KR20050019716A - Rolling part and power transmission part - Google Patents

Abstract

An object of the present invention is to provide a power component made of a steel material of medium carbon steel level that improves the rolling life to the level of bearing steel and improves the occurrence characteristics of surface cracks, and a power transmission component including the power component.

For this purpose, the steel constituting the electric component has a lower limit value (ΔKth) of the stress intensity factor range with respect to the tensile fatigue crack propagation in the high frequency hardening hardening portion, which is 6.2 MPa√m or more.

Description

ROLLING PART AND POWER TRANSMISSION PART}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a motor-driven part made of high-frequency quenched steel and a power transmission part including the motor-driven part, which are subjected to repeated tensile stress and are used under severe lubrication conditions or with slip.

Bearing steels such as SUJ2, which have excellent rolling life, are used for rolling parts having relatively simple shapes, including rolling bearings. However, since the bearing steel lacks workability, the bearing steel is not suitable for a complicated electric component. On the other hand, since medium carbon steels, such as S53C, have favorable workability, it is suitable for the electric component with a complicated shape. Medium carbon steel is usually used after being processed into a complicated shape and subjected to high frequency quenching to the transmission site. In addition, since medium carbon steel has a low content of expensive alloy elements, it is inexpensive and leads to saving of scarce resources.

However, in many cases, a complicatedly shaped power component is not simply subjected to a simple rolling load in the power portion. In addition to rolling, since slippage or repetitive tensile stresses other than rolling are overlapped, cracks are likely to occur at rolling sites, which may cause early propagation and fatal damage. This is considered to be the cause of the drawback that a heavy carbon steel falls in rolling life compared with a bearing steel.

In recent years, with energy saving and compactness, electric components tend to be used under severe conditions than before. In order to achieve long life while considering productivity and cost, there is a limit as a bearing steel lacking in workability. For this reason, the demand for the electric component manufactured from the steel material which reviewed content of the inexpensive alloy elements C, Si, and Mn contained in the conventional heavy carbon steel is increasing. Specifically, the demand for improving the following items (1) and (2) is increasing.

(1) With the medium carbon steel level, the rolling life of the high frequency hardened portion is improved to the bearing steel level.

(2) At the level of the medium carbon steel, the generation resistance of the surface cracks of the high frequency quenched portion is improved.

(1) is effective for improving the reliability against rolling fatigue, and (2) is effective for suppressing the occurrence of surface cracks caused by sliding.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the 3rd generation hub unit which the wheel bearing and the constant velocity joint combined using the electric component of this invention.

2 is a schematic view of a fourth generation hub unit in which a wheel bearing and a constant velocity joint are incorporated, in which the electric component of the present invention is used.

Fig. 3 is a diagram showing a relationship between actual values and predicted values of rolling fatigue life (L ₁₀ ) of rolling in the first embodiment.

Fig. 4 is a diagram showing a test piece used for the measurement of the fatigue crack propagation test in the second embodiment.

Fig. 5 is a diagram showing a relationship between a correction coefficient FI (a / W) and α (= a / W) in equation (4) for obtaining a stress intensity factor in a fatigue crack propagation test.

Fig. 6 is a diagram showing a method for obtaining the lower limit of the stress intensity factor range in the relationship between the crack growth rate (da / dN) and the stress intensity factor range (ΔK _I ) in the fatigue crack propagation test.

Figure 7 is a view showing the relationship between the measured value and the predicted value of the electric fatigue life (L ₁₀₎ of the cloud in the second embodiment.

An object of the present invention is to provide a power transmission component including an electric component made of a steel material of a medium carbon steel level that improves the rolling life to the level of bearing steel and further improves the occurrence characteristics of surface cracks.

