JP2007016271A - Steel for induction hardening for pinion having excellent machinability, method for producing the same, and pinion having excellent bending fatigue property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel for induction hardening for a pinion having excellent machinability for efficiently obtaining a pinion having excellent fatigue properties, and to provide a pinion having excellent bending fatigue properties obtained by subjecting the steel to induction hardening. <P>SOLUTION: The steel for induction hardening for a pinion having excellent machinability has a composition essentially consisting of prescribed amounts of Cr, B and Ti, containing prescribed amounts of C, Si, Mn, S, Al, P, N and Total oxygen, and comprising a prescribed amount(s) of one or more kinds selected from the group consisting of Te, Ca, Zr, Mg, Y and rare earth metals as inclusion form controlling elements, and the balance iron with inevitable impurities, and in which the average aspect ratio of MnS-containing inclusions is ≤10. Also, when high frequency heat treatment is performed under prescribed conditions, the steel exhibits prescribed bending fatigue properties. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steel for induction hardening for pinions excellent in machinability, a manufacturing method thereof, and a pinion excellent in bending fatigue characteristics.

  Among the various gears obtained by induction hardening, automotive components that make up the steering system of automobiles: Pinion has become more strongly oriented in recent years due to higher output of automobile engines and compliance with environmental regulations. ing. However, since the carbon concentration of the surface layer is lower than when carburizing is performed, the equivalent hardness can be ensured, but the wear resistance is often poor. For this reason, although higher carbonization of steel materials is requested | required, problems, such as causing the fall of the fatigue life by a machinability fall or toughness degradation, may arise when it raises carbon. When S is positively added to improve the machinability, there is a problem that the fatigue life is lowered.

  The pinion rotates on the rack (a round bar with teeth) during operation. At this time, the pinion is subjected to a very high load, so it is necessary to reliably prevent fatigue damage such as tooth root damage. Therefore, it is required to exhibit high bending fatigue characteristics. In particular, the pinion is also a steel part important for safety, so it is necessary to reliably exhibit the high bending fatigue characteristics.

  Therefore, as a characteristic of the steel material used for the production of the pinion, it is required to exhibit high strength after high-frequency heat treatment, reliably exhibit high bending fatigue characteristics, and exhibit excellent machinability in the manufacturing process.

  As a technique for improving the fatigue characteristics of induction hardening steel, for example, Patent Document 1 discloses that the generation of elongated MnS is suppressed, the MnS is granulated and refined, the ferrite fraction is regulated, and the ferrite grains are refined. It is shown that If the ferrite grains are coarse, the ferrite portion becomes low carbon martensite after induction hardening, causing hardness unevenness and reducing fatigue characteristics. However, this technology considers only the torsional fatigue characteristics of rod-like members such as drive shafts, and considers the bending fatigue characteristics assuming the case where a high load is applied to the tooth tip like the above pinion. It has not been.

Patent Document 2 also shows a technique that improves the fatigue characteristics of steel for induction hardening. In the longitudinal cross section passing through the axis of a linear or rod-shaped rolled material, the technique uses an imaginary line parallel to the axis and separated from the axis by 1/4 · D (D represents the diameter of the rolled material). Bending fatigue strength and rolling of induction hardening steel by reducing the number of oxide inclusions and sulfide composite inclusions with a diameter of 10 μm or more present in the test area 100 mm ² included as the center line to 20 or less. It has been shown to increase fatigue strength.

  However, it is considered that further improvement is necessary in the case where particularly high bending fatigue properties such as the pinion are required. Moreover, in order to manufacture a steel part such as a pinion that requires high accuracy, it is necessary to combine excellent machinability and the above fatigue characteristics.

