JP4649857B2 - Manufacturing method of hot forged products with excellent fatigue strength - Google Patents

Description

  The present invention relates to a method for producing a hot forged product excellent in fatigue strength, which is suitable for application to automobile parts using strip steel, such as a hub or a constant velocity joint.

In general, a steel bar product such as a hub or a constant velocity joint is manufactured by hot forging or rolling and then cutting. In recent years, high fatigue strength is required for products for such applications in order to reduce the weight of automobiles to which they are applied.
Conventionally, in order to improve fatigue strength, it is known that it is effective to add expensive component elements, reduce the maximum diameter of inclusions, or reduce the number of inclusions.

For example, with regard to the steel materials used in the above products, after appropriately adjusting each component such as Al, N, Ti, Zr and S, the maximum diameter of sulfide is 10 μm or less and the cleanliness is 0.05 mass% or more. Is proposed in Patent Document 1.
Patent Document 2 discloses a ferrite-pearlite having an average crystal grain size of 10 μm or less after hot forging by using steel containing martensite in an area ratio of 95 to 100% as a material for hot forging. It is described that a forged product having a structure consisting of
Japanese Patent Laid-Open No. 11-302778 Japanese Patent Laid-Open No. 2003-147481

  However, even if expensive component elements are added, the maximum diameter of inclusions is reduced, and the number of inclusions is reduced, crystal grains grow and become coarse in the cooling process after hot forging, and are required for the above products. However, there is a problem that the high fatigue strength is not obtained. Further, it is known that the refinement of the crystal grain size is effective for improving the fatigue strength. If the forged product is refined the crystal grain size as in the technique of Patent Document 2, the fatigue strength is improved. Although improvement can also be expected, since the structure of the material before forging is a martensite structure in the method of Patent Document 2, reheating after rolling in the manufacturing process of the material for forging, particularly in the hot rolling process, There is a problem in productivity because it requires rapid cooling. In addition, forged products such as the above hubs and constant velocity joints are formed into final product shapes by cold working or cutting after forging, but the grain size is refined for the purpose of increasing strength. Then, conversely, there is a problem that the required load at the time of cold working increases excessively or cracks occur at the time of cold working.

The present invention has been developed in view of the above circumstances, by properly controlling the tissue in hot forging step, rotating bending for example be requested from the increase in parts lighter, caused by compacting stress fatigue The purpose is to propose an advantageous method for producing a forged product having an excellent fatigue strength with a strength of 400 MPa or more .

Now, in order to achieve the above-mentioned object, the inventors have made extensive studies especially on the forging temperature, and as a result, have obtained the following knowledge.
(1) As the forging temperature is lowered from the high temperature γ region, the crystal grain size gradually decreases regardless of the applied strain, but the degree of grain refinement is saturated, and as expected in the present invention. The fatigue strength cannot be improved.
(2) When the forging temperature is set to the _Al point or less, the fatigue strength only expected in the present invention cannot be expected since the ferrite only exhibits a stretched structure.
(3) When the forging temperature was 2-phase region below ₃ points or more A _l points A, Ownership by the distortion added is significantly different, if distortion is small, the same organization and the crystal grain size and the (1) Thus, the fatigue strength cannot be improved as much as expected in the present invention. On the other hand, when the strain is large, two types of tissue forms are exhibited. That is, when the strain is large but only the uniaxial direction is large as a strain component, it shows a form in which the ferrite as in (2) is extended together with the crushed pearlite, which is close to the case of forging below the _Al point. Since the structure is obtained, the fatigue strength cannot be improved. However, when the strain has components in a plurality of directions and each component is relatively large, the crystal grain size becomes equiaxed and extremely fine. Only in this state, a marked improvement in fatigue strength appears. Specifically, when forging is performed so that strains composed of components in multiple directions are added, and strains of two or more of those components are each 0.5 or more, a significant improvement in fatigue strength is realized. To do.
(4) By adopting this forging condition, the above structure can be reproduced without adding an expensive component element, and an improvement in fatigue strength can be easily expected.
(5) Moreover, by setting the forging conditions only in the final forging step in the forging step, the above structure can be sufficiently reproduced, and is not affected by the hot forging in the previous step.
(6) When forming a forged product by forging, such forging conditions are applied to the part that requires fatigue characteristics, and then such forging condition is applied to the part to be cold worked. By not doing, it can suppress that the crystal grain diameter of the site | part which performs cold work refines | miniaturizes, and the forged product which can perform cold work easily is obtained.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. C: 0.3-0.9 mass%
Si: 0.01-1.2mass% and
Mn: 0.01-2.0mass%
When the hot forging product is manufactured by subjecting the steel material having a composition of Fe and inevitable impurities to a plurality of hot forgings in the final forging process, Heat with excellent fatigue strength characterized by applying multi-directional component strain under a temperature range of ₁ point or more and A ₃ points or less, and having multi-directional component strain of 2 or more components each 0.5 or more A method for manufacturing inter-forged products.

