JPH0558055B2 - - Google Patents

Description

[Detailed description of the invention]

Purpose of invention

[Industrial application field]

The present invention provides mechanical structural parts with increased fatigue strength,
Especially regarding gears.

[Conventional technology]

In general, mechanical structural parts are required to have high fatigue strength, so in addition to considering the selection of materials,
In particular, for applications where strong stress is applied to the surface, surface hardening treatment is often performed. Typical surface hardening treatment methods carried out for this purpose are carburizing and hardening and induction hardening. As is well known, carburizing and quenching can achieve a high degree of surface hardening, but it requires long heating times, consumes a lot of energy, and has the disadvantages of large deformation due to the treatment. On the other hand, induction hardening has the advantage that it can be carried out in a short time and is preferable from the viewpoint of energy saving, and that the finishing process is easy or insoluble due to small deformation, but the degree of surface hardening is not as good as that of carburizing hardening. do not have. For this reason, induction hardening is rarely used for applications that require high surface strength, such as mechanical structural parts such as gears in automobile transmissions.

[Problems to be solved by the invention]

An object of the present invention is to provide a mechanical structural component that can be applied to many cases by taking advantage of the above-mentioned advantages of induction hardening and obtaining a higher hardening effect. Composition of the invention

[Means to solve the problem]

The mechanical structural parts with high fatigue strength of the present invention contain, by weight, C: 0.30 to 0.60%, Si: exceeding 0.45 to 2.0%, Mn: 0.40 to 2.0%, and Cr: 2.0% or less, with the balance It is characterized by induction hardening of steel made of Fe and unavoidable impurities. In a typical embodiment where the mechanical structural part is a gear, induction hardening is performed using the formula log f=A/m [where f is the frequency (KHz), m is the gear module, and A is the proportionality constant. . ] It is preferable to use a high frequency wave having a frequency in which A is in the range of 3 to 10.

[Effect]

The reasons for limiting the above alloy composition are as follows. The C content of 0.30% to 0.60% is the range normally adopted for carbon steel for machine structures, the lower limit is the minimum amount required to obtain a specified surface hardness by induction hardening, and the upper limit is this. This was established because there is a risk of burn damage if the temperature is exceeded. Si content exceeding 0.45 ~ 2.0% is common in carbon steel
This is a high value outside the range of 0.15-0.35%. The lower limit is necessary to obtain a high surface effect through induction hardening, and the upper limit was selected as the limit at which a decrease in machinability can be tolerated. The Mn content ranges from 0.40 to 2.0% over a relatively wide range, including the range typical of carbon steel.
The lower limit is necessary to ensure deoxidation and hardenability, and the upper limit was determined in consideration of machinability as well as Si. Cr is added when it is desired to particularly improve the hardenability of induction hardening depending on the size of the part, and if the content exceeds the upper limit of 2.0%,
It was set as the boundary at which the effect is saturated. The above-mentioned preferable conditions for induction hardening are as follows.
The range of proportionality constant A=3 to 10 is a condition under which the residual stress after surface hardening of the fillet portion of the root of the gear becomes compressive rather than tensile. This increases the bending fatigue strength at the tooth root of the gear and reduces the risk. Example Steel having the chemical composition shown in Table 1 was melted. S35C,
S45C and S55C are carbon steels that have traditionally been used to manufacture mechanical structural parts by applying induction hardening, and SCM420 is a steel that is carburized and hardened.

【table】

[Table] Gear-shaped test pieces as shown in Table 2 were manufactured from each steel by cutting.

[Table] Each test piece was then induction hardened under the conditions shown in Table 3 to harden the surface. In addition, SCM420
was carburized and quenched.

[Table] These test pieces were subjected to a durability test under the conditions shown in Table 4, and the residual stress in the fillet portion of the dedendum of the test pieces made from test steel A was measured. The results of the durability test for the steels of Example 1 and Comparative Example are shown in the graph of the drawing, and the values of the root bending stress after applying stress ¹⁰⁷ times for the steels of Examples 1 to 4 and Comparative Example are shown in the graph. The results are summarized in Table 5. Table 4 Test conditions Gear system Hardening in place stress Hertzian stress ~ 250Kgf/mm ² Lubricating oil Idemitsu gear oil HE-90S (40℃) Life judgment Tooth breakage or tooth surface damage Rotation speed 5160rpm

[Table] It can be seen from the drawings and Table 5 that the gear according to the invention has excellent fatigue strength. Also the fifth
The data in the table confirms that the residual stress in the root fillet of gears obtained by induction hardening under favorable conditions is always on the compression side. Effects of the Invention The present invention can be widely applied to various mechanical structural parts that require a high degree of surface hardening. Specific examples include bearings, rolling parts such as universal joints, rack and pinions used in automobile steering, automobile transmission gears, differential gears, and transmission dogs. be. However, as mentioned in the introduction, among these parts, the present invention is most useful when applied to the manufacture of gears.

[Brief explanation of drawings]

The drawing is a graph showing the fatigue strength of a gear, which is a representative example of a mechanical structural part of the present invention, in comparison with a conventional product.

Claims (1)

[Claims] 1 C: 0.30~0.60%, Si: Exceeding 0.45% by weight
2.0% and Mn: 0.40-2.0% plus Cr: 2.0%
A mechanical structural part with high fatigue strength, characterized by induction hardening of steel containing the following, with the remainder consisting of Fe and unavoidable impurities.