JP4757831B2 - Induction hardening part and manufacturing method thereof - Google Patents

Description

  The present invention relates to parts such as continuously variable transmission (CVT) sheaves and gears having high surface pressure fatigue strength and toughness that are applied to mechanical structural parts, particularly power transmission parts such as automobiles.

  Power transmission parts such as CVT sheaves of continuously variable transmissions (CVT) and gears of automatic transmissions, for example, mechanical structural parts, are given high hardness on the surface, so that surface pressure fatigue strength, toughness, wear resistance In order to improve the property, case-hardened steel having C of about 0.2%, such as JIS SCr420 and SCM420, is used as a material. After actually forging such a material and cutting it into a part shape, carburizing and quenching is performed to make the surface of the part a martensite structure of about 0.8% and to improve the surface pressure fatigue strength. Use by improving. Incidentally, when these CVT sheaves and gears are embodied as relatively small parts, cold forging may be performed instead of the hot forging described above from the viewpoint of cost reduction. In such a case, the material is subjected to cold forging after being subjected to softening treatment such as spheroidizing annealing. However, even when either the hot forging step or the cold forging step is adopted, the subsequent carburizing and quenching treatment is generally required to be performed at a high temperature for a long time of the order of 5 hours to 10 hours at 930 ° C. Therefore, there is a problem that the manufacturing cost increases.

  In order to cope with such problems of the prior art, an induction quenching method capable of short-time processing of several seconds instead of carburizing and quenching processing has been proposed. For example, in Patent Document 1, an alloy composition is appropriately selected, the hardenability index is suppressed to a specific value or less, and a certain tempering hardness is ensured, whereby a high-frequency contour that is heated for a short time without quenching and tempering. A method that enables quenching has been proposed. The alloy composition in the technology disclosed in Patent Document 1 is such that C is 0.45 to 0.8% and contains other alloy elements. According to the technique disclosed in Patent Document 1, a gear having high fatigue strength can be manufactured without performing carburizing and quenching.

However, as evaluated by the present inventors, it has been confirmed that when C exceeds 0.6%, the machinability is remarkably deteriorated and the cutting cost is greatly deteriorated. Further, if C exceeds 0.6%, toughness deteriorates, so application to CVT sheaves and gears becomes difficult.
JP 2000-265241 A

  Therefore, the present invention has been devised in view of the above-mentioned problems, and has high surface pressure fatigue strength and toughness that can be applied particularly to power transmission parts such as automobiles including CVT sheaves and gears. Furthermore, an object is to provide an induction-hardened part excellent in machinability and a method for manufacturing the same.

  The inventors of the present invention performed a spheroidizing annealing process after the forging process and transferred C in the steel to a carbide to form a structure mainly composed of ferrite and a spheroidized carbide having a low C content, and C was 0.6%. By making the steel having a substantially low C amount even if it exceeds the steel material, the machinability and toughness are ensured, and further, only the surface layer is martensitic transformed by subsequent induction hardening to ensure the surface pressure fatigue strength. The present invention has been completed by finding out that the problems can be solved.

That is, in order to solve the above-described problems, the invention according to claim 1 of the present invention is in mass%, C: 0.4 to 1.2%, Si: 2.0% or less, Mn: 0.2 to 3 0.0%, P: 0.03% or less, S: 0.005-0.10%, Ni: 2.0% or less (including 0%), Cr: 3.0% or less (including 0%) , Mo: 1.0% or less (including 0%), O 2: 0.0025% or less, N: 0.005 to 0.03%, and Al: 0.005 to 0.05%, Ti: one or two of 0.005 to 0.05%, V: 0.3% or less (including 0%), Nb: one of 0.3% or less (including 0%) Alternatively, it is a component containing two types, the balance being made of steel consisting of iron and inevitable impurities, the surface layer of which is induction-hardened, and the structure in the region at a depth of 0.05 mm from the surface. The insite area ratio is 60% or more, the hardness at the part is HRC55 or more, and the core structure that is a non-frequency-hardened part is a substantial ferrite not containing bainite, and is present in the core structure. Ri substantially all of globular carbides der carbide, characterized in that it is applied to a continuously variable transmission (CVT).