Patent Document 3 discloses a steel material for machine structure with improved machinability, fatigue characteristics, and cold forgeability. In this technique, the test result by a rotating bending fatigue tester is shown, but it is a result when induction hardening is not performed. When induction hardening is performed, high strength is ensured and good bending fatigue characteristics are obtained. It is hard to say that it is demonstrated. That is, it has not been studied to improve the bending fatigue characteristics after the high-frequency heat treatment like the above-described pinion.
JP 2002-69566 A Japanese Patent Laid-Open No. 11-1749 JP 2004-52099 A

  The present invention has been made in view of such circumstances, and the object thereof is a steel for induction hardening for a pinion excellent in machinability and a method for producing the same for efficiently obtaining a pinion excellent in bending fatigue characteristics. And it is providing the pinion excellent in the bending fatigue property obtained by performing induction hardening using this steel.

With the steel for induction hardening for pinions according to the present invention,
C: 0.3 to 0.60% (meaning mass%, the same shall apply hereinafter)
Si: 0.01 to 1.0%,
Mn: 0.2 to 2.0%,
Cr: 0.50 to 2.0%,
S: 0.010 to 0.08%,
B: 0.0005 to 0.005%,
Al: 0.001 to 0.1%,
Ti: 0.005 to 0.05%,
P: 0.025% or less (excluding 0%),
N: 0.007% or less (excluding 0%),
Total oxygen: 15 ppm or less (excluding 0%)
Including
Te: 0.0005 to 0.02%,
Ca: 0.0005 to 0.02%,
Zr: 0.01 to 0.50%,
Mg: 0.0001 to 0.0055%,
Y: 0.001 to 0.1%, and REM: one or more selected from the group consisting of 0.001 to 0.15%,
The balance consists of iron and inevitable impurities,
The MnS-containing inclusions have an average aspect ratio of 10 or less, and have the following bending fatigue characteristics when induction hardening is performed under the following conditions.

<High-frequency heat treatment conditions>
In a high-frequency heat treatment machine, after quenching until the center of the test piece is cured under the following conditions, temper at 150 ° C. for 1 hour.
Test piece: D ₀ : 12 mm, D: 10 mm, R: 16 mm
Rotating bend test piece with a crack of α = 2.0 Frequency: 20 kHz
Output: 6.0 kV
Feeding speed: 5.0mm / sec
Quenching temperature: 850 ° C
Use of soluble liquid <Bending fatigue characteristics>
Bending fatigue test conditions: Rotational bending stress 280 MPa
(Stress on a test piece with a smooth notch bottom diameter)
・ Bending fatigue life: 1.0 × 10 ⁵ times or more

  In particular, those containing both Ca: 0.0005-0.02% and Mg: 0.0001-0.0055% have a smaller average aspect ratio of the MnS-containing inclusions of 3 or less, and high-frequency heat treatment It is preferable because it is excellent in later bending fatigue characteristics.

The present invention also defines a pinion having excellent bending fatigue characteristics, and the pinion is obtained by induction-quenching using a steel material having the above component composition, and is an average of MnS-containing inclusions. The aspect ratio is 10 or less, and the following bending fatigue characteristics are shown.
<Bending fatigue properties>
Bending fatigue test piece: D ₀ : 12 mm, D: 10 mm, R: 16 mm
α = 2.0 Rotating Bending Specimen with Crevice ・ Bending fatigue test condition: Rotating bending stress 280 MPa
(Stress on a test piece with a smooth notch bottom diameter)
・ Bending fatigue life: 1.0 × 10 ⁵ times or more

  The present invention also provides a method for producing the steel for induction hardening for pinions, wherein the method reduces Te, Ca, Zr, Mg, Y, And adding one or more elements selected from the group consisting of REM, adjusting to the above component composition, performing casting, and heating the steel material to 900 ° C. or higher during hot rolling. Yes.

The aspect ratio is 0.64 mm ² in total in the rolling direction cross section of the D / 4 (D: diameter of the rolled material) portion of the rolled material, as shown in the examples to be described later (resolution: 1 μm). The average value of the major axis / minor axis was calculated and obtained for MnS-containing inclusions having an area (major axis × minor axis) of 5 μm ² or more.

  According to the present invention, it is possible to realize a highly reliable pinion that exhibits high bending fatigue characteristics and is reliably suppressed from fatigue fracture such as tooth root damage. In addition, as a steel material for obtaining a pinion that exhibits the above characteristics, a steel material with improved machinability and excellent bending fatigue characteristics after induction hardening can be realized.

