及其制造方法
US20140251507A1 (en) * 2009-01-16 2014-09-11 Nippon Steel & Sumitomo Metal Corporation Steel for surface hardening for machine structural use and part for machine structural use
US9777343B2 (en) * 2009-01-16 2017-10-03 Nippon Steel & Sumitomo Metal Corporation Steel for surface hardening for machine structural use and part for machine structural use
EP2816128A4 (fr) * 2012-02-15 2015-05-20 Jfe Bars & Shapes Corp Acier à nitruration modérée et matière d'acier utilisant un composant à nitruration modérée
US10745772B2 (en) 2014-03-05 2020-08-18 Daido Steel Co., Ltd. Age hardening non-heat treated bainitic steel
US10272960B2 (en) 2015-11-05 2019-04-30 Caterpillar Inc. Nitrided track pin for track chain assembly of machine
WO2020178854A3 (fr) * 2019-03-04 2020-10-15 Bharat Forge Limited Acier pour carburation à haute température et son procédé de préparation

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