  The invention according to claim 2 of the present application is the invention according to claim 1, wherein the chemical composition of the steel is further, by mass%, Ca: 0.01% or less, Mg: 0.01% or less, Zr: 0.05 % Or less, Te: containing any one or more of 0.1% or less.

In order to solve the above-described problems, the invention according to claim 3 is mass%, C: 0.4 to 1.2%, Si: 2.0% or less, Mn: 0.2 to 3.0. %, P: 0.03% or less, S: 0.005 to 0.10%, Ni: 2.0% or less (including 0%), Cr: 3.0% or less (including 0%), Mo : 1.0% or less (including 0%), O: 0.0025% or less, N: 0.005 to 0.03%, Al: 0.005 to 0.05%, Ti: One or two of 0.005 to 0.05% and one or two of V: 0.3% or less (including 0%), Nb: 0.3% or less (including 0%) After the steel containing seeds and the balance consisting of iron and inevitable impurities is subjected to hot forging or cold forging, it is heated to 740 to 780 ° C. for 1 hour or longer, and the heating temperature to 550 ° C. Slow cooling at a cooling rate of ℃ / min or less, followed by induction hardening, so that the martensite area ratio in the tissue at a depth of 0.05 mm from the surface is 60% or more, and Hardness is HRC55 or more, the structure of the core part which is a non-high frequency quenching part is substantially ferrite not containing bainite, and substantially all of the carbides present in the core part structure are spherical carbides. Features.

The invention according to claim 4 of the present application is the invention according to claim 3, wherein the chemical components of the steel are further by mass% Ca: 0.01% or less, Mg: 0.01% or less, Zr: 0.05. % Or less, Te: containing any one or more of 0.1% or less.

  The invention according to claim 5 of the present application is characterized in that the induction-hardened component according to claim 3 or 4 is applied to a continuously variable transmission (CVT).

  It is possible to provide parts such as CVT sheaves and gears that have high surface pressure fatigue strength and toughness that can be applied to power transmission parts such as automobiles, and also have excellent machinability, thereby increasing the output of automobiles. In addition, it greatly contributes to cost reduction.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using an induction-hardened component as an example.

  In the present invention, the entire steel is obtained by performing a spheroidizing annealing treatment after hot forging a steel material in which the content of C is 0.4% to 1.2% in mass% and other components are appropriately added. After making the structure mainly composed of ferrite and spheroidized carbide with low C content with excellent toughness, and after cutting into the shape of the part, only the surface layer of the part is martensite to ensure the surface pressure fatigue strength by induction hardening Because the core part that is not induction hardened remains a structure mainly composed of ferrite and spheroidized carbide with low C content and excellent toughness, it is possible to obtain a component having both surface pressure fatigue strength and toughness Become. The present invention can also produce parts by cold forging in the case of relatively small parts. In this case, if necessary, cold forging may be performed after spheroidizing annealing, and then spheroidizing annealing may be performed again, and cutting and induction hardening may be performed to obtain a part.

  Below, the reason for limitation of each element component which comprises the induction hardening component to which this invention is applied is demonstrated. Hereinafter, the mass% in the composition is simply described as%.

C: 0.4-1.2%
C is an important element for obtaining the strength of steel, and ensures the surface hardness (HRC 55 or higher) after induction hardening, and improves the surface pressure fatigue strength, bending fatigue strength, torsional fatigue strength, and static strength. It is an element to be added. If the amount of C is less than 0.4%, the hardness after induction hardening becomes insufficient, fatigue life and wear resistance are greatly deteriorated, and desired mechanical properties cannot be obtained. For this reason, in the present invention, the lower limit of the C amount is set to 0.4% to ensure strength and the like. However, if the amount of C exceeds 1.2%, the surface hardness is lowered due to a large amount of retained austenite structure remaining after induction hardening. For this reason, the upper limit was made less than 1.2%. In addition, in order to ensure the effect mentioned above more stably, the most preferable content is 0.6 to 1.0%.

