JP5619366B2 - Aging treatment parts and method for manufacturing the same - Google Patents

Description

  The present invention relates to a steel for aging treatment, and particularly relates to a steel excellent in fatigue characteristics after aging treatment and preferable for automobiles, construction machinery and industrial machinery.

  Excellent fatigue properties are required for mechanical structural parts such as connecting rods, gears, etc. of automobiles, construction machines, and industrial machines.

  These machine parts have a desired strength after rough forming by forging, finishing to a predetermined shape by cutting, and then tempering by quenching and tempering or surface hardening treatment such as carburizing and nitriding. .

  If a desired strength can be obtained as it is without forging or surface hardening treatment, various non-heat treated steels are developed because the production cost reduction effect is great. 1. In order to ensure the strength of the component, a component design that increases the hardness after forging is adopted, and in order to improve the machinability that decreases due to this, a free cutting element such as S is added. After forging, that is, when cutting, the hardness is low, and is roughly classified into age-hardening dies that can be increased in hardness by aging treatment thereafter.

  In the latter case, for example, Patent Document 1 proposes an age-hardened steel using V carbonitride, Patent Document 2 proposes an age-hardened steel using Mo and V carbides, and Patent Document 3 discloses Age hardening steels utilizing age hardening of V carbides have been proposed.

JP 2000-17374 A JP 2006-37177 A JP 2008-88508 A

  However, the steel described in Patent Document 1 has a high hardness before aging of HV299 to 352, and it is difficult to say that sufficient workability is obtained from the viewpoint of cutting, and the addition amount of V has a lower limit of 0. .51%, so it was not economical.

  The age-hardened steel described in Patent Document 2 has a hardness before aging treatment of 40 or less in HRC, and HRC 40.0 to 27.9 (HV392 to 286) is considerably high in Examples, and it is difficult to say that the machinability is sufficient. However, although the steel described in Patent Document 3 utilizes age hardening of V carbide, the hardness after aging treatment is about 306.2 HV at the maximum, which is not necessarily sufficient.

  Therefore, an object of the present invention is to provide a steel for aging treatment that can increase the hardness after aging treatment at a relatively low production cost and can produce an aging treatment part having excellent fatigue characteristics.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on the effects of the structure and composition on the fatigue properties after aging treatment of steel, and precipitated fine nanometer-size precipitates during the aging treatment to increase the hardness. It has been found that excellent fatigue properties can be obtained after aging treatment when increased.