In the motor component of the present invention, the steel forming the motor component is 6.2 MPa√m as the lower limit value (ΔKth) of the stress intensity factor range for tensile fatigue crack growth in the high frequency hardening hardening portion. Have more than By providing the lower limit of 6.2 MPa√m or more in the range of the stress intensity factor, resistance to the occurrence and propagation of fatigue cracks due to repetition of tensile stress is higher than that of the conventional material (S53C). Conventionally, there is no example that the lower limit value (ΔKth) of the stress intensity factor range for tensile fatigue crack propagation is required for a high frequency quenched portion of a steel material used for an electric component. Moreover, about the medium carbon steel S53C for conventional electric components, it is not disclosed that the lower limit (DELTA Kth) of the above-mentioned stress intensity | strength expansion coefficient range was obtained in the high frequency quenching part.

By securing the lower limit value [Delta] Kth of the above-mentioned stress intensity factor range, occurrence of surface cracks and propagation in the transmission site are less likely to occur under conditions in which slippage other than rolling or overlapping repetitive tensile stress overlaps.

Next, the present invention will be described in detail with reference to Examples. 1 and 2 show a hub unit in which the electric component of the present invention is used. FIG. 1: is a schematic diagram of the 3rd generation hub unit H / U which is a hub joint which integrated the wheel bearing 6 and the constant velocity joint. 2 is a schematic diagram of the wheel bearing 6 including the 4th generation H / U which evolved further. In the third generation H / U shown in FIG. 1, one side of the inner race 2 is integrated with the hub wheel 4, and the other inner race 5 is caulked to the hub wheel 4. do. The outer ring 3 is structured to be directly fixed to the knuckle. In this third generation H / U, the constant velocity joint 1 is an independent component.

On the other hand, the fourth generation H / U shown in Fig. 2 has a more compact structure. It is the same as the third generation that one side 5 of the inner ring race is integrated with the hub wheel 4, but the other inner ring race is integrated with the joint outer ring 3. Therefore, the part requires both (I) rolling fatigue life as the bearing race portion, and (II) life with respect to the rolling fluctuation movement with sliding as the joint portion.

(First embodiment)

As shown in Table 1, steels (A1 to A9) within the component range of the present invention are used as examples of the present invention, and steels (B1 to B10) outside the component ranges of the present invention are used as comparative examples. As described in the remarks of Table 1, Comparative Example B1 is conventional material (S53C), and B10 is bearing steel (SUJ2).

TABLE 1

(1) rolling contact fatigue test

As mentioned above, the drawback of the medium carbon steel is that the rolling life is lower than that of the bearing steel. Given the use under the severe conditions expected in the future, it is desirable to have a rolling life at the level of bearing steel. The test piece was subjected to high frequency quenching so that the depth of the cured layer was about 2 mm. In this test, the number of tests N was 15 pieces, and the cloud life was evaluated as L ₁₀ (10% life). The conditions of a rolling fatigue test are shown below.

(Test Specimen Dimensions): Outer Diameter 12mm × Length 22mm

(Relative steel ball dimensions): Diameter 19.05 mm

Maximum contact surface pressure (Pmax): 5.88 GPa

(Load Speed): 46240 times / minute

Lubricant oil: turbine oil VG68

(2) rolling and sliding fatigue test

In the transmission site | part, such as the relative shaft of a needle bearing, a constant velocity joint, a ball screw, etc., there exists a site | part which slides in addition to a cloud. In addition to long life under pure cloud conditions, it is necessary to ensure long life even under the conditions in which sliding is affected. Rolling sliding fatigue test is a two-cylinder test which evaluates the lifetime under rolling sliding conditions. The test piece was subjected to high frequency quenching so that the depth of the cured layer was about 2 mm. Test conditions are shown below.

(Target test piece): Outside diameter 40 mm x width 12 mm, no outer diameter bending rate (straight)

(Relative test piece): outer diameter 40mm x width 12mm, outer diameter bending rate 60mm, the material is bearing steel (SUJ2)

Max Contact Surface Pressure (Pmax): 3.5GPa

(Speed): Target Test Specimen 1800rpm / Relative Test Specimen 2000rpm

Lubricant oil: turbine oil VG46

(3) test result

Table 2 shows the results of the rolling fatigue test and the rolling sliding fatigue test. Measured value of the cloud life (L _10), this 263O × 10 carbon steel (S53C) (Comparative Example B1) of a conventional ^four, bearing steel (SUJ2) (Comparative Example B10) is a 7300 × 10 ^4, S53C is half Bearing Steel Or less. In the example of the present invention, considering that the structure is made of only an inexpensive alloy component, it is not possible to reach the bearing steel, but it is preferable to have an L ₁₀ of 500 × 10 ⁴ or more, which is at least about twice that of S53C. In view of this, Examples A1 to A9 of the present invention all showed 5000 × 10 ⁴ or more, and in particular, A5, A8, and A9 had a life equivalent to that of bearing steel.