Si: 2.0% or less Si is an element inevitably contained in steel, and is an element effective for deoxidation during steelmaking. On the other hand, temper softening of the hardened layer is possible by adding it. The resistance can be improved, and the pitching life of the CVT sheave or gear is improved. In order to obtain such an effect, the Si content is preferably 0.2% or more. However, if the Si content exceeds 2.0%, decarburization during forging becomes significant, so 2.0% was made the upper limit. In addition, in order to ensure the effect mentioned above more stably, the most preferable content is 0.2 to 2.0%.

Mn: 0.2 to 3.0%
Mn is an element effective for improving the hardenability of steel, and is also an element effective for improving the temper softening resistance. In order to obtain the effect, addition of 0.2% or more is necessary. However, if it exceeds 3.0%, austenite remains on the surface part due to induction hardening, leading to a decrease in surface hardness. On the other hand, the amount of martensite increases in the core part, so it becomes too hard during steel production and the steel bar is cut. It may interfere with sex. For this reason, the upper limit of the amount of Mn is set to 3.0%. The most preferable addition amount is 0.2 to 2.0%.

P: 0.03% or less P is an element contained as an inevitable impurity in steel, and is not an element intentionally added. P needs to be reduced as much as possible because it segregates at the grain boundaries of austenite and lowers toughness, and should be limited to 0.03% or less.

S: 0.005-0.10%
S is a useful element that improves the machinability by forming MnS in steel. The lower limit of the amount of S is set to 0.005% from the viewpoint of improving the machinability. However, if it exceeds 0.10%, the ductility is lowered and forging cracks are likely to occur, so the upper limit of the amount of S was made 0.10%. In addition, the most preferable addition amount is 0.01 to 0.03%.

Ni: 2.0% or less (including 0%)
Ni need not be added. However, the addition has the effect of further improving toughness and strength. In order to exert these effects, the Ni content is preferably 0.2% or more. However, if it exceeds 2.0%, the effect is saturated and economically disadvantageous, and the machinability deteriorates, so 2.0% was made the upper limit.

Cr: 3.0% or less (including 0%)
It is not necessary to add Cr. However, if added, the tempering softening resistance of the hardened layer is improved, thereby improving the pitching life of the gear. In order to exert these effects, the Cr content is preferably 0.2% or more. However, if the Cr content exceeds 3.0%, the carbide is stabilized so that it does not dissolve even during high-frequency heating, so 3.0% was made the upper limit. The most preferable content of Cr is 0.2 to 2.0%.

Mo: 1.0% or less (including 0%)
Mo may not be added. However, the addition has an effect of strengthening the hardened layer and improving the bending fatigue strength. In order to exert these effects, the Mo amount is preferably 0.01% or more. However, even if added over 1.0%, the effect is saturated and the economic efficiency is impaired, so 1.0% was made the upper limit. The most preferred upper limit is 0.4%.

O: 0.0025% or less O is present in steel as oxide inclusions such as alumina and titania, but if there is a large amount of O, the oxide will increase in size, and this will cause damage to power transmission components. Therefore, it is necessary to limit it to 0.0025% or less. The amount of O is preferably as small as possible. In particular, it is preferably 0.0020% or less when applied to a part that requires contact fatigue characteristics, and more preferably 0.0015% or less when aiming at a long life.

N: 0.005 to 0.03%
N forms nitrides with Al, Ti, and the like and effectively works to refine austenite grains during induction hardening, and thus contributes to improvement of mechanical properties. In order to exert such effects, the N amount needs to be 0.005% or more. However, if the N content exceeds 0.03%, the forgeability is remarkably inhibited, so the upper limit was made 0.03%. The most preferable amount of N is 0.005 to 0.02%.

Al: 0.005 to 0.05%, Ti: 0.005 to 0.05%, one or two of Al, Ti precipitates and disperses in the steel as a nitride, and during induction hardening treatment There is an effect of preventing coarsening of the austenite structure, and in order to exert such an effect, one or two of Al and Ti are required to be 0.005% or more, respectively. However, if the Al content and Ti content exceed 0.05%, the precipitates become coarse and the steel becomes brittle. For this reason, the upper limit of Al amount and Ti amount was set to 0.05%. Most preferably, 0.005 to 0.05% of Al is added.