The present invention has been made on the basis of the above findings and further studies, that is, the present invention,
1. % By mass, C ≦ 0.15%, Si ≦ 0.5%, Mn ≦ 2.5%, Ti: 0.03 to 0.35%, Mo: 0.03 to 0.8%, Cr ≦ 2 % Or less, Al ≦ 0.1%, P ≦ 0.040%, S ≦ 0.1 % , a steel composition composed of the balance Fe and inevitable impurities, and has a structure with a bainite area ratio of 50% or more. An aging-treated part having a bainite average packet size of 80 μm or less and fine precipitates having a particle size of less than 10 nm dispersed and precipitated in the bainite phase by 90% by number or more of all precipitates.
2. 2. The aging-treated part according to 1, wherein the steel composition further satisfies the formula (1).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96)} ≦ 1.5 −−− (1)
However, the content of each element is set to mass (% by mass), and the content of elements not included is set to 0.
3. 3. The aging-treated part according to 1 or 2, wherein the fine precipitate is a carbide containing Ti and Mo.
4). 2. The aging-treated part according to 1, wherein the steel composition further contains one or more of Nb ≦ 0.08%, V ≦ 0.15%, and W ≦ 1.5% in terms of mass%.
5. The aging-treated part according to 4, wherein the steel composition further satisfies the formula (2).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} ≦ 1.5 −−− (2 )
However, the content of each element is set to mass (% by mass), and the content of elements not included is set to 0.
6). 6. The aging-treated part according to 4 or 5, wherein the fine precipitate is a carbide containing Ti, Mo, and at least one of Nb, V, and W.
7). The steel composition further contains B: 0.0003 to 0.005%, The aging-treated part according to any one of 1 to 6, wherein
8). % By mass, C ≦ 0.15%, Si ≦ 0.5%, Mn ≦ 2.5%, Ti: 0.03 to 0.35%, Mo: 0.03 to 0.8%, Cr ≦ 2 % Or less, Al ≦ 0.1%, P ≦ 0.040%, S ≦ 0.1 % , a steel having a steel composition composed of the balance Fe and inevitable impurities, the heating temperature is 950 ° C. to 1250 ° C., Rolling finish temperature is 800 ° C or more, rolling finish reduction ratio is 10% or more, and steel bar is formed by hot rolling with a cooling rate in the range of 700 to 550 ° C after rolling is over 0.5 ° C / sec. Forging and / or cutting to form a part shape, and thereafter performing an aging treatment with a heating temperature of 550 to 750 ° C. and a treatment time of 10 minutes or more , having a structure with a bainite area ratio of 50% or more, The bainite average packet size is 80 μm or less, and Fine precipitates of less than 10nm is particle size bets phase is 90% by number or more of the total precipitates manufacturing method of aging treatment components are dispersed and deposited.
9. % By mass, C ≦ 0.15%, Si ≦ 0.5%, Mn ≦ 2.5%, Ti: 0.03 to 0.35%, Mo: 0.03 to 0.8%, Cr ≦ 2 % Or less, Al ≦ 0.1%, P ≦ 0.040%, S ≦ 0.1 % , a steel having a steel composition composed of the balance Fe and inevitable impurities, the heating temperature is 950 ° C. to 1250 ° C., The forging finish temperature is 800 ° C. or higher, the forging finish reduction ratio is 10% or more, and the forging finish is hot forged with a cooling rate in the range of 700 to 550 ° C. exceeding 0.5 ° C./sec. A bainite area ratio of 50% or more , characterized by performing an aging treatment at 750 ° C. and a treatment time of 10 minutes or more, an average bainite packet size of 80 μm or less, and a particle size of less than 10 nm in the bainite phase 90% or more of all precipitates Manufacturing method of aging treatment components are dispersed and deposited.
10. The method for producing an aging-treated part according to 8 or 9, wherein the fine precipitate is a carbide containing Ti and Mo.
11. Steel composition is further characterized by satisfying the equation (1), the manufacturing method of the aging treatment component according to any one of 8 to 1 0.
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96)} ≦ 1.5 −−− (1)
However, each element is the content (wt%), has elements such contained is 0.
12 The manufacture of an aging-treated part according to 8 or 9, further comprising one or more of Nb ≦ 0.08%, V ≦ 0.15%, and W ≦ 1.5% in terms of steel composition as a steel composition. Method.
13. And fine precipitates are Ti, Mo and, Nb, V, characterized in that it is a carbide containing at least one kind of W, the manufacturing method of the aging treatment component according to 1 2.
14 The method for producing an aging-treated part according to 12 or 13 , wherein the steel composition further satisfies the formula (2).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} ≦ 1.5 −−− (2 )
However, each element is the content (wt%), has elements such contained is 0.
15. Steel composition further, B: production method of aging treatment component according to any one of 8 to 1 4, characterized in that it contains 0.0003 to .005%.

  According to the present invention, machinability is excellent before aging treatment, and after aging treatment, conventional steel: for example, aging treatment steel having strength and toughness equivalent to SCM420 steel and better fatigue properties, and the aging treatment. An aging-treated part using treatment steel is obtained, which is extremely useful industrially.

The figure which shows the outline manufacturing process which manufactures an aging treatment component.

The microstructure, component composition, and production conditions of the aging steel according to the present invention will be described in detail below. The microstructure is the microstructure after aging treatment.
1. Microstructure
The microstructure after the aging treatment is a structure in which fine precipitates having a bainite area ratio of 50% or more, an average bainite packet size of 80 μm or less, and a particle size of less than 10 nm are dispersed and precipitated in the bainite phase.

  When the parent phase is a bainite structure, the amount of fine precipitates after aging treatment is larger than that of other structures such as ferrite. To improve.

  When the bainite average packet size exceeds 80 μm, the fatigue strength decreases, so the bainite average packet size is set to 80 μm or less. The packet is a kind of substructure of the bainite structure, and is an assembly of structures called laths having a width of about 0.2 μm and a length of about 10 μm.