The present inventor has conducted excellent research to obtain a steel material exhibiting excellent bending fatigue characteristics after induction hardening, realizing a highly reliable pinion, and exhibiting excellent machinability during machining in the production of the pinion. . As a result, on the premise that a predetermined amount of S is included to ensure machinability, to improve the bending fatigue characteristics,
It has been found that it is important that (a) the specified amounts of Cr, Ti and B are essential, and (b) the aspect ratio of the MnS-containing inclusions is 10 or less.

  First, as described in (a) above, prescribed amounts of Cr, Ti, and B are essential. In the case of a rod-shaped steel part, the fatigue characteristic is how to generate a residual stress inside the steel part rather than ensuring the hardness of the surface of the steel part. On the other hand, in the case of a gear such as a pinion, the fatigue characteristics (bending fatigue characteristics) of the gear depend on the hardness. Therefore, in the present invention, by including these elements, the strength of the tooth root portion is increased within a range that does not impair other characteristics necessary in the manufacturing process such as machinability, and the bending fatigue characteristics are reliably improved. It was decided.

  In order to fully exhibit the said effect, it is necessary to contain Cr 0.50% or more. However, if the amount of Cr is excessive, the effect is saturated, and if it is rolled, the machinability such as cutting property and machinability is deteriorated, and the productivity and accuracy are lowered. Preferably it is 1.0% or less.

  B improves the fatigue strength and impact strength by imparting hardenability to the steel and improving the grain boundary strength of the hardened material. In order to exhibit this effect, 0.0005% or more of B is contained. Preferably it is 0.001% or more, More preferably, it is 0.002% or more. However, even if the amount of B becomes excessive, the effect is saturated, and it becomes a factor in generating wrinkles during melting, so it is suppressed to 0.005% or less. Preferably it is 0.003% or less.

  Ti is an element necessary for fixing solute N as TiN and imparting high hardenability by solute B. It is also useful for detoxifying other adverse effects caused by solute N. Furthermore, it is also an element having a deoxidizing action. Therefore, 0.005% or more, preferably 0.010% or more is contained. However, when the amount of Ti becomes excessive, precipitation hardening by TiC becomes remarkable, and machinability deteriorates remarkably. Therefore, the upper limit of Ti amount is set to 0.05%. Preferably it is 0.030% or less.

  Furthermore, in the present invention, as described in (b) above, the aspect ratio of the MnS-containing inclusions (major axis / minor axis of the MnS-containing inclusions) is 10 or less. When S is added to improve machinability, bending fatigue characteristics tend to decrease with increasing S amount, as shown in FIG. 1, which shows the relationship between the amount of S in steel and the bending fatigue life, as will be described later. is there. However, addition of S is indispensable for cutting to form a highly accurate pinion, and it is necessary to improve the bending fatigue characteristics on the assumption that a certain amount of S is contained.

  As described above, the inventor makes the specified amounts of Cr, Ti, and B essential, and can achieve both excellent machinability and bending fatigue characteristics when the aspect ratio of the inclusion containing MnS is 10 or less. I found. FIG. 2 shows a steel material containing 0.015% of S and a steel material containing 0.060% of S and changing the aspect ratio of MnS-containing inclusions, as shown in the examples described later. The results of heat treatment and subsequent measurement of bending fatigue life are organized. From FIG. 2, even in the case where the S content is as large as 0.060% in order to improve the machinability, by reducing the aspect ratio of the MnS-containing inclusions, the steel content of S content: 0.015% It can be seen that the same bending fatigue characteristics can be secured.

  The aspect ratio is preferably 5 or less, more preferably 3 or less.

  As the MnS-containing inclusions, in addition to MnS, a composite compound of MnS and an oxide of one or more elements selected from the group consisting of Te, Ca, Zr, Mg, Y, and REM described later is included. Can be mentioned.