One or two of V: 0.3% or less (including 0%) and Nb: 0.3% or less (including 0%) may not be added. However, when added, Al and Ti precipitate and disperse in the steel as nitrides, thereby further preventing coarsening of the austenite structure during induction hardening. In order to exert these effects, it is preferable to add 0.01% or more of one or two of V and Nb. However, even if added over 0.3%, the effect is saturated and the economy is impaired, so the upper limit was made 0.3%. Most preferably, 0.1 to 0.2% of V is added.

  Furthermore, when improving bending fatigue strength further, 1 or more types selected from the group which consists of Ca, Mg, Zr, and Te of the following content are added.

Any one or more of Ca: 0.01% or less, Mg: 0.01% or less, Zr: 0.05% or less, Te: 0.1% or less, and the bottom of splines of shaft parts It is an element that suppresses the extension of MnS and further improves the bending fatigue strength against fatigue fracture. That is, in order to give an effect of suppressing the stretching of MnS, any one or more of Ca 0.01% or less, Mg 0.01% or less, Zr 0.05% or less, and Te 0.1% or less. Containing. However, even if each element is contained in excess of the above content, the effect is saturated and the economy is impaired, so the upper limit is set as described above.

  Preferable content is Ca: 0.0005 to 0.003%, Mg: 0.0003 to 0.002%, Zr: 0.0005 to 0.004%, Te: 0.005 to 0.03% Any one or more.

  Next, the reasons for limitation in defining other components of the present invention will be described.

A component obtained by induction-hardening the surface layer, the martensite area ratio in the tissue at a site 0.05 mm deep from the surface is 60% or more, and the hardness at the site is HRC (Rockwell hardness) 55 As described above, the surface fatigue strength is ensured by subjecting the structure to martensite transformation by induction hardening and improving the hardness. However, the area where it is required to improve the hardness differs depending on which part the present invention is applied to. For example, for small parts such as planetary pinions, it is sufficient if the hardness is increased up to about 0.3 mm from the surface, but for large parts such as CVT sheave, the hardness is up to about 2 mm from the surface. Need to be increased.

  The region to be induction hardened can be adjusted by the magnitude of the frequency. If the region is 0.3 mm, it is about 400 kHz, and if it is about 2 mm, the region is about 5 kHz. The coolant used for quenching can be any of water, polymer quenching material, and quenching oil, and water is usually sufficient, but quenching with a slow cooling rate is necessary when the shape is prone to cracking during quenching. It is desirable to prevent cracking with oil.

  In any part, high hardness is required in the vicinity of the surface, and from the viewpoint of surface fatigue strength, higher hardness is required in the portion closer to the surface. Therefore, in the present invention, the hardness is 0.05 mm from the surface. It was decided to prescribe. If the hardness is less than HRC55, it is insufficient for ensuring the surface fatigue strength. Therefore, in the present invention, the hardness is set to HRC55 or more.

  In the steel material component of the present invention, the structure after induction hardening is mainly martensite, and in addition, retained austenite, ferrite, pearlite, and bainite may be present. However, when insufficient heating occurs during induction heating, the martensite area ratio is 60. %, And therefore, it may be less than HRC55 and the surface fatigue strength may not be satisfied. Therefore, in the present invention, the martensite area ratio is set to 60% or more.

  With this martensite area ratio, starting from a depth of 0.05 mm from the surface, a square region having a depth direction of 0.15 mm and a width direction of 0.15 mm is observed with a 400 × optical microscope, It refers to the area ratio of the martensite structure to the total area.

  In order to obtain the above-described hardness and martensite area ratio, it is necessary to set the high-frequency heating temperature to 910 ° C. or higher, which is equal to or higher than the Ac3 transformation point, but if it exceeds 1150 ° C., there is a concern of causing coarsening of crystal grains. Therefore, it is desirable that the upper limit is 1150 ° C. If the high-frequency heating time is too long, the heat conduction will reach the interior of the part beyond the Ac3 transformation point, and there is a concern that the spheroidized carbide in the core will dissolve and the toughness will decrease, so it is preferably within 10 seconds.