  The bainite average packet size is obtained by the following method. 1. After etching the structure with a nital etchant, the packet is observed with an optical microscope. 2. For the observed packet, the image analysis device calculates the packet area and converts it to the equivalent circle diameter to obtain the bainite average packet size.

  The particle size of the fine precipitate is less than 10 nm. When the particle size of fine precipitates is 10 nm or more, the precipitation strengthening after aging treatment is insufficient, the strength does not improve compared to the case of aging treatment using a quenching and tempering material, and the strength characteristics Since the yield ratio does not increase, the fatigue characteristics are not improved.

  In order to improve strength and fatigue characteristics, the smaller the particle size of the fine precipitate, the more effective, preferably 5 nm, more preferably 3 nm or less.

  Carbides containing Ti and Mo as such fine precipitates, and carbides further containing one or more of Nb, V and W are preferred. The distribution form of these fine precipitates is desirably dispersed and precipitated in the matrix. In the present invention, dispersion precipitation means uniform dispersion.

  Moreover, in this invention, if the fine precipitate mentioned above is 90% or more of all the precipitates, the target fatigue strength after an aging treatment will be obtained. However, a precipitate having a size of 10 nm or more consumes a precipitate-forming element when it is deposited, and adversely affects the strength.

  Even if it contains a small amount of Fe carbide in addition to the precipitates described above, the effect of the present invention is not impaired. However, if a large amount of Fe carbide having an average particle size of 1 μm or more is contained, the toughness is inhibited. The upper limit of the size of Fe carbide contained is preferably 5 μm, and the content is preferably 5% or less.

  The ratio of the fine precipitates in the present invention to the total precipitates can be determined by the following method. First, an electron microscope sample is prepared by an electropolishing method using a twin jet method and observed at an acceleration voltage of 200 kV.

  At that time, the crystal orientation of the parent phase is controlled so that the fine precipitates have a measurable contrast with respect to the parent phase, and the defocus is shifted from the normal focus in order to minimize the counting of the precipitates. Observe by method.

  Moreover, the thickness of the sample in the region where the precipitate particles are measured is evaluated by measuring the elastic scattering peak and the inelastic scattering peak intensity using electron energy loss spectroscopy.

By this method, the measurement of the number of particles and the measurement of the sample thickness can be executed for the same region. The measurement of the number of particles and the particle diameter was performed on four locations of 0.5 × 0.5 μm of the sample,
The precipitates distributed per 1 μm ² are calculated as the number for each particle size.

From the obtained value and the sample thickness, the number of precipitates distributed per 1 μm ³ is calculated for each particle diameter, and the ratio of the precipitates having a diameter of less than 10 nm to the measured total precipitates is calculated.

  Further, in the present invention, the structure having a bainite area ratio of 50% or more means that the area ratio of the bainite structure is 50% or more, preferably 60% or more, more preferably 70%, in cross-sectional structure observation (observation with 200 times optical microscope structure). That's it.

2. Ingredient composition
The steel of the present invention preferably has the following component composition. In the description,% is mass%.
C
C is added to form a bainite structure and ensure strength. If the content exceeds 0.15%, fine precipitates become coarse and the strength decreases, so the content is made 0.15% or less. More preferably, it is 0.02% or more and 0.12% or less. More preferably, it is 0.02% or more and less than 0.10%.

Si
Si is added for deoxidation, but if it exceeds 0.5%, it dissolves in the ferrite and bainite structure and deteriorates the machinability and cold workability, so the content is made 0.5% or less. More preferably, it is 0.3% or less.

Mn
Mn is added because it is effective for bainite structure formation and strength improvement. However, if it exceeds 2.5%, the machinability and the cold workability deteriorate, so the content is made 2.5% or less. More preferably, it is 0.5% or more and 2.0% or less. More preferably, it is more than 1.0% and not more than 2.0%.