TABLE 2

On the other hand, in the comparative example, although B2 and B3 showed 5000x10 <^4> or more, the thing with comparatively little content of other alloying elements became short life. The predicted value of L ₁₀ shown in Table 1 is a weighted regression analysis using the amounts of chemical components C, Si, and Mn as dependent variables with respect to the measured value of L ₁₀ . It is the value calculated | required from L of 1).

L = 11271 (C) +5796 (Si) +2665 (Mn) -6955... … … … … … … … (One)

There is a relationship of L ₁₀ = L × 10 ⁴ between L and L ₁₀ . Therefore, the following formula (2) is established between L ₁₀ and the content rate (wt%) of the component elements.

L ₁₀ (× 10 ⁻⁴ ) = 11271 (C) +5796 (Si) +2665 (Mn) -6955. … (2)

Fig. 3 is a diagram showing the relationship between the measured value of L ₁₀ and the predictive equation for each steel, and shows that there is a very good correlation between them. That is, it means that L ₁₀ can be predicted with high precision by the amount of alloying elements C, Si, and Mn. If this is to honor A1 to A9 of the predictive value of C, Si, which is available from as well as the composition range of Mn, Equation _{(2) L 10 5OO0 × 10} 4 or more configuration can be said to ensure a long life.

In life under cloud sliding conditions, Examples A1 to A9 of the present invention were all superior to S53C (Comparative Example B1). On the other hand, all the comparative examples were S53C or less. In view of the alloy composition, a balance of C, Si, and Mn is required for the rolling sliding life. In the right column of Table 2, as a measure of softening resistance, the half-width of the X-ray diffraction after the cloud sliding test for a predetermined time and then (dried 9 x 10 ⁵ times under the same conditions as the cloud sliding test) is shown. . As for the example of this invention, the fall of the half width | variety is generally small, and it can be said that fatigue by the influence of a slip hardly arises.

As mentioned above, it can be said that the cloud life can be improved by optimizing the amounts of C, Si, and Mn, and the cloud sliding life can be stably improved.

(Second embodiment)

As shown in Table 3, steels (A1 to A13) of 6.2 MPa√m or more having a lower limit value (ΔKth) of the stress intensity factor range for tensile fatigue crack growth were used as the examples of the present invention. In addition, as a comparative example, steel (B1 to B8) having a ΔKth smaller than 6.2 MPa √m was used as the material. In addition, as described in the remarks, Comparative Example B1 is a conventional material (S53C), and Comparative Example B8 is a bearing steel (SUJ2). Further, A1 to A9 have a DELTA Kth of 6.2 MPa √m or more, and C, Si, and Mn are in a composition range in which L ₁₀ is 5000 × 10 ⁴ or more in formula (2).

TABLE 3

(1) fatigue crack growth test

In order to evaluate the lower limit value (ΔKth) of the stress intensity factor range for the tensile fatigue crack growth of the high frequency hardening hardened portion, a three-point bending test was performed. The test piece was uniformly hardened inside to eliminate the influence of residual stress on fatigue crack growth. Test conditions are shown below.