  In particular, the present invention improves the bending fatigue characteristics of the pinion by controlling the content of Cr, Ti and B and the aspect ratio of the MnS-containing inclusion, and at the same time, achieves both the machinability required at the time of manufacturing the pinion. Although it has been achieved, in order to reliably exhibit the effects, it is necessary to control other components as follows.

<C: 0.3 to 0.60%>
C is an element necessary for securing the strength after induction hardening, and is contained in an amount of 0.3% or more in the present invention. Preferably it is 0.4% or more. On the other hand, when the amount of C becomes excessive, the hardness increases more than necessary and the machinability deteriorates. Moreover, since it becomes brittle and it becomes difficult to ensure fatigue characteristics, it is suppressed to 0.60% or less. Preferably it is 0.55% or less, more preferably 0.50% or less.

<Si: 0.01 to 1.0%>
Si is an element effective for deoxidation of steel, and is an element effective for imparting necessary strength and hardenability to steel and improving temper softening resistance. It is insufficient. On the other hand, if it exceeds 1.0%, the hardness increases and the machinability deteriorates. Preferably it is 0.5% or less, More preferably, it is 0.15% or less.

<Mn: 0.2 to 2.0%>
Mn is an element effective for improving the induction hardenability, and in order to exhibit this effect, it is necessary to contain 0.2% or more of Mn. However, when the amount of Mn becomes excessive, a large amount of hard bainite structure is formed and the machinability is deteriorated. Preferably it is 0.5% or less.

<S: 0.010 to 0.08%>
S is an element useful for forming MnS in steel and thereby improving machinability. In order to fully exhibit this effect, it is necessary to contain S 0.010% or more. Preferably it is 0.015% or more. However, when the amount of S is excessive, the bending fatigue characteristics are deteriorated, so the amount is suppressed to 0.08% or less. Preferably it is 0.04% or less, More preferably, it is 0.030% or less.

<Al: 0.001 to 0.1%>
Al is useful as a deoxidizer and is useful for securing solid solution B by fixing solid solution N existing in steel as AlN. In order to exhibit the effect sufficiently, Al is contained in an amount of 0.001% or more, preferably 0.01% or more. However, when the amount of Al is excessive, hard Al ₂ O ₃ is excessively generated and machinability is deteriorated. Therefore, the Al content is 0.1% or less, preferably 0.04% or less.

<P: 0.025% or less (excluding 0%)>
P is an element that contributes to improvement of chip disposal by making chips generated during cutting easy to break. However, since the grain boundaries of the parts after induction hardening and tempering are embrittled and the fatigue strength of the final product is deteriorated, it should be reduced as much as possible. In the present invention, it is suppressed to 0.025% or less. Preferably it is 0.015% or less.

<N: 0.007% or less (excluding 0%)>
Since N combines with B and suppresses the effect of imparting hardenability by solute B, it is preferable that N is as small as possible. As described above, Ti is added to fix the solid solution N, and the above effect of the solid solution B is ensured. However, if the amount of N is large, it is necessary to add a large amount of Ti and the cost increases. In addition, hard TiN increases, which adversely affects machinability. Therefore, the N content is suppressed to 0.007% or less. Preferably it is 0.005% or less.

<Te: 0.0005 to 0.02%,
Ca: 0.0005 to 0.02%,
Zr: 0.01 to 0.50%,
Mg: 0.0001 to 0.0055%,
Y: 0.001 to 0.1%, and REM (rare earth element): 0.001 to 0.15%
One or more selected from the group consisting of>
When these elements are added, oxides are formed to form nuclei of MnS, and MnS is compositionally modified to, for example, (Mn, Ca) S or (Mn, Mg) S. Such modification improves the stretchability of the MnS-containing inclusions during hot rolling and finely disperses the granular MnS-containing inclusions, so that the aspect ratio can be 10 or less as described above. The bending fatigue life after induction hardening can be improved.