Ti
Ti is added to finely precipitate Ti-based carbides and precipitates containing Ti-Mo-based carbides together with Mo and improve the fatigue strength of the aging treatment material. If it is less than 0.03%, the amount of precipitates is small and the desired fatigue strength cannot be obtained, so 0.03% or more is added. On the other hand, if added over 0.35%, the precipitates become coarse and the effect of improving fatigue strength decreases. Therefore, it is set to 0.03 to 0.35%. More preferably, it is 0.05 to 0.35%. More preferably, it is 0.13-0.35%.

Mo
Mo is added to finely precipitate Mo-based carbides and precipitates containing Ti-Mo-based carbides together with Ti and improve the fatigue strength of the aging treatment material. To improve fatigue strength, 0.03% or more is added. On the other hand, if over 0.8% is added, the machinability deteriorates, so the content is made 0.03 to 0.8%. More preferably, it is 0.10 to 0.6%. More preferably, it is 0.12-0.45%.

  Mo has a slow diffusion rate, and when it precipitates together with Ti, the growth rate of the precipitate is reduced, and a fine precipitate is easily obtained.

(C / 12) / {(Ti / 48) + (Mo / 96)}
This parameter formula affects the size of the precipitate. When the value is 0.5 or more and 1.5 or less, it becomes easy to form a fine precipitate having a particle diameter of less than 10 nm.

  The above is the basic component composition of the present invention. When further improving the characteristics, one or more of Nb, V, and W are added.

Nb
Nb, like Ti, contributes to improving fatigue strength by forming fine precipitates. If it exceeds 0.08%, the precipitate becomes coarse, so when added, the content is made 0.08% or less. More preferably, it is 0.05% or less.

V
V, like Ti, contributes to the improvement of fatigue strength by forming fine precipitates. However, if it exceeds 0.15%, the precipitates become coarser. To do. More preferably, it is less than 0.10%.

W
W forms fine precipitates with Ti and contributes to the improvement of fatigue strength. However, if it exceeds 1.5%, the precipitates become coarse, so when added, the content is made 1.5% or less. More preferably, it is 1.0% or less.

  In the addition of these elements, it is effective to define the atomic ratio of C, Ti, Mo, Nb, V, and W to refine the carbide (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} is 0.5 or more and 1.5 or less, it is easy to form fine precipitates having a particle size of less than 10 nm.

  In the steel of the present invention, when improving the machinability after forging or aging treatment, 0.03 ≦ S ≦ 0.1%, Pb ≦ 0.2%, Ca ≦ 0.005%, Bi ≦ One or more of 0.02% can be added.

  In the steel of the present invention, the balance other than the above-mentioned additive elements is Fe and inevitable impurities, but Al can be added as a deoxidizer in an amount of 0.1% or less. Further, when improving the cold forgeability of the material, P ≦ 0.040% and N ≦ 80 ppm, and when improving the strength, Cu ≦ 2%, Ni ≦ 2%, Cr ≦ 2%, B: 0.0003 One or more of ~ 0.005% can be added. In addition, the effect of this invention is not impaired by content of these elements, or the presence or absence of addition.

3. Manufacturing conditions
FIG. 1 shows a schematic manufacturing process for manufacturing an aging-treated part using the aging-treated steel according to the present invention, where S1 is a raw steel bar manufacturing process, S2 is a conveying process, and S3 is a product (aging-treated part) finishing process. Indicates. The steel ingot is hot-rolled into a steel bar in the steel bar manufacturing process (S1) and shipped after quality inspection.

  In the product (aging treated part) finishing step (S3), the steel bar is cut to a predetermined size, hot forged or cold forged, and the desired shape is obtained by cutting such as drilling or turning as necessary. After that, an aging treatment is performed to obtain a product.

  Further, the hot rolled material may be finished as it is by a cutting process such as turning or drilling, and then subjected to an aging treatment to obtain a product. In the case of hot forging, cold correction may be performed after hot forging. In addition, the final product may be subjected to a coating treatment such as paint or plating. A desirable manufacturing process will be described in detail below.

Rolling heating temperature
Rolling heating temperature shall be 950-1250 degreeC. The steel of the present invention dissolves carbides remaining from the time of melting during hot rolling so that fine precipitates are not deposited on the rolled material (bar steel used as the material of the forged part) and the forgeability is not impaired.