(Test piece dimensions): 80 mm x 20 mm x 2 mm (slit and fatigue cracks are introduced at the center)

Fig. 4 shows the test situation of the test piece shape (80 mm x 20 mm x 2 mm) and the repeated load addition by three-point bending. On one side of the test piece, a slit is inserted by a wire cut, and fatigue preheat is introduced before that. As shown in Fig. 4, the nominal bending stress σ ₀ when the load P is applied to the center of the test piece in the three-point bending arrangement of the distance S between the points is represented by the formula (3). The stress intensity factor K _I when the crack length is a (m) can be obtained by substituting sigma ₀ into equation (4). FI (a / W) in the formula is a correction factor. Fig. 5 shows the relationship between a / W and FI (a / W) obtained by the Finite Element Method (FEM).

sigma ₀ = 3SP / (2tW ² ). … … … … … … … … … … … … … … (3)

K _I = FI (a / W) sigma ₀ (? A) ^1/2 ... … … … … … … … … … … (4)

In the lower limit value (ΔKth) of the stress intensity factor range, the value of the most severe plane strain stress state (type I stress state) of restraint is represented by the symbol ΔK _I th. That is, ΔK _I th represents the lower limit of the stress intensity factor range of the planar strain stress. That is, the lower limit value (ΔKth) of the stress intensity factor range of the present invention is the lower limit value of the stress intensity factor range in the planar strain stress state. In the above description, the symbol indicating that it is an I type (plane strain stress state) has been omitted and simply recorded. Also in the following description, the indication of type I may be omitted, and the lower limit value of the stress intensity factor range in the planar deformation state may be described as ΔKth. Load is applied to the specimen by the following load method.

(Load Method): Load Control

(Load frequency): 8 Hz

(Stress ratio): 0.5

(2) crack fatigue test

In order to evaluate a crack fatigue strength, the crack fatigue test was done using the high frequency quenched ring test piece. The test piece was subjected to high frequency quenching so that the depth of the cured layer was about 2 mm. Test conditions are shown below. The number of tests was four and evaluated by the average lifetime.

(Test piece dimensions): 60 mm outside diameter x 45 mm inside diameter x 15 mm width

(Load): 9.5kN

(Rotation speed): 8000rpm

(3) cloud fatigue test

The rolling fatigue test was done under the same conditions as in the first example. That is, rolling fatigue test was done using the high frequency quenched cylindrical test piece. The test piece was subjected to high frequency quenching so that the depth of the cured layer was about 2 mm, and the cloud life L ₁₀ (10% life) was evaluated using the number of 15 pieces.

(4) cloud sliding fatigue test

It carried out on the conditions similar to 1st Example. That is, the rolling sliding test was done by the two-cylinder test, and the test piece was subjected to the high frequency quenching so that the depth of the hardened layer might be about 2 mm. The number of test pieces was two and evaluated by the average lifetime.

(5) trace lubrication cloud test

Under conditions where the lubricant oil is not sufficiently supplied, the oil film may partly crack, resulting in surface heat generation and surface cracks. In order to reproduce this, (4) in a test such as rolling slip fatigue test, the lubricant was applied at the initial stage of rolling, and then rolled without supplying lubricant. The number of test pieces was two, and it evaluated by the average lifetime.

(6) test result

Table 4 shows the results of the fatigue crack propagation test, crack fatigue test, rolling fatigue test, rolling slip fatigue test, and trace lubrication rolling test.

TABLE 4

Fig. 6 shows a method for obtaining ΔK _I th in the fatigue crack propagation test. 6 shows the relationship between the crack growth rate da / dN and the stress intensity factor range DELTA K _I of Inventive Example A1 and Comparative Example B8 (SUJ2). The lower limit value (ΔK _I th) in the range of stress intensity factor relates to the stress intensity factor when cracking does not progress even under load. From the plot of Figure 6, a △ K _I th of Invention Example A1 is 6.5MPa√m △ K _I th of a, Comparative Example B8 is 5.0MPa√m.

As a result of the fatigue crack propagation test, ΔKth of the inventive examples Al to A13 were all 6.2 MPa √m or more. On the other hand, DELTA Kth of Comparative Examples B1 to B8 had the largest B1 (S53C) of 6.0 MPa √m and the other was smaller than that.

As a result of the crack fatigue test, all of invention examples A1 to A13 showed the crack fatigue life more than 1.5 times compared with the comparative example B1 (S53C). On the other hand, Comparative Examples B2 to B7 are farther than Comparative Example B1 (S53C).