  In order to reliably exhibit the above effect, 0.0005% or more (preferably 0.0050% or more) is added when Te is added, 0.0005% or more (preferably 0.0015% or more) in the case of Ca, In the case of Zr, 0.01% or more (preferably 0.05% or more), in the case of Mg, 0.0001% or more (preferably 0.0005% or more), in the case of Y, 0.001% or more (preferably 0.002% or more), and in the case of REM, 0.001% or more (preferably 0.002% or more) is contained.

  However, even if these elements are present in excess, the above effects are saturated, coarse oxides such as CaO and MgO and clusters thereof are formed, and a large amount of hard precipitates such as ZrN are formed, resulting in machinability. It causes deterioration. Therefore, Te is 0.02% or less (preferably 0.01% or less), Ca is 0.02% or less (preferably 0.0050% or less), and Zr is 0.50% or less (preferably 0.15%). Or less), Mg is 0.0055% or less (preferably 0.0030% or less), Y is 0.1% or less (preferably 0.05% or less), and REM is 0.15% or less (preferably 0.05). % Or less).

  In addition, REM (rare earth element) as used in the field of this invention refers to the element of atomic number 57-71.

<Total oxygen: 15 ppm or less (excluding 0%)>
In order to reduce the aspect ratio of the MnS-containing inclusion, it is effective to add one or more elements selected from the group consisting of Te, Ca, Zr, Mg, Y, and REM as described above. In order to realize the reduction of Te, it is necessary to dissolve or combine the above Te and the like in MnS. However, when the dissolved oxygen concentration in the molten steel at the time of melting the steel material is high, most of the above elements become oxides, and it becomes difficult to form a solid solution or compound in MnS, so that the above-described modification of the inclusions becomes insufficient. Therefore, it is necessary to suppress the dissolved oxygen concentration to 30 ppm or less, preferably 20 ppm or less, more preferably 10 ppm or less in advance when the above elements are added. At this time, there is a correlation between the dissolved oxygen concentration and the total oxygen amount of the steel material. If the total oxygen is 15 ppm or less, more preferably 10 ppm or less, the dissolved oxygen concentration is reduced within the above range, The aspect ratio of the MnS-containing inclusions can be reduced by dissolving or combining the elements.

  The contained elements defined in the present invention are as described above, and the balance is iron and unavoidable impurities. As the unavoidable impurities, mixing of elements brought in depending on the situation of raw materials, materials, manufacturing facilities, etc. can be allowed.

  In order to control the aspect ratio of the MnS-containing inclusions as described above, the dissolved oxygen concentration is set to 30 ppm or less, preferably 20 ppm or less, more preferably 10 ppm or less as described above (as a specific method, as described above) before casting. Deoxidation), one or more elements selected from the group consisting of Te, Ca, Zr, Mg, Y, and REM must be added and adjusted to the above component composition before casting. It is also important to control the heating temperature at the time of rolling, and it is necessary to perform rolling after heating to 900 ° C or higher, preferably 1000 ° C or higher (temperature measured by a radiation thermometer of the steel material coming out of the heating furnace). There is.

  The pinion of the present invention can be obtained by using the above steel material, hot rolling, hot forging, then machining (cutting) into a gear, and then performing high frequency heat treatment. Thereafter, tempering, shot peening or finish polishing may be performed as necessary.

  The condition of induction heat treatment depends on the size of the pinion (steel part), but for example, quenching at the root of the tooth under the conditions of output: 150 kW, frequency: 200 kHz, moving speed: 1.15 mm / sec with an induction hardening machine Depth: quenching (water cooling) to 0.5 to 1.5 mm, followed by tempering as appropriate.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  The steel materials obtained by melting the test steels having the composition shown in Tables 1 and 2 were heated at the temperatures shown in Tables 1 and 2 and then hot-rolled to obtain a rolled material (diameter: 35 mm). Obtained. At the time of melting, except for J3 in Table 2 described later, Al is added before casting to reduce the dissolved oxygen content of the molten steel to 20 ppm or less, and then Te, Ca, Zr, Mg, Y, and REM One or more elements selected from the group consisting of: For J3, Mg and Ca were added at the time of melting without sufficiently lowering dissolved oxygen.