  When the rolling heating temperature is less than 950 ° C., the remaining carbide from the time of dissolution does not dissolve, so the temperature is set to 950 ° C. or higher. On the other hand, if the temperature exceeds 1250 ° C., the crystal grains become coarse and the forgeability deteriorates, so the heating temperature is set to 950 ° C. to 1250 ° C.

Rolling finish temperature
When the rolling finish temperature is less than 800 ° C., a ferrite structure is formed. In particular, when the aging treatment is performed after cold forging or cutting, the parent phase is formed into a bainite structure having an area ratio of 50% or more after the aging treatment. Is disadvantageous. Further, the rolling load is high, and the roundness of the rolled material is also deteriorated. For this reason, a rolling finishing temperature shall be 800 degreeC or more.

Rolling finish reduction ratio If the rolling finish reduction ratio is less than 10%, the bainite average packet size becomes coarse. In particular, when the aging treatment is performed after cold forging or cutting, the bainite average packet size is 80 μm or less after the aging treatment. This is disadvantageous. For this reason, the rolling finish reduction ratio is set to 10% or more.

Cooling rate
The cooling rate after rolling is regulated so that fine precipitates are deposited before forging and the forgeability is not impaired.
The precipitation temperature range of 700 to 550 ° C. of the fine precipitate is cooled at a rate exceeding the limit cooling rate (0.5 ° C./sec) at which the fine precipitate is obtained.

Aging treatment (precipitation treatment)
The obtained steel bar is used as a raw material, and after forging, it is formed into a part shape by cutting or the like. Thereafter, an aging treatment is performed. The aging treatment is performed at a heating temperature of 550 to 750 ° C. and a treatment time of 10 minutes or more so as to precipitate fine precipitates. When the temperature is lower than 550 ° C., a sufficient amount of precipitate cannot be obtained, and when the temperature exceeds 750 ° C., the precipitate becomes coarse, so the temperature is set to 550 to 750 ° C. In addition, More preferably, it shall be 550-700 degreeC.

  When hot forging is used, after aging treatment, the parent phase has a bainite structure with an area ratio of 50% or more and an average bainite packet size of 80 μm or less, and cold correction and cutting after hot forging. From the viewpoint of workability, the heating temperature during hot forging is 950 to 1250 ° C., the forging finishing temperature is 800 ° C. or more, the forging finish reduction ratio is 10% or more, and the cooling rate after forging so that fine precipitates do not precipitate. At 0.5 ° C./sec.

  Steel (No. 1-14) having the composition shown in Table 1 was melted in a 150 kg vacuum melting furnace, rolled at 1200 ° C. and finished at 980 ° C., then cooled to room temperature at 1 ° C./sec, and a 50 mmφ bar steel It was. No. Reference numeral 14 denotes a conventional material JIS SCM420.

  These materials are further heated to 1180 ° C., then hot forged at 1080 ° C. with a finishing reduction rate of 40%, 30 mmφ, 1 ° C./sec, and partially cooled to room temperature at 0.1 ° C./sec. did. In these microstructures, the 1 ° C./sec coolant was a bainite main structure, and the 0.1 ° C./sec coolant was a ferrite pearlite structure. Steel No. For comparison, for comparison, the material was heated to 1180 ° C., and then hot forged at 1080 ° C. with a finishing reduction rate of 4% to 48 mmφ and cooled to room temperature at 1 ° C./sec. These microstructures were bainite-based structures.

  About the said raw material, the machinability was evaluated by the drill cutting test. Using a hot forged material cut to a thickness of 20 mm as a test material, a JIS high-speed tool steel SKH51 6 mmφ straight drill is used to feed 0.15 mm / rev, a rotational speed of 745 rpm, and five through holes per cross section. Evaluation was made based on the total number of holes until the drill could not be drilled.

  Further, the hardness of these materials was measured. As a measuring method, a Vickers hardness tester was used, and at a test load of 10 kg, a cross section of the material was measured at four points at a quarter of the diameter, and an average value thereof was taken as a measured value.

