JP3458604B2 - Manufacturing method of induction hardened parts - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine part manufactured by induction hardening / tempering treatment using machine structural steel, particularly an induction hardened part which is suitable for manufacturing gears and which is excellent in economic efficiency. The present invention relates to a manufacturing method.

[0002]

Gears used in automobiles and industrial machines are
Manufactured by a method that imparts the necessary function as a gear by carburizing and tempering after processing to a predetermined shape by forging → cutting → turning → gear cutting using alloy steel for carburization containing about 0.2% carbon . The carburizing process is a mainstream manufacturing process for gears, but carburizing requires a carburizing process at a temperature of about 800 to 950 ° C for several hours. Since it is difficult to put the gear manufacturing process in-line, there is a limit to the improvement of productivity, which has been a major obstacle in reducing the manufacturing cost.

Generally, carburizing is generally carried out by a gas carburizing method, but an abnormal surface layer is inevitably formed on the surface layer of a material to be treated during gas carburizing, and this abnormal layer deteriorates fatigue strength and impact characteristics. Therefore, there is a limit to further improvement in fatigue strength and impact properties. Further, since the material to be treated is deformed by the heat treatment strain generated during carburizing and quenching, strict control of the heat treatment conditions is indispensable. In order to overcome the above problems, it is assumed that the carburizing process is adopted.
Developed high strength carburizing steel intended to improve fatigue strength and impact characteristics by reducing Si, Mn, Cr in steel and adding Mo, Ni etc. to reduce the abnormal surface layer generated during gas carburizing. However, since a large amount of expensive alloy components are used to increase the cost of steel materials and deteriorate machinability such as machinability, high strength can be achieved but the manufacturing cost is increased. was there.

On the other hand, it has been attempted to manufacture gears by induction hardening, which has a higher production efficiency than the carburizing and quenching process, using alloy steels for machine structures such as JIS standards SCM435 and S55C and carbon steels. It is difficult to apply to high-strength gears used in automobile transmissions and differentials, such as gears manufactured by the carburizing process because the composition is not originally determined in consideration of application to gears. It was only applied to gears with relatively low strength.

In order to solve these problems, for example, JP-A-60-169544 (parts for high-strength mechanical structures and a method of manufacturing the same) regulates the component composition and applies it to gear manufacturing by an induction hardening process. The technology is proposed and disclosed. However, according to the study by the inventors, there is a problem in this technique that the size of non-metallic inclusions is large and the fatigue strength and rolling fatigue life required for gear steels are still insufficient.

[0006]

The present invention advantageously solves the above-mentioned problems and is suitable for manufacturing gears and the like capable of ensuring quality characteristics equivalent to or better than those of conventional carburizing processes. It is intended to propose a method for manufacturing a hardened part.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the inventors have conducted various experiments and studies on the composition of the steel material in order to ensure the characteristics required for gears in an induction hardening process. We came to obtain such knowledge.

Gears are required to have root strength, tooth surface strength and impact characteristics. Here, the tooth root strength means the maximum stress at which the tooth portion is repeatedly stressed and does not cause fatigue fracture from the tooth root portion. This root strength has a good correlation with the fatigue strength of fatigue tests such as rotary bending, so the chemical composition of the steel was investigated by rotary bending fatigue tests. As a result, the basic factors affecting fatigue strength are material hardness, austenite grain size and non-metallic inclusions. If the material hardness decreases, the fatigue strength also decreases. In order to ensure the hardness of this material to be approximately the same as that of the carburized and hardened material by induction hardening, the C content must be about 0.5% or more. In order to secure the hardness of the material, it is effective to add the alloying component from the viewpoint of improving the hardenability, but this may be added in an appropriate amount according to the size of the gear.

Not only the hardness of the material but also the finer austenite grain size is effective for improving the fatigue strength. This is because fatigue cracks grow along the former austenite grain size, so making them finer increases the resistance to fatigue crack propagation, and segregates at grain boundaries such as P to cause this. This is because the concentration of the component that causes embrittlement decreases as the austenite grains become finer. Induction hardening is extremely effective for grain refinement of austenite because it is rapid heating for a short time, but addition of N, Al, etc., which forms precipitates that suppress the growth of austenite grains, is much more effective. Fine graining is effective for improving fatigue strength.