  The heating temperatures shown in Tables 1 and 2 are obtained by measuring the temperature of the steel slab with a radiation thermometer at the time of removal from the heating furnace.

And the aspect ratio of the MnS containing inclusion was measured as follows using the said rolling material. That is, in the cross section in the rolling direction of the D / 4 (D: diameter of the rolled material) part of the rolled material, the measurement visual field: 0.16 mm ² is observed by SEM (resolution: 1 μm), and MnS whose major axis × minor axis is 5 μm ² or more. The aspect ratio (major axis / minor axis) was measured for the inclusions included, and the average value was obtained with a total of four fields (0.64 mm ² ).

  The bending fatigue characteristics were evaluated as follows. That is, an Ono-type mini-rotation bending test piece (test piece shown in FIG. 3) was prepared from the rolled material, induction hardening (IHQ) was performed until the center portion was cured, and then tempered at 150 ° C. for 1 hour.

And the Ono type | formula rotation bending test was done using this test piece. In this test, the sample was rotated under a bending stress of 280 MPa, the number of rotations until failure (bending fatigue life) was measured, and a bending fatigue life of 1.0 × 10 ⁵ or more was excellent in bending fatigue characteristics. It was evaluated. These results are also shown in Tables 1 and 2.

For machinability, a cutting test was performed using the steel materials A1, C1, C2, and I3 in Tables 1 and 2 described later under the following conditions, and the drill wear index was obtained when the drill wear amount of A1 was 1.0. It was. As a result, it was 1.5 for C1, 2.0 for C2, and 3.0 for I3.
<Cutting test conditions>
・ Tool: SKH9, 10mmφ straight drill ・ Cutting speed: 15m / min
・ Feed: 0.33mm / rev
・ Dry type ・ Work material: Normalizing treatment (850 ° C. × 2 hr → AC)
・ Measurement item: Hole depth 30mm × 4 Wear during cutting

  The following can be considered from Tables 1 and 2 (note that the following symbols indicate the symbols in Tables 1 and 2).

  A1 to A7 are examples in which steel parts are manufactured by changing the manufacturing conditions using steel materials whose component composition is within the specified range of the present invention. Among them, A6 and A7 were rolled without being heated at the recommended temperature, so that the aspect ratio of the MnS-containing inclusions was increased, resulting in poor bending fatigue characteristics.

  B1 to B4 are examples in which the influence of the C amount is confirmed. From the result of B4, it is understood that if the C amount is excessive, excellent bending fatigue characteristics cannot be ensured. This is presumably because the steel material became brittle due to excess C.

  C1 and C2 are examples in which the Si amount is relatively high, but it is understood that excellent bending fatigue characteristics are exhibited.

  D1 and D2 are examples in which the amount of Mn is relatively high, but it is understood that excellent bending fatigue characteristics can be secured in this case as well.

  E1 and E2 are examples in which the amount of P is slightly high, but it can be seen that excellent bending fatigue characteristics can be ensured if within the specified range.

  F1 to F6 are examples in which the influence of the S amount is confirmed. From these examples, it can be seen that if the amount of S is excessive, it is difficult to ensure excellent bending fatigue characteristics even if the aspect ratio of MnS is reduced.

  G1 to G4 are examples in which the influence of the Cr amount is confirmed. From the result of G1, it is understood that the bending fatigue life is shortened when the Cr amount is insufficient. This is probably because the hardenability is insufficient.

  H1 and H2 are an example in which the amount of Al is relatively small and an example in which the amount of Al is relatively large.

  I1 to I6 are examples in which the effects of Ti amount and B amount are confirmed. From the results of I2 and I6, when the Ti amount is too small, the grain boundary strengthening mechanism of B does not work and the fatigue life is shortened. ing. Since the amount of Ti in I3 is excessive, the hardness is increased more than necessary and the machinability is inferior as described above. Since the amount of B in I4 is too small, the fatigue life is shortened. Also, from I5, when the amount of B was excessive, wrinkles were likely to occur during melting.