2. In 1 above, the steel material is further
Mo: 0.05-0.6mass%,
Al: 0.01-0.06mass%,
Ti: 0.005 to 0.050 mass%,
Ni: 1.0 mass% or less,
Cr: 1.0 mass% or less,
V: 0.1 mass% or less,
Cu: 1.0 mass% or less,
Nb: 0.05 mass% or less,
A method for producing a hot forged product excellent in fatigue strength, characterized in that the composition contains one or more selected from Ca: 0.008 mass% or less and B: 0.004 mass% or less.

3. In the above 1 or 2, the at least part is a portion where fatigue strength is required, and at least a portion subjected to cold working among portions other than the portion where fatigue strength is required is the final forging step A method for producing a hot forged product excellent in fatigue strength, characterized by performing hot forging in a temperature range of more than ₃ points.

  According to the present invention, it is possible to stably and easily produce a forged product having excellent fatigue strength with a rotational bending fatigue strength of 400 MPa or more.

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel material is limited to the above range in the present invention will be described.
C: 0.3-0.9mass%
C is an element necessary for increasing the strength of the base material. If the C content is less than 0.3 mass%, the required strength increase effect cannot be obtained. On the other hand, if the C content exceeds 0.9 mass%, the machinability, fatigue strength, and forgeability are further reduced. Was limited to the range of 0.3-0.9 mass%.

Si: 0.01-1.2mass%
Si not only acts as a deoxidizer, but also contributes to improving the strength effectively. However, if the content is less than 0.01 mass%, the additive effect is poor, while if it exceeds 1.2 mass%, the machinability is low. In order to reduce the forgeability, the Si content is limited to a range of 0.01 to 1.2 mass%.

Mn: 0.01-2.0mass%
Mn contributes not only to improving the strength but also to improving the fatigue strength. However, if the content is less than 0.01 mass%, the additive effect is poor, while if it exceeds 2.0 mass%, machinability and forgeability are reduced. Therefore, the amount of Mn was limited to a range of 0.01 to 2.0 mass%.

The basic components have been described above. However, when further improvement in fatigue strength is desired, the following elements can be appropriately contained.
Mo: 0.05-0.6mass%
Mo is an element useful for suppressing the growth of ferrite grains. To do so, at least 0.05 mass% is required, but if added over 0.6 mass%, machinability is deteriorated, so the amount of Mo Was limited to the range of 0.05 to 0.6 mass%.

Al: 0.01-0.06mass%
Al acts as a deoxidizer for steel. However, if the content is less than 0.01 mass%, the effect of addition is poor. On the other hand, if it exceeds 0.06 mss%, the machinability and fatigue strength are reduced, so the Al content is limited to the range of 0.01 to 0.06 mass%. .