Next, in order to improve fatigue strength,
In addition to ensuring the hardness of the above-mentioned materials and making the austenite grains fine, it is also important to reduce non-metallic inclusions. That is, even if the hardness of the material can be secured, if an oxide-based non-metallic inclusion is present, fatigue fracture will occur from this portion, and the fatigue strength will decrease. In particular, hard nonmetallic inclusions such as alumina are harmful, and for this purpose, reduction of O is essential. According to the examination result, O
The amount must be at least 0.0015% or less, but this is not sufficient, and the number and size of oxides must be limited to ensure fatigue strength equal to or higher than that of conventional carburized materials. Has been found to be important.

As described above, when non-metallic inclusions are present, fatigue fracture progresses starting from the inclusions.
The larger the non-metallic inclusion, the more remarkable the stress concentration in the inclusion becomes, and the easier the initial fatigue crack occurs.
In addition, the occurrence of initial cracks becomes more remarkable as the size of non-metallic inclusions and the degree of stress concentration increase, and once large initial cracks occur, fatigue cracks quickly expand and lead to fatigue failure.

According to the examination results, in order to secure the fatigue strength equal to or higher than that of the conventional carburized and hardened material by induction hardening, it is important that no oxide-based nonmetallic inclusion having a size exceeding 19 μm is present. I found out. further,
As a result of examining the influence of the number of non-metallic inclusions,
It was found that even if the number is 19 μm or less, if the number exceeds 2.5 pieces / mm ² , the fatigue strength equal to or higher than that of the conventional carburized and hardened material cannot be obtained. This is because when the nonmetallic inclusions are small, the initial cracks generated from that part are small, but when this grows, it becomes a large fatigue crack by coalescing with the fatigue cracks generated from other nonmetallic inclusions, and then the fatigue cracks rapidly develop. This is because it grows and leads to fatigue failure in a short time. As described above, in order to secure the fatigue strength, it is necessary to control not only the amount of O but also the number and size of oxide-based non-metallic inclusions.

Further, a method for reducing the amount and size of oxide-based non-metallic inclusions within the above range was investigated. As a result, it was found that by limiting the O content in the steel to 15 ppm or less, the amount of oxide-based non-metallic inclusions could be reduced to the target of 2.5 pieces / mm ² or less. Regulations alone are not enough. Therefore, as a result of various studies, the total area reduction rate when rolling to the final steel material from the slab size at the time of casting has a strong correlation with the nonmetallic inclusion size, and as the area reduction rate increases, We have found that the size of inclusions decreases. This is because the coarse nonmetallic inclusions are mechanically crushed by rolling. Further, it has been found that in order to achieve the target size of 19 μm or less, the O content is controlled to be 15 ppm or less, and the reduction of area is required to be 95% or more.

Next, fatigue damage called pitching occurs on the tooth surface due to repeated contact stress and friction. When this occurs, it becomes difficult for the gear to perform its normal function, and therefore the tooth surface strength that can withstand these is required. This tooth surface strength has a good correlation with the rolling fatigue test, and can be evaluated by this test. By the way, a relative slip occurs on the tooth flank of the gear, and this friction causes a remarkable temperature rise. This temperature rise softens the steel material and causes pitching on the tooth surface. In order to suppress this, it is effective to add Si, Mo, V, Nb, etc., which increase the tempering softening resistance of steel, and the addition of these can increase the tooth surface strength. Further, the rolling fatigue life is affected by the amount and size of the oxide-based non-metallic inclusions similarly to the fatigue strength. However, the control of the O amount and the reduction rate of the cross-section when rolling from the slab to the final steel material are performed. By controlling the amount and size of the non-metallic inclusions, it has been found that a rolling fatigue life equivalent to or higher than that of the conventional carburized steel can be secured.