Substantial ferrite in which core structure which is non-inductively hardened part does not contain bainite In order to ensure toughness and machinability, the component of the present invention is a real ferrite in which the structure of core part which is a non-inductively hardened part does not contain bainite. Need to be.

  Since bainite significantly deteriorates toughness and machinability, it must be completely eliminated. Further, the reason for making the ferrite substantially is to sufficiently secure a structure having a low C content and improve toughness. This substantial ferrite means that the ferrite area ratio in the structure is 95% or more, and pearlite and / or retained austenite is allowed for the balance. The ferrite area ratio is observed with an optical microscope of 400 times and refers to the area ratio of the ferrite structure with respect to the total area.

In the present invention, substantially all of the carbides present in the core structure are spherical carbides. The carbides are cementite in which Fe is bonded to C, cementite in which Fe and an alloy are bonded to C, and Fe and an alloy are bonded to C. An alloy-based carbide or an alloy-based carbonitride in which Fe, an alloy, and N are bonded to C. The term “substantially all” as used herein means that the spherical carbide ratio defined below is 95% or more.

   Spherical carbide ratio (%) = (number of carbides having an aspect ratio of less than 3 / total number of carbides) × 100

  Here, the aspect ratio means a ratio (L / D) of the maximum length L of carbides and the maximum length D in the perpendicular direction in the observation of the metal structure by a scanning electron microscope. The number of all carbides is This is the total number of carbides having an aspect ratio of less than 3 and carbides having an aspect ratio of 3 or more (however, including lamellar cementite in pearlite and not including cementite at grain boundaries). Carbide can be observed with a scanning electron microscope, and since a peak of C appears by EDS qualitative analysis, it can be identified.

  If the carbide spheroidization is insufficient, the lamellar shaped cementite in the pearlite remains without spheroidizing, and plastic deformation is hindered during large deformation due to high impact load on the part, so that the toughness is reduced. In addition, substantially all of the carbides present in the core structure were spherical carbides.

  Next, a description will be given below of a method in which the core structure, which is a non-induction hardened part, is substantially ferrite containing no bainite, and substantially all of the carbides present in the structure are made into spherical carbides.

  In order to obtain the core structure and carbide as described above, after hot forging or cold forging, it was heated for 1 hour or more at a temperature (740 to 780 ° C.) slightly higher than the Ac1 transformation point (around 730 ° C.). After that, the temperature from the heating temperature to 550 ° C. is gradually cooled at a cooling rate of 1 ° C./min or less. In addition, about 550 degrees C or less, even if a cooling rate will be 1 degree C / min or more, it does not interfere. By suppressing the cooling rate between the heating temperature and 550 ° C., the spheroidization of the carbide can be promoted and the formation of bainite can be suppressed. The spheroidized carbide can be coarsened so as to suppress the cooling rate between the heating temperature and 550 ° C. For example, when cooled at a cooling rate of 0.1 ° C / min, the carbide particle size is around 2 µm. However, it is preferable in terms of toughness. However, if the cooling rate between the heating temperature and 550 ° C. becomes too long, the productivity is lowered, so the cooling rate is preferably 0.1 to 0.5 ° C./min.

  In addition, when adopting hot forging, the reason for performing the heat treatment from the above heating to cooling after the hot forging is that the heat treatment before the hot forging makes the spheroidization by the heating during the hot forging. This is because the annealed structure disappears. In the case of adopting cold forging, the reason why the heat treatment from the heating to the cooling is performed after the cold forging is that the cold forging work hardening even if the heat treatment is performed before the cold forging if necessary. In addition to hindering the machinability, there is an adverse effect that the coarsening of the crystal grains is liable to occur by subsequent high-frequency heating due to the influence of processing distortion accumulated by cold forging. For this reason, the said heat processing after cold forging is needed.

