JPS6334423B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for measuring the degree of rolling fatigue occurring in rolling parts such as bearings, gears, cams, etc. As used herein, rolling fatigue refers to fatigue of materials due to rolling contact, even when accompanied by some slippage. Therefore, it specifically refers to fatigue due to repeated Hertzian rolling contact stress, surface friction force, stress when foreign objects are caught, etc. Until now, there has been no method to quantitatively express the degree of rolling fatigue in bearings, etc.; for example, it can be determined by visual observation, or more scientifically, changes in the material of rolling parts caused by rolling fatigue can be detected using an X-ray machine. Therefore, it was only possible to use the physical quantities obtained by measurement as a rough guide. In particular, the latter method of determining the physical quantity as a guideline will be described here, and the known methods are as follows. That is, the X-ray diffraction line half-width (unit: mm) of the martensitic phase (unit: mm) (hereinafter referred to as half-width) and rolling fatigue degree, and the amount of retained austenite (unit: Vol%) (hereinafter referred to as γ _R amount) and rolling fatigue degree. It is known that there is some kind of relationship between the two, and of course, the method for measuring the half width and the amount of γ _R is also known. However, using only the half-width width or the γ _R amount, there are too many variations for each measurement target, making it difficult to even approximate the degree of fatigue. It is not clear how to process the half-width and γ _R amount determined at the depth (inside the depth) and use them to determine the degree of fatigue. Therefore, the present invention provides a method for measuring the degree of fatigue due to rolling fatigue of each part of each object by separately processing the half-width and γ _R amount determined for each part of each object separately. It is an object.
In the present invention, this is determined by the fatigue degree parameter determined from the measurement value by an This also means that the remaining life of each measurement object is estimated by changing the criteria for determining the degree of fatigue progression. This is because internal fatigue tends to accumulate more before failure than surface fatigue, which is exposed to various environmental conditions. Hereinafter, specific examples of the present invention will be described. Figure 1 shows an example where the degree of fatigue is maximum near the surface of the measurement target.
Various flags related to surface fatigue of each measurement target shown in are shown. Figure 1a shows the change in half-width as surface fatigue progresses, and Figure 1b shows the same γ _R
This shows a decrease in quantity. The half width and the amount of γ _R reduction are obtained from measurements using an X-ray diffraction device.
The former is shown here in mm and the latter in volume percent (Vol%).
Further, the degree of progress of fatigue is expressed as a relative amount of durability test time (relative durability test time L), with the time until the final rolling fatigue failure being 100. As is clear from these two graphs, even in the case of the same type of metal material and the same surface fatigue, the degree of change in the half-value width with respect to L and the amount of reduction in γ _R vary considerably depending on the bearing type, lubrication conditions, etc. I understand that. Therefore, the degree of fatigue cannot be estimated just by looking at the measured values of the measurement target separately. However, as shown in Figure 1c, if you look at the graph of the amount of decrease in half-value width (△B) against the amount of decrease in γ _R (△R) for each L,
The quantity F=k・△R+△B (k=b/a, which is determined by the type of metal material) corresponds almost one-to-one to L, regardless of the bearing type, lubrication conditions, etc. . Therefore, if ΔR and ΔB of each measurement object are known, then F can be calculated, and furthermore, L can be found. For this reason, if a graph of F, that is, the fatigue degree parameter, against L in surface fatigue as shown in Figure 1d is created in advance, fatigue fatigue can be measured by measuring the amount of decrease in the half-power width and the amount of decrease in γ _R of each measurement target. The degree parameter F is calculated, and based on the value of this parameter, L of the subject is determined from the above graph, and the degree of fatigue progress can be estimated with considerable certainty. Next, FIG. 2 shows an example of internal fatigue, and specifically shows various graphs regarding internal fatigue of each measurement target shown in Table 2. The same thing can be said for internal fatigue as for surface fatigue, and the second
Since ΔR and ΔB are known from diagrams a and b, and k, which changes depending on the type of metal material, is known, F can be calculated and diagram 2c can be created. However, the difference from surface fatigue is that even if the fatigue degree parameter F is the same for surface fatigue and internal fatigue, L is different. The reason for this has been stated earlier. When measuring internal fatigue of a rolling part, remove the rolling part before and after rolling fatigue using a method such as electrolytic grinding that does not apply a processing load to expose the surface to be measured. The half width and amount of retained austenite are measured using an X-ray diffraction device as shown in the figure. The rest is the same as when measuring the degree of surface fatigue. Here, we will talk about how to calculate the γ _R amount and half-value width when not fatigued.It is possible to measure it on a new product of the same type, or extrapolate it from an internal measurement value that is not affected by fatigue. It can be found by measuring parts other than the rolling surface of the same object. By the way, as seen in Figures 1 and 2,
The reason why a certain relationship is recognized between the amount of γ _R reduction and the amount of half width reduction is considered as follows. The decrease in γ _R due to repeated stress appears to be due to martensitic transformation of γ _R due to stress-induced transformation. Since the martensite generated during this fatigue process is a newly generated phase, it is not yet fatigued, and it must be considered that its half-width is naturally large. It is thought that the half-width of the diffraction line becomes large because the diffraction line with a large half-width value overlaps the diffraction line with a small half-width of fatigued martensite. This effect is predicted to have a certain relationship with the amount of austenite. It is also possible that the internal strain of new martensite generated by stress-induced transformation differs depending on the material, and therefore the half-width value thereof differs. Another factor is that external energy is consumed for martensitic transformation of γ _R , and
Another possible effect is that the fatigue of martensite is delayed and the decrease in half-value width is delayed. However, since γ _R is originally an extremely unstable phase at room temperature and transforms into martensite through instantaneous sliding deformation, the energy consumption required for the martensitic transformation process itself is less than the energy of rolling contact stress. It is thought that much more of the potential energy originally possessed by _R itself is consumed. Therefore, considering a state in which γ _R has a very large internal strain due to fatigue and a state in which the austenite has transformed into martensite, martensite is The fatigue-reduced energy is only relatively small, and the influence of this second factor on the half-width is negligible compared to the first factor (the effect of the large half-width of new martensite). It is considered small. Therefore, correction of the half-value width should be considered mainly based on the first factor. Note that it is easy to make a measuring device by embodying the above measuring method. For this purpose, an X-ray diffraction device, calculation/recording device, microcomputer, etc. may be combined. As described above, the measurement method according to the present invention brings about the following advantageous results. The progress of fatigue damage, that is, the degree of fatigue, of bearings used in practical machines can be determined with considerable certainty, allowing highly reliable and rational design and maintenance. It is now possible to reliably detect abnormalities such as load inclinations and local stress concentrations, which were previously determined by visually inspecting the area. It is no longer necessary to carry out the durability test until the final failure, and by stopping the test in the middle, the test time can be significantly shortened and the number of test machines can be reduced. In fields where safety is strongly required, such as aircraft and railway vehicles, these can be used with an extremely high degree of safety by periodically measuring their remaining life.