When an impact load is applied to the tooth root, if the impact property of the steel material is low, the tooth is broken from the tooth root portion, and not only the gear but also the entire machine in which the gear is incorporated is damaged which is difficult to recover. Up to Therefore, the impact characteristics are extremely important characteristics. The amount of C has the greatest effect on the impact properties, but the C concentration of the carburized part after the carburizing process is about 0.8%, while the equivalent hardness of steel material by induction hardening. The amount of C required to obtain
Since it is about 0.5 to 0.7%, it is advantageous from the viewpoint of securing impact characteristics. Further, not only the factors that affect the impact characteristics but also the austenite grain size during induction hardening and the impurity components such as P segregated at the grain boundaries also influence, and the austenite grains become finer and the impurity components such as P are also affected. Is also effective for improving impact characteristics. However, when comparing only the non-hardened parts, the carburizing steel has a low C content of about 0.2%, while 0.5-0.7 for application to induction hardening.
The conventional carburized steel is more advantageous for the non-hardened part because it increases the% C and the amount of C.

In the case of the entire gear, the impact characteristics are determined by the action of these factors, so in the steel for induction hardening, it is important to improve the impact characteristics of the non-hardened part. Therefore, as a result of further studying measures for improving the impact characteristics of the non-hardened part, it is possible to further improve the impact characteristics of the entire gear by specifying the forging temperature and the subsequent cooling rate in the forging process from the steel material to the gear. I found it.

Generally, the improvement of the impact properties of steel materials is achieved by refining the microstructure of steel, but in the above study results, the forging temperature range was set to the range of Ac ₃ -100 ° C to Ac ₃ + 200 ° C. It has been clarified that the processing rate at 70% and the subsequent cooling rate at 0.005 ° C./s or more are most effective for the refinement of the structure.

The present invention is based on the above findings, and the gist of the invention is as follows.

C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 ma
ss% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.
05 mass% or less, P: 0.010 mass% or less, S: 0.020 mass
% Or less, O: 0.0015 mass% or less and N: 0.002 mass%
Above, 0.006 mass% or less is contained, the balance becomes composition of Fe and unavoidable impurities, and the number of oxide-based nonmetallic inclusions in the steel is 2.5 pieces / mm ² or less, maximum size:
For steel materials of 19 μm or less, Ac ₃ points −100 ° C or more, Ac ₃ points +20
It is heated to a temperature range below 0 ° C, and the processing rate is 70% in that temperature range.
% Or more, then 0.005 ℃ / s or more, 10 ℃ /
A method for manufacturing an induction-hardened component, which comprises cooling in a cooling rate range of s or less and then performing induction hardening and tempering treatment (first invention).

C: 0.5 mass% or more, 0.75 mass% or less
Lower, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 ma
ss% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.
05 mass% or less, P: 0.010 mass% or less, S: 0.020 mass
% Or less, O: 0.0015 mass% or less and N: 0.002 mass%
Above, including 0.006 mass% or less, and Ni: 0.1 mass%
Or more, 1.0 mass% or less, Mo: 0.05 mass% or more, 0.50mass
% Or less, Ti: 0.005 mass% or more, 0.05 mass% or less and
B: Select from 0.0003 mass% or more and 0.005 mass or less
Contains one or more of the
The composition of unavoidable impurities and the oxide-based non-
Number of metal inclusions: 2.5 / mm ²Below, maximum size:
Steel material of 19 μm or less₃Point -100 ° C or higher, Ac₃Point +20
It is heated to a temperature range below 0 ° C, and the processing rate is 70% in that temperature range.
% Or more, then 0.005 ℃ / s or more, 10 ℃ /
Cooling in the cooling rate range of s or less, then induction hardening
Induction-hardened parts characterized by being tempered
Manufacturing method (2nd invention).

C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 ma
ss% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.
05 mass% or less, P: 0.010 mass% or less, S: 0.020 mass
% Or less, O: 0.0015 mass% or less and N: 0.002 mass%
Above, including 0.006 mass% or less, and V: 0.05 mass%
Or more, 0.5 mass% or less and Nb: 0.01 mass% or more, 0.5
It contains one or two selected from mass% or less, the balance is Fe and inevitable impurities, and the number of oxide-based nonmetallic inclusions in the steel is 2.5 / mm. ² or less, maximum size: steel material of 19 μm or less is heated to a temperature range of Ac ₃ points −100 ° C. or more and Ac ₃ points + 200 ° C. or less,
After forging with a processing rate of 70% or more in that temperature range,
A method of manufacturing an induction-hardened component, which comprises cooling in a cooling rate range of 0.005 ° C./s or more and 10 ° C./s or less, and then performing induction hardening and tempering treatment (third invention).