  Usually, when steel material with C of 0.6% or more is used as a raw material, it is formed by hot forging. When steel material with C is less than 0.6%, it is formed by hot forging or cold forging. Is done.

  In addition, induction hardening parts to which the present invention is applied are subjected to induction hardening, and further processing such as sub-zero treatment, tempering treatment, shot peening treatment, WPC treatment, barrel polishing treatment, tooth polishing treatment, honing finishing processing, etc. Of course, you may go.

  Hereinafter, the present invention will be specifically described by way of examples. These examples are for explaining the present invention, and do not limit the scope of the present invention.

  Each hot-rolled steel material having the chemical composition shown in Table 1 is held at 760 ° C. for 300 minutes after hot forging or cold forging, then cooled to 560 ° C. at the cooling rate shown in Table 2, and then allowed to cool and spheroidized. After the annealing treatment, a small roller test piece having a cylindrical portion with a diameter of 26 mm and a width of 28 mm and a large roller test piece with a diameter of 130 mm and a width of 18 mm were manufactured for a roller pitting fatigue test by machining. Similarly, a U-notch impact test piece (shown in FIG. 2a of JIS Z 2202) and a φ65 mm round bar for machinability evaluation were manufactured. Thereafter, the small roller test piece and the large roller test piece were No. 1-No. No. 17 was subjected to induction hardening with a frequency of 100 kHz, a heating temperature of 980 ° C., and water as a refrigerant, and then subjected to a tempering treatment at 180 ° C. for 90 minutes to conduct a roller pitching fatigue test. No. 18 was subjected to induction hardening using a frequency of 100 kHz, a heating temperature of 900 ° C., and water as a refrigerant, and then subjected to a tempering treatment at 180 ° C. for 90 minutes to conduct a roller pitching fatigue test. The U-notch impact test piece is No. 1-No. 17 was subjected to induction hardening using a frequency of 400 kHz, a heating temperature of 980 ° C., and water as a refrigerant, followed by tempering at 180 ° C. for 90 minutes and subjected to an impact test. No. 18 was subjected to induction hardening using a frequency of 400 kHz, a heating temperature of 900 ° C., and water as a refrigerant, followed by tempering at 180 ° C. for 90 minutes and subjected to an impact test.

  A roller pitching fatigue test was performed using the large roller and the small roller produced as described above. In the roller pitching fatigue test, the large roller is pressed against the small roller with a surface pressure of 3000 MPa, the circumferential speed direction of both rollers at the contact portion is the same direction, and the slip rate is −40% (larger roller than the small roller). The rotation speed of the small roller until the occurrence of pitching in the small roller was defined as the life. The oil temperature of the gear oil supplied to the contact portion was 80 ° C. The occurrence of pitching was detected by a vibrometer provided in the testing machine, and after the vibration was detected, the rotation of both rollers was stopped and the occurrence of pitching and the number of rotations were confirmed.

  Next, the impact value at room temperature was measured using the U-notch impact test produced above. The φ65mm round bar for machinability evaluation was carried out using a TiN-coated carbide tool under dry conditions with a cutting depth of 2mm, a feed rate of 0.25mm / rev and a cutting rate of 200mm / min. The time reaching 0.2 mm was measured as the tool life. The test results and measurement results are shown in Table 2.

As shown in Table 2, No. of the present invention example. 1-No. It was revealed that No. 13 roller test piece has a life of 10 million times or more and has excellent pitting fatigue strength (surface pressure fatigue strength). Further, it was revealed that the U-notch impact test piece of the present invention example has an impact value of 20 J / cm ² or more and has excellent toughness. The tool life was also good over 20 minutes.

  On the other hand, No. of the comparative example which made C amount deviate from the component range prescribed | regulated in this invention. No. 14 had a short pitching fatigue test life of 4,832,000 times. This is because the hardness HRC at a depth of 0.05 mm from the surface was less than 55 due to the low C.

  In Comparative Example No. 1 in which the amount of Cr deviates from the component range defined in the present invention. 15 had a short pitching fatigue test life of 6,231,000 times. This is presumably because Cr was low and the temper softening resistance of the quenched layer was insufficient.

