JP2830064B2 - Manufacturing method of high-strength gear with excellent tooth root strength - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the invention]

The present invention relates to a high-strength gear which is used for manufacturing a high-strength gear, and in particular, has an excellent tooth-root strength capable of intentionally realizing a tooth root portion of the gear. And a method for producing the same. (Prior Art) Gears requiring high strength include transmission gears. In transmission gears, it is important to improve the fatigue strength of the gears in order to cope with higher output of the engine and to reduce costs by downsizing the transmission unit. Conventionally, when manufacturing such a transmission gear, in a normal case, a surface hardening treatment such as carburizing and quenching is performed on the coarse gear material, and when it is necessary to further improve the fatigue strength. Are subjected to a shot peening process (for example, JP-A-62-200071 and JP-A-64-31927). In order to further improve the fatigue strength, the surface roughening treatment such as carburizing and quenching is applied to the shaved gear coarse material, and the tooth root fillet including the shaving step is shot peened in two stages. In the first stage shot peening, the shaving step is removed or its shape is changed, and in the second stage shot peening, the tooth fillet portion is surface-finished in two stages. (For example, "a method for manufacturing a high-strength gear" described in JP-A-61-170511). (Problems to be Solved by the Invention) However, in such a conventional method for manufacturing a high-strength gear, the shot peening is simply performed without considering the relationship between the effective hardened layer depth and the shot peening. However, since the shot peening is performed only by focusing on the increase in the compressive residual stress on the outermost surface due to the above, there is a problem that it is still insufficient to effectively strengthen the gear. In addition, there has been a problem that hardly any research has been made on improving the fatigue strength of a helical gear, which is a gear that needs to have high strength, particularly for a transmission. (Object of the Invention) The present invention has been made in view of such a conventional problem, and has excellent fatigue strength in which gears such as helical gears and the like, in particular, have a sufficiently strengthened root portion. It is an object of the present invention to provide a method of manufacturing a high-strength gear excellent in tooth root strength capable of manufacturing a high-strength gear.