C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 ma
ss% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.
05 mass% or less, P: 0.010 mass% or less, S: 0.020 mass
% Or less, O: 0.0015 mass% or less and N: 0.002 mass%
Above, including 0.006 mass% or less, and Ni: 0.1 mass%
Or more, 1.0 mass% or less, Mo: 0.05 mass% or more, 0.50mass
% Or less, Ti: 0.005 mass% or more, 0.05 mass% or less and B: 0.0003 mass% or more, 0.005 mass or less, one or more kinds selected and V: 0.05 mass% or more, 0.5 ma
ss% or less and Nb: 1 or 2 selected from 0.01 mass% or more and 0.5 mass% or less, with the balance being Fe
And the composition of unavoidable impurities, and the number of oxide non-metallic inclusions in the steel is 2.5 pieces / mm ² or less, maximum size: 19 μm or less steel material, Ac ₃ points −100 ° C. or more,
Ac ₃ points +200 ℃ Heated to a temperature range of less than 200 ℃, forged with a working rate of 70% or more in that temperature range, then cooled in the cooling rate range of 0.005 ℃ / s or more, 10 ℃ / s Then, a method for manufacturing an induction-hardened component, characterized by performing induction hardening and tempering treatment (fourth invention).

The steel material has been subjected to rolling at a cross-section reduction rate of 95% or more from the cast slab, and a method for manufacturing an induction-hardened component according to any one of claims 1 to 4 (fifth invention). ).

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limitation in carrying out the present invention will be described below. First, the reasons for limiting the component composition will be described. C: 0.5 to 0.75 mass% C is an essential component for obtaining the same surface hardness as conventional carburized steel by induction hardening, and is at least 0.5 ma.
It is necessary to contain ss% or more. But 0.75ma
If it is contained in excess of ss%, the impact properties and machinability required for gears deteriorate. Therefore, its content is 0.5
Mass% or more and 0.75 mass% or less.

Si: 0.5 to 1.8 mass% Si is a component for improving the tempering softening resistance and improves the tooth surface strength. However, in order to secure the tooth surface strength comparable to that of the gear by the conventional carburizing process. At least 0.5 mass
%, But if it is contained in excess of 1.8 mass%, the solid solution hardening of ferrite raises the hardness and lowers the machinability. Therefore, its content is 0.5
The content is set to not less than mass% and not more than 1.8 mass%, but a more preferable range is 0.5 to 1.0 mass%.

Mn: 0.4 to 1.5 mass% Mn is an essential component for improving the hardenability and ensuring the hardening depth during induction hardening, but it is added positively.
If the content is less than 0.4 mass%, the effect is poor, and 1.5%
If it exceeds, the retained austenite after induction hardening is increased to rather lower the surface hardness and reduce the fatigue strength and rolling fatigue life. Therefore, the content is set to 0.4 mass% or more and 1.5 mass% or less, and a more preferable range is 0.7 to 1.3 mass%.

Al: 0.019 to 0.050 mass% Al is an effective component for deoxidation and is useful for lowering oxygen, and also combines with N to form AIN, which grows austenite grains during high frequency heating. Is added positively because it improves impact properties and root strength, but the effect is poor when the content is less than 0.019 mass%, and the effect is saturated even if added over 0.05 mass%. . Therefore, its content is 0.019 mass% or more, 0.05
It should be 0 mass% or less.

P: 0.01 mass% or less P is segregated at the grain boundaries of austenite and lowers the grain boundary strength, thereby not only lowering the tooth root strength, but
At the same time, impact properties are deteriorated, so it is desirable to reduce the content as much as possible, and the content is allowed up to 0.01 mass%.

S: 0.020 mass% or less S forms MnS, which acts as the starting point of fatigue fracture to lower the fatigue strength. On the other hand, MnS is also a component that improves machinability, so 0.020 mass% Can be included.

O: 0.0015 mass% or less O is preferably as small as possible. In order to control the amount and size of the nonmetallic inclusions to be equal to or less than the target value, O forming oxide type nonmetallic inclusions such as alumina is required. Although it is necessary to reduce the content, the content thereof should be 0.0015 mass% or less.