Cloud lifetime carbon steel of the measured value is, the conventional (L ₁₀₎ (S53C) (Comparative Example B1) is 2630 × 10 ^4, bearing steel (SUJ2) (Comparative Example B8) is 73O0 × 10 ⁴ and, S53C (Comparative Example B1 ) Is less than half of the bearing steel. Considering that the structure is made of only an inexpensive alloy component, it is not possible to reach the bearing steel, but it is preferable to have an L ₁₀ of 5000 × 10 ⁴ or more, which is at least about twice that of S53C. In view of this, Examples A1 to A13 of the present invention all exhibited 5000 × 10 ⁴ or more, and in particular, A5, A8, and A9 had a life equivalent to that of the bearing steel. On the other hand, all of Comparative Examples B2 to B7 had a short life of 5000 × 10 ⁴ or less. The predicted value of L ₁₀ shown in Table 3 is a value obtained from the formula (2) obtained by performing a regression analysis using the amounts of chemical components C, Si, and Mn as dependent variables with respect to the measured value of L ₁₀ .

Fig. 7 shows the relationship between the measured value of L ₁₀ and the predicted value, and shows a very good correlation between them. That is, it means that L ₁₀ can be predicted with high accuracy by the amount of alloying elements C, Si, and Mn, and it is obtained not only from the numerical range of C, Si, Mn of Examples A1 to A13 of the present invention, but also obtained from equation (2). It can be said that long life can be guaranteed if the L ₁₀ predicted value is 5000 × 10 ⁴ or more.

The service life under rolling sliding conditions was excellent in all of Examples A1 to A9 of S53C (Comparative Example B1). On the other hand, A10 to A13 resulted in an equivalent to or slightly inferior to S53C in rolling slip life, and the comparative examples were all less than S53C except for B8 (SUJ2). In view of the alloying component, regardless of the present invention and the comparative example, a large amount of Mn shows a tendency of excellent rolling sliding life.

In the result of the trace lubrication cloud test, Examples A1 to A13 of the present invention were all superior to S53C (Comparative Example B1). In the comparative example, B6 and B7, which had two of the higher amounts of C, Si, and Mn, showed relatively longer life, but the service life under the above-described rolling sliding test conditions was very long.

In view of the above, in order to be excellent in all of the crack fatigue life, the rolling life, the rolling sliding life, and the trace lubrication life in the medium carbon steel base material,? Kth must be 6.2 MPa? M or more. Moreover, in order to ensure the (DELTA) Kth, the reliability of other performance can also be improved by adjusting the amount of C, Si, and Mn.

The high frequency quenching transmission component of the present invention can suppress the occurrence and propagation of surface cracks under conditions where the high frequency quenching hardening portion, which is a transmission site, is accompanied by sliding or a cyclic tensile stress other than rolling is superimposed. Has excellent cloud life of river level. For this reason, in the power transmission component using the said electric component, high strength and long life can be made compatible.

Next, the embodiment and the effect of the present invention, including the above-described examples, will be described in general with respect to the effect of alloying elements.

As one embodiment of the electric component of the present invention, the steel material having the following alloy component range makes it possible to make the ΔKth at 6.2 MPa√m or more at the high frequency quenched portion, to further secure long life. Can be. That is, C: 0.5 to 0.7 wt%, Si: 0.6 to 1.2 wt%, Mn: 0.6 to 1.5 wt%, and the balance of the electric component in the component composition consisting of Fe and unavoidable impurities You may comprise.

The amount of carbon is 0.5 to 0.7 wt% because it is possible to guarantee a hardness or higher by high frequency quenching, coexist with a certain amount of Si or Mn, and ensure a rolling life under a large load condition. For this reason, the amount of carbon required is 0.5 wt% or more. In order to further improve hardness and rolling life, it is preferable to contain 0.55 wt% or more of carbon.

Carbon is good for making carbides and for obtaining a stable hardness. On the other hand, when there is too much carbon amount, material hardness will become high too much and workability will fall. In addition, since a special heat treatment such as high temperature diffusion heat treatment (soaking) or carbide spheroidization for preventing component segregation is required and the cost is increased, the upper limit is 0.7 wt%. In addition, after securing the above-mentioned effects of Mn, it is preferable to make the carbon amount 0.65 wt% or less in order to reduce the damage accompanying component segregation.