  Steel No. In Nos. 1 to 13, the hot forging material was further subjected to aging treatment, and steel No. In No. 14, the hot forging was quenched and tempered, and further subjected to aging treatment. The aging treatment was performed by heating to 525 to 775 ° C. and holding for 3 hours. These aging-treated materials were subjected to structure observation, hardness and fatigue property investigation.

  In the structure observation, the cross section was observed with an optical microscope, the precipitate was observed with a transmission electron microscope (TEM), and the composition was determined with an energy dispersive X-ray spectrometer (EDX).

  The hardness after the aging treatment was measured using a Vickers hardness tester at a test load of 10 kg, and the cross section of the aging treatment material was measured at four points at a quarter of the diameter, and the average value thereof was taken as the measured value.

  Fatigue characteristics were determined by the Ono type rotating bending fatigue test. An Ono-type rotating bending fatigue test piece (parallel portion 8 mmφ) was collected from a hot forged material and subjected to the aging treatment described above.

  Table 2 shows the test results. No. 1-8 are examples of the present invention, No.1. 9 to 17 are comparative examples. 18 is a conventional example of JIS SCM420 steel.

  As can be seen from the table, no. The aging treatment materials 1 to 8 are superior in fatigue strength to those obtained by aging treatment of the conventional material (No. 18) after quenching and tempering treatment. Regarding the hardness and drill cutting workability of the material (hot forged material) before aging treatment, In Nos. 1 to 8, the hardness is equal to or higher than that of the conventional material (No. 18), and the drill cutting workability is practically equivalent to that of the conventional material (No. 18).

  Comparative Example No. In Nos. 9 to 17, the chemical composition or the obtained microstructure is outside the scope of the present invention, and the fatigue strength or drillability is inferior.

  No. No. 9 has an aging treatment temperature higher than that of the examples of the present invention, so that the grain size of the precipitate after aging treatment is large and the amount of fine precipitates is small, so that precipitation strengthening is insufficient and fatigue strength is low.

  No. No. 10 has an aging treatment temperature lower than that of the example of the present invention, so that the amount of fine precipitates produced by aging treatment is small, precipitation strengthening is insufficient, and fatigue strength is low.

  No. No. 11 has a slower cooling rate after hot forging than the examples of the present invention, so a bainite structure cannot be obtained, the amount of fine precipitates produced by aging treatment is small, precipitation strengthening is insufficient, and fatigue strength is lower than that of the examples of the invention. Low.

  No. No. 12 has a hot forging finish reduction ratio lower than that of the examples of the present invention, so that the bainite particle size after aging treatment is large and the bainite particle size is 80 μm or less. Compared to 2, the fatigue strength is reduced.

  No. Since C is high outside the scope of the present invention, the amount of fine precipitates after aging treatment is small, sufficient precipitation strengthening cannot be obtained, and fatigue strength is lower than that of conventional materials.

  No. No. 14, since Si and Mn are high outside the scope of the present invention, the hardness of the rolled material is high, and the drill workability is reduced to about 40% of the conventional material.

  No. 15 is low outside the scope of the present invention, and C / (Ti + Mo) is also outside the scope of the present invention, so the amount of fine precipitates after aging treatment is small and sufficient precipitation strengthening cannot be obtained. Is low.

  No. Since No. 16 is low outside the scope of the present invention, the amount of fine precipitates after the aging treatment is small, and sufficient precipitation strengthening cannot be obtained. Therefore, the fatigue strength is lower than that of the conventional material.

  No. In No. 17, C / (Ti + Mo) is low outside the scope of the present invention, so the amount of fine precipitates after aging treatment is small, and sufficient precipitation strengthening cannot be obtained, so the fatigue strength is lower than that of conventional materials.