N: 0.002 to 0.006 mass% N combines with Al to form AIN. Since this improves impact properties and fatigue strength by suppressing the growth of austenite grains during high frequency heating, it is added positively.
If the content is less than 0.002 mass%, the effect is small,
If it exceeds 6 mass%, the hot deformability is lowered and the surface defects of the slab are increased during continuous casting. Therefore, the content is set to 0.002 mass% or more and 0.006 mass% or less.

In addition to the above component composition, in the present invention, Ni, Mo, Ti and B can be contained alone or in combination as the same effect components for improving fatigue strength, tooth surface strength and impact characteristics. These actions are as follows.

Ni: 0.1 to 1.0 mass% Ni is a component that not only improves hardenability and is effective in improving fatigue strength and tooth surface strength, but also improves impact properties. Therefore, when adjusting hardenability or It may be used especially when improvement of impact properties is required. Content is 0.1 mass%
If less than 1.0%, the effect is not sufficient. On the other hand, since Ni is an extremely expensive component, if it exceeds 1.0 mass%, the cost of the steel material increases, which is contrary to the object of the present invention. Therefore, the content is preferably 0.1 mass% or more and 1.0 mass% or less, and a more preferable range is 0.6 to 0.9 mass%.

Mo: 0.05 to 0.50 mass% Mo is a component useful for improving hardenability and various properties, and is used not only for adjusting hardenability, but also for significantly affecting the morphology of pearlite, Cementite forms divided pearlite, and as a result, machinability is significantly improved. Further, since the temper softening resistance is improved, the tooth surface strength can be improved, and further, the effect of improving the fatigue strength, the root strength and the impact characteristics by reducing the impurity components such as P segregated at the grain boundaries. There is. As described above, since it is a preferable component in the present invention, it is preferable to positively add it, but the content is 0.05 ma.
If it is less than ss%, its effect is poor, and if it exceeds 0.50 mass%, carbides that are difficult to dissolve in austenite are formed by heating for a short time such as induction hardening. Therefore, the content is preferably 0.05 mass% or more and 0.50 mass% or less, more preferably 0.10 to 0.30 mass%.

Ti: 0.005 to 0.05 mass% Ti is a component which is very likely to bond with N and forms TiN which has a function of refining austenite grains during high frequency heating. Therefore, Ti alone causes fatigue. It has the effect of improving strength, tooth surface strength and impact characteristics. On the other hand, Ti is B
As described above, since it is easily bonded to N, in the case of composite addition with B, the bond between B and N is suppressed and the hardenability of B is secured (the hardenability of B exists in the steel alone in the steel. There is also the effect). To achieve these effects, a content of less than 0.005 mass% is not enough,
If the content exceeds mass%, TiN will be excessively precipitated, and this will become the starting point of fatigue fracture, reducing fatigue strength and tooth surface strength. Therefore, its content is 0.005mass% or more, 0.05mass%
The following is preferable, but the range of 0.01 to 0.025 mass% is more preferable.

B: 0.0003 to 0.005 mass% B is a component that improves the hardenability by adding a trace amount, so that other alloy components can be reduced. Further, B segregates preferentially at the grain boundaries, and the concentration of P segregated at the grain boundaries is reduced, so that fatigue strength, root strength and impact characteristics are significantly improved. In order to bring out these effects
0.0003 mass% or more is desirable, but 0.005
Even if it is contained in excess of mass%, the effect is saturated. Therefore, its content is 0.0003 mass% or more, 0.005 mass%
The following is preferable, but a more preferable range is 0.0010 to 0.0030mass.
%.

Further, in the present invention, V and Nb having a precipitation strengthening effect can be added alone or in combination. These actions are as follows. When an induction hardening process is performed, it is common to perform a quenching and tempering process as a pre-heat treatment in order to secure the hardness of the central portion of the material to be processed. However, it is desirable to omit this heat treatment because it increases the cost. In order to omit the quenching and tempering as the pretreatment, it is important to raise the hardness of the material before induction hardening, but for that purpose, the addition of V and Nb, which have a precipitation strengthening effect, is effective. is there.