Configuration of the Invention

(Means for Solving the Problems) The method of manufacturing a high-strength gear having excellent root strength according to the present invention is a Vickers by the surface hardening treatment when a roughening material such as carburizing is subjected to a surface hardening treatment. Hardness Hv513
After reducing the effective hardened layer depth to less than (gear module × 0.2) [mm] especially at the tooth root of the gear,
20 ~ from tooth root surface by performing shot peening
It is characterized in that the maximum value of the compressive residual stress within the range of 100 [μm] is set to a negative value larger than −60 [kgf / mm ² ] or more. The structure of the manufacturing method is used as means for solving the conventional problem. In the method for manufacturing a high-strength gear having excellent tooth root strength according to the present invention, a surface hardening treatment is performed on a gear rough material. As the gear rough material, for example, various gears conventionally used as gear steel are used. The surface hardening treatment for the gear coarse material includes carburizing and quenching and carbonitriding. When performing this surface hardening treatment, the effective hardened layer depth, which becomes Vickers hardness Hv513 or more due to the surface hardening treatment, becomes shallow as less than (gear module × 0.2) [mm] especially at the tooth base. However, the reason why the effective hardened layer depth by the surface hardening treatment is controlled to be shallower is that the toughness is improved by making the effective hardened layer depth shallow, and the fatigue crack is reduced. This is due to the fact that since the occurrence time is delayed, further improvement in fatigue strength is realized. In this way, the effective hardened layer depth due to the surface hardening treatment is particularly determined at the tooth base of the gear (gear module × 0.2) [m
m], the maximum value of the compressive residual stress within the range of 20 to 100 [μm] from the tooth root surface is increased to a negative value of −60 [kgf / mm ² ] or more by performing shot peening. The reason is that the fatigue strength of the hardened gear has a correlation with the maximum value of the compressive residual stress in the range of 20 to 100 [μm] from the surface rather than the residual stress value of the surface. , From this surface 20-100 [μ
The maximum value of compressive stress in the range of “m” is -60 [kgf / mm
² ] By setting the negative value larger than the above value, the fatigue strength can be further improved. (Effect of the Invention) The method for manufacturing a high-strength gear having excellent root strength according to the present invention has the above-described configuration, and takes into account the relationship between the effective hardened layer depth and shot peening to obtain an effective hardened gear. By making the layer depth shallower than the conventional optimum and improving the toughness, the timing of fatigue cracking becomes slower, and at the same time from the surface slightly more than the innermost surface of the tooth root Since the maximum value of the compressive residual stress is made to have a larger value, the strengthening of the gear becomes remarkably effective, and the fatigue strength of the gear such as the helical gear, which has not been studied so far, is reduced. The effect of being further improved is brought about. (Example) In this example, chromium steel (SCr420H; 0.19% C-0.28
% Si-0.82% Mn-0.05% Ni-1.11% Cr-0.02% M0-Fe)
As shown in FIG. 1, a helical gear having a helical portion 1a having a pressure angle of 17.5 °, a module of 1.5, a number of teeth of 33, and a helix angle of 34 ° and a cylindrical portion 1b adjacent thereto. 1 is shown as an example. Therefore, for the helical gears made of chromium steel described above, gas carburizing (RΧ) was applied to No. 1, 2, 3, 4, 6, and 7 in Table 1.
Carburizing treatment in an atmosphere containing butane and ammonia using a gas as the carrier gas) and performing a surface hardening treatment by vacuum carburizing in No. 5 in Table 1 and then tempering. A surface hardening treatment for adjusting the effective hardened layer depth was performed. Next, after the surface hardening treatment for adjusting the effective hardened layer depth, the effective hardened layer depth at the tooth root having Vickers hardness of Hv513 or more was examined.
The results are shown in the table. For Nos. 1, 2, 4, and 5, the effective hardened layer depth at the root of about 0.35 to 0.40 [mm], which is the same as the conventional optimum However, in Nos. 3, 6, and 7, the effective hardened layer depth at the root of 0.20 to 0.25 [mm] shallower than the conventional optimum It was assumed to have. Next, for No. 2, 3, 4, 6, 7 shown in Table 1,
Shot peening was performed so that the arc height became 0.45 to 0.95 [mmA]. Then, after the shot peening shown in Nos. 2, 3, 4, 6, and 7, the shot peening shown in Nos. 1 and 5 is not performed, and the cylindrical portions (Nos. When the residual stress in 1b was examined by the X-ray diffraction method, it had a residual stress distribution in the depth direction as shown in FIG. On the other hand, the residual stress at the root (the root of the helical portion 1a in FIG. 1) which should be a broken part should be measured. However, the residual stress of the cylindrical portion 1b must be measured in FIG. The reason for this is that the measurement of the distribution of the residual stress at the root of the tooth is very difficult and takes time. Therefore, instead of measuring the residual stress distribution at the tooth root, the second
As shown in the figure, it is necessary to calculate the residual stress distribution of the cylindrical portion 1b and to convert the maximum value of the compressive residual stress obtained from the residual stress distribution of the cylindrical portion 1b into a value at the tooth root. As shown, the residual stress distribution at the tooth root was determined. As a result, the second
As shown in the figure, it can be seen that the maximum value of the residual stress at the root of the tooth is about 60% of that of the cylindrical portion. Therefore,
No.2,3,4,6,7 in which the shot peening was performed in the column of the maximum value of the compressive residual stress in Table 1, the compressive residual stress at the tooth root was calculated as the converted value of 60% of the cylindrical part, which was the measured value. Is shown. It should be noted that Nos. 1 and 5 for which shot peening was not performed are shown in parentheses without conversion. Next, each of the test gears Nos. 1 to 7 was subjected to a meshing fatigue tester to examine the bending fatigue strength at the root of each gear. These results are shown in FIG. In addition, all the damages at the time of this test were bending fatigue damages from the root portion of the helical gear. By the way, the effective hardened layer depth, which is higher than the hardness Hv513 by carburizing and quenching, is generally optimized to be a value obtained by multiplying the gear module by 0.2, and the fatigue strength is shallower or deeper than that. It is said to fall. FIG. 3 shows the optimum effective hardened layer depth of the gear of module 1.5 in the gears of Nos. 1, 2 and 4 in Table 1, which is 0.30 [m
m] as the target and carburizing and quenching.
The gear of No. 5 was subjected to vacuum carburization so that no abnormal surface layer was formed, and the gears of Nos. 3, 6 and 7 in Table 1 had the optimum effective hardened layer depth of the gear of Module 1.5 of 0.3 [m
3] shows the results of examining the effect on fatigue strength by the presence or absence of shot peening for each of carburizing and quenching shallower than m]. From this result, N without shot peening
The fatigue strength of shot peened Nos. 2, 3, and 4 is considerably higher than the fatigue strength of o.1 gears, and shot peening is quite effective in improving fatigue strength. it is obvious. In this case, the No. 4 gear was improved in workability by shot peening for No. 2 gear.
As a result, it is clear that the gear No. 4 has further improved fatigue strength. No.2
The gear of No. 3 has the effective hardened layer depth at the tooth root shallower than the value that was conventionally considered to be optimal for the gear of
As a result, it is clear that the No. 3 gear having a smaller effective hardened layer depth has a higher fatigue strength. On the other hand, the gear No. 5 was a case where vacuum carburizing was performed as a surface hardening treatment, and the hardening was confirmed when the surface abnormal layer generated by gas carburizing was eliminated and the compressive residual stress on the surface was increased. In other words, the No. 5 gear subjected to vacuum carburization has significantly improved fatigue strength despite the higher compressive residual stress at the tooth root surface compared to the No. 1 gear subjected to gas carburization. Was not. Therefore, N
From the viewpoint of compressive residual stress, the results obtained with the gears shown in o.1-5 show that there is a correlation between the maximum value of compressive residual stress that occurs slightly inside the surface and the fatigue strength. It was clear. On the other hand, in the gears according to the present invention of Nos. 6 and 7, the Vickers hardness is Hv513 and the effective hardened layer depth is 0.3 [mm].
(Ie, module x 0.2 [mm]), but despite the fact that the compressive residual stress is almost equal to that of No. 4 gear, the fatigue strength is large as shown in Fig. 3. It is evident that it has improved. That is, it was newly recognized that a shallower effective hardened layer depth than the conventionally-known value can increase the fatigue strength after shot peening. However, No.3
As is clear from the gears, the compressive residual stress at the root of the tooth was -60 [kg
f / mm ² ], the degree of improvement in fatigue strength is small. Here, the reason why the effective hardened layer depth shallower than the conventionally known value has higher fatigue strength is that the toughness is improved by making the effective hardened layer depth shallower, and the fatigue crack generation time Is estimated to be slow. Such an effect can be obtained in a similar manner for gears of other modules, and further improvement in fatigue strength can be obtained. From the results of such an implementation, the fatigue strength of the gear is smaller than the residual stress value on the surface, as shown in FIG. The maximum value of the compressive residual stress is set to -60 [kgf / mm ² ] or more (that is, to increase to the negative side), and the effective hardened layer depth by the surface hardening treatment is reduced. It was clarified that the fatigue strength was greatly improved by making it smaller than the conventional optimum (gear module x 0.2) [mm].

