JPH03166320A - Track bushing and its production - Google Patents

Abstract

PURPOSE:To obtain a track bushing excellent in wear resistance and strength by applying hardening and tempering to the whole of a track bushing to form the whole of the track bushing into a uniform hardened layer, applying induction heating to an outside cylindrical part and cooling to a bore part, and then performing low-temp. tempering at the time of producing the track bushing. CONSTITUTION:The whole of a track bushing material 1 composed of medium-carbon low-alloy steel and formed into a cylindrical state is subjected to oil quenching and tempering treatments, by which an outside cylindrical part 2, a core part 3, and a bore part 4 are provided with uniform hardness. Subsequently, while turning the track bushing material 1, induction heating is applied to an outside cylindrical surface 2a by means of a moving coil 5. At this time, a bore surface 4a is cooled by means of water spray from a cooling nozzle 6 in order to prevent thermal effect from extending to the inner part, and then the whole of the track bushing 1 is subjected to low-temp. tempering. By this method, the track bushing which has the high hardness outside cylindrical surface 2a subjected to temp. rise up to the austenitizing temp. or above by means of heating of the outside cylindrical part 2 and hardened, the tempered core part 3 region, and the high hardness bore part surface 4a free from thermal effect and also has toughness and superior wear resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a track bushing used in the tracks of tracked vehicles such as construction machinery, and more particularly to a track bushing with deep hardening and a method for manufacturing the same. (Prior art) Track bushings used in the tracks of tracked vehicles such as construction machinery require wear resistance because their outer and inner diameter parts constantly slide on the track links and bins, respectively. At the same time, it is necessary to have quality that has strength and toughness to withstand the loads that are applied to them. In order to satisfy such quality, ■ Carburizing, quenching, and tempering the entire product using a carburizing furnace.

■Entire quenching and tempering (material refining) in a heating furnace f&, induction quenching and tempering is applied to the inner and outer diameter surfaces separately. ■As seen in Japanese Patent Application Laid-Open No. 59-77979 "Crawler push and its production method", the whole body is not quenched and tempered,
The inner and outer diameters are induction hardened and tempered separately.

(2) As shown in Japanese Patent Application No. 62-323575, ``Deep Hardened Track Bushing and Method for Producing the Same'', which is an invention of the applicant, after the whole body is quenched and tempered, the inner diameter is induction heated, the outer diameter is cooled, and then the whole body is tempered.

Track bushings are manufactured using methods such as these, in which the inner and outer diameter surfaces are hard, and the core has a lower hardness than the inner and outer surfaces so as to have toughness.

(Problems to be Solved by the Invention) However, regarding item (1), these methods require a long processing time and are uneconomical in order to obtain the same hardened layer depth as i) induction hardening. When carburizing for a long time, the crystal grains become coarse and brittle. ii) When the depth of the hardened layer is increased, the crystal grains tend to become coarser and the impact value decreases.

Regarding (1) to (3), the inner diameter surface is directly induction heated to obtain a hardened layer of the inner diameter, but when the inner diameter becomes small, the efficiency of the heating coil becomes extremely poor, and it is practically impossible to apply this method when the inner diameter is less than φ25.

There are drawbacks such as. In view of this, the present invention makes it possible to obtain a hardened layer even if the inner diameter is small, and with fewer steps than conventional steps.
In other words, the purpose of this invention is to provide a rack push and its manufacturing method (which can shorten the number of manufacturing steps).

<Means for Solving the Problems> In order to achieve the above object, claim 1 of the present invention provides that the hardened layer region of the cylindrical track bushing is made of austonite from the outer diameter surface to the core. The core part is formed into a hardened region due to quenching at a temperature higher than the quenching temperature, the core part is a region tempered by the thermal influence of the quenching process, and the area from the core part to the surface of the inner diameter part is a hardened layer area that is not affected by the quenching process. Claim 2 is a method for obtaining the track bushing according to claim 1, comprising: a first step of forming the entire track bushing material into a uniform hardened layer by oil quenching and tempering the entire track bushing material; It consists of a second step in which the outer diameter part of the bushing material is induction heated by a moving coil and the inner diameter part is cooled, and a third step in which the entire track bushing material is subjected to low-temperature tempering, and the outer diameter part is heated to austenite. A head area of the outer diameter surface that has been quenched at a temperature higher than the temperature,
It is characterized by a method in which a region of the core that has undergone tempering and a region of the inner diameter surface that has not been affected by heat are formed simultaneously. (Function) In the track bushing having the above structure, the uniform hardened layer from the outer diameter part to the core part and from the core part to the inner diameter part is obtained by normal quenching and tempering, and is most suitable for the material. It is heat treated under the same conditions to make it hard and highly wear resistant. Then, the hardened layer of the core is heated by induction from the outer diameter 4, and
As a result of cooling the inner diameter part, a tough structure is created by tempering.

(Example) The present invention will be described below with reference to examples shown in FIGS. 1 to 6. The truck bush of claim 1 according to the present invention is claim 2.
This manufacturing method will be described below.

The track bush 1 used in this example is used for a small power excavator, and has an outer diameter of φ44.2. Inner diameter φ24
．． 6 pipe material (SCrB material) was machined to form the first pipe material (SCrB material).
Finish the shape as shown in the figure. The main precepts are shown in Table 1.

Table I Main components of SCrB material Next, Table 2 shows the heat treatment conditions from the first step to the third step in the manufacturing method.