Claims (15)

% By mass, C ≦ 0.15%, Si ≦ 0.5%, Mn ≦ 2.5%, Ti: 0.03 to 0.35%, Mo: 0.03 to 0.8%, Cr ≦ 2 % Or less, Al ≦ 0.1%, P ≦ 0.040%, S ≦ 0.1 % , a steel composition composed of the balance Fe and inevitable impurities, and has a structure with a bainite area ratio of 50% or more. An aging-treated part having a bainite average packet size of 80 μm or less and fine precipitates having a particle size of less than 10 nm dispersed and precipitated in the bainite phase by 90% by number or more of all precipitates. The aging-treated part according to claim 1, wherein the steel composition further satisfies the formula (1).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96)} ≦ 1.5 −−− (1)
However, the content of each element is set to mass (% by mass), and the content of elements not included is set to 0.   The aging-treated part according to claim 1 or 2, wherein the fine precipitate is a carbide containing Ti and Mo.   The aging-treated part according to claim 1, further comprising, as a steel composition, one or more of Nb ≦ 0.08%, V ≦ 0.15%, and W ≦ 1.5%. The aging-treated part according to claim 4, wherein the steel composition further satisfies the formula (2).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} ≦ 1.5 −−− (2 )
However, the content of each element is set to mass (% by mass), and the content of elements not included is set to 0.   The aging-treated part according to claim 4 or 5, wherein the fine precipitate is a carbide containing Ti, Mo, and at least one of Nb, V, and W.   The steel composition further contains B: 0.0003 to 0.005%, the aging-treated part according to any one of claims 1 to 6. % By mass, C ≦ 0.15%, Si ≦ 0.5%, Mn ≦ 2.5%, Ti: 0.03 to 0.35%, Mo: 0.03 to 0.8%, Cr ≦ 2 % Or less, Al ≦ 0.1%, P ≦ 0.040%, S ≦ 0.1 % , a steel having a steel composition composed of the balance Fe and inevitable impurities, the heating temperature is 950 ° C. to 1250 ° C., Rolling finish temperature is 800 ° C or more, rolling finish reduction ratio is 10% or more, and steel bar is formed by hot rolling with a cooling rate in the range of 700 to 550 ° C after rolling is over 0.5 ° C / sec. Forging and / or cutting to form a part shape, and thereafter performing an aging treatment with a heating temperature of 550 to 750 ° C. and a treatment time of 10 minutes or more , having a structure with a bainite area ratio of 50% or more, The bainite average packet size is 80 μm or less, and Fine precipitates of less than 10nm is particle size bets phase is 90% by number or more of the total precipitates manufacturing method of aging treatment components are dispersed and deposited. % By mass, C ≦ 0.15%, Si ≦ 0.5%, Mn ≦ 2.5%, Ti: 0.03 to 0.35%, Mo: 0.03 to 0.8%, Cr ≦ 2 % Or less, Al ≦ 0.1%, P ≦ 0.040%, S ≦ 0.1 % , a steel having a steel composition composed of the balance Fe and inevitable impurities, the heating temperature is 950 ° C. to 1250 ° C., The forging finish temperature is 800 ° C. or higher, the forging finish reduction ratio is 10% or more, and the forging finish is hot forged with a cooling rate in the range of 700 to 550 ° C. exceeding 0.5 ° C./sec. A bainite area ratio of 50% or more , characterized by performing an aging treatment at 750 ° C. and a treatment time of 10 minutes or more, an average bainite packet size of 80 μm or less, and a particle size of less than 10 nm in the bainite phase 90% or more of all precipitates Manufacturing method of aging treatment components are dispersed and deposited. The method for producing an aging-treated part according to claim 8 or 9, wherein the fine precipitate is a carbide containing Ti and Mo. Steel composition is further characterized by satisfying the equation (1), the manufacturing method of the aging treatment component according to any of claims 8 to 1 0.
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96)} ≦ 1.5 −−− (1)
However, each element is the content (wt%), has elements such contained is 0.   The aging-treated part according to claim 8 or 9, further comprising one or more of Nb ≦ 0.08%, V ≦ 0.15%, and W ≦ 1.5% as a steel composition. Manufacturing method. And fine precipitates are Ti, Mo and, Nb, V, characterized in that it is a carbide containing at least one kind of W, the manufacturing method of the aging treatment component according to claim 1 2. The method for producing an aging-treated part according to claim 12 or 13 , wherein the steel composition further satisfies the formula (2).
0.5 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (Nb / 93) + (V / 51) + (W / 184)} ≦ 1.5 −−− (2 )
However, each element is the content (wt%), has elements such contained is 0. Steel composition further, B: production method of aging treatment component according to any of claims 8 to 1 4, characterized in that it contains 0.0003 to .005%.

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