【The invention's effect】

In the method for manufacturing a high-strength gear having excellent tooth root strength according to the present invention, the Vickers hardness Hv51 by the surface hardening treatment when performing a surface hardening treatment such as carburizing and quenching on the gear coarse material.
After reducing the effective hardened layer depth of 3 or more to less than (gear module × 0.2) [mm] especially at the tooth root, by performing shot peening from the tooth root surface
Since the maximum value of the compressive residual stress within the range of 20 to 100 [μm] is set to a negative value larger than −60 [kgf / mm ² ], the fatigue strength of the gear is greatly improved. It is possible to improve the toughness because the effective hardened layer depth, which becomes Vickers hardness Hv 513 or more after surface hardening treatment, is smaller than before, so that the fatigue crack generation time As described above, it is possible to greatly improve the fatigue strength of the gears as described above, and it is possible to shorten the surface hardening treatment time, and to reduce the productivity by shortening the surface hardening treatment time. It is possible to improve the energy cost and reduce the energy cost. If the fatigue strength of the gears is the same, the processing strength during shot peening can be reduced, and Leads to significantly better effect can be assumed small.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the distance from the surface of each gear and the residual stress in the embodiment of the present invention, and FIG. 2 is a graph showing the distance from the surface of the cylindrical portion and the tooth root of the gear and the residual stress. FIG. 3 is a graph showing the result of examining the fatigue strength of each gear, and FIG. 3 is a graph showing the result of examining the correlation with stress.

Continuation of the front page (72) Inventor Makoto Yoshida 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-64-31927 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) C21D 7/00-7/10 B23P 15/14 B24C 1/10 F16H 51/00-55/30

Claims (1)

(57) [Claims] 1. A Vickers hardness by a surface hardening process when a surface hardening process such as carburizing and quenching is performed on a coarse gear material.
After reducing the effective hardened layer depth of Hv513 or more to less than (gear module × 0.2) [mm] especially at the tooth root, the shot peening is performed and the range of 20 to 100 [μm] from the tooth root surface is obtained. A method of manufacturing a high-strength gear having excellent tooth root strength, wherein the maximum value of the compressive residual stress in the gear is set to a negative value larger than −60 [kgf / mm ² ].