Ti: 0.005 to 0.050 mass%
Ti is a useful element for refining crystal grains due to the pinning effect of TiN. To obtain this effect, it is necessary to add at least 0.005 mass%, but if added over 0.050 mass% In order to cause a decrease in fatigue strength, the range is limited to 0.005 to 0.050 mass%.

Ni: 1.0 mass% or less
Ni is effective in increasing strength and preventing cracking when Cu is added, and is preferably added at 0.05 mass% or more. However, if Ni is added in excess of 1.0 mass%, it tends to cause fire cracking, so 1.0 mass% Limited to:

Cr: 1.0 mass% or less
Cr is effective for increasing the strength, and is preferably added at 0.05 mass% or more, but if added over 1.0 mass%, the carbide is stabilized to promote the formation of residual carbides, and the grain boundary strength is reduced. Moreover, since the fall of fatigue strength is also caused, it limited to 1.0 mass% or less.

V: 0.1 mass% or less V is a useful element that produces a microstructure refining effect by pinning by being precipitated as carbide, and is preferably added at 0.005 mass% or more, but even if added over 0.1 mass%, it is effective. Since it is saturated, it was limited to 0.1 mass% or less.

Cu: 1.0 mass% or less
Cu is a useful element that improves strength by solid solution strengthening and precipitation strengthening, and also contributes effectively to improving hardenability, so it is preferably added at 0.1 mass% or more, but the content is 1.0 mass%. If it exceeds 1, cracks are likely to occur during hot working and manufacturing becomes difficult, so it was limited to 1.0 mass% or less.

Nb: 0.05 mass% or less
Nb has the effect of pinning grain growth by precipitation, and is preferably added at 0.005 mass% or more, but even if added over 0.05 mass%, the effect is saturated, so it was limited to 0.05 mass% or less.

Ca: 0.008 mass% or less
Ca is a useful element that spheroidizes inclusions and improves fatigue properties, and is preferably added at 0.001 mass% or more, but if added over 0.008 mass%, inclusions tend to become coarse and deteriorate fatigue properties. Therefore, it is limited to 0.008 mass% or less.

B: 0.004 mass% or less B is a useful element that not only improves fatigue properties by strengthening grain boundaries but also improves strength. Preferably, B is added at 0.0003 mass% or more, but more than 0.004 mass% is added. However, since the effect is saturated, it was limited to 0.004 mass% or less.
The balance is Fe and inevitable impurities. Inevitable impurities include P, S, O, and N.

The preferred component composition has been described above, but in the present invention, in addition to limiting the component composition to the above range, it is essential to adjust the forging conditions as described below.
In other words, when the forging temperature is set to the γ region as the forging conditions, the degree of fine grain refinement is limited even if the forging temperature is lowered within the γ region, and thus the fatigue strength cannot be improved as expected. In the case where the forging temperature is set to the _Al point or less, since only the structure in which the ferrite is extended is exhibited, the expected improvement in fatigue strength cannot be expected in this case as well. In addition, the influence of strain is slight in these temperature ranges, and a great effect on the change of the structure and the improvement of fatigue strength by applying strain cannot be expected. Therefore, forging in a region where fatigue strength should be ensured, forging in the temperature range of the γ region and the α region single phase is not suitable.

On the other hand, when the forging temperature is set to a two-phase region of A ₁ point or more and A ₃ point or less, as described above, the fatigue strength is remarkably different from the structure morphology due to the applied strain. In other words, when the applied strain is appropriately controlled, it is effective for the forging temperature to be A ₁ point or more and A ₃ point or less. Therefore, first, it is necessary to regulate the forging temperature to A ₁ point or more and A ₃ point or less for a portion where fatigue strength should be ensured.

  Next, under such a temperature range, by applying forging that satisfies the conditions of applying strain of a multidirectional component and that strain of two or more components of the multidirectional component is 0.5 or more, The crystal grain size in the forged product structure becomes equiaxed and fine, and as a result, the fatigue strength is significantly improved.