  Comparative Example No. HRC deviated from the range defined in the present invention. No. 16 had a short pitching fatigue test life of 3,544,000 times. This is because the carbide is stabilized because Cr is high, and the hardness at a depth of 0.05 mm is lower than that of HRC55 due to the fact that C did not dissolve in the structure at the time of high-frequency heating.

Comparative Example No. 1 in which the cooling rate conditions, the core structure, and the shape of the carbides were different from the ranges defined in the present invention. No. 17 had a low impact value of 11 J / cm ² . This is because the cooling rate after spheroidizing annealing is as high as 1.5 ° C./min, and therefore the core structure contains bainite and the ferrite is 80%, and the tool life is greatly reduced to 20 minutes. .

  Comparative Example No. HRC deviated from the range defined in the present invention. No. 18 had a short pitching fatigue test life of 2,335,000 times. This is because the hardness at a depth of 0.05 mm was lower than HRC55 due to the fact that the high-frequency heating temperature was low and C did not dissolve in the tissue. In addition, the martensite area ratio also decreased as C did not dissolve in the structure.

Claims (5)

% By mass
C: 0.4 to 1.2%,
Si: 2.0% or less,
Mn: 0.2 to 3.0%
P: 0.03% or less,
S: 0.005 to 0.10%,
Ni: 2.0% or less (including 0%),
Cr: 3.0% or less (including 0%),
Mo: 1.0% or less (including 0%),
O: 0.0025% or less,
N: 0.005-0.03%
In addition,
Al: 0.005 to 0.05%,
Ti: 0.005 to 0.05%
One or two of them,
V: 0.3% or less (including 0%),
Nb: 0.3% or less (including 0%)
A martensite area in the structure at a depth of 0.05 mm from the surface, which is made of steel containing one or two of the above, the balance being made of steel consisting of iron and inevitable impurities, and the surface layer being induction-hardened The rate is 60% or more, the hardness at the part is HRC55 or more, and the structure of the core part which is a non-high-frequency quenching part is a substantial ferrite containing no bainite, and the carbides present in the core part structure induction hardening components substantially all of Ri globular carbides der, characterized in that it is applied to a continuously variable transmission (CVT).   Further, the steel has a chemical composition of at least one of Ca: 0.01% or less, Mg: 0.01% or less, Zr: 0.05% or less, Te: 0.1% or less. The induction-hardened component according to claim 1, which is contained. % By mass
C: 0.4 to 1.2%,
Si: 2.0% or less,
Mn: 0.2 to 3.0%
P: 0.03% or less,
S: 0.005 to 0.10%,
Ni: 2.0% or less (including 0%),
Cr: 3.0% or less (including 0%),
Mo: 1.0% or less (including 0%),
O: 0.0025% or less,
N: 0.005-0.03%
In addition,
Al: 0.005 to 0.05%,
Ti: 0.005 to 0.05%
One or two of them,
V: 0.3% or less (including 0%),
Nb: 0.3% or less (including 0%)
1 or 2 of the steel, and the remainder consisting of iron and inevitable impurities is subjected to hot forging or cold forging, and then heated to 740 to 780 ° C. for 1 hour or more, from the heating temperature to 550 ° C. Is gradually cooled at a cooling rate of 1 ° C./min or less, and then subjected to induction quenching, the martensite area ratio in the structure at a depth of 0.05 mm from the surface is 60% or more. And the hardness in the said part is HRC55 or more, the structure of the core part which is a non-high frequency hardening part is a substantial ferrite which does not contain a bainite, and substantially all of the carbide | carbonized_material which exists in this core part structure | tissue is a spherical carbide. A method for manufacturing an induction-hardened component, characterized by: Further, the steel has a chemical composition of at least one of Ca: 0.01% or less, Mg: 0.01% or less, Zr: 0.05% or less, Te: 0.1% or less. The method of manufacturing an induction-hardened component according to claim 3, wherein the component is contained . The induction hardening component according to claim 3 or 4, wherein the induction hardening component is applied to a continuously variable transmission (CVT).