V: 0.05 to 0.5 mass% V has an extremely strong precipitation strengthening effect and is a component that improves the tempering softening resistance of the steel material, so it is extremely effective in improving the tooth surface strength. Further, it is also effective to add it when it is necessary to omit the quenching and tempering treatment as a preheat treatment before induction hardening. If the content is less than 0.05 mass%, the effect is small, and if the content exceeds 0.5 mass%, the effect is saturated. Therefore, its content is 0.05 mass%
Above, 0.5 mass% or less is preferable.

Nb: 0.01 to 0.5 mass% Like V, Nb has a very strong precipitation strengthening effect and is a component for improving the tempering softening resistance of the steel material, so it is extremely effective for improving the tooth surface strength. Further, it is also effective to add it when it is necessary to omit the quenching and tempering treatment as a preheat treatment before induction hardening. If the content is less than 0.01 mass%, the effect is small, and if the content exceeds 0.5 mass%, the effect is saturated. Therefore, the content is preferably 0.01 mass% or more and 0.5 mass% or less.

Next, in the present invention, in order to secure the fatigue strength, the amount and size of the oxide-based nonmetallic inclusions are specified to be 2.5 pieces / mm ² or less and 19 μm or less, respectively. As mentioned above, the number of oxide-based non-metallic inclusions
If the number of oxides exceeds 2.5 pieces / mm ^{2, the} presence of oxides in excess of these will combine the fatigue cracks generated from the respective non-metallic inclusions to rapidly propagate the fatigue cracks, resulting in fatigue fracture. This is because it becomes difficult to secure the strength. In addition, the size is specified to be 19 μm or less because the presence of non-metallic inclusions exceeding this size facilitates and enlarges the initial cracks generated from these non-metallic inclusions, resulting in rapid fatigue crack growth and early fatigue. This is because destruction will occur.

Further, the reason why the cross-section reduction rate is 95% or more in the rolling from the cast slab to the steel material is to make the size of the oxide nonmetallic inclusions to be 19 μm or less which is the target, and the cross-section reduction below this This is because there are cases where the target size cannot be made smaller than the target size.

Next, the reasons for limiting the hot forging conditions will be described. Forging temperature is Ac ₃ -100 ℃ ~ Ac ₃ +200 ℃
The temperature range below Ac ₃ -100 ℃ is limited to
Deformation resistance is high, is because forging becomes difficult, Ac ₃ +
This is because at temperatures above 200 ° C., the initial austenite grain size becomes large and recrystallization and grain growth of the austenite grains after processing occur extremely rapidly, and the structure transformed from this austenite is not sufficiently refined.

The reason why the working rate is set to 70% or more is that the working rate lower than this is not sufficient for refining austenite and the microstructure of the transformed steel is not sufficiently fine. Further, the cooling rate is specified to be 0.005 ° C./s or more and 10 ° C./s or less because the transformation structure becomes coarse at a cooling rate lower than 0.005 ° C./s and a sufficient refining effect cannot be obtained. This is because the machinability may be significantly reduced due to the formation of the martensite structure at a cooling rate higher than ° C / s. A more preferable cooling rate range is 0.05 ° C / s to 1.5 ° C / s.

[0044]

EXAMPLES A converter (continuous cross-section casting process) was used to cast slabs (cross-sectional size: 200 × 225 mm) having a total of 23 kinds of component compositions of the compatible steel of the present invention, the comparative steel and the conventional steel shown in Table 1.

[0045]

[Table 1]

After that, each slab was rolled into a 150 mm square billet through a breakdown process, and then rolled into a steel bar having a different size (changing the cross-section reduction rate). Next, the steel materials sampled from each of these steel bars were forged under different conditions and then heated as pre-heat treatment at 850 ° C for 30 minutes,
After quenching, tempering treatment was performed at a temperature of 550 ° C. In addition,
For Steel Nos. 11 and 12, such pre-heat treatment was partially omitted.

Subsequently, a rotating bending fatigue test piece and a rolling fatigue test piece were prepared from each of the test materials, and a high-frequency of 15 kHz was used for those using compatible steel and comparative steel (steel Nos. 1 to 21). After hardening the surface with a hardening tester, 180
It was tempered at ℃ × 2 hours. The impact test pieces were subjected to the same induction hardening and tempering as described above, and then the impact test pieces having a 2 mm 10R notch were taken from the vicinity of the surface of the steel material.