  This is because strain can be introduced into a random grain interface by applying strain in a multidirectional component, and as a result, ferrite nucleation can be generated from the random grain interface. Furthermore, by setting the strains of two or more of the multidirectional component strains to 0.5 or more, the number of ferrite nucleation per unit grain interfacial area increases dramatically, and the generated ferrite collides with each other and grows. Therefore, fine ferrite grains are effectively formed. Incidentally, if the distortion of two or more components is 0.5 or more, the equivalent distortion is 1.0 or more.

  In addition, it is not necessary to set all the forging steps to the above-mentioned conditions. Even if forging in the γ region is performed in the previous stage, it is not affected by the structure formation in the next step. By doing so, a sufficiently fine and uniform desired structure can be reproduced. Of course, it is possible to set all the forging processes to the above conditions, but conversely, if all the forging processes are set to the above-mentioned conditions, the deformation resistance of the material increases due to the forging temperature drop, and the forging load in the whole process Is unfavorable from the viewpoint of forging function.

  Furthermore, it is preferable that only the desired part is set as the forging condition described above, because an increase in forging load can be better suppressed. In other words, since parts where high fatigue strength is required in a product such as a hub or a constant velocity joint are limited, a product with excellent fatigue characteristics can be obtained if the above forging conditions are satisfied only in a desired part. . Of course, all parts of the forged product can be forged under the above conditions, and the scope of application of the present invention may be determined according to the required characteristics.

Here, when cold working is performed after hot forging, at least a portion subjected to cold working other than a portion where fatigue strength is required is in a temperature range of more than A ₃ points. It is preferable to perform the final hot forging. This can be achieved by refining the grain size, although fatigue strength is improved, since the cold workability conversely deteriorate, that portions cold working is performed, the forging temperature A ₃ point This is because cold workability can be maintained by increasing the crystal grain size as described above.
In addition, in the temperature range of A ₁ point or more and A ₃ point or less, the portion where the final hot forging was performed so as to add the strain of the multi-directional component in which the strain of two or more components is 0.5 or more is the average grain size Becomes a structure having a high fatigue strength of 5 μm or less. Meanwhile, the portion subjected to final hot forging in a temperature range of A _3-point than the average crystal grain size of more than 8 [mu] m, a tissue that is suitable for cold working.

Here, a method for satisfying the forging conditions will be specifically described.
First, local water cooling may be adopted to reduce the temperature range of A ₁ point or more and A ₃ point or less for a portion requiring fatigue strength, and the method is not particularly limited.

Next, an example of means for partially applying the strain under the above conditions will be described with reference to the drawings in the case of manufacturing a hub as a forged product.
The hub is heated by using the steel bar (round bar) shown in FIG. 1 (a) as a raw material, and processed into the shape shown in FIGS. 1 (b), (c) and (d) (in the case of FIG. 1). In general, it is manufactured through three forging steps. In the hub 1 at the product stage shown in FIG. 1 (d), the flange root portion indicated by reference numeral 1a is a portion that requires a higher fatigue strength than the other portions. Therefore, the present invention is applied to this portion. The case where the fatigue strength is improved will be described with reference to FIG.

That is, the raw material and the shape after each forging step shown in FIGS. 2 (a) to 2 (d) correspond to the steps shown in FIGS. 1 (a) to 1 (d), and FIG. (B) is the same shape as FIG. 1 (a) and (b). Next, in the present invention, in the final forging process shown in FIGS. 2 (c) to 2 (d), in order to introduce strains having a multi-directional component, the strains having two or more components are each 0.5 or more. In the final forging of the last stage from FIG. 2 (b) to FIG. 2 (c), the part 1b corresponding to 1a in FIG. After that, it is subjected to a forging process in a temperature range of the final A ₁ point or more and A ₃ points or less, and in this final forging, processing that generates strains in a plurality of directions along with large strains in the 1b portion is realized. The hub 1 shown in FIG. 2 (d) thus obtained is finished into a product in which the portion 1 a has particularly excellent fatigue characteristics. Further, in the hub in the product stage shown in FIG. 2 (d), for example, cold caulking is performed on the shaft end portion 1c. preferable. Therefore, in the forging process in the temperature range of A ₁ point or more and A ₃ point or less, it is necessary to prevent the crystal grain size of the shaft end portion 1c from being refined. For that purpose, in FIG. the portion 1d corresponding to the shaft end portion 1c of the final product, it is effective to a forging temperature and a ₃ points greater.