[Table] Filter bearing with iron powder
Mix earth and sand
Enter

【table】 [Brief explanation of the drawing]

FIG. 1 shows various graphs for surface fatigue, and FIG. 2 shows various graphs for internal fatigue.

Claims (1)

[Scope of Claims] 1. A method for measuring the degree of fatigue due to rolling fatigue of a metallic material having a retained austenite structure, comprising the X-ray diffraction half-width of a martensitic phase before and after rolling fatigue of a rolling part of the metallic material. The amount of retained austenite (Vol%) is measured, K is the constant determined by the type of metal member, and △R is the difference between the amount of retained austenite (Vol%) when not fatigued and that when fatigued. △
When B, fatigue level parameter F=K△R+△
Substitute the reduction in the X-ray diffraction half-width of the martensitic phase and the reduction in the amount of retained austenite (Vol%) based on the above-mentioned measured values into the equation B to obtain the fatigue parameter, and use this fatigue parameter as A method for measuring the degree of fatigue due to rolling fatigue, characterized in that the degree of fatigue of each part is measured by evaluating according to a standard created in advance according to each part of the rolling part. 2. In the measuring method described in claim 1, the X-ray diffraction half-width and the amount of retained austenite (Vol%) of the martensitic phase before and after rolling fatigue on the surface of the rolling part are measured, The amount of decrease in half width and the amount of decrease in retained austenite amount (Vol%) based on the above measurement values are calculated as F=K△R+△
A method for measuring fatigue level due to rolling fatigue, characterized in that the fatigue level parameter is obtained by substituting it into the equation B, and the evaluation is performed based on a pre-prepared surface fatigue standard. 3. In the measuring method described in claim 1, the X-ray diffraction half-width and the amount of retained austenite (Vol%) of the martensitic phase before and after rolling fatigue inside the rolling part are measured, The amount of decrease in half width and the amount of decrease in retained austenite amount (Vol%) based on the above measurement values are calculated as F=K△R+△
A method for measuring fatigue level due to rolling fatigue, characterized in that the fatigue level parameter is obtained by substituting it into the equation B, and the evaluation is performed based on a pre-prepared surface fatigue criterion.