Table 2 Under such heat treatment conditions, the entire track bush 1 shown in Fig. 1 is oil quenched and low temperature tempered in the first step.
Uniform hardness HRC5 from outer diameter part 2, inner diameter part 4 to core part 3
Set it to 5-58. Therefore, the outer diameter portion 2 of the track bushing 1 shown in cross section in FIG. Core part 3, inner diameter part 4 (A-
The hardness distribution in section A) is as shown in Fig. 2.

Next, in a second step, as shown in FIG. 3, the outer diameter surface 2a is induction heated upward in the figure while rotating the track bushing 1 by the moving coil 5. At this time, a cooling nozzle 6 is inserted into the inner diameter surface 4a and cooled by water spray so that the inside is not affected by heat. That is, the push inner diameter surface 4
For a, a hardened layer is necessary to ensure pitch elongation life and fatigue life, but induction heating is applied from the outer diameter surface 2a so that a hardened layer of an appropriate thickness remains, and the inner diameter surface 4a is heated with water. It is cooled by spraying and tempered from the outer diameter surface 2a to the core 3 so that the inside is not affected by heat. During the second process, if the outer diameter surface 2a is heated above the austenitizing temperature and the inner diameter surface 4a is continued to be heated by water bubbles, the austenitized part transforms into martensite and hardens, and the core part 3 A three-layer composite structure can be obtained in a single treatment, in which a tough structure is obtained by high-temperature tempering, and the inner diameter portion 4 is a hardened structure that has been subjected to overnight quenching and low-temperature tempering. In this regard, in conventional technology, in order to obtain a hardened layer on the inner diameter part,
Since the inner diameter surface was directly induction heated, the heating efficiency was extremely low in the case of small diameters, making it extremely difficult to obtain a hard layer, but in the case of the present invention, heating is not necessary. This kind of problem will disappear. In addition, if a coolant is applied directly to the outer diameter heated part during the second process, the cooling speed will be too fast and a large tensile residual stress will be generated at the sintering boundary, making it more likely to cause quench cracking and place cracking, as well as causing fatigue. However, since the present invention employs indirect cooling that cools from the inner diameter part, there is no uneven heating, and therefore such problems do not occur. After the second step is completed, the entire track bushing 1 is tempered in a tempering furnace in the third step, thereby completing the entire process. The hardness distribution on the inner and outer surfaces (A-A cross section in Fig. 1) of the track bushing l made in this way has numerical regions ■, ■, and ■ as shown in Fig. 4.Next, the bench As shown in Fig. 5, the sample track bushing 1 manufactured by the method described above was assembled into the track link 7 of the track, and the assembled link 7 was placed on the test stand 8. Then, the weight W provided on the top of the test track bush 1 is allowed to fall naturally to apply an impact load to the test track bush 1.This impact load is repeatedly applied to an impact fatigue test until it breaks. A graph as shown in Figure 6 was obtained by comparing the carburized track bushings shown in Figure 6.This graph shows the impact load as an energy index on the vertical axis and the number of impacts on the horizontal axis. In the figure, O indicates the position of the crack in the push of the present invention, and ● indicates the position of the crack in the conventional push.According to this, it was found that the life of the present invention was about 5 times longer than that of the conventional push. (Effects of the Invention) As explained above, the method for manufacturing a truck bush according to the present invention includes the first step of forming the entire truck bush material into a uniform hardened layer by oil quenching and tempering the entire truck bush material; It consists of a second step in which the outer diameter portion is induction heated by a moving coil and the inner diameter portion is cooled, and a third step in which the entire track bushing material is subjected to low-temperature tempering. Since the hardened outer diameter surface area, the tempered core area, and the inner diameter surface area that was not affected by heat are formed at the same time, induction heating can be removed even with a small diameter push. Since heat treatment is performed from the radial side, heat treatment is possible easily and economically.Also, when you want to deepen the hardening depth for the purpose of improving wear life, for example, you can adjust the width of the heating zone that extends to the outer diameter. Alternatively, by appropriately adjusting the heating temperature, it is possible to change the hardening depth of either the inner or outer diameter.Furthermore, the track bushing manufactured in this way has extremely high performance as shown in the bench impact fatigue test results. It has the excellent effect of providing a product with a long lifespan.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the track bushing according to the present invention, Fig. 2 is a hardness distribution diagram of the entire track bushing shown in Fig. 1 after overnight quenching and tempering, and Fig. 3 is a heating of the outer diameter performed after the process shown in Fig. 2. An explanatory diagram showing the state of induction heating by a coil and water cooling of the inner diameter, Figure 4 is a hardness distribution diagram after outer diameter quenching and tempering according to Figure 3, and Figure 5 is a bench impact fatigue test of a truck bush manufactured by the method of the present invention. An explanatory diagram showing the method, FIG. 6 is a graph showing a life comparison between the push of the present invention and the conventional carburized push according to the test method of No. 5I2I.

Claims (1)

[Claims] 1) The area of the hardened layer of the cylindrical track bushing from the outer diameter surface to the core is a hardened area by quenching at a temperature equal to or higher than the austonitizing temperature, and the core is hardened by quenching at a temperature higher than the austonitizing temperature. A track bushing characterized in that a hardened layer is formed in a region tempered by the heat effect of the quenching process, and a hardened layer is formed in a region from the core portion to the inner diameter surface that is not affected by the heat effect of the quenching process. 2) A first step in which the entire track bushing material is oil quenched and tempered to form a uniform hardened layer, and a second step in which the outer diameter portion of the track bushing material is induction heated by a moving coil and the inner diameter portion is cooled. and a third step of subjecting the entire track bushing material to low-temperature tempering, the outer diameter surface area being quenched to a temperature equal to or higher than the austenitizing temperature due to the outer diameter heating, and the core area being tempered. and a region of the inner diameter surface that has not been affected by heat are simultaneously formed.