In addition, as a process for introducing a distortion of a multi-directional component, in which the distortion of the two or more components is 0.5 or more, other than the above, uniformly overlap in the circumferential direction as described above In addition to the shaped shape, it may be subjected to extra-stressing in the circumferential direction, and conversely, a recess is provided so that the plastic flow from other parts increases in the desired part in the final forging process. The shape may be any shape and is not particularly limited.
Incidentally, the amount of distortion of each direction component can be obtained by the finite element method.

  Cooling after forging is allowed to cool, but if the average cooling rate from forging to 400 ° C is slow, ferrite grains grow and the fatigue strength decreases, so the average cooling rate is 0.3 ° C. / s or more is preferable. Furthermore, it is preferably 0.5 ° C./s or more. In order to obtain the preferred average cooling rate, cooling is sufficient, but in the case of a large product having a large heat capacity, it can be achieved by blast cooling or the like.

Steel material of JIS S48C (C: 0.48 mass%, Si: 0.25 mass%, Mn: 0.7 mass%, P: 0.01 mass%, S: 0.01 mass%, A ₁ point: 730 ° C, A ₃ points: 780 ° C) After rolling to obtain a bar material of 60mmφ × 100mm, after warm forging according to the process shown in Fig. 3 so that the reduction ratio is 50% from three directions (up, down and longitudinal direction) at various temperatures. Air-cooled to obtain a 50 × 67 × 85 mm product. By this forging, a strain of 0.7 or more was added to each of the three directions in the bar material.

The average crystal grain size of the product thus obtained was investigated with an optical microscope and a scanning electron microscope after corrosion with nital, and a rotating bending fatigue test piece was collected and subjected to a rotating bending fatigue test. These investigations and test results are summarized in FIG.
The rotating bending fatigue test was performed with an Ono type rotating bending fatigue tester using a 10mmφ smooth shape test piece at a repetition rate of 3600cycle / min, and the 1 × 10 ⁷ fatigue limit as the rotating bending fatigue strength. evaluated.

  As shown in FIG. 4, in the product obtained under the conditions according to the present invention, it can be seen that the crystal grain size is remarkably fine and the fatigue strength is remarkably improved.

JIS S53C (C: 0.55 mass%, Si: 0.3 mass%, Mn: 0.65 mass%, P: 0.01 mass%, S: 0.005 mass%, A ₁ point: 730 ° C, A ₃ points: 775 ° C) Rolled to 60mmφ, material of 20.8mmφ × 47.3mm length from 1 / 4D part of 60mmφ was taken from rolling direction, followed by upset forging to 31mmφ × 21.3mm length at 1100 ° C, radiation thermometer When the surface temperature measured in step 750 became 750 ° C., backward extrusion forging and air cooling were performed to obtain a product having an outer diameter of 34.8 mmφ × length of 33.3 mm and an inner diameter of 25.0 mmφ × 27.9 mm (see FIG. 5). A structure investigation was carried out from each part indicated by numbers P _{1 to} P ₈ in FIG. 5 of this product. These survey results are listed in Table 1.
The strain amount and temperature of each part of the forged product were calculated by the finite element method using the Coulomb friction coefficient of 0.2 and the published thermophysical value of S53C. The crystal grain size investigation is the same as in Example 1 above.