Si is an element which strengthens the base of steel and increases cloud life. For this reason, by containing 0.6 wt% or more, softening at the time of exposure to high temperature is suppressed, and there exists an effect which slows the structure change and the crack generation by repetition of a large load. For this reason, the minimum of Si is made into 0.6 wt%. In order to further improve the softening resistance at high temperature, it is preferable to be 0.7 wt% or more.

On the other hand, even if the amount of Si is increased, Mn mentioned later does not contribute to an increase in material hardness, and when it exceeds 1.2 wt%, cold workability and hot workability are inferior, so 1.2 wt% was set as an upper limit. In addition, in order to suppress surface property deterioration resulting from internal oxidation of Si in the surface layer part during hot working, it is preferable to make Si 1.1 wt% or less. Moreover, in order to reduce surface decarburization, it is preferable to set it as 1.0 wt% or less.

By containing 0.6 wt% or more, Mn improves the hardenability of steel materials, solidifies the steel by solidifying it in steel, and increases the retained austenite useful for the life of the cloud. In addition, Mn is most effective for improving the lower limit value (ΔKth) of the stress intensity factor range for tensile fatigue crack growth. For this reason, Mn is contained 0.6 wt% or more. In order to further increase the retained austenite and to further improve the cloud life, the Mn is preferably contained 0.7 wt% or more.

On the other hand, Mn not only strengthens the base, but also acts to enter the carbide and increase the hardness of the carbide. By including 1.5 wt% or more, the hardness of the material is excessively increased, and workability and machinability are reduced. From these viewpoints, the upper limit of Mn content is made into 1.5%. In order to reduce the degree of segregation of components and to reduce soaking costs and the like, Mn is preferably 1.25 wt% or less. In addition, when the size of the ingot at the time of manufacture is large, component segregation occurs more strongly, and Mn is more preferably 1.0 wt% or less in consideration of the case where the ingot size is large.

In the case of electric furnace steel, since scrap is a main raw material, the impurity contained in scrap is mixed in steel. For example, 0.3 wt% or less of Cr, 0.3 wt% or less of copper (Cu), and other impurities are contained in the steel from scrap. Such impurities mixed from steelmaking raw materials are treated as impurities inevitably included. That is, even if it contains such an impurity, it corresponds to the electric component of this invention.

It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown by above-described not description but Claim, and it is intended that the meaning of a Claim and equality and all the changes within a range are included.

ADVANTAGE OF THE INVENTION According to this invention, by adjusting the composition of a medium carbon steel with respect to the steel material which forms a rolling component, the rolling life can be improved to the level of the bearing steel containing expensive alloying elements, and the surface crack generation characteristic can be improved. have. As a result, it is expected that the electric component of the present invention and the power transmission component using the same will be widely used in a power transmission system in which repeated tensile stresses other than sliding and electric power are superimposed in automobiles for energy saving and compactness. .

Claims (6)

As an electric component made of steel, The lower limit value (ΔKth) of the stress intensity factor range for tensile fatigue crack growth in the high frequency hardening hardened portion of the steel is within a range of 6.2 MPa√m or more. The method of claim 1, The steel comprises C: 0.5 to 0.7 wt%, Si: 0.6 to 1.2 wt%, Mn: 0.6 to 1.5 wt%, and the balance has a component composition consisting of Fe and unavoidable impurities . The method of claim 1, The said steel is a steel material which adjusted the content rate (wt%) of C, Si, and Mn so that it may satisfy L≥5000 in following formula (1). L = 11271 (C) +5796 (Si) +2665 (Mn) -6955... … … … … … … (One) A power transmission component comprising the electric component according to claim 1. The method of claim 4, wherein And the power transmission component is a hub joint incorporating a wheel bearing (6) and a constant velocity joint (1). The method of claim 4, wherein The transmission component is a power transmission component, characterized in that the sliding overlap on the rolling.