For conventional steels (Steel Nos. 22 and 23), instead of the induction hardening and tempering described above, 930 ° C. × 4
After carburizing and quenching treatment for a time (carbon potential 0.88), tempering was conducted at 180 ° C for 2 hours.

The test pieces thus obtained were subjected to a rotary bending fatigue test, a rolling fatigue test and an impact test, respectively.

Here, each test procedure is as follows. Fatigue test: Ono type rotary bending fatigue tester at room temperature
The rotation speed was 3600 rpm.・ Rolling fatigue test: A 130 mmφ roller was pressed against a 25 mmφ test piece to give a contact stress of 3677 MPa, and the life was evaluated by the number of stress repetitions until pitting occurred on the surface. -Impact test: A Charpy impact tester was used at a temperature of 20 ° C.

The rolling and forging conditions and the test results are shown in Tables 2 to 5, respectively.

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

[0055]

[Table 5]

Here, Table 2 is a conforming example in which the conforming steel of the present invention was used and rolling and forging were performed under the conditions conforming to the present invention, and Table 3 is the conforming steel, and the forging conditions outside the limited range of the present invention. Comparative Examples performed, Table 4 shows that compatible steel was used, and rolling was performed under rolling conditions outside the limit range of the present invention, so the size of oxide-based non-metallic inclusions was also outside the limit range of the present invention, and the forging temperature was also the limit of the present invention. Comparative examples conducted out of the range, and Table 5 is a summary of comparative examples and conventional examples using comparative steels and conventional steels whose component compositions are out of this invention.

As is apparent from these tables, the conforming examples of sample Nos. 1 to 12 and 11 'to 12' in Table 2 are sample N in Table 5.
Compared to the conventional examples (carburized and quenched materials) of o. 46 and 47, the impact value, fatigue strength and rolling contact fatigue life are far superior.

Further, using the same steel as that of the conforming example, samples No. 13 to No. 13 in Table 3 were forged under the conditions outside the limited range of the present invention.
In Comparative Example 24, since the forging temperature is high or the cooling rate after forging is slow, the micronization of the structure is not sufficient, and thus the impact value is inferior to the conforming example. However, compared with the conventional example, the fatigue strength and rolling fatigue life are naturally superior, but the impact values are very similar or higher.

Further, using the same steel as the conforming example, the reduction rate of rolling cross section, the maximum size of oxide-based non-metallic inclusions, and the forging temperature are out of the limits of the present invention.
In the comparative example, since the micronization of the structure is not sufficient and the maximum size of the inclusions is large, the impact value, the fatigue strength, and the rolling fatigue life are inferior to the conforming example.

On the other hand, the comparative examples of sample Nos. 37 to 45 in Table 5 in which the composition of the steel is out of the limited range of the present invention are, for example,
Sample No. 37, which has a large amount of C, has an impact value
In No. 38, the fatigue strength and rolling fatigue life were inferior, and in No. 39 with a small amount of Si and No. 45 with a large amount of O, the rolling fatigue life was inferior, respectively. ,
Either the fatigue strength or rolling fatigue life or overall is inferior to the conforming example.

From the above, it can be seen that the conforming example of the present invention is extremely excellent in the impact, fatigue and rolling contact fatigue characteristics required for gears.

[0062]

INDUSTRIAL APPLICABILITY The present invention is intended to produce an induction-hardened part by limiting the composition of steel and the number and size of oxide-based nonmetallic inclusions, and further defining forging conditions.
According to the present invention, induction hardening can be adopted in place of the conventional carburizing and hardening in the manufacturing process of gears, etc., and the manufacturing cost can be reduced, and the parts having remarkably excellent quality characteristics can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22C 38/14 C22C 38/14 (56) Reference JP-A-1-129952 (JP, A) JP-A-6-306542 (JP , A) JP-A-8-267548 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 8/00-8/10 C22C 38/00-38/60 B21J 5/00 B21K 1/30

Claims (5)