From the analysis results shown in Table 1, it can be seen that the strains of two or more components each show a value of 0.5 or more, and the crystal grain size in the temperature range of A ₁ point or more and A ₃ point or less is remarkably fine. In addition, even when the strains of two or more components are each 0.5 or more, the crystal grain becomes a stretched structure at a site where the temperature is A ₁ point or less, and no significant refining is observed at a site of A ₃ point or more.
These results, as the forging conditions for subsequent final forging step for hot forging, a strain of more than two components each 0.5 or more, it is clear that and temperature range ₃ points or less of _one or more points A A is preferred.

  After rolling the steel material having the composition shown in Table 2 into a bar material, the final forging process following the hot forging at a forging temperature of 1100 ° C. is set to the forging conditions shown in Table 3, and the bar material is 60 × 60 × 120 mm Got the product. The product thus obtained was subjected to a structure investigation, and a rotational bending fatigue test piece and a cold compression test piece were collected and subjected to a rotational bending fatigue test and a cold compression test, respectively. These surveys and test results are also shown in Table 3.

The amount of strain during forging was calculated by a finite element analysis method with a Coulomb friction coefficient of 0.2. Further, the structure investigation and the rotating bending fatigue test are the same as those in Example 1 described above.
In the cold compression test, a cylindrical compression test piece having a diameter of 8 mmφ × length of 12 mm was taken, and the test piece was subjected to 75% cold compression up to 3 mm with a strain rate of 1 / s in the length direction. Cold workability was evaluated by the presence or absence of cracks.

As apparent from Table 2, the forging temperature of the final forging step in A ₁ point or more A ₃ points below the temperature range, and two or more components of the distortion in a plurality of directions component was respectively 0.5 or more in accordance with the present invention, invention examples Nos. 1, 2, 9 to 12 were all able to obtain excellent fatigue strength with a rotational fatigue strength of 400 MPa or more.
On the other hand, No. _{3 in} which the forging temperature condition is more than A3 has a coarse crystal grain size and low fatigue strength. Further, No.4 forging temperature is less than ₁ point A is worked structure remains, the fatigue strength was low. Furthermore, the forging temperature is less than ₁ point A, and strain conditions will also worked structure remains in the No.6 not satisfied 0.5 or more per second direction component, a low fatigue strength.
Moreover, in the comparative examples of Nos. 7 and 8 and Nos. 13 to 15 that do not satisfy the component composition, the rotational bending fatigue strength was insufficient or the cold workability was lowered.

Steel material of JIS S48C (C: 0.48 mass%, Si: 0.25 mass%, Mn: 0.7 mass%, P: 0.01 mass%, S: 0.01 mass%, A ₁ point: 730 ° C, A ₃ points: 780 ° C) After rolling into a steel bar, this steel bar was subjected to three-stage hot forging as shown in FIG. 2 to form a hub for an automobile. At this time, the crystal grain size was variously changed for the root portion of the flange, which is the part where the rotational bending fatigue strength is most required, and the shaft end portion where the cold caulking is performed. The crystal grain size was adjusted by changing the forging conditions during final forging. That is, as shown in FIG. 2 (c), the shape after the intermediate forging is a shape having a surplus in the 1b portion corresponding to the root portion 1a of the flange in the final shape, and FIG. 2 (d) to FIG. In the final forging stage shown in FIG. 2), the axial strain amount is 0.7 or more and the circumferential strain amount is 0.5 or more. Further, in the forging stage from FIG. 2 (c) to FIG. 2 (d), heating is performed. The temperature was set to 900 ° C., the 1b portion and the 1d portion were locally cooled before forging and adjusted to the temperature range shown in Table 4, and then hot forging was performed. The obtained hub was subjected to a structure observation, a fatigue test, and a cold compression test in the following manner.