  J1 to J3 confirm the influence of the total oxygen amount. If the total oxygen content is high as in J3, the aspect ratio of MnS becomes high and excellent bending fatigue characteristics cannot be ensured. This means that a high total oxygen means a high dissolved oxygen concentration at the time of melting. When the dissolved oxygen concentration is high, Mg and Ca added to spheroidize MnS-containing inclusions are almost oxidized. Presumably because it was a product and did not work effectively.

  K1 to K6 are examples in which the influence of inclusion form control elements such as Te is examined. However, when no inclusion form control element such as Te is added as in K1, other factors such as heating temperature are set. It can be seen that the aspect ratio of the MnS-containing inclusions is increased even if controlled. Further, from K2 to K6, it is understood that the same effect as Mg can be obtained even when elements such as Zr, Y, REM, Ca, Te other than Mg are added.

It is the graph which showed the relationship between the amount of S in steel, and a bending fatigue life. It is the graph which showed the relationship between the aspect ratio of a MnS containing inclusion, and a bending fatigue life according to S amount. It is the side view which showed typically the rotation bending test piece used in the Example.

Claims (4)

C: 0.3 to 0.60% (meaning mass%, the same shall apply hereinafter)
Si: 0.01 to 1.0%,
Mn: 0.2 to 2.0%,
Cr: 0.50 to 2.0%,
S: 0.010 to 0.08%,
B: 0.0005 to 0.005%,
Al: 0.001 to 0.1%,
Ti: 0.005 to 0.05%,
P: 0.025% or less (excluding 0%),
N: 0.007% or less (excluding 0%),
Total oxygen: 15 ppm or less (excluding 0%)
Including
Te: 0.0005 to 0.02%,
Ca: 0.0005 to 0.02%,
Zr: 0.01 to 0.50%,
Mg: 0.0001 to 0.0055%,
Y: 0.001 to 0.1%, and REM: one or more selected from the group consisting of 0.001 to 0.15%,
The balance consists of iron and inevitable impurities,
A steel for induction hardening for pinions having excellent machinability, wherein the MnS-containing inclusions have an average aspect ratio of 10 or less and exhibit the following bending fatigue characteristics when subjected to induction heat treatment under the following conditions.
<High-frequency heat treatment conditions>
In a high-frequency heat treatment machine, after quenching until the center of the test piece is cured under the following conditions, temper at 150 ° C. for 1 hour.
Test piece: D ₀ : 12 mm, D: 10 mm, R: 16 mm
Rotating bend test piece with a crack of α = 2.0 Frequency: 20 kHz
Output: 6.0 kV
Feeding speed: 5.0mm / sec
Quenching temperature: 850 ° C
Use of soluble liquid <Bending fatigue characteristics>
Bending fatigue test conditions: Rotational bending stress 280 MPa
・ Bending fatigue life: 1.0 × 10 ⁵ times or more   2. The induction hardening for pinions according to claim 1, comprising 0.0005 to 0.02% of Ca and 0.0001 to 0.0055% of Mg, and an average aspect ratio of the MnS-containing inclusions being 3 or less. Steel. Using a steel material having the component composition according to claim 1 or 2, obtained by induction hardening,
The average aspect ratio of the MnS-containing inclusion is 10 or less,
A pinion excellent in bending fatigue characteristics characterized by exhibiting the following bending fatigue characteristics.
<Bending fatigue properties>
Bending fatigue test piece: D ₀ : 12 mm, D: 10 mm, R: 16 mm
α = 2.0 Rotating Bending Specimen with Crevice ・ Bending fatigue test condition: Rotating bending stress 280 MPa
・ Bending fatigue life: 1.0 × 10 ⁵ times or more   A method for producing an induction-quenched steel for pinions according to claim 1 or 2, comprising a Te, Ca, Zr, Mg, Y, and REM after the dissolved oxygen content of the molten steel is reduced to 20 ppm or less. One or more elements selected from the group are added to adjust the component composition according to claim 1 or 2 to perform casting, and the steel is heated to 900 ° C. or higher during hot rolling. A method for producing steel for induction hardening for pinions.

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