(57) [Claims] 1. C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 mass% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.05 masss % Or less, P: 0.010 mass% or less, S: 0.020 mass% or less, O: 0.0015 mass% or less, and N: 0.002 mass% or more, 0.
006 mass% or less is contained, the balance is composed of Fe and unavoidable impurities, and the number of oxide-based nonmetallic inclusions in the steel is 2.5 pieces / mm ² or less, maximum size: 19 μm or less Steel material is heated to a temperature range of Ac ₃ points -100 ℃ or more and Ac ₃ points +200 ℃ or less, and after forging with a working rate of 70% or more in that temperature range, 0.005 ℃ / s or more, 10 ℃ A method for producing an induction-hardened component, which comprises cooling in a cooling rate range of / s or less, and then performing induction hardening and tempering. 2. C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 mass% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.05 mass% or less, P: 0.010 mass% or less, S: 0.020 mass% or less, O: 0.0015 mass% or less and N: 0.002 mass% or more, 0.
006 mass% or less is included, and Ni: 0.1 mass% or more, 1.0 mass% or less, Mo: 0.05 mass% or more, 0.50 mass% or less, Ti: 0.005 mass% or more, 0.05 mass% or less and B: 0.00
One selected from 03 mass% or more and 0.005 mass or less
Or contains two or more kinds, the balance is Fe and unavoidable impurities
The composition of the product and the inclusion of oxide-based non-metals in the steel
Number of objects: 2.5 / mm ²Below, maximum size: 19 μm or less
The steel below, Ac₃Point -100 ° C or higher, Ac₃Add to the temperature range below +200 ℃
Heated and forged with a processing rate of 70% or more in that temperature range
After that, a cooling rate range of 0.005 ° C / s or more and 10 ° C / s or less
And then induction hardening and tempering treatment.
And a method for manufacturing an induction-hardened component. 3. C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 mass% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.05 masss % Or less, P: 0.010 mass% or less, S: 0.020 mass% or less, O: 0.0015 mass% or less, and N: 0.002 mass% or more, 0.
Contains 006 mass% or less and V: 0.05 mass% or more, 0.5 mass% or less and Nb: 0.01 ma
It contains one or two selected from ss% or more and 0.5 mass% or less, with the balance being the composition of Fe and unavoidable impurities, and the number of oxide-based nonmetallic inclusions in the steel : 2.5 pieces / mm ² or less, maximum size: 19 μm or less steel material is heated to a temperature range of Ac ₃ points −100 ° C. or more and Ac ₃ points + 200 ° C. or less, and processing rate: 70% or more in that temperature range. A method for producing an induction-hardened component, which comprises performing forging, cooling in a cooling rate range of 0.005 ° C./s or more and 10 ° C./s or less, and then performing induction hardening and tempering. 4. C: 0.5 mass% or more and 0.75 mass% or less, Si: 0.5 mass% or more, 1.8 mass% or less, Mn: 0.4 mass% or more, 1.5 mass% or less, Al: 0.019 mass% or more, 0.05 masss % Or less, P: 0.010 mass% or less, S: 0.020 mass% or less, O: 0.0015 mass% or less, and N: 0.002 mass% or more, 0.
006 mass% or less and Ni: 0.1 mass% or more, 1.0 mass% or less, Mo: 0.05 mass% or more, 0.50 mass% or less, Ti: 0.005 mass% or more, 0.05 mass% or less and B: 0.00
One or more selected from 03 mass% or more and 0.005 mass or less, and V: 0.05 mass% or more, 0.5 mass% or less and Nb: 0.01 ma
One or two selected from ss% or more and 0.5 mass% or less is contained, and the balance is composed of Fe and unavoidable impurities, and the oxide-based nonmetallic inclusions in the steel are
Number: 2.5 pieces / mm ² or less, maximum size: 19 μm or less steel material is heated to a temperature range of Ac ₃ points −100 ° C. or more and Ac ₃ points + 200 ° C. or less, and processing rate: 70% or more in that temperature range. After forging, the method for producing an induction-hardened component is characterized by cooling in a cooling rate range of 0.005 ° C./s or more and 10 ° C./s or less, and then performing induction hardening and tempering. 5. The method for producing an induction-hardened component according to claim 1, wherein the steel material is rolled from a cast slab at a cross-section reduction rate of 95% or more.