[Tissue observation]
From the obtained shaft end 1c of the hub and the base 1a of the flange (see FIG. 2D), a structure observation sample was cut out and the average crystal grain size was measured. The tissue observation method is the same as in Example 1.
[Fatigue test]
As shown in FIG. 6, the bolt hole 2 was drilled in the flange portion 1 e of the hub 1 and fixed to the rotating jig 4 using the bolt 3. Further, the bearing ball 5 is arranged on the outer peripheral surface of the shaft portion 1f of the hub 1 and the ball presser 6 is mounted, and the hub 1 is moved at a constant rotational speed (1500 rpm) with a constant load (10 kN) applied to the ball presser 6. The durability test for rotating was performed, and the time until the hub 1 was broken was measured and evaluated. Table 4 also shows the results of this durability test.
[Cold compression test]
A cylindrical compression test piece having a diameter of 8 mmφ and a length of 12 mm is taken from the shaft end 1 c of the hub 1, and is subjected to 75% cold compression up to 3 mm at a strain rate of 1 / s in the length direction of the test piece. The cold workability was evaluated by the presence or absence of. Here, the cylindrical specimen was collected so that the length direction of the cylindrical specimen was the axial direction of the hub.

From Table 4, it can be seen that No. 1 to 5 in which the average crystal grain size of the root portion of the flange is 5 μm or less has high durability. In this, the crystal grain size of No.2~5 the axial end portion of the forging temperature was A _3-point than the shaft end portion becomes more 8 [mu] m, also not recognized the occurrence of cracks due to cold compression test, cold The inter-processability was also excellent.
On the other hand, the No.6 was forging temperature of the root portion of the flange and 710 ° C. and A less than ₁ point, since the worked structure at the root portion of the flange was left, poor durability.
Further, the No.7 and the forging temperature of the root portion of the flange and 800 ° C. and A ₃ point than has the average crystal grain size of the root portion of the flange is increased, the durability was poor.

It is a figure which shows the conventional forge process in manufacture of a hub. It is a figure which shows the forge process according to this invention in manufacture of a hub. 3 is a schematic diagram of three-way forging according to Example 1. FIG. It is a figure which shows the relationship between forging conditions, rotation bending fatigue strength, and a product particle size. It is a schematic diagram which shows the site | part which measured the shape after back extrusion forging in Example 2, forging temperature, the amount of distortion, and the crystal grain diameter. It is a schematic diagram explaining the durability test of a hub.

Explanation of symbols

1 Hub 2 Bolt hole 3 Bolt 4 Rotating jig 5 Bearing ball 6 Ball retainer

Claims (3)

C: 0.3-0.9 mass%
Si: 0.01-1.2mass% and
Mn: 0.01-2.0mass%
When the hot forging product is manufactured by subjecting the steel material having a composition of Fe and inevitable impurities to a plurality of hot forgings in the final forging process, Heat with excellent fatigue strength characterized by applying multi-directional component strain under a temperature range of ₁ point or more and A ₃ points or less, and having multi-directional component strain of 2 or more components each 0.5 or more A method for manufacturing inter-forged products. In Claim 1, steel material is further
Mo: 0.05-0.6mass%,
Al: 0.01-0.06mass%,
Ti: 0.005 to 0.050 mass%,
Ni: 1.0 mass% or less,
Cr: 1.0 mass% or less,
V: 0.1 mass% or less,
Cu: 1.0 mass% or less,
Nb: 0.05 mass% or less,
A method for producing a hot forged product excellent in fatigue strength, characterized in that the composition contains one or more selected from Ca: 0.008 mass% or less and B: 0.004 mass% or less. 3. The final forging according to claim 1 or 2, wherein at least a part is a part for which fatigue strength is required, and at least a part subjected to cold working among parts other than the part for which fatigue strength is required. A method for producing a hot forged product excellent in fatigue strength, characterized by performing hot forging in a temperature range of more than A ₃ points in the process.

Images